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Sample records for miocene chado-libyan bioprovince

  1. Anthracothere dental anatomy reveals a late Miocene Chado-Libyan bioprovince.

    PubMed

    Lihoreau, Fabrice; Boisserie, Jean-Renaud; Viriot, Laurent; Coppens, Yves; Likius, Andossa; Mackaye, Hassane Taisso; Tafforeau, Paul; Vignaud, Patrick; Brunet, Michel

    2006-06-01

    Recent discovery of an abundant and diverse late Miocene fauna at Toros-Ménalla (Chad, central Africa) by the Mission Paléoanthropologique Franco-Tchadienne provides a unique opportunity to examine African faunal and hominid evolution relative to the early phases of the Saharan arid belt. This study presents evidence from an African Miocene anthracotheriid Libycosaurus, particularly well documented at Toros-Ménalla. Its remains reveal a large semiaquatic mammal that evolved an autapomorphic upper fifth premolar (extremely rare in Cenozoic mammals). The extra tooth appeared approximately 12 million years ago, probably in a small northern African population isolated by climate-driven fragmentation and alteration of the environments inhabited by these anthracotheriids [Flower, B. P. & Kennett, J. P. (1994) Palaeogeogr. Palaeoclimatol. Palaeoecol. 108, 537-555 and Zachos, J., Pagani, M., Sloan, L., Thomas, E. & Billups, K. (2001) Science 292, 686-693]. The semiaquatic niche of Libycosaurus, combined with the distribution and relationships of its late Miocene species, indicates that by the end of the Miocene, wet environments connected the Lake Chad Basin to the Libyan Sirt Basin, across what is now the Sahara desert.

  2. Before the flood: Miocene otoliths from eastern Amazon Pirabas Formation reveal a Caribbean-type fish fauna

    NASA Astrophysics Data System (ADS)

    Aguilera, Orangel; Schwarzhans, Werner; Moraes-Santos, Heloísa; Nepomuceno, Aguinaldo

    2014-12-01

    The Pirabas Formation of Early Miocene age represents the final stage of the central western Atlantic carbonate platform in northeastern South America, predating the emplacement of the Amazon delta system. The otolith-based fossil fish fauna is represented by 38 species typical of a shallow marine environment. A total of 18 species are described new to science from the families Congridae, Batrachoididae, Bythitidae, Sciaenidae and Paralichthyidae. The fish fauna was associated with high benthic and planktic primary productivity including seagrass meadows, calcareous algae and suspension-feeders. The break of todays shallow marine bioprovince at the Amazonas delta mouth is not evident from the fish fauna of the Pirabas Fm., which shows good correlation with the Gatunian/proto-Caribbean bioprovince known from an only slightly younger time window in Trinidad and Venezuela. Differences observed to those Early Miocene faunal associations are interpreted to be mainly due to stratigraphic and geographic and not environmental differences. We postulate that the emergence of the Amazonas river mouth close to its present day location has terminated the carbonate cycle of the Pirabas Fm. and pushed back northwards a certain proportion of the fish fauna here described.

  3. Miocene Coralline algae

    SciTech Connect

    Bosence, D.W.J.

    1988-01-01

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

  4. Antarctic Miocene Climate

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Fossils from Antarctic Miocene terrestrial deposits, coupled with stratigraphic, geochemical and paleontological data from marine boreholes, provide new insights into the climatic history of the continent. During the Miocene, ice caps coalesced to form ice sheets and vegetated surfaces gave way to barren expanses. The cryospheric changes especially have global climatic implications. The fossil data consists of diatoms, pollen and spores, and macroscopic remains of plants, ostracods, insects, molluscs and a fish. Plant fossils include wood and leaves of Nothofagus (southern beech), seeds of several vascular plants, including Ranunculus (buttercup), Hippuris (mare's-tail) and Myriophyllum (watermilfoil), megaspores of Isoetes (quillwort), and moss species. The insect chitin consists of larval head capsules of Chironomidae (midges) and exoskeletal parts of Coleoptera (beetles). The molluscs include freshwater gastropods and bivalves. The majority of these taxa are likely descendants of taxa that had survived on the continent from the Paleogene or earlier. Even though early Miocene glaciations may have been large, the climate was never cold enough to cause the extinction of the biota, which probably survived in coastal refugia. Early Miocene (c. 20 Ma) macrofossils from the McMurdo Dry Valleys (77°S) support palynological interpretations from the Cape Roberts and ANDRILL marine records that the upland vegetation was a shrub tundra. Mean summer temperature (MST) in the uplands was c. 6°C and possibly higher at the coast. The climate was wet, supporting mires and lakes. By the mid-Miocene, even though the climate continued to be wet. MST was c. 4°C which was too cold to support Nothofagus and most vascular plant species. Stratigraphic evidence indicates that the time between the Early and Mid-Miocene was a time of repeated ice advances and retreats of small glaciers originating from ice caps. At c. 14 Ma there appears to have been a modal shift in climate to

  5. Miocene Antarctic Terrestrial Realm

    NASA Astrophysics Data System (ADS)

    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

  6. Miocene reef corals: A review

    SciTech Connect

    Frost, S.H.

    1988-01-01

    Tectonic blockage in the Middle East of westward-flowing Tethys surface circulation during the latest Oligocene led to creation in the earliest Miocene of endemic Mediterranean, Western Atlantic-Caribbean, and Indo-Pacific realms. A great reduction in reef coral diversity from 60-80 Oligocene species to 25-35 early Miocene species occurred in the Western Atlantic-Caribbean and Mediterranean areas accompanied by a decrease in reef growth. A slower and less drastic change apparently occurred in the Indo-Pacific area. Early Miocene reef corals of the Western Atlantic-Caribbean comprise a transition between the cosmopolitan Oligocene fauna and its endemic mid-Miocene to modern counterpart. Although early Miocene reefs were dominated by a Porites-Montastrea assemblage, eastward flow of Pacific circulation brought with it ''exotic'' corals such as Coscinaraea and Pseudocolumnastrea. Also, many cosmopolitan genera persisted from the Oligocene. During the middle to late Miocene, most of the species still living on Holocene reefs evolved. As the Mediterranean basin became more restricted, there was a slow decline in reef corals from 20 - 25 species in the Aquitainian to less than five species in the Messinian. Eustatic lowstand led to the extinction of reef-building corals in the late Messinian. In the Indo-Pacific, Neogene evolution of reef corals was conservative. Excluding the Acroporidae and Seriatoporidae, most Holocene framework species had evolved by the middle Miocene. Interplay between regional tectonics and eustatic sea level changes led to extensive development of middle to late Miocene pinnacle reefs over the southwestern Pacific.

  7. An overview of Miocene reefs

    SciTech Connect

    Jordan, C.F. Jr. ); Colgan, M.W. ); Frost, S.H. ); Glenn, E.C. ); Bosence, D. ); Esteban, M. )

    1990-05-01

    Miocene reefs lived approximately within the latitudes of 27{degree}S to 48{degree}N compared with 25{degree}S and 32{degree}N for Holocene reefs. This expansion of reef-growing environments was the result of warm Miocene climates, aided by a eustatic sea level rise and tectonic styles that provided numerous foundations for reef development. The majority of Miocene reefs are found in three main areas: (1) Southeast Asia and the western Pacific, (2) the Mediterranean-Middle East, and (3) Middle America and the Caribbean. These regions, with their distinctive suites of coral and foramineral species, formed three biological provinces; respectively, they are the Indo-Pacific, Tethyan, and Western Atlantic provinces. Miocene reefs in Southeast Asia occur in several foreland basins as patch reef complexes on paleohighs and as barrier reefs in back-arc basins. Those reefs in the Mediterranean occur as fringing reefs, middle-shelf patch reefs, or as barrier reefs on the edges of tectonic blocks associated with Alpine thrust belts. Most reefs in the Caribbean grew on isolated open-ocean highs of volcanic origin. Miocene reefs display a diversity of framework types: (1) coral-encrusting, red algal boundstones with diverse coral faunas, (2) branching coral-encrusting, red algal boundstones with a limited Poritid fauna, (3) encrusting red algal boundstones. Barrier reef systems are especially rich in encrusting red algae and robust corals; grainstones are common as interbedded sediment. Patch reef complexes, however, display muddy carbonate textures, may have less diverse coral faunas, and commonly have larger foraminifera. The global distribution of Miocene reefs is important because (1) it provides insight into a paleoclimatic view of the earth during a major greenhouse stage and (2) Miocene buildups, such as the Arun (EUR of 14 tcf) and Bima fields (EUR of about 100 MMBO), are exploration targets.

  8. Middle Miocene dispersals of apes.

    PubMed

    Andrews, Peter; Kelley, Jay

    2007-01-01

    The earliest record of fossil apes outside Africa is in the latest early Miocene of Turkey and eastern Europe. There were at least 2, and perhaps 4, species of ape, which were found associated with subtropical mixed environments of forest and more open woodland. Postcranial morphology is similar to that of early Miocene primates and indicates mainly generalized arboreal quadrupedal behaviours similar to those of less specialized New World monkeys such as Cebus. Robust jaws and thick enamelled teeth indicate a hard fruit diet. The 2 best known species of fossil ape are known from the site of Paşalar in Turkey. They have almost identical molar and jaw morphology. Molar morphology is also similar to that of specimens from Germany and Slovakia, but there are significant differences in the anterior teeth of the 2 Paşalar species. The more common species, Griphopithecus alpani, shares mainly primitive characters with early and middle Miocene apes in Africa, and it is most similar phenetically to Equatorius africanus from Maboko Island and Kipsaramon. The second species is assigned to a new species of Kenyapithecus, an African genus from Fort Ternan in Kenya, on the basis of a number of shared derived characters of the anterior dentition, and it is considered likely that there is a phylogenetic link between them. The African sites all date from the middle Miocene, similar in age to the Turkish and European ones, and the earliest emigration of apes from Africa coincides with the closure of the Tethys Sea preceding the Langhian transgression. Environments indicated for the African sites are mixtures of seasonal woodlands with some forest vegetation. The postcrania of both African taxa again indicate generalized arboreal adaptation but lacking specialized arboreal function. This middle Miocene radiation of both African and non-African apes was preceded by a radiation of arboreal catarrhine primates in the early Miocene, among which were the earliest apes. The earliest

  9. Miocene reefs in western Mediterranean

    SciTech Connect

    Esteban, M.

    1988-01-01

    Coral reefs were particularly abundant and well developed during the late Tortonian and Messinian in southeastern Spain, the Balearic Islands, Italy, Sicily, Algeria, and Morocco. These reefs occurred just before and during the deposition of the thick Messinian evaporite units in the basinal areas and disappeared completely from Mediteranean during the early Pliocene. Most of the coral reefs are fringing terrigenous coastal fan complexes with very small lagoons and show progradation of less than 2 km. Some of the reefs occur on, or are intercalated with, Neogene volcanics or Messinian evaporites. Barrier-reef complexes are less common, have extensive lagoons behind them, and show complex progradational geometries more than 10 km wide. Excellent outcrops allow detailed reconstruction of paleogeography and sea level changes. Progradation predominated during phases of relative sea level drops and stillsands, while significant retrogradation occurred during sea level rises. The coral reef wall framework is commonly less than 20 m thick and is dominated by Porites and, locally, Tarbellastrae. Older Miocene reefs are less well developed, but show greater diversity of corals and reef organisms. Younger Miocene reef complexes occurring in open ocean settings are formed by only one branching coral genus (Porites or, locally, Tarbellastraea) with branching colonies up to 7 m high. Halimeda sands are particularly abundant in the upper reef slopes with occasional intercalations of red algae pavements that most likely coincide with episodes of terrigenous influx.

  10. Miocene benthic foraminiferal isotope records: A synthesis

    USGS Publications Warehouse

    Savin, S.M.; Douglas, R.G.; Keller, G.; Killingley, J.S.; Shaughnessy, L.; Sommer, M.A.; Vincent, E.; Woodruff, F.

    1981-01-01

    18O 16O and 13C 12C ratios of Miocene benthic foraminifera from a number of Atlantic, Pacific and Indian Ocean DSDP sites (71, 77B, 206, 208, 238, 279, 289, 296, 329, 357 and 366A) have been compiled. These provide a rather detailed history of Miocene deep water especially in the Pacific Ocean. Bottom-water temperatures rose during the early Miocene and then declined rapidly during the middle Miocene. This decline was accompanied by an increase in Antarctic glaciation. Late Miocene bottom temperatures and Antarctic ice volumes are inferred to be similar to today's, but exhibited some fluctuation. The early Miocene ocean was less thermally stratified at intermediate and abyssal depths while the late Miocene deep ocean had a thermal structure generally similar to the modern ocean. Foraminiferal carbon isotope ratios at most of the sites varied quasi-sympathetically throughout the Miocene. These variations must reflect comparable variations in the mean 13C 12C of marine HCO3-. However, the causes of such variations are not yet clear. ?? 1981.

  11. Marine mammals from the Miocene of Panama

    NASA Astrophysics Data System (ADS)

    Uhen, Mark D.; Coates, Anthony G.; Jaramillo, Carlos A.; Montes, Camilo; Pimiento, Catalina; Rincon, Aldo; Strong, Nikki; Velez-Juarbe, Jorge

    2010-12-01

    Panama has produced an abundance of Neogene marine fossils both invertebrate (mollusks, corals, microfossils etc.) and vertebrate (fish, land mammals etc.), but marine mammals have not been previously reported. Here we describe a cetacean thoracic vertebra from the late Miocene Tobabe Formation, a partial cetacean rib from the late Miocene Gatun Formation, and a sirenian caudal vertebra and rib fragments from the early Miocene Culebra Formation. These finds suggest that Central America may yet provide additional fossil marine mammal specimens that will help us to understand the evolution, and particularly the biogeography of these groups.

  12. Panafrican distribution of Lower Miocene Hominoidea

    NASA Astrophysics Data System (ADS)

    Senut, Brigitte; Pickford, Martin; Wessels, Dudley

    1997-11-01

    Palaeontological survey of the Neogene littoral deposits of the Namaqualand coastal strip, Northern Cape Province, South Africa, has resulted in the collection of the first Lower Miocene faunas from South Africa. Among the mammals from Ryskop and Hondeklip Bay is a gorilla-sized hominoid. This discovery greatly increases the geographic range of early Miocene hominoids and suggests that even at this remote epoch, the superfamily had a Panafrican distribution.

  13. Miocene reefs of Dominican Republic

    SciTech Connect

    Evans, C.C.

    1988-01-01

    The reefs are overlain by conglomeratic strata. The stratigraphic setting of these reefs suggests that they have developed along the stalled portions of rapidly prograding fan deltas. Thickets and layers of coral debris are found seaward and stratigraphically above the well-developed reef. The matrix sediments are exclusively fine-grained sand to mud, and the fauna are suggestive of more open shelf conditions. In thickets, branched (porites spp., Pocillopora spp.), small massive (Montastrea spp., Siderastrea spp.), and foliose or plate like (Agaricia spp.) corals are found upright in the muddy sediment. Similarities in coral species and areal proximity suggest that thickets are the source of most layers of coralline debris. The association of coral debris with graded bedding and cross-bedding suggests that coral debris has been reworked by storms. The growth of corals and development of coral reefs in the Miocene-Pliocene Yaque Group is limited only by opportunities created by the slowing of siliciclastic sedimentation. Soft, muddy, terrigenous substrates and a continuing supply of terrigenous mud exert only a limited, indirect effect on reef growth.

  14. The late early Miocene Sabine River

    SciTech Connect

    Manning, E. )

    1990-09-01

    Work on a new late early Miocene vertebrate fossil site, in a paleochannel deposit of the upper Carnahan Bayou Member of the lower Fleming Formation, has revealed unexpected data on the course and nature of the Sabine River of that time. Screen washing for smaller vertebrate remains at the site, just west of the Sabine River in Newton County, central eastern Texas, has resulted in the recovery of early Permian, Early Cretaceous, Late Cretaceous (Maestrichtian), Paleocene/Eocene, late Eocene, and Oligocene/Miocene fossils, in addition to the main early Miocene fauna. The reworked fossils, as well as distinctive mineral grains, show that the late early Miocene Sabine River was connected to the Texas/Oklahoma/Arkansas boundary section of the Red River, as well as to rivers draining the southern Ouachita Mountains. These rivers must have joined the Texas/Louisiana boundary section of the Sabine River somewhere in northwest Louisiana at that time. This suggests that the Louisiana section of the present Red River pirated the Texas/Oklahoma/Arkansas boundary section of the river some time after the early Miocene. The preservation of recognizable fossils transported hundreds of miles in a large river itself requires explanation. It is speculated here that the late early Miocene Sabine River incorporated a large amount of the then recently deposited volcanic ash from the Trans-Pecos Volcanic Field. Montmorillonite clay from the altered volcanic ash would have made the river very turbid, which could have allowed coarse sand-sized particles to be carried in the suspended load of the river, rather than in its bed load (where they would have been destroyed by the rolling chert gravel). Additional evidence for such long-distance fossil transport in the late early Miocene rivers of the western Gulf Coastal Plain comes from the abundant Cretaceous fossils of the upper Oakville Formation of southeast Texas and the Siphonina davisi zone of the southeast Texas subsurface.

  15. Miocene reef carbonates of Mariana Islands

    SciTech Connect

    Siegrist, H.G. Jr.

    1988-02-01

    Miocene carbonates in the southern Mariana Islands are impressive for their lithologic diversity, thicknesses (over 250 m), and geographic extent (> 20% combined outcrop coverage over four major high islands: Guam, Rota, Tinian and Saipan). Sections are dominated either by lagoonal algal-foraminiferal wackestones and mudstones with locally abundant high-energy shelly-skeletal facies, or by rubbly to muddy, fore-reef-to-bank deposits of packstones and grainstones with highly diverse and variable biogenic clasts. Fresh to deeply weathered volcaniclastic material may comprise at least 80% of some high-energy fore-reef facies, whereas lagoonal and bank deposits usually contain less than 0.5% terrigenous material. Surprisingly, the Miocene in the Marianas lacks almost completely any reef-core facies. Several poorly developed coral-rich mounds on Saipan and localized laminated red algal buildups on Guam appear to constitute the extant reef-wall facies in the Miocene. The lack of buildups may be a matter of differential survival; it may result from headland erosion and benching associated with emergence of narrow reef tracts as has been postulated by others for south Guam. Alternatively, the authors are proposing that Miocene bathymetry and the volume of terrigenous influx militated against significant reef core formation. Radiometric age dating of these reef carbonates has proven unsuccessful because pervasive diagenesis has transformed the entire Miocene section into low-magnesium calcite with minor and occasional dolomite. Freshwater phreatic diagenesis accounts for the principal porosity variation and trace element distribution.

  16. The Miocene Ocean: Paleoceanography and Biogeography

    NASA Astrophysics Data System (ADS)

    Schlanger, Seymour O.

    This volume brings together research carried out within the Cenozoic Paleoceanography Project (CENOP), a goal of which was to generate paleoceanographic reconstructions of the Miocene Epoch, 24 to 5 Ma. On the basis of stable isotope and quantitative micropaleontological studies, the authors have related these data bases to parameters and processes of the Miocene Ocean, including paleogeography, stratigraphy, circulation, water mass distributions, temperature variability, vertical water mass structure, biogeography, and biotic evolution.That these authors attained their goal is attested to by the quality and scope of the 14 chapters presented in this valuable treatise. The Miocene Epoch was chosen because it was in this interval of time that major ice sheets became a permanent feature of Earth's surface. The presentation of this stunning amount of data and interpretation is very well organized for the researcher as well as for the students and professors who will surely use the book as a basis for seminars.

  17. Miocene precursors to Great Barrier Reef

    SciTech Connect

    Davies, P.J.; Symonds, P.A.; Feary, D.A.; Pigram, C.

    1988-01-01

    Huge reefs of Miocene age are present in the Gulf of Papua north of the present-day Great Barrier Reef and to the east on the Marion and Queensland Plateaus. In the Gulf of Papua, Miocene barrier reefs formed the northern forerunner of the Great Barrier Reef, extending for many hundreds of kilometers along the eastern and northern margin of the Australian craton within a developing foreland basin. Barrier reefs, slope pinnacle reefs, and platform reefs are seen in seismic sections and drill holes. Leeside talus deposits testify to the high energy impinging on the eastern margin of these Miocene reefs. The Queensland Plateau is a marginal plateau east of the central Great Barrier Reef and separated from it by a rift trough. Miocene reefs occupied an area of about 50,000 km/sup 2/ and grew on salt-controlled highs on the western margin of the plateau and on a regional basement high extending from the platform interior to its southern margin. Reef growth has continued to the present day, although two major contractions in the area covered by reefs occurred during the Miocene. The Marion Plateau is present directly east of the Great Barrier Reef and during the Micoene formed a 30,000-km/sup 2/ platform with barrier reefs along its northern margin and huge platform reefs and laggons on the platform interior. These reefs grew on a flat peneplained surface, the whole area forming a large shallow epicontinental sea. In all three areas, the middle Miocene formed the acme of reef expansion in the region.

  18. Miocene reef carbonates of Mariana Islands

    SciTech Connect

    Siegrist, H.G. Jr.

    1988-01-01

    Miocene carbonates in the southern Mariana Islands are impressive for their lithologic diversity, thicknesses (over 250 m), and geographic extend (>20% combined outcrop coverage over four major high islands: Guam, Rota, Tinian and Saipan). Sections are dominated either by lagoonal algal-foraminiferal wackestones and mudstones with locally abundant high-energy shelly-skeletal facies, or by rubbly to muddy, fore-reef-to-bank deposits of packstones and grainstones with highly diverse and variable biogenic clasts. Fresh to deeply weathered volcaniclastic material may comprise at least 80% of some high-energy fore-reef facies, whereas lagoonal and bank deposits usually contain less than 0.5% terrigenous material. Surprisingly, the Miocene in the Marianas lacks almost completely any reef-core facies. Several poorly developed coral-rich mounds on Saipan and localized laminated red algal buildups on Guam appear to constitute the extant reef-wall facies in the Miocene. The lack of buildups may be a matter of differential survival; it may result from headland erosion and benching associated with emergency of narrow reef tracts as has been postulated by others for south Guam. Radiometric age dating of these reef carbonates has proven unsuccessful because pervasive diagenesis has transformed the entire Miocene section into low-magnesium calcite with minor and occasional dolomite. Freshwater phreatic diagenesis accounts for the principal porosity variation and trace element distribution.

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

    NASA Astrophysics Data System (ADS)

    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.

  20. El Nino-like events during Miocene

    SciTech Connect

    Casey, R.E.; Nelson, C.O.; Weinheimer, A.L.; Oeth, P.A.; Swanson, R.J.

    1988-03-01

    El Nino-like events have been recorded from the Miocene laminated siliceous facies of the Monterey Formation. These El Nino-like Miocene events are compared to El Nino events recorded from Holocene varved sediments deposited within the anoxic Santa Barbara basin. Strong El Nino events can be recognized from Holocene Santa Barbara basin sediments by increases in radiolarian flux to the sea floor during those events. For the last 100-plus years, frequency of strong El Ninos has been on the order of one extremely strong event about every 100 years, and one easily recognizable event about every 18 years. Frequencies in the laminated (varved) Miocene range from about every 4-5 years to over 20 years. The higher frequencies occur within generally warm intervals and the lower frequencies within generally cold intervals. Perhaps the frequencies of these events may, in fact, be an important indicator in determining whether the intervals were cold or warm. Reconstructions of the paleo-California Current system during El Nino-like periods have been made for the west coast from the Gulf of California to northern California. Strong El Nino-like events occurred 5.5 and 8 Ma, and a strong anti-El Nino-like event occurred at about 6.5 Ma. Evidence from the 5.5 and 8 Ma events combined with other evidence suggests that modern El Ninos, similar to today's, were initiated at 5.5 Ma or earlier.

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

    USGS Publications Warehouse

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

    2009-01-01

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

  2. Miocene mollusks from the Simojovel area in Chiapas, southwestern Mexico

    NASA Astrophysics Data System (ADS)

    del Carmen Perrilliat, María; Vega, Francisco J.; Coutiño, Marco A.

    2010-11-01

    The fauna of gastropods and bivalves from the amber-bearing lithostratigraphic units of the Simojovel area, Chiapas is reported, including the description of two new species and one subspecies: Turbinella maya new species, Melongena corona tzeltal new subspecies and Agladrillia ( Eumetadrillia) vermeiji new species. Stratigraphic affinities of the previously described species suggest an Early Miocene age for the Mazantic Shale, and a Middle Miocene age for the overlying Balumtum Sandstone. One specimen of gastropod, with a relatively large piece of amber attached to the adapertural part of the shell is representative for an Early Miocene age and estuarine paleoenvironmental interpretation for the Mazantic Shale. Mollusca, Miocene, Chiapas, Amber, Mexico.

  3. The dietary adaptations of European Miocene catarrhines.

    PubMed Central

    Ungar, P S; Kay, R F

    1995-01-01

    European Miocene "apes" have been known for nearly a century and a half but their phylogenetic significance is only now becoming apparent with the recent discovery of many relatively complete remains. Some appear to be close in time and morphology to the last common ancestor of modern great apes and humans. The current study is an attempt to reconstruct the diets of these fossils on the basis of quantitative data. Results suggest that these primates varied more greatly in their diets than modern apes, with adaptations ranging from hard-object feeding to soft-object frugivory to folivory. PMID:7777533

  4. Mammal extinctions in the Vallesian (Upper Miocene)

    NASA Astrophysics Data System (ADS)

    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.

  5. A molecular organic carbon isotope record of miocene climate changes.

    PubMed

    Schoell, M; Schouten, S; Damsté, J S; de Leeuw, J W; Summons, R E

    1994-02-25

    The difference in carbon-13 ((13)C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in (18)O (delta(18)O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes (delta(13)C = 25.4 +/- 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C(35) hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing (13)C concentrations in Middle and Late Miocene samples (delta(13)C = -29.5 to -31.5 per mil), consistent with the Middle Miocene formation of a carbon dioxide-rich cold water mass at the base of the photic zone.

  6. Miocene vertebrates and North Florida shorelines

    USGS Publications Warehouse

    Olsen, S.J.

    1968-01-01

    Vertebrate fossils from ten localities, spread across northern Florida, give evidence of shorelines and deltas that have previously been established on geologic evidence or invertebrates alone. Terrestrial mammal remains, in association with shallow-water forms, indicate a deltaic assemblage and in several instances specific animals suggest restricted water depths at the time of sediment deposition. Fortunately diagnostic fragments of Miocene horses, Merychippus and Parahippus, are present in these beds, allowing for a rather close age evaluation of these sediments. Adequate fossil material has been collected from these localities to suggest the past environment and ecological conditions for the forms represented. By utilizing a suggested course of experiments with stream table apparatus it is possible to use the orientation of the fossil vertebrate remains as aids in determining past conditions of sediment accumulation. ?? 1968.

  7. Geographic and stratigraphic distribution of Miocene palynomorphs in north Idaho

    NASA Astrophysics Data System (ADS)

    Jorstad, R. B.

    1983-02-01

    Acetolysis of Early and Middle Miocene sediments from the Clarkia, Idaho, area yielded 3,477 palynomorphs representing 37 taxa from eighteen samples for assemblage analysis. Relative pollen frequency data from various study sites suggest an older Coniferae-Mixed Dicotyledoneae-Pteridophyte Palynomorph Assemblage Zone, and a younger Fagaceae-TCT-Platanus Pollen Assemblage Zone. Two pollen based chronostratigraphic stages are proposed for at least part of the Miocene epoch: an older Clarkian Stage, and a younger Oviattian Stage. Palynomorph stratigraphic range charts document the youngest regional occurrence of Lygodium. Two palynomorph taxa are possible index fossils in the Pacific Northwest: (1) Sigmopollis (Incertae Sedis) for the Oligocene, and (2) Elaeagnus (Elaeagnaceae) for the Late Oligocene-Early Miocene. Palynostratigraphic and assemblage analyses of the fossil bearing sediments confirms prior models for the infilling of Miocene Clarkia Lake, and a regional change from a warm temperature to temperate climate.

  8. Wet Winters in the Eastern Siberian Arctic during the Miocene

    NASA Astrophysics Data System (ADS)

    Schubert, B.; Jahren, H.; Davydov, S. P.

    2015-12-01

    Eastern Siberia (a 7.3 million km2 area, similar to Australia in size) features numerous plant fossil localities, many with spectacularly preserved Neogene fossils (e.g., Baekovo and Nekkeiveem; Khapchan-Timmerdekh; Mamontova Gora). Although these sites have been described in full using classical methods (e.g., Baranova and Grinenko, 1989; Baranova et al., 1970; Biske, 1970; Dorofeev, 1969; Grinenko et al., 1989; Nikitin, 2006, 2007), geochemical proxy techniques have not yet been applied. Here we report the first stable isotope analyses of fossil wood from northeastern Siberia: 512 high-resolution intra-ring analyses of carbon isotopes (IRA-δ13C) in 6 specimens of Miocene wood from the Finish Creek site, located near Cherskiy, Sakha Republic, Russia. Using our model for reconstructing the ratio of summer to winter precipitation (Ps/Pw) from IRA-δ13C (Schubert and Jahren, 2011, GCA), we quantified the seasonal precipitation in far northeastern Siberia (~69 oN) during the Miocene. Although the median value for Ps/Pw during the Miocene was similar to today (Ps/Pw = ~2), we observed much greater variability in Ps/Pw during the Miocene than today. Specifically, years with Ps/Pw < 1/2 occurred ~4 times more frequently during the Miocene than today. When taken with independent estimates of mean annual precipitation based on nearest living relatives (581 to 1206 mm; Popova et al., 2012), our Miocene values for Ps/Pw suggest at least 2.8 times greater winter precipitation during the Miocene relative to today, and at least 5.5 times greater winter precipitation than today in ~10% of years sampled (6-month winter precipitation averages ~70 mm/yr today). Our result differentiates the Siberian Arctic Miocene from the Canadian Arctic Eocene which featured wet summers in the Eocene Arctic of Canada using similar methods, highlighting spatial and temporal variability in the Arctic paleoclimate record of the middle Cenozoic.

  9. Otavipithecus namibiensis, first Miocene hominoid from southern Africa.

    PubMed

    Conroy, G C; Pickford, M; Senut, B; Van Couvering, J; Mein, P

    1992-03-12

    We report here the discovery of a Miocene hominoid from Berg Aukas, Namibia, the first known from the African continent south of equatorial East Africa. This represents a major range extension of Miocene Hominoidea in Africa to latitude 20 degrees S. The holotype, a right mandibular corpus preserving the crowns of the P4-M3, partial crown and root of the P3, partial root of the canine, alveoli for all four incisors, and partial alveolus for the left canine, was found during paleontological explorations of karst-fill breccias in the Otavi region of northern Namibia. The mandible has unique characteristics that differentiate it from other middle Miocene hominoids of Africa and Eurasia and represents the only fossil evidence documenting a pre-australopithecine stage of hominoid evolution in southern Africa. Faunal analyses indicate that the breccia block containing the specimen accumulated during the latter part of the middle Miocene, about 13 +/- 1 Myr. Fauna from other breccia blocks at Berg Aukas are of diverse ages, including the earlier part of the middle Miocene, the upper Miocene, Plio-Pleistocene and Holocene. PMID:1545864

  10. The late Miocene Panama isthmian strait

    NASA Astrophysics Data System (ADS)

    Collins, Laurel S.; Coates, Anthony G.; Berggren, William A.; Aubry, Marie-Pierre; Zhang, Jijun

    1996-08-01

    Miocene sediments of the Caribbean Gatun and Chagres formations, Panama Canal basin, were deposited within an archipelagic strait that connected Caribbean and Pacific waters. Shallow-water (˜ 25 m) benthic foraminifera of the Gatun Formation have a strong Caribbean affinity, indicating that a significant interoceanic, biogeographic barrier had formed at ˜ 8 Ma. However, benthic foraminifera of the overlying Chagres Formation are bathyal and markedly Pacific in affinity, indicating that at ˜ 6 Ma, waters of the Panama isthmian strait deepened to ˜ 200 500 m and Pacific bathyal waters flowed into the Caribbean. The Chagres Formation crops out at the Caribbean entrance to the Panama Canal in a large wedge of cross-laminated sandstone and coquina. The cross-laminations and coarse grain size indicate high-energy currents atypical of bathyal settings. We infer that a jet of the Pacific North Equatorial Countercurrent Equatorial Undercurrent passed through the Panama isthmian strait to deposit these sediments on the Caribbean side. This later entry of Pacific taxa into the Caribbean had no apparent effect on the subsequent composition of Caribbean faunas.

  11. Allopolyploidy, diversification, and the Miocene grassland expansion

    PubMed Central

    Estep, Matt C.; McKain, Michael R.; Vela Diaz, Dilys; Zhong, Jinshun; Hodge, John G.; Hodkinson, Trevor R.; Layton, Daniel J.; Malcomber, Simon T.; Pasquet, Rémy; Kellogg, Elizabeth A.

    2014-01-01

    The role of polyploidy, particularly allopolyploidy, in plant diversification is a subject of debate. Whole-genome duplications precede the origins of many major clades (e.g., angiosperms, Brassicaceae, Poaceae), suggesting that polyploidy drives diversification. However, theoretical arguments and empirical studies suggest that polyploid lineages may actually have lower speciation rates and higher extinction rates than diploid lineages. We focus here on the grass tribe Andropogoneae, an economically and ecologically important group of C4 species with a high frequency of polyploids. A phylogeny was constructed for ca. 10% of the species of the clade, based on sequences of four concatenated low-copy nuclear loci. Genetic allopolyploidy was documented using the characteristic pattern of double-labeled gene trees. At least 32% of the species sampled are the result of genetic allopolyploidy and result from 28 distinct tetraploidy events plus an additional six hexaploidy events. This number is a minimum, and the actual frequency could be considerably higher. The parental genomes of most Andropogoneae polyploids diverged in the Late Miocene coincident with the expansion of the major C4 grasslands that dominate the earth today. The well-documented whole-genome duplication in Zea mays ssp. mays occurred after the divergence of Zea and Sorghum. We find no evidence that polyploidization is followed by an increase in net diversification rate; nonetheless, allopolyploidy itself is a major mode of speciation. PMID:25288748

  12. Calcareous Nannofossil Evolution Vs. Climatic Evolution In The Miocene

    NASA Astrophysics Data System (ADS)

    Raffi, I.; Backman, J.; Ciummelli, M.

    2013-12-01

    Miocene times were characterized by major changes in ocean circulation and global climate that were driven by a complex set of factors operating on tectonic, orbital and suborbital timescales (Zachos et al., 2001). This time dependent development of Miocene paleo-environmental conditions is reflected in the distribution and evolutionary patterns, often expressed in terms of biostratigraphic resolution, among the dominant sediment-forming oceanic plankton groups (Kennett & Srinivasan, 1983; Baldauf & Barron, 1990; Perch-Nielsen, 1985) including calcareous nannofossils. In the Miocene through Pleistocene interval, calcareous nannofossil evolutionary appearances or extinctions provide eight biostratigraphically useful biohorizons between 23 Ma and 14 Ma, giving an average rate of 1.5 biohorizon per million years. In the next following eight million years (14-5 Ma), the number of biohorizons are 29 (3.6 biohorizons/million years), representing well over a doubling of the rate of taxonomic evolution among open ocean calcareous nannofossils compared with that of the early half of the Miocene. This observation demonstrates that a distinct evolutionary response to climatic evolution throughout the Miocene, specifically to changing conditions in the photic zone of the middle and late Miocene oceans. This assumption is supported by the behavior of some nannofossil groups, in particular by the representatives of the genus Discoaster, a key group that gives nearly half (14 of 29) of biohorizons in the younger half of the Miocene. The Discoaster's environmental distribution and abundance may provide some information about the complex interaction between climatic evolution and biotic evolution in the plankton realm.

  13. Miocene sequence biostratigraphy of the northern Gulf of Mexico

    SciTech Connect

    Jiang, M.M. )

    1993-09-01

    The Miocene floral pulse model of Jiang and Watkins is revised. The new revision suggests that the Gulf of Mexico Miocene floral pulses, corresponding to the traditional foraminiferal tops, are transgression surfaces of the fourth-order sequences. These pulses show diverse magnitudes and when they are plotted on a depth (or time) tract, their relative magnitudes show an orderly wavy pattern comparable to the Haq et al.'s third-order cycles in the Miocene. After iterative comparison, the condensed intervals of these Miocene third-order sequences have been determined as, in descending order, Cyclammina 3, the second Cibicides carstensi, the second Textularia W, Cristellaria I, Robulus 43, Discorbis B, the third Marginulina A, and Textularia panamensis (= fauna unit II). The least prominent pulses suggesting the third-order cycle highstands (or shelf-margin wedges) are suggested as, in descending order, Textularia X, Bolivina thalmanni, Globorotalia fohsi robusta, Bigenerina humblei, Cibicides opima, Saracenaria schencki, Marginulina A (= second Robulus chambersi), and Siphonina davisi. Redeposited Cretaceous nanno species are an important component in the Gulf of Mexico middle and lower Miocene. Significant concentrations of these species are found primarily in the third-order cycle highstands, one exception being the Marginulina A third-order cycle highstand that in the High Island and West Cameron areas contained only rare redeposited Cretaceous nannos.

  14. A molecular organic carbon isotope record of miocene climate changes

    SciTech Connect

    Schoell, M. ); Schouten, S.; Sinninghe Damste', J.S.; Leeuw, J.W. de ); Summons, R.E. )

    1994-02-25

    The difference in carbon-13 ([sup 13]C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in [sup 18]O ([delta][sup 18]O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes ([delta][sup 13]C = 25.4 [+-] 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C[sub 35] hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing [sup 13]C concentrations in Middle and Late Miocene samples ([delta][sup 13]C = 29.5 to [minus]31.5 per mil), consistent with the Middle Miocene formation of a carbon dioxide-rich cold water mass at the base of the photic zone.

  15. Miocene-Oligocene sequence stratigraphy of the Malay Basin

    SciTech Connect

    Lovell, R.; Elias, M.R. ); Hill, R.E.; Feeley, M.H. )

    1994-07-01

    The Malay Basin has experienced extension of the Eocene ( ) through Oligocene, sag in the early Miocene, and compression in the middle Miocene through Pliocene-Pleistocene. The interaction of structurally induced and glacial-eustatic accommodation changes has resulted in complex, interrelated play elements, including multiple reservoirs, diverse nonmarine sources, discontinuous migration pathways, and thin seals. Extensional subbasins were filled with braided streams, associated coastal plain, lacustrine deltas, and thick lake shales (groups M-K). This initial rift fill comprises an overall second order progradational cycle punctuated by 3rd-order cycles. These 3rd-order cycles are capped by thick, source-rich, lacustrine shale packages. The lower Miocene section (groups I and J) consists of progradational to aggradational fluvial to tidally-dominated estuarine sands. Hydrocarbons are generated from interbedded coals and other coal-related lithologies.

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

    NASA Astrophysics Data System (ADS)

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

    2009-08-01

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

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

    SciTech Connect

    Bachman, S.B.

    1988-03-01

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

  18. Interpretation of Samburupithecus, an upper Miocene hominoid from Kenya

    NASA Astrophysics Data System (ADS)

    Pickford, Martin; Ishida, Hidemi

    1998-02-01

    Samburupithecus, an extinct great ape from upper Miocene (9.5 Ma) deposits in Kenya, is compared with other fossil and extant hominoids. It possesses features which are derived in comparison with Proconsul and other Lower and Middle Miocene hominoids, but it has none of the derived features which characterize the Eurasian large apes. It possesses characters which indicate that its closest relationships lie with the AAH clade (extant African apes and man). Within this clade it is closest dentally to primitive hominids such as Praeanthropus.

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

    PubMed Central

    Lu, Xiaoyu; Ni, Xijun; Li, Lüzhou; Li, Qiang

    2016-01-01

    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. PMID:27486803

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

    PubMed

    López-Antoñanzas, Raquel; Gutkin, Vitaly; Rabinovich, Rivka; Calvo, Ran; Grossman, Aryeh

    2016-01-01

    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.

  1. The lithostratigraphy of Miocene series from Tunisia, revisited

    NASA Astrophysics Data System (ADS)

    Mannaï-Tayech, Beya

    2009-06-01

    In the Mediterranean region, the Miocene is a rather particular tectonic, eustatic and climatic epoch. In Tunisia, the complex distribution of the sedimentary sequences has been controlled by the interaction of these factors. These sequences are composed mostly of silici-clastic packages filling usually rim-syncline, graben and half-graben basins. In the absence of a solid biostratigraphic framework, the dating and correlation of certain formations are not yet clearly perceived. In spite of the availability of some elements of dating (planktonic foraminifera, vertebrates), the solution remains as a whole unclear. The question thus remains as to the significance of the frequency and occurrence of discontinuities, and consequently of those hiatuses between Miocene Formations. Thus, in the light of the recent palynologic, sedimentological and vertebrate biostratigraphical data, a new reading of the paleogeography and paleoenvironment of the Miocene from Tunisia is essential. In this work, the results of multi-field studies supported by the compilation of the literature, enable sensible discussion of the proposed ages, analyze the depositional environments, and concomitantly support correlations between the Miocene Formations recognized to the South-East of the Eastern Dorsale of Tunisia. It is demonstrated that the Beglia and Saouaf Formations are partially equivalent rather than being superposed, as it has been previously surmised. A new, marine formation, the "Kef Ettir Formation", is also proposed.

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

    PubMed Central

    López-Antoñanzas, Raquel; Gutkin, Vitaly; Rabinovich, Rivka; Calvo, Ran; Grossman, Aryeh

    2016-01-01

    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. PMID:27049960

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

    PubMed

    López-Antoñanzas, Raquel; Gutkin, Vitaly; Rabinovich, Rivka; Calvo, Ran; Grossman, Aryeh

    2016-01-01

    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. PMID:27049960

  4. The early to mid-Miocene environment of Antarctica

    NASA Astrophysics Data System (ADS)

    Ashworth, A. C.; Lewis, A.

    2012-12-01

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

  5. A new pitheciin primate from the middle Miocene of Argentina.

    PubMed

    Kay, R F; Johnson, D; Meldrum, D J

    1998-01-01

    We report here a new fossil primate from the middle Miocene of Argentina. The material consists of isolated teeth, mandibular fragments, and a talus. The fossils were collected in the Collón Cura formation at Cañadón del Tordillo in Neuquén Province. An age of 15.71 +/- 0.07 Ma has been reported for the Pilcaniyeu Ignimbrite, which lies just below the paleosols in which the fossils were found. This material is thus the youngest occurrence of fossil primates in Argentina (hitherto documented in the Santacrucian and older land mammal ages) but still is older than the middle Miocene platyrrhine primates from La Venta, Colombia, in particular the pitheciins Nuciruptor and Cebupithecia. The material is recognized as a new genus and species of Pitheciinae, Propithecia neuquenensis. The mesiodistally compressed, high-crowned incisors are specialized and similar to species in the tribe Pithecini and to the nonpitheciin Soriacebus (early Miocene, Patagonia). We rule out a phylogenetic relationship to the latter because of differences in molar morphology. Propithecia does, however, fit well into the pattern of pitheciin evolution, being more derived than the middle Miocene pitheciin Nuciruptor but not as much as another middle Miocene taxon, Cebupithecia. As such, this makes Propithecia the oldest taxon that can be confidently placed within this modern New World monkey subfamily. By analogy with the molar structures and diets of extant platyrrhines, Propithecia has a molar structure consistent with a variety of low-fiber diets ranging from fruit and gum to seeds. Its incisors suggest seed-eating in much the same way as extant pitheciins, like Pithecia. The talus resembles that of Callicebus, suggesting arboreal quadrupedal locomotion. PMID:9702279

  6. Droughts in the Miocene of the Black Sea region

    NASA Astrophysics Data System (ADS)

    Vasiliev, Iuliana; Reichart, Gert-Jan; Grothe, Arjen; Krijgsman, Wout

    2016-04-01

    Since Miocene the Black Sea has been highly sensitive to fluctuations in the hydrological cycle. These fluctuations were principally determined by Black Sea's recurrently restricted connections to the Open Ocean and by its specific paleogeographic location between the dry Mediterranean domain and more humid higher northern latitudes. To determine the nature of changes in the hydrological budget of the Black Sea occurring during the late Miocene we use compound-specific hydrogen isotope ratios on terrestrial and aquatic biomarkers extracted from two different locations: 1) the sedimentary succession of Zhelezniy Rog land based section of Taman in Russia and 2) the deep sea sedimentary succession recovered in 1975 from the Black Sea (DSDP 42B, Hole 380A). The carbon and hydrogen isotopic composition of n-alkanes as well as alkenones and palynology indicate large environmental changes in the Black Sea and/or in the sources of the water entering the Black Sea during the late Miocene. The hydrogen isotopes of alkenones, showing an enrichment of more than 80 ‰ at the end of the Miocene, imply a major shift in basin hydrology, possibly resulting in severely increased salinity. These changes in hydrogen isotopic composition of the alkenones concur both with sharp shifts in reconstructed sea surface temperature and palynological assemblages. Two intervals with negative water budget were identified, most likely caused by enhanced evaporation. The older and longer dry/evaporative phase predates the Maeotian/Pontian boundary (regional stages) at ~6.1 Ma. The younger negative water budget phase is partly coeval to the Messinian salinity crisis of Mediterranean. Both shifts to highly evaporative conditions are recorded in both Taman Peninsula (Russia) and DSDP 42B 380A locations. These recurrent dryer phases were, most likely, the result of important hydrological changes over a significantly larger area around the Black Sea area during the upper Miocene.

  7. A new pitheciin primate from the middle Miocene of Argentina.

    PubMed

    Kay, R F; Johnson, D; Meldrum, D J

    1998-01-01

    We report here a new fossil primate from the middle Miocene of Argentina. The material consists of isolated teeth, mandibular fragments, and a talus. The fossils were collected in the Collón Cura formation at Cañadón del Tordillo in Neuquén Province. An age of 15.71 +/- 0.07 Ma has been reported for the Pilcaniyeu Ignimbrite, which lies just below the paleosols in which the fossils were found. This material is thus the youngest occurrence of fossil primates in Argentina (hitherto documented in the Santacrucian and older land mammal ages) but still is older than the middle Miocene platyrrhine primates from La Venta, Colombia, in particular the pitheciins Nuciruptor and Cebupithecia. The material is recognized as a new genus and species of Pitheciinae, Propithecia neuquenensis. The mesiodistally compressed, high-crowned incisors are specialized and similar to species in the tribe Pithecini and to the nonpitheciin Soriacebus (early Miocene, Patagonia). We rule out a phylogenetic relationship to the latter because of differences in molar morphology. Propithecia does, however, fit well into the pattern of pitheciin evolution, being more derived than the middle Miocene pitheciin Nuciruptor but not as much as another middle Miocene taxon, Cebupithecia. As such, this makes Propithecia the oldest taxon that can be confidently placed within this modern New World monkey subfamily. By analogy with the molar structures and diets of extant platyrrhines, Propithecia has a molar structure consistent with a variety of low-fiber diets ranging from fruit and gum to seeds. Its incisors suggest seed-eating in much the same way as extant pitheciins, like Pithecia. The talus resembles that of Callicebus, suggesting arboreal quadrupedal locomotion.

  8. A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids.

    PubMed

    Tanaka, Yoshihiro; Kohno, Naoki

    2015-01-01

    The modern walrus, Odobenus rosmarus, is specialized and only extant member of the family Odobenidae. They were much more diversified in the past, and at least 16 genera and 20 species of fossil walruses have been known. Although their diversity increased in the late Miocene and Pliocene (around 8-2 Million years ago), older records are poorly known. A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0-9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses. Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features. Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific. This rapid diversification of the archaic odobenids occurred with a combination of marine regression and transgression, which provided geological isolation among the common ancestors of extinct odobenids. PMID:26244784

  9. A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids

    PubMed Central

    Tanaka, Yoshihiro; Kohno, Naoki

    2015-01-01

    The modern walrus, Odobenus rosmarus, is specialized and only extant member of the family Odobenidae. They were much more diversified in the past, and at least 16 genera and 20 species of fossil walruses have been known. Although their diversity increased in the late Miocene and Pliocene (around 8–2 Million years ago), older records are poorly known. A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0–9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses. Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features. Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific. This rapid diversification of the archaic odobenids occurred with a combination of marine regression and transgression, which provided geological isolation among the common ancestors of extinct odobenids. PMID:26244784

  10. A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids.

    PubMed

    Tanaka, Yoshihiro; Kohno, Naoki

    2015-01-01

    The modern walrus, Odobenus rosmarus, is specialized and only extant member of the family Odobenidae. They were much more diversified in the past, and at least 16 genera and 20 species of fossil walruses have been known. Although their diversity increased in the late Miocene and Pliocene (around 8-2 Million years ago), older records are poorly known. A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0-9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses. Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features. Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific. This rapid diversification of the archaic odobenids occurred with a combination of marine regression and transgression, which provided geological isolation among the common ancestors of extinct odobenids.

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

    NASA Astrophysics Data System (ADS)

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

    2001-05-01

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

  12. New primate genus from the Miocene of Argentina.

    PubMed

    Tejedor, Marcelo F; Tauber, Adán A; Rosenberger, Alfred L; Swisher, Carl C; Palacios, María E

    2006-04-01

    Killikaike blakei is a new genus and species of anthropoid from the late Early Miocene of southeastern Argentina based on the most pristine fossil platyrrhine skull and dentition known so far. It is part of the New World platyrrhine clade (Family Cebidae; Subfamily Cebinae) including modern squirrel (Saimiri) and capuchin monkeys (Cebus) and their fossil relatives known from Early to Middle Miocene and subrecent periods. Living cebines are relatively large-brained, adroit predatory foragers and live within complex social groups, and wild capuchins exhibit a wide range of behaviors associated with enhanced intelligence. We show that K. blakei lacks diagnostic derived characteristics of the lower face and premolar dentition that are shared by modern cebines, but its strongly vaulted frontal bone and capacious anterior cranial fossa indicate the early evolution of an enlarged forebrain.

  13. Upper Miocene reef complex of Mallorca, Balearic Islands, Spain

    SciTech Connect

    Pomar, L.

    1988-02-01

    The late Tortonian-Messinian coral reef platform of south Mallorca onlaps a folded middle late Miocene carbonate platform on which progradation of up to 20 km occurs. Vertical sea cliffs (up to 100 m high) superbly show the last 5 km of this progradation and complement the numerous water-well cores from the island interior. The Mallorca reef presents the most complete facies zonation of the Miocene reefs of the western Mediterranean. The reef wall framework is up to 20 m thick and shows (1) erosional reef flat with reef breccia and small corals; (2) spur-and-grove zone with large, massive corals; (3) deep buttresses and pinnacles with terraces of branching corals; and (4) deep reef wall with flat, laminar coral colonies, branching red algae, and Halimeda sands.

  14. Late Miocene biogeography and paleoclimatology of the central North Atlantic

    USGS Publications Warehouse

    Poore, R.Z.

    1981-01-01

    Quantitative analyses of planktonic foraminiferal assemblages from Deep Sea Drilling Project (DSDP) Holes 334 and 410 demonstrate that subpolar and subtropical faunal provinces existed in the North Atlantic during the late Miocene. Climatic oscillations are clearly recorded in Hole 410 by variations in abundance of the Neogloboquadrina subpolar assemblage. These climatic oscillations have a period of about 1 m.y. Higher frequency oscillations with a periodicity of one to several hundred thousand years are evident from about 6.5 to 7.5 m.y. and are probably present throughout the entire late Miocene. A revised age of 7.0 m.y. is proposed for the first occurrence of the calcareous nannofossil Amaurolithus primus (the Amaurolithus datum). ?? 1981.

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

    NASA Astrophysics Data System (ADS)

    Fox, L. R.; Wade, B.; Holbourn, A. E.; Leng, M. J.

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  17. Miocene Oaks from Eastern Zhejiang, China and their Paleoenvironmental Significance

    NASA Astrophysics Data System (ADS)

    Jia, Hui; Ferguson, David

    2015-04-01

    The intertrappean fluvial-lacustrine beds belonging to the Upper Miocene Shengxian Formation in eastern China contain many exquisitely preserved plant fossils, e.g., leaves, fruits and seeds as well as plentiful pollen. The Fagaceae is the dominant taxon represented by 5 genera and 15 species, four of which belong to Quercus subgenus Cyclobalanopsis. Quercus species (oaks) are highly sensitive to environmental changes. The correlation between climate and trichome base density of Quercus glauca and Quercus delavayi of subg. Cyclobalanopsis, which are the NLRs of two fossil species, Quercus paraglauca and Quercus aff. delavayi, indicates that the trichome base density of Quercus glauca is comprehensively affected by various climate factors, but most influenced by solar radiation and latitude. The trichome base parametrics of Quercus paraglauca and the comparison of epidermal cell characteristics between Quercus paraglauca and Quercus aff. delavayi and their NLR species of subg. Cyclobalanopsis, show that the climate was warmer and more humid in the late Miocene than that of today in eastern Zhejiang, China. A study of the stomatal index of Quercus glauca and Quercus delavayi, collected in different years, demonstrates that they are very sensitive to the variation of atmospheric CO2 concentration. By comparing the stomatal ratio between the two fossil species and their NLRs, the paleoatmospheric CO2 concentration in the late Miocene is reconstructed as ca. 400 ppmv, i.e. higher than the present natural CO2 concentration eliminating the industrial influence.

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

    PubMed Central

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

    2016-01-01

    Australia has a fossil record of penguins reaching back to the Eocene, yet today is inhabited by just one breeding species, the little penguin Eudyptula minor. The description of recently collected penguin fossils from the re-dated upper Miocene Port Campbell Limestone of Portland (Victoria), in addition to reanalysis of previously described material, has allowed the Cenozoic history of penguins in Australia to be placed into a global context for the first time. Australian pre-Quaternary fossil penguins represent stem taxa phylogenetically disparate from each other and E. minor, implying multiple dispersals and extinctions. Late Eocene penguins from Australia are closest to contemporaneous taxa in Antarctica, New Zealand and South America. Given current material, the Miocene Australian fossil penguin fauna is apparently unique in harbouring ‘giant penguins’ after they went extinct elsewhere; and including stem taxa until at least 6 Ma, by which time crown penguins dominated elsewhere in the southern hemisphere. Separation of Australia from Antarctica during the Palaeogene, and its subsequent drift north, appears to have been a major event in Australian penguin biogeography. Increasing isolation through the Cenozoic may have limited penguin dispersal to Australia from outside the Australasian region, until intensification of the eastwards-flowing Antarctic Circumpolar Current in the mid-Miocene established a potential new dispersal vector to Australia. PMID:27115739

  19. Pre-transform early Miocene extension in western California

    SciTech Connect

    Tennyson, M.E. )

    1989-09-01

    Earliest Miocene (20-24 Ma) faulting and volcanism were widespread in western California, including the San Joaquin-La Honda basin, Coast Ranges, and Transverse Ranges. Evidence for strike slip on faults of this age is lacing. Their arrangement on a pre-San Andreas restoration suggest continuity with early Miocene extended terranes in eastern California and southwestern Arizona. Deformation was probably not an effect of transform or triple-junction-migration tectonics, because it was synchronous over 300 km of latitude and there is no direct evidence for a transform boundary until late in early Miocene time. Magnetic anomalies in the eastern Pacific permit an interpretation that a spreading ridge supplied a still-active subduction zone with young oceanic crust until sometime after 20 Ma. If so, extension evidently took place in an arc-related setting. A transform regime probably formed about 18 Ma, when most basins underwent episodes of deepening or uplift, strike-slip faults became active, and rotation of the western Transverse Ranges block began.

  20. Miocene reef platforms from northwestern Tuamotu Islands, central Pacific

    SciTech Connect

    Montaggioni, L.F.; Mnhn-Ephe, A.

    1988-02-01

    Reef deposits of Miocene age occur on several northwestern Tuamotu atolls as either pointed residual and scattered reliefs through the Holocene reef sequence (Mataiva, Rangiroa, Tikehau, Kaukura) or elevated atoll-shaped platforms (Makatea). Throughout the region considered, the depositional/diagenetic history of Miocene reefs can be reconstructed as follows. During early Miocene times (e-f range-biozones), reef platforms developed on top of older carbonate banks, capping a midplate volcanic ridge of early Tertiary age. More than 100 m thick, these platforms displayed concentrically zoned environments of deposition: a peripheral subemergent rim composed of coralgalforaminiferal boundstones, and a very shallow central area in which foraminiferal and molluscan fine sands and muds were subhorizontally deposited. Local evidence of internal unconformity surfaces and subaerially produced features indicates that periods of relative emergency occurred as the reef piles grew upward. The ultimate stage of platform development is believed to have been a complete upfilling of the back-reef areas and subsequent emergence. Correlatively, a freshwater lens would have been formed close to the surface level of each of the so-formed islands. Dolomitization may have been initiated in the marine water/freshwater phreatic mixing zone. During lowstands, severe meteoric alteration affected emergent carbonate deposits, forming incipient cavity systems; the usual atoll morphology is considered to have been initiated at this time (presumably middle Micoene).

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

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

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

    PubMed Central

    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

  3. Estimates of CO2 since the mid-Miocene

    NASA Astrophysics Data System (ADS)

    Stoll, Heather

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    PubMed

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

    2016-01-01

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

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

    PubMed

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

    2016-01-01

    Australia has a fossil record of penguins reaching back to the Eocene, yet today is inhabited by just one breeding species, the little penguin Eudyptula minor. The description of recently collected penguin fossils from the re-dated upper Miocene Port Campbell Limestone of Portland (Victoria), in addition to reanalysis of previously described material, has allowed the Cenozoic history of penguins in Australia to be placed into a global context for the first time. Australian pre-Quaternary fossil penguins represent stem taxa phylogenetically disparate from each other and E. minor, implying multiple dispersals and extinctions. Late Eocene penguins from Australia are closest to contemporaneous taxa in Antarctica, New Zealand and South America. Given current material, the Miocene Australian fossil penguin fauna is apparently unique in harbouring 'giant penguins' after they went extinct elsewhere; and including stem taxa until at least 6 Ma, by which time crown penguins dominated elsewhere in the southern hemisphere. Separation of Australia from Antarctica during the Palaeogene, and its subsequent drift north, appears to have been a major event in Australian penguin biogeography. Increasing isolation through the Cenozoic may have limited penguin dispersal to Australia from outside the Australasian region, until intensification of the eastwards-flowing Antarctic Circumpolar Current in the mid-Miocene established a potential new dispersal vector to Australia. PMID:27115739

  7. Oligocene to Miocene carbon isotope cycles and abyssal circulation changes

    NASA Astrophysics Data System (ADS)

    Miller, Kenneth G.; Fairbanks, Richard G.

    Three cycles of δ13C occurred in Oligocene to Miocene benthic and planktonic foraminifera at western North Atlantic Sites 558 and 563. Intervals of high δ13C occurred at about 35-33 Ma (early Oligocene), 25-22 Ma (across the Oligocene/Miocene boundary), and 18-14 Ma (across the early/middle Miocene boundary). Similar carbon isotopic fluctuations have been measured in benthic and planktonic foraminifera from the Atlantic, Pacific, and Indian oceans, suggesting that these cycles represent global changes in the δ13C of mean ocean water. The average duration of the carbon cycles is 50 times greater than the residence time of carbon in the oceans. Therefore, the mechanism controlling these cycles must be tied to changes in the input ratio of organic carbon to carbonate from weathering rocks or to changes in the output ratio of organic carbon to carbonate in marine sediments. Following a strategy used to study modern and Pleistocene oceans, benthic foraminiferal δ13C differences between the Atlantic and Pacific are used to infer Oligocene through Miocene abyssal circulation changes. The Atlantic was most enriched in l3C relative to the Pacific from about 36-33 Ma (early Oligocene) and 26-10 Ma (late Oligocene to late Miocene). We interpret this as indicating supply of nutrient-depleted bottom water in the North Atlantic, perhaps analogous to modern North Atlantic Deep Water. High benthic foraminiferal δ13O values at about 36-35 Ma, 31-28 Ma, 25-24 Ma, and younger than 15 Ma indicate the presence of ice sheets at these times. Covariance between benthic and planktonic foraminiferal δ18O records of 0.3-0.5°/ºº at 36 Ma, 31 Ma, and 25 Ma suggests that three periods of continental glaciation caused eustatic (global sea-level) lowerings of 30-50 m during the Oligocene epoch. The δ13C cycles do not correlate with sea-level changes deduced from oxygen isotopic data, nor do they correlate with other proxy indicators for sea level.

  8. Biofacies zonation of middle Miocene benthic foraminifera, southeastern San Joaquin basin, California

    SciTech Connect

    Olson, H.C.

    1987-05-01

    The quantitative distribution of benthic foraminifera across the middle Miocene margin of the southeastern San Joaquin basin constitutes a useful tool in applying benthic biofacies zonation to the interpretation of marine paleoenvironments. A middle Miocene transect (near the Luisian/Relizian boundary) was completed across the margin of the southeastern San Joaquin basin near Bakersfild, California. Surface and subsurface fauna encompass strandline through bathyal environments. Quantitative analyses of these fauna result in a useful biofacies zonation for the middle Miocene which can be applied to the interpretation of middle Miocene paleobathymetric and paleogeographic reconstructions, basin analysis, and subsidence histories of the San Joaquin basin. In addition, these data suggest that vertical faunal migration of continental slope fauna has occurred between the middle Miocene and Recent. During the early and middle Miocene, marine temperatures were warmer than today and lower latitudinal gradients prevailed. Stepwise climatic cooling since the middle Miocene has been accompanied by the latitudinal adjustment of surface isotherms, strengthening of the permanent thermocline, and the associated migration of temperature-sensitive planktonic and benthic biofacies. Sedimentologic and seismic evidence in the southeastern San Joaquin basin suggests that present-day lower bathyal biofacies may have been at shallower depths during the middle Miocene. Such migrations would have a significant impact on paleoenvironmental interpretations. Middle Miocene faunal transects from the southeastern San Joaquin basin are compared with equivalent Holocene transects from the eastern Pacific, and differences are discussed in light of this proposal.

  9. Middle Miocene Displacement Along the Rand Detachment Fault, Rand Mountains

    NASA Astrophysics Data System (ADS)

    Shulaker, D. Z.; Grove, M. J.

    2015-12-01

    Laramide flat-slab subduction extinguished Sierra Nevada pluton emplacement in southern California by ca. 85 Ma as trench-derived sediments were underthrust and accreted beneath arc basement. These relationships are well illustrated in the Rand Mountains, situated just south of the Garlock fault in the northwestern Mojave Desert. Here, accreted rocks within the Rand Mountains are referred to as Rand Schist. The Rand Detachment fault juxtaposes Rand Schist beneath 87 Ma Sierran granitoids. New zircon (U-Th)/He age results from schist and basement juxtaposed across the Rand Detachment fault are 15 ± 3 Ma and 30 ± 5 Ma, respectively. When considered within the context of previously reported thermochronology from the Rand Mountains, our data shows that the Rand Detachment fault in the Rand Mountains is a middle Miocene fault that facilitated extension of the northwest Mojave Desert. This timing is in temporal and spatial agreement with regional extension throughout the Mojave triggered by northern migration of the slab window after collision of the Mendocino Triple Junction with the southern California margin. Further evidence of slab-window-related magmatism in the easternmost Rand Mountains is provided by the 19 Ma Yellow Aster pluton and 19 Ma rhyolite porphyry. It is possible that Miocene extension re-activated an older structure within the Rand Mountains. For example, a similar low-angle fault juxtaposing schist and basement present in the San Emigdio Mountains is believed to have accommodated large scale Late Cretaceous displacement, exhuming Rand Schist and overlying deepest Sierran basement to shallow crustal levels by 77 Ma [1]. However, 68-72 Ma phengite cooling ages and other thermochronology from the Rand Mountains indicates that any pre-Miocene extension in this area must postdate that in the San Emigdio Mountains. [1] Chapman et al., 2012. Geosphere, 8, 314-341.

