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Sample records for middle miocene e-w

  1. Across the Pacific: Climate Evolution in the Middle Miocene

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    Fox, Lyndsey; Wade, Bridget; Holbourn, Ann; Leng, Melanie

    2014-05-01

    We present the first high-resolution (3 kyr) astronomically-tuned record of δ18O and δ13C from planktonic foraminifera for the equatorial Pacific Ocean (16.5-13.5 Myr). Our data provides exciting new information on sea surface temperatures and primary productivity changes at the tropics during the middle Miocene at a resolution not achieved in any previous study, which sheds new light on the middle Miocene climatic transition (MMCT) and associated carbon-isotope excursion. Reliable sea surface temperature estimates are crucial to any reconstruction and modelling of past ocean salinity and density, water column stratification, thermohaline circulation, and ice volume. Despite extensive studies of benthic foraminifera, existing planktonic foraminiferal records of this interval are extremely scarce and of low resolution, with samples representing time intervals of 2x105and 5x105 years. Previous studies have been hindered by the absence of biogenic carbonate (e.g., Leg 199). Consequently the impact of global warming and cooling on tropical surface waters and the propagation of orbital cycles in the Earth System are unknown. In 2009 Integrated Ocean Drilling Program Expedition 320/321 recovered lower-middle Miocene sediments with high sedimentation rates (30m/myr), continuous recovery, and orbital cyclicity from the east equatorial Pacific Ocean. At Site U1338 planktonic foraminifera are abundant and diverse in the lower and middle Miocene sediments and exceptionally well preserved. Scanning electron microscope studies revealed open pore spaces, little evidence of calcitic overgrowth on the wall surface and in many cases preserved spines (Fox and Wade, 2013). We compare our data from Site U1338 to Site 1146 in the western equatorial Pacific Ocean, to reconstruct bottom and surface water conditions and changes in ocean dynamics across the equatorial Pacific during this highly complex interval of climate history.

  2. Middle Miocene closure of the Central American Seaway

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    Montes, C.; Cardona, A.

    2014-12-01

    The final closure of the Panama Isthmus and permanent separation of Caribbean and Pacific waters is thought to have modified their salinity, faunistic assemblages, and ultimately, ocean circulation patterns and global climate. The Great American Biotic Interchange (GABI) is thought to have been the result of Plio-Pleistocene closure of the Isthmus that allowed land animals to massively cross the Isthmus. Similarly, the separation of Caribbean and Pacific waters by a rising Isthmus is thougth to be a prime example of vicariance. The role of Isthmus closure on global changes, however, remains controversial due in part to the difficulty of establishing a precise chronology of seaway closure. While timing of glaciation is well established, new data on the chronology of Isthmus emergence suggests that the process of closure is more complex, long, and old than previously thought. We sampled fluvial and shallow marine strata in northwesternmost South America to recover zircon grains for provenance analyses in the immediate vicinity of the docking site. Because the ages of magmatic provinces in northwestern South America and the Panama Isthmus are mutually exclusive, detrital zircon analyses provides a tool to evaluate land connections. We found that an uniquely Panamanian, 40-45 Ma (early Lutetian) detrital zircon fingerprint is abundant in middle Miocene strata, but absent in underlying lower Miocene and Oligocene strata of the northern Andes. This fingerprint represents the beginning of fluvial detrital exchange between the Panama arc and South America, and therefore marks the time of docking and the end of deep-water, and probably shallow-water connections by middle Miocene times.

  3. Middle Miocene carnivorans from the Monarch Mill Formation, Nevada

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    Kent Smith

    2016-02-01

    Full Text Available he lowest part of the Monarch Mill Formation in the Middlegate basin, west-central Nevada, has yielded a middle Miocene (Barstovian Land Mammal Age vertebrate assemblage, the Eastgate local fauna. Paleobotanical evidence from nearby, nearly contemporaneous fossil leaf assemblages indicates that the Middle Miocene vegetation in the area was mixed coniferous and hardwood forest and chaparral-sclerophyllous shrubland, and suggests that the area had been uplifted to 2700–2800 m paleoaltitude before dropping later to near its present elevation of 1600 m. Thus, the local fauna provides a rare glimpse at a medium- to high-altitude vertebrate community in the intermountain western interior of North America. The local fauna includes the remains of fish, amphibians, reptiles, birds, and 25 families of mammals. Carnivorans, the focus of this study, include six taxa (three of which are new belonging to four families. Canidae are represented by the borophagine Tomarctus brevirostris and the canine Leptocyon sp. indet. The earliest record and second North American occurrence of the simocyonine ailurid Actiocyon is represented by A. parverratis sp. nov. Two new mustelids, Brevimalictis chikasha gen. et sp. nov. and Negodiaetictis rugatrulleum gen. et sp. nov., may represent Galictinae but are of uncertain subfamilial and tribal affinity. The fourth family is represented by the felid Pseudaelurus sp. indet. Tomarctus brevirostris is limited biochronologically to the Barstovian land mammal age and thus is consistent with the age indicated by other members of the Eastgate local fauna as well as by indirect tephrochronological dates previously associated with the Monarch Mill Formation. Actiocyon parverratis sp. nov. extends the temporal range of the genus Actiocyon from late Clarendonian back to the Barstovian. The Eastgate local fauna improves our understanding of mammalian successions and evolution, during and subsequent to the Mid-Miocene Climatic Optimum

  4. Comments to Middle Miocene closure of the Central American Seaway

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    Coates, A.G.; Stallard, Robert F.

    2016-01-01

    In a recent paper proposing an early (mid-Miocene) closure of the Central American Seaway (CAS), Montes et al. 2015 (1) disregard existing paleogeographic data that invalidate Panama as a source for zircons, and inappropriately ignore the evidence for trans-isthmian marine connections until 4-3 Ma. They also fail to cite previous work (2, 3), that had reconstructed the Central American arc already docked with South America by 12 Ma. Montes et al. 2015 (1) (Fig. 1) disregard the Atrato-San Juan sedimentary basin (3), a shallowing Oligocene to Pliocene, Pacific to Caribbean seaway (3, 4, 5). This deep graben (6) is filled with thousands of meters of Pre-Pliocene marine sediments (3, 5, 6) that now occupy a lowland between the Baudo uplift to the west and the Western Cordillera to the east. The Mande Batholith and numerous Eocene and younger volcanic rocks (4), the most proximal source of the zircons, are situated to the east of this seaway and would have shed zircons eastward towards the Cordillera Central. There is no evidence for any rivers crossing the seaway (3, 5), and thus no Panamanian source of zircons. Instead this seaway is evidence of a significant marine connection between the Pacific and Atlantic oceans into the Pliocene. The authors assume that the middle Miocene closure of the CAS effectively creates a continuous land bridge connecting North and South America and separating the Atlantic from the Pacific. They acknowledge, but then discount, marine connections across the Isthmus until 4-3 Ma even though these satisfactorily explain (Coates and Stallard, 2014 (6)) the oceanographic, molecular and Great American Biological Interchange events ignore unexplained by Montes et al. 2015. Only by conspicuously ignoring these events can they imply that the Isthmus was formed at 15-13 Ma. References 1. C. Montes et al., Middle Miocene closure of the Central American Seaway. Science 348, 226-229 (2015). 2. A. G. Coates, R. F. Stallard, How old is the Isthmus of

  5. Oil and Gas Wells in Southern Louisiana that Penetrated the Middle Miocene Sequence

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    U.S. Geological Survey, Department of the Interior — The drilling history documents oil and gas wells in the Middle Miocene sequence as a whole and in 10-year intervals. The wells included in this interval are...

  6. Paleointensity determinations from Middle Miocene volcanic rocks, Far East, Russia

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    Shcherbakov, Valeriy; Shcherbakova, Valentina; Zhidkov, Grigoriy; Bretstein, Yury

    2010-05-01

    Paleomagnetic and paleointensity studies of a representative collection of Middle Miocene volcanic rocks of (12.4-10.0) Ma age from Far East, Russia were carried out. A comprehensive rock magnetic investigation has been performed in order to determine the mineralogy of magnetic fraction and to identify the origin of NRM. Successful Thellier palaeointensity determinations with pTRM checks were obtained for 4 sites (33 samples). The Thellier experiments were complimented by the Wilson's express method. Values of the VDMs range from 3.1 to 7.5 (10^22 Am^2) with the mean VDM = 5.5×10^22 Am^2. A total 88 Thellier-type palaeointensity determinations were found in the World Paleointensity database for the 5-23 Ma period with the overall mean VDM = 5×10^22 Am^2. The VDM distribution is characterized by high variance from 1.5 to 12 (10^22 Am^2). No significant difference between the VDM distributions for the normal and reverse polarity intervals was revealed.

  7. Early, middle, and late Miocene basin development, California

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    Bachman, S.B.

    1988-03-01

    Contrary to earlier models of progressive basin development related to northward migration of the Mendocino triple junction, it can now be documented that the major basins of coastal California developed at about the same time in the late Oligocene to early Miocene. This basin development is marked by rapid deepening of basin floors, subsequent changes in depositional facies from nonmarine and shallow marine to deep marine, and widespread volcanism dated at 23-20 Ma. The coastal basins likely formed by rifting and subsidence linked to the proximity of the Farallon-pacific spreading ridge and the subduction of hot young oceanic crust, but cannot be correlated to any existing models of triple junction migration. Indeed, strike-slip restored positions of the coastal basins at their inception indicate that the basins were spread out over about 800 km of the southern coast of California. The Miocene basins were likely larger than the present coastal basins, although their configurations are obscured by late Neogene faulting and erosion. It is likely, however, that paleohighs separated at least some of the margin into proximal and distal basins. With local exceptions, structuring in the Miocene basins was primarily extensional, with widespread strike-slip and thrust tectonics restricted mainly to latest Miocene and younger events. Plate reconstructions suggest several hundred kilometers of transform motion occurred along the California margin during the Miocene, but there is only limited evidence of this movement in the known history of either the basins or the major faults of California. Sedimentation during the Miocene was controlled by both oceanic conditions (biogenic component) and the relative abundance of clastic input. The clastic input was controlled by a combination of proximal vs distal basinal positions, eustatic sea level changes, and local tectonics.

  8. The Middle Miocene climate as modelled in an atmosphere-ocean-biosphere model

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    M. Krapp

    2011-11-01

    Full Text Available We present simulations with a coupled atmosphere-ocean-biosphere model for the Middle Miocene 15 million years ago. The model is insofar more consistent than previous models because it captures the essential interactions between ocean and atmosphere and between atmosphere and vegetation. The Middle Miocene topography, which alters both large-scale ocean and atmospheric circulations, causes a global warming of 0.7 K compared to present day. Higher than present-day CO2 levels of 480 and 720 ppm cause a global warming of 2.8 and 4.9 K. The associated water vapour feedback enhances the greenhouse effect which leads to a polar amplification of the warming. These results suggest that higher than present-day CO2 levels are necessary to drive the warm Middle Miocene climate, also because the dynamic vegetation model simulates a denser vegetation which is in line with fossil records. However, we do not find a flatter than present-day equator-to-pole temperature gradient as has been suggested by marine and terrestrial proxies. Instead, a compensation between atmospheric and ocean heat transport counteracts the flattening of the temperature gradient. The acclaimed role of the large-scale ocean circulation in redistributing heat cannot be supported by our results. Including full ocean dynamics, therefore, does not solve the problem of the flat temperature gradient during the Middle Miocene.

  9. The Middle Miocene climate as modelled in an atmosphere-ocean-biosphere model

    Directory of Open Access Journals (Sweden)

    M. Krapp

    2011-06-01

    Full Text Available We present simulations with a coupled ocean-atmosphere-biosphere model for the Middle Miocene 15 million years ago. The Middle Miocene topography, which alters both large-scale ocean and atmospheric circulations, causes a global warming of 0.7 K compared to present-day. Higher than present-day CO2 levels of 480 and 720 ppm cause a global warming of 2.8 and 4.9 K, thereby matching proxy-based Middle Miocene global temperature estimates of 3–6 K warming. Higher CO2 levels and the associated water vapour feedback enhance the greenhouse effect and lead to a polar amplification of the warming. Although oceanic and atmospheric poleward heat transport are individually altered by 10–30 % in the mid and high latitudes, changes of the total heat transport account only for 4–8 %, pointing toward a compensation between oceanic and atmospheric heat transport. Our model reproduces a denser vegetation in agreement with fossil records. These results suggest that higher than present-day CO2 levels are essential to drive the warm Middle Miocene climate.

  10. The Middle Miocene Climate Transition in the Central Mediterranean. Geologica Ultraiectina (326)

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    Mourik, A.A.

    2010-01-01

    The Middle Miocene Climate Transition (~15-13.7 Ma) is one of the major steps in Cenozoic climate evolution. The rapid expansion of the East Antarctic Ice Sheet at ~13.9 – 13.7 Ma caused important climate changes on a global scale. The aim of this PhD research has been to study the effects of the Mi

  11. A unique Middle Miocene European hominoid and the origins of the great ape and human clade

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    Moyà-Solà, Salvador; Alba, David M.; Almécija, Sergio; Casanovas-Vilar, Isaac; Köhler, Meike; De Esteban-Trivigno, Soledad; Robles, Josep M.; Galindo, Jordi; Fortuny, Josep

    2009-01-01

    The great ape and human clade (Primates: Hominidae) currently includes orangutans, gorillas, chimpanzees, bonobos, and humans. When, where, and from which taxon hominids evolved are among the most exciting questions yet to be resolved. Within the Afropithecidae, the Kenyapithecinae (Kenyapithecini + Equatorini) have been proposed as the sister taxon of hominids, but thus far the fragmentary and scarce Middle Miocene fossil record has hampered testing this hypothesis. Here we describe a male partial face with mandible of a previously undescribed fossil hominid, Anoiapithecus brevirostris gen. et sp. nov., from the Middle Miocene (11.9 Ma) of Spain, which enables testing this hypothesis. Morphological and geometric morphometrics analyses of this material show a unique facial pattern for hominoids. This taxon combines autapomorphic features—such as a strongly reduced facial prognathism—with kenyapithecine (more specifically, kenyapithecin) and hominid synapomorphies. This combination supports a sister-group relationship between kenyapithecins (Griphopithecus + Kenyapithecus) and hominids. The presence of both groups in Eurasia during the Middle Miocene and the retention in kenyapithecins of a primitive hominoid postcranial body plan support a Eurasian origin of the Hominidae. Alternatively, the two extant hominid clades (Homininae and Ponginae) might have independently evolved in Africa and Eurasia from an ancestral, Middle Miocene stock, so that the supposed crown-hominid synapomorphies might be homoplastic. PMID:19487676

  12. Paleomagnetic analyses on Badenian–Sarmatian drill cores from the North Carpathian foredeep (Middle Miocene, Poland)

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    Sant, K.; de Leeuw, Arjan; Chang, L.; Czapowski, Grzegorsz; Gasiewicz, Andrzej; Krijgsman, W.

    2015-01-01

    Accurate dating of the Badenian–Sarmatian transition, a boundary between two regional Middle Miocene stages of the semi-isolated Paratethys Sea, is crucial to understand what event caused the corresponding major turnover in faunal assemblage at that point in time. The general opinion is that this ev

  13. Seawater osmium isotope evidence for a middle Miocene flood basalt event in ferromanganese crust records

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    Klemm, Veronika; Frank, Martin; Levasseur, Sylvain; Halliday, Alex N.; Hein, James R.

    2008-08-01

    Three ferromanganese crusts from the northeast, northwest and central Atlantic were re-dated using osmium (Os) isotope stratigraphy and yield ages from middle Miocene to the present. The three Os isotope records do not show evidence for growth hiatuses. The reconstructed Os isotope-based growth rates for the sections older than 10 Ma are higher than those determined previously by the combined beryllium isotope (10Be/9Be) and cobalt (Co) constant-flux methods, which results in a decrease in the maximum age of each crust. This re-dating does not lead to significant changes to the interpretation of previously determined radiogenic isotope neodymium, lead (Nd, Pb) time series because the variability of these isotopes was very small in the records of the three crusts prior to 10 Ma. The Os isotope record of the central Atlantic crust shows a pronounced minimum during the middle Miocene between 15 and 12 Ma, similar to a minimum previously observed in two ferromanganese crusts from the central Pacific. For the other two Atlantic crusts, the Os isotope records and their calibration to the global seawater curve for the middle Miocene are either more uncertain or too short and thus do not allow for a reliable identification of an isotopic minimum. Similar to pronounced minima reported previously for the Cretaceous/Tertiary and Eocene/Oligocene boundaries, possible interpretations for the newly identified middle Miocene Os isotope minimum include changes in weathering intensity and/or a meteorite impact coinciding with the formation of the Nördlinger Ries Crater. It is suggested that the eruption and weathering of the Columbia River flood basalts provided a significant amount of the unradiogenic Os required to produce the middle Miocene minimum.

  14. The formation placement and palaeoenvironment of the Middle Miocene Los Atajos Member, Trinidad

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    Wilson, Brent; Farfan, Philip; Hughes, Chantelle

    2017-07-01

    The age, palaeoenvironment and formation placement of the conglomeratic Los Atajos Member of central Trinidad have long been unclear. Seven samples (four from calcareous silts near the member's base exposed by building work at the Los Atajos Community Centre, and three from the underlying calcareous claystones of the Brasso Formation) were examined for calcareous microfossils. These indicate a conformable succession encompassing an overall regression. The oldest of the claystone samples, of uppermost early Middle Miocene Globorotalia fohsi fohsi Zone age (N11), contained an upper bathyal benthic foraminiferal assemblage, while the younger claystone samples yielded abundant, shallow neritic Hanzawaia carstensi. The recovery of the planktonic foraminifera Globorotalia mayeri but absence of Globigerinoides subquadratus suggest a Middle Miocene age (Globorotalia mayeri planktonic foraminiferal Zone; N14) for both the uppermost Brasso claystone sample and the Los Atajos Member. The benthic foraminiferal fauna in the Los Atajos is dominated by Rosalina subaraucana, with subdominant Cibicides ex gr. aknerianus and C. floridanus sensu Galloway and Heminway, and common Elphidium spp. This faunal succession has a close affinity with that of parts of the Lower to Middle Miocene Brasso Formation, especially the N10 Guaracara Limestone Member and the clays on which it sits. However, the Los Atajos Member assemblage differs markedly from that of the overlying Late Miocene San José Calcareous Silt Member of the Manzanilla Formation, from which the Los Atajos is separated by an unconformity of Globorotalia menardii (N15) Zone age. On these grounds, the Los Atajos Member is here placed within the Brasso Formation. The low diversity, high dominance benthic foraminiferal fauna and the associated ostracod assemblage in the Los Atajos are indicative of inner to shallower middle neritic palaeodepths in a carbonate-prone palaeoenvironment with marine vegetation and strong current action

  15. A new age model for the early-middle Miocene in the North Alpine Foreland Basin

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    Reichenbacher, Bettina; Krijgsman, Wout; Pippèrr, Martina; Sant, Karin; Kirscher, Uwe

    2016-04-01

    The establishment of high-resolution age models for sedimentary successions is crucial for numerous research questions in the geosciences and related disciplines. Such models provide an absolute chronology that permits precise dating of depositional episodes and related processes such as mountain uplift or climate change. Recently, our work in the Miocene sediments of the North Alpine Foreland Basin (NAFB) has revealed a significantly younger age (16.6 Myr) for sediments that were thought to have been deposited 18 Myr ago. This implies that a fundamentally revised new age model is needed for the entire suite of lower-middle Miocene sedimentary rocks in the NAFB (20 to 15-Myr). Our new data also indicate that previously published reconstructions of early-middle Miocene palaeogeography, sedimentation dynamics, mountain uplift and climate change in the NAFB all require a critical review and revision. Further, the time-span addressed is of special interest, since it encompasses the onset of a global warming phase. However, it appears that a fundamentally revised new age model for the entire suite of lower-middle Miocene sedimentary rocks in the NAFB can only be achieved based on a 500 m deep drilling in the NAFB for which we currently seek collaboration partners to develop a grant application to the International Continental Deep Drilling Program (ICDP). Reference: Reichenbacher, B., W. Krijgsman, Y. Lataster, M. Pippèrr, C. G. C. Van Baak, L. Chang, D. Kälin, J. Jost, G. Doppler, D. Jung, J. Prieto, H. Abdul Aziz, M. Böhme, J. Garnish, U. Kirscher, and V. Bachtadse. 2013. A new magnetostratigraphic framework for the Lower Miocene (Burdigalian/Ottnangian, Karpatian) in the North Alpine Foreland Basin. Swiss Journal of Geosciences 106:309-334.

  16. Orbitally paced phosphogenesis in Mediterranean shallow marine carbonates during the middle Miocene Monterey event

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    Auer, Gerald; Hauzenberger, Christoph A.; Reuter, Markus; Piller, Werner E.

    2016-04-01

    During the Oligo-Miocene, major phases of phosphogenesis occurred in the Earth's oceans. However, most phosphate deposits represent condensed or allochthonous hemipelagic deposits, formed by complex physical and chemical enrichment processes, limiting their applicability for the study regarding the temporal pacing of Miocene phosphogenesis. The Oligo-Miocene Decontra section located on the Maiella Platform (central Apennines, Italy) is a widely continuous carbonate succession deposited in a mostly middle to outer neritic setting. Of particular interest are the well-winnowed grain to packstones of the middle Miocene Bryozoan Limestone, where occurrences of authigenic phosphate grains coincide with the prominent carbon isotope excursion of the Monterey event. This unique setting allows the analysis of orbital forcing on phosphogenesis, within a bio, chemo, and cyclostratigraphically constrained age-model. LA-ICP-MS analyses revealed a significant enrichment of uranium in the studied authigenic phosphates compared to the surrounding carbonates, allowing natural gamma-radiation (GR) to be used as a qualitative proxy for autochthonous phosphate content. Time series analyses indicate a strong 405 kyr eccentricity forcing of GR in the Bryozoan Limestone. These results link maxima in the GR record and thus phosphate content to orbitally paced increases in the burial of organic carbon, particularly during the carbon isotope maxima of the Monterey event. Thus, phosphogenesis during the middle Miocene in the Mediterranean was controlled by the 405 kyr eccentricity and its influence on large-scale paleoproductivity patterns. Rare earth element data were used as a tool to reconstruct the formation conditions of the investigated phosphates, indicating generally oxic formation conditions, which are consistent with microbially mediated phosphogenesis.

  17. Miocene climate seasonality in southern India - first direct evidence for a weak Indian monsoon during the Middle Miocene Climate Optimum

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    Piller, W. E.; Reuter, M.; Kern, A. K.; Harzhauser, M.

    2012-04-01

    The Asian monsoon is an integral component of the global climate system. This large-scale atmospheric circulation comprises the East Asian summer and winter monsoon and the Indian monsoon subsystems, all characterized by seasonal reversing winds and precipitation changes associated with asymmetric heating of land and sea. The Neogene monsoon history is mainly reconstructed from chemical and physical weathering rates recorded in widely continuous marine sequences of the Indus Fan, Bengal Fan and South China Sea, which, depending on the source, physiography and sediment, indicate drier or wetter climates. These indirect climate proxies display an unusually dry period during the Middle Miocene Climate Optimum (MMCO, 16.5-15 Ma). As part of the FWF-projects P18189, P21414 and P23492, we present an Early/Middle Miocene coastal palynoflora record from the siliciclastic Ambalapuzha Formation at the coastal cliff of Varkala (Kerala Basin, SW India). Pollen assemblages and facies document a coastal wetland with mangrove vegetation. The Coexistence Approach was applied for palaeoclimatic reconstructions. This method uses climatic tolerances of all nearest living relatives known for a fossil flora by assuming that the tolerances of a fossil taxon are not significantly different from its modern counterpart. The maximum overlap of the environmental tolerances of all nearest living relatives (coexistence interval) is then regarded as being indicative of the most likely palaeoenvironment. By enquiring the Palaeoflora Database (http://www.palaeoflora.de/), the palaeoclimatic parameters of the pollen flora were calculated. The reconstructed climatic parameters for the MMCO show a seasonal precipitation pattern with a dry and a wet period and moderate rainfalls during the warmest period, which is comparable to the present day annual precipitation cycle in coastal Kerala, and affirms the presence of a monsoon-like atmospheric circulation over South India during the MMCO. However, the

  18. A new Middle Miocene Niveria Jousseaume, 1884 (Mollusca: Gastropoda: Trivioidea) from Hungary

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    Fehse, Dirk

    2011-02-01

    A new species of Niveria from the Middle Miocene (Badenian) of the Paratethys of Borsodbóta, Hungary is described. This species is characterized by its callused dorsum and dorsal depression. Niveria jozefgregoi sp. nov. is discussed with comparative species from the Badenian of Hungary, the Pliocene of the Mediterranean region, Florida and Recent species from Madeira and the Islas Galápagos.

  19. Early to middle Miocene foraminifera from the deep-sea Congo Fan, offshore Angola

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    Kender, S; Kaminski, M.A.; Jones, R W

    2008-01-01

    Analysis of a 630m section of an exploration well penetrating the distal part of the Congo Fan (~2000m water depth) yielded high abundance and diversity assemblages of agglutinated and calcareous benthic foraminifera. Planktonic foraminifera constrain the age to Early – Middle Miocene, and \\delta 18O records reveal the Mi1 (~16.3 Ma) isotopic shift. Relatively few taxonomic studies of deep-water calcareous and agglutinated benthic foraminifera exist from this time period in this loca...

  20. Etisus evamuellerae, a new xanthid crab (Decapoda, Brachyura) from the Middle Miocene of Austria and Hungary

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    Hyžný, M.; van Bakel, B.W.M.; Guinot, D.

    2015-01-01

    On the basis of several carapaces, a new species of xanthid crab, Etisus evamuellerae, is described from the Middle Miocene of the Vienna (Austria) and Great Hungarian basins. It differs from the coeval xanthids, Xantho moldavicus and Pilodius vulgaris, in having a distinctly protruding front and comparatively longer carapace. Contrary to those two species, the new one makes up for just a small percentage in the decapod crustacean assemblages studied. PMID:25983383

  1. Gratkorn - A new late Middle Miocene vertebrate fauna from Styria (Late Sarmatian, Austria)

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    Gross, M.; Böhme, M.; Prieto, J.

    2009-04-01

    Integrated stratigraphic approaches provide precise correlations of global standard stages with regional Paratethys stages. Nevertheless, higher resolution stratigraphic matching of terrestrial deposits remains challenging due to the lack of a practical continental biostratigraphy. The mostly used tool for biostratigraphic correlation of non-marine deposits in the Old World is still the concept of Neogene Mammal-zones (MN-zones). However, at higher biostratigraphic resolution (imprints of gnawing structures. These taphonomic features point to a longer surface exposure before burial without considerable transportation. Trampling and the activity of scavengers (crunching, displacement of cadavers) are probable. Locally small- and medium-sized mammal remains (jaws and postcranial elements) of e.g., hamsters, flying squirrels, gymnures and shrews are concentrated, perhaps demonstrating feeding places of carnivores or more probably of birds of prey. Nonetheless, from geologic point of view, this paleosol represents an event horizon, which accumulated rapidly maybe within tens or hundreds of years. The vertebrate fauna comprises of scattered fishes (e.g. cyprinids, gobiids, ?channids), amphibians (e.g. salamandrids, ranids, discoglossids, bufonids, pelobatids,), reptiles (scincids, lacertids, gekkonids, anguids, varanids, colubrids, testudinids, emydids), birds (coliiformes), rodents and lagomorphs (cricetids, glirids, eomyids, sciurids, castorids), insectivores and chiropterans (erinaceids, soricids, talpids), and large mammals (suids, tragulids, moschids, cervids, ?palaeomerycids, equids, chalicotheriids, rhinos, proboscidians, carnivors). Litho- and biostratigraphy (terrestrial gastropods) as well as magnetostratigraphic data and the sequence stratigraphic and geodynamic frame indicate an age of 12-12.2 Ma (early Late Sarmatian s.str., chron 5An.1n) for the locality. Therefore, Gratkorn is one of richest and most complete fauna of the late Middle Miocene of Central

  2. Antarctic ice-sheet response to atmospheric CO2 and insolation in the Middle Miocene

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    M. Schulz

    2009-10-01

    Full Text Available Foraminiferal oxygen isotopes from deep-sea sediment cores suggest that a rapid expansion of the Antarctic ice sheet took place in the Middle Miocene around 13.9 million years ago. The origin for this transition is still not understood satisfactorily. One possible cause is a drop in the partial pressure of atmospheric carbon dioxide (pCO2 in combination with orbital forcing. A complication is the large uncertainty in the magnitude and timing of the reconstructed pCO2 variability and additionally the low temporal resolution of the available pCO2 records in the Middle Miocene. We used an ice sheet-climate model of reduced complexity to assess variations in Antarctic ice sheet volume induced by pCO2 and insolation forcing in the Middle Miocene. The ice-sheet sensitivity to atmospheric CO2 was tested for several scenarios with constant pCO2 forcing or a regular decrease in pCO2. This showed that small, ephemeral ice sheets existed under relatively high atmospheric CO2 conditions (between 640–900 ppm, whereas more stable, large ice sheets occurred when pCO2 was less than ~600 ppm. The main result of this study is that the pCO2-level must have declined just before or during the period of oxygen-isotope increase, thereby crossing a pCO2 glaciation threshold of around 615 ppm. After the decline, the exact timing of the Antarctic ice-sheet expansion depends also on the relative minimum in summer insolation at approximately 13.89 million years ago. Although the mechanisms described appear to be robust, the exact values of the pCO2 thresholds are likely to be model-dependent.

  3. New Bryozoa from the Sarmatian (Middle Miocene deposits of the Cerna-Strei Depression, Romania

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    Kamil Zágoršek

    2008-08-01

    Full Text Available A new species of the Sarmatian bryozoan, Crisia romanica sp. nov., is described from Sarmatian (Middle Miocene sediments of the Cerna-Strei Depression, near Răcăştia, Romania. The new species differs from all other known species of Crisia by having a frontal elongated gonozooecium with a prominent oeciopore situated on a short oeciostome. Crisia romanica sp. nov. is accompanied by Annectocyma corrugata (REUSS, 1869 occurring in a section nearby. The bryozoans found indicate normal marine conditions in the Cerna-Strei Depression during the Sarmatian.

  4. Otoliths in situ from Sarmatian (Middle Miocene) fishes of the Paratethys. Part I

    DEFF Research Database (Denmark)

    Schwarzhans, Werner; Carnevale, Giorgio; Bannikov, Alexandre F.

    2017-01-01

    Several well-preserved otoliths were extracted from four slabs containing fish specimens of Atherina suchovi. Atherina suchovi is one of the five Atherina species recorded from the Middle Miocene of the Central and Eastern Paratethys established on articulated skeletal remains. This corresponds...... it appears to be closely related to A. gidjakensis. A list is presented and briefly discussed showing Sarmatian skeleton-based fish records from the Central and Eastern Paratethys with an overview of known and currently studied fishes with otoliths in situ....

  5. Rapid middle Miocene extension and unroofing of the southern Ruby Mountains, Nevada

    Science.gov (United States)

    Colgan, Joseph P.; Howard, Keith A.; Fleck, Robert J.; Wooden, Joseph L.

    2010-01-01

    Paleozoic rocks in the northern Ruby Mountains were metamorphosed during Mesozoic crustal shortening and Cenozoic magmatism, but equivalent strata in the southern Ruby Mountains were never buried deeper than stratigraphic depths prior to exhumation in the footwall of a west dipping brittle normal fault. In the southern Ruby Mountains, Miocene sedimentary rocks in the hanging wall of this fault date from 15.2 to 11.6 Ma and contain abundant detritus from the Paleozoic section. Apatite fission track and (U-Th)/He samples of the Eocene Harrison Pass pluton record rapid cooling that peaked ca. 17–15 Ma, while apatite fission track data from Jurassic plutons east and west of the southern Ruby Mountains indicate near-surface temperatures (pluton to be partially reset rather than to directly record fault slip. Our new data, together with published data on the distribution and composition of Miocene basin fill, suggest that rapid middle Miocene slip took place on the west dipping brittle detachment that bounds the Ruby Mountains and East Humboldt Range for 150 km along strike. This fault was thus active during a period of rapid extension (ca. 17–15 to 12–10 Ma) documented widely across the northern Basin and Range Province.

  6. Paleo-environment in the upper amazon basin during early to middle Miocene times

    Science.gov (United States)

    van Soelen, Els; Hoorn, Carina; Santos, Roberto V.; Dantas, Elton L.; Sinninghe Damsté, Jaap S.; Kim, Jung-Hyun

    2014-05-01

    The Amazon River has the largest catchment in the world and is responsible for the largest water discharge from land to the ocean. The river system that flows from the Andes to the Atlantic Equatorial Margin exists since the late Miocene, and results from Andean uplift which strongly affected erosion/deposition and major flow patterns in northern South-America. Two outcrop sites from the Solimões basin, Mariñame (17.7-16.1 Ma) and Los Chorros (14.2-12.7 Ma), may shed light on the inland paleo-environmental conditions during a period of active Andean uplift in the early to middle Miocene. Earlier works revealed the Mariñame outcrops to represent a river born in Amazonia. Instead the Los Chorros outcrops are relics of the Amazon River system, characterized by extensive wetlands consisting of swamps, shallow lakes, crevasse splays channels and crevasse-delta lakes (e.g. Hoorn et al., 2010). The freshwater ecosystems alternate with some intervals that are rich in marine palynomorphs (such as dinocysts), mangrove pollen, brackish tolerant molluscs and ostracods, which indicate brackish conditions and a marine influence. It is thought that these marine incursion are related to phases of global sea-level rise and rapid subsidence in the Andean foreland (Marshall & Lundberg, 1996). Still, much remains unknown about the Miocene river systems, like the extent and diversity of the wetland system and the nature of the marine incursions. To get a better understanding of the sources of the (in)organic material, geochemical methods were used. Strontium (Sr) and Neodymium (Nd) isotopes were analyzed on bulk sediments, and used for a paleo-provenance study. The Sr and Nd isotopic signature in the older section (Mariñame) is in general more radiogenic compared to the Los Chorros section. The most radiogenic values are comparable to those found nowadays in the the Precambrian Guyana shield. A Guyana sediment source would suggest a distinctly different flow direction of the major

  7. Enamel thickness in the Middle Miocene great apes Anoiapithecus, Pierolapithecus and Dryopithecus

    Science.gov (United States)

    Alba, D. M.; Fortuny, J.; Moyà-Solà, S.

    2010-01-01

    On the basis of industrial computed tomography, relative enamel thickness (RET) is computed in three Middle Miocene (ca 11.9–11.8 Ma) hominoids from Abocador de Can Mata (Vallès-Penedès Basin, Catalonia, Spain): Pierolapithecus catalaunicus from BCV1 and Anoiapithecus brevirostris from C3-Aj, interpreted as stem hominids; and Dryopithecus fontani from C3-Ae of uncertain phylogenetic affinities. Pierolapithecus displays an average RET value of 19.5, Anoiapithecus of 18.6 and Dryopithecus of 10.6. The thick-enamelled condition of Pierolapithecus and Anoiapithecus is also characteristic of afropithecids, including the more derived kenyapithecins from the early Middle Miocene of Eurasia (Griphopithecus and Kenyapithecus). Given the presence of other dentognathic and craniofacial similarities, thick enamel may be interpreted as a symplesiomorphy of the Hominidae (the great ape and human clade), which would have been later independently modified along several lineages. Given the correlation between thick enamel and hard-object feeding, our results suggest that thick enamel might have been the fundamental adaptation that enabled the out-of-Africa dispersal of great-ape ancestors and their subsequent initial radiation throughout Eurasia. The much thinner enamel of Dryopithecus is difficult to interpret given phylogenetic uncertainties, being either a hominine synapomorphy or a convergently developed feature. PMID:20335211

  8. Occlusal enamel complexity in middle miocene to holocene equids (Equidae: Perissodactyla of North America.

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    Nicholas A Famoso

    Full Text Available Four groups of equids, "Anchitheriinae," Merychippine-grade Equinae, Hipparionini, and Equini, coexisted in the middle Miocene, but only the Equini remains after 16 Myr of evolution and extinction. Each group is distinct in its occlusal enamel pattern. These patterns have been compared qualitatively but rarely quantitatively. The processes influencing the evolution of these occlusal patterns have not been thoroughly investigated with respect to phylogeny, tooth position, and climate through geologic time. We investigated Occlusal Enamel Index, a quantitative method for the analysis of the complexity of occlusal patterns. We used analyses of variance and an analysis of co-variance to test whether equid teeth increase resistive cutting area for food processing during mastication, as expressed in occlusal enamel complexity, in response to increased abrasion in their diet. Results suggest that occlusal enamel complexity was influenced by climate, phylogeny, and tooth position through time. Occlusal enamel complexity in middle Miocene to Modern horses increased as the animals experienced increased tooth abrasion and a cooling climate.

  9. Hystricognath rodents from the Pinturas Formation, Early Middle Miocene of Patagonia, biostratigraphic and paleoenvironmental implications

    Science.gov (United States)

    Kramarz, Alejandro G.; Bellosi, Eduardo S.

    2005-01-01

    The Pinturas Formation is a continental succession, characterized by eolian sediments (mainly tuffaceous) and paleosols, originated in an upland setting of west central Patagonia. The main intraformational erosive surfaces and lithological changes define three sequences. The Formation bears a rich mammalian association (Florentino Ameghino's Astrapothericulan fauna), whose age in relation to the Santacrucian SALMA (middle Miocene) is still controversial. Recent collections from the Pinturas Formation, performed with stratigraphic control, allow differentiation of two distinct hystricognath rodent associations. The lower and middle sequences bear a particular combination of Colhuehuapian (early Miocene) and Santacrucian genera, mostly represented by species exclusively known to the Pinturas Formation ('Pinturan' association). The upper sequence bears typical Santacrucian species, more derived than its Pinturan counterparts. According to the rodent record, the lower and middle sequences of the Pinturas Formation are older than the base of the Santa Cruz Formation exposed at Monte Observación and Monte León, and the upper sequence may be correlated with the lowermost levels of the Santa Cruz Formation and deposits exposed at Karaiken that bear Ameghino's 'Notohippidian' fauna. These correlations agree with more recent radiometric dates and other biostratigraphic evidence, supporting Ameghino's original hypothesis. The Pinturan rodent assemblage of the lower and middle sequences suggests the presence of humid forests, in accordance with other faunal components and palynological data. Sedimentologic, paleopedologic, and ichnologic evidence, however, suggest environments dominated by herbaceous vegetation. This seeming contradiction is interpreted as the result of a marked environmental gradient due to the paleotopography and/or climatic fluctuations. The mammal record corresponds to the more humid intervals, which have less representation in the sedimentary record

  10. Prodeinotherium bavaricum (Proboscidea, Mammalia from the Middle Miocene tuffaceous sediments near Svinná (Danube Basin, Slovakia

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    Csaba Tóth

    2013-12-01

    Full Text Available An isolated p4 of Prodeinotherium bavaricum (von Meyer, 1831 from the Middle Miocene (Sarmatian sediments of Svinná (the Danube Basin, Slovakia is morphometrically described and compared with similarly preserved coeval material from the neighbouring countries. The material points to the taxonomic identification of isolated deinothere p4 teeth based on the combination of size, WI index and the paracristid morphology. The material presented herein is the only occurrence of the Middle Miocene deinothere from the Slovakian part of the Danube Basin.

  11. Palynostratigraphy and sedimentary facies of Middle Miocene fluvial deposits of the Amazonas Basin, Brazil

    Science.gov (United States)

    Dino, Rodolfo; Soares, Emílio Alberto Amaral; Antonioli, Luzia; Riccomini, Claudio; Nogueira, Afonso César Rodrigues

    2012-03-01

    Palynostratigraphic and sedimentary facies analyses were made on sedimentary deposits from the left bank of the Solimões River, southwest of Manaus, State of Amazonas, Brazil. These provided the age-dating and subdivision of a post-Cretaceous stratigraphic succession in the Amazonas Basin. The Novo Remanso Formation is subdivided into upper and lower units, and delineated by discontinuous surfaces at its top and bottom. The formation consists primarily of sandstones and minor mudstones and conglomerates, reflecting fluvial channel, point bar and floodplain facies of a fluvial meandering paleosystem. Fairly well-preserved palynoflora was recovered from four palynologically productive samples collected in a local irregular concentration of gray clay deposits, rich in organic material and fossilized wood, at the top of the Novo Remanso Formation upper unit. The palynoflora is dominated by terrestrial spores and pollen grains, and is characterized by abundant angiosperm pollen grains ( Tricolpites, Grimsdalea, Perisyncolporites, Tricolporites and Malvacearumpollis). Trilete spores are almost as abundant as the angiosperm pollen, and are represented mainly by the genera Deltoidospora, Verrutriletes, and Hamulatisporis. Gymnosperm pollen is scarce. The presence of the index species Grimsdalea magnaclavata Germeraad et al. (1968) indicates that these deposits belong to the Middle Miocene homonymous palynozone (Lorente, 1986; Hoorn, 1993; Jaramillo et al., 2011). Sedimentological characteristics (poorly sorted, angular to sub-angular, fine to very-coarse quartz sands facies) are typical of the Novo Remanso Formation upper part. These are associated with a paleoflow to the NE-E and SE-E, and with an entirely lowland-derived palinofloristic content with no Andean ferns and gymnosperms representatives. All together, this suggests a cratonic origin for this Middle Miocene fluvial paleosystem, which was probably born in the Purus Arch eastern flank and areas surrounding the

  12. Reappearance of Galerix (Erinaceomorpha, Mammalia) at the Middle to Late Miocene transition in South Germany: biostratigraphic and palaeoecologic implications

    NARCIS (Netherlands)

    Prieto, J.; Hoek Ostende, van den L.W.; Böhme, M.

    2011-01-01

    The presence of Galerix molars in the South German fossil locality Hammerschmiede 3 is interpreted as evidence for a reimmigration of West European origin into the North Alpine Foreland Basin at the transition of the Middle to Late Miocene. The brief re-appearence of Galerix in southern Germany can

  13. Middle Miocene pedological record of monsoonal climate from NW Himalaya (Jammu & Kashmir State), India

    Science.gov (United States)

    Ganjoo, R. K.; Shaker, Som

    2007-03-01

    The Lower Siwalik Subgroup represented by the Dodenal (Kamlial Formation) and Ramnagar Members (Chinji Formation) is well exposed at Ramnagar, District Udhampur, Jammu & Kashmir State. The Ramnagar Member consists of an alternating sequence of silt and mudstone formed under crevasse-splay and flood-plain environments of deposition. Argillisol and gleysol soils are developed on the Ramnagar Member deposits. Argillisols formed under well-drained conditions at high levels, whereas gleysols formed under poorly drained conditions at low levels of the palaeo-landscape. Geochemical and micromorphological studies of the Ramnagar Member palaeosols suggest formation under wet and humid climatic conditions. Early uplift of the Tibetan Plateau/Himalaya resulted in a contemporaneous change in precipitation and monsoonal climate conditions within the Indian region beginning in Middle Miocene.

  14. Extant cheilostomatous bryozoans of the Middle Miocene from the north Western Desert, Egypt

    Science.gov (United States)

    Ziko, Abdelmohsen; Eweda, Shehta; El-Khawaga, Samar

    2016-12-01

    Twenty-nine extant Bryozoan species, belonging to the order Cheilostomata are described. They are from the Middle Miocene Marmarica Formation of the northern Western Desert in Egypt. The described bryozoans are collected from Matruh and Siwa areas. Fourteen species belong to the suborder Anasca, and the other fifteen species belong to the suborder Ascophora. The identified bryozoan species exhibit many zoarial growth forms. The encrusting forms are membraniporiform and celleporiform, while the erect forms are adeoniforms, eschariforms, vinculariiforms, reteporiform, and cellariiforms. They extend in the geologic record from the Eocene to the Recent, distributed mainly in the Tethyan realm, and recorded also from North America. The extant species are mainly of Mediterranean affinity, some are of wider distribution in the Atlantic and Pacific oceans, and are rarely cosmopolitan.

  15. MIDDLE EOCENE TO EARLY MIOCENE FORAMINIFERAL BIOSTRATIGRAPHY IN THE EPILIGURIAN SUCCESSION (NORTHERN APENNINES, ITALY

    Directory of Open Access Journals (Sweden)

    NICOLETTA MANCIN

    2001-11-01

    Full Text Available A quantitative biostratigraphical study was performed on the foraminiferal assemblages from 15 stratigraphic sections of the Epiligurian Succession (Middle Eocene-Early Miocene, Northern Apennines, Italy. This study enabled us to identify the presence of some of the standard bioevents and to note that other bioevents are absent or show a different chronostratigraphic range. Other additional bioevents, identified throughout the area, have therefore been utilised to improve the biostratigraphical resolution of the Epiligurian sediments. These bioevents include the massive extinction of the muricate species at the Bartonian/Priabonian boundary; the increasing abundance of Paragloborotalia opima opima near Subzone P21a/P21b and the Rupelian/Chattian boundaries; and the FO of Globoquadrina dehiscens at the Subzone N4a/N4b boundary. 

  16. The genus Macroteleia Westwood in Middle Miocene amber from Peru (Hymenoptera, Platygastridae s.l., Scelioninae)

    Science.gov (United States)

    Perrichot, Vincent; Antoine, Pierre-Olivier; Salas-Gismondi, Rodolfo; Flynn, John J.; Engel, Michael S.

    2014-01-01

    Abstract A new species of the scelionine genus Macroteleia Westwood (Platygastridae s.l., Scelioninae) is described and figured from a female beautifully preserved in Middle Miocene amber from Peru. Macroteleia yaguarum Perrichot & Engel, sp. n., shows a unique combination of characters otherwise seen independently within its congeners. It is most similar to the modern M. surfacei Brues, but differs from it by the non-foveolate notauli, the contiguous punctures of the vertex, and the continuous propodeum. The new species is the first New World fossil of the genus, suggesting a Cretaceous origin for the group and a relatively old age of the South American, tropical African, and Australian faunas, and a younger age of the modern Holarctic faunas. PMID:25147461

  17. Rapid middle Miocene collapse of the Mesozoic orogenic plateau in north-central Nevada

    Science.gov (United States)

    Colgan, Joseph P.; Henry, Christopher D.

    2009-01-01

    The modern Sierra Nevada and Great Basin were likely the site of a high-elevation orogenic plateau well into Cenozoic time, supported by crust thickened during Mesozoic shortening. Although crustal thickening at this scale can lead to extension, the relationship between Mesozoic shortening and subsequent formation of the Basin and Range is difficult to unravel because it is unclear which of the many documented or interpreted extensional episodes was the most significant for net widening and crustal thinning. To address this problem, we integrate geologic and geochronologic data that bear on the timing and magnitude of Cenozoic extension along an ???200km east-west transect south of Winnemucca, Battle Mountain, and Elko, Nevada. Pre-Cenozoic rocks in this region record east-west Palaeozoic and Mesozoic compression that continued into the Cretaceous. Little to no tectonism and no deposition followed until intense magmatism began in the Eocene. Eocene and Oligocene ash-flow tuffs flowed as much as 200km down palaeovalleys cut as deeply as 1.5km into underlying Palaeozoic and Mesozoic rocks in a low-relief landscape. Eocene sedimentation was otherwise limited to shallow lacustrine basins in the Elko area; extensive, thick clastic deposits are absent. Minor surface extension related to magmatism locally accompanied intense Eocene magmatism, but external drainage and little or no surface deformation apparently persisted regionally until about 16-17Ma. Major upper crustal extension began across the region ca. 16-17Ma, as determined by cross-cutting relationships, low-temperature thermochronology, and widespread deposition of clastic basin fill. Middle Miocene extension was partitioned into high-strain (50-100%) domains separated by largely unextended crustal blocks, and ended by 10-12Ma. Bimodal volcanic rocks that erupted during middle Miocene extension are present across most of the study area, but are volumetrically minor outside the northern Nevada rift. The modern

  18. Mediterranean proto-sapropels in the Middle Miocene: implications for the strength of the African monsoon and link to Miocene glaciations

    Science.gov (United States)

    John, C. M.; Mutti, M.; Adatte, T.; Laskar, J.

    2003-04-01

    The strength of the African monsoon is known to have played a major role in determining sedimentation patterns in the Mediterranean during the Plio-Pleistocene. Increased meteoric water input by strong monsoons reduced surface water salinity, and the resulting slower water-mixing rate triggered the deposition of organic-rich layers called "sapropels". Here we present some proxy data coming from a mixed siliciclastic-carbonate section outcropping on the Maltese Islands that suggests that sapropels deposits already existed in the Middle Miocene. This implies that an enhanced monsoonal climate was likely active at that time. Our primary evidences for the existence of "proto-sapropels" are runoff proxies (clay mineral assemblages and abundance) coupled with oxygen isotopes. These indicate that a direct link existed between increased runoff regarded here as a proxy for the strength of the Monsoon- and Miocene global climate (Antarctic glaciation). Each Miocene phase of glaciation is reflected in the section as an increased flux of continental-derived material. Moreover, stable isotopes of carbon and Corg:Norg ratio analyses of organic matter revealed a higher mixing rate of terrigenous and marine organic matters during times of increased sedimentation. This is in good agreement with a monsoon model where increased sedimentation is linked to increased continental runoff. Spectral analysis of the section revealed the presence of Milankovitch-scaled cycles with a strong 100 k.y. frequency. Astronomically calibrated age model for the section shows that the African monsoon has probably initiated around 16.7 Ma and underwent a major strengthening around 13.8 Ma, a time corresponding to enhanced siliciclastic deposition on the Malta-Ragusa platform and to the global cooling phase of the Mi3 Antarctic ice-buildup phase. We argue that the strong coherence between Miocene glaciation phases and increased runoff into the Mediterranean is due to a link between Antarctic cooling

  19. The Middle Aragonian (Middle Miocene Micromammals from La Retama (Intermediate Depression, Tagus Basin Province of Cuenca, Spain

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    Sevilla, P.

    2006-12-01

    Full Text Available The micromammal fauna from the Middle Miocene (Middle Aragonian of La Retama, eastern central Spain, is described. It is a relatively poor rodent fauna composed by ten species only, associated to a highly diverse bat fauna, which includes five genera. The insectivores are represented by two species. This fossil assemblage has been correlated to zone Db (MN 5. The palaeoenvironmental reconstruction based on micromammals indicates open and dry conditions for this locality.Se describen los micromamíferos del Mioceno medio (Aragoniense medio de La Retama, sector centro-oriental español. La fauna de roedores es relativamente pobre y está compuesta únicamente por diez especies. Sin embargo, cabe destacar la elevada diversidad de los quirópteros, representados por cinco géneros. Se describe también dos taxa de insectívoros. Esta asociación fósil ha sido correlacionada con la zona Db (MN5. La reconstrucción paleoambiental de La Retama inferida a partir de la fauna de micromamíferos corresponde a un ambiente abierto y seco.

  20. Carnivores from the Middle Miocene Ngorora Formation (13-12 Ma, Kenya

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    Pickford, M.

    2005-12-01

    Full Text Available The late Middle Miocene Ngorora Formation has yielded several interesting carnivore fossils. Among these are a huge creodont, Megistotherium osteothlastes, at 12 Ma, possibly the youngest record of the species, an amphicyonid, two species of mustelids (an otter and a honey badger, two kinds of viverrids (one about the size of a civet, one the size of a genet and an extremely small herpestid the size of a dwarf mongoose. It has also yielded remains of a moderate sized percrocutid. Perhaps the most interesting carnivore is a new genus and species of bundont viverrid that is intermediate in size and morphology between Early Miocene Orangictis on the one hand and Plio-Pleistocene Pseudocivetta on the other. This lineage of bundont viverrids appears to have been restricted to Africa.La Formación Mioceno medio final de Ngorora (Kenia ha suministrado carnívoros muy interesantes. Entre los que se encuentran un enorme creodonto, Megistotherium osteothlastes, de 12 Ma, que posiblemente es el registro más moderno de la especie, un amphicyonido, dos especies de mustélidos (una nutria y un melivorino, dos diferentes tipos de vivérridos (uno de la talla de una civeta y el otro de la de una jineta y un herpéstido diminuto de la talla de una mangosta enana. También hay fósiles de un percrocútido de talla moderada. Tal vez el carnívoro más interesante es un nuevo género y especie de vivérrido bunodonto que presenta una talla y morfología intermedia entre Oragictis del Mioceno inferior y Pseudocivetta del Plio-Pleistoceno. Esta línea de vivérridos bunodontos parece estar restringida a Africa.

  1. New paleomagnetic constraints on middle Miocene strike-slip faulting along the middle Altyn Tagh Fault

    Science.gov (United States)

    Li, Bingshuai; Yan, Maodu; Zhang, Weilin; Fang, Xiaomin; Meng, Qingquan; Zan, Jinbo; Chen, Yi; Zhang, Dawen; Yang, Yongpeng; Guan, Chong

    2017-06-01

    Knowledge of the evolution of the Altyn Tagh Fault (ATF) has significant implications for our understanding of the tectonic deformation of the Tibetan Plateau. Controversy exists regarding the formation of the orocline-like arcuate structures or curved thrust faults south of the ATF. In this paper, we conducted a paleomagnetic rotation study of the Akatengnengshan (AK) and Youshashan (YSS) anticlines to determine whether the changes in the anticlines' axes were caused by frictional drag associated with sinistral strike-slip faulting along the ATF. No significant paleomagnetic rotations during the last 20 Ma were observed at the Xichagou and Laomangai localities, which are situated along the YSS anticline, whereas significant counterclockwise (CCW) rotations of 50° that occurred between 16.2 and 11.1 Ma were noted at the Yitunbulake locality, which lies along the western edge of the AK anticline. This amount of CCW rotation is consistent with the difference in axes between the AK and YSS anticlines. Combined with other geological evidence, we believe that the middle ATF was active between 16 and 11 Ma. Frictional drag associated with sinistral strike-slip motion likely resulted in the 50° CCW rotation of the AK anticline, which was originally straight or parallel to the YSS anticline. There was concentrated or insignificant strike-slip faulting along the middle ATF before 16 Ma, but rapid and distributed (< 40 km) strike-slip faulting occurred between 16 and 11 Ma at a rate of ≥10 mm/yr, and the minimum displacement was 50 km.

  2. Brachypotherium cf. brachypus and Lartetotherium sp. (Rhinocerotidae, Perissodactyla, Mammalia from the Middle Miocene Dúbravka-Pole site (western Slovakia

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    Júlia Zervanová

    2013-06-01

    Full Text Available The vertebrate fossil record from the Dúbravka-Pole site in the territory of Devínska Kobyla consists of Brachypotherium cf. brachypus and Lartetotherium sp. dental and osteological remains. The both taxa lived in swampy to forested land at the shore of shallow brackish sea (or lagoon? during the Early Sarmatian (MN 7/8. Their occurrence is probably a result of intermittent faunal migrations during changing environmental conditions at the end of the Middle Miocene.

  3. The nasal and paranasal architecture of the Middle Miocene ape Pierolapithecus catalaunicus (primates: Hominidae): phylogenetic implications.

    Science.gov (United States)

    Pérez de Los Ríos, Miriam; Moyà-Solà, Salvador; Alba, David M

    2012-09-01

    The internal (nasal and paranasal) cranial anatomy of the Middle Miocene (11.9 Ma [millions of years ago]) great ape Pierolapithecus catalaunicus (Hominidae: Dryopithecini) is described on the basis of computed-tomography scans of the holotype specimen (IPS21350), with particular emphasis on its phylogenetic implications. Pierolapithecus displays the following characters: an anteriorly-restricted maxillary sinus that posteriorly spreads towards the ethmoidal area (thus resembling the pongine condition), although being situated well above the molar roots (as in kenyapithecins, other dryopithecins and pongines); lack of frontal sinus (a synapomorphy of derived pongines, independently acquired by both cercopithecoids and hylobatids); posteriorly-situated turbinals (as in Pongo); anteriorly-projecting nasolacrimal canal (as in Pongo); and probably stepped nasal floor with non-overlapping premaxillary-maxillary contact (as in dryopithecines and stem hominoids, although it cannot be conclusively shown due to bone damage). Overall, Pierolapithecus displays a mosaic of primitive hominid and derived pongine features that are inconsistent with this taxon being a hominine (as previously suggested). Two alternative phylogenetic interpretations are possible: Pierolapithecus may be a stem member of the Hominidae as previously suggested in its original description, or alternatively this taxon may be a stem member of the Ponginae s.l. (with the European dryopithecines being the sister taxon to the Asian pongines). Copyright © 2012 Elsevier Ltd. All rights reserved.

  4. Morphology of the thoracolumbar spine of the middle Miocene hominoid Nacholapithecus kerioi from northern Kenya.

    Science.gov (United States)

    Kikuchi, Yasuhiro; Nakatsukasa, Masato; Nakano, Yoshihiko; Kunimatsu, Yutaka; Shimizu, Daisuke; Ogihara, Naomichi; Tsujikawa, Hiroshi; Takano, Tomo; Ishida, Hidemi

    2015-11-01

    A new caudal thoracic and a new lumbar vertebra of Nacholapithecus kerioi, a middle Miocene hominoid from northern Kenya, are reported. The caudal thoracic vertebral body of N. kerioi has a rounded median ventral keel and its lateral sides are moderately concave. The lumbar vertebral body has an obvious median ventral keel. Based on a comparison of vertebral body cranial articular surface size between the caudal thoracic vertebrae in the present study and one discussed in a previous study (KNM-BG 35250BO, a diaphragmatic vertebra), N. kerioi has at least two post-diaphragmatic vertebrae (rib-bearing lumbar-type thoracic vertebrae), unlike extant hominoids. It also has thick, rounded, and moderately long metapophyses on the lumbar vertebra that project dorsolaterally. The spinous process bases of its caudal thoracic and lumbar vertebrae originate caudally between the postzygapophyses, as described previously in the KNM-BG 35250 holotype specimen. In other words, the postzygapophyses of N. kerioi do not project below the caudal border of the spinous processes, similar to those of extant great apes, and unlike small apes and monkeys, which have more caudally projecting postzygapophyses. Nacholapithecus kerioi has a craniocaudally expanded spinous process in relation to vertebral body length, also similar to extant great apes. Both these spinous process features of N. kerioi differ from those of Proconsul nyanzae. The caudal thoracic vertebra of N. kerioi has a caudally-directed spinous process, whose tip is tear-drop shaped. These features resemble those of extant apes. The morphology of the spinous process tips presumably helps vertebral stability by closely stacking adjacent spinous process tips as seen in extant hominoids. The morphology of the spinous process and postzygapophyses limits the intervertebral space and contributes to the stability of the functional lumbar region as seen in extant great apes, suggesting that antipronograde activity was included

  5. Middle Miocene coralline algal facies from the NW Transylvanian Basin (Romania)

    Science.gov (United States)

    Chelaru, Ramona; Bucur, Ioan I.; Sǎsǎran, Emanoil; Bǎlc, Ramona; Tǎmas, Tudor

    2016-04-01

    The current study focus on the coralline algae from the Middle Miocene limestones in NW Transylvania to provide an outline for their systematics and palaeoecology. The investigated samples were collected from three carbonate outcrops: Vǎlenii Șomcutei, Ciolt 1 and Ciolt 2, named after the respective localities situated in the vicinity of the Țicǎu-Preluca Mountains (NW Romania). The microfacies analysis suggest shallowing upward tendency in middle to proximal shelf environments. The coralline algae are present in the carbonate successions as detritus, branches, crusts and rhodoliths. The Vǎlenii Șomcutei section shows a depositional model where large and spheroidal rhodoliths develop in high energy conditions, most probably generated by storm waves. The sections from the Ciolt area are distinguished by the presence of green algae in association with the encrusting and geniculate coralline specimens. The identified species belong to Ord. Corallinales (Hydrolithon, Spongites, Lithophyllum, Jania), Hapalidales (Lithothamnion and Mesophyllum) and Sporolithales (Sporolithon). In the taxonomic identification of coralline red algae we used as many diagnostic features as possible, known from the description of present - day species, such as: shape of epithallial cells and roof morphology for melobesioids; presence/absence of a layer of elongated cells below sporangial compartments and number of cells in paraphyses for sporolithoids. The identified coralline algal assemblages are discussed according to different paleoenvironmental conditions (paleo-depth, hydrodynamic energy) and then compared with similar fossil assemblages and recent analogs like modern maërl and rhodolith pavements. The study of the calcareous nannoplankton assemblages from the Vǎlenii Șomcutei section [1] and the presence of previously dated tuffite intercalations of Dej Tuff [2] in the two sections near the Ciolt village confirm the Badenian age (NN5) of these deposits. [1] Chelaru R., S

  6. A new Middle Miocene selachian assemblage (Chondrichthyes, Elasmobranchii) from the Central Paratethys (Nyirád, Hungary): implications for temporal turnover and biogeography

    Science.gov (United States)

    Szabó, Márton; Kocsis, László

    2016-12-01

    A new Middle Miocene (Langhian - early Serravallian) assemblage with shark and ray teeth from Nyirád (Hungary, Transdanubia, Veszprém County) consists of nine families, with 15 different species. The assemblage shares many common genera with other Middle Miocene assemblages in the Paratethys (Notorynchus, Carcharias, Otodus, Cosmopolitodus, Hemipristis, Galeocerdo, Carcharhinus, and Aetobatus), and reflects a subtropical climate and a close connection with the Mediterranean Sea. However, a detailed faunal compilation of Miocene selachians reveals that several taxa that were still present in the Mediterranean or lived in the Paratethys during the Lower Miocene disappeared or became very rare by the Middle Miocene in the Central Paratethys (e.g., Isistius, Centrophorus, Mitsukurina, Carcharoides, Parotodus, Alopias). The taxa that went locally extinct in the Paratethys are mainly represented by deep-water or pelagic forms. Their disappearance is most probably related to the gradual separation of the Paratethys from the Mediterranean. The common presence of some large, rather pelagic sharks (e.g., Otodus, Cosmopolitodus) in the Central Paratethys during the Middle Miocene is explained here by the widespread occurrence of their potential prey represented by marine mammals (e.g., whales and dolphins).

  7. A new Middle Miocene selachian assemblage (Chondrichthyes, Elasmobranchii from the Central Paratethys (Nyirád, Hungary: implications for temporal turnover and biogeography

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    Szabó Márton

    2016-12-01

    Full Text Available A new Middle Miocene (Langhian - early Serravallian assemblage with shark and ray teeth from Nyirád (Hungary, Transdanubia, Veszprém County consists of nine families, with 15 different species. The assemblage shares many common genera with other Middle Miocene assemblages in the Paratethys (Notorynchus, Carcharias, Otodus, Cosmopolitodus, Hemipristis, Galeocerdo, Carcharhinus, and Aetobatus, and reflects a subtropical climate and a close connection with the Mediterranean Sea. However, a detailed faunal compilation of Miocene selachians reveals that several taxa that were still present in the Mediterranean or lived in the Paratethys during the Lower Miocene disappeared or became very rare by the Middle Miocene in the Central Paratethys (e.g., Isistius, Centrophorus, Mitsukurina, Carcharoides, Parotodus, Alopias. The taxa that went locally extinct in the Paratethys are mainly represented by deep-water or pelagic forms. Their disappearance is most probably related to the gradual separation of the Paratethys from the Mediterranean. The common presence of some large, rather pelagic sharks (e.g., Otodus, Cosmopolitodus in the Central Paratethys during the Middle Miocene is explained here by the widespread occurrence of their potential prey represented by marine mammals (e.g., whales and dolphins.

  8. Wetter and cooler: pronounced temperate climate conditions in western Anatolia during the Middle Miocene Climatic Optimum

    Science.gov (United States)

    Güner, Tuncay H.; Bouchal, Johannes M.; Köse, Nesibe; Denk, Thomas

    2017-04-01

    proposed that has only a weak seasonality in precipitation (lower precipitation in winter). The findings of our study provide valuable information for inferring palaeoenvironments of middle Miocene rich ungulate faunas in western Turkey (e.g. Paşalar), for which seasonal tropical and subtropical forest communities have been proposed (Andrews, 1990). The fossil floras of the Tınaz and Salihpaşalar lignite mines, representing the Tınaz sub-basin and the main basin of the wider Yataǧan Basin, are investigated at the moment, and a synthesis paper combining and comparing evidence from the macro floral and palynological data is soon to be submitted. Andrews. (1990) Palaeoecology of the Miocene fauna from Paşalar, Turkey. Journal of Human evolution 19:569-582.

  9. Effects of CO2, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study

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    G. Munhoven

    2010-04-01

    Full Text Available The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma. Several proxy-based reconstructions support warmer and more humid climate during the MMCO. The mechanisms responsible for the warming at MMCO and particulary the role of the atmospheric carbon dioxide CO2 are still highly debated. Here we carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the absence of ice on the continents, the opening of the Central American and Eastern Tethys Seaways, the lowering of the topography on land, the effect of various atmospheric CO2 concentrations and the vegetation retroaction. Our results show that a higher than present-day CO2 concentration is necessary to generate a warmer climate at all latitudes at the Middle Miocene, in agreement with the terrestrial proxy reconstructions which suggest high atmospheric CO2 concentrations at MMCO. Nevertheless, the changes in sea-surface conditions and the lowering of the topography on land also produce significant local warming that may, locally, even be stronger than the CO2 induced temperature increases. The lowering of the topography leads to a more zonal atmospheric circulation and allows the westerly flow to continue over the lowered Plateaus at mid-latitudes. The reduced height of the Tibetan Plateau notably prevents the development of a monsoon-like circulation, whereas the reduction of elevations of the North American and European reliefs strongly increases precipitation from northwestern to eastern Europe. The changes in vegetation cover contributes to maintain and even to intensify the the warm and humid conditions produced by the other factors, suggesting that the vegetation-climate interactions could help to improve the model-data comparison.

  10. Geochemistry, environmental and provenance study of the Middle Miocene Leitha limestones (Central Paratethys

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    Ali Ahmed

    2017-06-01

    Full Text Available Mineralogical, major, minor, REE and trace element analyses of rock samples were performed on Middle Miocene limestones (Leitha limestones, Badenian collected from four localities from Austria (Mannersdorf, Wöllersdorf, Kummer and Rosenberg quarries and the Fertőrákos quarry in Hungary. Impure to pure limestones (i.e. limited by Al2O3 contents above or below 0.43 wt. % were tested to evaluate the applicability of various geochemical proxies and indices in regard to provenance and palaeoenvironmental interpretations. Pure and impure limestones from Mannersdorf and Wöllersdorf (southern Vienna Basin show signs of detrital input (REEs = 27.6 ± 9.8 ppm, Ce anomaly = 0.95 ± 0.1 and the presence of quartz, muscovite and clay minerals in impure limestones and diagenetic influence (low contents of, e.g., Sr = 221 ± 49 ppm, Na is not detected, Ba = 15.6 ± 8.8 ppm in pure limestones. Thus, in both limestones the reconstruction of original sedimentary palaeoenvironments by geochemistry is hampered. The Kummer and Fertőrákos (Eisenstadt–Sopron Basin comprise pure limestones (e.g., averages Sr = 571 ± 139 ppm, Na = 213 ± 56 ppm, Ba = 21 ± 4 ppm, REEs = 16 ± 3 ppm and Ce anomaly = 0.62 ± 0.05 and composed predominantly of calcite exhibiting negligible diagenesis. Deposition under a shallow-water, well oxygenated to intermittent dysoxic marine environment can be reconstructed. Pure to impure limestones at Rosenberg–Retznei (Styrian Basin are affected to some extent by detrital input and volcano-siliciclastic admixture. The Leitha limestones at Rosenberg have the least diagenetic influence among the studied localities (i.e. averages Sr = 1271 ± 261 ppm, Na = 315 ± 195 ppm, Ba = 32 ± 15 ppm, REEs = 9.8 ± 4.2 ppm and Ce anomaly = 0.77 ± 0.1 and consist of calcite, minor dolomite and quartz. The siliciclastic sources are characterized by immobile elemental ratios (i.e. La/Sc and Th/Co which apply not only for the siliciclastics, but also

  11. Middle miocene badenian transgression: New evidences from the Vrdnik coal basin (Fruška Gora Mt., Northern Serbia

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    Rundić Ljupko

    2013-01-01

    Full Text Available The latest field investigation of the Vrdnik Coal Basin as well as new data from numerous boreholes enabled the finding of an unconformity between the undivided continental-lacustrine Lower Miocene and the marine Middle Miocene Badenian. The different terrestrial-lacustrine sediments indicate a very mobile and dynamic environment (according to known drilling data, the total thickness of these deposits reaches up to 300 m. All these rocks belong to the Vrdnik series (Vrdnik Formation. The evolution of the Vrdnik series is distinguished by several stages (e.g. pre-lacustrine, lacustrine, peat-swamp, etc.. Each of these phases was proved by their sedimentologic and structural characteristics. On the other hand, among the fossils, only the swamp flora remains (Sequoia, Laurus, Taxodium, Glyptostrobus, etc. and poor and fragmented ostracode valves (Candona sp. were documented. Presently, the exact stratigraphic position of the Vrdnik series is unknown. Discordantly over the mentioned rocks, real marine sediments of the Paratethys Sea occur. To date, it was a completely unknown subsurface distribution of these sediments. Among a few types of rocks that have a small distribution, the so-called the Leitha limestones (Middle Miocene, Badenian have great significance (up to 98% of CaCO3. The total thickness of the limestones reaches up to 70 meters (borehole B-11. The findings of key foraminifer species (Orbulina - Globigerinoides Zone indicate an early Badenian (Moravian transgressive event (ca. 15 Ma. Lithologically, it is represented by gray, sandy marls and sandy clays, coarse-grained sands and microconglomerates in the base of the mentioned limestones (boreholes B-11, B-15, B-19, and B-21 with a total thickness of up to 15 meters. [Projekat Ministarstva nauke Republike Srbije, br. 176015

  12. Depositional environment, organic matter characterization and hydrocarbon potential of Middle Miocene sediments from northeastern Bulgaria (Varna-Balchik Depression

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    Zdravkov Alexander

    2015-10-01

    Full Text Available The depositional environments and hydrocarbon potential of the siliciclastic, clayey and carbonate sediments from the Middle Miocene succession in the Varna-Balchik Depression, located in the south-eastern parts of the Moesian Platform, were studied using core and outcrop samples. Based on the lithology and resistivity log the succession is subdivided from base to top into five units. Siliciclastic sedimentation prevailed in the lower parts of units I and II, whereas their upper parts are dominated by carbonate rocks. Unit III is represented by laminated clays and biodetritic limestone. Units IV and V are represented by aragonitic sediments and biomicritic limestones, correlated with the Upper Miocene Topola and Karvuna Formations, respectively. Biogenic silica in the form of diatom frustules and sponge spicules correlates subunit IIa and unit III to the lower and upper parts of the Middle Miocene Euxinograd Formation. Both (subunits contain organic carbon contents in the order of 1 to 2 wt. % (median: 0.8 for subunit IIa; 1.3 for unit III, locally up to 4 wt. %. Based on Hydrogen Index values (HI and alkane distribution pattern, the kerogen is mainly type II in subunit IIa (average HI= 324 mg HC/g TOC and type III in unit III (average HI ~200 mg HC/g TOC. TOC and Rock Eval data show that subunit IIa holds a fair (to good hydrocarbon generative potential for oil, whereas the upper 5 m of unit III holds a good (to fair potential with the possibility to generate gas and minor oil. The rocks of both units are immature in the study area. Generally low sulphur contents are probably due to deposition in environments with reduced salinity. Normal marine conditions are suggested for unit III. Biomarker composition is typical for mixed marine and terrestrial organic matter and suggests deposition in dysoxic to anoxic environments.

  13. LOWER TO MIDDLE MIOCENE MOLLUSC ASSEMBLAGES FROM THE TORINO HILLS (NW ITALY: SYNTHESIS OF NEW DATA AND CHRONOSTRATIGRAPHICAL ARRANGEMENT

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    MARTA ZUNINO

    2009-11-01

    Full Text Available The goal of this study is to correlate in chronostratigraphic order the fossil assemblages of selected, historical Lower and Middle Miocene localities of the Torino Hills. More than 18,000 specimens have been classified and assigned to 798 taxa (cf. Tab. I. The compositional analyses mainly concern the 672 listed gastropods, most of which were already described in classical monographies. The critical evaluation of the morphological and architectural shell parameters let to a significant reduction of the species that could be realistically maintained in comparison to those cited in literature from the Torino Hills Miocene. Six localities have been analyzed: Valle Ceppi (VC and Val Sanfrà (VS referred to the middle part of the Burdigalian stage (N7a Biozone, Villa Bertini at the topmost Burdigalian, Villa Allason (VA and Villa Forzano (VF at the early Langhian (N8 Biozone and Monte dei Cappuccini (MC at the late Langhian (N9 Biozone. On the whole, the fossil assemblages show a taxonomic variation of both biochronologic and palaeobiogeographic meaning. Actually, the similarity in specific biodiversity of VC, VS, VB, VA and VS reflects homogeneity among late Burdigalian to early Langhian palaeocommunities. As to MC, its deep difference on VC is correlatable with the eastern closing between the Mediterranean areas and the Tethyan Realm, at the boundary Burdigalian-Langhian, that brought to disjoint evolutions of the Mediterranean and Indo-Pacific palaeocommunities, the former being influenced by oceanic current changes and related climatic variations. 

  14. Paleointensity and paleodirection of the geomagnetic field in the middle Miocene: Evidence from late cenozoic volcanites of primorye

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    Shcherbakova, V. V.; Shcherbakov, V. P.; Bretshtein, Yu. S.; Zhidkov, G. V.

    2010-12-01

    We present the results of analyzing a representative collection of the middle Miocene 12.4-10.0 Ma basalts that compose the volcanic cover of the Shufan and Sovgavan plateaus, namely the Nikolo-L'vovsk (NL) and Sovetskaya Gavan (SG) volcanic fields. Preliminary data are obtained about the relicts of some volcanic edifices within the West and East Sikhote-Alin volcanic belts, namely the Shishlovskii, Malyshevo, and Truzhenik objects. It is established that the volcanic rocks from these localities are characterized by similar petrologic and magnetic properties. Thermal cleaning of the samples is carried out, and the coordinates of the paleomagnetic pole are determined as Λ = 190.2°E, Φ = 71.3°N for basalts of the Nokolo-L'vovsk area and Λ = 180.4°E, Φ = 71.9°N for rocks from the Sovgavan locality. These values are consistent with the data for coeval volcanics from other regions of Eurasia. Reliable determinations of the paleointensity H pal for a representative collection of samples were obtained using the Thellier method. The corresponding values of the virtual dipole moment (VDM) are almost half its present-day value. The analysis of the Miocene VDM values available from the world database revealed a low average field 5.06 × 1022 Am2 characterized by high variance σ = 2.13 × 1022 Am2 at that time. The similarity of VDM values for the Miocene characterized by frequent inversions and for the Cretaceous Superchron supports the hypothesis of the lack of a correlation between the VDM values and the frequency of geomagnetic inversions.

  15. The role of East-Tethys seaway closure in the middle Miocene climatic transition (ca. 14 Ma

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    N. Hamon

    2013-04-01

    Full Text Available The middle Miocene climatic transition (MMCT, approximately 14 Ma is a key period in Cenozoic cooling and cryospheric expansion. Despite it is well documented in isotopic record, the causes of the MMCT are still a matter of debate. Among various hypotheses, some authors suggested that it was linked with the final closure of the East-Tethys seaway and subsequent oceanic circulation reorganisation. The aim of the present study is to quantify the impact of varying East-Tethys seaway depths on middle Miocene ocean and climate, in order to better understand its role in the MMCT. We present four sensitivity experiments with a fully coupled ocean-atmosphere generalized circulation model. Our results indicate the presence of a warm and salty water source in the northern Indian Ocean when the East-Tethys is deep-open (4000 or 1000 m, which corresponds to the Tethyan Indian Saline Water (TISW described on the basis of isotopic studies. This water source is absent in the experiments with shallow (250 m and closed East-Tethys, inducing strong changes in the latitudinal density gradient and ultimately the reinforcement of the Antarctic Circumpolar Current (ACC. Moreover, when the East-Tethys seaway is shallow or closed, there is a westward water flow in the Gibraltar Strait that strengthens the Atlantic meridional overturning circulation (AMOC compared to the experiments with deep-open East-Tethys. Our results therefore suggest that the shoaling and final closure of the East-Tethys seaway played a major role in the oceanic circulation reorganisation during the middle Miocene. The results presented here provide new constraints on the timing of the East-Tethys seaway closure, and particularly indicate that, prior to 14 Ma, a deep-open East-Tethys should have allow the formation of TISW. Moreover, whereas the final closure of this seaway likely played a major role in the MMCT, we suggest that it was not the only driver of the global cooling and Antarctica ice

  16. Middle Miocene chitons (Polyplacophora from the Slovak part of the Vienna Basin and the Danube Basin (Central Paratethys

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    Ruman Andrej

    2015-12-01

    Full Text Available We describe species-rich chiton assemblages from the Middle Miocene of the Slovak part of the Vienna Basin and the Danube Basin (Central Paratethys. They were found at five localities, including Devínska Nová Ves brickyard, Devínska Nová Ves-Útočnica, Rohožník clay pit, Kúty-45 borehole and Dubová. Thirteen species belong to eight genera from the families Leptochitonidae, Hanleyidae, Callochitonidae, Chitonidae, Tonicellidae and Acanthochitonidae. They occur predominantly in redeposited, moderately-sorted rhodolith-rich or well-sorted bioclastic layers of the Late Badenian age, and belong to lineages that presently inhabit warm-temperate and tropical regions.

  17. Limpet-shaped gastropods of the genus Diodora (Vetigastropoda: Fissurellidae) from the Middle Miocene of Western Ukraine

    Science.gov (United States)

    Dell'Angelo, Bruno; Sosso, Maurizio; Anistratenko, Olga; Anistratenko, Vitaliy

    2017-06-01

    The genus Diodora Gray, 1821 is widely represented in the Middle Miocene of the Central Paratethys with specimens usually attributed to D. graeca (Linnaeus, 1758) or D. italica (Defrance, 1820), well-known recent species of the Atlantic / Mediterranean Basin. In samples from the Upper Badenian of Western Ukraine we found two clusters of Diodora specimens, showing a similarity with these species, but a review of shell diagnostic characters using a statistical approach has revealed their clear conchological separateness. The first species from Varovtsi and Horodok is attributed herein to D. nodosa (Eichwald, 1830), whereas the second species from Maksymivka is described as a new species, D. stalennuyi sp. nov. We consider that these molluscs inhabited the Polish-Ukrainian marginal part of the Late Badenian Basin. Detailed descriptions of the protoconch and teleoconch morphology of the taxa involved, including SEM images, are presented.

