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Sample records for eocene garford paleovalley

  1. Formation conditions of paleovalley uranium deposits hosted in upper Eocene-lower Oligocene rocks of Bulgaria

    NASA Astrophysics Data System (ADS)

    Vinokurov, S. F.; Strelkova, E. A.

    2016-03-01

    The uranium deposits of Bulgaria related to the Late Alpine tectonomagmatic reactivation are subdivided into two groups: exogenic-epigenetic paleovalley deposits related to the basins filled with upper Eocene-lower Oligocene volcanic-sedimentary rocks and the hydrothermal deposits hosted in the coeval depressions. The geological and lithofacies conditions of their localization, the epigenetic alteration of rocks, mineralogy and geochemistry of uranium ore are exemplified in thoroughly studied paleovalley deposits of the Maritsa ore district. Argumentation of the genetic concepts providing insights into both sedimentation-diagenetic and exogenic-epigenetic mineralization with development of stratal oxidation zones is discussed. A new exfiltration model has been proposed to explain the origin of the aforementioned deposits on the basis of additional analysis with consideration of archival factual data and possible causes of specific ningyoite uranium ore composition.

  2. Paleovalleys mapping using remote sensing

    NASA Astrophysics Data System (ADS)

    Baibatsha, A. B.

    2014-06-01

    For work materials used multispectral satellite imagery Landsat (7 channels), medium spatial resolution (14,25-90 m) and a digital elevation model (data SRTM). For interpretation of satellite images and especially their infrared and thermal channels allocated buried paleovalleys pre-paleogene age. Their total length is 228 km. By manifestation of the content of remote sensing paleovalleys distinctly divided into two types, long ribbon-like read in materials and space survey highlights a network of small lakes. By the nature of the relationship established that the second type of river paleovalleys flogs first. On this basis, proposed to allocate two uneven river paleosystem. The most ancient paleovalleys first type can presumably be attributed to karst erosion, blurry chalk and carbon deposits foundation. Paleovalleys may include significant groundwater resources as drinking and industrial purposes. Also we can control the position paleovalleys zinc and bauxite mineralization area and alluvial deposits include uranium mineralization valleys infiltration type and placer gold. Direction paleovalleys choppy, but in general they have a north-east orientation, which is controlled by tectonic zones of the foundation. These zones are defined as the burial place themselves paleovalleys and position of karst cavities in areas interfacing with other structures orientation. The association of mineralization to the caverns in the beds paleovalleys could generally present conditions of formation of mineralization and carry it to the "Niagara" type. The term is obviously best reflects the mechanism of formation of these ores.

  3. Paleovalley fills: Trunk vs. tributary

    USGS Publications Warehouse

    Kvale, E.P.; Archer, A.W.

    2007-01-01

    A late Mississippian-early Pennsylvanian eustatic sea level drop resulted in a complex lowstand drainage network being eroded across the Illinois Basin in the eastern United States. This drainage system was filled during the early part of the Pennsylvanian. Distinct differences can be recognized between the trunk and tributary paleovalley fills. Fills preserved within the trunk systems tend to be fluvially dominated and consist of bed-load deposits of coarse- to medium-grained sandstone and conglomerate. Conversely, the incised valleys of tributary systems tend to be filled with dark mudstone, thinly interbedded sandstones, and mudstones and siltstones. These finer grained facies exhibit marine influences manifested by tidal rhythmites, certain traces fossils, and macro- and microfauna. Examples of tributary and trunk systems, separated by no more than 7 km (4.3 mi) along strike, exhibit these styles of highly contrasting fills. Useful analogs for understanding this Pennsylvanian system include the Quaternary glacial sluiceways present in the lower Ohio, White, and Wabash river valleys of Indiana (United States) and the modern Amazon River (Brazil). Both the Amazon River and the Quaternary rivers of Indiana have (or had) trunk rivers that are (were) dominated by large quantities of bed load relative to their tributaries. The trunk valley systems of these analogs aggraded much more rapidly than their tributary valleys, which evolved into lakes because depositional rates along the trunk are (were) so high that the mouths of the tributaries have been dammed by bed-load deposits. These Holocene systems illustrate that sediment yields can significantly influence the nature of fill successions within incised valleys independent of rates of sea level changes or proximity to highstand coastlines. Copyright ?? 2007. The American Association of Petroleum Geologists. All rights reserved.

  4. Structural control on paleovalley development, muddy sandstone, Powder River basin, Wyoming

    SciTech Connect

    Gustason, E.R.; Wheeler, D.A.; Ryer, T.A.

    1988-07-01

    A subaerial unconformity within the Lower Cretaceous Muddy Sandstone in the Powder River basin developed during a late Albian sea level lowstand and resulted in a markedly rectangular drainage pattern. Numerous right-angle bends and perpendicular confluences of Muddy paleovalleys are believed to reflect syndepositional movement on basement faults and dissolution of salts in the Goose Egg Formation. A detailed subsurface analysis of geophysical logs from closely spaced wells reveals that up to 30 ft of vertical displacement occurred along northwest- and northeast-trending faults prior to and during the development of the subaerial unconformity. An analysis of a high-resolution magnetic survey (NewMag) of the Powder River basin reveals that numerous paleovalleys parallel the boundaries, or basement shear zones, between basement blocks. Small, irregularly shaped, thin intervals of the Permian Goose Egg Formation, which resemble karst topography, also occur along these northwest- and northeast-trending basement faults beneath Muddy paleovalleys. An arcuate Muddy paleovalley located in the northern Powder River basin parallels contours of isopach and trend surface maps of the Goose Egg Formation. These relationships suggest that the location and orientation of Muddy paleovalleys were controlled by a combination of movement along northwest- and northeast-trending faults and syntectonic dissolution of salt within the Goose Egg Formation. Simultaneous dissolution of Goose Egg salts and headward erosion of Muddy paleovalleys along this conjugate fault pattern also indicate that the Powder River basin was influenced by wrench fault tectonics during the late Albian.

  5. A late Quaternary multiple paleovalley system from the Adriatic coastal plain (Biferno River, Southern Italy)

    NASA Astrophysics Data System (ADS)

    Amorosi, Alessandro; Bracone, Vito; Campo, Bruno; D'Amico, Carmine; Rossi, Veronica; Rosskopf, Carmen M.

    2016-02-01

    A buried paleovalley system, up to 2 km wide and exceeding 50 m in relief, made up of multiple cross-cutting depressions incised into the Lower Pleistocene bedrock, is reported from the central Adriatic coastal plain at the mouth of Biferno River. Through a multi-proxy approach that included geomorphological, stratigraphic, sedimentological and paleontological (benthic foraminifers, ostracods and molluscs) investigations, the facies architecture of distinct, superposed valley fills is reconstructed and their relative chronology established along a transverse profile with extremely high data density (average borehole spacing 75 m). Regional tectonic uplift appears as the major controlling factor of initial (Middle Pleistocene) river down-cutting and paleovalley formation. In contrast, glacio-eustatic fluctuations drove fluvial-system response over the last 120 ky, when valley incision was primarily induced by the last glacial base-level lowering and climatic forcing. A fragmented record of coastal and shallow-marine deposits is available for the lower paleovalley fill, which is penetrated by a limited borehole dataset. Multiple erosion phases probably related to the post-MIS 5e sea-level fall are reconstructed from the upper paleovalley fill, where a buried fluvial terrace succession is identified a few tens of meters below the ground surface. The flat surfaces of two buried fluvial terraces suggest longer-term, stepped relative sea-level fall, and are correlated with fluvial incisions that took place possibly at the MIS 5/4 transition and at the MIS 3/2 transition, respectively. A laterally extensive gravel body developed on the valley floor during the Last Glacial Maximum. During the ensuing latest Pleistocene-early Holocene sea-level rise the Biferno paleovalley was transformed into an estuary. Upstream from the maximum shoreline ingression, the vertical succession of well-drained floodplain, poorly-drained floodplain, and swamp deposits evidences increasing

  6. Sedimentology of Upper Paleocene-Lower Eocene Sepultura Formation near Colonet, Baja California, Mexico

    SciTech Connect

    Miller, V.V.; Abbott, P.L.

    1988-03-01

    Upper Paleocene-lower Eocene braided-stream conglomerate of the Sepultura Formation crops out extensively within a paleovalley incised into the Cretaceous Peninsular Ranges batholith and the Alisitos Formation volcanics. The paleovalley trends just north of west as shown in 22-km long exposures within the modern San Telmo Canyon. Remnants of Sepultura fluvial-conglomerate infill reach a maximum thickness of 250 m and widths of 5-10 km. Conglomerate-clast assemblages are dominated by volcanic clasts (68-81%) along with the metamorphic (12-20%) and plutonic (2-8%) stones. The clast assemblage of andesitic and dacitic porphyries, volcaniclastics, granodiorites, aplites, and various metasediments appears to have been locally derived; all clasts are similar to the basement rocks exposed in the paleostream drainageway or just to the east of the metasedimentary belt. The Sepultura Formation contains none of the exotic, far-travelled, ultradurable rhyolitic gravels analogous to the Poway clasts that mark the time-equivalent deposits of the Mt. Soledad Formation in the San Diego area 220 km to the north. The Sepultura fluvial system supplied a gravel-rich braid delta that prograded westward over the inner shelf. Outcrops are up to 15 km wide and 23 km long, spanning braid-delta, transition-zone, and shallow-marine facies. Excellent exposures of reworked gravelly and biotite-rich sandy marine facies, some of which exhibit hummocky cross-stratification, occur in the vicinity of Punta Colonet. A late Paleocene age is indicated by the presence of turritella peninsularis. A late Paleocene age is indicated by the presence of Turritella peninsularis. A late Paleocene-early Eocene age is suggested by a sparse foraminiferal fauna (Ceratiopsos sp., Lanternosphaeridum lappaceum, Deflandrea speiosa, and Spindinium sp.).

  7. Age, distribution, and formation of late cenozoic paleovalleys of the lower Colorado River and their relation to river aggradation and degradation

    USGS Publications Warehouse

    Howard, K.A.; Lundstrom, S.C.; Malmon, D.V.; Hook, S.J.

    2008-01-01

    Distinctive far-traveled fluvial sediment of the lower Colorado River fills 20 paleo-valleys now stranded by the river downstream of Grand Canyon as it crosses the Basin and Range Province. These sediments resulted from two or more aggradational epi sodes in Pliocene and Pleistocene times following initial incision during the early Pliocene. A review of the stratigraphic evidence of major swings in river elevation over the last 5 m.y. from alternating degradation and aggradation episodes establishes a framework for understanding the incision and filling of the paleovalleys. The paleo-valleys are found mostly along narrow bedrock canyon reaches of the river, where divides of bedrock or old deposits separate them from the modern river. The paleo-valleys are interpreted to have stemmed from periods of aggradation that filled and broadened the river valley, burying low uplands in the canyon reaches into which later channel positions were entrenched during subsequent degradation episodes. The aggradation-degradation cycles resulted in the stranding of incised river valleys that range in elevation from near the modern river to 350 m above it. ?? 2008 The Geological Society of America.

  8. Petrographic-geochemical characteristics of granitoids and their epigenetic alteration products in paleovalley fields (Vitim uranium-ore site)

    NASA Astrophysics Data System (ADS)

    Kuznetsova, E. S.; Domarenko, V. A.; Matveenko, I. A.

    2016-09-01

    The study describes the results of the mineral and element composition of granitoids in basement and weathering crust of Khiagdinsk ore field in Vitim uranium ore site. It has been stated that granitoids in basement consist of leucocratic biotite granite of subalkaline group. The major rock-forming, accessory (apatite, zircon, sphene (titanite), magnetite, monazite, xenotime), and uranium-bearing minerals have been determined. Weathering crust is composed of unlithified or weakly lithified sediments, among which sandy and sandy medium gravel deposits have been distinguished in terms of mineralogical and granulometric texture. High radioactivity of granitoids was revealed in thorium-uranium basement and natural uranium. The combination of the specified factors presupposes that granitoids of Vitim uranium ore site may be a source of uranium in the fields of the paleovalley type.

  9. Eocene precipitation: a global monsoon?

    NASA Astrophysics Data System (ADS)

    Greenwood, D. R.; Huber, M.

    2011-12-01

    The Eocene was the warmest part of the Cenozoic, with warm climates extending across all continents including Antarctica, and extending into the Arctic. Substantive paleobotanical evidence (leaf floras and palynofloras) has demonstrated the existence of broadleaf and coniferous polar forests - a circumpolar rain forest - at both poles. North and South America, Australia, and China in the Eocene were well-forested and humid continents, in contrast to today where 2/3 of these continental areas are arid or semi-arid and lack forests. Each of these regions reflect past climate states - mesothermal moist climates with low thermal seasonality at high latitudes - that have no analog in the modern world. Recent modelling and paleontological proxy data, however, is revealing a high degree of seasonality to precipitation for these continental areas, indicating a monsoon-type precipitation regime may have characterized Eocene 'greenhouse climates'. Paleobotanical proxies offer 2 methods for estimated paleo-precipitation; leaf physiognomy (including both CLAMP and leaf area analysis), and quantitative analysis of nearest living relatives ('NLRs') of macrofloras. Presented here are 1) an updated leaf area analysis calibration with smaller errors of the estimate than previously provided, and 2) analyses of fossil floras from North America, Canada, the Arctic, and Australia. Analysis of the Canadian floras indicate moist climates (MAP >100cm/a) in the early and middle Eocene at middle and high paleolatitudes. Precipitation for western North America at mid-latitudes is also estimated as high, but a seasonally dry interior and south-east is indicated. For Australia, precipitation in the south-east is estimated >120 cm/a, but the macrofloras indicate a drier interior (MAP ~60 cm/a) and seasonal drought, contradicting estimates of ~120 cm/a based on NLR analysis of pollen floras. Recently published data show that north-eastern China in the Eocene had a monsoonal-type seasonality for

  10. Depositional controls on coal distribution and quality in the Eocene Brunner Coal Measures, Buller Coalfield, South Island, New Zealand

    USGS Publications Warehouse

    Flores, R.M.; Sykes, R.

    1996-01-01

    The Buller Coalfield on the West Coast of the South Island, New Zealand, contains the Eocene Brunner Coal Measures. The coal measures unconformably overlie Paleozoic-Cretaceous basement rocks and are conformably overlain by, and laterally interfinger with, the Eocene marine Kaiata Formation. This study examines the lithofacies frameworks of the coal measures in order to interpret their depositional environments. The lower part of the coal measures is dominated by conglomeratic lithofacies that rest on a basal erosional surface and thicken in paleovalleys incised into an undulating peneplain surface. These lithofacies are overlain by sandstone, mudstone and organic-rich lithofacies of the upper part of the coal measures. The main coal seam of the organic-rich lithofacies is thick (10-20 m), extensive, locally split, and locally absent. This seam and associated coal seams in the Buller Coalfield are of low- to high-volatile bituminous rank (vitrinite reflectance between 0.65% and 1.75%). The main seam contains a variable percentage of ash and sulphur. These values are related to the thickening and areal distribution of the seam, which in turn, were controlled by the nature of clastic deposition and peat-forming mire systems, marine transgression and local tidal incursion. The conglomeratic lithofacies represent deposits of trunk and tributary braided streams that rapidly aggraded incised paleovalleys during sea-level stillstands. The main seam represents a deposit of raised mires that initially developed as topogenous mires on abandoned margins of inactive braidbelts. Peat accumulated in mires as a response to a rise in the water table, probably initially due to gradual sea-level rise and climate, and the resulting raised topography served as protection from floods. The upper part of the coal measures consists of sandstone lithofacies of flu vial origin and bioturbated sandstone, mudstone and organic-rich lithofacies, which represent deposits of paralic (deltaic

  11. Multiple Early Eocene Thermal Maximums

    NASA Astrophysics Data System (ADS)

    Roehl, U.; Zachos, J. C.; Thomas, E.; Kelly, D. C.; Donner, B.; Westerhold, T.

    2004-12-01

    Periodic dissolution horizons signifying abrupt shoaling of the lysocline and CCD are characteristic features of deep-sea sections and often attributed to Milankovitch forcing via their diagnostic frequencies. Prominent dissolution horizons also correspond to abrupt climate events, such as the Paleocene-Eocene thermal maximum (PETM), as a result of input of significant CH4 - CO2 into the ocean-atmosphere system. The question arises whether other significant dissolution horizons identified in sediments of late Paleocene and early Eocene age similar to the recently identified ELMO (Lourens et al., 2004) were formed as a result of greenhouse gas input, or whether they were related to cumulative effects of periodic changes in ocean chemistry and circulation. Here we report the discovery of a 3rd thermal maximum in early Eocene (about 52 Ma) sediments recovered from the South Atlantic during ODP Leg 208. The prominent clay layer was named the "X" event and was identified within planktonic foraminifer zone P7 and calcareous nannofossil zone CP10 at four Walvis Ridge Transect sites with a water depth range of 2000 m (Sites 1262 to 1267). Benthics assemblages are composed of small individuals, have low diversity and high dominance. Dominant taxa are Nuttallides truempyi and various abyssaminids, resembling the post PETM extinction assemblages. High-resolution bulk carbonate \\delta13C measurements of one of the more shallow Sites 1265 reveal a rapid about 0.6 per mill drop in \\delta13C and \\delta18O followed by an exponential recovery to pre-excursion \\delta13C values well known for the PETM and also observed for the ELMO. The planktonic foraminiferal \\delta13C records of Morozovella subbotina and Acaranina soldadoensis in the deepest Site 1262 show a 0.8 to 0.9 per mill drop, whereas the \\delta13C drop of benthic foraminifera Nuttallides truempyi is slightly larger (about 1 per mill). We are evaluating mechanisms for the widespread change in deep-water chemistry, its

  12. Eocene ostracoda from Oshosun formation Southwestern Nigeria

    NASA Astrophysics Data System (ADS)

    Okosun, E. A.

    A biostratigraphic study of the phosphate-bearing Oshosun Formation in southwestern Nigeria (eastern Dahomey Embayment) gave ostracos which are diagnostic for the Eocene. The ostracod assemblage contains the early to middle Eocene zonal index Costa dahomeyi. The majority of the species are common to the phosphatic sequence in the western Dahomey Embayment. This paleontologic evidence, and the association of clay and shale with the phosphate occurrences in different parts of the basin, suggest that the phosphatic beds were deposited in the Dahomey Embayment under similar paleoenvironmental conditions. Phosphatic sedimentation in southwestern Nigeria is inferred to have occurred during an early to early middle Eocene minor marine transgression.

  13. The Eocene/Oligocene boundary event in the deep sea

    USGS Publications Warehouse

    Corliss, B.H.; Aubry, M.-P.; Berggren, W.A.; Fenner, J.M.; Keigwin, L.D.; Keller, G.

    1984-01-01

    Analysis of middle Eocene to early Oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the Eocene/Oligocene boundary. Biotic changes in the late Paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the Eocene/Oligocene boundary.

  14. Pre-Eocene rocks of Java, Indonesia

    USGS Publications Warehouse

    Ketner, Keith B.; Kastowo,; Modjo, Subroto; Naeser, C.W.; Obradovich, J.D.; Robinson, Keith; Suptandar, Tatan; Wikarno,

    1976-01-01

    The exposed pre-Eocene rocks of Java can be divided into two compound units for purposes of reconnaissance mapping and structural interpretation: a sedimentary sequence and melange. The sedimentary sequence consists of moderately deformed and little-metamorphosed conglomerate, sandstone, mudstone, claystone, chert, and limestone. The melange consists of a chaotic mechanical mixture of rocks identical to those of the sedimentary sequence and their metamorphic equivalents, such as schist, phyllite, quartzite, and marble. In addition, it contains a large proportion of quartz porphyry and smaller amounts of granite, basalt, gabbro, peridotite, pyroxenite, and serpentinite. The sedimentary sequence is at least partly of Early Cretaceous age and the melange is of Early Cretaceous to very early Paleocene age. They are overlain unconformably by Eocene rocks. The presence in the melange of blocks of quartz porphyry and granite is not easily reconcilable with current plate tectonic concepts in which the sites of formation of melange and plutonic rocks should be hundreds of kilometres apart.

  15. Geochronology of Early Eocene strata, Baja California

    SciTech Connect

    Flynn, J.J.; Cipolletti, R.M.

    1985-01-01

    Recent discoveries clearly indicate a Wasatchian (Early Eocene) land mammal age for fossil vertebrates from the Punta Prieta area, Baja California North, Mexico. This fauna provides a rare test for discriminating the temporal significance of mammalian faunas over a broad geographic area. The authors sampled intertonguing, fossiliferous terrestrial and marine strata for paleomagnetic and biostratigraphic analyses to provide an independent age determination for the Punta Prieta area mammal fauna. The marine macroinvertebrate assemblage is most likely upper Meganos to lower Capay West Coast Molluscan Stage based on the temporal ranges of all the taxa; also, none of the taxa occur in pre-Meganos stages. Two genera of planktonic forams indicate a probably Eocene age. They sampled seventeen paleomagnetic sites over 50 meters in the terrestrial mammal-bearing section, and thirteen sites over 25 meters in the marine section. The entire terrestrial sequence is reversely magnetized; initial results indicate the marine sequence probably also is reversely magnetized. Based on all the available biochronologic evidence this reversed sequence most likely should be correlated with the long reversed polarity Chron C24R. Clarkforkian to Early Wasatchian faunas in Wyoming also are associated with Chron C24R. All the available biostratigraphic and magnetostratigraphic evidence strongly supports an Early Eocene age for the Punta Prieta mammalian fauna and temporal equivalence of the Punta Prieta Wasatchian fauna with Wasatchian faunas from the Western United States. Land mammal ages are synchronous and applicable across broad geographic areas.

  16. Late Eocene rings around the earth

    NASA Technical Reports Server (NTRS)

    King, E. A.

    1980-01-01

    The suggestion of O'Keefe (1980) that the terminal Eocene event was caused by rings of tektite material encircling the earth is discussed. It is argued that the assumption that the tektites are of lunar volcanic origin is unwarranted and contrary to existing data, including the lack of lunar rocks of suitable composition, the lack of lunar rocks of the correct age, the lack of evidence that the North American tektites fell throughout a sedimentary rock column of a few million years, and the nondetection of a tektite with a measurable cosmic ray exposure age. Alternatively, it is suggested that the terminal Eocene event may be associated with volcanic ash, air-fall tuff and bentonite in the late Eocene. O'Keefe replies that the hypothesis of the terrestrial origin of the tektites conflicts with the laws of physics, for example in the glass structure and shaping of the tektites. Furthermore, evidence is cited for lunar rocks of the proper major-element composition and ages, and it is noted that the proposed solar Poynting-Robertson effect would account for the particle fall distributions and cosmic ray ages.

  17. Early Eocene uplift of southernmost San Joaquin basin, California

    SciTech Connect

    Reid, S.A.; Cox, B.F.

    1989-04-01

    Stratigraphic studies in the southern San Joaquin basin and in the El Paso Mountains of the southwestern Great Basin corroborate a hypothesized early Eocene regional uplift event. Eocene uplift and erosion of the southernmost San Joaquin basin south of Bakersfield were recently proposed because an early Paleogene fluviodeltaic sequence in the El Paso Mountains (Goler Formation) apparently had no seaward counterpart to the southwest. New microfossil data (coccoliths) indicate that marine deposits near the top of the Goler Formation are uppermost Paleocene (nannofossil zone CP8) rather than lower Eocene, as reported previously. These data (1) confirm that the oldest known Tertiary strata south of Bakersfield (Eocene Tejon Formation) are younger than the uppermost Goler Formation and (2) seem to restrict uplift to the earliest Eocene. The authors propose that the uppermost Cretaceous and Paleocene deposits were eroded and the Mushrush trough was cut and filled mainly in response to earliest Eocene uplift. The uplift was transverse to the northwest-trending forearc basin. Thus, it was distinct from late early Eocene (pre-Comengine Formation) regional tilting and uplift, which produced northwest-trending structures. Early Eocene uplift probably played only a minor role in the southward termination of pre-Maastrichtian parts of the forearc basin, which they instead attribute to massive uplift of the southernmost Sierra Nevada during the early(.) Late Cretaceous.

  18. Possible role of oceanic heat transport in early Eocene climate.

    PubMed

    Sloan, L C; Walker, J C; Moore, T C

    1995-04-01

    Increased oceanic heat transport has often been cited as a means of maintaining warm high-latitude surface temperatures in many intervals of the geologic past, including the early Eocene. Although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically, determining how additional oceanic heat transport would take place has yet to be accomplished. That the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked. Using early Eocene climate as an example, we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early Eocene conditions. Our interpolation of early Eocene paleotemperature data indicate that an approximately 30% increase in poleward heat transport would be required to maintain Eocene high-latitude temperatures. This increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early Eocene rates. Either oceanic processes were very different from those of the present to produce the early Eocene climate conditions or oceanic heat transport was not the primary cause of that climate. We believe that atmospheric processes, with contributions from other factors, such as clouds, were the most likely primary cause of early Eocene climate.

  19. Tectonic control of Eocene arkosic sediment deposition, Oregon and Washington

    SciTech Connect

    Armentrout, J.M.; Ulrich, A.R.

    1983-03-01

    Chronostratigraphic and geographic studies of Eocene arkosic sandstones suggest deposition during a volcanically quiet interval resulting from the westward jump of the Farallon-Kula plate subduction zone in Oregon and Washington. The Eocene arkosic sandstones were deposited as part of a broad fluvial plain-coastal plain-shelf margin basin complex extending throughout Oregon and Washington between uplands of Mesozoic rocks. Feldspathic-quartzose sediments were transported from the east by river systems draining granitic terrains perhaps as far away as the Idaho Batholith. Chronostratigraphic correlations suggest that the arkosic sandstones were deposited along the margins of the depositional system during the early Eocene, prograded westward during the middle Eocene, and then regressed during the latest Eocene and Oligocene simultaneously with the influx of abundant pyroclastic debris. During the early Eocene, a northwest-southeast seamount chain was extruded on the Farallon and Kula plates west of an eastward-dipping subduction zone. Subduction of the oceanic plates moved the seamount chain obliquely toward the subduction zone. In middle Eocene time-49 to 40 m.y.b.p-the seamount chain reached the subduction zone creating instability in the subduction system and resulting in the westward jump of the underthrust boundary between the Farallon-Kula and North American plates. Coincident with and continuing after the subduction zone jump and seamount accretion, eastwardly derived arkosic sediments prograded across Oregon and Washington spilling into the new fore-arc basin and enveloping the seamounts.

  20. Humidity estimate for the middle Eocene Arctic rain forest

    NASA Astrophysics Data System (ADS)

    Jahren, A. Hope; Silveira Lobo Sternberg, Leonel

    2003-05-01

    The exquisite preservation of fossilized Metasequoia trees that grew near 80°N latitude during the middle Eocene (ca. 45 Ma) in Nunavut, Canada, allowed for δD and δ18O analyses of cellulose, techniques previously restricted to wood <30,000 yr old. From the isotopic results, we determined that the middle Eocene Arctic atmosphere contained ˜2× the water found in the region's atmosphere today. This water vapor contributed to a middle Eocene greenhouse effect that insulated the polar region during dark polar winters.

  1. The Arctic Forest of the Middle Eocene

    NASA Astrophysics Data System (ADS)

    Jahren, A. Hope

    2007-05-01

    Lush forests, dominated by deciduous conifers, existed well north of the Arctic Circle during the middle Eocene (45 Ma). The Fossil Forest site, located on Axel Heiberg Island, Canada, has yielded a particularly rich assemblage of plant macro- and microfossils, as well as paleosols -- all exquisitely preserved. Methods ranging from classical paleobotany, to stable-isotope geochemistry, have been applied to materials excavated from the Fossil Forest and have revealed layers of diverse conifer forests with a rich angiosperm understory that successfully endured three months of continuous light and three months of continuous darkness. Paleoenvironmental reconstructions suggest a warm, ice-free environment, with high growing-season-relative humidity, and high rates of soil methanogenesis. Methods to evaluate intraseasonal variability highlight the switchover from stored to actively fixed carbon during the short annual growing season.

  2. Was the Arctic Eocene 'rainforest' monsoonal? Estimates of seasonal precipitation from early Eocene megafloras from Ellesmere Island, Nunavut

    NASA Astrophysics Data System (ADS)

    West, Christopher K.; Greenwood, David R.; Basinger, James F.

    2015-10-01

    The early Eocene was the warmest interval of the Cenozoic, and included within it were several hyperthermal events, with the Paleocene-Eocene Thermal Maximum (PETM) the most pronounced of these. These globally warm climates extended into the Arctic and substantive paleobotanical evidence for high Arctic precipitation (MAP > 150 cm/yr) is indicative of an Arctic rainforest, which contradicts some climate models that show low Arctic precipitation. Prior studies of Arctic early Eocene wood stable-isotope chemistry, however, have shown a summer peak in precipitation, which suggests modern analogs are best sought on the summer-wet east coast of the Asia (e.g., China, Japan, South Korea), not the winter-wet west coasts of the Pacific Northwest of North America). Furthermore, some prior modeling data suggest that highly seasonal 'monsoon-type' summer-wet precipitation regimes (i.e., summer:MAP > 55%) characterized certain mid and lower latitude regions in the early to mid-Eocene. Presented here is a new analysis using leaf physiognomy of 3 leaf megafloras (Split Lake, Stenkul Fiord and Strathcona Fiord) and palynofloral Bioclimatic Analysis from the Margaret Formation from Ellesmere Island, placed stratigraphically as early Eocene, possibly occurring during or following one of the early Eocene hyperthermals. These new data indicate high summer precipitation in the Arctic during the early Eocene, which in part corroborates the results from Eocene wood chemistry. Nevertheless, in contradiction to the wood analysis, monsoonal conditions are not indicated by our analysis, consistent with current modeling studies. High summer (light season) and winter (dark season) precipitation in the Eocene Arctic during hyperthermals would have contributed to regional warmth.

  3. The Terrestrial Eocene-Oligocene Transition in North America

    NASA Astrophysics Data System (ADS)

    Prothero, Donald R.; Emry, Robert J.

    1996-06-01

    The transition from the Eocene to the Oligocene epoch, occurring approximately 47 to 30 million years ago, was the most dramatic episode of climatic and biotic change since the demise of the dinosaurs. The mild tropical climates of the Paleocene and early Eocene were replaced by modern climatic conditions and extremes, including glacial ice in Antarctica. The first part of this book summarizes the latest information in the dating and correlation of the strata of late middle Eocene through early Oligocene age in North America. The second part reviews almost all the important terrestrial reptiles and mammals found near the Eocene-Oligocene boundary, in the White River Chronofauna--from the turtles, snakes and lizards to the common rodents, carnivores, oreodonts and deer of the Badlands. This is the first comprehensive treatment of these topics in over sixty years, and will be invaluable to vertebrate paleontologists, geologists, mammalogists and evolutionary biologists.

  4. Paleoclimatic analyses of middle Eocene through Oligocene planktic foraminiferal faunas

    USGS Publications Warehouse

    Keller, G.

    1983-01-01

    Quantitative faunal analyses and oxygen isotope ranking of individual planktic foraminiferal species from deep sea sequences of three oceans are used to make paleoceanographic and paleoclimatic inferences. Species grouped into surface, intermediate and deep water categories based on ??18O values provide evidence of major changes in water-mass stratification, and individual species abundances indicate low frequency cool-warm oscillations. These data suggest that relatively stable climatic phases with minor cool-warm oscillations of ???0.5 m.y. frequency are separated by rapid cooling events during middle Eocene to early Oligocene time. Five major climatic phases are evident in the water-mass stratification between middle Eocene through Oligocene time. Phase changes occur at P14/P15, P15/P16, P20/P21 and P21/P22 Zone boundaries and are marked by major faunal turnovers, rapid cooling in the isotope record, hiatuses and changes in the eustatic sea level. A general cooling trend between middle Eocene to early late Oligocene is indicated by the successive replacement of warm middle Eocene surface water species by cooler late Eocene intermediate water species and still cooler Oligocene intermediate and deep water species. Increased water-mass stratification in the latest Eocene (P17), indicated by the coexistence of surface, intermediate and deep dwelling species groups, suggest that increased thermal gradients developed between the equator and poles nearly coincident with the development of the psychrosphere. This pattern may be related to significant ice accumulation between late Eocene and early late Oligocene time. ?? 1983.

  5. Sediment budget of a terrestrial source-to-sink system: An example from the Eocene Escanilla Formation, Spanish Pyrenees

    NASA Astrophysics Data System (ADS)

    Michael, N.; Allen, P. A.; Carter, A.; Mange, M.

    2010-12-01

    This study examines the source-to-sink system of the Escanilla Formation in the South-Central Pyrenees(1). The Escanilla Formation is the fluvial segment of a sediment routing system that was deposited by ancient rivers in the Tremp-Graus and Ainsa wedge-top basins during the late Eocene, at the time of tectonic activity in the Pyrenean orogen(2-3). The study uses thermochronological and isotopic data (AFT and U-Pb geochronology) and heavy minerals as provenance tools, allowing correlation between the subunits and timelines within the Escanilla routing system(4-5) and pinpointing source areas. Volumetric analysis of the Escanilla routing system from the proximal depocenters of the Sis and Gurp Paleovalleys(2) to the distal fluvial depozones of the Tremp and Ainsa sub basins has been carried out. Additionally, granulometric data have been gathered throughout the sediment routing system. Using the combined sediment volume and grain size data, we estimate a probability density function for the sediment supply to the fluvial segment of the system within each chosen time interval. In addition, we calculate deposited sediment volumes per time interval that enable sediment discharges and catchment-averaged erosion rates to be estimated. Estimated erosion rates can be compared with estimates derived from thermochronological data. This study provides critical information on the pdf of the grain size distribution of the sediment supply, the sediment discharge from source area catchments, and the spatial distribution of subsidence in the basin within each of the time subdivisions of the Escanilla Formation. These factors comprise the main controls on down-system sedimentary architecture(6-8). References 1. Bentham, P.A. and Burbank, D.W. 1996 Chronology of Eocene foreland basin evolution along the western oblique margin of the South-Central Pyrenees. Tertiary basins of Spain: the stratigraphic record of crustal kinematics. Cambridge University Press, p400. 2. Vincent, S

  6. Constructing an Eocene Marine Ecosystem Sensitivity Scale

    NASA Astrophysics Data System (ADS)

    D'haenens, S.; Bornemann, A.; Speijer, R. P.; Hull, P. M.

    2014-12-01

    A key question in the face of current global environmental change is how marine ecosystems will respond and evolve in the future. To answer this, we first need to understand the relationship between environmental and ecosystem change - i.e., the ecosystem sensitivity. Addressing this question requires understanding of how biota respond to (a succession of) sudden environmental perturbations of varying sizes and durations in varying background conditions (i.e., climatic, oceanographic, biotic). Here, we compare new and published data from the Early to Middle Eocene greenhouse world to understand the sensitivity of marine ecosystems to background environmental change and hyperthermal events. This work focuses on the early Paleogene, because it is considered to be a good analog for a future high CO2 world. Newly generated high-resolution multiproxy datasets based on northern Atlantic DSDP Leg 48 and IODP Leg 342 material will allow us to compare the marine ecosystem responses (including bentho-pelagic systems) to abiotic drivers across climatic disruptions of differing magnitude. Initial results of a benthic foraminiferal community comparison including the PETM and ETM2 hyperthermals in the northeastern Atlantic DSDP sites 401 and 5501 suggest that benthic ecosystem sensitivity may actually be non-linearly linked to background climate states as reflected by a range of geochemical proxies (XRF, TOC, CaCO3, grain sizes, XRD clay mineralogy and foraminiferal δ18O, δ13C, Mg/Ca)2,3, in contrast to planktic communities4. Testing the type of scaling across different taxa, communities, initial background conditions and time scales may be the first big step to disentangle the often synergistic effects of environmental change on ecosystems5. References: 1D'haenens et al., 2012, in prep. 2Bornemann et al., 2014, EPSL 3D'haenens et al., 2014, PA 4Gibbs et al., 2012, Biogeosc. 5 Norris et al., 2013, Science

  7. Asian monsoons in a late Eocene greenhouse world

    NASA Astrophysics Data System (ADS)

    Licht, A.; van Cappelle, M.; Abels, H. A.; Ladant, J.-B.; Trabucho-Alexandre, J.; France-Lanord, C.; Donnadieu, Y.; Vandenberghe, J.; Rigaudier, T.; Lécuyer, C.; Terry, D., Jr.; Adriaens, R.; Boura, A.; Guo, Z.; Soe, Aung Naing; Quade, J.; Dupont-Nivet, G.; Jaeger, J.-J.

    2014-09-01

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.

  8. Widespread formation of cherts during the early Eocene climate optimum

    NASA Astrophysics Data System (ADS)

    Muttoni, G.; Kent, D. V.

    2007-12-01

    Radiolarian cherts in the Tethyan realm of Jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates. However, the widespread occurrence of cherts in the Eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones. In a new survey of the global spatiotemporal distribution of Cenozoic cherts in Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sediment cores, we found that cherts occur most frequently in the Paleocene and early Eocene, with a peak in occurrences at ~50 Ma that is coincident with the time of highest bottom water temperatures of the early Eocene climatic optimum (EECO) when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity. Cherts occur less commonly during the subsequent Eocene global cooling trend. Primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation. This timing of peak Eocene chert occurrence, which is supported by detailed stratigraphic correlations, contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and/or volcanism in a supposedly sluggish ocean of the EECO, followed during the subsequent middle Eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification, with the formation of chert as a result of biosilica transformation during diagenesis. Instead, we suggest that basin-basin fractionation by deep-sea circulation could have raised the concentration of EECO dissolved silica especially in the North Atlantic, where an alternative mode of silica burial involving widespread direct precipitation and/or absorption of silica by clay minerals could have

  9. High plant diversity in Eocene South America: Evidence from Patagonia

    USGS Publications Warehouse

    Wilf, P.; Cuneo, N.R.; Johnson, K.R.; Hicks, J.F.; Wing, S.L.; Obradovich, J.D.

    2003-01-01

    Tropical South America has the highest plant diversity of any region today, but this richness is usually characterized as a geologically recent development (Neogene or Pleistocene). From caldera-lake beds exposed at Laguna del Hunco in Patagonia, Argentina, paleolatitude ???47??S, we report 102 leaf species. Radioisotopic and paleomagnetic analyses indicate that the flora was deposited 52 million years ago, the time of the early Eocene climatic optimum, when tropical plant taxa and warm, equable climates reached middle latitudes of both hemispheres. Adjusted for sample size, observed richness exceeds that of any other Eocene leaf flora, supporting an ancient history of high plant diversity in warm areas of South America.

  10. Eocene precipitation: How wet do greenhouse climates get? (Invited)

    NASA Astrophysics Data System (ADS)

    Greenwood, D. R.; Smith, R. Y.

    2010-12-01

    The Eocene was the warmest part of the Cenozoic due to CO2 being at 2x - 4x Holocene levels, with warm climates extending across North America into the Arctic. Substantive paleobotanical evidence for this greenhouse time shows the existence of extensive broadleaf and coniferous polar forests - a circumpolar rain forest. Similarly, Australia in the Eocene - while 25° south of its present position - was a well-forested and humid continent, in contrast to today where 2/3 of the continent is arid or semi-arid and lacks forest. Both of these regions reflect past climate states - mesothermal moist climates with low thermal seasonality at high latitudes - that have no analog in the modern world; undiscovered earth climates. Paleontological temperature proxies provide a basis for understanding early Paleogene climates; however, there is a lack of corresponding proxy data on precipitation. Paleobotanical proxies offer 2 methods for estimated paleo-precipitation; leaf physiognomy (including leaf area analysis), and quantitative analysis of nearest living relatives (‘NLRs’) of macrofloras. Presented here is an exploration of this former greenhouse world, through analyses of macrofloras from mid-latitude North America and the Canadian Arctic, as well as from Australia. Analysis of the Canadian Arctic floras indicate upper microthermal to lower mesothermal moist climates (MAT ~13-15 °C, CMMT ~4 °C, MAP >100cm/a) in the early and middle Eocene. Leaf-area analysis of Paleocene and Eocene Arctic floras demonstrates precipitation for the Paleogene western and eastern Arctic estimated as >100 cm/yr. Sites from the Okanagan Highlands early Eocene lake macrofloras of British Columbia and northern Washington indicate comparable conditions in the early Eocene to those reconstructed for the Arctic in the middle Eocene, with MAP ~100cm/a for most sites along a 1000km North-South transect from Republic in Washington State to Driftwood Canyon near Smithers in northern British

  11. A new Late Eocene anthropoid primate from Thailand.

    PubMed

    Chaimanee, Y; Suteethorn, V; Jaeger, J J; Ducrocq, S

    1997-01-30

    The fossil record of anthropoid primates from the Middle Eocene of South Asia is so far restricted to two genera (Pondaungia cotteri Pilgrim, 1937 and Amphipithecus mogaungensis Colbert, 1937 from the Eocene Pondaung deposits of Burma) whose anthropoid status and phylogenetic position have long been under debate because they represent the oldest highly derived fossil primates of anthropoid grade. Moreover, several new African taxa, some of which are even older, have been recently included in the suborder Anthropoidea, suggesting an African origin for this group. Conversely, new fossil primates recently discovered in China (Eosimias) have been related to the most primitive representatives of Anthropoidea, alternatively suggesting an Asian origin and a probable Asian radiation centre. We report here the discovery of a new anthropoid from the Thai Late Eocene locality of Krabi, which displays several additional anthropoid characters with regard to those of the Eocene Burmese genera. This species, which is about the size of the Fayum Aegyptopithecus, can be related to the Burmese forms, and it further provides strong additional evidence for a southeast Asian evolutionary centre for anthropoids.

  12. High bat (Chiroptera) diversity in the Early Eocene of India

    NASA Astrophysics Data System (ADS)

    Smith, Thierry; Rana, Rajendra S.; Missiaen, Pieter; Rose, Kenneth D.; Sahni, Ashok; Singh, Hukam; Singh, Lachham

    2007-12-01

    The geographic origin of bats is still unknown, and fossils of earliest bats are rare and poorly diversified, with, maybe, the exception of Europe. The earliest bats are recorded from the Early Eocene of North America, Europe, North Africa and Australia where they seem to appear suddenly and simultaneously. Until now, the oldest record in Asia was from the Middle Eocene. In this paper, we report the discovery of the oldest bat fauna of Asia dating from the Early Eocene of the Cambay Formation at Vastan Lignite Mine in Western India. The fossil taxa are described on the basis of well-preserved fragments of dentaries and lower teeth. The fauna is highly diversified and is represented by seven species belonging to seven genera and at least four families. Two genera and five species are new. Three species exhibit very primitive dental characters, whereas four others indicate more advanced states. Unexpectedly, this fauna presents strong affinities with the European faunas from the French Paris Basin and the German Messel locality. This could result from the limited fossil record of bats in Asia, but could also suggest new palaeobiogeographic scenarios involving the relative position of India during the Early Eocene.

  13. Warm ocean processes and carbon cycling in the Eocene.

    PubMed

    John, Eleanor H; Pearson, Paul N; Coxall, Helen K; Birch, Heather; Wade, Bridget S; Foster, Gavin L

    2013-10-28

    Sea surface and subsurface temperatures over large parts of the ocean during the Eocene epoch (55.5-33.7 Ma) exceeded modern values by several degrees, which must have affected a number of oceanic processes. Here, we focus on the effect of elevated water column temperatures on the efficiency of the biological pump, particularly in relation to carbon and nutrient cycling. We use stable isotope values from exceptionally well-preserved planktonic foraminiferal calcite from Tanzania and Mexico to reconstruct vertical carbon isotope gradients in the upper water column, exploiting the fact that individual species lived and calcified at different depths. The oxygen isotope ratios of different species' tests are used to estimate the temperature of calcification, which we converted to absolute depths using Eocene temperature profiles generated by general circulation models. This approach, along with potential pitfalls, is illustrated using data from modern core-top assemblages from the same area. Our results indicate that, during the Early and Middle Eocene, carbon isotope gradients were steeper (and larger) through the upper thermocline than in the modern ocean. This is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm Eocene ocean, leading to more efficient recycling of organic matter and reduced burial rates of organic carbon.

  14. Possible methane-induced polar warming in the early Eocene.

    PubMed

    Sloan, L C; Walker, J C; Moore, T C; Rea, D K; Zachos, J C

    1992-05-28

    Reconstructions of early Eocene climate depict a world in which the polar environments support mammals and reptiles, deciduous forests, warm oceans and rare frost conditions. At the same time, tropical sea surface temperatures are interpreted to have been the same as or slightly cooler than present values. The question of how to warm polar regions of Earth without noticeably warming the tropics remains unresolved; increased amounts of greenhouse gases would be expected to warm all latitudes equally. Oceanic heat transport has been postulated as a mechanism for heating high latitudes, but it is difficult to explain the dynamics that would achieve this. Here we consider estimates of Eocene wetland areas and suggest that the flux of methane, an important greenhouse gas, may have been substantially greater during the Eocene than at present. Elevated methane concentrations would have enhanced early Eocene global warming, and also might specifically have prevented severe winter cooling of polar regions because of the potential of atmospheric methane to promote the formation of optically thick, polar stratospheric ice clouds.

  15. Arctic plant diversity in the Early Eocene greenhouse

    PubMed Central

    Harrington, Guy J.; Eberle, Jaelyn; Le-Page, Ben A.; Dawson, Mary; Hutchison, J. Howard

    2012-01-01

    For the majority of the Early Caenozoic, a remarkable expanse of humid, mesothermal to temperate forests spread across Northern Polar regions that now contain specialized plant and animal communities adapted to life in extreme environments. Little is known on the taxonomic diversity of Arctic floras during greenhouse periods of the Caenozoic. We show for the first time that plant richness in the globally warm Early Eocene (approx. 55–52 Myr) in the Canadian High Arctic (76° N) is comparable with that approximately 3500 km further south at mid-latitudes in the US western interior (44–47° N). Arctic Eocene pollen floras are most comparable in richness with today's forests in the southeastern United States, some 5000 km further south of the Arctic. Nearly half of the Eocene, Arctic plant taxa are endemic and the richness of pollen floras implies significant patchiness to the vegetation type and clear regional richness of angiosperms. The reduced latitudinal diversity gradient in Early Eocene North American plant species demonstrates that extreme photoperiod in the Arctic did not limit taxonomic diversity of plants. PMID:22072610

  16. Lower Eocene carbonate facies of Egypt: paleogeographic and tectonic implications

    SciTech Connect

    Garrison, R.E.

    1983-03-01

    The northern Arabo-Nubian craton witnessed a major Late Cretaceous-early Tertiary marine transgression that culminated in the deposition of widespread shelf-sea carbonates during Early Eocene (Ypresian) time. Outer shelf facies characterize exposures in central Egypt (Assiut, Luxor, Kharga), and are composed primarily of rhythmically interbedded chalk and micritic limestone with minor intercalated marine hardgrounds. To the south (Kurkur-Dungul), these fine-grained lithologies give way to inner shelf foraminiferal wackestones and grainstones, typical Tethyan Nummulitic facies. Missing in southern Egypt is the restricted dolomitic evaporitic facies predicted by the Irwin model and observed in the lower Eocene of the Sirte basin to the west and the Arabian Platform to the east. Comparing the areal distribution of these lower Eocene carbonates to coeval facies developed across the remained of northern Africa and Arabia reveals the presence of a broad marine embayment which extended through central and eastern Egypt into northern Sudan during Ypresian time. The widespread subsidence that resulted in the development of this features may have been an effect of regional crustal attenuation preceding the rifting of the Red Sea. Concomitant with this regional subsidence were localized uplift and extensional block faulting in the vicinity of the incipient Red Sea rift (the Safaga-Quseir coastal plain). Here, lower Eocene carbonate facies are indicative of shallow water platforms developed on horst blocks, and deeper water, turbidite-fed basins in intervening grabens.

  17. New taxa of Tanyderidae (Diptera) from Eocene Baltic amber.

    PubMed

    Krzeminski, Wiesław; Krzeminska, Ewa; Kania, Iwona; Ross, Andrew J

    2013-01-01

    Macrochile hornei sp. nov. from Baltic amber (Upper Eocene) is described and illustrated. Podemacrochile gen. nov. is described with Podemacrochile baltica (Podenas, 1997) as type species. A key to the genera and species of Tanyderidae known from Baltic amber is presented. PMID:24583815

  18. Eocene cooling linked to early flow across the Tasmanian Gateway

    PubMed Central

    Bijl, Peter K.; Bendle, James A. P.; Bohaty, Steven M.; Pross, Jörg; Schouten, Stefan; Tauxe, Lisa; Stickley, Catherine E.; McKay, Robert M.; Röhl, Ursula; Olney, Matthew; Sluijs, Appy; Escutia, Carlota; Brinkhuis, Henk; Klaus, Adam; Fehr, Annick; Williams, Trevor; Carr, Stephanie A.; Dunbar, Robert B.; Gonzàlez, Jhon J.; Hayden, Travis G.; Iwai, Masao; Jimenez-Espejo, Francisco J.; Katsuki, Kota; Kong, Gee Soo; Nakai, Mutsumi; Passchier, Sandra; Pekar, Stephen F.; Riesselman, Christina; Sakai, Toyosaburo; Shrivastava, Prakash K.; Sugisaki, Saiko; Tuo, Shouting; van de Flierdt, Tina; Welsh, Kevin; Yamane, Masako

    2013-01-01

    The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52–50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO2). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ∼49–50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2–4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO2 forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling. PMID:23720311

  19. Rapid Middle Eocene temperature change in western North America

    NASA Astrophysics Data System (ADS)

    Methner, Katharina; Mulch, Andreas; Fiebig, Jens; Wacker, Ulrike; Gerdes, Axel; Graham, Stephan A.; Chamberlain, C. Page

    2016-09-01

    Eocene hyperthermals are among the most enigmatic phenomena of Cenozoic climate dynamics. These hyperthermals represent temperature extremes superimposed on an already warm Eocene climate and dramatically affected the marine and terrestrial biosphere, yet our knowledge of temperature and rainfall in continental interiors is still rather limited. We present stable isotope (δ18O) and clumped isotope temperature (Δ47) records from a middle Eocene (41 to 40 Ma) high-elevation mammal fossil locality in the North American continental interior (Montana, USA). Δ47 paleotemperatures of soil carbonates delineate a rapid +9/-11 °C temperature excursion in the paleosol record. Δ47 temperatures progressively increase from 23 °C ± 3 °C to peak temperatures of 32 °C ± 3 °C and subsequently drop by 11 °C. This hyperthermal event in the middle Eocene is accompanied by low δ18O values and reduced pedogenic carbonate concentrations in paleosols. Based on laser ablation U/Pb geochronology of paleosol carbonates in combination with magnetostratigraphy, biostratigraphy, stable isotope, and Δ47 evidence, we suggest that this pronounced warming event reflects the Middle Eocene Climatic Optimum (MECO) in western North America. The terrestrial expression of northern hemisphere MECO in western North America appears to be characterized by warmer and wetter (sub-humid) conditions, compared to the post-MECO phase. Large and rapid shifts in δ18O values of precipitation and pedogenic CaCO3 contents parallel temperature changes, indicating the profound impact of the MECO on atmospheric circulation and rainfall patterns in the western North American continental interior during this transient warming event.

  20. Seasonal variability in Arctic temperatures during the early Eocene

    NASA Astrophysics Data System (ADS)

    Eberle, J. J.; Fricke, H. C.; Humphrey, J.; Hackett, L.; Newbrey, M.; Hutchison, H.

    2009-12-01

    As a deep time analog for today’s rapidly warming Arctic region, early Eocene (~53 Ma) rocks on Ellesmere Island, Arctic Canada (~79° N.) preserve evidence of lush swamp forests inhabited by turtles, alligators, primates, tapirs, and hippo-like Coryphodon. Although the rich flora and fauna of the early Eocene Arctic imply warmer, wetter conditions that at present, quantitative estimates of Eocene Arctic climate are rare. By analyzing oxygen isotope ratios of biogenic phosphate from mammal, fish, and turtle fossils from a single locality on central Ellesmere Island, we provide estimates of early Eocene Arctic temperature, including mean annual temperature (MAT) of ~ 8° C, mean annual range in temperature (MART) of ~ 16.5° C, warm month mean temperature (WMMT) of 16 - 19° C, and cold month mean temperature (CMMT) of 0 - 1° C. Our seasonal range in temperature is similar to the range in estimated MAT obtained using different proxies. In particular, unusually high estimates of early Eocene Arctic MAT and sea surface temperature (SST) by others that are based upon the distribution of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in terrestrial soil bacteria and marine Crenarchaeota fall within our range of WMMT, suggesting a bias towards summer values. Consequently, caution should be taken when using these methods to infer MAT and SST that, in turn, are used to constrain climate models. From a paleontologic perspective, our temperature estimates verify that alligators and tortoises, by way of nearest living relative-based climatic inference, are viable paleoclimate proxies for mild, above-freezing year-round temperatures. Although in both of these reptiles, past temperature tolerances were greater than in their living descendants.