  10. Rotation history of Chios Island, Greece since the Middle Miocene

    NASA Astrophysics Data System (ADS)

    Kondopoulou, D.; Sen, S.; Aidona, E.; van Hinsbergen, D. J. J.; Koufos, G.

    2011-05-01

    Superimposed on a regional pattern of oroclinal bending in the Aegean and west Anatolian regions, the coastal region of western Anatolia, shows a complex and chaotic pattern of coexisting clockwise and counterclockwise rotations. Here, we report new palaeomagnetic data from the eastern Aegean island of Chios, to test whether this fits the regional palaeomagnetic pattern associated with the Aegean orocline, or should be included in the narrow zone of chaotic palaeomagnetic directions. Therefore, a combined palaeomagnetic study of Miocene sediments and volcanic rocks has been carried out. Thermal and AF demagnetization of a 130-m thick Middle Miocene succession from the Michalos claypit allowed a stable component of both polarities to be isolated while rock magnetic experiments showed that the main magnetic carrier is magnetite. When compared with the Eurasian reference, the mean declination of 348 ± 5.1° implies 15° of counterclockwise rotation since Middle Miocene times. The obtained shallow inclination of 38 ± 6.7° was corrected to 61.8 ± 3.9°, by applying the elongation/inclination correction method for inclination shallowing. This result is similar to the expected inclination of 58° for the latitude of Chios. The palaeomagnetic analysis (demagnetization treatment and corresponding rock magnetic measurements) of the volcanic rocks identify a stable, predominantly normal, ChRM with poorly constrained mean declination of about 290 ± 19.8° based on five successfully resolved components. The significantly different palaeomagnetic results obtained from an island as small as Chios (and a very short distance), and the relatively large rotation amounts do not fit the regional palaeomagnetic direction of Lesbos and basins in northwestern Turkey which show little or no significant rotation. We thus prefer to include Chios in the coastal zone of chaotic rotations, which may represent a previously inferred tectonic transfer zone that accommodates lateral

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  12. Miocene reef facies of pelagian block, central Mediterranean

    SciTech Connect

    Pedley, H.M.

    1988-02-01

    Miocene reefs outcrop in the Maltese Islands, southeastern Sicily, and the pelagian island of Lampedusa. Several rapid eustatic sea level fluctuations affected these late Tortonian-early Messinian build-ups; normal salinities appear to have been maintained during these events. In addition to sea floor topography, reef development appears to have been controlled by turbulence. Encruster-dominated patch reefs are typical of platform and shallow ramp situations where turbulence is high. Branching and massive coral assemblages are typical of fore-reef curtains and steep slope substrates.

  13. Early Miocene mylonitization and detachment faulting, South Mountains, central Arizona

    SciTech Connect

    Reynolds, S.J.; Shafiqullah, M.; Damon, P.E.; DeWitt, E.

    1986-04-01

    The South Mountains of central Arizona are one of the geologically simplest metamorphic core complexes of the North American Cordillera. An early Miocene age of mylonitization is indicated by crosscutting relationships between mylonitic fabric and a composite pluton dated at 22-25 Ma by Rb-Sr, U-Th-Pb, and K-Ar techniques. The kinematic agreement and close temporal association of mylonitization and detachment faulting support models in which the two processes are related to an evolving crustal shear zone that accommodated mid-Tertiary continental extension. 19 references, 3 figures, 2 tables.

  14. The beaver Anchitheriomys from the Miocene of Central Europe

    SciTech Connect

    Stefen, C.; Mors, T.

    2008-09-15

    New finds of teeth and mandibles of Anchitheriomys from the Hambach opencast lignite mine in Northwest Germany and the first detailed descriptions of other mandibles from South Germany and Switzerland allow a review of the Central European specimens of this rare beaver genus. The metric variation of cheek teeth and especially the great differences in dimensions of incisors can be much better assessed. The observed range in size can be attributed to ontogenetic changes, and all material is assigned to Anchitheriomys suevicus. Stratigraphically, this species is restricted to the early middle Miocene, European Mammalian Neogene biozones MN 5-6.

  15. Upper Miocene reef complex of Mallorca, Balearic Islands, Spain

    SciTech Connect

    Pomar, L.

    1988-01-01

    The late Tortonian-Messinian coral reef platform of south Mallorca onlaps a folded middle late Miocene carbonate platform on which progradation of up to 20 km occurs. Vertical sea cliffs (up to 100 m high) superbly show the last 5 km of this progradation and complement the numerous water-well cores from the island interior. The coral reef platform consists of a series of progradational-accretional sequences and erosion surfaces of different orders of magnitude. The first-order sequence is bounded by significant erosion surfaces with breccias, major facies shifts, and vertical accretion. The second-order sequences show accretional events of up to 100 m thick with 1 to 2 km of progradation, and the third-order sequences occur in packages of tens of meters. Individual reef units are bounded by minor erosional surfaces and define the fourth-order sequences. This composite accretional-progradational architecture implies cyclic variations of relative sea level. Episodes of sea level rise were responsible for the vertical accretion. Sea level falls produced the erosional surfaces; most progradation occurred during lowering sea level episodes. This sedimentological framework of the Mallorca reef suggests late Miocene glacio-eustatic fluctuations of sea level similar to the Quaternary.

  16. Late Miocene hominids from the Middle Awash, Ethiopia.

    PubMed

    Haile-Selassie, Y

    2001-07-12

    Molecular studies suggest that the lineages leading to humans and chimpanzees diverged approximately 6.5-5.5 million years (Myr) ago, in the Late Miocene. Hominid fossils from this interval, however, are fragmentary and of uncertain phylogenetic status, age, or both. Here I report new hominid specimens from the Middle Awash area of Ethiopia that date to 5.2-5.8 Myr and are associated with a wooded palaeoenvironment. These Late Miocene fossils are assigned to the hominid genus Ardipithecus and represent the earliest definitive evidence of the hominid clade. Derived dental characters are shared exclusively with all younger hominids. This indicates that the fossils probably represent a hominid taxon that postdated the divergence of lineages leading to modern chimpanzees and humans. However, the persistence of primitive dental and postcranial characters in these new fossils indicates that Ardipithecus was phylogenetically close to the common ancestor of chimpanzees and humans. These new findings raise additional questions about the claimed hominid status of Orrorin tugenensis, recently described from Kenya and dated to approximately 6 Myr.

  17. Late Miocene magnetostratigraphy, biostratigraphy and cyclostratigraphy in the Mediterranean

    NASA Astrophysics Data System (ADS)

    Krijgsman, W.; Hilgen, F. J.; Langereis, C. G.; Santarelli, A.; Zachariasse, W. J.

    1995-12-01

    A new chronology for the late Miocene of the Mediterranean is presented by combining magnetostratigraphic, biostratigraphic (planktonic foraminifera and dinoflagellates) and cyclo-stratigraphic data. Long and continuous upper Miocene sections on Gavdos (Metochia section) and Sicily (Gibliscemi section) display cyclic alternations of homogeneous marls and sapropels and can be correlated on the basis of their distinct cyclic patterns. The Metochia section yields a good paleomagnetic signal and the position of 17 polarity reversals can be determined. The resulting polarity sequence allows an unambiguous correlation to the geomagnetic polarity time scale (GPTS). The paleomagnetic signal in the Gibliscemi section is too weak to determine a reliable polarity sequence, except for the lowermost part of the section. Detailed biostratigraphic analysis results in the identification of 13 planktonic foraminiferal and 9 dinoflagellate bioevents, which can all be accurately dated. The Tortonian/Messinian boundary, defined by the First Regular Occurrence (FRO) of the G. conomiozea group, is determined in chron C3Br.1r with an age of 7.12 Ma, according to the GPTS (CK95) of Cande and Kent [1].

  18. What controls early Miocene relief production of southeastern Tibet?

    NASA Astrophysics Data System (ADS)

    Cao, Kai

    2016-04-01

    When and how the high-elevation, low-relief relict surface originated in the SE Tibet remain debated. Tectono-geomorphologic analyses reveal that a NE-SW-strike topographic step is extended from the Longmen Shan to Jianchuan Basin, coincident with the trace of the Yalong-Yulong and Jinghe-Qinghe thrust system. This coincidence seems to tell the casual links between the relief generation of SE Tibet and thrusting. We conducted comprehensive work of geological mapping, structural analysis, sedimentology and apatite fission-track dating in the Tertiary Jianchuan Basin. Structural analysis examined a newly-defined thrust-Lijiang fault, viewed as the southeastward extending of the Yalong-Yulong thrust. Apatite fission-track data reveals rapid exhumation of the Jianchuan Basin at ~20-18 Ma in the hanging wall of the Lijiang thrust consistent with regional absence of Early Miocene sediments, indicating Early Miocene uplift of the Jianchuan Basin. We proposed that this event was likely related to the thrusting of the Yulong-Lijiang fault, broadly coeval with EW-oriented compression prevailed along the relief margins of the southeastern Tibet. Therefore, our new data supports that the relief production of the SE Tibet was controlled by thrusting, which predicts a revised block extrusion model.

  19. Plate-induced Miocene extension in southern California

    SciTech Connect

    Stuart, W.D. Univ. of California, Santa Barbara, CA )

    1992-01-01

    Miocene crustal extension in southern California can be explained by the interaction of tectonic plates in relative motion. The Pacific, Juan de Fuca, and Farallon (Guadalupe) plates are represented by flat elastic plates surrounded by an infinite elastic plate, the eastern part of which represents the North America plate. Forcing is by assigned subduction pull, and tractions at all plate boundaries satisfy a viscous constitutive law. Plate bottoms are stress-free. In the first part of the solution plate velocities and boundary tractions are found from static equilibrium. Then principal horizontal stresses and strains in plate interiors caused by tractions and subduction pull are found by a boundary element procedure. Using plate boundary geometry from Stock and Hodges for early- and mid-Miocene times, it is found that the portion of the North America plate margin between the Mendocino and Rivera triple junctions has maximum extensional strain directed westward. This result is generally consistent with directions associated with metamorphic core complex formation in southern California. The model is also consistent with extensional strain and rotation sense of crustal blocks in the vicinity of Los Angeles, as inferred by Luyendyk and others from paleomagnetic data. In the model the greatest extensional strain of the North America plate occurs near the Pacific-North America transform, in the area above the absent Farallon slab. Extension direction varies from northwest to southwest according to plate geometry, subduction pull (Juan de Fuca and Guadalupe), and plate boundary tractions.

  20. Early Miocene sequence development across the New Jersey margin

    USGS Publications Warehouse

    Monteverde, D.H.; Mountain, Gregory S.; Miller, K.G.

    2008-01-01

    Sequence stratigraphy provides an understanding of the interplay between eustasy, sediment supply and accommodation in the sedimentary construction of passive margins. We used this approach to follow the early to middle Miocene growth of the New Jersey margin and analyse the connection between relative changes of sea level and variable sediment supply. Eleven candidate sequence boundaries were traced in high-resolution multi-channel seismic profiles across the inner margin and matched to geophysical log signatures and lithologic changes in ODP Leg 150X onshore coreholes. Chronologies at these drill sites were then used to assign ages to the intervening seismic sequences. We conclude that the regional and global correlation of early Miocene sequences suggests a dominant role of global sea-level change but margin progradation was controlled by localized sediment contribution and that local conditions played a large role in sequence formation and preservation. Lowstand deposits were regionally restricted and their locations point to both single and multiple sediment sources. The distribution of highstand deposits, by contrast, documents redistribution by along shelf currents. We find no evidence that sea level fell below the elevation of the clinoform rollover, and the existence of extensive lowstand deposits seaward of this inflection point indicates efficient cross-shelf sediment transport mechanisms despite the apparent lack of well-developed fluvial drainage. ?? 2008 The Authors. Journal compilation ?? 2008 Blackwell Publishing.

  1. Miocene to Pliocene osmium isotopic records of Mediterranean sediments

    NASA Astrophysics Data System (ADS)

    Kuroda, Junichiro; Jiménez-Espejo, Francisco J.; Nozaki, Tatsuo; Gennari, Rocco; Lugli, Stefano; Manzi, Vinicio; Roveri, Marco; Flecker, Rachel; Suzuki, Katsuhiko; Yoshimura, Toshihiro; Sierro, Francisco; Ohkouchi, Naohiko

    2015-04-01

    In the late Miocene the Mediterranean Sea experienced a salinity crisis and thick sequences of evaporites precipitated across the basin. In this study we report Os isotopic records from drilled cores in the Mediterranean; the Balearic Sea, the Tyrrhenian Sea, the Ionian Basin and the Florence Rise. Pliocene sediments at all sites show 187Os/188Os values close to that of the coeval ocean water, indicating that the Mediterranean was connected to the North Atlantic. Evaporitic sediments deposited during the late Miocene however, have 187Os/188Os values lower than coeval ocean water values and samples from the eastern Mediterranean and Ionian basins are particularly low. Os isotopic ratios of the pre-evaporite sediments in the western Mediterranean are almost identical to that of the coeval ocean water. In contrast, equivalent sediments from the Florence Rise have significantly lower 187Os/188Os values. The offset of Mediterranean evaporite 187Os/188Os is attributed to limited exchange with the North Atlantic during the Messinian Salinity Crisis (MSC). The source of unradiogenic Os is likely to be weathering of ultramafic rocks (ophiolites) cropping out in the Mediterranean's drainage basins. The offset in the Os ratio on the Florence Rise is attributed either to limited water exchange between eastern and western Mediterranean, or to local effects associated with exhumation of ophiolites around the eastern Mediterranean Sea.

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

    PubMed

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

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

    2014-01-01

    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. PMID:25297009

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

    PubMed Central

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

    2014-01-01

    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. PMID:25297009

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

    NASA Astrophysics Data System (ADS)

    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.

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

    USGS Publications Warehouse

    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

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

    USGS Publications Warehouse

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

    1980-01-01

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

  9. Understanding the Miocene-Pliocene - The Mediterranean Point of View

    NASA Astrophysics Data System (ADS)

    Simon, D.; Marzocchi, A.; Lunt, D. J.; Flecker, R.; Hilgen, F. J.; Meijer, P. T.

    2015-12-01

    During the Miocene-Pliocene the Mediterranean region experienced major changes in paleogeography. Today, its only connection to the global ocean is the Strait of Gibraltar. This restricted nature causes the Mediterranean basin to react more sensitive to climatic and tectonic related phenomena than the global ocean: Not just eustatic sea-level and regional river run-off, but also gateway tectonics and connectivity between sub-basins are leaving an enhanced fingerprint in its geological record. To understand its evolution, it is crucial to understand how these different effects are coupled. The Miocene-Pliocene sedimentary record of the Mediterranean alternates in composition and colour. Around the Miocene-Pliocene Boundary the most extreme changes occur in the Mediterranean Sea: About 6% of the salt in the global ocean got deposited in the Mediterranean Region, forming an approximately 2km thick salt layer, which is still present today. This extreme event is named the Messinian Salinity Crisis (MSC, 5.97-5.33Ma). Before (and also after) the MSC, the sedimentary record demonstrates "marl dominated" alternations with variations in organic content (e.g. higher organic content = sapropel). During the MSC these change to mainly "evaporite (e.g. gypsum or halite) dominated" alternations, but also to brackish Black Sea-type of deposits towards the end of the crisis. Due to its relative short geological time span, the period before, during and after the MSC is ideal to study these extreme changes in sedimentation. We are investigating these couplings and evolutions in a box/budget model. With such a model we can study the responses to basin water exchange dynamics under the effect of different regional and global climatic and tectonic forcings, to predict the evolution of basin properties (e.g. salinity). By doing so we can isolate certain climatic and tectonic effects, to better understand their individual contribution, their interaction, but also the consequences due to

  10. A Miocene submarine volcano at Low Layton, Jamaica

    NASA Technical Reports Server (NTRS)

    Wadge, G.

    1982-01-01

    A submarine fissure eruption of Upper Miocene age produced a modest volume of alkaline basalt at Low Layton, on the north coast of Jamaica. The eruption occurred in no more than a few hundred meters of water and produced a series of hyaloclastites, pillow breccias and pillow lavas, massive lavas, and dikes with an ENE en echelon structure. The volcano lies on the trend of one of the island's major E-W strike-slip fault zones; the Dunavale Fault Zone. The K-Ar age of the eruption of 9.5 plus or minus 0.5 Ma. B.P. corresponds to an extension of the Mid-Cayman Rise spreading center inferred from magnetic anomalies and bathymetry of the Cayman Trough to the north and west of Jamaica. The Low Layton eruption was part of the response of the strike-slip fault systems adjacent to this spreading center during this brief episode of tectonic readjustment.

  11. Silica diagenesis in Santa Cruz mudstone, Late Miocene, California

    SciTech Connect

    El-Sabbagh, D.

    1987-05-01

    The silica-rich upper Miocene Santa Cruz Mudstone is similar to the Miocene Monterey Formation. Previous studies have suggested the Santa Cruz Mudstone was not buried deeply nor had it undergone extensive diagenesis. Because opaline diagenesis is temperature dependent, the author examined the silica diagenesis of the Santa Cruz Mudstone using scanning electron microscopy and x-ray diffraction methods to study its burial history. In a series of samples from Santa Cruz to Davenport, California (over 16 km), opal-CT is the dominant silica phase present and clay minerals are notably absent. The d(101)-spacing values of opal-CT range from 4.11 A (Santa Cruz area) to 4.06 A (north of Santa Cruz), exhibiting the complete range of d(101)-spacing values found in opal-CT zones. Scanning electron micrographs of crystalline microtextures show rosettes of opal-CT (lepispheres) in cavities of samples with medium to high d(101)-spacing values. The morphology of lepisphere crystallites grades from bladed to spiny with decreasing d(101)-spacing values, reflecting an internal crystal ordering with increased diagenesis. Further diagenetic changes occurred in a sample with 4.06 A d(101)-spacing where incipient quartz crystals signal the initial conversion of opal-CT to microcrystalline quartz. Silica diagenesis demonstrates that burial temperatures surpassed the range of opal-A to opal-CT conversion and approached conversion temperatures (55/sup 0/C to 110/sup 0/C) of opal-CT to microcrystalline quartz. The conversion occurred when the Santa Cruz Mudstone was buried over 1900 m (depth calculated from a geohistory diagram). This burial temperature brings the Santa Cruz Mudstone within the oil generation window, and could account for the presence of hydrocarbons in the unit.

  12. Miocene reef and nonreef carbonate rocks in Japan

    SciTech Connect

    Konishi, K.

    1988-01-01

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

  13. Miocene to Pleistocene osmium isotopic records of the Mediterranean sediments

    NASA Astrophysics Data System (ADS)

    Kuroda, Junichiro; Jiménez-Espejo, Francisco J.; Nozaki, Tatsuo; Gennari, Rocco; Lugli, Stefano; Manzi, Vinicio; Roveri, Marco; Flecker, Rachel; Sierro, Francisco J.; Yoshimura, Toshihiro; Suzuki, Katsuhiko; Ohkouchi, Naohiko

    2016-01-01

    In the late Miocene the Mediterranean Sea experienced a salinity crisis and thick sequences of evaporites precipitated across the deep and marginal basins. In this study we report Os isotopic records from Deep Sea Drilling Project and Ocean Drilling Project cores in the Mediterranean: the Balearic Sea (Site 372), the Tyrrhenian Sea (Site 654), the Ionian Basin (Site 374), and the Florence Rise (Sites 375-376), as well as Integrated Ocean Drilling Project Site U1387 in Gulf of Cadiz, North Atlantic. Pliocene-Pleistocene sediments at all sites show 187Os/188Os values close to that of the coeval ocean water, indicating that the Mediterranean was connected to the North Atlantic. Evaporitic sediments deposited during the latest Miocene, however, have 187Os/188Os values significantly lower than coeval ocean water values. The offset of the Mediterranean evaporite 187Os/188Os is attributed to limited exchange with the North Atlantic during the Messinian salinity crisis. The source of unradiogenic Os is likely to be weathering of ultramafic rocks (ophiolites) cropping out in the Mediterranean's drainage basins. Based on a box model we estimated the amount of unradiogenic Os and the Atlantic-Mediterranean exchange rate to explain this offset. Os isotopic ratios of the pre-evaporite sediments in the western Mediterranean are almost identical to that of the coeval ocean water. In contrast, equivalent sediments from the Florence Rise have significantly lower 187Os/188Os values. The offset in the Os isotopic ratio on the Florence Rise is attributed either to limited water exchange between eastern and western Mediterranean or to local effects associated with exhumation of the Troodos ophiolites (Cyprus).

  14. Miocene to Pleistocene Exhumation of the Southern European Alps

    NASA Astrophysics Data System (ADS)

    Reverman, R.; Fellin, M.; Herman, F.; Willett, S.

    2011-12-01

    We apply apatite fission-track, (U-Th-Sm)/He dating, 4He/3He diffusion profiles, and OSL thermochronology to construct a complete thermal history and constrain the exhumation and topographic evolution of the Adamello complex in the Southern European Alps. The Adamello complex is an Eocene-Oligocene pluton emplaced at a depth of 7 km, now exposed and dissected by deep valleys with a local relief of more than 2 km, which drain into larger fluvial systems overdeepened during the Messinian salinity crisis. Our aim is to determine which major erosional event during the Miocene-to-Pleistocene evolution of the Alps most affected the topographic development of the Adamello complex. We quantify exhumation rates using multiple methods: age-elevation relationships, estimates based on exhumation of a fossil partial retention zone, and cooling histories. We then compare these estimates with those predicted from a 3-D heat conduction model including topographic relief and erosion (Pecube; Braun, 2002) paired with the Neighborhood Algorithm, which is a two stage mathematical procedure that finds models, or parameters, which minimize the misfit to the data (Sambridge, 1999a,b). The predicted tectono-geomorphic history is tested for feasibility through comparison with known timing of tectonic and erosional events. Our apatite fission-track and (U-Th-Sm)/He results indicate that relief development alone cannot account for the episodic history and suggest a possible coupling between tectonics and erosion in the late Miocene, where the establishment of major drainages coincides with a period of increased rock uplift. The initial results from even lower temperature methods, 4He/3He diffusion profiles and OSL thermochronology, suggest an increase in exhumation rates in the Plio-Pleistocene, most likely associated with glacial reshaping.

  15. Gulf of Mexico miocene CO₂ site characterization mega transect

    SciTech Connect

    Meckel, Timothy; Trevino, Ramon

    2014-12-01

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

  16. Miocene ocean circulation inferred from marine carbon cycle modeling combined with benthic isotope records

    NASA Astrophysics Data System (ADS)

    Butzin, Martin; Lohmann, Gerrit; Bickert, Torsten

    2011-02-01

    In a modeling sensitivity study we investigate the evolution of the ocean circulation and of marine carbon isotope (δ13C) records during the Miocene (about 23-5 million years ago). For this purpose we ran an ocean-circulation carbon cycle model of intermediate complexity (Large Scale Geostrophic- Hamburg Ocean Carbon Cycle Model, version 2s) exploring various seaway configurations. Our investigations confirm that the Central American Seaway played a decisive role in the history of the Miocene ocean circulation. In simulations with a deep Central American Seaway (depth range 1-3 km), typical for the early to middle Miocene, deep water production in the North Atlantic is absent or weak, while the meridional overturning circulation is dominated by water mass formation in the Southern Ocean. Deep water formation in the North Atlantic begins when the Central American Seaway shoals to a few hundreds of meters, which is typical for the late Miocene. Our results do not support ideas that the mid-Miocene closing of the Eastern Tethys contributed to Antarctic glaciation. On the other hand, we find some water exchange between the Indian Ocean and the Atlantic via the Eastern Tethys during the early Miocene. Our model results for the Atlantic meridional overturning circulation and for Atlantic δ13C during the late Miocene are largely independent from depth variations of the Greenland-Scotland Ridge. To a large extent, the evolution of Miocene deep-sea δ13C records can be explained with large-scale ocean circulation changes. Our model-data comparison for the middle and early Miocene suggests that during the early Neogene the seaway effect on benthic δ13C may have been superimposed by further factors such as climate regime shifts and/or terrestrial carbon cycle changes.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  18. Late Miocene teeth from Middle Awash, Ethiopia, and early hominid dental evolution.

    PubMed

    Haile-Selassie, Yohannes; Suwa, Gen; White, Tim D

    2004-03-01

    Late Miocene fossil hominid teeth recovered from Ethiopia's Middle Awash are assigned to Ardipithecus kadabba. Their primitive morphology and wear pattern demonstrate that A. kadabba is distinct from Ardipithecus ramidus. These fossils suggest that the last common ancestor of apes and humans had a functionally honing canine-third premolar complex. Comparison with teeth of Sahelanthropus and Orrorin, the two other named late Miocene hominid genera, implies that these putative taxa are very similar to A. kadabba. It is therefore premature to posit extensive late Miocene hominid diversity on the basis of currently available samples.

  19. Late Miocene uplift and doming of Madagascar: topographic implications

    NASA Astrophysics Data System (ADS)

    Delaunay, Antoine; Robin, Cecile; Guillocheau, François; Dall'Asta, Massimo; Calves, Gérôme

    2016-04-01

    Madagascar is an Archean to Neoproterozoic continental crust surrounded by transform, oblique and divergent margins: the oblique Morondava Basin to the west, pounded by the Davie Fracture Zone, and to the north, the divergent Mahajanga (Majunga) Basin connected to the Somali Oceanic Basin. This 1600 km long island is a high axial plateau with elevations from 1200 to 1800m. The top of the plateau corresponds to weathered planation surfaces (etchplains), bounded by more or less high scarps. We here present geological arguments for the age and the timing of the Madagascar Plateau. This analysis is based on a double, coupled analysis of the onshore geomorphology (stepped planation surfaces) and the offshore margin stratigraphy (seismic stratigraphy and wells). The geomorphological analysis is based on a characterization, a mapping and dating of stepped planation surfaces (mantled to stripped etchplains, pediments to pediplains). The dating is based on their geometrical relationships with dated magmatic rocks. The difference of elevation between two planation surfaces (corresponding to local base level) provides a proxy of the uplift. The sequence stratigraphic analysis is based on a biostratigraphic reevaluation of 4 industrial wells (foraminifers and nannofossils on cuttings). Uplift periods are characterized by (1) seaward tiltings of the margins overlain by planar reflectors, (2) forced regression wedges and (3) upstream erosions of older sediments recorded by fauna/flora reworking. (1) During Paleocene to Middle Miocene times (66 to 13 Ma), Madagascar is a quite flat low elevation domain with remnants of an oldest pre-Madagascar Trap (90 Ma) surface. This low relief is highly weathered with growth of numerous lateritic profiles and surrounded by large carbonate platforms with no siliciclastic sands influx. (2) The Late Miocene is the paroxysm of uplift with (1) a tilting of the margin (Morondova), (2) an increase of the siliciclastic sand flux since middle Miocene

  20. Significant Role of the East Antarctic Ice Sheet in Miocene Global Climate Change

    NASA Astrophysics Data System (ADS)

    Cook, C. P.; Martin, E. E.

    2015-12-01

    The Miocene was a period of climatic extremes, with indirect records suggesting major retreat and advance of Antarctica's ice sheets. Climatic warmth of the Early Miocene and Miocene Climatic Optimum (MCO; ~17-15 Ma) was followed by cooler conditions and growth of the East Antarctic ice sheet (EAIS) during the middle Miocene Climate Transition (MMCT; ~14-15 Ma). This cooling occured with decreasing CO2 levels and deepening of the CCD. Weathering on Antarctica associated with ice sheet variability likely played a role in global climate, but the temporal and spatial evolution of the EAIS is not constrained well enough to characterize this relationship. We use Pb and Nd isotopes of authigenic Fe-Mn oxide coatings, which preserve bottom water compositions, and associated detrital bulk deep sea sediments, to provide new insights into continental weathering and ice sheet evolution during the Miocene. Comparison of Pb IC's of coupled detrital and authigenic phases are used to reconstruct chemical weathering patterns. In contrast, Nd IC's provide insights into bedrock erosion and ocean circulation patterns. Study sites are located on Maud Rise (ODP Sites 689 and 690) in the Atlantic sector, and on Kerguelen Plateau (ODP Site 744) off of Prydz Bay. Results reveal increased offsets between seawater and detrital Pb IC's during the Early Miocene and MCO, and decreased values and offsets during the MMCT and Late Miocene for all three sites, a pattern that is most pronounced at Maud Rise. There is a long-term trend to more unradiogenic Nd IC and more radiogenic Pb IC values of detrital sediments during the MMCT and Late Miocene. Comparison with modern day coretop data suggest this pattern indicates increased supply of local continental material. Our data suggest enhanced chemical weathering accompanied reduced ice volume and high atmospheric CO2 during the Early Miocene and MCO, likely contributing to the drawdown of CO2 that lead to the MMCT, as well as deepening of the CCD

  1. Early Miocene origin and cryptic diversification of South American salamanders

    PubMed Central

    2013-01-01

    Background The currently recognized species richness of South American salamanders is surprisingly low compared to North and Central America. In part, this low richness may be due to the salamanders being a recent arrival to South America. Additionally, the number of South American salamander species may be underestimated because of cryptic diversity. The aims of our present study were to infer evolutionary relationships, lineage diversity, and timing of divergence of the South American Bolitoglossa using mitochondrial and nuclear sequence data from specimens primarily from localities in the Andes and upper Amazon Basin. We also estimated time of colonization of South America to test whether it is consistent with arrival via the Panamanian Isthmus, or land bridge connection, at its traditionally assumed age of 3 million years. Results Divergence time estimates suggest that Bolitoglossa arrived in South America from Central America by at least the Early Miocene, ca. 23.6 MYA (95% HPD 15.9-30.3 MYA), and subsequently diversified. South American salamanders of the genus Bolitoglossa show strong phylogeographic structure at fine geographic scales and deep divergences at the mitochondrial gene cytochrome b (Cytb) and high diversity at the nuclear recombination activating gene-1 (Rag1). Species often contain multiple genetically divergent lineages that are occasionally geographically overlapping. Single specimens from two southeastern localities in Ecuador are sister to the equatoriana-peruviana clade and genetically distinct from all other species investigated to date. Another single exemplar from the Andes of northwestern Ecuador is highly divergent from all other specimens and is sister to all newly studied samples. Nevertheless, all sampled species of South American Bolitoglossa are members of a single clade that is one of several constituting the subgenus Eladinea, one of seven subgenera in this large genus. Conclusions The ancestors of South American salamanders

  2. Astrochronology of the Mediterranean Early and Middle Miocene

    NASA Astrophysics Data System (ADS)

    Hüsing, Silja Katherine; Hilgen, Frederik; Krijgsman, Wout; Turco, Elena

    2013-04-01

    An accurate high-resolution astronomical time scale is of crucial importance in Earth Sciences. It allows not only to reconstruct astronomical climate forcing but also to precisely date geological events, to determine rates of changes, and to discriminate between cause and effect related to fundamental processes controlling Earth's history. The accuracy, precision and resolution of the geological time scale for the Neogene have improved considerably over the last decades, thanks to the combination of an integrated stratigraphic approach and astronomical tuning, which resulted in the "Astronomically Tuned Neogene Time Scale" (ATNTS2004, ATNTS2012). The most recent ATNTS2012 (Gradstein et al. 2012) includes direct astronomical ages for chron boundaries back to ~15 Ma based on the tuning of marine successions from the Mediterranean. Reversal ages for the interval between 15 and 23 Ma were calculated from a seafloor-spreading-rate history model in combination with limited astronomical control. Completing the Neogene time scale should be exclusively based on deep marine sections. The most suitable section in the Mediterranean is the Monte dei Corvi-La Vedova-Spiaggia della Scalaccia composite section near Ancona in Italy as an integrated stratigraphy and astronomical tuning has been established for the Late to Middle Miocene interval (Hüsing et al. 2007, 2009, 2010, Mourik et al. 2010, Turco et al. 2011). The resultant astronomically tuned reversal ages have already been incorporated into the GTS (Gradstein et al. 2012). The section has now been further extended into the Early Miocene along the cliffs near Ancona (Spiaggia della Scalaccia composite section). We will present our high-resolution integrated stratigraphy including cyclostratigraphy, biostratigraphy, magnetostratigraphy, colour and elemental proxy records. The sedimentary cycle pattern is very complex in this interval, and we thus use the detailed colour and elemental proxy records to achieve a match with

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

    USGS Publications Warehouse

    Jayko, A.S.

    2009-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  5. Late Miocene calcareous nannofossil genus Catinaster: taxonomy, evolution and magnetobiochronology

    USGS Publications Warehouse

    Peleo-Alampay, A.; Bukry, D.; Liu, L.; Young, J.R.

    1998-01-01

    A systematic study on the evolution and stratigraphic distribution of the species of Catinaster from several DSDP/ODP sites with magnetostratigraphic records is presented. The evolution of Catinaster from Discoaster is established by documentation of a transitional nannofossil species, Dicoaster transitus. Two new subspecies, Catinaster coalitus extensus and Catinaster calyculus rectus are defined which appear to be intermediates in the evolution of Catinaster coalitus coalitus to Catinaster calyculus calyculus. The first occurrence of C. coalitus is shown to be in the lower part of C5n.2n at 10.7-10.9 Ma in the low to mid-latitude Atlantic and Pacific oceans. The last occurrence of C. coalitus coalitus varies from the upper part of C5n.2n to the lower portion of C4A. Magnetobiostratigraphic evidence suggests that the FO of C. calyculus rectus is diachronous. Catinaster mexicanus occurs in the late Miocene and has been found only in the eastern equatorial Pacific, the Indian Ocean and the Gulf of Mexico.

  6. Hydrologic cycling over Antarctica during the middle Miocene warming

    NASA Astrophysics Data System (ADS)

    Feakins, Sarah J.; Warny, Sophie; Lee, Jung-Eun

    2012-08-01

    From 20 to 15 million years (Myr) ago, a period of global warmth reversed the previous ice growth on Antarctica, leading to the retreat of the West Antarctic Ice Sheet and the contraction of the East Antarctic Ice Sheet. Pollen recovered from the Antarctic shelf indicates the presence of substantial vegetation on the margins of Antarctica 15.7Myr ago. However, the hydrologic regime that supported this vegetation is unclear. Here we combine leaf-wax hydrogen isotopes and pollen assemblages from Ross Sea sediments with model simulations to reconstruct vegetation, precipitation and temperature in Antarctica during the middle Miocene. Average leaf-wax stable hydrogen isotope (δD) values from 20 to 15.5Myr ago translate to average δD values of -50‰ for precipitation at the margins of Antarctica, higher than modern values. We find that vegetation persisted from 20 to 15.5Myr ago, with peak expansions 16.4 and 15.7Myr ago coinciding with peak global warmth and vegetation growth. Our model experiments are consistent with a local moisture source in the Southern Ocean. Combining proxy measurements with climate simulations, we conclude that summer temperatures were about 11°C warmer than today, and that there was a substantial increase in moisture delivery to the Antarctic coast.

  7. Late Miocene exhumation and uplift of the Washington Cascade Range

    NASA Astrophysics Data System (ADS)

    Reiners, Peter W.; Ehlers, Todd A.; Garver, John I.; Gran Mitchell, Sara; Montgomery, David R.; Vance, Joseph A.; Nicolescu, Stefan

    2002-09-01

    The Washington Cascade Range is a complex, polygenetic mountain range that dominates the topographic, climatic, and cultural configurations of Washington State. Although it has been the locus of ongoing arc magmatism since the Eocene, most of the range is distinct from the southern part of the arc in Oregon and California in that bedrock uplift has produced high surface elevations and topographic relief, rather than volcanic burial or edifice construction. (U-Th)/He and fission-track ages of bedrock samples on the east flank of the range record relatively rapid cooling in the early Tertiary, but slow exhumation rates (˜0.2 km/m.y.) through most of the Oligocene. Samples on the west flank suggest rapid cooling in the late Miocene (8 12 Ma), and age variations in vertical transects are consistent with a pulse of rapid exhumation (0.5 1.0 km/m.y.) at that time. Apatite He ages as young as 1 5 Ma in several areas suggest that high cooling and possibly exhumation rates persist locally. Accelerated exhumation rates ca. 10 Ma are also observed in the Coast Mountains of British Columbia and southeast Alaska, ˜1500 km to the north, suggesting a large-scale mechanism for the exhumation pulse at that time.

  8. Miocene detachment faulting predating EPR propagation: Southern Baja California

    NASA Astrophysics Data System (ADS)

    Bot, Anna; Geoffroy, Laurent; Authemayou, Christine; Bellon, Hervé; Graindorge, David; Pik, Raphaël.

    2016-05-01

    At the southern tip of the Baja California peninsula, we characterize the onshore structures and kinematics associated with crustal necking leading up to the Pliocene breakup and early East Pacific Rise seafloor spreading. From a combination of tectonic field investigations, K-Ar and cosmogenic isotope dating and geomorphology, we propose that the Los Cabos block represents the exhumed footwall of a major detachment fault. This north trending detachment fault is marked by a conspicuous low-dipping brittle-ductile shear zone showing a finite displacement with top to the SE ending to the ESE. This major feature is associated with fluid circulations which led to rejuvenation of the deformed Cretaceous magmatic rocks at a maximum of 17.5 Ma. The detachment footwall displays kilometer-scale corrugations controlling the present-day drainage pattern. This major detachment is synchronous with the development of the San José del Cabo Basin where syntectonic sedimentation took place from the middle Miocene to probably the early Pliocene. We propose that this seaward dipping detachment fault accommodates the proximal crustal necking of the Baja California passive margin, which predates the onset of formation of the East Pacific Rise spreading axis in the Cabo-Puerto Vallarta segment. Our data illustrate an apparent anticlockwise rotation of the stretching direction in Baja California Sur from ~17 Ma to the Pliocene.

  9. Miocene reef facies of Pelagian Block, central Mediterranean

    SciTech Connect

    Pedley, H.M.

    1988-01-01

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

  10. Porosity evolution of upper Miocene reefs, Almeria Province, Southern Spain

    SciTech Connect

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

    1980-02-01

    In the reef cores and fore-reef breccia beds, porosity in both primary and postdepositional. Primary porosity is of three types: (a) boring clam holes in the scleractinian coral heads, cemented reef rocks, and breccias; (b) intraparticle porosity within the corals, Halimeda plates, and vermetid worm tubes; and (c) interparticle porosity between bioclastic fragments and in the reef breccia. Postdepositional moldic porosity was formed by the solution of aragonitic material such as molluscan and coral fragments. The Polomo reef carbonate rocks have high porosity and permeability, and retain a great amount of depositional porosity. Pores range in size from a few micrometers to 30 cm. The extensive intercrystalline porosity and high permeability resulted from dolomitization of micritic matrix. Some porosity reduction has occured by incomplete and partial sparry calcite infilling of interparticular, moldic, and intercrystalline voids. The high porosity and permeability of these reefs make them important targets for petroleum exploration in the western Mediterranean off southern Spain. In these offshore areas in the subsuface the volcanic ridge and the Plomo reef complex are locally onlapped or overlapped by 350 m or more of Miocene and Pliocene fine-grained sedimentary rocks. The possibility exists that the buried Plomo reef deposits may form traps for oil and gas in the offshore areas southwest of the type locality. Stratigraphic traps also may occur where the Neogene sequence above the Plomo reef complex onlaps the volcanic ridge. 17 figures.

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

    PubMed

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

    2013-01-01

    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.

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

    PubMed

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

    2010-06-01

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

  13. Late Oligocene-early Miocene birth of the Taklimakan Desert.

    PubMed

    Zheng, Hongbo; Wei, Xiaochun; Tada, Ryuji; Clift, Peter D; Wang, Bin; Jourdan, Fred; Wang, Ping; He, Mengying

    2015-06-23

    As the world's second largest sand sea and one of the most important dust sources to the global aerosol system, the formation of the Taklimakan Desert marks a major environmental event in central Asia during the Cenozoic. Determining when and how the desert formed holds the key to better understanding the tectonic-climatic linkage in this critical region. However, the age of the Taklimakan remains controversial, with the dominant view being from ∼ 3.4 Ma to ∼ 7 Ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert. In this study, we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy. We constrained the initial desertification to be late Oligocene to early Miocene, between ∼ 26.7 Ma and 22.6 Ma. We suggest that the Taklimakan Desert was formed as a response to a combination of widespread regional aridification and increased erosion in the surrounding mountain fronts, both of which are closely linked to the tectonic uplift of the Tibetan-Pamir Plateau and Tian Shan, which had reached a climatically sensitive threshold at this time.

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

    PubMed Central

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

    2013-01-01

    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 (δ13C) values from tooth enamel imply the presence of a woodland ecosystem dominated by C3 plants. δ13C 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 δ13C 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, δ13C 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. PMID:23135673

  15. Late Oligocene–early Miocene birth of the Taklimakan Desert

    PubMed Central

    Zheng, Hongbo; Wei, Xiaochun; Tada, Ryuji; Clift, Peter D.; Wang, Bin; Jourdan, Fred; Wang, Ping; He, Mengying

    2015-01-01

    As the world’s second largest sand sea and one of the most important dust sources to the global aerosol system, the formation of the Taklimakan Desert marks a major environmental event in central Asia during the Cenozoic. Determining when and how the desert formed holds the key to better understanding the tectonic–climatic linkage in this critical region. However, the age of the Taklimakan remains controversial, with the dominant view being from ∼3.4 Ma to ∼7 Ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert. In this study, we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy. We constrained the initial desertification to be late Oligocene to early Miocene, between ∼26.7 Ma and 22.6 Ma. We suggest that the Taklimakan Desert was formed as a response to a combination of widespread regional aridification and increased erosion in the surrounding mountain fronts, both of which are closely linked to the tectonic uplift of the Tibetan–Pamir Plateau and Tian Shan, which had reached a climatically sensitive threshold at this time. PMID:26056281

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    SciTech Connect

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

    1986-05-01

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

  18. Miocene tephrochronology in the northern Basin and Range

    SciTech Connect

    Perkins, M.E.; Brown, F.H.; Nash, W.P. . Dept. of Geology and Geophysics)

    1993-04-01

    Silicic air-fall tephra layers with unaltered glass shards preserved in Miocene basins of the northern Basin and Range Province (NBR) were sampled from well-exposed sections in the Goose Creek (GCB) and Ibapah (IB) basins in the northeastern NBR, and the El Pasco basin (EPB) in the southwestern NBR. Each basin may contain up to 50 tephras. Glass shards from individual tephras in any one basin are compositionally distinct, as shown by XRF and electron microprobe analysis. Seventeen tephra correlate between two or more basins; 12 of these are regionally important, providing precise stratigraphic ties across the NbR. Four regionally correlative tephras are white biotitic ashes from southern Nevada sources, whereas eight are gray vitric ashes from Yellowstone hot spot sources. Dates on tephra layers and lava flows in the basins, and on ashflow units correlated with four other tephra provide a preliminary chronology for the tephra in the all basins. In each section [Delta]h/[Delta]t appears constant on time scales [>=]1 Ma, but variation in [Delta]h/[Delta]t is demonstrated from IB, and is likely typical of all basins. Sedimentation in all five basins begins in the time interval of 14.5--12.5 Ma, which may represent the beginning of a phase of regional extension in the NBR. Post-[approximately]9.5 Ma deformation has affected all basins and likely contributed to the termination of sedimentation in the exposed areas of these basins.

  19. Middle Miocene Hominoids dispersion and radiation: impact of climate and vegetation changes in Europe

    NASA Astrophysics Data System (ADS)

    Hamon, N.; Sepulchre, P.; Contoux, C.; Jaeger, J.-J.; Ramstein, G.

    2012-04-01

    The middle Miocene is a time of important climatic changes, and a crucial period for ape's evolution. The Middle Miocene Climatic Optimum (MMCO), that occurred approximately 17 to 15 Ma, was one of the last global warming event of the Cenozoic. This period also corresponds to the first dispersion of apes from Africa to Europe, which was made possible by tectonic and environmental changes, in particular the expansion of hominoids habitat: (sub-)tropical forest. Following the MMCO, an abrupt global cooling occurred that coincides with an important radiation of European hominoids. The most common view is that the widening of hominoids habitat during the MMCO was the main factor of their dispersion from Africa to Europe. Moreover, the major climatic change that followed induced an opening of the environment because of cooler and dryer conditions, which should have lead to a fragmentation of hominoids' habitat. This imply that hominoids evolved separately in refuges during the end of the Miocene, so the radiation observed in the fossil record of European Miocene apes is interpreted as a divergent evolution in a fragmented habitat. However, no study has yet demonstrated this evolutionary scenario. Our aim is to study the environmental changes during the middle Miocene, in particular climate and vegetation changes, and to link them with these two major events of hominoids' evolution. Using climate and vegetation models, we investigate the role of environmental variation in hominoids' evolution during the middle Miocene, in particular between 17 and 14 Ma. We perform two climatic experiments (16Ma and 14Ma) with the atmospheric general circulation model LMDZ. The results of these experiments will then be used to force the dynamic vegetation model CARAIB. This should help us to simulate hominoids' habitat for the two time period chosen, and to discuss the role of important climate change for Miocene apes evolution.

  20. New insights to the middle Miocene pCO2 problem (Invited)

    NASA Astrophysics Data System (ADS)

    Badger, M. P.; Foster, G. L.; Lear, C. H.; Pancost, R. D.; Bailey, T. R.; Leng, M. J.; Abels, H. A.

    2013-12-01

    The climate of the middle Miocene was substantially different to today with a much warmer world with boundary conditions (plate configurations, ocean circulation etc) that were very different to the present. The sustained warmth of the 'Middle Miocene Climate Optimum' prevailed prior to the second step of the descent into the ice-house - with the major expansion of Antarctic ice sheet and global cooling at the middle Miocene Climate Transition. Coincident with these major changes in global temperatures and the cryosphere were substantial perturbations of the carbon cycle, as documented by the large fluctuations in oceanic carbonate δ13C values during the 'Monterey Excursion' as well as the various 'CM' events superimposed upon it. Critical to our understanding of Miocene climate and carbon cycle dynamics is a full understanding of atmospheric pCO2 during this fascinating time. A number of Miocene atmospheric pCO2 estimates are now available (Kürschner, Kvaček and Dilcher, 2008; Foster, Lear and Rae, 2012; Badger et al., 2013) that help to better understand this relationship but differences between these new records and older published records (ie Pagani et al., 1999; Pearson and Palmer, 2000) raise interesting questions as to the drivers of Miocene climate and carbon cycling. Here we will discuss the implications of our records for the Monterey Excursion and the CM events, as well as presenting a novel probabilistic re-assessment of new and existing atmospheric pCO2 records. The combination of a larger dataset and more quantitative approach allows us to answer some of the outstanding questions about the operation of the Miocene climate system, and help to explain the apparent disparity between atmospheric pCO2 records and proxy temperature estimates.

  1. Miocene ungulates and terrestrial primary productivity: Where have all the browsers gone?

    PubMed Central

    Janis, Christine M.; Damuth, John; Theodor, Jessica M.

    2000-01-01

    Progressive changes are observed in both the composition of mammal faunas and vegetation during the Miocene epoch [24–5 mega-annum (Ma)]. These changes are usually interpreted as a response to climatic changes. In the traditional view, forests or woodlands gradually gave way to more open habitats, with grazing (grass-eating) ungulate (hoofed) mammal species replacing the browsing (leafy-vegetation-eating) species as grasslands expanded. However, data from fossil assemblages in the Great Plains region of North America show that this faunal change was not a one-for-one replacement of browsers by grazers, as usually thought. Typical late early Miocene (17 Ma) fossil communities included extraordinarily high numbers of browsing ungulate species, comprising a fauna that cannot be directly analogized with any present-day community. Both maximum species richness of all ungulates and the proportion of browsers declined steadily in ungulate communities through the middle Miocene, to levels comparable to those of the present by the late Miocene. The resulting dramatic, cumulative loss of browsing species constitutes one of the strongest faunal signals of the late Tertiary (but was not a single “event”). We suggest that the early Miocene browser-rich communities may reflect higher levels of primary productivity in Miocene vegetation, compared with equivalent present-day vegetation types. The observed decline in species richness may represent a gradual decline in primary productivity, which would be consistent with one current hypothesis of a mid-Miocene decrease in atmospheric CO2 concentrations from higher mid-Cenozoic values. PMID:10884422

  2. Fish Productivity in Open-Ocean Gyre Systems in the Late Oligocene and Miocene

    NASA Astrophysics Data System (ADS)

    Cuevas, J. M.; Sibert, E. C.; Norris, R. D.

    2015-12-01

    Understanding how marine ecosystems respond to climate change is very important as we continue to warm the climate. Fish represent a critical protein source for a significant portion of the global population, and as such, an understanding of fish production and its interactions with climate change may help better prepare for the future. Ichthyoliths, fossil fish teeth and shark scales, are a novel fossil group which can be used as an indicator for fish productivity. Several important climate events occurred during the Miocene (7 to 23 Ma), including the Middle Miocene Climatic Optimum. Here we reconstruct fish production from across the Miocene from Pacific and Atlantic Ocean gyres. South Atlantic samples, from Deep Sea Drilling Program (DSDP) Site 522 spanning from 30 to 20 Ma, show fairly variable numbers in the Oligocene (ranging from 100 to 800 ich/cm2/yr), but stabilization in the Early Miocene (around 400 ich/cm2/yr), suggesting that the beginning of the Miocene brought consistent conditions for fish production. In the North Pacific, our record from Ocean Drilling Program (ODP) Site 886 shows a distinct crash in fish productivity at 11 Ma, from 3500 ich/cm2/yr to a steady decline around 100 ich/cm2/yr for the next million years. This crash is followed by a marked increase in the presence of diatoms and biogenous opal. This is somewhat surprising, since in modern oceanic systems, an increase in diatoms and other large-celled phytoplankton is associated with shorter, more efficient food chains and higher levels of fish. It is also interesting to note that denticles remain consistently low at both sites, indicating consistently low shark populations through this time period. Together, these results suggest that the Late Oligocene and Miocene was a time of variable fish production and provide a window into understanding of dynamic ecosystem changes through the Miocene in open-ocean gyre ecosystems.

  3. Late Miocene “washhouse” climate in Europe

    NASA Astrophysics Data System (ADS)

    Böhme, Madelaine; Ilg, August; Winklhofer, Michael

    2008-11-01

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

  4. Post-Miocene extension in Central Anatolia; It's linkage to Aegean extension

    NASA Astrophysics Data System (ADS)

    Rojay, Bora; Özsayın, Erman

    2013-04-01

    Post-Miocene extension in Central Anatolia; It's linkage to Aegean extension Anatolian Plate, -where Central Anatolia situated on-, escapes westward onto African plate along Eastern Mediterranean-Cyprus subduction zone, sliding by North and East Anatolian faults. Central Anatolia is bounded by dextral North Anatolian Fault from north, Taurides from south and it is fragmented by strike slip faults evolving under N-S compression in east and by Aegean horst and grabens evolving under N-S extension in west. To be able to delineate and understand the deformational order in Central Anatolia and its linkage to Aegean region, various sectors with the Anatolia are chosen, namely, Ankara region (Beypazarı to Kazan Miocene basins), Eskişehir region (Mihallıçık to İnönü Miocene basins) in Central Anatolia, Gediz-Alaşehir Graben and Efes areas in Western Anatolia are selected. To sum up, in a wide region from Central Anatolia to Western Anatolia, i. Unconformities btw uppermost Late Miocene and Plio-Quaternary, and btw Plio-Quaternary and Quaternary are clearly identified in both regions, ii) ENE-WSW to N-S compression (intense post-Late Miocene - pre-Pliocene folding) with almost E-W extension operates during post-Miocene (during Pliocene) is followed by a short lived strike slip deformation during Early Pliocene, and finally by NW-SE to WNW-ESE oriented multi directional extension during post-Plio-Quaternary. And in Gediz-Alaşehir Graben and Efes (western Anatolia); a continuous NNE-SSW to NE-SW multi directed extension since post-Late Miocene following almost N-S compression (post-Early Miocene) operated. Dextral strike slip faulting with normal components and normal faulting with right lateral strike slip components are recorded on same fault planes, iii) Quaternary normal faulting post dates folding, reverse and strike slip faulting in both regions. However, right lateral strike slip faulting is recorded to the NW tip of the normal faults like Efes, Manisa and

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

    NASA Astrophysics Data System (ADS)

    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

  6. Effect of abyssal circulation changes on Oligocene to Miocene benthic foraminifera in the North Atlantic

    SciTech Connect

    Katz, M.E.; Miller, K.G.

    1985-01-01

    Benthic foraminiferal ranges at western North Atlantic Sites 563 and 558 show: 1) gradual Oligocene last occurrences in response to subsidence from the upper to lower abyssal zones; 2) a preponderance of extinctions in the early middle Miocene (about 15.5-13.5 Ma). Comparison of relative and absolute abundance changes at Site 563 sows that percentages of some taxa (e.g. Nuttallides umbonifera) reliably reflect their accumulations while percentages of others vary independently. Regional abundance changes include: 1) maxima N. umbonifera in the middle Oligocene of the deepest sites (10 and 119); 2) increased Planulina wuellerstorfi in the early middle Miocene; 3) increased N. umbonifera in the late middle Miocene. Seismic stratigraphic and delta/sup 13/C evidence indicates a northern bottom-water source for the North Atlantic throughout much of the Oligocene and Miocene. Benthic foraminifera apparently responded to bottom-water changes inferred from carbon isotopic comparisons. The extinction of relict Paleogene taxa and the ascendancy of P. wuellerstorfi in the middle Miocene apparently correlate with increased advection into the eastern Atlantic, subsidence of the Iceland-Faeroe Ridge and increased North Atlantic carbonate sedimentation. The authors speculate that this faunal reorganization was in response to global ocean chemistry changes resulting from increased ventilation of the North Atlantic.

  7. Oligocene-Miocene Sr-isotope stratigraphy: Examples from eastern North America

    SciTech Connect

    Sugarman, P.J. ); Owens, J.P.; Gibson, T.G.; McCartan, L. ); Feigenson, M.D. )

    1994-03-01

    Sr-isotopic age estimates from the coastal plain in New Jersey, Maryland Virginia, and Florida have allowed correlation of upper Oligocene-Miocene stratigraphic sequences with an accuracy of [+-] 0.5--2.0 m.y. The upper Oligocene sequence mapped in New Jersey has an age range of 28.7--24.2 Ma, and is tentatively correlated with the Old Church Formation in Virginia. Sr-isotope age estimates of 28.6--25.3 in the lower part of the Arcadia Formation in Florida provide a chronostratigraphic correlation with the upper Oligocene, N.J. sequence. Miocene Sr-isotopic correlations are better constrained by improved age resolution of [+-]1 m.y. and less in the Miocene. The uppermost lower Miocene sequence in N.J. with Sr-isotopic age estimates of 17.4--15.5 Ma, can be correlated with the Calvert Formation in Maryland and the upper part of the Arcadia Formation in Florida based on Sr-isotopic correlations. The uppermost calcareous marine sequence in New Jersey is lower middle Miocene, with a Sr-isotopic age range of 13.6--12.2 Ma. This sequence is correlative with the Choptank Formation in Maryland. The St. Mary's Formation in Maryland has a Sr-isotopic age range of 10--9.6 Ma, and may be equivalent to the Cohansey Formation in New Jersey.

  8. Lithostratigraphy and vertebrate biostratigraphy of the early Miocene Himalayan Foreland, Zinda Pir Dome, Pakistan

    NASA Astrophysics Data System (ADS)

    Downing, Kevin F.; Lindsay, Everett H.; Downs, William R.; Speyer, Stephen E.

    1993-09-01

    Deposits in the Sulaiman foothills and Zinda Pir Dome in west-central Pakistan provide new insight into the critical early Miocene record of Himalayan Foreland sedimentation and paleobiology. The Chitarwata Formation, which underlies the Vihowa Formation in the Sulaiman foothills predates the Siwalik deposits on the Potwar Plateau of north-central Pakistan and provides a record of mammals spanning the interval between the early Miocene Bugti fauna and middle Miocene to Pleistocene Siwalik faunas. Siwalik deposits on the Potwar Plateau are no older than middle Miocene; they represent fluvial environments. In contrast, the Chitarwata and Lower Vihowa Formations in the Zinda Pir Dome represent coastal-delta plain and fluvial environments, respectively. Biostratigraphic information from the Chitarwata Formation, coupled with paleomagnetic data (reported by Friedman et al., 1992) from coincident strata, suggest that coastal environments persisted in the area of the Sulaiman foothills until about 18.6 Ma when they were replaced by fluvial environments, probably representing the ancestral Indus River system. Apparently, during the early Miocene when sediments of the Chitarwata Formation were accumulating on the western portion of the Himalayan Foreland Basin much of the area of the Potwar Plateau to the north was being eroded. The overlying Vihowa Formation, along with the relatively contemporaneous Kamlial Formation on the Potwar Plateau, represent the appearance of widespread terrestrial sedimentation in the Himalayan Foreland Basin.

  9. Organic geochemical evaluations of bituminous rock and coals in Miocene Himmetoglu basin (Bolu, Turkey)

    SciTech Connect

    Sari, A.; Geze, Y.

    2008-07-01

    The studied area is a lake basin located in Bolu basin in Turkey. In the basin, from Upper Cretaceous to Upper Miocene 3,000-m thickness sediments were deposited. Upper Miocene Himmetoglu formation consisted of sandstone, claystone, and marl. To the middle level of the formation are located coal, bituminous limestone, and bituminous shales. In the basin, there are two coal beds whose thicknesses range from 1 to 13 m. The coals are easily breakable and black in color. In the coal beds exists some bituminous limestone and bituminous shales, and their thicknesses are between 5 and 45 cm. The amount of organic matter of the bituminous rocks from the Upper Miocene Himmetoglu formation are between 6.83 and 56.34 wt%, and the amount of organic matter of the bituminous limestone from the formation are between 13.58 and 57.16 wt%. These values indicate that these rocks have very good source potential. According to hydrogen index (HI), S2/S3, HI-T{sub max}, and HI-OI (oxygen index) parameters, kerogen types of the bituminous rocks and coals belonging to Upper Miocene Himmetoglu formation are Type I, Type II, and Type III. In accordance with HI, S2/S3, HI-T{sub max}, and HI-OI parameters, the bituminous rocks and coals from the Upper Miocene Himmetoglu formation are mostly immature.

  10. Paleomagnetism of the Ishikoshi Andesite: a Middle Miocene paleomagnetic pole for northeastern Japan and tectonic implications

    NASA Astrophysics Data System (ADS)

    Hoshi, Hiroyuki; Teranishi, Yuki

    2007-07-01

    To determine a Middle Miocene paleomagnetic pole for northeastern Japan and discuss its tectonic implications, we obtained new paleomagnetic results from Middle Miocene (about 14 Ma) dacite and andesite flows of the Ishikoshi Andesite. Characteristic remanent magnetizations were isolated from 12 lava sites by means of detailed alternating field and thermal demagnetizations. Analysis of demagnetization results and rock magnetic experiments indicated that magnetite or Ti-poor titanomagnetite is the main magnetic carrier. We obtained a formation mean direction ( D = 9.2°, I = 65.9°, α95 = 7.3°, k = 40.5, N = 11) and compared it with published paleomagnetic results from other areas of northeastern Japan to discuss tectonic rotation. This comparison provided a mean paleomagnetic pole (85.9°N, 236.6°E, A 95 = 6.2°, K = 115.9, N = 6) that we consider represents the Middle Miocene pole for northeastern Japan. It is statistically indistinguishable from coeval poles for southwestern Japan, South Korea, and northern China, and we therefore conclude that northeastern Japan as a whole has not been subjected to tectonic rotation since the Middle Miocene. A reassessment of geologic and paleomagnetic data suggests that a previous model of the Late Miocene or later counterclockwise rotation of northeastern Japan is based on tilt-uncorrected paleomagnetic directions from tilted rock units.

  11. Mineralogy and diagenesis of miocene and pleistocene sediments, Northeastern Gulf of Mexico

    SciTech Connect

    Conner, S.P.; Denham, M.E.; Tieh, T.T.

    1988-01-01

    Cored Miocene and Pleistocene sediments from the northeastern Gulf of Mexico (ranging in depth from 1,400 to 2,000 m) consist of interbedded sands, silts, and muds with varying degrees of consolidation. Samples selected from these sediments were studied for their mineralogy and diagenesis. The Miocene sediments represent various subenvironments of the ancestral Mississippi River delta complex; Pleistocene sediments are marine shelf deposits. Sands from both Miocene and Pleistocene cores are fine to very fine-grained feldspathic litharenites with abundant (approx. = 25%) matrix fines and minor (<7%) carbonate clasts and shell fragments. Carbonate diagenesis is a continuing process in these sediments. Clayey sands contain disseminated siderite crystallites formed during organic matter fermentation. In clean sands, scattered thin (<15 cm) bands of poikilotopic carbonate-cemented sand are present in the middle of thicker unconsolidated intervals. Cemented bands are thicker in the Miocene section, having grown during burial through dissolution of shell fragments and reprecipitation at the margin of cemented zones. Diagenetic events evident in the Miocene core illustrate processes that could occur in the Pleistocene sediments with continued burial. These are: (1) dolomitization of some calcite cements, (2) precipitation of Fe-carbonate as crystallites, rims on dolomite cements, and overgrowths on siderite crystallites, and (3) zeolite formation on amorphous silica substrates. Amorphous silica is associated with limited dissolution of feldspars or lithic fragments.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  13. A sphenodontine (Rhynchocephalia) from the Miocene of New Zealand and palaeobiogeography of the tuatara (Sphenodon)

    PubMed Central

    Jones, Marc E.H.; Tennyson, Alan J.D.; Worthy, Jennifer P.; Evans, Susan E.; Worthy, Trevor H.