  18. Sedimentary environment and paleosols of middle Miocene fluvial and lacustrine sediments in central Japan: Implications for paleoclimate interpretations

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    Hatano, Nozomi; Yoshida, Kohki

    2017-01-01

    Sedimentary facies analysis and description of paleosols were carried out for the middle Miocene Tokiguchi Porcelain Clay Formation (PCF) in central Japan in order to interpret the soil-forming environments during a long hiatus in the Japanese Islands. The sedimentary facies suggests that deposition occurred mainly in a lacustrine environment, with minor channel-fill and debris-flow deposits associated with alluvial fan environments. The coarse-grained sediments, which are inferred to have been deposited in channel-bar and debris-flow deposits, are present only in the marginal area of the sedimentary basin. Mature paleosols are identified in the Tokiguchi PCF, characterized by illuviated clay, identifiable soil horizons including Bt horizons and many in situ plant fossils, and are then similar to Ultisols. Most tree trunk fossils, however, were preserved by burial beneath debris-flow deposits. Most of paleosols formed on lacustrine deposits and were covered by lacustrine clay and silt deposits, without intervening coarse-grained deposits, such as flood-flow deposits. This change of sedimentary facies indicates a dramatic change of hydrologic environment, from stagnant water to entirely desiccated conditions, promoting weathering and soil formation. The relationship between sedimentary facies and Pedotypes, consequently, implies the repetition of specific events, i.e., submergence and emergence of lake bottom, most likely due to formation and drainage of a dammed lake. These isolated events and development of mature paleosols might suggest specific characteristics of middle Miocene weathering conditions, such as seasonally heavy rainfall and/or warm climatic conditions in the Japanese Islands.

  19. The Middle Miocene of the Fore-Carpathian Basin (Poland, Ukraine and Moldova)

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    Wysocka, Anna; Radwański, Andrzej; Górka, Marcin; Bąbel, Maciej; Radwańska, Urszula; Złotnik, Michał

    2016-09-01

    Studies of Miocene sediments in the Fore-Carpathian Basin, conducted by geologists from the University of Warsaw have provided new insights on the distribution of the facies infilling the basin, particularly in the forebulge and back-bulge zones. The origin of the large-scale sand bodies, evaporitic deposits and large-scale organic buildups is discussed, described and verified. These deposits originated in variable, shallow marine settings, differing in their water chemistry and the dynamics of sedimentary processes, and are unique with regard to the fossil assemblages they yield. Many years of taxonomic, biostratigraphic, palaeoecologic and ecotaphonomic investigations have resulted in the identification of the fossil assemblages of these sediments, their age, sedimentary settings and post-mortem conditions. Detailed studies were focused on corals, polychaetes, most classes of molluscs, crustaceans, echinoderms, and fishes.

  20. Decrease in coccolithophore calcification and CO2 since the middle Miocene

    Science.gov (United States)

    Bolton, Clara T.; Hernández-Sánchez, María T.; Fuertes, Miguel-Ángel; González-Lemos, Saúl; Abrevaya, Lorena; Mendez-Vicente, Ana; Flores, José-Abel; Probert, Ian; Giosan, Liviu; Johnson, Joel; Stoll, Heather M.

    2016-01-01

    Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone εp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity.

  1. Genesis of Middle Miocene Yellowstone hotspot-related bonanza epithermal Au-Ag deposits, Northern Great Basin, USA

    Science.gov (United States)

    Saunders, J. A.; Unger, D. L.; Kamenov, G. D.; Fayek, M.; Hames, W. E.; Utterback, W. C.

    2008-09-01

    Epithermal deposits with bonanza Au-Ag veins in the northern Great Basin (NGB) are spatially and temporally associated with Middle Miocene bimodal volcanism that was related to a mantle plume that has now migrated to the Yellowstone National Park area. The Au-Ag deposits formed between 16.5 and 14 Ma, but exhibit different mineralogical compositions, the latter due to the nature of the country rocks hosting the deposits. Where host rocks were primarily of meta-sedimentary or granitic origin, adularia-rich gold mineralization formed. Where glassy rhyolitic country rocks host veins, colloidal silica textures and precious metal-colloid aggregation textures resulted. Where basalts are the country rocks, clay-rich mineralization (with silica minerals, adularia, and carbonate) developed. Oxygen isotope data from quartz (originally amorphous silica and gels) from super-high-grade banded ores from the Sleeper deposit show that ore-forming solutions had δ 18O values up to 10‰ heavier than mid-Miocene meteoric water. The geochemical signature of the ores (including their Se-rich nature) is interpreted here to reflect a mantle source for the “epithermal suite” elements (Au, Ag, Se, Te, As, Sb, Hg) and that signature is preserved to shallow crustal levels because of the similar volatility and aqueous geochemical behavior of the “epithermal suite” elements. A mantle source for the gold in the deposits is further supported by the Pb isotopic signature of the gold ores. Apparently the host rocks control the mineralization style and gangue mineralogy of ores. However, all deposits are considered to have derived precious metals and metalloids from mafic magmas related to the initial emergence of the Yellowstone hotspot. Basalt-derived volatiles and metal(loid)s are inferred to have been absorbed by meteoric-water-dominated geothermal systems heated by shallow rhyolitic magma chambers. Episodic discharge of volatiles and metal(loid)s from deep basaltic magmas mixed with

  2. Plate interactions control middle late Miocene, proto-Gulf and Basin and Range extension in the southern Basin and Range

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    Henry, Christopher D.; Aranda-Gomez, J. Jorge

    2000-03-01

    Middle-late Miocene (proto-Gulf; ˜12-6 Ma) extension around the Gulf of California (Gulf Extensional Province) is commonly interpreted as resulting from partitioning of oblique Pacific-North American plate motion into strike-slip displacement along the margin and east-northeast extension perpendicular to the margin within the North American plate. We propose that this mechanism also applies to kinematically similar, predominantly east-northeast extension that occurred at the same time throughout the southern Basin and Range province, from southern Arizona and New Mexico to the Trans-Mexican Volcanic Belt. New field and 40Ar/ 39Ar data in Sinaloa and Durango confirm that this episode of extension occurred on the mainland side of the Gulf and in the Basin and Range east of the Sierra Madre Occidental, which is generally considered the eastern margin of the Gulf Extensional Province. Published data indicate the middle-late Miocene episode also occurred across the northern and southern ends of the Sierra Madre where the Gulf Extensional Province connects with the Basin and Range: (1) from central Sonora into southern Arizona and New Mexico, and (2) from Nayarit into central Mexico north of the Trans-Mexican Volcanic Belt. This episode appears to have affected an area that continues to the eastern edge of the Basin and Range province in Texas and San Luis Potosi. Recognition that this episode of extension affected the entire southern Basin and Range resolves the discrepancy between the amount of extension calculated based on plate reconstructions and that based on field data within the Gulf Extensional Province alone. Published plate reconstructions require 160 to 110 km of east-northeast extension between ˜12 and 6 Ma. If taken up solely within the Gulf Extensional Province, this would have generated 66 to 78% extension, which is much greater than observed. Spread across the entire southern Basin and Range it requires only ˜20% total extension, which is more

  3. Devínska Kobyla – a window into the Middle Miocene shallow-water marine environments of the Central Paratethys (Vienna Basin, Slovakia

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    Matúš Hyžný

    2012-10-01

    Full Text Available Middle Miocene strata exposed at Devínska Kobyla Hill (Malé Karpaty Mts document the temporal and spatial changes in shallow-water environments of the northern Vienna Basin during the Late Badenian and Early Sarmatian. Middle Miocene deposits of the Studienka and Holíč formations border this hill essentially along its full perimeter. The present overview of 16 localities based on published observations and new sampling shows that the Middle Miocene deposits contain species-rich micro- and macrofaunal assemblages as well as nannoflora. This contribution includes lists of all marine faunal (except tetrapods and microfloral taxa known to date. The localities can be divided into three groups on the basis of their lithology and the abundance of molluscs and foraminifers in fossil assemblages: Devín area, Dúbravka area and Devínska Nová Ves area. On the basis of foraminifers the localities in the Dúbravka area (Dúbravská hlavica, Pektenová lavica, Starý lom, partly Fuchsov lom can be assigned to the Early Sarmatian (based on benthic taxa, whereas the localities in the Devín (Šibeničný vrch, Štítová, Terasy, Lomnická, Lingulová lavica, Glosusová lavica and Devínska Nová Ves (Sandberg 1–2, Malý Sandberg, Waitov lom, Glavica, Štokeravská vápenka-Bonanza areas are predominantly of the Late Badenian age (based on benthic and planktonic taxa. However, molluscs imply that the deposits from the Dúbravka area are of Late Badenian age. The differences in the estimates of stratigraphic age between on molluscs and foraminifers can be explained with the persistence of typically Badenian mollusc taxa in the marginal parts of the Central Paratethys Sea during the Middle Miocene. For every studied locality palaeoenvironmental conditions based mostly on molluscs and foraminifers are inferred.

  4. The palaeoecologic and biostratigraphic evaluation of Middle Miocene freshwater sediments and microfossils near Denkendorf (Bavaria)

    Science.gov (United States)

    Pirkenseer, C.; Reichenbacher, B.

    2009-04-01

    foreland basin. Furthermore the ostracod assemblage is related to taxa recorded from the Miocene infill of the (isolated) Steinheim meteorite crater (e.g., Pseudocandona steinheimensis). According to the evaluation of the micromammal molars (Megacricetodon cf. M. minor and M. cf. M. bavaricus) the sediments of Denkendorf are attributed to the lower MN5 mammal zone (latest Karpatian to early Badenian) and are thus considered to be younger than the associations found near Hitzhofen and Heitensheim.

  5. A shell concentration of the Middle Miocene Crassostrea gryphoides (Schlotheim, 1813) from Siwa Oasis, Western Desert, Egypt

    Science.gov (United States)

    El-Sabbagh, Ahmed M.; El Hedeny, Magdy M.

    2016-08-01

    A concentration of heavy, thick-shelled, large-sized, and elongated population of the oyster Crassostrea gryphoides (Schlotheim, 1813) was recorded in shallow-marine deposits of the basal Oasis Member of the Middle Miocene Marmarica Formation exposed at Siwa Oasis, Egypt. The oyster assemblage is resedimented as a lens-shaped bank up to 80-100 cm thick and about 220 m long. Crassostrea gryphoides specimens are embedded in a yellowish green, soft marl matrix. This is the first documented occurrence of this lens at Siwa Oasis. The lensoid structure is bounded by a lower marl and an upper shale beds of about 2 m and 1.5 m thick, respectively. Assemblage within this lens is characterized by extreme variations of Crassostrea gryphoides, forming an almost monotypic assemblage. The shell packing was dense (shell percentages higher than 75%) at the base and the center of the lens, whereas it exhibits loose packing at the top and right and left sides of the lens (shell percentage less than 15%). Valves are poorly sorted and randomly orientated (both in surface and cross section views). Encrustation and bioerosion have observed on both sides of the left and right valves. The relatively limited varieties of encrusters together with moderate frequency of borings indicate moderate to high sedimentation rate. On the other hand, the low abundance of fragmented and abraded shells indicates good preservation and minimal transport. The studied lens concentration is interpreted as proximal tempestites assemblage.

  6. CALCAREOUS PLANKTON BIOSTRATIGRAPHY AND AGE OF THE MIDDLE MIOCENE DEPOSITS OF LONGANO FORMATION (EASTERN MATESE MOUNTAINS, SOUTHERN APENNINES

    Directory of Open Access Journals (Sweden)

    FABRIZIO LIRER

    2005-03-01

    Full Text Available The integrated calcareous plankton biostratigraphy (planktonic foraminifera and calcareous nannofossils and an accurate fieldwork, allowed us the reconstruction of the sedimentary evolution of the Longano Formation (Orbulina Marls. In particular the correlation between the bioevents recognised in the Orbulina Marls sequence and those recorded in astronomically calibrated Middle Miocene sections, offered the possibility to date the passage from the shallow-water Cusano Formation to the deep-water deposits of the Longano Formation at about 13.21 Ma and the successive onset of terrigenous deposits of the Pietraroia Formation at 10.54 Ma. In addition, an high resolution study of the terrigenous sequence, showed that this sedimentary event is not abrupt but it is characterised by a progressive increase, bed by bed, of the siliciclastic fraction up to the deposition of the sandstones. The recognition in all the studied sections of the base of the first Acme (AB1 of Paragloborotalia siakensis dated at 13.21 Ma, just above the phosphate-rich interval (this interval marks the transition between Cusano and Longano Formations, proved that the transgression which led to the deposition of the Orbulina Marls was synchronous in all the south-eastern Matese Mountains. 

  7. Trace fossils from Bhuban Formation, Surma Group (Lower to Middle Miocene) of Mizoram India and their palaeoenvironmental significance

    Indian Academy of Sciences (India)

    Raghavendra P Tiwari; Chinmoy Rajkonwar; Lalchawimawii; Paul Lalnuntluanga Jehova Malsawma; Victor Z Ralte; Satish J Patel

    2011-12-01

    A detailed ichnological study performed on the Bhuban Formation, Surma Group (Lower to Middle Miocene) of Mizoram, India reveals the occurrence of rich and diverse trace fossils. These have been collected from the two localities in Aizawl, i.e., Bawngkawn and Ropaiabawk, where sandstone-shale sequence is well exposed. Total 20 ichnospecies of 14 ichnogenera have been identified which include Arenicolites isp., Cochlichnus anguineus, Helminthopsis abeli, Laevicyclus mongraensis, Ophiomorpha borneensis, Palaeophycus tubularis, Palaeophycus heberti, Palaeophycus sulcatus, Palaeophycus alternatus, Pholeus abomasoformis, Pholeus bifurcatus, Planolites beverleyensis, Planolites annularis, Polykladichnus irregularis, Rhizocorallium isp., Skolithos linearis, Taenidium satanassi, Teichichnus rectus, Thalassinoides horizontalis and Thalassinoides paradoxicus. Ethologically these ichnogenera display dwelling and feeding activities of the infaunal organisms. Arenicolites, Ophiomorpha, Polykladichnus and Skolithos are the members of the Skolithos ichnofacies while Palaeophycus, Planolites, Rhizocorallium and Thalassinoides are the members of the Cruziana ichnofacies. The presence of Skolithos ichnofacies indicates sandy shifting substrate and high energy conditions in foreshore zone while the Cruziana ichnofacies indicate unconsolidated, poorly sorted soft substrate and low energy condition in the shoreface/offshore zone. These ichnogenera indicate foreshore to shoreface-offshore zone of shallow marine environment for the deposition of the rocks of the Bhuban Formation of Mizoram.

  8. Accelerated middle Miocene exhumation of the Talesh Mountains constrained by U-Th/He thermochronometry: Evidence for the Arabia-Eurasia collision in the NW Iranian Plateau

    Science.gov (United States)

    Madanipour, Saeed; Ehlers, Todd A.; Yassaghi, Ali; Enkelmann, Eva

    2017-08-01

    The Talesh Mountains at the NW margin of the Iranian Plateau curve around the southwestern corner of the South Caspian Block and developed in response to the collision of the Arabian-Eurasian Plates. The timing, rates, and regional changes in late Cenozoic deformation of the Talesh Mountains are not fully understood. In this study, we integrate 23 new apatite and zircon bedrock U-Th/He ages and structurally restored geologic cross sections with previously published detrital apatite fission track data to reconstruct the deformation history of the Talesh Mountains. Our results reveal that slow rock exhumation initiated during the late Oligocene ( 27-23 Ma) and then accelerated in the middle Miocene ( 12 Ma). These events resulted in the present-day high-elevation and curved geometry of the mountains. The spatial and temporal distribution of cooling ages suggest that the Oligocene bending of the Talesh Mountains was earlier than in the eastern Alborz, Kopeh Dagh, and central Alborz Mountains that initiated during the late Cenozoic. Late Oligocene and middle Miocene deformation episodes recorded in the Talesh Mountains can be related to the collisional phases of the Arabian and Eurasian Plates. The lower rate of exhumation recorded in the Talesh Mountains occurred during the initial soft collision of the Arabian-Eurasian Plates in the late Oligocene. The accelerated exhumation that occurred during final collision since the middle Miocene resulted from collision of the harder continental margin.

  9. Giant fossil tortoise and freshwater chelid turtle remains from the middle Miocene, Quebrada Honda, Bolivia: Evidence for lower paleoelevations for the southern Altiplano

    Science.gov (United States)

    Cadena, Edwin A.; Anaya, Federico; Croft, Darin A.

    2015-12-01

    We describe the first Miocene turtle remains from Bolivia, which were collected from the late middle Miocene (13.18-13.03 Ma) of Quebrada Honda, southern Bolivia. This material includes a large scapula-acromion and fragmentary shell elements conferred to the genus Chelonoidis (Testudinidae), and a left xiphiplastron from a pleurodire or side-necked turtle, conferred to Acanthochelys (Chelidae). The occurrence of a giant tortoise and a freshwater turtle suggests that the paleoelevation of the region when the fossils were deposited was lower than has been estimated by stable isotope proxies, with a maximum elevation probably less than 1000 m. At a greater elevation, cool temperatures would have been beyond the tolerable physiological limits for these turtles and other giant ectotherm reptiles.

  10. Lagerstroemia L. from the middle Miocene Siwalik deposits, northern India: Implication for Cenozoic range shifts of the genus and the family Lythraceae

    Indian Academy of Sciences (India)

    Gaurav Srivastava; Rajan Gaur; R C Mehrotra

    2015-02-01

    Fossil leaves of Lagerstroemia (Lythraceae) are described from the Siwalik deposits (middle Miocene) of Kathgodam, Uttarakhand, India. The fossil records of the Lythraceae indicate its worldwide distribution in the Cenozoic. The family had its widest distribution during the Miocene but became less widespread during the Pliocene, followed by range expansion during the Quaternary. The present leaf fossil, along with the previous fossil records of Lagerstroemia, indicates that the genus followed the same pattern of expansion and retraction as the entire family Lythraceae suggesting that both the genus and the family adapted in similar ways. The fossil plant assemblage from the Lower Siwalik deposits indicates warm and humid climate with plenty of rainfall in the region during the depositional period.

  11. Vertical thermal gradient history in the eastern equatorial Pacific during the early to middle Miocene: Implications for the equatorial thermocline development

    Science.gov (United States)

    Matsui, Hiroki; Nishi, Hiroshi; Kuroyanagi, Azumi; Hayashi, Hiroki; Ikehara, Minoru; Takashima, Reishi

    2017-07-01

    Knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical Pacific. Multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline. Although the secular thermocline development has been documented back to the late Miocene, the early to middle Miocene interval has rarely been examined. In addition, relationships with the dynamic Antarctic ice sheets remain unclear. Here we investigate the vertical thermal gradient in the upper water column at Integrated Ocean Drilling Program Site U1337 in the eastern equatorial Pacific (EEP) throughout the early to middle Miocene (23.1 to 11.7 Ma). The gradient increased over the Miocene Climatic Optimum, whereas it decreased during the East Antarctic Ice Sheet Expansion (EAIE). Comparison of the EEP record with its western equatorial Pacific (WEP) counterpart suggests that sea surface temperature was more stable in the WEP than in the EEP. We further estimated equatorial thermocline from two diagonal gradients between the EEP and the WEP: thermocline shoaled from 16.7 to 15.7 Ma and tilt weakened between 16.5 and 13.8 Ma. The onset of the "Monterey Excursion" and the reduced Antarctic ice sheet volume would have affected thermocline depth and tilt, respectively. Thermocline depth was likely much deeper compared to Pliocene-to-modern conditions. Furthermore, a 4-point-based distribution of isotherms (4DI index) was used as a metric of the evenness or unevenness of the isotherm distributions. The 4DI index considerably reduced at around the EAIE and other Mi-events, reflecting the evenly distributed isotherms under a more glaciated Antarctica.

  12. Zeros in. gamma. +e. -->. W+. nu

    Energy Technology Data Exchange (ETDEWEB)

    Mikaelian, K.O.

    1984-09-01

    We point out a misprint in the differential cross section for ..gamma..e..-->..W..nu.. reported recently by Ginzburg, Kotkin, Parful, and Serbo. The corrected expression has a zero in accordance with the general formula derived earlier by Mikaelian. We plot the angular distribution for different values of kappa, the anomalous-magnetic-moment parameter of the W. We suggest that the reaction ..gamma..e..-->..W..nu.. is an attractive way to measure kappa because the distributions are sensitive to it and the zero exists only if kappa = +1 as in the standard electroweak theory.

  13. Upper Cretaceous to Miocene tectonostratigraphy of the Azuero area (Panama) and the discontinuous accretion and subduction erosion along the Middle American margin

    Science.gov (United States)

    Buchs, David M.; Baumgartner, Peter O.; Baumgartner-Mora, Claudia; Flores, Kennet; Bandini, Alexandre N.

    2011-11-01

    The Central American forearc allows insight into the long-term evolution of the Middle American margin and possible shifts between accretionary and erosive periods of subduction. We present a revised tectonostratigraphic subdivision of the Azuero area based on new field observations and biochronologic data, and a synthesis of previous age, geochemical and stratigraphic data. The basement of the area is composed of an autochtonous oceanic plateau, the early Central American arc and accreted seamounts, which are unconformably overlain by forearc sediments. The nature and spatial arrangement of basement units combined with patterns of uplift and subsidence recorded in overlapping sediments allow reconstruction of the local evolution of subduction tectonics between the Upper Cretaceous and Miocene. Comparison of this evolution with that formerly proposed for the south Costa Rican margin based on a similar approach (Buchs et al., 2009, 2010) provides an insight into temporal and along-strike changes of subduction tectonics along a ~ 500 km-long segment of the Middle American margin. We find that subduction erosion (or non-accretion), punctuated by seamount accretion, was the dominant process along the margin between the late Campanian and Middle Eocene. In the Middle Eocene, uplift of the Central American forearc, initiation of a volcanic front retreat in Panama and a pulse of seamount accretion between south Costa Rica and west Panama are likely to relate to a reorganization of plate tectonics in the Pacific. A contrasted evolution occurred in south Costa Rica and Panama afterwards, with continued subduction erosion in the Azuero area and net accretion of olistostromal and hemipelagic sediments in south Costa Rica at least until the Middle Miocene. Our results show that tectononstratigraphic observations in the forearc may represent a valuable complement to offshore drilling and geophysical studies to understand modern subduction tectonics along the Middle American

  14. Vegetation and climatic changes during the Middle Miocene in the Wushan Basin, northeastern Tibetan Plateau: Evidence from a high-resolution palynological record

    Science.gov (United States)

    Hui, Zhengchuang; Li, Jijun; Song, Chunhui; Chang, Jing; Zhang, Jun; Liu, Jia; Liu, Shanpin; Peng, Tingjiang

    2017-10-01

    There remains no detailed record of the Middle Miocene vegetation and climatic changes which occurred in central Asia and their possible driving mechanisms. This is because there is still a lack of high resolution records. Here, we present a sporopollen record from the Wushan Basin on the northeastern Tibetan Plateau, central Asia, spanning the period ∼16.1-13.6 Ma. The sporopollen record shows that a dense mixed forest growing in rather warm and humid climatic conditions was affected by a general drying trend during the period ∼16.1-15 Ma. It demonstrates that although the climate was generally warm and humid during the Middle Miocene Climate Optimum (MMCO), it was also a time of climatic instability. The dense forest gave way to an open forest in response to a less humid climate between ∼15 and 14.4 Ma. Dense mixed forest made a return with an increasingly humid climate during ∼14.4-13.8 Ma. This vegetation and climatic succession could be associated with global cooling, or more particularly, a higher temperature rebound set against the background of a long-term cooling trend. A more open forest appearing in response to drier and colder climatic conditions dominated the study area during the ∼13.8-13.6 Ma period. This could be compared to the rapid global cooling event Mi-3b. This significant global cooling event exerted a major impact on terrestrial vegetation, climate and biota. Our high resolution sporopollen record demonstrates that global climate changes could have been the first order driving force for the Middle Miocene vegetation and climate changes seen in the Wushan Basin in central continental Asia, with the tectonic uplift of the Tibetan Plateau probably playing a subordinate role.

  15. The Middle Miocene lacustrine mollusc fauna of the Kupres Basin: palaeobiogeography, palaeoecology, and taxonomic implications (Dinaride Lake System, Bosnia and Herzegovina)

    Science.gov (United States)

    Neubauer, T. A.; Mandic, O.; Harzhauser, M.; Hrvatović, H.

    2012-04-01

    During the Early and Middle Miocene the Dinaride Lake System displayed one of the largest freshwater systems in the Neogene of Europe, forming a palaeogeographic barrier between the Paratethys and the Mediterranean seas. It is widely known for its exceptional mollusc fauna, which experienced major radiations resulting in a high level of endemicity. Despite advanced investigations in that region our knowledge on the mollusc fauna is still fragmentary or out-dated. A major problem for taxonomic revisions is the complex geographic and geologic setting with numerous basins. Therefore, most authors were unable to assign already described taxa and localities in the literature to discrete basins and palaeo-lakes. The herein presented results give insight into the outstandingly preserved mollusc fauna of the Kupres Basin. Except for few descriptions, partly dating back to the early 20th century, and a preliminary list of species, a concise taxonomic frame is entirely missing. Consequently, the presented results provide the base for a systematic revision of several supraspecific taxa among the Hydrobiidae. Moreover, the faunal composition allows inferences on palaeobiogeography and hydrological connections within the Dinaride Lake System during the early Middle Miocene. About one third of the described taxa are restricted to the Kupres basin. The other taxa document faunistic relations to the coeval faunas of the Sinj, Drniš, and Džepi basins. Phases of hydrological isolation, indicated by carbonate dominated lithology, coincide with a high frequency of sculptured morphologies within the gastropods. Phases of increased aridity led to high evaporation, a lowered lake level and enhanced carbonate production which seem to have promoted strongly calcified shells. The stratigraphic ranges of the species imply a depositional age of 15.5 ± 0.2 Ma (earliest Middle Miocene; Langhian).

  16. Tectonics of the Western Betics: the role of E-W strike slip fault corridors

    Science.gov (United States)

    Frasca, Gianluca; Gueydan, Frédéric; Brun, Jean-Pierre; Célérier, Bernard

    2014-05-01

    The tectonic origin of the arcuate Betic-Rif orogenic belt that surrounds the Alboran Sea at the western tip of the Mediterranean Sea remains debated. Here, we investigate the tectonic units cropping out in the Western Betics (Malaga region, Southern Spain) with the main goal of reconstructing the Oligo-Miocene evolution of the area. New structural data and geological mapping together with available data allow us to identify the main structural features of the area. Deformation is found to be extremely diffused but two E-W elongated tectonic blocks with different lithological composition are outlined by marked E-W dextral strike-slip corridors ending up in horse-tail splays. These E-W strike slip corridors are responsible for late Miocence tectonics of both the internal and external zones of the Betic Cordillera.

  17. Palaeo-oceanographical implications of Early-Middle Miocene subtropical ostracod faunas from the continental shelf of the SE Atlantic Ocean

    DEFF Research Database (Denmark)

    Dingle, R.V.; McMillan, I.K.; Majoram, Stefan

    2001-01-01

    palaeo-oceanography, miocene, SE Atlantic, ostracoda, upwelling, Benguela current, Agullas current......palaeo-oceanography, miocene, SE Atlantic, ostracoda, upwelling, Benguela current, Agullas current...

  18. Were West Antarctic Ice Sheet grounding events in the Ross Sea a consequence of East Antarctic Ice Sheet expansion during the middle Miocene?

    Science.gov (United States)

    Bart, Philip J.

    2003-11-01

    Seismic correlation of glacial unconformities from the Ross Sea outer continental shelf to chronostratigraphic control at DSDP sites 272 and 273 indicates that at least two West Antarctic Ice Sheet (WAIS) expansions occurred during the early part of the middle Miocene (i.e. well before completion of continental-scale expansion of the East Antarctic Ice Sheet (EAIS) inferred from δ 18O and eustatic shifts). Therefore, if the volume of the EAIS was indeed relatively low, and if the Ross Sea age model is valid, then these WAIS expansions/contractions were not a direct consequence of EAIS expansion over the Transantarctic Mountains onto West Antarctica. An in-situ development of the WAIS during the middle Miocene suggests that either West Antarctic land elevations were above sea level and/or that air and water temperatures were sufficiently cold to support a marine-based ice sheet. Additional chronostratigraphic and lithologic data are needed from Antarctic margins to test these speculations.

  19. Highly extended terrains, lateral segmentation of the substratum, and basin development: The middle-late Miocene Radicondoli Basin (inner northern Apennines, Italy)

    Science.gov (United States)

    Brogi, Andrea; Liotta, Domenico

    2008-09-01

    This paper deals with the evolution of sedimentary basins not delimited by normal faults, with a substratum characterized by an upward concave shape and with infilling sediments synclinally deformed. We describe the middle-late Miocene Radicondoli Basin, representing an example of such bowl-shaped basins. Its tectonic origin is controversial, being related both to compression and extension; these opposite interpretations bear significant consequences on the geodynamic context in which the inner northern Apennines developed during the middle-late Miocene. The results of our structural studies, carried out in the substratum and infilling sediments, indicate that the Radicondoli Basin is an example of a hanging wall basin developed in an extensional setting. Extensional tectonics determined the lateral segmentation of the substratum competent levels (i.e., Tuscan Nappe and Verrucano Group) and the consequent collapse of overlying less competent levels (i.e., the Ligurian units) with the formation of a bowl-shaped tectonic depression. Here, the syntectonic sediments (Serravallian-late Messinian) are deformed in a large syncline, characterized by minor gravity-driven folds, with vergences toward the depocenter and traces of their axial planes parallel to the basin margins. This paper highlights the role of the competence contrast during the postcollisional tectonic evolution and the influence of substratum lateral segmentation for the accommodation of syntectonic sediments.

  20. Paleontology, paleoclimatology and paleoecology of the late middle miocene Musselshell Creek flora, Clearwater County Idaho. A preliminary study of a new fossil flora

    Energy Technology Data Exchange (ETDEWEB)

    Baghai, N.L. [Univ. of Texas, Austin, TX (United States); Jorstad, R.B. [Eastern Illinois Univ., Charleston, IL (United States)

    1995-10-01

    The Musselshell Creek flora (12.0-10.5 Ma) of northern Idaho is used to reconstruct paleoclimatic and paleoecologic parameters of the Pacific Northwest during the late Middle Miocene. Other megafossil and microfossil floral records spanning 12.0-6.4 Ma are unknown from this region. The Musselshell Creek fossil flora, previously undescribed, is preserved in lacustrine clays and sediments that accumulated in a narrow valley surrounded by rugged terrain. Dominant taxa include dicotyledons and conifers. Most of the leaves are preserved as impressions or compressions. Some fossil leaves retained their original pigmentation, cellular anatomy, and organic constituents. Other fossils include excellent remains of pollen and spores, dispersed leaf cuticle, pyritized wood, and disarticulated fish bones. A destructive statistical analysis of one block of sediment, approximately 30 cm x 45 cm (1.5 sq. ft) recovered 14 orders, 23 families, and 34 genera of spermatophyte plant fossils. These floral elements are compared with two other earlier Miocene floras which were similarly sampled. Common megafossil genera include Quercus, Zizy-phoides, Taxodium, Alnus, Castanea, Magnolia, Acer, Ex-bucklandia, Sequoia, Populus, and Betula. The rare occurrence of Ginkgo leaves is a first record of this taxon in the Idaho Miocene. Additional plant taxa, are represented by palynomorphs. Common pollen taxa are Pinus, Abies, Carya, Quercus, and Tilia. Most of the megafossil and microfossil flora assemblage is characteristic of a streambank to floodplain environment that existed in a warm to cool temperate climate similar to the modern Mid-Atlantic coast of the United States. 47 refs., 5 figs., 4 tabs.

  1. Sedimentology of some facies from the Coris formation (Middle and Upper Miocene), Central Valley, Costa Rica, Central America; Sedimentologia de alunas facies de la formacion Coris (Mioceno Medio, Mioceno superiore), Valle Central, Costa Rica, America Central

    Energy Technology Data Exchange (ETDEWEB)

    Obando, L.G.; Bottazzi, G.; Alvarado, F. [Universidad de Costa Rica, San Jose (Costa Rica). Escuela Centroamericana de Geologia

    1991-10-01

    In the Central Valley of Costa Rica exists a principal sandy-quartz sequence (Middle Miocene to Upper Miocene). Occasionally these rocks are interbedded with coal seams (lignite 0.3 to 1m thick) and siltstones very rich in organic matter. New data and reinterpretation of the sequences has permitted definition of the sedimentary facies: silicoclastic platform (mixed facies), open bay facies, bar facies (bar front (middle shoreface) and upper shoreface). Those facies represent a strand plain, generated by Miocene inter-oceanic currents, through the channel genetic related with the sinistral Costa Rica transcurrent fault system. That fault has segmented the national territory and generated the pull-apart basin in the Central Valley. This rapid subsidence accumulated thick shallow deposits. 27 refs., 5 figs.

  2. Shirleya grahamae gen. et sp. nov. (Lythraceae), Lagerstroemia-like fruits from the middle Miocene Yakima Canyon flora, central Washington State, USA.

    Science.gov (United States)

    Pigg, Kathleen B; Devore, Melanie L

    2005-02-01

    Shirleya grahamae Pigg & DeVore gen. et sp. nov. (Lythraceae) is established for silicified fruits from the middle Miocene Yakima Canyon of central Washington State, USA. The capsules are 10 mm long × 11.5-12.5 mm wide, enclosed in a persistent floral tube and contain 5-7 locules. They are loculicidally dehiscent, fracturing into fragments and leaving the central axis free. Placentation is axile. Five to seven mature seeds are tightly packed per locule, often with several smaller seeds. Seeds are winged, anatropous, and narrowly attached subapically to the central axis, curving basally and radially within the fruit. They are up to ∼4.6 mm long × 1.9 mm wide, with a small, triangular embryo cavity and a prominent distal wing. The inflated wing is filled with a bilobed parenchymatous pad of tissue with a central cavity. Shirleya grahamae is assigned to the Lythraceae, and is most similar to Lagerstroemia, based on the synapomorphies of distally winged seeds and revolute cotyledons. Shirleya differs from Lagerstroemia in seed arrangement, and pericarp and wing anatomy. This study provides the first anatomical information about a Miocene Lagerstroemia-like fruit and documents further diversity of the Lythraceae in the Neogene of northwestern North America.

  3. Subsidence and conversion of the Dead Sea basin to an inland erosion base level in the early middle Miocene as inferred from geomorphological analysis of its ancient western fluvial outlet

    Science.gov (United States)

    Bar, Oded; Zilberman, Ezra

    2016-05-01

    The first major subsidence of the Dead Sea pull-apart basin (DSB) is evidenced by the thick Hufeira Member of the terrestrial Hazeva Formation. The age of the Hufeira Member and the conversion of the DSB to an inland erosion base level are not well constrained. For this purpose we studied the effect of the evolving basin on its ancient fluvial outlet to the Arad-Be'er Sheva Valley (ABSV), which served as a Miocene corridor between the embryonic DSB region in the east and the Mediterranean Sea in the west. We mapped and analyzed the morphostratigraphy of four series of rock-cut erosion surfaces (from top to bottom: the Barir, Kuseifa, Ar'ara, and Shemen surfaces). They are manifested in the east as fluvial erosion surfaces, capped by conglomerates, passing laterally westward to marine wave-cut surfaces, capped by a shallow marine limestone of the early middle Miocene Ziqlag Formation. The age of these surfaces is constrained to the early middle Miocene (Langhian) based on morphostratigraphy correlation with the Ziqlag Formation. Paleogeographic reconstruction of the two higher and older surfaces reveals transverse valleys, which drained the DSB region and crossed the present route of the regional water divide. These transverse valleys were presumably the western outlets to the Mediterranean Sea of the newly subsiding basin. Precambrian components in the assemblage of the clasts that cover the Kuseifa surface were not found in the Hufeira Member and thus reflect an ongoing post-Hufeira exumation of the DSB drainage basin. Hence, this early middle Miocene surface postdates the Hufeira Member, assigning an age of late early Miocene to the first major subsidence of the DSB. The two lower and younger surfaces represent local drainage systems confined to the ABSV. This transition from regional to local drainage system marks the establishment of the present regional water divide and the conversion of the DSB to an inland erosion base level during the early middle Miocene.

  4. Middle-Miocene (Serravallian) temperate carbonates in a seaway connecting the Atlantic Ocean and the Mediterranean Sea (North Betic Strait, S Spain)

    Science.gov (United States)

    Braga, Juan C.; Martín, José M.; Aguirre, Julio; Baird, Catherine D.; Grunnaleite, Ivar; Jensen, Niels Bo; Puga-Bernabéu, Angel; Sælen, Gunnar; Talbot, Michael R.

    2010-03-01

    Miocene deposits in the contact area between the Prebetic and Subbetic domains (Betic Cordillera, S Spain) record the last stages of marine deposition on the southern Iberian margin and the final closure of the North Betic Strait in the early Tortonian (Late Miocene). Serravallian (Middle Miocene) shallow-water carbonates and mixed carbonate-siliciclastics formed on a platform at the southern margin of the North Betic Strait. These shallow-water deposits, informally termed the La Escalera Formation, onlap an erosion surface carved into underlying Miocene and older rocks. Carbonate components are mainly bryozoans, coralline red algae, molluscs, and benthic and planktonic foraminifers, typical of heterozoan lithofacies. Several facies types can be distinguished based on different grain sizes and sedimentary structures. Large-scale geometries and stratigraphic facies relationships indicate that the La Escalera Formation was deposited on a homoclinal ramp attached to a deeply eroded, emergent relief to the south. A beach system developed at the southern margin, with backshore lagoons and local incursions of coarse terrigenous sediments. Seawards of the beach system was a submarine-dune belt that extended over several square kilometres at the northeastern end of the La Escalera Formation. Longshore currents shifted submarine dunes to the northeast. Maximum production of carbonate skeletons took place seawards of the dune field. From this factory area, skeletal debris was moved landwards and incorporated into the dunes and beaches, whereas other skeletal particles were transported downslope by storms and fed a facies belt with hummocky and swaley cross-stratified sediments. The finest-grained particles accumulated below a storm-wave base, along with significant planktic debris. Carbonate deposits change laterally westwards to terrigenous sediments formed in similar facies belts. Terrigenous influx limited carbonate production on the western part of the ramp by disturbing

  5. A Middle Miocene (13.5-12 Ma) deformational event constrained by volcanism along the Puna-Eastern Cordillera border, NW Argentina

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    Aramayo, Alejandro; Guzmán, Silvina; Hongn, Fernando; del Papa, Cecilia; Montero-López, Carolina; Sudo, Masafumi

    2017-04-01

    The features of Middle Miocene deposits in the Puna-Eastern Cordillera transition (Valles Calchaquíes) indicate that Cenozoic deformation, sedimentation and volcanism follow a complex spatiotemporal relationship. The intense volcanic activity recorded in the eastern Puna border between 14 and 11.5 Ma coincides with the occurrence of one of the most important deformation events of the Neogene tectonic evolution in the region. Studies performed across the Puna-Eastern Cordillera transition show different relationships between volcanic deposits of ca. 13.5-12.1 Ma and the Oligocene-Miocene Angastaco Formation. In this paper we describe the ash-flow tuff deposits which are the first of this type found concordant in the sedimentary fill of Valles Calchaquíes. Several analyses performed on these pyroclastic deposits allow a correlation to be made with the Alto de Las Lagunas Ignimbrite (ca. 13.5 Ma) of the Pucarilla-Cerro Tipillas Volcanic Complex located in the Puna. Outcrops of the ca. 13.5 Ma pyroclastic deposits are recognised within the Puna and the Valle Calchaquí. However, in the southern prolongation of the Valle de Hualfín (Tiopampa-Pucarilla depression) that separates the Puna from the Valle Calchaquí at these latitudes, these deposits are partially eroded and buried, and thus their occurrence is recorded only by abundant volcanic clasts included in conglomerates of the Angastaco Formation. The sedimentation of the Angastaco Formation was aborted at ca. 12 Ma in the Tiopampa-Pucarilla depression by the Pucarilla Ignimbrite, which unconformably covers the synorogenic units. On the contrary, in the Valle Calchaquí the sedimentation of the Angastaco Formation continued until the Late Miocene. The different relationships between the Miocene Angastaco Formation and the ignimbrites with ages of ca. 13.5 and ca. 12 Ma reveal that in this short period ( 1.5 m.y.) a significant deformation event took place and resulted in marked palaeogeographic changes, as

  6. A middle Miocene benthic foraminiferal stable isotope record from extensively recrystallised carbonate sediments of IODP Site U1336 in the Equatorial Pacific

    Science.gov (United States)

    Voigt, J.; Hathorne, E. C.; Holbourn, A. E.; Frank, M.

    2013-12-01

    The elemental and isotopic composition of foraminifera is widely used for reconstructing oceanic and climatic conditions in the past. However, ancient foraminiferal tests are altered after deposition through replacement of the original biogenic calcite by secondary (inorganic) calcite. Therefore, it is important to quantify changes in the elemental and isotopic composition of recrystallised tests to assess the reliability of proxy data. Here, we present benthic foraminiferal stable isotope data from IODP Site U1336 where the geochemistry of bulk carbonates and associated pore waters suggests extensive recrystallisation resulting from an enhanced thermal gradient. In sediments older than 20.3 Ma the 87Sr/86Sr ratios of bulk carbonates and associated pore waters exhibit lower values than contemporaneous seawater indicating the incorporation of Sr originating from older carbonates recrystallised deeper in the section. Furthermore, the generally lower Sr/Ca ratios of bulk carbonates from Site U1336 also suggest extensive recrystallisation. Despite the extensive recrystallisation at Site U1336, the stable isotope composition (δ13C and δ18O) of benthic foraminifera (C. wuellerstorfi and C. mundulus) from the middle Miocene (13-16 Ma) is in good agreement with existing records (e.g. Holbourn et al. 2007, Tian et al. 2013). The carbon-isotope events of the Monterey Excursion (including CM 3b, CM 4a, CM 5 and CM 6) can clearly be identified. The CM 3b event displays the highest δ13C values with a maximum of 1.78 ‰ at 15.61 Ma which is in accordance with values measured from Sites 1237 (Nazca Ridge off Peru) and U1337 (706 km southeast from U1336) of 1.72 and 1.74 ‰, respectively at 15.60 Ma. The Middle Miocene cooling at 13.91-13.84 Ma marks the onset of ice-sheet expansion over Antarctica and the drastic increase in δ18O (0.86 ‰) at Site U1336 during that cooling event (CM 6) is comparable to that at Site 1237 (0.79 ‰) (Holbourn et al. 2007) and U1337 (1.00

  7. Early to middle Miocene climate evolution: New insights from IODP Sites U1335, U1337 and U1338 (eastern equatorial Pacific Ocean)

    Science.gov (United States)

    Kochhann, Karlos G. D.; Holbourn, Ann; Kuhnt, Wolfgang; Lyle, Mitch; Raffi, Isabella; Channell, James E.; Andersen, Nils

    2015-04-01

    The lower to middle Miocene (~20 to 13 Ma) carbonate-rich sedimentary successions recovered at Integrated Ocean Drilling Program (IODP) Sites U1335, U1337 and U1338 allow unsurpassed resolution over the Climatic Optimum (16.9-14.7 Ma) and the transition into a colder climate mode after 13.9 Ma with re-establishment of permanent Antarctic ice sheets. High-resolution (1-10 kyr) stable carbon (δ13C) and oxygen (δ18O) isotopes of well-preserved epibenthic foraminifera (Cibicidoides mundulus and Planulina wuellerstorfi) from these three sites show that the Climatic Optimum was characterized by high-amplitude climate variations and intense perturbations of the carbon cycle. Episodes of peak warmth coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. The U1335 and U1337 records additionally reveal that the rapid global warming and/or polar ice melting event, marking the onset of the Climatic Optimum at ~16.9 Ma, was coupled to a massive increase in carbonate dissolution, indicated by sharp drops in carbonate percentages and accumulation rates and by the fragmentation or complete dissolution of planktonic foraminifers. After ~14.7 Ma, stepwise global cooling, culminating with extensive ice growth over Antarctica at ~13.8 Ma, coincide with enhanced opal and benthic foraminiferal accumulation rates, suggesting that increased siliceous productivity and organic carbon burial may have contributed to CO2 drawdown. Integration of age models derived from orbitally-tuned, high-resolution isotopes, biostratigraphic data and magnetic reversals allows further constraints on the temporal sequence of events and helps unravel the drivers of early to middle Miocene climate variations.

  8. Re-deposited rhodoliths in the Middle Miocene hemipelagic deposits of Vitulano (Southern Apennines, Italy): Coralline assemblage characterization and related trace fossils

    Science.gov (United States)

    Checconi, Alessio; Bassi, Davide; Carannante, Gabriele; Monaco, Paolo

    2010-03-01

    An integrated analysis of rhodolith assemblages and associated trace fossils (borings) found in hemipelagic Middle Miocene Orbulina marls (Vitulano area, Taburno-Camposauro area, Southern Apennines, Italy) has revealed that both the biodiversity of the constituent components and taphonomic signatures represent important aspects which allow a detailed palaeoecological and palaeoenvironmental interpretation. On the basis of shape, inner arrangement, growth forms and taxonomic coralline algal composition, two rhodolith growth stages were distinguished: (1) nucleation and growth of the rhodoliths, and (2) a final growth stage before burial. Nucleation is characterized by melobesioids and subordinately mastophoroids, with rare sporolithaceans and lithophylloids. The rhodolith growth (main increase in size) is represented by abundant melobesioids and rare to common mastophoroids; very rare sporolithaceans are also present. The final growth stage is dominated by melobesioids with rare mastophoroids and very rare sporolithaceans. Each rhodolith growth stage is characterized by a distinct suite of inner arrangement and growth form successions. Well diversified ichnocoenoeses ( Gastrochaenolites, Trypanites, Meandropolydora and/or Caulostrepsis, Entobia, Uniglobites, micro-borings) related to bivalves, sponges, polychaetes, barnacles, algae, fungi, and bacteria are distinguished in the inner/intermediate rhodolith growth stage, while mainly algal, fungal and bacterial micro-borings are present in the outer final growth stage. Rhodolith growth stages and associated ichnocoenoeses indicate significant change in the depositional setting during the rhodolith growth. In the Vitulano area, the Middle Miocene rhodolith assemblages formed in a shallow-water open-shelf carbonate platform, were susceptible to exportation from their production area and then to sedimentation down to deeper-water hemipelagic settings, where the rhodoliths shortly kept growth and were finally buried. Such

  9. Miocene to Quaternary tectonostratigraphic evolution of the middle section of the Burdur-Fethiye Shear Zone, south-western Turkey: Implications for the wide inter-plate shear zones

    Science.gov (United States)

    Elitez, İrem; Yaltırak, Cenk

    2016-10-01

    The Burdur-Fethiye Shear Zone (BFSZ) is a 75- to 90- km wide and 300-km-long transtensional left-lateral shear zone which is located in one of the most tectonically active regions in south-western Turkey. A considerable number of studies suggested contradictory models of the evolution and Neogene stratigraphy of the BFSZ and in most cases, the local river and alluvial fan deposits were mapped together with the lacustrine sediments and assigned a Pliocene age. We present new field data, fault kinematic analyses, and DEM and earthquake data to characterize the tectonic controls and extent of the middle section of the BFSZ including Acıpayam, Çameli and Gölhisar basins. Our field observations revealed two distinct sedimentary sequences that unconformably overlie the pre-Neogene basement. The first sequence begins with middle-upper Miocene meandering- and braided-river sediments of the Gölhisar Formation, which transition upward into lacustrine sediments of the upper Miocene-lower Pliocene İbecik Formation. This sequence is overlain by upper Pliocene-lower Quaternary alluvial fan conglomerates, mudstones and claystones of the Dirmil Formation. The basin deposits located in the middle section of the BFSZ consist of lacustrine sediments of a late Miocene lake that likely evaporated due to the Messinian salinity crisis. Fault kinematic analysis and DEM and earthquake data indicate that the middle BFSZ can be characterized as a heterogeneous left-lateral transtensional shear zone rather than a major fault system. Our findings suggest that the middle section of the BFSZ developed under the influence of progressive counter clockwise rotation of south-western Turkey, the Aegean graben system and the Cyprus and Hellenic arcs since the middle Miocene.

  10. Miocene progressive forearc extension in the Central Mediterranean

    Science.gov (United States)

    Milia, A.; Valente, A.; Cavuoto, G.; Torrente, M. M.

    2017-07-01

    Miocene extensional sedimentary basins are being increasingly recognized in Central Mediterranean. However the paleogeographic reconstruction of the Paleo-Tyrrhenian during this time span results a difficult task because the subsequent Pliocene-Quaternary backarc opening moved away these older sedimentary basins. Our study outlines principal deformation events recorded by sediments that were deposited within minor basins of the Tyrrhenian Sea region and provides constraints on the duration of these events. The interpretation of seismic profiles, wells, and outcrops data together with a review of the middle-upper Miocene successions permitted us to recognize Miocene third order depositional sequences, reconstruct the fault pattern, and furnish a detailed evolution of the sedimentary basins that preceded the Pliocene-Quaternary Tyrrhenian high stretching. Based on the stratigraphic and tectonic constraints together with the age migration of the depocenters, we reconstructed a detailed paleogeographic evolution of central Mediterranean. Sedimentary basins architecture and fault pattern indicate a system of approximately N-S oriented normal faults and approximately E-W transform faults that were active since the Late Oligocene. Two period of extensional/transtensional tectonics (late Oligocene-Lower Burdigalian and Upper Langhian-Tortonian) were interrupted by a compressional event (late Burdigalian-Lower Langhian). Tacking in account the position of the Miocene volcanic arc (Sardinia), we propose that the coeval sedimentary basins developed in the central Mediterranean as forearc extensional/transtensional basins during the progressive collision with the African plate and before the Tyrrhenian backarc opening. Unlike published late Oligocene-Tortonian reconstructions of the western-central Mediterranean realm that report a linear migration of backarc extension, our results support a geodynamic model characterized by a progressive deformation of the forearc extension

  11. Comparing Early to Middle Miocene floras and probable vegetation types of Oberdorf N Voitsberg (Austria), Bohemia (Czech Republic), and Wackersdorf (Germany).

    Science.gov (United States)

    Kovar-Eder, J; Kvacek, Z; Meller, B

    2001-03-01

    The Early Miocene vegetation of western Styria, Austria, is reconstructed on the basis of detailed investigations of leaves and diaspores from the mining area Oberdorf N Voitsberg. In this paper, the flora and probable vegetation are compared with other assemblages of similar age from the Czech Republic and Germany to elucidate the diversity of wetland and mesophytic plant communities. The floristic composition and the vegetational units represented in Oberdorf are compared to the middle part of the Most Formation (M Most Fm), Cypris Shale, Mydlovary Formation (Mydlovary Fm) of Bohemia, and the Wackersdorf mining area of Bavaria. Among these sites, Oberdorf is extremely poor in hydrophytes and reed-like monocotyledons, indicating rare pond-like habitats as well as possibly more closed swamp forest conditions than, e.g. in the M Most Fm. In Oberdorf, relatively high pH-values in the lignite-forming swamps and the possible scarcity of acidic, nutrient-poor (sandy) soils have probably influenced the floristic composition of the azonal communities. The peat-forming associations in all regions share the abundance of Glyptostrobus europaeus. However, distinct differences in the accompanying elements, such as Taxodium dubium (present and abundant only in the M Most Fm) indicate even stronger floristic variability of Early(/Middle) Miocene peat-forming and riparian plant communities than previously expected. The virtual absence of Pinus, Engelhardia, Comptonia, and probably also of Quercus kubinyii/Quercus drymeja in the megafossil record of Oberdorf can possibly be explained by the edaphic conditions. The abundance of Sequoia abietina (absent in all the other compared sites), which we assign to riparian (and mesophytic) forests in Oberdorf, may have been favoured by rich alluvial soils.In the mesophytic associations, thermophilous elements of the Lauraceae, Mastixiaceae, Symplocaceae, and Rutaceae are diverse. Usually they include Trigonobalanopsis rhamnoides

  12. Origin of the Red Earth sequence on the northeastern Tibetan Plateau and its implications for regional aridity since the middle Miocene

    Institute of Scientific and Technical Information of China (English)

    WANG; Xianyan; LU; Huayu; JI; Junfeg; WANG; Xiaoyong; ZHAO; Jingbo; HUANG; Baochun; LI; Zhen

    2006-01-01

    The Red Earth deposit around Xining, northeastern Tibetan Plateau, has been studied in terms of soil micro-structure, grain-size distribution, major- and trace-element chemistry and magnetostratigraphy. Field investigations indicate that the Red Earth sequence consists of 25 visually definable yellow-brown and weakly-developed soils interbedded with reddish strongly-developed soils, and has a similar structure to the aeolian Red Clay deposit on the Chinese Loess Plateau. Grain-size analysis shows that the Red Earth deposit is very fine-grained with a negligible sand fraction (>63μm). Thin-section observations under light microscopy show that the deposit has a clayey texture and the coarse fraction (>10μm) mainly consists of quartz, feldspar and micas. Pyroxene and hornblende were also observed. This mineralogical composition of the coarse fraction is similar to that of the Quaternary loess. In addition, all of the mineral grains are semi angular semi-angular and are generally finer than 63μm. There is a good agreement between the major and minor trace element chemistry of loess-soil units and the Red Earth deposit. The REE distributions of the loess-soil and the Red Earth deposit are similar in shape, with enriched LREE and fairly flat HREE profiles and a clear negative Eu anomaly. The geochemical characteristics of the Red Earth deposit are also identical to those of upper continental crust, thus indicating a wind-blown origin.Magnetostratigraphic investigation shows that onset of the Red Earth deposition predates 11.4 Ma BP (13.6 Ma at a nearby site). The distribution of the reported Miocene aeolian loess at Qin'an of the Loess Plateau is still unknown. Our results indicate that this aeolian deposit had extended to the northeastern Tibetan Plateau by at least the middle Miocene. The similarity of the element geochemistry between the Red Earth deposit and the overlying loess shows that they may have similar sources and dynamic transport system, and may indicate

  13. Paleogene-early miocene deformations of Bukulja-Venčac crystalline (Vardar zone, Serbia

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    Marović Milun

    2007-01-01

    Full Text Available Low-grade metamorphic rocks of the crystalline of Mts. Bukulja and Venčac, which are integral parts of the Vardar Zone, are of Late Cretaceous age. From the Middle Paleogene to the beginning of the Miocene, they were subjected to three phases of intensive deformations. In the first phase, during the Middle Paleogene, these rocks were subjected to intense shortening (approximately in the E-W direction, regional metamorphism and deformations in the ductile and brittle domains, when first-generation folds with NNE-SSW striking fold hinges were formed. In the second phase, during the Late Oligocene and up to the Early Miocene, extensional unroofing and exhumation of the crystalline occurred, which was followed by intrusion of the granitoid of Bukulja and refolding of the previously formed folds in a simple brachial form of Bukulja and Venčac with an ESE-WNW striking B-axis. The third phase was expressed in the Early lowermost Miocene (before the Ottnanghian, under conditions of NE-SW compression and NW-SE tension. It was characterized by wrench-tectonic activity, particularly by dextral movements along NNW-SSE striking faults.

  14. Samotragus pilgrimi n. sp., a new species of Oiocerini (Bovidae, Mammalia) from the Middle Miocene of SpainSamotragus pilgrimi n. sp., un nouvel Oicerini (Bovidae, Mammalia) du Miocène moyen d'Espagne

    Science.gov (United States)

    Azanza, Beatriz; Nieto, Manuel; Morales, Jorge

    1998-03-01

    A new Oiocerini, Samotragus pilgrimi n. sp., from the Middle Miocene of Spain is described. This medium sized bovid is characterized by large, massive, inverse-twisted horn cores with an abrupt narrowing of the section at mid-length. These features allow the inclusion of this form within the genus Samotragus. To date, this form is the earliest and westernmost record of this tribe.

  15. Lateral heterogeneity in rodent samples of the T1 level from the Middle Miocene of Somosaguas (Pozuelo de Alarcón, Madrid

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    F. Blanco

    2016-11-01

    Full Text Available Rodent associations are habitually used in palaeoenviromental inferences. Assuming lateral homogeneity in fossil content within stratigraphic levels, sometimes these inferences are performed using the relative abundances of species included in such associations. Nevertheless, this homogeneity has never been checked empirically in species proportions inside the same fossiliferous level. Because of that, in this work we compared two samples from T1 level of the Somosaguas fossil site (middle Miocene, which were separated laterally by 30 m. Although both samples show identical faunal composition from a qualitative viewpoint, analysis realized through Monte Carlo randomizations indicated the existence of significant differences in relative abundances of different species between the two samples. These results could be due to 1 different sedimentary behaviour of dental pieces from different species due to differences in size; 2 small size of sediment samples combined with high density of fossil remains in level T1 of Somosaguas; 3 differential time averaging related to presence of successive alluvial fans, associated to population changes due to environmental changes during the Aragonian. Our results show the need of cautiousness when palaeoenviromental inferences are based on relative abundances of micromammalian species.

  16. The bivalve Placuna (Indoplacuna) miocenica from the Middle Miocene of Siwa Oasis, Western Desert of Egypt: Systematic paleontology, paleoecology, and taphonomic implications

    Science.gov (United States)

    El-Sabbagh, Ahmed M.; El Hedeny, Magdy M.; Rashwan, Mohammed A.; Abdel Aal, Abdel Aal A.

    2016-04-01

    The present study investigated the epifaunal, free lying bivalve Placuna (Indoplacuna) miocenica (Fuchs, 1883) encountered in the Middle Miocene Marmarica Formation of Siwa Oasis, Western Desert, Egypt, in terms of systematic paleontology, paleoecology and taphonomy. Well to moderately preserved shells of this species were collected from three sections. They have been found embedded in sandy, marly and chalky limestones. Although they are extremely thin and fragile, they occurred as complete disarticulated and articulated valves. Specimens of P. (I.) miocenica are highly accumulated in the north Siwa section forming a coquinoid band (30 cm thick). In addition, they are generally distributed sporadically in different stratigraphic levels within the three studied sequences. Taphonomic observations indicated that these shells were affected by encrustation, bioerosion, disarticulation, fragmentation and abrasion. Moreover, valves of this species suffered minor chipping along their fragile margins. The occurrence of the studied species associated with oysters and other benthic faunal assemblages within carbonate sediments revealed shallow, low energy, warm and intertidal environments with periods of relatively agitated conditions.

  17. Community ecology of the Middle Miocene primates of La Venta, Colombia: the relationship between ecological diversity, divergence time, and phylogenetic richness.

    Science.gov (United States)

    Wheeler, Brandon C

    2010-04-01

    It has been suggested that the degree of ecological diversity that characterizes a primate community correlates positively with both its phylogenetic richness and the time since the members of that community diverged (Fleagle and Reed in Primate communities. Cambridge University Press, New York, pp 92-115, 1999). It is therefore questionable whether or not a community with a relatively recent divergence time but high phylogenetic richness would be as ecologically variable as a community with similar phylogenetic richness but a more distant divergence time. To address this question, the ecological diversity of a fossil primate community from La Venta, Colombia, a Middle Miocene platyrrhine community with phylogenetic diversity comparable with extant platyrrhine communities but a relatively short time since divergence, was compared with that of modern Neotropical primate communities. Shearing quotients and molar lengths, which together are reliable indicators of diet, for both fossil and extant species were plotted against each other to describe the dietary ''ecospace'' occupied by each community. Community diversity was calculated as the area of the minimum convex polygon encompassing all community members. The diversity of the fossil community was then compared with that of extant communities to test whether the fossil community was less diverse than extant communities while taking phylogenetic richness into account. Results indicate that the La Ventan community was not significantly less ecologically diverse than modern communities, supporting the idea that ecological diversification occurred along with phylogenetic diversification early in platyrrhine evolution.

  18. Middle Miocene reworked turbidites in the Baiyun Sag of the Pearl River Mouth Basin, northern South China Sea margin: Processes, genesis, and implications

    Science.gov (United States)

    Gong, Chenglin; Wang, Yingmin; Zheng, Rongcai; Hernández-Molina, F. Javier; Li, Yun; Stow, Dorrik; Xu, Qiang; Brackenridge, Rachel E.

    2016-10-01

    Our understanding of reworked turbidites is still in its infancy, and their flow processes and genesis still remain understudied. Core data from the middle Miocene Zhujiang Formation in the Pearl River Mouth Basin allow us to differentiate reworked turbidites, yielding two main contributions. Firstly, reworked turbidites are distinguished from turbidites by the association of traction structures and tidal signatures, which occur in discrete units rather than forming a classic "Bouma Sequence" for turbidites. Sedimentological characteristics of reworked turbidites proposed here will help to obtain a robust set of diagnostic criteria for the recognition of deep-water non-turbidite deepwater units as reservoirs. Secondly, our results suggest that, in the down-slope direction, classic detritus carried in turbidity flows would synchronously be bidirectionally reworked by internal tides and waves, resulting in tidal signatures seen in the interpreted reworked turbidites. In the along-slope direction, upper parts of dilute turbidity currents would mix vertically with seawater, and muddy fines would be winnowed away by contour currents, whereas lower parts of dilute turbidity currents would probably drop their coarse particles, resulting in traction structures recognized in the documented reworked turbidites. Our work highlights the influence of bottom currents on the development and modification of turbidites and suggests that reworked turbidites were created by the combined action of down-slope transport and reworking and along-slope winnowing and sorting, helping to better understand flow processes and genesis of non-turbidite reservoirs with a great economic interest.

  19. MIDDLE MIOCENE DEPOSITIONAL MODEL IN THE DRAVA DEPRESSION DESCRIBED BY GEOSTATISTICAL POROSITY AND THICKNESS MAPS (CASE STUDY: STARI GRADAC-BARCS NYUGAT FIELD

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    Tomislav Malvić

    2006-12-01

    Full Text Available Neogene depositional environments in the Drava depression can be classified in two groups. One group is of local alluvial fans, which were active during the period of Middle Miocene (Badenian extension through the entire Pannonian Basin. The second group is represented by continuous Pannonian and Pontian sedimentation starting with lacustrine environment of partly deep water and partly prodelta (turbidity fans and terminating at the delta plain sedimentation. The coarse-grained sediments of alluvial fans have the great hydrocarbon potential, because they often comprise reservoir rocks. Reservoir deposits are mostly overlain (as result of fan migration by pelitic seal deposits and sometimes including organic rich source facies. That Badenian sequences are often characterised by complete petroleum systems, what is confirmed by large number of oil and gas discoveries in such sediments in the Drava and other Croatian depressions. Alluvial environments are characterised by frequent changes of petrophysical properties, due to local character of depositional mechanism and material sources. In the presented paper, Stari Gradac-Barcs Nyugat field is selected as a case study for demonstrating the above mentioned heterogenic features of the Badenian sequences. Structural solutions are compared by maps of parameters related to depositional environment, i.e. porosity and thickness maps. Geostatistics were used for spatial extension of input dataset. The spatial variability of porosity values, i.e. reservoir quality, is interpreted by transition among different sub-environments (facies in the alluvial fan system.

  20. Middle Miocene near trench volcanism in northern Colombia: A record of slab tearing due to the simultaneous subduction of the Caribbean Plate under South and Central America?

    Science.gov (United States)

    Lara, M.; Cardona, A.; Monsalve, G.; Yarce, J.; Montes, C.; Valencia, V.; Weber, M.; De La Parra, F.; Espitia, D.; López-Martínez, M.

    2013-08-01

    Field, geochemical, geochronological, biostratigraphical and sedimentary provenance results of basaltic and associated sediments northern Colombia reveal the existence of Middle Miocene (13-14 Ma) mafic volcanism within a continental margin setting usually considered as amagmatic. This basaltic volcanism is characterized by relatively high Al2O3 and Na2O values (>15%), a High-K calc-alkaline affinity, large ion lithophile enrichment and associated Nb, Ta and Ti negative anomalies which resemble High Al basalts formed by low degree of asthenospheric melting at shallow depths mixed with some additional slab input. The presence of pre-Cretaceous detrital zircons, tourmaline and rutile as well as biostratigraphic results suggest that the host sedimentary rocks were deposited in a platform setting within the South American margin. New results of P-wave residuals from northern Colombia reinforce the view of a Caribbean slab subducting under the South American margin. The absence of a mantle wedge, the upper plate setting, and proximity of this magmatism to the trench, together with geodynamic constraints suggest that the subducted Caribbean oceanic plate was fractured and a slab tear was formed within the oceanic plate. Oceanic plate fracturing is related to the splitting of the subducting Caribbean Plate due to simultaneous subduction under the Panama-Choco block and northwestern South America, and the fast overthrusting of the later onto the Caribbean oceanic plate.

  1. Secular variation of the middle and late Miocene geomagnetic field recorded by the Columbia River Basalt Group in Oregon, Idaho and Washington, USA

    Science.gov (United States)

    Dominguez, Ada R.; Van der Voo, Rob

    2014-06-01

    database to the bottom of the middle Miocene. Many Miocene formations on a variety of continents are suitable targets for future analysis. Furthermore, the significant difference between the reversed and N-polarity dispersion parameters is intriguing and needs substantiation.

  2. A new fossil cichlid from the Middle Miocene in the East African Rift Valley (Tugen Hills, Central Kenya: First record of a putative Ectodini

    Directory of Open Access Journals (Sweden)

    Melanie Altner

    2015-11-01

    Full Text Available Identification of fossil cichlids is difficult, because the currently used diagnostic morphological characters for living cichlids are mostly soft tissue based and such characters are hardly preserved in fossils. During our recent fieldwork in the Central Kenya Rift (E-Africa, we discovered several exceptionally well-preserved fossil cichlids, which can be assigned to different lineages among the African Pseudocrenilabrinae. Here we present one of those new specimens. Its most conspicuous character is a lateral line divided into three segments. This specimen was found in the lacustrine sediments of the Middle Miocene site Waril, Tugen Hills, Kenya. The site represents the deposits of an ancient freshwater lake ca. 9-10 million years ago. Previous work on fossil leaves from the same site allow for the reconstruction of open vegetation surrounding the lake and pronounced dry seasons. Among the main further characteristics of the new fossil cichlid is a lachrimal with six lateral line canals, big cycloid scales and a low number of dorsal fin spines (XIII. The latter two characters are traceable in several members of tribes within the Pseudocrenilabrinae. However, a lachrimal with six lateral line canals is exclusively found in certain tribes of the EAR (East African Radiation within the Pseudocrenilabrinae. Moreover, the unique lateral line pattern is solely present in two genera of the EAR tribe Ectodini. However, the fossil shows cycloid scales, while modern Ectodini have ctenoid scales. Taken all evidence together, this fossil may perhaps represent an ancient lineage related to the Ectodini. Up to date, there is no definite fossil record of the members of the EAR. Our fossil may represent the first reliable calibration point for this group, which would be consistent with the previously reconstructed diversification time of the H-lineage (EAR tribes, except Boulengerochromini, Bathybatini, Trematocarini and Lamprologini and the Lamprologini ca

  3. Functional anatomy of the postcranial skeleton of Styriofelis lorteti (Carnivora, Felidae, Felinae from the Middle Miocene (MN 6 locality of Sansan (Gers, France

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    Peigné, S.

    2011-12-01

    Full Text Available The postcranial skeleton of the European Middle Miocene feline Styriofelis lorteti has been traditionally known on the basis of fragmentary fossils mainly from the French locality of Sansan. The discovery of an almost complete skeleton in the same site in the excavations of 1990 opened the possibility of unprecedented assessment of the morphology and function of this early felid. In this paper we describe this material, and compare it with a sample of modern and fossil felids, finding a combination of a generally modern morphology, with moderate adaptations to terrestrial locomotion, besides a set of primitive characters linking S. lorteti with earlier felids like Proailurus lemanensis.El esqueleto post-craneal del felino Styriofelis lorteti, del Mioceno medio de Europa, ha sido tradicionalmente conocido en base a fósiles fragmentarios, procedentes principalmente del yacimiento francés de Sansan. El descubrimiento en este yacimiento de un esqueleto casi completo, durante la campaña de 1990, abrió la posibilidad de llevar a cabo un análisis sin precedentes de la morfología y función de este félido primitivo. En este trabajo se describe este material, comparándose con una muestra de felinos fósiles y actuales, hallándose una combinación entre una morfología general moderna, con adaptaciones moderadas para la locomoción terrestre, junto con una serie de caracteres primitivos que relacionan a S. lorteti con los félidos más antiguos como Proailurus lemanensis.

  4. Taphonomy and differential diversity of the Middle Miocene decapod crustaceans from the Plášťovce Member of the Sebechleby Formation (Novohrad-Nógrad Basin, Slovakia, with remarks on palaeobiogeography

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    Hyžný Matúš

    2015-12-01

    Full Text Available Decapod crustacean assemblages from the Middle Miocene (lower ‘Badenian’=Langhian volcanoclastic Plášťovce Beds (Sebechleby Formation in the Slovakian part of the Novohrad-Nógrad Basin comprise five species in five families (Callianassidae, Laomediidae, Munididae, Cancridae and Retroplumidae and are dominated by the cancrid crab Tasadia carniolica (Bittner, 1884. Munida sp. constitutes the first record of this genus from Slovakia and the second from the European Neogene. Burrowing shrimp (Jaxea kuemeli Bachmayer, 1954 are associated with burrows tentatively attributed to this species. The occurrence of Retropluma slovenica Gašparič & Hyžný, 2014, previously recorded from the Lower Miocene of Slovenia, extends both the geographical distribution and stratigraphical range of the species. Differential decapod diversity at four localities in the Plášťovce area can be explained by collecting bias and palaeoenvironmental factors. The palaeosetting is interpreted as a muddy-bottom, nearshore zone with a water depth of approximately 100 m. Abundant articulated crabs suggest rapid burial. Third maxillipeds in open posture in some specimens may indicate respiratory stress of the animals, suggesting episodic events of rapid volcanoclastic flows responsible for killing crabs and promoting their preservation. Species composition of the decapod fauna of the Plášťovce Beds further strengthens similarities with Miocene faunas from the North Sea Basin.

  5. Integrated stratigraphy and 40Ar/39Ar chronology of the Early to Middle Miocene Upper Freshwater Molasse in eastern Bavaria (Germany)

    Science.gov (United States)

    Abdul Aziz, H.; Böhme, M.; Rocholl, A.; Zwing, A.; Prieto, J.; Wijbrans, J. R.; Heissig, K.; Bachtadse, V.

    2008-02-01

    A detailed integrated stratigraphic study was carried out on middle Miocene fluvial successions of the Upper Freshwater Molasse (OSM) from the North Alpine Foreland Basin, in eastern Bavaria, Germany. The biostratigraphic investigations yielded six new localities thereby refining the OSM biostratigraphy for units C to E (sensu; Heissig, Actes du Congres BiochroM’97. Mem Trav EPHE, Inst Montpellier 21, 1997) and further improving biostratigraphic correlations between the different sections throughout eastern Bavaria. Radioisotopic ages of 14.55 ± 0.19 and 14.88 ± 0.11 Ma have been obtained for glass shards from the main bentonite horizon and the Ries impactite: two important stratigraphic marker beds used for confirming our magnetostratigraphic calibration to the Astronomical Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). Paleomagnetic analysis was performed using alternating field (AF) and thermal (TH) demagnetization methods. The AF method revealed both normal and reverse polarities but proofs to yield unreliable ChRM directions for the Puttenhausen section. Using the biostratigraphic information and radioisotopic ages, the magnetostratigraphic records of the different sections are tentatively correlated to the Astronomical Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the main bentonite horizon coincides to chron C5ADn, which is corroborated by its radioisotopic age of 14.55 Ma, whereas the new fossil locality Furth 460, belonging to OSM unit E, probably correlates to chron C5Bn.1r. The latter correlation agrees well with the Swiss Molasse locality Frohberg. Correlations of the older sections are not straightforward. The Brock horizon, which comprises limestone ejecta from the Ries impact, possibly correlates to C5ADr (14.581 14.784 Ma), implying that, although within error, the radioisotopic age

  6. Erosional and depositional contourite features at the transition between the western Scotia Sea and southern South Atlantic Ocean: links with regional water-mass circulation since the Middle Miocene

    Science.gov (United States)

    Pérez, Lara F.; Hernández-Molina, F. Javier; Esteban, Federico D.; Tassone, Alejandro; Piola, Alberto R.; Maldonado, Andrés; Preu, Benedict; Violante, Roberto A.; Lodolo, Emanuele

    2015-08-01

    The aim of the present study was to characterise the morpho-sedimentary features and main stratigraphic stacking pattern off the Tierra del Fuego continental margin, the north-western sector of the Scotia Sea abyssal plain (Yaghan Basin) and the Malvinas/Falkland depression, based on single- and multi-channel seismic profiles. Distinct contourite features were identified within the sedimentary record from the Middle Miocene onwards. Each major drift developed in a water depth range coincident with a particular water mass, contourite terraces on top of some of these drifts being associated with interfaces between water masses. Two major palaeoceanographic changes were identified. One took place in the Middle Miocene with the onset of Antarctic Intermediate Water flow and the enhancement of Circumpolar Deep Water (CDW) flow, coevally with the onset of Weddell Sea Deep Water flow in the Scotia Sea. Another palaeoceanographic change occurred on the abyssal plain of the Yaghan Basin in the Late Miocene as a consequence of the onset of Southeast Pacific Deep Water flow and its complex interaction with the lower branch of the CDW. Interestingly, these two periods of change in bottom currents are coincident with regional tectonic episodes, as well as climate and Antarctic ice sheet oscillations. The results convincingly demonstrate that the identification of contourite features on the present-day seafloor and within the sedimentary record is the key for decoding the circulation of water masses in the past. Nevertheless, further detailed studies, especially the recovery of drill cores, are necessary to establish a more robust chronology of the evolutionary stages at the transition between the western Scotia Sea and the southern South Atlantic Ocean.

  7. Middle Miocene Hotspot-Related Uplift, Exhumation, and Extension north of the Snake River Plain: Evidence from Apatite (U-Th)/He Thermochronology

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    Foster, D. A.; Vogl, J.; Min, K. K.; Bricker, A.; Gelato, P. W.

    2013-12-01

    Passage of North America over the Yellowstone hotspot has had a profound influence on the topography of the northern Rocky Mountains. One of the most prominent topographic features is the Yellowstone crescent of high topography, which comprises two elevated shoulders bounding the eastern Snake River Plain (SRP) and converging at a topographic swell centered on the Yellowstone region. Kilometer-scale erosion has occurred locally within the topographic crescent, but it is unclear if rock exhumation is due to surface uplift surrounding the propagating hot spot, subsidence of the Snake River Plain after passage of the hot spot, or relief initiated by extension in the Northern Basin and Range Province. We have applied (U-Th/He) apatite (AHe) thermochronology to the Pioneer-Boulder Mountains (PBM) on the northern flank of the SRP, and the southern Beartooth Mountains (BM) directly north of the modern Yellowstone caldera, to constrain the timing, rates, and spatial distribution of exhumation. AHe ages from the PBM indicate that >2-3 km of exhumation occurred in the core of this topographic culmination since ~11 Ma. Age-elevation relationships suggest an exhumation rate of ~0.3 mm/yr between ~11 and 8 Ma. Eocene Challis volcanic rocks are extensively preserved and Eocene topographic highs are locally preserved to the north and south of the PBM, indicating minimal erosion adjacent to the PBM culmination. Spatial patterns of both exhumation and topography indicate that faulting was not the primary control on uplift and exhumation. Regional exhumation at 11-8 Ma was synchronous with silicic eruptions from the ~10.3 Ma Picabo volcanic field located immediately to the south and with S-tilting of the southern flank of the PBM that is likely the result of loading of the ESRP by mid-crustal mafic intrusions. AHe data from Archean rocks of the southern BM reveal Miocene-Pliocene cooling ages and include samples as young as ~2-6 Ma. Discordant single grain ages in samples with

  8. Post-Paleogene (post-Middle Eocene-pre-Miocene) Geodynamic evolution of the Upper Cretaceous-Paleogene Basins in Central Anatolia, Turkey

    Science.gov (United States)

    Rojay, Bora

    2017-04-01

    Central Anatolia is one of the key areas on the evolution of Cretaceous-Paleogene Tethys where stratigraphy of the region is well studied. However not well linked with tectonics. The so-called "Ankara Mélange" belt (AOM) and the basins on top are important elements in the understanding of the İzmir-Ankara-Erzincan suture belt (İAES) evolution in Anatolia (Turkey) and in the evolution of Tethys in minor Asia (Turkey). Some of the basins are directly situated on top of the tectonic slices of the accretionary prism (IAES). However, some are not tectonically well explained as in the case of Haymana basin. The southern continental fragments (eg. Kütahya-Bolkardaǧ and Kırşehir blocks from Gondwana) are approaching to northern continents (Pontides of Lauriasia) where basins like Haymana, Alçı, Kırıkkale and Orhaniye extensional basins are evolved in between the closing margins of two continents. Haymana basin is an extensional basin developed under contractional regime on top of both northward subducting oceanic fragments and an approaching fragments of southern continents. Paleogene (end of Eocene) is the time where the Seas were retreated to S-SE Anatolia leaving a continental setting in Anatolia during Oligocene-Miocene. The slip data gathered from the faults cross-cutting the Paleogene Units and the fabric from Cretaceous mélanges depicts a NNW-SSE to NNE-SSW compressional stress regime operated during post-Eocene-pre-Miocene period. Lately the slip surfaces were overprinted by post-Pliocene normal faulting. Key words: fault slip data, Paleogene, NNW-SSE compression, Anatolia.

  9. TECTONIC AND CLIMATIC CONTROL ON DEPOSITION OF SEEP-CARBONATES: THE CASE OF MIDDLE-LATE MIOCENE SALSOMAGGIORE RIDGE (NORTHERN APENNINES, ITALY

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    ANDREA ARTONI

    2014-11-01

    Full Text Available Seep-carbonates are generally related to hydrocarbon seepage on continental margins. Modern cold seeps are abundant in actively deforming tectonic settings, suggesting that tectonics is one of the major controlling factor on fluid emissions. Hydrocarbon seepages areconsidered major geological sources of atmospheric methane, one of the most important green-house gases, and have also been related to climate changes. However, the interplaybetween tectonics and climate change in forcing seepage is not clearly understood. Miocene seep-carbonates, formed in a collisional settingsuch as that ofthe Salsomaggiore area of the Northern Apennines(Italy, provide an opportunitytoassess accumulation and release of methane in response to tectonics and climate change along a convergent margin. Thestudiedseep-carbonatesarerelated to fluid emissions of various intensities coeval with tectonic pulses.Newplanktonic foraminiferal biostratigraphic datareveals thatdepositionof these seep-carbonatesislate Serravallian-early Tortonian in age and partiallycoeval with the Miller’s global cooling event Mi 5 (as used below. These seep-carbonates were deposited in two stages with different seepage modes. During the first stage, local tectonic pulses at the onset of the Mi5 event may have producedslow seepage, whereas during the second stage regional tectonics and more extreme climatic conditions (coolest peak of Mi5 event may have resulted inafast and more intense seepage as suggested by increasing occurrence of chaotic facies. In the Salsomaggiore Ridge, tectonics and the Mi5 cooling event actively concurredtothe deposition of seep-carbonates in both stages.

  10. The Middle Miocene ape Pierolapithecus catalaunicus exhibits extant great ape-like morphometric affinities on its patella: inferences on knee function and evolution.

