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Sample records for neogene valles-penedes half-graben

  1. Structural geology and 4D evolution of a half-graben: New digital outcrop modelling techniques applied to the Nukhul half-graben, Suez rift, Egypt

    Science.gov (United States)

    Wilson, Paul; Hodgetts, David; Rarity, Franklin; Gawthorpe, Rob L.; Sharp, Ian R.

    2009-03-01

    LIDAR-based digital outcrop mapping, in conjunction with a new surface modelling approach specifically designed to deal with outcrop datasets, is used to examine the evolution of a half-graben scale normal fault array in the Suez rift. Syn-rift deposition in the Nukhul half-graben was controlled by the graben-bounding Nukhul fault. The fault can be divided into four segments based on the strike of the fault, the morphology of hangingwall strata, and the variation in throw along strike. The segments of the fault became geometrically linked within the first 2.5 m.y. of rifting, as evidenced by the presence of early syn-rift Abu Zenima Formation strata at the segment linkage points. Fault-perpendicular folds in the hangingwall related to along-strike variations in throw associated with precursor fault segments persist for a further 1.8 m.y. after linkage of the segments, suggesting that the fault remains kinematically segmented. We suggest this occurs because of sudden changes in fault strike at the segment linkage points that inhibit earthquake rupture propagation, or because displacement is geometrically inhibited at fault linkage points where the orientation of the intersection line of the segments is significantly different from the orientation of the slip vector on the fault system. Length/throw plots and throw contour patterns for minor faults show that some faults initiated in pre-rift strata, whereas late east-striking faults initiated in the syn-rift basin fill. The late initiating faults are spatially associated with the east-striking Baba-Markha fault, which was active throughout the rift history, but developed as a transfer fault between major block-bounding fault systems around 6-7 Ma after rift initiation.

  2. Seismic Structure of the Half-Graben of Santiaguillo, Durango, Mexico

    Science.gov (United States)

    Gomez-Gonzalez, J. M.; Nieto-Samaniego, A. F.; Barajas-Gea, I.; Alaniz-Alvarez, S. A.; Diaz-Baez, I.

    2007-05-01

    The Santiaguillo half-graben is part of the San Luis-Tepehuanes fault system, which is a major structure separating two physiographic provinces, the Mesa Central and the Sierra Madre Occidental. The younger movement of the faults is Quaternary, which is affecting the rocks of the Durango volcanic field. In this work, we study the faults and grabens forming the complex structure of the Santiaguillo half-graben. These structures result from active extensional tectonics since the Oligocene. The contemporary tectonic deformations have been manifested in the last 50 years by a number of earthquakes occurred in the region (1.2 Laguna de Santiaguillo. This temporal and portable network has been installed for a period of roughly 12 months starting in April 2006, over an area of about 80 km length and 40 km width. The overall aim of our experiment is to understand the driven forces controlling the tectonics of the western side of the Mesa Central in western Mexico. We combine structural observations and recorded seismicity to locate the potential seismogenic structures. Another objective is characterizing some of the crustal properties in the region. Results show a sparsed and scattered seismic activity. We recorded about 50 microearthquakes, half of them were located out side of the array. Bulk of this activity does not coincide with previously reported activity, which implies a more difficult definition of the seismogenic zones.

  3. Active Extensional Faulting at the Southern Half-Graben Belt of the Tepic-Zacoalco Rift, Western Mexico

    Science.gov (United States)

    Rosas-Elguera, J.; Ferrari, L.; Delgado, M.; Uribe, A.; Valdivia, L.; Castillo, R.

    2003-12-01

    In the past decade much debate has centered upon the kinematics and the mechanism of continental deformation in western Mexico and the motion of the Jalisco block relative to North America. Two distinct models have been proposed. The first one suggest a NW-motion of the Jalisco block that would implies a right-lateral faulting along the Tepic-Zacoalco rift (TZR). More recently others authors have documented a N-NE extensional tectonics active since late Miocene and suggested that the continental boundaries of the Jalisco block, are older structures reactivated by plate boundary forces. Studies on the crustal seismicity and the kinematics of Quaternary faults provide another constraint on the direction of motion between the Jalisco block and North America. On November 4, 5, 6, and 7, 1995, one month after the October 09, 1995, Manzanillo earthquake (Mw = 8.0), a swarm of small events was felt in the Amatlan de Ca¤as half-graben and recorded by the regional seismic network of Comision Federal de Electricidad. The coda magnitude of the largest event was Mc = 2.5-3.6 and the events were located depth ranging from 6 to 10 km. This seismic activity provoked that people from Pie de la Cuesta and Yerbabuena villages were evacuated. After that a seismic station equipped with an analogic seismograph MEQ-800 at Pie de la Cuesta was installed for three months. During the same time, October, 1995, some houses distributed along a WNW trend in Ameca city underwent severe damages, they are. The digital elevations model of the Ameca city suggest that several structures tectonics are shorter than 2 km are present in the area. The present direction of motion of the Rivera plate relative to North America plate along Middle America Trench has been estimated between N19° E to N48° E (e.g. Bandy et al., 1996). During the October 09, 1995, subduction-related earthquake (Mw = 8.0) a GPS network recorded a SW motion of the Jalisco block which could be associated to an elastic deformation

  4. Miocene rifting in the Los Angeles basin: Evidence from the Puente Hills half-graben, volcanic rocks, and P-wave tomography

    Science.gov (United States)

    Bjorklund, Tom; Burke, Kevin; Zhou, Hua-Wei; Yeats, Robert S.

    2002-05-01

    Formation of the Puente Hills half-graben in the northeastern Los Angeles basin and eruption of the Glendora and El Modeno Volcanics (16 14 Ma) help to define the timing of extension in the basin. Normal faulting on the proto-Whittier fault ca. 14 Ma established the Puente Hills half-graben, in which sedimentary strata accumulated between ca. 14 and 10 Ma and into which diabase sills intruded. North-South contraction began to invert the Puente Hills half-graben ca. 7 Ma, leading to formation of the Puente Hills anticline and the Whittier fault. Our high-resolution three-dimensional P-wave velocity model shows two anomalous higher velocity (6.63 km/s) bodies at depths between 9 and 18 km, which we attribute to dioritic plutons named here for Whittier Narrows and El Modeno. The stocklike Whittier Narrows pluton could have been a source for the Glendora Volcanics and the diabase sills in the Puente Hills half-graben. The sill-shaped El Modeno pluton was a likely source for the El Modeno Volcanics. The northwesterly alignment of the plutons may mark the location of the northeastern Los Angeles basin rift boundary, which is associated with the clockwise rotation of the western Transverse Ranges. Three active faults, the Elysian Park blind thrust, the Puente Hills blind thrust, and the Whittier fault, converge on the Whittier Narrows pluton, which may have played a role in their location and segmentation.

  5. A 1.3 million year record of synchronous faulting in the hangingwall and border fault of a half-graben in the Malawi (Nyasa) Rift

    Science.gov (United States)

    McCartney, Tannis; Scholz, Christopher A.

    2016-10-01

    This paper analyzes throw-depth (T-z) profiles from a high resolution 2D reflection seismic grid in the central basin of Lake Malawi to investigate whether evidence exists: 1) for migration of faulting away from the border fault of the half-graben; and 2) that faults in the hangingwall lengthened over the last 1.3 million years. We use the high-precision age model from a 2005 scientific drilling project in our study area to constrain the ages of our seismic horizons and examine a fault array and two individual faults within the hangingwall of the central basin border fault. We account for climatic and sedimentological controls on stratal growth with a lake-level curve that accompanies the age model. A comparison of our hangingwall T-z profiles with published throw-distance (T-x) profiles for the border fault shows synchronous faulting over the last 1.3 m.y. rather than basinward migration of faulting. Furthermore, we find no evidence for significant propagation of the tips of the hangingwall faults in the last 1.3 m.y. and conclude that the lack of basinward migration of faulting is a consequence of strain localization on faults established at an early stage in basin development.

  6. Oblique half-graben inversion of the Mesozoic Neuquén Rift in the Malargüe Fold and Thrust Belt, Mendoza, Argentina: New insights from analogue models

    Science.gov (United States)

    Yagupsky, Daniel L.; Cristallini, Ernesto O.; Fantín, Julián; Valcarce, Gonzalo Zamora; Bottesi, Germán; Varadé, Roberto

    2008-07-01

    The Malargüe fold and thrust belt, located in the Andean mountains between 34°S and 36°30'S, formed in response to contraction during Cenozoic times. Its structural style and geometry was controlled by the Mesozoic rift system that formed the Neuquén basin in west-central Argentina. The rift architecture in the southern sector of this belt was previously interpreted in terms of the present N-S compressive structural trends, assuming the inversion of pre-existing normal faults with the same orientation. Here, we propose that the NW-SE-trending El Manzano-Liu Cullín lineament, located in the northern termination of the Sierra Azul, reflects the presence of a half-graben master fault in the subsurface. This hypothesis is supported by subsurface data, a balanced cross section, and it is tested using a series of scaled sandbox analogue models. We suggest that the lineament responds to a reactivated NW-trending half-graben fault, hidden by the mainly N-S-trending Andean structures. The proposed orientation is in agreement with the NE-SW extension developed in the Neuquén basin during the Triassic-Early Jurassic. The modeling of the inverted oblique half-graben reveals that the strikes of the main structures of inversion-related belts may often be independent of the orientation of the previously developed extensional system, providing a new perspective for their interpretation.

  7. Neogene sinistral transtension along the Hickman fault zone, southeastern Colorado Plateau, New Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Chamberlin, R.M. (New Mexico Bureau of Mines and Mineral Resources, Socorro, NM (United States))

    1993-04-01

    A north-northeast-trending crustal flaw known as the Hickman fault zone (HFZ) transects the southeastern margin of the Colorado Plateau from Mangas to Grants, New Mexico, a distance of 140 km. Recent reconnaissance mapping of the eastern half of the Quemado 1:100,000 sheet by the author indicates that the southern half of the HFZ is a Neogene oblique-slip zone that displays a normal-sinistral sense of shear. The vertical slip component is 150--200 m and the apparent horizontal component is as much as 120 m. Basaltic debris flows and fluvial deposits of the Miocene Fence Lake Formation are preferentially preserved on the downthrown western side of the HFZ. West of Pietown, Fence Lake strata define an asymmetric synclinal basin. Older northwest-striking Late Oligocene basaltic dikes are locally concealed where they pass under the shallow (200 m) northeast--trending basin. Within the 5-km-wide HFZ, north-trending segments appear to form releasing bends and east-northeast-trending segments appear to form weakly constraining bends, a pattern that implies distributed sinistral shear. Small alluvial basins (incipient half grabens) in the Mangas Mountains are associated with north-striking bends. An east-northeast-trending bend near Pietown is locally defined by an asymmetric anticline; also the Late Oligocene dike trend here bends westerly (counterclockwise) where it crosses the anticlinal axis. Near Hickman (a.k.a. Lehew), the HFZ shows two sinistral offsets of another Late Oligocene dike; cumulative offset is about 120 m.

  8. Neogene climate evolution in Amazonia and the Brazilian Northeast

    NARCIS (Netherlands)

    Hoorn, C.; Bernardes-de-Oliveira, M.E.C.; Dino, R.; Garcia, M.J.; Antonioli, L.; da Costa Casado, F.; Hooghiemstra, H.; de Souza Carvalho, I.; Garcia, M.J.; Strohschoen, O.; Cunha Lana, C.

    2014-01-01

    Climate change follows from the interaction between global atmospheric and oceanic processes with regional processes. In this chapter we review which factors determined climate evolution in Amazonia and the Brazilian Northeast and present a recompilation of Neogene palynological and paleobotanical

  9. 10Be dating of Neogene halite

    Science.gov (United States)

    Belmaker, Reuven; Lazar, Boaz; Beer, Jürg; Christl, Marcus; Tepelyakov, Natalya; Stein, Mordechai

    2013-12-01

    Direct radioactive dating of ancient halite formations is difficult because this mineral typically lacks conventionally datable material. We describe an attempt to date Neogene halite using the cosmogenic isotope 10Be (T1/2 = 1.39 Ma). We dated marine-derived salt deposits from the Sedom and Amora (The Hebrew forms of Sodom and Gomorrah) Formations, Dead Sea basin, Israel. To verify whether Be is incorporated into marine halite we measured the stable isotope 9Be, 7Be (the short lived “cosmogenic brother” of 10Be having T1/2 = 53.3 d), and 10Be in evaporation pans of sea-salt production plants. The data suggest that seawater beryllium is incorporated into the halite with a halite-brine distribution coefficient, (KD) of about unity. A 10Be/9Be decay curve constructed for Sedom Formation halite yielded an age that lies in the range of ∼2-6 Ma. The 10Be decay curve constructed for Sedom Formation halite yielded an age that lies in the range of 3-5 Ma. This age is consistent with previous estimates of the Sedom Formation age. Furthermore, this age lies in the same range of 10Be in situ ages obtained on the lacustrine Erq El Ahmer Formation located in the northern Jordan Valley. This may imply that during the Mid Pliocene the Sedom Lagoon, the water-body that deposited the Sedom Formation, might have been already disconnected from the open sea.

  10. Planktonic foraminiferal biostratigraphy of the late Neogene of Crete (Greece)

    NARCIS (Netherlands)

    Zachariasse, W.J.

    1975-01-01

    A planktonic foraminiferal zonation is established for the Middle/Upper Miocene - Pliocene interval in Crete. It is based upon the investigation of samples from 29 sections. Eight zones are distinguished. A comparison with samples from other Neogene sections from Italy, Spain, Algeria, and the islan

  11. Large Centrophorus (Chondrichthyes, Squaliformes) of the Belgian Neogene continental shelf

    NARCIS (Netherlands)

    Schutter, de P.J.; Wijnker, E.

    2012-01-01

    A number of isolated teeth of gulper sharks (genus Centrophorus Müller & Henle, 1837) have been recovered from Neogene sands in the Antwerp area, marking the first occurrence of the genus Centrophorus in the fossil record of Belgium and the North Sea Basin. The precise stratigraphic origin of th

  12. Neogene climate evolution in Amazonia and the Brazilian Northeast

    NARCIS (Netherlands)

    Hoorn, C.; Bernardes-de-Oliveira, M.E.C.; Dino, R.; Garcia, M.J.; Antonioli, L.; da Costa Casado, F.; Hooghiemstra, H.; de Souza Carvalho, I.; Garcia, M.J.; Strohschoen, O.; Cunha Lana, C.

    2014-01-01

    Climate change follows from the interaction between global atmospheric and oceanic processes with regional processes. In this chapter we review which factors determined climate evolution in Amazonia and the Brazilian Northeast and present a recompilation of Neogene palynological and paleobotanical r

  13. Aragonian : the stage concept versus Neogene mammal zones

    NARCIS (Netherlands)

    Daams, R.; Freudenthal, M.

    1981-01-01

    The system of Neogene Mammal Zones, as originally created by Mein (1975), is discussed, and found to be confusing. The Aragonian in the type section and in the surrounding area is discussed, and the evolution of its fauna described in some detail. It appears dubious to apply the MN-zones to the

  14. Aragonian : the stage concept versus Neogene mammal zones

    NARCIS (Netherlands)

    Daams, R.; Freudenthal, M.

    1981-01-01

    The system of Neogene Mammal Zones, as originally created by Mein (1975), is discussed, and found to be confusing. The Aragonian in the type section and in the surrounding area is discussed, and the evolution of its fauna described in some detail. It appears dubious to apply the MN-zones to the faun

  15. Wrench tectonics control on Neogene-Quaternary sedimentation along the Mid-Hungarian Mobile Belt

    Science.gov (United States)

    Pogacsas, Gyorgy; Juhász, Györgyi; Mádl-Szőnyi, Judit; Simon, Szilvia; Lukács, Szilveszter; Csizmeg, János

    2010-05-01

    terrain, lying originally between the Central Alpine and Southern Alpine units, reached its recent position by some hundred kilometers strike slip movement, resulting in shifting of depocenters from the SW toward NE. The TISZA unit was characterised by clockwise motion, while counterclockwise rotation of the ALPACA is inferred in Late Oligocene-Miocene. Lower Miocene layers were deposited in depocenters whose subsidence was initiated by escape tectonics, NE-ward displacement of the ALCAPA terrane, and uplifting of the NW-SE oriented Neo-Vardar zone. The Neo-Vardar zone was represented by wide area of continental and alluvial depositional systems. 2. During the middle-late Badenian (15.5-13.6Ma), the ALCAPA collided with the European platform, and the eastward movement of the Tisza-Dacia became pronounced. Because of that the former right lateral motion along the Mid-Hungarian Mobile Belt ceased and a long period of left lateral strike slipe began. Earlier development of pull-apart basins, related to the extensive strike-slip faulting inside the ALCAPA, changed to the graben opening driven by the westward subduction and the eastward motion of the Tisza-Dacia. The middle-late Badenian period was characterised by sediments deposited in listric fault bounded half grabens, in crestal collapse grabens related to (flat-ramp) listric faults, in wide and/or narrow rift systems. Migration of volcanic activity and facies belts took place during relatively short period of times. Large displacements along listric faults have resulted in tilting of originally horizontal strata, and the formation of a regional unconformity between the middle Miocene and the upper Miocene sediments. Wrench fault related pull apart basins were filled by terrestrial to marine sediments. 3. During the Sarmatian-Pannonian (13.6-6.2 Ma), while the eastward motion of the ALPACA was strictly restricted, the Tisza-Dacia unit was able still to move eastward until the last parts of the remnant Carpathian Flysch

  16. Neogene molluscan stages of the West Coast of North America

    Science.gov (United States)

    Marincovich, L.

    1984-01-01

    Neogene marine sediments of the West Coast of North America were deposited in a series of widely spaced basins that extended geographically from the western and northern Gulf of Alaska (60??N) to southern California (33??N). Rich molluscan faunas occur extensively throughout these deposits and form the basis for biostratigraphic schemes that are useful for correlating within and between individual basins. Early biostratigraphic work was concerned with faunas from particular horizons and with the stratigraphic range of diverse taxa, such as Pecten and Turritella, without reference to other fossil groups. Succeeding work increasingly dealt with the relationships of molluscan zones to benthic and, later, planktonic foraminiferal stages. In recent years the age limits of Neogene molluscan stages have become better documented by reference to planktonic microfossils from dated DSDP cores and onshore faunas. Neogene molluscan faunas from California, the Pacific Northwest states (Oregon and Washington), and southern Alaska have been treated separately due to differences in faunal composition and geographic isolation. As a result, a different biostratigraphic sequence has been described for each region. Pacific Northwest stages have been formally named and defined, and their names are also used informally for Alaskan faunas. California Neogene stages were proposed early in this century, are in need of redescription, and their usage is informal. Precise correlations between the three regional sequences have not yet been achieved, due to the low number of co-occurring species and the general lack of planktonic microfossils in these largely shallow-water faunas. The objectives of ongoing research include: fuller documentation of the faunas of California and Pacific Northwest stages; formal description of California stages; improved correlation between regional stage sequences; refinement of age estimates for stage boundaries; and, establishment of Neogene stages for Alaskan

  17. Neogene dinocyst zonation for the eastern North Sea Basin, Denmark

    DEFF Research Database (Denmark)

    Dybkjær, Karen; Piasecki, Stefan

    2010-01-01

    - and sequence stratigraphy. The dinocyst zonation and the foraminifer zonation of the Danish Miocene (based upon analysis of the same boreholes) were independently calibrated with the established nannoplankton zonation. This correlation revealed a mismatch generally corresponding to one nannoplankton zone...... for the Achomosphaera andalousiensis Zone. Neogene biostratigraphy in the North Sea Basin has been problematic due to the periodically limited connection between the North Sea Basin and the North Atlantic Ocean, especially with respect to stratigraphy based on foraminifers and calcareous nannoplankton. Many...

  18. Marine intervals in Neogene fluvial deposits of western Amazonia

    Science.gov (United States)

    Boonstra, Melanie; Troelstra, Simon; Lammertsma, Emmy; Hoorn, Carina

    2014-05-01

    Amazonia is one of the most species rich areas on Earth, but this high diversity is not homogeneous over the entire region. Highest mammal and tree-alpha diversity is found in the fluvio-lacustrine Pebas system, a Neogene wetland associated with rapid radiation of species. The estuarine to marine origin of various modern Amazonian fish, plants, and invertebrates has been associated with past marine ingressions into this freshwater Pebas system. The exact nature and age of these invasions is, however, debated. Here we present new evidence from fluvial and fluvio-lacustrine deposits of Neogene age in southeast Colombia, that point to periods of widespread marine conditions in western Amazonia. Our evidence is based on an analysis of marine palynomorphs, such as organic linings of foraminifera and dinoflagellate cysts, present in dark sandy clay sediments that outcrop along the Caqueta and Amazon rivers. Characteristically, the foraminiferal linings can be assigned to three benthic morphotypes only, e.g. Ammonia, Elphidium and Trochammina. This low diversity assemblage is associated with estuarine/marginal marine conditions. No distinct marine elements such as shelf or planktonic species were encountered. The observed foraminiferal linings and dinocyst assemblages are typical for a (eutrophic) shallow marine environment, suggesting that the Pebas freshwater wetland system occasionally changed to (marginal) marine. Although some reworked elements are found, a typical Neogene dinocyst taxon is commonly found supporting in situ deposition. Sedimentological features typical for tidal conditions that are reported for sites in Peru and northeastern Brazil likely relate to these marine ingressions. Sea level changes as well as foreland basin development related to Andes formation may have facilitated the entry of marine water during the Neogene.

  19. Coccolith Carbonate Burial in the Open Ocean: Neogene Patterns

    Science.gov (United States)

    Henderiks, J.

    2003-12-01

    Coccolithophorids, gold-brown algae, are prominent primary producers in the World's oceans. They produce calcite scales (coccoliths) that surround their cell, which represents a potential short-term CO2 source to the environment. The burial of coccoliths into marine sediments acts as a long-term sink of carbon. In fact, sedimentary carbonates are the largest reservoir of carbon on Earth, and hence play a vital role in the global carbon cycle. The contribution by coccolithophorids to this long-term sink can be expressed by accumulation rates of fine fraction carbonate. In more detail, absolute abundances of coccoliths combined with species-specific carbonate weights can resolve which taxa are most effective contributors to deep-sea carbonate. Surprisingly little has been done to link biogenic calcium carbonate budgets in the geological past to the general evolutionary patterns of calcifying plankton. Coccolithophorids have evolved relatively rapidly since their first appearance in the Mesozoic. Their evolutionary patterns are characterized by several periods of increasing species diversity and subsequent decline, as well as changes in their coccolith size and morphology. An overall decrease in the coccolith sizes is recorded during the Neogene, with the disappearance of large coccoliths (>10 micron) since the Middle Miocene. Because larger coccoliths are generally more resistant to dissolution, this observation cannot be due to (selective) carbonate dissolution. Hence, it implies significant variability in the amount of coccolith carbonate effectively buried through time, and potentially drastic changes in coccolithophorid productivity in the open ocean, with consequences for the short-term effects of biocalcification. This study focuses on Neogene proportions and accumulation rates of coccolith carbonate in selected well-preserved DSDP and ODP Sites from the Atlantic, Pacific and Indian Oceans, at a 1-2 M.y. resolution. Ultimately, the aim is to understand the

  20. The Neogene de-greening of Central Asia

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    Caves, J. K.; Moragne, D. Y.; Ibarra, D. E.; Bayshashov, B. U.; Gao, Y.; Jones, M. M.; Zhamangara, A.; Arzhannikova, A. V.; Arzhannikov, S. G.; Chamberlain, C. P.

    2016-12-01

    There remains substantial debate concerning the relative roles of tectonics and of global climate in driving the evolution of climate in Asia. Today, interior Asia—including the Taklimakan, Gobi, and Ordos deserts—is exceptionally arid and is surrounded by distinct rainfall boundaries, such as those generated by the Asian monsoon systems to the east and south and those generated by high topography to the north and west. Determining how and why these hydroclimatic boundaries have varied over the Neogene is hindered by the lack of a single proxy that can be broadly applied through space and time. We construct isoscapes of pedogenic carbonate δ13C over the Neogene in Asia by combining a compilation of 2,236 published measurements with new data from three localities in northern Central Asia. Pedogenic carbonate δ13C records local aridity—excepting localities impacted by C4 grasslands and during large changes in atmospheric pCO2—through variations in soil respiration, depth of carbonate formation, and the effect of water stress on plant δ13C. Together, these effects reflect changes in both primary productivity and mean annual precipitation (MAP). Throughout the Neogene, we find consistent and exceptionally high δ13C in interior Asia with a ring of lower δ13C that demarcates higher precipitation. This persistent ring of lower δ13C corresponds in the south and east with the influence of the Asian monsoon systems; in the west and north, it reflects both orographic rainfall due to uplift of the Tian Shan and to moisture delivery by the mid-latitude westerlies. Finally, δ13C and, hence, aridity increases regionally in the latest Neogene, reflecting the effects of Northern Hemisphere glaciation and cooling. The result is a stark decrease in soil respiration fluxes and primary productivity across much of Central Asia. This widespread "de-greening" would have increased regional albedo, and substantially modified basin-scale water balances, resulting in greater

  1. A calibrated mammal scale for the Neogene of Western Europe. State of the art

    NARCIS (Netherlands)

    Agustí, Jorge; Cabrera, L.; Garces, M.; Krijgsman, W.; Oms, O.; Pares, J.M.

    2002-01-01

    A magnetobiostratigraphically calibrated mammal scale for the Neogene of Western Europe is presented in this paper. The Mammal Neogene MN units originally proposed by Mein [Report on activity RCMNS-Working groups] 1975 have been re-defined here on the basis of first appearances of selected small and

  2. Neogene sharks and rays from the Brazilian 'Blue Amazon'.

    Science.gov (United States)

    Aguilera, Orangel; Luz, Zoneibe; Carrillo-Briceño, Jorge D; Kocsis, László; Vennemann, Torsten W; de Toledo, Peter Mann; Nogueira, Afonso; Amorim, Kamilla Borges; Moraes-Santos, Heloísa; Polck, Marcia Reis; Ruivo, Maria de Lourdes; Linhares, Ana Paula; Monteiro-Neto, Cassiano

    2017-01-01

    The lower Miocene Pirabas Formation in the North of Brazil was deposited under influence of the proto-Amazon River and is characterized by large changes in the ecological niches from the early Miocene onwards. To evaluate these ecological changes, the elasmobranch fauna of the fully marine, carbonate-rich beds was investigated. A diverse fauna with 24 taxa of sharks and rays was identified with the dominant groups being carcharhiniforms and myliobatiforms. This faunal composition is similar to other early Miocene assemblages from the proto-Carribbean bioprovince. However, the Pirabas Formation has unique features compared to the other localities; being the only Neogene fossil fish assemblage described from the Atlantic coast of Tropical Americas. Phosphate oxygen isotope composition of elasmobranch teeth served as proxies for paleotemperatures and paleoecology. The data are compatible with a predominantly tropical marine setting with recognized inshore and offshore habitats with some probable depth preferences (e.g., Aetomylaeus groups). Paleohabitat of taxa particularly found in the Neogene of the Americas (†Carcharhinus ackermannii, †Aetomylaeus cubensis) are estimated to have been principally coastal and shallow waters. Larger variation among the few analyzed modern selachians reflects a larger range for the isotopic composition of recent seawater compared to the early Miocene. This probably links to an increased influence of the Amazon River in the coastal regions during the Holocene.

  3. Gravity and Magnetic Survey of the Oaxaca-Juarez Terrane Boundary (Oaxaca Fault), Southern Mexico: Evidence for three Half Grabens

    Science.gov (United States)

    Campos-Enriquez, J. O.; Belmonte-Jimenez, S. I.; Ortega-Gutierrez, F.; Keppie-Moorhouse, J. D.; Martinez-Silva, J.; Martinez-Serrano, R.

    2007-05-01

    A geophysical survey of the Oaxaca Fault boundary between the Oaxaca (Oaxaquia) (Zapoteco) and Juarez (Cuicateco) terranes along the Etla and Zaachila valleys area, southern Mexico shows a series of NW-SE Bouguer and magnetic anomalies with stronger gradients towards the east. The basement from the Oaxaca terrane has a high density (2.8 gr/cm3 ) and magnetic susceptibility of up to 0.0051 cgs units, which contrast with the Juarez basement that has a lower density (2.67 gr/cm3) and a higher magnetic susceptibility (values ranging between 0.0025 to 0.0045 cgs units). The magnetic susceptibility is similar south of the Donaji fault. Interpretation of six combined gravity and magnetic NE-SW profiles perpendicular to the valleys indicates the presence of a composite depression comprising three N-S sub-basins with the Etla and Zachila sub-basins located at the northern and southern portions, respectively, separated by a third sub-basin relatively displaced westwards. They are bounded on the east by the steeply W-dipping Oaxaca master fault, and on the west by the gently E-dipping Huitzo-Zimatlan fault. Two interpretations are suggested for the southward continuation of the Oaxaca Fault: 1) it continues southwards at depth with the same strike. Together the Bouguer and total field magnetic anomalies suggest that the Oaxaca fault is continuous from Etla via Oaxaca City and Ocotlán de Morelos probably to Miahuatlán de Porfirio Díaz, and 2) it continues with the same strike but is displaced eastwards ~20 km along a sinistral transfer fault, which forms the northern boundary of the Zaachila sub-basin.

  4. Neogene Development of the Terror Rift, western Ross Sea, Antarctica

    Science.gov (United States)

    Sauli, C.; Sorlien, C. C.; Busetti, M.; De Santis, L.; Wardell, N.; Henrys, S. A.; Geletti, R.; Wilson, T. J.; Luyendyk, B. P.

    2015-12-01

    Terror Rift is a >300 km-long, 50-70 km-wide, 14 km-deep sedimentary basin at the edge of the West Antarctic Rift System, adjacent to the Transantarctic Mountains. It is cut into the broader Victoria Land Basin (VLB). The VLB experienced 100 km of mid-Cenozoic extension associated with larger sea floor spreading farther north. The post-spreading (Neogene) development of Terror Rift is not well understood, in part because of past use of different stratigraphic age models. We use the new Rossmap seismic stratigraphy correlated to Cape Roberts and Andrill cores in the west and to DSDP cores in the distant East. This stratigraphy, and new fault interpretations, was developed using different resolutions of seismic reflection data included those available from the Seismic Data Library System. Depth conversion used a new 3D velocity model. A 29 Ma horizon is as deep as 8 km in the south, and a 19 Ma horizon is >5 km deep there and 4 km-deep 100 km farther north. There is a shallower northern part of Terror Rift misaligned with the southern basin across a 50 km right double bend. It is bounded by steep N-S faults down-dropping towards the basin axis. Between Cape Roberts and Ross Island, the Oligocene section is also progressively-tilted. This Oligocene section is not imaged within northern Terror Rift, but the simplest hypothesis is that some of the Terror Rift-bounding faults were active at least during Oligocene through Quaternary time. Many faults are normal separation, but some are locally vertical or even reverse-separation in the upper couple of km. However, much of the vertical relief of the strata is due to progressive tilting (horizontal axis rotation) and not by shallow faulting. Along the trend of the basin, the relief alternates between tilting and faulting, with a tilting margin facing a faulted margin across the Rift, forming asymmetric basins. Connecting faults across the basin form an accommodation zone similar to other oblique rifts. The Neogene basin is

  5. Europe's Neogene and Quaternary lake gastropod diversity - a statistical approach

    Science.gov (United States)

    Neubauer, Thomas A.; Georgopoulou, Elisavet; Harzhauser, Mathias; Mandic, Oleg; Kroh, Andreas

    2014-05-01

    During the Neogene Europe's geodynamic history gave rise to several long-lived lakes with conspicuous endemic radiations. However, such lacustrine systems are rare today as well as in the past compared to the enormous numbers of "normal" lakes. Most extant European lakes are mainly results of the Ice Ages and are due to their (geologically) temporary nature largely confined to the Pleistocene-Holocene. As glacial lakes are also geographically restricted to glacial regions (and their catchment areas) their preservation potential is fairly low. Also deposits of streams, springs, and groundwater, which today are inhabited by species-rich gastropod assemblages, are rarely preserved. Thus, the pre-Quaternary lacustrine record is biased towards long-lived systems, such as the Late Miocene Lake Pannon, the Early to Middle Miocene Dinaride Lake System, the Middle Miocene Lake Steinheim and several others. All these systems have been studied for more than 150 years concerning their mollusk inventories and the taxonomic literature is formidable. However, apart from few general overviews precise studies on the γ-diversities of the post-Oligocene European lake systems and the shifting biodiversity in European freshwater systems through space and time are entirely missing. Even for the modern faunas, literature on large-scale freshwater gastropod diversity in extant lakes is scarce and lacks a statistical approach. Our preliminary data suggest fundamental differences between modern and pre-Pleistocene freshwater biogeography in central Europe. A rather homogenous central European Pleistocene and Holocene lake fauna is contrasted by considerable provincialism during the early Middle Miocene. Aside from the ancient Dessaretes lakes of the Balkan Peninsula, Holocene lake faunas are dominated by planorbids and lymnaeids in species numbers. This composition differs considerably from many Miocene and Pliocene lake faunas, which comprise pyrgulid-, hydrobiid-, viviparid-, melanopsid

  6. Neogene biomarker record of vegetation change in eastern Africa.

    Science.gov (United States)

    Uno, Kevin T; Polissar, Pratigya J; Jackson, Kevin E; deMenocal, Peter B

    2016-06-07

    The evolution of C4 grassland ecosystems in eastern Africa has been intensely studied because of the potential influence of vegetation on mammalian evolution, including that of our own lineage, hominins. Although a handful of sparse vegetation records exists from middle and early Miocene terrestrial fossil sites, there is no comprehensive record of vegetation through the Neogene. Here we present a vegetation record spanning the Neogene and Quaternary Periods that documents the appearance and subsequent expansion of C4 grasslands in eastern Africa. Carbon isotope ratios from terrestrial plant wax biomarkers deposited in marine sediments indicate constant C3 vegetation from ∼24 Ma to 10 Ma, when C4 grasses first appeared. From this time forward, C4 vegetation increases monotonically to present, with a coherent signal between marine core sites located in the Somali Basin and the Red Sea. The response of mammalian herbivores to the appearance of C4 grasses at 10 Ma is immediate, as evidenced from existing records of mammalian diets from isotopic analyses of tooth enamel. The expansion of C4 vegetation in eastern Africa is broadly mirrored by increasing proportions of C4-based foods in hominin diets, beginning at 3.8 Ma in Australopithecus and, slightly later, Kenyanthropus This continues into the late Pleistocene in Paranthropus, whereas Homo maintains a flexible diet. The biomarker vegetation record suggests the increase in open, C4 grassland ecosystems over the last 10 Ma may have operated as a selection pressure for traits and behaviors in Homo such as bipedalism, flexible diets, and complex social structure.

  7. Evolution of Chinese Neogene Rhinocerotidae and Its Response to Climatic Variations

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Chinese Neogene Rhinocerotidae has quite a complete record and its temporal range is the Early Miocene to Late Pliocene. The samples include 25 species in 4 tribes of 2 subfamilies. They are used as a foundation for the study of the evolution of the family and its relation to climatic changes. Taxonomic diversity, new records and extinctions are estimated for each Chinese Neogene mammal faunal unit (NMU). The diversity of Chinese Rhinocerotidae varies noticeably throughout the Neogene and is recognized within five stages: the Middle Miocene and Late Miocene are stages of high diversity and the Early Miocene, early Late Miocene and Pliocene are stages of low diversity. Rhinocerotid diversity and morphology are closely related to environmental factors and particularly sensitive to changes in ambient temperature and humidity. The interpretation of climatic variation reflected in the evolution of Rhinocerotidae corresponds precisely with the conclusions drawn from other workers and provides new evidence for research on the Neogene terrestrial ecosystem in China.

  8. The Neogene Environment of the Beardmore Glacier, Transantarctic Mountains

    Science.gov (United States)

    Ashworth, A. C.; Cantrill, D. J.; Francis, J. E.; Roof, S. R.

    2004-12-01

    Discontinuous sequences of Neogene marine and non-marine glacigenic sequences, including the Meyer Desert Formation (MDF), occur throughout the Transantarctic Mountains. The upper 85m of the MDF, consisting of interbedded diamictites, conglomerates, sandstones and siltstones, outcrops in the Oliver Bluffs on the Beardmore Glacier at 85° 07'S, 166° 35'E. The location is about 170 km south of the confluence of the Beardmore Glacier with the Ross Ice Shelf and about 500 km north of the South Pole The glacial, fluvioglacial and glaciolacustrine facies of the MDF represent a dynamic glacial margin which advanced and retreated on at least four occasions. On at least one occasion, the retreat was sufficiently long for plants and animals to colonize the head of a major fjord which existed in the place of the existing Beardmore Glacier. From the fossils we have identified at least 18 species of plants, 3 species of insects, 2 species of freshwater mollusks, and a species of fish. The plant fossils consist of pollen, seeds, fruits, flowers, leaves, wood, and in situ plants. The plants include a cryptogamic flora of mosses and liverworts, conifers, and angiosperms in the families Gramineae, Cyperaceae, Nothofagaceae, Ranunculaceae, Hippuridaceae, ?Caryophyllaceae, and ?Chenopodiaceae or ?Myrtaceae. The plants grew in a weakly developed soil developed on a complex periglacial environment that included moraines, glacial outwash streams, well-drained gravel ridges, and poorly drained depressions in which peat and marl were being deposited. The fossil assemblage represents a mosaic tundra environment of well- and poorly-drained micro-sites, in which nutrient availability would have been patchily distributed. Antarctica has been essentially in a polar position since the Early Cretaceous and at 85° S receives no sunlight from the middle of March until the end of September. Today, the annual radiation received is about 42% that of Tierra del Fuego at 55° S. During the Neogene

  9. Neogene biostratigraphy and paleoenvironments of Enewetak Atoll, equatorial Pacific Ocean

    Science.gov (United States)

    Cronin, T. M.; Bybell, L.M.; Brouwers, E.M.; Gibson, T.G.; Margerum, R.; Poore, R.Z.

    1991-01-01

    Micropaleontologic analyses of Neogene sediments from Enewetak Atoll, Marshall Islands, provide data on the age of lagoonal deposits, stratigraphic disconformities and the paleoenvironmental and subsidence history of the atoll. Benthic foraminifers, planktic foraminifers, calcareous nannofossils and ostracodes were studied from six boreholes, the deepest penetrating 1605 feet below the lagoon floor into upper Oligocene strata. The Oligocene-Miocene boundary occurs at about 1200 ft below the lagoon floor. The early and middle Miocene is characterized by brief periods of deposition and numerous hiatuses. Ostracodes and benthic foraminifers indicate a shallow-marine reefal environment with occasional brackish water conditions. Upper Miocene and lower Pliocene deposits placed in calcareous nannofossil Zones NN9-15 and in planktic foraminifer Zones N16-19 contain species-rich benthic microfaunas which indicate alternating reefal and brackish water mangrove environments. The upper Pliocene contains at least two major depositional hiatuses that coincide with a major faunal turnover in benthic foraminiferal and ostracode assemblages. The Quaternary is characterized by benthic microfaunas similar to those of modern atoll lagoons and is punctuated by at least 11 disconformities which signify periods of low sea level. Atoll subsidence rates during the last 10 Ma averaged 30 to 40 m/m.y. ?? 1991 Elsevier Science Publishers B.V. All rights reserved.

  10. A Palaeohydrological Shift during Neogene East Antarctic Ice Sheet Retreat

    Science.gov (United States)

    Rees-Owen, R. L.; Newton, R.; Ivanovic, R. F.; Francis, J.; Tindall, J. C.; Riding, J. B.

    2015-12-01

    The East Antarctic Ice Sheet is an important driver of global climate, playing a particular role in governing albedo and atmospheric circulation (eg. Singh et al., 2013). Recent evidence from marine sediment and terrestrial glaciovolcanic sequences suggests that the EAIS underwent periodic retreat and collapse in response to warmer climates during the late Neogene (14 to 3 million years ago). Mummified prostrate trees recovered from palaeosols at Oliver Bluffs in the Beardmore Glacier region, Transantarctic Mountains (85° S), represent a rare insight into the terrestrial palaeoclimate during one of these periods of retreat. Prostrate trees are an understudied but useful tool for interrogating endmember (e.g. periglacial) environments at high altitudes and latitudes. We present exciting new palaeoclimate data from the sequence at Oliver Bluffs. δ18O analysis of tree ring cellulose suggests that Antarctic summer palaeoprecipitation was enriched relative to today (-25 to -5‰ for ancient, -35 to -20‰ for modern); consistent with our isotope-enabled general circulation model simulations. The MBT/CBT palaeothermometer gives a summer temperature of 3-6ºC, consistent with other palaeobotanical climate indices. These geological and model data have wide-ranging implications for our understanding of the hydrological cycle during this time period. We present data suggesting that changes in moisture recycling and source region indicate a markedly different hydrological cycle.

  11. Himalaya evolution at Paleogene-Neogene boundary unraveled by zircon age spectrum from Arabian Sea Sediments

    Science.gov (United States)

    Feng, Han; Lu, Huayu; Zhang, Hanzhi

    2016-04-01

    Although virtually all the intensive orogenic activities of Himalaya occurred in Neogene, the tectonic evolution of this high mountain range in Paleogene is poorly understood. Investigations of tectonic change pattern at Paleogene-Neogene boundary are important to better understand the interaction between mountain building and climate evolution. Here we present new U-Pb ages of zircon grains from Indus Fan sediments to constrain the orogenic history of Himalaya at Paleogene-Neogene boundary. 11 samples between late Oligocene and early Miocene from ODP 117 cores are dated by the zircon U-Pb technique. We calculate relative contributions of potential sources by counting zircon grains for each sample, and the quantized results indicate Himalaya contributed sediments to the coring site, and an extremely high input from Great and Tethyan Himalaya during late Oligocene-early Miocene. Four samples in Pleistocene are also dated for comparison, which indicates that high proportion of Lesser Himalaya has contributed to the sediment in Pleistocene. Our results suggest that the high contribution of Great and Tethyan Himalaya at Paleogene-Neogene boundary might correlate with the beginning of activity of MCT and extension of STD with leucogranite intrusion along Himalaya, which give rise to the extensive Great Himalaya exhumation. Our study demonstrates that zircon U-Pb dating technique is a good tool to reconstruct erosional history of mountain building on a tectonic timescale. Key words: ODP, Himalaya, Indus Fan, zircon U-Pb dating, Paleogene-Neogene boundary

  12. Andean uplift and Neogene climate change in the Atacama Desert

    Science.gov (United States)

    Rech, J. A.; Currie, B. S.; Jordan, T. E.

    2006-12-01

    Today the Andean Cordillera and Altiplano provide a major obstacle to atmospheric circulation over South America. The Altiplano Plateau prevents moist air masses from the Amazon Basin from reaching the Atacama Desert, causing the Atacama to be one of the driest places on Earth. Although Neogene sedimentary records from the western flank of the Andes should record the dramatic shift to hyperaridity that resulted from the growth of the Altiplano Plateau, the climatic implications of many sedimentary sequences have been difficult to decipher. The causes of the difficulties are complex, such as the relative influences of tectonics and active volcanism versus climate, and the roles of local as well as regional precipitation on groundwater and on the deposition of paludal sediments in basin centers. Over the last few years our research group has focused on using paleosols and the isotopic composition of palustrine carbonates in the Calama Basin (22°S) to try to identify a local precipitation signal and determine the onset of extreme hyperaridity as a consequence of the growth of the Altiplano. We have determined the soil morphological characteristics, salt chemistry, and mass independent fractionation anomalies (Δ17O values) in dated paleosols to reconstruct a Middle Miocene climatic transition from semi-aridity to extreme hyperaridity in the Atacama Desert. Paleosols along the southeastern margin of the Calama Basin change from calcic Vertisols with root traces, slickensides, and gleyed horizons to an extremely mature salic Gypsisol with pedogenic nitrate. We interpret this transition, which occurred between 19 and 13 Ma, to represent a change in precipitation from >200 mm/yr to Calama Basin also show a marked change during this time period. δ13C values of palustrine carbonates increase from -7 to +7? VPDB and δ18O values increases from -7 to +1? VPDB over the late to Middle Miocene time. This major trend towards more positive values is likely the result of several

  13. Post-Neogene tectonism along the Aravalli Range, Rajasthan, India

    Science.gov (United States)

    Sen, Deepawati; Sen, Saurindranath

    1983-03-01

    The Aravalli Range runs southwest from Delhi for a distance of about 700 km. Its western margin is well defined, but the eastern margin is diffuse. Five geomorphic provinces are recognized in the study area: the western piedmont plains; the ridge and valley province which in the Central Aravallis occurs at two different heights separated by a fault scarp; the plateau province demarcated from the former by a fault scarp, confined to the Southern Aravallis, and occurring for a short stretch at two heights across another fault scarp; the BGC rolling plains east of the Range; and the BGC uplands south of the above. The scarps coincide with Precambrian faults. A series of rapids and water-falls, together with deeply entrenched river courses across the scarps and the youthful aspects of the escarpments with no projecting spurs, or straight river courses along their feet, all point unmistakably to a recent or post-Neogene vertical uplift along pre-existing faults. Presence of knickpoints at a constant distance from the Range in all west-flowing rivers, the ubiquitous terraces, and river courses entrenched within their own flood-plain deposits of thick gritty to conglomeratic sand, are indicative of a constant disturbance with a gradual rise of the Range east of the knickpoint, wherefrom the coarse materials were carried by the fast west-flowing streams. There is a differential uplift across the plateau scarp together with a right-lateral offset. This epeirogenic tectonism is ascribed to the collision of the Eurasian and the subducting Indian plates and to a locking of their continental crusts. By early Pleistocene, with the MBT gradually dying off, continued plate movement caused a flexural bending of the plate by a moment generated at the back, and a possible delinking of the continental crust along the zone of subduction. The felexural bending ripped open the Precambrian regional faults. The differential uplift and the difference in the distances of the nodes on two

  14. Reconstructing the cosmogenic 21Ne inventory of Neogene sedimentary sequences

    Science.gov (United States)

    Stuart, Finlay; Sinclair, Hugh; McCann, Louise

    2016-04-01

    Ne is ubiquitous. The data require minimum average pebble transport times of 150 kyr. A similar distribution of cosmogenic Ne concentrations is present in quartzite pebbles from gravels from the Pliocene Broadwater Formation and Miocene Ogallala Formation gravels indicates that the rates of transport and pebble recycling on flood plain have not changed over the Neogene. [1] Margerison et al. (2005) Earth Planet. Sci. Lett. 230, 163-175. [2] Codilean et al. (2008) Geology 36, 159-162.

  15. Decapod crustaceans from the Neogene of the Caribbean: diversity, distribution and prospectus

    NARCIS (Netherlands)

    Collins, J.S.H.; Portell, R.W.; Donovan, S.K.

    2009-01-01

    The Neogene decapod crustaceans are reviewed from Aruba, Bonaire and Curaçao, Anguilla, Barbados, Carriacou, Costa Rica, Cuba, Florida, Hispaniola (Haiti and Dominican Republic), Jamaica, Mexico, Panama, Puerto Rico, St. Kitts, Tintamare Island, Trinidad and Venezuela. The most widely distributed ta

  16. Neogene stratigraphy of the Langenboom locality (Noord-Brabant, the Netherlands)

    NARCIS (Netherlands)

    Wijnker, E.; Bor, T.J.; Wesselingh, F.P.; Munsterman, D.K.; Brinkhuis, H.; Burger, A.W.; Vonhof, H.B.; Post, K.; Hoedemakers, K.; Janse, A.C.; Taverne, N.

    2008-01-01

    The locality of Langenboom (eastern Noord-Brabant, the Netherlands), also known as Mill, is famous for its Neogene molluscs, shark teeth, teleost remains, birds and marine mammals. The stratigraphic context of the fossils, which have been collected from sand suppletions, was hitherto poorly understo

  17. Decapod crustaceans from the Neogene of the Caribbean: diversity, distribution and prospectus

    NARCIS (Netherlands)

    Collins, J.S.H.; Portell, R.W.; Donovan, S.K.

    2009-01-01

    The Neogene decapod crustaceans are reviewed from Aruba, Bonaire and Curaçao, Anguilla, Barbados, Carriacou, Costa Rica, Cuba, Florida, Hispaniola (Haiti and Dominican Republic), Jamaica, Mexico, Panama, Puerto Rico, St. Kitts, Tintamare Island, Trinidad and Venezuela. The most widely distributed

  18. The Late Neogene elephantoid-bearing faunas of Indonesia and their palaeozoogeographic implications

    NARCIS (Netherlands)

    Bergh, van den G.D.

    1999-01-01

    The stratigraphic framework of the Neogene fossil vertebrate bearing formations of the Indonesianislands Sulawesi and Flores is established and the sediments are dated by means of marinemicropalaeontological and/or palaeomagnetic methods. The results allow comparison of the faunaevolution on these i

  19. Lithofacies Associations and Depositional Environments of the Neogene Molasse succession, Pishin Belt, northwestern Pakistan

    DEFF Research Database (Denmark)

    Kasi, Aimal K.; Kassi, Akhtar M.; Friis, Henrik

    Formation and Oligocene Khojak Formation. The Early to Middle Miocene Dasht Murgha group comprises Zone-III, the Late Miocene-Pliocene Malthanai formation comprises Zone-IV, the Pleistocene Bostan Formation makes Zone-V, and the flat-laying Holocene deposits of the Zhob Valley comprise Zone-VI. The Neogene...

  20. Neogene stratigraphy of the Langenboom locality (Noord-Brabant, the Netherlands)

    NARCIS (Netherlands)

    Wijnker, T.G.; Bor, T.J.; Wesselingh, F.P.; Munsterman, D.K.; Brinkhuis, H.; Burger, A.W.; Vonhof, H.B.; Post, K.; Hoedemakers, K.; Janse, A.C.; Taverne, N.

    2008-01-01

    The locality of Langenboom (eastern Noord-Brabant, the Netherlands), also known as Mill, is famous for its Neogene molluscs, shark teeth, teleost remains, birds and marine mammals. The stratigraphic context of the fossils, which have been collected from sand suppletions, was hitherto poorly

  1. Extended stratigraphy, palynology and depositional environments record the initiation of the Himalayan Gyirong Basin (Neogene China)

    NARCIS (Netherlands)

    Xu, Y.; Zhang, K.; Wang, G.; Jiang, S.; Chen, F.; Xiang, S.; Dupont-Nivet, G.; Hoorn, C.

    2012-01-01

    Here we report new sedimentological and paleontological data from a 603.5 m thick Neogene sequence (Woma section) in the Gyirong Basin, a basin induced by east-west extension in the Himalayas of southern Tibet. We document the conglomeratic Danzengzhukang Formation, at the base of the section, and

  2. Magnetostratigraphy of the Neogene sediments of SW Uruguay

    Science.gov (United States)

    Sanchez Bettucci, L.; Orgeira, M. J.; Sanchez, G.; Bertoni-Machado, C.; Farina, R.

    2007-05-01

    Preliminary results on the magnetostratigraphy of three Neogene formations from SW Uruguay are presented: Camacho, Raigón and Libertad, and a relative age from the record of reversions in the Earth's magnetic field polarity is proposed. The sediments outcrop in the SW region of Uruguay,and have been received attention due to their fossil contents. The oldest is the late Miocene-Pliocene Camacho Fm, of Huayquerian to Montehermosan affinities. A Pliocene-early Pleistocene age has been assigned to Raigón Fm, of Chapadmalalan affinities. The overlying Libertad Fm has been considered early-middle Pleistocene in age, and to have Marplatan-Ensenadan affinities. The lithology of this facies of Camacho Fm is identified by the presence of fine to very fine sandstones and is composed of silty-sandy and bioturbed silty deposits. The marine facies of this formation is rich in fossil content, as several invertebrate and vertebrate taxa are found. The upper Raigón Fm is formed by sandstones of varied grain size and includes lenses and levels of claystones and conglomerates. It shows the sedimentological features of a deep, pebble-rich braided fluvial system. The 383 vertebrate specimens found in the sandy facies and studied in a taphonomically-oriented study belong to 19 genera and 13 higher taxa. The bones are disarticulated, with smooth fractures and little weathered or abraded, which is congruent with a short time of contact, as observed in strong and sudden flows. The elements belong to the three Voorhies groups and fractured specimens are found along with well preserved materials, implying different taphonomical histories and reworking. The consequent inferred time averaging urges caution at using these remains for defining precise ages. The Libertad Fm, top of the sequence, is conformed by greenish clays, clayey fine sandstones, medium sized sandstones and conglomeratic levels, corresponding to deposits of continental origin under a semiarid climate, which allowed the

  3. Deepwater Ventilation and Stratification in the Neogene South China Sea

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    cap buildup on northern high latitudes, a deepening sea basin due to stronger subduction eastward may also have triggered the influx of more corrosive waters from the deep western Pacific. Since 3 Ma, the evolution of the SCS deep water entered a modern phase, as characterized by relative stable 10% CaCO3 difference between the two sites and increase in infaunal benthic species which prefer a low oxygenated environment. The subsequent reduction of PBW and PDW marker species at about 1.2 Ma and 0.9 Ma and another significant negative excursion of benthic δ13C to a Neogene minimum at ~0.9 Ma together convey a clear message that the PBW largely disappeared and the PDW considerably weakened in the Mid-Pleistocene SCS. Therefore, the true modern mode SCS deep water started to form only during the "Mid-Pleistocene climatic transition" probably due to the rise of sill depths under the Bashi Strait.

  4. Paleomagnetism of the Late Paleogene and Neogene rocks of the Serbian Carpatho-Balkanides: Tectonic implications

    Directory of Open Access Journals (Sweden)

    Marović Milun

    2002-01-01

    Full Text Available This paper focuses on results of the paleomagnetic research conducted in the territory of Serbian Carpatho-Balkanides, within the following basinal domains: Babušnica-Koritnik (the Oligocene deposits, Žagubica (the upper part of the Lower Miocene and the lower part of the Middle Miocene deposits and Dacian (the Pontian deposits. The clockwise rotations are established for each basinal region: Babušnica-Koritnik 10°, Žagubica 5-10° and Dacia 5-20°. On the basis of these results and the available data on rotations in the Romanian Southern Carpathians, new tectonic implications are discussed as a contribution to understanding the genesis of the Paleogene-Neogene and Neogene fabric of the Carpatho-Balkanides in Serbia. It is shown that this region has been subjected not only to vertical, but also to horizontal mobility during the latest stage of its geological development.

  5. Neogene tectonics and climate forcing of carnivora dispersals between Asia and North America

    OpenAIRE

    2015-01-01

    Exchange records of terrestrial mammals can be combined with available tectonic and climatic documents to evaluate major biological and environmental events. Previous studies identified four carnivoran dispersals between Eurasia and North America in the Neogene, namely, at ∼ 20, 13–11, 8–7, and ∼ 4 Ma. In order to evaluate driving mechanism of these biological events, we collected, compared and analyzed a large number of published records. The result...

  6. Neogene stratigraphy, foraminifera, diatoms, and depositional history of Maria Madre Island, Mexico: Evidence of early Neogene marine conditions in the southern Gulf of California

    Science.gov (United States)

    McCloy, C.; Ingle, J.C.; Barron, J.A.

    1988-01-01

    Foraminifera and diatoms have been analyzed from an upper Miocene through Pleistocene(?) sequence of marine sediments exposed on Maria Madre Island, largest of the Tre??s Marias Islands off the Pacific coast of Mexico. The Neogene stratigraphic sequence exposed on Maria Madre Island includes a mid-Miocene(?) non-marine and/or shallow marine sandstone unconformably overlain by a lower upper Miocene to uppermost Miocene upper to middle bathyal laminated and massive diatomite, mudstone, and siltstone unit. This unit is unconformably overlain by lower Pliocene middle to lower bathyal sandstones and siltstones which, in turn, are unconformably overlain by upper Pliocene through Pleistocene(?) upper bathyal to upper middle bathyal foraminiferal limestones and siltstones. These beds are unconformably capped by Pleistocene terrace deposits. Basement rocks on the island include Cretaceous granite and granodiorite, and Tertiary(?) andesites and rhyolites. The upper Miocene diatomaceous unit contains a low diversity foraminiferal fauna dominated by species of Bolivina indicating low oxygen conditions in the proto-Gulf Maria Madre basin. The diatomaceous unit grades into a mudstone that contains a latest Miocene upper to middle bathyal biofacies characterized by Baggina californica and Uvigerina hootsi along with displaced neritic taxa. An angular unconformity separates the upper Miocene middle bathyal sediments from overlying lower Pliocene siltstones and mudstones that contain a middle to lower bathyal biofacies and abundant planktonic species including Neogloboquadrina acostaensis and Pulleniatina primalis indicating an early Pliocene age. Significantly, this Pliocene unit contains common occurrences of benthic species restricted to Miocene sediments in California including Bulimina uvigerinaformis. Pliocene to Pleistocene(?) foraminiferal limestones and siltstones characterize submarine bank accumulations formed during uplift of the Tre??s Marias Island area, and include

  7. Facies control on seismites in an alluvial-aeolian system: The Pliocene dunefield of the Teruel half-graben basin (eastern Spain)

    Science.gov (United States)

    Liesa, Carlos L.; Rodríguez-López, Juan Pedro; Ezquerro, Lope; Alfaro, Pedro; Rodríguez-Pascua, Miguel Ángel; Lafuente, Paloma; Arlegui, Luis; Simón, José L.

    2016-10-01

    The recognition of seismically induced soft-sediment deformation structures (SSDS) in sedimentary successions characterized by different facies, and hence by different rheology, is challenging. This is the case for high porosity and high permeability aeolian facies interbedded with muddy wet interdune deposits and alluvial conglomerates and sandstones. Several types of SSDS have been studied in two exposures of the Upper Pliocene (2.9-2.6 Ma) sediments of a fault-bounded intracontinental aeolian dune field in the Teruel Basin (Iberian Chain, eastern Spain). Among SSDS, load and fluid-escape structures, apart from several animal tracks, have been recognized. Those structures show an irregular distribution through the studied stratigraphic sections, being scarce in homogenous aeolian sands and frequent in water-related facies. A detailed study of the distribution and geometry of SSDS and their relationships with respect to the stratigraphic architecture and facies has allowed a critical discrimination of trigger mechanisms, i.e. biological or physical overloading vs. earthquakes. The seismically induced structures are concentrated into seven deformed beds, showing an uneven lateral distribution and geometry closely controlled by the hosting sedimentary facies and their rheology. These seismites resulted from liquefaction during moderate earthquakes (estimated magnitude from 5.0 to 6.8). The most probable seismogenic source was the Sierra del Pobo normal fault zone, located 2 km to the East. Results show how an appropriate recognition of sedimentary facies is crucial to understand the lateral variability of seismites in sedimentary environments characterized by sharp facies changes.

  8. The Baja California Borderland and the Neogene Evolution of the Pacific-North American Plate Boundary

    Science.gov (United States)

    Fletcher, J. M.; Eakins, B. W.

    2001-12-01

    New observational data on Neogene faulting in the borderland of Baja California places important constraints on tectonic models for the evolution of the Pacific-North American (P-NA) plate boundary and rifting in the Gulf of California. Neogene faults in the borderland range from strike slip to normal slip and accommodate integrated transtension. Most have east-facing escarpments and likely reactivate the former east-dipping accretionary complex. Numerous lines of evidence indicate that Neogene faults are still active and accomplish a significant component ( ~1-5 mm/yr) of Pacific-North American shearing. Quaternary volcanoes are found offshore and along the Pacific coastal margin, Quaternary marine terraces are warped and uplifted as high as 200 masl. Many of the offshore faults have fresh escarpments and cut Holocene sediments. Extensive arrays of Quaternary fault scarps are found throughout the coastal region and in Bahia Magdalena they are clearly associated with major faults that bound recently uplifted islands. A prominent band of seismicity follows the coast and eight earthquakes (Ms>5.0) were teleseismically recorded between 1973 and 1998. This evidence for active shearing indicates that the Baja microplate has not yet been completely transferred to the Pacific plate. The best lithologic correlation that can be used to define the total Neogene slip across the borderland faults is the offset between the Magdalena submarine fan and its Baja source terrane. The distal facies of the fan drilled during DSDP leg 63 is dominated by mudstone and siltstone that contain reworked Paleogene cocoliths derived from strata correlative with the Tepetate formation found throughout the borderland and fine-grained sandstone derived from a source terrane of granitoid basement. The Middle Miocene La Calera formation of the Cabo trough is one of many granitoid-clast syn-rift alluvial deposits that could form the continental counterpart of the submarine fan near the mouth of the

  9. Timing and sources of neogene and quaternary volcanism in South-Central Guatemala

    Science.gov (United States)

    Reynolds, James H.

    1987-08-01

    Five new and six existing radiometric age dates place constraints on the timing of volcanic episodes in a 1400-km 2 area east of Guatemala City. The source of the voluminous Miocene rhyolitic welded tuffs was the newly discovered Santa Rosa de Lima caldera, in the northern part of the area, not fissure eruptions as was previously believed. Resurgence during the Pliocene included the eruption of more silicic tuffs, followed by post-collapse volcanism around the perimeter. Volcanism in the southern part of the area occurred along the Neogene volcanic front. The sources for these Late Miocene and Pliocene andesitic lavas were not fissure eruptions, as was once believed, but were four large volcanic centers, Cerro Pinula, Ixhuatán, Teanzul, and Cerro La Gabia. The Santa Rosa de Lima caldera structure deflects the Jalpatagua Fault forming tensional fractures along which eruptions in the Quaternary Cuilapa-Barbarena cinder cone field took place. Pleistocene ash flows were erupted from Ixhuatán and Tecuamburro volcanoes in the southern part of the area. Tephras from Ayarza, Amatitlán, and Atitlán blanket the northern and central portions. Present-day activity is restricted to hot springs around the northern and eastern base of Tecuamburro volcano. Based on the work in this area it is proposed that rocks of the Miocene Chalatenango Formation throughout northern Central America were erupted from calderas behind the Neogene volcanic front. Rocks of the Mio-Pliocene Bálsamo Formation in Guatemala and El Salvador were erupted from discrete volcanic centers along the Neogene volcanic front. Pliocene rocks of the Cuscatlán Formation probably represent post-collapse volcanism around earlier caldera structures.

  10. Paleoatmospheric signatures in Neogene fossil leaves; Utrecht University, Utrecht (Netherlands). Lab. of Paleobotany and Palynology

    Energy Technology Data Exchange (ETDEWEB)

    Burgh, J. van der; Visscher, H.; Dilcher, D.L.; Kuerschner, W.M.

    1993-06-18

    An increase in the atmospheric carbon dioxide (CO[sub 2]) concentration results in a decrease in the number of leaf stomata. This relation is known both from historical observations of vegetation over the past 200 years and from experimental manipulations of microenvironments. Evidence from stomatal frequencies of fossil [ital Quercus petraea] leaves indicates that this relation can be applied as a bioindicator for changes in paleoatmospheric CO[sub 2] concentrations during the last 10 million years. The data suggest that late Neogene CO[sub 2] concentrations fluctuated between about 280 and 370 parts per million by volume. 20 refs., 3 figs.

  11. Seismic reflection survey at Llancanelo region (Mendoza, Argentina) and preliminary interpretation of Neogene stratigraphic features

    Science.gov (United States)

    Osella, A.; Onnis, L.; de la Vega, M.; Tassone, A.; Violante, R. A.; Lippai, H.; López, E.; Rovere, E. I.

    2015-07-01

    A shallow multichannel seismic survey reaching depths of 700/800 m was performed for the first time in the Llancanelo Lake region (Southern Mendoza Province, Argentina), in order to depict the major Neogene sedimentary-volcanic sequences that form the final infilling of the tectonic-volcanic basin where the lake is located. The seismic survey advances on the results of previous geoelectric and electromagnetic surveys carried out at early stages of the research that reached the uppermost 80-100 m of the sequences (Quaternary), and therefore they go deeper in the subsoil. All the surveys were supported by surface and subsoil geological observations. After explaining the details of the performed seismic methodology, the obtained results are discussed, which indicate the presence of three major sedimentary units with increasing volcanic (basaltic layers) intercalations with depth, that accommodate to the geometry of the depocenter. The entire sequence encompasses most of the Neogene. This research sets the methodological basis for future, more detailed shallow seismic surveys in the region.

  12. High-resolution sedimentological and subsidence analysis of the Late Neogene, Pannonian Basin, Hungary

    Science.gov (United States)

    Juhasz, E.; Muller, P.; Toth-Makk, A.; Hamor, T.; Farkas-Bulla, J.; Suto-Szentai, M.; Phillips, R.L.; Ricketts, B.

    1996-01-01

    Detailed sedimentological and paleontological analyses were carried out on more than 13,000 m of core from ten boreholes in the Late Neogene sediments of the Pannonian Basin, Hungary. These data provide the basis for determining the character of high-order depositional cycles and their stacking patterns. In the Late Neogene sediments of the Pannonian Basin there are two third-order sequences: the Late Miocene and the Pliocene ones. The Miocene sequence shows a regressive, upward-coarsening trend. There are four distinguishable sedimentary units in this sequence: the basal transgressive, the lower aggradational, the progradational and the upper aggradational units. The Pliocene sequence is also of aggradational character. The progradation does not coincide in time in the wells within the basin. The character of the relative water-level curves is similar throughout the basin but shows only very faint similarity to the sea-level curve. Therefore, it is unlikely that eustasy played any significant role in the pattern of basin filling. Rather, the dominant controls were the rapidly changing basin subsidence and high sedimentation rates, together with possible climatic factors.

  13. Record of C4 Photosynthesis Through the Late Neogene and Pleistocene

    Science.gov (United States)

    Cerling, T. E.

    2016-12-01

    C4 photosynthesis is an adaptation to the low atmospheric carbon dioxide concentrations experienced in the Neogene; it is found principally in tropical to sub-tropical/temperate regions where temperatures are high in the growing season. Although C4 photosynthesis makes up about 50% of Net Primary Productivity in tropical regions, its macroscopic fossil record is extremely sparse. Therefore, inferences to its significance in local ecosystems are based primarily on stable isotopes, with phytoliths become more important as phytolith morphology becomes better associated with plant structure and classification. Stable isotopes have been the principal recorder for understanding the history of C4 photosynthesis; however, different materials record different aspects of the C4 contribution to ecosystem structure and thus are telling different parts of the same story. With the fossil record so poorly known, we often assume similar ecosystem structures and functions as we observe in modern analogues. It is likely that large evolutionary changes have taken place within C4 plants as they went from 50% tropical NPP in the late Neogene.

  14. PALYNOLOGICAL MODEL OF THE LATE NEOGENE SEDIMENTS OF EASTERN SLAVONIA (CROATIA

    Directory of Open Access Journals (Sweden)

    Gabrijela Pecimotika

    2015-12-01

    Full Text Available By applying a palynological analysis of the Late Neogene sediments from one exploration well in the area of Eastern Slavonia, three vegetation zones (Z1, Z2, Z3 as conditioned by climate sensitivity were set. On the basis of mutual percentage relations of the occurrence of individual form-species and grouping them according to the results of cluster analysis, these zones reflect the changes of warm-cold and variable humidity periods. The age of zones has been determined: zone Z1 is Pontian, zone Z2 is Pliocene and zone Z3 is Pleistocene-Holocene. In the Pontian, 13 form-species of spores were determined that do not cross the Miocene/Pliocene boundary. In the Pliocene, 4 index form-species of spores were determined that were not found in the Quaternary in the study area. In the youngest sediments of the study area, i.e. Pleistocene and Holocene, 7 index form-species of spores were determined. Together with well logging (gamma ray and specific resistivity logs of the formation, a model was constructed for the local routine provision of age in the study area. The results are generally consistent with other results obtained from Early Neogene sediments in adjacent areas in the central part of Paratethys, and may serve as a model for the correlation of contemporaneous sediments in other areas of Croatia, e.g. Sava and Drava Depressions , which in effect may contribute to the more efficient investigation of potential hydrocarbon reservoirs.

  15. Uplift and volcanism of the SE Colombian Andes in relation to Neogene sedimentation in the Upper Magdalena Valley.

    NARCIS (Netherlands)

    Wiel, van der A.M.

    1991-01-01

    The present study deals with the relation between Neogene uplift and volcanism of the SE Colombian Andes and sedimentation processes in the Upper Magdalena Valley. The southernmost part of the Upper Magdalena Valley, the S. Neiva Basin, is located between latitudes 2°08'-2°31 N and longitudes 75°22'

  16. Contrasting neogene denudation histories of different structural regions in the transantarctic mountains rift flank constrained by cosmogenic isotope measurements

    NARCIS (Netherlands)

    Wateren, F.M. van der; Dunai, T.J.; Balen, R.T. van; Klas, W.; Verbers, A.L.L.M.; Passchier, S.; Herpers, U.

    1999-01-01

    Separate regions within the Transantarctic Mountains, the uplifted flank of the West Antarctic rift system, appear to have distinct Neogene histories of glaciation and valley downcutting. Incision of deep glacial outlet valleys occurred at different times throughout central and northern Victoria Lan

  17. Variations in sea surface temperature reconstructed by algal biomarker thermometry in the Neogene equatorial Pacific sediments

    Science.gov (United States)

    Sawada, K.; Nakamura, H.; Yamamoto, S.; Kobayashi, M.

    2012-12-01

    The eastern equatorial Pacific Ocean today sustains significant amounts of global marine productivity, and the region is one of the largest marine sources of CO2 to the atmosphere. However, geological time-scale variations of marine environment and ecological / biogeochemical systems in the equatorial Pacific have been still unclear. In this study, we reconstruct the variations of sea surface temperature (SST) by long chain alkenone and the newest long-chain diol thermometers from the equatorial Pacific sediments, and discuss fluctuations in paleoceanographic and paleoclimatic systems in this region during the Neogene. Integrated Ocean Drilling Program (IODP) Expeditions 320/321 (Pacific Equatorial Age Transect; PEAT) recovered a Cenozoic sediment record from the equatorial Pacific by coring above the palaeoposition of the Equator at successive crustal ages on the Pacific plate. We used a core U1337 in the present study. We identify C37 - C38 alkenones as well as saturated C28 and C30 1,13-diols, C28 and C30 1,14-diols, and C30 1,15-diol from almost all the Neogene sediments (23 - 0.23 Ma) in a core U1337. This indicates that diatom, haptophyte and eustigmatophyte algal productions were consistently significant in the equatorial Pacific throughout the Neogene. The UK'37 values were converted to temperatures by using the calibrations reported by Prahl et al. (1988) and Kienast et al. (2012). The alkenone-based SSTs in a core U1337 were nearly constant over the past 25 Ma, ranging from 26 to 28 C, although there were two much lower spikes of 15 - 20 C in 13.2 - 12.5 Ma and 6 Ma. The Long chain Diol Index (LDI; Rampen et al., 2012) values were converted to SSTs by using the calibrations reported by Rampen et al. (2012) and Sawada et al. (unpublished data). The LDI values were estimated to be 7 - 30 C and 12 - 27 C by the Rampen et al. and Sawada et al. calibrations, respectively. The decreasing spikes of SSTs in U1337 core are observed in the horizons of 12.5Ma, 11Ma

  18. New finds of lacertids (Sauria, Lacertidae from the Neogene of Slovakia and Czech Republic

    Directory of Open Access Journals (Sweden)

    Peter Joniak

    2009-01-01

    Full Text Available In the present paper, first finds of fossil lacertids from the Neogene of Slovakia and new finds from Czech Republic are described. The material comes from three localities: Merkur - North (Czech Republic, Early Miocene, Borský Svätý Jur (Slovakia, Late Miocene and Ivanovce (Slovakia, Early Pliocene, and consists of several isolated dentaries, maxillae and one vertebra. According to the morphology, the find of dentary from the Ivanovce locality can be attributed to Lacerta cf. agilis. Except one vertebra, the rest of the material can be assigned to Lacerta sp. The fragment of the anterior portion of the dentary from the Upper Miocene sediments of Borský Svätý Jur represents the oldest known occurrence of this taxon in Slovakia. Thus, the material enhances our rather poor knowledge of the paleoherpetofauna from the Slovakian territory.

  19. ESR dating of quartz extracted from quaternary and neogene sediments: method, potential and actual limits

    Science.gov (United States)

    Laurent, M.; Falguères, C.; Bahain, J. J.; Rousseau, L.; Van Vliet Lanoé, B.

    ESR dating of fluvial, fluvio-marine and beach sediment has been tested using the Al centre in quartz grains from a basin and fossil beaches located around the Manche Channel. Dating was performed in conjunction with sedimentological, stratigraphical and neotectonical studies. The technical basis of the method is presented in the light of the study made on recent and fossil sediment in order to establish a procedure for the determination of the palaeodose. The application on a Neogene Basin samples allows to push back the dating ESR limits. Results show that ESR dating of sediment can provide chronozons which are necessary to the uderstanding of the history of a basin where classical chronological markers do not exist.

  20. A Neogene structural dome in the Klamath Mountains, California and Oregon

    Science.gov (United States)

    Mortimer, N.; Coleman, R. G.

    1985-04-01

    Regional structural doming of Neogene age has affected rocks of the Klamath and Cascade mountains near the California-Oregon border. Evidence for this is seen in (1) subannular outcrop patterns of pre-Cretaceous lithotectonic units, (2) a crude pattern of radially oriented high-angle faults, (3) tilted Jurassic plutons, (4) tilted Cretaceous to Miocene strata, and (5) various geomorphological features. The age of doming is constrained by a major middle Miocene to earliest Pliocene angular unconformity within the Cascade Mountains and uplifted upper Miocene marine beds on the western edge of the Klamath Mountains. Uplift and doming may be the result of shortening in the Cascade fore-arc region or, more speculatively, the recent accretion of subducted material to the North American plate beneath the Klamath Mountains. *Present addresses: Mortimer, Department of Geological Sciences, University of British Columbia, Vancouver, British Columbia V6T 2B4, Canada; Coleman, U.S. Geological Survey, Menlo Park, California 94025

  1. Neogene to recent contraction and basin inversion along the Nubia-Iberia boundary in SW Iberia

    Science.gov (United States)

    Ramos, Adrià; Fernández, Oscar; Terrinha, Pedro; Muñoz, Josep Anton

    2017-02-01

    The SW of Iberia is currently undergoing compression related to the convergence between Nubia and Iberia. Multiple compressive structures, and their related seismic activity, have been documented along the diffuse Nubia-Iberia plate boundary, including the Gorringe bank west of the Gulf of Cadiz, and the Betic-Rif orogen to the east. Despite seismic activity indicating a dominant compressive stress along the Algarve margin in the Gulf of Cadiz, the structures at the origin of this seismicity remain elusive. This paper documents the contractional structures that provide linkage across the Gulf of Cadiz and play a major role in defining the present-day seismicity and bathymetry of this area. The structures described in this paper caused the Neogene inversion of the Jurassic oblique passive margin that formed between the central Atlantic and the Ligurian Tethys. This example of a partially inverted margin provides insights into the factors that condition the inversion of passive margins.

  2. A closer look at the Neogene erosion and accumulation rate increase

    Science.gov (United States)

    Willenbring, J.; von Blanckenburg, F.

    2008-12-01

    Glacial erosion and Quaternary cold-stage warm-stage climate cycling have been cited as mechanisms to explain observations of increased Neogene marine sedimentation rates. Quantification of long-term glacial erosion rates from cosmogenic radionuclides from large areas mostly covered by cold-based ice during the Quaternary show very low erosion rates over several glacial cycles. In addition, isotope ratio proxies of dissolved metals in seawater, measured in chemical ocean sediments, lack clear evidence for an increase in terrigenous denudation. In particular, the stable isotope 9Be, derived from continental erosion, shows no change in its ratio to meteoric cosmogenic nuclide 10Be, derived from rain over the past 10 My. Radiogenic Pb and Nd isotopes, mainly show a change in the style of denudation from more chemical to more physical processes in the Quaternary. These data are at odds with a suggested increase in marine sedimentation rates during the late Cenozoic. In order to resolve this contradiction we have scrutinized these sedimentation rate calculations from ocean cores to identify whether they might show only apparent increases in the Neogene sections. Potential explanations are that in some cases, measured sediment thicknesses for different time intervals lack corrections for sediment compaction. Compaction of the lower portions of the cores drastically increases the apparent thickness of the more recent (Quaternary) sediment. In addition, sedimentation rates often only appear higher for recent sections in cores due to an artifact of an averaging timescale that decreases up-core. Such an averaging time scale decrease arises from better chronological resolution in recent times (Sadler et al., 1999). Cannibalization of older sediment might add to this effect. Together, these data question a clear, global-scale Quaternary climate-erosion connection that would be unique in Earth's history.

  3. Linked basin sedimentation and orogenic uplift: The Neogene Barinas basin sediments derived from the Venezuelan Andes

    Science.gov (United States)

    Erikson, Johan P.; Kelley, Shari A.; Osmolovsky, Peter; Verosub, Kenneth L.

    2012-11-01

    The Venezuelan Andes are an asymmetric, doubly vergent orogen that is flanked on its southeastern side by the Barinas basin. Analyses of sedimentary facies, sandstone petrography, apatite fission-tracks, and magnetostratigraphy were completed on a 1750-m section of the syn-orogenic Neogene Parángula and Río Yuca formations in the Barinas side foothills of the Venezuelan Andes. Our sedimentary facies analyses record a progression of sedimentary environments from floodplain and floodplain channel deposits through the 560-m thick Parángula Formation transitioning to distal alluvial fan deposits in the lower Río Yuca Formation and finally to an alternation of distal alluvial fan and two, ˜100-m thick organic-rich lacustrine deposits in the upper third of the section. Major- and minor-mineral petrographic analysis reveals unroofing of the Venezuelan Andes, with quartz arenite composition low in the section succeeded by metamorphic and igneous clasts and potassium feldspar appearing near the base of the Río Yuca Formation. Apatite fission-track (AFT) analysis of sandstones and pebbles generated ages of 11.2 ± 1.3 - 13.8 ± 2.0 Ma over ˜1100 m of stratigraphic section. Thermal modeling of the detrital AFT and vitrinite data from the lower Río Yuca Formation indicates exhumation of the source area was occurring by 12-13 Ma, surface exposure at 10-9 Ma, maximum burial by 4-2 Ma and exhumation of the sedimentary package starting 3-2 Ma. Accumulation of the Río Yuca Formation is contemporaneous with a basinward migration of the deformation front. Regional considerations indicate that the Venezuelan Andes evolved from a primarily singly vergent orogen to its current double vergence over the interval of Neogene-Quaternary sedimentation.

  4. Punctuated Neogene tectonics and stratigraphy of the African-Iberian plate-boundary zone: concurrent development of Betic-Rif basins (southern Spain, northern Morocco)

    NARCIS (Netherlands)

    Sissingh, W.

    2008-01-01

    This paper integrates the sequence stratigraphic and tectonic data related to the Neogene geodynamic and palaeogeographic development of the African-Iberian plate boundary zone between Spain and Morocco. Though the dating of individual tectonostratigraphic sequences and their delimiting sequence

  5. Reliability of the nanopheres-DNA immunization technology to produce polyclonal antibodies directed against human neogenic proteins.

    Science.gov (United States)

    Arnaoty, Ahmed; Gouilleux-Gruart, Valérie; Casteret, Sophie; Pitard, Bruno; Bigot, Yves; Lecomte, Thierry

    2013-08-01

    The molecular domestication of several DNA transposons that occurred during the evolution of the mammalian lineage, has led to the emergence of at least 43 genes, known as neogenes. To date, the limited availability of efficient commercial antibodies directed against most of their protein isoforms hampers investigation of their expression in vitro and in situ. Since immunization protocols using peptides or recombinant proteins have revealed that it is difficult to recover antibodies, we planned to produce antisera in mice using a new technique of nanopheres/DNA immunization, the ICANtibodies™ technology. Here, we investigate the possibilities of obtaining polyclonal antibodies for 24 proteins or protein domains using this immunization strategy. We successfully obtained 13 antisera that were able to detect neogenic proteins by Western blotting and ELISA in protein extracts of transiently-transfected cells and various cancer cell lines, plus another two that only detected the in ELISA and in in situ hybridizations. The features required for the production of these antibodies are analyzed and discussed, and examples are given of the advantages they offer for the study of neogenic proteins.

  6. Neogene vegetation development in the Amazon Basin: evidence from marine well-2, Foz do Amazonas (Brazil)

    Science.gov (United States)

    Bogota-Angel, Raul; Chemale Junior, Farid; Davila, Roberto; Soares, Emilson; Pinto, Ricardo; Do Carmo, Dermeval; Hoorn, Carina

    2014-05-01

    Origen and development of the highly diverse Amazon tropical forest has mostly been inferred from continental sites. However, sediment records in the marine Foz do Amazonas Basin can provide important information to better understand the influence of the Andes uplift and climate change on its plant biomes evolution since the Neogene. Sediment analyses of samples from BP-Petrobras well 1 and 2, drilled in the Amazon Fan, allowed to infer the onset of the transcontinental Amazon river and the fan phase during the middle to late Miocene (c. 10.5 Ma). As part of the CLIMAMAZON research programme we performed pollen analysis on the 10.5 to 0.4 Ma time interval. 76 ditch cutting samples of the upper 4165 m sediments of well 2 permitted us to infer changes in floral composition in the Amazon Basin. The palynological spectra across this interval (nannofossil based age model) include pollen, fern spores, dinocysts and foram lignings. When possible pollen and fern spores were grouped in four vegetation types: estuarine, tropical, mountain forest and high mountain open treeless vegetation. Pollen is generally corroded and reflects the effects of sediment transportation while reworked material is also common. Good pollen producers such as Poaceae, Asteraceae and Cyperaceae are common and reflect indistinctive vegetation types particularly those associated to riverine systems. Rhizophora/Zonocostites spp. indicate "close-distance" mangrove development. Tropical forest biomes are represented by pollen that resemble Moraceae-Urticaceae, Melastomataceae-Combretaceae, Sapotaceae, Alchornea, Euphorbiaceae, Rubiaceae, Bignoniaceae, Mauritia and Arecaceae. Myrica, and particularly sporadic occurrences of fossil fern spores like Lophosoria, and Cyathea suggest the development of a moist Andean forest in areas above 1000 m. First indicators of high altitudes appear in the last part of late Miocene with taxa associated to current Valeriana and particularly Polylepis, a neotropical taxon

  7. Carbonatite metasomatized peridotite xenoliths from southern Patagonia: implications for lithospheric processes and Neogene plateau magmatism

    Science.gov (United States)

    Gorring, Matthew L.; Kay, Suzanne M.

