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Sample records for early miocene varved

  1. Miocene

    Indian Academy of Sciences (India)

    (Malvaceae s.l.), is described from the Sindhudurg Formation. (Miocene) at the ... described along with palynofossils (Phadtare and. Kulkarni 1980a ... D istrict,. Maharash tra,. India, star indicates fossil lo cality; and. ( b. ) litholog o f the. Kalviw adi .... Following collision of the two plates, land connections ... The occur- rence of ...

  2. Palynological Zonation of Oligocene to Early Miocene Sediments of ...

    African Journals Online (AJOL)

    ADOWIE PERE

    2017-12-31

    Dec 31, 2017 ... Keywords: Lithozones; Niger delta Basin; Palynomorphs; Oligocene to Early Miocene; Depobelt. The Niger Delta is ... province on the West African continental margin. It lies mainly in the ... Nigeria depends largely on the oil and gas derived from it. ... generation, accumulation and retention of hydrocarbons.

  3. Avian fossils from the Early Miocene Moghra Formation of Egypt ...

    African Journals Online (AJOL)

    Avian remains from the Early Miocene (~17 Ma) Moghra Formation of Egypt include new records of 'waterbirds' (storks, herons, pelicans and allies) and a ratite. Only a single avian fossil has been previously reported from Wadi Moghra and, thus, additional knowledge of the avifauna complements previously documented ...

  4. Two New Mylagaulid Rodents from the Early Miocene of China.

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    Xiaoyu Lu

    Full Text Available Mylagaulid fossorial rodents are a common component of North American Miocene fossil faunas. However outside of North America, only three species are known from Asia. Here we report two new mylagaulids, Irtyshogaulus minor gen. et sp. nov. and Irtyshogaulus major gen. et sp. nov., recovered from early Miocene sediments in the Junggar Basin in northwestern China. The two new taxa are small-sized, high-crowned promylagauline rodents. Their lower molars possess high metastylid crests, small mesostylids, broad and posterolingually expanded labial inflections, and transversely extending metalophid IIs. The mesoconid is absent in both species. The anterior and posterior fossettids are large and equally developed. Their upper M1-2s possess a square occlusal surface with five deep fossettes. The two new taxa are distinguished from each other mainly by their size, the morphology of fossettes and fossettids, development of mesial and distal lophs, posterior reduction of M3, and the orientation of m2 hypolophid. Our phylogenetic analysis indicates that Irtyshogaulus and Lamugaulus (another early Miocene Asian mylagaulid are sister taxa. The two genera are nested among the North American promylagaulines, and share a common ancestor from North America, indicating early Miocene intercontinental dispersal within this clade of rodents.

  5. 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

  6. 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

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

    OpenAIRE

    DANIEL ZOBOLI; GIAN LUIGI PILLOLA

    2017-01-01

    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 ...

  8. An Early Miocene bumble bee from northern Bohemia (Hymenoptera, Apidae

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    Jakub Prokop

    2017-10-01

    Full Text Available A new species of fossil bumble bee (Apinae: Bombini is described and figured from Early Miocene (Burdigalian deposits of the Most Basin at the Bílina Mine, Czech Republic. Bombus trophonius sp. n., is placed within the subgenus Cullumanobombus Vogt and distinguished from the several species groups therein. The species is apparently most similar to the Nearctic B. (Cullumanobombus rufocinctus Cresson, the earliest-diverging species within the clade and the two may be related only by symplesiomorphies. The age of the fossil is in rough accordance with divergence estimations for Cullumanobombus.

  9. 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.

  10. 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

  11. The early Miocene balaenid Morenocetus parvus from Patagonia (Argentina and the evolution of right whales

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    Mónica R. Buono

    2017-12-01

    Full Text Available Balaenidae (right and bowhead whales are a key group in understanding baleen whale evolution, because they are the oldest surviving lineage of crown Mysticeti, with a fossil record that dates back ∼20 million years. However, this record is mostly Pliocene and younger, with most of the Miocene history of the clade remaining practically unknown. The earliest recognized balaenid is the early Miocene Morenocetus parvus Cabrera, 1926 from Argentina. M. parvus was originally briefly described from two incomplete crania, a mandible and some cervical vertebrae collected from the lower Miocene Gaiman Formation of Patagonia. Since then it has not been revised, thus remaining a frequently cited yet enigmatic fossil cetacean with great potential for shedding light on the early history of crown Mysticeti. Here we provide a detailed morphological description of this taxon and revisit its phylogenetic position. The phylogenetic analysis recovered the middle Miocene Peripolocetus as the earliest diverging balaenid, and Morenocetus as the sister taxon of all other balaenids. The analysis of cranial and periotic morphology of Morenocetus suggest that some of the specialized morphological traits of modern balaenids were acquired by the early Miocene and have remained essentially unchanged up to the present. Throughout balaenid evolution, morphological changes in skull arching and ventral displacement of the orbits appear to be coupled and functionally linked to mitigating a reduction of the field of vision. The body length of Morenocetus and other extinct balaenids was estimated and the evolution of body size in Balaenidae was reconstructed. Optimization of body length on our phylogeny of Balaenidae suggests that the primitive condition was a relatively small body length represented by Morenocetus, and that gigantism has been acquired independently at least twice (in Balaena mysticetus and Eubalaena spp., with the earliest occurrence of this trait in the late

  12. The early Miocene balaenid Morenocetus parvus from Patagonia (Argentina) and the evolution of right whales

    Science.gov (United States)

    Cozzuol, Mario A.; Fitzgerald, Erich M.G.

    2017-01-01

    Balaenidae (right and bowhead whales) are a key group in understanding baleen whale evolution, because they are the oldest surviving lineage of crown Mysticeti, with a fossil record that dates back ∼20 million years. However, this record is mostly Pliocene and younger, with most of the Miocene history of the clade remaining practically unknown. The earliest recognized balaenid is the early Miocene Morenocetus parvus Cabrera, 1926 from Argentina. M. parvus was originally briefly described from two incomplete crania, a mandible and some cervical vertebrae collected from the lower Miocene Gaiman Formation of Patagonia. Since then it has not been revised, thus remaining a frequently cited yet enigmatic fossil cetacean with great potential for shedding light on the early history of crown Mysticeti. Here we provide a detailed morphological description of this taxon and revisit its phylogenetic position. The phylogenetic analysis recovered the middle Miocene Peripolocetus as the earliest diverging balaenid, and Morenocetus as the sister taxon of all other balaenids. The analysis of cranial and periotic morphology of Morenocetus suggest that some of the specialized morphological traits of modern balaenids were acquired by the early Miocene and have remained essentially unchanged up to the present. Throughout balaenid evolution, morphological changes in skull arching and ventral displacement of the orbits appear to be coupled and functionally linked to mitigating a reduction of the field of vision. The body length of Morenocetus and other extinct balaenids was estimated and the evolution of body size in Balaenidae was reconstructed. Optimization of body length on our phylogeny of Balaenidae suggests that the primitive condition was a relatively small body length represented by Morenocetus, and that gigantism has been acquired independently at least twice (in Balaena mysticetus and Eubalaena spp.), with the earliest occurrence of this trait in the late Miocene–early

  13. Simulating a Dynamic Antarctic Ice Sheet in the Early to Middle Miocene

    Science.gov (United States)

    Gasson, E.; DeConto, R.; Pollard, D.; Levy, R. H.

    2015-12-01

    There are a variety of sources of geological data that suggest major variations in the volume and extent of the Antarctic ice sheet during the early to middle Miocene. Simulating such variability using coupled climate-ice sheet models is problematic due to a strong hysteresis effect caused by height-mass balance feedback and albedo feedback. This results in limited retreat of the ice sheet once it has reached the continental size, as likely occurred prior to the Miocene. Proxy records suggest a relatively narrow range of atmospheric CO2 during the early to middle Miocene, which exacerbates this problem. We use a new climate forcing which accounts for ice sheet-climate feedbacks through an asynchronous GCM-RCM coupling, which is able to better resolve the narrow Antarctic ablation zone in warm climate simulations. When combined with recently suggested mechanisms for retreat into subglacial basins due to ice shelf hydrofracture and ice cliff failure, we are able to simulate large-scale variability of the Antarctic ice sheet in the Miocene. This variability is equivalent to a seawater oxygen isotope signal of ~0.5 ‰, or a sea level equivalent change of ~35 m, for a range of atmospheric CO2 between 280 - 500 ppm.

  14. Integrated stratigraphy and 40Ar/39Ar chronology of early Middle Miocene sediments from DSDP Leg 42A, Site 372 (Western Mediterranean)

    NARCIS (Netherlands)

    Abdul Aziz, H.; di Stefano, A.; Foresi, L. M.; Hilgen, Frederik J.; Iaccarino, S. M.; Kuiper, K. F.; Lirer, F.; Salvatorini, G.; Turco, E.

    2008-01-01

    An integrated magneto-biostratigraphic framework is presented for Middle Miocene sediments of DSDP Site 372 located in the Western Mediterranean. Detailed biostratigraphic analysis shows a nearly complete sequence of early Middle Miocene calcareous plankton bioevents in the Mediterranean, including

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

    Science.gov (United States)

    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. 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.

  17. 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

  18. 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.

  19. Dynamic Antarctic ice sheet during the early to mid-Miocene

    Science.gov (United States)

    Gasson, Edward; DeConto, Robert M.; Pollard, David; Levy, Richard H.

    2016-03-01

    Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate-ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet-climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52-0.66‰, or a sea level equivalent change of 30-36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability.

  20. Early Miocene benthic foraminifera and biostratigraphy of the Qom Formation, Deh Namak, Central Iran

    Science.gov (United States)

    Daneshian, Jahanbakhsh; Dana, Leila Ramezani

    2007-03-01

    A total of 165 samples were collected from the Qom Formation investigated in a stratigraphic section north of Deh Namak, in Central Iran. From these, 35 genera and 47 species of benthic foraminifera were identified. The age of the studied section is Early Miocene (Aquitanian to Early Burdigalian) based on the occurrence of Borelis melo curdica, Meandropsina anahensis, Meandropsina iranica, Elphidium sp. 14, Peneroplis farsensis, and Triloculina tricarinata. The thickness of the Qom Formation is 401 m of which 161.2 m is early Burdigalian in age. Foraminiferal assemblages in the Deh Namak section are referable to the Borelis melo group- Meandropsina iranica Assemblage Zone and Miogypsinoides- Archaias-Valvulinid Assemblage Zone of [Adams, T.D., Bourgeois, F., 1967. Asmari biostratigraphy. Iranian Oil Operating Companies, Geological and Exploration Division, Report1074 (unpublished) 1-37.] described originally from the Asmari Formation.

  1. Andegameryx andegaviensis Ginsburg, 1971 (Artiodactyla, Ruminantia, from the early Miocene site of Estrepouy (MN3, France

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    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.

  2. Palaeobotanical data for climate change during the late Miocene - early Pliocene in Western Bulgaria

    International Nuclear Information System (INIS)

    Hristova, Viktoria; Ivanov, Dimiter; Bozukov, Vladimir

    2015-01-01

    The Coexistence Approach (CA) analysis was applied to plant macro- and microfossils from the Late Miocene to Early Pliocene sites in western Bulgaria to obtain quantitative climate data and reconstruct climate dynamics. Calculated new values for the Sofia macro flora confirmed a warm-temperate and humid climate with mean annual temperature (MAT) between 12–170C, mean temperature of the warmest month (WMT) 23.6–280C, mean temperature of the coldest month (CMT) 0–50C and mean annual precipitation (MAP) 843–1179 mm. This is consistent with the climatic parameters obtained from the microflora – MAT 13.6–16, WMT 23.6–27.9, CMT 3.7–6 and MAP 803–1308mm. All presented data are in good accordance with other regional palaeoclimate reconstructions from Bulgarian and Europaean floras. Key words: Late Miocene–Early Pliocene, palaeoclimate, Sofia Basin

  3. Quality and petrographic characteristics of the lacustrine Ermenek coal (early Miocene), Turkey

    Energy Technology Data Exchange (ETDEWEB)

    Demirel, I.H.; Karayigit, A.I. [Hacettepe Univ., Beytepe-Ankara (Turkey). Dept. of Geological Engineering

    1999-05-01

    The early Miocene Yenimahalle Formation including alluvial-lacustrine sediments and a mineable coal steam with an average of 5 m in thickness rests unconformably upon the basement and is also unconformably overlain by marine limestones of the middle-late Miocene Mut Formation in the Ermenek coal basin. The coal basin in the present study has been subdivided into two areas, Canakci and Pamuklu-Tepebasi, which are separated by the basement and a fault, in order to determine coal properties in detail. The investigated subbituminous coals with an average of 0.40%Ro huminite reflectance often contain gastropod shells (Planorbidae) which commonly maintain the original aragonite and calcite composition. The coals have similar chemical properties and petrographic composition in the two areas, but their sulphur contents are clearly different. In the Canakci area the coals on an air-dried basis contain distinctly less total sulphur (avg. 1.3%) and organic sulphur contents (0.13--0.15%) than in the Pamuklu-Tepebasi area (avg. 4.5% and 4.25%, respectively). This difference is interpreted to be controlled by mire chemistry and sedimentation during peat formation.

  4. Quality and petrographic characteristics of the Lacustrine Ermenek Coal (Early Miocene), Turkey

    Energy Technology Data Exchange (ETDEWEB)

    Demirel, I.H.; Karayigit, A.I.

    1999-04-15

    The early Miocene Yenimahalle Formation including alluvial-lacustrine sediments and a mineable coal seam with an average of 5 m in thickness rests unconformably upon the basement and is also unconformably overlain by marine limestones of the middle-late Miocene Mut Formation in the Ermenek coal basin. The coal basin in the present study has been subdivided into two areas, Canakci and Pamuklu-Tepebasi, which are separated by the basement and a fault, in order to determine coal properties in detail. The investigated subbituminous coals with an average of 0.40% Ro huminite reflectance often contain gastropod shells (Planorbidae) which commonly maintain the original aragonite and calcite composition. The coals have similar chemical properties and petrographic composition in the two areas, but their sulphur contents are clearly different. In the Canakci area the coals on an air-dried basis contain distinctly less total sulphur (avg. 1.3%) and organic sulphur contents (0.13 0.15%) than in the Pamuklu-Tepebasi area (avg. 4.5% and 4.25%, respectively). This difference is interpreted to be controlled by mire chemistry and sedimentation during peat formation. (author)

  5. First North American fossil monkey and early Miocene tropical biotic interchange

    Science.gov (United States)

    Bloch, Jonathan I.; Woodruff, Emily D.; Wood, Aaron R.; Rincon, Aldo F.; Harrington, Arianna R.; Morgan, Gary S.; Foster, David A.; Montes, Camilo; Jaramillo, Carlos A.; Jud, Nathan A.; Jones, Douglas S.; MacFadden, Bruce J.

    2016-05-01

    New World monkeys (platyrrhines) are a diverse part of modern tropical ecosystems in North and South America, yet their early evolutionary history in the tropics is largely unknown. Molecular divergence estimates suggest that primates arrived in tropical Central America, the southern-most extent of the North American landmass, with several dispersals from South America starting with the emergence of the Isthmus of Panama 3-4 million years ago (Ma). The complete absence of primate fossils from Central America has, however, limited our understanding of their history in the New World. Here we present the first description of a fossil monkey recovered from the North American landmass, the oldest known crown platyrrhine, from a precisely dated 20.9-Ma layer in the Las Cascadas Formation in the Panama Canal Basin, Panama. This discovery suggests that family-level diversification of extant New World monkeys occurred in the tropics, with new divergence estimates for Cebidae between 22 and 25 Ma, and provides the oldest fossil evidence for mammalian interchange between South and North America. The timing is consistent with recent tectonic reconstructions of a relatively narrow Central American Seaway in the early Miocene epoch, coincident with over-water dispersals inferred for many other groups of animals and plants. Discovery of an early Miocene primate in Panama provides evidence for a circum-Caribbean tropical distribution of New World monkeys by this time, with ocean barriers not wholly restricting their northward movements, requiring a complex set of ecological factors to explain their absence in well-sampled similarly aged localities at higher latitudes of North America.

  6. Varves in lake sediments - a review

    Science.gov (United States)

    Zolitschka, Bernd; Francus, Pierre; Ojala, Antti E. K.; Schimmelmann, Arndt

    2015-06-01

    Downcore counting of laminations in varved sediments offers a direct and incremental dating technique for high-resolution climatic and environmental archives with at least annual and sometimes even seasonal resolution. The pioneering definition of varves by De Geer (1912) had been restricted to rhythmically deposited proglacial clays. One century later the meaning of 'varve' has been expanded to include all annually deposited laminae in terrestrial and marine settings. Under favourable basin configurations and environmental conditions, limnic varves are formed due to seasonality of depositional processes from the lake's water column and/or transport from the catchment area. Subsequent to deposition of topmost laminae, the physical preservation of the accumulating varved sequence requires the sustained absence of sediment mixing, for example via wave action or macrobenthic bioturbation. Individual (sub)laminae in varved lake sediments typically express contrasting colours, always differ in terms of their organic, chemical and/or mineralogical compositions, and often also differ with regard to grain-size. Various predominating climatic and depositional conditions may result in clastic, biogenic or endogenic (incl. evaporitic) varved sediments and their mixtures. To reliably establish a varve chronology, the annual character of laminations needs to be determined and verified in a multidisciplinary fashion. Sources and influences of possible errors in varve chronologies are best determined and constrained by repeated varve counts, and by including radioisotopes and correlation with historically documented events. A well-established varve chronology greatly enhances the scientific value of laminated limnic archives by securely anchoring the wealth of multi-proxy palaeoenvironmental information in the form of time-series for multidisciplinary investigations. Applications of varved records are discussed with special reference to advances since the 1980s. These span fields

  7. 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. 

  8. Astrochronology of a Late Oligocene to Early Miocene Magnetostratigraphy from the Northwest Atlantic

    Science.gov (United States)

    van Peer, T. E.; Xuan, C.; Liebrand, D.; Lippert, P. C.; Wilson, P. A.

    2016-12-01

    The Oligocene-Miocene Boundary is defined by the geomagnetic polarity reversal C6Cn.2n/C6Cn.2r with an astronomically tuned age of 23 Ma. For late Oligocene to early Miocene reversals, only a few records (mainly from the equatorial Pacific and South Atlantic) integrate magneto- and cyclo-stratigraphy with astronomical tuning. Reversal ages acquired from these records show differences up to 100 kyr. We report new astronomically tuned ages for reversals between 21-26.5 Ma, based on integrated palaeomagnetic and X-Ray Fluorescence (XRF) data from rapidly accumulated drift sediments (mean sedimentation rate of 2.5 cm/kyr) at Integrated Ocean Drilling Program (IODP) Site U1406 (northwest Atlantic). The natural remanence preserved in the sediments is relatively weak (especially at high demagnetisation steps) and prone to influence from measurement noise. We introduce an optimisation protocol to improve the estimation of component directions used to define the reversals. For each 1-cm interval measurement, the protocol searches for the combination of a fixed number of steps of demagnetisation data that minimises the maximum angular deviation, statistically excluding the noisy measurement steps. For the tuning, we use the logarithm of the calcium over potassium ratio ln(Ca/K) from XRF core scanning data, a proxy of carbonate content in the sediment. Spectral and wavelet analyses of the 140-m long ln(Ca/K) record highlight dominant obliquity (including the 178 and 1200 kyr modulation) and additional eccentricity forcing. Supported by preliminary stable isotope analysis on benthic foraminifera, we tuned ln(Ca/K) minima to obliquity minima and eccentricity maxima. The resulting age model yield new independent ages for all reversals between C6Ar/C6AAn to C8r/C9n. Our results are generally consistent (within an obliquity cycle) with the Ocean Drilling Program (ODP) Site 1090 age model [Billups et al., 2004], but deviate up to 80 kyr relative to ODP Site 1218 [Pälike et al

  9. K-Ar ages of Early Miocene arc-type volcanoes in northern New Zealand

    International Nuclear Information System (INIS)

    Hayward, B.W.; Black, P.M.; Smith, I.E.M.; Ballance, P.F.; Itaya, T.; Doi, M.; Takagi, M.; Bergman, S.; Adams, C.J.; Herzer, R.H.; Robertson, D.J.

    2001-01-01

    Understanding the temporal and spatial development of the Early Miocene Northland Volcanic Arc is critical to interpreting the patterns of volcanic activity in northern New Zealand through the Late Cenozoic. The northwesterly trending arc is considered to have developed above a southwest-dipping subduction system. The distribution of its constituent eruptive centres is described in terms of an eastern belt that extends along the eastern side of Northland and a complementary broad western belt which includes subaerial and submarine volcanic edifices. Critical examination of all 216 K-Ar ages available, including 180 previously unpublished ages, and their assessment against tectonic, lithostratigraphic, seismic stratigraphic, and biostratigraphic constraints, leads us to deduce a detailed chronology of periods of activity for the various Early (and Middle) Miocene arc-type volcanic complexes and centres of northern New Zealand: Waipoua Shield Volcano Complex (19-18 Ma, Altonian); Kaipara Volcanic Complex (23-16 Ma, Waitakian-Altonian); Manukau Volcanic Complex (c. 23-15.5 Ma, Waitakian-Clifdenian); North Cape Volcanic Centre (23-18 Ma, Waitakian-Altonian); Whangaroa Volcanic Complex (22.5-17.5 Ma, Waitakian-Altonian); Taurikura Volcanic Complex (22-15.5 Ma, Otaian-Clifdenian); Parahaki Dacites (22.5-18 Ma, Waitakian-Altonian); Kuaotunu Volcanic Complex (18.5-11 Ma, Altonian-Waiauan). In general, volcanic activity does not show geographic migration with time, and the western (25-15.5 Ma) and eastern (23-11 Ma) belts appear to have developed concurrently. (author). 123 refs., 9 figs., 1 tab

  10. Diagenetic history of late Oligocene-early Miocene carbonates in East Sabah, Malaysia

    Science.gov (United States)

    Zainal Abidin, N. S.; Raymond, R. R.; Bashah, N. S. I.

    2017-10-01

    Limestones are particularly susceptible to drastic early diagenesis modifications, mainly cementation and dissolution. During the early Miocene, a major tectonic deformation has caused a widespread of uplift in Sabah. This has resulted change in depositional environment from deep to shallow marine, which favours the deposition of Gomantong Limestone. This study aims to investigate the diagenetic history of Gomantong Limestone in East Sabah. Thorough understanding of the diagenetic processes may provide data to unravel the tectonic activities which affected the reservoir quality of the carbonates. Combining the data from comprehensive petrographic analysis, and Scanning Electron Microscopy (SEM) of 30 samples, two main cements type were identified. These are microcrystalline cement and Mg-calcite cement of granular and blocky mosaics which are dominantly seen in all samples. The sequence of diagenesis events are determined as (1) micritization; (2) grain scale compaction; (3) cementation (pore-filling); (4) mechanical compaction and cementation infilling fractures and (5) chemical compaction. These diagenetic events are interpreted as reflection of changes in diagenetic environment from shallow marine to deep burial. The massive cementation in the Gomantong Limestone has resulted into a poor reservoir quality.

  11. K-Ar Geochronology and isotopic composition of the late oligocene- early miocene Ancud volcanic complex, Chiloe

    International Nuclear Information System (INIS)

    Munoz B, Jorge; Duhart O, Paul; Farmer, G. Lang; Stern, Charles R

    2001-01-01

    The Ancud Volcanic Complex (Gally and Sanchez , 1960) forms a portion of the Mid-Tertiary Coastal Magmatic Belt which outcrops in the area of northern Chiloe island. Main exposures occur at Ancud, Punta Polocue, Punihuil, Pumillahue, Tetas de Teguaco and Bahia Cocotue. The Ancud Volcanic Complex consists of basaltic to basaltic andesites lava flows and volcanic necks and rhyolitic pyroclastic flows and vitric domes. Previous studies indicate a Late Oligocene-Early Miocene age (Garcia et al., 1988; Stern and Vergara, 1992; Munoz et al., 2000). The Ancud Volcanic Complex covers and intrudes Palaeozoic-Triassic metamorphic rocks and is partially covered by an early to middle Miocene marine sedimentary sequence known as Lacui Formation (Valenzuela, 1982) and by Pleistocene glacial deposits (Heusser, 1990). At Punihuil locality, lava flows are interbedded with the lower part of the marine sedimentary sequence, which includes significant amounts of redeposited pyroclastic components. Locally, the presence of hyaloclastic breccias suggests interaction of magma with marine water (au)

  12. Early Miocene amber inclusions from Mexico reveal antiquity of mangrove-associated copepods.

    Science.gov (United States)

    Huys, Rony; Suárez-Morales, Eduardo; Serrano-Sánchez, María de Lourdes; Centeno-García, Elena; Vega, Francisco J

    2016-10-12

    Copepods are aquatic microcrustaceans and represent the most abundant metazoans on Earth, outnumbering insects and nematode worms. Their position of numerical world predominance can be attributed to three principal radiation events, i.e. their major habitat shift into the marine plankton, the colonization of freshwater and semiterrestrial environments, and the evolution of parasitism. Their variety of life strategies has generated an incredible morphological plasticity and disparity in body form and shape that are arguably unrivalled among the Crustacea. Although their chitinous exoskeleton is largely resistant to chemical degradation copepods are exceedingly scarce in the geological record with limited body fossil evidence being available for only three of the eight currently recognized orders. The preservation of aquatic arthropods in amber is unusual but offers a unique insight into ancient subtropical and tropical ecosystems. Here we report the first discovery of amber-preserved harpacticoid copepods, represented by ten putative species belonging to five families, based on Early Miocene (22.8 million years ago) samples from Chiapas, southeast Mexico. Their close resemblance to Recent mangrove-associated copepods highlights the antiquity of the specialized harpacticoid fauna living in this habitat. With the taxa reported herein, the Mexican amber holds the greatest diversity of fossil copepods worldwide.

  13. The Early Miocene Critical Zone at Karungu, Western Kenya: An Equatorial, Open Habitat with Few Primate Remains

    Science.gov (United States)

    Lukens, William E.; Lehmann, Thomas; Peppe, Daniel J.; Fox, David L.; Driese, Steven G.; McNulty, Kieran P.

    2017-10-01

    Early Miocene outcrops near Karungu, Western Kenya, preserve a range of fluvio-lacustrine, lowland landscapes that contain abundant fossils of terrestrial and aquatic vertebrates. Primates are notably rare among these remains, although nearby early Miocene strata on Rusinga Island contain a rich assemblage of fossilized catarrhines and strepsirrhines. To explore possible environmental controls on the occurrence of early Miocene primates, we performed a deep-time Critical Zone (DTCZ) reconstruction focused on floodplain paleosols at the Ngira locality in Karungu. We specifically focused on a single stratigraphic unit (NG15), which preserves moderately developed paleosols that contain a microvertebrate fossil assemblage. Although similarities between deposits at Karungu and Rusinga Island are commonly assumed, physical sedimentary processes, vegetative cover, soil hydrology, and some aspects of climate state are notably different between the two areas. Estimates of paleoclimate parameters using paleosol B horizon elemental chemistry and morphologic properties are consistent with seasonal, dry subhumid conditions, occasional waterlogging, and herbaceous vegetation. The reconstructed small mammal community indicates periodic waterlogging and open-canopy conditions. Based on the presence of herbaceous root traces, abundant microcharcoal, and pedogenic carbonates with high stable carbon isotope ratios, we interpret NG15 to have formed under a warm, seasonally dry, open riparian woodland to wooded grassland, in which at least a subset of the vegetation was likely C4 biomass. Our results, coupled with previous paleoenvironmental interpretations for deposits on Rusinga Island, demonstrate that there was considerable environmental heterogeneity ranging from open to closed habitats in the early Miocene. We hypothesize that the relative paucity of primates at Karungu was driven by their environmental preference for locally abundant closed canopy vegetation, which was likely

  14. The Early Miocene Critical Zone at Karungu, Western Kenya: An Equatorial, Open Habitat with Few Primate Remains

    Directory of Open Access Journals (Sweden)

    William E. Lukens

    2017-10-01

    Full Text Available Early Miocene outcrops near Karungu, Western Kenya, preserve a range of fluvio-lacustrine, lowland landscapes that contain abundant fossils of terrestrial and aquatic vertebrates. Primates are notably rare among these remains, although nearby early Miocene strata on Rusinga Island contain a rich assemblage of fossilized catarrhines and strepsirrhines. To explore possible environmental controls on the occurrence of early Miocene primates, we performed a deep-time Critical Zone (DTCZ reconstruction focused on floodplain paleosols at the Ngira locality in Karungu. We specifically focused on a single stratigraphic unit (NG15, which preserves moderately developed paleosols that contain a microvertebrate fossil assemblage. Although similarities between deposits at Karungu and Rusinga Island are commonly assumed, physical sedimentary processes, vegetative cover, soil hydrology, and some aspects of climate state are notably different between the two areas. Estimates of paleoclimate parameters using paleosol B horizon elemental chemistry and morphologic properties are consistent with seasonal, dry subhumid conditions, occasional waterlogging, and herbaceous vegetation. The reconstructed small mammal community indicates periodic waterlogging and open-canopy conditions. Based on the presence of herbaceous root traces, abundant microcharcoal, and pedogenic carbonates with high stable carbon isotope ratios, we interpret NG15 to have formed under a warm, seasonally dry, open riparian woodland to wooded grassland, in which at least a subset of the vegetation was likely C4 biomass. Our results, coupled with previous paleoenvironmental interpretations for deposits on Rusinga Island, demonstrate that there was considerable environmental heterogeneity ranging from open to closed habitats in the early Miocene. We hypothesize that the relative paucity of primates at Karungu was driven by their environmental preference for locally abundant closed canopy vegetation

  15. A new genus and species of tettigarctid cicada from the early Miocene of New Zealand: Paratettigarcta zealandica (Hemiptera, Auchenorrhyncha, Tettigarctidae)

    Science.gov (United States)

    Kaulfuss, Uwe; Moulds, Max

    2015-01-01

    Abstract A new genus and species of primitive cicada (Hemiptera: Tettigarctidae) is described from the early Miocene of southern New Zealand. Paratettigarcta zealandica gen. et sp. n. is the first cicada (Cicadoidea) fossil from New Zealand and exhibits wing venation patterns typical for the subfamily Tettigarctinae. It differs from other fossil taxa and the extant genus Tettigarcta in the early divergence of CuA2 from the nodal line in the forewing, its parallel-sided subcostal cell, the early bifurcation of vein M and long apical cells of the hindwing, and in wing pigmentation patterns. PMID:25829843

  16. Global compilation of marine varve records

    Science.gov (United States)

    Schimmelmann, Arndt; Lange, Carina B.; Schieber, Juergen; Francus, Pierre; Ojala, Antti E. K.; Zolitschka, Bernd

    2017-04-01

    Marine varves contain highly resolved records of geochemical and other paleoceanographic and paleoenvironmental proxies with annual to seasonal resolution. We present a global compilation of marine varved sedimentary records throughout the Holocene and Quaternary covering more than 50 sites worldwide. Marine varve deposition and preservation typically depend on environmental and sedimentological conditions, such as a sufficiently high sedimentation rate, severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos, and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern. Additional oceanographic factors may include the strength and depth range of the Oxygen Minimum Zone (OMZ) and regional anthropogenic eutrophication. Modern to Quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions, but also in fjords, embayments and estuaries with thermohaline density stratification, and nearshore 'marine lakes' with strong hydrologic connections to ocean water. Marine varves have also been postulated in pre-Quaternary rocks. In the case of non-evaporitic laminations in fine-grained ancient marine rocks, such as banded iron formations and black shales, laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transported and sorted silt-sized particles, clay floccules, and organic-mineral aggregates in the form of migrating bedload ripples. Modern marine ecosystems on continental shelves and slopes, in coastal zones and in estuaries are susceptible to stress by anthropogenic pressures, for example in the form of eutrophication, enhanced OMZs, and expanding ranges of oxygen-depletion in bottom waters. Sensitive laminated sites may play the important role of a 'canary in the coal mine' where monitoring the character and geographical extent of laminations/varves serves as a diagnostic

  17. A new large squalodelphinid (Cetacea, Odontoceti) from Peru sheds light on the Early Miocene platanistoid disparity and ecology

    Science.gov (United States)

    Bianucci, Giovanni; Bosio, Giulia; Malinverno, Elisa; de Muizon, Christian; Villa, Igor M.; Urbina, Mario; Lambert, Olivier

    2018-04-01

    The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78 ± 0.08 Ma (Burdigalian, Early Miocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the Early Miocene radiation of crown odontocetes.

  18. Fruits and wood of Parinari from the early Miocene of Panama and the fossil record of Chrysobalanaceae.

    Science.gov (United States)

    Jud, Nathan A; Nelson, Chris W; Herrera, Fabiany

    2016-02-01

    Chrysobalanaceae are woody plants with over 500 species in 20 genera. They are among the most common trees in tropical forests, but a sparse fossil record has limited our ability to test evolutionary and biogeographic hypotheses, and several previous reports of Chrysobalanaceae megafossils are doubtful. We prepared fossil endocarps and wood collected from the lower Miocene beds along the Panama Canal using the cellulose acetate peel technique and examined them using light microscopy. We compared the fossil endocarps with previously published fossils and with fruits from herbarium specimens. We compared the fossil wood with photographs and descriptions of extant species. Parinari endocarps can be distinguished from other genera within Chrysobalanaceae by a suite of features, i.e., thick wall, a secondary septum, seminal cavities lined with dense, woolly trichomes, and two ovate to lingulate basal germination plugs. Fossil endocarps from the Cucaracha, Culebra, and La Boca Formations confirm that Parinari was present in the neotropics by the early Miocene. The earliest unequivocal evidence of crown-group Chrysobalanaceae is late Oligocene-early Miocene, and the genus Parinari was distinct by at least 19 million years ago. Parinari and other Chrysobalanaceae likely reached the neotropics via long-distance dispersal rather than vicariance. The presence of Parinari in the Cucaracha flora supports the interpretation of a riparian, moist tropical forest environment. Parinari was probably a canopy-dominant tree in the Cucaracha forest and took advantage of the local megafauna for seed dispersal. © 2016 Botanical Society of America.

  19. A new large squalodelphinid (Cetacea, Odontoceti) from Peru sheds light on the Early Miocene platanistoid disparity and ecology

    Science.gov (United States)

    Bosio, Giulia; Malinverno, Elisa; Villa, Igor M.; Urbina, Mario

    2018-01-01

    The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78 ± 0.08 Ma (Burdigalian, Early Miocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the Early Miocene radiation of crown odontocetes.

  20. A new baleen whale from the Late Miocene of Denmark and early mysticete hearing

    DEFF Research Database (Denmark)

    Steeman, Mette Elstrup

    2009-01-01

    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...

  1. Early Miocene rapid exhumation in southern Tibet: Insights from P-T-t-D-magmatism path of Yardoi dome

    Science.gov (United States)

    Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Kai; Zhang, Jin-Jiang; Liu, Xiao-Chi

    2018-04-01

    Reconstructing the evolution of Gneiss domes within orogenic belts poses challenges because domes can form in a variety of geodynamic settings and by multiple doming mechanisms. For the North Himalayan gneiss domes (NHGD), it is debated whether they formed during shortening, extension or collapse of the plateau, and what is the spatial and temporal relationship of magmatism, metamorphism and deformation. This study investigates the Yardoi dome in southern Tibet using field mapping, petrography, phase equilibria modelling and new monazite ages. The resulting P-T-time-deformation-magmatism path for the first time reveals the spatial and temporal relationship of metamorphism, deformation and magmatism in the Yardoi dome: a) the dome mantle recorded prograde loading to kyanite-grade Barrovian metamorphic conditions of 650 ± 30 °C and 9 ± 1 kbar (M2) in the Early Miocene (18-17 Ma); b) the main top-to-the-north deformation fabric (D2) formed syn- to post-peak-metamorphism; c) the emplacement of leucorgranites related to doming is syn-metamorphism at 19-17 Ma. The link between the detachment shear zone in the Yardoi dome and the South Tibetan detachment system (STDS) is confirmed. By comparing with orogen-scale tectonic processes in the Himalaya, we suggest that north-south extension in a convergent geodynamic setting during Early Miocene accounts for formation of the Yardoi dome. In a wider tectonic context, the Early Miocene rapid exhumation of deep crustal rocks was contemporaneous with the rapid uplift of southern Tibet and the Himalayan orogen.

  2. A long-living species of the hydrophiloid beetles: Helophorus sibiricus from the early Miocene deposits of Kartashevo (Siberia, Russia

    Directory of Open Access Journals (Sweden)

    Martin Fikácek

    2011-09-01

    Full Text Available The recent hydrophiloid species Helophorus (Gephelophorus sibiricus (Motschulsky, 1860 is recorded from the early Miocene deposits of Kartashevo assigned to the Ombinsk Formation. A detailed comparison with recent specimens allowed a confident identification of the fossil specimen, which is therefore the oldest record of a recent species for the Hydrophiloidea. The paleodistribution as well as recent distribution of the species is summarized, and the relevance of the fossil is discussed. In addition, the complex geological settings of the Kartashevo area are briefly summarized.

  3. Paleosoils and pedogenic calcretes formations in Fray Bentos (Oligocene - early miocene) Raigon (late pliocene and middle pleistocene) and Libertad (early - middle pleistocene)

    International Nuclear Information System (INIS)

    Tofalo, O.; Morras, H.; Sanchez-Bettucci, L.

    2012-01-01

    The Fray Bentos formation is composed by loessic deposits based on paleosoils and pedogenic calcretes (Oligocene - early miocene). In this deposits are tubular and lamellar formations which would have been formed in arid climates.The fluvial origen of Raigon Formation, (late pliocene and middle pleistocene) presents a paleosoil roof which is generated under a subhumid climate.The Libertad Formation during the glacial intervals consisted of loess deposits

  4. Monitoring the formation of clastic-biogenic varves to improve the quality of paleoclimate reconstructions

    Science.gov (United States)

    Ojala, A.; Kosonen, E.; Weckstrom, J.; Korkonen, S.

    2013-12-01

    Annually laminated (varved) sediments are excellent archives for studies of past climate and environmental changes, as they allow analysis of the undisturbed 'in-situ' sediment composition and structure with a seasonal-scale resolution. Among those, clastic-biogenic varved lake sediments have been found and investigated in Finland and Sweden during the last decades. An important prerequisite for applying varved sediments in palaeoenvironmental studies is understanding the mechanism of rhythmic sedimentation and the composition of different laminae representing annual sedimentation events. This knowledge is essential for verifying the annual nature of varves, for investigating the main factors controlling seasonal sedimentation, and for the interpretations of past environmental changes. Here, we report detailed information on the seasonal sedimentation of different varve components and palaeolimnological indicators (diatoms, chrysophycaean cysts) in Lake Nautajärvi, Finland, using near-bottom sediment trap monitoring. The monitoring results strongly support previous interpretations of the formation of clastic-biogenic varves in Fennoscandian lakes. The results also indicate that seasonal sediment fluxes correspond with regional climate and environmental changes. They clearly reveal differences in the amount of seasonal sediment flux between two climatologically and hydrologically different years. For example, higher snow storage in winter and the discharge intensity during the following spring snow melt clearly increases the suspended sediment load, transportation, and net accumulation of detrital mineral matter during spring and early summer. A prolonged autumn and subsequent freezing and thawing cycles in winter, conversely, results in an incremental but slow accumulation of assorted mineral matter and organic particles during winter, whereas the subsequent spring flooding and detrital sediment yield are diminished and thinner clastic laminae are formed. The

  5. Megalictis, the Bone-Crushing Giant Mustelid (Carnivora, Mustelidae, Oligobuninae) from the Early Miocene of North America

    Science.gov (United States)

    Valenciano, Alberto; Baskin, Jon A.; Abella, Juan; Pérez-Ramos, Alejandro; Álvarez-Sierra, M. Ángeles; Morales, Jorge; Hartstone-Rose, Adam

    2016-01-01

    We describe cranial and mandibular remains of three undescribed individuals of the giant mustelid Megalictis ferox Matthew, 1907 from the latest Arikareean (Ar4), Early Miocene mammal fauna of Nebraska, and Wyoming (USA) housed at the American Museum of Natural History (New York, USA). Our phylogenetic hypothesis indicates that Ar4 specimens assigned to M. ferox constitute a monophyletic group. We assign three additional species previously referred to Paroligobunis to Megalictis: M. simplicidens, M. frazieri, and “M.” petersoni. The node containing these four species of Megalictis and Oligobunis forms the Oligobuninae. We test the hypothesis that Oligobuninae (Megalictis and Oligobunis) is a stem mustelid taxon. Our results indicate that the Oligobuninae form the sister clade to the crown extant mustelids. Based on the cranium, M. ferox is a jaguar-size mustelid and the largest terrestrial mustelid known to have existed. This new material also sheds light on a new ecomorphological interpretation of M. ferox as a bone-crushing durophage (similar to hyenas), rather than a cat-like hypercarnivore, as had been previously described. The relative large size of M. ferox, together with a stout rostrum and mandible made it one of the more powerful predators of the Early Miocene of the Great Plains of North America. PMID:27054570

  6. Megalictis, the Bone-Crushing Giant Mustelid (Carnivora, Mustelidae, Oligobuninae from the Early Miocene of North America.

    Directory of Open Access Journals (Sweden)

    Alberto Valenciano

    Full Text Available We describe cranial and mandibular remains of three undescribed individuals of the giant mustelid Megalictis ferox Matthew, 1907 from the latest Arikareean (Ar4, Early Miocene mammal fauna of Nebraska, and Wyoming (USA housed at the American Museum of Natural History (New York, USA. Our phylogenetic hypothesis indicates that Ar4 specimens assigned to M. ferox constitute a monophyletic group. We assign three additional species previously referred to Paroligobunis to Megalictis: M. simplicidens, M. frazieri, and "M." petersoni. The node containing these four species of Megalictis and Oligobunis forms the Oligobuninae. We test the hypothesis that Oligobuninae (Megalictis and Oligobunis is a stem mustelid taxon. Our results indicate that the Oligobuninae form the sister clade to the crown extant mustelids. Based on the cranium, M. ferox is a jaguar-size mustelid and the largest terrestrial mustelid known to have existed. This new material also sheds light on a new ecomorphological interpretation of M. ferox as a bone-crushing durophage (similar to hyenas, rather than a cat-like hypercarnivore, as had been previously described. The relative large size of M. ferox, together with a stout rostrum and mandible made it one of the more powerful predators of the Early Miocene of the Great Plains of North America.

  7. Late Miocene-Early Pliocene reactivation of the Main Boundary Thrust: Evidence from the seismites in southeastern Kumaun Himalaya, India

    Science.gov (United States)

    Mishra, Anurag; Srivastava, Deepak C.; Shah, Jyoti

    2013-05-01

    Tectonic history of the Himalaya is punctuated by successive development of the faults that run along the boundaries between different lithotectonic terrains. The Main Boundary Fault, defining the southern limit of the Lesser Himalayan terrain, is tectonically most active. A review of published literature reveals that the nature and age of reactivation events on the Main Boundary Fault is one of the poorly understood aspects of the Himalayan orogen. By systematic outcrop mapping of the seismites, this study identifies a Late Miocene-Early Pliocene reactivation on the Main Boundary Thrust in southeast Kumaun Himalaya. Relatively friable and cohesionless Neogene sedimentary sequences host abundant soft-sediment deformation structures in the vicinity of the Main Boundary Thrust. Among a large variety of structures, deformed cross-beds, liquefaction pockets, slump folds, convolute laminations, sand dykes, mushroom structures, fluid escape structures, flame and load structures and synsedimentary faults are common. The morphological attributes, the structural association and the distribution pattern of the soft-sediment deformation structures with respect to the Main Boundary Fault strongly suggest their development by seismically triggered liquefaction and fluidization. Available magnetostratigraphic age data imply that the seismites were developed during a Late Miocene-Early Pliocene slip on the Main Boundary Thrust. The hypocenter of the main seismic event may lie on the Main Boundary Thrust or to the north of the study area on an unknown fault or the Basal Detachment Thrust.

  8. Volcaniclastic and sedimentary deposits in Late Oligocene/Early Miocene Smrekovec Volcanic Complex, northern Slovenia

    Science.gov (United States)

    Kralj, Polona

    2010-05-01

    Late Oligocene/Early Miocene volcanic activity in northern Slovenia is related to post-collisional accommodation of continental Apulian and oceanic European plates (von Blanckenburg and Davis, 1996). It occurred in one of small south-western marginal depressions of the Pannonian basin system, locally termed the Smrekovec Basin (Hanfland et al., 2004). Contemporaneous clastic sedimentation is evidenced by several hundred metres thick succession composed mainly of mudstone, siltstone and sand. Smrekovec Volcanic Complex (SVC) is an eroded and tectonically uplifted remain of a larger submarine stratovolcano edifice, built of lavas, shallow or subsurface intrusive bodies, and pyroclastic, hyaloclastic, syn-eruptively resedimented volcaniclastic and reworked volcaniclastic-sedimentary deposits (Kralj, 1996). The development of lithofacies of syn-eruptively resedimented deposits is controlled by the proximity to the ancient volcano summit and the volcano sloping. Moreover, close to the rising volcano edifice, distinct shallow-water environments with siliciclastic sedimentation developed. Syn-eruptively resedimented deposits are the most widespread and are related to volcaniclastic debris flows and volcaniclastic tubidity flows. Volcaniclastic debris flow deposits are subdivided into lithofacies Bx - polymict volcaniclastic breccia, and Bt - volcaniclastic tuff-breccia. Bx occurs as tabular, up to some ten metres thick bodies with abundant up to 5 dm large angular lava clasts and angular or rounded clasts of fine-grained tuff, and tuffaceous matrix. Bt forms basal, massive layers in fining-upward sequences. The main constituent is tuffaceous matrix; up to 1.5 dm large clasts of lavas and tuffs are subordinate. In a distance up to 2 km from the former volcano summit (proximal area), Bt predominates in the sequence lithofacies composition (~75 %), and attains a thickness of up to 4 m. At a distance of 2-4 km (distal area), a maximum Bt thickness rarely exceeds 5 dm, an

  9. A major Early Miocene thermal pulse due to subduction segmentation and rollback in the western Mediterranean region

    Science.gov (United States)

    Spakman, W.; Van Hinsbergen, D. J.; Vissers, R.

    2012-12-01

    Geological studies have shown that Eo-Oligocene subduction related high-pressure, low-temperature metasediments and peridotites of the Alboran region (Spain, Morocco) and the Kabylides (Algeria) experienced a major Early Miocene (~21 Ma) thermal pulse requiring asthenospheric temperatures at ~60 km depth. Despite earlier propositions, the cause of this thermal pulse is still controversial while also the paleogeographic origin of the Alboran and Kabylides units is debated. Here, we relate the thermal pulse to segmentation of the West Alpine-Tethyan slab under the SE Iberian margin (Baleares-Sardinia). We restore the Alboran rocks farther east than previously assumed, to close to the Balearic Islands, adjacent to Sardinia. We identify three major lithosphere faults, the NW-SE trending North Balearic Transform Zone (NBTZ) and the ~W-E trending Emile Baudot and North African transforms that accommodated the Miocene subduction evolution of slab segmentation, rollback, and migration of Alboran and Kabylides rocks to their current positions. The heat pulse occurred S-SE of the Baleares where slab segmentation along the NBTZ triggered radially outgrowing S-SW rollback opening a slab window that facilitated local ascent of asthenosphere below the rapidly extending Alboran-Kabylides accretionary prism. Subsequent slab rollback carried the Kabylides and Alboran domains to their present positions. Our new reconstruction is in line with tomographically imaged mantle structure and focuses attention on the crucial role of evolving subduction segmentation driving HT-metamorphism and subsequent extension, fragmentation, and dispersion of geological terrains.

  10. New contribution to the palaeoichnology and taphonomy of the Ahníkov fossil site, Early Miocene, Most Basin (The Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Ekrt, B.; Mikuláš, Radek; Wagner, J.; Čermák, Stanislav; Procházková, K.; Kadlecová, E.; Fejfar, O.

    2016-01-01

    Roč. 72, 3/4 (2016), s. 202-214 ISSN 2533-4050 Institutional support: RVO:67985831 Keywords : biting traces * bone-mammal interaction * Czech Republic * Early Miocene * Most Basin * palaeoichnology * Sciuridae * taphonomy Subject RIV: DB - Geology ; Mineralogy

  11. A lacustrine record of the early stage of the Miocene Climatic Optimum in Central Europe from the Most Basin, Ohre (Eger) Graben, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Matys Grygar, Tomáš; Mach, K.; Schnabl, Petr; Pruner, Petr; Laurin, Jiří; Martinez, M.

    2014-01-01

    Roč. 151, č. 6 (2014), s. 1013-1033 ISSN 0016-7568 R&D Projects: GA ČR(CZ) GAP210/11/1357 Institutional support: RVO:61388980 ; RVO:67985530 ; RVO:67985831 Keywords : cyclostratigraphy * lake sediments * climate dynamics * Milankovitch cycles * early Miocene Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.482, year: 2014

  12. Characterization of groundwater dynamics in landslides in varved clays

    NARCIS (Netherlands)

    Van der Spek, J.E.; Bogaard, T.A.; Bakker, M.

    2013-01-01

    Groundwater dynamics may play a significant role in landslides. A detailed model is developed of the groundwater dynamics in landslides in varved clays in the Trièves area in the French Alps. The varved clays consist of a sequence of alternating silt and clay layers, covered by a colluvium layer and

  13. Characterization of groundwater dynamics in landslides in varved clays

    NARCIS (Netherlands)

    Van der Spek, J.E.; Bogaard, T.A.; Bakker, M.

    2013-01-01

    Groundwater dynamics may play a significant role in landslides. A detailed model is developed of the groundwater dynamics in landslides in varved clays in the Trieves area in the French Alps. The varved clays consist of a sequence of alternating silt and clay layers, covered by a colluvium layer and

  14. Formation of early-middle Miocene red beds in the South China Sea: element geochemistry and mineralogy analysis

    Science.gov (United States)

    Lyu, X.; Liu, Z.

    2017-12-01

    The formation of oceanic red beds that usually present oxic and oligotrophic conditions with low sedimentation rate has been used to trace depositional paleoenvironment and paleoclimate change. Red beds overlying oceanic basalts were drilled at two adjacent Sites U1433 and U1434 of IODP Expedition 349 in the Southwest Subbasin of the South China Sea. The occurrence of early-middle Miocene red beds may indicate that at that time there was oxic and quiet marine environment in the deep South China Sea. To understand their formation of red-color, local depositional condition, and potential paleoceanographic significance, major elements (XRF), trace and rare earth elements (ICP-MS), Fe chemical speciation (modified sequential iron extraction procedure), and Fe oxic minerals (CBD and DRS) were analyzed. Geochemical and mineralogical data reveal that hematite and goethite are responsible for the reddish color and red beds were deposited under highly oxic, oligotrophic conditions with a little later hydrothermal influence in the South China Sea. Our results indicate that: (1) after treatment using the CBD procedure, the red samples presented a change in color to greenish, showing the iron oxides being responsible for the sediment color; (2) enriched Mn, depleted U, S enrichment factors, and negative Ce anomaly show that the water mass was pre-oxidized before transported to the study location; (3) low primary productivity was inferred from the lower P, Ba enrichment factors in red beds compared to non-red beds; (4) the excess Mo influx at the bottom may come from the later hydrothermal input; (5) the diverse Ca enrichment factors and correlations between Fe and Al suggest different allogenic sources for red beds at our two sites. We conclude that the red beds at Sites U1433 and U1434 despite their diverse sources both developed in externally oxidized water mass and low primary productivity conditions, and partially altered by hydrothermal fluids after their pelagic

  15. Quantifying incision rates since the early Miocene: novelties, potentialities and limitations

    Science.gov (United States)

    Sartégou, A.; Braucher, R.; Blard, P. H.; Bourlès, D. L.; Zimmermann, L.; Tibari, B.; Voinchet, P.; Bahain, J. J.; Sorriaux, P.; Leanni, L.; Team, A.

    2017-12-01

    The rates and chronologies of valley incision are closely modulated by the tectonic uplift of active mountain ranges and were controlled by repeated climate changes during the Quaternary. The Pyrenees are a continental collision between the Iberian and Eurasian plates induced a double vergence orogen, which has been considered as a mature mountain range in spite of significant seismicity and evidence of neotectonics. Nevertheless, recent studies indicate that the range may have never reached a steady state. One option for resolving this controversy is to quantify the incision rates since the Miocene by reconstructing the vertical movement of geometric markers. However, the few available ages from the Pyrenean terrace systems do not exceed the middle Pleistocene. To enlarge the time span of this dataset, we studied alluvium-filled horizontal epiphreatic passages in limestone karstic networks, which represent former valley floors. They record the transient position of former local base levels during the process of valley deepening. We used various suitable geochronological methods (26Al/10Be, 10Be/21Ne, ESR and OSL burial durations on quartz) on intrakarstic alluvial deposits from three valleys of the central and eastern Pyrenees, as well as on a recent analogue. In the Pyrenean context, under particular conditions, these geochronometers allow us to document incision processes since 16-13 Ma, and to study influences of external forcing and eustatism. In comparison with other studies, it appears that incision rates are higher in the central Pyrenees and for the Spanish slope. However, the density of horizontal levels on an altimetric range, the geodynamical and paleoclimatic contexts, the reorganization of the drainage networks can make the filling stories of the networks more complex than expected. Indeed, these radiometric approaches may be limited when some formations are reworked inside and/or outside the karst. The validity of dosimetric methods in a mountainous

  16. Individual to Community-Level Faunal Responses to Environmental Change from a Marine Fossil Record of Early Miocene Global Warming

    Science.gov (United States)

    Belanger, Christina L.

    2012-01-01

    Modern climate change has a strong potential to shift earth systems and biological communities into novel states that have no present-day analog, leaving ecologists with no observational basis to predict the likely biotic effects. Fossil records contain long time-series of past environmental changes outside the range of modern observation, which are vital for predicting future ecological responses, and are capable of (a) providing detailed information on rates of ecological change, (b) illuminating the environmental drivers of those changes, and (c) recording the effects of environmental change on individual physiological rates. Outcrops of Early Miocene Newport Member of the Astoria Formation (Oregon) provide one such time series. This record of benthic foraminiferal and molluscan community change from continental shelf depths spans a past interval environmental change (∼20.3-16.7 mya) during which the region warmed 2.1–4.5°C, surface productivity and benthic organic carbon flux increased, and benthic oxygenation decreased, perhaps driven by intensified upwelling as on the modern Oregon coast. The Newport Member record shows that (a) ecological responses to natural environmental change can be abrupt, (b) productivity can be the primary driver of faunal change during global warming, (c) molluscs had a threshold response to productivity change while foraminifera changed gradually, and (d) changes in bivalve body size and growth rates parallel changes in taxonomic composition at the community level, indicating that, either directly or indirectly through some other biological parameter, the physiological tolerances of species do influence community change. Ecological studies in modern and fossil records that consider multiple ecological levels, environmental parameters, and taxonomic groups can provide critical information for predicting future ecological change and evaluating species vulnerability. PMID:22558424

  17. The Early Burdigalian (MN3; Miocene large mammals from Estrepouy (Aquitaine basin, France: an updated faunal list

    Directory of Open Access Journals (Sweden)

    Ginsburg, L.

    2011-12-01

    Full Text Available The purpose of the present work is to describe the mammals from the Early Miocene locality of Estrepouy, Gers, France. We have identified 17 species belonging to 3 orders; Carnivora; Amphicyon lanthanicus, Cynelos helbingi, Plithocyon bruneti, Hemicyon gargan, Palaeogale hyaenoides, Semigenetta elegans y Pseudaelurus turnauensis. Perissodactyla; Anchitherium aurelianense, Protaceratherium minutum y Diaceratherium cf. aurelianense. Arctiodactyla; Aureliachoerus aurelianensis, Xenohyus venitor, Caenotherium aff. lintillae, Andegameryx andegaviensis, Oriomeryx willii, Procervulus praelucidus, Lagomeryx parvulus y Procervulus praelucidus. The Estrepouy mammal assemblage seems older than that represented in Wintershof-West (Alemania, MN 3 reference locality.

    [fr] Des grands mammifères sont determines pour le Miocène inférieur (MN3 de Etrepouy, Gers, France. 17 taxons appartenant à trois déterminés ont été identifies: Carnivora; Amphicyon lanthanicus, Cynelos helbingi, Plithocyon bruneti, Hemicyon gargan, Palaeogale hyaenoides, Semigenetta elegans et Pseudaelurus turnauensis. Perissodactyla; Anchitherium aurelianense, Protaceratherium minutum et Diaceratherium cf. aurelianense. Arctiodactyla; Aureliachoerus aurelianensis, Xenohyus venitor, Caenotherium aff. lintillae, Andegameryx andegaviensis, Oriomeryx willii, Procervulus praelucidus, Lagomeryx parvulus et Procervulus praelucidus. L’association des mammifères Estrepouy regarde un peu plus âgé que celui représenté à la localité de référence du MN3 á Wintershof-Ouest (Allemagne.

  18. Discordant Early Miocene palaeomagnetic directions at the vicinity of the North Aegean Trough: tectonic or palaeofield feature?

    Science.gov (United States)

    Kontopoulou, D.; Valet, J. P.; Zananiri, I.; Voidomatis, P.

    2017-12-01

    The North Aegean Trough (N.A.T) is a major tectonic feature of North Aegean Sea. This is a large NE-SW transcurrent lineament that is interpreted as the continuation of the North Anatolian Fault, with a prominent dextral strike-slip motion. IAn intense igneous activity has developed along the N.A.T to its north through the presence of abundant plutonism and volcanism from Early Oligocene to Pliocene. A considerable amount of palaeomagnetic data display a systematic pattern of clockwise rotations with angles varying between 20°-40° since the Early Oligocene. In order to document the impact of the N.A.T to regional rotations, early Miocene lava flows have been extensively sampled in the islands of Samothrace and Lemnos located to the north and south of N.A.T, respectively. Two sets of directions have been defined from the palaeomagnetic studies. The first one corresponds to the expected North-East declinations with positive inclinations or to reversed South-West declinations with negative inclinations that were previously interpreted as a dextral rotations of this area. The second set, exhibits discordant and apparently erratic directions despite quite acceptable demagnetization behaviour and magnetic characteristics. In order to constrain further these directions we performed new samplings. The new measurements which include Thellier absolute palaeointensity experiments reveal that the intermediate directions are associated with low field values for Samothrace with a transitional field recorded between 21 and 17 Ma. The presence of single magnetization component and the variability of the lavas do not favor the possibility of self-reversal mechanisms. The consistency of the directions within each flow but also between lava flows of comparable ages in the two islands and the presence of normal and reverse polarities point to records of transitional directions. In both islands, the intermediate virtual geomagnetic poles exhibit a preference for equatorial latitudes

  19. Declining Atmospheric pCO2 During the Late Miocene and Early Pliocene: New Insights from Paired Alkenone and Coccolith Stable Isotope Barometry

    Science.gov (United States)

    Phelps, S. R.; Polissar, P. J.; deMenocal, P. B.; Swann, J. P.; Guo, M. Y.; Stoll, H. M.

    2015-12-01

    806 combined with previous published measurements suggests atmospheric CO2 values declined across the late Miocene and early Pliocene. This decline is coincident with decreasing ocean temperatures suggesting the fundamental relationship between atmospheric CO2 and climate can qualitatively explain late Miocene warmth.

  20. Marine connections of Amazonia: Evidence from foraminifera and dinoflagellate cysts (early to middle Miocene, Colombia/Peru)

    NARCIS (Netherlands)

    Boonstra, M.; Ramos, M.I.F.; Lammertsma, E.I.; Antoine, P.-O; Hoorn, C.

    2015-01-01

    Species composition in the present-day Amazonian heartland has an imprint of past marine influence. The exact nature, timing and extent of this marine influence, however, are largely unresolved. Here we use calcareous tests of foraminifera and marine palynomorphs from Miocene sediments in

  1. Ar-Ar dating and petrogenesis of the Early Miocene Taşkapı-Mecitli (Erciş-Van) granitoid, Eastern Anatolia Collisional Zone, Turkey

    Science.gov (United States)

    Oyan, Vural

    2018-06-01

    The Early Miocene Taşkapı-Mecitli granitoid that is located in the northern section of the Eastern Anatolia Collision Zone has typical I-type, metaluminous and calk-alkaline characteristics. It also contains mafic microgranular / magmatic enclaves (MMEs). New Ar-Ar dating results show that the age of the Taşkapı-Mecitli granitoid is ∼23 Ma and it crystallised in the Early Miocene, in contrast to its previously known Cretaceous age. Identical crystallisation ages (∼23 Ma), similar mineral assemblages and geochemical compositions, and indistinguishable isotopic compositions of MMEs and host rocks imply that the MMEs are most consistent with a cumulate origin formed at earlier stages of the same magmatic system that produced the Taşkapı-Mecitli granitoid. MELTS modelling suggests that magma of the Taşkapı-Mecitli granitoid was the result of fractionation under a crustal pressure of 4 kbar, with a H2O content of 1.5%. EC-AFC model calculation reveals that the Taşkapı-Mecitli granitoid includes from 0.5% to 2% crustal assimilation rates. These rates indicate that crustal contamination can be negligible when compared to fractional crystallisation in the evolution of the magma beneath the Taşkapı-Mecitli granitoid. The partial melting model calculations and MORB-normalised trace element concentrations of the least evolved samples of the Taşkapı-Mecitli granitoid are consistent with those of mafic melts obtained from partial melting of interacting mantle- lower crust with a melting degree of 18%. The age (23 Ma) of the post- or syn-collisional Taşkapı-Mecitli granitoid suggests that the collision between Arabian and Eurasian plates could be before/around ∼23 Ma (Late Oligocene to Early Miocene).

  2. Discovery of the oldest .i.Gobius./i. (Teleostei, Gobiiformes) from a marine ecosystem of Early Miocene age

    Czech Academy of Sciences Publication Activity Database

    Reichenbacher, B.; Gregorová, R.; Holcová, K.; Šanda, R.; Vukić, J.; Přikryl, Tomáš

    2018-01-01

    Roč. 16, č. 6 (2018), s. 493-513 ISSN 1477-2019 R&D Projects: GA ČR(CZ) GA16-21523S Institutional support: RVO:67985831 Keywords : Gobiidae * Miocene * comparative anatomy * marine ecosystem * Outer Carpathian flysh zone * Outer Carpathian flysch zone * Ždánice-Hustopeče Formation Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Paleontology Impact factor: 2.963, year: 2016

  3. Sedimentology and biostratigraphy of the Early-Middle Miocene transition in NW Transylvanian Basin (Pâglişa and Dej sections

    Directory of Open Access Journals (Sweden)

    Claudia Beldean

    2013-01-01

    Full Text Available The Early - Middle Miocene transition can be studied in several sections from the north-western Transylvanian Basin, across the boundary between the Hida and Dej Formations. The Pâglişa and Râpa Dracului (Dej locally outcrop sections offer a very good record of the changes in the sedimentary facies and micropaleontological content across the boundary. The lower parts of the sections display the upper Hida Formation with prodelta fine grained sediments covered by coarser grained sediments related to a delta front progradation. Four sedimentary facies associations have been separated based on grain size and associated sedimentary structures. Micropaleontological assemblages are moderately to poorly preserved, with a low abundance and diversity. Planktonic Streptochilus pristinum is the main taxon associated with rare (< 10% calcareous benthic foraminifera (Bulimina, Bolivina, Cibibicidoides. The Dej Formation consists of stacked channel lag deposits associated with lateral accretion bars and crevasse splays followed by fall-out tuffs and redeposited low density tuffites interbedded with low density fine siliciclastics. The deposits of Dej Formation from the investigated areas were separated in four facies associations based on grain size/petrography and primary sedimentary structures. Micropaleontological assemblages contain typical early Badenian planktonic foraminifera (species of Orbulina, Praeorbulina, Globigerinoides, and Globorotalia associated to the main phase of the marine transgresion from the beginning of the Middle Miocene.

  4. Dispersals of Hyoscyameae and Mandragoreae (Solanaceae) from the New World to Eurasia in the early Miocene and their biogeographic diversification within Eurasia.

    Science.gov (United States)

    Tu, Tieyao; Volis, Sergei; Dillon, Michael O; Sun, Hang; Wen, Jun

    2010-12-01

    The cosmopolitan Solanaceae contains 21 tribes and has the greatest diversity in South America. Hyoscyameae and Mandragoreae are the only tribes of this family distributed exclusively in Eurasia with two centers of diversity: the Mediterranean-Turanian (MT) region and the Tibetan Plateau (TP). In this study, we examined the origins and biogeographical diversifications of the two tribes based on the phylogenetic framework and chronogram inferred from a combined data set of six plastid DNA regions (the atpB gene, the ndhF gene, the rps16-trnK intergenic spacer, the rbcL gene, the trnC-psbM region and the psbA-trnH intergenic spacer) with two fossil calibration points. Our data suggest that Hyoscyameae and Mandragoreae each forms a monophyletic group independently derived from different New World lineages in the early Miocene. Phylogenetic relationships within both tribes are generally well resolved. All genera of Hyoscyameae are found to be monophyletic and they diversified in middle to late Miocene. At nearly the same time, Mandragoreae split into two clades, corresponding to the MT region and the TP region, respectively. Both the phylogenetic relationships and the estimated ages of Hyoscyameae and Mandragoreae support two independent dispersal events of their ancestors from the New World into Eurasia. After their arrivals in Eurasia, the two tribes diversified primarily in the MT region and in the TP region via multiple biogeographic processes including vicariance, dispersal, recolonization or being preserved as relicts, from the mid Miocene to the late Quaternary. Published by Elsevier Inc.

  5. Comment on "Geochemistry of the Early Miocene volcanic succession of Northland, New Zealand, and implications for the evolution of subduction in the Southwest Pacific" by M.A. Booden, I.E.M. Smith, P.M. Black and J.L. Mauk

    NARCIS (Netherlands)

    Schellart, W. P.

    2012-01-01

    In a recent paper Booden et al. (2011) present new geochemical and petrological data of Early Miocene volcanics from the Northland region (Northland volcanic belt) in New Zealand, and interpret these data to support a particular regional tectonic model. This tectonic model involves Early Miocene

  6. 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.

  7. Geologic Reconnaissance of the Antelope-Ashwood Area, North-Central Oregon: With Emphasis on the John Day Formation of Late Oligocene and Early Miocene Age

    Science.gov (United States)

    Peck, Dallas L.

    1964-01-01

    This report briefly describes the geology of an area of about 750 square miles in Jefferson, Wasco, Crook, and Wheeler Counties, Oregon. About 16,000 feet of strata that range in age from pre-Tertiary to Quaternary are exposed. These include the following units: pre-Tertiary slate, graywacke, conglomerate, and meta-andesite; Clarno Formation of Eocene age - lava flows, volcanic breccia, tuff, and tuffaceous mudstone, chiefly of andesitic composition; John Day Formation of late Oligocene and early Miocene age - pyroclastic rocks, flows, and domes, chiefly of rhyolitic composition; Columbia River Basalt of middle Miocene age - thick, columnar jointed flows of very fine grained dense dark-gray basalt; Dalles Formation of Pliocene age - bedded tuffaceous sandstone, siltstone, and conglomerate; basalt of Pliocene or Pleistocene age - lava flows of porous-textured olivine basalt; and Quaternary loess, landslide debris, and alluvium. Unconformities separate pre-Tertiary rocks and Clarno Formation, Clarno and John Day Formations, John Day Formation and Columbia River Basalt, and Columbia River Basalt and Dalles Formation. The John Day Formation, the only unit studied in detail, consists of about 4,000 feet of tuff, lapilli tuff, strongly to weakly welded rhyolite ash flows, and less abundant trachyandesite flows and rhyolite flows and domes. The formation was divided into nine mappable members in part of the area, primarily on the basis of distinctive ledge-forming welded ash-flow sheets. Most of the sheets are composed of stony rhyolite containing abundant lithophysae and sparse phenocrysts. One sheet contains 10 to 20 percent phenocrysts, mostly cryptoperthitic soda sanidine, but including less abundant quartz, myrmekitic intergrowths of quartz and sanidine, and oligoclase. The rhyolitic ash flows and lava flows were extruded from nearby vents, in contrast to some of the interbedded air-fall tuff and lapilli tuff of dacitic and andesitic composition that may have been

  8. First report of bats (Mammalia: Chiroptera from the Gray Fossil Site (late Miocene or early Pliocene, Tennessee, USA

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    Nicholas J. Czaplewski

    2017-04-01

    Full Text Available Thousands of vertebrate fossils have been recovered from the Gray Fossil Site, Tennessee, dating to the Miocene-Pliocene boundary. Among these are but eight specimens of bats representing two different taxa referable to the family Vespertilionidae. Comparison of the fossils with Neogene and Quaternary bats reveals that seven of the eight specimens pertain to a species of Eptesicus that cannot be distinguished from recent North American Eptesicus fuscus. The remaining specimen, a horizontal ramus with m3, is from a smaller vespertilionid bat that cannot confidently be assigned to a genus. Although many vespertilionid genera can be excluded through comparisons, and many extinct named taxa cannot be compared due to nonequivalence of preserved skeletal elements, the second taxon shows morphological similarities to small-bodied taxa with three lower premolar alveoli, three distinct m3 talonid cusps, and m3 postcristid showing the myotodont condition. It resembles especially Nycticeius humeralis and small species of Eptesicus. Eptesicus cf. E. fuscus potentially inhabited eastern North America continuously since the late Hemphillian land mammal age, when other evidence from the Gray Fossil Site indicates the presence in the southern Appalachian Mountains of a warm, subtropical, oak-hickory-conifer forest having autochthonous North American as well as allochthonous biogeographical ties to eastern Asia and tropical-subtropical Middle America.