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    Marta Pina

    Full Text Available The mosaic nature of the Miocene ape postcranium hinders the reconstruction of the positional behavior and locomotion of these taxa based on isolated elements only. The fossil great ape Pierolapithecus catalaunicus (IPS 21350 skeleton; 11.9 Ma exhibits a relatively wide and shallow thorax with moderate hand length and phalangeal curvature, dorsally-oriented metacarpophalangeal joints, and loss of ulnocarpal articulation. This evidence reveals enhanced orthograde postures without modern ape-like below-branch suspensory adaptations. Therefore, it has been proposed that natural selection enhanced vertical climbing (and not suspension per se in Pierolapithecus catalaunicus. Although limb long bones are not available for this species, its patella (IPS 21350.37 can potentially provide insights into its knee function and thus on the complexity of its total morphological pattern. Here we provide a detailed description and morphometric analyses of IPS 21350.37, which are based on four external dimensions intended to capture the overall patellar shape. Our results reveal that the patella of Pierolapithecus is similar to that of extant great apes: proximodistally short, mediolaterally broad and anteroposteriorly thin. Previous biomechanical studies of the anthropoid knee based on the same measurements proposed that the modern great ape patella reflects a mobile knee joint while the long, narrow and thick patella of platyrrhine and especially cercopithecoid monkeys would increase the quadriceps moment arm in knee extension during walking, galloping, climbing and leaping. The patella of Pierolapithecus differs not only from that of monkeys and hylobatids, but also from that of basal hominoids (e.g., Proconsul and Nacholapithecus, which display slightly thinner patellae than extant great apes (the previously-inferred plesiomorphic hominoid condition. If patellar shape in Pierolapithecus is related to modern great ape-like knee function, our results suggest

  11. A Milankovitch climate control on the Middle Miocene Mediterranean Intermediate Water: evidence from benthic microfauna and isotope geochemistry of the Ras Il-Pellegrin composite section (Malta island, central Mediterranean)

    Science.gov (United States)

    Rocca, D.; Bellanca, A.; Neri, R.; Russo, B.; Sgarrella, F.; Sprovieri, M.

    2003-04-01

    The marly sediments of the Blue Clay Formation in the upper part of the Middle Miocene Ras il-Pellegrin composite section (Malta island, central Mediterranean) have been investigated by integrated analysis of benthic microfauna and planktonic and benthic oxygen isotopes. The astronomical calibration of the whole section, obtained by using the astronomical solution of Laskar et al. (1993), indicates for deposition of the analysed sediments a time interval ranging between 13.75 and 12.32 Ma (Sprovieri et al., 2002). This time interval is useful to investigate the oceanographic evolution of the (paleo)Mediterranean after the interruption of communications between the Mediterranean and Indo-Pacific areas. This important paleogeographic event, estimated at about 16 Ma by Johnson (1985) and at about 14.5 Ma by Woodruff and Savin (1991), represented the first step of a progressive oceanographic evolution of the Tethys region water masses towards present Mediterranean conditions. A comparison of long-term planktonic and benthic d18O trends suggests that the intermediate outflowing Mediterranean water (proto-MIW), originated in the surface eastern zone of upper Langhian lower Serravallian (paleo)Mediterranean, had hydrographic and hydrodynamic features similar to those of the present Levantine Intermediate Water (LIW). Focusing our attention on benthic species which can be considered the best recorders of variation of proto-MIW production, we elaborated benthic data by Q-mode varimax principal factor analysis. Spectral analysis was carried out only on two factors which have a clear paleoecological significance: Factor 1 (loaded by Cibicidoides ungerianus and Siphonina reticulata) indicative of oxic bottom waters and Factor 2 (loaded by Bulimina elongata group) indicative of oxygen stressed conditions. Results of these analyses show that Factor 1 and Factor 2 curves are respectively in and out of phase with maxima of the eccentricity (100 and 400 kyr). Factor 1 is

  12. Miocene Current-Modified Submarine Fans

    Science.gov (United States)

    Arce Perez, L. E.; Snedden, J.; Fisher, W. L.

    2016-12-01

    In the southwestern Gulf of Mexico, new and newly reprocessed seismic data has revealed a series of large bedforms, with set thicknesses of 130 to 250 meters. These exhibit hummocky, oblique and shingled to parallel seismic clinoform reflections. This seismic package has a paleowater depth of 450 meters. Those shingled seismic reflections in offshore east Mexico are interpreted as contourite drift deposits. These Miocene-age contourites may be related to strong ocean bottom currents that modified submarine fans and transported sediment to the north. Those contourites were identified on older seismic data, but are better imaged and interpreted on this new data. Plans are to map out and investigate the origin and extent of fans and contourites that extends over a large area of the Gulf of Mexico. In the Early Miocene several submarine fans systems were formed by the sediment input related to orogenic activity in Mexico. Submarine fan development persisted into the Middle Miocene due to continued uplift and erosion of the Mexican landmass. Initial, contourites are small and close proximity to the deep-water fan. In the Late Miocene time, contourite drift field reached its maximum extent in the Mexican deepwater area, anchored on its southern end by a submarine mound. This mounded submarine fan is located in the offshore northeast Veracruz and can be linked to increased uplift and erosion of the Trans-Mexican volcanic belt. In the Miocene-Pliocene, the large contourite drift begins to diminish in size and scale and is moribund by the Pliocene, with establishment of oceanic circulation similar to the present day. This research is important to understand more about the Gulf of Mexico and also for the Miocene timeframe that is a key phase in the earth's history. The role of the change in bottom water flow during progressive closure of the equatorial seaway separating North and South America will also be investigated.

  13. [Proceedings of the 5th Symposium on Mesozoic and Cenozoic Decapod Crustaceans, Krakow, Poland, 2013: A tribute to Pál Mihály Müller / R.H.B. Fraaije, M. Hyžný, J.W.M. Jagt, M. Krobicki & B.W.M. van Bakel (eds.)]: Etisus evamuellerae, a new xanthid crab (Decapoda, Brachyura) from the Middle Miocene of Austria and Hungary

    NARCIS (Netherlands)

    Hyžný, M.; Bakel, van B.W.M.; Guinot, D.

    2014-01-01

    On the basis of several carapaces, a new species of xanthid crab, Etisus evamuellerae, is described from the Middle Miocene of the Vienna (Austria) and Great Hungarian basins. It differs from the coeval xanthids, Xantho moldavicus and Pilodius vulgaris, in having a distinctly protruding front and co

  14. Miocene Coralline algae

    Energy Technology Data Exchange (ETDEWEB)

    Bosence, D.W.J.

    1988-01-01

    The coralline algae (Order Corallinales) were sedimentologically and ecologically important during the Miocene, a period when they were particularly abundant. The many poorly described and illustrated species and the lack of quantitative data in coralline thalli make specific determinations particularly difficult, but some species are well known and widespread in the Tethyan area. The sedimentologic importance of the Miocene coralline algae is reflected in the abundance of in-situ coralline buildups, rhodoliths, and coralline debris facies at Malta and Spain; similar sequences are known throughout the Tethyan Miocene. In-situ buildups vary from leafy crustose biostromes to walled reefs with dense coralline crusts and branches. Growth forms are apparently related to hydraulic energy. Rhodoliths vary from leafy, crustose, and open-branched forms in muddy sediments to dense, crustose, and radial-branching forms in coarse grainstones. Rhodolith form and internal structure correlate closely with hydraulic energy. Coralline genera are conservative and, as such, are useful in paleoenvironmental analysis. Of particular interest are the restricted depth ranges of recent coralline genera. More research is needed on the sedimentology, paleoecology, and systematics of the Cenozoic corallines, as they have particular value in paleoenvironmental analysis.

  15. Evidence for an Early-Middle Miocene age of the Navidad Formation (central Chile: Paleontological, paleoclimatic and tectonic implications Evidencias de una edad miocena temprana-media de la Formación Navidad: Implicancias paleontológicas, paleoclimáticas y tectónicas

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    Néstor M Gutiérrez

    2013-01-01

    Full Text Available The age of the Navidad Formation in central Chile has always been controversial, mainly due to the conflicting age ranges indicated by its macro- and microfossils. Macrofossils are generally interpreted as having been reworked from older, Early to Middle Miocene strata, whereas a Late Miocene-Pliocene age has been accepted on the basis of planktonic foraminifer index species. The results of this study, however, indicate that the macrofossils occur in situ, which necessitates a complete revision of the geochronological data. It is concluded that the evidence for an Early to Middle Miocene age is overwhelming, and that the planktonic foraminifer index species must have appeared in the SE Pacific earlier than elsewhere. These include Globoturborotalia apertura, Globorotalia puncticulata (Deshayes, Globorotalia spheriomizea (Walters, Neogloboquadrina pachyderma (Ehrenberg, and Neogloboquadrina acostaensis (Blow. An Early to Middle Miocene age for the Navidad Formation correlates well with a reinterpretation of its depo-sitional environment as a continental shelf instead of a deepwater continental slope, global and regional paleoclimatic events, and the tectonic development of the Andes Range.La edad de la Formación Navidad en Chile central siempre ha sido controversial, debido a los distintos rangos de edad indicados por los macro- y microfósiles. En general, se considera que los macro-fósiles han sido retrabajados de estratos del Mioceno Temprano a Medio, y se aceptó una edad miocena tardía para esta unidad sobre la base de especies indicadoras de foraminíferos planctónicos. Sin embargo, los resultados de este estudio indican que los macrofósiles ocurren in situ, lo cual hace necesario una revisión completa de los datos geocronológicos. Se concluye que la evidencia por una edad miocena temprana a media es contundente, y que los foraminíferos planctónicos que indicarían una edad miocena tardía aparecieron más temprano en el SE del oc

  16. Primitive Anourosoricini and Allosoricinae from the Miocene of Germany

    NARCIS (Netherlands)

    Prieto, J.; van Dam, Jan|info:eu-repo/dai/nl/323247644

    2012-01-01

    The origin of the peculiar and highly specialized shrew tribe Anourosoricini is poorly known. The oldest known genera, Crusafontina Gibert and Darocasorex van Dam, first occur in Europe and North America around the Middle-Late Miocene transition (12-11 Ma), with the extremely rare cf. Crusafontina

  17. Mammal extinctions in the Vallesian (Upper Miocene)

    Science.gov (United States)

    Agusti, J.; Moya-Sola, S.

    The term Vallesian was created by Crusafont (1950) to designate the first European Mammalian palaeofaunas containing the equid Hipparion, the remainder of the faunas being composed of typical elements coming from the Middle Miocene such as Micromeryx, Euprox, Sansanosmilus, Pseudaelurus, and Listriodon. Thus, the Aragonian-Vallesian boundary does not show a strong change among European Miocene mammalian faunas (Agusti et al., 1984). On the other hand, the Lower Vallesian/Upper Vallesian transition corresponds to a major biotic crisis. This boudnary is characterized by the disappearence of most of the Aragonian artiodactyl forms such as Protragocerus, Miotragocerus, Listriodon, Hyotherium, Parachleusastochoerus, etc. Among the rodents, this crisis affects the family Eomyidae and most of the cricetid and glirid species. On the other hand, a number of eastern elements appear in the area at the same time. This is the case of the suid Schizochoerus and the murid Progonomys. Other eastern forms are Tragoportax, Graecoryx, Adcrocuta, Paramachairodus, Microstonyx, etc. Most of these are typical elements of the next Mammal stage, the Turolian. Thus, whereas the Lower Vallesian fauna has a typical Aragonian composition except for Hipparion. After the Middle Vallesian event, the Upper Vallesian faunas are already largely Turolian in character. The possible factors involved in this extinction event are discussed.

  18. Miocene Antarctic Terrestrial Realm

    Science.gov (United States)

    Ashworth, A. C.; Lewis, A.; Marchant, D. R.

    2009-12-01

    The discovery of several locations in the Transantarctic Mountains that contain macrofossils and pollen is transforming our understanding of late Cenozoic Antarctica. The most southerly location is on the Beardmore Glacier (85.1°S) about 500 km from the South Pole. The environment was an active glacial margin in which plants, insects and freshwater mollusks inhabited the sand and gravel bars and small lakes on an outwash plain. In addition to leaves and wood of dwarf Nothofagus (Southern Beech) shrubs, achenes of Ranunculus (Buttercup), in situ cushion growth forms of mosses and a vascular plant, the assemblages contains various exoskeletal parts of carabid and curculionid beetles and a cyclorrhaphan fly, the shells of freshwater bivalve and gastropod species and a fish tooth. Initially the deposits were assigned a Pliocene age (3.5 Ma) but a mid- to early Miocene age is more probable (c. 14 - 25 Ma) based on correlation of fossil pollen from the deposits with 39Ar/40Ar dated pollen assemblages from the McMurdo Dry Valleys locations. The oldest location within the Dry Valleys also involved an active ice margin but was part of a valley system that was completely deglaciated for intervals long enough for thick paleosols to develop. The Friis Hills fossil deposits of the Taylor Valley region (77.8°S) are at least 19.76 Ma based on the 39Ar/40Ar age of a volcanic ash bed. The valley floor during the non-glacial phases had poorly-drained soils and the extensive development of mossy mires. Wood and leaves of Nothofagus are abundant in lacustrine deposits. The silts of shallow fluvial channels contain abundant megaspores and spiky leaves of the aquatic lycopod Isoetes (Quillwort). Fossils of beetles are also present in these deposits. During the glacial phases, proglacial lakes were surrounded by dwarfed, deciduous Nothofagus shrubs. The youngest fossils recovered from the Dry Valleys are from the Olympus Range (77.5°S) with an age of 14.07 Ma. The environment was an

  19. Tectono-stratigraphy of the Çankiri Basin: Late Cretaceous to early Miocene evolution of the Neotethyan Suture Zone in Turkey

    NARCIS (Netherlands)

    Kaymakçi, N.; Özçelik, Y.; White, S.H.; Dijk, P.M. van

    2009-01-01

    The Çankırı Basin straddles the İzmir–Ankara–Erzincan Suture Zone which demarcates the former position of the northern branch of the Neotethys. It includes more than 3 km of pre-Middle Miocene in-fill related to late Cretaceous to pre-Middle Miocene evolution of the region. The basin has developed

  20. An oceanic box model of the Miocene Mediterranean Sea with emphasis on the effects of closure of the eastern gateway

    NARCIS (Netherlands)

    Karami, M.P.; Meijer, P.Th.; Dijkstra, H.A.; Wortel, M.J.R.

    2009-01-01

    The early Miocene Mediterranean Sea had two gateways toward the open ocean: the Indian Ocean in the east and the Atlantic Ocean in the west. Closure of the eastern connection during the middle Miocene had important effects on the water properties and circulation of the Mediterranean Sea. To gain ins

  1. Primer registro de cráneos asignados a Palaeospheniscus (Aves, Spheniscidae procedentes de la Formación Bahía Inglesa (Mioceno Medio-tardío, Chile First record of skulls assigned to Palaeospheniscus (Aves, Spheniscidae from the Bahía Inglesa formation (middle-late Miocene, Chile

    Directory of Open Access Journals (Sweden)

    CAROLINA ACOSTA HOSPITALECHE

    2005-09-01

    Full Text Available Los cráneos de los Spheniscidae (como los de todas las aves, aunque escasos en el registro paleontológico, muestran importantes caracteres a nivel taxonómico. Hasta el momento se conocían solo seis cráneos en todo el mundo: Paraptenodytes antarctica y una nueva especie de Spheniscidae procedentes de las formaciones Gaiman (Mioceno temprano y Puerto Madryn (Mioceno tardío de Argentina, respectivamente; Spheniscus megaramphus y 3S. urbinai de la formación Pisco (Mioceno tardío de Perú, Marplesornis novaezealandiae del Plioceno de Nueva Zelanda y un resto de Sphenicidae cf Spheniscus procedente de la formación Bahía Inglesa (Mioceno medio-tardío. De esta última unidad provienen cinco restos craneanos recientemente descubiertos en la localidad de Caldera (Región de Atacama, Chile, los cuales fueron descritos y asignados preliminarmente a Palaeospheniscus. Estos materiales constituyen el primer registro de cráneos para la especie y significan un importante aporte al conocimiento de la avifauna fósil de Chile y en particular de la formación Bahía InglesaAlthough the skulls of the Spheniscidae are unusual in the paleontologic record, they show important features useful in the systematics of the group, as well as in the rest of the birds. Until now, fossil occurrences were restricted to six skulls: Paraptenodytes antarctica and one new species from the Gaiman formation (Early Miocene and Puerto Madryn formation (late Miocene of Argentina, respectively; Spheniscus megaramphus and S. urbinai from the Pisco Formation (Late Miocene, Perú; Marplesornis novaezealandiae from New Zealand (Pliocene; and Spheniscidae cf. Spheniscus from the Bahía Inglesa Formation (Middle-Late Miocene, Chile. Five new materials have been exhumed from this last unit. These skulls, which come from the Caldera locality (Region of Atacama, Chile, have been preliminarily assigned to Palaeospheniscus (Aves, Spheniscidae, constituting the first skulls described for

  2. [Contribution of E. W. Schmidt to the development of Soviet neurology and its international relations].

    Science.gov (United States)

    Schulze, H A

    1987-05-01

    A short retrospect, occasioned by the death on July 13, 1985, of E. W. Schmidt, of his career as director of the Neurological Research Institute at the Academy of Medical Sciences of the USSR, and his influence as scientist, medical man, and humanist on the development of neurology in the Soviet Union and its representation on the international scene.

  3. Palaeomagnetism of the Miocene Farellones formation (Chile)

    Science.gov (United States)

    Goguitchaichvili, A.; Chauvin, A.; Roperch, P.; Prévot, M.; Aguirre, L.; Vergara, M.

    2000-02-01

    We report on a detailed palaeomagnetic study of the Miocene Farellones volcanic formation in the Chilean Andes near Santiago (two sections, 37 sites, about 400 orientated cores). Petrological observations show evidence of low-grade metamorphism increasing downwards through the volcanic sequence. Optical observations of opaque minerals and magnetic experiments suggest that in many cases maghemitization is associated with hydrothermal alteration. However, thermal demagnetization data indicate that the low-grade metamorphism did not significantly modify the direction of the primary remanent magnetization recorded at the time of emplacement of the volcanic lava flows. Four intervals of polarity with two intermediate palaeodirections were observed in the ~650-m-thick composite section. According to the dispersion of flow average directions, palaeosecular variation was slightly larger than that observed in general during the Upper Cenozoic. The site mean directions obtained in this study differ significantly from the expected Miocene direction. Clockwise rotations of up to 20 deg of small blocks are probably associated with the deformation of the Andean Cordillera since middle Miocene times. Geomagnetic palaeointensity data were obtained, using the Thellier method, on 24 samples from eight distinct lava flows. The flow mean VDM varies from 1.4 to 4.0x1022Am-2. Altogether, our data seem to suggest the existence of a relatively low geomagnetic field undergoing large fluctuations. Although a linear relationship was observed between the natural remanent magnetization and the thermal remanent magnetization acquired during the Thellier-Thellier experiments, undetected chemical alteration of the magnetic minerals during hydrothermalism may also explain the unusually low palaeointensity obtained.

  4. Geological controls on groundwater chemistry and arsenic mobilization: Hydrogeochemical study along an E-W transect in the Meghna basin, Bangladesh

    Science.gov (United States)

    Aziz Hasan, M.; Bhattacharya, Prosun; Sracek, Ondra; Ahmed, Kazi Matin; von Brömssen, Mattias; Jacks, Gunnar

    2009-11-01

    SummaryHydrogeochemical investigations along an E-W transect in the middle Meghna basin show groundwater chemistry and redox condition vary considerably with the change in geology. Groundwater in the Holocene shallow ( 10 μg/l) and salinity. On the other hand, groundwater from the Pliocene Dupi Tila sandy aquifer in the eastern part is fresh and low in As (geological control (i.e. change in lithofacies) on groundwater chemistry and distribution of redox-sensitive elements such as As along the transect.

  5. A platyrrhine talus from the early Miocene of Peru (Amazonian Madre de Dios Subandean Zone)

    NARCIS (Netherlands)

    Marivaux, L.; Salas-Gismondi, R.; Tejada, J.; Billet, J.; Louterbach, M.; Vink, J.; Bailleul, J.; Roddaz, M.; Antoine, P.-O

    2012-01-01

    The earliest platyrrhines have been documented from the late Oligocene of Bolivia (Salla) and from the early and early middle Miocene of middle and high latitudes (central Chile and Argentinean Patagonia). Recent paleontological field expeditions in Peruvian Amazonia (Atalaya, Cusco; Upper Madre de

  6. The Miocene carnivore assemblage of Greece

    Directory of Open Access Journals (Sweden)

    Koufos, G. D.

    2011-12-01

    Full Text Available The Miocene carnivore assemblage of Greece includes a great number of taxa, described in numerous articles since the first decades of the 19th Century. The present article is a revision of all these taxa, providing information about their history, localities, age, as well as their stratigraphic distribution and palaeoenvironment. The Early/Middle Miocene carnivore record of Greece is poor as the available fossiliferous sites and material are rare. However, the Late Miocene one is quite rich, including numerous taxa. The Miocene localities with carnivores and their age are given in a stratigraphic table covering the European Mammal zones from MN 4 to MN 13. The type locality, holotype, and some historical and morphological remarks are given for each taxon. Several carnivore taxa were erected from Greek material and new photos of their holotypes are given. The stratigraphic distribution of the Greek carnivore taxa indicates that they are covering the time span from ~19.0-5.3Ma. The majority of the Miocene taxa (Adcrocuta, Hyaenictitherium, Plioviverrops, Protictitherium, Ictitherium, Indarctos, Dinocrocuta, Promephitis disappeared at the end of Miocene. The composition of the Early/Middle Miocene carnivore assemblage of Greece includes mainly viverrids (Lophocyon, Euboictis, while the hyaenids, percrocutids, felids and mustelids are very few. On the contrary the Late Miocene assemblage is richer, including more subfamilies and species; the hyaenids and mustelids dominate, while the viverrids are absent. The Late Miocene carnivore guild structure is similar to that of the modern Serengeti, indicating a relatively open, savannah-like environment.

    La asociación de carnívoros miocenos de Grecia incluye un gran número de taxones, descritos en numerosos artículos desde las primeras décadas del siglo XIX. El presente artículo supone un esfuerzo de síntesis de todos estos taxones, suministrando información sobre su

  7. Lithostratigraphy of the Upper Oligocene - Miocene succession of Denmark

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    Piasecki, Stefan

    2010-12-01

    Full Text Available This paper presents a revised lithostratigraphic scheme for the uppermost Upper Oligocene – Miocene succession of Denmark. The marine Oligocene Brejning Clay Member is upgraded to formation status and includes the Sydklint Member and the Øksenrade Member (new. The shallow marine and deltaic deposits of mainly Early Miocene age are included in the Ribe Group (new while the fully marine Middle and Upper Miocene clay-rich deposits are referred to the Måde Group (new. The Ribe Group is subdivided into 6 formations: the Vejle Fjord Formation is revised and includes the Skansebakke Member,the Billund Formation (new includes the Addit and Hvidbjerg Members (new, the Klintinghoved Formation is redefined formally and includes the Koldingfjord Member (new, the Bastrup Formation(new includes the Resen Member (new, the Vandel Member is a new member in the Arnum Formation (revised, the Odderup Formation is redefined and includes the Stauning Member (new and the coalbearing Fasterholt Member. The Måde Group is subdivided into the Hodde, Ørnhøj (new, Gram and Marbæk (new Formations. Subdivision of the Upper Oligocene – Miocene succession into two groups, the Ribe and Måde Groups, is compatible with the North Sea lithostratigraphic framework where they correlate with the upper part of the Hordaland Group and the Nordland Group, respectively. The revised lithostratigraphic framework correlated in three dimensions provides rigorous constraints on the palaeogeographic interpretation of the Late Oligocene – Miocene period. Three major deltaic units (Billund, Bastrup and Odderup Formations prograded from the north and north-east into the North Sea Basin during the Early – early Middle Miocene. Delta progradation was punctuated by deposition of marine clay and silt associated with minor transgressive events (Vejle Fjord, Klintinghoved and Arnum Formations. During the Middle–Late Miocene, marine depositional conditions dominated (Hodde, Ørnhøj and

  8. 77 FR 20622 - N.E.W. Hydro LLC; Notice of Application for Amendment of License and Soliciting Comments, Motions...

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    ... Energy Regulatory Commission N.E.W. Hydro LLC; Notice of Application for Amendment of License and...: Amendment of License. b. Project No.: 2744-041 & 042. c. Date Filed: March 14, 2012. d. Applicant: N.E.W... 167, 116 N. State Street, Neshkoro, WI 54869-0167, (920) 293-4628, Ext. 14. i. FERC Contact: John...

  9. A Transitional Gundi (Rodentia: Ctenodactylidae from the Miocene of Israel.

    Directory of Open Access Journals (Sweden)

    Raquel López-Antoñanzas

    Full Text Available We describe a new species of gundi (Rodentia: Ctenodactylidae: Ctenodactylinae, Sayimys negevensis, on the basis of cheek teeth from the Early Miocene of the Rotem Basin, southern Israel. The Rotem ctenodactylid differs from all known ctenodactylid species, including Sayimys intermedius, which was first described from the Middle Miocene of Saudi Arabia. Instead, it most resembles Sayimys baskini from the Early Miocene of Pakistan in characters of the m1-2 (e.g., the mesoflexid shorter than the metaflexid, the obliquely orientated hypolophid, and the presence of a strong posterolabial ledge and the upper molars (e.g., the paraflexus that is longer than the metaflexus. However, morphological (e.g., presence of a well-developed paraflexus on unworn upper molars and dimensional (regarding, in particular, the DP4 and M1 or M2 differences between the Rotem gundi and Sayimys baskini distinguish them and testify to the novelty and endemicity of the former. In its dental morphology, Sayimys negevensis sp. nov. shows a combination of both the ultimate apparition of key-characters and incipient features that would be maintained and strengthened in latter ctenodactylines. Thus, it is a pivotal species that bridges the gap between an array of primitive ctenodactylines and the most derived, Early Miocene and later, gundis.

  10. Miocene-Pliocene mantle depletion event in the northern Fossa Magna, western NE Japan

    Science.gov (United States)

    Okamura, Satoshi; Inaba, Mitsuru; Adachi, Yoshiko; Shinjo, Ryuichi

    2016-07-01

    New isotopic and trace element data presented here imply a temporal change in magma sources and thermal conditions beneath the northern Fossa Magna of NE Japan from the Miocene to the Pliocene. Less radiogenic 176Hf/177Hf and 143Nd/144Nd, high Zr/Hf, and little or no Hf anomaly characterize the Early Miocene volcanism in the northern Fossa Magna region. The mantle wedge consisted of chemically heterogeneous mantle source. Based on out isotope proxies, we propose that during the onset of subduction, influx of hot asthenospheric mantle provided sufficient heat to partially melt newly subducting sediment. Geochemical modeling demonstrates that slab-derived melt mixed with mantle wedge produces the observed isotopic and trace elemental characteristics. In the Middle Miocene, the injection of hot and depleted asthenospheric material replaced the mantle beneath the northern Fossa Magna region of NE Japan. This caused the isotopic signature of the rocks to change from enriched to depleted. Then, the mantle wedge was gradually cooled during the Middle Miocene to the Pliocene with back-arc opening ending in the Late Miocene. Slab surface temperatures were still high enough for sediments to melt but not too high (<∼780 °C) to lose zircon as a residual phase. The Late Miocene and Pliocene volcanism at the post stage of the back-arc opening is best explained by a partial melting of subducted metasediment saturated with trace quantities of zircon and rutile.

  11. Updated chronology for the Miocene hominoid radiation in Western Eurasia.

    Science.gov (United States)

    Casanovas-Vilar, Isaac; Alba, David M; Garcés, Miguel; Robles, Josep M; Moyà-Solà, Salvador

    2011-04-05

    Extant apes (Primates: Hominoidea) are the relics of a group that was much more diverse in the past. They originated in Africa around the Oligocene/Miocene boundary, but by the beginning of the Middle Miocene they expanded their range into Eurasia, where they experienced a far-reaching evolutionary radiation. A Eurasian origin of the great ape and human clade (Hominidae) has been favored by several authors, but the assessment of this hypothesis has been hampered by the lack of accurate datings for many Western Eurasian hominoids. Here we provide an updated chronology that incorporates recently discovered Iberian taxa and further reevaluates the age of many previously known sites on the basis of local biostratigraphic scales and magnetostratigraphic data. Our results show that identifiable Eurasian kenyapithecins (Griphopithecus and Kenyapithecus) are much younger than previously thought (ca. 14 Ma instead of 16 Ma), which casts serious doubts on the attribution of the hominoid tooth from Engelswies (16.3-16.5 Ma) to cf. Griphopithecus. This evidence is further consistent with an alternative scenario, according to which the Eurasian pongines and African hominines might have independently evolved in their respective continents from similar kenyapithecin ancestors, resulting from an early Middle Miocene intercontinental range extension followed by vicariance. This hypothesis, which would imply an independent origin of orthogrady in pongines and hominines, deserves further testing by accurately inferring the phylogenetic position of European dryopithecins, which might be stem pongines rather than stem hominines.

  12. Sex determination in miocene catarrhine primates.

    Science.gov (United States)

    Kelley, J

    1995-04-01

    Canines of fossil hominoids and primitive catarrhines from several early, middle, and late Miocene sites were analyzed according to the shape indices described in Kelley (1995) and compared to those of males and females of extant great apes. In bivariate plots of the fossil canines utilizing the indices, 90% of the upper canines and 85% of the lower canines fell within or just outside the exclusively male or exclusively female territories delimited by the extant great apes. The remainder fell in the male-female overlap zones. Sex assignments based on these distributions were nearly 100% concordant with classifications according to canine height, suggesting a high degree of accuracy. There were various taxon-specific shifts in bivariate space among fossil genera, reflecting subtle differences in canine shape between taxa within the overall pattern of similarity to extant great apes as a whole. In many cases these shifts are matched by particular extant-ape species and subspecies, while other fossil taxa have no exact analogue for canine shape among the extant great apes. However, the pattern of spatial segregation of canines identified as either male or female at each of the sites largely mirrors that of males and females within the extant-ape sample, indicating that Miocene catarrhines shared with extant great apes a common pattern of shape differences between male and female canines, regardless of taxon-specific morphologies. These observations demonstrate that the canines of fossil catarrhines can be sexed with a high degree of confidence based solely on intrinsic features of shape. This will permit more reliable characterizations of morphological sexual dimorphism among fossil species. It is also argued that canine shape is a more reliable indicator of sex in fossil taxa than are canine/molar size ratios.

  13. Mid Miocene Terrestrial Ecosystems: Information from Mammalian Herbivore Communities.

    Science.gov (United States)

    Janis, C. M.; Damuth, J.; Theodor, J. M.

    2001-05-01

    In present day ecosystems the numbers and proportions of different kinds of ecologically distinct ungulates (hoofed mammals) provide an indicator of the nature of the vegetation in the habitat. Different vegetation types (such as forest, savanna, or grassland) are characteristically associated with different arrays of ungulates, with species exhibiting differences in diet, body size, and type of digestive fermentation system. These biological attributes can also be inferred for fossil ungulate species, the first two from quantitative assessment of skull and dental anatomy, and the last from phylogenetic affinity. Thus fossil ungulate communities may be used as indicators of the vegetation types of the habitats in which they lived. Vegetation types, in turn, are determined largely by a number of physical environmental factors. Typical ungulate communities of the late early to early middle Miocene (17 - 15 Ma) from the Great Plains of North America contained a diversity of browsing (leaf-eating) and grazing (grass-eating) species, with proportions of dietary types and a diversity of body sizes indicative of a woodland savanna habitat. Paleobotanical evidence also indicates a woodland savanna type of vegetation. However, these communities included a much larger number of ungulate species than can be found in any present-day community. The "excess" ungulate species were primarily browsers. Throughout the rest of the middle Miocene both species numbers and the proportion of browsers in ungulate communities appear to have declined steadily. During this decline in browser species the numbers of grazer species remained relatively constant. Within-community species numbers comparable to the present day were attained by the late Miocene. We suggest that the early Miocene browser-rich communities, and their subsequent decline, carry an important paleoenvironmental signal. In particular, communities "over rich" in browsers may reflect higher levels of primary productivity in

  14. Miocene cyclopid copepod from a saline paleolake in Mojave, California

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    Maria Hołyńska

    2016-06-01

    Full Text Available There are remarkably few direct fossil records of Copepoda, which implies that current estimates of the lineage divergence times and inferences on the historical biogeography remain highly dubious for these small-sized crustaceans. The Cyclopidae, a predominantly freshwater copepod family with 1000+ species and distributed worldwide, has no fossil record at all. Recent collections from the middle Miocene Barstow Formation in Southern California resulted in ample material of finely preserved cyclopid fossils, including both adult and larval stages. To document the antennulary setation pattern in the adult and copepodid instars we used a coding system that is coherent between sexes and developmental stages. The majority of the cyclopid fossils, coming from saline lake environment, represent the modern genus Apocyclops, a euryhaline, thermophilic group occurring both in the New World and Old World. A new species Apocyclops californicus is described, based on the short medial spine and spiny ornamentation of the free segment of leg 5, spinule ornamentation of pediger 5, and well-developed protuberances of the intercoxal sclerite of leg 4. The presence of antennal allobasis and the features of the swimming legs unambiguously place the Miocene Apocyclops in the A. panamensis-clade, a predominantly amphi-Pacific group. The middle Miocene fossils with clear affinities to a subgroup of Apocyclops imply an early Miocene or Paleogene origin of the genus. Based on the geographic patterns of the species richness and morphology in Apocyclops and its presumed closest relative, genus Metacyclops, we hypothesize that: (i the ancestor of Apocyclops, similar in morphology to some cave-dweller Metacyclops occurring today in the peri-Mediterranean region, might have arrived in North America from Europe via the Thulean North Atlantic bridge in the late Paleocene–early Eocene; (ii Eocene termination of the Thulean land connection might have resulted in the

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    2010-03-25

    ... Marinette County, Wisconsin. No Federal lands are occupied by the project works or located within the... Division of Hydropower Licensing approved N.E.W. Hydro's request to use the Traditional Licensing Process...

  16. A major reorganization of Asian climate by the early Miocene

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    Z. T. Guo

    2008-08-01

    Full Text Available The global climate system experienced a series of drastic changes during the Cenozoic. In Asia, these include the climate transformation from a zonal pattern to a monsoon-dominated pattern, the disappearance of typical subtropical aridity, and the onset of inland deserts. Despite major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes.

    This paper addresses these issues mainly based on two lines of evidence. First, we compiled newly collected data from geological indicators of the Cenozoic environment in China as paleoenvironmental maps of ten intervals. In confirming the earlier observation that a zonal climate pattern was transformed into a monsoonal one, the maps within the Miocene indicate that this change was achieved by the early Miocene, roughly consistent with the onset of loess deposition in China. Although a monsoon-like regime would have existed in the Eocene, it was restricted to tropical-subtropical regions. The latitudinal oscillations of the climate zones during the Paleogene are likely attributable to the imbalance in evolution of polar ice-sheets between the two hemispheres.

    Secondly, we examine the relevant depositional and soil forming processes of the Miocene loess-soil sequences to determine the circulation characteristics with emphasis on the early Miocene. Continuous eolian deposition in the middle reaches of the Yellow River since the early Miocene firmly indicates the formation of inland deserts, which have been constantly maintained during the past 22 Ma. Grain-size gradients between loess sections indicate northerly dust-carrying winds from northern sources, a clear indication of an Asian winter monsoon system. Meanwhile, well-developed Luvisols show evidence that moisture from the oceans reached northern China. This evidence shows the coexistence of two kinds of

  17. Response of Mediterranean circulation to Miocene shoaling and closure of the Indian Gateway : A model study

    NARCIS (Netherlands)

    De La Vara, Alba; Meijer, Paul

    2016-01-01

    In this regional ocean model study, we explore the effect of the Early to Middle Miocene shoaling and closure of the Indian Gateway on Mediterranean circulation and its exchange with the adjacent oceans. For this we use the regional ocean circulation model "sbPOM" and a collection of bathymetries cr

  18. New Odostomia species (Gastropoda, Heterobranchia, Pyramidellidae) from the Miocene Pebas Formation of Western Amazonia (Peru, Colombia)

    NARCIS (Netherlands)

    Aartsen, van J.J.; Wesselingh, F.P.

    2000-01-01

    Odostomia nuttalli spec. nov. and O. coluhensis spec. nov. are described from the Miocene Pebas Formation of Peruvian and Columbian Amazonia. A third pyramidellid snail is also diagnosed. These species are indicators for marine influence in the late Middle to early Late Miocence of Western Amazonia.

  19. Estimates of CO2 since the mid-Miocene

    Science.gov (United States)

    Stoll, Heather

    2016-04-01

    For past warm climates, direct CO2 determinations are unavailable. Our inferences of Antarctic ice sheet thresholds and climate sensitivity to CO2 are therefore strongly conditioned by the reliability of CO2 proxy reconstructions. For the Miocene, these rely heavily on proxies using the carbon isotopic fractionation of marine phytoplankton during photosynthesis (ep). While recent records are beginning to reveal more clearly the long term CO2 trends since the middle Miocene , the absolute CO2 concentrations are subject to higher uncertainty. This in turn influences the ability of models to simulate dynamic Antarctic ice sheet behavior in the context of expected ice sheet hysteresis. In this contribution, I discuss a new approach for estimating CO2 from published and new measurements of phytoplankton carbon isotopic fractionation using the ACTI-CO cell model. This approach accounts for the physiological adaptations made by phytoplankton cells to avoid falling below optimal photosynthetic rates as CO2 declines, the carbon concentrating mechanism. The model yields CO2 estimates which can be significantly (up to 2-fold) higher than those estimated from classic equations. Given the large degree of cooling since the late Miocene in extratropical sea surface temperature records, such CO2 estimates are consistent with a more conservative estimate of climate sensitivity over the last 12 Ma.

  20. Deformation of the late Miocene to Pliocene Inyo Surface, eastern Sierra region, California

    Science.gov (United States)

    Jayko, A.S.

    2009-01-01

    A middle and late Miocene erosion surface, the Inyo Surface, underlies late Miocene mafic flows in the White Mountains and late Miocene and (or) early Pliocene flows elsewhere in the eastern Sierra region. The Inyo Surface is correlated with an erosion surface that underlies late Miocene mafic flows in the central and northern Sierra Nevada. The mafic flows had outpourings similar to flood basalts, although of smaller volume, providing paleohorizontal and paleolowland indicators. The flows filed and locally topped the existing landscape forming broad plateau-like flats. Topographic relief in the region was characterized by weathered and rounded slopesp rior to late Miocene mafic magmatism. Relicts of the older landscape lie adjacent to late Miocene and early Pliocene basalt-covered lowlands that now occur within the crests of ranges that have 2500-3000 m relief and dramatically steep escarpments. Late Miocene mafic flows that lie on the crest of the Sierra Nevada adjacent to the White Mountains predate significant activity on the Sierra Nevada frontal fault zone. These deposits and accompanying erosion surfaces provide excellent strain markers for reconstructing part of the Walker Lane north of the Garlock fault and west of the Amargosa drainage, here referred to as the eastern Sierra region. The Inyo Surface is a compound erosional surface that records at least four major erosion events during the Cenozoic. These four surfaces were first recognized on the Kern Plateau and named from oldest to youngest, the Summit Upland, the Subsummit Plateau, the Chagoopa Plateau, and the Canyon. The three older surfaces have also been subsequently modifi ed by Pleistocene glaciation. The compound erosion surface, which is locally overlain by late Miocene mafic flows in the northern and central Sierra Nevada, is here referred to as the Lindgren Surface. Correlatives in the eastern Sierra region are found in the White Mountains, Inyo Mountains, Darwin Plateau, Coso Range, and

  1. Lower Miocene echinoderms of Jamaica, West Indies

    NARCIS (Netherlands)

    Donovan, S.K.; Portell, R.W.; Veltkamp, C.J.

    2005-01-01

    Despite being diverse globally, Miocene echinoids are poorly known from Jamaica. Moderately diverse echinoids and other echinoderms have been identified mainly from fragmentary specimens collected from chalks and mass-flow deposits of the Lower Miocene Montpelier Formation, White Limestone Group, ne

  2. Miocene phosphate-rich sediments in Salento (southern Italy)

    Science.gov (United States)

    Föllmi, Karl B.; Hofmann, Hélène; Chiaradia, Massimo; de Kaenel, Eric; Frijia, Gianluca; Parente, Mariano

    2015-08-01

    The upper Middle to lower Upper Miocene (Serravallian to Tortonian) sedimentary succession in Salento (southern Italy) includes glauconite- and phosphate-rich deposits, which are associated with pelagic micrite. In Baia del Ciolo and Marittima (southern Salento), the succession is composed of shallow-water platform carbonates of Late Oligocene age (Chattian; Porto Badisco Formation), which are overlain by a 20- to 30-cm-thick level of glauconite-rich micrite with abundant reworked particles and fossils of the underlying Porto Badisco Formation. This interval is in turn covered by an up to 15 cm thick phosphatic crust ("Livello ad Aturia"), which itself is overlain either by a hemipelagic chalk-like carbonate of Middle to Late Miocene age ("Pietra Leccese"; Marittima) or directly by a micrite of Late Miocene age (Messinian; Novaglie Formation; Baia del Ciolo), which shallows upwards into a shallow-water platform carbonate. A large hiatus is present in this succession, which likely includes the Lower and lower Middle Miocene. In the region of Lecce, two discrete levels enriched in glauconite and phosphate-each associated with a major discontinuity-occur within the Pietra Leccese. The strontium-isotope ages derived on phosphate nodules and phosphatized and non-phosphatized fossils and calcareous nannofossil ages indicate a time interval of phosphogenesis between 13.5 and 7.5 Ma, with two clusters at 12 and 10.5 Ma. The glauconite and phosphate-rich sediments resulted from a current-dominated regime, which was characterized by low overall sedimentation rates, erosion and sediment reworking, and authigenesis. This regime was likely related to a generally westward-directed bottom current, which was forced to upwell once it arrived at the western border of the eastern Mediterranean basin. The timing of the principal phosphogenic phases can only partly be correlated to those of other occurrences in this part of the Mediterranean (Malta, Gozo, southern Sicily, Matese

  3. Miocene to recent extension in NW Sulawesi, Indonesia

    Science.gov (United States)

    Advokaat, Eldert L.; Hall, Robert; White, Lloyd T.; Watkinson, Ian M.; Rudyawan, Alfend; BouDagher-Fadel, Marcelle K.

    2017-10-01

    The Malino Metamorphic Complex (MMC) in the western part of the North Arm of Sulawesi (Indonesia) has previously been suggested to be a metamorphic complex exhumed in the Early - Middle Miocene. This idea was based on limited K-Ar and 40Ar/39Ar age data, but no structural data were presented to provide evidence for the mechanism of exhumation. Here we present new field observations, micro-structural analyses and a revised stratigraphy of NW Sulawesi based on new age data, to provide better constraints on the timing and mechanism of exhumation. The data presented here suggest that the MMC is a metamorphic core complex which underwent lithospheric extension during the Early - Middle Miocene. Although the MMC experienced significant extension, there is no evidence that it was exhumed during this time. There is no contact between the MMC and the Pliocene Ongka Volcanics, contradicting a previously inferred unconformable contact. Pliocene undeformed granitoids intruding the MMC indicate the complex was still at depth during their emplacement. Furthermore, Pliocene and Pleistocene cover sequences do not contain metamorphic detritus. A second phase of extensional uplift was accommodated by brittle faulting from the Late Miocene-Pliocene onwards, during which the MMC was exhumed. This extension is widespread, as indicated by synchronous exhumation of the adjacent Palu Metamorphic Complex in West Sulawesi, and rapid subsidence offshore in Gorontalo Bay. It is linked to northward slab rollback of the southward-subducting Celebes Sea since the Pliocene. GPS data show rapid northward motion of the North Arm of Sulawesi with respect to the Celebes Sea, indicating that this process is ongoing at present day.

  4. Mid-Late Miocene vegetation and environments in Southeast China: Insights from a marine palynological record in northwestern Taiwan

    Science.gov (United States)

    Hao, Xiu-dong; Weng, Chengyu; Huang, Chi-Yue; Ouyang, Xu-hong

    2017-05-01

    Taiwan Island represents the exposed accretionary prism developed by eastward subduction of South China Sea (SCS) oceanic lithosphere beneath the Philippine Sea Plate since the middle Miocene. There are many well-documented data about the biostratigraphic correlation, except for palynological studies. Here, we present a new palynological record of mid-Late Miocene deposits from the Chuhuangkeng section, Miaoli, northwestern Taiwan, which reveals a vegetation and paleoelevation reconstruction in Southeast China, during the Middle to Late Miocene, corresponding to the time interval of about 14.5-5.5 Ma. Most samples yielded well-preserved palynomorphs, and the palynological results suggest that the dominant vegetation was the mixed coniferous-broadleaved forests in the Coastal Mountains of Southeast China (CMSC) during the Mid-Late Miocene. Moreover, based on large amounts of Tsuga and Picea pollen, we hypothesized that a subalpine conifer forest then flourished in the CMSC, and the estimated maximum paleoelevation might be up to ∼3000 m above sea level (a.s.l.) during the Mid-Late Miocene, being 1000-1500 m higher than today. These findings offer a new perspective to comprehend the paleotopographic evolution of China and the source area of Taiwan's spruce forests. Additionally, the high abundance of Pinus, Tsuga, Picea pollen and fern spores also suggests an enhancement of the EASM during the Mid-Late Miocene.

  5. Miocene sediments distribution in the central and northern parts of the Vienna Basin, central Europe

    Science.gov (United States)

    Lee, E.; Wagreich, M.; Decker, K.

    2012-12-01

    The Vienna Basin is a Miocene sedimentary basin situated at the Alpine-Carpathian transition and spreading from Austria in the South to the Czech Republic and Slovakia in the north. The basin primarily developed as a piggy-back basin during the Lower Miocene (~18 - 16 Ma) on top of the NW-ward moving Eastern Alpine and West Carpathians thrust sheets. In the late Lower Miocene, the local stress regime changed by the lateral extrusion of the Eastern Alps towards the Pannonian area. It leads to the developing of the basin between two left stepping sinistral strike-slip faults of the Vienna Basin faults system during the Middle and Upper Miocene (~16 - 8 Ma). Structures related with this pull-apart stage are extensional sinistral strike-slip duplexes connected with large scale listric normal fraults. Our study area mainly covers the central and northern Vienna Basin that is not yet studied well for the stratigraphy. The goal of this study is the characterization and distribution of the Miocene sediments. For this purpose we investigated approximately 200 wells in 17 well-groups in order to obtain details on the Miocene sediments. Among them 84 wells drilled down to the Northern Calcareous Alps and the flysch units in the pre-Neogene basin subcrop. The initial phase of the Miocene deposition was related to the transgression and is characterized by the deposition of coarse clastic and marly clay sediments. These sediments are distributed locally in the northern part of the basin. The overlying sediments are more widely distributed than the underlying ones. During the late Lower Miocene, the depocenters shifted towards the south and sedimentation was dominated by marly clay intercalated with sand. An unconformity depicted for the regional stage boundary fits well with the regressive phase and the subsequent transgression. From Middle to Upper Miocene, sediments were deposited over a wide area of the Vienna Basin. The sedimentation was governed by combination of pull

  6. A fish assemblage from an early Miocene horizon from Jabal Zaltan, Libya

    Science.gov (United States)

    Argyriou, Thodoris; Cook, Todd D.; Muftah, Ahmed M.; Pavlakis, Paris; Boaz, Noel T.; Murray, Alison M.

    2015-02-01

    Recent excavations and prospecting in the early to middle Miocene deposits of the Maradah Formation in Jabal Zaltan, Libya, yielded a diverse fish assemblage coming from an early Miocene locality. The material described here includes more than 18 marine and freshwater taxa most of which were previously unreported from the area. Jabal Zaltan is one of the very few early Miocene Afroarabian fossil sites that produced such a diverse fish sample. Therefore, the fossils described here provide a unique insight into the composition of the early Miocene fish faunas from the northern African coast; a critical time period for faunas of the continent, as contact with Eurasia ended 100 million years of African isolation. In addition, the Jabal Zaltan fossils help consolidate the validity of Galeocerdo mayumbensis and extend its geographic range to include the Tethys. The Maradah deposits also host the first occurrences of two genera (Pteromylaeus, Distichodus) in the fossil record. The fish finds support the presumed depositional environment that of tropical shallow estuarine to deltaic conditions, and the freshwater fishes document the presence of a modern-type Nilosudanian fauna containing elements with both African and Asian affinities. The Jabal Zaltan ichthyofauna, with its diversity of taxa, has the potential to become a key reference fauna for future studies of early Miocene African fishes.

  7. Rifting, rotation, detachment faulting, and sedimentation: Miocene evolution of the southern California margin

    Energy Technology Data Exchange (ETDEWEB)

    Bachman, S.B.; Crouch, J.K. (Crouch, Bachman, and Associates, Inc., Santa Barbara, CA (USA))

    1990-05-01

    The evolution of the Los Angeles and adjacent offshore Santa Monica and San Pedro basins of southern California began during the earliest Miocene. The basins formed as the result of rifting and subsequent large scale rotation of segments within a preexisting Mesozoic-Paleogene forearc basin. Clockwise rotation (less than 90{degree}) of the outer two-thirds of this fore-arc basin during the early and middle Miocene moved these once north-trending forearc strata into an east-west trend (the modern Transverse Ranges). The eastern margin of the initial rift remains in its original location and is best documented from outcrop and subsurface data in the San Joaquin Hills. What was once the western margin of the rift has been rotated to a position north of the rift, along the southern Santa Monica Mountains. The early Miocene Vaqueros sandstones. which that are entirely shallow-marine and thousands of feet thick provide evidence for initial subsidence of the rift. Widening of the rift and separation of the Santa Monica Mountains and the San Joaquin Hills in the early and middle Miocene was accompanied by detachment faulting and volcanism along the rift margins. These detachment faults can be documented in the subsurface of the San Joaquin Hills and in outcrop in the Santa Monica Mountains. A unique aspect of this inner borderland rift is the rapid uplift, exposure, erosion, and then subsidence of high pressure/temperature metamorphic basement blocks (Catalina schist) within the rift itself. These basement rocks were buried 20 to 30 km beneath the ancestral fore arc prior to rifting. They were uplifted, perhaps due to thermal effects, during pervasive early and middle Miocene volcanism within the rift. Evidence of these dramatic events is provided by the distinctive San Onofre breccia deposit exposed along the margins of the rift.

  8. PALAEOECOLOGY OF AN EARLY-MIDDLE MIOCENE LAKE IN CHINA: PRELIMINARY INTERPRETATIONS BASED ON PHYTOLITHS FROM THE SHANWANG BASIN%中国-中新世湖泊的古生态:根据山旺盆地植硅体的初步解释

    Institute of Scientific and Technical Information of China (English)

    Caroline A.E.STR(O)MBERG; Else Marie FRIIS; 梁明媚; Lars WERDELIN; 张玉亮

    2007-01-01

    山东山旺中新世山旺组湖相沉积中富含保存精美的古生物化石.对于湖相沉积中的昆虫、植物和哺乳动物化石,前人已经做了大量的研究工作.其中植物大化石和孢粉的研究结果表明,中新世山旺组在沉积期间,山旺湖周围的植被处于湿润的暖温带到亚热带的古生态环境下.哺乳动物蝙蝠和貘化石的研究结果也支持这个结论.然而,迄今为止,还没有关于草本植物的种类组成及含量的研究报道.本文首次对山旺组样品中的植硅体进行了研究,为山旺中新世植被的研究提供了新的证据.对从6块山旺组样品中分析出的植硅体进行研究的结果表明,山旺中新世植硅体组合含有丰富的保存极好的草本植物植硅体,代表森林成分的双子叶植物植硅体,以及偶尔出现的棕榈科植硅体.草本植物的植硅体主要来自于C3/C4禾本科的PACCAD类群和早熟禾亚科的植物,少数可能来自于在林下封闭生活环境中生长的草本植物.山旺中新世植硅体组合显示,在湖边森林生活环境下,伴生大量的适合沼生到中生环境的草本植物,在较干旱的地区生长着早熟禾(和PACCAD)的草本植物.本文的研究结果进一步支持山旺中新世气候比现在更加湿润而且变动较小的观点.山旺中新世植硅体组合与土耳其和北美大平原中新世湖相沉积中的植硅体组合不同,后者的植硅体组合主要是由多种C3早熟禾亚科草本和不同种类的PACCAD类群草本植物组成.今后的研究工作将进一步揭示这种差异是否反映了草本植物群落在大尺度的生物地理上的差异,或者是由于地区性的局部气候不同所导致.%The lacustrine Early to Middle Miocene Shanwang Formation contains an exceptionally well-preserved biota including insects, plants, and vertebrates that has been subject to intense study. Palaeoecological work on plant macrofossils and palynofloras indicate that

  9. Bonefish-otoliths from the Anversian (Middle Miocene) of Antwerp

    NARCIS (Netherlands)

    Gaemers, P.A.M.

    1971-01-01

    31 species are listed from the Anversian in the neighbourhood of Antwerp (Belgium). Nine were previously known and one recorded species could not be found again. The relative abundances of the species are discussed, especially with reference to Trisopterus friedbergi and small species. The faunas

  10. Middle Miocene Rosarito Beach Formation, northwest Baja California, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Ledesma-Vasquez, J.

    1988-03-01

    The Rosarito Beach Formation was deposited on the continental borderland adjacent to the Peninsular Range province. This formation provides an insight to the paleo-oceanographic characteristics that are representative of marine sediments. The La Mision Member consists largely of basalts more than 150 m thick, which thin to the east. There are no pillow lavas or water-laid textures associated with this member. The Los Indios Member, which overlies the La Mision, consists of a wide variety of volcaniclastic marine sediments (tuffs, lapilli tuffs, tuffaceous sandstones) and 4-m thick diatomaceous layers. Basalts were emplaced through a series of fissures in the Mesozoic basement while the area was uplifted to the west. At the same time, the coastline receded to the east. The basalt flows that comprise the La Mision Member and the overlying pyroclastics were deposited at the same time that the coastline was moving east and the entire area was being faulted, building horst and graben structures (continental borderland). The diatomaceous sediments were deposited on this new shallow area associated with upwelling and an oxygen minimum layer, and were reinforced by the presence of grabens, which acted as silled basins. The silicic microfossils indicate a mixed environment of outer and inner shelves on a shallow platform no deeper than 200 m.

  11. Gulf Coast Estimated Thickness of the Middle Miocene Sequence

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The thickness contours were created using biostratigraphic data in the Paleo-Data, Inc., Tenroc Regional Geologic Database. The depths of the microfossil locations...

  12. NEOGLOBOQUADRINA ATLANTICA PRAEATLANTICA, NEW SUBSPECIESFROM LATE MIDDLE MIOCENE

    Directory of Open Access Journals (Sweden)

    LUCA M. FORESI

    2002-07-01

    Full Text Available A new subspecies of Neogloboquadrina atlantica atlantica previously reported under different names, is here distinguished and named Neogloboquadrina atlantica praeatlantica. Its first occurrence into the Mediterranean dated at 11.78 Ma, is not evolutionary appearance but is related to a global climatic cooling which pushed southwards from high latitude this taxon; however, the area of its evolutionary appearance is not clearly defined; its extinction occurs within the Globigerinoides obliquus extremus Zone. N. atlantica atlantica which evolves from N. atlantica praeatlantica occurs in the Mediterranean at 11.15 Ma, just after the Mediterranean exit of Paragloborotalia siakensis (Le Roy.   

  13. Structural studies on Miocene kerogen

    Energy Technology Data Exchange (ETDEWEB)

    Almendros, G.; Gonzalez-Vila, F.J.; Martin, F.; Alvarez-Ramis, C.

    1988-04-01

    The different characteristics of organic matter in Miocene sediment from Portazgo (Madrid, Spain) were studied by several physicochemical techniques. Then g.c.-m.s. was applied to bitumen and to oxidation degradation products of the insoluble organic residue. Both the palaeobotanic study and the composition of the bitumen fraction suggest an important contribution of vascular plants in the sediment; a predominance of odd-numbered alkanes, of straight-chain aliphatic compounds, and of high molecular weight homologues of the series were observed. The degradation methods employed yielded large proportions of aliphatic chains, but aromatic compounds amounted to approx. 25 wt% of the degradation products, suggesting a significant contribution of lignin. In addition to the degradation with potassium persulphate followed by alkaline permanganate oxidation, by depolymerization perborate was also applied. The latter degradation method yielded aromatic acids and polymethylene compounds, and residual kerogen was transformed into an alkali-soluble polymer, which can be studied by the usual techniques for humic acids. 23 refs., 4 figs., 2 tabs.

  14. Direct dating of Late Miocene-Early Pliocene compression on Elba Island: Is a new paradigm necessary for the opening of the Northern Tyrrhenian Sea?

    Science.gov (United States)

    Viola, Giulio; Torgersen, Espen; Mazzarini, Francesco; Musumeci, Giovanni; Garofalo, Paolo Stefano; van der Lelij, Roelant

    2017-04-01

    The northern Apennines accommodated the closure of the Liguro-Piemontese Ocean along the European and Adriatic continental margins. Crustal shortening via folding, eastward thrusting and stacking of oceanic and continental units during the westward subduction of Adria beneath the European plate shaped the orogenic prism starting in the Eocene and continuing to the Middle Miocene. Intrusive and volcanic rocks between 8.4 and 3 Ma crop out extensively in the northern Tyrrhenian Sea, and their emplacement in the inner portion of the belt is commonly interpreted as resulting from major crustal extension related to the Late Miocene-Pliocene opening of the northern Tyrrhenian Sea as a backarc basin. On the Island of Elba, which exposes the westernmost portion of the prism, the low-angle Zuccale fault (ZF) is generally interpreted as a major low-angle normal fault (LANF) whose Late Miocene activity would have greatly facilitated regional E-W extension in the geodynamic framework of the opening of the northern Tyrrhenian Sea between 10 and 5 Ma. In order to better constrain the kinematic meaning of the ZF and the timing of these important events, we have used the K-Ar method to date a set of brittle-ductile and brittle fault rocks cut by the ZF and sampled from its immediate footwall. A last sample from the brittle ZF itself is currently also being dated. The dated deformation zones in the ZF footwall are both thrusts with top-to-the east kinematics. They are undoubtedly cut by the brittle ZF and thus predate it; they are 1) the Calanchiole shear zone, formed by strongly sheared carbonate hornfelses and 2) the Capo Norsi fault, a brittle fault zone within serpentinites of the Ligurian sequence. While the Calanchiole shear zone developed coevally with the c. 6.2 Ma Porto Azzurro (PA) monzogranite, the Capo Norsi thrust led to the internal stacking of the PA contact aureole, and separates an upper complex that did not experience contact metamorphism from the underlying

  15. New reports of decapod Portunus monspeliensis A. Milne Edwards, 1860 from Miocene beds of eastern Slovenia with notes on palaeoecology and palaeobiogeography

    Directory of Open Access Journals (Sweden)

    Rok Gašparič

    2016-08-01

    Full Text Available In the present paper we report on several new occurrences of decapod Portunus monspeliensis A. Milne Edwards, 1860 from Miocene beds of eastern Slovenia, i. e. from the already known locality Šentilj in the northeastern Štajerska region and additional new localities in the Kozjansko and Dolenjska regions. These new reported occurrences of P. monspeliensis from the Middle Miocene (Badenian strata of eastern Slovenia improve our knowledge of this otherwise widespread decapod crustacean. Additionally, we also re-evaluate the environmental preferences of the species and its wider palaeobiogeographical distribution during the Miocene in the Mediterranean, Atlantic and Paratethys Seas.

  16. The thumb of Miocene apes: new insights from Castell de Barberà (Catalonia, Spain).

    Science.gov (United States)

    Almécija, Sergio; Alba, David M; Moyà-Solà, Salvador

    2012-07-01

    Primate hands display a major selective compromise between locomotion and manipulation. The thumb may or may not participate in locomotion, but it plays a central role in most manipulative activities. Understanding whether or not the last common ancestor of humans and Pan displayed extant-ape-like hand proportions (i.e., relatively long fingers and a short thumb) can be clarified by the analysis of Miocene ape hand remains. Here we describe new pollical remains-a complete proximal phalanx and a partial distal phalanx-from the middle/late Miocene site of Castell de Barberà (ca., 11.2-10.5 Ma, Vallès-Penedès Basin), and provide morphometric and qualitative comparisons with other available Miocene specimens as well as extant catarrhines (including humans). Our results show that all available Miocene taxa (Proconsul, Nacholapithecus, Afropithecus, Sivapithecus, Hispanopithecus, Oreopithecus, and the hominoid from Castell de Barberà) share a similar phalangeal thumb morphology: the phalanges are relatively long, and the proximal phalanges have a high degree of curvature, marked insertions for the flexor muscles, a palmarly bent trochlea and a low basal height. All these features suggest that these Miocene apes used their thumb with an emphasis on flexion, most of them to powerfully assist the fingers during above-branch, grasping arboreal locomotion. Moreover, in terms of relative proximal phalangeal length, the thumb of Miocene taxa is intermediate between the long-thumbed humans and the short-thumbed extant apes. Together with previous evidence, this suggests that a moderate-length hand with relatively long thumb-involved in locomotion-is the original hand morphotype for the Hominidae. Copyright © 2012 Wiley Periodicals, Inc.

  17. EARLY MIOCENE INSULAR VERTEBRATES FROM LAERRU (SARDINIA, ITALY: PRELIMINARY NOTE

    Directory of Open Access Journals (Sweden)

    DANIEL ZOBOLI

    2017-01-01

    Full Text Available A new vertebrate assemblage was discovered in an Early  Miocene lacustrine deposit near the village of Laerru (northern Sardinia, Italy. The assemblage is composed by mammals, reptiles and a bird. The mammals are represented by three ruminants (cf. Sardomeryx oschiriensis, Pecora indet. small size and Pecora indet. very small size and one dormouse (Peridyromys aff. murinus while reptiles are represented by turtles (Trionychidae? and crocodiles (cf. Diplocynodon sp.. A bird bone fragment is also reported and referred to Palaeortyx cf. brevipes (Galliformes. The assemblage can be related to the “Oschiri fauna”, one of the oldest endemic insular fauna known in the Mediterranean. The age of the Laerru vertebrates is early-middle Burdigalian, between 18.8 and 18.3 Ma, corresponding to the mammal unit of the main land MN3. The predominance of ruminants confirms the good capacity of these mammals to colonize insular environments.

  18. Miocene reef and nonreef carbonate rocks in Japan

    Energy Technology Data Exchange (ETDEWEB)

    Konishi, K.

    1988-01-01

    Japan's main islands experienced temperature climates throughout the Neogene with a tropical invasion around 16 Ma (early middle Miocene). This climatic warming, accompanied by a eustatic sea level rise, caused the unusual occurrence of reef facies, mangrove deposits, and lateritic beds in Japan. In cooler climates both before and after reef growth, sediments rich in bryozoan and algal material were widespread. Reef rocks emplaced as penecontemporaneous olistoliths in deep-water clastics at the Pacific coast of central Honshu are characterized by a wide lithologic spectrum, ranging from grainstone to bindstone. These rocks include rudstone and floatstone, which are rich in coralline algae (encrusting forms such as Lithophyllum and Mesophyllum and articulate forms such as Amphiroa) and codiacean algae (Halimeda) with hermatypic corals and large benthic formainifera (e.g., Nephrolepidina and Miogypsina) being less common. Two types of dolomite occur: (1) limpid dolomite with O/sup 18/ = -5.77 and with bipyramidal quartz and (2) microcrystalline dolomite with O/sup 18/ = 2.00 and with length-slow chalcedony. While microcrystalline dolomite tends to predominate in muddy matrix material, limpid dolomite appears to fill pores, some of which are moldic. Younger nonreef carbonate rocks, as occur on the Noto Peninsula of central Honshu, are commonly cross-bedded, contain Bryozoa, mollusks, small foraminifera, and echinoids, and are locally dolomitized. These dolomites are ascribed to a mixed-water origin. A different type of nonreef, yet reservoir-forming, dolostone occurs in the late middle Miocene of northeast Honshu and is interpreted to have formed as a transformation from bathyal opal.

  19. Petrogenesis of the Miocene volcanism along the İzmir-Balıkesir Transfer Zone in western Anatolia, Turkey: Implications for origin and evolution of potassic volcanism in post-collisional areas

    Science.gov (United States)

    Ersoy, Yalçın E.; Helvacı, Cahit; Uysal, İbrahim; Karaoğlu, Özgür; Palmer, Martin R.; Dindi, Fulya

    2012-10-01

    The Miocene volcanic rocks along the İzmir-Balıkesir Transfer Zone along the western margin of the Menderes Core Complex (MCC) in western Anatolian Volcanic Province (WAVP), where strike-slip deformation is dominant, comprise: (Group 1) early-middle Miocene high-K to shoshonitic rocks with high-Mg# and relatively low SiO2, (Group 2) middle Miocene phonolitic rocks with low-Mg# and intermediate SiO2, (Group 3) early-middle Miocene medium- to high-K series from andesites to rhyolites, (Group 4) middle Miocene rhyolites with distinct trace element compositions; and (Group 5) late Miocene high-MgO basalts, K-trachybasalts and (Group 6) late Miocene high-MgO basaltic andesites. The geochemical features of these rocks are comparable with the other Oligocene to Miocene volcanic rocks, but differ from the Eocene volcanic rocks in WAVP. The geochemical features of the most primitive early-middle Miocene Group 1 rocks indicate that they were derived from an anomalously metasomatized lithospheric mantle. The mineralogical and geochemical properties of garnet-amphibole peridotite from the Ulten Zone (UZP), Eastern Alps, which is thought to represent a fossil metasomatic mantle wedge contaminated by continental subduction, is similar to the model mantle composition previously proposed for the genesis of the mafic rocks. Together with the presence of Eocene to early Miocene continental subduction beneath the Aegean-west Anatolia region, this strongly suggests that continental subduction was an important factor in the genesis of the high-MgO shoshonitic to ultrapotassic volcanism in this post-collisional area. The origin of the Group 3 andesitic to rhyolitic rocks includes; (1) lower crustal melting, (2) mixing between lower crustally-derived and mantle-derived melts, and (3) FC-AFC processes. The late Miocene Group 5 and 6 rocks, however, derived from a more depleted mantle source, indicating that the mantle became depleted over time. The rhyolites of Group 4 are most probably

  20. Miocene extension in the East Range, Nevada: A two-stage history of normal faulting in the northern basin and range

    Science.gov (United States)

    Fosdick, J.C.; Colgan, J.P.

    2008-01-01

    The East Range in northwestern Nevada is a large, east-tilted crustal block bounded by west-dipping normal faults. Detailed mapping of Tertiary stratigraphic units demonstrates a two-phase history of faulting and extension. The oldest sedimentary and volcanic rocks in the area record cumulative tilting of -30??-45??E, whereas younger olivine basalt flows indicate only a 15??-20??E tilt since ca. 17-13 Ma. Cumulative fault slip during these two episodes caused a minimum of 40% extensional strain across the East Range, and Quaternary fault scarps and seismic activity indicate that fault motion has continued to the present day. Apatite fission track and (U-Th)/He data presented here show that faulting began in the East Range ca. 17-15 Ma, coeval with middle Miocene extension that occurred across much of the Basin and Range. This phase of extension occurred contemporaneously with middle Miocene volcanism related to the nearby northern Nevada rifts, suggesting a link between magmatism and extensional stresses in the crust that facilitated normal faulting in the East Range. Younger fault slip, although less well constrained, began after 10 Ma and is synchronous with the onset of low-magnitude extension in many parts of northwestern Nevada and eastern California. These findings imply that, rather than migrating west across a discrete boundary, late Miocene extension in western Nevada is a distinct, younger period of faulting that is superimposed on the older, middle Miocene distribution of extended and unextended domains. The partitioning of such middle Miocene deformation may reflect the influence of localized heterogeneities in crustal structure, whereas the more broadly distributed late Miocene extension may reflect a stronger influence from regional plate boundary processes that began in the late Miocene. ?? 2008 Geological Society of America.

  1. Miocene freshwater Mollusca from western Brazilian Amazonia

    NARCIS (Netherlands)

    Wesselingh, F.P.; Ranzi, A.; Räsänen, M.E.

    2006-01-01

    Thirteen species of fossil molluscs are reported from the Solimões Formation of western Brazilian Amazonia. Based on mammalian chronology of the Solimões Formation and radiometric ages reported from coeval deposits in adjacent Peru, the age of the fauna is established as Late Miocene. The fauna incl

  2. Global warming and South Indian monsoon rainfall-lessons from the Mid-Miocene.

    Science.gov (United States)

    Reuter, Markus; Kern, Andrea K; Harzhauser, Mathias; Kroh, Andreas; Piller, Werner E

    2013-04-01

    Precipitation over India is driven by the Indian monsoon. Although changes in this atmospheric circulation are caused by the differential seasonal diabatic heating of Asia and the Indo-Pacific Ocean, it is so far unknown how global warming influences the monsoon rainfalls regionally. Herein, we present a Miocene pollen flora as the first direct proxy for monsoon over southern India during the Middle Miocene Climate Optimum. To identify climatic key parameters, such as mean annual temperature, warmest month temperature, coldest month temperature, mean annual precipitation, mean precipitation during the driest month, mean precipitation during the wettest month and mean precipitation during the warmest month the Coexistence Approach is applied. Irrespective of a ~ 3-4 °C higher global temperature during the Middle Miocene Climate Optimum, the results indicate a modern-like monsoonal precipitation pattern contrasting marine proxies which point to a strong decline of Indian monsoon in the Himalaya at this time. Therefore, the strength of monsoon rainfall in tropical India appears neither to be related to global warming nor to be linked with the atmospheric conditions over the Tibetan Plateau. For the future it implies that increased global warming does not necessarily entail changes in the South Indian monsoon rainfall.

  3. Global dominance of coralline red-algal facies: A response to Miocene oceanographic events

    Science.gov (United States)

    Halfar, Jochen; Mutti, Maria

    2005-06-01

    Rhodoliths (free-living coralline red algae) can thrive under a wide range of temperatures, reduced light, and increased nutrient levels, and often form a distinct so-called rhodalgal lithofacies that is an important component of Cenozoic shallow-water carbonates. Global distributions illustrate that from the late-early to early-late Miocene (Burdigalian early Tortonian), rhodalgal facies reached peak abundances and commonly replaced coral-reef environments, accompanied by a decline in other carbonate-producing phototrophs. We argue that the dominance of red algae over coral reefs was triggered in the Burdigalian by enhanced trophic resources associated with a global increase in productivity, as evidenced by a long-term shift toward higher carbon isotope values. Rhodalgal lithofacies expanded further in the middle Miocene when strengthened thermal gradients associated with the establishment of the East Antarctic Ice Sheet led to enhanced upwelling while climate change generated increased weathering rates, introducing land-derived nutrients into the oceans. Globally cooler temperatures following a climatic optimum in the early-middle Miocene contributed to sustain the dominance of red algae and prevented the recovery of coral reefs. The global shift in nearshore shallow-water carbonate producers to groups tolerant of higher levels of trophic resources provides further evidence for increased nutrient levels during that time interval and shows the sensitivity of shallow-water carbonate facies as indicators of past oceanographic conditions.

  4. Age and stratigraphic context of Pliopithecus and associated fauna from Miocene sedimentary strata at Damiao, Inner Mongolia, China

    Science.gov (United States)

    Kaakinen, Anu; Abdul Aziz, Hayfaa; Passey, Benjamin H.; Zhang, Zhaoqun; Liu, Liping; Salminen, Johanna; Wang, Lihua; Krijgsman, Wout; Fortelius, Mikael

    2015-03-01

    Since the discovery of mammalian fossils in Central Inner Mongolia in the beginning of the 20th century, this area has produced a rich and diverse record of Miocene faunas. Nevertheless, the stratigraphy has remained poorly constrained owing to scattered faunal horizons and lack of continuous vertical exposures. Consequently, most age estimates of these Miocene sites are based on paleontological evidence alone, with very few sites having been dated independently. Our field investigations in Damiao, in Siziwang Qi, Inner Mongolia have yielded more than 30 new fossiliferous localities from three horizons, including a pliopithecid fauna. This study presents the litho-, bio- and magnetostratigraphy of the Damiao area and provides age estimates for the three fossil-bearing horizons. The sedimentary sequence is interpreted as the remains of a fluvial system comprising channels, subaerially exposed floodplains and floodbasin environments. The two local stratigraphic sections measured and sampled for paleomagnetic analysis coincide with species-rich vertebrate fossil localities. The paleomagnetic results and faunal evidence suggest a correlation of lowermost fossil horizon (DM16) producing relatively rich small mammal assemblage to the early Miocene chron C6Ar or C6An.1r, roughly in 20-21 Ma age range. The pliopithecid locality level (DM01) represents latest middle Miocene and has an age estimate of about 12.1 Ma while the youngest localities (DM02) with cervoids and abundant and diverse small mammal fauna represents the earliest late Miocene with an age estimate of about 11.6 Ma. Our magnetostratigraphic results confirm that the Damiao strata constitute one of the best sequences in Inner Mongolia with early, middle and late Miocene mammalian faunas in stratigraphic superposition. The results also provide constraints on the paleoenvironmental evolution and bioevents of the area. The occurrence of pliopithecid primates in the middle Miocene of Inner Mongolia suggests humid

  5. Evolution by structural polymorphism in a Miocene neogastropod

    Energy Technology Data Exchange (ETDEWEB)

    Allmon, W.D.

    1985-01-01

    Morphological change in the shallow marine species Bullia (Bulliopsis) quadrata (Nassariidae) from the middle to late Miocene of Maryland and Virginia seems to have been by anagenesis within a single lineage rather than by cladogenesis, or associated with a speciation event. The mechanism for this change seems to have been a shift in frequency of a shell form polymorphism. When B.quadrata first appears in the lower St. Mary's Fm., all individuals show a similar smooth shell form. In the middle St. Mary's a distinct carinate morphotype appears, represented by only a few individuals. In the upper St. Mary's a higher proportion of these more ornate forms occurs. Finally in the upper member of the overlying Eastover Fm. the ornate morphology becomes dominant. Specimens from the Eastover Fm. are not only mostly of the more ornate type, but maximum size has increased and the ornate morphology has become more pronounced. This occurs in an area geographically and ecologically marginal to the previous main species range and so may represent an ecophenotypic effect. The genetics of gastropod shell form are very poorly understood. This study represents one of the few documented examples of the role of structural polymorphism in gastropod evolution.

  6. New sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin area

    Directory of Open Access Journals (Sweden)

    Emílio Alberto Amaral Soares

    Full Text Available ABSTRACT The scarcity of stratigraphic data has hindered the demarcation of the outcropping area of Miocene deposits of the Amazon Basin, represented informally by the Novo Remanso Formation. Moreover, this unit is characterized by a sparse and irregular geographic distribution due to its sedimentological features and rare fossil content. Miocene deposits cropping out in central Amazonas Basin area were described in sedimentological terms and analyzed palynologically. All analyses were undertaken in samples collected at the Uatumã River banks (Itapiranga and São Sebastião do Uatumã cities. Lithostratigraphic data shows that Novo Remanso Formation consists of sandstones, with subordinate conglomerates and pelites, characteristic of a meandering fluvial paleosystem, with fluvial channel, point bar, floodplain and crevasse splay facies. The palynoflora retrieved from five samples consists exclusively of continental-origin palynomorphs dominated by angiosperms species. Trilete spores are well represented, while gymnosperms pollen grains are minor components. The presence of Psilastephanoporites tesseroporus, Syncolporites poricostatus, Jandufouria seamrogiformis and Polypodiaceoisporites potoniei ensure these deposits fits into the Grimsdalea magnaclavata palynozone (Regali et al. 1974a, b, and the Grimsdalea magnaclavata/Crassoretitriletes vanraadshooveni palynozones of Jaramillo et al. (2011 considered Middle Miocene age. This age is confirmed by the zonation of Jaramillo et al. (2011, based on the LADs of Bombacacidites baumfalki (11.57Ma and Crototricolpites annemariae (12.91Ma; and the FAD of Psilastephanoporites tesseroporus (14.00Ma. With these new data presented herein, it is possible to assume that the Miocene strata represented by the Novo Remanso Formation covers a larger area in the basin than previously considered, and that it may be extended for about 300 km until the Manacapuru village, indicating a Miocene subsidence phase.

  7. The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru.

    Science.gov (United States)

    Lambert, Olivier; Bianucci, Giovanni; Post, Klaas; de Muizon, Christian; Salas-Gismondi, Rodolfo; Urbina, Mario; Reumer, Jelle

    2010-07-01

    The modern giant sperm whale Physeter macrocephalus, one of the largest known predators, preys upon cephalopods at great depths. Lacking a functional upper dentition, it relies on suction for catching its prey; in contrast, several smaller Miocene sperm whales (Physeteroidea) have been interpreted as raptorial (versus suction) feeders, analogous to the modern killer whale Orcinus orca. Whereas very large physeteroid teeth have been discovered in various Miocene localities, associated diagnostic cranial remains have not been found so far. Here we report the discovery of a new giant sperm whale from the Middle Miocene of Peru (approximately 12-13 million years ago), Leviathan melvillei, described on the basis of a skull with teeth and mandible. With a 3-m-long head, very large upper and lower teeth (maximum diameter and length of 12 cm and greater than 36 cm, respectively), robust jaws and a temporal fossa considerably larger than in Physeter, this stem physeteroid represents one of the largest raptorial predators and, to our knowledge, the biggest tetrapod bite ever found. The appearance of gigantic raptorial sperm whales in the fossil record coincides with a phase of diversification and size-range increase of the baleen-bearing mysticetes in the Miocene. We propose that Leviathan fed mostly on high-energy content medium-size baleen whales. As a top predator, together with the contemporaneous giant shark Carcharocles megalodon, it probably had a profound impact on the structuring of Miocene marine communities. The development of a vast supracranial basin in Leviathan, extending on the rostrum as in Physeter, might indicate the presence of an enlarged spermaceti organ in the former that is not associated with deep diving or obligatory suction feeding.

  8. A major reorganization of Asian climate regime by the early Miocene

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    Z. T. Guo

    2008-05-01

    Full Text Available The global climate system has experienced a series of drastic changes during the Cenozoic. These include the climate transformation in Asia, from a zonal pattern to a monsoon-dominant pattern, the disappearance of subtropical aridity related to a planetary circulation system and the onset of inland deserts in central Asia. Despite of the major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes.

    This paper addresses these issues mainly based on two lines of evidence. Firstly, we newly collected the available Cenozoic geological indicators of environment in China to compile the paleoenvironmental maps of ten intervals with a more detailed examination within the Oligocene and Miocene. In confirming the earlier observation that a zonal climate pattern was transformed into a monsoonal one, the new maps within the Miocene indicate that this major change was achieved by the early Miocene, roughly consistent with the onset of loess deposition in China. Although a monsoon-like regime would have existed in the Eocene, it was restricted in the tropical-subtropical regions. The observed latitudinal oscillations of the climate zones during the Paleogene are likely attributable to the imbalanced evolution of polar ice-sheets between the two hemispheres.