  1. Eocene cooling linked to early flow across the Tasmanian Gateway.

    PubMed

    Bijl, Peter K; Bendle, James A P; Bohaty, Steven M; Pross, Jörg; Schouten, Stefan; Tauxe, Lisa; Stickley, Catherine E; McKay, Robert M; Röhl, Ursula; Olney, Matthew; Sluijs, Appy; Escutia, Carlota; Brinkhuis, Henk

    2013-06-11

    The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52-50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO2). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began ~49-50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2-4 °C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO2 forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling.

  2. Seasonal variability in Arctic temperatures during early Eocene time

    NASA Astrophysics Data System (ADS)

    Eberle, Jaelyn J.; Fricke, Henry C.; Humphrey, John D.; Hackett, Logan; Newbrey, Michael G.; Hutchison, J. Howard

    2010-08-01

    As a deep time analog for today's rapidly warming Arctic region, early Eocene (52-53 Ma) rock on Ellesmere Island in Canada's High Arctic (˜ 79°N.) preserves evidence of lush swamp forests inhabited by turtles, alligators, primates, tapirs, and hippo-like Coryphodon. Although the rich flora and fauna of the early Eocene Arctic imply warmer, wetter conditions than at present, the quantification of Eocene Arctic climate has been more elusive. By analyzing oxygen isotope ratios of biogenic phosphate from mammal, fish, and turtle fossils from a single locality on central Ellesmere Island, we infer early Eocene Arctic temperatures, including mean annual temperature (MAT) of ˜ 8 °C, mean annual range in temperature of ˜ 16.5-19 °C, warm month mean temperature of 19-20 °C, and cold month mean temperature of 0-3.5 °C. Our seasonal range in temperature is similar to the range in estimated MAT obtained using different proxies. In particular, relatively high estimates of early Eocene Arctic MAT and SST by others that are based upon the distribution of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in terrestrial soil bacteria and isoprenoid tetraether lipids in marine Crenarchaeota fall close to our warm month temperature, suggesting a bias towards summer values. From a paleontologic perspective, our temperature estimates verify that alligators and tortoises, by way of nearest living relative-based climatic inference, are viable paleoclimate proxies for mild, above-freezing year-round temperatures. Although for both of these reptilian groups, past temperature tolerances probably were greater than in living descendants.

  3. Late Eocene diatomite from the Peruvian coastal desert, coastal upwelling in the eastern Pacific, and Pacific circulation before the terminal Eocene event

    SciTech Connect

    Marty, R.; Dunbar, R.; Martin, J.B.; Baker, P.

    1988-09-01

    Previously undocumented late Eocene diatomaceous sediments are present near Fundo Desbarrancado (FD) in southern Peru. These sediments are similar to Miocene diatomite from the same area but, unlike the Miocene diatomite, the FD sediments contain cherty layers, are enriched in CaCO/sub 3/, have a diverse and abundant radiolarian fauna, and possess varved-massive and millimeter- and meter-scale biogenic-terrigenous alternations. The FD sediments are part of an Eocene sequence that includes the clastic sediments of the Paracas Formation, and they are correlative to the Chira Formation of northern Peru. The Paleogene biogenic sediments of western South America show that coastal upwelling developed in the eastern Pacific before the latest Eocene, argue for the existence of a proto-Humboldt current at this time, and suggest that the terminal Eocene event was the culmination of gradual changes and not a catastrophic event at the Eocene/Oligocene boundary.

  4. Environment and evolution through the Paleocene-Eocene thermal maximum.

    PubMed

    Gingerich, Philip D

    2006-05-01

    The modern orders of mammals, Artiodactyla, Perissodactyla and Primates (APP taxa), first appear in the fossil record at the Paleocene-Eocene boundary, c. 55 million years ago. Their appearance on all three northern continents has been linked to diversification and dispersal in response to rapid environmental change at the beginning of a worldwide 100 000-200 000-year Paleocene-Eocene thermal maximum (PETM) and carbon isotope excursion. As I discuss here, global environmental events such as the PETM have had profound effects on evolution in the geological past and must be considered when modeling the history of life. The PETM is also relevant when considering the causes and consequences of global greenhouse warming.

  5. Cretaceous and Eocene lignite deposits, Jackson Purchase, Kentucky

    USGS Publications Warehouse

    Hower, J.C.; Rich, F.J.; Williams, D.A.; Bland, A.E.; Fiene, F.L.

    1990-01-01

    Lignites occur in the Cretaceous McNairy Formation and the Eocene Claiborne Formation in the Jackson Purchase region of western Kentucky. The lone Cretaceous lignite sample has over 18 percent inertodetrinite and 32 percent humodetrinite which, along with the abundant mineral matter, suggests a possible allochthonous origin for the deposit. The Claiborne Formation lignites have higher humic maceral contents than the Cretaceous lignites. Palynology suggests that there was considerable variation in the plant communities responsible for the Claiborne deposits. Differences in the preservation of the various plants is also seen in the variations between the humic types, particularly in the ulminite and humodetrinite contents. Potter and Dilcher (1980) suggested that the Claiborne lignites in the Jackson Purchase and west Tennessee developed in the abandoned oxbows of Eocene rivers. Significant short-distance changes in the peat thickness, flora, and other depositional elements should be expected in such an environment and could easily account for the observed variations in composition. ?? 1990.

  6. Late Eocene impact microspherules - Stratigraphy, age and geochemistry

    NASA Astrophysics Data System (ADS)

    Keller, G.; D'Hondt, S. L.; Orth, C. J.; Gilmore, J. S.; Oliver, P. Q.; Shoemaker, E. M.; Molina, E.

    1987-03-01

    The stratigraphy, faunal changes, and geochemistry of deep-sea sediments associated with late Eocene microtektite and microspherule layers are reported. Microprobe analyses of major element compositions of microspherules show that, although there is some compositional overlap in all three late Eocene layers as well as with the Pleistocene Australasian and Ivory Coast microtektites, each microspherule population has characteristic compositional features. All three microspherule layers are associated with decreased carbonate, possibly due to a sudden productivity change, increased dissolution as a result of sea-level and climate fluctuations, or impact events. A discovery of microtektites in the Gl. cerroazulensis Zone off the New Jersey coast extends the North American strewn field from the Caribbean to the northwest Atlantic.

  7. The Middle Eocene flora of Csordakút (N Hungary)

    NASA Astrophysics Data System (ADS)

    Erdei, Boglárka; Rákosi, László

    2009-02-01

    The Middle Eocene fossil plant assemblage from Csordakút (N Hungary) comprises plant remains preserved exclusively as impressions. Algae are represented by abundant remains of Characeae, including both vegetative fragments and gyrogonites. Remains of angiosperms comprise Lauraceae (Daphnogene sp.), Fagaceae (cf. Eotrigonobalanus furcinervis), Ulmaceae (Cedrelospermum div. sp.), Myricaceae (Myrica sp., Comptonia div. sp.), Leguminosae (leaves and fruit), Rhamnaceae (?Zizyphus zizyphoides), Elaeocarpaceae (Sloanea nimrodi, Sloanea sp. fruit), Smilacaceae (Smilax div. sp.). The absence of gymnosperms is indicative of a floristic similarity to the coeval floras of Tatabánya (N Hungary) and Girbou in Romania. Sloanea nimrodi (Ettingshausen) Kvaček & Hably, a new element for the Hungarian fossil record indicates a floristic relation to the Late Eocene flora of Kučlin (Bohemia).

  8. Impact ejecta at the Paleocene-Eocene boundary

    NASA Astrophysics Data System (ADS)

    Schaller, Morgan F.; Fung, Megan K.; Wright, James D.; Katz, Miriam E.; Kent, Dennis V.

    2016-10-01

    Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.

  9. A New Eocene Casquehead Lizard (Reptilia, Corytophanidae) from North America.

    PubMed

    Conrad, Jack L

    2015-01-01

    A new fossil showing affinities with extant Laemanctus offers the first clear evidence for a casquehead lizard (Corytophanidae) from the Eocene of North America. Along with Geiseltaliellus from roughly coeval rocks in central Europe, the new find further documents the tropical fauna present during greenhouse conditions in the northern mid-latitudes approximately 50 million years ago (Ma). Modern Corytophanidae is a neotropical clade of iguanian lizards ranging from southern Mexico to northern South America.

  10. Climate directly influences Eocene mammal faunal dynamics in North America

    PubMed Central

    Woodburne, Michael O.; Gunnell, Gregg F.; Stucky, Richard K.

    2009-01-01

    The modern effect of climate on plants and animals is well documented. Some have cautioned against assigning climate a direct role in Cenozoic land mammal faunal changes. We illustrate 3 episodes of significant mammalian reorganization in the Eocene of North America that are considered direct responses to dramatic climatic events. The first episode occurred during the Paleocene–Eocene Thermal Maximum (PETM), beginning the Eocene (55.8 Ma), and earliest Wasatchian North American Land Mammal Age (NALMA). The PETM documents a short (<170 k.y.) global temperature increase of ≈5 °C and a substantial increase in first appearances of mammals traced to climate-induced immigration. A 4-m.y. period of climatic and evolutionary stasis then ensued. The second climate episode, the late early Eocene Climatic Optimum (EECO, 53–50 Ma), is marked by a temperature increase to the highest prolonged Cenozoic ocean temperature and a similarly distinctive continental interior mean annual temperature (MAT) of 23 °C. This MAT increase [and of mean annual precipitation (MAP) to 150 cm/y) promoted a major increase in floral diversity and habitat complexity under temporally unique, moist, paratropical conditions. Subsequent climatic deterioration in a third interval, from 50 to 47 Ma, resulted in major faunal diversity loss at both continental and local scales. In this Bridgerian Crash, relative abundance shifted from very diverse, evenly represented, communities to those dominated by the condylarth Hyopsodus. Rather than being “optimum,” the EECO began the greatest episode of faunal turnover of the first 15 m.y. of the Cenozoic. PMID:19666605

  11. Climate directly influences Eocene mammal faunal dynamics in North America.

    PubMed

    Woodburne, Michael O; Gunnell, Gregg F; Stucky, Richard K

    2009-08-11

    The modern effect of climate on plants and animals is well documented. Some have cautioned against assigning climate a direct role in Cenozoic land mammal faunal changes. We illustrate 3 episodes of significant mammalian reorganization in the Eocene of North America that are considered direct responses to dramatic climatic events. The first episode occurred during the Paleocene-Eocene Thermal Maximum (PETM), beginning the Eocene (55.8 Ma), and earliest Wasatchian North American Land Mammal Age (NALMA). The PETM documents a short (<170 k.y.) global temperature increase of approximately 5 degrees C and a substantial increase in first appearances of mammals traced to climate-induced immigration. A 4-m.y. period of climatic and evolutionary stasis then ensued. The second climate episode, the late early Eocene Climatic Optimum (EECO, 53-50 Ma), is marked by a temperature increase to the highest prolonged Cenozoic ocean temperature and a similarly distinctive continental interior mean annual temperature (MAT) of 23 degrees C. This MAT increase [and of mean annual precipitation (MAP) to 150 cm/y) promoted a major increase in floral diversity and habitat complexity under temporally unique, moist, paratropical conditions. Subsequent climatic deterioration in a third interval, from 50 to 47 Ma, resulted in major faunal diversity loss at both continental and local scales. In this Bridgerian Crash, relative abundance shifted from very diverse, evenly represented, communities to those dominated by the condylarth Hyopsodus. Rather than being "optimum," the EECO began the greatest episode of faunal turnover of the first 15 m.y. of the Cenozoic. PMID:19666605

  12. Asian Eocene monsoons as revealed by leaf architectural signatures

    NASA Astrophysics Data System (ADS)

    Spicer, Robert A.; Yang, Jian; Herman, Alexei B.; Kodrul, Tatiana; Maslova, Natalia; Spicer, Teresa E. V.; Aleksandrova, Galina; Jin, Jianhua

    2016-09-01

    The onset and development of the Asian monsoon systems is a topic that has attracted considerable research effort but proxy data limitations, coupled with a diversity of definitions and metrics characterizing monsoon phenomena, have generated much debate. Failure of geological proxies to yield metrics capable of distinguishing between rainfall seasonality induced by migrations of the Inter-tropical Convergence Zone (ITCZ) from that attributable to topographically modified seasonal pressure reversals has frustrated attempts to understand mechanisms underpinning monsoon development and dynamics. Here we circumvent the use of such single climate parameter metrics in favor of detecting directly the distinctive attributes of different monsoon regimes encoded in leaf fossils. Leaf form adapts to the prevailing climate, particularly under the extreme seasonal stresses imposed by monsoons, so it is likely that fossil leaves carry a unique signature of past monsoon regimes. Leaf form trait spectra obtained from fossils from Eocene basins in southern China were compared with those seen in modern leaves growing under known climate regimes. The fossil leaf trait spectra, including those derived from previously published fossil floras from northwestern India, were most similar to those found in vegetation exposed to the modern Indonesia-Australia Monsoon (I-AM), which is largely a product of seasonal migrations of the ITCZ. The presence of this distinctive leaf physiognomic signature suggests that although a monsoon climate existed in Eocene time across southern Asia the characteristics of the modern topographically-enhanced South Asia Monsoon had yet to develop. By the Eocene leaves in South Asia had become well adapted to an I-AM type regime across many taxa and points to the existence of a pervasive monsoon climate prior to the Eocene. No fossil trait spectra typical of exposure to the modern East Asia monsoon were seen, suggesting the effects of this system in southern

  13. A New Eocene Casquehead Lizard (Reptilia, Corytophanidae) from North America

    PubMed Central

    Conrad, Jack L.

    2015-01-01

    A new fossil showing affinities with extant Laemanctus offers the first clear evidence for a casquehead lizard (Corytophanidae) from the Eocene of North America. Along with Geiseltaliellus from roughly coeval rocks in central Europe, the new find further documents the tropical fauna present during greenhouse conditions in the northern mid-latitudes approximately 50 million years ago (Ma). Modern Corytophanidae is a neotropical clade of iguanian lizards ranging from southern Mexico to northern South America. PMID:26131767

  14. Temperate Pollen Genera in the Eocene (Claiborne) Flora, Alabama.

    PubMed

    Gray, J

    1960-09-23

    Pollen, spores, hystrichospherids, dinoflagellates, and the fresh-water alga Pediastrum occur in marine clays at the classic Claiborne Bluffs locality, Alabama. The presence of Ephedra pollen provides the first documented Tertiary record of this genus from the southeastern states. The occurrence of several characteristically temperate genera lends support to the idea that a deciduous hardwood forest was present in the Appalachian uplands during the Eocene.

  15. Eocene-Oligocene boundary problems, west coast, North America

    SciTech Connect

    Armentrout, J.M.

    1983-03-01

    Correlation of the international Eocene-Oligocene boundary with the provincial biostratigraphic framework of the northeast Pacific margin has been and continues to be controversial. The controversy centers about historical nomenclature and correlations, and current correlations based on planktonic fossil group. The Geological Society of America's C.E. Weaver Committee published the first interdisciplinary correlation chart for the Cenozoic rocks of the western United States in 1944. The committee placed the Eocene-Oligocene boundary at the base of the Keasey Molluscan Stage and Refugian Benthic Foraminiferal Stage. The most useful provincial boundaries of Late Eocene to Oligocene age are the Narizian-Refugian and Refugian-Zemorrian Benthic Foraminiferal Stage boundaries. Reevaluation of the Refugian Stage has recently been completed. The stage boundaries have been correlated to the international geologic time scale using planktonic microfossils. Planktonic assemblages are rare in samples from above and below the Refugian-Zemorrian Benthic Foraminiferal Stage boundary. In California this boundary is commonly at an unconformity or without superposition of diagnostic faunas. In southwestern Washington the Refugian-Zemorrian boundary occurs in continuously deposited and foraminiferally rich sections. Radiometric calibration of the provincial boundaries is not yet possible. Whole rock potassium-argon and fission track dates are available but both have very large error bars or lack adequate biostratigraphic control to be useful. Fossiliferous stratigraphic sections have rocks with sufficient remanent magnetism for magnetostratigraphic studies but to date only reconnaissance data are available.

  16. Late Eocene white pines (Pinus subgenus Strobus) from southern China

    PubMed Central

    Xu, Qingqing; Zhou, Wenjun; Kodrul, Tatiana M.; Naugolnykh, Serge V.; Jin, Jianhua

    2015-01-01

    Fossil records indicate that the genus Pinus L. split into two subgenera by the Late Cretaceous, although subgenus Strobus (D. Don) Lemmon is less well documented than subgenus Pinus L., especially in eastern Asia. In this paper, Pinus maomingensis sp. nov. is established based on a compressed seed cone from the upper Eocene of the Maoming Basin of southern China. This species is attributed to genus Pinus, subgenus Strobus, section Quinquefoliae Duhamel, subsection Strobus Loudon based on the combination of morphological characters obtained from the cone scales, specifically from the terminal umbo, rhombic apophysis, and cuticle structure. Associated fascicles of needle leaves with deciduous sheaths and bulbous bases are recognized as Pinus sp. and also represent Pinus subgenus Strobus. This new discovery from the Maoming Basin constitutes the first megafossil record of subgenus Strobus from southern China and implies that the members of this subgenus arrived in the southern region of China by the late Eocene. The extant species of subgenus Strobus are mainly distributed in northern temperate and tropical to subtropical mountainous regions. We propose that the Maoming Basin was adjacent to a mountainous region during the late Eocene. PMID:26548658

  17. Late Eocene white pines (Pinus subgenus Strobus) from southern China.

    PubMed

    Xu, Qingqing; Zhou, Wenjun; Kodrul, Tatiana M; Naugolnykh, Serge V; Jin, Jianhua

    2015-11-09

    Fossil records indicate that the genus Pinus L. split into two subgenera by the Late Cretaceous, although subgenus Strobus (D. Don) Lemmon is less well documented than subgenus Pinus L., especially in eastern Asia. In this paper, Pinus maomingensis sp. nov. is established based on a compressed seed cone from the upper Eocene of the Maoming Basin of southern China. This species is attributed to genus Pinus, subgenus Strobus, section Quinquefoliae Duhamel, subsection Strobus Loudon based on the combination of morphological characters obtained from the cone scales, specifically from the terminal umbo, rhombic apophysis, and cuticle structure. Associated fascicles of needle leaves with deciduous sheaths and bulbous bases are recognized as Pinus sp. and also represent Pinus subgenus Strobus. This new discovery from the Maoming Basin constitutes the first megafossil record of subgenus Strobus from southern China and implies that the members of this subgenus arrived in the southern region of China by the late Eocene. The extant species of subgenus Strobus are mainly distributed in northern temperate and tropical to subtropical mountainous regions. We propose that the Maoming Basin was adjacent to a mountainous region during the late Eocene.

  18. Asian monsoons in a late Eocene greenhouse world.

    PubMed

    Licht, A; van Cappelle, M; Abels, H A; Ladant, J-B; Trabucho-Alexandre, J; France-Lanord, C; Donnadieu, Y; Vandenberghe, J; Rigaudier, T; Lécuyer, C; Terry, D; Adriaens, R; Boura, A; Guo, Z; Soe, Aung Naing; Quade, J; Dupont-Nivet, G; Jaeger, J-J

    2014-09-25

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.

  19. Asian monsoons in a late Eocene greenhouse world.

    PubMed

    Licht, A; van Cappelle, M; Abels, H A; Ladant, J-B; Trabucho-Alexandre, J; France-Lanord, C; Donnadieu, Y; Vandenberghe, J; Rigaudier, T; Lécuyer, C; Terry, D; Adriaens, R; Boura, A; Guo, Z; Soe, Aung Naing; Quade, J; Dupont-Nivet, G; Jaeger, J-J

    2014-09-25

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago. PMID:25219854

  20. Stable warm tropical climate through the Eocene Epoch

    NASA Astrophysics Data System (ADS)

    Pearson, Paul N.; van Dongen, Bart E.; Nicholas, Christopher J.; Pancost, Richard D.; Schouten, Stefan; Singano, Joyce M.; Wade, Bridget S.

    2007-03-01

    Earth's climate cooled from a period of extreme warmth in the early Eocene Epoch (ca. 50 Ma) to the early Oligocene (ca. 33 Ma), when a large ice cap first appeared on Antarctica. Evidence from the planktonic foraminifer oxygen isotope record in deep-sea cores has suggested that tropical sea-surface temperatures declined by 5-10 degrees over this interval, eventually becoming much cooler than modern temperatures. Here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine Crenarcheota from new drill cores in Tanzania that indicate a warm and generally stable tropical climate over this period. We reinterpret the previously published isotope records in the light of comparative textural analysis of the deep-sea foraminifer shells, which shows that in contrast to the Tanzanian material, they have been diagenetically recrystallized. We suggest that increasingly severe alteration of the deep-sea plankton shells through the Eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea-surface cooling trend. This implies that the long-term Eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes.

  1. Eocene Diversification of Crown Group Rails (Aves: Gruiformes: Rallidae)

    PubMed Central

    García–R, Juan C.; Gibb, Gillian C.; Trewick, Steve A.

    2014-01-01

    Central to our understanding of the timing of bird evolution is debate about an apparent conflict between fossil and molecular data. A deep age for higher level taxa within Neoaves is evident from molecular analyses but much remains to be learned about the age of diversification in modern bird families and their evolutionary ecology. In order to better understand the timing and pattern of diversification within the family Rallidae we used a relaxed molecular clock, fossil calibrations, and complete mitochondrial genomes from a range of rallid species analysed in a Bayesian framework. The estimated time of origin of Rallidae is Eocene, about 40.5 Mya, with evidence of intrafamiliar diversification from the Late Eocene to the Miocene. This timing is older than previously suggested for crown group Rallidae, but fossil calibrations, extent of taxon sampling and substantial sequence data give it credence. We note that fossils of Eocene age tentatively assigned to Rallidae are consistent with our findings. Compared to available studies of other bird lineages, the rail clade is old and supports an inference of deep ancestry of ground-dwelling habits among Neoaves. PMID:25291147

  2. Hydrocarbon potential of Middle Eocene carbonates, Sirt Basin, Libya

    NASA Astrophysics Data System (ADS)

    Swei, Giuma H.; Tucker, Maurice E.

    2015-11-01

    Deposition of Middle Eocene carbonates in the Sirt Basin in Libya has been the subject of considerable study in recent years because of the importance of sediments of this age as hydrocarbon reservoirs. The Gialo Formation is an important gas-producing reservoir in the Assumood, Sahl and other nearby fields. The gas which is generated from the gas-prone Sirt Shale source rock of the northern Ajdabiya Trough probably migrated in to the Assumood Ridge from the northeast through late Cretaceous, Paleocene and early Eocene carbonates, before being trapped beneath the Augila Shale (Upper Eocene) which is the principal regional seal in the area. This integrated study has enhanced our understanding of reservoir heterogeneity and hydrocarbon potential of the Gialo carbonates and should lead to improved exploration in the future. Reservoir quality in the Gialo Formation is a function of grain types, pore types, grain size, sorting, cementation and compaction, and predicting areas of high reservoir quality has proved difficult; exploration should be oriented to positioning wells into the main trend of the mid-ramp, nummulite accumulation. Different nummulite facies can be reservoirs depending on their diagenetic history. A diagenetic reduction in porosity must be distinguished from a lack of porosity resulting from an unfavourable depositional environment, so that exploration alternatives can be assessed. This integrated study has demonstrated the presence of suitable reservoir rocks, hydrocarbon traps and the close proximity of potential source rocks. These features should encourage further hydrocarbon exploration in the area.

  3. The terminal eocene event and the polish connection

    USGS Publications Warehouse

    Van Couvering, J. A.; Aubry, M.-P.; Berggren, W.A.; Bujak, J.P.; Naeser, C.W.; Wieser, T.

    1981-01-01

    The Eocene/Oligocene boundary in Europe is marked by major discontinuities in all environments: the "Grande Coupure" in continental mammals; the elimination of semitropical elements from high-latitude floras; the virtually complete replacement of the shallow-marine malacofauna; and an extraordinary downslope excursion of carbonate deposition in deep-ocean basins (drop in the CCD). These phenomena collectively represent the "Terminal Eocene Event" (TEE). In the Carpathian Mountains, the TEE is manifested in the thin but regionally persistent Globigerina Marl, a calcareous unit containing abundant cool-water microplankton that occurs within very thick, siliceous, bathyal flysch sequences. In southern Poland, the marl is of very latest Eocene age, within planktonic foraminifera zone P17, calcareous nannoplankton zone NP19/20, and the zone of the dinoflagellate Rhomdodinium perforatum. Zircons from bentonites bracketing the marl are dated by fission-track analysis; at Polany, two underlying bentonites are 41.7 and 39.8 Ma, and at Znamirowice two overlying bentonites are 34.6 and 28.9 Ma, in sequence. This accords with glauconite K/Ar ages in Western Europe by which the Eo/Oligocene boundary age is estimated at 37-38 Ma. Global correlations indicate that the TEE corresponds to a major glacio-eustatic regression with a duration of about 0.5 Ma, in which a large Antarctic ice cap was formed, the ocean circulation was permanently changed to the psychrospheric condition, and world climate shifted irreversibly towards the modern state. ?? 1981.

  4. Late Eocene impact events recorded in deep-sea sediments

    NASA Technical Reports Server (NTRS)

    Glass, B. P.

    1988-01-01

    Raup and Sepkoski proposed that mass extinctions have occurred every 26 Myr during the last 250 Myr. In order to explain this 26 Myr periodicity, it was proposed that the mass extinctions were caused by periodic increases in cometary impacts. One method to test this hypothesis is to determine if there were periodic increases in impact events (based on crater ages) that correlate with mass extinctions. A way to test the hypothesis that mass extinctions were caused by periodic increases in impact cratering is to look for evidence of impact events in deep-sea deposits. This method allows direct observation of the temporal relationship between impact events and extinctions as recorded in the sedimentary record. There is evidence in the deep-sea record for two (possibly three) impact events in the late Eocene. The younger event, represented by the North American microtektite layer, is not associated with an Ir anomaly. The older event, defined by the cpx spherule layer, is associated with an Ir anomaly. However, neither of the two impact events recorded in late Eocene deposits appears to be associated with an unusual number of extinctions. Thus there is little evidence in the deep-sea record for an impact-related mass extinction in the late Eocene.

  5. Modern Mammals dispersion linked to the Paleocene Eocene thermal maximum (PETM) and early Eocene climatic optimum, new insights from India

    NASA Astrophysics Data System (ADS)

    Khozyem, H. M.; Adatte, T.; Keller, G.; Spangenberg, J.; Bajpai, S.; Samant, B.

    2012-12-01

    The Paleocene Eocene Thermal Maximum (PETM, 55.9Ma)) is globally related with the extinction of deep benthic foraminifera, the diversification of both planktic foraminifera and modern mammals. In India, the tempo and timing of modern mammal dispersion, their association with the PETM or EECO (Early Eocene Climatic Optimum) and the India-Asia collision remain uncertain. Four Indian sections (Giral, Bhavnagar, Vastan and Tadkeshware lignite mines) have been studied using sedimentology, micropaleontology, mineralogy (bulk and clay mineralogy) and geochemistry (stable isotopes, major and trace elements, organic matter). Both PETM and ETM2 (second Eocene Thermal Maximum, 53.7Ma), a short-lived warming episode that followed the PETM, are globally marked by a pronounced δ13Ccarb and δ13Corg negative excursion. Both isotopic excursions have been recognized in the Vastan and Tarkeswhar lignite mines (Cambay basin, Gujarat) associated with the main mammal bearing level. The lower shift is located above the first lignite seam and corresponds to the transition from continental to shallow marine conditions. The upper excursion appears to be linked to the ETM2 and corresponds to a second marine incursion containing bivalves, benthic (Nummulites burdigalensis) and planktic foraminifera located below the second lignite seam. A very pronounced δ13Corg peak has been detected in the Giral lignite mine (Barmer, Rajhastan) around 6m above the vertebrate bearing level and may correspond to the PETM. This correlation is confirmed by palynological data and more particularly by a dinoflagellate acme that globally characterizes the PETM interval. Our micropaleontological data combined with stable carbone isotopes indicate the presence of both PETM and ETM2 events and constrain the age of the early mammals in northwestern India in between these two thermal events in the early Eocene. These new data will significantly improve the ongoing debate on whether mammals originated in or out of

  6. Iridium and Spherules in Late Eocene Impact Deposits

    NASA Technical Reports Server (NTRS)

    Kyte, F. T.; Liu, S.

    2002-01-01

    We have been independently examining the Ir (FTK) and spherule (SL) contents of recently discovered late Eocene impact deposits from the south Atlantic and western Indian oceans. These include ODP Sites 1090 [14,15], 709 [lo], and 699 [Liu in prep.]. Iridium abundances at these sites are within the typical range reported for late Eocene deposits, with peak concentrations between 100 and 1000 pg/g. In Table 1 we present estimated net Ir fluences (in ng Ir/cm ) for these and nine other sites. Although there are fewer sites than the K/T boundary, the average of 9 ng Ir/cm2 is probably a good estimate of the late Eocene global flux. This is enough Ir for a 6 km comet (assuming 250 ng/g Ir, p=1.5), is sufficient to produce the Popigai or Chesapeake Bay structures, and is 16% of the flux estimated for the K/T boundary (55 ng/cm2 [ 161). Figure 1 shows the relative abundances of Ir, glassy microtektites and cpx-bearing spherules in sediments from Sites 699 and 1090, which are separated by only 3100 km. Although these two sites have similar Ir anomalies, the abundances of spherules are quite different. Site 1090 has well-defined peaks for both types of spherules, with a peak of 562 cpx spheruledg, while Site 699 contains only a few glassy microtektites and no cpx spherules. While the different abundances of spherules may reflect a heterogeneous distribution of spherules on the Earth s surface, an equally likely cause of this difference may be differential preservation of spherules in the sediment. recovered are only a trace residue of the initial impact deposit. Earlier work found 0.22 ng/g Ir in glassy microtektites from Site 689 [17], an insufficient concentration to support 0.16 ng/g in the bulk sediment at this site. We measured 15 ng/g Ir in a group of 95 cpx spherules from Site 1090 with sizes from 63 to -200 pm, a set typical of the size distribution at this site. Although this is a significant concentration it also cannot support the Ir peak. We presently lack

  7. New Eocene damselflies and first Cenozoic damsel-dragonfly of the isophlebiopteran lineage (Insecta: Odonata).

    PubMed

    Garrouste, Romain; Nel, André

    2015-01-01

    The study of a new specimen of Petrolestes hendersoni from the Eocene Green Formation allows a more precise description of the enigmatic damselfly and the diagnosis of the Petrolestini. Petrolestes messelensis sp. nov. is described from the Eocene Messel Formation in Germany, extending the distribution of the Petrolestini to the European Eocene. The new damsel-dragonfly family Pseudostenolestidae is described for the new genus and species Pseudostenolestes bechlyi, from the Eocene Messel Formation. It is the first Cenozoic representative of the Mesozoic clade Isophlebioptera. PMID:26624314

  8. New Eocene damselflies and first Cenozoic damsel-dragonfly of the isophlebiopteran lineage (Insecta: Odonata).

    PubMed

    Garrouste, Romain; Nel, André

    2015-10-09

    The study of a new specimen of Petrolestes hendersoni from the Eocene Green Formation allows a more precise description of the enigmatic damselfly and the diagnosis of the Petrolestini. Petrolestes messelensis sp. nov. is described from the Eocene Messel Formation in Germany, extending the distribution of the Petrolestini to the European Eocene. The new damsel-dragonfly family Pseudostenolestidae is described for the new genus and species Pseudostenolestes bechlyi, from the Eocene Messel Formation. It is the first Cenozoic representative of the Mesozoic clade Isophlebioptera.

  9. Palaeotectonic implications of increased late Eocene-early Oligocene volcanism from South Pacific DSDP sites

    USGS Publications Warehouse

    Kennett, J.P.; Von Der Borch, C.; Baker, P.A.; Barton, C.E.; Boersma, A.; Cauler, J.P.; Dudley, W.C.; Gardner, J.V.; Jenkins, D.G.; Lohman, W.H.; Martini, E.; Merrill, R.B.; Morin, R.; Nelson, Campbell S.; Robert, C.; Srinivasan, M.S.; Stein, R.; Takeuchi, A.; Murphy, M.G.

    1985-01-01

    Late Eocene-early Oligocene (42-35 Myr) sediments cored at two DSDP sites in the south-west Pacific contain evidence of a pronounced increase in local volcanic activity, particularly in close association with the Eocene-Oligocene boundary. This pulse of volcanism is coeval with that in New Zealand and resulted from the development of an Indo- Australian / Pacific Plate boundary through the region during the late Eocene. The late Eocene / earliest Oligocene was marked by widespread volcanism and tectonism throughout the Pacific and elsewhere, and by one of the most important episodes of Cenozoic climatic cooling. ?? 1985 Nature Publishing Group.

  10. Eocene to Miocene biostratigraphy of New Jersey core ACGS #4; implications for regional stratigraphy

    USGS Publications Warehouse

    Poore, Richard Z.; Bybell, Laurel M.

    1988-01-01

    A time versus depth plot controlled primarily by nannofossil zone boundaries shows that sediment accumulation rates during the early and middle Eocene were in the range of 6 to 15 feet per million years. During the late Eocene, accumulation rates were much higher, perhaps exceeding 70 feet per million years. The only clear hiatus detected in the Paleogene part of ACGS #4 on the basis of microfossils is between the early and (?)late Oligocene. However, hiatuses are suspected at the early-middle Eocene boundary and within the late Eocene. Occurrences of calcareous nannofossils and planktic foraminifers are documented, and a number of key taxa are illustrated.

  11. Comet or asteroid shower in the late Eocene?

    PubMed

    Tagle, Roald; Claeys, Philippe

    2004-07-23

    The passage of a comet shower approximately 35 million years ago is generally advocated to explain the coincidence during Earth's late Eocene of an unusually high flux of interplanetary dust particles and the formation of the two largest craters in the Cenozoic, Popigai and the Chesapeake Bay. However, new platinum-group element analyses indicate that Popigai was formed by the impact of an L-chondrite meteorite. Such an asteroidal projectile is difficult to reconcile with a cometary origin. Perhaps instead the higher delivery rate of extraterrestrial matter, dust, and large objects was caused by a major collision in the asteroid belt. PMID:15273387

  12. Exploring Terrestrial Temperature Changes during the Early Eocene Hyperthermals

    NASA Astrophysics Data System (ADS)

    Snell, K. E.; Clyde, W. C.; Fricke, H. C.; Eiler, J. M.

    2012-12-01

    The Early Eocene is marked by a number of rapid global warming events called hyperthermals. These hyperthermals are associated with negative carbon isotope excursions (CIE) in both marine and terrestrial records. Multiple theories exist to explain the connection of these hyperthermals with the CIEs and each theory predicts different responses by the climate system. Characterizing the timing, duration and magnitude of temperature change that is associated with these hyperthermals is important for determining whether the hyperthermals are all driven by the same underlying climate dynamics or perhaps differ from one another in cause and climatic consequences. In the simplest case, all share a common underlying mechanism; this predicts that the associated temperature changes scale in a predictable way with the magnitude of the CIE (and perhaps exhibit other similarities, such as the relative amplitudes of marine and terrestrial temperature change). To our knowledge, however, the only hyperthermal with paleotemperature data from land is the Paleocene-Eocene Thermal Maximum (PETM). Here we present preliminary carbonate clumped isotope paleotemperature estimates for Early Eocene hyperthermal ETM2/H2 from paleosol carbonates from the Bighorn Basin in Wyoming, USA. We compare the results to existing clumped isotope paleotemperature estimates for the PETM in the Bighorn Basin. Temperatures recorded by paleosol carbonates (which likely reflect near-peak summer ground temperatures) prior to each CIE are ~30°C and increase to ~40-43°C during the apex of each CIE. Following both CIEs, temperatures drop back to pre-CIE values. In the case of ETM2/H2, temperatures begin to rise again immediately, possibly in association with a later hyperthermal, though further work needs to be done to establish this with certainty. These preliminary data suggest that both the absolute values and the magnitudes of temperature changes associated with the PETM and ETM2/H2 are similar; the

  13. Comet or asteroid shower in the late Eocene?

    PubMed

    Tagle, Roald; Claeys, Philippe

    2004-07-23

    The passage of a comet shower approximately 35 million years ago is generally advocated to explain the coincidence during Earth's late Eocene of an unusually high flux of interplanetary dust particles and the formation of the two largest craters in the Cenozoic, Popigai and the Chesapeake Bay. However, new platinum-group element analyses indicate that Popigai was formed by the impact of an L-chondrite meteorite. Such an asteroidal projectile is difficult to reconcile with a cometary origin. Perhaps instead the higher delivery rate of extraterrestrial matter, dust, and large objects was caused by a major collision in the asteroid belt.

  14. Mass-movement deposits in the lacustrine Eocene Green River Formation, Piceance Basin, western Colorado

    USGS Publications Warehouse

    Johnson, Ronald C.; Birdwell, Justin E.; Brownfield, Michael E.; Mercier, Tracey J.

    2015-01-01

    The Eocene Green River Formation was deposited in two large Eocene saline lakes, Lake Uinta in the Uinta and Piceance Basins and Lake Gosiute in the Greater Green River Basin. Here we will discuss mass-movement deposits in just the Piceance Basin part of Lake Uinta.

  15. The oldest accurate record of Scenopinidae in the Lowermost Eocene amber of France (Diptera: Brachycera).

    PubMed

    Garrouste, Romain; Azar, Dany; Nel, Andre

    2016-01-01

    Eocenotrichia magnifica gen. et sp. nov. (Diptera: Scenopinidae: Metatrichini) is described and illustrated from the Lowermost Eocene amber of Oise (France) and represents the oldest definitive window fly fossil. The present discovery in the Earliest Eocene supports the Late Cretaceous-Paleocene age currently proposed for the emergence of Metatrichini. PMID:27394507

  16. Provenance of the Eocene Soebi Blanco formation, Bonaire, Leeward Antilles: Correlations with post-Eocene tectonic evolution of northern South America

    NASA Astrophysics Data System (ADS)

    Zapata, S.; Cardona, A.; Montes, C.; Valencia, V.; Vervoort, J.; Reiners, P.

    2014-07-01

    Middle to upper Eocene fluvial strata in the island of Bonaire contain detrital components that were tracked to Precambrian to Triassic massifs in northern Colombia and Venezuela. These detrital components confirm previous hypothesis suggesting that Bonaire and the Leeward Antilles were attached to South American basement massifs (SABM). These are composed of different fragmented South American blocks (Paraguana, Falcon, Maracaibo, Guajira, Perija, and Santa Marta) representing an Eocene, right-laterally displaced tectonic piercing point along the southern Caribbean plate margin. U-Pb LA-ICP-MS from the metamorphic boulders of the Soebi Blanco Formation in Bonaire yield Grenvillian peaks ages (1000-1200 Ma), while detrital zircons recovered from the sandy matrix of the conglomerates contain populations with peaks of 1000 Ma-1200 Ma, 750-950 Ma, and 200-300 Ma. These populations match with geochronological data reported for the northern South American massifs. Thermochronological results from the metamorphic clasts yield Paleocene-middle Eocene ages (65-50 Ma) that confirm a regional-scale cooling event in this time. These data imply a land connection between the SABM and the Leeward Antilles in late Eocene times, followed by a significant strike slip right-lateral displacement and transtensional basin opening starting in latest Eocene times. The succession of Eocene tectonic events recorded by the Soebi Blanco Formation and adjacent basins is a major tracer of the oblique convergence of the Caribbean plate against the South American margin.

  17. Early Eocene cyclicity at the Wilkes Land Margin, Antarctica: Orbital forcing and environmental response

    NASA Astrophysics Data System (ADS)

    Roehl, U.; Bijl, P.; Jiménez, F.; Pross, J.; Contreras, L.; Tauxe, L.; Bohaty, S. M.; Bendle, J.; Brinkhuis, H.; IODP Expedition 318 Scientists

    2011-12-01

    The early Eocene Greenhouse interval (~56-49 Ma) was punctuated by multiple transient global warming events, or hyperthermals - the most prominent of which was the Paleocene-Eocene Thermal Maximum (PETM). Additional thermal maxima identified in Eocene records exhibit negative carbon isotope excursions (CIEs), carbonate dissolution horizons, and biotic perturbations, although of reduced magnitude and duration relative to the PETM. Many hyperthermals have been identified or postulated in the early Eocene, but it is unclear which of these events are normal carbon-cycle variations that occurred at orbital frequencies and which are exceptional events outside the normal range of Eocene carbon-cycle variability. Here we present a high-resolution cyclostratigraphy for a new early Eocene drillcore from the Wilkes Land Margin in direct proximity to the Antarctic continent (Site U1356 drilled during IODP Expedition 318). Site U1356 was situated in a mid-shelf setting during the early Eocene and is characterized by a superb magnetostratigraphy and a robust biostratigraphic age control. Our investigation includes XRF core scanning and ICP-MS data as well as bulk organic carbon isotope ratios (delta13Corg) in combination with the concentration of the total organic carbon (TOC). The early Eocene at Site U1356 consists of well developed cyclic claystones including the interval of magnetochron C24 which is ideal to re-evaluate the early Eocene part of the Geomagnetic Polarity Time Scale (GPTS) and to provide new insights into the environmental responses as well as orbital configuration of early Eocene climatic cycles.

  18. Foraminiferal repopulation of the late Eocene Chesapeake Bay impact crater

    USGS Publications Warehouse

    Poag, C. Wylie

    2012-01-01

    The Chickahominy Formation is the initial postimpact deposit in the 85km-diameter Chesapeake Bay impact crater, which is centered under the town of Cape Charles, Virginia, USA. The formation comprises dominantly microfossil-rich, silty, marine clay, which accumulated during the final ~1.6myr of late Eocene time. At cored sites, the Chickahominy Formation is 16.8-93.7m thick, and fills a series of small troughs and subbasins, which subdivide the larger Chickahominy basin. Nine coreholes drilled through the Chickahominy Formation (five inside the crater, two near the crater margin, and two ~3km outside the crater) record the stratigraphic and paleoecologic succession of 301 indigenous species of benthic foraminifera, as well as associated planktonic foraminifera and bolboformids. Two hundred twenty of these benthic species are described herein, and illustrated with scanning electron photomicrographs. Absence of key planktonic foraminiferal and Bolboforma species in early Chickahominy sediments indicates that detrimental effects of the impact also disturbed the upper oceanic water column for at least 80-100kyr postimpact. After an average of ~73kyr of stressed, rapidly fluctuating paleoenvironments, which were destabilized by after-effects of the impact, most of the cored Chickahominy subbasins maintained stable, nutrient-rich, low-oxygen bottom waters and interstitial microhabitats for the remaining ~1.3myr of late Eocene time.

  19. Eocene Podocarpium (Leguminosae) from South China and its biogeographic implications.

    PubMed

    Xu, Qingqing; Qiu, Jue; Zhou, Zhekun; Jin, Jianhua

    2015-01-01

    Podocarpium A. Braun ex Stizenberger is one of the most common legumes in the Neogene of Eurasia, including fossil fruits, seeds, leaves, and possible flower and pollen grains. This genus is not completely consistent with any extant genera according to gross morphological characters and poorly preserved cuticular structures reported in previous studies. The fossil pods collected from the coal-bearing series of the Changchang Basin of Hainan Island and Maoming Basin of Guangdong, South China, are examined by morphologically comparative work, with special reference to venation patterns and placental position. These distinctive features, as well as the ovule development of pods from different developmental stages and the epidermal structure of the pods, as distinguished from previous records lead to the conclusion that these fossils can be recognized as a new species of Podocarpium, P. eocenicum sp. nov. This new discovery indicates that Podocarpium had arrived in South China by the Eocene. Investigation on the fossil records of this extinct genus shows that P. eocenicum is the earliest and lowest latitude fossil data. The possible occurrence pattern of this genus is revealed as follows: Podocarpium had distributed in the South China at least in the middle Eocene, and then migrated to Europe during the Oligocene; in the Miocene this genus reached its peak in Eurasia, spreading extensively across subtropical areas to warm temperate areas; finally, Podocarpium shrank rapidly and became extinct in Eurasia during the Pliocene. PMID:26579179

  20. Eocene Podocarpium (Leguminosae) from South China and its biogeographic implications

    PubMed Central

    Xu, Qingqing; Qiu, Jue; Zhou, Zhekun; Jin, Jianhua

    2015-01-01

    Podocarpium A. Braun ex Stizenberger is one of the most common legumes in the Neogene of Eurasia, including fossil fruits, seeds, leaves, and possible flower and pollen grains. This genus is not completely consistent with any extant genera according to gross morphological characters and poorly preserved cuticular structures reported in previous studies. The fossil pods collected from the coal-bearing series of the Changchang Basin of Hainan Island and Maoming Basin of Guangdong, South China, are examined by morphologically comparative work, with special reference to venation patterns and placental position. These distinctive features, as well as the ovule development of pods from different developmental stages and the epidermal structure of the pods, as distinguished from previous records lead to the conclusion that these fossils can be recognized as a new species of Podocarpium, P. eocenicum sp. nov. This new discovery indicates that Podocarpium had arrived in South China by the Eocene. Investigation on the fossil records of this extinct genus shows that P. eocenicum is the earliest and lowest latitude fossil data. The possible occurrence pattern of this genus is revealed as follows: Podocarpium had distributed in the South China at least in the middle Eocene, and then migrated to Europe during the Oligocene; in the Miocene this genus reached its peak in Eurasia, spreading extensively across subtropical areas to warm temperate areas; finally, Podocarpium shrank rapidly and became extinct in Eurasia during the Pliocene. PMID:26579179

  1. Episodic fresh surface waters in the Eocene Arctic Ocean

    USGS Publications Warehouse

    Brinkhuis, H.; Schouten, S.; Collinson, M.E.; Sluijs, A.; Damste, J.S.S.; Dickens, G.R.; Huber, M.; Cronin, T. M.; Onodera, J.; Takahashi, K.; Bujak, J.P.; Stein, R.; Van Der Burgh, J.; Eldrett, J.S.; Harding, I.C.; Lotter, A.F.; Sangiorgi, F.; Cittert, H.V.K.V.; De Leeuw, J. W.; Matthiessen, J.; Backman, J.; Moran, K.

    2006-01-01

    It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions that characterized the early Palaeogene period (55-45 Myr ago) probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes. Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (???50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an ???800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea. The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from ???10??C to 13??C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas. ?? 2006 Nature Publishing Group.

  2. Continental ice in Greenland during the Eocene and Oligocene

    NASA Astrophysics Data System (ADS)

    Eldrett, James S.; Harding, Ian C.; Wilson, Paul A.; Butler, Emily; Roberts, Andrew P.

    2007-03-01

    The Eocene and Oligocene epochs (~55 to 23 million years ago) comprise a critical phase in Earth history. An array of geological records supported by climate modelling indicates a profound shift in global climate during this interval, from a state that was largely free of polar ice caps to one in which ice sheets on Antarctica approached their modern size. However, the early glaciation history of the Northern Hemisphere is a subject of controversy. Here we report stratigraphically extensive ice-rafted debris, including macroscopic dropstones, in late Eocene to early Oligocene sediments from the Norwegian-Greenland Sea that were deposited between about 38 and 30million years ago. Our data indicate sediment rafting by glacial ice, rather than sea ice, and point to East Greenland as the likely source. Records of this type from one site alone cannot be used to determine the extent of ice involved. However, our data suggest the existence of (at least) isolated glaciers on Greenland about 20million years earlier than previously documented, at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher.

  3. Cretaceous to Eocene passive margin sedimentation in Northeastern Venezuela

    SciTech Connect

    Erikson, J.P. )

    1993-02-01

    Twenty two palinspastic paleogeographic maps are presented for the Cretaceous to Eocene strata of the Serrania del Interior of northeastern Venezuela. The mapped lithologies, environmental conditions, and evolving depositional systems record [approximately]90 m.y. of dominantly marine sedimentation on the only observable Mesozoic passive margin in the Western Hemisphere. The depositional systems of the passive margin are heterogeneous at lateral (i.e., along-margin) length scales greater than [approximately]40 km. The primary lateral heterogeneity is caused by a major Lower Cretaceous deltaic system that emanated southwest of the Serrania del Interior. All important intervals, such as the laterally variable Aptian-Albian El Cantil platform limestone and the hydrocarbon source rocks of the Upper Cretaceous Querecual and San Antonio formations, are related to probable causal mechanisms and environmental conditions. Stratigraphic events have been interpreted as of either local or regional extent; based on a combination of outcrop sedimentologic analyses and regional depositional systems interpretation. The 3-dimensional distribution of depositional systems and systems tracts reveals 4-6 regional sequence boundaries separated by 4-20 m.y. Subsidence analyses support the facies interpretation of a passive margin by showing continuous, thermally dominated subsidence during the Cretaceous to Eocene interval. Subsidence and accumulation rates increased and facies changed significantly in the Oligocene, indicating the end of passive margin sedimentation and the initiation of foredeep subsidence and accumulation associated with overthrusting the eastward-advancing Caribbean Plate.

  4. How many upper Eocene microspherule layers: More than we thought

    NASA Technical Reports Server (NTRS)

    Hazel, Joseph E.

    1988-01-01

    The scientific controversy over the origin of upper Eocene tektites, microtektites and other microspherules cannot be logically resolved until it is determined just how many events are involved. The microspherule-bearing beds in marine sediments have been dated using standard biozonal techniques. Although a powerful stratigraphic tool, zonal biostratigraph has its limitations. One is that if an event, such as a microspherule occurrence, is observed to occur in a zone at one locality and then a similar event observed in the same zone at another locality, it still may be unwarranted to conclude that these events exactly correlate. To be in a zone a sample only need be between the fossil events that define the zone boundaries. It is often very difficult to accurately determine where within a zone one might be. Further, the zone defining events do not everywhere occur at the same points in time. That is, the ranges of the defining taxa are not always filled. Thus, the length of time represented by a zone (but not, of course, its chronozone) can vary from place to place. These problems can be offset by use of chronostratigraphic modelling techniques such as Graphic Correlation. This technique was used to build a Cretaceous and Cenozoic model containing fossil, magnetopolarity, and other events. The scale of the model can be demonstrated to be linear with time. This model was used to determine the chronostratigraphic position of upper Eocene microspherule layers.

  5. Eocene Arctic Ocean and earth's Early Cenozoic climate

    SciTech Connect

    Clark, D.L.

    1985-01-01

    Seasonal changes of the Arctic Ocean are an approximate microcosm of the present advanced interglacial climate of the Earth. A similar relationship has existed for several million years but was the Early Cenozoic Arctic Ocean an analog of Earth's climate, as well. Absence of polar ice during the Cretaceous is relatively well established. During the Cenozoic a worldwide decrease in mean annual ocean temperature resulted from such factors as altered oceanic circulation and lower atmospheric CO/sub 2/ levels. Limited Arctic Ocean data for the middle or late Eocene indicate the presence of upwelling conditions and accompanying high productivity of diatoms, ebridians, silicoflagellates and archaeomonads. During this interval, some seasonality is suggested from the varve-like nature of a single sediment core. However, the absence of drop stones or any ice-rafted sediment supports the idea of an open water, ice-free central Arctic Ocean during this time. Latest Cretaceous Arctic Ocean sediment is interpreted to represent approximately the same conditions as those suggested for the Eocene and together with that data suggest that the central Arctic Ocean was ice-free during part if not all of the first 20 my of the Cenozoic. Sediment representing the succeeding 30 my has not been recovered but by latest Miocene or earl Pliocene, ice-rafted sediment was accumulating, both pack ice and icebergs covered the Arctic Ocean reflecting cyclic glacial climate.