    2009-01-01

    Jaws and dentition closely resembling those of the extant tuatara (Sphenodon) are described from the Manuherikia Group (Early Miocene; 19–16 million years ago, Mya) of Central Otago, New Zealand. This material is significant in bridging a gap of nearly 70 million years in the rhynchocephalian fossil record between the Late Pleistocene of New Zealand and the Late Cretaceous of Argentina. It provides the first pre-Pleistocene record of Rhynchocephalia in New Zealand, a finding consistent with the view that the ancestors of Sphenodon have been on the landmass since it separated from the rest of Gondwana 82–60 Mya. However, if New Zealand was completely submerged near the Oligo-Miocene boundary (25–22 Mya), as recently suggested, an ancestral sphenodontine would need to have colonized the re-emergent landmass via ocean rafting from a currently unrecorded and now extinct Miocene population. Although an Early Miocene record does not preclude that possibility, it substantially reduces the temporal window of opportunity. Irrespective of pre-Miocene biogeographic history, this material also provides the first direct evidence that the ancestors of the tuatara, an animal often perceived as unsophisticated, survived in New Zealand despite substantial local climatic and environmental changes. PMID:19203920

  14. Miocene-Pliocene transition in the southern Cyprus basins: The sedimentary expression of regional tectonic events

    SciTech Connect

    Orzag-Sperber, F.; Rouchy, J.M. )

    1988-08-01

    In the southern part of Cyprus, a Maastrichtian-Pleistocene sedimentary area fringes Troodos Mountain, a fragment of an ancient crust. During the Neogene, three basins formed in this area: Polemi, Pissouri, and Psematismenos. A deep marine condition has prevailed since the Maastrichtian. During the Paleocene and early Miocene, the sea gradually become shallower until the Messinian, where the most spectacular sedimentary event concerns the deposition of evaporites contemporaneous with other Mediterranean evaporites. Some sedimentary phenomena express the tectonic instability during the upper Miocene. A well-known tectonic event affecting the east Mediterranean region generally referred to as the Miocene-Pliocene phase occurs at the Miocene-Pliocene limit. Recent sedimentological studies indicate this event is in fact complex. The Tortonian-lower Pliocene period is marked by a constraint involving an N20 distension in the Polemi and Pissouri basins and an N100 distension in the Psematismenos basin. Sedimentologic studies have demonstrated three tectonic pulsations during the Messinian prior to the Pliocene transgression. These are expressed by two episodes of seismic brecciation and a paleoemersion indicated by paleosols and detrital discharges. These phenomena suggest brief tectonic instability during the Messinian. Microtectonic studies reveal that the main change in tectonic constraint does not coincide with the Miocene-Pliocene contact but occurs at the top of the lower Pliocene.

  15. Molluscan evidence for early middle Miocene marine glaciation in southern Alaska

    USGS Publications Warehouse

    Marincovich, L., Jr.

    1990-01-01

    Profound cooling of Miocene marine climates in southern Alaska culminated in early middle Miocene coastal marine glaciation in the northeastern Gulf of Alaska. This climatic change resulted from interaction of the Yakutat terrane with southern Alaska beginning in late Oligocene time. The ensuing extreme uplift of the coastal Chugach and St. Elias Mountains resulted in progressive regional cooling that culminated in coastal marine glaciation beginning in the early middle Miocene (15-16 Ma) and continuing to the present. The counterclockwise flow of surface water from the frigid northeastern Gulf of Alaska resulted in a cold-temperate shallow-marine environment in the western Gulf of Alaska, as it does today. Ironically, dating of Gulf of Alaska marine glaciation as early middle Miocene is strongly reinforced by the presence of a few tropical and subtropical mollusks in western Gulf of Alaska faunas. Shallow-marine waters throughout the Gulf of Alaska were cold-temperate to cold in the early middle Miocene, when the world ocean was undergoing peak Neogene warming. -Author

  16. Major Mid-Miocene Climate Change In The Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    Independent lines of evidence from paleoecology, glacial geology and marine isotopes indicate major climate change in the Dry Valley sector of the Transantarctic Mountains (TAM) at c.14 Ma. A fossil assemblage of pollen and spores, freshwater diatoms, ostracods, mosses, and insect remains has been recovered from lacustrine sediments preserved in a small morainic lake basin in the western Olympus Range. The diatom assemblage indicates that the lake existed for >103yr and was ice-free during summers. Based on the moss and insect fossils the minimum mean summer temperature (MST- Dec-Feb) was 2°C but could have been as high as 5°C. Today at the site the MST is c. -15°C. The lake-marginal vegetation was a sparse tundra dominated by mosses and liverworts. Based on pollen, Nothofagus (southern beech) was part of the lowland regional vegetation and individual dwarfed shrubs may have grown on the slopes surrounding the lake basin. The age of the deposits is well-constrained by an 40Ar/39Ar age of 14.11 ± 0.11 Ma from an in situ volcanic ash within related lacustrine sediments. Based on an independent study of the glacial stratigraphy of the western Wright and McKelvey valleys, diamictites of a wet-based glacial regime had been replaced by those of cold-based regime by 13.85 ± 0.03 Ma. The drop in temperatures and the cessation of meltwater at c. 14 Ma would have caused the regional extinction of all plant and insect life with the exception of the hardiest of soil-dwelling organisms. Paleobotanical evidence indicates that Antarctica had likely been vegetated throughout the Cenozoic, with forests replaced by tundra during the early Oligocene. The mid-Miocene extinction marks the end of tundra in the interior of Antarctica and its replacement by the polar desert biota which exists today. Changes in δ18O and Mg/Ca ratios from different sectors of the Southern Ocean indicate sea surface temperature cooling and ice sheet growth between 13.8 - 14.2 Ma. The close correlation

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

    PubMed

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

    2015-08-07

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

  18. Relation of peralkaline magmatism to heterogeneous extension during the Middle Miocene, southeastern Nevada

    USGS Publications Warehouse

    Scott, R.B.

    1995-01-01

    Volcanism migrated southward in the northern Basin and Range province in the Oligocene and early Miocene to produce voluminous calcalkaline silicic ash flow tuffs. Alkaline volcanism became dominant by middle Miocene (17-14 Ma) as smaller volumes of rhyolite-trachyte-basalt suites were erupted from the relatively small Kane Springs Wash caldera complex in southeastern Nevada. Only minor extension affected the Kane Wash area before the end of calcalkaline activity, but extension expressed by rate of progressive stratal tilt peaked (15-13.5 Ma) with peralkaline magmatism (14.7-14.4 Ma). Variations in distribution, degree, style, and timing of deformation demonstrate heterogeneous extension in the Kane Wash area. Only minor extension and tilting persisted post-middle Miocene (<12 Ma). All major eruptive sources overlap domains of rapid extension. -from Authors

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

    PubMed Central

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

    2015-01-01

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

  20. Oligocene-Miocene biostratigraphy, magnetostratigraphy, and isotopic stratigraphy of the western North Atlantic

    NASA Astrophysics Data System (ADS)

    Miller, Kenneth G.; Aubry, Marie-Pierre; Khan, M. J.; Melillo, A. J.; Kent, D. V.; Berggren, W. A.

    1985-04-01

    Magnetostratigraphic records from western North Atlantic Deep Sea Drilling Project (DSDP) Sites 563 and 558 are correlated with the geomagnetic polarity time scale (GPTS; Berggren et al., 1984a, 1984b) using marine magnetic anomalies and selected biostratigraphic datum levels. The magnetochronology established is used to make direct magnetobiostratigraphic correlations that agree with previous Oligocene early Miocene studies. However, we show that Zones NN8 partim and NN9 and associated Epoch 11 correlate with Magnetic Anomaly 5 (= Chron C5n). This contrasts with previous indirect correlations of Epoch 11 with Anomaly 5A and requires an upward adjustment of 1.5 2.0 m.y. for middle late Miocene calcareous nannofossil zones. We correlate the middle/late Miocene boundary with Zone NN8 and earliest Chron C5n (10.4 Ma). *Present address: Peshawar University, Peshawar, Pakistan

  1. Miocene non-marine diatoms from the western Cordillera basins of northern Peru

    USGS Publications Warehouse

    Fourtanier, E.; Gasse, F.; Bellier, O.; Bonhomme, M.G.; Robles, I.

    1993-01-01

    Diatom assemblages are documented from diatomite layers of two Miocene fluvio-lacustrine units from the basins of the western Cordillera of northern Peru: the Namora Formation and the Cajabamba Formation. Emphasis is given to taxa of particular stratigraphic interest. The diatom assemblages indicate for the Namora Formation the occurrence of swampy conditions with very dilute, low alkalinity water. The diatom assemblages of the Cajabamba Formation reflect the occurrence of fresh, slightly alkaline, eutrophic lakes with deep water in some samples, and swampy conditions with relatively high salt content in other samples. The Namora formation is late Miocene in age based on the diatom assemblages and radiometric analyses. The diatom layers of the Cajabamba Formation are dated as late middle to early late Miocene. -from Authors

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

    PubMed

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

    2012-07-01

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

  3. An age for Kajong, a Miocene fossil site east of Lake Turkana, Kenya

    NASA Astrophysics Data System (ADS)

    Brown, Francis H.; Jicha, Brian R.; Leakey, R. E.

    2016-02-01

    The Kajong Formation in Marsabit District, northern Kenya has yielded a Miocene mammalian fauna consisting of nine taxa. It is capped by a basalt 40Ar/39Ar dated at 19.1 ± 0.1 Ma, and a volcanic clast from a conglomerate within the formation yielded an age of 20.3 Ma, only slightly older. The entire fauna from this site thus lies close to the base of the Miocene Epoch and is older than 19.2 Ma. The site has yielded some of the oldest examples of Archaeobelodon filholi, Prodeinotherium hobleyi, and Gomphotherium sp. in east Africa.

  4. A giant termite from the Late Miocene of Styria, Austria (Isoptera)

    NASA Astrophysics Data System (ADS)

    Engel, Michael S.; Gross, Martin

    2009-02-01

    A giant termite is described and figured from the Late Miocene of the Styrian Basin in southeastern Austria. Gyatermes styriensis gen. n. et sp. n. is represented by a relatively complete forewing, with basal scale. The fossil approximates in size the largest of all termites today and is the largest fossil termite on record. The presence of this species in the Late Miocene fauna of Europe indicates that climatic conditions were appropriate for the persistence of species and colonies requiring relatively stable, warm conditions. The genus is primitive in overall features but shares some similarity with the dampwood termites.

  5. Upper Miocene-Eopleistocene terrestrial sediments of the northwestern Ciscaucasia region

    NASA Astrophysics Data System (ADS)

    Beluzhenko, E. V.; Pis'mennaya, N. S.

    2016-07-01

    On the basis of their stratigraphic, lithological, and genetic features, the Upper Miocene-Eopleistocene terrestrial sediments of the northwestern Ciscaucasia region are subdivided into the following local stratigraphic units (formations): Azov-Kuban, Srednyaya Kuban, Novoaleksandrovsk, Temizhbekskaya. The paleontological and paleomagnetic data are used for determining or specifying their age and correlating the formations between each other and with the regional stratigraphic scale. The obtained data make it possible to improve the Upper Miocene-Eopleistocene stratigraphic scale of the northwestern Ciscaucasia region.

  6. Stratigraphical investigations on a new Miocene fossil-bearing sequence in Central Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Central Inner Mongolia has been an area of great paleontological interest since the beginning of the 20th century. Although the area has produced numerous diverse collections of Miocene faunas, fossil records from the early Miocene of Inner Mongolia are relatively rare. The localities occur mainly as scattered faunal horizons and their stratigraphy is challenging owing to lack of continuous vertical exposures. Consequently, most age estimations of these Miocene sites are based on paleontological evidence alone, with very few sites having been dated independently based on paleomagnetics. The Damiao site in Siziwang Qi, Inner Mongolia, was discovered in 2006, and during the following four years extensive field activities were undertaken. The focus was on paleontological studies and on the stratigraphy of the Neogene sediments. The field survey led to the recovery of approximately 30 new fossiliferous localities, which have produced a rich mammalian fauna, including pliopithecid remains. The bulk of the vertebrate fossils and localities have been recovered from three main fossil horizons. We have interpreted the Damiao sequence as the remains of a fluvio-lacustrine system comprising channels, subaerially exposed floodplains and ephemeral/marginal lacustrine environments. This study presents the litho- and magnetostratigraphy of the Damiao area and provides age estimations for the important fossil-bearing localities. The two local stratigraphic sections measured and sampled for paleomagnetic analysis coincide with important vertebrate fossil localities. The western section is about 30 m thick and includes fossil locality DM16 while the eastern section spans up 40 m and comprises localities DM01 and DM02. The paleomagnetic results and faunal evidence suggest a correlation in the magnetozones C6Ar through C5r with an age range of ca 21 to 11 Ma. The interval of reversed polarity at the base of the section (C6Ar) coincides with fossil locality DM16. The pliopithecid

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

    NASA Astrophysics Data System (ADS)

    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 <200 mm thick zone of cataclasites developed between footwall carbonate ultramylonites, containing thin layers and cm-scale boudins of quartzite, and hanging wall breccias; no contacts with the footwall ultramylonites or hanging wall breccias has been found (yet). The cataclasite zone, which can be traced along-strike for at least 90 m, over ~20 m elevation, comprises several distinct layers. In the sample described, five layers occur. The lowest (A; >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 <30x5 mm-sized red carbonate clasts (+/- quartz fragments) of earlier cataclasite generations. These elongate clasts lie parallel to the overall banding, which is parallel to the ultramylonitic foliation (detachment surface

  8. Tracking Arabia-India motion from Miocene to Present

    NASA Astrophysics Data System (ADS)

    Chamot-Rooke, N. R.; Fournier, M.

    2009-12-01

    Although small, the present-day Arabia-India motion has been captured by several global and regional geodetic surveys that consistently show dextral motion of a few mm/yr, either transpressive or transtensive (Fournier et al., 2008). This motion is accommodated along the Owen Fracture Zone, an active strike-slip boundary that runs for more than 700 km from the Somalia-India-Arabia triple junction in the south to the Dalrymple trough in the north. Two recent marine cruises conducted along this fault aboard the BHO Beautemps-Beaupré (AOC 2006 and OWEN 2009) using a high resolution multibeam sounder (Simrad EM120, 10 m vertical resolution) provided a complete map of the active fault and confirmed a present-day pure dextral motion. The surface breaks closely follow a small circle of the Arabia-India motion, with several pull-part basins at the junctions between the main segments of the fault. Geomorphologic offsets reach 10 km, suggesting that the mapped fault has been active with the same style for past several million years. When did this motion start? The difficulty in tracking the past Arabia-India motion is that there is no direct kinematic indicator available, since the boundary has been strike-slip and/or convergent during the Tertiary. Motion was most probably sinistral during the rapid northward travelling of India towards Eurasia in the early Tertiary, Arabia being rigidly attached to Africa until the opening of the Gulf of Aden. However, the nature and location of the Arabia-India boundary at that time remain speculative. Throughout the Miocene, the relative motion between India and Arabia has been indirectly recorded at the Sheba and Carslberg ridges, the former recording Arabia-Somalia motion (opening of the Gulf of Aden) and the latter India-Somalia motion (Indian Ocean opening). Both ridges have been studied with some details recently, using up to date magnetic lineations identification (Merkouriev and DeMets, 2006; Fournier et al., 2009). We combine

  9. Foraminiferal record of Oligocene-Miocene shales from the Limon Basin, eastern Costa Rica

    SciTech Connect

    Cassell, D.T.; Sen Gupta, B.K.

    1985-01-01

    Foraminiferal analysis of an unusually thick and continuous section of Tertiary shales from the western margin of the Limon Basin, Costa Rica, indicates that rocks from this section are older than similar facies elsewhere in the basin. Approximately 620 meters of silty shales from the Quebrada Terciopelo belong to zones N3 through N9 while the oldest shales from the rest of the basin are in N12 to N13. The lowermost N3 zone is characterized by the presence of the Late Oligocene larger foraminifera Lepidocyclina waylandvaughani and Heterostegina antillea associated with oncolite clasts in a siltstone. Shales above contain typical Early to Middle Miocene planktonic foraminifera, including Catapsydrax stainforthi, Globorotalia kugleri, G. sicanus, and G. peripheroronda. The first two species, used widely as Early Miocene markers and reported to have nonoverlapping stratigraphic ranges, are found together within a short interval in this section. This Quebrada Terciopelo sedimentary section shows the transition from a shallow nearshore environment in the Late Oligocene to an open marine outer shelf or upper slope in the Miocene. The biostratigraphic analysis demonstrates than an approximately 70 meter thick Late Oligocene (N3) to Early Miocene (N5) section is repeated. This is apparently related to normal faulting associated with the uplift of the Talamanca Mountains.

  10. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene.

    PubMed

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Gasson, Edward; Kuhn, Gerhard; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco

    2016-03-29

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

  11. Early miocene subglacial basalts, the East antarctic ice sheet, and uplift of the transantarctic mountains.

    PubMed

    Stump, E; Sheridan, M F; Borg, S G; Sutter, J F

    1980-02-15

    Subglacially erupted volcanic rocks from Mount Early and Sheridan Bluff, Antarctica, yield whole-rock potassium-argon dates and argon-40/argon-39 release spectra of Early Miocene age. Field associations suggest the existence of the East Antarctic ice sheet and significant uplift of the Transantarctic Mountains by that time.

  12. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

    NASA Astrophysics Data System (ADS)

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Gasson, Edward; Kuhn, Gerhard; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco; SMS Science Team; Acton, Gary; Askin, Rosemary; Atkins, Clifford; Bassett, Kari; Beu, Alan; Blackstone, Brian; Browne, Gregory; Ceregato, Alessandro; Cody, Rosemary; Cornamusini, Gianluca; Corrado, Sveva; DeConto, Robert; Del Carlo, Paola; Di Vincenzo, Gianfranco; Dunbar, Gavin; Falk, Candice; Field, Brad; Fielding, Christopher; Florindo, Fabio; Frank, Tracy; Giorgetti, Giovanna; Grelle, Thomas; Gui, Zi; Handwerger, David; Hannah, Michael; Harwood, David M.; Hauptvogel, Dan; Hayden, Travis; Henrys, Stuart; Hoffmann, Stefan; Iacoviello, Francesco; Ishman, Scott; Jarrard, Richard; Johnson, Katherine; Jovane, Luigi; Judge, Shelley; Kominz, Michelle; Konfirst, Matthew; Krissek, Lawrence; Kuhn, Gerhard; Lacy, Laura; Levy, Richard; Maffioli, Paola; Magens, Diana; Marcano, Maria C.; Millan, Cristina; Mohr, Barbara; Montone, Paola; Mukasa, Samuel; Naish, Timothy; Niessen, Frank; Ohneiser, Christian; Olney, Mathew; Panter, Kurt; Passchier, Sandra; Patterson, Molly; Paulsen, Timothy; Pekar, Stephen; Pierdominici, Simona; Pollard, David; Raine, Ian; Reed, Joshua; Reichelt, Lucia; Riesselman, Christina; Rocchi, Sergio; Sagnotti, Leonardo; Sandroni, Sonia; Sangiorgi, Francesca; Schmitt, Douglas; Speece, Marvin; Storey, Bryan; Strada, Eleonora; Talarico, Franco; Taviani, Marco; Tuzzi, Eva; Verosub, Kenneth; von Eynatten, Hilmar; Warny, Sophie; Wilson, Gary; Wilson, Terry; Wonik, Thomas; Zattin, Massimiliano

    2016-03-01

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (˜280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (˜500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

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

    NASA Astrophysics Data System (ADS)

    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. First record of Mesopithecus (Cercopithecidae, Colobinae) from the Miocene of the Iberian Peninsula.

    PubMed

    Alba, David M; Montoya, Plini; Pina, Marta; Rook, Lorenzo; Abella, Juan; Morales, Jorge; Delson, Eric

    2015-11-01

    We report dental remains of the extinct colobine monkey Mesopithecus from the Turolian (MN13, Late Miocene, ca. 6.23 Ma) locality of Venta del Moro (Valencia, Spain). They include most of the deciduous dentition and the unerupted germs of the first molars of a single infantile individual, as well as two lower left lateral incisors from two additional individuals. On the basis of morphometric comparisons, mainly based on the M1s, these remains are attributed to the Late Miocene species Mesopithecus pentelicus. They represent a significant addition to the knowledge of the deciduous dentition of this taxon, much less well-known than the permanent dentition. Although this genus was widely distributed from the Late Miocene through the Pliocene across Europe, southwestern Asia, Pakistan, and China, until now its occurence in the Late Miocene of the Iberian Peninsula had not been documented conclusively. Hence, the reported remains considerably enlarge southwestwards the known geographic distribution of Mesopithecus. The presence of this genus at Venta del Moro must be understood within the framework of the significant faunal turnover that took place in European faunas during the latest Turolian (the second Messinian mammalian dispersal), which is further documented at this locality by the occurrence of other eastern immigrants. At the same time, the presence of M. pentelicus at this site agrees well with previous paleoenvironmental and sedimentological evidence, indicating a lacustrine depositional environment with strong hydrologic seasonality. PMID:26553814

  15. Evidence for ice-free summers in the late Miocene central Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Stein, Ruediger; Fahl, Kirsten; Schreck, Michael; Knorr, Gregor; Niessen, Frank; Forwick, Matthias; Gebhardt, Catalina; Jensen, Laura; Kaminski, Michael; Kopf, Achim; Matthiessen, Jens; Jokat, Wilfried; Lohmann, Gerrit

    2016-04-01

    Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene sediments close to the seafloor. Here we document the presence of IP25 as a proxy for spring sea-ice cover and alkenone-based summer sea-surface temperatures >4 °C that support a seasonal sea-ice cover with an ice-free summer season being predominant during the late Miocene in the central Arctic Ocean. A comparison of our proxy data with Miocene climate simulations seems to favour either relatively high late Miocene atmospheric CO2 concentrations and/or a weak sensitivity of the model to simulate the magnitude of high-latitude warming in a warmer than modern climate.

  16. Evidence for ice-free summers in the late Miocene central Arctic Ocean.

    PubMed

    Stein, Ruediger; Fahl, Kirsten; Schreck, Michael; Knorr, Gregor; Niessen, Frank; Forwick, Matthias; Gebhardt, Catalina; Jensen, Laura; Kaminski, Michael; Kopf, Achim; Matthiessen, Jens; Jokat, Wilfried; Lohmann, Gerrit

    2016-01-01

    Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene sediments close to the seafloor. Here we document the presence of IP25 as a proxy for spring sea-ice cover and alkenone-based summer sea-surface temperatures >4 °C that support a seasonal sea-ice cover with an ice-free summer season being predominant during the late Miocene in the central Arctic Ocean. A comparison of our proxy data with Miocene climate simulations seems to favour either relatively high late Miocene atmospheric CO2 concentrations and/or a weak sensitivity of the model to simulate the magnitude of high-latitude warming in a warmer than modern climate. PMID:27041737

  17. Evidence for sediment fan deposition on outer Texas shelf during Miocene eustatic sea level highstands

    SciTech Connect

    Riese, W.C.; Olsen, R.S.; Rosen, R.N.

    1988-02-01

    Four types of data were reviewed in an attempt to clearly define the environments of deposition for reservoir sands in the Matagorda 668 field: well log curve shapes, seismic amplitude responses, micropaleontology, and thin section sedimentary petrology. All four lines of evidence support the interpretation that these lower Miocene sands were deposited as fan complexes.

  18. Middle Miocene vertebrates from the Amazonian Madre de Dios Subandean Zone, Perú

    NASA Astrophysics Data System (ADS)

    Antoine, Pierre-Olivier; Roddaz, Martin; Brichau, Stéphanie; Tejada-Lara, Julia; Salas-Gismondi, Rodolfo; Altamirano, Ali; Louterbach, Mélanie; Lambs, Luc; Otto, Thierry; Brusset, Stéphane

    2013-03-01

    A new middle Miocene vertebrate fauna from Peruvian Amazonia is described. It yields the marsupials Sipalocyon sp. (Hathliacynidae) and Marmosa (Micoureus) cf. laventica (Didelphidae), as well as an unidentified glyptodontine xenarthran and the rodents Guiomys sp. (Caviidae), “Scleromys” sp., cf. quadrangulatus-schurmanni-colombianus (Dinomyidae), an unidentified acaremyid, and cf. Microsteiromys sp. (Erethizontidae). Apatite Fission Track provides a detrital age (17.1 ± 2.4 Ma) for the locality, slightly older than its inferred biochronological age (Colloncuran-early Laventan South American Land Mammal Ages: ˜15.6-13.0 Ma). Put together, both the mammalian assemblage and lithology of the fossil-bearing level point to a mixture of tropical rainforest environment and more open habitats under a monsoonal-like tropical climate. The fully fluvial origin of the concerned sedimentary sequence suggests that the Amazonian Madre de Dios Subandean Zone was not part of the Pebas mega-wetland System by middle Miocene times. This new assemblage seems to reveal a previously undocumented “spatiotemporal transition” between the late early Miocene assemblages from high latitudes (Patagonia and Southern Chile) and the late middle Miocene faunas of low latitudes (Colombia, Perú, Venezuela, and ?Brazil).

  19. Upper-miocene submarine volcanism in the strait of sicily (banco senza nome)

    NASA Astrophysics Data System (ADS)

    Beccaluva, L.; Colantoni, P.; Savelli, C.; di Girolamo, P.

    1981-09-01

    Two basaltic fragments dredged from a volcanic seamount in the Sicilian continental slope of the Strait of Sicily show petrochemical features typical of within plate alkalibasaltic lavas and K/Ar age of about 10 m.y. The data represent the first volcanic evidence of Upper Miocene tensional tectonics in this sector of the African plate.

  20. Evidence for ice-free summers in the late Miocene central Arctic Ocean

    PubMed Central

    Stein, Ruediger; Fahl, Kirsten; Schreck, Michael; Knorr, Gregor; Niessen, Frank; Forwick, Matthias; Gebhardt, Catalina; Jensen, Laura; Kaminski, Michael; Kopf, Achim; Matthiessen, Jens; Jokat, Wilfried; Lohmann, Gerrit

    2016-01-01

    Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene sediments close to the seafloor. Here we document the presence of IP25 as a proxy for spring sea-ice cover and alkenone-based summer sea-surface temperatures >4 °C that support a seasonal sea-ice cover with an ice-free summer season being predominant during the late Miocene in the central Arctic Ocean. A comparison of our proxy data with Miocene climate simulations seems to favour either relatively high late Miocene atmospheric CO2 concentrations and/or a weak sensitivity of the model to simulate the magnitude of high-latitude warming in a warmer than modern climate. PMID:27041737

  1. Miocene sandstone provenance relations in the Gulf of Suez: Insights into synrift unroofing and uplift history

    SciTech Connect

    Evans, A.L. )

    1990-09-01

    Time-compositional relations inferred from point counts of 46 upper Oligocene to middle Miocene syn-rift sandstones from Gulf of Suez outcrops are used to further constrain the uplift and unroofing history of this Neogene continental rift. Although earliest rifting began by approximately 24 Ma, as evidenced by minor basaltic volcanism, the main phase of crustal extension, tectonic subsidence of the axial trough, and rift-margin uplift began approximately 19 Ma. Oligocene and basal Miocene (Nukhul Formation) sandstones are dominated by monocrystalline quartz and clasts derived from only the youngest prerift strata (Eocene), indicating that relief was probably less than 200 m until 20 Ma. The lower Miocene Rudeis Formation records both major subsidence in the axial trough and peak unroofing of the prerift sedimentary sequence from 19-16 Ma. Middle Miocene sandstones derived from the Kareem and Belayim formations are increasingly dominated by crystalline basement-derived detritus, recording rapid increase in rift-margin relief after approximately 14 Ma. Diachronism in the first appearance of unroofed basement detritus across the rift indicates uplift of the western margin may have preceded that of the eastern margin by as much as 2 m.y. Once rapid uplift began, between about 20-17 Ma, unroofing of a maximum of 1000 m of the prerift strata occurred in less than 2 m.y. 9 figs., 2 tabs.

  2. A remarkable new pygmy grasshopper (Orthoptera, Tetrigidae) in Miocene amber from the Dominican Republic

    PubMed Central

    Heads, Sam W.; Thomas, M. Jared; Wang, Yinan

    2014-01-01

    Abstract A new genus and species of pygmy grasshopper (Orthoptera: Tetrigidae) is described from Early Miocene (Burdigalian) Dominican amber. Electrotettix attenboroughi Heads & Thomas, gen. et sp. n. is assigned to the subfamily Cladonotinae based on the deeply forked frontal costa, but is remarkable for the presence of tegmina and hind wings, hitherto unknown in this subfamily. PMID:25147472

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

    PubMed Central

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

    2009-01-01

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

  4. Late Oligocene and Early Miocene Muroidea of the Zinda Pir Dome

    PubMed Central

    Lindsay, Everett H.; Flynn, Lawrence J.

    2016-01-01

    A series of Oligocene through Early Miocene terrestrial deposits preserved in the foothills of the Zinda Pir Dome of western Pakistan produce multiple, superposed fossil mammal localities. These include small mammal assemblages that shed light on the evolution of rodent lineages, especially Muroidea, in South Asia. Nine small mammal localities span approximately 28–19 Ma, an interval encompassing the Oligocene–Miocene boundary. The Early Miocene rodent fossil assemblages are dominated by muroid rodents, but muroids are uncommon and archaic in earlier Oligocene horizons. The Zinda Pir sequence includes the evolutionary transition to modern Muroidea at about the Oligocene–Miocene boundary. We review the muroid record for the Zinda Pir Dome, which includes the early radiation of primitive bamboo rats (Rhizomyinae) and early members of the modern muroid radiation, which lie near crown Cricetidae and Muridae. The Zinda Pir record dates diversification of modern muroids in the Indian Subcontintent and establishment by 19 Ma of muroid assemblages characteristic of the later Siwaliks. PMID:26681836

  5. Gravity modeling reveals that the "Miocene Pyrenean peneplain" developed at high elevation

    NASA Astrophysics Data System (ADS)

    Bosch, Gemma V.; Van Den Driessche, Jean; Robert, Alexandra; Babault, Julien; Le Carlier, Christian

    2016-04-01

    Geodynamics that shaped the present morphology of the western Mediterranean are mostly linked to the African-Eurasia collision and the extension related to the Mediterranean opening. The Pyrenean chain formed by the collision between the Iberian microplate and the Eurasian plate from the Eocene to the late Oligocene. This resulted in lithosphere thickening especially below the Central Pyrenees that becomes thinner eastwards. Whether the later thinning of the lithosphere in the easternmost Pyrenees involves the removal of the lithospheric mantle or not is debated. This issue joins the problematics about the origin of the high-elevation of the "Miocene Pyrenean peneplain" remnants. Indeed the most striking feature of the Pyrenean morphology is the occurrence of high-elevation, low relief erosional surfaces that are interpreted as the remnants of a Miocene single planation surface, dissected and reworked by Quaternary fluvial and glacial erosion. Two end-member interpretations have proposed to explain the high elevation of this original surface. The first considers that the Miocene Pyrenean peneplain develops near sea-level and was later uplifted, the second claims that the planation surface developed at high elevation in response to the inhibition of erosion consecutively to the progressive rise of the base-level of the Pyrenean drainage network. The first interpretation implies the return to normal crustal thickness by erosion and later uplift by removal of the lithospheric mantle. The second interpretation considers that the mean elevation of the original planation surface matches the thickness of the lithosphere below the chain, taking into account some hundred meters of isostatic rebound due to Quaternary erosion. To test these interpretations, we first restore the Miocene original planation surface by mapping and interpolating the high-elevation, low relief surfaces across the Pyrenees. We then performed 1D and 2D gravity models that we compare with recent

  6. Distributional patterns of decapod crustaceans in the circum-Mediterranean area during the Oligo-Miocene

    NASA Astrophysics Data System (ADS)

    Hyžný, Matúš

    2015-04-01

    During the Oligocene and Miocene, the circum-Mediterranean area was a complex network of (mostly) shallow marine basins. Significant biogeographic differentiation of this area has been documented (Harzhauser et al. 2007), mainly during the Miocene, when connections between Proto-Mediterranean, Paratethys and Proto-Indo-West Pacific were intermittently opening and closing. These seaways allowed migration of marine faunas. Distributional patterns has so far been discussed for several different animal groups, especially for molluscs (e.g. Studencka et al. 1998; Harzhauser et al. 2002, 2003, 2007). To test these patterns with decapod crustaceans, a database has been compiled including all previously published Oligocene and Miocene decapod occurrences and newly gathered data from examined material deposited in the institutional collections. Decapod associations have been significant components of marine habitats since the Mesozoic times with ever-increasing importance throughout the Cenozoic. Müller (1979) argued that brachyuran decapods are among the best zoogeographical indicators. Although decapods were used as such indicators before (e.g. Schweitzer 2001; Feldmann & Schweitzer 2006), no detailed analysis of the circum-Mediterranean taxa has been conducted so far. Based on proposed anti-estuarine circulation pattern, decapods originated in the Proto-Mediterranean, and migrated both into the North Sea and the Paratethys. Moreover, during the Early Miocene the Rhine Graben served as a connection between the North Sea and the Paratethys which enabled faunal exchange. The Middle Miocene Proto-Mediterranean and Paratethys decapod assemblages as taken together were relatively homogeneous, although distinct due to increasing rate of endemites in the Paratethys during the Miocene. The research has been supported by FWF: Lise Meitner Program M 1544-B25. References Feldmann R.M. & Schweitzer C.E. 2006: Paleobiogeography of Southern Hemisphere decapod Crustacea. J. Paleontol

  7. Hominoid phalanges from the middle Miocene site of Paşalar, Turkey.

    PubMed

    Ersoy, A; Kelley, J; Andrews, P; Alpagut, B

    2008-04-01

    Eleven proximal and ten intermediate partial or complete hominoid phalanges have been recovered from the middle Miocene site of Paşalar in Turkey. Based on species representation at Paşalar, it is likely that most or all of the phalanges belong to Griphopithecus alpani rather than Kenyapithecus kizili, but both species may be represented. All of the complete or nearly complete phalanges appear to be manual, so comparisons to extant and other fossil primate species were limited to manual phalanges. Comparisons were made to extant hominoid and cercopithecoid primate genera expressing a variety of positional repertoires and varying degrees of arboreality and terrestriality. The comparisons consisted of a series of bivariate indices derived from previous publications on Miocene catarrhine phalangeal morphology. The proximal phalanges have dorsally expanded proximal articular surfaces, which is characteristic of cercopithecoids and most other Miocene hominoids, and indicates that the predominant positional behaviors involved pronograde quadrupedalism. Among the extant primates, many of the proximal and intermediate phalangeal indices clearly distinguish more habitually terrestrial taxa from those that are predominantly arboreal, and especially from taxa that commonly engage in suspensory activities. For nearly every index, the values of the Paşalar phalanges occupy an intermediate position-most similar to values for Pan and, to a lesser extent, Macaca-indicating a generalized morphology and probably the use of both arboreal and terrestrial substrates. At least some terrestrial activity is also compatible with reconstructions of the Paşalar habitat. Most proximal and intermediate phalanges of other middle and late Miocene hominoids have similar index values to those of the Paşalar specimens, revealing broadly similar manual phalangeal morphology among many Miocene hominoids.

  8. Depositional history of Oligocene-Miocene carbonate rocks of northeastern Puerto Rico

    SciTech Connect

    Scharlach, R. )

    1990-05-01

    The apparent tectonic stability of the northern Puerto Rico platform during the late Oligocene and early Miocene allows for the depositional history of subsurface carbonate rocks of northeastern Puerto Rico to be related to major changes in eustatic sea level. During a late Oligocene north to south transgression of sea level, fluvial/deltaic to shallow marine terrigenous sediments (San Sebastian Formation) and, subsequently, open-ramp carbonates (Lares Limestone) accumulated in the central basin. Following a minor regression (third-order cycle ), a more extensive early Miocene( ) transgression resulted in deposition of deeper ramp carbonate mudstone and marl (Mudstone unit) in an apparent trough in the central basin, and open-ramp reefal carbonate (upper Lares) was deposited over a wider area of the basin. The San Sebastian Formation/Lares Limestone/Mudstone Unit sequence was most likely deposited during the second-order supercycle, TB{sub 1}. An early Miocene relative fall in sea level resulted in deposition of interfingering inner-ramp limestone and terrigenous sediments (Cibao Formation) and the development of subaerial costs, especially in the upper part of the unit. During a sea level rise, terrigenous deposition decreased and gave way to inner- and middle-ramp carbonate sediments (Los Puertos Limestone). A middle Miocene highstand in sea level brought basin-wide deposition of open-ramp carbonate sediments (Aymamon Ls). The Cibao Formation/Los Puertos Limestone/Aymamon. Limestone sequence may correspond to the second-order supercycle, TB{sub 2}. During the late middle Miocene( ), the carbonate platform was exposed and extensively karsted, possibly in an event related to the sea level drop at the end of TB{sub 2}.

  9. Changes in the Indonesian Throughflow and southeast Asian hydroclimate during the Middle-Miocene Climate Transition

    NASA Astrophysics Data System (ADS)

    Frigola Boix, Amanda; Prange, Matthias; Schulz, Michael

    2013-04-01

    The present-day Indonesian Throughflow (ITF), a key component in the global ocean circulation, transports relatively cold low-salinity water from the Pacific to the Indian oceans. This ocean current is of course not a constant system, meaning that its characteristics have changed throughout its history, both due to local forcings, such as changes in the geometry of the passages, and changes in the global climate system, such as the Middle-Miocene Climate Transition. The Middle-Miocene Climate Transition leads from the warm Middle-Miocene Climatic Optimum into the subsequent "icehouse world". The transition is associated with an increase in Antarctic glaciation at ~13.9 Ma. The aim of this study is to investigate the differences in atmospheric and ocean circulation between the warm and cold climate states in the Middle Miocene, specifically on changes in the characteristics of the ITF and shifts in the tropical rainbelt. We test whether there was a northward movement of the tropical rainbelt in southeast Asia as has been suggested on the basis of palaeoclimatic proxy records. We employ the comprehensive Community Climate System Model (CCSM) version 3.0 in a medium resolution. All the experiments used Miocene boundary conditions, including topography, bathymetry and vegetation. Two simulations were carried out, representing the time before and after the climate transition. Different boundary conditions take into account changes in ice-sheet geometry, sea-level and atmospheric CO2 concentration. The state prior to the transition is characterized by Antarctica being partially glaciated, with one ice cap covering the Transantarctic Mountains and another over East Antarctica. The second simulation corresponds to a fully glaciated Antarctica with one single merged ice-sheet covering the whole continent. We will present initial analyses of hydrological fields and ocean circulation to assess the role of Antarctic glaciation on tropical climate.

  10. Palynological evidence for late Miocene stepwise aridification on the northeastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Liu, Jia; Li, Ji Jun; Song, Chun Hui; Yu, Hao; Jiang Peng, Ting; Chuang Hui, Zheng; Ye, Xi Yan

    2016-07-01

    Holding a climatically and geologically key position both regionally and globally, the northeastern Tibetan Plateau provides a natural laboratory for illustrating the interactions between tectonic activity and the evolution of the Asian interior aridification. Determining when and how the late Miocene climate evolved on the northeastern Tibetan Plateau may help us better understand the relationships among tectonic uplift, global cooling and ecosystem evolution. Previous paleoenvironmental research has focused on the western Longzhong Basin. Late Miocene aridification data derived from pollen now require corroborative evidence from the eastern Longzhong Basin. Here, we present a late Miocene pollen record from the Tianshui Basin in the eastern Longzhong Basin. Our results show that a general trend toward dry climate was superimposed by stepwise aridification: a temperate forest with a rather humid climate existed in the basin between 11.4 and 10.1 Ma, followed by a temperate open forest environment with a less humid climate between 10.1 and 7.4 Ma, then giving way to an open temperate forest-steppe environment with a relatively arid climate between 7.4 and 6.4 Ma. The vegetation succession demonstrates that the aridification of the Asian interior occurred after ˜ 7-8 Ma, which is confirmed by other evidence from Asia. Furthermore, the aridification trend on the northeastern Tibetan Plateau parallels the global cooling of the late Miocene; the stepwise vegetation succession is consistent with the major uplift of the northeastern Tibetan Plateau during this time. These integrated environmental proxies indicate that the long-term global cooling and the Tibetan Plateau uplift caused the late Miocene aridification of the Asian interior.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Paleogeographic and structural setting of Miocene strata in central western Nevada

    SciTech Connect

    Stewart, J.H. )

    1993-04-01

    Late Cenozoic sedimentary rocks as old as 19 Ma are widely distributed in central western Nevada. They are greatly more abundant than older Cenozoic strata and are commonly interpreted to have formed in fault-bounded basins that mark the onset of widespread extension in the Basin and Range Province. Miocene strata are largely coeval with a magmatic arc that extended south southeast near the boundary of the Basin and Range and Sierra Nevada Provinces. This arc produced voluminous andesitic flows and lahars that locally interfinger with the Miocene strata. Miocene depositional basins apparently varied greatly in size. The largest that can be defined clearly is the Esmeralda Basin that was at least 65 km long and 45 km wide. Other basins may have been larger but are difficult to reconstruct; still other basins may be small and isolated, particularly within the magmatic arc. Lacustrine deposits and minor interfingering deltaic and distal fluvial units predominate; near-source, coarse alluvial-fan and megabreccia landslide deposits are locally conspicuous. coarse near-source deposits, particularly landslide deposits, are interpreted to be adjacent to basin-bounding normal faults. The Esmeralda, Coal Valley, and Gabbs Valley-Stewart Valley-Tonopah Basins are interpreted to be related to large-scale Miocene extension. Other basins may be (1) pull-apart structures related to strike-slip faults, (2) downdropped blocks in areas of cross-cutting normal and/or strike-slip faults related to changes in the extension direction or (3) grabens or half-grabens related to uniform extension. Younger Cenozoic basins, including present-day basins, overprint and cut across the Miocene basins.

  13. The effect of a flexible hydrological discharge model on the climate of the Middle Miocene

    NASA Astrophysics Data System (ADS)

    Stärz, Michael; Ward, Andrew; Stepanek, Christian; Lohmann, Gerrit

    2016-04-01

    The Middle Miocene (~17‒14 Myrs ago) climate is characterized by much warmer temperatures and an amplified hydrological cycle with respect to present-day climate. Though it is well known that a change in the global freshwater distribution via the hydrological cycle can impact climate and large scale ocean circulation, most modelling studies encompassing tectonic time scales rather focus on the sensitivity of the climate to orography, ocean gateways, land surface, ice-sheets, and CO2 changes. Alternatively, here we study the effect of two different kinds of hydrological discharge models and their respective boundary conditions, that are fully implemented in the earth system model COSMOS, on the climate of the Middle Miocene. The standard hydrological discharge model (HD) of COSMOS requires the information of high spatial resolution orography for the Middle Miocene that is conventionally tuned to present-day conditions, to calculate river routing following the steepest slope of the terrain. Instead, the flexible hydrological discharge model (FHD) calculates river routing by using Middle Miocene orography at identical grid resolution as the atmosphere model and additionally taking the dynamic topography of continental water levels into account. We find that the anomaly between a climate simulation of the Middle Miocene with COSMOS and HD versus a comparable simulation based on COSMOS and FHD reveals strong differences in the redistribution of freshwater in form of continental discharge from land to the ocean. As a consequence, deep water formation and large scale ocean circulation significantly differ between both model versions, emphasizing the importance of representing a realistic freshwater redistribution from land towards the ocean. We therefore conclude that a more realistic representation of climate states at tectonic time scales necessitates geological constraints on the freshwater redistribution, and changes in the freshwater redistribution may have had a

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

    USGS Publications Warehouse

    Klemm, V.; Frank, M.; Levasseur, S.; Halliday, A.N.; Hein, J.R.

    2008-01-01

    Three ferromanganese crusts from the northeast, northwest and central Atlantic were re-dated using osmium (Os) isotope stratigraphy and yield ages from middle Miocene to the present. The three Os isotope records do not show evidence for growth hiatuses. The reconstructed Os isotope-based growth rates for the sections older than 10??Ma are higher than those determined previously by the combined beryllium isotope (10Be/9Be) and cobalt (Co) constant-flux methods, which results in a decrease in the maximum age of each crust. This re-dating does not lead to significant changes to the interpretation of previously determined radiogenic isotope neodymium, lead (Nd, Pb) time series because the variability of these isotopes was very small in the records of the three crusts prior to 10??Ma. The Os isotope record of the central Atlantic crust shows a pronounced minimum during the middle Miocene between 15 and 12??Ma, similar to a minimum previously observed in two ferromanganese crusts from the central Pacific. For the other two Atlantic crusts, the Os isotope records and their calibration to the global seawater curve for the middle Miocene are either more uncertain or too short and thus do not allow for a reliable identification of an isotopic minimum. Similar to pronounced minima reported previously for the Cretaceous/Tertiary and Eocene/Oligocene boundaries, possible interpretations for the newly identified middle Miocene Os isotope minimum include changes in weathering intensity and/or a meteorite impact coinciding with the formation of the No??rdlinger Ries Crater. It is suggested that the eruption and weathering of the Columbia River flood basalts provided a significant amount of the unradiogenic Os required to produce the middle Miocene minimum. ?? 2008 Elsevier B.V.

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

    PubMed Central

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

    2016-01-01

    Abstract During the Oligo‐Miocene, major phases of phosphogenesis occurred in the Earth's oceans. However, most phosphate deposits represent condensed or allochthonous hemipelagic deposits, formed by complex physical and chemical enrichment processes, limiting their applicability for the study regarding the temporal pacing of Miocene phosphogenesis. The Oligo‐Miocene Decontra section located on the Maiella Platform (central Apennines, Italy) is a widely continuous carbonate succession deposited in a mostly middle to outer neritic setting. Of particular interest are the well‐winnowed grain to packstones of the middle Miocene Bryozoan Limestone, where occurrences of authigenic phosphate grains coincide with the prominent carbon isotope excursion of the Monterey event. This unique setting allows the analysis of orbital forcing on phosphogenesis, within a bio, chemo, and cyclostratigraphically constrained age‐model. LA‐ICP‐MS analyses revealed a significant enrichment of uranium in the studied authigenic phosphates compared to the surrounding carbonates, allowing natural gamma‐radiation (GR) to be used as a qualitative proxy for autochthonous phosphate content. Time series analyses indicate a strong 405 kyr eccentricity forcing of GR in the Bryozoan Limestone. These results link maxima in the GR record and thus phosphate content to orbitally paced increases in the burial of organic carbon, particularly during the carbon isotope maxima of the Monterey event. Thus, phosphogenesis during the middle Miocene in the Mediterranean was controlled by the 405 kyr eccentricity and its influence on large‐scale paleoproductivity patterns. Rare earth element data were used as a tool to reconstruct the formation conditions of the investigated phosphates, indicating generally oxic formation conditions, which are consistent with microbially mediated phosphogenesis. PMID:27570497

  16. Orbital and suborbital-scale sedimentary rhythms in the Middle Miocene Onnagawa Formation, Northeastern Japan

    NASA Astrophysics Data System (ADS)

    Kurokawa, S.; Tada, R.; Takahashi, S.; Itaki, T.; Kubota, Y.

    2014-12-01

    Late Quaternary climate is characterized by millennial-scale abrupt climatic changes namely Dansgaard-Oeschger Cycles. Such millennial-scale changes are faithfully recorded in the Japan Sea sediments as alternation of dark and light colored silty clay, and the relationship between the millennial-scale variability and orbitally-driven changes in ice volume has been explored. On the other hand, presence of similar millennial-scale changes was reported from the Middle Miocene alternations of dark and light colored siliceous rocks in the Onnnagawa Formation, Northeastern Japan. Because large, unstable ice sheet was present during the Late Quaternary and the Middle Miocene, it is suggested that such millennial-scale variability and waxing and waning of unstable ice sheet could be interrelated. Thus, it is important to specify the cyclicity and the amplitude variability of millennial-scale cycles during the Middle Miocene to understand the underlying mechanism and the ultimate cause. The Middle Miocene Onnagawa Formation is known as bedded siliceous rocks equivalent to the Monterey Formation, California. Tada (1991) demonstrated that its cm-scale dark-light colored alternations reflected millennial-scale variability. However, the timing, periodicity, and duration of the millennial-scale variability are not fully understood. Thus, we aim to clarify when the millennial-scale variability became distinct and faded out, and examine its possible association with ice volume changes. We conducted a field survey in the Yashima area, Akita, Northeastern Japan to reconstruct a continuous sedimentary record throughout the Middle Miocene, and constructed the age model based on biostratigraphy. In addition, we identified cyclic changes in lithology, and applied cyclostratigraphy to produce the high-resolution age model. Based on this age model, we attempt correlation with δ18O curve to examine the relationship between cyclicity of δ18O changes and occurrence of millennial

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

    PubMed

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

    2010-07-01

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

  18. Correlation and zonation of miocene strata along the atlantic margin of North America using diatoms and silicoflagellates

    USGS Publications Warehouse

    Abbott, W.H.

    1978-01-01

    Six Atlantic Miocene siliceous microfossil zones are proposed based on onshore and offshore samples from the United States Atlantic Margin. Diatoms and silicoflagellates are used to establish the zones. These zones are from oldest to youngest: 1. Zone I Actinoptychus heliopelta Concurrent Range Zone - Early Miocene 2. Zone II Delphineis ovata Partial Range Zone - late Early to early Middle Miocene 3. Zone III Delphineis ovata/Delphineis penelliptica Concurrent Range Zone - early Middle Miocene 4. Zone IV Delphineis penelliptica Partial Range Zone - Middle Miocene 5. Zone V Delphineis penelliptica/Coscinodiscus plicatus Concurrent Range Zone - Middle Miocene 6. Zone VI Coscinodiscus plicatus Partial Range Zone - Middle Miocene. The six zones are easily traced along the Southern and Middle Atlantic Seaboard, but the older three are found for the most part between Cape Hatteras and New Jersey. There is some suggestion of sea-level change during Zone IV. Using rare planktonic diatoms that are index species from other regions and the zonal markers established in this study, correlation can be made with the Standard Foraminiferal Zones, the North Pacific Diatom Zones and with DSDP core 391A in the Blake-Bahama Basin. ?? 1978.

  19. Post-Miocene Tectonics from Black Sea to Mediterrenean Sea along Central Anatolian Plateau

    NASA Astrophysics Data System (ADS)

    Rojay, B.; Özsayın, E.; Çiner, A.

    2012-04-01

    The existences of the gross structures are crucial elements in the understanding of the Neogene evolution of the Anatolia. The structures, from north to south, are fairly documented extensional Black Sea coast structures, "N vergent tectonics" in Black Sea region, the cross cutting scar/shear zone -North Anatolian Fault- , S verging tectonics in central Anatolian overthrust belt (Cretaceous ophiolitic mélange belt), extensional Tuzgölü basin, basins like Cilicia, Mut situated to the back of the Cyprian arc and Cyprus locked subduction and accretionary tectonics (locked by approaching and colliding of the Eratosthenes and Hecatacus "seamount" obstacles). The closure of the northern Neotethys during post-Late Eocene- pre-Miocene end with the collision of the squeezed "Anatolian Block" from south with the Eurasian Continent. Consequently the linkage of the central Anatolian basins is lost with the Seas (Paratethys) in north by the evolution of Black Sea Mountains. However, the subduction in southern Neotethys continued with a complex array due to oblique subduction between "Anatolian Block" and downgoing African-Arabian plates. The growth of the accretionary wedge along southeast Anatolia resulted in retreat of the Miocene Seas towards Basra Bay (Iraq) and collision of the southeast Anatolian belt operated to the end of late Miocene where the marine realm in eastern Mediterrenean Sea continues. The rifting - sea-floor spreading in Red Sea, propagating of Dead Sea Transform to the north and oblique subduction in southern Tethys Ocean during different times in Miocene-Pliocene manifested a various different tectonic mechanism stories in the evolution of the Neogene basin in Anatolia. Consequently progressive closure of the Tethys Oceans resulted in the development Central Anatolian and Eastern Anatolian Plateaus. The growth of the Plateaus, in other words, the progressive shortening from north to south during Late Miocene, ended with the escape of the Anatolian Block

  20. Ocean Circulation and Gateway Closures During the Late Miocene (~13-5 Ma)

    NASA Astrophysics Data System (ADS)

    Nathan, S. A.; Leckie, R. M.

    2004-12-01

    Long-term climate change is driven by tectonic influences, including changes in ocean circulation that are the result of ocean gateway closure. During the middle to late Miocene (~13-5 Ma), both tropical ocean circulation and deep water production were reorganized due to the increasing constriction of the Indonesian and Central American seaways. For example, the waters of the modern Pacific equatorial current system do not move freely into the Indian Ocean (i.e., via the Indonesian Throughflow, ITF) but instead pile up to form the Western Pacific Warm Pool (a thermal anomaly that greatly influences tropical Pacific climate and ocean circulation). Here we use a continuous record of multispecies stable isotope stratigraphy and foraminiferal assemblage counts from Ontong Java Plateau to demonstrate that during middle to late Miocene time, progressive restriction of the ITF, modulated by sea level fluctuations, resulted in the waxing and waning of a proto-warm pool in the western equatorial Pacific (WEP). The proto-warm pool profoundly affected the early late Miocene "carbonate crash" (an anomalous decrease of carbonate in deep sea sediments) and the late Miocene "biogenic bloom" (sharp increase in carbonate accumulation rates across the tropical Indo-Pacific). We hypothesize that El Niño/La Niña-like alternations of tropical carbonate preservation and productivity between the western and eastern equatorial Pacific during the late Miocene were the consequence of early warm pool development and decay. A proto-warm pool was formed ~12.1-10.6 Ma, which initiated a nutrient-rich Equatorial Undercurrent and/or increased Trade Wind strength. These La Niña-like conditions sustained carbonate productivity in the eastern equatorial Pacific (EEP) at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening and El Niño-like conditions ~10.6-8.8 Ma intensified a "carbonate crash" in the EEP, while resurgence of the warm pool and La Ni

  1. Palynology of the Heath Formation (Miocene) from the Progreso Basin, Peru

    SciTech Connect

    Engelhardt, D.W. ); Wood, G.D. )

    1993-02-01

    A diverse and well preserved assemblage of pollen, spores, dinoflagellates, and acritarchs were recovered from outcrop samples of the Heath Formation, exposed along Bocapan Creek near Tumbes, Peru. The pollen and spores include representatives of Arecipites, Bombacacidites, Caryapollenites, Cicatricosisporites, Couperipollis, Cyathidites, Diporisporites, Distaverrusporites, Dyadosporites, Echiperiporites, Faramea, Foveodiporites, Foveotriletes, Fusiformisporites, Gothanipollis, Granitricolpites, Hymenophyllum, Hexpollenties, Involutisporites, Laevigatosporites, Lygodiumsporites, Magniperiporites, Malvacearumpollis, Monocolpopollenites, Perissyncolporites, Peritheciumites, Phragmothyrites, Polyadadporites, Polypodiaceisporites, Polypodiisporites, Retibrevitricolpites, Striadisporites, Tetracolporites, Tricolporopollenties, and Verrucosisporites. Plankton are assignable to Lejeunecysta, Operculodinium, Pterospermella, Selenopemphix, Spiniferites, Sumatradinium, Tythodiscus, and Tuberculodinium. The palynomorph assemblage can be placed in the Early Miocene based on the co-occurrence of Cicatricosisporites dorogensis, Couperipollis rarispinosus, Echiperiporites estelae, Magniperiporites echinatus, Perisyncolporites porkornii, Polypodiaceoisporites minor, P. potoniei, Reticolporites guianesnsis, R. irregularis, Scabriporites asymetricus, Selenopemphix nephroides and Tuberculodinium vancampoae. This is an agreement with foraminiferal evidence which positions the Heath Formation in the Early Miocene Catapsydrax dissimilis, Catapsydrax stainforthi and oldest portion of the Globigerinatella insueta zones.

  2. Sr-isotopic, paleomagnetic, and biostratigraphic calibration of horse evolution: Evidence from the Miocene of Florida

    SciTech Connect

    MacFadden, B.J.; Bryant, J.D.; Mueller, P.A. )

    1991-03-01

    During the middle Miocene an explosive adaptive radiation resulted in the advent of grazing horses with high-crowned teeth in North America. New Sr isotopic, paleomagnetic, and biostratigrahic evidence from the Miocene marine and nonmarine sequence of the Florida panhandle calibrates the base of this adaptive radiation. The transition from the primitive outgroup species 'Parahippus' leonensis to the most primitive high-crowned horse, 'Merychippus' gunteri occured after about 17.7 Ma. After this event, the lowest known stratigraphic level at which diversification (i.e., presence of two or more sympatric species) of grazing merychippine horses occurs is about 16.2 Ma, or within the early part of Chron C5BR. Although this currently is the only sequence where the parahippine-merychippine transition is directly calibrated, biochronologic evidence from other important, contemporaneous localities in Texas, Nebraska, and California indicate that diversification occured rapidly throughout North America between 15 and 16 Ma.

  3. Sensitivity of climate and Atlantic overturning circulation to uncertain ocean gateway configurations for the late Miocene

    NASA Astrophysics Data System (ADS)

    Bradshaw, C.; Lunt, D. J.; Flecker, R.; Martinez-Mendez, G.

    2013-12-01

    The palaeorecord documents late Miocene (11.6-5.3 Ma) climate to be much warmer and wetter than today yet CO2 reconstructions are similar to modern levels. Given the apparent decoupling between CO2 and warmth for this period we investigate here the role of the oceans. The late Miocene experienced significant tectonic change including the restriction of some of the last ocean gateways to close (Panama Gateway and Indonesian Seaway) and open (Bering Strait and Barents/Kara Sea). However, the timing and configuration of these tectonic changes is uncertain. The final closure of the Panama Gateway is dated to the Pliocene, but continental mammal exchange suggests the existence of a Central American archipelago from the mid-late Miocene. The Bering Strait is typically assumed to have opened at the very end of the late Miocene/early Pliocene based on diatom exchange, but other marine and terrestrial evidence points to a much earlier, perhaps intermittent, opening. The timing of the restriction of the Indonesian Seaway is very poorly constrained at middle Miocene to Pliocene. The Barents Sea and Kara Sea shelves are documented as having being subject to extensive glacial erosion and post-glacial uplift since the Pliocene and throughout the Quaternary but records of uplift and erosion during the earlier Cenozoic are limited. However, the presence of significant preglacial sediments suggests that this region underwent tectonic uplift, volcanism and subsequent erosion during the Eocene-Miocene period although the age assignment of the data remains controversial. The Panama Gateway has been suggested to influence North Atlantic Deep Water (NADW) production through numerous modelling studies, the Bering Strait has been suggested to greatly impact NADW during the Quaternary, and the strength of Indonesian Throughflow is hypothesised to influence Agulhas Leakage, which, in turn, has been speculated to influence Atlantic meridional overturning and thus NADW production. Here, we

  4. Eocene to post-Miocene kinematic evolution of the central Cyclades (Greece)

    NASA Astrophysics Data System (ADS)

    Draganits, E.; Huet, B.; Grasemann, B.; Schneider, D.; Ertl, A.

    2012-04-01

    Due to the extraordinary geotectonic location of the Aegean above an active subduction zone and an exceptional high seismicity, this area and especially the Cyclades have been in the focus of structural investigations for several decades. The present deformation is the result of ongoing plate tectonic movements in this area since at least the Miocene. The ductile structures of the Miocene extension and related metamorphic core type deformation are quite well studied and understood. Equally well investigated are the active tectonic deformation and associated brittle structures through several decades of seismic records. However, due to the difficulties of dating brittle faults, the kinematic evolution from the early to middle Miocene ductile structures, to later Miocene brittle-ductile and brittle faults is much less understood. For these reasons detailed structural fieldwork, combined with Ar-Ar geochronology and P-T studies, have been carried out on the uninhabited island of Despotiko, SW of Antiparos, which is situated virtually in the center of the Cycladic islands. This island has been selected because the existence of metamorphic rocks penetrated by Messinian rhyolite pipes and Pleistocene eolianites provide exceptional age constraints for Eocene to post-Miocene deformation structures. Despotiko is part of lower structural levels of the polymetamorphic Blueschist Unit of the Attic-Cycladic Metamorphic Belt and correlated lithologically with the Parikia gneisses and Marathi unit of Paros. Foliation is shallowly dipping towards the SSW. The main lithologies of the island, from the footwall to the hanging wall, consist of dark to pale grey, strongly foliated, mylonitic granite gneiss with abundant pegmatite dikes. The gneiss is overlain by prominent white, strongly foliated, mylonitic gneiss. Above are medium-grained, white calcite marble followed by greenish-white, mylonitic gneiss and an alternation of mica schist, greenschist, thin marble layers and some small

  5. Late Miocene evolution of the Black Sea: insights from palynology and strontium isotope ratios

    NASA Astrophysics Data System (ADS)

    Grothe, Arjen; van Baak, Christiaan; Vasiliev, Iuliana; Sangiorgi, Francesca; Reichart, Gert-Jan; Stoica, Marius; Krijgsman, Wout

    2016-04-01

    During the late Miocene, the connection(s) between the Mediterranean Basin and the Atlantic Ocean deteriorated, which ultimately culminated in thick evaporite deposits and a water level drop in the Mediterranean Basin during the so-called Messinian Salinity Crisis (MSC, 5.97 - 5.33 Ma). It has been claimed that Black Sea, in response to the MSC, also desiccated but these claims have been proven incorrectly. Here we present palynological (dinoflagellate cysts and pollen) and strontium isotope ratios from two Black Sea records: the Zheleznyi Rog outcrop section and Deep Sea Drilling Project Hole 380A. Organic walled cyst-producing dinoflagellates are highly sensitive to even small changes in surface waters and strontium isotope ratios are excellent recorders of changing connectivity. Our records provide therefore more insights in the sensitivity of the Black Sea to Messinian Salinity Crisis and the general evolution of the late Miocene Black Sea.

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

    PubMed

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

    2016-03-01

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

  7. The femur of Orrorin tugenensis exhibits morphometric affinities with both Miocene apes and later hominins.

    PubMed

    Almécija, Sergio; Tallman, Melissa; Alba, David M; Pina, Marta; Moyà-Solà, Salvador; Jungers, William L

    2013-01-01

    Orrorin tugenensis (Kenya, ca. 6 Ma) is one of the earliest putative hominins. Its proximal femur, BAR 1002'00, was originally described as being very human-like, although later multivariate analyses showed an australopith pattern. However, some of its traits (for example, laterally protruding greater trochanter, medially oriented lesser trochanter and presence of third trochanter) are also present in earlier Miocene apes. Here, we use geometric morphometrics to reassess the morphological affinities of BAR 1002'00 within a large sample of anthropoids (including fossil apes and hominins) and reconstruct hominoid proximal femur evolution using squared-change parsimony. Our results indicate that both hominin and modern great ape femora evolved in different directions from a primitive morphology represented by some fossil apes. Orrorin appears intermediate between Miocene apes and australopiths in shape space. This evidence is consistent with femoral shape similarities in extant great apes being derived and homoplastic and has profound implications for understanding the origins of human bipedalism.