    The mineral chemistry, major and trace element, and Sr-Nd isotopic composition of Cr-diopside, spinel peridotite xenoliths from the Estancia Lote 17 locality in southern Patagonia document a strong carbonatitic metasomatism of the backarc continental lithosphere. The Lote 17 peridotite xenolith suite consists of hydrous spinel lherzolite, wehrlite, and olivine websterite, and anhydrous harzburgite and lherzolite. Two-pyroxene thermometry indicates equilibration temperatures ranging from 870 to 1015°C and the lack of plagioclase or garnet suggests the xenoliths originated from between 40 and 60km depth. All of the xenoliths are LILE- and LREE-enriched, but have relatively low 87Sr/86Sr (0.70294 to 0.70342) and high ɛNd (+3.0 to +6.6), indicating recent trace element enrichment ( 25Ma, based on the low 87Sr/86Sr and high Rb concentrations of phlogopite separates) in the long-term, melt-depleted Patagonian lithosphere. Lote 17 peridotite xenoliths are divided into two basic groups. Group 1 xenoliths consist of fertile peridotites that contain hydrous phases (amphibole+/-phlogopite+/-apatite). Group 1 xenoliths are further subdivided into three groups (a, b, and c) based on distinctive textures and whole-rock chemistry. Group 1 xenolith mineralogy and chemistry are consistent with a complex metasomatic history involving variable extents of recent carbonatite metasomatism (high Ca/Al, Nb/La, Zr/Hf, low Ti/Eu) that has overprinted earlier metasomatic events. Group 2 xenoliths consist of infertile, anhydrous harzburgites and record cryptic metasomatism that is attributed to CO2-rich fluids liberated from Group 1 carbonatite metasomatic reactions. Extremely variable incompatible trace element ratios and depleted Sr-Nd isotopic compositions of Lote 17 peridotite xenoliths indicate that the continental lithosphere was neither the primary source nor an enriched lithospheric contaminant for Neogene Patagonian plateau lavas. Neogene plateau magmatism associated with formation

  8. Cryptic diversity of African tigerfish (genus Hydrocynus reveals palaeogeographic signatures of linked neogene geotectonic events.

    Directory of Open Access Journals (Sweden)

    Sarah A M Goodier

    tectonic events modified Africa's Neogene drainage. Haplotypes shared amongst extant Hydrocynus populations across northern Africa testify to recent dispersals that were facilitated by late Neogene connections across the Nilo-Sahelian drainage. These events in tigerfish evolution concur broadly with available geological evidence and reveal prominent control by the African Rift System, evident in the formative events archived in phylogeographic records of tigerfish.

  9. Late Neogene sedimentary facies and sequences in the Pannonian Basin, Hungary

    Science.gov (United States)

    Juhasz, E.; Phillips, L.; Muller, P.; Ricketts, B.; Toth-Makk, A.; Lantos, M.; Kovacs, L.O.

    1999-01-01

    This paper is part of the special publication No.156, The Mediterranean basins: Tertiary extension within the Alpine Orogen. (eds B.Durand, L. Jolivet, F.Horvath and M.Seranne). Detailed sedimentological, facies and numerical cycle analysis, combined with magnetostratigraphy, have been made in a number of boreholes in the Pannonian Basin, in order to study the causes of relative water-level changes and the history of the basin subsidence. Subsidence and infilling of the Pannonian Basin, which was an isolated lake at that time occurred mainly during the Late Miocene and Pliocene. The subsidence history was remarkably different in the individual sub-basins: early thermal subsidence was interrupted in the southern part of the basin, while high sedimentation rate and continuous subsidence was detected in the northeastern sub-basin. Three regional unconformities were detected in the Late Neogene Pannonian Basin fill, which represent 0.5 and 7.5 Ma time spans corresponding to single and composite unconformities. Consequently two main sequences build up the Late Neogene Pannonian Basin fill: a Late Miocene and a Pliocene one. Within the Late Miocene sequence there are smaller sedimentary cycles most probably corresponding to climatically driven relative lake-level changes in the Milankovitch frequency band. Considering the periods, the estimated values for precession and eccentricity in this study (19 and 370 ka) are close to the usually cited ones. In the case of obliquity the calculated period (71 ka) slightly deviates from the generally accepted number. Based on the relative amplitudes of oscillations, precession (sixth order) and obliquity (fifth order) cycles had the most significant impact on the sedimentation. Eccentricity caused cycles (fourth order) are poorly detectable in the sediments. The longer term (third order) cycles had very slight influence on the sedimentation pattern. Progradation, recorded in the Late Miocene sequence, correlates poorly in time

  10. Post-Neogene Structural Evolution:An Important Geological Stage in the Formation of Gas Reservoirs in China

    Institute of Scientific and Technical Information of China (English)

    WANG Tingbin

    2004-01-01

    Tectonic movements since the Neogene have been the major developmental and evolutional stages of the latest global crustal deformation and orogenic movements. China is located in a triangular area bounded by the Indian landmass, the West Siberian landmass and the Pacific Plate, characterized by relatively active tectonic movements since the Neogene, and in this region, natural gas would have been very easy to dissipate, or difficult to preserve. Therefore, the characteristics of post-Neogene tectonic movements offer important geological factors in researching the formation and preservation of gas reservoirs in China. Summarizing the reservoiring history of gas fields in China, although there are some differences between various basins, they are all affected by the tectonic movements since the Neogene. These movements have certainly caused destruction to the reservoiring and distribution of natural gas in China, which has resulted in a certain dissipation of natural gas in some basins. As a whole, however, they have mainly promoted the reservoiring and accumulation of natural gas: (1) a series of China-type foreland basins have been formed between basins and ridges in western China, which provide favorable conditions for the formation of large and medium gas fields, as well as controlling the finalization of gas reservoirs in the basins; (2) rows and belts of anticlines have been formed in the Sichuan Basin in central China, which have been the major stages of the formation and finalization of gas reservoirs in that basin; the integral and quick rising and lifting, and a further west-dipping in the Ordos Basin have resulted in a further accumulation of natural gas in gas fields from Jingbian to Uxin; (3) in eastem China, the Bohai movement in the late Pliocene has provided favorable geological conditions for lately-formed gas reservoirs in the Bohai Sea area mainly composed of the Bozhong depression; and it also resulted in secondary hydrocarbon generation and

  11. Neogene tectonics and climate forcing of carnivora dispersals between Asia and North America

    Directory of Open Access Journals (Sweden)

    H. Jiang

    2015-08-01

    Full Text Available Exchange records of terrestrial mammals can be combined with available tectonic and climatic documents to evaluate major biological and environmental events. Previous studies identified four carnivoran dispersals between Eurasia and North America in the Neogene, namely, at ∼ 20, 13–11, 8–7, and ∼ 4 Ma. In order to evaluate driving mechanism of these biological events, we collected, compared and analyzed a large number of published records. The results indicate that the carnivoran dispersal from Eurasia to North America at ∼ 20 Ma was probably caused by intense tectonic movements in Asia. During 13–11 Ma, global cooling possibly drove the mammal exchanges between Eurasia and North America. By comparison, the carnivoran dispersal from Eurasia to North America at 8–7 Ma was probably caused by the combination of global cooling and tectonic movements of the Tibetan Plateau. Similar to during 13–11 Ma, the carnivoran exchanges between Eurasia and North America at ∼ 4 Ma were possibly driven by global cooling.

  12. Neogene tectonics and climate forcing of carnivora dispersals between Asia and North America

    Science.gov (United States)

    Jiang, H.; Deng, T.; Li, Y.; Xu, H.

    2015-08-01

    Exchange records of terrestrial mammals can be combined with available tectonic and climatic documents to evaluate major biological and environmental events. Previous studies identified four carnivoran dispersals between Eurasia and North America in the Neogene, namely, at ∼ 20, 13-11, 8-7, and ∼ 4 Ma. In order to evaluate driving mechanism of these biological events, we collected, compared and analyzed a large number of published records. The results indicate that the carnivoran dispersal from Eurasia to North America at ∼ 20 Ma was probably caused by intense tectonic movements in Asia. During 13-11 Ma, global cooling possibly drove the mammal exchanges between Eurasia and North America. By comparison, the carnivoran dispersal from Eurasia to North America at 8-7 Ma was probably caused by the combination of global cooling and tectonic movements of the Tibetan Plateau. Similar to during 13-11 Ma, the carnivoran exchanges between Eurasia and North America at ∼ 4 Ma were possibly driven by global cooling.

  13. Lithostratigraphy of the Palaeogene – Lower Neogene succession of the Danish North Sea

    Directory of Open Access Journals (Sweden)

    Rasmussen, Jan A.

    2007-06-01

    Full Text Available As a result of a lithological, sedimentological and biostratigraphic study of well sections from the Danish sector of the North Sea, including some recently drilled exploration wells on the Ringkøbing–Fyn High, the lithostratigraphic framework for the siliciclastic Palaeogene to Lower Neogene sediments of the Danish sector of the North Sea is revised. The sediment package from the top of the Chalk Group to the base of the Nordland Group is subdivided into seven formations containing eleven new members. The existing Våle, Lista, Sele, Fur, Balder, Horda and Lark Formations of previously published lithostratigraphic schemes are adequate for a subdivision of the Danish sector at formation level. Bor is a new sandstone member of the Våle Formation. The Lista Formation is subdivided into three new mudstone members: Vile, Ve and Bue, and three new sandstone members: Tyr, Idun and Rind. Kolga is a new sandstone member of the Sele Formation. Hefring is a new sandstone member of the Horda Formation. Freja and Dufa are two new sandstone members of the Lark Formation. Danish reference sections are established for the formations, and the descriptions of their lithology, biostratigraphy, age and palaeoenvironmental setting are updated.

  14. Migration history of air-breathing fishes reveals Neogene atmospheric circulation patterns

    Science.gov (United States)

    Böhme, M.

    2004-05-01

    The migration history of an air-breathing fish group (Channidae; snakehead fishes) is used for reconstructing Neogene Eurasian precipitation and atmospheric circulation patterns. The study shows that snakeheads are sensitive indicators of summer precipitation maxima in subtropical and temperate regions, and are present regularly if the wettest month exceeds 150 mm precipitation and 20 °C mean temperature. The analysis of 515 fossil freshwater fish deposits of the past 50 m.y. from Africa and Eurasia shows two continental-scale migration events from the snakeheads' center of origin in the south Himalayan region, events that can be related to changes in the Northern Hemisphere circulation pattern. The first migration, ca. 17.5 Ma, into western and central Eurasia may have been caused by a northward shift of the Intertropical Convergence Zone that brought western Eurasia under the influence of trade winds that produced a zonal and meridional precipitation gradient in Europe. During the second migration, between 8 and 4 Ma, into Africa and East Asia, snakeheads reached their present-day distribution. This migration could have been related to the intensification of the Asian monsoon that brought summer precipitation to their migratory pathways in East Africa Arabia and East Asia.

  15. Neogene Tectonics And Paleomagnetism Of The Western And Eastern Of Palu Bay, Central Sulawesi, Indonesia

    Science.gov (United States)

    Muin, M. R.; Pramumijoyo, S.; Warmada, I. W.; Suryanto, W.

    2017-04-01

    Geologic observations and paleo magnetic studies of the western and eastern Palu Bay was undertaken, in order to study the extent of rotated areas and to develop constraints on tectonic models concerning the formation of this bay. Characteristic of remanent magentization (ChRM) results from Palu bay, the western show that; yield a pole at -39.116°N, 119.895°E with R=13.99, α95 =0,42, Dm/Im=61.76/-26.7 and the Eastern Palu bay show that; yield a pole at -81.855°N, 52.913°E, R=8.99, α95=0.29, Dm/Im =67.1/-5.42. The granitic rocks in these areas are dominated by granite and Monzonit-Quartz in composition, with high-K calc-alkaline photasik (KAP) and show metaluminous-peraluminous affinity. This suggests that the rotational motion on both sides of the bay are similar during the Neogen.

  16. The Neogene genus Streptochilus (Brönnimann and Resig, 1971) from the Gulf of California

    Science.gov (United States)

    Miranda Martínez, A.Y.; Carreño, A.L.; McDougall, Kristin

    2017-01-01

    Four species of the planktonic foraminiferal genus Streptochilus from key Neogene marine localities are documented in relation to the evolution of the Gulf of California: S. globigerus, S. latus, S. macdougallae sp. nov., and S. inglei sp. nov. Planktonic foraminiferal bioevents and strontium isotopes in the Bouse, Tirabuzón, Carmen and Ojo de Buey lithostratigraphic units constrain the local distribution range between 6 and 5.3 Ma for the last three species, whereas S. globigerus appears locally at 5.5 Ma and disappears between 3.79 and 3.46 Ma in the Imperial and Trinidad Formations. The last occurrence of Streptochilus latus, and the first and last occurrences of S. globigerus in the ancient Gulf of California are correlated with bioevents calibrated in the equatorial Pacific; therefore, they can be used as reliable local biostratigraphic markers. The presence of Streptochilus in the ancient Gulf of California seems to correlate with upwelling, in a pattern similar to that observed in the modern oceans.

  17. Late Neogene Mountain Building of Eastern Kunlun Orogen: Constrained by DEM Analysis

    Institute of Scientific and Technical Information of China (English)

    Wang An; Wang Guocan; Zhang Kexin; Xiang Shuyuan; Li Dewei; Liu Demin

    2009-01-01

    Topography, as a net result of the dynamic interaction between endogenesis and exogenesis, holds immense information on tectonic uplift, surface erosion and thus mountain building. The eastern Kunlun (昆仑) orogen, which experienced significant Late Neogene tectonic uplift and is located in an arid environment, is advantageous for morphotectonlc analysis based on well-preserved tectonic landforms. The digital elevation model (DEM) analysis was carried out for the central segment of the eastern Kunlun orogen based on shuttle radar topography mission (SRTM) data. River longitudinal profile analysis indicates that major rivers across the orogen are characterized by high river gradient indexes and intensive tectonic uplift. Differential uplift was also identified in swath-topography analysis in the studied area, which can be divided into three major tectonic-geomorphic units by orogenicstrike-parallel faults. It is indicated that the most active region is located to the south of the Xidatan (西大滩) fault with significant differential uplift. Another identified fault with differential uplift is the Middle Kuninn fault; however, the timing of which is suggested to be much older than that of the Xidatan fault. These analyses are eoneordantly supported by both field survey and studies of thermochronology, which in turn indicates that the DEM analysis bears great potential in morphotectonic analysis.

  18. Neogene marine isotopic evolution and the erosion of Lesser Himalayan strata: Implications for Cenozoic tectonic history

    Science.gov (United States)

    Myrow, Paul M.; Hughes, Nigel C.; Derry, Louis A.; Ryan McKenzie, N.; Jiang, Ganqing; Webb, A. Alexander G.; Banerjee, Dhiraj M.; Paulsen, Timothy S.; Singh, Birendra P.

    2015-05-01

    An extensive, northward deepening blanket of Neoproterozoic and Cambrian sedimentary rocks once extended from the Himalayan margin far onto the Indian craton. Cambrian deposits of this "upper Lesser Himalayan" succession, which include deposits of the "outer" Lesser Himalaya tectonic unit, are enriched in radiogenic 187Os. They make up part of a proximal marine facies belt that extends onto the craton and along strike from India to Pakistan. By contrast, age-equivalent facies in the Tethyan Himalaya are more distal in nature. Neoproterozoic to Cambrian strata of the upper Lesser Himalayan succession are now missing in much of the Lesser Himalaya, with their erosion exposing older Precambrian Lesser Himalayan strata. We suggest that exhumation and weathering of the upper Lesser Himalaya and related strata caused dramatic changes in the 187Os/188Os and 87Sr/86Sr Neogene record of seawater starting at ∼ 16 Ma. First-order estimates for the volume of upper Himalayan strata, as well as the volume of all LH rock eroded since this time, and geochemical box modeling, support this idea. Exhumation at 16 Ma is a fundamental event in the evolution of the Himalayan orogeny and the geochemical evolution of the oceans, and will be a critical part of the construction of future models of Himalayan thrust belt evolution.

  19. Neogene sedimentary evolution of Baja California in relation to regional tectonics

    Science.gov (United States)

    Helenes, J.; Carreño, A. L.

    1999-11-01

    During the Neogene, the tectonic and sedimentary evolution of the Baja California Peninsula followed four stages: (1) during the early Miocene (22 Ma), the initiation of transform motion between Pacific and North American plates, caused a rapid subsidence in the Continental Borderland Province and in some adjacent areas.This subsidence coincided in time with with a global rise in sea level. At this time, the eastern and southern parts of the peninsula did not show any evidence of subsidence. (2) During the middle Miocene (12 Ma), normal and strike slip faulting migrated eastward, causing subsidence in the northern part of the Gulf of California, where the oldest Tertiary marine sedimentary rocks were deposited. The areas in central Baja California Sur and the central part of the Gulf itself received abundant volcanic deposits related to continental extension. (3) During the late Miocene (8 Ma), the western margin of the Peninsula changed to a slightly compressive regime, while the northern part of the Gulf contained a marine basin with upper bathyal environments. The central area of the Gulf continued receiving abundant volcanic deposits, while the Los Cabos block received marine sedimentation, correlatable with sedimentary units reported from the continental margins in Nayarit, Jalisco and Michoacán. (4) Beginning in the early Pliocene (5 Ma), the present configuration of the Gulf of California developed through right-lateral strike slip and extension in the Gulf itself. Since Pliocene times, the Gulf presents widespread marine sedimentation with deep basins reaching lower bathyal depths.

  20. Paleomagnetic investigation of late Neogene vertical axis rotation and remagnetization in central coastal California

    Science.gov (United States)

    Horns, Daniel M.; Verosub, Kenneth L.

    1995-03-01

    Outcrops of shallow marine sedimentary rocks of the Neogene Purisima Formation and Santa Cruz Mudstone occur throughout the Santa Cruz Mountains and along the coast of Santa Cruz and San Mateo counties in California. Within the Santa Cruz Mountains, the Purisima Formation has been extensively folded and offset by reverse faults. Along the coast, the Purisima Formation and Santa Cruz Mudstone are only gently folded although the Purisima Formation is cut by the San Gregorio Fault Zone. Previous paleomagnetic studies have shown that vertical axis rotation has occurred within some parts of the San Gregorio Fault Zone. As part of a kinematic study of the San Gregorio Fault Zone, this paleomagnetic investigation of the Purisima Formation and Santa Cruz Mudstone was conducted to determine the extent of the vertical axis rotation. The characteristic paleomagnetic directions of the Purisima Formation and Santa Cruz Mudstone, which we interpret as the primary directions, indicate that a clockwise vertical axis rotation of 35 deg to 60 deg has occurred throughout the San Gregorio Zone, whereas no rotation has occurred away from the fault zone. This result suggests that vertical axis rotation is fundamentally related to shear across the San Gregorio Fault Zone. Our work also indicates that while the Purisima Formation and Santa Cruz Mudstone along the coast have retained their primary magnetizations, the Purisima Formation within the Santa Cruz Mountains has been remagnetized after folding.

  1. Neogene oxygen isotopic stratigraphy, ODP Site 1148,northern South China Sea

    Institute of Scientific and Technical Information of China (English)

    ZHAO; Quanhong

    2001-01-01

    paleoceanography in the southwest Pacific: Relating with East Antarctic ice sheet development, Paleaceanogr., 1995, 10(6): 1095-1112.[21]Pagani, M., Arthus, M. A., Freeman, K. H., Miocene evolution of atmospheric carbon dioxide, Paleoceanogr., 1999, 14(3):273-292.[22]Hodell, D. A., Woodruff, F., Variations in the strontium isotopic ratio of seawater during the Miocene: Stratigraphic and geochemical implications, Paleoceanogr., 1994, 9(3): 405-426.[23]Kennen, J. P., Marine Geology, Englewood: Prentice-Hall, Inc., 1982, 813. [24]Shackleton, N. J., Opdyke, N. D., Oxygen isotope and paleomagnetic stratigraphy of equatorial Pacific core V28-238:Oxygen isotope temperatures and ice volumes on a 106 year scale, Quat. Res., 1973, 3: 39-55.[25]Elmstrom, K. M., Kennett, P., Late Neogene paleoceanographic evolution of Site 590: Southwest Pacific, in Init Rep.DSDP (eds. Kennett, J. P., yon der Borch, C. C., Baker, P. A. et al.), 1983, 90(Part 2): 1361-1381.[26]Whitman, J. M., Berger, W. H., Pliocene-Pleistocene carbon isotope record, Site 586, Ontong Java Plateau, in Proc. ODP Sci. Res.(eds. Berger, W. H., Kroenke, L. W., Janecek, T. R. et al.), 1993, 130: 333-348.[27]Tiedemann, R., Sarnthein, M., Shackleton, N. J., Astronomic timescale for the Pliocene Atlantic δ 18O and dust flux re cords of Ocean Drilling Program site 659, Paleoceanogr., 1994, 9(4): 619-638.[28]Mix. A. C., Pisias, N. G., Rugh, W. et al., Benthic Foraminifera stable isotope record from Site 849 (0-5 Ma): Local and global climate changes, in Proc. ODP Sci. Res. (eds. Pisias, N. G., Mayer, L. A., Jenecek, T. R. et al.), 1995, 138: 371-412.[29]Tsuchi, R., Neogene events in Japan and the Pacific, in Pacific Neogene Event Studies (ed. Tsuchi, R.), Shizuoka: Kuro fune Printing Co. Ltd., 1987, 102-104.[30]Tsuchi, R., Neogene Events in Japan and Southeast Asia, in Annual Technical Meeting 1989 and IGCP-246, Proceedings,Thailand: Chiang Mai Univ., 1991, 169-177[31]Barron, J. A., Baldauf, J

  2. Chemical and Isotope Compositions of Neogene Hippopotamidae Teeth From Lake Albert (Uganda): Implications for Environmental Change

    Science.gov (United States)

    Brugmann, G. E.; Brachert, T. C.; Ssemmanda, I.; Mertz, D. F.

    2008-12-01

    The Neogene was a period of long-term global cooling and increasing climatic variability on astronomical time scales. Lake systems strongly depend on rainfall patterns and size or geographical distribution of river networks. To unravel environmental change and watershed dynamics in the western branch of the East African Rift (Lake Albert, Uganda) during the Late Neogene, we use proxy data (trace elements, O, C and Sr isotopes) from Hippopotamidae teeth. Laser ablation ICPMS profiles in enamel measured from the outside rim towards the dentin show an asymmetric trace element distribution in that the concentrations continuously decrease by up to 5 orders of magnitude within a distance of about 1 mm until a minimum is reached (migration pathways and palaeoenvironmental changes. On geological time scales δ13C compositions reflect a transition from pure C3 browsers (-11 per mil PDB) at 5 to 6 Ma towards C4 dominated grazers (0 per mil PDB) at 2.0 to 2.5 Ma. The oxygen stable isotope (δ18O) composition of enamel rises from 26 per mil at 5 to 6 Ma to a maximum of 32 per mil SMOW at 2.3 Ma. Increasing δ18O values suggest enhanced evaporation of the lake due to rising aridity. This is in agreement with a synchronous spread of C4 vegetation in the reach of Hippopotamid populations. The Sr isotopic composition of enamel displays a large variation and 87Sr/86Sr is 0.714 about 5 Ma ago, reaches a maximum of 0.717 at about 2.3 Ma and decreases from there on to about 0.708. Thus, Sr and O isotopic compositions correlate with each other on the geological time scale. This is plausible if the Sr isotopic composition of Hippopotamid enamel dominantly reflects the changes of the water chemistry of the lake, and is therefore a powerful tool for tracing ancient hydrological networks. The large variation of the Sr isotope composition can be explained if the lake is fed by different sources: water draining Cenozoic volcanic terrains have low 87Sr/86Sr (~ 0.704), whereas Proterozoic

  3. Delineating shallow Neogene deformation structures in northeastern Pará State using Ground Penetrating Radar

    Directory of Open Access Journals (Sweden)

    Dilce F. Rossetti

    2003-06-01

    Full Text Available The geological characterization of shallow subsurface Neogene deposits in northeastern Pará State using Ground Penetrating Radar (GPR revealed normal and reverse faults, as well as folds, not yet well documented by field studies. The faults are identified mostly by steeply-dipping reflections that sharply cut the nearby reflections causing bed offsets, drags and rollovers. The folds are recognized by reflections that are highly undulating, configuring broad concave and convex-up features that are up to 50 m wide and 80 to 90 ns deep. These deformation structures are mostly developed within deposits of Miocene age, though some of the faults might continue into younger deposits as well. Although the studied GPR sections show several diffractions caused by trees, differential degrees of moisture, and underground artifacts, the structures recorded here can not be explained by any of these ''noises''. The detailed analysis of the GPR sections reveals that they are attributed to bed distortion caused by brittle deformation and folding. The record of faults and folds are not widespread in the Neogene deposits of the Bragantina area. These GPR data are in agreement with structural models, which have proposed a complex evolution including strike-slip motion for this area from the Miocene to present.A caracterização geológica de depósitos neógenos ocorrentes em sub-superfície rasa no nordeste do Estado do Pará, usando Radar de Penetração no Solo (GPR, revelou a presença de falhas normais e reversas, bem como dobras, ainda não documentadas em estudos de campo prévios. As falhas são identificadas por reflexões inclinadas que cortam bruscamente reflexões vizinhas, causando freqüentes deslocamentos de camadas. As dobras são reconhecidas por reflexões fortemente ondulantes, configurando feições côncavas e convexas que medem até 50 m de amplitude e 80 a 90 m de profundidade. Estas estruturas deformacionais desenvolvem-se, principalmente

  4. Seismic architecture and morphology of Neogenic sediment waves and drifts, offshore West Africa

    Science.gov (United States)

    Baglioni, Luca; Bonamini, Enrico

    2013-04-01

    The three dimension visualisation softwares of seismic data and the recent development of semi-automatic interpretation tools allow to define the 3D morphology of ancient depositional systems at a resolution never achieved before. This study analyses a Neogenic stratigraphic interval in the deep water of the West African margin. The purpose of the work is the understanding of the sedimentary architectures and the link with the genetic depositional processes. The study is mainly based on the interpretation of seismic geometries and amplitude/isochron maps derived from newly-interpreted seismic horizons. The seismic stratigraphy reveals abrupt changes in depositional styles and sedimentary processes. Transitions between Sediment Drifts (SD), Sediment Waves (SWs) and Mass Transport Complexes (MTCs) are here frequently observed, suggesting that cyclically either bottom-current intensity decreased or gravity-flow input overwhelmed the bottom-current signal. The lower studied interval corresponds to a SD sequence, made up of stacked individual packages and having a maximum thickness of 300 ms. The landward drift morphology is characterized by convex-upward, mounded seismic reflections. Each drift onlaps on a seaward-dipping reflection interpreted as paleo-slope. These contouritic deposits are concentrated near the base of slope, and fade out downdip. The drift appears to be grown from the deeper part of the basin and backstepped up the slope. It is inferred that the deposition of the drifts took place under the influence of a marine current, subparallel to the southern margin of West African coast. The backstepping of the onlapping architecture may have resulted from bottom current acceleration across the ramp. The intermediate studied interval represents a transitional sequence in which SW are alternated with MTDs of minor size (up to 60 ms thick). In this transition interval, onlap relationships and thickness variations suggest that gravity flow deposits preferentially

  5. Neogene and Quaternary history of vegetation, climate, and plant diversity in Amazonia

    Science.gov (United States)

    van der Hammen, Thomas; Hooghiemstra, Henry

    2000-04-01

    The neotropical Amazonian and Andean plant diversity developed mainly during the Tertiary. In Amazonia, Miocene floral diversity seems considerably higher than today. During the Neogene, tropical taxa entered newly created montane area, and montane taxa entered the tropical lowlands. The general decrease of temperature during the upper Neogene and especially during the Quaternary glacial periods may have caused considerable extinctions in the lowlands. Representation of pollen of apparently principally montane taxa ( Podocarpus, Hedyosmum) in Miocene, Pliocene, and Quaternary sediments of Amazonia and surroundings, is still difficult to interpret in terms of temperature decrease at low elevation. Changes in precipitation may have profound impact on the composition of vegetation communities; Ilex and Melastomataceae increase significantly in many glacial pollen records. Increase of Weinmannia in Amazonian pollen records seems the best indicator of downward migration of montane vegetation belts. A temperature lowering at sea-level of 4.5 ±1°C during the Last Glacial Maximum (LGM) seems reasonable; it may have caused a downslope migration of some 700 m of the lower montane vegetation belt; lower montane arboreal species may have been able to grow in higher elevation areas (>500 m) of Amazonia, increasing background pollen values of montane taxa in the area. Difference between a cool and wet Middle Pleniglacial (60-28 ka BP), and a cold and dry Upper Pleniglacial (28-14 ka BP; thus including the LGM) is evident in Andean and Amazonian records; statements about environmental conditions of the ice-age Amazon should be specified chronologically. The Middle Pleniglacial is a time of accumulation of fluvial sediments. The Upper Pleniglacial is a time of incision of the rivers in their sediments; sedimentation started again in the Lateglacial (since ca. 13 ka BP) and the Holocene, when lake levels rose again. Based on simplified considerations of precipitation changes and

  6. Neogene Uplift and Exhumation of Plutonic Bodies in the Beni Bou Ifrour Massif (Nador, northeastern Morocco)

    Science.gov (United States)

    Lebret, Noëmie; Jolivet, Laurent; Branquet, Yannick; Bourdier, Jean-Louis; Jolivet, Marc; Marcoux, Eric

    2013-04-01

    In Neogene times, the whole Mediterranean Sea was the center of an intense magmatic activity. This post-collisional magmatism produced a large amount of volcanic edifices through the Alpine belts, together with some intrusives. These plutonic bodies can be associated with skarn-type mineralization, well-known in Elba Island or Serifos Island (Cyclades), where they are generally exhumed by detachment faults. In Morocco, the plutons hosted by the Beni Bou Ifrour massif are connected to the biggest skarn-type iron concentrations of the country (production > 60 Mt, reserves ≈ 25 Mt). The purpose of this work is to explain the late uplift of this massif and subsequent exhumation of the intrusives. As a final product of the Africa-Eurasia plate convergence since ca. 70 Ma, the Rif Mountains constitute the westernmost segment of the Mediterranean Alpine belts. In the oriental part of this range, volcanic summits and Paleozoic to Mesozoic massifs outcrop in the surrounding Mio-Pliocene plains. The Beni Bou Ifrour massif, in the Nador province, consists in a dome-shaped folded Mesozoic series (Domerian to Barremian) affected by a slight epizonal regional metamorphism (ca. 14-12 Ma), dislocated by Neogene NE-SW faults and eventually sealed by upper Miocene transgressive sediments. The hosted intrusives (7.58 ± 0.03 Ma; Duggen et al., 2005) are the plutonic equivalents to the potassic calc-alkaline lavas (andesites mainly) from the surrounding "satellite" volcanic massifs. They turn out to stand in higher topographic position than the younger shoshonitic lavas of the neighboring Gourougou stratovolcano (6.12 ± 0.01 Ma; Duggen et al., 2005). Previous studies have attributed this uplift to the action of normal faults (pull-apart basins; Guillemin & Houzay, 1982), thrusting (Kerchaoui, 1985; 1995) or even of a caldeira resurgence (El Bakkali, 1995). To discriminate against those exhumation mechanisms, field work has been performed, coming along with new cross-sections to

  7. Analysis of Neogene deformation between Beaver, Utah and Barstow, California: Suggestions for altering the extensional paradigm

    Science.gov (United States)

    Anderson, R. Ernest; Beard, Sue; Mankinen, Edward A.; Hillhouse, John W.

    2013-01-01

    For more than two decades, the paradigm of large-magnitude (~250 km), northwest-directed (~N70°W) Neogene extensional lengthening between the Colorado Plateau and Sierra Nevada at the approximate latitude of Las Vegas has remained largely unchallenged, as has the notion that the strain integrates with coeval strains in adjacent regions and with plate-boundary strain. The paradigm depends on poorly constrained interconnectedness of extreme-case lengthening estimated at scattered localities within the region. Here we evaluate the soundness of the inferred strain interconnectedness over an area reaching 600 km southwest from Beaver, Utah, to Barstow, California, and conclude that lengthening is overestimated in most areas and, even if the estimates are valid, lengthening is not interconnected in a way that allows for published versions of province-wide summations.We summarize Neogene strike slip in 13 areas distributed from central Utah to Lake Mead. In general, left-sense shear and associated structures define a broad zone of translation approximately parallel to the eastern boundary of the Basin and Range against the Colorado Plateau, a zone we refer to as the Hingeline shear zone. Areas of steep-axis rotation (ranging to 2500 km2) record N-S shortening rather than unevenly distributed lengthening. In most cases, the rotational shortening and extension-parallel folds and thrusts are coupled to, or absorb, strike slip, thus providing valuable insight into how the discontinuous strike-slip faults are simply parts of a broad zone of continuous strain. The discontinuous nature of strike slip and the complex mixture of extensional, contractional, and steep-axis rotational structures in the Hingeline shear zone are similar to those in the Walker Lane belt in the west part of the Basin and Range, and, together, the two record southward displacement of the central and northern Basin and Range relative to the adjacent Colorado Plateau. Understanding this province

  8. Tectonostratigraphic history of the Neogene Maimará basin, Northwest Argentina

    Science.gov (United States)

    Galli, Claudia I.; Coira, Beatriz L.; Alonso, Ricardo N.; Iglesia Llanos, María P.; Prezzi, Claudia B.; Kay, Suzanne Mahlburg

    2016-12-01

    This paper presents the tectonostratigraphic evolution of the Maimará Basin and explores the relationship between the clastic sediments and pyroclastic deposits in the basin and the evolution of the adjacent orogeny and magmatic arc. The sedimentary facies in this part of the basin include, in ascending order, an ephemeral fluvial system, a deep braided fluvial system and a medial to distal ephemeral fluvial system. We interpret that Maimará Formation accumulated in a basin that has developed two stages of accumulation. Stage 1 extended from 7 to 6.4 Ma and included accelerated tectonic uplift in the source areas, and it corresponds to the ephemeral fluvial system deposits. Stage 2, which extended from 6.4 to 4.8 Ma, corresponds to a tectonically quiescent period and included the development of the deep braided fluvial system deposits. The contact between the Maimará and Tilcara formations is always characterized by a regional unconformity and, in the study area, also shows pronounced erosion. Rare earth element and other chemical characteristics of the tuff intervals in the Maimará Formation fall into two distinct groups suggesting the tuffs were erupted from two distinct late Miocene source regions. The first and most abundant group has characteristics that best match tuffs erupted from the Guacha, Pacana and Pastos Grandes calderas, which are located 200 and 230 km west of the study area at 22º-23º30‧S latitude. The members the second group are chemically most similar to the Merihuaca Ignimbrite from the Cerro Galán caldera 290 km south-southwest of the studied section. The distinctive geochemical characteristics are excellent tools to reconstruct the stratigraphic evolution of the Neogene Maimará basin from 6.4 to 4.8 Ma.

  9. Paleogene and Early Neogene Lacustrine Reefs in the Western Qaidam Basin, China

    Institute of Scientific and Technical Information of China (English)

    ZHONG Jianhua; WEN Zhifeng; GUO Zeqing; WANG Haiqiao; GAO Jianbo

    2004-01-01

    Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef and thrombolite reef with distinct reef structures, fore-reef, back-reef and reef-plateau. The fore-reef is characterized by a combination of pinnacle reef, thrombolite and algal reef. The back reef is composed of stromatolite reef and algal reef. The pinnacle reefs (micro-atoll), most of which are several tens of centimeters in diameter (whereas some exceptionally big ones are over 200 cm in diameter), and several tens of centimeter to 2 m in height, are situated on the far front-edge of the reef; the pinnacle reef is also often of recumbent form with a gravel-filled circular hole in the center. The algal reef is in the form of dome and irregular beds, and filled with algal detritus, ostracodes, spirorbis fossils, ooid and terrigenous debris, and worm traces;cavities and scour marks are often developed. The algal reef is gray commonly when fresh and weathers to a brown color.The lacustrine thrombolite in the Qaidam Basin is light gray or deep gray when fresh, white-gray or brown when weathered, dense and homogeneous with abundant pores filled by oil and bitumen. Observed under the microscope, the thrombolite consists mainly of brown or brown-black clots with a little algal debris, ooid, pellet, ostracodes, spirorbis fossils and terrigenous debris, in some cases, terrigenous debris, even gravel, is abundant. Many features of the thrombolite suggest that it is formed in a high-energy environment. The stromatolite reefs developed on the lacustrine algal reef in the Qaldam Basin are very complex whether in shape or in internal structure. The simplest ones form laminated layers and the most complex ones have intensely branching structures. The size is also variable.

  10. Dated Plant Phylogenies Resolve Neogene Climate and Landscape Evolution in the Cape Floristic Region.

    Science.gov (United States)

    Hoffmann, Vera; Verboom, G Anthony; Cotterill, Fenton P D

    2015-01-01

    In the context of molecularly-dated phylogenies, inferences informed by ancestral habitat reconstruction can yield valuable insights into the origins of biomes, palaeoenvironments and landforms. In this paper, we use dated phylogenies of 12 plant clades from the Cape Floristic Region (CFR) in southern Africa to test hypotheses of Neogene climatic and geomorphic evolution. Our combined dataset for the CFR strengthens and refines previous palaeoenvironmental reconstructions based on a sparse, mostly offshore fossil record. Our reconstructions show remarkable consistency across all 12 clades with regard to both the types of environments identified as ancestral, and the timing of shifts to alternative conditions. They reveal that Early Miocene land surfaces of the CFR were wetter than at present and were dominated by quartzitic substrata. These conditions continue to characterize the higher-elevation settings of the Cape Fold Belt, where they have fostered the persistence of ancient fynbos lineages. The Middle Miocene (13-17 Ma) saw the development of perennial to weakly-seasonal arid conditions, with the strongly seasonal rainfall regime of the west coast arising ~6.5-8 Ma. Although the Late Miocene may have seen some exposure of the underlying shale substrata, the present-day substrate diversity of the CFR lowlands was shaped by Pliocene-Pleistocene events. Particularly important was renewed erosion, following the post-African II uplift episode, and the reworking of sediments on the coastal platform as a consequence of marine transgressions and tectonic uplift. These changes facilitated adaptive radiations in some, but not all, lineages studied.

  11. Stratigraphy of the Neogene Sahabi units in the Sirt Basin, northeast Libya

    Science.gov (United States)

    El-Shawaihdi, M. H.; Mozley, P. S.; Boaz, N. T.; Salloum, F.; Pavlakis, P.; Muftah, A.; Triantaphyllou, M.

    2016-06-01

    A revision of the nomenclature of lithostratigraphic units of Neogene strata at As Sahabi, northeast Libya, is presented, based on new fieldwork conducted during 2006-2008. The Sahabi units are correlated across the Ajdabya Sheet (NH 34-6) in northeastern Libya. Major conclusions are: (1) Miocene (Langhian through Messinian) strata are predominantly carbonate and should be referred to as formation "M"; (2) A local unconformity of Miocene (early Messinian) age overlies strata of the formation "M"; (3) This unconformity is overlain by Messinian gypsiferous sand and mud (formerly formation "P" and partially member "T"), which are designated as the "lower member" (gypsiferous) of the Sahabi Formation; (4) The "lower member" is overlain by sand and mud of late Messinian age (formerly partially member "T" and members "U1", "UD", and "U2") in a generally fining-upwards sequence, and are designated as the "upper member" (non-gypsiferous) of the Sahabi Formation; (5) The latest Miocene sand and mud of the "upper member" are capped by an unconformity that is correlated with the regression and desiccation of the Mediterranean Sea during the Messinian Salinity Crisis and with Eosahabi Channel cutting; (6) The unconformity is overlain by Pliocene medium, coarse, and pebbly sands, which are referred to as the Qarat Weddah Formation (formerly Garet Uedda Formation); (7) The Pliocene sands of Qarat Weddah Formation are overlain by carbonate soil (calcrete) of Late Pliocene age, which is referred to as formation "Z" (formerly member "Z"). The major outcome of this study is a revised stratigraphic description and nomenclature of the Sahabi units that helps to provide a formal and unified context for understanding paleontological discoveries in northeastern Libya, which will serve to facilitate a broader correlation of the Sahabi units with their equivalents elsewhere in Africa and in Europe and Asia.

  12. Magnetostratigraphy of the late Neogene purisima formation, Santa Cruz County, California

    Science.gov (United States)

    Madrid, Victor M.; Stuart, Robert M.; Verosub, Kenneth L.

    1986-09-01

    The magnetic polarity zonation of a late Neogene sedimentary sequence in Santa Cruz County, California, has provided a chronologic framework for studies of the sedimentologic and tectonic processes involved in an episode of basin formation in the vicinity of the San Andreas fault system in central coastal California. The zonation is based on the analysis of samples from 79 horizons in a 300 m thick section of the Purisima Formation and a portion of the overlying Aromas Formation. Although rock magnetic studies support the hypothesis that the primary carrier of the remanence is magnetite, many samples contain a secondary overprint which cannot be completely removed by alternating field demagnetization. Nevertheless, systematic analysis of the behavior of the samples during demagnetization has led to an unambiguous determination of the polarity of each horizon and to the development of a magnetic polarity zonation containing thirteen magnetozones. These magnetozones can be correlated to the magnetic polarity time scale using biostratigraphic constraints provided by diatoms in the lower portion of the section and invertebrates and vertebrates in the upper portion. The studied section is found to span the interval from the Epoch 5/Epoch 6 boundary (6.07 Mya) to the Matuyama/Gauss boundary (2.47 Mya) with a hiatus corresponding to the upper part of the Gilbert epoch (4.5 Mya to 3.5 Mya). This hiatus does not coincide with major regressions in the global sea-level curve and is interpreted as a period of tectonic uplift. The compression which generated this uplift was probably caused by interplay between the San Andreas fault east of the study area and the San Gregorio-Hosgri fault west of it.

  13. Impact of tectonic and volcanism on the Neogene evolution of isolated carbonate platforms (SW Indian Ocean)

    Science.gov (United States)

    Courgeon, S.; Jorry, S. J.; Jouet, G.; Camoin, G.; BouDagher-Fadel, M. K.; Bachèlery, P.; Caline, B.; Boichard, R.; Révillon, S.; Thomas, Y.; Thereau, E.; Guérin, C.

    2017-06-01

    Understanding the impact of tectonic activity and volcanism on long-term (i.e. millions years) evolution of shallow-water carbonate platforms represents a major issue for both industrial and academic perspectives. The southern central Mozambique Channel is characterized by a 100 km-long volcanic ridge hosting two guyots (the Hall and Jaguar banks) and a modern atoll (Bassas da India) fringed by a large terrace. Dredge sampling, geophysical acquisitions and submarines videos carried out during recent oceanographic cruises revealed that submarine flat-top seamounts correspond to karstified and drowned shallow-water carbonate platforms largely covered by volcanic material and structured by a dense network of normal faults. Microfacies and well-constrained stratigraphic data indicate that these carbonate platforms developed in shallow-water tropical environments during Miocene times and were characterized by biological assemblages dominated by corals, larger benthic foraminifera, red and green algae. The drowning of these isolated carbonate platforms is revealed by the deposition of outer shelf sediments during the Early Pliocene and seems closely linked to (1) volcanic activity typified by the establishment of wide lava flow complexes, and (2) to extensional tectonic deformation associated with high-offset normal faults dividing the flat-top seamounts into distinctive structural blocks. Explosive volcanic activity also affected platform carbonates and was responsible for the formation of crater(s) and the deposition of tuff layers including carbonate fragments. Shallow-water carbonate sedimentation resumed during Late Neogene time with the colonization of topographic highs inherited from tectonic deformation and volcanic accretion. Latest carbonate developments ultimately led to the formation of the Bassas da India modern atoll. The geological history of isolated carbonate platforms from the southern Mozambique Channel represents a new case illustrating the major

  14. Neogene reef coral assemblages of the Bocas del Toro region, Panama: the rise of Acropora palmata

    Science.gov (United States)

    Klaus, J. S.; McNeill, D. F.; Budd, A. F.; Coates, A. G.

    2012-03-01

    Temporal patterns are evaluated in Neogene reef coral assemblages from the Bocas del Toro Basin of Panama in order to understand how reef ecosystems respond to long-term environmental change. Analyses are based on a total of 1,702 zooxanthellate coral specimens collected from six coral-bearing units ranging in age from the earliest Late Miocene to the Early Pleistocene: (1) Valiente Formation (12-11 Ma), (2) Fish Hole Member of the Old Bank Formation (5.8-5.6 Ma), (3) La Gruta Member of the Isla Colon Formation (2.2-1.4 Ma), (4) Ground Creek Member of the Isla Colon Formation (2.2-1.4 Ma), (5) Mimitimbi Member of the Urracá Formation (1.2-0.8 Ma), and (6) Hill Point Member of the Urracá Formation (1.2-0.8 Ma). Over 100 coral species occur in the six units, with faunal assemblages ranging from less than 10% extant taxa (Valiente Formation) to over 85% extant taxa (Ground Creek Member). The collections provide new temporal constraints on the emergence of modern Caribbean reefs, with the La Gruta Member containing the earliest occurrence of large monospecific stands of the dominant Caribbean reef coral Acropora palmata, and the Urracá Formation containing the last fossil occurrences of 15 regionally extinct taxa. Canonical correspondence analysis of 41 Late Miocene to Recent reef coral assemblages from the Caribbean region suggests changes in community structure coincident with effective oceanic closure of the Central American Seaway (~3.5 Ma). These changes, including increased Acropora dominance, may have contributed to a protracted period of elevated extinction debt prior to the major peak in regional coral extinctions (~2-1 Ma).

  15. Dated Plant Phylogenies Resolve Neogene Climate and Landscape Evolution in the Cape Floristic Region.

    Directory of Open Access Journals (Sweden)

    Vera Hoffmann

    Full Text Available In the context of molecularly-dated phylogenies, inferences informed by ancestral habitat reconstruction can yield valuable insights into the origins of biomes, palaeoenvironments and landforms. In this paper, we use dated phylogenies of 12 plant clades from the Cape Floristic Region (CFR in southern Africa to test hypotheses of Neogene climatic and geomorphic evolution. Our combined dataset for the CFR strengthens and refines previous palaeoenvironmental reconstructions based on a sparse, mostly offshore fossil record. Our reconstructions show remarkable consistency across all 12 clades with regard to both the types of environments identified as ancestral, and the timing of shifts to alternative conditions. They reveal that Early Miocene land surfaces of the CFR were wetter than at present and were dominated by quartzitic substrata. These conditions continue to characterize the higher-elevation settings of the Cape Fold Belt, where they have fostered the persistence of ancient fynbos lineages. The Middle Miocene (13-17 Ma saw the development of perennial to weakly-seasonal arid conditions, with the strongly seasonal rainfall regime of the west coast arising ~6.5-8 Ma. Although the Late Miocene may have seen some exposure of the underlying shale substrata, the present-day substrate diversity of the CFR lowlands was shaped by Pliocene-Pleistocene events. Particularly important was renewed erosion, following the post-African II uplift episode, and the reworking of sediments on the coastal platform as a consequence of marine transgressions and tectonic uplift. These changes facilitated adaptive radiations in some, but not all, lineages studied.

  16. A Neogene seawater sulfur isotope age curve from calcareous pelagic microfossils

    Science.gov (United States)

    Burdett, James W.; Arthur, Michael A.; Richardson, Mark

    1989-09-01

    Until now, our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites. Owing to the sporadic occurrence of evaporites through time, the secular sulfur isotope age curve contains many gaps with little or no data. In order to fill in some of these gaps, particularly the Neogene, we have analyzed the sulfur isotopic composition of carbonate-associated sulfate in carbonate tests of planktonic foraminifera. Other investigators have shown that sulfate may occur in biogenic calcites either lattice-bound, as micro-fluid inclusions, in adsorbed phases, or as protein polysaccharides. Whatever the origin, the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived, as shown by results on recent calcareous foraminifera and macrofossils. Using this approach for study of Miocene to Recent pelagic marine sediments supplemented by new data for Miocene marine evaporites from the Gulf of Suez, we have found that the δ 34S of seawater has decreased about 2.5‰ over the past 25 m.y. and that most of the decrease has occurred over the past 5 m.y., parallelling a decrease in the δ 13C of dissolved oceanic bicarbonate from the same interval. Sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m.y. Alternatively, an increase in weathering rates over the past 5 m.y. would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species. In either case, the net result would be a decrease in atmospheric p O 2.

  17. Extended stratigraphy, palynology and depositional environments record the initiation of the Himalayan Gyirong Basin (Neogene China)

    Science.gov (United States)

    Xu, Ya-Dong; Zhang, Ke-Xin; Wang, Guo-Can; Jiang, Shang-Song; Chen, Fen-Ning; Xiang, Shu-Yuan; Dupont-Nivet, Guillaume; Hoorn, Carina

    2012-01-01

    Here we report new sedimentological and paleontological data from a 603.5 m thick Neogene sequence (Woma section) in the Gyirong Basin, a basin induced by east-west extension in the Himalayas of southern Tibet. We document the conglomeratic Danzengzhukang Formation, at the base of the section, and the overlying finer grained Woma Formation that includes a Hipparion fauna. Based on stratigraphic correlations and earlier thermochronology and magnetostratigraphic results, we bracket the depositional age of this section between 10.8 Ma and 1.7 Ma. Lithology, paleo-current directions and provenance analysis, together with palynological and paleontological data, have revealed three depositional environments for the deposition of the studied section. (1) Alluvial-fan to braided river environments with ESE transport directions (Danzengzhukang Formation, coniferous- and broad-leaved mixed forest. (2) Lacustrine dominated conditions (Lower Woma Formation, ˜7.2 to 3.2 Ma) with WSW transport directions were associated with locally warm and humid environments in the low-lying areas while input from a new source area suggests the presence of a high-altitude, cold and arid deciduous coniferous-leaved forests. (3) A fan delta dominated environment (Upper Woma Formation, 3.2 to >1.7 Ma) with increased denudation and WSW paleo-currents was associated with a deciduous coniferous and broad-leaved mixed forest that suggests an increase in climate variability. Our data indicate that the Gyirong Basin was under overall warm and humid conditions throughout most of its history, in agreement with high-resolution oxygen and carbon isotope data collected from the same section (this issue). We interpret our warm climate in the Gyirong Basin to reflect the prevalence of the monsoonal influence and the distal pollen sources to result from orographic effects.

  18. Gastropoda-Bivalvia Fauna And Neogene-Quaternary Stratigraphy of the Southwest of Dardanelles (Çanakkale-NWAnatolia)

    Science.gov (United States)

    Kapan, Sevinç; Kabasakal, Sinem

    2016-04-01

    Gastropoda-Bivalvia Fauna And Neogene-Quaternary Stratigraphy of the Southwest of Dardanelles (Çanakkale-NWAnatolia) Sevinç KAPAN, Sinem KABASAKAL, Çanakkale Onsekiz Mart University, Engineering Faculty, Geological Engineering Department sevinckapan_yesilyurt@hotmail.com In this study, paleontology and stratigraphy of Neogene and Quaternary units around south of the Dardanelles have been examined using Gastropoda and Bivalvia fauna. In the investigation area, the base of the sediments that belongs to Neogene, consist of the volcanics which are formed with basalts, andesites and tuff. Neogene begins unconformity with basal conglomerate which are formed with basalt and tuff gravels. The measurable thickness of the Neogene sediments is approximately 200meters in total. First fossiliferius level which consist of Lymnocardium (Euxinicardium) nobile Sabba has showed similarities with the Pontian (Late Miocene) fauna of the Eastern Paratethys. The existence of Melanopsis and Psidium species indicate that the basin has been brackish water feeding by fresh water in the Early Pliocene. Theodoxus fluviatilis (Linne), Theodoxus (Calvertia) aff. imbricata Brusina, Theodoxus (Calvertia) licherdopoli scriptus (Stefanescu), Viviparus mammatus (Stefanescu), Valvata (Valavata) sulekiana Brusina, Valvata (Cincinna) crusitensis Fontannes, Hydrobia cf grandis Cobalcescu, Hydrobia ventrosa Monfort, Melanopsis (Melanopsis) cf. bergeroni Stefanescu, , Melanopsis (Melanopsis) sandbergeri rumana Tournouer, Melanopsis (Canthidomus) hybostoma anili Taner, Melanopsis (Canthidomus) hybostoma amaradica Fontannes, Melanopsis (Canthidomus) lanceolata Neumayr, Amphimelania fossariformis (Tournouer), Melanoides tuberculata monolithica (Bukowski), Radix (Radix) peregra (Müller), Planorbarius thiollierei (Michaud), Potamida (Potamida) craiovensis craiovensis (Tournouer), Potamida (Potamida) berbestiensis (Fontannes), Unio pristinus davilai Porumbaru, Unio subexquisitus Jatzko, Anadonta zmaji

  19. Late Neogene-Recent uplift of the Cabo de Gata volcanic province, Almerı´a, SE Spain

    Science.gov (United States)

    Martín, José M.; Braga, Juan C.; Betzler, Christian

    2003-02-01

    Cabo de Gata is a Miocene volcanic province in the Betic Cordillera in southeastern Spain. The distribution of coastal deposits in the successive marine sedimentary units overlying the last volcanic episode (about 7.5 Ma old) has been used to reconstruct the post-volcanic palaeogeographic evolution of the region during the Late Neogene. The current elevation of well-dated shoreline marker rocks has been used to estimate uplift amount and rates. Since the late Tortonian, a N45°E-aligned (the strike of the Carboneras fault system) topographic relief was emergent in the Cabo de Gata region. The extension and height of this island increased throughout the late Neogene. Smaller, independent islands were emergent and finally became connected to the main island during the Messinian. The Carboneras and Agua Amarga Pliocene sub-basins were the last two marine basins prior to the final emergence of the region. Since the last volcanic eruption (ca. 7.5 Ma), maximum uplift of sedimentary rocks in Cabo de Gata has taken place on the western margin of the N45°E-aligned palaeorelief. The altitude of the shoreline marker rocks in the successive sedimentary units decreases eastwards to the present-day coast and northwards of the Rambla del Plomo. Uplift rates since deposition remain nearly constant for the successive Messinian rocks and decrease slightly for the lower Pliocene outcrops. Most of the uplift took place before the Pliocene while the main island enlarged. Uplift amounts and rates since deposition of the upper Neogene sedimentary units in the Cabo de Gata area are similar to the ones estimated for laterally equivalent units in the eastern Betic basins (approximately 50 m/Ma). Despite its volcanic nature and the occurrence of the Carboneras fault system, the Cabo de Gata probably became elevated as a consequence of regional uplift in connection with the rest of the Betic Cordillera.

  20. The Progreso Basin Province of Northwestern Peru and Southwestern Ecuador: Neogene and Cretaceous-Paleogene Total Petroleum Systems

    Science.gov (United States)

    Higley, Debra K.

    2004-01-01

    The Progreso Basin province (6083) in northwestern Peru and southwestern Ecuador consists of the Paleogene Santa Elena block and Peru Bank, and the Neogene Tumbes-Progreso subbasin. The Santa Elena block and Peru Bank are part of the Cretaceous-Paleogene Total Petroleum System (TPS)(608302), which contains the Cretaceous-Paleogene Santa Elena Block Assessment Unit (60830201). The Tumbes- Progreso subbasin includes the Neogene TPS (608301) and associated Neogene Pull-Apart Basin Assessment Unit (60830101). The complex tectonic history of the Progreso Basin province influenced depositional and erosional patterns across the region, and also the location, timing, and types of seals, traps, possible source and reservoir rocks, and hydrocarbon generation and migration. Marine shales that are interbedded with and overlie reservoir intervals are the probable hydrocarbon source rocks. Timing of hydrocarbon generation and migration was probably Miocene and younger, following creation of the Tumbes-Progreso subbasin by movement along the Dolores-Guayaquil megashear. More than 220 million barrels of oil (MMBO) and 255 billion cubic feet of gas (BCFG) have been produced from the Progreso Basin province. The means of estimated recoverable oil, gas, and natural gas liquids (NGL) resources from undiscovered fields in the province are 237 MMBO, 695 BCFG, and 32 MMB NGL, respectively. The means of estimated recoverable oil, gas, and NGL resources from undiscovered onshore fields are 45 MMBO, 113 BCFG, and 5 MMBNGL, and from undiscovered offshore fields are 192 BBO, 582 BCFG, and 27 MMBNGL. These are USGS grown undiscovered resources that were determined by using a minimum field size of 1 million barrels of oil equivalent.

  1. New allocyclic dimensions in a prograding carbonate bank: Evidence for eustatic, tectonic, and paleoceanographic control (late Neogene, Bahamas)

    Science.gov (United States)

    Lidz, B.H.; McNeill, D.F.

    1997-01-01

    The deep-sea record, examined recently for the first time in a shallow-depocenter setting, has unveiled remarkable evidence for new sedimentary components and allocyclic complexity in a large, well-studied carbonate bank, the western Great Bahama Bank. The evidence is a composite foraminiferal signature - Paleocene to early Miocene (allogenic or reworked) and late Miocene to late Pliocene (host) planktic taxa, and redeposited middle Miocene shallow benthic faunas. Ages of the oldest and youngest planktic groups range from ??? 66 to ??? 2 Ma. The reworked and redeposited taxa are a proxy for significant sediment components that otherwise have no lithofacies or seismic resolution. The composite signature, reinforced by a distinctive distribution of the reworked and redeposited faunas, documents a much more complex late Neogene depositional system than previously known. The system is more than progradational. The source sequences that supplied the constituent bank-margin grains formed at different water depths and over hundreds of kilometers and tens of millions of years apart. New evidence from the literature and from data obtained during Ocean Drilling Program (OOP) Leg 166 in the Santaren Channel (Bahamas) support early interpretations based on the composite fossil record and provide valuable new dimensions to regional allocyclicity. The middle Miocene taxa were confined to the lower part of the section by the latest Miocene-earliest Pliocene(?) lowstand of sea level. An orderly occurrence of the allogenic taxa is unique to the global reworked geologic record and appears to have been controlled by a combination of Paleogene-early Neogene tectonics at the source, eustatic changes, and late Neogene current activity at the source and across the bank. The allogenic taxa expand the spatial and temporal range of information in the northern Bahamas by nearly an order of magnitude. In essence, some of the major processes active in the region during ??? 64 m.y. of the

  2. High resolution stratigraphy and paleoenvironmental changes in the southern North Sea during the Neogene : An integrated study of Late Cenozoic marine deposits from the northern part of the Dutch offshore area

    NARCIS (Netherlands)

    Kuhlmann, G.

    2004-01-01

    This thesis is the result of a multidisciplinary study on the prograding marine Neogene sedimentary succession of the southern North Sea Basin. To date, sediment material available from the Neogene North Sea is very scarce. Its location between 400 and 1500 m below the seabed in the depocentre of th

  3. High resolution stratigraphy and paleoenvironmental changes in the southern North Sea during the Neogene : an integrated study of Late Cenozoic marine deposits from the northern part of the Dutch offshore area

    NARCIS (Netherlands)

    Kuhlmann, Gesa

    2004-01-01

    This thesis is the result of a multidisciplinary study on the prograding marine Neogene sedimentary succession of the southern North Sea Basin. To date, sediment material available from the Neogene North Sea is very scarce. Its location between 400 and 1500 m below the seabed in the depocentre of th

  4. High resolution stratigraphy and paleoenvironmental changes in the southern North Sea during the Neogene : An integrated study of Late Cenozoic marine deposits from the northern part of the Dutch offshore area

    NARCIS (Netherlands)

    Kuhlmann, G.

    2004-01-01

    This thesis is the result of a multidisciplinary study on the prograding marine Neogene sedimentary succession of the southern North Sea Basin. To date, sediment material available from the Neogene North Sea is very scarce. Its location between 400 and 1500 m below the seabed in the depocentre of th

  5. High resolution stratigraphy and paleoenvironmental changes in the southern North Sea during the Neogene : an integrated study of Late Cenozoic marine deposits from the northern part of the Dutch offshore area

    NARCIS (Netherlands)

    Kuhlmann, Gesa

    2004-01-01

    This thesis is the result of a multidisciplinary study on the prograding marine Neogene sedimentary succession of the southern North Sea Basin. To date, sediment material available from the Neogene North Sea is very scarce. Its location between 400 and 1500 m below the seabed in the depocentre of th

  6. Paleogeographic and Depositional Model for the Neogene fluvial succession, Pishin Belt Northwest Pakistan: the effect of post collisional tectonics on sedimentation in peripheral foreland setting

    DEFF Research Database (Denmark)

    Kasi, Aimal Khan; Kassi, Akhtar Muhammad; Umar, Muhammad

    2017-01-01

    channels, lateral accretion surfaces (point bars) and alluvial fans. Neogene sedimentation in the Pishin Belt was mainly controlled by active tectonism and thrusting in response to oblique collision of the Indian Plate with Afghan Block of the Eurasian Plate along the Chaman-Nushki Fault. Post Miocene......Detailed facies analysis of the Neogene successions of the Pishin Belt (Katawaz Basin) has enabled documentation of successive depositional systems and palaeogeographic settings of the basin formed by the collision of northwestern continental margin of Indian Plate and Afghan Block. During Early...

  7. Chemical and isotopic characteristics of hot springs along the along the Neogene Malawi rift.

    Science.gov (United States)

    Atekwana, E. A.; Tsokonombwe, G. W.; Elsenbeck, J.; Wanless, V. D.; Atekwana, E. A.

    2015-12-01

    We measured the concentrations of major ions and dissolved inorganic carbon (DIC) and the stable isotopes of carbon (δ13CDIC), hydrogen (δD) and oxygen (δ18O) of hot springs along the Neogene Malawi rift. We compared the results with those of streams and a cold spring. We aimed to assess the hot springs for evidence of addition of mantle mass, specifically water and carbon and (2) determine the processes that control the chemical and isotopic evolution of the hot springs. Understanding the source(s) of heat for the springs and if the chemical and isotopic characteristics show evidence of mantle processes is an important goal of the Project for Rift Initiation, Development and Evolution (PRIDE). The temperature of the hot springs ranged from 35 to 80 ºC. High temperature anomalies are observed between latitudes 10 to 11, 12 to 13 and 15 to 16 degrees south along the rift axis. The δD and δ18O for the cold spring, hot springs and streams had a similar range, were positively correlated and lie on the trend of the local meteoric water line. We suggest negligible contribution of water from a connate or magmatic source and limited oxygen exchange from water-rock interaction or CO2 exchange from deep sedimentary carbonates. The DIC concentrations of the hot springs are higher (5 to 61 mg C/L) than those of streams (2 to 28 mg C/L) indicating addition of carbon to the DIC pool during the circulation of some springs. The range in the δ13CDIC of the hot springs (-17 to -8‰) is broader and lower compared to streams (-12 to -5‰) due to addition of carbon with a δ13CDIC of -15‰ to the spring water during circulation. Our results indicate that (1) the source of water for the hot springs is meteoric, (2) the hot springs have not experienced extensive water-rock interaction due to fast circulation suggesting highly permeable fault zones, (3) the source of carbon in the DIC of the hot springs is mostly CO2(g) from the soil zone and (4) the springs are heated by normal

  8. Neogene kinematic history of Nazca-Antarctic-Phoenix slab windows beneath Patagonia and the Antarctic Peninsula

    Science.gov (United States)

    Breitsprecher, Katrin; Thorkelson, Derek J.

    2009-01-01

    The Patagonian slab window is a subsurface tectonic feature resulting from subduction of the Nazca-Antarctic spreading-ridge system (Chile Rise) beneath southern South America. The geometry of the slab window had not been rigorously defined, in part because of the complex nature of the history of ridge subduction in the southeast Pacific region, which includes four interrelated spreading-ridge systems since 20 Ma: first, the Nazca-Phoenix ridge beneath South America, then simultaneous subduction of the Nazca-Antarctic and the northern Phoenix-Antarctic spreading-ridge systems beneath South America, and the southern Phoenix-Antarctic spreading-ridge system beneath Antarctica. Spreading-ridge paleo-geographies and rotation poles for all relevant plate pairs (Nazca, Phoenix, Antarctic, South America) are available from 20 Ma onward, and form the mathematical basis of our kinematic reconstruction of the geometry of the Patagonia and Antarctic slab windows through Neogene time. At approximately 18 Ma, the Nazca-Phoenix-Antarctic oceanic (ridge-ridge-ridge) triple junction enters the South American trench; we recognize this condition as an unstable quadruple junction. Heat flow at this junction and for some distance beneath the forearc would be considerably higher than is generally recognized in cases of ridge subduction. From 16 Ma onward, the geometry of the Patagonia slab window developed from the subduction of the trailing arms of the former oceanic triple junction. The majority of the slab window's areal extent and geometry is controlled by the highly oblique (near-parallel) subduction angle of the Nazca-Antarctic ridge system, and by the high contrast in relative convergence rates between these two plates relative to South America. The very slow convergence rate of the Antarctic slab is manifested by the shallow levels achieved by the slab edge (< 45 km); thus no point on the Antarctic slab is sufficiently deep to generate "normal" mantle-derived arc-type magmas

  9. Early Neogene unroofing of the Sierra Nevada de Santa Marta along the Bucaramanga -Santa Marta Fault

    Science.gov (United States)

    Piraquive Bermúdez, Alejandro; Pinzón, Edna; Bernet, Matthias; Kammer, Andreas; Von Quadt, Albrecht; Sarmiento, Gustavo

    2016-04-01

    Plate interaction between Caribbean and Nazca plates with Southamerica gave rise to an intricate pattern of tectonic blocks in the Northandean realm. Among these microblocks the Sierra Nevada de Santa Marta (SNSM) represents a fault-bounded triangular massif composed of a representative crustal section of the Northandean margin, in which a Precambrian to Late Paleozoic metamorphic belt is overlain by a Triassic to Jurassic magmatic arc and collateral volcanic suites. Its western border fault belongs to the composite Bucaramanga - Santa Marta fault with a combined left lateral-normal displacement. SE of Santa Marta it exposes remnants of an Oligocene marginal basin, which attests to a first Cenoizoic activation of this crustal-scale lineament. The basin fill consists of a sequence of coarse-grained cobble-pebble conglomerates > 1000 m thick that unconformably overlay the Triassic-Jurassic magmatic arc. Its lower sequence is composed of interbedded siltstones; topwards the sequence becomes dominated by coarser fractions. These sedimentary sequences yields valuable information about exhumation and coeval sedimentation processes that affected the massif's western border since the Upper Eocene. In order to analyse uplifting processes associated with tectonics during early Neogene we performed detrital zircon U-Pb geochronology, detrital thermochronology of zircon and apatites coupled with the description of a stratigraphic section and its facies composition. We compared samples from the Aracataca basin with analog sequences found at an equivalent basin at the Oca Fault at the northern margin of the SNSM. Our results show that sediments of both basins were sourced from Precambrian gneisses, along with Mesozoic acid to intermediate plutons; sedimentation started in the Upper Eocene-Oligocene according to palynomorphs, subsequently in the Upper Oligocene a completion of Jurassic to Cretaceous sources was followed by an increase of Precambrian input that became the dominant

  10. The Neogene Redbeds of Iceland - a High-Latitude Terrestrial Paleoclimate Monitor Driven by Chemical Weathering

    Science.gov (United States)

    Riishuus, M. S.; Bird, D. K.

    2012-12-01

    Chemical weathering of tephra and aeolian dust of basaltic composition produces clays and iron oxide/hydroxide minerals preserved in reddened layers referred to as redbeds, boles or paleosols. We propose that the extent of weathering of Neogene redbeds in Iceland and the isotopic composition of structurally bound water in associated weathering clay preserve records of high-latitude paleoclimatic and hydrologic conditions. In support we present whole-rock geochemistry and smectite D/H compositions of redbed horizons from Iceland for comparative analysis with global paleoclimate trends and local independent proxy data. Smectite δD values of 35 basaltic tephras in Iceland (~15-2 Ma) display a general decrease in δD compositions from -110 to -105 ‰ at ~15-13 Ma to -115 to -118 ‰ at ~3-2 Ma which correlates well with the global cooling trend from the Middle Miocene Climatic Optimum (17-15 Ma) to present day. Furthermore, the extent of weathering expressed by the Chemical Index of Weathering increases from 40-50 at 2-3 Ma to 80-90 at 15-16 Ma suggesting enhanced chemical weathering rates during the warmer climate conditions. The weathering extent of modern andosols in Iceland is temperature-dependant and allows construction of a paleo-climate proxy [1]. Application of this proxy suggests that mean annual temperatures (MATs) increased from ~0°C at ~2 Ma to ~9°C at 15-16 Ma in general agreement with independent local proxy data. The δD values of paleo meteoric waters in Iceland, estimated using a smectite-water fractionation factor and model MATs, decrease from -41 ‰ at 15-16 Ma (9°C) to -45 ‰ at 2 Ma (0°C). The paleo meteoric water compositions are increasingly enriched in deuterium relative to present day meteoric water in Iceland (δD ≤ -50 ‰). This is in agreement with global cooling since Middle Miocene toward ice-dominated conditions with greater equator-to-pole temperature contrasts, affecting the distillation process between ocean, atmosphere and

  11. Neogene-Quaternary Volcanic forms in the Carpathian-Pannonian Region: a review

    Science.gov (United States)

    Lexa, Jaroslav; Seghedi, Ioan; Németh, Karoly; Szakács, Alexandru; Koneĉny, Vlastimil; Pécskay, Zoltan; Fülöp, Alexandrina; Kovacs, Marinel

    2010-09-01

    Neogene to Quaternary volcanic/magmatic activity in the Carpathian-Pannonian Region (CPR) occurred between 21 and 0.1 Ma with a distinct migration in time from west to east. It shows a diverse compositional variation in response to a complex interplay of subduction with rollback, back-arc extension, collision, slab break-off, delamination, strike-slip tectonics and microplate rotations, as well as in response to further evolution of magmas in the crustal environment by processes of differentiation, crustal contamination, anatexis and magma mixing. Since most of the primary volcanic forms have been affected by erosion, especially in areas of post-volcanic uplift, based on the level of erosion we distinguish: (1) areas eroded to the basement level, where paleovolcanic reconstruction is not possible; (2) deeply eroded volcanic forms with secondary morphology and possible paleovolcanic reconstruction; (3) eroded volcanic forms with remnants of original morphology preserved; and (4) the least eroded volcanic forms with original morphology quite well preserved. The large variety of volcanic forms present in the area can be grouped in a) monogenetic volcanoes and b) polygenetic volcanoes and their subsurface/intrusive counterparts that belong to various rock series found in the CPR such as calc-alkaline magmatic rock-types (felsic, intermediate and mafic varieties) and alkalic types including K-alkalic, shoshonitic, ultrapotassic and Na-alkalic. The following volcanic/subvolcanic forms have been identified: (i) domes, shield volcanoes, effusive cones, pyroclastic cones, stratovolcanoes and calderas with associated intrusive bodies for intermediate and basic calclkaline volcanism; (ii) domes, calderas and ignimbrite/ash-flow fields for felsic calc-alkaline volcanism and (iii) dome flows, shield volcanoes, maars, tuffcone/tuff-rings, scoria-cones with or without related lava flow/field and their erosional or subsurface forms (necks/ plugs, dykes, shallow intrusions

  12. Heterogeneous sources of marlstone in a piggy-back basin: the Neogene Lopare basin in Dinarides

    Science.gov (United States)

    Grba, Nenad; Neubauer, Franz; Šajnović, Aleksandra; Jovančićević, Branimir

    2014-05-01

    The chemical composition of marlstones is commonly not used to investigate to provenance of the sedimentary basin fill because of variable dilution by authigenic carbonate and the assumed uniformity of the clay fraction. Here, we report geochemical compositions of marlstone from the Neogene Lopare basin in Internal Dinarides, which have an unusual chemical composition reflecting at least two different sources. The Lopare basin formed as a piggy-back basin on top of the growing Dinaric orogenic wedge. Much of its Miocene evolution, this basin represented a partly hypersaline lake in a warm climate likely formed during the Miocene Climatic Optimum during Early Miocene. Several lithofacies of marlstone reflect basin center deposits and the chemical composition could be considered as well mixed from external siliciclastic input (clay fraction) and internal carbonate precipitation. Sandstone layers are very thin and are not considered here. A total of 46 samples from two boreholes POT-3 (depth to 344 m) and POT-1 (depth to 193 m) were selected for geochemical investigation. The contents of major, minor and trace including rare earth elements were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The qualitative composition of the mineral part was determined by means of X-ray diffractometry. The main chemical features of the Lopare basin marlstone are variable but high contents of most metals like Fe (5.36 ± 1.05 wt%), Cr (215 ± 34 ppm), Ni (183 ± 36 ppm), Pb (173 ± 43 ppm), but also of some alkalies like Li (340 ± 123 ppm). Particularly the heavy metal contents like Cr, Ni, Fe are much higher than for average continental mudstones (e.g., Taylor and McLennan, 1985). These contrasting compositions may result from two geochemically different sources: (1) Ophiolites (oceanic source) occurring in the neighborhood are responsible for high Cr, Ni, Fe contents, while (2) the increased alkali contents (e.g., Li; continental source) likely

  13. Genesis of economic relevant fresh groundwater resources in Pleistocene/ Neogene aquifers in Nam Dinh (Red River Delta, Vietnam).

    Science.gov (United States)

    Wagner, F.; Ludwig, R. R.; Noell, U.; Hoang, H. V.; Pham, N. Q.; Larsen, F.; Lindenmaier, F.

    2012-04-01

    In the Southern Red River Delta (Nam Dinh Province, Vietnam), a local lens of low saline pore water of high quality has been identified in unconsolidated Pleistocene and Neogene aquifers, which are regionally known to contain brackish and saline pore waters. Since the 1990ies, ongoing overexploitation of the fresh groundwater results in decreasing GW heads up to 0.6 m/a and the development of a regional abstraction cone. The presented study focuses on distribution and genesis of fresh and saline pore waters and reflects the results in frame of the regional hydrogeological context. Observations of the geological structure and groundwater dynamics combined with hydrochemical and isotopic studies suggest adjacent Triassic hard rock aquifers as the major source for fresh Pleistocene and Neogene groundwater. Salinization status in the economically most relevant Pleistocene aquifer has been studied based on archive and new hydrochemical and geophysical data. Own hydrochemical field studies as well as laboratory measurements of the specific resistivity of dry sediment samples allow the translation of induction logging data from existing monitoring wells into vertical pore water salinity profiles. This approach suggests the regional occurrence of saline pore water in shallow Holocene sediments in the working area, as confirmed by pore water studies in Hoan et al. (2010). Interpretation of induction logging and stable isotope data suggest vertical diffusion of saline pore water in shallow Holocene sediments as a source for high saline pore water in deeper aquifers. Analytical diffusion modeling for a period of 3000 years confirms that vertical diffusion of Holocene paleo-sea water can explain saline pore water in Pleistocene and Neogene aquifers in a stagnant environment. The constant influx of fresh groundwater from adjacent Triassic hard rocks results in flushing of the primary Pleistocene and Neogene pore water and inhibits the infiltration of saline water from marine

  14. Punctuated Neogene tectonics and stratigraphy of the African-Iberian plate-boundary zone: concurrent development of Betic-Rif basins (southern Spain, northern Morocco)

    NARCIS (Netherlands)

    Sissingh, W.

    2008-01-01

    This paper integrates the sequence stratigraphic and tectonic data related to the Neogene geodynamic and palaeogeographic development of the African-Iberian plate boundary zone between Spain and Morocco. Though the dating of individual tectonostratigraphic sequences and their delimiting sequence bou

  15. Reconsideration of the so-called Oligocene fauna in the asphaltic deposits of Buton (Malay Archipelago) — 2. Young-Neogene Foraminifera and calcareous Algae

    NARCIS (Netherlands)

    Keyzer, F.G.

    1952-01-01

    Miopliocene marls from the island of Buton yield a large marine foraminiferal fauna and some calcareous algae. Three-hundred and thirthy-three species have been identified. Two genera, twenty-three species and four varieties are described as new. The existence of mud-volcanoes in young neogene time

  16. Punctuated Neogene tectonics and stratigraphy of the African-Iberian plate-boundary zone: concurrent development of Betic-Rif basins (southern Spain, northern Morocco)

    NARCIS (Netherlands)

    Sissingh, W.

    2008-01-01

    This paper integrates the sequence stratigraphic and tectonic data related to the Neogene geodynamic and palaeogeographic development of the African-Iberian plate boundary zone between Spain and Morocco. Though the dating of individual tectonostratigraphic sequences and their delimiting sequence bou

  17. Kinematics of the Neogene Terror Rift: Constraints from calcite twinning strain in AND-1B core, McMurdo Ice Shelf

    Science.gov (United States)

    Paulsen, T.; Wilson, T. J.; Demosthenous, C.; Millan, C.; Jarrard, R. D.; Laufer, A.

    2013-12-01

    Strain analyses of mechanically twinned calcite in veins and faults hosted by Neogene (13.6 Ma to 4.3 Ma) sedimentary and volcanic rocks recovered within the ANDRILL AND-1B drill core from the Terror Rift in the southern Ross Sea, Antarctica, yield prolate and oblate ellipsoids with principal shortening and extension strains ranging from 0.1% to 8.5%. The majority of samples show homogeneous coaxial strain predominantly characterized by subvertical shortening, which we attribute to lithostatic loading in an Andersonian normal faulting stress regime during sedimentary and ice sheet burial of the stratigraphic sequence. The overall paucity of a non-coaxial layer-parallel shortening signal in the AND-1B twin populations suggests that horizontal compressive stresses predicted by Neogene transtensional kinematic models for the rift system have been absent or of insufficient magnitude to cause a widespread noncoaxial strain overprint. Limited numbers of oriented samples yield a possible average ESE extension direction for the rift that is subparallel to other indicators of Neogene extension. The lack of horizontal shortening in the twin data suggests the Neogene Terror Rift system either lacks a strong longitudinal strike-slip component, or that spatial partitioning of strain controls the maximum shortening axes seen in rocks of this age.

  18. Neogene amphibians and reptiles (Caudata, Anura, Gekkota, Lacertilia, and Testudines) from the south of Western Siberia, Russia, and Northeastern Kazakhstan

    Science.gov (United States)

    Zazhigin, Vladimir S.

    2017-01-01

    Background The present-day amphibian and reptile fauna of Western Siberia are the least diverse of the Palaearctic Realm, as a consequence of the unfavourable climatic conditions that predominate in this region. The origin and emergence of these herpetofaunal groups are poorly understood. Aside from the better-explored European Neogene localities yielding amphibian and reptile fossil remains, the Neogene herpetofauna of Western Asia is understudied. The few available data need critical reviews and new interpretations, taking into account the more recent records of the European herpetofauna. The comparison of this previous data with that of European fossil records would provide data on palaeobiogeographic affiliations of the region as well as on the origin and emergence of the present-day fauna of Western Siberia. An overview of the earliest occurrences of certain amphibian lineages is still needed. In addition, studies that address such knowledge gaps can be useful for molecular biologists in their calibration of molecular clocks. Methods and Results In this study, we considered critically reviewed available data from amphibian and reptile fauna from over 40 Western Siberian, Russian and Northeastern Kazakhstan localities, ranging from the Middle Miocene to Early Pleistocene. Herein, we provided new interpretations that arose from our assessment of the previously published and new data. More than 50 amphibians and reptile taxa were identified belonging to families Hynobiidae, Cryptobranchidae, Salamandridae, Palaeobatrachidae, Bombinatoridae, Pelobatidae, Hylidae, Bufonidae, Ranidae, Gekkonidae, Lacertidae, and Emydidae. Palaeobiogeographic analyses were performed for these groups and palaeoprecipitation values were estimated for 12 localities, using the bioclimatic analysis of herpetofaunal assemblages. Conclusion The Neogene assemblage of Western Siberia was found to be dominated by groups of European affinities, such as Palaeobatrachidae, Bombina, Hyla, Bufo

  19. Inversion tectonics in the Neogene basins of Tuscany (Northern Apennines, Italy): Insights from the Pisa-Viareggio basin.

    Science.gov (United States)

    Argnani, A.; Rogledi, S.

    2012-04-01

    Several sedimentary basins are located in the internal portion of the Northern Apennines, bordering the eastern side of the Northern Tyrrhenian sea. These basins trend almost parallel to the Apennine range and are filled by Neogene sediments with thickness ranging between few 100's m to few km (Martini et al., 2001). Sediments belonging to these basins crop out extensively in western Tuscany, often appearing heavily deformed. Although classically interpreted as extensional basins (e.g., Martini and Sagri, 1993 and references therein), some papers call for an initial thrust-related origin (Finetti et al., 2001; Bonini and Sani, 2002), and the long-lasting debate about the origin of the Neogene basins of Tuscany is still ongoing (cfr. Brogi 2011 and Sani et al., 2004). This contribution aims at presenting the case of the Pisa-Viareggio basin, which is the northernmost one among the large basins of Tuscany (Pascucci et al., 2007). This basin straddles the coastline and has been investigated through the interpretation of a grid of industrial seismic profiles covering the Pisa plain and tied to exploration wells. In the Pisa-Viareggio basin seismic profiles show a west-dipping listric extensional fault that bounds the basin to the east, supporting an extensional origin. The basin is filled with up to 3 seconds of upper Messinian to Quaternary sediments, and extension mostly occurred during late Messinian-early Pliocene, although continuing with reduced intensity till the Quaternary. The southern part of this basin shows a superimposed contractional deformation (tectonic inversion), that progressively increases to the south, where the basin appears completely overturned and eroded in the Livorno Mountains. The basin-boundary fault trends roughly NNW-SSE and is buried in the Quaternary sediments of the Pisa plain, but it turns rather abruptly to N-S and NNE-SSW in the south, near Livorno. Inspection of detailed geological maps (Lazzarotto et al., 1990) suggests that the

  20. Neogene paleogeography provides context for understanding the origin and spatial distribution of cryptic diversity in a widespread Balkan freshwater amphipod

    Directory of Open Access Journals (Sweden)

    Michał Grabowski

    2017-02-01

    Full Text Available Background The Balkans are a major worldwide biodiversity and endemism hotspot. Among the freshwater biota, amphipods are known for their high cryptic diversity. However, little is known about the temporal and paleogeographic aspects of their evolutionary history. We used paleogeography as a framework for understanding the onset of diversification in Gammarus roeselii: (1 we hypothesised that, given the high number of isolated waterbodies in the Balkans, the species is characterised by high level of cryptic diversity, even on a local scale; (2 the long geological history of the region might promote pre-Pleistocene divergence between lineages; (3 given that G. roeselii thrives both in lakes and rivers, its evolutionary history could be linked to the Balkan Neogene paleolake system; (4 we inspected whether the Pleistocene decline of hydrological networks could have any impact on the diversification of G. roeselii. Material and Methods DNA was extracted from 177 individuals collected from 26 sites all over Balkans. All individuals were amplified for ca. 650 bp long fragment of the mtDNA cytochrome oxidase subunit I (COI. After defining molecular operational taxonomic units (MOTU based on COI, 50 individuals were amplified for ca. 900 bp long fragment of the nuclear 28S rDNA. Molecular diversity, divergence, differentiation and historical demography based on COI sequences were estimated for each MOTU. The relative frequency, geographic distribution and molecular divergence between COI haplotypes were presented as a median-joining network. COI was used also to reconstruct time-calibrated phylogeny with Bayesian inference. Probabilities of ancestors’ occurrence in riverine or lacustrine habitats, as well their possible geographic locations, were estimated with the Bayesian method. A Neighbour Joining tree was constructed to illustrate the phylogenetic relationships between 28S rDNA haplotypes. Results We revealed that G. roeselii includes at least

  1. Magnetostratigraphy of the Neogene Siwalik Group of far eastern Himalaya, Kameng section, Arunashal Pradesh, India

    Science.gov (United States)

    Chirouze, Francois; Huyghe, Pascale; Dupont-Nivet, Guillaume

    2010-05-01

    Foreland basins act as receptacles for synorogenic sediments and store materials eroded off a convergent mountain belt (DeCelles and Giles, 1996, DeCelles and Giles, 1996). Their infill records tectonic, climatic and erosional processes that govern the development of the mountain belt and the foreland basin. Consequently, studying the infill of foreland basins can give clues as to the reconstruction of the orogen tectonic growth and the interaction with global or regional climate (e.g. Molnar & England, 1990). The Himalaya, the highest range in the world, is used as a natural laboratory to test the interactions between these processes, in particular because of the effect of the Tibetan Plateau uplift on the intensity and variability of the Asian monsoon (Kutzbach et al., 1993; Fluteau et al., 1999). Exhumation, erosion and climate events affecting the Himalaya are recorded in the Neogene Siwalik foreland basin deposits (e.g. DeCelles et al., 1998, 2000; Galy et al., 1999; Huyghe et al., 2001, 2005; Najman, 2005). Dating these deposits is a key element to reconstruct the Himalaya's evolution. Despite a wealth of studies in the central and western Himalayan foreland, very few studies have been carried out in the eastern part (Yin et al., 2006, Cina et al 2009). Understanding the evolution of this eastern part is essential for reconstructing the regional migration of the Himalayan deformation. In addition, the eastern Himalayan foreland potentially records the evolution of processes associated to the eastern syntaxis drainage networks (Singh and France-Lanord, 2002) and the Shillong plateau uplift (Grujic et al., 2006). Therefore, accurate dating of the sediments of the Eastern part of the Siwalik foreland basin using magnetostratigraphy is a crucial initial step for further investigations such as sedimentological and structural field studies, fission tracks, provenance and isotopic stable laboratory analysis. These investigations aim at constraining the exhumation

  2. Making Earth's earliest continental crust - an analogue from voluminous Neogene silicic volcanism in NE-Iceland

    Science.gov (United States)

    Berg, Sylvia E.; Troll, Valentin R.; Burchardt, Steffi; Riishuus, Morten S.; Deegan, Frances M.; Harris, Chris; Whitehouse, Martin J.; Gústafsson, Ludvik E.