  6. A Phororhacoid bird from the Eocene of Africa

    NASA Astrophysics Data System (ADS)

    Mourer-Chauviré, Cécile; Tabuce, Rodolphe; Mahboubi, M'hammed; Adaci, Mohammed; Bensalah, Mustapha

    2011-10-01

    The bird fossil record is globally scarce in Africa. The early Tertiary evolution of terrestrial birds is virtually unknown in that continent. Here, we report on a femur of a large terrestrial new genus discovered from the early or early middle Eocene (between ˜52 and 46 Ma) of south-western Algeria. This femur shows all the morphological features of the Phororhacoidea, the so-called Terror Birds. Most of the phororhacoids were indeed large, or even gigantic, flightless predators or scavengers with no close modern analogs. It is likely that this extinct group originated in South America, where they are known from the late Paleocene to the late Pleistocene (˜59 to 0.01 Ma). The presence of a phororhacoid bird in Africa cannot be explained by a vicariant mechanism because these birds first appeared in South America well after the onset of the mid-Cretaceous Gondwana break up (˜100 million years old). Here, we propose two hypotheses to account for this occurrence, either an early dispersal of small members of this group, which were still able of a limited flight, or a transoceanic migration of flightless birds from South America to Africa during the Paleocene or earliest Eocene. Paleogeographic reconstructions of the South Atlantic Ocean suggest the existence of several islands of considerable size between South America and Africa during the early Tertiary, which could have helped a transatlantic dispersal of phororhacoids.

  7. Continental ice in Greenland during the Eocene and Oligocene.

    PubMed

    Eldrett, James S; Harding, Ian C; Wilson, Paul A; Butler, Emily; Roberts, Andrew P

    2007-03-01

    The Eocene and Oligocene epochs (approximately 55 to 23 million years ago) comprise a critical phase in Earth history. An array of geological records supported by climate modelling indicates a profound shift in global climate during this interval, from a state that was largely free of polar ice caps to one in which ice sheets on Antarctica approached their modern size. However, the early glaciation history of the Northern Hemisphere is a subject of controversy. Here we report stratigraphically extensive ice-rafted debris, including macroscopic dropstones, in late Eocene to early Oligocene sediments from the Norwegian-Greenland Sea that were deposited between about 38 and 30 million years ago. Our data indicate sediment rafting by glacial ice, rather than sea ice, and point to East Greenland as the likely source. Records of this type from one site alone cannot be used to determine the extent of ice involved. However, our data suggest the existence of (at least) isolated glaciers on Greenland about 20 million years earlier than previously documented, at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher.

  8. Composition of Eocene Ice-Rafted Debris, Central Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Ramstad, C.; St. John, K.

    2007-12-01

    IODP Expedition 302 drilled a 400-m sediment record which contains physical evidence of ice-rafting in the Eocene and Neogene in the Arctic (Backman et al., 2006; Moran et al., 2006, St. John, in press). An increase in the terrigenous sand abundance occurs above 246 mcd (~46 Ma), with a flux similar to that in the Neogene. Higher resolution sampling in an interval of good recovery from 246-236 mcd shows evidence of cyclic input of IRD and biogenic components that fits with Milankovitch forcing at the obliquity period (Sangiorgi et al., in press). The question remains - what areas of the Arctic were ice-covered at this early stage in the Cenozoic? To address this provenance issue the composition of the terrigenous sands (250 micron fraction) in cores 55-56X is being quantified. Grains in 75 samples are being point-counted and their compositions categorized. Quartz grains are the dominant component (greater than 10,000 grains per gram), with some being hematite-stained, and there are lesser amounts of mafic minerals. No carbonate grains are identified so far in this study. Possible sources areas for Eocene IRD are the Eastern European and Russian Arctic margins. Tracking compositional variations of the IRD over the interval of cyclic deposition, should indicate whether the cyclic IRD deposition was consistently derived from one source region or multiple regions during this time.

  9. Diversity of Scydmaeninae (Coleoptera: Staphylinidae) in Upper Eocene Rovno amber.

    PubMed

    Jałoszyński, Paweł; Perkovsky, Evgeny

    2016-01-01

    Among nearly 1270 inclusions of Coleoptera found in Upper Eocene Rovno amber, 69 were identified as ant-like stone beetles (Scydmaeninae); 34 were possible to unambiguously determine to the tribal level and were studied in detail. Rovnoleptochromus ableptonoides gen. & sp. n. (Mastigitae: Clidicini), Vertheia quadrisetosa gen. & sp. n. (Cephenniitae: Eutheiini), Cephennomicrus giganteus sp. n. (Cephenniitae: Cephenniini), Glaesoconnus unicus gen. & sp. n. (Scydmaenitae: Glandulariini), Rovnoscydmus frontalis gen. & sp. n. (Scydmaenitae: Glandulariini; type species of Rovnoscydmus), Rovnoscydmus microscopicus sp. n., Euconnus (incertae sedis, near Cladoconnus) palaeogenus sp. n. (Scydmaenitae: Glandulariini), and Stenichnus (s. str.) proavus sp. n. (Scydmaenitae: Glandulariini) are described. Additionally, specimens representing one undescribed species of Vertheia, one of Cephennodes, five of Cephennomicrus, one of Euconnus, one of Microscydmus are recorded, and nine specimens representing an unknown number of species of Rovnoscydmus (and two putative Rovnoscydmus), one Euconnus (and one putative Euconnus), two putative Microscydmus and one putative Scydmoraphes were found in the studied material. The composition of Scydmaeninae fauna in Rovno amber is discussed in the context of ecological preferences and distribution of extant taxa. It is concluded that subtropical and tropical taxa were present in the region where Rovno amber has formed, most notably the second genus and species of the extant tribe Clidicini known from the Eocene of Europe, and six species of the extant genus Cephennomicrus, for the first time found in the fossil record. An annotated catalog of nominal species of Scydmaeninae known in the fossil record is given. PMID:27615867

  10. Eocene paleosols of King George Island, Maritime Antarctica

    NASA Astrophysics Data System (ADS)

    Spinola, Diogo; Portes, Raquel; Schaefer, Carlos; Kühn, Peter

    2016-04-01

    Red layers between lava flows on King George Island, Maritime Antarctica, were formed during the Eocene, which was one of the warmest periods on Earth in the Cenozoic. Our hypothesis is that these red layers are paleosols formed in periods of little or no volcanic activity. Therefore, our main objective was to identify the main pedogenic properties and features to distinguish these from diagenetic features formed after the lava emplacement. Additionally, we compared our results with volcanic soils formed under different climates to find the best present analogue. The macromorphological features indicate a pedogenic origin, because of the occurrence of well-defined horizons based on colour and structure. Micromorphological analyses showed that most important pedogenic features are the presence of biological channels, plant residues, anisotropic b-fabric, neoformed and illuvial clay and distinct soil microstructure. Although the paleosols are not strongly weathered, the geochemical data also support the pedogenic origin despite of diagenetic features as the partial induration of the profiles and zeolites filling nearly all voids in the horizons in contact with the overlying lava flow, indicating circulation of hydrothermal fluids. The macromorphological and micromorphological features of these paleosols are similar to the soils formed under seasonal climates. Thus, these paleosol features do not correspond to the other proxies (e.g. sediment, plant fossils), which indicate a wet, non-seasonal climate, as in Valdivian Forest, Chile, during the Eocene in King George Island

  11. Diachronous ranges of benthonic Foraminifera in the Eocene of Alabama and South Carolina

    SciTech Connect

    Willard, G.D.; Fallaw, W.C. . Dept. of Geology); Price, V. ); Snipes, D.S. . Dept. of Earth Sciences)

    1994-03-01

    Seventeen species of benthonic Foraminifera reported by Bandy (1949) from the Eocene of Little Stave Creek in Clarke County, Alabama were identified from the middle eocene Santee Limestone and the upper Eocene Dry Branch Formation in Aiken and Barnwell counties, South Carolina. Of the 17 species, seven occurred in South Carolina stratigraphically above or below the ranges listed by Bandy. Bandy made a detailed study of Foraminifera from the Claibornian and Jacksonian Tallahatta, Lisbon, Gosport, Moodys Branch, and Yazoo formations exposed on Little Stave Creek and plotted the stratigraphic ranges within the section of numerous species. The authors' samples came from well cores at the Savannah River Site in South Carolina. Of 13 species from the middle Eocene Santee and also reported by Bandy, four are stratigraphically below the lowest occurrence listed by Bandy, and one is stratigraphically above the highest occurrence. Of four species from the upper Eocene Dry Branch Formation and also listed by Bandy, two are stratigraphically above his highest occurrence. Dockery and Nystrom (1992) and Campbell (1993) have described diachroneity among mollusks in the Eocene of South Carolina. Caution should be used in relying on a small number of species in correlating Eocene deposits in the Atlantic and Gulf coastal plains.

  12. Calcareous phytoplankton perturbations through the Eocene/Oligocene Transition

    NASA Astrophysics Data System (ADS)

    Bown, P. R.; Dunkley Jones, T.; Expedition 320/321 Shipboard Party

    2010-12-01

    The Eocene-Oligocene transition (E/OT) witnessed the most significant climatic change in the Cenozoic with a fundamental reordering of the planet’s oceanic and atmospheric circulation, the cooling of deep and high-latitude waters and the formation of continental scale ice sheets on Antarctica. Records from the equatorial Pacific show rapid and highly correlated increases in deep-ocean oxygen and carbon isotopes and a drop in the Calcium Carbonate Compensation Depth (CCD) of over a kilometre (Coxall et al. 2005). The role of surface ocean productivity changes, especially at low latitudes, within this carbon cycle perturbation remains open to question. Detailed micropalaeontological analyses from shelf-slope sections of Tanzania, which host exceptionally well preserved calcareous microfossils, indicate a significant reorganization of planktonic niches coincident with the E/OT (Pearson et al. 2008). These include major assemblage shifts within the calcareous phytoplankton closely coupled to the isotopic excursions (Dunkley Jones et al. 2008). Here, we integrate the Tanzanian records with patterns of calcareous nannofossil turnover observed in historic DSDP Site 242 (Davie Ridge, Indian Ocean), the US Gulf Coast and preliminary data from new E/OT successions recovered during the recent IODP Expedition 320 in the eastern equatorial Pacific and discuss their implications for nutrient cycling and surface ocean productivity across the E/OT. Coxall, H. K., Wilson, P. A., Palike, H., Lear, C. H. & Backman, J. 2005. Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean. Nature 433: 53-57. Dunkley Jones, T., Bown, P. R., Pearson, P. N., Wade, B. S., Coxall, H. K. & Lear, C. H. 2008. Major shifts in calcareous phytoplankton assemblages through the Eocene-Oligocene transition of Tanzania and their implications for low-latitude primary production, Paleoceanography, 23, PA4204, doi:10.1029/2008PA001640. Pearson, P.N, McMillan, I. K

  13. First Record of Eocene Bony Fishes and Crocodyliforms from Canada’s Western Arctic

    PubMed Central

    Eberle, Jaelyn J.; Gottfried, Michael D.; Hutchison, J. Howard; Brochu, Christopher A.

    2014-01-01

    Background Discovery of Eocene non-marine vertebrates, including crocodylians, turtles, bony fishes, and mammals in Canada’s High Arctic was a critical paleontological contribution of the last century because it indicated that this region of the Arctic had been mild, temperate, and ice-free during the early – middle Eocene (∼53–50 Ma), despite being well above the Arctic Circle. To date, these discoveries have been restricted to Canada’s easternmost Arctic – Ellesmere and Axel Heiberg Islands (Nunavut). Although temporally correlative strata crop out over 1,000 km west, on Canada’s westernmost Arctic Island – Banks Island, Northwest Territories – they have been interpreted as predominantly marine. We document the first Eocene bony fish and crocodyliform fossils from Banks Island. Principal Findings We describe fossils of bony fishes, including lepisosteid (Atractosteus), esocid (pike), and amiid, and a crocodyliform, from lower – middle Eocene strata of the Cyclic Member, Eureka Sound Formation within Aulavik National Park (∼76°N. paleolat.). Palynology suggests the sediments are late early to middle Eocene in age, and likely spanned the Early Eocene Climatic Optimum (EECO). Conclusions/Significance These fossils extend the geographic range of Eocene Arctic lepisosteids, esocids, amiids, and crocodyliforms west by approximately 40° of longitude or ∼1100 km. The low diversity bony fish fauna, at least at the family level, is essentially identical on Ellesmere and Banks Islands, suggesting a pan-High Arctic bony fish fauna of relatively basal groups around the margin of the Eocene Arctic Ocean. From a paleoclimatic perspective, presence of a crocodyliform, gar and amiid fishes on northern Banks provides further evidence that mild, year-round temperatures extended across the Canadian Arctic during early – middle Eocene time. Additionally, the Banks Island crocodyliform is consistent with the phylogenetic hypothesis of a Paleogene divergence

  14. Paleocene and Lower Eocene sections in the southern part of the Crimean Peninsula

    NASA Astrophysics Data System (ADS)

    Bugrova, I. Yu.; Bugrova, E. M.

    2015-11-01

    This work summarizes updated data on Paleocene and Lower Eocene deposits of the Crimean Peninsula concerning the systematics of assemblages of small foraminifers (and partly data on other microfossils) and results of biostratigraphic subdivision of sections. It is shown that Lower Paleocene and Lower-Middle Eocene deposits accumulated during two cycles of carbonate sedimentation in a warm-water shallow basin. These deposits are separated by Upper Paleocene deep-water deposits. The systematic composition of foraminifers testifies that there were different facies conditions in different parts of the Crimean basin and its connection to Western European and Tethyan basins during the Paleocene-early Eocene.

  15. Biochronology and paleoclimatic implications of Middle Eocene to Oligocene planktic foraminiferal faunas

    USGS Publications Warehouse

    Keller, G.

    1983-01-01

    Planktic foraminiferal assemblages have been analyzed quantitatively in six DSDP sites in the Atlantic (Site 363), Pacific (Sites 292, 77B, 277), and Indian Ocean (Sites 219, 253) in order to determine the nature of the faunal turnover during Middle Eocene to Oligocene time. Biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the Atlantic, Pacific and Indian oceans. A high resolution biochronology, based on dominant faunal characteristics and 55 datum events, permits correlation between all three oceans with a high degree of precision. Population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during Middle Eocene to Oligocene time. Planktic foraminiferal assemblage changes indicate a general cooling trend between Middle Eocene to Oligocene time, consistent with previously published oxygen isotope data. Major faunal changes, indicating cooling episodes, occur, however, at discrete intervals: in the Middle Eocene 44-43 Ma (P13), the Middle/Late Eocene boundary 41-40 Ma ( P14 P15), the Late Eocene 39-38 Ma ( P15 P16), the Eocene/Oligocene boundary 37-36 Ma (P18), and the Late Oligocene 31-29 Ma ( P20 P21). With the exception of the E 0 boundary, faunal changes occur abruptly during short stratigraphic intervals, and are characterized by major species extinctions and first appearances. The Eocene/Oligocene boundary cooling is marked primarily by increasing abundances of cool water species. This suggests that the E 0 boundary cooling, which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes. Planktic foraminiferal faunas indicate that the E 0 boundary event is part of a continued cooling trend which began during the Middle Eocene. Two hiatus intervals are recognized in low and high latitude sections at the Middle/Late Eocene

  16. Geochemical evidence for a comet shower in the late Eocene.

    PubMed

    Farley, K A; Montanari, A; Shoemaker, E M; Shoemaker, C S

    1998-05-22

    Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began approximately 1 My before and ended approximately 1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters approximately 36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud. PMID:9596575

  17. Eocene Hyperthermal Event Offers Insight Into Greenhouse Warming

    NASA Astrophysics Data System (ADS)

    Bowen, Gabriel J.; Bralower, Timothy J.; Delaney, Margaret L.; Dickens, Gerald R.; Kelly, Daniel C.; Koch, Paul L.; Kump, Lee R.; Meng, Jin; Sloan, Lisa C.; Thomas, Ellen; Wing, Scott L.; Zachos, James C.

    2006-04-01

    What happens to the Earth's climate, environment, and biota when thousands of gigatons of greenhouse gases are rapidly added to the atmosphere? Modern anthropogenic forcing of atmospheric chemistry promises to provide an experiment in such change that has not been matched since the early Paleogene, more than 50 million years ago (Ma),when catastrophic release of carbon to the atmosphere drove abrupt, transient, hyperthermal events. Research on the Paleocene-Eocene Thermal Maximum (PETM)-the best documented of these events, which occurred about 55 Ma-has advanced significantly since its discovery 15 years ago. During the PETM, carbon addition to the oceans and atmosphere was of a magnitude similar to that which is anticipated through the 21st century. This event initiated global warming, biotic extinction and migration, and fundamental changes in the carbon and hydrological cycles that transformed the early Paleogene world.

  18. Identification of Late Eocene Impact Deposits at ODP Site 1090

    NASA Technical Reports Server (NTRS)

    Kyte, Frank T.

    2001-01-01

    Anomalous concentrations of Ir have been found in upper Eocene sediments from Ocean Drilling Program (ODP) Hole 1090B. Clear and dark-colored spherules that are believed to be microtektites and clinopyroxene- bearing microkrystites, respectively, were found in the samples with highest Ir. The peak Ir concentration in Sample 177- 1090B-30X-5,105-106 cm (954 pg/g) and the net Ir fluence (14 ng/cm2) at this site are higher that at most other localities except for Caribbean site RC9-58. The Ir anomaly and impact debris are probably correlative with similar deposits found at ODP Site 689 on the Maude Rise and at other localities around the world.

  19. High latitude hydrological changes during the Eocene Thermal Maximum 2

    NASA Astrophysics Data System (ADS)

    Krishnan, Srinath; Pagani, Mark; Huber, Matthew; Sluijs, Appy

    2014-10-01

    The Eocene hyperthermals, including the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2), represent extreme global warming events ∼56 and 54 million years ago associated with rapid increases in atmospheric greenhouse gas concentrations. An initial study on PETM characteristics in the Arctic region argued for intensification of the hydrological cycle and a substantial increase in poleward moisture transport during global warming based on compound-specific carbon and hydrogen isotopic (2H/1H) records from sedimentary leaf-wax lipids. In this study, we apply this isotopic and hydrological approach on sediments deposited during ETM2 from the Lomonosov Ridge (Integrated Ocean Drilling Program Expedition 302). Our results show similar 2H/1H changes during ETM2 as during the PETM, with a period of 2H-enrichment (∼20‰) relative to “pre-event” values just prior to the negative carbon isotope shift (CIE) that is often taken as the onset of the hyperthermal, and more negative lipid δ2H values (∼-15‰) during peak warming. Notably, lipid 2H-enrichment at the base of the event is coeval with colder TEX86H temperatures. If 2H/1H values of leaf waxes primarily reflect the hydrogen isotopic composition of precipitation, the observed local relationship between temperature and 2H/1H values for the body of ETM2 is precisely the opposite of what would be predicted using a simple Rayleigh isotope distillation model, assuming a meridional vapor trajectory and a reduction in equator-pole temperature gradients. Overall, a negative correlation exists between the average chain length of n-alkanes and 2H/1H suggesting that local changes in ecology could have impacted the hydrogen isotopic compositions of leaf waxes. The negative correlation falls across three separate intervals - the base of the event, the initial CIE, and during the H2 hyperthermal (of which the assignment is not fully certain). Three possible mechanisms potentially explain 2H

  20. Geochemical evidence for a comet shower in the late Eocene.

    PubMed

    Farley, K A; Montanari, A; Shoemaker, E M; Shoemaker, C S

    1998-05-22

    Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began approximately 1 My before and ended approximately 1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters approximately 36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.

  1. Geochemical evidence for a comet shower in the late Eocene

    USGS Publications Warehouse

    Farley, K.A.; Montanari, A.; Shoemaker, E.M.; Shoemaker, C.S.

    1998-01-01

    Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ~1 My before and ended ~1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ~36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.

  2. Isotopic interrogation of a suspected late Eocene glaciation

    NASA Astrophysics Data System (ADS)

    Scher, Howie D.; Bohaty, Steven M.; Smith, Brian W.; Munn, Gabrielle H.

    2014-06-01

    Ephemeral polar glaciations during the middle-to-late Eocene (48-34 Ma) have been proposed based on far-field ice volume proxy records and near-field glacigenic sediments, although the scale, timing, and duration of these events are poorly constrained. Here we confirm the existence of a transient cool event within a new high-resolution benthic foraminiferal δ18O record at Ocean Drilling Program (ODP) Site 738 (Kerguelen Plateau; Southern Ocean). This event, named the Priabonian oxygen isotope maximum (PrOM) Event, lasted ~140 kyr and is tentatively placed within magnetochron C17n.1n (~37.3 Ma) based on the correlation to ODP Site 689 (Maud Rise, Southern Ocean). A contemporaneous change in the provenance of sediments delivered to the Kerguelen Plateau occurs at the study site, determined from the <63 µm fraction of decarbonated and reductively leached sediment samples. Changes in the mixture of bottom waters, based on fossil fish tooth ɛNd, were less pronounced and slower relative to the benthic δ18O and terrigenous ɛNd changes. Terrigenous sediment ɛNd values rapidly shifted to less radiogenic signatures at the onset of the PrOM Event, indicating an abrupt change in provenance favoring ancient sources such as the Paleoproterozoic East Antarctic craton. Bottom water ɛNd reached a minimum value during the PrOM Event, although the shift begins much earlier than the terrigenous ɛNd excursion. The origin of the abrupt change in terrigenous sediment provenance is compatible with a change in Antarctic terrigenous sediment flux and/or source as opposed to a reorganization of ocean currents. A change in terrigenous flux and/or source of Antarctic sediments during the oxygen isotope maximum suggests a combination of cooling and ice growth in East Antarctica during the early late Eocene.

  3. Cretaceous and Eocene poroid hymenophores from Vancouver Island, British Columbia.

    PubMed

    Smith, Selena Y; Currah, Randolph S; Stockey, Ruth A

    2004-01-01

    Two fossil poroid hymenophore fragments, one from the Cretaceous Period and the other from the Eocene Epoch, are described. The permineralized specimens were obtained from marine calcareous concretions on Vancouver Island, British Columbia, Canada, and were studied using the cellulose acetate peel technique. Size and distribution of pores in the hymenophores, as well as the hyphal anatomy of the dissepiments and some hymenial elements, were examined. In the Cretaceous specimen, Quatsinoporites cranhamii sp. nov., pores are round to elliptical, three per mm, and 130-540 μm diam. Dissepiments consist of narrow, simple septate, hyphae. Neither basidia nor basidiospores are present, but acuminate hymenial cystidia, up to 54 μm in length, are common. The Eocene specimen, Appianoporites vancouverensis sp. nov., has a pore density of six per mm and pores are 130-163 μm in diam. Dissepiments consist of narrow, simple septate, thin-walled hyphae. Neither basidia nor basidiospores are present, but acuminate, thick-walled hymenial cystidia, up to 32 μm in length, are common. The poroid hymenophore is a characteristic of a number of extant basidiomycete taxa, including the Boletales, Polyporales and Hymenochaetales. It is unlikely that the fleshy, ephemeral, terrestrial basidiomata of the Boletales would be preserved in a marine environment, and thus the specimens are interpreted as belonging to basidiomycete lineages, with persistent, leathery or corky basidiomata. The simple septate hyphae, the minute pores and presence of cystidia most closely resemble taxa of the Hymenochaetales. These fossils unequivocally push back the minimum age of homobasidiomycetes and extend their paleogeographical range.

  4. Differing Eocene floral histories in southeastern North America and Western Europe: influence of paleogeography

    USGS Publications Warehouse

    Frederiksen, N.O.

    1995-01-01

    Pollen data show that in southeastern North America, the Eocene angiosperm flora attained its maximum relative diversity some 8 m.y. after the late early Eocene to earliest middle Eocene to earliest middle Eocene climatic maximum. Increasing diversity resulted in part from the flora's position on a large continent which allowed easy migration. In western Europe, the floral diversity began decreasing even before the climatic maximum. Paleogeography played large roles in this diversity decrease. In western Europe, terrestrial floras were on islands and peninsulas in the sea, so that the floras underwent increasing isolation and partial local extermination. Temperate plants generally did not migrate to western Europe, because of a lack of nearby uplands, lack of northern terrestrial source areas for these plants, and presence of the Turgai Straights barrier. -from Authors

  5. Fossil palm beetles refine upland winter temperatures in the Early Eocene Climatic Optimum

    PubMed Central

    Archibald, S. Bruce; Morse, Geoffrey E.; Greenwood, David R.; Mathewes, Rolf W.

    2014-01-01

    Eocene climate and associated biotic patterns provide an analog system to understand their modern interactions. The relationship between mean annual temperatures and winter temperatures—temperature seasonality—may be an important factor in this dynamic. Fossils of frost-intolerant palms imply low Eocene temperature seasonality into high latitudes, constraining average winter temperatures there to >8 °C. However, their presence in a paleocommunity may be obscured by taphonomic and identification factors for macrofossils and pollen. We circumvented these problems by establishing the presence of obligate palm-feeding beetles (Chrysomelidae: Pachymerina) at three localities (a fourth, tentatively) in microthermal to lower mesothermal Early Eocene upland communities in Washington and British Columbia. This provides support for warmer winter Eocene climates extending northward into cooler Canadian uplands. PMID:24821798

  6. Fragments of Late Eocene Earth-Impacting Asteroids Linked to Disturbance of Asteroid Belt

    NASA Astrophysics Data System (ADS)

    Schmitz, B.; Boschi, S.; Cronholm, A.; Heck, P. R.; Monechi, S.; Montanari, A.; Terfelt, F.

    2015-07-01

    The impactors that created the large Popigai and Chesapeake Bay craters represent two different meteorite types. A Late Eocene multi-type asteroid shower may reflect solar-system instability and indicate an astronomical trigger of ice-house climate.

  7. Late Eocene- Oligocene magnetostratigraphy and biostratigraphy at South Atlantic DSDP site 522.

    USGS Publications Warehouse

    Poore, R.Z.; Tauxe, L.; Percival, S.F., Jr.; Labrecque, J.L.

    1982-01-01

    Upper Eocene to lowest Miocene sediments recovered at DSDP Site 522 in the S Atlantic Ocean allow direct calibration of magnetostratigraphy and calcareous plankton biostratigraphy. The results from Site 522 show that the Eocene/Oligocene boundary occurs in the reversed interval of magnetic Chron C13 (= C13R) and that the Oligocene/Miocene boundary probably occurs in the upper part of Chron C6C.-Authors

  8. The palaeobiology of high latitude birds from the early Eocene greenhouse of Ellesmere Island, Arctic Canada.

    PubMed

    Stidham, Thomas A; Eberle, Jaelyn J

    2016-02-12

    Fossils attributable to the extinct waterfowl clade Presbyornithidae and the large flightless Gastornithidae from the early Eocene (~52-53 Ma) of Ellesmere Island, in northernmost Canada are the oldest Cenozoic avian fossils from the Arctic. Except for its slightly larger size, the Arctic presbyornithid humerus is not distinguishable from fossils of Presbyornis pervetus from the western United States, and the Gastornis phalanx is within the known size range of mid-latitude individuals. The occurrence of Presbyornis above the Arctic Circle in the Eocene could be the result of annual migration like that of its living duck and geese relatives, or it may have been a year-round resident similar to some Eocene mammals on Ellesmere and some extant species of sea ducks. Gastornis, along with some of the mammalian and reptilian members of the Eocene Arctic fauna, likely over-wintered in the Arctic. Despite the milder (above freezing) Eocene climate on Ellesmere Island, prolonged periods of darkness occurred during the winter. Presence of these extinct birds at both mid and high latitudes on the northern continents provides evidence that future increases in climatic warming (closer to Eocene levels) could lead to the establishment of new migratory or resident populations within the Arctic Circle.

  9. A redescription of Lithornis vulturinus (Aves, Palaeognathae) from the Early Eocene Fur Formation of Denmark.

    PubMed

    Bourdon, Estelle; Lindow, Bent

    2015-10-20

    The extinct Lithornithidae include several genera and species of flying palaeognathous birds of controversial affinities known from the Early Paleogene of North America and Europe. An almost complete, articulated skeleton from the Early Eocene marine deposits of the Fur Formation (Denmark) was recently assigned to Lithornis vulturinus Owen, 1840. This study provides a detailed redescription and comparison of this three-dimensionally preserved specimen (MGUH 26770), which is one of the best preserved representatives of the Lithornithidae yet known. We suggest that some new features might be diagnostic of Lithornis vulturinus, including a pterygoid fossa shallower than in other species of Lithornis and the presence of a small caudal process on the os palatinum. We propose that Lithornis nasi (Harrison, 1984) is a junior synonym of Lithornis vulturinus and we interpret minor differences in size and shape among the specimens as intraspecific variation. To date, Lithornis vulturinus is known with certainty from the latest Paleocene-earliest Eocene to Early Eocene of the North Sea Basin (Ølst, Fur and London Clay Formations). Among the four species of the genus Lithornis, the possibility that Lithornis plebius Houde, 1988 (Early Eocene of Wyoming) is conspecific with either Lithornis vulturinus or Lithornis promiscuus Houde, 1988 (Early Eocene of Wyoming) is discussed. The presence of closely related species of Lithornis on either side of the North Atlantic in the Early Eocene reflects the existence of a high-latitude land connection between Europe and North America at that time.

  10. Cross section through the Toa Baja drillsite: Evidence for northward change in Late Eocene deformation intensity

    SciTech Connect

    Larue, D.K. ); Berrong, B. )

    1991-03-01

    A 55 km geologic cross section through the Toa Baja Drillsite, generated by integrating geologic mapping data from the foothills of the Central Mountains of Puerto Rico with onshore and offshore multichannel seismic reflection data, provides an opportunity to examine in profile from the arc interior northward to within 40 km of the current trench slope break. Three structural divisions are recognized. In the foothills of Puerto Rico, Cretaceous and Eocene rocks are separated by transpressional strike-slip faults. In the vicinity of the Toa Baja drillsite where both seismic reflection and borehole data are available, Eocene rocks, deformed by thrust faults, .ie above a lower unit, interpreted to be of Cretaceous age. Offshore, north of the drilling site, seismic reflections suggest Eocene rocks onlap structural basement, thought to be Cretaceous rocks, and both units appear only slightly deformed. All Eocene and Eocene ( ) rocks are overlain by little deformed Oligocene to Recent rocks. From south to north, or from the arc massif interior toward the present-day trench, there is an apparent decrease in amount of Late Eocene to Middle Oligocene strike-slip and shortening deformation. Deformation events occurred mostly in the arc-interior and were not directly associated with the plate boundary which was probably near the Puerto Rico Trench.

  11. The palaeobiology of high latitude birds from the early Eocene greenhouse of Ellesmere Island, Arctic Canada

    PubMed Central

    Stidham, Thomas A.; Eberle, Jaelyn J.

    2016-01-01

    Fossils attributable to the extinct waterfowl clade Presbyornithidae and the large flightless Gastornithidae from the early Eocene (~52–53 Ma) of Ellesmere Island, in northernmost Canada are the oldest Cenozoic avian fossils from the Arctic. Except for its slightly larger size, the Arctic presbyornithid humerus is not distinguishable from fossils of Presbyornis pervetus from the western United States, and the Gastornis phalanx is within the known size range of mid-latitude individuals. The occurrence of Presbyornis above the Arctic Circle in the Eocene could be the result of annual migration like that of its living duck and geese relatives, or it may have been a year-round resident similar to some Eocene mammals on Ellesmere and some extant species of sea ducks. Gastornis, along with some of the mammalian and reptilian members of the Eocene Arctic fauna, likely over-wintered in the Arctic. Despite the milder (above freezing) Eocene climate on Ellesmere Island, prolonged periods of darkness occurred during the winter. Presence of these extinct birds at both mid and high latitudes on the northern continents provides evidence that future increases in climatic warming (closer to Eocene levels) could lead to the establishment of new migratory or resident populations within the Arctic Circle. PMID:26867798

  12. The palaeobiology of high latitude birds from the early Eocene greenhouse of Ellesmere Island, Arctic Canada.

    PubMed

    Stidham, Thomas A; Eberle, Jaelyn J

    2016-01-01

    Fossils attributable to the extinct waterfowl clade Presbyornithidae and the large flightless Gastornithidae from the early Eocene (~52-53 Ma) of Ellesmere Island, in northernmost Canada are the oldest Cenozoic avian fossils from the Arctic. Except for its slightly larger size, the Arctic presbyornithid humerus is not distinguishable from fossils of Presbyornis pervetus from the western United States, and the Gastornis phalanx is within the known size range of mid-latitude individuals. The occurrence of Presbyornis above the Arctic Circle in the Eocene could be the result of annual migration like that of its living duck and geese relatives, or it may have been a year-round resident similar to some Eocene mammals on Ellesmere and some extant species of sea ducks. Gastornis, along with some of the mammalian and reptilian members of the Eocene Arctic fauna, likely over-wintered in the Arctic. Despite the milder (above freezing) Eocene climate on Ellesmere Island, prolonged periods of darkness occurred during the winter. Presence of these extinct birds at both mid and high latitudes on the northern continents provides evidence that future increases in climatic warming (closer to Eocene levels) could lead to the establishment of new migratory or resident populations within the Arctic Circle. PMID:26867798

  13. A redescription of Lithornis vulturinus (Aves, Palaeognathae) from the Early Eocene Fur Formation of Denmark.

    PubMed

    Bourdon, Estelle; Lindow, Bent

    2015-01-01

    The extinct Lithornithidae include several genera and species of flying palaeognathous birds of controversial affinities known from the Early Paleogene of North America and Europe. An almost complete, articulated skeleton from the Early Eocene marine deposits of the Fur Formation (Denmark) was recently assigned to Lithornis vulturinus Owen, 1840. This study provides a detailed redescription and comparison of this three-dimensionally preserved specimen (MGUH 26770), which is one of the best preserved representatives of the Lithornithidae yet known. We suggest that some new features might be diagnostic of Lithornis vulturinus, including a pterygoid fossa shallower than in other species of Lithornis and the presence of a small caudal process on the os palatinum. We propose that Lithornis nasi (Harrison, 1984) is a junior synonym of Lithornis vulturinus and we interpret minor differences in size and shape among the specimens as intraspecific variation. To date, Lithornis vulturinus is known with certainty from the latest Paleocene-earliest Eocene to Early Eocene of the North Sea Basin (Ølst, Fur and London Clay Formations). Among the four species of the genus Lithornis, the possibility that Lithornis plebius Houde, 1988 (Early Eocene of Wyoming) is conspecific with either Lithornis vulturinus or Lithornis promiscuus Houde, 1988 (Early Eocene of Wyoming) is discussed. The presence of closely related species of Lithornis on either side of the North Atlantic in the Early Eocene reflects the existence of a high-latitude land connection between Europe and North America at that time. PMID:26624382

  14. The crazy hollow formation (Eocene) of central Utah

    USGS Publications Warehouse

    Weiss, M.P.; Warner, K.N.

    2001-01-01

    The Late Eocene Crazy Hollow Formation is a fluviatile and lacustrine unit that was deposited locally in the southwest arm of Lake Uinta during and after the last stages of the lake the deposited the Green River Formation. Most exposures of the Crazy Hollow are located in Sanpete and Sevier Counties. The unit is characterized by a large variety of rock types, rapid facies changes within fairly short distances, and different lithofacies in the several areas where outcrops of the remnants of the formation are concentrated. Mudstone is dominant, volumetrically, but siltstone, shale, sandstone, conglomerate and several varieties of limestone are also present. The fine-grained rocks are mostly highly colored, especially in shades of yellow, orange and red. Sand grains, pebbles and small cobbles of well-rounded black chert are widespread, and "salt-and-pepper sandstone" is the conspicuous characteristic of the Crazy Hollow. The salt-and-pepper sandstone consists of grains of black chert, white chert, quartz and minor feldspar. The limestone beds and lenses are paludal and lacustrine in origin; some are fossiliferous, and contain the same fauna found in the Green River Formation. With trivial exceptions, the Crazy Hollow Formation lies on the upper, limestone member of the Green River Formation, and the beds of the two units are always accordant in attitude. The nature of the contact differs locally: at some sites there is gradation from the Green River to the Crazy Hollow; at others, rocks typical of the two units intertongue; elsewhere there is a disconformity between the two. A variety of bedrock units overlie the Crazy Hollow at different sites. In the southeasternmost districts it is overlain by the late Eocene formation of Aurora; in western Sevier County it is overlain by the Miocene-Pliocene Sevier River Formation; in northernmost Sanpete County it is overlain by the Oligocene volcanics of the Moroni Formation. At many sites bordering Sanpete and Sevier Valleys

  15. Response of Deep Ocean Carbon Cycling to Astronomical Forcing in the Non-Glaciated Eocene 'Greenhouse' World

    NASA Astrophysics Data System (ADS)

    Sexton, P. F.; Wilson, P. A.; Pälike, H.

    2007-12-01

    Atmospheric carbon dioxide concentrations predicted for 2100 may not have existed on Earth since the early part of the Eocene epoch when global conditions were much warmer and less glaciated than today. Yet our understanding of carbon cycling and climate stability within the Eocene is extremely rudimentary. Here we present the first high-resolution paleoceanographic records across the early to middle Eocene boundary. Our records reveal multiple prominent perturbations to Eocene climate and the carbon cycle. We also observe breakdown in the post-Eocene/Oligocene boundary spatial pattern of astronomical pacing of deep ocean sediment calcium carbonate content. We attribute this divergent response to astronomical forcing to the deglaciated early Eocene climate state.

  16. Was the Eocene Arctic a Source Area for Exotic Plants and Mammals? (Invited)

    NASA Astrophysics Data System (ADS)

    Eberle, J. J.; Harrington, G. J.; Fricke, H. C.; Humphrey, J.; Hackett, L.; Newbrey, M.; Hutchison, J. H.

    2010-12-01

    Today’s High Arctic is undergoing rapid warming, but the impact on its animal and plant communities is not clear. As a deep time analog to better understand and predict the impacts of global warming on the Arctic biota, early Eocene (52-53 Ma) rocks on Ellesmere Island, Nunavut in Canada’s High Arctic (~79°N latitude) preserve evidence of diverse terrestrial ecosystems that supported dense forests inhabited by turtles, alligators, snakes, primates, tapirs, brontotheres, and hippo-like Coryphodon. The fossil localities were just a few degrees further south and still well above the Arctic Circle during the early Eocene; consequently, the biota experienced months of continuous sunlight as well as darkness, the Arctic summer and winter, respectively. The flora and fauna of the early Eocene Arctic imply warmer, wetter conditions than at present, and recently published analyses of biogenic phosphate from fossil fish, turtle, and mammal estimate warm summers (19 - 20 C) and mild, above-freezing winters. In general, temperature estimates for the early Eocene Arctic can be compared to those found today in temperate rainforests in the Pacific Northwest of the United States. The early Eocene Arctic mammalian fauna shares most genera with coeval mid-latitude faunas thousands of kilometers to the south in the US Western Interior, and several genera also are shared with Europe and Asia. Recent analyses suggest that the large herbivores such as hippo-like Coryphodon were year-round inhabitants in the Eocene Arctic forests. Although several of the Eocene Arctic mammalian taxa are hypothesized to have originated in either mid-latitude North America or Asia, the earlier occurrence of certain clades (e.g., tapirs) in the Arctic raises the possibility of a northern high-latitude origin. Analysis of the early Eocene Arctic palynoflora indicates comparable richness to early Eocene plant communities in the US Western Interior, but nearly 50% of its species (mostly angiosperms) are

  17. Anthropoid humeri from the late Eocene of Egypt

    PubMed Central

    Seiffert, Erik R.; Simons, Elwyn L.; Fleagle, John G.

    2000-01-01

    A number of recent studies have, by necessity, placed a great deal of emphasis on the dental evidence for Paleogene anthropoid interrelationships, but cladistic analyses of these data have led to the erection of phylogenetic hypotheses that appear to be at odds with biogeographic and stratigraphic considerations. Additional morphological data from the cranium and postcranium of certain poorly understood Paleogene primates are clearly needed to help test whether such hypotheses are tenable. Here we describe humeri attributable to Proteopithecus sylviae and Catopithecus browni, two anthropoids from late Eocene sediments of the Fayum Depression in Egypt. Qualitative and morphometric analyses of these elements indicate that humeri of the oligopithecine Catopithecus are more similar to early Oligocene propliopithecines than they are to any other Paleogene anthropoid taxon, and that Proteopithecus exhibits humeral similarities to parapithecids that may be symplesiomorphies of extant (or “crown”) Anthropoidea. The humeral morphology of Catopithecus is consistent with certain narrowly distributed dental apomorphies—such as the loss of the upper and lower second premolar and the development of a honing blade for the upper canine on the lower third premolar—which suggest that oligopithecines constitute the sister group of a clade containing propliopithecines and Miocene-Recent catarrhines and are not most closely related to Proteopithecus as has recently been proposed. PMID:10963669

  18. Primate postcrania from the late middle Eocene of Myanmar

    PubMed Central

    Ciochon, Russell L.; Gingerich, Philip D.; Gunnell, Gregg F.; Simons, Elwyn L.

    2001-01-01

    Fossil primates have been known from the late middle to late Eocene Pondaung Formation of Myanmar since the description of Pondaungia cotteri in 1927. Three additional primate taxa, Amphipithecus mogaungensis, Bahinia pondaungensis and Myanmarpithecus yarshensis, were subsequently described. These primates are represented mostly by fragmentary dental and cranial remains. Here we describe the first primate postcrania from Myanmar, including a complete left humerus, a fragmentary right humerus, parts of left and right ulnae, and the distal half of a left calcaneum, all representing one individual. We assign this specimen to a large species of Pondaungia based on body size and the known geographic distribution and diversity of Myanmar primates. Body weight estimates of Pondaungia range from 4,000 to 9,000 g, based on humeral length, humeral midshaft diameter, and tooth area by using extant primate regressions. The humerus and ulna indicate that Pondaungia was capable of a wide variety of forelimb movements, with great mobility at the shoulder joint. Morphology of the distal calcaneus indicates that the hind feet were mobile at the transverse tarsal joint. Postcrania of Pondaungia present a mosaic of features, some shared in common with notharctine and adapine adapiforms, some shared with extant lorises and cebids, some shared with fossil anthropoids, and some unique. Overall, Pondaungia humeral and calcaneal morphology is most consistent with that of other known adapiforms. It does not support the inclusion of Pondaungia in Anthropoidea. PMID:11438722

  19. Continental warming preceding the Palaeocene-Eocene thermal maximum.

    PubMed

    Secord, Ross; Gingerich, Philip D; Lohmann, Kyger C; Macleod, Kenneth G

    2010-10-21

    Marine and continental records show an abrupt negative shift in carbon isotope values at ∼55.8 Myr ago. This carbon isotope excursion (CIE) is consistent with the release of a massive amount of isotopically light carbon into the atmosphere and was associated with a dramatic rise in global temperatures termed the Palaeocene-Eocene thermal maximum (PETM). Greenhouse gases released during the CIE, probably including methane, have often been considered the main cause of PETM warming. However, some evidence from the marine record suggests that warming directly preceded the CIE, raising the possibility that the CIE and PETM may have been linked to earlier warming with different origins. Yet pre-CIE warming is still uncertain. Disentangling the sequence of events before and during the CIE and PETM is important for understanding the causes of, and Earth system responses to, abrupt climate change. Here we show that continental warming of about 5 °C preceded the CIE in the Bighorn Basin, Wyoming. Our evidence, based on oxygen isotopes in mammal teeth (which reflect temperature-sensitive fractionation processes) and other proxies, reveals a marked temperature increase directly below the CIE, and again in the CIE. Pre-CIE warming is also supported by a negative amplification of δ(13)C values in soil carbonates below the CIE. Our results suggest that at least two sources of warming-the earlier of which is unlikely to have been methane-contributed to the PETM.

  20. Seawater calcium isotope ratios across the Eocene-Oligocene transition

    USGS Publications Warehouse

    Griffith, E.M.; Paytan, A.; Eisenhauer, A.; Bullen, T.D.; Thomas, E.

    2011-01-01

    During the Eocene-Oligocene transition (EOT, ca. 34 Ma), Earth's climate cooled significantly from a greenhouse to an icehouse climate, while the calcite (CaCO3) compensation depth (CCD) in the Pacific Ocean increased rapidly. Fluctuations in the CCD could result from various processes that create an imbalance between calcium (Ca) sources to, and sinks from, the ocean (e.g., weathering and CaCO3 deposition), with different effects on the isotopic composition of dissolved Ca in the oceans due to differences in the Ca isotopic composition of various inputs and outputs. We used Ca isotope ratios (??44/40Ca) of coeval pelagic marine barite and bulk carbonate to evaluate changes in the marine Ca cycle across the EOT. We show that the permanent deepening of the CCD was not accompanied by a pronounced change in seawater ??44/40Ca, whereas time intervals in the Neogene with smaller carbonate depositional changes are characterized by seawater ??44/40Ca shifts. This suggests that the response of seawater ??44/40Ca to changes in weathering fluxes and to imbalances in the oceanic alkalinity budget depends on the chemical composition of seawater. A minor and transient fluctuation in the Ca isotope ratio of bulk carbonate may reflect a change in isotopic fractionation associated with CaCO3 precipitation from seawater due to a combination of factors, including changes in temperature and/or in the assemblages of calcifying organisms. ?? 2011 Geological Society of America.

  1. Paleoecology of Early eocene strata near Buffalo, Wyoming

    SciTech Connect

    Durkin, T.V.; Rich, F.J.

    1986-08-01

    Palynological investigation has helped illustrate the paleoecology of a vertical section of strata from the Wasatch Formation between the Healy and Walters coal burns near Buffalo, Wyoming. Numerous silicified logs and stumps of cypress and sequoia have been preserved at the site and drew initial attention to it. Flood-basin deposits enclose the trees and include sandstones, siltstones, shale, and coal beds that accumulated as channel, levee, crevasse-splay, and swamp/marsh sediments. Detrital sediments were probably derived from the Bighorn Mountains and accumulated as they were carried into the Powder River basin fluvial system. One hundred five polynomorph taxa have been distinguished, as well as 10 types of fungal spores. Platycarya, Tilia, Sparganium, and Platanus pollen indicate an early Eocene age for the strata. Other pollen, as well as the genera of trees and megafossil remains from a clinker bed several miles from the study area, reinforce the interpretation of a warm-temperature or subtropical climate at the time of deposition. The megafossil assemblage includes pinnae of the aquatic fern Marsilea, never before described from the fossil record. Variations in the species composition of the polynomorph assemblages show that several plant communities existed in succession at the site. These varied from pond or marsh types to mature forests.

  2. Middle Eocene seagrass facies from Apennine carbonate platforms (Italy)

    NASA Astrophysics Data System (ADS)

    Tomassetti, Laura; Benedetti, Andrea; Brandano, Marco

    2016-04-01

    Two stratigraphic sections located in the Latium-Abruzzi (Monte Porchio, Central Apennines, Central Italy) and in the Apulian carbonate platform (S. Cesarea-Torre Tiggiano, Salento, Southern Italy) were measured and sampled to document the sedimentological characteristic and the faunistic assemblages of Middle Eocene seagrass deposits. The faunistic assemblages are dominated by porcellaneous foraminifera Orbitolites, Alveolina, Idalina, Spiroloculina, Quinqueloculina, Triloculina and abundant hooked-shaped gypsinids, associated with hooked red algae and green algae Halimeda. Fabiania, rotaliids and textulariids as well as nummulitids are subordinated. The samples were assigned to Lutetian (SBZ13-16) according to the occurrence of Nummulites cf. lehneri, Alveolina ex. gr. elliptica, Idalina berthelini, Orbitolites complanatus, Slovenites decastroi and Medocia blayensis. At Santa Cesarea reticulate nummulites occur in association with Alveolina spp. and Halkyardia minima marking the lower Bartonian (SBZ17). Three main facies associations have been recognised: I) larger porcellaneous foraminiferal grainstones with orbitolitids and alveolinids deposited into high-energy shallow-water settings influenced by wave processes that reworked the sediments associated with a seagrass; II) grainstone to packstone with small porcellaneous foraminifera and abundant permanently-attached gypsinids deposited in a more protected (e.g., small embayment) in situ vegetated environment; III) bioclastic packstone with parautochthonous material reworked from the seagrass by rip currents and accumulated into rip channels in a slightly deeper environment. The biotic assemblages suggest that the depositional environment is consistent with tropical to subtropical vegetated environments within oligotrophic conditions.

  3. Late Eocene stable isotope stratigraphy of North Atlantic IODP Site U1411: Orbitally paced climatic heartbeat at the close of the Eocene greenhouse

    NASA Astrophysics Data System (ADS)

    Coxall, Helen; Bohaty, Steve; Wilson, Paul; Liebrand, Diederik; Nyberg, Anna; Holmström, Max

    2016-04-01

    Integrated Ocean Drilling Program (IODP) Expedition 342 drilled sediment drifts on the Newfoundland margin to recover high-resolution records of North Atlantic ocean-climate history and track the evolution of the modern climate system through the Late Cretaceous and Early Cenozoic. An early Paleogene deep-sea benthic stable isotope composite record from multiple Exp. 342 sites is currently in development and will provide a key reference section for investigations of Atlantic and global climate dynamics. This study presents initial results for the late Eocene slice of the composite from Site U1411, located at mid depth (˜2850m Eocene paleodepth) on the Southeast Newfoundland Ridge. Stable oxygen (δ18O) and carbon (δ13C) isotope ratios were measured on 640 samples hosting exceptionally well-preserved epifaunal benthic foraminifera obtained from the microfossil-rich uppermost Eocene clays at 4cm spacing. Sedimentation rates average 2-3 cm/kyr through the late Eocene, such that our sampling resolution is sufficient to capture the dominant Milankovitch frequencies. Late Eocene Site U1411 benthic δ18O values (1.4 to 0.5‰ VPDB) are comparable to the Pacific and elsewhere in the Atlantic at similar depths; however, δ13C is lower by ˜0.5 ‰ with values intermediate between those of the Southern Labrador Sea to the north (-1 to 0) and mid latitude/South Atlantic (0.5 to 1.5) to the south, suggesting poorly ventilated bottom waters in the late Eocene North Atlantic and limited production of North Atlantic deep water. Applying the initial shipboard magneto-biostratigraphic age framework, the Site U1411 benthic δ13C and δ18O records display clear cyclicity on orbital timescales. Spectral analysis of the raw unfiltered datasets identifies eccentricity (400 and 100 kyr), obliquity (40 kyr) and precession (˜20 kyr) signals imprinted on our time series, revealing distinct climatic heart beats in the late Eocene prior to the transition into the 'ice house'.

  4. Late paleogene (eocene to oligocene) paleoceanography of the northern North Atlantic. Doctoral thesis

    SciTech Connect

    Miller, K.G.

    1982-11-01

    Seismic stratigraphic evidence indicates that a major change in abyssal circulation occurred in the latest Eocene-earliest Oligocene of the North Atlantic. Reflector R4 reflects a change from weakly (Eocene) to vigorously circulating bottom water (early Oligocene). Sediment distribution studies indicate a northern source for this bottom water, probably from the Arctic via the Norwegian-Greenland Sea/Faeroe-Shetland Channel. Current-controlled sedimentation and erosion continued through the Oligocene; however, above reflector R3 (upper Oligocene), the general intensity of abyssal currents decreased. Above reflector R2 (lower Miocene) a further reduction in abyssal currents resulted in more coherent current-controlled sedimentation and a major phase of sediment drift development. Major deep-sea benthic foraminiferal changes occurred between the middle Eocene and earliest Oligocene: an agglutinated assemblage was replaced by a calcareous assemblage (abyssal Labrador Sea), and an indigenous Eocene calcareious fauna became extinct (abyssal Bay of Biscay). In shallower Atlantic sites (< 3km paleodepth), a Nuttallides truempyi assemblage was replaced by an assemblage of long- and wide-ranging taxa in the early late Eocene.

  5. The oldest African bat from the early Eocene of El Kohol (Algeria)

    NASA Astrophysics Data System (ADS)

    Ravel, Anthony; Marivaux, Laurent; Tabuce, Rodolphe; Adaci, Mohammed; Mahboubi, Mohammed; Mebrouk, Fateh; Bensalah, Mustapha

    2011-05-01

    The Afro-Arabian Paleogene fossil record of Chiroptera is very poor. In North Africa and Arabia, this record is limited, thus far, to a few localities mainly in Tunisia (Chambi, late early Eocene), Egypt (Fayum, late Eocene to early Oligocene), and Sultanate of Oman (Taqah, early Oligocene). It consists primarily of isolated teeth or mandible fragments. Interestingly, these African fossil bats document two modern groups (Vespertilionoidea and Rhinolophoidea) from the early Eocene, while the bat fossil record of the same epoch of North America, Eurasia, and Australia principally includes members of the "Eochiroptera." This paraphyletic group contains all primitive microbats excluding modern families. In Algeria, the region of Brezina, southeast of the Atlas Mountains, is famous for the early Eocene El Kohol Formation, which has yielded one of the earliest mammalian faunas of the African landmass. Recent fieldwork in the same area has led to the discovery of a new vertebrate locality, including isolated teeth of Chiroptera. These fossils represent the oldest occurrence of Chiroptera in Africa, thus extending back the record of the group to the middle early Eocene (Ypresian) on that continent. The material consists of an upper molar and two fragments of lower molars. The dental character association matches that of "Eochiroptera." As such, although very fragmentary, the material testifies to the first occurrence of "Eochiroptera" in Algeria, and by extension in Africa. This discovery demonstrates that this basal group of Chiroptera had a worldwide distribution during the early Paleogene.