  9. Correlating carbon and oxygen isotope events in early to middle Miocene shallow marine carbonates in the Mediterranean region using orbitally tuned chemostratigraphy and lithostratigraphy

    Science.gov (United States)

    Auer, Gerald; Piller, Werner E.; Reuter, Markus; Harzhauser, Mathias

    2015-04-01

    During the Miocene prominent oxygen isotope events (Mi-events) reflect major changes in glaciation, while carbonate isotope maxima (CM-events) reflect changes in organic carbon burial, particularly during the Monterey carbon isotope excursion. However, despite their importance to the global climate history they have never been recorded in shallow marine carbonate successions. The Decontra section on the Maiella Platform (central Apennines, Italy), however, allows to resolve them for the first time in such a setting during the early to middle Miocene. The present study improves the stratigraphic resolution of parts of the Decontra section via orbital tuning of high-resolution gamma ray (GR) and magnetic susceptibility data to the 405 kyr eccentricity metronome. The tuning allows, within the established biostratigraphic, sequence stratigraphic, and isotope stratigraphic frameworks, a precise correlation of the Decontra section with pelagic records of the Mediterranean region, as well as the global paleoclimatic record and the global sea level curve. Spectral series analyses of GR data further indicate that the 405 kyr orbital cycle is particularly well preserved during the Monterey Event. Since GR is a direct proxy for authigenic uranium precipitation during increased burial of organic carbon in the Decontra section, it follows the same long-term orbital pacing as observed in the carbon isotope records. The 405 kyr GR beat is thus correlated with the carbon isotope maxima observed during the Monterey Event. Finally, the Mi-events can now be recognized in the δ18O record and coincide with plankton-rich, siliceous, or phosphatic horizons in the lithology of the section.

  10. Facies associations, depositional environments and stratigraphic framework of the Early Miocene-Pleistocene successions of the Mukah-Balingian Area, Sarawak, Malaysia

    Science.gov (United States)

    Murtaza, Muhammad; Rahman, Abdul Hadi Abdul; Sum, Chow Weng; Konjing, Zainey

    2018-02-01

    Thirty-five stratigraphic section exposed along the Mukah-Selangau road in the Mukah-Balingian area have been studied. Sedimentological and palynological data have been integrated to gain a better insight into the depositional architecture of the area. Broadly, the Mukah-Balingian area is dominated by fluvial, floodplain and estuarine related coal-bearing deposits. The Balingian, Begrih and Liang formations have been described and interpreted in terms of seven facies association. These are: FA1 - Fluvial-dominated channel facies association; FA2 - Tide-influenced channel facies association; FA3 - Tide-dominated channel facies association; FA4 - Floodplain facies association; FA5 - Estuarine central basin-mud flats facies association; FA6 - Tidal flat facies association and FA7 - Coastal swamps and marshes facies association. The Balingian Formation is characterised by the transgressive phase in the base, followed by a regressive phase in the upper part. On the basis of the occurrence of Florscheutzia trilobata with Florscheutzia levipoli, the Early to Middle Miocene age has been assigned to the Balingian Formation. The distinct facies pattern and foraminifera species found from the samples taken from the Begrih outcrop imply deposition in the intertidal flats having pronounced fluvio-tidal interactions along the paleo-margin. Foraminiferal data combined with the pronounced occurrence of Stenochlaena laurifolia suggest at least the Late Miocene age for the Begrih Formation. The internal stratigraphic architecture of the Liang Formation is a function of a combination of sea level, stable tectonic and autogenic control. Based on stratigraphic position, the Middle Pliocene to Pleistocene age for the Liang Formation is probable. The Balingian, Begrih and Liang formations display deposits of multiple regressive-transgressive cycles while the sediments were derived from the uplifted Penian high and Rajang group.

  11. Revised Late Oligocene to Early Miocene magnetic stratigraphy recorded by drift sediments at Sites U1405 and U1406, IODP Expedition 342 (Newfoundland, NW Atlantic)

    Science.gov (United States)

    van Peer, Tim; Xuan, Chuang; Wilson, Paul; Liebrand, Diederik; Lippert, Peter

    2015-04-01

    The nannofossil oozes drilled at IODP Expedition 342 (Paleogene Newfoundland Sediment Drifts) Sites U1405 and U1406 provide an exceptional sedimentary archive of the Late Oligocene to Early Miocene due to high sedimentation rates (2-6 cm/kyr at U1406 and up to 20 cm/kyr at U1405) and their ideal location below the Deep Western Boundary Current. These drift sediment sequences provide a unique opportunity to study the Oligocene-Miocene Transition (OMT) and Mi1-event (a transient 1‰ positive oxygen isotope excursion) at an unprecedented resolution from a Northern Hemisphere perspective. The exact timing of the OMT and its rate of change require a reliable and high-resolution magnetic stratigraphic age control, as Chron C6Cn with its three subchrons roughly spans the Mi1 event and the reversal C6Cn.2n/C6Cn.2r defines the Oligocene-Miocene boundary. Natural Remanent Magnetisation (NRM) was measured on 140 m of u-channel samples at U1405 and 190 m at U1406. The u-channel sample based magnetostratigraphy is in good agreement with that based on the shipboard data and reveal distinctive well-defined patterns of normal and reversed polarities, which can be correlated to the Geomagnetic Polarity Time Scale between C6Bn.2n and C9n (ca. 22.2 to 27 Ma) at U1406 and between C6Bn.2n and C6Cr (ca. 22.2 to 23.5 Ma) at U1405. Furthermore, putative cryptochrons in Chron C6Br and C7Ar, previously reported at Site U1334 (IODP Expedition 320), are observed in the u-channel magnetic stratigraphy for Sites U1405 and U1406. Anhysteretic Remanent Magnetisation (ARM) intensity variations are combined with X-Ray Fluorescence (XRF) generated elemental measurements to refine the shipboard splice of both U1405 and U1406. Latest Oligocene to earliest Miocene splice refinements are complicated by the presence of large-scale stratigraphic gaps (up to 25 m at U1405) unrelated to drilling disturbances. The depth and estimated age of these stratigraphic gaps vary from hole to hole, and do not appear

  12. 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

  13. The taphonomy of a remarkable leaf bed assemblage from the Late Oligocene-Early Miocene Gore Lignite Measures, southern New Zealand

    Energy Technology Data Exchange (ETDEWEB)

    Ferguson, David K.; Zetter, Reinhard; Vavra, Norbert [Department of Paleontology, University of Vienna, Althanstrasse 14, A-1090 Vienna (Austria); Lee, Daphne E. [Department of Geology, University of Otago, PO Box 56, Dunedin (New Zealand); Bannister, Jennifer M. [Department of Botany, University of Otago, PO Box 56, Dunedin (New Zealand); Jordan, Gregory J. [School of Plant Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001 (Australia); Mildenhall, Dallas C. [GNS Science, PO Box 30-368, Lower Hutt (New Zealand)

    2010-08-01

    A diverse assemblage of fossil leaves showing cellular detail is reported from the Late Oligocene-Early Miocene Gore Lignite Measures, southern New Zealand. The leaf-remains include at least five conifers, such as the genera Agathis, Dacrycarpus, Phyllocladus and Dacrydium, as well as a number of angiosperms including Gymnostoma, Nothofagus Subgenus Brassospora, Phormium, Proteaceae, Sapindaceae and Ericaceae. A parallel palynological study has identified a number of the same elements. The leaf layers represent litter horizons laid down in pools on the surface of a subtropical ombrotrophic forest mire that formed on an extensive low-lying coastal plain. Highly acidic water ponded in tree-fall depressions prevented microbial decay of the foliage. Taxa represented by both leaves and pollen are considered to have been components of the autochthonous swamp forest. Some other pollen grains are thought to represent local elements, based on the pollination biology of their nearest living relatives. Other taxa whose extant representatives are wind-pollinated may have grown further away. (author)

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

    NARCIS (Netherlands)

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

    2008-01-01

    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

  15. Evaluating climatic response to external radiative forcing during the late Miocene to early Pliocene: New perspectives from eastern equatorial Pacific (IODP U1338) and North Atlantic (ODP 982) locations

    Science.gov (United States)

    Drury, Anna Joy; John, Cédric M.; Shevenell, Amelia E.

    2016-01-01

    Orbital-scale climate variability during the latest Miocene-early Pliocene is poorly understood due to a lack of high-resolution records spanning 8.0-3.5 Ma, which resolve all orbital cycles. Assessing this variability improves understanding of how Earth's system sensitivity to insolation evolves and provides insight into the factors driving the Messinian Salinity Crisis (MSC) and the Late Miocene Carbon Isotope Shift (LMCIS). New high-resolution benthic foraminiferal Cibicidoides mundulus δ18O and δ13C records from equatorial Pacific International Ocean Drilling Program Site U1338 are correlated to North Atlantic Ocean Drilling Program Site 982 to obtain a global perspective. Four long-term benthic δ18O variations are identified: the Tortonian-Messinian, Miocene-Pliocene, and Early-Pliocene Oxygen Isotope Lows (8-7, 5.9-4.9, and 4.8-3.5 Ma) and the Messinian Oxygen Isotope High (MOH; 7-5.9 Ma). Obliquity-paced variability dominates throughout, except during the MOH. Eleven new orbital-scale isotopic stages are identified between 7.4 and 7.1 Ma. Cryosphere and carbon cycle sensitivities, estimated from δ18O and δ13C variability, suggest a weak cryosphere-carbon cycle coupling. The MSC termination coincided with moderate cryosphere sensitivity and reduced global ice sheets. The LMCIS coincided with reduced carbon cycle sensitivity, suggesting a driving force independent of insolation changes. The response of the cryosphere and carbon cycle to obliquity forcing is established, defined as Earth System Response (ESR). Observations reveal that two late Miocene-early Pliocene climate states existed. The first is a prevailing dynamic state with moderate ESR and obliquity-driven Antarctic ice variations, associated with reduced global ice volumes. The second is a stable state, which occurred during the MOH, with reduced ESR and lower obliquity-driven variability, associated with expanded global ice volumes.

  16. Trace element analysis provides insight into the diets of early Late Miocene ungulates from the Rudabánya II locality (Hungary)

    Energy Technology Data Exchange (ETDEWEB)

    Eastham, L.C.; Feranecc, R.S.; Begun, D.R.

    2017-11-01

    The early Late Miocene vertebrate locality of Rudabánya II (R. II) in northeastern Hungary preserves an abundance of forest-adapted ungulate species. To better understand the ecological relationships within this ancient ecosystem, we used analysis of enamel strontium/calcium (Sr/Ca) ratios to infer dietary preferences. The goals of the analysis were to: i) determine whether these ungulate species specialized in specific plants or plant parts; ii) discern whether the Sr/Ca ratios support what was previously suggested about the ecology of these species; and iii) evaluate the factors that may have acted to promote coexistence within this diverse community of predominantly browsing herbivores. Results show significant differences in the diets of the sampled species. The highest Sr/Ca ratios were displayed by the suids Parachleuastochoerus kretzoii [B1] and Propotamochoerus palaeochoerus implying a preference for Sr-rich underground plant parts. Elevated Sr/Ca ratios yielded by the cervid Lucentia aff. pierensis and equid Hippotherium intrans are indicative of intermediate feeding. The bovid Miotragocerus sp. showed higher Sr/Ca ratios than the gomphothere Tetralophodon longirostris, which is incongruent with morphological and stable isotope data, and suggested browsing by both taxa. This finding is likely the result of a difference in digestive physiology (ruminant vs. monogastric) rather than a difference in dietary behaviour. The lowest Sr/Ca ratios were displayed by the traguild Dorcatherium naui and moschid Micromeryx flourensianussuggesting a preference for Sr-poor fruits. Resource specialization and partitioning within the local environment likely acted to decrease interspecific competition and promote coexistence within the diverse ungulate community at R. II.

  17. Trace element analysis provides insight into the diets of early Late Miocene ungulates from the Rudabánya II locality (Hungary)

    International Nuclear Information System (INIS)

    Eastham, L.C.; Feranecc, R.S.; Begun, D.R.

    2017-01-01

    The early Late Miocene vertebrate locality of Rudabánya II (R. II) in northeastern Hungary preserves an abundance of forest-adapted ungulate species. To better understand the ecological relationships within this ancient ecosystem, we used analysis of enamel strontium/calcium (Sr/Ca) ratios to infer dietary preferences. The goals of the analysis were to: i) determine whether these ungulate species specialized in specific plants or plant parts; ii) discern whether the Sr/Ca ratios support what was previously suggested about the ecology of these species; and iii) evaluate the factors that may have acted to promote coexistence within this diverse community of predominantly browsing herbivores. Results show significant differences in the diets of the sampled species. The highest Sr/Ca ratios were displayed by the suids Parachleuastochoerus kretzoii [B1] and Propotamochoerus palaeochoerus implying a preference for Sr-rich underground plant parts. Elevated Sr/Ca ratios yielded by the cervid Lucentia aff. pierensis and equid Hippotherium intrans are indicative of intermediate feeding. The bovid Miotragocerus sp. showed higher Sr/Ca ratios than the gomphothere Tetralophodon longirostris, which is incongruent with morphological and stable isotope data, and suggested browsing by both taxa. This finding is likely the result of a difference in digestive physiology (ruminant vs. monogastric) rather than a difference in dietary behaviour. The lowest Sr/Ca ratios were displayed by the traguild Dorcatherium naui and moschid Micromeryx flourensianussuggesting a preference for Sr-poor fruits. Resource specialization and partitioning within the local environment likely acted to decrease interspecific competition and promote coexistence within the diverse ungulate community at R. II.

  18. The tide-influenced Pétervására sandstone, early Miocene, Northern Hungary : sedimentology, palaeogeography and basin development

    NARCIS (Netherlands)

    Sztanó, O.

    1994-01-01

    The objectives of this thesis are: - to determine the main sedimentary units, the dominant depositional processes, and to reconstruct the depositional environment of the Lower Miocene Petervasara Sandstone (Chapter 3), - to show the pattern of sediment dispersal in connection with the potential

  19. Asymmetrical, inversely graded, upstream-migrating cyclic steps in marine settings: Late Miocene-early Pliocene Fish Creek-Vallecito Basin, southern California

    Science.gov (United States)

    Gong, Chenglin; Chen, Liuqin; West, Logan

    2017-10-01

    Cyclic steps are ubiquitous in modern sedimentary environments, yet their recognition remains sparse in the rock record. Here, we interpret three sets of undulating backsets (1 to 3) recognized in the late Miocene-early Pliocene Latrania Formation in the Anza-Borrego Desert, the Fish Creek-Vallecito Basin, southern California, USA as the first cm- to dm-scale outcrop record of cyclic steps, based on asymmetrical cross-sections, upstream migration, and inversely graded laminae. Upstream migration and asymmetrical cross-sections of backsets and concomitant backset laminae are attributed to supercritical-to-subcritical flow transitions through weak hydraulic jumps, which are composed of: (i) thin (tens of centimetres) and slower (reported as flow velocities (Ū) of 0.45 to 1.45 m s- 1, with mean value of Ū = 0.89 m s- 1) subcritical (represented by internal Froude numbers (Fr) of 0.67 to 0.99, with mean value of Fr = 0.84) turbidity currents on the stoss sides, and (ii) thin (tens of centimetres) and faster (reported as Ū of 0.99 to 4.03 m s- 1, with mean value of Ū = 2.24 m s- 1) supercritical (represented by Fr of 1.84 to 3.07, with mean value of Fr = 2.42) turbidity flows on the lee sides. The inversely graded laminae in the troughs of backsets are 2 to 5 cm thick, and consist of two discrete divisions: (i) 1 to 2 cm thick, lower finer-grained divisions made up of parallel laminated siltstones, overlain by very fine- to fine-grained sandstones, and (ii) 2 to 3 cm thick, upper divisions composed of medium- to coarse-grained sandstones, with sporadic occurrence of subrounded pebbles. These inversely graded laminae are related to stratified, collisional and/or frictional traction carpets under conditions of high fall-out rates. Due to the poor preservation potential of cyclic steps, the rock record of cyclic steps is generally considered to be rare. The present outcrop-based study presents a detailed analysis of sedimentary facies, growth patterns, and flow

  20. The Varve Record of Puyehue Lake (Meridional Chile), AD 1412-2002 .

    Science.gov (United States)

    Boes, X.; Arnaud, F.; Fagel, N.

    2004-12-01

    Puyehue Lake is located in the Southern Volcanic Zone of Chile (Southern Lake District, 40°S). This monomictic lake is under the influence of the oceanic winter polar front (WPF) and constitutes a powerful sedimentary archive for paleoenvironmental reconstruction. The underflow (PUI) and interflow (PUII) coring sites were selected by a high resolution seismic survey (RUG). The sedimentation is driven by the annual blooms of diatoms in association with thermal lake cycles. For each site, one short core (50-60 cm) is analyzed by continuous cover of thin sections for varve counting and chronology for the AD 1412-2002 time window. The varve chronology is constrained by 210Pb,137Cs sedimentation rate estimates, and by the AD 1960 Valdivia'seismite. The sediment laminations are especially emphasized by the continuous grey-scale measurements from thin sections. Detrital clayey material characterizes the dark levels, and biogenic diatom mud defines the light levels. Varve counting is derived from the occurrence of light layers, i.e. formed at the end of winter after nutrient turn-over. In both cores, the grey-scale is influenced by instantaneous tephra layers related to the regional volcanic activity (Puyehue and Cordon Caulle volcanoes). For instance, in PUII, we identify major historical eruptions (AD 1921, 1837, 1790, 1564, and 1544) in accordance with the varve age model. In addition, we measure the total varve thickness. Lower than 500 µm until AD 1780, the varve thickness gradually increases by a factor of four in PUII. The first period suggests a decrease of lake productivity, in agreement with a cooling. The age fits with the end of Little Ice Age in Southern America. Between AD 1780-2002, the thicker varves could be driven by a reinforcement of the WPF since the 19e century. Our local observations require further investigations to be extrapolated over regional or global scale.

  1. Ecomorphological and taphonomic gradients in clypeasteroid-dominated echinoid assemblages along a mixed siliciclastic-carbonate shelf from the early Miocene of northern Sardinia, Italy

    Directory of Open Access Journals (Sweden)

    Andrea Mancosu

    2017-09-01

    Full Text Available Clypeasteroid echinoids are widespread and abundant within Miocene sedimentary sequences of the Mediterranean area within both siliciclastic and carbonate deposits. Herein, three clypeasteroid-dominated echinoid assemblages from the mixed siliciclastic-carbonate succession of the Mores Formation (lower Miocene cropping out within the Porto Torres Basin (northern Sardinia are described. These assemblages were compared to previously described clypeasteroid-bearing deposits from the Miocene of northern Sardinia with the purpose of investigating their palaeoecology and taphonomy along a shelf gradient. These goals are accomplished by various methods including (i logging sedimentary facies, (ii analysing the functional morphology of sea urchin skeletons, (iii comparing the relative abundance of taxa and taphonomic features, and (iv studying associated fauna, flora, and trace fossils. The clypeasteroid-bearing deposits differ greatly with respect to echinoid diversity, accompanying fauna and flora, sedimentological signatures, and taphonomic features. They also show variations in depositional environments and the mechanism of formation of the deposits. Three different shelf settings are distinguished: littoral, inner sublittoral, and outer sublittoral environments. Furthermore, an ecomorphological gradient along the shelf is recognized with respect to echinoid taxa and their morphologies. This gradient ranges from shallow water to a moderately deep shelf and is interpreted with respect to both abiotic and biotic factors as well as the taphonomy of the echinoid tests.

  2. Tracking the Transformation and Preservation of Organic Biomarkers in a Varved Sediment-Core Series

    Science.gov (United States)

    Tolu, J.; Bigler, C.; Bindler, R.

    2014-12-01

    An important premise for reconstructing environmental changes using sediment records is to understand which environmental information reaches the lake bottom and how diagenetic processes may affect the proxies, such as terrestrial and aquatic organic biomarkers. We can tackle this question using a unique series of varved sediment cores collected from the lake Nylandssjön (northern Sweden). In addition to limnological and sediment trap sampling since 2001, we have a collection of freeze cores taken in late winter and stored since 1979, which allows us to track individual varve years (e.g., 1978) over time (~30 years). A previous study using this collection showed that 23 % of C and 35 % of N were lost during the first 25 years with a C:N ratio increase of ≈21, suggesting important implications for diagenetic effects on organic biomarkers. To assess the preservation/transformation of organic biomarkers, we developed a new Pyrolysis-Gas Chromatography/Mass Spectrometry method that allows the rapid determination of biomarkers from the common OM classes (e.g., plant waxes, microbial lipids, lignins) using sub-mg sample sizes and thus applicable to high-resolution sampling of the varved sediment (Tolu et al., under review). Our results show that the different biomarkers exhibit a broad spectrum of reactivities over ~30 years -% change determined by ([Peak area at t] - [Peak area at t=0])/ [peak area at t=0] x 100-. For example: 67-80 % of the algal chlorophyll-derived product 'phytene' is lost depending which single varve year is followed over time (e.g., 1979). Only 12-32 % of "pristene", the degraded form of algal chlorophyll, is lost. The guaiacyl and syringyl lignin units are affected by a smaller loss, i.e. 5-15 %, and the S/G ratio, indicative of angiosperm/gymnosperm plant input remains stable, which is contrary to previous work on non-varved lake sediments. Considering all biomarkers, the degradation/production plateaued after ~15 years, which indicates that

  3. Using palynology to re-assess the Dead Sea laminated sediments - Indeed varves?

    Science.gov (United States)

    Bookman, Revital; Lopez-Merino, Lourdes; Belmaker, Reuven; Eshel, Amram; Epshtein Epshtein, Valentina; Leroy, Suzanne

    2017-04-01

    Lacustrine laminated sediments are often varves representing annual rhythmic deposition. The Dead Sea high-stand laminated sections consist of mm-scale alternating detrital and authigenic aragonite laminae. Previous studies assumed these laminae were varves; detritus deposition during the winter and aragonite in the summer. These sequences were used for varve counting and chronology, however this assumption has never been robustly validated. Here, we report an examination of the seasonal deposition of detrital and aragonite couplets from two well-known Late Holocene laminated sections at the Ze'elim fan-delta using palynology and grain-size distribution analyses. These analyses are complemented by the study of contemporary flash-flood samples and multivariate statistical analysis. Because transport affects the pollen preservation state, well-preserved (mostly) air-borne transported pollen was analysed separately from badly-preserved pollen and fungal spores, which are more indicative of water transport and reworking from soils. Our results indicate that (i) both detrital and aragonite laminae were deposited during the rainy season; (ii) aragonite laminae have significantly lower reworked pollen and fungal spore concentrations than detrital and flash-flood samples; and (iii) detrital laminae are composed of recycling of local and distal sources, with coarser particles that were initially deposited in the Dead Sea watershed and later transported via run-off to the lake. The conclusions suggest that detrital and aragonite couplets in the Dead Sea laminated sediments are most likely not varves and that the laminae deposition is related to the occurrence of flash-flood events. Consequently, at least for the Holocene sequences, laminated sediments cannot be considered as varves and Quaternary laminated sequences should be re-evaluated. The Dead Sea Basin laminated sequences (as the ICDP Dead Sea Deep Drilling Project record) should be used for the reconstruction of

  4. Larger benthic foraminifera in Miocene carbonates of Indonesia

    NARCIS (Netherlands)

    Novak, Vibor

    2014-01-01

    Present day Southeast Asia represents the region that supports the most diverse marine ecosystems on Earth. The origin of this biodiversity is still unresolved, but it is proposed to be present at least since the Early Miocene. Therefore, the data acquired from the fossil assemblages may contribute

  5. 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.

  6. The Miocene carnivore assemblage of Greece

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    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. History of human activity in last 800 years reconstructed from combined archive data and high-resolution analyses of varved lake sediments from Lake Czechowskie, Northern Poland

    Science.gov (United States)

    Słowiński, Michał; Tyszkowski, Sebastian; Ott, Florian; Obremska, Milena; Kaczmarek, Halina; Theuerkauf, Martin; Wulf, Sabine; Brauer, Achim

    2016-04-01

    The aim of the study was to reconstruct human and landscape development in the Tuchola Pinewoods (Northern Poland) during the last 800 years. We apply an approach that combines historic maps and documents with pollen data. Pollen data were obtained from varved lake sediments at a resolution of 5 years. The chronology of the sediment record is based on varve counting, AMS 14C dating, 137Cs activity concentration measurements and tephrochronology (Askja AD 1875). We applied the REVEALS model to translate pollen percentage data into regional plant abundances. The interpretation of the pollen record is furthermore based on pollen accumulation rate data. The pollen record and historic documents show similar trends in vegetation development. During the first phase (AD 1200-1412), the Lake Czechowskie area was still largely forested with Quercus, Carpinus and Pinus forests. Vegetation was more open during the second phase (AD 1412-1776), and reached maximum openness during the third phase (AD 1776-1905). Furthermore, intensified forest management led to a transformation from mixed to pine dominated forests during this period. Since the early 20th century, the forest cover increased again with dominance of the Scots pine in the stand. While pollen and historic data show similar trends, they differ substantially in the degree of openness during the four phases with pollen data commonly suggesting more open conditions. We discuss potential causes for this discrepancy, which include unsuitable parameters settings in REVEALS and unknown changes in forest structure. Using pollen accumulation data as a third proxy record we aim to identify the most probable causes. Finally, we discuss the observed vegetation change in relation the socio-economic development of the area. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape Evolution Analysis - ICLEA- of the Helmholtz Association and National Science Centre, Poland (grant No. 2011/01/B/ST10

  8. A 900-Year Diatom and Chrysophyte Record of Spring Mixing and Summer Stratification From Varved Lake Mina, West-Central Minnesota, USA

    Science.gov (United States)

    St. Jacques, J.; Cumming, B. F.; Smol, J. P.

    2009-05-01

    A high-resolution, independent pollen-inferred paleoclimate record and direct algal seasonality data from the actual time of sediment deposition are used to interpret the high-resolution diatom and chrysophyte record of varved Lake Mina, west-central Minnesota, USA during AD 1116-2002. This direct algal seasonality information was obtained by a new technique of splitting varves into constituent winter-spring and summer lamina, and separately analyzing the siliceous algae in each layer. Analyses of integrated, continuous four-year diatom and chrysophyte samples from a sedimentary sequence show that the time period AD 1116-1478 (i.e. the Atlantic- centered Medieval Climate Anomaly (MCA)) was characterized by periods of vigorous and prolonged spring mixing, suggesting that ice-out occurred early. However, the warm summer temperatures in the MCA, particularly in a massive drought spanning AD 1300-1400, frequently caused the lake to stratify strongly, leading to nutrient depletion. During AD 1478-1870 (i.e. the Atlantic-centered Little Ice Age (LIA)), Lake Mina was characterized by weak spring circulation and increasing nutrient depletion, suggesting late ice-out conditions. Strong summer stratification and/or nutrient depletion in both time periods is shown by the occurrence of the nutrient-poor oligotrophic taxon Cyclotella pseudostelligera. The diatom and chrysophyte assemblages of the period of Euro-American settlement AD 1870-2002 show higher nutrient availability and increased spring mixing intensity, due to forest clearance and increasingly earlier ice-out (documented in regional historical records).

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

    Directory of Open Access Journals (Sweden)

    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 Earlyearly 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

  10. A 12,000-Year-Long, Annually-Resolved Varve Record Spanning the Last Interglacial from Lake Bosumtwi, Southern Ghana

    Science.gov (United States)

    McKay, N.; Overpeck, J. T.; Shanahan, T. M.; Peck, J. A.; Heil, C. W.; King, J. W.; Scholz, C. A.

    2012-12-01

    The impact of continued global warming on the likelihood of severe drought in sub-Saharan West Africa remains uncertain, as climate models generally do not simulate realistic climate dynamics in the region and have inconsistent projections for the future. The Last Interglacial period (LIG), occurring between 128 and 116 thousand years ago, is a partial analog for future warming because at its peak, global temperatures were slightly higher, and this warming was accentuated in Northern Hemisphere terrestrial summer temperatures. Here we present a new, annually-resolved, 12,100-year-long varve record for the LIG from Lake Bosumtwi in southern Ghana (6.5°N, 1.4°W). The abundance of terrigenous elements in the sediment, varve thickness, and the isotope geochemistry and mineralogy of authigenic carbonates in the sediment were used to infer changes in lake level. The varve chronology, varve thickness and elemental abundance records were developed with a new ensemble approach that allows for a more robust determination of uncertainty in the record. The new records reveal a dynamic history of hydrologic variability during the LIG. The LIG lake highstand was lower and shorter-lived than the the prolonged highstand in the early Holocene, and unlike the Holocene, the lake never overflowed during LIG. The overall drier conditions during the LIG are most likely driven by amplified precessional forcing during the interval, resulting in a northward shift in the rainbelt. The LIG, like the Holocene, had two distinct millennial-scale moist intervals, from 125 - 123 and 121 - 120 ka. In both the LIG and the Holocene, these peaks occurred during times of precession-driven insolation maxima in July and October, corresponding to the two rainy seasons in the modern climatology. This suggests that, at least during interglacials, prolonged wet conditions occur at the lake when rainy season insolation is highest. Over the course of the LIG, lake level generally tracked sea surface

  11. Palaeogene to Early Miocene sedimentary history of the Sierra Espuña (Malaguide complex, internal zone of the Betic cordilleras, SE Spain. Evidence for extra-Malaguide (Sardinian? provenance of oligocene conglomerates: Palaeogeographic implications

    Directory of Open Access Journals (Sweden)

    Geel, T.

    1996-12-01

    Full Text Available The Sierra Espuña is situated at the northern edge of the Internal Zone in the eastern Betic Cordilleras and is part of the unmetamorphosed Malaguide Complex. Palaeontological and sedimentological analysis of the Eocene to Aquitanian sediments on the northwest side of the Espuña yielded unexpected new information of importance for the reconstruction of the history of the Espuña itself and the Malaguides in general. The socalled Upper Eocene (Auversian rocks are of Early Oligocene (P20 age and contain supermature detritus derived from outside the Malaguide realm. The hundreds of meters thick limestone conglomerate formation of the Espuña is of Middle Oligocene (P21 age and represents a backstepping fan delta complex at the margin of a carbonate platform situated to the northeast of the Espuña. Analysis of the clasts suggests that this platform was a part of the north Sardinian block given the majority of fragments of Upper Jurassic sheltered inner platform (Clypeina-Trocholina limestones and dolomites. Contrary to former views (Paquet, 1966; Lonergan, 1993, the conglomerates cannot be considered to be the erosional products of Malaguide imbricated units. Therefore, one of the main arguments for early (Late Eocene to Oligocene thrusting and nappe emplacement in the Espuña area is not valido Other arguments for early kinematics are discussed, among others the allegedly continuous sedimentation from the Late Eocene until the Langhian northwest of the Espuña. Our data indicate the existence of a stratigraphic gap, comprising the middle Aquitanian to middle Burdigalian. A new model for the development of the Espuña within the Malaguide realm during the Palaeogene to Early Miocene is presented. Main thrusting and nappe emplacement is thought to have been taken place during the late Aquitanian. Finally, the recently proposed 2000 clockwise rotation of the Espuña as a coherent block during the Early to Middle Miocene (AlIerton el al., 1993 is

  12. Architecture and growth history of a Miocene carbonate platform from 3D seismic reflection data; Luconia province, offshore Sarawak, Malaysia

    NARCIS (Netherlands)

    Zampetti, V.; Schlager, W.; van Konijnenburg, J.H; Everts, A.J.

    2004-01-01

    Using 3D seismic reflection data and wireline logs we reconstruct in detail the architecture and growth history of a Miocene carbonate platform in the Luconia province, offshore Sarawak, Malaysia. Platform growth started in the Late Oligocene to Early Miocene, by coalescence of isolated patch reefs.

  13. Rb-Sr geochronology of some Miocene West Australian lamproites

    International Nuclear Information System (INIS)

    Allsopp, H.L.; Scott Smith, B.H.; Danchin, R.V.

    1985-01-01

    Rb-Sr ages are presented for four lamproite intrusions (Mount North, Old Leopold Hill, Mount Rose and Seltrust Pipe 2) located in the west Kimberley region of West Australia. The data are in agreement with the early Miocene ages previously obtained for the lamproites of this area. The lamproites are characterized by high initial-Sr ratios, indicative of derivation from an enriched source. Localized and regional mantle heterogeneity is indicated by new and existing data

  14. Response of deep-sea benthic foraminifera to Miocene paleoclimatic events, DSDP site 289

    International Nuclear Information System (INIS)

    Woodruff, F.; Douglas, R.G.

    1981-01-01

    Changes in the Miocene deep-sea benthic foraminifera at DSDP Site 289 closely correlate to the climatically induced variations in deep and bottom waters in the Pacific Ocean. In early Miocene time, oxygen and carbon isotopes indicate that bottom waters were relatively warm and poorly oxygenated. Benthic foraminiferal assemblages are characterized by various species inherited from the Oligocene. Expansion of the Antarctic icecap in the early middle Miocene, 14-16 m.y. ago, increased oxygen isotope values, produced cold, more oxygenated bottom waters and lead to a turnover in the benthic foraminifera. An Oligocene-early Miocene assemblage was replaced by a cibicidoid-dominated assemblage. Some species became extinct and benthic faunas became more bathymetrically restricted with the increased stratification of deep waters in the ocean. In mid-Miocene time, Epistominella exigua and E. umbonifera, indicative of young, oxygenated bottom waters, are relatively common at DSDP Site 289. Further glacial expansion 5-9 m.y. ago lowered sealevel, increased oceanic upwelling and associated biological productivity and intensified the oxygen minima. Abundant hispid and costate uvigerines become a dominant faunal element at shallow depths above 2500 m as E. umbonifera becomes common to abundant below 2500 m. By late Miocene time, benthic faunas similar in species composition and proportion to modern faunas on the Ontong-Java plateau, had become established. (Auth.)

  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

    Directory of Open Access Journals (Sweden)

    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. Tectonic/climatic control on sediment provenance in the Cape Roberts Project core record (southern Victoria Land, Antarctica): A pulsing late Oligocene/early Miocene signal from south revealed by detrital thermochronology

    Science.gov (United States)

    Olivetti, V.; Balestrieri, M. L.; Rossetti, F.; Talarico, F. M.

    2012-04-01

    , three peaks are detected reflecting different bedrock provenance areas. Two peaks older than 40 Ma (P2 and P3) are compatible with thermochronological data from TAM bedrock that underwent a stepwise denudation in Cretaceous times. A Peak younger than 40 Ma (P1) has been detected occasionally, recording the signal of a source area exhumed during late Oligocene /early Miocene with a constant denudation rate of 0.4 mm/yr (constant lag-time up-section), but absent in the onshore portion of the proximal TAM. Indeed, when compared with AFT data from ANDRILL cores, the relatively young P1 ages, suggest that part of sediments in the Cape Robert Rift basin have a provenance from source regions probably located far away in the south (i.e. Skelton-Byrd glaciers region) where bedrock experienced compatible thermal histories. This provenance would imply glacial systems with main flow patterns from south to the north, therefore orthogonal to the orientation of present-day drainage. We thus infer that the post-Eocene glacial and erosional history of the TAM front was significantly controlled by the N-S-trending transtensional regime that affected the western Ross Sea margin during transition from orthogonal to oblique rifting in the region. The appearance and disappearance of P1 along the drill-cored stratigraphic succession seems to be linked to the oscillation in the extent of the ice sheet.

  17. POLYPLACOPHORA FROM THE MIOCENE OF NORTH ITALY. PART 2: CALLOCHITONIDAE, CHITONIDAE, LEPIDOCHITONIDAE, ACANTHOCHITONIDAE AND CRYPTOPLACIDAE

    Directory of Open Access Journals (Sweden)

    BRUNO DELL’ ANGELO

    2016-10-01

    Full Text Available This study completes the description of the chiton fauna (Mollusca, Polyplacophora from deposits of the Miocene marine sequence of North Italy, located in Piedmont and Emilia Romagna regions. This second and final part describes chitons belonging to five families: Callochitonidae, Chitonidae, Lepidochitonidae, Acanthochitonidae and Cryptoplacidae. Nineteen species were identified, of which two are described as new (Chiton sulcomarginatus sp. n. and Craspedochiton brunettii sp. n., and 17 were already known. Craspedochiton mutinocrassus is the new name attributed to the species previously known as Acanthochiton costatus or A. costatus var. mutinocrassa; Chiton sulcomarginatus sp. n., Lepidochitona monterosatoi, L. pliocinerea, and Acanthochitona oblonga, previously known only up to Pliocene, are reported for the first time from the Miocene of Italy. The stratigraphic distribution of numerous species thought to first appear in the Late Miocene (Callochiton doriae, Chiton olivaceus, C. corallinus, Acanthochitona fascicularis, A. crinita, and Craspedochiton altavillensis is here extended to the Early Miocene. The distribution of Cryptoplax weinlandi is extended to the Middle Miocene (Serravallian. In total 35 chiton species (with 3.003 valves were identified in the Italian Miocene (including both parts of this series. Ten species became extinct at the end of the Miocene, six in the Pliocene, two in the Pleistocene, and 17 are extant. Of the extant species nine occur both in the Atlantic and Mediterranean, two exclusively in the Atlantic and six only in the Mediterranean. The number of species reported from the Torino Hill assemblages (Burdigalian? is increased from three listed by Sacco (1897 to nine. Thirty-four of the 35 species (excluding only Lepidopleurus benoisti occur in the Tortonian-Messinian Po Basin. Thirteen (37% of the species are also found in the Miocene Paratethys (Austria, Poland, Czech Republic, Hungary, Romania and Ukraine, which

  18. POLYPLACOPHORA FROM THE MIOCENE OF NORTH ITALY. PART 1: LEPTOCHITONIDAE, HANLEYIDAE, ISCHNOCHITONIDAE AND CALLISTOPLACIDAE

    Directory of Open Access Journals (Sweden)

    BRUNO DELL’ANGELO

    2015-11-01

    Full Text Available This study describes the chiton fauna (Mollusca, Polyplacophora from deposits of the Miocene marine sequence of North Italy, located in Piedmont and Emilia Romagna regions. This first part of the work describes the chitons pertaining to four families: Leptochitonidae, Hanleyidae, Ischnochitonidae and Callistoplacidae. The studied fossils consist of 377 valves from 13 sites (Sciolze, Valle Ceppi, Rocco di Passerano, Albugnano, Monchio di Sarzano Casina, Villa Monti, Rio di Bocca d’Asino, Sant’Agata Fossili, Vargo, Vigoleno, Montegibbio, Borelli, and Moncucco Torinese ranging from the Early Miocene (Burdigalian to the Late Miocene (Messinian. We identified 16 species, 12 of which were already known, two are identified only at generic level (Stenosemus sp. A & sp. B, and two are described as new: Parachiton statianus sp. n., and Callistochiton borellianus sp. n. Some species found are particularly noteworthy; Lepidopleurus benoisti is the new name attributed to the species previously known as Middendorffia subcajetana or Gymnoplax orbignyi, based on the study of the type material; Leptochiton salicensis, previously known only from the Early Pleistocene of Salice (Messina, Sicily; Hanleya mediterranea is reported for the first time from the Miocene of Italy; Ischnochiton ligusticus, previously known only from the Early Pliocene of Western Liguria; the distribution of Stenoplax paviai, recently described from the Late Miocene (Rio di Bocca d’Asino, is extended to the Early Miocene (Langhian. A complete discussion on the chiton fauna from the North Italian Miocene, consisting of all the species treated in both parts, will be given in the second part of this work.

  19. Deformability Parameters of Varved Clays From the Iłów (Central Poland Area Based on the Selected Field Tests

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    Zawrzykraj Piotr Zbigniew

    2017-03-01

    Full Text Available This publication presents the results of research carried out for the ice-dammed clays of the Iłów region, formed during Vistula glaciation. Pressuremeter tests, dilatometer tests and static probes were made. The tests were performed on the study site in Piskorzec near Iłów. In this region, ice-dammed clays are present almost from the land surface reaching the thickness of about 11 m. This site is the westernmost experimental site of clays of the “Warsaw Ice-Dammed Lake” among those presented in the literature. Research and their analysis showed differences in deformability due to the test procedure in connection with the structure of varved clays. Pressuremeter test, even though it is the most time consuming and challenging among the tests performed, allows the most complete characteristics of deformability of varved clays to be obtained. Vertical profile of clays being studied appears to be fairly homogeneous in terms of mechanical properties. Nevertheless, some parts of the profile clearly differ from the average values. This indicates the rate of post sedimentary changes varied in different parts of research profile. The data obtained are consistent with the values for ice-dammed clays from Radzymin and Sochaczew areas. Comparison of the engineering properties of varved clays to other experimental sites points to their similar geological history. It confirms that the experimental sites belong to one ice-dammed lake covering the areas of the Warsaw Basin.

  20. Isotope shifts in the late Permian of the Delaware Basin, Texas, precisely timed by varved sediments

    International Nuclear Information System (INIS)

    Magaritz, M.; Oregon Univ., Eugene; Anderson, R.Y.; Holser, W.T.; Saltzmann, E.S.; Garber, J.

    1983-01-01

    Closely spaced samples (285 in number) of varved sediments from the Upper Permian in Delaware Basin, Texas, have been analyzed for delta 13 Csub(carb), delta 13 Csub(org), delta 18 Osub(carb), Csub(org), Csub(carb) and calcite/dolomite. delta 13 C records a dramatic rise from -2.8 to + 5.7per mille in only 4400 years, detected in three sections across the basin, extrapolating smoothly through a 600-year interruption by a local (west side of the basin) fresh-water inflow evidenced by low delta 18 O. This continuity and low Csub(org) within the basin, both indicate that the excess net deposition of Csub(org), necessary to generate the rise in delta 13 C, took place in the ocean external to the Delaware Basin, Correlation with similar records from the Zechstein Basin suggest that the event was world-wide, although this poses obvious difficulties for the carbon cycle. The rate of rise of delta 13 C, and its sustained high level, must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved. (orig.)

  1. 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

    2011-01-01

    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. PMID:21436034

  2. The significance of marine microfossils for paleoenvironmental reconstruction of the Solimões Formation (Miocene), western Amazonia, Brazil

    Science.gov (United States)

    Linhares, Ana Paula; Gaia, Valber do Carmo de Souza; Ramos, Maria Inês Feijó

    2017-11-01

    Micropalaeontological studies of borehole cores 1AS-7D-AM and 1AS-8-AM, from Atalaia do Norte, Amazonas state, Brazil, support previous evidence for Miocene marine ingressions in Western Amazonia. Three marine incursion events are recorded: the first in the Early/early Middle Miocene (in both cores), the second in the late Middle/early Late Miocene (1AS-8-AM), and the third in the Late Miocene (1AS-7D-AM). The first event is characterized by exclusively mangrove taxa, and the last two present a mixture of marine, fresh, and brackish water taxa. However, at the end of the third event an increase of fluvial influence is demonstrated by the predominance of freshwater taxa. These marine incursions reached the study area through narrow and geographically limited connections, controlled by the tectonic setting, at a time between the Early/early Middle Miocene and late Middle/Late Miocene. Thereafter, fluvial conditions were reestablished before Pliocene times.

  3. Parametrization of environment by geochemistry of the varved clastic and bio- chemogenic lake sediments

    Science.gov (United States)

    Kalugin, Ivan; Darin, Andrey; Babich, Valery; Markovich, Tatiana; Meydan, Feray

    2017-04-01

    As it well known, recent quantitative estimations of high-resolution environmental variability are based on geochemical records in lake sediments. Naturally, annually laminated sediments (varves) are the best objects for paleoclimatic study, because they allow to investigate seasonal variability for understanding long-term environmental pattern. Also, varved sediments seem to be applied as the model for identification of element-indicators for non-laminated sediments. The XRF scanner on Synchrotron Radiation provides big geochemical dataset for next mathematic treatment, including time series construction. XRF scanning realizes rapid and non-destructive determinations more than 30 trace elements in a range of concentration from 1 up to 10000 ppm in annual layers. That makes sedimentary cores comparable with tree-rings. Geochemical and physicochemical investigation of lake sediments provides basic information to identify geochemical signals with paleoclimate. In general, sediment consists of mineral component, organics and carbonates. The proportions between these components are affected by environmental parameters, because measured element content or their combinations show correlation with meteodata on instrumental time interval. That allows applying geochemical variability to reconstruct the environmental parameters in the form of time series. The proportions between main components are controlled by temperature, atmospheric precipitation, water salinity and other external forcings. So, layered structure of lake bottom sediments and detectable elements content variability both represent a continuous record of environmental history. Element composition and it's climatic response. Bottom sediments represent conditions of physical weathering, temperate bioproductivity and aridity, which concern to mountain lakes within extra tropical zone. The numerical values of the parameters can be computed by software of physical-chemical modeling for gas+water+rock multisystems

  4. Hypsodont Myomiminae (Gliridae, Rodentia) from the Miocene and the Oligocene-Miocene boundary interval of Spain

    NARCIS (Netherlands)

    Daams, R.

    1990-01-01

    Fifty-one localities from the Oligocene-Miocene boundary interval and the Miocene of Spain have yielded nearly 4000 teeth of hypsodont Gliridae (Armantomys and Praearmantomys). The phylogeny and palaeoecology are discussed. Two new species of Armantomys (A. parsani sp. nov. from Ramblar 1 and A.

  5. Spring temperature variability and eutrophication history inferred from sedimentary pigments in the varved sediments of Lake Żabińskie, north-eastern Poland, AD 1907-2008

    Science.gov (United States)

    Amann, Benjamin; Lobsiger, Simon; Fischer, Daniela; Tylmann, Wojciech; Bonk, Alicja; Filipiak, Janusz; Grosjean, Martin

    2014-12-01

    Varved lake sediments are excellent natural archives providing quantitative insights into climatic and environmental changes at very high resolution and chronological accuracy. However, due to the multitude of responses within lake ecosystems it is often difficult to understand how climate variability interacts with other environmental pressures such as eutrophication, and to attribute observed changes to specific causes. This is particularly challenging during the past 100 years when multiple strong trends are superposed. Here we present a high-resolution multi-proxy record of sedimentary pigments and other biogeochemical data from the varved sediments of Lake Żabińskie (Masurian Lake District, north-eastern Poland, 54°N-22°E, 120 m a.s.l.) spanning AD 1907 to 2008. Lake Żabińskie exhibits biogeochemical varves with highly organic late summer and winter layers separated by white layers of endogenous calcite precipitated in early summer. The aim of our study is to investigate whether climate-driven changes and anthropogenic changes can be separated in a multi-proxy sediment data set, and to explore which sediment proxies are potentially suitable for long quantitative climate reconstructions. We also test if convoluted analytical techniques (e.g. HPLC) can be substituted by rapid scanning techniques (visible reflectance spectroscopy VIS-RS; 380-730 nm). We used principal component analysis and cluster analysis to show that the recent eutrophication of Lake Żabińskie can be discriminated from climate-driven changes for the period AD 1907-2008. The eutrophication signal (PC1 = 46.4%; TOC, TN, TS, Phe-b, high TC/CD ratios total carotenoids/chlorophyll-a derivatives) is mainly expressed as increasing aquatic primary production, increasing hypolimnetic anoxia and a change in the algal community from green algae to blue-green algae. The proxies diagnostic for eutrophication show a smooth positive trend between 1907 and ca 1980 followed by a very rapid increase

  6. A Miocene wave-dominated estuarine system in the Paraíba Basin, northeastern Brazil

    Science.gov (United States)

    Gandini, Rosana; Rossetti, Dilce de Fátima; Netto, Renata Guimarães; Góes, Ana Maria

    2017-11-01

    A number of publications have documented the effect of the Miocene transgression on several coasts of the world. However, this event is incompletely documented along the Brazilian margin, despite the existence of an impressive record of Miocene deposits exposed mostly as several coastal cliffs along more than 5000 km of distance. The transgressive nature of Miocene deposits, so far recognized only in a few localities of northeastern Brazil, needs to be amplified in order to better characterize the impact of the Miocene transgression in eastern South America. In this work, we provide facies analysis of early/middle Miocene strata exposed in the Paraíba Basin, northeastern Brazil, aiming reconstruct the depositional paleoenvironments and analyze their evolution within the context of relative sea-level fluctuations data. The results revealed deposits characterized by several features that were related to the action of tidal currents, such as alternating thicker/thinner forest packages, abundant reactivation surfaces, mud drapes and oppositely-dipping (herringbone) cross sets. These sedimentary structures were associated with an ichnological assemblage indicative of marine-influenced and brackish water, best represented by Ophiomorpha, Planolites-Palaeophycus-Thalassinoides and Thallassinoides-Planolites-Palaeophycus ichnofabrics. Sedimentation occurred in environments consisting of estuarine channel, estuarine central basin, tidal inlet/tidal channel, tidal delta/washover, tidal flat/shoal and foreshore, which were related to an estuarine setting, at least in part of a wave-dominated type. Analysis of facies stratal patterns led to suggest that the estuarine deposits of the Paraíba Basin reflect a rise in relative sea level probably during the transgressive and/or highstand stage of a depositional sequence formed directly overlying Cretaceous rocks. This rise can be correlated with the worldwide early/mid Miocene marine transgression. However, while the eustatic sea

  7. 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

  8. The development of the Amazonian mega-wetland (Miocene; Brazil, Colombia, Peru, Bolivia)

    NARCIS (Netherlands)

    Hoorn, C.; Wesselingh, F.P.; Hovikoski, J.; Guerrero, J.; Hoorn, C.; Wesselingh, F.P.

    2010-01-01

    The scenery of Western Amazonia once consisted of fluvial systems that originated on the Amazonian Craton and were directed towards the sub-Andean zone and the Caribbean. In the course of the Early Miocene these fluvial systems were largely replaced by lakes, swamps, tidal channels and marginal

  9. 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.

  10. Eocene and miocene rocks off the northeastern coast of the United States

    Science.gov (United States)

    Gibson, T.G.

    1965-01-01

    A grab sample from a depth of 1675 m at a point south of Cape Cod contains early Eocene planktonic Foraminifera and is correlated with the Globorotalia rex zone of Trinidad. The assemblage indicates a depth comparable to that existing today. Regional relations suggest that the Cretaceous and Eocene deposits deepen to the west toward New Jersey. Two mollusk-bearing blocks dredged from the northern side of Georges Bank are correlative with the Miocene Yorktown Formation. Rocks from two other stations are probably Miocene. Benthonic Foraminifera in one sample indicate deposition in cool temperate waters of less than 60 m depth. ?? 1965.

  11. BENTHIC FORAMINIFERAL BIOSTRATIGRAPHY OF MALATYA OLIGO-MIOCENE SUCCESSION (EASTERN TAURIDS, EASTERN TURKEY

    Directory of Open Access Journals (Sweden)

    Fatma GEDİK

    2015-10-01

    Full Text Available The benthic foraminiferal biostratigraphy of Oligo-Miocene aged Muratlı and Petekkaya formations which crop out over wide regions around Akçadağ town, west of Malatya pro- vince in Eastern Taurids were revealed in this study. Systematical sampling was carried out in measured stratigraphical sections in four locations in order to perform stratigraphical and paleontological investigations. Benthic foraminifera taken from 182 hard rock samples were defined and three biozones were determined as; SBZ 21-22, belonging to Oligocene (Rupe- lian - Early Chattian, SBZ 23 (Late Chattian and SBZ 25 belonging to Lower Miocene in shallow marine deposits in the region. It was stated that the assemblage of planktic forami- nifer and nannoplankton which stratigraphically detected within Chattian - Burdigalian units in the succession most probably indicated Aquitanian age. Besides; Oligo-Miocene transition in the region was approved with this study based on biostratigraphical locations of benthic foraminiferal taxa.

  12. Reconstructing Late Holocene Climate Variability in North East China From Varved Maar Lake Sediments

    Science.gov (United States)

    Panizzo, V. N.; Mackay, A. W.; Rioual, P.; Chu, G.; Leng, M. J.

    2008-12-01

    Reconstructing climatic variability over the past c. 2 ka years is recognised as a key PAGES timeframe (focus 2). However few high-resolution records exist from the climate sensitive region of N) China which receives the majority of its precipitation from the east Asian summer monsoon (EASM). Interactions between the EASM and the global climate system have great resonance. Such examples include how the EASM responded to changes in climate over the documented e.g. "Medieval Warm Period" (c. AD 900 - 1300), "Little Ice Age" (c. AD 1350-1850) and recent warming. At present, literature remains contradictory to such environmental changes in NE China over this time-frame due to poor chronological control, low resolution of existing studies and even due to the inexact terminology of these climatic periods. Xiaolongwan Lake (XLW) is a small, closed, maar lake located in the Long Gang Volcanic Field, NE China (42°18'N; 126°19'E). It is at an elevation of 655 m a.s.l. with a maximum depth of 15 m. A varve chronology has been created for a 143 cm composite core (2 cores collected in 2006), and here we present diatoms and organic geochemistry (δ13C, TOC, C/N) evidence for environmental change over the past c. 2 ka years. Results show a gradual change in diatom species, moving from a composition where opportunistic species (e.g. Achnanthidium minutissimum) dominate (between c. 100 BC to 500 years AD) at the beginning of the record to one comprised of benthic/epiphytic species (e.g. Staurosira construens var venter, Punctastriata discoidea, Gomphonema parvulum). The introduction after c. 1850 years AD of the planktonic diatom species, Discotella woltereckii, not previously seen in the record, coincides with recent warming. This may be a response to changing limnological conditions, such as decreasing duration of lake ice-cover. Bulk organic δ13C results conducted on a short core collected from XLW in summer 2007, show that over the past c. 350 years there is a distinct

  13. Monitoring climate signal transfer into the varved lake sediments of Lake Czechowskie, Poland

    Science.gov (United States)

    Groß-Schmölders, Miriam; Ott, Florian; Brykała, Dariusz; Gierszewski, Piotr; Kaszubski, Michał; Kienel, Ulrike; Brauer, Achim

    2015-04-01

    In 2012 we started a monitoring program at Lake Czechowskie, Poland, because the lake comprises a long Holocene time series of calcite varves until recent times. The aim of the program is to understand how environmental and climatic conditions influence the hydrological conditions and, ultimately, the sediment deposition processes of the lake. Lake Czechowskie is located in the north of Poland in the Pomeranian Lake District and is part of the national park Tuchola Forest. The landscape and the lake is formed by the glacier retreat after the last glaciation (Weichselian). Lake Czechowskie is a typical hardwater lake and has a length of 1.4 km, an average width of 600 m and a lake surface area of ca 4 km. The maximum depth of 32 m is reached in a rather small hollow in the eastern part of the lake. Two different types of sediment traps provide sediment samples with monthly resolution from different water depths (12m, 26m). In addition, hydrological data including water temperature in different depths, water inflow, throughflow and outflow and the depth of visibility are measured. These data allow to describe strength and duration of lake mixing in spring and autumn and its influence on sedimentation. The sediment samples were analyzed with respect to their dry weight (used to calculate mean daily sediment flux), their inorganic and organic carbon contents, the stable C- and O-isotopes of organic matter and calcite as well as N-isotopes of organic matter. For selected samples dominant diatom taxa are determined. Our first results demonstrate the strong influence of the long winter with ice cover until April in 2013 on the sedimentation. A rapid warming in only 9 days starting on April 9th from -0,3 C° to 15,2 C° resulted in fast ice break-up and a short but intensive lake mixing. In consequence of this short mixing period a strong algal bloom especially of Fragilaria and Crysophycea commenced in April and had its maximum in May. This bloom further induced biogenic

  14. Miocene shale tectonics in the Moroccan margin (Alboran Sea)

    Science.gov (United States)

    Do Couto, D.; El Abbassi, M.; Ammar, A.; Gorini, C.; Estrada, F.; Letouzey, J.; Smit, J.; Jolivet, L.; Jabour, H.

    2011-12-01

    The Betic (Southern Spain) and Rif (Morocco) mountains form an arcuate belt that represents the westernmost termination of the peri-mediterranean Alpine mountain chain. The Miocene Alboran Basin and its subbasins is located in the hinterland of the Betic-Rif belt. It is considered to be a back-arc basin that developed during the coeval westward motion of the Alboran domain and the extensional collapse of previously thickened crust of the Betic-Rif belt. The Western Alboran Basin (WAB) is the major sedimentary depocenter with a sediment thickness in excess of 10 km, it is bordered by the Gibraltar arc, the volcanic Djibouti mounts and the Alboran ridge. Part of the WAB is affected by shale tectonics and associated mud volcanism. High-quality 2D seismic profiles acquired on the Moroccan margin of the Alboran Basin during the last decade reveal the multiple history of the basin. This study deals with the analysis of a number of these seismic profiles that are located along and orthogonal to the Moroccan margin. Seismic stratigraphy is calibrated from industrial wells. We focus on the interactions between the gravity-driven tectonic processes and the sedimentation in the basin. Our seismic interpretation confirms that the formation of the WAB began in the Early Miocene (Aquitanian - Burdigalian). The fast subsidence of the basin floor coeval to massive sedimentation induced the undercompaction of early miocene shales during their deposition. Downslope migration of these fine-grained sediments initiated during the deposition of the Langhian siliciclastics. This gravity-driven system was accompanied by continuous basement subsidence and induced disharmonic deformation in Mid Miocene units (i.e. not related to basement deformation). The development of shale-cored anticlines and thrusts in the deep basin is the result of compressive deformation at the front of the gravity-driven system and lasted for ca. 15 Ma. The compressive front has been re-activated by strong

  15. Toward a quantitative reconstruction of hypoxia from varve records in the large perialpin Lake Bourget over the last 150 years

    Science.gov (United States)

    Jenny, J.-P.; Arnaud, F.; Dorioz, J. M.; Giguet Covex, C.; Frossard, V.; Sabatier, P.; Millet, L.; Reyss, J. L.; Tachikawa, K.; Romeyer, O.; Pignol, C.; Mallet, E.; Perga, M. E.

    2012-04-01

    Hypoxia -defined as dissolved oxygen ≤2 mg/l- is a severe detrimental factor for aquatic environments. In lakes, despit the importance for management, it is generally still hard to estimate hypoxia because of the lack of appropriate proxies or restricted number of sample cores. In this study, by using (40) sediment core data from chosen depths, we propose to go a step further toward a quantitative reconstruction of hypoxia integrating the extension of hypoxic water layer, both through space (volume) and time (yearly value). For that we went a step further in using an existing proxy: varve preservation. It is generally well-adapted for hypoxia detection, but not yet developed for small scale time and space variations through a complete large lake basin. Varves preservation is the consequence of the death of most of benthic macro-organisms that normally mix-up first millimetres of sediments, due to oxygen depletion. In Lake Bourget recent laminated sediments correspond to biochemical varves. We assume that their preservation results from a threshold in dissolved oxygen concentrations induced by seasonal hypoxia. Chironomids, organic matter and Mn/Fe ratio (XRF) were used as complementary proxies of hypoxia to validate our assumptions concerning varves. Our results show that volume of hypoxia can be annually estimated according to varve records through lake. Volumes of hypoxia varied through time in the Lake Bourget. Sediments recorded first the onset of severe hypoxia in the deepest part of the basin (-140m) in AD 1935±1, corresponding to 11.103m3 of hypoxic waters. Then hypoxic surface progressively extended on the slope until reaching a maximum at -90m in AD 1960, leading to 306.103m3 of hypoxic waters. After a retreat dated to AD 1980, hypoxia seemed to re-extend until today. Those fluctuations over the "oscillating zone" of hypoxia (-90 to -133m) were compared with potential forcing factors. The onset of hypolimnetic hypoxia is commonly attributed to

  16. Emplacement of the La Peña alkaline igneous complex, Mendoza, Argentina (33° S): Implications for the early Miocene tectonic regime in the retroarc of the Andes

    Science.gov (United States)

    Pagano, D. S.; Galliski, M. A.; Márquez-Zavalía, M. F.

    2014-03-01

    The La Peña alkaline complex (LPC) of Miocene age (18-19 Ma) lies on the eastern front of the Precordillera (32°41ʹ34ʺS, 68°59ʹ48″W, 1400-2900 m a.s.l.), 30 km northwest of Mendoza city, Argentina. It is a subcircular massif of 19 km2 and 5 km in diameter, intruded in the metasedimentary sequence of the Villavicencio Formation of Silurian-Devonian age. It is the result of integration of multiple pulses derived from one or more deep magma chambers, which form a suite of silicate rocks grouped into: a clinopyroxenite body, a central syenite facies with a large breccia zone at the contact with the clinopyroxenite, bodies of malignite, trachyte and syenite porphyry necks, and a system of radial and annular dikes of different compositions. Its subcircular geometry and dike system distribution are frequent features of intraplate plutons or plutons emplaced in post-orogenic settings. These morphostructural features characterize numerous alkaline complexes worldwide and denote the importance of magmatic pressures that cause doming with radial and annular fracturing, in a brittle country rock. However, in the LPC, the attitude of the internal fabric of plutonic and subvolcanic units and the preferential layout of dikes match the NW-SE extensional fractures widely distributed in the host rock. This feature indicates a strong tectonic control linked to the structure that facilitate space for emplacement, corresponding to the brittle shear zone parallel to the N-S stratigraphy of the country rock. Shearing produced a system of discontinuities, with a K fractal fracture pattern, given by the combination of Riedel (R), anti-Riedel (R‧), (P) and extensional (T) fracture systems, responsible for the control of melt migration by the opening of various fracture branches, but particularly through the NW-SE (T) fractures. Five different pulses would have ascent, (1) an initial one from which cumulate clinopyroxenite was formed, (2) a phase of mafic composition represented by

  17. Tropical sea surface temperature variability near the Oligocene - Miocene boundary

    Science.gov (United States)

    Zhang, Y.; Pagani, M.

    2010-12-01

    The Oligocene/Miocene (O-M) boundary is characterized by a period of rapid and intense glaciation labeled Mi-1 at ~ 23.1 Ma. An abrupt 1.5‰ increase in the benthic foraminifera oxygen isotope composition that characterizes Mi-1 may indicate a (1) significant deep-water temperature decrease; (2) major ice-sheet expansion, or the combination of both. Current coarse Mg/Ca-based temperature estimations for the early Miocene suggests that deep-ocean temperatures were ~2°C warmer than Today [1, 2]. However, Mg/Ca based temperatures can also be influenced by changes in the carbonate ion concentration, vital effects, and diagenesis. In particular, recent evidence from mid-ocean ridge flank carbonate veins shows dramatic seawater Mg/Ca ratio changes during the Neogene (Mg/Ca from ~2.2 to 5.3, [3]), which further challenges the application of Mg/Ca thermometry. Owing to poor temperature constraints, current ice volume estimations for the late Oligocene/early Miocene range from 125% of the present-day East Antarctic Ice Sheet (EAIS) to a nearly complete collapse of the Antarctic glaciers [4]. Here we present tropical sea surface temperatures (SSTs) records based on TEX86 and alkenone UK37 near the O-M boundary. Sediment samples from Ocean Drilling Program (ODP) Site 926 in the Ceara Rise (tropical Atlantic) and Site 1148 in the South China Sea (tropical Pacific) were subject to lipid extraction, separation, gas chromatography, and liquid chromatography-mass spectrometry analysis. TEX86-based SST indicates that the tropics were ~3-4°C warmer than today and relatively stable during Mi-1. This suggests that ice-sheet dynamics, rather than temperature, might be responsible for the observed oxygen isotope changes during the O-M boundary. Further, O-M boundary averaged temperatures recorded at site 926 is ~ 0.5°C higher relative to the late Eocene from site 925 (a nearby site [5]). Given late Oligocene benthic δ18O that suggests at least 1‰ enrichment relative to the late

  18. 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

  19. Late Miocene magnetostratigraphy in the Mediterranean

    NARCIS (Netherlands)

    Langereis, C.G.

    1984-01-01

    Reversals of the geomagnetic field In the geological past are recorded globally in the natural remanent magnetization (NRM) of igneous and sedimentary rock sequences. The accurate and rei iable reconstruction of this record is the basis of magnetostratigraphy. The magnetostratigraphy of Late Miocene

  20. Mastritherium (Artiodactyla, Anthracotheriidae) from Wadi Sabya, southwestern Saudi Arabia; an earliest Miocene age for continental rift-valley volcanic deposits of the Red Sea margin

    Science.gov (United States)

    Madden, Gary T.; Schmidt, Dwight Lyman; Whitmore, Frank C.

    1983-01-01

    A lower jaw fragment with its last molar (M/3) from the Baid formation in Wadi Sabya, southwestern Saudi Arabia, represents the first recorded occurrence in the Arabian Peninsula of an anthracotheriid artiodactyl (hippo-like, even-toed ungulate). This fossil is identified as a primitive species of Masritherium, a North and East African genus restricted, previously to the later early Miocene. This identification indicates that the age of the Baid formation, long problematical, is early Miocene and, moreover, shows that the age of the fossil site is earliest Miocene (from 25 to 21Ma). The Wadi Sabya anthracothere is the first species of fossil mammal recorded from western Saudi Arabia, and more important, it indicates an early Miocene age for the volcanic deposits of a continental rift-valley that preceded the initial sea-floor spreading of the Red Sea.

  1. Plate tectonic model for the oligo-miocene evolution of the western Mediterranean

    Science.gov (United States)

    Cohen, Curtis R.

    1980-10-01

    This paper outlines a plate tectonic model for the Oligo-Miocene evolution of the western Mediterranean which incorporates recent data from several tectonic domains (Corsica, Sardinia, the Kabylies, Balearic promontory, Iberia, Algero-Provençal Basin and Tunisian Atlas). Following late Mesozoic anticlockwise rotation of the Iberian peninsula (including the Balearic promontory and Sardinia), late Eocene collision occurred between the Kabylies and Balearic promontory forming a NE-trending suture with NW-tectonic polarity. As a result of continued convergence between the African and European plates, a polarity flip occurred and a southward-facing trench formed south of the Kabylie—Balearic promontory suture. During late Oligocene time an E-W-trending arc and marginal basin developed behind the southward-facing trench in the area of the present-day Gulf of Lion. Opening of this basin moved the Corsica—Sardinia—Calabria—Petit Kabylie—Menorca plate southward, relative to the African plate. Early Miocene back-arc spreading in the area between the Balearic promontory and Grand Kabylie emplaced the latter in northern Algeria and formed the South Balearic Basin. Coeval with early Miocene back-arc basin development, the N-S-extension in the Gulf of Lion marginal basin changed to a more NW-SE direction causing short-lived extension in the area of the present-day Valencia trough and a 30° anticlockwise rotation of the Corsica-Sardinia-Calabria—Petit Kabylie plate away from the European plate. Early—middle Miocene deformation along the western Italian and northeastern African continental margins resulted from this rotation. During the early late Miocene (Tortonian), spreading within a sphenochasm to the southwest of Sardinia resulted in the emplacement of Petit Kabylie in northeastern Algeria.

  2. Holocene surge-history of the Eyjabakkajökull glacier inferred from varved lake sediments on eastern Iceland

    Science.gov (United States)

    Striberger, J.; Bjorck, S.; Ingolfsson, O.; Kjaer, K.; Snowball, I.; Uvo, C. B.