    2014-05-01

    Borgarfjörður Eystri in NE-Iceland represents the second-most voluminous exposure of silicic eruptive rocks in Iceland and is a superb example of bimodal volcanism (Bunsen-Daly gap), which represents a long-standing controversy that touches on the problem of crustal growth in early Earth. The silicic rocks in NE-Iceland approach 25 % of the exposed rock mass in the region (Gústafsson et al., 1989), thus they significantly exceed the usual ≤ 12 % in Iceland as a whole (e.g. Walker, 1966; Jonasson, 2007). The origin, significance, and duration of the voluminous (> 300 km3) and dominantly explosive silicic activity in Borgarfjörður Eystri is not yet constrained (c.f. Gústafsson, 1992), leaving us unclear as to what causes silicic volcanism in otherwise basaltic provinces. Here we report SIMS zircon U-Pb ages and δ18O values from the region, which record the commencement of silicic igneous activity with rhyolite lavas at 13.5 to 12.8 Ma, closely followed by large caldera-forming ignimbrite eruptions from the Breiðavik and Dyrfjöll central volcanoes (12.4 Ma). Silicic activity ended abruptly with dacite lava at 12.1 Ma, defining a ≤ 1 Myr long window of silicic volcanism. Magma δ18O values estimated from zircon range from 3.1 to 5.5 (± 0.3; n = 170) and indicate up to 45 % assimilation of a low-δ18O component (e.g. typically δ18O = 0 ‰, Bindeman et al., 2012). A Neogene rift relocation (Martin et al., 2011) or the birth of an off-rift zone to the east of the mature rift associated with a thermal/chemical pulse in the Iceland plume (Óskarsson & Riishuus, 2013), likely brought mantle-derived magma into contact with fertile hydrothermally-altered basaltic crust. The resulting interaction triggered large-scale crustal melting and generated mixed-origin silicic melts. Such rapid formation of silicic magmas from sustained basaltic volcanism may serve as an analogue for generating continental crust in a subduction-free early Earth (e.g. ≥ 3 Ga, Kamber et

  3. Reconstructing Vegetation and Hydrological Changes from Biomarkers in Modern Soils and Late Neogene Paleosols, Meade Basin, KS, USA

    Science.gov (United States)

    Fischer-Femal, B.; Uno, K. T.; Polissar, P. J.; Fox-Dobbs, K.; Feinberg, J. M.; Fox, D. L.; Snell, K. E.; Martin, R.

    2014-12-01

    Paleoclimate and paleovegetation proxies can help us understand how C4 grasslands have expanded worldwide and responded to climate change during the late Neogene. The Miocene-Holocene deposits of the Meade Basin, southwestern Kansas preserve a record of C4 ecosystem expansion as well as a rich fossil record of small mammals. These records combined provide an excellent opportunity to study the cause(s) of the C4 ecosystem expansion and the consequences for faunal evolution. As part of an interdisciplinary project, we are investigating the organic geochemical record of vegetation and hydrological change in the Meade Basin. Preliminary findings from three modern soil pits suggest n-alkane δ¹³C values have similar trends to n-alkanoic acid δ¹³C values in each soil profile, but the absolute values of these two different types of plant-wax compounds are offset by up to 6.8‰. This result was unexpected because the absolute δ¹³C values of n-alkanes and n-alkanoic acids are assumed to be very similar in the plants themselves. Moreover, the δ¹³C values of the n-alkanoic acids more accurately reflect the modern vegetation at our sites. Few studies compare carbon isotope data in n-alkanes and n-alkanoic acids and it is important to constrain how these two types of plant-wax compounds reflect vegetation differently. We will use hydrogen isotope measurements on these same plant-wax samples to evaluate how the modern precipitation isotopic ratios are recorded in biomarkers, which in turn will be used to interpret hydrogen isotope data from paleosol biomarkers. Ongoing work will use plant-wax isotopic records from the modern soil profiles as a framework for interpreting the plant-wax isotopic records from Meade Basin paleosol and fluvial sediments to reconstruct the late Neogene C4 grassland expansion and hydroclimate change in this region.

  4. The Neogene molasse deposits of the Zagros Mountains in central Dezful Embayment: facies, sedimentary environments and controls

    Directory of Open Access Journals (Sweden)

    Ali Hossein Jalilian

    2016-03-01

    Full Text Available The upper part of Neogene sequence of the Zagros Mountains consists of a clastic succession which is identified as Aghajari and Bakhtyari formations. The sequence is an excellent example of synorogenic sedimentation or molasse deposited in northern portion of the Zagros foreland basin. Sedimentological analysis of an outcrop section representing Miocene-Pliocene sediments in central Dezful Embayment resulted in recognizing 9 lithofacies and 4 architectural elements. These lithofacies include conglometate (Gt, Gh, Gmm, sandstone (Sp, Sh, Sr, St and mudstone (Fm, Fl that were deposited in meandering stream, braided river and alluvial fan environments. Paleocurrent analysis of cross-beds, channels and asymmetric ripple marks indicate that these Neogene clastics were mainly drived from Cretaceous to Paleogene highlands in the Zagros Mountains on the north. This stratigraphic record is coarsening-upward and formed by a regressive depositional megacycle under arid climate. Facies and depositional history analysis show that sedimentation of the Zagros molasse was primarily controlled by base-level changes rather than catchment lithology or climate. The sedimentary record of this regressive megacycle reveales the base-level was constantly falling down on one hand and the provenance was uplifting on the other hand. Tectonic activities and Zagros Mountains rising in the Late Miocene resulted in deposition of fining-upward point-bar and floodplain sequences of the Aghajari Formation in low-gradient meandering streams. The Lahbari Member of the Aghajari Formation represents deposition in braided rivers that composed predominantly of flood-plain deposits in the Early Pliocene. Finally, the sedimentary cycle of the Zagros molasse deposits terminated with massive conglomerates of the Bakhtyari Formation deposited in large alluvial fans near the source area.

  5. Role of Neogene Exhumation and Sedimentation on Critical-Wedge Kinematics in the Zagros Orogenic Belt, Northeastern Iraq, Kurdistan

    Science.gov (United States)

    Koshnaw, R. I.; Horton, B. K.; Stockli, D. F.; Barber, D. E.; Tamar-Agha, M. Y.; Kendall, J. J.

    2014-12-01

    The Zagros orogenic belt and foreland basin formed during the Cenozoic Arabia-Eurasia collision, but the precise histories of shortening and sediment accumulation remain ambiguous, especially at the NW extent of the fold-thrust belt in Iraqi Kurdistan. This region is characterized by well-preserved successions of Cenozoic clastic foreland-basin fill and deformed Paleozoic-Mesozoic hinterland bedrock. The study area provides an excellent opportunity to investigate the linkage between orogenic wedge behavior and surface processes of erosion and deposition. The aim of this research is to test whether the Zagros orogenic wedge advanced steadily under critical to supercritical wedge conditions involving in-sequence thrusting with minimal erosion or propagated intermittently under subcritical condition involving out-of-sequence deformation with intense erosion. These endmember modes of mountain building can be assessed by integrating geo/thermochronologic and basin analyses techniques, including apatite (U-Th)/He thermochronology, detrital zircon U-Pb geochronology, stratigraphic synthesis, and seismic interpretations. Preliminary apatite (U-Th)/He data indicate activation of the Main Zagros Fault (MZF) at ~10 Ma with frontal thrusts initiating at ~8 Ma. However, thermochronometric results from the intervening Mountain Front Flexure (MFF), located between the MZF and the frontal thrusts, suggest rapid exhumation at ~6 Ma. These results suggest that the MFF, represented by the thrust-cored Qaradagh anticline, represents a major episode of out-of-sequence deformation. Detrital zircon U-Pb analyses from the Neogene foreland-basin deposits show continuous sediment derivation from sources to the NNE in Iraq and western Iran, suggesting that out-of-sequence thrusting did not significantly alter sedimentary provenance. Rather, intense hinterland erosion and recycling of older foreland-basin fill dominated sediment delivery to the basin. The irregular distribution of

  6. Species diversity variations in Neogene deep-sea benthic foraminifera at ODP Hole 730A, western Arabian Sea

    Indian Academy of Sciences (India)

    Yuvaraja Arumugm; Anil K Gupta; Mruganka K Panigrahi

    2014-10-01

    Deep-sea benthic foraminifera are an important and widely used marine proxy to understand paleoceanographic and paleoclimatic changes on regional and global scales, owing to their sensitivity to oceanic and climatic turnovers. Some species of benthic foraminifera are sensitive to changes in water mass properties whereas others are sensitive to organic fluxes and deep-sea oxygenation. Benthic faunal diversity has been found closely linked to food web, bottom water oxygen levels, and substrate and water mass stability. The present study is aimed at analyzing species diversity trends in benthic foraminifera and their linkages with Indian monsoon variability during the Neogene. Species diversity of benthic foraminifera is examined in terms of number of species (S), information function (H), equitability (E) and Sanders’ rarefied values, which were combined with relative abundances of high and low productivity benthic foraminifera at Ocean Drilling Program Hole 730A, Oman margin, western Arabian Sea. The Oman margin offers the best opportunity to understand monsoon-driven changes in benthic diversity since summer monsoon winds have greater impact on the study area. The species diversity was higher during the early Miocene Climatic Optimum (∼17.2–16.4 Ma) followed by a decrease during 16.4–13 Ma coinciding with a major increase in Antarctic ice volume and increased formation of Antarctic Bottom Water. All the diversity parameters show an increase during 13–11.6 Ma, a gradual decrease during 11.6–9 Ma and then an increase with a maximum at 7 Ma. Thereafter the values show little change until 1.2 Ma when all the parameters abruptly decrease. The benthic foraminiferal populations and diversity at Hole 730A were mainly driven by the Indian monsoon, and polar waters might have played a minor or no role since early Neogene period as the Arabian Sea is an enclosed basin.

  7. Late Neogene shift from polythermal to cold polar conditions of the Antarctic ice sheet indicated by glacial stratigraphy and sea-ice history

    Science.gov (United States)

    Harwood, D.; Hambrey, M.; McKelvey, B.; Webb, P.; Whitehead, J.

    2003-04-01

    Discussions on the Neogene history of the East Antarctic Ice Sheet center on the age of the switch from a 'dynamic' mode (polythermal) to the modern, 'stable' mode (cold-polar) of Antarctic glaciation. Interpretations derived from landscape evolution, ash deposits and polar desert pavements in the Dry Valley region support a persistent cold-polar climate by middle Miocene time. In contrast, interpretations based on glacigene strata of the Sirius Group in the Transantarctic Mts. and Pagodroma Group of the Prince Charles Mts. support the persistence of a dynamic, polythermal ice sheet until the late Pliocene. Marine sediments on the continental shelf preserve a record of sea-ice history, as indicated by sea-ice diatom assemblages, that bears on the timing of the switch in glacial regime. Through most of the Late Neogene and into the late Pliocene, the sea-ice diatom flora was weakly developed to absent. The reduced influence of sea-ice during the Late Neogene would impact the terrestrial glacial regime by lowered albedo of the ocean surface and higher ocean to atmospheric heat and moisture transfer, both of which would result in prolonged regional warming and polythermal ice. This paper will review the history of Neogene sea-ice and present stratigraphic evidence on characteristics of glacigene deposition in terrestrial and glacimarine environments during the Miocene and Pliocene, which suggest deposition by an ice sheet of quite different character than the present ice sheet, and a glacial regime of significant erosion and deposition. In situ marine fossils of the Pagodroma Group indicate that this warmer than present climate and polythermal character of the East Antarctic ice sheet continued into the Pliocene. The floating ice margin retreated up the Lambert Valley by as much as 300 km south of the present limit, where distal glacimarine facies deposited diatomaceous mud. The grounding zone of the paleo-Lambert Glacier/Amery Ice Shelf system fluctuated across a

  8. Petrogenesis and its significance to continental dynamics of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang, Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    赖绍聪; 刘池阳; S.Y.O’Reilly

    2001-01-01

    Detailed studies indicate that the main rock type of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang is andesite, dacite and rhyolite. They belong to typical crust-generation magmatic system and originate from the special thickened crust of the Tibetan Plateau by dehydration melting. This group of rocks exhibits LREE enrichment but no remarkable Eu anomaly that shows their source region should be a thickened deep crust consisting of eclogitic mass group, implying that the crust had been thickened and an eclogitic deep crust had been formed during the Neogene period in Qiangtang area. This understanding is important and significant to making further discussion on the uplift mechanism and continental dynamics of the Tibetan Plateau.

  9. Neogene Tiporco Volcanic Complex, San Luis, Argentina: An explosive event in a regional transpressive - local transtensive setting in the pampean flat slab

    Science.gov (United States)

    Ibañes, Oscar Damián; Sruoga, Patricia; Japas, María Silvia; Urbina, y. Nilda Esther

    2017-07-01

    The Neogene Tiporco Volcanic Complex (TVC) is located in the Sierras Pampeanas of San Luis, Argentina, at the southeast of the Pampean flat-slab segment. Based on the comprehensive study of lithofacies and structures, the reconstruction of the volcanic architecture has been carried out. The TVC has been modeled in three subsequent stages: 1) initial updoming, 2) ignimbritic eruptive activity and 3) lava dome emplacement. Interplay of magma injection and transtensional tectonic deformation has been invoked to reproduce TVC evolution.

  10. Cosmogenic nuclide concentrations in Neogene rivers of the Great Plains reveal the evolution of fluvial storage and recycling

    Science.gov (United States)

    Sinclair, Hugh; Stuart, Fin; McCann, Louise; Tao, Zui

    2016-04-01

    The measurement of the duration of near surface residence of sediment grains from the stratigraphic record has the potential to quantitatively reconstruct processes such as stratal condensation, sediment recycling and the exposure histories of unconformities. Geomorphological measurements of dates and rates of surfaces and erosion respectively has enabled significant advances in understanding, however, the radiogenic half life of typical cosmogenic nuclides such as 10Be and 26Al means they are not suitable for the stratigraphic record. Instead, we have applied the stable cosmogenic nuclide of 21Ne to quartz-rich sediment to quantify the routing history of the river systems that have drained the southern Rockies of Wyoming and Colorado during Neogene times. The Neogene sediments of Nebraska record fluvial systems of the Great Plains that flow from the Rockies towards the east and into the Mississippi catchment. This succession is climate change. As part of an evaluation of the application of 21Ne to the stratigraphic record, we sampled quartzite pebbles from an Upper Miocene, Pliocene and modern river channel of the North Platte approximately 400 km from their mountainous source. The quartzite is derived from a single exposure of the Medicine Bow quartzites in Wyoming, therefore all three intervals recorded the same travel distance from source. Additionally, we know the erosion rate of the Medicine Bow quartzites from detrital 10Be analyses, and we also sampled shielded bedrock samples from the quartzite to evaluate for any non-cosmogenic 21Ne. This means that the concentrations of 21Ne in detrital pebbles >400 km from their source could be corrected for both inherited non-cosmogenic and erosion induced accumulation at source. Therefore, any additional amounts of 21Ne must record storage and exposure during transport down the river systems. Based on 40 analyses of pebbles from these intervals, we are able to demonstrate that approximately half of the pebbles record

  11. The mode of emplacement of Neogene flood basalts in eastern Iceland: Facies architecture and structure of simple aphyric basalt groups

    Science.gov (United States)

    Óskarsson, Birgir V.; Riishuus, Morten S.

    2014-12-01

    Simple flows (tabular) in the Neogene flood basalt sections of Iceland are described and their mode of emplacement assessed. The flows belong to three aphyric basalt groups: the Kumlafell group, the Hólmatindur group and the Hjálmadalur group. The groups can be traced over 50 km and originate in the Breiðdalur-Thingmuli volcanic zone. The groups have flow fields that display mixed volcanic facies architecture and can be classified after dominating type morphology. The Kumlafell and the Hólmatindur groups have predominantly simple flows of pāhoehoe and rubbly pāhoehoe morphologies with minor compound or lobate pāhoehoe flows. The Hjálmadalur group has simple flows of rubbly pāhoehoe, but also includes minor compound or lobate flows of rubble and 'a'ā. Simple flows are most common in the distal and medial areas from the vents, while more lobate flows in proximal areas. The simple flows are formed by extensive sheet lobes that are several kilometers long with plane-parallel contacts, some reaching thicknesses of ~ 40 m (aspect ratios inflation structures. Their internal structure consists generally of a simple upper vesicular crust, a dense core and a thin basal vesicular zone. The brecciated flow-top is formed by clinker and crustal rubble, the clinker often welded or agglutinated. The simple flows erupted from seemingly short-lived fissures and have the characteristics of cooling-limited flows. We estimate the effusion rates to be ~ 105 m3/s for the simple flows of the Kumlafell and Hólmatindur groups and ~ 104 m3/s for the Hjálmadalur group. The longest flows advanced 15-20 km from the fissures, with lava streams of fast propagating flows inducing tearing and brecciation of the chilled crust. Compound or lobate areas appear to reflect areas of low effusion rates or the interaction of the lava with topographic barriers or wetlands, resulting in chaotic flowage. Slowing lobes with brecciated flow-tops developed into 'a'ā flows. The groups interdigitated

  12. Variations in terrigenous matter transport evaluated by plant terpenoid analysis in the Neogene eastern equatorial Pacific sediment

    Science.gov (United States)

    Nakamura, H.; Sawada, K.; Yamamoto, S.; Kobayashi, M.

    2012-12-01

    We analyze land plant biomarkers in sediments recovered during the IODP Expeditions 320/321, the Pacific Equatorial Age Transect (PEAT), to reconstruct variations in terrestrial input in the eastern equatorial Pacific Ocean, as well as to evaluate transport systems of terrigenous matter from land to ocean. We used the Neogene sediments (23-0.23 Ma) recovered from site U1337. We could identify cadalene (sesquiterpenoid), as well as series of aromatic abietane type diterpenoids (e.g. retene) from most samples. These terpenoids are derived from biomolecules that constitute plant resin and supportive tissues. Plant-derived compounds in deep-sea sediments are considered that initially transported via fluvial process, followed by redistribution by gravity flow to the deeper part. Although, the typical pelagic setting of site U1337, even far from land across the mid-ocean-ridge, exclude such pathway. Therefore, the variations in mass accumulation rate (MAR) of plant terpenoids in this site depend eolian transportation and can be used as an indicator of change in atmospheric circulation. The increasing spikes in MAR of plant terpenoids were observed in the horizons of 16 Ma, 14 Ma, 12 Ma, 10 Ma, 9 - 8 Ma, 7 Ma and 2.5 - 1Ma. It is found that some of the spikes, 14 Ma, 7 Ma, 2.5 - 1 Ma correspond to the East Antarctica Ice Sheet event (EAIS), the Biogenic bloom event, and the Northern Hemisphere Glaciation (NHG), respectively. Furthermore, the degree of aromatization in diterpenoids, which represented by retene to the sum of abietane type diterpenoids, tends to increase concurrently with the MAR of total plant terpenoids. The aromatization of plant terpenoids take place under thermal maturation after deposition as well as in earlier processes such as biomass burning. In the U1337 sediments, the degree of aromatization of diterpenoids was uncorrelated with the age or depositional depth, suggesting its variations retain potential for paleoclimatic application. For example

  13. High molecular weight (C35+)n-alkanes of Neogene heavily biodegraded oil in the Qianmiqiao region, North China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    With wax content of 1.62%, heavy oil has been produced from the sandstone reservoirs of Neogene Guantao Formation (Ng1Ⅲ). In the GC and GC-MS RIC profiles of its aliphatic fraction, n-alkanes are totally lost, which shows the result of heavy biodegradedation. However, the remaining trace C13-C36 n-alkanes can be still seen from its m/z 85 mass chromatogram. In addition, a complete series of C35-C73 high molecular weight (HMW) n-alkanes was detected by high-temperature gas chromatography (HTGC). The HMW n-alkane series shows a normal distribution pattern, a major peak at nC43, obvious odd-carbon-number predominance, CPI37-55 and OEP45-49 values up to 1.17 and 1.16-1.20 respectively. The present study not only has conformed the strong resistibility of HMW n-alkanes to biodegradation in crude oils as concluded by previous researchers, but also has provided some significant information on source input and maturity for the heavily biodegraded oil in the Qianmiqiao region.

  14. Geochronology and paleothermometry of Neogene sediments from the Vøring Plateau using Sr, C and O isotopes

    Science.gov (United States)

    Smalley, P. C.; Nordaa, A.; Råheim, A.

    1986-07-01

    The Neogene sediments from DSDP site 341 on the Vøring Plateau, Norwegian Sea, contain a thin glauconitic pellet-bearing subunit, which separates underlying pelagic clays from overlying glacial-marine sediments. Oxygen isotope measurements of benthic foraminifera show aδ 18O shift of + 1%. during deposition of this subunit, probably a combined effect of a drop in bottom water temperature and a rise in seawaterδ 18O. The chronology of this sedimentological and O isotope transition is, however, poorly constrained by fossil evidence. Rb sbnd Sr dating of glauconitic pellets indicates that the lower part of the glauconitic subunit was deposited 11.6 ± 0.2 Ma ago. Further geochronological evidence, derived from the Sr and C isotopic compositions of foraminifera compared with known seawater-time variations, indicates that the lower pelagic clays are early to middle Miocene, deposited at a mean rate of ˜ 15 m/Ma. The glauconitic subunit contains part of the middle Miocene and probably all of the late Miocene in a condensed sequence with a very low mean depositional rate (˜ 0.2 m/Ma). The overlying glacial marine sediments are probably Pliocene, with a high mean rate of deposition, ˜ 45 m/Ma. This is the first application of C, O and Sr isotopic stratigraphy combined with Rb sbnd Sr dating of glauconitic minerals, and it illustrates the applications of this integrated approach in geochronology.

  15. Neogene magnetostratigraphy and rock magnetic study of the Kashi Depression, NW China: Implications to neotectonics in the SW Tianshan Mountains

    Science.gov (United States)

    Qiao, Qingqing; Huang, Baochun; Piper, John D. A.; Deng, Tao; Liu, Chengying

    2016-03-01

    The southwest Tianshan Mountains of China are bordered by the Tarim foreland and comprise an actively deforming segment of the India-Asia collisional system. We report a detailed magnetostratigraphic study of the Dashankou section in the Kashi Depression of the Tarim Basin to improve the understanding of the history of sedimentation, denudation, and mountain building in this region. The preferred correlation of the succession with the geomagnetic polarity timescale defines a depositional history between 12.4 and 3.0 Ma with a substantial increase in sedimentation rates identified at ~6.7 Ma corresponding to a pulse of rapid uplift in the southwest Tianshan Mountains. Although climatic changes may have modulated the record during Neogene times, they do not appear to have had an important influence on sediment accumulation rates between 7.0 and 2.6 Ma. Magnetic fabrics identify the influence of a regional stress field imparted by ongoing India-Asia collision in the lower part of the succession contrasting with predominantly sedimentary fabrics in the higher part of the succession. A major clastic influx with a maximum age estimate of ~3.6 Ma comprises the Xiyu conglomerates, and integration with other magnetostratigraphic investigations around the Tianshan demonstrates unambiguously that depositional onset of this coarse clastic episode is diachronous. Hence, the Xiyu Formation cannot be considered as a chronostratigraphic marker related to any specific tectonic or climatic event.

  16. Late Miocene breccia of Menorca (Balearic Islands) a basis for the interpretation of a Neogene ramp deposit

    Science.gov (United States)

    Obrador, A.; Pomar, L.; Taberner, C.

    1992-08-01

    Neogene (Tortonian) ramp facies associations crop out in the southern sector of Menorca (Balearic island). These are made mainly by sigmoidal and oblique clinoform units comprising rhodoliths, bryozoans, molluscs and foraminifera. These units are interpreted as outer-ramp deposits. A breccia deposit infilling an erosional surface is found at the top of the carbonate ramp sequence. The breccia components (mainly rhodoliths and oolite clasts) may represent erosion of the underlying ramp deposits and inner-ramp counterparts, which do not crop out on the island. The study of components in the breccia deposits confirms the indigenous character of the outer-ramp facies associations, which suggests that the ramp was steepened distally. The breccia deposits correspond laterally to a discontinuity surface locally showing karstic features. Transgressive sediments (including a phosphatic crust) are found above the discontinuity surface. All together these features, and the dolomitisation of the uppermost ramp sediments and breccia deposits, suggest that the breccia originated from erosion of the ramp after a major relative sea-level fall. The breccia and discontinuity surface separate the ramp sequence from an overlying prograding sequence. A correlation of this sequence boundary to other areas in the western Mediterranean is proposed.

  17. Preliminary Investigations of Creep Strain of Neogene Clay from Warsaw in Drained Triaxial Tests Assisted by Computed Microtomography

    Science.gov (United States)

    Kaczmarek, Łukasz Dominik; Dobak, Paweł Józef; Kiełbasiński, Kamil

    2017-06-01

    The study concerns soil creep deformation in multistage triaxial stress tests under drained conditions. High resolution X-ray computed microtomography (XμCT) was involved in structure recognition before and after triaxial tests. Undisturbed Neogene clay samples, which are widespread in central Poland, were used in this study. XμCT was used to identify representative sample series and informed the detection and rejection of unreliable ones. Maximum deviatoric stress for in situ stress confining condition was equal 95.1 kPa. This result helped in the design of further multistage investigations. The study identified the rheological strain course, which can be broken down into three characterizations: decreasing creep strain rate, transitional constant creep velocity, and accelerating creep deformation. The study found that due to multistage creep loading, the samples were strengthened. Furthermore, there is a visibly "brittle" character of failure, which may be the consequence of the microstructure transformation as a function of time as well as collapse of voids. Due to the glacial tectonic history of the analyzed samples, the reactivation of microcracks might also serve as an explanation. The number of the various sizes of shear planes after failure is confirmed by XμCT overexposure.

  18. Late Neogene stratigraphy and tectonic control on facies evolution in the Laguna Salada Basin, northern Baja California, Mexico

    Science.gov (United States)

    Martín-Barajas, A.; Vázquez-Hernández, S.; Carreño, A. L.; Helenes, J.; Suárez-Vidal, F.; Alvarez-Rosales, J.

    2001-10-01

    The Laguna Salada Basin (LSB) in northeastern Baja California records late-Neogene marine incursions in the Salton Trough and progradation of the Colorado River delta. Early subsidence and subsequent tectonic erosion are related to evolution of the Sierra El Mayor detachment fault during late Miocene time (geothermal exploratory well on the eastern margin of LSB. Interfingering fluvial-sandstone deposits and prograding alluvial fanglomerates with coarse debris-flow and rock-avalanche deposits crudely mark the onset of vertical slip along the Laguna Salada fault and rapid uplift of Sierra Cucapa and Sierra El Mayor. Up to 2 km of Quaternary alluvial-fan and lacustrine deposits accumulated along the eastern margin of LSB, whereas lower subsidence rates produced a thinner sedimentary wedge over a ramp-like crystalline basement along the western margin. In early Pleistocene time (˜2-1 Ma), the Laguna Salada became progressively isolated from the Colorado River delta complex, and the Salton Trough by activity on the Elsinore and Laguna Salada fault zones.

  19. Bloc tectonic rotations recorded in the Neogene and Quaternary magmatic rocks from Northwestern Algeria: preliminary paleomagnetic results.

    Science.gov (United States)

    El Messaoud Derder, Mohamed; Robion, Philippe; Maouche, Said; Bayou, Boualem; Amenna, Mohamed; Henry, Bernard; Missenard, Yves; Ouabadi, Aziouz; Bestandji, Rafik; Ayache, Mohamed

    2016-04-01

    The seismic activity of the Western Mediterranean area is partly concentrated in northern Africa, particularly in northern Algeria, as it was shown by the strong earthquakes of Zemmouri 21 May 2003 Mw=6.9 and the El Asnam 10 October 1980 Ms= 7.3. This seismicity is due to the convergence between Africa and Eurasia plates since the Oligocene. This convergence involves a tectonic transpression with N-S to NNW-SSE shortening direction, which is expressed by active deformation along the plate boundary. Along the Tellian Atlas (Northern Algeria), active structures define NE-SW trending folds and NE-SW sinistral transpressive faults affecting the intermountain and coastal Neogene to Quaternary sedimentary basins (e.g. Cheliff and Mitidja Plioquaternary intramontaneous basins, …). The NE-SW reverse active faults are coupled with NW-SE to E-W trending strike-slip deep faults. The active deformation in northern Algeria can be explained by a kinematics model of blocks rotation: the transpressive tectonics with NNW-SSE direction of convergence defines NE-SW oriented blocks, which have been subjected to clockwise rotation. In north Algeria, paleomagnetic studies were carried out in the central area, on Neogene sedimentary and magmatic formations (Derder et al, 2009, 2011; 2013). They pointed out tectonic rotation of large blocks, in agreement with the kinematic model. Narrow zones represent important shear zone with strong rotation of smaller blocks (Derder et al., 2013). A new paleomagnetic study was conducted on the recent magmatic rocks outcropping in the Northwestern Algeria, in order to validate this model on a regional scale. The study is still in progress and the preliminary results show presence of systematic clockwise blocks rotation. These results confirm that the Africa-Europe convergence is partly accommodated in northern Africa by blocks rotations. They highlight that rotations are not homogeneous in north Algeria and thus the importance of future works in this

  20. New stratigraphic, chronologic, and magnetic fabric constraints for Neogene and Quaternary ignimbrites in the Central Andes (South Peru)

    Science.gov (United States)

    De La Rupelle, A.; Thouret, J. C.; Cubukcu, H. E.; Jicha, B.; Bréard, E.; Gerbe, M.-C.; Le Pennec, J.-L.; Diot, H.; Boivin, P.

    2012-04-01

    Central Andean deformation history in southern Peru is recorded in Neogene volcanic units of Ocoña and Cotahuasi canyons that cut across the western Cordillera. Acceleration (100 km3) Nazca (c.24.6 Ma), Alpabamba (19.4-18.0 Ma), and Huaylillas (14.25-12.7 Ma) ignimbrite sheets preceded the canyon incision, whereas sheets of smaller volume (welded, eutaxitic, crystal-rich facies overlain by a thick, multi-bedded ash-flow tuff and a lithic-rich, indurated flow unit. The Huaylillas ignimbrite sheet comprises a strongly welded, crystal-rich, lithic-poor, columnar lithofacies, with devitrified pumice. The Caraveli ignimbrite sheet has a jointed vitrophyre overlain by a welded, blocky, crystal-rich flow unit. A vacuolar, saccharolytic unit forms the top of the sequence. The Lower Sencca ignimbrite sheet comprises of a basal vitrophyre and a slightly welded, fibrous pumice-rich flow unit, which grades into a welded, vapor-phase unit that contains more crystals than pumice and lithics. The Upper Sencca ignimbrite sheet consists of a black vitrophyre, grading into a strongly welded, crystal-rich, eutaxitic cooling unit. The latter is capped by a slightly welded unit, and an indurated pumice-rich, crystal-poor vapour-phase facies. Quaternary valley-fill termed Las Lomas consists of unwelded, crystal-poor pumice-flow deposits. Eighteen new 40Ar/39Ar analyses have been carried out on feldspar/glass separates from pumice and lavas. Results for the Caraveli ignimbrite (9.35±0.06 Ma), Upper Barroso lavas (2.24±0.45 Ma) and Upper Sencca ignimbrite (2.00-2.06±0.09 Ma) are in good agreement with previous data. New ages for the Lower Barroso lavas (7.32±0.05; 5.36±0.12 Ma) and Lower Sencca ignimbrites (5.13±0.01, 5.09±0.03, 4.65±0.11, 4.36 ± 0.16) extend their temporal history towards older times. Lower Barroso lava flow activity occurred as early as~7.3 and lasted until 5.4 Ma just before the Lower Sencca eruptions. The Lower Sencca ignimbrites spanned at least 1.5 Ma and

  1. Evidence for the development of the Andean rain shadow from a Neogene isotopic record in the Atacama Desert, Chile

    Science.gov (United States)

    Rech, Jason A.; Currie, Brian S.; Shullenberger, Eric D.; Dunagan, Stan P.; Jordan, Teresa E.; Blanco, Nicolás; Tomlinson, Andrew J.; Rowe, Harry D.; Houston, John

    2010-04-01

    Varying ages from Triassic to Pliocene have been proposed for the onset of hyperaridity in the Atacama Desert. The exact timing for the initiation of hyperaridity is critical for determining potential causes, which range from regional effects of global cooling to Andean uplift above elevations conducive to extreme rain shadows. Analysis of the stable isotopic composition of lower Miocene-Quaternary (21-0.015 Ma) palustrine and lacustrine carbonates in the Calama Basin reveals extreme changes in their oxygen and carbon isotopic composition during the Miocene. Limestone δ18O values increased by ˜ 5‰ from middle to late Miocene, ranging from - 5.5‰ at 12 Ma to - 1‰ at ˜ 6 Ma. Carbon isotopic values increase by 9‰ over the Neogene, from average values of - 3‰ at 21 Ma to + 3‰ at 12 Ma, and reaching a maximum of + 6‰ at 5 Ma. The increase in oxygen isotopic values occurred over a time span in which the catchment area of the basin experienced significant uplift, causing the δ18O value of precipitation to become more negative. We attribute the shift towards higher δ18O values to enhanced evaporative enrichment both of soil water or snow prior to infiltration, and within shallow lakes or wetlands prior to carbonate precipitation. The large increase in δ13C values was likely caused by a transition from a vegetated landscape influenced primarily by soil-respired CO 2 to a landscape largely devoid of vegetation and influenced by atmospheric and volcanic CO 2. Isotopic values of palustrine carbonates therefore indicate that hyperaridity commenced in the Calama Basin during the middle to late Miocene, in agreement with other paleoclimatic records from the basin. The cause for the onset of this climate change is thought to be due to the development of a strong Andean rain shadow associated with the uplift of the Andes to mean elevations > 2 km.

  2. Ant-nest ichnofossils in honeycomb calcretes, Neogene Ogallala Formation, High Plains region of western Kansas, U.S.A.

    Science.gov (United States)

    Smith, J.J.; Platt, B.F.; Ludvigson, Greg A.; Thomasson, J.R.

    2011-01-01

    Two new ant-nest trace fossils are described from calcic sandy paleosols of the Neogene Ogallala Formation in western Kansas. The ichnofossils are preserved within and below calcrete beds weathering in positive relief as carbonate-filled casts or as cavities in negative relief. Daimoniobarax ichnogenus nov. is established for burrow systems composed of vertically tiered, horizontally oriented pancake-shaped chambers connected by predominantly vertical and cylindrical shafts ~. 0.8. cm in diameter. Ichnospecies of Daimoniobarax are differentiated based on differences in the plan view outline of chambers, shaft orientation, and junctions between chambers and shafts.Daimoniobarax nephroides ichnospecies nov. is composed of an ~. 24-76. cm long vertical sequence of distinctly lobed chambers (~. 2-20. cm wide and ~. 1. cm high) arranged along sinuous to helical shafts. Chamber shape in plan view ranges from small teardrops to larger kidney- and U-shaped forms. Shafts intersect at chamber edges such that chambers appear to bud from the central shafts. Daimoniobarax nephroides is most similar to the nests of extant seed-harvester ants of the New World genus Pogonomyrmex. Such ants are specialized granivores and prefer sandy soils in arid to semi-arid grassland and desert regions.Daimoniobarax tschinkeli ichnospecies nov. is ~. 30-80. cm in vertical extent. Chambers (~. 2-30. cm wide and ~. 1. cm high) are circular to elongate or pseudopodial in plan view. Vertical shafts are straight to slightly sinuous and intersect most often toward the center of the chambers. The generalized architecture of D. tschinkeli is similar to that of the nests or nest portions of several extant ant genera, though it does not closely resemble any known modern nest.Ant ichnofossils provide valuable information on hidden biodiversity, paleohydrologic regimes, paleopedogenic processes, and paleoclimate during the time of nest occupation. Depth-related changes in chamber size and vertical spacing

  3. Neogene non-tropical carbonate sedimentation in a warm temperate biogeographic province (Rethymnon Formation, Eastern Crete, Greece)

    Science.gov (United States)

    Pomoni-Papaioannou, F.; Drinia, H.; Dermitzakis, M. D.

    2003-01-01

    The Apostoli Basin, in the central-west part of Crete, was formed as a fore-arc type basin related to the convergent plate boundary between the African and the Eurasian plates. Most of the Neogene sediments filling the basin were deposited in a terrestrial to shallow marine environment. The succession is a transgressive cycle, which culminates in the alternation of Rethymnon bioclastic limestones with marls, documenting the important Tortonian marine transgression. The Rethymnon limestones are classified as a typical non-tropical carbonate lithofacies. Two particular lithofacies have been recognized: (a) a rhodalgal-type lithofacies, characterized by predominance of encrusting coralline algae and bryozoans, and (b) an echinofor-type lithofacies, characterized by predominance of echinoderms and/or benthic foraminifera. The coralline algae occur mostly as in situ spheroidal or branched rhodoliths, whereas benthic foraminifera are mainly represented by larger foraminifera. In both lithofacies, typical tropical carbonate elements are lacking. Skeletal elements consisted of low- and high-Mg calcite. Although the observed lithofacies possess many similarities with facies of non-tropical carbonates, the presence of large benthic foraminifera suggests development in a warm temperate biogeographic province. The depositional environment corresponds to a shallow ramp, the sediments being deposited in a nearshore environment and under conditions analogous to those prevailing in the present-day circalittoral bottoms of the Mediterranean Sea. The main carbonate accumulation area is located at the factory area itself (rhodalgal-type sediments), and downslope from the factory area (echinofor-type sediments). In the classic zonation of Mediterranean benthic assemblages of Peres and Picard [Rec. Trav. Stn. Mar. (1964)], the rhodalgal-type sediments of the Rethymnon Fm correspond to the "Facies a Pralines", developed in areas strongly controlled by currents (e.g., tops of plateaus

  4. New insights into late Neogene glacial dynamics, tectonics, and hydrocarbon migrations in the Atlantic-Arctic gateway region.

    Science.gov (United States)

    Knies, J.; Baranwal, S.; Fabian, K.; Grøsfjeld, K.; Andreassen, K.; Husum, K.; Mattingsdal, R.; Gaina, C.; De Schepper, S.; Vogt, C.; Andersen, N.

    2012-04-01

    Notwithstanding the recent IODP drilling on the Lomonosov Ridge, the Late Cenozoic history of the Arctic Ocean still remains elusive. The tectonic processes leading to the development of the only deep-water connection to the Arctic Ocean via the Fram Strait are still poorly understood. Also, the influence of the gateway region on changes in Arctic-Atlantic ocean circulation, uplift/erosion on the adjacent hinterland, as well as glacial initiation and its consequences for the petroleum systems in the regions, remain unclear. By revisiting Ocean Drilling Program (ODP) Leg 151, holes 911A and 910C and interpreting new multi-channel seismic data, we have now established a new comprehensive chronological framework for the Yermak Plateau and revealed important paleoenvironmental changes for the Atlantic-Arctic gateway during the late Neogene. The improved chronostratigraphic framework is established through continuous paleomagnetic and biostratigraphic data as well as selected intervals with stable ?18O and ?13C data derived from benthic foraminifera Cassidulina teretis. Supported by acoustic profiling, the new data indicate a continuous late Miocene/early Pliocene age (~5-6 Ma) for the base of both holes. The depositional regime north (Yermak Plateau) and south of the Fram Strait (Hovgaard Ridge) was rather shallow during the late Miocene and water mass exchange between the Arctic and Atlantic was restricted. Ice sheets on the Svalbard Platform evolved during the late Miocene, however did not reach the coastline before 3.3 Ma. Migration of gaseous hydrocarbons occurred prior to the intensification of the Northern Hemisphere Glaciations (~2.7 Ma) as indicated by high-amplitude reflections, corroborating the occurrence of greigite mineralization and stable carbon isotope excursions in planktic/benthic foraminifera. The data indicate that Pleistocene erosion and uplift in the Barents Sea region had probably only minor effects on reservoir leakages than previously thought.

  5. A review of Neogene and Quaternary snakes of central and eastern Europe. Part 1: Scolecophidia, Boidae, Colubrinae

    Directory of Open Access Journals (Sweden)

    Szyndlar, Z.

    1991-04-01

    Full Text Available Remains of Neogene and Quaternary seoleeophidians, boids and «eolubrine» eolubrids, including snakes previously deseribed and those undeseribed yet, eoming fram Poland, Ukraine, Moldavia, Czeehoslovakia, Austria, Hungary, Romania, Bulgaria, and Greece are diseussed. The following taxa, including 7 extinet speeies, were reeognized: Seoleeophidia indet.; Boidae: Bransateryx septentrionalis, Bransateryx sp., Albaneryx volynicus, cf., Gongylophis sp., Eryx jaculus, Eryx sp., eL Eryx sp., Eryeinae indet.; Colubridae: Texasophis bohemiacus, Coluber dolnicensis, Coluber planicarinatus, Coluber viridij1avus, cf. Coluber viridiflavus, Coluber caspius, Coluber gemonensis, cf. Coluber gemonensis, Coluber sp., Coronella austriaca, Coronella sp., cf. Coronella sp., Elaphe kohfidischi, cf. Elaphe kohfidischi, Elaphe paralongissima, Elaphe longissima, cf. Elaphe longissima, Elaphe quatuorlineata, cf. Elaphe quatuorlineata, eL Elaphe situla, Elaphe sp., cf. Malpolon sp., Telescopus sp., «Colubrinae» indet.Revisión de las serpientes neógenas y cuaternarias de Europa central y oriental. Parte 1: Scolecophidia, Boidae, Colubrinae. Se estudian restos neógenos y cuaternarios de escolecofidios, boidos y colúbridos «colubrinos», incluyendo tanto formas ya descritas como inéditas, y procedentes de Polonia, Ucrania, Moldavia, Checoslovaquia, Austria, Hungría, Rumanía, Bulgaria y Grecia. Se reconocen los siguientes taxones: Scolecophidia indet.; Boidae: Bransateryx septentrionalis, Bransateryx sp., Albaneryx volynicus, cf. Gongylophis sp., Eryx jaculus, Eryx sp., cf. Eryx sp., Erycinae indet.; Colubridae: Texasophis bohemiacus, Coluber dolnicensis, Coluber planicarinatus, Coluber viridij1avus, cf., Coluber viridiflavus, Coluber caspius, Coluber gemonensis, eL Coluber gemonensis, Coluber sp., Coronella austriaca, Coronella sp., cf. Coronella sp., Elaphe kohfidischi, cf. Elaphe kohfidischi, Elaphe paralongissima, Elaphe longissima, cf. Elaphe

  6. Variation of palaeostress patterns along the Oriente transform wrench corridor, Cuba: significance for Neogene Quaternary tectonics of the Caribbean realm

    Science.gov (United States)

    Rojas-Agramonte, Y.; Neubauer, F.; Handler, R.; Garcia-Delgado, D. E.; Friedl, G.; Delgado-Damas, R.

    2005-02-01

    In this study, we address the late Miocene to Recent tectonic evolution of the North Caribbean (Oriente) Transform Wrench Corridor in the southern Sierra Maestra mountain range, SE Cuba. The region has been affected by historical earthquakes and shows many features of brittle deformation in late Miocene to Pleistocene reef and other shallow water deposits as well as in pre-Neogene, late Cretaceous to Eocene basement rocks. These late Miocene to Quaternary rocks are faulted, fractured, and contain calcite- and karst-filled extension gashes. Type and orientation of the principal normal palaeostress vary along strike in accordance with observations of large-scale submarine structures at the south-eastern Cuban margin. Initial N-S extension is correlated with a transtensional regime associated with the fault, later reactivated by sinistral and/or dextral shear, mainly along E-W-oriented strike-slip faults. Sinistral shear predominated and recorded similar kinematics as historical earthquakes in the Santiago region. We correlate palaeostress changes with the kinematic evolution along the boundary between the North American and Caribbean plates. Three different tectonic regimes were distinguished for the Oriente transform wrench corridor (OTWC): compression from late Eocene-Oligocene, transtension from late Oligocene to Miocene (?) (D 1), and transpression from Pliocene to Present (D 2-D 4), when this fault became a transform system. Furthermore, present-day structures vary along strike of the Oriente transform wrench corridor (OTWC) on the south-eastern Cuban coast, with dominantly transpressional/compressional and strike-slip structures in the east and transtension in the west. The focal mechanisms of historical earthquakes are in agreement with the dominant ENE-WSW transpressional structures found on land.

  7. Geochemical characterization of Neogene sediments from onshore West Baram Delta Province, Sarawak: paleoenvironment, source input and thermal maturity

    Science.gov (United States)

    Togunwa, Olayinka S.; Abdullah, Wan H.

    2017-08-01

    The Neogene strata of the onshore West Baram Province of NW Borneo contain organic rich rock formations particularly within the Sarawak basin. This basin is a proven prolific oil and gas province, thus has been a subject of great interest to characterise the nature of the organic source input and depositional environment conditions as well as thermal maturation. This study is performed on outcrop samples of Lambir, Miri and Tukau formations, which are of stratigraphic equivalence to the petroleum bearing cycles of the offshore West Baram delta province in Sarawak. The investigated mudstone samples are organic rich with a total organic carbon (TOC) content of more than 1.0 wt.%. The integration of elemental and molecular analyses indicates that there is no significant variation in the source input between these formations. The investigated biomarkers parameters achieved from acyclic isoprenoids, terpanes and steranes biomarkers of a saturated hydrocarbon biomarkers revealed that these sediments contain high contribution of land plants with minor marine organic matter input that was deposited and preserved under relatively oxic to suboxic conditions. This is further supported by low total sulphur (TS), high TOC/TN ratios, source and redox sensitive trace elements (V, Ni, Cr, Co and Mo) concentrations and their ratios, which suggest terrigenous source input deposited under oxic to suboxic conditions. Based on the analysed biomarker thermal maturity indicators, it may be deduced that the studied sediments are yet to enter the maturity stage for hydrocarbon generation, which is also supported by measured vitrinite reflectance values of 0.39-0.48% Ro.

  8. Neogene shortening and exhumation of the Zagros fold-thrust belt and foreland basin in the Kurdistan region of northern Iraq

    Science.gov (United States)

    Koshnaw, Renas I.; Horton, Brian K.; Stockli, Daniel F.; Barber, Douglas E.; Tamar-Agha, Mazin Y.; Kendall, Jerome J.

    2017-01-01

    The Zagros fold-thrust belt in the Kurdistan region of Iraq encroached southward toward a rapidly subsiding Neogene foreland basin and was later partitioned by out-of-sequence shortening focused along the Mountain Front Flexure (MFF), as defined by new low-temperature thermochronologic, stratigraphic, and provenance results. Apatite (U-Th)/He ages document rapid deformation advance from the Main Zagros Fault to southern frontal structures (Kirkuk, Shakal, and Qamar thrusts) at 10-8 Ma, followed by potential basement-involved out-of-sequence development of the MFF (Qaradagh anticline) by 5 Ma. Distinct shifts in detrital zircon U-Pb provenance signatures for Neogene foreland basin fill provide evidence for drainage reorganization during fold-thrust belt advance. U-Pb age spectra and petrologic data from the Injana (Upper Fars) Formation indicate derivation from a variety of Eurasian, Pan-African, ophiolitic and Mesozoic-Cenozoic volcanic terranes, whereas the Mukdadiya (Lower Bakhtiari) and Bai-Hasan (Upper Bakhtiari) Formations show nearly exclusive derivation from the Paleogene Walash-Naopurdan volcanic complex near the Iraq-Iran border. Such a sharp cutoff in Eurasian, Pan-African, and ophiolitic sources is likely associated with drainage reorganization and tectonic development of the geomorphic barrier formed by the MFF. As a result of Zagros crustal shortening, thickening and loading, the Neogene foreland basin developed and accommodated an abrupt influx of fluvial clastic sediment that contains growth stratal evidence of synkinematic accumulation. The apparent out-of-sequence pattern of upper crustal shortening in the hinterland to foreland zone of Iraqi Kurdistan suggests that structural inheritance and the effects of synorogenic erosion and accumulation are important factors influencing the irregular and episodic nature of orogenic growth in the Zagros.

  9. Neogene sedimentary history of the Outer Cilicia Basin, eastern Mediterranean: a contribution to the TopoEurope VAMP project

    Science.gov (United States)

    Piercey, Tiffany; Akhun, Selin; Hall, Jeremy; Aksu, Ali; Ćifçi, Günay

    2010-05-01

    The Vertical Anatolian Movements Project (VAMP) addresses the Neogene uplift of the Taurides and the Central Anatolian Plateau. While terrestrial studies are focussed on erosion in the sediment source area, and deposition within the Turkish landmass, our marine work is intended to provide a history of deposition in one of the ultimate sinks: the eastern Mediterranean. In particular, we are mapping the distribution in space and time of sediment deposited from the Göksu River into the Cilicia Basin. In 2008 we obtained km of high-resolution marine multi-channel seismic profiles radiating out from the river delta across the basin. Many of the profiles are processed and images of the data are presented. Interpretation of the available industry seismic reflection profiles show that during the the Miocene the northeastern Mediterranean, including the Cilicia Basin, experienced regional compression, which resulted in the formation of a broad and arcuate fold-thrust belt extending from the Taurides in the north, across the Troodos ophiolite complex into the Cyprus Arc in the south. Two prominent culminations were developed: one was located along the Misis-Kyrenia Fault Zone, another developed in the Amanos-Larnaka-Troodos Fault Zone. Stratigraphic and structural relationships demonstrated that the late Pliocene-Quaternary Cilicia-Adana Basin complex evolved as an asymmetric piggyback basin on the hanging-wall of the south-verging Misis-Kyrenia thrust culmination. Detailed mapping demonstrated that the S/SE-directed contraction culminated in the latest Miocene, and is followed in the early Pliocene by a progressive transition to partitioned contraction and extension related to the initiation of strike slip along the eastern Anatolian Transform Fault and its marine extensions. The shift in kinematics is expressed by the development of major NE-SW trending (Inner Cilicia Basin) and E-W trending (Outer Cilicia Basin) steep faults with extensional separations bounding the

  10. Stratigraphic and structural analysis of the Neogene sediments of the offshore portion of the Salina del Istmo Basin, southeastern Mexico

    Science.gov (United States)

    Gomez-Cabrera, Pedro Tomas

    2003-10-01

    Southeastern Mexico has been affected by regional and local tectonic events. Regional tectonic events are the Gulf of Mexico opening and the lateral movement of micro-plates on the Pacific margin. The local tectonic events are related to salt tectonics. Autochthonous Jurassic salt serves as the detachment level for the main compressional event in the late Miocene. Jurassic salt was allochthonously emplaced in the late Miocene, then partially displaced by a huge quantity of terrigenous sediments during the Plio-Pleistocene. This research is a study of the main geological processes that have influenced the structural and stratigraphic evolution of the Neogene sediments in the offshore portion of the Salina del Istmo basin known as the Marbella area. Owing to data availability, the project was divided into regional and local studies. The regional study is based on 2D multi-channel seismic reflection data, and the local study is based on a 3D seismic streamer survey. Structural analysis in the regional study permits the recognition of four buried fold belts (Agua Dulce, Catemaco, Marbella, and Marbella Norte) trending roughly NE. These fold belts are the result of tectonic convergence in the pacific margin during late Miocene. The Agua Dulce and Marbella Norte fold belts are separated by an enormous salt withdrawal basin called the Pescadores basin. The Pescadores basin is bounded on the north by a spectacular stepped, counter-regional structure. Beyond the Pescadores basin, a salt mini-basin area is recognized in the upper continental slope. Another important structural element is the Sal Somera canopy in the southern part of the study area. Sedimentation-rate analysis, based on isochore mapping in the local study area, indicates that from SB-2.4 to SB-2.6 Ma, deposition rate peaked with a maximum of 7.5 mm/yr. Regional and local structural restorations show that, in general, the maximum allochthonous salt mobilization was during the Plio-Pleistocene because of the

  11. The Neogene-Quaternary geodynamic evolution of the central Calabrian Arc: A case study from the western Catanzaro Trough basin

    Science.gov (United States)

    Brutto, F.; Muto, F.; Loreto, M. F.; Paola, N. De; Tripodi, V.; Critelli, S.; Facchin, L.

    2016-12-01

    The Catanzaro Trough is a Neogene-Quaternary basin developed in the central Calabrian Arc, between the Serre and the Sila Massifs, and filled by up to 2000 m of continental to marine deposits. It extends from the Sant'Eufemia Basin (SE Tyrrhenian Sea), offshore, to the Catanzaro Basin, onshore. Here, onshore structural data have been integrated with structural features interpreted using marine geophysical data to infer the main tectonic processes that have controlled the geodynamic evolution of the western portion of the Catanzaro Trough, since Upper Miocene to present. The data show a complex tectonostratigraphic architecture of the basin, which is mainly controlled by the activity of NW-SE and NE-SW trending fault systems. In particular, during late Miocene, the NW-SE oriented faults system was characterized by left lateral kinematics. The same structural regime produces secondary fault systems represented by E-W and NE-SW oriented faults. The ca. E-W lineaments show extensional kinematics, which may have played an important role during the opening of the WNW-ESE paleo-strait; whereas the NE-SW oriented system represents the conjugate faults of the NW-SE oriented structural system, showing a right lateral component of motion. During the Piacenzian-Lower Pleistocene, structural field and geophysical data show a switch from left-lateral to right-lateral kinematics of the NW-SE oriented faults, due to a change of the stress field. This new structural regime influenced the kinematics of the NE-SW faults system, which registered left lateral movement. Since Middle Pleistocene, the study area experienced an extensional phase, WNW-ESE oriented, controlled mainly by NE-SW and, subordinately, N-S oriented normal faults. This type of faulting splits obliquely the western Catanzaro Trough, producing up-faulted and down-faulted blocks, arranged as graben-type system (i.e Lamezia Basin). The multidisciplinary approach adopted, allowed us to constrain the structural setting of

  12. Stratigraphic architecture and forcing processes of the late Neogene Miradouro da Lua sedimentary prism, Cuanza Basin, Angola

    Science.gov (United States)

    Cauxeiro, C.; Durand, J.; Lopez, M.

    2014-07-01

    The Miradouro da Lua cliffs, which are 60 km south of Luanda, record the building and uplift of the late Neogene Palaeo-Cuanza delta. The detailed study of the sedimentary architecture and stacking pattern permitted separation of the pile into five depositional units bounded by erosional surfaces and characterised by separate facies associations (genetic sequences = units in this paper). At the base of the series, aeolian deposits (Unit 1) mark the development of a possible coastal desert during the late Miocene aridification. The major Pliocene sea-level rise (Transgressive Systems Tract) led to the drowning of the continental platform into a discrete shoreface-foreshore sequence (Unit 2), followed by an expanded deltaic sequence (Unit 3) that represents the main outcrop of the area. The sedimentary fabric of this prograding wedge during the Highstand Systems Tract reveals laterally stacked pluri-hectometic mouth bars built by the abrupt switching of a bird-foot delta during the Pliocene highstand. The clinoforms are deeply incised by submarine gullies filled both by periodic river-driven turbidite and tidal currents (Unit 4) during the coeval growing of the delta. The topset of the prograding wedge and associated gullies infill is truncated by an overall erosional unconformity that marks the widespread development of an extensive braid-delta system (Unit 5) during the lower Pleistocene sea-level drop (Lowstand Systems Tract). The last 6 m of the Braid-delta unit is overprinted by a ferallitic profile, forming the surface of the plateau and indicating long-term subaerial exposure and weathering processes consistent with the maximum warming of the middle to late Pleistocene interglacial periods. The successive abrupt shifts of the depositional systems through the sedimentary pile indicate a high-amplitude sea level amplified by major coastal uplifts and the reorganisation of the fluvial network. In this context, the palaeo-Cuanza prograding wedge signals the

  13. Neogene sea surface temperature reconstructions from the Southern McMurdo Sound and the McMurdo Ice Shelf (ANDRILL Program, Antarctica)

    Science.gov (United States)

    Sangiorgi, Francesca; Willmott, Veronica; Kim, Jung-Hyun; Schouten, Stefan; Brinkhuis, Henk; Sinninghe Damsté, Jaap S.; Florindo, Fabio; Harwood, David; Naish, Tim; Powell, Ross

    2010-05-01

    During the austral summers 2006 and 2007 the ANtarctic DRILLing Program (ANDRILL) drilled two cores, each recovering more than 1000m of sediment from below the McMurdo Ice-Shelf (MIS, AND-1B), and sea-ice in Southern McMurdo Sound (SMS, AND-2A), respectively, revealing new information about Neogene Antarctic cryosphere evolution. Core AND-1B was drilled in a more distal location than core AND-2A. With the aim of obtaining important information for the understanding of the history of Antarctic climate and environment during selected interval of the Neogene, we applied novel organic geochemistry proxies such as TEX86 (Tetra Ether IndeX of lipids with 86 carbon atoms) using a new calibration equation specifically developed for polar areas and based on 116 surface sediment samples collected from polar oceans (Kim et al., subm.), and BIT (Branched and Isoprenoid Tetraether), to derive absolute (sea surface) temperature values and to evaluate the relative contribution of soil organic matter versus marine organic matter, respectively. We will present the state-of-the-art of the methodology applied, discussing its advantages and limitations, and the results so far obtained from the analysis of 60 samples from core AND-2A covering the Miocene Climatic Optimum (and the Mid-late Miocene transition) and of 20 pilot samples from core AND-1B covering the late Pliocene.

  14. TAXONOMY AND EVOLUTIONARY PROCESS OF NEOGENE BOVIDAE FROM CHINA%中国新近纪牛科分类及演化规律

    Institute of Scientific and Technical Information of China (English)

    陈冠芳; 张兆群

    2009-01-01

    Bovidae is one of the most diversified groups of Neogene mammals. The study of Chinese Neogene Bovidae traced back to the beginning of the 20~(th) century (Schlosser, 1903). During the 1920's and 1930's, Neogene bovid fossil collecting and describing reached a peak. From the 1950's on, not only some new bovid taxa have been reported based on the materials obtained from Northern and Southwest China, but also the systematic positions of some bovid genera have been revised by Chinese paleontologists.In this paper, we try to review the taxonomy based on the most recent progress. Till now, 30 genera belonging to 5 subfamilies of Bovidae have been recognized from Chinese Neogene (Table 1). Most of the genera were found from North China. There discovered few taxa from the Late Miocene of Southwest China.Analysis of the geological and geographical distribution of fossil Bovidae from China shows 5 evolutionary phases and 4 turnovers during the Neogene:Phase 1; Late Oligocene-Early Miocene. Fossil Bovidae is only represented by Sinopalaeoceros Chen, 1988 ( Hypsodontinae). It occurred in the Early Miocene of Qinghai and in the Late Oligocene of Xinjiang.Phase 2; Middle Miocene ( Tunggurian) . Bovids are characterized by the presence of Tur-cocerus K(o)hler, 1987 and Kubanotragus Sokolov, 1973. They distributed only in North China.Phase 3 : Late Miocene ( Bahean-Baodean) . Bovids are characterized by the flourishing of Urmiatheriini, and a specialized group belonging to Caprinae. Gazella ( Antilopinae) is also one of the most common genera. Phase 4: Early Pliocene. The dominant elements are Gazella and endemic forms of Caprinae.Phase 5 Late Pliocene. Bovids are characterized by the occurrence of extant genera and species, e. g. Ovis and Gazella subgutturosa.These phases also indicate 4 turnover events of bovid faunas during the Neogene.The first turnover event happened after the first phase, in between the Early and Middle Miocene. Sinopalaeoceros went extinct, and there

  15. Mangrove associated lignite beds of Malvan, Konkan: Evidence for higher sea-level during the Late Tertiary (Neogene) along the west coast of India

    Energy Technology Data Exchange (ETDEWEB)

    Kumaran, K.P.N.; Shindikar, M.; Limaye, R.B. [Agharkar Research Inst., Pune (India)

    2004-01-25

    Fossil pneumatophores (breathing roots) of Avicennia are recovered and reported from the lignite beds exposed in Kolamb well-section near Malvan, Konkan area of western Maharashtra. The accrued palynoflora is dominated by mangroves (Avicennia, Aegialitis, Excoecaria, Rhizophora and Sonneratia). The spores of mangrove fern (Acrostichum aureum) an estuarine fungus Cirrenalia indicate that these lignites are autochthonous and deposited in a near-shore environment. Presence of foraminiferal linings (= microforaminifera), dinoflagellate cysts, a few calcareous nannofossils and scolecodonts is an irrefutable proof of marine and brackish water influence during the deposition of lignites under intertidal/tidal swampy condition (mangrove influenced) with fair input from freshwater swamps and hinterland. Freshwater-related forms, viz. Ceratopteris thalictroides, Nymphaeaceae, Ctenolophonaceae and hinterland taxa (Cullenia/Durio) of Bombacaceae along with abundance of microthyriaceous fungi in the palynoflora imply a warm humid tropical climate with high precipitation during the depositional period. The presence of Ctenolophon englerianus (= Ctenolophonidites costatus) in Kolamb lignites suggests the Late Neogene (Late Miocene-Early Pliocene) age. The occurrence of pneumatophores and associated lignite deposits about 37 m above the present mean sea-level, and much inland, clearly indicates the higher sea-level strand during Late Neogene along the west coast of India.

  16. Late Neogene changes in North America and Antarctica absolute plate motions inferred from the Mid-Atlantic and Southwest Indian Ridges spreading histories

    Science.gov (United States)

    Iaffaldano, G.; DeMets, C.

    2016-08-01

    Reconstructions of absolute plate motions underpin our understanding of the plate torque balance, but are challenging due to difficulties in inferring well-dated rates and directions of plate movements from hot spot tracks. Useful information about plate dynamics can be inferred from rapid absolute plate motion changes, as these are linked only to the torque(s) that changed. Here we infer late Neogene changes in the absolute motions of North America and possibly Antarctica from changes in the easier-to-determine relative plate motions recorded along the Arctic, northern Mid-Atlantic and Southwest Indian Ridges. We show that Eurasia/North America and Nubia/North America motions changed by the same amount between 8 and 5 Ma, as may have Nubia/Antarctica and Somalia/Antarctica plate motions. By considering additional, independent constraints on Somalia/India plate motion, we argue that a scenario in which North America and Antarctica absolute motions changed is the simplest one that explains the observed changes in relative motions. We speculate that these changes are linked to the late Neogene dynamics of the Pacific plate.

  17. Relative roles of Neogene vicariance and Quaternary climate change on the historical diversification of bunchgrass lizards (Sceloporus scalaris group) in Mexico.

    Science.gov (United States)

    Bryson, Robert W; García-Vázquez, Uri Omar; Riddle, Brett R

    2012-01-01

    Neogene vicariance during the Miocene and Pliocene and Quaternary climate change have synergistically driven diversification in Mexican highland taxa. We investigated the impacts of these processes on genetic diversification in the widely distributed bunchgrass lizards in the Sceloporus scalaris group. We searched for correlations between timing in diversification and timing of (1) a period of marked volcanism across the Trans-Mexican Volcanic Belt in central Mexico 3-7.5million years ago (Ma) and (2) a transition to larger glacial-interglacial cycles during the mid-Pleistocene. From our phylogenetic analyses of mitochondrial DNA we identified two major clades that contained 13 strongly supported lineages. One clade contained lineages from the two northern sierras of Mexico, and the other clade included lineages associated with the Trans-Mexican Volcanic Belt and Central Mexican Plateau. Results provided support for Neogene divergences within the S. scalaris group in response to uplift of the Trans-Mexican Volcanic Belt, a pattern observed in several co-distributed taxa, and suggested that Quaternary climate change likely had little effect on diversification between lineages. Uplift of the Trans-Mexican Volcanic Belt during specific time periods appears to have strongly impacted diversification in Mexican highland taxa.

  18. Constraints on the history and topography of the Northeastern Sierra Nevada from a Neogene sedimentary basin in the Reno-Verdi area, Western Nevada

    Science.gov (United States)

    Trexler, James; Cashman, Patricia; Cosca, Michael

    2012-01-01

    Neogene (Miocene–Pliocene) sedimentary rocks of the northeastern Sierra Nevada were deposited in small basins that formed in response to volcanic and tectonic activity along the eastern margin of the Sierra. These strata record an early phase (ca. 11–10 Ma) of extension and rapid sedimentation of boulder conglomerates and debrites deposited on alluvial fans, followed by fluvio-lacustrine sedimentation and nearby volcanic arc activity but tectonic quiescence, until ~ 2.6 Ma. The fossil record in these rocks documents a warmer, wetter climate featuring large mammals and lacking the Sierran orographic rain shadow that dominates climate today on the eastern edge of the Sierra. This record of a general lack of paleo-relief across the eastern margin of the Sierra Nevada is consistent with evidence presented elsewhere that there was not a significant topographic barrier between the Pacific Ocean and the interior of the continent east of the Sierra before ~ 2.6 Ma. However, these sediments do not record an integrated drainage system either to the east into the Great Basin like the modern Truckee River, or to the west across the Sierra like the ancestral Feather and Yuba rivers. The Neogene Reno-Verdi basin was one of several, scattered endorheic (i.e., internally drained) basins occupying this part of the Cascade intra-arc and back-arc area.

  19. Constraints on Neogene deformation in the southern Terror Rift from calcite twinning analyses of veins within the ANDRILL MIS core, Victoria Land Basin, Antarctica

    Science.gov (United States)

    Paulsen, T. S.; Demosthenous, C.; Wilson, T. J.; Millan, C.

    2009-12-01

    The ANDRILL MIS (McMurdo Ice Shelf) Drilling Project obtained over 1200 meters of Neogene sedimentary and volcanic rocks in 2006/2007. Systematic fracture logging of the AND-1B core identified 1,475 natural fractures, i.e. pre-existing fractures in the rock intersected by coring. The most abundant natural fractures are normal faults and calcite veins; reverse faults, brecciated zones, and sedimentary intrusions are also present. In order to better understand Neogene deformation patterns within the southern Terror Rift, we have been conducting strain analyses on mechanically twinned calcite within healed fractures in the drill core. Twinning strains using all of the data from each sample studied to date range from 2% to 10%. The cleaned data (20% of the largest magnitude deviations removed) typically show ≤30% negative expected values, consistent with a single deformation episode or multiple ~coaxial deformation episodes. The majority of the samples record horizontal extension, similar to strain patterns expected in a normal fault regime and/or vertical sedimentary compaction in a continental rift system. The morphology, width, and intensity of twins in the samples suggest that twinning typically occurred at temperatures <170° C. Twinning intensities suggest differential stress magnitudes that caused the twinning ranged from 216 to 295 MPa.

  20. [The fossil record of the Eurasian Neogene insectivores (Erinaceomorpha, Soricomorpha, Mammalia) : Part I / L.W. van den Hoek Ostende, C.S. Doukas and J.W.F. Reumer (editors)]: WINE: putting the fossil insectivores on record

    NARCIS (Netherlands)

    Hoek Ostende, van den L.W.; Doukas, C.S.; Reumer, J.W.F.

    2005-01-01

    Introduction In their report of a meeting at Reisensburg, the RCMNS working group on fossil mammals presented ranges of Neogene mammal genera (De Bruijn et al, 1992). However, no erinaceid, talpid or shrew can be found in the tables. The working group concluded (p. 70); "The omission of all the inse

  1. [The fossil record of the Eurasian Neogene insectivores (Erinaceomorpha, Soricomorpha, Mammalia) : Part I / L.W. van den Hoek Ostende, C.S. Doukas and J.W.F. Reumer (editors)]: Greece

    NARCIS (Netherlands)

    Doukas, C.S.

    2005-01-01

    Introduction The Neogene insectivores from Greece span an interval from Early Miocene to Biharian but certainly do not represent a continuous succession. The first reference of small mammals in Greece is by Dames (1883), who described Mus [=Parapodemus] gaudryi from the classical locality of Pikermi

  2. Neogene sedimentary history of the Inner Cilicia Basin, eastern Mediterranean: a contribution to the TopoEurope VAMP project

    Science.gov (United States)

    Walsh, Susan; Kurtboǧan, Bahar; Akhun, Selin; Aksu, Ali; Hall, Jeremy; Ćifçi, Günay

    2010-05-01

    The Vertical Anatolian Movements Project (VAMP) addresses the Neogene uplift of the Taurides and the Central Anatolian Plateau. While terrestrial studies are focused on erosion in the sediment source area and deposition within the Turkish landmass, our marine work is focused to provide a history of deposition in one of the ultimate sinks: the eastern Mediterranean. In particular, we are mapping the distribution in space and time of sediment deposited from the Göksu River into the Cilicia Basin. In 2008 we collected ~2000 km of high-resolution marine multi-channel seismic reflection profiles radiating out from the present-day mouth of the Göksu River across the basin. The Göksu River delta is located on a narrow shelf at the junction of the Inner and Outer Cilicia Basins. The Inner Cilicia Basin consists of a 40 km-wide shelf linking to the onshore Adana Basin and a slope down to the deeper water (~ 1 km) of the Outer Cilicia Basin. The shelf is built out of a >2.5 km-thick sequence of Pliocene-Quaternary sediment overlying Messinian evaporites or older Miocene sediments. The evaporites have been mobilised to move down slope during the Pliocene-Quaternary so that the shelf is located above an extensional fault fan, complemented by a salt-cored fold/thrust belt in deeper water (see poster by Piercey et al., this meeting). The 2008 seismic reflection profiles show that the western margin of the Inner Cilicia Basin seaward of the mouth of the Göksu River is constructed by numerous vertically stacked and east-prograded delta successions. Detailed mapping in this region revealed that the sediment input from the Göksu River can be readily distinguished from the larger influxes from the coalescing Tarsus, Seyhan and Ceyhan Rivers to the north. The bases of major delta packages supplied by the Göksu River are marked by strong reflections, defining shelf-crossing unconformities, which can be correlated across the Inner Cilicia Basin. Industry exploration wells in the

  3. Numerical analysis of palynological data from Neogene fluvial sediments as evidence for rainforest dynamics in western Amazonia

    Science.gov (United States)

    Salamanca, Sonia; van Manen, Milan; Hoorn, Carina

    2014-05-01

    Deep-time records that give an insight into the composition and dynamics of the ancestral Amazon rain forest are rare. Yet to understand the modern biodiversity patterns it is important to untangle the long-term evolution of this forest. Sampling Neogene strata requires drilling operations or complex fieldwork along the rivers where outcrops generally are small. In the nineties an exceptionally good exposure of fluvial sediments of early Miocene age (17.7-16.1 Ma) was documented near the island of Mariñame (Caquetá River, Colombian Amazonia) (Hoorn, 1994). This 60 m sediment succession consists of quartz-rich sands with a circa 10 m black, sandy clay intercalation. Palynomorphs are well preserved in these organic-rich clays and palynological analysis indicated high pollen diversity and changes in composition following changes in the sedimentary environment and water composition (see van Soelen et al., this session). A numerical analysis in R (2013) of the existing data, using a number of multivariate and other statistical techniques now shows a gradient of change in the composition of the Miocene palynological assemblages. Non-metric-multidimensional scaling using distance matrixes (Oksanen, 2012) and their visualizations in correlograms (Friendly, 2002) indicate that the regional (palm) swamp forests of Mauritiides franciscoi (Mauritia), frequently found together with other palms such as Psilamonocolpites amazonicus (Euterpe?) and Psilamonocolpites rinconii, were affected by a marine incursion. The latter is suggested by the change of composition and the presence of estuarine elements such as Zonocostites ramonae (Rhizophora), foraminifer linings and dinoflagellate cysts, which became common during the marine event. In the older part of the section, and at the top, Rhoipites guianensis (Sterculiaceae/Tiliaceae) is quite abundant, in contrast with the relatively low abundance of M. franciscoi. The numerical analysis allowed us to: a) group the pollen data into 3

  4. A review of neogene and quaternary snakes of Central and Eastern Europe. Part 11: natricinae, elapidae, viperidae

    Directory of Open Access Journals (Sweden)

    Szyndlar, Z.

    1991-08-01

    Full Text Available Remains of Neogene and Quaternary "natricine" colubrids, elapids and viperids, including snakes previously described and those undescribed yet, coming from Poland, Ukraine, Moldavia, Czechoslovakia, Austria, Hungary, Romania, Bulgaria, and Greece are discussed. The following taxa, including 11 extinct species, were recognized: "Natricinae": Neonatrix nova, Neonatrix sp., Palaeonatrix silesiaca, Palaeonatrix lehmani, Natrix longivertebrata, Natrix cf. N. longivertebrata, Natrix natrix, Natrix tesselata, Natrix cf. N. tesselata, Natrix sp., "Natricinae" indet.; Elapidae: Naja romani, Naja sp., cf. Naja sp.; Viperidae: Vipera platyspondyla, Vipera sarmatica, Vipera burgenlandica, Vipera gedulyi, Vipera kuchurganica, Vipera antiqua, Vipera cf. V. ammodytes, Vipera berus, Vipera sp ('Oriental vipers' group, Vipera sp. ('aspis' group, Vipera sp. ('berus' group, Vipera sp. . (status unknown. Taxonomic status of two other extinct species, Natrix parva and Laophis crotaloides, is uncertain. Modern species appeared fírst in Central and East Europe in the middle Pliocene (MN 15. Older snakes belonged to extinct species of either extinct or extant genera; taxonomic distinction of most extinct genera is, however, not fully demonstrated. Best recognized oldest snakes from the area (Elapidae, Viperidae, and sorne Colubridae are clearly referable to modern genera and intrageneric subdivisions occurring today are observed in oldest (Iower Miocene remains; closest living relatives of these fossils are presently distributed in the Oriental Realm.Se revisan y estudian los restos neógenos y cuaternarios de colúbridos «natricinos», elápidos y vipéridos, incluyendo tanto serpientes previamente descritas como- otras inéditas. Los materiales analizados proceden de Polonia, Ukrania, Moldavia, Checoslovaquia, Austria, Hungría, Rumania, Bulgaria y Grecia. Se reconocen los siguientes taxones, incluyendo 11 especies extinguidas: Natricinae: Neonatrix nova

  5. Mud volcanism and authigenic carbonates related to methane-rich fluids migration in the late Neogene marls of S.E. Spain

    Science.gov (United States)

    Pierre, C.; Blanc-Valleron, M. M.; Rouchy, J. M.

    2015-12-01

    Methane-rich fluids that are generated at depth in organic-rich deposits migrate within the sediments to the seafloor where they are expelled to form mud volcanoes or pockmarks. Moreover, these migrating fluids are involved in diagenetic processes as authigenic carbonate formation and they may participate to gas hydrate formation. These features are well-known in the present-day continental margins but their fossil records are relatively scarce. The outcropping Tortonian and Messinian marls in S.E. Spain basins (Lorca, Fortuna, Columbares, Huercal Overa) contain abundant authigenic dolomite nodules. The oxygen and carbon isotopic compositions of these dolomites exhibit wide ranges (-1.4 migration in the marly deposits of the western Mediterranean basins during the late Neogene, which was the time of major paleoenvironmental changes in the Mediterranean sea climaxing during the Messinian salinity crisis.

  6. Close evolutionary affinities between freshwater corbulid bivalves from the Neogene of western Amazonia and Paleogene of the northern Great Plains, USA

    Science.gov (United States)

    Anderson, Laurie C.; Hartman, Joseph H.; Wesselingh, Frank

    2006-03-01

    Freshwater corbulid bivalves found in Miocene deposits of western Amazonia have been considered products of an endemic radiation of a marine clade within the large lacustrine system occupying the region at that time. Our reexamination of Paleocene freshwater corbulids of the Tongue River Formation of western North Dakota and eastern Montana, however, extends the stratigraphic and geographic range of three Amazonian taxa— Pachydon, Ostomya, and Anticorbula—to the Paleocene of the northern Great Plains of the United States. Both Paleocene and Miocene freshwater corbulid taxa occur in large freshwater systems with an intermittent marine connection. To test the phylogenetic relationships of one particularly widespread Paleocene species ( Pachydon mactriformis), we conducted cladistic analyses using maximum parsimony and heuristic searches of matrices of conchologic characters. Seven species of Pachydon and Pebasia dispar from the western Amazonian Neogene, Pachydon mactriformis from the Paleocene of North Dakota, representative species of eight neotropical marine corbulid genera, and three additional corbulid taxa were included. Corbula was the outgroup. All analyses produced similar regions of stability within trees. One such area is a Pachydon crown group that includes P. mactriformis, indicating that Paleocene and Miocene Pachydon are not convergent. Our results also indicate that Pachydon does not represent a separate basal radiation within the family. However, we have not resolved a robust sister clade relationship for the Pachydon crown group. Two Amazonian Neogene taxa do not fall within the Pachydon crown group, and their phylogenetic position is not resolved. At this time, we do not have sufficient evidence to refine the definitions of Pachydon and Pachydontinae as monophyletic clades. Although we have evidence that three genera of corbulid bivalves ( Pachydon, Ostomya, and Anticorbula) in the Pebas Formation are not endemic and have long geologic

  7. Inheritance of Jurassic rifted margin architecture into the Apennines Neogene mountain building: a case history from the Lucretili Mts. (Latium, Central Italy)

    Science.gov (United States)

    Bollati, Andrea; Corrado, Sveva; Marino, Maurizio

    2012-06-01

    The western Lucretili Mts. in the central Apennines (Latium, Italy) have been recently re-mapped in great detail and are the subject of combined stratigraphic, sedimentological and structural investigations. In this paper, we present a new stratigraphic interpretation of the Jurassic paleogeography of western Lucretili Mts., where a rift-derived intrabasinal paleo-high of the Alpine Tethys has been identified for the first time by means of facies analysis and biostratigraphic dating. Recognised facies associations, combined with dated stratigraphic sections, allow to define the morphology of the structural paleo-high and to identify the associated gravity-driven deposits (olistoliths) accumulated in the surrounding basin. Furthermore, we investigated the modes of interaction between Jurassic extensional structures and the subsequent contractional patterns developed during the Tertiary mountain building. In detail, the role played during Apennines tectonics by the paleo-escarpments bounding the paleo-high and by the surrounding olistoliths has been analysed. The paleo-escarpments either acted as focussing features for ENE-directed frontal thrust ramp localisation and were offset with small shortening amounts or reactivated as NNE striking high angle transpressional faults or preserved the original geometries as a result of variable orientation of paleo-escarpments with respect to the Neogene compressive stress field (with ENE oriented sigma1). Newly formed ENE striking tear faults connect these either inherited or neo-formed discontinuities. This complex stratigraphic and structural pattern is substantially different from the previous interpretations of this portion of the central Apennines based on a hypothesised layer-cake stratigraphy deformed by neo-formed Neogene thrusts. This contribution strengthens the importance of integrating facies analyses and structural investigations to detect the influence of pre-orogenic structures on compressive structural patterns

  8. Neogene basin development around Söke-Kuşadası (western Anatolia) and its bearing on tectonic development of the Aegean region

    Science.gov (United States)

    Gürer, Ömer Feyzi; Bozcu, Mustafa; Yılmaz, Kamil; Yılmaz, Yücel

    There is a N-S lying narrow strip of Neogene outcrop between the towns of Kuşadası and Söke in western Anatolia. It contains remnants of successive Neogene graben basins. The first graben began to form under the control of a N40-70°E-trending oblique fault system during the Early Miocene. At the initial phase of the opening coarse clastic rocks were deposited in front of the fault-elevated blocks as scree deposits and fanglomerates. Later the graben advanced into a large lake basin. Towards the end of the Middle Miocene the lacustrine sediments of the Early-Middle Miocene age underwent an approximately N-S compressional deformation and elevated above the lake level, and were partly eroded. During the Late Miocene a new graben basin began to form as a consequence of the development of E-W-trending normal faults, formed under the N-S extensional regime. This graben also turned later into a lake environment. The lake extended far beyond the limits of the fault zones, and covered the entire regions stretching from the south of Bafa Lake in the south to Kuşadası and beyond in the north. Micritic clayey limestones were predominantly deposited in the lake. A severe erosional phase followed the termination of the lake basin. This corresponds to the cessation of the N-S extension. When the N-S extension regenerated during the Pliocene(?)-Pleistocene, the Büyük Menderes graben system began to form. In the western part of the graben, a conjugated pair of oblique faults, the Priene-Sazlı fault and the Kuşadası fault, have formed. The faults having important strike-slip components, bounded a tectonic wedge, which began to move westward into the Aegean Sea region. Major morphological features of the region were formed under the effective control of these fault zones.

  9. New insight on the recent tectonic evolution and uplift of the southern Ecuadorian Andes from gravity and structural analysis of the Neogene-Quaternary intramontane basins

    Science.gov (United States)

    Tamay, J.; Galindo-Zaldívar, J.; Ruano, P.; Soto, J.; Lamas, F.; Azañón, J. M.