  6. Multiple microtektite horizons in upper Eocene marine sediments: No evidence for mass extinctions

    USGS Publications Warehouse

    Keller, G.; D'Hondt, S.; Vallier, T.L.

    1983-01-01

    Microtektites have been recovered from three horizons in eight middle Eocene to middle Oligocene marine sediment sequences. Five of these occurrences are coeval and of latest Eocene age (37.5 to 38.0 million years ago); three are coeval and of early late Eocene age (38.5 to 39.5 million years ago); and three are of middle Oligocene age (31 to 32 million years ago). In addition, rare probable microtektites have been found in sediments with ages of about 36.0 to 36.5 million years. The microtektite horizon at 37.5 to 38.0 million years can be correlated with the North American tektite-strewn field, which has a fission track age (minimum) of 34 to 35 million years and a paleomagnetic age of 37.5 to 38.0 million years. There is no evidence for mass faunal extinctions at any of the microtektite horizons. Many of the distinct faunal changes that occurred in the middle Eocene to middle Oligocene can be related to the formation of the Antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large-scale dissolution of calcium carbonate and erosion, which created areally extensive hiatuses in the deep-sea sediment records. The occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle Eocene to middle Oligocene time.

  7. Multiple microtektite horizons in upper eocene marine sediments: no evidence for mass extinctions.

    PubMed

    Keller, G; D'Hondt, S; Vallier, T L

    1983-07-01

    Microtektites have been recovered from three horizons in eight middle Eocene to middle Oligocene marine sediment sequences. Five of these occurrences are coeval and of latest Eocene age (37.5 to 38.0 million years ago); three are coeval and of early late Eocene age (38.5 to 39.5 million years ago); and three are of middle Oligocene age (31 to 32 million years ago). In addition, rare probable microtektites have been found in sediments with ages of about 36.0 to 36.5 million years. The microtektite horizon at 37.5 to 38.0 million years can be correlated with the North American tektite-strewn field, which has a fission track age (minimum) of 34 to 35 million years and a paleomagnetic age of 37.5 to 38.0 million years. There is no evidence for mass faunal extinctions at any of the microtektite horizons. Many of the distinct faunal changes that occurred in the middle Eocene to middle Oligocene can be related to the formation of the Antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large-scale dissolution of calcium carbonate and erosion, which created areally extensive hiatuses in the deep-sea sediment records. The occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle Eocene to middle Oligocene time.

  8. Larger benthic foraminiferal turnover across the Eocene-Oligocene transition at Siwa Oasis, Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Orabi, H.; El Beshtawy, M.; Osman, R.; Gadallah, M.

    2015-05-01

    In the Eocene part of the Siwa Oasis, the larger foraminifera are represented by the genera Nummulites, Arxina, Operculina, Sphaerogypsina, Asterocyclina, Grzybowskia, Silvestriella, Gaziryina and Discocyclina in order of abundance. Operculina continues up to the early Oligocene as modern representatives in tropical regions, while the other genera became extinct. Nevertheless, the most common larger foraminiferal genus Lepidocyclina (Nephrolepidina) appears only in the lowermost Oligocene. In spite of the Eocene-Oligocene (E/O) transition is thought to have been attended by major continental cooling at northern middle and high latitudes, we discover that at the Siwa Oasis, there is a clear warming trend from the late Eocene (extinction level of Nummulites, Sphaerogypsina, Asterocyclina, Grzybowskia, Silvestriella and Discocyclina) to the early Oligocene is observed due to the high abundance of Operculina and occurrence of kaolinite and gypsiferous shale deposits in both Qatrani and El Qara formations (Oligocene) at this transition. The El Qara Formation is a new rock unit proposed herein for the Oligocene (Rupelian age) in the first time. Several episodes of volcanic activity occurred in Egypt during the Cenozoic. Mid Tertiary volcanicity was widespread and a number of successive volcanic pulses are starting in the late Eocene. The release of mantle CO2 from this very active volcanic episode may have in fact directly caused the warm Eocene-Oligocene greenhouse climate effect.

  9. Fossil plant stomata indicate decreasing atmospheric CO2 prior to the Eocene-Oligocene boundary

    NASA Astrophysics Data System (ADS)

    Steinthorsdottir, Margret; Porter, Amanda S.; Holohan, Aidan; Kunzmann, Lutz; Collinson, Margaret; McElwain, Jennifer C.

    2016-02-01

    A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany has been used to derive an atmospheric pCO2 record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the inverse relationship between the density of stomata and pCO2, we show that pCO2 decreased continuously from the late middle to late Eocene, reaching a relatively stable low value before the end of the Eocene. Based on the subsequent records, pCO2 in parts of the Oligocene was similar to latest Eocene values. These results suggest that a decrease in pCO2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene-Oligocene transition and that when a certain threshold of pCO2 change was crossed, the cumulative effects of this and other factors resulted in rapid temperature decline, ice build up on Antarctica and hence a change of climate mode.

  10. Fossil plant stomata indicate decreasing atmospheric CO2 prior to the Eocene-Oligocene boundary

    NASA Astrophysics Data System (ADS)

    Steinthorsdottir, M.; Porter, A. S.; Holohan, A.; Kunzmann, L.; Collinson, M.; McElwain, J. C.

    2015-10-01

    A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany has been used to derive an atmospheric pCO2 record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the inverse relationship between the density of stomata and pCO2, we show that pCO2 decreased continuously from the late middle to late Eocene, reaching a relatively stable low value before the end of the Eocene. Based on the subsequent records, pCO2 in parts of the Oligocene was similar to latest Eocene values. These results show that a decrease in pCO2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene-Oliogocene transition. This may be related to the "hysteresis effect" previously proposed - where a certain threshold of pCO2 change was crossed before the cumulative effects of this and other factors resulted in rapid temperature decline, ice build up on Antarctica and hence a change of climate mode.

  11. The oldest African bat from the early Eocene of El Kohol (Algeria).

    PubMed

    Ravel, Anthony; Marivaux, Laurent; Tabuce, Rodolphe; Adaci, Mohammed; Mahboubi, Mohammed; Mebrouk, Fateh; Bensalah, Mustapha

    2011-05-01

    The Afro-Arabian Paleogene fossil record of Chiroptera is very poor. In North Africa and Arabia, this record is limited, thus far, to a few localities mainly in Tunisia (Chambi, late early Eocene), Egypt (Fayum, late Eocene to early Oligocene), and Sultanate of Oman (Taqah, early Oligocene). It consists primarily of isolated teeth or mandible fragments. Interestingly, these African fossil bats document two modern groups (Vespertilionoidea and Rhinolophoidea) from the early Eocene, while the bat fossil record of the same epoch of North America, Eurasia, and Australia principally includes members of the "Eochiroptera." This paraphyletic group contains all primitive microbats excluding modern families. In Algeria, the region of Brezina, southeast of the Atlas Mountains, is famous for the early Eocene El Kohol Formation, which has yielded one of the earliest mammalian faunas of the African landmass. Recent fieldwork in the same area has led to the discovery of a new vertebrate locality, including isolated teeth of Chiroptera. These fossils represent the oldest occurrence of Chiroptera in Africa, thus extending back the record of the group to the middle early Eocene (Ypresian) on that continent. The material consists of an upper molar and two fragments of lower molars. The dental character association matches that of "Eochiroptera." As such, although very fragmentary, the material testifies to the first occurrence of "Eochiroptera" in Algeria, and by extension in Africa. This discovery demonstrates that this basal group of Chiroptera had a worldwide distribution during the early Paleogene. PMID:21442243

  12. Sonora, Mexico, source for the Eocene Poway Conglomerate of southern California

    NASA Astrophysics Data System (ADS)

    Abbott, Patrick L.; Smith, T. E.

    1989-04-01

    Alluvial-fan conglomerates of the Eocene Poway Group are composed largely of exotic rhyolite and dacite clasts derived from far to the east of their Eocene depositional site. Remnants of the Upper Jurassic bedrock source of the Poway rhyolite clasts may yet be exposed in hills in Sonora, Mexico. For this study, pieces of bedrock were taken from hills 13 km west of El Plomo in Sonora. Clasts texturally and mineralogically similar to the Sonoran bedrock were collected from the apex of the Eocene alluvial fan in San Diego County, California Nine couplets of bedrock and conglomerate clast samples (textural twins) were analyzed for 16 trace elements selected for their wide range of behaviors during magmatic and alteration processes. Statistical comparisons of the trace-element data, by using the standard error-of-the-difference method, show that there are no significant differences between the two populations. These data strongly suggest that the rhyolitic bedrock hills west of El Plomo were part of the source terrane for the Eocene conglomerate in San Diego. The latitudinal separation between bedrock source and the site of deposition is only the 2° created by the opening of the Gulf of California This implies that any boundary separating a paleomagnetically efined, Baja-Borderland terrane from the craton since Eocene time was at least 100 km east of the Gulf of California in northernmost Sonora.

  13. Geochronology of upper Paleocene and lower Eocene strata, eastern Gulf Coastal Plain

    SciTech Connect

    Mancini, E.A.; Tew, B.H. Geological Survey of Alabama, Tuscaloosa, AL )

    1994-03-01

    Four samples of glauconitic sand from upper Paleocene and lower Eocene strata of the eastern Gulf Coastal Plain were analyzed for conventional potassium-argon (K-Ar) age determination. Results from these analyses are as follows: Coal Bluff Marl Member of the Naheola Formation of the Midway Group (58.2 [+-] 1.5 MA), Ostrea thirsae beds of the Nanafalia Formation of the Wilcox Group (56.3 [+-] 1.5 MA), upper Tuscahoma Sand of the Wilcox Group (54.5 [+-] 1.4 MA), and Bashi Marl Member of the Hatchetigbee Formation of the Wilcox Group (53.4 [+-] 1.4 MA). The Nanafalia Formation (Wilcox Group) disconformably overlies the Naheola Formation (Midway Group), and based on the data presented here, the age of this unconformity is bracketed between 59.7 and 54.8 MA. The Paleocene-Eocene Epoch boundary occurs in the Wilcox Group and coincides with the lithostratigraphic contact of the upper Paleocene Tuscahoma Sand with the lower eocene Hatchetigbee Formation. The age of this boundary, which is also an unconformity, can be placed between 55.9 and 52.0 MA. The K-Ar age dates for this boundary in the Gulf Coastal Plain compare favorably with the numerical limits placed on the Paleocene-Eocene boundary in the published literature. Generally, the Paleocene-Eocene Epoch boundary is reported as approximately 54 to 55 MA.

  14. Astronomical calibration of the middle Eocene Contessa Highway section (Gubbio, Italy)

    NASA Astrophysics Data System (ADS)

    Coccioni, R.; Florindo, F.; Jovane, L.; Marsili, A.; Sprovieri, M.

    2008-12-01

    The Earth's Eocene to early Oligocene climatic system experienced an important transition with a long-term cooling trend from warm greenhouse to icehouse conditions. Today, it is a priority to understand the causes and consequences that drove this major climatic change. In this context, a multidisciplinary study has been carried out on the middle Eocene sedimentary succession of the Contessa Highway (Gubbio, Italy). Spectral analysis and CWT technique of seven multidisciplinary high-resolution records demonstrate that climatic changes, in the western Neo-Tethys (Umbria-Marche basin) during the middle Eocene, are sensitive to eccentricity, obliquity and precession astronomical variations. In the Contessa Highway section, the lithology shows high-frequency cyclicity, which is strongly modulated by insolation. The lithologic cyclostratigraphy combined with the ~7 My-long astronomically driven climate proxy records, provide a first astronomical calibration of the middle Eocene. Here, we present astronomical age for the bio-magnetostratigraphic events along the middle Eocene Contessa Highway section. These astronomically calibrated ages mark significant improvements for the dating of biostratigraphic events and minimal correction to chronostratigraphy. Based on the available high-resolution bio-, isotope- and magnetostratigraphy and the precise multi-proxy astronomical tuning of the sedimentary record we retain that the Contessa Highway section represents an excellent candidate as GSSP for the Lutetian/Bartonian boundary.

  15. The Massignano Eocene-Oligocene golden spike section revisited

    NASA Astrophysics Data System (ADS)

    van Mourik, C. A.; Brinkhuis, H.

    2004-12-01

    In common practice, the Eocene/Oligocene (E/O) boundary is linked to the Oi-1 δ 18 O benthic isotope event, reflecting the oldest phase of major Antarctic glaciation, calibrated against magnetosubchron C13n. Yet, the IUGS-ratified, current E/O GSSP at the pelagic Massignano Quarry section, central Italy, occurs within the older magnetosubchron C13r, at metre 19 of the 23 m section. To promote further high-resolution stratigraphic and paleoecological studies at Massignano, and to extend the lower Oligocene record, the so-called Massicore was drilled about 110 m south of the stratotype section. By means of high-resolution organic-walled dinoflagellate cyst (dinocyst) analysis, in combination with biotite-rich horizons an almost perfect linear correlation between the core and the quarry was obtained, resulting in the establishment of the Massignano GSSP composite section, spanning from magnetosubchron16-2n to 12r (van Mourik and Brinkhuis, in press). The revised paleomagnetic ages of this interval (Pḋ {a}like et al., in prep) were used for a preliminary age model of the composite section. The paleoecological dinocysts proxies were plotted along this agemodel. A straightforward correlation of the (relative) Sea Surface Temperature (SST) curve to the 400 ky eccentricity curve of Laskar et al.'s (2004) was possible. In two intervals (5.60 to 10.50 m and 17 to 35 m) the correlation could be made to the 100 ky eccentricity curve (Laskar et al., 2004). The first astronomical timescale for the Massignano GSSP composite section could be composed, placing the GSSP (19 m) at age of 33.96 ± 0.05 Ma. The age of the onset of the Oi-1 event appears around 33.55 ± 0.01 Ma, and towards the top of the section the cold peaks in the SST get more and more pronounced. The cooler conditions are substantiated by the occurrence of restricted high latitude dinocyst species (G. inflata and Sv. cooksoniae) from 33.30 ± 0.01 Ma until the top of the section (van Mourik et al., in prep

  16. Upper Eocene Spherules at ODP Site 1090B

    NASA Technical Reports Server (NTRS)

    Liu, S.; Kyte, F. T.; Glass, B. P.; Gersonde, R.

    2000-01-01

    Our two labs independently discovered upper Eocene microtektites and microkrystites at ODP Site 1090, a new South Atlantic locality near the Agulhus Ridge. This is a significant new data point for the strewn fields of these spherules, which were recently extended into the Atlantic sector of the Southern Ocean when they were reported at ODP Site 689 on the Maude Rise. The microtektites have been regarded as related to North American tektites and the microkrystites as belonging to the clinopyroxene-bearing (cpx) spherule strewn field. Initial reports indicate that Site 1090 contains a complete sequence of upper Eocene sediments composed of diatom and nannofossil oozes. The magneto- and bio-stratigraphy indicate that impact-age sediments should occur in core 30X of Hole 1090B. One of us (FTK) took 2 cc samples at 10 cm intervals over 600 cm of core for Ir analyses and the senior author (SL) took 3 cc samples at 20 cm intervals to search for spherules. Both studies proved successful and additional samples were obtained to confirm initial results and better define the Ir anomaly and spherule abundances. Peak Ir concentrations of 0.97 ng/g were found at 1090B-30X-5, 105-106cm and 0.78 ng/g at 115-116 cm. Anomalous Ir concentrations (greater than 0.1 ng/g) extend over about 100 cm of core. Preliminary results indicate that the excess Ir at this site is about 25 ng per sq cm. About 380 microtektites (>63 pm) and 2492 microkrystites (>63 pm) were recovered over a 1.8 m interval with a peak abundance of microtektites (106/gram) and microkrystites (562/gram) at 1090B-30X- 5, 114-115 cm. The largest microtektite is approximately 960 x 1140 micron in size. About 55 % are spherical, and the rest are disc, cylinder, dumbbell, teardrop, or fragments. Most of the microtektites are transparent colorless, but a few are transparent pale brown or green. Preliminary data indicate that the microtektites at Site 1090 have similar major oxide compositions to those at Site 689. About 50% of

  17. The Eocene turbidities of the Trujillo Formation, Venezuelan Andes

    SciTech Connect

    Ghosh, S.K.; Zambrano, E.

    1996-08-01

    The Trujillo Formation, overlying the Paleocene Cerro Verde and Valle Hondo formations, reveals a turbiditic origin in a lowstand shelf-edge and bathyal setting in two excellent road sections on the Valera-Carache road and many creek sections. The basal outcrop shows well developed fining upward (FU) sequences of proximal channel turbidite and overbank origin (abandonment phase) and minor coarsening upward (CU) sequences representing progradational pulse in overbank areas. The FU (and thinning-upward) sequence, overlying a shale, consists of: (a) basal stacked conglomeratic arenites (probably inner fan channels) with graded beds, imbricate casts and transported shells; (b) a sand/shale alternating unit (channel margin/interchannel) with flame structure, lenticular bedding, infrequent Tb-d Sequence, rippled flats, and rare Planolites; and (c) a dark shale (overbank-interchannel lows) with scarce Chondrites and Scaladtuba traces. The CU sequence consists of thickening-upward heterolithic facies overlain by lenticular stacked pebbly arenites. The upper unit exposed near Puente Gomez is a typical progradational lobe starting with a basal shale, with intraformational diastems and slumped beds, and Tb-d and Tb-e sequences in thin intercalated sandstones; a heterolithic facies with flute/groove casts, Planolites, Thalassinoides and Neonereites occurs between the shale and a thick cross-stratified sandstone at the top. This CU lobe sequence is discordantly(?) overlain by a thin wedge of massive bedded pebbly sandstones of Middle Eocene(?) Misoa Formation. Unlike the southwesterly sourced subsurface turbidites, those in this area were probably sourced from both the south and north, though locally the southern source might have been more important.

  18. Age of Eocene/Oligocene boundary based on extrapolation from North American microtektite layer

    SciTech Connect

    Glass, B.P.; Crosbie, J.R.

    1982-04-01

    Microtektites believed to belong to the North American tektite strewn field have been found in upper Eocene sediments in cores from nine Deep Sea Drilling Project sites in the Caribbean Sea, Gulf of Mexico, equatorial Pacific, and eastern equatorial Indian Ocean. The microtektite layer has an age of 34.2 +- 0.6 m.y. based on fission-track dating of the microtektites and K-Ar and fission-track dating of the North American tektites. Extrapolation from the microtektite layer to the overlying Eocene/Oligocene boundary indicates an age of 32.3 +- 0.9 m.y. for the Eocene/Oligocene boundary as defined at each site in the Initial Reports of the Deep Sea Drilling Project. This age is approximately 5 m.y. younger than the age of 37.5 m.y. that is generally assigned to the boundary based on recently published Cenozoic time scales. 3 figures, 5 tables.

  19. Latitudinal gradients in greenhouse seawater δ(18) O: evidence from Eocene sirenian tooth enamel.

    PubMed

    Clementz, Mark T; Sewall, Jacob O

    2011-04-22

    The Eocene greenhouse climate state has been linked to a more vigorous hydrologic cycle at mid- and high latitudes; similar information on precipitation levels at low latitudes is, however, limited. Oxygen isotopic fluxes track moisture fluxes and, thus, the δ(18)O values of ocean surface waters can provide insight into hydrologic cycle changes. The offset between tropical δ(18)O values from sampled Eocene sirenian tooth enamel and modern surface waters is greater than the expected 1.0 per mil increase due to increased continental ice volume. This increased offset could result from suppression of surface-water δ(18)O values by a tropical, annual moisture balance substantially wetter than that of today. Results from an atmospheric general circulation model support this interpretation and suggest that Eocene low latitudes were extremely wet.

  20. Latitudinal gradients in greenhouse seawater δ(18) O: evidence from Eocene sirenian tooth enamel.

    PubMed

    Clementz, Mark T; Sewall, Jacob O

    2011-04-22

    The Eocene greenhouse climate state has been linked to a more vigorous hydrologic cycle at mid- and high latitudes; similar information on precipitation levels at low latitudes is, however, limited. Oxygen isotopic fluxes track moisture fluxes and, thus, the δ(18)O values of ocean surface waters can provide insight into hydrologic cycle changes. The offset between tropical δ(18)O values from sampled Eocene sirenian tooth enamel and modern surface waters is greater than the expected 1.0 per mil increase due to increased continental ice volume. This increased offset could result from suppression of surface-water δ(18)O values by a tropical, annual moisture balance substantially wetter than that of today. Results from an atmospheric general circulation model support this interpretation and suggest that Eocene low latitudes were extremely wet. PMID:21512030

  1. Post-Eocene movement on the Coast Range thrust, northern Sacramento Valley, California

    SciTech Connect

    Ramirez, V. )

    1990-05-01

    Subsurface structure mapping with more than 600 wells and 200 miles of seismic data in a portion of the northern Sacramento basin and surface geologic mapping in the Rumsey Hills area to the west indicates that Upper Cretaceous strata along the western edge of the basin are doubled in thickness along thrust faults. These east-dipping detachments are part of the Coast Range thrust fault system. Eocene strata crop out in the fault zone and indicate that considerable post-Eocene movement occurred. Cretaceous movement on these faults can be surmised but not proven from reconstructions. Similarly, analysis from five subsurface structure maps to the east shows that deformation there also is post-Eocene; only minor Upper Cretaceous deformation can be discerned. Underthrusting of Franciscan accretionary rocks best accounts for the development of these faults and a western high along the basin margin.

  2. Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures.

    PubMed

    Douglas, Peter M J; Affek, Hagit P; Ivany, Linda C; Houben, Alexander J P; Sijp, Willem P; Sluijs, Appy; Schouten, Stefan; Pagani, Mark

    2014-05-01

    Paleoclimate studies suggest that increased global warmth during the Eocene epoch was greatly amplified at high latitudes, a state that climate models cannot fully reproduce. However, proxy estimates of Eocene near-Antarctic sea surface temperatures (SSTs) have produced widely divergent results at similar latitudes, with SSTs above 20 °C in the southwest Pacific contrasting with SSTs between 5 and 15 °C in the South Atlantic. Validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites. Here, we present multiproxy data from Seymour Island, near the Antarctic Peninsula, that provides well-constrained evidence for annual SSTs of 10-17 °C (1σ SD) during the middle and late Eocene. Comparison of the same paleotemperature proxy at Seymour Island and at the East Tasman Plateau indicate the presence of a large and consistent middle-to-late Eocene SST gradient of ∼7 °C between these two sites located at similar paleolatitudes. Intermediate-complexity climate model simulations suggest that enhanced oceanic heat transport in the South Pacific, driven by deep-water formation in the Ross Sea, was largely responsible for the observed SST gradient. These results indicate that very warm SSTs, in excess of 18 °C, did not extend uniformly across the Eocene southern high latitudes, and suggest that thermohaline circulation may partially control the distribution of high-latitude ocean temperatures in greenhouse climates. The pronounced zonal SST heterogeneity evident in the Eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands.

  3. Effects of Proto-Antarctic Circumpolar Current circulation in the middle to late Eocene

    NASA Astrophysics Data System (ADS)

    Katz, M.; Cramer, B. S.; Toggweiler, J. R.

    2011-12-01

    Progressive development of the Antarctic Circumpolar Current (ACC) and reorganization of global ocean circulation accompanied the critical climate transition from the late middle Eocene to mid-Oligocene (~38-28 Ma), marked by global cooling and development of continental-scale Antarctic ice sheets. The ACC began to develop in the middle Eocene through a shallow Drake Passage, with deepwater flow likely established by 29 Ma (Livermore et al. 2004). Rapid deepening of the Tasman gateway occurred in the late Eocene to early Oligocene). The timing of the earliest impact of the (proto-) ACC on global circulation and climate has been debated for decades. Here, we present new middle to late Eocene (~36-40 Ma) benthic foraminiferal stable isotopic (δ18O, δ13C) records and %CaCO3 data from ODP Site 1090 that extend published late Eocene-early Oligocene records (Pusz et al. 2011). Comparisons with published isotopic records (Cramer et al. 2009) highlight the development of a significant carbon isotopic (δ13C) offset between Site 1090 (values ~ 0.7% lower) and other sites from ~37.5 to 34 Ma, reminiscent of similar low δ13C values in this region during the Plio-Pleistocene (Hodell & Venz-Curtis, 2006). The low δ13C interval coincides with elevated opaline silica deposition at Site 1090 (Diekmann et al. 2004), and with the development of small, but significant, meridional δ18O gradients within the deep Atlantic basin. We interpret these observations as indicative of enhanced primary production at the northern edge of the polar front accompanied by increased thermal differentiation of northern- and sourthern-sourced deepwaters. These records are consistent with model predictions for the effects of proto-ACC development in the late Eocene (Heinze and Crowley, 1997; Toggweiler and Bjornsson, 2000).

  4. Eocene Underplating Along the Kodiak Shelf, Alaska: Implications and Regional Correlations

    NASA Astrophysics Data System (ADS)

    Byrne, Tim

    1986-06-01

    Structural geology and geophysical data from the Kodiak Shelf suggest that the Mesozoic rocks exposed on the shelf are structurally underlain (at about 12 km depth) by several kms of Eocene age strata. Kinematic data from the Late Cretaceous to Paleocene Ghost Rocks Formation indicate that this formation and probably all of the Kodiak Islands, were uplifted vertically to nearly their present elevations. Landward tilting and imbrication are not indicated. The age of uplift is indicated by a regional, angular unconformity of Early Eocene to Early Oligocene age that separates deep-sea rocks from shallow water to non-marine rocks. The uplift of the accretionary prism is believed to have been caused by underplating of an Eocene sedimentary sequence because (1) a band of seismic reflections that occur 12 to 20 km beneath the shelf is interpreted as the top of the underplated material and (2) an obductively offscraped sequence of Eocene deep-sea rocks crops out on the seaward side of the Kodiak Shelf, suggesting that a thick trench-fill sequence may have been present prior to uplift of the prism. The underplated material is interpreted to be part of either a previously unrecognized turbidite fan of Early Eocene age or a proximal equivalent of the Zodiac fan of Late Eocene to Early Oligocene age. Other possible on-land remnants of the underplated material may be present in Prince William Sound (the Montague belt), the Gulf of Alaska (lower sections of the Yakutat block) and in the Coast Ranges of Oregon and Washington. The large volume of underplated material beneath the Kodiak shelf suggests that underplating may be the dominant process in the growth of convergent margins.

  5. Orbitally tuned timescale and astronomical forcing in the middle Eocene to early Oligocene

    NASA Astrophysics Data System (ADS)

    Westerhold, T.; Röhl, U.; Pälike, H.; Wilkens, R.; Wilson, P. A.; Acton, G.

    2014-05-01

    Deciphering the driving mechanisms of Earth system processes, including the climate dynamics expressed as paleoceanographic events, requires a complete, continuous, and high-resolution stratigraphy that is very accurately dated. In this study, a robust astronomically calibrated age model was constructed for the middle Eocene to early Oligocene interval (31-43 Ma) in order to permit more detailed study of the exceptional climatic events that occurred during this time, including the middle Eocene climate optimum and the Eocene-Oligocene transition. A goal of this effort is to accurately date the middle Eocene to early Oligocene composite section cored during the Pacific Equatorial Age Transect (PEAT, IODP Exp. 320/321). The stratigraphic framework for the new timescale is based on the identification of the stable long eccentricity cycle in published and new high-resolution records encompassing bulk and benthic stable isotope, calibrated XRF core scanning, and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199-1218, and 207-1260 as well as IODP Sites 320-U1333, and 320-U1334 spanning magnetic polarity Chrons C12n to C20n. Subsequently orbital tuning of the records to the La2011 orbital solution was conducted. The resulting new timescale revises and refines the existing orbitally tuned age model and the geomagnetic polarity timescale from 31 to 43 Ma. The newly defined absolute age for the Eocene-Oligocene boundary validates the astronomical tuned age of 33.89 Ma identified at the Massignano, Italy, global stratotype section and point. The compilation of geochemical records of climate-controlled variability in sedimentation through the middle-to-late Eocene and early Oligocene demonstrates strong power in the eccentricity band that is readily tuned to the latest astronomical solution. Obliquity driven cyclicity is only apparent during 2.4 myr eccentricity cycle minima around 35.5, 38.3, and 40.1 Ma.

  6. Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures

    PubMed Central

    Douglas, Peter M. J.; Affek, Hagit P.; Ivany, Linda C.; Houben, Alexander J. P.; Sijp, Willem P.; Sluijs, Appy; Schouten, Stefan; Pagani, Mark

    2014-01-01

    Paleoclimate studies suggest that increased global warmth during the Eocene epoch was greatly amplified at high latitudes, a state that climate models cannot fully reproduce. However, proxy estimates of Eocene near-Antarctic sea surface temperatures (SSTs) have produced widely divergent results at similar latitudes, with SSTs above 20 °C in the southwest Pacific contrasting with SSTs between 5 and 15 °C in the South Atlantic. Validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites. Here, we present multiproxy data from Seymour Island, near the Antarctic Peninsula, that provides well-constrained evidence for annual SSTs of 10–17 °C (1σ SD) during the middle and late Eocene. Comparison of the same paleotemperature proxy at Seymour Island and at the East Tasman Plateau indicate the presence of a large and consistent middle-to-late Eocene SST gradient of ∼7 °C between these two sites located at similar paleolatitudes. Intermediate-complexity climate model simulations suggest that enhanced oceanic heat transport in the South Pacific, driven by deep-water formation in the Ross Sea, was largely responsible for the observed SST gradient. These results indicate that very warm SSTs, in excess of 18 °C, did not extend uniformly across the Eocene southern high latitudes, and suggest that thermohaline circulation may partially control the distribution of high-latitude ocean temperatures in greenhouse climates. The pronounced zonal SST heterogeneity evident in the Eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands. PMID:24753570

  7. Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures.

    PubMed

    Douglas, Peter M J; Affek, Hagit P; Ivany, Linda C; Houben, Alexander J P; Sijp, Willem P; Sluijs, Appy; Schouten, Stefan; Pagani, Mark

    2014-05-01

    Paleoclimate studies suggest that increased global warmth during the Eocene epoch was greatly amplified at high latitudes, a state that climate models cannot fully reproduce. However, proxy estimates of Eocene near-Antarctic sea surface temperatures (SSTs) have produced widely divergent results at similar latitudes, with SSTs above 20 °C in the southwest Pacific contrasting with SSTs between 5 and 15 °C in the South Atlantic. Validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites. Here, we present multiproxy data from Seymour Island, near the Antarctic Peninsula, that provides well-constrained evidence for annual SSTs of 10-17 °C (1σ SD) during the middle and late Eocene. Comparison of the same paleotemperature proxy at Seymour Island and at the East Tasman Plateau indicate the presence of a large and consistent middle-to-late Eocene SST gradient of ∼7 °C between these two sites located at similar paleolatitudes. Intermediate-complexity climate model simulations suggest that enhanced oceanic heat transport in the South Pacific, driven by deep-water formation in the Ross Sea, was largely responsible for the observed SST gradient. These results indicate that very warm SSTs, in excess of 18 °C, did not extend uniformly across the Eocene southern high latitudes, and suggest that thermohaline circulation may partially control the distribution of high-latitude ocean temperatures in greenhouse climates. The pronounced zonal SST heterogeneity evident in the Eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands. PMID:24753570

  8. Gateways, Supergyre, and proto-Antarctic Circumpolar Current in the middle to late Eocene

    NASA Astrophysics Data System (ADS)

    Katz, M. E.; Cramer, B. S.; Toggweiler, J.

    2013-12-01

    The (proto-)Antarctic Circumpolar Current (ACC) began to develop in the middle Eocene through a shallow Drake Passage and Tasman Gateway. Progressive deepening of these gateways and northward migration of Australia through the Eocene impacted global ocean circulation. We present middle to late Eocene (~36-40 Ma) benthic foraminiferal stable isotope (δ18O, δ13C) records from ODP Site 1090 that extend published late Eocene-early Oligocene records (Pusz et al. 2011). Comparisons with published isotope records highlight that the deep (~3000m) eastern and western South Atlantic (Sites 699 (Mead et al. 1993) and 1090) was warmer than the shallower (~1500-2500m) Southern Ocean Sites 689 (Diester-Haass and Zahn, 1996; Bohaty et al., 2012). The divergence in the δ18O records began in the late middle Eocene and continued through the late Eocene, as the Drake and Tasman gateways progressively deepened, and Australia moved northward. We speculate that these paleogeographic changes resulted in the development of circulation analogous to the modern Supergyre, which transported warm Indian and Pacific water westward into the South Atlantic and cooler South Atlantic water eastward into the Pacific Ocean via the Tasman Seaway, and acted as a barrier that prevented subtropical water from flowing to high southern latitudes. At the same time, a significant carbon isotopic (δ13C) offset developed between Site 1090 (values ~ 0.7‰ lower) and other sites from ~37.5 to 34 Ma, coinciding with onset of elevated opaline silica (Diekmann et al. 2004), barite, carbonate, and phosphorous (Anderson and Delaney 2005) deposition at Site 1090; these changes are consistent with enhanced primary productivity at the northern edge of the developing polar front, consistent with model predictions for the effects of proto-ACC development (Heinze and Crowley, 1997; Toggweiler and Bjornsson, 2000).

  9. Orbitally tuned time scale and astronomical forcing in the middle Eocene to early Oligocene

    NASA Astrophysics Data System (ADS)

    Westerhold, T.; Röhl, U.; Pälike, H.; Wilkens, R.; Wilson, P. A.; Acton, G.

    2013-12-01

    Deciphering the driving mechanisms of Earth system processes, including the climate dynamics expressed as paleoceanographic events, requires a complete, continuous, and high-resolution stratigraphy that is very accurately dated. In this study, we construct a robust astronomically calibrated age model for the middle Eocene to early Oligocene interval (31-43 Ma) in order to permit more detailed study of the exceptional climatic events that occurred during this time, including the Middle Eocene Climate Optimum and the Eocene/Oligocene transition. A goal of this effort is to accurately date the middle Eocene to early Oligocene composite section cored during the Pacific Equatorial Age Transect (PEAT, IODP Exp. 320/321). The stratigraphic framework for the new time scale is based on the identification of the stable long eccentricity cycle in published and new high-resolution records encompassing bulk and benthic stable isotope, calibrated XRF core scanning, and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199-1218, and 207-1260 as well as IODP Sites 320-U1333, and -U1334 spanning magnetic polarity Chrons C12n to C20n. Subsequently we applied orbital tuning of the records to the La2011 orbital solution. The resulting new time scale revises and refines the existing orbitally tuned age model and the Geomagnetic Polarity Time Scale from 31 to 43 Ma. Our newly defined absolute age for the Eocene/Oligocene boundary validates the astronomical tuned age of 33.89 Ma identified at the Massignano (Italy) global stratotype section and point. Our compilation of geochemical records of climate-controlled variability in sedimentation through the middle-to-late Eocene and early Oligocene demonstrates strong power in the eccentricity band that is readily tuned to the latest astronomical solution. Obliquity driven cyclicity is only apparent during very long eccentricity cycle minima around 35.5, 38.3 and 40.1 Ma.

  10. The 40Ar/39Ar ages and tectonic setting of the Middle Eocene northeast Nevada volcanic field

    USGS Publications Warehouse

    Brooks, W.E.; Thorman, C.H.; Snee, L.W.

    1995-01-01

    Widespread middle to late Eocene calc-alkalic volcanism, which formed the Northeast Nevada Volcanic Field, marks the earliest Tertiary volcanism in the northern Basin and Range. The central part of this major field in northest Nevada and adjacent Utah is herein defined by 23 40Ar/39Ar ages that arange from 42.6 to 39.0 Ma, rock chemistry from 12 localities, stratigraphic position of the volcanic rocks above a regional middle Eocene unconformity, volcanic setting, and lithology. The type area is at Nanny Creek, in the northern Pequop Mountains, Nevada. In the western and southeastern parts of the field these middle Eocene volcanic rocks rest with depositional angular discordance on lower Eocene lacustrine strata of the Elko and White Sage Formations, respectively. This angular discordance documents a middle Eocene deformational event previously unrecognized in the region. -from Authors

  11. Igneous geology of the Carlin trend, Nevada: The importance of Eocene magmatism in gold mineralization

    NASA Astrophysics Data System (ADS)

    Ressel, Michael Walter, Jr.

    Igneous rocks of five ages are present in the Carlin trend, Nevada, and include: (1) Paleozoic basalt of the Roberts Mountains allochthon, (2) the Jurassic (˜158 Ma) Goldstrike intrusive complex, which includes the Goldstrike diorite laccolith and abundant dikes and sills, (3) a Cretaceous (112 Ma) granite stock, (4) lavas and intrusions of the Emigrant Pass volcanic field and widespread epizonal plugs and dikes of Eocene (˜40-36 Ma) age that range from rhyolite through basalt, and (5) Miocene (15 Ma) rhyolite lava and tuff. Jurassic and Eocene igneous rocks are by far the most important volumetrically and are spatially associated with nearly all ore deposits of the Carlin trend. This study focuses on the field relations, isotopic dating, and geochemistry of Eocene dikes that intrude sedimentary rocks in many deposits of the Carlin trend, because they are the youngest pre-mineral rocks and have simpler alteration histories than other host rocks. In the Beast, Genesis, Deep Star, Betze-Post, Rodeo-Goldbug, Meikle-Griffin, and Dee-Storm deposits, Eocene dikes are altered, commonly mineralized, and locally constitute ore. Gold-bearing dikes and sedimentary rocks have similar ore mineralogy, including arsenian pyrite, marcasite, and arsenopyrite, with late barite and stibnite. At Beast, as much as half the ore is hosted in a 37.3 Ma rhyolite dike. Post-gold alunite is ˜18.6 Ma. At Meikle and Griffin, porphyritic dacite dikes yield concordant U/Pb zircon and 40Ar/39Ar biotite emplacement ages of ˜39.2 Ma, and illite from the same QSP-altered dacite, with as much 9 ppm Au, yields similar, although imprecise 40Ar/39Ar ages. Thus, gold mineralization at these deposits closely followed emplacement of Eocene dikes. Carlin-type gold deposits in northeastern Nevada have been variously interpreted as partly syngenetic with Paleozoic carbonate rocks, products of Mesozoic contraction and metamorphism with or without significant magmatism, and of Tertiary age and related or

  12. A new primate from the Middle Eocene of Myanmar and the Asian early origin of anthropoids.

    PubMed

    Jaeger, J; Thein, T; Benammi, M; Chaimanee, Y; Soe, A N; Lwin, T; Tun, T; Wai, S; Ducrocq, S

    1999-10-15

    A new genus and species of anthropoid primate, Bahinia pondaungensis gen. et sp. nov., is described from the Yashe Kyitchaung locality in the Late Middle Eocene Pondaung Formation (Myanmar). It is related to Eosimias, but it is represented by more complete remains, including upper dentition with associated lower jaw fragment. It is interpreted as a new representative of the family Eosimiidae, which corresponds to the sister group of the Amphipithecidae and of all other anthropoids. Eosimiidae are now recorded from three distinct Middle Eocene localities in Asia, giving support to the hypothesis of an Asian origin of anthropoids.

  13. Pulses of middle Eocene to earliest Oligocene climatic deterioration in southern California and the Gulf Coast

    USGS Publications Warehouse

    Frederiksen, N.O.

    1991-01-01

    A general deterioration of terrestrial climate took place during middle Eocene to earliest Oligocene time in southern California and in the Gulf Coast. Pollen data, calibrated by calcareous nannofossil ages, indicate four events of rapid floral and/or vegetational change among angiosperms during this time interval. The events can be correlated between the two regions even though these regions lay within different floristic provinces, and each event of angiosperm change is interpreted to indicate a pulse of rapid climatic shift. The most distinct of these events is the Middle Eocene Diversity Decline, which resulted from a peak in last appearances (extinctions, emigrations) centered in the early Bartonian. -from Author

  14. An eocene hystricognathous rodent from Texas: its significance in interpretations of continental drift.

    PubMed

    Wood, A E

    1972-03-17

    The earliest known representative of the fundamentally South American and African hystricognathous rodents has recently been found in the middle or late Eocene of southwestern Texas; this discovery supports the postulate of a northern and independent origin for the two southern groups and increases the evidence against mid-Tertiary trans-Atlantic migration of these rodents at a time when the South Atlantic was narrower than it is at present. The fossil seems to be related to the North American Eocene family Sciuravidae.

  15. Monophyly and extensive extinction of advanced eusocial bees: insights from an unexpected Eocene diversity.

    PubMed

    Engel, M S

    2001-02-13

    Advanced eusociality sometimes is given credit for the ecological success of termites, ants, some wasps, and some bees. Comprehensive study of bees fossilized in Baltic amber has revealed an unsuspected middle Eocene (ca. 45 million years ago) diversity of eusocial bee lineages. Advanced eusociality arose once in the bees with significant post-Eocene losses in diversity, leaving today only two advanced eusocial tribes comprising less than 2% of the total bee diversity, a trend analogous to that of hominid evolution. This pattern of changing diversity contradicts notions concerning the role of eusociality for evolutionary success in insects.

  16. Hydrogen isotopes in Eocene river gravels and paleoelevation of the Sierra Nevada.

    PubMed

    Mulch, Andreas; Graham, Stephan A; Chamberlain, C Page

    2006-07-01

    We determine paleoelevation of the Sierra Nevada, California, by tracking the effect of topography on precipitation, as recorded in hydrogen isotopes of kaolinite exposed in gold-bearing river deposits from the Eocene Yuba River. The data, compared with the modern isotopic composition of precipitation, show that about 40 to 50 million years ago the Sierra Nevada stood tall (>/=2200 meters), a result in conflict with proposed young surface uplift by tectonic and climatic forcing but consistent with the Sierra Nevada representing the edge of a pre-Eocene continental plateau.

  17. Paleomagnetism of Eocene and Miocene sediments from the Qaidam basin: Implication for no integral rotation since the Eocene and a rigid Qaidam block

    NASA Astrophysics Data System (ADS)

    Yu, Xiangjiang; Fu, Suotang; Guan, Shuwei; Huang, Baochun; Cheng, Feng; Cheng, Xiang; Zhang, Tuo; Guo, Zhaojie

    2014-06-01

    Qaidam basin is the largest topographic depression inside the Tibetan Plateau and it is a key factor to understanding the Cenozoic evolution of the northern Tibetan Plateau. Paleomagnetic data was obtained from the middle to late Eocene Xiaganchaigou Formation and the early to middle Miocene Xiayoushashan Formation from seven localities. The paleomagnetic results indicate that the Qaidam basin has not undergone obvious basin-scale vertical axis rotation with respect to the Eurasia Plate since the Eocene. Local clockwise rotation took place only at a few special locations along the northern margin of the Qaidam basin. The uniform paleomagnetic results at different localities support that the Qaidam basin is a relatively rigid block. Regional paleomagnetic and geodetic observations also suggest that crust south of the Kunlun fault moves eastward faster than crust north of the Kunlun fault.

  18. Nonexplosive and explosive magma/wet-sediment interaction during emplacement of Eocene intrusions into Cretaceous to Eocene strata, Trans-Pecos igneous province, West Texas

    USGS Publications Warehouse

    Befus, K.S.; Hanson, R.E.; Miggins, D.P.; Breyer, J.A.; Busbey, A.B.

    2009-01-01

    Eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified, Upper Cretaceous (Maastrichtian) to Eocene fluvial strata in part of the Trans-Pecos igneous province in West Texas produced an array of features recording both nonexplosive and explosive magma/wet-sediment interaction. Intrusive complexes with 40Ar/39Ar dates of ~ 47-46??Ma consist of coherent basalt, peperite, and disrupted sediment. Two of the complexes cutting Cretaceous strata contain masses of conglomerate derived from Eocene fluvial deposits that, at the onset of intrusive activity, would have been > 400-500??m above the present level of exposure. These intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the Trans-Pecos province. Disrupted Cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions. Eocene conglomerate slumped downward from higher levels during vent excavation. Coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate, within disrupted Cretaceous strata in the conduit walls, and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism. A younger series of intrusions with 40Ar/39Ar dates of ~ 42??Ma underwent nonexplosive interaction with Upper Cretaceous to Paleocene mud and sand. Dikes and sills show fluidal, billowed, quenched margins against the host strata, recording development of surface instabilities between magma and groundwater-rich sediment. Accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment. More intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite, but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions. This work suggests that

  19. Middle Eocene Equatorial Pacific Paleoceanography: Insights From Bulk Sediment Geochemistry, ODP Site 1218

    NASA Astrophysics Data System (ADS)

    Tripati, A. K.; Lyle, M.; Backman, J.

    2002-12-01

    The deep equatorial Pacific was dominated by siliceous sedimentation from ~45 Ma to the Eocene-Oligocene boundary. Inspection of Paleogene sediments recovered during Ocean Drilling Program (ODP) Leg 199 and Deep Sea Drilling Program Leg 16 indicate several episodes of carbonate deposition during the Middle Eocene. The well-preserved and expanded sedimentary sequence recovered at ODP Site 1218 presents an opportunity to document the Middle Eocene paleoceanographic history of the equatorial Pacific, and to determine whether the occurrence of Middle Eocene carbonates in Chron C18 is coincident with a sequence of rapid paleoceanographic and climatic changes. Here we present high-resolution bulk sediment oxygen and carbon isotope records, carbonate, opal, and organic carbon accumulation data, and coarse sand fraction data for chalks and radiolarites spanning Chron C18 from ODP Site 1218. Stable isotope and % carbonate records exhibit large-amplitude oscillations corresponding to obliquity and eccentricity frequencies. In addition, a series of stepwise oxygen isotope excursions of 0.5 to 0.8 per mil at roughly 40.5, 40.4, and 40.3 Ma, occur in coincidence with large-scale drops in % carbonate. These data may record rapid CCD fluctuation associated with transient warming and cooling events and/or ephemeral polar ice sheets.

  20. A new dermochelyid turtle from the Late Paleocene-Early Eocene of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Tong, Haiyan; Buffetaut, Eric; Thomas, Herbert; Roger, Jack; Halawani, Mohammed; Memesh, Abdallah; Lebret, Patrick

    1999-12-01

    A new dermochelyid sea turtle, Arabemys crassiscutata n. gen, n. sp., is described on the basis of epithecal shell mosaic ossicles from the Late Paleocene—Early Eocene of Saudi Arabia. This is the oldest and the most primitive known representative of the dermochelyids having an epithecal shell mosaic.

  1. The first Late Eocene continental faunal assemblage from tropical North America

    NASA Astrophysics Data System (ADS)

    Jiménez-Hidalgo, Eduardo; Smith, Krister T.; Guerrero-Arenas, Rosalia; Alvarado-Ortega, Jesus

    2015-01-01

    To date, the terrestrial faunal record of the North American late Eocene has been recovered from its subtropical and temperate regions. We report the first late Eocene continental faunal assemblage from tropical North America, in southern Mexico. Fossil specimens were collected from mudstones that crop out in the Municipality of Santiago Yolomécatl, in northwestern Oaxaca. Previously published K-Ar ages of 32.9 ± 0.9 and 35.7 ± 1.0 Ma in overlain nearby volcanic rocks and biostratigraphy of these new localities suggests a Chadronian mammal age for this new local fauna. The assemblage is composed by two turtle taxa, Rhineura, two caniform taxa, a sciurid, a jimomyid rodent, a geomyine rodent, Gregorymys, Leptochoerus, Perchoerus probus, Merycoidodon, a protoceratid, Poebrotherium, Nanotragulus, Miohippus assinoboiensis, a chalicotherid, a tapiroid, cf. Amynodontopsis, Trigonias and the hymenopteran ichnofossils Celliforma curvata and Fictovichnus sciuttoi. The records of these taxa in northwestern Oaxaca greatly expand southerly their former geographic distribution in North America. The records of the geomorph rodents and Nanotragulus extend their former known biochronological range to the late Eocene. The hymenopteran ichnofossils in the localities suggest the presence of a bare soil after periodic waterlogging, under a sub-humid to sub-arid climate. This new local fauna represents the first glimpse of Eocene vertebrate and invertebrate terrestrial life from tropical North America.

  2. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography

    PubMed Central

    Antoine, Pierre-Olivier; Marivaux, Laurent; Croft, Darin A.; Billet, Guillaume; Ganerød, Morgan; Jaramillo, Carlos; Martin, Thomas; Orliac, Maëva J.; Tejada, Julia; Altamirano, Ali J.; Duranthon, Francis; Fanjat, Grégory; Rousse, Sonia; Gismondi, Rodolfo Salas

    2012-01-01

    The long-term isolation of South America during most of the Cenozoic produced a highly peculiar terrestrial vertebrate biota, with a wide array of mammal groups, among which caviomorph rodents and platyrrhine primates are Mid-Cenozoic immigrants. In the absence of indisputable pre-Oligocene South American rodents or primates, the mode, timing and biogeography of these extraordinary dispersals remained debated. Here, we describe South America's oldest known rodents, based on a new diverse caviomorph assemblage from the late Middle Eocene (approx. 41 Ma) of Peru, including five small rodents with three stem caviomorphs. Instead of being tied to the Eocene/Oligocene global cooling and drying episode (approx. 34 Ma), as previously considered, the arrival of caviomorphs and their initial radiation in South America probably occurred under much warmer and wetter conditions, around the Mid-Eocene Climatic Optimum. Our phylogenetic results reaffirm the African origin of South American rodents and support a trans-Atlantic dispersal of these mammals during Middle Eocene times. This discovery further extends the gap (approx. 15 Myr) between first appearances of rodents and primates in South America. PMID:21993503

  3. Reevaluation of conflicting Eocene tropical temperature estimates: Molluskan oxygen isotope evidence for warm low latitudes

    NASA Astrophysics Data System (ADS)

    Kobashi, Takuro; Grossman, Ethan L.; Yancey, Thomas E.; Dockery, David T., III

    2001-11-01

    Oxygen isotope data from planktonic foraminifera for the warm Eocene epoch suggest that tropical sea-surface temperatures (SSTs) may have been cooler than at present. Such data have stimulated various explanations involving, e.g., major changes in ocean heat transport. However, the planktonic data disagree with terrestrial climate proxies, which suggest significantly warmer low-latitude temperatures. We examined this discrepancy by analyzing seasonal oxygen isotope variations in shallow-marine mollusks from the Mississippi Embayment. Results indicate that mean annual SSTs decreased from 26 27 °C in the early Eocene to 22 23 °C in the Oligocene, agreeing well with temperatures inferred from terrestrial climate proxies. These cooling trends, with more significant winter cooling (5 °C) than summer cooling (3 °C), are consistent with the predicted consequences of decreasing atmospheric CO2 concentration through the Paleogene, suggesting that atmospheric CO2 change was a major controlling factor for Paleogene climate change. That winter SST estimates from the mollusks agree well with the foraminiferal SST estimates suggests that planktonic foraminiferal growth in low latitudes occurred mainly during the cooler winter months throughout the Eocene. We hypothesize that the unusual hydrography of Eocene oceans shifted foraminiferal productivity primarily to winter, biasing foraminiferal SST estimates of mean annual SSTs.