    2009-12-01

    Properties of varved lake sediments from Lake Lögurinn on eastern Iceland and their link to glacial processes of Eyjabakkajökull, a surging outlet glacier of the Vatnajökull ice cap, is examined. An 18 m long sediment sequence obtained from the lake, covering at least the past ~ 9 200 years, displays a distinct recurring pattern of light-coloured clay dominated laminae sections. The thickness of the light-coloured laminae is mainly controlled by the amount of glacial rock flour transported from Eyjabakkajökull. These light laminae are interlaid by coarser dark-coloured laminae mainly formed by suspended matter transported to the lake by the large non-glacial river Grímsá. During the recent surge of Eyjabakkajökull in 1972, the amount of suspended matter transported to the lake increased significantly. The surge was followed by years of recurring drainages of Lake Háöldulón, an ice-dammed lake that was formed shortly after the surge. As a result, the amount of glacial rock flour transported to Lake Lögurinn was higher than usual as long as Lake Háöldulón continued to drain (i.e. as long as the ice front was in an advanced position enough to dam the lake). This increase in glacially derived rock flour is reflected in the sediments, as the varve that was formed in 1972 constitutes the thickest light-coloured laminae deposited during the 20th century, which is followed by the second thickest light-coloured laminae, deposited in 1973. From there on, the thicknesses of the light-coloured laminae gradually fade out. Based on these modern observations, we suggest that the recurring cyclic pattern of light-coloured clay dominated laminae sections in the sediment sequence is related to past surges of Eyjabakkajökull, followed by drainages of Lake Háöldulón. Recurring cycles of light-coloured clay dominated laminae began to develop close to the Hekla-3 and Hekla-4 tephras (ca. 3000-4000 years BP), which also coincides with the time when the varves became

  3. Miocene Soil Database: Global paleosol and climate maps of the Middle Miocene Thermal Maximum

    Science.gov (United States)

    Metzger, C. A.

    2013-12-01

    Paleosols, which record past climatic, biologic, and atmospheric conditions, can be used as a proxy to understand ancient terrestrial landscapes, paleoclimate, and paleoenvironment. In addition, the middle Miocene thermal maximum (~16 Ma) provides an ancient analog for understanding the effects of current and future climate change on soil and ecosystem regimes, as it contains records of shifts similar in magnitude to expected global climate change. The Miocene Soil Database (MSDB) combines new paleosol data from Australia and Argentina with existing and previously uncollated paleosol data from the literature and the Paleobiology Database. These data (n = 507) were then used to derive a paleogeographic map of climatically significant soil types zones during the Middle Miocene. The location of each diagnostic paleosol type (Aridisol, Alfisol, Mollisol, Histosol, Oxisol, and Ultisol) was plotted and compared with the extent of these soil types in the modern environment. The middle Miocene soil map highlights the extension of tropical soils (Oxisols, Ultisols), accompanied by thermophilic flora and fauna, into northern and southern mid-latitudes. Peats, lignites, and Histosols of wetlands were also more abundant at higher latitudes, especially in the northern hemisphere, during the middle Miocene. The paleosol changes reflect that the Middle Miocene was a peak of global soil productivity and carbon sequestration, with replacement of unproductive Aridisols and Gelisols with more productive Oxisols, Alfisols, Mollisols and Histosols. With expansion to include additional data such as soil texture, moisture, or vegetation type, the MSDB has the potential to provide an important dataset for computer models of Miocene climate shifts as well as future land use considerations of soils in times of global change.

  4. New method to estimate paleoprecipitation using fossil amphibians and reptiles and the middle and late Miocene precipitation gradients in Europe

    Science.gov (United States)

    Böhme, M.; Ilg, A.; Ossig, A.; Küchenhoff, H.

    2006-06-01

    Existing methods for determining paleoprecipitation are subject to large errors (±350 400 mm or more using mammalian proxies), or are restricted to wet climate systems due to their strong facies dependence (paleobotanical proxies). Here we describe a new paleoprecipitation tool based on an indexing of ecophysiological groups within herpetological communities. In recent communities these indices show a highly significant correlation to annual precipitation (r2 = 0.88), and yield paleoprecipitation estimates with average errors of ±250 280 mm. The approach was validated by comparison with published paleoprecipitation estimates from other methods. The method expands the application of paleoprecipitation tools to dry climate systems and in this way contributes to the establishment of a more comprehensive paleoprecipitation database. This method is applied to two high-resolution time intervals from the European Neogene: the early middle Miocene (early Langhian) and the early late Miocene (early Tortonian). The results indicate that both periods show significant meridional precipitation gradients in Europe, these being stronger in the early Langhian (threefold decrease toward the south) than in the early Tortonian (twofold decrease toward the south). This pattern indicates a strengthening of climatic belts during the middle Miocene climatic optimum due to Southern Hemisphere cooling and an increased contribution of Arctic low-pressure cells to the precipitation from the late Miocene onward due to Northern Hemisphere cooling.

  5. Middle Miocene E-W tectonic horst structure of Crete through extensional detachment faults

    International Nuclear Information System (INIS)

    Papanikolaou, D; Vassilakis, E

    2008-01-01

    Two east-west trending extensional detachment faults have been recognized in Crete, one with top-to-the-north motion of the hanging wall toward the Cretan Sea and one with top-to-the-south motion of the hanging wall toward the Libyan Sea. The east-west trending zone between these two detachment faults, which forms their common footwall, comprises a tectonic horst formed during Middle Miocene slip on the detachment faults. The detachment faults disrupt the overall tectono-stratigraphic succession of Crete and are localized along pre-existing thrust faults and along particular portions of the stratigraphic sequence, including the transition between the Permo-Triassic Tyros Beds and the base of the Upper Triassic-Eocene carbonate platform of the Tripolis nappe. By recognizing several different tectono-stratigraphic formations within what is generally termed the 'phyllite-quartzite', it is possible to distinguish these extensional detachment faults from thrust faults and minor discontinuities in the sequence. The deformation history of units within Crete can be summarized as: (i) compressional deformation producing arc-parallel east-west trending south-directed thrust faults in Oligocene to Early Miocene time (ii) extensional deformation along arc-parallel, east-west trending detachment faults in Middle Miocene time, with hanging wall motion to the north and south; (iii) Late Miocene-Quaternary extensional deformation along high-angle normal and oblique normal faults that disrupt the older arc-parallel structures

  6. The Late Glacial Chronology from Lake Suigestu: A new approach to varve interpolation using frequency distributions of annual sub-layers

    Science.gov (United States)

    Schlolaut, Gordon; Marshall, Michael; Brauer, Achim; Nakagawa, Takeshi; Lamb, Henry; Staff, Richard; Bronk Ramsey, Christopher; Brock, Fiona; Bryant, Charlotte; 2006 Project Members, Suigetsu

    2010-05-01

    The 1993 sediment core from Lake Suigetsu is one of the most comprehensive terrestrial radiocarbon records. It is extremely rich in leaf fossils, providing a unique, truly atmospheric record of radiocarbon for the last 10-50 kyr BP (Kitagawa & van der Plicht, 2000). Since the Lake Suigetsu sediment is annually laminated (varved) for much of its depth it is suitable for extending the terrestrial radiocarbon calibration model up to 50 kyr BP. However, the data presented by Kitagawa & van der Plicht (2000) significantly diverged from alternative, marine-based calibration datasets, due to gaps in the sediment profile and varve counting uncertainties (Staff et al., 2009). In 2006 four new parallel cores were recovered from Lake Suigetsu and combined to construct a new complete and continuous master profile (SG06). Along with a new program of AMS radiocarbon measurement, varve counting is being carried out using two different techniques: i) thin section microscopy and ii) high-resolution X-ray fluorescence and X-radiography. In addition, a novel interpolation approach has been developed. First results are presented for the Late Glacial (10,200 - 15,000 kyr BP). The U-Oki Tephra at the top of this interval is used as tie point for the floating varve count chronology. Initially, the two counting methods are carried out independently. The results are then compared in detail to identify the differences down to the sub-mm scale. This new approach substantially reduces internal error and results in a greater degree of accuracy than previously possible. Due to poor varve preservation in some sediment intervals, the counts of these sections have to be interpolated. Commonly, interpolation is carried out manually using sedimentation rate estimates from neighbouring sections. The new approach presented here is based on an automated analysis of frequency distributions of annual sub-layers from the compromised section itself, allowing an estimate of the sedimentation rate unbiased

  7. The first fossil brown lacewing from the Miocene of the Tibetan Plateau (Neuroptera, Hemerobiidae

    Directory of Open Access Journals (Sweden)

    Qiang Yang

    2018-01-01

    Full Text Available A new species of Hemerobiidae, Wesmaelius makarkini Yang, Pang & Ren, sp. n. is described from the Lower Miocene, Garang Formation of Zeku County, Qinghai Province (northeastern Tibetan Plateau, China. The species is assigned to the widely distributed extant genus Wesmaelius Krüger (Hemerobiinae. The species represents the first named fossil of this family from China, which sheds light on the historical distribution of Wesmaelius and early divergences within Hemerobiinae.

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

    Science.gov (United States)

    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

  9. Changing seasonality patterns in Central Europe from Miocene Climate Optimum to Miocene Climate Transition deduced from the Crassostrea isotope archive

    Science.gov (United States)

    Harzhauser, Mathias; Piller, Werner E.; Müllegger, Stefan; Grunert, Patrick; Micheels, Arne

    2011-03-01

    The Western Tethyan estuarine oyster Crassostrea gryphoides is an excellent climate archive due to its large size and rapid growth. It is geologically long lived and allows a stable isotope-based insight into climatic trends during the Miocene. Herein we utilised the climate archive of 5 oyster shells from the Miocene Climate Optimum (MCO) and the subsequent Miocene Climate Transition (MCT) to evaluate changes of seasonality patterns. MCO shells exhibit highly regular seasonal rhythms of warm-wet and dry-cool seasons. Optimal conditions resulted in extraordinary growth rates of the oysters. δ 13C profiles are in phase with δ 18O although phytoplankton blooms may cause a slight offset. Estuarine waters during the MCO in Central Europe display a seasonal temperature range of c. 9-10 °C. Absolute water temperatures have ranged from 17 to 19 °C during cool seasons and up to 28 °C in warm seasons. Already during the early phase of the MCO, the growth rates are distinctly declining, although gigantic and extremely old shells have been formed at that time. Still, a very regular and well expressed seasonality is dominating the isotope profiles, but episodically occurring extreme climate events influence the environments. The seasonal temperature range is still c. 9 °C but the cool season temperature seems to be slightly lower (16 °C) and the warm season water temperature does not exceed c. 25 °C. In the later MCT at c. 12.5-12.0 Ma the seasonality pattern is breaking down and is replaced by successions of dry years with irregular precipitation events. No correlation between δ 18O and δ 13C is documented maybe due to a suboptimal nutrition level which would explain the low growth rates and small sizes. The amplitude of seasonal temperature range is decreasing to 5-8 °C. No clear cooling trend can be postulated for that time as the winter season water temperatures range from 15 to 20 °C. This may point to unstable precipitation rhythms on a multi-annual to

  10. A 900-year pollen-inferred temperature and effective moisture record from varved Lake Mina, west-central Minnesota, USA

    Science.gov (United States)

    St. Jacques, Jeannine-Marie; Cumming, Brian F.; Smol, John P.

    2008-04-01

    Drought is endemic to the North American Great Plains, causing severe economic consequences. However, instrumental climate data only exist from ca AD 1890, and limited tree-ring, paleolimnological, archeological and eolian records document the last two millennia. To address this lack of monitoring and paleoclimatic data, the pollen preserved in the varved sediments of Lake Mina, Minnesota, on the northeastern border of the Great Plains, were analyzed. May and February mean monthly temperatures and "annual precipitation minus potential evapotranspiration" were reconstructed at a 4-year resolution using a pre-settlement pollen-climate calibration set. The period of the so-called Little Ice Age (LIA) (AD 1500-1870) was colder than the Medieval Climate Anomaly (MCA) (AD 1100-1500) in west-central Minnesota. Winter temperatures in the LIA declined more than summer ones. The pollen record suggests that the LIA occurred in three phases: an initial cold phase from AD 1505 to AD 1575, a warmer phase, and then a very cold phase from AD 1625 to AD 1775. There were severe droughts detected in the Lake Mina record from AD 1660 to AD 1710 and AD 1300 to AD 1400, suggesting that high-resolution pollen records can detect events previously defined from the tree-ring records. This latter century-scale drought is concurrent with the widely reported "AD 1250-1400 mega-drought", which exceeds the severity of 20th century droughts.

  11. Molluscan radiations and landscape evolution in Miocene Amazonia

    NARCIS (Netherlands)

    Wesselingh, F.P.

    2008-01-01

    This PhD study aims to exploit the rich archive provided by the Miocene mollusc fauna of the Pebas Formation and other inland Miocene Amazonian formations to reconstruct landscape evolution and biotic development in lowland Amazonia during the Neogene. Over 160 samples from more than 70 Pebas

  12. 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.

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

    Science.gov (United States)

    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 (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 Europe and will be confidentially one of the key faunas for a high-resolution continental biostratigraphy and the comprehension of the faunal succession and interchanges near the Middle/Late Miocene transition. Acknowledgements This is a preliminary overview of the Gratkorn vertebrate fauna. Several taxa are still under investigation. We are especially grateful to Gudrun Daxner-Höck, Ursula Göhlich (both Natural History Museum Vienna) and Getrud Rössner (University of Munich) for their comments to the rodents, ruminants, proboscidians and bird remains. References Böhme, M., Ilg, A., Winklhofer, M. 2008. Late Miocene "washhouse" climate in Europe.- Earth and Planetary Science Letters, 275: 393-401. Gross, M., 2008. A limnic ostracod fauna from the surroundings of the Central

  14. The identification of Oligo-Miocene mammalian palaeocommunities from the Riversleigh World Heritage Area, Australia and an appraisal of palaeoecological techniques

    Science.gov (United States)

    Black, Karen H.; Archer, Michael; Hand, Suzanne J.

    2017-01-01

    Fourteen of the best sampled Oligo-Miocene local faunas from the Riversleigh World Heritage Area, north-western Queensland, Australia are analysed using classification and ordination techniques to identify potential mammalian palaeocommunities and palaeocommunity types. Abundance data for these faunas are used, for the first time, in conjunction with presence/absence data. An early Miocene Faunal Zone B and two middle Miocene Faunal Zone C palaeocommunities are recognised, as well as one palaeocommunity type. Change in palaeocommunity structure, between the early Miocene and middle Miocene, may be the result of significant climate change during the Miocene Carbon Isotope Excursion. The complexes of local faunas identified will allow researchers to use novel palaeocommunities in future analyses of Riversleigh’s fossil faunas. The utility of some palaeoecological multivariate indices and techniques is examined. The Dice index is found to outperform other binary similarity/distance coefficients, while the UPGMA algorithm is more useful than neighbour joining. Evidence is equivocal for the usefulness of presence/absence data compared to abundance. PMID:28674663

  15. Miocene Fossils Reveal Ancient Roots for New Zealand's Endemic Mystacina (Chiroptera and Its Rainforest Habitat.

    Directory of Open Access Journals (Sweden)

    Suzanne J Hand

    Full Text Available 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.

  16. Equatorial Precession Drove Mid-Latitude Changes in ENSO-Scale Variation in the Earliest Miocene

    Science.gov (United States)

    Fox, B.; D'Andrea, W. J.; Lee, D. E.; Wilson, G. S.

    2014-12-01

    Foulden Maar is an annually laminated lacustrine diatomite deposit from the South Island of New Zealand. The deposit was laid down over ~100 kyr of the latest Oligocene and earliest Miocene, during the peak and deglaciation phase of the Mi-1 Antarctic glaciation event. At this time, New Zealand was located at approximately the same latitude as today (~45°S). Evidence from organic geochemical proxies (δD, δ13C) and physical properties (density, colour) indicates the presence of an 11-kyr cycle at the site. Although it is known that 11-kyr insolation (half-precession) cycles occur between the Tropics, this cycle is rarely seen in sedimentary archives deposited outside the immediate vicinity of the Equator. Records from Foulden Maar correlate well with the amplitude and phase of the modelled equatorial half-precession cycle for the earliest Miocene. High-resolution (50 µm) colour intensity measurements and lamina thickness measurements both indicate the presence of significant ENSO-like (2-8 year) variation in the Foulden Maar sediments. Early results from targeted lamina thickness measurements suggest that ENSO-band variation is modulated by the 11-kyr cycle, with power in the ENSO band increasing during periods of increased insolation at the Equator. This implies that equatorial half-precession had a significant effect on ENSO-like variation in the early Miocene, and that this effect was felt as far afield as the mid-latitudes of the Southern Hemisphere.

  17. Pollen analysis of coal-bearing Miocene sedimentary rocks from the Seyitomer basin (Kutahya), western Anatolia

    Energy Technology Data Exchange (ETDEWEB)

    Yavuz-Isik, N. [Ondokuz Mayis University, Kurupelit (Turkey). Dept. of Civil Engineering

    2007-09-15

    The late Early-Middle Miocene sequences of the Seyitomer Basin (western Anatolia) were palynologically investigated. Fifty-five taxa belonging to seven gymnospermous and 48 angiospermous pollen genera were identified in the 19 productive samples. Two pollen zones were recognised based on the changing abundance of individual tree taxa. Zone 1 is characterized by predominance of Pinus and Cedrus. Zone 2 is characterized by predominance of deciduous Quercus and evergreen Quercus and a marked reduction in representation of Taxodiaceae. The differences in the pollen spectra between Zone 1 and Zone 2 may reflect the global Middle Miocene cooling. These results are largely comparable to pollen data derived from the neighbouring areas. The vegetation of the Seyitomer Basin was dominated by trees. This palynological analysis reveals the existence of a swamp-forest developed in a subtropical to warm-temperate humid climate.

  18. Miocene isotope zones, paleotemperatures, and carbon maxima events at intermediate water-depth, Site 593, Southwest Pacific

    International Nuclear Information System (INIS)

    Cooke, P.J.; Nelson, C.S.; Crundwell, M.P.

    2008-01-01

    Oxygen and carbon isotopic stratigraphies are presented from both benthic and planktic foraminifera for the late early Miocene to earliest Pliocene interval (c. 19-5 Ma) of intermediate water-depth DSDP Site 593 in the southern Tasman Sea. The benthic values are interpreted as recording Miocene Southern Component Intermediate Water, while the planktic species record the Miocene mode and surface water signals. Comparisons are made between temperate Site 593 and the intermediate-depth polar Site 747 in the southern Indian Ocean. Glacial Mi zones Mi1b-Mi6, representing extreme glacial events, are evident in both the Site 593 intermediate and surface water records. Miocene Southern Component Intermediate Water δ 18 O values are generally lighter than the Holocene equivalent (Antarctic Intermediate Water), indicating slightly warmer intermediate waters and/ or less global ice volume. The benthic-planktic gradient is interpreted as indicating a less stratified Tasman Sea during the Miocene. The benthic δ 13 C record contains most of the global carbon maxima (CM) events, CM1-7 (CM1-6 = the Monterey Excursion). Like global deep-water records, the Tasman Sea intermediate water δ 13 C values indicate that most CM events correspond with Mi glacials, including Mi4 at Site 593, not reported previously. Intermediate waters play an important role in propagating climatic changes from the polar regions to the tropics, and the Site 593 dataset provides a full water column record of the structure of Miocene intermediate to surface watermasses prior to the modern situation. (author). 132 refs., 8 figs., 4 tabs

  19. Paleo-environmental Reconstruction of Oligocene to Early Miocene ...

    African Journals Online (AJOL)

    ADOWIE PERE

    province on the West African continental margin. It lies mainly in the ... basin are favorable for the generation, accumulation ... reconstruction as well as recognition of oil and gas deposits .... zone which covers from 1640ft to 11,100ft of the well.

  20. Palynological zonation of oligocene to early miocene sediments of ...

    African Journals Online (AJOL)

    573) which represents the base of P620 zone and top of P580 zone were undefined. P560 Zone was defined by the appearance of quantitative base Peregrinipollis nigericus at 7620ft and increase Retibrevitricolporites obodoensis at 11580ft.

  1. Late Miocene mollusks from the Queen Charlotte Islands, British Columbia, Canada

    Science.gov (United States)

    Addicott, Warren O.

    1978-01-01

    A fauna of bivalve mollusks, scattered gastropods, and an echinoid from exposures of the Skonun Formation in the northeastern part of Graham Island is indicative of an early late Miocene age and correlation with the provincial Wishkahan Stage. The molluscan assemblages are from the upper 600 of the 1800-m-thick marine and nonmarine formation, which appears to be entirely of late Miocene age. The Skonun Formation is the strandline fa.cies of marginal marine and nonmarine deposits of the northwestern part of the Queen Charlotte basin, a Nieogene embayment paralleling the modern mainland coast. The molluscan fauna and associated lignite beds are known from a few widely scattered outcrops; they are indicative of alternating marine and nonmarine to brackish-water environments in the upper part of the formation. The Skonun fauna occurs near the northern boundary of the Pacific Northwest Neogene molluscan province. It is the only marine Neogene molluscan fauna known from the British Columbia coast. The fauna has strong taxonomic ties with the fauna of the Empire Formation of southwestern Oregon and has several species in common with the upper Miocene of the Lituya district, southeastern Alaska, implying that these three faunas are coeval.

  2. Modern limnology, sediment accumulation and varve formation processes in Lake Żabińskie, northeastern Poland: comprehensive process studies as a key to understand the sediment record

    Directory of Open Access Journals (Sweden)

    Alicja Bonk

    2014-12-01

    Full Text Available Reconstructions of paleoclimatic and paleoenvironmental data from sediment records require a thorough knowledge of the physical, chemical and biological factors that influence sediment-formation processes and signal preservation in lake sediments. Lake Żabińskie, an eutrophic hardwater lake located in northeastern Poland (Masurian Lake District, provides an unique environment for the investigation of processes that lead to the varve formation. During a two-year long observation period we investigated limnological and hydrochemical conditions within the water column, recent sediment fluxes and laminations preserved in the sediments of this lake to understand the relationship between the lake water properties and the sediment formation processes. We demonstrate that different mixing patterns may occur in Lake Żabińskie, from dimictic to meromictic depending on the meteorological conditions. Regardless of the water mixing pattern, the lake was stratified during much of the year which led to significant differences between surface and near-bottom water environments. The hypolimnion was characterized by higher conductivity and anoxic conditions with only short periods of better oxygenation, which created conditions ideal for the formation and preservation of biogenic varves. The material collected from the sediment trap revealed notable changes in sediment fluxes with characteristic spring maxima and, optionally, a second late fall maxima. Considerable variability was also observed for the fluxes of total organic carbon, biogenic silica and calcite. Microscopic investigation of the topmost sediments revealed a complex structure of the varves showing a distinct spring calcite lamina followed by several fine calcite laminae interbedded with diatom-rich laminae and, finally, by an organic-rich lamina with minerogenic admixtures deposited during winter. This seasonal variability was also reflected in the chemical composition inferred from high

  3. Miocene block uplift and basin formation in the Patagonian foreland: The Gastre Basin, Argentina

    Science.gov (United States)

    Bilmes, A.; D'Elia, L.; Franzese, J. R.; Veiga, G. D.; Hernández, M.

    2013-08-01

    The intraplate fault-block mountains and intermontane deposits of the Gastre Basin, which are recorded more than 550 km east of the Andean trench in central Patagonia, Argentina, are analyzed. The Gastre Basin is one of the largest Patagonian intermontane basins, limited by uplifted blocks strongly oblique to the Andean chain. It was originated by reverse faulting and inversion of pre-existing normal faults associated with a Mesozoic rift basin and defined by older crustal heterogeneities. The deformational event occurred during the middle Miocene, related to a short contractional episode (16.1-14.86 Ma), probably in response to an eastward migration of the Andean fold and thrust belt. During Pliocene to Quaternary times, neither younger fault-block uplifts nor reconfigurations of the basin occurred. Similarities between the study area and other parts of the Patagonian foreland - such as the presence of Miocene reverse or inversion tectonics, as well as the accommodation of the Miocene sedimentary successions - suggest that the Gastre Basin is part of a major late early to middle Miocene broken foreland system (i.e. the Patagonian broken foreland) that exhumed discrete fault-block mountains and generated contemporary basins along more than 950 km parallel to the Andean trench (i.e. between 40°00' and 48°00' south latitude). Based on recent studies on the southern Andean Margin, this continental-scale contractional episode may be the result of a flat-slab subduction segment. Nevertheless, such a hypothesis is very difficult to support when analyzing such a large flat subduction segment along the entire Patagonian trench. This suggests the need to consider alternative flat-slab trigger mechanisms or other factors in the generation of broken foreland systems.

  4. Miocene to Recent structural evolution of the Nevado de Toluca volcano region, Central Mexico

    Science.gov (United States)

    García-Palomo, A.; Macías, J. L.; Garduño, V. H.

    2000-03-01

    Based on aerial photography, satellite imagery, and detailed field work, a geological and structural model of Nevado de Toluca and its surroundings is presented. The Nevado de Toluca volcano is built upon the intersection of three complex fault systems of different age, orientation, and kinematics. These systems from the older to the younger are: (a) The Taxco-Querétaro Fault System (NNW-SSE) with clear expression south of the volcano; (b) The San Antonio Fault System (NE-SW) that runs between the San Antonio and Nevado de Toluca volcanoes; and (c) The Tenango Fault System (E-W) located to the east of Nevado de Toluca volcano. Our field data, supported by previous studies, suggest that these systems have coexisted since the late Miocene. In addition, the stratigraphy, chronology, and kinematics of fault planes point to the existence of at least three main deformation events that have affected the region since the late Miocene. During the early Miocene, an extensional phase with the same deformation style as the Basin and Range tectonics of northern Mexico caused the formation of horsts and grabens south of Nevado de Toluca and allowed the intrusion of sub-vertical dikes oriented NW-SE and NNW-SSE. During the middle Miocene, a transcurrent episode generated NE-SW faults that presented two main motions: the first movement was left-lateral with a σ3 oriented NW-SE and later turned into normal through a counter-clockwise rotation of σ3 up to a N-S position. The latest deformation phase started during the late Pliocene and produced oblique extension ( σ3 oriented NE-SW) along E-W-trending faults that later changed to pure extension by shifting of σ3 to a N-S orientation. These faults appear to control the late Pleistocene to Holocene monogenetic volcanism, the flank collapses of Nevado de Toluca volcano and the seismic activity of the region.

  5. Smilax (Smilacaceae) from the Miocene of western Eurasia with Caribbean biogeographic affinities.

    Science.gov (United States)

    Denk, Thomas; Velitzelos, Dimitrios; Güner, H Tuncay; Ferrufino-Acosta, Lilian

    2015-03-01

    • Recent molecular studies provide a phylogenetic framework and some dated nodes for the monocot genus Smilax. The Caribbean Havanensis group of Smilax is part of a well-supported "New World clade" with a few disjunct taxa in the Old World. Although the fossil record of the genus is rich, it has been difficult to assign fossil taxa to extant groups based on their preserved morphological characters.• Leaf fossils from Europe and Asia Minor were studied comparatively and put into a phylogenetic and biogeographic context using a molecular phylogeny of the genus.• Fossils from the early Miocene of Anatolia represent a new species of Smilax with systematic affinities with the Havanensis group. The leaf type encountered in the fossil species is exclusively found in species of the Havanensis group among all modern Smilax. Scattered fossils of this type from the Miocene of Greece and Austria, previously referred to Quercus (Fagaceae), Ilex (Aquifoliaceae), and Mahonia (Berberidaceae) also belong to the new species.• The new Smilax provides first fossil evidence of the Havanensis group and proves that this group had a western Eurasian distribution during the Miocene. The age of the fossils is in good agreement with the (molecular-based) purported split between the Havanensis and Hispida groups within Smilax. The Miocene Smilax provides evidence that all four subclades within the "New World clade" had a disjunct intercontinental distribution during parts of the Neogene involving trans-Atlantic crossings (via floating islands or the North Atlantic land bridge) and the Beringia land bridge. © 2015 Botanical Society of America, Inc.

  6. Some observations on the Miocene foraminifera from Kachchh, Western India

    Digital Repository Service at National Institute of Oceanography (India)

    Jauhri, A.K.; Khare, N.

    The foraminiferal species described from the Miocene sequence exposed at the village Vinjhan of Kachchh are widely distributed in the comparable successions of the Middle East and Greece. They can be used for inter-regional correlation...

  7. Paleofaunal and Environmental Research on Miocene Fossil Sites TVOR SE and TVOR S on Fort Polk, Louisiana, with Continued Survey, Collection, Processing, and Documentation of other Miocene Localities

    National Research Council Canada - National Science Library

    Schiebout, Judith

    2004-01-01

    Focus of paleontological research on the Miocene of Fort Polk is currently the marine locality TVOR SE, which also has yielded large and small terrestrial Miocene vertebrates, and a single Cretaceous...

  8. Petrologic evolution of Miocene-Pliocene mafic volcanism in the Kangal and Gürün basins (Sivas-Malatya), central east Anatolia: Evidence for Miocene anorogenic magmas contaminated by continental crust

    Science.gov (United States)

    Kocaarslan, Ayça; Ersoy, E. Yalçın

    2018-06-01

    This study discusses the geochemical features of the Early-Middle Miocene and Pliocene basaltic (SiO2 = 46-52; MgO = 6-10 wt%) to andesitic (SiO2 = 59; MgO = 4 wt%) rocks exposed in the Gürün and Kangal basins (Sivas, eastern part of central Anatolia), respectively. The basaltic rocks are characterized by alkaline to tholeiitic affinities, while the more evolved andesitic samples show calc-alkaline affinity. Trace element variations reveal that they can be evaluated in three sub-groups, each represented by different contents of trace elements for given Nb contents. Primary magmas of each groups were likely produced by different degrees of partial melting ( 1-2, 2-3, 7-10% respectively) from a common mantle source, subsequently underwent different degrees of fractionation and crustal contamination. Derivation from a common mantle source of the primitive magmas of each group is supported by similar Sr, Nd and Pb isotopic ratios. Increasing degrees of partial melting seem to be responsible for the alkaline to tholeiitic variation among the basaltic samples, while higher degrees of crustal contamination (AFC) resulted in calc-alkaline affinity of the more evolved samples. Most primitive Pliocene samples show intra-plate (anorogenic) geochemical features, while the more evolved Miocene calc-alkaline samples resemble geochemically subduction-related (orogenic) magmatic rocks. However, on the basis of detailed geochemical models, we propose that the calc-alkaline affinity among the Miocene samples can also be gained by crustal contamination of their primary magmas which were also anorogenic in character. If this is true, overall, the Miocene and Pliocene basaltic to andesitic rocks in the Gürün and Kangal basins appear to may have formed by variable degrees of partial melting of a common anorogenic mantle that had not been subject to subduction-related metasomatism. This is an alternative approach to the general view assuming the Early-Middle Miocene magmatic activity

  9. Mid-Miocene C4 expansion on the Chinese Loess Plateau under an enhanced Asian summer monsoon

    Science.gov (United States)

    Dong, Jibao; Liu, Zhonghui; An, Zhisheng; Liu, Weiguo; Zhou, Weijian; Qiang, Xiaoke; Lu, Fengyan

    2018-06-01

    Atmospheric CO2 starvation, aridity, fire and warm season precipitation have all been proposed as major contributors to C4 plant expansion during the Late Miocene. However, the driving factors responsible for the distribution of C4 plants in the early and mid-Miocene still remain enigmatic. Here we report pedogenic carbon and oxygen isotope data (δ13Cpedo, δ18Opedo), along with magnetic susceptibility (MS) results, from the Zhuang Lang drilling core on the Chinese Loess Plateau (CLP). Elevated δ13Cpedo values (>-5‰) signal a prominent C4 expansion and substantially increased δ18Opedo and MS values indicate enhanced Asian summer monsoon (ASM) precipitation. Both of these conditions are observed during the Mid-Miocene Climatic Optimum (MMCO), 14.5-17 million years ago. The marked increase in C4 plants, associated with warm temperatures and increased precipitation, strongly suggests the control of an enhanced ASM on C4 expansion on the CLP during the MMCO. This finding contrasts with the late-Miocene C4 expansion associated with cooling and drying conditions observed in low latitudes and argues for regionally specific control of C4 plant distribution/expansion.

  10. 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.

  11. The Late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system

    Science.gov (United States)

    Latrubesse, Edgardo M.; Cozzuol, Mario; da Silva-Caminha, Silane A. F.; Rigsby, Catherine A.; Absy, Maria Lucia; Jaramillo, Carlos

    2010-05-01

    On the basis of paleontological content (vertebrates and palynology) and facies analysis from river banks, road cuts, and three wells, we have assigned the uppermost levels of the Solimões Formation in western Amazonia, Brazil, to the Late Miocene. The vertebrate fossil record from outcropping sediments is assigned to the Huayquerian-Mesopotamian mammalian biozones, spanning 9-6.5 Ma. Additionally, we present results that demonstrate that deposits in Peruvian Amazonia attributed to Miocene tidal environments are actually fluvial sediments that have been misinterpreted (both environmentally and chronologically) by several authors. The entire Late Miocene sequence was deposited in a continental environment within a subsiding basin. The facies analysis, fossil fauna content, and palynological record indicate that the environment of deposition was dominated by avulsive rivers associated with megafan systems, and avulsive rivers in flood basins (swamps, lakes, internal deltas, and splays). Soils developed on the flatter, drier areas, which were dominated by grasslands and gallery forest in a tropical to subtropical climate. These Late Miocene sediments were deposited from westward of the Purus arch up to the border of Brazil with Peru (Divisor Ranges) and Bolivia (Pando block). Eastward of the Iquitos structural high, however, more detailed studies, including vertebrate paleontology, need to be performed to calibrate with more precision the ages of the uppermost levels of the Solimões Formation. The evolution of the basin during the late Miocene is mainly related to the tectonic behavior of the Central Andes (˜ 3°-15°S). At approximately 5 Ma, a segment of low angle of subduction was well developed in the Nazca Plate, and the deformation in the Subandean foreland produced the inland reactivation of the Divisor/Contamana Ranges and tectonic arrangements in the Eastern Andes. During the Pliocene southwestern Brazilian Amazonia ceased to be an effective sedimentary

  12. Late Eocene to middle Miocene (33 to 13 million years ago) vegetation and climate development on the North American Atlantic Coastal Plain (IODP Expedition 313, Site M0027)

    Science.gov (United States)

    Kotthoff, U.; Greenwood, D. R.; McCarthy, F. M. G.; Müller-Navarra, K.; Prader, S.; Hesselbo, S. P.

    2014-08-01

    We investigated the palynology of sediment cores from Site M0027 of IODP (Integrated Ocean Drilling Program) Expedition 313 on the New Jersey shallow shelf to examine vegetation and climate dynamics on the east coast of North America between 33 and 13 million years ago and to assess the impact of over-regional climate events on the region. Palynological results are complemented with pollen-based quantitative climate reconstructions. Our results indicate that the hinterland vegetation of the New Jersey shelf was characterized by oak-hickory forests in the lowlands and conifer-dominated vegetation in the highlands from the early Oligocene to the middle Miocene. The Oligocene witnessed several expansions of conifer forest, probably related to cooling events. The pollen-based climate data imply an increase in annual temperatures from ∼11.5 °C to more than 16 °C during the Oligocene. The Mi-1 cooling event at the onset of the Miocene is reflected by an expansion of conifers and mean annual temperature decrease of ∼4 °C, from ∼16 °C to ∼12 °C around 23 million years before present. Relatively low annual temperatures are also recorded for several samples during an interval around ∼20 million years before present, which may reflect the Mi-1a and the Mi-1aa cooling events. Generally, the Miocene ecosystem and climate conditions were very similar to those of the Oligocene. Miocene grasslands, as known from other areas in the USA during that time period, are not evident for the hinterland of the New Jersey shelf, possibly reflecting moisture from the proto-Gulf Stream. The palaeovegetation data reveal stable conditions during the mid-Miocene climatic optimum at ∼15 million years before present, with only a minor increase in deciduous-evergreen mixed forest taxa and a decrease in swamp forest taxa. Pollen-based annual temperature reconstructions show average annual temperatures of ∼14 °C during the mid-Miocene climatic optimum, ∼2 °C higher than today

  13. On Prophoca and Leptophoca (Pinnipedia, Phocidae from the Miocene of the North Atlantic realm: redescription, phylogenetic affinities and paleobiogeographic implications

    Directory of Open Access Journals (Sweden)

    Leonard Dewaele

    2017-02-01

    Full Text Available Background Prophoca and Leptophoca represent the oldest known genera of phocine seals, dating from the latest early to middle Miocene. Originally, Prophoca rousseaui and Prophoca proxima were described based on fragmentary remains from the Miocene of Belgium. However, several researchers contested the union of Prophoca rousseaui and Prophoca proxima into one genus, without providing evidence. The stratigraphic context of Prophoca remained poorly constrained due to the lack of precise data associated with the original specimens collected in the area of Antwerp (north of Belgium. Methods Prophoca and Leptophoca are redescribed and their phylogenetic position among Phocidae is reassessed using PAUP. Dinoflagellate biostratigraphy has been carried out on sediment samples associated with specimens from Prophoca and Leptophoca to elucidate their approximate ages. Results Whereas the species Prophoca rousseaui is redescribed, Prophoca proxima is considered synonymous to Leptophoca lenis, with the proposal of a new combination Leptophoca proxima (Van Beneden, 1877. Sediment samples from specimens of both taxa have been dated to the late Langhian–early Serravallian (middle Miocene. Following a reinvestigation of Leptophoca amphiatlantica, characters from the original diagnosis are questioned and the specimens of Leptophoca amphiatlantica are considered Leptophoca cf. L. proxima. In a phylogenetic analysis, Prophoca rousseaui and Leptophoca proxima constitute early branching stem-phocines. Discussion Leptophoca proxima from the North Sea Basin is younger than the oldest known find of Leptophoca proxima from North America, which does not contradict the hypothesis that Phocinae originated along the east coast of North America during the late early Miocene, followed by dispersal to Europe shortly after. Morphological features of the appendicular skeleton indicate that Prophoca rousseaui and Leptophoca proxima have archaic locomotory modes, retaining a more

  14. Regional stratigraphy, sedimentology, and tectonic significance of Oligocene-Miocene sedimentary and volcanic rocks, northern Baja California, Mexico

    Science.gov (United States)

    Dorsey, Rebecca J.; Burns, Beverly

    1994-01-01

    Upper Oligocene (?) to middle Miocene sedimentary and volcanic rocks in northern Baja California were deposited along the western margin of North America during subduction of the Guadalupe plate and southward migration of the Rivera Triple Junction. Regional mapping and compilation of stratigraphic data reveal a sequence of three regionally traceable stratigraphic units. (1) Oligocene (?) to lower Miocene Mesa Formation: basal quartz-rich fluvial sandstone, grus, conglomerate, and accessory facies, whose detrital compositions reflect the composition of local pre-Tertiary basement rock. (2) Lower to middle Miocene Comondú Formation: laterally variable sequence of volcaniclastic conglomerate, breccia, sandstone, tuff and minor volcanic flow units. (3) Widespread mesa-capping rhyolite tuff, typically welded and crystal-rich, probably upper Miocene in age. The Mesa Formation overlies a highly irregular and deeply dissected erosional surface developed on pre-Tertiary basement rock. The shift from pre-Mesa erosion to widespread (though localized) deposition and valley-filling records the final phase of late Cretaceous to middle Tertiary regional subsidence and eastward transgression that resulted from slow cooling and thermal contraction of Cretaceous arc crust during a temporal gap in magmatic activity along the western Cordilleran margin. Nonmarine sediments of the Mesa Formation were deposited in small, steep-walled paleovalleys and basins that gradually filled and evolved to form through-going, low-energy ephemeral stream systems. The gradational upward transition from the Mesa to Comondú Formation records the early to middle Miocene onset of subduction-related arc magmatism in eastern Baja California and related westward progradation of alluvial volcaniclastic aprons shed from high-standing eruptive volcanic centers. Pre-existing streams were choked with the new influx of volcanic detritus, causing the onset of rapid sediment deposition by stream flows and dilute

  15. Earthquake-induced soft-sediment deformations and seismically amplified erosion rates recorded in varved sediments of Köyceğiz Lake (SW Turkey)

    KAUST Repository

    Avsar, Ulas

    2016-06-06

    Earthquake-triggered landslides amplify erosion rates in catchments, i.e. catchment response to seismic shocks (CR). In addition to historical eyewitness accounts of muddy rivers implying CRs after large earthquakes, several studies have quantitatively reported increased sediment concentrations in rivers after earthquakes. However, only a few paleolimnological studies could detect CRs within lacustrine sedimentary sequences as siliciclastic-enriched intercalations within background sedimentation. Since siliciclastic-enriched intercalations can easily be of non-seismic origin, their temporal correlation with nearby earthquakes is crucial to assign a seismic triggering mechanism. In most cases, either uncertainties in dating methods or the lack of recent seismic activity has prevented reliable temporal correlations, making the seismic origin of observed sedimentary events questionable. Here, we attempt to remove this question mark by presenting sedimentary traces of CRs in the 370-year-long varved sequence of Köyceğiz Lake (SW Turkey) that we compare with estimated peak ground acceleration (PGA) values of several nearby earthquakes. We find that earthquakes exceeding estimated PGA values of ca. 20 cm/s2 can induce soft-sediment deformations (SSD), while CRs seem only to be triggered by PGA levels higher than 70 cm/s2. In Köyceğiz Lake, CRs produce Cr- and Ni-enriched sedimentation due to the seismically mobilized soils derived from ultramafic rocks in the catchment. Given the varve chronology, the residence time of the seismically mobilized material in the catchment is determined to be 5 to 10 years.

  16. Two fossil species of Metrosideros (Myrtaceae) from the Oligo-Miocene Golden Fleece locality in Tasmania, Australia.

    Science.gov (United States)

    Tarran, Myall; Wilson, Peter G; Macphail, Michael K; Jordan, Greg J; Hill, Robert S

    2017-06-01

    The capsular-fruited genus Metrosideros (Myrtaceae) is one of the most widely distributed flowering plant genera in the Pacific but is extinct in Australia today. The center of geographic origin for the genus and the reason for and timing of its extinction in Australia remain uncertain. We identify fossil Metrosideros fruits from the newly discovered Golden Fleece fossil flora in the Oligo-Miocene of Tasmania, Australia, shedding further light on these problems. Standard paleopalynological techniques were used to date the fossil-bearing sediments. Scanning electron microscopy and an auto-montage camera system were used to take high-resolution images of fossil and extant fruits taken from herbarium specimens. Fossils are identified using a nearest-living-relative approach. The fossil-bearing sediments are palynostratigraphically dated as being Proteacidites tuberculatus Zone Equivalent (ca. 33-16 Ma) in age and provide a confident Oligo-Miocene age for the macrofossils. Two new fossil species of Metrosideros are described and are here named Metrosideros dawsonii sp. nov. and Metrosideros wrightii sp. nov. These newly described fossil species of Metrosideros provide a second record of the genus in the Cenozoic of Australia, placing them in the late Early Oligocene to late Early Miocene. It is now apparent not only that Metrosideros was present in Australia, where the genus is now extinct, but that at least several Metrosideros species were present during the Cenozoic. These fossils further strengthen the case for an Australian origin of the genus. © 2017 Botanical Society of America.

  17. A partial skeleton of a new lamniform mackerel shark from the Miocene of Europe

    Directory of Open Access Journals (Sweden)

    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.

  18. Climate aberrations during the middle Miocene: evidence from the eastern North Atlantic Ocean

    NARCIS (Netherlands)

    Quaijtaal, W.; Donders, T.H.; Schouten, S.; Louwye, S.

    2013-01-01

    During the Middle Miocene Climatic Optimum (MMCO; 17-14.5 Ma) the relatively warm climate of the Miocene reached peak temperatures. After the MMCO, the global climate started cooling through several short-lived cooling events, represented by positive oxygen isotope excursions: the Mi-events (Miocene

  19. Eocene and Miocene extension, meteoric fluid infiltration, and core complex formation in the Great Basin (Raft River Mountains, Utah)

    Science.gov (United States)

    Methner, Katharina; Mulch, Andreas; Teyssier, Christian; Wells, Michael L.; Cosca, Michael A.; Gottardi, Raphael; Gebelin, Aude; Chamberlain, C. Page

    2015-01-01

    Metamorphic core complexes (MCCs) in the North American Cordillera reflect the effects of lithospheric extension and contribute to crustal adjustments both during and after a protracted subduction history along the Pacific plate margin. While the Miocene-to-recent history of most MCCs in the Great Basin, including the Raft River-Albion-Grouse Creek MCC, is well documented, early Cenozoic tectonic fabrics are commonly severely overprinted. We present stable isotope, geochronological (40Ar/39Ar), and microstructural data from the Raft River detachment shear zone. Hydrogen isotope ratios of syntectonic white mica (δ2Hms) from mylonitic quartzite within the shear zone are very low (−90‰ to −154‰, Vienna SMOW) and result from multiphase synkinematic interaction with surface-derived fluids. 40Ar/39Ar geochronology reveals Eocene (re)crystallization of white mica with δ2Hms ≥ −154‰ in quartzite mylonite of the western segment of the detachment system. These δ2Hms values are distinctively lower than in localities farther east (δ2Hms ≥ −125‰), where 40Ar/39Ar geochronological data indicate Miocene (18–15 Ma) extensional shearing and mylonitic fabric formation. These data indicate that very low δ2H surface-derived fluids penetrated the brittle-ductile transition as early as the mid-Eocene during a first phase of exhumation along a detachment rooted to the east. In the eastern part of the core complex, prominent top-to-the-east ductile shearing, mid-Miocene 40Ar/39Ar ages, and higher δ2H values of recrystallized white mica, indicate Miocene structural and isotopic overprinting of Eocene fabrics.

  20. Molluscan fauna from the Miocene sediments of Kachchh, Gujarat ...

    Indian Academy of Sciences (India)

    geological mapping of Kachchh was assigned to. Fedden and Wynne in the late ... Figure 1. Geological map of parts of Kachchh Region, Gujarat State, India; slightly modified after Biswas and Deshpande. Formational boundaries ...... division and correlation of Oligo–Miocene petroleum bearing strata in India and future ...

  1. A southern North Sea Miocene dinoflagellate cyst zonation

    NARCIS (Netherlands)

    Munsterman, D.K.; Brinkhuis, H.

    2004-01-01

    An integrated stratigraphical analysis emphasizing organic-walled dinoflagellate cyst (dinocyst) distribution has been carried out on multiple boreholes penetrating the Miocene in the subsurface of the Netherlands (southern North Sea Basin). The bulk of the investigated successions is attributed to

  2. 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

    , Palaeoecology 77, 203-234. Figueiredo, J., Hoorn, C., van der Veen, P., Soares, E. (2009): Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin. Geology; v. 37, no. 7; p. 619-622. Lear, C.H., Rosenthal, Y., Wright, J.D. (2003): The closing of a seaway: ocean water masses and global climate change. Earth and Planetary Science Letters 210, 425-436. Wright, J.D., Miller, K.G., Fairbanks, R.G. (1992): Early and middle Miocene stable isotopes: implications for deepwater circulation and climate. Paloceanography 7(3): 357-398.

  3. Late Miocene (Proto-Gulf) Extension and Magmatism on the Sonoran Margin

    Science.gov (United States)

    Gans, P.; MacMillan, I.; Roldan-Quintana, J.

    2003-12-01

    Constraints on the magnitude and character of late Miocene (Proto-Gulf) deformation on the Sonoran margin of the Gulf of California extensional province are key to understanding how and when Baja California was captured by the Pacific plate and how strain was partitioned during the early stages of this transtensional rift system. Our new geologic mapping in southwestern Sonora and 40Ar/39Ar dating of pre-, syn-, and post-tectonic volcanic units indicate that late Miocene deformation and volcanic activity were largely restricted to a NW-trending, 100-120 km wide belt adjacent to the coast. Inboard of this belt, NW-SE extension is mainly older (>15 Ma) and occurred in an intra-arc or back-arc setting. Proto-Gulf deformation within the coastal belt was profoundly transtensional, with NW-striking, dextral strike slip faults operating in concert with N-S and NNE-striking normal and oblique slip faults to produce an inferred NW or NNW tectonic transport direction. The total amount of late Miocene NW directed dextral shear within the coastal belt is still poorly constrained, but may exceed 100 km. The locus of deformation and volcanic activity migrated westward or northwestward within the Sonoran coastal belt. in the eastern portion (Sierra Libre and Sierra El Bacatete) major volcanic activity commenced at ˜13.0 Ma and peaked at 12.0 Ma, and major faulting and tilting is bracketed between 12.0 and 10.6 Ma. Further west in the Sierra El Aguaje/San Carlos region, major volcanic activity commenced at 11.5 Ma and peaked at 10.5 Ma, and most faulting and tilting is bracketed between 10.7 and 9.3 Ma. On the coastal mountains northwest of San Carlos, rift related faulting and tilting continued after 8.5 Ma. Voluminous late Miocene (13-8 Ma) volcanic rocks within the Sonoran coastal belt were erupted from numerous centers (e.g. Sierra Libre, Guaymas, Sierra El Aguaje). These thick volcanic sections are compositionally diverse (basalt to rhyolite, with abundant dacite and

  4. 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.

  5. A MIDDLE MIOCENE BALEEN WHALE FROM BELE VODE IN BELGRADE, SERBIA

    Directory of Open Access Journals (Sweden)

    PAVEL GOL’DIN

    2018-01-01

    Full Text Available There was a fauna of baleen whales (Cetacea: Mysticeti in the Central Paratethys, a Miocene water body which covered the area of present-day Central Europe. Most of the fossil baleen whales from the Central Paratethys have been found in strata assigned to the regional Badenian age and comprise endemic forms, known only from this region. Here a new description is provided for a fragmentary skeleton of a whale found in Belgrade, Serbia, and its age context and biological aspects are discussed. This specimen, consisting of a fragmentary horizontal ramus of the mandible and eight caudal vertebrae, is tentatively identified as ?Parietobalaena sp., a globally known Miocene taxon, with related forms having been recorded earlier from the Eastern Paratethys. An early Sarmatian age (i.e., about 12.7-12.4 Ma is proposed for the specimen. Based on epiphyseal fusion of caudal vertebrae, the specimen’s age is identified as a subadult, with a body length of around 2.5 m and an estimated adult body length around 3-3.5 m, which is extremely small for baleen whales. This find represents one of the latest records of baleen whales in the Central Paratethys and one of the latest published records of Parietobalaena-like taxa in the world.

  6. ON THE PRESENCE OF PYRAMIODONTHERIUM (MAMMALIA, XENARTHRA, MEGATHERIIDAE IN THE LATE MIOCENE OF NORTHEASTERN ARGENTINA AND ITS BIOGEOGRAPHICAL IMPLICATIONS

    Directory of Open Access Journals (Sweden)

    DIEGO BRANDONI

    2009-03-01

    Full Text Available The biochron of the subfamily Megatheriinae, large to very large terrestrial sloths typified by Megatherium Cuvier, in Argentina extends from the middle Miocene of Patagonia to the late Pleistocene-early Holocene. Megatheriines reached their highest diversity in the lower levels (="conglomerado osífero", late Miocene of the Ituzaingó Formation in Entre Ríos Province, northeastern Argentina. Among the four megatheriines that occur in this unit, the genera Promegatherium Ameghino, Eomegatherium Kraglievich and Pliomegatherium Kraglievich represent relatively small to medium-sized taxa. Here we describe new material assigned to Pyramiodontherium, the largest of the four genera from the same bed and comparable in size to some Quaternary species of Megatherium. Three valid species of Pyramiodontherium have been recognized, all distributed mainly in northwestern Argentina, from the late Miocene in Catamarca Province (and probably also in Tucumán Province, and the late Pliocene in La Rioja Province. The presence of this genus in northeastern Argentina extends its known paleobiogeographical distribution. 

  7. A southern species of the tropical catfish genus Phractocephalus (Teleostei: Siluriformes) in the Miocene of South America

    Science.gov (United States)

    Azpelicueta, María de las Mercedes; Cione, Alberto Luis

    2016-04-01

    Catfish bones from Tortonian (Miocene) freshwater beds of central Argentina are here identified as pertaining to a new species of the tropical pimelodid genus Phractocephalus. The new species differs from the other recent and fossil species of the genus in skull, pectoral girdle and spine characters. The material was found in different localities near the city of Paraná, Entre Ríos Province. The bearing horizon is the so-called "Conglomerado osífero" which constitutes the lowermost beds of the fluvial Ituzaingó Formation. The aquatic vertebrate fauna occurring in the bearing bed shows a similar generic composition to several northern South American Miocene units where Phractocephalus remains were found. This report extends the range of Phractocephalus more than 2000 km to the South. The record is in agreement with higher global temperatures and putative ample hydrographic connections of the river basins in the Paraná area with the Amazon basin until at least the early late Miocene.

  8. The Rajang Unconformity: Major provenance change between the Eocene and Miocene sequences in NW Borneo

    Science.gov (United States)

    Breitfeld, H. T.; Hennig, J.; BouDagher-Fadel, M.; Hall, R.

    2017-12-01

    The offshore Sarawak Basin NW of North Sarawak is a major hydrocarbon province in SE Asia. A very thick sedimentary sequence of Oligocene to ?Early Miocene age, named Cycle 1, is an important hydrocarbon source and reservoir. Despite numerous wells the stratigraphy and tectonic history is not very well understood. The Nyalau Formation of onshore North Sarawak is the supposed equivalent of the offshore Cycle 1 sequence. The Nyalau Formation is a thick sedimentary sequence of mainly tidal to deltaic deposits. The formation is dominated by well-bedded sandstone-mudstone alternations and thicker sandstones with abundant bioturbation. The sandstones are predominantly arenaceous. Various lithic fragments and feldspar indicate multiple sources and fresh input from igneous and metamorphic rocks. Interbedded thin limestone beds and marls yielded Early Miocene foraminifera for the upper part of the succession. Zircons separated from the sandstones yielded mainly Cretaceous and Triassic ages. The Triassic is the dominant age population. The Nyalau Formation conformably overlies the Buan Shale and the Tatau Formation, and in places unconformably overlies the Belaga Formation. The Belaga Formation is part of the Rajang Group that represents remnants of a large submarine fan deposited in the Late Cretaceous to Eocene in Central Sarawak. In contrast to the Nyalau Formation, the majority of zircons from the Rajang Group have Cretaceous ages. This marks an important change in provenance at the major unconformity separating the Belaga and Nyalau Formations. This unconformity was previously interpreted as the result of an orogeny in the Late Eocene. However, there is no evidence for a subduction or collision event at this time in Sarawak. We interpret it to mark plate reorganisation in the Middle Eocene and name it the Rajang Unconformity. Borneo is the principal source of Cretaceous zircons which were derived from the Schwaner Mountains and West Sarawak. The dominant Triassic zircon

  9. Late Miocene extensional systems in northern Tunisia and their relation with SE directed delamination of the African subcontinental mantle lithosphere

    Science.gov (United States)

    Booth-Rea, Guillermo; Gaidi, Seif; Melki, Fetheddine; Pérez-Peña, Vicente; Marzougui, Wissem; Azañón, Jose Miguel; Galve, Jorge Pedro

    2017-04-01

    Recent work has proposed the delamination of the subcontinental mantle lithosphere under northern Tunisia during the late Miocene. This process is required to explain the present location of the Tunisian segment of the African slab, imaged by seismic tomography, hanging under the Gulf of Gabes to the south of Tunisia. Thus, having retreated towards the SE several hundred km from its original position under the Tellian-Atlas nappe contact that crops out along the north of Tunisia. However, no tectonic structures have been described which could be related to this mechanism of lithospheric mantle peeling. Here we describe for the first time extensional fault systems in northern Tunisia that strongly thinned the Tellian nappes, exhuming rocks from the Tunisian Atlas in the core of folded extensional detachments. Two normal fault systems with sub-orthogonal extensional transport occur. These were active during the late Miocene associated to the extrusion of 13 Ma granodiorite and 9 Ma rhyodacite in the footwall of the Nefza detachment. We have differentiated an extensional system formed by low-angle normal faults with NE- and SW-directed transport cutting through the Early to Middle Miocene Tellian nappen stack and a later system of low and high-angle normal faults that cuts down into the underlying Tunisian Atlas units with SE-directed transport, which root in the Nefza detachment. Both normal fault systems have been later folded and cut by thrusts during Plio-Quaternary NW-SE directed compression. These findings change the interpretation of the tectonic evolution of Tunisia that has always been framed in a transpressive to compressive setting, manifesting the extensional effects of Late Miocene lithospheric mantle delamination under northern Tunisia.

  10. Reduction in Surface Ocean Carbon Storage across the Middle Miocene

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    Babila, T. L.; Sosdian, S. M.; Foster, G. L.; Lear, C. H.

    2017-12-01

    During the Middle Miocene, Earth underwent a profound climate shift from the warmth of the Miocene Climatic Optimum (MCO; 14-17 Ma) to the stable icehouse of today during the Middle Miocene Climate transition (MMCT). Elevated atmospheric carbon dioxide concentrations (pCO2) revealed by boron isotope records (δ11B) link massive volcanic outputs of Columbia River Flood Basalts to the general warmth of MCO. Superimposed on the long-term cooling trend (MMCT) is a gradual pCO2 decline and numerous positive carbon isotope (δ13C) excursions that indicate dynamic variations in the global carbon cycle. Enhanced organic carbon burial via marine productivity, increased silicate weathering and volcanic emission cessation are each invoked to explain the drawdown of pCO2. To better constrain the oceanic role in carbon sequestration over the Middle Miocene detailed records of carbonate chemistry are needed. We present high resolution Boron/Calcium (B/Ca) and δ13C records in planktonic foraminifer T.trilobus spanning 12-17 Ma at ODP 761 (tropical eastern Indian Ocean) to document changes in surface ocean carbonate chemistry. An overall 30% increase in B/Ca ratios is expressed as two stepwise phases occurring at 14.7 and 13 Ma. Cyclic B/Ca variations are coherent with complimentary δ13C records suggesting a tight coupling between ocean carbonate chemistry parameters. Lower resolution B/Ca data at DSDP 588 (Pacific) and ODP 926 (Atlantic) corroborate the trends observed at ODP 761. We employ a paired approach that combines B/Ca (this study) to δ11B (Foster et al., 2012) and an ad hoc calibration to estimate changes in surface ocean dissolved inorganic carbon (DIC). We estimate a substantial decrease in surface ocean DIC spanning the Middle Miocene that culminates with modern day like values. This gradual decline in surface ocean DIC is coeval with existing deep-ocean records which together suggests a whole ocean reduction in carbon storage. We speculate that enhanced weathering

  11. Dental remains of cebid platyrrhines from the earliest late Miocene of Western Amazonia, Peru: Macroevolutionary implications on the extant capuchin and marmoset lineages.

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    Marivaux, Laurent; Adnet, Sylvain; Altamirano-Sierra, Ali J; Pujos, François; Ramdarshan, Anusha; Salas-Gismondi, Rodolfo; Tejada-Lara, Julia V; Antoine, Pierre-Olivier

    2016-11-01

    Undoubted fossil Cebidae have so far been primarily documented from the late middle Miocene of Colombia, the late Miocene of Brazilian Amazonia, the early Miocene of Peruvian Amazonia, and very recently from the earliest Miocene of Panama. The evolutionary history of cebids is far from being well-documented, with notably a complete blank in the record of callitrichine stem lineages until and after the late middle Miocene (Laventan SALMA). Further documenting their evolutionary history is therefore of primary importance. Recent field efforts in Peruvian Amazonia (Contamana area, Loreto Department) have allowed for the discovery of an early late Miocene (ca. 11 Ma; Mayoan SALMA) fossil primate-bearing locality (CTA-43; Pebas Formation). In this study, we analyze the primate material, which consists of five isolated teeth documenting two distinct Cebidae: Cebus sp., a medium-sized capuchin (Cebinae), and Cebuella sp., a tiny marmoset (Callitrichinae). Although limited, this new fossil material of platyrrhines contributes to documenting the post-Laventan evolutionary history of cebids, and besides testifies to the earliest occurrences of the modern Cebuella and Cebus/Sapajus lineages in the Neotropics. Regarding the evolutionary history of callitrichine marmosets, the discovery of an 11 Ma-old fossil representative of the modern Cebuella pushes back by at least 6 Ma the age of the Mico/Cebuella divergence currently proposed by molecular biologists (i.e., ca. 4.5 Ma). This also extends back to > 11 Ma BP the divergence between Callithrix and the common ancestor (CA) of Mico/Cebuella, as well as the divergence between the CA of marmosets and Callimico (Goeldi's callitrichine). This discovery from Peruvian Amazonia implies a deep evolutionary root of the Cebuella lineage in the northwestern part of South America (the modern western Amazon basin), slightly before the recession of the Pebas mega-wetland system (PMWS), ca. 10.5 Ma, and well-before the subsequent

  12. An initial examination of carbonate variability in the western equatorial Pacific: XRF results from the lower to middle Miocene of IODP Site U1490

    Science.gov (United States)

    Valerio, D. A.; Kulhanek, D. K.; Rosenthal, Y.; Holbourn, A. E.

    2017-12-01

    International Ocean Discovery Program (IODP) Expedition 363 sought to determine the nature of and driving forces behind climate variability in the Western Pacific Warm Pool (WPWP) region throughout the Neogene on millennial, orbital, and geologic timescales. Our research focuses on the Miocene (19-9 Ma) sediment record from IODP Site U1490 to examine changes in carbonate production and burial in the WPWP as a record of variations in the regional/global carbon cycle. This interval is of particular interest because it spans the Middle Miocene Climatic Optimum, the Middle Miocene Climate Transition, and the late Miocene carbonate crash. Site U1490 is located on the northern edge of Eauripik Rise at 05°58.95'N, 142°39.27'E in the northern part of the WPWP. At 2341 m water depth, today the site is bathed in Upper Circumpolar Deepwater. Miocene sediment at Site U1490 primarily consists of clay-bearing to clay-rich foraminifer-rich nannofossil ooze, although biogenic silica (primarily radiolaria) is a significant component in the lowermost part of the record. The sedimentation rate in the early to middle Miocene was very low (calcium carbonate content of 87 wt% throughout the site, with the most significant variations in the lower to middle Miocene, where contents range from 20 to 85 wt%. We collected X-ray fluorescence (XRF) data at 1 cm resolution along the composite stratigraphic section over the 19-9 Ma interval to obtain a qualitative measure of the bulk chemistry of the sediment. We will use the weight percent calcium carbonate of discrete samples to calibrate the XRF data to generate a high-resolution carbonate record. We observe cyclical variations in the Ca/Ba, which may reflect variations in productivity and/or dissolution through this interval, although additional work is needed to fully interpret these data. Ultimately our research will allow for comparison between records obtained from these cores located in the western equatorial Pacific to those obtained

  13. Fluids circulation during the Miocene rifting of the Penedès half-graben, NE Iberian Peninsula

    Science.gov (United States)

    Baqués, Vinyet; Travé, Anna; Cantarero, Irene

    2013-04-01

    The Penedès half-graben, located in the north-western part of the Mediterranean, is a NE-SW oriented basin generated during the Miocene rifting. This graben is bounded to the northwest by the SE-dipping Vallès-Penedès fault, which places the Mesozoic rocks in contact with the Miocene basin-fill. The basin is filled with an up to 4 km thick succession of sediments divided into three lithostratigraphic units. From base to top: (1) a lower continental complex, (2) a continental to marine complex and (3) an upper continental complex. These units are covered by Pliocene deposits which onlap a Messinian regional erosive surface. The structural features within the Penedès half-graben allow defining three deformational phases during the Miocene rifting. The first, during the syn-rift, two successive stages of NE-SW normal faults were formed. The second, during the early post-rift, one stage of NE-SW normal faults and one minor compression phase with a dextral directional developed. The third, during the late post-rift, two successive stages of N-S trending extensional fractures (faults and joints) and one minor compression with a sinistral component developed. The fractures related to the syn-rift stage acted as conduits for meteoric fluids both, in the phreatic and in the vadose zone. During the early post-rift, Fe2+- rich fluids precipitated oxides along the NE-SW fault planes. The dextral directional faults served as conduits for meteoric fluids which reequilibrated totally the marine Miocene host rocks under the phreatic environment. The late post-rift stage was characterized by marine fluids upflowing through the N-S fractures, probably derived from the Miocene marine interval, which mixed with meteoric fluids producing dolomitization. The second set of N-S fractures served as conduits for meteoric fluids characterised by δ13C-depleted soil-derived CO2 attributed to precipitation in the vadose zone. The change from phreatic to vadose meteoric environment and the

  14. Exceptional preservation of Miocene pollen: plasmolysis captured in salt?

    Energy Technology Data Exchange (ETDEWEB)

    Durska, W.

    2016-07-01

    Exceptionally well-preserved Miocene pollen from the Bochnia salt mine of southern Poland is reported herein. The halite deposits within the salt mine belonging to Late Badenian (Miocene) marine evaporites originated in the Paratethys. Rounded and angular structures are present inside pollen grains. On the basis of the similarity with plasmolyzed pollen grains of modern plants, these structures are considered to represent cytoplasms plasmolyzed in the condensed brine prior to fossilization. Two forms of plasmolyzed cytoplasms (concave and convex) can be observed in modern pollen. Both are distinguished in the investigated fossil material. In porate and colporate grains the shape of the plasmolyzed cellular content is concave while in inaperturate it is convex. The plasmolysis form depends on the type of apertures and pollen shape. The percentage of pollen with fossilized cytoplasms within individual taxa is a valuable environmental indicator, as it depends on the proximity of the pollen-producing plant assemblages to the depositional setting. (Author)

  15. 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.

  16. PROPOTAMOCHOERUS SP. (SUIDAE, MAMMALIA FROM THE LATE MIOCENE OF GRAVITELLI (MESSINA, SICILY, ITALY REDISCOVERED

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    GIANNI GALLAI

    2006-07-01

    Full Text Available This paper describes two casts of a suid from the Late Miocene of Gravitelli (Messina, Sicily, originally described by Seguenza in 1902. The entire Gravitelli faunal collection was lost in the early 1900¡¦s. The recent rediscovery of two casts in the collections of the Museo di Storia Naturale of the University of Florence represent the only available material from this locality (in addition to the original description and illustration by Seguenza. The study of these casts allow a revision of the Gravitelli suid and its attribution to the genus Propotamochoerus. Although a specific determination is not possible, we suggest probable affinities with the species P. hysudricus or P. provincialis.

  17. Miocene volcanism in the Oaş-Gutâi Volcanic Zone, Eastern Carpathians, Romania: Relationship to geodynamic processes in the Transcarpathian Basin

    Science.gov (United States)

    Kovacs, Marinel; Seghedi, Ioan; Yamamoto, Masatsugu; Fülöp, Alexandrina; Pécskay, Zoltán; Jurje, Maria

    2017-12-01

    We present the first comprehensive study of Miocene volcanic rocks of the Oaş-Gutâi Volcanic Zone (OGVZ), Romania, which are exposed in the eastern Transcarpathian Basin (TB), within the Eastern Alpine-Western Carpathian-Northern Pannonian (ALCAPA) block. Collision between the ALCAPA block and Europe at 18-16 Ma produced the Carpathian fold-and-thrust belt. This was followed by clockwise rotation and an extensional regime forming core complexes of the separated TB fragment. Based on petrographic and geochemical data, including Srsbnd Nd isotopic compositions and Ksbnd Ar ages, we distinguish three types of volcanic activity in the OGVZ: (1) early Miocene felsic volcanism that produced caldera-related ignimbrites in the Gutâi Mountains (15.4-14.8 Ma); (2) widespread middle-late Miocene intermediate/andesitic volcanism (13.4-7.0 Ma); and (3) minor late Miocene andesitic/rhyolitic volcanism comprising the Oraşu Nou rhyolitic volcano and several andesitic-dacitic domes in the Oaş Mountains (11.3-9.5 Ma). We show that magma evolution in the OGVZ was controlled by assimilation-fractional crystallization and magma-mixing processes within an interconnected multi-level crustal magmatic reservoir. The evolution of volcanic activity within the OGVZ was controlled by the geodynamics of the Transcarpathian Basin. The early felsic and late intermediate Miocene magmas were emplaced in a post-collisional setting and were derived from a mantle source region that was modified by subduction components (dominantly sediment melts) and lower crust. The style of volcanism within the eastern TB system exhibits spatial variations, with andesitic composite volcanoes (Gutâi Mountains) observed at the margins, and isolated andesitic-rhyolitic monogenetic volcanoes (Oaş Mountains) in the center of the basin.