    2016-10-01

    The sedimentary basins of Loja, Malacatos-Vilcabamba and Catamayo belong to the Neogene-Quaternary synorogenic intramontane basins of South Ecuador. They were formed during uplift of the Andes since Middle-Late Miocene as a result of the Nazca plate subduction beneath the South American continental margin. This E-W compressional tectonic event allowed for the development of NNE-SSW oriented folds and faults, determining the pattern and thickness of sedimentary infill. New gravity measurements in the sedimentary basins indicate negative Bouguer anomalies reaching up to -292 mGal related to thick continental crust and sedimentary infill. 2D gravity models along profiles orthogonal to N-S elongated basins determine their deep structure. Loja Basin is asymmetrical, with a thickness of sedimentary infill reaching more than 1200 m in the eastern part, which coincides with a zone of most intense compressive deformation. The tectonic structures include N-S, NW-SE and NE-SW oriented folds and associated east-facing reverse faults. The presence of liquefaction structures strongly suggests the occurrence of large earthquakes just after the sedimentation. The basin of Malacatos-Vilcabamba has some folds with N-S orientation. However, both Catamayo and Malacatos-Vilcabamba basins are essentially dominated by N-S to NW-SE normal faults, producing a strong asymmetry in the Catamayo Basin area. The initial stages of compression developed folds, reverse faults and the relief uplift determining the high altitude of the Loja Basin. As a consequence of the crustal thickening and in association with the dismantling of the top of the Andes Cordillera, extensional events favored the development of normal faults that mainly affect the basins of Catamayo and Malacatos-Vilcabamba. Gravity research helps to constrain the geometry of the Neogene-Quaternary sedimentary infill, shedding some light on its relationship with tectonic events and geodynamic processes during intramontane basin

  10. Geologic history of the Neogene “Qena Lake” developed during the evolution of the Nile Valley: A sedimentological, mineralogical and geochemical approach

    Science.gov (United States)

    Philobbos, Emad R.; Essa, Mahmoud A.; Ismail, Mustafa M.

    2015-01-01

    Siliciclastic and carbonate sediments were laid down in southern Wadi Qena and around the Qena Nile bend (Middle Egypt) in a lacustrine-alluvial environment which dominated a relatively wide lake, the "Qena Lake" that interrupted the Nile course during the Neogene time. These sediments are represented mainly by the oldest dominantly lacustrine chocolate brown mudstones of the Khuzam Formation that accumulated nearer to the center of that lake (now forming a 185 m terrace above sea level), overlain by the dominantly lacustrine carbonates and marls of the Durri Formation which accumulated during semi-arid conditions, mainly nearer to the periphery of the lake (now forming 170, 180 and 185 m terraces a.s.l. in the studied sections). The water level of the "Qena Lake" reached 240 m. above sea level, as indicated by the maximum carbonate elevation reached in the region. Finally fanglomerates of the Higaza Formation with its chert and limestone conglomerates accumulated during torrential periods at higher elevations (forming 240, 300 and 400 m terraces a.s.l.). These three formations accumulated in this particular area before and during the unroofing of the basement rocks of the Eastern Desert, west of the watershed. According to the known Early Miocene initial development of the Nile Valley, beside the occurrence of similar deposits of Oligocene age along the eastern side of the basement range, the earlier known Pliocene age given for these sediments in the Qena area is here questioned. It might belong to earlier Miocene?-Pliocene times. As the basement rocks of the Eastern Desert were still covered by Cretaceous-Paleogene sedimentary rocks while the Khuzam, Durri and Higaza Formations were accumulating in the Qena Lake region, it is believed, contrary to the belief of some authors, that the basement rocks of the Eastern Desert were not the source of these sediments. The carbonate petrographic study, beside the X-ray, and the11 major oxides and 22 trace elements

  11. Lithology and palynology of Neogene sediments on the narrow edge of the Kitakami Massif (basement rocks), northeast Japan: significant change for depositional environments as a result of plate tectonics

    Energy Technology Data Exchange (ETDEWEB)

    Koji Yagishita; Akiko Obuse; Hiroshi Kurita [Iwate University, Morioka-City (Japan). Department of Geology, Faculty of Education

    2003-09-01

    A controversial stratigraphic section, the Taneichi Formation, is exposed along the Pacific Coast of northeastern Honshu, the main island of the Japanese Archipelago. Although most sediments of the formation have long been dated as late Cretaceous, the northern section of it has been assigned to (I) the Upper Cretaceous; (ii) the Paleogene; or (iii) the Neogene. In the present report, we present the data of palynological and sedimentological studies, showing that the northern section should be assigned to the Neogene. A more important point in the present study is that we invoke some basic principles of fluvial sedimentology to resolve this stratigraphic subject. The lignite layers full of PaleogeneMiocene dinoflagellate cysts and pollen assemblages drape over the boulder-sized ({gt}40 cm in diameter) clasts in the northern section. However, the layers totally consist of aggregates of small lignite chips, indicating that the lignites are allochthonous materials. The mega-clasts with derived microfossils in the lignites are thought to have been deposited as Neogene fluvial (flood) sediments in the newly formed Japanese Archipelago. Prior to the Miocene, the northern Honshu was part of the Eurasian Plate, thus the boulder-sized clasts cannot be envisaged as long river flood deposits along the continental Paleogene Pacific Coast. Instead, the mega-clasts with the draping lignites were probably derived from nearby Miocene highlands in the newly born island arc.

  12. The Amazon at sea: Onset and stages of the Amazon River from a marine record, with special reference to Neogene plant turnover in the drainage basin

    Science.gov (United States)

    Hoorn, Carina; Bogotá-A, Giovanni R.; Romero-Baez, Millerlandy; Lammertsma, Emmy I.; Flantua, Suzette G. A.; Dantas, Elton L.; Dino, Rodolfo; do Carmo, Dermeval A.; Chemale, Farid

    2017-06-01

    The Amazon submarine fan is a large sediment apron situated offshore Pará (Brazil) and represents the most distal extent of the Amazon River. The age of onset of this transcontinental river remains debated, yet is of great importance for understanding biotic evolutionary processes on land and at sea. Here we present new geochemical and palynological data from a borehole drilled at the continental slope and dated based on nannofossil biostratigraphy. We found that sediments of mixed source (craton and adjacent) occur at least from the late Oligocene (NP25) to late Miocene (NN9), and that the earliest Andes-derived sediments occur in NN10 (late Miocene). Our geochemical record indicates an onset of the transcontinental Amazon River between 9.4 and 9 Ma, which postdates the regional unconformity by 1 to 1.5 My. The shift in sediment geochemistry is more gradually replicated in the palynological record by a change from coastal plain and tropical lowland taxa to a mixture of tropical lowland, and montane forest to open Andean taxa. In particular, the appearance of taxa such as Jamesonia and Huperzia, followed by Valeriana, Polylepis-Acaena, Lysipomia and Plantago (with a current altitudinal range from 3200 to 4000 m) suggests the development of open, treeless, vegetation between 9.5 and 5.4 Ma, and highlight the presence of a high Andes in the late Miocene hinterland. Poaceae progressively increased from 9 Ma, with a notable rise from 4 Ma onwards, and percentages well above post-glacial and modern values, particularly between 2.6 and 0.8 Ma. We hypothesize that the rise of the grasses is a basin-wide phenomenon, but that the Plio-Pleistocene expansion of open, treeless vegetation on the Andean slopes and foothills are the main contributor. This rise in grasses was likely caused by climatic fluctuations, and subsequent changes in relief and erosion rates. We conclude that the onset of the Amazon River is coupled with Neogene Andean tectonism and that subsequent

  13. Neogene-quaternary Ostracoda and paleoenvironments, of the Limón basin, Costa Rica, and Bocas del Toro basin, Panama

    Science.gov (United States)

    Borne, P.F.; Cronin, T. M.; Hazel, J.E.

    1999-01-01

    Tropical marine ostracodes from Neogene and Quaternary sediments of the Central American Caribbean region have been the subject of biostratigraphic, ecological, taxonomic, and evolutionary studies. As part of the Panama Paleontology Project (PPP), Neogene and Quaternary ostracodes are being studied from the Central American region. The overall goal of this research is to evaluate the impact of the emergence of the Central American Isthmus as a land barrier between the Caribbean/tropical Atlantic and the Pacific oceans on marine ostracode biodiversity and the oceanic environments in which extant ostracodes evolved. Due to the ecological specificity of many living tropical ostracode species, they are ideally suited for reconstructing paleoenvironments on the basis of their occurrence in fossil assemblages, which in turn can lead to a better understanding of the tropical climatic and tectonic history of Central America. The principal aims of this chapter are: (a) to document the composition of the ostracode assemblages from the Limón Basin of Costa Rica and the Bocas del Toro Basin of Panama, two areas yielding extensive ma rine ostracode assemblages; (b) to describe the environments of deposition within these basins; and (c) to document the stratigraphic distribution of potentially agediagnostic ostracode species in the Limón and Bocas del Toro basins in order to enhance their use in Central American biostratigraphy. A secondary, but none-the-less important goal is to assemble a database on the distribution of modem ostracode species in the Caribbean and adjacent areas as a basis for comparison with fossil assemblages. Although the ecological, biostratigraphic and paleoenvironmental conclusions presented here will improve as additional material is studied, these fossil and modem ostracode databases constitute the foundation for future evolutionary and geochernical studies of tropical Caribbean and eastern Pacific Ocean ostracodes. Moreover, we present here evidence

  14. Stable isotope variation in tooth enamel from Neogene hippopotamids: monitor of meso and global climate and rift dynamics on the Albertine Rift, Uganda

    Science.gov (United States)

    Brachert, Thomas Christian; Brügmann, Gerhard B.; Mertz, Dieter F.; Kullmer, Ottmar; Schrenk, Friedemann; Jacob, Dorrit E.; Ssemmanda, Immaculate; Taubald, Heinrich

    2010-10-01

    The Neogene was a period of long-term global cooling and increasing climatic variability. Variations in African-Asian monsoon intensity over the last 7 Ma have been deduced from patterns of eolian dust export into the Indian Ocean and Mediterranean Sea as well as from lake level records in the East African Rift System (EARS). However, lake systems not only depend on rainfall patterns, but also on the size and physiography of river catchment areas. This study is based on stable isotope proxy data (18O/16O, 13C/12C) from tooth enamel of hippopotamids (Mammalia) and aims in unravelling long-term climate and watershed dynamics that control the evolution of palaeolake systems in the western branch of the EARS (Lake Albert, Uganda) during the Late Neogene (7.5 Ma to recent). Having no dietary preferences with respect to wooded (C3) versus grassland (C4) vegetation, these territorial, water-dependant mammals are particularly useful for palaeoclimate analyses. As inhabitants of lakes and rivers, hippopotamid tooth enamel isotope data document mesoclimates of topographic depressions, such as the rift valleys and, therefore, changes in relative valley depth instead of exclusively global climate changes. Consequently, we ascribe a synchronous maximum in 18O/16O and 13C/12C composition of hippopotamid enamel centred around 1.5-2.5 Ma to maximum aridity and/or maximum hydrological isolation of the rift floor from rift-external river catchment areas in response to the combined effects of rift shoulder uplift and subsidence of the rift valley floor. Structural rearrangements by ~2.5 Ma within the northern segment of the Albertine Rift are well constrained by reversals in river flow, cannibalisation of catchments, biogeographic turnover and uplift of the Rwenzori horst. However, a growing rain shadow is not obvious in 18O/16O signatures of the hippopotamid teeth of the Albertine Rift. According to our interpretation, this is the result of the overriding effect of evaporation on 18

  15. Evidence for pre-Cretaceous history and partial Neogene (19-9 Ma) reequilibration in the Karakorum (NW Himalayan Syntaxis) from 40Ar- 39Ar amphibole dating

    Science.gov (United States)

    Rolland, Yann; Villa, Igor M.; Guillot, Stéphane; Mahéo, Gweltaz; Pêcher, Arnaud

    2006-09-01

    Amphiboles and a biotite from amphibolites and amphibolitic gneisses of the Karakorum Metamorphic Complex (KMC, NW Himalaya), were dated using the 40Ar/ 39Ar method. Isotope correlations were compared to electron-microprobe analyses. Both Al IV and Al VI contents of amphibole increase from the south near the Shyok Suture Zone to the Dassu-Askole Area in the north, with an increase in metamorphic grade (from anchizone to upper amphibolite facies). In the lower metamorphic zone, discordant age spectra were obtained. They are related to epidote-amphibolite overgrowth of amphibole rims on older (Precambrian to Mesozoic) magmatic cores. In the Shyok Suture Zone Ar/Ar ages of 38-62 Ma are contemporaneous with the emplacement of the Ladakh Batholith granodiorites, while middle Cretaceous magmatic Ar/Ar ages (˜ 120 Ma) are locally preserved in tschermakite relics. In the Southern Karakorum basement, a minimum Ar/Ar age of 651 Ma was preserved, while an age of 208.5±2 Ma was preserved in Panjal Trap-like diorites. At the margin of the domes zone, more recent metamorphism resulted in mineral growth at 20-5 Ma. In the domes zone, amphibole Ar/Ar ages of 17 Ma (Askole) and bimodal age spectra of 15-17 and 9-13 Ma (Dassu) extend towards the east the zone of Neogene amphibolite to granulite facies metamorphism known in the Nanga Parbat Syntaxis.

  16. Relationship Between Faults Oriented Parallel and Oblique to Bedding in Neogene Massive Siliceous Mudstones at The Horonobe Underground Research Laboratory, Japan

    Science.gov (United States)

    Hayano, Akira; Ishii, Eiichi

    2016-10-01

    This study investigates the mechanical relationship between bedding-parallel and bedding-oblique faults in a Neogene massive siliceous mudstone at the site of the Horonobe Underground Research Laboratory (URL) in Hokkaido, Japan, on the basis of observations of drill-core recovered from pilot boreholes and fracture mapping on shaft and gallery walls. Four bedding-parallel faults with visible fault gouge, named respectively the MM Fault, the Last MM Fault, the S1 Fault, and the S2 Fault (stratigraphically, from the highest to the lowest), were observed in two pilot boreholes (PB-V01 and SAB-1). The distribution of the bedding-parallel faults at 350 m depth in the Horonobe URL indicates that these faults are spread over at least several tens of meters in parallel along a bedding plane. The observation that the bedding-oblique fault displaces the Last MM fault is consistent with the previous interpretation that the bedding- oblique faults formed after the bedding-parallel faults. In addition, the bedding-parallel faults terminate near the MM and S1 faults, indicating that the bedding-parallel faults with visible fault gouge act to terminate the propagation of younger bedding-oblique faults. In particular, the MM and S1 faults, which have a relatively thick fault gouge, appear to have had a stronger control on the propagation of bedding-oblique faults than did the Last MM fault, which has a relatively thin fault gouge.

  17. Provenance of the Late Neogene Siwalik sandstone, Kumaun Himalayan Foreland Basin: Constraints from the metamorphic rank and index of detrital rock fragments

    Indian Academy of Sciences (India)

    Poonam Jalal; Sumit K Ghosh

    2012-06-01

    An understanding about lithology, tectonics and unroofing history of provenance is mostly drawn from the compositional and textural parameters of the detrital fragments. We here use different metamorphic ranks (Rm) and metamorphic index (MI) values of rock fragments present in Late Neogene Siwalik sandstone of the Ramganga sub-basin to infer the provenance history. The study indicates maximum contribution from metamorphic ranks 1 and 2 (Rm1 and Rm2; meta-sedimentary and very low grade metamorphic rocks) and minimum from metamorphic rank 4 (Rm4; high metamorphic grade rocks). The metamorphic index (MI) values range from 118 to 224, with an average of 186. The meta-sedimentary and very low-grade metamorphic rock fragments are derived from the Lesser Himalayan domain. The medium-to-high grade metamorphic fragments are derived from the Lesser Himalayan Crystalline bodies. The abundance of Rm2 and Rm3 detrital modes suggest the exhumation of crystalline bodies of the Ramgarh and Almora most likely occurred prior to 7 Ma and subsequently the source area shifted and resulted abundant supply of Rm1 fragments due to the upliftment along Main Boundary Thrust around 5.55 Ma.

  18. Zeolitisation of Neogene sedimentary and pyroclastic rocks exposed in Paipa (Boyacá, in the Colombian Andes: simulating their natural formation conditions

    Directory of Open Access Journals (Sweden)

    Quintero Ortíz Fredy Alberto

    2011-12-01

    Full Text Available The present study concerns the synthesis of zeolites from Neogene sedimentary and pyroclastic rocks exposed around the Sochagota Lake, Paipa (Boyacá. Two synthesis methods were used: conventional hydrothermal treatment and alkaline fusion followed by hydrothermal reaction. Both raw materials and synthesised zeolytic products were characterised by X-ray diffraction (XRD, Fourier transform infrared spectroscopy (FTIR and nuclear magnetic resonance (NMR. Several zeolytic phases were synthesised, including faujasite (FAU, phillipsite(PHI and sodalite (SOD. The results showed that the alkaline fusion approach was more efficient regarding hydrothermal conversion of the raw materials than conventional hydrothermal treatment, taking into accountthat zeolytic products having a higher degree of crystallinity and few impurities were obtained in this way. This study was aimed at applying experimental mineralogy to a laboratory simulation of the geological conditions in which zeolites can occur as the basis for defining criteria for exploring natural zeolites in Colombia, with prospects for the profitable exploitation of these mineral resources in different parts of Colombia

  19. Glowing seashells: diversity of fossilized coloration patterns on coral reef-associated cone snail (Gastropoda: Conidae shells from the Neogene of the Dominican Republic.

    Directory of Open Access Journals (Sweden)

    Jonathan R Hendricks

    Full Text Available The biology of modern Conidae (cone snails--which includes the hyperdiverse genus Conus--has been intensively studied, but the fossil record of the clade remains poorly understood, particularly within an evolutionary framework. Here, ultraviolet light is used to reveal and characterize the original shell coloration patterns of 28 species of cone snails from three Neogene coral reef-associated deposits from the Cibao Valley, northern Dominican Republic. These fossils come from the upper Miocene Cercado Fm. and lower Pliocene Gurabo Fm., and range in age from about 6.6-4.8 Ma. Comparison of the revealed coloration patterns with those of extant species allow the taxa to be assigned to three genera of cone snails (Profundiconus, Conasprella, and Conus and at least nine subgenera. Thirteen members of these phylogenetically diverse reef faunas are described as new species. These include: Profundiconus? hennigi, Conasprella (Ximeniconus ageri, Conus anningae, Conus lyelli, Conus (Atlanticonus? franklinae, Conus (Stephanoconus gouldi, Conus (Stephanoconus bellacoensis, Conus (Ductoconus cashi, Conus (Dauciconus garrisoni, Conus (Dauciconus? zambaensis, Conus (Spuriconus? kaesleri, Conus (Spuriconus? lombardii, and Conus (Lautoconus? carlottae. Each of the three reef deposits contain a minimum of 14-16 cone snail species, levels of diversity that are similar to modern Indo-Pacific reef systems. Finally, most of the 28 species can be assigned to modern clades and thus have important implications for understanding the biogeographic and temporal histories of these clades in tropical America.

  20. Sr isotopic composition of gypsic paleosols as a proxy for Neogene forearc uplift in the South America - Nazca plate system at latitudes 19 to 22° S

    Science.gov (United States)

    Cosentino, N. J.; Jordan, T. E.

    2011-12-01

    Quantification of uplift of a continental surface relative to sea level is challenging. The study area comprises the forearc associated with the South America - Nazca plate margin in northern Chile. The Coastal Cordillera (CdlC) is a mountain range 800 to 2300 m in elevation that ends abruptly to the west at the Pacific Ocean, terminated at a 400 m to 1700 m high scarp. The CdlC is formed mainly of Jurassic - Early Cretaceous igneous rocks, the remnants of a Mesozoic magmatic arc. To the east, the Central Depression (CD) is a forearc basin filled with Cenozoic sediments derived from the arc to the east. Arid to hyperarid climate conditions dominated throughout the Neogene. Profiles from rivers draining the CD and cutting through the CdlC are strongly suggestive that at least 1 km of relative surface uplift occurred since 10 Ma. Paleogeographic reconstructions of continental deposits, marine terraces and tilted originally horizontal depositional surfaces in the CdlC constrain surface uplift histories. However, we seek quantitative information about the magnitude as well as ages of uplift, so that numerical models of forearc geodynamics can be tested against uplift history. We are testing a new paleoaltimetry proxy based on the 87Sr/86Sr ratio of gypsum-rich paleosols. Published studies show that modern pedogenic gypsum in the study area is derived from two sources of distinguishable Sr isotopic values; salts precipitate from aerosols in persistent winter marine fogs and dust comes from the weathering of Andean rocks. It has been shown for modern soils that a transect from the coast to the Andes reveals a progressive decline in 87Sr/86Sr, corresponding to the mixing of marine aerosols and weathered dust. Below 1.5 km altitude, the marine signal diminishes as altitude rises. The low mass difference between 87Sr and 86Sr leads to little fractionation by environmental processes, which is ideal for studying the primary marine vs. Andean signal. Because the Neogene strata

  1. Seismostratigraphy and tectonic architecture of the Carboneras Fault offshore based on multiscale seismic imaging: Implications for the Neogene evolution of the NE Alboran Sea

    Science.gov (United States)

    Moreno, Ximena; Gràcia, Eulàlia; Bartolomé, Rafael; Martínez-Loriente, Sara; Perea, Héctor; de la Peña, Laura Gómez; Iacono, Claudio Lo; Piñero, Elena; Pallàs, Raimon; Masana, Eulàlia; Dañobeitia, Juan José

    2016-10-01

    In the SE Iberian Margin, which hosts the convergent boundary between the European and African Plates, Quaternary faulting activity is dominated by a large left-lateral strike-slip system referred to as the Eastern Betic Shear Zone. This active fault system runs along more than 450 km and it is characterised by low to moderate magnitude shallow earthquakes, although large historical events have also occurred. The Carboneras Fault is the longest structure of the Eastern Betic Shear Zone, and its southern termination extends further into the Alboran Sea. Previously acquired high-resolution data (i.e. swath-bathymetry, TOBI sidescan sonar and sub-bottom profiler) show that the offshore Carboneras Fault is a NE-SW-trending upwarped zone of deformation with a length of 90 km long and a width of 0.5 to 2 km, which shows geomorphic features typically found in subaerial strike-slip faults, such as deflected drainage, pressure ridges and "en echelon" folds. However, the neotectonic, depth architecture, and Neogene evolution of Carboneras Fault offshore are still poorly known. In this work we present a multiscale seismic imaging of the Carboneras Fault (i.e. TOPAS, high-resolution multichannel-seismic reflection, and deep penetration multichannel-seismic reflection) carried out during three successive marine cruises, from 2006 to 2010. The new dataset allowed us to define a total of seven seismostratigraphic units (from Tortonian to Late Quaternary) above the basement, to characterise the tectonic architecture and structural segmentation of the Carboneras Fault, and to estimate its maximum seismic potential. We finally discuss the role of the basement in the present-day tectonic evolution of the Carboneras Fault, and explore the northern and southern terminations of the fault and how the strain is transferred to nearby structures.

  2. Orogen-parallel brittle extension as a major tectonic imprint in the Neogene evolution of the south-western Alpine arc

    Science.gov (United States)

    Beucher, Romain; Sue, Christian; Tricart, Pierre

    2017-04-01

    We present a new analysis of the late Alpine brittle deformation in the southern branch of the western Alpine arc, focusing on the stack of internal metamorphic nappes east of the Argentera external crystalline massif. The regional-scale fault network is dominated by a NW-SE-striking right-lateral fault system that follows the general curvature of the arc and controls the overall morphology of the area. A second fault set strikes N-S and is mainly represented by normal faults which accommodate orogen-parallel extension. Structural analysis and paleostress tensors derived from inversion of fault-slip data reveal a complex pattern of deformation involving extensional and strike-slip deformation events. The orogen-parallel extension previously described in the internal zones at the east of the Pelvoux massif is confirmed further south, and we show that it is combined with right-lateral strike-slip deformation that increases in intensity towards the south-west. The stability of the minimum stress axis (σ3) direction suggests that extensional and transcurrent regimes are contemporaneous and highlights regional interferences between inner brittle extension, parallel to the strike of the belt, and the strike-slip strain field driven by the counterclockwise rotation of the Apulia-Adria plate. The curved geometry of the belt constrains the direction of extension and the coupling relationship between the internal and external Alpine zones. We propose that the Neogene tectonic history is a result of the unique curved tectonic architecture of the south-western Alps with respect to the rotation of the Apulia-Adria indenting plate. The southern tip of the western Alpine arc represents a transitional zone between extension in the inner chain and strike-slip/compression in the outer parts.

  3. Composite Phymatoderma from Neogene deep-marine deposits in Japan: Implications for Phanerozoic benthic interactions between burrows and the trace-makers of Chondrites and Phycosiphon

    Directory of Open Access Journals (Sweden)

    Kentaro Izumi

    2015-12-01

    Full Text Available Among composite trace fossils, one of the most common structures throughout the Phanerozoic are structures (e.g., dwelling trace, feeding trace reworked by Chondrites and/or Phycosiphon. However, differences in the nature of the reworking behaviors of these two ichnogenera remain unknown. Thus, in this study, composite Phymatoderma specimens from the Neogene deep-marine Shiramazu Formation in Japan, particularly those reworked by Chondrites and Phycosiphon, were analyzed to reveal the specific conditions that might control the activities of these trace-makers. Phymatoderma reworked by Phycosiphon is significantly larger than non-reworked Phymatoderma, whereas Phymatoderma reworked by Chondrites shows no significant difference in burrow diameter compared with non-reworked Phymatoderma. The recognized size selectivity (i.e., preference for larger burrows by the Phycosiphon trace-maker can be explained by considering the different feeding strategies of these two ichnogenera; namely deposit-feeding Phycosiphon-makers, which must have processed a significant mass of sediment to obtain sufficient organic matter, whereas chemosymbiotic Chondrites-producers did not require a lot of sediment to obtain nutrients. In order to test these interpretations, a dataset of Phanerozoic trace fossils reworked by Chondrites/Phycosiphon were compiled. Consequently, the Phycosiphon-producers’ preference toward relatively larger burrows was recognized, quantitatively supporting the results of this study. The compilation also indicates that the burrow size might have become one of the important limiting factors for the Phycosiphon-producers that tried to rework the sediments within previous subsurface burrows, at least for 80 million years.

  4. The role of pleistocene strike-slip tectonics in the neogene-quaternary evolution of the southern Apennine orogenic belt: implications for oil trap development

    Energy Technology Data Exchange (ETDEWEB)

    Monaco, C.; Tortorici, L.; Catalano, S. [Universita degli Studi di Catania (Italy). Dipt. di Scienze Geologiche; Paltrinieri, W.; Steel, N. [British Gas Rimi, Milan (Italy)

    2001-07-01

    The Southern Apennine orogenic belt is composed of allochthonous continental units derived from the African and European palaeo-margins of NeoTethys (the Adria and Corsica-Sardinia Blocks, respectively), together with oceanic units derived from the intervening NeoTethyan domain. The frontal part of the belt has been thrust over a foredeep-foreland system consisting of the Bradano Trough and Apulian Platform. The belt can be divided into two structural levels which are separated by a major detachment surface. The upper level consists of a multilayer complex made up of allochthonous NeoTethyan nappes; these were deformed during oceanic subduction, and are now emplaced on the Adria Block as a consequence of continent-continent collision. The lower structural level is characterised by large-scale duplexes involving the Mesozoic-Cenozoic sedimentary cover of the Adria Block which in recent years has formed an important target for oil exploration. On top of these allochthonous terranes, a series of small Plio-Pleistocene basins developed during the final phases of the thrust belt's migration into the foreland. During the last stages of orogenesis, thrust migration became locked as a result of collisional thickening of the continental crust, and deformation in the southern Apennines was taken up by strike-slip faults which now cut across the fold and thrust belt. In this paper, we describe the major Pleistocene strike-slip structures in the southern Apennines between the Pollino Mountains in the south and the Potenza region in the north, and investigate the role of wrench tectonics in the belt's Neogene-Quaternary evolution. The study combines field mapping with analyses of satellite images and aerial photographs. Sinistral WNW-ESE trending strike-slip faults are accommodated by thrusts and folds which cross-cut the preexisting tectonic layering, giving rise to an interference pattern in which culminations may act as structural traps suitable for oil and gas

  5. Spatial distribution of cones and satellite-detected lineaments in the Pali Aike Volcanic Field (southernmost Patagonia): insights into the tectonic setting of a Neogene rift system

    Science.gov (United States)

    Mazzarini, Francesco; D'Orazio, Massimo

    2003-07-01

    The relationships between the distribution and morphometric features of eruptive structures (scoria and spatter cones, maar, tuff rings) and the fracture network were investigated in the Pliocene-Quaternary Pali Aike Volcanic Field (southernmost Patagonia, Argentina-Chile). The alkali basaltic/basanitic magmas which erupted in this area have nearly primary magma compositions and often bear mantle xenoliths; hence magma ascent from deep-seated reservoirs was probably very fast, with no significant stagnation at crustal levels. Field surveys and satellite image analysis led to the identification of up to 467 eruptive structures and four main NW-SE, NE-SW, E-W and N-S fracture systems. The spatial distribution of eruptive cones and fractures was investigated through the computation of power-law exponents ( Df) for self-similar clustering. The self-similarity of cones and fractures was defined between lower and upper cut-offs which were in turn related to the thickness of the fractured mechanical layer. The fractal character of cones and fracture distribution (clustering) in the Pali Aike Volcanic Field area was thus correlated with crustal thickness. The self-similarity of fractures was used to establish the relative chronology of the detected fracture systems. The self-similar clustering exponent is highest in the E-W and NW-SE fracture systems ( Df=1.78 and 1.77, respectively), and lowest in the N-S system ( Df=1.65). The self-similar clustering of eruptive structures is well defined ( Df=1.45). The intense volcano-tectonic activity in the Pali Aike area marks a major Pliocene-Quaternary phase in the development of the Magellan Neogene Rift System.

  6. Geology, geochemistry, geochronology, and economic potential of Neogene volcanic rocks in the Laguna Pedernal and Salar de Aguas Calientes segments of the Archibarca lineament, northwest Argentina

    Science.gov (United States)

    Richards, J. P.; Jourdan, F.; Creaser, R. A.; Maldonado, G.; DuFrane, S. A.

    2013-05-01

    This study presents new geochemical, geochronological, isotopic, and mineralogical data, combined with new geological mapping for a 2400 km2 area of Neogene volcanic rocks in northwestern Argentina near the border with Chile, between 25°10‧S and 25°45‧S. The area covers the zone of intersection between the main axis of the Cordillera Occidental and a set of NW-SE-trending structures that form part of the transverse Archibarca lineament. This lineament has localized major ore deposits in Chile (e.g., the late Eocene La Escondida porphyry Cu deposit) and large volcanic centers such as the active Llullaillaco and Lastarría volcanoes on the border between Chile and Argentina, and the Neogene Archibarca, Antofalla, and Cerro Galán volcanoes in Argentina. Neogene volcanic rocks in the Laguna Pedernal and Salar de Aguas Calientes areas are mostly high-K calc-alkaline in composition, and range from basaltic andesites, through andesites and dacites, to rhyolites. Magmatic temperatures and oxidation states, estimated from mineral compositions, range from ~ 1000 °C and ∆FMQ ≈ 1.0-1.5 in andesites, to ~ 850 °C and ∆FMQ ≈ 1.5-2.0 in dacites and rhyolites. The oldest rocks consist of early-middle Miocene andesite-dacite plagioclase-pyroxene-phyric lava flows and ignimbrites, with 40Ar/39Ar ages ranging from 17.14 ± 0.10 Ma to 11.76 ± 0.27 Ma. Their major and trace element compositions are typical of the Andean Central Volcanic Zone, and show strong crustal contamination trends for highly incompatible elements such as Cs, Rb, Th, and U. These rocks are geochemically grouped as sub-suite 1. This widespread intermediate composition volcanism was followed in the middle-late Miocene by a period of more focused rhyodacitic flow-dome complex formation. These felsic rocks are characterized by less extreme enrichments in highly incompatible elements, and increasing depletion of heavy rare earth elements. These rocks are geochemically grouped as sub-suite 2. The

  7. Changes in grain-size and sedimentation rate of the Neogene Red Clay deposits along the Chinese Loess Plateau and implications for the palaeowind system

    Institute of Scientific and Technical Information of China (English)

    WEN Lingjuan; LU Huayu; QIANG Xiaoke

    2005-01-01

    The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to investigate spatiotemporal changes in grain-size and sedimentation rate of the Neogene Red Clay deposits in north China and to explore palaeoclimatic changes during the late Miocene and Pliocene, in particular the palaeowind system that transported dust. Samples were collected from eight Red Clay sections on the Loess Plateau. Measurement and analysis show that there is a clear southward decrease in the mean grain-size index and in the coarse particle fraction (>20 μm). At Jiaxian site on the northern Loess Plateau, the average mean grain-size is around 20 μm, while at Lantian site in the south, the mean is around 9 μm. The coarse particle fraction >20 μm makes up 24.4% and 5.6%, at the two sites respectively. This distinct diversity of grain-size in the aeolian Red Clay deposit between the north and south indicate that the palaeodust was transported mainly by northerly low-level winds. The grain-size variations in the Red Clay deposits can also be divided into three stages (the lower, the middle and the upper interval): grain-size of the lower stage is significantly coarser than that of the middle stage, but finer than that of the upper stage. As a consequence, the intensity of palaeowind and desiccation of the dust source region during the late Miocene and Pliocene can be divided into three stages: 6.2-5.4 Ma, 5.4-3.5 Ma and 3.5-2.6 Ma. Strength of the palaeowind during the middle stage (5.4-3.5 Ma) is weaker than that of the previous and subsequent stages and the intensity of palaeowind during the latest stage (3.5-2.6 Ma) is stronger than that of the early time (6.2-5.4 Ma). Variations in the sedimentation rate of the Red Clay deposit can also be divided into three stages: the earlier, the middle and the later interval. The sedimentation rate of the

  8. Polen y esporas de la Formación Navidad, Neógeno de Chile Pollen and spores of the Navidad Formation, Neogene from Chile

    Directory of Open Access Journals (Sweden)

    VIVIANA BARREDA

    2011-09-01

    with the co-existence of Gondwanan (Podocarpaceae, Araucariaceae, Nothofagaceae and neotropical (Sapotaceae, Malphigiaceae, Arecaceae, Chloranthaceae, Tiliaceae/Bombacaceae taxa -Mixed Paleoflora- supporting previous assumptions based on the macroflora. On the forest margins, patches of sclerophyllous formations with Anacardiaceae and Fabaceae as prevailing components may have also established. Xerophitic and halophytic shrubby-herbaceous elements (Chenopodiaceae, Calyceraceae may have developed in sandy soils and costal salt marshes. Endemic components such as Calyceraceae and Asteraceae (Barnadesioideae were recorded for the first time in Chile. This flora would have developed under warm and humid climatic conditions. The spore-pollen assemblages support a Neogene age for the Navidad Formation.

  9. U-Pb geochronology of modern river sands from the flat-slab segment of the southern central Andes, Argentina, 29-31°S: Implications for Neogene foreland and hinterland basin evolution

    Science.gov (United States)

    Capaldi, T.; Horton, B. K.; McKenzie, R.; Stockli, D. F.

    2015-12-01

    This study investigates how Andean river sediments in the flat-slab segment of western Argentina record active mixing of lithologically and geochemically distinct source regions comprising the Principal Cordillera, Frontal Cordillera, Precordillera fold-thrust belt, Sierras Pampeanas basement uplifts, and recycled Neogene basin fill. Detrital zircon U-Pb geochronological results for modern river sands discriminate variations from hinterland source regions, through river tributaries and main trunks of the Bermejo, Jachal, San Juan, and Mendoza rivers, and their respective fluvial megafans within the active foreland basin. Proportions of proximal zircon populations in the hinterland trunk rivers (with extensive Permian-Triassic and Cenozoic igneous exposures) diminish downstream with progressive contributions from the frontal Precordillera fold-thrust belt (dominantly Paleozoic sedimentary rocks) and Pampean basement uplifts. However, this systematic downstream dilution is perturbed in several catchments by significant recycling of older foreland basin fill. The degree of recycling depends on the position and extent of Oligocene-Pliocene exposures within the catchments. To discern the effects of the variable detrital zircon sources, multiple statistical methods are utilized. Quantitative comparisons suggest that variations in detrital zircon age distributions among the modern sands, and with older foreland basin fill and exposed bedrock, are dependent on spatial and temporal variations in exhumation and drainage network evolution within their respective Andean catchments. The present surface area of competing source regions and the configuration of hinterland tributary rivers largely dictate the degree of downstream dilution and/or recycling. This study provides a modern analogue and baseline for reconstructing Neogene shifts in foreland basin provenance, depositional systems, and drainage configurations during a critical transition to flat-slab subduction.

  10. 中国新近纪植被和环境研究中的几个问题讨论%REMARKS ON SOME POSSIBLE BIAS IN RECONSTRUCTING NEOGENE VEGETATION AND ENVIRONMENT IN CHINA

    Institute of Scientific and Technical Information of China (English)

    王伟铭

    2011-01-01

    探索新近纪植被和环境的发展规律,是了解当今地球生物多样性和环境的形成过程、预测今后可能变化趋势的重要途径,已成为当今学术界研究的一个热点.鉴于中国新近纪植被和环境演化的错综复杂性,为使相关研究工作的开展真实有效,特提出下列几个问题进行讨论,以期引起大家的重视:1)资料的不均衡性.现有的有关中国新近纪古植物资料因研究时期、产地和化石类型的不同,存在着很大的不均衡性,如一些源于油田的孢粉资料,大多是以孢粉组合的形式陈述,孢粉组合所涵盖的地层往往很厚,其精度远比以样品为单元的资料为低.2)地质年代的精确对比.中国陆相地层年代的确定以往主要参照化石证据,其中孢粉为重要证据之一.鉴于新近纪植被分异的增大,大区域间的孢粉对比存在着较大的风险,工作中需要更多地运用其他证据,如古地磁等.3)大植物与孢粉资料运用的利弊.用综合化石证据来恢复古植被,需要根据不同化石的保存特性区别对待,如孢粉的产出层位一般比较连续,但更多地代表区域性植被面貌;而大植物的分布层位比较局限,主要反映本地植物的情况.此外,由于保存的缘故,草本植物的花粉比大植物更容易被保存.4)定量方法的运用.对原始资料需要建立一个严格的取舍标准,以去除因资料的不均衡所引起的误差.对孢粉和大植物资料要区别对待,因孢粉组分的百分含量对决定植被的类型至关重要.%Neogene is an important period for the evolution of vegetations. The distribution pattern of modern vegetation on the earth is largely affected and restricted by the Late Cenozoic environment changes to a great extent. Consequently, the relevant Neogene vegetation and its relationship with environment have got more and more attention in the academic circle. Some new approaches, such as various related

  11. 西沙海域新近纪生物礁的发育演化及控制因素%Development and controlling factors of Neogene reefs in Xisha sea area

    Institute of Scientific and Technical Information of China (English)

    杨振; 张光学; 张莉; 夏斌

    2016-01-01

    南海北部西沙海域发育大量的生物礁,活跃于整个新近纪,蕴含有丰富的油气资源。对西沙海域高精度地震数据及钻井数据的研究表明,早中新世时期,少量的生物礁初始发育于地势高点之上。至中中新世早期,生物礁进入了全面发育阶段,礁体类型众多,如点礁、台地边缘礁、塔礁等,广泛分布于西沙隆起西部的斜坡之上。在发育过程中,随着水体的加深,生物礁逐渐向隆起等地势高部位迁移。至中中新世晚期,进入衰退阶段,以马趾礁、台地边缘礁为代表,主要分布于西沙隆起之上。晚中新世以来,生物礁的发育进入了淹没阶段,并以垂向生长的环礁为代表,主要分布于西沙隆起之上的岛礁周缘。构造作用和相对海平面变化为西沙海域新近纪生物礁发育演化的主要控制因素,其中构造断裂产生的构造高点控制生物礁初始发育的位置,后期基底构造沉降和相对海平面变化控制了生物礁发育演化的各个阶段,三级相对海平面周期性浮动也影响了生物礁旋回性的退积过程。%During the Neogene a large number of reefs developed in the Xisha sea area with a great potential for oil and gas exploration. High⁃resolution seismic data and extensive well drilling data provided an opportunity to under⁃stand the evolution of reefs in this area. A few reefs initially developed on a basement high in the early Miocene. In the early Middle Miocene, the reefs, such as point reefs, platform⁃edge reefs, and pinnacle reefs, flourished on the western slope of Xisha Uplift. They gradually back stepped to the elevated topographic highs in response to a relative sea level rise. In the late Middle Miocene, reefs began to wither and mainly grew on the Xisha Uplift represented by horse toe reefs and platform⁃edge reefs. Since the Late Miocene, many reefs formerly developing on the edge of the Xisha Uplift

  12. 南海北部大陆架琼东南盆地西南部新近纪沟鞭藻类%NEOGENE DINOFLAGELLATES FROM THE SOUTHWESTERN QIONG DONGNAN BASIN IN THE NORTH CONTINENTAL SHELF OF THE SOUTH CHINA SEA

    Institute of Scientific and Technical Information of China (English)

    何承全; 祝幼华; 麦文

    2005-01-01

    首次报道的低纬度晚第三纪(新近纪)丰富多样的海相沟鞭藻类,产自南海北部大陆架琼东南盆地西南部的两钻孔(主要是Ya21-1-2井,少量为Ya21-1-1井),经鉴定达40余种.文中仅对其中的31种4亚种进行了照相和对15种2亚种和1新种 (Impletosphaeridium capillare sp. nov.)在我国进行了首次描述;在新近系建立2个沟鞭藻组合:即 Hystrichosphaeropsis obscura组合(下部)和Reticulatosphaera actinocoronata-Polysphaeridium zoharyi组合(上部),并讨论了它们的组合特征及其地质时代,认为其下部的组合时代为中新世,上部的组合时代为上新世.%Rich and varied dinoflagellate cysts dealt with in this paper are obtained from the Neogene subsurface sediments of two offshore wells (mainly from well Ya21-1-2 with a depth of 1827.77-4562.79m, but a few from well Ya21-1-1 with a depth of 2413.98-3703.87m) drilled in the southwestern Qiong Dongnan(or Southeast) Basin, the North Continental Shelf of the South China Sea. More than fourty species belonging to 20 genera of dinoflagellates, Granodiscus granulatus of acritarchs, Pterospermella spp. of chlorophytes, and microforaminifer linings have been identified from well Ya21-1-2, of which 31 species of dinoflagellates are only illustrated and described in this work, including one new species, Impletosphaeridium capillare sp. nov. Two dinoflagellate assemblages have been recognized from the Neogene sediments of well Ya21-1-2 which are as follows in ascending order. 1. Hystrichosphaeropsis obscura Assemblage (at a depth of 3727.65-4562.79m) is marked by the latest occurrences of several species including Cordosphaeridium cantharellus, Bosedinia granulata, Hystrichosphaeropsis obscura and by the presence of Edwardsiella sexispinosa, Selenopemphix crenata and Impletosphaeridium capillare sp. nov. In the assemblage Hystrichokolpoma rigaudiae, H. denticulatum, Lingulodinium machaerophorum, Operculodinium centrocarpum, Polysphaeridium

  13. 柴西南古近系——新近系盐湖盆地层序地层分析%Sequence Stratigraphic Study of Paleogene and Neogene Salt Lake, Southwestern Qaidam Basin

    Institute of Scientific and Technical Information of China (English)

    王宏波; 陈启林; 王朴

    2011-01-01

    Sequence stratigraphic study of the salt lake with lately started and weak foundations in Qaidam Basin is important in many respects. In order to analyze the sequence stratigraphy in Paleogene and Neogene in southwestern Qaidam Basin and provide a foundation for lithologic hydrocarbon reservoir exploration, this paper studies the sequence boundary identification and the sequence classification in Paleogene and Neogene in southwestern Qaidam Basin by using sequence stratigraphic method, and applyin8 outcrop data, core, drilling data and seismic data. It is shown that the classification in terms of 13 long-term circles is reasonable, and there are 4 sequence developing patterns: gentle slope zone, abrupt slope zone, low uplift zone and Lake Basin. And it is also shown that the sequence circle structure plays a significant role in controlling the lithologic trap, the development of sandstone reservoir is closely related to the midterm circle, and favorable reservoirs mainly develop at the bottom of the circle structure with a trend of "becoming deeper upward".%为了探讨柴达木盆地西南古近系-新近系层序地层,为岩性油气藏勘探提供依据,本文在Cross高分辨率层序地层学理论指导下,综合利用露头、岩心、钻井、地震等资料,结合盐湖盆地的沉积特殊性,对柴西南古近系-新近系层序界面进行识别与层序划分.研究认为将柴达木盆地柴西南古近系-新近系地层划分为13个长期旋回更为合理,提出缓坡带、陡坡带、低凸地区和湖盆区4种不同沉积单元的层序发育模式,指出层序旋回结构对岩性圈闭具有重要的控制作用,储集砂岩的发育状况与中期旋回密切相关,有利储层主要发育在旋回结构向上"变深"的非对称型下部.

  14. 山东济宁杨营煤矿工业广场新近系砂层水井回灌量分析%Yangying Coalmine Surface Installation Area Neogene Sand Layer Wells Recharge Rate Analysis in Jining, Shandong

    Institute of Scientific and Technical Information of China (English)

    田立强; 范士彦; 许京丰; 王红梅

    2015-01-01

    The Yangying coalmine is intended to use water-source heat pump air-conditioning system to substitute traditional heating and air-conditioning facilities. To satisfy water-source heat pump air-conditioning system outdoor ground source heat exchange design requirements, need to determine hydrostatic and hydrodynamic unpressurized recharging effects, number of pumping and recharging wells and intervals between them. Through Yangying coalmine surface installation area Neogene sand layer water-bearing characteris-tics and Neogene deep well pumping and recharging tests, carried out hydrostatic and hydrodynamic unpressurized recharging compari-son have found that the effect of hydrodynamic unpressurized recharging is better with larger recharge rate and recharging ratio can be 67%as high. Thus determined the total recharging wells layout:according to system required water amount, using proportion of pump-ing, recharging wells 1:2 or 2:3 to set well numbers, and interval between wells not less than 75m.%杨营煤矿拟采用水源热泵空调系统替代传统的取暖、空调设施.为满足水源热泵空调系统室外地能换热系统设计的需要,需确定静水和动水无压回灌的效果,抽水井、回灌井的数量和间距.通过对杨营煤矿工业广场新生界砂层含水特征及新近系深水井的抽水和回灌试验,进行了静水和动水无压回灌的比较,发现动水无压回灌的效果较好,回灌量较大,回灌比达67%,从而确定了实现全部回灌的井群布置方式:根据系统需水量大小,采用抽水井、回灌井为1:2或2:3的比例设置水井数量,井间距不小于75 m.

  15. Provenance of the Neogene Surma Group from the Chittagong Tripura Fold Belt, southeast Bengal Basin, Bangladesh: Constraints from whole-rock geochemistry and detrital zircon U-Pb ages

    Science.gov (United States)

    Rahman, M. Julleh Jalalur; Xiao, Wenjiao; McCann, Tom; Songjian, Ao

    2017-10-01

    Miocene Surma Group from the Chittagong Tripura Fold Belt (CTFB), southeast Bengal Basin has been analyzed to evaluate their provenance, tectonic settings and paleoweathering conditions. The sandstones show moderate to high contents of SiO2 (65-80%; 75% on average), and Al2O3 (9.94% on average), with Fe2O3 (total Fe as Fe2O3) + MgO contents of 5.1%, TiO2 (0.57% on average). Compared to the upper continental crust (UCC), the sandstones are depleted in CaO (1.49%) and enriched in Al2O3, Fe2O3 and Na2O. The Neogene shales of the Surma Group are in fair concurrence when compared to the NASC (North American Shale Composite), UCC (the upper continental crust) with the exception of the low content of CaO but when compared with the PAAS (Post-Archaean Australian Shale), the Neogene shales are a little more depleted in Al2O3 content. Sandstones and shales have Eu/Eu∗ ∼0.61 and ∼0.65, (La/Lu)N ∼9.06 and ∼8.70, La/Sc- ∼3.90 and ∼2.86, Th/Sc ∼1.19 and ∼1.41, La/Co- ∼3.69 and ∼2.42, Th/Co ∼1.08 and ∼1.20 and Cr/Th ∼7.90 and ∼5.88 ratios as well as Chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate the derivation from predominantly felsic sources subjected to low to moderate chemical weathering [Chemical index of alteration (CIA) values of sandstones- 31.11-74.46, av. 60.08); shales- 43.96-73.07, av. 61.80]. Integrated geochemical and zircon U-Pb studies reveal that main sediment input might have been from the Himalaya with mixing influence from the east of the Indo-Burman Ranges in an active margin setting at the convergence of the Indian and Burmese plates.

  16. Hallazgo de sedimentitas sinorogénicas neógenas en los alrededores de Chos Malal, Cuenca Neuquina, Argentina Finding of Neogene synorogenic sedimentites around Chos Malal, Neuquén Basin, Argentina

    Directory of Open Access Journals (Sweden)

    Martín Cervera

    2009-06-01

    Full Text Available Se propone la Formación Chos Malal nov. para agrupar a un conjunto de 140,50 m de sedimentitas neógenas de naturaleza epiclástica que incluyen areniscas, fangolitas y arcilitas con aporte tobáceo, previamente adjudicadas a la Formación Rayoso del Cretácico inferior. Las mismas se acumularon durante la gestación de un sinclinal de rumbo NNO-SSE, quedando apoyadas en discordancia angular sobre el Miembro Rincón de la Formación Rayoso, y cubiertas de la misma forma por la Formación Rincón Bayo del Mioceno Medio-Plioceno Temprano Por posición estratigráfica y correlaciones con unidades geográficamente cercanas, la nueva unidad es adjudica al Mioceno medio.The Chos Malal Formation nov. is proposed to group a 140,50 m thick neogene succession of epiclastic sedimentites including sandstones, silstones and mudstones with tuffaceous input, which were previously ascribed to the Early Cretaceous Rayoso Formation. They were accumulated during the formation of a syncline elongated in a NNW-SSE direction, being deposited in angular unconformity on the Rincon Member of the Rayoso Formation, and covered in the same way by the Middle Miocene-Early Pliocene Rincón Bayo Formation. According to its stratigraphic position and correlations with near geographically situated units, they are ascribed to the Middle Miocene.

  17. Geologic map of the eastern half of the Vail 30' x 60' quadrangle, Eagle, Summit, and Grand Counties, Colorado

    Science.gov (United States)

    Kellogg, Karl S.; Shroba, Ralph R.; Premo, Wayne R.; Bryant, Bruce

    2011-01-01

    Recent mapping and geochronologic studies for the eastern half of the Vail 1:100,000-scale quadrangle have significantly improved our understanding of (1) Paleoproterozoic history of the basement rocks of the Gore Range and Williams Fork Mountains (western margin of the Front Range), (2) the Late Paleozoic history of the Gore fault system, (3) Laramide contractional tectonism, including deformation along the Gore fault and Williams Range thrust, (4) Oligocene and younger extensional history of the Blue River half graben (The northern extent of the Rio Grande rift), and (5) late Neogene and Quaternary surficial history. The recently active Gilman mining district, a major producer of zinc and lead, is in the southwestern corner of the map area. Marine sediments and mafic to felsic volcanic rocks deposited between about 1,740 and 1,780 m.y. were generally metamorphosed to amphibolite grade and intruded and deformed by mostly calc-alkalic granitic rocks during an orogenic episode that lasted about 110 m.y. The distribution of well-studied Upper Cambrian to thick Upper Cretaceous platform sediments is now greatly improved, which allows a better definition of the late Paleozoic uplift, erosion, and flanking sedimentation of the ancestral Front Range. Detailed mapping has also better defined the geometry of Late Cretaceous to early Tertiary Laramide deformation along both the Gore fault system and Williams Range thrust, as well as increased understanding of the details of mostly Neogene extension along the Blue River normal fault system (the western margin of the Blue River half graben). Scarps along the latter fault system indicate movement may be as young as Holocene. Detailed mapping of surficial deposits has defined and described (1) six ages of terrace alluvium, (2) three general ages of landslides, (3) glacial and periglacial deposits, and (4) fan, pediment, talus, and debris-flow deposits.

  18. 新近系松散一半胶结砂砾石含水层的注浆改造试验及效果%Neogene Loose-Weakly Cemented Sandy Gravel Aquifer Grouting Reformation Test and Effect

    Institute of Scientific and Technical Information of China (English)

    赵兰春; 李经海; 高祥川; 牛淑敏

    2012-01-01

    Safely driving through the Neogene sandy gravel is a common hard nut in inclined shaft opening out. To provide basis for surface advance grouting or concrete curtain grouting, the Xinwen Group has carried out special grouting test and pumping test, coring etc. to contrast and validated for Neogene gravel layer (intercalated with sandy clay) with total thickness 20~30m near the Heiliang coalmine main and auxiliary inclines, Shanghaimiao west mine area, Inner Mongolia. The result has demonstrated that although the loose-weakly cemented gravel layer has certain groutability beyond the IMPa grouting pressure "threshold" , but the slurry diffusive extent is less than 2~3m; also, the diffusive mode is irregular, uncontrollable and cannot form a reliable slurry diffusive consolidated ring, thus no improved effects on gravel layer water-bearing property and transmissibility have been found. Through this test, has grappled grouting performance in loose -weakly cemented gravel layer better, and obtained related grouting parameters and experiences, thus have guiding significance in grouting reformation and underground engineering construction safety in similar strata.%矿井斜井开拓安全通过新近系砂砾石含水层是一个普遍的难题,为给斜井地面预注浆或帷幕注浆法过砾石层提供依据,新矿集团在内蒙古自治区上海庙西矿区黑梁煤矿主副斜井附近对总厚20~30m的新近系砾石层(夹砂质粘土层)进行了专门注浆试验及抽水、取心等对比验证工作.结果表明,松散-半胶结砾石层虽然在超过1MPa的注浆压力“阀值”后具有一定的可注性,但浆液扩散范围小于2~3m,而且扩散方式不规则、不可控、形不成可靠的浆液扩散加固圈,对砾石层的含、导水性未发现有改善效果.通过本次试验,较好地掌握了松散-半胶结砾石层注浆性能,获得了有关注浆参数和经验,对类似地层的注浆改造和井巷工程的安全施工具有指导意义.

  19. PROGRESS AND PROSPECT OF STUDY ON NEOGENE CLIMATE EVOLUTION IN EURASIA (NECLIME)%欧亚大陆新近纪气候演化(NECLIME)研究进展与展望

    Institute of Scientific and Technical Information of China (English)

    王伟铭; 李建国; 毛礼米

    2012-01-01

    “欧亚大陆新近纪气候演化”国际研究团体成立于2000年,其前期工作主要集中在欧洲.随着研究的不断深入,亚洲地区的工作开始受到越来越多的关注.2010年11月在昆明举办了首届亚洲NECLIME年会,今年5月下旬又在南京成功召开了NECLIME研讨会,讨论的内容也有了更多的拓展.为使国内相关研究人员对这一国际研究团体及其目标有更多的了解,本文拟对NECLIME的发展史、研究进展和南京会议作一简要介绍,并对NECLIME的今后工作进行展望,以期对国内的相关研究提供帮助.%The international research group on "Neogene climate evolution in Eurasia" came into existence in 2000. Its prophase work is mainly concentrated in Europe. With the development of the study in recent years, more and more attention has been transferred to Asia. The first Asian NECLIME meeting was held in Kunming in November 2010. In the late May 2012, the second one was successfully held in Nanjing, with broadened contents for discussion. This paper attempts to give a brief introduction on the NECLIME history, its major progress, the Nanjing NECLIME meeting, along with a short prospect, so that the related domestic scientists could learn more about this international research project, and benefit from its renewed results by making more intensified exchange with the activities and members in the group.

  20. 柴北缘西段新近系上干柴沟组沉积相特征分析%Sedimentary facies in the Neogene Upper Ganchaigou Formation on the northern margin of the Qaidam Basin, Qinghai

    Institute of Scientific and Technical Information of China (English)

    刘琪; 潘晓东; 李凤杰

    2011-01-01

    根据野外露头、岩心观察及录井、测井资料,研究了柴北缘西段新近系上干柴沟组沉积相类型和沉积特征.结果表明:上干柴沟组发育冲积扇、扇三角洲、辫状河、辫状河三角洲、湖泊及颗粒流等六种沉积相类型,其中在鄂博梁-冷湖-潜西发育了一套扇三角洲-湖泊沉积体系,在马海-南八仙地区发育冲积扇-辫状河-辫状河三角洲-湖泊沉积体系.%The examination of the sedimentary facies is based on the field outcrops, core observation and well logs for the Neogene Upper Ganchaigou Formation on the northern margin of the Qaidam Basin, Qinghai. The Upper Ganchaigou Formation is built up of the alluvial fan, fan delta, braided stream, braided delta, lacustrine facies and grain flow deposits. Two depositional systems have been recognized, including the fan delta-lacustrine depositional system in the Eboliang-Lenghu-Qianxi zone, and alluvial fan-braided stream-braided delta-lacustrine depositional system in the Mahai-Nanbaxian zone. The results of research in the western part of the northern margin of the Qaidam Basin may provide reliable geological information for further petroleum exploration.

  1. Données nouvelles sur le Néogène et le Quaternaire des escarpements ioniens (Méditerranée orientale New Data on the Neogene and Quaternary in Lonian Scarps (Eastern Mediterranean

    Directory of Open Access Journals (Sweden)

    Bizon G.

    2006-11-01

    Full Text Available Les études micropaléontologiques réalisées sur les échantillons prélevés soit par dragage, soit avec le bras articulé de la soucoupe plongeante Cyana apportent des résultats nouveaux sur la stratigraphie du Néogène en mer Ionienne et sur l'interprétation paléobathymétrique des associations faunistiques. Si le Miocène reste encore mal caractérisé, toutes les zones du Pliocène (MPL1 à MPL6 ont été reconnues. Les cotes des différents prélèvements et la faible puissance de chaque série qui leur permet d'affleurer en différents points des escarpements rendent probable un mécanisme de dépôt sur une pente préexistante. Les échantillons quaternaires très nombreux sont souvent caractérisés par la formation de croûtes ou par leur lithification complète. L'étude des vases holocènes a montré des associations relativement peu diversifiées. Ceci semble lié beaucoup plus à une stratification permanente des eaux entraînant une diminution de la teneur en oxygène et en éléments nutritifs qu'à d'autres facteurs comme la température ou la salinité. Micropaleontological analyses of samples taken either by dredging or by the articulated arm of the Cyana have provided new findings on the submersible Neogene stratigraphy of the lonian Sea and on the paleobathymetric interpretation of faunistic associations. Although the Miocene has not yet been fully characterized, all the Pliocene zones (MPL1 to MPL6 have been recognized. The depths of the different samples and the shallowness of each series outcropping at different points in the scarps make a deposit mechanism probable on a preexisting slope. The very numerous Quaternary samples are often characterized by crust formation or by complete lithification. An analysis of Holocene muds has shown relatively little diversified associations. This seems linked much more to a permanent stratification of the waters, causing a decrease in the oxygen content and in the nutritive

  2. Neogene foreland tectonics in the southern Appenines

    Energy Technology Data Exchange (ETDEWEB)

    Roure, F.; Casero, P.; Moretti, I.; Mueller, C.; Sage, L.; Vially, R. (Institut Francais du Petrole, Rueil-Malmaison)

    1988-08-01

    Combined structural and biostratigraphic analyses and seismic interpretation help them to balance cross sections through the southern Apennines from the Adriatic to the Tyrrhenian Sea and to propose an overall model for the evolution of the belt. Three lithostratigraphic units have been distinguished according to their Mesozoic facies and style of deformation: the western platform (upper unit), the Lagonegro-Molise basin, and the eastern platform. Foreland deformation migrated from west to east, and external domains were reached progressively by synorogenic flysch deposits (foredeep) and later incorporated into the thrust sheets. Presently, only the most external part of the eastern platform is still unaffected by thrusting, while internal parts are building the overthrust belt at depth, which is masked on the surface by allochthonous basinal nappes. The evolutive geometry of thrust and piggy-back basins results from the continuous understacking of new material at the bottom of the tectonic prism. The deeper basement is also progressively involved in the deformation, giving rise to large nappe anticlines. Despite the early subsidence and deformation of the western platform and basinal domains in Langhian to Tortonian time, all the deformation of the eastern platform has occurred since Messinian time. These compressive structures are thus contemporaneous with the opening of the Tyrrhenian Sea. To the west, the upper tectonic units of the Apennines are indeed affected by listric normal faulting, with previous thrust planes having been locally reactivated during the distension. Post-Messinian shortening in the sedimentary cover is accompanied by a crustal thickening outlined by the Moho's geometry. The authors interpret it as a result of the subduction of the Apulian continental lithosphere. Recent uplift of the Apennines is indeed directly related to this crustal root.

  3. Neogene vertebrates from the Gargano Peninsula, Italy

    NARCIS (Netherlands)

    Freudenthal, M.

    1971-01-01

    Fissure-fillings in Mesozoic limestones in the Gargano Peninsula yield rich collections of fossil vertebrates, which are characterized by gigantism and aberrant morphology. Their age is considered to be Vallesian or Turolian. The special features of the fauna are probably due to isolation on an isla

  4. 辽宁盘锦新近系馆陶组地下热水分布特征及成因分析%Neogene Guantao Formation Underground Hot Water Distribution Features and Genetic Analysis in Panjin, Liaoning

    Institute of Scientific and Technical Information of China (English)

    邱立军

    2012-01-01

    辽宁盘锦新近系馆陶组地下热水埋藏较深,开发历史较早,但利用率较低.研究认为,该区地温场变化主要受地幔隆起相对程度控制;东西两侧幔隆带部位,地壳的厚度相对较薄,结晶岩基底埋藏浅,深部热能传导到储热层消耗能量少,地温及地温梯度值相对较高;中部幔凹带地温以中凸起最高,凹陷区相对较低.在地幔隆起的控制下,区内馆陶组地下水水温受储热层埋藏深度的影响,储热层的埋藏深度大,降低了热能向地表的散失速度,所以水温相对较高;反之,水温相对较低.地下水水温变化规律为:西部的谷坡区,受地下水径流影响,水温一般25℃~28℃,而凹陷区则为30℃~35℃;到中部隆起区水温升高到35℃~50℃;东部凹陷区为31℃~38℃,谷坡为29℃.深部上地幔幔源热源(岩浆热)构成本区生热层,经构造导热作用传输到储热层.最后指出,中央凸起区是该区馆陶组地下热水勘查开发的有利地区,重点开发应在温热水(Ⅰ区).%The Neogene Guantao Formation underground hot water in Panjin, Liaoning is rather deeply buried with rather early exploitation history, but rather low rate of utilization. The study considered that the geothermal field in the area is mainly controlled by relative degree of mantle uplift. In both east and west sides' mantle uplift part, crust thickness is relatively thinner, crystalline rock basement shallower, deep part heat energy conducting to reservoir has less consumption, geotemperature and geothermal gradient is relatively high; while geotemperature is the highest in the middle bulge of middle mantle depression zone, while relatively low in sag parts. Under the control of mantle uplift, the groundwater temperature in the Guantao Formation is impacted by reservoir buried depth, since the larger reservoir buried depth can lower down heat energy dissipation pace toward surface, thus has relatively high water temperature; if on

  5. The mode of emplacement of Neogene flood basalts in Eastern Iceland: Facies architecture and structure of the Hólmar and Grjótá olivine basalt groups

    Science.gov (United States)

    Óskarsson, Birgir V.; Riishuus, Morten S.

    2013-11-01

    Hólmar and Grjótá are two stratigraphically distinct transitional alkaline olivine basalt lava groups within the westward-dipping Neogene flood basalts of eastern Iceland. The Hólmar olivine basalt group, separated from the overlying Grjótá olivine basalt group by only a few tholeiite flows, can be traced over 80 km north-south, with thicknesses varying from ~ 250 m where thickest to ~ 30 m where thinnest. The Grjótá group can be traced over 50 km also north-south, reaching thicknesses of ~ 250 m and thinning down-dip to ~ 10 m. In contrast to other groups in eastern Iceland that thicken down-dip, the studied olivine basalt groups thicken up-dip. The groups filled topographic confinements and formed aprons around central volcanoes. We have estimated the minimum volumes to be ~ 119 km3 for Hólmar and ~ 86 km3 for Grjótá. Scoria cones are found in the Hólmar group, and two thick olivine dolerite sills cross-cut the Hólmar group and probably belong to the plumbing system that fed the Grjótá group. The architecture of the lava groups are near identical. The architecture is compound, with lobes stacked horizontally and vertically, varying from 1-15 m thick and 2-200 m long, but do also encompass a number of thicker (15-20 m) and more extensive (> 1 km long) lava lobe in the stacks. Filled lava tubes are commonly observed within the lava flows. The constituent lobes of the flows are often directly emplaced or welded together, suggesting rapid buildup, but are also found interbedded with redbeds and thicker tuff deposits, and occasionally preserve tree molds. The internal structure follows the characteristics for lava lobe morphology in general, with an upper vesicular crust forming half to one third of the total thickness, a massive core with abundant vesicle cylinders, and a thin basal vesicular crust. Flow tops are of the pahoehoe type, seldom found with scoria or clinker. Inflation structures such as tumuli and inflation clefts were identified in the

  6. Mountain building processes at the orogenic front: A study of the unroofing in Neogene foreland sequence (37°S Procesos orogénicos en el frente Andino: Estudio de una secuencia de destechado correspondiente a la cuenca de antepaís neógena

    Directory of Open Access Journals (Sweden)

    Lucía Sagripanti

    2012-05-01

    Full Text Available The orogenic front at 37°S has been mainly formed through at least two contraccional stages, as inferred from the exhumed major angular unconformities at the Late Eocene and the Late Miocene times respectively. A Late Cretaceous event is restricted to the hinterland zones in the Main Cordillera. A series of syntectonic sedimentary packages, that thin to the east is identified through a detailed description of the cannibalized westernmost Neogene foreland basin associated with the Sierra de Reyes. Their detrital microscopic and macroscopic descriptions reveal that the Neogene basin was fed from the west and particularly from the eastern Sierra de Reyes slope at the time of mountain incision. Detrital composition of the upper section reveals that a metamorphic component is present, implying that a domain further east has been exhumed, and therefore that the westernmost foreland basin has been cannibalized. This also implies that exhumation previous to Miocene times should have been minimum in the area, since the Neogene succession represents a complete unroofing. The structural cross sections show Neogene shortening of about 20%, leaving in comparison Eocene contraction as negligible.El frente orogénico a los 37°S ha sido construido por, al menos, dos episodios con-traccionales, determinados a partir de discordancias angulares entre los depósitos del Eoceno Superior y del Mioceno Superior. Un episodio contraccional del Cretácico Superior, ampliamente descrito con anterioridad, se encuentra parcialmente restringido a las zonas internas de la Cordillera Principal. A partir de un detallado análisis de la cuenca de antepaís neógena asociada, canibalizada por el frente de levantamiento de la sierra de Reyes, se puede distinguir una secuencia sedimentaria que experimenta una disminución de su espesor hacia el este. Las descripciones microscópicas y macroscópicas de estos depósitos sinorogénicos revelan que la cuenca neógena fue alimentada

  7. The Sequence Stratigraphy of Neogene Shizigou Formation of North Slope in Sanhu Depression and the Prediction of Potential Targets%三湖坳陷北斜坡新近系狮子沟组层序地层特征及有利勘探目标预测

    Institute of Scientific and Technical Information of China (English)

    芮华松; 关平

    2012-01-01

    伊深1井在柴达木盆地三湖地区新近系狮子沟组试气获得工业气流,指示新近系狮子沟组中可能存在生物气。为突破柴达木盆地一直局限于第四系寻找生物气的局面,拓宽生物气的勘探领域,采用钻/测井、地震及米兰科维奇旋回相结合的方法,对三湖坳陷北斜坡新近系狮子沟组进行高分辨率层序地层学研究。狮子沟组相当于一个三级层序(长期基准面旋回),在狮子沟组可识别出6个层序界面,进而划分出5个四级层序(中期基准面旋回)。每个层序内部可进一步划分为基准面上升半旋回和基准面下降半旋回。层序Ⅲ(Sq3)基准面上升半旋回时期发育的三角洲前缘砂体尖灭及砂岩透镜体圈闭是进一步勘探的有利目标。%Yishen-1 well has obtained commercial gas flow in the Neogene Shizigou Formation.Results show that the Sanhu area of the Neogene Shizigou Formation has biogenic gas,but the study of the Neogene in Sanhu area is very poor and lack of drilling targets.In order to make a breakthrough of the situation to find biogenic gas in the Quaternary and widen the biogenic gas exploration field,this paper combined drilling/logging,seismic and Milankovitch cycles to study the high resolution sequence stratigraphy of the Neogene in Sanhu depression,Qaidam basin.Results show that Shizigou Formation equals to a Ⅲ sequence(long-term datum plane cycles).Six sequence boundaries can be further identified and divided into five Ⅳ sequence(medium-term datum plane cycles) in Shizigou Formation.Each sequence can be further divided into half cycle of increasing and half cycle of descending.The delta front sandstone thinning out and sand lens trap which develop in half cycle of increasing period of Sequence III(sq3) are favorable target for further exploration.

  8. Tectonostratigraphic evolution of the Danube Basin: inferences from gravity, magnetic and seismic data

    Science.gov (United States)

    Zalai, Zsófia; Balázs, Attila; Balázs, László

    2017-04-01

    The 220-290 km of Miocene extension observed in the Pannonian basin system of Central Europe was driven by the rapid roll-back of the Carpathian slab. Basin formation was coupled with the extrusion of the Eastern Alps with large amounts of translation and vertical axis rotations. In the hanging wall of low-angle normal faults and detachments few kilometers thick syn-rift sediments deposited during the Early to Middle Miocene (Karpatian, Badenian and Sarmatian). Following a spectacular unconformity they are overlain by the gently folded thick Pannonian to Quaternary deposits. A novel tectono-stratigraphic interpretation was carried out in the Csapod and Győr-Kenyeri sub-basins using a dense network of reflection seismic data supported by gravity and magnetic anomaly maps. Incorporating new biostratigraphical data from deep wells the spatial and temporal patterns of the Miocene deformation was analyzed. 3D geological model was constructed using the gravity and magnetic forward modeling software (IGMAS+, e.g., Götze & Lahmeyer, 1988) based on the potential field anomalies (). Dz magnetic anomalies imply the location of buried volcanic bodies while the gravity anomalies indicate the buried basement highs. Our seismic interpretation revealed that asymmetric extension (Tari et al. 1992) was diachronous in the basin system. Oldest half-grabens closer to the basin margins were characterized by Karpatian (ca. 17.2-16.3 Ma) extension with limited amount of Badenian post-kinematic sedimentation. Toward the basin centre, in the Csapod Through the culmination of extension is Badenian (16-13 Ma) in age. Further to the deepest depocenters, in the Győr-Kenyeri depression, half-graben formation was still active during late Badenian - Sarmatian (14-11.6 Ma). Uplift and exhumation of the footwalls of the half-grabens are shown by the interpretation of depth-converted seismic data. Our estimations on this uplift of the footwalls are in the order of a few hundreds of meters, up to 1

  9. 3D Geometry of Salt Controlled Normal Faults on Friesland Platform - NW Netherlands

    Science.gov (United States)

    Yucel, Kivanc; Kaymakci, Nuretdin; Arda Ozacar, A.

    2010-05-01

    A detailed 3D structural modeling was carried out using the available 3D seismic reflection and borehole data, in order to reveal the structures and deformation history, associated with the dynamic evolution of the Middle-Late Permian age Zechstein salt layer in Northern Friesland - Netherlands. The model includes major structures and seismostratigraphic units of Permian to recent, revealing salt and salt induced structures, formed during the periods of active salt movement in the study area. The model indicates a thick salt layer formed on N-S oriented grabens and half grabens of South Permian Basin that acted as the primary control for the location of salt diapirs and reflected the basement deformation pattern to the cover. A major salt movement was initiated in Triassic, during E-W Mesozoic rifting i.e breaking up of Pangea, evidenced by rim-synclines on Triassic mini-basins. Structurally conformable layers of Cretaceous and Early Cenozoic units overlie Triassic units unconformably by base Cretaceous unconformity, deposited during a tectonic quiescence when salt movement was ceased. A second phase of salt movement took place during the Early Cenozoic that was triggered possily due to the compressional tectonism related to Late Cretaceous - Early Tertiary Alpine Orogeny. A final and still ongoing phase is observed in the slightly deformed Neogene and Quaternary units. The model represents a N-S oriented salt cored anticline and a convergent transfer zone between a pair of segmented normal growth faults, controlled by the salt movement. Major faults associated with the transfer zone have assymetrical half graben geometry away from the transfer zone and symmetrical graben structure with small scale synthetic and antithetic faults at the center of the transfer zone. Detailed study of the structural model in 3D with the aid of cross sections, allows the establishment of the architecture of the transfer zone and its relation with the salt deformation process.

  10. Review of the stratigraphy and paleoclimatology study of the Paleogene-Neogene Longzhong Basin%陇中盆地古近纪-新近纪地层学与古气候学研究进展

    Institute of Scientific and Technical Information of China (English)

    张鹏; 敖红; 安芷生

    2016-01-01

    Background aim and scope The well-developed long continuous Paleogene—Neogene fluvio-lacustrine strata (the Tertiary red beds) are exposed in the Longzhong Basin, Northwestern China. The abundant mammalian faunas and phytolite in the red beds provide valuable material for the stratigraphic correlation and paleoenvironmental reconstruction. In recent decades, paleontological, sedimentological, magnetostratigraphical and palynological studies have been conducted in the Longzhong Basin (e.g., Xining Basin, Lanzhou Basin and Linxia Basin). The environmental evolution in the Longzhong Basin since Cenzoic is likely to be associated with the land-sea redistributions the uplift of the Tibetan Plateau and/or the global cooling. Materials and methods In this study, we review the achievements mentioned above based on the stratigraphic and paleoclimatic research published in recent decades and bring out questions to be solved in future studies. Results The Tertiary beds in the Xining Basin unconformably overlie the Cretaceous Minhe Group, and the initiation of Tertiary beds began at least 55—52 Ma ago. Between 52—17 Ma, the continuous deposits in this basin implied a relatively stable sedimentary environment. The Tertiary beds of the Lanzhou Basin unconformably overlie the Cretaceous Hekou Group with an basal age of over 58 Ma. Given the formation of the basin systems in and around the Tibetan Plateau at that time, we speculate that the initiation of Paleogene deposits in these two basins at 58—52 Ma may be linked to the Indian-Eurasian continental collision at 65—55 Ma. The low sedimentary rate before late Paleogene (32—29 Ma) implied a relatively weak tectonic activity in the northeast margin of the Tibetan Plateau after the collision of Indian and Eurasian continent. However, the sedimentary rate increased from 32—29 Ma in both basins and a hiatus was observed in the Lanzhou Basin at the boundary of Yehucheng Formation and Xianshuihe Formation (~31 Ma

  11. CUTICULAR STRUCTURE OF TWO ANGIOSPERM FOSSILS IN NEOGENE FROM TENGCHONG, YUNNAN PROVINCE AND ITS PALAEOENVIRONMENTAL SIGNIFICANCE%云南腾冲新近纪两种被子植物化石的角质层构造及其古环境意义

    Institute of Scientific and Technical Information of China (English)

    孙柏年; 丛培允; 阎德飞; 解三平

    2003-01-01

    This paper emphatically describes the cuticular characteristics of two fossil angiosperm species Betula mioluminifera Hu et Chaney and Carpinus subcordata Nathorst collected from Neogene in Tengchong, Yunnan. The cuticular characteristics of their Nearest Living Relative species (NLR species), Betula luminifera Winkler and Carpinus cordata B1.var. mollis Cheng et Chen, are analysed. In this experiment, we have got the lower epidermis of C.subcordata, whose characteristics are described as follows: Only the middle and lower parts of leave preserved; length about 7.5 cm, width 5 cm. Midrib strong; angle between ventricumbent and midrib 40°-50°; nearer to the base, bigger the angle; venulose, more than 12 pairs. Upper epidermis a little thicker and net-veined, stomata not found; epidermic cells arrayed rotundly, polygonal, length and width 20-30 μm; length of the net about 350 μm, width about 200 μm; width of nervecourses 50 μm with 3-4 rows of parallel cells; cells in nervecourses oblong, length about 2-3 times of width. Lower epidermis thin with stomata; trichome found; arrangement of epidermic cells as the same of upper epidermis. Distribution of stomata ruleless; type of stomatal apparatus Anomocytic; stomata slightly sunken; guard cells kidney-shaped and slightly lower than surrounding cells; inner surface of guard cells thick; guard cell surrounded by several epidermic cells. The cuticle, with its stomatal pores, represents the interface between plants and atmosphere, and its features such as cuticle thickness, stomatal density (SD), stomatal index (SI) and stomatal ratio (SR) are well used as a palaeoenvironmental indicator. Therefore, we can analyse changes in palaeoenvironment by studying the stomatal parameter of fossil plants which are sensitive to the change in atmospheric CO2 concentration. In this experiment, we have got the stomatal parameter of C.subcordata which indicates that atmospheric CO2 concentration in Neogene was higher than that of

  12. Analysis of Neogene sequence-structure control over hydrocarbon distribution and accumulation in Huanghekou sag%层序—构造对黄河口凹陷新近系油气分布及成藏的控制作用

    Institute of Scientific and Technical Information of China (English)

    于海波; 王德英; 牛成民; 曾萱; 黄江波

    2012-01-01

    The hydrocarbon is mainly distributed in shallow water delta system of N1m1 in the Huanghekou sag. The hydrocarbon distribution and accumulation are analyzed according to sequence - structure herein. The lower member of Minghuazhen Formation is recognized as 3 long-term cycles and 8 middle-term cycles with high resolution sequence stratigraphy in Neogene. The early phase of ascending half cycles and middle-late phase of descending half cycles form sandbodies development favorable position are the main position of hydrocarbon distribution. Structure setting controls the direction of hydrocarbon migration, and positive structure zones are favorable areas of petroleum migration and accumulation. The faults of connecting deep and shallow strata are the main pathway of petroleum migrating to Neogene in the vertical direction. And, the late-stage faults adjust and distribute hydrocarbon. The sequence-structure controls the hydrocarbon accumulation layer and enrichment degree, and the good matching relation between faults (especially oil-migrating faults) and reservoir-seal assemblage is the main reason accounting for high hydrocarbon accumulation. The sequence-structure determine the effectiveness of the Neogene traps, and formed lithologic-structure, structure-lithologic and lithologic hydrocarbon reservoir.%黄河口凹陷的油气主要分布于新近系明化镇组下段的浅水三角洲沉积体系,从层序—构造角度对其油气分布及成藏进行分析.高分辨率层序地层分析表明,明下段可划分为3个长期基准面旋回和8个中期基准面旋回,基准面上升半旋回早期和下降半旋回中、晚期是储集砂体发育的有利部位,也是油气分布的主要部位;构造背景控制了油气的运移指向,正向构造带是油气长期运移、聚集成藏的有利地区,纵贯深、浅层的断裂是油气垂向运移至新近系的主要通道,晚期断裂主要对油气起到调整和再分配的作用.层序—构造耦

  13. Tectónica neógena en el extremo sur de la Cordillera Patagónica Septentrional: Cuenca de los lagos la Plata y Fontana (45°S Neogene tectonics in the southernmost extreme of the Northern Patagonian Cordillera: La Plata-Fontana lakes basin (45°S

    Directory of Open Access Journals (Sweden)

    A. Folguera

    2003-06-01

    Full Text Available Nuevos datos acerca de la anisotropía del manto, debajo de los Andes entre los 45° y los 46°S han revelado un rasgo sorprendente: un eje de polarización con orientación NO coincide con la segmentación estructural, derivada de la geometría de la cuenca cretácica inferior a estas latitudes. La geometría de la litosfera inferior induciría flujo astenosférico, en forma no paralela al tren andino. Adicionalmente se relaciona este mismo, con el desarrollo de una serie de pequeños depocentros extensionales en el retroarco de edad neógena a cuaternaria, los cuales se encuentran alineados con la estructura extensional cretácica. ¿Fue la reactivación transtensional de estructuras de basamento, durante el Neógeno, la que modificó la geometría de la litosfera inferior, a través de la actividad de un antiguo detachment, induciendo corrientes convectivas en el manto superior? ¿O simplemente la actividad de este detachment se relacionó con los efectos de arrastre que produjera la apertura de una ventana astenosférica, en la litosfera inferior, provocando la ruptura de la corteza a través de discontinuidades fósiles?New anisotropic seismic data below the Andes at 45°- 46°S have revealed a striking feature: a fast polarization NW axis coinciding with the Lower Cretaceous segmentation derived from basin geometry. The geometry of the lower lithosphere would induce astenospheric flux which is not parallel to the Andean trend. Moreover, a series of Quaternary-Neogene small basins in the retro-arc are aligned with the Cretaceous extensional structure. Did transtensional reactivation of basement structures during the Neogene modify lower lithosphere geometry through activity of ancient detachments, inducing convective cells in the upper mantle? Or would the activity of the ancient detachment be linked to the opening of a slab astenospheric window and to its drag in the lower lithosphere, making the crust yield through fossilized

  14. The sequence stratigraphic response to the basin-orogene coupling process of Cretaceous- Neogene in Tarim Basin, China%塔里木盆地白垩纪-新近纪盆山耦合过程的层序地层响应

    Institute of Scientific and Technical Information of China (English)

    丁孝忠; 林畅松; 刘景彦; 韩坤英; 庞健峰; 庞维华

    2011-01-01

    On the basis of the comprehensive analyses of the depositional sequence of the Cretaceous- Neogene outcrop sections, and the seismic sequence and drill-hole information in Tarim Basin, the authors hold that the Cretaceous - Neogene strata can be divided into 32 depositional sequences in the southwestern depression and 27 depositional sequences in the northwestern depression. According to the study of ordered stacking of several 3rd-order sequences and tectonic sequences, 4 tectonic sequence interfacies with the form of unconformity can be identified in Tarim Basin, And the Cretaceous - Neogene strata may be redivided into 4 supersequences(SSl - 4) which can be correlated synchronously in Tarim Basin, and the supersequence stratigraphic framework of the Cretaceous - Neogene in Tarim Basin can be established. Each supersequence represented the evolution cycle from progradation to retrogradation of 3rd-order sequence group and possesses the different characteristics of sequence association in different directions. The analysis of tectonic subsidence and depositional provenances indicate that the processes of subsidence and deposition in the depression in front of Tianshan and Kunlunshan Mts. Possess the characteristics of subsection and double provenances of foreland basin: Middle subsidence in the Early Cretaceous, slow subsidence in the Late Cretaceous and rapid subsidence in the Paleogence and Neo-gence. The change of the provenance areas is recycled orogen-inner craton-recycled orogen. And at the same time, the subarea occurred in terms of sequence constitution, depositional speed and depositional system collocation along the orogen due to the difference in the impact of tectonic movements to the provenance area, which was stronger in the western area than in the east This proves the characteristics of the basin-orogene coupling evolution between the depositional filling of southwestern depression and northwestern depression and lifting-fall process of Tianshan

  15. MAMMAL FOSSILS AND ECOLOGICAL ENVIRONMENT FEATURES OF THE NEOGENE FROM QIN'AN AREA,GANSU PROVINCE%甘肃秦安崖湾剖面新近纪哺乳动物化石及其生态环境特征

    Institute of Scientific and Technical Information of China (English)

    张军; 颉光普; 李吉均; 宋春晖; 赵志军; 王修喜; 惠争闯

    2011-01-01

    甘肃东南部的天水盆地新近纪沉积十分发育,其中富含哺乳动物化石,自20世纪六、七十年代发现铲齿象等哺乳动物化石后,一直鲜有关于这一地区化石发现的报道.近几年,在对天水盆地北部秦安一带的新生代地层研究过程中,经过野外考察和测量,确认秦安县城西北部约15.5km郭嘉镇附近的崖湾剖面属于新近系沉积,其沉积地层大致可以划分为3段(共37层),并于第二段的23层(褐红色砂质泥岩层)和28层(褐红色粉砂质泥岩层)中发现了丰富的哺乳动物化石,经有关专家鉴定属于三趾马动物群,共包含有5目10科11属13种.其中上化石层(第28层)三趾马动物群主要代表性属种有Hipparion chiai,H.weihoense,H.fossatum,H.plocodus,Acerorhinusfuguensis,Chilotherium wimani,Ch.habereri,Chleuastochoerus stehlini,Palaeotragus microdon等,其化石组合时代大致与府谷喇嘛沟动物群和临夏盆地大深沟动物群相当,时代可能为保德期早期,相当于欧洲MN11.下化石层(第23层)哺乳类可能为晚中新世灞河期晚期,相当于欧洲MN10.由于本地区正好位于我国东部季风区向青藏高原区的过渡区,因此,崖湾剖面上化石层动物群代表了晚中新世华北三趾马动物群与青藏高原三趾马动物群之间过渡区域的三趾马动物群面貌,其化石组合特征反映出当时该区可能属于亚热带稀树草原的生态环境特征,气候相对较为适宜,是比较适合大型哺乳动物生存的.该区具有过渡性质三趾马动物群的发现,对于研究三趾马动物群在我国境内的分异与东西演化、确定该区地层年代以及古生态环境都具有重要的意义.%The Tianshui Basin at southeast Cansu preserved well developed Neogene strata, in which enclose rich mammal fossils. However,there are few reports on these fossils after the Platybelodon fauna were discovered during the 1960s and 1970s. For the last decades, we have carried out

  16. Paleoambientes y magnetoestratigrafía del Neógeno de la Sierra de Mogna, y su relación con la Cuenca de Antepaís Andina Depositional environments and magnetostratigraphy of the Neogene Mogna sequence and its relation to the Andean Foreland Basin

    Directory of Open Access Journals (Sweden)

    JP Milana

    2003-09-01

    Full Text Available Se presenta un análisis preciso de la historia de acumulación del Neógeno de Mogna utilizando magnetoestratigrafía, dataciones absolutas, determinaciones de vertebrados fósiles y correlaciones con secciones vecinas. Esta secuencia, la más completas de la cuenca de antepaís del Bermejo, evolucionó debido a dos fases tectónicas moduladas por cambios fisiográficos y climáticos. Se estudiaron cronológica y sedimentológicamente ocho formaciones neógenas, determinándose una gran diacronicidad de sus límites, hasta de 1 Ma. El Neógeno se acumuló entre los 19 y 1 Ma ininterrumpidamente salvo entre los 15 y 12 Ma, donde la correlación magnetoestratigráfica es dudosa. La formación basal, Río Salado, se depositó en un ambiente de playa lake (centro de cuenca, mientras que las cuatro unidades siguientes (Formaciones Quebrada del Jarillal, Huachipampa, Qa. del Cura y Río Jáchal caracterizan sistemas fluviales efímeros, distinguiéndose en la relación arena/pelita, morfología de canal, bioturbación, y composición. Las formaciones superiores, Mogna y El Corral son gravosas y se interdigitan lateral y verticalmente. La primera fue depositada por un importante río entrelazado gravoso mientras que la segunda se acumuló como una bajada aluvial. Toda la secuencia caracteriza la progradación de una cuña aluvial, empujada por la deformación que avanzó hacia el este. La evolución asociada a las fases tectónicas sugiere una reología del basamento disímil a lo largo del eje de cuenca. Durante la deformación inicial la subsidencia disminuyó hacia el sur, acomodada por fallas sinsedimentarias expuestas en Loma de los Pozos, mientras que durante la deformación principal la subsidencia del antepaís fue más homogénea.A precise history of accumulation has been depicted for the Mogna Neogene sequence, using magnetostratigraphy, absolute dating, vertebrate fossil determinations and comparisons with neighboring sections. A two

  17. Geomorphic response of an active metamorphic core-complex in a collisional orogen: Example from the Lunggar Shan, Southern Tibet

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, M H; Stockli, D F [Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Lawrence, KS 66044 (United States); Kapp, P A [Department of Geosciences, University of Arizona, Tucson, AZ (United States)], E-mail: mht@ku.edu

    2008-07-01

    We present structural and neotectonic mapping from the Lunggar Shan rift in southern Tibet. The Lunggar Shan is a N-trending mountain range {approx}70 km long N-S and up to 40 km wide E-W. The Lunggar Shan is bounded on its east side by a low-angle (<40{sup 0}) east-dipping detachment fault that juxtaposes mylonitic gneiss and variably deformed granites in its footwall against alluvial fans and Neogene gravels in its hangingwall. Foliations in the mylonitic footwall dip < 40 deg. east and stretching lineations are east plunging. The range front detachment is presently inactive as indicated by undisturbed moraines and Quaternary sediments that overlie it. However, we consider the Lunggar Shan detachment to be an active structure, as inferred by range parallel fault scarps cutting Quaternary alluvium located 4-5 km into the hangingwall basin, with >40 m of throw on individual scarps. An intriguing observation is that an intrabasinal topographic high is actively developing near areas of inferred maximum extension, with lacustrine sediments being uplifted and eroded. This observation indicates that the rift basin initially developed as a typical half-graben system that underwent a transition from deposition, to uplift and erosion perhaps as a result of isostatic rebound of the footwall at depth, warping the overlying hangingwall basin. If correct, the Lunggar Shan may represent a modern analogue to the supradetachment basin model.