  4. New euprimate postcrania from the early Eocene of Gujarat, India, and the strepsirrhine-haplorhine divergence.

    PubMed

    Dunn, Rachel H; Rose, Kenneth D; Rana, Rajendra S; Kumar, Kishor; Sahni, Ashok; Smith, Thierry

    2016-10-01

    The oldest primates of modern aspect (euprimates) appear abruptly on the Holarctic continents during a brief episode of global warming known as the Paleocene-Eocene Thermal Maximum, at the beginning of the Eocene (∼56 Ma). When they first appear in the fossil record, they are already divided into two distinct clades, Adapoidea (basal members of Strepsirrhini, which includes extant lemurs, lorises, and bushbabies) and Omomyidae (basal Haplorhini, which comprises living tarsiers, monkeys, and apes). Both groups have recently been discovered in the early Eocene Cambay Shale Formation of Vastan lignite mine, Gujarat, India, where they are known mainly from teeth and jaws. The Vastan fossils are dated at ∼54.5 Myr based on associated dinoflagellates and isotope stratigraphy. Here, we describe new, exquisitely preserved limb bones of these Indian primates that reveal more primitive postcranial characteristics than have been previously documented for either clade, and differences between them are so minor that in many cases we cannot be certain to which group they belong. Nevertheless, the small distinctions observed in some elements foreshadow postcranial traits that distinguish the groups by the middle Eocene, suggesting that the Vastan primates-though slightly younger than the oldest known euprimates-may represent the most primitive known remnants of the divergence between the two great primate clades. PMID:27650579

  5. Eocene prevalence of monsoon-like climate over eastern China reflected by hydrological dynamics

    NASA Astrophysics Data System (ADS)

    Wang, Dehai; Lu, Shicong; Han, Shuang; Sun, Xiaoyan; Quan, Cheng

    2013-01-01

    Hydrological dynamics of sedimentary basins are essential for understanding regional climatic pattern in the geological past. In previous qualitative studies lithologically depending on the occurrence of featured sedimentary rocks, the Eocene climate of China had been subdivided into three latitudinal zones, with one subtropical high-controlled arid zone throughout middle China, and two humid zones respectively in the north and south. However, recent advances on mammalian fauna distribution, plant fossil-based quantitative paleoclimatic reconstruction, and modeling experiment jointly suggest that the relatively humid monsoonal climate might have prevailed over the territory. Here we examine and compare sedimentary sequences of 10 Eocene sections across eastern China, and hence the lake level fluctuations, to discuss the nature of climate type. Our results show that, instead of the categorically zonal pattern, the hydroclimate dynamics is intensified landward. This is demonstrated by the fact that, in contrast to the wide developed coal layers around the periphery, evaporites are growingly occurred endocentrically to the central part of middle China. However, although we have had assumed that all evaporites are indicator of extreme aridity, the highly oscillated climate in the central part of middle China was humid in the majority of the Eocene, distinct from permanent arid as seen in deserts or steppe along modern horse latitude. From the upcountry distribution pattern of the Eocene hydrological dynamics, it appears that the relatively dry climate in central China was caused by the impact of continentality or rain shadow effect under monsoonal, or monsoon-like climate.

  6. A new libelluloid family from the Eocene Green River Formation (Colorado, USA) (Odonata, Anisoptera).

    PubMed

    Zeiri, Asma; Nel, Andre; Garrouste, Romain

    2015-01-01

    The new family Urolibellulidae is proposed for the new genus and species Urolibellula eocenica, based on a fossil dragonfly from the Eocene Green River Formation (USA). This new taxon is considered as the sister group of the extant Libellulidae. As the oldest libellulid dragonfly is dated from the Turonian, the Urolibellulidae should also be at least Late Cretaceous. PMID:26624363

  7. Emplacement and geochemical evolution of eocene plutonic rocks in the Colville batholith

    SciTech Connect

    Holder, R.W.

    1986-01-01

    Eocene plutonic rocks in the Colville batholith are divided on the basis of field evidence and chemical composition into, in order of decreasing age, (1) several calc-alkalic biotite-hornblende monzodiorite to granodiorite intrusions referred to as the Devils Elbow suite, and (2) compositionally variable calc-alkalic to alkali-calcic intrusions referred to as the Herron Creek suite. These Eocene suites are distinct from older, more voluminous, leucocratic granite and granodiorite intrusions, designated the Keller Butte suite, which are calcic and characteristically lack hornblende. Results of qualitative and computer modeling of major element variation and quantitative models of trace element variation in the chemically coherent Bridge Creek intrusions, a member of the Herron Creek suite, are compatible with fractionation of plagioclase feldspar + hornblende + biotite + magnetite + apatite from a parent magma of andesitic composition to account for the observed variation. Strongly curved variation trends preclude mixing as the primary mechanism for the observed variation. It is suggested that parallel variation trends in the other Eocene intrusions are also the result of crystal fractionation. Lateral chemical variations including a decrease in silica saturation suggest the chemical characteristics of these rocks reflect those of parental magmas derived from the mantle, with an unknown amount of crustal contribution. Rotated and angular xenoliths, discordant contacts, and temporal and spatial proximity to graben structures indicate that the Eocene plutons were passively implaced into the upper crust along graben-bounding faults during graben formation, the earlier stages of which appear to have been contemporaneous with regional mylonitic deformation.

  8. New occurrence of Lower Eocene (Capay Stage) strata, lower Piru Creek, Topatopa Mountains, southern California

    SciTech Connect

    Squires, R.L.; Yamashiro, D.A.

    1986-04-01

    A 900-m thick siltstone unit between Canton Canyon and Piru Creek, 16 km north of the town of Piru, California, previously was unnamed and considered as undifferentiated Eocene or middle Eocene in age. The Siltstone unconformably overlies the Whitaker Peak granodiorite basement complex. At the base of the siltstone is a veneer of gruss (weathered granodiorite). The gruss is usually overlain by about a few meters of shoreface carbonaceous sandstone that grades vertically upward into transition-zone siltstone (500 m) with storm-deposit accumulations of macrofossils. Collections made at 53 localities from these lower 500 m of strata yielded numerous shallow marine gastropods and bivalves, as well as specimens of discocyclinid foraminifers, colonial corals, calcareous worm tubes, and spataganoid echinoids. This fauna is indicative of the West Coast provincial molluscan Capay Stage (lower Eocene). Common age-diagnostic species are Turritella uvasana infera, T. Andersoni, and Ostrea haleyi. Overlying and gradational with the transition-zone siltstone is 400 m of muddy siltstone with rare storm-deposit accumulations of macrofossils. This muddy siltstone thickens westward and passes into deep-sea slope and inner-fan turbidite deposits. Collections made at three localities in the muddy siltstone yielded many shallow marine gastropods and bivalves indicative of the Domengine stage (upper lower through lower middle Eocene). Common age-diagnostic species are Turritella uvasana applinae and Pitar (Lamelliconcha) joaquinensis.

  9. Early Eocene hyperthermals record orbitally controlled changes in high latitude climates

    NASA Astrophysics Data System (ADS)

    Galeotti, S.; DeConto, R. M.; Lanci, L.; Pagani, M.; Rohl, U.; Westerhold, T.; Zachos, J. C.

    2012-04-01

    The Late Paleocene to Early Eocene records a succession of short-term (104 yr) negative carbon isotope excursions (CIEs) in marine carbonates and organic carbon. Available data indicate that at least three of these episodes, including the Paleocene Eocene Thermal Maximum (PETM) at ca. 55.5, the Eocene Thermal Maximum (ETM)2 at ca. 53.5 Ma and the ETM3 at ca. 52 Ma, were associated with rapid warming, and widespread marine carbonate dissolution forced by shoaling of the carbonate lysocline and lowering of the carbonate saturation state. Large temperature raises associated with decreased δ13C values in both terrestrial and oceanic records and concomitant acidification of oceanic waters implies that hyperthermals were caused by the addition of massive amounts of 13C-depleted greenhouse gases (CH4 and/or CO-2) into the atmosphere and subsequent sequestration by oceanic waters. Cyclostratigraphic analyses of marine sequences provided evidence that CIEs and associated carbonate dissolution episodes were linked to orbital changes in insolation. Here we show grounds that Early Eocene hyperthermals are part of a continuum of δ13C anomaly and carbonate dissolution episodes and are triggered by long-term orbitally-controlled changes in local climates at high latitudes.

  10. Towards closing the Eocene Astronomical Time Scale Gap: Cyclostratigraphic Implications from IODP Expedition 342

    NASA Astrophysics Data System (ADS)

    Vahlenkamp, M.; De Vleeschouwer, D.; Palike, H.; Boulila, S.; Yamamoto, Y.; Laskar, J.

    2015-12-01

    Astronomical tuning using the 405-kyr eccentricity component as a prime target has been established as a standard technique for the Cenozoic timescale. There is an astronomically-tuned time scale across most of the Cenozoic. However, no definite astronomical tuning exists in the so-called "Eocene gap". The main reason for the existence of this Eocene gap is the very shallow carbonate compensation depth (CCD) during this time (Pälike et al., 2012), preventing the deposition of cyclic carbonate-rich sediments. IODP Expedition 342 however drilled Eocene cyclic carbonate-rich sequences, which were deposited in sediment drifts offshore Newfoundland at a palaeodepth above the CCD while large parts of the ocean were starved of carbonate. As the variations in the studied sites are predominantly obliquity induced, we assess and use the 173-kyr obliquity amplitude modulation cycle as a tuning target. These 173-kyr cycles result from the resonance or "beat" between the (present-day) 41 and 53 kyr obliquity cycles, determined by the precession constant and the frequency of the ascending node precession of the Earth and Saturn (p+s3)-(p+s6). We use physical property measurements, as well as the ratio between the elemental intensities of calcium and iron (Ca/Fe) of the sediments from sites U1408, U1409 and U1410 to construct an astronomically-tuned chronology between (and including) magnetochrons C19r and C22n (~41 - 50 Ma), spanning the "Eocene gap".

  11. Synchronous turnover of flora, fauna, and climate at the Eocene-Oligocene Boundary in Asia

    NASA Astrophysics Data System (ADS)

    Sun, Jimin; Ni, Xijun; Bi, Shundong; Wu, Wenyu; Ye, Jie; Meng, Jin; Windley, Brian F.

    2014-12-01

    The Eocene-Oligocene Boundary (~34 million years ago) marks one of the largest extinctions of marine invertebrates in the world oceans and of mammalian fauna in Europe and Asia in the Cenozoic era. A shift to a cooler climate across this boundary has been suggested as the cause of this extinction in the marine environment, but there is no manifold evidence for a synchronous turnover of flora, fauna and climate at the Eocene-Oligocene Boundary in a single terrestrial site in Asia to support this hypothesis. Here we report new data of magnetostratigraphy, pollen and climatic proxies in the Asian interior across the Eocene-Oligocene Boundary; our results show that climate change forced a turnover of flora and fauna, suggesting there was a change from large-size perissodactyl-dominant fauna in forests under a warm-temperate climate to small rodent/lagomorph-dominant fauna in forest-steppe in a dry-temperate climate across the Eocene-Oligocene Boundary. These data provide a new terrestrial record for this significant Cenozoic environmental event.

  12. Tectonic implications of Paleocene-Eocene Foreland Basin, Lake Maracaibo, Venezuela

    SciTech Connect

    Lugo, J. ); Mann, P. )

    1993-02-01

    A compilation of industry geological and geophysical data indicates that Paleocene-Eocene clastic sedimentation in the Maracaibo basin records the first manifestation of Cenozoic foreland basin tectonics in northern South America. Isopach maps based on industry seismic data and well logs suggest that the Maracaibo foreland basin formed a 100 to 200 km wide elongate trough along the northeastern edge of the present-day Lake Maracaibo. The basin is asymmetric with a deep (7 km) northeastern margin adjacent to an exposed southwest-verging thrust belt mapped by previous workers. Isopach mapping of seven seismic units within the Eocene suggest a nor-northwest to southeast migration of the depocenter from Paleocene to Middle Eocene time at a rate of 0.6 cm/year. A similar style of foreland basin has been previously identified over a distance of 1000 Km from western central Venezuela to Trinidad. Eocene to Pliocene ages of foreland basin sedimentation in these areas suggest time transgressive, oblique collision of the Caribbean plate along the northern margin of South America. Comparison of the age of deformation along both the northern and southern edges of the pro-Caribbean plate yield reasonable estimates for the rate of relative motion of this small plate relative to the larger America plates.

  13. Synchronous turnover of flora, fauna, and climate at the Eocene-Oligocene Boundary in Asia.

    PubMed

    Sun, Jimin; Ni, Xijun; Bi, Shundong; Wu, Wenyu; Ye, Jie; Meng, Jin; Windley, Brian F

    2014-01-01

    The Eocene-Oligocene Boundary (~34 million years ago) marks one of the largest extinctions of marine invertebrates in the world oceans and of mammalian fauna in Europe and Asia in the Cenozoic era. A shift to a cooler climate across this boundary has been suggested as the cause of this extinction in the marine environment, but there is no manifold evidence for a synchronous turnover of flora, fauna and climate at the Eocene-Oligocene Boundary in a single terrestrial site in Asia to support this hypothesis. Here we report new data of magnetostratigraphy, pollen and climatic proxies in the Asian interior across the Eocene-Oligocene Boundary; our results show that climate change forced a turnover of flora and fauna, suggesting there was a change from large-size perissodactyl-dominant fauna in forests under a warm-temperate climate to small rodent/lagomorph-dominant fauna in forest-steppe in a dry-temperate climate across the Eocene-Oligocene Boundary. These data provide a new terrestrial record for this significant Cenozoic environmental event. PMID:25501388

  14. Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary.

    PubMed

    Ivany, L C; Patterson, W P; Lohmann, K C

    2000-10-19

    The Eocene/Oligocene boundary, at about 33.7 Myr ago, marks one of the largest extinctions of marine invertebrates in the Cenozoic period. For example, turnover of mollusc species in the US Gulf coastal plain was over 90% at this time. A temperature change across this boundary--from warm Eocene climates to cooler conditions in the Oligocene--has been suggested as a cause of this extinction event, but climate reconstructions have not provided support for this hypothesis. Here we report stable oxygen isotope measurements of aragonite in fish otoliths--ear stones--collected across the Eocene/Oligocene boundary. Palaeo-temperatures reconstructed from mean otolith oxygen isotope values show little change through this interval, in agreement with previous studies. From incremental microsampling of otoliths, however, we can resolve the seasonal variation in temperature, recorded as the otoliths continue to accrete new material over the life of the fish. These seasonal data suggest that winters became about 4 degrees C colder across the Eocene/Oligocene boundary. We suggest that temperature variability, rather than change in mean annual temperature, helped to cause faunal turnover during this transition. PMID:11057663

  15. Occurrence and distribution of bacterial tetraether lipids in the Eocene Canadian Arctic paleosols: paleoclimate implications (Invited)

    NASA Astrophysics Data System (ADS)

    Mehay, S.; Jahren, A.; Schubert, B.; Eberle, J. J.; Summons, R. E.

    2010-12-01

    The Early to Middle Eocene (~56-45 Ma) was a “greenhouse” interval with average global temperatures warmer than any other time in the Cenozoic. This period was characterized by warm climates at high latitude leading to lush forests and the arrival of new mammal groups north of the Arctic Circle (>73°N). Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane-spanning lipids characteristic of certain archaea and bacteria and it has been demonstrated that branched and cyclic GDGTs derived from soil bacteria vary in structure as a function of environmental factors. Proxies based on the relative abundances of methyl branched and cyclopentyl bacterial tetraethers are hypothesized to correlate with mean annual air temperature and soil pH. Here we present the occurrence and distribution of GDGTs in a range of paleosol and sediment samples from Axel Heiberg Island and Ellesmere Island, Nunavut (eastern Canadian Arctic) and Banks Island in the Northwest Territories (western Canadian Arctic). Preliminary results on 11 paleosol samples from the middle Eocene-aged Geodetic Hills Fossil Forest on Axel Heiberg Island indicate a mean annual air temperature of about 9°C. Earlier paleotemperature estimates for Axel Heiberg Island led to values ranging from 9°C to 15°C for the Middle Eocene. Recent temperature prediction for Ellesmere Island (Early Eocene) based upon oxygen isotope ratios of biogenic phosphate from mammal and fish fossils led to ~8°C. In contrast, GDGTs from a marine sedimentary sequence from Lomonosov Ridge in the central Arctic Ocean led to much higher Early Eocene temperature. Thus, the evaluation of the paleotemperature for the Early to Middle Eocene is still a subject of controversy. Ongoing GDGTs analysis of samples from Ellesmere and Banks Islands should give a more comprehensive paleoenvironmental description of the Eocene Arctic. Differences observed between the various paleotemperature estimates will also be discussed. GDGTs distributions are

  16. The Early Eocene equable climate problem: can perturbations of climate model parameters identify possible solutions?

    PubMed

    Sagoo, Navjit; Valdes, Paul; Flecker, Rachel; Gregoire, Lauren J

    2013-10-28

    Geological data for the Early Eocene (56-47.8 Ma) indicate extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable data-model differences in the prediction of these polar surface temperatures, resulting in the so-called 'equable climate problem'. In this paper, for the first time an ensemble with a perturbed climate-sensitive model parameters approach has been applied to modelling the Early Eocene climate. We performed more than 100 simulations with perturbed physics parameters, and identified two simulations that have an optimal fit with the proxy data. We have simulated the warmth of the Early Eocene at 560 ppmv CO2, which is a much lower CO2 level than many other models. We investigate the changes in atmospheric circulation, cloud properties and ocean circulation that are common to these simulations and how they differ from the remaining simulations in order to understand what mechanisms contribute to the polar warming. The parameter set from one of the optimal Early Eocene simulations also produces a favourable fit for the last glacial maximum boundary climate and outperforms the control parameter set for the present day. Although this does not 'prove' that this model is correct, it is very encouraging that there is a parameter set that creates a climate model able to simulate well very different palaeoclimates and the present-day climate. Interestingly, to achieve the great warmth of the Early Eocene this version of the model does not have a strong future climate change Charney climate sensitivity. It produces a Charney climate sensitivity of 2.7(°)C, whereas the mean value of the 18 models in the IPCC Fourth Assessment Report (AR4) is 3.26(°)C±0.69(°)C. Thus, this value is within the range and below the mean of the models included in the AR4.

  17. Greenland ice sheet initiation and Arctic sea ice coincide with Eocene and Oligocene CO2 changes

    NASA Astrophysics Data System (ADS)

    Tripati, Aradhna; Darby, Dennis

    2016-04-01

    Earth's modern ocean-climate system is largely defined by the presence of glacial ice on landmasses in both hemispheres. Northern Hemisphere ice was previously thought to have formed no earlier than the Miocene or Oligocene, about 20-30 million years after the widespread onset of Antarctic glaciation at the Eocene-Oligocene boundary. Controversially, the episodic presence of seasonal Arctic sea ice and glacial ice in the Northern Hemisphere beginning in the early Oligocene to Middle Eocene has been inferred from multiple observations. Here we use precise source determinations based on geochemical measurements of ice-rafted debris (IRD) from an ODP core in the Greenland Sea (75° N) to constrain glacial ice and sea ice-rafting in the Northern Hemisphere during the middle Eocene through early Oligocene. The chemical fingerprint of 2,334 detrital Fe oxide grains indicates most of these grains are from Greenland with >98% certainty. Thus the coarse IRD in the Greenland Sea originates from widespread areas of east Greenland as far south as the Denmark Strait area (~68° N), with additional IRD sources from the circum-Arctic Ocean. This is the first definitive evidence that mid-Eocene IRD in the Greenland Sea is from Greenland. Episodic glaciation of different source regions on Greenland is synchronous with times of ice-rafting in the western Arctic and ephemeral perennial Arctic ice cover. Intervals of bipolar glacial ice storage in the middle Eocene through early Oligocene coincide with evidence for periods of reduced CO2, associated with carbon cycle perturbations.

  18. Depositional and diagenetic signatures of Late Eocene Oligocene sediments, South Carolina

    NASA Astrophysics Data System (ADS)

    Segall, M. P.; Siron, D. L.; Colquhoun, D. J.

    2000-07-01

    Surficial and near-surface soils of the South Carolina Coastal Plain reflect a variety of lithologies and depositional environments that are difficult to differentiate because of intense leaching and abrupt or laterally inconsistent facies changes. Binocular microscopic examination, scanning electron microscopic/energy dispersive X-ray (SEM/EDX) observations, and X-ray diffraction (XRD) analyses indicate that onshore Late Eocene to Late Oligocene Barnwell Group sediments are transitional facies ranging from high-energy fluvial deposits to offshore siliciclastic shelf sands. Interfingering of the units results in alternation of mineralogic signatures within a low-gradient fluvial/transitional/marine depositional system. Late Eocene and Early Oligocene offshore sediments were deposited in a mixed carbonate-siliciclastic, middle- to outer-shelf environment that was subjected to periods of erosion or non-deposition during transgressive events. Detrital and diagenetic characteristics of the onshore kaolinite-enriched, Late Oligocene Upland Unit sediments reflect deposition in a high- to low-energy fluvial system. Differentiation between these uppermost sediments and the underlying low-energy fluvial deposits of the Late Eocene Tobacco Road Sand is based on distinctive hydroxy-interlayered vermiculite (HIV) signatures. Intervals of HIV-enrichment are coincident with accumulations of carbonaceous material and identified as paleosols; these "soils" are used to infer offshore transgressive periods. Onshore sediments of the Late Eocene Dry Branch Formation contain high concentrations of smectite and flocculated, relatively poorly crystallized kaolinite flakes reflective of marine depositional conditions. At the base of this unit, authigenic Ca-minerals (Ca-zeolites and calcite) and quartz lepispheres (opal-CT) form coatings on and between sand grains. Late Eocene siliceous microfossils that contribute to opal-CT formation are identified in southwestern North Atlantic

  19. Descent toward the Icehouse: Eocene sea surface cooling inferred from GDGT distributions

    NASA Astrophysics Data System (ADS)

    Inglis, Gordon N.; Farnsworth, Alexander; Lunt, Daniel; Foster, Gavin L.; Hollis, Christopher J.; Pagani, Mark; Jardine, Phillip E.; Pearson, Paul N.; Markwick, Paul; Galsworthy, Amanda M. J.; Raynham, Lauren; Taylor, Kyle. W. R.; Pancost, Richard D.

    2015-07-01

    The TEX86 proxy, based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids (GDGTs), is increasingly used to reconstruct sea surface temperature (SST) during the Eocene epoch (56.0-33.9 Ma). Here we compile published TEX86 records, critically reevaluate them in light of new understandings in TEX86 palaeothermometry, and supplement them with new data in order to evaluate long-term temperature trends in the Eocene. We investigate the effect of archaea other than marine Thaumarchaeota upon TEX86 values using the branched-to-isoprenoid tetraether index (BIT), the abundance of GDGT-0 relative to crenarchaeol (%GDGT-0), and the Methane Index (MI). We also introduce a new ratio, %GDGTRS, which may help identify Red Sea-type GDGT distributions in the geological record. Using the offset between TEX86H and TEX86L (ΔH-L) and the ratio between GDGT-2 and GDGT-3 ([2]/[3]), we evaluate different TEX86 calibrations and present the first integrated SST compilation for the Eocene (55 to 34 Ma). Although the available data are still sparse some geographic trends can now be resolved. In the high latitudes (>55°), there was substantial cooling during the Eocene (~6°C). Our compiled record also indicates tropical cooling of ~2.5°C during the same interval. Using an ensemble of climate model simulations that span the Eocene, our results indicate that only a small percentage (~10%) of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change. Collectively, this indicates that atmospheric carbon dioxide (pCO2) was the likely driver of surface water cooling during the descent toward the icehouse.

  20. Diachronous seawater retreat from the southwestern margin of the Tarim Basin in the late Eocene

    NASA Astrophysics Data System (ADS)

    Sun, Jimin; Windley, Brian F.; Zhang, Zhiliang; Fu, Bihong; Li, Shihu

    2016-02-01

    In contrast to the present hyper-arid inland basin surrounded by the high mountains of Central Asia, the western Tarim Basin was once connected with the Tajik Basin at least in the late Eocene, when an epicontinental sea extended from the western Tarim Basin to Europe. Western Tarim is a key site for studying the retreat of seawater, which was likely caused by the northward indentation of the Pamir arc and facilitated by the climatic cooling and eustatic sea level change in the Cenozoic. Here we present a new magnetostratigraphic record from the Tarim Basin that provides evidence of diachronous seawater retreat from its southwestern margin. We studied about 1360 m of well-exposed Eocene-Oligocene strata at Keliyang in the folded foreland of the West Kunlun orogen. Until now, the age of the strata has only been minimally constrained by the presence of late mid-Eocene marine fossils. Our biostratigraphic and magnetostratigraphic results demonstrate that the age of the sedimentary sequence ranges from ∼46 Ma to ∼26 Ma (mid-Eocene to late-Oligocene) and the seawater retreat at Keliyang took place at ∼40 Ma. Considering the stepwise northward indentation and uplift of the Pamir orogen, together with the other previous results, we propose that seawater retreat from the southwestern margin of the Tarim Basin was diachronous in the late Eocene ranging from 47 Ma to 40 Ma. The regional indentation, uplift and erosion of the Pamir orogen played the dominant and important role in controlling the seawater retreat from the southwestern margin of the Tarim Basin.

  1. Origin of a Voluminous Pulse of Eocene Arc Magmatism in Iran

    NASA Astrophysics Data System (ADS)

    Verdel, C.; Wernicke, B.; Hassanzadeh, J.

    2008-12-01

    The Late Triassic to Miocene closure of Neotethys via subduction beneath central Iran was characterized by slow (~2-3 cm/yr) and relatively constant convergence between Arabia and Eurasia. Despite this protracted history of subduction, the record of shallow marine arc volcanism in Iran is dominated by an Eocene pulse that is not readily explainable by changes in the rate or style of plate interactions between south Asian and Neotethyan lithosphere. New U-Pb and 40Ar/39Ar geochronology of volcanic arcs in central and northern Iran constrains the duration of this pulse to <22 My. Eocene volcanic rocks are enriched in large ion lithophile elements (LILE) and depleted in high-field strength elements (HFSE), a pattern typical of arc magmatism. In contrast, Oligocene basalts from the Urumieh-Dokhtar arc and the Alborz Mtns. are enriched in both LILE and HFSE. Together with the recent recognition of Eocene metamorphic core complexes in central and east-central Iran and stratigraphic evidence for Eocene subsidence, these geochemical and geochronological data suggest that the magmatic pulse was generated by extension-related decompression melting of lithosphere hydrated by slab-derived fluids, followed by Oligocene upwelling and melting of enriched mantle that was less extensively modified by hydrous fluids. Based on the inboard position of Cretaceous arc magmas relative to Eocene volcanism, we suggest that extension was driven by an episode of slab retreat or rollback, analogous to the western US. In contrast to the western US, slow subduction rate and restricted Mesozoic magmatism in Iran resulted in a long (~150 My) period of "preconditioning" the arc lithosphere, resulting in a much more voluminous magmatic episode during extension than in the western US.

  2. Provenance and depositional environments of middle Eocene Canoe Formation, Big Bend National Park, Brewster County, Texas

    SciTech Connect

    Rigsby, C.A.

    1984-04-01

    The middle Eocene Canoe Formation contains the first sedimentologic evidence of local volcanism in the Big Bend region. Sediments comprising the formation's lower member, the Big Yellow Sandstone, were deposited by sandy braided streams which were scoured by ancient carbonate highlands and volcanic terranes to the west. The unit represents a continuation of the depositional styles and compositional trends recorded in the Paleocene and early Eocene strata of the region. In contrast, sediments comprising the upper, unnamed member of the Canoe Formation were deposited as a volcanic sediment apron of the fringes of the newly forming Chisos Mountains volcanic center. The sandstones (feldspathic litharenites and lithic arkoses) are dominated by volcanic rock fragments and, as such, document an abrupt change in depositional style and sediment composition brought about by the onset of local volcanism. A comparison of Canoe Formation and earlier Tertiary sediment compositions results in the delineation of distinct petrologic trends which record the tectonic evolution of the early Tertiary sediment source area. The Paleocene sediments of the area were derived primarily from ancient magmatic arcs in northeastern Mexico. With the onset of the Laramide orogeny in late Paleocene-early Eocene, a new source of sediment - newly uplifted carbonate highlands - was added. Local volcanism in the middle Eocene produced yet another source of sediment, lava flows, ash flow tuffs, and sand-size pyroclastic materials from the Chisos Mountain volcanic center. Rapid erosion of these materials produced volcanic sediment aprons such as the one described here. As regional volcanic activity increased, typical Paleocene and early Eocene depositional styles may have been completely abandoned, especially in areas proximal to the volcanic centers.

  3. Reconstructing a Hot and High Eocene Sierra Nevada Using Oxygen and Hydrogen Isotopes in Kaolinite

    NASA Astrophysics Data System (ADS)

    Mix, H.; Ibarra, D. E.; Mulch, A.; Graham, S. A.; Chamberlain, C. P.

    2014-12-01

    Despite the broad interest in determining the topographic and climatic histories of mountain ranges, the evolution of California's Sierra Nevada remains actively debated. Prior stable isotope-based studies of Sierra Nevada have relied exclusively on hydrogen isotopes in kaolinite, hydrated volcanic glass and leaf n-alkanes. Additional constraints from the oxygen isotope composition of phyllosilicates increase the robustness of findings from a single isotope system and allow for the reconstruction of paleotemperatures. Here, we reconstruct the temperature and elevation of the Early Eocene Sierra Nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral Yuba and American Rivers. We evaluate the possible contributions of hydrogen isotope exchange by direct comparison with more robust oxygen isotope measurements. Next, we utilize differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain paleotemperature. Oxygen isotope geochemistry of in-situ kaolinites indicates upstream (eastward) depletion of 18O in the northern Sierra Nevada. δ18O values ranging from 11.4 - 14.4 ‰ at the easternmost localities correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a Pacific source using Eocene boundary conditions. This finding is consistent with stable isotope studies of the northern Sierra, but oxygen isotope based paleoelevation estimates are systematically ~500 - 1000 m higher than those from hydrogen-based estimates from the same samples. Kaolinite geothermometry from 16 samples measured in duplicate or triplicate produce an average Early Eocene temperature of 24.2 ± 2.0 °C (1s). This kaolinite temperature reconstruction is in agreement with paleofloral and geochemical constraints and general circulation model simulations from Eocene California. Our results confirm prior hydrogen isotope-based paleoelevations and further substantiate the existence of a

  4. Multiple microtektite horizons in upper eocene marine sediments: no evidence for mass extinctions.

    PubMed

    Keller, G; D'Hondt, S; Vallier, T L

    1983-07-01

    Microtektites have been recovered from three horizons in eight middle Eocene to middle Oligocene marine sediment sequences. Five of these occurrences are coeval and of latest Eocene age (37.5 to 38.0 million years ago); three are coeval and of early late Eocene age (38.5 to 39.5 million years ago); and three are of middle Oligocene age (31 to 32 million years ago). In addition, rare probable microtektites have been found in sediments with ages of about 36.0 to 36.5 million years. The microtektite horizon at 37.5 to 38.0 million years can be correlated with the North American tektite-strewn field, which has a fission track age (minimum) of 34 to 35 million years and a paleomagnetic age of 37.5 to 38.0 million years. There is no evidence for mass faunal extinctions at any of the microtektite horizons. Many of the distinct faunal changes that occurred in the middle Eocene to middle Oligocene can be related to the formation of the Antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large-scale dissolution of calcium carbonate and erosion, which created areally extensive hiatuses in the deep-sea sediment records. The occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle Eocene to middle Oligocene time. PMID:17769212

  5. Stable isotope study of fluid inclusions in fluorite from Idaho: implications for continental climates during the Eocene

    USGS Publications Warehouse

    Seal, R.R.; Rye, R.O.

    1993-01-01

    Isotopic studies of fluid inclusions from meteoric water-dominated epithermal ore deposits offer a unique opportunity to study paleoclimates because the fluids can provide direct samples of ancient waters. Fluorite-hosted fluid inclusions from the Eocene (51-50 Ma) epithermal deposits of the Bayhorse mining district, have low salinities and low to moderate homogenization temperatures indicating meteoric origins for the fluids. Oxygen and hydrogen isotope data on inclusion fluids are almost identical to those of modern meteoric waters in the area. The equivalence of the isotope composition of the Eocene inclusion fluids and modern meteoric waters indicates that the Eocene climatic conditions were similar to those today. -from Authors

  6. Late Eocene obliquity domination and impact of the Eocene/Oligocene climate transition on central Asian climate at the northeastern margin of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Xiao, Guoqiao; Abels, Hemmo A.; Yao, Zhengquan; Dupont-Nivet, Guillaume; Hilgen, Frederik J.

    2010-05-01

    At the boundary between the Eocene and Oligocene epochs, approximately 34 million years ago (Ma), the Earth experienced a significant change from a greenhouse world to an icehouse world. The present understanding of the triggering mechanisms, processes and environmental effects of this climatic event is mostly based upon ocean sediment records and climatic modeling results. Terrestrial records of the critical interval are rare and, where available, often poorly constrained in time. Here, we present a continuous continental record (Tashan section) from the Xining basin at the northeastern edge of Tibetan Plateau, covering the period between ~35 to 33 Ma. Lithology supplemented with high-resolution magnetic susceptibility (MS), median grain size (MGS) and color reflectance (a*) records show clear Late Eocene basic cyclicity of ~3.5 m in length. Our detailed magnetostratigraphic age model indicates that this cycle was most likely forced by the 41-kyr obliquity cycle driving drier and wetter periods in northern hemisphere Asian interior climates already 1 million year before the Eocene-Oligocene Climate Transition (EOCT). Detailed comparison of the E/O boundary interval in the Tashan section with marine records show that the most pronounced lithofacies change in the Xining Basin corresponds to the first of two widely recognized steps in oxygen isotopes making up the EOCT. This first step is reported to precede the major and second step (base of the Oi-1 phase) by around 0.2 to 0.3 Myr and has recently been suggested to be mainly related to atmospheric cooling rather than ice volume growth.

  7. Highly-seasonal monsoons controlled by Central Asian Eocene epicontinental sea

    NASA Astrophysics Data System (ADS)

    Bougeois, Laurie; Tindall, Julia; de Rafélis, Marc; Reichart, Gert-Jan; de Nooijer, Lennart; Dupont-Nivet, Guillaume

    2015-04-01

    Modern Asian climate is mainly controlled by seasonal reverse winds driven by continent-ocean thermal contrast. This yields monsoon pattern characterized by a strong seasonality in terms of precipitation and temperature and a duality between humidity along southern and eastern Asia and aridity in Central Asia. According to climate models, Asian Monsoons and aridification have been governed by Tibetan plateau uplift, global climate changes and the retreat of a vast epicontinental sea (the Proto-Paratethys sea) that used to cover Eurasia in Eocene times (55 to 34 Myr ago). Evidence for Asian aridification and monsoons a old as Eocene, are emerging from proxy and model data, however, the role of the Proto-Paratethys sea remains to be established by proxy data. By applying a novel infra-annual geochemical multi-proxy methodology on Eocene oyster shells of the Proto-Paratethys sea and comparing results to climate simulations, we show that the Central Asian region was generally arid with high seasonality from hot and arid summers to wetter winters. This high seasonality in Central Asia supports a monsoonal circulation was already established although the climate pattern was significantly different than today. During winter months, a strong influence of the Proto-Paratethys moisture is indicated by enhanced precipitations significantly higher than today. Precipitation probably dwindled because of the subsequent sea retreat as well as the uplift of the Tibetan and Pamir mountains shielding the westerlies. During Eocene summers, the local climate was hotter and more arid than today despite the presence of the Proto Paratethys. This may be explained by warmer Eocene global conditions with a strong anticyclonic Hadley cell descending at Central Asian latitudes (25 to 45 N). urthermore, the Tibetan plateau emerging at this time to the south must have already contributed a stronger Foehn effect during summer months bringing warm and dry air into Central Asia. Proto

  8. A model-model and data-model comparison for the early Eocene hydrological cycle

    NASA Astrophysics Data System (ADS)

    Carmichael, Matthew J.; Lunt, Daniel J.; Huber, Matthew; Heinemann, Malte; Kiehl, Jeffrey; LeGrande, Allegra; Loptson, Claire A.; Roberts, Chris D.; Sagoo, Navjit; Shields, Christine; Valdes, Paul J.; Winguth, Arne; Winguth, Cornelia; Pancost, Richard D.

    2016-02-01

    A range of proxy observations have recently provided constraints on how Earth's hydrological cycle responded to early Eocene climatic changes. However, comparisons of proxy data to general circulation model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised. In this work, we undertake an intercomparison of GCM-derived precipitation and P - E distributions within the extended EoMIP ensemble (Eocene Modelling Intercomparison Project; Lunt et al., 2012), which includes previously published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure, and precipitation-relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to the preindustrial conditions. This is primarily due to elevated atmospheric paleo-CO2, resulting in elevated temperatures, although the effects of differences in paleogeography and ice sheets are also important in some models. For a given CO2 level, globally averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP/dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa, and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that GCMs generally underestimate precipitation rates at high latitudes, although a possible seasonal bias of the proxies cannot be excluded. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a

  9. Fossil plants indicate that the most significant decrease in atmospheric CO2 happened prior to the Eocene-Oligocene boundary

    NASA Astrophysics Data System (ADS)

    Steinthorsdottir, Margret; Porter, Amanda; Holohan, Aidan; Kunzmann, Lutz; Collinson, Margaret; McElwain, Jennifer

    2016-04-01

    A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany was utilized to derive an atmospheric pCO2 record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the stomatal proxy, which relies on the inverse relationship between pCO2 and leaf stomatal density, we show that a ~40% decrease in pCO2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene-Oliogocene climate transition. The results endorse the theory that pCO2 drawdown was the main forcer of the Eocene-Oligocene climate change, and a 'tipping point' was reached in the latest Eocene, triggering the plunge of the Earth System into icehouse conditions.

  10. Evolutionary, biostratigraphic, and taxonomic study of calcareous nannofossils from a continuous Paleocene-Eocene boundary section in New Jersey

    USGS Publications Warehouse

    Bybell, L.M.; Self-Trail J.M.

    1994-01-01

    Calcareous nannofossils of late Paleocene and early Eocene age were examined from six coreholes located in southern New Jersey. Fossil data indicate that four of these coreholes (GL 913, GL 915, GL 917, and the Clayton Core) contain an apparently continuous depositional sequence across the Paleocene-Eocene boundary. There are four new species described from this material, along with six new combinations, and several species were put into synonymy. Evolutionary trends within several species are recognized and discussed.

  11. Occurence and preservation of Eocene squamariacean and coralline rhodoliths: Eau, Tonga: Chapter 9 in Paleoalgology: contemporary research and applications

    USGS Publications Warehouse

    Buchbinder, Binyamin; Halley, Robert B.; Toomey, Donald F.; Nitecki, Matthew H.

    1985-01-01

    A widespread rhodolith facies occurs within middle Eocene limestones of Eua, Tonga (Fig. 1). These limestones, first described by Hoffmeister (1932), represent a portion of a broad, early Tertiary platform that developed in the Tonga area prior to disruption and uplift by later Tertiary plate movements (Kroenke and Tongilava 1975). Algal rhodoliths form beds several meters thick within Eocene limestones and occur at localities several kilometers apart along the length of Eua.

  12. First records of Chevrolatiini and Cephenniini in Eocene Baltic amber (Coleoptera, Staphylinidae, Scydmaeninae).

    PubMed

    Jałoszyński, Paweł; Kubisz, Daniel

    2016-01-01

    Fossils of two tribes of the ant-like stone beetles, previously unknown in Eocene deposits, are recorded, based on inclusions in Baltic amber. Well-preserved specimens of Chevrolatia sp. (Chevrolatiini) and Cephennodes sp. (Cephenniini) are described, but the species lack reliable diagnostic characters and remain unnamed. This is the first record of a fossil of Chevrolatiini, an extant tribe that includes only one genus, Chevrolatia Jacquelin du Val, distributed in the Holarctic, Mexico, West Palaearctic and Afrotropical regions. The extant tribe Cephenniini, in turn, is cosmopolitan, but the only fossil unambiguously assigned to this taxon, an unnamed genus, was known from Upper Cretaceous Burmese amber. Many extant species of Cephennodes Reitter are known from Palaearctic, but they predominantly inhabit its eastern part, with only two species occurring in Europe. The Eocene specimen of Cephennodes sp. is also the first known fossil of this genus. PMID:27395147

  13. Anthracobunids from the middle eocene of India and pakistan are stem perissodactyls.

    PubMed

    Cooper, Lisa Noelle; Seiffert, Erik R; Clementz, Mark; Madar, Sandra I; Bajpai, Sunil; Hussain, S Taseer; Thewissen, J G M

    2014-01-01

    Anthracobunidae is an Eocene family of large mammals from south Asia that is commonly considered to be part of the radiation that gave rise to elephants (proboscideans) and sea cows (sirenians). We describe a new collection of anthracobunid fossils from Middle Eocene rocks of Indo-Pakistan that more than doubles the number of known anthracobunid fossils and challenges their putative relationships, instead implying that they are stem perissodactyls. Cranial, dental, and postcranial elements allow a revision of species and the recognition of a new anthracobunid genus. Analyses of stable isotopes and long bone geometry together suggest that most anthracobunids fed on land, but spent a considerable amount of time near water. This new evidence expands our understanding of stem perissodactyl diversity and sheds new light on perissodactyl origins.

  14. Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls

    PubMed Central

    Cooper, Lisa Noelle; Seiffert, Erik R.; Clementz, Mark; Madar, Sandra I.; Bajpai, Sunil; Hussain, S. Taseer; Thewissen, J. G. M.

    2014-01-01

    Anthracobunidae is an Eocene family of large mammals from south Asia that is commonly considered to be part of the radiation that gave rise to elephants (proboscideans) and sea cows (sirenians). We describe a new collection of anthracobunid fossils from Middle Eocene rocks of Indo-Pakistan that more than doubles the number of known anthracobunid fossils and challenges their putative relationships, instead implying that they are stem perissodactyls. Cranial, dental, and postcranial elements allow a revision of species and the recognition of a new anthracobunid genus. Analyses of stable isotopes and long bone geometry together suggest that most anthracobunids fed on land, but spent a considerable amount of time near water. This new evidence expands our understanding of stem perissodactyl diversity and sheds new light on perissodactyl origins. PMID:25295875

  15. Seafloor hydrothermal activity and spreading rates - The Eocene carbon dioxide greenhouse revisited

    NASA Technical Reports Server (NTRS)

    Kasting, J. F.; Richardson, S. M.

    1985-01-01

    A suggestion has been made that enhanced rates of hydrothermal activity during the Eocene could have caused a global warming by adding calcium to the ocean and pumping CO2 into the atmosphere (Owen and Rea, 1984). This phenomenon was purported to be consistent with the predictions of the CO2 geochemical cycle model of Berner, Lasaga and Garrels (1983) (henceforth BLAG). In fact, however, the BLAG model predicts only a weak connection between hydrothermal activity and atmospheric CO2 levels. By contrast, it predicts a strong correlation between seafloor spreading rates and pCO2, since the release rate of CO2 from carbonate metamorphism is assumed to be proportional to the mean spreading rate. The Eocene warming can be conveniently explained if the BLAG model is extended by assuming that the rate of carbonate metamorphism is also proportional to the total length of the midocean ridges from which the spreading originates.

  16. Fine structure of the late Eocene Ir anomaly in marine sediments

    NASA Technical Reports Server (NTRS)

    Asaro, F.

    1991-01-01

    The Late Eocene Ir abundance profile in deep sea cores from Ocean Drilling Program Leg 113 Hole 689B on the Maude Rise off of Antarctica was studied with 410 samples continuously in 10 cm increments and measured with the Iridium Coincidence (ICS). The ICS was subsequently modified to measure 13 other elements simultaneously with the Ir. The abundance profiles of these elements were then determined in the Late Eocene Massignano section in central Italy with 250 samples (encompassing roughly 2 million years of accumulation) which were collected about every 5 cm in about 2 cm increments. These studies augmented a previous one (which included many elements) of deep sea cores from Deep Sea Drilling Project Site 592 on the Lord Howe Rise in the Tasman Sea between Australia and New Zealand. In the latter study, 50 samples (encompassing roughly 0.7 million years of accumulation) were collected continuously in 10 cm increments. The results from these studies are discussed.

  17. New marine ostracod species from the Middle Eocene of west-central Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Morsi, Abdel-Mohsen M.; Hewaidy, Abdel-Galil A.; Samir, Ahmed

    2016-05-01

    The study of two Eocene sections exposed at Wadi Nukhul and Wadi Tayiba in west-central Sinai, Egypt for ostracods yielded diverse fauna. Investigation of the recorded taxa revealed findings of eight new marine ostracod species, one belonging to the family Krithidae, Parakrithe tayibaensis n. sp., three to the family Cytheruridae, Cytheropteron bicostsatum n. sp., Cytheropteron nukhulensis n. sp. and Cytheropteron speijeri n. sp., three to the family Trachyleberididae: Digmocythere centroreticulata n. sp. in subfamily Brachycytherinae and Buntonia bassiounii n. sp. and Buntonia posteroacuta n. sp. in subfamily Buntoniinae, and one, Xestoleberis posterotruncata n. sp., to the family Xestoleberididae. The newly erected species have been described and compared with nearest known and probably related taxa. Their records in the studied sections are stratigraphically confined to the Middle Eocene (Lutetian-Bartonian) interval.

  18. The organic geochemistry of the Eocene-Oligocene black shales from the Lunpola Basin, central Tibet

    NASA Astrophysics Data System (ADS)

    Sun, Tao; Wang, Chengshan; Duan, Yi; Li, Yalin; Hu, Bin

    2014-01-01

    This paper reports on the depositional paleoenvironment and the potential hydrocarbons of the Eocene-Oligocene black shales from the Dingqinghu and Niubao Formations in the Lunpola Basin, central Tibet. Nineteen samples from two outcrop profiles were analysed. The contents of the total organic carbon (TOC) and sulphur were measured; other analyses included Rock-Eval pyrolysis, solvent extraction and gas chromatography-mass spectrometer (GC-MS). The results indicated that the shales from the Dingqinghu and Niubao Formations are thermally immature. The pyrolysis data show that the shales contain Type I organic matter and that lacustrine algal are the main organic matter sources. The low pristane to phytane ratios and the high gammacerane indices indicate that the shales were deposited in a reducing, stratified, and hypersaline palaeo-lake, which is consistent with the climate information provided by the development history of palaeo-lakes from the Eocene to the Oligocene epochs.

  19. Biostratigraphic implications of the first Eocene land-mammal fauna from the North American coastal plain

    NASA Astrophysics Data System (ADS)

    Westgate, James W.

    1988-11-01

    A newly discovered vertebrate fossil assemblage, the Casa Blanca local fauna, comes from the Laredo Formation, Claiborne Group, of Webb County, Texas, and is the first reported Eocene land-mammal fauna from the coastal plain of North America. The mammalian fauna is correlated with the Serendipity and Candelaria local faunas of west Texas, the Uinta C faunas of the Rocky Mountains, the Santiago Formation local fauna of southern California, and the Swift Current Creek local fauna of Saskatchewan. The vertebrate-bearing deposit lies about 32 m above a horizon containing the marine gastropod Turritella cortezi, which ranges from east Texas to northeast Mexico in the lower half of the Cook Mountain and Laredo Formations and is a guide fossil to the Hurricane Lentil in the Cook Mountain Formation. Nannoplankton found in these middle Eocene formations belong to the upper half of Nannoplankton Zone I6 and allow correlation with European beds of late Lutetian to early Bartonian age.

  20. A roller-like bird (Coracii) from the Early Eocene of Denmark

    PubMed Central

    Bourdon, Estelle; Kristoffersen, Anette V.; Bonde, Niels

    2016-01-01

    The fossil record of crown group birds (Neornithes) prior to the Cretaceous-Paleogene boundary is scarce and fragmentary. Early Cenozoic bird fossils are more abundant, but are typically disarticulated and/or flattened. Here we report the oldest roller (Coracii), Septencoracias morsensis gen. et sp. nov. (Primobucconidae), based on a new specimen from the Early Eocene (about 54 million years ago) Fur Formation of Denmark. The new fossil is a nearly complete, three-dimensionally preserved and articulated skeleton. It lies at the lower end of the size range for extant rollers. Salient diagnostic features of Septencoracias relative to other Coracii include the proportionally larger skull and the small, ovoid and dorsally positioned narial openings. Our discovery adds to the evidence that the Coracii had a widespread northern hemisphere distribution in the Eocene. Septencoracias is the oldest substantial record of the Picocoraciae and provides a reliable calibration point for molecular phylogenetic studies. PMID:27670387

  1. Biostratigraphic implications of the first Eocene land-mammal fauna from the North American coastal plain

    SciTech Connect

    Westgate, J.W. )

    1988-11-01

    A newly discovered vertebrate fossil assemblage, the Casa Blanca local fauna, comes from the Laredo Formation, Claiborne Group, of Webb County, Texas, and is the first reported Eocene land-mammal fauna from the coastal plain of North America. The mammalian fauna is correlated with the Serendipity and Canderlaria local faunas of west Texas, the Uinta C faunas of the Rocky Mountains, the Santiago Formation local fauna of southern California, and the Swift Current Creek local fauna of Saskatchewan, The vertebrate-bearing deposit lies about 32 m above a horizon containing the marine gastropod Turritella cortezi, which ranges from east Texas to northeast Mexico in the lower half of the Cook Mountain and Laredo Formations and is a guide fossil to the Hurricane Lentil in the Cook Mountain Formation. Nannoplankton found in these middle Eocene formations belong to the upper half of Nannoplankton Zone 16 and allow correlation with European beds of late Lutetian to early Bartonian age.

  2. Richness of plant-insect associations in Eocene Patagonia: a legacy for South American biodiversity.

    PubMed

    Wilf, Peter; Labandeira, Conrad C; Johnson, Kirk R; Cúneo, N Rubén

    2005-06-21

    South America has some of the most diverse floras and insect faunas that are known, but its Cenozoic fossil record of insects and insect herbivory is sparse. We quantified insect feeding on 3,599 leaves from the speciose Laguna del Hunco flora (Chubut, Argentina), which dates to the early Eocene climatic optimum (52 million years ago) and compared the results with three well preserved, rich, and identically analyzed early- and middle-Eocene floras from the following sites in North America: Republic, WA; Green River, UT; and Sourdough, WY. We found significantly more damage diversity at Laguna del Hunco than in the North American floras, whether measured on bulk collections or on individual plant species, for both damage morphotypes and feeding groups. An ancient history of rich, specialized plant-insect associations on diverse plant lineages in warm climates may be a major factor contributing to the current biodiversity of South America.

  3. Major element compositional variation within and between different late Eocene microtektite strewnfields

    NASA Astrophysics Data System (ADS)

    D'Hondt, S. L.; Keller, G.; Stallard, R. F.

    1987-03-01

    The major element composition of microspherules from all three late Eocene stratigraphic layers was analyzed using an electron microprobe. The results indicate a major element compositional overlap beween individual microspherules of different microtektite layers or strewn fields. However, multivariate factor analysis shows that the microtektites of the three late Eocene layers follow recognizably different compositional trends. The microtektite population of the North American strewn field is characterized by high concentrations of SiO2, Al2O3, and TiO2; the microspherules of an older layer, the Gl. cerroazulensis Zone, are relatively enriched in FeO and MgO and impoverished in SiO2 and TiO2; while those of the oldest layer in the uppermost G. semiinvoluta Zone are relatively enriched in CaO and impoverished in Al2O3 and Na2O.

  4. Bipolar Atlantic deepwater circulation in the middle-late Eocene: Effects of Southern Ocean gateway openings

    NASA Astrophysics Data System (ADS)

    Borrelli, Chiara; Cramer, Benjamin S.; Katz, Miriam E.

    2014-04-01

    We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ18Obf and δ13Cbf) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning ~38.5 Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ18Obf values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene, ~1-4 Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (~34 Ma) and the consequent development of a circumpolar proto-ACC.

  5. Geochemical anomalies near the Eocene-Oligocene and Permian-Triassic boundaries

    SciTech Connect

    Asaro, F.; Alvarez, L.W.; Alvarez, W.; Michel, H.V.