  8. Late Miocene hominin teeth from the Gona Paleoanthropological Research Project area, Afar, Ethiopia.

    PubMed

    Simpson, Scott W; Kleinsasser, Lynnette; Quade, Jay; Levin, Naomi E; McIntosh, William C; Dunbar, Nelia; Semaw, Sileshi; Rogers, Michael J

    2015-04-01

    Since 2000, significant collections of Latest Miocene hominin fossils have been recovered from Chad, Kenya, and Ethiopia. These fossils have provided a better understanding of earliest hominin biology and context. Here, we describe five hominin teeth from two periods (ca. 5.4 Million-years-ago and ca. 6.3 Ma) that were recovered from the Adu-Asa Formation in the Gona Paleoanthropological Research Project area in the Afar, Ethiopia that we assign to either Hominina, gen. et sp. indet. or Ardipithecus kadabba. These specimens are compared with extant African ape and other Latest Miocene and Early Pliocene hominin teeth. The derived morphology of the large, non-sectorial maxillary canine and mandibular third premolar links them with later hominins and they are phenetically distinguishable and thus phyletically distinct from extant apes. PMID:25795338

  9. Miocene Shark and Batoid Fauna from Nosy Makamby (Mahajanga Basin, Northwestern Madagascar).

    PubMed

    Andrianavalona, Tsiory H; Ramihangihajason, Tolotra N; Rasoamiaramanana, Armand; Ward, David J; Ali, Jason R; Samonds, Karen E

    2015-01-01

    Madagascar is well known for producing exceptional fossils. However, the record for selachians remains relatively poorly known. Paleontological reconnaissance on the island of Nosy Makamby, off northwest Madagascar, has produced a previously undescribed assemblage of Miocene fossils. Based on isolated teeth, ten taxonomic groups are identified: Otodus, Carcharhinus, Galeocerdo, Rhizoprionodon, Sphyrna, Hemipristis, Squatina, Rostroraja, Himantura and Myliobatidae. Six are newly described from Madagascar for the Cenozoic (Galeocerdo, Rhizoprionodon, Sphyrna, Squatina, Rostroraja and Himantura). In association with these specimens, remains of both invertebrates (e.g., corals, gastropods, bivalves) and vertebrates (e.g., bony fish, turtles, crocodylians, and sirenian mammals) were also recovered. The sedimentary facies are highly suggestive of a near-shore/coastal plain depositional environment. This faunal association shares similarities to contemporaneous sites reported from North America and Europe and gives a glimpse into the paleoenvironment of Madagascar's Miocene, suggesting that this region was warm, tropical shallow-water marine. PMID:26075723

  10. Depositional and structural evolution of the Middle Miocene depositional episode, east-central Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Combellas Bigott, Ricardo Ignacio

    Two widespread, transgressive deposits associated with the faunal top Amphistegina B (15.5 Ma) and Textularia W (12.1 Ma) define the Middle Miocene depositional episode. An extensive stratigraphic correlation framework established in this study allowed tracing of the middle Miocene sediment dispersal system from the shelf through the slope to the basin floor in the complex paleogeography of the east-central Gulf of Mexico. The Middle Miocene depositional episode is recorded in four genetic cycles (˜1 to 2 Ma), bounded by regional maximum flooding surfaces in the shelf and shelf margin setting, and three equivalent seismic sequences punctuated by condensed sections in the slope and basin floor. Two principal, long-lived extrabasinal fluvial/delta axes, the ancestral Mississippi and the Tennessee systems, provided the bulk of sediments that infilled the middle Miocene depocenters. Salt-related structural provinces controlled the configuration of the depocenters. Structural linked systems, dominated by gravity spreading, and a minibasin province, driven by differential subsidence, were established during the Middle Miocene depositional episode. Sediment supply coupled with wave energy flux, high-frequency sea-level changes, and salt tectonism determined the time and space distribution of progradation, aggradation, and retrogradation of system tracts. Middle Miocene shelf margins have prograded 20 to 40 miles from the relict lower Miocene shelf margin. Two depositional systems tracts characterize the constructional shelf margin: (1) a mixed-load fluvial-dominated platform delta/shelf-margin delta/delta-fed apron systems tract; and (2) a strandplain/shelf/muddy slope systems tract. However, the constructional, offlapping shelf margin systems were locally punctuated by a large-scale phase of retreat and erosion, named the Harang collapse system, in which a large volume of sediments bypassed the shelf margin to be deposited on the slope and basin floor. The Harang

  11. Faunal change in the Turkana Basin during the late Oligocene and Miocene.

    PubMed

    Leakey, Meave; Grossman, Ari; Gutiérrez, Mercedes; Fleagle, John G

    2011-01-01

    Faunal evolution over the last 65 million years of earth's history was dominated by mammalian radiations, but much of this era is poorly represented in Africa. Mammals first appeared early in the Mesozoic, living alongside dinosaurs for millions of years, but it was not until the extinction of dinosaurs 65 myr ago that the first major explosion of mammalian taxa took place. The Cenozoic (65 Ma to Recent) witnessed repeated and dynamic events involving the radiation, evolution, and extinction of mammalian faunas. Two of these events, each marking the extinction of one diverse fauna and subsequent establishment of another equally diverse fauna, both involving advanced catarrhine primates, are recorded in sites in the Turkana Basin, despite the poorly represented record of Cenozoic faunas elsewhere in sub-Saharan Africa. The first of these events occurred at the Oligocene-Miocene transition and the other at the Miocene-Pliocene transition.

  12. Miocene Shark and Batoid Fauna from Nosy Makamby (Mahajanga Basin, Northwestern Madagascar).

    PubMed

    Andrianavalona, Tsiory H; Ramihangihajason, Tolotra N; Rasoamiaramanana, Armand; Ward, David J; Ali, Jason R; Samonds, Karen E

    2015-01-01

    Madagascar is well known for producing exceptional fossils. However, the record for selachians remains relatively poorly known. Paleontological reconnaissance on the island of Nosy Makamby, off northwest Madagascar, has produced a previously undescribed assemblage of Miocene fossils. Based on isolated teeth, ten taxonomic groups are identified: Otodus, Carcharhinus, Galeocerdo, Rhizoprionodon, Sphyrna, Hemipristis, Squatina, Rostroraja, Himantura and Myliobatidae. Six are newly described from Madagascar for the Cenozoic (Galeocerdo, Rhizoprionodon, Sphyrna, Squatina, Rostroraja and Himantura). In association with these specimens, remains of both invertebrates (e.g., corals, gastropods, bivalves) and vertebrates (e.g., bony fish, turtles, crocodylians, and sirenian mammals) were also recovered. The sedimentary facies are highly suggestive of a near-shore/coastal plain depositional environment. This faunal association shares similarities to contemporaneous sites reported from North America and Europe and gives a glimpse into the paleoenvironment of Madagascar's Miocene, suggesting that this region was warm, tropical shallow-water marine.

  13. Late Miocene hominin teeth from the Gona Paleoanthropological Research Project area, Afar, Ethiopia.

    PubMed

    Simpson, Scott W; Kleinsasser, Lynnette; Quade, Jay; Levin, Naomi E; McIntosh, William C; Dunbar, Nelia; Semaw, Sileshi; Rogers, Michael J

    2015-04-01

    Since 2000, significant collections of Latest Miocene hominin fossils have been recovered from Chad, Kenya, and Ethiopia. These fossils have provided a better understanding of earliest hominin biology and context. Here, we describe five hominin teeth from two periods (ca. 5.4 Million-years-ago and ca. 6.3 Ma) that were recovered from the Adu-Asa Formation in the Gona Paleoanthropological Research Project area in the Afar, Ethiopia that we assign to either Hominina, gen. et sp. indet. or Ardipithecus kadabba. These specimens are compared with extant African ape and other Latest Miocene and Early Pliocene hominin teeth. The derived morphology of the large, non-sectorial maxillary canine and mandibular third premolar links them with later hominins and they are phenetically distinguishable and thus phyletically distinct from extant apes.

  14. Some palynological aspects of Oligocene to Early Miocene transition Southern Alaska

    SciTech Connect

    Wiggins, V.D.

    1985-04-01

    The Oligocene to early Miocene transition in southern Alaska perhaps represents one of the most dramatic floristic changes in the entire Tertiary of Alaska. The basic modification is from a dominant deciduous, broadleaved forest biome in the late Eocene - early Oligocene (early Zemorrian) to a dominant moist, temperate, coniferous forest biome in the early Miocene (Saucesian). A similar change can be seen between the deciduous broad-leaved forests and the montane boreal coniferous forest of China today. This change in flora - and from a palynological perspective this change in microflora - reflects the onset of global cooling in the Neogene and the concurrent change from a dominant marine transgressive to a dominant nonmarine regressive mode of sedimentation.

  15. Basal Adare volcanics, Robertson Bay, North Victoria Land, Antarctica: Late Miocene intraplate basalts of subaqueous origin

    USGS Publications Warehouse

    Mortimer, N.; Dunlap, W.J.; Isaac, M.J.; Sutherland, R.P.; Faure, K.

    2007-01-01

    Late Cenozoic lavas and associated hyaloclastite breccias of the Adare volcanics (Hallett volcanic province) in Robertson Bay, North Victoria Land rest unconformably on Paleozoic greywackes. Abundant hyaloclastite breccias are confined to a paleovalley; their primary geological features, and the stable isotope ratios of secondary minerals, are consistent with eruption in a subaqueous environment with calcite formation probably involving seawater. In contrast, the lavas which stratigraphically overlie the hyaloclastites on Mayr Spur probably were erupted subaerially. K-Ar dating of eight samples from this basal sequence confirms the known older age limit (Late Miocene) of the Hallett volcanic province. Geochemical data reveal an ocean island basalt-like affinity, similar to other Cenozoic igneous rocks of the Hallett volcanic province. If a submarine eruptive paleoenvironment is accepted then there has been net tectonic or isostatic post-Late Miocene uplift of a few hundred metres in the Robertson Bay-Adare Peninsula area

  16. Miocene Shark and Batoid Fauna from Nosy Makamby (Mahajanga Basin, Northwestern Madagascar)

    PubMed Central

    Andrianavalona, Tsiory H.; Ramihangihajason, Tolotra N.; Rasoamiaramanana, Armand; Ward, David J.; Ali, Jason R.; Samonds, Karen E.

    2015-01-01

    Madagascar is well known for producing exceptional fossils. However, the record for selachians remains relatively poorly known. Paleontological reconnaissance on the island of Nosy Makamby, off northwest Madagascar, has produced a previously undescribed assemblage of Miocene fossils. Based on isolated teeth, ten taxonomic groups are identified: Otodus, Carcharhinus, Galeocerdo, Rhizoprionodon, Sphyrna, Hemipristis, Squatina, Rostroraja, Himantura and Myliobatidae. Six are newly described from Madagascar for the Cenozoic (Galeocerdo, Rhizoprionodon, Sphyrna, Squatina, Rostroraja and Himantura). In association with these specimens, remains of both invertebrates (e.g., corals, gastropods, bivalves) and vertebrates (e.g., bony fish, turtles, crocodylians, and sirenian mammals) were also recovered. The sedimentary facies are highly suggestive of a near-shore/coastal plain depositional environment. This faunal association shares similarities to contemporaneous sites reported from North America and Europe and gives a glimpse into the paleoenvironment of Madagascar’s Miocene, suggesting that this region was warm, tropical shallow-water marine. PMID:26075723

  17. The Miocene Cyprideis species flock (Ostracoda; Crustacea) of western Amazonia (Solimões Formation)

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The Miocene mega-wetland of western Amazonia holds a diverse, largely endemic aquatic invertebrate fauna (e.g., molluscs, ostracods). Among ostracods, the genus Cyprideis experienced a remarkable radiation. Micropalaeontologic investigations of a 400-m-long sediment core (~62 km SW Benjamin Constant, Amazonia, Brazil) permitted a taxonomic revision of about two-thirds of hitherto described Cyprideis species. Ostracod index species enabled a biostratigraphic allocation of the well succession to the Cyprideis minipunctata to Cyprideis cyrtoma biozones (late middle to early late Miocene age). The current study underlines once more Cyprideis' remarkable capability to produce species flocks and western Amazonian Cyprideis comply with the criteria of a species flock: i) endemicity: up to now not a single species is recorded in adjacent areas; ii) monophyly: although hardly verifiable to date and probably Amazonian Cyprideis is not monophyletic s.str., several closely related, quite rapidly evolving species are proved; iii) speciosity: due to the present study, 30 formally described species exist; several further species, left in open nomenclature, are recorded in the literature, which strongly hints to a much higher, still unrecorded species richness; iv) ecological diversity: based on rare sedimentologic cross-references, ecological diversity within a highly structured wetland is possible; the current results demonstrate the sympatric occurrence of up to 12 Cyprideis species, which may indicate adaptations to different microhabitats; v) habitat dominance: regularly Cyprideis holds more than >90 % in western Amazonian ostracod assemblages during the early and middle Miocene. Explanations for this extreme habitat monopolisation are still arguable and touch the highly disputed question about the nature of western Amazonia's environments during the Miocene. It seems, however, evident that a strictly actualistic approach to endemic Neogene Amazonian biota is highly

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

    PubMed Central

    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

  19. The age of the Miocene-Pliocene boundary in the Capo Rossello area (Sicily)

    NASA Astrophysics Data System (ADS)

    Hilgen, F. J.; Langereis, C. G.

    1988-12-01

    Detailed correlations of magnetostratigraphy, biostratigraphy and lithostratigraphy reveal that the basal Pliocene is equally complete in the Eraclea Minoa and Capo Rossello sections (Sicily) and the Singa section (Calabria), and that, in accordance with the model of the Pliocene flooding event in the Mediterranean, the deposition of the pelagic marls of the Trubi Formation started synchronously on Sicily and in adjacent Calabria. In addition, the data obtained from the Trubi in the Eraclea Minoa section allows the age of the Miocene-Pliocene boundary to be adjusted slightly from 4.83-4.84 [1] to 4.86 Ma because downward extrapolation of both sedimentation rate and average duration of small-scale sedimentary cycles in the Trubi yields this age for the boundary in this section. Linearly interpolated ages for the top of the Sphaeroidinellopsis acme and the first substantial increase in Globorotalia margaritae (the FOD of this species is non-existent in the Mediterranean Pliocene) at Eraclea Minoa arrive at 4.74 and 4.63 Ma respectively. Because of the detailed magnetostratigraphy and the very accurate dating of the Miocene-Pliocene boundary, it is preferable to select the Eraclea Minoa section as the boundary stratotype rather than the Capo Rossello section. Finally, this age of 4.86 Ma for the Miocene-Pliocene boundary suggests that the beginning of the Pliocene is connected with the termination of a series of latest Miocene glaciations and that the re-establishment of open marine conditions in the Mediterranean might be of glacio-eustatic origin.

  20. Paleoenvironmental conditions in the Spanish Miocene-Pliocene boundary: isotopic analyses of Hipparion dental enamel.

    PubMed

    Domingo, Laura; Grimes, Stephen T; Domingo, M Soledad; Alberdi, M Teresa

    2009-04-01

    Expansion of C(4) grasses during Late Miocene and Early Pliocene constitutes one of the most remarkable biotic events of the Cenozoic era. The Teruel-Alfambra region (northeastern Spain) contains one of the most complete Miocene-Pliocene sequences of mammalian fossil sites in the world. In this study, stable isotope (delta (13)C and delta (18)O) analyses have been performed on the tooth enamel from the equid Hipparion from 19 localities spanning a time interval from approximately 10.9 to 2.7 Ma. This time range starts with the first appearance of this genus in Spain and ends at its extinction. An increase in delta (13)C at about 4.2 Ma has been observed, indicative of a shift toward a more open habitat. This shift may be related to a large scale vegetation change which occurred across the Miocene-Pliocene boundary when C(4) grasses expanded. This expansion might in turn be linked to global tectonic events such as the uplift of the Himalaya and/or the closure of the Panama Isthmus. However, other more regional factors may have ultimately enhanced the trend toward more open habitats in the Western Mediterranean Basin. The Messinian Salinity Crisis was a major environmental event that may have been responsible for the isotopic changes seen in the equid Hipparion from the Iberian Peninsula along with an increase in the aridity detected approximately 4.6 Ma ago in the Sahara. Even though the exact factor triggering the isotopic change observed in the Hipparion enamel remains mostly unknown, this study demonstrates that the global environmental changes detected across the Miocene-Pliocene boundary are also recorded in the realm of the Iberian Peninsula. PMID:19190888

  1. Confirmation of a late Oligocene-early Miocene age of the Deseadan Salla Beds of Bolivia

    SciTech Connect

    Naeser, C.W.; McKee, E.H.; Johnson, N.M.; MacFadden, B.J.

    1987-11-01

    Three new fission-track (zircon) and four new K-Ar (biotite) dates corroborate a late Oligocene-early Miocene age (22-28 Ma) for the Salla Beds of Bolivia. These ages contrast markedly with the previously accepted age of about 35 Ma for these strata and their contained faunas, and recasts of order and chronology of interchange between New World and Old World mammals.

  2. Confirmation of a late Oligocene-early Miocene age of the Deseadan Salla Beds of Bolivia.

    USGS Publications Warehouse

    Naeser, C.W.; McKee, E.H.; Johnson, N.M.; Macfadden, B.J.

    1987-01-01

    Three new fission-track (zircon) and four new K-Ar (biotite) dates corroborate a late Oligocene-early Miocene age (22-28 Ma) for the Salla Beds of Bolivia. These ages contrast markedly with the previously accepted age of about 35 Ma for these strata and their contained faunas, and recasts of order and chronology of interchange between New World and Old World mammals. -Authors

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

    SciTech Connect

    Reid, J.A.; Plumley, P.W. ); Schellekens, J.H. )

    1991-03-01

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

  4. A new Late Miocene hominoid from Kenya: Samburupithecus kiptalami gen. et sp. nov.

    NASA Astrophysics Data System (ADS)

    Ishida, Hidemi; Pickford, Martin

    1997-11-01

    A new genus and species of hominoid, Samburupithecus kiptalami, is erected on the basis of a maxillary specimen with complete post canine dentition. Its age is established as upper Miocene (9.5 Ma) on the basis of radioisotopic dating and associated mammalian fauna. The new genus is more closely related to the African ape —human clade (AAH) than is any other known extinct hominoid and it may well be on the line leading to hominids.

  5. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene.

    PubMed

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Gasson, Edward; Kuhn, Gerhard; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco

    2016-03-29

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene. PMID:26903644

  6. A molecular stable carbon isotope study of organic matter in immature Miocene Monterey sediments, Pismo basin

    SciTech Connect

    Schouten, S.; Rijpstra, I.C.; De Leeuw, J.W.

    1997-05-01

    The 300 m section of the Miocene Monterey Formation outcropping at Shell Beach is composed of calcareous phosphatic (15.1 -14.5 Ma) and siliceous facies (14.5-11.0 Ma). An objective of this paper is to document lateral paleoenvironmental changes in the Miocene Monterey Formation by comparing the Shell Beach (SB) profile with the Naples Beach (NB) section in the Santa Barbara-Ventura basin. Eight samples (one sample representing, on average, a time period of ca. 2000 y) from this section were analyzed for variations of extractable biomarkers and their carbon isotopic signatures as indicators for paleoenvironmental change during the Miocene. Saturated hydrocarbons present include 28,30-dinorhopane, phytane, n-alkanes (C{sub 17}-C{sub 31}), lycopane, and 17{beta}, 21{beta}(H)-homohopane. The biomarkers released after desulfurization of the polar fractions predominantly consist of phytane, 2,6.10,14-tetramethyl-7-(3-methylpentyl)pentadecane, C{sub 17}-C{sub 31} n-alkanes. regular 5{alpha}- and 5{beta}-steranes, dinosteranes, and (22R)-17{beta},21{beta}(H)-pentakishomohopane. Steranes have similar carbon isotopic compositions (-25 to -27{per_thousand}) throughout the section and are isotopically similar at both sites, indicating laterally similar and vertically stable environmental conditions for algae living in the upper part of the photic zone. Free and S-bound n-alkanes at SB mainly originate from marine organisms and not from terrestrial sources as in the NB section. S-bound pentakishomohopane is ca. 1-49{per_thousand} depleted compared to the steranes and is thought to be derived from the deeper water dwelling cyanobacteria. These findings are consistent with stable carbon isotopic data obtained for these compounds from Middle Miocene Monterey sediments at Naples Beach and indicates similar environmental conditions in the depositional environments of the Santa Barbara-Ventura and the Pismo basin. 64 refs., 14 figs., 6 tabs.

  7. Antarctic Ice Sheet Sensitivity to Atmospheric CO2 Variations During the Early to Mid-Miocene

    NASA Astrophysics Data System (ADS)

    Levy, R. H.; Harwood, D. M.; Florindo, F.; Sangiorgi, F.; Eagle, R.; von Eynatten, H.; Gasson, E.; Kuhn, G.; Tripati, A.; Deconto, R. M.; Fielding, C. R.; Field, B.; Golledge, N. R.; Mckay, R. M.; Naish, T.; Olney, M.; Pollard, D.; Schouten, S.; Talarico, F. M.; Warny, S.; Willmott, V.

    2015-12-01

    The Early to mid-Miocene (23 to 14 million years ago) is a compelling interval to study Antarctic ice sheet sensitivity to changes in atmospheric CO2 as oceanic and atmospheric circulation patterns in the southern hemisphere were broadly similar to present and reconstructed atmospheric CO2 concentrations were analogous to those projected for the next several decades. This time interval includes the Miocene Climatic Optimum (MCO), a period of global warmth during which average surface temperatures were 3 to 4°C higher than today. Miocene sediments in the AND-2A drill core from the Western Ross Sea, Antarctica provide direct information regarding ice sheet variability through this key time interval and offer insight into the potential Antarctic contribution to future sea level rise. A multi-proxy dataset derived from AND-2A identifies four distinct environmental "motifs" based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of marine-based ice across the Ross Sea. They all correlate with major positive shifts in benthic oxygen isotope records and episodes of sea-level fall, and generally coincide with intervals when atmospheric CO2 concentrations were below current levels (~400 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for significant ice mass loss during episodes of high (>400 ppm) atmospheric CO2. These results suggest that polar climate and the Antarctic Ice Sheet (AIS) were highly sensitive to relatively small changes in CO2 during the early to mid-Miocene, which is supported by numerical ice sheet and climate modelling.

  8. Functional anatomy of the limbs of erethizontidae (Rodentia, Caviomorpha): Indicators of locomotor behavior in Miocene porcupines.

    PubMed

    Candela, Adriana M; Picasso, Mariana B J

    2008-05-01

    Functional analysis of the limb bones of the erethizontid Steiromys duplicatus, one of the most abundant Miocene porcupines from Patagonia, provides evidence to infer their locomotor behavior. Remains of the giant Neosteiromys pattoni (Late Miocene of Northeast Argentina) are also analyzed. Osteological and myological features of extant porcupines were evaluated and used as a model to interpret the functional significance of Miocene species' limbs. Several features in erethizontids are compatible with the ability to climb: the low humeral tuberosities indicate a mobile gleno-humeral joint; the prominent and distally extended deltopectoral crest indicates a powerful pectoral muscle, which is particularly active when climbing; the humero-ulnar and humero-radial joints are indicative of pronation-supination movements; the well-developed lateral epicondylar ridge and the medially protruding entepicondyle are in agreement with an important development of the brachioradialis, supinator, flexor digitorum profundus, and pronator teres muscles, acting in climbing and grasping functions; the mechanical advantage of the biceps brachii would be emphasized because of its distal attachment on the bicipital tuberosity. As with extant porcupines, in Miocene species, the large femoral head would have permitted a broad range of abduction of the femur, and the medially protruding lesser trochanter would have emphasized the abduction and outward rotation of the femur by the action of the ilio-psoas complex. In S. duplicatus, the shape of the hip, knee, and cruro-astragalar, calcaneo-astragalar, and astragalo-navicular joints would have allowed lateral and rotational movements, although probably to a lesser degree than in extant porcupines. Foot features of S. duplicatus (e.g., great medial sesamoid bone, medial astragalar head, complete hallux) indicate that this species would have had grasping ability, but would not have achieved the high degree of specialization of Coendou

  9. Late Miocene Pliocene intensification of the East Asian monsoon linked to Antarctic ice-sheet development

    NASA Astrophysics Data System (ADS)

    Ao, H.; An, Z.; Dekkers, M. J.; Liu, X.

    2013-12-01

    Recent evidence indicates that an East Asian monsoon broadly similar to the present may have occurred in China as early as the late Oligocene or early Miocene, but its variability and possible driving forces prior to the Quaternary epoch remain poorly known, due to rare reconstructions of continuous long-term East Asian monsoon records extending to the earlier periods. Here we report Late MiocenePliocene records of magnetic property variations of an eolian red clay sequence on the eastern Chinese Loess Plateau, which is dated using magnetostratigraphy. The high-resolution magnetic records indicate a long-term increasing trend in the East Asian summer monsoon intensity from ca 8 to 2.6 Ma. This is supported by studies from central Chinese Loess Plateau and South China Sea. We further find that this Late MiocenePliocene monsoon intensification is broadly correlated the long-term increasing trend in the Southern Hemisphere ice volume, suggesting a possible linkage between them. Combing a numerical climate-model experiment that simulates the East Asian summer monsoonal responses to the idealized stepwise increases of ice sheets from East to West Antarctic, we suggested that the Southern Hemisphere ice-sheet development is a driver of this late MiocenePliocene intensification of the East Asian summer monsoon. The Southern Hemisphere ice-sheet development could have intensified the East Asian monsoon mainly via weakening the low pressures over Asia and enhancing the high pressures over western Pacific Ocean and Australia, implying sensitivity of the Asian monsoon to the interhemispheric temperature gradient modulated by Southern Hemisphere climate.

  10. A Miocene termite nest from southern Argentina and its paleoclimatological implications

    USGS Publications Warehouse

    Bown, T.M.; Laza, J.H.

    1990-01-01

    A Miocene termitarium attributable to the extant termite Syntermes (Isoptera: Termitidae, Nasutitermitinae) is the first fossil termite nest reported from South America and possibly the oldest record of the Isoptera from that continent. A new ichnogenus and ichnospecies, Syntermesichnus fontanae, is proposed for this distinctive trace fossil. It differs from nests constructed by other members of the Nasutitermitinae in its architectural organization and its large size. -from Authors

  11. The demise of the Oligo-Miocene fluvial system of the Levant and its geodynamic significance

    NASA Astrophysics Data System (ADS)

    Vachtman, Dina; Mart, Yossi

    2015-04-01

    The Levant rift system is a linear assemblage of axial rifts and their mountainous flanks that comprises two structurally distinct sections. The southern segment is built of series of secondary axial grabens, which trend northwards and are separated from each other by poorly rifted threshold zones, which is the northern extension of the Red Sea continental break-up. The northern section comprises the SW-trending Karasu - Hatay rifts, from which the Ghab graben branches southwards, which is tectonically attributed to the westward migration of Anatolia. A system of large rivers transected the southern section of the Levant from central Arabia in the east to the Mediterranean Sea in the west during the Oligo-Miocene, leaving behind 5 km thick series of clastic deposits at sea, and sandstones and conglomerates of variable thickness on land. The demise of that fluvial system was gradual, stretching from the late Miocene to the early Pleistocene, where coastal rivers were truncated from their sources due to the growth of segmented rift. The geodynamic process that constrains the development of the rifts of the southern Levant and their elevated flanks is oblique rifting, where several small rifts start the evolution along a weakness zone concurrently, separated by wide and inactive threshold zones. Gradually the rifts grow along their long axes to interconnect, shrinking the threshold zone to their disappearence. Such geodynamic history best accounts for the observations of relicts of late Miocene fluvial deposits on mountaintops, large river beds dated to the late Miocene-early Pliocene, and large marine fan deposits of early Pliocene age, where rivers continued to flow in the threshold zones, but truncated by the emerging rifts.

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

    USGS Publications Warehouse

    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 (<60°C) since the Cretaceous. We interpret these data to record rapid unroofing of the southern Ruby Mountains during slip on the west dipping brittle detachment between 17–16 and 10–12 Ma, followed by minor high-angle faulting. We interpret published Oligocene to early Miocene K-Ar biotite and zircon fission track dates from the Harrison Pass 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.

  13. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

    PubMed Central

    Levy, Richard; Harwood, David; Florindo, Fabio; Sangiorgi, Francesca; Tripati, Robert; von Eynatten, Hilmar; Tripati, Aradhna; DeConto, Robert; Fielding, Christopher; Field, Brad; Golledge, Nicholas; McKay, Robert; Naish, Timothy; Olney, Matthew; Pollard, David; Schouten, Stefan; Talarico, Franco; Warny, Sophie; Willmott, Veronica; Acton, Gary; Panter, Kurt; Paulsen, Timothy; Taviani, Marco

    2016-01-01

    Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23–14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3–4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene. PMID:26903644

  14. Middle Miocene hiatus in volcanic activity in the Great Basin area of the Western United States

    USGS Publications Warehouse

    McKee, E.H.; Noble, D.C.; Silberman, M.L.

    1970-01-01

    A summary of potassium-argon dates shows that a high level of igneous activity in the Great Basin and adjacent regions during middle Tertiary time (40 to 20 my ago) was followed by a period of relative quiescence in middle Miocene time that lasted for several million years (from 20 to 17 my ago). Volcanism resumed 16 my ago mainly at the margins of the region and has continued to the present. ?? 1970.

  15. The Miocene Topanga Group of Southern California - A 100-Year History of Changes in Stratigraphic Nomenclature

    USGS Publications Warehouse

    Campbell, Russell H.; McCulloh, Thane H.; Vedder, John G.

    2007-01-01

    A review of selected literature summarizes the origin and chronology of changes in usage of 'Topanga' in the Miocene stratigraphic nomenclature of the Los Angeles Basin and adjacent areas in southern California. The review was done to summarize and reconcile some differences in Miocene stratigraphic nomenclature as applied to geologic map compilations of the Santa Ana (Morton, 2004), San Bernardino (Morton and Miller, 2003), Long Beach (Saucedo and others, 2003) and Los Angeles (Yerkes and Campbell, 2005) 30' x 60' quadrangles, all of which are products of the cooperative (California Geological Survey-U.S. Geological Survey) Southern California Areal Mapping Project (SCAMP). The deposition of the Topanga Group spans about 6 my (from as old as about 18 ma to as young as about 12 ma), and the sequence of included strata records changes in provenance and depositional environments that are contemporaneous with part of a major Miocene tectonic episode in southern California -- the 'basin-inception phase' in the evolution of the Neogene Los Angeles basin (Yerkes and others, 1965). The area of Topanga deposition extends to the southern, eastern, northern, and northwestern sides of the Los Angeles basin, as well as the southern part of the eastern Ventura Basin. Topanga beds are inferred to underlie the thick upper Miocene and Pliocene deposits of the central Los Angeles Basin and the southern part of the eastern Ventura Basin; however, they have been reached by drilling only in marginal areas, where the overlying deposits are relatively thin. Post-Topanga strata were deposited in more-restricted areas of rapid subsidence. Selected papers are summarized as they relate to the Topanga nomenclature, and are presented in chronological order.

  16. Functional anatomy of the limbs of erethizontidae (Rodentia, Caviomorpha): Indicators of locomotor behavior in Miocene porcupines.

    PubMed

    Candela, Adriana M; Picasso, Mariana B J

    2008-05-01

    Functional analysis of the limb bones of the erethizontid Steiromys duplicatus, one of the most abundant Miocene porcupines from Patagonia, provides evidence to infer their locomotor behavior. Remains of the giant Neosteiromys pattoni (Late Miocene of Northeast Argentina) are also analyzed. Osteological and myological features of extant porcupines were evaluated and used as a model to interpret the functional significance of Miocene species' limbs. Several features in erethizontids are compatible with the ability to climb: the low humeral tuberosities indicate a mobile gleno-humeral joint; the prominent and distally extended deltopectoral crest indicates a powerful pectoral muscle, which is particularly active when climbing; the humero-ulnar and humero-radial joints are indicative of pronation-supination movements; the well-developed lateral epicondylar ridge and the medially protruding entepicondyle are in agreement with an important development of the brachioradialis, supinator, flexor digitorum profundus, and pronator teres muscles, acting in climbing and grasping functions; the mechanical advantage of the biceps brachii would be emphasized because of its distal attachment on the bicipital tuberosity. As with extant porcupines, in Miocene species, the large femoral head would have permitted a broad range of abduction of the femur, and the medially protruding lesser trochanter would have emphasized the abduction and outward rotation of the femur by the action of the ilio-psoas complex. In S. duplicatus, the shape of the hip, knee, and cruro-astragalar, calcaneo-astragalar, and astragalo-navicular joints would have allowed lateral and rotational movements, although probably to a lesser degree than in extant porcupines. Foot features of S. duplicatus (e.g., great medial sesamoid bone, medial astragalar head, complete hallux) indicate that this species would have had grasping ability, but would not have achieved the high degree of specialization of Coendou

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

    NASA Astrophysics Data System (ADS)

    Fehse, Dirk

    2011-02-01

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

  18. Inferred relation of Miocene Bealville Fanglomerate to Edison Fault, Caliente Canyon area, Kern County, California

    SciTech Connect

    Dibblee, T.W. Jr.; Warne, A.H.

    1986-04-01

    The Bealville Fanglomerate is a very coarse, local, eastern torrential facies of the middle Tertiary marine sedimentary sequence of southern San Joaquin basin. This fanglomerate is exposed in lower Caliente Canyon east of Bakersfield. It is composed of unsorted boulder-size detritus of granitic rocks now exposed in the highlands on the east and south. The fanglomerate intertongues northwestward into the overlying Miocene fluvial Bena Gravel and probably partly into the underlying Oligocene-Miocene fluvial Walker Formation. In its eastern exposure, the Bealville Fanglomerate laps onto granitic basement. The Bealville Fanglomerate, as thick as 7000 ft (2200 m), dips southward into the north-dipping Edison fault. Pre-Tertiary granitic basement was elevated on the Edison fault to the south when the fault was contemporaneously active during the Miocene. Both the fanglomerate terrane north of the fault and the adjacent granitic basement terrane south of it are now eroded to low relief, so the fault is not expressed physiographically and is inactive. In contrast, the active White Wolf fault to the southeast is expressed by the northwest-facing escarpment slope of Bear Mountain. The Bealville Fanglomerate was deposited during the early and middle Miocene as coarse alluvial detritus on the western base of the rising Sierra Nevada uplift of granitic terrane. This southward-dipping fanglomerate is coarser and thicker than other formations deposited on the eastern margin of the San Joaquin basin. These conditions indicate that the fanglomerate was deposited rapidly on a southward-tilting block against a block of granitic basement being elevated on the Edison fault to the south, and it was derived from the adjacent granitic terrane to the east and from that elevated on the Edison fault to the south.

  19. Plate kinematics of the central Atlantic during the Oligocene and early Miocene

    NASA Astrophysics Data System (ADS)

    Schettino, Antonio; Macchiavelli, Chiara

    2016-04-01

    A new plate motions model for the northwest Africa-North America Plate pair during the Oligocene and early Miocene is presented. The model is accompanied by a high-resolution isochron map for the central Atlantic region, resulting from a re-examination of 423 ship tracks from the NGDC data base for the area between the 15°20' FZ and the Azores triple junction. A new digital model of fracture zones for this region and a set of 309 magnetic profiles crossing the Oligocene to recent oceanic crust within the study area allowed to determine accurate finite reconstruction poles for the North America-northwest Africa conjugate plate pair between the early Miocene (Chron 6) and the early Oligocene (Chron 13). For times older than Chron 7 (˜25 Ma), the finite reconstruction poles were calculated using a reliable data set coming exclusively from the region south of the Canary Islands FZ (˜32°N), which allowed to test the rigidity of the northwest African oceanic lithosphere during the Oligocene-early Miocene phase of Atlas orogeny. A comparison of theoretical magnetic isochrons with observed magnetic lineations systematically shows that anomalously high spreading rates occurred in the area north of the Canary Islands FZ before Chron 7, thereby suggesting that the formation of the Atlas mountain, rather than being a localized intracontinental process, was logically linked to the central Atlantic spreading history. Thus, an independent Moroccan Plate could have existed during the Oligocene-early Miocene time interval, which included both the oceanic lithosphere north of the Canary Islands FZ and the northern Maghrebian areas of Morocco, Algeria and Tunisia. In this eventuality, the Atlas mountain belt should be reinterpreted as a giant flower structure associated with dextral transpression.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  1. Role of Marine Gateways in the Paleoceanography of the Miocene Mediterranean Sea; A Model Study

    NASA Astrophysics Data System (ADS)

    de la Vara, A.; Meijer, P. T.

    2015-12-01

    During the Miocene, due to the convergence of the African plate and the Eurasian plate, the Mediterranean region was subject to profound paleogeographic changes. The evolving coastline and bathymetry of the Mediterranean Sea and, in particular, the opening and closure of the marine connections between the Mediterranean and the outside oceans, triggered important changes in Mediterranean circulation and, indirectly, also affected the global-scale ocean circulation. Until about the Middle Miocene the proto-Mediterranean Sea was open to the Indo-Pacific Ocean through the so-called Indian Gateway. Although the exact age of closure of this gateway is still debated, it is accepted that it substantially affected the paleoceanography of the Mediterranean Sea. Later in time, during the Late Miocene, the Mediterranean was only connected to the Atlantic Ocean but by two marine corridors: the Betic and Rifian corridors. Closure of these narrow passages resulted in the Messinian Salinity Crisis, during which a sequence of evaporites was deposited throughout the Mediterranean basin. In this work we use a regional-scale ocean general circulation model (the Princeton Ocean Model) to gain insight into the role of the evolving gateways. The analysis focuses on large-scale (overturning) circulation, patterns of exchange in the gateways and properties of the Mediterranean water. By comparing our model results to geological data we are able to propose new scenarios or rule out previously proposed ones, and determine the conditions evidenced by the geological observations. More specifically we investigate two different topics: (i) the effects of shoaling and closure of the Indian Gateway and (ii) the functioning of the Late Miocene double gateway to the Atlantic.

  2. Clay mineralogy indicates a mildly warm and humid living environment for the Miocene hominoid from the Zhaotong Basin, Yunnan, China

    NASA Astrophysics Data System (ADS)

    Zhang, Chunxia; Guo, Zhengtang; Deng, Chenglong; Ji, Xueping; Wu, Haibin; Paterson, Greig A.; Chang, Lin; Li, Qin; Wu, Bailing; Zhu, Rixiang

    2016-02-01

    Global and regional environmental changes have influenced the evolutionary processes of hominoid primates, particularly during the Miocene. Recently, a new Lufengpithecus cf. lufengensis hominoid fossil with a late Miocene age of ~6.2 Ma was discovered in the Shuitangba (STB) section of the Zhaotong Basin in Yunnan on the southeast margin of the Tibetan Plateau. To understand the relationship between paleoclimate and hominoid evolution, we have studied sedimentary, clay mineralogy and geochemical proxies for the late Miocene STB section (~16 m thick; ca. 6.7–6.0 Ma). Our results show that Lufengpithecus cf. lufengensis lived in a mildly warm and humid climate in a lacustrine or swamp environment. Comparing mid to late Miocene records from hominoid sites in Yunnan, Siwalik in Pakistan, and tropical Africa we find that ecological shifts from forest to grassland in Siwalik are much later than in tropical Africa, consistent with the disappearance of hominoid fossils. However, no significant vegetation changes are found in Yunnan during the late Miocene, which we suggest is the result of uplift of the Tibetan plateau combined with the Asian monsoon geographically and climatically isolating these regions. The resultant warm and humid conditions in southeastern China offered an important refuge for Miocene hominoids.

  3. Middle-Miocene counterclockwise rotation of rocks from west-central Nevada; implications for Basin and Range extension

    SciTech Connect

    Hudson, M.R.; Geissman, J.W.

    1985-01-01

    Drilling and geophysical data from Dixie Valley and Fallon Basin of west-central Nevada have shown that dip-slip normal faults accommodated post-Miocene Basin and Range extension in this area, but the presence of an earlier, less-understood phase of Basin and Range deformation is suggested in the adjacent West Humboldt, Stillwater, and Clan Alpine Ranges where the late-Miocene basalts lie in angular unconformity on Oligocene to early-Miocene ash-flow tuffs. Paleomagnetic components obtained from the tuffs and underlying gabbroic and basaltic rocks of the Jurassic Humboldt Lopolith have declinations that are statistically different and counterclockwise from the expected Oligo-Miocene and Jurassic directions for the area. Paleomagnetic components from the late-Miocene basalts statistically overlap their expected direction. These data imply that the rocks were rotated counterclockwise during middle-Miocene. The common association of such rotations with strike-slip faulting suggests that this earlier phase of Basin and Range extension was largely a strike-slip faulting deformation. If so, the total amount of extension in the area may be significantly larger than estimates based solely on the moderate tilts (<30/sup 0/) of the ranges.

  4. Clay mineralogy indicates a mildly warm and humid living environment for the Miocene hominoid from the Zhaotong Basin, Yunnan, China.

    PubMed

    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

  5. Clay mineralogy indicates a mildly warm and humid living environment for the Miocene hominoid from the Zhaotong Basin, Yunnan, China

    PubMed Central

    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

  6. Slowing extrusion tectonics: Lowered estimate of post-Early Miocene slip rate for the Altyn Tagh fault

    USGS Publications Warehouse

    Yue, Y.; Ritts, B.D.; Graham, S.A.; Wooden, J.L.; Gehrels, G.E.; Zhang, Z.

    2004-01-01

    Determination of long-term slip rate for the Altyn Tagh fault is essential for testing whether Asian tectonics is dominated by lateral extrusion or distributed crustal shortening. Previous slip-history studies focused on either Quaternary slip-rate measurements or pre-Early Miocene total-offset estimates and do not allow a clear distinction between rates based on the two. The magmatic and metamorphic history revealed by SHRIMP zircon dating of clasts from Miocene conglomerate in the Xorkol basin north of the Altyn Tagh fault strikingly matches that of basement in the southern Qilian Shan and northern Qaidam regions south of the fault. This match requires that the post-Early Miocene long-term slip rate along the Altyn Tagh fault cannot exceed 10 mm/year, supporting the hypothesis of distributed crustal thickening for post-Early Miocene times. This low long-term slip rate and recently documented large pre-Early Miocene cumulative offset across the fault support a two-stage evolution, wherein Asian tectonics was dominated by lateral extrusion before the end of Early Miocene, and since then has been dominated by distributed crustal thickening and rapid plateau uplift. ?? 2003 Elsevier B.V. All rights reserved.

  7. First occurrence of Platycladus from the upper Miocene of Southwest China and its phytogeographic implications.

    PubMed

    Wu, Jing-Yu; Ding, Su-Ting; Li, Qi-Jia; Zhao, Zhen-Rui; Sun, Bai-Nian

    2014-01-01

    Platycladus Spach is native to Central China, but its natural occurrences are very difficult to establish. According to molecular phylogenetic data, this genus might have originated since the Oligocene, but no fossil record has been reported. Here, we describe eight foliage branches from the upper Miocene in western Yunnan, Southwest China as a new species, P. yunnanensis sp. nov., which is characterized by foliage branches spread in flattened sprays, and leaves decussate, imbricate, scale-like and dimorphic. The leaves are amphistomatic, and the stomata are elliptical or oblong, haplocheilic, and monocyclic type. Based on a detailed comparison with the extant genera of Cupressaceae sensu lato, our fossils are classified into the genus Platycladus. The occurrence of P. yunnanensis sp. nov. indicates that this genus had a more southernly natural distribution in the late Miocene than at present. Molecular phylogeny and fossil records support a pre-Oligocene common ancestor for the genera Platycladus, Microbiota and Calocedrus. The separation of the three taxa was most likely caused by the arid belt across Central China during the Oligocene. In addition, the cooling down of the global temperature and the strengthening of Asian monsoon since the Miocene will further promote the migration of these genera.

  8. Badenian (Middle Miocene) echinoids and starfish from western Ukraine, and their biogeographic and stratigraphic significance

    NASA Astrophysics Data System (ADS)

    Radwański, Andrzej; Górka, Marcin; Wysocka, Anna

    2014-06-01

    Echinoderms from the Badenian (Middle Miocene) of the Fore-Carpathian Basin of western Ukraine are facies restricted. The Mykolaiv Beds, stratigraphically older, yielded the starfish Astropecten forbesi (complete skeletons), two genera of sand dollars (Parascutella, Parmulechinus), and numerous other echinoids of the genera Psammechinus , Echinocyamus, Spatangus, Hemipatagus, Echinocardium, Clypeaster, Echinolampas, and Conolampas. The stratigraphically younger, calcareous Ternopil Beds yielded Eucidaris (complete coronae, isolated spines), Arbacina , Brissus, and Rhabdobrissus. Sixteen species of echinoids are distinguished and/or commented. A new brissid, Rhabdobrissus tarnopolensis sp. nov., is established. A mass occurrence of some species (Psammechinus dubius and Hemipatagus ocellatus) contrasts with that of mass aggregations (sand dollars and Echinocardium leopolitanum) by dynamic events in selected layers of proximal tempestites. Of special note is the occurrence of very small specimens, interpreted as juveniles (`babies') having been swept out of their restricted biotopes (`nurseries'). Some species hitherto regarded as of Early Miocene age, and the problem of their persistence beyond the Fore-Carpathian Basin and/or migration into that basin during the Middle Miocene transgression are discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Early Miocene granitoids from the Leo Pargil gneiss dome, northwest Himalaya

    NASA Astrophysics Data System (ADS)

    Hassett, W.; Leech, M. L.

    2007-12-01

    The Leo Pargil gneiss dome is comprised of upper amphibolite-facies metasedimentary rocks of the lower Tethyan Himalayan sequence (known as the Haimantas Group), that are intruded by numerous small granitoid bodies and leucogranite dikes. The dome is located in northern India/southwestern Tibet at the junction of the Sutlej and Spiti rivers, west of the Zada basin. U-Pb SHRIMP dating of zircon yield concordant ages ranging from Late Archean to Late Proterozoic for paragneisses (2.6 Ga to 970 Ma) corresponding to the Haimantas group, and Early Oligocene to Middle Miocene ages for granitoid intrusions (33 Ma to 15 Ma). Concordant analyses and lower intercept ages from Tera-Wasserburg concordia plots range from 28.1-17.2 Ma. Late Oligocene to Early Miocene ages are from zircon domains with consistently high U contents (1500 to over 25000 ppm). Linear regression of age vs. U content scatter plots show a trend toward younger ages (22-20 Ma) corresponding to ages from zircon with lower U contents (1000-3000 ppm) and that is consistent with lower intercept ages. These Early Miocene ages for Leo Pargil granitoids correspond to the ages for the widespread leucogranite bodies exposed throughout the Himalaya and granites from the North Himalayan gneiss domes further east.

  11. Fossil wood from the Miocene and Oligocene epoch: chemistry and morphology.

    PubMed

    Bardet, Michel; Pournou, Anastasia

    2015-01-01

    Fossil wood is the naturally preserved remain of the secondary xylem of plants that lived before the Holocene epoch. Typically, fossil wood is preserved as coalified or petrified and rarely as mummified tissue. The process of fossilization is very complex and it is still unknown why in the same fossil record, wood can be found in different fossilisation forms. In 2007, a fossil forest was found in the Bükkábrány open-pit coal mine in Hungary. The non-petrified forest is estimated to be 7 million years old (Miocene epoch) and its trees were found standing in an upright position. This fossil assemblage is exceptionally rare because wood has been preserved as soft waterlogged tissue. This study aimed to investigate this remarkable way of fossil wood preservation, by examining its chemistry with (13)C CPMAS NMR and its morphology with light and electron microscopy. For comparison reasons, a petrified wood trunk from the Oligocene epoch (30 Myr) found in 2001 at Porrentruy region in Switzerland and two fresh wood samples of the modern equivalents of the Miocene sample were also examined. The results obtained showed that the outstanding preservation state of the Miocene fossil is not owed to petrification or coalification. Mummification is a potential mechanism that could explain Bükkábrány trunks' condition, however this fossilisation process is not well studied and therefore this hypothesis needs to be further investigated. PMID:25294390

  12. Miocene structural features of north and south Padre Island and OCS areas, offshore south Texas

    SciTech Connect

    Al-Ghamdi, A.M.; Watkins, J.S.

    1996-12-31

    Integration of 2-D seismic reflection data, paleontological reports, velocity analysis, and well logs has provided a new structural model for North and South Padre Island OCS areas. The Clemente-Tomas fault system (Late Oligocene-Early Miocene) is located above overpressured shale ridges. Sediment loading initiated the faulting over the compacted shale. The Corsair fault system (Early-Middle Miocene) is located seaward of Clemente-Tomas and was formed due to a huge sediment influx that forced the salt to withdraw basinward. The Wanda fault system formed during the Late Miocene because of the further salt withdrawal. Study area is dominated by shale ridges and the salt are only formed beneath the present shelf edge as salt diapirs. Overpressured shale was mapped throughout the study area. Well logs show overpressured shale between 8,800 to 12,000 feet. Berg and Avery suggested that growth faults can seal the faults sheared zones which may cause a structural hydrocarbon trap. We examined most of the responses of the dip logs in the study area and we found that the seal general trend is the drag (non seal) type.

  13. Miocene structural features of north and south Padre Island and OCS areas, offshore south Texas

    SciTech Connect

    Al-Ghamdi, A.M.; Watkins, J.S. )

    1996-01-01

    Integration of 2-D seismic reflection data, paleontological reports, velocity analysis, and well logs has provided a new structural model for North and South Padre Island OCS areas. The Clemente-Tomas fault system (Late Oligocene-Early Miocene) is located above overpressured shale ridges. Sediment loading initiated the faulting over the compacted shale. The Corsair fault system (Early-Middle Miocene) is located seaward of Clemente-Tomas and was formed due to a huge sediment influx that forced the salt to withdraw basinward. The Wanda fault system formed during the Late Miocene because of the further salt withdrawal. Study area is dominated by shale ridges and the salt are only formed beneath the present shelf edge as salt diapirs. Overpressured shale was mapped throughout the study area. Well logs show overpressured shale between 8,800 to 12,000 feet. Berg and Avery suggested that growth faults can seal the faults sheared zones which may cause a structural hydrocarbon trap. We examined most of the responses of the dip logs in the study area and we found that the seal general trend is the drag (non seal) type.

  14. New magnetochronology of Late Miocene mammal fauna, NE Tibetan Plateau, China: Mammal migration and paleoenvironments

    NASA Astrophysics Data System (ADS)

    Ao, Hong; Zhang, Peng; Dekkers, Mark J.; Roberts, Andrew P.; An, Zhisheng; Li, Yongxiang; Lu, Fengyan; Lin, Shan; Li, Xingwen

    2016-01-01

    Lanzhou Basin lies on the northeastern margin of the Tibetan Plateau in western China and is a rich source of Oligocene-Miocene mammalian fossils. Obtaining precise age determinations for these fossils is important to address key questions concerning mammalian and environmental evolution in Asia associated with stepwise Tibetan Plateau uplift. Here we report a new magnetostratigraphic record for the Xingjiawan fluvio-lacustrine section from the northwestern margin of Lanzhou Basin that can be correlated to the geomagnetic polarity timescale with two options. The Late Miocene Xingjiawan Fauna is located either at the boundary between reversed polarity chron C4r.1r and normal polarity chron C4n.2n or at the boundary between subchrons C5r.1r and C5n.2n, with an estimated age of at least ∼8 Ma or perhaps as early as ∼11 Ma. Both age estimations imply that the fossil Stegodon in the Lanzhou Basin is the oldest known record of Stegodon worldwide; it predates the formerly oldest Stegodon find from Africa by at least one million years and perhaps by as many as four million years. This provides new evidence for an Asian origin of Stegodon. Together with other faunal components, a mixed woodland/grassland setting existed in the Lanzhou Basin during the Late Miocene, in contrast to its modern arid environment.

  15. Chaungtha, a new Middle Miocene mammal locality from the Irrawaddy Formation, Myanmar

    NASA Astrophysics Data System (ADS)

    Chavasseau, Olivier; Chaimanee, Yaowalak; Tun, Soe Thura; Soe, Aung Naing; Barry, John C.; Marandat, Bernard; Sudre, Jean; Marivaux, Laurent; Ducrocq, Stéphane; Jaeger, Jean-Jacques

    2006-12-01

    We describe here a mammalian assemblage originating from the locality of Chaungtha (Irrawaddy Formation, Myanmar). It represents one of the rare descriptions of a precisely located, in space, vertical section and time, fossil mammal fauna from the Irrawaddy Formation. Classically the fossil record of Irrawaddy Formation is essentially known from isolated fossils of imprecise or unknown provenance, especially concerning the stratigraphic position of the fossils along several hundred meter thick sections. The Chaungtha faunal association consists of the rhino Brachypotherium fatehjangense, the pig Conohyus thailandicus, the ruminants cf. Siamotragulus sanyathanai, cf. Siamotragulus sp. and a gomphotheriid proboscidean. This assemblage indicates that the locality is Miocene in age, and not Late Eocene as previously claimed, and roughly contemporaneous with the Chinji Formation of India-Pakistan (ca. 14-11 Ma) and with the Mae Moh Group of northern Thailand. The Chaungtha fauna, even if it displays regional characteristics, shows a strong resemblance to those of the Middle Miocene of India-Pakistan and of Thailand and reinforces the idea that South-East Asia and Pakistan were part of the same biogeographical province during the Middle Miocene.

  16. Fire and fire-adapted vegetation promoted C4 expansion in the late Miocene.

    PubMed

    Scheiter, Simon; Higgins, Steven I; Osborne, Colin P; Bradshaw, Catherine; Lunt, Dan; Ripley, Brad S; Taylor, Lyla L; Beerling, David J

    2012-08-01

    Large proportions of the Earth's land surface are covered by biomes dominated by C(4) grasses. These C(4)-dominated biomes originated during the late Miocene, 3-8 million years ago (Ma), but there is evidence that C(4) grasses evolved some 20 Ma earlier during the early Miocene/Oligocene. Explanations for this lag between evolution and expansion invoke changes in atmospheric CO(2), seasonality of climate and fire. However, there is still no consensus about which of these factors triggered C(4) grassland expansion. We use a vegetation model, the adaptive dynamic global vegetation model (aDGVM), to test how CO(2), temperature, precipitation, fire and the tolerance of vegetation to fire influence C(4) grassland expansion. Simulations are forced with late Miocene climates generated with the Hadley Centre coupled ocean-atmosphere-vegetation general circulation model. We show that physiological differences between the C(3) and C(4) photosynthetic pathways cannot explain C(4) grass invasion into forests, but that fire is a crucial driver. Fire-promoting plant traits serve to expand the climate space in which C(4)-dominated biomes can persist. We propose that three mechanisms were involved in C(4) expansion: the physiological advantage of C(4) grasses under low atmospheric CO(2) allowed them to invade C(3) grasslands; fire allowed grasses to invade forests; and the evolution of fire-resistant savanna trees expanded the climate space that savannas can invade. PMID:22712748

  17. Middle Miocene to present sediment transport and deposits in the Southeastern Weddell Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Huang, Xiaoxia; Jokat, Wilfried

    2016-04-01

    Understanding the transport and deposition of sediments along the Antarctic continental shelves helps to provide constraints on past ice sheet dynamics. Seismic stratigraphic and scientific drilling data from the Antarctic continental margins have provided much direct evidence concerning ice sheet evolution and sedimentation history. In this study, we describe a series of sedimentary features along the continental margin of the southeastern Weddell Sea to constrain glacial-influenced sedimentation processes from the Middle Miocene to the present. The Crary Trough Mouth Fan (CTMF), channel systems, Mix-system turbidity-contourites are investigated by using seismic reflection, sub-bottom profiler, and results from ODP Site 693. The sinuous, NE-SW-oriented turbidity-contourites are characterized by bathymetric highs that are more than 150 km wide, 700 km long, and have a sediment thickness of up to 2 km. The unique sedimentation environment of the southeastern Weddell Sea is controlled by a large catchment area and its fast (paleo-)ice streams feeding the Filchner Ronne Ice Shelf, turbidity/bottom currents as well as sea level changes. A remarkable increase in mass transport deposits (MTDs) in the Late Miocene and Early Pliocene strata has been related to, ice sheet loading, eustatic sea level fall, earthquakes, and overpressure of rapid sediment accumulation. Our seismic records also imply that fluctuations of East Antarctic ice sheet similar to those that occurred during the last glacial cycle might have been typical for southeastern Weddell Sea during glacial periods since the Late Miocene or even earlier.

  18. Simulating a dynamic Antarctic ice sheet in the early to middle Miocene

    NASA Astrophysics Data System (ADS)

    Gasson, Edward; DeConto, Robert; Pollard, David; Levy, Richard

    2016-04-01

    A variety of sources of geological data suggest that there were major variations in Antarctic ice sheet volume and extent during the early to middle Miocene. Simulating such large-scale changes is problematic due to a strong hysteresis effect, which results in limited retreat of the terrestrial ice sheet once it has reached continental size. A relatively narrow range of atmospheric CO2 concentrations shown by proxy records exacerbates this problem. Here we use a new asynchronous climate-ice sheet coupling method, using a high-resolution atmospheric component, to account for ice sheet-climate feedbacks. Accounting for these processes results in increased retreat when compared with standard offline simulations. Combined with recently proposed mechanisms for ice retreat into deep subglacial basins, we are able to simulate large-scale variability of the Miocene Antarctic ice sheet. This variability 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 - 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, and provides a mechanistic explanation for new ice-proximal records emerging from sedimentological drill cores.

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

    USGS Publications Warehouse

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

    2004-01-01

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

  20. Seastacks buried beneath newly reported Lower Miocene sandstone, northern Santa Barbara County, California

    SciTech Connect

    Fritsche, A.E.; Hanna, F.M.

    1985-04-01

    Three large, isolated exposures of a light-gray, coarse-grained, thick-bedded sandstone unit occur in the northern San Rafael Mountains of Santa Barbara County, California. These rocks are moderately fossiliferous and contain Vertipecten bowersi, Amussiopecten vanvlecki, Aequipecten andersoni, Otrea howelli, shark teeth, whale bones, and regular echinoid spines. The fossils indicate that the sandstone unit, although previously reported as upper(.) Miocene, correlates best with the lower Miocene Vaqueros Formation. This unit was deposited in angular unconformity on a Cretaceous, greenish-gray turbidite sequence of interbedded sandstone and shale, and onlaps the unconformity erosion surface from west to east, the unit being thicker in the west and older at its base. The underlying Cretaceous sandstone beds are well indurated, and during the eastward transgression of the early Miocene sea, they resisted wave erosion and stood as seastacks offshore of the advancing coastline, thus creating a very irregular topographic surface upon which the Vaqueros Formation was deposited. Some seastacks were as much as 4 m tall, as indicated by inliers of Cretaceous rock surrounded by 4-m thick sections of the Vaqueros Formation.

  1. Middle Miocene environmental and climatic evolution at the Wilkes Land margin, East Antarctica

    NASA Astrophysics Data System (ADS)

    Sangiorgi, Francesca; Bijl, Peter; Passchier, Sandra; Salzmann, Ulrich; Schouten, Stefan; Pross, Jörg; Escutia, Carlota; Brinkhuis, Henk

    2015-04-01

    Integrated Ocean Drilling Program (IODP) Expedition 318 successfully drilled a Middle Miocene (~ 17 - 12.5 Ma) record from the Wilkes Land Margin at Site U1356A (63°18.6138'S, 135°59.9376'E), located at the transition between the continental rise and the abyssal plain at 4003 mbsl. We present a multiproxy palynological (dinoflagellate cyst, pollen and spores), sedimentological and organic geochemical (TEX86, MBT/CBT) study, which unravels the environmental and climate variability across the Miocene Climatic Optimum (MCO, ~17-15 Ma) and the Mid Miocene Climate Transition (MMCT). Several independent lines of evidence suggest a relatively warm climate during the MCO. Dinocyst and pollen assemblage diversity at the MCO is unprecedented for a Neogene Antarctic record and indicates a temperate, sea ice-free marine environment, with woody sub-antarctic vegetation with elements of forest/shrub tundra and peat lands along the coast. These results are further confirmed by relatively warm TEX86-derived Sea Surface Temperatures and mild MBT-derived continental temperatures, and by the absence of glacially derived deposits and very few ice-rafted clasts. A generally colder but highly dynamic environment is suggested for the interval 15-12.5 Ma.

  2. Middle Miocene environmental and climatic evolution at the Wilkes Land margin, East Antarctica

    NASA Astrophysics Data System (ADS)

    Sangiorgi, F.; Passchier, S.; Salzmann, U.; Schouten, S.; Pross, J.; Bijl, P.; Tauxe, L.; Bendle, J. A.; Escutia, C.; Brinkhuis, H.

    2012-12-01

    Integrated Ocean Drilling Program (IODP) Expedition 318 successfully drilled a Middle Miocene (~ 17 - 12.5 Ma) record from the Wilkes Land Margin at Site U1356A (63°18.6138'S, 135°59.9376'E), located at the transition between the continental rise and the abyssal plain at 4003 mbsl. We present a multiproxy palynological (dinoflagellate cyst, pollen and spores), sedimentological and organic geochemical (TEX86, MBT/CBT) study, which unravels the environmental and climate variability across the Miocene Climatic Optimum (MCO, ~17-15 Ma) and the Mid Miocene Climate Transition (MMCT). Several independent lines of evidence indeed suggest a relatively warm climate during the MCO. Dinocyst and pollen assemblage diversity at the MCO is unprecedented for a Neogene Antarctic record and indicates a temperate, sea ice-free marine environment, with woody sub-antarctic vegetation with elements of forest/shrub tundra and peat lands along the coast. These results are further confirmed by relatively warm TEX86-derived Sea Surface Temperatures and mild MBT-derived continental temperatures, and by the absence of glacially derived deposits and very few ice-rafted clasts. A generally colder but highly dynamic environment is suggested for the interval 15-12.5 Ma.

  3. Dental microwear profilometry of African non-cercopithecoid catarrhines of the Early Miocene.

    PubMed

    Shearer, Brian M; Ungar, Peter S; McNulty, Kieran P; Harcourt-Smith, William E H; Dunsworth, Holly M; Teaford, Mark F

    2015-01-01

    The Early Miocene of Kenya has yielded the remains of many important stem catarrhine species that provide a glimpse of the East African primate radiation at a time of major faunal turnover. These taxa have been subject to innumerable studies, yet there is still no consensus on their dietary niches. Here we report results of an analysis of dental microwear textures of non-cercopithecoid catarrhines from the Early Miocene of Kenya. Scanning confocal profilometry of all available molar specimens with undamaged occlusal surfaces revealed 82 individuals with unobscured antemortem microwear, representing Dendropithecus, Micropithecus, Limnopithecus, Proconsul, and Rangwapithecus. Scale-sensitive fractal analysis was used to generate microwear texture attributes for each individual, and the fossil taxa were compared with each other using conservative non-parametric statistical tests. This study revealed no discernible variation in microwear texture among the fossil taxa, which is consistent with results from a previous feature-based microwear study using smaller samples. Our results suggest that, despite their morphological differences, these taxa likely often consumed foods with similar abrasive and fracture properties. However, statistical analyses of microwear texture data indicate differences between the Miocene fossil sample and several extant anthropoid primate genera. This suggests that the African non-cercopithecoid catarrhines included in our study, despite variations in tooth form, had generalist diets that were not yet specialized to the degree of many modern taxa. PMID:25282274

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

    PubMed

    Hand, Suzanne J; Lee, Daphne E; Worthy, Trevor H; Archer, Michael; Worthy, Jennifer P; Tennyson, Alan J D; Salisbury, Steven W; Scofield, R Paul; Mildenhall, Dallas C; Kennedy, Elizabeth M; Lindqvist, Jon K

    2015-01-01

    The New Zealand endemic bat family Mystacinidae comprises just two Recent species referred to a single genus, Mystacina. The family was once more diverse and widespread, with an additional six extinct taxa recorded from Australia and New Zealand. Here, a new mystacinid is described from the early Miocene (19-16 Ma) St Bathans Fauna of Central Otago, South Island, New Zealand. It is the first pre-Pleistocene record of the modern genus and it extends the evolutionary history of Mystacina back at least 16 million years. Extant Mystacina species occupy old-growth rainforest and are semi-terrestrial with an exceptionally broad omnivorous diet. The majority of the plants inhabited, pollinated, dispersed or eaten by modern Mystacina were well-established in southern New Zealand in the early Miocene, based on the fossil record from sites at or near where the bat fossils are found. Similarly, many of the arthropod prey of living Mystacina are recorded as fossils in the same area. Although none of the Miocene plant and arthropod species is extant, most are closely related to modern taxa, demonstrating potentially long-standing ecological associations with Mystacina.