  18. Oligocene stratigraphy across the Eocene and Miocene boundaries in the Valley of Lakes (Mongolia).

    Science.gov (United States)

    Daxner-Höck, Gudrun; Badamgarav, Demchig; Barsbold, Rinchen; Bayarmaa, Baatarjav; Erbajeva, Margarita; Göhlich, Ursula Bettina; Harzhauser, Mathias; Höck, Eva; Höck, Volker; Ichinnorov, Niiden; Khand, Yondon; López-Guerrero, Paloma; Maridet, Olivier; Neubauer, Thomas; Oliver, Adriana; Piller, Werner; Tsogtbaatar, Khishigjav; Ziegler, Reinhard

    2017-01-01

    Cenozoic sediments of the Taatsiin Gol and TaatsiinTsagaan Nuur area are rich in fossils that provide unique evidence of mammal evolution in Mongolia. The strata are intercalated with basalt flows. 40 Ar/ 39 Ar data of the basalts frame the time of sediment deposition and mammal evolution and enable a composite age chronology for the studied area. We investigated 20 geological sections and 6 fossil localities of Oligocene and early Miocene deposits from this region. Seventy fossil beds yielded more than 19,000 mammal fossils. This huge collection encompasses 175 mammal species: 50% Rodentia, 13% Eulipotyphla and Didelphomorphia, and 12% Lagomorpha. The remaining 25% of species are distributed among herbivorous and carnivorous large mammals. The representation of lower vertebrates and gastropods is comparatively poor. Several hundred SEM images illustrate the diversity of Marsupialia, Eulipotyphla, and Rodentia dentition and give insight into small mammal evolution in Mongolia during the Oligocene and early Miocene. This dataset, the radiometric ages of basalt I (∼31.5 Ma) and basalt II (∼27 Ma), and the magnetostratigraphic data provide ages of mammal assemblages and time ranges of the Mongolian biozones: letter zone A ranges from ∼33 to ∼31.5 Ma, letter zone B from ∼31.5 to ∼28 Ma, letter zone C from ∼28 to 25.6 Ma, letter zone C1 from 25.6 to 24 Ma, letter zone C1-D from 24 to ∼23 Ma, and letter zone D from ∼23 to ∼21 Ma.

  19. Chronology of Eocene-Miocene sequences on the New Jersey shallow shelf: implications for regional, interregional, and global correlations

    Science.gov (United States)

    Browning, James V.; Miller, Kenneth G.; Sugarman, Peter J.; Barron, John; McCarthy, Francine M.G.; Kulhanek, Denise K.; Katz, Miriam E.; Feigenson, Mark D.

    2013-01-01

    Integrated Ocean Drilling Program Expedition 313 continuously cored and logged latest Eocene to early-middle Miocene sequences at three sites (M27, M28, and M29) on the inner-middle continental shelf offshore New Jersey, providing an opportunity to evaluate the ages, global correlations, and significance of sequence boundaries. We provide a chronology for these sequences using integrated strontium isotopic stratigraphy and biostratigraphy (primarily calcareous nannoplankton, diatoms, and dinocysts [dinoflagellate cysts]). Despite challenges posed by shallow-water sediments, age resolution is typically ±0.5 m.y. and in many sequences is as good as ±0.25 m.y. Three Oligocene sequences were sampled at Site M27 on sequence bottomsets. Fifteen early to early-middle Miocene sequences were dated at Sites M27, M28, and M29 across clinothems in topsets, foresets (where the sequences are thickest), and bottomsets. A few sequences have coarse (∼1 m.y.) or little age constraint due to barren zones; we constrain the age estimates of these less well dated sequences by applying the principle of superposition, i.e., sediments above sequence boundaries in any site are younger than the sediments below the sequence boundaries at other sites. Our age control provides constraints on the timing of deposition in the clinothem; sequences on the topsets are generally the youngest in the clinothem, whereas the bottomsets generally are the oldest. The greatest amount of time is represented on foresets, although we have no evidence for a correlative conformity. Our chronology provides a baseline for regional and interregional correlations and sea-level reconstructions: (1) we correlate a major increase in sedimentation rate precisely with the timing of the middle Miocene climate changes associated with the development of a permanent East Antarctic Ice Sheet; and (2) the timing of sequence boundaries matches the deep-sea oxygen isotopic record, implicating glacioeustasy as a major driver

  20. Metasomatized mantle as the source of Mid-Miocene-Quaternary volcanism in NW-Iranian Azerbaijan: Geochronological and geochemical evidence

    Science.gov (United States)

    Lechmann, Anna; Burg, Jean-Pierre; Ulmer, Peter; Guillong, Marcel; Faridi, Mohammad

    2018-04-01

    Middle Miocene to Quaternary volcanic rocks cover large areas of the Azerbaijan Province in NW Iran. This study reports two separate age clusters out of 23 new LA-ICP-MS U-Pb zircon ages: (1) Middle Miocene (16.2-10.6 Ma) and (2) Latest Miocene-Late Pleistocene (5.5-0.4 Ma). Major and trace element bulk rock geochemistry and initial Sr, Nd, Pb radiogenic isotope data on the dated rocks provide new constraints on the Mid-Miocene to Quaternary volcanism in this region. The analyses are distributed over a large compositional range from low-K to high-K calc-alkaline andesites and dacites/rhyolites to more alkaline trachybasalts and dacites with shoshonitic affinities. Chondrite-normalized REE patterns are steep with significant enrichment in LREE and low abundances of HREE indicating a garnet control. Plots of primitive mantle-normalized trace elements show negative Ti and Nb-Ta anomalies indicative of an arc signature. The wide compositional range and the ubiquitous presence of an arc signature reveal that the source mantle is heterogeneous and metasomatically altered. Sr, Nd and Pb radiogenic isotope data further point towards an enriched mantle source and/or crustal contamination. Crustal contamination is best recognized by inherited zircon cores, which yield Late Neoproterozoic to Early Cambrian ages typical for the Iranian basement. The occurrence of adakite-like compositions with elevated magnesium numbers, Cr and Ni concentrations argue against a fractionation-driven process but point to a subcrustal origin. Overall, the analyzed lavas show no spatial and temporal relation to a potential subduction zone, confirming the dated volcanics to be post-collisional and not related to singular processes such as slab retreat or delamination of a continuous lower crustal sliver. We propose three hypotheses to explain the reported disparity in distribution, age and composition and favour small-scale sublithospheric convection or incorporation of crustal material into the

  1. Miocene vegetation shift and climate change: Evidence from the Siwalik of Nepal

    Science.gov (United States)

    Srivastava, Gaurav; Paudayal, Khum N.; Utescher, Torsten; Mehrotra, R. C.

    2018-02-01

    We reconstruct climate and vegetation applying the Coexistence Approach (CA) methodology on two palaeofloras recovered from the Lower (middle Miocene; 13-11 Ma) and Middle Siwalik (late Miocene; 9.5-6.8 Ma) sediments of Surai Khola section, Nepal. The reconstructed mean annual temperature (MAT) and cold month mean temperature (CMT) show an increasing trend, while warm month mean temperature (WMT) remains nearly the same during the period. The reconstructed precipitation data indicates that the summer monsoon precipitation was nearly the same during the middle and late Miocene, while the winter season precipitation significantly decreased in the late Miocene. The overall precipitation infers increased rainfall seasonality during the late Miocene. The vegetation during the middle Miocene was dominated by wet evergreen taxa, whereas deciduous ones increased significantly during the late Miocene. The reconstructed climate data indicates that high temperature and significantly low precipitation during the winter season (dry season) in the late Miocene might have enhanced forest fire which favoured the expansion of C4 plants over C3 plants during the period. This idea gets further support not only from a recent forest fire in northern India that was caused by the weakening of winter precipitation, but also from the burnt wood recovered from the late Miocene Siwalik sediments of northern India.

  2. Origin, evolution and sedimentary processes associated with a late Miocene submarine landslide, southeast Spain

    Science.gov (United States)

    Sola, F.; Puga-Bernabéu, Á.; Aguirre, J.; Braga, J. C.

    2018-02-01

    A submarine landslide, the Alhama de Almería Slide, influenced late Tortonian and early Messinian (late Miocene) sedimentary processes in the vicinity of Alhama de Almería in southeast Spain. Its 220-m-high headscarp and deposits are now subaerially exposed. The landslide occurred at the northern slope of the antecedent relief of the present-day Sierra de Gádor mountain range. This is a large antiform trending east-west to east-northeast-west-southwest, which has been uplifting since the late Miocene due to convergence of the African and Eurasian plates. During the Tortonian, this relief was an island separated from the Iberian Peninsula mainland by the Alpujarra corridor, a small and narrow intermontane basin of the Betic Cordillera in the western Mediterranean Sea. The materials involved in the slope failure were Triassic dolostones and phyllites from the metamorphic Alpujárride Complex and Tortonian marine conglomerates, sandstones, and marls that formed an initial sedimentary cover on the basement rocks. Coherent large masses of metamorphic rocks and Miocene deposits at the base of the headscarp distally change to chaotic deposits of blocks of different lithologies embedded in upper Tortonian marine marls, and high-strength cohesive debrites. During downslope sliding, coherent carbonate blocks brecciated due to their greater strength. Phyllites disintegrated, forming a cohesive matrix that engulfed and/or sustained the carbonate blocks. Resedimented, channelized breccias were formed by continuing clast collision, bed fragmentation, and disaggregation of the failed mass. The conditions leading to rock/sediment failure were favoured by steep slopes and weak planes at the contact between the basement carbonates and phyllites. Displacement of collapsed rocks created a canyon-like depression at the southeast edge of the landslide. This depression funnelled sediment gravity flows that were generated upslope, promoting local thick accumulations of sediments during

  3. Late oligocene and miocene faulting and sedimentation, and evolution of the southern Rio Grande rift, New Mexico, USA

    Science.gov (United States)

    Mack, Greg H.; Seager, William R.; Kieling, John

    1994-08-01

    The distribution of nonmarine lithofacies, paleocurrents, and provenance data are used to define the evolution of late Oligocene and Miocene basins and complementary uplifts in the southern Rio Grande rift in the vicinity of Hatch, New Mexico, USA. The late Oligocene-middle Miocene Hayner Ranch Formation, which consists of a maximum of 1000 m of alluvial-fan, alluvial-flat, and lacustrine-carbonate lithofacies, was deposited in a narrow (12 km), northwest-trending, northeast-tilted half graben, whose footwall was the Caballo Mountains block. Stratigraphic separation on the border faults of the Caballo Mountains block was approximately 1615 m. An additional 854 m of stratigraphic separation along the Caballo Mountains border faults occurred during deposition of the middle-late Miocene Rincon Valley Formation, which is composed of up to 610 m of alluvial-fan, alluvial-flat, braided-fluvial, and gypsiferous playa lithofacies. Two new, north-trending fault blocks (Sierra de las Uvas and Dona Ana Mountains) and complementary west-northwest-tilted half graben also developed during Rincon Valley time, with approximately 549 m of stratigraphic separation along the border fault of the Sierra de las Uvas block. In latest Miocene and early Pliocene time, following deposition of the Rincon Valley Formation, movement continued along the border faults of the Caballo Mountains, Dona Ana Mountains, and Sierra de las Uvas blocks, and large parts of the Hayner Ranch and Rincon Valley basins were segmented into smaller fault blocks and basins by movement along new, largely north-trending faults. Analysis of the Hayner Ranch and Rincon Valley Formations, along with previous studies of the early Oligocene Bell Top Formation and late Pliocene-early Pleistocene Camp Rice Formation, indicate that the traditional two-stage model for development of the southern Rio Grande rift should be abandoned in favor of at least four episodes of block faulting beginning 35 Ma ago. With the exception of

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

    Directory of Open Access Journals (Sweden)

    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.

  5. Description of Karaganops n. gen. perratus (Daniltshenko 1970) with otoliths in situ, an endemic Karaganian (Middle Miocene) herring (Clupeidae) in the Eastern Paratethys

    DEFF Research Database (Denmark)

    Baykina, Eugenia M.; Schwarzhans, Werner

    2017-01-01

    Karaganops is established as a new fossil genus of the family Clupeidae, subfamily Clupeinae, to encompass the nominal species Sardinella perrata Daniltshenko 1970 from the Karaganian of southern Russia. Karaganops belongs to the group of genera characterized by the presence of two elongated rays...... fossil record reaches back in time to Early Miocene and possibly Late Oligocene in the North Sea Basin....

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

    Directory of Open Access Journals (Sweden)

    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

  7. Natural product terpenoids in Eocene and Miocene conifer fossils.

    Science.gov (United States)

    Otto, Angelika; White, James D; Simoneit, Bernd R T

    2002-08-30

    Numerous saturated and aromatic hydrocarbons, but not polar compounds, originating from plants and microorganisms (biomarkers) have been reported in sediments, coals, and petroleum. Here we describe natural product terpenoids found in two fossil conifers, Taxodium balticum (Eocene) and Glyptostrobus oregonensis (Miocene). A similar terpenoid pattern is also observed in extant Taxodium distichum. The preservation of characteristic terpenoids (unaltered natural products) in the fossil conifers supports their systematic assignment to the Cypress family (Cupressaceae sensu lato). The results also show that fossil conifers can contain polar terpenoids, which are valuable markers for (paleo)chemosystematics and phylogeny.

  8. Shark-bitten vertebrate coprolites from the Miocene of Maryland

    Science.gov (United States)

    Godfrey, Stephen J.; Smith, Joshua B.

    2010-05-01

    Coprolites (fossilized feces) preserve a wide range of biogenic components, from bacteria and spores to a variety of vertebrate tissues. Two coprolites from the Calvert Cliffs outcrop belt (Miocene-aged Chesapeake Group), MD, USA, preserve shark tooth impressions in the form of partial dental arcades. The specimens are the first known coprolites to preserve vertebrate tooth marks. They provide another example of trace fossils providing evidence of prehistoric animal behaviors that cannot be directly approached through the study of body fossils. Shark behaviors that could account for these impressions include: (1) aborted coprophagy, (2) benthic or nektonic exploration, or (3) predation.

  9. High resolution biostratigraphy of Oligo-Miocene Leon and Chama Formations: An integrated approach for sequence stratigraphy analysis

    Energy Technology Data Exchange (ETDEWEB)

    Pittelli, R.; Rull, V. (Maraven S.A., Caracas (Venezuela))

    1993-02-01

    Based on foraminiferal and palynological high resolution studies, a set of Sequence Boundaries (SB) and Maximum Flooding Surfaces (MSF) were identified for the Venezuelan Northwestern Andean Foothills Leon and Chama formations. Changes in abundance patterns of forminifera palynomorphs, in faunal/floral composition and distribution, together with quantitative studies of particulate organic matter allowed picking SB 30, 21 and 15.5 (very low values of fossil abundance and faunal discontinuities, recognized by a rapid stratigraphic change in biofacies and faunal assemblage and the associated mineralogical contents) and MFS 18.5, 16, and 15 (abundant fossils). The Leon Formation represents coastal plain and swamp deposits with some minor fluctuations in the seawater level. The top of the Leon Formation shaly unit is bounded by SB 30, according to Hag B.U. et al (version 1992), marked by a decrease in fossil abundance. An increase in faunal/floral content close to the top of the section coincides with the MFS 18.5. The upper part of the formation is marked by a sandy unit with SB 16.5, characterized again by a decrease in fossil abundance at its top. The Chama Formation was deposited in a transitional environment, with minor seawater level fluctuations. Climate type was tropical humid, with seasonal precipitations, except at the Early Miocene arid or semiarid phase. Mangrove and rain forest vegetation dominated throughout the Early to Middle Miocene. MFS 16 was picked on the basis of a high abundance of microforams and glauconite.

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

    Directory of Open Access Journals (Sweden)

    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. 

  11. Remarkable preservation of terpenoids and record of volatile signalling in plant-animal interactions from Miocene amber.

    Science.gov (United States)

    Dutta, Suryendu; Mehrotra, Rakesh C; Paul, Swagata; Tiwari, R P; Bhattacharya, Sharmila; Srivastava, Gaurav; Ralte, V Z; Zoramthara, C

    2017-09-08

    Plants produce and release a large array of volatile organic compounds that play many ecological functions. These volatile plant metabolites serve as pollinator attractants, herbivore and pathogen repellents and protect plants from abiotic stresses. To date, the geological evolution of these organic compounds remains unknown. The preservation potential of these metabolites in the fossil record is very poor due to their low boiling points. Here we report a series of volatile sesquiterpenoids, including δ-elemene, α-copaene, β-elemene, β-caryophyllene, α-humulene, germacrene D, δ-cadiene and spathunenol, from early Miocene (~17 million year) amber from eastern India. The survival of these unaltered bioterpenoids can be attributed to the existence of extraordinary taphonomic conditions conducive to the preservation of volatile biomolecules through deep time. Furthermore, the occurrence of these volatiles in the early Miocene amber suggests that the plants from this period had evolved metabolic pathways to synthesize these organic molecules to play an active role in forest ecology, especially in plant-animal interactions.

  12. Paleoclimatic and paleoenvironmental records of the Oligocene-Miocene transition, central Jylland, Denmark

    NARCIS (Netherlands)

    Sliwinska, K.K.; Dybkjær, K.; Schoon, P.L.; Beyer, C.; King, C.; Schouten, S.; Nielsen, O.B.

    2014-01-01

    A multidisciplinary study of the Oligocene/Miocene (O/M) transition was carried in two boreholes (Harre-1 and Horn-1) from the Danish land area in order to improve the understanding of the paleodimatological and environmental changes across the Mi-1, the earliest Miocene cooling event.

  13. Miocene fish faunas from the northwestern Amazonia basin (Colombia, Peru, Brazil) with evidence of marine incursions

    NARCIS (Netherlands)

    Monsch, KA

    1998-01-01

    New evidence indicates marine influences during the Miocene in the northwestern Amazonia basin. This is the first major survey of the ichthyofauna from this area in the Miocene. Fossil fish remains from taxa such as the Dasyatoidea, Myliobatoidea, Characiformes, Siluriformes and Sciaenidae are

  14. A macroecological glance at the structure of late Miocene rodent assemblages from Southwest Europe

    Science.gov (United States)

    Cano, Ana Rosa Gómez; Cantalapiedra, Juan L.; Álvarez-Sierra, M. Ángeles; Fernández, Manuel Hernández

    2014-10-01

    Deep-time perspectives in macroecology are essential with regard to understanding the impact of climate forcing on faunal communities. Using late Miocene rodent faunas (12 to 5 Ma) from two different biogeographical provinces from southwestern Europe, we asked whether the waxing and waning of faunas with dissimilar ecological affinities tracked climate in different ways. The latest middle Miocene featured a fauna dominated by dormice with forest and mixed-habitat affinities. This group declined towards the Upper Miocene. Rodent taxa with the highest values of richness at the beginning of the Upper Miocene are generalists in the southern province and specialists of forested habitats in the northern province. Finally, we identified a third, increasingly significant group of rodents linked to open landscapes towards the end of the Miocene. These three broad ecological groups showed differential responses to a complex set of interconnected circumstances, including the biogeographic structure of the study area and climatic changes throughout time.

  15. A new species of Nyanzachoerus (Cetartiodactyla: Suidae from the late Miocene Toros-Ménalla, Chad, central Africa.

    Directory of Open Access Journals (Sweden)

    Jean-Renaud Boisserie

    Full Text Available During the latest Miocene and the early Pliocene, tetraconodontine suids were the most predominant large omnivorous mammals in Africa. Yet, new species were often identified on the grounds of limited evidence, a situation impacting their value for biochronological correlations as well as for environmental and biogeographical reconstructions. The description of the most abundant known collection of craniodental remains attributed to the tetraconodontine Nyanzachoerus helps to improve this situation. These specimens were collected in the upper Miocene deposits at Toros-Ménalla, northern Chad, central Africa, by the Mission Paléoanthropologique Franco-Tchadienne. We compared them with Nyanzachoerus from eastern and southern Africa, using extant species as a reference for patterns of morphological variation. Thanks to a large sample of observations, our work focused as much on craniomandibular morphology as on dental morphology and metrics (improved by an index scoring for the complexity of distal third molars and a detailed investigation of premolar-molar ratios. We recognized two taxa at Toros-Ménalla: Nyanzachoerus khinzir nov. sp. and Ny. cf. australis. We also revised the taxonomic status for other species, including: the restriction of Ny. syrticus to its holotype specimen from Sahabi (Libya, the resurrection of the nomen Ny. tulotos, and the synonymy of Ny. kuseralensis with Ny. waylandi. At Toros-Ménalla, Ny. khinzir was the only suid coexisting with the anthracotheriid Libycosaurus and the hominid Sahelanthropus, whereas Ny. cf. australis was associated with a different, probably younger faunal context. Nyanzachoerus. khinzir, which probably had a diversified diet, supports a latest Miocene biogeographical distinction between central Africa and eastern Africa.

  16. The role of the Anaxagoras Mountain in the Miocene to Recent tectonic evolution of the eastern Mediterranean

    Science.gov (United States)

    Colbourne, Mark; Hall, Jeremy; Aksu, Ali; Çifçi, Günay

    2014-05-01

    The Anaximander Mountains are one of the many enigmatic structures situated along the morphologically and structurally complicated junction between the Hellenic and Cyprus Arcs, in the eastern Mediterranean. Interpretation of ~750 km of marine multi-channel seismic reflection data show that the present day Anaximander Mountains underwent several distinct phases of tectonic activity since Miocene. During the mid-late Miocene, a protracted, contractional tectonic regime produced the east-west trending, south-verging fold-thrust belt observed in the area. The Messinian was a period of relatively low tectonic activity, and is marked by the deposition of an evaporite layer. This phase lasted until the latest Miocene - earliest Pliocene, when a major erosional event associated with the Messinian salinity crisis occurred. Beginning in the early-mid Pliocene-Quaternary a transpressional and rotational tectonic regime prevailed over the area. The Anaximander Mountain (sensu stricto) and Anaximenes Mountain developed in the Pliocene-Quaternary associated with the reactivation, uplift and rotation of a linked, thick skinned pre-Messinian imbricate thrust fan. Back thrusting in the region accentuated the morphology of these mountains. The Anaxagoras Mountain differs both lithologically and morphologically from the Anaximander Mountain (sensu stricto) and the Anaximenes Mountain. It is probably developed associated with the emplacement of the ophiolitic Antalya Nappe Complex. Faulting in the Anaxagoras region is characterized by southwest striking thrust and/or oblique thrust faults. Due to the similarities in morphology between the Isparta Angle of southwestern Turkey and the Anaximander Mountains (sensu lato), it is hypothesized that the tectonic evolution of the two regions are similar in nature. The Anaximander Mountains (sensu lato) can thus be considered the offshore replication of the Isparta Angle, produced by similar mechanisms, but being of a younger age.

  17. Chronology of Miocene-Pliocene deposits at Split Mountain Gorge, Southern California: A record of regional tectonics and Colorado River evolution

    Science.gov (United States)

    Dorsey, R.J.; Fluette, A.; McDougall, K.; Housen, B.A.; Janecke, S.U.; Axen, G.J.; Shirvell, C.R.

    2007-01-01

    Late Miocene to early Pliocene deposit at Split Mountain Gorge, California, preserve a record of basinal response to changes in regional tectonics, paleogeography, and evolution of the Colorado River. The base of the Elephant Trees Formation, magnetostratigraphically dated as 8.1 ?? 0.4 Ma, provides the earliest well-dated record of extension in the southwestern Salton Trough. The oldest marine sediments are ca. 6.3 Ma. The nearly synchronous timing of marine incursion in the Salton Trough and northern Gulf of California region supports a model for localization of Pacific-North America plate motion in the Gulf ca. 6 Ma. The first appearance of Colorado River sand at the Miocene-Pliocene boundary (5.33 Ma) suggests rapid propagation of the river to the Salton Trough, and supports a lake-spillover hypothesis for initiation of the lower Colorado River. ?? 2007 Geological Society of America.

  18. Sedimentologic development of a Late Oligocene Miocene forearc embayment, Valdivia Basin Complex, southern Chile

    Science.gov (United States)

    le Roux, J. P.; Elgueta, Sara

    2000-01-01

    Deposition of Tertiary sediments in the southeastern part of the Valdivia Basin commenced during the Late Oligocene with the rapid incision of rivers draining the Palaeo-Coastal Range. Alluvial fans developing along the steep valley flanks joined gravelly braided streams transporting bedload to the coast. Tectonic and eustatic stability lasting into the Early Miocene subsequently allowed lateral erosion of the valley flanks and the development of extensive fluvial and estuarine peat swamps. This stable period was interrupted briefly by a volcanic eruption at 23.5 Ma. Shortly after 23 Ma, rapid uplift caused by an acceleration in plate convergence resulted in renewed erosion of the landscape, as reflected in the deposition of coarse river gravels. Basin subsidence and marine transgression proceeding up the river valleys subsequently formed still, deep embayments, occasionally disturbed by debris flows and turbidity currents originating on the steep, wooded valley flanks. At the upper limits of the inlets, bayhead deltas, tidal flats and beaches existed. In some areas, fan deltas prograded into the embayments, as reflected in the interfingering relationship between conglomerates and marine mudrocks. In the deeper parts of the embayments, the frequency of debris flows and turbidity currents increased markedly during periods of relative sea-level lowstand. The landscape was eventually inundated by continued subsidence and marine transgression, which lasted until a possibly eustatic sea-level fall in the early Tortonian.

  19. 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

  20. Constraints on the Miocene landscape evolution of the Eastern Alps from the Kalkspitze region, Niedere Tauern (Austria)

    Science.gov (United States)

    Dertnig, Florian; Stüwe, Kurt; Woodhead, Jon; Stuart, Finlay M.; Spötl, Christoph

    2017-12-01

    In order to unravel aspects of the Miocene landscape evolution of the eastern European Alps, we present geomorphic and isotopic data from the western Niedere Tauern region (Austria). The region is critical for such interpretations, because it is one of the few regions along the topographic axis of the Eastern Alps where the highest peaks (up to 2500 m a.s.l.) are dominated by limestone. As such, the region contains a record of Miocene landscape-forming events that survived the Pleistocene glaciations, not preserved elsewhere in the central Eastern Alps. This record includes karst caves, karstified planation surfaces and crystalline fluvial pebbles (Augenstein Formation) preserved on planation surfaces and in karst caves. Caves in the region occur in three distinct levels that correlate with well-known cave levels in the Northern Calcareous Alps, although they are somewhat higher in the Niedere Tauern. In part, these cave elevations also correlate with three planation surfaces and knickpoints of major streams draining the region, testifying their pre-glacial origin. We report details of a karst cave (Durchgangshöhle) from the highest cave level located at 2340 m a.s.l. In this cave, allochthonous fluvial gravels are present, overgrown by speleothems. One speleothem yielded an early middle Pleistocene U-Pb age (682 ± 17 ka). We regard this as a minimum age for the erosion of the fluvial cave deposits during Marine Isotope Stages 17 or 16. Carbon and oxygen isotope data of these speleothems imply a climate that is consistent with this interpretation. Cosmogenic 21Ne data of fluvial quartz clasts collected from the surface on plateaus of the Northern Calcareous Alps suggest minimum exposure durations of 115 and 262 ka. They probably reflect successive exposure since removal of the sediment cover of the Oligocene Augenstein Formation during the Pleistocene. While our geochronological data fail to record aspects of the earlier Miocene uplift history, they are

  1. Provenance evolution in the northern South China Sea and its implication of paleo-drainage systems from Eocene to Miocene

    Science.gov (United States)

    Cui, Y.; Shao, L.; Qiao, P.

    2017-12-01

    Geochemistry analysis and detrital zircon U-Pb geochronology aim to fully investigate the "source to sink" patterns of northern South China Sea (SCS) from Eocene to Miocene. Evolutional history of the surrounding drainage system has been highly focused on, in comparison to sedimentary characteristics of the SCS basins. Rapid local provenances were prevailed while large-scale fluvial transport remained to evolve during Eocene. Since early Oligocene, sediments from the South China were more abundantly delivered to the northeastern Pearl River Mouth Basin in addition to Dongsha volcanism supplement. Aside from intrabasinal provenances, long-distance transport started to play significant role in Zhu1 Depression, possibly reaching western and southern Baiyun Sag, partially. Western Qiongdongnan Basin might accept sediments from central Vietnam with its eastern area more affected from Hainan Island and Southern Uplift. In the late Oligocene, due to drastic sea-level changes and rapid exhumation, mafic to altramafic sediments were transported in abundance to Central Depression from Kontum Massif, while multiple provenances casted integrated influence on eastern sedimentary sequences. Southern Baiyun Sag was also affected by an increased supplement from the west Shenhu Uplift or even central Vietnam. Overall pattern did not change greatly since early Miocene, but long-distance transport has become dominant in the northern SCS. Under controlled by regional tectonic cycles, Pearl River gradually evolved into the present scale and exerted its influence on basinal provenances by several stages. Zhu1 Depression was partially delivered sediments from its tributaries in early Oligocene while northern Zhu2 Depression has not been provided abundant materials until late Oligocene. Meanwhile, although detailed transportation routine remains uncertain and controversial, an impressive paleo-channel spanning the whole Qiongdongnan Basin was presumed to supply huge amount of mafic to

  2. Paleoenvironmental reconstruction of the Oligocene-Miocene deposits of the Tethyan Seaway, Qom Formation, Central Iran

    Science.gov (United States)

    Dabaghi Sadr, Fatemeh; Schmiedl, Gerhard

    2017-04-01

    The Cenozoic climate transition from greenhouse to icehouse conditions was associated with major paleogeographic changes in the Tethyan realm. The closure of the Tethyan Seaway and its Iranian gateways during the terminal Paleogene and early Neogene, between approximately 28 and 18 million years, influenced the latitudinal exchange of water masses and energy and is documented in sediment successions of the Qom formation in central Iran. Little is known on the spatial expression and the exact depositional histories of the Qom Formation on orbital time-scales, including a lack of quantitative sea-level reconstructions and studies on the impact of climatic and tectonic changes on marine ecosystems and sedimentation processes. The PhD project focuses on the investigation of lithostratigraphy, biostratigraphy, paleoecology and paleoenvironmental evolution of the Iranian gateways based on late Oligocene to early Miocene foraminiferal faunas and carbonate facies from selected sediment sections of the Qom Basin. The Qom Formation was deposited in the Central Iranian back-arc basin during the Oligocene-Miocene. In this study foraminiferal faunas and carbonate microfacies were studied based on total 191 samples of two section of Qom Formation. One of them is Molkabad section, which is located northwest of Molkabad mountains, southeast of Garmsar. The section mainly consists of limestones, calcareous marls, marls, and gypsum-bearing marls with a total thickness of 760 meters. The Qom Formation at Molkabad section overlies Eocene rocks with an unconformity and consists of the following lithostratigraphic units (from the lower to upper part): Lithothamnium Limestone, Lower Marl Limestone, Bryozoa Limestone, and Upper Marl Group. The Molkabad fault separates the Qom Formation from the overlying Upper Red Formation. The other section is located at Navab anticline in Qom Formation .The section mainly consist of limestone, marl, and gypsum with a total thickness of 318 meters Navab

  3. Quantitative summer temperature reconstruction derived from a combined biogenic Si and chironomid record from varved sediments of Lake Silvaplana (south-eastern Swiss Alps) back to AD 1177

    Science.gov (United States)

    Trachsel, M.; Grosjean, M.; Larocque-Tobler, I.; Schwikowski, M.; Blass, A.; Sturm, M.

    2010-09-01

    High-resolution quantitative temperature records are needed for placing the recent warming into the context of long-term natural climate variability. In this study we present a quantitative high-resolution (9-year) summer (June-August) temperature reconstruction back to AD 1177 for the south-eastern Swiss Alps. This region is a good predictor for summer temperatures in large parts of western and central Europe. Our reconstruction is based on a combination of the high-frequency component of annually resolved biogenic silica (bSi flux) data and the low-frequency component of decadal chironomid-inferred temperatures from annually laminated well dated sediments (varves) from proglacial Lake Silvaplana, eastern Swiss Alps. For the calibration (period AD 1760-1949) we assess systematically the effects of six different regression methods (Type I regressions: Inverse Regression IR, Inverse Prediction IP, Generalised Least Squares GLS; Type II regressions: Major Axis MA, Ranged Major Axis RMA and Standard Major Axis SMA) with regard to the predicted amplitude and the calibration statistics such as root-mean-square error of prediction (RMSEP), reduction of error (RE) and coefficient of efficiency (CE). We found a trade-off in the regression model choice between a good representation of the amplitude and good calibration statistics. The band-pass filtered bSi flux record is in close agreement both in the structure and the amplitude with two fully independent reconstructions spanning back to AD 1500 and AD 1177, respectively. All known pulses of negative volcanic forcing are represented as cold anomalies in the bSi flux record. Volcanic pulses combined with low solar activity (Spörer and Maunder Minimum) are seen as particularly cold episodes around AD 1460 and AD 1690. The combined chironomid and bSi flux temperature record (RMSEP = 0.57 °C) is in good agreement with the glacier history of the Alps. The warmest (AD 1190) and coldest decades (17th century; 1680-1700) of our

  4. 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

  5. Out of Africa:Miocene Dispersal, Vicariance, and Extinction within Hyacinthaceae Subfamily Urgineoideae

    Institute of Scientific and Technical Information of China (English)

    Syed Shujait Ali; Martin Pfosser; Wolfgang Wetschnig; Mario MartnezAzorn; Manuel B. Crespo; Yan Yu

    2013-01-01

    Disjunct distribution patterns in plant lineages are usually explained according to three hypotheses:vicariance, geodispersal, and long-distance dispersal. The role of these hypotheses is tested in Urgineoideae (Hyacinthaceae), a subfamily disjunctly distributed in Africa, Madagascar, India, and the Mediterranean region. The potential ancestral range, dispersal routes, and factors responsible for the current distribution in Urgineoideae are investigated using divergence time estimations. Urgineoideae originated in Southern Africa approximately 48.9 Mya. Two independent dispersal events in the Western Mediterranean region possibly occurred during Early Oligocene and Miocene (29.9-8.5 Mya) via Eastern and Northwestern Africa. A dispersal from Northwestern Africa to India could have occurred between 16.3 and 7.6 Mya. Vicariance and extinction events occurred approximately 21.6 Mya. Colonization of Madagascar occurred between 30.6 and 16.6 Mya, after a single transoceanic dispersal event from Southern Africa. The current disjunct distributions of Urgineoideae are not satisfactorily explained by Gondwana fragmentation or dispersal via boreotropical forests, due to the younger divergence time estimates. The flattened winged seeds of Urgineoideae could have played an important role in long-distance dispersal by strong winds and big storms, whereas geodispersal could have also occurred from Southern Africa to Asia and the Mediterranean region via the so-called arid and high-altitude corridors.

  6. Morphometry, bite-force, and paleobiology of the late miocene caiman Purussaurus brasiliensis.

    Directory of Open Access Journals (Sweden)

    Tito Aureliano

    Full Text Available Purussaurus brasiliensis thrived in the northwestern portion of South America during the Late Miocene. Although substantial material has been recovered since its early discovery, this fossil crocodilian can still be considered as very poorly understood. In the present work, we used regression equations based on modern crocodilians to present novel details about the morphometry, bite-force and paleobiology of this species. According to our results, an adult Purussaurus brasiliensis was estimated to reach around 12.5 m in length, weighing around 8.4 metric tons, with a mean daily food intake of 40.6 kg. It was capable of generating sustained bite forces of 69,000 N (around 7 metric tons-force. The extreme size and strength reached by this animal seems to have allowed it to include a wide range of prey in its diet, making it a top predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates, and, being unmatched by any other carnivore, it avoided competition. The evolution of a large body size granted P. brasiliensis many advantages, but it may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts.

  7. Miocene tectonics of the Maramures area (Northern Romania): implications for the Mid-Hungarian fault zone

    Science.gov (United States)

    Tischler, M.; Gröger, H. R.; Fügenschuh, B.; Schmid, S. M.

    2007-06-01

    The interplay between the emplacement of crustal blocks (e.g. “ALCAPA”, “Tisza”, “Dacia”) and subduction retreat is a key issue for understanding the Miocene tectonic history of the Carpathians. Coeval thrusting and basin formation is linked by transfer zones, such as the Mid-Hungarian fault zone, which seperates ALCAPA from Tisza-Dacia. The presented study provides new kinematic data from this transfer zone. Early Burdigalian (20.5 to ˜18.5 Ma) SE-directed thrusting of the easternmost tip of ALCAPA (Pienides), over Tisza-Dacia is linked to movements along the Mid-Hungarian fault zone and the Periadriatic line, accommodating the lateral extrusion of ALCAPA. Minor Late Burdigalian (˜18.5 to 16 Ma) NE-SW extension is interpreted as related to back-arc extension. Post Burdigalian (post-16 Ma) NE SW shortening and NW SE extension correlate with “soft collision” of Tisza-Dacia with the European foreland coupled with southward migration of active subduction. During this stage the Bogdan-Voda and Dragos-Voda faults were kinematically linked to the Mid-Hungarian fault zone. Sinistral transpression (16 to 12 Ma) at the Bogdan-Voda fault was followed by sinistral transtension (12 10 Ma) along the coupled Bogdan-Dragos-Voda fault system. During the transtensional stage left-lateral offset was reduced eastwards by SW trending normal faults, the fault system finally terminating in an extensional horse-tail splay.

  8. Morphometry, Bite-Force, and Paleobiology of the Late Miocene Caiman Purussaurus brasiliensis

    Science.gov (United States)

    Aureliano, Tito; Ghilardi, Aline M.; Guilherme, Edson; Souza-Filho, Jonas P.; Cavalcanti, Mauro; Riff, Douglas

    2015-01-01

    Purussaurus brasiliensis thrived in the northwestern portion of South America during the Late Miocene. Although substantial material has been recovered since its early discovery, this fossil crocodilian can still be considered as very poorly understood. In the present work, we used regression equations based on modern crocodilians to present novel details about the morphometry, bite-force and paleobiology of this species. According to our results, an adult Purussaurus brasiliensis was estimated to reach around 12.5 m in length, weighing around 8.4 metric tons, with a mean daily food intake of 40.6 kg. It was capable of generating sustained bite forces of 69,000 N (around 7 metric tons-force). The extreme size and strength reached by this animal seems to have allowed it to include a wide range of prey in its diet, making it a top predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates, and, being unmatched by any other carnivore, it avoided competition. The evolution of a large body size granted P. brasiliensis many advantages, but it may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts. PMID:25689140

  9. Reinvestigation of the Miocene palynoflora from the Daotaiqiao Formation of north-eastern China using SEM

    Science.gov (United States)

    Akyurt, Elvan; Grímsson, Friðgeir; Zetter, Reinhard; Leng, Qin; Bouchal, Johannes Martin

    2016-04-01

    : Grímsson F, Zetter R, Leng Q. 2012. Diverse fossil Onagraceae pollen from a Miocene palynoflora of north-east China: early steps in resolving the phytogeographic history of the family. Plant Systematics and Evolution 298: 671-687.

  10. Lower Miocene stratigraphy along the Panama Canal and its bearing on the Central American Peninsula.

    Directory of Open Access Journals (Sweden)

    Michael Xavier Kirby

    Full Text Available Before the formation of the Central American Isthmus, there was a Central American Peninsula. Here we show that southern Central America existed as a peninsula as early as 19 Ma, based on new lithostratigraphic, biostratigraphic and strontium chemostratigraphic analyses of the formations exposed along the Gaillard Cut of the Panama Canal. Land mammals found in the Miocene Cucaracha Formation have similar body sizes to conspecific taxa in North America, indicating that there existed a terrestrial connection with North America that allowed gene flow between populations during this time. How long did this peninsula last? The answer hinges on the outcome of a stratigraphic dispute: To wit, is the terrestrial Cucaracha Formation older or younger than the marine La Boca Formation? Previous stratigraphic studies of the Panama Canal Basin have suggested that the Cucaracha Formation lies stratigraphically between the shallow-marine Culebra Formation and the shallow-to-upper-bathyal La Boca Formation, the latter containing the Emperador Limestone. If the La Boca Formation is younger than the Cucaracha Formation, as many think, then the peninsula was short-lived (1-2 m.y., having been submerged in part by the transgression represented by the overlying La Boca Formation. On the other hand, our data support the view that the La Boca Formation is older than the Cucaracha Formation. Strontium dating shows that the La Boca Formation is older (23.07 to 20.62 Ma than both the Culebra (19.83-19.12 Ma and Cucaracha (Hemingfordian to Barstovian North American Land Mammal Ages; 19-14 Ma formations. The Emperador Limestone is also older (21.24-20.99 Ma than the Culebra and Cucaracha formations. What has been called the "La Boca Formation" (with the Emperador Limestone, is re-interpreted here as being the lower part of the Culebra Formation. Our new data sets demonstrate that the main axis of the volcanic arc in southern Central America more than likely existed as a

  11. Lower Miocene stratigraphy along the Panama Canal and its bearing on the Central American Peninsula.

    Science.gov (United States)

    Kirby, Michael Xavier; Jones, Douglas S; MacFadden, Bruce J

    2008-07-30

    Before the formation of the Central American Isthmus, there was a Central American Peninsula. Here we show that southern Central America existed as a peninsula as early as 19 Ma, based on new lithostratigraphic, biostratigraphic and strontium chemostratigraphic analyses of the formations exposed along the Gaillard Cut of the Panama Canal. Land mammals found in the Miocene Cucaracha Formation have similar body sizes to conspecific taxa in North America, indicating that there existed a terrestrial connection with North America that allowed gene flow between populations during this time. How long did this peninsula last? The answer hinges on the outcome of a stratigraphic dispute: To wit, is the terrestrial Cucaracha Formation older or younger than the marine La Boca Formation? Previous stratigraphic studies of the Panama Canal Basin have suggested that the Cucaracha Formation lies stratigraphically between the shallow-marine Culebra Formation and the shallow-to-upper-bathyal La Boca Formation, the latter containing the Emperador Limestone. If the La Boca Formation is younger than the Cucaracha Formation, as many think, then the peninsula was short-lived (1-2 m.y.), having been submerged in part by the transgression represented by the overlying La Boca Formation. On the other hand, our data support the view that the La Boca Formation is older than the Cucaracha Formation. Strontium dating shows that the La Boca Formation is older (23.07 to 20.62 Ma) than both the Culebra (19.83-19.12 Ma) and Cucaracha (Hemingfordian to Barstovian North American Land Mammal Ages; 19-14 Ma) formations. The Emperador Limestone is also older (21.24-20.99 Ma) than the Culebra and Cucaracha formations. What has been called the "La Boca Formation" (with the Emperador Limestone), is re-interpreted here as being the lower part of the Culebra Formation. Our new data sets demonstrate that the main axis of the volcanic arc in southern Central America more than likely existed as a peninsula

  12. Late Miocene climate and time scale reconciliation: Accurate orbital calibration from a deep-sea perspective

    Science.gov (United States)

    Drury, Anna Joy; Westerhold, Thomas; Frederichs, Thomas; Tian, Jun; Wilkens, Roy; Channell, James E. T.; Evans, Helen; John, Cédric M.; Lyle, Mitch; Röhl, Ursula

    2017-10-01

    Accurate age control of the late Tortonian to early Messinian (8.3-6.0 Ma) is essential to ascertain the origin of benthic foraminiferal δ18O trends and the late Miocene carbon isotope shift (LMCIS), and to examine temporal relationships between the deep-sea, terrasphere and cryosphere. The current Tortonian-Messinian Geological Time Scale (GTS2012) is based on astronomically calibrated Mediterranean sections; however, no comparable non-Mediterranean stratigraphies exist for 8-6 Ma suitable for testing the GTS2012. Here, we present the first high-resolution, astronomically tuned benthic stable isotope stratigraphy (1.5 kyr resolution) and magnetostratigraphy from a single deep-sea location (IODP Site U1337, equatorial Pacific Ocean), which provides unprecedented insight into climate evolution from 8.3-6.0 Ma. The astronomically calibrated magnetostratigraphy provides robust ages, which differ by 2-50 kyr relative to the GTS2012 for polarity Chrons C3An.1n to C4r.1r, and eliminates the exceptionally high South Atlantic spreading rates based on the GTS2012 during Chron C3Bn. We show that the LMCIS was globally synchronous within 2 kyr, and provide astronomically calibrated ages anchored to the GPTS for its onset (7.537 Ma; 50% from base Chron C4n.1n) and termination (6.727 Ma; 11% from base Chron C3An.2n), confirming that the terrestrial C3:C4 shift could not have driven the LMCIS. The benthic records show that the transition into the 41-kyr world, when obliquity strongly influenced climate variability, already occurred at 7.7 Ma and further strengthened at 6.4 Ma. Previously unseen, distinctive, asymmetric saw-tooth patterns in benthic δ18O imply that high-latitude forcing played an important role in late Miocene climate dynamics from 7.7-6.9 Ma. This new integrated deep-sea stratigraphy from Site U1337 can act as a new stable isotope and magnetic polarity reference section for the 8.3-6.0 Ma interval.

  13. Late Miocene radiolarian biostratigraphy and paleoceanography of Sawai Bay formation, Neill Island, Andamans, India

    Digital Repository Service at National Institute of Oceanography (India)

    Gupta, S.M.; Srinivasan, M.S.

    Late Miocene radiolarian zones are encountered from mudstone strata of Sawai Bay Formation, Neill Island, Andamans. Percentage data of forty-five coarser taxonomic groups of radiolarians were subjected to Q-mode cluster analysis. Based...

  14. Miocene transgression in the central and eastern parts of the Sivas Basin (Central Anatolia, Turkey) and the Cenozoic palaeogeographical evolution

    Science.gov (United States)

    Poisson, André; Vrielynck, Bruno; Wernli, Roland; Negri, Alessandra; Bassetti, Maria-Angela; Büyükmeriç, Yesim; Özer, Sacit; Guillou, Hervé; Kavak, Kaan S.; Temiz, Haluk; Orszag-Sperber, Fabienne

    2016-01-01

    We present here a reappraisal of the tectonic setting, stratigraphy and palaeogeography of the central part of the Sivas Basin from Palaeocene to late Miocene. The Sivas Basin is located in the collision zone between the Pontides (southern Eurasia) and Anatolia (a continental block rifted from Gondwana). The basin overlies ophiolites that were obducted onto Anatolia from Tethys to the north. The Central Anatolian Crystalline Complex (CACC) experienced similar ophiolite obduction during Campanian time, followed by exhumation and thrusting onto previously emplaced units during Maastrichtian time. To the east, crustal extension related to exhumation of the CACC created grabens during the early Tertiary, including the Sivas Basin. The Sivas Basin underwent several tectonic events during Paleogene-Neogene. The basin fill varies, with several sub-basins, each being characterised by a distinctive sequence, especially during Oligocene and Miocene. Evaporite deposition in the central part of the basin during early Oligocene was followed by mid-late Oligocene fluvio-lacustrine deposition. The weight of overlying fluvial sediments triggered salt tectonics and salt diapir formation. Lacustrine layers that are interbedded within the fluviatile sediments have locally yielded charophytes of late Oligocene age. Emergent areas including the pre-existing Sivas Basin and neighbouring areas were then flooded from the east by a shallow sea, giving rise to a range of open-marine sub-basins, coralgal reef barriers and subsiding, restricted-marine sub-basins. Utilising new data from foraminifera, molluscs, corals and nannoplankton, the age of the marine transgression is reassessed as Aquitanian. Specifically, age-diagnostic nannoplankton assemblages of classical type occur at the base of the transgressive sequence. However, classical stratigraphic markers have not been found within the planktic foraminiferal assemblages, even in the open-marine settings. In the restricted-marine sediments

  15. Bilobate leaves of Bauhinia (Leguminosae, Caesalpinioideae, Cercideae) from the middle Miocene of Fujian Province, southeastern China and their biogeographic implications.

    Science.gov (United States)

    Lin, Yanxiang; Wong, William Oki; Shi, Gongle; Shen, Si; Li, Zhenyu

    2015-11-16

    Morphological and molecular phylogenetic studies suggest that the pantropical genus Bauhinia L. s.l. (Bauhiniinae, Cercideae, Leguminosae) is paraphyletic and may as well be subdivided into nine genera, including Bauhinia L. s.s. and its allies. Their leaves are usually characteristic bilobate and are thus easily recognized in the fossil record. This provides the opportunity to understand the early evolution, diversification, and biogeographic history of orchid trees from an historical perspective under the framework of morphological and molecular studies. The taxonomy, distribution, and leaf architecture of Bauhinia and its allies across the world are summarized in detail, which formed the basis for classifying the bilobate leaf fossils and evaluating the fossil record and biogeography of Bauhinia. Two species of Bauhinia are described from the middle Miocene Fotan Group of Fujian Province, southeastern China. Bauhinia ungulatoides sp. nov. is characterized by shallowly to moderately bilobate, pulvinate leaves with shallowly cordate bases and acute apices on each lobe, as well as paracytic stomatal complexes. Bauhinia fotana F.M.B. Jacques et al. emend. possesses moderately bilobate, pulvinate leaves with moderately to deeply cordate bases and acute or slightly obtuse apices on each lobe. Bilobate leaf fossils Bauhinia ungulatoides and B. fotana together with other late Paleogene - early Neogene Chinese record of the genus suggest that Bauhinia had been diverse in South China by the late Paleogene. Their great similarities to some species from South America and South Asia respectively imply that Bauhinia might have undergone extensive dispersals and diversification during or before the Miocene. The fossil record, extant species diversity, as well as molecular phylogenetic analyses demonstrate that the Bauhiniinae might have originated in the Paleogene of low-latitudes along the eastern Tethys Seaway. They dispersed southwards into Africa, migrated from Eurasia to

  16. Differential denudation across the Judea Range, Israel, suggests the persistence of a rain-shadow since mid Miocene

    Science.gov (United States)

    Ryb, U.; Matmon, A.; Erel, Y.; Haviv, I.; Benedetti, L. C.

    2013-12-01

    The Judea Range which is composed of a thick sequence of Cretaceous marine carbonate rises up to ~1000 m between the Mediterranean Sea and the Dead Sea basins. The western flank of the range faces predominant winds which deliver humidity from the Mediterranean and thus maintains a sub-humid Mediterranean climate (Mean Annual Precipitation (MAP) of 500-700 mm). Over the eastern, leeward side, rain-shadow orographic effect imposes a climatic gradient from Mediterranean near the water divide to hyper-arid near the Dead Sea rift escarpment (MAPMAP values, indicating that chemical weathering is the dominant process of erosion. Long-term denudation rates of interfluves reflect the climatic gradient between the two flanks of the Judea range; over the western, windward, flank of the Judea range, exposed bedrock denude at an average rate of 21×7 mm kyr-1, while over the leeward flank denudation rates drop dramatically, reaching 1-3 mm kyr-1 near the Dead Sea rift escarpment. As a rough measure to the erosion of the Judea Range since it began uplifting in Senonian time, we compare the present envelope-topography (T) of the range with the top-Turonian structural datum (S). We found that over the windward flank topography lay ~300 meters below the datum, while over the leeward flank topography generally follows the datum. Can this difference result from differential denudation, similar to the one observed over 10-1-105 year timescales? S-T values are well correlated with present MAP values, suggesting a positive answer. Assuming that the late Pleistocene denudation pattern calculated from 36Cl data was maintained, ~15 million years are required to form the observed 300 difference between the eastern and western flanks of the range. Indeed, previous studies suggest that by mid Miocene the Judea Range was uplifted to about ~500 m above sea level, while the Mediterranean was the immediate source for humidity in the region as of the early Miocene. The integrated data could

  17. Application of carbon isotope stratigraphy to late miocene shallow marine sediments, new zealand.

    Science.gov (United States)

    Loutit, T S; Kennett, J P

    1979-06-15

    A distinct (0.5 per mil) carbon-13/carbon-12 isotopic shift in the light direction has been identified in a shallow marine sedimentary sequence of Late Miocene age at Blind River, New Zealand, and correlated with a similar shift in Late Miocene Deep Sea Drilling Project sequences throughout the Indo-Pacific. A dated piston core provides an age for the shift of 6.2 +/- 0.1 million years. Correlations based on the carbon isotopic change require a revision of the previously established magnetostratigraphy at Blind River. The carbon shift at Blind River occurs between 6.2 and 6.3 +/- 0.1 million years before present. A new chronology provides an age for the evolutionary first appearance datum of Globorotalia conomiozea at 6.1 +/- 0.1 million years, the beginning of a distinct latest Miocene cooling event associated with the Kapitean stage at 6.2 +/- 0.1 million years, and the beginning of a distinct shallowing of water depths at 6.1 +/- 0.1 million years. The Miocene-Pliocene boundary as recognized in New Zealand is now dated at 5.3 +/- 0.1 million years. Extension of carbon isotope stratigraphy to other shallow Late Miocene sequences should provide an important datum for international correlation of Late Miocene shallow and deep marine sequences.

  18. 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.

  19. New gadiform fishes (Teleostei, Gadiformes) from the Miocene of Algeria

    Science.gov (United States)

    Carnevale, Giorgio

    2007-02-01

    As part of the completion of studies on the Miocene fishes of the Chelif Basin (north-western Algeria), this paper represents a contribution to the knowledge of the Messinian gadiform diversity of this western Mediterranean, semi-enclosed, Neogene basin. A new genus and species of the family Macrouridae is erected ( Razelainia paradoxa n. gen. et sp.), two specimens are tentatively referred to already existing taxa ( Gadiculus cf. jonas; Merluccius cf. merluccius), and a species formerly assigned to the gadid genus Brosme is transferred to the genus Gaidropsarus ( Gaidropsarus murdjadjensis). The macrourid Razelainia paradoxa n. gen. et sp. is characterized by an unusual combination of: plesiomorphic gadiform features, such as low vertebral number (presumed), well-developed caudal-fin rays, presence of a single continuous dorsal fin originating just posterior to the neurocranium, anal-fin rays slightly longer than dorsal-fin rays; and derived, typically macrourid features, such as the presence of spinoid scales and the anterior anal-fin pterygiophores extending forward over the abdominal wall. A paleoecological analysis reveals that the Messinian gadiform assemblage of the Chelif Basin had a subtropical/warm temperate affinity, with a marked north-eastern Atlantic-Mediterranean biogeographic character.

  20. Resource partitioning among top predators in a Miocene food web.

    Science.gov (United States)

    Domingo, M Soledad; Domingo, Laura; Badgley, Catherine; Sanisidro, Oscar; Morales, Jorge

    2013-01-07

    The exceptional fossil sites of Cerro de los Batallones (Madrid Basin, Spain) contain abundant remains of Late Miocene mammals. From these fossil assemblages, we have inferred diet, resource partitioning and habitat of three sympatric carnivorous mammals based on stable isotopes. The carnivorans include three apex predators: two sabre-toothed cats (Felidae) and a bear dog (Amphicyonidae). Herbivore and carnivore carbon isotope (δ(13)C) values from tooth enamel imply the presence of a woodland ecosystem dominated by C(3) plants. δ(13)C values and mixing-model analyses suggest that the two sabre-toothed cats, one the size of a leopard and the other the size of a tiger, consumed herbivores with similar δ(13)C values from a more wooded portion of the ecosystem. The two sabre-toothed cats probably hunted prey of different body sizes, and the smaller species could have used tree cover to avoid encounters with the larger felid. For the bear dog, δ(13)C values are higher and differ significantly from those of the sabre-toothed cats, suggesting a diet that includes prey from more open woodland. Coexistence of the sabre-toothed cats and the bear dog was likely facilitated by prey capture in different portions of the habitat. This study demonstrates the utility of stable isotope analysis for investigating the behaviour and ecology of members of past carnivoran guilds.

  1. Horizontal drilling in Miocene thin sand of Lake Maracaibo

    Energy Technology Data Exchange (ETDEWEB)

    Partidas, C. [PDVSA Exploration and Production (Venezuela)

    1998-12-31

    Horizontal drilling in the mature Lake Maracaibo field in Venezuela as a means of stimulating production are discussed. The Miocene sand where the horizontal well technology was applied, presented a number of intervals of unconsolidated sand of varied continuity, pay intervals at ten to twenty feet thickness, and reservoir pressures mostly at hydrostatic or below hydrostatic values. This paper evaluates a horizontal drilling program in the Lagunallis Lago Production Unit of Maracaibo, involving 91 wells to date (since 1995). When assessed in economic terms, results indicate that horizontal wells are a better economic alternative than vertical wells. The same results also showed that drainage from thin sand reservoirs resulted in better production with horizontal well technology than production from vertical wells. Payout was less than two years for 50 per cent of the horizontal wells while 40 per cent had payouts of between two and four years. Profit to investment ratio was greater than two in the case of about 70 per cent of the horizontal wells drilled in 1996. 2 tabs., 10 figs.

  2. 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. 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. 2010 Elsevier Inc. All rights reserved.

  3. Ecological tolerances of Miocene larger benthic foraminifera from Indonesia

    Science.gov (United States)

    Novak, Vibor; Renema, Willem

    2018-01-01

    To provide a comprehensive palaeoenvironmental reconstruction based on larger benthic foraminifera (LBF), a quantitative analysis of their assemblage composition is needed. Besides microfacies analysis which includes environmental preferences of foraminiferal taxa, statistical analyses should also be employed. Therefore, detrended correspondence analysis and cluster analysis were performed on relative abundance data of identified LBF assemblages deposited in mixed carbonate-siliciclastic (MCS) systems and blue-water (BW) settings. Studied MCS system localities include ten sections from the central part of the Kutai Basin in East Kalimantan, ranging from late Burdigalian to Serravallian age. The BW samples were collected from eleven sections of the Bulu Formation on Central Java, dated as Serravallian. Results from detrended correspondence analysis reveal significant differences between these two environmental settings. Cluster analysis produced five clusters of samples; clusters 1 and 2 comprise dominantly MCS samples, clusters 3 and 4 with dominance of BW samples, and cluster 5 showing a mixed composition with both MCS and BW samples. The results of cluster analysis were afterwards subjected to indicator species analysis resulting in the interpretation that generated three groups among LBF taxa: typical assemblage indicators, regularly occurring taxa and rare taxa. By interpreting the results of detrended correspondence analysis, cluster analysis and indicator species analysis, along with environmental preferences of identified LBF taxa, a palaeoenvironmental model is proposed for the distribution of LBF in Miocene MCS systems and adjacent BW settings of Indonesia.

  4. Miocene squat lobsters (Decapoda, Anomura, Galatheoidea) of the Central Paratethys - a review, with description of a new species of Munidopsis.

    Science.gov (United States)

    Hyžný, M; Gašparič, R; Robins, C M; Schlögl, J

    2014-10-01

    All squat lobsters of the families Galatheidae, Munididae and Munidopsidae from the Miocene of the Central Paratethys are reviewed taxonomically. Based on additional observations emended diagnoses are provided for Agononida cerovensis and Galathea weinfurteri , from the Lower and Middle Miocene, respectively. Munidopsis is represented by two species in the study area; additional data for M. lieskovensis from the Lower Miocene of Slovakia are presented and a new species, M. palmuelleri , from the Middle Miocene of Slovenia is erected. Implications for palaeoenvironmental reconstructions are briefly discussed for each taxon.

  5. Stratigraphy, age, and depositional setting of the Miocene Barstow Formation at Harvard Hill, central Mojave Desert, California

    Science.gov (United States)

    Leslie, Shannon R.; Miller, David M.; Wooden, Joseph L.; Vazquez, Jorge A.

    2010-01-01

    New detailed geologic mapping and geochronology of the Barstow Formation at Harvard Hill, 30 km east of Barstow, CA, help to constrain Miocene paleogeography and tectonics of the central Mojave Desert. A northern strand of the Quaternary ENE-striking, sinistral Manix fault divides the Barstow Formation at Harvard Hill into two distinct lithologic assemblages. Strata north of the fault consist of: a green rhyolitic tuff, informally named the Shamrock tuff; lacustrine sandstone; partially silicified thin-bedded to massive limestone; and alluvial sandstone to pebble conglomerate. Strata south of the fault consist of: lacustrine siltstone and sandstone; a rhyolitic tuff dated at 19.1 Ma (U-Pb); rock-avalanche breccia deposits; partially silicified well-bedded to massive limestone; and alluvial sandstone and conglomerate. Our U-Pb zircon dating of the Shamrock tuff by SHRIMP-RG yields a peak probability age of 18.7 ± 0.1 Ma. Distinctive outcrop characteristics, mineralogy, remanent magnetization, and zircon geochemistry (Th/U) suggest that the Shamrock tuff represents a lacustrine facies of the regionally extensive Peach Spring Tuff (PST). Here we compare zircon age and geochemical analyses from the Shamrock tuff with those of the PST at Stoddard Wash and provide new insight into the age of zircon crystallization in the PST rhyolite. Results of our field studies show that Miocene strata at Harvard Hill mostly accumulated in a lacustrine environment, although depositional environments varied from a relatively deep lake to a very shallow lake or even onshore setting. Rock-avalanche breccias and alluvial deposits near the base of the exposed section indicate proximity to a steep basin margin and detrital studies suggest a southern source for coarse-grained deposits; therefore, we may infer a southern basin-margin setting at Harvard Hill during the early Miocene. Our geochronology demonstrates that deposition of the Barstow Formation at Harvard Hill extended from before

  6. Petrography and stable isotope geochemistry of Oligocene-Miocene continental carbonates in south Texas: Implications for paleoclimate and paleoenvironment near sea-level

    Science.gov (United States)

    Godfrey, Conan; Fan, Majie; Jesmok, Greg; Upadhyay, Deepshikha; Tripati, Aradhna

    2018-05-01

    Cenozoic sedimentary rocks in the southern Texas Gulf Coastal Plains contain abundant continental carbonates that are useful for reconstructing terrestrial paleoclimate and paleoenvironment in a region near sea-level. Our field observations and thin section characterizations of the Oligocene and Miocene continental carbonates in south Texas identified three types of pedogenic carbonates, including rhizoliths, carbonate nodules, and platy horizons, and two types of groundwater carbonates, including carbonate-cemented beds and carbonate concretions, with distinctive macromorphologic and micromorphologic features. Based on preservations of authigenic microfabrics and variations of carbon and oxygen isotopic compositions, we suggest these carbonates experienced minimal diagenesis, and their stable isotopic compositions reflect paleoclimate and paleoenvironment in south Texas. Our Oligocene and Miocene carbonate clumped isotope temperatures (T(Δ47)) are 23-28 °C, slightly less than or comparable to the range of modern mean annual and mean warm season air temperature (21-27 °C) in the study area. These T(Δ47) values do not show any dependency on carbonate-type, or trends through time suggesting that groundwater carbonates were formed at shallow depths. These data could indicate that air temperature in south Texas was relatively stable since the early Oligocene. The reconstructed paleo-surface water δ18O values are similar to modern surface water which could indicate that meteoric water δ18O values also remained stable since the early Oligocene. Mean pedogenic carbonate δ13C values increased - 4.6‰ during the late Miocene, most likely reflecting an expansion of C4 grassland in south Texas. This study provides the first mid- and late Cenozoic continental records of paleoclimate and paleoecology in a low-latitude, near sea-level region.

  7. Provenance of the lower Miocene of the Gulf of Mexico from detrital zircon double dating

    Science.gov (United States)

    xu, J.

    2013-12-01

    The lower Miocene interval of the Gulf of Mexico (GOM) has recently gained increasing attention from oil and gas industry due to its hydrocarbon potential below the salt canopy. However, it has been less well studied than both the underlying Oligocene and overlying middle Miocene strata. The lower Miocene worldwide is a transitional period of tectonic, climatic, and oceanographic change. In particular, it is a period of major tectonic reorganization in the western interior of North America (Rocky Mountains), involving a shift from the Oligocene thermal phase, with abundant volcanic activity recorded in the thick Frio/Vicksburg succession of the GOM, to the Miocene Basin-Range extensional phase. Climatic conditions also changed from a relatively arid Oligocene to wetter Miocene, resulting in increased sediment yields from exhumed tectonic structures. Previous provenance studies used proportions of quartz, feldspar and lithic fragments and consideration of likely river courses through known paleogeomorphological elements. Only limited detrital zircon (DZ) U-Pb studies on Paleocene strata have been undertaken and there has been no previous U-Pb and (U-Th)/He double dating in the GOM. In this study we apply the latest analytical approaches, such as DZ U-Pb dating to gain robust source terranes ages and more fully elucidate the complex sediment provenance and dispersal history of GOM. We also employ DZ (U-Th)/He (ZHe) dating, combined with DZ U-Pb, to not only define sedimentary provenance but also the exhumation histories of detrital source regions. Samples of lower Miocene outcrop exposures in Texas and Louisiana have been collected to discriminate the varied tectonic and drainage system changes across the basin in lateral. In addition, samples from the Eocene, Oligocene and middle Miocene have been obtained to reveal vertical shift of source terranes contributions. Our initial age data show detrital zircons of lower Miocene sediments come from a wide range of source

  8. New Evidence For A Late Miocene Onset Of The Amazon River Following Andean Tectonics And Quaternary Climate Change

    Science.gov (United States)

    Hoorn, M. C.; Bogota-Angel, G.; Romero-Baez, M.; Lammertsma, E.; Flantua, S. G. A.; Dantas, E. L.; Dino, R.; do Carmo, D.; Chemale, F., Jr.

    2017-12-01

    The Amazon River influenced biotic evolution on land and at sea, but its onset and development are still debated. Terrestrial sedimentary records are sparse, far apart, and do not present a continuous stratigraphy and thus greatly complicate the reconstruction of the history of this river system. At sea the stratigraphic record is better known thanks to hydrocarbon exploration efforts, but these data are not in the public domain. Renewed exploration in the Amazon submarine fan (Brazilian Equatorial Margin) has provided novel data and materials from wells drilled along the slope of the Amazon submarine fan, that are now partially available for scientific research. Here we report on the results of a geochemical and palynological study of `Well 2' based on which we determined the age and provenance of early Miocene to Pleistocene sediments. The palynological data were also used to reconstruct past biomes on land, which ranged from mangrove and lowland forest to alpine vegetation. A distinct change in provenance was observed between 9.4 Ma and 9 Ma, which represented a change from Amazonian to Andean sediment source. This signal is replicated in the palynological record, which shows a shift from lowland to high-mountain taxa. Furthermore, we observed a very large increase of grass pollen from the Pliocene onwards with a further rise in the Pleistocene. These changes coincide with a rise in sedimentation rates. We interpret these results as following: a) the arrival of Andean sediments is related to the onset of the transcontinental river, b) the two-step rise of grass pollen and manifold increase in sediment discharge are related to Quaternary climatic change. These results agree with earlier and recent findings on the Ceara Rise and firmly place the birth of this river in the late Miocene. This study exemplifies the continental scale of tectonic changes on fluvial environments and biota across a W-E transect of South America. The study of this well is continued and we

  9. Migrations of European honey bee lineages into Africa, Asia, and North America during the Oligocene and Miocene

    Science.gov (United States)

    Kotthoff, Ulrich; Wappler, Torsten; Engel, Michael

    2013-04-01

    Today honey bees, principally the western honey bee, Apis mellifera, represent a multi-billion dollar agricultural industry. Through the efforts of humans they have become established well outside of their modern native ranges, having been introduced multiple times into the Americas, Australia, New Zealand, New Caledonia, and many areas of Oceania. The native, i.e., non-human influenced, distribution and migration of honey bee species and populations has been a matter of serious and continued debate. Apicultural dogma informs us that the center of origin of honey bees (genus Apis) resides in Asia, with subsequent migration and diversification into Europe and Asia. Recent population genetic studies of the western honey bee, Apis mellifera, slightly modified this received wisdom by suggesting that this species originated in Africa and subsequently reinvaded Eurasia. Research into the historical biogeography of honey bees has ignored entirely the abundant fossil evidence distributed through a variety of Late Paleogene (Oligocene) and Early Neogene (Miocene) deposits, a diversity which is predominantly European in origin, particularly among the most basal species of the genus. We have examined the morphological disparity and affinities of the full living and fossil diversity of honey bees ranging from their earliest origins to the present day. This analysis indicates that honey bees exhibited a greater morphological disparity during the Oligocene and Miocene epochs, a time when the principal lineages were established, and that Apis apparently originated in Europe, spreading from there into Asia, Africa, and North America, with subsequent diversification in the former two regions and extinction in the latter. During the human migrations and colonization honey bees were once again introduced multiple times into the Americas, as well as into Australia and Asia.