    1981-10-01

    Evidence is presented to support the theory that several mass extinctions, i.e., those that define the Permian-Triassic boundary, the Cretaceous-Tertiary boundary, and the Eocene-1 Oligocene boundary, were caused by impact on the earth of extraterrestrial objects having the composition of carbonaceous chondrites and diameters of about 10 km. The evidence consists of anomalously high concentrations of iridium and other siderophile elements at the stratigraphic levels defining the extinctions. (ACR)

  6. Primate tarsal bones from Egerkingen, Switzerland, attributable to the middle Eocene adapiform Caenopithecus lemuroides

    PubMed Central

    Costeur, Loïc

    2015-01-01

    The middle Eocene species Caenopithecus lemuroides, known solely from the Egerkingen fissure fillings in Switzerland, was the first Paleogene fossil primate to be correctly identified as such (by Ludwig Rütimeyer in 1862), but has long been represented only by fragmentary mandibular and maxillary remains. More recent discoveries of adapiform fossils in other parts of the world have revealed Caenopithecus to be a biogeographic enigma, as it is potentially more closely related to Eocene adapiforms from Africa, Asia, and North America than it is to any known European forms. More anatomical evidence is needed, however, to provide robust tests of such phylogenetic hypotheses. Here we describe and analyze the first postcranial remains that can be attributed to C. lemuroides—an astragalus and three calcanei held in the collections of the Naturhistorisches Museum Basel that were likely recovered from Egerkingen over a century ago. Qualitative and multivariate morphometric analyses of these elements suggest that C. lemuroides was even more loris-like than European adapines such as Adapis and Leptadapis, and was not simply an adapine with an aberrant dentition. The astragalus of Caenopithecus is similar to that of younger Afradapis from the late Eocene of Egypt, and parsimony and Bayesian phylogenetic analyses that include the new tarsal data strongly support the placement of Afradapis and Caenopithecus as sister taxa to the exclusion of all other known adapiforms, thus implying that dispersal between Europe and Africa occurred during the middle Eocene. The new tarsal evidence, combined with previously known craniodental fossils, allows us to reconstruct C. lemuroides as having been an arboreal and highly folivorous 1.5–2.5 kg primate that likely moved slowly and deliberately with little or no capacity for acrobatic leaping, presumably maintaining consistent powerful grasps on branches in both above-branch and inverted postures. PMID:26131376

  7. No extreme bipolar glaciation during the main Eocene calcite compensation shift.

    PubMed

    Edgar, Kirsty M; Wilson, Paul A; Sexton, Philip F; Suganuma, Yusuke

    2007-08-23

    Major ice sheets were permanently established on Antarctica approximately 34 million years ago, close to the Eocene/Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world's oceans. Until recently, it was thought that Northern Hemisphere glaciation began much later, between 11 and 5 million years ago. This view has been challenged, however, by records of ice rafting at high northern latitudes during the Eocene epoch and by estimates of global ice volume that exceed the storage capacity of Antarctica at the same time as a temporary deepening of the calcite compensation depth approximately 41.6 million years ago. Here we test the hypothesis that large ice sheets were present in both hemispheres approximately 41.6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial Atlantic Ocean. These records allow, at most, an ice budget that can easily be accommodated on Antarctica, indicating that large ice sheets were not present in the Northern Hemisphere. The records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled, ocean temperatures increased and carbon isotope values decreased in the equatorial Atlantic. The nature of these changes around 41.6 million years ago implies common links, in terms of carbon cycling, with events at the Eocene/Oligocene boundary and with the 'hyperthermals' of the Early Eocene climate optimum. Our findings help to resolve the apparent discrepancy between the geological records of Northern Hemisphere glaciation and model results that indicate that the threshold for continental glaciation was crossed earlier in the Southern Hemisphere than in the Northern Hemisphere. PMID:17713530

  8. Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris.

    PubMed

    Stickley, Catherine E; St John, Kristen; Koç, Nalân; Jordan, Richard W; Passchier, Sandra; Pearce, Richard B; Kearns, Lance E

    2009-07-16

    Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice, IRD records are restricted to providing a history of general ice-rafting only. It is critical to differentiate sea ice from glacial (land-based) ice as climate feedback mechanisms vary and global impacts differ between these systems: sea ice directly affects ocean-atmosphere exchanges, whereas land-based ice affects sea level and consequently ocean acidity. An earlier report assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists, these data are neither comprehensive nor quantified. Here we show the presence of middle Eocene Arctic sea ice from an extraordinary abundance of a group of sea-ice-dependent fossil diatoms (Synedropsis spp.). Analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of IRD at this time. Together with new information on cosmopolitan diatoms and existing IRD records, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas approximately 47.5 Myr ago, followed approximately 0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic. Our data establish a 2-Myr record of sea ice, documenting the transition from a warm, ice-free environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase.

  9. Upper Eocene glauconites from the Bahariya depression: An evidence for the marine regression in Egypt

    NASA Astrophysics Data System (ADS)

    El-Habaak, Galal; Askalany, Mohamed; Galal, Mohamed; Abdel-Hakeem, Mahmoud

    2016-05-01

    Glauconite deposits at the Bahariya Oasis are reported as Cenomanian and Upper Eocene deposits. The Upper Eocene glauconite deposits have received little attention in comparison with the Cenomanian counterpart. In the present study, glauconite deposits belonging to the Hamra Formation were investigated in terms of petrography, mineralogy and geochemistry to determine their origin and demonstrate their significance as proxies for the paleoenvironmental conditions. Petrographically, glauconite occurs as green to yellowish green, oval, sub-oval, rounded, fine to medium-grained (150-400 μm), moderately sorted pellets set in clayey matrix. Mineralogically, the studied deposit consists mainly of glauconite in association with quartz, feldspar, hematite, alunite, halloysite and calcite, whereas clay fractions (<2 μm) are composed essentially of glauconite with small amounts of illite-smectite mixed layer and kaolinite. Chemically, the studied glauconite contains K2O at average of 7.47%. Thus, it can be classified as evolved glauconite. The morphology of glauconite as oval, sub-oval, rounded pellets with deeply penetrating fractures on some grain surfaces, the moderate sort of these pellets and the occurrence of argillaceous matrix consisting of glauconitic plasma, illite-smectite mixed layer and kaolinite are considered criteria for the parautochthonous origin of the Upper Eocene glauconite. Moreover, the geochemistry of rare earth elements along with stratigraphy and the occurrences of many glauconitic ironstone horizons within the studied section proposed that the deposition of the studied glauconite, at depth of 100 m, started with marine transgression and terminated by marine regression during the Upper Eocene.

  10. Cool-water Eocene-Oligocene carbonate sedimentation on a paleobathymetric high, Kangaroo Island, southern Australia

    NASA Astrophysics Data System (ADS)

    James, Noel P.; Matenaar, Joanne; Bone, Yvonne

    2016-07-01

    The Kingscote Limestone is a thin, biofragmental ~ 41 m thick Paleogene subtropical to cool-temperate carbonate interpreted to have accumulated in a seaway developed between a series of mid-shelf islands. It is a pivotal section that allows interpretation of a region in which there is little exposure of early Cenozoic shelf sediments. Sedimentation occurred on part of the shelf along the northern margin of an extensive Eocene embayment that evolved into a narrow Oligocene ocean following collapse of the Tasman Gateway. Eocene strata are subtropical echinoid-rich floatstones with conspicuous bryozoans, and mollusks, together with large and small benthic foraminifers. Numerous echinoid rudstone storm deposits punctuate the succession. Correlation with coeval Eocene strata across southern Australia supports a regional facies model wherein inner neritic biosiliceous spiculitic sediments passed outboard into calcareous facies. The silica was derived from land covered by a thriving subtropical forest and attendant deep weathering. Oligocene rocks are distinctively cooler cyclic cross-bedded bryozoan rudstones and floatstones with a similar benthic biota but dominated by bryozoans and containing no large benthic foraminifers. These deposits are interpreted as flood-dominated tidal subaqueous dunes that formed in a flood-tide dominated inter-island strait. Omission surfaces at the top of the Eocene and at the top of most Oligocene cycles are Fe-stained hardgrounds that underwent extensive multigeneration seafloor and meteoric diagenesis prior to deposition of the next cycle. Cycles in the Kingscote Limestone, although mostly m-scale and compositionally distinct are similar to those across the region and point to a recurring cycle motif controlled by icehouse eustasy and local paleogeography.

  11. Background- versus event-level biotic variability: Hyperthermals of the late Paleocene and early Eocene

    NASA Astrophysics Data System (ADS)

    Gibbs, S.; Murphy, B. H.; Pälike, H.

    2009-12-01

    The Paleocene-Eocene Thermal Maximum (PETM) was an abrupt global warming event 55 million years ago (Ma) which has received much attention in recent years as an analogue for anthropogenic carbon emissions. We now know that the PETM was not unique, but was perhaps the most extreme of a number of abrupt carbon cycle perturbations throughout the late Paleocene and early Eocene. These inferred transient warming events, or ‘hyperthermals’, all have characteristic negative carbon isotope excursions (CIE). Unlike the PETM, it is currently unclear whether there was a significant biotic response to these additional CIEs, and if so, whether the amplitude of response varied systematically with excursion magnitude. Here, we present high-resolution nannofossil records from a two million year interval spanning the Paleocene-Eocene boundary at Ocean Drilling Program (ODP) Site 1209 in the paleo-subequatorial Pacific. This interval, from ~55 to 53 Ma, includes the PETM, a second hyperthermal named the Eocene Thermal Maximum 2 (ETM2 or ‘Elmo’), and a further number of smaller excursions. These data allow us to look for common biotic signatures and to document the level of assemblage variability relative to the inferred levels of environmental change associated with each CIE. We use this dataset as a case-study for investigating different statistical means of quantifying and comparing biotic responses to background and event-level perturbation. Preliminary analyses suggest that, as expected, the PETM exhibited the greatest level of assemblage variability, well above background levels, followed in order of CIE magnitude by the ETM2. Several of the smaller excursions have no significant assemblage variability above background levels, pointing to a critical threshold level of environmental perturbation.

  12. Atmospheric pCO2 Reconstructed across the Early Eocene Hyperthermals

    NASA Astrophysics Data System (ADS)

    Cui, Y.; Schubert, B.

    2015-12-01

    Negative carbon isotope excursions (CIEs) are commonly associated with extreme global warming. The Early Eocene is punctuated by five such CIEs, the Paleocene-Eocene thermal maximum (PETM, ca. 55.8 Ma), H1 (ca. 53.6 Ma), H2 (ca. 53.5 Ma), I1 (ca. 53.3 Ma), and I2 (ca. 53.2 Ma), each characterized by global warming. The negative CIEs are recognized in both marine and terrestrial substrates, but the terrestrial substrates exhibit a larger absolute magnitude CIE than the marine substrates. Here we reconcile the difference in CIE magnitude between the terrestrial and marine substrates for each of these events by accounting for the additional carbon isotope fractionation by C3 land plants in response to increased atmospheric pCO2. Our analysis yields background and peak pCO2 values for each of the events. Assuming a common mechanism for each event, we calculate that background pCO2 was not static across the Early Eocene, with the highest background pCO2 immediately prior to I2, the last of the five CIEs. Background pCO2 is dependent on the source used in our analysis with values ranging from 300 to 720 ppmv provided an injection of 13C-depleted carbon with δ13C value of -60‰ (e.g. biogenic methane). The peak pCO2 during each event scales according to the magnitude of CIE, and is therefore greatest during the PETM and smallest during H2. Both background and peak pCO2 are higher if we assume a mechanism of permafrost thawing (δ13C = -25‰). Our reconstruction of pCO2 across these events is consistent with trends in the δ18O value of deep-sea benthic foraminifera, suggesting a strong link between pCO2 and temperature during the Early Eocene.

  13. Microfacies and depositional environment of the Paleocene-Eocene Jahrum Formation (SW Iran)

    NASA Astrophysics Data System (ADS)

    Noormohammadi, Zohreh; Vazirimoghadam, Hossein

    2010-05-01

    The Jahrum Formation a thick carbonate succession of the Paleocene-Eocene in Zagros Mountains (south west Iran), has been studied to determine its microfacies and paleoenvironments. Detailed petrograhic analysis of the deposits led to the recognition, four major depositional environments were identified in the Jahrum Formation. These include tidal flat, lagoon, barrier and open marine environmental setting and are interpreted as a carbonate platform developed in a homoclinal ramp situation.

  14. Integrated stratigraphy and astronomical tuning of Smirra cores, lower Eocene, Umbria-Marche basin, Italy.

    NASA Astrophysics Data System (ADS)

    Lauretano, Vittoria; Turtù, Antonio; Hilgen, Frits; Galeotti, Simone; Catanzariti, Rita; Reichart, Gert Jan; Lourens, Lucas J.

    2016-04-01

    The early Eocene represents an ideal case study to analyse the impact of increase global warming on the ocean-atmosphere system. During this time interval, the Earth's surface experienced a long-term warming trend that culminated in a period of sustained high temperatures called the Early Eocene Climatic Optimum (EECO). These perturbations of the ocean-atmosphere system involved the global carbon cycle and global temperatures and have been linked to orbital forcing. Unravelling this complex climatic system strictly depends on the availability of high-quality suitable geological records and accurate age models. However, discrepancies between the astrochronological and radioisotopic dating techniques complicate the development of a robust time scale for the early Eocene (49-54 Ma). Here we present the first magneto-, bio-, chemo- and cyclostratigraphic results of the drilling of the land-based Smirra section, in the Umbria Marche Basin. The sediments recovered at Smirra provide a remarkably well-preserved and undisturbed succession of the early Palaeogene pelagic stratigraphy. Bulk stable carbon isotope and X-Ray Fluorescence (XRF) scanning records are employed in the construction of an astronomically tuned age model for the time interval between ~49 and ~54 Ma based on the tuning to long-eccentricity. These results are then compared to the astronomical tuning of the benthic carbon isotope record of ODP Site 1263 to evaluate the different age model options and improve the time scale of the early Eocene by assessing the precise number of eccentricity-related cycles comprised in this critical interval.

  15. Changes in the strength of Atlantic Ocean overturning circulation across repeated Eocene warming events

    NASA Astrophysics Data System (ADS)

    Kirtland Turner, S.; Sexton, P. F.; Norris, R. D.; Wilson, P. A.; Charles, C. D.; Ridgwell, A.

    2015-12-01

    The Paleogene Period (~65 to 34 Ma) was a time of acute climatic warmth, with deep ocean temperatures exceeding 12°C at the height of the Early Eocene Climatic Optimum (~53 to 50 Ma). Multiple rapid warming events, associated with transient deep sea temperature increases of 2 to 4°C (termed 'hyperthermals'), potentially related to orbital forcing of the carbon cycle and climate, occurred from the late Paleocene through at least the early middle Eocene and onset of long-term Cenozoic cooling (~47 Ma). While deep ocean circulation patterns associated with the great glaciations of the Plio-Pleistocene have been studied extensively, the behavior of the ocean's overturning circulation on orbital-timescales in the extreme warmth of the early Cenozoic is largely unknown. Here we present new evidence for changing patterns of ocean overturning in the southern hemisphere associated with four orbitally paced hyperthermal events in the early-middle Eocene (~50 to 48 Ma) based on a combination of multi-site bulk carbonate and benthic foraminiferal stable isotope measurements and Earth system modeling. Our results suggest that southern-sourced overturning weakens and shoals in response to modest atmospheric carbon injections and consequent warming, and is replaced by invasion of nutrient-rich North Atlantic-sourced deep water, leading to predictable spatial patterns in deep-sea carbon isotope records. The changes in abyssal carbon isotope 'aging' gradients associated with these hyperthermals are, in fact, two to three times larger than the change in aging gradient associated with the switch in Atlantic overturning between the Last Glacial Maximum and today. Our results suggest that the Atlantic overturning circulation was sensitive to orbital-scale climate variability during Eocene extreme warmth, not just to interglacial-glacial climatic variability of the Plio-Pleistocene.

  16. Eocene global warming events driven by ventilation of oceanic dissolved organic carbon.

    PubMed

    Sexton, Philip F; Norris, Richard D; Wilson, Paul A; Pälike, Heiko; Westerhold, Thomas; Röhl, Ursula; Bolton, Clara T; Gibbs, Samantha

    2011-03-17

    'Hyperthermals' are intervals of rapid, pronounced global warming known from six episodes within the Palaeocene and Eocene epochs (∼65-34 million years (Myr) ago). The most extreme hyperthermal was the ∼170 thousand year (kyr) interval of 5-7 °C global warming during the Palaeocene-Eocene Thermal Maximum (PETM, 56 Myr ago). The PETM is widely attributed to massive release of greenhouse gases from buried sedimentary carbon reservoirs, and other, comparatively modest, hyperthermals have also been linked to the release of sedimentary carbon. Here we show, using new 2.4-Myr-long Eocene deep ocean records, that the comparatively modest hyperthermals are much more numerous than previously documented, paced by the eccentricity of Earth's orbit and have shorter durations (∼40 kyr) and more rapid recovery phases than the PETM. These findings point to the operation of fundamentally different forcing and feedback mechanisms than for the PETM, involving redistribution of carbon among Earth's readily exchangeable surface reservoirs rather than carbon exhumation from, and subsequent burial back into, the sedimentary reservoir. Specifically, we interpret our records to indicate repeated, large-scale releases of dissolved organic carbon (at least 1,600 gigatonnes) from the ocean by ventilation (strengthened oxidation) of the ocean interior. The rapid recovery of the carbon cycle following each Eocene hyperthermal strongly suggests that carbon was re-sequestered by the ocean, rather than the much slower process of silicate rock weathering proposed for the PETM. Our findings suggest that these pronounced climate warming events were driven not by repeated releases of carbon from buried sedimentary sources, but, rather, by patterns of surficial carbon redistribution familiar from younger intervals of Earth history.

  17. Magnetostratigraphy in the Lodo Formation, CA: An Attempt to Locate Hyperthermals of the Early Eocene

    NASA Astrophysics Data System (ADS)

    Aldrich, N. C.; Pluhar, C. J.; Gibbs, S.; Rieth, J. A.

    2015-12-01

    The Lodo Formation in the California Coast Range, Fresno County records the Paleocene Eocene Thermal Maximum (PETM) and possibly other Early Eocene hyperthermal events. The Eocene Thermal Maximum 2 (ETM2, ELMO, or H1) represents a hyperthermal event that occurred approximately 2 million years after the PETM and just prior to the C24r - C24n magnetic reversal (≈ 53.9 Ma) in the Ypresian. While the ETM2 event has been located in offshore samples, it has been more difficult to locate in a terrestrial section. This project attempts to locate the ETM2 magnetostratigraphically by finding the paleomagnetic reversal at C24r-C24n.3n, provide geochronological framework, and assess sedimentation rate changes during this time. This area is known to have had a high rate of deposition (16.8 cm/kyr ) during the PETM, which is found lower in the section. We collected 36 new samples from a 13.44m section spanning stratigraphy thought to cover the ETM2 along with 31 previous samples spanning the PETM, and prepared them for paleomagnetic and paleontological analysis. We analyzed samples using standard paleomagnetic methods including low-temperature and thermal demagnetization. Preliminary results suggest that the magnetostratigraphy spans the C24r-C24n boundary, while the micropaleontology shows the NP10-NP11 boundary, which occurs near the ETM2 as well as the NP11-NP12 boundary. The data indicate an order-of-magnitude drop in sedimentation rate in the lower Eocene at this site, concomitant with a drop in grain size, compared with the PETM.

  18. Goulds Belt, Interstellar Clouds, and the Eocene-Oligocene Helium-3 Spike

    NASA Technical Reports Server (NTRS)

    Rubincam, David Parry

    2015-01-01

    Drag from hydrogen in the interstellar cloud which formed Gould's Belt may have sent small meteoroids with embedded helium to the Earth, perhaps explaining part or all of the (sup 3) He spike seen in the sedimentary record at the Eocene-Oligocene transition. Assuming the Solar System passed through part of the cloud, meteoroids in the asteroid belt up to centimeter size may have been dragged to the resonances, where their orbital eccentricities were pumped up into Earth-crossing orbits.

  19. Warm Eocene climate enhanced petroleum generation from Cretaceous source rocks: A potential climate feedback mechanism?

    NASA Astrophysics Data System (ADS)

    Kroeger, K. F.; Funnell, R. H.

    2012-02-01

    Earth surface temperatures, including in the deep sea increased by 5-10°C from the late Paleocene ca. 58 Myr ago to the Early Eocene Climatic Optimum (EECO) centered at about 51 Myr ago. A large (˜2.5‰) drop in δ13C of carbonate spans much of this interval. This suggests a long-term increase in the net flux of 13C-depleted carbon to the ocean and atmosphere that is difficult to explain by changes in surficial carbon cycling alone. We reveal a relationship between surface temperature increase and increased petroleum generation in sedimentary basins operating on 100 kyr to Myr time scales. We propose that early Eocene warming has led to a synchronization of periods of maximum petroleum generation and enhanced generation in otherwise unproductive basins through extension of the volume of source rock within the oil and gas window across hundreds of sedimentary basins globally. Modelling the thermal evolution of four sedimentary basins in the southwest Pacific predicted an up to 50% increase in petroleum generation that would have significantly increased leakage of light hydrocarbons and oil degeneration products into the atmosphere. Extrapolating our modelling results to hundreds of sedimentary basins worldwide suggests that globally increased leakage could have caused a climate feedback effect, driving or enhancing early Eocene climate warming.

  20. Carbon sequestration during the Palaeocene-Eocene Thermal Maximum by an efficient biological pump

    NASA Astrophysics Data System (ADS)

    Ma, Zhongwu; Gray, Ellen; Thomas, Ellen; Murphy, Brandon; Zachos, James; Paytan, Adina

    2014-05-01

    A perturbation of the carbon cycle and biosphere, linked to globally increased temperatures about 55.9 million years ago, characterized the Palaeocene-Eocene Thermal Maximum. Its effect on global oceanic productivity is controversial. Here we present records of marine barite accumulation rates that show distinct peaks during this time interval, suggesting a general increase in export productivity. We propose that changes in marine ecosystems, resulting from high atmospheric partial pressure of CO2 and ocean acidification, led to enhanced carbon export from the photic zone to depth, thereby increasing the efficiency of the biological pump. Higher seawater temperatures at that time increased bacterial activity and organic matter regeneration. Through this process much of the sinking particulate organic matter was probably converted to dissolved inorganic and organic carbon. We estimate that an annual carbon export flux out of the euphotic zone and into the deep ocean waters could have amounted to about 15 Gt during the Palaeocene-Eocene Thermal Maximum. About 0.4% of this carbon is expected to have entered the refractory dissolved organic pool, where it could be sequestered from the atmosphere for tens of thousands of years. Our estimates are consistent with the amount of carbon redistribution expected for the recovery from the Palaeocene-Eocene Thermal Maximum.

  1. The role of fire during the Eocene-Oligocene transition in southern South America

    NASA Astrophysics Data System (ADS)

    Strömberg, C. A. E.; Selkin, P. A.; Boyle, J.; Carlini, A. A.; Davies-Vollum, K. S.; Dunn, R. E.; Kohn, M. J.; Madden, R. H.

    2014-12-01

    The geological record of wildfire, particularly across climate transitions, can help elucidate the complex relationships between climate, vegetation, and fire at long temporal scales. Across Eocene-Oligocene Transition (EOT), previous workers have proposed climate changes (drying and changes in seasonality) contemporaneous with the growth of the Antarctic ice sheet that would have changed the likelihood of wildfires in terrestrial ecosystems. We document short-lived changes in fire regime and plant community in Patagonia near the time of the EOT. Specifically, the concentration of magnetic oxide minerals in Eocene-Oligocene loessites from the Sarmiento Formation correlates with the fraction of burnt palm phytoliths as well as with the fraction of non-palm phytoliths. We interpret the magnetic mineral assemblage magnetite + maghemite ± hematite as pyrogenic, forming in reducing conditions at temperatures between 300 and 600°C. The disappearance of fire-related characteristics near the EOT is possible if seasonal drought was suppressed due to a northward shift in the westerlies - a process consistent with changes in modal particle sizes in the Vera Member. Although the transitory nature of the changes in fire regime remains a puzzle, these results imply a more important role for fire in structuring Eocene-Oligocene landscapes than previously thought.

  2. Provenance and palaeogeographic implications of Eocene-Oligocene sedimentary rocks in the northwestern Basin and Range

    USGS Publications Warehouse

    Egger, A.E.; Colgan, J.P.; York, C.

    2009-01-01

    A thick sequence of uppermost Eocene to lower Oligocene volcaniclastic and sedimentary rocks is exposed at the base of the Warner Range in northeastern California. This isolated exposure provides insight into the palaeogeographic setting of the northwestern Basin and Range during this time period. Significant thinning of the unit over 35km of lateral exposure and predominantly volcanic clast compositions suggest that the sequence was deposited in an alluvial plain adjacent to a volcanic arc. Palaeocurrent indicators in the conglomerates define a NNE transport direction. Detrital zircon analysis on coarse sandstones and dating of individual granite cobbles show a range of ages consistent with a local, volcanic source area primarily from the SSW with some far-travelled input from northern Nevada; the far-travelled component increases in influence as the unit thins to the north. Comparison with other sedimentary sequences of Eocene age and integration with palaeofloral and geophysical data help to define drainage divides, and suggest that this sequence accumulated in a relatively isolated, intra-arc basin. This localized accumulation differs markedly from contemporaneous drainages to the south that transported material westwards from central Nevada to the palaeoshoreline, and suggests that ongoing volcanism had a strong influence on palaeogeography in this region during the Eocene and Oligocene.

  3. Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India

    PubMed Central

    Rust, Jes; Singh, Hukam; Rana, Rajendra S.; McCann, Tom; Singh, Lacham; Anderson, Ken; Sarkar, Nivedita; Nascimbene, Paul C.; Stebner, Frauke; Thomas, Jennifer C.; Solórzano Kraemer, Monica; Williams, Christopher J.; Engel, Michael S.; Sahni, Ashok; Grimaldi, David

    2010-01-01

    For nearly 100 million years, the India subcontinent drifted from Gondwana until its collision with Asia some 50 Ma, during which time the landmass presumably evolved a highly endemic biota. Recent excavations of rich outcrops of 50–52-million-year-old amber with diverse inclusions from the Cambay Shale of Gujarat, western India address this issue. Cambay amber occurs in lignitic and muddy sediments concentrated by near-shore chenier systems; its chemistry and the anatomy of associated fossil wood indicates a definitive source of Dipterocarpaceae. The amber is very partially polymerized and readily dissolves in organic solvents, thus allowing extraction of whole insects whose cuticle retains microscopic fidelity. Fourteen orders and more than 55 families and 100 species of arthropod inclusions have been discovered thus far, which have affinities to taxa from the Eocene of northern Europe, to the Recent of Australasia, and the Miocene to Recent of tropical America. Thus, India just prior to or immediately following contact shows little biological insularity. A significant diversity of eusocial insects are fossilized, including corbiculate bees, rhinotermitid termites, and modern subfamilies of ants (Formicidae), groups that apparently radiated during the contemporaneous Early Eocene Climatic Optimum or just prior to it during the Paleocene-Eocene Thermal Maximum. Cambay amber preserves a uniquely diverse and early biota of a modern-type of broad-leaf tropical forest, revealing 50 Ma of stasis and change in biological communities of the dipterocarp primary forests that dominate southeastern Asia today. PMID:20974929

  4. Tectonic rotations and internal structure of Eocene plutons in Chuquicamata, northern Chile

    NASA Astrophysics Data System (ADS)

    Somoza, R.; Tomlinson, A. J.; Zaffarana, C. B.; Singer, S. E.; Puigdomenech Negre, C. G.; Raposo, M. I. B.; Dilles, J. H.

    2015-07-01

    A paleomagnetic and AMS study on Eocene plutonic complexes in the Calama area, northern Chile, reveals high-temperature, high-coercivity magnetizations of dominantly thermoremanent origin and magnetic fabrics controlled by magnetite. The paleomagnetic results indicate that ~ 43 Ma plutons underwent clockwise tectonic rotation, whereas adjacent ~ 39 Ma plutons did not undergo discernible rotation. This points to a middle Eocene age for the younger tectonic rotations associated with the Central Andean Rotation Pattern in the Chuquicamata-Calama area. The petrofabric in these rocks formed under conditions ranging from purely magmatic (i.e. before full crystallization) to low-temperature solid-state deformation. AMS and paleomagnetism suggest that the plutonic bodies were formed by progressive amalgamation of subvertical magma sheets spanning multiple magnetic polarity chrons. The parallelism between magmatic and tectonic foliations suggests that regional tectonic stress controlled ascent, emplacement and rock deformation during cooling. In this context, we suggest that magma ascent and emplacement in the upper crust likely exploited Mesozoic structures which were locally reactivated in the Eocene.

  5. Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India.

    PubMed

    Rust, Jes; Singh, Hukam; Rana, Rajendra S; McCann, Tom; Singh, Lacham; Anderson, Ken; Sarkar, Nivedita; Nascimbene, Paul C; Stebner, Frauke; Thomas, Jennifer C; Solórzano Kraemer, Monica; Williams, Christopher J; Engel, Michael S; Sahni, Ashok; Grimaldi, David

    2010-10-26

    For nearly 100 million years, the India subcontinent drifted from Gondwana until its collision with Asia some 50 Ma, during which time the landmass presumably evolved a highly endemic biota. Recent excavations of rich outcrops of 50-52-million-year-old amber with diverse inclusions from the Cambay Shale of Gujarat, western India address this issue. Cambay amber occurs in lignitic and muddy sediments concentrated by near-shore chenier systems; its chemistry and the anatomy of associated fossil wood indicates a definitive source of Dipterocarpaceae. The amber is very partially polymerized and readily dissolves in organic solvents, thus allowing extraction of whole insects whose cuticle retains microscopic fidelity. Fourteen orders and more than 55 families and 100 species of arthropod inclusions have been discovered thus far, which have affinities to taxa from the Eocene of northern Europe, to the Recent of Australasia, and the Miocene to Recent of tropical America. Thus, India just prior to or immediately following contact shows little biological insularity. A significant diversity of eusocial insects are fossilized, including corbiculate bees, rhinotermitid termites, and modern subfamilies of ants (Formicidae), groups that apparently radiated during the contemporaneous Early Eocene Climatic Optimum or just prior to it during the Paleocene-Eocene Thermal Maximum. Cambay amber preserves a uniquely diverse and early biota of a modern-type of broad-leaf tropical forest, revealing 50 Ma of stasis and change in biological communities of the dipterocarp primary forests that dominate southeastern Asia today. PMID:20974929

  6. Paleogeographic considerations of the Barbacoas Platform western border during Paleocene-Middle Eocene, Trujillo State, Venezuela

    SciTech Connect

    Muller, K. ); Falcon, R. )

    1993-02-01

    Stratigraphic and sedimentological field information of the Chejende-Cuicas area, and subsurface well data (Butaque-1S) have been integrated to analyze the paleogeographic evolution of Barbacoas Platform. Both localities are in the Trujillo state, western Venezuela and they are 18 km apart. A relatively narrow continental platform during Paleocene times can be inferred from the existence of Paleocene rocks of the Rancheria Formation, deposited in outer and middle neritic environments. This formation probably grades laterally towards the east and northeast, into the Trujillo Formation (Paleocene-early Eocene), which was deposited in a middle to upper bathyal environment in turbiditic conditions. Paleocene units grade upwards into the Misoa Formation, deposited in deltaic to coastal marine environments. This suggests a regressive progradation over slope and platform during early to early middle Eocene times. Eocene sedimentation ends with the transgressive Caus and Pauji formations, typical of upper bathyal to outer neritic conditions. Low sedimentation and subsidence rates in the platform in the Chejende area is inferred by the marked difference between Rancheria and Misoa formation thicknesses in this area (95 m and 40 m) and the Butaque-S well (520 and 175 m).

  7. A new tarkadectine primate from the Eocene of Inner Mongolia, China: phylogenetic and biogeographic implications.

    PubMed

    Ni, Xijun; Meng, Jin; Beard, K Christopher; Gebo, Daniel L; Wang, Yuanqing; Li, Chuankui

    2010-01-22

    Tarka and Tarkadectes are Middle Eocene mammals known only from the Rocky Mountains region of North America. Previous work has suggested that they are members of the Plagiomenidae, an extinct family often included in the order Dermoptera. Here we describe a new primate, Tarkops mckennai gen. et sp. nov., from the early Middle Eocene Irdinmanha Formation of Inner Mongolia, China. The new taxon is particularly similar to Tarka and Tarkadectes, but it also displays many features observed in omomyids. A phylogenetic analysis based on a data matrix including 59 taxa and 444 dental characters suggests that Tarkops, Tarka and Tarkadectes form a monophyletic group--the Tarkadectinae--that is nested within the omomyid clade. Within Omomyidae, tarkadectines appear to be closely related to Macrotarsius. Dermoptera, including extant and extinct flying lemurs and plagiomenids, is recognized as a clade nesting within the polyphyletic group of plesiadapiforms, therefore supporting the previous suggestion that the relationship between dermopterans and primates is as close as that between plesiadapiforms and primates. The distribution of tarkadectine primates on both sides of the Pacific Ocean basin suggests that palaeoenvironmental conditions appropriate to sustain primates occurred across a vast expanse of Asia and North America during the Middle Eocene. PMID:19386655

  8. The Best Modern Analog for Eocene Arctic Forests is within Today's Korean Peninsula

    NASA Astrophysics Data System (ADS)

    Schubert, B.; Jahren, H.; Eberle, J.; Sternberg, L. O.; Ellsworth, P.; Eberth, D.; Sweet, A.

    2011-12-01

    In the 25 years that have passed since the first extensive descriptions of the Fossil Forests that persisted above the Arctic Circle during the Eocene (~45-54 Ma), no less than four locations have been suggested as modern analogs. These locations represent a diverse collection of biomes and temperature/precipitation environments, and include the southeastern Unites States and southeastern Asia (based on flora and fauna assemblages), southern Chile and the U.S. Pacific Northwest (based on biomass and productivity estimates), and Pacific Northwestern U.S. and Canada (based on mean annual temperature and mean annual precipitation). Here we report on new isotope datasets that allow for a prediction of best modern analog based on a quantitative characterization of paleoseasonality. First, we report high-resolution carbon isotope data from fossil tree rings that record the ratio of summer to winter precipitation. Second, we report analyses of the oxygen isotope composition of phenylglucosazone, a compound isolated from fossil cellulose that straightforwardly records the oxygen isotope composition of meteoric water available to the tree. Together, our analyses indicate that the fossil forests of the Eocene Arctic thrived under a summer-dominated, high-intensity, seasonal precipitation regime, with at least 279 mm of rainfall during the wettest month. A quantitative comparison of mean-annual temperature and precipitation, fossil and modern plant communities, and the seasonality indices, highlights the Korean peninsula as the most appropriate modern analog for the Arctic Eocene forests, in preference to the North and South American analogs previously proposed.

  9. Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water.

    PubMed

    Fahlke, Julia M; Gingerich, Philip D; Welsh, Robert C; Wood, Aaron R

    2011-08-30

    Eocene archaeocete whales gave rise to all modern toothed and baleen whales (Odontoceti and Mysticeti) during or near the Eocene-Oligocene transition. Odontocetes have asymmetrical skulls, with asymmetry linked to high-frequency sound production and echolocation. Mysticetes are generally assumed to have symmetrical skulls and lack high-frequency hearing. Here we show that protocetid and basilosaurid archaeocete skulls are distinctly and directionally asymmetrical. Archaeocete asymmetry involves curvature and axial torsion of the cranium, but no telescoping. Cranial asymmetry evolved in Eocene archaeocetes as part of a complex of traits linked to directional hearing (such as pan-bone thinning of the lower jaws, mandibular fat pads, and isolation of the ear region), probably enabling them to hear the higher sonic frequencies of sound-producing fish on which they preyed. Ultrasonic echolocation evolved in Oligocene odontocetes, enabling them to find silent prey. Asymmetry and much of the sonic-frequency range of directional hearing were lost in Oligocene mysticetes during the shift to low-frequency hearing and bulk-straining predation.

  10. Sensitivity of the Palaeocene-Eocene Thermal Maximum climate to cloud properties.

    PubMed

    Kiehl, Jeffrey T; Shields, Christine A

    2013-10-28

    The Palaeocene-Eocene Thermal Maximum (PETM) was a significant global warming event in the Earth's history (approx. 55 Ma). The cause for this warming event has been linked to increases in greenhouse gases, specifically carbon dioxide and methane. This rapid warming took place in the presence of the existing Early Eocene warm climate. Given that projected business-as-usual levels of atmospheric carbon dioxide reach concentrations of 800-1100 ppmv by 2100, it is of interest to study past climates where atmospheric carbon dioxide was higher than present. This is especially the case given the difficulty of climate models in simulating past warm climates. This study explores the sensitivity of the simulated pre-PETM and PETM periods to change in cloud condensation nuclei (CCN) and microphysical properties of liquid water clouds. Assuming lower levels of CCN for both of these periods leads to significant warming, especially at high latitudes. The study indicates that past differences in cloud properties may be an important factor in accurately simulating past warm climates. Importantly, additional shortwave warming from such a mechanism would imply lower required atmospheric CO2 concentrations for simulated surface temperatures to be in reasonable agreement with proxy data for the Eocene.

  11. Crown Group Lejeuneaceae and Pleurocarpous Mosses in Early Eocene (Ypresian) Indian Amber

    PubMed Central

    Heinrichs, Jochen; Scheben, Armin; Bechteler, Julia; Lee, Gaik Ee; Schäfer-Verwimp, Alfons; Hedenäs, Lars; Singh, Hukam; Pócs, Tamás; Nascimbene, Paul C.; Peralta, Denilson F.; Renner, Matt; Schmidt, Alexander R.

    2016-01-01

    Cambay amber originates from the warmest period of the Eocene, which is also well known for the appearance of early angiosperm-dominated megathermal forests. The humid climate of these forests may have triggered the evolution of epiphytic lineages of bryophytes; however, early Eocene fossils of bryophytes are rare. Here, we present evidence for lejeuneoid liverworts and pleurocarpous mosses in Cambay amber. The preserved morphology of the moss fossil is inconclusive for a detailed taxonomic treatment. The liverwort fossil is, however, distinctive; its zig-zagged stems, suberect complicate-bilobed leaves, large leaf lobules, and small, deeply bifid underleaves suggest a member of Lejeuneaceae subtribe Lejeuneinae (Harpalejeunea, Lejeunea, Microlejeunea). We tested alternative classification possibilities by conducting divergence time estimates based on DNA sequence variation of Lejeuneinae using the age of the fossil for corresponding age constraints. Consideration of the fossil as a stem group member of Microlejeunea or Lejeunea resulted in an Eocene to Late Cretaceous age of the Lejeuneinae crown group. This reconstruction is in good accordance with published divergence time estimates generated without the newly presented fossil evidence. Balancing available evidence, we describe the liverwort fossil as the extinct species Microlejeunea nyiahae, representing the oldest crown group fossil of Lejeuneaceae. PMID:27244582

  12. Upper Cretaceous and lower Eocene conglomerates of Western Transverse Ranges: evidence for tectonic rotation

    SciTech Connect

    Reed, W.E.; Krause, R.G.F.

    1989-04-01

    Stratigraphic and paleomagnetic studies have suggested that the western Transverse Ranges (WTR) microplate is allochthonous, and may have experienced translational and rotational motions. Present paleocurrent directions from the Upper Cretaceous Jalama Formation of the Santa Ynez Mountains are north-directed; these forearc sediments (Great Valley sequence) contain magmatic arc-derived conglomerate clasts from the Peninsular Ranges in southern California. Paleocurrents in the lower Eocene Juncal and Cozy Dell Formations are south-directed. This juxtaposition is best explained by 90/degrees/ or more of clockwise rotation of the WTR microplate, so that Upper Cretaceous forearc sediments sourced from the Peninsular Ranges magmatic arc were deposited by west-directed currents. Eocene sediments were derived from an uplifted portion of the western basin margin and deposited by east-directed currents. Franciscan olistoliths in the Upper Cretaceous sediments indicate deposition adjacent to an accretionary wedge; conglomeratic clasts recycled from the Upper Cretaceous sequence, and radiolarian cherts and ophiolitic boulders in the Eocene strata indicate derivation from an outer accretionary ridge.

  13. A new tarkadectine primate from the Eocene of Inner Mongolia, China: phylogenetic and biogeographic implications

    PubMed Central

    Ni, Xijun; Meng, Jin; Beard, K. Christopher; Gebo, Daniel L.; Wang, Yuanqing; Li, Chuankui

    2010-01-01

    Tarka and Tarkadectes are Middle Eocene mammals known only from the Rocky Mountains region of North America. Previous work has suggested that they are members of the Plagiomenidae, an extinct family often included in the order Dermoptera. Here we describe a new primate, Tarkops mckennai gen. et sp. nov., from the early Middle Eocene Irdinmanha Formation of Inner Mongolia, China. The new taxon is particularly similar to Tarka and Tarkadectes, but it also displays many features observed in omomyids. A phylogenetic analysis based on a data matrix including 59 taxa and 444 dental characters suggests that Tarkops, Tarka and Tarkadectes form a monophyletic group—the Tarkadectinae—that is nested within the omomyid clade. Within Omomyidae, tarkadectines appear to be closely related to Macrotarsius. Dermoptera, including extant and extinct flying lemurs and plagiomenids, is recognized as a clade nesting within the polyphyletic group of plesiadapiforms, therefore supporting the previous suggestion that the relationship between dermopterans and primates is as close as that between plesiadapiforms and primates. The distribution of tarkadectine primates on both sides of the Pacific Ocean basin suggests that palaeoenvironmental conditions appropriate to sustain primates occurred across a vast expanse of Asia and North America during the Middle Eocene. PMID:19386655

  14. Late Jurassic to Eocene geochemical evolution of volcanic rocks in Puerto Rico

    SciTech Connect

    Schellekens, J.H. )

    1991-03-01

    The Late Jurassic to Eocene deformed volcanic, volcaniclastic and sedimentary rocks of Puerto Rico are divided into three igneous provinces, the southwestern, central, and northeastern igneous province. Based on the stratigraphic position approximate ages could be assigned to the flow rocks in these provinces. Ba/Nb and La/Sm diagrams are presented to illustrate the origin and evolution of the flow rocks. The oldest rock in the southwestern province may include MORB. Early Cretaceous volcanic rocks in the central and northeastern province have low Ba/nb and La/Sm, that are interpreted as an early island arc stage, with none or only minor contribution of slab-derived material. The Late Cretaceous to Eocene volcanic rocks have a wide range of values for the Ba/Nb and La/Sm that are interpreted as the result of admixture of a variable amount of slab-derived material. The Maricao Basalt (Maastrichtian to Eocene) in the southeastern igneous province has the geochemical signature of magmas formed in an extensional setting.

  15. Intercontinental dispersal of giant thermophilic ants across the Arctic during early Eocene hyperthermals

    PubMed Central

    Archibald, S. Bruce; Johnson, Kirk R.; Mathewes, Rolf W.; Greenwood, David R.

    2011-01-01

    Early Eocene land bridges allowed numerous plant and animal species to cross between Europe and North America via the Arctic. While many species suited to prevailing cool Arctic climates would have been able to cross throughout much of this period, others would have found dispersal opportunities only during limited intervals when their requirements for higher temperatures were met. Here, we present Titanomyrma lubei gen. et sp. nov. from Wyoming, USA, a new giant (greater than 5 cm long) formiciine ant from the early Eocene (approx. 49.5 Ma) Green River Formation. We show that the extinct ant subfamily Formiciinae is only known from localities with an estimated mean annual temperature of about 20°C or greater, consistent with the tropical ranges of almost all of the largest living ant species. This is, to our knowledge, the first known formiciine of gigantic size in the Western Hemisphere and the first reported cross-Arctic dispersal by a thermophilic insect group. This implies intercontinental migration during one or more brief high-temperature episodes (hyperthermals) sometime between the latest Palaeocene establishment of intercontinental land connections and the presence of giant formiciines in Europe and North America by the early middle Eocene. PMID:21543354

  16. “Terror Birds” (Phorusrhacidae) from the Eocene of Europe Imply Trans-Tethys Dispersal

    PubMed Central

    Angst, Delphine; Buffetaut, Eric; Lécuyer, Christophe; Amiot, Romain

    2013-01-01

    Background Phorusrhacidae was a clade including middle-sized to giant terrestrial carnivorous birds, known mainly from the Cenozoic of South America, but also occurring in the Plio-Pleistocene of North America and the Eocene of Africa. Previous reports of small phorusrhacids in the Paleogene of Europe have been dismissed as based on non-phorusrhacid material. Methodology we have re-examined specimens of large terrestrial birds from the Eocene (late Lutetian) of France and Switzerland previously referred to gastornithids and ratites and have identified them as belonging to a phorusrhacid for which the name Eleutherornis cotei should be used. Conclusions/Significance The occurrence of a phorusrhacid in the late Lutetian of Europe indicates that these flightless birds had a wider geographical distribution than previously recognized. The likeliest interpretation is that they dispersed from Africa, where the group is known in the Eocene, which implies crossing the Tethys Sea. The Early Tertiary distribution of phorusrhacids can be best explained by transoceanic dispersal, across both the South Atlantic and the Tethys. PMID:24312212

  17. Virtual endocranial cast of earliest Eocene Diacodexis (Artiodactyla, Mammalia) and morphological diversity of early artiodactyl brains.

    PubMed

    Orliac, M J; Gilissen, E

    2012-09-22

    The study of brain evolution, particularly that of the neocortex, is of primary interest because it directly relates to how behavioural variations arose both between and within mammalian groups. Artiodactyla is one of the most diverse mammalian clades. However, the first 10 Myr of their brain evolution has remained undocumented so far. Here, we used high-resolution X-ray computed tomography to investigate the endocranial cast of Diacodexis ilicis of earliest Eocene age. Its virtual reconstruction provides unprecedented access to both metric parameters and fine anatomy of the most complete endocast of the earliest artiodactyl. This picture is assessed in a broad comparative context by reconstructing endocasts of 14 other Early and Middle Eocene representatives of basal artiodactyls, allowing the tracking of the neocortical structure of artiodactyls back to its simplest pattern. We show that the earliest artiodactyls share a simple neocortical pattern, so far never observed in other ungulates, with an almond-shaped gyrus instead of parallel sulci as previously hypothesized. Our results demonstrate that artiodactyls experienced a tardy pulse of encephalization during the Late Neogene, well after the onset of cortical complexity increase. Comparisons with Eocene perissodactyls show that the latter reached a high level of cortical complexity earlier than the artiodactyls. PMID:22764165

  18. Astronomical calibration of the geological timescale: closing the middle Eocene gap

    NASA Astrophysics Data System (ADS)

    Westerhold, T.; Röhl, U.; Frederichs, T.; Bohaty, S. M.; Zachos, J. C.

    2015-09-01

    To explore cause and consequences of past climate change, very accurate age models such as those provided by the astronomical timescale (ATS) are needed. Beyond 40 million years the accuracy of the ATS critically depends on the correctness of orbital models and radioisotopic dating techniques. Discrepancies in the age dating of sedimentary successions and the lack of suitable records spanning the middle Eocene have prevented development of a continuous astronomically calibrated geological timescale for the entire Cenozoic Era. We now solve this problem by constructing an independent astrochronological stratigraphy based on Earth's stable 405 kyr eccentricity cycle between 41 and 48 million years ago (Ma) with new data from deep-sea sedimentary sequences in the South Atlantic Ocean. This new link completes the Paleogene astronomical timescale and confirms the intercalibration of radioisotopic and astronomical dating methods back through the Paleocene-Eocene Thermal Maximum (PETM, 55.930 Ma) and the Cretaceous-Paleogene boundary (66.022 Ma). Coupling of the Paleogene 405 kyr cyclostratigraphic frameworks across the middle Eocene further paves the way for extending the ATS into the Mesozoic.

  19. Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water

    PubMed Central

    Fahlke, Julia M.; Gingerich, Philip D.; Welsh, Robert C.; Wood, Aaron R.

    2011-01-01

    Eocene archaeocete whales gave rise to all modern toothed and baleen whales (Odontoceti and Mysticeti) during or near the Eocene-Oligocene transition. Odontocetes have asymmetrical skulls, with asymmetry linked to high-frequency sound production and echolocation. Mysticetes are generally assumed to have symmetrical skulls and lack high-frequency hearing. Here we show that protocetid and basilosaurid archaeocete skulls are distinctly and directionally asymmetrical. Archaeocete asymmetry involves curvature and axial torsion of the cranium, but no telescoping. Cranial asymmetry evolved in Eocene archaeocetes as part of a complex of traits linked to directional hearing (such as pan-bone thinning of the lower jaws, mandibular fat pads, and isolation of the ear region), probably enabling them to hear the higher sonic frequencies of sound-producing fish on which they preyed. Ultrasonic echolocation evolved in Oligocene odontocetes, enabling them to find silent prey. Asymmetry and much of the sonic-frequency range of directional hearing were lost in Oligocene mysticetes during the shift to low-frequency hearing and bulk-straining predation. PMID:21873217

  20. Increased seasonality through the Eocene to Oligocene transition in northern high latitudes.

    PubMed

    Eldrett, James S; Greenwood, David R; Harding, Ian C; Huber, Matthew

    2009-06-18

    A profound global climate shift took place at the Eocene-Oligocene transition ( approximately 33.5 million years ago) when Cretaceous/early Palaeogene greenhouse conditions gave way to icehouse conditions. During this interval, changes in the Earth's orbit and a long-term drop in atmospheric carbon dioxide concentrations resulted in both the growth of Antarctic ice sheets to approximately their modern size and the appearance of Northern Hemisphere glacial ice. However, palaeoclimatic studies of this interval are contradictory: although some analyses indicate no major climatic changes, others imply cooler temperatures, increased seasonality and/or aridity. Climatic conditions in high northern latitudes over this interval are particularly poorly known. Here we present northern high-latitude terrestrial climate estimates for the Eocene to Oligocene interval, based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the Norwegian-Greenland Sea. Our data indicate a cooling of approximately 5 degrees C in cold-month (winter) mean temperatures to 0-2 degrees C, and a concomitant increased seasonality before the Oi-1 glaciation event. These data indicate that a cooling component is indeed incorporated in the delta(18)O isotope shift across the Eocene-Oligocene transition. However, the relatively warm summer temperatures at that time mean that continental ice on East Greenland was probably restricted to alpine outlet glaciers.

  1. Studies in neotropical paleobotany. XIV. A palynoflora from the middle Eocene Saramaguacan formation of Cuba

    USGS Publications Warehouse

    Graham, A.; Cozadd, D.; Areces-Mallea, A.; Frederiksen, N.O.

    2000-01-01

    An assemblage of 46 fossil pollen and spore types is described from a core drilled through the middle Eocene Saramaguacan Formation, Camaguey Province, eastern Cuba. Many of the specimens represent unidentified or extinct taxa but several can be identified to family (Palmae, Bombacaceae, Gramineae, Moraceae, Myrtaceae) and some to genus (Pteris, Crudia, Lymingtonia?). The paleo-climate was warm-temperate to subtropical which is consistent with other floras in the region of comparable age and with the global paleotemperature curve. Older plate tectonic models show a variety of locations for proto-Cuba during Late Cretaceous and later times, including along the norther coast of South America. More recent models depict western and central Cuba as two separate parts until the Eocene, and eastern Cuba (joined to northern Hispaniola) docking to central Cuba also in the Eocene. All fragments are part of the North American Plate and none were directly connected with northern South America in late Mesozoic or Cenozoic time. The Saramaguacan flora supports this model because the assemblage is distinctly North American in affinities, with only one type (Retimonocolpites type 1) found elsewhere only in South America.

  2. Sensitivity of the Palaeocene-Eocene Thermal Maximum climate to cloud properties.

    PubMed

    Kiehl, Jeffrey T; Shields, Christine A

    2013-10-28

    The Palaeocene-Eocene Thermal Maximum (PETM) was a significant global warming event in the Earth's history (approx. 55 Ma). The cause for this warming event has been linked to increases in greenhouse gases, specifically carbon dioxide and methane. This rapid warming took place in the presence of the existing Early Eocene warm climate. Given that projected business-as-usual levels of atmospheric carbon dioxide reach concentrations of 800-1100 ppmv by 2100, it is of interest to study past climates where atmospheric carbon dioxide was higher than present. This is especially the case given the difficulty of climate models in simulating past warm climates. This study explores the sensitivity of the simulated pre-PETM and PETM periods to change in cloud condensation nuclei (CCN) and microphysical properties of liquid water clouds. Assuming lower levels of CCN for both of these periods leads to significant warming, especially at high latitudes. The study indicates that past differences in cloud properties may be an important factor in accurately simulating past warm climates. Importantly, additional shortwave warming from such a mechanism would imply lower required atmospheric CO2 concentrations for simulated surface temperatures to be in reasonable agreement with proxy data for the Eocene. PMID:24043867

  3. Crown Group Lejeuneaceae and Pleurocarpous Mosses in Early Eocene (Ypresian) Indian Amber.

    PubMed

    Heinrichs, Jochen; Scheben, Armin; Bechteler, Julia; Lee, Gaik Ee; Schäfer-Verwimp, Alfons; Hedenäs, Lars; Singh, Hukam; Pócs, Tamás; Nascimbene, Paul C; Peralta, Denilson F; Renner, Matt; Schmidt, Alexander R

    2016-01-01

    Cambay amber originates from the warmest period of the Eocene, which is also well known for the appearance of early angiosperm-dominated megathermal forests. The humid climate of these forests may have triggered the evolution of epiphytic lineages of bryophytes; however, early Eocene fossils of bryophytes are rare. Here, we present evidence for lejeuneoid liverworts and pleurocarpous mosses in Cambay amber. The preserved morphology of the moss fossil is inconclusive for a detailed taxonomic treatment. The liverwort fossil is, however, distinctive; its zig-zagged stems, suberect complicate-bilobed leaves, large leaf lobules, and small, deeply bifid underleaves suggest a member of Lejeuneaceae subtribe Lejeuneinae (Harpalejeunea, Lejeunea, Microlejeunea). We tested alternative classification possibilities by conducting divergence time estimates based on DNA sequence variation of Lejeuneinae using the age of the fossil for corresponding age constraints. Consideration of the fossil as a stem group member of Microlejeunea or Lejeunea resulted in an Eocene to Late Cretaceous age of the Lejeuneinae crown group. This reconstruction is in good accordance with published divergence time estimates generated without the newly presented fossil evidence. Balancing available evidence, we describe the liverwort fossil as the extinct species Microlejeunea nyiahae, representing the oldest crown group fossil of Lejeuneaceae. PMID:27244582

  4. Integrated stratigraphy of a shallow marine Paleocene-Eocene boundary section, MCBR cores, Maryland (USA)

    NASA Astrophysics Data System (ADS)

    Self-Trail, J. M.; Robinson, M. M.; Edwards, L. E.; Powars, D. S.; Wandless, G. A.; Willard, D. A.