  5. First Occurrence of Platycladus from the Upper Miocene of Southwest China and Its Phytogeographic Implications

    PubMed Central

    Li, Qi-Jia; Zhao, Zhen-Rui; Sun, Bai-Nian

    2014-01-01

    Platycladus Spach is native to Central China, but its natural occurrences are very difficult to establish. According to molecular phylogenetic data, this genus might have originated since the Oligocene, but no fossil record has been reported. Here, we describe eight foliage branches from the upper Miocene in western Yunnan, Southwest China as a new species, P. yunnanensis sp. nov., which is characterized by foliage branches spread in flattened sprays, and leaves decussate, imbricate, scale-like and dimorphic. The leaves are amphistomatic, and the stomata are elliptical or oblong, haplocheilic, and monocyclic type. Based on a detailed comparison with the extant genera of Cupressaceae sensu lato, our fossils are classified into the genus Platycladus. The occurrence of P. yunnanensis sp. nov. indicates that this genus had a more southernly natural distribution in the late Miocene than at present. Molecular phylogeny and fossil records support a pre-Oligocene common ancestor for the genera Platycladus, Microbiota and Calocedrus. The separation of the three taxa was most likely caused by the arid belt across Central China during the Oligocene. In addition, the cooling down of the global temperature and the strengthening of Asian monsoon since the Miocene will further promote the migration of these genera. PMID:25517767

  6. Late Miocene sedimentary environments in south-western Amazonia (Solimões Formation; Brazil)

    PubMed Central

    Gross, Martin; Piller, Werner E.; Ramos, Maria Ines; Douglas da Silva Paz, Jackson

    2011-01-01

    In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ18O and δ13C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake (“Lake Pebas”) or any influx of marine waters can be excluded for that region during the Late Miocene. PMID:26523089

  7. Late Miocene sedimentary environments in south-western Amazonia (Solimões Formation; Brazil)

    NASA Astrophysics Data System (ADS)

    Gross, Martin; Piller, Werner E.; Ramos, Maria Ines; Douglas da Silva Paz, Jackson

    2011-08-01

    In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ18O and δ13C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake (“Lake Pebas”) or any influx of marine waters can be excluded for that region during the Late Miocene.

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

    NASA Astrophysics Data System (ADS)

    Halfar, Jochen; Mutti, Maria

    2005-06-01

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

  9. Palynology, paleoclimatology and correlation of middle Miocene beds from Porcupine River (locality 90-1), Alaska

    USGS Publications Warehouse

    White, J.M.; Ager, T.A.

    1994-01-01

    Beds in the Upper Ramparts Canyon of the Porcupine River, Alaska (67?? 20' N, 141?? 20' W), yielded a flora rich in pollen of hardwood genera now found in the temperate climates of North America and Asia. The beds are overlain or enclosed by two basalt flows which were dated to 15.2 ?? 0.1 Ma by the 40Ar 39Ar method, fixing the period of the greatest abundance of warm-loving genera to the early part of the middle Miocene. The assemblage is the most northern middle Miocene flora known in Alaska. Organic bed 1 underlies the basalt and is older than 15.2 Ma, but is of early to middle Miocene age. The pollen assemblage from organic bed 1 is dominated by conifer pollen from the pine and redwood-cypress-yew families with rare occurrences of temperate hardwoods. Organic bed 2 is a forest floor containing redwood trees in life position, engulfed by the lowest basalt flow. A pine log has growth rings up to 1 cm thick. Organic beds 3 and 4 comprise lacustrine sediment and peat between the two basalt flows. Their palynoflora contain conifers and hardwood genera, of which about 40% have modern temperate climatic affinities. Hickory, katsura, walnut, sweet gum, wingnut, basswood and elm pollen are consistently present, and beech and oak alone make up about 20% of the pollen assemblage. A warm high latitude climate is indicated for all of the organic beds, but organic bed 3 was deposited under a time of peak warmth. Climate data derived by comparison with modern east Asian vegetation suggest that, at the time of deposition of organic bed 3, the Mean Annual Temperature (MAT) was ca. 9??C, the Warm Month Mean Temperature (WMMT) was ??? 20??C and the Cold Month Mean Temperature (CMMT) was ca. -2??C. In contrast, the modern MAT for the region is -8.6??C, WMMT is 12.6??C and CMMT is -28??C. Organic beds 3 and 4 correlate to rocks of the middle Miocene-late Seldovian Stage of Cook Inlet and also probably correlate to, and more precisely date, the lower third of the Suntrana Formation

  10. High resolution sequence stratigraphic analysis of the Late Miocene Abu Madi Formation, Northern Nile Delta Basin

    NASA Astrophysics Data System (ADS)

    Sarhan, Mohammad Abdelfattah

    2015-12-01

    Abu Madi Formation represents the Upper Miocene Messinian age in the Nile Delta basin. It consists mainly of sandstones and shale intercalations and because of its richness in hydrocarbon, it has been subdivided by the petroleum companies into Level-I, Level-II and Level-III, respectively according to the increase in the sandstone to the shale ratio. The Miocene cycle in the northern subsurface section of the Nile Delta encompasses three main formations namely from the base; Sidi Salim formation, Qawasim Formation and Abu Madi Formation at the top. The high resolution sequence stratigraphic analysis, using gamma ray responses, has been done for the Late Miocene formation in the northern part of the Nile delta subsurface section. For this purpose, the gamma-ray logs of ten deep wells, arranged in four cross-sections trending in almost north-south direction throughout the northern region of the Nile Delta, were analyzed. The analysis has revealed that the interpreted 4th order depositional cycles within Abu Madi Formation display great variations in both number and gamma ray responses in each investigated well, and cannot be traced laterally, even in the nearest well. These variations in the interpreted 4th order depositional sequences could be attributed to the presence of normal faults buried in the inter-area laying between the investigated wells. This finding matches with the conclusion of that Abu Madi Formation represents a part of the Upper Miocene Nile Delta syn-rift megasequence, developed during the Upper Miocene rift phase of the Red Sea - Gulf of Suez province in Egypt. Accordingly, in the sequence stratigraphic approach, the depositional history of Abu Madi Formation was strongly overprinted by the tectonic controls rather than the relative sea-level changes which are assumed to be of a secondary influence. Regarding the hydrocarbon aspects of the Abu Madi Formation, the present work recommends to direct the drilling efforts into the stratigraphic traps

  11. The strontium isotope seawater curve during the early Middle Miocene and its relation to paleoceanographic events

    SciTech Connect

    Hodell, D.A. . Dept. of Geology); Woodruff, F. . Dept. Geological Sciences)

    1992-01-01

    Breaks in slope of the strontium isotope seawater curve signal fundamental changes in either rates of continental weathering, seafloor spreading (i.e., tectonic reorganizations), or submarine dissolution of marine carbonates. The authors conducted a detailed study of the change in slope of the strontium isotopic seawater curve that occurred during the early middle Miocene in three Pacific DSDP sites (289, 574, and 588). The change in slope from the rapid rise in Sr-87/Sr-86 of the early Miocene (60 ppm/Ma) to the less rapid increase of the mid- and late Miocene (22 ppm/Ma) occurred between two periods of maximum [delta]C-13 values dated between 15.5 and 15.2 Ma. This internal was followed by relatively constant Sr-87/Sr-86 values (averaging 0.70878) between 15.2 and 14.2 Ma. Sr-87/Sr-86 ratios began to increase again after 14.2 Ma, but at a reduced rate compared to the early Miocene. The break in slope in Sr-87/Sr-86 preceded the mid-Miocene increase in [delta]O-18 that represents ice growth on Antarctica, which began at 14.9 Ma and increased rapidly after 14.2 Ma. In 2 out of 3 of the sites, the break in Sr-slope between 15.5 and 15.2 Ma is accompanied by a small, but significant, decrease in Sr-87/Sr-86 values. They speculate, that this decrease in Sr-87/Sr-86 may have been related to massive dissolution of older carbonate on the sea floor associated with NH2B (Neogene Hiatus 2 of Keller and Barron, 1983). This event may have important implications for changes in carbonate chemistry of the oceans. Numerical modeling of the strontium isotope budget will be used to test the feasibility of this mechanism and to estimate the volume and age of dissolved carbonate needed to produce the observed decrease in Sr-87/Sr-86.

  12. The Cenozoic Diversity of Agglutinated Foraminifera - Evidence for a late Oligocene to early Miocene diversification event

    NASA Astrophysics Data System (ADS)

    Kaminski, Michael; Setoyama, Eiichi; Kender, Sev; Cetean, Claudia

    2014-05-01

    The agglutinated foraminifera are among the most abundant micro-organisms in the deep marine environment and have a diversity record extending back to the late Precambrian. We present an updated diversity curve for agglutinated foraminiferal genera based on the stratigraphic ranges of all the agglutinated genera recognized as valid in the classification of Kaminski (2014). The data set for this analysis is based on the stratigraphic ranges of agglutinated genera published in Foraminiferal Genera and their Classification, which has been subsequently updated based on published studies and our new observations. The mean standing diversity of agglutinated foraminiferal genera was compiled by counting the number of boundary crossers rather than the number of genera in each stage. In this study, we report the stratigraphic and geographical occurrence of a benthic foraminiferal diversification event that has previously received little attention. In the latest Oligocene to earliest Miocene a number of trochospiral agglutinated genera with alveolar or canaliculate walls first appeared in the fossil record. Our studies of late Oligocene of the Congo fan, offshore Angola (Kender et al., 2008; Cetean and Kaminski, 2011) have revealed a diverse assemblage that includes new taxa of deep-water agglutinated foraminifera. In a biostratigraphic study of the Miocene foraminiferal assemblages Kender et al. (2008) noted steadily increasing diversity and proportions of infaunal agglutinated foraminiferal morphotypes over the lower Miocene interval. The proportion of infaunal agglutinated foraminifera assigned to the order Textularida increased dramatically in the lower mid-Miocene, suggesting expansion of the oxygen minimum zone into deeper waters. In addition to the trochospiral alveolar genera, several species of Reticulophragmium and Cyclammina display rapid diversification into numerous separate lineages that are at present not reflected in our generic diversity record owing to

  13. Paleomagnetic quantification of upper-plate deformation during Miocene detachment faulting in the Mohave Mountains, Arizona

    USGS Publications Warehouse

    Pease, V.; Hillhouse, J.W.; Wells, R.E.

    2005-01-01

    Paleomagnetic data from Miocene (???20 Ma) volcanic rocks and dikes of west central Arizona reveal the tilt history of Proterozoic crystalline rocks in the hanging wall of the Chemehuevi-Whipple Mountains detachment fault. We obtained magnetization data from dikes and flows in two structural blocks encompassing Crossman Peak and Standard Wash in the Mohave Mountains. In the Crossman block the dike swarm records two components of primary magnetization: (1) CNH, a normal polarity, high-unblocking-temperature or high-coercivity component (inclination, I = 48.5??, declination, D = 6.4??), and (2) CRHm, a reversed polarity, high-temperature or high-coercivity component (I = -33.6??, D = 197.5??). Argon age spectra imply that the dikes have not been reheated above 300??C since their emplacement, and a baked-contact test suggests that the magnetization is likely to be Miocene in age. CRHm deviates from the expected direction of the Miocene axial dipole field and is best explained as a result of progressive tilting about the strike of the overlying andesite flows. These data suggest that the Crossman block was tilted 60?? to the southwest prior to intrusion of the vertical dike swarm, and the block continued to tilt during a magnetic field reversal to normal polarity (CNH). Miocene dikes in the Crossman block are roughly coplanar, so the younger dikes with normal polarity magnetization intruded along planes of weakness parallel to the earlier reversed polarity swarm. An alternative explanation involves CNH magnetization being acquired later during hydrothermal alteration associated with the final stages of dike emplacement. In the Standard Wash block, the primary component of magnetization is a dual-polarity, high-temperature or high-coercivity component (SWHl, I = 7.2??,D= 0.7??). To produce agreement between the expected Miocene magnetic direction and the SWH component requires (1) correcting for a 56?? tilt about the strike of flow bedding and (2) removing a

  14. Uplift and Deformation of the Western Andean Slope, Northernmost Chile: Insights from Deformed Early Miocene Ignimbrites

    NASA Astrophysics Data System (ADS)

    van Zalinge, M. E.; Sparks, R. S. J.; Cooper, F. J.; Evenstar, L.; Aslin, J.; Condon, D. J.

    2015-12-01

    In northern Chile and southern Peru, deformed early Miocene ignimbrites characterize the Western Andean Slope (WAS). In this study we use the emplacement and subsequent deformation of these large-volume ignimbrites to reconstruct the pre-eruptive paleotopography and constrain Miocene uplift rates across the WAS in northernmost Chile. Our results provide evidence that the uplift of the WAS began as early as Eocene-Oligocene time, with elevated rates of uplift during the middle-late Miocene. In northernmost Chile, the WAS is covered by the early Miocene Oxaya Formation (22.7 Ma - 19.6 Ma), a series of ignimbrites and minor sediments that includes the large-volume (>3000 km3), 21.9 Ma Cardones ignimbrite. Following eruption, these ignimbrites were faulted, tilted, and folded into the long-wavelength Huaylillas anticline, which forms a steep slope rising ~2300 m over a distance of ~40 km. Based on the assumption that large-volume ignimbrites like the Cardones infill existing topography to create a relatively uniform low-gradient surface slope of ~1°, we performed a line-balanced reconstruction of this surface. Results suggest the existence of a proto-WAS, with an elevation up to ~1800 m, prior to 21.9 Ma. This proto-WAS had local paleo-lows, in which the Cardones ignimbrite was able to reach thicknesses exceeding 1000 m. We interpret these lows as river valleys that transported sediment from the proto-WAS westwards towards the Central Basin, creating an Eocene-Oligocene (~50-22.7 Ma) clastic wedge, expressed today as the Azapa Formation. After deposition of the Oxaya Formation, the WAS experienced <1° of westward tilting, faulting, and folding resulting in ~2000 m of uplift along the hinge of the Huaylillas anticline. U-Pb geochronology of zircons from intercalated volcanic units in the syn-tectonic Huaylas Basin on the eastern limb of the anticline suggest that the majority of this Miocene uplift occurred between 16 and 6 Ma.

  15. An objective statistical test for eccentricity forcing of Oligo-Miocene climate

    NASA Astrophysics Data System (ADS)

    Proistosescu, C.; Huybers, P.; Maloof, A. C.

    2008-12-01

    We seek a maximally objective test for the presence of orbital features in Oligocene and Miocene δ18O records from marine sediments. Changes in Earth's orbital eccentricity are thought to be an important control on the long term variability of climate during the Oligocene and Miocene Epochs. However, such an important control from eccentricity is surprising because eccentricity has relatively little influence on Earth's annual average insolation budget. Nevertheless, if significant eccentricity variability is present, it would provide important insight into the operation of the climate system at long timescales. Here we use previously published data, but using a chronology which is initially independent of orbital assumptions, to test for the presence of eccentricity period variability in the Oligocene/Miocene sediment records. In contrast to the sawtooth climate record of the Pleistocene, the Oligocene and Miocene climate record appears smooth and symmetric and does not reset itself every hundred thousand years. This smooth variation, as well as the time interval spanning many eccentricity periods makes Oligocene and Miocene paleorecords very suitable for evaluating the importance of eccentricity forcing. First, we construct time scales depending only upon the ages of geomagnetic reversals with intervening ages linearly interpolated with depth. Such a single age-depth relationship is, however, too uncertain to assess whether orbital features are present. Thus, we construct a second depth-derived age-model by averaging ages across multiple sediment cores which have, at least partly, independent accumulation rate histories. But ages are still too uncertain to permit unambiguous detection of orbital variability. Thus we employ limited tuning assumptions and measure the degree by orbital period variability increases using spectral power estimates. By tuning we know that we are biasing the record toward showing orbital variations, but we account for this bias in our

  16. Palinspastic reconstruction of southeastern California and southwestern Arizona for the middle Miocene

    NASA Technical Reports Server (NTRS)

    Richard, Stephen M.

    1992-01-01

    A paleogeographic reconstruction of southeastern California and southwestern Arizona at 10 Ma was made based on available geologic and geophysical data. Clockwise rotation of 39 deg was reconstructed in the eastern Transverse Ranges, consistent with paleomagnetic data from late Miocene volcanic rocks, and with slip estimates for left-lateral faults within the eastern Transverse Ranges and NW-trending right lateral faults in the Mojave Desert. This domain of rotated rocks is bounded by the Pinto Mountain fault on the north. In the absence of evidence for rotation of the San Bernardino Mountains or for significant right slip faults within the San Bernardino Mountains, the model requires that the late Miocene Pinto Mountain fault become a thrust fault gaining displacement to the west. The Squaw Peak thrust system of Meisling and Weldon may be a western continuation of this fault system. The Sheep Hole fault bounds the rotating domain on the east. East of this fault an array of NW-trending right slip faults and south-trending extensional transfer zones has produced a basin and range physiography while accumulating up to 14 km of right slip. This maximum is significantly less than the 37.5 km of right slip required in this region by a recent reconstruction of the central Mojave Desert. Geologic relations along the southern boundary of the rotating domain are poorly known, but this boundary is interpreted to involve a series of curved strike slip faults and non-coaxial extension, bounded on the southeast by the Mammoth Wash and related faults in the eastern Chocolate Mountains. Available constraints on timing suggest that Quaternary movement on the Pinto Mountain and nearby faults is unrelated to the rotation of the eastern Transverse Ranges, and was preceded by a hiatus during part of Pliocene time which followed the deformation producing the rotation. The reconstructed Clemens Well fault in the Orocopia Mountains, proposed as a major early Miocene strand of the San

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

    NASA Astrophysics Data System (ADS)

    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

  18. Palaeoecological construction from the Oligo-Miocene coal deposits of Gelibolu Peninsula, NW Turkey.

    NASA Astrophysics Data System (ADS)

    Demirtaş, Ferdi; Koşun, Erdal; Serkan Akkiraz, Mehmet; Bozcu, Mustafa; Koç, Koray

    2015-04-01

    The palynomorph composition of the Upper Oligocene and Miocene coal deposits from Gelibolu peninsula, NW Turkey, was analyzed to determine the palaeoclimate conditions. The samples were collected from two different abandoned coal mines. Also two different palynological assemblages were reported. The first one belongs to the Late Oligocene (Osmancik Formation). The other one is the Miocene (Gazhanedere Formation). The Late Oligocene palynological assemblage consist mainly of Alnus, Myricaceae, Cyrillaceae-Clethraceae, Calamus and Castanea. Riparian vegetation or wetland forest community incorporate high amounts of Alnus, and low percentages of deciduous Salix, Pterocarya and Carya. Calamus, which is a stratigraphical marker for the Late Oligocene of the Thrace Basin, was also recorded in high quantities. The content of the Miocene palynological assemblage is different from the Late Oligocene assemblage, and is mainly made up of Polypodiaceae, Poaceae, Chenopodiaceae, Myricaceae, Oleaceae, Cyrillaceae-Clethraceae and Sapotaceae. Calamus and Alnus totally disappear here. In contrast, open vegetation elements such Poaceae and Chenopodiaceae occur frequently. The palaeoclimate calculations were made by the help of coexistence approach method. The late Oligocene association contains a total of 18 taxa, 11 of which were used for calculating the coexistence intervals. The values obtained 15.6 to 21.1 ° C for annual temperature, 5.0 to 13.3 ° C for winter temperature, 24.7 to 28.1 ° C for summer temperature and, 1096 to 1355 mm annual rainfall. In the Miocene palynological assemblage 23 taxa were identified. The palaeoclimate calculation is based on the 21 taxa. Quantitative data indicate the values for the mean annual temperature 15.6-21.3 ° C, for the winter temperature 5.0 to 13.3 ° C, 24.7- 27.9 ° C for summer temperature and 823-1520 mm for the annual rainfall. The palaeoclimate was warm and contained dry seasons due to lower boundary of annual precipitation

  19. A Synthesis of Late Miocene Through Pliocene Evolution of Glaciation as Inferred From Deep Sea Geochemical Records

    NASA Astrophysics Data System (ADS)

    Billups, K.

    2008-12-01

    During the Miocene through Pliocene climate evolved from an early Miocene climatic optimum (~16 Ma) followed by major expansion of the Antarctic ice sheet during the middle Miocene (~15 Ma), to an early Pliocene interval of relative global warmth (5 to 3.5 Ma) followed by the onset of wide spread Northern Hemisphere Glaciation during the late Pliocene (~3 Ma). Here I review the evolution of Miocene/Pliocene glaciation as recorded in the geochemistry of deep sea sediments. Much of what we know about past climate change comes from the oxygen isotopic composition of benthic foraminifera. Although this proxy outlines large scale changes in the degree of polar glaciation, the absolute magnitude and the relationship between ice extent and ocean temperature cannot be uniquely determined. The recent development of foraminiferal Mg/Ca ratios as a proxy for paleotemperatures provides an opportunity to improve our understanding of Miocene/Pliocene climate change on both tectonic and orbital time scales. For example, paired δ18O and Mg/Ca deep water records show that middle Miocene expansion of ice predates cooling of Southern Ocean surface waters providing evidence for the importance of heat and moisture transport in Antarctic ice growth (Shevenell and Kennett, 2007). Relatively few deep sea studies have focused on late Miocene climate, and foraminiferal δ18O records do not support major oceanographic and climatic changes. Although, the late Miocene may have been a time of global cooling, especially in the circum- Antarctic region, with the establishment of a grounded West Antarctic ice sheet. The early Pliocene, in contrast, has been the focus of much research because of the relevance to understanding intervals of sustained global climatic warmth with near modern-day tectonic configuration, warm upwelling regions, and elevated CO2 levels with respect to the pre-industrial atmosphere. The deep sea δ18O record, however, suggests that Antarctic ice sheet size remained

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    Potter, P. E.; Szatmari, P.

    2012-12-01

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

  2. Evidence for Late Oligocene-Early Miocene episode of transtension along San Andreas Fault system in central California

    SciTech Connect

    Stanley, R.G.

    1986-04-01

    The San Andreas is one of the most intensely studied fault systems in the world, but many aspects of its kinematic history remain controversial. For example, the period from the late Eocene to early Miocene is widely believed to have been a time of negligible strike-slip movement along the San Andreas fault proper, based on the rough similarity of offset of the Eocene Butano-Point of rocks Submarine Fan, the early Miocene Pinnacles-Neenach volcanic center, and an early Miocene shoreline in the northern Gabilan Range and San Emigdio Mountains. Nonetheless, evidence indicates that a late Oligocene-early Miocene episode of transtension, or strike-slip motion with a component of extension, occurred within the San Andreas fault system. The evidence includes: (1) about 22-24 Ma, widespread, synchronous volcanic activity occurred at about 12 volcanic centers along a 400-km long segment of the central California coast; (2) most of these volcanic centers are located along faults of the San Andreas system, including the San Andreas fault proper, the San Gregorio-Hosgri fault, and the Zayante-Vergeles fault, suggesting that these and other faults were active and served as conduits for magmas rising from below; (3) during the late Oligocene and early Miocene, a pull-apart basin developed adjacent to the San Andreas fault proper in the La Honda basin near Santa Cruz; and (4) during the late Oligocene and early Miocene, active faulting, rapid subsidence, and marine transgression occurred in the La Honda and other sedimentary basins in central California. The amount of right-lateral displacement along the San Andreas fault proper during this transtentional episode is unknown but was probably about 7.5-35 km, based on model studies of pull-apart basin formation. This small amount of movement is well within the range of error in published estimates of the offset of the Eocene to early Miocene geologic features noted.

  3. Miocene and Pliocene lacustrine and fluvial sequences, Upper Ramparts and Canyon village, Porcupine river, east-central Alaska

    USGS Publications Warehouse

    Fouch, T.D.; Carter, L.D.; Kunk, M.J.; Smith, C.A.S.; White, J.M.

    1994-01-01

    Cenozoic strata exposed along the Porcupine River between the Upper Ramparts and Canyon Village, Alaska, can be divided into five unconformity-bounded units (sequences) which are: lower and middle Miocene unit A, the white sandy fluvial sequence with peat beds; middle Miocene unit B, the basalt sequence-part B1 is basalt, and part B2 is organic-rich sedimentary beds; upper Miocene unit C, mudrock-dominated lake sequence; late Miocene or Pliocene to Pleistocene unit D, terrace gravels, detrital organic matter and associated sediments, and Holocene unit E, mixed sand and gravel-rich sediment and other sedimentary material including peat and eolian silt. The sequence (unit A) of lower and middle Miocene fluvial deposits formed in streams and on flood plains, just before the inception of local volanism. Fossil pollen from unit A suggests conifer-dominated regional forests and cool temperate climates. Peat beds and lake deposits from unit B contain pollen that indicates a warmer temperate climate coinciding with the middle Miocene thermal maximum. The lake deposits (unit C) downstream from the basalts accumulated in a small basin which resulted from a hydrologic system that was dammed in the late Miocene but breached soon thereafter. The lower part of the terrace gravels (unit D) expresses breaching of the dammed hydrologic system (of unit C). The Porcupine River became a major tributary of the Yukon River in late Pleistocene time when Laurentide ice blocked drainage from the Yukon interior basins causing meltwater to spill over the low divide separating it from the Porcupine River drainage initiating erosion and capture of the Yukon interior basins. ?? 1994.

  4. Early to middle Miocene vegetation history of Antarctica supports eccentricity-paced warming intervals during the Antarctic icehouse phase

    NASA Astrophysics Data System (ADS)

    Griener, Kathryn W.; Warny, Sophie; Askin, Rosemary; Acton, Gary

    2015-04-01

    Recent palynological evidence from the upper section (< 664 mbsf) of the Miocene ANDRILL 2A (AND-2A) core in the Ross Sea indicated a brief warm period during the Mid Miocene Climatic Optimum (MMCO), during Antarctica's icehouse phase. The nature of other Miocene climate fluctuations in Antarctica remains poorly resolved. Here, we present new palynological data from the lower section of the AND-2A core (> 664 mbsf) that reveal additional intervals of increased palynomorph abundance and diversity during the Antarctic early to middle Miocene. This evidence is consistent with a relatively dynamic early Miocene Antarctic icehouse climate with intervals of increased temperature and moisture, prior to the MMCO. Comparison with previous AND-2A studies indicates that periods of increased palynomorph abundance in the lower stratigraphic section largely coincide with ice sheet minima, distal ice conditions, and the presence of freshwater (i.e. increased precipitation, meltwater run-off, and freshwater ponds). Decreases in plant productivity mostly coincide with increased glaciation, decreased freshwater, and ice-proximal conditions during the Antarctic Miocene. Comparing the palynological data with other AND-2A data and global climate proxies (e.g., pCO2, δ18O, relative sea level, Milankovitch cycles) helps to resolve questions regarding the driving forces behind climate and vegetation change. We found that palynomorph assemblages reflecting generally warmer conditions are largely associated with 400-kyr eccentricity maxima, while assemblages indicative of colder conditions coincide with 400-kyr eccentricity minima. These data are consistent with other findings that indicate the early to middle Miocene climate was eccentricity-paced.

  5. Depositional patterns and hydrocarbon occurrence in middle to upper Miocene strata in part of the western Niger Delta Basin, Nigeria

    NASA Astrophysics Data System (ADS)

    Agyingi, C. M.; Agagu, O. K.; Fozao, K. F.; Njoh, O. A.; Ngalla, N.

    2013-04-01

    The relation of depositional patterns to hydrocarbon occurrence in middle to upper Miocene strata of part of the western Niger Delta Basin is postulated from the study of electrical logs, radiometric logs, lithologic logs, bottom hole temperatures, intervals of hydrocarbon occurrence and paleontological data. Alternating sands and shales of the Agbada Formation were deposited in the area (up to 720 m, middle Miocene and 510 m, upper Miocene) mainly as regressive off lap sequences in a paralic environment with depo-centers located in the south of the study area. Three deltaic facies can be recognized based on the relative amounts of shale and sand including, proximal delta front facies (>70% sand), distal delta front facies (30-70% sand) and prodelta facies (<30% sand). The upper Miocene is generally sandier than the middle Miocene as a result of south-westerly progradation of delta front facies from middle to upper Miocene. Geothermal gradients in the area range from 2.5 °C/100 m to 4.4 °C/100 m. Isothermal maps show that some middle to upper Miocene shales could have undergone catagenesis to become mature source rocks. Three depositional zones (A, B, C) corresponding to dominant depositional facies i.e., proximal delta, distal delta and prodelta respectively, have been delineated from sand percentage maps. There is a progression of these zones from A through B to C in a generally south-westerly direction (the direction of delta progradation). Data for hydrocarbon intervals reveal the predominance of hydrocarbons in Zone C due to high entrapment potentials and to a lesser extent in Zone B. Zone A is barren as a result of poor entrapment potentials. The juxtaposition of distal delta front sands and prodelta mud could have initiated growth faults which constitute the major types of traps in the basin.

  6. Fission track evidence for widespread early to Middle miocene extension in the northern Basin and Range province

    SciTech Connect

    Dumitru, T.; Miller, E.; Savage, C. . Geological Dept.); Gans, P. . Geological Science Dept.); Brown, R. . Geology Dept.)

    1993-04-01

    The northern Basin and Range province has experienced multiple periods of extension but the precise timing and relative importance of the various periods is poorly known. Geologic data in many areas suggest inception of extension was closely tied with the southward sweep in earliest magmatism, which is Eocene in southern Idaho, Oligocene in east-central Nevada, and Miocene in southern Nevada. Ar/Ar ages suggest that extension continued into the Early Miocene in areas such as the Raft River, Albion, Ruby, and Snake Range metamorphic core complexes. Youthful topography and recent faulting have been taken as indicating that faulting leading to present physiography is commonly younger than [approximately]10 Ma. New apatite fission track cooling age and track length data, supplemented by other information, point to the Early to Middle Miocene as an additional time of very significant extension-induced uplift and range formation. Many ranges in a 700-km-long north-south corridor from the Utah-Nevada-Idaho border to southernmost Nevada experience extension and major exhumation in Early to Middle Miocene time. Whether extension of Early to Middle Miocene age is restricted to this corridor or is more widespread is unclear due to the paucity of similar data to the east and west. Reconnaissance apatite ages from the Toiyabe Range and environs (NV) are [approximately]15 Ma and geologic data indicate Early to Middle Miocene extension at Yerington NV (Proffet and Dillis, 1984). Thus, it appears from the available data that the Early to Middle Miocene was an important, and previously little recognized, period of major extension over broad areas of the northern Basin and Range.

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

    PubMed Central

    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

  8. Middle to late Miocene canyon cutting on the New Jersey continental slope: biostratigraphic and seismic stratigraphic evidence

    SciTech Connect

    Miller, K.G.; Melillo, A.J.; Mountain, G.S.; Farre, J.A.; Poag, C.W.

    1987-06-01

    The authors have identified and dated a major Miocene erosional surface (M1) on the New Jersey continental slope. This surface was penetrated at Deep Sea Drilling Project (DSDP) Site 612, which was drilled near the thalweg of a buried V-shaped canyon. Biostratigraphic data at Site 612 firmly constrain the age of strata above the buried canyon surface as Zones CN7 (N=NN9) and N16 (lowermost upper Miocene); the upper Miocene surface at Site 612 lies above lowermost Oligocene strata because of coalesced unconformities. The authors traced the M1 erosional surface to the COST B-3 well where upper middle Miocene strata underlie it. Biostratigraphic studies of other New Jersey continental slope boreholes (ASP 14, ASP 15) suggest that elsewhere the sediments immediately below the M1 surface encompass the Globorotalia fohsi robusta Zone (=Zone N12-earliest N13; middle middle Miocene). The best age estimate is that M1 was eroded between 11.5 and 10.0 Ma. This erosional event apparently correlates with a similar even on the Irish and Florida continental margins and with oxygen-isotope evidence for a glacio-eustatic lowering.

  9. A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia.

    PubMed

    Rybczynski, Natalia; Dawson, Mary R; Tedford, Richard H

    2009-04-23

    Modern pinnipeds (seals, sea lions and the walrus) are semi-aquatic, generally marine carnivores the limbs of which have been modified into flippers. Recent phylogenetic studies using morphological and molecular evidence support pinniped monophyly, and suggest a sister relationship with ursoids (for example bears) or musteloids (the clade that includes skunks, badgers, weasels and otters). Although the position of pinnipeds within modern carnivores appears moderately well resolved, fossil evidence of the morphological steps leading from a terrestrial ancestor to the modern marine forms has been weak or contentious. The earliest well-represented fossil pinniped is Enaliarctos, a marine form with flippers, which had appeared on the northwestern shores of North America by the early Miocene epoch. Here we report the discovery of a nearly complete skeleton of a new semi-aquatic carnivore from an early Miocene lake deposit in Nunavut, Canada, that represents a morphological link in early pinniped evolution. The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing. The new fossil shows evidence of pinniped affinities and similarities to the early Oligocene Amphicticeps from Asia and the late Oligocene and Miocene Potamotherium from Europe. The discovery suggests that the evolution of pinnipeds included a freshwater transitional phase, and may support the hypothesis that the Arctic was an early centre of pinniped evolution. PMID:19396145

  10. Miocene Indian Ocean Circulation: A High-Resolution Multivariate Analysis of Interbasinal Records

    NASA Astrophysics Data System (ADS)

    Irving, D. H.; Smart, C.; Ramsay, A. T.; Thomas, E.

    2006-12-01

    Ocean circulation in the Indian Ocean during the Miocene progresses through three configurations in response to changes in plate movement and global climate. Principal Component Analysis (PCA) was carried out on benthic foraminifera, stable isotope and sedimentological data sampled at 100 kyr intervals from cores recovered from ODP sites 237, 707, 709 and 710 in the Somali Basin (SOB) and sites 214, 216 and 238 in the Mid-Indian Basin (MIB). These analyses provide insight into the structure and dynamics of the Indian Ocean through most of the Miocene (25--6 Ma) and suggest forcing mechanisms of the circulation system in this and adjacent ocean basins. Bulk responses of infaunal and epifaunal species mask local and regional oceanic signals that this study extracts by analysis at the species level. Isotopic ratios are used to describe the depth structure of the two basins. Coupled with sedimentological data, the dynamics of the basins is described in terms of the major events of the Miocene, namely Tethyan closure, the growth of the West Antarctic Ice Sheet (WAIS) and the initiation of the monsoon. PCA of the time series data show three separate components which correlate with these three phases in the history of the Indian Ocean. These are: i) 25-18 Ma, a stratified SOB with warm dense Tethyan outflow waters (TOW) underlying cooler, less dense water that is weakly coupled across the Chagos- Laccadive Ridge (CLR) with an unstratified MIB; ii) 18-12 Ma, mixing in the SOB as TOW diminishes due to seaway closure, and increasing cool bottom waters which penetrate further north with time, accompanied by stratification of the MIB and stronger coupling of surface waters promoting nutrient transfer eastwards; iii) 12-6 Ma, overturn and upwelling in the SOB with occasional strong fluxes of cooler WAIS bottom water and strong stratification in the MIB, with a westerly flux of warm water overtopping a more greatly subsided CLR.

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

    PubMed

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

    2016-03-29

    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. PMID:26903645

  12. The stratigraphy, geochronology and paleophysiography of a Miocene fresh-water interarc basin, southern Chile

    NASA Astrophysics Data System (ADS)

    Suarez, M.; Emparan, C.

    1995-01-01

    During Miocene time, the Andean region between 38° and 39°S was an area where active volcanoes, lakes and rivers formed under a temperate to cold humid climate. The volcanic products and sedimentary deposits which accumulated in lakes and rivers adjacent to the volcanoes constitute the Cura-Mallín Formation. The deep roots of the volcanic chain are represented by middle to late Miocene granitoids which formed a north-south trending belt that separated a marine fore-arc basin (Temuco basin) to the west from the continental sedimentary deposits of the Cura-Mallín Formation to the east. Twenty-three KAr dates ranging between 20 and 11 Ma, constrain the age of the Cura-Mallin Formation to the early to middle Miocene. The alternation of pyroclastic strata and lava flows in the Guapitrío Member of the Cura-Mallín Formation suggests the former existence of strato-volcanoes, whilst the presence of ignimbrites suggests caldera formation. A major lacustrine basin ( >100 km long) represented by some facies of the Rio Pedregoso Member of the Cura-Mallín Formation existed from at least 17.5 ± 0.6 to 13 ± 1.6 Ma. Lacustrine accumulations terminated during the progradation of deltas and infilling of volcanic material. The Cura-Mallín Formation lakes could have been formed, in part, by intra-arc extension, by the damming of rivers caused by volcanic products and/or by the filling of calderas. The occurrence of Gilbert-type delta complexes in the Rio Pedregoso Member may indicate a steep basin margin generated by faulting and/or volcanic accretion.

  13. Late Miocene Global Ocean Cooling Linked to Terrestrial Aridification and Evolutionary Events

    NASA Astrophysics Data System (ADS)

    Herbert, T.; Lawrence, K. T.; Tzanova, A.; Kelly, C. S.; Peterson, L.

    2015-12-01

    The path of global temperatures between the permanent establishment of the East Antarctic ice sheet at ~13.9 Ma and the onset of cyclical northern hemisphere glaciation at circa 2.7 Ma is poorly known. Enormous changes to terrestrial environments and ecosystems occurred approximately halfway between these polar glaciation milestones. What is perplexing is that this environmental upheaval on land occurred without any substantial evidence for late Miocene temperature change. Our single best marine index of the global climate state, the marine oxygen isotope record derived from benthic foraminifera is singularly devoid of a strong trend that would suggest notable climatic change during this time period. We present a globally distributed data set of estimated marine sea surface temperatures (SST) for the past 12 Ma reconstructed via the alkenone unsaturation method. Our reconstruction reveals what may be the strongest directional cooling of the Neogene, which occurred broadly synchronously in both hemispheres and culminated with ocean temperatures dipping to values close to the present between ~7 and 5.8 Ma before rebounding to warmer conditions in the Pliocene. The cold interval from circa 7-5.8 Ma that we reconstruct coincides very closely in time with previously enigmatic evidence of late Miocene glaciations of southeast Greenland, southeastern Alaska, and South America, with pulses of ice rafted detritus off Wilkes Land and Adelie Land and, perhaps the formation of an ice sheet on West Antarctica. A large scale forcing mechanism, such as a previously hypothesized decline in atmospheric CO2 levels from 8-6 Ma [T.E. Cerling and colleagues] seems required to coordinate the increase in late Miocene Equator-Pole temperature gradients with evidence for a contemporaneous increase in aridity on land, restructuring of terrestrial plant and animal communities, and a pronounced shift in the marine carbon cycle.

  14. Steps in the intensification of Benguela upwelling over the Walvis Ridge during Miocene and Pliocene

    NASA Astrophysics Data System (ADS)

    Hoetzel, Sebastian; Dupont, Lydie M.; Marret, Fabienne; Jung, Gerlinde; Wefer, Gerold

    2016-03-01

    Upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient-rich cold waters to the surface and therefore influencing ocean productivity and global climate. The Benguela upwelling system (BUS) is one of the major upwelling areas in the world. Previous reconstructions of the BUS mainly focused on the onset and intensification in southern and central parts, but changes of the northern part have been rarely investigated in detail. Using the Late Miocene to Pliocene organic-walled dinoflagellate cyst record of ODP Site 1081, we reconstruct and discuss the early upwelling history over the Walvis Ridge with a special focus on the movement of the Angola-Benguela Front (ABF). We suggest that during the Late Miocene the Angola Current flowed southwards over the Walvis Ridge more frequently than today because the ABF was probably located further south as a result of a weaker meridional temperature gradient. A possible strengthening of the meridional gradient during the latest Miocene to early Pliocene in combination with uplift of south-western Africa intensified the upwelling along the coast and increased the upwelling's filaments over the Walvis Ridge. An intermediate period from 6.2 to 5.5 Ma is shown by the dominance of Habibacysta tectata, cysts of a cool-tolerant dinoflagellate known from the northern Atlantic, indicating changing oceanic conditions contemporaneous with the Messinian Salinity Crisis. From 4.3 Ma on, the upwelling signal got stronger again and waters were well-mixed and nutrient-rich. Our results indicate a northward migration of the ABF as early as 7 Ma and the initial stepwise intensification of the BUS.

  15. Sedimentary facies, mineralogy, and geochemistry of the sulphate-bearing Miocene Dam Formation in Qatar

    NASA Astrophysics Data System (ADS)

    Dill, H. G.; Botz, R.; Berner, Z.; Stüben, D.; Nasir, S.; Al-Saad, H.

    2005-01-01

    The Miocene deposits of the Dam Formation were deposited in a narrow seaway stretching along the western edge of the Qatar Arch. During the initial stages of basin evolution the rising Zagros Mts. delivered debris in this fore deep basin. The paleocurrent and paleogeographic zonation are reflected by the heavy mineral assemblage, by the spatial distribution of phyllosilicates and the various types of sulphate. From NW towards the SE, the contents of smectite and palygorskite increase, whereas the illite and kaolinite contents decrease. Mega crystals of gypsum are found in the NW and massive fine-grained gypsum in the SE of the basin. During the waning stages of basin subsidence, the Arabian Shield became more and more important as a source for the Miocene sediments. In this study, the Dam Formation was subdivided into 7 members/lithofacies associations (lower, middle, upper Salwa, and Al Nakhsh Members, Abu Samrah Member). The Salwa Members at the base of the Dam Formation consists of heterolithic siliciclastic-calcareous sediments which were laid down under meso- to microtidal conditions. The Al Nakhsh Members formed under macrotidal conditions with sub- to supratidal depositional environments passing into continental ones. Celestite, gypsum, and microbial mats (stromatolites) are very widespread in these sabkha sediments. Crystals of gypsum and the thickness of stromatolites tremendously increase towards younger sediments indicating thereby a close genetic link between growth of microbial domes and gypsum precipitation. Throughout the Abu Samrah Member marine calcareous sediments were deposited in a microtidal wave-dominated environment. Dissolution of Eocene evaporites at depth governed the lithofacies differentiation in the Miocene Dam Formation.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Atmosphere, ecology and evolution: what drove the Miocene expansion of C(4) grasslands?

    PubMed

    Osborne, Colin P

    2008-01-01

    Grasses using the C(4) photosynthetic pathway dominate today's savanna ecosystems and account for approximately 20% of terrestrial carbon fixation. However, this dominant status was reached only recently, during a period of C(4) grassland expansion in the Late Miocene and Early Pliocene (4-8 Myr ago). Declining atmospheric CO(2) has long been considered the key driver of this event, but new geological evidence casts doubt on the idea, forcing a reconsideration of the environmental cues for C(4) plant success.Here, I evaluate the current hypotheses and debate in this field, beginning with a discussion of the role of CO(2) in the evolutionary origins, rather than expansion, of C(4) grasses. Atmospheric CO(2) starvation is a plausible selection agent for the C(4) pathway, but a time gap of around 10 Myr remains between major decreases in CO(2) during the Oligocene, and the earliest current evidence of C(4) plants.An emerging ecological perspective explains the Miocene expansion of C(4) grasslands via changes in climatic seasonality and the occurrence of fire. However, the climatic drivers of this event are debated and may vary among geographical regions.Uncertainty in these areas could be reduced significantly by new directions in ecological research, especially the discovery that grass species richness along rainfall gradients shows contrasting patterns in different C(4) clades. By re-evaluating a published data set, I show that increasing seasonality of rainfall is linked to changes in the relative abundance of the major C(4) grass clades Paniceae and Andropogoneae. I propose that the explicit inclusion of these ecological patterns would significantly strengthen climate change hypotheses of Miocene C(4) grassland expansion. Critically, they allow a new series of testable predictions to be made about the fossil record.Synthesis. This paper offers a novel framework for integrating modern ecological patterns into theories about the geological history of C(4) plants.

  18. Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing.

    PubMed

    LaRiviere, Jonathan P; Ravelo, A Christina; Crimmins, Allison; Dekens, Petra S; Ford, Heather L; Lyle, Mitch; Wara, Michael W

    2012-06-06

    Deep-time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration (that is, the atmospheric partial pressure of CO(2), p(co(2))). Although past studies have explored these responses during portions of the Cenozoic era (the most recent 65.5 million years (Myr) of Earth history), comparatively little is known about the climate of the late Miocene (∼12-5 Myr ago), an interval with p(co(2)) values of only 200-350 parts per million by volume but nearly ice-free conditions in the Northern Hemisphere and warmer-than-modern temperatures on the continents. Here we present quantitative geochemical sea surface temperature estimates from the Miocene mid-latitude North Pacific Ocean, and show that oceanic warmth persisted throughout the interval of low p(co(2)) ∼12-5 Myr ago. We also present new stable isotope measurements from the western equatorial Pacific that, in conjunction with previously published data, reveal a long-term trend of thermocline shoaling in the equatorial Pacific since ∼13 Myr ago. We propose that a relatively deep global thermocline, reductions in low-latitude gradients in sea surface temperature, and cloud and water vapour feedbacks may help to explain the warmth of the late Miocene. Additional shoaling of the thermocline after 5 Myr ago probably explains the stronger coupling between p(co(2)), sea surface temperatures and climate that is characteristic of the more recent Pliocene and Pleistocene epochs.

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

    PubMed

    Sánchez, Israel M; Cantalapiedra, Juan L; Ríos, María; Quiralte, Victoria; Morales, Jorge

    2015-01-01

    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.

  20. The Superimposed Paleocene-Miocene Tectonics of the middle part of the Nallihan Wedge (NW Turkey)

    NASA Astrophysics Data System (ADS)

    Şahin, Murat; Yaltirak, Cenk

    2015-04-01

    In the NW Turkey, the area between the suture zones of the Rhodope-Pontide Ocean and Izmir-Ankara Ocean, and North Anatolian Fault Zone (NAFZ) and Thrace-Eskişehir Fault Zone (TEFZ) is known as the Nallıhan Wedge. The shape of Nallıhan Wedge is a 90 degree counter-clockwise rotated isosceles triangle. The northwestern boundary is a part of NAFZ and the southwestern boundary is a part of TEFZ. The 160 km-long eastern boundary is located at around Beypazarı and western corner is on the Bursa Plain. Nallıhan is situated at the centre of this isosceles triangle. While all the thrusts and folds shrink towards to the west and show an imbricate-like structure, the characteristics of the folds turn into to the open folds. Thrusts faults are locally observed as blind and almost perpendicular thrusts at the fold limbs towards to the east. The rocks of the study area show different characteristics according to their types and basins of formation. On the other hand the structural properties of these rocks display the effects of the closure of the Intra-Pontide and Izmir-Ankara Oceans in between Paleocene and Early Oligocene. During Miocene, the thrust faults reactivated and a deformation formed the NEE-SWW left lateral strike-slip faults parallel to these thrust faults. Whereas the first events are related to the closure of the branches of Neo-Tethys, the Miocene deformation is probably based on the Miocene tectonics of the Western Anatolia by the reason of equivalent age of the TEFZ. In this framework, the deformation of the Nallıhan Wedge presents significant information about the period between the evolution of Paleotectonic and Neotectonic of Turkey.

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

    PubMed

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

    2016-03-29

    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.

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

    PubMed Central

    Sánchez, Israel M.; Cantalapiedra, Juan L.; Ríos, María; Quiralte, Victoria; Morales, Jorge

    2015-01-01

    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. PMID:26630174

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

    PubMed Central

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

    2016-01-01

    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. PMID:26903645

  4. Late Oligocene to Late Miocene Antarctic Climate Reconstructions Using Molecular and Isotopic Biomarker Proxies

    NASA Astrophysics Data System (ADS)

    Duncan, B.; Mckay, R. M.; Bendle, J. A.; Naish, T.; Levy, R. H.; Ventura, G. T.; Moossen, H. M.; Krishnan, S.; Pagani, M.

    2015-12-01

    Major climate and environmental changes occurred during late Oligocene to the late Miocene when atmospheric CO2 ranged between 500 and 300ppm, indicating threshold response of Antarctic ice sheets and climate to relatively modest CO2 variations. This implies that the southern high latitudes are highly sensitive to feedbacks associated with changes in global ice sheet and sea-ice extent, as well as terrestrial and marine ecosystems. This study focuses on two key intervals during the evolution of the Antarctic Ice Sheet: (1) The Late Oligocene and the Oligocene/Miocene boundary, when the East Antarctic Ice Sheet expanded close to present day volume following an extended period of inferred warmth. (2) The Mid-Miocene Climate Optimum (MMCO ~17-15 Ma), a period of global warmth and moderately elevated CO2 (350->500 ppm) which was subsequently followed by rapid cooling at 14-13.5 Ma. Reconstructions of climate and ice sheet variability, and thus an understanding of the various feedbacks that occurred during these intervals, are hampered by a lack of temperature and hydroclimate proxy data from the southern high latitudes. We present proxy climate reconstructions using terrestrial and marine organic biomarkers that provide new insights into Antarctica's climate evolution, using Antarctic drill cores and outcrop samples from a range of depositional settings. Bacterial ether-lipids have been analysed to determine terrestrial mean annual temperatures and soil pH (via the methylation and cyclisation indexes of branched tetraethers - MBT and CBT, respectively). Tetraether-lipids of crenarchaeota found in marine sediments sampled from continental shelves around Antarctica have been used to derive sea surface temperatures using the TEX86 index. Compound specific stable isotopes on n-alkanes sourced from terrestrial plants have been analysed to investigate changes in the hydrological and carbon cycles.

  5. Late Miocene-Pleistocene Stability of upper Ferrar Glacier, Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Staiger, J. W.; Marchant, D. R.; Schaefer, J. M.; Johnson, J. V.; Oberholzer, P.

    2005-12-01

    Vernier Valley (78o S, 161o E) opens onto a peripheral lobe of upper Ferrar glacier in the Dry Valleys of southern Victoria Land, Antarctica. The areal distribution of Ferrar drifts, along with a relative and numerical chronology afforded by surface-weathering characteristics and 3He - 21Ne exposure-age data, are used to reconstruct the Late Miocene-to-Pleistocene history of upper Ferrar Glacier. Applying a modest erosion rate correction of 10 cm Ma-1, our results show that the glacial record provided by Ferrar (1, 2, 3, and 4) drifts in Vernier Valley extends back into late Miocene time. Cosmogenic ages for clasts on the modern, ice-cored Ferrar 1 moraine suggest that nuclide inheritance is negligible. The development of weathering pits and desert varnish on surface cobbles varies linearly with cosmogenic age. Ice-surface profiles reconstructed from the moraine distribution and exposure-ages of boulders atop the moraines indicate that the ice-surface elevation of upper Ferrar Glacier has lowered roughly 50 m throughout the Quaternary Period and roughly 125 m since late Miocene time. Conversely, during MIS 2, the ice-surface elevation of upper Ferrar Glacier was likely no higher than today and may have been below modern levels. The moraine now forming through ice sublimation and debris accumulation at the modern, cold-based Ferrar Glacier margin is texturally similar to older drifts up-valley. The slow recession of cold-based glacier ice (and without surface melting ablation zones) in lower Vernier Valley implies enduring cold-desert conditions, much like those of today, for at least the last ~6.5 Ma. Results from a 2-D glacier flow-band model also demonstrate that upper Ferrar Glacier lacked basal-melting zones even during the Pliocene optimum. The overall stability of this glacial system has implications for the response of ice in this sector of Antarctica to future polar warming.

  6. Early Miocene subduction in the western Mediterranean: Constraints from Rb-Sr multimineral isochron geochronology

    NASA Astrophysics Data System (ADS)

    Kirchner, Kory L.; Behr, Whitney M.; Loewy, Staci; Stockli, Daniel F.

    2016-05-01

    The Betic Cordillera of southern Spain is a complex orogen formed in the context of convergence between Africa and Iberia from the Mesozoic to the present. The internal zone of the orogen includes three tectonic complexes, two of which have been subducted to high-pressure conditions, then exhumed back to the surface during subsequent extension. Subduction in the structurally lower complex, known as the Nevado-Filabride Complex (NFC), has been a topic of debate for several years due to conflicting geochronological data. Here we use multimineral isochron 87Rb/86Sr dating on carefully selected mineral samples from high-pressure metamorphic rocks in the NFC to better constrain the timing of high-pressure metamorphism and subduction in the region. Out of five samples analyzed, statistically valid multimineral isochrons were obtained for one eclogite and two schists, yielding ages of 20.1 ± 1.1, 16.0 ± 0.3, and 13.3 ± 1.3 Ma, respectively. Despite that the other two eclogite samples appeared to preserve prograde mineral assemblages, low 87Rb/86Sr ratios in white mica precluded precise age calculations. These new ages are in close agreement with previously published Lu-Hf ages on garnet and U-Pb ages on metamorphic zircon overgrowths for the same rocks, but are substantially younger than published data from the 40Ar/39Ar technique. Combined with recently published tomographic images of slab structure beneath the Alboran Sea, the new ages support a tectonic model in which subduction occurred both prior to the Miocene and during the early to mid-Miocene, but that it was punctuated in time by a pulse of extensional exhumation in the early Miocene associated with lithospheric delamination and/or slab tearing.

  7. Correlating Mediterranean shallow water deposits with global Oligocene–Miocene stratigraphy and oceanic events☆

    PubMed Central

    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

  8. Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama

    PubMed Central

    Pimiento, Catalina; Ehret, Dana J.; MacFadden, Bruce J.; Hubbell, Gordon

    2010-01-01

    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. PMID:20479893

  9. Miocene-Pleistocene Paleoclimate and Paleoenvironment in the Meade Basin, Kansas

    NASA Astrophysics Data System (ADS)

    Snell, K. E.; Uno, K. T.; Fetrow, A. C.; Burgess, C.; Lukens, W. E.; Fox, D. L.; Fox-Dobbs, K.; Polissar, P. J.

    2015-12-01

    The Meade Basin in southwestern Kansas preserves a unique record of paleovegetation and small mammal faunal change from the Miocene to the Pleistocene. Many of the paleosols preserved in this basin contain paleosol carbonate nodules, thick calcretes and abundant organic-rich horizons, which makes it ideally suited for a multiproxy study that explores the role of paleoenvironmental change in driving floral and faunal change. Here we focus on the carbonate samples where we measured carbon and oxygen isotopes (δ13Cc and δ18Oc, respectively); used clumped isotope thermometry (Δ47) to estimate soil temperature and soil water δ18O; and assessed the preservation state and additional paleoenvironmental features of the samples using optical and cathodoluminescence (CL) microscopy. The carbon isotope record matches previous studies from the region and shows an increase in the relative abundance of C4 biomass on the landscape since the late Miocene. The Δ47 temperatures and the δ18O of soil water, while variable, show no significant change in average values through time. The textural and luminescenece characteristics suggest some samples have undergone moderate to extensive diagenetic alteration from groundwater fluids, perhaps causing some of the variability in the geochemical records. Soil depth may also account for some of the variability. Overall, these data suggest that temperature is unlikely to be the dominant factor driving paleovegetation and faunal change in this region from the Miocene to Pleistocene. In addition, these data highlight the importance of assessing preservation for all carbonate samples, regardless of whether or not the samples have been deeply buried.

  10. Early and Middle Miocene Antarctic Ice Sheet Behavior: results from the ANDRILL SMS Project

    NASA Astrophysics Data System (ADS)

    Harwood, D. M.; Florindo, F.; Levy, R. H.; SMS Project Science Team http://andrill. org/projects/sms/team. html

    2011-12-01

    A 1138-meter sediment drillcore (AND-2A) recovered by the SMS Project of the ANDRILL Program from the McMurdo Sound sector of the western Ross Sea contains a near-continuous, coastal record of Antarctic climate and ice sheet variability through the early Miocene (20.2 to ~14.5 million years ago), including an interval of global warmth known as the Mid-Miocene Climatic Optimum (MMCO). The AND-2A drillcore was deposited in the subsiding Victoria Land Basin, during a period of relatively steady thermal subsidence, on the coastal plain and continental shelf seaward of the rising Transantarctic Mountains. Analysis of this drillcore indicates prolonged periods when the ice sheet margin remained retreated from the coastline, and other periods when the ice sheet was highly dynamic, advancing and retreating on orbital timescales. It preserves a record of the pace and scale of climate and ice sheet variation, and allows for the evaluation of climate sensitivity through data and numerical modeling integration. Stratigraphic sequences and facies interpretations reveal a cyclical history of climate changes, glacial advance and retreat cycles. Under warm, equable climate conditions recorded in a variety of climate indicators, the behavior of the early Miocene Antarctic ice sheet evident in the AND-2A core was varied, ranging between two modes: (1) persistent absence/retreat of low elevation ice sheets from coastal regions, and (2) periods of dynamic but subdued fluctuations with the ice margin of larger volume ice sheets entering across the coastal zone. The glacial regime varied from sub-polar with significant meltwater through proximal and distal high-latitude temperate glacial conditions with abundant meltwater. A well-developed chronostratigraphic framework allows for the comparison of events recognized in this drillcore with events identified in distal proxy records from deep-sea stable isotope studies. This dynamic response of Antarctic climate during times when CO2 levels

  11. New constrains on the thermal history of the Miocene Jarando basin (Southern Serbia)

    NASA Astrophysics Data System (ADS)

    Andrić, Nevena; Životić, Dragana; Fügenschuh, Bernhard; Cvetković, Vladica

    2013-04-01

    The Jarando basin, located in the internal Dinarides, formed in the course of the Miocene extension affecting the whole Alpine-Carpathian-Dinaride system (Schmid et al., 2008). In the study area Miocene extension led to the formation of a core-complex in the Kopaonik area (Schefer et al., 2011) with the Jarando basin located in the hanging wall of the detachment fault. The Jarando basin is characterized by the presence of bituminous coals, whereas in the other intramontane basins in Serbia coalification did not exceed the subbituminous stage within the same stratigraphic level. Furthermore, the basin hosts boron mineralizations (borates and howlite) and a magnesite deposit, which again implies elevated temperatures. This thermal overprint is possibly due to post-magmatic activity related to the emplacement of Oligocene I-type Kopaonik and Miocene S-type Polumir granitoid (Schefer et al., 2011.). This research project is aimed at providing new information about the thermal history of the Jarando basin. Fifteen core samples from three boreholes and 10 samples from the surrounding outcrops were processed for apatite fission-track analysis. Additionally, vitrinite reflectance was measured for 11 core samples of shales from one borehole and 5 samples of coal from an underground mine. VR data of Early to Middle Miocene sediments reveal a strong post-depositional overprint. Values increase with the depth from 0.66-0.79% to 0.83-0.90%. Thus organic matter reached the bituminous stage and experienced temperatures of around 110-120˚C (Barker and Pawlewicz, 1994). FT single grain ages for apatite scatter between 45 Ma to 10 Ma with a general trend towards younger ages with depth. Both, the spread in single grain ages together with the bimodal track lengths distribution clearly point to partial annealing of the detrital apatites. With the temperature given from the VR values the partial annealing points to a rather short-lived thermal event. This is assisted by thermal

  12. C4 expansion in the central Inner Mongolia during the latest Miocene and early Pliocene

    NASA Astrophysics Data System (ADS)

    Zhang, Chunfu; Wang, Yang; Deng, Tao; Wang, Xiaoming; Biasatti, Dana; Xu, Yingfeng; Li, Qiang

    2009-10-01

    The emergence of C4 photosynthesis in plants as a significant component of terrestrial ecosystems is thought to be an adaptive response to changes in atmospheric CO 2 concentration and/or climate during Neogene times and has had a profound effect on the global terrestrial biosphere. Although expansion of C4 grasses in the latest Miocene and Pliocene has been widely documented around the world, the spatial and temporal variations in the C4 expansion are still not well understood and its driving mechanisms remain a contentious issue. Here we present the results of carbon and oxygen isotope analyses of fossil and modern mammalian tooth enamel samples from the central Inner Mongolia. Our samples represent a diverse group of herbivorous mammals including deer, elephants, rhinos, horses and giraffes, ranging in age from the late Oligocene to modern. The δ13C values of 91 tooth enamel samples of early late-Miocene age or older, with the exception of two 13 Ma rhino samples (- 7.8 and - 7.6‰) and one 8.5 Ma suspected rhino sample (- 7.6‰), were all less than - 8.0‰ (VPDB), indicating that there were no C4 grasses present in their diets and thus probably few or no C4 grasses in the ecosystems of the central Inner Mongolia prior to ~ 8 Ma. However, 12 out of 26 tooth enamel samples of younger ages (~ 7.5 Ma to ~ 3.9 Ma) have δ13C values higher than - 8.0‰ (up to - 2.4‰), indicating that herbivores in the area had variable diets ranging from pure C3 to mixed C3-C4 vegetation during that time interval. The presence of C4 grasses in herbivores' diets (up to ~ 76% C4) suggests that C4 grasses were a significant component of the local ecosystems in the latest Miocene and early Pliocene, consistent with the hypothesis of a global factor as the driving mechanism of the late Miocene C4 expansion. Today, C3 grasses dominate grasslands in the central Inner Mongolia area. The retreat of C4 grasses from this area after the early Pliocene may have been driven by regional

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  14. Miocene to Quaternary volcanism in NW Iran Azerbaijan: new geochemical and geochronological data

    NASA Astrophysics Data System (ADS)

    Lechmann, Anna; Burg, Jean-Pierre; Faridi, Mohammad

    2016-04-01

    The Mesozoic to Present geology of Iran has been shaped by the northward subduction of the Neo-Tethys Ocean during convergence and subsequent collision between Arabia and Eurasia, leading to the generation of magmatic arcs and seeding the conditions for the formation of the Turkish-Iranian Plateau. Over this Plateau, Miocene to Quaternary magmatic rocks cover vast areas. Processes, such as lithospheric delamination or slab break-off, which led to this widespread magmatism are still debated. We present major and trace element analyses together with LA-ICP-MS U-Pb zircon ages of domes and lavas from NW Iran Azerbaijan, with the goal to shed light on the generation and evolution of these recent magmatic rocks and compare them with previously published information. We focused on morphologically prominent domes scattered over the region. The sampled domes, dominantly dacitic to rhyolitic in composition, and the lavas, showing a wide range from basaltic to dacitic and few alkaline compositions, have tholeiitic to calc-alkaline and shoshonitic chemical features. REE patterns are steep and flatten towards the HREE. Plots of primitive mantle normalized trace elements systematically show a negative Nb-Ta anomaly indicating a subduction-modified component in the mantle source and/or crustal contamination. U-Pb zircon ages on one lava, two tuffs and 12 dacitic domes yield two distinct age distributions: (1) middle Miocene (ca. 10-12 Ma) and (2) latest Miocene - late Pleistocene (ca. 2-5.5 Ma). Ascribing these two age clusters to trace element compositions reveals that REE patterns became more depleted from middle Miocene to late Pleistocene. On a plot of Rb/Sr vs Ba/Rb the samples follow a low Rb/Sr trend typical for an amphibole-bearing mantle source. First Sr-Nd isotope results lie within or near the mantle array, making crustal contamination enigmatic. Coeval lavas in neighbouring regions (e.g. Ararat) show similar major/trace element and Sr-Nd isotopic compositions and the

  15. Mid Miocene volcanism in Nicaragua and implications for the formation of the Nicaraguan Depression

    NASA Astrophysics Data System (ADS)

    Saginor, I.; Gazel, E.; Carr, M. J.