  10. Paleocene-middle Miocene flexural-margin migration of the non marine llanos Foreland basin of Colombia

    International Nuclear Information System (INIS)

    Bayona, German; Jaramillo, Carlos; Rueda, Milton; Reyes Harker, Andres; Torres, Vladimir

    2007-01-01

    A foreland basin is a dynamic system whose depositional systems migrate in response to changes in tectonic uplift patterns, sedimentary filling processes and isostatic rebound of the lithosphere. The Paleocene-middle Miocene foreland system of the llanos foothills and llanos basin of Colombia includes regional unconformities, abrupt changes in lithology/stacking patterns and flooding surfaces bounding reservoir and seal units. Here we integrate a systematic biostratigraphic study, strata architecture and tectonic subsidence analyses, regional seismic profiles, and provenance data to define the diachronism of such surfaces and to document the direction of migration of foreland depozones. Line a flexural-deformed basin, sandstone composition, rates of accommodation and sediment supply vary across and along the basin. we show how a coeval depositional profile in the llanos foothills-llanos foreland basin consists of lithoranites inter b edded with mudstones (seal rock, supplied from the orogenic front to the west) that correlate craton ward with organic-rich mudstones and coal (source rock), and to amalgamated fluvial-estuarine quartzarenites (reservoir rock, supplied from the craton to the east) adjacent to a sub-aerial fore-bulge (unconformity). This system migrated northward and eastward during the Paleocene, westward during the early-middle Eocene, and eastward during the Oligocene. In the lower-middle Miocene succession of the llanos basin, identification of flooding events indicates a westward encroaching of a shallow-water lacustrine system that covered an eastward-directed fluvial-deltaic system. A similar process has been documented in other basins in Venezuela and Bolivia, indicating the regional extent of such flooding event may be related to the onset of Andean-scale mountain-building processes

  11. Provenance and evolution of miocene turbidite sedimentation in the central Apennines, Italy

    Science.gov (United States)

    Chiocchini, Ugo; Cipriani, Nicola

    1992-05-01

    A study of the siliciclastic detritus within the calcareous Miocene turbidite sandstones of the central Apennines has elucidated the provenance of these sandstones. Three ratios: Q/(Q+F), K/F, and Mc/M, have been used and binary correlations of these parameters show that: (1) the sandstones of the Marnoso-Arenacea are characterized by a northern Alpine supply, mainly derived from metamorphic rocks and subordinately from granitic rocks; (2) a secondary supply of western provenance, interbedded within the Marnoso-Arenacea, shows a typical arkosic composition and suggests that granitic rocks of Alpine-type were associated with the Ligurides; (3) the Urbania and Serraspinosa sandstones consist of detritus derived from sources almost identical to those supplying the Marnoso-Arenacea; (4) all the sandstones of the remaining central Apennine basins are characterized by a siliciclastic supply similar to the arkosic one; the rare carbonate fragments can be referred to the Apennine units. The continuity of the Alpine are in the Tyrrhenian area strongly suggests a connection between the western crystalline units and turbidite sedimentation in the basins examined. The crystalline units are associated with a segment of the Alpine chain tectonically linked to the Liguride nappes (Apennine source areas) during the eastwards migration of the Apennines deformation. The crystalline units were gradually eroded during the Burdigalian to Early Pliocene interval when the Laga basin was completely filled. Currently the term "Alpine" is used as synonymous with northern provenance. However, a detailed study carried out over ten years, revealed a western Alpine supply associated with an Apennine source area; we therefore suggest that it is necessary to distinguish a northern Alpine provenance from a western Alpine supply.

  12. Aridification of the Sahara desert caused by Tethys Sea shrinkage during the Late Miocene

    Science.gov (United States)

    Zhang, Zhongshi; Ramstein, Gilles; Schuster, Mathieu; Li, Camille; Contoux, Camille; Yan, Qing

    2014-09-01

    It is widely believed that the Sahara desert is no more than ~2-3 million years (Myr) old, with geological evidence showing a remarkable aridification of north Africa at the onset of the Quaternary ice ages. Before that time, north African aridity was mainly controlled by the African summer monsoon (ASM), which oscillated with Earth's orbital precession cycles. Afterwards, the Northern Hemisphere glaciation added an ice volume forcing on the ASM, which additionally oscillated with glacial-interglacial cycles. These findings led to the idea that the Sahara desert came into existence when the Northern Hemisphere glaciated ~2-3 Myr ago. The later discovery, however, of aeolian dune deposits ~7 Myr old suggested a much older age, although this interpretation is hotly challenged and there is no clear mechanism for aridification around this time. Here we use climate model simulations to identify the Tortonian stage (~7-11 Myr ago) of the Late Miocene epoch as the pivotal period for triggering north African aridity and creating the Sahara desert. Through a set of experiments with the Norwegian Earth System Model and the Community Atmosphere Model, we demonstrate that the African summer monsoon was drastically weakened by the Tethys Sea shrinkage during the Tortonian, allowing arid, desert conditions to expand across north Africa. Not only did the Tethys shrinkage alter the mean climate of the region, it also enhanced the sensitivity of the African monsoon to orbital forcing, which subsequently became the major driver of Sahara extent fluctuations. These important climatic changes probably caused the shifts in Asian and African flora and fauna observed during the same period, with possible links to the emergence of early hominins in north Africa.

  13. Aridification of the Sahara desert caused by Tethys Sea shrinkage during Late Miocene

    Science.gov (United States)

    Zhang, Z.; Ramstein, G.; Schuster, M.; Li, C.; Contoux, C.; Yan, Q.

    2014-12-01

    It is widely believed that the Sahara desert is no more than ~2-3 million years (Myr) old, with geological evidence showing a remarkable aridification of north Africa at the onset of the Quaternary ice ages. Before that time, north African aridity was mainly controlled by the African summer monsoon (ASM), which oscillated with Earth's orbital precession cycles. Afterwards, the Northern Hemisphere glaciation added an ice volume forcing on the ASM, which additionally oscillated with glacial-interglacial cycles. These findings led to the idea that the Sahara desert came into existence when the Northern Hemisphere glaciated ~2-3 Myr ago. The later discovery, however, of aeolian dune deposits ~7 Myr old suggested a much older age, although this interpretation is hotly challenged and there is no clear mechanism for aridification around this time. Here we use climate model simulations to identify the Tortonian stage (~7-11 Myr ago) of the Late Miocene epoch as the pivotal period for triggering north African aridity and creating the Sahara desert. Through a set of experiments with the Norwegian Earth System Model and the Community Atmosphere Model, we demonstrate that the African summer monsoon was drastically weakened by the Tethys Sea shrinkage during the Tortonian, allowing arid, desert conditions to expand across north Africa. Not only did the Tethys shrinkage alter the mean climate of the region, it also enhanced the sensitivity of the African monsoon to orbital forcing, which subsequently became the major driver of Sahara extent fluctuations. These important climatic changes probably caused the shifts in Asian and African flora and fauna observed during the same period, with possible links to the emergence of early hominins in north Africa.

  14. Carbonate pseudotachylite? from a Miocene extensional detachment, W. Cyclades, Greece.

    Science.gov (United States)

    Rice, A. Hugh N.; Grasemann, Bernhard

    2016-04-01

    Most pseudotachylites, both impact- and fault-related, occur in silicate-rich rocks, typically with 'granitoid' compositions. Examples of melting in carbonate rocks, excluding magmatic sources, are restricted to impact-events, except for a carbonate pseudotachylite in the Canalone Fault, S. Italy (Viganò et al. 2011). Another potential example of carbonate pseudotachylite, shown here, comes from the Miocene-aged W. Cycladic Detachment System, in Greece. Top-SSE ductile to brittle movement on this detachment, with a maximum displacement estimated at tens of kilometers, exhumed of HP-rocks. The carbonate pseudotachylite occurs within an 43 mm thick), consists of dark (hematitic) red, ultra-fine grained unlayered carbonate with up to 40x10 mm rather rounded clasts of earlier generations of cataclasite, many with a quartzite composition. These clasts are fractured and partially separated, with a fine red carbonate matrix. No layering of the matrix or clasts is apparent. The clasts become finer and more abundant towards the boundary with Layer B. Layers B and D (~57 & ~20 mm thick) dominantly comprises protocataclasite with greyish quartz fragments separated by a carbonate matrix along narrow fractures. Zone C and E (~23 m & >15 mm thick) comprise pale pink carbonate-dominated rocks with abundant material and may have darker (?reaction) rims. No layering is seen in the pale pink groundmass although this is present in some elongate clasts. All layer boundaries are irregular and no principle slip surfaces have been seen. Injection veins from 1 to 9 mm wide and up to at least 100 mm long derive from the central layer (C), cutting the overall layering at a high angle and branching in several places. These veins contain clasts comparable to those in Layer C. Both thick and thin injection-veins are rimmed by impersistent white calcite suggesting that injection was associated with precipitation of calcite. Whether Layer C (and perhaps E also) is a carbonate pseudotachylite is

  15. 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

  16. Latest Miocene-Pliocene Tiliviche Paleolake, Atacama Desert, Northern Chile 19.5°S: Paleoclimatic and Paleohydrologic Implications

    Science.gov (United States)

    Kirk-Lawlor, N. E.; Jordan, T. E.; Rech, J.; Lehmann, S.

    2010-12-01

    Endorheic paleolake deposits of diatomite, mudstone, sandstone, and evaporites are exposed in the Atacama Desert of northern Chile. This study focuses on a major latest Miocene-Pliocene paleolake system centered at 19.5°S, near Tiliviche. A diatiomite unit, up to 35m thick, composed of 0.2-1.5m thick beds of massive, white diatiomite, free of plant matter and root traces, is interpreted have formed from lacustrine diatom blooms. At its maximum extent, the lake would have had a surface area of roughly 200 km2, based on the extent of the diatomite unit, and might have been 50-100 m deep, as inferred by the relationship between the diatomite unit and modern topography. The Tiliviche paleolake initially formed before 6.4 Ma, and much of its sedimentary record formed under a wetter climatic and hydrologic regime than the present. Prior to 3.5 Ma, the lake had evolved into a groundwater-fed saltpan. Polygonally fractured efflorescent halite evaporite and bedded gypsum and gypsarenite evaporite deposits that overlie the diatomite unit are evidence of this saltpan environment. The modern Atacama Desert is hyperarid, with an average precipitation of 2 mm/yr in the driest areas. The paleosol record demonstrates that hyperarid conditions dominated this region since the middle Miocene, albeit with multiple fluctuations to less arid conditions of short to moderately long duration. This hyperaridity is due to the desert’s latitude, ocean currents and the rainshadow created by the Andes. There is no evidence that the rainshadow effect has diminished since the late Miocene, hence global climate changes affecting ocean temperatures and atmospheric patterns likely caused the wetter periods in the Atacama. In particular, prior workers noted wetter conditions in the region ~6-5 Ma, followed by a return to hyper-arid conditions. The regional Pliocene return to hyperaridity coincided with the desiccation of the Tiliviche endorheic lake system. During the late Miocene (~6-5 Ma) wetter

  17. Miocene magmatism and tectonics within the Peri-Alboran orogen (western Mediterranean)

    Science.gov (United States)

    El Azzouzi, M.; Bellon, H.; Coutelle, A.; Réhault, J.-P.

    2014-07-01

    The aim of this paper concerns Miocene igneous activity in the Alboran Sea and Peri-Alboran area (northern Morocco, western Algeria and Betic Cordilleras in Spain), considering its age and its location with regard to major tectonics structures. We have compiled previous K-Ar isotopic ages of lavas and plutonic boulders and intrusives with an error of ±1σ and completed this set by a new K-Ar isotopic age for andesitic tuffites from Alboran Island. Geochemistry of most of these samples has been considered after previous analyses completed with new data for Spain magmatism. These two sets of data allow us to place the magmatic activity within the regional stratigraphy and tectonics and their chronological framework of the three major tectonic phases of the Maghrebian orogen, at 17 Ma (Burdigalian), 15 Ma (Langhian) and 9 Ma (Tortonian). Petro-geochemical characteristics are compared through time and geographical locations. A major goal of this coupled approach is to help the elaboration of possible geodynamical processes. As an application, we present the case study of the Dellys, Djinet and Thenia region (east of Algiers) where the successive magmatic events between 19.4 ± 1 and 11.6 ± 0.5 Ma are closely related to the local tectonics and sedimentation. The Peri-Alboran igneous activity is placed in a multidisciplinary framework. Timing of activity is defined according to the ages of the neighbouring sedimentary units and the K-Ar ages of igneous rocks. In Spain, the Cabo de Gata-Carboneras magmatic province displays late Oligocene and early Miocene leucogranitic dikes, dated from 24.8 ± 1.3 to 18.1 ± 1.2 Ma; three following andesitic to rhyolitic events took place around 15.1 ± 0.8 to 14.0 ± 0.7 Ma, 11.8 ± 0.6 to 9.4 ± 0.4 Ma, 8.8 ± 0.4 to 7.9 ± 0.4 Ma; this last event displays also granitic rocks. Lamproitic magmas dated between 8.4 ± 0.4 and 6.76 ± 0.04 Ma were emplaced after the Tortonian phase. In Morocco, after the complex building of the Ras Tarf

  18. Late Miocene to early Pliocene climate variability off NW Africa (ODP Site 659)

    NARCIS (Netherlands)

    Colin, C.; Siani, G.; Liu, Z.; Blamart, D.; Skonieczny, C.; Zhao, Y.; Bory, A.; Frank, N.; Duchamp-Alphonse, S.; Thil, F.; Richter, T.; Kissel, C.; Gargani, J.

    2014-01-01

    A high resolution delta O-18 record obtained on benthic foraminifera (Cibicides wuellerstorfi) combined with clay mineralogy, major element concentrations and Sr-Nd isotopes have been investigated for the ODP Site 659 located off North Africa in order to reconstruct African monsoon intensity between

  19. 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

  20. Amazon forest dynamics under changing abiotic conditions in the early Miocene (Colombian Amazonia)

    NARCIS (Netherlands)

    Salamanca, S.; van Soelen, E.E.; Teunissen van Manen, Milan L.; Flantua, Suzette G.A.; Ventura Santos, Roberto; Roddaz, M.; Dantas, Elton Luiz; van Loon, Emiel; Sinninghe Damsté, J.S.; Kim, J.H.; Hoorn, Carina

    2016-01-01

    Aim We analysed in detail a past marine incursion event in north-western Amazonia and measured its effect on the forest composition. We also determined the sediment provenance in the fluvio-estuarine system and reconstructed the overall floral composition of the Amazon lowland forest during the

  1. A fruit wing of Shorea Roxb. from the Early Miocene sediments of ...

    Indian Academy of Sciences (India)

    Previously recorded plant megafossils from the Khari River Formation, Kachchh. Fossil species .... Origin and evolution of ... era of vascular plants V: Flowering plant-Dicotyledons- ... Hickey L J 1979 A revised classification of the architecture.

  2. Precipitation history of the central Atacama Desert since the Miocene as reconstructed from clay pan records of the Costal Cordillera/ N Chile

    Science.gov (United States)

    Wennrich, V.; Melles, M.; Diederich, J. L.; Fernández Galego, E.; Ritter, B.; Brill, D.; Niemann, K.; Rolf, C.; Dunai, T. J.

    2017-12-01

    Hyperaridity is a major limitation of Earth-surface processes and biological activity in the Atacama Desert of N Chile, one of the oldest and the driest deserts on Earth. But even the hyperarid core of the Atacama Desert of N Chile has experienced sever precipitation events, e.g., during the flash floods in 2015. On geological timescales, the overall aridity that is postulated to have lasted at least since the early Miocene was punctuated by distinct pluvial events. Such wetter conditions, e.g. during the Miocene, caused widespread lake-formation in the Central Depression and Coastal Cordillera, but also caused amplified surface processes, changes in vegetation dynamics, and enabled the dispersal of species. Unfortunately, due to the limited number and heterogeneous appearance of climate archives from the central Atacama, it's longer-scale precipitation history is still a matter of controversy. This study aims to study continuous longterm (Pleistocene-Miocene) paleoclimatic and environmental records from the hyperarid core of the Atacama Desert covering the last >10 Ma. Therefor we investigate clay pans records from endorheic basins in the Coastal Cordillera mostly formed by blocking of drainage by tectonic movement. The clay pans under study are located along a latitudinal transect across the hyperarid core of the Atacama, and thus, are assumed to have recorded local and regional precipitation variations on different timescales. The investigated sequences exhibit significant changes in the sedimentological, geochemical, and mineralogical properties due to changes in precipitation, but also in the weathering and erosion in the catchments. Diatom and phytolith remains preserved in these records clearly point to significant water bodies during the wettest periods and a significant vegetation cover. The results shed a new light on the timing, frequency, and the driving mechanisms of the intervening pluvial phases.

  3. Miocene-Recent sediment flux in the south-central Alaskan fore-arc basin governed by flat-slab subduction

    Science.gov (United States)

    Finzel, Emily S.; Enkelmann, Eva

    2017-04-01

    The Cook Inlet in south-central Alaska contains the early Oligocene to Recent stratigraphic record of a fore-arc basin adjacent to a shallowly subducting oceanic plateau. Our new measured stratigraphic sections and detrital zircon U-Pb geochronology and Hf isotopes from Neogene strata and modern rivers illustrate the effects of flat-slab subduction on the depositional environments, provenance, and subsidence in fore-arc sedimentary systems. During the middle Miocene, fluvial systems emerged from the eastern, western, and northern margins of the basin. The axis of maximum subsidence was near the center of the basin, suggesting equal contributions from subsidence drivers on both margins. By the late Miocene, the axis of maximum subsidence had shifted westward and fluvial systems originating on the eastern margin of the basin above the flat-slab traversed the entire width of the basin. These mud-dominated systems reflect increased sediment flux from recycling of accretionary prism strata. Fluvial systems with headwaters above the flat-slab region continued to cross the basin during Pliocene time, but a change to sandstone-dominated strata with abundant volcanogenic grains signals a reactivation of the volcanic arc. The axis of maximum basin subsidence during late Miocene to Pliocene time is parallel to the strike of the subducting slab. Our data suggest that the character and strike-orientation of the down-going slab may provide a fundamental control on the nature of depositional systems, location of dominant provenance regions, and areas of maximum subsidence in fore-arc basins.

  4. Primate fauna from the Miocene La Venta, in the Tatacoa desert, department of Huila, Colombia Primate fauna from the Miocene La Venta, in the Tatacoa desert, department of Huila, Colombia

    Directory of Open Access Journals (Sweden)

    Setoguchi Takeshi

    1986-12-01

    Full Text Available Los ejemplares aquí descritos aumentan el conocimiento sobre la diversidad de los primates del Mioceno medio de América del Sur. Nótese, sin embargo que se discutirá y se mencionará solo el material que ya ha sido descrito previamente; el resto de fósiles se prepara para otra publicación (SETOGOUCHI y ROSENBERGER, en preparación, razón por la cual no se mencionan en este manuscrito. Estos datos proporcionan un panorama más claro sobre la diversificación de la fauna primatológica durante el Mioceno medio.  En esta área, ahora periférica a la Cuenca del Amazonas, donde los primates platirrinos son muy abundantes, pudieron haber vivido 10 especies, en forma simpátrica, sin tenerse en cuenta las diferencias temporales. El arreglo adaptativo de insectívoros-frugívoros-folívoros que tipifica las comunidades del bosque Neotropical en la actualidad, parece guardar similitud con las comunidades de primates fósiles de La Venta. Estos fósiles también parecen corroborar la hipótesis (ROSENBERGER,1979; DELSON & ROSENBERGER, 1984 de que los géneros de monos vivientes del Nuevo Mundo (Callithrix, AIouatta y Ateles representan una rama filogenética que se separó hace mucho tiempo y que guarda una estrecha relación con los fósiles encontrados en el sitio Kyoto en La Venta, los cuales, posiblemente fueron sus ancentros.The Tatacoa desert in Department of Huila of Republic of Colombia,is one of the richest classical continental South American localitiesyielding Tertiary vertebrate faunas, known as the La Venta fauna. The LaVenta is within the Miocene Honda Group and its fauna has been correlated with Argentine deposits of the Friasian Land Mammal Age, dated at about 14 Ma (million years ago. The original collection yielded three primate species: Neosaimiri fieldsi, Cebu pithecia sarmient oi, and Stirt onia tatacoensis.Other fossil platyrrhine primates are known by four or five additionalgenera from the early Oligocene through early

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

    NARCIS (Netherlands)

    Mourik, A.A.|info:eu-repo/dai/nl/304849383

    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

  6. 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.

  7. 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.

  8. 3-D seismic characterization of submarine landslides on a Miocene carbonate platform (Luconia Province, Malaysia)

    NARCIS (Netherlands)

    Zampetti, V.; Schlager, W.; van Konijnenburg, J.H; Everts, A.J.

    2004-01-01

    3-D seismic reflection data and a variance cube are used to determine the architecture and investigate the triggering processes of submarine landslides affecting the flanks of a Miocene carbonate platform in the Luconia Province, Malaysia. The slide masses exhibit, in time-slice displays, chaotic,

  9. Geochemical history of a Lower Miocene lake, the Cypris Formation, Sokolov Basin, Czech Republic

    Czech Academy of Sciences Publication Activity Database

    Kříbek, B.; Knésl, I.; Rojík, P.; Sýkorová, Ivana; Martínek, K.

    2017-01-01

    Roč. 58, č. 2 (2017), s. 169-190 ISSN 0921-2728 R&D Projects: GA ČR GA205/09/1162 Institutional support: RVO:67985891 Keywords : intracontinental Miocene * Czech Republic * geochemistry * organic matter * paleolake evolution Subject RIV: DD - Geochemistry OBOR OECD: Geology Impact factor: 2.017, year: 2016

  10. A new short-rostrum odontocete (Mammalia: Cetacea) from the middle Miocene of the Eastern Netherlands

    NARCIS (Netherlands)

    Bianucci, G.; Landini, W.

    2002-01-01

    An incomplete odontocete (Mammalia, Cetacea) skull from Middle Miocene Miste Bed (near Winterswijk in the eastern part of The Netherlands) is described as Vanbreenia trigonia, a new genus and species. The skull exhibits a short rostrum with only two maxillary teeth for each toothrow and with narrow

  11. Whiting–related sediment export along the Middle Miocene carbonate ramp of Great Bahama Bank.

    NARCIS (Netherlands)

    Turpin, M.; Emmanuel, L.; Reijmer, J.J.G.; Renard, M.

    2011-01-01

    Modern aragonite needles are present all along the modern leeward margin of Great Bahama Bank (ODP Leg 166), while Middle Miocene sediments contain needles only in more distal areas (Sites 1006 and 1007). In contrast to the rimmed, flat-topped platform topography during the Plio-Pleistocene, the

  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. The influence of late Miocene exhumation on the petroleum systems of the greater Caucasus foreland basins

    International Nuclear Information System (INIS)

    Andy, A.; Colin, D.; Sally, H.; Simon, O.

    2002-01-01

    Full text: Northwards impingement of Arabia during the Cenozoic led to the inversion of the Mesozoic Greater Caucasus Basin and the associated development of areas of enhanced subsidence. However, there is great debate regarding the timing of initiation of thrusting and uplift in the Caucasus region.Traditionally, ages ranging from Middle Eocene through to Middle Miocene have been proposed.More recently. It has become clear that although deformation and flexural subsidence may have initiated during the Late Miocene to Pliocene.The potential causative mechanisms for this late uplift and exhumation did not begin until the Late Miocene to Pliocene.The potential causative mechanisms for this late uplift event have been identified.The late Miocene to Pliocene event influenced a broad region and had important implications for reservoir rock deposition and the generation,migration,trapping and preservation of hydrocarbons in the surrounding basins (e.g. Indolo-Kuban,Terek-Caspian, South Caspian, Kura-Kartli, Rion, Black Sea).One area of particular interest is the development of the Stavropol Arch through time,since foreland basins are presently restricted to the Indolo-Kuban and Terek-Caspian Sub-basins.The Stavropol Arch lies immediately north of the central, most elevated parts of the Caucasus Mountains and separates the main areas of enhanced foreland subsidence.Although in most palaeogeographic reconstructions of the area, the Stavropol Arch is shown as an uplifted massif during much of the Mesozoic and Lower Cenozoic, it seems likely from recent studies that it is a feature of Late Miocene to Pliocene exhumation.One major potential implication is that an Oligocene to Miocene (foreland) succession developed in a major basin across the whole region north of the Greater Caucasus.Much of this was subsequently eroded from the Stavropol Arch during uplift and exhumation, separating the Indolo-Kuban and Terek-Caspian foreland basins.From qualitative section balancing we

  14. Miocene denudation history of Himalaya deduced from IODP Exp. 354 Bengal Fan

    Science.gov (United States)

    Kohki, Y.; Cruz, J. W.; Osaki, A.; Manoj, M. C.; Hatano, N.; France-Lanord, C.; Spiess, V.; Klaus, A.

    2017-12-01

    The submarine Bengal Fan is the largest submarine fan on Earth and covers the whole Bay of Bengal. The sediments are fed by the Ganges and Brahmaputra rivers reflecting India-Asia plate collision. The sediments recovered from IODP Expedition 354 Bengal Fan record the uplift history of the Himalayan orogenic system. We examined the chemical composition of detrital garnets in the Miocene deposits from Site U1451, where drilling reached to basal horizon of the fan deposits, in order to reveal the detailed denudation history of Himalayan metamorphic rocks. For this purpose, the comparison of chemical composition between detrital garnet in the Bengal Fan deposits and metamorphic garnet in Himalayan metamorphic rocks was carried out. The chemical composition of the metamorphic garnet from Higher Himalayan Crystalline (HHC) in Karnali and Kaligandaki areas, western Nepal, was examined for chemical reference to detrital garnets in Bengal Fan. The metamorphic garnets in "Formation I (Le Fort, 1975)" in HHC are characterized by almandine-rich garnet with high pyrope content. Also, the garnets in "Formation II" are remarked by two types of garnets, i.e., almandine-rich and grandite-rich garnets. Meanwhile, the composition of garnets in "Formation III" is almandine-rich garnet with low pyrope content. In the Bengal Fan deposits, the characteristic garnets, which show the similarity to the metamorphic garnet in HHC, is not found from the Lower Miocene (Burdigalian) deposits. In the Middle and Upper Miocene deposits, the almandine-rich garnets characteristic in Formation I, are normally included. At the basal part of the Middle Miocene (Langhian), almandine-rich garnets with low pyrope content, suggesting the derivation from Formation III, are remarkable. The grandite-rich garnets from Formation II are sporadically found In the Upper Miocene deposits (Tortonian-Messinian). Above chemical comparison between the detrital garnets in Bengal Fan and metamorphic garnets from HHC

  15. Pleistocene to Miocene Calcareous Nannofossil Biostratigraphy from IODP Expedition 334 Hole U1381A and Expedition 352 Hole U1439A

    Science.gov (United States)

    Power, M.; Scientists, I. E.; Avery, A. J.

    2015-12-01

    Samples for this study were collected from drill cores taken during the Integrated Ocean Drilling Program (IODP) Expeditions 334 and 352 at Sites U1381 and U1439, respectively. Both of these expeditions were focused around subduction zones and, therefore, had priorities to determine time frames for the initiation of subduction. There are two main objectives for this study, the first being to age-date Pleistocene to Miocene sediments from the western offshore continental margin of Costa Rica (IODP Expedition 334) via calcareous nannofossils. The second objective is to age-date the Miocene sediments from the fore-arc of the Izu-Bonin-Mariana system, east of Japan (IODP Expedition 352), using calcareous nannofossils. Shore-based analysis allows for high-resolution study to determine exact biostratigraphic zonations. These zonations reflect specific time frames based on the occurrence or non-occurrence of certain nannofossil species. Once these zonations are determined, scientists can use the data to identify the initiation of seismic processes that often occur in these regions. Calcareous nannofossil biostratigraphy has now provided zonations for the samples taken from IODP Expedition 334 cores. Samples from core 6R are assigned to the Pleistocene nannofossil Zone NN19 due to the presence ofPseudoemiliania lacunosa and the absence of Emiliania huxleyi. Using the zonal scheme by de Kaenel (1999), this can further be broken down into Event 18 due to the presence of Gephyrocapsa oceanica larger than 4 μm but less than 5 μm, the presence of Calcidiscus macintyrei smaller than 11 μm, and the absence ofGephyrocapsa caribbeanica larger than 4 μm. De Kaenel (1999) has assigned this event datum an age of 1.718 Ma using orbital time scales and oxygen isotope data. Below these samples, an extensive hiatus ranges from the Pleistocene to the early Miocene. Samples from cores 7R through 10R are assigned to nannofossil zone NN5; however, it is impossible to constrain the top of

  16. Miocene magmatism in the Bodie Hills volcanic field, California and Nevada: A long-lived eruptive center in the southern segment of the ancestral Cascades arc

    Science.gov (United States)

    John, David A.; du Bray, Edward A.; Blakely, Richard J.; Fleck, Robert J.; Vikre, Peter; Box, Stephen E.; Moring, Barry C.

    2012-01-01

    The Middle to Late Miocene Bodie Hills volcanic field is a >700 km2, long-lived (∼9 Ma) but episodic eruptive center in the southern segment of the ancestral Cascades arc north of Mono Lake (California, U.S.). It consists of ∼20 major eruptive units, including 4 trachyandesite stratovolcanoes emplaced along the margins of the field, and numerous, more centrally located silicic trachyandesite to rhyolite flow dome complexes. Bodie Hills volcanism was episodic with two peak periods of eruptive activity: an early period ca. 14.7–12.9 Ma that mostly formed trachyandesite stratovolcanoes and a later period between ca. 9.2 and 8.0 Ma dominated by large trachyandesite-dacite dome fields. A final period of small silicic dome emplacement occurred ca. 6 Ma. Aeromagnetic and gravity data suggest that many of the Miocene volcanoes have shallow plutonic roots that extend to depths ≥1–2 km below the surface, and much of the Bodie Hills may be underlain by low-density plutons presumably related to Miocene volcanism.Compositions of Bodie Hills volcanic rocks vary from ∼50 to 78 wt% SiO2, although rocks with Bodie Hills rocks are porphyritic, commonly containing 15–35 vol% phenocrysts of plagioclase, pyroxene, and hornblende ± biotite. The oldest eruptive units have the most mafic compositions, but volcanic rocks oscillated between mafic and intermediate to felsic compositions through time. Following a 2 Ma hiatus in volcanism, postsubduction rocks of the ca. 3.6–0.1 Ma, bimodal, high-K Aurora volcanic field erupted unconformably onto rocks of the Miocene Bodie Hills volcanic field.At the latitude of the Bodie Hills, subduction of the Farallon plate is inferred to have ended ca. 10 Ma, evolving to a transform plate margin. However, volcanism in the region continued until 8 Ma without an apparent change in rock composition or style of eruption. Equidimensional, polygenetic volcanoes and the absence of dike swarms suggest a low differential horizontal stress regime

  17. The role of changing geodynamics in the progressive contamination of Late Cretaceous to Late Miocene arc magmas in the southern Central Andes

    Science.gov (United States)

    Jones, Rosemary E.; Kirstein, Linda A.; Kasemann, Simone A.; Litvak, Vanesa D.; Poma, Stella; Alonso, Ricardo N.; Hinton, Richard; EIMF

    2016-10-01

    The tectonic and geodynamic setting of the southern Central Andean convergent margin changed significantly between the Late Cretaceous and the Late Miocene, influencing magmatic activity and its geochemical composition. Here we investigate how these changes, which include changing slab-dip angle and convergence angles and rates, have influenced the contamination of the arc magmas with crustal material. Whole rock geochemical data for a suite of Late Cretaceous to Late Miocene arc rocks from the Pampean flat-slab segment (29-31 °S) of the southern Central Andes is presented alongside petrographic observations and high resolution age dating. In-situ U-Pb dating of magmatic zircon, combined with Ar-Ar dating of plagioclase, has led to an improved regional stratigraphy and provides an accurate temporal constraint for the geochemical data. A generally higher content of incompatible trace elements (e.g. Nb/Zr ratios from 0.019 to 0.083 and Nb/Yb from 1.5 to 16.4) is observed between the Late Cretaceous ( 72 Ma), when the southern Central Andean margin is suggested to have been in extension, and the Miocene when the thickness of the continental crust increased and the angle of the subducting Nazca plate shallowed. Trace and rare earth element compositions obtained for the Late Cretaceous to Late Eocene arc magmatic rocks from the Principal Cordillera of Chile, combined with a lack of zircon inheritance, suggest limited assimilation of the overlying continental crust by arc magmas derived from the mantle wedge. A general increase in incompatible, fluid-mobile/immobile (e.g., Ba/Nb) and fluid-immobile/immobile (e.g., Nb/Zr) trace element ratios is attributed to the influence of the subducting slab on the melt source region and/or the influx of asthenospheric mantle. The Late Oligocene ( 26 Ma) to Early Miocene ( 17 Ma), and Late Miocene ( 6 Ma) arc magmatic rocks present in the Frontal Cordillera show evidence for the bulk assimilation of the Permian-Triassic (P

  18. 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.

  19. Controls on the quality of Miocene reservoirs, southern Gulf of Mexico

    Science.gov (United States)

    Gutiérrez Paredes, Hilda Clarisa; Catuneanu, Octavian; Hernández Romano, Ulises

    2018-01-01

    An investigation was conducted to determine the main controls on the reservoir quality of the middle and upper Miocene sandstones in the southern Gulf of Mexico based on core descriptions, thin section petrography and petrophysical data; as well as to explore the possible link between the sequence stratigraphic framework, depositional facies and diagenetic alterations. The Miocene deep marine sandstones are attributed to the falling-stage, lowstand, and transgressive systems tracts. The middle Miocene falling-stage systems tract includes medium-to very fine-grained, and structureless sandstones deposited in channels and frontal splays, and muddy sandstones, deposited in lobes of debrites. The lowstand and transgressive systems tracts consist of medium-to very fine-grained massive and normally graded sandstones deposited in channel systems within frontal splay complexes. The upper Miocene falling-stage systems tract includes medium-to coarse-grained, structureless sandstones deposited in channel systems and frontal splay, as well as lobes of debrites formed by grain flows and hybrid-flow deposits. The lowstand and transgressive systems tracts include fine-grained sandstones deposited in overbank deposits. The results reveal that the depositional elements with the best reservoir quality are the frontal splays deposited during the falling-stage system tracts. The reservoir quality of the Miocene sandstones was controlled by a combination of depositional facies, sand composition and diagenetic factors (mainly compaction and calcite cementation). Sandstone texture, controlled primarily by depositional facies appears more important than sandstone composition in determining reservoir quality; and compaction was more important than cementation in porosity destruction. Compaction was stopped, when complete calcite cementation occurred.

  20. Palynology of carcinolites and limestones from the Baunilha Grande Ecofacies of the Pirabas Formation (Miocene of Pará state, northeastern Brazil)

    Science.gov (United States)

    Antonioli, Luzia; de Araújo Távora, Vladimir; Dino, Rodolfo

    2015-10-01

    The Pirabas Formation records important transgressive/regressive marine events in northern Brazil during the Miocene. Here, we present the results of a palynological analysis of four samples from finely stratified gray limestone and associated carbonate concretions bearing decapod crustacean remains. These sampled strata are representatives of the Baunilha Grande Ecofacies, and our analysis enhances the knowledge of local biostratigraphy and paleoecology. The palynoflora is dominated by taxa typical of Neogene tropical areas, such as Zonocostites ramonae (the most common species), together with Retitricolpites and Retitricolporites genera. Commonly represented are the smooth and apiculate trilete/monolete spores (Polypodiisporites, Verrucosisporites, Magnastriatites, and Deltoidospora), in conjunction with some freshwater algae (Ovoidites and Botryococcus). Gymnosperm pollen grains were absent. Marine microplankton (dinoflagellate cysts, acritarchs and foraminiferal test linings) are scarce, although present in all samples. The presence of the index species, Malvacipolloides maristellae and Pachydermites diederixii, co-occurring with Zonocostites ramonae and Lanagiopollis crassa, suggests that these sediments and concretions belong to the "T-13 Malvacipolloides maristellae" palynozone (Jaramillo et al., 2011), considered as late-Early Miocene in age. Palynological and sedimentological evidence further points to a predominantly continental depositional environment with a weak marine influence, as indicated by the persistent presence of sparse dinoflagellate cysts, acritarchs and foraminiferal test linings, typical of a mangrove environment.

  1. A WELL PRESERVED SKELETON OF THE FOSSIL SHARK COSMOPOLITODUS HASTALIS FROM THE LATE MIOCENE OF PERU, FEATURING FISH REMAINS AS FOSSILIZED STOMACH CONTENTS

    Directory of Open Access Journals (Sweden)

    ALBERTO COLLARETA

    2017-01-01

    Full Text Available Both the preservation of the poorly mineralized skeleton of sharks and the preservation of stomach contents are rarely observed in the fossil record. Here we report on a partial skeleton of a lamniform shark, including portions of the visceral arches and the anterior segment of the vertebral column, collected from the late Miocene beds of the Pisco Formation exposed at Cerro Yesera (Ica Desert, South Peru. Based on the morphology of the preserved teeth, this specimen was determined as a juvenile of the extinct lamnid species Cosmopolitodus hastalis. The shark skeleton includes remains of fish (featuring a pilchard determined as Sardinops sp. cf. S. sagax in the abdominal region. These fish remains are interpreted herein as the fossilized stomach contents of the shark. For the first time, piscivory is demonstrated in a juvenile individual of Cosmopolitodus hastalis. This result is consistent with the current knowledge about the feeding habits of immature individuals of extant lamniform shark species (including Carcharodon carcharias and Isurus oxyrinchus. Our report further outlines the fundamental role of schooling pilchards in the late Miocene trophic chains of the highly productive coastal waters off present South Peru. Moreover, the find of this well preserved shark skeleton strengthens the qualification of the Pisco Formation as a Fossil-Lagerstätte, and emphasizes the role of early mineralization processes in cases of exceptional preservation.

  2. Insights into the diagenetic environment of fossil marine vertebrates of the Pisco Formation (late Miocene, Peru) from mineralogical and Sr-isotope data

    Science.gov (United States)

    Gioncada, A.; Petrini, R.; Bosio, G.; Gariboldi, K.; Collareta, A.; Malinverno, E.; Bonaccorsi, E.; Di Celma, C.; Pasero, M.; Urbina, M.; Bianucci, G.

    2018-01-01

    The late Miocene Pisco Formation of Peru is an outstanding example of richness and high-quality preservation of fossil marine vertebrates. In order to reconstruct the fossilization path, we present new textural, mineralogical and Sr-isotope data of diagenetic minerals formed in correspondence of fossil specimens such as marine vertebrates and mollusks. These fossil specimens were found at Cerro los Quesos, in the Ica Desert, within the diatomaceous strata of the Pisco Formation. Dolomite, gypsum, anhydrite and Mn minerals are the main phases found, while the calcium carbonate originally forming the mollusk valves is replaced by gypsum. An early formation of dolomite and of Mn minerals, triggered by the modifications of the geochemical environment due to organic matter degradation, is suggested by the textural relationships and is confirmed by the Sr isotopic ratio of dolomite, which agrees with that of seawater at the time of sedimentation. Instead, gypsum Sr isotopic ratios indicate a pre-Miocene seawater-derived brine circulating within the sedimentary sequence as a source for Sr. Oxidation of diagenetic sulfide causing a lowering of the pH of porewater is proposed as an explanation for Ca-carbonate dissolution. The diagenetic chemical environment was, nevertheless, favorable to bone preservation.

  3. The occurrence of an abdominal fauna in an articulated tapir (Tapirus polkensis) from the Late Miocene Gray Fossil Site, Northeastern Tennessee.

    Science.gov (United States)

    McCONNELL, Shannon M; Zavada, Michael S

    2013-03-01

    The analysis of samples recovered from the abdominal area of an articulated tapir (Tapirus polkensis) from the Late Miocene (4.5-7 million BP) Gray Fossil Site (GFS) revealed a rich palyno-fauna comprised of about 94% egg/oocyst-like structures and 6% pollen and other palynomorphs. In addition, a group of 6 hickory nuts (Carya) was recovered from the same area suggesting that the samples represent the abdominal contents. The analysis of a sample from immediately outside the tapir produced a sample with 98% pollen and less than 0.5% egg/oocyst-like structures. The size, shape, and general morphology of egg/oocyst-like structures were analyzed with light and scanning electron microscopy and were compared to a variety of intestinal parasites found in extant ungulates, and the Perissodactyla in particular. We also compared fossil structures to the numbers and kind of intestinal parasites recovered from fecal samples from the Baird's tapir (T. bairdii) in Costa Rica and from samples collected from the lowland tapir (T. terrestris) from Ecuador to assess their similarity to our fossil sample. Based on these data, we discuss what role parasites may have played in the biology of T. polkensis during the Late Miocene-Early Pliocene. © 2012 Wiley Publishing Asia Pty Ltd, ISZS and IOZ/CAS.

  4. A new, large-bodied omnivorous bat (Noctilionoidea: Mystacinidae) reveals lost morphological and ecological diversity since the Miocene in New Zealand.

    Science.gov (United States)

    Hand, Suzanne J; Beck, Robin M D; Archer, Michael; Simmons, Nancy B; Gunnell, Gregg F; Scofield, R Paul; Tennyson, Alan J D; De Pietri, Vanesa L; Salisbury, Steven W; Worthy, Trevor H

    2018-01-10

    A new genus and species of fossil bat is described from New Zealand's only pre-Pleistocene Cenozoic terrestrial fauna, the early Miocene St Bathans Fauna of Central Otago, South Island. Bayesian total evidence phylogenetic analysis places this new Southern Hemisphere taxon among the burrowing bats (mystacinids) of New Zealand and Australia, although its lower dentition also resembles Africa's endemic sucker-footed bats (myzopodids). As the first new bat genus to be added to New Zealand's fauna in more than 150 years, it provides new insight into the original diversity of chiropterans in Australasia. It also underscores the significant decline in morphological diversity that has taken place in the highly distinctive, semi-terrestrial bat family Mystacinidae since the Miocene. This bat was relatively large, with an estimated body mass of ~40 g, and its dentition suggests it had an omnivorous diet. Its striking dental autapomorphies, including development of a large hypocone, signal a shift of diet compared with other mystacinids, and may provide evidence of an adaptive radiation in feeding strategy in this group of noctilionoid bats.

  5. Eocene to Miocene Out-of-Sequence Deformation in the Eastern Tibetan Plateau: Insights From Shortening Structures in the Sichuan Basin

    Science.gov (United States)

    Tian, Yuntao; Kohn, Barry P.; Qiu, Nansheng; Yuan, Yusong; Hu, Shengbiao; Gleadow, Andrew J. W.; Zhang, Peizhen

    2018-02-01

    A distinctive NNE trending belt of shortening structures dominates the topography and deformation of the eastern Sichuan Basin, 300 km east of the Tibetan Plateau. Debate continues as to whether the structures resulted from Cenozoic eastward growth of the Tibetan Plateau. A low-temperature thermochronology (AFT and AHe) data set from four deep boreholes and adjacent outcrops intersecting a branch of the shortening structures indicates distinctive differential cooling at 35-28 Ma across the structure, where stratigraphy has been offset vertically by 0.8-1.3 km. This result forms the first quantitative evidence for the existence of a late Eocene-Oligocene phase of shortening in the eastern Sichuan Basin, synchronous with the early phase of eastward growth and extrusion of the Tibetan Plateau. Further, a compilation of regional Cenozoic structures reveals a Miocene retreat of deformation from the foreland basin to the hinterland areas. Such a tectonic reorganization indicates that Eocene to Miocene deformation in the eastern Tibetan Plateau is out-of-sequence and was probably triggered by enhanced erosion in the eastern Tibetan Plateau.

  6. Diagenetic history of the Surma Group sandstones (Miocene) in the Surma Basin, Bangladesh

    Science.gov (United States)

    Rahman, M. Julleh Jalalur; McCann, Tom

    2012-02-01

    This study examines the various diagenetic controls of the Miocene Surma Group sandstones encountered in petroleum exploration wells from the Surma Basin, which is situated in the northeastern part of the Bengal Basin, Bangladesh. The principal diagenetic minerals/cements in the Surma Group sandstones are Fe-carbonates (with Fe-calcite dominating), quartz overgrowths and authigenic clays (predominantly chlorite, illite-smectite and minor kaolin). The isotopic composition of the carbonate cement revealed a narrow range of δ 18O values (-10.3‰ to -12.4‰) and a wide range of δ 13C value (+1.4‰ to -23.1‰). The δ 13C VPDB and δ 18O VPDB values of the carbonate cements reveal that carbon was most likely derived from the thermal maturation of organic matter during burial, as well as from the dissolution of isolated carbonate clasts and precipitated from mixed marine-meteoric pore waters. The relationship between the intergranular volume (IGV) versus cement volume indicates that compaction played a more significant role than cementation in destroying the primary porosity. However, cementation also played a major role in drastically reducing porosity and permeability in sandstones with poikilotopic, pore-filling blocky cements formed in early to intermediate and deep burial areas. In addition to Fe-carbonate cements, various clay minerals including illite-smectite and chlorite occur as pore-filling and pore-lining authigenic phases. Significant secondary porosity has been generated at depths from 2500 m to 4728 m. The best reservoir rocks found at depths of 2500-3300 m are well sorted, relatively coarse grained; more loosely packed and better rounded sandstones having good porosities (20-30%) and high permeabilities (12-6000 mD). These good quality reservoir rocks are, however, not uniformly distributed and can be considered to be compartmentalized as a result of interbedding with sandstone layers of low to moderate porosities, low permeabilities owing to poor

  7. Tectonic implications of a paleomagnetic direction obtained from a Miocene dike swarm in central Honshu, Japan

    Science.gov (United States)

    Hoshi, H.; Sugisaki, Y.

    2017-12-01

    Central Honshu of Japan is an ideal field for the study of crustal deformation related to arc-arc collision. In this study we obtained rock magnetic and paleomagnetic results from early Miocene igneous rocks in central Honshu in order to examine rotational deformation caused by the collision of the Izu-Bonin-Mariana (IBM) arc with central Honshu. In Takane of the Hida region, gabbro intrusions and older sedimentary rocks are intruded by numerous andesitic dikes that comprise a parallel dike swarm. The dikes formed under two different normal-faulting paleostress conditions, which were suggested using a method of clustering dike orientations. Cross-cutting relationships indicate that the two paleostress conditions existed during the same period. More than 240 oriented cores were taken at 38 sites in two localities for magnetic study. The andesites and gabbros generally have magnetite, and some andesites also contain pyrrhotite. The magnetite records easterly deflected remanent magnetization directions of dual polarities that pass the reversals test. Positive baked contact tests at two sites demonstrate that the easterly deflected direction is a thermoremanent magnetization acquired at the time of intrusion. The overall in situ (i.e., in geographic coordinates) mean direction for andesitic dikes is judged to be highly reliable, although there are two possible scenarios for explaining the easterly deflection: (1) clockwise rotation and (2) tilting to the northwest. We prefer the former scenario and conclude that 45° clockwise rotation occurred in Takane with respect to the North China Block of the Asian continent. This rotation must represent the clockwise rotation of entire Southwest Japan during the opening period of the Japan Sea. Very little difference is observed between the amount of the easterly deflection in Takane and those in the Tokai and Hokuriku regions, indicating no significant relative rotation. Thus, the crust beneath Takane has not suffered rotation

  8. Early stages of clastic deposition in the Most Basin (Ohre Rift, Czech Republic, Early Miocene): timing and possible controls

    Czech Academy of Sciences Publication Activity Database

    Matys Grygar, Tomáš; Mach, K.; Hošek, Michal; Schnabl, Petr; Martinez, M.; Koubová, M.

    2017-01-01

    Roč. 92, č. 3 (2017), s. 337-355 ISSN 1214-1119 R&D Projects: GA ČR(CZ) GA16-00800S Institutional support: RVO:61388980 ; RVO:67985831 Keywords : cyclostratigraphy * chemostratigraphy * lake sediments * climate forcing * Burdigalian Subject RIV: DD - Geochemistry; DB - Geology ; Mineralogy (GLU-S) OBOR OECD: Geology Impact factor: 1.175, year: 2016

  9. Metal sources in Jurassic to miocene ore deposits of Ecuador

    International Nuclear Information System (INIS)

    Chiaradia, M.; Fontbote, L

    2001-01-01

    The Ecuadorian crust is a mosaic of NNE-SSW-trending terranes representing different geotectonic domains. These terranes, composed by oceanic and continental crust, were formed during the Triassic separation of the North and South American continents and were accreted to the Amazon craton during subduction of the Farallon/Nazca plate, from Early Cretaceous to Early Tertiary (Litherland et al., 1994). In the southwestern part of Ecuador, EW-striking crustal-scale faults, related to the Huancabamba deflection, mark the transition between the Central and Northern Andes. In this study we discuss more than 200 lead isotope compositions of ores as well as magmatic and metamorphic rocks of Ecuador. The interest of carrying out a large-scale isotope survey in the Northern Andes derives from a geotectonic evolution characterized by multi-accretionary episodes which is not recognized in the Central Andes (au)

  10. Sr isotope evidence for a lacustrine origin for the upper Miocene to Pliocene Bouse Formation, lower Colorado River trough, and implications for timing of Colorado Plateau uplift

    Science.gov (United States)

    Spencer, J.E.; Patchett, P.J.

    1997-01-01

    The upper Miocene to Pliocene Bouse Formation in the lower Colorado River trough, which consists largely of siltstone with basal tufa and marl, has been interpreted as estuarine on the basis of paleontology. This interpretation requires abrupt marine inundation that has been linked to early rifting in the Gulf of California and Salton trough. New strontium isotope measurements reported here from carbonates and invertebrate shells in the Bouse Formation reveal no evidence of marine water, but are consistent with deposition in a lake or chain of lakes fed by the Colorado River. Furthermore, the absence of a southward decrease in 87Sr/86Sr within the Bouse Formation does not support the estuarine model in which low 87Sr/86Sr marine Sr would have dominated the mouth of the hypothetical Bouse estuary. Elevation of originally marine 87Sr/86Sr in the Bouse Formation to its present level, due to postdepositional interaction with ground water, is unlikely because Sr from secondary calcite above, below, and within the Bouse Formation is consistently less radiogenic, not more, than Bouse marl and shells. In contrast to Bouse Sr, strontium from mollusks in tidal-flat and delta-front paleoenvironments in the contemporaneous Imperial Formation in the Salton trough and from the subsurface south of Yuma was derived from sea water and confirms the dominance of marine strontium near or at the mouth of the late Miocene to early Pliocene Colorado River. Inferred post-early Pliocene uplift of the Bouse Formation from below sea level to modern elevations of up to 550 m has been used to support a late Cenozoic uplift age for the nearby Colorado Plateau. This constraint on uplift timing is eliminated if the Bouse Formation is lacustrine.

  11. 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

  12. "Species" radiations of symbiotic dinoflagellates in the Atlantic and Indo-Pacific since the Miocene-Pliocene transition.

    Science.gov (United States)

    Lajeunesse, Todd C

    2005-03-01

    Endosymbiotic dinoflagellates, or "zooxanthellae," are required for the survival of a diverse community of invertebrates that construct and dominate shallow, tropical coral reef ecosystems. Molecular systematics applied to this once understudied symbiont partner, Symbiodinium spp., divide the group into divergent lineages or subgeneric "clades." Within each clade, numerous closely related "types," or species, exhibit distinctive host taxon, geographic, and/or environmental distributions. This diversity is greatest in clade C, which dominates the Indo-Pacific host fauna and shares dominance in the Atlantic-Caribbean with clade B. Two "living" ancestors in this group, C1 and C3, are common to both the Indo-Pacific and Atlantic-Caribbean. With these exceptions, each ocean possesses a diverse clade C assemblage that appears to have independently evolved (adaptively radiated) through host specialization and allopatric differentiation. This phylogeographic evidence suggests that a worldwide selective sweep of C1/C3, or their progenitor, must have occurred before both oceans separated. The probable timing of this event corresponds with the major climactic changes and low CO(2) levels of the late Miocene and/or early Pliocene. Subsequent bursts of diversification have proceeded in each ocean since this transition. An ecoevolutionary expansion to numerous and taxonomically diverse hosts by a select host-generalist symbiont followed by the onset of rapid diversification suggests a radical process through which coral-algal symbioses respond and persist through the vicissitudes of planetary climate change.

  13. High-precision zircon U-Pb geochronology of astronomically dated volcanic ash beds from the Mediterranean Miocene

    NARCIS (Netherlands)

    Wotzlaw, Jörn Frederik; Hüsing, Silja K.; Hilgen, Frederik J.; Schaltegger, Urs

    2014-01-01

    Several orbitally tuned Miocene sedimentary sequences around the Mediterranean contain abundant intercalated volcanic ash beds. These sequences provide the rare opportunity to directly compare radioisotopic dating methods with independent and accurate deposition ages derived from astrochronology. We

  14. Supra-generic radiolarian transfer function based late Miocene palaeomonsoonal changes in the northeastern tropical Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Gupta, S.M.; Fernandes, A.A.

    and PPT changes using % data of the late Miocene radiolarian sequence from the Sawai Bay Formation, Neill Island, Andamans. Estimated SST and salinity during southwest monsoon are not only conformable with the qualitative paleoceanography in terms...

  15. Stratigraphy, geochronology, and paleoenvironments of Miocene - Pliocene boundary of San Fernando, Belén (Catamarca, northwest of Argentina)

    Science.gov (United States)

    Bonini, Ricardo A.; Georgieff, Sergio M.; Candela, Adriana M.

    2017-11-01

    the Miocene-Pliocene boundary is represented in this area. The lower tuff beds, outcropping at the southwest of San Fernando Sur, provided an age of 5.59 ± 0.04 Ma (late Miocene, Messinian). The others tuffs beds, both outcropping at the west-northwest of San Fernando Norte and overlaying the first one, gave an age of 4.79 ± 0.15 Ma and 4.72 ± 0.08 Ma (early Pliocene, Zanclean), respectively. These absolutes ages, together with the results of a sedimentological analysis, indicate that westward from San Fernando River, much of the areas mapped as Corral Quemado Formation correspond to the Andalhuala Formation; while part of the area considered as Punaschotter unit must be assigned to Corral Quemado Formation. Also, a thick tuff bed, recognized at the contact of Corral Quemado and Punaschotter, was considered as the previous one dated in 3.66 Ma, in Puerta de Corral Quemado locality.

  16. 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

  17. lower and Middle Miocene Foraminiferal Paleoecology of Southwest Sinai Area, Egypt

    International Nuclear Information System (INIS)

    El Ashwah, A.A.E.; Mandur, M.M.; Obeid, F.L.

    2005-01-01

    The planktonic and benthonic foraminifera content of the lower and middle miocene successions exposed at southwest Sinai in Egypt have been studied. One hundred and thirty three foraminifera species were identified (30 planktonic species and 103 benthonic species). This study aims to contribute in the understanding of the paleoecology, paleobathymetry and tectonic history of these sedimentary sequences. These sediments are subdivided into four rock units, from base to top, as follow: Nukhul, Rudeis, Kareem and Balayim formations. According to the foraminifera content the studied successions are subdivided into five eco zones. The environment of each ec ozone is deduced. These environments point to outer neritic for the Nukhul formation, middle to inner neritic for the Rudeis formation, inner to littoral neritic for the Kareem formation and littoral neritic for the Belayim formation. A proposed paleobathymetric curve is presented. The interpretation of this curve helped to deduce the tectonic history of the lower and Middle Miocene sediments in the studied area

  18. Miocene small-bodied ape from Eurasia sheds light on hominoid evolution.

    Science.gov (United States)

    Alba, David M; Almécija, Sergio; DeMiguel, Daniel; Fortuny, Josep; Pérez de los Ríos, Miriam; Pina, Marta; Robles, Josep M; Moyà-Solà, Salvador

    2015-10-30

    Miocene small-bodied anthropoid primates from Africa and Eurasia are generally considered to precede the divergence between the two groups of extant catarrhines—hominoids (apes and humans) and Old World monkeys—and are thus viewed as more primitive than the stem ape Proconsul. Here we describe Pliobates cataloniae gen. et sp. nov., a small-bodied (4 to 5 kilograms) primate from the Iberian Miocene (11.6 million years ago) that displays a mosaic of primitive characteristics coupled with multiple cranial and postcranial shared derived features of extant hominoids. Our cladistic analyses show that Pliobates is a stem hominoid that is more derived than previously described small catarrhines and Proconsul. This forces us to reevaluate the role played by small-bodied catarrhines in ape evolution and provides key insight into the last common ancestor of hylobatids (gibbons) and hominids (great apes and humans). Copyright © 2015, American Association for the Advancement of Science.

  19. Differential responses of Miocene rodent metacommunities to global climatic changes were mediated by environmental context.

    Science.gov (United States)

    Blanco, Fernando; Gómez Cano, Ana Rosa; Cantalapiedra, Juan L; Domingo, M Soledad; Domingo, Laura; Menéndez, Iris; Flynn, Lawrence J; Hernández Fernández, Manuel

    2018-02-06

    The study of how long-term changes affect metacommunities is a relevant topic, that involves the evaluation of connections among biological assemblages across different spatio-temporal scales, in order to fully understand links between global changes and macroevolutionary patterns. We applied multivariate statistical analyses and diversity tests using a large data matrix of rodent fossil sites in order to analyse long-term faunal changes. Late Miocene rodent faunas from southwestern Europe were classified into metacommunities, presumably sharing ecological affinities, which followed temporal and environmental non-random assembly and disassembly patterns. Metacommunity dynamics of these faunas were driven by environmental changes associated with temperature variability, but there was also some influence from the aridity shifts described for this region during the late Miocene. Additionally, while variations in the structure of rodent assemblages were directly influenced by global climatic changes in the southern province, the northern sites showed a pattern of climatic influence mediated by diversity-dependent processes.

  20. Petrology of the Miocene igneous rocks in the Altar region, main Cordillera of San Juan, Argentina. A geodynamic model within the context of the Andean flat-slab segment and metallogenesis

    Science.gov (United States)

    Maydagán, Laura; Franchini, Marta; Chiaradia, Massimo; Pons, Josefina; Impiccini, Agnes; Toohey, Jeff; Rey, Roger

    2011-07-01

    The Altar porphyry Cu-(Au-Mo) deposit (31° 29' S, 70° 28' W) is located in the Andean Main Cordillera of San Juan Province (Argentina), in the southern portion of the flat-slab segment (28-33°S), 25 km north of the world-class porphyry Cu-Mo deposits of Los Pelambres and El Pachón. Igneous rocks in the area have been grouped into the Early Miocene Lower Volcanic Complex -composed of intercalations of lava flows and thin volcaniclastic units that grade upwards to a thick massive tuff- and the Middle-Late Miocene Upper Subvolcanic Suite that consists of a series of porphyritic stocks and dikes and magmatic and hydrothermal breccias. The Lower Volcanic Complex represents an Early Miocene arc (20.8 Ma ± 0.3 Ma; U-Pb age) erupted over a steep subduction zone. Their magmas equilibrated with an assemblage consisting of plagioclase- and pyroxene-dominated mineral residues, and experienced fractional crystallization and crustal contamination procesess. Their radiogenic signatures are interpreted to indicate conditions of relatively thickened continental crust in Altar during the Early Miocene, compared to the south and west. The Upper Subvolcanic Suite represents the development of a Middle-Late Miocene arc (11.75 ± 0.24 Ma, 10.35 ± 0.32 Ma; U-Pb ages) emplaced over a shallow subduction zone. A magmatic gap in Altar area betwen the Lower Volcanic Complex and Upper Subvolcanic Suite correlates with documented higher rates of compression in this period, that may have favored the storage of the USS magmas in cameras within the crust. Magmas of the Upper Subvolcanic Suite require a hornblende-bearing residual mineral assemblage that is interpreted to reflect their higher water contents. The relatively uniform radiogenic isotope compositions of the Upper Subvolcanic Suite magmas suggest a homogeneously mixed crust-mantle contribution in the source region. They have similar REE signatures as other fertile intrusives of the flat-slab. The differences observed in their

  1. Large mammal burrows in late Miocene calcic paleosols from central Argentina: paleoenvironment, taphonomy and producers

    Directory of Open Access Journals (Sweden)

    María Cristina Cardonatto

    2018-05-01

    Full Text Available Large cylindrical sediment-filled structures interpreted as mammal burrows occur within the loess-paleosol sequence of the late Miocene Cerro Azul Formation of central Argentina. A total of 115 burrow fills from three localities were measured. They are typically shallowly dipping, subcylindrical, unbranched structures with rounded ends and lacking enlargements. The horizontal diameter of the burrows range between 0.15 and 1.50 m, with most of the burrows in the interval of 0.39 to 0.98 m. Geometric morphometric analysis of transverse cross-sections support their distinct subcircular and elliptical (horizontally flattened shapes. Burrow fills are typically laminated in the lower part and massive in the upper part. The laminated intervals reflect pulses of flowing water entering the abandoned burrow during moderate rains, whereas massive intervals reflect mass flow input of dense sediment-water mixtures during heavy rains that produced sheet floods. Approximately 1% of the burrows contained fragmentary, disarticulated and weathered mammal bones that were introduced in the open burrow by currents along with other sedimentary particles. Analysis of the tetrapod burrow fossil record suggests that Miocene burrows, including those studied herein, reflect a remarkable increase in the average size of the fossorial fauna. We conclude that large late Miocene mammals dug burrows essentially as a shelter against environmental extremes and to escape predation. The simple architecture of the burrows suggests that the producers essentially foraged aboveground. Several mammal groups acquired fossorial habits in response to cold and seasonally dry climatic conditions that prevailed during the late Miocene in southern South America. The considerable range of horizontal diameters of the studied burrows can be attributed to a variety of producers, including dasypodids, the notoungulate Paedotherium minor, Glyptodontidae and Proscelidodon sp.

  2. Miocene climate variations in the Moesian Platform sediments based on sedimentology and biomarkers

    Science.gov (United States)

    Butiseaca, Geanina; Vasiliev, Iuliana; Rabagia, Traian; Dinu, Corneliu; Mulch, Andreas

    2017-04-01

    During the Miocene the Moesian Platform (southern Romania and northern Bulgaria) had a complicated flexural behavior due to the mobility of the nearby orogens. The different behavior induced varying sediment charges, sediment distribution and sediment types. The northern part of the study area (on which the Dacian Basin is overlaid) is characterized by siliciclastic units with dominantly deep facieses, while the southern part is characterized by carbonate production in shallower basin waters. Since the Miocene, the Dacian and Black Sea basins have been highly sensitive to fluctuations in the hydrological cycle. To establish the dynamic evolution of the basin and the climate variations during the Miocene, we have sampled both northern and southern margins of the basin. To discriminate between the tectonic imprint and the eustatic influence over the sedimentation rate we have chosen a multidisciplinary approach including sedimentology, tectonics and organic geochemistry based reconstructions. The sedimentary succession is interrupted by few unconformities correspondent with the main phases of orogeny (in the Carpathian Foredeep) while the southern part seems to have been exposed more often expressed in the geological record by a higher number of unconformities and paleo-soils levels. The n-alkanes distribution recovered from the lipids extracted from the sedimentary rocks indicates a mixture of terrestrial and marine input in the northern, Romanian, closer to Carpathians, part of the Dacian Basin. Surprisingly, the southern, Bulgarian side, showed a more predominant terrestrial input (with higher contribution of the long chain n-alkanes) at least for the Sarmatian (arround 10 Ma). The estimated paleotemperatures based on branched GDGT's indicate much warmer conditions than present day, up to a value of 20 C mean annual temperatures. We will further investigate the paleoenvironmental changes during the latest Miocene of the Dacian basin, using the biomarker approach

  3. Petrology and organic geochemistry of the lower Miocene lacustrine sediments (Most Basin, Eger Graben, Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Havelcová, Martina; Sýkorová, Ivana; Mach, K.; Trejtnarová, Hana; Blažek, Jaroslav

    2015-01-01

    Roč. 139, Special issue (2015), s. 26-39 ISSN 0166-5162 R&D Projects: GA ČR(CZ) GA13-18482S Institutional support: RVO:67985891 Keywords : Most Basin * Miocene * coal facies indices * coal petrology * organic geochemistry Subject RIV: DD - Geochemistry Impact factor: 3.294, year: 2015 http://www.sciencedirect.com/science/article/pii/S0166516214001529#

  4. Influence of leachate on the Oligocene-Miocene clays of the İstanbul area, Turkey

    OpenAIRE

    ÖZTOPRAK, SADIK; LAÇİN, DAVUT

    2018-01-01

    Oligo-Miocene clay outcrops on the European side (west and northwest part) of İstanbul were analysed. Formerly, a landfill and sanitary landfill were built on the clay. Mineral liners of the current and extending parts of the İstanbul landfill consist of these clays, since they include a considerable amount of smectite, illite, and kaolinite. With this feature, these clays are also an important candidate for the buffer material of repositories for nuclear wastes of newly planned nuclear power...

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

    Science.gov (United States)

    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

  6. Magnetostratigraphy of the Miocene sediments at Háj u Duchcova and Sokolov (West Bohemia)

    Czech Academy of Sciences Publication Activity Database

    Schnabl, Petr; Man, Otakar; Matys Grygar, Tomáš; Mach, K.; Kdýr, Šimon; Čížková, Kristýna; Pruner, Petr; Martínek, K.; Rojík, P.

    2017-01-01

    Roč. 19, EGU General Assembly 2017 (2017) ISSN 1029-7006. [European Geosciences Union General Assembly. 23.04.2017-28.04.2017, Vienna] R&D Projects: GA ČR(CZ) GA16-00800S Institutional support: RVO:67985831 ; RVO:61388980 Keywords : DP-333-09 * JP-585-10 * Burdigalian * spectral analysis * magnetostratigraphy * Miocene Subject RIV: DE - Earth Magnetism, Geodesy, Geography http://meetingorganizer.copernicus.org/EGU2017/EGU2017-19330.pdf

  7. 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

    2016-01-01

    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. PMID:26829756

  8. Terpenoid Compositions and Botanical Origins of Late Cretaceous and Miocene Amber from China

    Science.gov (United States)

    Shi, Gongle; Dutta, Suryendu; Paul, Swagata; Wang, Bo; Jacques, Frédéric M. B.

    2014-01-01

    The terpenoid compositions of the Late Cretaceous Xixia amber from Central China and the middle Miocene Zhangpu amber from Southeast China were analyzed by gas chromatography-mass spectrometry (GC-MS) to elucidate their botanical origins. The Xixia amber is characterized by sesquiterpenoids, abietane and phyllocladane type diterpenoids, but lacks phenolic abietanes and labdane derivatives. The molecular compositions indicate that the Xixia amber is most likely contributed by the conifer family Araucariaceae, which is today distributed primarily in the Southern Hemisphere, but widely occurred in the Northern Hemisphere during the Mesozoic according to paleobotanical evidence. The middle Miocene Zhangpu amber is characterized by amyrin and amyrone-based triterpenoids and cadalene-based sesquiterpenoids. It is considered derived from the tropical angiosperm family Dipterocarpaceae based on these compounds and the co-occurring fossil winged fruits of the family in Zhangpu. This provides new evidence for the occurrence of a dipterocarp forest in the middle Miocene of Southeast China. It is the first detailed biomarker study for amber from East Asia. PMID:25354364

  9. A middle Pleistocene through middle Miocene moraine sequence in the central Transantarctic Mountains, Antarctica

    Science.gov (United States)

    Balter, A.; Bromley, G. R.; Balco, G.; Thomas, H.; Jackson, M. S.

    2017-12-01

    Ice-free areas at high elevation in the central Transantarctic Mountains preserve extensive moraine sequences and drift deposits that comprise a geologic record of former East Antarctic Ice Sheet thickness and extent. We are applying cosmogenic-nuclide exposure dating to determine the ages of these moraine sequences at Roberts Massif and Otway Massif, at the heads of the Shackleton and Beardmore Glaciers, respectively. Moraines at these sites are for the most part openwork boulder belts characteristic of deposition by cold-based ice, which is consistent with present climate and glaciological conditions. To develop our chronology, we collected samples from 30 distinct ice-marginal landforms and have so far measured >100 3He, 10Be, and 21Ne exposure ages. Apparent exposure ages range from 1-14 Ma, which shows that these landforms record glacial events between the middle Pleistocene and middle Miocene. These data show that the thickness of the East Antarctic Ice Sheet in this region was similar to or thicker than present for long periods between the middle Miocene and today. The time range represented by these moraine sequences indicates that they may also provide direct geologic evidence for East Antarctic Ice Sheet behavior during past periods of warmer-than-present climate, specifically the Miocene and Pliocene. As the East Antarctic Ice Sheet is the largest ice sheet on earth, understanding its sensitivity to warm-climate conditions is critical for projections of ice sheet behavior and sea-level rise in future warm climates.

  10. 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.