    2013-12-01

    An exceptional Paleocene-Eocene boundary section occurs in a cluster of six short (<15m) coreholes (MCBR 1 through 6) drilled near Mattawoman Creek in western Charles County, Maryland. The sediments consist of glauconite-rich sand of the upper Paleocene Aquia Formation and silty clay of the lower Eocene Marlboro Clay. Sediment samples were analyzed for carbon and oxygen isotopes, percent calcium carbonate, calcareous nannofossils, planktic and benthic foraminifera, dinoflagellates, pollen, and lithology. A well-defined carbon isotope excursion (CIE) documents a gradual negative shift in δ13C values that starts below the lithologic break between the Aquia Formation and the Marlboro Clay. A benthic foraminifer extinction event, reduction of calcareous nannofossil assemblages, and change in core color from gray to alternating gray and pink also occurs within the CIE transition. These alternating changes in color coincide with cyclic peaks in the carbon isotope and percent calcium carbonate curves, where gray color corresponds to a positive shift in carbon isotope values and to a corresponding increase in percent benthic and planktic foraminifera. The upper third of the Marlboro Clay is barren of all calcareous microfossil material, although the presence of foraminiferal molds and linings proves that deposition occurred in a marine environment. Co-occurrence of the dinoflagellates Apectodinium augustum and Phthanoperidinium crenulatum at the top of the Marlboro Clay suggests that the Marlboro Clay at Mattawoman Creek is truncated. This is corroborated by the absence in the Marlboro of specimens of the calcareous nannofossil Rhomboaster-Discoaster assemblage, which is restricted to early Eocene Zone NP9b. Based on planktic/benthic foraminifera ratios, deposition of sediments at Mattawoman Creek occurred predominantly in an inner neritic environment, at water depths between 25-50 m. Occasional deepening to approximately 75m (middle neritic environment) occurred in the

  5. Refinement of Eocene lapse rates, fossil-leaf altimetry, and North American Cordilleran surface elevation estimates

    NASA Astrophysics Data System (ADS)

    Feng, Ran; Poulsen, Christopher J.

    2016-02-01

    Estimates of continental paleoelevation using proxy methods are essential for understanding the geodynamic, climatic, and geomorphoric evolution of ancient orogens. Fossil-leaf paleoaltimetry, one of the few quantitative proxy approaches, uses fossil-leaf traits to quantify differences in temperature or moist enthalpy between coeval coastal and inland sites along latitudes. These environmental differences are converted to elevation differences using their rates of change with elevation (lapse rate). Here, we evaluate the uncertainty associated with this method using the Eocene North American Cordillera as a case study. To do so, we develop a series of paleoclimate simulations for the Early (∼55-49 Ma) and Middle Eocene (49-40 Ma) period using a range of elevation scenarios for the western North American Cordillera. Simulated Eocene lapse rates over western North America are ∼5 °C/km and 9.8 kJ/km, close to moist adiabatic rates but significantly different from modern rates. Further, using linear lapse rates underestimates high-altitude (>3 km) temperature variability and loss of moist enthalpy induced by non-linear circulation changes in response to increasing surface elevation. Ignoring these changes leads to kilometer-scale biases in elevation estimates. In addition to these biases, we demonstrate that previous elevation estimates of the western Cordillera are affected by local climate variability at coastal fossil-leaf sites of up to ∼8 °C in temperature and ∼20 kJ in moist enthalpy, a factor which further contributes to elevation overestimates of ∼1 km for Early Eocene floras located in the Laramide foreland basins and underestimates of ∼1 km for late Middle Eocene floras in the southern Cordillera. We suggest a new approach for estimating past elevations by comparing proxy reconstructions directly with simulated distributions of temperature and moist enthalpy under a range of elevation scenarios. Using this method, we estimate mean elevations for

  6. Eocene seasonality and seawater alkaline earth reconstruction using shallow-dwelling large benthic foraminifera

    NASA Astrophysics Data System (ADS)

    Evans, David; Müller, Wolfgang; Oron, Shai; Renema, Willem

    2013-11-01

    Intra-test variability in Mg/Ca and other (trace) elements within large benthic foraminifera (LBF) of the family Nummulitidae have been investigated using laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). These foraminifera have a longevity and size facilitating seasonal proxy retrieval and a depth distribution similar to 'surface-dwelling' planktic foraminifera. Coupled with their abundance in climatically important periods such as the Paleogene, this means that this family of foraminifera are an important but under-utilised source of palaeoclimatic information. We have calibrated the relationship between Mg/Ca and temperature in modern Operculina ammonoides and observe a ˜2% increase in Mg/Ca °C-1. O. ammonoides is the nearest living relative of the abundant Eocene genus Nummulites, enabling us to reconstruct mid-Eocene tropical sea surface temperature seasonality by applying our calibration to fossil Nummulites djokdjokartae from Java. Our results indicate a 5-6 °C annual temperature range, implying greater than modern seasonality in the mid-Eocene (Bartonian). This is consistent with seasonal surface ocean cooling facilitated by enhanced Eocene tropical cyclone-induced upper ocean mixing, as suggested by recent modelling results. Analyses of fossil N. djokdjokartae and Operculina sp. from the same stratigraphic interval demonstrate that environmental controls on proxy distribution coefficients are the same for these two genera, within error. Using previously published test-seawater alkaline earth metal distribution coefficients derived from an LBF of the same family (Raitzsch et al., 2010) and inorganic calcite, with appropriate correction systematics for secular Mg/Casw variation (Evans and Müller, 2012), we use our fossil data to produce a more accurate foraminifera-based Mg/Casw reconstruction and an estimate of seawater Sr/Ca. We demonstrate that mid-Eocene Mg/Casw was ≲2 molmol, which is in contrast to the model most

  7. Water mass stability reconstructions from greenhouse (Eocene) to icehouse (Oligocene) for the northern Gulf Coast continental shelf (USA)

    NASA Astrophysics Data System (ADS)

    Kobashi, Takuro; Grossman, Ethan L.; Dockery, David T.; Ivany, Linda C.

    2004-03-01

    Shallow water mass characteristics such as temperature and density profile play a critical role in the climate system. We have developed a new method by which to reconstruct the ancient shallow water mass stability on the continental shelf using oxygen isotope variation within mollusc shells and fish otoliths and applied the method to an important interval in Earth history, the most recent transition from Greenhouse (Eocene) to Icehouse (Oligocene) climate modes. We define the slope of summer temperature (density) versus the seasonal range in temperature (density) as an indicator of water mass stability. In addition, extrapolation of the regression to zero seasonality is a proxy for temperature at the bottom of the seasonal thermocline (TBST). During the greenhouse world (the early Eocene and middle Eocene) the water mass plot shows an unstable water mass, agreeing with previous planktonic foraminiferal studies showing that temperature gradients at this time were much smaller than at present. During the middle to late Eocene transition, a substantial increase in water mass stability occurred. Significant cooling (˜5°C) of the TBST at this transition indicates that the greater cooling of deeper water relative to surface water caused the increase in water mass stability. The changes in water column structure at this transition were the most likely cause of a major extinction of planktonic foraminifera from warm to cold water taxa. The late Eocene T-ΔT profile is very similar to modern profiles, suggesting that shallow water mass structure became similar to that of the modern Gulf Coastal shelf by the late Eocene. At the Eocene/Oligocene (E/O) boundary, no major change in water mass structure is identified. This agrees with the observation that no major extinction of planktonic foraminifera is found at the E/O boundary.

  8. Remnants of the late Eocene erosion surface in the region between the Kaibab uplift and the Rio Grande rift

    SciTech Connect

    Ely, R.W. )

    1993-04-01

    A widespread low-relief erosion surface is thought to have formed in the Colorado Plateau region during the late Eocene between the end of the Laramide orogeny and the beginning of widespread Oligocene volcanism. The present configuration of the late-Eocene surface (LES) is depicted on east-west cross sections that extend from the Kaibab uplift to the Rio Grande rift. The LES is best preserved underneath the Oligocene Chuska Sandstone on the Defiance uplift at about 8,000 ft. MSL. The Chuska is an aeolian arkose that contains rhyolitic ash beds, and was eroded to hilly surface by 30 my ago prior to eruption of the Navajo volcanic field. To the north, the Paleocene Carrizo Mtns. intrusive appear to have been an isolated upland that stood above surrounding plains during the late Eocene. To the west, the north rim of Black Mesa is close to the elevation of the LES on the Defiance Plateau. Siliceous lag-gravels on the rim of Black Mesa may have been derived from sediments originally deposited on the LES. Farther west the Kaibab uplift rises above 9,000 ft. MSL for 14 miles along its crest. The Kaibab uplift probably was a karst plateau that stood above alluviated late Eocene lowlands to the east, north and west. East of the Defiance Plateau, the early Eocene San Jose Formation of the San Juan basin is preserved at elevations as high as 7,500 ft. under the eastern part of the basin, and as high as 8,450 ft. along the deformed eastern flank of the basin. Several thousand feet of middle Eocene deposits probably were once present in the basin. Several thousand feet of middle Eocene deposits probably were once present in the basin, putting the LES at about 9,000--10,000 ft MSL along the eastern side.

  9. POST-Eocene subsidence of the Marshall Islands recorded by drowned atolls on Harrie and Sylvania guyots

    NASA Astrophysics Data System (ADS)

    Schlanger, S. O.; Campbell, J. F.; Jackson, M. W.

    Geophysical and geological surveys of Harrie and Sylvania Guyots in the northern Marshall Islands show that both of these volcanic edifices are capped by drowned atolls of Early Eocene age. The volcanic eruptions that formed both of these guyots were apparently coeval with the eruptions that formed the volcanic edifice below Enewetak Atoll. These Eocene eruptions took place in an off-ridge setting in a region that had experienced a complex history of Cretaceous mid-plate volcanism. Present depths to the tops of these drowned Eocene atolls are 1520 m at Harrie and 1480 m at Sylvania which, taken together with the coeval subsidence of Enewetak atoll of ˜1300-1400 m and the post-Late Cretaceous subsidence of the Nauru Basin of ˜1600 m, show that this region has subsided rapidly, as a unit, atop a thermally rejuvenated lithosphere of Middle Jurassic age. The Eocene atolls on Harrie and Sylvania Guyots drowned during a rapid sea level rise ˜49 Ma that followed a period of relatively high sea levels in Early Eocene time.

  10. Climatic and stratigraphic implications of clay mineral changes in Paleocene/Eocene boundary strata -- Eastern United States

    SciTech Connect

    Gibson, T.G.; Bybell, L.M.; Owens, J.P.; Mason, D.B.; McCartan, L.; Snow, J.N. )

    1994-03-01

    A major change in the clay mineral suite from predominantly illite/smectite and illite to predominantly kaolinite is present in uppermost Paleocene neritic deposits in the Salisbury embayment of the northeastern US. The clay mineral change occurred during a time of relatively high sea level and is associated with biotic, climatic, and oceanographic changes. This kaolinite increase in middle-latitude areas of the western North Atlantic Ocean, and similar increases in coeval deep-marine sediments off Antarctica and in the eastern North Atlantic Ocean, suggests that intensified weathering due to increased temperature and precipitation was widespread in the latest Paleocene. In the Salisbury embayment, kaolinite proportions rapidly increase from less than 5% in upper Paleocene strata to maximum values of 50 to 60% near the top of the Paleocene (top of calcareous nannofossil Zone NP 9). High kaolinite proportions continue into the lowest Eocene strata (lowermost zone NP 10), but the kaolinite proportion rapidly decreases to 5% or less within the lower part of Zone NP 10. The pattern of kaolinite increasing to maximum values in the latest Paleocene, followed by decreasing values in the earliest Eocene can be used for correlation within the upper Paleocene and lower Eocene units in the Salisbury embayment. On this basis, it is suggested that during the early Eocene, large parts of the uppermost Paleocene and lowermost Eocene clay were eroded from landward parts of the basin.

  11. Nummulite biostratigraphy of the Eocene succession in the Bahariya Depression, Egypt: Implications for timing of iron mineralization

    NASA Astrophysics Data System (ADS)

    Afify, A. M.; Serra-Kiel, J.; Sanz-Montero, M. E.; Calvo, J. P.; Sallam, E. S.

    2016-08-01

    In the northern part of the Bahariya Depression (Western Desert, Egypt) the Eocene carbonate succession, unconformably overlying the Cretaceous deposits, consists of three main stratigraphic units; the Naqb, Qazzun and El Hamra formations. The Eocene carbonates are relevant as they locally host a large economic iron mineralization. This work revises the stratigraphic attribution of the Eocene formations on the basis of larger benthic foraminifers from both carbonate and ironstone beds. Eight Nummulites species spanning the late Ypresian - early Bartonian (SBZ12 to SBZ17) were identified, thus refining the chronostratigraphic framework of the Eocene in that region of Central Egypt. Moreover, additional sedimentological insight of the Eocene carbonate rocks is presented. The carbonate deposits mainly represent shallow marine facies characteristic of inner to mid ramp settings; though deposits interpreted as intertidal to supratidal are locally recognized. Dating of Nummulites assemblages from the youngest ironstone beds in the mines as early Bartonian provides crucial information on the timing of the hydrothermal and meteoric water processes resulting in the formation of the iron ore mineralization. The new data strongly support a post-depositional, structurally-controlled formation model for the ironstone mineralization of the Bahariya Depression.

  12. Paleomagnetism of Eocene Intrusive Rocks, Black Hills of South Dakota and Wyoming

    NASA Astrophysics Data System (ADS)

    Housen, B. A.; Fawcett, T. C.; Gregiore, P.

    2003-12-01

    The Black Hills of South Dakota and Wyoming are a large Precambrian-cored Laramide uplift. Intruding the Black Hills are a diverse suite of igneous rocks, which include phonolites, trachytes, latites, garnet-bearing rhyolites, and pyroxenites. These intrusive bodies range in size from several meter outcrop-scale bodies, to several 10s of km wide intrusive complexes. New geochronology (40Ar-39Ar) data indicate many of these intrusive rocks are between 58 and 45 Ma in age (Duke at al, 2002). As part of a larger paleomagnetic study aimed at Jurassic strata surrounding the Black Hills, a collection of 20 sites and 145 samples of the Eocene intrusive rocks was made. A combination of alternating field, thermal, and liquid nitrogen step-wise demagnetization revealed that, with a few exceptions, these rocks have two well-defined magnetization components. The first-removed component is interpreted to be a present (dipole) field magnetization, and is removed by 10 to 30 mT a.f., or 200 C thermal demagnetization steps. The second-removed components have either positive or negative inclinations, and are defined by demagnetization steps between 30 and 200 mT a.f., or 300 to 630 C thermal demagnetization steps. These components are interpreted to be ancient, presumably Eocene, magnetizations. A preliminary mean of the normal-polarity sites is D=352, I=59.3, k=26.7, a95=18.2, N=4, and of the reverse-polarity sites is D=154.9, I=-61.3, k=23.1, a95=18.2, N=4. The combined mean direction is D=344.9, I=60.3, k=28.8, a95=10.5, N=8. Two sites of rhyolites at Mt. Theodore Roosevelt have well-defined magnetization components, but either mixed polarity (Site 99Trr1), or reverse-polarity with what might be a transitional-field direction (D=27.7, I=-37.4, k=18.0, a95=18.6, n=5), and are not included in the calculation of means. The magnetizations recorded by these Eocene rocks are essentially identical to the expected direction for the Black Hills calculated from the Diehl et al., 1983

  13. Metasequoia glyptostroboides and its Utility in Paleoecological Reconstruction of Eocene High Latitude Forests

    NASA Astrophysics Data System (ADS)

    Williams, C. J.; LePage, B. A.; Vann, D. R.; Johnson, A. H.

    2001-05-01

    Abundant fossil plant remains are preserved in the Eocene-aged deposits of the Buchanan Lake formation on Axel Heiberg Island, Nunavut, Canada. Intact leaf litter, logs, and stumps preserved in situ as mummified remains present an opportunity to determine forest composition, structure, and productivity of a Taxodiaceae-dominated forest that once grew north of the Arctic Circle (paleolatitude 75-80° N). We excavated 37 tree stems for dimensional analysis from mudstone and channel-sand deposits. Stem length ranged from 1.0 m to 14.8 m (average = 3.2 m). Stem diameter ranged from less than 10 cm to greater than 75 cm (average = 32.2 cm). All stem wood was tentatively identified to genus as Metasequoia sp. The diameters and parabolic shape of the preserved tree trunks indicate that the Metasequoia were about 39 m tall across a wide range of diameters. The allometric relationships we derived for modern Metasequoia (n=70) allowed independent predictions of Metasequoia height given the stand density and stump diameters of the fossil forest. The two height estimates of 40 and 40.5 m match the results obtained from measurements of the Eocene trees. We used stump diameter data (n =107, diameter > 20 cm) and an uniform canopy height of 39 m to calculate parabolic stem volume and stem biomass for a 0.22 ha area of fossil forest. Stem volume equaled 2065 m3 ha-1 and stem biomass equaled 560 Mg ha-1 . In the Eocene forest, as determined from length of stems that were free of protruding branches and from 7 exhumed tree tops, the uppermost 9 m of the trees carried live branches with foliage. In living conifers, branch weights and the amount of foliage carried by branches are well correlated with branch diameters measured where the branch joins the main stem. To determine the biomass in branches and foliage in the Eocene forest, we used relationships derived from large modern Metasequoia. Based on the regression of branch weight v. branch diameter (r2 = 0.97) and foliar biomass v

  14. Late Eocene sea surface cooling of the western North Atlantic (ODP Site 647A)

    NASA Astrophysics Data System (ADS)

    Sliwinska, Kasia K.; Coxall, Helen K.; Schouten, Stefan

    2016-04-01

    The initial shift out of the early Cenozoic greenhouse and into a glacial icehouse climate occurred during the middle to late Eocene and culminated in the abrupt growth of a continental-scale ice cap on Antarctica, during an episode known as the Oligocene Isotope Event 1 (Oi-1) ˜33.7 Ma. Documenting the patterns of global and regional cooling prior to Oi-1 is crucial for understanding the driving force and feedback behind the switch in climate mode. Well-dated high-resolution temperature records, however, remain sparse and the climatic response in some of the most climatically sensitive regions of the Earth, including the high latitude North Atlantic (NA), where today large amounts of ocean heat are exchanged, are poorly known. Here we present a sea surface palaeotemperature record from the late Eocene to the early Oligocene (32.5 Ma to 35 Ma) of ODP Hole 647A based on archaeal tetraether lipids (TEX86H). The site is located in the western North Atlantic (Southern Labrador Sea) and is the most northerly located (53° N) open ocean site with a complete Eocene-Oligocene sequence which yields both calcareous and organic microfossils suitable for detailed proxy reconstructions. Our record agrees with the magnitude of temperature decrease (˜3 ° C sea surface cooling) recorded by alkenones and pollen data from the Greenland Sea, but our higher resolution study reveals that the high latitude NA cooling step occurred about 500 kyrs prior to the Oi-1 Antarctic glaciation, at around ˜34.4 Ma. This cooling can be explained by regional effects related to local NA tectonics including ocean gateways, known to have changed at the time, with potential to effect NA overturning circulation due to adjustments in the thermohaline density balance. Alternatively, the cooling itself may be due to changes in NA circulation, suggesting that global ocean circulation played a role in pre-conditioning the Earth for Antarctic glaciation.

  15. Summer Temperatures of Late Eocene to Early Oligocene Freshwaters: a Multi-proxy Approach

    NASA Astrophysics Data System (ADS)

    David, M. P.; Grimes, S. T.; Hooker, J. J.; Collinson, M.

    2004-12-01

    We report northern hemisphere summer palaeotemperatures derived from multiple palaeoproxies from the Hamphire Basin Eocene-Oligocene succession. Continental freshwater \\delta18O values have been determined at six horizons spanning a 3 ma interval across the Eocene-Oligocene boundary from large sets of analyses of rodent tooth enamel phosphate. Surface water \\delta18O values permit use of associated carbonate and phosphate thermometers (gastropods, charophyte gyrogonites and fish otoliths) to bracket either the mean summer growing season temperature (gastropods), the mean temperature of the warmest months of the growing season (fish otoliths) and the mean temperature of a single month in the latter part of the growing season (charophtyte gyrogonites). We argue that calculated temperatures, which range from 26\\deg C to 37\\deg C are independent of freshwater evaporation effects and of variations in initial seawater \\delta18O that may be modified by distal changes in ice volume. The time averaged mean palaeotemperatures for each fossil horizon are generally indicative of warm mesothermal conditions. However, the large standard deviations on each of the summer season palaeotemperatures suggest climate perturbations during these times and/or that the period of mineralization of the rodent teeth encompasses some seasonal variation. This succession is a key interval where the positive \\delta18O shift in the early Oligocene marine foraminiferal isotope record identifies the onset of the Antarctic Oi-1 glaciation. The data suggest there was no significant summer temperature fall across the Oi-1 glaciation itself. This result is concordant with several other recent studies in suggesting that the majority of the isotopic shift in the marine realm across the Oi-1 glaciation is linked to ice volume, not temperature change. Our new approach has allowed us to put numerical values on summer season temperatures as well as to reconstruct relative temperature change across this

  16. Paleolimnology of Lake Tubutulik, an iron-meromictic Eocene Lake, eastern Seward Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    Dickinson, Kendell A.

    1988-01-01

    Sideritic lacustrine mudstone was found in drill core from a uranium deposit in the Death Valley area in the eastern part of the Seward Peninsula, Alaska. The precursor sediments for this rock were deposited in an unusual "iron-meromictic" Eocene lake, herein named Lake Tubutulik, which occupied part of the Boulder Creek basin, a structural graben that is probably a southern extension of the larger Death Valley basin. The Boulder Creek basin is bounded on the west by granite of the Late Cretaceous Darby Pluton, on the east by Precambrian to Paleozoic metasedimentary rocks. The lake basin was formed by basaltic flows that dammed the river valley of the ancestral Tubutulik River in early Eocene time. Lake Tubutulik contained a nearshore facies of fine-grained organic mud and an offshore facies of laminated sideritic mud. The offshore (profundal) laminated mudstone consists of alternating layers of authigenic siderite and detrital layers containing mostly quartz and clay minerals. Both lacustrine facies contain turbidities. The lacustrine sediments graded laterally into an onshore facies of colluvial and fluvial sandstone, paludal mudstone, and coal. The ancient lake apparently occupied a small deep basin in a tectonically active area of high relief. Meromixus was probably stabilized by reduced iron and bicarbonate dissolved in the monimolimnion. The intensity of meromixus decreased as the lake became shallower from sediment filling. The source of the iron, abundant in the monimolimnion of Lake Tubutulik, was probably the Eocene basalt. Based on carbon isotope analysis of the siderite, the dissolved bicarbonate in the profundal facies was largely inorganic. Sideritic carbon in one sample from the onshore paludal facies has an isotopic signature ( δ13C = +16.9) consistent with residual carbon formed during methanogenic fermentation.

  17. Iberian-Europe convergence: evolution of the Cretaceous and Eocene basins in Pyrenees and Provence

    SciTech Connect

    Muller, J.; Ducassel, L.; Guieu, G.; Razin, P.; Rochet, J.; Roussel, J.; Velasque, P.C.; Villeneuve, M. )

    1988-08-01

    During Cretaceous time the geodynamic evolution of Northern and Western Pyrenean basins was related to scissors-shaped rifting which evolved as a passive margin filled by thick flysch deposits. In Provence, the carbonate platform was marked since the late Albian by the arrival of significant detrital flows originated from an uplifted Paleozoic block situated in the Gulf of Lion. In Provence the northward migration of the basin from Cenomanian to Eocene and Oligocene indicates the growing of the Gulf of Lion-South Provence crustal uplift and its northward displacement. The Cretaceous opening of the western Pyrenean, Parentis, and Bay of Biscay basins is synchronous with the first stages of compression in the Gulf of Lion. These features are induced by the rotation of Iberia. During the Eocene the compression, resulting from the Iberian-Europe convergence, affected nearly the whole Pyrenean-Provencal area. In the southern part of the Pyrenees east of the Pamplona fault, the successive dislocations of carbonate platforms, migration of reefs, and filling of foreland basins became the signature of the intracontinental subduction of Iberia. The transform fault pattern, still well preserved in spite of the Eocene compression, prevents any important strike-slip movement between Europe and Iberia, especially along the so-called North Pyrenean fault zone, which shows several discontinuities in the western part of Pyrenees. The final evolution of Gulf of Lion crustal uplift generated a gliding of its cover (Provence overthrusts) and, during Oligocene, the opening of the Ligurian-Provencal basin by a propagating rift process.

  18. Modifications in calcareous nannofossil assemblages during the Early Eocene: a tethyan perspective.

    NASA Astrophysics Data System (ADS)

    Agnini, Claudia; Rio, Domenico; Dallanave, Edoardo; Spofforth, David J. A.; Muttoni, Giovanni; Pälike, Heiko

    2010-05-01

    The available oxygen isotope records indicate a long-term warming trend from the late Paleocene through the early Eocene (ca. 59-52 Ma) that peaked at the Early Eocene Climatic Optimum (EECO) (Zachos et al., 2001). This trend was interrupted by at least two or more prominent carbon cycle perturbations, the PETM at ca. 55.5 Ma and the Eocene thermal maximum 2 (ETM2; also referred to as Elmo, H-1) at ca. 53,6 Ma (Kennett and Stott, 1991; Lourens et al., 2005). Here we present calcareous nannofossil data from the hemipelagic Cicogna section located in the Piave River Valley in north eastern Italy (Dallanave et al., 2009). This continuous sedimentary record was studied to reconstruct the main features in the calcareous nannoplankton communities during this critical interval. As is clearly shown by the results, some of the observed prominent modifications are related to short-lived phases of climate perturbation, as for instance the transient and abrupt appearance of odd species during the PETM or the prominent variations in the relative abundance within the assemblages during these events. These short-term changes are usually transitory and calcareous nannoplankton seem to be able to return back to pre-event state. Nonetheless, the overall shape of calcareous nannofossil assemblages showed long lasting or gradual changes, for example the extinction of genera Fasciculithus and Prinsius, the explosion of Zyghrablithus bijugatus and the gradual decrease of heterococcoliths/nannoliths ratio. Either transient or permanent modifications in calcareous nannofossils are associated to dramatic perturbation of paleoenviromental conditions or long trend climate evolution, respectively. References: Dallanave et al., 2009. Earth and Planetary Science Letters, 285, 39-51. Kennett and Stott, 1991. Nature, 353, 225-229. Lourens et al., 2005. Nature, 235, 1083-1087. Zachos et al., 2001. Science, 292, 686-693.

  19. New fauna of archaeocete whales (Mammalia, Cetacea) from the Bartonian middle Eocene of southern Morocco

    NASA Astrophysics Data System (ADS)

    Gingerich, Philip D.; Zouhri, Samir

    2015-11-01

    Six genera and species of archaic whales are present in a new fauna from the Aridal Formation at Gueran in the Sahara Desert of southwestern Morocco. Three of the archaeocete species represent semiaquatic Protocetidae and three species are fully aquatic Basilosauridae. Protocetids are characteristic of Lutetian lower middle Eocene strata, and basilosaurids are characteristic of Priabonian late Eocene beds. Similar representation of both families is restricted to intervening Bartonian strata and indicative of a late middle Eocene age. Archaeocetes from Gueran include (1) a small protocetid represented by a partial humerus, teeth, and vertebrae; (2) a middle-sized protocetid represented by a partial innominate and proximal femur; (3) the very large protocetid Pappocetus lugardi represented by teeth, a partial innominate, and two partial femora; (4) a new species of the small basilosaurid Chrysocetus represented by a dentary, teeth, humeri, and many vertebrae; (5) a new species of the larger basilosaurid Platyosphys (resurrected as a distinct genus) represented by a partial braincase, tympanic bulla, and many vertebrae; and (6) the large basilosaurid Eocetus schweinfurthi represented by teeth, a tympanic bulla, and lumbar vertebrae. The Gueran locality is important geologically because it constrains the age of a part of the Aridal Formation, and biologically because it includes a diversity of archaic whales represented by partial skeletons with vertebrae in sequence and by forelimb and hind limb remains. With further collecting, Gueran archaeocete skeletons promise to clarify the important evolutionary transition from foot-powered swimming in Protocetidae to the tail-powered swimming of Basilosauridae and all later Cetacea.

  20. Revised East-West Antarctic plate motions since the Middle Eocene

    NASA Astrophysics Data System (ADS)

    Granot, R.; Cande, S. C.; Stock, J.; Damaske, D.

    2010-12-01

    The middle Cenozoic (43-26 Ma) rifting between East and West Antarctica is defined by an episode of ultraslow seafloor spreading in the Adare Basin, located off northwestern Ross Sea. The absence of fracture zones and the lack of sufficient well-located magnetic anomaly picks have resulted in a poorly constrained kinematic model (Cande et al., 2000). Here we utilize the results from a dense aeromagnetic survey (Damaske et al., 2007) collected as part of GANOVEX IX 2005/06 campaign to re-evaluate the kinematics of the West Antarctic rift system since the Middle Eocene. We identify marine magnetic anomalies (anomalies 12o, 13o, 16y, and 18o) along a total of 25,000 km of the GPS navigated magnetic profiles. The continuation of these anomalies into the Northern Basin has allowed us to use the entire N-S length of this dataset in our calculations. A distinct curvature in the orientation of the spreading axis provides a strong constraint on our calculated kinematic models. The results from two- (East-West Antarctica) and three- (Australia-East Antarctica-West Antarctica) plate solutions agree well and create a cluster of rotation axes located south of the rift system, near the South Pole. These solutions reveal that spreading rate and direction, and therefore motion between East and West Antarctica, were steady between the Middle Eocene and Early Oligocene. Our kinematic solutions confirm the results of Davey and De Santis (2005) that the Victoria Land Basin has accommodated ~95 km of extension since the Middle Eocene. This magnetic pattern also provides valuable constraints on the post-spreading deformation of the Adare Basin (Granot et al., 2010). The Adare Basin has accommodated very little extension since the Late Oligocene (<7 km), but motion has probably increased southward. The details of this younger phase of motion are still crudely constrained.

  1. Paleolimnology of Lake Tubutulik, an iron-meromictic Eocene Lake, eastern Seward Peninsula, Alaska

    USGS Publications Warehouse

    Dickinson, K.A.

    1988-01-01

    Sideritic lacustrine mudstone was found in drill core from a uranium deposit in the Death Valley area in the eastern part of the Seward Peninsula, Alaska. The precursor sediments for this rock were deposited in an unusual "iron-meromictic" Eocene lake, herein named Lake Tubutulik, which occupied part of the Boulder Creek basin, a structural graben that is probably a southern extension of the larger Death Valley basin. The Boulder Creek basin is bounded on the west by granite of the Late Cretaceous Darby Pluton, on the east by Precambrian to Paleozoic metasedimentary rocks. The lake basin was formed by basaltic flows that dammed the river valley of the ancestral Tubutulik River in early Eocene time. Lake Tubutulik contained a nearshore facies of fine-grained organic mud and an offshore facies of laminated sideritic mud. The offshore (profundal) laminated mudstone consists of alternating layers of authigenic siderite and detrital layers containing mostly quartz and clay minerals. Both lacustrine facies contain turbidities. The lacustrine sediments graded laterally into an onshore facies of colluvial and fluvial sandstone, paludal mudstone, and coal. The ancient lake apparently occupied a small deep basin in a tectonically active area of high relief. Meromixus was probably stabilized by reduced iron and bicarbonate dissolved in the monimolimnion. The intensity of meromixus decreased as the lake became shallower from sediment filling. The source of the iron, abundant in the monimolimnion of Lake Tubutulik, was probably the Eocene basalt. Based on carbon isotope analysis of the siderite, the dissolved bicarbonate in the profundal facies was largely inorganic. Sideritic carbon in one sample from the onshore paludal facies has an isotopic signature (??13C = +16.9) consistent with residual carbon formed during methanogenic fermentation. ?? 1988.

  2. Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology

    PubMed Central

    Franzen, Jens L.; Gingerich, Philip D.; Habersetzer, Jörg; Hurum, Jørn H.; von Koenigswald, Wighart; Smith, B. Holly

    2009-01-01

    Background The best European locality for complete Eocene mammal skeletons is Grube Messel, near Darmstadt, Germany. Although the site was surrounded by a para-tropical rain forest in the Eocene, primates are remarkably rare there, and only eight fragmentary specimens were known until now. Messel has now yielded a full primate skeleton. The specimen has an unusual history: it was privately collected and sold in two parts, with only the lesser part previously known. The second part, which has just come to light, shows the skeleton to be the most complete primate known in the fossil record. Methodology/Principal Findings We describe the morphology and investigate the paleobiology of the skeleton. The specimen is described as Darwinius masillae n.gen. n.sp. belonging to the Cercamoniinae. Because the skeleton is lightly crushed and bones cannot be handled individually, imaging studies are of particular importance. Skull radiography shows a host of teeth developing within the juvenile face. Investigation of growth and proportion suggest that the individual was a weaned and independent-feeding female that died in her first year of life, and might have attained a body weight of 650–900 g had she lived to adulthood. She was an agile, nail-bearing, generalized arboreal quadruped living above the floor of the Messel rain forest. Conclusions/Significance Darwinius masillae represents the most complete fossil primate ever found, including both skeleton, soft body outline and contents of the digestive tract. Study of all these features allows a fairly complete reconstruction of life history, locomotion, and diet. Any future study of Eocene-Oligocene primates should benefit from information preserved in the Darwinius holotype. Of particular importance to phylogenetic studies, the absence of a toilet claw and a toothcomb demonstrates that Darwinius masillae is not simply a fossil lemur, but part of a larger group of primates, Adapoidea, representative of the early haplorhine

  3. Eocene climate and Arctic paleobathymetry: A tectonic sensitivity study using GISS ModelE-R

    NASA Astrophysics Data System (ADS)

    Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

    2009-12-01

    The early Paleogene (65-45 million years ago, Ma) was a ‘greenhouse’ interval with global temperatures warmer than any other time in the last 65 Ma. This period was characterized by high levels of CO2, warm high-latitudes, warm surface-and-deep oceans, and an intensified hydrological cycle. Sediments from the Arctic suggest that the Eocene surface Arctic Ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions remain uncertain. We present equilibrium climate conditions derived from a fully-coupled, water-isotope enabled, general circulation model (GISS ModelE-R) configured for the early Eocene. We also present model-data comparison plots for key climatic variables (SST and δ18O) and analyses of the leading modes of variability in the tropical Pacific and North Atlantic regions. Our tectonic sensitivity study indicates that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the seaways connecting the Arctic to the Atlantic and Tethys. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~6 psu and warming of sea-surface temperatures by 2°C in the North Atlantic and 5-10°C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We also suggest that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates in the Atlantic.

  4. Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene-Oligocene transition.

    PubMed

    Kennedy, A T; Farnsworth, A; Lunt, D J; Lear, C H; Markwick, P J

    2015-11-13

    The glaciation of Antarctica at the Eocene-Oligocene transition (approx. 34 million years ago) was a major shift in the Earth's climate system, but the mechanisms that caused the glaciation, and its effects, remain highly debated. A number of recent studies have used coupled atmosphere-ocean climate models to assess the climatic effects of Antarctic glacial inception, with often contrasting results. Here, using the HadCM3L model, we show that the global atmosphere and ocean response to growth of the Antarctic ice sheet is sensitive to subtle variations in palaeogeography, using two reconstructions representing Eocene and Oligocene geological stages. The earlier stage (Eocene; Priabonian), which has a relatively constricted Tasman Seaway, shows a major increase in sea surface temperature over the Pacific sector of the Southern Ocean in response to the ice sheet. This response does not occur for the later stage (Oligocene; Rupelian), which has a more open Tasman Seaway. This difference in temperature response is attributed to reorganization of ocean currents between the stages. Following ice sheet expansion in the earlier stage, the large Ross Sea gyre circulation decreases in size. Stronger zonal flow through the Tasman Seaway allows salinities to increase in the Ross Sea, deep-water formation initiates and multiple feedbacks then occur amplifying the temperature response. This is potentially a model-dependent result, but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography, and highlights the need for coupled ice sheet-climate simulations to properly represent and investigate feedback processes acting on these time scales. PMID:26438285

  5. Ironstone deposits hosted in Eocene carbonates from Bahariya (Egypt)-New perspective on cherty ironstone occurrences

    NASA Astrophysics Data System (ADS)

    Afify, A. M.; Sanz-Montero, M. E.; Calvo, J. P.

    2015-11-01

    This paper gives new insight into the genesis of cherty ironstone deposits. The research was centered on well-exposed, unique cherty ironstone mineralization associated with Eocene carbonates from the northern part of the Bahariya Depression (Egypt). The economically important ironstones occur in the Naqb Formation (Early Eocene), which is mainly formed of shallow marine carbonate deposits. Periods of lowstand sea-level caused extensive early dissolution (karstification) of the depositional carbonates and dolomitization associated with mixing zones of fresh and marine pore-water. In faulted areas, the Eocene carbonate deposits were transformed into cherty ironstone with preservation of the precursor carbonate sedimentary features, i.e. skeletal and non-skeletal grain types, thickness, bedding, lateral and vertical sequential arrangement, and karst profiles. The ore deposits are composed of iron oxyhydroxides, mainly hematite and goethite, chert in the form of micro- to macro-quartz and chalcedony, various manganese minerals, barite, and a number of subordinate sulfate and clay minerals. Detailed petrographic analysis shows that quartz and iron oxides were coetaneous and selectively replaced carbonates, the coarse dolomite crystals having been preferentially transformed into quartz whereas the micro-crystalline carbonates were replaced by the iron oxyhydroxides. A number of petrographic, sedimentological and structural features including the presence of hydrothermal-mediated minerals (e.g., jacobsite), the geochemistry of the ore minerals as well as the structure-controlled location of the mineralization suggest a hydrothermal source for the ore-bearing fluids circulating through major faults and reflect their proximity to centers of magmatism. The proposed formation model can contribute to better understanding of the genetic mechanisms of formation of banded iron formations (BIFs) that were abundant during the Precambrian.

  6. Magnetic microspherules associated with the K/T and upper Eocene extinction events

    NASA Technical Reports Server (NTRS)

    Cisowski, Stanley M.

    1988-01-01

    Magnetic microspherules were identified in over 20 K/T boundary sites, and in numerous Deep Sea Drilling Project (DSDP) cores from the Caribbean and Pacific, synchronous with the extinction of several radiolarian species near the end of the Eocene. The K/T magnetic spherules are of particular interest as carriers of Ir and other siderophiles generally found in abundance in K/T boundary clay. Furthermore the textures and unusual chemistry of their component magnetic phases indicate an origin at high temperature, possibly related to (an) unusual event(s) marking the end of the Cretaceous and Eocene periods. Their origin, along with the non-magnetic (sanidine) spheules, is generally ascribed directly to megaimpact events hypothesized to have periodically disrupted life on Earth. A survey of microspherical forms associated with known meteorite and impact derived materials reveals fundamental differences from the extinction related spherules. Low temperature magnetic experiments on the K/T and Upper Eocene spheroids indicate that, unlike tektites, extremely small superparamagnetic carriers are not present in abundance. The extensive subaerial exposure of Cretaceous combustible black shale during sea level regression in the latest Cretaceous represents a potential source for the magnetic spheroids found in certain K/T boundary clays. The recent discovery of high Ir abundances distributed above and below the K/T boundary within shallow water sediments in Israel, which also contain the most extensive known zones of combustion metamorphism, the so called Mottled Zone, adds a further dramatic footnote to the proposed association between the magnetic spheroids and combustion of organic shales. Interestingly, the Mottled Zone also contains the rare mineral magnesioferrite, which was identified both within the K/T magnetic spheroids and as discrete crystals in boundary clay from marine and continental sites.

  7. Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene-Oligocene transition.

    PubMed

    Kennedy, A T; Farnsworth, A; Lunt, D J; Lear, C H; Markwick, P J

    2015-11-13

    The glaciation of Antarctica at the Eocene-Oligocene transition (approx. 34 million years ago) was a major shift in the Earth's climate system, but the mechanisms that caused the glaciation, and its effects, remain highly debated. A number of recent studies have used coupled atmosphere-ocean climate models to assess the climatic effects of Antarctic glacial inception, with often contrasting results. Here, using the HadCM3L model, we show that the global atmosphere and ocean response to growth of the Antarctic ice sheet is sensitive to subtle variations in palaeogeography, using two reconstructions representing Eocene and Oligocene geological stages. The earlier stage (Eocene; Priabonian), which has a relatively constricted Tasman Seaway, shows a major increase in sea surface temperature over the Pacific sector of the Southern Ocean in response to the ice sheet. This response does not occur for the later stage (Oligocene; Rupelian), which has a more open Tasman Seaway. This difference in temperature response is attributed to reorganization of ocean currents between the stages. Following ice sheet expansion in the earlier stage, the large Ross Sea gyre circulation decreases in size. Stronger zonal flow through the Tasman Seaway allows salinities to increase in the Ross Sea, deep-water formation initiates and multiple feedbacks then occur amplifying the temperature response. This is potentially a model-dependent result, but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography, and highlights the need for coupled ice sheet-climate simulations to properly represent and investigate feedback processes acting on these time scales.

  8. Paleoenvironmental setting and description of an estuarine oyster reef in the Eocene of Patagonia, southern Argentina

    NASA Astrophysics Data System (ADS)

    Raising, Martín Rodríguez; Casadío, Silvio; Pearson, Nadine; Mángano, Gabriela; Buatois, Luis; Griffin, Miguel

    2014-12-01

    A middle Eocene Crassostrea sp. reef near Río Turbio, southwestern Patagonia (Argentina), represents the earliest record of an oyster reef associated with estuarine facies in the southern hemisphere, and also one of the few known worldwide occurring in Paleogene rocks. The reef grew in an outer estuary environment subject to periodic changes in salinity and may have reached a maturing phase. The Río Turbio reef - by its dimensions, geometry, and substrate lithology- would have been located in a tidal channel convergence area. This reef provides new evidence suggesting that estuaries served as refuges for Crassostrea populations allowing them to disperse into fully marine environments many times throughout the Cenozoic.

  9. Systematic catalogue of vertebrata of the Eocene of New Mexico, collected in 1874

    USGS Publications Warehouse

    Wheeler, George Montague; Cope, E.D.

    1875-01-01

    The present essay completes the determination of the species of vertebrata obtained by the geographical survey under your charge in the Eocene formation of New Mexico during the field-season of 1874. The descriptions which have already appeared in your [George M. Wheeler] report to the Chief of Engineers, as published in the annual report of the latter for 1874, are not now repeated. The total number of mammalia is forty-seven species, of which the present report introduces twenty-four for the first time.

  10. Sedimentology and depositional environments of middle Eocene terrigenous-carbonate strata, southeastern atlantic coastal plain, USA

    NASA Astrophysics Data System (ADS)

    Harris, Mary K.; Thayer, Paul A.; Amidon, Mark B.

    1997-02-01

    Basin-margin sediments of middle Eocene age in the Savannah River Site area consist of five terrigenous-carbonate lithofacies: quartz sand; calcareous quartz sand; sandy carbonate; muddy carbonate; and a transitional lithofacies that ranges from sandy, muddy carbonate to calcareous mud. The middle Eocene sediment package, which includes calcareous parts of the upper Congaree, Warley Hill, and Santee Formations, dips southeast at 4.7 m/km and thickens from 2 m at its updip edge to 95 m downdip. The presence of glauconite and a diverse faunal assemblage in all lithofacies suggests deposition in clear, well-oxygenated, open-marine waters of normal salinity on the inner to middle shelf with periods of marginal marine, nearshore, and deltaic influence. Coarse-grained terrigenous sand and calcareous sand, deposited in higher-energy, nearshore environments, occur near the updip limit. Fine-grained terrigenous mud, calcareous mud, and sandy and muddy carbonate are located downdip and accumulated in quieter water conditions on the inner and middle shelf. The transition from terrigenous to carbonate sediment occurs near the updip limit in a narrow zone less than 5 km wide. Three depositional sequences, which contain transgressive and highstand system tracts, are recognized within the middle Eocene calcareous interval. One is assigned to the upper Congaree Formation ( TA{3.5}/{3.6}cycles). The main control on areal distribution Hill Formation (TA3.4 cycle), and one to the Santee Formation ( TA{3.5}/{3.6}cycles). The main control on areal distribution of facies was depositional environment, which was controlled primarily by sea-level eustasy and the amount, rate and locus of terrigenous influx. In updip areas, however, sediment distribution and thickness were also influenced by middle Eocene growth faulting. Diagenetic pathways vary with facies type, but generally include: (1) marine phreatic — boring of skeletal fragments by algae and fungi, grain micritization, and

  11. Influence of Large Lakes on Methane Greenhouse Forcing in the Early Eocene

    NASA Astrophysics Data System (ADS)

    Whiteside, J. H.; Granberg, D. L.; Kasprak, A. H.; Taylor, K. W.; Pancost, R. D.

    2011-12-01

    Long-duration elevated global temperatures and increased atmospheric pCO2 levels (~1000-2000 ppm) characterized the earliest portion of the Eocene (Ypressian; ~55 to 49 Ma). This extended period of global warmth was also punctuated by a series of short (sub-precessional) hyperthermal events in which atmospheric CO2 (>2000 ppm) and global temperatures rose with unprecedented and (as of yet) unexplained rapidity. This interval is perhaps the best temporal analog for assessing contemporary response of the biosphere and global carbon cycle to increased CO2 emissions. Although these hyperthermals appear paced by 100 Ka and 1 Ma scale orbital (eccentricity) cycles in the marine realm, high frequency forcing processes have not yet been examined, and long continental records have yet to be explored for their expression. To identify sub-eccentricity (<100,000 year) scale variability in Early Eocene carbon cycling, we examined lacustrine records of organic carbon isotopes and carbon content from a ~5 Ma record in the Green River Formation (GRF) in the Uinta Basin of Utah, U.S.A. and a ~1 Ma record from the Messel Shale, (Darmstadt, Germany.) We demonstrate that in addition to the expected 100 Ka eccentricity cycle, the 40 Ka cycle of obliquity is also an important component of climate variability as reflected in the lacustrine carbon cycle and hence a potential driver of global carbon cycling. We further investigated carbon cycle dynamics by examining biomarker evidence for changes in the terrestrial methane cycle during this time interval. Due to their increased volumes (>60,000 km2), highly stratified and cyclically anoxic lakes of the Eocene could have provided enough methane to alter global radiative forcing. This is consistent with our data, which demonstrate that the GRF and Messel Shale both exhibit strongly reducing conditions as well as abundant methanogen and methanotroph biomarkers. Further, the GRF lacustrine environment was highly stratified with, at times

  12. Paleoceanographic, and paleoclimatic constraints on the global Eocene diatom and silicoflagellate record

    USGS Publications Warehouse

    Barron, John A.; Stickley, Catherine E.; Bukry, John D.

    2015-01-01

    Tabulation of the first and last occurrences of 132 biostratigraphically-important diatoms suggests increased species turnover during the latest Paleocene to earliest Eocene that may be in part due to a monographic effect. An increasing rate of evolution of new diatom species between ~ 46 and 43 Ma and after ~ 40 Ma coincides respectively with the widespread expansion of diatom deposition in the Atlantic and with an increased pole-to-equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings.

  13. Paleocene-Eocene transition at Naqb Assiut, Kharga Oasis, Western Desert, Egypt: Stratigraphical and paleoenvironmental inferences

    NASA Astrophysics Data System (ADS)

    El-Dawy, Moustafa, Hassan; Obaidalla, Nageh Abdelrahman; Mahfouz, Kamel Hussien; Abdel Wahed, Samar Adel

    2016-05-01

    This work depends on the study of the lower part of the Esna Formation which encompasses the Paleocene-Eocene (P-E) transition in Egypt as well as at Naqb Assiut section, Kharga Oasis, Western Desert. The Paleocene/Eocene (P/E) boundary is represented by El Dababiya Quarry Member which consists of five distinctive beds (nos. 1-5) at the GSSP. On the other hand, at Naqb Assiut section this boundary is only represented by the upper two beds (nos. 4&5), whereas, the lower three beds (nos. 1-3) are missing due to a hiatus. This hiatus is marked by the occurrence of an irregular surface contains pebbles and phosphatic materials. This hiatus may be related to the echo of Sryian Arc Orogeny at the P/E time. Biostratigraphically; four planktonic foraminiferal zones are defined from base to top as: Acarinina soldadoensis/Globanomalina pseudomenardii and Morozovella velascoensis (late Paleocene), Acarinina sibaiyaensis and Pseudohastigerina wilcoxensis/Morozovella velascoensis (early Eocene). The Acarinina sibaiyaensis Zone which represents the P//E/boundary is characterized by the occurrence of intrazonal hiatus at it's lower part. The benthonic foraminiferal taxa contain abundant representatives of Midway-type fauna (∼91% of the whole assemblages), beside few Velasco-type faunal ones (∼9%), indicating an outer neritic (150-200 m) water depth of deposition during the P-E transition. Quantitative analysis and composition of benthonic foraminiferal assemblages are indicative for various environmental changes around the P/E boundary. They reflected a high diversity, increase of epifaunal taxa, and low-intermediate productivity conditions, which indicates a well-ventilated bottom water and oligo - to mesotrophic conditions during the late Paleocene age. Rapid extinction of about 18% of the entire benthonic foraminiferal species started at the P/E boundary, where the last occurrence of Angulogavelinella avnimelechi is pronounced at the base of this boundary. There is a

  14. Paleocene-Early Eocene larger foraminiferal biostratigraphy of Yemen and Oman

    NASA Astrophysics Data System (ADS)

    Di Carlo, M.; Serra-Kiel, J.; Pignatti, J.

    2012-04-01

    The Paleogene larger foraminiferal biostratigraphy is today rather well assessed for the Tethyan domain. In order to contribute to the full integration of the Middle-East in the widely employed Shallow Benthic Zonation, a preliminary report on the Paleocene-Early Eocene larger foraminiferal assemblages from Yemen and Oman is provided here. The sections investigated in Yemen range in age from the Upper Cretaceous to the Oligocene. The Paleogene of Yemen is widely affected by dolomitization and only by analyzing over 1,700 thin sections from 60 stratigraphic sections (mainly from Hadramaut and Socotra) it has been possible to adequately investigate the fossil assemblages. In contrast, the deposits from northern Oman are characterized by rich and extraordinarily well-preserved Paleocene-Lower Eocene larger foraminiferal assemblages. This preliminary report focuses mainly on the Paleocene-Early Eocene deposits of the Umm-er-Radhuma formation. The Paleocene-Lower Eocene assemblages are characterized by strong affinities with northern Somalia. Hyaline forms such as Daviesina khatiyahi, Miscellanea gr. rhomboidea/dukhani, M. miscella, Saudia, Sakesaria, Lockhartia, Ranikothalia, Dictyokathina largely prevail in SBZ 3-4 deposits. Nummulites, Ranikothalia and Daviesina ruida characterize the Lower Ypresian. Subordinately, porcelaneous forms such as "Taberina" daviesi and conical agglutinated (Daviesiconus) also occur; alveolinids (such as Alveolina vredenburgi and A. decipiens) are relatively abundant in the basal Lower Ypresian of Socotra. In contrast to the coeval deposits from Yemen, the Paleocene section of Oman (Wadi Duqm, Abat-Tiwi platform) yields very well-preserved larger foraminiferal assemblages and agglutinated and porcelaneous forms are well represented. The occurrence of abundant Globoreticulina paleocenica is noteworthy along with an as yet undescribed Lacazinella species. The co-occurrence of Coskinon sp., "Plumokathina dienii", Dictyoconus turriculus and

  15. Simplified stratigraphic cross sections of the Eocene Green River Formation in the Piceance Basin, northwestern Colorado

    USGS Publications Warehouse

    Dietrich, John D.; Johnson, Ronald C.