    2009-12-01

    Northwest Nicaragua contains Mid Miocene volcanism on either side of the Nicaraguan Depression consisting of portions of the Coyol Formation to the East and the Tamarindo Formation to the West. The Tamarindo Formation is a narrow band of basaltic to andesitic lavas interlayered with thick ignimbrite deposits and volcaniclastic sediments that parallel Nicaragua’s Pacific coast to the west of the modern volcanic front with ages from 14.7-11.7 Ma. The Coyol represents primarily Miocene volcanism from 25-7 Ma and lies east of the active front. The presence of Mid Miocene volcanism on either side of the Nicaraguan Depression has led to speculation that the two coeval units, which are currently separated by almost 100km, were once connected and have since been separated by extension. Here, we present data that show the Tamarindo and Coyol are geochemically distinct and therefore cannot be considered part of the same unit. First, the Tamarindo has lower La/Yb values than Coyol, which suggests that the Tamarindo was formed by a higher degree of partial melting, assuming that mantle source compositions are similar for both units. In addition, the Tamarindo has higher Zr/Nb values than Coyol, which are indicative of High Field Strength Element (HFSE) depletion common in arc volcanics. Because the degree of partial melting and HFSE depletion is expected to increase towards the trench, both Tamarindo’s La/Yb and Zr/Nb values are consistent with its being emplaced closer to the trench than Coyol and the presence of these two units of Mid-Miocene age on opposite sides of the Nicaraguan Depression cannot be used as proof of significant extension. In addition, currently available data do not show the significant crustal thinning and large-scale structural surface features that would be expected if the Tamarindo and Coyol were once connected and later separated by extension. Fault displacement along the Nicaraguan Depression is insufficient to accommodate this extension and

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

    NASA Astrophysics Data System (ADS)

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

    1999-02-01

    The recently collected fauna of Armantes 1A in Chron C5Br of the Armantes section necessitates reinterpretation of the previous bio- and magnetostratigraphical correlations between the Armantes and Vargas sections (Calatayud-Daroca Basin, Central Spain) [W. Krijgsman, M. Garcés, C.G. Langereis, R. Daams, J. van Dam, A.J. van der Meulen, J. Agustı´, L. Cabrera, A new chronology for the Middle to Late Miocene continental record in Spain, Earth Planet. Sci. Lett. 142 (1996) 367-380]. The long reversal in the Vargas section is now correlated to C5Br, instead of to C5Cr, on the basis of the biostratigraphical correlation of Armantes 1A to the faunas of Fuente Sierra 2 and 3 (in the Vargas section), which are situated in the basal part of the Middle Aragonian (MN5). This leads to the revised age of 16.0 Ma for the Early-Middle Aragonian (MN 4/5) boundary. Our age estimate of the MN5/6 boundary is maintained at ca. 13.75 Ma. The Vargas section is now considered to start in Chron C5Cn.2r and to end in C5Bn.1n. As a result of the revised correlation the duration of the time gap between the fossiliferous parts of Vargas and the younger Aragón section, previously estimated as ca. 1.5 Myr, is now reduced to less than 200,000 years. The tie points of the European mammal units (MN4-MN6) to the geomagnetic polarity time scale [F.F. Steininger, W.A. Berggren, D.V. Kent, R.L. Bernor, S. Sen, J. Agustı´, Circum-Mediterranean Neogene (Miocene and Pliocene) marine-continental chronologic correlations of European mammal units, in: R.L Bernor, V. Fahlbusch, H.-W. Mittmann (Eds.), The Evolution of Western Eurasian Neogene Mammal Faunas, Columbia Univ. Press, New York, 1996, pp. 7-46] are evaluated. Our age estimates of the MN4/5 and MN5/6 boundaries are compatible with the new magnetostratigraphic calibration of middle Miocene mammal zones in the Swiss Molasse basin [O. Kempf, T. Bolliger, D. Kälin, B. Engesser, A. Matter, New magnetostratigraphic calibration of Early to Middle

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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 isotope events). One of the more severe events, Mi-3, is associated with East Antarctic Ice Sheet growth and potential Northern Hemisphere ice expansion, as well as marine and terrestrial species turnover and aridification. The causes and consequences of the Mi-events are not well constrained yet. CO2 reconstructions combined with the abovementioned consequences suggest that a drawdown of CO2 and/or changes in ocean led to the changes surrounding Mi-3. A minimum node in both eccentricity and obliquity amplitude modulation, an orbital configuration creating favourable conditions for ice growth, has been suggested as a possible triggering mechanism as well. However, an exact cause cannot be pinpointed yet and more high-resolution records are needed in order to investigate the impact and order of events surrounding the Mi-events. Integrated Ocean Drilling Program (IODP) Leg 307 recovered such a high resolution record from the middle Miocene of the Porcupine Basin (offshore south-western Ireland). We have analyzed well-preserved palynomorphs (mainly organic-walled dinoflagellate cysts, acritarchs and pollen) and organic molecules for paleothermometry (e.g. TEX86 and UK'37) from site U1318. With these proxies, the development of the Mi-3 event and following Mi-4 have been reconstructed in high resolution (ca. 13 kyr), by assessing e.g. temperature, sea level, thermocline depth and productivity. A pronounced cooling can be observed at Mi-3, and to a lesser degree in Mi-4 as well, together with a sea-level fall and a turnover in the dinocyst record. Our findings also include indications of aridification and a change in wind patterns during Mi-3. This confirms the dramatic

  18. Combination of hand mapping and automatic mapping to reveal the Miocene high elevation Pyrenean peneplain

    NASA Astrophysics Data System (ADS)

    Bosch, Gemma V.; Babault, Julien; Van Den Driessche, Jean

    2016-04-01

    A striking feature of the morphology of the Pyrenees is the occurrence of high-elevation, low-relief surfaces, which are interpreted as remnants of a single Miocene planation surface. Whether the original surface was uplifted or developed at high altitude is debated. This "Miocene Pyrenean peneplain" has been dissected by fluvial and glacial erosion during the Quaternary. Reworking by glacial erosion also provides new smooth surfaces such as glacial cirque floors that must not be confused with the remnants of the original planation surface. The later are convex-up landforms whereas glacial cirque floors are concave-up landforms. To reveal the Miocene high-elevation Pyrenean peneplain, we combined hand mapping and automatic mapping at the scale of the whole chain. From previous mapping in literature and from our own field work, we first perform a map of both the Miocene planation surface remnants and the Quaternary glacial cirque floors. Using Digital Elevation Models, numerical parameters were extracted from this map to characterize the two types of smooth surfaces. The slope is the parameter that helps to delimitate and differentiate the smooth surfaces from the rest of the Pyrenean topography. To distinguish between the two types of smooth surfaces we used the Topographic Index (TPI). This parameter is the difference between the elevation of a point and the mean elevation. Choosing the pertinent radius according to the scale of the landform to map, and the pertinent values interval, we can differentiate the planation surface (convex-up) from the glacial cirque floors (concave-up). A sensitivity test was performed to determine the best radius and the best interval for TPI and slope values to distinguish between the two types of smooth surfaces. Finally, we used a combination of slope values, TPI values and radius to determine automatically the high-elevation, low-relief surfaces in the entire Pyrenees. We verified in the field the presence of the newly mapped high

  19. Biostratigraphy and paleoenvironment of Miocene- Pliocene hemipelagic limestone: Kingshill Seaway, St. Croix, US Virgin Islands.

    USGS Publications Warehouse

    Lidz, B.H.

    1982-01-01

    The Kingshill Limestone and younger carbonate rocks constitute the central portion of St. Croix, forming the remains of an ancient seaway that was flanked by emergent highlands. The seaway has been filled with thick epipelagic sediments alternating with carbonate turbidites and ash falls and capped with shallow-water reefal and terrigenous debris. Planktonic foraminifera indicate that ages of these rocks range sequentially in a SW direction from the middle Miocene to lower Pliocene. Scanning electron micrographs illustrate 42 species and subspecies of pelagic foraminifera and 13 selected paleoenvironmentally significant aberrant forms.-from Author

  20. Global climate and monsoons response to orbital forcing in the Late Miocene

    NASA Astrophysics Data System (ADS)

    Marzocchi, A.; Lunt, D. J.; Flecker, R.; Farnsworth, A.; Bradshaw, C.

    2014-12-01

    Global climate during the Late Miocene (11.61-5.33 Ma) is thought to have been generally warmer and wetter than at present day. The Northern Hemisphere was characterised by nearly ice-free conditions (with respect to the extent of the Greenland ice sheet) and some of the main marine gateways were undergoing opening or closure (e.g. Central American gateway, Bering Strait, and Indonesian Throughflow). Vegetation distribution was also generally more extensive than it is today, both at high and low latitudes. There is geological evidence of orbitally-forced cyclicity in sedimentary sections throughout the globe, especially in marginal basins such as the Mediterranean Sea. In the Late Miocene the entire North African catchment drained in the Eastern Mediterranean, constituting the main fresh water input into the basin, regulated by the North African monsoon. In addition, the Tibetan Plateau underwent substantial uplift throughout this time period, which strengthened the Asian monsoon system. The Late Miocene therefore represents an ideal scenario to investigate the impact of orbital forcing on the North African and Asian monsoon systems, the establishment of their teleconnections, and the associated vegetation changes. There still is considerable uncertainty in the reconstructed atmospheric CO2 levels for this time period, due to the patchy distribution (both spatially and temporally) of the available proxy record. Hence, we also explore the sensitivity of global climate to changing CO2 levels with different orbital configurations. We carried out a new series of 22 fully coupled atmosphere-ocean-vegetation numerical simulations, run at evenly spaced intervals (1kyr) through a full late Miocene precession cycle (~6.5 Ma), using a full-complexity general circulation model (HadCM3L). These model results show substantial changes to sea surface temperatures and regional atmospheric circulation on sub-precessional time scales. This triggers responses in the North African and

  1. Coarse-grained deltaic sedimentation in the Miocene Cuyama strike-slip basin, California Coast Ranges

    USGS Publications Warehouse

    Alan, Bartow J.

    1990-01-01

    The Cuyama basin, located in the southern Coast Ranges of California southwest of the San Andreas fault, developed early in the history of the San Andreas transform system. The Miocene marine basin formed in a transtensional setting along a dextral strike-slip fault of the transform system following Oligocene non-marine basin formation in an extensional setting. The lower and middle Miocene Vaqueros Formation in the northwestern part of the basin, which represents the first of two transgressive-regressive cycles, is described here in terms of nine facies in two broad facies groups. The 400-m-thick Soda Lake Shale Member (of the Vaqueros) comprises deep-basin and starved-basin facies. A thin transgressive facies occurs locally at the base of the formation. The overlying Painted Rock Sandstone Member (of the Vaqueros), which is more than 2200 m thick and consists mostly of coarse-grained sandstone and pebbly sandstone, constitutes a delta complex of prodelta, slope channel, delta front, tide-influenced distributary channel, interdistributary bay, and fluvial channel facies. The basinal depositional system consisted of turbidite mud and sand, and hemipelagic and pelagic sediments of the basinal facies deposited in a rapidly subsiding basin. The delta depositional system consisted of the delta complex facies that prograded into the deep basin and had a steep prodelta slope that extended to bathyal depths. The delta is inferred to be a mixed fluvial-wave-dominated fan delta, analogous in its delta-front morphology and processes to a fjord delta, in which coarse sediment delivered to the delta front by braided streams was transported down the prodelta slope into deep water by sediment gravity flows. Transgression and rapid deepening of the basin in the early Miocene coincided with rapid tectonic subsidence. Deepening culminated with deposition of a starved-basin facies or condensed section at the time of maximum transgression, which was followed by the beginning of a

  2. A molecular stable carbon isotope study of organic matter in immature Miocene Monterey sediments, Pismo basin

    NASA Astrophysics Data System (ADS)

    Schouten, Stefan; Schoell, Martin; Rijpstra, W. Irene C.; Sinninghe Damsté, Jaap S.; de Leeuw, Jan W.

    1997-05-01

    The 300 m section of the Miocene Monterey Formation outcropping at Shell Beach (Pismo basin; ca. 15-11 Ma) is composed of calcareous phosphatic (15.1-14.5 Ma) and siliceous facies (14.5-11.0 Ma). An objective of this paper is to document lateral paleoenvironmental changes in the Miocene Moneterey Formation by comparing the Shell Beach (SB) profile with the Naples Beach (NB) section in the Santa Barbara-Ventura basin (Schouten et al., 1997) which is ˜80 km to the south. Eight samples (one sample representing, on average, a time period of ca. 2000 y) from this section were analyzed for variations of extractable biomarkers and their carbon isotopic signatures as indicators for paleoenvironmental change during the Miocene. Saturated hydrocarbons present include 28,30-dinorhopane, phytane, n-alkanes (C 17sbnd C 31), lycopane, and 17β,21β(H)-homohopane. The biomarkers released after desulfurization of the polar fractions predominantly consist of phytane, 2,6,10,14-tetramethyl-7-(3-methylpentyl)pentadecane, C 17sbnd C 31n-alkanes, regular 5α- and 5β-steranes, dinosteranes, and (22R)-17β,21β(H)-pentakishomohopane. Steranes have similar carbon isotopic compositions (-25 to -27‰) throughout the section and are isotopically similar at both sites, indicating laterally similar and vertically stable environmental conditions for algae living in the upper part of the photic zone. Free and S-bound n-alkanes at SB mainly originate from marine organisms and not from terrestrial sources as in the NB section. S-bound pentakishomohopane is ca. 1-4‰ depleted compared to the steranes and is thought to be derived from the deeper water dwelling cyanobacteria. These findings are consistent with stable carbon isotopic data obtained for these compounds from Middle Miocene Monterey sediments at Naples Beach and indicates similar environmental conditions in the depositional environments of the Santa Barbara-Ventura and the Pismo basin. S-bound highly branched isoprenoids have, at both

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

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Heinrich, Sonja; Zonneveld, Karin A. F.; Willems, Helmut

    2010-05-01

    The middle- and upper Miocene represent a time-interval of major changes in palaeoclimate leading to global cooling forming the precursor of the onset of Northern Hemisphere Glaciations (NHG). These climate changes are thought to be strongly controlled by oceanographic modifications although the nature of the relationship between ocean and climate change is far from clear. It has for instance been observed that in this time interval the modern deepwater circulation system; the thermohaline circulation was established. It is thought that tectonic events, such as the narrowing of the Panama gateway, played a key role in the progressing of these Miocene oceanographic changes (e.g. Duque-Caro 1990; Lear et al. 2003). However, the complex interaction between the closing of the Panama Gateway, the development of NADW, and thus the oceanographic progression towards our present day circulation is far from being fully understood. A key region to study these interactions is the Caribbean region, notably the Ceara Rise since it is an area of highest sensitivity to global deep water circulation changes. Here we intent to improve the understanding of these processes by establishing a detailed palaeoceanographic reconstruction of the western equatorial Atlantic Ocean on the basis of calcareous dinoflagellate cyst (dinocyst) associations. For this, we investigated sediment samples from ODP Site 926A by defining the calcareous dinocyst assemblage. Site 926A is located at the southwestern flank of the Ceara Rise, an area of highest sensitivity to global deep water circulation changes. At about 11 Ma, we see a distinct increase in the absolute abundances of the calcareous dinocysts suggesting enhanced productivity and better carbonate preservation that can be related to the intensification of NADW formation (Woodruff & Savin 1989). At 11.3 Ma, Leonella granifera, a species known to be strongly related to terrestrial input increases. This could be a signal for the initiation of the

  5. Miocene zircon crystals in dacite from Ilopango Caldera, El Salvador: Evidence for recycling of plutonic rocks

    NASA Astrophysics Data System (ADS)

    Garrison, J. M.; Korm, S.; Schmitt, A. K.; Economos, R. C.

    2011-12-01

    Ilopango Caldera is located in El Salvador and is part of the Central American Volcanic Arc (CAVA) that extends from southern Mexico to Panama. The volcanic arc is situated on crust that ranges in age from 150-28 Ma and is covered with Miocene-Recent volcanic ash and pyroclastic flow deposits. Several large eruptions are associated with Ilopango Caldera, the most recent are from the Tierra Blanca Joven (TBJ) eruption, which produced massive pyroclastic flows 1600 years BP. Older eruptions from Ilopango Caldera are referred to as the Tierra Blanca (TB) deposits, and the TB2 ignimbrite has been dated at 12,000 years. The objective of this research is to use the ages of zircon crystals from the TBJ and TB2 eruptions to establish and compare storage times for these magma reservoirs. We used a CAMECA ims 1270 at UCLA's NSF National Ion Microprobe Facility in order to obtain U-Pb and U-Th ages for individual zircon crystals from each eruption. Depth profiling and U-Pb analyses were performed on both of the zircon crystals using established analysis techniques. The data show that zircon from both eruptions have 15 Ma old cores with thin rims (few μm) that are consistent with the young eruption ages. In both cases, however the transition from core to rim composition is abrupt and does not record continuous crystallization of the zircon crystals. We conclude that the presence of the old cores is consistent with assimilation of middle Miocene plutonic rock by juvenile magma during Quaternary activity of Ilopango Caldera. The most likely source of 15 Ma old zircon are the plutons associated with middle Miocene explosive volcanism in Central America. Ash deposits recovered from the sea floor (via ODP studies) record extensive explosive volcanism from 13-15 Ma that can be traced to ignimbrite deposits of the Chalatenango Formation in south-central Guatemala and El Salvador. We conclude that 1) the zircon crystals record only brief pre-eruptive crystallization histories for the

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

    NASA Astrophysics Data System (ADS)

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

    2002-11-01

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

  7. Depositional setting and hydrocarbon source potential of the Miocene Gulf of Suez syn-rift evaporites

    SciTech Connect

    Richardson, M.; Arthur, M.A.; Quinn, J.S.; Whelan, J.K.; Katz, B.J. )

    1988-08-01

    The Red Sea rift basin and its northern continuation, the Gulf of Suez, has experienced continuous deposition of marine evaporites throughout much of its development from the early Miocene to the Pliocene resulting in the accumulation of up to 5 km of evaporite strata in the rift. In this paper, the geologic history of these evaporites are discussed, along with their petroleum source rock potential. The authors hypothesize that rapid deposition of organic matter occurred during episodic storms and freshening events in which a less saline surface layer developed.

  8. Miocene woods from the Qaidam Basin on northern Qinghai-Tibet Plateau with implications for paleoenvironmental change

    NASA Astrophysics Data System (ADS)

    Cheng, Ye-Ming; Yang, Xiao-Nan

    2016-02-01

    The Qaidam Basin with the most complete Cenozoic sedimentary preservation in northern Qinghai-Tibet Plateau is a key area for studying uplift and environmental change of the plateau. Three types of woods, Ulmus (Ulmaceae), Leguminosae (?) (angiosperm) and Cupressaceae (gymnosperm) were recognized from the large-scale preservation of fossil woods in late Miocene Shang Youshashan Formation in northern Qaidam Basin on the Qinghai-Tibet Plateau. Both investigations of their Nearest Living Relatives (NLRs) and previous grassland mammal evidences suggest that there have been temperate deciduous broad-leaved forest and needle-leaved forest with grass in northern Qaidam Basin during the late Miocene in contrast to the desert vegetation found there nowadays. The presence of the ancient forest steppe further implies that the southern part of the plateau used to be adequately low, so that the Indian and East Asian monsoons could approach the northern area and to accommodate the vegetation in late Miocene.

  9. Investigating Tectonic Drivers of Miocene - Pliocene Polar Climate Evolution using the HadCM3 Climate Model.

    NASA Astrophysics Data System (ADS)

    Hunter, S. J.; Knies, J.; Haywood, A. M.; Dolan, A. M.; Pound, M. J.

    2015-12-01

    We model the climate of the Miocene (Tortonian and the Messinian) and the Pliocene (Piacenzian) using the HadCM3 Atmosphere-Ocean GCM. We use baseline Miocene and Pliocene geographies that have different reconstruction lineages so we describe methods to create a set of self-consistent paleogeographies that represent the main features of the three stages. We present large-scale features of the evolving climate and examine model fidelity by comparing modelled climatology against palaeoenvironmental proxy data. We focus on the climate of the Arctic region and investigate tectonic drivers of sea ice expansion by comparing and interpreting model predictions against borehole data from the North Atlantic and Arctic Ocean. In particular how Late Miocene/ early Pliocene tectonic uplift in the Svalbard/Barents Sea and Greenland region, the opening of the Bering Strait, and the onset of deep water Atlantic-Arctic exchange influenced the development of modern sea ice cover.

  10. Subtropical forest expansion in the middle Miocene Europe: pCO2, Antarctic ice volume and oceanic changes

    NASA Astrophysics Data System (ADS)

    Hamon, N.; Sepulchre, P.; Donnadieu, Y.; Ramstein, G.

    2012-04-01

    The middle Miocene is a crucial period for ape's evolution and corresponds to their appearance in Europe. The dispersion of apes was made possible by tectonic changes and the expansion of their habitat, which is tropical to subtropical forest, in Europe. The context in which the Middle Miocene Climatic Optimum occurred still lacks constraints in terms of atmospheric pCO2 and Antarctic ice sheet volume and extent. Using the coupled atmosphere - ocean GCM FOAM and the dynamic vegetation model CARAIB, we investigate the sensitivity of Miocene climate and vegetation to pCO2 levels and Antarctic ice sheet configurations. We performed sensitivity experiments to test the impact of varying pCO2 (280 ppmv, 560 ppmv and 700 ppmv) and Antarctic albedo (ice and tundra) on the European vegetation during the Middle Miocene Climatic Optimum. Our results indicate that higher than present pCO2 is necessary to simulate subtropical forest in Western and Central Europe during the middle Miocene. However, a threshold between 560 and 700 ppmv makes subtropical forest partly collapse, which is due to colder and slightly dryer conditions in Europe. This can be explained by the fact that CO2-induced warming of the high latitudes strongly reduces North Atlantic Deep Water formation, therefore reducing the heat transport in this region. Moreover, the albedo change over Antarctica, which is directly linked to the ice surface, leads to further warming in Europe, and the expansion of subtropical forest. These results suggest that a small East Antarctic Ice Sheet (25% of present-day ice volume) together with higher than present pCO2 are in better agreement with available European middle Miocene data.

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

    NASA Astrophysics Data System (ADS)

    Sandroni, Sonia; Talarico, Franco M.

    2011-01-01

    This paper includes the results of a detailed quantitative provenance investigation on gravel-size clasts occurring within the late Early to Late Miocene sedimentary glacimarine section recovered for the first time by the AND-2A core in the SW sector of the Ross Sea (southern McMurdo Sound, Antarctica). This period of time is of crucial interest, as it includes two of the major Cenozoic events in the global climatic evolution: the mid-Miocene climatic optimum and the middle Miocene climate transition. Petrographical and mineral chemistry data on basement clasts allow to individuate two different diagnostic clast assemblages, which clearly suggest two specific sectors of southern Victoria Land as the most likely sources: the Mulock-Skelton glacier and the Koettlitz-Blue glacier regions. Distribution patterns reveal high fluctuations of the detritus source areas throughout the investigated core interval, variations which can be interpreted as the direct result of an evolving McMurdo Sound paleogeography during the late Early to Late Miocene. Consistently with sedimentological studies, gravel-fraction clast distribution patterns clearly testify that the Antarctic ice sheet experienced a dramatic contraction at ca. 17.35 ± 0.14 Ma (likely correlated to the onset of the climatic optimum), and in a < ca. 100 ka time window passing from a glacial scenario comparable to the last glacial maximum (Phase 1) to a very dynamic glacial environment (Phase 2). Phase 2 conditions persisted through the early Middle Miocene (to ca. 14.2 Ma), when a major expansion of the Antarctic ice sheet is hypothesized, likely contemporaneously to the onset of the middle Miocene climate transition. Therefore, provenance and distribution studies of gravel-fraction clasts show that the variations of paleoenvironmental drivers characterising this period were able to exert deep transformation of the Antarctic ice sheet and reveal the methodology to be a powerful tool for the reconstruction of paleo

  12. Geology and tectonic setting of early miocene travertine deposits, Dominican Republic

    SciTech Connect

    Rodriguez, J.; Llinas, R.; Lebron, M.C.

    1985-01-01

    An extensive, ancient travertine deposit occurs immediately above a major unconformity within early Miocene carbonate rocks (Sombrerito Fm.) in the western Enriquillo Basin, Dominican Republic. The authors have mapped the area at a scale of 1:20,000 in order to better understand the geology and economic potential of the travertine which is widely used as an ornamental building stone in the Dominican Republic. The travertine occurs as a discontinuous tabular layer up to 15 m thick that outcrops within the complexly faulted Canoa Dome that forms the western plunging end of the reverse fault-bounded Sierra Martin Garcia. The measured stratigraphy of the dome from the oldest rocks in the center outwards consists of: 1) 100 m of grey to buff, chalky to crystalline limestones: 2) slight angular unconformity with 0 to 0.5 m of overlying conglomerate with limestone cobble clasts; 3) 0.5 to 15 m of grey to buff, indurated, microcrystalline travertine with zones of .1 to 1 cm, elongate cavities parallel to bedding; and 4) 250 m of interbedded siltstones and calcarenties. The genesis of the travertine deposit appears related to a previously unrecognized, widespread deformational, uplift, and thermal event that affected a shallow marine carbonate shelf in early Miocene time.

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

    PubMed Central

    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 <10.0 million years ago (MYA), rather than in situ diversification. In contrast, the Andes, 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

  14. Global Sea Surface Temperature and Ecosystem Change Across the Mid-Miocene Climatic Optimum

    NASA Astrophysics Data System (ADS)

    Veenstra, T. J. T.; Bakker, V. B.; Sangiorgi, F.; Peterse, F.; Schouten, S.; Sluijs, A.

    2015-12-01

    The Mid-Miocene Climatic Optimum (MMCO) (ca. 17 to 14 Ma) is generally considered as the warmest episode of the Neogene based on deep marine oxygen isotope records and terrestrial plant fossils. To date, however, reasonable resolution high-quality sea surface temperature (SST) proxy records spanning its onset are scarce at best. For the remainder of the MMCO, reliable SST records are absent from the tropics and very scarce in temperate and polar regions. This leaves the question if the MMCO was truly associated with global warming and if this warming was associated with biotic change. We use organic biomarker paleothermometry (Uk'37 and TEX86) to reconstruct SST across the MMCO at four locations along a pole-to-pole transect in the Atlantic and Pacific Ocean. Additionally, we use marine palynology (mostly dinoflagellate cysts) to assess ecosystem change at these locations. This study includes the first tropical biomarker-based SST records of the MMCO. Together with new and existing SST records from higher latitudes and the corresponding palynological records, they provide new insights in the temporal and spatial development of the MMCO. Our results indicate that Mid-Miocene warming was most prominent in the Norwegian Sea, showed a more complex, perhaps upwelling-related pattern in a tropical location, and was small in the Southern Hemisphere.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    SciTech Connect

    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.

  17. An Amphisbaenian Skull from the European Miocene and the Evolution of Mediterranean Worm Lizards

    PubMed Central

    Bolet, Arnau; Delfino, Massimo; Fortuny, Josep; Almécija, Sergio; Robles, Josep M.; Alba, David M.

    2014-01-01

    The evolution of blanid amphisbaenians (Mediterranean worm lizards) is mainly inferred based on molecular studies, despite their fossils are common in Cenozoic European localities. This is because the fossil record exclusively consists in isolated elements of limited taxonomic value. We describe the only known fossil amphisbaenian skull from Europe – attributed to Blanus mendezi sp. nov. (Amphisbaenia, Blanidae) – which represents the most informative fossil blanid material ever described. This specimen, from the Middle Miocene of Abocador de Can Mata (11.6 Ma, MN7+8) in the Vallès-Penedès Basin (Catalonia, NE Iberian Peninsula), unambiguously asserts the presence of Blanus in the Miocene of Europe. This reinforces the referral to this genus of the previously-known, much more incomplete and poorly-diagnostic material from other localities of the European Neogene. Our analysis – integrating the available molecular, paleontological and biogeographic data – suggests that the new species postdates the divergence between the two main (Eastern and Western Mediterranean) extant clades of blanids, and probably precedes the split between the Iberian and North-Western African subclades. This supports previous paleobiogeographic scenarios for blanid evolution and provides a significant minimum divergence time for calibrating molecular analyses of blanid phylogeny. PMID:24896828

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

    PubMed

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

    2007-06-21

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

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

    PubMed Central

    Jaeger, Jean-Jacques; Naing Soe, Aung; Chavasseau, Olivier; Coster, Pauline; Emonet, Edouard-Georges; Guy, Franck; Lebrun, Renaud; Maung, Aye; Aung Khyaw, Aung; Shwe, Hla; Thura Tun, Soe; Linn Oo, Kyaw; Rugbumrung, Mana; Bocherens, Hervé; Benammi, Mouloud; Chaivanich, Kamol; Tafforeau, Paul; Chaimanee, Yaowalak

    2011-01-01

    For over a century, a Neogene fossil mammal fauna has been known in the Irrawaddy Formation in central Myanmar. Unfortunately, the lack of accurately located fossiliferous sites and the absence of hominoid fossils have impeded paleontological studies. Here we describe the first hominoid found in Myanmar together with a Hipparion (s.l.) associated mammal fauna from Irrawaddy Formation deposits dated between 10.4 and 8.8 Ma by biochronology and magnetostratigraphy. This hominoid documents a new species of Khoratpithecus, increasing thereby the Miocene diversity of southern Asian hominoids. The composition of the associated fauna as well as stable isotope data on Hipparion (s.l.) indicate that it inhabited an evergreen forest in a C3-plant environment. Our results enlighten that late Miocene hominoids were more regionally diversified than other large mammals, pointing towards regionally-bounded evolution of the representatives of this group in Southeast Asia. The Irrawaddy Formation, with its extensive outcrops and long temporal range, has a great potential for improving our knowledge of hominoid evolution in Asia. PMID:21533131

  20. Paleomagnetic Evidence for Spatially Distributed Post-Miocene Rotation of Western Washington and Oregon

    NASA Astrophysics Data System (ADS)

    Sheriff, Steven D.

    1984-06-01

    Anomalous paleomagnetic directions have been determined for 17 sites in the Frenchmans Springs member of the Wanapum basalt formation, Columbia River basalt group. These sites are located in the Ginkgo flows from near Vantage, Washington, to Portland, Oregon, a distance of approximately 300 km. The average paleomagnetic direction for six of these sites, centered around Vantage is D = 147°, I = 41°, α95 = 4.5°. The expected Miocene field direction is D = 355°, I = 65°. At some localities there are two distinct Ginkgo flows, in direct stratigraphic succession, with statistically identical anomalous directions. Their anomalous paleomagnetic direction makes these flows a valuable marker horizon in the Columbia River basalt group. The nondipole field direction of the Ginkgo flows correlates well with available results from the Miocene Cape Foulweather basalts of Oregon. This correlation strongly supports the hypothesis that these coastal basalts of Oregon are the distal ends of Columbia Plateau derived basalt flows. The spatial distribution of these anomalous field directions suggests about 14° of clockwise rotation between Vantage and Portland. Combining these data with data from the Oregon Coast basalts allows a maximum declination difference of about 35°. The increase in declination can be best explained by clockwise rotation, about nearby vertical axes, increasing to the southwest across the Columbia Plateau and Oregon coast.

  1. A geochemical study of macerals from a Miocene lignite and an Eocene bituminous coal, Indonesia

    USGS Publications Warehouse

    Stankiewicz, B.A.; Kruge, M.A.; Mastalerz, Maria

    1996-01-01

    Optical and chemical studies of maceral concentrates from a Miocene lignite and an Eocene high-volatile bituminous C coal from southeastern Kalimantan, Indonesia were undertaken using pyro-Lysis, optical, electron microprobe and FTIR techniques Pyrolysis products of vitrinite from bituminous coal were dominated by straight-chain aliphatics and phenols. The huminite of the Miocene lignite produced mostly phenolic compounds upon pyrolysis. Differences in the pyrolysis products between the huminite and vitrinite samples reflect both maturation related and paleobotanical differences. An undefined aliphatic source and/or bacterial biomass were the likely contributors of n-alkyl moieties to the vitrinite. The resinite fraction in the lignite yielded dammar-derived pyrolysis products, as well as aliphatics and phenols as the products of admixed huminite and other liptinites. The optically defined resinite-rich fraction of the bituminous coal from Kalimantan produced abundant n-aliphatic moieties upon pyrolysis, but only two major resin markers (cadalene and 1,6-dimethylnaphthalene). This phenomenon is likely due to the fact that Eocene resins were not dammar-related. Data from the electron microprobe and Fourier transform infrared spectrometry strongly support the results obtained by Py GC MS and microscopy.

  2. Paleoclimatic controls on sedimentation, diagnesis, and reservior quality: Lessons from Miocene carbonates

    SciTech Connect

    Sun, S.Q. ); Esteban, M. )

    1994-04-01

    Miocene carbonates worldwide were deposited in a wide range of paleogeographic and tectonic settings and form important reservoirs in several regions. The reservoir quality of these carbonates appears to have been primarily controlled by the prevailing paleoclimate, which exerted a major control of both the depositional patterns and diagenetic pathways. Two end members are discussed here: (1) humid, oceanic tropical-subtropical settings, and (2) arid, land-locked temperate-subtropical settings. In humid, oceanic tropical-subtropical settings (e.g., Miocene of Southeast Asia), a warming trend paralleled by generally rising sea level allowed thick coral reefs and skeletal banks to develop, most of which are seismically resolvable. These carbonates typically represent several stages or cycles of development (largely third-order) separated by discontinuities in platform growth with episodic subaerial exposure. Development of economic reservoirs is mainly related to relative sea level falls and associated meteoric diagenesis. Trends and patterns of reservoir distribution can be predicted within a sequence stratigraphic framework. Basal transgressive carbonates are mostly tight because of their relatively fine-grained textures, intense compaction, and isolation from meteoric water influence. Best reservoir quality is commonly developed beneath subaerial unconformities in highstand buildups where effect of meteoric water leaching and karstification are most intense. 80 refs., 18 figs., 1 tab.

  3. Detailed view into the dynamics of the Late Miocene glaciation episode that accompanied terrestrial evolution

    NASA Astrophysics Data System (ADS)

    Tzanova, A.; Herbert, T.; Lawrence, K. T.; Peterson, L.; Kelly, C. S.

    2015-12-01

    We focus on the period of ~ 9 - 5 Ma when an episode of notably cool temperatures corresponds to evidence of high latitude Northern Hemisphere glaciation and mid-latitude terrestrial evolution. Alkenone-based sea surface temperatures (SST) from six globally distributed sites: ODP Sites 907 and 982 in the North Atlantic, ODP Site 1088 in the South Atlantic and ODP Sites 883, 884 and 887 in the North Pacific, and the Monte dei Corvi marine section in the Mediterranean unequivocally establish a dramatic, Late Miocene cold episode that persisted over approximately 2.5 Myr. In this work we establish the timing and synchronization of temperature decrease as well as rebound at orbital timescales. All sites were notably warmer than their modern annual average at ~9 Ma and exhibit sustained cooling beginning at ~8 Ma. SSTs rebound close to ~5.9 Ma at most locations suggesting that the cooling trend that began in the Late Miocene slowed down or even reversed in some locations in the Pliocene. The newly reconstructed SSTs highlight the role of cooling and an increase in equator to pole temperature gradients in terrestrial evolution at this pivotal time.

  4. Late Miocene episodic lakes in the arid Tarim Basin, western China.

    PubMed

    Liu, Weiguo; Liu, Zhonghui; An, Zhisheng; Sun, Jimin; Chang, Hong; Wang, Ning; Dong, Jibao; Wang, Huanye

    2014-11-18

    The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (δ(18)O) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (δ(11)B) and δ(18)O records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at ∼4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period. PMID:25368156

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

    NASA Astrophysics Data System (ADS)

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

    1998-12-01

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

  6. Amazonian amphibian diversity is primarily derived from late Miocene Andean lineages.

    PubMed

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

    2009-03-10

    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 <10.0 million years ago (MYA), rather than in situ diversification. In contrast, the Andes, 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

  7. Geology and palaeontology of the Late Miocene Middle Awash valley, Afar rift, Ethiopia.

    PubMed

    WoldeGabriel, G; Haile-Selassie, Y; Renne, P R; Hart, W K; Ambrose, S H; Asfaw, B; Heiken, G; White, T

    2001-07-12

    The Middle Awash study area of Ethiopia's Afar rift has yielded abundant vertebrate fossils (approximately 10,000), including several hominid taxa. The study area contains a long sedimentary record spanning Late Miocene (5.3-11.2 Myr ago) to Holocene times. Exposed in a unique tectonic and volcanic transition zone between the main Ethiopian rift (MER) and the Afar rift, sediments along the western Afar rift margin in the Middle Awash provide a unique window on the Late Miocene of Ethiopia. These deposits have now yielded the earliest hominids, described in an accompanying paper and dated here to between 5.54 and 5.77 Myr. These geological and palaeobiological data from the Middle Awash provide fresh perspectives on hominid origins and early evolution. Here we show that these earliest hominids derive from relatively wet and wooded environments that were modulated by tectonic, volcanic, climatic and geomorphic processes. A similar wooded habitat also has been suggested for the 6.0 Myr hominoid fossils recently recovered from Lukeino, Kenya. These findings require fundamental reassessment of models that invoke a significant role for global climatic change and/or savannah habitat in the origin of hominids. PMID:11449271

  8. Miocene temblor formation and related basin evolution, southwestern San Joaquin Basin, California

    SciTech Connect

    Gillespie, B.W.

    1988-01-01

    The southwestern San Joaquin basin is an area of great importance for the energy industry and academic basin analysts. Understanding basin evolution is a key concern for explorationists in this essentially pristine province. Temblor Formatio is exposed in an east-west-trending belt that comprises the north flank of the San Emigdio Mountains. Field and subsurface evidence were used to elucidate the geology, depositional environments, and age of the Temblor Formation. The formation represents sand-rich borderland sedimentation in a predominantly deep-marine setting. Deposition of Temblor clastics reflects deformation due to the impingement of the Farallon Pacific ridge with the California-North American plate margin during the middle Oliocene. As a result, severe uplift along the margins of the southern San Joaquin basin, reinforced by a lowstand of global seal level, caused large volumes of coarse, immature clastics to be shed into the rapidly subsiding deep-marine depocenter. Deposition of the Temblor was thus concurrent with the transformation from a convergent margin tectonic regime to one of dextral strike-slip. This transformation was marked by an episode of transform-extension indicated by volcanism, rapid subsidence, and marine transgression during the early Miocene. The Maricopa trough or oceanic connection from the San Joaquin basin to the Pacific Ocean is inferred to have existed between Recruit Pass and Maricopa. The age of the Temblor Formation is late Oligocene to early Miocene. Petroleum production is limited to the upper member in small oil fields flanking the northern Sam Emigdio Mountains.

  9. Occlusal Enamel Complexity in Middle Miocene to Holocene Equids (Equidae: Perissodactyla) of North America

    PubMed Central

    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. PMID:24587267

  10. Biostratigraphic sequence analysis of Oligocene-Lower Miocene sections in the Orocual Field, Eastern Venezuela Basin

    SciTech Connect

    Giffuni, G.; Castro-Mora, M.

    1996-08-01

    A detailed biostratigraphic study of the Oligocene-Miocene boundary was carried out in sections 1000 ft thick of ten wells of the Orocual Field, Eastern Venezuela, The sequences under investigation carry a rich microfauna of benthic and planktonic foraminifera and calcareous nannoplankton. About 500 samples were analyzed and nearly 150 species of foraminifera and 60 of nannoplankton calcareous were identified. The planktonic assemblages allow the identification of zones N3 and N4 of Blow, 1969; zones NP23, NP24, NP25 and NN1 of Martini, 1971; and zones F and E of Stainforth et al., 1959 of the Carapita Formation. The paleoenvironments of these sediments were determined rather precisely and vary from inner shelf to middle slope. Paleobathymetric curves of several wells are included. High and low fossil abundance and diversity peaks were used to recognize two sequences of the third order and five of the fourth order between 24.8 Ma and 26.5 Ma. A generalized transgressive trend is evident from the Late Oligocene to the Early Miocene.

  11. Sedimentology and diagenesis of Miocene Lirio Limestone, Isla de Mona, Puerto Rico

    SciTech Connect

    Ruiz, H.; Gonzalez, L.A.; Budd, A.F. )

    1991-03-01

    Isla de Mona is a carbonate plateau, 50 mi west of Puerto Rico. The island lies on the southern portion of the Mona Platform. It is composed mostly of two Miocene carbonate units: Isla de Mona Dolomite overlain by Lirio Limestone. The Lirio Limestone was deposited on a sloping erosional surface over the Isla de Mona Dolomite. The Miocene Lirio Limestone consists mostly of backreef sands (packstones) with a reefal sequence (boundstones and grainstones) present in the southwestern portion of the island. The reefal sequence is made up mostly of Stylophora, Porites, and Millepora. Thin, discreet pockets of carbonate mud, rich in planktonic foraminifera and radiolarians and mixed with shallow benthic fauna/flora (foraminifera, echinoderms, red algae, and corals) interpreted as storm deposits, are found throughout the unit. An extensive reefal zone can be inferred to be present throughout the southwestern to southern portions of the Mona Platform. The Lirio Limestone is heavily karstified and is riddled with sinkholes on the plateau surfaces and caves around the periphery of the island. Caves are exposed around the periphery of the island, radiating from a depression in the central portions of the Lirio Limestone, near contacts with the Isla de Mona Dolomite, are partially dolomitized. The southwestern outcrops exhibit partial dolomitization throughout. The distribution of sinkholes, seaward caverns, and partial dolomitization of the lowermost Lirio Limestone suggests diagenetic modifications by meteoric fluids in central exposed portions of the island and by marine-meteoric fluids in the lowermost portions of the phreatic lens.

  12. Did tectonic activity stimulate oligo-miocene speciation in the Indo-West Pacific?

    PubMed

    Williams, Suzanne T; Duda, Thomas F

    2008-07-01

    Analyses of molecular phylogenies of three unrelated tropical marine gastropod genera, Turbo, Echinolittorina, and Conus, reveal an increase in the rate of cladogenesis of some Indo-West Pacific (IWP) clades beginning in the Late Oligocene or Early Miocene between 23.7 and 21.0 million years ago. In all three genera, clades with an increased rate of diversification reach a maximum of diversity, in terms of species richness, in the central IWP. Congruence in both the geographical location and the narrow interval of timing suggests a common cause. The collision of the Australia and New Guinea plate with the southeast extremity of the Eurasian plate approximately 25 Mya resulted in geological changes to the central IWP, including an increase in shallow-water areas and length of coastline, and the creation of a mosaic of distinct habitats. This was followed by a period of rapid diversification of zooxanthellate corals between 20 and 25 Mya. The findings reported here provide the first molecular evidence from multiple groups that part of the present-day diversity of shallow-water gastropods in the IWP arose from a rapid pulse of speciation when new habitats became available in the Late Oligocene to Early Miocene. After the new habitats were filled, the rate of speciation likely decreased and this combined with high levels of extinction (in some groups), resulted in a slow down in the rate of diversification in the genera examined.

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

    NASA Astrophysics Data System (ADS)

    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 (<1 million years) this concept looses its practicability and has to be replaced by a taxon-range-zonation. To solve this problem a higher number of independently dated small-mammal localities are needed. This is especially crucial for the late Middle to earliest Late Miocene, for which vertebrate faunas in the (Central-)Paratethyan area rare. Recently, a new vertebrate fauna was discovered at the locality Gratkorn (clay pit St. Stefan) just beyond the northwestern margin of the Styrian Basin (Gratkorn Basin; 10 km NW Graz; 15°20'55"E/47°08'15"N). The fauna originates from a c. 0.5 m thick hydromorphic paleosol, underlain by fluvial sands and gravels and topped by c. 15 m thick limnic pelites (Gross, 2008). Sedimentological data as well as the gastropod (Harzhauser et al., 2008) and vertebrate faunas point to a highly structured, more or less vegetated alluvial fan/braided river landscape. Active and abandoned fluvial channels, moist floodplain-soils and ephemeral ponds but also nearby dryer open areas and limestone screes of the up-lifting Palaeozoic basement offered a wide range of habitats. The occurrence of xero- and thermophile terrestrial gastropods and ectothermic vertebrates correspond well with the late Middle/early Late Miocene dry-spell in Central Europe (Böhme et al., 2008). Furthermore, an overall semiarid climate is supported by the development of a calcrete horizon c. 0.6 m below the fossiliferous horizon. The vertebrate remains are irregularly distributed throughout the

  14. Depositional styles from Miocene through Pleistocene in the North Central Gulf of Mexico: An historical reconstruction

    SciTech Connect

    Hunt, J.L. Jr.; Burgess, G.

    1995-10-01

    During the past two years, Minerals Management Service, U.S. Department of the Interior, has classified the reservoir sands from the approximately 1,100 fields across the entire Northern Gulf of Mexico into groups of genetically related plays defined by production, chronostratigraphy, lithostratigraphy, and structure. This study was undertaken in part for the 1995 National Gas and Oil Assessment. Each field was assigned a structural code, and each producible sand was classified by depositional environment. Correlation of the composite type logs with biostratigraphic and seismic data established twelve chronozones from lower Miocene to upper Pleistocene. Sands within each chronozone were classified as transgressive, aggradational, progradational, or deep-sea fan facies. Proved reserves plays, hydrocarbon extents, as well as facies sand limits were mapped for each chronozone. Dramatic changes in depositional styles from the Miocene through the Pliocene are observed in the north-central Gulf of Mexico as the ancestral Mississippi River delta moved both basinward and eastward across offshore Louisiana. The depocenter moved back to the west and significantly basinward during the Pleistocene. Depositional patterns were strongly influenced by localized salt structure and major growth faulting. Salt ridges on the paleo-slope had a damming effect on deposition. When the ridges were breached, the focused sediment supply created areas of slope fan deposits. The results of this study are useful hydrocarbon exploration and development tools.

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

    PubMed

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

    2007-06-21

    Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic's deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ('ventilated') conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events. PMID:17581581

  16. Late Miocene episodic lakes in the arid Tarim Basin, western China.

    PubMed

    Liu, Weiguo; Liu, Zhonghui; An, Zhisheng; Sun, Jimin; Chang, Hong; Wang, Ning; Dong, Jibao; Wang, Huanye

    2014-11-18

    The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (δ(18)O) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (δ(11)B) and δ(18)O records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at ∼4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period.

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

    PubMed

    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.

  18. Amazonian amphibian diversity is primarily derived from late Miocene Andean lineages.

    PubMed

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

    2009-03-10

    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 <10.0 million years ago (MYA), rather than in situ diversification. In contrast, the Andes, 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.

  19. Late Miocene-Pliocene Asian monsoon intensification linked to Antarctic ice-sheet growth

    NASA Astrophysics Data System (ADS)

    Ao, Hong; Roberts, Andrew P.; Dekkers, Mark J.; Liu, Xiaodong; Rohling, Eelco J.; Shi, Zhengguo; An, Zhisheng; Zhao, Xiang

    2016-06-01

    Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene-Pliocene (∼8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene-Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.

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

    PubMed

    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. PMID:25256056

  1. Late Miocene episodic lakes in the arid Tarim Basin, western China

    PubMed Central

    Liu, Weiguo; Liu, Zhonghui; An, Zhisheng; Sun, Jimin; Chang, Hong; Wang, Ning; Dong, Jibao; Wang, Huanye

    2014-01-01

    The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (δ18O) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (δ11B) and δ18O records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at ∼4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period. PMID:25368156

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

    PubMed

    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.

  3. Did tectonic activity stimulate oligo-miocene speciation in the Indo-West Pacific?

    PubMed

    Williams, Suzanne T; Duda, Thomas F

    2008-07-01

    Analyses of molecular phylogenies of three unrelated tropical marine gastropod genera, Turbo, Echinolittorina, and Conus, reveal an increase in the rate of cladogenesis of some Indo-West Pacific (IWP) clades beginning in the Late Oligocene or Early Miocene between 23.7 and 21.0 million years ago. In all three genera, clades with an increased rate of diversification reach a maximum of diversity, in terms of species richness, in the central IWP. Congruence in both the geographical location and the narrow interval of timing suggests a common cause. The collision of the Australia and New Guinea plate with the southeast extremity of the Eurasian plate approximately 25 Mya resulted in geological changes to the central IWP, including an increase in shallow-water areas and length of coastline, and the creation of a mosaic of distinct habitats. This was followed by a period of rapid diversification of zooxanthellate corals between 20 and 25 Mya. The findings reported here provide the first molecular evidence from multiple groups that part of the present-day diversity of shallow-water gastropods in the IWP arose from a rapid pulse of speciation when new habitats became available in the Late Oligocene to Early Miocene. After the new habitats were filled, the rate of speciation likely decreased and this combined with high levels of extinction (in some groups), resulted in a slow down in the rate of diversification in the genera examined. PMID:18410535

  4. Ribosomal RNA gene fragments from fossilized cyanobacteria identified in primary gypsum from the late Miocene, Italy.

    PubMed

    Panieri, G; Lugli, S; Manzi, V; Roveri, M; Schreiber, B C; Palinska, K A

    2010-03-01

    Earth scientists have searched for signs of microscopic life in ancient samples of permafrost, ice, deep-sea sediments, amber, salt and chert. Until now, evidence of cyanobacteria has not been reported in any studies of ancient DNA older than a few thousand years. Here, we investigate morphologically, biochemically and genetically primary evaporites deposited in situ during the late Miocene (Messinian) Salinity Crisis from the north-eastern Apennines of Italy. The evaporites contain fossilized bacterial structures having identical morphological forms as modern microbes. We successfully extracted and amplified genetic material belonging to ancient cyanobacteria from gypsum crystals dating back to 5.910-5.816 Ma, when the Mediterranean became a giant hypersaline brine pool. This finding represents the oldest ancient cyanobacterial DNA to date. Our clone library and its phylogenetic comparison with present cyanobacterial populations point to a marine origin for the depositional basin. This investigation opens the possibility of including fossil cyanobacterial DNA into the palaeo-reconstruction of various environments and could also be used to quantify the ecological importance of cyanobacteria through geological time. These genetic markers serve as biosignatures providing important clues about ancient life and begin a new discussion concerning the debate on the origin of late Miocene evaporites in the Mediterranean. PMID:20059556

  5. Ribosomal RNA gene fragments from fossilized cyanobacteria identified in primary gypsum from the late Miocene, Italy.

    PubMed

    Panieri, G; Lugli, S; Manzi, V; Roveri, M; Schreiber, B C; Palinska, K A

    2010-03-01

    Earth scientists have searched for signs of microscopic life in ancient samples of permafrost, ice, deep-sea sediments, amber, salt and chert. Until now, evidence of cyanobacteria has not been reported in any studies of ancient DNA older than a few thousand years. Here, we investigate morphologically, biochemically and genetically primary evaporites deposited in situ during the late Miocene (Messinian) Salinity Crisis from the north-eastern Apennines of Italy. The evaporites contain fossilized bacterial structures having identical morphological forms as modern microbes. We successfully extracted and amplified genetic material belonging to ancient cyanobacteria from gypsum crystals dating back to 5.910-5.816 Ma, when the Mediterranean became a giant hypersaline brine pool. This finding represents the oldest ancient cyanobacterial DNA to date. Our clone library and its phylogenetic comparison with present cyanobacterial populations point to a marine origin for the depositional basin. This investigation opens the possibility of including fossil cyanobacterial DNA into the palaeo-reconstruction of various environments and could also be used to quantify the ecological importance of cyanobacteria through geological time. These genetic markers serve as biosignatures providing important clues about ancient life and begin a new discussion concerning the debate on the origin of late Miocene evaporites in the Mediterranean.

  6. Evidence for deep-water evaporite deposition in the Miocene Kareem Formation, Gemsa basin, eastern Egypt

    SciTech Connect

    May, J.A.; Stonecipher, S.A.; Steinmetz, J.C. ); Dyess, J.N. )

    1991-03-01

    The correct interpretation of intercalated Miocene siliciclastics and evaporites of Gemsa basin is crucial for understanding early rift tectonics of the Gulf of Suez, pinpointing the timing of isolation of the Gulf from the Mediterranean, and developing exploration plays. Evaporites of the Kareem Formation comprise celestites and massive, 'chicken-wire,' and laminated anhydrites. Although previously interpreted as sabkha deposits; sedimentologic, petrographic, and paleontologic analyses indicate these evaporites more likely formed in a submarine setting. Marls that encase the evaporites contain a diverse and abundant assemblage of nannoplankton, planktonic foraminifera, diatoms, pteropods, and fish scales indicative of basinal deposition. Associated turbidites also denote deep-water sedimentation. The paucity of benthic diatoms and foraminifera, plus the presence of unburrowed shales, phosphate nodules, early ferroan carbonate cements, and authigenic pyrite, suggest periodic anoxic, or at least disaerobic, bottom waters. These sequences probably represent partial isolation of the Gulf of Suez by middle Miocene, producing periodic basin restriction and evaporative drawdown. Episodes of increasing salinity likely caused the progressive decreases in foram abundance and diversity in marls beneath the anhydrites, culminating in subaqueous evaporite formation. Diverse, indigenous nannoplankton assemblages from shale seams within the anhydrites suggest Gemsa basin was stratified; shallow open-marine conditions coexisted with anhydrite crystallization from deeper hypersaline waters.

  7. Middle Miocene Paleoceanography in the Southern High-Latitudes Off Tasmania: Stable Isotope Records from ODP Sites 1170 and 1172

    NASA Astrophysics Data System (ADS)

    Ennyu, A.; Arthur, M. A.

    2002-12-01

    The middle Miocene encompasses one of the major steps in a global cooling trend towards the permanent establishment of east Antarctica ice sheet (EAIS), as inferred from the worldwide ca. 1\\permil increase in benthic foraminiferal δ18O. It has been suggested that an intensified Antarctic Circumpolar Current (ACC) prompted the mid-Miocene cooling, thereby increasing the meridional thermal gradient in the southern high-latitudes, and, ultimately, accumulation of the EAIS. At the same time, the southwest Pacific sector is thought to have ameliorated regionally through the incursion of a warm western boundary current, i.e., the proto-East Australian Current (EAC). In order to test the potentially contrasting effects of the EAC and ACC on evolution of the meridional thermal gradient in the southern high-latitudes across the middle Miocene climate transition, we have reconstructed near-surface paleohydrography by measuring δ18O and δ13C of planktic foraminifer Globigerina bulloides and Orbulina universa and bulk fine-fraction carbonates from ODP Sites 1170 (South Tasman Rise; Indian Ocean sector) and 1172 (East Tasman Plateau; Pacific sector) off Tasmania for the interval 8-20 Ma. Our results show no significant differences in the δ18O values between Sites 1170 and 1172. This suggests that the both sites were influenced by the same water mass in the middle Miocene. Long-term trends in the fine-fraction δ18O from the both sites indicate a signal of the early middle Miocene "climatic optimum" (MMCO) and the subsequent EAIS positive δ18O shift, and are similar to those reported from other lower latitude sites. In contrast, the planktic foraminiferal δ18O records from Sites 1170 and 1172 do not exhibit significant long-term trends, with values ranging from ca. 0.6 to 1.6\\permil. This implies that near-surface seawater temperatures at Sites 1170 and 1172 increased across the middle Miocene EAIS event (after ca. 14.5 Ma), as assuming that the mid-Miocene increase in

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  9. Seismic interpretation of the post-Middle Miocene section of the northeastern Northern South Sea Yellow Basin, Yellow Sea

    NASA Astrophysics Data System (ADS)

    Kim, Hyeonju; Lee, Gwang H.; Kim, Han J.; Yi, BoYeon

    2016-04-01

    The Yellow Sea is a very shallow (< 90 m), semi-enclosed epicontinental sea, lying between China and the Korean Peninsula. The Yellow Sea has undergone gradual, regional subsidence since the Middle Miocene when the major plate reorganization in East Asia led to regional uplift and subsequent erosion in many parts of the marginal basins of the western Pacific, including the Yellow Sea. In this study, we analyzed about 2500 km of 2-D multi-channel seismic data from the northeastern part of the Northern South Yellow Sea Basin to investigate the post-Middle Miocene geologic history of the area. We identified and mapped the Middle Miocene unconformity (MMU) and two horizons (H1 and H2) which are correlatable over much of the area. H1 and H2 were inferred to be of the early Late Miocene (ca. 10 Ma) and of the late Late Miocene (ca. 6.7 Ma), respectively, assuming a constant sediment accumulation rate. MMU forms the top of the basement except for the southwestern corner of the area and is interrupted by numerous volcanic bodies, suggesting active post-Middle Miocene volcanism. The volcanic bodies are oriented largely parallel to the basement faults. H1 and H2 are also affected by volcanic bodies in the northern part of the area, suggesting continued volcanism until the late Late Miocene. The depth of MMU increases southwestward from about 250 m to over 750 m, indicating progressive tilting (i.e., differential subsidence) of the basement toward the depocenter in the southwest. The depths of H1 and H2 increase west- and southwestward from about 200 m to over 450 m and from about 150 m to over 300 m, respectively. Detailed seismic facies were not analyzed due to poor data quality; nevertheless, continuous reflectors, suggesting uniform and thus marine deposition, appear to increase upward and northeastward. This, together with the amount of subsidence estimated from the depth of MMU, strongly suggests that subsidence has been dominant in the area over the global sea

  10. Environmental changes in Southwest Africa during the Miocene C4 plant expansion

    NASA Astrophysics Data System (ADS)

    Dupont, L. M.; Rommerskirchen, F.; Condon, T.; Mollenhauer, G.; Schefuss, E.

    2009-12-01

    The Late Miocene epoch is characterized by fundamental changes in Earth's climate system: sea-level variability, changes in surface- and deep-water circulation, increase in upwelling intensity along the coasts and turnover in marine and terrestrial biota [1,2]. It is thought that plants using the CO2 concentrating C4 mechanism for photosynthesis potentially evolved during times of a global drop in atmospheric CO2 content and at relatively hot and dry habitats. During the Late Miocene C4 plants expanded nearly simultaneously at different places in the world, while temperatures declined and global CO2 levels exhibited no corresponding change [1,3]. Our objectives concern the climatic and environmental change of Miocene Southwest Africa between ~14 to ~5 Myrs BP and how these conditions may be linked to the C4 plant expansion. We use a variety of organic geochemical techniques combined with palynology on sediments of ODP Site 1085. The site is situated in the Cape Basin at the south-west African continental margin, within the today’s upwelling zone of the Benguela Coastal Current. Miocene sea surface temperature (SST) estimates applying two indices (TEX86 and UK'37) suggest a transition to cooler temperatures from above 27 to 18°C over a time period from ~14 to ~5 Myrs BP, but are different in rate and timing. Increased upwelling leads to cooler SSTs and enhanced marine primary production as implied by a small but clear overall shift in total organic carbon content after 11 Myrs BP. Concurrently, the abundance of both marine cysts and terrestrial pollen and spores increase and the relative contribution river run-off from the nearby Orange River declines, as indicated by the BIT-index (from ~0.8 to <0.1). We connect these findings to a change in strength and the predominant direction of the wind combined with an intensification of the Benguela upwelling current bringing cold, nutrient-rich waters from the South Atlantic and the Antarctic circumpolar current

  11. Late Miocene biomarker and pollen records in Southeast Atlantic Ocean sediments indicate environmental changes

    NASA Astrophysics Data System (ADS)

    Rommerskirchen, Florian; Dupont, Lydie; Condon, Tegan; Mollenhauer, Gesine; Schefuß, Enno

    2010-05-01

    The Late Miocene epoch is characterized by fundamental changes in Earth‘s climate system: sea-level variability, changes in surface- and deep-water circulation, increase in upwelling intensity along the coasts and turnover in marine and terrestrial biota [1,2]. It is thought that plants using the CO2 concentrating C4 mechanism for photosynthesis potentially evolved during times of a global drop in atmospheric CO2 content and at relatively hot and dry habitats. During the Late Miocene C4 plants expanded nearly simultaneously at different places in the world, while temperatures declined and global CO2 levels exhibited no corresponding change [1,3]. Our objectives concern the climatic and environmental change of Miocene Southwest Africa between ~14 to ~5 Myrs BP and how these conditions may be linked to the C4 plant expansion. We use a variety of organic geochemical techniques combined with palynology on sediments of ODP Site 1085. The site is situated in the Cape Basin at the south-west African continental margin, within the today's upwelling zone of the Benguela Coastal Current. Miocene sea surface temperature (SST) estimates applying two indices (TEX86 and UK'37) suggest a transition to cooler temperatures from above 27 to 18°C over a time period from ~14 to ~5 Myrs BP, but are different in rate and timing. Increased upwelling leads to cooler SSTs and enhanced marine primary production as implied by a small but clear overall shift in total organic carbon content after 11 Myrs BP. Concurrently, the abundance of both marine cysts and terrestrial pollen and spores increase and the relative contribution river run-off from the nearby Orange River declines, as indicated by the BIT-index (from ~0.8 to <0.1). We connect these findings to a change in strength and the predominant direction of the wind combined with an intensification of the Benguela upwelling current bringing cold, nutrient-rich waters from the South Atlantic and the Antarctic circumpolar current

  12. Oligocene and Miocene Vegetation and climate development on the Atlantic Coastal Plain (IODP Expedition 313)

    NASA Astrophysics Data System (ADS)

    Kotthoff, Ulrich; McCarthy, Francine; Greenwood, David; Hesselbo, Stephen

    2013-04-01

    The major aims of IODP Expedition 313 are estimating amplitudes, rates and mechanisms of sea-level change and the evaluation of sequence stratigraphic facies models that predict depositional environments, sediment compositions, and stratal geometries in response to sea-level change. Cores from three Sites (313-M0027, M0028, and M0029; 45 to 67 km off the coast of New Jersey) from the New Jersey shallow shelf (water depth approximately 35 m) were retrieved during May to July 2009, using an ECORD "mission-specific" jack-up platform. The recovery rate for the three sites exceeded 80%; in total, more than 1300 m core length were achieved. The oldest sediments were recovered from Hole M0027A, and dated as late Eocene/early Oligocene according to biostratigraphy, sequence-stratigraphy, and Sr-isotopy-based age estimates. We have investigated the palynology of sediment cores from Sites M0027 and M0029. The cores examined span ca. 33 to 13 million years before present together with additional samples from younger sediments. The palynological results were complemented with pollen-based quantitative climate reconstructions using bioclimatic analysis, a mutual climate range NLR approach. Until the Pleistocene, the hinterland vegetation of the New Jersey shelf was characterized by oak-hickory forests in the lowlands and conifers in the highlands. The Oligocene witnessed several downward expansions of conifer forest, which were probably related to cooling events. The pollen-based climate data show a temperature increase during the Rupelian and at the Chattian-Aquitanian transition, with mean annual temperatures surpassing 15 °C. For the Miocene, mean annual temperatures varied around ~13.5 °C. Generally, the Miocene ecosystem and climate conditions were similar to those of the Oligocene in the hinterland of the New Jersey shelf. We conjecture that the Miocene uplift of the Appalachian Mountains led to the proliferation of mountainous taxa and thus to an increase of related

  13. Phylogenetics and molecular clocks reveal the repeated evolution of ant-plants after the late Miocene in Africa and the early Miocene in Australasia and the Neotropics.

    PubMed

    Chomicki, Guillaume; Renner, Susanne S

    2015-07-01

    Ant-plant symbioses involve over 110 ant species in five subfamilies that are facultative or obligate occupants of stem, leaf or root domatia formed by hundreds of ant-plant species. The phylogenetic distribution and geological ages of these associations, and the frequency of gains or losses of domatium, are largely unknown. We compiled an up-to-date list of ant domatium-bearing plants, estimated their probable true number from model-based statistical inference, generated dated phylogenies that include c. 50% of ant-plant lineages, and traced the occurrence of domatia and extrafloral nectaries on a 1181-species tree, using likelihood and Bayesian methods. We found 681 vascular plants with domatia (159 genera in 50 families) resulting from minimally 158 inferred domatium origins and 43 secondary losses over the last 19 Myr. The oldest African ant-plant symbioses are younger than those in Australasia and the Neotropics. The best statistical model suggests that the true number of myrmecophytes may approach 1140 species. The phylogenetic distribution of ant-plants shows that domatia evolved from a range of pre-adapted morphological structures and have been lost frequently, suggesting that domatia have no generalizable effect on diversification. The Miocene origin of ant-plant symbioses is consistent with inferred changes in diet and behaviour during ant evolution.