  18. Superposed deformation straddling the continental-oceanic transition in deep-water Angola

    Energy Technology Data Exchange (ETDEWEB)

    Cramez, C. [TotalFina Elf Exploration and Production, Paris La Defense (France); Jackson, M.P.A. [Texas Univ., Austin, TX (United States). Bureau of Economic Geology

    2000-12-01

    The Angolan margin is the type area for raft tectonics. New seismic data reveal the contractional buffer for this thin-skinned extension. A 200-km-long composite section from the Lower Congo Basin and Kwanza Basin illustrates a complex history of superposed deformation caused by: (1) progradation of the margin; and (2) episodic Tertiary epeirogenic uplift. Late Cretaceous tectonics was driven by a gentle slope created by thermal subsidence; extensional rafting took place updip, contractional thrusting and buckling downdip; some distal folds were possibly unroofed to form massive salt walls. Oligocene deformation was triggered by gentle kinking of the Atlantic Hinge Zone as the shelf and coastal plain rose by 2 or 3 km; relative uplift stripped Paleogene cover off the shelf, provided space for Miocene progradation, and steepened the continental slope, triggering more extension and buckling. In the Neogene, a subsalt half graben was inverted or reactivated, creating keystone faults that may have controlled the Congo Canyon; a thrust duplex of seaward-displaced salt jacked up the former abyssal plain, creating a plateau of salt 3-4 km thick on the present lower slope. The Angola Escarpment may be the toe of the Angola thrust nappe, in which a largely Cretaceous roof of gently buckled strata, was transported seawards above the thickened salt by up to {approx}20 km. (author)

  19. Genetic analysis on Neogene multiple oil & water system fault-block reservoirs in the sea area of Yellow River Mouth Sag%渤海海域黄河口凹陷新近系多油水系统油藏成因分析

    Institute of Scientific and Technical Information of China (English)

    胡光义; 杨希濮; 古莉; 范廷恩; 王晖; 汪珍宇; 高云峰

    2012-01-01

    为明确同类油田的开发调整方向和潜力目标,以滚动勘探开发为目的,以A油田为例,探讨了黄河口凹陷中央构造脊北端新近系多油水系统油藏成因。储层与油源断层的有效配置是控制该类油气聚集的关键因素。基于已开发油田井震一体化精细地层对比和储层展布研究,细化了储层空间展布,并结合油源断层特征剖析,系统分析了储-断耦合对油气分布的控制作用。首先,油源断裂垂向活动强弱的差异与储层的匹配控制着油气垂向上主要聚集层位;其次,断裂平面发育程度的差异与储层展布的耦合控制着油气在平面上的分布;再次,储-断接触关系影响着油气的富集和赋存规律。%To clarify the development orientation and potential target in the similar fields,taking A oilfield located at the northern end of the central structural ridge of Yellow River Mouth Sag as an example,genesis of Neogene multiple oil water system fault-block reservoirs is systematically researched.The effective matching of sand reservoir and fault connecting source rocks is a key factor that controls hydrocarbon accumulation.The reservoir distribution of A oilfield is studied on the basis of fine stratigraphic classification and reservoir characterization by the integration of well logs and seismic data.Reservoir characterization combined with the analysis of source-connected faults,the controlling effect of reservoir-fault coupling on oil and gas distribution is systematically studied.Firstly,the vertical distribution of hydrocarbon accumulation may be controlled by a "coupling" between the differences of vertical fault activity and relevant sand reservoir distribution.Secondly,the horizontal distribution of hydrocarbon may be controlled by the "coupling" between the differences in horizontal fault activity and the abundance of sand reservoir.Finally,the contact patterns of sand reservoir and fault affect the oil and gas

  20. The diffuse seismicity of the Sierra Nevada of Santa Marta, the Perijá Range, and south of the La Guajira peninsula, Colombia and Venezuela: Result of the convergence between Caribbean plate and the South American margin during the Late Neogene?

    Science.gov (United States)

    Chicangana, G.; Pedraza, P.; Mora-paez, H.; Ordonez Aristizabal, C. O.; Vargas-Jimenez, C. A.; Kammer, A.

    2012-12-01

    A diffuse low deep microseismicity located overall between the Guajira peninsula and the Sierra Nevada de Santa Marta (SNSM) was registered with the recent installation (2008 to Present) of three seismological stations in northeastern Colombia by the Colombian Seismological Network (RSNC), but mainly with the Uribia station in (the) central region of La Guajira peninsula, The microseismicity is characterized by a great population of events with 1.2 Colombia impedes to locate the origin of the local seismicity; however, this seismic activity is associated to the tectonic activity of the Oca fault because with the GPS displacement analysis, neotectonics evidence found in faults traces associated to the Oca fault and the historical earthquake that affected the Colombian city of Santa Marta in 1834, lead us to conclude this. This is a big cortical fault that sets the limit between La Guajira peninsula and the SNSM. Its cortical characteristics were verified from geological data together with gravimetric and seismic exploration. The SNSM limits toward the southeast with the Cesar - Ranchería basin, and this basin in turn limits with the Perijá Range that is localized in the Colombia - Venezuela border. The SNSM, Cesar - Ranchería basin and Perijá Range limit toward the southwest with the Bucaramanga - Santa Marta fault (BSMF), the Oca fault toward the north, and Perijá - El Tigre fault toward the southeast defining a pyramidal orogenic complex. Using remote sensing images data with geological and regional geophysical information, we proposed that this orogenic complex was originated as a result of the Panama arc with the northwestern South America accretion. The final adjustment of the Caribbean plate (CP) between North America and South America during the Late Neogene produced the big cortical faults systems activation like Oca - Moron - El Pilar in Colombia and Venezuela toward the south of the Caribbean Plate (CP), and Motegua - Walton - Enriquillo - Plantain

  1. Neogene climate change and uplift in the Atacama Desert, Chile

    Science.gov (United States)

    Rech, Jason A.; Currie, Brian S.; Michalski, Greg; Cowan, Angela M.

    2006-09-01

    The relationship between Andean uplift and extreme desiccation of the west coast of South America is important for understanding the interplay between climate and tectonics in the Central Andes, yet it is poorly understood. Here we use soil morphological characteristics, salt chemistry, and mass independent fractionation anomalies (Δ17O values) in dated paleosols to reconstruct a middle Miocene climatic transition from semiaridity to extreme hyperaridity in the Atacama Desert. Paleosols along the southeastern margin of the Calama Basin change from calcic Vertisols with root traces, slickensides, and gleyed horizons to an extremely mature salic Gypsisol with pedogenic nitrate. We interpret this transition, which occurred between 19 and 13 Ma, to represent a change in precipitation from >200 mm/yr to 2 km; the uplift blocked moisture from the South American summer monsoon from entering the Atacama. The mid-Miocene Gypsisol with pedogenic nitrate is located at elevations between 2900 and 3400 m in the Calama Basin, significantly higher than modern nitrate soils, which occur below ˜2500 m. Modern and Quaternary soils in this elevation zone contain soil carbonate and lack pedogenic gypsum and nitrate. We infer that >900 m of local surface uplift over the past 10 m.y. displaced these nitrate paleosols relative to modern nitrate soils and caused a return to wetter conditions in the Calama Basin by decreasing local air temperatures and creating an orographic barrier to Pacific air masses.

  2. Neogene Caribbean plate rotation and associated Central American tectonic evolution

    Science.gov (United States)

    Wadge, G.; Burke, K.

    1983-01-01

    A theoretical model of the opening of the Cayman Trough is developed on the basis of geological evidence from a wide area. It is proposed that strike slip motion began about 30 Myr ago and proceeded at a rate of 37 + or - 6 mm/yr for a total of 1100 km of relative plate displacement, and that Central America Underwent an anticlockwise rotation with internal plate deformation. Maps of the reconstructed motion are provided.

  3. Neogene volcanism in Gutai Mts. (Eastern Carpathains: a review

    Directory of Open Access Journals (Sweden)

    Marinel Kovacs

    2003-04-01

    Full Text Available Two types of volcanism developed in Gutâi Mts. (inner volcanic chain of Eastern Carpathians: a felsic, extensional/“back-arc” type and an intermediate, arc type. The felsic volcanism of explosive origin, consisting of caldera-related rhyolitic ignimbrites and resedimented volcaniclastics, had taken place during Early-Middle Badenian and Early Sarmatian. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The geochemical study on the volcanic rocks shows the calc-alkaline character of both felsic and intermediate volcanism and typical subduction zones geochemical signatures for the intermediate one. The felsic volcanism shows affinities with subduction-related rocks as well. The main petrogenetic process in Gutâi Mts. was crustal assimilation, strongly constrained by trace element and isotope geochemistry.

  4. Neogene history of the Carapita Formation, Eastern Venezuela basin

    Science.gov (United States)

    Sanchez Zambrano, Dennis Alberto

    The planktonic and benthic foraminifera from the lower to middle Miocene shales of the Carapita Formation of Eastern Venezuela in three exploration wells and one outcrop section are analyzed with the objectives of establishing a precise biostratigraphy of the formation and its bathymetric history. Comparison with the well-preserved microfaunas of the correlative Cipero Formation of Trinidad made possible the achievement of these objectives. The formation, up to 4500 to 6000 m thick in outcrops, extends from northeastern Anzoategui and North of Monagas States to the Gulf of Paria and is both an important oil reservoir towards the east and the main seal rock for the Oligocene reservoir in the north of Monagas State. In the area studied the Carapita Formation spans lower to lower middle Miocene Zones N6/M3 to N9/M6; its upper part is unconstrained as only rare long ranging early Miocene to early Pliocene planktonic foraminifera occur above the Orbulina datum. Unexpectedly, we found that the four lower to middle Miocene sections are highly discontinuous, with hiastuses as long as 4 Myr. Based on the abundance patterns of sixty-nine species of benthic foraminifera and analysis of morphotype abundance following the methodology of Corliss and Chen (1988) and Corliss and Fois (1993), we show that the Carapita Formation was deposited at outer neritic to middle bathyal depths (≥200--1000 m), whereas the Cipero Formation was deposited at middle to lower bathyal depths (≥600--2000 m). Importantly, the bathymetric changes are associated with unconformities in all sections, strongly suggesting that both (shallowing and associated unconformities) were tectonically induced.

  5. Neogene origins and implied warmth tolerance of Amazon tree species.

    Science.gov (United States)

    Dick, Christopher W; Lewis, Simon L; Maslin, Mark; Bermingham, Eldredge

    2012-01-01

    Tropical rain forest has been a persistent feature in South America for at least 55 million years. The future of the contemporary Amazon forest is uncertain, however, as the region is entering conditions with no past analogue, combining rapidly increasing air temperatures, high atmospheric carbon dioxide concentrations, possible extreme droughts, and extensive removal and modification by humans. Given the long-term Cenozoic cooling trend, it is unknown whether Amazon forests can tolerate air temperature increases, with suggestions that lowland forests lack warm-adapted taxa, leading to inevitable species losses. In response to this uncertainty, we posit a simple hypothesis: the older the age of a species prior to the Pleistocene, the warmer the climate it has previously survived, with Pliocene (2.6-5 Ma) and late-Miocene (8-10 Ma) air temperature across Amazonia being similar to 2100 temperature projections under low and high carbon emission scenarios, respectively. Using comparative phylogeographic analyses, we show that 9 of 12 widespread Amazon tree species have Pliocene or earlier lineages (>2.6 Ma), with seven dating from the Miocene (>5.6 Ma) and three >8 Ma. The remarkably old age of these species suggest that Amazon forests passed through warmth similar to 2100 levels and that, in the absence of other major environmental changes, near-term high temperature-induced mass species extinction is unlikely.

  6. Neogene Caribbean plate rotation and associated Central American tectonic evolution

    Science.gov (United States)

    Wadge, G.; Burke, K.

    1983-01-01

    A theoretical model of the opening of the Cayman Trough is developed on the basis of geological evidence from a wide area. It is proposed that strike slip motion began about 30 Myr ago and proceeded at a rate of 37 + or - 6 mm/yr for a total of 1100 km of relative plate displacement, and that Central America Underwent an anticlockwise rotation with internal plate deformation. Maps of the reconstructed motion are provided.

  7. New perspectives on the geometry of the Albuquerque Basin, Rio Grande rift, New Mexico: Insights from geophysical models of rift-fill thickness

    Science.gov (United States)

    Grauch, V. J.; Connell, Sean D.

    2013-01-01

    Discrepancies among previous models of the geometry of the Albuquerque Basin motivated us to develop a new model using a comprehensive approach. Capitalizing on a natural separation between the densities of mainly Neogene basin fill (Santa Fe Group) and those of older rocks, we developed a three-dimensional (3D) geophysical model of syn-rift basin-fill thickness that incorporates well data, seismic-reflection data, geologic cross sections, and other geophysical data in a constrained gravity inversion. Although the resulting model does not show structures directly, it elucidates important aspects of basin geometry. The main features are three, 3–5-km-deep, interconnected structural depressions, which increase in size, complexity, and segmentation from north to south: the Santo Domingo, Calabacillas, and Belen subbasins. The increase in segmentation and complexity may reflect a transition of the Rio Grande rift from well-defined structural depressions in the north to multiple, segmented basins within a broader region of crustal extension to the south. The modeled geometry of the subbasins and their connections differs from a widely accepted structural model based primarily on seismic-reflection interpretations. Key elements of the previous model are an east-tilted half-graben block on the north separated from a west-tilted half-graben block on the south by a southwest-trending, scissor-like transfer zone. Instead, we find multiple subbasins with predominantly easterly tilts for much of the Albuquerque Basin, a restricted region of westward tilting in the southwestern part of the basin, and a northwesterly trending antiform dividing subbasins in the center of the basin instead of a major scissor-like transfer zone. The overall eastward tilt indicated by the 3D geophysical model generally conforms to stratal tilts observed for the syn-rift succession, implying a prolonged eastward tilting of the basin during Miocene time. An extensive north-south synform in the

  8. Paleogene-Neogene Sedimentary Facies and Sequence Stratigraphic Characteristics in Qixinghe Coal-bearing Basin, Heilongjiang%黑龙江七星河含煤盆地古近纪-新近纪沉积相及层序地层特征

    Institute of Scientific and Technical Information of China (English)

    商晓旭; 邵龙义; 马立军; 野兆瑞; 曲延林

    2014-01-01

    The Qixinghe Basin in eastern Heilongjiang is a Cenozoic coal accumulation basin. Its coal-bearing strata belong to Paleo-gene Baoquanling Formation and Neogene Fujin Formation. The Baoquanling Formation is comprised of siltstone, sandstone of various grain sizes, mudstone, carbonaceous mudstone and lignite;developed littoral-shallow lacustrine facies, deep-semideep lacustrine fa-cies, delta plain facies belong to lake sedimentary system, lake delta sedimentary system. The Fujin Formation is comprised of mud-stone, siltstone, medium-grained sandstone, pebbly coarse-grained sandstone, coal, carbonaceous mudstone and diatomite;developed littoral-shallow lacustrine facies, fan delta plain facies, belong to lake sedimentary system and fan delta sedimentary system respective-ly. Sequence SI is corresponding to Baoquanling Formation;developed lowstand system tract, lacustrine transgressive system tract and highstand system tract. Coal seams were mainly developed during middle to late stages of highstand system tract;coal-forming environ-ment was mainly littoral-shallow lacustrine silting bog. Sequence SII is corresponding to Fujin Formation;mainly developed lacustrine transgressive system tract, highstand system tract, locally lowstand system tract. Also, coal seams were mainly developed during middle to late stages of highstand system tract;coal-forming environment was mainly fan delta silting bog and littoral-shallow lacustrine silt-ing bog. During sequences SI, SII middle to late stages of highstand system tract, basin basement settlement rate and sediment supply were in a relatively balanced state, mainly developed fan delta silting bog, in littoral-shallow lacustrine and littoral-shallow lacustrine silting bog environments have developed mineable coal seams.%黑龙江省东部七星河盆地是一新生代聚煤盆地,其含煤地层为古近系宝泉岭组、新近系富锦组。宝泉岭组由各级砂岩、泥岩、炭质泥岩以及褐煤组成,发育滨浅

  9. Los cuerpos ígneos neógenos del cerro de Las Minas (35,3°S - 69,9°O, Cordillera Principal de los Andes, SO de Mendoza: geología, petrografía y geoquímica The Neogene igneous bodies of the Cerro de las Minas (35.3°S-69.9°W, Main Cordillera of the Andes, SW of Mendoza: geology, petrography and geochemistry

    Directory of Open Access Journals (Sweden)

    M.J. Pons

    2007-06-01

    dikes and sills. These units are part of the Neogene magmatic arc of SW Mendoza (Andesita Huincán. They intrude the sedimentary Jurassic Puchenque and Auquilco Formations. Near the contacts with plutons, the sedimentary rocks are modified to biotite and pyroxene hornfels, recrystallized limestones and superimposed banded Fe-skarns. Geochemically, they are cogenetic plutons with a wide compositional range. They are metaluminous, subalkaline with a calc-alkaline affinity, I- type plutons, like other plutons from convergent margins associated with Fe skarns. They evolved through a fractional crystallization process involving their main mineral components, (plagioclase-piroxene-anphibol-magnetite-titanite, and mingling between the diorite and granodiorite magmas. Their incompatible trace elements and REE patterns are similar to igenous rocks a from the Neogene volcano-plutonic arc (Andesita Huincán, b associated with Fe skarns of SW Mendoza (Hierro Indio and El Kaiser, c of the cerro Nevazón, from the Paleogene volcano-plutonic Arc of NW Neuquén, and c of the Andean Quaternary volcanic segment of the TSVZ (34.5°-37° SL, wich are emplaced on a relatively thin continental crust (35-50 km. This suggests that the parental magma of the cerro de las Minas plutons came from calc-alkaline and metaluminous magmas derived from primary magmas generated in a similar mantle source, with little or no residual garnet.

  10. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Sound Velocity Profiles (SVP)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  11. Geophysical Surveys of Bear Lake, Utah-Idaho, 2002 - JPEG Images of Seismic Data

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  12. 5 meter bathymetric contours derived from data collected during U.S. Geological Survey Geophysical Surveys of Bear Lake, Utah-Idaho, September, 2002 cruise 02031(02031_BATHY_5M)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  13. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Chirp Seismic Tracklines (CHRPTRK)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  14. Geophysical Surveys of Bear Lake, Utah-Idaho, 2002 - JPG Images of Seismic Data

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  15. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Shot Point Navigation (CHRPSHT)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  16. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Shot Point Navigation 500 shot interval (CHRP_500)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  17. 1 meter resolution sidescan sonar image of data acquired during the U.S. Geological Survey Geophysical Surveys 02031 of Bear Lake, Utah-Idaho, September, 2002 (BEARLAKE.TIF, UTM)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  18. Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Grab Sample Data (GRABS)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  19. Geophysical Surveys of Bear Lake, Utah-Idaho, September, 2002 - Bathymetry (5m contours)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  20. Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Bathymetric Grid (BATHYGRD.TIF)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  1. Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - JPEG Images of Grab Samples

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  2. Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - JPEG Images of Sound Velocity Profiles

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  3. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September, 2002 - Bathymetry Tracklines (BATHY_TRK)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  4. GRABS - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Grab Sample Data

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  5. Geophysical Surveys of Bear Lake, Utah-Idaho, 2002 - JPG Images of Seismic Data

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  6. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Sidescan-sonar Tracklines (SSS_TRK)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  7. 02031 : Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Seismic Navigation: Start of Line (CHRP_SOL)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  8. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Sidescan-sonar Tracklines (SSS_TRK)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  9. Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Grab Sample Data (GRABS)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  10. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Shot Point Navigation (CHRPSHT)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  11. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Shot Point Navigation 500 shot interval (CHRP_500)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  12. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Chirp Seismic Tracklines (CHRPTRK)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  13. 1 meter resolution sidescan sonar image of data acquired during the U.S. Geological Survey Geophysical Surveys 02031 of Bear Lake, Utah-Idaho, September, 2002 (BEARLAKE.TIF, UTM)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  14. 02031 : Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Seismic Navigation: Start of Line (CHRP_SOL)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  15. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Sound Velocity Profiles (SVP)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  16. Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Bathymetric Grid (BATHYGRD.TIF)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  17. 02031 - Geophysical Surveys of Bear Lake, Utah-Idaho, September, 2002 - Bathymetry Tracklines (BATHY_TRK)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  18. 5 meter bathymetric contours derived from data collected during U.S. Geological Survey Geophysical Surveys of Bear Lake, Utah-Idaho, September, 2002 cruise 02031(02031_BATHY_5M)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  19. Geophysical Surveys of Bear Lake, Utah-Idaho, September, 2002 - Bathymetry (5m contours)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped...

  20. Deciphering Past and Present Tectonics of the Rio Grande Rift in New Mexico Utilizing Apatite Fission Track Thermochronology, Geochronology, Quaternary Faulting, and Cross-Section Restoration

    Science.gov (United States)

    Ricketts, J. W.; Karlstrom, K. E.; Kelley, S. A.; Priewisch, A.; Crossey, L. J.; Asmerom, Y.; Polyak, V.; Selmi, M.

    2011-12-01

    The Rio Grande rift provides an excellent laboratory for understanding styles and processes of extensional tectonics, and their driving forces. We apply apatite fission track (AFT) thermochronology, geochronology, fracture analysis, and cross-section restoration to decipher past and present tectonics of the Rio Grande rift. AFT data has been compiled from rift flank uplifts along the Rio Grande rift in an attempt to recognize long wavelength spatial and temporal patterns. AFT ages record time of cooling of rocks below ~110°C and, when cooling is due to exhumation, age elevation traverses can record upward advection of rocks through paleo 110°C isotherms. The relatively passive sides of half-grabens (e.g. Manzanos and Santa Fe Range) preserve Laramide AFT ages ranging from 45-70 Ma, indicating they were cooled during the Laramide Orogeny and have remained cooler than 110°C since then. Rift flanks on the tectonically active sides of half-grabens, (e.g. Sierra Ladrones, Sandias, Taos Range, and Sierra Blanca) have AFT ages that range from 35 Ma to <10 Ma, and record cooling that initiated with the Oligocene ignimbrite flare-up and continues through the Neogene. Our analysis tracks the approximate elevation of paleo 110°C isotherms in 10 Ma intervals from the Laramide to the present and shows that reconstructed paleoisotherms have been differentially uplifted, warped, and faulted since their time of formation, and hence serve as markers of uplift history and its mechanisms. AFT data at Ladron Peak, an active rift flank along the western margin of the Rio Grande rift in central New Mexico, indicates that it was rapidly unroofed between 20-10 Ma. Preliminary apatite helium data gives a similar age vs. elevation trend, but apatites have highly radiogenically damaged lattices and hence have corrected closure temperatures tens of degrees higher than AFT ages. The style of faulting at Ladron Peak is unusual because it is bounded by the anomalously low-angle (~15°) Jeter

  1. Sedimentology and ichnology of Neogene Coastal Swamp deposits in the Niger Delta Basin, Nigeria

    Science.gov (United States)

    Ezeh, Sunny C.; Mode, Wilfred A.; Ozumba, Berti M.; Yelwa, Nura A.

    2016-09-01

    Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mudstones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log signatures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamma ray logs, described sedimentological cores showing sedimentary features and ichnological characteristics; these were integrated to define the depositional settings. Some portions from one of the well sections reveal a blocky gamma ray well log signature instead of a coarsening-upward trend that characterises a shoreface setting while in other wells the signatures for heteroliths at some sections are bell blocky in shaped rather than serrated. Besides, heteroliths and mudstones within the proximal facies and those of distal facies were difficult to distinguish solely on well log signatures. However, interpretation based on sedimentology and ichnology of cores from these facies was used to correct these inconsistencies. It follows that depositional environment interpretation (especially in multifarious depositional environments such as the Niger Delta) should ideally be made together with other raw data for accuracy and those based solely on well log signatures should be treated with caution.

  2. Late Neogene Sequence Stratigraphic Evolution of the Foz do Amazonas Basin, Brazil

    Science.gov (United States)

    Gorini, Christian; Haq, Bilal U.; Tadeu dos Reis, Antonio; Guizan Silva, Cleverson; Cruz, Alberto; Soares, Emilson; Grangeon, Didier

    2014-05-01

    The margin of the Foz do Amazonas Basin saw a shift from predominantly carbonate to siliciclastic sedimentation in the early late Miocene. By this time the Amazon shelf had also been incised by a canyon that allowed direct influx of sediment to the basin floor, thus confirming that the paleo-Amazon fan had already initiated by that time (9.5-8.3Ma). Above this interval, during a prolonged lowstand, Messinian third-order sequences are preserved only in the incised-valley fills of the canyon with no equivalent strata on the shelf. Third and fourth-order sequences younger than Messinian are preserved on the shelf after sea-level rise above the shelf by early Pliocene. Sequences younger than 3.8 Ma often show fourth-order cyclicity with average duration of 400 kyr (larger scale eccentricity cycles) often preserved in high sedimentation rate areas of river deltas. Mass wasting and transportation of slope sediments to the basin began to play an important role in sediment dispersal at least as far back as mid Pliocene, after rapid progradation had produced steeper slopes 23 more prone to failure.

  3. Neogene magmatism and its possible causal relationship with hydrocarbon generation in SW Colombia

    Science.gov (United States)

    Vásquez, Mónica; Altenberger, Uwe; Romer, Rolf L.

    2009-07-01

    The Cretaceous oil-bearing source and reservoir sedimentary succession in the Putumayo Basin, SW Colombia, was intruded by gabbroic dykes and sills. The petrological and geochemical character of the magmatic rocks shows calc-alkaline tendency, pointing to a subduction-related magmatic event. K/Ar dating of amphibole indicates a Late Miocene to Pliocene age (6.1 ± 0.7 Ma) for the igneous episode in the basin. Therefore, we assume the intrusions to be part of the Andean magmatism of the Northern Volcanic Zone (NVZ). The age of the intrusions has significant tectonic and economic implications because it coincides with two regional events: (1) the late Miocene/Pliocene Andean orogenic uplift of most of the sub-Andean regions in Peru, Ecuador and Colombia and (2) a pulse of hydrocarbon generation and expulsion that has reached the gas window. High La/Yb, K/Nb and La/Nb ratios, and the obtained Sr-Nd-Pb isotopic compositions suggest the involvement of subducted sediments and/or the assimilation of oceanic crust of the subducting slab. We discuss the possibility that magma chamber(s) west of the basin, below the Cordillera, did increase the heat flow in the basin causing generation and expulsion of hydrocarbons and CO2.

  4. Lithofacies Associations and Depositional Environments of the Neogene Molasse succession, Pishin Belt, northwestern Pakistan

    DEFF Research Database (Denmark)

    Kasi, Aimal K.; Kassi, Akhtar M.; Friis, Henrik

    southwestern extension of the Neo-Tethys) in the Early Miocene. Uplifted orogens of the Muslim Bagh-Zhob Ophiolite and marine successions of the Nisai and Khojak formations served as the major source terrains for the Miocene through Holocene molasse succession in the south and southeast verging successive...

  5. Why does the convergence rate between Nazca and South America decrease since the Neogene?

    Science.gov (United States)

    Quinteros, J.; Sobolev, S. V.

    2012-12-01

    The classic example of the poorly understood rapid change of tectonic plates motion is the increase and then decrease of the convergence rate between the Nazca and South America plates during the last 25-20 Myr that has coincided with the growth of the Andes Mountains. Currently, the decrease in convergence rate is explained either by the increasing load of the Andes or by the appearance of flat slab segments beneath South America. Here, we present an alternative view derived from a thermomechanical self-consistent (gravity driven) model of Nazca plate subduction. Reconstructions of global plate velocities suggest that before some 25 Ma subduction of the Faralon/Nazca plate was almost perfectly parallel to the coastline of South America south of 20°S. After some 22 Ma direction of subduction became almost perpendicular to the trench. Based on these data as well as seismic tomographic images, we assume that the tip of the oceanic slab was still in the upper mantle under the central and southern parts of South America till 22 Ma. We run 2D thermomechanical models of gravity driven subduction starting at 22 Ma in the 1200 km deep mantle domain considering all the most important phase transformations. In all our numerical experiments we get a large increment in convergence velocity related to the penetration of the tip of the slab into the mantle transition zone. The subduction velocity is later reduced when the slab interacts with the spinel/perovskite phase transition and underlying more viscous lower mantle. Our models fit quite well the observed variations of convergence rate and are consistent with seismic tomographic images of the Nazca plate beneath South America. In a number of experiments we also added thick crust and high topography of Andes. These experiments demonstrate that presence of the Andes does not affect much the convergence rate between Nazca and South America plates. From our models we conclude that the variations in the convergence rate between Nazca and South America plates since 22 Ma are not related to the appearance of Andes. They are rather natural consequences of the first penetration of the Nazca plate into the transition zone and lower mantle beneath the southern part of South America after ending of the long-term oblique subduction.

  6. New Extinct Carp Fish Species (Teleostei, Cyprinidae from the Late Neogene of Southeastern Europe

    Directory of Open Access Journals (Sweden)

    Kovalchuk М.

    2014-10-01

    Full Text Available Новые вымершие виды карповых рыб (Teleostei, Cyprinidae из позднего неогена юга Восточ- ной Европы. Ковальчук А. Н. - Описаны новые виды вымерших карповых рыб из отложений верхнего неогена юга Восточной Европы. Rutilus robustus Kovalchuk, sp. n. из раннего плиоцена Приозерного (Республика Молдова отличается от других известных видов рода Rutilus массивной высокой ceratobranchiale, длинным передним неозубленным отростком, а также широкими пере- городками между септами кавернозной поверхности. Scardinius ponticus Kovalchuk, sp. n. из позд- него миоцена Лектостратотипа понта (Украина характеризуется большими глоточными зубами и увеличенным количеством зубцов на их внешнем жевательном крае.

  7. Neogene uplift of south Western Australia as constrained by river profiles

    CERN Document Server

    Barnett-Moore, Nicholas; Flament, Nicolas; Butterworth, Nathaniel; Müller, R Dietmar

    2013-01-01

    The relative tectonic quiescence of the Australian continent during the Cenozoicmakes it an excellent natural laboratory to study recent large-scale variations insurface topography and the processes influencing these changes. A part of this landscape is a fluvial network that is sensitive to variations in landscape horizontaland vertical motions. The notion that a river acts as a "tape recorder" for vertical perturbations (Pritchard et al., 2009) suggests that one can deduce changes in spatial and temporal characteristics of uplift via the analysis of river "channel-parallel", or longitudinal, profiles. Here we analysed 21 longitudinal river profiles, around the Australian continent. Steady-state concave upward profiles in northeast Australia indicate an absence of recent uplift. In contrast, pronounced convex upward undulations and major knickpoints within longitudinal profiles of rivers in southwest Australia suggest recent landscape uplift. This requires an explanation given the lackof recent, large-scale ...

  8. Sodium sulphate deposits of Neogene age: the Kirmir Formation, Beypazari Basin, Turkey

    Science.gov (United States)

    Ortí, Federico; Gündogan, Ibrahim; Helvaci, Cahit

    2002-01-01

    The Evaporite Member of the Kirmir Formation was deposited in shallow lacustrine environments during the upper Miocene. The most soluble minerals of this member can be currently observed in the Çayirhan mine. The Evaporite Member, which is composed of secondary gypsum at outcrop, can be subdivided into a bedded lower unit and a massive upper unit. In the bedded lower unit, most of the gypsum throughout the basin can be identified as having been transformed from glauberite. In the glauberite layers of the Çayirhan mine, some glauberite textures ('clear glauberite') suggest a primary, subaqueous, free precipitation on a depositional floor. More common, however, are the glauberite textures indicating an interstitial growth within a clayey-magnesitic matrix. In the thenardite layers accompanying the glauberite in the Çayirhan mine, some disruption structures can be assigned to synsedimentary dissolution. These structures together with the textures of the thenardite suggest that the original sodium sulphate was mirabilite, thenardite being a secondary phase, which formed during early to moderate burial diagenesis. The massive upper unit, in which evidence of sodium-bearing minerals is absent, is characterized by laminated to banded gypsum and nodular gypsum in the marginal areas of the evaporitic basin, whereas thick, clast-supported gypsum breccias prevail in the northern, deeper part of the basin. The brecciation of these calcium sulphate layers occurred as a result of synsedimentary, gravitative slumping under tectonic control. Although the sulphur isotopic values (δ 34S) of the sulphates of the Kirmir Formation suggest a marine-derived brine supply, the oxygen isotopic values (δ 18O) and the strontium ratios ( 87Sr/ 86Sr) do not support such a supply. The origin of the mother brines, the glauberite genesis, the depositional model of the sodium sulphates, and the salinity evolution are discussed.

  9. Before the 'Big Chill': Patterns of plant-insect associations from the Neogene of Iceland

    Science.gov (United States)

    Wappler, Torsten; Grímsson, Friðgeir

    2016-07-01

    Iceland is the only known terrestrial place in the subarctic North Atlantic providing a fairly continuous sedimentary and plant fossil record over the past 15 million years. While the basic palaeobotanical framework of this pattern has been well established during the last decade, less attention has been paid to the abundant insect traces on fossil leaves/leaflets. Here, we assess the diversity and frequency of insect herbivory on 4349 fossil angiosperm leaves/leaflets from six plant-bearing sedimentary formations exposed at 18 localities. By combining analyses of environmental factors, species interactions, ecology, biogeography, and the geological history, our results demonstrate how patterns of herbivory have changed over time in relation to temperature fluctuations that profoundly influenced levels of insect-mediated damage diversity and frequency. In addition, higher structural complexity, particularly the establishment of species-rich herb layer communities seems to have positively influenced the structure of insect communities in early late Miocene palaeoforests of Iceland.

  10. The evolutionary history of the extinct ratite moa and New Zealand Neogene paleogeography

    DEFF Research Database (Denmark)

    Bunce, M; Worthy, T H; Phillips, M J

    2009-01-01

    of the species of an extinct order. We also present an important new geological/paleogeographical model of late Cenozoic NZ, which suggests that terrestrial biota on the North and South Island landmasses were isolated for most of the past 20-30 Ma. The data reveal that the patterns of genetic diversity within......The ratite moa (Aves: Dinornithiformes) were a speciose group of massive graviportal avian herbivores that dominated the New Zealand (NZ) ecosystem until their extinction approximately 600 years ago. The phylogeny and evolutionary history of this morphologically diverse order has remained...

  11. Flexibility along the neck of the neogene terror bird Andalgalornis steulleti (Aves Phorusrhacidae.

    Directory of Open Access Journals (Sweden)

    Claudia P Tambussi

    Full Text Available BACKGROUND: Andalgalornis steulleti from the upper Miocene-lower Pliocene (≈6 million years ago of Argentina is a medium-sized patagornithine phorusrhacid. It was a member of the predominantly South American radiation of 'terror birds' (Phorusrhacidae that were apex predators throughout much of the Cenozoic. A previous biomechanical study suggests that the skull would be prepared to make sudden movements in the sagittal plane to subdue prey. METHODOLOGY/PRINCIPAL FINDINGS: We analyze the flexion patterns of the neck of Andalgalornis based on the neck vertebrae morphology and biometrics. The transitional cervical vertebrae 5th and 9th clearly separate regions 1-2 and 2-3 respectively. Bifurcate neural spines are developed in the cervical vertebrae 7th to 12th suggesting the presence of a very intricate ligamentary system and of a very well developed epaxial musculature. The presence of the lig. elasticum interespinale is inferred. High neural spines of R3 suggest that this region concentrates the major stresses during downstrokes. CONCLUSIONS/SIGNIFICANCE: The musculoskeletal system of Andalgalornis seems to be prepared (1 to support a particularly big head during normal stance, and (2 to help the neck (and the head rising after the maximum ventroflexion during a strike. The study herein is the first interpretation of the potential performance of the neck of Andalgalornis in its entirety and we considered this an important starting point to understand and reconstruct the flexion pattern of other phorusrhacids from which the neck is unknown.

  12. Evolution of Neogene Mammals in Eurasia: Environmental Forcing and Biotic Interactions

    Science.gov (United States)

    Fortelius, Mikael; Eronen, Jussi T.; Kaya, Ferhat; Tang, Hui; Raia, Pasquale; Puolamäki, Kai

    2014-05-01

    The relative weights of physical forcing and biotic interaction as drivers of evolutionary change have been debated in evolutionary theory. The recent finding that species, genera, clades, and chronofaunas all appear to exhibit a symmetrical pattern of waxing and waning lends support to the view that biotic interactions shape the history of life. Yet, there is similarly abundant evidence that these primary units of biological evolution arise and wane in coincidence with major climatic change. We review these patterns and the process-level explanations offered for them. We also propose a tentative synthesis, characterized by interdependence between physical forcing and biotic interactions. We suggest that species with evolutionary novelties arise predominantly in "species factories" that develop under harsh environmental conditions, under dominant physical forcing, whereas exceptionally mild environments give rise to "oases in the desert," characterized by strong competition and survival of relics.

  13. Neogene oceanographic variations recorded in manganese nodules from the Somali Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Banakar, V.K.; Nair, R.R.; Tarkian, M.; Haake, B.

    in the Western Indian ocean, Leg 25. Init. Rep. DSDP, 25: 743-760. Segl, M., Mangini, A., Beer, J., Bonani, G., Suter, M. and Wolfli, W., 1989. Growth rate variation of manganese nod- ules and crusts induced by paleoceanographic events. Paleo- ceanography, 4...:511-530. Segl, M., Mangini, A., Bonani, G, Hofmann, H.J., Nessi, M., Suter, M., Wolfli, W., Friedrich, G., Pluger, W.L,, Wiechow- ski, A. and Beer, J., 1984. Be-10 dating of a manganese crust from Central North Pacific and implications for ocean paleo...

  14. Carbonate replacement of lacustrine gypsum deposits in two Neogene continental basins, eastern Spain

    Science.gov (United States)

    Anadón, P.; Rosell, L.; Talbot, M. R.

    1992-07-01

    Bedded nonmarine gypsum deposits in the Miocene Teruel and Cabriel basins, eastern Spain, are partly replaced by carbonate. The Libros gypsum (Teruel Graben) is associated with fossiliferous carbonate wackestones and finely laminated, organic matter-rich mudstones which accumulated under anoxic conditions in a meromictic, permanent lake. The gypsum is locally pseudomorphed by aragonite or, less commonly, replaced by calcite. Low δ 13C values indicate that sulphate replacement resulted from bacterial sulphate reduction processes that were favoured by anacrobic conditions and abundant labile organic matter in the sediments. Petrographic evidence and oxygen isotopic composition suggest that gypsum replacement by aragonite occurred soon after deposition. A subsequent return to oxidising conditions caused some aragonite to be replaced by diagenetic gypsum. Native sulphur is associated with some of these secondary gypsum occurrences. The Los Ruices sulphate deposits (Cabriel Basin) contain beds of clastic and selenitic gypsum which are associated with limestones and red beds indicating accumulation in a shallow lake. Calcite is the principal replacement mineral. Bacterial sulphate reduction was insignificant in this basin because of a scarcity of organic matter. Stable isotope composition of diagenetic carbonate indicates that gypsum replacement occurred at shallow burial depths due to contact with dilute groundwaters of meteoric origin. Depositional environment evidently has a major influence upon the diagenetic history of primary sulphate deposits. The quantity of preserved organic matter degradable by sulphate-reducing bacteria is of particular importance and, along with groundwater composition, is the main factor controlling the mechanism of gypsum replacement by carbonate.

  15. Neogene to Recent Mafic Volcanism in Death Valley Reveals Architecture of Deep Mojavia Lithosphere

    Science.gov (United States)

    Rämö, O. T.; Calzia, J.

    2015-12-01

    At 10-0 m.y., the evolution of the Death Valley region, SE California, was characterized by repeated extrusion of mafic and intermediate lavas. The volume of these lavas appears to have diminished with time, from the relatively extensive (now faulted) Sheephead, Death Valley, Shoshone, and Funeral basalts to small monogenic volcanic centers (Split Cinder Cone, Ubehebe). A common denominator of these lavas is their transitional alkaline character (in general, trachybasalts to trachydacites with Na > K), relatively low MgO (1.5 to 6 wt.%), varying Fe2O3(tot) (4 to 12 wt.%) and Ni (10 to 80 ppm). They are all strongly enriched in the LREE: Chondrite-normalized La/Yb varies between 10 and 28, with the earlier, more voluminous lavas being less enriched (10 to 18) than the youngest volcanics (27 to 28). The initial Nd isotope composition of the lavas is outstandingly varying and does not correlate with fractionation stage. Their epsilon-Nd values vary from -10 to -2 and none of them thus registers a major asthenospheric component. Overall, these transitional mafic magmas probably represent relatively low-degree melts from the subcontinental lithosphere underneath the cratonic Mojavia crust. The 147Sm/144Nd ratios of the lavas show a restricted range (0.0930 to 0.1140) and, together with the measured 143Nd/144Nd ratios of the lavas, define Meso- to Neoproterozoic depleted mantle model ages between 800 and 1200 Ma. These have now spatial control across the Death Valley region and are clearly lower than those measured for the exposed craton. This suggest that the Mojavia cratonic mantle lithosphere may be a random amalgamation of ultramafic domains that vary in the degree of metasomatism and rejuvenation.

  16. Growth response of a deep-water ferromanganese crust to evolution of the Neogene Indian Ocean

    Science.gov (United States)

    Banakar, V.K.; Hein, J.R.

    2000-01-01

    A deep-water ferromanganese crust from a Central Indian Ocean seamount dated previously by 10Be and 230Th(excess) was studied for compositional and textural variations that occurred throughout its growth history. The 10Be/9Be dated interval (upper 32 mm) yields an uniform growth rate of 2.8 ?? 0.1 mm/Ma [Frank, M., O'Nions, R.K., 1998. Sources of Pb for Indian Ocean ferromanganese crusts: a record of Himalayan erosion. Earth Planet. Sci. Lett., 158, pp. 121-130.] which gives an extrapolated age of ~ 26 Ma for the base of the crust at 72 mm and is comparable to the maximum age derived from the Co-model based growth rate estimates. This study shows that Fe-Mn oxyhydroxide precipitation did not occur from the time of emplacement of the seamount during the Eocene (~ 53 Ma) until the late Oligocene (~ 26 Ma). This paucity probably was the result of a nearly overlapping palaeo-CCD and palaeo-depth of crust formation, increased early Eocene productivity, instability and reworking of the surface rocks on the flanks of the seamount, and lack of oxic deep-water in the nascent Indian Ocean. Crust accretion began (older zone) with the formation of isolated cusps of Fe-Mn oxide during a time of high detritus influx, probably due to the early-Miocene intense erosion associated with maximum exhumation of the Himalayas (op. cit.). This cuspate textured zone extends from 72 mm to 42 mm representing the early-Miocene period. Intense polar cooling and increased mixing of deep and intermediate waters at the close of the Oligocene might have led to the increased oxygenation of the bottom-water in the basin. A considerable expansion in the vertical distance between the seafloor depth and the CCD during the early Miocene in addition to the influx of oxygenated bottom-water likely initiated Fe-Mn crust formation. Pillar structure characterises the younger zone, which extends from 40 mm to the surface of the crust, i.e., ~ 15 Ma to Present. This zone is characterised by > 25% higher content of oxide-bound elements than in the older zone, possibly corresponding to further increased oxygenation of bottom-waters, increased stability of the seamount slope, and gradually reduced input of continental detritus from the erosion of the Himalayas. Middle Miocene Antarctic glaciation, which peaked ~ 12-13 Ma ago, increased the oxic bottom-water influx to the basin resulting in accretion of the crust with low detritus. Therefore, the younger crust started to accrete in response to a shift in bottom-water circulation towards the contemporary pattern, which produced a uniform growth rate and pillar structure up to the present. (C) 2000 Published by Elsevier Science B.V.

  17. Flexibility along the Neck of the Neogene Terror Bird Andalgalornis steulleti (Aves Phorusrhacidae)

    Science.gov (United States)

    Tambussi, Claudia P.; de Mendoza, Ricardo; Degrange, Federico J.; Picasso, Mariana B.

    2012-01-01

    Background Andalgalornis steulleti from the upper Miocene–lower Pliocene (≈6 million years ago) of Argentina is a medium-sized patagornithine phorusrhacid. It was a member of the predominantly South American radiation of ‘terror birds’ (Phorusrhacidae) that were apex predators throughout much of the Cenozoic. A previous biomechanical study suggests that the skull would be prepared to make sudden movements in the sagittal plane to subdue prey. Methodology/Principal Findings We analyze the flexion patterns of the neck of Andalgalornis based on the neck vertebrae morphology and biometrics. The transitional cervical vertebrae 5th and 9th clearly separate regions 1–2 and 2–3 respectively. Bifurcate neural spines are developed in the cervical vertebrae 7th to 12th suggesting the presence of a very intricate ligamentary system and of a very well developed epaxial musculature. The presence of the lig. elasticum interespinale is inferred. High neural spines of R3 suggest that this region concentrates the major stresses during downstrokes. Conclusions/Significance The musculoskeletal system of Andalgalornis seems to be prepared (1) to support a particularly big head during normal stance, and (2) to help the neck (and the head) rising after the maximum ventroflexion during a strike. The study herein is the first interpretation of the potential performance of the neck of Andalgalornis in its entirety and we considered this an important starting point to understand and reconstruct the flexion pattern of other phorusrhacids from which the neck is unknown. PMID:22662194

  18. Newfoundland Neogene sediment drifts : Transition from the Paleogene greenhouse to the modern icehouse

    NARCIS (Netherlands)

    Friedrich, O.; Norris, R. D.; Wilson, P. A.; Opdyke, B. N.; Badger, Markus; Bailey, Ian; Beddow-Twigg, Helen; Bohaty, Steven; Bolton, Clara; Bornemann, André; Crocker, Anja; Grützner, Jens; Herbert, Timothy; Holbourn, Ann; Hull, Pincelli; Liebrand, Diederick; Lippert, Peter; Lourens, Lucas; Lyle, Mitch; die, Jo; Rosenthal, Yair; Sexton, Phil; Stärz, Michael; Westerhold, Thomas

    2015-01-01

    This workshop brought together specialists from various fields to develop a drilling proposal to fill the "Oligo-Miocene Gap" that exists in our understanding of the functions of Earth's systems. We propose to establish the first continuous high-deposition record of the Oligo-Miocene through new Int

  19. Sedimentology and ichnology of Neogene Coastal Swamp deposits in the Niger Delta Basin, Nigeria

    Directory of Open Access Journals (Sweden)

    Ezeh Sunny C.

    2016-09-01

    Full Text Available Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mudstones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log signatures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamma ray logs, described sedimentological cores showing sedimentary features and ichnological characteristics; these were integrated to define the depositional settings. Some portions from one of the well sections reveal a blocky gamma ray well log signature instead of a coarsening-upward trend that characterises a shoreface setting while in other wells the signatures for heteroliths at some sections are bell blocky in shaped rather than serrated. Besides, heteroliths and mudstones within the proximal facies and those of distal facies were difficult to distinguish solely on well log signatures. However, interpretation based on sedimentology and ichnology of cores from these facies was used to correct these inconsistencies. It follows that depositional environment interpretation (especially in multifarious depositional environments such as the Niger Delta should ideally be made together with other raw data for accuracy and those based solely on well log signatures should be treated with caution.

  20. TRANSGRESSIVE SEQUENCES ON FORELAND MARGINS: A CASE STUDY OF THE NEOGENE CENTRAL GUADALQUIVIR BASIN, SOUTHERN SPAIN

    Directory of Open Access Journals (Sweden)

    J. GABRIEL PENDÓN

    2004-07-01

    Full Text Available The Guadalquivir foreland basin, located between the Iberian basement northward and the Betic orogen to the South, represents the western sector of the earlier foredeep basin of the Betic Cordillera. Along the northern foreland margin, the sedimentary fill of this basin includes a Tortonian Basal Transgressive Complex (BTC, composed of five internal sequences bounded by transgressive surfaces. Two main parts are distinguished within each sequence: the lower transgressive lag deposits, and the upper stillstand/prograding sediments. Three facies associations were distinguished within this stratigraphic succession along the central sector of this basin margin: unfossiliferous conglomerates and coarse-grained sands (A, fossiliferous conglomerates and coarse-grained sands (B, and yellow medium-coarse-grained fossiliferous sands (C. A fourth facies association (D: blue silty marlstones and shales overlies the BTC. Deposits of alluvial sediments (facies association A and shallow-marine/foreshore sediments (facies association C, were recurrently interrupted by transgressive pulses (facies associations B and C. Every pulse is recorded by an erosional, cemented sandy-conglomerate bar with bivalves (Ostreidae, Isognomon, balanids, gastropods and other marine bioclasts; or their transgressive equivalents. The lateral facies changes in each individual sequence of the BTC are related to: (1 the influence on the northern foreland margin of the tectonic activity of the southern orogenic margin; (2 the palaeorelief formed by irregularities of the substrate which controls the sediment dispersal; and (3 the evolution stages of the sedimentary systems. 

  1. Neogene and active shortening offshore the reactivated Levant margin in Lebanon: results of the SHALIMAR cruise

    Science.gov (United States)

    Briais, A.; Singh, S. C.; Tapponnier, P.; Elias, A.; Sursock, A.; Jomaa, R.; Carton, H.; Daeron, M.; King, G.; Jacques, E.

    2004-12-01

    The objectives of the SHALIMAR cruise were to study recent deformation of the Mediterranean seafloor west of Mt Lebanon. We collected multibeam bathymetry and back-scatter images, reflection seismic profiles - surface and deep-towed, 3.5 kHz echo-sounder data, gravity and magnetic data over an 80 km-wide zone offshore the entire Lebanese coast. The bathymetry reveals a very steep slope between Beyrouth and Batroun, with a water depth of 1500 m only 5 km offshore. Between Saida and Tripoli (33.5N to 34.5N), both the bathymetry and seismic lines show a series of ramp anticlines affecting Plio-Quaternary deposits and a seismically transparent layer with variable thickness corresponding to the Messinian evaporites (5.6 Ma). This fold-and-thrust belt is the offshore expression of shortening related to the formation of Mt Lebanon. It is limited westwards by a prominent fold front 30 km from shore. Some ramps appear to be submarine continuations of faults documented ashore (e.g., Aabde and Tripoli thrusts). The strikes of fold axes are consistent with WNW-ESE shortening and slip-partitioning along the 30° Lebanese bend of the Levant fault. North of Tripoli and south of Saida, the continental margin displays a wider shelf (20 km) and gentler slope. In the south, at 1200-1500 m depth small, closely spaced, NE-trending scarps attest to young, distributed dip-slip faulting, although deformation is much less than north of Beyrouth. At the southern extremity of our survey, NW-trending normal fault scarps roughly aligned with the Mt Carmel-Haifa fault vanish 50 km offshore in the Levant basin. Bouguer gravity anomalies, estimated by removing from free-air gravity data the effect of bathymetry, display a very steep gradient between Beyrouth and Tripoli, marking the passage from thickened Mt Lebanon crust to thin crust in the Levant basin. Gravity anomalies also outline large, NE-SW trending steps between the basin crust and thinned continental crust near and south of Beyrouth. The particularly large negative anomalies in the north likely reflect flexure of the lithosphere due to subduction under Cyprus and underthrusting beneath Lebanon. The SHALIMAR data suggest that local compression induced by the bend in the Dead Sea Transform reactivated faults of the Mesozoic Levant margin into lateral ramps and thrusts whose evolution may lead to subduction. It is possible that the shorter distance between the transform and margin in central Lebanon (35 km) than in Syria (65 km) is one measure of continental shortening. That the oceanic lithosphere is strong may explain why the Carmel and Roum faults did not extend into the Levant basin.

  2. The Neogene tectonic evolution and climatic change of the Tianshui Basin, NE Tibetan Plateau

    Science.gov (United States)

    Peng, T.; Li, J.; Song, C.; Zhao, Z.; Zhang, J.; Wang, X.; Hui, Z.

    2013-12-01

    The Tianshui Basin, located at the conjunction of NE Tibetan Plateau and Chinese Loess Plateau, has received intensive attention recently. Fine-grained Miocene sediment was identified as loess in its north part and this pushes the onset of Asian aridification into 22 Ma. However, our sedimentological, biomarker, pollen, diatom and mammalian fossils evidence propose that these sediments were suggested to be mudflat/distal fan and floodplain deposit instead of eolian deposit. So detailed tectonic background and climate reconstruction may illustrate the controversy and shed light on the tectonic, climate and ecology interactions. Here we report our integrated studies on the tectonic evolution, climate change and paleoecology reconstruction in the Tianshui basin. Based on the magnetostratigraphy and fossil mammal ages, sedimentological and detrital fission-track thermochronologic (DFT) analysis reveals four episodic tectonic uplift events occurred at ~20 Ma, ~14 Ma, ~9.2-7.4 Ma and ~3.6 Ma along the basin and its adjacent mountains. The timing of these activities at Western Qinling have been documented at many segments of the Tibetan Plateau, so most likely they were the remote response to the ongoing India-Asia collision. Pollen, mammalian fossils and biomarker data permit us to illustrate the paleoenvironment in the Tianshui Basin. During the period of ~17-10 Ma, the climate was generally warm-humid revealed by the broad-leaved forest and low Average Chain Length (ACL) values, when the Paltybelodon and Gomphotherium were roaming near an extensive aquatic setting. In addition, the observed Middle Miocene Climatic Optimum and Middle Miocene Climatic Transition events may be a terrestrial response to global climate changes. During the interval of ~10-6 Ma, the climate was relatively arid characterized by the rapid development of steppe and appearance of the Hipparion fauna, consistent with the biomarker proxy. Although the NE Tibetan Plateau experienced a phase of active uplift around ~8 Ma, we mainly ascribe this arid interval to global change known as the C4 grass expansion, because the subsequent early Pliocene turned back to humid-warm climate again. Since ~4 Ma, it became obviously drier than the previous two arid intervals via the biomarker perspective. This dramatic dry trend may be related to the Tibetan Plateau uplift and/or global cooling, highlighting the importance and complexity of tectonic-climate interaction. Acknowledgements: This work was co-supported by the "Strategic Priority Research Program" of the CAS (XDB03020402), the (973) National Basic Research Program of China (2013CB956400) and the National Natural Science Foundation of China (41021091, 41101012).

  3. Evolutionary Patterns among Living and Fossil Kogiid Sperm Whales: Evidence from the Neogene of Central America.

    Science.gov (United States)

    Velez-Juarbe, Jorge; Wood, Aaron R; De Gracia, Carlos; Hendy, Austin J W

    2015-01-01

    Kogiids are known by two living species, the pygmy and dwarf sperm whale (Kogia breviceps and K. sima). Both are relatively rare, and as their names suggest, they are closely related to the sperm whale, all being characterized by the presence of a spermaceti organ. However, this organ is much reduced in kogiids and may have become functionally different. Here we describe a fossil kogiid from the late Miocene of Panama and we explore the evolutionary history of the group with special attention to this evolutionary reduction. The fossil consists of cranial material from the late Tortonian (~7.5 Ma) Piña facies of the Chagres Formation in Panama. Detailed comparison with other fossil and extant kogiids and the results of a phylogenetic analysis place the Panamanian kogiid, herein named Nanokogia isthmia gen. et sp. nov., as a taxon most closely related to Praekogia cedrosensis from the Messinian (~6 Ma) of Baja California and to Kogia spp. Furthermore our results show that reduction of the spermaceti organ has occurred iteratively in kogiids, once in Thalassocetus antwerpiensis in the early-middle Miocene, and more recently in Kogia spp. Additionally, we estimate the divergence between extant species of Kogia at around the late Pliocene, later than previously predicted by molecular estimates. Finally, comparison of Nanokogia with the coeval Scaphokogia cochlearis from Peru shows that these two species display a greater morphological disparity between them than that observed between the extant members of the group. We hypothesize that this reflects differences in feeding ecologies of the two species, with Nanokogia being more similar to extant Kogia. Nanokogia shows that kogiids have been part of the Neotropical marine mammal communities at least since the late Miocene, and gives us insight into the evolutionary history and origins of one of the rarest groups of living whales.

  4. Reconstruction of different wetland plant habitats of the Pannonian basin system (Neogene, Eastern Austria)

    Energy Technology Data Exchange (ETDEWEB)

    Hofmann, C.C.; Zetter, R. [University of Vienna, Vienna (Austria). Inst. of Palaeontology

    2005-06-01

    Sedimentary and palynofacies analysis, total organic carbon content (TOC), and palynology from a densely sampled, small, lignite-bearing succession of Late Miocene age at Badersdorf, SE Austria, were compared with modern wetland ecologies. From this, six hydrologically controlled palynofacies types and six associated paleo-plant habitats in an ancient wetland system were differentiated. The associated woody and herbaceous hinterland flora also were distinguished. At least four horizons with relatively high fusinite content have been preserved, indicating occurrence of paleo-wildfires in either the wetland or the hinterland. The palynofacies types were used to determine the taphonomic bias of the associated palynomorph assemblages, which, together with a comparison with modern wetland vegetation, led to differentiation of the paleo-plant habitats. The paleo-wetland was dominated mainly by Glyptostrobus-containing vegetation, and comprised clastic swamp forests with woody angiosperms, natural levee forests, fern- and Glyptostrobus-dominated organic swamps, freshwater marshes, and wet prairies. The occurrence of more than 40 herbaceous taxes at this locality indicates that the lowland vegetation was not composed of only different closed-forest types, but also of areas with herbaceous vegetation. The more zonal vegetation of the adjacent hinterland has been interpreted as a mix of Pinaceae and woody angiosperms with patches of more herbaceous xeric layers.

  5. Early neogene history of the central American arc from Bocas del Toro, western Panama

    Science.gov (United States)

    Coates, A.G.; Aubry, M.-P.; Berggren, W.A.; Collins, Luke S.; Kunk, M.

    2003-01-01

    A newly discovered sequence of lower to middle Miocene rocks from the eastern Bocas del Toro archipelago, western Panama, reveals the timing and environment of the earliest stages in the rise of the Isthmus of Panama in this region. Two new formations, the Punta Alegre Formation (lower Miocene, Aquitanian to Burdigalian) and the Valiente Formation (middle Miocene, Langhian to Serravallian), are here named and formally described. The Punta Alegre Formation contains a diagnostic microfauna of benthic and planktic foraminifera and calcareous nannofossils that indicate deposition in a 2000-m-deep pre-isthmian neotropical ocean from as old as 21.5-18.3 Ma. Its lithology varies from silty mudstone to muddy foraminiferal ooze with rare thin microturbidite layers near the top. The Valiente Formation, which ranges in age from 16.4 to ca. 12.0 Ma, lies with slight angular unconformity on the Punta Alegre Formation and consists of five lithofacies: (1) columnar basalt and flow breccia, (2) pyroclastic deposits, (3) coarse-grained volcaniclastic deposits, (4) coral-reef limestone with diverse large coral colonies, and (5) marine debris-flow deposits and microturbidities. These lithofacies are interpreted to indicate that after ca. 16 Ma a volcanic arc developed in the region of Bocas del Toro and that by ca. 12 Ma an extensively emergent archipelago of volcanic islands had formed. 39Ar/40Ar dating of basalt flows associated with the fossiliferous sedimentary rocks in the upper part of the Valiente Formation strongly confirms the ages derived from planktic foraminifera and nannofossils. Paleobathymetric analysis of the two new formations in the Valiente Peninsula and Popa Island, in the Bocas del Toro archipelago, shows a general shallowing from lower- through upper-bathyal to upper-neritic and emergent laharic and fluviatile deposits from ca. 19 to 12 Ma. The overlying nonconformable Bocas del Toro Group contains a lower transgressive sequence ranging from basal nearshore sandstone to upper-bathyal mudstone (ca. 8.1-5.3. Ma) and an upper regressive sequence (5.3-3.5 Ma). A similar paleobathymetric pattern is observed from the Gatun to Chagres Formations (12-6 Ma) in the Panama Canal Basin area and in the Uscari, Rio Banana, Quebrada Chocolate, and Moin Formations (8-1.7 Ma) in the southern Limo??n Basin of Costa Rica.

  6. Neogene-Quaternary magmatic activity and its geodynamic implications in the Central Mediterranean region

    Directory of Open Access Journals (Sweden)

    G. Serri

    1997-06-01

    Full Text Available The petrogenesis and time/space distribution of the magmatism associated with the formation of the Northern and Southern Tyrrhenian basins, together with the directions and ages of lithospheric extension and/or spreading north and south of the 410N discontinuity, show that the two arc/back-arc systems have undergone a different structural evolution at least since the middle Miocene (Langhian. The geochemical components involved in the genesis of the heterogeneities of the mantle sources of this magmatism require two separate, compositionally different slabs: 1 an old oceanic (Ionian lithosphere still seismically active below the Calabrian arc and the Southern Tyrrhenian region; 2 an almost seismically inactive continental (Adriatic lithosphere which carried large amounts of upper crustal materials within the upper mantle under the NW Roman Province/Tuscan/Northern Tyrrhenian region. The proposed geodynamic models require: 1 for the Northern Tyrrhenian/Northern Apenninic arc/back-arc system, the delamination and foundering of the Adriatic continental lithosphere as a consequence of the continental collision between the Corsica block and the Adriatic continental margin. This delamination process, which is still ongoing, probably started in the early-middle Miocene, but earlier than 15-14 Ma, as indicated by the age and petrogenesis of the first documented magmatic episode (the Sisco lamproite of the Northern Apennine orogenesis; 2 for the Southern Tyrrhenian/Southern Apenninic-Calabrian arc/back-arc system, the roll-back subduction and back-arc extension driven by gravitational sinking of the Ionian oceanic subducted lithosphere. This process started after the end of the arc volcanism of Sardinia (about 13 Ma but earlier than the first recorded episode of major rifting (about 9 Ma in the Southern Tyrrhenian back-arc basin.

  7. Increased rates of large-magnitude explosive eruptions in Japan in the late Neogene and Quaternary

    Science.gov (United States)

    Mahony, S. H.; Sparks, R. S. J.; Wallace, L. M.; Engwell, S. L.; Scourse, E. M.; Barnard, N. H.; Kandlbauer, J.; Brown, S. K.

    2016-07-01

    Tephra layers in marine sediment cores from scientific ocean drilling largely record high-magnitude silicic explosive eruptions in the Japan arc for up to the last 20 million years. Analysis of the thickness variation with distance of 180 tephra layers from a global data set suggests that the majority of the visible tephra layers used in this study are the products of caldera-forming eruptions with magnitude (M) > 6, considering their distances at the respective drilling sites to their likely volcanic sources. Frequency of visible tephra layers in cores indicates a marked increase in rates of large magnitude explosive eruptions at ˜8 Ma, 6-4 Ma, and further increase after ˜2 Ma. These changes are attributed to major changes in tectonic plate interactions. Lower rates of large magnitude explosive volcanism in the Miocene are related to a strike-slip-dominated boundary (and temporary cessation or deceleration of subduction) between the Philippine Sea Plate and southwest Japan, combined with the possibility that much of the arc in northern Japan was submerged beneath sea level partly due to previous tectonic extension of northern Honshu related to formation of the Sea of Japan. Changes in plate motions and subduction dynamics during the ˜8 Ma to present period led to (1) increased arc-normal subduction in southwest Japan (and resumption of arc volcanism) and (2) shift from extension to compression of the upper plate in northeast Japan, leading to uplift, crustal thickening and favorable conditions for accumulation of the large volumes of silicic magma needed for explosive caldera-forming eruptions.

  8. Blockfields in Reinheimen Nationalpark, Norway – Neogene weathering remnants or Quaternary periglacial origin?

    DEFF Research Database (Denmark)

    Andersen, Jane Lund; Egholm, David Lundbek; Knudsen, Mads Faurschou;

    rates of landscape evolution of the mountain summit. References Goodfellow B W, 2012. A granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins. Quaternary Science Reviews, 57, 121- 135. Strømsøe J R, Paasche Ø, 2011....... Weathering patterns in high-latitude regolith. Journal of Geophysical Research: Earth Surface, 116 (F3)...

  9. Orbital signatures in lacustrine sediments : the Late Neogene intramontane Florina-Ptolemais-Servia Basin, northwestern Greece

    NARCIS (Netherlands)

    Steenbrink, J.

    2001-01-01

    Zwabberende aardas verklaart klimaatcycli Klimaatwisselingen tijdens de ijstijden blijken niet het gevolg te zijn van het periodiek afsmelten van poolijs. Er is ontdekt dat dezelfde wisselingen voorkwamen toen de noordpool nog geen ijskappen had. Zwabberingen in de stand van de aa

  10. A revision of the Neogene Conidae and Conorbidae (Gastropoda) of the Paratethys Sea.

    Science.gov (United States)

    Harzhauser, Mathias; Landau, Bernard

    2016-12-22

    The Miocene Conidae and Conorbidae of the central- and south-eastern European Paratethys Sea are revised. In total, 74 species are described of which 10 are new species and 5 are documented for the first time from Paratethyan localities. Species descriptions and delimitations are partly based on morphometric data. In addition, colour patterns are described for the first time for the majority of species. In respect to the ongoing discussion on the supraspecific treatment of extant Conidae, we strongly focus on generic allocations and provide a key for the genera as understood herein. Biogeographically, the larger part of the assemblage indicates affiliation with modern western African faunas as indicated by the occurrence of genera such as Lautoconus, Kalloconus, Monteiroconus and Pseudonoduloconus. The relationship with Indo-West Pacific faunas is comparatively low. The high alpha-diversities observed for localities in the Pannonian, Transylvanian and Vienna basins, with up to 44 species, is a marker of tropical conditions in the Paratethys Sea during middle Miocene times.        Conasprella minutissima nov. sp., Kalloconus hendricksi nov. sp., Kalloconus letkesensis nov. sp., Kalloconus pseudohungaricus nov. sp., Lautoconus kovacsi nov. sp., Lautoconus pestensis nov. sp., Lautoconus quaggaoides nov. sp., Leporiconus paratethyianus nov. sp., Plagioconus breitenbergeri nov. sp. and Plagioconus bellissimus nov. sp. are described as new species; Conilithes eichwaldi nov. nom. is proposed as new name for Conus exiguus Eichwald, 1830 [non Lamarck, 1810].

  11. Multiple evolutionary origins of Australian soil-burrowing cockroaches driven by climate change in the Neogene.

    Science.gov (United States)

    Lo, Nathan; Tong, K Jun; Rose, Harley A; Ho, Simon Y W; Beninati, Tiziana; Low, David L T; Matsumoto, Tadao; Maekawa, Kiyoto

    2016-02-24

    Parallel evolution is the independent appearance of similar derived phenotypes from similar ancestral forms. It is of key importance in the debate over whether evolution is stochastic and unpredictable, or subject to constraints that limit available phenotypic options. Nevertheless, its occurrence has rarely been demonstrated above the species level. Climate change on the Australian landmass over the last approximately 20 Myr has provided conditions conducive to parallel evolution, as taxa at the edges of shrinking mesic habitats adapted to drier biomes. Here, we investigate the phylogeny and evolution of Australian soil-burrowing and wood-feeding blaberid cockroaches. Soil burrowers (subfamily Geoscapheinae) are found in relatively dry sclerophyllous and scrubland habits, whereas wood feeders (subfamily Panesthiinae) are found in rainforest and wet sclerophyll. We sequenced and analysed mitochondrial and nuclear markers from 142 specimens, and estimated the evolutionary time scale of the two subfamilies. We found evidence for the parallel evolution of soil-burrowing taxa from wood-feeding ancestors on up to nine occasions. These transitions appear to have been driven by periods of aridification during the Miocene and Pliocene across eastern Australia. Our results provide an illuminating example of climate-driven parallel evolution among species. © 2016 The Author(s).

  12. Neogene biogenic sediments of onshore Peru: part I, sedimentology and stratigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Marty, R.C.; Dunbar, R.B.; Baker, P.

    1985-01-01

    The Sechura (approx.6/sup 0/S) and Pisco (approx.14/sup 0/S) Basins of onshore Peru contain Miocene diatom and phosphate rich sediments which sharply contrast with underlying clastics. In the Sechura Basin the Miocene clastic Mancora, Heath and Montera Formations are overlain by the Zapallal Formation which grades upwards from a weakly biogenic base into fairly pure diatomites (biogenic silica >20%) and ore grade phosphorite (P/sub 2/O/sub 5/>20%). Biogeneic content decreases in the eastern basin as clastic content increases. The base of the Zapallal Formation has been dated at between 12.2 and 14.0 mybp using radiolaria correlated to magnetic stratigraphy by Theyer, et al (1978), and the phosphatic section yields dates of between 8.0 and 11.2 my. In the Pisco Basin the Eocene clastic Paracas Formation is overlain unconformably by the Miocene Pisco Formation which contains a basal sequence of cross-bedded clastics, tuffs, and partially recrystallized diatomites; a phosphorite bearing middle sequence; and a diatom rich top. Current direction from the cross beds of the basal Pisco Formation indicate a generally southerly transport direction but with considerable directional variability. This may be related to the Peru under-current which shows highly variable strength and direction near 15/sup 0/S.

  13. Unraveling tectonics and climate forcing in the late-Neogene exhumation history of South Alaska

    Science.gov (United States)

    Valla, Pierre; Champagnac, Jean-Daniel; Shuster, David; Herman, Frédéric; Giuditta Fellin, Maria

    2015-04-01

    The southern Alaska range presents an ideal setting to study the complex interactions between tectonics, climate and surface processes in landscape evolution. It exhibits active tectonics with the ongoing subduction/collision between Pacific and North America, and major active seismogenic reverse and strike-slip faults. The alpine landscape, rugged topography and the important ice-coverage at present reveal a strong glacial imprint associated with high erosion and sediment transport rates. Therefore, the relative importance of climatically-driven glacial erosion and tectonics for the observed late-exhumation history appears to be quite complex to decipher. Here, we first perform a formal inversion of an extensive bedrock thermochronological dataset from the literature to quantify the large-scale 20-Myr exhumation history over the entire southern Alaska. We show that almost half of the variability within the thermochronological record can be explained by modern annual precipitations spatial distribution, the residuals clearly evidencing localized exhumation along major tectonic structures of the frontal fold and thrust belt. Our results confirm high exhumation rates in the St Elias "syntaxis" and frontal zones for the last 0-2 Myr, where major ice fields and high precipitation rates likely sustained high exhumation rates; however the impact of late Cenozoic glaciations is difficult to constrain because of the low resolution on the exhumation history older than ~2 Myr. On the contrary, our inversion outcomes highlight that north of the Bagley Icefield the long-term exhumation has remained quite slow and continuous over the last ~20 Myr, with no late-stage signal of exhumation change since the onset of glaciations despite a clear glacial imprint on the landscape. We thus focus on the Granite Range (Wrangell-St Elias National Park, Alaska), an area presenting a strong glacial imprint but minor tectonic activity with only localized brittle deformation. We sampled four elevation profiles over an East-West transect for low-temperature thermochrometry. Apatite (U-Th-Sm)/He dating provides ages between ~10 and 30 Ma, in agreement with published data, and shows apparent low long-term exhumation rates (~0.1 km/Myr). 4He/3He thermochronometry on a subset of samples reveals a more complex exhumation history, with a significant increase in exhumation since ~6-4 Ma that we relate to the early onset of glaciations and associated glacial erosion processes. Our results, in agreement with offshore sediment records, thus confirm an early glacial activity and associated erosion response in Alaska, well before the onset of Pliocene-Pleistocene Northern Hemisphere glaciations.

  14. Neogene seismites and seismic volcanic rocks in the Linqu area, Shandong Province, E China

    Directory of Open Access Journals (Sweden)

    Tian H.S.

    2014-07-01

    Full Text Available The Yishu Fault Zone runs through the centre of Shandong Province (E China; it is a deep-seated large fault system that still is active. Two volcanic faulted basins (the Shanwang and Linqu Basins in the Linqu area, west of the fault zone, are exposed to rifting, which process is accompanied by a series of tectonic and volcanic earthquakes with a magnitude of 5-8. Lacustrine sediments in the basins were affected by these earthquakes so that seismites with a variety of soft-sediment deformation structures originated. The seismites form part of the Shanwang Formation of the Linqu Group. Semi-consolidated fluvial conglomerates became deformed in a brittle way; these seismites are present at the base of the Yaoshan Formation. Intense earthquakes triggered by volcanic activity left their traces in the form of seismic volcanic rocks associated with liquefied-sand veins in the basalt/sand intercalations at the base of the Yaoshan Formation. These palaeo-earthquake records are dated around 14-10 Ma; they are responses to the intense tectonic extension and the basin rifting in this area and even the activity of the Yishu Fault Zone in the Himalayan tectonic cycle.

  15. Clay minerals assemblage in the Neogene fluvial succession of the Pishin Belt, Pakistan

    DEFF Research Database (Denmark)

    Kasi, Aimal Khan; Kassi, Akhtar Muhammad; Friis, Henrik

    2014-01-01

    and metasedimentary successions. The source of kaolinite seems to be pedogenic or lateritic. The clay minerals assemblage in mudstones and sandstones of the Dasht Murgha group, Malthanai formation and Bostan formation appears to have been derived from the nearby-exposed Pre-Miocence mafic/ultramafic rocks...

  16. Clay minerals assemblage in the Neogene fluvial succession of the Pishin Belt, Pakistan

    DEFF Research Database (Denmark)

    Kasi, Aimal Khan; Kassi, Akhtar Muhammad; Friis, Henrik

    2014-01-01

    and kaolinite. Smectite and chlorite are most probably derived from the metavolcanic and mafic volcanic rocks, respectively. Presence of serpentine in samples of the Bostan Formation indicates altered ultramafic rocks as one of the source terrains. Illite is probably recycled from the older sedimentary...... and metasedimentary successions. The source of kaolinite seems to be pedogenic or lateritic. The clay minerals assemblage in mudstones and sandstones of the Dasht Murgha group, Malthanai formation and Bostan formation appears to have been derived from the nearby-exposed Pre-Miocence mafic/ultramafic rocks...

  17. Geomorphology and Neogene tectonic evolution of the Palomares continental margin (Western Mediterranean)

    Science.gov (United States)

    Gómez de la Peña, Laura; Gràcia, Eulàlia; Muñoz, Araceli; Acosta, Juan; Gómez-Ballesteros, María; R. Ranero, César; Uchupi, Elazar

    2016-10-01

    The Palomares continental margin is located in the southeastern part of Spain. The margin main structure was formed during Miocene times, and it is currently part of the wide deformation zone characterizing the region between the Iberian and African plates, where no well-defined plate boundary occurs. The convergence between these two plates is here accommodated by several structures, including the left lateral strike-slip Palomares Fault. The region is characterized by sparse, low to moderate magnitude (Mw tectonic history of the margin we analyze new high-resolution multibeam bathymetry data and re-processed three multichannel seismic reflection profiles crossing the main structures. The analysis of seafloor morphology and associated subsurface structure provides new insights of the active tectonic features of the area. In contrast to other segments of the southeastern Iberian margin, the Palomares margin contains numerous large and comparatively closely spaced canyons with heads that reach near the coast. The margin relief is also characterized by the presence of three prominent igneous submarine ridges that include the Aguilas, Abubacer and Maimonides highs. Erosive processes evidenced by a number of scars, slope failures, gullies and canyon incisions shape the present-day relief of the Palomares margin. Seismic images reveal the deep structure distinguishing between Miocene structures related to the formation of the margin and currently active features, some of which may reactivate inherited structures. The structure of the margin started with an extensional phase accompanied by volcanic accretion during the Serravallian, followed by a compressional pulse that started during the Latemost Tortonian. Nowadays, tectonic activity offshore is subdued and limited to few, minor faults, in comparison with the activity recorded onshore. The deep Algero-Balearic Basin is affected by surficial processes, associated to halokinesis of Messinian evaporites.

  18. Abundance of color bands in Neogene carbonate sediments on Ontong Java Plateau:

    DEFF Research Database (Denmark)

    Berger, W.H.; Lind, Ida

    1997-01-01

    When comparing color-band abundances within one sediment section with those of others of the same age but deposited at different depths along a transect on the northeastern flank of Ontong Java Plateau in the western equatorial Pacific (ODP Leg 130), one notes that the sections with the highest s...