    Secondly, we examine the relevant depositional and soil-forming processes of the Miocene loess-soil sequences to determine the circulation characteristics with special emphasis given to the early Miocene. Continuous eolian deposition in the middle reaches of the Yellow River since the early Miocene firmly indicates the formation of inland deserts, which has been constantly maintained in the past 22 Ma. Inter-section grain-size gradients indicate northerly dust-carrying winds and source location, as is regarded as the main criteria of the Asian winter monsoon

  9. FIRST CETACEAN FOSSIL RECORDS FROM ECUADOR, COLLECTED FROM THE MIOCENE OF ESMERALDAS PROVINCE

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    GIOVANNI BIANUCCI

    2005-07-01

    Full Text Available Cetacean fossils from Ecuador are reported for the first time on the basis of fragmentary remains referred to odontocetes, collected during our investigations of Neogene stratigraphic sequences outcropping along the northern coast (Esmeraldas Province. One specimen was collected near Las Peñas village in the Lower-Middle Miocene sediments of the Viche Formation and consists of ear bones and mandibular fragments surely belonging to Ziphiidae. It represents the oldest record of this family in the southeastern Pacific and one of the few records of this family in South America. The other fossil was collected near Rio Verde village in the Upper Miocene sediments of the Angostura Formation and consists of an isolated tooth exhibiting some ziphiid affinities. Pdf

  10. A new Mammutidae (Proboscidea, Mammalia) from the Late Miocene of Gansu Province, China.

    Science.gov (United States)

    Mothé, Dimila; Avilla, Leonardo S; Zhao, Desi; Xie, Guangpu; Sun, Boyang

    2016-03-01

    The "Yanghecun specimen", a proboscidean specimen represented by a mandible from Miocene of China and previously described as Gomphotheriidae, is here reviewed and described as a new genus and species of Mammutidae: Sinomammut tobieni. This taxon is a longirostrine mastodon, lacking lower tusks, and bearing a wide last molar with oblique and non-inflated lophids, broad transverse interlophids, and yoke-like wear figures. Phylogenetic analysis of Mammutidae based on dental and mandibular features recovered S. tobieni as sister group of the mastodon Mammut. The longirostrine condition and the well-developed lower incisors seem to be primitive for Mammutidae, while the brevirostry is the derived condition, probably emerged during the middle Miocene (12-11 Mya). However, two derived conditions are recognized to the lower tusks: the absence of lower tusks (S. tobieni) and the occasional presence of vestigial lower tusks (Mammut).

  11. A new Mammutidae (Proboscidea, Mammalia from the Late Miocene of Gansu Province, China

    Directory of Open Access Journals (Sweden)

    DIMILA MOTHÉ

    2016-03-01

    Full Text Available ABSTRACT The "Yanghecun specimen", a proboscidean specimen represented by a mandible from Miocene of China and previously described as Gomphotheriidae, is here reviewed and described as a new genus and species of Mammutidae: Sinomammut tobieni. This taxon is a longirostrine mastodon, lacking lower tusks, and bearing a wide last molar with oblique and non-inflated lophids, broad transverse interlophids, and yoke-like wear figures. Phylogenetic analysis of Mammutidae based on dental and mandibular features recovered S. tobieni as sister group of the mastodon Mammut. The longirostrine condition and the well-developed lower incisors seem to be primitive for Mammutidae, while the brevirostry is the derived condition, probably emerged during the middle Miocene (12-11 Mya. However, two derived conditions are recognized to the lower tusks: the absence of lower tusks (S. tobieni and the occasional presence of vestigial lower tusks (Mammut.

  12. Paleomagnetic evidence for Late Miocene counterclockwise rotation of north coast carbonate sequence, Puerto Rico

    Energy Technology Data Exchange (ETDEWEB)

    Reid, J.A.; Plumley, P.W. (Syracuse Univ., NY (United States)); Schellekens, J.H. (Univ. of Puerto Rico, Mayaguez (Puerto Rico))

    1991-03-01

    A paleomagnetic study of the essentially undeformed middle Tertiary carbonate sequence along the north coast of Puerto Rico reveals statistically significant pre-Pliocene discordance of characteristic component directions against those expected from cratonic North America for much of the section. Despite generally weak to moderately weak magnetic intensities, confirmation of the magnetization as primary in origin comes from the presence of two distinct components of magnetization, intrasite bipolarity, and/or the reproducibility of measurements. The mean geographic direction for the upper Oligocene to middle Miocene strata is 335.2{degree}/32.9{degree} and the corrected mean paleomagnetic pole is 207.6{degree}/66.5{degree}, (N = 3, {alpha}95 = 4.3{degree}). This suggests a counter-clockwise (CCW) block rotation of Puerto Rico and its microplate of 24.5{degrees} ({plus minus} 5.8{degrees}) during the late Miocene. Using a width of 250 km for the Northern Caribbean Plate Boundary Zone (NCPBZ) between the North American Plate and Caribbean Plate, the mean left lateral displacement implied is 1.8 to 2.4 cm/yr, which agrees fairly well with published relative motion rates for the two plates. Average rotation rate for 50 Ma to 20 Ma was 0.7{degree}/my but perhaps as great as 4{degree}/my in the Miocene. Resolution of mean paleolatitude indicates northward motion of a degree or less during the period of rotation. Causes of this short-lived rotation may include (1) tectonic escape from the inhibiting presence of the Bahama Banks and Beata Ridge during eastward motion of Puerto Rico along the sinistral transpressive Puerto Rico Trench and Muertos Trough fault systems or (2) changes in relative plate motions of the Caribbean and North American Plate during the late Miocene.

  13. Oligocene-miocene mammalian fossils from Hongyazi Basin and its bearing on tectonics of Danghe Nanshan in northern Tibetan plateau.

    Science.gov (United States)

    Li, Qiang; Wang, Xiaoming; Xie, Guangpu; Yin, An

    2013-01-01

    A shortage of Cenozoic vertebrate fossils in the Tibetan Plateau has been an obstacle in our understanding of biological evolution in response to changes in tectonism, topography, and environment. This is especially true for Paleogene records, so far known by only two sites along the northern rim of the Plateau. We report a Hongyazi Basin in northern Tibetan Plateau that produces at least three mammalian faunas that span Oligocene through late Miocene. Located at the foothills of the Danghe Nanshan and presently connected to the northern margin of the Suganhu Basin through the Greater Haltang River, the intermountain basin is controlled by the tectonics of the Danghe Nanshan to the north and Chahan'ebotu Mountain to the south, making the basin sediments well suited for inferring the evolutionary history of these two mountain ranges. At the bottom of the local section, the Oligocene Haltang Fauna is best compared to the early Oligocene Desmatolagus-Karakoromys decessus assemblage in the Dingdanggou Fauna in Tabenbuluk Basin. The Middle Miocene Ebotu Fauna from the middle Hongyazi section shares many taxa with the late Middle Miocene Tunggur mammal assemblage in Inner Mongolia, such as Heterosminthus orientalis, Megacricetodon sinensis, Democricetodon lindsayi, and Alloptox gobiensis. Toward the top of the section, the Hongyazi Fauna includes late Miocene elements typical of Hipparion faunas of North China. All three faunas are of typical North China-Central Asian characteristics, suggesting a lack of geographic barriers for faunal differentiation through the late Miocene. Sedimentary packages producing these faunas are arrayed from north to south in progressively younger strata, consistent with a compressive regime to accommodate shortening between Danghe Nanshan and Chahan'ebotu Mountain by thrust faults and folds. With additional constraints from vertebrate fossils along the northern flanks of the Danghe Nanshan, an eastward propagation of the Danghe Nanshan is

  14. Oligocene-Miocene Mammalian Fossils from Hongyazi Basin and Its Bearing on Tectonics of Danghe Nanshan in Northern Tibetan Plateau

    Science.gov (United States)

    Li, Qiang; Wang, Xiaoming; Xie, Guangpu; Yin, An

    2013-01-01

    A shortage of Cenozoic vertebrate fossils in the Tibetan Plateau has been an obstacle in our understanding of biological evolution in response to changes in tectonism, topography, and environment. This is especially true for Paleogene records, so far known by only two sites along the northern rim of the Plateau. We report a Hongyazi Basin in northern Tibetan Plateau that produces at least three mammalian faunas that span Oligocene through late Miocene. Located at the foothills of the Danghe Nanshan and presently connected to the northern margin of the Suganhu Basin through the Greater Haltang River, the intermountain basin is controlled by the tectonics of the Danghe Nanshan to the north and Chahan’ebotu Mountain to the south, making the basin sediments well suited for inferring the evolutionary history of these two mountain ranges. At the bottom of the local section, the Oligocene Haltang Fauna is best compared to the early Oligocene Desmatolagus-Karakoromys decessus assemblage in the Dingdanggou Fauna in Tabenbuluk Basin. The Middle Miocene Ebotu Fauna from the middle Hongyazi section shares many taxa with the late Middle Miocene Tunggur mammal assemblage in Inner Mongolia, such as Heterosminthus orientalis, Megacricetodon sinensis, Democricetodon lindsayi, and Alloptox gobiensis. Toward the top of the section, the Hongyazi Fauna includes late Miocene elements typical of Hipparion faunas of North China. All three faunas are of typical North China-Central Asian characteristics, suggesting a lack of geographic barriers for faunal differentiation through the late Miocene. Sedimentary packages producing these faunas are arrayed from north to south in progressively younger strata, consistent with a compressive regime to accommodate shortening between Danghe Nanshan and Chahan’ebotu Mountain by thrust faults and folds. With additional constraints from vertebrate fossils along the northern flanks of the Danghe Nanshan, an eastward propagation of the Danghe Nanshan

  15. Oligocene-miocene mammalian fossils from Hongyazi Basin and its bearing on tectonics of Danghe Nanshan in northern Tibetan plateau.

    Directory of Open Access Journals (Sweden)

    Qiang Li

    Full Text Available A shortage of Cenozoic vertebrate fossils in the Tibetan Plateau has been an obstacle in our understanding of biological evolution in response to changes in tectonism, topography, and environment. This is especially true for Paleogene records, so far known by only two sites along the northern rim of the Plateau. We report a Hongyazi Basin in northern Tibetan Plateau that produces at least three mammalian faunas that span Oligocene through late Miocene. Located at the foothills of the Danghe Nanshan and presently connected to the northern margin of the Suganhu Basin through the Greater Haltang River, the intermountain basin is controlled by the tectonics of the Danghe Nanshan to the north and Chahan'ebotu Mountain to the south, making the basin sediments well suited for inferring the evolutionary history of these two mountain ranges. At the bottom of the local section, the Oligocene Haltang Fauna is best compared to the early Oligocene Desmatolagus-Karakoromys decessus assemblage in the Dingdanggou Fauna in Tabenbuluk Basin. The Middle Miocene Ebotu Fauna from the middle Hongyazi section shares many taxa with the late Middle Miocene Tunggur mammal assemblage in Inner Mongolia, such as Heterosminthus orientalis, Megacricetodon sinensis, Democricetodon lindsayi, and Alloptox gobiensis. Toward the top of the section, the Hongyazi Fauna includes late Miocene elements typical of Hipparion faunas of North China. All three faunas are of typical North China-Central Asian characteristics, suggesting a lack of geographic barriers for faunal differentiation through the late Miocene. Sedimentary packages producing these faunas are arrayed from north to south in progressively younger strata, consistent with a compressive regime to accommodate shortening between Danghe Nanshan and Chahan'ebotu Mountain by thrust faults and folds. With additional constraints from vertebrate fossils along the northern flanks of the Danghe Nanshan, an eastward propagation of the

  16. Phylogenetic and paleobotanical evidence for late Miocene diversification of the Tertiary subtropical lineage of ivies (Hedera L., Araliaceae).

    Science.gov (United States)

    Valcárcel, V; Guzmán, B; Medina, N G; Vargas, P; Wen, J

    2017-06-22

    Hedera (ivies) is one of the few temperate genera of the primarily tropical Asian Palmate group of the Araliaceae, which extends its range out of Asia to Europe and the Mediterranean basin. Phylogenetic and phylogeographic results suggested Asia as the center of origin and the western Mediterranean region as one of the secondary centers of diversification. The bird-dispersed fleshy fruits of ivies suggest frequent dispersal over long distances (e.g. Macaronesian archipelagos), although reducing the impact of geographic barriers to gene flow in mainland species. Genetic isolation associated with geographic barriers and independent polyploidization events have been postulated as the main driving forces of diversification. In this study we aim to evaluate past and present diversification patterns in Hedera within a geographic and temporal framework to clarify the biogeographic history of the genus. Phylogenetic (biogeographic, time divergence and diversification) and phylogeographic (coalescence) analyses using four DNA regions (nrITS, trnH-psbA, trnT-trnL, rpl32) revealed a complex spatial pattern of lineage divergence. Scarce geographic limitation to gene flow and limited diversification are observed during the early-mid Miocene, followed by a diversification rate increase related to geographic divergence from the Tortonian/Messinian. Genetic and palaeobotanical evidence points the origin of the Hedera clade in Asia, followed by a gradual E-W Asian extinction and the progressive E-W Mediterranean colonization. The temporal framework for the E Asia - W Mediterranean westward colonization herein reported is congruent with the fossil record. Subsequent range expansion in Europe and back colonization to Asia is also inferred. Uneven diversification among geographic areas occurred from the Tortonian/Messinian onwards with limited diversification in the newly colonized European and Asian regions. Eastern and western Mediterranean regions acted as refugia for Miocene and

  17. Miocene cercopithecoidea from the Tugen Hills, Kenya.

    Science.gov (United States)

    Gilbert, Christopher C; Goble, Emily D; Hill, Andrew

    2010-11-01

    Miocene to Pleistocene fossiliferous sediments in the Tugen Hills span the time period from at least 15.5 Ma to 0.25 Ma, including time periods unknown or little known elsewhere in Africa. Consequently, the Tugen Hills deposits hold the potential to inform us about crucial phylogenetic events in African faunal evolution and about long-term environmental change. Among the specimens collected from this region are a number of discoveries already important to the understanding of primate evolution. Here, we describe additional cercopithecoid material from the Miocene deposits in the Tugen Hills sequence, including those from securely dated sites in the Muruyur Beds (16-13.4 Ma), the Mpesida Beds (7-6.2 Ma) and the Lukeino Formation (∼ 6.2-5.7 Ma). We also evaluate previously described material from the Ngorora Formation (13-8.8 Ma). Identified taxa include Victoriapithecidae gen. et sp. indet., cf. Parapapio lothagamensis, and at least two colobines. Specimens attributed to cf. Pp. lothagamensis would extend the species' geographic range beyond its type locality. In addition, we describe specimens sharing derived characters with modern African colobines (Tribe: Colobina), a finding that is congruent with previous molecular estimates of colobine divergence dates. These colobine specimens represent some of the earliest known members of the modern African colobine radiation and, in contrast to previous hypotheses, suggest that early African colobines were mainly arboreal and that semi-terrestrial Late Miocene and Plio-Pleistocene colobine taxa were secondarily derived in their locomotor adaptations.

  18. A record of Miocene carbon excursions in the South China Sea

    Institute of Scientific and Technical Information of China (English)

    ZHAO; Quanhong

    2001-01-01

    [1]Mackensen, A., Bickert, T., Stable isotopes in benthic Foraminifera: Proxies for deep and bottom water circulation and new production, in Use of Proxies in Paleoceanography: Examples From the South Atlantic (eds. Fischer, G., Wefer, G.),Berlin-Heiderberg: Springer-Verlag, 1999, 229-254.[2]Shackleton, N. J., Pisias, N. G., Atmospheric carbon dioxide, orbital forcing, and climate, Geophys. Monogr. Ser., 1985,32: 303-317.[3]Shackleton, N. J., Carbon-13 in Uvigerina: Tropical rainforest history and the Equatorial Pacific carbonate dissolution cy cles, in The Fate of Fossil Fuel CO2 in the Oceans (eds. Andersen, N. R., Malahoff, A.), New York: Plenum Publ. Corp.,1977, 401-427.[4]Wang Pinxian, Neogene stratigraphy and paleoenvironments of China, Palaeogeogr. Palaeoclim. Palaeoecol., 1990, 77:315-334.[5]Jian Zhimin, Stable isotopic evidences of the glacial deep water properties in the South China Sea, Science in China, Ser.D, 1998, 41(4): 337-344.[6]Hao Yichun, Xu Yulin, Xu Shice et al., Research on Micropaleontology and Paleoceanography in Pear River Mouth Basin,South China Sea (in Chinese), Beijing: China Univ. of Geosci. Press, 1996, 136.[7]Wang, P, Prell, W. L.. Blum, P. et al.. Proceedings of the Ocean Drilling Program, Initial Reports Volume 184 (CD-ROM),Beijing Nat. Sci. Found. & Joint Oceanogr. Inst., Inc., 2000.[8]Zhao Quanhong, Jian Zhimin, Wang Jiliang et al., Neogene oxygen isotopic stratigraphy, ODP Site 1148, northern South China Sea, Sciences in China, Ser. D (in press).[9]Vincent, E., Killingley, J. S., Oxygen and carbon isotope record for the Early and Middle Miocene in the central equatorial Pacific (Leg 85) and paleoceanographic implications, in Init. Rep. DSDP (ed. Mayer, L.), 1985, 85: 749-769.[10]Miller, K. G., Fairbanks, R. G., Oligocene to Miocene carbon isotope cycles and abyssal circulation changes, Geophys.Monogr., 1985, 32: 469-486.[11]Wright, J. D., Miller, N. G., Miocene stable isotope

  19. Oligocene and Miocene arc volcanism in northeastern California: evidence for post-Eocene segmentation of the subducting Farallon plate

    Science.gov (United States)

    Colgan, J.P.; Egger, A.E.; John, D.A.; Cousens, B.; Fleck, R.J.; Henry, C.D.

    2011-01-01

    The Warner Range in northeastern California exposes a section of Tertiary rocks over 3 km thick, offering a unique opportunity to study the long-term history of Cascade arc volcanism in an area otherwise covered by younger volcanic rocks. The oldest locally sourced volcanic rocks in the Warner Range are Oligocene (28–24 Ma) and include a sequence of basalt and basaltic andesite lava flows overlain by hornblende and pyroxene andesite pyroclastic flows and minor lava flows. Both sequences vary in thickness (0–2 km) along strike and are inferred to be the erosional remnants of one or more large, partly overlapping composite volcanoes. No volcanic rocks were erupted in the Warner Range between ca. 24 and 16 Ma, although minor distally sourced silicic tuffs were deposited during this time. Arc volcanism resumed ca. 16 Ma with eruption of basalt and basaltic andesite lavas sourced from eruptive centers 5–10 km south of the relict Oligocene centers. Post–16 Ma arc volcanism continued until ca. 8 Ma, forming numerous eroded but well-preserved shield volcanoes to the south of the Warner Range. Oligocene to Late Miocene volcanic rocks in and around the Warner Range are calc-alkaline basalts to andesites (48%–61% SiO2) that display negative Ti, Nb, and Ta anomalies in trace element spider diagrams, consistent with an arc setting. Middle Miocene lavas in the Warner Range are distinctly different in age, composition, and eruptive style from the nearby Steens Basalt, with which they were previously correlated. Middle to Late Miocene shield volcanoes south of the Warner Range consist of homogeneous basaltic andesites (53%–57% SiO2) that are compositionally similar to Oligocene rocks in the Warner Range. They are distinctly different from younger (Late Miocene to Pliocene) high-Al, low-K olivine tholeiites, which are more mafic (46%–49% SiO2), did not build large edifices, and are thought to be related to backarc extension. The Warner Range is ∼100 km east of the

  20. Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin

    NARCIS (Netherlands)

    Figueiredo, J.; Hoorn, C.; van der Ven, P.; Soares, E.

    2009-01-01

    New biostratigraphic, isotopic, and well log data from exploration wells on the outer continental shelf and uppermost Amazon deep-sea fan, Brazil, reveal that the Amazon River was initiated as a transcontinental river between 11.8 and 11.3 Ma ago (middle to late Miocene), and reached its present sha

  1. Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin

    NARCIS (Netherlands)

    Figueiredo, J.; Hoorn, C.; van der Ven, P.; Soares, E.

    2009-01-01

    New biostratigraphic, isotopic, and well log data from exploration wells on the outer continental shelf and uppermost Amazon deep-sea fan, Brazil, reveal that the Amazon River was initiated as a transcontinental river between 11.8 and 11.3 Ma ago (middle to late Miocene), and reached its present sha

  2. Miocene mass-transport sediments, Troodos Massif, Cyprus

    Science.gov (United States)

    Lord, A.R.; Harrison, R.W.; BouDagher-Fadel, M.; Stone, B.D.; Varol, O.

    2009-01-01

    Sediment mass-transport layers of submarine origin on the northern and southern flanks of the Troodos ophiolitic massif are dated biostratigraphically as early Miocene and late Miocene, respectively and therefore represent different seismogenic events in the uplift and erosional history of the Troodos terrane. Analysis of such events has potential for documenting Miocene seismic and uplift events regionally in the context of changing stress field directions and plate vectors through time. ?? 2009 The Geologists' Association.

  3. Lower miocene larger foraminifera and petroleum potential of the Tai Formation, Mergui Group, Andaman Sea

    Science.gov (United States)

    Polachan, Songpope; Racey, Andrew

    Tertiary larger foraminifera are recorded for the first time from Thailand. The fauna studied is restricted mainly to the reefal carbonate of the Tai Formation, which rests unconformably on the pre-Late Eocene quartz-chlorite schist basement in the Central High region of the Mergui Basin. The formation is broadly correlatable with the Peutu Formation of the North Sumatra Basin. The Tai Formation can be divided into three units at the type locality; a basal unit of interbedded anhydrite, dolomite, shale and sandstone; a middle unit of coral/algal reefal limestones, and an upper unit of calcarenites interbedded with silty shales and sandstones. The middle and upper units have yielded a fauna comprising; Lepidocyclina (Nephrolepidina) japonica, Spiroclypeus yabeii, Cycloclypeus eidae, Cycloclypeus sp. A, Heterostegina sp. A, Lepidocyclina (N) sp. A, Miogypsina sp. A, and Miogypsinoides sp. L. (N) japonica and Miogypsinoides sp. can range up into the Middle Miocene (Lower Tf) whilst C. eidae can range down into the Upper Oligocene (Lower Te). The fauna is typical of the Indo-West Pacific Miocene faunal province of Adams (1970) and shows closer affinities to the faunas of Indonesia than those of India-Pakistan.

  4. First hominoid from the Miocene of Ethiopia and the evolution of the catarrhine elbow.

    Science.gov (United States)

    Richmond, B G; Fleagle, J G; Kappelman, J; Swisher, C C

    1998-03-01

    The first known fossil ape from the early-middle Miocene of Fejej, Ethiopia, is described here. The specimen, FJ-18SB-68, is a partial ulna from a locality dated by 40Ar/39Ar and paleomagnetic methods to a minimum age of 16.18 MYA. Compared to a variety of extant and fossil ulnae, FJ-18SB-68 is most similar to Turkanapithecus, Proconsul, and Pliopithecus, and appears to have been an arboreal quadruped with substantial forearm rotational mobility. Among the extant ulnae, canonical variates analysis successfully discriminates platyrrhines from catarrhines and within the latter, cercopithecoids from hominoids. Basal catarrhines (e.g., Aegyptopithecus) are platyrrhine-like in their morphology. Two basic trends appear to evolve from this generalized template: one with less mobile and more habitually pronated forearms, as seen in living and fossil cercopithecoids (including Victoriapithecus and Paracolobus), and another with greater forearm rotational mobility in fossil and modern hominoids. Primitive Miocene apes, including Proconsul, Turkanapithecus, and FJ-18SB-68, share with extant hominoids a more laterally positioned and laterally facing radial notch and an incipient trochlear keel. This morphology, along with a large insertion area for m. brachialis, suggests a departure from the more habitually pronated hand posture of monkeys and may indicate greater climbing abilities in these arboreally quadrupedal apes. Later Miocene apes, such as Oreopithecus and Dryopithecus share additional morphological features with hominoids, indicating considerable suspensory and climbing capabilities.

  5. Late Miocene remagnetization within the internal sector of the Northern Apennines, Italy

    Science.gov (United States)

    Aiello, I.W.; Hagstrum, J.T.; Principi, G.

    2004-01-01

    Paleomagnetic and geologic evidence indicates that Upper Jurassic radiolarian cherts of both the Tuscan Cherts Formation (continental margin, Tuscan Units) and the Monte Alpe Cherts Formation (oceanic crust, Ligurian Units) were remagnetized during Miocene orogenesis of the Northern Apennines of Italy. Characteristic overprint magnetizations with reversed polarities have been found over a large area within the internal sector of the Northern Apennines, including eastern Liguria, Elba Island and the Thyrrenian margin, and west of the Middle Tuscan Ridge. The reversed-polarity overprint (average direction: D=177??, I=-52??, ??95=15??) was most likely acquired during Late Miocene uplift and denudation of the orogenic chain, and thermochemical remagnetization was a probable consequence of increased circulation of orogenic fluids. Similarly, mostly reversed-polarity directions of magnetization have been found by other workers in overlying post-orogenic Messinian sediments (D=177??, I=-57??, ??95=3??), which show little counterclockwise (CCW) vertical-axis rotation with respect to stable Europe (-8??5??). The Monte Alpe Cherts sampled at sites in the external sector of the Northern Apennines, close to major tectonic features, have normal- polarity overprint directions with in situ W-SW declinations. Since the overlying post-orogenic Messinian sediments have not been substantially rotated about vertical axes, the evidence points to an earlier,pre-Late Miocene remagnetization in the external parts of the orogenic chain. ?? 2004 Elsevier B.V. All rights reserved.

  6. The Tunggurian Stage of the Continental Miocene in China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Tunggurian Age was nominated in 1984, and the Second National Commission on Stratigraphy of China formally suggested establishing the corresponding chronostratigraphic unit, the Tunggurian Stage, based on the Tunggurian Age in 1999. The name of this stage comes from a lithostratigraphic unit, the Tunggur Formation, and the stratotype section is located at the Tunggur tableland, 15 km southeast of Saihan Gobi Township, Sonid Left Banner, Inner Mongolia. The Tunggurian Age is correlated to the Astaracian of the European land mammal ages, and they share the same definition of the lower boundary at the base of the paleomagnetic Chron C5Bn.1r with an age of 15.0 Ma. In the Tairum Nor section on the southeastern edge of the Tunggur tableland, this boundary is situated within the successive deposits of reddish-brown massive mudstone of the lower part of the Tunggur Formation, with a distance of 7.6 m from the base of the grayish-white sandstones in the middle part of the section. The Tunggurian is approximately correlated to the upper part of the marine Langhian and the marine Serravallian in the International Stratigraphical Chart. The Tunggurian Stage includes two Neogene mammal faunal units, i.e. NMU 6 (MN 6) and NMU 7 (MN 7/8). The Tairum Nor fauna from the Tairum Nor section corresponds to NMU 6, and the Tunggur fauna (senso stricto) from the localities on the northwestern edge of the Tunggur tableland, such as Platybelodon Quarry, Wolf Camp and Moergen, corresponds to NMU 7. Among the Middle Miocene mammalian faunas in China, the Laogou fauna from the Linxia Basin, Gansu, the Quantougou fauna from the Lanzhou Basin, Gansu, the Halamagai fauna from the northern Junggar Basin, Xinjiang,and the Dingjiaergou fauna from Tongxin, Ningxia correspond to NMU 6.

  7. The Miocene Nullarbor Limestone, southern Australia; deposition on a vast subtropical epeiric platform

    Science.gov (United States)

    O'Connell, Laura G.; James, Noel P.; Bone, Yvonne

    2012-05-01

    The early to middle Miocene Nullarbor Limestone forms the vast, karsted Nullarbor Plain in southern Australia, and may be the most extensive Miocene carbonate deposit described to date. These carbonates were deposited at southern paleolatitudes of ~ 40°S and are interpreted to be subtropical to warm-temperate in character because of the presence of certain genera of tropical coralline algae (rhodoliths and articulated types), large benthic foraminifera, tropical molluscs, zooxanthellate corals, and micrite envelopes. Facies are dominated by skeletal grainstones and floatstones that accumulated in three interpreted paleoenvironments: (1) seagrass banks (upper photic zone), (2) rhodolith pavements (lower photic zone), and (3) open seafloors (lower photic to subphotic zone). A decrease of tropical components from west to east across the platform implies that warm oceanic currents (possibly related to a proto-Leeuwin Current), as well as a period of warm climate (Miocene Climatic Optimum), resulted in subtropical deposition at southern latitudes. The Southern Ocean extended inboard ~ 450 km from the shelf edge during Nullarbor Limestone deposition, but interpreted paleodepths did not extend much below the base of the photic zone. A small slope angle (~ 0.02°) over a wide shelf (~ 300,000 km2) implies deposition on an epeiric platform or epeiric ramp. A Miocene barrier reef was likely coeval with Nullarbor Limestone deposition. Therefore, the inboard portion of the Nullarbor Limestone can be considered part of an extensive back-reef lagoon system on a rimmed epeiric platform, perhaps attaining a size similar to the modern Great Barrier Reef system.

  8. A rhinoceros from the late miocene of Fort Ternan, Kenya

    NARCIS (Netherlands)

    Hooijer, D.A.

    1968-01-01

    SYNOPSIS A rhinoceros from the Fort Ternan site, Kenya, Late Miocene in age, represents a form distinctly more advanced than the genera and species known from the Early Miocene although it is not directly ancestral to the Quaternary forms. It is a collaterally developed tuskless, two-horned, browsin

  9. Understanding the murky history of the Coral Triangle: Miocene corals and reef habitats in East Kalimantan (Indonesia)

    Science.gov (United States)

    Santodomingo, Nadiezhda; Renema, Willem; Johnson, Kenneth G.

    2016-09-01

    Studies on ancient coral communities living in marginal conditions, including low light, high turbidity, extreme temperatures, or high nutrients, are important to understand the current structure of reefs and how they could potentially respond to global changes. The main goal of this study was to document the rich and well-preserved fossil coral fauna preserved in Miocene exposures of the Kutai Basin in East Kalimantan, Indonesia. Our collections include almost forty thousand specimens collected from 47 outcrops. Seventy-nine genera and 234 species have been identified. Three different coral assemblages were found corresponding to small patch reefs that developed under the influence of high siliciclastic inputs from the Mahakam Delta. Coral assemblages vary in richness, structure, and composition. Platy coral assemblages were common until the Serravallian (Middle Miocene), while branching coral assemblages became dominant in the Tortonian (Late Miocene). By the late Tortonian massive coral assemblages dominated, similar to modern-style coral framework. Our results suggest that challenging habitats, such as the Miocene turbid habitats of East Kalimantan, might have played an important role during the early diversification of the Coral Triangle by hosting a pool of resilient species more likely to survive the environmental changes that have affected this region since the Cenozoic. Further research that integrates fossil and recent turbid habitats may provide a glimpse into the dynamics and future of coral reefs as "typical" clear-water reefs continue to decline in most regions.

  10. 78 FR 63570 - Proposed Collection; Comment Request for Forms W-8BEN, W-8BEN-E, W-8ECI, W-8EXP, and W-8IMY

    Science.gov (United States)

    2013-10-24

    ... Internal Revenue Service Proposed Collection; Comment Request for Forms W-8BEN, W-8BEN-E, W-8ECI, W-8EXP, and W-8IMY AGENCY: Internal Revenue Service (IRS), Treasury. ACTION: Notice and request for comments... Form W-8BEN, Certificate of Foreign Status of Beneficial Owner for United States Tax Withholding,...

  11. Facies analysis and depositional environments of the OligoceneeMiocene Asmari Formation, Zagros Basin, Iran

    Institute of Scientific and Technical Information of China (English)

    Mohammad Sahraeyan; Mohammad Bahrami; Solmaz Arzaghi

    2014-01-01

    The Asmari Formation (a giant hydrocarbon reservoir) is a thick carbonate sequence of the Oligocenee Miocene in the Zagros Basin, southwest of Iran. This formation is exposed at Tang-e-Lendeh in the Fars interior zone with a thickness of 190 m comprising medium and thick to massive bedded carbonates. The age of the Asmari Formation in the study area is the late Oligocene (Chattian)eearly Miocene (Burdigalian). Ten microfacies are defined, characterizing a gradual shallowing upward trend;the related environments are as follows:open marine (MF 8e10), restricted lagoon (MF 6e7), shoal (MF 3e5), lagoon (MF 2), and tidal flat (MF 1). Based on the environmental interpretations, a homoclinal ramp consisting of inner and middle parts prevails. MF 3e7 are characterized by the occurrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp, influenced by wave and tidal pro-cesses. MF 8e10, with large particles of coral and algae, represent a deeper fair weather wave base of a middle ramp setting.

  12. A Miocene breeding ground of an extinct baleen whale (Cetacea: Mysticeti).

    Science.gov (United States)

    Tsai, Cheng-Hsiu

    2017-01-01

    Locating breeding sites is definitely a key to understanding the ecological requirements and maintaining the sustainability of populations/species. Here I re-examined published specimens of an extinct baleen whale, Parietobalaena yamaokai, from the lower part of Itahashi Formation (16.1-15.6 Ma, Middle Miocene) in Shobara, Hiroshima, Japan. A critical and previously unnoticed feature, the open suture between the supraoccipital and exoccipital, in one specimen indicates the preservation of a very young individual-under six months old and even close to a new-born calf. Given the occurrence of a new-born whale and relatively abundant assemblage of Parietobalaena yamaokai, I propose a previously hidden and unknown breeding ground for the extinct baleen whale, P. yamaokai, in the Middle Miocene of Shobara (16.1-15.6 Ma), Hiroshima. Discovery of paleo-breeding sites of extinct populations/species should further help us to understand biological extinctions from a long-term perspective as conservation paleobiology aims to offer new insights into policy making for conserving endangered populations/species.

  13. Relating Major Surface Processes to the Deep Earth — The Importance of the Miocene

    Science.gov (United States)

    Potter, P. E.; Szatmari, P.

    2012-12-01

    Many global scale tectonic, oceanic and climate changes began in the Tertiary with global tectonics as the underlying driving force and changed the world. In full flower by the beginning of the Middle Miocene around 16 Ma, these changes continued through the Late Miocene into the present so we can firmly say that most of our modern world, continental glaciations excepted, began in the Middle and Late Miocene. We summarize in a flow diagram how the major earth surface processes active in the Miocene are related to the Deep Earth as understood by recent advances in seismic tomography. This 11 Ma interval had two global orogenic zones, the Alpine-Tethyan orogen from Gibraltar across southern Asia into Vietnam and around the Pacific Rim, both crustal expressions of downwellings taking place, especially in the upper mantle. These downwellings are balanced by upwellings in the lower mantle in and on the rim of the African and Pacific superplumes, which are large, low-shear velocity provinces; part of the rising plumes originated from the most extensively melted regions of the core-mantle boundary layer, D", where heat flow from the outer core is highest. Together these up-and downwellings indicate that mantle convection extended, at least periodically, through the whole mantle and reflected lateral variations in convection and heat flow in the cooling and slowly crystallizing outer core. Correlation of mantle convection with surface features is most evident in the uppermost mantle whose dynamic topography is readily reflected by the subsidence and tilting of continents moving toward the downwelling zones. Because they are closely synchronous, these two orogenic belts had enormous consequences for the earth's surface, and because they are close to us in time, they are easy to study and sample. Thus the Miocene is ideal to study for both its many global intra connections and for their link to the Deep Earth. As these two orogenies developed, they changed a global warm

  14. Paleotopography of the Miocene European Central Alps

    Science.gov (United States)

    Campani, M.; Mulch, A.; Kempf, O.; Schlunegger, F.; Mancktelow, N.

    2011-12-01

    Reconstructing the surface elevation, surface uplift, and relief evolution histories is fundamental to understanding the growth of mountain ranges, to explore their topographic limits, and relate these to geodynamic and Earth surface processes. Recent geologic and geodynamic models for the Central European Alps propose that the bulk of topography was built through the Pliocene, mainly based on the observation of a strong increase in sedimentation and erosion rates during the last 5-6 Ma, suggesting that the Alps never attained elevations as high as today. Here, we aim to quantify the Miocene (20-14 Ma) paleoelevation of the Central Alps through stable isotope paleoaltimetry. The novelty of the approach presented here, which renders it rather insensitive to past climate change, is to analyze stable isotope proxies of identical age, both from high internal parts of the Alpine orogen and from the adjacent foreland basin that was at or near sea level. We first exploit the hydrogen isotopic ratio in phyllosilicates (mica and chlorite) that interacted with meteoric water during activity of the Simplon detachment, a major normal fault that developed during orogen-parallel extension in high elevation regions. We then contrast the resulting meteoric water compositions with those recorded in carbonate-bearing paleosols of the North-Alpine foreland basin to provide an estimate of relative elevation differences. In the North-Alpine foreland basin, we present oxygen and carbon isotopic compositions of pedogenic mudstones and carbonate concretions. These terrestrial paleosols, dated with ca. 100 ka precision, serve as our point of reference for stable isotope paleoaltimetry, since they formed at or near sea level. Here, δ18O and δ13C values vary between +19 to +25% (SMOW) and -7 to +1% respectively and show close correspondence to global climate change during the mid-Miocene climatic optimum. In the Simplon fault zone, detachment-related muscovite (-126%) and chlorite (-135

  15. 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.

  16. Miocene oceanographic changes of the western equatorial Atlantic (Ceara Rise) based on calcareous dinoflagellate cysts

    Science.gov (United States)

    Heinrich, S.; Zonneveld, K. A. F.; Willems, H.

    2010-09-01

    The middle- and upper Miocene represent a time-interval of major changes in palaeoceanography that favoured the cooling of the climate and culminated in the Northern Hemisphere Glaciation (NHG). The basis for the development of the modern deepwater circulation pattern, e.g. thermohaline circulation, was hereby established. Tectonic events played a key role in the progressing Miocene oceanography, such as the narrowing of the Panama gateway (e.g. Duque-Caro 1990) and the possible linked changes in North Atlantic Deep Water formation (Lear et al. 2003). However, the complex interaction between the closing of the Panama Gateway, the development of NADW, and thus the oceanographic progression towards our present day circulation is far from being fully understood. We want to improve the understanding of these processes by establishing a detailed palaeoceanographic reconstruction of the western equatorial Atlantic Ocean on the basis of calcareous dinoflagellate cyst (dinocyst) associations. Within this study, we investigated sediment samples from ODP Site 926A by defining the calcareous dinocyst assemblage. Site 926A is located at the southwestern flank of the Ceara Rise, an area of highest sensitivity to global deep water circulation changes. At about 12 Ma, when NADW production increased (e.g. Wright et al. 1992), we see a distinct increase in the absolute abundances of the calcareous dinocysts. This might be related to enhanced productivity or to better carbonate preservation. At 11.3 Ma, Leonella granifera, a species known to be strongly related to terrestrial input occurs. This could be a signal for the initiation of the Amazon River as a transcontinental river with the development of the Amazon fan (11.8 - 11.3 Ma; Figueiredo et al. 2009) in relation to Andean tectonism. References: Duque-Caro, H. (1990): Neogene stratigraphy, paleoceanography and palebiology in Northwest South America and the evolution of the Panama Seaway. Palaeogeography, Palaeoclimatology

  17. Stratigraphical and palaeontological characteristics of the Miocene deposits at Soluq area, NE Libya: First Results

    Science.gov (United States)

    Abdulsamad, E. O.; El Zanati, S. M.

    2012-04-01

    The north-south scarp that runs in the middle of Soluq area, about 70 km southeast of Benghazi, attains altitudes towards the north, reaching a maximum of about 300 meters above sea level at wadi al Qattarah. The scarp fades gradually towards the south till at Antelat area and is represented by few meters high hills. The plateau, however, extends eastwards rising to altitudes more than 450 meters above sea level. The plain (known as Soluq plain) extends westwards till near the Mediterranean coast with average width of about 50 kilometers. Several outcrops along the main escarpment have been visited and spot sampled and two carbonate rock units separated by reduced deposits of clastic origin have been recognised based on lithology and faunal contents. The oldest rock unit is representing by the Benghazi Formation and the youngest rock unit is representing by Wadi al Qattarah Formation. Both rock units, nevertheless, are belonging to the Miocene Ar Rajmah Group and cover the greater part of the Soluq area. The lower Benghazi Formation has been dated as Middle Miocene based on the presence of Lepidocyclina (Eulepidina) dilatat (Michelotti) and Borelis melo melo (Fichiteli). The latter taxon was recognized in different local areas of the same time-interval. The inconsistent occurrences and broken nature of tests of Borelis melo melo in some levels in the upper Wadi al Qattarah Formation, however, indicates that this taxon has been subjected to extensive reworking and Late Miocene age is ascribed to the major deposits of the later rock unit. This assumption may explain the occurrences of a number of lenses and irregular bodies of gypsum of the Messenian event in study region. The high variety of the microfacies and fossil assemblages recognised in this study reflects (1) the variety of environmental settings and (2) the effect of the lithofacies on the fossil recovery. In general, larger and small foraminifera from the Miocene Ar Rajmah Group are a mix of infaunal and

  18. Late Miocene “washhouse” climate in Europe

    Science.gov (United States)

    Böhme, Madelaine; Ilg, August; Winklhofer, Michael

    2008-11-01

    We present two eight-million year long proxy records of precipitation for Southwest and Central Europe, covering the middle to late Miocene (5.3-13 Ma) at a temporal resolution of about 60 kyr and 150 kyr, respectively. The estimates of precipitation are based on the ecophysiological structure of herpetological assemblages (amphibians and reptiles). From 13.0 Ma until about 9 Ma, both records show a similar trend, evolving from a long dry period (13-11 Ma) into a "washhouse climate" (10.2-9.8 Ma), characterized by global warm conditions and several times more precipitation than present. The transition from washhouse to a dryer climate between 9.7 and 9.5 Ma and the concomitant cooling episode appear to have triggered a severe biotic event known as the Vallesian crisis, which included the extinction of hominoids in Western Europe. A second washhouse period (9.0-8.5 Ma), coeval with a global warm episode, was unprecedentedly intense in Southwest Europe, but less pronounced in Central Europe. From 8 Ma onward, a divergence in the two precipitation records is observed, with Southwest Europe staying wetter and Central Europe becoming dryer than present. Both precipitation records are combined into a common run-off curve as a measure of the relative intensity of the hydrological cycle for moderate latitudes of continental Europe. The run-off curve shows a remarkable positive correlation with Atlantic deep-water temperatures from Ceará Rise by Lear et al. (2003), which are significantly higher (up to + 3 °C) during the two washhouse periods and show no other positive excursion of comparable magnitude. We discuss potential links and the role of the coeval temporary restriction of the Central American Seaway on ocean and atmosphere circulation.

  19. A Miocene ostrich fossil from Gansu Province, northwest China

    Institute of Scientific and Technical Information of China (English)

    HOU Lianhai; ZHOU Zhonghe; ZHANG Fucheng; WANG Zhao

    2005-01-01

    @@ A pelvic skeleton, recognized as a large terrestrial bird in the field, was recently collected by our paleomammalogist colleagues from the Institute of Vertebrate Paleontology and Paleoanthropology from the late Miocene sandy mudstones in the Linxia Basin in Gansu Province, northwest China. We have further referred this bird to as an early representative of ostrich. Ostrich fossils usually coexisted with the famous Hipparion Fauna from the Miocene to Pliocene.

  20. Systematics and Evolution of the Miocene Three-Horned Palaeomerycid Ruminants (Mammalia, Cetartiodactyla.

    Directory of Open Access Journals (Sweden)

    Israel M Sánchez

    Full Text Available Palaeomerycids were strange three-horned Eurasian Miocene ruminants known through fossils from Spain to China. We here study their systematics, offering the first cladistic phylogeny of the best-known species of the group, and also reassess their phylogenetic position among ruminants, which is currently disputed. The beautifully preserved remains of a new palaeomerycid from middle Miocene deposits of Spain, Xenokeryx amidalae gen. et sp. nov., helps us to better understand palaeomerycid anatomy, especially that of the nuchal region in the skull, significantly improving our current knowledge on these enigmatic ruminants. Our results show two main lineages of palaeomerycids, one containing the genus Ampelomeryx diagnosed by a characteristic type of cranium / cranial appendages and some dental derived traits, and another one that clusters those forms more closely related to Triceromeryx than to Ampelomeryx, characterized by a more derived dentition and a set of apomorphic cranial features. Xenokeryx branches as a basal offshoot of this clade. Also, we find that Eurasian palaeomerycids are not closely related to North American dromomerycids, thus rejecting the currently more accepted view of palaeomerycids as the Eurasian part of the dromomerycid lineage. Instead of this, palaeomerycids are nested with the African Miocene pecoran Propalaeoryx and with giraffoids. On the other hand, dromomerycids are closely related to cervids. We define a clade Giraffomorpha that includes palaeomerycids and giraffids, and propose an emended diagnosis of the Palaeomerycidae based on cranial and postcranial characters, including several features of the cranium not described so far. We also define the Palaeomerycidae as the least inclusive clade of pecorans containing Triceromeryx and Ampelomeryx. Finally, we reassess the taxonomy of several palaeomerycid taxa.

  1. The early Miocene onset of a ventilated circulation regime in the Arctic Ocean.

    Science.gov (United States)

    Jakobsson, Martin; Backman, Jan; Rudels, Bert; Nycander, Jonas; Frank, Martin; Mayer, Larry; Jokat, Wilfried; Sangiorgi, Francesca; O'Regan, Matthew; Brinkhuis, Henk; King, John; Moran, Kathryn

    2007-06-21

    Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic's deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ('ventilated') conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events.

  2. Rapid diversification of falcons (Aves: Falconidae) due to expansion of open habitats in the Late Miocene.

    Science.gov (United States)

    Fuchs, Jérôme; Johnson, Jeff A; Mindell, David P

    2015-01-01

    Understanding how and why lineages diversify is central to understanding the origins of biological diversity. The avian family Falconidae (caracaras, forest-falcons, falcons) has an uneven distribution of species among multiple well-supported clades, and provides a useful system for testing hypotheses about diversification rate and correlation with environmental changes. We analyzed eight independent loci for 1-7 individuals from each of the 64 currently recognized Falconidae species, together with two fossil falconid temporal calibrations, to assess phylogeny, absolute divergence times and potential shifts in diversification rate. Our analyses supported similar diversification ages in the Early to Middle Miocene for the three traditional subfamilies, Herpetotherinae, Polyborinae and Falconinae. We estimated that divergences within the subfamily Falconinae began about 16mya and divergences within the most species-rich genus, Falco, including about 60% of all Falconidae species, began about 7.5mya. We found evidence for a significant increase in diversification rate at the basal phylogenetic node for the genus Falco, and the timing for this rate shift correlates generally with expansion of C4 grasslands beginning around the Miocene/Pliocene transition. Concomitantly, Falco lineages that are distributed primarily in grassland or savannah habitats, as opposed to woodlands, and exhibit migratory, as opposed to sedentary, behavior experienced a higher diversification rate. Published by Elsevier Inc.

  3. Lower Miocene plant assemblage with coastal-marsh herbaceous monocots from the Vienna Basin (Slovakia)

    Science.gov (United States)

    Kvaček, Zlatko; Teodoridis, Vasilis; Kováčová, Marianna; Schlögl, Ján; Sitár, Viliam

    2014-06-01

    A new plant assemblage of Cerová-Lieskové from Lower Miocene (Karpatian) deposits in the Vienna Basin (western Slovakia) is preserved in a relatively deep, upper-slope marine environment. Depositional conditions with high sedimentation rates allowed exceptional preservation of plant remains. The plant assemblage consists of (1) conifers represented by foliage of Pinus hepios and Tetraclinis salicornioides, a seed cone of Pinus cf. ornata, and by pollen of the Cupressaceae, Pinaceae, Pinus sp. and Cathaya sp., and (2) angiosperms represented by Cinnamomum polymorphum, Platanus neptuni, Potamogeton sp. and lauroid foliage, by pollen of Liquidambar sp., Engelhardia sp. and Craigia sp., and in particular by infructescences (so far interpreted as belonging to cereal ears). We validate genus and species assignments of the infructescences: they belong to Palaeotriticum Sitár, including P. mockii Sitár and P. carpaticum Sitár, and probably represent herbaceous monocots that inhabited coastal marshes, similar to the living grass Spartina. Similar infructescences occur in the Lower and Middle Miocene deposits of the Carpathian Foredeep (Slup in Moravia), Tunjice Hills (Žale in Slovenia), and probably also in the Swiss Molasse (Lausanne). This plant assemblage demonstrates that the paleovegetation was represented by evergreen woodland with pines and grasses in undergrowth, similar to vegetation inhabiting coastal brackish marshes today. It also indicates subtropical climatic conditions in the Vienna Basin (central Paratethys), similar to those implied by other coeval plant assemblages from Central Europe

  4. Climatic and tectonic implications of the late Miocene Jakokkota flora, Bolivian Altiplano

    Science.gov (United States)

    Gregory-Wodzicki, Kathryn M.; McIntosh, W. C.; Velasquez, Kattia

    1998-12-01

    When compared to a database of modern foliar physiognomy and climate, the physiognomy of a new collection of dicotyledonous leaves from the 10.66±0.06 Ma Jakokkota flora, Bolivian Altiplano, implies a mean annual temperature (MAT) of 18.6-21.0±2.5°C. Similarly, a literature-derived sample of the early-middle Miocene Potosı´flora, Cordillera Oriental, implies a MAT of 21.5-21.7±2.1°C. We estimate that both floras experienced a growing season precipitation of 50±40 cm. The paleoclimate thus appears considerably warmer than the current highland climate, with MATs of 8-9°C; the paleoprecipitation is indistinguishable from modern levels. A comparison of the Miocene MATs with the modern MATs, with the effects of latitudinal continental drift and global climate change subtracted, suggests that the Jakokkota flora grew at an elevation of 590-1610±1000 m, and the Potosı´flora grew at an elevation of 0-1320±1000 m. Both paleoelevation estimates are significantly lower than the present elevations of 3940 and 4300 m, respectively, requiring a substantial component of Andean uplift since 10.7 Ma. This uplift history is consistent with two-stage tectonic models of Andean orogeny.

  5. Lower Miocene plant assemblage with coastal-marsh herbaceous monocots from the Vienna Basin (Slovakia

    Directory of Open Access Journals (Sweden)

    Kvaček Zlatko

    2014-06-01

    Full Text Available A new plant assemblage of Cerová-Lieskové from Lower Miocene (Karpatian deposits in the Vienna Basin (western Slovakia is preserved in a relatively deep, upper-slope marine environment. Depositional conditions with high sedimentation rates allowed exceptional preservation of plant remains. The plant assemblage consists of (1 conifers represented by foliage of Pinus hepios and Tetraclinis salicornioides, a seed cone of Pinus cf. ornata, and by pollen of the Cupressaceae, Pinaceae, Pinus sp. and Cathaya sp., and (2 angiosperms represented by Cinnamomum polymorphum, Platanus neptuni, Potamogeton sp. and lauroid foliage, by pollen of Liquidambar sp., Engelhardia sp. and Craigia sp., and in particular by infructescences (so far interpreted as belonging to cereal ears. We validate genus and species assignments of the infructescences: they belong to Palaeotriticum Sitár, including P. mockii Sitár and P. carpaticum Sitár, and probably represent herbaceous monocots that inhabited coastal marshes, similar to the living grass Spartina. Similar infructescences occur in the Lower and Middle Miocene deposits of the Carpathian Foredeep (Slup in Moravia, Tunjice Hills (Žale in Slovenia, and probably also in the Swiss Molasse (Lausanne. This plant assemblage demonstrates that the paleovegetation was represented by evergreen woodland with pines and grasses in undergrowth, similar to vegetation inhabiting coastal brackish marshes today. It also indicates subtropical climatic conditions in the Vienna Basin (central Paratethys, similar to those implied by other coeval plant assemblages from Central Europe

  6. Paleosecular variation record of geomagnetic full vector during late Miocene, from the Nayarit area, Mexico

    Science.gov (United States)

    Goguitchaichvili, Avto; Alva Valdivia, Luis M.; Elguera, Jose Rosas; Fucugauchi, Jaime Urrutia; Cervantes, Miguel Angel; Morales, Juan

    2002-11-01

    We have sampled a sequence of 45 late Miocene consecutive lava flows in the Tepic area (Nayarit State, Mexico). The age of the volcanic units lies between 8 and 9 million years (Ma) according to available radiometric data. All samples were stepwise demagnetized, partly with alternating field (AF), partly thermally with very similar results. Most of the rocks exhibited well-defined one component remanent magnetisation with high unblocking temperatures (mostly above 525 °C) and high median destructive fields (MDF) (40-50 mT). Rock-magnetic experiments combined with microscopy show that, in most cases, the main magnetic mineral is Ti-poor titanomagnetite associated with exsoluted ilmenite. Continuous susceptibility measurements with temperature and hysteresis experiments yield in most cases nearly reversible curves with Curie points close to that of magnetite and pseudo-single-domain characteristics. Characteristic remanent magnetisations (ChRM) isolated after the first steps of demagnetisation are all normal polarity. According to the dispersion of virtual geomagnetic pole (VGP) directions, paleosecular variation was abnormally lower than the one observed in general during Miocene. Considering our paleomagnetic results together with available radiometric data, it seems that the volcanic units have been emplaced during a very short time span of about 0.08 million years. The mean paleomagnetic directions obtained from this study do not differ significantly from that expected for the middle Miocene. Thirty-one samples from eight individual flows yielded acceptable paleointensity estimates. The site mean paleointensities range from 27.8±0.9 to 42.0±7.9 μT. The virtual dipole moments (VDM) range from 5.9 to 9.5×10 22 Am 2. This corresponds to a mean value of 7.6±1.4×10 22 Am 2, which is higher than the average VDM value for late Miocene. Altogether our data suggest the existence of relatively high geomagnetic field strength undergoing low fluctuations. These

  7. On the Miocene Cyprideis species flock (Ostracoda; Crustacea) of Western Amazonia (Solimões Formation): Refining taxonomy on species level.

    Science.gov (United States)

    Gross, Martin; Ramos, Maria Ines F; Piller, Werner E

    2014-12-18

    The Miocene mega-wetland of western Amazonia holds a diverse, largely endemic ostracod fauna. Among them, especially the genus Cyprideis experienced a remarkable radiation. Micropalaeontologic investigations of a 400 m long sediment core (~62 km SW Benjamin Constant, Amazonia, Brazil) permitted a taxonomic revision of about two-thirds of hitherto described Cyprideis species. We evaluate the diagnostic value of shell characters and provide an extensive illustration of the intraspecific variability of species. Based on comparative morphology, the 20 recorded Cyprideis species are arranged in groups and subgroups. The "smooth" group comprises C. amazonica, C. kotzianae, C. kroemmelbeini, C. machadoi, C. multiradiata, C. olivencai, C. paralela and C. simplex; the "ornate" group C. curucae nom. nov., C. cyrtoma, C. aff. graciosa, C. inversa, C. ituiae n. sp., C. matorae n. sp., C. minipunctata, C. munoztorresi nom. nov., C. pebasae, C. reticulopunctata, C. schedogymnos and C. sulcosigmoidalis. Five species have been revalidated, two renamed, two synonymised and two are new descriptions. Along with 10 further formally established species, for which a review is pending, Cyprideis keeps at least 30 endemic species in that region during Miocene times. Up to 12 Cyprideis species have been found to occur sympatrically, representing >90% of the entire ostracod fauna. Ostracod index species enable a biostratigraphic allocation of the well succession to the Cyprideis minipunctata to Cyprideis cyrtoma biozones, corresponding to a late Middle to early Late Miocene age (late Serravallian-early Tortonian).

  8. Modeling geologically abrupt climate changes in the Miocene

    Directory of Open Access Journals (Sweden)

    B. J. Haupt

    2010-12-01

    Full Text Available The gradual cooling of the Cenozoic, including the Miocene epoch, was punctuated by many geologically abrupt warming and cooling episodes – strong deviations from the cooling trend with time span of ten to hundred thousands of years. Our working hypothesis is that some of those warming episodes at least partially might have been caused by dynamics of the emerging Antarctic Ice Sheet, which, in turn, might have caused strong changes of sea surface salinity in the Miocene Southern Ocean. Feasibility of this hypothesis is explored in a series of coupled ocean-atmosphere computer experiments. The results suggest that relatively small and geologically short-lived changes in freshwater balance in the Southern Ocean could have significantly contributed to at least two prominent warming episodes in the Miocene. Importantly, the experiments also suggest that the Southern Ocean was more sensitive to the salinity changes in the Miocene than today, which can attributed to the opening of the Central American Isthmus as a major difference between the Miocene and the present-day ocean-sea geometry.

  9. Evolution of the Climate Continuum from the Mid-Miocene Climatic Optimum to the Present

    Science.gov (United States)

    Aswasereelert, W.; Meyers, S. R.; Hinnov, L. A.; Kelly, D.

    2011-12-01

    The recognition of orbital rhythms in paleoclimate data has led to a rich understanding of climate evolution during the Neogene and Quaternary. In contrast, changes in stochastic variability associated with the transition from unipolar to bipolar glaciation have received less attention, although the stochastic component likely preserves key insights about climate. In this study, we seek to evaluate the dominance and character of stochastic climate energy since the Middle Miocene Climatic Optimum (~17 Ma). These analyses extend a previous study that suggested diagnostic stochastic responses associated with Northern Hemisphere ice sheet development during the Plio-Pleistocene (Meyers and Hinnov, 2010). A critical and challenging step necessary to conduct the work is the conversion of depth data to time data. We investigate climate proxy datasets using multiple time scale hypotheses, including depth-derived time scales, sedimentologic/geochemical "tuning", minimal orbital tuning, and comprehensive orbital tuning. To extract the stochastic component of climate, and also explore potential relationships between the orbital parameters and paleoclimate response, a number of approaches rooted in Thomson's (1982) multi-taper spectral method (MTM) are applied. Importantly, the MTM technique is capable of separating the spectral "continuum" - a measure of stochastic variability - from the deterministic periodic orbital signals (spectral "lines") preserved in proxy data. Time series analysis of the proxy records using different chronologic approaches allows us to evaluate the sensitivity of our conclusion about stochastic and deterministic orbital processes during the Middle Miocene to present. Moreover, comparison of individual records permits examination of the spatial dependence of the identified climate responses. Meyers, S.R., and Hinnov, L.A. (2010), Northern Hemisphere glaciation and the evolution of Plio-Pleistocene climate noise: Paleoceanography, 25, PA3207, doi:10

  10. The record of Miocene climatic events in AND-2A drill core (Antarctica): Insights from provenance analyses of basement clasts

    Science.gov (United States)

    Sandroni, Sonia; Talarico, Franco M.

    2011-01-01

    This paper includes the results of a detailed quantitative provenance investigation on gravel-size clasts occurring within the late Early to Late Miocene sedimentary glacimarine section recovered for the first time by the AND-2A core in the SW sector of the Ross Sea (southern McMurdo Sound, Antarctica). This period of time is of crucial interest, as it includes two of the major Cenozoic events in the global climatic evolution: the mid-Miocene climatic optimum and the middle Miocene climate transition. Petrographical and mineral chemistry data on basement clasts allow to individuate two different diagnostic clast assemblages, which clearly suggest two specific sectors of southern Victoria Land as the most likely sources: the Mulock-Skelton glacier and the Koettlitz-Blue glacier regions. Distribution patterns reveal high fluctuations of the detritus source areas throughout the investigated core interval, variations which can be interpreted as the direct result of an evolving McMurdo Sound paleogeography during the late Early to Late Miocene. Consistently with sedimentological studies, gravel-fraction clast distribution patterns clearly testify that the Antarctic ice sheet experienced a dramatic contraction at ca. 17.35 ± 0.14 Ma (likely correlated to the onset of the climatic optimum), and in a gravel-fraction clasts show that the variations of paleoenvironmental drivers characterising this period were able to exert deep transformation of the Antarctic ice sheet and reveal the methodology to be a powerful tool for the reconstruction of paleo-glacial-flow direction and paleogeographic scenarios.

  11. Chad Basin: Paleoenvironments of the Sahara since the Late Miocene

    Science.gov (United States)

    Schuster, Mathieu; Duringer, Philippe; Ghienne, Jean-François; Roquin, Claude; Sepulchre, Pierre; Moussa, Abderamane; Lebatard, Anne-Elisabeth; Mackaye, Hassan Taisso; Likius, Andossa; Vignaud, Patrick; Brunet, Michel

    2009-08-01

    Since the mid 1990s, the Mission paléoanthropologique francotchadienne (MPFT) conducts yearly paleontological field investigations of the Miocene-Pliocene of the Chad Basin. This article synthesizes some of the results of the MPFT, with focus on the Chad Basin development during the Neogene. We propose an overview of the depositional paleoenvironments of this part of Africa at different scales of time and space, based on a multidisciplinary approach (sedimentary geology, geomorphology, geophysic, numerical simulations and geochronology). The Miocene-Pliocene paleoenvironments are examined through the sedimentary archives of the early hominids levels and the Holocene Lake Mega-Chad episode illustrates the last major paleoenvironmental change in this area. The sedimentary record of the Chad Basin since the Late Miocene can be schematized as the result of recurrent interactions from lake to desert environments.

  12. Miocene to Pleistocene floras and climate of the Eastern Himalayan Siwaliks, and new palaeoelevation estimates for the Namling-Oiyug Basin, Tibet

    Science.gov (United States)

    Khan, Mahasin Ali; Spicer, Robert A.; Bera, Subir; Ghosh, Ruby; Yang, Jian; Spicer, Teresa E. V.; Guo, Shuang-xing; Su, Tao; Jacques, Frédéric; Grote, Paul J.

    2014-02-01

    Four fossil floras ranging in age from the mid Miocene to the early Pleistocene from the eastern Siwaliks near Darjeeling and in Arunachal Pradesh (AP) were compared taxonomically and subjected to a CLAMP (Climate Leaf Analysis Multivariate Program) analysis using a new calibration dataset that includes sites from India, southern China and Thailand and high resolution gridded climate data. Two lower Siwalik mid Miocene floras yielded almost the same values suggesting mean annual temperatures (MATs) of 25.4 and 25.3 °C ± 2.8 °C (all uncertainties ± 2 sigma) with warm month mean temperatures (WMMTs) of 28.4 and 27.8 ± 3.39 °C and cold month mean temperatures (CMMTs) of 17.9 and 21.3 ± 4 °C. Precipitation estimates have high uncertainties but suggest a weak monsoon with growing season precipitations of 242 ± 92 cm for Darjeeling and 174 ± 92 cm for AP. Leaves from the middle Siwalik (Pliocene) sediments of AP indicate a lowering of the MAT to 23.7 °C, a function of cooler winter months (CMMT 16.9 °C). The AP early Pleistocene temperatures and rainfall were similar to those of the mid Miocene. Changes in the monsoon index suggest that in the AP area there has been little change in the intensity of the monsoon since mid Miocene time, while further west at Darjeeling there has been an intensification since the mid Miocene. Mid Miocene CLAMP-derived enthalpy estimates provide sea level (flora from the Namling-Oiyug Basin, southern Tibet. Enthalpy values from Darjeeling and AP were 354.1 and 355.8 ± 10.3 kJ/kg respectively, while that derived from the Namling-Oiyug flora was 296.3 kJ/kg. This yields a palaeoelevation of 5888 m for the Namling site using the Darjeeling enthalpy estimate as a sea level datum and 6065 m using the AP assemblage. The combined uncertainty is ± 728 m. Model corrected enthalpy trends at sea level across palaeolatitude and longitude reduce the mean elevation to 5.54 km. These elevations are higher than earlier estimates from the same

  13. Late Miocene Tidal Deposits in the Amazonian Foreland Basin

    Science.gov (United States)

    Rasanen, Matti E.; Linna, Ari M.; Santos, Jose C. R.; Negri, Francisco R.

    1995-07-01

    Late Miocene tidal sediments of Acre, Brazilian Amazonia, were deposited in an embayment or interior seaway located in the sub-Andean zone. This late Tertiary embayment system may once have connected the Caribbean with the South Atlantic. The tidal coasts of the embayment-seaway have provided an avenue for the earliest waif (over water) dispersal phases of the great American biotic interchange in the late Miocene. The subsequent change from semimarine to terrestrial environments is of value in assessing the importance of earlier hypotheses on the evolution of the western Amazonian landscape and gives insight into the formation of several observed biogeographic patterns, especially of aquatic biota.

  14. Effect of vegetation on the Late Miocene ocean circulation

    Directory of Open Access Journals (Sweden)

    G. Lohmann

    2006-08-01

    Full Text Available A weak and shallow thermohaline circulation in the North Atlantic Ocean is related to an open Central American gateway and exchange with fresh Pacific waters. We estimate the effect of vegetation on the ocean general circulation using the atmospheric circulation model simulations for the Late Miocene climate. Caused by an increase in net evaporation in the Miocene North Atlantic, the North Atlantic water becomes more saline which enhances the overturning circulation and thus the northward heat transport. This effect reveals a potentially important feedback between the ocean circulation, the hydrological cycle and the land surface cover for Cenozoic climate evolution.

  15. Reconnaissance geochronology of tuffs in the Miocene Barstow Formation: implications for basin evolution and tectonics in the central Mojave Desert

    Science.gov (United States)

    Miller, D.M.; Leslie, S.R.; Hillhouse, J.W.; Wooden, J.L.; Vazquez, J.A.; Reynolds, R.E.

    2010-01-01

    Early to middle Miocene lacustrine strata of the Barstow Formation are well dated in just a few places, limiting our ability to infer basin evolution and regional tectonics. At the type section in the Mud Hills, previous studies have shown that the lacustrine interval of the Barstow Formation is between ~16.3 Ma and ~13.4 Ma. Elsewhere, lake beds of the Barstow Formation have yielded vertebrate fossils showing the Hemingfordian/Bartovian transition at ~16 Ma but are otherwise poorly dated. In an attempt to clarify the age and depositional environments of the lake deposits, we are mapping the Barstow Formation and dating zircons from interbedded tuffs, as well as testing ash-flow tuffs for the distinctive remanent magnetization direction of the widespread Peach Spring Tuff. Thus far, our new U-Pb zircon ages inficate that the Barstow lake beds contain tuff beds as old as 19.1 Ma and as young as 15.3 Ma. At Harvard Hill, Barstow lake beds contain a thick tuff dated at 18.7 Ma. On the basis of zircon ages, mineralogy, zircon chemistry, and paleomagnetic results, we consider the thick tuff to be a lacustrine facies of the Peach Spring Tuff. We have identified the Peach Spring Tuff by similar methods at eight localities over a broad area, providing a timeline for several fluvial and lacustrine sections. The new dates indicate that long-lived lacustrine systems originated before 19 Ma and persisted to at least 15 Ma. The onset of lacustrine conditions predates the Peach Spring Tuff in most Barstow Formation sections and may be older than 19.5 Ma in some places. The new data indicate that the central Mojave Desert contained narrow to broad lake basins during and after extension, and that Barstow lacustrine deposits did not exclusively postdate extensional tectonics. At present, it is unclear whether several separate, small lake basins coexisted during the early to middle Miocene, or if instead several small early Miocene basins gradually coalesced over about 6 millions

  16. On the timing and forcing mechanism of a mid-Miocene arid climate transition at the NE margins of the Tibetan Plateau: stratigraphic and sedimentologic evidence from the Sikouzi Section

    Science.gov (United States)

    Lin, Xiubin; Wyrwoll, Karl-Heinz; Chen, Hanlin; Cheng, Xiaogan

    2016-04-01

    The Sikouzi Section is located towards the northern limits of the East Asian summer monsoon, providing the opportunity of placing the stratigraphic record into the context of the East Asian summer monsoon history. We present here the results of the details of the sedimentology of the Neogene succession of the section and use these to provide insights into the evolving history of the East Asian summer monsoon. The record is marked by a strongly expressed early Miocene lacustrine phase. A well-defined evaporate bed defines the top of the lacustrine succession, marking the onset of more arid conditions during the middle Miocene. The overlying succession is dominated by a series of alluvial packages, extending into the late Pleistocene with varying stratigraphic architectures and including a subordinate lacustrine component. Given the regional setting, the onset of drier conditions during the middle Miocene must relate to a downturn of summer monsoon activity. We focus on the question: what `forced' this palaeoclimate event? Earlier biostratigraphic work places the explanation of this change into the context of the global-scale middle Miocene climate reorganisation. Here we explore this question in the context of regional-scale climate dynamics and propose that the onset of drier conditions over the study area was a response to atmospheric subsidence driven by circulation changes related to the growth of the Tibetan Plateau.

  17. Paleobiogeography of scleractinian reef corals: Changing patterns during the Oligocene-Miocene climatic transition in the Mediterranean

    Science.gov (United States)

    Perrin, Christine; Bosellini, Francesca R.

    2012-02-01

    geographically-restricted genera with a moderate to short stratigraphical range and a few long-ranging widespread genera. A major consequence of this structure is that the extinction pattern has proceeded through the preferential extinction of rare-occurrence genera through time. The potential rapid long-distance dispersal of most coral larvae compared to the size of the Oligocene-Miocene Mediterranean, explains why no biogeographical subprovinces can be distinguished for the z-coral fauna. On a local scale, ecological processes tend to sort coral taxa by limiting z-coral development to geographically restricted and discontinuous areas. This accounts for the large amount of geographically-restricted taxa forming the Mediterranean coral fauna. The interaction of plate-tectonics, Alpine orogenesis and climate at local to subregional scales exerts strong controls over the spatio-temporal distribution of z-coral assemblages within the circum-Mediterranean realm. In particular, we suggest that the richness and composition of the Eastern Atlantic coral fauna are indirectly related to the opening and closure of the eastern seaway connection with the Indian Ocean, which controlled the E-W circulation of surface waters and hence the westwards dispersal of pelagic larvae. At the scale of the whole region, the gradual regional climatic change produced by the northwards migration of the entire area, superimposed on the global cooling, appears in large part responsible for the extinction pattern of z-corals through time in the Mediterranean biogeographical Province.

  18. Soft-sediment deformation structures in seismically affected deep-sea Miocene turbidites (Cilento Basin, southern Italy

    Directory of Open Access Journals (Sweden)

    Valente Alessio

    2014-07-01

    Full Text Available Soft-sediment deformation structures (SSDS are widespread in the upper part of the S. Mauro Formation (Cilento Group, Middle-Late Miocene. The succession is represented mainly by thick and very thick, massive, coarse-grained sandstones, deposited by rapid sedimentation of high-density turbidity currents. The most common SSDS are short pillars, dishes, sedimentary sills and convolutions. They occur mostly in the upper parts of sandstone beds. Vertical tubes of 4-5 cm in diameter and up to 50 cm long constitute the most striking structures. They begin in the middle part of sandstone beds, which are basically massive or contain faint dish structures. These tubes can bifurcate upwards and/ or pass into bedding-parallel veins or dikes. The vertical tubes sometimes form sand volcanoes on the then sedimentary surface.

  19. Late Miocene Sciuridae (Mammalia, Rodentia) from Anatolia, Turkey

    NARCIS (Netherlands)

    Bosma, A.A.; de Bruijn, H.; Wessels, W.

    2013-01-01

    Isolated cheek teeth of Sciuridae (Rodentia, Mammalia) from nine late Miocene localities in central Anatolia (Turkey) are described. The teeth represent at least 12 different species, five of which belong to the ground squirrel genus Tamias, two to the ground squirrel genus Spermophilinus, one to th

  20. Lithostratigraphy of the upper Oligocene–Miocene succession in Denmark

    DEFF Research Database (Denmark)

    Rasmussen, Erik Skovbjerg; Dybkjær, Karen; Piasecki, Stefan

    2010-01-01

    The Upper Oligocene – Miocene succession of onshore Denmark is about 250 m thick and is composed of interdigitating, coarse-grained fluvio-deltaic and mud-rich marine sediments; it is best exposed in coastal cliffs in eastern and northern Jylland but is also seen locally inland. These sediments...

  1. Late Miocene Sciuridae (Mammalia, Rodentia) from Anatolia, Turkey

    NARCIS (Netherlands)

    Bosma, A.A.; de Bruijn, H.; Wessels, W.

    Isolated cheek teeth of Sciuridae (Rodentia, Mammalia) from nine late Miocene localities in central Anatolia (Turkey) are described. The teeth represent at least 12 different species, five of which belong to the ground squirrel genus Tamias, two to the ground squirrel genus Spermophilinus, one to

  2. Proboscidea (Mammalia) from the Upper Miocene of Crevillente (Alicante, Spain)

    NARCIS (Netherlands)

    Mazo, A.V.; Montoya, P.

    2003-01-01

    The fossil Proboscidea from the Spanish Turolian (Upper Miocene) sites of Crevillente 2 (MN11) and Crevillente 15 and 16 (MN12) are described. The mastodont from Crevillente 2 is assigned to Tetralophodon cf. longirostris ‘grandincisivoid form’, recognised for the first time in the Iberian Peninsula

  3. A Miocene perspective on the evolution of the Amazonian biota

    NARCIS (Netherlands)

    Wesselingh, F.P.; Salo, J.A.

    2006-01-01

    Between c. 23 and 8 Ma, western Amazonia was occupied by the vast Pebas long-lived lake/wetland system. The Pebas system had a variety of influences over the evolution of Miocene and modern Amazonian biota; it formed a barrier for the exchange of terrestrial biota, a pathway for the transition of ma

  4. The early to mid-Miocene environment of Antarctica

    Science.gov (United States)

    Ashworth, A. C.; Lewis, A.

    2012-12-01

    Paleoecological studies in the Transantarctic Mountains of the McMurdo region provide evidence that the climate was both warmer and wetter in the early to mid-Miocene than it was during the late Miocene. The climate change was accompanied by a shift from wet- to cold-based glaciation in the TAM and the probable growth of the polar ice sheet. Terrestrial and freshwater aquatic fossil assemblages from the Friis Hills (77°S) and the Olympus Range (77°S), with endpoint 40Ar/39Ar ages on tephras of 19.76 Ma and 14.07 Ma, respectively, indicate climatic cooling during the interval. At c.14 Ma, the temperature dropped below the threshold required to support the plants and insects of a tundra biome, and they became extinct. This interpretation is supported by pollen studies from Ross Sea cores. The extinction of the tundra biota on the continent appears to have been time-transgressive, occurring at 12.8 Ma on the Antarctic Peninsula. Evidence of climatic cooling from early to mid-Miocene is based on a decrease in biodiversity. During interglacial phases of the early Miocene, the poorly drained valley of the Friis Hills supported a sexually-reproducing moss community dominated by Campylium cf. polygamum, which today grows on the margins of lakes and in soil between boulders. Wood and leaves of Nothofagus (Southern Beech), and the seeds of at least five other angiosperm species are preserved as fossils. In addition, there are abundant megaspores and spiny, curved leaves of the aquatic lycopod Isoetes (Quillwort), as well as chitinous remains of curculionid beetles and Chironomidae (midges). During glacial phases, the only fossils found are Nothofagus leaves of a species which appears to be different than that associated with the interglacial phases. Pollen supports the interpretation that there was more than one species of Nothofagus in the vegetation. The types and numbers of species indicate that the vegetation was a shrub tundra. The closest modern analog for the fossil

  5. Optimization of the Acetic Acid method for microfossil extraction from lithified carbonate rocks: Examples from the Jurassic and Miocene of Saudi Arabia

    Science.gov (United States)

    Chan, Septriandi; Malik, Muhammad; Kaminski, Michael; Babalola, Lamidi

    2016-04-01

    We report the first ever use of the acetic acid processing method for the extraction of microfossils from indurated limestones in Saudi Arabia. Two different limestone samples from Middle Jurassic and Middle Miocene formation in Saudi Arabia were tested under different concentrations of acid from 50% to 100% and with processing times from 2 hours to 10 hours, in an attempt to optimize the processing methodology. The recovery of acid residues shows a similar trend for both Jurassic and Miocene samples. The weight percentage of residue particle size > 1 mm decreases as acid concentration increases, especially in the 50 to 80% acid concentration range, and the weight percentage of the smallest size particles >0.063 mm increases as acid concentration increases. The small fraction of residue between 0.50 - 0.063 mm was split into 3 g subsamples and picked for microfossils in order to assess their preservation. All concentrations of acetic acid tested show promising results for both the Jurassic Dhruma and Miocene Dam formation carbonates. Higher acid concentrations with longer reaction times yield better recovery than higher concentrations with less reaction time. Based on our experiment, we recommended a 60% concentration of acetic acid to be the optimal concentration for use on routine micropaleontological samples of Saudi Arabian carbonate rocks. By lowering the concentration of acetic acid from 80% to 60%, the consumption of acid is reduced without compromising the recovery of microfossils, and the sample can be processed in a more environmentally friendly manner.

  6. Magmatic evolution of the Sarapiqui Miocene Arc, Costa Rica, Central America

    Science.gov (United States)

    Gazel, E.; Alvarado, G. E.; Carr, M. J.; Obando, J.; Alfaro, A.

    2005-12-01

    The Sarapiqui Miocene Arc (22.2-11.4 Ma) is located in the modern back-arc region of northern Costa Rica, Central America. The arc basement is represented by serpentinized peridotites, Albian silicic pelagites, and Paleocene to Middle Eocene turbidites. Magmatic units vary from basalts to rhyolites and include lavas, pyroclastic deposits, and a few subvolcanic bodies. The magmatic evolution of the Sarapiqui Miocene Arc consists of three distinct stages: 1) Jardin Basalts (22.2 Ma) showing a primary tendency with high MgO, Ni, Cr, and Nb, high initial La/Yb ratios, and low Ba/La which increase with the slab fluids addition; 2) Arrepentidos Basaltic-andesites, Chaparron Pyroclasts, Hito Sar Basalts, Boca Tapada Gabro, and Chamorro Andesites, that represent the island arc evolution from 17.2 to 11.4 Ma; and 3) Crucitas Rhyolites (14.3 Ma) characterizated by low TiO2 and very high Ba/La ratios represent non-cogenetic, but contemporaneous felsic magmas produced by remelting of pre-existing intrusives. The REE patterns indicate a plagioclase rich, amphibole bearing source for this last unit. The Zr/Nb ratios (7-36) are evidence of the coalescing of a minor OIB source with a dominant MORB source, both modified by subduction. 87Sr/86Sr correlate positively with Ba/La; however, they are still within the OIB field. An inverse model using the REEs of the mafic units is consistent with a source mantle composition of garnet peridotite. All but one of the units show LILE enrichments and HFSE depletions typical of the island arc environment. The exception is a suite of near primary magmas, included in the Jardin Basalts, which probably originated by decompression melting. The Ba/La and La/Yb ratios of the Sarapiqui Miocene Arc are very similar to those of the modern Northern Costa Rican Arc, suggesting that the subduction fluid composition and the degree of partial melting have not changed significantly in the last 20 Ma.