  14. The Brahmaputra tale of tectonics and erosion: Early Miocene river capture in the Eastern Himalaya

    NASA Astrophysics Data System (ADS)

    Bracciali, Laura; Najman, Yani; Parrish, Randall R.; Akhter, Syed H.; Millar, Ian

    2015-04-01

    The Himalayan orogen provides a type example on which a number of models of the causes and consequences of crustal deformation are based and it has been suggested that it is the site of a variety of feedbacks between tectonics and erosion. Within the broader orogen, fluvial drainages partly reflect surface uplift, different climatic zones and a response to crustal deformation. In the eastern Himalaya, the unusual drainage configuration of the Yarlung Tsangpo-Brahmaputra River has been interpreted either as antecedent drainage distorted by the India-Asia collision (and as such applied as a passive strain marker of lateral extrusion), latest Neogene tectonically-induced river capture, or glacial damming-induced river diversion events. Here we apply a multi-technique approach to the Neogene paleo-Brahmaputra deposits of the Surma Basin (Bengal Basin, Bangladesh) to test the long-debated occurrence and timing of river capture of the Yarlung Tsangpo by the Brahmaputra River. We provide U-Pb detrital zircon and rutile, isotopic (Sr-Nd and Hf) and petrographic evidence consistent with river capture of the Yarlung Tsangpo by the Brahmaputra River in the Early Miocene. We document influx of Cretaceous-Paleogene zircons in Early Miocene sediments of the paleo-Brahmaputra River that we interpret as first influx of material from the Asian plate (Transhimalayan arc) indicative of Yarlung Tsangpo contribution. Prior to capture, the predominantly Precambrian-Paleozoic zircons indicate that only the Indian plate was drained. Contemporaneous with Transhimalayan influx reflecting the river capture, we record arrival of detrital material affected by Cenozoic metamorphism, as indicated by rutiles and zircons with Cenozoic U-Pb ages and an increase in metamorphic grade of detritus as recorded by petrography. We interpret this as due to a progressively increasing contribution from the erosion of the metamorphosed core of the orogen. Whole rock Sr-Nd isotopic data from the same samples

  15. Provenance, Offset Equivalent and Palinspastic Reconstruction of the Miocene Cajon Valley Formation, Southern California

    NASA Astrophysics Data System (ADS)

    Stang, Dallon Michael

    Petrographic, conglomerate and detrital-zircon analyses of formations in southern California can determine consanguineous petrofacies and lithofacies that help constrain paleotectonic and paleogeographic reconstructions of the southwestern United States. Arkosic sandstone of the lower Middle Miocene Cajon Valley formation is exposed on the southwest edge of the Mojave block and juxtaposed against Mesozoic and Paleozoic rocks by the San Andreas fault (SAf). Early work in Cajon Valley referred to the formation as Punchbowl, due to its similar appearance to the Punchbowl Formation at Devil's Punchbowl (northwest along the SAf). However, paleontological work placed Cajon Valley strata in the Hemingfordian-Barstovian (18-14 Ma), as opposed to the Clarendonian-Hemphillian (13-9 Ma) Punchbowl Formation. Since the Cajon Valley formation was deposited prior to being truncated by the San Andreas fault, the 2400m-thick, laterally extensive subaerial deposits likely were deposited across what is now the fault trace. Restoring 310 km of dextral slip on the SAf system should indicate the location of offset equivalent sandstone. Restoration of slip on the SAf system places Cajon Valley adjacent to the Caliente and La Panza Ranges, east of San Luis Obispo. Although analysis of detrital zircon from Cenozoic sandstone throughout southern California has been crucial in establishing paleodrainage areas, detrital zircon from the Cajon Valley and equivalent formations had not been analyzed prior to this study. Paleocurrents measured throughout the Cajon Valley formation indicate a source to the NE, in the Mojave Desert. Sandstone samples analyzed in thin section using the Gazzi-Dickinson method of point-counting are homogeneously arkosic, with slight compositional variability, making differentiation of the Cajon Valley formation and potential offset equivalents problematic. However, Branch Canyon Sandstone and Santa Margarita Formation samples are compositionally the best match for the

  16. Stratigraphical links between Miocene Alpine Foreland basin and Gulf of Lion Passive Margin during lowstands

    NASA Astrophysics Data System (ADS)

    Rubino, Jean-Loup; Gorini, Christian; Leroux, Estelle; Aslanian, Daniel; Rabineau, Marina; Parize, Olivier; Besson, David

    2015-04-01

    Miocene peri-alpine foreland basin is connected toward the south with the Gulf of Lion passive margin and is predominantly filled by marine shallow water molassic deposits ranging from lower Miocene to Pliocene in age. Nine to ten depositional sequences are recorded and partly preserved in this basin and can be traced into the post rift part of the Gulf of Lion. One of the most surprising feature of the stratigraphic infill is the total lack of lowstand deposits within the foreland basin ; All superimposed sequences only includes transgressive and highstand System Tracts separated by erosional sequence boundaries and the development of incised valley networks filled by tidal deposits during transgression; Besson et al. 2005. It means that the entire foreland basin in SE France is exposed during lowstand periods without any preservation of fluvial deposits. By place few forced regression wedges are preserved at the transition between the foreland and the passive margin, close to the present day coastline. To date no real lowstand wedges have never been reported in the offshore of the Gulf of Lion. A reinterpretation of the best old vintage 2D dip seismic profiles along the passive margin validates the idea that the foreland basin is entirely exposed as well as the proximal part of the passive margin; first because some incised valleys can be occasionally picked on the shelf and second mainly because well defined superimposed or juxtaposed prograding lowstand wedges with nicely defined clinoforms onlapping the sequence boundaries can be recognized on the distal part of the shelf from the Burdigalian to the Messinian. Their ages being constrains by the Calmar well calibration. Unfortunately, they can't be continuously mapped all along the shelf break because of the strong erosion related to the Messinian Unconformity and the associated huge sea level fall.So we have to explain why during the lowstands, exceptionally long fluvial valley networks (more than 300km) can

  17. Small mammal carbon isotope ecology across the Miocene-Pliocene boundary, northwestern Argentina

    NASA Astrophysics Data System (ADS)

    Hynek, Scott A.; Passey, Benjamin H.; Prado, José Luis; Brown, Francis H.; Cerling, Thure E.; Quade, Jay

    2012-03-01

    The late Miocene expansion of plants using the C4 photosynthetic pathway in South America has been documented by tooth enamel carbon isotope ratios (δ13Cen). However, a more detailed understanding of this ecological event is hampered by poor chronological control on the widespread fossil localities from which isotopic data are derived. This study develops a δ13Cen record from a single 2500 m-thick stratigraphic section in subtropical South America. Strata at Puerta de Corral Quemado (PCQ), northwestern Argentina, span 9 to 3.5 Ma in age, and existing paleosol carbonate data (δ13Cpc) document C4 expansion across the Miocene-Pliocene boundary. Comparison of δ13Cen data with δ13Cpc data at high stratigraphic resolution refines understanding of this ecological event in South America. Small mammal δ13Cen data in particular are complementary to that of large mammal and paleosol δ13C data. Small mammal teeth integrate isotopic data over much shorter temporal and spatial scales than large mammal teeth, providing a sensitive measure of local vegetation and placing constraints on the landscape distribution of C3 and C4 plants. Explicit consideration of the distinctive carbon isotope enrichment factor between enamel and diet for rodents (ɛ*en-diet = 11‰, as opposed to 14‰ for large mammals) allows for unequivocal inference of C4 vegetation ~ 1 Ma prior to that inferred from large mammal δ13Cen data, and ~ 2 Ma prior to δ13Cpc data. This multiproxy record demonstrates that C4 plants were a stable component of the ecosystem hundreds of thousands of years prior to their major ecological expansion, and that the expansion of C4 plants was pulsed at PCQ. Two periods of ecological change are demonstrated by δ13C and δ18O data at ~ 7 Ma and 5.3 Ma (coincident with the Miocene-Pliocene boundary). Development of small mammal δ13Cen records on other continents may provide similar insight into the early stages of the global C4 event.

  18. Geochemistry and diagenesis of Miocene lacustrine siliceous sedimentary and pyroclastic rocks, Mytilinii basin, Samos Island, Greece

    USGS Publications Warehouse

    Stamatakis, M.G.; Hein, J.R.; Magganas, A.C.

    1989-01-01

    A Late Miocene non-marine stratigraphic sequence composed of limestone, opal-CT-bearing limestone, porcelanite, marlstone, diatomaceous marlstone, dolomite, and tuffite crops out on eastern Samos Island. This lacustrine sequence is subdivided into the Hora Beds and the underlying Pythagorion Formation. The Hora Beds is overlain by the clastic Mytilinii series which contains Turolian (Late Miocene) mammalian fossils. The lacustrine sequence contains volcanic glass and the silica polymorphs opal-A, opal-CT, and quartz. Volcanic glass predominantly occurs in tuffaceous rocks from the lower and upper parts of the lacustrine sequence. Opal-A (diatom frustules) is confined to layers in the upper part of the Hora Beds. Beds rich in opal-CT underlie those containing opal-A. The occurrence of opal-CT is extensive, encompassing the lower Hora Beds and the sedimentary rocks and tuffs of the Pythagorion Formation. A transition zone between the opal-A and opal-CT zones is identified by X-ray diffraction patterns that are intermediate between those of opal-CT and opal-A, perhaps due to a mixture of the two polymorphs. Diagenesis was not advanced enough for opal-CT to transform to quartz or for volcanic glass to transform to opal-C. Based on geochemical and mineralogical data, we suggest that the rate of diagenetic transformation of opal-A to opal-CT was mainly controlled by the chemistry of pore fluids. Pore fluids were characterized by high salinity, moderately high alkalinity, and high magnesium ion activity. These pore fluid characteristics are indicated by the presence of evaporitic salts (halite, sylvite, niter), high boron content in biogenic silica, and by dolomite in both the opal-A and opal-CT-bearing beds. The absence of authigenic K-feldspar, borosilicates, and zeolites also support these pore fluid characteristics. Additional factors that influenced the rate of silica diagenesis were host rock lithology and the relatively high heat flow in the Aegean region from

  19. Miocene Evaporites in the Intermountain Tuzluca -Iǧdir Neogene Basin, Eastern Turkey

    NASA Astrophysics Data System (ADS)

    Ayyıldız, T.; Varol, B.; Sözeri, K.; Karakaş, Z.

    2012-04-01

    The study area, which continues into Armenia south of Yerevan as Aras/Araxes or Hoktemberian Basin, is located within the Eastern Turkish High Plateau lying east of the intersection point of the North and East Anatolian faults at Karlıova, where folds, thrust and strike-slip faults, and large-scale extensional fractures related to a shortening regime have been developing as a result of continent-continent collision during the Neotectonic episode. Simultaneously with the shortening phase, structural basins developed such as intermountane. Detailed mapping of the Neogene deposits (Early Oligocene - Middle to early Late Miocene) in the eastern part of this basin studied allowed the recognition of four successive sedimentary units composed of fluvial, fluvio-deltaic, lake and saline pan. The depositional units were ended by intensive volcanic activity started in the Late Miocene epoch. Pre-evaporitic stage, some levels with siliciclastic and carbonate might be important for petroleum potential, which consists of bituminous mudstone (TOC: % 0.67 - 6.14; Tmax: 422 - 4620C; HI: 37-54). Evaporites are mainly represented by bedded/banded halite that were formed as four separate layers (10-40 m thick) intersected by red siliciclastic deposits with single selenitic gypsum and cubic halite crystals. Bedded gypsum was formed as marginal evaporites, laterally interfingering with the halite layers. On the other hand, it was precipitated as final evaporite deposits on the top of the halite-dominated succession, indicating upward increasing value of SO4 to Cl, probably resulted from a climatic changing leading to transition from saline pan to sulphate lake. As based on the different kinds of precipitation, the evaporite succession includes following 1) evaporitic red mudstone inner-sabkha mud flats; 2) bedded/banded halite and mudstone with organic matter in inner-sabkha salt pan; 3) interdigitated gypsum in marginal sabkha; 4) sealed gypsum in sulphate lake / floodwater sabkha

  20. Middle Miocene kinematic shift in northeastern Tibet from collision-related northward growth to eastward contraction

    NASA Astrophysics Data System (ADS)

    Lease, R. O.; Burbank, D. W.; Hough, B. G.; Clark, M. K.; Zhang, H.; Farley, K. A.; Wang, Z.

    2009-12-01

    Variations in the direction and timing of range growth demonstrate how India-Asia convergence was manifest in northeastern Tibet (near 36°N, 103°E) throughout the Cenozoic. We detect a >45° change in shortening direction in middle Miocene time by examining thermochronological relief transects from contractional ranges in combination with stratigraphic successions from adjacent foreland basins. Apatite (U-Th)/He and fission track age-elevation relationships suggest an onset of rapid exhumation in the north-directed Laji Shan at ~23 Ma. Rapid exhumation of the adjacent east-directed Jishi Shan, however, did not commence until ~12 Ma. Furthermore, diachronous Miocene range growth is expressed in the subsidence, provenance, and paleoclimatic records from magnetostratigraphically dated sections in adjacent Xunhua and Linxia basins. Emergence of the north-directed Laji Shan is highlighted in Xunhua basin by a doubling of sediment accumulation rates between 24 and 22 Ma, enhanced flexural loading from 25 to 22 Ma, and the introduction of proximal alluvial facies at 20.7 Ma that detrital zircon U/Pb age spectra show were sourced from basement terranes within the Laji Shan. In contrast, growth of the east-directed Jishi Shan is expressed by an acceleration in Xunhua accumulation rates between 12 and 9 Ma and a doubling of detrital zircons derived from Jishi Shan sources by 11.5 Ma in Linxia. Additionally, the divergence of Linxia and Xunhua oxygen isotopic values signals topographic isolation of these two basins by surface uplift of the intervening Jishi Shan by 11 Ma. Together these diverse observations document a middle Miocene change in the kinematic style of plateau growth from initial north-directed contraction along a trajectory that mimicked the India-Asia collision to later east-directed contraction. This kinematic shift in northeastern Tibet coincides with expansion of the plateau margin in southeastern Tibet, as well as the onset of normal faulting in the high

  1. Geometry and kinematics of the southern part of the Miocene Pohang basin, SE Korea

    NASA Astrophysics Data System (ADS)

    Song, C.; Son, M.; Kim, I.

    2008-12-01

    Several kinematic models have been proposed for the East Sea opening. One major model is the fan-shaped opening and another is the pull-apart opening. In order to solve the controversies, diverse geologic data from both the seafloor and the surrounding landmasses, including the Miocene basins in SE Korea, should be synthesized. This study has carried out detailed field mapping and observations of basin structures together with analyses of basin-fill characteristics in the southern part of the Pohang basin. The southern part of the basin has an elongated shape in NS direction. The basin-fill is composed of conglomerates and sandstones accumulated under shallow-marine environment during late Early to early Middle Miocene. The conglomerates occur predominantly in the western and eastern marginal areas of the basin, and the west is much thicker and broader than the east. And the strata are gently dipping east to southeastward. These stratal configurations seem to imply that the sediments were supplied from the both margins into the center, but more dominantly from the western margin. Both western and eastern margins of the basin are bounded by faults which are zigzag-shaped in planar view. The faults are composed of two different trending segments: NNE- and NW-trending segments. The former shows the features of normal faults, while the latter those of dextral oblique-slip faults. The western bounding fault of the Pohang basin has been generally known as the northern part of the Yangsan fault which is known to have acted as major dextral strike-slip fault during the basin extension. Detailed mapping of this study, however, reveals that the western marginal fault is about 2 km easterly away from the Yangsan fault. Quite a number of syn-depositional structures including growth faults are observed in the basin-fill. Most of them indicate a tensional stress regime trending EW to WNW. Based on the geometric and kinematic features of basin-bounding faults as well as minor

  2. The role of hydroclimate in the late-Miocene expansion of C4 grasses in India

    NASA Astrophysics Data System (ADS)

    Polissar, P. J.; Uno, K. T.; Phelps, S. R.; Pensky, J. L.

    2015-12-01

    The dramatic expansion of C4 grasslands in northern India, Pakistan and and Nepal during the late Miocene has been well documented from carbon isotope changes in paleosols and marine sediments. This expansion is part of a trend in the late Miocene towards increasing tropical C4 savannah vegetation worldwide. The roles that evolution, global boundary conditions, and local factors played in this trend remain uncertain. The expansion of C4 grasses in India has been variously ascribed to uplift of the Tibetan plateau, changes in the Indian monsoon, declining atmospheric CO2 levels, and global cooling. However, the ultimate cause of this expansion remains unknown. Here we investigate the role that hydrologic change may have played in driving the expansion of C4 grasslands in India. We analyzed the molecular distribution of leaf-wax n-alkanes in the Bengal Fan and their carbon and hydrogen isotopic composition to determine the history of vegetation, aridity and hydroclimate associated with the expansion. Ocean Drilling Program sites 717 and 718 on the distal Bengal Fan preserve lipid molecules from terrestrial vegetation transported to the core site by deep-sea turbidites. We found that changes in the molecular distribution and hydrogen isotopic composition of terrestrial leaf wax n-alkanes precede changes in the carbon isotopic composition of these molecules. These data suggest that vegetation and hydroclimate changes preceded the expansion of C4 grasses, implying a more nuanced ecological and environmental trajectory. The hydrogen isotope data indicate a substantial enrichment in the δD of source water prior to the C4 transition. Some combination of increasing aridity and rainfall δD could lead to the observed δD changes. Comparison with soil carbonate δ18O suggests that changes in rainfall δD is the more likely cause, reflecting the moisture source, rainfall amount, or seasonality of rainfall. Overall, the timing of changes in molecular distribution and

  3. Oligocene to Miocene terrestrial climate change and the demise of forests on Wilkes Land, East Antarctica

    NASA Astrophysics Data System (ADS)

    Salzmann, Ulrich; Strother, Stephanie; Sangiorgi, Francesca; Bijl, Peter; Pross, Joerg; Woodward, John; Escutia, Carlota; Brinkhuis, Henk

    2016-04-01

    The question whether Cenozoic climate was warm enough to support a substantial vegetation cover on the Antarctic continent is of great significance to the ongoing controversial debate on the dynamic behaviour of Antarctic land ice during the transition from a greenhouse to an icehouse world. Here we present palynological results from an Oligocene to Miocene sediment record provided by the Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin (East Antarctica). The Oligocene assemblages (33.9-23 Ma) are dominated by pollen and spores from temperate forest and sub-Antarctic shrub vegetation inhabiting different altitudinal zones. These include a lowland cold temperate forest with Dacrydium and Lagarostrobos (both common in southern forests of New Zealand and Tasmania today) and a high altitude tundra shrubland comprising Microcachrys, Nothofagus (southern beech) and Podocarpaceae conifers. A decline in pollen percentages of Dacrydium and Lagarostrobos and absence of Proteaceae indicate climate cooling during the late Oligocene (~25-23 Ma). However, the continuous presence of Lagarostrobos suggests that the full transition to a tundra environment had not yet occurred and climate on Wilkes Land during the late Oligocene was still warm enough to support forest vegetation in sheltered areas. Temperature reconstructions derived from the fossil pollen assemblages using the Coexistence Approach suggest mean annual temperatures (MATs) between 6.7-13.7°C during the early Oligocene and a drop of minimum MATs to 5.8°C in the late Oligocene. Pollen of "unambiguous" forest indicators, such as Lagarostrobos, are absent in the Miocene sediment record (16.2 -12.5 Ma) but temperatures were still high enough (minimum MATs > 5°C) to sustain a woody sub-Antarctic vegetation under partially ice-free conditions. Wilkes Land provides a unique record of Antarctic vegetation change from a subtropical, highly diverse Eocene rainforest to an Oligocene cold temperate

  4. Transitional directions from Early Miocene Lavas at Samothraki Island, N. Greece

    NASA Astrophysics Data System (ADS)

    Kondopoulou, Despina; Valet, Jean-Pierre; Zananiri, Irene; Voidomatis, Philippos

    2014-05-01

    The North Hellenic orogen was formed at the expenses of the Variscan and Jurassic oceanic crust, preserved in scattered ophiolitic massifs. Strong post-orogenic extension with coeval emplacement of granodioritic plutons, deposition of clastic sediments and calc-alkaline volcanism appeared from the Middle-Late Eocene to the Middle Miocene. These widespread Tertiary volcanic products, outcropping also in north and central Aegean, have been extensively studied as far as their emplacement conditions are concerned. In parallel, they have been the object of several palaeomagnetic studies, all consistently indicating a general pattern of clockwise rotations. The island of Samothraki belongs to the Circum-Rhodope Zone, a series of Triassic-Jurassic continental margin sedimentary and volcanic rocks that surround the crystalline Serbo-Macedonian and Rhodope Massifs. The geochronological data, along with the morphology and the eruption mode of the Samothraki Tertiary volcanic rocks, allow a division into three groups, namely the "old", the "intermediate" and the "young" ones. Several radiometric ages have been assigned to the three groups, spanning from 25 to 19 Ma. Isotope and trace-element modeling do not favor a continuous evolution of these magmas. The major granitic and volcanic formations of the island have been subjected to paleomagnetic studies. The results revealed a complex pattern with coexisting straightforward directions and puzzling ones, only within the younger lavas, mostly domes. These samples are characterized by a medium temperature component with an eastward declination and a positive inclination and a high temperature one with a negative inclination. Experiments of absolute paleointensity have been conducted on twenty-eight samples from 3 separate domes with ages between 22-19 Ma using a modified Thellier technique with very narrow 4°C to 10°C temperature steps between 500°C and 595°C. The results indicate significantly low field values at two sites

  5. Thermochronologic evidence for Miocene mid-crustal tectonic exhumation of the Huachuca Mountains, southeast Arizona

    NASA Astrophysics Data System (ADS)

    King, C. C.; Orme, D. A.; Biswas, A.; Reiners, P. W.

    2011-12-01

    Zircon double dating of detrital grains from the northward flowing upper San Pedro river valley at Murray Springs in southeastern Arizona yields abundant zircons with variable U/Pb crystallization ages of ~70-1400 Ma, but a restricted range of (U-Th)/He cooling ages of ~18-25 Ma. This combination of diverse formation ages but uniform mid-Miocene cooling ages is characteristic of zircons from the core complexes and deeply exhumed Santa Catalina, Rincon, and Pinaleno Mountains, which experienced tectonic exhumation from mid-crustal depths during mid-Miocene extension. But all these sources are far downstream or outside the watershed of the upper San Pedro valley. To trace the source of these detrital grains and understand the implications for regional tectonics, we also measured U/Pb and (U-Th)/He dates of zircons from the Tombstone Hills and Huachuca Mountains, proximal to the Murray Springs site. Magmatic rocks in the Tombstone Hills yielded U/Pb dates of 76-83 Ma and zircon He ages of 53-60 Ma. In contrast, crystalline basement of the Huachucas yields Cretaceous through 1.5-Ga U/Pb ages and zircon He ages of 17-25 Ma, with most between 21-22 Ma. These data require that a large region of the Huachucas contains rocks that cooled rapidly below temperatures of at least 180 oC in the mid-Miocene. Assuming typical geothermal gradients of 20-30 oC, this requires exhumation of at least 7-9 km of crust, likely within 1-2 Myr. While it is possible that erosion contributed, it is more likely that denudation was accommodated by deep tectonic exhumation. Faults are observed on the basin-bounding east-side of the Huachucas, but most are inferred to accommodate Laramide-age thrusting, and the normal faults have been interpreted as high-angle and unlikely to cause significant tectonic exhumation. Our new data suggest that a large part of the presently exposed Huachucas was exhumed from depths at least as great as ~7-9 km, requiring a considerable revision of structural

  6. Spatiotemporal variation in C4-grass abundance during the early to middle Miocene in Spain

    NASA Astrophysics Data System (ADS)

    Urban, M. A.; Nelson, D. M.; Jimenez-Moreno, G.; Hu, F.

    2014-12-01

    Carbon-isotope analyses on a variety of substrates (e.g., leaf waxes, teeth, carbonates) suggest a pronounced increase in C4 plant biomass during the late Miocene and early Pliocene in many regions of the world. This spread of C4-dominated grasslands is thought to have occurred at the expense of C3-dominated grasslands. However, the earlier history of C4 grasses is uncertain, primarily because of difficulty assessing the presence and abundance of C4 grasses when they are relatively rare on the landscape. We measure d13C of individual grass pollen grains using SPIRAL (Single Pollen Isotope Ratio AnaLysis) to distinguish the relative abundance of C3 and C4 grasses during the early to middle Miocene in Spain. We analyzed a total of 3251 pollen grains isolated from 7 samples from Andalucia A1 (10-13.5 Ma), 7 samples from Gor (13-15 Ma) and 24 sediment samples from (Rubielos de Mora, (16-22 Ma). Palynological data indicate that grasses were not a significant component (5-20% of total terrestrial pollen) of the regional vegetation, which was composed of herbs, shrubs, and thermophilous (e.g., Taxodiaceae, Engelhardia) and mesothermic (Quercus, Carya) trees. Based on our SPIRAL data, 21-72% of the grasses were C4, with the older northern site (Rubielos de Mora) having lower C4-grass abundance (average of 39%) than the younger and more southern sites (average of 62%). Paleoclimate reconstructions suggest that the region was mainly subtropical (warm and semi-arid/highly seasonal) at that time, and pollen spectra suggest that the regional vegetation was similar to that found today in northern Africa where C4 grasses dominate. Our pollen-isotope results imply an increase in C4-grass abundance through time, and/or a north-south climatic gradient, with wetter and less seasonal conditions that were less favorable to C4 grasses in the north. Overall, these results suggest that C4 grasses were relatively abundant in southwestern Europe during the early and middle Miocene, prior to

  7. Unlocking the Ice House: Oligocene-Miocene oxygen isotopes, eustasy, and margin erosion

    NASA Astrophysics Data System (ADS)

    Miller, Kenneth G.; Wright, James D.; Fairbanks, Richard G.

    1991-04-01

    Oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on Antarctica since the earliest Oligocene (circa 35 Ma). The growth and decay of ice sheets during the Oligocene to modern "ice house world" caused glacioeustatic sea level changes. The early Eocene was an ice-free "greenhouse world," but it is not clear if ice sheets existed during the middle to late Eocene "doubt house world." Benthic foraminiferal δ18O records place limits on the history of glaciation, suggesting the presence of ice sheets at least intermittently since the earliest Oligocene. The best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic δ18O records. Although planktonic isotope records from the western equatorial regions are limited, subtropical planktonic foraminifera may also record such ice volume changes. It is difficult to apply these established principles to the Cenozoic δ18O record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events. We improved Oligocene to Miocene correlations of δ18O records and erected eight oxygen isotope zones (Oi1-Oi2, Mi1-Mi6). Benthic foraminiferal δ18O increases which are associated with the bases of Zones Oil (circa 35.8 Ma), Oi2 (circa 32.5 Ma), and Mil (circa 23.5 Ma) can be linked with δ18O increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near Antarctica. Our new correlations of middle Miocene benthic and western equatorial planktonic δ18O records show remarkable agreement in timing and amplitude. We interpret benthic-planktonic covariance to reflect substantial ice volume increases near the bases of Zones Mi2 (circa 16.1 Ma), Mi3 (circa 13.6 Ma), and possibly Mi5 (circa 11.3 Ma). Possible glacioeustatic lowerings are associated with the δ18O increases which culminated with the bases of Zone Mi4 (circa 12.6 Ma) and Mi6 (circa 9

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  9. Reconstructing Paleovegetation in mid-Miocene Tropical South America: An Analysis of Carbon and Oxygen Stable Isotopes

    NASA Astrophysics Data System (ADS)

    Jenkins, H. S.; Madden, R. H.

    2006-12-01

    The advance of the C4 photosynthetic pathway in the late Miocene (~7 Ma) has typically been associated with a global shift from cold, wet conditions to a warmer, dryer climatic regime (MacFadden, 1997; Cerling et al., 1997; Winslow et al., 2003; Balasse and Ambrose, 2005). Because C4 photosynthesis is energetically advantageous at low levels (<400 ppm) of CO2, a global decrease in atmospheric CO2 may have initiated this shift (Cerling et al., 1993). However, changes in precipitation, temperature, and humidity would also have affected the evolutionary growth of C4 plant biota (Winslow et al., 2003). Reconstructing vegetation and temperature records just prior to the global radiation of C4 plants may therefore provide valuable insight into the exact cause and timing of this shift. Here we present new data obtained from ungulate tooth enamel from the Villavieja Formation (mid-Miocene) in central Colombia (5° North). An analysis of the carbon and oxygen isotopic signals embedded in fossilized toxodontid tooth enamel reveals a reconstruction of vegetation and temperature in central Colombia during the mid-Miocene. By correlating the presence of C3 versus C4 plant biota with paleotemperature, we attempt to analyze the biogeography and paleoclimatic implications of these plant types during the Miocene and further constrain the parameters that drive biotic change.

  10. Miocene climate change recorded in the chemical and isotopic (Pb, Nd, Hf) signature of Southern Ocean sediments

    NASA Astrophysics Data System (ADS)

    VlastéLic, Ivan; Carpentier, Marion; Lewin, ÉRic

    2005-03-01

    The Middle Miocene transition from carbonate to biosilica sedimentation at DSDP site 266 (Australian-Antarctic basin) reflects a global transition toward a colder climate. The 143Nd/144Nd, 176Hf/177Hf, and Al/Ti of bulk sediments display systematic, coupled variations through time, which have been attributed to a change of the detrital source. This change could correspond to a reduction of input from the Antarctic continent, an increase of input from the Kerguelen volcanic province, or both. Mixing models based on Nd isotopes and Al/Ti suggest a 30-40% reduction of Antarctic input and an equivalent increase of Kerguelen input during the Miocene. Reduction of Antarctic input may result from the formation of a stable East Antarctic ice sheet. Consistently, Pb isotopes and trace element systematics suggest a change of weathering style during the Miocene, with an increase in physical weathering, or a reduction of chemical weathering, after 15 Ma. Increase of Kerguelen input may reflect the initiation, or enhancement, of the Antarctic Circumpolar Current (ACC), thus raising the possibility of a simultaneous onset of North Atlantic Deep Water production and the ACC during the Middle Miocene. In addition, large geochemical oscillations occurred during the Pliocene, possibly reflecting fluctuation in strength of the ACC or, alternatively, periods of instability of the Antarctic ice sheet.

  11. Palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin, northern South China Sea.

    PubMed

    Li, Wenhao; Zhang, Zhihuan; Wang, Weiming; Lu, Shuangfang; Li, Youchuan; Fu, Ning

    2014-01-01

    The main factors of the developmental environment of marine source rocks in continental margin basins have their specificality. This realization, in return, has led to the recognition that the developmental environment and pattern of marine source rocks, especially for the source rocks in continental margin basins, are still controversial or poorly understood. Through the analysis of the trace elements and maceral data, the developmental environment of Miocene marine source rocks in the Qiongdongnan Basin is reconstructed, and the developmental patterns of the Miocene marine source rocks are established. This paper attempts to reveal the hydrocarbon potential of the Miocene marine source rocks in different environment and speculate the quality of source rocks in bathyal region of the continental slope without exploratory well. Our results highlight the palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin of the northern South China Sea and speculate the hydrocarbon potential of the source rocks in the bathyal region. This study provides a window for better understanding the main factors influencing the marine source rocks in the continental margin basins, including productivity, preservation conditions, and the input of terrestrial organic matter.

  12. The Late Oligocene to Early Miocene early evolution of rifting in the southwestern part of the Roer Valley Graben

    NASA Astrophysics Data System (ADS)

    Deckers, Jef

    2016-06-01

    The Roer Valley Graben is a Mesozoic continental rift basin that was reactivated during the Late Oligocene. The study area is located in the graben area of the southwestern part of the Roer Valley Graben. Rifting initiated in the study area with the development of a large number of faults in the prerift strata. Some of these faults were rooted in preexisting zones of weakness in the Mesozoic strata. Early in the Late Oligocene, several faults died out in the study area as strain became focused upon others, some of which were able to link into several-kilometer-long systems. Within the Late Oligocene to Early Miocene northwestward prograding shallow marine syn-rift deposits, the number of active faults further decreased with time. A relatively strong decrease was observed around the Oligocene/Miocene boundary and represents a further focus of strain onto the long fault systems. Miocene extensional strain was not accommodated by further growth, but predominantly by displacements along the long fault systems. Since the Oligocene/Miocene boundary coincides with a radical change in the European intraplate stress field, the latter might have contributed significantly to the simultaneous change of fault kinematics in the study area.

  13. Palaeoenvironment and Its Control on the Formation of Miocene Marine Source Rocks in the Qiongdongnan Basin, Northern South China Sea

    PubMed Central

    Li, Wenhao; Zhang, Zhihuan; Wang, Weiming; Lu, Shuangfang; Li, Youchuan; Fu, Ning

    2014-01-01

    The main factors of the developmental environment of marine source rocks in continental margin basins have their specificality. This realization, in return, has led to the recognition that the developmental environment and pattern of marine source rocks, especially for the source rocks in continental margin basins, are still controversial or poorly understood. Through the analysis of the trace elements and maceral data, the developmental environment of Miocene marine source rocks in the Qiongdongnan Basin is reconstructed, and the developmental patterns of the Miocene marine source rocks are established. This paper attempts to reveal the hydrocarbon potential of the Miocene marine source rocks in different environment and speculate the quality of source rocks in bathyal region of the continental slope without exploratory well. Our results highlight the palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin of the northern South China Sea and speculate the hydrocarbon potential of the source rocks in the bathyal region. This study provides a window for better understanding the main factors influencing the marine source rocks in the continental margin basins, including productivity, preservation conditions, and the input of terrestrial organic matter. PMID:25401132

  14. Stratigraphic framework, sedimentology and structural setting of Miocene-Pliocene sediments of the Abu Qir area, offshore Nile delta

    SciTech Connect

    Ince, D.M.; Deibis, S.; McSherry, A.; Seymour, W.P.

    1988-08-01

    The offshore Nile delta contains significant gas resources which are currently undergoing both production and appraisal in the Abu Qir field and adjacent areas. The principal reservoir occurs in sandstones of the upper Abu Madi Member (upper Miocene), but excellent potential reservoirs exist in the lower Abu Madi Member (upper Miocene), Sidi Salem (middle-upper Miocene), and Moghra (middle Miocene) Formations. Gas is trapped in fault-bounded anticlinal structures sealed by shales of the Pliocene Kafr el Sheikh Formation. Early wells in the Abu Qir field revealed an apparently simple stratigraphic picture. More recently, however, drilled wells have revealed a more complex stratigraphic situation. Integrated biostratigraphic and sedimentologic studies demonstrate the existence of a fault block or horst structure beneath part of the field, giving rise to the observed stratigraphic complexity. Such a structure was not visible on seismic data due to inhibited reflection quality beneath the overlying Messinian anhydrite but has since been demonstrated by reprocessing and reinterpreting seismic data. The presence of a structural style of this type provides a new concept for hydrocarbon exploration in the area. Reservoir sandstones of the Abu Madi, Sidi Salem, and Moghra Formations are interpreted as sediment gravity flow deposits whose distribution is strongly influenced by syndepositional tectonics. This interpretation, supported by microfossil assemblages, provides important constraints for both reservoir modeling and further exploration.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  16. Clay mineralogy indicates the living environment of the terminal Miocene hominoid of the Zhaotong Basin, Yunnan, China

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Guo, Z.; Deng, C.; Ji, X.; Wu, H.; Paterson, G. A.; Lin, C.; Li, Q.; Ling, B.; Zhu, R.

    2015-12-01

    Global and regional environmental changes have profoundly influenced the evolutionary processes of hominoid primates, particularly during the mid to late Miocene. Recently, a new fossil hominoid was discovered in the Shiutangba (STB) section of the Zhaotong Basin in Yunnan on the southeast margin of the Tibetan Plateau, and was assigned to the species of Lufengpithecus cf. lufengensis with the age of ~6.2 Ma, the terminal Miocene. To understand the relationship between paleoclimate and hominoid evolution, here we present sedimentary, clay mineralogy and geochemical proxies for the 16 m thick late Miocene sedimentary sequence (ca. 6.7-6.0 Ma) from the STB section. Our results show that Lufengpithecus cf. lufengensis lived in a mildly warm and humid climate in a lacustrine or swamp environment rather than hot and humid conditions. A comprehensive comparison among mid to late Miocene records from Yunnan hominoid sites, Siwalik and tropical Africa indicates that warm and humid ecological shifts in South and Southeast Asia are much later than tropical Africa. The presence of the Tibetan plateau may have influenced regional climatic conditions, and the warm and humid condition in the southern China (and perhaps Southeast Asia in general) offered an important refuge for hominoids.

  17. Reappraisal of the relationship between the northern Nevada rift and Miocene extension in the northern Basin and Range Province

    USGS Publications Warehouse

    Colgan, Joseph P.

    2013-01-01

    The northern Nevada rift is a prominent mafic dike swarm and magnetic anomaly in north-central Nevada inferred to record the Middle Miocene (16.5-15.0 Ma) extension direction in the northern Basin and Range province in the western United States. From the 245°-250° rift direction, Basin and Range extension is inferred to have shifted 45° clockwise to a modern direction of 290°-300° during the late Miocene. The region surrounding the northern Nevada rift was actively extending while the rift formed, and these domains are all characterized by extension oriented 280°-300°. This direction is distinctly different from the rift direction and nearly identical to the modern Basin and Range direction. Although the rate, structural style, and distribution of Basin and Range extension appear to have undergone a significant change in the late Miocene (ca. 10 Ma), the overall spreading direction does not. Middle Miocene extension was directed perpendicular to the axis of the thickest crust formed during Mesozoic shortening and this orientation may reflect gravitational collapse of this thick crust. Orientation of northern Nevada rift dikes may reflect a short-lived regional stress field related to the onset of Yellowstone hotspot volcanism.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  19. Geometry-Lithology-Origin: Solving the mystery of the Late Miocene mounded features below Lake Balaton

    NASA Astrophysics Data System (ADS)

    Visnovitz, Ferenc; Horváth, Ferenc; Surányi, Gergely

    2014-05-01

    The Department of Geophysics and Space Sciences of Eötvös University has carried out single- and multichannel water seismic surveys at the Lake Balaton since 1993. The dense grid of 2D profiles offers a high resolution image of the Late Miocene sedimentary strata (Tihany, Somló and Szák Formations) up to a thickness of 200 meters below the lake. These strata can be divided into smaller sedimentary units by numerous parasequence boundaries (Sztanó&Magyar, 2007). In one of these parasequence interesting, high amplitude mounded features have been observed that follow a seismic horizon over large area. It means that these features indicate a Late Miocene regional event. In terms of their shape these mounds are few tens of meters wide, several tens to a hundreds of meters long and few meters high. Their geometry and inner structure were mapped from 2D segments that were used for 3D reconstructions. The shape and stratigraphic position of these features have inspired Sacchi and Horvath (1999) to interpret them as the subsurface equivalent of the fresh-water siliceous-limestone mounds exposed on the Tihany Peninsula. They held these mounds as an evidence of dryland conditions in the time period of the formation of a Late Miocene erosional surface (PAN-2) that they regarded as a 3rd order sequence boundary. In addition to this so called "travertine" concept another explanation was also formulated as the mounds are the product of sedimentary failures e.g. slumps or water escape. To solve the problem an offshore drilling with a total depth of 19 meters was accomplished in October 2013 to sample one of these mounds and determine their origin. The well has not crossed any travertine body, instead alternating layers of clay-silt and very fine sand - without any convincing sign of fluid escape structures - were found in the core (typical lithology of the Tihany Formation). 3D structural analysis of the mounds revealed spherical organization composing bodies that are

  20. Latest Oligocene through early middle Miocene diatom biostratigraphy of the eastern tropical Pacific

    USGS Publications Warehouse

    Barron, J.A.

    1983-01-01

    Study of DSDP Sites 71, 77, and 495 has allowed the development of a refined diatom biostratigraphy for the latest Oligocene through early middle Miocene of the eastern tropical Pacific which is well correlated to the low-latitude zonations for planktonic foraminifers, coccoliths, and radiolarians. Six zones and 7 subzones are proposed, and correlation with high-latitude diatoms zonations for the North Pacific, the Norwegian Sea, and the Southern Ocean is suggested by the discovery of selected diatoms in these tropical sediments which were previously thought to be restricted to high latitudes. Six new species and one new variety of diatoms which are stratigraphically useful are proposed: Actinocyclus hajosiae, n. sp., A. radionovae, n. sp., Coscinodiscus blysmos, n. sp., C. praenodulifer, n. sp., Craspedodiscus rydei, n. sp., Thalassiosira bukryi, n. sp., and Coscinodiscus lewisianus var. robustus n. var. ?? 1983.

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

    NASA Astrophysics Data System (ADS)

    Ganjoo, R. K.; Shaker, Som

    2007-03-01

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

  2. The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina

    PubMed Central

    Chatterjee, Sankar; Templin, R. Jack; Campbell, Kenneth E.

    2007-01-01

    We calculate the flight performance of the gigantic volant bird Argentavis magnificens from the upper Miocene (≈6 million years ago) of Argentina using a computer simulation model. Argentavis was probably too large (mass ≈70 kg) to be capable of continuous flapping flight or standing takeoff under its own muscle power. Like extant condors and vultures, Argentavis would have extracted energy from the atmosphere for flight, relying on thermals present on the Argentinean pampas to provide power for soaring, and it probably used slope soaring over the windward slopes of the Andes. It was an excellent glider, with a gliding angle close to 3° and a cruising speed of 67 kph. Argentavis could take off by running downhill, or by launching from a perch to pick up flight speed. Other means of takeoff remain problematic. PMID:17609382

  3. The fossil land and freshwater snails of Gündlkofen (Middle Miocene, Germany).

    PubMed

    Salvador, Rodrigo B

    2014-01-01

    The molluscan fauna from the Middle Miocene (MN 5-6) fossil site of Gündlkofen in southern Germany was first reported by Gall (1980: Mitt. Bayer. Staatssaml. Paläont. hist. Geol., 20, 51-77). He listed 34 continental gastropod species, which were neither figured nor properly described in many cases. Here a revision of his identifications is presented, with a full description of the material and illustration of the best preserved specimens. Following this revision, 20 species are listed for Gündlkofen. Unfortunately, part of the original material was missing and the record of a few species could not be confirmed. The depositional environment seems to have been a temporary water body, like an oxbow lake, surrounded by a humid and warm forest and scrubland. PMID:24872183

  4. Hyaenidae (Carnivora) from the late Miocene of Toros-Menalla, Chad

    NASA Astrophysics Data System (ADS)

    Bonis, Louis de; Peigné, Stéphane; Guy, Franck; Mackaye, Hassane Taisso; Likius, Andossa; Vignaud, Patrick; Brunet, Michel

    2010-10-01

    The late Miocene Hyaenidae of Toros-Menalla (Chad) belong to four different middle or large body size taxa. The large Chasmaporthetes was a hunting predator probably adapted to open environments. The middle sized Hyaenictitherium minimum was the most abundant hyenid; it probably hunted in packs and, with a dentition far less specialized for bone-cracking than that of extant hyenas, occupied an ecological niche close to that of some extant canids. The wear on the teeth of the middle sized Belbus displays a pattern that could indicate a carcass consumer. The last hyenid, a new genus, was probably adapted to bone-cracking with a major horizontal wear of the premolars and a relatively shallow but robust mandible. Chasmaporthetes did survive until the Pleistocene but the other taxa disappeared during the Pliocene when replaced by the canids and modern hyenids.

  5. Remnants of an ancient forest provide ecological context for Early Miocene fossil apes.

    PubMed

    Michel, Lauren A; Peppe, Daniel J; Lutz, James A; Driese, Steven G; Dunsworth, Holly M; Harcourt-Smith, William E H; Horner, William H; Lehmann, Thomas; Nightingale, Sheila; McNulty, Kieran P

    2014-01-01

    The lineage of apes and humans (Hominoidea) evolved and radiated across Afro-Arabia in the early Neogene during a time of global climatic changes and ongoing tectonic processes that formed the East African Rift. These changes probably created highly variable environments and introduced selective pressures influencing the diversification of early apes. However, interpreting the connection between environmental dynamics and adaptive evolution is hampered by difficulties in locating taxa within specific ecological contexts: time-averaged or reworked deposits may not faithfully represent individual palaeohabitats. Here we present multiproxy evidence from Early Miocene deposits on Rusinga Island, Kenya, which directly ties the early ape Proconsul to a widespread, dense, multistoried, closed-canopy tropical seasonal forest set in a warm and relatively wet, local climate. These results underscore the importance of forested environments in the evolution of early apes.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  7. Evidence for sediment fan deposition on outer Texas Shelf during Miocene Eustatic Sea level highstands

    SciTech Connect

    Riese, W.C.; Olson, R.S.; Rosen, R.N.

    1988-01-01

    Four types of data were reviewed in an attempt to clearly define the environments of deposition for reservoir sands in the Matagorda 668 field; well log curve shapes, seismic amplitude responses, micropaleontology, and thin section sedimentary petrology. All four lines of evidence support the interpretation that these lower Miocene sands were deposited as fan complexes. The sands exhibit three distinctive curve forms: coarsening upward, fining upward, and cylindrical-serrate. These represent respectively fringe settings around the perimeter of the fan where deposition from turbid flow dominates, proximal fan settings where settling from suspension is the more dominant process, and a collection of environments in medial settings intermediate between the two end members just described.

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

    PubMed

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

    2014-01-01

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

  9. European Miocene hominids and the origin of the African ape and human clade.

    PubMed

    Begun, David R; Nargolwalla, Mariam C; Kordos, László

    2012-01-01

    In 1871, Darwin famously opined, "In each great region of the world the living mammals are closely related to the extinct species of the same region. It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere." Although this quote is frequently recalled today, Darwin's next line is rarely acknowledged: "But it is useless to speculate on this subject, for an ape nearly as large as a man, namely the Dryopithecus of Lartet, which was closely allied to the anthropomorphous Hylobates, existed in Europe during the Upper Miocene period; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale."

  10. Remnants of an ancient forest provide ecological context for Early Miocene fossil apes.

    PubMed

    Michel, Lauren A; Peppe, Daniel J; Lutz, James A; Driese, Steven G; Dunsworth, Holly M; Harcourt-Smith, William E H; Horner, William H; Lehmann, Thomas; Nightingale, Sheila; McNulty, Kieran P

    2014-01-01

    The lineage of apes and humans (Hominoidea) evolved and radiated across Afro-Arabia in the early Neogene during a time of global climatic changes and ongoing tectonic processes that formed the East African Rift. These changes probably created highly variable environments and introduced selective pressures influencing the diversification of early apes. However, interpreting the connection between environmental dynamics and adaptive evolution is hampered by difficulties in locating taxa within specific ecological contexts: time-averaged or reworked deposits may not faithfully represent individual palaeohabitats. Here we present multiproxy evidence from Early Miocene deposits on Rusinga Island, Kenya, which directly ties the early ape Proconsul to a widespread, dense, multistoried, closed-canopy tropical seasonal forest set in a warm and relatively wet, local climate. These results underscore the importance of forested environments in the evolution of early apes. PMID:24549336

  11. Careful climbing in the Miocene: the forelimbs of Ardipithecus ramidus and humans are primitive.

    PubMed

    Lovejoy, C Owen; Simpson, Scott W; White, Tim D; Asfaw, Berhane; Suwa, Gen

    2009-10-01

    The Ardipithecus ramidus hand and wrist exhibit none of the derived mechanisms that restrict motion in extant great apes and are reminiscent of those of Miocene apes, such as Proconsul. The capitate head is more palmar than in all other known hominoids, permitting extreme midcarpal dorsiflexion. Ar. ramidus and all later hominids lack the carpometacarpal articular and ligamentous specializations of extant apes. Manual proportions are unlike those of any extant ape. Metacarpals 2 through 5 are relatively short, lacking any morphological traits associable with knuckle-walking. Humeral and ulnar characters are primitive and like those of later hominids. The Ar. ramidus forelimb complex implies palmigrady during bridging and careful climbing and exhibits none of the adaptations to vertical climbing, forelimb suspension, and knuckle-walking that are seen in extant African apes.

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

    PubMed

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

    2016-01-01

    Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone ɛp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity. PMID:26762469

  13. European Miocene hominids and the origin of the African ape and human clade.

    PubMed

    Begun, David R; Nargolwalla, Mariam C; Kordos, László

    2012-01-01

    In 1871, Darwin famously opined, "In each great region of the world the living mammals are closely related to the extinct species of the same region. It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere." Although this quote is frequently recalled today, Darwin's next line is rarely acknowledged: "But it is useless to speculate on this subject, for an ape nearly as large as a man, namely the Dryopithecus of Lartet, which was closely allied to the anthropomorphous Hylobates, existed in Europe during the Upper Miocene period; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale." PMID:22307721

  14. Miocene Lonchocarpus (Papilionoideae) in San Esteban Tizatlán, Tlaxcala, Mexico

    NASA Astrophysics Data System (ADS)

    Hernández-Damián, Ana Lilia; Calvillo-Canadell, Laura; Cevallos-Ferriz, Sergio R. S.; Sousa, Mario

    2016-03-01

    New leaflets from San Esteban Tizatlán, Tlaxcala, Mexico, are described and identified based on their leaf architecture. They have elliptic leaflets with pulvinate petiolule, entire margin, convex apex and base, well developed primary and craspedodromous secondary venation, with decurrent secondary veins with fused the mid-vein, a pair of obtuse basal veins, weak intersecundary veins, mixed percurrent tertiary venation dominated by the opposite type with sinuous course, alternate percurrent fourth-order venation, regular reticulate with few non ramified veinlets. All these characteristics are closely compared with members of sections Obtusifolii and Standleyi of Lonchocarpus (Leguminosae, Papillionoideae, Millettieae), but the mosaic of characters found in the fossil material granted recognition of a new species Lonchocarpus miocenicus sp. nov. This new record of Lonchocarpus from central Mexico further supports the presence of an evergreen tropical forest during the Miocene in the area, a plant community that developed from the Boreotropical Flora and contributed latter to the Neotropical Flora.

  15. Paleomagnetic data bearing on style of Miocene deformation in the Lake Mead area, Southern Nevada

    USGS Publications Warehouse

    Wawrzyniec, T.F.; Geissman, J.W.; Anderson, R.E.; Harlan, S.S.; Faulds, J.

    2001-01-01

    Paleomagnetic and structural data from intermediate to mafic composition lava flows and related dikes in all major blocks of the late Miocene Hamblin-Cleopatra Volcano, which was structurally dismembered during the development of the Lake Mead Fault System (LMFS), provide limits on the magnitude and sense of tilting and vertical axis rotation of crust during extension of this part of the Basin and Range province. Sinistral separation along the fault system dissected the volcano into three major blocks. The eastern, Cleopatra Lobe of the volcano is structurally the most intact section of the volcano. Normal and reverse polarity data from paleomagnetic sites collected along traverses in the Cleopatra Lobe yield an in situ grand mean of Declination (D) = 339??, Inclination (I) = +54??, ??95 = 3.1??, k = 27.2, N = 81 sites. The rocks of the central core of the volcano yield an in situ grand mean of D = 3??, I = + 59??, ??95 = 6.8??, k = 42.5, N = 11 sites (six normal, five reverse polarity). Sites collected within the western Hamblin Lobe of the volcano are exclusively of reverse polarity and yield an overall in situ mean of D = 168??, I = -58??, ??95 = 6.5??. k = 28.9, N = 18 sites. Interpretation of the paleomagnetic data in the context of the structural history of the volcano and surrounding area, considers the possibility of two different types of structural corrections. A stratigraphic tilt correction involves restoring flows to the horizontal using the present strike. This correction assumes no initial, possibly radial, dip of flows of the volcano and is considered invalid. A structural tilt correction to the data assumes that dikes of the radiating swarm associated with the volcano were originally vertical and results in block mean directions of D = 9??, I = +53??, ??95 = 3.1??, k = 27.2, and D = 58??, I = + 78??, ??95 = 6.8, k = 42.5, for the Cleopatra Lobe and the central intrusive core, respectively. The data from the Cleopatra Lobe are slightly discordant

  16. Paleomagnetic data bearing on style of Miocene deformation in the Lake Mead area, southern Nevada

    NASA Astrophysics Data System (ADS)

    Wawrzyniec, Tim F.; Geissman, John W.; Anderson, R. Ernest; Harlan, Steve S.; Faulds, James

    2001-08-01

    Paleomagnetic and structural data from intermediate to mafic composition lava flows and related dikes in all major blocks of the late Miocene Hamblin-Cleopatra Volcano, which was structurally dismembered during the development of the Lake Mead Fault System (LMFS), provide limits on the magnitude and sense of tilting and vertical axis rotation of crust during extension of this part of the Basin and Range province. Sinistral separation along the fault system dissected the volcano into three major blocks. The eastern, Cleopatra Lobe of the volcano is structurally the most intact section of the volcano. Normal and reverse polarity data from paleomagnetic sites collected along traverses in the Cleopatra Lobe yield an in situ grand mean of Declination ( D)=339°, Inclination ( I)=+54°, α95=3.1°, k=27.2, N=81 sites. The rocks of the central core of the volcano yield an in situ grand mean of D=3°, I=+59°, α95=6.8°, k=42.5, N=11 sites (six normal, five reverse polarity). Sites collected within the western Hamblin Lobe of the volcano are exclusively of reverse polarity and yield an overall in situ mean of D=168°, I=-58°, α95=6.5°, k=28.9, N=18 sites. Interpretation of the paleomagnetic data in the context of the structural history of the volcano and surrounding area, considers the possibility of two different types of structural corrections. A stratigraphic tilt correction involves restoring flows to the horizontal using the present strike. This correction assumes no initial, possibly radial, dip of flows of the volcano and is considered invalid. A structural tilt correction to the data assumes that dikes of the radiating swarm associated with the volcano were originally vertical and results in block mean directions of D=9°, I=+53°, α95=3.1°, k=27.2, and D=58°, I=+78°, α95=6.8°, k=42.5, for the Cleopatra Lobe and the central intrusive core, respectively. The data from the Cleopatra Lobe are slightly discordant, in a clockwise sense, from expected middle

  17. HELIOTHERMAL LAKE MODEL OF BORATE DEPOSITION IN THE MIOCENE FURNACE CREEK FORMATION, DEATH VALLEY REGION, CALIFORNIA.

    USGS Publications Warehouse

    Barker, Charles E.; Barker, James M.; ,

    1988-01-01

    Heliothermal lakes are density-stratified with shallow submerged margins surrounding areally restricted deep pool(s) containing a dense brine overlain by a much less dense brine. The reflective brine interface allows solar energy to be trapped in the dense brine which may warm to over 90 degree C. Carbonate precipitated from the dense brine is the typical sediment produced in warm deep pool. Miocene borate deposits of the Death Valley region are typically contained within areally limited carbonate-rich pods that interfinger with a finely interlaminated (varve-like) mudstone and limestone. Primary borates there are predominately either Na-Ca borates or Ca-borates. This bimodal evaporite assemblage suggests that brine chemistries and (or) crystallization paths varied significantly in temporally and spatially related portions of this apparently continuous lacustrine deposit.

  18. A new Late Miocene chondrichthyan assemblage from the Chagres Formation, Panama

    NASA Astrophysics Data System (ADS)

    Carrillo-Briceño, Jorge D.; De Gracia, Carlos; Pimiento, Catalina; Aguilera, Orangel A.; Kindlimann, René; Santamarina, Patricio; Jaramillo, Carlos

    2015-07-01

    The lLate Miocene Chagres Formation from northern Panama contains the youngest outcrops of the Panama Canal Basin. Here we report two chondrichthyan assemblages that include 30 taxa from both the Rio Indio and Chagres Sandstone Members of the Chagres Formation. We report 18 new fossil records for Panama and four for tropical America, constituting the most diverse chondrichthyan association for the Cenozoic of Panama. We performed a paleobathymetry analysis based on the modern water depth preference of extant chondrichthyan taxa. The assemblage from the Rio Indio Member is characterized by taxa with neritic affinities, suggesting depths <100 m, whereas the assemblage from the Chagres Sandstone Member is dominated by taxa with oceanic affinities, suggesting 200-300 m water depths. The Chagres Sandstone Member could have accumulated at the edge of a platform-upper slope, bordered by a deep oceanic margin.

  19. Paleoenvironmental reconstruction of the Early to Middle Miocene Central Paratethys using stable isotopes from bryozoan skeletons

    NASA Astrophysics Data System (ADS)

    Key, Marcus M.; Zágoršek, Kamil; Patterson, William P.

    2013-01-01

    Stable carbon and oxygen isotope values from single bryozoan colonies were used to reconstruct the paleoenvironments of the Early to Middle Miocene (Ottnangian to Badenian) sediments of the Central Paratethys. This approach utilizes a locally abundant allochem while avoiding matrix and multiple allochem contamination from bulk rock samples. Bryozoan colonies (and a few foraminifera and rock matrix samples) from 14 localities yielded 399 carbon and oxygen isotope values. Data from six of the localities (15 % of the total number of samples) were interpreted as having been diagenetically altered and were rejected. The remaining data indicate a primarily localized upwelling signal with lesser variation caused by global climatic and regional tectonic forcing of sea level, salinity, and temperature. Paleotemperatures were calculated to range from 12 to 21 °C. Despite potential taxonomic and diagenetic problems, bryozoan colonies are a powerful, underutilized source of paleoenvironmental carbon and oxygen isotope data.

  20. A New Miocene-Divergent Lineage of Old World Racer Snake from India

    PubMed Central

    Vyas, Raju; Maheta, Jaydeep

    2016-01-01

    A distinctive early Miocene-divergent lineage of Old world racer snakes is described as a new genus and species based on three specimens collected from the western Indian state of Gujarat. Wallaceophis gen. et. gujaratenesis sp. nov. is a members of a clade of old world racers. The monotypic genus represents a distinct lineage among old world racers is recovered as a sister taxa to Lytorhynchus based on ~3047bp of combined nuclear (cmos) and mitochondrial molecular data (cytb, ND4, 12s, 16s). The snake is distinct morphologically in having a unique dorsal scale reduction formula not reported from any known colubrid snake genus. Uncorrected pairwise sequence divergence for nuclear gene cmos between Wallaceophis gen. et. gujaratenesis sp. nov. other members of the clade containing old world racers and whip snake is 21–36%. PMID:26934509

  1. Levoglucosan and other cellulose markers in pyrolysates of Miocene lignites: geochemical and environmental implications

    SciTech Connect

    Daniele Fabbri; Leszek Marynowski; Monika J. Fabianska; Michal Zaton; Bernd R.T. Simoneit

    2008-04-15

    Using the pyrolysis-gas chromatography-mass spectrometry and off-line pyrolysis/silylation methods for lignites from three Miocene brown coal basins of Poland resulted in the characterization of many organic compounds, including dominant cellulose degradation products such as levoglucosan, 1,6-anhydro-{beta}-D-glucofuranose, and 1,4:3,6-dianhydroglucopyranose. Levoglucosan is a general source-specific tracer for wood smoke in the atmosphere and recent sediments. The presence of unusually high levels of this compound in brown coal pyrolysates suggests that a portion of this compound concentration in some airsheds may originate from lignite combustion. On the other hand, nonglucose anhydrosaccharides, in particular, mannosan and galactosan, typical of hemicellulose, are not detected in those lignite pyrolysates investigated. This indicates that mannosan and galactosan are better specific tracers for combustion of contemporary biomass in those regions where the utilization of brown coals containing fossilized cellulose is important. 7 refs., 2 figs., 3 tabs.

  2. A Miocene river in northern Arizona and its implications for the Colorado River and Grand Canyon

    USGS Publications Warehouse

    Lucchitta, I.; Holm, R.F.; Lucchitta, B.K.

    2011-01-01

    The southwesterly course of the pre–late Miocene Crooked Ridge River can be traced continuously for 48 km and discontinuously for 91 km in northern Arizona. It is visible today in inverted relief. Pebbles in the river gravel came from at least as far northeast as the San Juan Mountains. The river valley was carved out of easily eroded Jurassic and Cretaceous rocks, whose debris overloaded the river with abundant detritus, possibly steepening the gradient. After the river became inactive, the regional drainage network was rearranged twice, and the Four Corners region was lowered by erosion 1–2 km. The river provides constraints on the history of the Colorado River and Grand Canyon; its continuation into lakes in Arizona or Utah is unlikely, as is integration of the Colorado River through Grand Canyon by lake spillover. The downstream course of the river was probably across the Kaibab Arch in a valley roughly coincident with the present eastern Grand Canyon.

  3. The Early Miocene Cape Melville Formation fossil assemblage and the evolution of modern Antarctic marine communities

    NASA Astrophysics Data System (ADS)

    Whittle, Rowan J.; Quaglio, Fernanda; Griffiths, Huw J.; Linse, Katrin; Crame, J. Alistair

    2014-01-01

    The fossil community from the Early Miocene Cape Melville Formation (King George Island, Antarctica) does not show the archaic retrograde nature of modern Antarctic marine communities, despite evidence, such as the presence of dropstones, diamictites and striated rocks, that it was deposited in a glacial environment. Unlike modern Antarctic settings, and the upper units of the Eocene La Meseta Formation on Seymour Island, Antarctica, which are 10 million years older, the Cape Melville Formation community is not dominated by sessile suspension feeding ophiuroids, crinoids or brachiopods. Instead, it is dominated by infaunal bivalves, with a significant component of decapods, similar to present day South American settings. It is possible that the archaic retrograde structure of the modern community did not fully evolve until relatively recently, maybe due to factors such as further cooling and isolation of the continent leading to glaciations, which resulted in a loss of shallow shelf habitats.

  4. Spirochete and protist symbionts of a termite (Mastotermes electrodominicus) in Miocene amber.

    PubMed

    Wier, Andrew; Dolan, Michael; Grimaldi, David; Guerrero, Ricardo; Wagensberg, Jorge; Margulis, Lynn

    2002-02-01

    Extraordinary preservation in amber of the Miocene termite Mastotermes electrodominicus has led to the discovery of fossil symbiotic microbes. Spirochete bacteria and wood-digesting protists were identified in the intestinal tissue of the insect. Fossil wood (xylem: developing vessel-element cells, fibers, pit connections), protists (most likely xylophagic amitochondriates), an endospore (probably of the filamentous intestinal bacterium Arthromitus = Bacillus), and large spirochetes were seen in thin section by light and transmission electron microscopy. The intestinal microbiota of the living termite Mastotermes darwiniensis, a genus now restricted to northern Australia, markedly resembles that preserved in amber. This is a direct observation of a 20-million-year-old xylophagus termite fossil microbial community.