  19. Small mammal tooth enamel carbon isotope record of C4 grasses in late Neogene China

    Science.gov (United States)

    Arppe, Laura; Kaakinen, Anu; Passey, Benjamin H.; Zhang, Zhaoqun; Fortelius, Mikael

    2015-10-01

    The spatiotemporal pattern of the late Cenozoic spread of C4 vegetation is an important indicator of environmental change that is intertwined with the uplift of the Himalaya and Tibetan Plateau, and the development of the East Asian monsoons. To explore the spread of C4 vegetation in China and shed new light on regional climatic evolution, we measured δ13C values of more than 200 small mammal teeth (primarily rodents and lagomorphs) using a laser ablation isotope ratio mass spectrometry approach. Small mammals are highly sensitive indicators of their environment because they have limited spatial ranges and because they have minimal time-averaging of carbon isotope signatures of dietary components. The specimens originate from four classic Late Miocene fossil localities, Lufeng, Yuanmou, Lingtai, and Ertemte, along a southwest-northeast transect from Yunnan Province to Inner Mongolia. In Yunnan (Lufeng, Yuanmou) and on the Loess Plateau (Lingtai), the small mammal δ13C values record nearly pure C3 ecosystems, and mixed but C3-based ecosystems, respectively, in agreement with previous studies based on carbon isotopes of large herbivores and soil carbonates. In Inner Mongolia, the micromammalian tooth enamel δ13C record picks up the presence of C4 vegetation where large mammal samples do not, indicating a mixed yet C3-dominated ecosystem at ~ 6 Ma. As a whole, the results support a scenario of northward increasing C4 grass abundance in a pattern that mirrors northward decreasing precipitation of the summer monsoon system. The results highlight differences between large and small mammals as indicators of C4 vegetation in ancient ecosystems, particularly the ability of small mammal δ13C values to detect the presence of minor components of the vegetation structure.

  20. The vegetation and climate of a Neogene petrified wood forest of Mizoram, India

    Science.gov (United States)

    Tiwari, R. P.; Mehrotra, R. C.; Srivastava, Gaurav; Shukla, Anumeha

    2012-11-01

    Eleven fossil woods belonging to seven families are described from a petrified wood forest of Mizoram. This fossil assemblage is derived from sediments belonging to the Tipam Group considered to be Late Miocene-Early Pliocene in age. The modern counterparts of the identified taxa are: Gluta L., Mangifera L. (Anacardiaceae), Bursera Jacq. ex L. (Burseraceae), Terminalia L. (Combretaceae), Shorea Roxb. (Dipterocarpaceae), Cynometra Linn., Dalbergia L. f., Millettia Wight et Arn.-Pongamia Vent, Ormosia Jacks. (Fabaceae), Artocarpus Forst. (Moraceae) and Madhuca Gmelin. (Sapotaceae). The genus Dalbergia is described for the first time from India. The modern environmental tolerances of the above taxa indicate the existence of a tropical warm and humid climate in Mizoram during the depositional period. The reconstructed climate data using Coexistence Approach (CoA) based on palaeoflora database of Mosbrugger and Utescher, along with other published data sets indicates an MAT (mean annual temperature) of 26.1-27.7 °C, a mean temperature of the warmest month (WMT) of 25.4-28.1 °C, a mean temperature of the coldest month (CMT) of 25.6-26 °C, and a mean annual precipitation (MAP) of 3180-3263 mm. These climatic interpretations are congruent with the data obtained from the anatomical features of all the fossil taxa. As all the fossil taxa possess diffuse porous wood, they further indicate a tropical climate with little seasonality. The majority of the taxa in the fossil assemblage generally have large vessels and simple perforation plates which indicate high precipitation. The present study provides vital evidence of floral exchange or migration between India and southeast Asia.

  1. Phosphatic hardgrounds and hiatus concretions in neogene marine sequences of California coastal ranges

    Energy Technology Data Exchange (ETDEWEB)

    Garrison, R.E.; Foellmi, K.B.; Friede, K.M.; Kastner, M.; Ramirez, P.C.

    1988-03-01

    Distinctive phosphatic intervals mark hiatuses of varying durations at several localities along the central California coast. At Capitola in the La Honda basin, a complex series of carbonate-cemented hardgrounds containing authigenic phosphatic nodules and marine vertebrate bones occurs within 50 cm of the upper Purisima Formation (Pliocene). Paleomagnetic measurements and diatom stratigraphy indicate that this 50-cm interval represents a hiatus of about 1 m.y. (4.5-3.5 Ma). At Naples Beach in the Santa Barbara basin, a severely condensed section of about 7 m of interbedded nodular phosphatic hardgrounds, phosphatic marlstones, and dolomites appears to represent as much as 5 m.y. (14.5-9.5 Ma). In the Lompoc Quarry of the Santa Maria basin, a thin phosphatic hardground at the contact between the Monterey and the Sisquoc Formations represents about 0.5-0.7 m.y. (between 7.0 and 6.0 Ma). At Mussel Rock in the Santa Maria basin, a nodular phosphatic conglomerate occurs at the boundary between the Monterey and Sisquoc Formations; the age of the conglomerate determined from diatom biostratigraphy is approximately 6.2 Ma (Messinian), but no time gap can be recognized given the resolution of diatom age dating. The phosphatic hardgrounds of Capitola, Lompoc Quarry, and Naples Beach appear to correspond to high sea level stands, whereas the conglomerate at Mussel Rock coincides with a sea level lowstand. During high sea level stands, depocenters shifted landward, leading to clastic-sediment starvation possibly accompanied by current-induced erosion and winnowing, which in term led to condensation and early diagenetic carbonate and phosphatic cementation.

  2. Preliminary correlations of lithology and seismic reflectors in prograding Neogene carbonate of Great Bahama Bank

    Energy Technology Data Exchange (ETDEWEB)

    Eberli, G.P. (Geological Inst., Zurich (Switzerland)); Ginsburg, R.N.; Swart, P.K.; McNeill, D.F.; Kenter, J.A.M. (Univ. of Miami, FL (United States))

    1991-03-01

    Excellent overall recovery of 80% in two continuous core borings provides the data on lithology necessary to calibrate prograding late Cenozoic sequences and their seismic signatures. Hole UNDA, 10 km inside the modern platform edge of Great Bahama Bank (GBB), penetrated onlapping and topset reflectors and a buried platform rim. The 500 m core revealed two platform sequences alternating with fine grainstone units with internal hardground surfaces. At hole CLINO, 5.5 km farther basinward, 657 m of core document the progradation of GBB with 150 m of shallow platform deposits and reefal sequences over mostly fine-grained, foraminifera-rich periplatform slope sediments with intercalations of coarser beds, some of which contain platform lithoclasts. Within these slope deposits, there is significant variation in the degree of cementation; friable, porous limestones alternate with well cemented beds. Preliminary correlations between lithofacies and seismic signatures suggest a strong influence of both the sedimentologic and diagenetic facies on the seismic signal. Major lithologic changes, such as from mudstone to coral-bearing packstone or from skeletal sand to reefal limestone, produce strong reflectors. These latter transitions also coincide with seismic sequence boundaries. Within the more homogeneous slope sections, where seismic reflection horizons are not characterized by a facies change, differential cementation seems to be responsible for the seismic signal. Nevertheless, three reflectors identified as sequence boundaries are overlain by units containing coarse-grained beds with platform lithoclasts and blackened grains, indicating that these deposits were shed during low sea level and represent parts of the lowstand systems tract.

  3. Growth response of a deep-water ferromanganese crust to evolution of the Neogene Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Banakar, V.K.; Hein, J.R.

    in the vertical distance between the seafloor depth and the CCD during the early Miocene in addition to the influx of oxygenated bottom-water likely initiated Fe–Mn crust formation. Pillar structure characterises the younger zone, which extends from 40 mm... with low detritus. Therefore, the younger crust started to accrete in response to a shift in bottom-water circulation towards the contemporary pattern, which produced a uniform growth rate and pillar structure up to the present. q 2000 Published by Elsevier...

  4. Global Climate Change and Sedimentation Patterns in the Neogene Baringo Basin, Central Kenya Rift

    Science.gov (United States)

    Deino, A. L.; Kingston, J. D.; Wilson, K. E.; Hill, A.

    2010-12-01

    The Tugen Hills are part of a ~100 km N-S tilted fault block, just west of Lake Baringo within the Central Kenyan Rift Valley. Sediments exposed in this block span the last 16 Ma and have yielded abundant and diverse fossil assemblages including a number of hominoid and hominid specimens. Much research has also focused on documenting the paleoecology of the succession through analyses of fossil floral, faunal, and biogeochemical proxies. Data from the Tugen Hills have revealed a complex evolutionary history of ecosystems characterized by spatial and temporal heterogeneity with no clear evidence of any long-term trends. While these studies suggest that the patterns of heterogeneity may be shifting at short time-scales (104-105 ka), limited temporal resolution has until now generally precluded assessments of environmental change at these scales. Recently published investigations in the Baringo Basin have provided evidence of orbitally mediated environmental change over periods which include hominid fossil localities (Deino et al., 2006; Kingston et al., 2007). The Baringo data represent the only empirical evidence for significant local environmental shifts that can directly be correlated with insolation patterns in equatorial Africa. Sedimentation patterns in the Baringo Basin between ca. 2.70 and 2.55 Ma, controlled by climatic factors, provide a detailed paleoenvironmental record including a sequence of diatomites that record rhythmic cycling of major freshwater lake systems consistent with ~23 kyr Milankovitch precessional periodicity modulated by eccentricity. The timing of the paleolakes most closely approximates insolation maximum for the June/July 30○N insolation curve, suggesting that precipitation patterns in the region are controlled by the African monsoon system. More recent fieldwork has identified older sequences that similarly demonstrate rhythmic cycling of freshwater lake systems. Preliminary 40Ar/39Ar dating of intercalated tephra reveals that these deposits occur at ~3.7-3.8 Ma, ~4.8-4.9 Ma, and ~5.7-5.8 Ma, though each occurrence is unique in terms of the number of cycles recorded, the thickness of diatomites, and the nature of the non-lacustrine sediments. The oldest of these packages is characterized by very thick (>50 m), continuous diatomite accumulation interrupted only by deposition of pyroclastic deposits. This unit is laterally quite extensive, with exposures extending over 150 km2, indicating the establishment of a large, deep, and persistent paleolake. The development of this major water body, possibly the largest recorded in the Baringo Basin, may be in part a consequence of hemisphere-wide climate disruptions accompanying dessication events in the Mediterranean during the Messinian.

  5. Genetic model of hanging wall syncline and central dome in extensional fault

    Institute of Scientific and Technical Information of China (English)

    刘德来; 丁贵明; 鲁兵

    2002-01-01

    Hanging wall syncline and central dome are special extension structures, developing over the hanging wall in an extensional ramp-flat fault. Under the condition that the flat is sub-horizontal, the hanging wall syncline is separated from the half graben by the central dome. And on the dome forms an erosional surface. Both sediments in the half graben and erosional surface on the top of the central dome extended over the dome and entered into the hanging wall syncline with extension going on. Meanwhile, those having entered were overlapped by new sedimentary layers in the hanging wall syncline, so that there is a together-threaded, diachronic unconformity to form in the same epoch stratum. The layers in the hanging wall syncline also have an attribute of migrating laterally and getting tilted with extension. There is no sedimentation on the central dome. But sediments, which came from the half graben, got thicker over the dome in extension.

  6. Tectonics of the Qinling (Central China): Tectonostratigraphy, geochronology, and deformation history

    Science.gov (United States)

    Ratschbacher, L.; Hacker, B.R.; Calvert, A.; Webb, L.E.; Grimmer, J.C.; McWilliams, M.O.; Ireland, T.; Dong, S.; Hu, Jiawen

    2003-01-01

    The Qinling orogen preserves a record of late mid-Proterozoic to Cenozoic tectonism in central China. High-pressure metamorphism and ophiolite emplacement (Songshugou ophiolite) assembled the Yangtze craton, including the lower Qinling unit, into Rodinia during the ~1.0 Ga Grenvillian orogeny. The lower Qinling unit then rifted from the Yangtze craton at ~0.7 Ga. Subsequent intra-oceanic arc formation at ~470-490 Ma was followed by accretion of the lower Qinling unit first to the intra-oceanic arc and then to the Sino-Korea craton. Subduction then imprinted a ~400 Ma Andean-type magmatic arc onto all units north of the northern Liuling unit. Oblique subduction created Silurian-Devonian WNW-trending, sinistral transpressive wrench zones (e.g., Lo-Nan, Shang-Dan), and Late Permian-Early Triassic subduction reactivated them in dextral transpression (Lo-Nan, Shang-Xiang, Shang-Dan) and subducted the northern edge of the Yangtze craton. Exhumation of the cratonal edge formed the Wudang metamorphic core complex during dominantly pure shear crustal extension at ~230-235 Ma. Post-collisional south-directed shortening continued through the Early Jurassic. Cretaceous reactivation of the Qinling orogen started with NW-SE sinistral transtension, coeval with large-scale Early Cretaceous crustal extension and sinistral transtension in the northern Dabie Shan; it presumably resulted from the combined effects of the Siberia-Mongolia-Sino-Korean and Lhasa-West Burma-Qiangtang-Indochina collisions and Pacific subduction. Regional dextral wrenching was active within a NE-SW extensional regime between ~60 and 100 Ma. An Early Cretaceous Andean-type continental magmatic arc, with widespread Early Cretaceous magmatism and back-arc extension, was overprinted by shortening related to the collision of Yangtze-Indochina Block with the West Philippines Block. Strike-slip and normal faults associated with Eocene half-graben basins record Paleogene NNE-SSW contraction and WNW-ESE extension

  7. National Assessment of Oil and Gas - Neogene System Assessment Units of the Gulf Coast (Provinces 047, 048 and 049)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The Assessment Unit is the fundamental unit used in the National Assessment Project for the assessment of undiscovered oil and gas resources. The Assessment Unit is...

  8. Tectonic and unroofing history of Neogene Manantiales foreland basin deposits, Cordillera Frontal (32°30'S), San Juan Province, Argentina

    Science.gov (United States)

    Pérez, Daniel J.

    2001-12-01

    The Miocene Manantiales foreland basin is located in Cordillera Frontal of San Juan, between 32°30' and 33°S. The unroofing study of the synorogenic Miocene deposits provides information about the structural evolution of Cordón de La Ramada fold-and-thrust belt. These Tertiary deposits are represented by the Chinches Formation and comprise seven members (Tc0-Tc6). They are the result of the uplift of Mesozoic sequences that crop out in La Ramada fold-and-thrust belt of the Cordillera Principal. Quaternary deposits unconformably overlying the Chinches Formation are composed of granitic and rhyolitic blocks, and represent the final uplift of the Cordón del Espinacito and a series of out-of-sequence thrusts. The unroofing studies also provide sufficient information to establish the out-of-sequence timing of the deformation at this latitude. Initial deposition of the Tertiary deposits can be dated at about 20 Ma, or early Miocene. Andesitic lavas dated in 9.2±0.3, 10.7±0.7, and 12.7±0.7 Ma unconformably overlie the structure of La Ramada fold-and-thrust belt. These facts constrain the uplift of the High Andes between 20 and 10 Ma at this latitude. The unconformity between Tertiary and Quaternary deposits suggests final uplift during Pliocene-Pleistocene times.

  9. Modern and long-term evaporation of central Andes surface waters suggests paleo archives underestimate Neogene elevations

    Science.gov (United States)

    Fiorella, Richard P.; Poulsen, Christopher J.; Pillco Zolá, Ramiro S.; Jeffery, M. Louise; Ehlers, Todd A.

    2015-12-01

    Central Andean paleoelevations reconstructed from stable isotope and paleofloral data imply a large magnitude (>2 km) Miocene-to-modern surface uplift. However, the isotopic relationships between precipitation, surface waters, and soil waters upon which these reconstructions are based remain poorly constrained for both past, and in many cases, modern conditions. We quantify the relationships between central Andean precipitation and surface waters by measuring the isotopic composition of 249 stream water samples (δ18O and δD) collected between April 2009 and October 2012. The isotopic compositions of stream waters match precipitation along the eastern flank. In contrast, Altiplano surface waters possess a lower δD-δ18O slope (4.59 vs ∼8 for meteoric waters) not observed in precipitation, which signals heavy isotope evaporative enrichment in surface waters. Paleoclimate models indicate that highly evaporative conditions have persisted on the plateau throughout Andean uplift, and that conditions may have been more evaporative when the Andes were lower. Thus, more ancient proxy materials may have a greater evaporative bias than previously recognized and paleoelevation reconstructions from stable isotope based central Andean plateau proxy materials likely overstate Miocene-to-present surface uplift. We propose Altiplano paleoelevations of 1-2 km at 24.5 Ma, 1.5-2.9 km by 11.45 Ma, and modern elevations by ∼6 Ma based on the lightest isotopic compositions observed in Altiplano proxy materials, which are least likely to be influenced by evaporation. These constraints limit total late-Miocene-to-modern uplift to <2.2 km, are more consistent with crustal shortening records, and suggest that plateau uplift may have been more spatially uniform than suggested by previous interpretations of stable isotope proxies.

  10. Neogene residual subsidence and its response to a sinking slab in the deep mantle of eastern China

    Science.gov (United States)

    Yao, Xiang; Liu, ShaoFeng; Bai, Yu; Ji, HuiLi

    2017-08-01

    Mantle convection could have a significant effect on basin evolution; however, research quantifying this relationship is controversial. To understand the formation mechanism and evolution of the Cenozoic rift basins in eastern China, we applied the back-stripping technique and strain rate inversion modeling to 119 wells from Sangjiang Basin, Bohai Bay Basin, North Yellow Sea Basin, South Yellow Sea Basin, East China Sea Shelf Basin, and four basins within the northern South China Sea margin. The modeled results can be used to reconstruct the tectonic subsidence history and further assess the potential subsidence mechanisms of eastern China. Residual subsidence is defined as the difference between the theoretical and observed tectonic subsidences. Our results show that the residual subsidence since 20 Ma in eastern China generally increases from ∼100 to 300 m in terrestrial areas to ∼1.2-1.8 km on the continental shelf. Our observed residual subsidence is generally consistent with the present-day dynamic topography that is predicted from mantle flow models, and it is associated with a stagnant slab within the mantle that has been observed by seismic tomography. The migration pathway of the residual subsidence since 20 Ma is consistent with the movement direction of the Pacific and Philippine plates. Therefore, we suggest that the residual subsidence might be a dynamic subsidence induced by a negative buoyancy of the sinking slab in the deep mantle beneath eastern China.

  11. A CONSIDERATION OF THE PALEONTOLOGICAL CONTRIBUTIONS OF WILL DOWNS WITH A GENERAL CORRELATION OF CHINESE NEOGENE LOCALITIES

    Institute of Scientific and Technical Information of China (English)

    Louis H. TAYLOR

    2004-01-01

    @@ William R. Downs, Ⅲ, known as Dong Weilin to many friends, died a relatively young man ( 1950 ~ 2002) at the height of his career in paleontology.His career began at the Museum of Northern Arizona in 1975. One of his early tasks was the preparation of Triassic cynodonts from Antarctica for Edwin H.Colbert, then Curator Emeritus of the American Museum of Natural History and Curator of Vertebrate Paleontology at the Museum of Northern Arizona (Colbert and Kitching, 1977). Will prepared the Early Jurassic armored ornithischian Scutellosaurus for Colbert (1981), and he collected and prepared a skull of Pentaceratops from the Cretaceous of the San Juan Basin (Rowe et al., 1981 ).One of his early ventures into screen-washing was near the Pentaceratops site in the San Juan Basin (Flynn, 1986) where mammals were poorly represented. In the mid-1980' s, Will left the Museum of Northern Arizona to become affiliated with Northern Arizona University, also in Flagstaff. In addition, he was briefly employed to revamp the fossil preparation laboratories at Southern Methodist University in Dallas, during which time he joined in excavations of a large series of small primitive ornithopods in Texas (Winkler et al.,1988). He maintained an office at the Bilby Research Center, and then the Department of Geology,at Northern Arizona University until the time of his death.

  12. Late Neogene slip transfer and extension within the curved Whisky Flat fault system central Walker Lane, west-central Nevada

    Science.gov (United States)

    Biholar, Alexander Kenneth Casian

    In Whisky Flat of west-central Nevada, northwest-striking faults in the Walker Lane curve to east-northeast orientations at the northern limits of the Mina deflection. This curve in strike results in the formation of ˜685 m deep depression bounded by north-south convex to the east range-front faults that at the apex of fault curvature are bisected at a high angle by a structural stepover. We use the vertical offset of a late Miocene erosional surface mapped in the highlands and inferred from gravity depth inversion in the basin to measure the magnitude of displacement on faults. A N65°W extensional axis determined through fault-slip inversion is used to constrain the direction in displacement models. Through the use of a forward rectilinear displacement model, we document that the complex array of faults is capable of developing with broadly contemporaneous displacements on all structures since the opening of the basin during the Pliocene.

  13. A Plagioclase Ultraphyric Basalt group in the Neogene flood basalt piles of eastern Iceland: Volcanic architecture and mode of emplacement

    Science.gov (United States)

    Oskarsson, B. V.; Riishuus, M. S.

    2013-12-01

    3D photogrammetry in conjunction with ground mapping was applied in order to assess the architecture of a Plagioclase Ultraphyric Basalt (PUB) group in eastern Iceland, namely the Grænavatn group. The ~10 Myr old group is exposed in steep glacially carved fjords and can be traced over 60 km along strike. Two feeder dikes have been found and show that the group erupted along the trend of the dike swarm associated with the Breiddalur central volcano. The group has 9--14 flows where thickest, and thins to about 3--4 flows up-dip to the east within the distance of 15-20 km from the source. We have estimated the volume of the group to exceed 40 km3. The flows have mixed architecture of simple and compound morphology. The flow lobes have thicknesses from 1--24 m and many reach lengths over 1000 m. The surface morphology varies from rubbly to scoriaceous, but is dominantly of pahoehoe style. The internal structure of the lava flows is well preserved and the flows display abundant vesicle cylinders. The modal percentage of An-rich plagioclase macrocrysts varies from 25--50 % and they are in the range of 5--30 mm. The aspect ratio of the group and the nature of the flows indicate fissure-fed eruptions. A thick flow found at the base of the group in various locations seems to record the largest eruption episode in the formation of the group. This phase is also the most abundant in macrocryst. An asymmetric buildup is seen in one location and may have characterized the general buildup of the group. The general morphology of the lava flows suggests low viscous behavior, at odds with the high crystal content. Petrographic observations and mineral chemistry shows that the plagioclase macrocrysts are very calcic (An80-85) and in disequilibrium with the groundmass and plagioclases therein (An50-70). Thus the apparent lava rheology and emplacement of the PUBs was likely achieved due to fast ascent of the magma through the crust and transfer of heat from the primitive macrocrysts to the host melt during surface flow. The simple flows represent likely flows that erupted rapidly during episodes with high effusion rates. The compound flows suggest eruptions or fissure segments of lower effusion rates that developed preferred pathways controlled by the topography. Several flows accounted for inflation, and occasionally surges disrupted the crust to form rubbly pahoehoe. The eruption of the Grænavatn group, when compared to the eruption of the 140 km long Holocene PUB lava flow of Thjórsá (up to 30% macrocrysts and 21 km3), shows a similar magmatic event. Nevertheless, the eruption styles seem to have differed. The Grænavatn eruptions were mostly short-lived confined to the surroundings of the fissures with flows that were volume and cooling-limited. Thjórsá represents seemingly one single eruption with continuous supply of lava, channeling the flow units far away from their source in well insulated channels. Grænavatn and Thjórsá lava flows reveal the great scale and diversity in eruption styles that PUB effusive volcanism may display, but the latter warns about how close to us such events may be.

  14. El volcanismo cuaternario en el retroarco de Payenia: una revisión Retroarc Neogene volcanism at Payenia: A review

    Directory of Open Access Journals (Sweden)

    Eduardo J Llambías

    2010-10-01

    Full Text Available La provincia basáltica Payenia se desarrolló al pie de los Andes entre 33º40'S y 38ºS. Es una típica asociación de retroarco con dos picos de actividad, el más antiguo es mayormente mioceno (26 a 8 Ma y el más joven es Plioceno - Holoceno (The Payenia basaltic province is a typical retroarc association developed along the foothills of the Andes between 33º40'S and 38º00'S. It records two main events, an older, mostly Miocene one (26 to 8 Ma and a younger Pliocene to Holocene one (younger than 5 Ma. It covers an N-S lowland belt named here the central depression. To the North of 36°20'S, the region was described as Los Huarpes depression, a partially deformed sedimentary basin characterized by a 1000 m-thick, undifferentiated Cenozoic sequence. To the south, Upper Cretaceous to Lower Paleogene layers, instead of the undifferentiated Cenozoic deposits, are covered by basalts. The volcanism additionally covers the western side of the San Rafael Block as well as the fold and thrust belt of the Andean foothills. The Payenia province consists of more than 800 monogenetic basaltic cones, and scarce polygenetic volcanos fed by shallow magmatic chambers. Among the latter, the following examples can be mentioned: Miocene Chachahuén volcano (7 to 5 Ma, composed of andesites, rhyodacites and basalts with high-K and amphibole; Pliocene El Nevado volcano, with calc-alkaline, basaltic trachyandesites, trachytes, dacites and rhyolites; and Upper Pleistocene to Holocene Payún Matrú volcano, composed of trachytes, trachyandesites and trachybasalts. The southernmost area of the central depression is covered by the Pleistocene, Auca Mahuida basaltic shield (1.7 to 0.88 Ma, consisting of trachybasalts, basaltic trachyandesites and trachyandesites. This shield is aligned with Tromen and Domuyo volcanos, defining an NW-SE volcanic belt, oblique to the Andes, whose southern tip corresponds to the Cortaderas lineament. Some of the monogenetic cones are of hydromagmatic origin, whereas a few others exhibit small mantle inclusions. The Payenia retroarc province develops to the south of the Pampean flat slab segment, where the heights of the Andes are smaller. This height difference might have been caused by a higher thermal gradient that softened the crust in the steeper subduction segment, while the colder lithosphere in the flat slab segment allowed greater crustal thickening and height. From the tectonic point of view the height difference has been attributed to a smaller orogenic contraction in the southern segment. Holocene volcanism appears exclusively at Payun Matru volcano. The associated thermal anomaly may explain the segmentation of the central depression, separating the Cenozoic Los Huarpes basin in the north and the section without coeval sedimentation in the south. The only surface evidence of this segmentation is the E-W, La Carbonilla fault, running both sides of the Payun Matru volcano. Other authors have explained this thermal anomaly as a process of crustal thinning and stretching associated with hot injection from the asthenosphere.

  15. Replacement names and nomenclatural comments for problematic species-group names in Europe's Neogene freshwater Gastropoda. Part 2

    Directory of Open Access Journals (Sweden)

    Thomas Neubauer

    2014-07-01

    Full Text Available In the course of a new database project on Miocene to Recent freshwater gastropods of Europe, a great many of primary and secondary homonyms were revealed. Such nomenclatural issues need clarification in order to avoid misunderstandings and wrong statements about geographical distributions and temporal ranges. The following 16 new names are introduced to replace existing homonyms: Theodoxus militaris jurisicpolsakae nom. n., Viviparus stevanovici nom. n., Melanopsis haueri ripanjensis nom. n., Melanopsis wolfgangfischeri nom. n., Micromelania ramacanensis nom. n., Pseudamnicola welterschultesi nom. n., Muellerpalia haszprunari nom. n., Muellerpalia pseudovalvatoides nom. n., Lithoglyphus gozhiki nom. n., Valvata heidemariae willmanni nom. n., Radix macaleti nom. n., Gyraulus okrugljakensis nom. n., Gyraulus rasseri nom. n., Gyraulus vrapceanus nom. n., Planorbarius halavatsi nom. n., and Segmentina mosbachensis nom. n. Additionally, six cases of homonyms are discussed that are not replaced by new names, because they are considered junior synonyms.

  16. Late Neogene exhumation of the Piceance basin, N.W. Colorado, USA: Integrated analysis of multiple thermochronometers and subsidence modeling

    Science.gov (United States)

    Vernon, A. J.; Kendall, J. J.; Becker, T. P.; Patterson, P. E.; Reiners, P. W.; Kapp, J.

    2010-12-01

    The retrograde history of sedimentary basins is often poorly constrained by the study of subsidence, compaction, and thermal diffusion models. As part of industry/academic collaborative research on the fundamental processes active in convergent tectonics we combined multiple paleothermometers, paleobarometers, and thermochronometers on deep borehole samples with modern heat flow measurements to provide powerful constraint for estimating the exhumation history in an area. The Piceance basin (N.W. Colorado) lies east of the leading edge of the Cretaceous to early Eocene Sevier thrust belt, and is flanked by several basement-involved structures (Douglas Creek arch, White River dome, Uinta uplift, White River uplift) that exhibit growth from the Maastrichtian through the late Eocene. The youngest preserved strata within the Piceance basin are within the early Oligocene Uinta Formation, although there are deposits as young as Miocene locally preserved in the region that may have also capped the basin. The timing of uplift, river incision, and plateau-scale exhumation within this region fits into the larger context of the evolution of the Colorado River drainage system. A series of core, cutting, and surface samples were compiled to develop a synthetic well (or vertical section) of over 5000 m. Samples were collected from stratigraphic intervals ranging from the Jurassic to the Eocene and analyzed for apatite and zircon U-Th/He ages, as well as apatite fission track length distributions and ages. As the exhumation model was the unconstrained parameter, the timing and magnitude of the cooling associated with such an event was systematically varied. Thermal histories of each sampled interval were extracted from differing exhumation scenarios in the Piceance basin model (which tracks the temperature and pressure evolution during burial and denudation) and forward modeled using HeFTy. The combined use of several thermochronometers (apatite and zircon U-Th/He, apatite fission tracks), as well as vitrinite reflectance and multi-phase fluid inclusion thermometry and barometry yields a best-fit thermal history that corresponds to ~ 1.5 km of exhumation in the last 4 million years (~0.38 mm/yr). The timing of the thermal lapse associated with the epierogenic uplift of the western United States is not well constrained, but did figure into these estimates of exhumation timing in the Piceance basin region. Estimates of modern rates of denudation derived from suspended sediment yields are considerably lower than our datasets suggest (~0.011 mm/yr), which suggest a transient period of Plio-Pleistocene unroofing. The onset of volcanism and hydrothermal mineralization within the Colorado mineral belt may constitute an additional factor to consider within the plateau exhumation history.

  17. Neogene tectonic block rotations and margin curvature at the Pampean flat slab segment (28º-33º SL, Argentina

    Directory of Open Access Journals (Sweden)

    M.S Japas

    2012-06-01

    Full Text Available Available paleomagnetic data from the Pampean flat slab segment reveal a heterogeneous rotation pattern that is interpreted herein as the result of the overprinting of late NNW-WNW left-lateral brittle-ductile megashear zones that would be also responsible for the continental margin bending.La base de datos paleomagnéticos disponible para el segmento de losa plana Pampeano revela un patrón de rotaciones heterogéneo como resultado de la sobreimposición de zonas de cizalla frágil-dúctiles regionales, de desplazamiento lateral izquierdo y rumbo NNO a ONO, las que habrían producido además la curvatura del margen continental.

  18. New Miocene sulid birds from Peru and considerations on their Neogene fossil record in the Eastern Pacific Ocean

    Directory of Open Access Journals (Sweden)

    Marcelo Stucchi

    2016-06-01

    Full Text Available Boobies and gannets (family Sulidae are the most specialized plunge divers among seabirds. Their fossil record along the Pacific coast of South America extends to the early Middle Miocene. Here we describe three new species of sulids: Sula brandi sp. nov., Sula figueroae sp. nov., and Ramphastosula aguirrei sp. nov., from the early Late Miocene of the Pisco Formation (Peru. Two of them are relatives of the living genus Sula, which represents medium and large-sized boobies. A new species of the extinct genus Ramphastosula is also described, adding to the discussion of possible alternative feeding strategies among sulids. The fossil record suggests that sympatric sulids exhibit different body sizes at least since the Oligocene epoch, a strategy related with resource partitioning. Furthermore, we find current analysis and knowledge of the fossil record unsuitable to evaluate properly seabird diversity changes through time.

  19. Chronostratigraphic relations of Neogene formations of the Great Hungarian Plain based on interpretation of seismic and paleomagnetic data

    Energy Technology Data Exchange (ETDEWEB)

    Pogacsas, G.; Lakatos, L.; Simon, E.; Vakaros, G.; Varkonyi, L.; Varnai, P. (Geofizikai, Budapest (Hungary)); Jambor, A.; Hamor, T.; Lantos, M. (Magyar Allami Foeldtani Intezet, Budapest (Hungary)); Mattick, R.E. (Geological Survey, Reston, VA (USA)); Elston, D.P. (Geological Survey, Flagstaff, AZ (USA))

    1990-05-01

    This cooperative study by Hungarian and American geologists and geophysicists, demonstrates the power of the combination of modern paleomagnetic techniques and seismic profiling in working out the stratigraphy of a basin, with only limited paleontologic and isotopic control. Indirect evidence suggests that lake levels in the Pannonian inland sea (a remnant of the Paratethys), although isolated from the world's oceans, were affected by eustatic sea-level changes. Four hiatuses identified by seismic profiles near the northern margin of the Pannonian Basin and inferred to represent non-deposition between 11.5 and 10.5, 7.9 and 7.6, 6.8 and 5.7, 5.4 and 4.6 million years ago. Comparing these hiatuses with the eustatic sea level change curves the accordance is close and systematic. This indicates that the sea level of the Pannonian Inland Sea that became gradually isolated from the world oceans fluctuated in the same phase as global sea level. The hiatus between 6.8 and 5.7 Ma is tentatively correlated with the Messinian global stage during which time evaporite deposition in the Mediterranean was widespread--the so-called Messinian salinity crisis.

  20. Sediment Volume Record of Paleogene-Neogene Transantarctic Mountains Erosion and Landscape Modification, McMurdo Sound Region, Antarctica

    Science.gov (United States)

    Hall, T.; Wilson, T. J.; Henrys, S.; Speece, M. A.

    2016-12-01

    The interplay of tectonics and climate is recorded in the sedimentary strata within Victoria Land Basin, McMurdo Sound, Antarctica. Patterns of Cenozoic sedimentation are documented from interpretation of seismic reflection profiles calibrated by drillhole data in McMurdo Sound, and these patterns provide enhanced constraints on the evolution of the coupled Transantarctic Mountains-West Antarctic Rift System and on ice sheet advance/retreat through multiple climate cycles. The research focuses on shifts from warm based to cold based ice sheets through the variable climate and ice sheet conditions that characterized the early to middle Miocene. The study seeks to test the view that cold based ice sheets in arid, polar deserts minimally erode the landscape by calculating sediment volumes for critical climatic intervals. Revised seismic mapping through McMurdo Sound has been completed, utilizing the seismic stratigraphic framework first established by Fielding et al. (2006) and new reflectors marking unconformities identified from the AND-2A core (Levy et al., 2016). Reflector age constraints are derived by tying surfaces to the Cape Roberts Project, CIROS-1, and AND-2A drillholes. Seismic facies coupled with AND-2A core provenance information provides insight into depositional mechanisms and ice sheet behavior. Seismic facies transitions occur across the major unconformity surfaces in the AND-2A core. Sediment volume calculations for subareas within McMurdo Sound where reflectors are most continuous indicate substantial decreases in preserved sediment volume between the Oligocene and Early Miocene sequences, and between the early and mid-Miocene sequences. Sediment volumes, used in combination with an ice sheet model in a backstacking procedure, provide constraints on landscape modification and further understanding of how landscapes erode under warm and cold based ice sheet regimes.

  1. El volcanismo cuaternario en el retroarco de Payenia: una revisión Retroarc Neogene volcanism at Payenia: A review

    OpenAIRE

    Eduardo J. Llambías; Bertotto, Gustavo W.; Corina Risso; Irene Hernando

    2010-01-01

    La provincia basáltica Payenia se desarrolló al pie de los Andes entre 33º40'S y 38ºS. Es una típica asociación de retroarco con dos picos de actividad, el más antiguo es mayormente mioceno (26 a 8 Ma) y el más joven es Plioceno - Holoceno (

  2. Milankovitch orbital cycles encoded by diagenetic iron sulfides in Neogene sediments, Stirone River section, Northern Apennines, Italy

    Science.gov (United States)

    Gunderson, K. L.; Kodama, K. P.; Anastasio, D. J.; Pazzaglia, F. J.

    2009-12-01

    We used rock magnetic parameters to identify Milankovitch orbital cycles in the marine sediments of the Messinian-Early Pleistocene Stirone River section, Northern Apennines, Italy. These measurements provide excellent proxies for subtle changes in depositional environment, including climate, in stratigraphic sections where facies variations are not evident. We measured 636 meters of section and collected samples every 1 meter, for which we measured magnetic susceptibility (MS), natural remanent magnetization (NRM), anhysteretic magnetization in a 40 mT peak alternating field(40mT ARM), and anhysteretic remanent magnetization in a 100 mT peak alternating field (100mT ARM). We present the results of our time-series analysis of the MS, 40mT ARM, and 100mT ARM stratigraphic series for 310 meters of section, encompassing the time period between 3.1 My and 1.8 My. During this time period, the power spectra produced from the MS stratigraphic series exhibits peaks with frequencies at 1/24m, 1/10m, and 1/6m. Based on our calculated mean sedimentation rate of 0.24 m/ky, we interpret the spectral peaks to be associated with the eccentricity, obliquity, and precessional orbital cycles, respectively. The 40mT ARM spectra exhibits peaks at similar periodicities, but the corresponding spectral peaks are broader and the spectral power is much lower. The 100mT ARM spectra shows an increase in spectral power with respect to the 40mT ARM, but it also exhibits broad spectral peaks. Low temperature (77 K) susceptibility (LT-MS) and isothermal remanent magnetization (IRM) acquisition experiments were conducted to determine which magnetic minerals carry the MS signal. The observed increase of the MS at low temperature (6-140%) was not large enough to conclude that the MS is dominated by paramagnetic grains. IRM acquisition modeling indicates two components of magnetization: (1) a major component comprising ~85% of the magnetization with a mean coercivity of 67 mT and (2) a minor component with a mean coercivity of 23 mT. We interpret the high coercivity component to represent magnetic iron-sulfides, which have been previously recognized in the Stirone section (Mary et al, 1993). A biplot of SIRM/MS versus 40mT ARM/ 100mT ARM suggests greigite is possibly the dominant magnetic iron sulfide and is responsible for encoding Milankovitch orbital cycles in the Stirone section.

  3. DITRUPA BREVIS N.SP., A NEW SERPULID FROM THE MEDITERRANEAN NEOGENE WITH COMMENTS ON THE ECOLOGY OF THE GENUS

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    ROSSANA SANFILIPPO

    1999-11-01

    Full Text Available The new species Ditrupa brevis (Polychaeta, Serpulidae is described from Middle Pliocene silts of southern Italy. It is also reported from Late Miocene sediments of southern Italy. The associated faunas suggest an infralittoral or upper-circalittoral distribution. A morphometrical and microstructural analysis of tube was carried out. D. brevis closely resembles Ditrupa arietina but several morphometrical differences allow to discriminate the two species. The Ditrupa tubes provide a substrate for a diversified epifauna. Their high density greatly affects species composition and diversity of soft-bottom communities. It is concluded that Ditrupa can live in various positions with respect to the sediment surface, depending on local sedimentation rate and dynamics. 

  4. An organic geochemical investigation on organic rich sediments from two Neogene formations in the Klias Peninsula area, West Sabah, Malaysia

    Institute of Scientific and Technical Information of China (English)

    Amer M. Burgan; Che Aziz Ali

    2009-01-01

    Twenty organic rich outcrop samples from the Belait and Setap Shale formations in the Klias Peninsula area, West Sabah, were analysed by means of organic petrology and geochemical techniques. The aims of this study are to assess the type of organic matter, thermal maturity and established source rock characterization based primarily on Rock-Eval pyrolysis data. The shales of the Setap Shale Formation have TOC values varying from 0.6 wt%-1.54 wt% with a mean hydrogen index (HI) of 60.1 mg/g, whereas the shales of the Belait Formation have TOC values ranging from 0.36 wt%-0.61 wt% with a mean (HI) of 38.2 mg/g, indicating that both formations have TOC>0.5 wt% the minimum limit for hydrocarbon generation. The samples do not contain sufficient hydrogen-rich organic matter (types I, II and III) to be considered good quality source rocks. The kerogen of type II is predominantly of marine origin. This organic matter was deposited in clastic algal environments. Geochemical data (Rock-Eval, Tmax values ranging from 377-451℃ for shales of the Setap Shale Formation and ranging from 466-498℃ for shales of the Belait Formation, typical of high maturity), indicate variable maturation histories in both formations. The maturation level varied from the beginning to the peak stage of oil generation in the Setap Shale Formation and it has reached the over-mature level in the samples of the Belait Formation.

  5. Biochronostratigraphy and paleoenvironment analysis of Neogene deposits from the Pelotas Basin (well 2-TG-96-RS, Southernmost Brazil

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    WAGNER G. SILVA

    2015-09-01

    Full Text Available This paper presents the integration of micropaleontological (palynology and foraminifera and isotopic (87Sr/86Sr analysis of a selected interval from the well 2-TG-96-RS, drilled on the onshore portion of the Pelotas Basin, Rio Grande do Sul, Brazil. A total of eight samples of the section between 140.20 and 73.50 m in depth was selected for palynological analysis, revealing diversified and abundant palynomorph associations. Species of spores, pollen grains and dinoflagellate cysts are the most common palynomorphs found. Planktic and benthic calcareous foraminifera were recovered from the lowest two levels of the section (140.20 and 134.30 m. Based on the stratigraphic range of the species of dinoflagellate cysts and sporomorphs, a span age from Late Miocene to Early Pliocene is assigned. The relative age obtained from the 87Sr/86Sr ratio in shells of calcareous foraminifers indicates a Late Miocene (Messinian correspondence, corroborating the biostratigraphic positioning performed with palynomorphs. Paleoenvironmental interpretations based on the quantitative distribution of organic components (palynomorphs, phytoclasts and amorphous organic matter throughout the section and on foraminiferal associations indicate a shallow marine depositional environment for the section. Two palynologicals intervals were recognized based on palynofacies analysis, related to middle to outer shelf (140.20 to 128.90 m and inner shelf (115.75 to 73.50 m conditions.

  6. Ordovician sponges (Porifera and other silicifications from Baltica in Neogene and Pleistocene fluvial deposits of the Netherlands and northern Germany

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    Rhebergen, Freek

    2009-03-01

    Full Text Available Fluvial deposits of Miocene to Early Pleistocene age in Germany and the Netherlands were laid down in the delta of the Eridanos River System, but the exact provenance of this material continues to be a subject of discussion. The aim of the present study is twofold. Firstly, a comparison of Ordovician sponges in these deposits with those from northern Estonia and the St Petersburg region (Russia demonstrates that these erratics originated from the drainage area of the Pra Neva, a tributary of the Eridanos. Secondly, the importance of Late Ordovician silicified boulders, which yield forms of preservation that are unknown in comparable fossils, preserved in situ, is outlined. Some recommendations for future studies are made.

  7. Late neogene and early quaternary paleoenvironmental and paleoclimatic conditions in southwestern Europe: isotopic analyses on mammalian taxa.

    Science.gov (United States)

    Domingo, Laura; Koch, Paul L; Hernández Fernández, Manuel; Fox, David L; Domingo, M Soledad; Alberdi, María Teresa

    2013-01-01

    Climatic and environmental shifts have had profound impacts on faunal and floral assemblages globally since the end of the Miocene. We explore the regional expression of these fluctuations in southwestern Europe by constructing long-term records (from ~11.1 to 0.8 Ma, late Miocene-middle Pleistocene) of carbon and oxygen isotope variations in tooth enamel of different large herbivorous mammals from Spain. Isotopic differences among taxa illuminate differences in ecological niches. The δ(13)C values (relative to VPDB, mean -10.3 ± 1.1‰; range -13.0 to -7.4‰) are consistent with consumption of C3 vegetation; C4 plants did not contribute significantly to the diets of the selected taxa. When averaged by time interval to examine secular trends, δ(13)C values increase at ~9.5 Ma (MN9-MN10), probably related to the Middle Vallesian Crisis when there was a replacement of vegetation adapted to more humid conditions by vegetation adapted to drier and more seasonal conditions, and resulting in the disappearance of forested mammalian fauna. The mean δ(13)C value drops significantly at ~4.2-3.7 Ma (MN14-MN15) during the Pliocene Warm Period, which brought more humid conditions to Europe, and returns to higher δ(13)C values from ~2.6 Ma onwards (MN16), most likely reflecting more arid conditions as a consequence of the onset of the Northern Hemisphere glaciation. The most notable feature in oxygen isotope records (and mean annual temperature reconstructed from these records) is a gradual drop between MN13 and the middle Pleistocene (~6.3-0.8 Ma) most likely due to cooling associated with Northern Hemisphere glaciation.

  8. Late neogene and early quaternary paleoenvironmental and paleoclimatic conditions in southwestern Europe: isotopic analyses on mammalian taxa.

    Directory of Open Access Journals (Sweden)

    Laura Domingo

    Full Text Available Climatic and environmental shifts have had profound impacts on faunal and floral assemblages globally since the end of the Miocene. We explore the regional expression of these fluctuations in southwestern Europe by constructing long-term records (from ~11.1 to 0.8 Ma, late Miocene-middle Pleistocene of carbon and oxygen isotope variations in tooth enamel of different large herbivorous mammals from Spain. Isotopic differences among taxa illuminate differences in ecological niches. The δ(13C values (relative to VPDB, mean -10.3 ± 1.1‰; range -13.0 to -7.4‰ are consistent with consumption of C3 vegetation; C4 plants did not contribute significantly to the diets of the selected taxa. When averaged by time interval to examine secular trends, δ(13C values increase at ~9.5 Ma (MN9-MN10, probably related to the Middle Vallesian Crisis when there was a replacement of vegetation adapted to more humid conditions by vegetation adapted to drier and more seasonal conditions, and resulting in the disappearance of forested mammalian fauna. The mean δ(13C value drops significantly at ~4.2-3.7 Ma (MN14-MN15 during the Pliocene Warm Period, which brought more humid conditions to Europe, and returns to higher δ(13C values from ~2.6 Ma onwards (MN16, most likely reflecting more arid conditions as a consequence of the onset of the Northern Hemisphere glaciation. The most notable feature in oxygen isotope records (and mean annual temperature reconstructed from these records is a gradual drop between MN13 and the middle Pleistocene (~6.3-0.8 Ma most likely due to cooling associated with Northern Hemisphere glaciation.

  9. Erosional Reduction of an Orogenic Wedge: Structural Response to Neogene Climate Change within the St. Elias Orogen, Alaska

    Science.gov (United States)

    Berger, A. L.; Spotila, J. A.; Chapman, J. B.; Pavlis, T. L.; Enkelmann, E.; Buscher, J. T.

    2007-12-01

    The kinematics and architecture of orogenic systems may be heavily influenced by climate, but little research has focused on the long term effects of glacial erosion on orogenesis. Apatite and zircon (U-Th)/He thermochronometry on >75 bedrock samples across the St. Elias orogen, one of the best examples of a glaciated orogenic wedge, is the basis for a new kinematic model and demonstrates an association between glacial denudation and orogenic architecture. The spatial pattern of low temperature cooling indicates that exhumation and deformation are focused within a thin-skinned fold and thrust belt on the windward flank, whereas the leeward flank of the orogen functions as a deformational backstop. A previously unrecognized structure beneath the Bagley ice field must separate these domains with south-side-up motion. We propose this structure is a backthrust making the orogen doubly-vergent. Suggestive of accelerated backthrust motion in response to climate change, cooling rates within the hanging wall block and across the entire windward flank of the orogen accelerated ten-fold coeval with enhanced glaciation. As backthrust motion increased, glacial unroofing also coincided with a regional shift in deformation away from prominent forethrusts including the North American-Yakutat terrane suture (Chugach St. Elias fault) and the seaward deformation front (Pamplona zone). Across the windward flank of the orogen, exhumation, at rates of up to 5 mm/yr, is focused within a narrow zone, where the glacial equilibrium line altitude (ELA) intersects the orogenic wedge. This zone of rapid exhumation, not present prior to the onset of enhanced glaciation, cuts across the structural trend of the orogen and is more narrowly focused than orographic precipitation. Accelerated denudation at the ELA thus appears to have redistributed strain along a series of forethrusts that lie at the zone of heaviest glacial flux, while the backthrust progressively truncates the southward-vergent forethrusts. In a cause and effect response, the expansion of glaciers therefore appears to have resulted in a narrowing of the orogenic wedge due to increased backthrust motion and a landward propagation of deformation in order to preserve topographic slope. This focusing of long- term glacial erosion and deformation at the ELA matches predictions from analytical models of orogenic wedges (i.e. Tomkin and Braun, 2002) and implies a high degree of coupling between climate and tectonics in this glacially-dominated orogen.

  10. Linear and non-linear response of late Neogene glacial cycles to obliquity forcing and implications for the Milankovitch theory

    NARCIS (Netherlands)

    Lourens, L.J.; Becker, J.; Bintanja, R.; Hilgen, F.J.; Tuenter, E.; Wal, R.S.W. van de; Ziegler, M.

    2010-01-01

    Constraints are given for the geometry and time lags of the prominent obliquity-paced glacial stages 100, 98 and 96, which mark a major phase in Northern Hemisphere (NH) glaciations during the late Pliocene (2.56–2.4 Ma ago). For this purpose a high-resolution benthic δ18O record was constructed fro

  11. Untangling inconsistent magnetic polarity records through an integrated rock magnetic analysis: A case study on Neogene sections in East Timor

    NARCIS (Netherlands)

    Aben, F.M.; Dekkers, M.J.; Bakker, R.R.; van Hinsbergen, D.J.J.; Zachariasse, W.J.; Tate, G.W.; McQuarrie, N.; Harris, R.; Duffy, B.

    2014-01-01

    Inconsistent polarity patterns in sediments are a common problem in magnetostratigraphic and paleomagnetic research. Multiple magnetic mineral generations result in such remanence "haystacks." Here we test whether end-member modeling of isothermal remanent magnetization acquisition curves as a basis

  12. Thylacinus (Marsupialia: Thylacinidae) from the Mio-Pliocene boundary and the diversity of Late Neogene thylacinids in Australia.

    Science.gov (United States)

    Yates, Adam M

    2015-01-01

    Thylacinus yorkellus is described as a new, moderately small-bodied species of thylacinid from the latest Miocene or, more likely, earliest Pliocene of South Australia. The new species can be diagnosed by the autapomorphic presence a strongly developed precingulid that terminates in a cuspidule on the anterobuccal face of the paraconid of the lower molars and a tiny basal anterior cuspidule on P 2, P 3 and the lower molars. It is found by cladistic analysis to be the sister species of the recently extinct Th. cynocephalus and distinct from the approximately coeval Th. megiriani from the Northern Territory. New dentary material is described and referred to Th. megiriani. These add character data and allow this species to be re-diagnosed based on autapomorphic character traits. Each of the three known late Miocene to early Pliocene Thylacinus species (Th. potens, Th. megiriani and Th. yorkellus) suggest that, instead of declining, there was a modest radiation of Thylacinus in the late Miocene.

  13. Long-lasting transcurrent tectonics in SW Alps evidenced by Neogene to present-day stress fields

    Science.gov (United States)

    Bauve, Victorien; Plateaux, Romain; Rolland, Yann; Sanchez, Guillaume; Bethoux, Nicole; Delouis, Bertrand; Darnault, Romain

    2014-05-01

    The SW Alps are an active orogen undergoing intra-mountainous extension and peripheral compression. We discuss the significance of syn-orogenic extension based on a comparison of paleo-stress derived from fault-slip data inversion reflecting the long-term (< 12 Ma) evolution of SW Alps and the present-day stress state obtained by the inversion of the focal mechanisms of the last 30-years seismicity. The resulting stress states of long-term and active tectonic regimes are in good agreement, showing that extension accompanies strike-slip and reverse faulting in the southern part of the belt. The extensional deformation regime is limited to specific tectonic domains that can be interpreted as ‘transitional' between pure strike-slip segments where the deformation concentrates on inherited ductile shear zones that were formed between 32° and 20 Ma ago. We thus propose that the extensional deformation in the SW Alps can be defined as a local deformation in a pull-apart type domain (High Durance - Jausiers area) or above slowly exhuming internal massifs (Dora Maira - Ivrea Body) along a curved boundary between the slowly rotating Apulian block and the relatively immobile Western Europe. The transcurrent fault system merges into a compressional front along the Mediterranean - Ligurian coast mainly to the east of San Remo.

  14. Late Neogene and Early Quaternary Paleoenvironmental and Paleoclimatic Conditions in Southwestern Europe: Isotopic Analyses on Mammalian Taxa

    Science.gov (United States)

    Domingo, Laura; Koch, Paul L.; Hernández Fernández, Manuel; Fox, David L.; Domingo, M. Soledad; Alberdi, María Teresa

    2013-01-01

    Climatic and environmental shifts have had profound impacts on faunal and floral assemblages globally since the end of the Miocene. We explore the regional expression of these fluctuations in southwestern Europe by constructing long-term records (from ∼11.1 to 0.8 Ma, late Miocene–middle Pleistocene) of carbon and oxygen isotope variations in tooth enamel of different large herbivorous mammals from Spain. Isotopic differences among taxa illuminate differences in ecological niches. The δ13C values (relative to VPDB, mean −10.3±1.1‰; range −13.0 to −7.4‰) are consistent with consumption of C3 vegetation; C4 plants did not contribute significantly to the diets of the selected taxa. When averaged by time interval to examine secular trends, δ13C values increase at ∼9.5 Ma (MN9–MN10), probably related to the Middle Vallesian Crisis when there was a replacement of vegetation adapted to more humid conditions by vegetation adapted to drier and more seasonal conditions, and resulting in the disappearance of forested mammalian fauna. The mean δ13C value drops significantly at ∼4.2−3.7 Ma (MN14–MN15) during the Pliocene Warm Period, which brought more humid conditions to Europe, and returns to higher δ13C values from ∼2.6 Ma onwards (MN16), most likely reflecting more arid conditions as a consequence of the onset of the Northern Hemisphere glaciation. The most notable feature in oxygen isotope records (and mean annual temperature reconstructed from these records) is a gradual drop between MN13 and the middle Pleistocene (∼6.3−0.8 Ma) most likely due to cooling associated with Northern Hemisphere glaciation. PMID:23717470

  15. Neogene fallout tuffs from the Yellowstone hotspot in the Columbia Plateau region, Oregon, Washington and Idaho, USA.

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    Barbara P Nash

    Full Text Available Sedimentary sequences in the Columbia Plateau region of the Pacific Northwest ranging in age from 16-4 Ma contain fallout tuffs whose origins lie in volcanic centers of the Yellowstone hotspot in northwestern Nevada, eastern Oregon and the Snake River Plain in Idaho. Silicic volcanism began in the region contemporaneously with early eruptions of the Columbia River Basalt Group (CRBG, and the abundance of widespread fallout tuffs provides the opportunity to establish a tephrostratigrahic framework for the region. Sedimentary basins with volcaniclastic deposits also contain diverse assemblages of fauna and flora that were preserved during the Mid-Miocene Climatic Optimum, including Sucker Creek, Mascall, Latah, Virgin Valley and Trout Creek. Correlation of ashfall units establish that the lower Bully Creek Formation in eastern Oregon is contemporaneous with the Virgin Valley Formation, the Sucker Creek Formation, Oregon and Idaho, Trout Creek Formation, Oregon, and the Latah Formation in the Clearwater Embayment in Washington and Idaho. In addition, it can be established that the Trout Creek flora are younger than the Mascall and Latah flora. A tentative correlation of a fallout tuff from the Clarkia fossil beds, Idaho, with a pumice bed in the Bully Creek Formation places the remarkably well preserved Clarkia flora assemblage between the Mascall and Trout Creek flora. Large-volume supereruptions that originated between 11.8 and 10.1 Ma from the Bruneau-Jarbidge and Twin Falls volcanic centers of the Yellowstone hotspot in the central Snake River Plain deposited voluminous fallout tuffs in the Ellensberg Formation which forms sedimentary interbeds in the CRBG. These occurrences extend the known distribution of these fallout tuffs 500 km to the northwest of their source in the Snake River Plain. Heretofore, the distal products of these large eruptions had only been recognized to the east of their sources in the High Plains of Nebraska and Kansas.

  16. Neogene fallout tuffs from the Yellowstone hotspot in the Columbia Plateau region, Oregon, Washington and Idaho, USA.

    Science.gov (United States)

    Nash, Barbara P; Perkins, Michael E

    2012-01-01

    Sedimentary sequences in the Columbia Plateau region of the Pacific Northwest ranging in age from 16-4 Ma contain fallout tuffs whose origins lie in volcanic centers of the Yellowstone hotspot in northwestern Nevada, eastern Oregon and the Snake River Plain in Idaho. Silicic volcanism began in the region contemporaneously with early eruptions of the Columbia River Basalt Group (CRBG), and the abundance of widespread fallout tuffs provides the opportunity to establish a tephrostratigrahic framework for the region. Sedimentary basins with volcaniclastic deposits also contain diverse assemblages of fauna and flora that were preserved during the Mid-Miocene Climatic Optimum, including Sucker Creek, Mascall, Latah, Virgin Valley and Trout Creek. Correlation of ashfall units establish that the lower Bully Creek Formation in eastern Oregon is contemporaneous with the Virgin Valley Formation, the Sucker Creek Formation, Oregon and Idaho, Trout Creek Formation, Oregon, and the Latah Formation in the Clearwater Embayment in Washington and Idaho. In addition, it can be established that the Trout Creek flora are younger than the Mascall and Latah flora. A tentative correlation of a fallout tuff from the Clarkia fossil beds, Idaho, with a pumice bed in the Bully Creek Formation places the remarkably well preserved Clarkia flora assemblage between the Mascall and Trout Creek flora. Large-volume supereruptions that originated between 11.8 and 10.1 Ma from the Bruneau-Jarbidge and Twin Falls volcanic centers of the Yellowstone hotspot in the central Snake River Plain deposited voluminous fallout tuffs in the Ellensberg Formation which forms sedimentary interbeds in the CRBG. These occurrences extend the known distribution of these fallout tuffs 500 km to the northwest of their source in the Snake River Plain. Heretofore, the distal products of these large eruptions had only been recognized to the east of their sources in the High Plains of Nebraska and Kansas.

  17. Phylogeography of Liquidambar styraciflua (Altingiaceae) in Mesoamerica: survivors of a Neogene widespread temperate forest (or cloud forest) in North America?

    Science.gov (United States)

    Ruiz-Sanchez, Eduardo; Ornelas, Juan Francisco

    2014-02-01

    We investigate the genetic variation between populations of the American sweetgum (Liquidambar styraciflua), a tree species with a disjunct distribution between northeastern Texas and Mexico, by analyzing sequences of two chloroplast DNA plastid regions in Mesoamerica. Our results revealed phylogeographical structure, with private haplotypes distributed in unique environmental space at either side of the Trans-Mexican Volcanic Belt, and a split in the absence of gene flow dating back ca. 4.2-1.4 million years ago (MYA). Species distribution modeling results fit a model of refugia along the Gulf and Atlantic coasts but the present ranges of US and Mesoamerican populations persisted disjunct during glacial/interglacial cycles. Divergence between the US and Mesoamerican (ca. 8.4-2.8 MYA) populations of L. styraciflua and asymmetrical gene flow patterns support the hypothesis of a long-distance dispersal during the Pliocene, with fragmentation since the most recent glacial advance (120,000 years BP) according to coalescent simulations and high effective migration rates from Mesoamerica to the USA and close to zero in the opposite direction. Our findings implicate the Trans-Mexican Volcanic Belt as a porous barrier driving genetic divergence of L. styraciflua, corresponding with environmental niche differences, during the Pliocene to Quaternary volcanic arc episode 3.6 MYA, and a Mesoamerican origin of populations in the USA.

  18. Neogene weathering and terrestrial sedimentation in southern New Caledonia; inference on post-obduction tectonics and climate change

    Science.gov (United States)

    Folcher, Nicolas; Ricordel-Prognon, Caroline; Sevin, Brice; Maurizot, Pierre; Cluzel, Dominique; Quesnel, Florence

    2014-05-01

    Iron-rich sediments that fill up karst-like depressions and paleo-valleys in southern New Caledonia are mainly composed of re-sedimented laterite and saprolite. These fluvial sediments come from the erosion of an older regolith that developed upon peridotites and gabbros of the Peridotite Nappe during Late Oligocene times. At the bottom, conglomeratic facies fill incised valleys and contain some metre-size cobbles of ferricrete that record dissection of pre-existing weathering profiles and were deposited in alluvial fan environment. The basal conglomerate is overlain by sand, then dominantly silty fluvial sediments 40 to 50 m thick, with a few thin conglomerate channels. Brutal grain size reduction suggests that erosion was short-lived and followed by quiescence. Multiple interbedded ferruginous duricrusts and rhizocretions made of goethite (and secondary hematite) and liesegang rings reveal iron mobility and several iron oxi-hydroxides concretion/ cementation episodes alternating with sedimentation, probably as a consequence of water table variations. The top of the succession is overlain by a weathering profile and capped by a nodular lateritic ferricrete. Finally, reactivated erosion profoundly incised the fluvial succession and locally reached the bedrock which today crops out upstream along the main river beds. In southern New Caledonia some ferricretes and ferruginous duricrusts have been dated at -25 Ma and -20 to -10 Ma by paleomagnetic method (in progress). They could be correlated to some warming events of the Late Oligocene and Early Miocene or to the Middle Miocene Climatic Optimum. Erosion that predates the accumulation of terrestrial sediments may be tentatively correlated to the uplift that accompanied the emplacement of the Saint-Louis and Koum plutons, and some internal dissection episodes could be related to the Lower Miocene post-obduction slab break off. The final erosion is most probably related to the southward tilt of New Caledonia due to Recent SW Pacific tectonics and to sea level drops during the Quaternary as well.

  19. Interaction between trench retreat and Anatolian escape as recorded by neogene basins in the northern Aegean Sea

    NARCIS (Netherlands)

    Beniest, A.; Brun, J. P.; Gorini, C.; Crombez, V.; Deschamps, R.; Hamon, Y.; Smit, Jeroen

    2016-01-01

    The evolution of the North Aegean Sea is studied through the development of three deep basins: the North Aegean Trough, the North Skyros Basin and the Ikaria Basin. Bathymetric data, a 2D seismic dataset and the well-investigated stratigraphic records of the onshore deep basins of northern Greece

  20. Sedimentation History of Neogene Lacustrine Sediments of Suseocka Bela Stena Based on Geochemical Parameters (Valjevo-Mionica Basin, Serbia)

    Institute of Scientific and Technical Information of China (English)

    Aleksandra (S)AJNOV1(C); Vladimir SIMI(C); Branimir JOVAN(C)I(C)EVI(C); Olga CVETKOVI(C); Radovan DIMITRIJEVI(C); Nenad GRUBIN

    2008-01-01

    Sediments of the western part of the Valjevo-Mionica basin (Serbia) were examined both geochemically and mineralogically to explain, on the basis of their sedimentological characteristics, the causes of changes in their qualitative and quantitative composition. A total of 62 samples obtained from the drillhole at depths up to 400 m was investigated. Using correlation of the obtained data, six geochemical zones were defined, two of which being specially distinguished by their mineralogical, geochemical and sedimentological characteristics. The first one, upper zone A, consists of banded marlstones interbedded with clay and oil shales and is characterized by presence of analcite and searlesite. These minerals and very high contents of Na2O indicate sedimentation in alkaline conditions with increased salinity in arid climate. That provided pronounced water stratification, as well as higher bioproductivity in the basin and sedimentary organic matter preservation. Therefore, the zone A sediments are characterized by high organic matter contents of the type which provides good potential for production of liquid hydrocarbons. Another specific zone, zone F, contains sediments with very high MgO, K2O and Li concentrations. Their geochemical correlation, as well as almost complete absence of illite in this zone, indicates the presence of interstratified clay mineral type illite-saponite (lithium-bearing Mg-smectite).

  1. Vertical Migration of Petroleum via Faults in Zhu Ⅲ Subbasin, Pearl River Mouth Basin, South China Sea

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The problem that faults act as a conduit for hydrocarbon-bearing fluid flow has been under debate for a long time. The southern boundary fault (FS) and No.2 fault belt in the Zhu Ⅲ subbasin in the Pearl River Mouth basin (PRMB) of South China Sea (SCS) are considered as the conduit of hydrocarbons for the oil and gas fields in the hydrocarbon-generating half grabens. Based upon the basin modeling and seismic velocity inversion simulation, there are abnormal-pressure compartments in the central part of half grabens. Wenchang, Enping and Zhuhai FormationⅡare seated within the abnormal-pressure zone, while the Zhuhai Formation Ⅰ is within the pressure-transition zone. The abnormal pressure was mainly caused by undercompaction due to the high rate of sedimentation for layers with an abnormal pressure. The increase of temperature of inclusions as the increase of depth supports vertical migration via faults in the study area.

  2. Structural and Seismic Stratigrapic study in the Center of the Magdalena Shelf in the Western Margin of Baja California Based on Seismic Reflection Data

    Science.gov (United States)

    González-Escobar, Mario; Salazar-Cárdenas, Rosa M.; Munguía, Luis; Martín, Arturo; Suárez-Vidal, Francisco

    2016-09-01

    The Magdalena Shelf is a shallow, low-relief surface located along the Baja California Pacific margin. As part of a forearc basin, the shelf was a convergent margin setting before the oblique divergent plate boundary formed in the Gulf of California at 12 Ma. It is thought that since 12-8 Ma, this basin has been a transtensional or strike-slip basin. To constrain the geometry, structural characteristics and some stratigraphic relationships, an active-source, seismic-reflection study was carried out in the central part of the shelf. As a result, the analyzed data show faults, basins and unconformities. Two out of four observed basins are clearly controlled by the Santa Margarita and San Lázaro faults that dip ~40° NE; a third basin is controlled by the Tosco-Abreojos fault. These three basins are part of the deformation zone that is associated with the Tosco-Abreojos fault system. The Iray-Margarita basin, on the other hand, is a fourth basin located at the northeast sector of the study area. An additional feature observed is a stepover lying between the overlapping ends of the Santa Margarita and San Lázaro faults. Small faults oriented sub-parallel to the above major faults are present, mainly throughout the western sector of the study area. Some of those minor faults cut through the seafloor indicating recent tectonic activity. Santa Margarita, San Lázaro and Tosco-Abreojos are also the names given to half-grabens controlled by the active faults that have the same names. The first two basins are affected by many more small faults in comparison with what we see in the third basin. Tectonically, this means that those two basins are the more active in the area of study. In all four basins, the upper seismic sequence consists of sediments controlled by faults of Neogene age. We found that the Iray-Santa Margarita basin is the deepest of all four basins (beyond the resolution of the data, >5 km), and lack of minor faults there indicates that the basin is not

  3. Structural and Seismic Stratigrapic study in the Center of the Magdalena Shelf in the Western Margin of Baja California Based on Seismic Reflection Data

    Science.gov (United States)

    González-Escobar, Mario; Salazar-Cárdenas, Rosa M.; Munguía, Luis; Martín, Arturo; Suárez-Vidal, Francisco

    2016-10-01

    The Magdalena Shelf is a shallow, low-relief surface located along the Baja California Pacific margin. As part of a forearc basin, the shelf was a convergent margin setting before the oblique divergent plate boundary formed in the Gulf of California at 12 Ma. It is thought that since 12-8 Ma, this basin has been a transtensional or strike-slip basin. To constrain the geometry, structural characteristics and some stratigraphic relationships, an active-source, seismic-reflection study was carried out in the central part of the shelf. As a result, the analyzed data show faults, basins and unconformities. Two out of four observed basins are clearly controlled by the Santa Margarita and San Lázaro faults that dip ~40° NE; a third basin is controlled by the Tosco-Abreojos fault. These three basins are part of the deformation zone that is associated with the Tosco-Abreojos fault system. The Iray-Margarita basin, on the other hand, is a fourth basin located at the northeast sector of the study area. An additional feature observed is a stepover lying between the overlapping ends of the Santa Margarita and San Lázaro faults. Small faults oriented sub-parallel to the above major faults are present, mainly throughout the western sector of the study area. Some of those minor faults cut through the seafloor indicating recent tectonic activity. Santa Margarita, San Lázaro and Tosco-Abreojos are also the names given to half-grabens controlled by the active faults that have the same names. The first two basins are affected by many more small faults in comparison with what we see in the third basin. Tectonically, this means that those two basins are the more active in the area of study. In all four basins, the upper seismic sequence consists of sediments controlled by faults of Neogene age. We found that the Iray-Santa Margarita basin is the deepest of all four basins (beyond the resolution of the data, >5 km), and lack of minor faults there indicates that the basin is not

  4. Geomorphologic, stratigraphic and sedimentologic evidences of tectonic activity in Sone–Ganga alluvial tract in Middle Ganga Plain, India

    Indian Academy of Sciences (India)

    Sudarsan Sahu; Dipankar Saha

    2014-08-01

    The basement of the Ganga basin in the Himalayan foreland is criss-crossed by several faults, dividing the basin into several sub-blocks forming horsts, grabens, or half-grabens. Tectonic perturbations along basement faults have affected the fluvial regime and extent of sediment fill in different parts of the basin during Late Quaternary. The East Patna Fault (EPF) and the West Patna Fault (WPF), located in Sone–Ganga alluvial tract in the southern marginal parts of Middle Ganga Plain (MGP), have remained tectonically active. The EPF particularly has acted significantly and influenced in evolving the geomorphological landscape and the stratigraphic architecture of the area. The block bounded by the two faults has earlier been considered as a single entity, constituting a half-graben. The present investigation (by morpho-stratigraphic and sedimentologic means) has revealed the existence of yet another fault within the half-graben, referred to as Bishunpur–Khagaul Fault (BKF). Many of the long profile morphological characters (e.g., knick-zone, low width–depth ratio) of the Sone River at its lower reaches can be ascribed to local structural deformation along BKF. These basement faults in MGP lie parallel to each other in NE–SW direction.

  5. SYNSEDIMENTARY TECTONICS AND SEDIMENTATION IN THE TERTIARY PIEDMONT BASIN, NORTHWESTERN ITALY

    Directory of Open Access Journals (Sweden)

    ROMANO GELATI

    1998-07-01

    Full Text Available The Late Oligocene/Early Miocene tectonic and sedimentary evolution of the eastern sector of the Langhe Sub-Basin (Teriary Piedmont Basin is proposed and discussed. The area is located between the villages of Roccaverano and Mombaldone, along the western side of the Bormida di Spigno River Valley (see attached geologic map. Synsedimentary tectonics strongly influenced the geologic evolution of the region during the time span examined, being particularly evident at three specific "times" that were chosen as models. During "Time 1" (Late Oligocene gentle anticlines, aligned WNW-ESE and NW-SE, started to form, affecting only hemipelagic mudstones and creating structural highs that controlled the areal distribution of both turbidites (i.e.T. Ovrano High and a thick pelitic slump sheet (i.e.M. Pisone High. During "Time 2"(Aquitanian the C. Mazzurini Half-Graben developed, separated by W-E and WNW-ESE growth faults from the M. Ovrano High to the north and gradually connecting, through a gently sloping ramp, with the Rocchetta High to the south. Turbidity currents and debris flows were channeled into the half-graben, while hemipelagic limestones were deposited onto the adjacent higher areas. During "Time 3" (Early Burdigalian the depocenter of the depression shifted southward, while the half-graben evolved into a wide trough (Piantivello Trough characterized by turbidites. Subsequently, the strongly irregular topography was progressively leveled to the quite homogeneous landscape on which the Cortemilia Formation (Late Burdigalian was deposited. 

  6. Anisotropy of Magnetic Susceptibility (AMS) of the Neogene Volcanic Succession at the Sierra Juarez - Las PintasVolcanic Province, Northeastern Baja California, Mexico: Preliminary Results

    Science.gov (United States)

    Mendoza-Borunda, R.; Cañón-Tapia, E.; Suárez-Vidal, F.; Gradilla-Martínez, L.

    2010-12-01

    The Sierra Juarez-Las Pintas Volcanic Province is among the largest in northern Baja California. For this work, we focused on a bimodal volcanic succession of late Miocene age, composed of an extensive ignimbrite unit and few dispersed basaltic flows that crop out in central Sierra Juarez and northern Sierra Las Tinajas. The ignimbrite is zoned, composed by three distinctive members: a basal unwelded white tuff, a mid-section unwelded orange tuff, and an upper red welded tuff. The basaltic flows are olivine-rich. Samples were collected in five sites that define a NE-SW section across the Sierra Juarez Escarpment, in the western boundary of the so-called Gulf Extensional Province. In each of these sites a stratigraphic column composed of more than one geologic unit was sampled. The total number of analyzed cores is ca. 160. The preliminary results show vertical and lateral variations of the AMS of the ignimbrite that can be interpreted in terms of the local flow direction and processes of emplacement of these volcanic deposits. Such variations, in turn, are likely to reflect variations in the dynamics of the eruptive process that produced them. Although the AMS of all the rocks in this province display a complex set of orientations, in this work is shown that when examined in detail important clues concerning the geological evolution of the province can be obtained from these data.

  7. Cenozoic tectono-thermal history of the Tordrillo Mountains, Alaska: Paleocene-Eocene ridge subduction, decreasing relief, and late Neogene faulting

    Science.gov (United States)

    Benowitz, Jeff A.; Haeussler, Peter J.; Layer, Paul W.; O'Sullivan, Paul B.; Wallace, Wes K.; Gillis, Robert J.

    2012-04-01

    Topographic development inboard of the continental margin is a predicted response to ridge subduction. New thermochronology results from the western Alaska Range document ridge subduction related orogenesis. K-feldspar thermochronology (KFAT) of bedrock samples from the Tordrillo Mountains in the western Alaska Range complement existing U-Pb, 40Ar/39Ar and AFT (apatite fission track) data to provide constraints on Paleocene pluton emplacement, and cooling as well as Late Eocene to Miocene vertical movements and exhumation along fault-bounded blocks. Based on the KFAT analysis we infer rapid exhumation-related cooling during the Eocene in the Tordrillo Mountains. Our KFAT cooling ages are coeval with deposition of clastic sediments in the Cook Inlet, Matanuska Valley and Tanana basins, which reflect high-energy depositional environments. The Tordrillo Mountains KFAT cooling ages are also the same as cooling ages in the Iliamna Lake region, the Kichatna Mountains of the western Alaska Range, and Mt. Logan in the Wrangell-St. Elias Mountains, thus rapid cooling at this time encompasses a broad region inboard of, and parallel to, the continental margin extending for several hundred kilometers. We infer these cooling events and deposition of clastic rocks are related to thermal effects that track the eastward passage of a slab window in Paleocene-Eocene time related to the subduction of the proposed Resurrection-Kula spreading ridge. In addition, we conclude that the reconstructed KFATmax negative age-elevation relationship is likely related to a long period of decreasing relief in the Tordrillo Mountains.

  8. Sedimentary evolution of Neogene continental deposits (Ñirihuau Formation) along the Ñirihuau River, North Patagonian Andes of Argentina

    Science.gov (United States)

    Paredes, J. M.; Giacosa, R. E.; Heredia, N.

    2009-07-01

    The sedimentary evolution of the Ñirihuau Formation (late Oligocene-middle Miocene) was studied along the southern margin of the Ñirihuau River, in the North Patagonian Andes. The 1300-m-thick section includes 15 epiclastic and volcaniclastic lithofacies which are grouped into five lithofacies associations: deep lacustrine, shallow lacustrine, fluvial channels, subaerial floodplains and volcaniclastic flows (lahar). Syn-eruptive and inter-eruptive stages are recorded along the Ñirihuau River section. The former consist of highly aggradational packages several tens of meters thick of ash-fall beds and lahar deposits. During inter-eruptive periods sedimentation took place mostly in shallow and deep lacustrine environments, with four cycles of lake expansion and contraction, and a minor proportion of fluvial deposits. Sedimentary supply originated from the northeast and northwest in the lower part of the unit through low to moderate sinuosity fluvial systems, flowing into a lake with high-gradient margins, and forming Gilbert-type deltas. The younger sections were sourced from the northeast, east and southeast, indicating changes in the basin morphology. Basic and intermediate volcanic rocks similar to those of the Ventana Formation (Oligocene) are interstratified at the beginning of the sedimentation. The syn-orogenic nature of the Ñirihuau Formation is evidenced by the changes in the basin shape, but mainly by the differences in styles and intensities of deformation between the Ñirihuau River section and the overlying outcrops of La Buitrera Hill, both separated by a folded unconformity.

  9. Calcareous nannofossil biostratigraphy and geochronology of Neogene trench-slope cover sediments in the south Boso Peninsula, central Japan: Implications for the development of a shallow accretionary complex

    Science.gov (United States)

    Chiyonobu, Shun; Yamamoto, Yuzuru; Saito, Saneatsu

    2017-07-01

    The geological structure and calcareous nannofossil biostratigraphy of the Middle to Late Miocene trench-slope succession in the southern Boso Peninsula, central Japan, were examined to obtain chronological constraints on the accretion and formation of the trench-slope architecture. As a result, trench-slope cover sediments (Kinone and Amatsu Formations) are clearly distinguishable from the Early Miocene Hota accretionary complex (Hota Group). The Hota accretionary complex was deposited below the carbonate compensation depth (CCD) and was affected by intense shearing, forming an east-west trending and south-verging fold and thrust belt. In contrast, the trench-slope cover sediments basically have a homoclinal dip, except at the northern rim where they are bounded by fault contact. They contain many species of calcareous nannofossils and foraminifers, which are indicative of their depositional environment above the CCD, and they show shallowing-upward sedimentary structures. Biostratigraphy revealed that the depositional age of the trench-slope sediments is ca. 15-5.5 Ma, suggesting that there is an approximately 2 myr hiatus beween the Miura Group and the underlying accretionary prism. Based on these results, the age of accretion of the Hota Group is inferred to be between ca. 17-15 Ma, and the group is covered by trench-slope sediments overlain on it after ca. 15 Ma. The timing of accretion and the age of the trench-slope basin tend to be younger southward of the Boso Peninsula. The accretionary system of the Boso Peninsula apparently developed in two stages, in the Middle Miocene and in the Late Miocene to Pliocene.

  10. Neogene felsic volcanic rocks in the Hoggar province: Volcanology, geochemistry and age of the Azrou trachyte-phonolite association (Algerian Sahara)

    Science.gov (United States)

    Ben El Khaznadji, Riad; Azzouni-Sekkal, Abla; Benhallou, Amel; Liégeois, Jean-Paul; Bonin, Bernard

    2017-03-01

    The Azrou volcanic district, located to the south-east to the Atakor district in the Hoggar, has a landscape is governed by a number of felsic volcanic highs and dissected mafic plateau lavas. Our new Rb-Sr age (i.e. 23.1 ± 1.6 Ma) indicates that the Azrou felsic lavas are contemporaneous with the Achkal ring complexes (Anahef region). The Azrou felsic lavas (mainly trachyte and phonolite) show remarkably homogeneous compositions both in major elements (57.5 ≤ SiO2≤ 63.1 wt%; 10.8 ≤(Na2O + K2O)≤12.4 wt%), trace elements (33.2 ≤ Th ≤ 107 ppm; 170 ≤ La≤472 ppm; 8.7<(La/Yb)N < 27.3) and radiogenic isotopes (0.703359 < 87Sr/86Sr < 0.706539; 0.512727 <143Nd/144Nd < 0.512925; 2<εNd <5.84. These data indicate that the lavas have been only very weakly contaminated by the Precambrian basement. Geodynamically, this genesis coupled with the low volume of both trachytic and phonolitic trends implies the reworking of pre-existing shear-zones allowing the rapid ascent of these small batches of magmas. This is in agreement with the general model of linear delamination along these shear zones due to the Africa-Europe convergence developed by Liégeois et al. (2005) and recently imaged by the magneto-telluric investigation of Bouzid et al. (2015).

  11. Magmatic evidence for Neogene lithospheric evolution of the central Andean ``flat-slab'' between 30°S and 32°S

    Science.gov (United States)

    Kay, S. M.; Abbruzzi, J. M.

    1996-06-01

    Geochemical data from Andean Miocene magmas erupted through the now volcanically-inactive "flat-slab" between 30°S to 32°S, coupled with geological and geophysical data, illuminate details on magmatic and continental lithospheric evolution over a progressively shallowing subduction zone. Pb, Sr and Nd isotopic and trace-element data show that Main Cordilleran, Precordilleran and Pampean magmas were contaminated in both the mantle and crust, and that the nature of the contaminants varied in time and space, reflecting tectonic events. Contaminants included both "enriched" (high LIL-element, high Sr and Pb, and low Nd isotopic ratios) and "depleted" (low LILE-element, low Sr and Pb, and high Nd isotopic ratios) types. In the western region, Main Cordilleran earlier Miocene lavas had contaminants with less "enriched" signatures than later Miocene lavas. Progressive "enrichment" is attributed to: (a) increasing amounts of sediment and tectonically eroded crust being subducted into the mantle wedge; and (b) contamination in a thickening Main Cordilleran lower crust whose composition was progressively "enriched". This "enrichment" occurred through addition of upper crust by an intracrustal mixing process driven by a propagating wedge tip associated with westward wedging, heating and deformation of crust from beneath the shortening Precordillera thrust belt to the east. Further east, magmas erupted through back-arc crust have more "depleted" signatures. Those erupted in the central part through the evolving Precordilleran thrust belt were contaminated by an older, thinner Grenville (˜ 1100 Ma) basement whose "depleted" signature is unique among Central Andean terranes. Late Miocene Pocho lavas erupted further east in conjunction with uplift of the Sierras Pampeanas show "enrichment" through time. Arguably, these magmas could contain a component mechanically removed from the base of the thinning continental lithosphere to the west, and progressively incorporated into the convecting asthenosphere. First-order mass balance calculations comparing the lithospheric geometry proposed for 20 Ma with that today suggests that ˜ 60% of the lithosphere within 600 km of the trench at 20 Ma has been lost. This lithospheric loss is required to accommodate simultaneous shallowing of the oceanic slab, and thickening and shortening of the crust. Continental lithosphere recycled into the asthenosphere could contribute to the sources of the "enriched" EM1 and EM2 mantle components in oceanic island basalts.

  12. Aggradation and progradation controlled clinothems and deep-water sand delivery model in the Neogene Lake Pannon, Makó Trough, Pannonian Basin, SE Hungary

    Science.gov (United States)

    Sztanó, Orsolya; Szafián, Péter; Magyar, Imre; Horányi, Anna; Bada, Gábor; Hughes, Daniel W.; Hoyer, Darrel L.; Wallis, Roderick J.