  7. Eccentricity pacing of eastern equatorial Pacific carbonate dissolution cycles during the Miocene Climatic Optimum

    Science.gov (United States)

    Kochhann, Karlos G. D.; Holbourn, Ann; Kuhnt, Wolfgang; Channell, James E. T.; Lyle, Mitch; Shackford, Julia K.; Wilkens, Roy H.; Andersen, Nils

    2016-09-01

    The Miocene Climatic Optimum (MCO; ~16.9 to 14.7 Ma) provides an outstanding opportunity to investigate climate-carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (δ18O) and carbon (δ13C) isotope records (5-12 kyr time resolution) spanning the late early to middle Miocene interval (18 to 13 Ma) at Integrated Ocean Drilling Program (IODP) Site U1335 (eastern equatorial Pacific Ocean). The U1335 stable isotope series track the onset and development of the MCO as well as the transitional climatic phase culminating with global cooling and expansion of the East Antarctic Ice Sheet at ~13.8 Ma. We integrate these new data with published stable isotope, geomagnetic polarity, and X-ray fluorescence (XRF) scanner-derived carbonate records from IODP Sites U1335, U1336, U1337, and U1338 on a consistent, astronomically tuned timescale. Benthic isotope and XRF scanner-derived CaCO3 records depict prominent 100 kyr variability with 400 kyr cyclicity additionally imprinted on δ13C and CaCO3 records, pointing to a tight coupling between the marine carbon cycle and climate variations. Our intersite comparison further indicates that the lysocline behaved in highly dynamic manner throughout the MCO, with >75% carbonate loss occurring at paleodepths ranging from ~3.4 to ~4 km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (δ18O minima) and δ13C decreases, implying that climate-carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial-interglacial pattern, where dissolution maxima correspond to δ13C maxima and δ18O minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.

  8. Diagenesis of Miocene, incised valley-filling limestones; Provence, Southern France

    Science.gov (United States)

    Seibel, Margaret J.; James, Noel P.

    2017-01-01

    The Cenozoic of southeastern France is characterized by a series of incised valleys that were filled by a succession of marine carbonate and then siliciclastic sediments culminating in the modern Rhone River depositional system. The earliest of these paleovalleys (Miocene - Burdigalian) is located in the Pernes Hills between the towns of Saumane and Venasque. It was filled by a succession of marine carbonates in the form of two third-order stratigraphic sequences (S1 and S2) and three fourth-order subsequences (S1a, S1b and S1c). The deposits are heterozoan throughout, composed of echinoids, bryozoans, coralline algae, mollusks, and benthic foraminifers. They comprise a succession of spectacular cross-bedded calcarenites that accumulated in the seaward part of a tide-dominated estuary. Diagenesis is interpreted to have taken place in four stages: 1) minor synsedimentary precipitation of inclusion-rich carbonate cements, 2) shallow burial physical and chemical compaction, 3) subaerial exposure and widespread precipitation of clear, zoned, epitaxial and isopachous, followed by subsequent clear, unzoned, calcite cements and, 4) prolonged subaerial exposure (middle Miocene to Holocene), that involved dissolution, karstification, and precipitation of minor clear and locally pendant calcite cement. The rocks were essentially uncemented during shallow burial only to be well lithified during the early phases of subsequent telogenesis. The main controls on such lithification are interpreted to have been: 1) the dissolution of minor aragonite biofragments and precipitation of some LMC cement, 2) the abundance of echinoid particle nuclei for epitaxial cement nucleation, and 3) increasing rainfall together with regional tectonic uplift to the east that resulted in increased subsurface water flow. This study not only emphasizes the variable paragenesis of calcite-rich, heterozoan carbonates but also highlights the utility of these Cenozoic limestones with extant components as

  9. Listriodon guptai Pilgrim, 1926 (Mammalia, Suidae) from the early Miocene of the Bugti Hills, Balochistan, Pakistan: new insights into early Listriodontinae evolution and biogeography

    Science.gov (United States)

    Orliac, Maeva Judith; Antoine, Pierre-Olivier; Métais, Grégoire; Marivaux, Laurent; Crochet, Jean-Yves; Welcomme, Jean-Loup; Baqri, Syed Rafiqul Hassan; Roohi, Ghazala

    2009-08-01

    New dental remains of listriodont suids are described from the lower member of the early to middle Miocene Vihowa Formation of the Bugti Hills, Pakistan. The material is homogeneous in terms of morphology and dimensions and referred as a whole to Listriodon guptai Pilgrim, 1926. This species is also mentioned in coeval deposits of the Zinda Pir Dome, Pakistan, dating back to ca. 19 Ma. The early occurrence of an advanced listriodont in Pakistan constrains the age of acquisition of several characters correlated to lophodonty within Listriodontini, and raises major questions about the early history of the Old World Listriodontinae. Strong morphological similarity between Listriodon guptai and the African species Listriodon akatikubas found in the late early Miocene of Maboko (Kenya, ca. 16.5 Ma) suggests that this latter is most probably a migrant originating from Asia.

  10. Fish vertebra from Miocene beds at Govce, Slovenia

    Directory of Open Access Journals (Sweden)

    Vasja Mikuž

    2014-07-01

    Full Text Available The article discusses a vertebra and a small shark tooth found in the Miocene Govce sandstone near Govce west of Laško in central Slovenia. The vertebra belongs to a shark of the superorder Galeomorphii but we could not determine it with greater precision. The small tooth was assigned to Carcharias cf. taurus Rafinesque, 1810. The nannofossils in the sample are scarce and did not allow dating at biozone precision.

  11. New Miocene Fossils and the History of Penguins in Australia.

    Science.gov (United States)

    Park, Travis; Fitzgerald, Erich M G; Gallagher, Stephen J; Tomkins, Ellyn; Allan, Tony

    2016-01-01

    Australia has a fossil record of penguins reaching back to the Eocene, yet today is inhabited by just one breeding species, the little penguin Eudyptula minor. The description of recently collected penguin fossils from the re-dated upper Miocene Port Campbell Limestone of Portland (Victoria), in addition to reanalysis of previously described material, has allowed the Cenozoic history of penguins in Australia to be placed into a global context for the first time. Australian pre-Quaternary fossil penguins represent stem taxa phylogenetically disparate from each other and E. minor, implying multiple dispersals and extinctions. Late Eocene penguins from Australia are closest to contemporaneous taxa in Antarctica, New Zealand and South America. Given current material, the Miocene Australian fossil penguin fauna is apparently unique in harbouring 'giant penguins' after they went extinct elsewhere; and including stem taxa until at least 6 Ma, by which time crown penguins dominated elsewhere in the southern hemisphere. Separation of Australia from Antarctica during the Palaeogene, and its subsequent drift north, appears to have been a major event in Australian penguin biogeography. Increasing isolation through the Cenozoic may have limited penguin dispersal to Australia from outside the Australasian region, until intensification of the eastwards-flowing Antarctic Circumpolar Current in the mid-Miocene established a potential new dispersal vector to Australia.

  12. Connectivity controls on the late Miocene eastern Mediterranean fish fauna

    Science.gov (United States)

    Agiadi, Konstantina; Antonarakou, Assimina; Kontakiotis, George; Kafousia, Nefeli; Moissette, Pierre; Cornée, Jean-Jacques; Manoutsoglou, Emmanouil; Karakitsios, Vasileios

    2016-06-01

    Environmental change significantly affects the production of fish resources and their dependent societies. The paleontological record offers unique insight into the effects of long-term paleoenvironmental variability on the fish species' distributions and abundances. In the present study, we investigate the late Miocene (7.5-6.5 Ma) fish assemblages of the Potamida section in western Crete (eastern Mediterranean). The determined fish taxa are examined in a paleobiogeographic context, with regard to their geographic and stratigraphic distribution from the early Miocene (~13 Ma) through today. In addition, present-day ecological data are used to reconstruct the paleoenvironmental conditions in the study area. Planktonic foraminifer biostratigraphy significantly improves the earlier dating of the studied sequence. The late Miocene fish fauna of Potamida includes 35 taxa (seven in open nomenclature) from 13 teleost families. The eastern Mediterranean biostratigraphic and geographic distribution of 32 taxa is significantly expanded into the Tortonian, whereas 13 species are recorded for the first time from the Messinian. Four stages are distinguished in the area's paleoenvironmental evolution. (1) The Potamida area was an open marine environment with depths exceeding 150 m between ~7.5-7.45 Ma. (2) Between 7.45-7.36 Ma, the results suggest depths between 300-400 m. (3) The depositional depth increases between 7.36-7.28 Ma to 400-550 m. (4) Later on, approximately between 6.8-6.6 Ma, the depth is again estimated around 100-150 m.

  13. Ventilation of the Miocene Arctic Ocean: An idealized model study

    Science.gov (United States)

    Thompson, Bijoy; Nilsson, Johan; Nycander, Jonas; Jakobsson, Martin; Döös, Kristofer

    2010-11-01

    A model study of an idealized early Miocene Arctic Ocean has been undertaken. The work is motivated by the first drill core retrieved from the Lomonosov Ridge in the central Arctic Ocean, which suggests a transition from anoxic to oxic condition during the early Miocene, a feature presumably related to the opening of the Fram Strait. Here, the ventilation in a semienclosed basin, connected with the ocean through a strait with a sill, is examined using an ocean circulation model that includes a passive age tracer. In particular, we investigate how the ventilation depends on strait geometry, freshwater influx, and surface wind stress. We find that the turnover time, characterizing the bulk ventilation rate, is primarily controlled by the strait width and the wind stress. Generally, the oldest water in the basin is encountered near the sill depth, but wind forcing displaces the oldest water downward. For narrow straits, the turnover time gives an upper bound on the mean age of the basin water. The results have implications when translating local oxygen conditions, recorded in the sediment sequence from the Lomonosov Ridge, to basin-scale circulation patterns. Further, the results indicate that the early Miocene Arctic Ocean became well ventilated when the Fram Strait reached a width of about 100 km.

  14. New Miocene Fossils and the History of Penguins in Australia.

    Directory of Open Access Journals (Sweden)

    Travis Park

    Full Text Available Australia has a fossil record of penguins reaching back to the Eocene, yet today is inhabited by just one breeding species, the little penguin Eudyptula minor. The description of recently collected penguin fossils from the re-dated upper Miocene Port Campbell Limestone of Portland (Victoria, in addition to reanalysis of previously described material, has allowed the Cenozoic history of penguins in Australia to be placed into a global context for the first time. Australian pre-Quaternary fossil penguins represent stem taxa phylogenetically disparate from each other and E. minor, implying multiple dispersals and extinctions. Late Eocene penguins from Australia are closest to contemporaneous taxa in Antarctica, New Zealand and South America. Given current material, the Miocene Australian fossil penguin fauna is apparently unique in harbouring 'giant penguins' after they went extinct elsewhere; and including stem taxa until at least 6 Ma, by which time crown penguins dominated elsewhere in the southern hemisphere. Separation of Australia from Antarctica during the Palaeogene, and its subsequent drift north, appears to have been a major event in Australian penguin biogeography. Increasing isolation through the Cenozoic may have limited penguin dispersal to Australia from outside the Australasian region, until intensification of the eastwards-flowing Antarctic Circumpolar Current in the mid-Miocene established a potential new dispersal vector to Australia.

  15. Tectonic drift versus climatic variations: rhodoliths as indicators of limits between tropical and nontropical sedimentary conditions: examples from Pacific Miocene

    Energy Technology Data Exchange (ETDEWEB)

    Bourrouilh-le Jan, F.G.

    1986-05-01

    Modern examples show that rhodoliths or red algal nodules are forming around the 18/sup 0/C winter isocline and that huge amounts of these red coralline algae are living and accumulating in the subtidal zones, from -60 m to sea level, of temperate seas, such as the English Channel and Rockall. In the Pacific Ocean, several high carbonate platforms, so-called uplifted atolls, show uniform, extended, and thick accumulation of rhodoliths. These accumulations have been recognized in the Solomon Islands (Rennell) and in the Loyalty Islands (Mare and Lifu, New Caledonia), but also in the Vanuatu (Vila), in the Austral Archipelago (Rurutu), where their age can be proved or estimated as middle Miocene. They are also mentioned in the literature on the Emperor Rise (northwest Pacific). On other high carbonate islands, such as Makatea (Tuamotu), red algae and rhodolith formations appear at the top of a sedimentary pile of lower Miocene coral accumulation. The same observations and perhaps the same age can be said for Nauru (central Pacific). Such a wide distribution, from the east to the west part of the Pacific Ocean and between the tropics, seems to be due to climate variations during the Miocene, more than tectonic drift due to oceanic spreading. Temperate conditions shown by this shallow platform sedimentation, just under the coral growth conditions, seem to be confirmed by isotopic studies on pelagic and benthic Foraminifera and could confirm the existence of climate variations affecting the surface water of the Pacific in an extensive area that does not consider the presence of trenches, arcs, and ridges.

  16. A Middle-Upper Miocene fluvial-lacustrine rift sequence in the Song Ba Rift, Vietnam

    DEFF Research Database (Denmark)

    Lars H., Nielsen; Henrik I., Petersen; Nguyen D., Dau

    2007-01-01

    subsidence rate and possibly a higher influx of water from the axial river systems the general water level in the graben rose and deep lakes formed. High organic preservation in the lakes prompted the formation of two excellent oil-prone lacustrine source-rock units. In the late phase of the graben...... fluvial activity. It is likely that the resulting interbedding of fluvial sandstones and lacustrine sediments reflects variations in precipitation. In periods of little precipitation the lakes diminished and lake bottoms became exposed. After heavy precipitation, transverse river systems transported sands...... as carrier beds, whereas the braided fluvial sandstones and conglomerates along the graben margins may form reservoirs. The Krong Pa graben thus contains oil-prone lacustrine source rocks, effective conduits for generated hydrocarbons and reservoir sandstones side-sealed by the graben faults toward...

  17. The interaction between Aegean back-arc extension and Anatolia escape since Middle Miocene

    NARCIS (Netherlands)

    Philippon, M.; Brun, J.-P.; Gueydan, F.; Sokoutis, D.

    2014-01-01

    The Aegean domain is a key area for understanding the processes of back-arc extension. Observed deformation pattern and present day kinematics result from the interaction between the southward retreat of the Hellenic trench and the westward escape of Anatolia. Lithosphere-scale analogue models were

  18. Stratigraphy Konkian-Sarmatian deposits in the south of Ukraine by molluscs (Middle - Upper Miocene

    Directory of Open Access Journals (Sweden)

    Staryn D.A.

    2014-12-01

    Full Text Available The results of study marine bivalve and gastropod from konkian-sarmatian deposits of the Southern Ukraine are gave. Their lateral and vertical distribution is studied. Local stratigraphic schemes for the Northern Black Sea region,Flat Crimea and Kerch peninsula.

  19. Relations of petrographical and geochemical parameters in the middle Miocene Lavanttal lignite (Austria)

    Energy Technology Data Exchange (ETDEWEB)

    Bechtel, A. [Department Angewandte Geowissenschaften und Geophysik, Montanuniversitaet Leoben, Peter-Tunner-Str. 5, A-8700 Leoben (Austria); Mineralogisch-Petrologisches Institut, Universitaet Bonn, Poppelsdorfer Schloss, D-53115 Bonn (Germany); Reischenbacher, D.; Sachsenhofer, R.F.; Gratzer, R. [Department Angewandte Geowissenschaften und Geophysik, Montanuniversitaet Leoben, Peter-Tunner-Str. 5, A-8700 Leoben (Austria); Luecke, A. [Institut fuer Chemie und Dynamik der Geosphaere V: Sedimentaere Systeme (ICG V), Forschungszentrum Juelich, D-52425 Juelich (Germany); Puettmann, W. [Institute of Atmospheric and Environmental Sciences, Department of Environmental Chemistry, J. W. Goethe-Universitaet, Georg-Voigt-Str. 14, D-60054 Frankfurt a.M. (Germany)

    2007-05-01

    Samples from two lignite seams (Lower Seam, Upper Seam) of the Lavanttal basin (Austria) and additional xylite were investigated for variations in maceral composition, petrography-based facies indicators, bulk geochemical parameters, and molecular composition of hydrocarbons. Both seams originated in a topogenous mire and evolved within a transgressive setting. The final drowning of the mire is indicated by sapropelic shales. Whereas the sapropelic shale overlying the Lower Seam was deposited in a freshwater lake, the sapropelic shale above the Upper Seam represents a brackish lake. Numerous relationships are found between petrography-based facies indicators and the geochemical composition of organic matter. The contents of macerals of the liptinite group are positively correlated with soluble organic matter (SOM) yields and hydrogen index (HI). Consistent with maceral composition and high HI values, enhanced proportions of short-chain n-alkanes, which are predominantly found in algae and microorganisms, are obtained from samples of the sapropelic shales. The final drowning of the mire is reflected by decreasing pristane/phytane ratios, due to the rise in (ground)water table and the establishment of anaerobic conditions, as well as by decreasing ratios of diasterenes/sterenes, indicating increasing pH values in the mire. The degree of gelification of plant tissue (gelification index) is governed by the microbial activity in the mire, as indicated by the hopanes concentration. The differences in floral assemblage during the formation of the Lavanttal lignite seams are reflected by major differences in tissue preservation. Preservation of plant tissue (TPI) in the Lavanttal lignite is obviously controlled by the presence/absence of decay-resistant gymnosperms in the peat-forming vegetation, and additionally influenced by the relative contribution of wood to coal formation. The results provide evidence that valuable information for coal facies characterization could be obtained by petrography-based and geochemical facies indicators. An influence of the floral assemblage (gymnosperms/angiosperms ratio) and of the contribution of algal biomass on carbon isotopic composition of the organic matter ({delta}{sup 13}C = - 24.2 to - 28.6 permille) is proposed. Carbon cycling during biogeochemical decomposition of plant tissue by bacteria is suggested to affect the {delta}{sup 13}C values of the coal. The chemotaxonomical classification of the xylites as gymnosperm remnants, based on the molecular composition of terpenoid biomarkers, is corroborated by the carbon isotopic composition of the xylites (mean {delta}{sup 13}C = - 24.1 permille) and the extracted cellulose (mean {delta}{sup 13}C = - 20.2 permille). The higher isotopic difference of about 3.9 permille between cellulose and total organic carbon of the xylites, compared to the difference between cellulose and wood found in modern trees, is explained by the smaller effect of decomposition on {delta}{sup 13}C of cellulose. (author)

  20. The brachiopod Lingula from the Middle Miocene – Badenian beds of Slovenia

    Directory of Open Access Journals (Sweden)

    Špela Ulaga

    2012-12-01

    Full Text Available The article discusses the first find of an inarticulate brachiopod in Slovenia. The fossil was discovered in Miocenebeds in Badenian sandy and marly limestones outcropping in the Plesko quarry near Trbovlje. It belongs to thespecies Lingula dregeri Andreae, 1893.

  1. Bryozoan Nodules as a Frame-Builder of Bryozoan-Microreef, Middle Miocene Sediments, Egypt

    Institute of Scientific and Technical Information of China (English)

    Abdelbaset S. El-Sorogy

    2015-01-01

    Bryozoan nodules, coralline algae, scleractinian corals and oysters form an important or-ganic buildup, 1.2–4.5 m thick in the Langhian-Serravaliann sediments of Egypt. Based on type, shape and size of the substrate, bryozoan nodules take tree-like and globular morphologies. Tree-like speci-mens reach 10 cm in maximum height and 3 cm in diameter, while Globular ones attain 9 cm in maxi-mum diameter. Most tree-like nodules are perforated with wide or narrow pores, few are non-perforated. Globulars and few tree-like forms are with mamelon-like structures. Perforations on the outer surfaces may indicate a symbiotic relationship between bryozoans and a live plant substrate. Nod-ules from Homiera and Gharra areas of the Cairo-Suez District with wider perforations may indicate growth in slightly lighter or turbid areas of the continental shelf than those of North Western Desert of narrower perforations. Non-perforated nodules may assume an incrustation on ephemeral substrate.

  2. Otoliths in situ from Sarmatian (Middle Miocene) fishes of the Paratethys. Part II

    DEFF Research Database (Denmark)

    Schwarzhans, Werner; Carnevale, Giorgio; Bratishko, Andriy

    2017-01-01

    previously described by Fedotov (1976). The new data allow further synonymization of otolith-based species, such as P. insectus (Weiler 1943) and possibly also P. irregularis (Gaemers 1973). Moreover, Properca sabbai Pauca 1929 is removed from the faunal list of Sarmatian fishes in the Paratethys. Kner...

  3. Aragonian stratigraphy reconsidered, and a re-evaluation of the middle Miocene mammal biochronology in Europe

    NARCIS (Netherlands)

    Daams, R.; Meulen, A.J. van der; Alvarez Sierra, M.A.; Peláez-Campomanes, P.; Krijgsman, W.

    1998-01-01

    The recently collected fauna of Armantes 1A in Chron C5Br of the Armantes section necessitates reinterpretation of the previous bio- and magnetostratigraphical correlations between the Armantes and Vargas sections (Calatayud-Daroca Basin, Central Spain) [W. Krijgsman, M. Garcés, C.G. Langereis, R.

  4. Structure Contour of the Top of the Middle Miocene Sequence, Gulf Coast

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The structure contours were created using biostratigraphic data in the Paleo-Data, Inc., Tenroc Regional Geologic Database. The depths of the microfossil locations...

  5. A new family of bizarre durophagous carnivorous marsupials from Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland

    Science.gov (United States)

    Archer, M.; Hand, S. J.; Black, K. H.; Beck, R. M. D.; Arena, D. A.; Wilson, L. A. B.; Kealy, S.; Hung, T.-T.

    2016-05-01

    A new specimen of the bizarrely specialised Malleodectes mirabilis from middle Miocene deposits in the Riversleigh World Heritage Area provides the first and only information about the molar dentition of this strange group of extinct marsupials. Apart from striking autapomorphies such as the enormous P3, other dental features such as stylar cusp D being larger than B suggest it belongs in the Order Dasyuromorphia. Phylogenetic analysis of 62 craniodental characters places Malleodectes within Dasyuromorphia albeit with weak support and without indication of specific relationships to any of the three established families (Dasyuridae, Myrmecobiidae and Thylacinidae). Accordingly we have allocated Malleodectes to the new family, Malleodectidae. Some features suggest potential links to previously named dasyuromorphians from Riversleigh (e.g., Ganbulanyi) but these are too poorly known to test this possibility. Although the original interpretation of a steeply declining molar row in Malleodectes can be rejected, it continues to seem likely that malleodectids specialised on snails but probably also consumed a wider range of prey items including small vertebrates. Whatever their actual diet, malleodectids appear to have filled a niche in Australia’s rainforests that has not been occupied by any other mammal group anywhere in the world from the Miocene onwards.

  6. The time-space distribution of Eocene to Miocene magmatism in the central Peruvian polymetallic province and its metallogenetic implications

    Science.gov (United States)

    Bissig, Thomas; Ullrich, Thomas D.; Tosdal, Richard M.; Friedman, Richard; Ebert, Shane

    2008-07-01

    rocks west of Tarma (21-20 Ma). A relationship between the Oligocene intrusions and polymetallic mineralization at Uchucchacua is possible, but evidence remains inconclusive. Widespread magmatism resumed in the middle Miocene and includes large igneous complexes in the Cordillera Occidental to the south of Domo de Yauli, and smaller scattered intrusive centers to the north thereof. Ore deposits of modest size are widely associated with middle Miocene intrusions along the Cordillera Occidental, north of Domo de Yauli. However, small volcanic centers were also active up to 50 km east of the continental divide and include dacitic dikes and domes, spatially associated with major base and precious metal mineralization at Cerro de Pasco and Colquijirca. Basaltic volcanism (14.54 ± 0.49 Ma) is locally observed in the back-arc domain south of Domo de Yauli approximately 30 km east of the Cordillera Occidental. After about 10 Ma intrusive activity decreased throughout Central Perú and ceased between 6 and 5 Ma. Late Miocene magmatism was locally related to important mineralization including San Cristobal (Domo de Yauli), Huarón and Yauricocha. Overall, there is no evidence for a systematic eastward migration of the magmatic arc through time. The arc broadened in the late Eocene to early Oligocene, and thereafter ceased over wide areas until the early Miocene, when magmatism resumed in a narrow arc. A renewed widening and subsequent cessation of the arc occurred in the late middle and late Miocene. The pattern of magmatism probably reflects two cycles of flattening of the subduction in the Oligocene and late Miocene. Contrasting crustal architecture between areas south and north of Domo de Yauli probably account for the differences in the temporal and aerial distribution of magmatism in these areas. Ore deposits are most abundant between Domo de Yauli and Cerro de Pasco and were generally emplaced in the middle and late Miocene during the transition to flat subduction and

  7. Brachyplatystom a promagdalena, new species, a fossil goliath catfish (Siluriformes: Pimelodidae from the Miocene of Colombia, South America

    Directory of Open Access Journals (Sweden)

    John G. Lundberg

    Full Text Available A fossil Weberian complex of a large pimelodid catfish from the middle Miocene La Venta fauna of central Colombia originally identified as Brachyplatystoma sp. is described as a new, extinct species. Brachyplatystoma promagdalena, new species, is diagnosed by three autapomorphic characters: fifth centrum with a massive midventral expansion containing deep cavities and heavy ridges; first and compound centra contribute to a pair of prominent anterolateral processes before the ventral ends of the ossa suspensoria; and compound centrum with an anteriorly concave low ridge crossing its ventral surface posterior to aortic canal foramen. Brachyplatystoma promagdalena is compared to modern congeneric species and placed in the subgenus Malacobagrus with B. filamentosum, B. capapretum and B. rousseauxii. This group is characterized by synapomorphies of the texture and form of the first vertebra; texture and form of the dorsal side of the fourth transverse process; and presence of a bony gas bladder platform on the ventral side of the fourth transverse process. Today Brachyplatystoma ranges widely across the lowland Orinoco and Amazon and some river basins of the Guianas. The genus does not occur west or north of the Andes or Venezuelan coastal ranges. The Miocene species of Brachyplatystoma signals the former large river and biotic connection between the paleo-Amazonas-Orinoco system and central Colombia, a region now drained by the río Magdalena. Other fossils of aquatic vertebrates from the La Venta fauna show this same biogeographic relationship.

  8. MIOCENE MAMMALIAN FAUNAL SUCCESSION FROM DAMIAO,CENTRAL NEI MONGOL AND THE ENVIRONMENTAL CHANGES%内蒙古大庙中新世哺乳动物群序列与环境变化

    Institute of Scientific and Technical Information of China (English)

    张兆群; 王李花; AnuKaakinen; 刘丽萍; 傅明楷

    2011-01-01

    Nei Mongol (Inner Mongolia) has been well-known in the paleontological society by rich vertebrate fossils, however, there are few well developed sections with superimposition of fossil levels. Here we present the preliminary results of our field seasons during 2006 ~2009 in the Damiao area,Central Nei Mongol. Three main fossil horizons represented by over 20 localities produce three faunas covering Early Miocene,latest Middle Miocene and earliest Late Miocene respectively. The Early Miocene Xiejian fauna is represented by 21 species of 13 families in 5 orders. Large mammals include mainly small sized cervoids, e. G. Lagomeryx sp., Stephanocemas sp. Nov, and Micromeryx sp. Small mammals are dominated by Metexallerix gaolanshanensis, Sinolagomys ulunguensis, Tachyoryctoides sp. Nov, Prodistylomys wangae, Distylomys cf. D.tedfordi, Sinodonomys sp.,Plesiosminthus sp.,Heterosminthus sp. Pseudotheridomys sp. Nov.,and Eomyidae gen. Et sp. Nov.The late Middle Miocene fauna includes more than 30 species,sharing with the classical Tunggur fauna Mioechinust gobknsis, Desmanella storchi, Bellatona forsythmajori, Atlantoxerus orkntalis, Heterosminthus orientalis, Protalactaga grabaui, Gobicricetodon flynni, and Stenofiber hesperus, however, with more diversified cervoids and a species of pliopithecid. The early Late Miocene fauna show great similarity with the previous fauna,except with the earliest record of Late Miocene elements Lophocricetus, Eozapus, Nannocricetus etc, and disappearance of the typical Middle Miocene Atlantoxerus ,Democricetodon, and Heterosminthus. All three faunas have rich small mammals (insectivores, rodents and lagomorphs) and diversified cervoids. The similar faunal community structure and continuity of main lineages suggest a relatively stable moderate humid and warm forest-grassland environment from the Early Miocene to early Late Miocene. The significant environment change seems to have happened after the earliest Late Miocene.%中新世是现代

  9. A minute ostracod (Crustacea: Cytheromatidae) from the Miocene Solimões Formation (western Amazonia, Brazil): evidence for marine incursions?

    Science.gov (United States)

    Gross, Martin; Ramos, Maria Ines F.; Piller, Werner E.

    2016-01-01

    A huge wetland (the ‘Pebas system’) covered western Amazonia during the Miocene, hosting a highly diverse and endemic aquatic fauna. One of the most contentious issues concerns the existence, potential pathways and effects of marine incursions on this ecosystem. Palaeontological evidences (body fossils) are rare. The finding of a new, presumably marine ostracod species (Pellucistoma curupira sp. nov.) in the upper middle Miocene Solimões Formation initiated a taxonomic, ecological and biogeographical review of the genus Pellucistoma. We demonstrate that this marine (sublittoral, euhaline), subtropical–tropical taxon is biogeographically confined to the Americas. The biogeographical distribution of Pellucistoma largely depends on geographical, thermal and osmotic barriers (e.g. land bridges, deep and/or cold waters, sea currents, salinity). We assume an Oligocene/early Miocene, Caribbean origin for Pellucistoma and outline the dispersal of hitherto known species up to the Holocene. Pellucistoma curupira sp. nov. is dwarfed in comparison to all other species of this genus and extremely thin-shelled. This is probably related to poorly oxygenated waters and, in particular, to strongly reduced salinity. The associated ostracod fauna (dominated by the eurypotent Cyprideis and a few, also stunted ostracods of possibly marine ancestry) supports this claim. Geochemical analyses (δ18O, δ13C) on co-occurring ostracod valves (Cyprideis spp.) yielded very light values, indicative of a freshwater setting. These observations point to a successful adaptation of P. curupira sp. nov. to freshwater conditions and therefore do not signify the presence of marine water. Pellucistoma curupira sp. nov. shows closest affinities to Caribbean species. We hypothesize that Pellucistoma reached northern South America (Llanos Basin) during marine incursions in the early Miocene. While larger animals of marine origin (e.g. fishes, dolphins, manatees) migrated actively into the Pebas

  10. A minute ostracod (Crustacea: Cytheromatidae) from the Miocene Solimões Formation (western Amazonia, Brazil): evidence for marine incursions?

    Science.gov (United States)

    Gross, Martin; Ramos, Maria Ines F; Piller, Werner E

    2016-07-02

    A huge wetland (the 'Pebas system') covered western Amazonia during the Miocene, hosting a highly diverse and endemic aquatic fauna. One of the most contentious issues concerns the existence, potential pathways and effects of marine incursions on this ecosystem. Palaeontological evidences (body fossils) are rare. The finding of a new, presumably marine ostracod species (Pellucistoma curupira sp. nov.) in the upper middle Miocene Solimões Formation initiated a taxonomic, ecological and biogeographical review of the genus Pellucistoma. We demonstrate that this marine (sublittoral, euhaline), subtropical-tropical taxon is biogeographically confined to the Americas. The biogeographical distribution of Pellucistoma largely depends on geographical, thermal and osmotic barriers (e.g. land bridges, deep and/or cold waters, sea currents, salinity). We assume an Oligocene/early Miocene, Caribbean origin for Pellucistoma and outline the dispersal of hitherto known species up to the Holocene. Pellucistoma curupira sp. nov. is dwarfed in comparison to all other species of this genus and extremely thin-shelled. This is probably related to poorly oxygenated waters and, in particular, to strongly reduced salinity. The associated ostracod fauna (dominated by the eurypotent Cyprideis and a few, also stunted ostracods of possibly marine ancestry) supports this claim. Geochemical analyses (δ(18)O, δ(13)C) on co-occurring ostracod valves (Cyprideis spp.) yielded very light values, indicative of a freshwater setting. These observations point to a successful adaptation of P. curupira sp. nov. to freshwater conditions and therefore do not signify the presence of marine water. Pellucistoma curupira sp. nov. shows closest affinities to Caribbean species. We hypothesize that Pellucistoma reached northern South America (Llanos Basin) during marine incursions in the early Miocene. While larger animals of marine origin (e.g. fishes, dolphins, manatees) migrated actively into the Pebas

  11. Effective heat transport of Gulf Stream to subarctic North Atlantic during Miocene cooling: evidence from "Köppen signatures" of fossil plant assemblages

    Directory of Open Access Journals (Sweden)

    T. Denk

    2013-08-01

    Full Text Available Shallowing of the Panama Sill and the closure of the Central American Seaway initiated the modern Loop Current/Gulf Stream circulation pattern during the Miocene but no direct evidence has yet been provided for effective heat transport to the northern North Atlantic during that time. Climatic signals from 11 precisely-dated plant-bearing sedimentary rock formations in Iceland, spanning 15–0.8 million years (Myr, resolve the impacts of the developing Miocene global thermohaline circulation on terrestrial vegetation in the subarctic North Atlantic region. "Köppen signatures" were implemented to express climatic properties of fossil plant taxa and their potential modern analogues using the principal concept of the generic Köppen–Geiger climate system, which is based on plant distribution patterns. Using Köppen signatures and the correlation between Köppen climate zones and major global vegetation zones, fossil assemblages were used to trace major vegetation shifts. This evidence was combined with evidence from tectonics and palaeoceanography. In contrast to the global climatic trend, the vegetation record reveals no cooling between ~ 15 and 12 Myr, whereas periods of climatic deterioration between 12–10 Myr, 8–4 Myr, and in the Pleistocene are in phase with increased pulses of ice-rafted debris in the Northern Hemisphere. The observed sequence of climate change in the northern North Atlantic can only be explained by an effective Gulf Stream-mediated heat transport from the middle Miocene onwards.

  12. Space-time variations of stresses in the Miocene-Quaternary along the Calama-Olacapato-El Toro Fault Zone, Central Andes

    Science.gov (United States)

    Lanza, F.; Tibaldi, A.; Bonali, F. L.; Corazzato, C.

    2013-05-01

    We describe the temporal and spatial changes in the tectonic state of stress occurred during the Miocene-Quaternary in the trans-orogen area of the Calama-Olacapato-El Toro (COT) fault zone in the Central Andes, at about 24°S within the northern portion of the Puna Plateau. This work sheds new light on the complexity of stress pattern distribution in general, and contributes to the analysis of the relationships between tectonics and volcanism, and of the seismic hazard of the area. Field geological surveys, along with kinematic analysis and numerical inversion of ~ 140 new fault-slip measurements, have revealed that this portion of the COT zone, previously considered a continuous, long-lived lineament, in reality has been subjected to three different kinematic regimes: 1) a Miocene transpressional phase with the maximum principal stress (σ1) chiefly trending NNE-SSW; 2) an extensional phase that started by 9 Ma, with a horizontal NW-SE-trending minimum principal stress (σ3), and 3) a left-lateral strike-slip phase with a horizontal ~ E-W σ1 and ~ N-S σ3 dating to the late Pliocene-Quaternary, which decreases toward the westernmost part of the studied zone, where it transitions to extension producing a N-S-trending graben structure. Hence, even if transcurrence is still active in the eastern portion of the COT, as focal mechanisms of crustal earthquakes indicate, our study demonstrates that extension is becoming the predominant structural style of deformation, at least in the western region. The major changes in the tectonic regimes are attributed to changes in the magnitude of the boundary forces due to subduction processes, whereas gravitational effect of a thickened crust might be responsible for the overall orogen-perpendicular extension.

  13. Reconstruction of floral changes during deposition of the Miocene Embalut coal from Kutai Basin, Mahakam Delta, East Kalimantan, Indonesia by use of aromatic hydrocarbon composition and stable carbon isotope ratios of organic matter

    Energy Technology Data Exchange (ETDEWEB)

    Widodo, S.; Bechtel, A.; Anggayana, K.; Puttmann, W. [University of Frankfurt, Frankfurt (Germany)

    2009-02-15

    The distribution of aromatic hydrocarbons and stable carbon isotope ratios of organic matter in a series of nine Miocene Embalut coal samples obtained from nine coal seams of Kutai Basin, East Kalimantan, Indonesia were studied. The rank of the Embalut coals ranged from lignites to low rank sub-bituminous coals (0.36-0.50% Rr), based on measurements of huminite reflectance. The aromatic hydrocarbon fractions of all coal samples were dominated by cadalene in the lower boiling point range and picene derivatives in the higher boiling point range of the gas chromatograms. Cadalene can be attributed to the contribution of Dipterocarpaceae and various hydrated picenes to the contribution of additional angiosperms to the coal forming vegetation. The picenes originate from {alpha}- and {beta}-amyrin. However, in some coal samples minor amounts of simonellite and retene were also detected which argues for an additional contribution of gymnosperms (conifers) to coal forming vegetation preferentially in the Middle Miocene and at the beginning of the Late Miocene. The results of stable carbon isotope ratios ({delta}{sup 13}C in most of the coal samples are consistent with their origin from angiosperms {delta}{sup 13}C between -27.09, and -28.0%). During the Miocene the climate of Mahakam Delta was not uniformly moist and cooler than the present day climate. This would have been favourable for the growth of conifers, especially in the montane forests. The contribution of conifers to the Embalut coals might be a result of the cool Middle/Late Miocene climate during peat accumulation in the Kutai Basin.

  14. A Miocene hyperdiverse crocodylian community reveals peculiar trophic dynamics in proto-Amazonian mega-wetlands

    Science.gov (United States)

    Salas-Gismondi, Rodolfo; Flynn, John J.; Baby, Patrice; Tejada-Lara, Julia V.; Wesselingh, Frank P.; Antoine, Pierre-Olivier

    2015-01-01

    Amazonia contains one of the world's richest biotas, but origins of this diversity remain obscure. Onset of the Amazon River drainage at approximately 10.5 Ma represented a major shift in Neotropical ecosystems, and proto-Amazonian biotas just prior to this pivotal episode are integral to understanding origins of Amazonian biodiversity, yet vertebrate fossil evidence is extraordinarily rare. Two new species-rich bonebeds from late Middle Miocene proto-Amazonian deposits of northeastern Peru document the same hyperdiverse assemblage of seven co-occurring crocodylian species. Besides the large-bodied Purussaurus and Mourasuchus, all other crocodylians are new taxa, including a stem caiman—Gnatusuchus pebasensis—bearing a massive shovel-shaped mandible, procumbent anterior and globular posterior teeth, and a mammal-like diastema. This unusual species is an extreme exemplar of a radiation of small caimans with crushing dentitions recording peculiar feeding strategies correlated with a peak in proto-Amazonian molluscan diversity and abundance. These faunas evolved within dysoxic marshes and swamps of the long-lived Pebas Mega-Wetland System and declined with inception of the transcontinental Amazon drainage, favouring diversification of longirostrine crocodylians and more modern generalist-feeding caimans. The rise and demise of distinctive, highly productive aquatic ecosystems substantially influenced evolution of Amazonian biodiversity hotspots of crocodylians and other organisms throughout the Neogene. PMID:25716785

  15. Impacts of orbital forcing and atmospheric carbon dioxide on Miocene ice-sheet expansion.

    Science.gov (United States)

    Holbourn, Ann; Kuhnt, Wolfgang; Schulz, Michael; Erlenkeuser, Helmut

    2005-11-24

    The processes causing the middle Miocene global cooling, which marked the Earth's final transition into an 'icehouse' climate about 13.9 million years ago (Myr ago), remain enigmatic. Tectonically driven circulation changes and variations in atmospheric carbon dioxide levels have been suggested as driving mechanisms, but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult. Here we present high-resolution climate proxy records, covering the period from 14.7 to 12.7 million years ago, from two complete sediment cores from the northwest and southeast subtropical Pacific Ocean. Using new chronologies through the correlation to the latest orbital model, we find relatively constant, low summer insolation over Antarctica coincident with declining atmospheric carbon dioxide levels at the time of Antarctic ice-sheet expansion and global cooling, suggesting a causal link. We surmise that the thermal isolation of Antarctica played a role in providing sustained long-term climatic boundary conditions propitious for ice-sheet formation. Our data document that Antarctic glaciation was rapid, taking place within two obliquity cycles, and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change.

  16. Herds Overhead: Nimbadon lavarackorum (Diprotodontidae), Heavyweight Marsupial Herbivores in the Miocene Forests of Australia

    Science.gov (United States)

    Black, Karen H.; Camens, Aaron B.; Archer, Michael; Hand, Suzanne J.

    2012-01-01

    The marsupial family Diprotodontidae (Diprotodontia, Vombatiformes) is a group of extinct large-bodied (60–2500 kg) wombat-like herbivores that were common and geographically widespread in Cenozoic fossil deposits of Australia and New Guinea. Typically they are regarded to be gregarious, terrestrial quadrupeds and have been likened in body form among placental groups to sheep, rhinoceros and hippopotami. Arguably, one of the best represented species is the zygomaturine diprotodontid Nimbadon lavarackorum which is known from exceptionally well-preserved cranial and postcranial material from the middle Miocene cave deposit AL90, in the Riversleigh World Heritage Area, northwestern Queensland. Here we describe and functionally analyse the appendicular skeleton of Nimbadon lavarackorum and reveal a far more unique lifestyle for this plesiomorphic and smallest of diprotodontids. Striking similarities are evident between the skeleton of Nimbadon and that of the extant arboreal koala Phascolarctos cinereus, including the powerfully built forelimbs, highly mobile shoulder and elbow joints, proportionately large manus and pes (both with a semi-opposable digit I) and exceedingly large, recurved and laterally compressed claws. Combined with the unique (among australidelphians) proportionately shortened hindlimbs of Nimbadon, these features suggest adept climbing ability, probable suspensory behaviour, and an arboreal lifestyle. At approximately 70 kg, Nimbadon is the largest herbivorous mammal to have occupied the forest canopies of Australia - an ecological niche that is no longer occupied in any Australian ecosystem and one that further expands the already significant niche diversity displayed by marsupials during the Cenozoic. PMID:23185250

  17. An overview of lithotype associations of Miocene lignite seams exploited in Poland

    Science.gov (United States)

    Widera, Marek

    2016-09-01

    Currently, three stratigraphically distinct lignite seams of Early to Middle Miocene age are exploited in Poland, namely the third Ścinawa lignite seam (ŚLS-3), the second Lusatian lignite seam (LLS-2) and the first Mid-Polish lignite seam (MPLS-1). All of these are composed of numerous macroscopically distinguishable layers defined as lignite lithotypes. In the present paper, the lithotypes of Polish lignites are grouped into seven major lithotype associations that originated in various types of mire. Therefore, an approximate reconstruction of mire type can be based on lignite lithotypes. Within the Polish lignite seams examined, the commonest in order of importance are: xylodetritic (XDL), detroxylitic (DXL), detritic (DL) and xylitic (XL) lithotype associations, mostly with a massive (m) or horizontal (h) structure. They are particularly dominant in lignite opencasts belonging to the Konin and Adamów mines. However, in the lowermost seams at the Turów and Bełchatów mines, a substantial part of the seams comprises the bitumen-rich (BL) lithotype association. These seams also lignite lithotypes that in large quantities have a gelified (g) and/or nodular (n) structure. In contrast, lignites from the Sieniawa mine are characterised by an admixture of the best-developed lithotype associations of both fusitic (FL) and weathered (WL) lignites. Moreover, the vast majority of these lignites have a folded (fo) and/or faulted (fa) structure, because they were completely deformed by glaciotectonics.

  18. An overview of lithotype associations of Miocene lignite seams exploited in Poland

    Directory of Open Access Journals (Sweden)

    Widera Marek

    2016-09-01

    Full Text Available Currently, three stratigraphically distinct lignite seams of Early to Middle Miocene age are exploited in Poland, namely the third Ścinawa lignite seam (ŚLS-3, the second Lusatian lignite seam (LLS-2 and the first Mid-Polish lignite seam (MPLS-1. All of these are composed of numerous macroscopically distinguishable layers defined as lignite lithotypes. In the present paper, the lithotypes of Polish lignites are grouped into seven major lithotype associations that originated in various types of mire. Therefore, an approximate reconstruction of mire type can be based on lignite lithotypes. Within the Polish lignite seams examined, the commonest in order of importance are: xylodetritic (XDL, detroxylitic (DXL, detritic (DL and xylitic (XL lithotype associations, mostly with a massive (m or horizontal (h structure. They are particularly dominant in lignite opencasts belonging to the Konin and Adamów mines. However, in the lowermost seams at the Turów and Bełchatów mines, a substantial part of the seams comprises the bitumen-rich (BL lithotype association. These seams also lignite lithotypes that in large quantities have a gelified (g and/or nodular (n structure. In contrast, lignites from the Sieniawa mine are characterised by an admixture of the best-developed lithotype associations of both fusitic (FL and weathered (WL lignites. Moreover, the vast majority of these lignites have a folded (fo and/or faulted (fa structure, because they were completely deformed by glaciotectonics.

  19. Hipparion macedonicum revisited: New data on evolution of hipparionine horses from the Late Miocene of Greece

    Directory of Open Access Journals (Sweden)

    George D. Koufos

    2016-08-01

    Full Text Available The new expeditions to the Axios Valley (Macedonia, Greece provided a new set of fossils from the various localities. Among the material collected from the Late Miocene hominoid bearing mammal locality Ravin de la Pluie (RPl were some remains of Hipparion macedonicum, which was originally described from this locality. The most important is the skull and associated mandible, the first from the type locality. The new material is compared with the previously collected material of the taxon from the Vallesian and Turolian levels of Greece, as well as with corresponding material from Eurasia. The RPl skull is compared with the type skull of H. matthwei, a taxon, which several times has been referred as synonym to H. macedonicum. The comparison indicated several differences which distinguish the two species. Hipparion macedonicum has a continuous stratigraphic range from the Vallesian to middle Turolian and it is possibly present in the late Turolian. The comparison of the chronologically different samples of H. macedonicum indicates that the Vallesian form of H. macedonicum has larger size, shorter narial opening, longer tooth rows, rich enamel plication, more elongated and narrow plis, more robust metapodials and less running legs than the Turolian form. Some of the morphological changes are related to the habitat, which was more closed, warmer and wetter in the Vallesian than Turolian.

  20. Geochemistry and petrology of the Early Miocene lamproites and related volcanic rocks in the Thrace Basin, NW Anatolia

    Science.gov (United States)

    Ersoy, Yalçın E.; Palmer, Martin R.; Uysal, İbrahim; Gündoğan, İbrahim

    2014-08-01

    The extensional Thrace basin (NW Anatolia) contains an association of early Miocene diopside-leucite-phlogopite (Doğanca) and diopside-phlogopite (Korucuköy) lamproites with Oligocene medium-K calc-alkaline andesites (Keşan volcanics), early Miocene shoshonitic rocks (Altınyazı trachyte) and middle Miocene Na-alkaline basalts (Beğendik basalts). The Doğanca lamproite (K2O = 5.1-5.5 wt.%; K/Na = 2.78-2.89; MgO = 11.4-11.8 wt.%) consists of olivine (Fo71-86), diopside (Al2O3 = 1.0-5.0, Na2O = 0.2-0.6), phlogopite (TiO2 = 1.1-9.4, Al2O3 = 11.1-13.9), spinel (Mg# = 22.9-32.6; Cr# = 64-83.4), leucite, apatite, zircon, Fe-Ti-oxides and magnetite in a poikilitic sanidine matrix. The potassic volcanic units (lamproites and trachytes) in the region have similarly high Sr and low Nd isotopic compositions (87Sr/86Sr(i) = 0.70835-0.70873 and 143Nd/144Nd(i) = 0.51227-0.51232). The major and trace element compositions and Sr-Nd-Pb isotopic ratios of the shoshonitic, ultrapotassic and lamproitic units closely resemble those of other Mediterranean ultrapotassic lamproites (i.e., orogenic lamproites) from Italia, Serbia, Macedonia and western Anatolia. The Beğendik basalts show intraplate geochemical signatures with an Na-alkaline composition, an absence of Nb negative anomalies on primitive mantle-normalized multi-element diagrams, as well as low Sr (~ 0.70416) and high Nd (0.51293) isotopic ratios; and include olivine (Fo72-84), diopside, spinel, Fe-Ti-oxides and magnetite. The Oligocene Keşan volcanics were emplaced in the earlier stages of extension in Thrace, and represent the typical volcanic products of post-collisional volcanism. The continental crust-like trace element abundances and isotopic compositions of the most primitive early Miocene ultrapotassic rocks (Mg# up to 74) indicate that their mantle sources were intensely contaminated by the continental material. By considering the geodynamic evolution of the region, including oceanic subduction, crustal

  1. Milankovitch cycles in an equatorial delta from the Miocene of Borneo

    Science.gov (United States)

    Marshall, Nathan; Zeeden, Christian; Hilgen, Frederik; Krijgsman, Wout

    2017-08-01

    The factors controlling sedimentary cyclicity in deltaic systems are a subject of intense debate, and more research, in different deltaic environments and time periods, is needed to better understand the possible mechanisms. Offshore and Pleistocene case studies are more common than proximal and more ancient, greenhouse-climate examples. Furthermore, many studies lack a (statistical) cyclostratigraphic element. The paleo-Mahakam delta of Eastern Kalimantan, Borneo developed during the globally warm middle Miocene, in an equatorial setting, making it of interest to comprehend cyclic sedimentation in a period of warmer yet rapidly changing climate. In this study, statistical analysis of lithological changes shows that regular sandstone/shale alternations occur in a distinct pattern of cycles with thicknesses of ∼90, ∼30, and ∼17 m. Using independent dating, these thicknesses translate into periods of about 100, 40, and 20 kyr, matching the known periods of Earth's orbital eccentricity, obliquity and precession. The obliquity dominance in the middle interval is markedly similar to that observed in the global marine isotope (benthic δ18O) and other cyclic proxy records for this time interval. Despite a mismatch in the number of 40 kyr cycles compared to the global record that can be plausibly linked to the major sea-level drop at ∼13.8 Ma and facies shifts, it appears that the proximal setting of the paleo-Mahakam's sedimentation was dominantly controlled by allogenic orbital forcing, probably as a consequence of glacioeustasy. In particular, the observed obliquity dominance at paleo-equatorial latitudes, as seen in other records, highlights the dominance of orbital forcing, and potentially glacioeustatic sea level change, during this crucial period of warmer climate.

  2. Clay mineral stratigraphy of Miocene to recent marine sediments in the central Mediterranean

    NARCIS (Netherlands)

    Visser, J.P. de

    1992-01-01

    X-ray diffraction analyses were made of the smaller than 2 J..Lm fraction from about 1250 samples of the central Mediterranean Miocene to Recent and the southeastern North-Atlantic Miocene in order to reconstruct climatic changes. Relative quantities of the clay minerals chlorite, illite, pyrophylli

  3. The first record of Deinotherium (Proboscidea, Mammalia) in the Miocene of Adygea.

    Science.gov (United States)

    Tarasenko, K K; Lopatin, A V; Maschenko, E N

    2015-01-01

    The data on an isolated upper tooth (P4) of Deinotherium sp. from the Late Miocene beds of the Maikop 1 locality (Maikop, Republic of Adygea) are reported. This is the first record of Deinotherium from the Upper Miocene of Russia. The tooth crown of P4 is similar in size to D. proavum Eichwald, 1831 (= D. gigantissimum Stefanescu, 1892).

  4. A new Miocene baleen whale from the Peruvian desert

    Science.gov (United States)

    Marx, Felix G.; Kohno, Naoki

    2016-10-01

    The Pisco-Ica and Sacaco basins of southern Peru are renowned for their abundance of exceptionally preserved fossil cetaceans, several of which retain traces of soft tissue and occasionally even stomach contents. Previous work has mostly focused on odontocetes, with baleen whales currently being restricted to just three described taxa. Here, we report a new Late Miocene rorqual (family Balaenopteridae), Incakujira anillodefuego gen. et sp. nov., based on two exceptionally preserved specimens from the Pisco Formation exposed at Aguada de Lomas, Sacaco Basin, southern Peru. Incakujira overall closely resembles modern balaenopterids, but stands out for its unusually gracile ascending process of the maxilla, as well as a markedly twisted postglenoid process of the squamosal. The latter likely impeded lateral (omega) rotation of the mandible, in stark contrast with the highly flexible craniomandibular joint of extant lunge-feeding rorquals. Overall, Incakujira expands the still meagre Miocene record of balaenopterids and reveals a previously underappreciated degree of complexity in the evolution of their iconic lunge-feeding strategy.

  5. Geodynamics along an increasingly curved convergent plate margin: Late Miocene-Pleistocene Rhodes, Greece

    Science.gov (United States)

    ten Veen, Johan H.; Kleinspehn, Karen L.

    2002-06-01

    Neogene-Holocene outward migration of the absolute position of the convergent Hellenic plate boundary produced simultaneous increased curvature of the plate boundary, changing obliquity of plate convergence vectors and boundary-parallel stretching of the forearc region. To study the effects of the plate boundary migration and curvature, a tectonostratigraphy is constructed from the middle Miocene-Pleistocene Apolakkia basin on Rhodes, whose easternmost location makes it a key island to assess the inner forearc's kinematic response to expansion of the overriding Aegean-Anatolian block and thus obliquity of convergence with the African plate. The basin fill provides temporal and paleogeographic control to interpret its syndepositional and postdepositional structural assemblages. Five fault populations in the Apolakkia basin record two neotectonic deformation phases separated by a kinematic change at ~4.5 Ma, both of which are consistent with outward expansion of the Aegean-Anatolian block. The Apolakkia basin originated as a late Miocene fault wedge basin in response to syndepositional southwest-northeast D1 extension with similar strain patterns in the adjacent offshore Hellenic inner forearc. The kinematic change at ~4-5 Ma is attributed to a threshold of obliquity whereby the inner forearc started to experience sinistral-oblique divergence. The Plio-Pleistocene D2 transtensional phase reoriented the basin and resulted in combined syndepositional west-northwest-east-southeast extension (283°) and 070° sinistral shear, orientations that are best attributed to simultaneous outward expansion of the Hellenic forearc, increasing curvature of the plate boundary and associated boundary-parallel stretching of the forearc. Principal shear zones offshore also occur consistently at ~070°, mimicking the D2 kinematic history of the Apolakkia basin and suggesting a consistent geodynamic regime throughout the inner eastern Hellenic forearc. Effects of sinistral-oblique plate

  6. Drivers and Dynamics of Ecological Responses to Abrupt Environmental Change on the Early Miocene Oregon Shelf

    Science.gov (United States)

    Belanger, C. L.

    2012-12-01

    We know that the biosphere responds to abrupt climate change, but know less about the dynamics of those changes and their proximal drivers. Studies of well-preserved fossil time-series spanning past climate events that utilize multiple environmental proxies and examine multiple taxonomic groups can provide critical insight into (a) the specific environmental factors to which the biota respond, (b) the rate and tempo of those responses, and (c) whether taxonomic groups respond similarly or differently to the same stresses. I examine the drivers and dynamics of ecological changes in continental shelf benthic foraminifera and molluscs from the Early Miocene Newport Member of the Astoria Formation in Oregon (20.3-16.3 mya), which spans a time of global warming leading into the Middle Miocene Climate Optimum. Stable isotope (δ18O) data from three species of benthic foraminifera from the Astoria sediments indicate that the region abruptly warmed by 2-4°C approximately 19 mya. In addition, δ13C values from epifaunal and infaunal foraminifera indicate an increase in productivity and organic carbon flux over time. Further, an increase in δ15N from bulk sediment and an increase in sedimentary laminations suggest oxygen levels declined. Multivariate analyses demonstrate a strong correlation between foraminiferal community metrics and δ15N suggesting that the foraminiferal community is tracking oxygenation levels while correlations to productivity changes appear indirect. Molluscan community metrics also have an approximately linear relationship to δ15N. Temperature itself had little direct influence on community composition. Changes in community composition and structure of both the foraminifera and the molluscs are abrupt relative to the duration of community states, but each group responds differently to the climate change. The foraminiferal community increases in the number of species and the evenness of species abundances while the molluscan community decreases in

  7. The Randeck Maar: Facies development and habitat differentiation of a Miocene lacustrine system

    Science.gov (United States)

    Rasser, Michael W.; Kern, Andrea K.

    2015-04-01

    The Randeck Maar in S Germany is a well-known fossil lagerstätte (Early/Middle Miocene, MN5) with exceptionally preserved fossils. Although it is a locally restricted succession of lake sediments with a diameter of only 1200 m and less than 60 m of preserved sediments, it appears to comprise a complex structure with a high scientific potential on a global scale, because the lake sediments and their fossils can provide evidence for the impact of the Mid-Miocene Climatic Optimum (MMCO) on the environment and its organisms as well as the ecological interactions between animals and/or plants during that interval. No other European locality provides such a rich insight into an ecosystem that existed during the MMCO. Excavations of Staatliches Museum für Naturkunde Stuttgart provided new insights into the facies types of this maar lake. They showed that a high variety of facies types existed beside the traditional separation into a basal tuffitic development, followed by calcareous and bituminous ('dysodil') laminates, and terminal massive freshwater limestones. Palaeoenvironmental reconstructions are based on the mentioned excavations and re-evaluations of collection material. They show that the Randeck Maar was a typical maar lake with a rich flora and fauna. Based on all plant remains, the IPR vegetational analysis points towards subhumid sclerophyllous forests, suggesting seasonal drought. 380 taxa in all are known thus far, which are dominated by plants (168) and insects (79). The taxonomic re-evaluation combined with palaeoecological considerations allows for the reconstruction of a palaeoenvironmental model. In brief, three main sections can be differentiated for the habitats of the Randeck Maar lake system: (1) Deep- and open-water lake habitats with local and short-termed mass occurrences of insect larvae, amphibians, and/or gastropods, while fish are particularly scarce. The interpretation of the water chemistry is problematic because palaeoenvironmental

  8. A revision of the fossil genus Miocepphus and other Miocene Alcidae (Aves: Charadriiformes) of the Western North Atlantic Ocean

    OpenAIRE

    Wijnker, T.G.; Olson, S. L.

    2009-01-01

    This study reviews and describes all known fossils of Alcidae from the Miocene of the western North Atlantic. Because the majority of alcid fossils recovered from Miocene sediments are allied with the genus Miocepphus Wetmore, 1940, the genus is revised here. Three new species of Miocepphus are described: Miocepphus bohaskai and Miocepphus blowi from the Early to Late Miocene, and Miocepphus mergulellus of uncertain Neogene age but probably Miocene. A new genus and species, Pseudocepphus tere...

  9. Porosity evolution of upper Miocene reefs, Almeria Province, southern Spain

    Science.gov (United States)

    Armstrong, A.K.; Snavely, P.D.; Addicott, W.O.

    1980-01-01

    Sea cliffs 40 km east of Almeria, southeastern Spain, expose upper Miocene reefs and patch reefs of the Plomo formation. These reefs are formed of scleractinian corals, calcareous algae, and mollusks. The reef cores are as much as 65 m thick and several hundred meters wide. Fore-reef talus beds extend 1,300 m across and are 40 m thick. The reefs and reef breccias are composed of calcific dolomite. They lie on volcanic rocks that have a K-Ar date of 11.5 m.y. and in turn are overlain by the upper Miocene Vicar Formation. In the reef cores and fore-reef breccia beds, porosity is both primary and postdepositional. Primary porosity is of three types: (a) boring clam holes in the scleractinian coral heads, cemented reef rocks, and breccias; (b) intraparticle porosity within the corals, Halimeda plates, and vermetid worm tubes; and (c) interparticle porosity between bioclastic fragments and in the reef breccia. Postdepositional moldic porosity was formed by the solution of aragonitic material such as molluscan and coral fragments. The Plomo reef carbonate rocks have high porosity and permeability, and retain a great amount of depositional porosity. Pores range in size from a few micrometers to 30 cm. The extensive intercrystalline porosity and high permeability resulted from dolomitization of micritic matrix. Dolomite rhombs are between 10 and 30 μ across. More moldic porosity was formed by the dissolution of the calclte bioclasts. Some porosity reduction has occurred by incomplete and partial sparry calcite infilling of interparticular, moldic, and intercrystalline voids. The high porosity and permeability of these reefs make them important targets for petroleum exploration in the western Mediterranean off southern Spain. In these offshore areas in the subsurface the volcanic ridge and the Plomo reef complex are locally onlapped or overlapped by 350 m or more of Miocene(?) and Pliocene fine-grained sedimentary rocks. The possibility exists that the buried Plomo reef

  10. Miocene tectonism and the separation of cis- and trans-Andean river basins: Evidence from Neotropical fishes

    Science.gov (United States)

    Albert, James S.; Lovejoy, Nathan R.; Crampton, William G. R.

    2006-03-01

    Maracaibo and trans-Andean Magdalena basins. The compound origin of the Maracaibo ichthyofauna may be due to partial extinction of cis-Andean taxa that resulted from a marine incursion in the Late Miocene and subsequent invasion by congeners from the adjacent Magdalena Basin. In combination, the pooled data on species phylogenies and distributions suggest that the origins of the trans-Andean freshwater fish fauna predate the Miocene tectonic events that dissected the landscape. Among families of freshwater teleosts from northwestern South America, species diversity is significantly correlated with a minimum number of cis-/ trans-Andean clades, which indicates that the relative species diversity and biogeographic distributions of Amazonian fishes were effectively modern by the late Middle Miocene. The diverse taxonomic composition of the trans-Andean ichthyofauna further suggests that Miocene tectonism fragmented the entire aquatic fauna of northwestern South America, leaving a clear signal on all major taxa.

  11. Tectono-sedimentary constraints to the Oligocene-to-Miocene evolution of the Peloritani thrust belt (NE Sicily)

    Science.gov (United States)

    Giunta, G.; Nigro, F.

    1999-12-01

    proximal-to-distal (Early Miocene) Stilo-Capo d'Orlando facies on the constructing mobile belt; and (g) the presence of various thrust-faults, distinguished in a sequential order. The collected data allow us to hypothesise that the Oligo-Miocene tectono-sedimentary history was characterised by a foredeep with a deforming internal flank, probably lying in onlap on the constructing tectonic edifice (Frazzanò-lower Stilo-Capo d'Orlando Fms), and then deformed and covered by a piggy-back like sequence (middle-upper Stilo-Capo d'Orlando Fm), which was subsequently also deformed. The tectono-sedimentary evolution of the Peloritani belt has been probably developed through a progressive migration towards the foreland of a foredeep-compressional front couple and the chain body. The thrust stack progressively incorporates terrigenous foredeep deposits and in turn carried piggy-back basins.

  12. Miocene amber inclusions from the Bitterfeld area. [German Democratic Republic

    Energy Technology Data Exchange (ETDEWEB)

    Barthel, M.; Hetzer, H.

    1982-07-01

    This paper presents color and black and white photographs enlarged from 1:10 to 1:100 of insect inclusions in amber from a new amber field located in a sandy-silty layer between two brown coal seams, the main Bitterfeld brown coal seam and the Breitenfeld brown coal seam. The amber is 22 million years old, which is 12 million years younger than Baltic amber. The brown coal seams are Miocene formations. The origin of the amber is resin from the Mesozoic conifer Cupressospermum saxonicum Mai. Insect inclusions are well preserved, 55 photographs are provided, showing samples of mosquitoes, spiders, beetles, flies and other insects, from insect groups Arachnida, Myriapoda, and Hexapoda. Each insect sample from the inclusions is described in detail by scientists from the Museum of Natural History in Berlin. Infrared spectrograms of different amber pieces are also analyzed and aspects of amber genesis in the Bitterfeld area are discussed.

  13. Aliphatic biological markers in Miocene Maritz-Iztok lignite, Bulgaria

    Energy Technology Data Exchange (ETDEWEB)

    Stefanova, M.; Magnier, C. [Bulgarian Academy of Sciences, Sofia (Bulgaria). Inst. of Organic Chemistry

    1997-12-31

    Chromatographic separation and mass spectral studies of bitumens extracted from lithotypes (humovitrain, xylain, liptain and humoclarain) from the Miocene Maritza-Iztok lignite reveal the following: (1) A preponderance of the {alpha}-phyllocladane skeleton over the pimaranes/abietanes. The variety of tricyclic diterpanes confirms that the generation biota included gymnosperms; (2) The presence of dicotyledonous angiosperms in the generation biota is indicated by the occurrence of widely distributed des-A-lupane structure; (3) The dominance of terpanes over steranes confirms the prevailing contribution of terrigenous input; (4) The preponderance of C{sub 27{beta}} hopane and the presence {beta}{beta} hopanes indicates a low degree of thermal maturation. 23 refs., 6 figs., 4 tabs.

  14. Late Miocene Hydrological Change in the Indus River Catchment

    Science.gov (United States)

    Liddy, H.; Feakins, S. J.; Clift, P. D.; Tauxe, L.; Kulhanek, D. K.; Scardia, G.; Warny, S.; Bendle, J. A.; Galy, V.; Zhou, P.; Science Party, E.

    2016-12-01

    The cause of the late Miocene proliferation of C4 grasslands in the Indo-Asian region is a long-standing question. Terrestrial records suggest that changes in regional hydrological processes drove changes in C4 plant expansion. However, part of the ambiguity lies in the geographic extent of existing proxy records as well as the particular aspect of hydrology that they record. Therefore a better understanding of the hydrological influence on C4 expansion requires the direct reconstruction of precipitation changes. Turbidite sedimentation in the Indus Fan captures the history of the terrestrial environment and erosional change in the Indus catchment. With Indus Fan sediments from IODP Expedition 355, we resolve hydrological change in this region using geochemical (both inorganic and organic) and pollen approaches. Provenance analysis using Nd isotopes verifies that changes in hydrology occurred independently of changes in sediment sourcing prior to 6 Ma. Therefore, we infer that shifts in plant wax hydrogen isotopes (up to 60‰) after 8.3 Ma and 7 Ma reflect changes in the dominant moisture source region (the Indian Ocean versus the Mediterranean and other inland seas). Vegetation also tracks hydrology: pollen and plant wax carbon isotopes (including n-alkanoic acid C28-C34 and n-alkane C27-C35) suggest that C4 grassland was present in the Indus floodplains prior 8.3 Ma and expanded after 7 Ma. The early 10 Ma C4 expansion is observed in other regions surrounding the Arabian Sea at this time and the later C4 expansion ( 7-6 Ma) occurs coeval records from the Siwalik Formation of the Himalayan foreland and Bengal Fan sediments. New evidence from plant wax hydrogen isotopes suggests that changing precipitation triggered ecological changes in the Indus catchment during the late Miocene.

  15. Gulf of Mexico miocene CO₂ site characterization mega transect

    Energy Technology Data Exchange (ETDEWEB)

    Meckel, Timothy [Univ. of Austin, Austin, TX (United Staes); Trevino, Ramon [Univ. of Austin, Austin, TX (United Staes)

    2014-12-01

    This project characterized the Miocene-age sub-seafloor stratigraphy in the near-offshore portion of the Gulf of Mexico adjacent to the Texas coast. The large number of industrial sources of carbon dioxide (CO₂) in coastal counties and the high density of onshore urbanization and environmentally sensitive areas make this offshore region extremely attractive for long-term storage of carbon dioxide emissions from industrial sources (CCS). The study leverages dense existing geologic data from decades of hydrocarbon exploration in and around the study area to characterize the regional geology for suitability and storage capacity. Primary products of the study include: regional static storage capacity estimates, sequestration “leads” and prospects with associated dynamic capacity estimates, experimental studies of CO₂-brine-rock interaction, best practices for site characterization, a large-format ‘Atlas’ of sequestration for the study area, and characterization of potential fluid migration pathways for reducing storage risks utilizing novel high-resolution 3D (HR3D) seismic surveys. In addition, three subcontracted studies address source-to-sink matching optimization, offshore well bore management and environmental aspects. The various geologic data and interpretations are integrated and summarized in a series of cross-sections and maps, which represent a primary resource for any near-term commercial deployment of CCS in the area. The regional study characterized and mapped important geologic features (e.g., Clemente-Tomas fault zone, the regionally extensive Marginulina A and Amphistegina B confining systems, etc.) that provided an important context for regional static capacity estimates and specific sequestration prospects of the study. A static capacity estimate of the majority of the Study area (14,467 mi2) was estimated at 86 metric Gigatonnes. While local capacity estimates are likely to be lower due to reservoir-scale characteristics, the

  16. Gulf of Mexico miocene CO₂ site characterization mega transect

    Energy Technology Data Exchange (ETDEWEB)

    Meckel, Timothy [Univ. of Austin, Austin, TX (United Staes); Trevino, Ramon [Univ. of Austin, Austin, TX (United Staes)

    2014-09-30

    This project characterized the Miocene-age sub-seafloor stratigraphy in the near-offshore portion of the Gulf of Mexico adjacent to the Texas coast. The large number of industrial sources of carbon dioxide (CO₂) in coastal counties and the high density of onshore urbanization and environmentally sensitive areas make this offshore region extremely attractive for long-term storage of carbon dioxide emissions from industrial sources (CCS). The study leverages dense existing geologic data from decades of hydrocarbon exploration in and around the study area to characterize the regional geology for suitability and storage capacity. Primary products of the study include: regional static storage capacity estimates, sequestration “leads” and prospects with associated dynamic capacity estimates, experimental studies of CO₂-brine-rock interaction, best practices for site characterization, a large-format ‘Atlas’ of sequestration for the study area, and characterization of potential fluid migration pathways for reducing storage risks utilizing novel high-resolution 3D (HR3D) seismic surveys. In addition, three subcontracted studies address source-to-sink matching optimization, offshore well bore management and environmental aspects. The various geologic data and interpretations are integrated and summarized in a series of cross-sections and maps, which represent a primary resource for any near-term commercial deployment of CCS in the area. The regional study characterized and mapped important geologic features (e.g., Clemente-Tomas fault zone, the regionally extensive Marginulina A and Amphistegina B confining systems, etc.) that provided an important context for regional static capacity estimates and specific sequestration prospects of the study. A static capacity estimate of the majority of the Study area (14,467 mi2) was estimated at 86 metric Gigatonnes. While local capacity estimates are likely to be lower due to reservoir-scale characteristics, the

  17. Geochemistry of phosphatic-shales and associated authigenic minerals of the Miocene Monterey Formation: Implications for paragenetic evolution

    Science.gov (United States)

    Sandoval, A.; Loyd, S. J.

    2016-12-01

    The Monterey Formation is a petroleum source and reservoir rock in California that was deposited in several basins during the tectonically-active Middle Miocene. The middle carbonaceous marl member of the Monterey Formation contains intervals of phosphatic-shales that are rhythmically cemented by dolomite as layers and concretions. Diagenetic minerals can form as the result of organic matter remineralization facilitated by microbes utilizing oxygen, nitrate, iron (III), sulfate and fermentation products as electron acceptors. Precipitation of phosphate and carbonate minerals tends to occur in suboxic-anoxic sediments, generally experiencing sulfate reduction, where degradation of organic matter yields alkalinity, sulfide and phosphate ions. Here, we present sulfur and carbon geochemical data in order to better characterize the conditions that led to the precipitation of phosphorous-rich minerals (e.g., carbonate-fluorapatite (CFA)) and dolomite that occur in close stratigraphic proximity. These data include concentration of CFA-associated sulfate, carbonate associated sulfate (CAS) and the respective δ°S values. The concentration of inorganic/organic carbon and associated δC values have been determined for CFA, dolomite and the host-shale, in order to further characterize the diagenetic environment of precipitation. These data indicate that authigenesis occurred in pore waters influenced by multiple microbial reactions, including respiration and methanogenesis reactions, and ultimately highlight the complexity of the Monterey diagenetic environment.

  18. Ostracoda (Arthropoda, Crustacea) in a Miocene oxygen minimum zone, Trinidad, West Indies: A test of the Platycopid Signal Hypothesis

    Science.gov (United States)

    Wilson, Brent; Coimbra, João C.; Hayek, Lee-Ann C.

    2014-10-01

    Studies of Recent ostracodes around the area of South America shed little light on the paleoenvironmental interpretation of Miocene assemblages. Consequently, interpretations of the Miocene ostracode assemblages must be supplemented using evidence from better documented taxa. Benthic foraminifera in samples from the Lower to Middle Miocene Brasso Formation at Brasso Village, Trinidad, have previously been used to distinguish three sample groupings (Beneath, Within and Above) around an oxygen minimum zone (OMZ), this being a layer of water within which dissolved oxygen concentrations can be as low as 0.1-1.0 mL/L. Using these same samples and the foraminiferal assemblage demarcations relative to the OMZ, this paper examines the associated and rich ostracode fauna of the Brasso Formation. The mean recovery of ostracode valves per sample was approximately three times greater in the Within OMZ sample group than in either of the Beneath OMZ or Above OMZ groups, perhaps reflecting the exclusion of macro-predators from within the OMZ. Individual rarefaction of species richness S to N = 300 valves was conducted for each sample group. This showed that S did not differ between the sample groups, ranging from 22.4 to 24.8. We used all ostracode species to model group separation. Based upon the Mahalanobis' criterion, we obtained significant group separation using a model with four taxa: Munseyella ex gr. minuta, Argilloecia posterotruncata, Munseyella sp. and Xestoleberis sp., while a fifth, Argilloecia spp., provided a significant but minor increase in separation probabilities over all groups. The two most abundant species (Bradleya sp., Gangamocytheridea reticulata) were thus not the best species for detecting the OMZ. Platycopid ostracodes of the genus Cytherella were found throughout the section, rather than concentrated within the OMZ, which contradicts the Platycopid Signal Hypothesis that OMZs are characterized by platycopid dominance. The total distribution and

  19. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic.

    Science.gov (United States)

    Døssing, Arne; Japsen, Peter; Watts, Anthony; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans

    2016-04-01

    Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone - East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of syn-rift deposition in the deep-sea basins and onset of: (i) thermo-mechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf-progradation on the NE Greenland margin. Given an estimated middle-to-late Miocene (~15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the East and West Greenland margins. The correlation between margin uplift and plate-motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.

  20. Isotopic evidence for complex microbial ecosystems in the phosphate-rich interval of the Miocene Monterey Formation

    Science.gov (United States)

    Theiling, B. P.; Coleman, M. L.

    2014-12-01

    The middle Miocene Monterey Formation has long been debated as a crucial global sink for organic carbon that led to global cooling. We evaluate proxies for the microbial ecosystem to investigate organic carbon burial within the phosphate-rich interval of the Monterey Formation at Naples Beach, California by combining mineralogical evidence with δ34S analyses of carbonate associated sulfate (CAS). All δ34S are below Miocene seawater values (~22‰, VCDT) and range from +12.2‰ to +18.5‰. δ34SCAS Sulfate reducing bacteria then consume the excess, residual sulfate, generating free H2S in the absence of available iron. H2S diffuses upward towards the sediment-water interface (an oxic-suboxic mixing zone) where H2S is oxidized to 34S-depleted sulfate either aerobically or coupled to nitrate reduction, and lowers seawater pH. The high phosphate content and low carbonate content of this interval of the Monterey Formation supports a model of precipitation in lower pH waters. Assuming a -40‰ fractionation of δ34S due to microbial sulfate reduction, we estimate at least a 10%-20% contribution of sulfate from sulfide oxidation to marine porewater sulfate. These results suggest that the phosphate-rich interval of the Monterey Formation housed a complex suite of iron and sulfate reducing bacteria as well as sulfide oxidizing bacteria, suggesting that significant organic carbon was consumed during early diagenesis and may account for low organic carbon content described in previous studies.

  1. Sequence stratigraphic model and Evolution of the Channelized depositional systems during Miocene in Ulleung Basin southeastern margin, East Sea

    Science.gov (United States)

    Baek, Y.; Lee, S. H.; Kim, H. J.; Jou, H. T.

    2015-12-01

    The southwestern margin of Ulleung Basin consists of broad and gentle slope continental shelf and shelf break. The sedimentary succession of the continental shelf is divided into nine sequences (S1-S9). The sedimentary succession is consists of the lower pro-graded sequences (from S2 to S6; 16.5-8.2 Ma) and upper channelized depositional sequences (S7 and S8; 8.2-5.5 Ma) in the Miocene. It progressively thickens northeast ward, suggesting a significant contribution of sediments into the basin margin. The channelized depositional system of S7 is divided into two subunits in which lower boundaries of each subunit are indicated by erosional truncation and channel incision. The underlying subunit 1 has two main streams; the progressive directions are to the NNE (a) and ENE (b). The main stream of subunit 2, developed after giving rise to the low-relief topography of the subunit 1, is only overlapping main stream (a) of subunit 1. The gentle sloped proximal-middle zone has different internal reflector, subunit 1 is characterized by parallel to chaotic reflections, whereas the subunit 2 is dominated by continuous and inclined reflectors, which can be interpreted that sediments supply is increase in subunit 2 than subunit 1. The steep sloped distal zone of channelized depositional systems connected the shelf break. The slope gradient is more slanted subunit 2 than 1. The internal structures are dis-continuous and inclined chaotic internal reflectors, which is interpreted mass transport deposits (MTDs). The slope failures commonly start near the shelf break, but some others are connected perpendicular to the main stream. The upper boundary of subunit 2 is truncated by transgressive surface. The stacking pattern of sequence 7 suggests the type-1 sequence controlled by sea level change, and the internal erosional surface in the channelized depositional systems can be interpreted that formed by tectonic or relative sea level flocculation during late Miocene in East Sea.

  2. Climate variations in the late Miocene - early Pliocene in the Black Sea region (Taman peninsula) inferred from palynological analyses.

    Science.gov (United States)

    Grundan, Ekaterina; Kürschner, Wolfram; Krijgsman, Wout

    2017-04-01

    A palynological study of Neogene sediments from the cape "Zhelezny Rog" (Taman peninsula, the Black Sea area) was carried out as part of integrated micropaleontological, lithological and paleomagnetic research. The Neogene section of the cape "Zhelezny Rog" (the Zhelezny Rog section) is one of the most representative Upper Miocene to Lower Pliocene succession of Eastern Paratethys. The section covers the Sarmatian, Maeotian, Pontian (upper Miocene) and Kimmerian (lower Pliocene) local stages. One hundred and eighteen samples were selected from the Zhelezny rog section for quantitative palynological analysis. Using PCA analysis and additional proxy such as "steppe index", art/chen and poa/ast ratios the regional climate history was reconstructed. The Early Maeotian is characterized by a warm, warm-temperate climate on the background of relatively high humidity. During the Late Maeotian it became colder and dryer. The coldest and driest conditions during the Maeotian correspond to the middle part of the Late Maeotian. There were a high number of steppe elements (as Artemisia) and low amount of thermophilous ones. Climate of the end of the Maeotian was characterized by warmer and wetter conditions. In the beginning of the Pontian there was a cooling trend, as evidenced by the decreasing thermophilous elements and the increasing high-latitude trees. Most significant changes were found within the Pontian-Kimmerian boundary beds. This level is characterized by decreasing of thermophilous elements, increasing of cool-temperate pollen and Sphagnum spores that are considered as an evidence of a temperature decrease in the background of high humidity conditions. The results will be discussed and correlated to Neogene global climate trends.

  3. Temporal size changes of Miocene planktonic foraminifera Paragloborotalia siakensis in the eastern Equatorial Pacific associated with Mi-events

    Science.gov (United States)

    Okada, H.; Hayashi, H.