  11. Miocene and Pleistocene mollusks from San Andres Island (Caribbean Sea, Colombia) and Paleogeographic considerations

    International Nuclear Information System (INIS)

    Diaz M, Juan Manuel; Garcia Llano, Cesar Fernando

    2010-01-01

    San Andres Island is the largest emerged portion of the oceanic archipelago of San Andres and Providencia, southwestern Caribbean Sea; it originated as a coralline atoll during Miocene times. The central and highest part of the island consists of a calcareous crest, the San Andres Formation, formed by Neogene lagoonal and reefal deposits. This crest is surrounded by a calcareous platform of Pleistocene age (San Luis Formation) which emerges only along the island coast, whereas its most part is submerged and covered by a Recent reef complex. Fossil material of molluscs from these two formations was collected in various sites throughout the island and taxonomically identified. In the four sites sampled in the San Andres Formation, material belonging to 19 gastropod and 37 bivalve species was obtained, most of them relatively well represented in other geologic formations of the Caribbean region that are stratigraphically situated between the upper Miocene and the middle Pliocene. Some elements occurring in this formation, such as Ostrea haitiensis, Meretrix dariena and Siphocypraea henekeni, were widely distributed in the Caribbean Miocene Province. In the San Luis Formation, material belonging to 18 gastropod and 11 bivalve species was obtained, most of them also represented in the Recent molluscan fauna of the region. The estimated age of this formation is Sangamonian, hence corresponding to similar formations occurring in Grand Cayman, Jamaica, Hispaniola, the Netherlands Antilles and other Caribbean islands, with which it also shows a great similarity in the composition of the molluscan fauna.

  12. 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.

  13. Miocene to recent tectonic and sedimentary evolution of the Anaximander Seamounts; eastern Mediterranean Sea

    Science.gov (United States)

    Cranshaw, Jennifer

    This thesis is focused on the Messinian to Recent tectonic and sedimentary evolution of the Anaximander Mountains and surrounding environs in the eastern Mediterranean Sea. It is based on processing of high-resolution seismic reflection data and the interpretation and mapping of seismic reflection profiles collected from this area during the 2001 and 2007 research cruises. The data show that the greater Anaximander Mountains region experienced a short interval of tectonic quiescence during the Messinian when a thin evaporite unit was deposited across a major erosional surface. This phase of limited tectonic activity ended in the latest Miocene and was replaced by an erosional phase. Major unconformities in the area are interpreted to develop during the desiccation of the eastern Mediterranean associated with the so-called Messinian salinity crisis. During the early Pliocene, the region experienced an increase in tectonic activity, dominated by transpression. Small amounts of growth observed in Pliocene-Quaternary sediments suggested that the tectonic activity remained low during the early Pliocene-Quaternary. However, the extensive growth strata wedges developed in older sediments indicate a period of accelerated tectonic activity during the mid-late Pliocene-Quaternary. This study suggests that the Anaximander Mountain (sensu stricto ) and the Anaximenes Mountain developed during the Pliocene-Quaternary as the result of a crustal-scale thick-skinned linked imbricate thrust fan. The development of back thrusts in both mountains heightened the seafloor morphology of these submarine mountains and brought Eocene-Oligocene sediments into the core of these mountains. The Sim Erinc Plateau represents a 30-40 km wide transpressional fault zone developed during the Pliocene-Quaternary. In this region the corrugated seafloor morphology observed in the multibeam bathymetry map is the reflection of high-angle faults. It is speculated that this transpressional fault zone

  14. A long-term multi-proxy record of varved sediments highlights climate-induced mixing-regime shift in a large hard-water lake ~5000 years ago

    Directory of Open Access Journals (Sweden)

    Walter Finsinger

    2014-06-01

    Full Text Available The long-term terrestrial and aquatic ecosystem dynamics spanning between approximately 6200 and 4800 cal BP were investigated using pollen, diatoms, pigments, charcoal, and geochemistry from varved sediments collected in a large stratified perialpine lake, Lago Grande di Avigliana, in the Italian Alps. Marked changes were detected in diatom and pigment assemblages and in sediment composition at ~4900 cal BP. Organic matter rapidly increased and diatom assemblages shifted from oligotrophic to oligo-mesotrophic planktonic assemblages suggesting that nutrients increased at that time. Because land cover, erosion, and fire frequency did not change significantly, external nutrient sources were possibly not essential in controlling the lake-ecosystem dynamics. This is also supported by redundancy analysis, which showed that variables explaining significant amounts of variance in the diatom data were not the ones related to changes in the catchment. Instead, the broad coincidence between the phytoplankton dynamics and rising lake-levels, cooler temperatures, and stronger spring winds in the northern Mediterranean borderlands possibly points to the effects of climate change on the nutrient recycling in the lake by means of the control that climate can exert on mixing depth. We hypothesize that the increased P-release rates and higher organic-matter accumulation rates, proceeded by enhanced precipitation of iron sulphides, were possibly caused by deeper and stronger mixing leading to enhanced input of nutrients from the anoxic hypolimnion into the epilimnion. Although we cannot completely rule out the influence of minor land-cover changes due to human activities, it may be hypothesized that climate-induced cumulative effects related to mixing regime and P-recycling from sediments influenced the aquatic-ecosystem dynamics.

  15. Volcanic complexes in the eastern ridge of the Canary Islands: the Miocene activity of the island of Fuerteventura

    Science.gov (United States)

    Ancochea, E.; Brändle, J. L.; Cubas, C. R.; Hernán, F.; Huertas, M. J.

    1996-03-01

    Fuerteventura has been since early stages of its growth the result of three different adjacent large volcanic complexes: Southern, Central and Northern. The definition of these volcanic complexes and their respective growing episodes is based on volcano-stratigraphic, morphological and structural criteria, particularly radial dyke swarms. Each complex has its own prolonged history that might be longer than 10 m.y. During that time, several periods of activity alternating with gaps accompanied by important erosion took place. The evolution of each volcanic complex has been partially independent but all the three are affected by at least three Miocene tectonic phases that controlled considerably their activity. The volcanic complexes are deeply eroded and partially submerged. In the core of the Northern and the Central volcanic complexes there is a set of submarine and plutonic rocks intensely traversed by a dyke swarm, known as the Basal Complex. The Basal Complex has been interpreted in different ways but all previous authors have considered it to be prior to the subaerial shield stage of the island. Here we advance the idea that the Basal Complex represent the submarine growing stage of the volcanic complexes and the hypabyssal roots (plutons and dykes) of their successive subaerial growing episodes. Two seamounts situated nearby, southwest of the island, might be interpreted as remains of two other major volcanoes. These two volcanoes, together with those forming the present emerged island of Fuerteventura, and finally those of Famara and Los Ajaches situated further north on Lanzarote constitute a chain of volcanoes located along a lineation which is subparallel to the northwestern African coastline and which may relate to early Atlantic spreading trends in the area.

  16. Miocene squat lobsters (Decapoda, Anomura, Galatheoidea) of the Central Paratethys – a review, with description of a new species of Munidopsis

    Science.gov (United States)

    Hyžný, M.; Gašparič, R.; Robins, C.M.; Schlögl, J.

    2015-01-01

    All squat lobsters of the families Galatheidae, Munididae and Munidopsidae from the Miocene of the Central Paratethys are reviewed taxonomically. Based on additional observations emended diagnoses are provided for Agononida cerovensis and Galathea weinfurteri, from the Lower and Middle Miocene, respectively. Munidopsis is represented by two species in the study area; additional data for M. lieskovensis from the Lower Miocene of Slovakia are presented and a new species, M. palmuelleri, from the Middle Miocene of Slovenia is erected. Implications for palaeoenvironmental reconstructions are briefly discussed for each taxon. PMID:26005283

  17. Intraplate volcanism in the Danube Basin of NW Hungary: 3D geophysical modelling of the Late Miocene Pásztori volcano

    Science.gov (United States)

    Pánisová, Jaroslava; Balázs, Attila; Zalai, Zsófia; Bielik, Miroslav; Horváth, Ferenc; Harangi, Szabolcs; Schmidt, Sabine; Götze, Hans-Jürgen

    2017-12-01

    Three-dimensional geophysical modelling of the early Late Miocene Pásztori volcano (ca. 11-10 Ma) and adjacent area in the Little Hungarian Plain Volcanic Field of the Danube Basin was carried out to get an insight into the most prominent intra-crustal structures here. We have used gridded gravity and magnetic data, interpreted seismic reflection sections and borehole data combined with re-evaluated geological constraints. Based on petrological analysis of core samples from available six exploration boreholes, the volcanic rocks consist of a series of alkaline trachytic and trachyandesitic volcanoclastic and effusive rocks. The measured magnetic susceptibilities of these samples are generally very low suggesting a deeper magnetic source. The age of the modelled Pásztori volcano, buried beneath a 2 km-thick Late Miocene-to-Quaternary sedimentary sequence, is 10.4 +/- 0.3 Ma belonging to the dominantly normal C5 chron. Our model includes crustal domains with different effective induced magnetizations and densities: uppermost 0.3-1.8 km thick layer of volcanoclastics underlain by a trachytic-trachyandesitic coherent and volcanoclastic rock units of a maximum 2 km thickness, with a top situated at minimal depth of 2.3 km, and a deeper magmatic pluton in a depth range of 5-15 km. The 3D model of the Danube Basin is consistent with observed high ΔZ magnetic anomalies above the volcano, while the observed Bouguer gravity anomalies correlate better with the crystalline basement depth. Our analysis contributes to deeper understanding of the crustal architecture and the evolution of the basin accompanied by alkaline intraplate volcanism.

  18. Constrained Magnetostratigraphic Dating of a Continental Middle Miocene Section in the Arid Central Asia

    Directory of Open Access Journals (Sweden)

    Verena Verestek

    2018-05-01

    Full Text Available The Neogene succession of the Aktau Mountains in the Ili Basin, southeast Kazakhstan, is a terrestrial archive well suited for researching the role of Central Asia in Miocene climate evolution. We present an integrated approach for dating the well-exposed Bastau Formation, based on magnetostratigraphy and constraints from cyclostratigraphy and biostratigraphy. Stepwise demagnetization yielded characteristic remanence directions that are consistent with those expected for the Miocene in Central Asia. The reddish-colored alluvial floodplain deposits and gray lacustrine deposits show partly complex magnetic behavior with magnetite and hematite as the main magnetic carriers, with variable demagnetization behavior and non-dipolar normal and reverse polarity directions. The observed magnetic properties are best explained by depositional variability and magneto-mineralogical alteration effects of both dissolution and neo-formation of magnetite, including significant secondary magnetization. The mean of reverse polarity directions is flatter than the expected Middle Miocene Earth magnetic field, which is an indicator for the existence of inclination shallowing that supports a primary origin. Detailed rock magnetic analyses are used to analyze the nature of the characteristic remanent magnetization and to discriminate primary and secondary remanence directions in order to obtain a reliable magnetostratigraphic result. The proposed age of 15.3–13.9 Ma for the Bastau Formation corresponds to the known biostratigraphic setting, matches with typical sedimentation rates of foreland basins in Central Asia, and coincides with spectral analysis of geochemical proxies of that section. The resulting age model serves as a robust framework for paleoclimate reconstruction of Neogene climate dynamics in Central Asia.

  19. Ancient nursery area for the extinct giant shark megalodon from the Miocene of Panama.

    Directory of Open Access Journals (Sweden)

    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.

  20. 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

    2013-01-01

    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. PMID:25844021

  1. 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.

  2. 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 CaCO 3 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.

  3. Magnetostratigraphy of the Vallesian (late Miocene) in the Vallès-Penedès Basin (northeast Spain)

    Science.gov (United States)

    Garcés, M.; Agustí, J.; Cabrera, L.; Parés, J. M.

    1996-08-01

    The magnetostratigraphic analysis of the late Miocene continental deposits from the Vallès-Penedès Basin, combined with its well-documented fossil mammal record, has provided a well-resolved chronology for the upper basin infill. The study is based on the biostratigraphic and magnetostratigraphic cross-correlation of 12 sections throughout the alluvial sequences in the western Vallès area. The biostratigraphic framework consists of 21 mammal localities corresponding to the Mammal Neogene MN9 and MN10 units. The composite magnetic polarity sequence is based on 400 paleomagnetic sites. Correlation with the Geomagnetic Polarity Time Scale (GPTS) has led to an absolute dating of the faunal events and a precise chronostratigraphy of the Vallesian mammal stage in its type area. The Hipparion First Appearance Datum (FAD), at the MN8/MN9 boundary, is dated at 11.1 Ma in the Vallès-Penedès Basin. This age, compared to other radiometrically dated localities in Europe, North Africa and Turkey, is consistent with an isochronous dispersal of this equid through the Mediterranean region. A possible isochrony at a larger geographical scale (Old World, Mesogea) must await more reliable ages of the Hipparion FAD in Asia and Africa. The Cricetulodon FAD ( MN9a/MN9b boundary) is dated to 10.4 Ma, in chron C5n. The Progonomys FAD ( MN9/MN10 boundary), corresponding to the intra-Vallesian faunal crisis, is dated at 9.7 Ma (C4Ar.3r). The Vallesian spans 2.4 Myr, from 11.1 Ma (C5r.1n) to 8.7 Ma (C4An) and correlates to the early Tortonian.

  4. Sedimentology, provenance and geochronology of the Miocene Qiuwu Formation: Implication for the uplift history of Southern Tibet

    Directory of Open Access Journals (Sweden)

    Jiawei Zhang

    2017-07-01

    Full Text Available Located on the south of the Gangdese, the Qiuwu Formation has traditionally been considered as Eocene coal-bearing clastic sediments consisting of sandstone, mudstone and conglomerate, unconformably on top of Gangdese batholith. However, its precise age and depositional environment remain ambiguous. Here, we present a newly measured stratigraphic section near the Ngamring County, western Xigaze. Detrital zircon U–Pb ages were also applied to trace the provenance of sediments and to constrain the maximum depositional age of the Qiuwu Formation. Sedimentary facies analyses indicate subaqueous fan and alluvial fan depositional environments. Clast composition of the conglomerate is dominated by magmatic rocks at the lower part, while chert and mafic detritus occur in the upper part, suggesting a southern source. Sandstone modal analyses indicate that the compositions of quartz, feldspar and lithic grains changed from transitional arc to dissected arc, implying the unroofing of the Gangdese arc. Detrital zircon U–Pb ages of the Qiuwu Formation are compared with those from Gangdese magmatic rocks and Yarlung-Zangbo ophiolites, suggesting that the Gangdese arc is a main source of the Qiuwu detritus and that the southern source played a role during the later stage. The major peak of detrital zircon ages is at 45–55 Ma, which corresponds to Linzizong volcanic rocks in southern Gangdese arc. The weighted mean age of the five youngest zircons from the lower part of the section is 21.0 ± 2.2 Ma, suggesting that the Qiuwu Formation was deposited in early Miocene, coeval with other conglomerates exposed along the southern margin of Gangdese. Combining new observations with previously published data, we propose that the provenance of the Qiuwu Formation had shifted from a single northern source to double sources from both the north and the south. Activities of Great Counter Thrust were primarily responsible for the shift by making the south area a

  5. Miocene metamorphism of pan-African granites in the Edough Massif (NE Algeria)

    International Nuclear Information System (INIS)

    Hammor, D.; Lancelot, J.

    1998-01-01

    The Edough Massif is the eastern most crystalline core of the Maghrebides that represents the African segment of the west Mediterranean Alpine belt. U-Pb zircon dating provides upper intercept ages of 595± My and 606±55 My and orthogneiss of the lower unit and a deformed leucogranite of the upper pelitic unit, respectively. These ages suggest emplacement of the two granitoids during the Pan-African orogeny. Monazites from a paragneiss sample gave a 18± My U-Pb age that points to a Miocene age of the high-temperature metamorphism. (authors)

  6. The Evolution of Indian and Pacific Ocean Denitrification and Nitrogen Dynamcs since the Miocene

    Science.gov (United States)

    Ravelo, A. C.; Carney, C.; Rosenthal, Y.; Holbourn, A.; Kulhanek, D. K.

    2017-12-01

    The feedbacks between geochemical cycles and physical climate change are poorly understood; however, there has been tremendous progress in developing coupled models to help predict the direction and strength of these feedbacks. As such, there is a need for more data to validate and test these models. To this end, the nitrogen (N) cycle, and its links to the biological pump and to climate, is an active area of paleoceanographic research. Using N isotope records, Robinson et al. (2014) showed that pelagic denitrification in the Indian and Pacific Oceans intensified as climate cooled and subsurface ventilation decreased since the Pliocene. They pointed out that a more ventilated warm Pliocene contrasts with glacial-interglacial patterns wherein more ventilation occurs during cold phases, indicating that different mechanisms may occur at different timescales. Our objective is to better understand the nature of the feedbacks between the oceanic N cycle and climate by focusing on the large dynamic range of conditions that occurred during and since the Miocene. We used new cores drilled during IODP Expedition 363 to generate bulk sediment N isotope records at three western tropical Pacific sites (U1486, U1488, U1490) and one southeastern tropical Indian Ocean site (U1482). We find that the N isotope trends since the Pliocene are in agreement with previous studies showing increasing denitrification as climate cooled. In the Miocene, the Indian Ocean record shows no long-term N isotope trend whereas the Pacific Ocean records show a trend that is roughly coupled to changes in global climate suggesting that pelagic denitrification in the Pacific was strongly influenced by greater ventilation during global warmth. However, there are notable deviations from this coupling during several intervals in the Miocene, and there are site-to-site differences in trends. These deviations and differences can be explained by changes in tropical productivity (e.g., late Miocene biogenic

  7. Ferroan dolomites in Miocene sediments of the Xisha Islands and their genetic model

    Science.gov (United States)

    Xu, Hong; Zhang, Weiwei; Wei, Kai; He, Qingkun; Jiang, Yunshui; Xu, Tingting; Jiang, Xuejun; Yan, Guijing; Song, Hongying; Wang, Jianghai

    2018-01-01

    Carbonate rocks are important reservoirs for global petroleum exploration. The largest oilfield in the South China Sea, Liuhua 11-1, is distributed in the massive carbonate reef area of the Zhujiang (Pearl) River Mouth Basin. Previous studies showed that one 802.17-m-long core from well Xichen-1 in the South China Sea mainly consisted of white and light gray-white organic reefs. Recently, a Miocene whole core (161.9 m long) of well Xiyong-2, near well Xichen-1, was found to contain six layers of yellowish brown, light yellowish gray, iron black, or light yellowish gray-white organic reefs. Scanning electron microscope images of these layers reveal a typical ferroan dolomite rich in Fe (up to 29%), with the high concentrations of Mn, Cu, W, Zn, Cr, Ni, and Co. Systematic X-ray powder diffraction analysis yields a 1.9-6.1 match in phase ratio with ankerite, 5.4-26.9 with dolomite, and zero with calcite, which indicate that the samples can be classified as ferroan dolomite. The iron and heavy metals are inferred to be originated from multiple volcanic eruptions of Gaojianshi Island in the Dongdao Atoll during the middle-late Miocene. These elements were dissolved in seawater, likely as a sol, and carried to Yongxing Island in the Xuande Atoll by sea currents and tides enhanced by prevailing winds, and deposited as a part of the sedimentation process in the study area. The ferroan dolomite has Sr content of (125-285)×10-6, which is lower than the accepted Sr boundary value of dolomite. This finding suggests that dolomitization occurred during large-scale global glacial regression in the late Miocene. The isolated Xisha carbonate platform, exposed to air, underwent freshwater leaching and dolomitization induced by mixed water, and caused the extensive Fe-Mg exchange along the organic reef profile to form ankerite and ferroan dolomite. These results may help to understand paleoceanographic environmental changes in the South China Sea during the Miocene.

  8. Biostratigraphy of the Miocene of Zeven, county of Bremervoerde, based on mollusks

    Energy Technology Data Exchange (ETDEWEB)

    Hinsch, W

    1969-06-01

    Cores from 2 water wells and a gas well, containing a very rich assemblage of fossil mollusks, were used to clarify the biostratigraphy of the Miocene near Zeven, especially in the sands corresponding to the brown coal deposits. The overburden contains the fauna of the Reinbek, the underburden 2 faunas of the Hemmoor, one of brachyhaline and one of euhaline characteristics. A list of the 174 species found, and of those most useful for age determinations, is given. The correspondence between several local nomenclatures in the Helvetian, Burdigalian and Aquitanian formations is tabulated. (12 refs.)

  9. 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...... drivers of this kinematic change....

  10. Late Miocene marine tephra beds : recorders of rhyolitic volcanism in North Island, New Zealand

    International Nuclear Information System (INIS)

    Shane, P.; Black, T.; Eggins, S.; Westgate, J.

    1998-01-01

    A deep-sea sequence of 72 rhyolitic tephra beds, now exposed at Mahia Peninsula in the Hawke's Bay region of the east coast, North Island, New Zealand, provides a record of Late Miocene volcanism of the Coromandel Volcanic Zone (CVZ): the precursor to large-scale explosive volcanism of the Quaternary Taupo Volcanic Zone (TVZ). The geochemical signature of the glasses in the Miocene tephra has been protected from hydrothermal alteration and prolonged subaerial exposure that have affected proximal CVZ deposits. The tephra beds are primarily eruption-driven sediment gravity flows that have been emplaced into a trench-slope basin, some 300 km from active volcanoes. Their occurrence is consistent with long-distance fluvial transport followed by a point-source discharge into the deep-sea environment, and has no implications for the paleogeographic location of the basins relative to the volcanic arc. The tephra beds are calc-alkaline rhyolites with SiO 2 contents in the range 72-78 wt% (recalculated on a volatile-free basis), and are broadly similar to glassy rocks of the CVZ. Their major oxide, trace element, and REE compositions are indistinguishable from glasses of TVZ rhyolites. The trace element and REE compositional variability in the Late Miocene tephra beds, which were erupted over an estimated duration of c. 0.5-2.4 m.y. is no greater than that of large silicic eruptives of the last 350 ka, and is suggestive of a long-lived source and/or similar magmatic processes. However, the individual tephra beds are products of discrete homogeneous magma batches. New fission track ages of the Miocene tephra beds suggest the main period of volcaniclastic deposition occurred in the interval c. 9-7 Ma. This corresponds well with the initiation of rhyolitic volcanism in the CVZ at c. 10 Ma, and a major period of caldera formation that took place to c. 7 Ma. The ages suggest a sediment accumulation rate of between 0.23 and 1.2 m/ka (av. 0.4 m/ka), and a frequency of eruption of

  11. 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

  12. Sedimentary petrography of the Early Proterozoic Pretoria Group, Transvaal Sequence, South Africa: implications for tectonic setting

    Science.gov (United States)

    Schreiber, U. M.; Eriksson, P. G.; van der Neut, M.; Snyman, C. P.

    1992-11-01

    Sandstone petrography, geochemistry and petrotectonic assemblages of the predominantly clastic sedimentary rocks of the Early Proterozoic Pretoria Group, Transvaal Sequence, point to relatively stable cratonic conditions at the beginning of sedimentation, interrupted by minor rifting events. Basement uplift and a second period of rifting occurred towards the end of Pretoria Group deposition, which was followed by the intrusion of mafic sill swarms and the emplacement of the Bushveld Complex in the Kaapvaal Craton at about 2050 Ma, the latter indicating increased extensional tectonism, and incipient continental rifting. An overall intracratonic lacustrine tectonic setting for the Pretoria Group is supported by periods of subaerial volcanic activity and palaeosol formation, rapid sedimentary facies changes, significant arkosic sandstones, the presence of non-glacial varves and a highly variable mudrock geochemistry.

  13. Provenance of Miocene Hinterland Basins in Ecuador: Implications for the Growth of Topographic Barriers in the Northern Andes

    Science.gov (United States)

    George, S. W. M.; Horton, B. K.; Vallejo, C.; Nogales, V.

    2017-12-01

    Establishment of the Eastern Cordillera of Ecuador as an Andean topographic barrier caused significant drainage reorganization, perhaps even as dramatic as the reversal of the Amazon River. Cenozoic growth of this barrier coincided with substantial increases in speciation rates in Andean and Amazonian environments. Situated in the Interandean Depression between the Eastern Cordillera and Western Cordillera of Ecuador, a series of well-preserved Miocene intermontane basins offer a unique opportunity to constrain the along-strike development of the flanking north-trending cordilleras as drainage divides in the Northern Andes. Here were provide detrital zircon U-Pb geochronological results for 17 samples from Ecuadorian hinterland basins (Cuenca, Giron-Santa Isabel, Nabón, Loja, and Vilcabamba), supplemented with measured sections in the Cuenca Basin, to provide insights on orogenic development of the cordilleras of Ecuador during the Miocene. In addition, we characterize the age distributions of basement units to more precisely determine sediment routing patterns through time. Detrital zircon geochronological data yields regional upsection trends throughout Miocene stratigraphic sections marked by: (1) middle Miocene deposits containing a strong syndepositional age peak, with a complementary Eocene-Oligocene peak in varying abundances, and subsidiary low-intensity Paleozoic-Proterozoic age peaks; and (2a) upper Miocene deposits maintaining similar trends to that of the middle Miocene, or (2b) upper Miocene deposits showing a dramatic shutoff of most Cenozoic populations and a switch to Paleozoic-Proterozoic sources, as seen in the Nabón and Loja basins. Syndepositional signatures reflect derivation from the magmatic arc, while varying inputs of Eocene-Oligocene zircons were derived from the Eocene-Oligocene volcanic rocks that comprise the effective basement of much of the Interandean Depression. The late Miocene shift to Paleozoic-Proterozoic sources observed in

  14. Migration of sharks into freshwater systems during the Miocene and implications for Alpine paleoelevation

    Science.gov (United States)

    Kocsis, László; Vennemann, Torsten W.; Fontignie, Denis

    2007-05-01

    Trace-element and isotopic compositions of fossilized shark teeth sampled from Miocene marine sediments of the north Alpine Molasse Basin, the Vienna Basin, and the Pannonian Basin generally show evidence of formation in a marine environment under conditions geochemically equivalent to the open ocean. In contrast, two of eight shark teeth from the Swiss Upper Marine Molasse locality of La Molière have extremely low δ18O values (10.3‰ and 11.3‰) and low 87Sr/86Sr ratios (0.707840 and 0.707812) compared to other teeth from this locality (21.1‰ 22.4‰ and 0.708421 0.708630). The rare earth element (REE) abundances and patterns from La Molière not only differ between dentine and enameloid of the same tooth, but also between different teeth, supporting variable conditions of diagenesis at this site. However, the REE patterns of enameloid from the “exotic” teeth analyzed for O and Sr isotopic compositions are similar to those of teeth that have O and Sr isotopic compositions typical of a marine setting at this site. Collectively, this suggests that the two “exotic” teeth were formed while the sharks frequented a freshwater environment with very low 18O-content and Sr isotopic composition controlled by Mesozoic calcareous rocks. This is consistent with a paleogeography of high-elevation (˜2300 m) Miocene Alps adjacent to a marginal sea.

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

    Directory of Open Access Journals (Sweden)

    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.

  16. 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.

  17. Amazonian Amphibian Diversity Is Primarily Derived from Late Miocene Andean Lineages

    Science.gov (United States)

    Santos, Juan C; Coloma, Luis A; Summers, Kyle; Caldwell, Janalee P; Ree, Richard; Cannatella, David C

    2009-01-01

    The Neotropics contains half of remaining rainforests and Earth's largest reservoir of amphibian biodiversity. However, determinants of Neotropical biodiversity (i.e., vicariance, dispersals, extinctions, and radiations) earlier than the Quaternary are largely unstudied. Using a novel method of ancestral area reconstruction and relaxed Bayesian clock analyses, we reconstructed the biogeography of the poison frog clade (Dendrobatidae). We rejected an Amazonian center-of-origin in favor of a complex connectivity model expanding over the Neotropics. We inferred 14 dispersals into and 18 out of Amazonia to adjacent regions; the Andes were the major source of dispersals into Amazonia. We found three episodes of lineage dispersal with two interleaved periods of vicariant events between South and Central America. During the late Miocene, Amazonian, and Central American-Chocoan lineages significantly increased their diversity compared to the Andean and Guianan-Venezuelan-Brazilian Shield counterparts. Significant percentage of dendrobatid diversity in Amazonia and Chocó resulted from repeated immigrations, with radiations at Venezuelan Highlands, and Guiana Shield have undergone extended in situ diversification at near constant rate since the Oligocene. The effects of Miocene paleogeographic events on Neotropical diversification dynamics provided the framework under which Quaternary patterns of endemism evolved. PMID:19278298

  18. Geology, geochemistry and 40K-40Ar geochronometry of Miocene magmatism in Algiers area, Northern Algeria

    International Nuclear Information System (INIS)

    Belanteur, O.; Ouabadi, A.; Semroud, B.; Megartsi, M.H.; Fourcade, S.

    1995-01-01

    Miocene magmatic rocks outcrop within a narrow coastal strip east of Algiers. They include basaltic and andesitic lava flows and intrusions (Dellys, Cap Djinet), the Thenia granodioritic plug and the dacitic to rhyolitic lavas and pyroclastic flows from Zemmouri El Bahri and El Kerma. Despite the effects of hydrothermal alteration, 40 K- 40 Ar ages coupled with micropalaeontological data lead to recognition of two emplacement events at 16-15 and 14-12 Ma, respectively. All the studied calc-alkaline to potassic calc-alkaline rocks are enriched in highly incompatible elements and display negative Nb anomalies. Acid magmas have a pronounced crustal imprint ( 87 Sr 86 Sr i =3D 0.7082 to 0.7155; δ 18 O =3D +9 to +13 per mill) which together with La/Nb ratios argues for the occurrence of upper crustal contamination processes. However, the Nb-depletion of the associated basalts suggest that the studied magmas derive from a mantle source which underwent subduction-related metasomatic enrichments prior to their Miocene emplacement. (authors). 13 refs., 3 figs., 2 tabs

  19. First hominoid from the Late Miocene of the Irrawaddy Formation (Myanmar.

    Directory of Open Access Journals (Sweden)

    Jean-Jacques Jaeger

    2011-04-01

    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.

  20. Sedimentologic indicators of the Miocene tectonic evolution in the Nunchia syncline

    International Nuclear Information System (INIS)

    Ramirez Arias, Juan Carlos; Mora, Andres; Parra, Mauricio

    2010-01-01

    The study area corresponds to the Nunchia syncline, which is located in the eastern foothills of the eastern cordillera of Colombia. This structure is bounded by the Yopal thrust to the east, and Guaicaramo thrust to the west. This syncline has mostly outcrops of Miocene units, which belong to the Carbonera (C1-C5), Leon and Guayabo formations. Here we use sedimentologic data, especially in the Guayabo Formation, in order to determine the influence of active tectonics during its deposition. Petrographic analyses of sandstones indicate the presence of components associated with upper Cretaceous - Paleocene formations in the eastern cordillera. Paleocurrent orientation shows a preferential trend towards the se during the deposition of most of the studied formations, with a reversal in flow direction towards the W-NW during the deposition of the middle Guayabo Formation preserved in the Nunchia syncline. The collected data allows establishing a structural evolution in the Nunchia syncline which was therefore active during most of the Miocene. This evolution appears to be continuous, although fragmentation of the geological record shows more specific periods of tectonic activity.

  1. Development of Miocene-Pliocene reef trend, St. Croix, U. S. Virgin Islands

    Energy Technology Data Exchange (ETDEWEB)

    Gill, I.; Eby, D.E.; Hubbard, D.K.; Frost, S.H.

    1988-01-01

    The Miocene-Pliocene reef trend on St. Croix, U.S. Virgin Islands, rims the present southern western coasts of the island and includes accompanying lagoonal and forereef facies. The reef trend was established on a foram-algal bank facies that represents basinal shallowing from the deep-water pelagic and hemipelagic facies of the Miocene Kingshill Limestone. Information on facies distribution and thickness is derived from rock exposures and 22 test wells drilled to a maximum depth of 91 m. The greatest thickness of the reef facies exists in a subsidiary graben on the south coast of St. Croix. The thickness of the reef section in this locality is due to preservation of the section in a downdropped block. Reef faunas include extant corals, as well as several extinct genera. Extant corals (e.g. Montastrea annularis, Diploria sp., and Porites porites) and extinct corals (e.g., Stylophora affinis, Antillea bilobata, and Thysanus sp.) are the main reef frame-builders. Coralline algea and large benthic foraminifera are significant contributors to the sediments both prior to and during scleractinian reef growth. Dolomitization and calcite cementation occur prominantly in an area corresponding to a Holocene lagoon. The spatial distribution of the dolomite suggests that the lagoon is a Tertiary feature directly related to the dolomitization process. Stable isotopic values suggest dolomitization of fluids of elevated salinity.

  2. Enhanced Structural Interpretation Using Multitrace Seismic Attribute For Oligo-Miocene Target at Madura Strait Offshore

    Science.gov (United States)

    Pratama Wahyu Hidayat, Putra; Hary Murti, Antonius; Sudarmaji; Shirly, Agung; Tiofan, Bani; Damayanti, Shinta

    2018-03-01

    Geometry is an important parameter for the field of hydrocarbon exploration and exploitation, it has significant effect to the amount of resources or reserves, rock spreading, and risk analysis. The existence of geological structure or fault becomes one factor affecting geometry. This study is conducted as an effort to enhance seismic image quality in faults dominated area namely offshore Madura Strait. For the past 10 years, Oligo-Miocene carbonate rock has been slightly explored on Madura Strait area, the main reason because migration and trap geometry still became risks to be concern. This study tries to determine the boundary of each fault zone as subsurface image generated by converting seismic data into variance attribute. Variance attribute is a multitrace seismic attribute as the derivative result from amplitude seismic data. The result of this study shows variance section of Madura Strait area having zero (0) value for seismic continuity and one (1) value for discontinuity of seismic data. Variance section shows the boundary of RMKS fault zone with Kendeng zone distinctly. Geological structure and subsurface geometry for Oligo-Miocene carbonate rock could be identified perfectly using this method. Generally structure interpretation to identify the boundary of fault zones could be good determined by variance attribute.

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

    Science.gov (United States)

    Famoso, Nicholas A; Davis, Edward Byrd

    2014-01-01

    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.

  4. Early evolution of Tubulogenerina during the Paleogene of Europe

    Science.gov (United States)

    Gibson, T.G.; Barbin, V.; Poignant, A.; Sztrakos, K.

    1991-01-01

    The early evolution of Tubulogenerina took place in Europe where eight species occur in lower Eocene to uppermost Oligocene or lower Miocene strata. Species diversity within Tubulogenerina dropped significantly in the early Oligocne; only a single species persisted from the late Eocene, and it became extinct before the end of the early Oligocene. Morphologic changes during the European phylogeny of Tubulogenerina include (1) the development of costate and more complex tubulopore ornamentation, and (2) the change from a single elongated apertural slit with a single toothplate to multiple apertures and toothplates. Three new Tubulogenerina species are described. -from Authors

  5. Evidence for a dynamic East Antarctic ice sheet during the mid-Miocene climate transition

    Science.gov (United States)

    Pierce, Elizabeth L.; van de Flierdt, Tina; Williams, Trevor; Hemming, Sidney R.; Cook, Carys P.; Passchier, Sandra

    2017-11-01

    The East Antarctic ice sheet underwent a major expansion during the Mid-Miocene Climate Transition, around 14 Ma, lowering sea level by ∼60 m. However, direct or indirect evidence of where changes in the ice sheet occurred is limited. Here we present new insights on timing and locations of ice sheet change from two drill sites offshore East Antarctica. IODP Site U1356, Wilkes Land, and ODP Site 1165, Prydz Bay are located adjacent to two major ice drainage areas, the Wilkes Subglacial Basin and the Lambert Graben. Ice-rafted detritus (IRD), including dropstones, was deposited in concentrations far exceeding those known in the rest of the Miocene succession at both sites between 14.1 and 13.8 Ma, indicating that large amounts of IRD-bearing icebergs were calved from independent drainage basins during this relatively short interval. At Site U1356, the IRD was delivered in distinct pulses, suggesting that the overall ice advance was punctuated by short periods of ice retreat in the Wilkes Subglacial Basin. Provenance analysis of the mid-Miocene IRD and fine-grained sediments provides additional insights on the movement of the ice margin and subglacial geology. At Site U1356, the dominant 40Ar/39Ar thermochronological age of the ice-rafted hornblende grains is 1400-1550 Ma, differing from the majority of recent IRD in the area, from which we infer an inland source area of this thermochronological age extending along the eastern part of the Adélie Craton, which forms the western side of the Wilkes Subglacial Basin. Neodymium isotopic compositions from the terrigenous fine fraction at Site U1356 imply that the ice margin periodically expanded from high ground well into the Wilkes Subglacial Basin during periods of MMCT ice growth. At Site 1165, MMCT pebble-sized IRD are sourced from both the local Lambert Graben and the distant Aurora Subglacial Basin drainage area. Together, the occurrence and provenance of the IRD and glacially-eroded sediment at these two marine

  6. Two new species of .i.Prolagus./i. (Lagomorpha, Mammalia) from the Late Miocene of Hungary: taxonomy, biochronology, and palaeobiogeography

    Czech Academy of Sciences Publication Activity Database

    Angelone, Ch.; Čermák, Stanislav

    2015-01-01

    Roč. 89, č. 4 (2015), s. 1023-1038 ISSN 0031-0220 Institutional support: RVO:67985831 Keywords : evolutionary trends * Hungary * isolated species * Late Miocene * P. latiuncinatus sp. nov * Prolagus pannonicus sp. nov Subject RIV: EG - Zoology Impact factor: 1.545, year: 2015

  7. A box model of the Late Miocene Mediterranean Sea: implications from combined 87Sr/86Sr and salinity data

    NARCIS (Netherlands)

    Topper, R.P.M.; Flecker, R.; Meijer, P.Th.; Wortel, M.J.R.

    2011-01-01

    Under certain conditions the strontium isotope ratio in the water of a semi‐enclosed basin is known to be sensitive to the relative size of ocean water inflow and river input. Combining Sr‐isotope ratios measured in Mediterranean Late Miocene successions with data on past salinity, one can derive

  8. Updated chronology for Middle to Late Miocene mammal sites of the Daroca area (Calatayud-Montalbán Basin, Spain)

    NARCIS (Netherlands)

    van Dam, Jan A.; Krijgsman, Wout; Abels, Hemmo A.; Álvarez-Sierra, Maria A.; Garci´a-Paredes, Israel; Lo´pez-Guerrero, Paloma; Peláez-Campomanes, Pablo; Ventra, Dario

    The micromammal sequence of the Calatayud-Montalbán Basin in Northeast Central Spain is exceptional in terms of its faunal richness and dating accuracy. However, until now, several classical localities with ages close to the Middle to Late Miocene transition have never been directly tied to the

  9. Evolutionary history of the thicket rats (genus Grammomys) mirrors the evolution of African forests since late Miocene

    Czech Academy of Sciences Publication Activity Database

    Bryja, J.; Šumbera, R.; Kerbis Peterhans, J. C.; Aghová, T.; Bryjová, A.; Mikula, Ondřej; Nicolas, V.; Denys, C.; Verheyen, E.

    2017-01-01

    Roč. 44, č. 1 (2017), s. 182-194 ISSN 0305-0270 Institutional support: RVO:67985904 Keywords : Arvicanthini * coastal forests * late Miocene Subject RIV: EA - Cell Biology OBOR OECD: Biology (theoretical, mathematical, thermal, cryobiology, biological rhythm), Evolutionary biology Impact factor: 4.248, year: 2016

  10. Evolutionary history of the thicket rats (genus Grammomys) mirrors the evolution of African forests since late Miocene

    Czech Academy of Sciences Publication Activity Database

    Bryja, Josef; Šumbera, R.; Kerbis Peterhans, J. C.; Aghová, Tatiana; Bryjová, Anna; Mikula, Ondřej; Nicolas, V.; Denys, C.; Verheyen, E.

    2017-01-01

    Roč. 44, č. 1 (2017), s. 182-194 ISSN 0305-0270 Institutional support: RVO:68081766 Keywords : Arvicanthini * coastal forests * late Miocene * lowland forests * mountain forests * phylogeography * Plio-Pleistocene climate changes * Rodentia * tropical Africa Subject RIV: EG - Zoology OBOR OECD: Ecology Impact factor: 4.248, year: 2016

  11. Four new species of deep water agglutinated foraminifera from the Oligocene-Miocene of the Congo Fan (offshore Angola)

    OpenAIRE

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

    2006-01-01

    Four new species of deep-water agglutinated benthic foraminifera are described from the Oligocene and Miocene of the Congo Fan, offshore Angola. Scherochorella congoensis n.sp., Paratrochamminoides goroyskiformis n.sp., Haplophragmoides nauticus n.sp. and Portatrochammina profunda n.sp. all occur in deep-sea turbiditic shales and sands from the distal section of the Congo Fan.

  12. The Mendel Formation: Evidence for Late Miocene climatic cyclicity at the northern tip of the Antarctic Peninsula

    Czech Academy of Sciences Publication Activity Database

    Nývlt, D.; Košler, J.; Mlčoch, B.; Mixa, P.; Lisá, Lenka; Bubík, M.; Hendriks, B. W. H.

    2011-01-01

    Roč. 299, 1/2 (2011), s. 363-384 ISSN 0031-0182 Institutional research plan: CEZ:AV0Z30130516 Keywords : Mendel Formation * Late Miocene * chmate * Antarctic Peninsula Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.392, year: 2011

  13. 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

  14. Microfacies models and sequence stratigraphic architecture of the Oligocene–Miocene Qom Formation, south of Qom City, Iran

    Directory of Open Access Journals (Sweden)

    Mahnaz Amirshahkarami

    2015-07-01

    Full Text Available The Oligocene–Miocene Qom Formation has different depositional models in the Central Iran, Sanandaj–Sirjan and Urumieh-Dokhtar magmatic arc provinces in Iran. The Kahak section of the Qom Formation in the Urumieh-Dokhtar magmatic arc has been studied, in order to determinate its microfacies, depositional model and sequence stratigraphy. The textural analysis and faunal assemblages reveal ten microfacies. These microfacies are indicative of five depositional settings of open marine, patch reef, lagoon, tidal flat and beach of the inner and middle ramp. On the basis of the vertical succession architecture of depositional system tracts, four third-order sequences have been recognized in the Oligocene–Miocene Kahak succession of Qom Formation. Based on the correlation charts, the transgression of the Qom Sea started from the southeast and continued gradually towards the north. This resulted in widespread northward development of the lagoon paleoenvironment in the Aquitanian-Burdigalian stages. Also, the sequence stratigraphic model of the Oligocene–Miocene Qom Formation has an architecture similar to those that have developed from Oligocene–Miocene global sea level changes.

  15. The Miocene fish Marosichthys, a putative tetraodontiform, actually a perciform surgeon fish (Acanthuridae) related to the recent Naso

    NARCIS (Netherlands)

    Tyler, James C.

    1997-01-01

    Marosichthys huismani (de Beaufort, 1926), a fish from the Miocene of the Celebes, was described in the tripod fish family Triacanthidae, Tetraodontiformes. It is shown here to be a valid genus of the surgeon fish family Acanthuridae, Perciformes, and closely related to the Recent genus Naso.

  16. Rodents from the Upper Miocene Tuğlu Formation (Çankırı Basin, Central Anatolia, Turkey)

    NARCIS (Netherlands)

    Joniak, Peter; de Bruijn, Hans

    2015-01-01

    The upper Miocene assemblages of rodents collected from two layers of the type section of the Tuğlu Formation (Çankırı Basin, Central Anatolia, Turkey) are described. The assemblage from the lower level is considerably less diverse than that from the upper level. It contains Progonomys together with

  17. 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

    to two otolith-based species so far identified from the same time interval in the Paratethys---Atherina austriaca and Atherina gidjakensis. Our correlation of isolated otoliths and otolith in situ documents in this case that A. suchovi is not synonymous to any of the otolith-based species, although...... 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.......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...

  18. 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

    The small Neogene Krong Pa graben is situated within the continental Song Ba Rift, which is bounded by strike-slip faults that were reactivated as extensional faults in Middle Miocene time. The 500 m thick graben-fill shows an overall depositional development reflecting the structural evolution...... 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...... 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...

  19. Enhanced Continental Weathering on Antarctica During the Mid Miocene Climatic Optima Based on Pb Isotopes

    Science.gov (United States)

    Martin, E. E.; Fenn, C.; Basak, C.

    2012-12-01

    Feedbacks between climate and continental weathering can be monitored over geologic time scales using Pb isotopes preserved in marine sediments. During chemical weathering, radiogenic Pb is preferentially released to the dissolved phase, producing weathering solutions with more radiogenic isotopic values than the parent rock. The offset between the composition of the solution and rock tend to increase with the intensity of incongruent weathering (von Blanckenburg and Nägler, 2001; Harlavan and Erel, 2002). The seawater isotopic signal extracted from Fe-Mn oxides on bulk marine sediments is interpreted to represent the composition of local dissolved weathering inputs. For example, increasing seawater Pb isotopes observed during the most recent deglaciation are believed to reflect enhanced weathering of newly exposed glacial rock flour under warm conditions (Foster and Vance, 2006; Kurzweil et al., 2010). For this study we evaluated Nd and Pb isotopes from both the seawater fraction (extracted from Fe-Mn oxides) and parent rock (the detrital fraction of marine sediment) during the Mid-Miocene Climatic Optimum (MMCO) and subsequent cooling and East Antarctic Ice Sheet (EAIS) expansion (18 to 8 Ma) from Ocean Drilling Program site 744 on Kerguelen Plateau (2300 m; Indian sector) and sites 689 and 690 on Maud Rise (2080 m and 2914 m; Atlantic sector). The absolute value of seawater 206Pb/204Pb and separation between values for seawater and detrital fractions increased during the MMCO, suggesting enhanced weathering in proglacial and deglaciated areas exposed by ice sheet meltback during the warm interval. During the ensuing cooling, seawater values and the offset between the two archives decreased. Similar trends are displayed by 207Pb/204Pb and 208Pb/204Pb, although 207Pb/204Pb detrital values tend to be higher than seawater values. Reconstructions of atmospheric pCO2 in the Miocene have suggested both 1) decoupling between pCO2 and climate with consistently low

  20. Paleomagnetic record of a geomagnetic field reversal from late miocene mafic intrusions, southern nevada.

    Science.gov (United States)

    Ratcliff, C D; Geissman, J W; Perry, F V; Crowe, B M; Zeitler, P K

    1994-10-21

    Late Miocene (about 8.65 million years ago) mafic intrusions and lava flows along with remagnetized host rocks from Paiute Ridge, southern Nevada, provide a high-quality paleomagnetic record of a geomagnetic field reversal. These rocks yield thermoremanent magnetizations with declinations of 227 degrees to 310 degrees and inclinations of -7 degrees to 49 degrees , defining a reasonably continuous virtual geomagnetic pole path over west-central Pacific longitudes. Conductive cooling estimates for the intrusions suggest that this field transition, and mafic magmatism, lasted only a few hundred years. Because this record comes principally from intrusive rocks, rather than sediments or lavas, it is important in demonstrating the longitudinal confinement of the geomagnetic field during a reversal.

  1. A new Miocene baleen whale from Peru deciphers the dawn of cetotheriids

    Science.gov (United States)

    Marx, Felix G.; Lambert, Olivier; de Muizon, Christian

    2017-09-01

    Cetotheriidae are an iconic, nearly extinct family of baleen whales (Mysticeti) with a highly distinct cranial morphology. Their origins remain a mystery, with even the most archaic species showing a variety of characteristic features. Here, we describe a new species of archaic cetotheriid, Tiucetus rosae, from the Miocene of Peru. The new material represents the first mysticete from the poorly explored lowest portion of the highly fossiliferous Pisco Formation (allomember P0), and appears to form part of a more archaic assemblage than observed at the well-known localities of Cerro Colorado, Cerro los Quesos, Sud-Sacaco and Aguada de Lomas. Tiucetus resembles basal plicogulans (crown Mysticeti excluding right whales), such as Diorocetus and Parietobalaena, but shares with cetotheriids a distinct morphology of the auditory region, including the presence of an enlarged paroccipital concavity. The distinctive morphology of Tiucetus firmly places Cetotheriidae in the context of the poorly understood `cetotheres' sensu lato, and helps to resolve basal relationships within crown Mysticeti.

  2. Anatomy and origin of carbonate structures in a Miocene cold-seep field

    Science.gov (United States)

    Aiello, Ivano W.; Garrison, Robert E.; Moore, J. Casey; Kastner, Miriam; Stakes, Debra S.

    2001-12-01

    Miocene calcite concretions resembling modern carbonate structures that form at cold seeps are present in fractured opal- CT porcelanites that are interbedded with mudstones in coastal cliffs at Santa Cruz, California. The morphologies of the carbonate structures differ markedly from conventional concretions and are spatially aligned with orthogonal joints in the porcelanites. The structures contain tubular holes that are identical to fluid and gas conduits in modern carbonate seep structures; the orientations of these tubes suggest that fluid and gas flow was both vertical and horizontal, the latter along extensional joints that formed preferentially in the brittle, silica-rich layers that had enhanced bedding- parallel permeability. Petrographic and isotopic characteristics of the carbonate structures indicate that calcite precipitation occurred in a shallow, subseafloor environment in either the zone of microbial sulfate reduction or of methanogenesis, prior to or possibly simultaneously with the silica phase transformation of opal- A in diatom shells to opal-CT.

  3. Oligo-Miocene reservoir sequence characterization and structuring in the Sisseb El Alem-Kalaa Kebira regions (Northeastern Tunisia)

    Science.gov (United States)

    Houatmia, Faten; Khomsi, Sami; Bédir, Mourad

    2015-11-01

    The Sisseb El Alem-Enfidha basin is located in the northeastern Tunisia, It is borded by Nadhour - Saouaf syncline to the north, Kairouan plain to the south, the Mediterranean Sea to the east and Tunisian Atlassic "dorsale" to the west. Oligocene and Miocene deltaic deposits present the main potential deep aquifers in this basin with high porosity (25%-30%). The interpretation of twenty seismic reflection profiles, calibrated by wire line logging data of twelve oil wells, hydraulic wells and geologic field sections highlighted the impact of tectonics on the structuring geometry of Oligo-Miocene sandstones reservoirs and their distribution in raised structures and subsurface depressions. Miocene seismostratigraphy analysis from Ain Ghrab Formation (Langhian) to the Segui Formation (Quaternary) showed five third-order seismic sequence deposits and nine extended lenticular sandy bodies reservoirs limited by toplap and downlap surfaces unconformities, Oligocene deposits presented also five third- order seismic sequences with five extended lenticular sandy bodies reservoirs. The Depth and the thickness maps of these sequence reservoir packages exhibited the structuring of this basin in sub-basins characterized by important lateral and vertical geometric and thichness variations. Petroleum wells wire line logging correlation with clay volume calculation showed an heterogeneous multilayer reservoirs of Oligocene and Miocene formed by the arrangement of fourteen sandstone bodies being able to be good reservoirs, separated by impermeable clay packages and affected by faults. Reservoirs levels correspond mainly to the lower system tract (LST) of sequences. Intensive fracturing by deep seated faults bounding the different sub-basins play a great role for water surface recharge and inter-layer circulations between affected reservoirs. The total pore volume of the Oligo-Miocene reservoir sandy bodies in the study area, is estimated to about 4 × 1012 m3 and equivalent to 4

  4. Enamel microwear texture properties of IGF 11778 (Oreopithecus bambolii) from the late Miocene of Baccinello, Italy.

    Science.gov (United States)

    L' Engle Williams, Frank

    2013-01-01

    Late Miocene Oreopithecus bambolii has been posited as a folivore from its pronounced molar shearing crests. However, scanning electron microscopy yields conflicting results with one study of Oreopithecus showing folivory and another indicating a coarser diet was consumed. To address this debate, the dietary proclivities of the well-known IGF 11778 Oreopithecus bambolii specimen are reconstructed by comparing the enamel texture properties of this specimen to extant Alouatta palliata (n = 11), Cebus apella (n = 13), Gorilla gorilla (n = 9), Lophocebus albigena (n = 15), Pan troglodytes (n = 17) and Trachypithecus cristatus (n = 12). Dental microwear is captured by scanning facet 9, a Phase II facet on the hypoconid surface, using white-light confocal microscopy at 100x. The scanning was followed by scale-sensitive fractal analysis, yielding four texture characteristics. These were ranked before ANOVA with post-hoc tests of significance and multivariate analyses were conducted. Oreopithecus specimen IGF 11778 does not match any of the extant taxa consistently but in some analyses is associated with Lophocebus, and secondarily with Pan, Gorilla and Cebus outliers suggesting mixed-fruit and hard-object feeding characterized at least a portion of its diet. The partially open habitat of late Miocene Baccinello may have had resources with mechanically resistant foods, or foods found near ground level were consumed. Hard, brittle foods, insects, and or extraneous grit may have contributed to the greater use-wear complexity of the enamel surface observed in IGF 11778 compared to extant folivores. IGF 11778 does not exhibit the degree of anisotropy characterizing Trachypithecus and Alouatta. The partial resemblance of IGF 11778 to some great ape specimens may indicate intermittent extractive and or terrestrial foraging.

  5. Life-history traits of the Miocene Hipparion concudense (Spain inferred from bone histological structure.

    Directory of Open Access Journals (Sweden)

    Cayetana Martinez-Maza

    Full Text Available Histological analyses of fossil bones have provided clues on the growth patterns and life history traits of several extinct vertebrates that would be unavailable for classical morphological studies. We analyzed the bone histology of Hipparion to infer features of its life history traits and growth pattern. Microscope analysis of thin sections of a large sample of humeri, femora, tibiae and metapodials of Hipparion concudense from the upper Miocene site of Los Valles de Fuentidueña (Segovia, Spain has shown that the number of growth marks is similar among the different limb bones, suggesting that equivalent skeletochronological inferences for this Hipparion population might be achieved by means of any of the elements studied. Considering their abundance, we conducted a skeletechronological study based on the large sample of third metapodials from Los Valles de Fuentidueña together with another large sample from the Upper Miocene locality of Concud (Teruel, Spain. The data obtained enabled us to distinguish four age groups in both samples and to determine that Hipparion concudense tended to reach skeletal maturity during its third year of life. Integration of bone microstructure and skeletochronological data allowed us to identify ontogenetic changes in bone structure and growth rate and to distinguish three histologic ontogenetic stages corresponding to immature, subadult and adult individuals. Data on secondary osteon density revealed an increase in bone remodeling throughout the ontogenetic stages and a lesser degree thereof in the Concud population, which indicates different biomechanical stresses in the two populations, likely due to environmental differences. Several individuals showed atypical growth patterns in the Concud sample, which may also reflect environmental differences between the two localities. Finally, classification of the specimens' age within groups enabled us to characterize the age structure of both samples, which is

  6. Oligo-Miocene peatland ecosystems of the Gippsland Basin and modern analogues

    Science.gov (United States)

    Korasidis, Vera A.; Wallace, Malcolm W.; Wagstaff, Barbara E.; Holdgate, Guy R.

    2017-02-01

    A detailed examination of the brown coal facies preserved in the Latrobe Valley Morwell 1B seam indicates that the type of peat-forming environment and the associated hydrological regime are the main factors influencing the development of lithotypes in brown coal deposits. New palynological data from the Morwell 1B seam suggests that each respective lithotype in the lightening-upwards lithotype cycles was deposited in a particular depositional environment that was characterised by a distinct floral community. The laminated dark lithotype represents a fire-prone emergent marsh that grew on the margins of a coastal lagoon and/or freshwater swamp. This facies grades into the dark lithotype, representing the transition from a meadow marsh to a periodically flooded ombrogenous forested bog. The medium and lighter lithotypes are interpreted as being deposited in an angiosperm-dominated ombrogenous forest bog that was intolerant of fire. These peat-forming environments are interpreted as being largely controlled by moisture and relative depth to water table. Each environment produces distinct lithotypes and lightening-upwards cycles are interpreted as terrestrialization cycles. As the peat grew upwards and above the water table, less moist conditions prevailed and lighter lithotypes were produced. The observed change in colour, from darker to lighter lithotypes, results from the environment evolving from anaerobic/inundated to less anaerobic/less moist settings via terrestrialization. The thin and laterally extensive light and pale lithotypes that top the cycles are interpreted to represent a residual layer of concentrated, oxidation resistant peat-forming elements that result from intense weathering and aerobic degradation of the peats. At a generic level, modern lowland bogs of South Westland in New Zealand have remarkably similar floral/ecological gradients to those of the Oligo-Miocene Morwell 1B brown coal cycles in Australia. This suggests that modern New Zealand

  7. Temporal and geochemical evolution of Miocene volcanism in the Andean back-arc between 36°S and 38°S and U-series analyses of young volcanic centers in the arc and back-arc, Argentina

    DEFF Research Database (Denmark)

    Dyhr, Charlotte Thorup

    New 40Ar/39Ar, major and trace element, and Sr, Nd and Pb isotopic data for the c. 24-7 Ma volcanic rocks from the Andean back-arc (35°S – 38°S) in the Mendoza and Neuquén (Argentina) regions shed light on the Miocene evolution of the back-arc of the Southern Volcanic Zone. Incipient shallowing......-Sr-Pb isotopic compositions. The arc-like component that dominates the geochemistry of the Palaoco rocks is absent in both the Early Miocene and the Pliocene-Pleistocene in the same area. Young volcanic Provinces in the main arc, retro-arc and back-arc are further investigated by U-series analyses which confirm...... the fluid-enriched nature of arc-related rocks (U-excess are found in most rocks) and the more OIB-like nature of the Payún Matrú complex (Th-exsess is observed in all rocks). The fluid addition to the mantle source is modeled revealing timescales of 10 – 100 ka for the fluid enrichment. For the back...

  8. Morphology and distribution of Oligocene and Miocene pockmarks in the Danish North Sea -implications for bottom current activity and fluid migration

    DEFF Research Database (Denmark)

    Andresen, Katrine Juul; Huuse, Mads; Clausen, O.R.

    2008-01-01

    This study gives the first description of 33 mid-Oligocene and 646 late Miocene pockmarks mapped in the Danish part of the central North Sea. The pockmarks are all highly elongated, with average long- and short axes of 2.5 km and 700 m, and average internal depth of 30 m. The Miocene pockmarks...... the timing and location of the pockmarks. The pockmarks thus tell a story of thermogenic gas venting to the surface and paleo-current scour of the seabed in the eastern part of the central North Sea during the mid Oligocene and late Miocene....

  9. THE BRECCE DELLA RENGA FORMATION: AGE AND SEDIMENTOLOGY OF A SYN-TECTONIC CLASTIC UNIT IN THE UPPER MIOCENE OF CENTRAL APENNINES. INSIGHTS FROM FIELD GEOLOGY

    Directory of Open Access Journals (Sweden)

    SIMONE FABBI

    2014-07-01

    Full Text Available In the NE Simbruini Mountains, the “Brecce della Renga Fm.” is a clastic unit documenting sedimentation controlled by late Miocene extensional tectonics.The unit has been subdivided into three lithofacies and six sublithofacies, based on the arenite/rudite/pelite ratio. Massive and coarser (up to megablock size intervals are interpreted as rockfall deposits (likely induced by earthquakes at the toe of steep submarine escarpments. By contrast, finer levels are interpreted as having been sedimented through avalanching and turbidity flows in more distal settings, and are partly lateral to basinal hemipelagites and siliciclastic turbidites. Pelite lenses, found at various stratigraphic levels, are the result of ponded sedimentation along the clastic margin. Calcareous nannofossils analyses have been performed for age determinations on 60 fossiliferous samples, which were collected in each sublithofacies of the “Brecce della Renga Fm.”. The unit ranges from early Tortonian (MNN8b to early Messinian (MNN11c. The age and field geometries of the older breccias document the existence of a Tortonian extensional phase, which predated the late Messinian thrusting. A progradation of the clastic wedge can be observed in the Tortonian, while Messinian deposits show a fining upwards trend. The distribution curve of clastics over time can, given the number of synsedimentary faults mapped in the area, be put in relation with the seismicity induced by the activity along such faults, which after reaching an acme in the Tortonian gradually reached a quiescent state in the early Messinian, causing the backstepping of clastic facies.

  10. Post-early Messinian counterclockwise rotations on Crete: implications for Late Miocene to Recent kinematics of the southern Hellenic arc

    NARCIS (Netherlands)

    Duermeijer, C.E.; Krijgsman, W.; Langereis, C.G.; Veen, J.H. ten

    1998-01-01

    Most geodynamical models for the kinematics of the central Mediterranean recognise that major tectonic rotations must have played an important role during the Neogene. The Hellenic arc is believed to have been subjected to clockwise rotations in the west and counterclockwise rotations in the east,

  11. Possible linkage between supernovae, increased terrestrial lightning, and wildfire activity in the Late Miocene and Early Pleistocene

    Science.gov (United States)

    Thomas, B. C.; Feulner, G.; Melott, A. L.; Kirsten, T.; von Bloh, W.

    2017-12-01

    Radioisotopes from deep-sea deposits show that Earth was affected by nearby supernovae about 2.5 and 8 million years ago. Recent modelling work shows that high-energy particles from these events resulted in greatly enhanced ionization of the troposphere. This could have led to an increase in wildfires via more frequent lightning. Here we show that published data on global fire activity from charcoal records reveal a marked increase in wildfires around the times of the supernova explosions. We use a dynamic global vegetation model to assess the impact of increased lightning frequency on vegetation patterns, finding a patchy global decrease in tree cover. Regionally, vegetation changes are particularly pronounced in western North America, the Mediterranean, Central Asia, Northern Indochina, subtropical South America, Africa and Australia, and notably East Africa, in agreement with empirical evidence for a global shift towards savannas during the Pleistocene. Our results demonstrate that moderately nearby supernovae have the potential to affect life on Earth even if they are too distant to initiate a mass extinction. Finally, we note that the shift from forest to savannah biomes in the East African Rift Valley region has been tentatively linked to hominin evolution in this region.

  12. 87Sr/86Sr variations in basalts of Late Eocene-Early Miocene series in Eastern Sikhoteh-Alin

    International Nuclear Information System (INIS)

    Esin, S.V.; Ponomarchuk, V.A.; Shipitsyn, Yu.G.; Palesskij, Yu.G.

    1993-01-01

    Late Eocene high-alumina and Oligocene high-alumina and magnesian basalts of the Neogene calc-alkaline series from the Eastern Sikhoteh-Alin are shown to have the following 87 Sr/ 86 Sr ratios: 0.70390-0.70465; 0.70347-0.70401, and the 0.70330-0.70347. Analysis of variations of Sr ratios, REE, HFSE, and LILE suggests that they are the products of successive melting of a multicomponent source containing the peridotite material of OIB- and MORB-types altered by fluids to a different degree and the pelagic sediments

  13. THE BAIKAL RIFT: PLIOCENE (MIOCENE – QUATERNARY EPISODE OR PRODUCT OF EXTENDED DEVELOPMENT SINCE THE LATE CRETACEOUS UNDER VARIOUS TECTONIC FACTORS. A REVIEW

    Directory of Open Access Journals (Sweden)

    V. D. Mats

    2015-01-01

    Full Text Available The article reviews three typical concepts concerning the age of the Baikal rift (BR which development is still underway: 5 Ma (the BR development start in the Late Pliocene, 30 Ma (Miocene or Oligocene, and 60–70 Ma (the Late Cretaceous. Under the concept of the young BR age (Pliocene–Quaternary [Artyushkov, 1993; Nikolaev et al., 1985; Buslov, 2012], according to E.V. Artyushkov, BR is not a rift, but a graben due to the fact that the pre‐Pliocene structure of BR does not contain any elements that would be indicative of tensile stresses. However, field studies reported in [Lamakin, 1968; Ufimtsev, 1993; Zonenshain et al., 1995; Mats, 1993, 2012; Mats et al., 2001] have revealed that extension structures, such as tilted blocks and listric faults, are abundant in the Baikal basin (BB, and thus do not supportE.V. Artyushkov’s argumentation. The opinion that BR is young is shared by M.M. Buslov [2012]; he refers to studies of  Central Asia and states that only the Pliocene‐Quaternary structure of BB is a rift, while the oldest Cenozoic structures (Upper Cretaceous – Miocene are just fragments of the large Cenozoic Predbaikalsky submontane trough (PBT which are not related to the rift. However, the coeval Cenozoic lithological compositions, thicknesses of sediment layers and types of tectonic structures in PBT and BB have nothing in common. Across the area separating PBT and BB, there are no sediments or structures to justify a concept that BR and PBT may be viewed as composing a single region with uniform structures and formations. The idea of the Pliocene‐Quaternary age of BR should be rejected as it contradicts with the latest geological and geophysical data. Seismic profiling in BB has revealed the syn‐rift sedimentary bed which thickness exceeds 7.5 km. Results of drilling through the 600‐metre sedimentary sequence of Lake Baikal suggest the age of 8.4 Ma [Horiuchi et al., 2004], but M.M. Buslov believes

  14. 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.

  15. Application of organic facies in sedimentological-stratigraphical model of the Oligo-Miocene and Miocene of the Campos Basin; Aplicacao da faciologia organica no modelo sedimentologico-estratigrafico do Oligo-Mioceno e Mioceno da Bacia de Campos

    Energy Technology Data Exchange (ETDEWEB)

    Mendonca Filho, Joao Graciano; Mendonca, Joalice de Oliveira; Oliveira, Antonio Donizeti de; Torres, Jaqueline [Universidade Federal do Rio de Janeiro (UFRJ). Centro de Ciencias Exatas e da Natureza. Inst. de Geociencias (Brazil)], e-mails: graciano@geologia.ufrj.br, donizeti@lafo.geologia.ufrj.br, joalice@lafo.geologia.ufrj.br, jaqueline@lafo.geologia.ufrj.br; Menezes, Taissa Rego [Centro de Pesquisas da Petrobras (CENPES), RJ (Brazil). P e D em Geociencias. Gerencia de Geoquimica], e-mail: taissamenezes@petrobras.com.br; Santos, Viviane Sampaio Santiago dos; Arienti, Luci Maria [Centro de Pesquisas da Petrobras (CENPES), RJ (Brazil). P e D em Geociencias. Gerencia de Sedimentologia e Estratigrafia], e-mails: vsss@petrobras.com.br, arienti@petrobras.com.br

    2010-05-15

    This study integrates palynofacies analyses and the sedimentological and stratigraphic model of the Oligo-Miocene/Miocene siliciclastic deposits from the stratigraphic interval of the shallow continental platform up to the slope/basin of the Oligo-Miocene/ Miocene of the Campos Basin proposed. The main objective of the palynofacies study was to characterize the particulate sedimentary organic matter to obtain information about the proximal-distal relationship and the sedimentary organic matter preservation and depositional environmental conditions. The 158 core samples collected in 29 wells of the 9 oil production fields (Albacora, Barracuda, Marlim Sul, Marlim, Voador, Marlim Leste, Moreia and Albacora Leste), were studied. This technique provides information about the proximal-distal relationship and the paleoenvironmental conditions of deposition and preservation of sedimentary organic matter, to facilitate the evaluation and comparisons between the associations of particulate organic components. Thus, the palynofacies technique can be used as another tool in the characterization of depositional systems, based on the spatial and temporal distribution of sedimentary intervals. In general the palynofacies assemblages showed the predominance of the Phytoclast Group (terrestrial derived organic matter) at various degradation stages due to the selective preservation process diagnosed in the studied samples. Some samples, revealed high dinocysts percentages indicative of transgressive depositional conditions. From the obtained data, it was possible to characterize the stratigraphic sequences according to the distribution of particulate organic content (e.g. influence of fluvio-deltaic systems, oxygen system, regressive-transgressive tendencies of each sequence). Additional analyses of Total Organic Carbon (% wt) showed the control of the particulate components from the Phytoclast Group on the TOC (% wt) content, suggesting that the relative sea-level variation curves

  16. New Late Miocene .i.Alilepus./i. (Lagomorpha, Mammalia) from Eastern Europe - a new light on the evolution of the earliest old world Leporinae

    Czech Academy of Sciences Publication Activity Database

    Čermák, Stanislav; Angelone, Ch.; Sinitsa, M. V.

    2015-01-01

    Roč. 90, č. 2 (2015), s. 431-451 ISSN 1214-1119 Institutional support: RVO:67985831 Keywords : Alilepus * Eastern Europe * Late Miocene * phylogeny * Pliocene * taxonomy Subject RIV: EG - Zoology Impact factor: 1.700, year: 2015

  17. Large-scale gravity sliding in the Miocene Shadow Valley Supradetachment Basin, Eastern Mojave Desert, California

    Science.gov (United States)

    Davis, G. A.; Friedmann, S. J.