    2013-04-01

    In the Late Miocene-Early Pliocene Lake Pannon, regression went on for about 6 Ma. Sediments arriving from the Alpine-Carpathian source area were partly accumulated on the flat-lying morphological shelf of the lake, whereas other portions of the sediment were passing through to the slope and deposited on the deep basin floor. The height of the slope exceeded 400-500 m based on correlated well and seismic data. An extended 3D seismic volume covering the Makó Trough, one of the largest and deepest depressions within the Pannonian Basin, provided an opportunity to study sequences and shelf-margin trajectories generated as a result of continuous slope advancement. The lithology of these shelf, slope and basin centre deposits was inferred from seven well logs and 220 m core material. In the Makó Trough the southeastward migrating shelf-margin was formed by alternating aggradational and progradational clinothems. Aggradational clinothems, i.e. aggradation accompanied by subordinate progradation, are characterised by rising shelf-margin trajectories. The shelf built up from inner-shelf to shelf-edge deltaic lobes which compose a few dozen metre thick coarsening-up units. The majority of the sand, however, was transported by effective turbidity currents through leveed channels into the basin, and deposited as thick, extended slope-detached turbidite lobes up to a distance of 30 km from the shelf edge. In aggradational clinothems both the shelf and the basin floor accreted vertically. Development of progradational clinothems resulted in horizontal (flat) shelf-margin trajectories. Corresponding reflections toplap at the shelf edge and downlap within a distance of few kilometres from the toe of the slope. The shelf was bypassed, sediments accumulated on the slope and directly at the slope-toe region as small simple lobes. Short-distance transport was the result of clay-poor, non-effective turbidity currents. Consequently, the thickness of coeval basin-centre sediments remained negligible in progradational clinothems. Alternations of rising and horizontal shelf margin trajectories indicate that the climate- and subsidence-controlled lacustrine base-level rose continuously, though at varying rates. Descending trajectories were not observed. It means that base-level drops larger in amplitude than the seismic resolution (20-30 m), did not occur during the studied time interval, i.e. at 7-5 Ma ago, approximately corresponding to the Messinian age. As a result, major forced-regressive wedges or lowstand fans did not develop. This is in contrast with former stratigraphic models claiming that several 3rd-order sequences, including the intra-Messinian unconformity supposedly induced by hundred metres large lake-level drop, developed in Lake Pannon with significant volume of lowstand deposits as turbidites. Instead, aggradational and progradational clinothems are interpreted as fourth-order transgressive, early and late highstand systems tracts. These incomplete sequences represent less than 100 kyr time intervals. Due to climate control both on high rate of sediment supply and the water budget of Lake Pannon, conditions were more favourable for deposition of large volumes of well-developed turbidite systems during base-level rise than during stagnation or minor base-level fall. Therefore, sand delivery to the basin centre was at maximum during the early highstand aggradational stage and at minimum during the late highstand progradational stage. The timing and position of sand accumulation in the Makó Trough of Lake Pannon is different from those predicted by "traditional" sequence stratigraphic considerations.

  13. The Neogene rise of the tropical Andes facilitated diversification of wax palms (Ceroxylon: Arecaceae) through geographical colonization and climatic niche separation

    DEFF Research Database (Denmark)

    Sanín, María José; Kissling, W. Daniel; Bacon, Christine D.;

    2016-01-01

    out in the palm family (Arecaceae) due to its adaptation to cold, mountainous environments. Here, we reconstruct the biogeography and climatic preference of this lineage to test the hypothesis that Andean uplift allowed diversification by providing suitable habitats along climatic and elevational...

  14. Tectono-sedimentary evolution of the Neuquén basin (Argentina) between 39°S and 41°S during the Neogene

    Science.gov (United States)

    Huyghe, D.; Bonnel, C.; Nivière, B.; Messager, G.; Dhont, D.; Fasentieux, B.; Hervouët, Y.; Xavier, J.-P.

    2012-04-01

    Sedimentary rocks deposited in foreland basins are of primary interest, because they record the interactions between the growth of the orogenic wedge, the isostatic readjustment of the lithosphere, the variations of base-level and earth surface process. The Neuquén basin (32°S - 41°S) is a triangular shape foreland basin located on the eastern flank of the Andes. Its filling began during the late Triassic, first as back arc basin context and as compressive foreland basin since the upper Cretaceous. The structural inheritance is thus important and old basement structures, like the Huincul Ridge, generate significant variations of both deformation and shortening. Its Mesozoic history is well constrained due to its hydrocarbon potential. In comparison, its Cenozoic history remains poorly documented. The modern configuration of this basin results from several successive compressive tectonic phases. The last one is dated from the Miocene (Quechua phase) and has conditioned the segmentation of the foreland basin in several intra-mountainous sub-basins, whose sedimentary filling could reach several hundred meters. In this work, we document the relative chronology of the geological events and the sedimentary processes that have governed the Cenozoic history of the southern part of the Neuquen basin, to discriminate the relative rules of climatic and structural controlling factors on the evolution of the depocentres. Several NNW-SSE oriented intra-mountainous basins exist in this part of the Andes (Collon Cura basin and Catan Lil basin). On the contrary the associated foreland basin (Picun Leufu basin) is relatively underformed and is bounded to the North by the Huincul ridge and the North Patagonian massif to the South. Fifteen sedimentary sections have been studied along the Rio Limay River in the southern border of the basin, from the range to the external part of the foreland. The sedimentation is discontinuous in time and important retrogradations of the depocentres are observed from the outer part of the foreland to the intra-mountainous basins. Tertiary sedimentation begins at the end of the Oligocene until the end of the middle Miocene in the Picun Leufu basin. During the paroxysm of the Quechua tectonic phase, (middle Miocene to Pliocene) the Picun Leufu basin is characterised by a sedimentary hiatus of ~10 Ma that illustrates the closure of the Collon Cura basin and a migration to the internal zone of the range of the depocentres. The filling of the Collon Cura basin is characterised by a continental fining upward sequence of a thickness of several hundred meters. This sedimentation begins with lacustrine and alluvial plain paleoenvironments with some syn-eruptive events (ignimbrites) and ends with continental conglomerates and paleosoils. A first reconnexion with the foreland basin occurs at the beginning of the Pliocene, with the deposition of an alluvial fan. Since the end of the Pliocene another anticline grew in the Picun Leufu basin and controlled the deposition of more recent alluvial fans with the arrival of coarse conglomerates (Pampa Curaco and Bayo Messa Formations). The modern drainage network is established during the Pleistocene in the Collon Cura and Picun Leufu basins, which are since only characterised by the construction of erosional surfaces (terraces) and the apparition of the Rio Limay system on the Miocene and Cretaceous deposits.

  15. Evidence for a long-lived accommodation/transfer zone beneath the Snake River Plain: A possible influence on Neogene magmatism?

    Science.gov (United States)

    Konstantinou, Alexandros; Miller, Elizabeth

    2015-12-01

    Geochronologic data compiled from 12 metamorphic core complexes and their flanking regions outline important differences in tectonic and magmatic histories north and south of the Snake River Plain-Yellowstone Province (SRP-Y). Magmatism, crustal flow, metamorphism, and extensional exhumation of core complexes north of the SRP occurred mostly between 55 and 42 Ma as compared to 42-25 Ma south of the SRP, with final exhumation of the southern complexes occurring only during younger Miocene (20-0 Ma) Basin and Range faulting. These significant differences in the timing of events suggest that the now lava-covered SRP, which is at a high angle to Cordilleran trends, may have at times operated as a steep shear or transfer zone accommodating difference in strain to the north and south. Following previous suggestions, we infer that this proposed accommodation or transfer zone developed above an important lithospheric boundary localized above a tear in the subducting slab (shallower slab angle to the south) used to explain both the locus of Late Cretaceous-Paleocene magmatism and the different ages and mechanisms of slab reconfiguration and removal north and south of the SRP during the Cenozoic. The details of these different histories help outline the complex evolution of this zone and also suggest that this zone of lithospheric weakness may have subsequently focused Miocene SRP-Y hot spot magmatism.

  16. U-Pb zircon geochronology of the Paleogene - Neogene volcanism in the NW Anatolia: Its implications for the Late Mesozoic-Cenozoic geodynamic evolution of the Aegean

    Science.gov (United States)

    Ersoy, E. Yalçın; Akal, Cüneyt; Genç, Ş. Can; Candan, Osman; Palmer, Martin R.; Prelević, Dejan; Uysal, İbrahim; Mertz-Kraus, Regina

    2017-10-01

    The northern Aegean region was shaped by subduction, obduction, collision, and post-collisional extension processes. Two areas in this region, the Rhodope-Thrace-Biga Peninsula to the west and Armutlu-Almacık-Nallıhan (the Central Sakarya) to the east, are characterized by extensive Eocene to Miocene post-collisional magmatic associations. We suggest that comparison of the Cenozoic magmatic events of these two regions may provide insights into the Late Mesozoic to Cenozoic tectonic evolution of the Aegean. With this aim, we present an improved Cenozoic stratigraphy of the Biga Peninsula derived from a new comprehensive set of U-Pb zircon age data obtained from the Eocene to Miocene volcanic units in the region. The compiled radiometric age data show that calc-alkaline volcanic activity occurred at 43-15 Ma in the Biga Peninsula, 43-17 Ma in the Rhodope and Thrace regions, and 53-38 Ma in the Armutlu-Almacık-Nallıhan region, which are slightly overlapping. We discuss the possible cause for the distinct Cenozoic geodynamic evolution of the eastern and western parts of the region, and propose that the Rhodope, Thrace and Biga regions in the north Aegean share the same Late Mesozoic to Cenozoic geodynamic evolution, which is consistent with continuous subduction, crustal accretion, southwestward trench migration and accompanying extension; all preceded by the Late Cretaceous - Paleocene collision along the Vardar suture zone. In contrast, the Armutlu-Almacık-Nallıhan region was shaped by slab break-off and related processes following the Late Cretaceous - Paleocene collision along the İzmir-Ankara suture zone. The eastern and western parts of the region are presently separated by a northeast-southwest trending transfer zone that was likely originally present as a transform fault in the subducted Tethys oceanic crust, and demonstrates that the regional geodynamic evolution can be strongly influenced by the geographical distribution of geologic features on the subducting plate.

  17. National Assessment of Oil and Gas Quarter-Mile Cells - Neogene System of the Gulf Coast (Provinces 047, 048 and 049)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Cell maps for each Miocene and Plio-Pleistocene oil and gas assessment unit were created by the USGS to illustrate the degree of exploration, type of production, and...

  18. Paleogene and Neogene magmatism in the Valle del Cura region: New perspective on the evolution of the Pampean flat slab, San Juan province, Argentina

    Science.gov (United States)

    Litvak, Vanesa D.; Poma, Stella; Kay, Suzanne Mahlburg

    2007-09-01

    The Valle del Cura region is characterized by a thick volcanic and volcaniclastic sequence that records the Tertiary arc and backarc magmatic evolution of the Argentine Main Cordillera over the modern Pampean flatslab at 29.5-30°S. During the Eocene, a retroarc basin developed, represented by the Valle del Cura Formation synorogenic volcanosedimentary sequence, which includes rhyolites and dacitic tuffs. These silicic volcanic rocks have weak arc chemical signatures and high lithophile element concentrations and are isotopically enriched relative to the late Oligocene-early Miocene volcanic rocks that followed them. Their chemical characteristics fit with eruption through a thin crust. The Valle de Cura Formation was followed by the Oligocene-early Miocene Doña Ana Group volcanic sequence, which erupted at and near the arc front west of the border with Chile. The Doña Ana Group volcanic rocks have calc-alkaline chemical characteristics consistent with parental magmas forming in a mantle wedge and erupting through a normal thickness crust (35 km). Subsequent shallowing of the downgoing Nazca plate caused the volcanic front to migrate eastward. The volcanic sequences of the middle Miocene Cerro de las Tórtolas Formation erupted at this new arc front, essentially at the Argentine border. Two stages are recognized: an older one (16-14 Ma) in which magmas appear to have erupted through a normal thickness crust (30-35 km) and a younger one (13-10 Ma) in which the steeper REE pattern suggests the magmas last equilibrated with higher pressure residual mineral assemblages in a thicker crust. Isotopic ratios in the younger group are consistent with an increase in original crustal components and crust introduced into the mantle source by forearc subduction erosion. A peak in forearc subduction erosion near 12-10 Ma is consistent with when the main part of the Juan Fernandez Ridge began to subduct beneath the region. In addition to late Miocene Tambo Formation dacitic ignimbrites, the younger Cerro de las Tórtolas Formation volcanic rocks erupted at the height of contractional deformation in the Valle del Cura and to the east. The last important volcanic sequence to erupt in the Valle del Cura is the late Miocene Vacas Heladas Ignimbrite, the most isotopically enriched Tertiary magmas in the Valle del Cura that contain the highest proportion of crustal components. Subsequently volcanism ceased in the region in response to shallowing of the subduction zone.

  19. 3D models related to the publication: Neogene sloth assemblages (Mammalia, Pilosa) of the Cocinetas Basin (La Guajira, Colombia): implications for the Great American Biotic Interchange

    OpenAIRE

    Amson, Eli; Carrillo, Juan David; Jaramillo, Carlos

    2016-01-01

    INTRODUCTION : We here present the surface models of two specimens of sloths(Mammalia, Tardigrada) coming from the Late Pliocene WareFormation (Cocinetas Basin, La Guajira, Colombia, see Table 1). Along with three additional sloth taxa found in the same Formation, these specimens document the great diversity of this Neotropical locality. Furthermore, they represent a sloth assemblage from a locality just a few hundred thousand years older than the classically recognized first main pulse of th...

  20. The mode of emplacement of Neogene flood basalts in Eastern Iceland: The plagioclase ultraphyric basalts in the Grænavatn group

    Science.gov (United States)

    V. Óskarsson, Birgir; B. Andersen, Christina; S. Riishuus, Morten; Sørensen, Erik Vest; Tegner, Christian

    2017-02-01

    Plagioclase ultraphyric basalt lava with high fraction of solids have a mode of emplacement that is poorly understood. In this study we conduct detailed mapping of a PUB group in eastern Iceland, namely the Grænavatn group, and assess the group architecture, flow morphology and internal structure with additional constraints from petrography, petrology and crystal size distribution, to derive information on emplacement dynamics of plagioclase ultraphyric basalts. We also derive information on the plumbing system of the group with reference to the source of the macrocysts. The group is exposed in steep glacially carved fjords and can be traced for more than 70 km along strike. The flows have mixed architecture of simple and compound flows. Individual flow lobes have thicknesses in the range of 1-24 m and many reach widths and lengths exceeding 1000 m. The flows vary from rubbly to slabby pahoehoe, but are predominantly of pahoehoe type. The aspect ratio of the group and the nature of the flows indicate fissure-fed eruptions. The plagioclase macrocrysts (5-30 mm) are An-rich, exhibit bimodal size distribution and the modal proportions within the group varies from 15-40%. Clinopyroxene macrocrysts are also present ranging from 1-6%. The lowermost flow is thickest and carries the greatest crystal cargo load. The morphology of the lava flows suggests low viscous behavior, at odds with the high crystal content. The very calcic plagioclase macrocrysts (An80-85) are in disequilibrium with the groundmass and plagioclase microlaths therein (An50-70), meaning that the crystal-laden magmas quickly ascended from deeper crustal levels to the surface. The flows with highest crystal content may have maintained high temperatures by heat exchange with the primitive macrocrysts in the flows and developed non-Newtonian behavior such as shear thinning. Such conditions would have enabled the flows to advance rapidly during episodes with high effusion rates forming the simple flows, and subsequently maintained by insulated lobe-by-lobe emplacement. Occasionally surges disrupted the crust to form rubbly and slabby pahoehoe. A Herschel-Bulkley model is applied to the flows yielding effusion rates in the order of 103-104 m 3/s for the largest eruptions. Variation in crystal proportions within the group and individual flows is considered to be the result of magmas penetrating a crystal mush, followed by disaggregation and mobilization, sorting by flotation, mixing of magma batches and transportation of heterogeneous crystal-laden magmas to the surface with opportunities for staging en route.

  1. Slab Detachment, Flat Subduction and Slab Rollback in Central Mexico: Fitting the Neogene Evolution of the Trans-Mexican Volcanic Belt into the History and Dynamics of Subduction

    Science.gov (United States)

    Ferrari, L.

    2001-12-01

    I present a comparative analysis of the volcanic record of the Trans-Mexican Volcanic Belt (TMVB) and the plate tectonic history since 16 Ma in central Mexico that has important implications for the dynamic of the Cocos-Rivera subduction system. The TMVB volcanism has occurred in episodes characterized by across-arc and along strike variation and/or migration. In its first stage (16 to 10 Ma) the TMVB consisted of a broad andesitic arc emplaced between Long. 102° and 97° 30' (central Mexico). During this period volcanism was absent in the western and eastern TMVB. Between 11 and 6 Ma a voluminous mafic volcanism was emplaced to the northof the previous arc with ages progressively younger from west (Tepic-Guadalajara) to east (Queretaro-Hidalgo). Large calderas and silicic dome complexes developed in latest Miocene and early Pliocene (7.5 to 3.5 Ma) west of the Taxco-San Miguel de Allende fault system (TSMA). East of the TSMA a volcanic gap is clearly observed between ~9 and 3.5 Ma. In the western TMVB small amount of lavas with an intra-plate affinity started to be emplaced since 5 Ma. At the same time the volcanic front migrated to the south by about 70 km. East of the TSMA volcanism resumed at about 3.5 Ma in the Mexico City region and at the end of Pliocene in the eastern TMVB (excluding the Palma Sola area). In the Toluca - Mexico City area the volcanic front migrated trenchward in the Quaternary. No southward migration of the volcanic front is observed in the eastern TMVB. The Middle Miocene volcanism represent a "normal" volcanic arc developed after a gap of ~15 Ma following the formation of the Acapulco trench. I propose that the following unusual volcanic evolution was controlled by the detachment of the deeper part of the Cocos slab and the resulting variation in slab inclination. Slab must have detached after 12.5 following the end of subduction off Baja California. This is a kinematic-dynamic requirement, also supported by the fact that the present seismic slab is short. The slab detached from the Gulf of California toward the ESE from ~12 to 7.5 Ma producing a migrating mafic pulse along the propagating tear. Once deprived by its deeper part the slab started to decrease its dip, due to the buoyancy of the young crust. This is the most likely cause for flat subduction of the Cocos plate. No oceanic plateau is obvious on the mirror image on the Pacific plate and the absence of a subducted thickened crust explains why there is no seismic coupling between the two plates and no shortening occurred in the upper plate. The ~9 to 3.5 to volcanic gap in the central TMVB marks the period of flat subduction of the Cocos plate. Indeed, Pacific-Cocos relative motion decrease by 70% after 10 Ma. Flat subduction delays the basalt/gabbro to eclogite transition for some Ma. However the resuming of volcanism in late Pliocene indicate that the leading edge of the Cocos plate completed its transformation to eclogite and started to rollback. The slab rollback enhances the advection of geochemically enriched material into the mantle wedge, which is the most likely cause for the occurrence of intraplate-type volcanism in the TMVB.

  2. Reappraisal of the extinct seal “Phoca” vitulinoides from the Neogene of the North Sea Basin, with bearing on its geological age, phylogenetic affinities, and locomotion

    Directory of Open Access Journals (Sweden)

    Leonard Dewaele

    2017-05-01

    Full Text Available Background Discovered on the southern margin of the North Sea Basin, “Phoca” vitulinoides represents one of the best-known extinct species of Phocidae. However, little attention has been given to the species ever since its original 19th century description. Newly discovered material, including the most complete specimen of fossil Phocidae from the North Sea Basin, prompted the redescription of the species. Also, the type material of “Phoca” vitulinoides is lost. Methods “Phoca” vitulinoides is redescribed. Its phylogenetic position among Phocinae is assessed through phylogenetic analysis. Dinoflagellate cyst biostratigraphy is used to determine and reassess the geological age of the species. Myological descriptions of extant taxa are used to infer muscle attachments, and basic comparative anatomy of the gross morphology and biomechanics are applied to reconstruct locomotion. Results Detailed redescription of “Phoca” vitulinoides indicates relatively little affinities with the genus Phoca, but rather asks for the establishment of a new genus: Nanophoca gen. nov. Hence, “Phoca” vitulinoides is recombined into Nanophoca vitulinoides. This reassignment is confirmed by the phylogenetic analysis, grouping the genus Nanophoca and other extinct phocine taxa as stem phocines. Biostratigraphy and lithostratigraphy expand the known stratigraphic range of N. vitulinoides from the late Langhian to the late Serravallian. The osteological anatomy of N. vitulinoides indicates a relatively strong development of muscles used for fore flipper propulsion and increased flexibility for the hind flipper. Discussion The extended stratigraphic range of N. vitulinoides into the middle Miocene confirms relatively early diversification of Phocinae in the North Atlantic. Morphological features on the fore- and hindlimb of the species point toward an increased use of the fore flipper and greater flexibility of the hind flipper as compared to extant Phocinae, clearly indicating less derived locomotor strategies in this Miocene phocine species. Estimations of the overall body size indicate that N. vitulinoides is much smaller than Pusa, the smallest extant genus of Phocinae (and Phocidae, and than most extinct phocines.

  3. Understanding the kinematic evolution and genesis of a back-arc continental “sag” basin: The Neogene evolution of the Transylvanian Basin

    NARCIS (Netherlands)

    Tiliță, M.; Matenco, L.C.; Dinu, C.; Ionescu, L.; Cloetingh, S.

    2013-01-01

    Formation and evolution of back-arc basins is related to the interplay between subduction and convergence velocities during the formation of an orogenic chain. Sedimentary basins lacking fault systems that are genetically associated can be locally observed in the hinterland of the main orogenic belt

  4. Cenozoic tectono-thermal history of the Tordrillo Mountains, Alaska: Paleocene-Eocene ridge subduction, decreasing relief, and late Neogene faulting

    Science.gov (United States)

    Benowitz, Jeff A.; Haeussler, Peter J.; Layer, Paul W.; O'Sullivan, Paul B.; Wallace, Wes K.; Gillis, Robert J.

    2012-01-01

    Topographic development inboard of the continental margin is a predicted response to ridge subduction. New thermochronology results from the western Alaska Range document ridge subduction related orogenesis. K-feldspar thermochronology (KFAT) of bedrock samples from the Tordrillo Mountains in the western Alaska Range complement existing U-Pb, 40Ar/39Ar and AFT (apatite fission track) data to provide constraints on Paleocene pluton emplacement, and cooling as well as Late Eocene to Miocene vertical movements and exhumation along fault-bounded blocks. Based on the KFAT analysis we infer rapid exhumation-related cooling during the Eocene in the Tordrillo Mountains. Our KFAT cooling ages are coeval with deposition of clastic sediments in the Cook Inlet, Matanuska Valley and Tanana basins, which reflect high-energy depositional environments. The Tordrillo Mountains KFAT cooling ages are also the same as cooling ages in the Iliamna Lake region, the Kichatna Mountains of the western Alaska Range, and Mt. Logan in the Wrangell-St. Elias Mountains, thus rapid cooling at this time encompasses a broad region inboard of, and parallel to, the continental margin extending for several hundred kilometers. We infer these cooling events and deposition of clastic rocks are related to thermal effects that track the eastward passage of a slab window in Paleocene-Eocene time related to the subduction of the proposed Resurrection-Kula spreading ridge. In addition, we conclude that the reconstructed KFATmax negative age-elevation relationship is likely related to a long period of decreasing relief in the Tordrillo Mountains.

  5. U/Pb ages on detrital zircons in the southern central Andes Neogene foreland (36°-37°S): Constraints on Andean exhumation

    Science.gov (United States)

    Sagripanti, Lucía; Bottesi, Germán; Naipauer, Maximiliano; Folguera, Andrés; Ramos, Victor A.

    2011-12-01

    U/Pb dating on detrital zircons was performed in the Pampa de Carrizalito depocenter of the Late Miocene foreland basin associated with the Southern Central Andes orogenic front. This reveals Andean and pre-Andean components in magmatic derived zircons inhomogeneously distributed through the sequence. Andean, Grenville, Pampean, Famatinian and Gondwanic components reveal a complex source distribution from either the Main Andes, Coastal Cordillera and basement foreland areas. These are discussed showing different patterns in the context of the Andean orogenic cycle. Cretaceous and Jurassic components that are partly related to Mesozoic batholiths, developed at the western slope of the Andes at these latitudes, have a very contrasting behavior through the sequence: While Jurassic grains are represented from base to top, Cretaceous ones dilute upwardly. This is explained through the progressive uplift of the Southern Central Andes that could have created a barrier to Cretaceous and Jurassic detritus, while the older ones could have had either an alternative source area represented by the inverted rift system of the Huincul Ridge in the foreland area and the Cordillera del Viento in the hinterland area or the reworking of Jurassic sedimentary sequences of the Neuquén basin. Finally, a progressive enrichment in pre-Andean components to the top of the sequence is interpreted as related to the development of a broken foreland and the consequent rapid expansion of the orogenic front at the time of development of a slab shallowing setting in the region as shown by previous works.

  6. The Neogene and Quaternary Clay-with-flints north and south of the English Channel: comparisons of distribution, age, genetic processes and geodynamics

    Science.gov (United States)

    Quesnel, Florence; Catt, John; Laignel, Benoît; Bourdillon, Chantal; Meyer, Robert

    2003-02-01

    Weathered residual accumulations termed Clay-with-flints (Argiles à silex) overlying Cretaceous deposits are widespread in southern England and northwestern France. Geological and pedological studies and some field surveys indicate their distribution, nature, age and origin. In France, the microfaunas preserved in the hollow flints of the Clay-with-flints demonstrate the preservation of the parent Chalk stratigraphy in the sections studied, i.e. the Clay-with-flints corresponds to in situ weathering profiles. However, in England and in France, an important part of the clay component is derived from a thin veneer of basal Tertiary sediment overlying sub-Tertiary marine erosion surfaces of various Palaeogene transgressions. In England as in France, the youngest generation of Clay-with-flints can be dated from Late Pliocene to Quaternary. It formed after removal of different Cenozoic deposits on many plateaus and during the downcutting of Pleistocene rivers. The most visible effect of subsequent weathering profile development is irregular dissolution of the underlying Chalk to produce deep karstic pipes into which the Clay-with-flints has slumped; other pedological processes include rubification, clay illuviation and cryoturbation. Clay-with-flints also provides evidence of Quaternary palaeoenvironments, Cenozoic continental palaeosurfaces, and their vertical deformation.

  7. Morphological modifications of the Kerguelen Islands (South Indian Ocean) in response to Neogene climate change: evidence from 40Ar/39Ar and (U-Th)/He thermochronology

    Science.gov (United States)

    Ahadi, Floriane; Delpech, Guillaume; Gautheron, Cécile; Nomade, Sébastien; Pinna-jamme, Rosella; Ponthus, Léandre; Guillaume, Damien

    2016-04-01

    The processes driving erosion in geodynamic contexts in which regional tectonics is of minor importance, such as in oceanic islands, can be seen as a combination of positive/negative retroactions between climate change, isostasy or dynamic topography. The Kerguelen Islands (48-50° S, 68.5-70.5° E) are of particular interest to understand the impact of Cenozoïc climatic variations on the long-term geomorphological evolution of emerged reliefs at mid-latitudes. The Kerguelen Islands (6700 km2) are the emerged part of the vast Kerguelen oceanic plateau and reach a maximum height of 1852m asl. The archipelago is mostly made up of Oligocene basaltic traps (≈25 Ma) up to 1000m asl that are cross-cut by a dense network of large and deep valleys. The impact of glacial erosion during the last Quaternary glaciations on the landscape morphology is attested by the occurrence of U-shaped valleys, abundant moraines, erratic blocs and glacial lakes, as well as remnants of glaciers. Numerous plutonic complexes of various age (25-4.5 Ma) locally intrude theses traps and cover about 15% of the main island's surface; the largest being located in the Rallier du Baty peninsula (800 km2). This plutonic complex is mainly constituted of syenites with minor occurrence of gabbros and monzonites. The southern part of this complex has a laccolith structure with satellites plutons and formed between 13.7 and 8.0 Ma. The cooling history of syenites from the Rallier du Baty plutonic complex was investigated in order to identify one or several denudation periods and to understand the potential role of climate change on the geomorphological evolution of the islands since the Oligocene. We conducted the first thermochronological study on the Kerguelen Islands using the biotite 40Ar/39Ar thermochronometer and the apatite (U-Th)/He thermochronometer (AHe). The 40Ar/39Ar ages range from 9.44 ± 0.13 Ma to 13.84 ± 0.07 Ma for the various parts of the southern complex. These ages are identical to high-temperature crystallisation ages (U-Pb on zircon) and suggest an extremely rapid cooling between ≈700 and ≈300° C and that these rocks were emplaced at shallow depth. The mean AHe ages range between 4.4 ± 0.3 Ma and 7.4 ± 0.7 Ma. Theses ages agree with a model implying a rapid erosion of the upper volcanic rock pile that occurred several My after emplacement of these plutonic rocks at the Miocene-Pliocene transition. This transition coincides with a global climatic cooling which is particularly strong at these mid-latitudes. It is suggested that the morphological evolution of this part of the main island results from global climate changes at this period, with a possible contribution from positive retroaction between climate cooling and local isostatic accommodation. This study further strengthens the link between climatic variations and increase in erosion rates at mid latitudes since 6 Ma as recently demonstrated for Patagonian Andes.

  8. Petrology and provenance of the Neogene fluvial succession in Pishin Belt (Katawaz Basin) western Pakistan: Implications for sedimentation in peripheral forelands basins

    DEFF Research Database (Denmark)

    Kasi, Aimal Khan; Kassi, Aktar Muhammad; Friis, Henrik;

    2017-01-01

    FL and QmFLt diagrams show recycled and transitional recycled orogenic source for both the successions. The Dasht Murgha Group is rich in sedimentary and metamorphic lithics and poor in volcanic fragments (Lm35Lv18Ls47). The LmLvLs plot indicate that most of the samples lie in the fields of suture belts...

  9. Tectonic control of the damaged areas by land subsidence: Ameca, Jalisco Mexico, a study case

    Science.gov (United States)

    Rosas-Elguera, J.; Malagon, A.; Maciel, R.; Alatorre, M. A.; Perez, G.

    2009-04-01

    The Miocene to Quaternary Trans-Mexican Volcanic Belt (TMVB), one of the largest mexican volcanic arcs built on the North America plate, covers about 1000 km along central Mexico from the Pacific ocean to the Gulf of Mexico. The structure of west-central Mexico is dominated by a complex assemblage of crustal blocks bounded by major tectonic structures of the TMVB. These are the NW-SE Tepic-Zacoalco, the N-S Colima, and the E-W Chapala grabens, which separate the Jalisco and Michoacan blocks from the stable North American plate. The three grabens join south of Guadalajara to form what has been long interpreted as an active triple junction. The Tepic-Zacoalco rift is composed of the eastern part of the Plan de Barrancas-Santa Rosa graben and by the Ameca and Zacoalco half-grabens. The Ameca city is located in the Ameca half-graben. From 80´s several houses and buildings (more than 300) have been affected by land subsidence for more than two decades. The damage area follows a specific pattern with NW trend which is similar to the regional faults. The land subsidence is associated with the water extraction. We suggest that the distribution of the damage area is controlled by the fault system in combination with the water extraction. Because of the Ameca half-graben has been affected by historical and present day earthquakes and considering the subsurface geology (sandstones, siltstone intercalated with conglomerates) sudden collapses can be expected.

  10. Magma sources during Gondwana breakup: chemistry and chronology of Cretaceous magmatism in Westland, New Zealand

    DEFF Research Database (Denmark)

    van der Meer, Quinten Har Adriaan; Waight, Tod Earle; Scott, James M.

    2013-01-01

    by emplacement of granitoid plutons, the deposition of terrestrial Pororari Group sediments in extensional half-grabens across on- and offshore Westland, and the intrusion of mafic dikes from 90 Ma. These dikes are concentrated in the swarms of the Paparoa and Hohonu Ranges and were intruded prior...... to and simultaneous with volumetrically minor A-type plutonism at 82 Ma. The emplacement of mafic dikes and A-type plutonism at 82 Ma is significant as it coincides with the age of the oldest seafloor in the Tasman Sea, therefore it represents magmatism coincident with the initiation of seafloor spreading which...

  11. The thin-skinned style of the South Atlas Front in Central Algeria

    Energy Technology Data Exchange (ETDEWEB)

    Bracene, R.; Bellahcene, A.; Bekkouche, D [Sonatrach Exploration (Algeria); Mercier, E.; Frizon de Lamotte, D. [Universite de Cergy-Pntoise, Cedex (France). Departement des Sciences de la Terre

    1998-12-31

    Seismic lines cutting through the southern front of the Sahara Atlas show that the front is not superimposed on a major basement fault. Folded Cretaceous rocks can be observed on these lines to overlie a decollement surface climbing from Triassic to Early Cretaceous, below which flat-lying sediments can be recognized. The structural style is thus interpreted to be thin skinned and the folds underlining the front as ramp-related features. The development of duplexes in the core of some anticlines explains the apparent thickening of Cretaceous and/or Jurassic strata revealed by boreholes. This thickening was previously interpreted to be related to now-inverted extensional half-grabens, a model which cannot now be supported. This new interpretation allows a reassessment of other parts of the Sahara Atlas system, the large-scale structural model for which is that of large half-graben system that has undergone inversion because of shortening between the High Plateau massif and the Sahara Platform. (author)

  12. Sediment infill within rift basins: Facies distribution and effects of deformation: Examples from the Kenya and Tanganyika Rifts, East Africa

    Energy Technology Data Exchange (ETDEWEB)

    Tiercelin, J.J.; Lezzar, K.E. (Universite de Bretagne Occidentale, Brest (France)); Richert, J.P. (Elf Aquitaine, Pau (France))

    1994-07-01

    Oil is known from lacustrine basins of the east African rift. The geology of such basins is complex and different depending on location in the eastern and western branches. The western branch has little volcanism, leading to long-lived basins, such as Lake Tanganyika, whereas a large quantity of volcanics results in the eastern branch characterized by ephemeral basins, as the Baringo-Bogoria basin in Kenya. The Baringo-Bogoria basin is a north-south half graben formed in the middle Pleistocene and presently occupied by the hypersaline Lake Bogoria and the freshwater Lake Baringo. Lake Bogoria is fed by hot springs and ephemeral streams controlled by grid faults bounding the basin to the west. The sedimentary fill is formed by cycles of organic oozes having a good petroleum potential and evaporites. On the other hand, and as a consequence of the grid faults, Lake Baringo is fed by permanent streams bringing into the basin large quantities of terrigenous sediments. Lake Tanganyika is a meromictic lake 1470 m deep and 700 km long, of middle Miocene age. It is subdivided into seven asymmetric half grabens separated by transverse ridges. The sedimentary fill is thick and formed by organic oozes having a very good petroleum potential. In contrast to Bogoria, the lateral distribution of organic matter is characterized by considerable heterogeneity due to the existence of structural blocks or to redepositional processes.

  13. Petroleum systems of the Malay Basin Province, Malaysia

    Science.gov (United States)

    Bishop, Michele G.

    2002-01-01

    The offshore Malay Basin province is a Tertiary oil and gas province composed of a complex of half grabens that were filled by lacustrine shales and continental clastics.These deposits were overlain by clastics of a large delta system that covered the basin.Delta progradation was interupted by transgressions of the South China Sea to the southeast, which finally flooded the basin to form the Gulf of Thailand.Oil and gas from the Oligocene to Miocene lacustrine shales and Miocene deltaic coals is trapped primarily in anticlines formed by inversion of the half grabens during the late Miocene.Hydrocarbon reserves that have been discovered amount to 12 billion barrels of oil equivalent.The U.S. Geological Survey assessment of the estimated quantities of conventional oil, gas and condensate that have the potential to be added to reserves by the year 2025 for this province is 6.3 billion barrels of oil equivalent (BBOE) (U. S. Geological Survey World Energy Assessment Team, 2000).

  14. Simultaneous development of semigrabens orthogonal and oblique to the extension direction: physical modeling of natural analogues in Northeastern Brazil

    Directory of Open Access Journals (Sweden)

    André João Palma Conde Blanco

    2014-03-01

    Full Text Available The physical modeling tool is being increasingly used in geology to provide information about the evolutionary stages (nucleation, growth and geometry of geological structures at various scales. In the simulations of extensional tectonics, modeling provides a better understanding of fault geometry and evolution of the tectonic-stratigraphic architecture of rift basins. In this study a sandbox type apparatus was used to study the nucleation and development of basins influenced by previous structures in the basement, variably oriented as regards to the main extensional axis. Two types of experiments were conducted in order to: (i simulate the individual (independent development of half-grabens oriented orthogonal or oblique to the extension direction; (ii simulate the simultaneous development of such half-grabens, orthogonal or oblique to the extension direction. In both cases the same materials (sand mixed with gypsum were used and the same boundary conditions were maintained. The results were compared with a natural analogue represented by the Rio do Peixe Basin (one of the eocretaceous interior basins of Northeast Brazil. The obtained models allowed to observe the development of segmented border faults with listric geometry, often forming relay ramps, and the development of inner basins faults that affect only the basal strata, like the ones observed in the seismic sections of the natural analogue. The results confirm the importance of basement tectonic heritage in the geometry of rift depocenters.

  15. Positive inversion of extensional footwalls in the southern Serra do Espinhaço, Brazil--insights from sandbox laboratory experiments.

    Science.gov (United States)

    Gomes, Caroline J S; Martins-Neto, Marcelo A; Ribeiro, Valéria E

    2006-06-01

    Analogue experiments were carried out to get insights into the processes governing positive inversion during the foreland propagating thrust tectonics in the southern Serra do Espinhaço, a Brasiliano/Panafrican foldthrust belt in southeast Brazil. In particular, model listric half-grabens were inverted by applying contractional displacement to the footwall blocks. We investigated two different inversion conditions in listric half-grabens: (i) extensional and contractional detachments at the same level and (ii) at different positions. The models revealed that the development of a forward-breaking thrust system occurs in the basin synrift deposits, by contractional translation of the extensional footwall block when the extensional and contractional master faults do not coincide. Our experiments show the tectonic imbrication between basement and synrift sequences which characterizes the southern Serra do Espinhaço, and support the location in the eastern mountain range domain of the Espinhaço rift master fault system, which is not exposed at the surface.

  16. Tectónica extensional triásica en el sector norte de la cuenca Cuyana: primeros datos cinemáticos Triassic extensional tectonics at the northern branch of the Cuyana basin (South Precordillera: First kinematic data

    Directory of Open Access Journals (Sweden)

    María S. Japas

    2008-06-01

    . 35º- 40° obtenida en los afloramientos de la quebrada El Salto, se infiere en forma preliminar una importante componente sinestral durante la extensión en el tramo norte de la cuenca.Triassic clastic and volcanic rocks from the Precordillera were deposited in the Cuyana rift basin filling half-graben systems. Contractional/ transpressional Andean tectonics leads to the almost complete inversion of some portions of the basin which resulted in present-day isolated, structurally controlled outcrops of these Triassic rocks. In the Southern Precordillera both the degree of Neogene tectonic inversion and structural compexities are variable. At the regional scale, these variations in Andean deformation are related to first order anisotropies like the Cuyana basin borders and previous shear zones of Permian age (San Rafael orogenic phase. This paper focuses on the kinematic analysis done in the Cerro Manantial thrust sheet area (Cordón San Bartolo, central sector of the South Precordillera where tectonic inversion was not that strong and the influence of oblique strain zones is practically null. Four sets of extensional / transtensional faults were recognized affecting Triassic sedimentary rocks of the El Cielo Formation (Uspallata Group at the Quebrada El Salto. Fault displacements are of decimetric to metric scale. Mesoscopic kinematic indicators (en-échèlon tensional gashes, Riedel shear fractures, sigmoidal fractures were measured. Once Andean deformation was restored, a NNE direction for the Triassic extension was determined. Considering a northern branch of the Cuyana basin trending NNW (Az. 150° and oblique to the direction of extension (Az. 35-40°, a sinistral strike-slip component could be inferred for this portion of the basin.

  17. 渤海湾沙北地区盆地结构构造及其演化分析%Structure and Evolution Analyses of the Shabei Area of Bohai Gulf Basin

    Institute of Scientific and Technical Information of China (English)

    陈树光; 任建业; 辛云路; 张建丽; 吴峰

    2015-01-01

    本文以覆盖全区的3D 地震和钻井资料为基础,追踪并闭合了盆内重要的层序界面,精细解释了盆内主要构造和地震反射特征,新识别出了中生代逆冲构造体系,包括逆冲反转构造和逆冲未反转构造两种型式,它们分别形成了中生代的半地堑盆地和古潜山。分析了新生代不同时期盆地结构构造特征和古构造格架,发现在E2s3-E3s1时期,盆地受到NW-SE向伸展作用,到Ed3-Ed1时期盆地应力场转变成了近SN向伸展,表明东营组底界面是古近纪应力场发生变化的重要构造变革界面,反映了盆地由沙河街时期走滑伸展到东营时期斜向走滑拉分的演化过程。研究了不同时期控盆断裂体系特征,认为盆地中、新生代主要经历了四期构造演化阶段,分别为中生代的挤压剥蚀,沙河街时期NW-SE向伸展,东营时期近SN向伸展以及新近纪的热沉降和共轭走滑阶段。根据以上盆地结构构造特征和演化过程分析,结合区域动力学背景,认为地幔物质上拱导致的地壳减薄是盆地发生裂陷作用的直接因素,周缘板块重组事件是控制并影响断陷盆地演化和不同期次断裂体系展布方向不同的重要因素。%Based on the 3D seismic and drilling data of the Shabei area of the Bohai Gulf Basin, we tracked the important basin sequence boundaries and interpreted the structure styles and seismic reflection characteristics. Two types of Mesozoic thrust structures, i.e., the negative inversion and non-negative inversion structures, were identified in the study area, which led to the formation of the Mesozoic half-grabens and buried hills, respectively. Analyzing the basin-structure characteristics and tectonic framework of different period, we found that the basin was influenced by the NW-SE trending stretching in E2s3-E3s1 and the nearly SN trending stretching forces in Ed3-Ed1. The change of the Paleogene stress

  18. Sedimentary Basins of the Republic of Yemen : Their Structural Evolution and Geological Characteristics Evolution structurelle et caractéristiques géologiques des bassins sédimentaires de la république du Yemen

    Directory of Open Access Journals (Sweden)

    Beydoun Z. R.

    2006-11-01

    rejuvenation of the ancient NW-SE Najd fault system with subordinate strike-slip motion. The Tertiary basins are related to separation of Arabia from Africa in the Neogene along the Gulf of Aden and Red Sea trends. The principal uplifts are of equal antiquity, the oldest and most persistent being the Hadhramawt Arch. All the tectonic activity is linked to Gondwanan fragmentation and breakup from the initial closure of the paleo-Tethys and opening of the neo-Tethys in late Carboniferous to Permian times, and the development of the African Karoo system, through separation of India from Afro-Arabia in the Cretaceous to ultimate separation of Arabia from Africa in the Neogene. Within individual basins, compartmentalisation by sub-parrallel highs into graben-like and half-graben sub-basins or sectors is related to local adjustments to this continuing motion within the overall structural framework. Il y a peu de temps encore, on ne disposait que de peu d'informations sur la distribution et l'évolution des bassins sédimentaires au Yemen, puisque les données existantes reposaient entièrement sur la géologie de surface et les corrélations des formations stratigraphiques anciennes étudiées uniquement dans les redressements situés en bordure du golfe d'Aden et de la mer Rouge, ou sur le haut plateau au nord-ouest où l'on a réalisé des coupes en profondeur. Partout ailleurs, la couche tabulaire de sédiments du Tertiaire et de laves du groupe volcanique du Tertiaire masquait les principaux éléments structurels précénozoïques sous-jacents ainsi que les diverses successions sédimentaires. Les premières tentatives de délinéation de la structure des sols du pays furent donc rudimentaires et/ou ne pouvaient être que partiellement correctes. La découverte de champs de pétrole et de gaz rentables dans plusieurs fossés d'effondrement mesozoïques, à l'intérieur du Yemen, à la fin des années quatre-vingt et au début des années quatre-vingt-dix après l

  19. Effects of a regional décollement level for gravity tectonics on late Neogene-Quaternary deep-sea clastic sedimentation in the Foz do Amazonas Basin, Brazil

    Science.gov (United States)

    Cruz, A. M.; Gorini, C.

    2015-12-01

    Sets of 2D multi-channel seismic and chronostratigraphic data allowed us to undertake analyses of source to sink processes and triggering mechanisms of the gigantic megaslides previously documented off the NW and SE steep slope settings of the Foz do Amazonas basin. These megaslides comprise two sets of stacked allochthonous masses within the Upper Miocene-Quaternary sedimentary record, now described as Mass-Transport Complexes (MTCs): the Amapá Megaslide Complex (AMC) and the Pará-Maranhão Megaslide Complex (PMMC). Individual megaslides of both MTCs can mobilize to deep waters up to kilometer thick sedimentary series as allochthonous masses with different flow directions, degrees of sediment disruption and internal coherence. Megaslides spread downslope over areas as large as thousands of km2, attaining dimensions comparable to the world's largest mass-transport deposits. The basal and largest megaslide of the AMC (AM1 megaslide) is a quite unique example of mass-transport deposit, since it is interpreted as a dominant carbonate allochthonous mass sourced from a mixed carbonate-siliciclastic platform. According to stratigraphic correlations with global sea-level positions, platform instability would have been triggered between the late Miocene and the end of the Early Pliocene by gravitational collapse of the mixed platform under its own weight, after successive subaerial exposures which were able to generate karstification processes. Siliciclastic-type megaslides, on the other hand, are all sourced from large upslope slide and/or rotated blocks (up to 60 km large in the case of the PMMC).Stratigraphic correlations evidenced that horizon equally acts as the upper décollement level for the gravity tectonic system that operates in the regional scale of the Foz do Amazonas basin. In such a context, results of this work evidence complex links between variable modes of gravity deformation (gravity tectonics and mass wasting), all induced by instability created from a condensed section prone to produce pore fluid overpressure.

  20. Neogene to Quaternary stratigraphic evolution of the Antarctic Peninsula, Pacific Margin offshore of Adelaide Island: Transitions from a non-glacial, through glacially-influenced to a fully glacial state

    Science.gov (United States)

    Hernández-Molina, F. Javier; Larter, Robert D.; Maldonado, Andrés

    2017-09-01

    A detailed morphologic and seismic stratigraphic analysis of the continental margin offshore of Adelaide Island on the Pacific Margin of the Antarctic Peninsula (PMAP) is described based on the study of a regular network of reflection multichannel seismic profiles and swath bathymetry. We present an integrated study of the margin spanning the shelf to the continental rise, establish novel chronologic constraints and offer new interpretations on tectonic evolution and environmental changes affecting the PMAP. The stratigraphic stacking patterns record major shifts in the depositional style of the margin that outline three intervals in its evolution. The first non-glacial interval (Early Cretaceous to middle Miocene) encompasses a transition from an active to a passive margin (early Miocene). The second glacially-influenced interval (middle to late Miocene) is marked by pronounced aggradational sedimentary stacking and subsidence. Ice sheets advanced over the middle shelf of the margin at the end of this second interval, while the outer shelf experienced rare progradational events. The third, fully glaciated interval shows clear evidence of glacially dominated conditions on the margin. This interval divides into three minor stages. During the first stage (late Miocene to the beginning of the Pliocene), frequent grounded ice advances to the shelf break began, depositing an initial progradational unit. A major truncation surface marked the end of this stage, which coincided with extensive mass transport deposits at the base of the slope. During the second progradational glacial margin stage (early Pliocene to middle Pleistocene), stacking patterns record clearly prograding glacial sequences. The beginning of the third aggradational glacial margin stage (middle Pleistocene to present) corresponded to an important shift in global climate during the Mid-Pleistocene Transition. Morphosedimentary characteristics observed along the margin today began to develop during the latest Miocene but did not become fully established until sometime during the interval between the end of the Pliocene and middle Pleistocene. Between these two time intervals, the northeastward lateral migration of the Marguerite Trough also played a critical role in margin evolution, as it controlled ice sheet drainage pathways across the shelf, which in turn influenced development of slope and rise morphologies. Areas offshore from Adelaide Island differ from other areas of the PMAP due to changes in sedimentary processes that resulted from migration of the trough. This study confirms that the PMAP represents an exceptional locality for decoding, reconstructing and linking past tectonic and climatic changes. The study area specifically records not only the most relevant changes in depositional style, but also the relative importance of persistent along- and down-slope sedimentary processes. Our study approach can be extended to other areas and integrated with additional techniques to understand the evolution and the global linkages of the entire Antarctic continental margin and the ice sheets.

  1. [Biostratigraphy and paleoecology of the Neogene micromammalian faunas from the Calatayud-Teruel Basin (Spain) / Freudenthal, M. (editor)]: Rodents and lagomorphs from a lower Vallesian fissure filling near Molina de Aragon (Prov. Guadalajara, Spain)

    NARCIS (Netherlands)

    Anduenza, J.I.L.

    1988-01-01

    A new lower Vallesian micromammalian fauna from a locality near Molina de Aragon is described. Five species of Cricetidae, three species of Sciuridae - including a new one (Heteroxerus molinensis) -, two species of Gliridae, and one lagomorph species are described. Also, the paleoecological

  2. Sedimentological processes in a scarp-controlled rocky shoreline to upper continental slope environment, as revealed by unusual sedimentary features in the Neogene Coquimbo Formation, north-central Chile

    Science.gov (United States)

    Le Roux, J. P.; Gómez, Carolina; Fenner, Juliane; Middleton, Heather

    2004-03-01

    Exceptionally good outcrops of Miocene to Pliocene deposits in the vicinity of submarine Paleozoic basement scarps at Carrizalillo, north of La Serena, reveal a wealth of sedimentary features not commonly observed. The most proximal facies consist of rock fall and coarse-grained debris flow deposits directly abutting the basement wall from which they originated. Angular basement clasts are mixed with well-rounded cobbles, which probably formed as a basal gravel on a wave-cut platform at the beginning of marine flooding, subsequently accumulated at the scarp edge and were incorporated into the debris when the latter collapsed. The poor sorting, inverse grading, and protruding cobbles and boulders are classical debris flow features, with good clast imbrication indicating a laminar shearing action. A medial facies is represented by secondary channels running parallel to the major scarp about 1 km downslope of the first locality. In the largest channel, megaflutes at the base indicate the passage of highly turbulent, nondepositing flows eroding the soft, silty substrate. In the deepest, central part of the channel, a pebbly coquina shows horizontal and trough cross-stratification, with most of the bivalves oriented convex side up. Meter-scale rip-up clasts of the underlying siltstone are also present, indicating turbulent flow with a density sufficiently high to retard settling. The coquina is interpreted as a detachment deposit resulting from a hydroplaning debris flow along the central part of the channel, where the velocity and rate of pore pressure decay were highest. This deposit is overlain by fining upward, massive to horizontally stratified sandstone very similar in texture and composition to the matrix of the debris flow, suggesting its formation by surface transformation and elutriation of the latter. Along the channel margin, a basal centimeter-scale sandstone layer is virtually unaffected by the megaflute topography and clearly represents a subsequent event. It is interpreted as a basal shear carpet driven by the overlying debris flow. Within the shear carpet, a basal friction zone and an overlying collision zone containing a higher concentration of shell hash can be distinguished. The overlying debris flow deposit is represented by massive coquina with scattered, angular to rounded basement clasts. It contains disarticulated bivalves oriented with their concave side up, indicating large-scale upward fluid escape during deposition. A smaller secondary channel shows large rip-up rafts of the underlying substrate. Some rafts appear to have been plucked from the substrate by a process of sand injection from an overriding high-density sandy debris flow, which probably originated during a tsunami. Such clasts can climb upward into a laminar flow by down-current tilting and tumbling. The most distal facies occurs below a second scarp oriented more or less parallel to the present coastline, where finer-grained turbidites onlap and backlap onto the stoss and lee sides of an obstacle formed by eroded boulder conglomerates. The onlap deposits resemble inclined sandy macroforms recently described in submarine canyon settings. They are interbedded with diatom-containing, volcanic ash beds with cross-stratification dipping eastwards and containing deepwater microflora typical of continental upwelling zones.

  3. Hoplitomerycidae fam. nov. (Ruminantia, Mammalia) from Neogene fissure fillings in Gargano (Italy) Part 1: The cranial osteology of Hoplitomeryx gen. nov. and a discussion on the classification of pecoran families

    NARCIS (Netherlands)

    Leinders, J.

    1984-01-01

    It is concluded that the endemic Ruminantia from the Late Miocene island-fauna of Monte Gargano (Italy) originated from antlerless Cervidae. This in spite of the fact that these Ruminantia from Gargano evidently had horncore-like cranial appendages. The presence of horncores, in combination with the

  4. Uplift history of a Betic fold nappe inferred from Neogene-Quaternary sedimentation and tectonics (in the Sierra Alhamilla and Almeria, Sorbas and Tabernas Basins of the Betic Cordilleras, SE Spain)

    NARCIS (Netherlands)

    Weijermars, R.; Roep, Th.B.; Eeckhout, B. van den; Postma, G.; Kleverlaan, K.

    2007-01-01

    Structural, stratigraphical and sedimentological studies of the Alhamilla region show that the Sierra Alhamilla was elevated relative to the surrounding basins by open folding towards the end of the Tortonian period (about 7 Ma ago) and before the onset of Messinian sedimentation. The main arguments

  5. Post-collisional volcanism in a sinking slab setting—crustal anatectic origin of pyroxene-andesite magma, Caldear Volcanic Group, Neogene Alborán volcanic province, southeastern Spain

    Science.gov (United States)

    Zeck, H. P.; Kristensen, A. B.; Williams, I. S.

    1998-12-01

    Caldear Volcanic Group (CVG), a stratigraphically well defined, calc-alkaline rock complex within S a de Gata in the eastern part of the Alpine Betic mountain chain, S Spain, consists of three distinct formations: Hernández pyroxene andesites, Bujo hornblende-bearing pyroxene andesites and Viuda hornblende-bearing pyroxene dacites-rhyolites. The letter rock formation may have developed through crystal fractionation of mainly plagioclase and pyroxenes, however there is no direct relation between two formations. CVG has a domainal structure with a northeastern domain where Hernández formation is overlain by Bujo formation while Viuda formation is absent, and a southwestern domain where Viuda formation forms the only fractionate after Hernández formation. Hernández parent magma is thought generated through crustal anatexis by dehydration melting of a predominantly amphibolitic source rock complex which was formed by metamorphism from c. 500 Ma volcano-sedimentary parent material. The domainal structure of CVG is explained by compositional variation within this protogenetic complex. Single crystal U-Pb ages of c. 500 Ma to 1800 Ma for inherited zircon support the presence of clastic material of Proterozoic derivation within the original volcano-sedimentary complex. Regional study of syn-collisional rock formations (Alpine nappe complexes) indicate that the collisional tectonic stage in the Betic-Rif orogenic belt took place rather early (25-30 Ma?) and was followed by a stage of rapid regional rock uplift, fast cooling (c. 500°C/my) and extensional tectonics in the period 22-17 Ma. This later tectonic stage was set into motion by slab break-off which set the stage for a high temperature regime in the overlying lithosphere, providing the framework for the crustal melting and magma production responsible for the calc-alkaline rocks of Alborán volcanic province. Miocene zircon with ages ranging from c. 17 to 11 Ma indicate a rather protracted magmatic development prior to eruption at c. 11 Ma. Post-collisional character of Caldear Volcanic Group thus seems well established.

  6. [The fossil record of the Eurasian Neogene insectivores (Erinaceomorpha, Soricomorpha, Mammalia) : Part I / L.W. van den Hoek Ostende, C.S. Doukas and J.W.F. Reumer (editors)]: Romania

    NARCIS (Netherlands)

    Rzebik-Kowalska, B.

    2005-01-01

    Introduction The oldest descriptions of Romanian fossil insectivores date from the 1930s. At that time, I. Simionescu described two Early Pliocene localities, Măluşteni (in 1930) and Bereşti (in 1932), both containing a rich mammal fauna. Among the insectivores, Simionescu identified such genera as

  7. [The fossil record of the Eurasian Neogene insectivores (Erinaceomorpha, Soricomorpha, Mammalia) : Part I / L.W. van den Hoek Ostende, C.S. Doukas and J.W.F. Reumer (editors)]: Germany

    NARCIS (Netherlands)

    Ziegler, R.; Dahlmann, Th.; Reumer, J.W.F.; Storch, G.

    2005-01-01

    Introduction Research of Miocene and Pliocene insectivores has a long history in Germany. Already in the middle of the 19th century Miocene insectivore species have been described from South German localities. Most of these were authored by Herman von Meyer, who deserves to be named a pioneer of Ger

  8. [The fossil record of the Eurasian Neogene insectivores (Erinaceomorpha, Soricomorpha, Mammalia) : Part I / L.W. van den Hoek Ostende, C.S. Doukas and J.W.F. Reumer (editors)]: Czech Republic and Slovak Republic

    NARCIS (Netherlands)

    Fejfar, O.; Sabol, M.

    2005-01-01

    Introduction The fossil record of insectivores in Czech Republic comes from two different settings: A. in the stratified deposits in the North Bohemian tectonic rift (the sites; Tuchořice, the Open Mine Merkur-Nord near Chomutov, Dolnice and Františkovy Lázně (Franzensbad), and Β. in the karstic fil

  9. Discussion on ;Neogene-Quaternary evolution of the Tefenni basin on the Fethiye-Burdur fault zone, SW Anatolia-Turkey. Journal of African Earth Science 118, 137-148; by R. Aksoy, S. Aksarı

    Science.gov (United States)

    Alçiçek, M. Cihat; Mayda, Serdar; Demirel, F. Arzu

    2017-10-01

    The study by Aksoy and Aksarı (2016); (1) omits key fossil localities resulting in erroneous age estimates for their rock units, and (2) excludes and/or refers incorrectly pre-existing key studies in their research field. As the study is based on no age data, their proposal of NW-SE directed crustal extension that transitions to transtension is flawed. In this comment we summarize pre-existing age data and highlight its vital importance for yielding accurate information on the evolution of the Burdur Basin.

  10. [The fossil record of the Eurasian Neogene insectivores (Erinaceomorpha, Soricomorpha, Mammalia) : Part I / L.W. van den Hoek Ostende, C.S. Doukas and J.W.F. Reumer (editors)]: Spain

    NARCIS (Netherlands)

    Hoek Ostende, van den L.W.; Furió, M.

    2005-01-01

    Introduction Spain, with its many Cenozoic continental basins, has one of the finest fossil records of mammals in the world. The presence of nearly continuous sections with mammal localities make some of these basins ideal for defining mammalian continental stages, such as the Ramblian, Aragonian,

  11. Reply to comment by J.L. Díaz-Hernández and R. Julià on “Quaternary landscape evolution and erosion rates for an intramontane Neogene basin (Guadix-Baza basin, SE Spain)”

    Science.gov (United States)

    Pérez-Peña, José Vicente; Azañón, José Miguel; Azor, Antonio; Sánchez-Almazo, Isabel María; Tuccimei, Paola; Della Seta, Marta; Soligo, Michele

    2012-10-01

    We demonstrate that the age of 43 ka obtained for the topmost calcrete layer in the Guadix-Baza remains the only reliable numerical dating of the flat geomorphic surface that marks the end of the sedimentation in the basin. Consequently, the late Pleistocene to Holocene erosion rates derived from the incision of the present-day drainage network into the flat geomorphic surface remain valid. The calcrete radiometric ages reported by Díaz-Hernández and Julià (2012) in their comment are untenable due to the contamination with detrital 230Th (not corrected with the applied U/Th technique) and the possible mix of textural elements with different ages (older inherited grains and newly formed grains). Díaz-Hernández and Julià also quote U/Th ages for travertine terraces formed later than the calcrete layer. These ages lack internal consistency probably due to systematic contamination and/or weathering of the samples. The archaeological ages reported by Díaz-Hernández and Julià are subjected to great uncertainties, but independently of the age assumed as most realistic, they are completely compatible with the age of 43 ka that we obtained for the topmost calcrete layer in the Guadix-Baza basin.

  12. Control estructural en el emplazamiento del volcanismo y mineralizaciones neógenas, distrito Cañada Honda, San Luis Structural control on Neogene volcanism and related ore deposits at Cañada Honda district, San Luis province

    OpenAIRE

    María Silvia Japas; Nilda Esther Urbina; Patricia Sruoga

    2010-01-01

    Emplazada en la zona de transición sur del segmento de flat-slab pampeano y directamente vinculada a la horizontalización de la placa de Nazca, la faja volcánica terciaria de San Luis delata la migración que experimentó el arco magmático andino a la latitud de los 33º S en tiempos mio-pliocenos. Esta faja volcánica comprende una serie de distritos metalogenéticos de gran importancia en las Sierras Pampeanas de San Luis. Las rocas volcánicas y mineralizaciones de la faja volcánica terciaria se...

  13. [Biostratigraphy and paleoecology of the Neogene micromammalian faunas from the Calatayud-Teruel Basin (Spain) / Freudenthal, M. (editor)]: Rodents and lagomorphs from a lower Vallesian fissure filling near Molina de Aragon (Prov. Guadalajara, Spain)

    NARCIS (Netherlands)

    Anduenza, J.I.L.

    1988-01-01

    A new lower Vallesian micromammalian fauna from a locality near Molina de Aragon is described. Five species of Cricetidae, three species of Sciuridae - including a new one (Heteroxerus molinensis) -, two species of Gliridae, and one lagomorph species are described. Also, the paleoecological implicat

  14. Características texturales y petrofacies de depósitos neógenos, Bancalari, provincia de Buenos Aires Textural and petrofacies characteristics of the Neogene deposits of Bancalari, Buenos Aires Province

    Directory of Open Access Journals (Sweden)

    O.R. Tofalo

    2005-06-01

    Full Text Available Se estudian el sector cuspidal de la Formación Puelches y los sedimentos pampeanos y postpampeanos, especialmente el intervalo designado como preensenadense, a fin de definir sus características texturales y petrofacies y determinar su evolución paleoambiental y paleoclimática. Se utilizaron muestras de cuatro perforaciones realizadas en la localidad bonaerense de Bancalari, las que permitieron diferenciar seis grupos texturales, (I a VI y dos petrofacies (A y B. Los grupos I a III representan subambientes fluviales genéticamente vinculados, incluyendo típicos niveles arenosos de la Formación Puelches (I, gradualmente cubiertos por sedimentos depositados en lagunas (II-III, formadas en planicies de inundación de muy baja pendiente, con buen drenaje y bajo condiciones oxidantes. Los grupos II y III se asignan al preensenadense. Los tres grupos basales presentan petrofacies A (Qt:F:L = 43:49:8, procedente de rocas sedimentarias derivadas de basamento, con suite pesada igneo metamórfica, escasa hornblenda y smectita predominando sobre illita. Los tres grupos cuspidales fueron depositados en distintos ambientes. El IV es loéssico y se asigna a la Formación Ensenada. El V representa depósitos de charcos de agua poco profundos en la planicie de inundación y corresponde al Miembro Río Salado de la Formación Luján, acumulado bajo condiciones climáticas templadas y húmedas. Los sedimentos limo arcillosos que constituyen el grupo VI, representan el avance del mar y se atribuyen a los designados como querandino. Los tres grupos cuspidales presentan petrofacies B (12:56:32, procedente del arco magmático andino, con neto predominio de plagioclasa, contribución de volcaniclastos y vitroclastos, con asociación pesada dominada por hornblenda e illita predominando sobre smectita.Samples obtained from four wells located at Bancalari, Buenos Aires Province, have been analysed in order to define textural parameters, petrofacies, palaeoenvironments and palaeoclimate evolution. The samples were obtained from the upper part of the Puelches Formation and from the Pampean and Postpampean sediments; in particular this paper highlights the informally named Preensenadense interval. Six textural groups (I to VI and two petrofacies (A and B have been recognised. Groups I to III represent fluvial sands (I, gradually overlain by backswamp and lake deposits (II -III, generated on very low slope and well-drained floodplains, with oxidizing conditions. Groups II and III are assigned to Preensenadense interval. The three groups are included in petrofacies A (Qt:F:L = 43:49:8, of sedimentary and basement provenance, which has an igneous metamorphic heavy suite, scarce hornblende and dominance of smectite over illite. By contrast the upper groups (IV to VI show more varied depositional settings, including aeolian, fluvial and marine environments. Group IV is loessic and corresponds to the Ensenada Formation. Group V, the Lujan Formation (Río Salado Member, is composed of fluvial plain deposits deposited during a wet and temperate climate. Marine silts and clays (group VI represent a transgression over terrestrial environments and record of the so-called Querandino event. The three upper groups are included in petrofacies B (12:56:32, and have a magmatic arc provenance, with plagioclase dominance and contributions of volcaniclastic and vitroclastic material. It contains a heavy-mineral suite mainly composed of hornblende and it has more illite than smectite.

  15. [The fossil record of the Eurasian Neogene insectivores (Erinaceomorpha, Soricomorpha, Mammalia) : Part I / L.W. van den Hoek Ostende, C.S. Doukas and J.W.F. Reumer (editors)]: Poland

    NARCIS (Netherlands)

    Rzebik-Kowalska, B.

    2005-01-01

    Introduction Despite the 19th century tradition of mammalian palaeontology in the present territory of Poland, the oldest records of insectivores are found in the papers of Andreae (1904), Schlosser (in Zittel, 1911) and Wegner (1913), who described the fauna from the Middle Miocene (MN 6) locality

  16. Dating the Indo-Asia collision in NW Himalaya: constraints from Sr-Nd isotopes and detrital zircon (U-Pb) and Hf isotopes of Paleogene-Neogene rocks in the Katawaz basin, NW Pakistan

    Science.gov (United States)

    Zhuang, Guangsheng; Najman, Yani; Millar, Ian; Chauvel, Catherine; Guillot, Stephane; Carter, Andrew

    2015-04-01

    The time of collision between the Indian and Asian plates is key for understanding the convergence history and the impact on climatic systems and marine geochemistry. Despite much active research, the fundamental questions still remain elusive regarding when and where the Indian plate collided with the Asian plate. Especially in the west Himalaya, the questions become more complex due to disputes on the amalgamation history of interoceanic Kohistan-Ladakh arcs (KLA) with Karakoram of the Asian plate and the Indian plate. Here, we present a result of multiple-isotopic geochemistry and geochronology study in the Katawaz Basin in NW Pakistan, a remnant oceanic basin on the western Indian plate which was the repository for the sediments eroded from the west Himalaya ( Qayyum et al., 1996, 1997a, 1997b, 2001; Carter et al., 2010), to evaluate the time and character of collision in this region. In this study, we analyzed 22 bulk mudstone samples for Sr-Nd isotopes and 11 medium-grained sandstones for detrital zircon (U-Pb) geochronology and Hf isotopes. We constructed the Cenozoic chronology in the Katawaz Basin based on our newly collected detrital zircon U-Pb ages and fission track ages. We present the first record of Katawaz chronology that constrained the Khojak Formation to be current study revealed that the Katawaz sedimentary sequence ranges in age from Eocene to the earliest Miocene. The samples from the Nisai Formation show the 87Sr/86Sr - ɛNd values overlapping those of the end member of the Karakoram of Asian origin, revealing the arrival of Asian detritus on the Indian plate prior to 50 Ma. There are two parallel lines of evidence supporting this conclusion: (1) young zircon grains (Journal of the Geological Society 154, 753-756. Qayyum, M., Lawrence, R.D., Niem, A.R., 1997b. Molasse-Delta-flysch continuum of the Himalayan orogeny and closure of the Paleogene Katawaz Remnant Ocean, Pakistan. International geology review 39, 861-875. Qayyum, M., Niem, A.R., Lawrence, R.D., 1996. Newly discovered Paleogene deltaic sequence in Katawaz basin, Pakistan, and its tectonic implications. Geology 24, 835-838. Qayyum, M., Niem, A.R., Lawrence, R.D., 2001. Detrital modes and provenance of the Paleogene Khojak Formation in Pakistan: Implications for early Himalayan orogeny and unroofing. Geological Society of America Bulletin 113, 320-332.

  17. The Analysis and Significance of N-alkane in the Neogene Red-earth in Northern China%中国北方新近系红土的正构烷烃构成分析

    Institute of Scientific and Technical Information of China (English)

    张勇; 李吉均; 赵志军; 宋春晖; 张军; 张建明

    2007-01-01

    中国北方晚新生代红层沉积及其发育,但对其成因尚不清楚.通过籍由分子标志化合物中的正构烷烃对天水盆地新近系红土的成因进行探讨表明:天水盆地晚新生代沉积物正构烷烃碳数分布范围为C14-C33,正构烷烃的主峰碳主要集中于低碳的nC16、nC18,高碳峰主要集中于nC25与nC26.nC27/nC31、nC31/nC17、Paq等参数的综合分析表明天水盆地新近系红色沉积物具有明显的水生来源组份,推测它们可能系滨浅湖沉积物经后期改造而成,天水盆地新近系红层可能为水成起因.

  18. On the Paleogene coal-measure distribution over the China sea area

    Institute of Scientific and Technical Information of China (English)

    LI Zeng-xue; LI Ying; ZHOU Jing; LIU Hai-yan; L(U) Da-wei; WANG Ping-li

    2012-01-01

    The Paleogene coal accumulation basins of China are part of the global Tertiary coal-accumulated zone of the Pacific Rim located in the eastern coastal provinces and areas.Although the coal-bearing basins of the China Sea area are faults and depressed basins,they come up in groups.The overall structures are suitable for the development of coal-bearing deposition.The continuity of basin groups are good,and the coal-bearing depositions are thick.For example,the coal-bearing deposition is more than a kilometer thick at the Qiongdongnan Basin and Xihu Sag in the East China Sea,which the continental Paleogene coal basins cannot reach.Research shows that the coal accumulation basins in the sea area consist of many sags.There are two types of coal accumulation sags:half-graben sag and graben sag.In terms of water depth,coal accumulation sags can also be classified as deep-water half-graben sag and shallow-water half-graben sag; the graben sag is the deep-water sag.There are two distinct coal-accumulated zones in the basin:gentle slope and steep slope,with the gentle slope being the dominant one.The marshes of the supratidal zone and intertidal zone in a tidal flat system is favorable for the coal accumulation process widely taking place.There are two types of peat accumulation:autochthonous accumulation and allochthonous accumulation.Because of tectonic activities in the basins,allochthonous accumulations may be the more important form of coal-forming activities in the sea area.The very thick coal-bearing deposition in the sea area provides a rich material base for the assemblage of coal-related gas.Also,as a result of the deep burial depth,the degree of coal metamorphism is relatively high,so the coal-bearing strata become good hydrocarbon source rocks.

  19. Lower crustal intrusions beneath the southern Baikal Rift Zone

    DEFF Research Database (Denmark)

    Nielsen, Christoffer; Thybo, Hans

    2009-01-01

    The Cenozoic Baikal Rift Zone (BRZ) is situated in south-central Siberia in the suture between the Precambrian Siberian Platform and the Amurian plate. This more than 2000-km long rift zone is composed of several individual basement depressions and half-grabens with the deep Lake Baikal at its...... centre. The BEST (Baikal Explosion Seismic Transect) project acquired a 360-km long, deep seismic, refraction/wide-angle reflection profile in 2002 across southern Lake Baikal. The data from this project is used for identification of large-scale crustal structures and modelling of the seismic velocities...... of the crust and uppermost mantle. Previous interpretation and velocity modelling of P-wave arrivals in the BEST data has revealed a multi layered crust with smooth variation in Moho depth between the Siberian Platform (41 km) and the Sayan-Baikal fold belt (46 km). The lower crust exhibits normal seismic...

  20. No Moho uplift below the Baikal Rift Zone

    DEFF Research Database (Denmark)

    Nielsen, Christoffer; Thybo, Hans

    2009-01-01

    The late Cenozoic Baikal Rift Zone (BRZ) in southern Siberia is composed of several individual topographic depressions and half grabens with the deep Lake Baikal at its center. We have modeled the seismic velocity structure of the crust and uppermost mantle along a 360 km long profile of the Baikal...... Explosion Seismic Transects (BEST) project across the rift zone in the southern part of Lake Baikal. The seismic velocity structure along the profile is determined by tomographic inversion of first arrival times and 2-D ray tracing of first arrivals and reflections. The velocity model shows a gently...... deepening Moho from the Siberian Platform (41 km depth) into the Sayan-Baikal Fold Belt (46 km depth). We can exclude the presence of any Moho uplift around the ~10 km deep sedimentary graben structure of southern Lake Baikal. The lower crust includes a distinct 50-80 km wide high-velocity anomaly (7...

  1. LATE CARBONIFEROUS BRACHIOPODS FROM KARAKORUM, PAKISTAN

    Directory of Open Access Journals (Sweden)

    LUCIA ANGIOLINI

    1999-03-01

    Full Text Available Carboniferous rocks from North Karakorum display sharp lateral variations in lithology and thickness suggesting accumulation in half-grabens during continental rifting between the Karakorum block and northern Gondwana. Different Carboniferous successions, belonging to distinct tectonic units, have been detected. Thin, poorly fossiliferous successions of arenites and crinoidal limestones contrast with very thick terrigenous-carbonate successions comprising two distinct fossiliferous horizons. The lower fossiliferous horizon yielded brachiopods (Pustula sp., Rhipidomella sp., Choristites sp., Martiniopsis sp., Afghanospirifer sp., Gypospirifer sp., Composita sp. of Bashkirian age. The upper fossiliferous horizon, lying about 90 m above the former, contains corals, crinoids and brachiopods (Densepustula cf. losarensis, Dowhatania sulcata n. sp., Brachythyris sp., Rhipidomella sp., Septacamera dowhatensis, Alispirifer middlemissi of Moscovian to Kasimovian age. The Carboniferous brachiopods of North Karakorum are similar to those collected in the Late Carboniferous of Central Afghanistan, Himalaya (Manang, Spiti, Tibet, and Lhasa Block (Xainza area. 

  2. Orthorhombic faults system at the onset of the Late Mesozoic-Cenozoic Barents Sea rifting

    Science.gov (United States)

    Collanega, Luca; Breda, Anna; Massironi, Matteo

    2016-04-01

    The structures of the Late Mesozoic/Cenozoic Barents Sea rifting have been investigated with multichannel 3D seismics, covering an area of 7700 sqKm in the Hoop Fault Complex, a transitional area between the platform and the marginal basins. The main structural lineaments have been mapped in a time domain 3D surface and their activity ranges have been constrained through the sin-sedimentary thickness variations detected in time-thickness maps. Two main fault systems have been identified: an orthorhombic fault system consisting of two fault sets trending almost perpendicularly one to the other (WNW-ESE and NNE-SSW) and a graben/half-graben system, elongated approximately N-S in the central part of the study area. While the graben/half-graben system can be explained through the theory of Anderson, this landmark theory fails to explain the simultaneous activity of the two fault sets of the orthorhombic system. So far, the models that can better explain orthorhombic fault arrangements are the slip model by Reches (Reches, 1978; Reches, 1983; Reches and Dieterich, 1983) and the odd-axis model by Krantz (Krantz, 1988). However, these models are not definitive and a strong quest to better understand polymodal faulting is actual (Healy et al., 2015). In the study area, the presence of both a classical Andersonian and an orthorhombic system indicates that these models are not alternative but are both effective and necessary to explain faulting in different circumstances. Indeed, the Andersonian plain strain and the orthorhombic deformation have affected different part of the succession during different phases of the rifting. In particular, the orthorhombic system has affected only the Late Mesozoic-Cenozoic interval of the succession and it was the main active system during the initial phase of the rifting. On the other hand, the graben/half-graben system has affected the whole sedimentary succession, with an increasing activity during the development of the rifting. It has

  3. Petroleum systems of the Northwest Java Province, Java and offshore southeast Sumatra, Indonesia

    Science.gov (United States)

    Bishop, Michele G.

    2000-01-01

    Mature, synrift lacustrine shales of Eocene to Oligocene age and mature, late-rift coals and coaly shales of Oligocene to Miocene age are source rocks for oil and gas in two important petroleum systems of the onshore and offshore areas of the Northwest Java Basin. Biogenic gas and carbonate-sourced gas have also been identified. These hydrocarbons are trapped primarily in anticlines and fault blocks involving sandstone and carbonate reservoirs. These source rocks and reservoir rocks were deposited in a complex of Tertiary rift basins formed from single or multiple half-grabens on the south edge of the Sunda Shelf plate. The overall transgressive succession was punctuated by clastic input from the exposed Sunda Shelf and marine transgressions from the south. The Northwest Java province may contain more than 2 billion barrels of oil equivalent in addition to the 10 billion barrels of oil equivalent already identified.

  4. ALLOSTRATIGRAPHY AND SEISMIC STRATIGRAPHY OF THE MIOCENE SEDIMENTS OF THE SPICCHIAIOLA - POMARANCE AREA, SOUTHERN SIDE OF THE VOLTERRA BASIN (TUSCANY, ITALY

    Directory of Open Access Journals (Sweden)

    ALESSANDRO BOSSIO LUCA MARIA FORESI

    1997-11-01

    Full Text Available The objective of this work is to analyze the Miocene depositional units of the southern side of the Volterra Basin (Tuscany, Italy utilizing outcrop and seismic data and to establish the major events that led to their formation. Four depositional units have been recognized: Unit 1 is characterized by marine sediments of late Serravallian-early Tortonian age; Unit 2 is characterized by fluvio-lacustrine and brackish deposits of late Tortonian-early Messinian age; Unit 3 is characterized by marine deposits of early Messinian age; Unit 4 is characterized by the lacustrine deposits ("Lago-mare" facies of late Messinian age. The deposition of these four units is associated with an extensional tectonic regime that has been active in Tuscany since the late Tortonian. This regime generated half graben type structures in which deposition occurred. The recognized unconformities between the units are mainly related to uplift as a consequence of the extensional tectonic regime.    

  5. Structural evolution of the Abu Gharadig field area, Northern Western Desert, Egypt

    Science.gov (United States)

    El Gazzar, A. M.; Moustafa, A. R.; Bentham, P.

    2016-12-01

    Discovered in 1969, the Abu Gharadig (AG) Field was the first large hydrocarbon discovery in the Abu Gharadig Basin of the Western Desert of Egypt. Oil production began in 1973, with gas brought into production in 1975. The field produces mainly from upper Cretaceous clastic reservoirs. The AG Basin is an E-W trending intracratonic rift basin, about 330 km long and 50-75 km wide. It was initially formed as a large half graben basin during the Jurassic time in response to Tethyan rifting and continued to subside throughout the Cretaceous time. The half graben was subsequently inverted during the Late Cretaceous as part of the Syrian Arc deformation which affected northern Egypt. The Mid-Basin Arch, the AG Anticline, and the Mubarak High are three NE-SW oriented main inversion anticlines located within the AG Basin and are controlled by inversion of pre-existing Jurassic rift faults. The AG Anticline has an overall NE-SW orientation with a gentle plunge towards the NE and SW. It is locally bounded by two NE-SW-trending inverted faults on the southwest and northeast, accounting for the asymmetry of the anticline. Reverse offset of Cretaceous horizons is obvious at these inverted faults. Fault propagation folding is developed above the tips of the inverted faults at the Late Cretaceous Abu Roash and Khoman Formations. Based on thickness changes and stratigraphic relationships, inversion started during the Santonian time and continued into the Campanian-Maastrichtian. Inversion continued during deposition of the Paleocene-Middle Eocene Apollonia Formation and the Late Eocene-Oligocene Dabaa Formation.

  6. Facies pattern of the middle Permian Barren Measures Formation, Jharia basin, India: The sedimentary response to basin tectonics

    Indian Academy of Sciences (India)

    Prabir Dasgupta

    2005-06-01

    In the Lower Gondwana succession of the Jharia basin of eastern India, the Barren Measures Formation is characterized by the cyclic disposition of fine-grained lacustrine deposits and relatively coarse-grained fluvial deposits. The cyclic variation in the rate of coarse clastic input is attributed to the sedimentary response to basin tectonics. The sandstone–shale alternations of the Barren Measures succession can be correlated with the tectonic cyclothems developed on the hangingwall dip-slope and adjoining trough in a continental half-graben setting. Enhancement of the gradient of the hangingwall dip-slope during reactivation of the basin margin faults led to progradation of the existing fluvial system towards the half-graben trough and deposition of the coarser clastics on the fine-grained lacustrine deposits of the trough. Peneplanation of the hangingwall slope and slow increase in the lake level caused lacustrine transgression and retrogration of the fluvial system on the hangingwall block. The fluvial sediments were onlapped by the fine-grained lacustrine deposits. Episodic rejuvenation of the basin margin faults thus caused development of tectonic cyclothem on the hangingwall block. The paleocurrent pattern indicates that a persistent northward paleoslope was maintained during Barren Measures sedimentation. The inferred depositional settings were much more extensive than the present limit of the outcrop. The faults, presently defining the northern limit of the Barren Measures Formation, were possibly emplaced after Barren Measures sedimentation. The final movement along these fault planes caused preservation of the downthrown hangingwall block and the Barren Measures sediments on the footwall block were eroded during subsequent denudation. The Southern Boundary Fault came into existence after the deposition of the Barren Measures sediments.

  7. Mode of opening of an oceanic pull-apart: The 20°N Basin along the Owen Fracture Zone (NW Indian Ocean)

    Science.gov (United States)

    Rodriguez, Mathieu; Chamot-Rooke, Nicolas; Fournier, Marc; Huchon, Philippe; Delescluse, Matthias

    2013-09-01

    basins are common features observed at releasing bends along major strike-slip faults. The formation and structural evolution of such basins have mostly been investigated in the continental domain and by sandbox laboratory experiments or numerical models. Here we present recently acquired multibeam bathymetry, 3.5 kHz echo sounder, and seismic profiles across the 20°N pull-apart Basin along the India-Arabia transform boundary, known as the Owen Fracture Zone (OFZ). Using nearby oceanic drilling (Deep Sea Drilling Project 222), we constrain the structural evolution of the basin since opening some 3 Myr ago. The 20°N Basin is large (90 km long and 35 km wide) despite limited transcurrent motion (~10 km). The first stage involved the formation of a step over along the OFZ and the subsequent isolation of a subsiding half graben. Extension and subsidence were further partitioned over three distinct subbasins separated by complex sets of transverse faults. The size of the basin was enhanced by gravity-driven collapse. The 20°N Basin has been a catchment for Indus turbidites since its opening, which provide a good record of syn-sedimentary deformation. The deformation related to the subsidence of the half graben mimics rollover structures commonly encountered in salt tectonics, suggesting that subsidence was accommodated by one or several décollement layers at depth. Despite a different rheological context, the subsurface structure of the nascent oceanic 20°N Basin is very similar to the more mature continental Dead Sea Basin along the Levant Fault, which also displays subbasins separated by transverse faults.