    2013-12-01

    Temporal changes in test size of planktonic foraminifera have been variously studied as a key for knowing evolution related to paleoceanographic changes. With respect to recent studies, rapid size reducing ('dwarfing') in several species have been observed around the last occurrence horizon. Generically, size changes of calcareous nannofossils have been used for global correlation. However, there are few previous studies of such temporal size changes for Miocene planktonic foraminifera. Paragloborotalia siakensis (LeRoy, 1939) is one of important index species in the middle Miocene. The upper boundary of planktonic foraminieral Zone N.14 is defined by the top occurrence of this species. It is a well known fact that P. siakensis is a dominant species in the tropical high-productivity area such as the eastern equatorial Pacific. The aims of this study are to reveal size changes of P. siakensis collected from IODP Site U1338 in the eastern equatorial Pacific and to correlate the size changes with paleoceanographic events. We measured maximum length of P. siakensis (50-200 individuals for each horizon) at approximately every 0.1 million years from 16.0 to 10.5 Ma. At the same time, we also conducted morphometric analyses of selected five horizons (14.96 Ma, 14.03 Ma, 13.00 Ma, 12.29 Ma and 11.11 Ma) by means of image analysis software (ImageJ). According to the morphometric analyses, the population from Site U1338 should be compared with the holotype of P. siakensis. The maximum length of P. siakensis shows significant reducing ('dwarfing') at cooling intervals inferred by previous studies based on alkenone and isotope data. It is possible to say that dwarfing of P. siakensis at Site U1338 might be induced by shallowing of the thermocline in the eastern equatorial Pacific.

  4. Developing a High-Resolution Sequence Stratigraphic Framework for Upper Lower Miocene Strata (18-16 Ma) From the ANDRILL AND-2A Drillcore, Southern McMurdo Sound Project, Antarctica

    Science.gov (United States)

    Koss, H. C.; Pekar, S. F.

    2008-12-01

    A high resolution sequence stratigraphic framework was developed for the upper lower Miocene (18-16 Ma) in Southern McMurdo Sound. Southern McMurdo Sound Project (SMS) of the ANDRILL Program completed the AND-2A drillcore (77° 45.488 S; 165° 16.613 E) from a floating sea-ice platform over approximately 380 meters of water, reaching a total depth of 1138.54 mbsf, during the 2007 austral spring/summer. One objective of the SMS Project was to recover a history of ice-proximal paleoenvironmental variation during the early to middle Miocene, which includes the Early Miocene Climatic Optimum (EMCO, 17.8-16.1 Ma), the Middle Miocene Climatic Optimum (16.0-14.2 Ma), and the climatic cooling that followed. The AND-2A drillcore recovered several distinct stratigraphic intervals including a thick middle Miocene section (400 to 223 mbsf) and an expanded upper lower Miocene section (700-400 mbsf) that includes the Early Miocene Climatic Optimum, with the latter being the focus of this study. Three motifs of stratigraphic stacking patterns were recognized in the AND-2A borehole of which two are observed between 700-400 mbsf. Motif 2, which dominates above 523 mbsf, is characterized by a sharp-based conglomerate and sandstone overlain by stratified, clast-poor diamictite. This is overlain by bioturbated clayey siltstone with interlaminated sandstone and siltstone above it. This is overlain by diamictite. Motif 3 is only recognized below 523 mbsf and is characterized by a sharp-based conglomerate and clast-rich sandstone overlain by stratified diamictite which grades upward into interlaminated siltstone and very fine sandstone with diamictite interbeds. This is overlain by fossiliferous diamictite. Each motif of stratigraphic stacking is capped with a sharp-based conglomerate. A minimum of 15 cycles of stratigraphic stacking, occurring at roughly 20-meter intervals between 700 and 400 mbsf, are recognized in core photographs and observations made on-ice during core description

  5. Albanerpetontid amphibian (Lissamphibia: Albanerpetontidae from the Early Miocene of the locality Merkur–North (north-west of the Czech Republic: data and a description of a new material

    Directory of Open Access Journals (Sweden)

    Andrej Čerňanský

    2010-01-01

    Full Text Available This paper deals with the first description of an albanerpetontid amphibian from the Early Miocene locality Merkur–North. The material comes from grey calcareous marls at the base of the so-called “Main Brown Coal Seam”. The marls are interpreted as reworked volcanic ash (Most Formation. The genus Albanerpeton was already known from this locality, but the material has never been described or illustrated. The new material of dentaries extends our knowledge about the state of the Merkur–North population. The extinct clade of Albanerpetontidae represents primarily Laurasian lissamphibians known from the Middle Jurassic to Pliocene periods. The Late Oligocene to Early Miocene albanerpetontids of central Europe belong to the species A. inexpectatum. The material described here allocated a big similarity closed to this species.

  6. Palynological and palaeobotanical investigations in the Miocene of the Yatağan basin, Turkey: High-resolution taxonomy and biostratigraphy

    Science.gov (United States)

    Bouchal, Johannes Martin; Güner, Tuncay H.; Denk, Thomas

    2015-04-01

    The subject of this study is the palynology (biostratigraphic and taxonomic) and the plant remains of the lignite strip mines of Eskihisar, Salihpasalar, and Tinaz (Muğla province, western Turkey). In the Yatağan basin two Miocene to Pliocene formations are present, the Eskihisar Formation (early to middle Miocene) and the Yatağan Formation (late Miocene to early Pliocene). Both formations represent river and lake deposits consisting mainly of conglomerate, sandstone, claystone, limestone, tuffite, and intercalated lignite; the thickest, actively mined lignite seams occur in the Sekköy member of the Eskihisar Formation. Previous palynological studies of the palynoflora of the Yatağan basin mainly focussed on its biostratigraphic and palaeoclimatic significance, using conventional morphological nomenclature and light microscopy (LM). In this study the "single grain method" is applied. Using this method, the same individual pollen grains are investigated by using both LM and scanning electron microscopy (SEM). The resulting high-resolution pictographs enable a much higher taxonomic resolution. The studied palynoflora is very rich and taxonomically diverse. Cryptogams are represented by more than ten spore morphotypes of at least three families (Osmundaceae, Pteridaceae, Polypodiaceae). Gymnosperm pollen is dominated by Cupressaceae, Gnetales (Ephedra), and Pinaceae (Cathaya, Keteleeria, Pinus). Angiosperm pollen can be assigned to 57 different genera belonging to Poaceae, Typhaceae, Altingiaceae, Amaranthaceae (Chenopodieae), Anacardiaceae, Apiaceae (three types), Asteraceae (Asteroideae, Cichoriodeae), Betulaceae (Alnus, Betula, Carpinus, Ostrya) Buxaceae, Campanulaceae, Caprifoliaceae (Lonicera), Caryophyllaceae, Dipsacaceae, Eucommiaceae, Euphorbiaceae, Fabaceae, Fagaceae (Fagus, Quercus, Trigonobalanopsis) Geraniaceae, Juglandaceae, Linaceae, Malvaceae (Tilia), Myricaceae, Oleaceae (four different types), Plumbaginaceae, Polygonaceae (Rumex), Rosaceae

  7. Miocene alluvial fan-alkaline playa lignite-trona bearing deposits from an inverted basin in Anatolia: sedimentology and tectonic controls on deposition

    Science.gov (United States)

    İnci, Uǧur

    1991-04-01

    During the Middle through Late Miocene, over 1200 m of clastics, carbonates and evaporites accumulated in the depositional basin situated in northwestern Ankara province of Central Anatolia. Detailed stratigraphic and sedimentological analyses of the exposed sequence exhibits three major facies: (1) lower alluvial, (2) upper alluvial, and (3) lacustrine. The lower alluvial facies consists primarily of volcaniclastic debris-flow, boulder and channel conglomerate, sandstone, siltstone, mudstone and two lignite horizons. These rock assemblages were deposited in alluvial fans and a braided-river system. The lower and upper lignite seams were laid down in swamps and lake-margin mud-flat environments associated with this river system. The upper alluvial facies is characterized by red conglomerate, fine-grained and cross-bedded sandstone, mudstone and calcareous mudstone units. The dominant depositional environments are interpreted to be alluvial fan, braided-river, and mud-flat. The base of the lacustrine deposits interfingers with the lower alluvial facies and consists of dolomitic claystone, bituminous shale, trona and intraformational conglomerate lithofacies. The sedimentary features of the dolomitic claystone and trona lithofacies suggest deposition in a playa-lake type environment. The bituminous shale is a transgressive deposit laid down in a shallow, but expanded lake environment. Sedimentological and structural characteristics of the intraformational conglomerate lithofacies indicate synsedimentary tectonism, intrabasinal erosion, redeposition and sediment selection toward the deposition centre of the lake environment. The green claystone lithofacies has three units: (a) the claystone-bedded chert-analcitized tuff alternation and siliceous carbonate lithofacies of the lacustrine system, deposited in a perennial lake environment; (b) montmorillonitic olive-green claystone containing mud-cracks, ripple mark and desiccation cracks filled by gypsum, deposited in a

  8. Sedimentological and palaeoecological integrated analysis of a Miocene channelized carbonate margin, Matese Mountains, Southern Apennines, Italy

    Science.gov (United States)

    Bassi, Davide; Carannante, Gabriele; Checconi, Alessio; Simone, Lucia; Vigorito, Mario

    2010-10-01

    Lower-Middle Miocene temperate marine carbonates occur in the Matese Mountains, Southern Apennines (Italy). These carbonates formed in an open-shelf depositional system with an uneven margin, 10 km long and up to 6 km wide. Shelf margin morphology shows multiple submarine channelized carbonate deposits which are dominated by coralline red algae and subordinate bryozoans. Two main channel networks (Pietraroia and Regia Piana channels) with their sedimentary bodies were analysed. The studied submarine channels grew by sediment accumulation as prograding bodies on a tectonic modelled substrate. Shallow-water rhodalgal skeletal debris, from moderately re-mobilized up to significantly re-worked, built up the complex channel-system fills in which sedimentary lenses overlapped and partially amalgamated one another when they were still unlithified. The early channelized succession is characterized by parautochthonous bryozoan floatstone and rhodolith/bryozoan floatstone representing soft muddy substrates in a low water turbulence and high turbidity setting. The rhodoliths, dominated by melobesioid coralline algae, are sub-discoidal and sub-spheroidal in shape with a characteristic loosely-packed inner arrangement. These sediments, whose latter portion underwent submarine diagenetic processes (incipient to evoluted hard-grounds), were eroded and successively covered by shallower water gravitative deposits constituted by rhodolith floatstone/rudstone. Their rhodoliths, constituted by melobesioids, mastophoroids and subordinate lithophylloids and sporolithaceans, are mainly spheroidal/sub-spheroidal in shape with subordinate sub-discoidal specimens, with massive and laminar inner arrangements. The lack in early lithification can be drawn back to the physiography of the channelized shelf margin, to the active tectonic as well as to the temperate-type carbonate dominant biogenic components. The depositional surface profile and local hydrodynamic conditions were the major

  9. Oil and Gas Wells in Southern Louisiana that Penetrated the Lower Miocene 1 Sequence

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The drilling history documents oil and gas wells in the Lower Miocene 1 sequence as a whole and in 10-year intervals. The wells included in this interval are...

  10. Oil and Gas Wells in Southern Louisiana that Penetrated the Upper Miocene Sequence

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The drilling history documents oil and gas wells in the Upper Miocene sequence as a whole and in 10-year intervals. The wells included in this interval are...

  11. Oil and Gas Wells in Southern Louisiana that Penetrated the Lower Miocene 2 Sequence

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The drilling history documents oil and gas wells in the Lower Miocene 2 sequence as a whole and in 10-year intervals. The wells included in this interval are...

  12. Generalized Representation of the Oil and Gas Producing Areas from the Miocene in Southern Louisiana

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — For each of the four Miocene sequences, polygons representing producing areas within fields were created by constructing a grid of ¼ sq. mi. cells and proximal...

  13. Aphotic zone carbonate production on a Miocene ramp, Central Apennines, Italy

    Science.gov (United States)

    Corda, Laura; Brandano, Marco

    2003-09-01

    The lower Miocene Latium-Abruzzi platform was a low-angle ramp that developed under tropical-to-subtropical conditions, but was dominated by bryomol and rhodalgal sediment associations. The Aquitanian to Serravallian sequence described here paraconformably overlies the Cretaceous limestones. It consists of a lowstand systems tract, a transgressive systems tract and a highstand systems tract. Based on facies analysis and on the light dependence of biotic associations, the ramp is divided into three parts: an inner ramp, a middle ramp and an outer ramp. The inner ramp facies are represented by a few metres of coral framestone, rhodolith floatstone-rudstone and balanid macroids floatstone without wave-related structures. The middle ramp consists of structureless bioclastic grainstone to packstone, floatstone and rudstone with rhodoliths and larger foraminifera. The outer ramp facies—proximal sector—are composed of crudely stratified bryozoan-dominated packstone to floatstone which extend over the whole platform. The outer ramp facies—intermediate sector—are represented by wackestone, packstone and rarely grainstone with foraminifera and echinoid fragments. The final depositional profile of the ramp was strongly influenced by the main organisms producing sediment. During the lowstand, the resulting profile is a ramp type. During the transgressive phase, the rapid spreading of the outer ramp facies belt, as a consequence of the enhanced productivity of the light-independent biota, is believed to be promoted by a change from oligotrophic to eutrophic conditions. Climate and/or tectonics are presumed to have played an important role in continental runoff and then in the nutrients delivery. During the highstand phase, the system returns to rates of production uniform throughout the platform. The high rates of carbonate production occurring in the aphotic zone are quite unusual in tropical settings and represent a provocative trend in apparent contrast with the

  14. The history of Post-Miocene sea level change: Inferences from stratigraphic modeling of Enewetak Atoll

    Science.gov (United States)

    Quinn, Terrence M.

    1991-04-01

    The history of post-Miocene sea level change has been investigated using a quantitative, one-dimensional stratigraphic forward model. The stratigraphic model produces synthetic stratigraphies, including mineralogy and sediment age versus depth, in response to changes in sea level, subsidence, sedimentation, and diagenesis. Model outputs, using sea level curves inferred from passive margin sequence stratigraphy and deep-sea foraminiferal oxygen isotope stratigraphy, were compared to the post-Miocene stratigraphy of Enewetak Atoll. Modeling results support high-frequency (104 to 105 years) fluctuations of post-Miocene sea level. Post-Miocene sea level elevations significantly greater than modern sea level elevation are not easily reconciled with the stratigraphy of Enewetak Atoll. Model/data fit is maximized when a rapid subsidence rate for Enewetak Atoll is used. Alternatively, model/data fit may be maximized using a lower subsidence rate for Enewetak and having post-Miocene sea level elevations significantly lower than modem sea level elevation. Given the present state of knowledge, much work is still needed to accurately decipher the record of post-Miocene sea level change.

  15. Miocene fossil plants from Bukpyeong Formation of Bukpyeong Basin in Donghae City, Gangwon-do Province, Korea and their palaeoenvironmental implications

    Science.gov (United States)

    Jeong, Eun Kyoung; Kim, Hyun Joo; Uemura, Kazuhiko; Kim, Kyungsik

    2016-04-01

    The Tertiary sedimentary basins are distributed along the eastern coast of Korean Peninsula. The northernmost Bukpyeong Basin is located in Donghae City, Gangwon-do Province, Korea. The Bukpyeong Basin consists of Bukpyeong Formation and Dogyeongri Conglomerate in ascending order. The geologic age of Bukpyeong Formation has been suggested as from Early Miocene to Pliocene, In particular, Lee & Jacobs (2010) suggested the age of the Bukpyeong Formation as late Early Miocene to early Middle Miocene based on the fossils of rodent teeth. Sedimentary environment has been thought as mainly fresh water lake and/or swamp partly influenced by marine water. Lately, new outcrops of Bukpyeong Formation were exposed during the road construction and abundant fossil plants were yielded from the newly exposed outcrops. As a result of palaeobotanical studies 47 genera of 23 families have been found. This fossil plant assemblage is composed of gymnosperms and dicotyledons. Gymnosperms were Pinaceae (e.g., Pinus, Tsuga), Sciadopityaceae (e.g., Sciadopitys) and Cupressaceae with well-preserved Metasequoia cones. Dicotyledons were deciduous trees such as Betulaceae (e.g., Alnus, Carpinus) and Sapindaceae (e.g., Acer, Aesculus, Sapindus), and evergreen trees such as evergreen Fagaceae (e.g., Castanopsis, Cyclobalanopsis, Pasania) and Lauraceae (e.g., Cinnamomum, Machilus). In addition, fresh water plants such as Hemitrapa (Lytraceae) and Ceratophyllum (Ceratophyllaceae) were also found. The fossil plant assemblage of the Bukpyeong Formation supported the freshwater environment implied by previous studies. It can be suggested that the palaeoflora of Bukpyeong Formation was oak-laurel forest with broad-leaved evergreen and deciduous trees accompanying commonly by conifers of Pinaceae and Cupressaceae under warm-temperate climate.

  16. Miocene reef facies of Pelagian Block, central Mediterranean

    Energy Technology Data Exchange (ETDEWEB)

    Pedley, H.M.

    1988-01-01

    Miocene reefs outcrop in the Maltese Islands, southeastern Sicily, and the pelagian island of Lampedusa. Several rapid eustatic sea level fluctuations affected these late Tortonian-early Messinian build-ups; normal salinities appear to have been maintained during these events. Substrate, topography, sedimentation rate, and tectonic/eustatic events controlled reef development, which can be grouped into three settings: The most stable situation, the oldest Maltese and southeastern Sicilian reefs, has a ramp profile 15-30 km wide. The outermost zone consists of a broad belt of the large benthic foraminifer Heterostegina (compared with the underyling Oligocene beds rich in Lepidocyclina). Coralline algal carbonates, commonly rhodolitic, form a broad biostromal up-ramp association, kilometers in width, which commonly extends into the shallowest parts of the shelf. Scattered across the shallower ramp areas, in water depths generally less than 10 m, are coral-algal patch reefs, rarely larger than 20-50 m in diameter, commonly with truncated tops, and dominated by crustose coralline algae and the corals Porites and Tarbellastraea.

  17. Peatmoss (Sphagnum) diversification associated with Miocene Northern Hemisphere climatic cooling?

    Science.gov (United States)

    Shaw, A Jonathan; Devos, Nicolas; Cox, Cymon J; Boles, Sandra B; Shaw, Blanka; Buchanan, Alex M; Cave, Lynette; Seppelt, Rodney

    2010-06-01

    Global climate changes sometimes spark biological radiations that can feed back to effect significant ecological impacts. Northern Hemisphere peatlands dominated by living and dead peatmosses (Sphagnum) harbor almost 30% of the global soil carbon pool and have functioned as a net carbon sink throughout the Holocene, and probably since the late Tertiary. Before that time, northern latitudes were dominated by tropical and temperate plant groups and ecosystems. Phylogenetic analyses of mosses (phylum Bryophyta) based on nucleotide sequences from the plastid, mitochondrial, and nuclear genomes indicate that most species of Sphagnum are of recent origin (ca. <20 Ma). Sphagnum species are not only well-adapted to boreal peatlands, they create the conditions that promote development of peatlands. The recent radiation that gave rise to extant diversity of peatmosses is temporally associated with Miocene climatic cooling in the Northern Hemisphere. The evolution of Sphagnum has had profound influences on global biogeochemistry because of the unique biochemical, physiological, and morphological features of these plants, both while alive and after death.

  18. Miocene drowning of temperate (Foramol) carbonate platform: upper Miami Terrace

    Energy Technology Data Exchange (ETDEWEB)

    Carannante, G.; Simone, L.; Neumann, C.

    1986-05-01

    Oligocene neritic rocks dredged from 350 m on the upper Miami Terrace exhibit repeated phosphatization as well as a filled void system containing post-Burdigalian foraminifera. During drowning, a neritic hardground was subjected to both pelagic deposition (infills) and repeated marine exposure (borings, P-coatings, etc). The neritic grainstone-packstone contains large benthic foraminifera, red algae, bryozoans, pelecypods, ahermatypic corals, echinoids, and some planktonic foraminifera. This composition association is the Foramol type characteristic of temperate to subtropical neritic environments such as the present Mediterranean, Brazilian, and New Zealand shelves. These temperate sediments derive from the local biocoenose, and accumulate slowly in deep sheets of loose skeletal debris. They become relict seaward where they are often bored, corroded, stained, glauconitized, and cemented into hardgrounds. Locally, hemipelagic cover might produce a palimpsest sequence. Recent Foramol-type platforms are undergoing drowning. The Miami Terrace is compared to very similar Miocene Foramol-type platforms now exposed in the southern Apennines. Both are characterized by neritic sequences passing upward into hemipelagics, via a palimpsest interval marked by glauconitic, phosphatic, iron-stained grains often mineralized into hardgrounds. The drowning of the Miami Terrace hence coincided with and, the authors suppose, was a result of the shift from a rapid, oligotrophic, tropical accumulation to a slow, temperate, eutrophic carbonate accumulation caused in turn by a temporary paleo-oceanographic shift to cooler, richer, neritic conditions within the history of this now subtropical setting.

  19. A new calymmate mimosoid polyad from the Miocene of Argentina.

    Science.gov (United States)

    Caccavari; Barreda

    2000-05-01

    A palynomorph with an unequivocal relationship to the eight-grain polyads of the mimosoid genus Calliandra Benth., is described from the Miocene sediments of San Juan Province, Argentina. Comparison of the fossil palynomorph with polyads of the extant Calliandra species shows a resemblance to those which have one, highly specialized, appendiculate monad. The new palynomorph has a rudimentary appendix, apparently transitional in the path leading to the more highly developed appendiculate forms in the extant Calliandra group. This specialized polyad type is considered to be one of the most highly evolved forms in subfamily Mimosoideae. The closest affinity of the new fossil polyad is with the eight-grain calymmate polyads of Calliandra chilensis Benth., a species which has developed in the extra-tropical, xerophilous shrub, habitat of north-central Chile. The disappearance of Calliandra species in San Juan Province is thought to be related to the culmination of the Andean rising, and the consequent interruption to the Pacific Ocean climatic influence. This new discovery is the first fossil record of Calliandra for Argentina, as well as being the most southerly and the oldest. It reinforces the hypothesis of an early origin and diversification for the Leguminosae in Tropical America.

  20. The palaeoclimatic significance of Eurasian Giant Salamanders (Cryptobranchidae: Zaissanurus, Andrias) - indications for elevated humidity in Central Asia during global warm periods (Eocene, late Oligocene warming, Miocene Climate Optimum)

    Science.gov (United States)

    Vasilyan, Davit; Böhme, Madelaine; Winklhofer, Michael

    2010-05-01

    Cryptobranchids represent a group of large sized (up to 1.8 m) tailed amphibians known since the Middle Jurassic (Gao & Shubin 2003). Two species are living today in eastern Eurasia: Andrias davidianus (China) and A. japonicus (Japan). Cenozoic Eurasian fossil giant salamanders are known with two genera and two or three species from over 30 localities, ranging from the Late Eocene to the Early Pliocene (Böhme & Ilg 2003). The Late Eocene species Zaissanurus beliajevae is restricted to the Central Asian Zaissan Basin (SE-Kazakhstan, 50°N, 85°E), whereas the Late Oligocene to Early Pliocene species Andrias scheuchzeri is distributed from Central Europe to the Zaissan Basin. In the latter basin the species occur during two periods; the latest Oligocene and the late Early to early Middle Miocene (Chkhikvadse 1982). Andrias scheuchzeri is osteological indistinguishable from both recent species, indicating a similar ecology (Westfahl 1958). To investigate the palaeoclimatic significance of giant salamanders we analyzed the climate within the present-day distribution area and at selected fossil localities with independent palaeoclimate record. Our results indicate that fossil and recent Andrias species occur in humid areas where the mean annual precipitation reach over 900 mm (900 - 1.300 mm). As a working hypothesis (assuming a similar ecology of Andrias and Zaissanurus) we interpret occurrences of both fossil Eurasian giant salamanders as indicative for humid palaeoclimatic conditions. Based on this assumption the Late Eocene, the latest Oligocene (late Oligocene warming) and the late Early to early Middle Miocene (Miocene Climatic Optimum) of Central Asia (Zaissan Basin) are periods of elevated humidity, suggesting a direct (positive) relationship between global climate and Central Asian humidity evolution. Böhme M., Ilg A. 2003: fosFARbase, www.wahre-staerke.com/ Chkhikvadze V.M. 1982. On the finding of fossil Cryptobranchidae in the USSR and Mongolia. Vertebrata

  1. Structure and provenance of Late Cretaceous-Miocene sediments located near the NE Dinarides margin: Inferences from kinematics of orogenic building and subsequent extensional collapse

    Science.gov (United States)

    Stojadinovic, Uros; Matenco, Liviu; Andriessen, Paul; Toljić, Marinko; Rundić, Ljupko; Ducea, Mihai N.

    2017-07-01

    The NE part of the Dinarides Mountain chain, located near their junction with the Carpatho-Balkanides, is an area where sedimentary basins associated with the Neotethys subduction and collision are still exposed. We performed a provenance study, based on detrital fission track thermochronology combined with zircon Usbnd Pb magmatic geochronology, and existing studies of kinematics and exhumation. Our study shows rapid sedimentation in the trench and forearc basin overlying the upper European tectonic plate. A number of latest Cretaceous-Early Paleocene igneous provenance ages show a dominant magmatic source area, derived from a Late Cretaceous subduction-related arc. This arc shed short time lag sediments in the forearc and the trench system, possibly associated with focused exhumation in the Serbo-Macedonian margin. This was followed by burial of the trench sediments and a novel stage of Middle-Late Eocene exhumation driven by continued continental collision that had larger effects than previously thought. The collision was followed by Late Oligocene-Miocene exhumation of the former lower Adriatic plate along extensional detachments that reactivated the inherited collisional contact along the entire Dinarides margin. This event re-distributed sediments at short distances in the neighboring Miocene basins. Our study demonstrates that the Dinarides orogenic system is characterized by short lag times between exhumation and re-deposition, whereas the upper tectonic plate is significantly exhumed only during the final stages of collision. Such an exhumation pattern is not directly obvious from observing the overall geometry of the orogen.

  2. Oligocene sivaladapid primate from the Bugti Hills (Balochistan, Pakistan) bridges the gap between Eocene and Miocene adapiform communities in Southern Asia.

    Science.gov (United States)

    Marivaux, Laurent; Welcomme, Jean-Loup; Ducrocq, Stéphane; Jaeger, Jean-Jacques

    2002-04-01

    A new species of Guangxilemur (Sivaladapidae, Adapiformes) is described from the early Oligocene Chitarwata Formation (Bugti Member) of the Bugti Hills, Sulaiman geological Province, Balochistan, Pakistan. Guangxilemur singsilai n. sp. provides further diagnostic morphological characters from its newly described upper and lower dentitions, confirming its intermediate phylogenetic position between Eocene and Miocene Asian sivaladapid adapiforms. G. singsilai possesses moderately developed shearing and puncturing molar features and maintains lingual cusps on upper molars as in Eocene hoanghoniines; in contrast, it possesses a typical molariform P(4) as in Miocene sivaladapines. The important paleogeographic changes that have affected South Asia during the Tertiary (related to the collision between the Indian and Eurasian Plates) have played a critical role in reforming circulation and climatic differentiation. The presence in Pakistan of an unique and well-diversified Oligocene primate fauna, clearly demonstrates that South Asia maintained favourable environmental conditions during the middle Caenozoic global climatic deterioration that coincides with drastic changes in faunal structure on the whole Holarctic Province, including the extinction of adapiform primates.

  3. Polyphase basin evolution of the Vienna Basin inferred from 3D visualization of sedimentation setting and quantitative subsidence

    Science.gov (United States)

    Lee, Eun Young; Novotny, Johannes; Wagreich, Michael

    2016-04-01

    This study analyzed and visualized data from 210 wells using a MATLAB-based program (BasinVis 1.0) for 3D visualization of sediment distribution, thickness, and quantitative subsidence of the northern and central Vienna Basin. The sedimentation settings for selected horizons were visualized to 3D sediment distribution maps, isopach maps, and cross-sections. Subsidence of the study area resulted in 3D subsidence depth and rate maps of basement and tectonic subsidences. Due to the special position of the Vienna Basin, the basin evolution was influenced by the regional tectonics of surrounding units. The 2D/3D maps provided insights into the polyphase evolution of the Vienna Basin, which is closely related to changes in the changing regional stress field and the paleoenvironmental setting. In the Early Miocene, the sedimentation and subsidence were shallow and E-W/NE-SW trending, indicating the development of piggy-back basins. During the late Early Miocene, maps show wider sedimentation and abruptly increasing subsidence by sinistral strike-slip faults, which initiated the Vienna pull-apart basin system. The sediments of the Early Miocene were supplied through a small deltaic system entering from the south. After thin sedimentation and shallow subsidence of the early Middle Miocene, the development of the Vienna Basin was controlled and accelerated mainly by NE-SW trending synsedimentary normal faults, especially the Steinberg fault. From the Middle Miocene, the subsidence was decreasing overall, however the tectonic subsidence show regionally different patterns. This study suggests that a major tensional regime change, from transtension to E-W extension, caused laterally varying subsidence across the Vienna Basin. The Late Miocene was characterized by the slowing down of basement and tectonic subsidence. From the middle Middle to Late Miocene, enormous amount of sediments supplied by a broad paleo-Danube delta complex on the western flank of the basin. The latest

  4. Tectonic implications of Early Miocene OIB magmatism in a near-trench setting: The Outer Zone of SW Japan and the northernmost Ryukyu Islands

    Science.gov (United States)

    Kiminami, Kazuo; Imaoka, Teruyoshi; Ogura, Kazuki; Kawabata, Hiroshi; Ishizuka, Hideo; Mori, Yasushi

    2017-03-01

    The Outer Zone of the SW Japan and northernmost Ryukyu arcs was affected by intense igneous activity during the Miocene, characterized by MORB-like basalts, alkaline basalts, and S-type (with subordinate I-type) felsic to intermediate volcano-plutonic complexes. These igneous rocks are inferred to be the products of near-trench magmatism. Early Miocene (∼18 Ma) alkaline basalt dikes from the Shingu-Otoyo area in central northern Shikoku, and an alkaline lamprophyre dike from Tanegashima, one of the northernmost Ryukyu Islands, pre-date the Middle Miocene felsic to intermediate igneous rocks. The basalts and lamprophyre have compositions of basanite, basalt, trachybasalt and phonotephrite. They are characterized by elevated large-ion lithophile elements (LILEs; e.g., Sr, Ba, and Th) and high concentrations of high-field strength elements (HFSEs; e.g., TiO2, Nb, and Zr). The geochemical signatures of the basalts and lamprophyre suggest an ocean island basalt-type (OIB-type) mantle source. The occurrence of alkaline basalts and lamprophyre with OIB-type, intraplate geochemical signatures in a near-trench setting is unusual with regard to plate tectonic processes. We propose that trench-ward motion of the overriding plate during the period around the Early Miocene resulted in a shallowly dipping slab, and interplate coupling between the subducting Philippine Sea Plate (PSP) and the overlying crust beneath most of the Outer Zone in the western part of SW Japan and the northernmost Ryukyu Islands. The OIB-type magmatism in the near-trench environment is most plausibly explained by the upwelling of asthenospheric material from beneath the subducting slab, which migrated through fractures and/or tears in the slab. We envisage two possible scenarios for the formation of these fractures or tears: (1) the shallowing dip angle of the subducted PSP resulted in concave-upwards flexure of the slab, generating fractures in the flexed region; and (2) differential motion within

  5. Organic geochemical characteristics and paleoclimate conditions of the Miocene coals at the Çan-Durali (Çanakkale)

    Science.gov (United States)

    Hoş-Çebi, Fatma

    2017-05-01

    In this study, n-alkane and isoprenoid, saturated and aromatic biomarker distributions of Miocene coals in the Çan (Çanakkale) region, were studied to investigate organic geochemical characteristics, depositional environment, and hydrocarbon potential of these coals. Çan formation (Middle Miocene) unconformably overlies the basement Çan volcanites (Upper Oligocene-Lower Miocene). This formation is composed of lignite, clayey lignite, and ligniferous clayey levels of various thicknesses interlayering with clay and tuffite. The formation represents sediments of small lacustrine basins that are isolated by faults that are formed contemporaneously with Early-Middle Eocene volcanism. Coaliferous units are overlain by lower agglomerate levels. The Rock Eval analyses show that the average TOC (Total Organic Carbon) content of the coal is 53.71% and the average HI (Hydrogen Index) value is 180.5 mgHC/gTOC. OI (Oxygen Index) values (avg. 22.33 mgCO2/gTOC) show that the depositional environment of peat deposits is suboxic. According to HI-Tmax, S2-TOC classification diagrams and Pr/n-C17vs. Ph/n-C18 diagram, the organic matter is composed of Type II and Type III kerogen mixing and represents a transitional environment. In gas chromatograms, n-alkanes with high, mostly odd-numbered carbons are dominant and they are associated with a slight algal contribution. CPI22-30 (Carbon Preference Index) and TARHC (Terrigenous/Aquatic Ratio) values indicate a dominance of high-carbon numbered n-alkanes, indicating the presence of terrestrial organic matter. Paq (aquatic plant n-alkane proxy) values (0.2; 0.3) indicate a climate with relatively wet conditions or low precipitation, the presence of emergent macrophyteses, and the scarcity of hydrophilic plants. Pwax (vascular plant n-alkane proxy) ratio (0.8; 0.7) shows moderately wet conditions and a relatively low water level. The TOC, ACL (n-alkane average chain length), Qwood/grass, Qwood/plant, and Qgrass/plant values indicate the

  6. Orbitally-paced variations of water availability in the SE Asian Monsoon region following the Miocene Climate Transition

    Science.gov (United States)

    Heitmann, Emma O.; Ji, Shunchuan; Nie, Junsheng; Breecker, Daniel O.

    2017-09-01

    Middle Miocene Earth had several boundary conditions similar to those predicted for future Earth including similar atmospheric pCO2 and substantial Antarctic ice cover but no northern hemisphere ice sheets. We describe a 12 m outcrop of the terrestrial Yanwan Section in the Tianshui Basin, Gansu, China, following the Miocene Climate Transition (13.9-13.7 Ma). It consists of ∼25 cm thick CaCO3-cemented horizons that overprint siltstones every ∼1 m. We suggest that stacked soils developed in siltstones under a seasonal climate with a fluctuating water table, evidenced by roots, clay films, mottling, presence of CaCO3 nodules, and stacked carbonate nodule δ13 C and δ18 O profiles that mimic modern soils. We suggest that the CaCO3-cemented horizons are capillary-fringe carbonates that formed in an arid climate with a steady water table and high potential evapotranspiration rates (PET), evidenced by sharp upper and basal contacts, micrite, sparite, and root-pore cements. The CaCO3 of the cemented horizons and the carbonate nodules have similar mean δ18 O and δ13 C values but the cements have significantly smaller variance in δ13 C and δ18 O values and a different δ18 O versus δ13 C slope, supporting the conclusion that these carbonates are from different populations. The magneto-stratigraphic age model indicates obliquity pacing of the arid conditions required to form the CaCO3-cemented horizons suggesting an orbital control on water availability. We suggest two possible drivers for the obliquity pacing of arid conditions: 1) variability in the cross-equatorial pressure gradient that controls summer monsoon (ASM) strength and is influenced by obliquity-paced variations of Antarctic ice volume and 2) variability in Western Pacific Ocean-East Asian continent pressure gradient controlled by the 25-45°N meridional insolation gradient. We also suggest that variations in aridity were influenced by variations in PET and sensible heating of the regional land

  7. Late Miocene extension partitioning in the eastern Betics: from W- to E-directed extension between the Sorbas and Vera basins (SE Spain).

    Science.gov (United States)

    Giaconia, Flavio; Booth-Rea, Guillermo; Martínez-Martínez, Jose Miguel; Azañon, Jose Miguel

    2014-05-01

    Late Miocene westward-directed extension in the Betics produced elongated core-complexes like Sierra Nevada and the Sierra de Filabres, tilted-block domains and associated basins. This extension represents the superficial manifestation of the rupture of the Tethyan slab and associated edge delamination along a lithospheric transform fault beneath the northern branch of the Gibraltar Arc orogenic system. However, crustal thinning at the eastern Betics occurs progressively towards the east suggesting an eastward-directed extension, probably related to the late Miocene opening of the Algero-Balearic basin. In order to define the kinematics and timing of such a heterogeneous extension at the eastern Betics we have carefully mapped a key area at the transition between the Sorbas and Vera basins. Field data indicate that extension in the area started at the southern margin of the Vera basin during the Serravallian (13.8 Ma) and continued until the Tortonian (approximately 8 Ma). This extension was characterized by a set of NE- to E-directed normal faults to the east, in the Vera basin, and a set of SW-directed normal faults to the west, towards the Sorbas basin. This opposite-directed extension is segmented by E-W to WNW-ESE strike-slip faults like the North Cabrera dextral transfer fault that accommodates NE- to E-directed extension to the north and SW-directed extension to the south. This structure resulted in westward tilted blocks that lead to Serravallian-Tortonian depocenters deepening towards the east at the Vera basin along the northern side of Sierra Cabrera. Meanwhile, at the western termination of Sierra Cabrera, westward-directed extension migrated SW-ward forming the Sorbas basin during the Tortonian (approximately 9-7.24 Ma). This extension was characterized by a listric fan of SW-directed normal faults highly segmented by E-W to NE-SW transfer. This extensional system produced tiled-blocks defining a Tortonian depocenter at the eastern margin of the Sorbas

  8. Linear magnetic anomalies and tectonic development of the middle Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    -By analyzing the magnetic anomalies, the linear magnetic anomalies in the middle Okinawa Trough are identified. It means that the crust along the spreading axis is broken, and new oceanic crust is formed. Geophysical data have revealed that a model of three extensive episodes occurs in the Okinawa Trough, which can be named as "doming episode" from the Middle to Late Miocene (Phase I), the episode from the Pliocence to Early Pleistocene (Phase Ⅱ ), and the recent "spreading episode" (Phase Ⅲ ). The magnetic anomalies in the middle Okinawa Trough are very similar to those found in the middle Red Sea, indicating that the Okinawa Trough is developing towards the "Red Sea stage". Similar to the Red Sea, there are a "main trough" and a "axial trough" in the Okinawa Trough.

  9. Strong winter monsoon wind causes surface cooling over India and China in the Late Miocene

    Directory of Open Access Journals (Sweden)

    H. Tang

    2015-01-01

    Full Text Available Modern Asian winter monsoon characterised by the strong northwesterly wind in East Asia and northeasterly wind in South Asia, has a great impact on the surface temperature of the Asian continent. Its outbreak can result in significant cooling of the monsoon region. However, it is still unclear whether such an impact existed and is detectable in the deep past. In this study, we use temperature reconstructions from plant and mammal fossil data together with climate model results to examine the co-evolution of surface temperature and winter monsoon in the Late Miocene (11–5 Ma, when a significant change of the Asian monsoon system occurred. We find that a stronger-than-present winter monsoon wind might have existed in the Late Miocene due to the lower Asian orography, particularly the northern Tibetan Plateau and the mountains north of it. This can lead to a pronounced cooling in southern China and northern India, which counteracts the generally warmer conditions in the Late Miocene compared to present. The Late Miocene strong winter monsoon was characterised by a marked westerly component and primarily caused by a pressure anomaly between the Tibetan Plateau and Northern Eurasia, rather than by the gradient between the Siberian High and the Aleutian Low. As a result, the close association of surface temperature with winter monsoon strength on inter-annual scale as observed at present may not have established in the Late Miocene.

  10. Chewing through the Miocene: an examination of the feeding musculature in the ground sloth Hapalops from South America (Mammalia: Pilosa).

    Science.gov (United States)

    Naples, Virginia L; McAfee, Robert K

    2014-01-01

    Hapalops, a smaller-sized and early sloth of the Megatheroidea, appeared in the middle Miocene Santa Cruz formation of Argentina. This genus is part of the group from which later, larger megatheroids arose, i.e., Nothrotheriops and Megatherium. Many cranial characters support this idea; however Hapalops is not merely a smaller antecedent of the later forms. Specifically, Hapalops retains short anterior caniniform teeth, and a temporomandibular joint elevated above the cheek tooth row; a combination distinct among sloths. An elevated temporomandibular joint occurs in Bradypus, a tree sloth with anterior chisel-shaped teeth instead of caniniforms, and the tree sloth Choloepus, which is aligned with the megalonychids, has anterior caniniforms. Hapalops has an elongated zygomatic ascending process that is reminiscent of that in Bradypus; however, the Bradypus skull is extremely foreshortened while that of Hapalops is elongated, as in nothrotheres, but not deepened as in megatheres. Previous work identified many sloth cranial character complexes, and functional limitations on skull feature combinations. The unique Hapalops character patterns indicate a selective feeder with a mediolaterally oriented grinding stroke during mastication.

  11. How could sympatric megaherbivores coexist? Example of niche partitioning within a proboscidean community from the Miocene of Europe

    Science.gov (United States)

    Calandra, Ivan; Göhlich, Ursula B.; Merceron, Gildas

    2008-09-01

    Although low in diversity, megaherbivores (mammals weighting over 103 kg) and especially proboscideans have a powerful impact on the structure and dynamics of present-day ecosystems. During the Neogene (23 to 2.6 Ma) of Europe, the diversity and geographic distribution of these megaherbivores was much greater. Nonetheless, their role in past ecosystems is unclear. Nutrition is one of the main bonds between organisms and their environment. Therefore, the ecology of organisms can be inferred from their dietary habits. The present study is aimed at characterizing the feeding habits of diverse megaherbivores through dental microwear analyses. This method was applied on cheek teeth of three sympatric species of proboscideans from the middle/late Miocene of the Molasse Basin in Southern Germany: Gomphotherium subtapiroideum, Gomphotherium steinheimense, and Deinotherium giganteum. The microwear signatures are significantly different between these taxa, suggesting differences in feeding habits and ecological niches within a woodland environment. D. giganteum probably browsed on dicotyledonous foliages whereas the two species of gomphotheres were neither strict grazers nor strict browsers and instead probably fed on a large spectrum of vegetal resources. The differences of occlusal molar morphology between the two gomphotheres are supported by the dental microwear pattern. Indeed, G. subtapiroideum probably ingested more abrasive material than G. steinheimense. Thus, our results suggest that these proboscideans did not compete for food resources.

  12. Stratigraphy and structural development of the southwest Isla Tiburón marine basin: Implications for latest Miocene tectonic opening and flooding of the northern Gulf of California

    Science.gov (United States)

    Bennett, Scott E K.; Oskin, Michael; Dorsey, Rebecca; Iriondo, Alexander; Kunk, Michael J.

    2015-01-01

    Accurate information on the timing of earliest marine incursion into the Gulf of California (northwestern México) is critical for paleogeographic models and for understanding the spatial and temporal evolution of strain accommodation across the obliquely divergent Pacific-North America plate boundary. Marine strata exposed on southwest Isla Tiburón (SWIT) have been cited as evidence for a middle Miocene marine incursion into the Gulf of California at least 7 m.y. prior to plate boundary localization ca. 6 Ma. A middle Miocene interpretation for SWIT marine deposits has played a large role in subsequent interpretations of regional tectonics and rift evolution, the ages of marine basins containing similar fossil assemblages along ~1300 km of the plate boundary, and the timing of marine incursion into the Gulf of California. We report new detailed geologic mapping and geochronologic data from the SWIT basin, an elongate sedimentary basin associated with deformation along the dextral-oblique La Cruz fault. We integrate these results with previously published biostratigraphic and geochronologic data to bracket the age of marine deposits in the SWIT basin and show that they have a total maximum thickness of ~300 m. The 6.44 ± 0.05 Ma (Ar/Ar) tuff of Hast Pitzcal is an ash-flow tuff stratigraphically below the oldest marine strata, and the 6.01 ± 0.20 Ma (U/Pb) tuff of Oyster Amphitheater, also an ash-flow tuff, is interbedded with marine conglomerate near the base of the marine section. A dike-fed rhyodacite lava flow that caps all marine strata yields ages of 3.51 ± 0.05 Ma (Ar/Ar) and 4.13 ± 0.09 Ma (U/Pb) from the base of the flow, consistent with previously reported ages of 4.16 ± 1.81 Ma (K-Ar) from the flow top and (K-Ar) 3.7 ± 0.9 Ma from the feeder dike. Our new results confirm a latest Miocene to early Pliocene age for the SWIT marine basin, consistent with previously documented latest Miocene to early Pliocene (ca. 6.2-4.3 Ma) planktonic and benthic

  13. Characterization of a Miocene carbonate reservoir analog in Southern Mallorca (Balearic Islands, Spain)

    Science.gov (United States)

    Vandeginste, V.; Camoin, G.; Eisenhauer, A.; Pézard, P.; Lapointe, P.

    2009-04-01

    Carbonate reservoirs contain more than half the world's oil reserves, including highly productive reservoirs in Cretaceous and Cenozoic carbonates from the Middle East and Southeastern Asia. They are usually characterized by the complexity both of their internal architecture and of the distribution of their diagenetic fabrics which hampers crosshole correlations at various scales, and predictions regarding flow paths and volumes of fluids. Reservoir analogs can have the advantage of easier accessibility and sampling and less severe diagenetic alteration. Their study often provides information complementary to the knowledge of hydrocarbon reservoirs and it leads to a better understanding of carbonate systems, important to make better predictions on other potential reservoirs. Significant advances can be made from joint research in natural laboratories integrating outcrops and shallow boreholes, with extensive control on geophysical, geological and petrophysical parameters. The southern part of the island of Mallorca appears as a natural laboratory where a direct comparison between outcrop and shallow subsurface datasets is the objective of the current study. This region is characterized both by spectacular outcrops, especially in the Cabo Blanco area, which were previously studied [e.g. 1], and by shallow holes, 100 m deep on average, that have been drilled especially at Can Roses, Ses Pastores and Ses Sitjoles, from west to east. This geographical extension of the study area provides the opportunity to better explore and understand the Miocene carbonate complex which comprises the Llucmajor platform. This study incorporates a wide range of analytical techniques to characterize the reservoir aspects, such as conventional microscopy of thin sections, XRD analysis, isotopic carbon and oxygen analysis, isotopic strontium dating analysis, petrophysical measurements, high-resolution borehole images and CT scan data. These techniques are used to unravel the sedimentology

  14. Technique for cleaning Tarragona miocene age dolomitized silty limestone, altered by urban pollution

    Directory of Open Access Journals (Sweden)

    Guasch, Nuria

    2008-06-01

    Full Text Available This paper reports the results of studies conducted to evaluate the most suitable cleaning technique for highly dolomitized, middle Miocene (Serravallian calcisiltite from Tarragona, Spain, used to build Les Saleses Convent Church in Barcelona. This stone material was widely used in the decorative and sculptural details on Catalonian modernist buildings.On the church, as on most of the modernist buildings made of this material, the limestone was found to be greatly decayed, with highly reactive black crusts, soluble salts and disaggregation. The cause of these pathologies lay in both the surrounding environment and the original crystalline water-repellent coating applied to the stone surface. Based on the results of an analysis of the stone, the coating and the alterations, water-based procedures and chemical poultices were ruled out as cleaning methods. In subsequent testing, low pressure abrasive blasting and the localized use of laser techniques were found to yield good results. These two techniques were checked for effectiveness and their parameters were determined.En este trabajo se exponen los estudios realizados para valorar la técnica de limpieza más apropiada de la calcisiltita muy dolomitizada del Mioceno medio (Serravalliense de Tarragona empleada en la Iglesia del Convento de Les Saleses (Barcelona, material pétreo muy empleado en el modernismo catalán para la talla de elementos decorativos y escultóricos.El material, al igual que en la mayoría de los edificios modernistas donde se ha utilizado, presentaba degradación importante con costras negras muy reactivas, sales solubles y arenizaciones. Además del origen ambiental de las patologías, éstas también estaban relacionadas con la pátina original de tratamiento, cristalina e hidrófuga, aplicada en toda su superficie. Tras el análisis del material pétreo, de la pátina, y de las alteraciones, que hicieron descartar los métodos de limpieza basados en agua y los qu

  15. Source components and magmatic processes in the genesis of Miocene to Quaternary lavas in western Turkey: constraints from HSE distribution and Hf-Pb-Os isotopes

    Science.gov (United States)

    Aldanmaz, Ercan; Pickard, Megan; Meisel, Thomas; Altunkaynak, Şafak; Sayıt, Kaan; Şen, Pınar; Hanan, Barry B.; Furman, Tanya

    2015-08-01

    Hf-Pb-Os isotope compositions and highly siderophile element (HSE) abundance variations are used to evaluate the mantle source characteristics and possible effects of differentiation processes in lavas from western Turkey, where the eruption of Late Miocene to Quaternary OIB-type intraplate mafic alkaline lavas followed pre-Middle Miocene convergent margin-type volcanism. Concentrations of Os, Ir, and Ru (IPGE) in the OIB-type intraplate lavas decrease with fractionation for primitive melts (MgO > 10 wt%), suggesting that these elements reside predominantly in olivine and associated HSE retaining trace phases and behave compatibly during olivine-dominated fractionation. Fractional crystallization trends indicate distinctly lower bulk partition coefficients for IPGE in more evolved lavas, possibly reflecting a change in the fractionating assemblages. Pd and Re in the primitive melts display negative correlations with MgO, demonstrating moderately incompatible behavior of these elements during fractionation, while the significantly scattered variation in Pt against MgO may indicate the effects of micronuggets of a Pt-rich alloy. Os-rich alkaline primary lavas (>50 ppt Os) exhibit a limited range of 187Os/188Os (0.1361-0.1404), with some xenolith-bearing lavas displaying depletions in 187Os/188Os (0.1131-0.1232), suggesting slight compositional modification of primitive melts through contamination with highly depleted, Os-rich mantle lithosphere. More radiogenic Os isotope ratios (187Os/188Os > 0.1954) in the evolved lavas reflect contamination of the magmas by high187Os/188Os crustal material during shallow differentiation. The OIB-type lavas show limited variations in Hf and Pb isotopes with 176Hf/177Hf = 0.282941-0.283051, 206Pb/204Pb = 18.683-19.091, 207Pb/204Pb = 15.579-15.646, 208Pb/204Pb = 38.550-38.993; 176Hf/177Hf ratios correlate negatively with 208Pb*/206Pb*, suggesting the effects of similar mantle processes on the evolution of time-integrated Th/U and Lu

  16. First Miocene rodent from Lebanon provides the 'missing link' between Asian and African gundis (Rodentia: Ctenodactylidae).

    Science.gov (United States)

    López-Antoñanzas, Raquel; Knoll, Fabien; Maksoud, Sibelle; Azar, Dany

    2015-08-07

    Ctenodactylinae (gundis) is a clade of rodents that experienced, in Miocene time, their greatest diversification and widest distribution. They expanded from the Far East, their area of origin, to Africa, which they entered from what would become the Arabian Peninsula. Questions concerning the origin of African Ctenodactylinae persist essentially because of a poor fossil record from the Miocene of Afro-Arabia. However, recent excavations in the Late Miocene of Lebanon have yielded a key taxon for our understanding of these issues. Proafricanomys libanensis nov. gen. nov. sp. shares a variety of dental characters with both the most primitive and derived members of the subfamily. A cladistic analysis demonstrates that this species is the sister taxon to a clade encompassing all but one of the African ctenodactylines, plus a southern European species of obvious African extraction. As such, Proafricanomys provides the 'missing link' between the Asian and African gundis.

  17. The flora of the Early Miocene Brandon Lignite, Vermont, USA. 8 Caldesia (Alismastaceae)

    Energy Technology Data Exchange (ETDEWEB)

    Haggard, K.K.; Tiffney, B.H. [University of California at Santa Barbara, Santa Barbara, CA (United States). Dept. of Geological Science

    1997-02-01

    Caldesia, a genus of aquatic monocotyledons, is represented by four living species, which are widely distributed in the temperate and tropical Old World. The genus has an extensive Oligocene through Pleistocene fossil record in Eurasia. This paper surveys the morphology of the extant and fossil fruits of the Alismataceae, and provides a detailed review of the morphology and anatomy of living and fossil Caldesia fruits. The latter exhibit substantial similarity, making the recognition of separate species on the basis of fruit morphology difficult. A new species Caldesia brandoniana is erected from the Early Miocene Brandon Lignite of Vermont primarily on the basis of its geographic isolation; careful revision of all fossil fruiting material of Caldesia might require placement of the Brandon specimens in a more inclusive form species. Together with leaves of Caldesia from the Miocene Clarkia flora of Idaho, this occurrence indicates that Caldesia was in the New World as recently as the Early Miocene.

  18. First Miocene rodent from Lebanon provides the 'missing link' between Asian and African gundis (Rodentia: Ctenodactylidae)

    Science.gov (United States)

    López-Antoñanzas, Raquel; Knoll, Fabien; Maksoud, Sibelle; Azar, Dany

    2015-01-01

    Ctenodactylinae (gundis) is a clade of rodents that experienced, in Miocene time, their greatest diversification and widest distribution. They expanded from the Far East, their area of origin, to Africa, which they entered from what would become the Arabian Peninsula. Questions concerning the origin of African Ctenodactylinae persist essentially because of a poor fossil record from the Miocene of Afro-Arabia. However, recent excavations in the Late Miocene of Lebanon have yielded a key taxon for our understanding of these issues. Proafricanomys libanensis nov. gen. nov. sp. shares a variety of dental characters with both the most primitive and derived members of the subfamily. A cladistic analysis demonstrates that this species is the sister taxon to a clade encompassing all but one of the African ctenodactylines, plus a southern European species of obvious African extraction. As such, Proafricanomys provides the 'missing link' between the Asian and African gundis. PMID:26250050

  19. The evolution of the primate foot from the earliest primates to the Miocene hominoids.

    Science.gov (United States)

    Conroy, G C; Rose, M D

    1983-01-01

    The fossil evidence relating to the evolution of the primate foot is reviewed and evaluated. Many of the characteristic features of the primate foot had evolved by the early Tertiary over 40 million years ago. Probably the most significant of these developments was the progressive migration of the talus to a position over the calcaneum. These morphological features are followed through the Miocene hominoid genera from East Africa, Europe, and South Asia. While some features of Miocene hominoids, especially those relating to climbing abilities, are still evident in the predominantly bipedal earliest hominids of the Plio-Pleistocene, there is no evidence yet from the Miocene of the first stages in the evolution of that bipedalism.

  20. Middle Ear Infections

    Science.gov (United States)

    ... Listen Español Text Size Email Print Share Middle Ear Infections Page Content Article Body What are the ... illness. What if a child with a middle ear infection is in great pain and discomfort? The ...

  1. Ear Infection (Middle Ear)

    Science.gov (United States)

    Ear infection (middle ear) Overview By Mayo Clinic Staff An ear infection (acute otitis media) is most often a bacterial or viral infection that affects the middle ear, the air-filled space behind the eardrum that ...

  2. Evolutionary ecology of the Pachydontinae (Bivalvia, Corbulidae) in the Pebas lake/wetland system (Miocene, western Amazonia)

    NARCIS (Netherlands)

    Wesselingh, F.P.

    2006-01-01

    Miocene deposits in western Amazonia and adjacent areas of South America harbour a diverse suite of endemic corbulid bivalves, commonly referred to as Pachydontinae, that show a wide variety of morphologies. Especially in the Miocene Pebas Formation (Peru, Colombia and Brazil), this group diversifie

  3. A new magnetostratigraphic framework for the Lower Miocene (Burdigalian/Ottnangian, Karpatian) in the North Alpine Foreland Basin

    NARCIS (Netherlands)

    Reichenbacher, B.; Krijgsman, W.|info:eu-repo/dai/nl/148529763; Lataster, Y.; Pippèrr, M.; van Baak, C.G.C.|info:eu-repo/dai/nl/341133361; Chang, L.; Kälin, D.; Jost, J.; Doppler, G.; Jung, D.; Prieto, J.; Abdul Aziz, H.; Böhme, M.; Garnish, J.; Kirscher, U.; Bachtadse, V.

    2013-01-01

    Oligocene-Miocene chronostratigraphic correlations within the Paratethys domain are still highly controversial. This study focuses on the late Early Miocene of the Swiss and S-German Molasse Basin (Late Burdigalian, Ottnangian-Karpatian). Previous studies have published different chronologies for th

  4. Biostratigraphical and palaeoecological implications of the small mammal assemblage from the late early Miocene of Montalvos2, Teruel Basin, Spain

    NARCIS (Netherlands)

    Hordijk, Kees; Bosma, Anneke; de Bruijn, Hans; van Dam, Jan; Geraedts, Caspar; van den Hoek Ostende, Lars; Reumer, Jelle; Wessels, Wilma

    The rich early Miocene small mammal assemblage from Montalvos2, collected from lacustrine deposits directly overlying the basement, is unique within the Teruel Basin, a basin that is otherwise well known for its late Miocene/Pliocene mammal faunas. The presence of Democricetodon decipiens,

  5. A revision of the fossil genus Miocepphus and other Miocene Alcidae (Aves: Charadriiformes) of the Western North Atlantic Ocean

    NARCIS (Netherlands)

    Wijnker, T.G.; Olson, S.L.

    2009-01-01

    This study reviews and describes all known fossils of Alcidae from the Miocene of the western North Atlantic. Because the majority of alcid fossils recovered from Miocene sediments are allied with the genus Miocepphus Wetmore, 1940, the genus is revised here. Three new species of Miocepphus are desc

  6. A revision of the fossil genus Miocepphus and other Miocene Alcidae (Aves: Charadriiformes) of the Western North Atlantic Ocean

    NARCIS (Netherlands)

    Wijnker, T.G.; Olson, S.L.

    2009-01-01

    This study reviews and describes all known fossils of Alcidae from the Miocene of the western North Atlantic. Because the majority of alcid fossils recovered from Miocene sediments are allied with the genus Miocepphus Wetmore, 1940, the genus is revised here. Three new species of Miocepphus are

  7. METAXYTHERIUM MEDIUM (MAMMALIA: SIRENIA FROM UPPER MIOCENE SEDIMENTS OF THE ARENARIA DI PONSANO FORMATION (TUSCANY, ITALY

    Directory of Open Access Journals (Sweden)

    GIOVANNI BIANUCCI

    2003-11-01

    Full Text Available Records of Metaxytherium medium (Mammalia: Sirenia from Tononian (Late Miocene sediments from che Arenaria di Ponsano Formation (Tuscany, Italy are described. They consist of fragmentary specimens, including several partial cranial elements representing at least three skulls, two humeri, fragments of venebrae and some incomplete ribs. The new Tuscan records confirm che wide diffusion of Metaxytherium in the Mediterranean during the Miocene. This sirenian's occurrence in the Arenaria di Ponsano sediments is in accordance with the shelf environment indicated by other fossils. The low sea bottom was at least partially covered by segrass meadows, the food source of this dugongid. 

  8. An age for Kajong, a Miocene fossil site east of Lake Turkana, Kenya

    Science.gov (United States)

    Brown, Francis H.; Jicha, Brian R.; Leakey, R. E.

    2016-02-01

    The Kajong Formation in Marsabit District, northern Kenya has yielded a Miocene mammalian fauna consisting of nine taxa. It is capped by a basalt 40Ar/39Ar dated at 19.1 ± 0.1 Ma, and a volcanic clast from a conglomerate within the formation yielded an age of 20.3 Ma, only slightly older. The entire fauna from this site thus lies close to the base of the Miocene Epoch and is older than 19.2 Ma. The site has yielded some of the oldest examples of Archaeobelodon filholi, Prodeinotherium hobleyi, and Gomphotherium sp. in east Africa.

  9. A new baleen whale from the Late Miocene of Denmark and early mysticete hearing

    DEFF Research Database (Denmark)

    Steeman, Mette Elstrup

    2009-01-01

    The extinct mysticete fauna of the North East Atlantic is primarily known from the abundant but fragmented Belgian specimens. Compared to the well-preserved contemporary mysticete fauna from deposits in North America, there are only few near complete European Miocene mysticete fossils. Presented...... here is a new, almost complete fossil baleen whale Uranocetus gramensis gen. et sp. nov. from the Upper Miocene Gram Formation in South West Denmark. It is the first stem-balaenopterid that has an initial stage of reduction in the mandibular cavity and a rostral configuration that is intermediate...

  10. Miocene core complex development and coeval supradetachment basin evolution of Paros, Greece, insights from (U-Th)/He thermochronometry

    Science.gov (United States)

    Bargnesi, Evan A.; Stockli, Daniel F.; Mancktelow, Neil; Soukis, Konstantinos

    2013-06-01

    Middle to Late Miocene.

  11. Model study of the circulation of the Miocene Mediterranean Sea and Paratethys: closure of the Indian Gateway

    Directory of Open Access Journals (Sweden)

    A. de la Vara

    2013-08-01

    Full Text Available The early Mediterranean Sea and the Paratethys were both connected to the Indian Ocean until the Early/Middle Miocene, when the convergence of the Eurasian and African-Arabian plates caused the constriction and final closure of the Indian Gateway. Although little is certain concerning the timing of the closure and the consequences that it entailed, it is broadly accepted that it had a large effect on water properties and ocean dynamics on the regional and global scales and, in that way, may have also played a role in the evolution of climate. The purpose of this work is to investigate the palaeocirculation of the Mediterranean Sea and the Paratethys during different stages of closure and the impact of this event on the water exchange between the Mediterranean and the adjacent Indian and Atlantic oceans. To this extent we use a regional ocean model and an Early Miocene palaeogeographic map. In addition to varying the depth of the Indian Gateway, different sets of values for the atmospheric forcing have been applied in order to check the robustness of our results and to understand the role of the temperature and net evaporation on the marine circulation and the strait dynamics. The series of experiments performed shows that, with an Indian Gateway ranging from 1000 to 460 m deep, the Mediterranean accommodates anti-estuarine exchange to the Indian and Atlantic oceans. The shoaling of the Indian Gateway results in a progressive decrease in the water exchanged between the Indian Ocean and the Mediterranean basin, and increases the spatial extension of the Atlantic inflow. When the gateway is as shallow as 220 m, there is no effective water exchange between the Indian Ocean and the Mediterranean basin, suggesting that the gateway may have been closed in an oceanographical sense, even while a water passage was still in existence. On a basinal scale, closure results in a rearrangement of the circulation pattern which leads to changes in salinity and

  12. Evidence for Repeated Early Miocene Glaciation and the Cutting of Upper Taylor Valley from the Friis Hills, Antarctica

    Science.gov (United States)

    Lewis, A.; Ashworth, A. C.; Marchant, D. R.; Hemming, S. R.

    2009-12-01

    preservation of the ash adjacent to Taylor Glacier suggests that cutting had already deepened the Taylor trough enough to protect the deposit from erosion during later glacier advances. The Friis Hills deposits are the first to show terrestrial evidence for Early Miocene-aged (or older) glacier cycles and the biota will provide novel constraints on paleoclimate. These tills may also help shed light on how Sirius Group deposits relate to the well-dated Middle Miocene-aged glacial record from the western Dry Valleys. Sirius Group tills occur on Table Mountain only 20 km to the south of the Friis Hills and at the same elevation. The lithology of these sediments is similar to that of the older tills in the Friis Hills and like them these sediments show ice flow into the Ferrar trough. One major difference is the degree of lithification. Tills in the Friis Hills are only weakly consolidated, whereas Sirius Group deposits are strongly lithified. This suggests that the Sirius Group in the southwestern Dry Valleys may be older than 19.76 Ma and could date to a period not long before deposition began on the Friis Hills. This research is supported by NSF OPP 0739693.

  13. Small suoids from the Miocene of Europe and Asia

    Directory of Open Access Journals (Sweden)

    Pickford, M.

    2011-12-01

    Full Text Available The history of study of small suoids from the Miocene of Eurasia is complex for several reasons: scarcity of fossil material, a high degree of dental convergence and parallelism between closely and distantly related lineages, and frequent misattribution of fossils, resulting in the gradual development of a confusing taxonomy. Changes in taxonomy above the genus level, have added to the complexity; European lineages classified in Suidae in 1924 are now arranged into three separate families; Suidae, Palaeochoeridae and Sanitheriidae. Recent studies have considerably clarified the situation, but there remain several problematic issues to resolve, especially among the Palaeochoeridae. The fossil register of some taxa is limited, so it is necessary to put on record newly recognised specimens in order to fill out our knowledge concerning them. This paper includes previously undescribed material of Palaeochoeridae and small Suidae, as well as reinterpretation of some fossils published in “obscure” scientific journals. The latter include some taxa that have priority over more recently proposed names. A systematic revision of these forms is carried out, and the paper ends with a proposal for a revised taxonomy of the Palaeochoeridae, a family that has recently taken on importance in the debate about the origins of Hippopotamidae.

    La historia del estudio de los suoideos de talla pequeña del Mioceno de Eurasia es compleja por varias razones: la escasez de material fósil, un grado alto de convergencia y paralelismo dental entre linajes cercana y lejanamente relacionados, y la frecuente errónea identificación de los fósiles, teniendo como resultado el desarrollo gradual de una taxonomía confusa. Los cambios en la taxonomía por encima del nivel de género, han contribuído a esta complejidad; linajes europeos clasificados como Suidae en 1924 ahora se reparten en tres familias separadas; Suidae, Palaeochoeridae y Sanitheriidae. Estudios

  14. Zeros in γ+e-->W

    Science.gov (United States)

    Mikaelian, Karnig O.

    1984-09-01

    We point out a misprint in the differential cross section for γe-->Wν reported recently by Ginzburg, Kotkin, Panfil, and Serbo. The corrected expression has a zero in accordance with the general formula derived earlier by Mikaelian. We plot the angular distributions for different values of κ, the anomalousmagnetic-moment parameter of the W. We suggest that the reaction γe-->Wν is an attractive way to measure κ because the distributions are sensitive to it and the zero exists only if κ=+1 as in the standard electroweak theory.

  15. Polyphase tectonic subsidence evolution of the Vienna Basin inferred from quantitative subsidence analysis of the northern and central parts

    Science.gov (United States)

    Lee, Eun Young; Wagreich, Michael

    2016-04-01

    The Vienna Basin is a tectonically complex Neogene basin situated at the Alpine-Carpathian transition. This study analyzes a detailed quantification of subsidence in the northern and central parts of the Vienna Basin to understand its tectonic subsidence evolution. About 200 wells were used to arrange stratigraphic setting, and wells reaching the pre-Neogene basement were analyzed for subsidence. To enhance the understanding of the regional subsidences, the wells were sorted into ten groups based on their position on major fault blocks. In the Early Miocene, subsidence was slow and along E-W to NE-SW trending axis, indicating the development of thrust-controlled piggyback basins. During the late Early Miocene data show abruptly increasing subsidence, making the initiation of the Vienna pull-apart basin system. From the Middle Miocene, the tectonic subsidence curves show regionally different patterns. The tectonic subsidence during the Middle Miocene varies laterally across the Vienna Basin, and the differential subsidence can be related to the changing tensional regime of weakening transtension and strengthening extension toward the late Middle Miocene. From the late Middle Miocene to the Late Miocene, the tectonic subsidence occurred dominantly along the regional active faults, and corresponds to the axis of E-W trending extension of the western parts of the Pannonian Basin system. In the Quaternary the Vienna Basin has been reactivated, and resulted in subsidence along the NE-SW trending Vienna Basin transfer fault system.

  16. Integrated Chronology, Flora and Faunas, and Paleoecology of the Alajuela Formation, Late Miocene of Panama

    Science.gov (United States)

    MacFadden, Bruce J.; Jones, Douglas S.; Jud, Nathan A.; Moreno-Bernal, Jorge W.; Morgan, Gary S.; Portell, Roger W.; Perez, Victor J.; Moran, Sean M.; Wood, Aaron R.

    2017-01-01

    The late Miocene was an important time to understand the geological, climatic, and biotic evolution of the ancient New World tropics and the context for the Great American Biotic Interchange (GABI). Despite this importance, upper Miocene deposits containing diverse faunas and floras and their associated geological context are rare in Central America. We present an integrated study of the geological and paleontological context and age of a new locality from Lago Alajuela in northern Panama (Caribbean side) containing late Miocene marine and terrestrial fossils (plants, invertebrates, and vertebrates) from the Alajuela Formation. These taxa indicate predominantly estuarine and shallow marine paleoenvironments, along with terrestrial influences based on the occurrence of land mammals. Sr-isotope ratio analyses of in situ scallop shells indicate an age for the Alajuela Formation of 9.77 ± 0.22 Ma, which also equates to a latest Clarendonian (Cl3) North American Land Mammal Age. Along with the roughly contemporaneous late Miocene Gatun and Lago Bayano faunas in Panama, we now have the opportunity to reconstruct the dynamics of the Central America seaway that existed before final closure coincident with formation of the Isthmus of Panama. PMID:28107398

  17. Effect of ocean gateways on the global ocean circulation in the late Oligocene and early Miocene

    NARCIS (Netherlands)

    von der Heydt, A.S.|info:eu-repo/dai/nl/245567526; Dijkstra, H.A.|info:eu-repo/dai/nl/073504467

    2006-01-01

    We investigate the effect of changes in the tectonic boundary conditions on global ocean circulation patterns. Using a fully coupled climate model in an idealized setup, we compare situations corresponding to the late Oligocene, the early Miocene, and present day. The model results show the

  18. Evidence for ice-free summers in the late Miocene central Arctic Ocean

    Science.gov (United States)

    Stein, Ruediger; Fahl, Kirsten; Schreck, Michael; Knorr, Gregor; Niessen, Frank; Forwick, Matthias; Gebhardt, Catalina; Jensen, Laura; Kaminski, Michael; Kopf, Achim; Matthiessen, Jens; Jokat, Wilfried; Lohmann, Gerrit

    2016-01-01

    Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene sediments close to the seafloor. Here we document the presence of IP25 as a proxy for spring sea-ice cover and alkenone-based summer sea-surface temperatures >4 °C that support a seasonal sea-ice cover with an ice-free summer season being predominant during the late Miocene in the central Arctic Ocean. A comparison of our proxy data with Miocene climate simulations seems to favour either relatively high late Miocene atmospheric CO2 concentrations and/or a weak sensitivity of the model to simulate the magnitude of high-latitude warming in a warmer than modern climate. PMID:27041737

  19. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

    Science.gov (United States)

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Gasson, Edward; Kuhn, Gerhard; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco; SMS Science Team; Acton, Gary; Askin, Rosemary; Atkins, Clifford; Bassett, Kari; Beu, Alan; Blackstone, Brian; Browne, Gregory; Ceregato, Alessandro; Cody, Rosemary; Cornamusini, Gianluca; Corrado, Sveva; DeConto, Robert; Del Carlo, Paola; Di Vincenzo, Gianfranco; Dunbar, Gavin; Falk, Candice; Field, Brad; Fielding, Christopher; Florindo, Fabio; Frank, Tracy; Giorgetti, Giovanna; Grelle, Thomas; Gui, Zi; Handwerger, David; Hannah, Michael; Harwood, David M.; Hauptvogel, Dan; Hayden, Travis; Henrys, Stuart; Hoffmann, Stefan; Iacoviello, Francesco; Ishman, Scott; Jarrard, Richard; Johnson, Katherine; Jovane, Luigi; Judge, Shelley; Kominz, Michelle; Konfirst, Matthew; Krissek, Lawrence; Kuhn, Gerhard; Lacy, Laura; Levy, Richard; Maffioli, Paola; Magens, Diana; Marcano, Maria C.; Millan, Cristina; Mohr, Barbara; Montone, Paola; Mukasa, Samuel; Naish, Timothy; Niessen, Frank; Ohneiser, Christian; Olney, Mathew; Panter, Kurt; Passchier, Sandra; Patterson, Molly; Paulsen, Timothy; Pekar, Stephen; Pierdominici, Simona; Pollard, David; Raine, Ian; Reed, Joshua; Reichelt, Lucia; Riesselman, Christina; Rocchi, Sergio; Sagnotti, Leonardo; Sandroni, Sonia; Sangiorgi, Francesca; Schmitt, Douglas; Speece, Marvin; Storey, Bryan; Strada, Eleonora; Talarico, Franco; Taviani, Marco; Tuzzi, Eva; Verosub, Kenneth; von Eynatten, Hilmar; Warny, Sophie; Wilson, Gary; Wilson, Terry; Wonik, Thomas; Zattin, Massimiliano

    2016-03-01

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (˜280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (˜500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

  20. Miocene Bryozoa from East Kalimantan, Indonesia. Part II: ‘Ascophoran’ Cheilostomata

    NARCIS (Netherlands)

    Martino, Di E.; Taylor, P.D.

    2015-01-01

    We describe 72 ascophoran-grade cheilostomes, ranging in age from Early to Late Miocene (late Burdigalian to Messinian), collected from 17 sections in the vicinities of Samarinda, Bontang and Sangkulirang in East Kalimantan, Indonesian Borneo. Two genera (Oviexechonella gen. nov. and Sendinopora

  1. Integrated Chronology, Flora and Faunas, and Paleoecology of the Alajuela Formation, Late Miocene of Panama.

    Science.gov (United States)

    MacFadden, Bruce J; Jones, Douglas S; Jud, Nathan A; Moreno-Bernal, Jorge W; Morgan, Gary S; Portell, Roger W; Perez, Victor J; Moran, Sean M; Wood, Aaron R

    2017-01-01

    The late Miocene was an important time to understand the geological, climatic, and biotic evolution of the ancient New World tropics and the context for the Great American Biotic Interchange (GABI). Despite this importance, upper Miocene deposits containing diverse faunas and floras and their associated geological context are rare in Central America. We present an integrated study of the geological and paleontological context and age of a new locality from Lago Alajuela in northern Panama (Caribbean side) containing late Miocene marine and terrestrial fossils (plants, invertebrates, and vertebrates) from the Alajuela Formation. These taxa indicate predominantly estuarine and shallow marine paleoenvironments, along with terrestrial influences based on the occurrence of land mammals. Sr-isotope ratio analyses of in situ scallop shells indicate an age for the Alajuela Formation of 9.77 ± 0.22 Ma, which also equates to a latest Clarendonian (Cl3) North American Land Mammal Age. Along with the roughly contemporaneous late Miocene Gatun and Lago Bayano faunas in Panama, we now have the opportunity to reconstruct the dynamics of the Central America seaway that existed before final closure coincident with formation of the Isthmus of Panama.

  2. Amazon forest dynamics under changing abiotic conditions in the early Miocene (Colombian Amazonia)

    NARCIS (Netherlands)

    Salamanca Villegas, S.; van Soelen, E.; Teunissen van Manen, M.L.; Flantua, S.G.A.; Santos, R.V.; Roddaz, M.; Dantas, E.L.; van Loon, E.; Sinninghe Damsté, J.S.; Kim, J.-H.; Hoorn, C.

    2016-01-01

    Aim We analysed in detail a past marine incursion event in north-westernAmazonia and measured its effect on the forest composition. We also deter-mined the sediment provenance in the ?uvio-estuarine system and recon-structed the overall ?oral composition of the Amazon lowland forest duringthe Miocen

  3. A new species of Sphenotrochus (Scleractinia: Turbinoliidae) from the Late Miocene (Tortonian) of Chile

    NARCIS (Netherlands)

    Cairns, S.D.

    2003-01-01

    A new species of azooxanthellate Scleractinia, Sphenotrochus denhartogi, is described from the Late Miocene (Tortonian, Navidad Formation) of Chile. Comparisons are made to three other closely related species which, based on their distinctive costal morphology, form a species complex: S. claibornens

  4. Fish remains from Miocene beds of Višnja vas near Vojnik, Slovenia

    Directory of Open Access Journals (Sweden)

    Aleš Šoster

    2013-06-01

    Full Text Available This paper discusses fossil teeth of sharks (Elasmobranchii, Neoselachii and porgies (Teleostei, Sparidae fromthe Miocene glauconite sandstones of Vi{nja vas near Vojnik. The remains of fish teeth, mostly tooth crowns, belongto cartilaginous fishes of the genera Notorynchus, Carcharias, Carcharoides, Isurus and Cosmopolitodus and to abony fish genus Pagrus.

  5. On the Late Miocene continentalization of the Guadix Basin: More evidence for a major Messinian hiatus

    NARCIS (Netherlands)

    Hüsing, S.K.; Oms, O.; Agustí, J.; Garcés, M.; Kouwenhoven, T.J.; Krijgsman, W.; Zachariasse, W.J.

    2012-01-01

    The chronology of the Late Miocene Mediterranean-Atlantic gateways through southern Iberia is a key issue to better understand the geodynamic processes that lead to the Messinian salinity crisis. The timing of the North Betic corridor continentalization has recently been constrained by integrated ma

  6. A stratigraphical framework for Miocene (MN4-MN13) continental sediments of Central Spain

    Science.gov (United States)

    Daams, Remmert; Alcalá, Luis; de los Angeles Alvarez Sierra, María; Azanza, Beatriz; Arie van Dam, Jan; van der Meulen, Albert-Jan; Morales, Jorge; Nieto, Manuel; Peláez-Campomanes, Pablo; Soria, Dolores

    1998-11-01

    New bio- and magnetostratigraphic data from the Miocene continental sediments of Central Spain are used to update the existing stratigraphical framework. Our revised record is based on the study of more than two hundred mammal faunas, ranging from the Late Ramblian (ca 18 Ma) to the Late Turolian (ca 6 Ma).

  7. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene.

    Science.gov (United States)

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Gasson, Edward; Kuhn, Gerhard; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco

    2016-03-29

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

  8. Anthracothere dental anatomy reveals a late Miocene Chado-Libyan bioprovince.

    Science.gov (United States)

    Lihoreau, Fabrice; Boisserie, Jean-Renaud; Viriot, Laurent; Coppens, Yves; Likius, Andossa; Mackaye, Hassane Taisso; Tafforeau, Paul; Vignaud, Patrick; Brunet, Michel

    2006-06-01

    Recent discovery of an abundant and diverse late Miocene fauna at Toros-Ménalla (Chad, central Africa) by the Mission Paléoanthropologique Franco-Tchadienne provides a unique opportunity to examine African faunal and hominid evolution relative to the early phases of the Saharan arid belt. This study presents evidence from an African Miocene anthracotheriid Libycosaurus, particularly well documented at Toros-Ménalla. Its remains reveal a large semiaquatic mammal that evolved an autapomorphic upper fifth premolar (extremely rare in Cenozoic mammals). The extra tooth appeared approximately 12 million years ago, probably in a small northern African population isolated by climate-driven fragmentation and alteration of the environments inhabited by these anthracotheriids [Flower, B. P. & Kennett, J. P. (1994) Palaeogeogr. Palaeoclimatol. Palaeoecol. 108, 537-555 and Zachos, J., Pagani, M., Sloan, L., Thomas, E. & Billups, K. (2001) Science 292, 686-693]. The semiaquatic niche of Libycosaurus, combined with the distribution and relationships of its late Miocene species, indicates that by the end of the Miocene, wet environments connected the Lake Chad Basin to the Libyan Sirt Basin, across what is now the Sahara desert.

  9. Do stable carbon isotopes of brown coal woods record changes in Lower Miocene palaeoecology?

    NARCIS (Netherlands)

    Poole, I.J.; Dolezych, M.; Kool, J.; Burgh, J. van der; Bergen, P.F. van

    2006-01-01

    Stable carbon isotope ratios of fossil wood from the Miocene brown coal deposits in former East Germany are compared with palaeobotanical and sedimentological data to test the use of stable isotopes in determining palaeoenvironment. Significant differences in the chemical composition of samples from

  10. Miocene rodent evolution and migration. Muroidea from Pakistan, Turkey and Northern Africa. Geologica Ultraiectina (307)

    NARCIS (Netherlands)

    Wessels, W.