    2005-12-01

    The Miocene Shadow Valley basin in the eastern Mojave Desert of California developed above the active west-dipping Kingston Range-Halloran Hills extensional detachment fault system between 13.5 and ca. 7 mybp. Although mass-wasting processes are common phenomena in supradetachment basins, the Shadow Valley basin is an exceptional locale for the study of such processes, especially rock-avalanches and gravity sliding. A score of megabreccias, interpreted as rock-avalanche deposits, and half that number of very large (> 1 km 2, up to 200 m thick), internally intact gravity-driven slide sheets are interbedded with various sedimentary facies. The slide sheets, variably composed of Proterozoic crystalline rocks and Proterozoic, Paleozoic, and Tertiary sedimentary strata, moved across both depositional and erosional surfaces in the basin. Although the majority consist of Paleozoic carbonate rocks, the largest slide sheet, the Eastern Star crystalline allochthon, contains Proterozoic gneisses and their sedimentary cover and is now preserved as klippen atop Miocene lacustrine and alluvial fan deposits over an area > 40 km 2. Estimates of slide sheet runouts into the basin from higher eastern and northern source terranes range from approximately a few km to > 10 km; in most cases the exact provenances of the slide blocks are not known. The basal contacts of Shadow Valley slide sheets are characteristically knife sharp, show few signs of lithologic mixing of upper- and lower-plate rocks, and locally exhibit slickensided and striated, planar fault-like bases. Pronounced folding of overridden Miocene lacustrine and fan deposits beneath the Eastern Star allochthon extends to depths up to 40 m at widely scattered localities. We conclude that this slow moving slide sheet encountered isolated topographic asperities (hills) and that stress transfer across the basal slide surface produced folding of footwall strata. Synkinematic gypsum veins in footwall playa sediments, with fibers

  18. Revised stratigraphy and reinterpretation of the Miocene Pohang basinfill, SE Korea: sequence development in response to tectonism and eustasy in a back-arc basin margin

    Science.gov (United States)

    Sohn, Y. K.; Rhee, C. W.; Shon, H.

    2001-09-01

    The Miocene Pohang Basin is a pull-apart basin formed along the eastern continental margin of Korea (ECMK) during the back-arc opening of the East Sea (Sea of Japan). The basin is filled by more than 1 km thick, nonmarine to deep-marine strata. These strata show extreme vertical and lateral lithofacies changes and have caused decades-long controversies on their nature and stratigraphy. Previous sedimentological studies suggest that the basinfill was deposited by a series of contemporaneously developed depositional systems, including fan delta, prodelta, slope apron, and basin plain. Detailed mapping and magnetotelluric surveying show, however, that the basinfill is composed of several packages of strata (sequences) that are bounded by distinct and laterally persistent stratigraphic discontinuities (sequence boundaries). This suggests that the depositional systems in the Pohang Basin developed sequentially rather than contemporaneously. Six packages of strata are identified in the basin: a nonmarine to shallow marine (transgressive) sequence (Sequence 1), a Gilbert-type-delta conglomerate (Sequence 2), and alternations of submarine conglomerates and hemipelagic mudstones (Sequences 3-6). The conglomerates and hemipelagic mudstones of the latter four sequences are interpreted to represent lowstand depositional systems (slope apron, submarine fan, and high-gradient delta) and condensed intervals, respectively. Compilation of geochronologic, paleomagnetic, and biostratigraphic data suggests that Sequence 1 formed during the gradual subsidence of the ECMK prior to 17 Ma, whereas Sequence 2 formed in response to abrupt downfaulting of the Pohang Basin at about 17 Ma. Both sequences are interpreted to have developed in response to the early Miocene back-arc-opening tectonism of the East Sea. On the other hand, Sequences 3-6 formed between 17 and about 10.5 Ma. The Pohang Basin was subject to only minor tectonism during this period and could record global sea

  19. New Insights to the Mid Miocene Calc-alkaline Lavas of the Strawberry Volcanics, NE Oregon Surrounded by the Coeval Tholeiitic Columbia River Basalt Province

    Science.gov (United States)

    Steiner, A. R.; Streck, M. J.

    2013-12-01

    The Strawberry Volcanics (SV) of NE Oregon were distributed over 3,400 km2 during the mid-Miocene and comprise a diverse volcanic suite, which span the range of compositions from basalt to rhyolite. The predominant composition of this volcanic suite is calc-alkaline (CA) basaltic andesite and andesite, although tholeiitic (TH) lavas of basalt to andesite occur as well. The coeval flood basalts of the Columbia River province surround the SV. Here we will discuss new ages and geochemical data, and present a new geologic map and stratigraphy of the SV. The SV are emplaced on top of pre-Tertiary accreted terranes of the Blue Mountain Province, Mesozoic plutonic rocks, and older Tertiary volcanic rocks thought to be mostly Oligocene of age. Massive rhyolites (~300 m thick) are exposed mainly along the western flank and underlie the intermediate composition lavas. In the southern portion of this study area, alkali basaltic lavas, thought to be late Miocene to early Pliocene in age, erupted and overlie the SV. In addition, several regional ignimbrites reach into the area. The 9.7 Ma Devine Canyon Tuff and the 7.1 Ma Rattlesnake Tuff also overlie the SV. The 15.9-15.4 Ma Dinner Creek Tuff is mid-Miocene, and clear stratigraphic relationships are found in areas where the tuff is intercalated between thick SV lava flows. All of the basalts of the SV are TH and are dominated by phenocryst-poor (≤2%) lithologies. These basalts have an ophitic texture dominated by plagioclase, clinopyroxene and olivine (often weathered to iddingsite). Basalts and basaltic andesites have olivine Fo #'s ranging from 44 at the rims (where weathered to iddingsite) and as high as 88 at cores. Pyroxene Mg #'s range from 65 to 85. Andesites of the SV are sub-alkaline, and like the basalts, are exceedingly phenocryst-poor (≤3%) with microphenocrysts of plagioclase and lesser pyroxene and olivine, which occasionally occur as crystal clots of ~1-3 mm instead of single crystals. In addition, minimal

  20. Lineage-Specific Responses of Tooth Shape in Murine Rodents (Murinae, Rodentia) to Late Miocene Dietary Change in the Siwaliks of Pakistan

    OpenAIRE

    Kimura, Yuri; Jacobs, Louis L.; Flynn, Lawrence J.

    2013-01-01

    Past ecological responses of mammals to climate change are recognized in the fossil record by adaptive significance of morphological variations. To understand the role of dietary behavior on functional adaptations of dental morphology in rodent evolution, we examine evolutionary change of tooth shape in late Miocene Siwalik murine rodents, which experienced a dietary shift toward C4 diets during late Miocene ecological change indicated by carbon isotopic evidence. Geometric morphometric analy...

  1. Evolution and classification of Elaphoglossum and Asplenium ferns on Cuba, and discovery of a Miocene Elaphoglossum in Dominican amber

    OpenAIRE

    Lóriga Piñero, Josmaily

    2018-01-01

    This dissertation deals with the systematics and evolution of Neotropical ferns of the genera Elaphoglossum and Asplenium, with particular focus on the species of Cuba and the West Indies. It also includes an analysis and description of an Elaphoglossum frond fragment preserved in Miocene Dominican amber. The worldwide genera Elaphoglossum with 600 species and Asplenium with 685 species are the most species-rich groups of leptosporangiate ferns. On Cuba, Elaphoglossum has 34 species and Asple...

  2. Coexisting Miocene Alkaline Volcanic Series Associated with the Cheb-Domažlice Graben (W Bohemia): Geochemical Characteristics

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Štěpánková, Jana; Lloyd, F. E.; Balogh, K.

    2003-01-01

    Roč. 54, č. 1 (2003), s. 53-64 ISSN 1335-0552 R&D Projects: GA ČR GA205/99/0907 Grant - others:Hungarian Academy of Sciences Foundation(HU) T 014961 Institutional research plan: CEZ:AV0Z3013912 Keywords : W Bohemia * Miocene volkanism * geochemistry Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.397, year: 2003 http://www.geologicacarpathica.sk/src/main.php

  3. Paleocene to Middle Miocene planktic foraminifera of the southwestern Salisbury Embayment, Virginia and Maryland: biostratigraphy, allostratigraphy, and sequence stratigraphy

    Science.gov (United States)

    Poag, C.W.; Commeau, J.A.

    1995-01-01

    The Paleocene to Middle Miocene sedimentary fill of the southwestern Salisbury Embayment contains a fragmental depositional record, interrupted by numerous local diastems and regional unconformities. Using planktic foraminiferal biostratigraphy, 15 unconformity-bounded depositional units have been identified, assigned to six formations and seven alloformations previously recognized in the embayment. The units correlate with second- and third-order sequences of the Exxon sequence stratigraphy model, and include transgressive and highstand systems tracts. Alloformation, formation, and sequence boundaries are marked by abrupt, scoured, burrowed, erosional surfaces, which display lag deposits, biostratigraphic gaps, and intense reworking of microfossils above and below the boundaries.Paleocene deposits represent the upper parts of upper Pleocene Biochronozones P4 and P5, and rest uncomformably  on Cretaceous sedimentary beds of various ages (Maastrichtian to Albian). Lower Eocene deposits represent parts of Biochronozones P6 and P9. Middle Eocene strata represent mainly parts of Biochronozones P11, P12, and P14. Upper Eocene sediments include parts of Biochronozones P15, P16, and P17. Oligocene deposits encompass parts of Biochronozones. N4b to N7 undifferentiated, P21a, and, perhaps, N4a. Lower Miocene deposits encompass parts of Biochronozones N4b to N7 undifferentiated. Middle Miocene strata represent mainly parts of Biochronorones N8, N9, and N10.Nine plates of scanning electron micrographs illustrate the principal planktic foraminifera used to establish the biostratigraphic framework. Two new informal formine of Praeterenuitella praegemma Li, 1987, are introduced.

  4. Thermochronometrically constrained anatomy and evolution of a Miocene extensional accommodation zone and tilt domain boundary: The southern Wassuk Range, Nevada

    Science.gov (United States)

    Gorynski, Kyle E.; Stockli, Daniel F.; Douglas Walker, J.

    2013-06-01

    (AHe) and Zircon (ZHe) (U-Th)/He thermochronometric data from the southern Wassuk Range (WR) coupled with 40Ar/39Ar age data from the overlying tilted Tertiary section are used to constrain the thermal evolution of an extensional accommodation zone and tilt-domain boundary. AHe and ZHe data record two episodes of rapid cooling related to the tectonic exhumation of the WR fault block beginning at ~15 and ~4 Ma. Extension was accommodated through fault-block rotation and variably tilted the southern WR to the west from ~60°-70° in the central WR to ~15°-35° in the southernmost WR and Pine Grove Hills, and minimal tilting in the Anchorite Hills and along the Mina Deflection to the south. Middle Miocene geothermal gradient estimates record heating immediately prior to large-magnitude extension that was likely coeval with the extrusion of the Lincoln Flat andesite at ~14.8 Ma. Geothermal gradients increase from ~19° ± 4°C/km to ≥ 65° ± 20°C/km toward the Mina Deflection, suggesting that it was the focus of Middle Miocene arc magmatism in the upper crust. The decreasing thickness of tilt blocks toward the south resulted from a shallowing brittle/ductile transition zone. Postmagmatic Middle Miocene extension and fault-block advection were focused in the northern and central WR and coincidentally moderated the large lateral thermal gradient within the uppermost crust.

  5. First fossil occurrence of a filefish (Tetraodontiformes; Monacanthidae) in Asia, from the Middle Miocene in Nagano Prefecture, central Japan.

    Science.gov (United States)

    Miyajima, Yusuke; Koike, Hakuichi; Matsuoka, Hiroshige

    2014-04-10

    A new fossil filefish, Aluterus shigensis sp. nov., with a close resemblance to the extant Aluterus scriptus (Osbeck), is described from the Middle Miocene Bessho Formation in Nagano Prefecture, central Japan. It is characterized by: 21 total vertebrae; very slender and long first dorsal spine with tiny anterior barbs; thin and lancet-shaped basal pterygiophore of the spiny dorsal fin, with its ventral margin separated from the skull; proximal tip of moderately slender first pterygiophore of the soft dorsal fin not reaching far ventrally; soft dorsal-fin base longer than anal-fin base; caudal peduncle having nearly equal depth and length; and tiny, fine scales with slender, straight spinules. The occurrence of this fossil filefish from the Bessho Formation is consistent with the influence of warm water currents suggested by other fossils, but it is inconsistent with the deep-water sedimentary environment of this Formation. This is the first fossil occurrence of a filefish in Asia; previously described fossil filefishes are known from the Pliocene and Pleistocene of Italy, the Pliocene of Greece, and the Miocene and Pliocene of North America. These fossil records suggest that the genus Aluterus had already been derived and was widely distributed during the Middle Miocene with taxa closely resembling Recent species.

  6. Variation in the pelvic and pectoral girdles of Australian Oligo–Miocene mekosuchine crocodiles with implications for locomotion and habitus

    Directory of Open Access Journals (Sweden)

    Michael D. Stein

    2017-06-01

    Full Text Available Australian Oligo–Miocene mekosuchines (Crocodylia; Crocodyloidea display wide diversity in cranial shape and inferred hunting strategies. Terrestrial habitus has been inferred for these distinctive predators. A direct morphological signal for locomotion can be expected in the postcrania, particularly the pelvic and pectoral girdles. Here we describe fossil materials of the girdles, which chart their morphological variation in the subfamily from Eocene through to Middle Miocene. Over this period, both girdles undergo significant morphological changes. Notably, an enclosed, ventrally orientated acetabulum in the ilium is developed in one lineage. This recapitulates the erect parasagittal configuration of the pelvic limb seen in many Mesozoic crocodylomorph lineages, suggesting consistent use of erect high-walking in these mekosuchines. Other pelves from the same Oligo–Miocene deposits display morphology closer to modern crocodilians, suggesting a partitioning of locomotory strategy among sympatric mekosuchines. Plesiomorphic and derived pelvic girdles are distinguishable by parsimony analysis, and the earliest examples of the mekosuchine pelvis more closely resemble gavialids and alligatorids while latter forms converge on crown group crocodylids in the morphology of the iliac crest. This suggests that a revaluation of the base relationship of Mekosuchinae within Eusuchia is necessary.

  7. Reciprocal sedimentation and noncorrelative hiatuses in marine-paralic siliciclastics: Miocene outcrop evidence

    Energy Technology Data Exchange (ETDEWEB)

    Kidwell, S.M.

    1988-07-01

    Deepening-upward paralic sequences present within a thicker record of shallowing-upward shelf and nonmarine sequences in Miocene siliciclastics of Maryland provide rare stratigraphic evidence for (1) coastal trapping of sediment during marine transgression, with simultaneous starvation on the open shelf (recorded by condensed skeletal lags), and (2) reciprocal switching of depositional and nondepositional conditions during regression. It follows that the regressive disconformities that define hemicyclic coastal sequences are not laterally continuous with the transgressive disconformities and condensed lags that define open-shelf hemicyclic sequences, although they are commonly depicted or assumed as such. Nor are these disconformities age correlative: marine-to-nonmarine correlations that assume lateral continuity of small-scale sequences (1 to 10 m thick; seismic parasequences) will err by as much as one-half cycle, restricting the applicability of models of punctuated aggradational cycles. The stratigraphic anatomy of parasequences is most comparable to reciprocal patterns inherent in hierarchically larger scale sequences in passive margins, where subaerial unconformities and submarine condensed intervals have recently been biostratigraphically verified as offset in age.

  8. Acoustic Impedance Inversion To Identify Oligo-Miocene Carbonate Facies As Reservoir At Kangean Offshore Area

    Science.gov (United States)

    Zuli Purnama, Arif; Ariyani Machmud, Pritta; Eka Nurcahya, Budi; Yusro, Miftahul; Gunawan, Agung; Rahmadi, Dicky

    2018-03-01

    Model based inversion was applied to inversion process of 2D seismic data in Kangean Offshore Area. Integration acoustic impedance from wells and seismic data was expected showing physical property, facies separation and reservoir quality of carbonate rock, particularly in Kangean Offshore Area. Quantitative and qualitative analysis has been conducted on the inversion results to characterize the carbonate reservoir part of Kujung and correlate it to depositional facies type. Main target exploration in Kangean Offshore Area is Kujung Formation (Oligo-Miocene Carbonate). The type of reservoir in this area generate from reef growing on the platform. Carbonate rock is a reservoir which has various type and scale of porosity. Facies determination is required to to predict reservoir quality, because each facies has its own porosity value. Acoustic impedance is used to identify and characterize Kujung carbonate facies, also could be used to predict the distribution of porosity. Low acoustic impedance correlated with packstone facies that has acoustic impedance value below 7400 gr/cc*m/s. In other situation, high acoustic impedance characterized by wackestone facies above 7400 gr/cc*m/s. The interpretation result indicated that Kujung carbonate rock dominated by packstone facies in the upper part of build-up and it has ideal porosity for hydrocarbon reservoir.

  9. Chemical evolution of Miocene wood: Example from the Belchatow brown coal deposit, central Poland

    Science.gov (United States)

    Drobniak, A.; Mastalerz, Maria

    2006-01-01

    Miocene conifer wood samples from the Belchatow brown coal deposit in Poland were studied in order to discuss a range of chemical variations that occur as a result of biochemical coalification. Petrographic analysis, ultimate analysis, electron microprobe technique, and FTIR spectroscopy were used in this study. Our data show several progressive trends in functional groups distribution that take place during the wood transformation from group 1 to group 4, such as an overall increase in aromaticity, an increase in lignin/cellulose ratio, and an increase in oxygen functionalities. Other observations include an increase in aliphatic stretching and bending functionalities from groups 1 to 3; followed by a decrease in the wood of group 4; appearance of aliphatic out-of-plane bands in group 3 and increase in group 4; an increase in CH2/CH3 in group 4 compared to the other groups; and decrease in O-H groups in group 4 compared to other groups. These observations, together with other chemical and petrological observations, indicate that the progressive elimination of cellulose and modification of lignin are dominant processes of the wood transformation. ?? 2005 Elsevier B.V. All rights reserved.

  10. STRONTIUM ISOTOPE STRATIGRAPHY AS A CONTRIBUTION FOR DATING MIOCENE SHELF CARBONATES (S. MARINO FM., NORTHERN APENNINES

    Directory of Open Access Journals (Sweden)

    CLAUDIO ARGENTINO

    2017-01-01

    Full Text Available This paper provides new data on strontium isotope stratigraphy applied to the Miocene heterozoan shelfal carbonates of the S. Marino Fm. (Marecchia Valley, northern Apennines. Sr isotopic analyses were carried out on oyster shells, bryozoans and bulk-rocks from the lower-middle carbonate portion of the section. In the upper part of the succession that shows evidence of detrital influx,87Sr/86Sr analyses were performed on foraminifera tests, separating planktonic and benthic forms. Results were compared with calcareous nannofossil biostratigraphic data from the same levels, in order to test the reliability of Sr dating in mixed carbonate-siliciclastic sediments. Mean ages obtained from oysters range between 16.9 Ma and 16.3 Ma. Very similar results are obtained using bryozoans (16.5 Ma to 16.1 Ma and bulk-rocks (16.8 Ma to 16.2 Ma. These results allow to better constrain the age of the massive carbonate shelf, referable to the upper Burdigalian. In the upper carbonate-siliciclastic portion of the shelf, numerical ages obtained from planktonic and benthic foraminifera are in good agreement with nannofossil biozones (mean ages respectively around 15.3 Ma and 14.5 Ma although they display wide confidence intervals. These wide age uncertainties depend on the slow rate of change of marine 87Sr/86Sr through time that characterizes the interval between ~15 and ~13.5 Ma.

  11. The Miocene "Pteropod event" in the SW part of the Central Paratethys (Medvednica Mt., northern Croatia)

    Science.gov (United States)

    Bošnjak, Marija; Sremac, Jasenka; Vrsaljko, Davor; Aščić, Šimun; Bosak, Luka

    2017-08-01

    Deep marine Miocene deposits exposed sporadically in the Medvednica Mt. (northern Croatia) comprise pelagic organisms such as coccolithophores, planktic foraminifera and pteropods. The pteropod fauna from yellow marls at the Vejalnica locality (central part of Medvednica Mt.) encompasses abundant specimens of Vaginella austriaca Kittl, 1886, accompanied with scarce Clio fallauxi (Kittl, 1886). Calcareous nannoplankton points to the presence of NN5 nannozone at this locality. Highly fossiliferous grey marls at the Marija Bistrica locality (north-eastern area of Medvednica Mt.) comprise limacinid pteropods: Limacina valvatina (Reuss, 1867), L. gramensis (Rasmussen, 1968) and Limacina sp. Late Badenian (NN5 to NN6 nannozone) age of these marls is presumed on the basis of coccolithophores. Most of the determined pteropods on species level, except V. austriaca have been found and described from this region for the first time. New pteropod records from Croatia point to two pteropod horizons coinciding with the Badenian marine transgressions in Central Paratethys. These pteropod assemblages confirm the existence of W-E marine connection ("Transtethyan Trench Corridor") during the Badenian NN5 nannozone. Limacinids point to the possible immigration of the "North Sea fauna" through a northern European marine passage during the Late Badenian (end of NN5-beginning of NN6 zone), as previously presumed by some other authors.

  12. 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.

  13. Subaqueous rhyolite block lavas in the Miocene Ushikiri Formation, Shimane Peninsula, SW Japan

    Science.gov (United States)

    Kano, Kazuhiko; Takeuchi, Keiji; Yamamoto, Takahiro; Hoshizumi, Hideo

    1991-06-01

    A rhyolite mass of the Miocene Ushikiri Formation in the western part of the Shimane Peninsula, SW Japan, is a small subaqueous edifice about 600 m high and 4 km wide, formed at water depths between 200 and 1000 m. It consists mainly of three relatively flat, lava-flow units 50-300 m in maximum thickness, each of which includes lobes and their polyhedral fragments. The lava lobes are poorly to well vesiculated, glassy to microcrystalline and flow-banded and -folded. Compared with mafic pillows, they are large, having thick, quenched and brecciated, glassy crusts because of their high viscosity, surface tension and thermal conductivity. Their surfaces disintegrate into polyhedral fragments and grade into massive volcanic breccia. The massive volcanic breccia composed of the lobe fragments is poorly sorted and covered with stratified volcanic breccia of the same rock type. The rhyolite lavas commonly bifurcate in a manner similar to mafic pillow lavas. However, they are highly silicic with 1-5 vol.% phenocrysts and have elongated vesicles and flow-folds, implying that they were visco-plastic during flowage. Their surface features are similar to those of subaerial block lava. With respect to rheological and morphological features, they are subaqueous equivalents of block lava.

  14. C4 Photosynthesis Promoted Species Diversification during the Miocene Grassland Expansion

    Science.gov (United States)

    Spriggs, Elizabeth L.; Christin, Pascal-Antoine; Edwards, Erika J.

    2014-01-01

    Identifying how organismal attributes and environmental change affect lineage diversification is essential to our understanding of biodiversity. With the largest phylogeny yet compiled for grasses, we present an example of a key physiological innovation that promoted high diversification rates. C4 photosynthesis, a complex suite of traits that improves photosynthetic efficiency under conditions of drought, high temperatures, and low atmospheric CO2, has evolved repeatedly in one lineage of grasses and was consistently associated with elevated diversification rates. In most cases there was a significant lag time between the origin of the pathway and subsequent radiations, suggesting that the ‘C4 effect’ is complex and derives from the interplay of the C4 syndrome with other factors. We also identified comparable radiations occurring during the same time period in C3 Pooid grasses, a diverse, cold-adapted grassland lineage that has never evolved C4 photosynthesis. The mid to late Miocene was an especially important period of both C3 and C4 grass diversification, coincident with the global development of extensive, open biomes in both warm and cool climates. As is likely true for most “key innovations”, the C4 effect is context dependent and only relevant within a particular organismal background and when particular ecological opportunities became available. PMID:24835188

  15. Late Miocene Pacific plate kinematic change explained with coupled global models of mantle and lithosphere dynamics

    Science.gov (United States)

    Stotz, I. L.; Iaffaldano, G.; Davies, D. R.

    2017-07-01

    The timing and magnitude of a Pacific plate motion change within the past 10 Ma remains enigmatic, due to the noise associated with finite-rotation data. Nonetheless, it has been hypothesized that this change was driven by the arrival of the Ontong Java Plateau (OJP) at the Melanesian arc 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, building on previous efforts to mitigate the impact of finite-rotation data noise. We find that the largest change in Pacific plate-motion direction occurred between 10 and 5 Ma, with the plate rotating clockwise. We subsequently develop and use coupled global numerical models of the mantle/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 drivers of this kinematic change.

  16. 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

    2015-04-07

    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. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  17. Paleoecology of benthic foraminifera from the Miocene of the San Jacinto Basin, Colombia

    Science.gov (United States)

    Poveda, John Sebastian; Fiorini, Flavia; Andres Trejos, Raul; Vallejo, Diego Felipe; Pardo, Andres

    2015-04-01

    Quantitative benthic foraminifera analysis was conducted on 34 samples collected from a borehole core (393.72m deep) drilled by Colombian Hydrocarbon Agency (ANH) on 2009 in the San Jacinto basin (Northern Colombia). The aims of the research were to define a taxonomical data-bank of Miocene benthic foraminifera for this region, to use the benthic foraminifera assemblages to interpret the paleoenvironment and to identify paleoenvironmental changes. The bottom of the section was dated between lowest Burdigalian to middle Langhian (20.393-17.721 Ma) based on calcareous nannofossils bioevents: LO Helicosphaera ampliaperta, HCO Sphenolithus belemnos and LCO Sphenolithus heteromorphus. The benthic foraminifera fauna identified in the studied samples is composed for the majority of calcareous hyaline tests and is dominated by infaunal taxas. Species belonging to the genera Uvigerina and Lenticulina are commonly occurring in the studied section together with other species typical of outer-shelf upper-bathyal environment. Cibicidoides spp., abundant in the lower part of the section, abruptly decreases in abundance in the upper part. Species belonging to the opportunistic genera Bulimina and Bolivina are more abundant in the upper part of the section. Variability in the abundance of opportunistic species can be associated with tectonic disturbance on the Sinu-San Jacinto fold belt (NW of Colombia) as a result of collision of the Caribbean plate against NW of South America. The tectonics could lead a perturbation on deep ocean sedimentation and circulation.

  18. From Late Miocene to Holocene: processes of differentiation within the Telestes genus (Actinopterygii: Cyprinidae.

    Directory of Open Access Journals (Sweden)

    Vincent Dubut

    Full Text Available Investigating processes and timing of differentiation of organisms is critical in the understanding of the evolutionary mechanisms involved in microevolution, speciation, and macroevolution that generated the extant biodiversity. From this perspective, the Telestes genus is of special interest: the Telestes species have a wide distribution range across Europe (from the Danubian district to Mediterranean districts and have not been prone to translocation. Molecular data (mtDNA: 1,232 bp including the entire Cyt b gene; nuclear genome: 11 microsatellites were gathered from 34 populations of the Telestes genus, almost encompassing the entire geographic range. Using several phylogenetic and molecular dating methods interpreted in conjunction with paleoclimatic and geomorphologic evidence, we investigated the processes and timing of differentiation of the Telestes lineages. The observed genetic structure and diversity were largely congruent between mtDNA and microsatellites. The Messinian Salinity Crisis (Late Miocene seems to have played a major role in the speciation processes of the genus. Focusing on T. souffia, a species occurring in the Danube and Rhone drainages, we were able to point out several specific events from the Pleistocene to the Holocene that have likely driven the differentiation and the historical demography of this taxon. This study provides support for an evolutionary history of dispersal and vicariance with unprecedented resolution for any freshwater fish in this region.

  19. Oligocene-Miocene burial and exhumation of the southernmost Gangdese mountains from sedimentary and thermochronological evidence

    Science.gov (United States)

    Ge, Yukui; Li, Yalin; Wang, Xiaonan; Qian, Xinyu; Zhang, Jiawei; Zhou, Aorigele; Liu-Zeng, Jing

    2018-01-01

    The Kailas conglomerates crop out ubiquitously along the southernmost boundary of the Gangdese batholith. They unconformably overlie the Gangdese batholith and are displaced by the Great Counter thrust (GCT) fault, forming a fault contact with the Xigaze forearc basin, the associated subduction complex and the Tethyan Himalayan sequence. These strata furnish a record of uplift and paleoenvironmental change in the Indus-Yarlung suture zone during the Oligocene-Miocene. Our new and previously published low-temperature thermochronometric data from the Gangdese batholith and the Kailas conglomerates indicate a period of rapid exhumation beginning approximately 17-15 Ma centered on the southern margin of the Gangdese batholith, whereas regional uplift commenced significantly earlier during the deposition of the Kailas conglomerates, based on the presence of an abrupt facies transition from deep-water lacustrine deposits to red alluvial fan or fluvial deposits. The period of rapid exhumation probably lagged behind the initiation of faster uplift, while the related changes in the depositional environment were most likely recorded immediately in the basin stratigraphy. Subsequently, the Kailas conglomerates were buried in association with the development of the north-directed Great Counter thrust, while rapid exhumation was facilitated by efficient incision by the paleo-Yarlung river at approximately 17-15 Ma.

  20. The Miocene Roof Mapping Using Microtremor Recording and Electrical Survey Method in Blida City, Algeria

    Science.gov (United States)

    Bouchelouh, Assia; Bensalem, Rabah; Zaourar, Naima; Machane, Djamel; Moulouel, Hakim; Oubaiche, El Hadi

    2018-01-01

    Bedrock depths in the Mitidja basin in general and in the Blida region in particular are still poorly known despite, the existence of some relatively deep hydraulic boreholes that intersect only superficial alluvial formations. To assess the seismic risk of Blida town, knowledge of soil amplification requires the thickness and properties of sedimentary formations that cover the substratum. For the purposes of our study, the thicknesses obtained by the vertical electric soundings, carried out in the hydrogeological study of the basin, were combined with horizontal-to-vertical spectral ratio (HVSR) microtremor recordings. This combination made it possible to determine an empirical relationship between frequency and thickness specific to the Blida site area, which enabled the roof of the Miocene to be mapped and shows slight undulations with directions compatible with the tectonic constraints of the region. The boundaries between the low and high frequencies obtained by HVSR are well materialized, at south by Sidi El Kebir river, at west by Chiffa river and in the central part by a line of direction SE-NW corresponding to the old passage of Sidi El Kebir river. The presence of low frequencies attributed to the old alluvial deposits with significant thicknesses that originate just after Sidi El Kebir river confirms that the South Mitidjian contact is subvertical.

  1. 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

  2. Frontier seismic geologic techniques and the exploration of the Miocene reefs in offshore Palawan, Philippines

    Science.gov (United States)

    Biswas, Buddhadeb

    An 88 km grid of Seislog sections (synthetic sonic log traces) was used to supplement the conventional seismic interpretation to assess the hydrocarbon potential of Lower Miocene reefs of offshore Palawan, Philippines. The porosity distribution in the zone of interest as well as the oil-water contact in and around the Tara and Libro patch reefs were mapped. The structural mapping was also fine tuned, including mapping of faults with small displacements. The paradox of pooling of hydrocarbons is evident in the maximum fill in the front line of traps near the shelf-slope break that are in the lowest structural position. Progressively dwindling amounts of fill in the structurally higher updip basin positions are interpreted to be due to the migration of hydrocarbons from the hydrocarbon kitchen in the Palawan Trough. The front line of traps had the benefit of maximum fill, the traps at the rear only of residual fill that spilled past the frontal traps. Three play types corresponding to the front line of traps, the rear line of traps and the most remote line of traps have been identified. Frontal reefs are considered to have the highest hydrocarbon potential. Diminishing hydrocarbon potential is inferred for closures in the updip direction. A thorough screening of all available seismic control for mapping all the patch reefs that might compensate for their dimensions by their numbers as well as for detecting possible pinnacle reefs in the downdip basin position has been suggested.

  3. 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

  4. Herds overhead: Nimbadon lavarackorum (Diprotodontidae, heavyweight marsupial herbivores in the Miocene forests of Australia.

    Directory of Open Access Journals (Sweden)

    Karen H Black

    Full Text Available 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.

  5. SILICEOUS SPONGE SPICULES FROM THE MIOCENE MEM MONIZ MARLS (PORTUGAL AND THEIR ENVIRONMENTAL SIGNIFICANCE

    Directory of Open Access Journals (Sweden)

    ANDRZEJ PISERA

    2006-07-01

    Full Text Available The Miocene (middle Serravalian Mem Moniz marls from Algarve (Portugal contain a rich and well preserved assemblage of siliceous sponge spicules, which is described here for the first time. The assemblage indicates that the sponge fauna was dominated by Astrophorida, and in particular by Geodiidae. The presence of Eurylus sp. and probably Geodia sp. (both Astrophorida, Samus sp. (Spirophorida and Alectona wallichii (Hadromerida is also reported. Samus sp. and Alectona wallichii are reported from the fossil record for the first time. Additionally, the occurrence of lithistid demosponges (represented by Theonellidae and rhizomorinids, Hadromerida, Spirophorida and Hexactinellida is also shown. Ancorinidae, Pachastrellidae (and/or Cathropellidae, both Astrophorida, were also clearly recognized. Less certain is the occurrence, in the Mem Moniz marls, of Tethyidae (Hadromerida. Bathymetric reconstructions based on sponges are imprecise due to the fact that these organisms often have very wide bathymetric ranges. However, the studied sponge assemblage is clearly neither characteristic of very shallow nor very deep marine environments. The dominance of astrophorids and the presence of lithistids and hexactinellids suggest a depth of at least several tens to one hundred metres, or even more.

  6. How We Got to the Northern Hemisphere Ice Ages: Late Miocene Global Cooling and Plate Tectonic CO2 Forcing

    Science.gov (United States)

    Herbert, T.; Dalton, C. A.; Carchedi, C.

    2017-12-01

    The evolution of Earth's climate between "refrigeration" of East Antarctica and the onset of cyclic Northern Hemisphere glaciation spanned more than 11 Myr. In the latest Miocene (Messinian) time, approximately half way on this journey, changes on land, ranging from the expansion of arid zones to major floral and faunal ecosystem shifts, accelerated. Recent compilations of marine surface temperatures reveal that global cooling from the Miocene Optimum (14-16Ma) also accelerated in late Miocene (7-5.35 Ma) time to reach temperatures not much above Holocene conditions. Both hemispheres cooled in parallel, with the changes amplified at higher latitudes in comparison to the tropics. Despite the strong circumstantial case for CO2 decline as the dominant cause of late Miocene climatic and evolutionary change, proxy indicators of CO2concentrations paint an equivocal picture of greenhouse forcing. Here we provide evidence that global sea floor spreading (SFS) rates decelerated at exactly the times of major climatic cooling, linking a decline in tectonic degassing (at both subduction zones and mid-ocean ridges) to fundamental shifts in the global carbon cycle. Our work utilizes newly available global compilations of seafloor fabric and marine magnetic anomalies provided by the NSF-funded Global Seafloor Fabric and Magnetic Lineation Data Base Project. Previous global compilations of SFS typically binned estimates over 10 Myr increments, losing critical resolution on the timescale of late Neogene climate changes. We further improve the signal:noise of SFS estimates by incorporating recent advances in the astronomical calibration of the Miocene geomagnetic polarity timescale. We use two approaches to compile spreading rate estimates over the past 20 Myr at each spreading system: optimized finite rotation calculations, and averages of sea floor-spreading derived from the distances of magnetic lineations along flow lines on the sea floor. Weighted by ridge length, we find an 25

  7. Miocene tectonic history of the Central Tauride intramontane basins, and the paleogeographic evolution of the Central Anatolian Plateau

    Science.gov (United States)

    Koç, Ayten; Kaymakci, Nuretdin; Van Hinsbergen, Douwe J. J.; Kuiper, Klaudia F.

    2017-11-01

    Marine Lower-Upper Miocene deposits uplifted to > 2 km elevation in the Tauride mountains of southern Turkey are taken as evidence for the rise of a nascent plateau. The dynamic causes of this uplift are debated, but generally thought to be a regional dynamic topographic effect of slab motions or slab break-off. Immediately adjacent to the high Tauride mountains lie the Central Tauride Intramontane Basins, which consist of Miocene and younger fluvio-lacustrine basins, at much lower elevations than the highly uplifted marine Miocene rocks. These basins include the previously analyzed Altınapa and Yalvaç basins, as well as the until now undescribed Ilgın Basin. In this paper, we aim to constrain the paleogeography of the Central Tauride Intramontane Basins and determine the role of the tectonics driving the formation of the high Miocene topography in southern Turkey. Therefore, we provide new data on the stratigraphy, sedimentology and structure of the continental Ilgın Basin. We provide an 40Ar/39Ar age of 11.61 ± 0.05 Ma for pumice deposits in the stratigraphy. We provide paleostress inversion analysis based on growth faults showing that the basin formed during multi-directional extension, with NE-SW to E-W dominating over subordinate Nsbnd S extension. We conclude that major, still-active normal faults like the Akşehir Fault also controlled Miocene Ilgın basin formation, with proximal facies close to the basin margins grading upwards and basinwards into lacustrine deposits representing the local depocenter. The Ilgın Basin was a local depocenter, but it may have connected with the adjacent Altınapa Basin during high lake levels in late Serravallian time. The Ilgın Basin and the other continental basins provide key constraints on the paleogeography and tectonic history of the region. These continental basins were likely close to the paleo-coastline during the Late Miocene after which there must have been major differential uplift of the Taurides. We

  8. Stable isotope stratigraphy of Latest Miocene sequences in northwest Morocco: The Bou Regreg section

    Science.gov (United States)

    Hodell, David A.; Benson, Richard H.; Kennett, James P.; Rakic-El Bied, Kruna

    1989-08-01

    Oxygen and carbon isotopic ratios of foraminifers were measured from outcrop and drill core sequences from the Bou Regreg Section, northwest Morocco. This composite section was located at the western end of the Rifian Corridor during the late Miocene and thus potentially contains a record of water exchange between the Atlantic and Mediterranean during the late Tortonian and Messinian stages. Here we correlate isotopic and sedimentologic events in the Bou Regreg Section with Mediterranean and deep-sea sequences during the time leading up to and including the deposition of the Messinian evaporites. The late Miocene chron 6 carbon shift was identified in two Moroccan sequences, providing a valuable 6.3-Ma datum level. In both sections, the carbon shift coincides with the first occurrence of Globorotalia conomiozea and the Tortonian/Messinian boundary. Near this boundary, a major faunal turnover occurred in ostracod, planktonic foraminiferal, and nannofossil assemblages that indicates a cooling of surface and deep water in the Rifian Corridor. At 6.1 Ma, just above the Tortonian/Messinian boundary, mean ∂18O values of benthic foraminifers increased by 0.4-0.5‰ suggesting decreased temperature and/or increased continental ice volume. The faunal and isotopic changes are interpreted as reflecting a reversal in the direction of deep water flow through the Rifian Corridor that occurred between 6.3 and 6.1 Ma. At this time, cold, nutrient-rich waters filled the Mediterranean basins from intermediate depths of the Atlantic, and the production of Mediterranean Outflow Water ceased. The upwelling of nutrient-rich Atlantic intermediate water stimulated productivity in the Mediterranean, which led to the deposition of organic-rich strata such as those found in the Tripoli Formation. At ˜5.5 Ma, coincident with a coiling shift in Neogloboquadrina acostaensis, the variability of the benthic ∂18O signal increased markedly, and strong color variations appeared in the sediments

  9. A possible cause of the Miocene uplift and volcanism in the central Anatolian plateau

    Science.gov (United States)

    Bartol, J.; Govers, R. M.; Wortel, M. J.

    2010-12-01

    During the middle and late Miocene (13-5Ma) several seemingly unrelated events occurred in central Anatolia, Turkey; (1) a new epoch of widespread volcanic activity with a mantle signature, (2) sudden uplift and disruption of a Oligocene-lower Miocene palaeo drainage system in the Western Taurus (southwest Turkey) and (3) a regional regression across southern Turkey (Antalya, Adana, Mut) coeval with volcanic activity. These observations suggest an uplift (>1000 meters) of the central Anatolian plateau by a mechanism which also triggered widespread volcanic activity. In eastern Anatolia, similar events are attributed to delamination of the lithospheric mantle [e.g. Keskin et al., 2003]. Results from tomography [W.Spakman, pers. com]) suggest that the (deeper) Bitlis slab was laterally continuous below the eastern and central Anatolian plateau. We therefore propose that the scenario developed for eastern Anatolian plateau also applies to the central Anatolian plateau. In this scenario, delamination started along the Izmir-Ankara-Erzincan suture zone and was possibly induced by remnants of a northern Neotethys slab or continental collision between Arabia and Eurasia. As the lithospheric mantle separated from the crust it sank into the asthenosphere and was replaced by hot mantle material. If true, delamination is expected to have had a thermal and isostatic imprint. Using a three-dimensional thermal-flexural model and taking changes of the effective elastic thickness due to thermal perturbation into account, we aim to quantify the possible imprints in the geological record of the central and eastern Anatolian plateau. Our model results show that delamination of the lithospheric mantle can explain the present day elevation (1500 m) of the central Anatolian plateau. For the eastern Anatolian plateau, however, delamination of the lithospheric mantle alone can only explain half (1000 m) of the present day elevation. Thickening of the eastern Anatolia crust by 1-5 km (β=1

  10. Combined tide and storm influence on facies sedimentation of miocene Miri Formation, Sarawak

    International Nuclear Information System (INIS)

    Yuniarta Ulfa; Nasiman Sapari; Zuhar Zahir Tuan Harith

    2011-01-01

    This study was conducted on the sedimentary rocks belonging to the Miri Formation (Middle - Late Miocene). The primary objective of the present study is to provide additional interpretation on the stratigraphy of the Miri Formation in the Miri Field based on the new information gathered from new outcrops in the area. Five outcrops were examined in detail on sedimentology and stratigraphy. Based on lithology, sedimentary structures, bedding geometry and traces fossil, the sediments of the Miri Formation were grouped into fourteen lithofacies. Influence of tide and storm during the depositional processes of the formation were indicated by the group of two main facies associations which are: (i) tide-dominated estuary; and (ii) wave-and-storm dominated facies associations. The tide-dominated estuary system of the Miri Formation are includes variety of sub environments: estuary mouth or tidal channel and sand bars (characterized by trough cross-stratified sandstone with mud drapes facies), estuary channel or upper flow regime of sand flat (characterized by parallel stratified sandstone with mud-laminas facies), mixed-tidal flat (characterized by wavy and flaser bedded sandstone facies), and mud-tidal flat (characterized by rhythmic stratified sandstone-mudstone and lenticular bedding facies). The wave-and-storm dominated varied from lower to middle shore face (characterized by hummocky cross-stratified sandstone and rhythmic parallel stratified sandstone and laminated siltstone facies), upper shore face (characterized by swaley cross-stratified sandstone), lower shore face inter bedded to bioturbated sandstone and siltstone facies), and offshore transitional (characterized by bioturbated sandstone and mudstone inter bedding with parallel to hummocky cross-stratified sandstone facies). (author)

  11. Stratigraphic condensation of marine transgressive records: Origin of major shell deposits in the Miocene of Maryland

    Energy Technology Data Exchange (ETDEWEB)

    Kidwell, S.M. (Univ. of Chicago, IL (USA))

    1989-01-01

    Cyclic stratigraphic sequences in shallow marine records are commonly charaterized by a condensed transgressive lag at the base of thicker, shallowing-upward facies. The standard actualistic model for these thin fossiliferous lags, by which most of the shelf is starved owing to coastal trapping of sediment and fossils are suspected of being reworked because of the association with an erosional ravinement, is contradicted by detailed stratigraphic and taphonomic analysis of Miocene examples in the Maryland coastal plain. The complex internal stratigraphies of the shell deposits and the mixture of soft- and shell-bottom faunas indicate condensation under a regime of dynamic bypassing rather than complete sediment starvation; bypassed fine sediments accumulated in deeper water environments below storm wavebase. Deeper, even more basinward parts of the shelf were starved of all sediment size fractions and accumulated shell-poor, bone-rich condensed deposits that lie mid-cycle (bracketing the time of maximum water depth). The base-of-cycle shell deposits and mid-cycle bone bed differ not only in composition and in environment and dynamics of condensation, but also in chronostratigraphic value: the onlapping shell deposits must be diachronous to some degree, whereas the mid-cycle bone bed approximates an isochronous marker for correlation. Thus, in some settings at least, transgressive shelves present a spatial mosaic of condensational and depositional regimes. Regardless of origin, all condensed intervals can time-average assemblages and telescope biostratigraphic datums. They otherwise differ widely, however, in paleontologic attributes and are characterized by highly variable and complex stratigraphic anatomies.

  12. A new species of great ape from the late Miocene epoch in Ethiopia.

    Science.gov (United States)

    Suwa, Gen; Kono, Reiko T; Katoh, Shigehiro; Asfaw, Berhane; Beyene, Yonas

    2007-08-23

    With the discovery of Ardipithecus, Orrorin and Sahelanthropus, our knowledge of hominid evolution before the emergence of Pliocene species of Australopithecus has significantly increased, extending the hominid fossil record back to at least 6 million years (Myr) ago. However, because of the dearth of fossil hominoid remains in sub-Saharan Africa spanning the period 12-7 Myr ago, nothing is known of the actual timing and mode of divergence of the African ape and hominid lineages. Most genomic-based studies suggest a late divergence date-5-6 Myr ago and 6-8 Myr ago for the human-chimp and human-gorilla splits, respectively-and some palaeontological and molecular analyses hypothesize a Eurasian origin of the African ape and hominid clade. We report here the discovery and recognition of a new species of great ape, Chororapithecus abyssinicus, from the 10-10.5-Myr-old deposits of the Chorora Formation at the southern margin of the Afar rift. To the best of our knowledge, these are the first fossils of a large-bodied Miocene ape from the African continent north of Kenya. They exhibit a gorilla-sized dentition that combines distinct shearing crests with thick enamel on its 'functional' side cusps. Visualization of the enamel-dentine junction by micro-computed tomography reveals shearing crest features that partly resemble the modern gorilla condition. These features represent genetically based structural modifications probably associated with an initial adaptation to a comparatively fibrous diet. The relatively flat cuspal enamel-dentine junction and thick enamel, however, suggest a concurrent adaptation to hard and/or abrasive food items. The combined evidence suggests that Chororapithecus may be a basal member of the gorilla clade, and that the latter exhibited some amount of adaptive and phyletic diversity at around 10-11 Myr ago.

  13. Investigating Miocene Mediterranean-Atlantic Gateway Exchange (IMMAGE) - an amphibious drilling proposal

    Science.gov (United States)

    Flecker, Rachel

    2017-04-01

    Today Mediterranean seawater flows out through the Gibraltar Straits, forming a saline plume at intermediate depths in the Atlantic. The plume's sedimentary record of distinctive, contouritic deposits has recently been recovered during IODP Leg 339 in the Gulf of Cadiz documenting a Mediterranean contribution to Atlantic thermohaline circulation since the Pliocene. However, before the Pliocene, the conduit for Mediterranean-Atlantic exchange is unclear. Gibraltar may have already been open, but two additional marine corridors also existed through northern Morocco and southern Spain. The restriction and closure of these Miocene connections resulted in extreme salinity fluctuations in the Mediterranean, leading to the precipitation of thick evaporites. This event is known as the Messinian Salinity Crisis (MSC) and recovering a complete record of the MSC is the target of current IODP drilling proposals (e.g. DREAM). Understanding both the causes of high-amplitude salinity change in the Mediterranean and its global consequences for thermohaline circulation in the Atlantic is dependent on recovering a complete record of Mediterranean-Atlantic exchange before, during and after the MSC. This key objective of the IMMAGE drilling proposal requires core recovery on-shore at the mouths of the Betic and Rifian corridors which are now exposed on land, as well as offshore, in the Alborán Sea and on the Atlantic continental margin. Consequently to meet this objective, an amphibious drilling strategy is necessary, involving both IODP and ICDP targets. In addition to allowing us to reconstruct Mediterranean-Atlantic exchange during high amplitude salinity fluctuations and identify the conduit through which exchange occurred, the sediments recovered from IMMAGE drilling will also provide us with a unique and explicit test for ocean physics hypotheses describing the location, size and velocity of overflow plumes under conditions where the density contrast between the two water

  14. The Oligocene-Miocene stratigraphic evolution of the Majella carbonate platform (Central Apennines, Italy)

    Science.gov (United States)

    Brandano, Marco; Cornacchia, Irene; Raffi, Isabella; Tomassetti, Laura

    2016-03-01

    The stratigraphic architecture of the Bolognano Formation documents the evolution of the Majella carbonate platform in response to global and local changes that affected the Mediterranean area during the Oligocene-Miocene interval. The Bolognano Formation consists of a homoclinal ramp that developed in a warm, subtropical environment. Five different lithofacies associations have been identified: Lepidocyclina calcarenites, cherty marly limestones, bryozon calcarenites, hemipelagic marls and marly limestones, and Lithothamnion limestones. Each association corresponds to a single lithostratigraphic unit except for the Lepidocyclina calcarenites that form two distinct lithostratigraphic units (Lepidocyclina calcarenites 1 and 2). These six units reflect alternation of shallow-water carbonate production and drowning. Specifically, two of the three stages of shallow-water carbonate production regard the development of wide dune fields within the middle ramp, one stage dominated by red algae and a sea-grass carbonate factory, whereas the two drowning phases are represented by marly cherty limestones and calcareous marls. A new biostratigraphic framework for Bolognano Formation is presented, based on high-resolution analysis of calcareous nannofossil assemblages, which proved to be very useful for biostratigraphic constraints also in shallow-water settings. Using this approach, we have linked the first drowning phase, late Chattian-Aquitanian p.p. in age, to western Mediterranean volcanism and the Mi-1 event, and the second drowning phase, late Burdigalian-Serravallian in age, to the closure of the Indo-Pacific passage and the occurrence of the global Monterey event. These results permit a new deciphering, in terms of sequence stratigraphy, of the Bolognano Formation that is interpreted as a 2nd-order super-sequence that can be subdivided into 3 transgressive-regressive sequences.

  15. FIRST RECORD OF FOSSIL CYSTOPHORINAE (CARNIVORA, PHOCIDAE: MIDDLE MIOCENE SEALS FROM THE NORTHERN PARATETHYS

    Directory of Open Access Journals (Sweden)

    IRINA A. KORETSKY

    2013-11-01

    Full Text Available Despite a long history of phocid studies, no fossil members of the Subfamily Cystophorinae have ever been described. New fossil material from the Middle Sarmatian (11.2-12.3 Ma in the Paratethyan Basin of Ukraine allows emended diagnoses and redescriptions to help clarify phylogenetic relationships within the Family Phocidae. After cladistic and morphological analyses of the material, a new genus ( Pachyphoca  was erected, with two new species of extinct fossil true seals ( Pachyphoca ukrainica and Pachyphoca chapskii , belonging to the Subfamily Cystophorinae. This new material shows exceptional pachyosteosclerotic bones, which is uncommon for the family as a whole. The new Miocene genus shares numerous characters with several Recent species of Cystophora and Mirounga , providing the first opportunity to study sexual dimorphism of limb bones and mandibles in the Subfamily Cystophorinae. Sexual dimorphism in postcranial bones and mandibles in living members of Cystophorinae is more obvious than in other representatives of true seals. Examination of anatomical traits demonstrated that both new species are more primitive and better adapted for terrestrial locomotion than any living representatives of Cystophorinae. The smaller Pachyphoca ukrainica is more adapted to terrestrial locomotion than its larger relative, P . chapskii . Phylogenetic analysis suggests that seals with 10 incisors (Phocinae are more primitive than those with 8 (Monachinae, and that Monachinae are more primitive than seals with 6 incisors (Cystophorinae.These findings indicate that the Subfamily Cystophorinae includes not only elephant and hooded seals, but also the two new Middle Sarmatian pachyosteosclerotic seals. 

  16. Origin of an Assemblage Massively Dominated by Carnivorans from the Miocene of Spain

    Science.gov (United States)

    Domingo, M. Soledad; Alberdi, M. Teresa; Azanza, Beatriz; Silva, Pablo G.; Morales, Jorge

    2013-01-01

    Carnivoran-dominated fossil sites provide precious insights into the diversity and ecology of species rarely recovered in the fossil record. The lower level assemblage of Batallones-1 fossil site (Late Miocene; Madrid Basin, Spain) has yielded one of the most abundant and diversified carnivoran assemblage ever known from the Cenozoic record of mammals. A comprehensive taphonomic study is carried out here in order to constrain the concentration mode of this remarkable assemblage. Another distinctive feature of Batallones-1 is that the accumulation of carnivoran remains took place in the context of a geomorphological landform (cavity formation through a piping process) practically unknown in the generation of fossil sites. Two characteristics of the assemblage highly restrict the probable causes for the accumulation of the remains: (1) the overwhelming number of carnivorans individuals; and (2) the mortality profiles estimated for the four most abundant taxa do not correspond to the classic mortality types but rather were the consequence of the behavior of the taxa. This evidence together with other taphonomic data supports the hypothesis that carnivoran individuals actively entered the cavity searching for resources (food or water) and were unable to exit. The scarcity of herbivores implies that the shaft was well visible and avoided by these taxa. Fossil bones exhibit a very good preservation state as a consequence of their deposition in the restricted and protective environment of the chamber. Batallones-1 had another assemblage (upper level assemblage) that was dominated by herbivore remains and that potentially corresponded to the final stages of the cavity filling. PMID:23650542

  17. Stratigraphy, age and environments of the late Miocene Mpesida Beds, Tugen Hills, Kenya.

    Science.gov (United States)

    Kingston, John D; Fine Jacobs, Bonnie; Hill, Andrew; Deino, Alan

    2002-01-01

    Interpretations of faunal assemblages from the late Miocene Mpesida Beds in the Tugen Hills of the Central Kenyan Rift Valley have figured prominently in discussions of faunal turnover and establishment of the modern East African communities. These faunal changes have important implications for the divergence of the human lineage from the African apes ca. 8-5 Ma. While fossil material recovered from the Mpesida Beds has traditionally been analyzed collectively, accumulating evidence indicates that Mpesida facies span the 7-6 Ma interval and are scattered more than 25 km along the eastern flanks of the Tugen Hills. Stratigraphic distinctions between Mpesida facies and younger sediments in the sequence, such as the Lukeino Formation, are not yet fully resolved, further complicating temporal assessments and stratigraphic context of Mpesida facies. These issues are discussed with specific reference to exposures of Mpesida facies at Rurmoch, where large fossil tree fragments were swept up in an ancient ash flow. Preserved anatomical features of the fossil wood as well as estimated tree heights suggest a wet, lowland rainforest in this portion of the rift valley. Stable isotopic analyses of fossil enamel and paleosol components indicate the presence of more open habitats locally. Overlying air-fall tuffs and epiclastic debris, possibly associated with the ash flow, have yielded an assemblage of vertebrate fossils including two teeth belonging to one of the earliest colombines of typical body size known from Africa, after the rather small Microcolobus. Single-crystal, laser-fusion,(40)Ar/(39)Ar dates from a capping trachyte flow as well as tuffs just below the lava contact indicate an age of greater than 6.37 Ma for the fossil material. Copyright 2002 Academic Press.

  18. Middle Miocene paleoenvironmental crises in Central Eurasia caused by changes in marine gateway configuration

    Science.gov (United States)

    Palcu, D. V.; Golovina, L. A.; Vernyhorova, Y. V.; Popov, S. V.; Krijgsman, W.

    2017-11-01

    Marine gateways prove to be important factors for changes in the ecology and biochemistry of marginal seas. Changes in gateway configuration played a dominant role in the Middle Miocene paleogeographic evolution of the Paratethys Sea that covered Central Eurasia. Here, we focus on the connection between the Central (CP) and Eastern Paratethys (EP) to understand the paleoenvironmental changes caused by the evolution of this marine gateway. We first construct an integrated magneto-biostratigraphic framework for the late Langhian-Serravallian (Chokrakian-Karaganian-Konkian-Volhynian) sedimentary record of the eastern domain, which allows a correlation to the well-dated successions west of the gateway. The magneto-biostratigraphic results from the Zelensky-Panagia section on the Black Sea coast of Russia show that the Chokrakian/Karaganian boundary has an age of 13.8 Ma, the Karaganian/Konkian boundary is dated at 13.4 Ma, and the Konkian/Volhynian boundary at 12.65 Ma. We identify three major phases on gateway functioning that are reflected in specific environmental changes. During the Karaganian, the EP turned into a lake-sea that supplied a unidirectional flow of low-salinity waters to the west, where the CP sea experienced its Badenian Salinity Crisis. This configuration is remarkably similar to the Mediterranean during its Messinian Salinity Crisis. The second phase is marked by a marine transgression from the west, reinstalling open-marine conditions in the CP and causing marine incursions in the EP during the Konkian. The Volhynian is characterized by a new gateway configuration that allows exchange between CP and EP, creating unified conditions all over the Paratethys. We hypothesize that a density driven pumping mechanism is triggered by the increase in connectivity at the Konkian/Volhynian boundary, which simultaneously caused major paleoenvironmental changes at both sides of the gateway and led to the Badenian-Sarmatian extinction event in the CP.

  19. Electron microscopy and microanalysis of uranium phases in primary ores, Eocene and Miocene of south Texas

    International Nuclear Information System (INIS)

    Liang, L.C.; Price, J.G.; Bobeck, P.

    1984-01-01

    Two contrasting types of roll-front uranium deposits occur in south Texas. In the barrier-bar sands of the Eocene Jackson Group, organic matter was essential to uranium reduction, whereas in the fluvial sands of the Miocene Oakville Formation, epigenetic pyrite was the reductant. In a sample of reduced Oakville ore, a uranium phase with grains ranging in diameter from < 1 to 20μm was recognized by SEM backscattered-electron imaging and wavelength-dispersive spectrometer (WDS) elemental-dot mapping. Quantitative microprobe analyses indicated that the phase is a uranium-calcium silicate-phosphate with molar Ca/P approximately equal to 1.0, U/P equal to 2.8 +/- 0.4 (n = 27), and U/Si approaching 1.0 in samples uncontaminated with quartz, feldspar, or clay minerals. Highest uranium content is 59%. Oakville ore is typically easy to leach by in-situ methods. Jackson ore contains 2 uranium phases. Sulfur-rich organic matter contains 4.1 +/- 1.6% uranium (n = 27). Although individual grains of a possible uranium mineral within the organic matter are too small to be resolved by electron imaging, a consistent molar U/Fe (0.5 +/- 0.1) suggests a uranium-iron oxide phase. Alternatively, uranium is adsorbed by or otherwise bound to the organic matter. The second phase is a uranium-calcium silicate-phosphate that differs from the Oakville ore. Molar Ca/P equals 0.8 +/- 0.2 (n = 13), and U/P equals 4.7 +/- 0.4. Small grain size (generally less than 1 μm) prevented analysis of samples uncontaminated with quartz and pyrite. The grain with highest uranium content (43%) has U/Si equal to 0.34. Jackson ore is less favorable for in-situ leaching than Oakville ore in part because the organic-associated uranium is difficult to extract

  20. Shallow Miocene basaltic magma reservoirs in the Bahia de Los Angeles basin, Baja California, Mexico

    Science.gov (United States)

    Delgado-Argote, Luis A.; García-Abdeslem, Juan

    1999-01-01

    The basement in the Bahía de Los Angeles basin consists of Paleozoic metamorphic rocks and Cretaceous granitoids. The Neogene stratigraphy overlying the basement is formed, from the base to the top, by andesitic lava flows and plugs, sandstone and conglomeratic horizons, and Miocene pyroclastic flow units and basaltic flows. Basaltic dikes also intrude the whole section. To further define its structure, a detailed gravimetric survey was conducted across the basin about 1 km north of the Sierra Las Flores. In spite of the rough and lineal topography along the foothills of the Sierra La Libertad, we found no evidence for large-scale faulting. Gravity data indicates that the basin has a maximum depth of 120 m in the Valle Las Tinajas and averages 75 m along the gravimetric profile. High density bodies below the northern part of the Sierra Las Flores and Valle Las Tinajas are interpreted to be part of basaltic dikes. The intrusive body located north of the Sierra Las Flores is 2.5 km wide and its top is about 500 m deep. The lava flows of the top of the Sierra Las Flores, together with the distribution of basaltic activity north of this sierra, suggests that this intrusive body continues for 20 km along a NNW-trending strike. Between the sierras Las Flores and Las Animas, a 0.5-km-wide, 300-m-thick intrusive body is interpreted at a depth of about 100 m. This dike could be part of the basaltic activity of the Cerro Las Tinajas and the small mounds along the foothills of western Sierra Las Animas. The observed local normal faulting in the basin is inferred to be mostly associated with the emplacement of the shallow magma reservoirs below Las Flores and Las Tinajas.

  1. Petrographic characteristics and depositional environment of Miocene Can coals, Canakkale-Turkey

    Energy Technology Data Exchange (ETDEWEB)

    Guerdal, Guelbin; Bozcu, Mustafa [Canakkale Onsekiz Mart University, Engineering and Architecture Faculty (Turkey)

    2011-01-01

    In this study, petrographic examinations along with proximate, calorific value, ultimate, sulphur form and XRD analyses were performed in order to determine the coal characteristics and the depositional environment of the Miocene Can coals. Seventy coal samples were taken from cores and open pit mines. The investigated Can coals are humic coals and classified as lignite to sub-bituminous coal based on the random huminite reflectance (0.38-0.54% R{sub r}), volatile matter (45.50-62.25 wt.%, daf) and calorific value (3419-6479 kcal/kg, maf). The sulphur content of the Can coals changes from 0.30 up to 12.23 wt.%, and a broad range of ash contents was observed varying between 2.46 wt.% and 41.19 wt.%. Huminite is the most abundant maceral group (74-95 vol.% mmf) consisting of mostly humocollinite (gelinite) which is followed by relatively low liptinite (2-18 vol.% mmf) and inertinite content (2-13 vol.% mmf). In general, major mineral contents of coal samples are clay minerals, quartz, mica, pyrite and feldspar. The Can-Etili lignite basin consists of mainly volcano-clastics, fluviatile and lacustrine clastic sediments and contains only one lignite seam with 17 m average thickness. In order to assess the development of paleo-mires, coal facies diagrams were obtained from maceral composition. According to the Vegetation Index (VI) and Ground Water Index (GWI), the Can coal accumulated in inundated marsh, limnic and swamp environments under a rheotrophic hydrological regime. In general, the facies interpretations are in accordance with the observed sedimentalogical data. (author)

  2. A secondary nursery area for the copper shark Carcharhinus brachyurus from the late Miocene of Peru

    Science.gov (United States)

    Landini, Walter; Collareta, Alberto; Pesci, Fabio; Di Celma, Claudio; Urbina, Mario; Bianucci, Giovanni

    2017-10-01

    The life history strategies of sharks often include the use of protected nursery areas by young-of-the-year and juveniles. Nursery areas can be primary (i.e., grounds where the sharks are born and spend the very first part of their lives) or secondary (i.e., grounds inhabited by slightly older but not yet mature individuals). Criteria utilized to recognize these strategic habitats include: high concentration of young sharks, high food availability, and low predation risk. Since the fossil record of sharks consists mainly of isolated teeth, identification of paleonurseries involves a series of problems due to difficult application of actualistic criteria. A rich shark tooth-bearing level (ST-low1) has recently been discovered in the upper Miocene deposits of the Pisco Formation exposed at Cerro Colorado (southern coast of Peru). Most of the teeth collected from this level belong to the extant copper shark Carcharhinus brachyurus. These teeth are small and compatible with those of extant juveniles. This observation, coupled with other paleoenvironmental considerations, indicates that the ST-low1 horizon could have represented a nursery ground for juvenile individuals of C. brachyurus. The absence of very small-sized teeth (i.e., referable to young-of-the-year) suggests a secondary nursery ground inhabited by immature copper sharks. Observations on the tooth size of other Lamniformes, Carcharhiniformes, and Myliobatiformes occurring along with C. brachyurus point to a significantly juvenile structure of this elasmobranch assemblage, thus supporting the hypothesis of a communal use of the Cerro Colorado paleonursery.

  3. 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

    2017-12-01

    -style mineralization during the early Miocene (˜18 Ma). The subsequent exhumation history of the Mo-Cu-bearing Pınarbaşı intrusion is attributed to regional-scale uplift, and further exhumation along detachment faults of the associated core complexes during the middle to late Miocene.

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

    Directory of Open Access Journals (Sweden)

    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.

  5. Entrapment bias of arthropods in Miocene amber revealed by trapping experiments in a tropical forest in Chiapas, Mexico.

    Science.gov (United States)

    Solórzano Kraemer, Mónica M; Kraemer, Mónica M Solórzano; Kraemer, Atahualpa S; Stebner, Frauke; Bickel, Daniel J; Rust, Jes

    2015-01-01

    All entomological traps have a capturing bias, and amber, viewed as a trap, is no exception. Thus the fauna trapped in amber does not represent the total existing fauna of the former amber forest, rather the fauna living in and around the resin producing tree. In this paper we compare arthropods from a forest very similar to the reconstruction of the Miocene Mexican amber forest, and determine the bias of different trapping methods, including amber. We also show, using cluster analyses, measurements of the trapped arthropods, and guild distribution, that the amber trap is a complex entomological trap not comparable with a single artificial trap. At the order level, the most similar trap to amber is the sticky trap. However, in the case of Diptera, at the family level, the Malaise trap is also very similar to amber. Amber captured a higher diversity of arthropods than each of the artificial traps, based on our study of Mexican amber from the Middle Miocene, a time of climate optimum, where temperature and humidity were probably higher than in modern Central America. We conclude that the size bias is qualitatively independent of the kind of trap for non-extreme values. We suggest that frequent specimens in amber were not necessarily the most frequent arthropods in the former amber forest. Selected taxa with higher numbers of specimens appear in amber because of their ecology and behavior, usually closely related with a tree-inhabiting life. Finally, changes of diversity from the Middle Miocene to Recent time in Central and South America can be analyzed by comparing the rich amber faunas from Mexico and the Dominican Republic with the fauna trapped using sticky and Malaise traps in Central America.

  6. Impacts of Evolutionary History on Endangerment in a Changing Climate: Miocene upwelling, Holocene Pluvial Cycles and Endemics at the Mouth of the Colorado River.

    Science.gov (United States)

    Jacobs, D. K.

    2006-12-01

    The environmental conditions communities experienced during their diversification and recent geologic history informs us as to which environmental changes are most likely to impact species in those communities. Three examples follow: 1) Recent compilation of molecular and paleontological data document that higher aspects of the trophic chain in the Pacific Northwest, including the salmon genus Onchoyrhynchus, alcid birds (Auks & Puffins) and crabs of the genus Cancer speciated dramatically in response to enhanced upwelling of the mid Miocene (Jacobs et al. 2004). Consistent with this evolutionary origin, population dynamics and endangerment of these taxa are associated with the changing productivity regime of the Pacific as well as more direct human impacts. 2) Pluvials in the Eurasian and African continent respond to the precession cycle, as a result wetland habitats were much more expansive in the early and middle Holocene. Late Holocene wetland habitat contraction combines with increasing anthropogenic manipulation of these cyclically limited hydrologic resources to yield a suite of endangered taxa across these continents as is statistically documented by analysis of Redbook data. 3) Our recent work documents the evolution of endemic fish and Molluscan taxa in association with the Colorado River Delta. These endemic taxa are then vulnerable to the to impacts on the Colorado Delta where anthropogenic use of water resources combine with the threat of climate provide combined threats to this ecosystem. The Environmental/Evolutionary history of lineages clearly has strong implications for how anthropogenic changes impacts and endangers those lineages. Jacobs D.K. et al. Annu. Rev. Earth Planet. Sci. 2004. 32:601 52

  7. Two flat-backed polydesmidan millipedes from the Miocene Chiapas-amber Lagerstätte, 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.

  8. Two Flat-Backed Polydesmidan Millipedes from the Miocene Chiapas-Amber Lagerstätte, Mexico

    Science.gov (United States)

    Riquelme, Francisco; Hernández-Patricio, Miguel; Martínez-Dávalos, Arnulfo; Rodríguez-Villafuerte, Mercedes; Montejo-Cruz, Maira; Alvarado-Ortega, Jesús; Ruvalcaba-Sil, José L.; Zúñiga-Mijangos, Luis

    2014-01-01

    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. PMID:25162220

  9. Paleoecology and environments of bioestromes and path reefs , its ostreid , enhdolith and epibionts ( Camacho formation - middle upper Miocene; Uruguay)

    International Nuclear Information System (INIS)

    Sprechmann, P.; Verde, M.; Martinez, S.; Gaucher, C.