  8. Patterns and Dynamics of Rifting on Passive Continental Margin from Shelf to Slope of the Northern South China Sea:Evidence from 3D Analogue Modeling

    Institute of Scientific and Technical Information of China (English)

    Sun Zhen; Zhou Di; Wu Shimin; Zhong Zhihong; Myra Keep; Jiang Jianqun; Fan Hao

    2009-01-01

    Affected by thermal perturbation due to mantle uprising,the rheological structure of the lithosphere could be modified,which could lead to different rifting patterns from shelf to slope in a passive continental margin.From the observed deformation style on the northern South China Sea and analogue modeling experiments,we find that the rift zone located on the shelf is characterized by half grabens or simple grabens controlled mainly by long faults with large vertical offset,supposed to be formed with normal lithasphere extension.On the slope,where the lithosphere is very hot due to mantle upwelling and heating,composite grabens composed of symmetric grabens developed.The boundary and inner faults are all short with small vertical offset.Between the zones with very hot and normal lithosphere,composite half grnbens composed of half grabens or asymmetric grabens formed,whose boundary faults are long with large vertical offset,while the inner faults are relatively short.Along with the thickness decrease of the brittle upper crust due to high temperature,the deformation becomes more sensitive to the shape of a pre-existing weakness zone and shows orientation variation along strike.When there was a bend in the pre-existing weakness zone,and the basal plate was pulled by a clockwise rotating stress,the strongest deformation always occurs along the middle segment and at the transition area from the middle to the eastern segments,which contributes to a hotter lithosphere in the middle segment,where the Baiyun (白云) sag formed.

  9. A structurally controlled fan-delta complex at the southern margin of the peninsular range forearc basin complex (Baja California)

    Energy Technology Data Exchange (ETDEWEB)

    Morris, W.R.; Busby-Spera, C. (Univ. of California, Santa Barbara (USA))

    1990-05-01

    A confined trunk fan delta and its structurally controlled tributary fan deltas are extremely well exposed along the southern margin of the Rosario embayment. This fan-delta complex consists of nonmarine to deep marine deposits almost continuously exposed for over 20 km in the down-paleoslope direction. Facies and stratal patterns in the fan-delta complex were controlled by local faulting, climatic variation, and eustasy, resulting in relative sea level fluctuations. Basin bathymetry and drainage patterns were controlled by a series of half-grabens that formed along north-south-trending faults that lay along the northern margin of an east-west-trending depression. Breccias were initially shed into the north-south-trending half-grabens; axial drainage systems were later established within the grabens, making up the tributary fan deltas. These tributary fan deltas fed a voluminous trunk fan delta confined to the east-west-trending depression. The trunk and tributary fan delta deposits show two major progradational to retrogradational cycles that record relative sea level fluctuations. Progradation in the shallow-marine environment is represented by conglomerate channels cut into ripple-laminated or bioturbated siltstone and HCS sandstones, overlain by conglomerate mouth bar deposits interstratified with nearshore sandstone deposits. Retrogradation in the shallow marine environment is recorded by either a vertical clastic facies transition or a clastic-carbonate facies transition. The clastic facies transition consists of nearshore sandstone deposits overlain by offshore bioturbated siltstones. The clastic-carbonate facies transition consists of the development of red algal patch reefs and rhodoliths on top of fan-delta conglomeratic lobes, mudstone and sandstone bank channel margins, or paleobasement highs. The clastic-carbonate facies transition reflects low sediment supply controlled by climatic conditions.

  10. Tectonic and gravity extensional collapses in overpressured cohesive and frictional wedges

    Science.gov (United States)

    Yuan, X. P.; Leroy, Y. M.; Maillot, B.

    2015-03-01

    Two modes of extensional collapse in a cohesive and frictional wedge of arbitrary topography, finite extent, and resting on an inclined weak décollement are examined by analytical means. The first mode consists of the gravitational collapse by the action of a half-graben, rooting on the décollement and pushing seaward the frontal part of the wedge. The second mode results from the tectonics extension at the back wall with a similar half-graben kinematics and the landward sliding of the rear part of the wedge. The predictions of the maximum strength theorem, equivalent to the kinematic approach of limit analysis and based on these two collapse mechanisms, not only match exactly the solutions of the critical Coulomb wedge theory, once properly amended, but generalizes them in several aspects: wedge of finite size, composed of cohesive material and of arbitrary topography. This generalization is advantageous to progress in our understanding of many laboratory experiments and field cases. For example, it is claimed from analytical results validated by experiments that the stability transition for a cohesive, triangular wedge occurs with the activation of the maximum length of the décollement. It is shown that the details of the topography, for the particular example of the Mejillones peninsula (North Chile) is, however, responsible for the selection of a short length-scale, dynamic instability corresponding to a frontal gravitational instability. A reasonable amount of cohesion is sufficient for the pressures proposed in the literature to correspond to a stability transition and not with a dynamically unstable state.

  11. Tiber delta CO2-CH4 degassing: A possible hybrid, tectonically active Sediment-Hosted Geothermal System near Rome

    Science.gov (United States)

    Ciotoli, G.; Etiope, G.; Marra, F.; Florindo, F.; Giraudi, C.; Ruggiero, L.

    2016-01-01

    Fiumicino town in the Tiber River delta, near Rome International Airport (Italy), is historically affected by large amounts of carbon dioxide (CO2) in the ground and gas eruptions triggered by shallow drilling. While it is known that CO2 originates from carbonate thermometamorphism and/or mantle degassing, the origin of methane (CH4) associated with CO2 is uncertain and the outgassing spatial distribution is unknown. Combining isotope gas geochemistry, soil gas, and structural-stratigraphic analyses, we provide evidence for a hybrid fluid source system, classifiable as Sediment-Hosted Geothermal System (SHGS), where biotic CH4 from sedimentary rocks is carried by deep geothermic CO2 through active segments of a half-graben. Molecular and isotopic composition of CH4 and concentration of heavier alkanes (ethane and propane), obtained from gas vents and soil gas throughout the delta area, reveal that thermogenic CH4 (up to 3.7 vol% in soil gas; δ13CCH4: -37 to -40‰ VPDB-Vienna Peedee Belemnite, and δ2HCH4: -162 to -203‰ VSMOW - Vienna Standard Mean Ocean Water in gas vents) prevails over possible microbial and abiotic components. The hydrocarbons likely result from known Meso-Cenozoic petroleum systems of the Latium Tyrrhenian coast. Overmaturation of source rocks or molecular fractionation induced by gas migration are likely responsible for increased C1/C2+ ratios. CO2 and CH4 soil gas anomalies are scattered along NW-SE and W-E alignments, which, based on borehole, geomorphologic, and structural-stratigraphic analyses, coincide with active faults of a half-graben that seems to have controlled the recent evolution of the Tiber delta. This SHGS can be a source of considerable greenhouse gas emissions to the atmosphere and hazards for humans and buildings.

  12. Structural differences between the western and eastern Qiongdongnan Basin: evidence of Indochina block extrusion and South China Sea seafloor spreading

    Science.gov (United States)

    Zhang, Cuimei; Wang, Zhenfeng; Sun, Zhipeng; Sun, Zhen; Liu, Jianbao; Wang, Zhangwen

    2013-12-01

    Located at the intersection between a NW-trending slip system and NE-trending rift system in the northern South China Sea, the Qiongdongnan Basin provides key clues for us to understand the proposed extrusion of the Indochina Block along with Red River Fault Zone and extensional margins. In this paper we for the first time systematically reveal the striking structural differences between the western and eastern sector of the Qiongdongnan Basin. Influenced by the NW-trending slip faults, the western Qiongdongnan Basin developed E-W-trending faults, and was subsequently inverted at 30-21 Ma. The eastern sector was dominated by faults with NE orientation before 30 Ma, and thereafter with various orientations from NE, to EW and NW during the period 30-21 Ma; rifting display composite symmetric graben instead of the composite half graben or asymmetric graben in the west. The deep and thermal structures in turn are invoked to account for such deformation differences. The lithosphere of the eastern Qiongdongnan Basin is very hot and thinned because of mantle upwelling and heating, composite symmetric grabens formed and the faults varied with the basal plate boundary. However, the Southern and Northern Uplift area and middle of the central depression is located on normal lithosphere and formed half grabens or simple grabens. The lithosphere in the western sector is transitional from very hot to normal. Eventually, the Paleogene tectonic development of the Qiongdongnan Basin may be summarized into three stages with dominating influences, the retreat of the West Pacific subduction zone (44-36 Ma), slow Indochina block extrusion together with slab-pull of the Proto-South China Sea (36-30 Ma), rapid Indochina block extrusion together with the South China Sea seafloor spreading (30-21 Ma).

  13. The Northern Boundary of the Michoacan Block: As Inferred From Aeromagnetic Data

    Science.gov (United States)

    Rosas-Elguera, J.; Lopez Loera, H.; Fregoso, E.; Maciel Flores, R.; Peña, L.; Alatorre-Zamora, M. A.

    2015-12-01

    The western part of the Guerrero terrane is comprised of the Jalisco and Michoacan Blocks (Rosas-Elguera et al., 1996 and references therein), a fault-bounded crustal blocks at western of Mexico. The Michoacan block is bounded by the N-NE segment of the Rio Balsas in the east, and the Colima graben in the west, the Chapala-Oaxaca fault to the north, and the Middle America Trench to the south. Northern boundary is formed with the Chapala-Oaxaca fault zone (Harrison y Johnson, 1985). The Cotija half-graben is the end-tip of this fault zone. A combined radiometric and paleomagnetic analyses in the Cotija half-graben were carried out (Rosas-Elguera, et al, 2003). Radiometric dates between 31.60 and 8.39 Ma confirm both the southern extension of the Sierra Madre Occidental and the early mafic Tans-Mexican Volcanic Belt succession at the northern part of the Michoacan block. Paleomagnetic data indicate a counterclockwise rotation of ~ 24° about a vertical axis for the Michoacan block. The Michoacan-Guanajuato Volcanic Field forms an area of extensive monogenetic volcanism. This volcanic field contains more than 1000 eruptive centers distributed over an area of 40,000 Km2. The Chapala-Oaxaca fault zone separates the northern MGVF and the southern MGVF. Hasenaka and Carmichael (1987) recognized three different petrologic associations in the MGVF: calc-alkaline rocks typical arc characteristic, K2O-rich alkaline rocks with relatively high MgO contents and TiO2-rich alkaline rocks with relatively low MgO contents. We present the aeromagnetic results (after Consejo de Recursos Minerales, 1999) which suggest a clear relationship between the geologic features and the magnetic response.

  14. BIOSTRATIGRAPHIC SUBDIVIDING OF THE NEOGENE DINGJIA'ERGOU MAMMALIAN FAUNA, TONGXIN COUNTY, NINGXIA PROVINCE, AND ITS BACKGROUND FOR THE UPLIFT OF THE TIBETAN PLATEAU%宁夏同心丁家二沟哺乳动物群生物地层学研究进展及青藏高原隆升背景

    Institute of Scientific and Technical Information of China (English)

    王世骐; 宗立一; 杨卿; 孙博阳; 李雨; 史勤勤; 杨湘雯; 叶捷; 吴文裕

    2016-01-01

    宁夏同心丁家二沟哺乳动物群是中国中中新世早期最具代表性的地方动物群,但长期以来,对这一动物群产出层位的认识处于模糊和混乱的状态.本文通过对丁家二沟一带新生界地层的划分和对比,将出产丁家二沟动物群的彰恩堡组划分为下、中、上3个层位,其中下部和中部的层位分别产出两个时代不同的动物群:下部的印子岭动物群以Alloptox gobiensis-Protanancus tobieni-Caementodon tongxinensis-Turcocerus sp.1组合为代表,时代对应于欧洲陆相哺乳动物分期的MN5;中部的马二嘴子沟动物群则以Alloptox gobiensis-Platybelodon tongxinensis-Hispanotherium matritense-Turcocerus sp.2组合为代表,时代对应于欧洲陆相哺乳动物分期的MN6;而上部的地层则需要进一步研究划分.同时,丁家二沟地区彰恩堡组的下部层位的时代约为17~ 15Ma,跨越了中中新统的下界,可以考虑在这一地区重新建立中国陆相通古尔阶下界,使其与中中新统的下界相一致.此外,丁家二沟地区北部彰恩堡组与下伏清水营组成不整合接触,南部干河沟组中发育了生长断层,可能代表了这一地区对约20Ma和10Ma青藏高原两次强烈构造事件在东北部的远程响应.

  15. Neogene deformation and its implications for the structural framework of the oil fields in the Icapui-Ponta Grossa (CE) region, onshore Potiguar Basin, Brazil; Deformacao neogena e suas implicacoes na estruturacao dos campos de petroleo na regiao de Icapui-Ponta Grossa (CE), Bacia Potiguar emersa

    Energy Technology Data Exchange (ETDEWEB)

    Sousa, Debora do Carmo [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil). Programa de Pos-Graduacao em Geodinamica e Geofisica]. E-mail: debora@geologia.ufrn.br; Sa, Emanuel Ferraz Jardim de; Antunes, Alex Francisco [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil). Dept. de Geologia

    2008-06-15

    In coastal cliffs at the western portion of the Potiguar Basin (so-called Aracati Platform), the Barreiras Formation, of miocene age, displays structures pointing to high strain deformation. Detailed mapping of faults and folds geometry in the Barreiras Formation leads to recognition of extensional structures (at Ponta Grossa village) and contractional oblique structures (Vila Nova, next to Icapui town), both of them related to a trans current system bearing NE (at these locations) and NW trends (Afonso Bezerra Fault, in the central portion of the basin). These data point to a neo gene stress field which generated faults, folds and hydro plastics structures, including SL fabrics and shear zones, as well as reactivated older structures in the underlying neocretaceous sedimentary section. Reinterpretation of seismic sections from this region and other geological data at several places in the Potiguar Basin outline structures which are correlated (in style and kinematic regime) throughout the siliciclastic rocks of the Acu Formation, limestones of the Jandaira Formation and younger basalts of the Macau Formation, whose age straddles the Oligocene-Miocene boundary. This structural framework recognized at the surface has to be compatible with subsurface deformation as observed in seismic sections, which includes pulses/events of older, Neocretaceous to Paleocene age. This model has important implications as regards the structure (geometry, kinematics, age of traps) of oil reservoirs (especially the sandstones of the Acu Formation, in the Fazenda Belem Oil Field) and the processes of migration and hydrocarbon entrapment at this region of the Potiguar Basin. (author)

  16. Reply to discussion by M. C. Alçiçek et al. on ;Neogene-Quaternary evolution of the Tefenni basin on the Fethiye-Burdur fault zone, SW Anatolia-Turkey;, Journal of African Earth Sciences, 118, 137-148, by R. Aksoy and S. Aksarı

    Science.gov (United States)

    Aksoy, Rahmi; Aksarı, Süleyman

    2017-10-01

    In their discussion on the Aksoy and Aksarı (2016) article, Alçiçek et al. (2017) claim that our stratigraphic interpretation, age assignment for the rock units and kinematic analysis depended on incorrect data. They also claim that there is no evidence for a NE-trending fault zone (Fethiye-Burdur Fault Zone) from Fethiye to Burdur with left-lateral strike-slip movement. Our opposing views on the above-mentioned issues are given below.

  17. 尼日尔三角洲盆地Akpo油田新近系深水浊积水道储层构型表征%Characterization of reservoir architectures for Neogene deepwater turbidity channels of Akpo oilfield, Niger Delta Basin

    Institute of Scientific and Technical Information of China (English)

    赵晓明; 吴胜和; 刘丽

    2012-01-01

    由于深水浊积水道油藏多位于深海区,受作业成本的限制,其开发井距往往较大,利用现行的针对密井网区的多井模式拟合方法进行该类油藏的地下储层构型表征,其精度较低.为此,利用西非尼日尔三角洲盆地深水区Akpo油田稀井条件下的钻井与地震资料,提出了基于井-震联合的该区深水浊积水道储层构型表征技术,论述了其表征思路与方法.深水浊积水道储层构型可分为水道体系、复合水道和单一水道3个层次,其中复合水道层次又可细分为复合水道系列和复合水道2个亚层次,不同层次构型单元规模差异大,需要在构型模式指导下,分别开展基于油组、小层及小层内部切片的井-震联合,将不同层次的构型模式与钻井、地震资料进行拟合,完成深水浊积水道的储层构型表征.这一研究不仅对高效开发深水浊积水道油藏具有实用价值,对利用井-震联合方法开展储层构型研究也具有重要参考价值.%Deepwater turbidity channel reservoirs are usually located in deep sea areas, where a distant spacing pattern for development wells is often allocated due to the cost constraint of prospecting operation. Consequently, the characterization of such underground reservoir architectures of deepwater turbidity channels with the current overlay method for multi-well models used mainly under dense-well pattern conditions usually achieves a poor precision. Therefore, based on drilling and seismic data of a distant well spacing pattern for deepwater turbidity channel reservoirs of the Akpo oilfield in Niger Delta Basin, West Africa, we introduced a novel method to characterize such turbidity channel reservoir architectures in terms of well-to-seismic integration, and discussed its conception and procedures as well. Reservoir architectures of deepwater turbidity channels can be classified into three orders, channel system, channel complex and single channel. Of which the channel complex can be further subdivided into two suborders, channel complex series and channel complex. Various orders of architecture units differ significantly from each other in scale, thus, a well-to-seismic integration of individual oil measures, sublayers and internal sections within sublayers guided by architecture models should be applied to adapting an architecture model of different orders to downhole data (including dynamic data) and seismic information as well as to fulfilling the characterization of reservoir architectures of deepwater turbidity channels. This study will not only have a significantly economic value in efficiently developing deepwater turbidity channel reservoirs but also be of guiding significance for integrating well data with seismic data to characterize architecture elements.

  18. 西藏冈底斯地块尼木地区新第三纪构造热史的磷灰石裂变径迹约束%Apatite Fission Track Evidences for Neogene Tectono-Thermal History in Nimu Area, Southern Gangdese Terrane, Tibet Plateau

    Institute of Scientific and Technical Information of China (English)

    袁万明; 董金泉; 保增宽; 朱炳玉

    2008-01-01

    文章报道冈底斯地块尼木地区磷灰石裂变径迹研究新成果.获得的5个磷灰石裂变径迹年龄为(6.8±0.6)~(9.7±1.2) Ma,均属同一组年龄;径迹长度为(12.9±1.7)~(14.2±2.3) μm,具单峰分布.这与近期9~5 Ma挤压事件并导致藏北盆地快速沉积作用相一致.样品模拟揭示有3阶段地质热历史:从大于12 Ma到8 Ma,温度120~110 ℃,属于稳定阶段;8~4 Ma,约从110 ℃到15 ℃地表温度,是快速冷却阶段;4~0 Ma,处于地表演化阶段.受喜马拉雅碰撞作用的影响,第2阶段使本区急剧隆升剥露,形成现今的山貌特征.在8~4 Ma期间,平均隆升速率为1.41 mm/a,累计隆升量达5 940 m.

  19. APPLICATION OF SEISMIC SEDIMENTOLOGY TO MICROFACIES IDENTIFICATION FOR J2I OIL FORMATION,THE 2ND MEMBER OF THE NEOGENE JIAOWEI FORMATION IN OIL FIELD A, WEIXINAN DEPRESSION%地震沉积学在涠西南凹陷A油田新近系角尾组二段I油组沉积微相刻画中的应用

    Institute of Scientific and Technical Information of China (English)

    付英娟; 林承焰; 孟祥君; 张宪国; 文子桃; 陈仕臻

    2016-01-01

    A油田位于北部湾盆地的涠西南凹陷,新近系角尾组二段I油组(J2I)为主要的储层,油组内部不同微相砂体厚度、岩性存在差异,并且A油田为海上油田,钻井少,井网分布不规则,这些因素制约了J2I油组井间沉积微相刻画.本文从井点出发,通过岩心资料确定了井点沉积微相特征.充分利用地震资料,运用地震沉积学的研究方法,对研究区井间沉积微相进行精细刻画.运用分频解释技术和等时地层切片生成层位技术,井震结合,确定了最小等时研究单元,即J2I油组的I-1小层和I-2小层.将小层界面作为地震属性提取的时窗,并对提取的地震属性进行属性—砂厚的相关性分析,将相关性最大的属性作为沉积相划分的主要依据.通过J2I油组2个小层的沉积微相的刻画,分析了J2I油组“临滨砂坝—浅滩”的纵向沉积演化.

  20. A calculation of denudation amount on Palaeogene-Neogene unconformity in Shengtuo area of Dongying sag using Milankovitch cycle method%利用米氏旋回法计算东营凹陷胜坨地区古近-新近系不整合的剥蚀量

    Institute of Scientific and Technical Information of China (English)

    张海峰; 姚益民; 何青芳; 边雪梅

    2008-01-01

    东营凹陷古近系与新近系之间存在一区域不整合面,该不整合面抬升剥蚀过程的恢复和剥蚀量计算,对恢复区内埋藏史、热史以及生烃史有重要意义.通过对东营凹陷胜坨地区24口钻井测井资料的分析研究,利用米氏旋回地层学方法获得的地层地质年龄、沉积速率作为沉积速率剥蚀量计算方法的参数,计算出了该地区古近-新近系不整合的剥蚀量,所获得的结果与现有的地质认识吻合较好.

  1. Element geochemistry of the Neogene Zhujiang formation mudstones in Lufeng depression, Pearl River Mouth Basin and its geological implication%珠江口盆地陆丰凹陷珠江组泥岩元素地球化学组成及意义

    Institute of Scientific and Technical Information of China (English)

    焦鹏; 郭建华; 张向涛; 张琳婷; 王张虎

    2016-01-01

    在珠江口盆地陆丰凹陷,选择5口井19件珠江组泥岩样品,分析元素(包括常量、微量和稀土)地球化学组成,并在此基础上,结合区域地质背景,探讨地质意义,主要是该沉积时期的沉积环境、物源区性质、构造背景及物源区的风化特征。研究结果表明:研究区泥岩的Al2O3,K2O,MgO,SiO2与PAAS的质量分数相近,富集Na2O和CaO,贫MnO和P2O5。不相容元素Th质量分数较高,指示物源区供应的中酸性碎屑组分较多,高强场元素Sr的平均质量分数接近于后太古宙页岩(PAAS)质量分数平均值而远低于大陆上地壳(UCC)质量分数平均值;Ta 的平均质量分数介于 UCC 和 PAAS 的之间,而 Hf 的平均质量分数比 UCC 的低,比 PAAS 的高;w(∑LREE)/w(∑HREE)和[w(La)/w(Yb)]N均值分别为8.89和10.16,轻重稀土分异明显;陆丰凹陷早中新世属于潮湿气候下的海陆过渡沉积,总体处于弱氧化−还原、半咸水沉积环境,西北部和中部沉积水体较深,东北部次深,东南部较浅,而东北部和东南部的水体盐度要比西北部和中部的水体盐度高。珠江组源岩主要为来源于上地壳的长英质岩石,西北部源区的构造背景具有类似活动大陆边缘的特征,东北部源区的构造背景具有类似被动大陆边缘的特征,东南部源区的构造背景具有类似岛弧的特征,中部为东北部和西北部物源交汇区。利用指数CIA指数和ICV揭示出东沙隆起、华南沿海气候条件相似(温暖、湿润),其中西北部源区经历的化学风化作用最强,东南部次之,东北部最弱。%According to regional geological background, the geological significance mainly including the sedimentary environment, provenance attribute, tectonic setting and weathering of provenance were investigated based on the geographical and chemical formation of elements including the major elements, trace elements and rare earth elements analysis of 5 wells with 19 Zhujiang mudstone samples collected from the Lufeng depression, Pearl River Mouth Basin. The results show that the mass fraction of Al2O3,K2O,MgO and SiO2 is similar to that of PAAS of the mudstone in the research areas, with the enriched Na2O and CaO, lacking of MnO and P2O5. The mass fraction of the incompatibleelements The is higher and the acidic clastic components supplied in the indicating source area are more. The average mass fraction of the high field-strength element (HFSE) Sr is close to that of the post archean shale (PAAS),but is much lower than that of the upper continental crust(UCC).The average mass fraction of Ta is between that of UCC and PAAS, nevertheless, the average mass fraction of Hf is lower than that of UCC and higher than that of PAAS. The ratio of mass fraction of∑LREE to∑HREE (8.89) and that La to Yb (10.16) suggests a distinct difference between LREE and HREE. Lufeng depression is marine-continental transition depositional sediment which is formed in humid climate, and its paleo-environment is under weak oxidation-education and brackish half-salt water condition. The sedimentary water during Early Miocene in the northwest and central is relatively deep, while that in the northeast is less deep and that in southeast is comparatively shallow. The water salinity in the southeast and northeast is higher than that in the northwest and central part. The parental rocks of Zhujiang formation are mainly supracrustal felsic rocks, the tectonic background of active continental margin in northwest, the tectonic background of passive continental margin in northeast, the tectonic background of arc in southeast, and the provenance in central part is an intersectional area of the ones in northeast and northwest. Chemical index of alteration (CIA) and index chemical variation (ICV) reveal that the climatic conditions of the Dongsha Massif and coastal region of South China in early Miocene are similar (warm and humid),and the order of the chemical intensity of the source areas is in the northwest, southeast and northeast.

  2. Les Cricetidae (Mammalia, Rodentia) du Néogène Moyen de Vieux-Collonges. Partie 2 : Cricetodontinae incertae sedis, Melissiodontinae, Platacanthomyinae, et Anomalomyinae = Cricetidae (Mammalia, Rodentia) of the middle Neogene of Vieux Collonges. France. Part 2 : Cricetodontinae incertae sedis, Melissiodontinae, Platacanthomyinae, et Anomalomyinae

    NARCIS (Netherlands)

    Mein, P.; Freudenthal, M.

    1981-01-01

    Apart from the common cricetid fauna, the site of Vieux-Collonges contains a number of rare forms: Lartetomys, Melissiodon, Neocometes, and Anomalomys. This scarce material is described and compared with material from other European localities. The stratigraphie position of Vieux-Collonges is discus

  3. Submarine topography and faulting in Bahia de Banderas, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez, Roman [Instituto de Investigaciones en Matematicas Aplicadas y en Sistemas, Universidad Nacional Autonoma de Mexico, Mexico D.F (Mexico)

    2007-04-15

    A digital elevation model of Bahia de Banderas and its offshore continuation to the Middle America Trench (MAT) is built from a data set of 6872 bathymetric soundings. Two new, offshore basins and several, previously unknown faults within the bay are also identified. The south flank of Banderas canyon is considerably steeper than the north one. This asymmetry and the seismic activity present lead to propose that Banderas Canyon has a half-graben structure of the fault growth type, and reverse drag geometry, which originates in an extensional basin oriented N-S. The canyon is divided in two sections that trend in different directions. The older section of the canyon, trending E-W, is probably Late Miocene; the associated Banderas Fault is suggested to extend westward, down to the MAT along a section that complements that of the half-graben. The section of Banderas Canyon trending NE and continuing into Banderas Valley is identified as a younger portion of the structure. The older and the younger portions of the canyon appear to be active presently. A group of faults also trending NE seem to be associated with the change in direction of the canyon. These results support the hypothesis that the structure of Banderas Canyon is a half-graben, and they strengthen the idea that it is the limit between the region to the north that underwent extension in the Miocene, and the region to the south that did not experienced it. [Spanish] Un modelo digital de elevacion de Bahia de Banderas y su continuacion costa afuera hasta la Trinchera Mesoamericana se construye con 6872 sondeos batimetricos. Se identifi can dos nuevas cuencas costa afuera y tambien varias fallas, hasta ahora no reportadas, dentro de la bahia. El fl anco sur del Canon de Banderas es considerablemente mas empinado que el flanco norte. Esta asimetria, junto con la actividad sismica presente, lleva a proponer que el Canon de Banderas tiene una estructura de semi-graben del tipo de crecimiento de falla, con

  4. Acoustic profiling and surface imaging of the coastal area near the subduction zone: the eastern coastal area of Boso Peninsula, Central Japan.

    Science.gov (United States)

    Furuyama, S.; Sato, T.

    2016-12-01

    The plate motion of the Philippine Sea plate and the Pacific plate influences geology of coastal area in the Pacific side in Japan and sometime causes extensive damage of human activity, such as the Great East Japan Earthquake. It is important to understand the geological structures in a coastal area for disaster prevention. Especially, rapid equipment of geoinformations is highly demanded in the Kanto region where covers capital Tokyo area. Geological Survey of Japan investigated the eastern coastal area in Boso Peninsula, eastern part of the Kanto region, Japan within two years from 2014 to 2015. We obtained seismic sections of ca. 1100 km in total length with a boomer and multi-channel streamer (24 channel with 3.125 m spacing) and report the geological significance of the subsurface structures. The survey area is divided into the northern part of Kujukuri area, the southern part of Kujukuri area, the coastal part of Kujukuri area based on topography and geological structures. In these Kujukuri areas, two strata that show distinct stratification bounded by distinct unconformity distribute and we define them as the Kujukuri A Unit and the Kujukuri B Unit, in ascending order. The lower sequence has some folds and normal faults. These folds that deformed the Kujukuri B Unit extend toward north-northeast in the northern part of Kujukuri area. They contributed to development of wide shelf distributed in this area. In the southern part of Kujukuri area, a lot of faults deformed the Kujukuri B Unit and some of them displaced the Kujukuri A Unit over 10 msec (two way travel). Normal faults developed in the Kujukuri B Unit over 10 msec made grabens and half grabens in the coastal part of Kujukuri area and these grabens and half grabens could make the lowland in the Kujukuri coastal area. The combination of these geological structures identified in the Kujukuri areas could reflect the transition of stress field associated with the subduction of the Philippine Sea plate

  5. Late Mesozoic basin and range tectonics and related magmatism in Southeast China

    Directory of Open Access Journals (Sweden)

    Dezi Wang

    2012-03-01

    Full Text Available During the Late Mesozoic Middle Jurassic–Late Cretaceous, basin and range tectonics and associated magmatism representative of an extensional tectonic setting was widespread in southeastern China as a result of Pacific Plate subduction. Basin tectonics consists of post-orogenic (Type I and intra-continental extensional basins (Type II. Type I basins developed in the piedmont and intraland during the Late Triassic to Early Jurassic, in which coarse-grained terrestrial clastic sediments were deposited. Type II basins formed during intra-continental crustal thinning and were characterized by the development of grabens and half-grabens. Graben basins were mainly generated during the Middle Jurassic and were associated with bimodal volcanism. Sediments in half-grabens are intercalated with rhyolitic tuffs and lavas and are Early Cretaceous in age with a dominance of Late Cretaceous–Paleogene red beds. Ranges are composed of granitoids and bimodal volcanic rocks, A-type granites and dome-type metamorphic core complexes. The authors analyzed lithological, geochemical and geochronological features of the Late Mesozoic igneous rock assemblages and proposed some geodynamical constraints on forming the basin and range tectonics of South China. A comparison of the similarities and differences of basin and range tectonics between the eastern and western shores of the Pacific is made, and the geodynamical evolution model of the Southeast China Block during Late Mesozoic is discussed. Studied results suggest that the basin and range terrane within South China developed on a pre-Mesozoic folded belt was derived from a polyphase tectonic evolution mainly constrained by subduction of the western Pacific Plate since the Late Mesozoic, leading to formation of various magmatism in a back-arc extensional setting. Its geodynamic mechanism can compare with that of basin and range tectonics in the eastern shore of the Pacific. Differences of basin and range

  6. Crustal shortening followed by extensional collapse of the Cordilleran orogenic belt in northwestern Montana: Evidence from vintage seismic reflection profiles acquired in the Swan Range and Swan Valley

    Science.gov (United States)

    Rutherford, B. S.; Speece, M. A.; Stickney, M. C.; Mosolf, J. G.

    2013-12-01

    half-graben fill suggest up to 1.5 km of Cenozoic basin filling sediments are present. Refraction tomography velocity modeling of distinct refracted arrivals, prevalent in the gathers, constrain a half-graben geometry for the Swan Valley. Signal attenuation within the low-velocity valley fill make correlation of reflectors at the depth of the décollement impossible underneath the Swan Valley. Prestack depth migration of the sections is anticipated to improve geometric constraints on major structural features of the Swan Range and Swan Valley.

  7. Geophysical evidence of crustal-heterogeneity control of fault growth in the Neocomian Iguatu basin, NE Brazil

    Science.gov (United States)

    de Castro, David L.; Bezerra, Francisco H. R.; Castelo Branco, Raimundo M. G.

    2008-11-01

    Models of fault growth propose that rift initiation starts with short fault segments. Knowledge of the growth of these segments and their interactions is important to understanding rift geometry and evolution. In the northern part of the Borborema Province, northeastern Brazil, a continental-scale, Cretaceous extensional system of faults has been observed to have reactivated ductile Precambrian shear zones. The faults form small grabens that represent the rift stage of the sedimentary basins. We integrated airborne radiometric and magnetic data with terrestrial gravity survey to investigate the influence of crustal heterogeneity on fault growth and the development of the extensional faults in one of these grabens, the Iguatu basin. Previous studies presented geophysical data, which provide evidence that the Iguatu basin contains a half-graben geometry. In our study, gravity and airborne geophysical data indicate that the basement of the Iguatu basin is part of a heterogeneous structural framework composed of two structural domains, is affected by several ductile shear zones and intruded by a few granite bodies. The gravity modeling reveals that this basin is composed of three right-bend en echelon fault segments. They form a sigmoid system of normal faults that accommodate the strong ˜90° bend of the Precambrian shear zones from E-W to roughly N-S. The growth of these segments led to the generation of two isolated depocenters. The overlapping fault segments link through relay ramps. Release faults that are nearly perpendicular or oblique to the three main fault segments form marginal strike ramps and horst structures in both depocenters. 3D-gravity modeling incorporates the presence of interfering sources of a heterogeneous structural framework. The modeling reveals a maximum sedimentary cover 1620 m thick, which occurs at the bend of the reactivated shear zones. The gravity signature of a possible granite body, after removal of the gravity effect of the basin

  8. Early-stage rifting of the northern Tyrrhenian Sea Basin: Results from a combined wide-angle and multichannel seismic study

    Science.gov (United States)

    Moeller, S.; Grevemeyer, I.; Ranero, C. R.; Berndt, C.; Klaeschen, D.; Sallares, V.; Zitellini, N.; Franco, R.

    2013-08-01

    Extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins. The mechanisms that operate during the early stage of crustal extension are still intensely debated. We present the results from coincident multichannel seismic and wide-angle seismic profiles that transect across the northern Tyrrhenian Sea Basin. The profiles cross the Corsica Basin (France) to the Latium Margin (Italy) where the early-rift stage of the basin is well preserved. We found two domains, each with a distinct tectonic style, heat flow and crustal thickness. One domain is the Corsica Basin in the west that formed before the main rift phase of the northern Tyrrhenian Sea opening (˜8-4 Ma). The second domain is rifted continental crust characterized by tilted blocks and half-graben structures in the central region and at the Latium Margin. These two domains are separated by a deep (˜10 km) sedimentary complex of the eastern portion of the Corsica Basin. Travel-time tomography of wide-angle seismic data reveals the crustal architecture and a subhorizontal 15-17 ± 1 km deep Moho discontinuity under the basin. To estimate the amount of horizontal extension we have identified the pre-, syn-, and post-tectonic sedimentary units and calculated the relative displacement of faults. We found that major faults initiated at angles of 45°-50° and that the rifted domain is horizontally stretched by a factor of β ˜ 1.3 (˜8-10 mm/a). The crust has been thinned from ˜24 to ˜17 km indicating a similar amount of extension (˜30%). The transect represents one of the best imaged early rifts and implies that the formation of crustal-scale detachments, or long-lived low-angle normal faults, is not a general feature that controls the rift initiation of continental crust. Other young rift basins, like the Gulf of Corinth, the Suez Rift or Lake Baikal, display features resembling the northern Tyrrhenian Basin, suggesting that half-graben

  9. Fault kinematic and Mesozoic paleo-stress evolution of the Hoop fault complex, Barents Sea

    Science.gov (United States)

    Etchebes, Marie; Athmer, Wiebke; Stueland, Eirik; Robertson, Sarah C.; Bounaim, Aicha; Steckhan, Dirk; Hellem Boe, Trond; Brenna, Trond; Sonneland, Lars; Reidar Granli, John

    2016-04-01

    The Hoop fault complex is an extensional fault system characterized by a series of multiscale half- and full-grabens trending NNE-SSW, NE-SW and E-W, and transfer zones striking ENE-WSW. In a joint collaboration between OMV Norge and Schlumberger Stavanger Research, the tectonic history of the Hoop area was assessed. A dense fault network was extracted from 3D seismic data using a novel workflow for mapping large and complex fault systems. The characterization of the fault systems was performed by integrating observations from (1) fault plane analysis, (2) geometrical shapes and crosscutting relationships of the different fault sets, (3) time-thickness maps, and (4) by establishing the relative timing of the tectonic events on key seismic lines orthogonal to the main fault strike azimuths. At least four successive extensional tectonic events affecting the Hoop fault complex have been identified in the Mesozoic. The first tectonic event is characterized by an Upper Triassic extensional event with an E-W trending maximum horizontal paleo-stress direction (Phase 1). This event led to new accommodation space established as a set of full-grabens. The grabens were orthogonally crosscut during the Middle Jurassic by a set of NNE-SSW striking grabens and half-grabens (Phase 2). Phase 3 was inferred from a set of E-W striking reactivated normal faults sealed by the Upper Jurassic-Lower Cretaceous sequence. In the Lower Cretaceous, the general trend of the maximum horizontal paleo-stress axis of Phase 2 rotates clockwise from NNE-SSW to NE-SW (Phase 4). This stress rotation induced the reactivation of Phase 2 and Phase 3 normal fault sets, producing west-dipping half-grabens/tilt-block systems and transtensional fault zones. A comparison between our results and the Mesozoic regional-scale tectonic events published for the Atlantic-Arctic region agrees with our reconstructed paleo-stress history. This implies that the Hoop fault complex is the result of far-field forces

  10. Positive inversion of extensional footwalls in the southern Serra do Espinhaço, Brazil - insights from sandbox laboratory experiments

    Directory of Open Access Journals (Sweden)

    Caroline J.S. Gomes

    2006-06-01

    Full Text Available Analogue experiments were carried out to get insights into the processes governing positive inversion during the foreland propagating thrust tectonics in the southern Serra do Espinhaço, a Brasiliano/Panafrican foldthrust belt in southeast Brazil. In particular, model listric half-grabens were inverted by applying contractional displacement to the footwall blocks. We investigated two different inversion conditions in listric half-grabens: (i extensional and contractional detachments at the same level and (ii at different positions. The models revealed that the development of a forward-breaking thrust system occurs in the basin synrift deposits, by contractional translation of the extensional footwall block when the extensional and contractional master faults do not coincide. Our experiments show the tectonic imbrication between basement and synrift sequences which characterizes the southern Serra do Espinhaço, and support the location in the eastern mountain range domain of the Espinhaço rift master fault system, which is not exposed at the surface.Em experimentos de areia foi simulada a inversão positiva com o intuito de investigar os processos que governam a tectônica da Cordilheira do Espinhaço Meridional na borda sudeste do Cráton São Francisco. Analisou-se, em particular, a evolução progressiva de hemigrabens, com falha de borda lístrica, na qual o fechamento da bacia ocorreu através da translação do bloco do muro da falha mestra. Duas condições foram investigadas: (i os descolamentos distensivos e compressivos ocorrem na mesma cota e (ii os descolamentos situam-se em posições diferentes. Os modelos revelaram que um sistema de falhas de cavalgamento com estilo colapso da lapa se desenvolve no interior do depósito sinrift quando os descolamentos não coincidem. O imbricamento entre escamas do pré- e sinrift, nos modelos, permite esboçar uma analogia com a tectônica da porção sul da Cordilheira do Espinhaço e situar a

  11. China's Beech Forests in the Pre-Quaternary

    Directory of Open Access Journals (Sweden)

    L. Yu-Sheng

    1998-01-01

    Full Text Available Fagus in China is never dominant in Late Cretaceous and Tertiary floras although it might reach its highest diversity in the Miocene. The genus Fagus was more widely distributed during the Palaeogene than in the Neogene. Furthermore, the ecological requirements of Fagus in the Palaeogene seem much broader than those in the Neogene onwards. This is because the Palaeogene floras containing Fagus lived in various conditions from an arid and hot climate to a humid and warm habitat. Additionally, Fagus then coexisted with many kinds of hygrophilous, thermophilous and xerophilous plants. However, the wide distribution, broad ecological adaptation and species composition changed greatly in the Neogene. The Neogene Fagus-containing floras are slightly more similar to the modern beech forests than the Palaeogene ones, although a big difference remains. Chinese fossil data document the post-Tertiary development of the modern beech forests. doi:10.1002/mmng.19980010111

  12. Holocene benthonic foraminifera from the shelf sediments of Kerala coast

    Digital Repository Service at National Institute of Oceanography (India)

    Setty, M.G.A.P.

    Of the 32 species of benthic foraminifera recovered here some show definite Indo-Pacific affinity. Ecological parameters which govern this offshore region are considered. Several species show similarities with those found in the Neogene while...

  13. Tucano Sul Basin: petroleum habitat; Bacia de Tucano Sul - habitat do petroleo

    Energy Technology Data Exchange (ETDEWEB)

    Schaller, Hannfried; Magalhaes, Celso Carvalho; Carvalho, Renato Kramberger

    2008-07-01

    The South Tucano Basin is located in the State of Bahia, and is an integrating part of the Northeast Brazilian intracratonic graben system which embraces the Jatoba, Tucano (North, Central and South), and Reconcavo Basins. It comprises a Late Jurassic - Early Cretaceous system of half grabens that evolved during the preliminary stages of continental break related to the South Atlantic opening, from which it was aborted during the Aptian. Close to one hundred wells have so far been drilled in the area, leading to the discovery of about 35 million m{sup 3} (220 mmboe) of oil equivalent, comprised in about ten small oil and gas pools, among which Conceicao, Querera, Lagoa Branca, Estacao de Irai and Sempre Viva . Organic shales, that area found in the lower half of the Candeias Fm, are interpreted as the main source rocks, and in regard to the stratigraphic position of the oil pool, three petroleum-systems are recognized in the basin: Candeias-Sergi; Candeias-Candeias, and Candeias-Ilhas. (author)

  14. Regional correlation of deposition sequences in the southern Mesozoic marine province, northwestern Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Satterfield, J.I.; Oldow, J.S. (Rice Univ., Houston, TX (United States). Dept. of Geology and Geophysics)

    1993-04-01

    Strata of the Mesozoic marine province of a northwestern Nevada, deposited in subaerial to deep marine environment in a backarc basin, underwent severe deformation during the late Mesozoic. Restoration of stratigraphic relations among constituent volcanic, volcanogenic, carbonate, and continentally-derived siliciclastic rocks has been hampered by sparse biostratigraphic age control. Regional correlation of coeval facies is made possible by coupling depositional sequences with biostratigraphic control in the southwestern Gabbs Valley Range, the southern Shoshone Mountains, and the southern Clan Alpine Mountains, which serve as reference sections for Late Triassic and Early Jurassic ammonite zonation of western North America. Differentiation between regionally significant sequence boundaries and those of limited areal extent is possible only by linking the biostratigraphy and physical stratigraphic relations, such as abrupt vertical transitions in lithology corresponding to large facies changes. Physical stratigraphic relations alone are not adequate for correlation ad indicated by the diachronous initiation of Early to Middle( ) Jurassic deposition in half-graben basins (Dunlap Formation) which locally cloaks eustatically( ) controlled depositional sequences. Within these limitations, three regionally extensive sequences are recognized in the reference sections and have lower boundaries at the base of Upper Triassic shallow marine to deltaic carbonate-clastic rocks (Luning Formation) and at the base and within subtidal to offshore-marine carbonate and clastic rocks (Triassic and Jurassic Volcano Peak Group).

  15. Facies analysis of a Toarcian-Bajocian shallow marine/coastal succession (Bardas Blancas Formation) in northern Neuquén Basin, Mendoza province, Argentina

    Science.gov (United States)

    Bressan, Graciela S.; Kietzmann, Diego A.; Palma, Ricardo M.

    2013-04-01

    Strata of the Bardas Blancas Formation (lower Toarcian-lower Bajocian) are exposed in northern Neuquén Basin. Five sections have been studied in this work. Shoreface/delta front to offshore deposits predominate in four of the sections studied exhibiting a high abundance of hummocky cross-stratified, horizontally bedded and massive sandstones, as well as massive and laminated mudstones. Shell beds and trace fossils of the mixed Skolithos-Cruziana ichnofacies appear in sandstone beds, being related with storm event deposition. Gravel deposits are frequent in only one of these sections, with planar cross-stratified, normal graded and massive orthoconglomerates characterizing fan deltas interstratified with shoreface facies. A fifth outcrop exhibiting planar cross-stratified orthoconglomerates, pebbly sandstones with low-angle stratification and laminated mudstones have been interpreted as fluvial channel deposits and overbank facies. The analysis of the vertical distribution of facies and the recognition of stratigraphic surfaces in two sections in Río Potimalal area let recognized four transgressive-regressive sequences. Forced regressive events are recognized in the regressive intervals. Comparison of vertical distribution of facies also shows differences in thickness in the lower interval among the sections studied. This would be related to variations in accommodation space by previous half-graben structures. The succession shows a retrogradational arrangement of facies related with a widespread transgressive period. Lateral variation of facies let recognize the deepening of the basin through the southwest.

  16. Venus: Geology of Beta Regio rift system

    Science.gov (United States)

    Nikishin, A. M.; Borozdin, V. K.; Bobina, N. N.

    1992-01-01

    Beta Regio is characterized by the existence of rift structures. We compiled new geologic maps of Beta Regio according to Magellan data. There are many large uplifted tesserae on beta upland. These tesserae are partly buried by younger volcanic cover. We can conclude, using these observations, that Beta upland formed mainly due to lithospheric tectonic uplifting and was only partly constructed by volcanism. Theia Mons is the center of the Beta rift system. Many rift belts are distributed radially to Theia Mons. Typical widths of rifts are 40-160 km. Rift valleys are structurally represented by crustal grabens or half-grabens. There are symmetrical and asymmetrical rifts. Many rifts have shoulder uplifts up to 0.5-1 km high and 40-60 km wide. Preliminary analysis for rift valley structural cross sections lead to the conclusion that rifts originated due to 5-10 percent crustal extension. Many rifts traverse Beta upland and spread to the surrounding lowlands. We can assume because of these data that Beta rift system has an active-passive origin. It formed due to regional tectonic lithospheric extension. Rifting was accelerated by upper-mantle hot spot origination under the center of passive extension (under the Beta Regio).

  17. Quaternary evolution of the Southern Apennines coastal plains: a review

    Science.gov (United States)

    Santangelo, Nicoletta; Romano, Paola; Ascione, Alessandra; Russo Ermolli, Elda

    2017-02-01

    The Quaternary evolution of the main coastal basins located along the southwestern margin of the Southern Apennines has been reconstructed by integrating the huge amount of existing stratigraphical and geomorphological data. The information produced in the last twenty years has shed new light on the recent (late Middle Pleistocene to Present) history of the Campanian and Sele plains or basins. During the early Quaternary, the analysed coastal basins originated as half-grabens in response to opening processes active since the late Tortonian in the southern Tyrrhenian back-arc basin. In some of these basins (e.g. the Campanian Plain), volcanism has also played an important role. In the inner sectors of the coastal basins, the complex interplay between block faulting, sedimentary inputs and glacioeustatic fluctuations gave rise to relative sea-level change and related coastline migrations, leading to the formation of the present-day coastal plains. In the Sele Plain basin, the construction of the present-day landscape mainly resulted from the substantial ceasing of subsidence in the final part of the Middle Pleistocene. Conversely, a strong contribution to the recent evolution of the Campanian Plain has been provided by abundant volcaniclastic aggradation, able to hinder the effect of the vertical motions that occurred in the last 100 ka.

  18. Shallow marine sedimentation within an active margin basin, James Ross Island, Antarctica

    Science.gov (United States)

    Pirrie, Duncan

    1989-06-01

    The Santa Marta Formation exposed on northern James Ross Island, Antarctica, represents shallow marine shelf sedimentation within an active margin basin. The formation is approximately 1000 m thick, is of uppermost Santonian to Campanian age and represents part of a 5000-6000 m thick sedimentary sequence forming the Larsen Basin. The Larsen Basin represents either a back-arc basin, or a half-graben basin, developed on the extending margin of the Weddell Sea. Twelve sedimentary facies have been recognised, which can be subdivided into two groups: those which are controlled by shelf processes and those which are related to active arc volcanism. Background shelf processes include fair-weather suspension sedimentation, storm sands and rare tidal current reworking. Active arc processes include direct settling of airfall detritus and rapid resedimentation of volcaniclastic detritus by sandy debris-flows and both high- and low-concentration turbidity currents. In addition sheet conglomerates represent debris flows that evolved from syn-sedimentary slumps. Two facies associations representing a mid to outer shelf and an inner shelf depositional setting respectively can be distinguished, with an apparent regression in the ?mid to late Campanian.

  19. Late Ordovician glaciogenic reservoir heterogeneity: An example from the Murzuq Basin, Libya

    Energy Technology Data Exchange (ETDEWEB)

    Le Heron, Daniel Paul [CASP, Department of Earth Sciences, University of Cambridge, West Building, 181A Huntingdon Road, CB30DH Cambridge (United Kingdom); Craig, Jonathan [ENI E and P, V. Emilia, 1, San Donato Milanese, MI 20097 (Italy); Sutcliffe, Owen E. [Neftex Petroleum Consultants Ltd., 80A Corinthian Court, Milton Park, Abingdon, Oxfordshire OX14 4RY (United Kingdom); Whittington, Robert [IGES, University of Wales, Aberystwyth, Ceredigion SY23 3DB (United Kingdom)

    2006-07-15

    In North Africa, Late Ordovician glaciogenic reservoirs contain large volume of recoverable hydrocarbon reserves, but their heterogeneity and internal complexity means they are poorly understood. To improve this understanding, this paper presents the case study of the Murzuq Basin, SW Libya, and a synthesis of the stratigraphic architecture of Upper Ordovician glaciogenic reservoirs (the Mamuniyat Formation) within it. Particular attention is paid to regionally extensive stratigraphic boundaries and the geometry of sandstone units of potential reservoir quality. Four disconformity-bound units are recognised, the bounding surfaces of which are flat or of high relief. Unit 1 (the oldest) and Unit 3 are mud-dominated and tend towards non-reservoir. In contrast, Units 2 and 4 (the youngest) are sand-dominated, have poor to excellent reservoir quality but distinctly different sedimentological architectures across the basin. Unit 2 comprises transitions from glaciofluvial/intertidal sandstones to offshore turbidites and formed exclusively during glacial retreat. The occurrence of a significant palaeotopography affected sandbody geometry with glaciofluvial/intertidal deposits concentrating in the lee of these palaeohighs or infilling the bottom of tunnel valleys. Unit 4 is a compound stratigraphic unit recording the effects of glacial retreat and isostatic rebound. In deep marine settings, turbidite fans were deposited during retreat but in shallow water settings, structural reactivation and sediment reworking had a more profound effect on sedimentation. Sedimentological architectures are variable at this level and include prograding coarse clastic wedges (away from a palaeohigh) or the infill of half-graben basins during isostatic rebound. (author)

  20. Low Angle Normal Fault System Controls the Structure Evolution of Baiyun Deepwater Basin and Its Lithosphere Thinning, Northern South China Sea

    Science.gov (United States)

    Zhao, Y.; Ren, J.; Yang, L.

    2015-12-01

    The discovery of the transition area from ~30 km to weakly thinned continental crust (<12 km) in Baiyun deepwater basin, Northern South China Sea leads to two questions: What controls extreme crustal thinning and what is the nature of Baiyun basin. The 3D seismic data newly acquired show that Baiyun basin is an asymmetric half graben mainly controlled by a set of north-dipping normal faults converging in deep. By employing the principle of back-stripping, we estimate the fault dips and slip amount would be in the absence of post-rift sediments and seawater loading. Results show these Middle Eocene faults were extremely active, with a high accumulation horizontal displacement (> 10 km) and an initial very low angle (<7°), followed by a rotated into sub-horizontal. A general scenario for extension of the uppermost continental crust probably includes simultaneous operation of low angle normal fault (F1) as well as parallel arrays of step-faults (domino-faults, f2-f9). Under such a scenario, it shows no obvious extension discrepancy in Baiyun basin. Our results indicate that Baiyun sag preserves information recording the continent thinning before the seafloor spreading, and it could be an abandoned inner rifted basin.

  1. Anatomy of a rift system: Triassic-Jurassic basins of eastern North America

    Energy Technology Data Exchange (ETDEWEB)

    Schlische, R.W. (Rutgers Univ., New Brunswick, NJ (United States)); Olsen, P.E. (Columbia Univ., Palisades, NY (United States))

    1991-03-01

    Basins containing the early Mesozoic Newark Supergroup formed during the incipient rifting of Pangaea. The basins are characterized by the following: (1) The border fault systems (BFS) represent reactivated older faults. (2) A regionally persistent northwest-southeast to west-northeast-east-southeast extension direction reactivated northeast- to north-striking structures as predominantly normal dip-slip faults. (3) The half-grabens are lozenge-shaped basins in which subsidence-fault slip was greatest at or near the center of the BFS and decreased to zero toward either end. (4) Transverse folds in the hanging walls immediately adjacent to the BFS formed as a result of higher-frequency variations in subsidence. (5) Subsidence also decreased in a direction perpendicular to the BFS. (6) Intrabasinal faults are overwhelmingly synthetic and predominantly post-depositional. (7) Younger strata progressively onlap prerift rocks of the hanging wall block; this indicates that the basins grew both in width and length as they filled. (8) In all basins initial sedimentation was fluvial, reflecting an oversupply of sediment with respect to basin capacity. (9) Sediments were derived largely from the hanging wall block, which sloped toward the basin, and from streams that entered the basin axially; a direct footwall source was minor, owing to footwall uplift. (10) In strike-slip-dominated basins, subsidence was considerably less than in dip-slip basins, and mosaics of strike- and dip-slip faults are common.

  2. 3-D numerical models of viscous flow applied to fold nappes and the Rawil depression in the Helvetic nappe system (western Switzerland)

    Science.gov (United States)

    von Tscharner, M.; Schmalholz, S. M.; Epard, J.-L.

    2016-05-01

    The Helvetic nappe system exhibits three-dimensional (3-D) features such as the lateral variation in geometry between the Morcles and Doldenhorn fold nappes or the Rawil depression. We perform 3-D finite element simulations of linear and power-law viscous flow to investigate fold nappe formation during shortening of a half graben with laterally varying thickness. 3-D ellipsoids and corresponding 2-D intersection ellipses are used to quantify finite strain. Fold nappes which formed above a thicker graben have (i) larger amplitudes, (ii) a less sheared and thinned overturned limb, and (iii) a larger thickness than fold nappes formed above a thinner graben. These results agree with observations for the Morcles and Doldenhorn nappes. We also perform 3-D simulations for a tectonic scenario suggested for the evolution of the Rawil depression. The basement is shortened and extended laterally and includes a graben which is oblique to the shortening direction and acts as mechanical weak zone. The graben causes laterally varying basement uplift generating a depression whose amplitude depends on the graben orientation and the stress exponent of basement and sediments. The axial plunge of the depression is smaller (approximately 10°) than the observed plunge (approximately 30°) indicating that additional processes are required to explain the geometry of the Rawil depression.

  3. Continental rift-setting and evolution of Neoproterozoic Sindreth Basin in NW-India

    Indian Academy of Sciences (India)

    Stefan Schöbel; Kamal K Sharma; Thorsten Hörbrand; Theresa Böhm; Ines Donhauser; Helga de Wall

    2017-08-01

    The Neoproterozoic Sindreth Basin, NW India, and its surrounding area represent a half graben structure situated between the undeformed Malani Igneous Suite (MIS) in the west and a corridor of coeval Cryogenian ductile deformation, anatexis and granite intrusion in the east. The main lithologies observed in the basin are conglomerate, fanglomerate, debris flow and lake deposits derived from a nearby continental provenance, intercalated with concurrent mafic and felsic lava flows. Based on geological traverses across the strike of the basin, we propose a three-fold classification comprising Lower Clastic Unit and an Upper Clastic Unit and a Bimodal (basalt–rhyolite) Volcanic Unit separating the two. Tilting due to basin inversion and faulting has been observed; however, the rocks are unmetamorphosed and show undisturbed primary sedimentary features. The stratigraphic record of the basin is characteristic for deposition and magmatism in a fault-related continental setting. Implications of the findings have been discussed in the context of Neoproterozoic crustal dynamics in NW India. This study provides conclusive evidence for a continental setting for Sindreth Basin evolution and contests the recent models of active subduction setting (either back-arc basin or accretionary sediments over a subduction zone).

  4. Tectonic characteristics and structural styles of a continental rifted basin: Revelation from deep seismic reflection profiles

    Directory of Open Access Journals (Sweden)

    Yuan Li

    2016-09-01

    Full Text Available The Fushan Depression is a half-graben rifted sub-basin located in the southeast of the Beibuwan Basin, South China Sea. The Paleogene Liushagang sequence is the main hydrocarbon-bearing stratigraphic unit in the sub-basin. Using three-dimensional (3-D seismic data and logging data over the sub-basin, we analyzed structural styles and sedimentary characteristics of the Liushagang sequence. Five types of structural styles were defined: ancient horst, traditional slope, flexure slope-break, faulted slope-break and multiple-stage faults slope, and interpretations for positions, background and development formations of each structural style were discussed. Structural framework across the sub-basin reveals that the most remarkable tectonic setting is represented by the central transfer zone (CTZ which divides the sub-basin into two independent depressions, and two kinds of sequence architectures are summarized: (i the western multi-stage faults slope; (ii the eastern flexure slope break belt. Combined with regional stress field of the Fushan Depression, we got plane combinations of the faults, and finally built up plan distribution maps of structural system for main sequence. Also, we discussed the controlling factors mainly focused on subsidence history and background tectonic activities such as volcanic activity and earthquakes. The analysis of structural styles and tectonic evolution provides strong theoretical support for future prospecting in the Fushan sub-basin and other similar rifted basins of the Beibuwan Basin in South China Sea.

  5. Oil exploration and development in Marib/Al Jawf basin, Yemen Arab Republic

    Energy Technology Data Exchange (ETDEWEB)

    Maycock, I.D.

    1988-02-01

    In 1981, Yemen Hunt Oil Company (YHOC) negotiated a production-sharing agreement covering 12,600 km/sup 2/ in the northeast part of the Yemen Arab Republic. A reconnaissance seismic program of 1864 km acquired in 1982 revealed the presence of a major half graben, designated the Marib/Al Jawf basin by YHOC. A sedimentary section up to 18,000 ft thick has been recognized. Geologic field mapping identified Jurassic carbonates covered by Cretaceous sands overlying Permian glaciolacustrine sediments, Paleozoic sandstones, or Precambrian basement. The first well, Alif-1, drilled in 1984, aimed at a possible Jurassic carbonate objective, encountered hydrocarbon-bearing sands in the Jurassic-Cretaceous transition between 5000 and 6000 ft. Appraisal and development drilling followed. The Alif field is believed to contain in excess of 400 million bbl of recoverable oil. Subsequent wildcat drilling has located additional accumulations while further amplifying basin stratigraphy. Rapid basin development took place in the Late Jurassic culminating with the deposition of Tithonian salt. The evaporites provide an excellent seal for hydrocarbons apparently sourced from restricted basin shales and trapped in rapidly deposited clastics.

  6. Oil exploration and development in Marib/Al Jawf basin, Yemen Arab Republic

    Energy Technology Data Exchange (ETDEWEB)

    Maycock, I.D.

    1986-07-01

    In 1981, Yemen Hunt Oil Company (YHOC) negotiated a production-sharing agreement covering 12,600 km/sup 2/ in the northeast part of the Yemen Arab Republic. A reconnaissance seismic program of 1864 km acquired in 1982 revealed the presence of a major half graben, designated the Marib/Al Jawf basin by YHOC. A sedimentary section up to 18,000 ft thick has been recognized. Geologic field mapping identified Jurassic carbonates covered by Cretaceous sands overlying Permian glaciolacustrine sediments, Paleozoic sandstones, or Precambrian basement. The first well drilled in 1984, aimed at a possible Jurassic carbonate objective, encountered hydrocarbon-bearing sands in the Jurassic-Cretaceous transition between 5000 and 6000 ft. A successful appraisal drilling program has demonstrated satisfactory lateral reservoir continuity. Further wildcat drilling demonstrates macro-unit correlation within the eastern part of the basin. Rapid basin development apparently commenced in the late Kimmeridgian, culminating with the deposition of Tithonian evaporites. Available geochemical analysis indicates sourcing from restricted-basin sediments. Excellent traps, reservoirs, and source beds underlying the Tithonian evaporites indicate that a significant new petroliferous province is present.

  7. Seismic stratigraphy of rift basins: techniques, methods and its application in the Reconcavo Basin; Sismoestratigrafia de bacias rifte: tecnicas, metodos e sua aplicacao na Bacia do Reconcavo

    Energy Technology Data Exchange (ETDEWEB)

    Kuchle, Juliano [Universidade Federal do Rio Grande do Sul (UFRGS). Inst. de Geociencias. Programa de Pos-Graduacao em Geociencias (Brazil)], e-mail: julianokuchle@yahoo.com.br; Scherer, Claiton Marlon dos Santos [Universidade Federal do Rio Grande do Sul (UFRGS). Inst. de Geociencias. Dept. de Paleontologia e Estratigrafia (Brazil)], e-mail: claiton.scherer@ufrgs.br

    2010-05-15

    This paper aims a proposal of interpretation and seismic stratigraphy systematic mapping of rift basins based on genetic concepts, as offered by the basic development of the Sequence Stratigraphy - the temporal interpretation of units based on concepts derived from variables and observable in depositional trends. So, rift basins are controlled by specifically variables and its relationships, which results in theoretical evolutional models. Those theoretical models are detailed as depositional trends denominated stacking patterns. Thus, from the stacking patterns, it is able to establish the inverse way analysis, picturing evolutional models and controlling variables. The main objective of this paper is the migration of the genetic tectonic-stratigraphic model of rift basins to the seismic platform, supported by the key-concepts of the seismic stratigraphy. This analysis is based on the recognition of seismic stratigraphic units which composes the tectonic system tracts - basic units of the framework, and these system tracts are formed by specific stacking patterns for each portion of the half Graben. As those stacking patterns reflect changes in the accommodation, stratigraphic surfaces and strata termination patterns are established. Therefore, a whole conceptual basis of seismic stratigraphy recognition and mapping is proposed, as well as a time determination of evolutional models in chronostratigraphic diagrams (Wheeler charts), to supply a useful tectonic-stratigraphic framework to hydrocarbon exploration. (author)

  8. Formation Laws of Inorganic Gas Pools in the Northern Jiangsu Basin

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In the Northern Jiangsu basin there are high pure CO2 gas pools, low condensed oil-containing CO2 gas pools, high condensed oil-containing CO2 gas pools and He-containing natural gas pools, with the d 13Cco2 (PDB) values ranging from - 2.87to - 6.50 3He/4He 3.71×10- 6 to 6.42×10- 6, R/Ra 2.64 to 4.5, 40Ar/36Ar 705 to 734, belonging to typical mantle source inorganic gas pools which are related to young magmatic activity. The gas layers occur in two major reservoir-caprock systems, the terrestrial Meso-Cenozoic clastic rock system and the marine Meso-Palaeozoic carbonate rock-clastic rock system. Controlled by the difference in the scale of traps in the two reservoir-caprock systems, large and medium-scale inorganic gas pools are formed in the marine Meso-Palaeozoic Group and only small ones are formed in the terrestrial Meso-Cenozoic strata. Inorganic gas pools in this basin are distributed along the two deep lithospheric faults on the west and south boundaries of the basin. Gas pools are developed at the intersected part of the ENE-trending faults that control the half graben and the E-W tenso-shear faults, mainly distributed near the Es1, Ny1 and Ny2-Q basalt eruption centres.

  9. Geometry of the inverted Cretaceous Chañarcillo Basin based on 2-D gravity and field data. An approach to the structure of the western Central Andes of northern Chile

    Directory of Open Access Journals (Sweden)

    F. Martínez

    2015-08-01

    Full Text Available This paper discusses an integrated approach that provides new ideas about the structural geometry of the NNE-striking, Cretaceous Chañarcillo Basin located along the eastern Coastal Cordillera in the western Central Andes of northern Chile (27–28° S. The results obtained from the integration of two transverse (E–W gravity profiles with previous geological information, show that the architecture of this basin is defined by a large NNE–SSE-trending and east-vergent anticline ("Tierra Amarilla Anticlinorium", which is related to the positive reactivation of a former Cretaceous normal fault (Elisa de Bordos Master Fault. Moreover, intercalations of high and low gravity anomalies and steep gravity gradients reveal a set of buried, west-tilted half-grabens associated with a synthetic normal fault pattern. These results, together with the uplift and folding style of the Cretaceous syn-rift recognized within the basin, suggest that their complete structural geometry could be explained by an inverted fault system linked to the shortening of pre-existing Cretaceous normal fault systems. Ages of the synorogenic deposits exposed unconformably over the frontal limb of the Tierra Amarilla Anticlinorium confirm a Late Cretaceous age for the Andean deformation and tectonic inversion of the basin.

  10. The link between tectonics and sedimentation in back-arc basins: New genetic constraints from the analysis of the Pannonian Basin

    Science.gov (United States)

    Balázs, A.; Matenco, L.; Magyar, I.; Horváth, F.; Cloetingh, S.

    2016-06-01

    The architecture of sedimentary basins reflects the relationship between accommodation space and sediment supply, their rates and localization being variable during basin evolution. The mechanisms driving the interplay between tectonics and sedimentation in extensional back-arc basins overlying rheological weak zones inherited from an earlier orogenic evolution are less understood. A typical example is the Pannonian back-arc basin of Central Europe. It is floored by continental lithosphere and was affected by large amounts of extension driven by the subduction rollback that took place in the Carpathians and/or Dinarides. A novel kinematic and seismic sequence stratigraphic interpretation calibrated by wells allows the quantification of the link between the formation of half grabens and coeval sedimentation in the Great Hungarian Plain part of the basin. While the lower order tectonic-induced cycles characterize the main phases of extension in various subbasins, the higher-order cyclicity and associated unconformities define individual moments of fault (re)activation. Our novel interpretation of a temporal and spatial migration of extension during Miocene times explains the contrasting present-day strike of various subbasins as a result of their gradual clockwise rotation. Incorporating the observed asymmetry, in particular the associated footwall exhumation, infers that the amount of extension is much larger than previously thought. The quantitative link between tectonics and sedimentation has allowed the definition of a novel model of sedimentation in asymmetric basins that can be ported to other natural scenarios of similarly hyperextended back-arc basins observed elsewhere.

  11. Cordilleran front range structural features in northwest Montana interpreted from vintage seismic reflection data

    Science.gov (United States)

    Porter, Mason C.; Rutherford, Bradley S.; Speece, Marvin A.; Mosolf, Jesse G.

    2016-04-01

    Industry seismic reflection data spanning the Rocky Mountain Cordillera front ranges of northwest Montana were reprocessed and interpreted in this study. Five seismic profiles represent 160 km of deep reflection data collected in 1983 that span the eastern Purcell anticlinorium, Rocky Mountain Trench (RMT), Rocky Mountain Basal Décollement (RMBD), and Lewis thrust. The data were reprocessed using modern techniques including refraction statics, pre-stack time migration (PSTM), and pre- and post-stack depth migration. Results indicate the RMBD is 8-13 km below the Earth's surface and dip 3-10° west. Evidence for the autochthonous Mesoproterozoic Belt and basal Cambrian rocks beneath the RMBD is present in all of the profiles and appears to extend east of the RMT. The Lewis thrust was identified in the seismic profiles and appears to sole into the RMBD east of the RMT. The RMT fault system has a dip displacement of 3-4 km and forms a half graben filled with 1 km of unconsolidated Tertiary sedimentary deposits. The RMT and adjacent Flathead fault systems are interpreted to be structurally linked and may represent a synthetic, en echelon fault system.

  12. Quaternary structural evolution of Terracina and Gaeta basins (Eastern Tyrrhenian margin, Italy)

    Energy Technology Data Exchange (ETDEWEB)

    Aiello, G.; Marsella, E.; Sacchi, M. [Consiglio Nazionale delle Ricerche, Naples (Italy). Ist. di Ricerca Geomare Sud

    2000-07-01

    In the Terracina and Gaeta basins (Italy) quaternary sediments are displaced by normal faults, which affect also Meso-Cenozoic tectonic units of the acoustic basement. The extensional tectonics is characterized by normal faults systems trending NE-SW and E-W. In the Terracina basin, roughly N-S oriented, half-graben structures are down thrown seaward through normal faults; the Gaeta extensional basin, E-W oriented, has two main depo centers and is bounded to the north and to the south by E-W trending normal faults and to the east by a NW-SE trending normal faults. [Italian] I bacini di Terracina e Gaeta mostrano un significativo controllo tettonico sulla sedimentazione quaternaria, causato dalla presenza di faglie normali: esse dislocano le unita' tettoniche meso-cenozoiche che rappresentano il basamento acustico. Sistemi di faglie normali ad andamento NE-SW e E-W determinano nel bacino di Terracina una struttura di tipo semi-graben orientata N-S- e ribassata verso mare da faglie dirette. Il bacino di Gaeta rappresenta un bacino estensionale ad andamento E-W, articolato in due principali depocentri e delimitato verso nord e verso sud da faglie normali ad andamento E-W e verso est da una faglia diretta ad andamento NW-SE.

  13. The role of inherited crustal structures and magmatism in the development of rift segments: Insights from the Kivu basin, western branch of the East African Rift

    Science.gov (United States)

    Smets, Benoît; Delvaux, Damien; Ross, Kelly Ann; Poppe, Sam; Kervyn, Matthieu; d'Oreye, Nicolas; Kervyn, François

    2016-06-01

    The study of rift basin's morphology can provide good insights into geological features influencing the development of rift valleys and the distribution of volcanism. The Kivu rift segment represents the central section of the western branch of the East African Rift and displays morphological characteristics contrasting with other rift segments. Differences and contradictions between several structural maps of the Kivu rift make it difficult to interpret the local geodynamic setting. In the present work, we use topographic and bathymetric data to map active fault networks and study the geomorphology of the Kivu basin. This relief-based fault lineament mapping appears as a good complement for field mapping or mapping using seismic reflection profiles. Results suggest that rifting reactivated NE-SW oriented structures probably related to the Precambrian basement, creating transfer zones and influencing the location and distribution of volcanism. Both volcanic provinces, north and south of the Kivu basin, extend into Lake Kivu and are connected to each other with a series of eruptive vents along the western rift escarpment. The complex morphology of this rift basin, characterized by a double synthetic half-graben structure, might result from the combined action of normal faulting, magmatic underplating, volcanism and erosion processes.

  14. South Sumatra Basin Province, Indonesia; the Lahat/Talang Akar-Cenozoic total petroleum system

    Science.gov (United States)

    Bishop, Michele G.

    2000-01-01

    Oil and gas are produced from the onshore South Sumatra Basin Province. The province consists of Tertiary half-graben basins infilled with carbonate and clastic sedimentary rocks unconformably overlying pre-Tertiary metamorphic and igneous rocks. Eocene through lower Oligocene lacustrine shales and Oligocene through lower Miocene lacustrine and deltaic coaly shales are the mature source rocks. Reserves of 4.3 billion barrels of oil equivalent have been discovered in reservoirs that range from pre-Tertiary basement through upper Miocene sandstones and carbonates deposited as synrift strata and as marine shoreline, deltaic-fluvial, and deep-water strata. Carbonate and sandstone reservoirs produce oil and gas primarily from anticlinal traps of Plio-Pleistocene age. Stratigraphic trapping and faulting are important locally. Production is compartmentalized due to numerous intraformational seals. The regional marine shale seal, deposited by a maximum sea level highstand in early middle Miocene time, was faulted during post-depositional folding allowing migration of hydrocarbons to reservoirs above the seal. The province contains the Lahat/Talang Akar-Cenozoic total petroleum system with one assessment unit, South Sumatra.

  15. Structural style of the Chos Malal fold and thrust belt, Neuquén basin, Argentina: Relationship between thick- and thin-skinned tectonics

    Science.gov (United States)

    Sánchez, Natalia; Turienzo, Martín; Lebinson, Fernando; Araujo, Vanesa; Coutand, Isabelle; Dimieri, Luis

    2015-12-01

    The Chos Malal fold and thrust belt (FTB) is a thick-skinned mountain belt formed by Mesozoic deposits of the Neuquén Basin during the Andean orogeny. Four structural cross-sections in the entire deformed area, supported by field and subsurface data, suggest a strong link between thick and thin-skinned structures. Major Andean thrusts branching from a detachment placed 12 km into the crust created large basement wedges, which were inserted in the cover producing minor order structures. The westernmost of these wedges is exposed forming the Cordillera del Viento, while others basement slices at depth were interpreted from seismic lines. These thick-skinned structures transferred deformation to the cover along the Auquilco Formation and contributed to create all thin-skinned structures surveyed in the Chos Malal FTB. We recognized half-graben geometries in the seismic lines, preserving their extensional configuration, which suggests that the main normal faults were not inverted. Shortenings calculated from the restoration of the four cross-sections are 16.9 km (29.7%), 16.9 km (29.7%), 14.7 km (26.9%) and 14.15 km (26.3%), which evidence a slight diminution of the contraction toward the south probably associated with the plunge of the Cordillera del Viento structure in this segment of the Chos Malal FTB.

  16. Geometry and kinematics of the Triassic rift basin in Jameson Land (East Greenland)

    Science.gov (United States)

    Guarnieri, Pierpaolo; Brethes, Anaïs.; Rasmussen, Thorkild M.

    2017-04-01

    The Triassic rift basin along the east Greenland margin described in this paper is represented by NE-SW trending basins and highs segmented by NW-SE trending transfer zones. Coarse-grained sediments along the eastern side of Jameson Land are shown to be hosted in half-graben structures belonging to the Carlsberg Fjord Basin that is bounded by NW dipping normal faults mapped and described after fieldwork in the Klitdal area in Liverpool Land. New aeromagnetic and electromagnetic data together with new drill cores allow the reinterpretation of available seismic lines showing the continuation of the Triassic rift basin toward the SW where it is buried under the Upper Triassic postrift sediments and the Jurassic successions of the Jameson Land Basin. The N-S trending Liverpool Land, interpreted as the boundary block of the Triassic basin, is shown to represent a structural high inherited from the Late Carboniferous tectonics and faulted during the Triassic rifting. The Carlsberg Fjord Basin and the Klitdal Fault System described in this paper should be seen as analogues to the Helgeland Basin in the Norwegian offshore that is bounded by the Ylvingen Fault Zone and to the Papa and West of Shetlands Basins that are bounded by the Spine Fault. The Triassic rift zone and transfer faults on both conjugate margins show a straightforward correlation with the trends of the initial spreading line and fracture zones of the northeast Atlantic indicating a possible inheritance of the Triassic rifting.

  17. Seismic Interpretation of the Nam Con Son Basin and its Implication for the Tectonic Evolution

    Directory of Open Access Journals (Sweden)

    Nguyen Quang Tuan

    2016-08-01

    Full Text Available The Nam Con Son Basin covering an area of circa 110,000 km2 is characterized by complex tectonic settings of the basin which has not fully been understood. Multiple faults allowed favourable migration passageways for hydrocarbons to go in and out of traps. Despite a large amount of newly acquired seismic and well data there is no significant update on the tectonic evolution and history of the basin development. In this study, the vast amount of seismic and well data were integrated and reinterpreted to define the key structural events in the Nam Con Son Basin. The results show that the basin has undergone two extentional phases. The first N - S extensional phase terminated at around 30 M.a. forming E - W trending grabens which are complicated by multiple half grabens filled by Lower Oligocene sediments. These grabens were reactivated during the second NW - SE extension (Middle Miocene, that resulted from the progressive propagation of NE-SW listric fault from the middle part of the grabens to the margins, and the large scale building up of roll-over structure. Further to the SW, the faults of the second extentional phase turn to NNE-SSW and ultimately N - S in the SW edge of the basin. Most of the fault systems were inactive by Upper Miocene except for the N - S fault system which is still active until recent time.

  18. Base- level Chang and Sequence Stratigraphy of Lishu Fault Lacustrine Basin

    Institute of Scientific and Technical Information of China (English)

    Wang Simin; Liu Zhaojun; Liu Kui

    2000-01-01

    Base - level is a kind of surface which controls sedimentation and erosion. So, it can be concluded that it is baselevel change that controls the formation and internal structure of a sequence. A single cycle of base- level change can generate four sets of different stacking patterns. They are two sets of aggradation, one progradation and one retrogradation, which affects the features of the internal structure of a sequence. Lishu fault subsidence of Songliao basin is a typical half - graben lacustrine basin. Comprehensive base - level change analysis indicates that six base - level cycles and their related six sequences can be recognized between T4 and T5 seismic reflection surface. The contemporaneous fault is the main controlling factor of the fault lacustrine basin. There are obvious differences exist in the composition of sedimentary systems and all systems tracts between its steep slope (the side that basin control fault existed) and flat slope. Except highstand systems tract is composed of fan delta - lacustrine system, lowstand systems tract, transgressive systems tract and regressive systems tract are all made up of fan delta - underwater fan- lacustrine sedimentary systems in the side of steep slope.

  19. Quaternary evolution of the Southern Apennines coastal plains: a review

    Directory of Open Access Journals (Sweden)

    Santangelo Nicoletta

    2017-02-01

    Full Text Available The Quaternary evolution of the main coastal basins located along the southwestern margin of the Southern Apennines has been reconstructed by integrating the huge amount of existing stratigraphical and geomorphological data. The information produced in the last twenty years has shed new light on the recent (late Middle Pleistocene to Present history of the Campanian and Sele plains or basins. During the early Quaternary, the analysed coastal basins originated as half-grabens in response to opening processes active since the late Tortonian in the southern Tyrrhenian back-arc basin. In some of these basins (e.g. the Campanian Plain, volcanism has also played an important role. In the inner sectors of the coastal basins, the complex interplay between block faulting, sedimentary inputs and glacioeustatic fluctuations gave rise to relative sea-level change and related coastline migrations, leading to the formation of the present-day coastal plains. In the Sele Plain basin, the construction of the present-day landscape mainly resulted from the substantial ceasing of subsidence in the final part of the Middle Pleistocene. Conversely, a strong contribution to the recent evolution of the Campanian Plain has been provided by abundant volcaniclastic aggradation, able to hinder the effect of the vertical motions that occurred in the last 100 ka.

  20. Analysis Method for Predicting Strain in Interior Beds and Sub-Resolution Faults from Area Balance Theory in Extensional Basins

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Extensional basins include mainly grabens and half grabens displaced along a lower detachment. Based on area balance theory, there is a linear relationship between a height of regional and the lower detachment h on the outside of the basin and "lost area S" from the regional in the basin. The pre-growth beds above lower detachment are of the same extensional displacement so that an "S-h diagram" can be used to determine the depth to lower detachment and to calculate the total extensional displacement of the beds above the lower detachment. The extensional displacement is dominated by the heave of various scale normal faults. The displacement of obvious faults can be immediately figured out from the measured bed-length. The requisite extension calculated by area balance is the layer-parallel strain, which could be accommodated by displacement on sub-resolution faults. Accordingly, the layer-parallel strain can help us predict the magnitude and distribution of sub-resolution faults on the basis of analysis of the structural style and rheological behavior.

  1. Seismic Interpretation of the Nam Con Son Basin and its Implication for the Tectonic Evolution

    Directory of Open Access Journals (Sweden)

    Nguyen Quang Tuan

    2016-06-01

    Full Text Available DOI:10.17014/ijog.3.2.127-137The Nam Con Son Basin covering an area of circa 110,000 km2 is characterized by complex tectonic settings of the basin which has not fully been understood. Multiple faults allowed favourable migration passageways for hydrocarbons to go in and out of traps. Despite a large amount of newly acquired seismic and well data there is no significant update on the tectonic evolution and history of the basin development. In this study, the vast amount of seismic and well data were integrated and reinterpreted to define the key structural events in the Nam Con Son Basin. The results show that the basin has undergone two extentional phases. The first N - S extensional phase terminated at around 30 M.a. forming E - W trending grabens which are complicated by multiple half grabens filled by Lower Oligocene sediments. These grabens were reactivated during the second NW - SE extension (Middle Miocene, that resulted from the progressive propagation of NE-SW listric fault from the middle part of the grabens to the margins, and the large scale building up of roll-over structure. Further to the SW, the faults of the second extentional phase turn to NNE-SSW and ultimately N - S in the SW edge of the basin. Most of the fault systems were inactive by Upper Miocene except for the N - S fault system which is still active until recent time.

  2. Le bassin du Souss (Zone de Faille du Tizi n'Test, Haut Atlas occidental, Maroc): résultat d'une inversion tectonique contrl̂ée par une faille de détachement profonde

    Science.gov (United States)

    Mustaphi, H.; Medina, F.; Jabour, H.; Hoepffner, C.

    1997-02-01

    Analysis of seismic reflection profiles and boreholes performed in the Souss Basin, which constitutes the southern foreland of the western High Atlas and the western continuation of the Tizi n'Test Fault Zone, allows an accurate inventory of several structures related to the rifting and opening of the Central Atlantic, and inversion related to the collision of Africa and Europe to be made. The most conspicuous structure is a deep north-northwestward gently dipping detachment, from which the El Klee and Biougra Faults diverge, striking northeast with a northwesterly dip. These faults are normal, have a Triassic to Middle Jurassic age, and delimit half-graben structures tilted to the south-southeast. The amount of extension (β) is at least 1.19. The obliquity of the faults with respect to the trend of the final rift gives them appearance of transfer faults. The Tertiary to present-day inversion is outlined by the reactivation of the detachment and some associated former normal faults as the El Kléa Fault, and by the creation of new decollement levels at the base, or within, the Triassic evaporites. The present study supports the idea that most of the High Atlas structures may be largely controlled by upper to mid-crustal gently northward dipping detachment planes.

  3. The mesoproterozoic midcontinent rift system, Lake Superior region, USA

    Science.gov (United States)

    Ojakangas, R.W.; Morey, G.B.; Green, J.C.

    2001-01-01

    Exposures in the Lake Superior region, and associated geophysical evidence, show that a 2000 km-long rift system developed within the North American craton ??? 1109-1087 Ma, the age span of the most of the volcanic rocks. This system is characterized by immense volumes of mafic igneous rocks, mostly subaerial plateau basalts, generated in two major pulses largely by a hot mantle plume. A new ocean basin was nearly formed before rifting ceased, perhaps due to the remote effect of the Grenville continental collision to the east. Broad sagging/subsidence, combined with a system of axial half-grabens separated along the length of the rift by accommodation zones, provided conditions for the accumulation of as much as 20 km of volcanic rocks and as much as 10 km of post-rift clastic sediments, both along the rift axis and in basins flanking a central, post-volcanic horst. Pre-rift mature, quartzose sandstones imply little or no uplift prior to the onset of rift volcanism. Early post-rift red-bed sediments consist almost entirely of intrabasinally derived volcanic sediment deposited in alluvial fan to fluvial settings; the exception is one gray to black carbon-bearing lacustrine(?) unit. This early sedimentation phase was followed by broad crustal sagging and deposition of progressively more mature red-bed, fluvial sediments with an extra-basinal provenance. ?? 2001 Elsevier Science B.V. All rights reserved.

  4. Preliminary Geologic Map of the Vermejo Peak area, Colfax and Taos Counties, New Mexico and Las Animas and Costilla Counties, Colorado