    2009-01-01

    Detailed research on fossil rodents from Pakistan, Turkey, northern Africa and Europe provides a better understanding of the evolutionary history of the Muroidea, especially of the Murinae, Myocricetodontinae and Rhizomyinae. The origin of these rodent groups lies in the Early Miocene of south-weste

  11. New magnetochronology of Late Miocene mammal fauna, NE Tibetan Plateau, China : Mammal migration and paleoenvironments

    NARCIS (Netherlands)

    Ao, Hong; Zhang, Peng; Dekkers, Mark J.; Roberts, Andrew P.; An, Zhisheng; Li, Yongxiang; Lu, Fengyan; Lin, Shan; Li, Xingwen

    2016-01-01

    Lanzhou Basin lies on the northeastern margin of the Tibetan Plateau in western China and is a rich source of Oligocene-Miocene mammalian fossils. Obtaining precise age determinations for these fossils is important to address key questions concerning mammalian and environmental evolution in Asia

  12. The westernmost tarsier: A new genus and species from the Miocene of Pakistan

    NARCIS (Netherlands)

    Zijlstra, Jelle S.; Flynn, Lawrence J.; Wessels, Wilma

    2013-01-01

    As the closest living sister group of anthropoids, tarsiers (Family Tarsiidae) are an important group in primate evolution. However, their fossil record is poor: only four species have been described, two from the Eocene of China and two from the Miocene of Thailand. All are from outside the range

  13. Composition of clastic sediments in the Somosaguas area (middle Miocene, Madrid Basin): insights into provenance and palaeoclimate

    OpenAIRE

    Fesharaki, Omid; Arribas, J.; López-Martínez, Nieves

    2015-01-01

    [ES] La zona occidental de la cuenca de Madrid no ha sido adecuadamente estudiada. Esto, combinado con la alta homogeneidad de facies detríticas dificulta la correlación estratigráfica con otras áreas de la cuenca. En consecuencia, sólo una caracterización detallada de diferentes zonas de estudio puede permitir posteriores trabajos de correlación regional. En los últimos años se han descubierto varios yacimientos de fósiles de vertebrados en esta área que permiten la datación de los ...

  14. Contours that Represent the Percentage of Sandstone for the Lower, Middle and Upper Miocene in Southern Louisiana

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The sand percent contours were produced by the Louisiana Geological Survey and were digitized from Chapter 11, Cenozoic, in The Gulf of Mexico Basin, Volume J, The...

  15. Gravity modeling reveals that the "Miocene Pyrenean peneplain" developed at high elevation

    Science.gov (United States)

    Bosch, Gemma V.; Van Den Driessche, Jean; Robert, Alexandra; Babault, Julien; Le Carlier, Christian

    2016-04-01

    Geodynamics that shaped the present morphology of the western Mediterranean are mostly linked to the African-Eurasia collision and the extension related to the Mediterranean opening. The Pyrenean chain formed by the collision between the Iberian microplate and the Eurasian plate from the Eocene to the late Oligocene. This resulted in lithosphere thickening especially below the Central Pyrenees that becomes thinner eastwards. Whether the later thinning of the lithosphere in the easternmost Pyrenees involves the removal of the lithospheric mantle or not is debated. This issue joins the problematics about the origin of the high-elevation of the "Miocene Pyrenean peneplain" remnants. Indeed the most striking feature of the Pyrenean morphology is the occurrence of high-elevation, low relief erosional surfaces that are interpreted as the remnants of a Miocene single planation surface, dissected and reworked by Quaternary fluvial and glacial erosion. Two end-member interpretations have proposed to explain the high elevation of this original surface. The first considers that the Miocene Pyrenean peneplain develops near sea-level and was later uplifted, the second claims that the planation surface developed at high elevation in response to the inhibition of erosion consecutively to the progressive rise of the base-level of the Pyrenean drainage network. The first interpretation implies the return to normal crustal thickness by erosion and later uplift by removal of the lithospheric mantle. The second interpretation considers that the mean elevation of the original planation surface matches the thickness of the lithosphere below the chain, taking into account some hundred meters of isostatic rebound due to Quaternary erosion. To test these interpretations, we first restore the Miocene original planation surface by mapping and interpolating the high-elevation, low relief surfaces across the Pyrenees. We then performed 1D and 2D gravity models that we compare with recent

  16. Paleogeographic and structural setting of Miocene strata in central western Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, J.H. (Geological Survey, Menlo Park, CA (United States))

    1993-04-01

    Late Cenozoic sedimentary rocks as old as 19 Ma are widely distributed in central western Nevada. They are greatly more abundant than older Cenozoic strata and are commonly interpreted to have formed in fault-bounded basins that mark the onset of widespread extension in the Basin and Range Province. Miocene strata are largely coeval with a magmatic arc that extended south southeast near the boundary of the Basin and Range and Sierra Nevada Provinces. This arc produced voluminous andesitic flows and lahars that locally interfinger with the Miocene strata. Miocene depositional basins apparently varied greatly in size. The largest that can be defined clearly is the Esmeralda Basin that was at least 65 km long and 45 km wide. Other basins may have been larger but are difficult to reconstruct; still other basins may be small and isolated, particularly within the magmatic arc. Lacustrine deposits and minor interfingering deltaic and distal fluvial units predominate; near-source, coarse alluvial-fan and megabreccia landslide deposits are locally conspicuous. coarse near-source deposits, particularly landslide deposits, are interpreted to be adjacent to basin-bounding normal faults. The Esmeralda, Coal Valley, and Gabbs Valley-Stewart Valley-Tonopah Basins are interpreted to be related to large-scale Miocene extension. Other basins may be (1) pull-apart structures related to strike-slip faults, (2) downdropped blocks in areas of cross-cutting normal and/or strike-slip faults related to changes in the extension direction or (3) grabens or half-grabens related to uniform extension. Younger Cenozoic basins, including present-day basins, overprint and cut across the Miocene basins.

  17. Palynological evidence for late Miocene stepwise aridification on the northeastern Tibetan Plateau

    Science.gov (United States)

    Liu, Jia; Li, Ji Jun; Song, Chun Hui; Yu, Hao; Jiang Peng, Ting; Chuang Hui, Zheng; Ye, Xi Yan

    2016-07-01

    Holding a climatically and geologically key position both regionally and globally, the northeastern Tibetan Plateau provides a natural laboratory for illustrating the interactions between tectonic activity and the evolution of the Asian interior aridification. Determining when and how the late Miocene climate evolved on the northeastern Tibetan Plateau may help us better understand the relationships among tectonic uplift, global cooling and ecosystem evolution. Previous paleoenvironmental research has focused on the western Longzhong Basin. Late Miocene aridification data derived from pollen now require corroborative evidence from the eastern Longzhong Basin. Here, we present a late Miocene pollen record from the Tianshui Basin in the eastern Longzhong Basin. Our results show that a general trend toward dry climate was superimposed by stepwise aridification: a temperate forest with a rather humid climate existed in the basin between 11.4 and 10.1 Ma, followed by a temperate open forest environment with a less humid climate between 10.1 and 7.4 Ma, then giving way to an open temperate forest-steppe environment with a relatively arid climate between 7.4 and 6.4 Ma. The vegetation succession demonstrates that the aridification of the Asian interior occurred after ˜ 7-8 Ma, which is confirmed by other evidence from Asia. Furthermore, the aridification trend on the northeastern Tibetan Plateau parallels the global cooling of the late Miocene; the stepwise vegetation succession is consistent with the major uplift of the northeastern Tibetan Plateau during this time. These integrated environmental proxies indicate that the long-term global cooling and the Tibetan Plateau uplift caused the late Miocene aridification of the Asian interior.

  18. Beijing Tibet Middle School

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The year marks the 20th anniversary of the Central Government decision to run Tibet middle schools in the hinterland. At present, there are such schools or Tibetan classes in 26 provinces and municipalities directly under the Central Government. They work to train technical personnel and teachers for Tibet. Launched in 1987, the Beijing Tibet Middle School has since trained more than 2,800 middle and high school students for Tibet. Many of them returned to Tibet for construction.

  19. Fostering a Middle Class

    Institute of Scientific and Technical Information of China (English)

    YAO BIN

    2011-01-01

    Though there is no official definition of "middle class" in China,the tag has become one few Chinese people believe they deserve anyway.In early August,the Chinese Academy of Social Sciences released a report on China's urban development,saying China had a middle-class population of 230 million in 2009,or 37 percent of its urban residents.It also forecast half of city dwellers in China would be part of the middle class by 2023.

  20. Depositional architecture and evolution of the Late Miocene slope channel-fan-system in the northeastern shelf-margin of South China Sea

    Science.gov (United States)

    Jiang, Jing; Lin, Changsong; Zhang, Zhongtao; Tian, Hongxun; Tao, Ze; Liu, Hanyao

    2016-04-01

    The Upper Miocene in the Pearl River Mouth Basin of northwestern shelf-margin of South China Sea Basin contains a series of slope channel - fan systems. Their depositional architecture and evolution are documented in this investigation based on an integrated analysis of cores, logs, and seismic data. Four depositional-palaeogeomorphological elements have been identified in the slope channel-fan systems as follows: broad, shallow and unconfined or partly confined outer-shelf to shelf-break channels; deeply incised and confined unidirectionally migrating slope channels; broad or U-shaped, unconfined erosional-depositional channels; frontal splays-lobes and nonchannelized sheets. The slope channels are mostly oriented NW-SE, which migrated unidirectionally northeastwards and intensively eroded almost the whole shelf-slope zone. The channel infillings are mainly mudstones, interbedded with siltstones. They might be formed by gravity flow erosion as bypassing channels. They were filled with limited gravity flow sediments at the base and mostly filled with lateral accretionary packages of bottom current deposits. At the end of the channels, a series of small-scale slope fans developed and coalesced into fan aprons along the base of the slope. The unconfined erosional-depositional channels at the upper parts of the fan-apron-systems display compound infill patterns, and commonly have concave erosional bases and convex tops. The frontal splays-lobes representing middle to distal deposits of fan-apron-systems have flat-mounded or gull-wing geometries, and the internal architectures include bidirectional downlap, progradation, and chaotic infillings. The distal nonchannelized turbidite sheets are characterized by thin-bedded, parallel to sub-parallel sheet-like geometries. Three major unconformities or obvious erosional surfaces in the channel-fan systems of the Upper Miocene are recognized, and indicate the falling of sea-level. The depositional architecture of sequences

  1. An evaluation of the evolution of the latest miocene to earliest pliocene bouse lake system in the lower Colorado river valley, southwestern USA

    Science.gov (United States)

    Spencer, J.E.; Pearthree, P.A.; House, P.K.

    2008-01-01

    The upper Miocene to lower Pliocene Bouse Formation in the lower Colorado River trough of the American Southwest was deposited in three basins - from north to south, the Mohave, Havasu, and Blythe Basins - that were formed by extensional fault ing in the early to middle Miocene. Fossils of marine, brackish, and freshwater organ isms in the Bouse Formation have been interpreted to indicate an estuarine environment associated with early opening of the nearby Gulf of California. Regional uplift since 5 Ma is required to position the estuarine Bouse Formation at present elevations as high as 555 m, where greater uplift is required in the north. We present a compilation of Bouse Formation elevations that is consistent with Bouse deposition in lakes, with an abrupt 225 m northward increase in maximum Bouse elevations at Topock gorge north of Lake Havasu. Within Blythe and Havasu Basins, maximum Bouse elevations are 330 m above sea level in three widely spaced areas and reveal no evidence of regional tilting. To the north in Mohave Basin, numerous Bouse outcrops above 480 m elevation include three widely spaced sites where the Bouse Formation is exposed at 536-555 m. Numerical simulations of initial Colorado River inflow to a sequence of closed basins along the lower Colorado River corridor model a history of lake filling, spilling, evaporation and salt concentration, and outflow-channel incision. The simulations support the plausibility of evaporative concentration of Colorado River water to seawater-level salinities in Blythe Basin and indicate that such salinities could have remained stable for as long as 20-30 k.y. We infer that fossil marine organ isms in the Bouse Formation, restricted to the southern (Blythe) basin, reflect coloniza tion of a salty lake by a small number of species that were transported by birds.

  2. The development of miocene extensional and short-lived basin in the Andean broken foreland: The Conglomerado Los Patos, Northwestern Argentina

    Science.gov (United States)

    del Papa, Cecilia E.; Petrinovic, Ivan A.

    2017-01-01

    The Conglomerado Los Patos is a coarse-grained clastic unit that crops out irregularly in the San Antonio de los Cobres Valley in the Puna, Northwestern Argentina. It covers different units of the Cretaceous-Paleogene Salta Group by means of an angular unconformity and, in turn, is overlaid in angular unconformity by the Viscachayoc Ignimbrite (13 ± 0.3 Ma) or by late Miocene tuffs. Three lithofacies have been identified in the Corte Blanco locality; 1) Bouldery matrix-supported conglomerate (Gmm); 2) Clast-supported conglomerate (Gch) and 3) Imbricated clast-supported conglomerate (Gci). The stratigraphic pattern displays a general fining upward trend. The sedimentary facies association suggests gravitational flow processes and sedimentation in alluvial fan settings, from proximal to medial fan positions, together with a slope decrease upsection. Provenance studies reveal sediments sourced from Precambrian to Ordovician units located to the southwest, except for volcanic clasts in the Gmm facies that shows U/Pb age of 14.5 ± 0.5 Ma. This new age represents the maximum depositional age for the Conglomerado Los Patos, and it documents that deposition took place simultaneously during a period of increased tectonic and volcanic activity in the area. The structural analysis of the San Antonio de los Cobres Valley and the available thermochronological ages, indicate active N-S main thrusts and NW-SE transpressive and locally normal faults during the middle Miocene. In this context, we interpret the Conglomerado Los Patos to represent sedimentation in a small, extensional and short-lived basin associated with the compressional Andean setting.

  3. Late Oligocene-Early Miocene compressional tectosedimentary episode and associated land-mammal faunas in the Andes of central Chile and adjacent Argentina (32 37°s)

    Science.gov (United States)

    Semper, Thierry; Marshall, Larry G.; Rivano, Sergio; Godoy, Estanislao

    1994-01-01

    A reassessment of the geologic and land-mammal fossil evidence used in attribution of a tectosedimentary episode in the Andes between 32 and 37°S to the Middle Eocene "Incaic tectonic phase" of Peru indicates that the episode occurred during Late Oligocene-Early Miocene times(~ 27-20 Ma). From west to east, three structural domains are recognized for this time span in the study area: a volcanic arc (Chile); a thin-skinned, E-verging fold-thrust belt (Cordillera Principal, Chile-Argentina border strip); and a foreland basin (Argentina). Initiation of thrusting in the Cordillera Principal fold-thrust belt produced the coeval initiation of sedimentation in the foreland basin of adjacent Argentina. This onset of foreland deposition postdates strata bearing a Divisaderan Land Mammal Age fauna (i.e. ~ 35-30 Ma) and is marked at ~ 36°30'S by the base of the "Rodados Lustrosos" conglomerates, which are conformably overlain by sedimentary rocks containing a Deseadan Land Mammal Age fauna (i.e. ~ 29-21 Ma). Geologic relationships between the thick volcanic Abanico (Coya-Machalí) and Farellones formations also demonstrate that this tectosedimentary episode practically ended at ~ 20 Ma at least in the volcanic arc, and was therefore roughly coeval with the major tectonic crisis (~ 27-19 Ma) known in northwestern Andean Bolivia some 1500 km to the north. This strongly suggests that a long, outstanding tectonic upheaval affected at least an extended 12-37°S segment of the Andean margin of South America during Late Oligocene and Early Miocene times.

  4. Tracing multiple resedimentation on an isolated karstified plateau: The bauxite-bearing Miocene red clay of the Southern Bakony Mountains, Hungary

    Science.gov (United States)

    Kelemen, Péter; Dunkl, István; Csillag, Gábor; Mindszenty, Andrea; von Eynatten, Hilmar; Józsa, Sándor

    2017-08-01

    The Vöröstó (= Red Lake) Formation, located in the Southern Bakony Mountains and the Balaton Highlands (Hungary), is a red, clayey continental assemblage containing hard, up to fist-sized bauxite pebbles, occurring in a large apparent stratigraphic gap between underlying karstified Triassic carbonates and mid' Miocene to Quaternary cover. The origin and the exact stratigraphic position of the assemblage have been controversial for a long time. In this study, petrographic observations on the bauxite pebbles revealed common features with Cretaceous bauxite deposits known in the region, whereas heavy mineral composition of the red clay matrix is similar to those known from the Eocene bauxite horizon of the region. Single grain zircon U-Pb ages obtained from the bauxite pebbles and their red clayey matrix show similar late Archean to Jurassic age components. Additionally, Cenozoic U-Pb ages are well represented in the mostly euhedral zircon crystals separated from the red clays, whereas this volcanogenic contribution completely missing from the bauxite pebbles. SEM morphology and related EDX chemical analysis of clay minerals indicate polygenetic, detrital origin for the red clays. The main source material of the bauxite bearing Vöröstó Formation is most probably local Cretaceous and Eocene bauxite deposits exposed during the middle-late Miocene. These tropical weathering products were partly decomposed and degraded, but dilution by siliciclastic contribution is negligible. We suggest a transport mechanism dominated by local redeposition of mostly pelitic and allitic material through seasonal muddy debris flows within a karstic landscape.

  5. The Middle East.

    Science.gov (United States)

    Blouin, Virginia; And Others

    This sixth grade resource unit focuses on Middle East culture as seen through five areas of the social sciences: anthropology-sociology, geography, history, economics, and political science. Among objectives that the student is expected to achieve are the following: 1) given general information on the Middle East through the use of film, visuals,…

  6. Middle East Respiratory Syndrome

    Centers for Disease Control (CDC) Podcasts

    2014-07-07

    This podcast discusses Middle East Respiratory Syndrome, or MERS, a viral respiratory illness caused by Middle East Respiratory Syndrome Coronavirus—MERS-CoV.  Created: 7/7/2014 by National Center for Immunization and Respiratory Diseases (NCIRD).   Date Released: 7/7/2014.

  7. DEFINING THE MIDDLE CLASS

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Classifying the middle class remains controversial despite its alleged growth China’s cities housed more than 230 million middle-class residents in 2009 or 37 percent of the urban population,according to the 2011 Blue Book of Cities in China released on August 3.

  8. DEFINING THE MIDDLE CLASS

    Institute of Scientific and Technical Information of China (English)

    WANG HAIRONG

    2011-01-01

    China's cities housed more than 230 million middle-class residents in 2009ot 37 percent of the urban population,according to the 2011 Blue Book of Cities in China released on August 3.In China's main urban centers,Beijing and Shanghai,the middle class accounted for 46 percent and 38 percent,respectively,of the local population.

  9. Miocene Bahean stratigraphy in the Longzhong Basin,northern central China and its implications in environmental change

    Institute of Scientific and Technical Information of China (English)

    LI; Jijun; ZHANG; Jun; SONG; Chunhui; ZHAO; Zhijun; ZHANG; Yong; WANG; Xiuxi; ZHANG; Jianming; CUI; Qiaoyu

    2006-01-01

    Fossil mammal-riched Neogene strata are widely distributed in the southeast corner of the huge Longzhong Basin at Tianshui,Gansu Province,northern central China.Hipparion weihoense,a typical member of late Middle Miocene Bahean stage,was recently excavated at Yaodian along a well-exposed outcrop.Owing to the importance of the Bahean stage in the mammalian evolution and its potential for environmental change,we suggested a name of Yaodian Formation for the stratigraphy,which is correlated to the Bahe Formation at Lantian,Shaanxi.High resolution paleomagnetic dating of the section shows that the Yaodian Formation covers the period between 11.67 Ma and 7.43 Ma,with the site bearing Hipparion weihoense being estimated at about 10.54-10.30 Ma,providing first magnetostratigraphic chronology for the Bahean Stage.The Yaodian Formation consists of fluvial channel deposits (11.67-10.40 Ma) at the bottom,floodplain deposits in the middle (10.40-9.23 Ma) and shallow lake sediments at the top (9.23-7.43 Ma).This upward fining sequence suggests that the relief in nearby mountain ranges such as West Qinling to the south and Huajia Ling to the north was greatly reduced after long-term denudation,fluvial transport capacity was low,and finally the drainage system was disintegrated,replaced with broad-shallow lakes in which only fine sediments like mud and marlite were deposited,indicating an old stage of development of a planation surface.A remarkable shift in ecology and climatic environment was found at 7.4-7.7 Ma when paleoclimate changed from early warm humid to late dry as indicated by sedimentary facies changed from early shallow lake sequence to late eolian red clays and a former coniferous-deciduous mixed forest was replaced by grassland,leading to great growth of Hipparion Fauna of Baodean stage in the region.Therefore,it is estimated that the present high relief of Qinling and drainage pattern did not come into being until Late Pliocene in response to intensive

  10. The Sarikavak Tephra, Galatea, north central Turkey: a case study of a Miocene complex plinian eruption deposit

    Science.gov (United States)

    Schumacher, Rolf; Mues-Schumacher, Ulrike; Toprak, Vedat

    2001-12-01

    The Sarikavak Tephra from the central Galatean Volcanic Province (Turkey) represents the deposit of a complex multiple phase plinian eruption of Miocene age. The eruptive sequence is subdivided into the Lower-, Middle-, and Upper Sarikavak Tephra (LSKT, MSKT, USKT) which differ in type of deposits, lithology and eruptive mechanisms. The Lower Sarikavak Tephra is characterised by pumice fall deposits with minor interbedded fine-grained ash beds in the lower LSKT-A. Deposits are well stratified and enriched in lithic fragments up to >50 wt% in some layers. The upper LSKT-B is mainly reversely graded pumice fall with minor amounts of lithics. It represents the main plinian phase of the eruption. The LSKT-A and B units are separated from each other by a fine-grained ash fall deposit. The Middle Sarikavak Tephra is predominantly composed of cross-bedded ash-and-pumice surge deposits with minor pumice fall deposits in the lower MSKT-A and major pyroclastic flow deposits in the upper MSKT-B unit. The Upper Sarikavak Tephra shows subaerial laminated surge deposits in USKT-A and subaqueous tephra beds in USKT-B. Isopach maps of the LSKT pumice fall deposits as well as the fine ash at the LSKT-A/B boundary indicate NNE-SSW extending depositional fans with the source area in the western part of the Ovaçik caldera. The MSKT pyroclastic flow and surge deposits form a SW-extending main lobe related to paleotopography where the deposits are thickest. Internal bedding and lithic distribution of the LSKT-A result from intermittent activity due to significant vent wall instabilities. Reductions in eruption power from (partial) plugging of the vent produced fine ash deposits in near-vent locations and subsequent explosive expulsion of wall rock debris was responsible for the high lithic contents of the lapilli fall deposits. A period of vent closure promoted fine ash fall deposition at the end of LSKT-A. The subsequent main plinian phase of the LSKT-B evolved from stable vent

  11. Miocene Shark and Batoid Fauna from Nosy Makamby (Mahajanga Basin, Northwestern Madagascar).

    Science.gov (United States)

    Andrianavalona, Tsiory H; Ramihangihajason, Tolotra N; Rasoamiaramanana, Armand; Ward, David J; Ali, Jason R; Samonds, Karen E

    2015-01-01

    Madagascar is well known for producing exceptional fossils. However, the record for selachians remains relatively poorly known. Paleontological reconnaissance on the island of Nosy Makamby, off northwest Madagascar, has produced a previously undescribed assemblage of Miocene fossils. Based on isolated teeth, ten taxonomic groups are identified: Otodus, Carcharhinus, Galeocerdo, Rhizoprionodon, Sphyrna, Hemipristis, Squatina, Rostroraja, Himantura and Myliobatidae. Six are newly described from Madagascar for the Cenozoic (Galeocerdo, Rhizoprionodon, Sphyrna, Squatina, Rostroraja and Himantura). In association with these specimens, remains of both invertebrates (e.g., corals, gastropods, bivalves) and vertebrates (e.g., bony fish, turtles, crocodylians, and sirenian mammals) were also recovered. The sedimentary facies are highly suggestive of a near-shore/coastal plain depositional environment. This faunal association shares similarities to contemporaneous sites reported from North America and Europe and gives a glimpse into the paleoenvironment of Madagascar's Miocene, suggesting that this region was warm, tropical shallow-water marine.

  12. Miocene Shark and Batoid Fauna from Nosy Makamby (Mahajanga Basin, Northwestern Madagascar.

    Directory of Open Access Journals (Sweden)

    Tsiory H Andrianavalona

    Full Text Available Madagascar is well known for producing exceptional fossils. However, the record for selachians remains relatively poorly known. Paleontological reconnaissance on the island of Nosy Makamby, off northwest Madagascar, has produced a previously undescribed assemblage of Miocene fossils. Based on isolated teeth, ten taxonomic groups are identified: Otodus, Carcharhinus, Galeocerdo, Rhizoprionodon, Sphyrna, Hemipristis, Squatina, Rostroraja, Himantura and Myliobatidae. Six are newly described from Madagascar for the Cenozoic (Galeocerdo, Rhizoprionodon, Sphyrna, Squatina, Rostroraja and Himantura. In association with these specimens, remains of both invertebrates (e.g., corals, gastropods, bivalves and vertebrates (e.g., bony fish, turtles, crocodylians, and sirenian mammals were also recovered. The sedimentary facies are highly suggestive of a near-shore/coastal plain depositional environment. This faunal association shares similarities to contemporaneous sites reported from North America and Europe and gives a glimpse into the paleoenvironment of Madagascar's Miocene, suggesting that this region was warm, tropical shallow-water marine.

  13. Dominant 100,000-year precipitation cyclicity in a late Miocene lake from northeast Tibet.

    Science.gov (United States)

    Nie, Junsheng; Garzione, Carmala; Su, Qingda; Liu, Qingsong; Zhang, Rui; Heslop, David; Necula, Cristian; Zhang, Shihong; Song, Yougui; Luo, Zeng

    2017-03-01

    East Asian summer monsoon (EASM) precipitation received by northern China over the past 800 thousand years (ky) is characterized by dominant 100-ky periodicity, mainly attributed to CO2 and Northern Hemisphere insolation-driven ice sheet forcing. We established an EASM record in the Late Miocene from lacustrine sediments in the Qaidam Basin, northern China, which appears to exhibit a dominant 100-ky periodicity similar to the EASM records during the Late Quaternary. Because evidence suggests that partial or ephemeral ice existed in the Northern Hemisphere during the Late Miocene, we attribute the 100-ky cycles to CO2 and Southern Hemisphere insolation-driven Antarctic ice sheet forcing. This indicates a >6-million year earlier onset of the dominant 100-ky Asian monsoon and, likely, glacial and CO2 cycles and may indicate dominant forcing of Northern Hemisphere climate by CO2 and Southern Hemisphere ice sheets in a warm world.

  14. Chemical composition and palaeobotanical origin of Miocene resins from Kerala–Konkan Coast, western India

    Indian Academy of Sciences (India)

    Suryendu Dutta; Monalisa Mallick; Runcie Paul Mathews; Ulrich Mann; Paul F Greenwood; Rakesh Saxena

    2010-10-01

    The terpenoid composition of resins from the Miocene lignite horizons from the Kerala –Konkan Coast,western India was analyzed by Curie-point pyrolysis –gas chromatography –mass spectrometry (Cupy –GC –MS).The major pyrolysates were cadalene-based bicyclic sesquiterpenoids including some C30-C31 bicadinenes and bicadinanes typical of dammar resin from angiosperm plants of Dipterocarpaceae family.These plants are typically supported by tropical climates which the western Indian region was known to have experienced during early Tertiary period.The present study suggests that these palaeoclimatic conditions persisted until at least the Miocene epoch.These sesquiterpenoids which are commonly detected in many SE Asian crude oils may be utilised as useful biomarkers for petroleum exploration in the western Indian region.

  15. Depositional models and reservoir properties of Miocene reefs, Visayan Islands, Philippines

    Energy Technology Data Exchange (ETDEWEB)

    Carozzi, A.V. [Illinois Univ., Urbana, IL (United States)

    1995-01-01

    Recent commercial discoveries offshore Palawan have propelled the Philippines into the list of oil- and gas-producing countries, and have focussed on the importance of Miocene reefs as reservoirs. This new situation has motivated the update of earlier depositional-diagenetic models for the Miocene reefs in the Visayan Islands, which is presented in this paper. These reefs consisted of an association of corals, red algae, bryozoans, and encrusting foraminifers, which formed wave-resistant, constructed, barrier-and-atoll systems along the edge of narrow shelves, with associated back-reef patch reefs and frontal pinnacle reefs. The latter also grew on structural and depositional highs and platforms among deeper water carbonate mudstones and shales. Reservoirs developed in all the various types of buildups by extensive burial dissolution, often preceded (with the exception of some pinnacle reefs) by subaerial exposure generating secondary porosity by vadose to phreatic undersaturated dissolution. (author)

  16. Terpenoids Preserved in Fossils from Miocene-aged Japanese Conifer Wood.

    Science.gov (United States)

    Ludwiczuk, Agnieszka; Asakawa, Yoshinori

    2015-06-01

    The compositions of terpenoids from the solvent extracts of two silicified wood samples were analyzed using a GC/MS method. Chromatographic analysis showed that several biomolecules were preserved unaltered in the Miocene-aged Japanese wood. These were α-terpineol, α-cedrene, thujopsene, widdrol and ferruginol, among others. In addition to the bioterpenoids, the fossil woods contained a series of geoterpenoids that were generated from their biological precursors before and after burial. These were cadalene, daucalene, pseudowiddrene and cuparene. The chemical composition of both analyzed fossil samples suggest that the silicified woods collected in the Noto Peninsula belong to the Cupressaceae family; this was confirmed by morphological analysis. Both samples were identified as Taxodioxylon cunninghamioides, which is the most common Miocene wood in Japan.

  17. Late Miocene evolution of the Black Sea: insights from palynology and strontium isotope ratios

    Science.gov (United States)

    Grothe, Arjen; van Baak, Christiaan; Vasiliev, Iuliana; Sangiorgi, Francesca; Reichart, Gert-Jan; Stoica, Marius; Krijgsman, Wout

    2016-04-01

    During the late Miocene, the connection(s) between the Mediterranean Basin and the Atlantic Ocean deteriorated, which ultimately culminated in thick evaporite deposits and a water level drop in the Mediterranean Basin during the so-called Messinian Salinity Crisis (MSC, 5.97 - 5.33 Ma). It has been claimed that Black Sea, in response to the MSC, also desiccated but these claims have been proven incorrectly. Here we present palynological (dinoflagellate cysts and pollen) and strontium isotope ratios from two Black Sea records: the Zheleznyi Rog outcrop section and Deep Sea Drilling Project Hole 380A. Organic walled cyst-producing dinoflagellates are highly sensitive to even small changes in surface waters and strontium isotope ratios are excellent recorders of changing connectivity. Our records provide therefore more insights in the sensitivity of the Black Sea to Messinian Salinity Crisis and the general evolution of the late Miocene Black Sea.

  18. The presence of Lower Miocene (Eggenburgian in borehole 575 Cetea (East of Borod Basin, NW Romania

    Directory of Open Access Journals (Sweden)

    I. Petrescu

    2000-09-01

    Full Text Available The microfloral record evidenced in borehole 575 Cetea is very rich, consisting of 114 taxa, some of them being new species for the Tertiary of Romania. At the same time, it includes species of Eggenburgian age of the host rocks. The whole microflora assemblage suggests a forest-type vegetation developed in a warm, subtropical climate, characteristic for the Eggenburgian age of the Early Miocene. The Eggenburgian of Romania shows the same microfloral features as the Eggenburgian of Central Paratethys.

  19. Cretaceous to miocene palaeogegraphic evolution of Turkey: implications for hydrocarbon potential

    Energy Technology Data Exchange (ETDEWEB)

    Gorur, N. [Tubitak Mam, Gebze (Turkey)

    2001-04-01

    The Cretaceous to Miocene palaeogeographic development of Turkey in general reflects the evolution of the various oceanic branches of Neo-Tethys together with interactions between the Laurasian and Gondwanan margins. At the beginning of the Cretaceous, the first-order palacotectonic units which make up present-day Turkey either formed parts of these supercontinents or were isolated continental blocks within the Neo-Tethys. In Aptian to Albian times, north-dipping subduction commenced along the southern margins of these units and resulted in the development of magmatic arcs and arc-related sedimentary basins. Coeval with the start of subduction, large-scale ophiolite abduction occurred on the units' passive margins. Terminal closure of the oceans' branches took place between the latest Cretaceous and the Miocene, forming the Anatolian orogenic collage whose outline defines present-day Turkey. Post-collisional intra-continental convergence continued until the late Miocene and resulted in north-south shortening of the collage. This shortening led to internal imbrication, thrusting and crustal thickening. It forced the Anatolian landmass westwards, away from east Anatolia where there has been continuous north-south compression since the Miocene between Laurasia and the Arabian Platform. Both the continental and the oceanic palaeotectonic units pose significant problems regarding their original geometry, size, depth, extent, contact relations, motion paths, subduction polarity, stratigraphy and timing of formation. Clarification of these issues is essential if the units' original paleogeographic relationships with respect to Neo-Tethys are to be reconstructed. This paper reviews some of these problems with the aid of a number of palinspastic and non-palinspastic maps. These maps are intended to provide a basis for evaluating the hydrocarbon potential of Turkey. (author)

  20. Phylogenetic evidence for Miocene origin of Mediterranean lineages: species diversity, reproductive traits and geography.

    Science.gov (United States)

    Vargas, Pablo; Fernández-Mazuecos, Mario; Heleno, Ruben

    2017-09-11

    A review of 27 species-rich and species-poor plant clades (26 genera) of angiosperms of the Mediterranean floristic region was performed considering phylogenetic and biological data. The emergent pattern is that a majority of the Mediterranean plant clades split from their sister groups between the Miocene (23-5 Ma) and the Oligocene (40-23 Ma), far earlier than the historically proposed onset of the Mediterranean climate (c. 3.2 Ma). In addition, 12 clades of the species-poor group (14 clades) have stem ages inferred for each clade in the Miocene or older, and six clades within the species-rich group (13 clades) show divergence of each stem clade within the Oligocene and/or Miocene. High levels of species diversity may be related not only to an ancient (Paleocene-Miocene) origin but also to recent origin (Pliocene-Pleistocene) followed by active speciation and even explosive radiations - i.e. many species and lineages generated in a short period of time - in some Mediterranean clades (Aquilegia, Cistus, Dianthus, Linaria sect. Supinae, Reseda). In the species-rich group, reproductive key characters were found to be significantly more important for species recognition than vegetative key characters in eight clades, but no difference was found in four clades, and vegetative characters were predominant in one clade (Saxifraga). Geographical differentiation is proposed as predominant over divergence driven by pollination ecology.. We hypothesize an evolutionary process in which lineages adapted to pre-Mediterranean (pre-Pliocene) conditions in relatively small, xeric areas became strongly competitive and expanded when the Mediterranean climate became dominant (Pliocene-Quaternary) across the whole Mediterranean basin. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

  1. The challenge of simulating warmth of the mid-Miocene Climate Optimum in CESM1

    Directory of Open Access Journals (Sweden)

    A. Goldner

    2013-06-01

    Full Text Available The mid-Miocene Climatic Optimum (MMCO is an intriguing climatic period due to its above-modern temperatures in mid-to-high latitudes in the presence of close-to-modern CO2 concentrations. We use the recently released Community Earth System Model (CESM1.0 with a slab ocean to simulate this warm period, incorporating recent Miocene CO2 reconstructions of 400 ppm. We simulate a global mean annual temperature (MAT of 18 °C, ~4 °C above the pre-industrial value, but 4 °C colder than the global Miocene MAT we calculate from climate proxies. Sensitivity tests reveal that the inclusion of a reduced Antarctic ice sheet, eastern equatorial Pacific Ocean temperature anomalies, increased CO2 to 560 ppm, and variations in obliquity only marginally improve model-data agreement. All MMCO simulations have an equator to pole temperature gradient which is at least ~ 10 °C larger than the reconstruction from proxies. The MMCO simulation most comparable to the proxy records requires a CO2 concentration of 800 ppm. Our results illustrate that MMCO warmth is not reproducible using the CESM1.0 forced with CO2 concentrations reconstructed for the Miocene or including various proposed Earth system feedbacks; the remaining discrepancy in the MAT is comparable to that introduced by a CO2 doubling. The models tendency to underestimate proxy derived global MAT and overestimate the equator to pole temperature gradient suggests a major climate problem in the MMCO akin to those in the Eocene. Our results imply that this latest model, as with previous generations of climate models, is either not sensitive enough or additional forcings remain missing that explain half of the anomalous warmth and pronounced polar amplification of the MMCO.

  2. Miocene catfishes (Ariidae,Bagridae) from Lisbon: a Nilotic (or Sudanian) type fauna

    OpenAIRE

    Antunes, M. Telles

    2010-01-01

    Miocene catfishes from Lisbon are dealt with. Two distinct sets of pectoral and dorsal pterygiophores are described. That from the Langhian V-b is referred to Arius sp. probably close to A. heudeloti. Another ser from the uppermost Burdigalian V-a may be ascribed to a bagrid, cf. Chrysichthys sp., identified for the first time in this region. The catfish and Lates association is sctrikingly similar to African, nilotic or sudanian ones as far as freshwaters are concerned. In marine, coastal...

  3. Miocene c4tfishes (Ariidae, Bagridae) from Lisbon: a Nilotic (or Sudanian) type fauna

    OpenAIRE

    Antunes, M. Telles

    1989-01-01

    Miocene catfishes from Lisbon are dealt with. Two distinct sets of pectoral and dorsal pterygiophores are described. That from the Langhian V-b is referred to Arius sp. probably close to A. Beudeloti. Another set from the uppermost Burdigalian V-a may be ascribed to a bagtid, cf, Chrysichthys sp., identified for the first time in this region. The catfish and Lates association is strikingly similar to African, nilotic or sudanian ones as far as freshwaters are concerned. In marine, co...

  4. Turbidites as indicators of paleotopography, Upper Miocene Lake Pannon, Western Mecsek Mountains (Hungary)

    OpenAIRE

    Sztanó Orsolya; Sebe Krisztina; Csillag Gábor; Magyar Imre

    2015-01-01

    The floor of Lake Pannon covering the Pannonian Basin in the Late Miocene had considerable relief, including both deep sub-basins, like the Drava Basin, and basement highs, like the Mecsek Mts, in close proximity. The several km thick lacustrine succession in the Drava Basin includes profundal marls, basin-center turbidites, overlain by shales of basin-margin slopes, coarsening-upward deltaic successions and alluvial deposits. Along the margin of the Mecsek Mts locally derived shoreface sands...

  5. Clay mineralogy indicates a mildly warm and humid living environment for the Miocene hominoid from the Zhaotong Basin, Yunnan, China

    Science.gov (United States)

    Zhang, Chunxia; Guo, Zhengtang; Deng, Chenglong; Ji, Xueping; Wu, Haibin; Paterson, Greig A.; Chang, Lin; Li, Qin; Wu, Bailing; Zhu, Rixiang

    2016-02-01

    Global and regional environmental changes have influenced the evolutionary processes of hominoid primates, particularly during the Miocene. Recently, a new Lufengpithecus cf. lufengensis hominoid fossil with a late Miocene age of ~6.2 Ma was discovered in the Shuitangba (STB) section of the Zhaotong Basin in Yunnan on the southeast margin of the Tibetan Plateau. To understand the relationship between paleoclimate and hominoid evolution, we have studied sedimentary, clay mineralogy and geochemical proxies for the late Miocene STB section (~16 m thick; ca. 6.7-6.0 Ma). Our results show that Lufengpithecus cf. lufengensis lived in a mildly warm and humid climate in a lacustrine or swamp environment. Comparing mid to late Miocene records from hominoid sites in Yunnan, Siwalik in Pakistan, and tropical Africa we find that ecological shifts from forest to grassland in Siwalik are much later than in tropical Africa, consistent with the disappearance of hominoid fossils. However, no significant vegetation changes are found in Yunnan during the late Miocene, which we suggest is the result of uplift of the Tibetan plateau combined with the Asian monsoon geographically and climatically isolating these regions. The resultant warm and humid conditions in southeastern China offered an important refuge for Miocene hominoids.

  6. Tertiary evolution of the Shimanto belt (Japan): A large-scale collision in Early Miocene

    Science.gov (United States)

    Raimbourg, Hugues; Famin, Vincent; Palazzin, Giulia; Yamaguchi, Asuka; Augier, Romain

    2017-07-01

    To decipher the Miocene evolution of the Shimanto belt of southwestern Japan, structural and paleothermal studies were carried out in the western area of Shikoku Island. All units constituting the belt, both in its Cretaceous and Tertiary domains, are in average strongly dipping to the NW or SE, while shortening directions deduced from fault kinematics are consistently orientated NNW-SSE. Peak paleotemperatures estimated with Raman spectra of organic matter increase strongly across the southern, Tertiary portion of the belt, in tandem with the development of a steeply dipping metamorphic cleavage. Near the southern tip of Ashizuri Peninsula, the unconformity between accreted strata and fore-arc basin, present along the whole belt, corresponds to a large paleotemperature gap, supporting the occurrence of a major collision in Early Miocene. This tectonic event occurred before the magmatic event that affected the whole belt at 15 Ma. The associated shortening was accommodated in two opposite modes, either localized on regional-scale faults such as the Nobeoka Tectonic Line in Kyushu or distributed through the whole belt as in Shikoku. The reappraisal of this collision leads to reinterpret large-scale seismic refraction profiles of the margins, where the unit underlying the modern accretionary prism is now attributed to an older package of deformed and accreted sedimentary units belonging to the Shimanto belt. When integrated into reconstructions of Philippine Sea Plate motion, the collision corresponds to the oblique collision of a paleo Izu-Bonin-Mariana Arc with Japan in Early Miocene.

  7. Miocene Fossils Reveal Ancient Roots for New Zealand's Endemic Mystacina (Chiroptera) and Its Rainforest Habitat.

    Science.gov (United States)

    Hand, Suzanne J; Lee, Daphne E; Worthy, Trevor H; Archer, Michael; Worthy, Jennifer P; Tennyson, Alan J D; Salisbury, Steven W; Scofield, R Paul; Mildenhall, Dallas C; Kennedy, Elizabeth M; Lindqvist, Jon K

    2015-01-01

    The New Zealand endemic bat family Mystacinidae comprises just two Recent species referred to a single genus, Mystacina. The family was once more diverse and widespread, with an additional six extinct taxa recorded from Australia and New Zealand. Here, a new mystacinid is described from the early Miocene (19-16 Ma) St Bathans Fauna of Central Otago, South Island, New Zealand. It is the first pre-Pleistocene record of the modern genus and it extends the evolutionary history of Mystacina back at least 16 million years. Extant Mystacina species occupy old-growth rainforest and are semi-terrestrial with an exceptionally broad omnivorous diet. The majority of the plants inhabited, pollinated, dispersed or eaten by modern Mystacina were well-established in southern New Zealand in the early Miocene, based on the fossil record from sites at or near where the bat fossils are found. Similarly, many of the arthropod prey of living Mystacina are recorded as fossils in the same area. Although none of the Miocene plant and arthropod species is extant, most are closely related to modern taxa, demonstrating potentially long-standing ecological associations with Mystacina.

  8. On Mesopithecus habitat: Insights from late Miocene fossil vertebrate localities of Bulgaria.

    Science.gov (United States)

    Clavel, Julien; Merceron, Gildas; Hristova, Latinka; Spassov, Nikolaï; Kovachev, Dimitar; Escarguel, Gilles

    2012-07-01

    The aim of this study is to describe the environments where the cercopithecid Mesopithecus was found during latest Miocene in Europe. For this purpose, we investigate the paleoecology of the herbivorous ungulate mesofauna of three very rich late Miocene fossil localities from southwestern Bulgaria: Hadjidimovo, Kalimantsi and Strumyani. While Mesopithecus has been found in the two first localities, no primate remains have yet been identified in Strumyani. Comparison between localities with and without primates using the herbivore mesofauna allows the cross-corroboration of paleoenvironmental conditions where this primate did and did not live. A multi-parameter statistical approach involving 117 equid and 345 bovid fossil dental and postcranial (phalanges, metapodia, astragali) remains from these three localities provides species to generic-level diet and locomotor habit information in order to characterize the environment in which Mesopithecus evolved. The analysis of dental mesowear indicates that the bovids were mainly mixed feeders, while coeval equids were more engaged in grazing. Meanwhile, postcranial remains show that the ungulate species from Hadjidimovo and Kalimantsi evolved in dry environments with a continuum of habitats ranging from slightly wooded areas to relatively open landscapes, whereas the Mesopithecus-free Strumyani locality was in comparison reflecting a rather contrasted mosaic of environments with predominant open and some more closed and wet areas. Environments in which Mesopithecus is known during the late Miocene were not contrasted landscapes combining open grassy areas and dense forested patches, but instead rather restricted to slightly wooded and homogeneous landscapes including a developed grassy herbaceous layer.

  9. C4 plant expansion since the late Miocene and the evolution of Asian summer monsoon

    Science.gov (United States)

    Wu, H.; Guo, Z.; Guiot, J.; Yu, Y.; Ge, J.; Zhang, Y.; Peng, S.

    2015-12-01

    A dramatic expansion of C4 plant distribution occurred in the South Asia during the late Miocene and in the East Asia during the Pliocene period, with broad spatial and temporal variations. Although the event is well documented, whether subsequent expansions were caused by a decreased atmospheric CO2 concentration or climate change is a contentious issue. In this study, we used an improved inverse vegetation modeling approach that accounts for the physiological responses of C3 and C4 plants to quantitatively reconstruct the paleoclimate in the Siwalik of South Asia and in the Loess Plateau of East Asia, based on pollen and carbon isotope data. We also studied the sensitivity of the C3 and C4 plants to changes in the climate and the atmospheric CO2 concentration. We suggest that the expansion of the C4 plant distribution since the late Miocene was unlikely caused by reduced CO2 levels alone. The expansion may have been primarily triggered by regional aridification, and seasonal analysis revealed that this climate shift mainly attributed to the summer rainfall decrease. Our findings suggest that this abrupt ecological shift mainly resulted from the weakening of the Asian summer monsoon, which may related to the decrease of SST in the tropic since the late Miocene.

  10. Molluscan fauna from the Miocene sediments of Kachchh, Gujarat, India – Part 3. Gastropods

    Indian Academy of Sciences (India)

    Kantimati G Kulkarni; Satarupa Bhattacharjee Kapoor; Vidyadhar D Borkar

    2010-06-01

    Systematic description of 25 gastropod species from the Khari Nadi Formation (Aquitanian) and Chhasra Formation (Burdigalian) from the Kachchh District, Gujarat, India is given. A checklist of 116 forms including those reported by earlier researchers, emending taxonomic identifications wherever necessary, is also provided. Vredenburg had referred these two formations together as ‘the Gaj Beds of Kachchh’. He noticed the affinity of molluscs among the Miocene deposits of Kachchh and Kathiawar regions of Gujarat, and Sind province of Pakistan. He also observed that molluscs from his ‘Lower Gaj’ and ‘Upper Gaj’ Formations showed relationship respectively with the Rembang (Aquitanian) and Njalindung (Burdigalian) series of the East Indies. Aquitanian and Burdigalian ages assigned by him were later substantiated by Raju on the basis of foraminifera. Present studies corroborated that the molluscan assemblage from the Miocene rocks of Kachchh is closely related to that from the Gaj Beds of Sind and the Ashapura Clay Member of Kathiawar; besides revealing that the fauna from these three formations taken together is essentially endemic. Discovery of certain species from the Quilon Beds in the Miocene of Kachchh evinces a close affinity between these two formations. The present fauna includes five extant forms, while 29 forms have related species in the Recent fauna.

  11. Late Miocene sedimentary environments in south-western Amazonia (Solimões Formation; Brazil).

    Science.gov (United States)

    Gross, Martin; Piller, Werner E; Ramos, Maria Ines; Douglas da Silva Paz, Jackson

    2011-08-01

    In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ(18)O and δ(13)C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake ("Lake Pebas") or any influx of marine waters can be excluded for that region during the Late Miocene.

  12. On middle cube graphs

    Directory of Open Access Journals (Sweden)

    C. Dalfo

    2015-10-01

    Full Text Available We study a family of graphs related to the $n$-cube. The middle cube graph of parameter k is the subgraph of $Q_{2k-1}$ induced by the set of vertices whose binary representation has either $k-1$ or $k$ number of ones. The middle cube graphs can be obtained from the well-known odd graphs by doubling their vertex set. Here we study some of the properties of the middle cube graphs in the light of the theory of distance-regular graphs. In particular, we completely determine their spectra (eigenvalues and their multiplicities, and associated eigenvectors.

  13. Mixing and melt sources in the Miocene Aztec Wash pluton (Nevada, USA) as revealed by zircon Hf and O and whole rock Sr, Nd, and Hf isotopes

    Science.gov (United States)

    Ryan, M.; Miller, J. S.; Miller, C. F.; Bromley, S.; Davies, G. R.; Schmitt, A. K.

    2011-12-01

    The 15.6 Ma Aztec Wash Pluton (AWP) is one of several Miocene intrusions located within the northern Colorado River extensional corridor. Extensive E-W tilting of fault blocks has exposed the pluton from the roof to 5 km structural depth. Earlier field and petrologic studies subdivided the AWP into two distinct zones: (1) a Granite Zone (GZ) comprised of relatively homogeneous granite with subtle differences in textures and mineralogy; (2) a Heterogeneous Zone (HZ), which interfingers the GZ, contains evidence for mafic and felsic magma input with a wide compositional range (42-78 wt% SiO2), and abundant field evidence for hybridization. Previous whole rock geochemistry and zircon trace element analyses indicated that compositional variation was produced by multi-component mixing between mafic and felsic melts within the HZ. New whole rock Sr, Nd, and Hf isotope data from the HZ show that all rocks (including high-silica granites) formed by mixing Precambrian crust and enriched mantle, with mixtures having a large mantle fraction (≥50%). New Hf (n=189) and O (n=241) isotope analyses of zircon from samples in the HZ confirm these melt sources and provide a broader perspective on hybridization processes within the AWP. Zircon grains from all samples show heterogeneous Hf and O isotopic compositions (-5 to -18 ɛHf; 4.5-7.5% δ18O), but despite the clear signature of Precambrian crust in the whole rock data, obvious Precambrian zircons (or cores) were mostly absent; only one zircon was clearly Precambrian (ɛHf = -25). Resolvable intragrain variability is relatively limited (including the Precambrian grain, which is unzoned). Zircons from hand samples and from compositional groups also show heterogeneous ɛHf and δ18O values, although the spreads are more restricted than in the whole data set (6-10 ɛHf in granites, 5-7 ɛHf in intermediate "hybrids", 5-6 ɛHf in gabbro/diorite sheets). Oxygen isotope values for the zircons also show intra-handsample heterogeneity

  14. Displaced/re-worked rhodolith deposits infilling parts of a complex Miocene multistorey submarine channel: A case history from the Sassari area (Sardinia, Italy)

    Science.gov (United States)

    Murru, Marco; Bassi, Davide; Simone, Lucia

    2015-08-01

    In the Sassari area (north-western Sardinia, Italy), the Miocene Porto Torres sub-basin sequences represent the complex multistorey mixed carbonate-siliciclastic submarine feature called the Sassari Channel. During the late Burdigalian-early Serravallian, repeated terrigenous supplies from uplifted Paleozoic crystalline substrata fed the Sassari Channel system by means of turbidity and locally hyper-concentrated turbidity flows. Shelfal areas were the source of terrigenous clasts, but open shelf rhodalgal/foramol carbonate areas were very productive and largely also contributed to the channel infilling. Re-worked sands and skeletal debris were discontinuously re-sedimented offshore as pure terrigenous, mixed and/or carbonate deposits. Major sediment supply was introduced between the latest Burdigalian and the start of the middle Langhian, during which a large amount of carbonate, mixed and siliciclastic sediments reached the Porto Torres Basin (Sassari Channel I). Contributions from shallow proximal source areas typify the lower intervals (Unit A) in marginal sectors of the channel. Upward, these evolve into autochthonous rhodolith deposits, winnowed by strong currents in relatively shallow well lit settings within a complex network of narrow tidally-controlled channels (Unit D) locally bearing coral assemblages. Conversely, re-sedimented rhodoliths from the Units B and C accumulated under conditions of higher turbidity. In deeper parts of the channel taxonomically diversified rhodoliths point to the mixing of re-deposited skeletal components from different relatively deep bathmetric settings. In the latest early Langhian, major re-sedimentation episodes, resulting in large prograding bodies (Unit D), triggered by repeated regression pulses in a frame of persistent still stand. During these episodes photophile assemblages dwelled in the elevated margin sectors of the channel. A significant latest early Langhian drop in relative sea-level resulted in impressive mass

  15. Characteristics of porosity and permeability layer of fossil Halimeda reef mineral rock of Miocene in the Xisha Islands and its genetic model

    Institute of Scientific and Technical Information of China (English)

    XU Hong; WEI Kai; CUI Ruyong; ZHU Yurui; EBERLI G P; LUO Wei; ZHAO Xinwei; CAI Ying; LIU Xinyu; YAN Guijing; ZHANG Bolin

    2015-01-01

    Halimeda is one of the major reef-building algas in the middle Miocene of Xisha, and one of the significant reef-building algas in the algal reef oil and gas field of the South China Sea. However, there have been few reports regarding the characteristics of mineral rocks, reservoir porosity and permeability layers, and sedimentation-diagenetic-evolution of fossil Halimeda systems. The present paper briefly introduces the relevant studies on chlorophyta Halimeda and the research status of oil and gas exploration. Through the 1 043 m core of the Xichen-1 well, we studied the characteristics of the mineral rocks and porosity and permeability of the middle Miocene Halimeda of the Yongle Atoll, identified and described the segments of fossil Halimeda, and pointed out that most of the segment slides are vertical sections in ovular, irregular or long strips. The overwhelming majority of these fossil Halimeda found and studied are vertical sections instead of cross sections. In this paper, knowledge regarding the cross sections of fossil Halimeda is reported and proven to be similar with the microscopic characteristics of modern living Halimeda;fossil Halimeda are buried in superposition;it is shown that there are different structures present, including typical bio-segment structure, and due to its feature of coexisting with red alga, tying structure, twining structure and encrusting structure are all present;and finally, it is suggested to classify the fossil Halimeda into segment algal reef dolomites. In addition, all of the studied intervals are moderately dolomitized. Secondary microcrystalline-dolosparite dominates the original aragonite raphide zones, and aphanitic-micrite dolomite plays the leading role in the cortexes and medullas;in the aragonite raphide zones between medulla and cysts, secondary dissolved pores and intercrystalline pores are formed inside the segments, and algal frame holes are formed between segments;therefore, a pore space network system

  16. Middle Helladic Period

    DEFF Research Database (Denmark)

    Sarri, Kalliopi

    1999-01-01

    The Middle Bronze Age on Mainland Greece is also known as the Middle Helladic period. The chronological framework of this period extends from the beginnings of the second millenium - roughly 1900 - until 1550 BC, that is until the beginnings of the Mycenaean period. The Middle Helladic period...... is considered as the dark period of the cultural decline. The remains of the material culture reveal a clear retrogression while the information available on the social stratification and economy are so few and problematic in interpretation that this period is considered as the "Middle Age of Greek Prehistory......". About 1900 BC, the period during which the first palaces of Crete were being built, Mainland Greece was entering a long period of decline during which economic features changed radically. A large number of metals and imported products became particularly rare while composite forms of economic...

  17. An objective statistical test for eccentricity forcing of Oligo-Miocene climate

    Science.gov (United States)

    Proistosescu, C.; Huybers, P.; Maloof, A. C.

    2008-12-01

    We seek a maximally objective test for the presence of orbital features in Oligocene and Miocene δ18O records from marine sediments. Changes in Earth's orbital eccentricity are thought to be an important control on the long term variability of climate during the Oligocene and Miocene Epochs. However, such an important control from eccentricity is surprising because eccentricity has relatively little influence on Earth's annual average insolation budget. Nevertheless, if significant eccentricity variability is present, it would provide important insight into the operation of the climate system at long timescales. Here we use previously published data, but using a chronology which is initially independent of orbital assumptions, to test for the presence of eccentricity period variability in the Oligocene/Miocene sediment records. In contrast to the sawtooth climate record of the Pleistocene, the Oligocene and Miocene climate record appears smooth and symmetric and does not reset itself every hundred thousand years. This smooth variation, as well as the time interval spanning many eccentricity periods makes Oligocene and Miocene paleorecords very suitable for evaluating the importance of eccentricity forcing. First, we construct time scales depending only upon the ages of geomagnetic reversals with intervening ages linearly interpolated with depth. Such a single age-depth relationship is, however, too uncertain to assess whether orbital features are present. Thus, we construct a second depth-derived age-model by averaging ages across multiple sediment cores which have, at least partly, independent accumulation rate histories. But ages are still too uncertain to permit unambiguous detection of orbital variability. Thus we employ limited tuning assumptions and measure the degree by orbital period variability increases using spectral power estimates. By tuning we know that we are biasing the record toward showing orbital variations, but we account for this bias in our

  18. The Cenozoic Diversity of Agglutinated Foraminifera - Evidence for a late Oligocene to early Miocene diversification event

    Science.gov (United States)

    Kaminski, Michael; Setoyama, Eiichi; Kender, Sev; Cetean, Claudia

    2014-05-01

    The agglutinated foraminifera are among the most abundant micro-organisms in the deep marine environment and have a diversity record extending back to the late Precambrian. We present an updated diversity curve for agglutinated foraminiferal genera based on the stratigraphic ranges of all the agglutinated genera recognized as valid in the classification of Kaminski (2014). The data set for this analysis is based on the stratigraphic ranges of agglutinated genera published in Foraminiferal Genera and their Classification, which has been subsequently updated based on published studies and our new observations. The mean standing diversity of agglutinated foraminiferal genera was compiled by counting the number of boundary crossers rather than the number of genera in each stage. In this study, we report the stratigraphic and geographical occurrence of a benthic foraminiferal diversification event that has previously received little attention. In the latest Oligocene to earliest Miocene a number of trochospiral agglutinated genera with alveolar or canaliculate walls first appeared in the fossil record. Our studies of late Oligocene of the Congo fan, offshore Angola (Kender et al., 2008; Cetean and Kaminski, 2011) have revealed a diverse assemblage that includes new taxa of deep-water agglutinated foraminifera. In a biostratigraphic study of the Miocene foraminiferal assemblages Kender et al. (2008) noted steadily increasing diversity and proportions of infaunal agglutinated foraminiferal morphotypes over the lower Miocene interval. The proportion of infaunal agglutinated foraminifera assigned to the order Textularida increased dramatically in the lower mid-Miocene, suggesting expansion of the oxygen minimum zone into deeper waters. In addition to the trochospiral alveolar genera, several species of Reticulophragmium and Cyclammina display rapid diversification into numerous separate lineages that are at present not reflected in our generic diversity record owing to

  19. Post-Miocene Right Separation on the San Gabriel and Vasquez Creek Faults, with Supporting Chronostratigraphy, Western San Gabriel Mountains, California

    Science.gov (United States)

    Beyer, Larry A.; McCulloh, Thane H.; Denison, Rodger E.; Morin, Ronald W.; Enrico, Roy J.; Barron, John A.; Fleck, Robert J.

    2009-01-01

    on the Vasquez Creek Fault adds to the generally accepted 22-23 km of middle-late Miocene right separation established for the San Gabriel Fault east of the bifurcation, resulting in total right separation of 34-35 km northwest of the bifurcation. Clast sizes and lithologies in Saugus Formation deformed alluvial fan deposits in the Gold and Little Tujunga Canyons area indicate that alluvial stream flow was from the north or north-northeast. The alluvial fan complex is beheaded at the San Gabriel Fault Zone, and no correlative deposits have been found north of the fault zone. Likely sources of several distinctive clast types are east of the bifurcation and north of the Vasquez Creek Fault. Combining these data with right slip caused by the 34 deg +-6 deg of clockwise local block rotation suggests that post-Saugus Formation (Big Tujunga Canyons gives an age of 16.14+-0.05 Ma from 40Ar/39Ar analysis. Improved understanding of the upper Miocene stratigraphy indicates large early movement on the eastern Santa Susana Fault at about 7-6 Ma.

  20. Rescuing Middle School Astronomy

    Science.gov (United States)

    Mayo, L. A.; Janney, D.

    2010-12-01

    There is a crisis in education at the middle school level (Spellings, 2006). Recent studies point to large disparities in middle school performance in schools with high minority populations. The largest disparities exist in areas of math and science. Astronomy has a universal appeal for K-12 students but is rarely taught at the middle school level. When it is taught at all it is usually taught in isolation with few references in other classes such as other sciences (e.g. physics, biology, and chemistry), math, history, geography, music, art, or English. The problem is greatest in our most challenged school districts. With scores in reading and math below national averages in these schools and with most state achievement tests ignoring subjects like astronomy, there is little room in the school day to teach about the world outside our atmosphere. Add to this the exceedingly minimal training and education in astronomy that most middle school teachers have and it is a rare school that includes any astronomy teaching at all. In this presentation, we show how to develop and offer an astronomy education training program for middle school teachers encompassing a wide range of educational disciplines that are frequently taught at the middle school level. The prototype for this program was developed and launched in two of the most challenged and diverse school systems in the country; D.C. Public Schools, and Montgomery County (MD) Public Schools.

  1. Evaluating the mid Miocene paleoclimate of Lower Carinthia (Austria) based on high resolution palynological studies from the Lavanttal Basin

    Science.gov (United States)

    Grímsson, Friðgeir; Bouchal, Johannes Martin; Zetter, Reinhard; Grimm, Guido

    2016-04-01

    , characteristic for the humid and semi-humid, summer-rain areas of the meridional and nemoral zone. (Co-)Dominant genera in these forests are the various members of the northern hemispheric Fagales. Important indicator taxa include Fagus, one of the most common and widespread genera in temperate, mixed mesophytic forests of North America, China and Japan, and Quercus Group Ilex, a co-dominant group in the East Asian monsoon influenced, winter-dry or fully humid southern foothills of the Himalayas and montane regions of south-western and central China. Equally informative is Corylus, and the co-occurrence of Carya, Juglans, Pterocarya and Engelhardioideae, pinpointing towards forests as today found in south-western China and the warm subtropical parts of the southeastern United States. References: Denk T, Grimm GW, Grímsson F, Zetter R. 2013. Evidence from "Köppen signatures" of fossil plant assemblages for effective heat transport of Gulf Stream to subarctic North Atlantic during Miocene cooling. Biogeosciences 10: 7927-7942. Grímsson F, Grimm GW, Meller B, Bouchal JM, Zetter R. 2015. Combined LM and SEM study of the middle Miocene (Sarmatian) palynoflora from the Lavanttal Basin, Austria: part IV. Magnoliophyta 2 - Fagales to Rosales. Grana: http://dx.doi.org/10.1080/00173134.2015.1096566 Velitzelos D, Bouchal JM, Denk T. 2014. Review of the Cenozoic floras and vegetation of Greece. Review of Palaeobotany and Palynology 204: 56-117.

  2. Mid-Miocene thermal Impact on the Lithosphere of Asia by sub-lithospheric convective Mantle Material: Temporal Transition from high- to moderate-Mg Magmatism beneath Vitim Plateau, Southern Siberia

    Science.gov (United States)

    Chuvashova, Irina; Rasskazov, Sergei

    2015-04-01

    In Inner Asia, high-Mg lavas is characteristic of the Middle Miocene volcanism. In the Vitim plateau, we studied the high- and moderate-Mg volcanics, erupted at 16-14 and 14-13 Ma, respectively. In the former (small volume) unit, initial basaltic melts, contaminated by crustal material, were followed by uncontaminated high-Mg basanites and basalts of transitional (K-Na-K) compositions and afterwards by picrobasalts and basalts of K series. In the latter (high-volume) unit, initial basalts and basaltic andesites of transitional (Na-K-Na) compositions and basalts of Na series were overlain by basalts and trachybasalts of K-Na series. From pressure estimates after equation [Scarrow, Cox, 1995], we infer that the high-Mg melts were derived from the sub-lithospheric mantle as deep as 115-150 km, unlike the moderate-Mg ones that were produced by melting of the shallow lithospheric mantle. We suggest that the studied transition from high- and moderate-Mg magmatism reflected the mid-Miocene thermal impact on the lithosphere by a hot sub-lithospheric mantle material from the Transbaikalian low-velocity domain with potential temperature estimates up to 1510 oC. This thermal impact triggered rifting in the lithosphere of the Baikal Rift System. The study is supported by the Russian Foundation for Basic Research (Grant 14-05-31328).

  3. Evidence for Late Oligocene-Early Miocene episode of transtension along San Andreas Fault system in central California

    Energy Technology Data Exchange (ETDEWEB)

    Stanley, R.G.

    1986-04-01

    The San Andreas is one of the most intensely studied fault systems in the world, but many aspects of its kinematic history remain controversial. For example, the period from the late Eocene to early Miocene is widely believed to have been a time of negligible strike-slip movement along the San Andreas fault proper, based on the rough similarity of offset of the Eocene Butano-Point of rocks Submarine Fan, the early Miocene Pinnacles-Neenach volcanic center, and an early Miocene shoreline in the northern Gabilan Range and San Emigdio Mountains. Nonetheless, evidence indicates that a late Oligocene-early Miocene episode of transtension, or strike-slip motion with a component of extension, occurred within the San Andreas fault system. The evidence includes: (1) about 22-24 Ma, widespread, synchronous volcanic activity occurred at about 12 volcanic centers along a 400-km long segment of the central California coast; (2) most of these volcanic centers are located along faults of the San Andreas system, including the San Andreas fault proper, the San Gregorio-Hosgri fault, and the Zayante-Vergeles fault, suggesting that these and other faults were active and served as conduits for magmas rising from below; (3) during the late Oligocene and early Miocene, a pull-apart basin developed adjacent to the San Andreas fault proper in the La Honda basin near Santa Cruz; and (4) during the late Oligocene and early Miocene, active faulting, rapid subsidence, and marine transgression occurred in the La Honda and other sedimentary basins in central California. The amount of right-lateral displacement along the San Andreas fault proper during this transtentional episode is unknown but was probably about 7.5-35 km, based on model studies of pull-apart basin formation. This small amount of movement is well within the range of error in published estimates of the offset of the Eocene to early Miocene geologic features noted.

  4. The Decahedrella-event in ODP Hole 909C - Implications for Miocene stratigraphic and paleoclimatic interpretations across the Fram Strait gateway

    Science.gov (United States)

    Schreck, Michael; Nam, Seung-il; Matthiessen, Jens

    2014-05-01

    -water acritarch have been reported from several ODP sites in the Norwegian-Greenland Sea and Labrador Sea displaying its supraregional prevalence in the high northern latitudes. This acme, as well as the highest and lowest occurrence of this species, has been independently calibrated to the pristine magnetostratigraphy of ODP Site 907 providing new tie-points for the construction of the ODP Site 909 age model and the interpretation of the paleomagnetic record. Initial results indicate that the existing age models may have to be shifted by roughly 2 Ma towards a younger age within the Middle to Late Miocene interval, resulting in a much younger age for the base of the hole than previously thought. Here we present a revised age model for the late Middle to Late Miocene of ODP Site 909 and discuss resulting implications for previous paleoceanographic and paleoclimatic interpretations, e.g. initiation of deep-water exchange through Fram Strait, establishment and strengthening of the East Greenland current, and the onset of modern like ice drift pattern.

  5. Middle managers service leadership

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    Lucio Roberto Lescano Duncan

    2011-12-01

    Full Text Available A big challenge in modern service organization is to focus on customers and to forge their satisfaction and loyalty. Innovation, information technology and value added are decisive factors, however the main aspect to consider is the human factor. It is necessary to focus on people in order to improve the service capability within the organization.Middle manager is the link between the strategy designed by top management and the execution to deliver services, that is realized by employees guided by leaders of middle level. Our study is focused on middle manager service orientation as the pillar to get a customer focus and to forge the service employees' performance.We consider that middle managers have to asume a service leadership in order to foster the productivity and employees' commitment. In that sense we focus especially on middle managers' main roles. Those are the key aspect to deploy a service culture, and at the same time to promote employees' satisfaction that drives their performance and development.

  6. Tectonic evolution of the Lorca sector from the Late Miocene to the Quaternary; Evolucion tectonica del sector de Lorca desde el Mioceno superior al Cuaternario

    Energy Technology Data Exchange (ETDEWEB)

    Sanz de Galdeano, C.; Garcia-Mondejar, J.; Ferrairo, J. M.

    2012-07-01

    The Alhama de Murcia Fault presents several parallel surfaces, forming a wide fault zone. Even at distances of several km, there are other faults belonging to the same system. These faults created subsidiary structures, some of kilometric lengths, as in the case of the progressive uplift of the Pena Rubia sector, occurring from the end of the Middle Miocene. Later and partially coeval, was the formation of the Castillo anti form. The sinistral displacement of the large Alhama de Murcia Fault and that of smaller dextral conjugated faults was caused by stress from a nearly N-S compression and a related perpendicular extension. At some points in time, the positions of s1 and s2 axes switched, permitting normal movements, particularly in faults with approximately N-S directions, and hence raising the possibility of this type of focal mechanism in some earthquakes.The NE border of Pena Rubia (on the eastern end of Sierra de Las Estancias), also the SE border of the Lorca Basin, is affected by small (compared with the main ones) strike-slip and reverse faults that are also consistent with the palaeostress deduced. Nevertheless, along this border no significant or continuous fault is detected. (Author) 32 refs.

  7. {Gamma}-ray prospecting of major faults of Miocene basins; Chushinto taisekibon no keisei ni kakawaru danso wo taisho to shita hoshano tansa

    Energy Technology Data Exchange (ETDEWEB)

    Iwata, A. [Shimada Technical Consultants, Ltd., Shimane (Japan); Yamauchi, S.; Adachi, K. [Shimane University, Shimane (Japan); Yoon, S.; Kil, R, [Pusan National University, Pusan (Korea, Republic of)

    1997-05-27

    The Masuda basin in the western edge of Shimane Prefecture and the Pohang basin in the southern part of the east cost of Korea had been formed in the middle of Miocene epoch of Neogene period, and show similarity in their geology and structure. A gamma-ray prospecting was carried out on major faults that have had been involved in forming these basins. A portable gamma-ray analysis device, model 8630 made by Clearpulse Corporation was used for the measurement. Emanation of radon and its migration are known generally, whereas rise in radon is recognized above crevices with deep opening trend. The present faults having been involved in forming the basins are thought to have large falls in positive faults and often accompany crevices with opening trend. This estimation is thought endorsed by the result of the present prospecting. In addition, such faults may often form geological boundaries, and the present survey has had geological division made easily with total gamma-ray. A gamma-ray exploration using both of the spectrum method and the total count method is a process sufficiently utilizable in geological surveys on structures in peripheries of sedimentary basins. 6 refs., 7 figs.

  8. Cones, Seeds, and Foliage of Tetraclinis Salicornioides (Cupressaceae) from the Oligocene and Miocene of Western North America: A Geographic Extension of the European Tertiary Species.

    Science.gov (United States)

    Kvacek; Manchester; Schorn

    2000-03-01

    The cupressaceous genus Tetraclinis is recognized from the Oligocene and Miocene of western North America on the basis of co-occurring seed cones, seeds, and foliage branches. Morphological and anatomical comparisons with the two previously recognized European Tertiary species indicate that the North American specimens are morphologically inseparable from Tetraclinis salicornioides (Unger) Kvacek. The North American taxon is treated as a new variety, T. salicornioides (Unger) Kvacek var. praedecurrens (Knowlton) comb. et stat. nov., and is distinguished from the European representatives, T. salicornioides (Unger) Kvacek var. salicornioides, by slight anatomical differences in the leaf epidermis. Although cones and seeds of the fossil species are closely similar to those of extant Tetraclinis articulata, the foliage is more "spreading," composed of flattened segments with fused facial and lateral leaves that are apparently adaptive for a more mesic climate. The recognition of T. salicornioides in western North America along with the absence of Tetraclinis in the fossil and recent flora of eastern Asia provide evidence for communication of the species across the North Atlantic during the early or middle Tertiary.

  9. THE MIOCENE AND DEVONIAN MAGMATISM AT THE JUNCTION BETWEEN THE TUVA-MONGOLIAN MASSIF AND SIBERIAN CRATON: COMMON COMPONENT OF MANTLE SOURCES AND ITS ORIGIN

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    Sergey V. Rasskazov

    2015-09-01

    Full Text Available Devonian dikes of the Urik-Belaya and Shagayte-Gol-Urik zones and Miocene lavas of the Urik volcanic field are spatially associated with each other at the structural junction between the Neoproterozoic Tuva-Mongolian massif and Siberian craton. The former dike belt is represented by basalts and basaltic andesites of tholeiitic series and the latter one by trachybasalts, trachyandesitic basalts of moderately alkaline series and trachybasalts, phonotephrites of highly alkaline one. The Urik volcanic field is composed of trachybasalts and trachyandesitic basalts of moderately alkaline series. A partial similarity between magmatic series of different age is found in terms of major oxides, trace elements, and Sr, Pb isotopes. The common component corrected for age was defined through its converging mixing trends with those of the lithospheric mantle and crust. The component identification was a basis for deciphering the nature of isotopic and geochemical heterogeneity of evolved magmatic sources. It was inferred that the common component characterizes either a modified (depleted reservoir of the lower mantle or, more likely, a local region of the convecting asthenospheric mantle that underlies the Tuva-Mongolian massif. The latter interpretation assumes the formation of a locally convecting asthenosphere in the middle Neoproterozoic, along with the development of the Oka zone at the massif, and puts constrains on later sufficient processing of the asthenosphere due to rising plumes or subducting slabs.

  10. Sphene and zircon in the Highland Range volcanic sequence (Miocene, southern Nevada, USA): Elemental partitioning, phase relations, and influence on evolution of silicic magma

    Science.gov (United States)

    Colombini, L.L.; Miller, C.F.; Gualda, G.A.R.; Wooden, J.L.; Miller, J.S.

    2011-01-01

    Sphene is prominent in Miocene plutonic rocks ranging from diorite to granite in southern Nevada, USA, but it is restricted to rhyolites in coeval volcanic sequences. In the Highland Range volcanic sequence, sphene appears as a phenocryst only in the most evolved rocks (72-77 mass% SiO2; matrix glass 77-78 mass% SiO2). Zr-in-sphene temperatures of crystallization are mostly restricted to 715 and 755??C, in contrast to zircon (710-920??C, Ti-in-zircon thermometry). Sphene rim/glass Kds for rare earth elements are extremely high (La 120, Sm 1200, Gd 1300, Lu 240). Rare earth elements, especially the middle REE (MREE), decrease from centers to rims of sphene phenocrysts along with Zr, demonstrating the effect of progressive sphene fractionation. Whole rocks and glasses have MREE-depleted, U-shaped REE patterns as a consequence of sphene fractionation. Within the co-genetic, sphene-rich Searchlight pluton, only evolved leucogranites show comparable MREE depletion. These results indicate that sphene saturation in intruded and extruded magmas occurred only in highly evolved melts: abundant sphene in less silicic plutonic rocks represents a late-stage 'bloom' in fractionated interstitial melt. ?? 2011 Springer-Verlag.

  11. Oligocene-to-Early Miocene depositional and structural evolution of the Calabria-Peloritani Arc southern terrane (Italy) and geodynamic correlations with the Spain Betics and Morocco Rif

    Science.gov (United States)

    Bonardi, Glauco; de Capoa, Paola; Di Staso, Angelida; Estévez, Antonio; Martín-Martín, Manuél; Martín-Rojas, Iván; Perrone, Vincenzo; Tent-Manclús, José Enrique

    2003-11-01

    The Calabria-Peloritani Arc southern terrane is a stack of crystalline basement nappes, some of them provided with a widely outcropping Alpine sedimentary cover, sealed by clastics of the Stilo-Capo d'Orlando Formation (SCOF). New field observations in the Stilo area lead to define a Pignolo Formation as a sedimentary cycle predating the emplacement of the uppermost nappe (Stilo Unit) of the tectonic pile. It includes the well-known Lithothamnium and larger foraminifers bearing calcarenites, previously interpreted as a basal member of the SCOF. The biostratigraphic revision of both formations, together with recently published data about other preorogenic deposits, point to a stacking of the whole terrane between the Aquitanian and the middle-late Burdigalian. A comparison between the sedimentary cycles characterising the Calabria-Peloritani southern terrane during the Oligocene-Early Miocene and those almost coeval of the Betic-Rifian internal units highlights their quite similar evolution. Thus it is reliable that both the orogenic belts originated from contiguous paleogeographic realms. These considerations confirm that the present western Mediterranean Chains were originally segments of a continuous orogenic belt disrupted by the opening of the Balearic and Tyrrhenian basins.

  12. Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing.

    Science.gov (United States)

    LaRiviere, Jonathan P; Ravelo, A Christina; Crimmins, Allison; Dekens, Petra S; Ford, Heather L; Lyle, Mitch; Wara, Michael W

    2012-06-06

    Deep-time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration (that is, the atmospheric partial pressure of CO(2), p(co(2))). Although past studies have explored these responses during portions of the Cenozoic era (the most recent 65.5 million years (Myr) of Earth history), comparatively little is known about the climate of the late Miocene (∼12-5 Myr ago), an interval with p(co(2)) values of only 200-350 parts per million by volume but nearly ice-free conditions in the Northern Hemisphere and warmer-than-modern temperatures on the continents. Here we present quantitative geochemical sea surface temperature estimates from the Miocene mid-latitude North Pacific Ocean, and show that oceanic warmth persisted throughout the interval of low p(co(2)) ∼12-5 Myr ago. We also present new stable isotope measurements from the western equatorial Pacific that, in conjunction with previously published data, reveal a long-term trend of thermocline shoaling in the equatorial Pacific since ∼13 Myr ago. We propose that a relatively deep global thermocline, reductions in low-latitude gradients in sea surface temperature, and cloud and water vapour feedbacks may help to explain the warmth of the late Miocene. Additional shoaling of the thermocline after 5 Myr ago probably explains the stronger coupling between p(co(2)), sea surface temperatures and climate that is characteristic of the more recent Pliocene and Pleistocene epochs.