    1998-01-01

    A special lithofacies of the Camacho formation (Middle-Upper Miocene, Uruguay), exposed at Puerto Arazati, is studied from a sedimentologic and paleontologic point of view. Ostreid biostromes and patch reefs show different kinds of growings patterns. Two kinds of ostreid concentration s, biogenic and sedimentologic were distinguished in Puerto Arazati based on taphonomic evidence. Endolith association and epibionts from biostrome and patch reef hardgrounds were also analysed in Puerto Arazati. Both sedimentologic and paleontologic evidence indicates a free of sediment, shallow water depositional environment, in the photic zone. Complementary data about endoliths from other outcrops of the Camacho Formation are included (author)

  10. Rodents from the Upper Miocene Tuğlu Formation (Çankırı Basin, Central Anatolia, Turkey)

    OpenAIRE

    Joniak, Peter; de Bruijn, Hans

    2015-01-01

    The upper Miocene assemblages of rodents collected from two layers of the type section of the Tuğlu Formation (Çankırı Basin, Central Anatolia, Turkey) are described. The assemblage from the lower level is considerably less diverse than that from the upper level. It contains Progonomys together with Megacricetodon, which is a very unusual association. The assemblage from the upper layer shows a relatively high diversity with four species of Gliridae instead of only one in the lower layer. Apa...

  11. Geology, geochemistry and {sup 40}K-{sup 40}Ar geochronometry of Miocene magmatism in Algiers area, Northern Algeria; La magmatisme miocene de l`Est Algerois, geologie, geochimie et geochronologie {sup 40}K-{sup 40}Ar

    Energy Technology Data Exchange (ETDEWEB)

    Belanteur, O; Ouabadi, A; Semroud, B; Megartsi, M H [Algiers Univ. (Algeria). Faculte des Sciences; Bellon, H; Maury, R C; Coutelle, A [Brest Univ., 29 (France); Fourcade, S [Rennes-1 Univ., 35 (France)

    1996-12-31

    Miocene magmatic rocks outcrop within a narrow coastal strip east of Algiers. They include basaltic and andesitic lava flows and intrusions (Dellys, Cap Djinet), the Thenia granodioritic plug and the dacitic to rhyolitic lavas and pyroclastic flows from Zemmouri El Bahri and El Kerma. Despite the effects of hydrothermal alteration, {sup 40}K-{sup 40}Ar ages coupled with micropalaeontological data lead to recognition of two emplacement events at 16-15 and 14-12 Ma, respectively. All the studied calc-alkaline to potassic calc-alkaline rocks are enriched in highly incompatible elements and display negative Nb anomalies. Acid magmas have a pronounced crustal imprint ({sup 87}Sr{sup 86}Sr{sub i} =3D 0.7082 to 0.7155; {delta}{sup 18}O =3D +9 to +13 per mill) which together with La/Nb ratios argues for the occurrence of upper crustal contamination processes. However, the Nb-depletion of the associated basalts suggest that the studied magmas derive from a mantle source which underwent subduction-related metasomatic enrichments prior to their Miocene emplacement. (authors). 13 refs., 3 figs., 2 tabs.

  12. A first possible chameleon from the late Miocene of India (the hominoid site of Haritalyangar): a tentative evidence for an Asian dispersal of chameleons.

    Science.gov (United States)

    Sankhyan, Anek R; Čerňanský, Andrej

    2016-12-01

    Miocene rare fossils from India, tentatively attributed to chameleons, are described for the first time. The material consists of a fragment of the left squamosal and an element interpreted as a posterodorsal process of the parietal. The specimens come from a late Miocene site of the Nagri Formation (Middle Siwaliks, ~ 9 Mya) at Haritalyangar, North India. This material presents a possible evidence for a chameleon dispersal to Asia. Based on molecular data, the dispersion of an Asian chamaeleonid lineage from Africa to Arabia/Asia is dated at approximately 13 Mya and its diversification in situ at around 6-8 Mya. However, till now, no Miocene-age fossil record has been described to support crown chamaeleonid presence in this area. The material described herein is very fragmented. If correctly allocated, the Haritalyangar chameleons show the oldest known occurrence of this clade in India, at least approximately 9 Mya ago.

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

    Science.gov (United States)

    Ali, Ahmed; Wagreich, Michael

    2017-06-01

    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 for marls and

  14. Understanding climate's influence on the extinction of Oreopithecus (late Miocene, Tusco-Sardinian paleobioprovince, Italy).

    Science.gov (United States)

    DeMiguel, Daniel; Rook, Lorenzo

    2018-03-01

    Despite its long history of scientific study, the causes underlying the extinction of the insular hominoid Oreopithecus bambolii are still a matter of ongoing debate. While some authors consider intense tectonism and invading species the cause of its extinction ca. 6.7 Ma, others propose climatic change as the main contributing factor. We rely on long-term patterns of tooth wear and hypsodonty of the Baccinello and Fiume Santo herbivore-faunas to reconstruct changes in habitat prior to, during and after the extinction. While a mosaic of habitats was represented in Baccinello V1 (as shown by a record of browsers, mixed feeders and species engaged in grazing), more closed forests (higher proportion of browsers, shortage of mixed feeders and lack of grazers) characterised Baccinello V2. Finally, there was a partial loss of canopy cover and development of open-patches and low-abrasive grasses in Baccinello V3 (as denoted by new records of taxa involved in grazing)-although still dominated by a forested habitat (since browse was a component in all diets). Our results provide evidence for two perceptible shifts in climate, one between 8.1 and 7.1 Ma and other ca. 6.7 Ma, though this latter was not drastic enough to lead to intensive forest loss, substantially alter the local vegetation or affect Oreopithecus lifestyle-especially if considering the growing evidence of its versatile diet. Although the disappearance of Oreopithecus is complex, our data reject the hypothesis of environmental change as the main factor in the extinction of Oreopithecus and Maremma fauna. When our results are analysed together with other evidence, faunal interaction and predation by invading species from mainland Europe seems to be the most parsimonious explanation for this extinction event. This contrasts with European hominoid extinctions that were associated with major climatic shifts that led to environmental uniformity and restriction of the preferred habitats of Miocene apes. Copyright

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

    Directory of Open Access Journals (Sweden)

    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

  16. Late Miocene (Pannonian) Vegetation from the Northern Part of Central Paratethys

    Science.gov (United States)

    Kováčová, M.; Doláková, N.

    2009-04-01

    During Late Miocene, the Western Carpathian paleogeography started to change. The Lake Pannon retreated southwards, and the northern coast of the back arc basin was slightly elevated due to progradation of deltaic and alluvial facies, especially in the lowlands. The studied „Pannonian lake" sediments come from the Czech and Slovak parts of Central Paratethys. Changes of the sedimentary environment from deep to shallow lake and deltaic environment, followed by development of alluvial plains were noticed. Salinity crisis due to Paratethys isolation led to development of total freshwater environment to the end of this period. Samples from 3 surficial localities and 15 boreholes were palynologically studied. Occasional occurences of Dinoflagellates indicate a slightly higher salinity, whereas green algae Pediastrum, aquatic ferns Azolla, and aquatic and coastal plants (Nelumbo, Nymphaea, Myriophyllum, Sparganium, Potamogeton, Cyperaceae etc.) represent a freshwater environment. Due to paleogeographic changes and climatic oscillations the number of thermophilous taxa decreased and some of them disappeared completely from this area (f. e. Sapotaceae, Palmae). Mostly broad-leaved deciduous elements of mixed mesophytic forests (Quercus, Celtis, Carya, Tilia, Carpinus, Betula, Juglans) with some thermophilous elements admixture of Engelhardia, Castanea, Trigonobalanopsis, Symplocos, Cornaceaepollis satzveyensis generally dominate. Variously high relief of the uplifted mountainy chains created ideal conditions for higher presence of extrazonal vegetation (Cedrus, Tsuga, Picea, Cathaya) in the investigated area. Zonal type of vegetation including marshes, riparian forests with Alnus, Salix, Pterocarya, Liquidambar, Betula, Fraxinus, shrubs and lianas on dryer substrates associated riparian forest (Buxus, Ericaceae, Vitaceae, Lonicera, Rosaceae type Rubus), and coastal swamps with Taxodiaceae, Nyssa, Myrica, Sciadopitys were growing in the floodplain lowlands of Vienna Basin

  17. Paleomagnetism and Anisotropy of Magnetic Susceptibility study of the Miocene Jack Springs Tuff (Nevada, USA)

    Science.gov (United States)

    Shields, S.; Petronis, M. S.; Pluhar, C. J.; Gordon, L.

    2014-12-01

    The mid-Miocene Jack Springs Tuff (JST) outcrops across the western Mina Deflection accommodation zone, west-central Nevada and into eastern California. Previously, the source location for the JST was unknown, yet recent studies northwest of Mono Lake, CA have identified a relatively un-rotated structural block in which to reference the paleomagnetic data. Although new studies have indicated that this block may be rotated up to 13º, we argue that the probable source area is located near the Bodie Hills, CA. At this site, the paleomagnetic reference direction is D = 353°, I = 43°, α95 = 7.7° (Carlson et al, 2013). Based on these data, the JST can be used to measure absolute vertical-axis rotation as well as enable reconstruction of the paleo-topography using the corrected anisotropy of magnetic susceptibility (AMS) data. A total of 19 sites were sampled to constrain Cenozoic to recent vertical axis rotation within the region and AMS experiments were conducted to determine the flow direction of the JST. Curie point estimates indicate that the JST ranges in titanium concentration from 0.042 to 1.10, indicating a low to moderate titanomagnetite phase (Akimoto, 1962). Demagnetization experiments reveal mean destructive fields of the NRM ranging between 15mT and 40mT suggesting that both multi-domain to pseudo-single domain grains are the dominant ferromagnetic phases that carry the remanence and AMS fabric. Preliminary paleomagnetic data yield stable single component demagnetization behavior for most sites that, after structural correction, indicate clockwise vertical axis rotation ranging from +20°± 10° to +60°± 11° between multiple fault blocks. The uncorrected AMS data yield oblate magnetic fabrics that can be used to infer the transport direction, source region, and paleovalley geometry of the JST. These data are tentatively interpreted to indicate west to east transport of the JST across the Mono Basin region into the Mina Deflection that was erupted and

  18. Large landslides, composed of megabreccia, interbedded in Miocene basin deposits, southeastern Arizona

    Science.gov (United States)

    Krieger, Medora Louise Hooper

    1977-01-01

    The landslides in the Kearny and El Capitan Mountain quadrangles, Pinal and Gila Counties, Ariz., are tabular or lens like masses of megabreccia enclosed in Miocene basin deposits. The megabreccias within individual slide blocks are composed of pervasively brecciated Precambrian and younger formations that remain in normal stratigraphic sequence, indicating that each landslide moved as a fairly coherent mass. The megabreccias consist of fresh, mostly angular rock fragments in a comminuted matrix of the same composition as the fragments. The matrix ranges in amount from sparse to abundant. Where the matrix is sparse, the fragments fit tightly with little or no rotation. Locally fragments are rotated but not moved far; most units within a slide block are lithologically homogeneous. The Kearny landslides are conformably interbedded in steeply east-dipping playa and alluvial deposits. They form map units from a few tens of meters to nearly 4 km long and from less than 1 to 270 m wide. Narrow ridges expose sections through the landslides at about right angles to the direction of movement. The upper (proximal) ends have been eroded; the lower (distal) ends are buried. The El Capitan landslide dips very gently southward. Although partly dissected during erosion of the enclosing alluvial and lakebed deposits, its approximate original outline is still preserved. It forms a thin sheet, 5-15 m thick and at least 3.8 km long; the maximum outcrop width, near its distal end, is about 1.5 km. The Kearny landslides show little evidence of having exerted differential pressure on the underlying soft playa and alluvial deposits, and the contacts with the underlying sediments have little relief. The distal end of the El Capitan landslide, on the other hand, has considerable relief. As the landslide came to an abrupt stop, the end plowed into the underlying sediments, compressing them into fol9.s and forming sandstone dikes. The source of the El Capitan landslide is a well

  19. Petrophysical characterization of three commercial varieties of miocene sandstones from the Ebro valley

    Directory of Open Access Journals (Sweden)

    Gisbert, J.

    2007-08-01

    Full Text Available Miocene sandstones studied were used extensively to build Aragon’s architectural heritage, are still used in modern construction. The quarries presently located on the edge of the Ebro Valley depression. The present paper describes an exhaustive petrophysical study of these materials, which while, of the same age and from the same deposition basin, exhibit different mineralogical and textural characteristics and as a result, different physical and mechanical properties and durability. The petrographic and petrophysical characteristics of these materials were evaluated with tests prescribed in UNE (Spanish, NORMAL and ASTM standards. All the results were subjected to statistical analysis to identify possible textural and compositional nonuniformities in the material that may underlie behavioural changes. The results of the present paper show that their petrophysical characteristics afford these sandstones substantial industrial value as construction materials. Durability was found to be longest in the Alcañiz stone, as a result of the geometry of its pore network.Las areniscas miocenas estudiadas han sido y son ampliamente utilizadas en patrimonio histórico y en obra civil moderna, localizándose las canteras actuales en el borde de la depresión del Ebro. Se ha realizado un exhaustivo estudio de las características petrofísicas de estos materiales, que pese a presentar la misma edad y pertenecer a la misma cuenca sedimentaria presentan características mineralógicas y texturales diferentes que les confieren diferentes propiedades físicas, mecánicas y una diferente durabilidad. Las características petrográficas y petrofísicas se han evaluado mediante la realización de ensayos según las normas UNE, NORMAL y ASTM. Para todos los ensayos se ha realizado un tratamiento estadístico de los resultados para evaluar las posibles inhomogeneidades texturales y composicionales presentes en el material y que pueden originar modificaciones en

  20. Lateral variations in vegetation in the Himalaya since the Miocene and implications for climate evolution

    Science.gov (United States)

    Vögeli, Natalie; Najman, Yani; van der Beek, Peter; Huyghe, Pascale; Wynn, Peter M.; Govin, Gwladys; van der Veen, Iris; Sachse, Dirk

    2017-08-01

    The Himalaya has a major influence on global and regional climate, in particular on the Asian monsoon system. The foreland basin of the Himalaya contains a record of tectonics and paleoclimate since the Miocene. Previous work on the evolution of vegetation and climate has focused on the central and western Himalaya, where a shift from C3 to C4 vegetation has been observed at ∼7 Ma and linked to increased seasonality, but the climatic evolution of the eastern part of the orogen is less well understood. In order to track vegetation as a marker of monsoon intensity and seasonality, we analyzed δ13 C and δ18 O values of soil carbonate and associated δ13 C values of bulk organic carbon from previously dated sedimentary sections exposing the syn-orogenic detrital Dharamsala and Siwalik Groups in the west, and, for the first time, the Siwalik Group in the east of the Himalayan foreland basin. Sedimentary records span from 20 to 1 Myr in the west (Joginder Nagar, Jawalamukhi, and Haripur Kolar sections) and from 13 to 1 Myr in the east (Kameng section), respectively. The presence of soil carbonate in the west and its absence in the east is a first indication of long-term lateral climatic variation, as soil carbonate requires seasonally arid conditions to develop. δ13 C values in soil carbonate show a shift from around -10‰ to -2‰ at ∼7 Ma in the west, which is confirmed by δ13 C analyses on bulk organic carbon that show a shift from around -23‰ to -19‰ at the same time. Such a shift in isotopic values is likely to be associated with a change from C3 to C4 vegetation. In contrast, δ13 C values of bulk organic carbon remain at ∼ - 23 ‰ in the east. Thus, our data show that the current east-west variation in climate was established at 7 Ma. We propose that the regional change towards a more seasonal climate in the west is linked to a decrease of the influence of the Westerlies, delivering less winter precipitation to the western Himalaya, while the east

  1. Environmental significance of Upper Miocene phosphorites at hominid sites in the Lukeino Formation (Tugen Hills, Kenya)

    Science.gov (United States)

    Dericquebourg, Perrine; Person, Alain; Ségalen, Loïc; Pickford, Martin; Senut, Brigitte; Fagel, Nathalie

    2015-08-01

    The Lukeino Formation contains an important sedimentary and fossiliferous record of the late Miocene (6.09-5.68 Ma), which has in particular yielded the fossil remains of the oldest East African bipedal hominid called Orrorin tugenensis. This fluvio-lacustrine sedimentary succession crops out in the Kenyan part of the East African Rift. It is mainly composed of clay to sandy clay deposits intercalated with volcanic ash horizons, and localized layers of carbonates and diatomites. A detailed sedimentological and mineralogical study of the Lukeino Formation was conducted to throw light on the environmental conditions in which the hominids lived. Several centimetric, relatively continuous and indurated phosphatic horizons, of sedimentary origin, were identified at two sites (Sunbarua and Kapcheberek). Mineralogical (XRD) and geochemical analyses as well as observations by SEM, which was coupled with an energy dispersive spectroscopy (EDS) microprobe, indicate that the autochthonous phosphate layers are composed of a micritic matrix of francolite (38-93%), with incorporation of silicates in variable proportions from one layer to another. The phosphate matrix contains very well preserved and abundant diatom frustules in the basal phosphate layer. These diatoms are identified as Aulacoseira granulata, implying a pH of 7.8-8.2 for freshwaters of the Palaeolake Lukeino. Calcitic tubular structures, linked to a possible bacterial origin, are also observed locally. Phosphate layers occur abruptly within a thick clay-sandy series, associated with an intense runoff phase during the deposition of this interval of the Lukeino Formation. The massive and cyclic input of phosphorus to the lake promoted productivity to the stage where it caused a diatom bloom. The establishment of several phosphate horizons testifies to successive phases of eutrophication of Palaeolake Lukeino. The diatom cells provided some of the organic matter, which was decomposed by bacterial activity at the

  2. Climate Proxy Signals in the Plio-Pleistocene Chemeron and Miocene Lukeino Formations, Baringo Basin, Kenya

    Science.gov (United States)

    Deino, A. L.; Kingston, J.; Hill, A.; Wilson, K. E.; Edgar, R.; Goble, E.

    2009-12-01

    in the Tugen Hills to diatomaceous sequences between ~8-6 Ma that would specifically implicate precessional control as a pervasive factor in the formation of rift lake systems and by inference climate. Reconnaissance in summer ’09 of these older strata have revealed extensive lacustrine deposits indicating that this portion of the rift was inundated by major lake systems during the upper Miocene.

  3. A new species of Miocene terrestrial gastropod Gastrocopta from Poland and the validity of 'Pupa (Vertigo) suevica'

    Energy Technology Data Exchange (ETDEWEB)

    Stworzewicz, E.; Prisyazhnyuk, V.A. [Polish Academy of Science, Krakow (Poland)

    2006-03-15

    We describe Gastrocopta sandbergeri sp. nov. from the Miocene brown coal deposits of the open-cast mine Belchatow (central Poland) and identify it as conspecific with Pupa (Vertigo) suevica Sandberger, 1875 (nomen nudum) from the Miocene of Steinheim. The new species is most similar to Gastrocopta nouletiana (Dupuy, 1850) but differs in having smaller and always slender shell, less convex whorls, much weaker crest on the body whorl (or even absent) and generally rather weakly developed teeth (6-7) in the aperture.

  4. D/H of late Miocene meteoric waters in Western Australia: Paleoenvironmental conditions inferred from the δD of (U-Th)/He-dated CID goethite

    Science.gov (United States)

    Yapp, Crayton J.; Shuster, David L.

    2017-09-01

    Nineteen (U-Th)/He ages were determined for eight samples from a core drilled in an ore-grade channel iron deposit (CID) of the Robe Pisolite (Robe Formation) of Mesa J in Western Australia. With one exception, uncorrected ages of the analyzed aliquots range from 6.7(±0.4) Ma to 30.2(±3.1) Ma, while molar ratios of Th/U range from 0.42 to 5.06. The exception is an aliquot with an apparent age of 2.7 Ma and Th/U of 5.70. A three-component mixing model involving one generation of goethite and two generations of hematite suggests that the age of crystallization of the oolitic goethites is ∼7(±1) Ma. If so, the goethites have effectively been closed systems for ∼7 million years and should preserve a stable hydrogen isotope record of late Miocene rainfall in the vicinity of Mesa J. Cenozoic movement of the Australian continent had placed Mesa J and environs in the subtropics at a paleolatitude of about 29 °S during the late Miocene. Al-adjusted δD values of oolitic goethite in the eight CID samples range from -153‰ to -146‰ and imply that the δD of the late Miocene meteoric waters ranged from -61‰ to -53‰, with an average of -56‰. These relatively negative δD values might indicate that near-coastal, late Miocene rain was derived primarily from summer-season tropical cyclones with storm tracks that extended into the subtropics of western Australia. The postulated late Miocene tropical cyclones would have occurred more often and/or exhibited greater intensity at a paleolatitude of 29 °S than is the case for modern sites at approximately 30 °S on the west coast of Australia (e.g., Perth). Higher fluxes of meteoric water in the Miocene summers would have facilitated dissolution and removal of BIF-sourced silica with concomitant enrichment in oxidized Fe. Moreover, wetter late Miocene summers could have promoted multiple cycles of microbially mediated dissolution and recrystallization of Fe(III) oxides in the aerobic systems. The oolitic textures may

  5. Stable carbon isotope ratios and intrinsic water-use efficiency of Miocene fossil leaves compared to modern congeners

    Energy Technology Data Exchange (ETDEWEB)

    Marshall, J.D.; Zhang, J.; Rember, W.C.; Jennings, D.; Larson, P. (Univ. of Idaho, Moscow, ID (United States))

    1994-06-01

    Miocene fossil leaves of forest trees were extracted from the Clarkia, Idaho fossil beds and their stable carbon isotope ratios were analyzed. Fossils had higher lignin concentrations and lower cellulose concentrations that modern leaves due to diagenesis and the HF used to extract the fossils. Therefore, [delta][sup 13]C of extracted fossil lignin was compared to that of modern lignin. Fossil lignin [delta][sup 13]C was significantly different from that of congeneric modern leaves (paired t-test, P<0.0001), but was 1.9% less negative. Gymnosperms (Metasequoia, Taxodium) were less negative than angiosperms (e.g., Magnolia, Quercus, Acer, Persea), but no difference between evergreen and deciduous species was detected. Using published estimates of the concentration and [delta][sup 13]C of atmospheric CO[sub 2] during the Miocene was estimated the CO[sub 2] partial pressure gradient across the stomata (intrinsic water-use efficiency). Intrinsic water-use efficiency was at least 70% higher during this past [open quotes]greenhouse[close quotes] period than at present.

  6. Paleomagnetism of the Miocene intrusive suite of Kidd Creek: Timing of deformation in the Cascade arc, southern Washington

    Science.gov (United States)

    Hagstrum, J.T.; Swanson, D.A.; Snee, L.W.

    1998-01-01

    Paleomagnetic study of the intrusive suite of Kidd Creek in the southern Washington Cascades (23 sites in dikes and sills) was undertaken to help determine if these rocks are comagmatic and whether they postdate regional folding of the volcanic arc. Fission track and 40Ar-39Ar age determinations indicate an age of ???12.7 Ma (middle Miocene) for these rocks. The similarity of normal-polarity characteristic directions for most samples corroborate the available geochemical data indicating that these rocks are most likely comagmatic. Reversed-polarity directions for samples from four sites, however, show that emplacement of Kidd Creek intrusions spanned at least one reversal of the geomagnetic field. The paleomagnetic directions for the dikes and sills fail a fold test at the 99% confidence level indicating that the Kidd Creek rocks postdate regional folding. The mean in situ direction also indicates that the Kidd Creek and older rocks have been rotated 22?? ?? 6?? clockwise about a vertical or near-vertical axis from the expected Miocene direction. Compression and regional folding of the Cascade arc in southern Washington therefore had ended by ???12 Ma prior to the onset of deformation resulting in rotation of these rocks.

  7. Distinguishing fluvio-deltaic facies by bulk geochemistry and heavy minerals: an example from the Miocene of Denmark

    DEFF Research Database (Denmark)

    Olivarius, Mette; Rasmussen, Erik S.; Siersma, Volkert Dirk

    2011-01-01

    Interpretations of seismic profiles, gamma-ray logs and sediment descriptions were used to classify seven facies in Miocene fluvio-deltaic deposits ofDenmark. An impartial approach was adopted by not including analytical data in the facies definition. This approach allowed identification of signi......Interpretations of seismic profiles, gamma-ray logs and sediment descriptions were used to classify seven facies in Miocene fluvio-deltaic deposits ofDenmark. An impartial approach was adopted by not including analytical data in the facies definition. This approach allowed identification...... grain size of quartz and heavy minerals from the channel facies towards the delta shoreface facies and further along the coast to the spit shoreface facies is associated with an increase in sorting and textural maturity. This trend is related to longshore drift. Increasing heavy mineral grain size...... is found from the delta slope facies offshore to the delta toe and shelf facies. This trend is interpreted as a result of sorting by turbidity currents. The mixed origin of the transgressive lag facies is shown by the poorer sorting in this facies. By indicating the amount of alteration the sediments have...

  8. 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

    During the Oligocene-Miocene Greenhouse-to-Icehouse climatic transition, the biogeography of reef corals or zooxanthellate-like scleractinian corals was gradually changing from a pan-tropical Tethyan Province in the Eocene to three reef-coral Provinces of the Western Atlantic-Caribbean, Indo-Pacific and Mediterranean. Our REEFCORAL database encompasses updated and homogenized data on paleoenvironmental and systematics of scleractinian corals occurring in the Oligocene and Miocene outcrops from circum-Mediterranean regions, provided by most of relatively recently published data in the literature and by the study of published and unpublished collections of coral specimens from the same area, including the important collections housed at the MNHN (Paris) and our own collections. As there is no validated direct criterion for the identification of the coral-zooxanthellate symbiosis in the fossil record, and considering the difficulty to use the biogeochemical approaches in the context of this study, the subjectivity of the morphological criteria and the relative recent age of the fossil corals we are dealing with, a uniformitarian approach has been used for inferring the symbiotic status of scleractinian genera in REEFCORAL. Among the 158 genera included in our database, 93 can be considered as zooxanthellate and 10 have a doubtful zooxanthellate status. This relatively exhaustive database was used to reconstruct the temporal and spatial distribution of scleractinian corals in the Mediterranean during the Oligocene-Miocene time in order to discuss the interplaying effects of the global cooling at that time, the re-organization of the Tethyan realm resulting from the African, Arabian and Eurasian plate collision and the emergence of the Alpine chains, driving the gradual northward movement of the whole region outside the tropical/subtropical belt. It is shown that the structure of the Mediterranean z-coral Oligocene-Miocene paleobiodiversity was characterized by many

  9. Astronomical tunings of the Oligocene-Miocene transition from Pacific Ocean Site U1334 and implications for the carbon cycle

    Science.gov (United States)

    Beddow, Helen M.; Liebrand, Diederik; Wilson, Douglas S.; Hilgen, Frits J.; Sluijs, Appy; Wade, Bridget S.; Lourens, Lucas J.

    2018-03-01

    Astronomical tuning of sediment sequences requires both unambiguous cycle pattern recognition in climate proxy records and astronomical solutions, as well as independent information about the phase relationship between these two. Here we present two different astronomically tuned age models for the Oligocene-Miocene transition (OMT) from Integrated Ocean Drilling Program Site U1334 (equatorial Pacific Ocean) to assess the effect tuning has on astronomically calibrated ages and the geologic timescale. These alternative age models (roughly from ˜ 22 to ˜ 24 Ma) are based on different tunings between proxy records and eccentricity: the first age model is based on an aligning CaCO3 weight (wt%) to Earth's orbital eccentricity, and the second age model is based on a direct age calibration of benthic foraminiferal stable carbon isotope ratios (δ13C) to eccentricity. To independently test which tuned age model and associated tuning assumptions are in best agreement with independent ages based on tectonic plate-pair spreading rates, we assign the tuned ages to magnetostratigraphic reversals identified in deep-marine magnetic anomaly profiles. Subsequently, we compute tectonic plate-pair spreading rates based on the tuned ages. The resultant alternative spreading-rate histories indicate that the CaCO3 tuned age model is most consistent with a conservative assumption of constant, or linearly changing, spreading rates. The CaCO3 tuned age model thus provides robust ages and durations for polarity chrons C6Bn.1n-C7n.1r, which are not based on astronomical tuning in the latest iteration of the geologic timescale. Furthermore, it provides independent evidence that the relatively large (several 10 000 years) time lags documented in the benthic foraminiferal isotope records relative to orbital eccentricity constitute a real feature of the Oligocene-Miocene climate system and carbon cycle. The age constraints from Site U1334 thus indicate that the delayed responses of the

  10. The stratigraphy and regional structure of Miocene deposits in western Amazonia (Peru, Colombia and Brazil), with implications for late Neogene landscape evolution

    NARCIS (Netherlands)

    Wesselingh, F.P.; Hoorn, M.C.; Guerrero, J.; Räsänen, M.E.; Romero Pittmann, L.; Salo, J.A.

    2006-01-01

    A biozonation based on molluscs is proposed for Miocene deposits of western Amazonia (Peru, Colombia and Brazil), commonly referred to as the Pebas Formation. The new zonation refines existing pollen zonations and provides a key for the quick assessment of the stratigraphic position of Neogene

  11. Geochemical constraints on the relationship between the Miocene-Pliocene volcanism and tectonics in the Palaoco and Fortunoso volcanic fields, Mendoza Region, Argentina

    DEFF Research Database (Denmark)

    Dyhr, Charlotte Thorup; Holm, Paul Martin; Llambias, Eduardo J.

    2013-01-01

    New 40Ar/39Ar analyses constrain the formation of the volcanic succession of Sierra de Palaoco in the present back-arc of the Andean Southern Volcanic Zone (SVZ), near 36°S, to the Late Miocene and assigns them to the Huincán II Formation. The composition of major and trace elements, Sr, Nd and P...

  12. Perseverance of pikas in the Miocene : Interplay of climate and competition in the evolution of Spanish Ochotonidae (Lagomorpha, Mammalia). Geologica Ultraiectina (333)

    NARCIS (Netherlands)

    Hordijk, K.

    2010-01-01

    The sedimentary succession near the village of Villafeliche in the Calatayud-Montalbán Basin (Spain) is well known for its very rich, densely sampled and well dated fossil mammal record of Miocene age and roughly spans the time interval between 17 and 10 million years ago. The exceptional quality of

  13. Petrology and geochemistry of the Miocene-Pliocene fluvial succession, Katawaz Basin, Western Pakistan: Implications on provenance and source area weathering

    DEFF Research Database (Denmark)

    Kasi, Aimal K.; Kassi, Aktar Muhammad; Friis, Henrik

    Petrology and geochemistry of sandstones and mudstones of the Miocene Dasht Murgha Group (DMG) and Pliocene Malthanai Formation (MF) of the Pishin Belt (Katawaz Basin), northwestern Pakistan have been carried out to find out their provenance and source area weathering. Sandstones of the Dasht...

  14. Morphological indicators of growth stages in carbonates platform evolution: comparison between present-day and Miocene platforms of Northern Borneo, Malaysia.

    Science.gov (United States)

    Pierson, B.; Menier, D.; Ting, K. K.; Chalabi, A.

    2012-04-01

    Satellite images of present-day reefs and carbonate platforms of the Celebes Sea, east of Sabah, Malaysia, exhibit large-scale features indicative of the recent evolution of the platforms. These include: (1) multiple, sub-parallel reef rims at the windward margin, suggestive of back-stepping of the platform margin; (2) contraction of the platform, possibly as a result of recent sea level fluctuations; (3) colonization of the internal lagoons by polygonal reef structures and (4) fragmentation of the platforms and creation of deep channels separating platforms that used to be part of a single entity. These features are analogue to what has been observed on seismic attribute maps of Miocene carbonate platforms of Sarawak. An analysis of several growth stages of a large Miocene platform, referred to as the Megaplatform, shows that the platform evolves in function of syn-depositional tectonic movements and sea level fluctuations that result in back-stepping of the margin, illustrated by multiple reef rims, contraction of the platform, the development of polygonal structures currently interpreted as karstic in origin and fragmentation of the megaplatform in 3 sub-entities separated by deep channels that precedes the final demise of the whole platform. Comparing similar features on present-day to platforms and Miocene platforms leads to a better understanding of the growth history of Miocene platforms and to a refined predictability of reservoir and non-reservoir facies distribution.

  15. 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

  16. 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

  17. Constraining controls on carbonate sequences with high-resolution chronostratigraphy: Upper Miocene, Cabo de Gata region, SE Spain

    Science.gov (United States)

    Montgomery, P.; Farr, M.R.; Franseen, E.K.; Goldstein, R.H.

    2001-01-01

    A high-resolution chronostratigraphy has been developed for Miocene shallow-water carbonate strata in the Cabo de Gata region of SE Spain for evaluation of local, regional and global factors that controlled platform architecture prior to and during the Messinian salinity crisis. Paleomagnetic data were collected from strata at three localities. Mean natural remanent magnetization (NRM) ranges between 1.53 ?? 10-8 and 5.2 ?? 10-3 Am2/kg. Incremental thermal and alternating field demagnetization isolated the characteristic remanent magnetization (ChRM). Rock magnetic studies show that the dominant magnetic mineral is magnetite, but mixtures of magnetite and hematite occur. A composite chronostratigraphy was derived from five stratigraphic sections. Regional stratigraphic data, biostratigraphic data, and an 40Ar/39Ar date of 8.5 ?? 0.1 Ma, for an interbedded volcanic flow, place the strata in geomagnetic polarity Chrons C4r to C3r. Sequence-stratigraphic and diagenetic evidence indicate a major unconformity at the base of depositional sequence (DS)3 that contains a prograding reef complex, suggesting that approximately 250 000 yr of record (Subchrons C3Br.2r to 3Br.1r) are missing near the Messinian-Tortonian boundary. Correlation to the GPTS shows that the studied strata represent five third- to fourth-order DSs. Basal units are temperate to subtropical ramps (DS1A, DS1B, DS2); these are overlain by subtropical to tropical reefal platforms (DS3), which are capped by subtropical to tropical cyclic carbonates (Terminal Carbonate Complex, TCC). Correlation of the Cabo de Gata record to the Melilla area of Morocco, and the Sorbas basin of Spain indicate that early - Late Tortonian ramp strata from these areas are partially time-equivalent. Similar strata are extensively developed in the Western Mediterranean and likely were influenced by a cool climate or influx of nutrients during an overall rise in global sea-level. After ramp deposition, a sequence boundary (SB3) in

  18. Modernist architecture in Barcelona reveals a new trace fossil from the Miocene of Montjuïc (NE Spain)

    Energy Technology Data Exchange (ETDEWEB)

    Belaústegui, Z.; Belaústegui, A.

    2017-11-01

    A new ichnotaxon, Lapillitubus montjuichensis n. i gen. n. isp., is described from the middle Miocene (Serravallian) of Montjuïc mountain (Barcelona, northeastern Spain). This ichnotaxon consists of a horizontal to vertical, cylindrical burrow with an agglutinated lining exclusively composed of lithoclasts. Lapillitubus montjuichensis is interpreted as the result of the burrowing activity of a deposit- or suspension-feeding annelid worm. This new ichnotaxon extends the record of the informal group known as clast-armored or agglutinated trace fossils. In addition, since part of its type material is located in the blocks that make up the façades of several modernist buildings in the city of Barcelona, this new ichnotaxon highlights the importance of fossils in urban settings for those cases in which natural outcrops are reduced, restricted or even missing.

  19. The Upper Miocene of the Rostov Dome (Eastern Paratethys: Implication of the chronostratigraphy and bivalvia-based biostratigraphy

    Directory of Open Access Journals (Sweden)

    Ruban Dmitry A.

    2005-01-01

    Full Text Available The Rostov Dome is located in the south of the Russian Platform. In the Late Miocene this area was embraced by the Eastern Paratethys. The implications of a recently developed Neogene chronostratigraphy to the studied area are discussed. The Sarmatian regional stage corresponds to the upper part of the Langhian, the entire Serravalian and the lower part of the Tortonian global stages; the Maeotian regional stage corresponds to the upper part of the Tortonian and the lowermost horizons of the Messinian global stages; the Pontian regional stage corresponds to most of the Messinian and the lowermost Zanclean global stages. A first Bivalvia-based bio-stratigraphic framework is proposed for the territory of the Rostov Dome. Five biozones were established within the Serravalian-Messinian: Tapes vitalianus, Cerastoderma fittoni-Cerastoderma subfittoni, Congeria panticapaea, Congeria amygdaloides navicula and Monodacna pseudocatillus-Prosodacna schirvanica.

  20. 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.

  1. Modernist architecture in Barcelona reveals a new trace fossil from the Miocene of Montjuïc (NE Spain)

    International Nuclear Information System (INIS)

    Belaústegui, Z.; Belaústegui, A.

    2017-01-01

    A new ichnotaxon, Lapillitubus montjuichensis n. i gen. n. isp., is described from the middle Miocene (Serravallian) of Montjuïc mountain (Barcelona, northeastern Spain). This ichnotaxon consists of a horizontal to vertical, cylindrical burrow with an agglutinated lining exclusively composed of lithoclasts. Lapillitubus montjuichensis is interpreted as the result of the burrowing activity of a deposit- or suspension-feeding annelid worm. This new ichnotaxon extends the record of the informal group known as clast-armored or agglutinated trace fossils. In addition, since part of its type material is located in the blocks that make up the façades of several modernist buildings in the city of Barcelona, this new ichnotaxon highlights the importance of fossils in urban settings for those cases in which natural outcrops are reduced, restricted or even missing.

  2. The extinct river shark Glyphis pagoda from the Miocene of Myanmar and a review of the fossil record of the genus Glyphis (Carcharhiniformes: Carcharhinidae).

    Science.gov (United States)

    Shimada, Kenshu; Egi, Naoko; Tsubamoto, Takehisa; Maung-Maung, Maung-Maung; Thaung-Htike, Thaung-Htike; Zin-Maung-Maung-Thein, Zin-Maung-Maung-Thein; Nishioka, Yuichiro; Sonoda, Teppei; Takai, Masanaru

    2016-09-05

    We redescribe an extinct river shark, Glyphis pagoda (Noetling), on the basis of 20 teeth newly collected from three different Miocene localities in Myanmar. One locality is a nearshore marine deposit (Obogon Formation) whereas the other two localities represent terrestrial freshwater deposits (Irrawaddy sediments), suggesting that G. pagoda from the Irrawaddy sediments was capable of tolerating low salinity like the extant Glyphis. Glyphis pagoda likely reached up to at least 185 cm in total body length and was probably piscivorous. The fossil species occurs in rocks of Myanmar and eastern and western India and stratigraphically ranges at least from the Lower Miocene (Aquitanian) to the lower Upper Miocene (mid-Tortonian). It has been classified under at least eight other genera to date, along with numerous taxonomic synonyms largely stemming from the lack of understanding of the heterodonty in extant Glyphis in the original description. Our literature review suggests that known Miocene shark faunas, particularly those in India, are manifested with unreliable taxonomic identifications and outdated classifications that warrant the need for a comprehensive taxonomic review in order to evaluate the evolutionary history and diversity pattern of Miocene shark faunas. The genus Glyphis has a roughly 23-million-year-long history, and its success may be related to the evolution of its low salinity tolerance. While extant Glyphis spp. are considered to be particularly vulnerable to habitat degradation and overfishing, the fossil record of G. pagoda provides renewed perspective on the natural history of the genus that can be taken into further consideration for conservation biology of the extant forms.

  3. Analysis of a multiple-well interference test in Miocene tuffaceous rocks at the C-Hole complex, May--June 1995, Yucca Mountain, Nye County, Nevada

    International Nuclear Information System (INIS)

    Geldon, A.L.; Umari, A.M.A.; Earle, J.D.; Fahy, M.F.; Gemmell, J.M.; Darnell, J.

    1998-01-01

    A multiple-well interference (pumping) test was conducted in Miocene tuffaceous rocks at the C-hole complex at Yucca Mountain, Nev., from May 22 to June 12, 1995, by the US Geological Survey, in cooperation with the US Department of Energy. This pumping test was conducted as part of investigations to determine the suitability of Yucca Mountain as a potential site for the storage of high-level nuclear waste in a mined geologic repository. During the test, borehole UE-25 c number-sign 3 was pumped for 10 days at an average rate of 17.9 liters per second. Drawdown in 6 observation wells completed in Miocene tuffaceous rocks 29.0--3,525.6 meters from the pumping well ranged from 0 to 0.42 meters 14,000 minutes after pumping started. The spatial distribution of this drawdown indicates that a northwest-trending zone of discontinuous faults might be affecting ground-water movement in the Miocene tuffaceous rocks near the C-holes. No drawdown was observed in a borehole completed in a regional Paleozoic carbonate aquifer 630.0 meters from the pumping well. Consequently, it could not be determined during the pumping test if the Miocene tuffaceous rocks are connected hydraulically to the regional aquifer. Analyses of drawdown and recovery indicate that the Miocene tuffaceous rocks in the vicinity of the C-holes have transmissivity values of 1,600--3,200 meters squared per day, horizontal hydraulic conductivity values of 6.5--13 meters per day, vertical hydraulic conductivity values of 0.2--1.7 meters per day, storativity values of 0.001--0.003, and specific yield values of 0.01--0.2

  4. Koristocetus pescei gen. et sp. nov., a diminutive sperm whale (Cetacea: Odontoceti: Kogiidae from the late Miocene of Peru

    Directory of Open Access Journals (Sweden)

    A. Collareta

    2017-12-01

    Full Text Available Among odontocetes, members of the family Kogiidae (pygmy and dwarf sperm whales are known as small-sized and in many respects enigmatic relatives of the great sperm whale Physeter macrocephalus. Most of the still scanty fossil record of Kogiidae is represented by isolated skulls and ear bones from Neogene deposits of the Northern Hemisphere, with the significant exception of Scaphokogia, a highly autapomorphic genus from late Miocene deposits of the Pisco Formation exposed along the southern coast of Peru. Here we report on a new fossil kogiid from Aguada de Lomas, a site where the late Miocene beds of the Pisco Formation are exposed. This specimen consists of an almost complete cranium representing a new taxon of Kogiidae: Koristocetus pescei gen. et sp. nov. Koristocetus mainly differs from extant Kogia spp. by displaying a larger temporal fossa and well-individualized dental alveoli on the upper jaws. Coupled with a relatively elongated rostrum, these characters suggest that Koristocetus retained some degree of raptorial feeding abilities, contrasting with the strong suction feeding specialization seen in Recent kogiids. Our phylogenetic analysis recognizes Koristocetus as the earliest branching member of the subfamily Kogiinae. Interestingly, Koristocetus shared the southern coast of present-day Peru with members of the genus Scaphokogia, whose unique convex rostrum and unusual neurocranial morphology seemingly indicate a peculiar foraging specialization that has still to be understood. In conclusion, Koristocetus evokes a long history of high diversity, morphological disparity, and sympatric habits in fossil kogiids, thus suggesting that our comprehension of the evolutionary history of pygmy and dwarf sperm whales is still far from being exhaustive.

  5. Changes of deep Pacific overturning circulation and carbonate chemistry during middle Miocene East Antarctic ice sheet expansion

    Science.gov (United States)

    Ma, Xiaolin; Tian, Jun; Ma, Wentao; Li, Ke; Yu, Jimin

    2018-02-01

    East Antarctic ice sheet expansion (EAIE) at ∼13.9 Ma in the middle Miocene represents a major climatic event during the long-term Cenozoic cooling, but ocean circulation and carbon cycle changes during this event remain unclear. Here, we present new fish teeth isotope (εNd) and benthic foraminiferal B/Ca records from the South China Sea (SCS), newly integrated meridional Pacific benthic foraminiferal δ18O and δ13C records and simulated results from a biogeochemical box model to explore the responses of deep Pacific Ocean circulation and carbon cycle across EAIE. The εNd and meridional benthic δ13C records reveal a more isolated Pacific Deep Water (PDW) and a sluggish Pacific meridional overturning circulation during the post-EAIE with respect to the pre-EAIE owing to weakened southern-sourced deep water formation. The deep-water [CO23-] and calcium carbonate mass accumulation rate in the SCS display markedly similar increases followed by recoveries to the pre-EAIE level during EAIE, which were probably caused by a shelf-basin shift of CaCO3 deposition and strengthened weathering due to a sea level fall within EAIE. The model results show that the ∼1‰ positive δ13C excursion during EAIE could be attributed to increased weathering of high-δ13C shelf carbonates and a terrestrial carbon reservoir expansion. The drawdown of atmospheric CO2 over the middle Miocene were probably caused by combined effects of increased shelf carbonate weathering, expanded land biosphere carbon storage and a sluggish deep Pacific meridional overturning circulation.

  6. Late Miocene volcanic sequences in northern Victoria Land, Antarctica: products of glaciovolcanic eruptions under different thermal regimes

    Science.gov (United States)

    Smellie, J. L.; Rocchi, S.; Armienti, P.

    2011-01-01

    Late Miocene (c. 13-5 Ma) volcanic sequences of the Hallett Volcanic Province (HVP) crop out along >250 km of western Ross Sea coast in northern Victoria Land. Eight primary volcanic and six sedimentary lithofacies have been identified, and they are organised into at least five different sequence architectures as a consequence of different combinations of eruptive and/or depositional conditions. The volcanoes were erupted in association with a Miocene glacial cover and the sequences are overwhelmingly glaciovolcanic. The commonest and most representative are products of mafic aa lava-fed deltas, a type of glaciovolcanic sequence that has not been described before. It is distinguished by (1) a subaerially emplaced relatively thin caprock of aa lavas lying on and passing down-dip into (2) a thicker association of chaotic to crudely bedded hyaloclastite breccias, water-chilled lava sheets and irregular lava masses, collectively called lobe-hyaloclastite. A second distinctive sequence type present is characterised by water-cooled lavas and associated sedimentary lithofacies (diamictite (probably glacigenic) and fluvial sands and gravels) similar to some mafic glaciovolcanic sheet-like sequences (see Smellie, Earth-Science Reviews, 74, 241-268, 2008), but including (for the first time) examples of likely sheet-like sequences with felsic compositions. Other sequence types in the HVP are minor and include tuff cones, cinder cones and a single ice-marginal lacustrine sequence. The glacial thermal regime varied from polar, characterised by sequences lacking glacial erosion, glacigenic sediments or evidence for free water, to temperate or sub-polar for sequences in which all of these features are conspicuously developed.

  7. Body-size structure of Central Iberian mammal fauna reveals semidesertic conditions during the middle Miocene Global Cooling Event.

    Directory of Open Access Journals (Sweden)

    Iris Menéndez

    Full Text Available We developed new quantitative palaeoclimatic inference models based on the body-size structure of mammal faunas from the Old World tropics and applied them to the Somosaguas fossil site (middle Miocene, central Iberian Peninsula. Twenty-six mammal species have been described at this site, including proboscideans, ungulates, carnivores, insectivores, lagomorphs and rodents. Our analyses were based on multivariate and bivariate regression models correlating climatic data and body-size structure of 63 modern mammal assemblages from Sub-Saharan Africa and the Indian subcontinent. The results showed an average temperature of the coldest month higher than 26°C for the Somosaguas fossil site, a mean annual thermal amplitude around 10°C, a drought length of 10 months, and an annual total precipitation greater than 200 mm per year, which are climate conditions typical of an ecotonal zone between the savanna and desert biomes. These results are congruent with the aridity peaks described over the middle Aragonian of Spain and particularly in the local biozone E, which includes Somosaguas. The aridity increase detected in this biozone is associated with the Middle Miocene Global Cooling Event. The environment of Somosaguas around 14 Ma was similar to the current environment in the Sahel region of North Africa, the Horn of Africa, the boundary area between the Kalahari and the Namib in Southern Africa, south-central Arabia, or eastern Pakistan and northwestern India. The distribution of modern vegetation in these regions follows a complex mosaic of plant communities, dominated by scattered xerophilous shrublands, semidesert grasslands, and vegetation linked to seasonal watercourses and ponds.

  8. Body-size structure of Central Iberian mammal fauna reveals semidesertic conditions during the middle Miocene Global Cooling Event.

    Science.gov (United States)

    Menéndez, Iris; Gómez Cano, Ana R; García Yelo, Blanca A; Domingo, Laura; Domingo, M Soledad; Cantalapiedra, Juan L; Blanco, Fernando; Hernández Fernández, Manuel

    2017-01-01

    We developed new quantitative palaeoclimatic inference models based on the body-size structure of mammal faunas from the Old World tropics and applied them to the Somosaguas fossil site (middle Miocene, central Iberian Peninsula). Twenty-six mammal species have been described at this site, including proboscideans, ungulates, carnivores, insectivores, lagomorphs and rodents. Our analyses were based on multivariate and bivariate regression models correlating climatic data and body-size structure of 63 modern mammal assemblages from Sub-Saharan Africa and the Indian subcontinent. The results showed an average temperature of the coldest month higher than 26°C for the Somosaguas fossil site, a mean annual thermal amplitude around 10°C, a drought length of 10 months, and an annual total precipitation greater than 200 mm per year, which are climate conditions typical of an ecotonal zone between the savanna and desert biomes. These results are congruent with the aridity peaks described over the middle Aragonian of Spain and particularly in the local biozone E, which includes Somosaguas. The aridity increase detected in this biozone is associated with the Middle Miocene Global Cooling Event. The environment of Somosaguas around 14 Ma was similar to the current environment in the Sahel region of North Africa, the Horn of Africa, the boundary area between the Kalahari and the Namib in Southern Africa, south-central Arabia, or eastern Pakistan and northwestern India. The distribution of modern vegetation in these regions follows a complex mosaic of plant communities, dominated by scattered xerophilous shrublands, semidesert grasslands, and vegetation linked to seasonal watercourses and ponds.

  9. Facies architecture of basin-margin units in time and space: Lower to Middle Miocene Sivas Basin, Turkey

    Science.gov (United States)

    Çiner, A.; Kosun, E.

    2003-04-01

    The Miocene Sivas Basin is located within a collision zone, forming one of the largest basins in Central Turkey that developed unconformably on a foundered Paleozoic-Mesozoic basement and Eocene-Oligocene deposits. The time and space relationships of sedimentary environments and depositional evolution of Lower to Middle Miocene rocks exposed between Zara and Hafik towns is studied. A 4 km thick continuous section is subdivided into the Agilkaya and Egribucak Formations. Each formation shows an overall fining upward trend and contains three members. Although a complete section is present at the western part (near Hafik) of the basin, to the east the uppermost two members (near Zara) are absent. The lower members of both formations are composed of fluvial sheet-sandstone and red mudstone that migrate laterally on a flood basin within a semi-arid fan system. In the Agilkaya Formation that crops out near Zara, alluvial fans composed of red-pink volcanic pebbles are also present. The middle members are composed of bedded to massive gypsum and red-green mudstone of a coastal and/or continental sabkha environment. While the massive gypsum beds reach several 10’s of m in Hafik area, near Zara, they are only few m thick and alternate with green mudstones. In Hafik, bedded gypsums are intercalated with lagoonal dolomitic limestone and bituminous shale in the Agilkaya Formation and with fluvial red-pink sandstone-red mudstone in the Egribucak Formation. The upper members are made up of fossiliferous mudstone and discontinuous sandy limestone beds with gutter casts, HCS, and 3-D ripples. They indicate storm-induced sedimentation in a shallow marine setting. The disorganized accumulations of ostreid and cerithiid shells, interpreted as coquina bars, are the products of storm generated reworking processes in brackish environments. Rapid vertical and horizontal facies changes and the facies associations in both formations reflect the locally subsiding nature of this molassic

  10. Late Miocene ignimbrites at the southern Puna-northern Sierras Pampeanas border (˜27°S): Stratigraphic correlation

    Science.gov (United States)

    Montero-López, Carolina; Guzmán, Silvina; Barrios, Fabiola

    2015-10-01

    New field observations and petrographic and geochemical data of pyroclastic deposits exposed along the Las Papas valley (border between southern Puna and northern Sierras Pampeanas, Argentina) and further north, lead us to propose a new stratigraphic correlation and classification of the late Miocene volcanism in this area. We redefine the Las Papas, Las Juntas, Aguada Alumbrera and Rosada ignimbrites and define the Agua Caliente and Del Medio ignimbrites. The whole set of ignimbrites are rhyolites and less frequently dacites of calc-alkaline affinity. In the present contribution we divide ignimbrites into the Agua Negra and Rincón groups, based mainly on their geochemical signature. The Agua Negra Group is formed by the Las Papas and Las Juntas ignimbrites, indurated and welded, lithic-rich, with crystal-poor pumices and crystal-rich matrix. The Rincón Group comprises the Agua Caliente, Aguada Alumbrera, Rosada and Del Medio ignimbrites, with variable welding degrees, lithic and crystal content. The greater enrichment of crystals in the matrix in comparison with the crystal content in pumices indicates significant elutriation during flow transport and thus volume estimations are to be considered lower bounds for the actual erupted volume. The total minimum estimated volume for the ignimbrites of the Agua Negra and Rincón groups is 2.8 km3 (2.3 km3 DRE). Field relationships and new analytical data indicate that the different acid ignimbrites that crop out in this small area are related to at least two different magma chambers. The widespread Quaternary volcanism in this area covers the older deposits, thus making it difficult to recognize the volcanic centers that produced these late Miocene ignimbrites.

  11. Stable isotope ecology of Miocene bovids from Northern Greece and the ape/monkey turnover in the Balkans.

    Science.gov (United States)

    Merceron, Gildas; Kostopoulos, Dimitris S; Bonis, Louis de; Fourel, François; Koufos, George D; Lécuyer, Christophe; Martineau, François

    2013-08-01

    Eurasia was home to a great radiation of hominoid primates during the Miocene. All were extinct by the end of the Miocene in Western Eurasia. Here, we investigate the hypothesis of climate and vegetation changes at a local scale when the cercopithecoid Mesopithecus replaced the hominoid Ouranopithecus along the Axios River, Greece. Because they are herbivorous and were much more abundant than primates, bovids are preferred to primates to study climate change in the Balkans as a cause of hominoid extinction. By measuring carbon stable isotope ratios of bovid enamel, we conclude that Ouranopithecus and Mesopithecus both evolved in pure C3 environments. However, the large range of δ(13)C values of apatite carbonate from bovids combined with their molar microwear and mesowear patterns preclude the presence of dense forested landscapes in northern Greece. Instead, these bovids evolved in rather open landscapes with abundant grasses in the herbaceous layer. Coldest monthly estimated temperatures were below 10°C and warmest monthly temperatures rose close to or above 20°C for the two time intervals. Oxygen isotope compositions of phosphate from bulk samples did not show significant differences between sites but did show between-species variation within each site. Different factors influence oxygen isotope composition in this context, including water provenience, feeding ecology, body mass, and rate of amelogenesis. We discuss this latter factor in regard to the high intra-tooth variations in δ(18)Op reflecting important amplitudes of seasonal variations in temperature. These estimations fit with paleobotanical data and differ slightly from estimations based on climate models. This study found no significant change in climate before and after the extinction of Ouranopithecus along the Axios River. However, strong seasonal variations with relatively cold winters were indicated, conditions quite usual for extant monkeys but unusual for great apes distributed today in

  12. Compositional variations and differential diagenesis in Miocene turbidites from the western coast of Mallorca (Balearic Islands, Spain)

    Science.gov (United States)

    Felder, Sonja; Westphal, Hildegard; Munnecke, Axel; Mateu Vicens, Guillem

    2010-05-01

    Compositional variations and differential diagenesis in Miocene turbidites from the western coast of Mallorca (Balearic Islands, Spain) Sonja Felder (1), Hildegard Westphal (1), Axel Munnecke (2), Guillem Mateu Vicens (1,3) (1) MARUM and Department of Geosciences, Universität Bremen, Leobener Straße, 28359 Bremen, Germany (2) GeoZentrum Nordbayern, Universität Erlangen-Nürnberg, Loewenichstr. 28, 91054 Erlangen, Germany (3) Dipartimento di Scienze della Terra, Università di Roma "La Sapienza", Ple Aldo 7 Moro, 5. I-00185 Roma, Italy Cyclic alternations of limestone and marl beds crop out along the western coast of the Island of Mallorca. This Miocene succession is traditionally interpreted to represent more weathering-resistant turbidites interlayered by softer hemipelagic background sediment. However, the cementation patterns that dominate the appearance of the outcrop do not always consistently follow sedimentary layering; locally the cemented beds are systematically oblique to the sedimentary layers. Compositional studies demonstrate that differences in non-carbonate fraction, carbonate concentration and fossil content (e.g. foraminiferal assemblages) trace sedimentary bedding, regardless the diagenetic style. Limestone versus marl lithology, in contrast, is defined by the diagenetic style, tight cementation by calcite cements in the limestones versus low porosity and compaction in the marls. The reason for this striking pattern of diagenetic bedding cross-cutting sedimentary layers is assumed to be related to tectonic fracturing, opening pathways for diagenetic fluids. This example cautions the straight-forward interpretation of limestone-marl alternations as direct witnesses of environmental or climatic variations.

  13. Extension of the astronomically calibrated (polarity) time scale to the Miocene/Pliocene boundary

    NARCIS (Netherlands)

    Hilgen, F.J.

    1991-01-01

    The early Pleistocene to late Pliocene astronormcally calibrated time scale of Shackleton et al. [1] and Hllgen [2] is extended to the Mlocene/Pllocene boundary This is done by correlating the detailed record of CaCO 3 cycles in the Trubl and the lower part of the overlying Narbone Formation

  14. Strong climate coupling of terrestrial and marine environments in the Miocene of northwest Europe

    NARCIS (Netherlands)

    Donders, T.H.; Weijers, J.W.H.; Munsterman, D.K.; Kloosterboer-van Hoeve, M.L.; Buckles, L.K.; Pancost, R.D.; Schouten, S.; Sinninghe Damsté, J.S.; Brinkhuis, H.

    2009-01-01

    A palynological and organic geochemical record from a shallow marine paleoenvironmental setting in SE Netherlands documents the coupled marine and terrestrial climate evolution from the late Burdigalian (∼ 17 Ma) through the early Zanclean (∼ 4.5 Ma). Proxy climate records show several coeval

  15. Changes in Eocene-Miocene shallow marine carbonate factories along the tropical SE Circum-Caribbean responded to major regional and global environmental and tectonic events

    Science.gov (United States)

    Silva-Tamayo, Juan Carlos

    2015-04-01

    Changes in the factory of Cenozoic tropical marine carbonates have been for long attributed to major variations on climatic and environmental conditions. Although important changes on the factories of Cenozoic Caribbean carbonates seem to have followed global climatic and environmental changes, the regional impact of such changes on the factories of shallow marine carbonate along the Caribbean is not well established. Moreover, the influence of transpressional tectonics on the occurrence, distribution and stratigraphy of shallow marine carbonate factories along this area is far from being well understood. Here we report detailed stratigraphic, petrographic and Sr-isotope chemostratigraphic information of several Eocene-Miocene carbonate successions deposited along the equatorial/tropical SE Circum-Caribbean (Colombia and Panama) from which we further assess the influence of changing environmental conditions, transtentional tectonics and sea level change on the development of the shallow marine carbonate factories. Our results suggest that during the Eocene-early Oligocene interval, a period of predominant high atmospheric pCO2, coralline algae constitute the principal carbonate builders of shallow marine carbonate successions along the SE Circum-Caribbean. Detailed stratigraphic and paragenetic analyses suggest the developed of laterally continuous red algae calcareous build-ups along outer-rimmed carbonate platforms. The predominance of coralline red algae over corals on the shallow marine carbonate factories was likely related to high sea surface temperatures and high turbidity. The occurrence of such build-ups was likely controlled by pronounce changes in the basin paleotopography, i.e. the occurrence of basement highs and lows, resulting from local transpressional tectonics. The occurrence of these calcareous red algae dominated factories was also controlled by diachronic opening of different sedimentary basins along the SE Circum Caribbean resulting from

  16. Can Pallars i Llobateres: A new hominoid-bearing locality from the late Miocene of the Vallès-Penedès Basin (NE Iberian Peninsula).

    Science.gov (United States)

    Alba, David M; Casanovas-Vilar, Isaac; Furió, Marc; García-Paredes, Israel; Angelone, Chiara; Jovells-Vaqué, Sílvia; Luján, Àngel H; Almécija, Sergio; Moyà-Solà, Salvador

    2018-05-18

    In the Iberian Peninsula, Miocene apes (Hominoidea) are generally rare and mostly restricted to the Vallès-Penedès Basin. Here we report a new hominoid maxillary fragment with M 2 from this basin. It was surface-collected in March 2017 from the site of Can Pallars i Llobateres (CPL, Sant Quirze del Vallès), where fossil apes had not been previously recorded. The locality of provenance (CPL-M), which has delivered no further fossil remains, is located very close (ca. 50 m) to previously known CPL outcrops, and not very far (ca. 500 m in NW direction) from the classical hominoid-bearing locality of Can Poncic 1. Here we describe the new fossil and, based on the size and proportions of the M 2 , justify its taxonomic attribution to Hispanopithecus cf. laietanus, a species previously recorded from several Vallesian sites of the Vallès-Penedès Basin. Based on the associated mammalian fauna from CPL, we also provide a biochronological dating and a paleoenvironmental reconstruction for the site. The associated fauna enables an unambiguous correlation to the Cricetulodon hartenbergeri - Progonomys hispanicus interval local subzone, with an estimated age of 9.98-9.73 Ma (late Vallesian, MN10). Therefore, CPL-M is roughly coeval with the Hispanopithecus laietanus-bearing localities of Can Llobateres 1 and Can Feu 1, and minimally older than those of La Tarumba 1 and Can Llobateres 2. In contrast, CPL-M is younger than the early Vallesian (MN9) localities of Can Poncic 1 (the type locality of Hispanopithecus crusafonti) as well as Polinyà 2 (Gabarró) and Estació Depuradora d'Aigües Residuals-Riu Ripoll 13, where Hispanopithecus sp. is recorded. The associated fauna from CPL indicates a densely forested and humid paleoenvironment with nearby freshwater. This supports the view that Hispanopithecus might have been restricted to dense wetland forests soon before its extinction during the late Vallesian, due to progressive climatic deterioration. Coupled with the

  17. Chewing through the Miocene: an examination of the feeding musculature in the ground sloth Hapalops from South America (Mammalia: Pilosa [v1; ref status: indexed, http://f1000r.es/2pu

    Directory of Open Access Journals (Sweden)

    Virginia L. Naples

    2014-04-01

    Full Text Available 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.

  18. Plastome phylogeny and early diversification of Brassicaceae.

    Science.gov (United States)

    Guo, Xinyi; Liu, Jianquan; Hao, Guoqian; Zhang, Lei; Mao, Kangshan; Wang, Xiaojuan; Zhang, Dan; Ma, Tao; Hu, Quanjun; Al-Shehbaz, Ihsan A; Koch, Marcus A

    2017-02-16

    The family Brassicaceae encompasses diverse species, many of which have high scientific and economic importance. Early diversifications and phylogenetic relationships between major lineages or clades remain unclear. Here we re-investigate Brassicaceae phylogeny with complete plastomes from 51 species representing all four lineages or 5 of 6 major clades (A, B, C, E and F) as identified in earlier studies. Bayesian and maximum likelihood phylogenetic analyses using a partitioned supermatrix of 77 protein coding genes resulted in nearly identical tree topologies exemplified by highly supported relationships between clades. All four lineages were well identified and interrelationships between them were resolved. The previously defined Clade C was found to be paraphyletic (the genus Megadenia formed a separate lineage), while the remaining clades were monophyletic. Clade E (lineage III) was sister to clades B + C rather than to all core Brassicaceae (clades A + B + C or lineages I + II), as suggested by a previous transcriptome study. Molecular dating based on plastome phylogeny supported the origin of major lineages or clades between late Oligocene and early Miocene, and the following radiative diversification across the family took place within a short timescale. In addition, gene losses in the plastomes occurred multiple times during the evolutionary diversification of the family. Plastome phylogeny illustrates the early diversification of cruciferous species. This phylogeny will facilitate our further understanding of evolution and adaptation of numerous species in the model family Brassicaceae.

  19. 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

  20. Investigation of Laramide Deformation in North-Central New Mexico and Its Role in Guiding Miocene Extension

    Science.gov (United States)

    Freer, C. M.; Hamilton, J.; Murphy, M. A.

    2009-12-01

    North-trending Laramide age dextral faults in New Mexico help to explain shortening features along the northern margin of the Colorado Plateau. However, a palinspastic reconstruction of aeromagnetic anomalies that are cut by these dextral faults, do not explain shortening in the Tusas-Brazos uplift suggesting that the geometry of the Laramide structural system needs to be reassessed. We conducted geologic mapping and structural analysis of a series of Laramide asymmetric anticlines as well as Miocene normal faults between the Tusas-Brazos and Nacimento uplift to assess alternative models describing Laramide deformation. The kinematics of Laramide features in Northern New Mexico has been interpreted in multiple conflicting models. One model suggests that Laramide deformation in this region was characterized by several (4-6) large N-S striking faults with net dextral slip estimates ranging from ~55-170km. A second model suggests a hybrid of the two models above, suggesting a counter-clockwise rotation in the maximum shortening direction from E-W to NNE-SSW. The anticlines investigated lie between the north-trending east-vergent Tusas-Brazos uplift and the west-vergent Nacimento uplift. They form an en echelon set of km-scale folds that trend ~N40E and verge to the east and west. The estimated shortening direction from conjugate fractures and lineations are close to agreeing on an orientation of N30E, with conjugates at N10W and N50E. Fracture data throughout the specific areas are not easily explained by east-west extension during Rio Grande rifting but instead correlate to Laramide deformation. The regional fracture pattern suggests a vertically oriented σ2 advocating for a strike-slip deformation regime. Also apparent from the fracture pattern is a possible change in σ1 direction, with both E-W and NNE-SSW possible, though timing is uncertain. Mineral stretching lineations in Proterozoic rocks of the Laramide-uplifted Tusas Mountains display an average NE

  1. Petrographic and geochemical analyisis for determination of provenance of the Slovenj Gradec Miocene Basin fill (Western Central Paratethys)

    Science.gov (United States)

    Ivančič, Kristina; Trajanova, Mirka; Skaberne, Dragomir; Šmuc, Andrej

    2017-04-01

    The Slovenj Gradec Basin (SGB) is located in northern Slovenia between eastern margin of the Northern Karavanke and the western Pohorje Mts. Structurally, it belongs to Eastern Alps. It is filled with Miocene clastic sediments. Modal composition of sandstones was determined on thin sections by point-counter and presented with the QFL and QmFLt diagrams. Their geochemical composition was determined by classical method and by Inductively Coupled Plasma-Mass Spectrometry. Based on petrography, sedimentary fill of the SGB consists mostly of lithic grains and quartz, derived from metamorphic and carbonate rocks. Locally, fragments of granitoids occur. Binder consists of carbonate, subordinately quartz cement, and carbonate matrix. Recycled orogen (lithic and transitional recycled) provenance of the grains was determined. Geochemical composition shows that: - Sandstones from the SGB belong to the fields of shale, wacke, litharenite, arkose and subarkose (Pettijohn, 1972). - In the ternary diagram of weathering trends (cf. Nesbitt & Young 1984), the samples group near the CaO+Na2OAl2O3 conjunctive. Calculated minimum CIA (Fedo et al., 1995) is 40.06, indicating that the source rocks were not subjected to considerable weathering. - According to discriminant function (cf. Roser & Korsch, 1988) all samples from SGB originate from quartzose sedimentary rocks. - For determination of tectonic setting of source rocks (Verma & Armstrong-Altrin, 2013) the studied samples plot in the field of collision zone. - In the multidimensional discriminant function diagram for the discrimination of active and passive margin after Verma and Armstrong (2016), the samples plot into the field of passive margin. The data indicate that source rocks of the SGB sedimentary fill were derived from Eastern Alps and Southern Alps. It is suggested that SGB was detached from the Styrian and Mura-Zala Basins in the course of the Pohorje Mts. oblique transpressive uplift during the late Miocene to Pliocene

  2. [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.)]: Miocene squat lobsters (Decapoda, Anomura, Galatheoidea) of the Central Paratethys – a review, with description of a new species of Munidopsis

    NARCIS (Netherlands)

    Hyžný, M.; Gašparič, R.; Robins, C.M.; Schlögl, J.

    2014-01-01

    All squat lobsters of the families Galatheidae, Munididae and Munidopsidae from the Miocene of the Central Paratethys are reviewed taxonomically. Based on additional observations emended diagnoses are provided for Agononida cerovensis and Galathea weinfurteri, from the Lower and Middle Miocene,

  3. [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.)]: Miocene squat lobsters (Decapoda, Anomura, Galatheoidea) of the Central Paratethys – a review, with description of a new species of Munidopsis: erratum

    NARCIS (Netherlands)

    Hyžný, M.; Gašparič, R.; Robins, C.M.; Schlögl, J.

    2015-01-01

    All squat lobsters of the families Galatheidae, Munididae and Munidopsidae from the Miocene of the Central Paratethys are reviewed taxonomically. Based on additional observations emended diagnoses are provided for Agononida cerovensis and Galathea weinfurteri, from the Lower and Middle Miocene,

  4. Study of fossil wo