  5. The fossil land and freshwater snails of Gündlkofen (Middle Miocene, Germany).

    PubMed

    Salvador, Rodrigo B

    2014-04-03

    The molluscan fauna from the Middle Miocene (MN 5-6) fossil site of Gündlkofen in southern Germany was first reported by Gall (1980: Mitt. Bayer. Staatssaml. Paläont. hist. Geol., 20, 51-77). He listed 34 continental gastropod species, which were neither figured nor properly described in many cases. Here a revision of his identifications is presented, with a full description of the material and illustration of the best preserved specimens. Following this revision, 20 species are listed for Gündlkofen. Unfortunately, part of the original material was missing and the record of a few species could not be confirmed. The depositional environment seems to have been a temporary water body, like an oxbow lake, surrounded by a humid and warm forest and scrubland.

  6. A diverse assemblage of fossil hardwood from the Upper Tertiary (Miocene?) of the Arauco Peninsula, Chile

    NASA Astrophysics Data System (ADS)

    Schöning, Meike; Bandel, Klaus

    2004-09-01

    Silicified woods of 10 dicotyledonous tree families of probably Miocene age from the Arauco Peninsula, central Chile are described and classified according to their anatomy. The diversity is surprisingly high, in that of the 19 samples analyzed, virtually every one could belong to a different species of tree or shrub. Almost all species document a damp climate, and most have related species living in the central zone of modern Chile. The samples were collected in a narrow zone on Punta El Fraile, west of the town of Arauco. The following families are based on woods from the Arauco Peninsula: Anacardiaceae, Boraginaceae, Euphorbiaceae, Fagaceae, Lauraceae, Leguminosae, Monimiaceae, the first report of fossil Myristicaceae, Myrtaceae, and Proteaceae. Their diagenetic history is connected to tuffaceous material and calcareous concretions.

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

    PubMed

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

    2016-01-14

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

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

    NASA Astrophysics Data System (ADS)

    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 (<1 million years) this concept looses its practicability and has to be replaced by a taxon-range-zonation. To solve this problem a higher number of independently dated small-mammal localities are needed. This is especially crucial for the late Middle to earliest Late Miocene, for which vertebrate faunas in the (Central-)Paratethyan area rare. Recently, a new vertebrate fauna was discovered at the locality Gratkorn (clay pit St. Stefan) just beyond the northwestern margin of the Styrian Basin (Gratkorn Basin; 10 km NW Graz; 15°20'55"E/47°08'15"N). The fauna originates from a c. 0.5 m thick hydromorphic paleosol, underlain by fluvial sands and gravels and topped by c. 15 m thick limnic pelites (Gross, 2008). Sedimentological data as well as the gastropod (Harzhauser et al., 2008) and vertebrate faunas point to a highly structured, more or less vegetated alluvial fan/braided river landscape. Active and abandoned fluvial channels, moist floodplain-soils and ephemeral ponds but also nearby dryer open areas and limestone screes of the up-lifting Palaeozoic basement offered a wide range of habitats. The occurrence of xero- and thermophile terrestrial gastropods and ectothermic vertebrates correspond well with the late Middle/early Late Miocene dry-spell in Central Europe (Böhme et al., 2008). Furthermore, an overall semiarid climate is supported by the development of a calcrete horizon c. 0.6 m below the fossiliferous horizon. The vertebrate remains are irregularly distributed throughout the

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

    PubMed Central

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

    2014-01-01

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

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

    USGS Publications Warehouse

    Colgan, Joseph P.; Henry, Christopher D.

    2009-01-01

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

  11. The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina.

    PubMed

    Chatterjee, Sankar; Templin, R Jack; Campbell, Kenneth E

    2007-07-24

    We calculate the flight performance of the gigantic volant bird Argentavis magnificens from the upper Miocene ( approximately 6 million years ago) of Argentina using a computer simulation model. Argentavis was probably too large (mass approximately 70 kg) to be capable of continuous flapping flight or standing takeoff under its own muscle power. Like extant condors and vultures, Argentavis would have extracted energy from the atmosphere for flight, relying on thermals present on the Argentinean pampas to provide power for soaring, and it probably used slope soaring over the windward slopes of the Andes. It was an excellent glider, with a gliding angle close to 3 degrees and a cruising speed of 67 kph. Argentavis could take off by running downhill, or by launching from a perch to pick up flight speed. Other means of takeoff remain problematic.

  12. Tephra Deposits in Lake Mead Miocene Sediments: Characteristics, Chronology, and Sources

    NASA Astrophysics Data System (ADS)

    Dunbar, N. W.; McIntosh, W. C.; Umhoefer, P. J.; Lamb, M. A.; Hickson, T.

    2013-12-01

    The Lake Mead extensional domain, in the east central Basin and Range Province, contains Miocene basin sediments that have undergone complex faulting and deformation. A rich tephra record in the basin sediments provides a chronological and correlation framework that can help understand the depositional and deformational processes during Miocene and post-Miocene time. The tephra layers, up to 10s of cm thick, range from white deposits containing glassy shards to bright green layers in which all original glass has been altered to the zeolite mordenite. The tephra layers range from aphyric to extremely crystal rich. Many appear to be primary ashfall deposits based on depositional geometry, uniform crystal size, and good preservation of glass or relict glass shard structures. However, some layers show evidence of reworking as evidenced by variable crystal size, and the presence of plutonic feldspar and rock fragments. Electron microprobe analyses of preserved glass reveal that compositions of almost all of the tephra layers are high silica rhyolite, typically with FeO and CaO contents of 1wt% or lower. Where present, the glass in the tephra layers is invariably hydrated, consistent with their age, but although the alkali concentrations in the glass are likely to have been modified by the hydration process, other elements, particularly Fe, Ca, Ti, and Cl appear to yield robust concentrations. The compositions of individual layers with respect to these elements are very homogeneous, based on analysis of 20-30 glass shards per sample, and can be used to correlate individual tephra layers between different parts of the sedimentary basin, although a number of layers have very similar compositions. Some higher Fe rhyolites/dacites (up to 4 wt.% FeO) are also observed. Crystal-bearing tephra layers contain some combination of quartz, one or two feldspars (typically a chemically uniform sanidine and a range of plagioclase compositions), biotite, amphibole, and magnetite

  13. Spirochete and protist symbionts of a termite (Mastotermes electrodominicus) in Miocene amber

    PubMed Central

    Wier, Andrew; Dolan, Michael; Grimaldi, David; Guerrero, Ricardo; Wagensberg, Jorge; Margulis, Lynn

    2002-01-01

    Extraordinary preservation in amber of the Miocene termite Mastotermes electrodominicus has led to the discovery of fossil symbiotic microbes. Spirochete bacteria and wood-digesting protists were identified in the intestinal tissue of the insect. Fossil wood (xylem: developing vessel-element cells, fibers, pit connections), protists (most likely xylophagic amitochondriates), an endospore (probably of the filamentous intestinal bacterium Arthromitus = Bacillus), and large spirochetes were seen in thin section by light and transmission electron microscopy. The intestinal microbiota of the living termite Mastotermes darwiniensis, a genus now restricted to northern Australia, markedly resembles that preserved in amber. This is a direct observation of a 20-million-year-old xylophagus termite fossil microbial community. PMID:11818534

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

    PubMed Central

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

    2016-01-01

    Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone ɛp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity. PMID:26762469

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

    PubMed

    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. PMID:17816684

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

    PubMed

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

    2013-01-01

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

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

    PubMed Central

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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

  19. Oligocene-Miocene deformational and depositional history of the Andean hinterland basin in the northern Altiplano plateau, southern Peru

    NASA Astrophysics Data System (ADS)

    Perez, Nicholas D.; Horton, Brian K.

    2014-09-01

    Cenozoic basin fill of the northern Altiplano plateau records the tectonic development of the flanking Western Cordillera magmatic arc and Eastern Cordillera fold-thrust belt. The Ayaviri hinterland basin of southern Peru contains a ~2300 m thick succession of fluvial sandstones and overbank siltstones (upper Oligocene Puno Group and lower Miocene lower Tinajani Formation) capped by ~400 m of alluvial fan conglomerates (middle Miocene upper Tinajani Formation). New U-Pb zircon chronostratigraphic constraints from ~30 to 15 Ma yield sediment accumulation rates of 110-660 m/Myr. Newly dated growth strata highlight the genetic role played by thrust displacement in basin evolution. A several phase accumulation history derived from chronostratigraphic, provenance, and structural data reveals Oligocene basin filling by fluvial sand and mud that changes provenance from Western Cordillera Mesozoic-Cenozoic volcanic rocks to Paleozoic-Mesozoic Eastern Cordillera sedimentary rocks driven by deformation along the southwest directed, northeastern basin margin Ayaviri thrust at 28-26 Ma. Continued early Miocene fluvial deposition was sourced solely from the Eastern Cordillera. An abrupt middle Miocene shift to coarse alluvial fan deposition sourced from the Western Cordillera was driven by out-of-sequence deformation along the northeast directed, southwestern basin margin Pasani thrust at 18-16 Ma. This northern Altiplano out-of-sequence deformation was coincident with increased Eastern and Western Cordillera exhumation and thrusting and may be symptomatic of changes in critical wedge dynamics. The overall record of basin sedimentation and syndepositional fold-thrust deformation emphasizes the role of regional shortening in governing crustal thickening and basin evolution in the central Andes during the Oligocene to Miocene.

  20. Apatite fission track evidence for Miocene extensional faulting east-central Nevada, northern Basin and Range province

    SciTech Connect

    Miller, E.L.; Dumitru, T.A. . Geology Dept.); Gans, P.B. . Geological Sciences Dept.); Brown, R.W. . Geology Dept.)

    1993-04-01

    Apatite fission track ages indicates that a large component of motion along many of the present range-bounding faults occurred in the Early to Middle Miocene, tilting and uplifting rocks through the apatite annealing zone (120--60 C) between 18--13 Ma (n = 20, Deep Creeks), 18--15 Ma (northern Snake Range, n = 20), 25--17 Ma (n = 7, southern Snake Range), 24--15 Ma (Egan Range, n = 6), 23--18 Ma (Kern Mts., n = 2) and 28--16 ma (Schell Creek Range, n = 2). Long track length distributions indicate rapid cooling through the 120--60 C interval followed by residence at low, near surface temperatures. The data set also indicates that the combined Deep Creek-Kern Mountains-northern and southern Snake Range constitutes a single coherent footwall crustal block beneath a > 150 km-long system of east-dipping Miocene faults which includes at least the eastern portions of faults that have been mapped as the Snake Range decollement (NSRD). Conglomerates deposited in hanging wall basins along this fault system contain metamorphic and granitic boulders whose FT ages are coeval with footwall unroofing. The deposits themselves are now known to be younger than previously reported (Oligocene) as ages from boulders are Miocene. The thick (> 2 km) sequences of synorogenic conglomerate indicates rapid unroofing; large slide blocks attest to generation of steep, fault-controlled topography. Faults that cut this sequence are now known to be younger than 15 Ma. Thus, protracted extensional faulting affected the region, beginning in the Early Oligocene and continuing to the Recent, but a significant part of this extension, including a large component of the slip on the NSRD, was accomplished in the Early to Middle Miocene. Data from this region is compatible with a growing base of apatite fission track data from elsewhere in the northern Basin and Range, which, together with geologic relationships, suggest an important episode of Miocene extension and Basin and Range development.

  1. Integrated biostratigraphy of the upper Oligocene-middle Miocene successions in west central Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Hewaidy, Abdel Galil A.; Farouk, Sherif; Ayyad, Haitham M.

    2014-12-01

    The nannofossil and planktonic foraminiferal biostratigraphy in four upper Oligocene-middle Miocene sections are examined in Nukhul-Sudr area of west central Sinai, Egypt. The integration of calcareous nannofossils and planktonic foraminifera is used to verify the ages and determine the biozones of the upper Oligocene-middle Miocene units in the studied area. This target is important in the light of the great lithofacies changes during the time interval. The detailed examination of the nannofossil and planktonic foraminiferal contents in these sections led to identification of 86 calcareous nannofossil species belonging to 22 genera, 10 families and 3 orders, in addition to 64 planktonic foraminiferal species belonging to 11 genera, 4 families and 2 superfamilies. The identified nannofossil and planktonic foraminiferal assemblages allow to distinguish five calcareous nannofossil biozones and six planktonic foraminiferal biozones. The biostratigraphic integration suggested the Chattian-Aquitanian age for the Nukhul Formation where the Globigerina ciperoensis Zone (P22) and Globigerinoides primordius Zone (M1a) correspond to calcareous nannofossil Sphenolithus ciperoensis Zone (NP25) and Discoaster druggii Zone (NN2), respectively. The Rudeis Formation is assigned to the Burdigalian-Langhian age depending on correspondence of Catpsydrax dissimilis Zone (M2), Globigerinoides bisphericus Zone (M4b) and Praeorbulina sicana Zone (M5) with Discoaster druggii zone (NN2), Sphenolithus belemnos Zone (NN3) and Helicosphaera ampliaperta Zone (NN4). The Somar Formation is found barren ofany microfossils, but it contains index pectens and oysters of Burdigalian age which may be equivalent to the lower part of the Rudeis Formation. The Kareem and Sarbut El-Gamal formations are represented by evaporitic and conglomeratic succession, where no foraminifera or nannofossils are recorded and assigned to the Langhian age according to their stratigraphic position. The Belayim Formation

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Late Oligocene-early Miocene volcanism, faulting, and sedimentation in west-central California

    SciTech Connect

    Stanley, R.G.

    1988-03-01

    Abundant evidence from the rock record indicates that volcanism, active faulting, and sedimentary-basin development were widespread and nearly synchronous in west-central California during the late Oligocene and early Miocene. Volcanic activity occurred about 24-22 Ma at more than 20 eruptive centers in a northwest-trending belt, extending from Point Arena to the Orocopia Mountains. Volcanism was accompanied by marine transgression, rapid bathymetric deepening, and accumulation of thick piles of predominantly marine clastic sediment in the Point Arena, La Honda, San Joaquin, Pescadero-Ano Nuevo, Salinas, Husana-San Luis Obispo, and Cuyama basins, as well as in several other basins presently situated offshore. Concurrent movement along basin-margin normal faults resulted in localized deposition of wedges of very coarse nonmarine and deltaic sediment in the La Honda, Cuyama, Lockwood, Soledad, and Diligencia basins. Also, at about the same time, right-lateral strike-slip faulting apparently caused en enchelon folding in both the Cuyama and San Joaquin basins, and formation of a pull-apart feature in the La Honda basin. Late Oligocene-early Miocene volcanism, faulting, and basin development in west-central California were nearly synchronous over the entire area rather than sequential from south to north, and therefore cannot be explained simply as the effects of the northwestward-migrating Mendocino triple junction. An alternative explanation is that volcanism, faulting, and basin development were caused by an episode of regional extension or transtension (strike-slip with a component of extension) related to a change in plate motions in the circum-Pacific area.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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

    2016-05-12

    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. PMID:27096364

  6. Paleoecologic and biostratigraphic models for pleistocene through miocene foraminiferal assemblages of the Gulf Coast Basin

    SciTech Connect

    Breard, S.Q.; Callender, A.D.; Nault, M.J. )

    1993-09-01

    We have developed operationally oriented paleoecologic models used in hydrocarbon exploration of the Gulf Coast basin for Pleistocene through Miocene foraminifera and an updated, refined biostratigraphic chart. We also present estimated paleoecologic tolerances for major benthic and planktic foraminiferal markers, and discuss a number of rules and problems encountered in oil industry paleoenvironmental reconstruction. Key benthic paleoenvironmental markers for particular depth zones are graphically presented for the Pleistocene through Miocene. Improvements over previous models include greater use of calcareous and arenaceous foraminiferal species not used or recognized in earlier studies. Finer subdivisions of bathyal paleoenvironments are of particular significance due to current Gulf of Mexico deep-water exploration. Operationally, the abyssal environmental is difficult to recognize due to a reliance of faunal abundance to delineate abyssal from bathyal and the lack of abyssal zone markers. A number of genera and species are identified as having changed habitat preference through time. Some forms have moved progressively into deeper water (Ceratobulimina Cyclammina cancellata and Nonion pompiloides). Conversely, the movement of species into progressively shallower occurrences through time (Pullenia bullodies) appears to be less common. The widespread occurrence of known Gulf of Mexico foraminiferal species from countries such as Mexico, Venezuela, Ecuador, Jamaica, Trinidad, and the Dominican Republic, suggest that these; models have direct application to Neogene studies in Central America, South America, the Caribbean, and the U.S. Gulf Coast. We introduce a variety of deep-water benthic marker foraminifera, many for the first time. These taxa help fill gaps for deeper-water sections where standard benthic marker foraminifera do not occur, helping debunk the popular myth that benthic foraminifera are useless as markers in the exploration of deep-water sections.

  7. Miocene to Present Sea Level and the Origin of Modern Rimmed Atoll Morphology

    NASA Astrophysics Data System (ADS)

    Toomey, M.; Perron, J. T.; Raymo, M. E.; Ashton, A. D.

    2014-12-01

    Rising sea-level over the next century will reshape our coastlines and make low-lying islands more vulnerable to extreme events. Atolls could potentially provide unique geologic records from periods of high sea level analogous to those we might experience over the coming centuries. However, sea-level records from atolls have been largely overlooked, in part because the processes that shape coral reef and atoll form are often complex and, in many cases, remain unexplored. Darwin's canonical model, which proposes an evolution from fringing reef to barrier reef to atoll as an ocean island ages and subsides, cannot explain the stratigraphy or morphology of many island reefs. We will present a study that combines a numerical model of reef development with existing stratigraphic records from Pacific atolls. The model, driven by sea level, simulates the evolution of atoll morphology using parameterizations of coral growth, rim derived sediment and in situ production, dissolution, and subsidence. We use it to solve for late-Miocene to present sea level by iteratively changing the ice volume and deep-ocean temperature corrections for converting deep-ocean, benthic, δ18O to sea level and finding the best-fit between the model output and corelog stratigraphy from Enewetak Atoll. We then compare lagoon depths produced by the model for different island sizes and dissolution rates (but the same subsidence and sediment production rates) to an independent dataset of real-world observations from the Marshall, Gilbert and Caroline Island chains. Our model results suggest that a period of sustained low sea level occurred during the late Miocene before rising above present moving into the Pliocene. We propose that it was atoll exposure and enhanced lagoon dissolution during the subsequent sea-level fall since the late Pliocene, ~2.7 Ma - not crustal subsidence, as Darwin's canonical model of atoll evolution presumes - that likely drove the development of modern rimmed atoll

  8. Giant slide in the South Alboran margin: Upper Miocene margin inversion or Messinian sea level fall?

    NASA Astrophysics Data System (ADS)

    Gorini, C.; d'Acremont, E.; El Abbassi, M.; Do Couto, D.; Migeon, S.; Ammar, A.; Estrada, F.; Ercilla, G.; Alonso, B.; Poort, J.; Jabour, H.

    2012-04-01

    A series of submarine slides, from different periods and origin, were identified offshore Morroco using a new seismic reflection database available in the South Alboran Sea. The latest seismic reflection survey, used for this study, was acquired during the Marlboro-1 cruise (July 2011). This high resolution, two dimensional seismic data , provide evidence for a giant submarine landslide (mega-slide) with a volume of 200 km3, an area of 550 km2 and a maximum thickness of 540 m. It extends for over 40 km from the Xauen/Tofino banks at 200 m water depth to the deep basin floor of the Western Alboran Basin. The landslide is located on a steep, tectonically active margin and confined between structural highs. The seismic data allow a detailed imaging of internal structures, erosional headwall and the basal sliding surface of this mass transport deposit (MTD). The landslide is a complex deposit, involving a chaotic matrix, and preserved continuous reflectors evoquing floating giant blocks. The basal sliding surface reveals that significant amounts of seafloor erosion occured that cut into the Upper Miocene sediments. We will discuss the factors triggering the slope failure and the mechanism that caused the weakening. The origin of the mega-slide is the Xauen-Tofino banks bounded by thrust faults whose tectonic activity is recorded since the late Miocene. An acceleration of the uplift and compressional activity is evidenced during the Messinian with an increase of the volume of mass transport at the front of these thrusts. The top of the mega-slide is eroded by the Zanclean (5.33Ma) flooding event and thus occurred before or during the Messinian crisis. This timing correponds in the South Alboran Sea to a peak of tectonic activity and a huge and rapid sea level fall (about 1000m). We propose that both have played a role in triggering the South Alboran mega-slide.

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

    PubMed

    Martinez-Maza, Cayetana; Alberdi, Maria Teresa; Nieto-Diaz, Manuel; Prado, José Luis

    2014-01-01

    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 typical of

  10. Petrography, diagenesis, and reservoir properties of Miocene Reefs, Visayan Islands, Philippines

    SciTech Connect

    Carozzi, A.V.

    1988-01-01

    The Miocene reefs of the volcanic island arcs making up the Visayan Islands, Philippines, consist of an association of corals, red algae, bryozoans, and encrusting foraminifers forming barriers along the edge of narrow shelves. Bioclasts and intraclasts derived from these wave-resistant barriers were shed as frontal aprons of calcirudites and calcarenites that sometimes support pinnacle coralling buildups. These aprons were intersected by tidal-channel calcarenites grading seaward into carbonate turbidite submarine fans that interfingered with deep-water pelagic argillaceous micrites and shales. Lagoons with low energy micritic and pelletoidal muds. although intersected by numerous well-sorted tidal channel calcarenites, displayed an ecologically zoned succession of small buildups that, in a landward direction, were: (1) finger-coral constructed; (2) larger, benthic foraminifer bioaccumulated; (3) small arenaceous foraminifer, gastropod, and red algae bioaccumulated. The shoreface environment consisted of mixed carbonates and andesitic grkaywackes grading landward into mangrove tidal flats and estuaries. Reservoirs were mainly developed in constructed barriers and in immediately adjacent frontal aprons and rear bioclastic carbonates. Many of these high-energy carbonates show interstitial micritic matrix. Porosity (reaching 30%) and permeability (reaching 146 md) result from a locally variable combination of the effects of subaerial exposure introducing secondary porosity by vadose to upper phreatic undersaturated dissolution,followed by extensive burial dissolution. Seals are provided between superposed barriers by andesitic volcaniclastics and basaltic flows. Uplifted Pleistocene reefs of Barbados, West Indies, which are nearly identical to Holocene West Indian reefs are excellent analogs of the Miocene examples except for the lack of active volcanism.

  11. Preserved aragonite cements in Miocene coral reefs: a record of Messinian salinity crises in Mediterranean

    SciTech Connect

    Esteban, M.; Prezbindowski, D.R.

    1985-02-01

    Layers of fibrous aragonite cement up to 2 cm thick, developed on aragonitic corals and micritic cements, occur in outcrops of Miocene coral reefs in western Sicily. These aragonitic fabrics show only minor amounts of corrosion after subaerial exposure for at least 3 m.y. Their preservation is attributed to encasement by subsequent gypsum cements. Although these botryoidal, banded aragonite cements are strontium-rich (7000 ppm) and resemble modern marine examples, they were precipitated in secondarily enlarged pores that formed during erosional episodes. Multiple cycles of enrichment in oxygen and carbon stable isotopes are recorded in the aragonite cement layers. The delta/sup 18/O values of these cycles range from -0.9 to +6.8 per thousand, whereas the delta/sup 13/C values range from +0.6 to +3.8 per thousand (PDB). These cyclic variations, indicated by isotopic data together with the petrology of the cements, are believed to record major changes in salinity, temperature, and organic productivity of the Mediterranean waters during the Miocene-Pliocene transition. These Messinian reefs were subaerially exposed and later onlapped by the upper evaporite unit with multiple cycles of marine hypersaline carbonate and evaporite deposition separated by periods of erosion. Aragonite cements formed in the enlarged cavities of the lower Messinian reefs during time of deposition of the upper evaporite and recorded the changes in Mediterranean water chemistry. This cementation is believed to have continued into the early Pliocene when colder Atlantic waters invaded the Mediterranean, ending reef growth and evaporite deposition.

  12. Coral distribution patterns in Miocene Reefs of Anguilla, Leeward Islands, West Indies

    SciTech Connect

    Foster, A.B.; Johnson, K.G.

    1988-01-01

    Anguilla, a 27 by 5 km island at 18/sup 0/13'N, 63/sup 0/05'W, parallels the northwest edge of the Anguilla bank (St. Martin plateau) in the outer lesser Angilles volcanic arc, which was active from the Eocene to Oligocene. Except for scattered exposures of tuff or basalt, the island is composed predominantly of reefal limestones and marls of the 70-m thick, middle Miocene Anguilla Formation, deposited on a shallow inner shelf platform extending from volcanoes near St. Martin. The reef framework consists of branched and platy corals interspersed with calcareous sand lenses. Although the limestones have been uplifted and subjected to minor faulting, little evidence supports extensive transport across a slope. Coral distribution patterns have been quantified across the reefal units by point-counting species occurrences at 0.16-m intervals within 1-m/sup 2/ quadrants placed haphazardly across vertical exposures. Eight coral species (of possibly 18 total) were recorded. Cluster analysis delineated four facies: (1) a low-diversity facies dominated by branched Porites, (2) an intermediate diversity facies dominated by branched Porites, (3) a high-diversity facies dominated by massive Montastraea, Siderastrea, and Porites, and (4) an intermediate diversity facies dominated by platy Porites. These facies consists of lenses, no more than 100 m long and 2 m high, arranged in no apparent regular sequence. Thus, they do not represent zones across a depth gradient. Comparisons with living Caribbean reefs suggests that the Anguilla Miocene reefs were similar to small, modern, backreef fringing and patch reefs near the San Blas Islands of Panama, reefs whose variable composition and patchy distribution depend largely on sedimentation and current patterns.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  14. The interaction between Aegean back-arc extension and Anatolia escape since Late Miocene

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The Aegean domain is a key area for understanding the processes of back-arc extension. Observed deformation pattern and present day kinematics result from the interaction between the southward retreat of the Hellenic trench and the westward escape of Anatolia. Using laboratory experiments designed to study lithosphere-scale deformation, we show that the overall pattern of Aegean extension requires not only the combination of trench retreat and Anatolia escape since 15 Ma but also the presence of an inherited lithosphere-scale mechanical discontinuity: the Vardar Suture Zone (VSZ). The reactivation in dextral shear of the eastern branch of the VSZ accommodates both the trench retreat (NS stretching) and the westward escape of Anatolia (EW shortening) in the Cyclades area since 15 Ma. Additionally, our model shows that the North Anatolian Fault (NAF) is a late structure in the evolution of the Aegean, initiated 10 Ma after the onset of Anatolia escape. The model displays displacement sub-domains, which result from strain partitioning instead of being "rigid microplates", directly comparable to the present-day displacement field (GPS) of the Aegean and western Anatolia. Our modelling provides a simple way to look at the dynamics of Aegean extension in two main stages. From middle Eocene to middle Miocene, extension was only driven by the southward retreat of the Hellenic trench at a rate lower than 1 cm.y-1. Since middle Miocene, the combination of slab rollback with Anatolia westward escape, resulted in a southwest direction of trench retreat, with an accelerating rate of up to 3 cm.y-1.

  15. Deep Ocean Circulation and Climate During the Miocene: Data vs. Modelling

    NASA Astrophysics Data System (ADS)

    Bickert, T.; Butzin, M.; Lohmann, G.

    2005-12-01

    A series of configurations for Neogene ocean circulation sensitivity experiments, i.e. different stages in the shoaling of the Central American Isthmus and of the eastern Tethys as well as different sea-ice coverage scenarios were used as input for a marine carbon cycle model (HAMOCC2s). Using d13C and sedimentary carbonate as model output variables, the geochemical experiments provided a new framework to interpret Neogene paleoenvironmental data. Assuming the Isthmus of Panama to be open and no sea-ice coverage in the southern hemisphere, deep water is formed in the North Atlantic as well as in the sub-Antarctic realm, in agreement with Neogene carbon isotope pattern. However, the formation rate of NADW is reduced by about 75o/o compared to the control experiment, consistent with very low d13C gradients between the North Atlantic and Southern Ocean. The sill depth greater than 1000 m allows for the passage of NADW into the Pacific ocean, forming a deep boundary current along the western Pacific margin. The export of NADW is compensated by an influx of low-salinity Pacific Intermediate water, which enters the Caribbean with a maximum strength of 3 Sv at a depth of about 500 m. Forming of sea-ice related to the Middle Miocene build-up of a permanent Antarctic ice sheet intensifies the sub-Antarctic deep water production while NADW formation is suppressed. This scenario is corroborated by the convergence of Atlantic and Pacific benthic d13C values between 15 and 11 Ma. Finally, the re-establishment of the formation of NADW in the late Miocene and the evolution of the modern ocean conveyor is predicted in the model experiments assuming further shoaling of the Central American Isthmus and evolution of sea-ice in the Artic Ocean.

  16. Source-To-Sink Perspectives On The Mississippi River System, Miocene To Present, Mountain To Abyss

    NASA Astrophysics Data System (ADS)

    Bentley, S. J.; Blum, M. D.

    2013-12-01

    . The objective of this study is to present a synthesis of the Mississippi River source-to-sink system, from montane source to abyssal sink, to elucidate specific geomorphic components and boundaries in the system, controls on mass transfer, and resultant geomorphic and statigraphic development. The Mississippi River source-to-sink system constitutes one of the largest sources, conduits, and depocenters of sediment on Earth, extending from elevations of 3.7 km in the Rocky Mountains to the Gulf of Mexico abyssal plain. Despite being one of the most intensely studied fluvial-marine systems in the world, comprehensive understanding and management of the system's resources remain a challenge. The system is valuable in many ways: it provides navigation and water to the heart of North America, and sustains extensive marine fisheries. The river has built a delta that is home to millions of people and yet is subsiding rapidly. Ancestral Mississippi fluvial-marine deposits continue to yield high-value petroleum resources to exploration. To address the range of temporal and spatial scales over which the system has developed and continues to evolve, we will focus on three geological time spans that display contrasting geologic forcing and response: Miocene, Pleistocene, and late Holocene. The present configuration of source, conduit, and sink were established during the Miocene epoch, when tectonics (via the uplifting southern Rockies, and later the rejuvenated Appalachians) and climate (wet in the east and dry in the west) provided abundant water and sediment to prograde the shelf margin and initiate deep-sea fan growth. Pleistocene continental glaciation, eustasy, and catastrophic drainage events further sculpted the alluvial valley, and extended the shelf margin, and fan. Studies of Modern processes and Holocene delta development have provided keys to both the delta's past and future evolution, in terms of cyclic autogenic lobe-switching, mass-transport events, storm

  17. Geometric and sedimentologic characteristic of Mid-Miocene lowstand reservoir sandstones, offshore northwest Java, Indonesia

    SciTech Connect

    Lowry, P.; Kusumanegara, Y.; Warman, S.

    1996-12-31

    Numerous reservoirs in the Upper Cibulakan Formation (Mid-Miocene) of the Offshore Northwest Java shelf occur in sharp-based sandbodies that range from less than 1 m up to 10 m in thickness. Well-log derived net-sand isopach and seismic amplitude maps of these sandbodies depict elongate features, that are 1-2 km wide and 5-8 km long. The orientation of the longest axis of these sandbodies is predominantly north-south. Conventional cores reveal that these sandbodies are burrowed to completely bioturbated sandstones. Common trace fossils associated with these sandbodies include Ophiomorpha, Teichichnus and Thalassinoides. The lower contact of these sands is typically sharp and is commonly associated with a Glossifungites surface and siderite mud clasts. Overlying and underlying mudstones are relatively devoid of burrowing. Benthonic foraminifera assemblages within these mudstones indicate inner to outer neritic conditions in a relatively restricted marine setting. The upper contact of these sandstones is gradational over a 0.5 to 1m interval. Sandbodies of the same age and similar facies were observed in outcrops in onshore west Java. Here, they can be observed to pinch out over a distance of 500 m. The lower bounding contact appears discordant with underlying interbedded sandstones and mudstones. Several of the sandstones contain abundant accumulations of the large, open marine, benthonic foraminifera Cycloclypeus and Lepidocyclina. Occasionally the concentration of these large foraminifera form limestones within the sharp-based sandbodies. These bioclastic deposits commonly exhibit planar-tabular and trough cross-stratification. The sandbodies are interpreted as having been emplaced during relative falls in sea-level within a large Mid-Miocene embayment. Our understanding of their geometry and sedimentologic characteristics is leading to a more effective exploitation strategy for these sandbodies in the Offshore Northwest Java area.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  19. Regional depositional history of the Miocene-Pleistocene Louisiana Slope, Green Canyon and Mississippi Canyon

    SciTech Connect

    Risch, D.L.; Chowdhury, A.N.; Hannan, A.E.

    1994-09-01

    A regional sequence-stratigraphic analysis was recently completed for the Tertiary slope sediments in Green Canyon, Ewing Bank, and Mississippi Canyon to provide a chronostratigraphic framework for basin reconstructions and predict lithofacies distributions of reservoir and seal rocks. Sixteen third-order sequences of lowstand deep-water deposits were interpreted for the middle Miocene-Pleistocene section. Thirty regional lithofacies maps were made of predominantly lowstand deposits showing the distribution of shale and sand-prone sediments, slumping, channel levee systems, and fan lobes based on distinctive seismic reflection and well log patterns. These maps were combined with isochrons of selected sequences to identify depositional fairways, depocenters, and paleosalt positions that constantly changed through time. Depositional trends were principally north to south but were also observed to be east-west as salt modified the gradient on the gently dipping slope. In some cases, the structural and stratigraphic trends could be projected under allochthonous tabular salt. Miocene channel and fan lobe sands were found concentrated on the middle-lower paleoslope across the study area. The sedimentation rate doubled (0.7 m/1000 yr) in the early-middle Pliocene, which caused large-scale salt movements and trapped sand-prone turbidites along the upper-middle slope. A four-fold decrease in sediment influx during the late Pliocene-early Pleistocene produced a stacked condensed section of four sequences over the eastern Louisiana slope. A return to rapid sedimentation (up to 2.1 m/1000 yr.) during the Pleistocene reactivated salt movements and depocenters in the Green Canyon, Ewing Bank, and Mississippi Trough areas.

  20. Regional depositional history of the miocene-pleistocene Louisiana slope, Green Canyon-Mississippi Canyon

    SciTech Connect

    Risch, D.L.; Choudhury, A.N.; Hannan, A.E.

    1994-12-31

    A regional sequence stratigraphic analysis was recently completed for the Tertiary slope sediments in Green Canyon, Ewing Bank, and Mississippi Canyon to provide a chronostratigraphic framework for basin reconstructions and to predict lithofacies distributions of reservoir and seal rocks. Sixteen third-order sequences of lowstand deepwater deposits were interpreted for the Middle Miocene-Pleistocene section. Thirty regional lithofacies maps were made of predominantly lowstand deposits showing the distribution of shale and sand-prone sediments, slumps, channel/levee systems, and fan lobes based on distinctive seismic reflection and well log patterns. These maps were combined with isochrons of selected sequences to identify depositional fairways, depocenters, and paleosalt positions that constantly changed through time. Depositional trends were principally north-south but were also observed to be east-west as salt modified the gradient on the gently dipping slope. In some cases, the structural and stratigraphic trends could be projected under allochthonous tabular salt. Miocene channel and fan lobe sands were concentrated on the middle-lower paleoslope across the study area. The sedimentation rate doubled to 2.3 m/1000 yr in the early Middle Pliocene, which caused large-scale salt movements and trapped sand-prone turbidities along the upper to middle slope. A four-fold decrease in sediment influx during the Late Pliocene-Early Pleistocene produced a stacked condensed section of four sequences over the eastern Louisiana slope. A return to rapid sedimentation (up to 6.9 m/1,000 yr) during the Late Pleistocene reactivated salt movements and depocenters in the Green Canyon, Ewing Bank, and Mississippi Trough areas.

  1. Regional-scale variation in size and abundance of the bivalve Varicorbula (Middle Miocene, Central Paratethys)

    NASA Astrophysics Data System (ADS)

    Fuksi, Tomáš; Tomašových, Adam; Rušin, Luboš

    2016-04-01

    Varicorbula gibba (Olivi, 1792) is a geologically long-ranging and ecologically generalistic bivalve species that appears in the Oligocene and persists to present, occurring in the tropical and northern temperate Eastern Atlantic and in the Mediterranean. Although it is one of the most frequent species in the benthic communities in the Paratethys during the Middle Miocene, spatial variation in its abundance, size, and shape is poorly known. Using bulk samples sieved with 1 mm mesh size, we investigate size and abundance variation of this taxon in molluscan communities in two basins in the Middle Miocene (Serravalian) sediments of the Central Paratethys. Bulk samples are derived from boreholes from the western (Vienna Basin) and eastern (Danube Basin) margins of the Malé Karpaty Mountains (Slovakia). We find that this taxon shows significant regional-scale differences in size distribution between the Vienna and Danube basins. In subtidal muds in the northern parts of the Vienna Basin, it achieves very high proportional community-level abundance and its median shell width ranges between 6-10 mm. In contrast, in muddy sands on the northeastern margin of the Danube Basin, community composition is more even and median width ranges just between 3-4 mm. The higher sandy content and lower sedimentation rates (as evidenced by higher taphonomic damage, with higher proportion of bored specimens, in the Danube Basin) imply that the size can partly positively correlate with nutrient supply. Morphometric analyses indicate that height and width of individuals of this taxon undergo significant allometry and that smaller-sized individuals in the Danube Basin have a smaller width/height ratio, suggesting that some shape differences between the two basins are unrelated to size differences.

  2. Composition and provenance of the Puente Formation (Miocene), Los Angeles Basin

    SciTech Connect

    Critelli, S. ); Rumelhart, P.E.; Ingersoll, R.V. )

    1994-04-01

    The Puente Formation (PFm) is a middle to upper Miocene clastic unit lying unconformably on the middle to lower Miocene El Modeno Volcanics and Topanga Group, within the Los Angeles basin (LAB). The PFm, about 3900m thick, is composed of sandstone, conglomerate, and mudrock deposited on a submarine fan at bathyal depths. Several intrabasinal discordances suggest active tectonics during deposition. The succession consists of two main upward thickening and coarsening megacycles reflecting submarine fan progradation. The PFm is characterized up-section by: (1) thin-bedded fine sandstone and shale (La Vida M.) grading to thick-bedded coarse sandstone an conglomerate (soquel M.); (2) thin-bedded siltstone, mudrock and sandstone (Yorba M.) grading to thick- to very thick-bedded coarse-grained sandstone and conglomerate (Sycamore Canyon M.). Sandstones of the PFm are quartzofeldspathic and suggest a probable local provenance from the plutonic, volcanic, and metamorphic rocks of the San Gabriel Mountains. Petrological parameters, however, suggest variable contribution of these source rock units through time. Coarse-grained plutonic rock fragments are abundant for the entire succession and consist of plagioclase-rich plutonic rocks perhaps sourced from the Lowe granodiorite. Microlitic, lathwork to felsitic volcanic lithic grains are also present in the lower and middle part. In the Yorba M. there is a local increase of volcanic detritus (Lv/L - 0.80), represented by larger volcanic lithics and abundant volcaniclastic matrix. Metamorphic detritus is not very abundant; it is concentrated in the La Vida M. the PFm represents sedimentation during tectonically active time in the evolution of southern California.

  3. Middle Miocene climate cooling linked to intensification of eastern equatorial Pacific upwelling

    NASA Astrophysics Data System (ADS)

    Holbourn, A. E.; Kuhnt, W.; Lyle, M. W.; Schneider, L. J.; Romero, O. E.; Andersen, N.

    2013-12-01

    During the middle Miocene, Earth's climate transitioned from a relatively warm phase (Miocene climatic optimum, ~17-15 Ma) into a colder mode with re-establishment of permanent ice sheets on Antarctica. Carbon sequestration and atmospheric CO2 drawdown through increased terrigenous and/or marine productivity have been proposed as the main drivers of this fundamental transition. However, comparatively little is known about the processes initially sustaining global warmth and about the chain of climate events that reversed this trend and promoted ice growth on Antarctica after ~15 Ma. We integrate high-resolution (1-3 kyr) benthic stable isotope data with XRF-scanner derived biogenic silica and carbonate accumulation estimates in an exceptionally well-preserved sedimentary archive to reconstruct variations in eastern equatorial Pacific upwelling and to investigate temporal linkages between high- and low-latitude climate change over the interval 16-13 Ma. Our records show that the climatic optimum (16.8-14.7 Ma) was characterized by high amplitude climate variations, marked by intense perturbations of the carbon cycle. Episodes of peak warmth at (southern hemisphere) insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. A switch to obliquity-paced climate variability after 14.7 Ma concurred with a general improvement in carbonate preservation and the onset of stepwise global cooling, culminating with extensive ice growth over Antarctica at ~13.8 Ma (Mi3 event). We find that two massive increases in opal accumulation at ~14.0 and ~13.8 Ma occurred just before and during the final and most prominent cooling step, supporting the hypothesis that increased primary productivity due to enhancement of the eastern equatorial Pacific cold tongue contributed to CO2 drawdown and promoted global cooling.

  4. Unlocking the ice house: Oligocene-Miocene oxygen isotopes, eustasy, and margin erosion

    SciTech Connect

    Miller, K.G. Columbia Univ., Palisades, NY ); Wright, J.D.; Fairbanks, R.G. )

    1991-04-10

    Benthic foraminiferal {delta}{sup 18}O records place limits on the history of glaciation, suggesting the presence of ice sheets at least intermittently since the earliest Oligocene. The best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic {delta}{sup 18}O records. Although planktonic isotope records from the western equatorial regions are limited, subtropical planktonic foraminifera may also record such ice volume changes. It is difficult to apply these established principles to the Cenozoic {delta}{sup 18}O record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events. The authors improved Oligocene to Miocene correlations of {delta}{sup 18}O records and erected eight oxygen isotope zones (Oi1-Oi2, Mi1-Mi6). Benthic foraminiferal {delta}{sup 18}O increases which can be linked with {delta}{sup 18}O increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near Antarctica. These new correlations of middle Miocene benthic and western equatorial planktonic {delta}{sup 18}O records show remarkable agreement in timing and amplitude. They interpret benthic-planktonic covariance to reflect substantial ice volume increases near the bases of Zones Mi2 (circa 16.1 Ma), Mi3 (circa 13.6 Ma), and possibly Mi5 (circa 11.3 Ma). Possible glacioeustatic lowerings are associated with the {delta}{sup 18}O increases which culminated with the bases of Zone Mi4 (circa 12.6 Ma) and Mi6 (circa 9.6 Ma), although low-latitude planktonic {delta}{sup 18}O records are required to test this. These inferred glacioeustatic lowerings can be linked to seismic and rock disconformities.

  5. Provenance of the upper Miocene-Pliocene Red Clay deposits of the Chinese loess plateau

    NASA Astrophysics Data System (ADS)

    Nie, Junsheng; Peng, Wenbin; Möller, Andreas; Song, Yougui; Stockli, Daniel F.; Stevens, Thomas; Horton, Brian K.; Liu, Shanpin; Bird, Anna; Oalmann, Jeffrey; Gong, Hujun; Fang, Xiaomin

    2014-12-01

    A clear understanding of the provenance of late Cenozoic Chinese loess and the underlying Red Clay deposits will shed light on the history and mechanisms of Asian aridification. Although much progress has been made in understanding the source of Quaternary loess on the Chinese Loess Plateau (CLP), the provenance of the underlying upper Miocene-Pliocene Red Clay sequence is largely unknown. Here we present the first provenance history of the Red Clay sequence based on zircon U-Pb ages from the central CLP. Visual and statistical analyses of the U-Pb age populations and comparison with results from potential source regions reveals that (1) the lowermost Red Clay of the late Miocene (depositional age of ∼8 Ma) is likely sourced from the nearby Liupan Mountains and the Qaidam Basin; (2) the middle Red Clay (5.5-4 Ma) of the early-mid Pliocene is sourced mainly from the Taklamakan desert, transported via lower-level westerly winds; (3) the upper Red Clay of the late Pliocene (∼3 Ma) is sourced from mixed areas, although western source materials from middle-northern Tibetan plateau (including Qaidam Desert sediments and materials eroded from the Qilian Mountains) sediments appear to dominate; and (4) the Quaternary loess is also sourced from mixed source regions, albeit with dominant northern CLP proximal desert sediments transported via winter monsoon winds, which in turn may be transported from mountain source regions of the northeastern Tibet and Gobi Altai via major river systems. This long term shift in sources suggests a progressive eastward aridification during the Pliocene in Asia with the specific timing of provenance shifts synchronous with large-scale climatic transitions and Tibetan uplift, demonstrating that Asian desertification is controlled by both factors.

  6. The significance of Rzehakia shell accumulations in the Lower Miocene of the Central Paratethys

    NASA Astrophysics Data System (ADS)

    Mandic, O.

    2009-04-01

    Rzehakia is a bivalve genus endemic for the Paratethys. Rzehakia bearing deposits can be traced from the Western Alpine Foredeep of the Swabian Alb (Kirchberg Formation; Upper Marine Molasse) over the Eastern Alpine and Carpathian Foredeep (upper Ottnangian of the Central Paratethys) up to Georgia in the East (Kotsakhurian of the Eastern Paratethys). Their deposition coincides with the tectonic inversion and the final onset of lacustrine and terrestrial environment in the Alpine Foredeep. Furthermore they are time equivalents of the initial subsidence and rifting of the Pannonian Basin System. Rzehakia shell accumulations mark the most prominent Lower Miocene restriction and endemic event in the Central Paratethys. They represent the major regression in the late Ottnangian before the last Lower Miocene marine pulse of the Karpatian. The Rzehakiidae representatives are accompanied in corresponding deposits by endemic Lymnocardiidae bivalves and different lacustrine to marginal marine gastropod species. Their faunal distribution pattern provides strong evidence for the well established paleogeographic connection throughout the Paratethys during late Ottnangian. In the Central Paratethys, however, conspicuous West-East faunal gradient is present with the western assemblage characterized through Rzehakia guembeli and Limnopagetia bavarica and the eastern assemblage bearing Rzehakia socialis, Limnopagetia moravica and Limnopagetia ammoni. Mandic & Ćorić (2007: Eine neue Molluskenfauna aus dem oberen Ottnangium von Rassing (NÖ) - taxonomische, biostratigraphische, paläoökologische und paläobiogeographische Auswertung. - Jahrbuch der Geologischen Bundesanstalt, 147: 387-398) located currently their transitional contact in the Lower Austrian Eastern Alpine Foredeep, showing co-occurrence of species from both paleobiogeographic entities. The study is part of the Austrian FWF Project P18519-B17.

  7. Syn-rift carbonate depositional patterns: Miocene, Gulf of Suez, Egypt

    SciTech Connect

    Hurst, J.M.

    1987-05-01

    The Suez rift, initiated in the Miocene, consists of asymmetric fault blocks, separated by transfer zones. Syn-rift Miocene carbonates developed on highs; the intricate relations are illustrated at Gebel Gharamul and Esh El Mellaha. Gebel Gharamul is a rollover, cut by antithetic faults, located on a transfer zone. Small coralgal rimmed shelves initially developed over the eroded footwall nick of an early western antithetic. Steepening depositional dips reflect increasing graben subsidence. Subsequently, the main easterly antithetic regionally lowered the rollover, promoting stacked coral rimmed shelf sequences with increasing dip filling the graben, with the back reef onlapping the main rollover crest. Simultaneously, a low-angle flexure (2/sup 0/-3/sup 0/) developed along the northern rollover margin. Low-angle (5/sup 0/) biostromal rimmed shelves, exhibiting sigmoidal clinoforms rapidly accreted laterally, as reflected in flat-based sequences. Depositional pattern eventually merged over the rollover to produce laterally complex rimmed shelf sequences. Esh El Mellaha is a footwall to a major extensional fault. In a southerly extensional cusp (20 km), the fault throw decreases from kilometers to flexural (2-3/sup 0/) displacement. Coralgal rimmed shelves and escarpment fringing reefs mantle the footwall. Initial, thick, and most laterally extensive sequences develop over the flexure. Accretion is primarily subvertical, reflecting continuous flexural subsidence. Where the fault cusp has less than a 30/sup 0/ inclination, carbonate sequences exhibiting oblique and oblique sigmoid clinoforms (40/sup 0/) prograded over and heeled the fault during periods of fault inactivity. With a fault plane inclination over 40/sup 0/, slope progradation was precluded and thin vertically accreting escarpment sequences developed.

  8. Reconstructing a Miocene pitfall trap: Recognition and interpretation of fossiliferous Cenozoic palaeokarst

    NASA Astrophysics Data System (ADS)

    Arena, Derrick A.; Black, Karen H.; Archer, Michael; Hand, Suzanne J.; Godthelp, Henk; Creaser, Philip

    2014-05-01

    The middle Miocene cave deposit at AL90 Site in the Riversleigh World Heritage Area of Queensland, Australia, is the largest excavated palaeokarst deposit within the extensive Cenozoic freshwater limestones of the region. Stratigraphic relationships between various lithological components of the cave deposit indicate a dynamic, complex depositional history including dissolution, infill and reworking of cave materials. Euhedral spar, shelf-stone, calcite rafts and desiccation cracks on cave sediments suggest standing water was variably present in the cave environment. The AL90 Local Fauna is moderately diverse comprising at least 20 vertebrate families and 32 species, yet is taphonomically biased towards large marsupial herbivores (families Diprotodontidae, Macropodidae, and Balbaridae) and cave-dwelling hipposiderid bats. Fossil material is generally exceptionally well-preserved with, in many cases, articulated skeletons recovered. The cave entrance appears to have acted as a natural pit-fall trap. The complex (unconformable) depositional structure and lithology, vertebrate taphonomy and faunal composition at AL90 Site are typical of deposits and assemblages formed in the inner environment of the upper vadose zone. In the past, some similar unroofed cave deposits have been interpreted as clastic fluvio-lacustrine sedimentary deposits formed by surface processes. Analysis of characteristic palaeokarst features at AL90 Site has enabled the identification of other less well-preserved, poorly-exposed or relict cave deposits at Riversleigh and has facilitated interpretation of the depositional and palaeoenvironmental history of those deposits. The findings presented here confirm earlier interpretations that specific, highly-fossiliferous early Miocene to early Pliocene fossil deposits at Riversleigh represent relict caves whose roofs and walls are no longer intact.

  9. Life-History Traits of the Miocene Hipparion concudense (Spain) Inferred from Bone Histological Structure

    PubMed Central

    Martinez-Maza, Cayetana; Alberdi, Maria Teresa; Nieto-Diaz, Manuel; Prado, José Luis

    2014-01-01

    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 typical of

  10. Age and depositional setting of the type Lospe Formation (Lower Miocene), Santa Maria basin, central California

    SciTech Connect

    Stanley, R.G. ); Johnson, S.Y.; Obradovich, J.D.; Tuttle, M.L. ); Thornton, M.L.C.; Vork, D.R.; Filewicz, M.V. ); Mason, M.A. ); Swisher, C.C. III )

    1990-05-01

    The Lospe Formation is an 800-m-thick sequence of sedimentary and minor volcanic rocks at the base of the petroliferous Neogene Santa Maria basin of central California. In its type area in the Casmalia Hills, the Lospe rests unconformably on Jurassic ophiolite, is conformably overlain by the lower Miocene (Sauceian and Relizian) Point Sal Formation, and is of earliest Miocene (Saucesian) age on the basis of palynomorphs, benthic foraminifers, and radiometric dating of tuffs. Alluvial fan and fan-delta facies at the base of the Lospe are as much as 200 m thick and consist mainly of conglomerate and sandstone derived from nearby fault-bounded uplifts of Mesozoic rocks. These coarse sediments grade upward into a sequence of interbedded turbidite sandstone and mudstone that accumulated in a lake or restricted coastal embayment. Lenses of tuff as much as 20 m thick occur sporadically throughout this sequence and contain blocks of Jurassic ophiolite up to 50 m long and 20 m across. The uppermost 30 m of the Lospe consist of storm-deposited sandstone and mudstone containing shallow marine microfossils. That these shelf deposits are abruptly overlain by black shale of the Point Sal Formation indicates rapid deepening to oxygen-poor bathyal environments. Overall, the Lospe Formation is a fining-upward sequence that records active faulting, volcanism, and a change from nonmarine to marine depositional environments during the initial formation of the Neogene Santa Maria basin. This history is consistent with several competing tectonic models that variously explain the origin of the basin as the result of regional rifting or local rotation of small crustal blocks.

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

    PubMed

    Martinez-Maza, Cayetana; Alberdi, Maria Teresa; Nieto-Diaz, Manuel; Prado, José Luis

    2014-01-01

    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 typical of

  12. Sequence stratigraphy of the Miocene, Pohokura field, Taranaki Basin, New Zealand

    SciTech Connect

    Kalid, Nur Zulfa Abdul; Hamzah, Umar

    2014-09-03

    A sequence stratigraphic study of the Miocene age was conducted in the Pohokura field, that is located offshore from the northern coast of Taranaki Penisula, New Zealand. It is a low-relief, north-south elongated anticline approximately 16 km long and 5 km wide. The study was carried out with two objectives which are to identify the Miocene seismic facies and to identify the sequence stratigraphic parameters. One seismic line and Pohokura-2 well was use in the study. Various seismic facies were observed in the seismic section including parallel, subparallel, continuous, subcontinuous, wavy, free reflection, subchaotic, high amplitude-high frequency and high amplitude-low frequency reflection. The interpreted seismic line showed three chronostratigraphic units which is sequence boundary 1 (SB1) represent top Manganui, sequence boundary 2 (SB2) represent top Mount Messenger and sequence boundary 3 (SB3) represent top Urenui. SB1, was separated by two distinct seismic facies namely sub-parallel and sub-chaotic. Parallel and sub-parallel reflection was observed on top of the sequence boundary SB2 while sub-chaotic and wavy seismic facies is found below the sequence boundary. SB3 is characterize by erosional truncation as shown by the present of toplap and downlap terminations in the western part of the seismic section. It is also supported by the clear difference of very high amplitud-high frequency reflection on top of SB3 overlying low amplitud-low frequency reflection of Urenui Formation. A complete depositional system including highstand, lowstand and transgressive system tracts are observed in the incised valley within the Urenui Formation.

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

    PubMed

    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

    2016-05-12

    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.

  14. Paleoproductivity during the middle Miocene carbon isotope events: A data-model approach

    NASA Astrophysics Data System (ADS)

    Diester-Haass, Liselotte; Billups, Katharina; Jacquemin, Ingrid; Emeis, Kay C.; Lefebvre, Vincent; FrançOis, Louis

    2013-06-01

    To what extent are individual middle Miocene eccentricity-scale benthic foraminiferal carbon isotope maxima (the so-called CM events) related to changes in marine export productivity? Here we use benthic foraminiferal accumulation rates from three sites in the Pacific and Southern Oceans and a geochemical box model to assess relationships between benthic foraminiferal δ13C records, export productivity, and the global carbon cycle. Results from Deep Sea Drilling Project Hole 588 and Ocean Drilling Program Site 747 show a distinct productivity maximum during CM 6 at 13.8 Ma, the time of major expansion of ice on Antarctica. Productivity maxima during other CM events are only recorded at high-latitude Site 747. A set of numerical experiments tests whether changes in foraminiferal δ13C records (CM events) and export productivity can be simulated solely by sea level fluctuations and the associated changes in global weathering-deposition cycles, by sea level fluctuations plus global climatic cooling, and by sea level fluctuations plus invigorated ocean circulation. Consistent with data, the periodic forcing of sea level and albedo (and associated weathering cycles) produces δ13C variations of the correct temporal spacing, albeit with a reduced amplitude. A productivity response of the correct magnitude is achieved by enhancing ocean circulation during cold periods. We suggest that the pacing of middle Miocene δ13C fluctuations is associated with cyclical sea level variations. The amplitude, however, is muted perhaps due to the competing effects of a time-lagged response to sea level lowstands but an immediate response to invigorated ocean circulation during cold phases.

  15. Miocene climate as recorded on slope carbonates : examples from Malta (Central Mediterranean) and Northeastern Australia (Marion Plateau, ODP LEG 194)

    NASA Astrophysics Data System (ADS)

    John, Cédric Michaël

    2003-08-01

    This study investigated the slope carbonates of two Miocene carbonate systems: the Maltese Islands (in the Central Mediterranean) and the Marion Plateau (Northeastern Australia, drilled during ODP Leg 194). The aim of the study was to trace the impact of the Miocene cooling steps (events Mi1-Mi6) in these carbonate systems, especially the Mi3 event, which took place around 13.6 Ma and deeply impacted the marine oxygen isotope record. This event also profoundly impacted oceanographic and climatic patterns, eventually leading to the establishment of the modern ice-house world. In particular, East Antarctica became ice covered at that period. The rational behind the present study was to investigate the impact that this event had on shallow water systems in order to complement the deep-sea record and hence acquire a more global perspective on Miocene climate change. The Maltese Islands were investigated for trends in bulk-rock carbon and oxygen isotopes, as well as bulk-rock mineralogy, clay minerals analysis and organic geochemisty. Results showed that the mid Miocene cooling event deeply impacted sedimentation at that location by changing sedimentation from carbonate to clay-rich sediments. Moreover, it was discovered that each phase of Antarctic glaciation, not just the major mid Miocene event, resulted in higher terrigenous input on Malta. Mass accumulation rates revealed that this was linked to increased runoff during periods when Antarctica was glaciated, and thus that the carbonate sediments were “diluted” by clay-rich sediments. The model subsequently developed to explain this implies feedback from Antarctic glaciations creating cold, dense air masses that push the ITCZ Northward, thus increasing precipitation on the North African subcontinent. Increased precipitation (or stronger African monsoon) accelerated continental weathering and runoff, thus bringing more terrigenous sediment to the paleo-location of the slope sediments of Malta. Spectral

  16. Palynology of latest Neogene (Middle Miocene to late Pliocene) strata in the Delmarva Peninsula of Maryland and Virginia

    USGS Publications Warehouse

    Sirkin, L.; Owens, J.P.

    1998-01-01

    Palynology of Miocene and Pliocene formations in the Delmarva Peninsula of Maryland and Virginia reveals a significant representation of exotic pollen interspersed in pollen assemblages that are otherwise comparable to those from the modern vegetation of the Mid-Alantic coastal plain region. The late Tertiary arboreal pollen (AP) assemblages are dominated by oak, hickory, pine, birch and alder with minor amounts of mid- and southern coastal tree taxa, as well as minor spruce and hemlock and a trace of fir. Nonarboreal pollen (NAP) include grass, sedge, composite and aquatic taxa. Exotic pollen in these assemblages represent plants now foreign to this region. They may be placed in three categories. First, there are extinct forms, such as Labrapollis, Plicatopollis, and Multiporopollenites, that can be traced from the Cretaceous or Early Tertiary into the Late Tertiary. The second group includes forms, such as Podocarpus, Engelhardtia, Pterocarya, Ephedra, Eucommia, Ulmus-Zelkova, Glyptostrobus, Palmae, and Cyathea, that are not found in this region today and not found in early Pleistocene sediments in the eastern United States. Many of these taxa are subtropical or greatly restricted in geographic range. A third group of exotics, mainly Cyrilla, Planera, Gordonia, Jussiaea, and Sapotacaea, including Minusops, are generally found south of the study area or have their northern limit here at this time. The lack of the extinct or distant exotics in early to mid-Pleistocene sediments in the mid-Atlantic coastal plain and the last appearance of Pterocarya, as the last exotic taxon in the early Pleistocene of western Europe, support the stratigraphic assignment of the Pliocene units. The number of exotic taxa diminish markedly between the Miocene pollen assemblages and those of the Late Pliocene. Climatic fluctuations characterize the Late Tertiary environments. The Miocene, for example, incorporates a warming trend between the upper, middle Miocene and the Manokin beds

  17. Cooling Mediterranean Sea surface temperatures during the Late Miocene provide a climate context for evolutionary transitions in Africa and Eurasia

    NASA Astrophysics Data System (ADS)

    Tzanova, Alexandrina; Herbert, Timothy D.; Peterson, Laura

    2015-06-01

    In the Late Miocene, grasslands proliferated, succulent plants diversified in the mid-latitudes, and the desert-like conditions appeared in the Sahara. Despite this major environmental change on land, the coeval deep-sea oxygen isotope record does not provide evidence for significant high latitude cooling or continental ice growth, making it difficult to relate widespread terrestrial environmental change to global climatic changes. A U37K‧ -derived sea surface temperature (SST) reconstruction spanning 13 to 6 Ma from uplifted hemipelagic sediments in Northern Italy provides the first continuous mid-latitude temperature record with which to compare the evolution of aridity and biotic events at similar latitudes in Northern Africa and Pakistan. Between 13 and 8.8 Ma, Mediterranean SST lay near the upper limit of the alkenone temperature proxy (∼28 °C), exceeding modern SST at the site by as much as 10 °C. Throughout the record, sapropel layers correspond to local SST maxima, suggesting that Late Miocene hydrological conditions in the Mediterranean responded to insolation forcing via mechanisms similar to those documented for the Plio-Pleistocene. Mediterranean SST cooled rapidly beginning at ∼8 Ma, with an episode of intense cooling to ∼19 °C between 7.2 Ma and 6.6 Ma, followed by a rebound to ∼25 °C preceding the Messinian Salinity Crisis at 5.9 Ma. These observations establish, for the first time, a direct relationship between increasing aridity in the Northern hemisphere mid-latitudes and significant cooling. Evidently, this cooling was not accompanied by significant growth in continental ice volume. The extreme warmth and subsequent cooling of the Mediterranean Sea are not well-represented in current Late Miocene climate models, which our results suggest underestimate regional warmth prior to the Late Miocene cooling. Evidence of secular cooling during the Late Miocene gives new support to the much-debated link between a possible decline in

  18. Post-Miocene Deformation in Central Anatolia and its link to Horst and Graben System of Western Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Rojay, B.

    2009-04-01

    The western Anatolian multi-directional extensional terrain developed as a result of the anti-clockwise westward migration of the Anatolian Block onto African Plate along the Mediterranean Ridge in between the North Anatolian Fault in north and East Anatolian-Dead Sea Fault in south-southeast. The multi-directed horst-graben system of the western Anatolian neotectonic domain is bisected by NW-SE to WNW-ESE extending faults. To understand the deformational pattern in the western Anatolia, five tectonic domains are differentiated in the area between Central Anatolian in the northeast and Kucuk Menderes sector in the southwest; i. central Anatolian domain (S of Galatian Volcanic province and Kazan Basin), ii. Eskişehir-Cihanbeyli Fault Zone, iii. Kütahya Fault and Simav-Afyon-Akşehir Fault Zone, iv. Gediz-Alaşehir Graben and v. Kücük Menderes basin. The results of the slip data analysis for the post-Late Miocene to Quaternary period from the northeastern sector (central Anatolia) to southwestern sector (K. Menderes) of the five domains are indicate that the style and tectonic setting of deformation phases are similar. In central Anatolia, the deformation is expressed by three distinct stages as (i) post-Late Miocene - pre-Pliocene NW-SE to N-S compression, (ii) Pliocene almost E-W extension and (iii) NNE-SSW to NW-SE multi-directed extension since the Pliocene. Similarly, the history of deformation in the Kucuk Menderes area is expressed by three distinct episodes as: (i) post-Late Miocene-pre-Pliocene N-S compression, (ii) ENE-WSW extension during Plio-Quaternary and (iii) NE-SW extension since the Quaternary. The fault-slip analyses from the five domains are consistent with continuum of continental extension since Pliocene which follows the post-Late Miocene - pre-Pliocene compression. The s1 - s3 relationship manifests a rotation of principal stress s1 axes from eithe