  13. Steps in the intensification of Benguela upwelling over the Walvis Ridge during Miocene and Pliocene

    Science.gov (United States)

    Hoetzel, Sebastian; Dupont, Lydie M.; Marret, Fabienne; Jung, Gerlinde; Wefer, Gerold

    2017-01-01

    Upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient-rich cold waters to the surface and therefore influencing ocean productivity and global climate. The Benguela upwelling system (BUS) is one of the major upwelling areas in the world. Previous reconstructions of the BUS mainly focused on the onset and intensification in southern and central parts, but changes of the northern part have been rarely investigated in detail. Using the Late Miocene to Pliocene organic-walled dinoflagellate cyst record of ODP Site 1081, we reconstruct and discuss the early upwelling history over the Walvis Ridge with a special focus on the movement of the Angola-Benguela Front (ABF). We suggest that during the Late Miocene the Angola Current flowed southwards over the Walvis Ridge more frequently than today because the ABF was probably located further south as a result of a weaker meridional temperature gradient. A possible strengthening of the meridional gradient during the latest Miocene to early Pliocene in combination with uplift of south-western Africa intensified the upwelling along the coast and increased the upwelling's filaments over the Walvis Ridge. An intermediate period from 6.2 to 5.5 Ma is shown by the dominance of Habibacysta tectata, cysts of a cool-tolerant dinoflagellate known from the northern Atlantic, indicating changing oceanic conditions contemporaneous with the Messinian Salinity Crisis. From 4.3 Ma on, the upwelling signal got stronger again and waters were well-mixed and nutrient-rich. Our results indicate a northward migration of the ABF as early as 7 Ma and the initial stepwise intensification of the BUS.

  14. Steps in the intensification of Benguela upwelling over the Walvis Ridge during Miocene and Pliocene

    Science.gov (United States)

    Hoetzel, Sebastian; Dupont, Lydie M.; Marret, Fabienne; Jung, Gerlinde; Wefer, Gerold

    2016-03-01

    Upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient-rich cold waters to the surface and therefore influencing ocean productivity and global climate. The Benguela upwelling system (BUS) is one of the major upwelling areas in the world. Previous reconstructions of the BUS mainly focused on the onset and intensification in southern and central parts, but changes of the northern part have been rarely investigated in detail. Using the Late Miocene to Pliocene organic-walled dinoflagellate cyst record of ODP Site 1081, we reconstruct and discuss the early upwelling history over the Walvis Ridge with a special focus on the movement of the Angola-Benguela Front (ABF). We suggest that during the Late Miocene the Angola Current flowed southwards over the Walvis Ridge more frequently than today because the ABF was probably located further south as a result of a weaker meridional temperature gradient. A possible strengthening of the meridional gradient during the latest Miocene to early Pliocene in combination with uplift of south-western Africa intensified the upwelling along the coast and increased the upwelling's filaments over the Walvis Ridge. An intermediate period from 6.2 to 5.5 Ma is shown by the dominance of Habibacysta tectata, cysts of a cool-tolerant dinoflagellate known from the northern Atlantic, indicating changing oceanic conditions contemporaneous with the Messinian Salinity Crisis. From 4.3 Ma on, the upwelling signal got stronger again and waters were well-mixed and nutrient-rich. Our results indicate a northward migration of the ABF as early as 7 Ma and the initial stepwise intensification of the BUS.

  15. Correlating Mediterranean shallow water deposits with global Oligocene-Miocene stratigraphy and oceanic events.

    Science.gov (United States)

    Reuter, Markus; Piller, Werner E; Brandano, Marco; Harzhauser, Mathias

    2013-12-01

    Shallow-marine sediment records have the strong potential to display sensitive environmental changes in sedimentary geometries and skeletal content. However, the time resolution of most neritic carbonate records is not high enough to be compared with climatic events as recorded in the deep-sea sediment archives. In order to resolve the paleoceanographic and paleoclimatic changes during the Oligocene-Miocene transition in the Mediterranean shallow water carbonate systems with the best possible time resolution, we re-evaluated the Decontra section on the Maiella Platform (central Apennines, Italy), which acts as a reference for the correlation of Oligocene-Miocene shallow water deposits in the Mediterranean region. The 120-m-thick late Oligocene-late Miocene carbonate succession is composed of larger foraminiferal, bryozoan and corallinacean limestones interlayered with distinct planktonic foraminiferal carbonates representing a mostly outer neritic setting. Integrated multi-proxy and facies analyses indicate that CaCO3 and total organic carbon contents as well as gamma-ray display only local to regional processes on the carbonate platform and are not suited for stratigraphic correlation on a wider scale. In contrast, new biostratigraphic data correlate the Decontra stable carbon isotope record to the global deep-sea carbon isotope record. This links relative sea level fluctuations, which are reflected by facies and magnetic susceptibility changes, to third-order eustatic cycles. The new integrated bio-, chemo-, and sequence stratigraphic framework enables a more precise timing of environmental changes within the studied time interval and identifies Decontra as an important locality for correlating not only shallow and deep water sediments of the Mediterranean region but also on a global scale.

  16. A model study of the first ventilated regime of the Arctic Ocean during the early Miocene

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    Bijoy Thompson

    2012-07-01

    Full Text Available The tectonic opening of Fram Strait during the Neogene was a significant geological event that transferred the Arctic Ocean from a poorly ventilated enclosed basin, with weak exchange with the North Atlantic, to a fully ventilated “ocean stage”. Previous tectonic and physical oceanographic analyses suggest that the early Miocene Fram Strait was likely several times narrower and less than half as deep as the present-day 400 km wide and 2550 m deep strait. Here we use an ocean general circulation model with a passive age tracer included to further address the effect of the Fram Strait opening on the early Miocene Arctic Ocean circulation. The model tracer age exhibits strong spatial gradient between the two major Arctic Ocean deep basins: the Eurasian and Amerasian basins. There is a two-layer stratification and the exchange flow through Fram Strait shows a bi-layer structure with a low salinity outflow from the Arctic confined to a relatively thin upper layer and a saline inflow from the North Atlantic below. Our study suggests that although Fram Strait was significantly narrower and shallower during early Miocene, and the ventilation mechanism quite different in our model, the estimated ventilation rates are comparable to the chemical tracer estimates in the present-day Arctic Ocean. Since we achieved ventilation of the Arctic Ocean with a prescribed Fram Strait width of 100 km and sill depth of 1000 m, ventilation may have preceded the timing of a full ocean depth connection between the Arctic Ocean and North Atlantic established through seafloor spreading and the development of the Lena Trough.

  17. Ancient nursery area for the extinct giant shark megalodon from the Miocene of Panama.

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    Catalina Pimiento

    Full Text Available BACKGROUND: As we know from modern species, nursery areas are essential shark habitats for vulnerable young. Nurseries are typically highly productive, shallow-water habitats that are characterized by the presence of juveniles and neonates. It has been suggested that in these areas, sharks can find ample food resources and protection from predators. Based on the fossil record, we know that the extinct Carcharocles megalodon was the biggest shark that ever lived. Previous proposed paleo-nursery areas for this species were based on the anecdotal presence of juvenile fossil teeth accompanied by fossil marine mammals. We now present the first definitive evidence of ancient nurseries for C. megalodon from the late Miocene of Panama, about 10 million years ago. METHODOLOGY/PRINCIPAL FINDINGS: We collected and measured fossil shark teeth of C. megalodon, within the highly productive, shallow marine Gatun Formation from the Miocene of Panama. Surprisingly, and in contrast to other fossil accumulations, the majority of the teeth from Gatun are very small. Here we compare the tooth sizes from the Gatun with specimens from different, but analogous localities. In addition we calculate the total length of the individuals found in Gatun. These comparisons and estimates suggest that the small size of Gatun's C. megalodon is neither related to a small population of this species nor the tooth position within the jaw. Thus, the individuals from Gatun were mostly juveniles and neonates, with estimated body lengths between 2 and 10.5 meters. CONCLUSIONS/SIGNIFICANCE: We propose that the Miocene Gatun Formation represents the first documented paleo-nursery area for C. megalodon from the Neotropics, and one of the few recorded in the fossil record for an extinct selachian. We therefore show that sharks have used nursery areas at least for 10 millions of years as an adaptive strategy during their life histories.

  18. Miocene fossil hydrothermal system associated with a volcanic complex in the Andes of central Chile

    Science.gov (United States)

    Fuentes, Francisco; Aguirre, Luis; Vergara, Mario; Valdebenito, Leticia; Fonseca, Eugenia

    2004-11-01

    Cenozoic deposits in the Andes of central Chile have been affected by very low-grade burial metamorphism. At about 33°S in the Cuesta de Chacabuco area, approximately 53 km north of Santiago, two Oligocene and Miocene volcanic units form a ca. 1300-m-thick rock pile. The Miocene unit corresponds to a volcanic complex composed of two eroded stratovolcanoes. Secondary mineral assemblages in both units were studied petrographically and using X-ray diffraction and electron microprobe analyses. Most of the igneous minerals are wholly or partially preserved, and the ubiquitous secondary minerals are zeolites and mafic phyllosilicates. The alteration pattern observed is characterized by a lateral zonation in secondary mineralogy related to a lateral increase in temperature but not to stratigraphic depth. The following three zones were established, mainly based on the distribution of zeolites: zone I comprises heulandite, thomsonite, mesolite, stilbite and tri-smectite; zone II contains laumontite, yugawaralite, prehnite, epidote and chlorite; and zone III comprises wairakite, epidote, chlorite, diopside, biotite and titanite. For each zone, the following temperature ranges were estimated: zone I, 100-180 °C; zone II, 180-270 °C; and zone III, 245-310 °C. The alteration episode was characterized by a high Pfluid/ Ptotal ratio (ca. 1.0), although slightly variable, a high geothermal gradient of ca. 160 °C km -1 and fluid pressures below 500 bars. Although temperature was the main control on the mineral zonation, several interrelated parameters, mainly fluid composition, porosity and permeability, were also important. Hot, near neutral to slightly alkaline pH, alkali chloride hydrothermal fluids with very low dissolved CO 2 contents deposited the secondary minerals. The alteration pattern is the result of depositing fluids in outflow regions from a hydrothermal system developed inside a volcanic complex during the Miocene. The hydrothermal system has been eroded to a

  19. Miocene-Pleistocene Paleoclimate and Paleoenvironment in the Meade Basin, Kansas

    Science.gov (United States)

    Snell, K. E.; Uno, K. T.; Fetrow, A. C.; Burgess, C.; Lukens, W. E.; Fox, D. L.; Fox-Dobbs, K.; Polissar, P. J.

    2015-12-01

    The Meade Basin in southwestern Kansas preserves a unique record of paleovegetation and small mammal faunal change from the Miocene to the Pleistocene. Many of the paleosols preserved in this basin contain paleosol carbonate nodules, thick calcretes and abundant organic-rich horizons, which makes it ideally suited for a multiproxy study that explores the role of paleoenvironmental change in driving floral and faunal change. Here we focus on the carbonate samples where we measured carbon and oxygen isotopes (δ13Cc and δ18Oc, respectively); used clumped isotope thermometry (Δ47) to estimate soil temperature and soil water δ18O; and assessed the preservation state and additional paleoenvironmental features of the samples using optical and cathodoluminescence (CL) microscopy. The carbon isotope record matches previous studies from the region and shows an increase in the relative abundance of C4 biomass on the landscape since the late Miocene. The Δ47 temperatures and the δ18O of soil water, while variable, show no significant change in average values through time. The textural and luminescenece characteristics suggest some samples have undergone moderate to extensive diagenetic alteration from groundwater fluids, perhaps causing some of the variability in the geochemical records. Soil depth may also account for some of the variability. Overall, these data suggest that temperature is unlikely to be the dominant factor driving paleovegetation and faunal change in this region from the Miocene to Pleistocene. In addition, these data highlight the importance of assessing preservation for all carbonate samples, regardless of whether or not the samples have been deeply buried.

  20. A partial skeleton of a new lamniform mackerel shark from the Miocene of Europe

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    Jürgen Kriwet

    2015-12-01

    Full Text Available Cenozoic lamniform sharks are mostly represented by isolated teeth and vertebrae, whereas articulated skeletal remains are usually very scarce. Here, we describe a partial skeleton of an extinct lamniform shark consisting of 42 slightly disarticulated teeth, 49 vertebrae, and additional unidentifiable cranial and postcranial remains. The specimen originates from the Miocene mica-clay of Groß Pampau (North Germany, which is of late Langenfeldian age (= Serravallian-Tortonian boundary; middle–late Miocene. A total of 13 measurements of each tooth, as well as morphological features, were used to reconstruct the dentition of this specimen and to provide detailed taxonomic information. Additionally, the total body size and age at death were established using methodologies based on vertebral and tooth measurements and vertebral centra growth ring counts, respectively. The specimen undoubtedly represents the most complete individual of “Carcharodon (= Isurus escheri”, previously known only from a few isolated teeth. The dental pattern (e.g., marked dignathic and monognathic heterodonty patterns; only slightly labio-lingually compressed upper teeth; upper teeth slender with distally inclined or curved main cusps; massive, hook-like upper intermediate tooth; main cusps with crenulated cutting edges; lateral cusplets in teeth of all ontogenetic stages clearly separates this shark from all hitherto known Cenozoic and Recent lamnids and a new genus, Carcharomodus, consequently is introduced. Carcharomodus escheri comb. nov. is a characteristic element of late early Miocene to the Pliocene Western and Central European fish faunas. All previously identified Pacific occurrences represent a different taxon. We estimate that the specimen had a total body length of about 4 m and that it was older than 10 years and thus might have reached maturity before death, as indicated by all available evidence.

  1. Stacked, Lower Miocene tide-dominated estuary deposits in a transgressive succession, Western Desert, Egypt

    Science.gov (United States)

    Hassan, Safiya M.; Steel, Ronald J.; El Barkooky, Ahmed; Hamdan, Mohamed; Olariu, Cornel; Helper, Mark A.

    2012-12-01

    The net transgressive Lower Miocene Moghra Formation of Egypt is a sandy estuarine complex consisting of a series of stratigraphic units that reflect repeated transgressive to regressive shoreline movements across the Burdigalian (Lower Miocene) coastal landscape. The transgressive part of each unit is preserved atop a deep erosional scour surface, and consists of tidal-fluvial sandstones with tree logs and vertebrate bones that transition up to cross-stratified, tidal estuarine channel deposits and then to open-marine, shelf mudstones and limestones. In contrast, the regressive part is thinly developed and consists of thin-bedded, fossiliferous shelf mudstones that pass upward to thin, tide-influenced delta-front deposits. Each of the nine transgressive-regressive units of the Moghra Formation is capped by a river-scour surface that severely truncates the underlying regressive half-unit. Regional tectonic subsidence and an overall decreasing influx of clastic sediment accounts for the accumulation of the Moghra Formation and its overall transgressive character. The high frequency relative base-level changes reflected by the transgressive-regressive units (averaging < 350 kyr) that punctuate the overall transgressive stratigraphic trend are thought to have been driven by (1) sea-level changes caused by recently-documented variations in East Antarctic ice-sheet volume during the Lower Miocene, and/or by (2) variation in the large-scale influx of sediment to the region (during continuous tectonic subsidence). The relative importance of the sea-level (eustatic fall) vs. supply drive (deep fluvial scour) mechanisms for producing the repeated and widespread Burdigalian incision surfaces in the Moghra succession cannot easily be determined.

  2. A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia.

    Science.gov (United States)

    Rybczynski, Natalia; Dawson, Mary R; Tedford, Richard H

    2009-04-23

    Modern pinnipeds (seals, sea lions and the walrus) are semi-aquatic, generally marine carnivores the limbs of which have been modified into flippers. Recent phylogenetic studies using morphological and molecular evidence support pinniped monophyly, and suggest a sister relationship with ursoids (for example bears) or musteloids (the clade that includes skunks, badgers, weasels and otters). Although the position of pinnipeds within modern carnivores appears moderately well resolved, fossil evidence of the morphological steps leading from a terrestrial ancestor to the modern marine forms has been weak or contentious. The earliest well-represented fossil pinniped is Enaliarctos, a marine form with flippers, which had appeared on the northwestern shores of North America by the early Miocene epoch. Here we report the discovery of a nearly complete skeleton of a new semi-aquatic carnivore from an early Miocene lake deposit in Nunavut, Canada, that represents a morphological link in early pinniped evolution. The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing. The new fossil shows evidence of pinniped affinities and similarities to the early Oligocene Amphicticeps from Asia and the late Oligocene and Miocene Potamotherium from Europe. The discovery suggests that the evolution of pinnipeds included a freshwater transitional phase, and may support the hypothesis that the Arctic was an early centre of pinniped evolution.

  3. New fossil records of Ceratozamia (Zamiaceae, Cycadales from the European Oligocene and lower Miocene

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    Kvaček Zlatko

    2014-12-01

    Full Text Available New compression leaf material of Ceratozamia (Zamiaceae has been recognised in the European Cenozoic. A leaflet of Ceratozamia floersheimensis (Engelhardt Kvaček was recovered among unidentified material from the Oligocene of Trbovlje, former Trifail, Slovenia, housed in old collections of the Austrian Geological Survey, Vienna. It is similar in morphology and epidermal anatomy to other specimens previously studied from the lower Oligocene of Flörsheim, Germany and Budapest, Hungary. A fragmentary leaflet assigned to C. hofmannii Ettingsh. was recovered in the uppermost part of the Most Formation (Most Basin in North Bohemia, Czech Republic and dated by magnetostratigraphy and cyclostratigraphy to CHRON C5Cn.3n, that is, the latest early Miocene. It yielded excellently preserved epidermal structures, permitting confirmation of the generic affinity and a more precise comparison with this lower Miocene species previously known from Austria (Münzenberg, Leoben Basin and re-investigated earlier. Both the Oligocene and Miocene populations of Ceratozamia are based on isolated disarticulated leaflets matching some living representatives in the size and slender form of the leaflets. Such ceratozamias thrive today in extratropical areas near the present limits of distribution of the genus along the Sierra Madre Orientale in north-eastern Mexico, in particular C. microstrobila Vovides & J.D. Rees and others of the C. latifolia complex, as well as C. hildae G.P. Landry & M.C. Wilson (“bamboo cycad”. The occurrence of Ceratozamia suggests subtropical to warm-temperate, almost frostless climate and a high amount of precipitation. The accompanied fossil vegetation of both species corresponds well with the temperature regime. While the Oligocene species in Hungary probably thrived under sub-humid conditions, the remaining occurrences of fossil Ceratozamia were connected with humid evergreen to mixed-mesophytic forests.

  4. Middle matching mining algorithm

    Institute of Scientific and Technical Information of China (English)

    GUO Ping; CHEN Li

    2003-01-01

    A new algorithm for fast discovery of sequential patterns to solve the problems of too many candidate sets made by SPADE is presented, which is referred to as middle matching algorithm. Experiments on a large customer transaction database consisting of customer_id, transaction time, and transaction items demonstrate that the proposed algorithm performs better than SPADE attributed to its philosophy to generate a candidate set by matching two sequences in the middle place so as to reduce the number of the candidate sets.

  5. On the middle class

    OpenAIRE

    MacLennan, Michael; Magalhães, Beatrix Judice

    2013-01-01

    The Middle class as a concept has evolved over time, taking on various meanings at various points throughout history, becoming an object to aspire to for poor people, an object of desire for a strong government, a buzzword for politicians the world over, and the source of new customers for firms, and the global economy more broadly. This special issue of Poverty in Focus, exclusively devoted to the exploration of themes related to the middle class is part of a larger endeavour initiated by Th...

  6. Two flat-backed polydesmidan millipedes from the Miocene Chiapas-amber Lagerstatte, Mexico.

    Directory of Open Access Journals (Sweden)

    Francisco Riquelme

    Full Text Available Two species of fossil polydesmidan millipedes (Diplopoda: Polydesmida embedded in amber are described from Miocene strata near Simojovel, in the Chiapas Highlands, Mexico. Maatidesmus paachtun gen. et sp. nov., placed into Chelodesmidae Cook, 1895, and Anbarrhacus adamantis gen. et sp. nov., assigned in the family Platyrhacidae Pocock, 1895. Morphological data from fossil specimens have been recovered using 3D X-ray micro-computed tomography and regular to infrared-reflected microscopy. Both fossil species are recognizable as new primarily but not exclusively, by collum margin modification and remarkable paranotal and metatergite dorsal sculpture.

  7. Combination of hand mapping and automatic mapping to reveal the Miocene high elevation Pyrenean peneplain

    Science.gov (United States)

    Bosch, Gemma V.; Babault, Julien; Van Den Driessche, Jean

    2016-04-01

    A striking feature of the morphology of the Pyrenees is the occurrence of high-elevation, low-relief surfaces, which are interpreted as remnants of a single Miocene planation surface. Whether the original surface was uplifted or developed at high altitude is debated. This "Miocene Pyrenean peneplain" has been dissected by fluvial and glacial erosion during the Quaternary. Reworking by glacial erosion also provides new smooth surfaces such as glacial cirque floors that must not be confused with the remnants of the original planation surface. The later are convex-up landforms whereas glacial cirque floors are concave-up landforms. To reveal the Miocene high-elevation Pyrenean peneplain, we combined hand mapping and automatic mapping at the scale of the whole chain. From previous mapping in literature and from our own field work, we first perform a map of both the Miocene planation surface remnants and the Quaternary glacial cirque floors. Using Digital Elevation Models, numerical parameters were extracted from this map to characterize the two types of smooth surfaces. The slope is the parameter that helps to delimitate and differentiate the smooth surfaces from the rest of the Pyrenean topography. To distinguish between the two types of smooth surfaces we used the Topographic Index (TPI). This parameter is the difference between the elevation of a point and the mean elevation. Choosing the pertinent radius according to the scale of the landform to map, and the pertinent values interval, we can differentiate the planation surface (convex-up) from the glacial cirque floors (concave-up). A sensitivity test was performed to determine the best radius and the best interval for TPI and slope values to distinguish between the two types of smooth surfaces. Finally, we used a combination of slope values, TPI values and radius to determine automatically the high-elevation, low-relief surfaces in the entire Pyrenees. We verified in the field the presence of the newly mapped high

  8. Late Miocene Pacific plate kinematic change explained with coupled global models of mantle and lithosphere dynamics

    DEFF Research Database (Denmark)

    Stotz, Ingo Leonardo; Iaffaldano, Giampiero; Davies, DR

    2017-01-01

    and the consequent subduction polarity reversal. The uncertainties associated with the timing of this event, however, make it difficult to quantitatively demonstrate a dynamical association. Here, we first reconstruct the Pacific plate's absolute motion since the mid-Miocene (15 Ma), at high-temporal resolution....../lithosphere system to test hypotheses on the dynamics driving this change. These indicate that the arrival of the OJP at the Melanesian arc, between 10 and 5 Ma, followed by a subduction polarity reversal that marked the initiation of subduction of the Australian plate underneath the Pacific realm, were the key...

  9. Regional climate model experiments to investigate the Asian monsoon in the Late Miocene

    Directory of Open Access Journals (Sweden)

    H. Tang

    2011-03-01

    Full Text Available The Late Miocene (11.6–5.3 Ma is a crucial period for the Asian monsoon evolution. However, the spatiotemporal changes of the Asian monsoon system in the Late Miocene are still ambiguous, and the mechanisms responsible for these changes are debated. Here, we present a simulation of the Asian monsoon climate (0 to 60° N and 50 to 140° E in the Tortonian (11–7 Ma using the regional climate model CCLM3.2. We employ relatively high spatial resolution (1° × 1° and adapt the physical boundary conditions such as topography, land-sea distribution and vegetation in the regional model to represent the Late Miocene. As climatological forcing, the output of a Tortonian run with a fully-coupled atmosphere-ocean general circulation model is used. Our results show a stronger-than-present E-Asian winter monsoon wind in the Tortonian, as a result of the enhanced mid-latitude westerly wind of our global forcing and the lowered northern Tibetan Plateau in the regional model. The summer monsoon circulation is generally weakened in our regional Tortonian run compared to today. However, the changes of summer monsoon precipitation exhibit major regional differences. The precipitation decreases in N-China and N-India, but increases in S-China, the western coast and the southern tip of India. This can be attributed to the combined effect of both the regional topographical changes and the other forcings related to our global model. The spread of the dry summer conditions over N-China and NW-India further implies that the monsoonal climate may not be fully established over these regions in the Tortonain. Compared with the global model, the high resolution regional model highlights the spatial differences of the Asian monsoon climate in the Tortonian, and better characterizes the convective activity and its response to topographical changes. It therefore provides a useful and compared to global models complementary tool to improve our understanding of the Asian

  10. Mid Miocene volcanism in Nicaragua and implications for the formation of the Nicaraguan Depression

    Science.gov (United States)

    Saginor, I.; Gazel, E.; Carr, M. J.

    2009-12-01

    Northwest Nicaragua contains Mid Miocene volcanism on either side of the Nicaraguan Depression consisting of portions of the Coyol Formation to the East and the Tamarindo Formation to the West. The Tamarindo Formation is a narrow band of basaltic to andesitic lavas interlayered with thick ignimbrite deposits and volcaniclastic sediments that parallel Nicaragua’s Pacific coast to the west of the modern volcanic front with ages from 14.7-11.7 Ma. The Coyol represents primarily Miocene volcanism from 25-7 Ma and lies east of the active front. The presence of Mid Miocene volcanism on either side of the Nicaraguan Depression has led to speculation that the two coeval units, which are currently separated by almost 100km, were once connected and have since been separated by extension. Here, we present data that show the Tamarindo and Coyol are geochemically distinct and therefore cannot be considered part of the same unit. First, the Tamarindo has lower La/Yb values than Coyol, which suggests that the Tamarindo was formed by a higher degree of partial melting, assuming that mantle source compositions are similar for both units. In addition, the Tamarindo has higher Zr/Nb values than Coyol, which are indicative of High Field Strength Element (HFSE) depletion common in arc volcanics. Because the degree of partial melting and HFSE depletion is expected to increase towards the trench, both Tamarindo’s La/Yb and Zr/Nb values are consistent with its being emplaced closer to the trench than Coyol and the presence of these two units of Mid-Miocene age on opposite sides of the Nicaraguan Depression cannot be used as proof of significant extension. In addition, currently available data do not show the significant crustal thinning and large-scale structural surface features that would be expected if the Tamarindo and Coyol were once connected and later separated by extension. Fault displacement along the Nicaraguan Depression is insufficient to accommodate this extension and

  11. Miophasianus and Palaeoperdix (Galliformes, Aves from three Miocene localities of Spain

    Directory of Open Access Journals (Sweden)

    Sánchez Marco, A.

    2006-12-01

    Full Text Available The occurrence of two genus of phasianids in some Miocene localities of Spain are reported. The fossil remains from two of the outcrops, Can Mas and Hostalets, were studied long time ago, and it seemed suitable to reconsider their corresponding taxonomical identifications.Este trabajo trata sobre la aparición de dos géneros de Phasianidae en localidades españolas del Mioceno. Los restos fósiles de dos de los yacimientos, Can Mas y Hostalets, fueron estudiados hace mucho tiempo y, en consecuencia, parecía conveniente reconsiderar sus identificaciones taxonómicas.

  12. Effects of Prolonged Flat Subduction on the Miocene Magmatic Record of the Central Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Mori, L.; Gomez-Tuena, A.; Goldstein, S. L.

    2006-12-01

    Temporal modifications in the chemical compositions of middle to late Miocene rocks from the central Trans- Mexican Volcanic Belt elucidate how a process of prolonged flat subduction influences arc magmatism. These are recorded in the Palo Huerfano-La Joya-Zamorano Volcanic Complex (PH-LJ-Z; 16-9 Ma), a group of andesitic to dacitic stratovolcanoes located at ~500 km from the current trench, and in the Queretaro Volcanic Succession (QVS; 9-6 Ma), a basaltic to basaltic-andesitic plateau which stratigraphically overlies the stratovolcanoes. The two rock groups have typical arc-like trace element patterns, but the PH-LJ-Z suite has higher Sr/Y and LREE(MREE)/HREE ratios with MORB-like Sr, Nd and Pb isotopic compositions; geochemical features that are typical of experimental and natural slab melts. In contrast, rocks from the QVS have an overall weaker subduction signature, do not show slab melt signals, and have higher FeO^{tot} and MgO contents at equivalent Na2O and Mg# (40-70) than the PH-LJ-Z suite. Since Fe in arc magmas is a sensitive proxy of melting pressure and/or water contents (Gaetani &Grove, CMP, 1998), and Na could be either sensitive to slab melt additions (Kelemen et al., Tr. Geoch., 2003) or to the thickness of the mantle column that controls the extent of melting (Plank &Langmuir, EPSL, 1998), the overall chemical differences of both rock suites can only be reconciled if they equilibrated with the mantle wedge at the same pressures but with different amounts of dissolved water. The geochemical evidence thus indicates that the compositional differences between the two magmatic episodes are mainly related to different mechanisms of element recycling that occurred without major changes in the local tectonic configuration. The slab melt features of PH- LJ-Z rocks, and their emplacement at a large distance from the trench, are consistent with a sub-horizontal subduction geometry which favors slab melting at relatively low pressures (Gutscher et al

  13. Post-collisional magmatism and ore-forming systems in the Menderes massif: new constraints from the Miocene porphyry Mo-Cu Pınarbaşı system, Gediz-Kütahya, western Turkey

    Science.gov (United States)

    Delibaş, Okan; Moritz, Robert; Chiaradia, Massimo; Selby, David; Ulianov, Alexey; Revan, Mustafa Kemal

    2017-01-01

    The Pınarbaşı Mo-Cu prospect is hosted within the Pınarbaşı intrusion, which is exposed together with the NW-SE-trending Koyunoba, Eğrigöz, and Baklan plutons along the northeastern border of the Menderes massif. The Pınarbaşı intrusion predominantly comprises monzonite, porphyritic granite, and monzodiorite. All units of the Pınarbaşı intrusion have sharp intrusive contacts with each other. The principal mineralization style at the Pınarbaşı prospect is a porphyry-type Mo-Cu mineralization hosted predominantly by monzonite and porphyritic granite. The porphyry type Mo-Cu mineralization consists mostly of stockwork and NE- and EW-striking sub-vertical quartz veins. Stockwork-type quartz veins hosted by the upper parts of the porphyritic granite within the monzonite, are typically enriched in chalcopyrite, molybdenite, pyrite, and limonite. The late NE- and EW-striking normal faults cut the stockwork vein system and control the quartz-molybdenite-chalcopyrite-sphalerite-fahlore-galena veins, as well as molybdenite-hematite-bearing silicified zones. Lithogeochemical and whole-rock radiogenic isotope data (Sr, Nd and Pb) of the host rocks, together with Re-Os molybdenite ages (18.3 ± 0.1 Ma - 18.2 ± 0.1 Ma) reveal that the monzonitic and granitic rocks of the Pınarbaşı intrusion were derived from an enriched lithospheric mantle-lower crust during Oligo-Miocene post-collisional magmatism. The lithospheric mantle was metasomatised by fluids and subducted sediments, and the mantle-derived melts interacted with lower crust at 35-40 km depth. This mechanism explains the Mo and Cu enrichments of the Pınarbaşı intrusion during back-arc magmatism. We conclude that the melt of the Pınarbaşı intrusion could have rapidly ascended to mid-crustal levels, with only limited crustal assimilation along major trans-lithospheric faults as a result of thinning of the middle to upper crust during regional extension, and resulted in the development of porphyry

  14. Investigating Tectonic Drivers of Miocene - Pliocene Polar Climate Evolution using the HadCM3 Climate Model.

    Science.gov (United States)

    Hunter, S. J.; Knies, J.; Haywood, A. M.; Dolan, A. M.; Pound, M. J.

    2015-12-01

    We model the climate of the Miocene (Tortonian and the Messinian) and the Pliocene (Piacenzian) using the HadCM3 Atmosphere-Ocean GCM. We use baseline Miocene and Pliocene geographies that have different reconstruction lineages so we describe methods to create a set of self-consistent paleogeographies that represent the main features of the three stages. We present large-scale features of the evolving climate and examine model fidelity by comparing modelled climatology against palaeoenvironmental proxy data. We focus on the climate of the Arctic region and investigate tectonic drivers of sea ice expansion by comparing and interpreting model predictions against borehole data from the North Atlantic and Arctic Ocean. In particular how Late Miocene/ early Pliocene tectonic uplift in the Svalbard/Barents Sea and Greenland region, the opening of the Bering Strait, and the onset of deep water Atlantic-Arctic exchange influenced the development of modern sea ice cover.

  15. A New Fossil Termite(Isoptera,Stolotermitidae,Stolotermes)from the Early Miocene of Otago,New Zealand

    Institute of Scientific and Technical Information of China (English)

    Uwe KAULFUSS; Anthony C.HARRIS; Daphne E.LEE

    2010-01-01

    The forewing of a termite from Eady Miocene lake sediments in Otago,southern New Zealand is figured and described.It exhibits the generic characters of the damp-wood termite Stolotermes Hagen,but differs from forewings of the known species in size and venation pattern and is described as Stolotermes kupe sp.nov.S.kupe represents the first confident record of fossil Stolotermitidae and extends the fossil record of the family back to the Early Miocene.It also is the first direct evidence of fossil Isoptera from New Zealand.though silicified termite faecal pellets.referable to Kalotermes brauni,have been previously described.S.kupe indicates that Stolotermitidae has been present in the Australasian re#on since at least the Early Miocene.

  16. Middle East Reform Halts

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The chaos in Iraq poses a great threat to the U.S. plan in the Middle East While the fighting between Israel and Lebanon-based Hezbollah becomes fiercer, security in Iraq also keeps deteriorating, making the region a petrol can that may blow up anytime.

  17. Utopia Middle School

    Science.gov (United States)

    Cloud, Michelle

    2006-01-01

    The following excerpt allows the reader to briefly peer into an ideal school setting: For the purposes of this paper, the fictitious school will be named Utopia Middle School or U.M.S. U.M.S embodies and exemplifies the perfect school. At U.M.S., the campus administrators perform at a level of excellence that motivates, empowers and supports all…

  18. Fostering a Middle Class

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Though there is no official definition of "middle class" in China, the tag has become one few Chinese people believe they deserve anyway.In early August, the Chinese Academy of Social Sciences released a report on China’s urban development,

  19. Model Middle Schools

    Science.gov (United States)

    Shapiro, Arthur; And Others

    1973-01-01

    Provides three models as approaches to organizing the middle school in a variety of exciting ways: (1) an oscillating system, where students in communities move between basic studies and related arts and physical education, (2) an immersion system, where students in communities spend full time moving between interdisciplinary areas, and (3) a…

  20. Lower Miocene fishes and turtle from Žvarulje near Mlinše, Slovenia (Central Paratethys

    Directory of Open Access Journals (Sweden)

    Vasja Mikuž

    2013-12-01

    Full Text Available The article discusses fossil finds of Miocene vertebrates from the vicinity of Žvarulje near Mlinše in Central Slovenia. The fossils were found in the Lower Miocene Govce formation. Most common in the assemblage were tooth coronas, usually without their root parts of cartilaginous fishes, belonging to the genera Notorynchus, Carcharias, Cosmopolitodus, Isurus, Carcharhinus and Sphyrna. Fragments of dental plates and caudal spines ascribed of the genera Myliobatis, Aetobatus and Rhinoptera were also relatively common. A few tooth crowns of bony fishes assigned of the genus Pagrus were also found along with two modest fragments of a turtle shell ascribed of the genus Trionyx.

  1. Late Miocene-Pliocene Asian monsoon intensification linked to Antarctic ice-sheet growth

    Science.gov (United States)

    Ao, Hong; Roberts, Andrew P.; Dekkers, Mark J.; Liu, Xiaodong; Rohling, Eelco J.; Shi, Zhengguo; An, Zhisheng; Zhao, Xiang

    2016-06-01

    Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene-Pliocene (∼8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene-Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.

  2. Late Miocene to recent plate tectonic history of the southern Central America convergent margin

    Science.gov (United States)

    Morell, Kristin D.

    2015-10-01

    New plate reconstructions constrain the tectonic evolution of the subducting Cocos and Nazca plates across the southern Central American subduction zone from late Miocene to recent. Because of the strong relationships between lower and upper (Caribbean) plate dynamics along this margin, these constraints have wide-ranging implications for the timing and growth of upper plate deformation and volcanism in southern Central America. The reconstructions outline three important events in the Neogene history of this margin: (1) the coeval development of the Panama Triple Junction with the initiation of oblique subduction of the Nazca plate at ˜8.5 Ma; (2) the initiation of seamount and rough crust subduction beginning at ˜3-4 Ma; and (3) Cocos Ridge subduction from ˜2 to 3 Ma. A comparison of these events with independent geologic, geomorphic, volcanic, and stratigraphic data sets reveals that the timing, rates, and origin of subducting crust directly impacted the Neogene growth of upper plate deformation and volcanism in southern Central America. These analyses constrain the timing, geometry, and causes of a number of significant tectonic and volcanic processes, including rapid Plio-Quaternary arc-fore arc contraction due to Cocos Ridge subduction, the detachment of the Panama microplate at ˜1-3 Ma, and the late Miocene cessation of mantle-wedge-derived volcanism across ˜300 km of the subduction zone.

  3. Swietenia (Meliaceae) flower in Late Oligocene Early Miocene amber from Simojovel de Allende, Chiapas, Mexico.

    Science.gov (United States)

    Castañeda-Posadas, Carlos; Cevallos-Ferriz, Sergio R S

    2007-11-01

    The amber of Simojovel de Allende, Chiapas, Mexico, of Late Oligocene-Early Miocene age, has yielded a new flower representing the Meliaceae. The flower of Swietenia miocenica Castañeda-Posadas & Cevallos-Ferriz sp. nov. is characterized by small size; free calyx composed of five glabrous lobes, ciliolated along the margin lobes; corolla composed of five free, contortedly inserted petals with ciliolated margins; cylindrical staminal tube ending in 10 acuminate or toothed accessories and 10 sessile anthers; and a discoid stigma divided in five lobular stigmatic glands. The morphology of S. miocenica is well represented among Meliaceae. Although the new species shares many characters with Swietenia microphylla, small differences in the length and width of petals and the length of staminal tube support its recognition as a new species. The presence of this genus demonstrates the establishment of tropical communities in southern Mexico by the early Miocene and highlights the influence of the northern hemisphere flora on the extant neotropical flora of the area.

  4. Post-Miocene diagenetic and eustatic history of Enewetak Atoll: Model and data comparison

    Science.gov (United States)

    Quinn, Terrence M.; Matthews, R. K.

    1990-10-01

    The post-Miocene diagenetic and eustatic history of Enewetak Atoll was investigated using a one-dimensional forward model. Comparison of model and data suggests that the post-Miocene history of Enewetak Atoll was dominated by multiple episodes of meteoric phreatic diagenesis attendant with high-frequency (104 to 105 yr) fluctuations in sea level and a subsidence rate of 39.0 m/m.y. Sensitivity testing indicates that subaerial erosion results in the preservation of additional subaerial unconformities because stratigraphic shortening permits a succeeding sea-level rise to flood the exposure surface and deposit sediment, whereas without subaerial erosion this sea-level rise would be recorded as a paleophreatic lens. Model results indicate that less than 10% of lapsed time is recorded by sediment deposition during periods of high-frequency changes in sea level. Incompleteness of the stratigraphic record suggests that magnetostratigraphy may give erroneous ages for shallow-marine carbonate sequences deposited during times of high-frequency changes in sea level and frequent magnetic polarity reversals.

  5. Andegameryx andegaviensis Ginsburg, 1971 (Artiodactyla, Ruminantia, from the early Miocene site of Estrepouy (MN3, France

    Directory of Open Access Journals (Sweden)

    Morales, J.

    2011-12-01

    Full Text Available Several dental remains from the Early Miocene of Estrepouy (MN3, France previously reported as Amphitragulus aurelianensis by Roman & Viret (1934 are described in this work and assigned to Andegameryx andegaviensis Ginsburg, 1971. The re-study of this material and the comparison with other remains of A. andegaviensis from several european localities of the early Miocene, including the type locality of the species, have permitted us to confirm the presence of A. andegaviensis in the ruminant fauna from Estrepouy.En esta nota describimos algunos de los restos del yacimiento del Mioceno inferior de Estrepouy (MN3, Francia atribuidos por Roman & Viret (1934 a Amphitragulus aruelianensis, cambiando su asignación a Andegameryx andegaviensis Ginsburg, 1971. El reestudio del material y su comparación con los restos de A. andegaviensis de otras localidades europeas del Mioceno inferior, incluyendo la localidad tipo de la especie, permiten confirmar su presencia entre la fauna de rumiantes fósiles de Estrepouy.

  6. Did tectonic activity stimulate oligo-miocene speciation in the Indo-West Pacific?

    Science.gov (United States)

    Williams, Suzanne T; Duda, Thomas F

    2008-07-01

    Analyses of molecular phylogenies of three unrelated tropical marine gastropod genera, Turbo, Echinolittorina, and Conus, reveal an increase in the rate of cladogenesis of some Indo-West Pacific (IWP) clades beginning in the Late Oligocene or Early Miocene between 23.7 and 21.0 million years ago. In all three genera, clades with an increased rate of diversification reach a maximum of diversity, in terms of species richness, in the central IWP. Congruence in both the geographical location and the narrow interval of timing suggests a common cause. The collision of the Australia and New Guinea plate with the southeast extremity of the Eurasian plate approximately 25 Mya resulted in geological changes to the central IWP, including an increase in shallow-water areas and length of coastline, and the creation of a mosaic of distinct habitats. This was followed by a period of rapid diversification of zooxanthellate corals between 20 and 25 Mya. The findings reported here provide the first molecular evidence from multiple groups that part of the present-day diversity of shallow-water gastropods in the IWP arose from a rapid pulse of speciation when new habitats became available in the Late Oligocene to Early Miocene. After the new habitats were filled, the rate of speciation likely decreased and this combined with high levels of extinction (in some groups), resulted in a slow down in the rate of diversification in the genera examined.

  7. IODP Expeditions 303 and 306 Monitor Miocene- Quaternary Climate in the North Atlantic

    Directory of Open Access Journals (Sweden)

    Carlos Alvarez-Zarikian

    2006-03-01

    Full Text Available Introduction The IODP Expeditions 303 and 306 drilling sites were chosen for two reasons: (1 to capture Miocene-Quaternary millennial-scale climate variability in sensitive regions at the mouth of the Labrador Sea and in the North Atlantic icerafted debris (IRD belt (Ruddiman et al., 1977, and (2 to provide the sedimentary and paleomagnetic attributes, including adequate sedimentation rates, for constructinghigh-resolution isotopic and magnetic stratigraphies.High accumulation rates, reaching 20 cm ky-1, permit the study of millennial-scale variations in climate and in the Earth's magnetic fi eld over the past several million years, when the amplitude and frequency of climate variability changed substantially. Shipboard logging and scanning data (magnetic susceptibility and remanence, density, natural gamma radiation, digital images and color refl ectance and post-expedition x-ray fl uorescence (XRF scanning datahave revealed that the sediment cores recovered on Expeditions 303 and 306 contain detailed histories of millennial-scale climate and geomagnetic fi eld variability throughout the late Miocene to Quaternary epochs. The climate proxies will be integrated with paleomagnetic data to place the records of millennial-scale climate change into a high resolution stratigraphy based on oxygen isotope andrelative paleomagnetic intensity (RPI. The paleomagnetic record of polarity reversals, excursions and RPI in these cores is central to the construction of the stratigraphic template and will provide detailed documentation of geomagnetic fi eld behavior.

  8. First Hominoid from the Late Miocene of the Irrawaddy Formation (Myanmar)

    Science.gov (United States)

    Jaeger, Jean-Jacques; Naing Soe, Aung; Chavasseau, Olivier; Coster, Pauline; Emonet, Edouard-Georges; Guy, Franck; Lebrun, Renaud; Maung, Aye; Aung Khyaw, Aung; Shwe, Hla; Thura Tun, Soe; Linn Oo, Kyaw; Rugbumrung, Mana; Bocherens, Hervé; Benammi, Mouloud; Chaivanich, Kamol; Tafforeau, Paul; Chaimanee, Yaowalak

    2011-01-01

    For over a century, a Neogene fossil mammal fauna has been known in the Irrawaddy Formation in central Myanmar. Unfortunately, the lack of accurately located fossiliferous sites and the absence of hominoid fossils have impeded paleontological studies. Here we describe the first hominoid found in Myanmar together with a Hipparion (s.l.) associated mammal fauna from Irrawaddy Formation deposits dated between 10.4 and 8.8 Ma by biochronology and magnetostratigraphy. This hominoid documents a new species of Khoratpithecus, increasing thereby the Miocene diversity of southern Asian hominoids. The composition of the associated fauna as well as stable isotope data on Hipparion (s.l.) indicate that it inhabited an evergreen forest in a C3-plant environment. Our results enlighten that late Miocene hominoids were more regionally diversified than other large mammals, pointing towards regionally-bounded evolution of the representatives of this group in Southeast Asia. The Irrawaddy Formation, with its extensive outcrops and long temporal range, has a great potential for improving our knowledge of hominoid evolution in Asia. PMID:21533131

  9. Late Miocene-Pliocene Asian monsoon intensification linked to Antarctic ice-sheet growth

    Science.gov (United States)

    Ao, H.; Roberts, A. P.; Dekkers, M. J.; Liu, X.; Rohling, E. J.; Shi, Z.; An, Z.; Zhao, X.

    2016-12-01

    Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene-Pliocene (˜8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene-Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.

  10. First hominoid from the Late Miocene of the Irrawaddy Formation (Myanmar.

    Directory of Open Access Journals (Sweden)

    Jean-Jacques Jaeger

    Full Text Available For over a century, a Neogene fossil mammal fauna has been known in the Irrawaddy Formation in central Myanmar. Unfortunately, the lack of accurately located fossiliferous sites and the absence of hominoid fossils have impeded paleontological studies. Here we describe the first hominoid found in Myanmar together with a Hipparion (s.l. associated mammal fauna from Irrawaddy Formation deposits dated between 10.4 and 8.8 Ma by biochronology and magnetostratigraphy. This hominoid documents a new species of Khoratpithecus, increasing thereby the Miocene diversity of southern Asian hominoids. The composition of the associated fauna as well as stable isotope data on Hipparion (s.l. indicate that it inhabited an evergreen forest in a C3-plant environment. Our results enlighten that late Miocene hominoids were more regionally diversified than other large mammals, pointing towards regionally-bounded evolution of the representatives of this group in Southeast Asia. The Irrawaddy Formation, with its extensive outcrops and long temporal range, has a great potential for improving our knowledge of hominoid evolution in Asia.

  11. Upper Cretaceous to Holocene magmatism and evidence for transient Miocene shallowing of the Andean subduction zone under the northern Neuquén Basin

    Science.gov (United States)

    Kay, Suzanne M.; Burns, W. Matthew; Copeland, Peter; Mancilla, Oscar

    2006-01-01

    Evidence for a Miocene period of transient shallow subduction under the Neuquén Basin in the Andean backarc, and an intermittent Upper Cretaceous to Holocene frontal arc with a relatively stable magma source and arc-to-trench geometry comes from new 40Ar/39Ar, major- and trace-element, and Sr, Pb, and Nd isotopic data on magmatic rocks from a transect at ∼36°–38°S. Older frontal arc magmas include early Paleogene volcanic rocks erupted after a strong Upper Cretaceous contractional deformation and mid-Eocene lavas erupted from arc centers displaced slightly to the east. Following a gap of some 15 m.y., ca. 26–20 Ma mafic to acidic arc-like magmas erupted in the extensional Cura Mallín intra-arc basin, and alkali olivine basalts with intraplate signatures erupted across the backarc. A major change followed as ca. 20–15 Ma basaltic andesite–dacitic magmas with weak arc signatures and 11.7 Ma Cerro Negro andesites with stronger arc signatures erupted in the near to middle backarc. They were followed by ca. 7.2–4.8 Ma high-K basaltic to dacitic hornblende-bearing magmas with arc-like high field strength element depletion that erupted in the Sierra de Chachahuén, some 500 km east of the trench. The chemistry of these Miocene rocks along with the regional deformational pattern support a transient period of shallow subduction that began at ca. 20 Ma and climaxed near 5 Ma. The subsequent widespread eruption of Pliocene to Pleistocene alkaline magmas with an intraplate chemistry in the Payenia large igneous province signaled a thickening mantle wedge above a steepening subduction zone. A pattern of decreasingly arc-like Pliocene to Holocene backarc lavas in the Tromen region culminated with the eruption of a 0.175 ± 0.025 Ma mafic andesite. The northwest-trending Cortaderas lineament, which generally marks the southern limit of Neogene backarc magmatism, is considered to mark the southern boundary of the transient shallow subduction zone.

  12. Deformation Along the Southeast Extension of the Lake Mead Fault System Evaluated with Paleomagnetic Data From Miocene Igneous Rocks, Hoover Dam area, Nevada and Arizona

    Science.gov (United States)

    Geissman, J. W.

    2002-12-01

    At and near Hoover Dam, southeast of Las Vegas, Cenozoic left-slip offset along the NE-SW trending Lake Mead fault system (LMFS) has resulted in the apparent rotation of structures and total displacement of up to 65 km. Defining any rotation of blocks within and near the LMFS is critical to assessing the kinematics of strike-slip faulting and attending extension. Paleomagnetic data from Miocene volcanic and some sedimentary rocks and intrusions (over 160 sites) deposited on Precambrian basement show that part of the Hoover Dam locality has experienced counterclockwise rotation . The middle Miocene (ca. 14.2 Ma)Tuff of Hoover Dam (THD)(sampled at over 90 sites) yields a well-grouped characteristic magnetization (ChRM); about 5 km south and east of the dam, gently east-dipping, north-striking rocks of the THD yield a corrected ChRM of moderate positive inclination and northwest declination (D=324.8°, I=27.4°, a95=10.7°, k=24, N=9 sites). Structural corrections, based on compaction fabrics in the THD are consistent with stratigraphic contacts. The anomalous shallow inclination for the THD ChRM implies that it was emplaced over a short period of time during a field instability. contact and conglomerate test results are interpreted to show that the THD ChRM is primary. Corrected data from north and west of the dam (D=289.7°, I=30.2°,a95=8.6°,k=32, N=10) are interpreted to indicate about 35° of counterclockwise rotation (R= -35.1°, delR= 12.4, F= -2.8°, delF = 10.8, relative to data from south of the dam) of crust across the dam site, consistent with progressive changes in strike of tilted fault blocks. The transition from apparently unrotated crust to rotated crust occurs over a zone about 1 km wide, where blocks of THD and older strata have been tilted up to 50°, probably concurrent with rotation. Rotation of crust northwest of Hoover Dam may reflect differential extension northwest of the LMFS (e.g.,River Mountains area) as strain is partitioned into west to

  13. Miocene to Present evolution of the Calabria Tyrrhenian continental margin (Southern Tyrrhenian Sea)

    Science.gov (United States)

    Pepe, F.; Sulli, A.; Bertotti, G.; Cella, F.

    2009-04-01

    The Miocene to Present evolution of the Calabria Tyrrhenian Continental Margin (CTCM, Southern Tyrrhenian Sea) are reconstructed using two ENE-WSW oriented, near-vertical seismic profiles (CROP-M27 and SISTER 11 lines). The interpreted profiles were time-to-depth converted, merged and translated in a geological section, which was also extended to the Tyrrhenian bathial plain and the Calabrian arc using wide-angle seismic data [Scarascia et al., 1994], and tested with gravity modelling. Across the CTCM, top of KCU is laterally variable in depth forming basins filled by Oligo-Miocene clastic to terrigenous deposits up to 1500m thick. Basins are separated by major structures with contractional or transcurrent kinematics, where faults are arranged in a positive flower structure fashion, affecting the KCU as well as lower Oligocene to Miocene deposits. The Messinian evaporites display essentially a constant thickness of ~-400m with the exception of the Paola Basin where deep-water Messinian evaporites are up to 1000 m thick. Plio-Quaternary deposits display a remarkable variation in thickness from ~-4.5 km in the Paola Basin to less then 400m in the central sector of the margin. Plio-Quaternary sediments are internally sub-divisible into four sub-units separated by tectonics enhanced angular unconformities. W-ward vergent reverse faults with limited vertical displacement offset the top of KCU as well as the Oligo-Miocene sedimentary and evaporitic units in the eastern side of the Paola basin and in the distal part of the CTCM where a number of closely spaced, W-vergent thrust faults are also observed in the Plio-Pleistocene deposits. Along the CTCM, the only significant normal fault which was identified is located around its central sector, dips to the W and has a displacement of ~-580m. Across the margin, the Moho was inferred at ~-35 km beneath the Calabria Arc and shallows up to 24 km in correspondence with the coastline. Moho deepens again to a depth of ~-28 km in

  14. Middle Ear Infections (For Parents)

    Science.gov (United States)

    ... Feeding Your 1- to 2-Year-Old Middle Ear Infections KidsHealth > For Parents > Middle Ear Infections Print ... 3 years old. A Close Look at the Ear To understand how ear infections develop, let's review ...

  15. The Early Miocene-Early Pliocene Vegetation and Climate Changes at the north to northwest Çankırı -Çorum Basin (Central Anatolian Plateau)

    Science.gov (United States)

    Atalar, Müge; Kováčová, Marianna; Sezgül Kayseri Ozer, Mine; Utescher, Torsten; Mazzini, Ilaria; Gliozzi, Elsa; Cosentino, Domenico

    2016-04-01

    The ALErT project targets on climate and tectonic hazards in the densely populated regions in the Central Anatolian Plateau (CAP), within the framework of the Marie Curie FP7-PEOPLE-2013-ITN program, The CAP extends in a wide area in between zone the Aegean extensional zone and Bitlis /Zagros compressional zone. Çankırı Basin (in the middle CAP) is a key to understand aridification plateau interior and it was a deep pelagic Basin from Late Cretaceous -Early Tertiary as a result of the closure of Neo- Tethyan till the Middle Eocene. North to south of the Çankırı Basin; the Plio - Quaternary Deǧim formation (fluvial deposits) consist of massive mudstones and sandstones and it unconformable overlies the Bozkır formation (lacustrine deposits). That is a Messinian succession mainly by a 200 m-thick cyclic sequence of continental gypsum layers, clays and sandy clays in gypsum with different thicknesses crops. Bozkır formation, the lower being the contact with the Süleymanlı formation. It is overlay the Tuǧlu formation with uncomformably, which is an Upper Miocene succession mainly composed of dark grey silty and organic rich clays. Following formation, which outcrops in the northwest of Çankırı basin, is Hançili formation. The unit is covered by grey sediments of the Hançili Formation, showing alternations of channel sandstones and clay stones over 100 m thick in Early - Middle Miocene in the Çankırı basin. In this study, samples were analyzed for biotic proxy data (palynology) to figure the paleo-environmental and paleoclimate changes. Additionally only for Bozkir formation (longest section in the study area) were sampled for geochemical (δ18O - δ13C isotopes analyses and CaCO3) analysis and the rest of the formations were interpreted using the previous study. In the most pollen spectra the herbs and shrubs prevail: in Deǧim formation (50%), in Bozkır formation (75%), in Süleymanlı formation (47%), in Tuǧlu formation (60%) and in Han

  16. Phylogenetics and molecular clocks reveal the repeated evolution of ant-plants after the late Miocene in Africa and the early Miocene in Australasia and the Neotropics.

    Science.gov (United States)

    Chomicki, Guillaume; Renner, Susanne S

    2015-07-01

    Ant-plant symbioses involve over 110 ant species in five subfamilies that are facultative or obligate occupants of stem, leaf or root domatia formed by hundreds of ant-plant species. The phylogenetic distribution and geological ages of these associations, and the frequency of gains or losses of domatium, are largely unknown. We compiled an up-to-date list of ant domatium-bearing plants, estimated their probable true number from model-based statistical inference, generated dated phylogenies that include c. 50% of ant-plant lineages, and traced the occurrence of domatia and extrafloral nectaries on a 1181-species tree, using likelihood and Bayesian methods. We found 681 vascular plants with domatia (159 genera in 50 families) resulting from minimally 158 inferred domatium origins and 43 secondary losses over the last 19 Myr. The oldest African ant-plant symbioses are younger than those in Australasia and the Neotropics. The best statistical model suggests that the true number of myrmecophytes may approach 1140 species. The phylogenetic distribution of ant-plants shows that domatia evolved from a range of pre-adapted morphological structures and have been lost frequently, suggesting that domatia have no generalizable effect on diversification. The Miocene origin of ant-plant symbioses is consistent with inferred changes in diet and behaviour during ant evolution. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

  17. My Middle School Life

    Institute of Scientific and Technical Information of China (English)

    高懿; 吕静

    2004-01-01

    It is generally believed that the best time of one's hfe is their youth, and we spend most of it in our schools. So school is like a cradle which supports us from our childhood through adulthood. It also serves as a bridge between family and society. As a teenager, I have already studied more than 6 years in middle school, during which period I have gained notonly a great deal of knowledge but some valuable experience as well. The most important of all are the many unforgettable activities of school, which make my hfe more colorful.Looking back on my nearly 7 years' middle school hfe, I'd hke to divide it into two parts,that is, help and enjoyment.

  18. Stuck in the Middle

    Institute of Scientific and Technical Information of China (English)

    YIN PUMIN

    2011-01-01

    Sun Lijun works as a software engineer at a Beijing-based IT company and earns around 8,000 yuan ($1254)a month.His relative y high income means his friends and colleagues,as well as China's statistical agencies,regard him as middle class.Sun,however,does not think he is worthy of being included in a category that is traditionally associated with security and comfort.

  19. Thermochronologic evidence for Miocene mid-crustal tectonic exhumation of the Huachuca Mountains, southeast Arizona

    Science.gov (United States)

    King, C. C.; Orme, D. A.; Biswas, A.; Reiners, P. W.

    2011-12-01

    Zircon double dating of detrital grains from the northward flowing upper San Pedro river valley at Murray Springs in southeastern Arizona yields abundant zircons with variable U/Pb crystallization ages of ~70-1400 Ma, but a restricted range of (U-Th)/He cooling ages of ~18-25 Ma. This combination of diverse formation ages but uniform mid-Miocene cooling ages is characteristic of zircons from the core complexes and deeply exhumed Santa Catalina, Rincon, and Pinaleno Mountains, which experienced tectonic exhumation from mid-crustal depths during mid-Miocene extension. But all these sources are far downstream or outside the watershed of the upper San Pedro valley. To trace the source of these detrital grains and understand the implications for regional tectonics, we also measured U/Pb and (U-Th)/He dates of zircons from the Tombstone Hills and Huachuca Mountains, proximal to the Murray Springs site. Magmatic rocks in the Tombstone Hills yielded U/Pb dates of 76-83 Ma and zircon He ages of 53-60 Ma. In contrast, crystalline basement of the Huachucas yields Cretaceous through 1.5-Ga U/Pb ages and zircon He ages of 17-25 Ma, with most between 21-22 Ma. These data require that a large region of the Huachucas contains rocks that cooled rapidly below temperatures of at least 180 oC in the mid-Miocene. Assuming typical geothermal gradients of 20-30 oC, this requires exhumation of at least 7-9 km of crust, likely within 1-2 Myr. While it is possible that erosion contributed, it is more likely that denudation was accommodated by deep tectonic exhumation. Faults are observed on the basin-bounding east-side of the Huachucas, but most are inferred to accommodate Laramide-age thrusting, and the normal faults have been interpreted as high-angle and unlikely to cause significant tectonic exhumation. Our new data suggest that a large part of the presently exposed Huachucas was exhumed from depths at least as great as ~7-9 km, requiring a considerable revision of structural

  20. Small mammal carbon isotope ecology across the Miocene-Pliocene boundary, northwestern Argentina

    Science.gov (United States)

    Hynek, Scott A.; Passey, Benjamin H.; Prado, José Luis; Brown, Francis H.; Cerling, Thure E.; Quade, Jay

    2012-03-01

    The late Miocene expansion of plants using the C4 photosynthetic pathway in South America has been documented by tooth enamel carbon isotope ratios (δ13Cen). However, a more detailed understanding of this ecological event is hampered by poor chronological control on the widespread fossil localities from which isotopic data are derived. This study develops a δ13Cen record from a single 2500 m-thick stratigraphic section in subtropical South America. Strata at Puerta de Corral Quemado (PCQ), northwestern Argentina, span 9 to 3.5 Ma in age, and existing paleosol carbonate data (δ13Cpc) document C4 expansion across the Miocene-Pliocene boundary. Comparison of δ13Cen data with δ13Cpc data at high stratigraphic resolution refines understanding of this ecological event in South America. Small mammal δ13Cen data in particular are complementary to that of large mammal and paleosol δ13C data. Small mammal teeth integrate isotopic data over much shorter temporal and spatial scales than large mammal teeth, providing a sensitive measure of local vegetation and placing constraints on the landscape distribution of C3 and C4 plants. Explicit consideration of the distinctive carbon isotope enrichment factor between enamel and diet for rodents (ɛ*en-diet = 11‰, as opposed to 14‰ for large mammals) allows for unequivocal inference of C4 vegetation ~ 1 Ma prior to that inferred from large mammal δ13Cen data, and ~ 2 Ma prior to δ13Cpc data. This multiproxy record demonstrates that C4 plants were a stable component of the ecosystem hundreds of thousands of years prior to their major ecological expansion, and that the expansion of C4 plants was pulsed at PCQ. Two periods of ecological change are demonstrated by δ13C and δ18O data at ~ 7 Ma and 5.3 Ma (coincident with the Miocene-Pliocene boundary). Development of small mammal δ13Cen records on other continents may provide similar insight into the early stages of the global C4 event.

  1. Geochemistry and diagenesis of Miocene lacustrine siliceous sedimentary and pyroclastic rocks, Mytilinii basin, Samos Island, Greece

    Science.gov (United States)

    Stamatakis, M.G.; Hein, J.R.; Magganas, A.C.

    1989-01-01

    A Late Miocene non-marine stratigraphic sequence composed of limestone, opal-CT-bearing limestone, porcelanite, marlstone, diatomaceous marlstone, dolomite, and tuffite crops out on eastern Samos Island. This lacustrine sequence is subdivided into the Hora Beds and the underlying Pythagorion Formation. The Hora Beds is overlain by the clastic Mytilinii series which contains Turolian (Late Miocene) mammalian fossils. The lacustrine sequence contains volcanic glass and the silica polymorphs opal-A, opal-CT, and quartz. Volcanic glass predominantly occurs in tuffaceous rocks from the lower and upper parts of the lacustrine sequence. Opal-A (diatom frustules) is confined to layers in the upper part of the Hora Beds. Beds rich in opal-CT underlie those containing opal-A. The occurrence of opal-CT is extensive, encompassing the lower Hora Beds and the sedimentary rocks and tuffs of the Pythagorion Formation. A transition zone between the opal-A and opal-CT zones is identified by X-ray diffraction patterns that are intermediate between those of opal-CT and opal-A, perhaps due to a mixture of the two polymorphs. Diagenesis was not advanced enough for opal-CT to transform to quartz or for volcanic glass to transform to opal-C. Based on geochemical and mineralogical data, we suggest that the rate of diagenetic transformation of opal-A to opal-CT was mainly controlled by the chemistry of pore fluids. Pore fluids were characterized by high salinity, moderately high alkalinity, and high magnesium ion activity. These pore fluid characteristics are indicated by the presence of evaporitic salts (halite, sylvite, niter), high boron content in biogenic silica, and by dolomite in both the opal-A and opal-CT-bearing beds. The absence of authigenic K-feldspar, borosilicates, and zeolites also support these pore fluid characteristics. Additional factors that influenced the rate of silica diagenesis were host rock lithology and the relatively high heat flow in the Aegean region from

  2. The Brahmaputra tale of tectonics and erosion: Early Miocene river capture in the Eastern Himalaya

    Science.gov (United States)

    Bracciali, Laura; Najman, Yani; Parrish, Randall R.; Akhter, Syed H.; Millar, Ian

    2015-04-01

    The Himalayan orogen provides a type example on which a number of models of the causes and consequences of crustal deformation are based and it has been suggested that it is the site of a variety of feedbacks between tectonics and erosion. Within the broader orogen, fluvial drainages partly reflect surface uplift, different climatic zones and a response to crustal deformation. In the eastern Himalaya, the unusual drainage configuration of the Yarlung Tsangpo-Brahmaputra River has been interpreted either as antecedent drainage distorted by the India-Asia collision (and as such applied as a passive strain marker of lateral extrusion), latest Neogene tectonically-induced river capture, or glacial damming-induced river diversion events. Here we apply a multi-technique approach to the Neogene paleo-Brahmaputra deposits of the Surma Basin (Bengal Basin, Bangladesh) to test the long-debated occurrence and timing of river capture of the Yarlung Tsangpo by the Brahmaputra River. We provide U-Pb detrital zircon and rutile, isotopic (Sr-Nd and Hf) and petrographic evidence consistent with river capture of the Yarlung Tsangpo by the Brahmaputra River in the Early Miocene. We document influx of Cretaceous-Paleogene zircons in Early Miocene sediments of the paleo-Brahmaputra River that we interpret as first influx of material from the Asian plate (Transhimalayan arc) indicative of Yarlung Tsangpo contribution. Prior to capture, the predominantly Precambrian-Paleozoic zircons indicate that only the Indian plate was drained. Contemporaneous with Transhimalayan influx reflecting the river capture, we record arrival of detrital material affected by Cenozoic metamorphism, as indicated by rutiles and zircons with Cenozoic U-Pb ages and an increase in metamorphic grade of detritus as recorded by petrography. We interpret this as due to a progressively increasing contribution from the erosion of the metamorphosed core of the orogen. Whole rock Sr-Nd isotopic data from the same samples

  3. Regional climate model experiments to investigate the Asian monsoon in the Late Miocene

    Directory of Open Access Journals (Sweden)

    H. Tang

    2011-08-01

    Full Text Available The Late Miocene (11.6–5.3 Ma is a crucial period in the history of the Asian monsoon. Significant changes in the Asian climate regime have been documented for this period, which saw the formation of the modern Asian monsoon system. However, the spatiotemporal structure of these changes is still ambiguous, and the associated mechanisms are debated. Here, we present a simulation of the average state of the Asian monsoon climate for the Tortonian (11–7 Ma using the regional climate model CCLM3.2. We employ relatively high spatial resolution (1° × 1° and adapt the physical boundary conditions such as topography, land-sea distribution and vegetation in the regional model to represent the Late Miocene. As climatological forcing, the output of a Tortonian run with a fully-coupled atmosphere-ocean general circulation model is used. Our regional Tortonian run shows a stronger-than-present East Asian winter monsoon wind as a result of the enhanced mid-latitude westerly wind of our global forcing and the lowered present-day northern Tibetan Plateau in the regional model. The summer monsoon circulation is generally weakened in our regional Tortonian run compared to today. However, the changes of summer monsoon precipitation exhibit major regional differences. Precipitation decreases in northern China and northern India, but increases in southern China, the western coast and the southern tip of India. This can be attributed to the changes in both the regional topography (e.g. the lower northern Tibetan Plateau and the global climate conditions (e.g. the higher sea surface temperature. The spread of dry summer conditions over northern China and northern Pakistan in our Tortonian run further implies that the monsoonal climate may not have been fully established in these regions in the Tortonian. Compared with the global model, the high resolution regional model highlights the spatial differences of the Asian monsoon climate in the Tortonian, and better

  4. Oligocene to Miocene terrestrial climate change and the demise of forests on Wilkes Land, East Antarctica

    Science.gov (United States)

    Salzmann, Ulrich; Strother, Stephanie; Sangiorgi, Francesca; Bijl, Peter; Pross, Joerg; Woodward, John; Escutia, Carlota; Brinkhuis, Henk

    2016-04-01

    The question whether Cenozoic climate was warm enough to support a substantial vegetation cover on the Antarctic continent is of great significance to the ongoing controversial debate on the dynamic behaviour of Antarctic land ice during the transition from a greenhouse to an icehouse world. Here we present palynological results from an Oligocene to Miocene sediment record provided by the Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin (East Antarctica). The Oligocene assemblages (33.9-23 Ma) are dominated by pollen and spores from temperate forest and sub-Antarctic shrub vegetation inhabiting different altitudinal zones. These include a lowland cold temperate forest with Dacrydium and Lagarostrobos (both common in southern forests of New Zealand and Tasmania today) and a high altitude tundra shrubland comprising Microcachrys, Nothofagus (southern beech) and Podocarpaceae conifers. A decline in pollen percentages of Dacrydium and Lagarostrobos and absence of Proteaceae indicate climate cooling during the late Oligocene (~25-23 Ma). However, the continuous presence of Lagarostrobos suggests that the full transition to a tundra environment had not yet occurred and climate on Wilkes Land during the late Oligocene was still warm enough to support forest vegetation in sheltered areas. Temperature reconstructions derived from the fossil pollen assemblages using the Coexistence Approach suggest mean annual temperatures (MATs) between 6.7-13.7°C during the early Oligocene and a drop of minimum MATs to 5.8°C in the late Oligocene. Pollen of "unambiguous" forest indicators, such as Lagarostrobos, are absent in the Miocene sediment record (16.2 -12.5 Ma) but temperatures were still high enough (minimum MATs > 5°C) to sustain a woody sub-Antarctic vegetation under partially ice-free conditions. Wilkes Land provides a unique record of Antarctic vegetation change from a subtropical, highly diverse Eocene rainforest to an Oligocene cold temperate

  5. Carbon-isotope stratigraphy from terrestrial organic matter through the Monterey event, Miocene, New Jersey margin (IODP Expedition 313)

    DEFF Research Database (Denmark)

    Fang, Linhao; Bjerrum, Christian J.; Hesselbo, Stephen P.

    2013-01-01

    The stratigraphic utility of carbon-isotope values from terrestrial organic matter is explored for Miocene siliciclastic sediments of the shallow shelf, New Jersey margin, USA (Integrated Ocean Drilling Program [IODP] Expedition 313). These shallow marine strata, rich in terrestrial organic matte...

  6. A Miocene molluscan faunule from Caucagua (Miranda State, Venezuela), with the description of a new species of Tryonia (Mollusca, Gastropoda)

    NARCIS (Netherlands)

    Wesselingh, F.P.; Macsotay, O.

    2006-01-01

    A molluscan faunule from the Miocene Cumaca Formation of the western margin of the Tuy Basin (Venezuela) is described. The fauna yields two species of freshwater snails and a single terrestrial snail species. Tryonia vivasi nov. spec. is described from the fauna, and its biogeographical significance

  7. A Miocene molluscan faunule from Caucagua (Miranda State, Venezuela), with the description of a new species of Tryonia (Mollusca, Gastropoda)

    NARCIS (Netherlands)

    Wesselingh, F.P.; Macsotay, O.

    2006-01-01

    A molluscan faunule from the Miocene Cumaca Formation of the western margin of the Tuy Basin (Venezuela) is described. The fauna yields two species of freshwater snails and a single terrestrial snail species. Tryonia vivasi nov. spec. is described from the fauna, and its biogeographical significance

  8. The nature of aquatic landscapes in the Miocene of western Amazonia: an integrated palaeontological and geochemical approach

    NARCIS (Netherlands)

    Wesselingh, F.P.; Kaandorp, R.J.G.; Vonhof, H.B.; Räsänen, M.E.; Renema, W.; Gingras, M.

    2006-01-01

    The Miocene Pebas Formation from the section Santa Rosa de Pichana (Loreto, Peru) was investigated using a combination of analyses of sedimentary facies, molluscan communities and taphonomy, and stable isotopes of both entire shells and growth bands in bivalves. Three sequences, comprising a success

  9. VIVERRA HOWELLI N. SP., A NEW VIVERRID (CARNIVORA, MAMMALIA FROM THE BACCINELLO-CINIGIANO BASIN (LATEST MIOCENE, ITALY

    Directory of Open Access Journals (Sweden)

    LORENZO ROOK

    2004-11-01

    Full Text Available We describe a new viverrid species (Viverra howelli n. sp.. Viverra howelli n. sp. is identified in Late Miocene (Messinian localities in the circum Mediterranean area (Italy and Lybia and in East Africa (Kenya. Morphologically, the new species is characterized by a relatively small size and a lower carnassial with short talonid.

  10. Orbital forcing and climate response : astronomically-tuned age models and stable isotope records for the Oligocene-Miocene

    NARCIS (Netherlands)

    Beddow-Twigg, H.M.

    2016-01-01

    The primary aim of this thesis is to reconstruct the evolution of the cryosphere, global ocean temperatures and the carbon cycle during the Oligocene-Miocene interval; using high-resolution foraminiferal stable isotope records with accurate chronological control provided by astronomically tuned age

  11. Age and stratigraphic context of Pliopithecus and associated fauna from Miocene sedimentary strata at Damiao, Inner Mongolia, China

    NARCIS (Netherlands)

    Kaakinen, Anu; Abdul Aziz, Hayfaa; Passey, Benjamin H.; Zhang, Zhaoqun; Liu, Liping; Salminen, Johanna; Wang, Lihua; Krijgsman, Wout; Fortelius, Mikael

    2015-01-01

    Since the discovery of mammalian fossils in Central Inner Mongolia in the beginning of the 20th century, this area has produced a rich and diverse record of Miocene faunas. Nevertheless, the stratigraphy has remained poorly constrained owing to scattered faunal horizons and lack of continuous vertic

  12. The Late Oligocene to Early Miocene early evolution of rifting in the southwestern part of the Roer Valley Graben

    Science.gov (United States)

    Deckers, Jef

    2016-06-01

    The Roer Valley Graben is a Mesozoic continental rift basin that was reactivated during the Late Oligocene. The study area is located in the graben area of the southwestern part of the Roer Valley Graben. Rifting initiated in the study area with the development of a large number of faults in the prerift strata. Some of these faults were rooted in preexisting zones of weakness in the Mesozoic strata. Early in the Late Oligocene, several faults died out in the study area as strain became focused upon others, some of which were able to link into several-kilometer-long systems. Within the Late Oligocene to Early Miocene northwestward prograding shallow marine syn-rift deposits, the number of active faults further decreased with time. A relatively strong decrease was observed around the Oligocene/Miocene boundary and represents a further focus of strain onto the long fault systems. Miocene extensional strain was not accommodated by further growth, but predominantly by displacements along the long fault systems. Since the Oligocene/Miocene boundary coincides with a radical change in the European intraplate stress field, the latter might have contributed significantly to the simultaneous change of fault kinematics in the study area.

  13. Miocene long-lived lake Pebas as a stage of mollusc radiations, with implications for landscape evolution in western Amazonia

    NARCIS (Netherlands)

    Wesselingh, F.P.

    2006-01-01

    The Miocene Pebas system was a huge (> 1 million km2) system of long-lived lakes and wetlands that occupied most of western Amazonia between c. 23 and 8 Ma. Remarkable endemic radiations of molluscs and ostracods occurred in the Pebas system. The continuity of many of the endemic lineages between c.

  14. 欧亚大陆中部盆地群大剖面的编制及其构造意义%Characteristics of the Basins from the E-W Inter-continent Profile in Central Eurasia

    Institute of Scientific and Technical Information of China (English)

    李维波; 李江海; 王洪浩; 傅臣建; 毛翔

    2015-01-01

    盆地结构记录了盆地演化特征,盆地群结构和构造特征由其所处的构造背景和板块边界决定。随着油气勘探的不断深入,积累了大量地震剖面,为盆地群剖面特征对比,提供了大量的基础资料。本文从大地构造背景着手,通过筛选地震与地质剖面,大致沿北纬39°绘制了欧亚大陆东西向剖面(在东部北黄海盆地有向南的偏转):西起黑海盆地,东至琉球海沟,剖面长约12000km,横穿18个盆地,涵盖克拉通盆地(塔里木原型盆地等)、裂谷盆地(太原盆地、渤海湾盆地等)、前陆盆地(黑海盆地、南里海盆地等)和弧后盆地(东海盆地)等多种盆地类型。其中,陆壳上的盆地发育在前寒武基底上,演化历史悠久;褶皱基底、洋壳基底和洋陆过渡壳基底上发育的盆地主要发育在中新生代。通过详细对比剖面各段结构和构造演化特征,发现中新生代构造活动决定了欧亚大陆中部盆地群最终格架,盆地多具有多期叠合改造的特征。剖面西段盆地群普遍具有中生代伸展断陷,叠加后期挤压坳陷的特征;剖面东段盆地群具有中生代断陷,叠加后期坳陷的特征。现今构造格架由西到东表现为前陆坳陷到弧后坳陷,鄂尔多斯盆地和沁水盆地是本剖面线结构特征分段的枢纽。%Basin’s structure records its evolution,and can be decided by the tectonic backgrounds and plate boundaries.As the increasing exploration in oil and gas,lots of seismic sections have been accumulated. This provides a large number of basic data for the comparison of the characteristics of the basins. Beginning from the tectonic backgrounds and selecting seismic profiles,this article draws E-W inter-continent profile in central Eurasian,mainly along N39°(turning southward in the East ).The profile begins from the Black Sea basin in the west and ends to the Ryukyu trench in the east.The profile is about 12000km long,crossing 18 major

  15. New observations on the Middle Fork Eel River coal-bearing beds, Mendocino County, California, USA

    Energy Technology Data Exchange (ETDEWEB)

    Bartley, Russell H. [Mendocino County Museum, 400 East Commercial Street, Willits, CA 95490 (United States); Bartley, Sylvia E. [Noyo Hill House, 28953 Highway 20, Fort Bragg, CA 95437 (United States); Springer, David J. [College of the Redwoods-Mendocino Coast, 1211 Del Mar Drive, Fort Bragg, CA 95437 (United States); Erwin, Diane M. [Museum of Paleontology, 1101 Valley Life Sciences Building, University of California, Berkeley, CA 94720 (United States)

    2010-08-01

    Mid-19th century reports of ''immense'' coal outcrops in the Middle Fork Eel River (MFER) drainage near Round Valley in California's northern Coast Ranges fueled the early geological interest in this area, with mine development the primary focus of many studies. It was not until Samuel G. Clark's 1940 ''Geology of the Covelo District, Mendocino County, California,'' that the coal was placed in its regional geologic context and assigned to the Miocene, a determination that relied primarily on a Desmostylus hesperus molar found in shale overlying the coal and an associated equivocal, though Miocene-compatible, marine molluscan fauna. Our investigation of the MFER coal-bearing beds has provided new data from foraminifera, marine mollusks, fish remains, and the first reported fossil plants, which as a whole support Clark's Miocene age assignment. We also present an updated stratigraphy proposing under modern-day stratigraphic protocols that the informal name Sand Bank beds (SBb) be used in place of the Temblor Formation to refer to the SBb coal-bearing fluvial-marine unit. Analysis of the SBb stratigraphy and sedimentology reveals the presence of a fluvial system that flowed from a distal upland region southward toward the paleocoast of California. An abundant diverse palynoflora containing lycophytes, ferns, conifers, and mesic, thermophillic herbaceous and woody angiosperms indicates the drainage flowed through a coastal swampy forested bottomland and estuarine environment before emptying into a coastal basin. Presence of Taxodium-like wood, foliage, pollen, and other ''hydrophiles'' suggests the MFER coal was a local mire buried by the progradation of the SBb fluvial system during a regressive phase, an interpretation to be tested with future field work and detailed compositional analysis of the coal. (author)

  16. Spirochete and protist symbionts of a termite (Mastotermes electrodominicus) in Miocene amber.

    Science.gov (United States)

    Wier, Andrew; Dolan, Michael; Grimaldi, David; Guerrero, Ricardo; Wagensberg, Jorge; Margulis, Lynn

    2002-02-05

    Extraordinary preservation in amber of the Miocene termite Mastotermes electrodominicus has led to the discovery of fossil symbiotic microbes. Spirochete bacteria and wood-digesting protists were identified in the intestinal tissue of th