    2013-01-01

    Thirteen stratigraphic cross sections of the Eocene Green River Formation in the Piceance Basin of northwestern Colorado are presented in this report. Originally published in a much larger and more detailed form by Self and others (2010), they are shown here in simplified, page-size versions that are easily accessed and used for presentation purposes. Modifications to the original versions include the elimination of the detailed lithologic columns and oil-yield histograms from Fischer assay data and the addition of ground-surface lines to give the depth of the various oil shale units shown on the cross section.

  16. Penguin response to the Eocene climate and ecosystem change in the northern Antarctic Peninsula region

    NASA Astrophysics Data System (ADS)

    Jadwiszczak, Piotr

    2010-08-01

    Eocene Antarctic penguins are known solely from the La Meseta Formation (Seymour Island, James Ross Basin). They are most numerous and taxonomically diverse (at least ten species present) within strata formed at the end of this epoch, which is concomitant with a significant cooling trend and biotic turnover prior to the onset of glaciation. Moreover, all newly appeared taxa were small-bodied, and most probably evolved in situ. Interestingly, some chemical proxies suggest enhanced nutrient upwelling events that coincided with obvious changes in the record of La Meseta penguins.

  17. Gould's Belt, interstellar clouds, and the Eocene-Oligocene helium-3 enhancement

    NASA Astrophysics Data System (ADS)

    Rubincam, David Parry

    2016-01-01

    Drag from hydrogen in the interstellar cloud which formed Gould's Belt may have sent interplanetary dust particle (IDPs) and small meteoroids with embedded helium to the Earth, perhaps explaining part the helium-3 flux increase seen in the sedimentary record near the Eocene-Oligocene transition. Assuming the Solar System passed through part of the cloud, IDPs in the inner Solar System may have been dragged to Earth, while dust and small meteoroids in the asteroid belt up to centimeter size may have been dragged to the resonances, where their orbital eccentricities were pumped up into Earth-crossing orbits; however, this hypotheses does not explain the Popigai and Chesapeake Bay impacts.

  18. Local response to warm Antarctic terrestrial temperatures in the Eocene: evidence from terrestrial biomarkers

    NASA Astrophysics Data System (ADS)

    Toney, J. L.; Bendle, J. A.; Inglis, G.; Bijl, P.; Pross, J.; Contreras, L.; van de Flierdt, T.; Huck, C. E.; Jamieson, S.; Huber, M.; Schouten, S.; Roehl, U.; Bohaty, S. M.; Brinkhuis, H.

    2011-12-01

    The early Eocene (~55 to 49 Ma) was characterized by long-term, high global temperatures and elevated atmospheric pCO2 levels (ca. 1000 ppm to more than 2000 ppm). Superimposed on top of this long-term warmth were a series of abrupt high pCO2 (>2000 ppm) and high temperature events. This greenhouse world may be used as an analogue for the future response of the biosphere and global carbon cycle to recent anthropogenic, atmospheric CO2 emissions. A major uncertainty, however, is the response of high polar latitudes to these climate conditions. Here we show evidence of early Eocene warmth measured from terrestrial, bacteria-derived tetraethers at IODP Site U1356, situated along the Wilkes Land margin in East Antarctica. The presence of soil bacteria-derived hopanes and higher plant n-alkanes in drillcores obtained from this site are also used to help understand the terrestrial Antarctic climate evolution in a warmer world. Methyl-branched and cyclised tetraether compounds are derived from terrestrial, soil bacteria. The number of branches and cycles are related directly to the environmental temperature and pH. These compounds indicate that temperatures on Eastern Antarctica likely exceeded 22°C during the Eocene. These temperatures reflect locally sourced terrestrial material input from a variety of elevations along the coastal plain and from the hinterland. A local source region is supported by the palynological and neodymium isotope records and by the presence of hopanes that suggest input from terrigenous soil and/or wetland environments. In particular, the existence of the C31 (17α,21β) homohopane within a relatively immature hopane assemblage is reported at Site U1356 and suggests the presence of methane-producing, wetland environments on Antarctica. Compound-specific carbon isotopes analyzed on the bacterial derived hopanes are used to characterize changes in wetland carbon cycling and methanogenesis. Local adiabatic lapse rate and precipitation amount

  19. Reconstruction of Middle Eocene - Late Oligocene Southern Ocean paleoclimate through calcareous nannofossils and stable isotopes

    NASA Astrophysics Data System (ADS)

    Villa, Giuliana; Fioroni, Chiara; Persico, Davide; Pea, Laura; Bohaty, Steve

    2010-05-01

    The transition from the ice free early Paleogene world to the glaciated conditions of the early Oligocene has been matter of discussion in the last years. This transition has not been monotonic but punctuated by numerous transient cooling and warming events. Here we present a summary of recent studies based on Nannofossil response to climatic changes during the Eocene and Oligocene. Collected data issue from high latitudes ODP Sites 748, 738, 744, 689 and 690. Based on a detailed revision of the biostratigraphy carried out through quantitative analysis, we conducted paleoecological studies on calcareous nannofossils through the late middle Eocene to the - late Oligocene interval to identify abundance variations of selected taxa in response to changes in sea surface temperature (SST) and trophic conditions. The nannofossil-based interpretation has been compared with detailed oxygen and carbon stable isotope stratigraphy confirming the climate variability in the Southern Ocean for this time interval. We identify the Middle Eocene Climatic optimum (MECO) event, related with the regional exclusion of Paleogenic warm-water taxa from the Southern Ocean, followed by the progressive cooling trend particularly emphasized during the cooling events at about 39 Ma, 37 Ma and 35.5 Ma. In the earliest Oligocene, marked changes in calcareous nannofossil assemblages are strikingly associated with the Oi-1 event recorded in perfect accordance with the oxygen isotope records. For most of the Oligocene we recorded a cold phase, while a warming trend is detected in the late Oligocene. In addiction, a marked increase of taxa thriving in eutrophic conditions coupled with a decrease in oligotrophic taxa, suggests the presence of a time interval (from about 36 Ma to about 26 Ma) with prevailing eutrophic conditions that correspond to an increase of the carbon stable isotope curve. This interval well corresponds with the clay mineral concentration that shows at Site 738 a higher

  20. Subfamily Limoniinae Speiser, 1909 (Diptera, Limoniidae) from Baltic amber (Eocene): the genus Elephantomyia Osten Sacken, 1860.

    PubMed

    Kania, Iwona

    2015-01-01

    A revision of the genus Elephantomyia Osten Sacken (Diptera: Limoniidae) from Baltic amber (Eocene) is presented. Four species--E. baltica Alexander, E. brevipalpa Loew, E. longirostris Loew, and E. pulchella Loew--are redescribed and documented with photographs and drawings. In addition, two new species of the genus are described: Elephantomyia bozenae sp. nov., and Elephantomyia irinae sp. nov. All these fossil species are placed within the subgenus Elephantomyia. A key to the extinct species of Elephantomyia is provided, and the genus' ecological pattern and evolutionary aspects are discussed. PMID:25706127

  1. Subfamily Limoniinae Speiser, 1909 (Diptera, Limoniidae) from Baltic Amber (Eocene): The Genus Elephantomyia Osten Sacken, 1860

    PubMed Central

    Kania, Iwona

    2015-01-01

    A revision of the genus Elephantomyia Osten Sacken (Diptera: Limoniidae) from Baltic amber (Eocene) is presented. Four species—E. baltica Alexander, E. brevipalpa Loew, E. longirostris Loew, and E. pulchella Loew—are redescribed and documented with photographs and drawings. In addition, two new species of the genus are described: Elephantomyia bozenae sp. nov., and Elephantomyia irinae sp. nov. All these fossil species are placed within the subgenus Elephantomyia. A key to the extinct species of Elephantomyia is provided, and the genus’ ecological pattern and evolutionary aspects are discussed. PMID:25706127

  2. Mammal Dispersion linked to The Paleocene Eocene Thermal Maximum (PETM): New Insights from India.

    NASA Astrophysics Data System (ADS)

    Khozyem, H.; Adatte, T.; Keller, G.; Spangenberg, J. E.; Bajpai, S.; Samant, B.; Mathur, S.

    2012-04-01

    The Paleocene Eocene Thermal Maximum (PETM, 55.5Ma) is globally related with the extinction of deep benthic foraminifera, the diversification of both plancktic foraminifera and mammals. In India, the tempo and timing of mammals dispersion, their association with the PETM or EECO (Early Eocene Climatic Optimum) and the India- Asia collision remain uncertain (Smith et al., 2006 Clementz, 2010). Three sections located in north and northwest India have been studied using sedimentology, micropaleontology, mineralogy (bulk and clay mineralogy) and geochemistry (stable isotopes, major and trace elements, organic matter). Both PETM and ETM2 (second Eocene Thermal Maximum, 53.7Ma), a short-lived warming episode that followed the PETM, are globally marked by a pronounced δ13Ccarb and org negative peak. Both isotopic excursions have been recognized in the Vastan and Tarkeswhar lignite mines (Cambay basin, Gujarat), above the main mammals bearing level. The lower shift is located above the first lignite seam (=lignite 2 of Sahni et al, 2004, 2009) and corresponds to the transition from continental to shallow marine conditions marked by benthic foraminifera and bivalves. The upper excursion appears to be linked to the ETM2 and corresponds to a second marine incursion containing bivalves, benthic (Nummulites burdigalensis) and planktic foraminifera located below the second lignite seam (lignite 1 of Sahni et al, 2004, 2009). A single but very pronounced δ13Corg peak has been detected in the Giral Lignite mine (Barmer, Rajhastan), around 6m above the vertebrates bearing level and may correspond to the PETM. This correlation is confirmed by palynological data (Tripathi et al., 2009, Sahni et al., 2004, 2009) and more particularly by an acme in the dinoflagellate Apectodinium that globally characterizes the PETM interval (Sluijs et al. 2007). Our micropaleontological data combined with stable carbone isotopes indicate the presence of both PETM and ETM2 events and constrain the

  3. Calcareous nannofossil and planktonic foraminifera biostratigraphy through the Middle to Late Eocene transition of Fayum area, Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Marzouk, Akmal Mohamed; El Shishtawy, Ahmed Moustafa; Kasem, Atef Masoud

    2014-12-01

    The Eocene sequence exposed at Gebel Naalun (Fayum-Nile divide), Guta section-I (West of Birket Qarun near Guta Village) and Guta section-II (Northwest of Birket Qarun near Guta Village) is differentiated, from base to top, into two formations; Gehannam Formation (Middle-Late Eocene) and Birket Qarun Formation (Late Eocene), respectively. Two calcareous nannofossil zones were recognized from the Eocene succession at Gebel Naalun; Discoaster saipanensis (NP17) and Chiasmolithus oamaruensis (NP18) zones as well as one planktonic foraminiferal zone; Truncorotaloides (Acaranina) rohri (P14) zone. However, at Guta section-I, two nannofossil zones were defined; Discoaster saipanensis (NP17) and Chiasmolithus oamaruensis (NP18) zones; the preservation of planktonic foraminiferal assemblage is too poor to enable us to recognize marker species as a result of many diagenetic processes. At Guta section-II, two nannofossil zones; Chiasmolitus oamaruensis (NP18) and Isthmolithus recurvus (NP19) and two planktonic foraminiferal zones; T. pseudoampliapertura zone and G. semiinvoluta zone are recorded. Several authors found that the lowest occurrence of Chiasmolithus oamaruensis is a poor criterion for defining the base of NP18 Zone, which is confirmed here. The same criticism has been applied to the lowest occurrence of Isthmolithus recurvus which defines the NP18/NP19 zonal boundary. It is generally agreed that NP19 Zone falls in the Priabonian (Late Eocene). As a result of the occurrence of the nannofossil marker species; Isthmolithus recurvus only in side views below and above the first appearance of Chiasmolithus oamaruensis at both Naalun and Guta section-I, this species is not reliable to define the NP18/NP19 zonal boundary. At Guta section-II, the Middle/Upper Eocene boundary can be delineated by the first appearance of Globigerinatheka semiinvoluta above the first occurrence of Isthmolithus recurvus in both plane and side views.

  4. The demise of the early Eocene greenhouse - Decoupled deep and surface water cooling in the eastern North Atlantic

    NASA Astrophysics Data System (ADS)

    Bornemann, André; D'haenens, Simon; Norris, Richard D.; Speijer, Robert P.

    2016-10-01

    Early Paleogene greenhouse climate culminated during the early Eocene Climatic Optimum (EECO, 50 to 53 Ma). This episode of global warmth is subsequently followed by an almost 20 million year-long cooling trend leading to the Eocene-Oligocene glaciation of Antarctica. Here we present the first detailed planktic and benthic foraminiferal isotope single site record (δ13C, δ18O) of late Paleocene to middle Eocene age from the North Atlantic (Deep Sea Drilling Project Site 401, Bay of Biscay). Good core recovery in combination with well preserved foraminifera makes this site suitable for correlations and comparison with previously published long-term records from the Pacific Ocean (e.g. Allison Guyot, Shatsky Rise), the Southern Ocean (Maud Rise) and the equatorial Atlantic (Demerara Rise). Whereas our North Atlantic benthic foraminiferal δ18O and δ13C data agree with the global trend showing the long-term shift toward heavier δ18O values, we only observe minor surface water δ18O changes during the middle Eocene (if at all) in planktic foraminiferal data. Apparently, the surface North Atlantic did not cool substantially during the middle Eocene. Thus, the North Atlantic appears to have had a different surface ocean cooling history during the middle Eocene than the southern hemisphere, whereas cooler deep-water masses were comparatively well mixed. Our results are in agreement with previously published findings from Tanzania, which also support the idea of a muted post-EECO surface-water cooling outside the southern high-latitudes.

  5. The Ostracoda assemblage of the Eocene-Oligocene transition in northwestern Thrace: Kırklareli-Edirne area (northwestern Turkey)

    NASA Astrophysics Data System (ADS)

    Şafak, Ümit; Güldürek, Manolya

    2016-05-01

    The aim of the study is to investigate the Eocene-Oligocene transition in detail in northwest Thrace (NW Turkey) with heavy reliance on ostracod fauna. The lithologies formed and the environmental changes during this time period were also studied. The study was carried out in northwest Thrace within the outcropping Koyunbaba, Soğucak, and Ceylan Formations; Mezardere, Osmancık, and Danişmen Formations of the Yenimuhacir Group; and the Taşlısekban and Pınarhisar members of the Danişmen Formation. Rich ostracod fauna indicating an Eocene and Oligocene age and environment are found within these units. The Ostracoda fauna identified were ostracods Triebelina punctata, Bairdia cymbula, Bairdia tenuis, Cyamocytheridea nova, Krithe bartonensis, Krithe angusta, Krithe rutoti, Krithe parvula, Echinocythereis isabenana, Leguminocythereis genappensis, Grinioneis triebeli, Xestoleberis subglobosa and Xestoleberis muelleriana from the Mid-Late Eocene epoch; Cytheromorpha zinndorfi, Hemicyprideis montosa, Neocyprideis williamsoniana, Cladarocythere apostolescui, Hammatocythere hebertiana, Haplocytheridea helvetica, Cytheridea pernota, Callistocythereis vitilis, Cushmanidea cf. scrobiculata, Pterygocythereis fimbriata, Pokornyella limbata, Grinioneis paijenborchiana, Cytheretta tracensis, Macrocypris wrightii and Paracypris bouldnorensis from the Late Eocene-Early Oligocene epoch; and Novocypris eocenana, Novocypris striata, Moenocypris forbesi, Candona (Pseudocandona) fertilis, Candona (Lineocypris) sp. and Cypridopsis soyeri from the Early-Late Oligocene epoch. The study was also correlated to previous research conducted on Eocene-Oligocene age ostracods around the area, in northwestern Europe, and in the Paris-Akiten Basin, in view of similar age-environment relationships determined by said studies. On the basis of evidence from the lithologic content of the beds and the micropaleontological investigation, the fossil community identified in this study indicates that the

  6. Sequential palynostratigraphy of the Queen City and Weches formations (Middle Eocene Claiborne Group), southeast central Texas

    SciTech Connect

    Elsik, W.C. )

    1993-02-01

    Palynomorph sequences of several orders of magnitude were found in the Queen City and Weches formations respectively at Six Mile and Burleson bluffs on the Brazos River, Milam and Burleson counties, Texas. The long term development of the subtropical to tropical Claibornian palynoflora included Engelhardtia spp., Friedrichipollis claibornensis, Nudopollis terminalis, Pollenites laesius and Symplocoipollenites spp. Shorter term fluctuations in sea level were reflected by common herbaceous pollen in the Queen City, and common mangrove pollen in the Weches. Paleoenvironments were marginally to fully marine; dinocysts occurred throughout. The Wetzeliella group of dinocysts were present only in the Queen City at Six Mile Bluff. Late Paleocene to Early Eocene pollen, and Early Middle Eocene pollen with last effective occurrences near the Queen City and Weches boundary included Aesculiidites circumstriatus, Annona foveoreticulata and a new species of Platycarya. Five short term warmer-cooler couplet events were represented by successive abundance peaks of Juglandaceae followed by Ulmus; Alnus supports the three upper Ulmus peaks. One deep water event was recorded by an abundance of fresh water Pediastrum at the Queen City and Weches boundary. That boundary event was bracketed by two of the Alnus and Ulmus peaks.

  7. Characterization of petroleum reservoirs in the Eocene Green River Formation, Central Uinta Basin, Utah

    USGS Publications Warehouse

    Morgan, C.D.; Bereskin, S.R.

    2003-01-01

    The oil-productive Eocene Green River Formation in the central Uinta Basin of northeastern Utah is divided into five distinct intervals. In stratigraphically ascending order these are: 1) Uteland Butte, 2) Castle Peak, 3) Travis, 4) Monument Butte, and 5) Beluga. The reservoir in the Uteland Butte interval is mainly lacustrine limestone with rare bar sandstone beds, whereas the reservoirs in the other four intervals are mainly channel and lacustrine sandstone beds. The changing depositional environments of Paleocene-Eocene Lake Uinta controlled the characteristics of each interval and the reservoir rock contained within. The Uteland Butte consists of carbonate and rare, thin, shallow-lacustrine sandstone bars deposited during the initial rise of the lake. The Castle Peak interval was deposited during a time of numerous and rapid lake-level fluctuations, which developed a simple drainage pattern across the exposed shallow and gentle shelf with each fall and rise cycle. The Travis interval records a time of active tectonism that created a steeper slope and a pronounced shelf break where thick cut-and-fill valleys developed during lake-level falls and rises. The Monument Butte interval represents a return to a gentle, shallow shelf where channel deposits are stacked in a lowstand delta plain and amalgamated into the most extensive reservoir in the central Uinta Basin. The Beluga interval represents a time of major lake expansion with fewer, less pronounced lake-level falls, resulting in isolated single-storied channel and shallow-bar sandstone deposits.

  8. Late Middle Eocene primate from Myanmar and the initial anthropoid colonization of Africa

    PubMed Central

    Chaimanee, Yaowalak; Chavasseau, Olivier; Beard, K. Christopher; Kyaw, Aung Aung; Soe, Aung Naing; Sein, Chit; Lazzari, Vincent; Marivaux, Laurent; Marandat, Bernard; Swe, Myat; Rugbumrung, Mana; Lwin, Thit; Valentin, Xavier; Zin-Maung-Maung-Thein; Jaeger, Jean-Jacques

    2012-01-01

    Reconstructing the origin and early evolutionary history of anthropoid primates (monkeys, apes, and humans) is a current focus of paleoprimatology. Although earlier hypotheses frequently supported an African origin for anthropoids, recent discoveries of older and phylogenetically more basal fossils in China and Myanmar indicate that the group originated in Asia. Given the Oligocene-Recent history of African anthropoids, the colonization of Africa by early anthropoids hailing from Asia was a decisive event in primate evolution. However, the fossil record has so far failed to constrain the nature and timing of this pivotal event. Here we describe a fossil primate from the late middle Eocene Pondaung Formation of Myanmar, Afrasia djijidae gen. et sp. nov., that is remarkably similar to, yet dentally more primitive than, the roughly contemporaneous North African anthropoid Afrotarsius. Phylogenetic analysis suggests that Afrasia and Afrotarsius are sister taxa within a basal anthropoid clade designated as the infraorder Eosimiiformes. Current knowledge of eosimiiform relationships and their distribution through space and time suggests that members of this clade dispersed from Asia to Africa sometime during the middle Eocene, shortly before their first appearance in the African fossil record. Crown anthropoids and their nearest fossil relatives do not appear to be specially related to Afrotarsius, suggesting one or more additional episodes of dispersal from Asia to Africa. Hystricognathous rodents, anthracotheres, and possibly other Asian mammal groups seem to have colonized Africa at roughly the same time or shortly after anthropoids gained their first toehold there. PMID:22665790

  9. A fossil primate of uncertain affinities from the earliest late Eocene of Egypt

    PubMed Central

    Seiffert, Erik R.; Simons, Elwyn L.; Boyer, Doug M.; Perry, Jonathan M. G.; Ryan, Timothy M.; Sallam, Hesham M.

    2010-01-01

    Paleontological work carried out over the last 3 decades has established that three major primate groups were present in the Eocene of Africa—anthropoids, adapiforms, and advanced strepsirrhines. Here we describe isolated teeth of a previously undocumented primate from the earliest late Eocene (≈37 Ma) of northern Egypt, Nosmips aenigmaticus, whose phylogenetic placement within Primates is unclear. Nosmips is smaller than the sympatric adapiform Afradapis but is considerably larger than other primate taxa known from the same paleocommunity. The species bears an odd mosaic of dental features, combining enlarged, elongate, and molariform premolars with simple upper molars that lack hypocones. Phylogenetic analysis across a series of different assumption sets variously places Nosmips as a stem anthropoid, a nonadapiform stem strepsirrhine, or even among adapiforms. This phylogenetic instability suggests to us that Nosmips likely represents a highly specialized member of a previously undocumented, and presumably quite ancient, endemic African primate lineage, the subordinal affinities of which have been obscured by its striking dental autapomorphies. Discriminant functions based on measurements of lower molar size and topography reliably classify extant prosimian primates into their correct dietary groups and identify Nosmips and Afradapis as omnivores and folivores, respectively. Although Nosmips currently defies classification, this strange and unexpected fossil primate nevertheless provides additional evidence for high primate diversity in northern Africa ≈37 million years ago and further underscores the fact that our understanding of early primate evolution on that continent remains highly incomplete. PMID:20457923

  10. Late Middle Eocene primate from Myanmar and the initial anthropoid colonization of Africa.

    PubMed

    Chaimanee, Yaowalak; Chavasseau, Olivier; Beard, K Christopher; Kyaw, Aung Aung; Soe, Aung Naing; Sein, Chit; Lazzari, Vincent; Marivaux, Laurent; Marandat, Bernard; Swe, Myat; Rugbumrung, Mana; Lwin, Thit; Valentin, Xavier; Zin-Maung-Maung-Thein; Jaeger, Jean-Jacques

    2012-06-26

    Reconstructing the origin and early evolutionary history of anthropoid primates (monkeys, apes, and humans) is a current focus of paleoprimatology. Although earlier hypotheses frequently supported an African origin for anthropoids, recent discoveries of older and phylogenetically more basal fossils in China and Myanmar indicate that the group originated in Asia. Given the Oligocene-Recent history of African anthropoids, the colonization of Africa by early anthropoids hailing from Asia was a decisive event in primate evolution. However, the fossil record has so far failed to constrain the nature and timing of this pivotal event. Here we describe a fossil primate from the late middle Eocene Pondaung Formation of Myanmar, Afrasia djijidae gen. et sp. nov., that is remarkably similar to, yet dentally more primitive than, the roughly contemporaneous North African anthropoid Afrotarsius. Phylogenetic analysis suggests that Afrasia and Afrotarsius are sister taxa within a basal anthropoid clade designated as the infraorder Eosimiiformes. Current knowledge of eosimiiform relationships and their distribution through space and time suggests that members of this clade dispersed from Asia to Africa sometime during the middle Eocene, shortly before their first appearance in the African fossil record. Crown anthropoids and their nearest fossil relatives do not appear to be specially related to Afrotarsius, suggesting one or more additional episodes of dispersal from Asia to Africa. Hystricognathous rodents, anthracotheres, and possibly other Asian mammal groups seem to have colonized Africa at roughly the same time or shortly after anthropoids gained their first toehold there.

  11. Molecular composition and paleobotanical origin of Eocene resin from northeast India

    NASA Astrophysics Data System (ADS)

    Rudra, Arka; Dutta, Suryendu; Raju, Srinivasan V.

    2014-06-01

    The molecular composition of fossil resins from early to middle Eocene coal from northeast India, has been analyzed for the first time to infer their paleobotanical source. The soluble component of fossil resin was analyzed using gas chromatography-mass spectrometry (GC-MS). The resin extracts are composed of cadalene-based C15 sesquiterpenoids and diagenetically altered triterpenoids. The macromolecular composition was investigated using pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) and Fourier transform infrared (FTIR) spectroscopy. The major pyrolysis products are C15 bicyclic sesquiterpenoids, alkylated naphthalenes, benzenes and a series of C17-C34 n-alkene- n-alkane pairs. Spectroscopic analysis revealed the dominance of aliphatic components. The presence of cadalene-based sequiterpenoids confirms the resin to be Class II or dammar resin, derived from angiosperms of Dipterocarpaceae family. These sesquiterpenoids are often detected in many SE Asian fluvio-deltaic oils. Dipterocarpaceae are characteristic of warm tropical climate suggesting the prevalence of such climate during early Eocene in northeast India.

  12. Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum.

    PubMed

    Wright, James D; Schaller, Morgan F

    2013-10-01

    The Paleocene/Eocene thermal maximum (PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE's onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). These couplets have corresponding δ(18)O cycles that imply a climatic origin. Seasonal insolation is the only regular climate cycle that can plausibly account for δ(18)O amplitudes and layer counts. High-resolution stable isotope records show 3.5‰ δ(13)C decrease over 13 couplets defining the CIE onset, which requires a large, instantaneous release of (13)C-depleted carbon. During the CIE, a clear δ(13)C gradient developed on the shelf with the largest excursions in shallowest waters, indicating atmospheric δ(13)C decreased by ~20‰. Our observations and revised release rate are consistent with an atmospheric perturbation of 3,000-gigatons of carbon (GtC). PMID:24043840

  13. Eocene climates, depositional environments, and geography, greater Green River basin, Wyoming, Utah, and Colorado

    SciTech Connect

    Roehler, H.W.

    1993-12-31

    The climates, depositional environments, and geography of Eocene rocks in the greater Green River basin are investigated to determine the origin, mode of deposition, and areal distribution of the Wasatch, Green River, Bridger, and Washakie Formations. The data indicate that Eocene climates ranged from cool temperature to tropical and were affected by both terrestrial and astronomical factors. The terrestrial factors were mainly latitude, altitude, regional geography, tectonism, and volcanism. The astronomical factors are interpreted from reptitious rock sequences in the Wilkins Peak Member of the Green River Formation that record seasonal changes, 21,000 year precession of the equinox cycles, 100,000 year eccentricity cycles, and an undetermined cycle of 727,000 years. Eight depositional environments are identified, discussed, and illustrated by diagrams, columnar sections, and photographs. They are: (1) fluvial, (2) paludal, (3) freshwater lacustrine, (4) saltwater lacustrine, (5) pond and playa lake, (6) evaporite (salt pan), (7) mudflat, and (8) volcanic and fluviovolcanic. The areal distribution of the eight depositional environments in the Wasatch, Green River, Bridger, and Washakie Formations is illustrated by photographs and 13 paleogeographic maps. 76 refs., 90 figs.

  14. Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum.

    PubMed

    Wright, James D; Schaller, Morgan F

    2013-10-01

    The Paleocene/Eocene thermal maximum (PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE's onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). These couplets have corresponding δ(18)O cycles that imply a climatic origin. Seasonal insolation is the only regular climate cycle that can plausibly account for δ(18)O amplitudes and layer counts. High-resolution stable isotope records show 3.5‰ δ(13)C decrease over 13 couplets defining the CIE onset, which requires a large, instantaneous release of (13)C-depleted carbon. During the CIE, a clear δ(13)C gradient developed on the shelf with the largest excursions in shallowest waters, indicating atmospheric δ(13)C decreased by ~20‰. Our observations and revised release rate are consistent with an atmospheric perturbation of 3,000-gigatons of carbon (GtC).

  15. An example of mixing-zone dolomite, Middle Eocene Avon Park Formation, Floridan aquifer system

    SciTech Connect

    Cander, H.S. )

    1994-07-01

    A late-formed dolomite cement in a core of the Middle Eocene Avon Park Formation, peninsular Florida, provides an example of dolomite cement from a mixing zone and illustrates how dolomite textural alteration and stabilization can occur at earth-surface conditions. The Avon Park Formation is a pervasively dolomitized peritidal platform carbonate 400 m thick in the Florida aquifer system. Typical Avon Park dolomite is inclusion-rich, fine-grained (< 40 mm), noncathodoluminescent, highly porous (average, 20%), and formed during the Eocene by normal to hypersaline seawater ([delta][sup 18]O = + 3.7[per thousand] PDB; [delta][sup 13]C = + 2.0[per thousand]; [sup 87]Sr/[sup 86]Sr = 0.70778; Sr = 167 ppm). In a 20 m interval in a core from southwest Florida, inclusion-free, cathodoluminescent dolomite overgrows the early-formed noncathodoluminescent marine dolomite. The cathodoluminescent dolomite cement profoundly alters the texture of Avon Park dolomite from typical Cenozoic-like porous, poorly crystalline dolomite to hard, dense, low-porosity, highly crystalline Paleozoic-like dolomite. The dolomite cement is not a replacement of limestone but an overgrowth of early-formed marine dolomite and pore-occluding cement. This study demonstrates that: (1) dolomite precipitated from a 75% seawater mixing-zone fluid that was both calcite saturated and sulfate-rich, and (2) dramatic textural maturation and stabilization in dolomite can occur in the near surface environment, without elevated temperature and burial conditions.

  16. The Paleocene-Eocene Thermal Maximum at DSDP Site 277, Campbell Plateau, southern Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Hollis, C. J.; Hines, B. R.; Littler, K.; Villasante-Marcos, V.; Kulhanek, D. K.; Strong, C. P.; Zachos, J. C.; Eggins, S. M.; Northcote, L.; Phillips, A.

    2015-07-01

    Re-examination of sediment cores from Deep Sea Drilling Project (DSDP) Site 277 on the western margin of the Campbell Plateau (paleolatitude of ~65° S) has identified an intact Paleocene-Eocene (P-E) boundary overlain by a 34 cm thick record of the Paleocene-Eocene Thermal Maximum (PETM) within nannofossil chalk. The upper part of the PETM is truncated, either due to drilling disturbance or a sedimentary hiatus. An intact record of the onset of the PETM is indicated by a gradual decrease in δ13C values over 20 cm, followed by a 14 cm interval in which δ13C is 2 ‰ lighter than uppermost Paleocene values. After accounting for effects of diagenetic alteration, we use δ18O and Mg/Ca values from foraminiferal tests to determine that intermediate and surface waters warmed by ~5-6° at the onset of the PETM prior to the full development of the negative δ13C excursion. After this initial warming, sea temperatures were relatively stable through the PETM but declined abruptly across the horizon that truncates the event at this site. Mg/Ca analysis of foraminiferal tests indicates peak intermediate and surface water temperatures of ~19 and ~32 °C, respectively. These temperatures may be influenced by residual diagenetic factors and changes in ocean circulation, and surface water values may also be biased towards warm-season temperatures.

  17. 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.

  18. Global vegetation distribution and terrestrial climate evolution at the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Pound, Matthew; Salzmann, Ulrich

    2016-04-01

    The Eocene - Oligocene transition (EOT; ca. 34-33.5 Ma) is widely considered to be the biggest step in Cenozoic climate evolution. Geochemical marine records show both surface and bottom water cooling, associated with the expansion of Antarctic glaciers and a reduction in the atmospheric CO2 concentration. However, the global response of the terrestrial biosphere to the EOT is less well understood and not uniform when comparing different regions. We present new global vegetation and terrestrial climate reconstructions of the Priabonian (late Eocene; 38-33.9 Ma) and Rupelian (early Oligocene; 33.9-28.45 Ma) by synthesising 215 pollen and spore localities. Using presence/absence data of pollen and spores with multivariate statistics has allowed the reconstruction of palaeo-biomes without relying on modern analogues. The reconstructed palaeo-biomes do not show the equator-ward shift at the EOT, which would be expected from a global cooling. Reconstructions of mean annual temperature, cold month mean temperature and warm month mean temperature do not show a global cooling of terrestrial climate across the EOT. Our new reconstructions differ from previous global syntheses by being based on an internally consistent statistically defined classification of palaeo-biomes and our terrestrial based climate reconstructions are in stark contrast to some marine based climate estimates. Our results raise new questions on the nature and extent of terrestrial global climate change at the EOT.

  19. Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Goldner, A.; Herold, N.; Huber, M.

    2014-07-01

    Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future.

  20. Stability of the vegetation-atmosphere system in the early Eocene climate

    NASA Astrophysics Data System (ADS)

    Port, U.; Claussen, M.

    2015-05-01

    We explore the stability of the atmosphere-vegetation system in the warm, almost ice-free early Eocene climate and in the interglacial, pre-industrial climate by analysing the dependence of the system on the initial vegetation cover. The Earth system model of the Max Planck Institute for Meteorology is initialised with either dense forests or bare deserts on all continents. Starting with desert continents, an extended desert remains in Central Asia in early Eocene climate. Starting with dense forest coverage, this desert is much smaller because the initially dense vegetation cover enhances water recycling in Central Asia relative to the simulation with initial deserts. With a smaller Asian desert, the Asian monsoon is stronger than in the case with a larger desert. The stronger Asian monsoon shifts the global tropical circulation leading to coastal subtropical deserts in North and South America which are significantly larger than with a large Asian desert. This result indicates a global teleconnection of the vegetation cover in several regions. In present-day climate, a bi-stability of the atmosphere-vegetation system is found for Northern Africa only. A global teleconnection of bi-stabilities in several regions is absent highlighting that the stability of the vegetation-atmosphere system depends on climatic and tectonic boundary conditions.

  1. Calcareous nannofossils and paleoenvironments of the Paleocene-Eocene thermal maximum (PETM) interval in central Egypt

    NASA Astrophysics Data System (ADS)

    Youssef, Mohamed

    2016-02-01

    The Paleocene-Eocene Thermal Maximum (PETM) interval was examined from four outcrops in Central Egypt to document the response of the floral communities across the PETM. The four outcrops are: Gebel Taramsa west of Qena, Gebel Duwi in the Red Sea Coast, and Gebel Qeryia, Gebel Arras sections in Wadi Qena. The qualitative and quantitative analyses of calcareous nannofossils used samples on a high resolution scale. The PETM is characterized by distinguished lithological succession, the Dababyia Quarry Beds (DQB) which extend over the Nile Valley, the Eastern Desert and the Western Desert. The calcareous nannofossils changes across the Paleocene/Eocene boundary (NP9a/NP9b) is marked by the following events: 1) abrupt decreases in both diversity and abundance, 2) dramatic decrease of Fasciculithus both in diversity and abundance, 3) first acme of Coccolithus pelagicus/Coccolithus subpertusus, and 4) first occurrence of excursion taxa including Discoaster araneus, Discoaster. anartios, Discoaster aegyptiacus and Rhomboaster spp). These events may refer to relatively warm and oligotrophic surface waters. The abundance of Toweius spp. in the upper part of the PETM which associated with Campylosphaera characterizes the return to normal conditions.

  2. Early Eocene Molluscan biostratigraphy, Mount Pinos-Lockwood Valley area, northern Ventura County, southern California

    SciTech Connect

    Squires, R.L.; Wilson, M.

    1987-05-01

    A 600-m thick unnamed marine, predominantly transition-zone siltstone unit along the south flank of the Mount Pinos uplift, in the northern Lockwood Valley area, previously has been suggested to be early Eocene (Capay Stage) in age at its base. This present study shows the entire unit to be this age. Unconformably overlying the pre-Tertiary granite basement is 30 m of unfossiliferous muddy siltstone that grades upward into 50 m of very fine sandstone with rarely fossiliferous lenses of medium to coarse sandstone. Gradationally above the sandstone is 100 m of muddy siltstone with less rarely fossiliferous lenses of conglomeratic sandstone. Macrofossil collections made at 10 localities in these lower 180 m yielded a sparse fauna of subtropical shallow-marine gastropods and bivalves, as well as rare specimens of discocyclinid foraminifera. from 180 to 500 m above the base of the section is unfossiliferous siltstone with local occurrences of lower shoreface, alternating laminated and bioturbated very fine sandstone. The uppermost 100 m of the section is siltstone with rarely fossiliferous lenses of fine to medium sandstone. Collections made at five localities yielded subtropical shallow-marine mollusks. Evidence of a West Coast provincial molluscan Capay Stage (early Eocene) age for all the fossiliferous beds of the siltstone unit is the presence of Turritella andersoni, a species diagnostic of this stage. Commonly associated mollusks are Cryptoconus cooperi, Cylichnina tantilla, Ectinochilus (Macilentos) macilentus, and Turritella buwaldana. Unconformably overlying the unit is the Oligocene-lower Miocene nonmarine Plush Ranch Formation.

  3. Anatomically preserved seeds of Nuphar (Nymphaeaceae) from the Early Eocene of Wutu, Shandong Province, China.

    PubMed

    Chen, Iju; Manchester, Steven R; Chen, Zhiduan

    2004-08-01

    Well-preserved seeds from the early Eocene of Wutu, Shandong, China are assigned to the genus Nuphar (Nymphaeaceae) based on morphology and anatomy. The seeds of Nuphar wutuensis sp. nov. are ellipsoidal to ovoid, 4-5 mm long with a clearly visible raphe ridge, and a truncate apex capped by a circular operculum ca. 1 mm in diameter bearing a central micropylar protrusion. These features, along with the testa composed of a uniseriate outer layer of equiaxial pentagonal to hexagonal surface cells and a middle layer 4-6 cells thick composed of thick-walled, periclinally elongate sclereids, correspond to the morphology and anatomy of extant Nuphar and distinguish this fossil species from all other extant and extinct genera of Nymphaeales. These seeds provide the oldest record for the genus in Asia and are supplemented by a similar well-preserved specimen from the Paleocene of North Dakota, USA. These data, together with the prior recognition of Brasenia (Cabombaceae) in the middle Eocene, indicate that the families Nymphaeaceae and Cabombaceae had differentiated by the early Tertiary.

  4. Scale insect larvae preserved in vertebrate coprolites (Le Quesnoy, France, Lower Eocene): paleoecological insights

    NASA Astrophysics Data System (ADS)

    Robin, Ninon; Foldi, Imre; Godinot, Marc; Petit, Gilles

    2016-10-01

    Coprolites of terrestrial vertebrates from the Sparnacian Le Quesnoy locality (Ypresian, Eocene, MP7, 53 Ma; Oise, France) were examined for possible parasitic helminth eggs. The extraction of the coprolite components was performed by a weak acetolyse and a slide mounting in glycerin. This long examination did not reveal paleoparasite remains, which may be explained through several arguments. However, some pollen grains, some enigmatic components, and two well-preserved first-instar cochineal nymphs (Hemiptera: Sternorrhyncha: Coccoidea) were evidenced in coprolites. Identified as Coccidae, these larvae are the earliest stage of the scale insect development ever reported as fossil, revealing the specific environment of preservation that fossilized scats may provide. These observations, combined to the coprolites morphotype, enable to ascribe the fossil scats producer to a small herbivorous mammal present in the deposit (early perissodactyls or Plesiadapidae). Regarding the ecology of extant representatives of Coccidae, this mammal was a likely foliage consumer, and the abundant Juglandaceae and/or Tiliaceae from Le Quesnoy might have lived parasitized by scale insects. These Early Eocene parasites had an already well-established dissemination strategy, with prevalent minute first-instar larvae. The herein performed extraction technique appears well-suited for the study of carbonate coprolites and could certainly be useful for evidencing other kind of microorganisms (including internal parasites).

  5. Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition.

    PubMed

    Goldner, A; Herold, N; Huber, M

    2014-07-31

    Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future.

  6. Flat meridional temperature gradient in the early Eocene in the subsurface rather than surface ocean

    NASA Astrophysics Data System (ADS)

    Ho, Sze Ling; Laepple, Thomas

    2016-08-01

    The early Eocene (49-55 million years ago) is a time interval characterized by elevated surface temperatures and atmospheric CO2 (refs ,), and a flatter-than-present latitudinal surface temperature gradient. The multi-proxy-derived flat temperature gradient has been a challenge to reproduce in model simulations, especially the subtropical warmth at the high-latitude surface oceans, inferred from the archaeal lipid-based palaeothermometry, . Here we revisit the interpretation by analysing a global collection of multi-proxy temperature estimates from sediment cores spanning millennia to millions of years. Comparing the variability between proxy types, we demonstrate that the present interpretation overestimates the magnitude of past climate changes on all timescales. We attribute this to an inappropriate calibration, which reflects subsurface ocean but is calibrated to the sea surface, where the latitudinal temperature gradient is steeper. Recalibrating the proxy to the temperatures of subsurface ocean, where the signal is probably formed, yields colder -temperatures and latitudinal gradient consistent with standard climate model simulations of the Eocene climate, invalidating the apparent, extremely warm polar sea surface temperatures. We conclude that there is a need to reinterpret -inferred marine temperature records in the literature, especially for reconstructions of past warm climates that rely heavily on this proxy as reflecting subsurface ocean.

  7. Eocene/Oligocene ocean de-acidification linked to Antarctic glaciation by sea-level fall.

    PubMed

    Merico, Agostino; Tyrrell, Toby; Wilson, Paul A

    2008-04-24

    One of the most dramatic perturbations to the Earth system during the past 100 million years was the rapid onset of Antarctic glaciation near the Eocene/Oligocene epoch boundary (approximately 34 million years ago). This climate transition was accompanied by a deepening of the calcite compensation depth--the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution. Changes in the global carbon cycle, rather than changes in continental configuration, have recently been proposed as the most likely root cause of Antarctic glaciation, but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear. Here we use a global biogeochemical box model to test competing hypotheses put forward to explain the Eocene/Oligocene transition. We find that, of the candidate hypotheses, only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor. In our simulations, glacioeustatic sea-level fall associated with the growth of Antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves, leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth. At the same time, fresh limestones are exposed to erosion, thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater delta13C. Our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the Cenozoic era. PMID:18432242

  8. Eocene primates of South America and the African origins of New World monkeys.

    PubMed

    Bond, Mariano; Tejedor, Marcelo F; Campbell, Kenneth E; Chornogubsky, Laura; Novo, Nelson; Goin, Francisco

    2015-04-23

    The platyrrhine primates, or New World monkeys, are immigrant mammals whose fossil record comes from Tertiary and Quaternary sediments of South America and the Caribbean Greater Antilles. The time and place of platyrrhine origins are some of the most controversial issues in primate palaeontology, although an African Palaeogene ancestry has been presumed by most primatologists. Until now, the oldest fossil records of New World monkeys have come from Salla, Bolivia, and date to approximately 26 million years ago, or the Late Oligocene epoch. Here we report the discovery of new primates from the ?Late Eocene epoch of Amazonian Peru, which extends the fossil record of primates in South America back approximately 10 million years. The new specimens are important for understanding the origin and early evolution of modern platyrrhine primates because they bear little resemblance to any extinct or living South American primate, but they do bear striking resemblances to Eocene African anthropoids, and our phylogenetic analysis suggests a relationship with African taxa. The discovery of these new primates brings the first appearance datum of caviomorph rodents and primates in South America back into close correspondence, but raises new questions about the timing and means of arrival of these two mammalian groups. PMID:25652825

  9. Intra-arc sedimentation in a low-lying marginal arc, Eocene Clarno Formation, central Oregon

    SciTech Connect

    White, J.D.L.; Robinson, P.T. . Centre for Marine Geology)

    1993-04-01

    The largely Eocene Clarno Formation consists of andesitic volcaniclastic rocks interstratified with clayey paludal sediments and lava flows, and cut locally by irregular hypabyssal stocks, dikes and sills. Lateral lithofacies variations are pronounced, and intrusive and extrusive volcanic rocks appear haphazardly emplaced throughout the formation. A range of sedimentary environments is represented, including near-vent flow and breccia accumulations, bouldery high-gradient braided streams, and relatively low-gradient sandy-tuff braidplains associated with paludal deposits. The authors infer that the coarse-grained volcaniclastic rocks of the Clarno Formation accumulated largely in volcanic flank and apron settings. The stratigraphy of the formation indicates that it was formed in sedimentary lowlands into which many small volcanoes erupted; only a few, scattered remnants of large central vent volcanoes are known. The absence of systematic variation across the unit's large outcrop belt argues against the derivation of the succession from a line of volcanoes beyond the reaches of the present outcrop. The authors infer that the arc was composed of small to medium-sized volcanoes arranged non-systematically over a broad area. The sedimentary succession most probably accumulated in a series of shallow intra-arc depressions formed by crustal stretching and diffuse block rotation driven by oblique subduction during the Eocene.

  10. Eocene primates of South America and the African origins of New World monkeys

    NASA Astrophysics Data System (ADS)

    Bond, Mariano; Tejedor, Marcelo F.; Campbell, Kenneth E.; Chornogubsky, Laura; Novo, Nelson; Goin, Francisco

    2015-04-01

    The platyrrhine primates, or New World monkeys, are immigrant mammals whose fossil record comes from Tertiary and Quaternary sediments of South America and the Caribbean Greater Antilles. The time and place of platyrrhine origins are some of the most controversial issues in primate palaeontology, although an African Palaeogene ancestry has been presumed by most primatologists. Until now, the oldest fossil records of New World monkeys have come from Salla, Bolivia, and date to approximately 26 million years ago, or the Late Oligocene epoch. Here we report the discovery of new primates from the ?Late Eocene epoch of Amazonian Peru, which extends the fossil record of primates in South America back approximately 10 million years. The new specimens are important for understanding the origin and early evolution of modern platyrrhine primates because they bear little resemblance to any extinct or living South American primate, but they do bear striking resemblances to Eocene African anthropoids, and our phylogenetic analysis suggests a relationship with African taxa. The discovery of these new primates brings the first appearance datum of caviomorph rodents and primates in South America back into close correspondence, but raises new questions about the timing and means of arrival of these two mammalian groups.

  11. Eocene bunoselenodont Artiodactyla from southern Thailand and the early evolution of Ruminantia in South Asia

    NASA Astrophysics Data System (ADS)

    Métais, Grégoire; Chaimanee, Yaowalak; Jaeger, J.-J.; Ducrocq, Stéphane

    2007-06-01

    Although Asia is thought to have played a critical role in the basal radiation of Ruminantia, the fossil record of early selenodont artiodactyls remains poorly documented in this region. Dental remains of a new bunoselenodont artiodactyl are described from the late Eocene of Krabi, southern Thailand. This new form, Krabitherium waileki gen. et sp. nov, is tentatively referred to the Tragulidae (Ruminantia) on the basis of several dental features, including a weak Tragulus fold and the presence of a deep groove on the anterior face of the entoconid. Although this new form is suggestive of the enigmatic ? Gelocus gajensis Pilgrim 1912 from the “base of the Gaj” (lower Chitarwata Formation) of the Bugti Hills (Central Pakistan), K. waileki most likely represents an early representative of a relatively bunodont group of tragulids that includes the genus Dorcabune, known from the Miocene of south Asia. This addition to the Eocene record of early ruminants attests to the antiquity of the group in Southeast Asia and lends support to the hypothesis that the Tragulidae represents one of the first offshoots in the evolutionary history of Ruminantia.

  12. Organic petrology and coalbed gas content, Wilcox Group (Paleocene-Eocene), northern Louisiana

    USGS Publications Warehouse

    Hackley, P.C.; Warwick, P.D.; Breland, F.C.

    2007-01-01

    Wilcox Group (Paleocene-Eocene) coal and carbonaceous shale samples collected from four coalbed methane test wells in northern Louisiana were characterized through an integrated analytical program. Organic petrographic analyses, gas desorption and adsorption isotherm measurements, and proximate-ultimate analyses were conducted to provide insight into conditions of peat deposition and the relationships between coal composition, rank, and coalbed gas storage characteristics. The results of petrographic analyses indicate that woody precursor materials were more abundant in stratigraphically higher coal zones in one of the CBM wells, consistent with progradation of a deltaic depositional system (Holly Springs delta complex) into the Gulf of Mexico during the Paleocene-Eocene. Comparison of petrographic analyses with gas desorption measurements suggests that there is not a direct relationship between coal type (sensu maceral composition) and coalbed gas storage. Moisture, as a function of coal rank (lignite-subbituminous A), exhibits an inverse relationship with measured gas content. This result may be due to higher moisture content competing for adsorption space with coalbed gas in shallower, lower rank samples. Shallower ( 600??m) coal samples containing less moisture range from under- to oversaturated with respect to their CH4 adsorption capacity.

  13. Eocene sediment dispersal pattern records asymmetry of Laramide Green River basin, southwestern Wyoming

    SciTech Connect

    Baldwin, R.J.; Andersen, D.W.

    1987-05-01

    Provenance and paleocurrent data from synorogenic fluvial sandstones can be used to constrain theories about the timing and structural style of Laramide foreland uplifts and associated basins. The Green River basin of southwestern Wyoming is a large ellipsoidal basin bounded by uplifts with diverse orientations and basement rock compositions. Sandstone from the main body of the Eocene Wasatch Formation in the Green River basin was sampled along the south and west flanks of the Rock Springs uplift. Petrographic examination and paleocurrent measurements reveal two main facies. The first facies is rich in feldspar and metamorphic rock fragments derived from the Wind River Mountains to the north. The second facies is dominated by quartz and sedimentary rock fragments, reflecting a source in the Uinta Mountains to the south. Distribution of these facies indicates that a sediment lobe extends 15 km into the basin from the Uinta Mountains. Another sediment lobe originates from the Wind River Mountains and extends approximately 100 km south into the basin. This pattern suggests that the topographic axis of the depositional basin was an east-west-trending trough about 15 km north of the Uinta Mountains. The position of the basin axis is inferred to reflect greater subsidence near the Uinta Mountains. The asymmetric distribution of the two facies of the Wasatch Formation thus supports the model of basin subsidence caused by thrust-loading and indicates the Uinta Mountains were the dominant active thrust block bounding the Green River basin during the early Eocene.

  14. Abrupt reversal in ocean overturning during the Palaeocene/Eocene warm period.

    PubMed

    Nunes, Flavia; Norris, Richard D

    2006-01-01

    An exceptional analogue for the study of the causes and consequences of global warming occurs at the Palaeocene/Eocene Thermal Maximum, 55 million years ago. A rapid rise of global temperatures during this event accompanied turnovers in both marine and terrestrial biota, as well as significant changes in ocean chemistry and circulation. Here we present evidence for an abrupt shift in deep-ocean circulation using carbon isotope records from fourteen sites. These records indicate that deep-ocean circulation patterns changed from Southern Hemisphere overturning to Northern Hemisphere overturning at the start of the Palaeocene/Eocene Thermal Maximum. This shift in the location of deep-water formation persisted for at least 40,000 years, but eventually recovered to original circulation patterns. These results corroborate climate model inferences that a shift in deep-ocean circulation would deliver relatively warmer waters to the deep sea, thus producing further warming. Greenhouse conditions can thus initiate abrupt deep-ocean circulation changes in less than a few thousand years, but may have lasting effects; in this case taking 100,000 years to revert to background conditions.

  15. Fossils and Fossil Climate: The Case for Equable Continental Interiors in the Eocene

    NASA Astrophysics Data System (ADS)

    Wing, Scott L.; Greenwood, David R.

    1993-08-01

    There are many methods for inferring terrestrial palaeoclimates from palaeontological data, including the size and species diversity of ectothermic vertebrates, the locomotor and dental adaptations of mammals, characteristics of leaf shape, size, and epidermis, wood anatomy, and the climatic preferences of nearest living relatives of fossil taxa. Estimates of palaeotemperature have also been based on stable oxygen isotope ratios in shells and bones. Interpretation of any of these data relies in some way on uniformitarian assumptions, although at different levels depending on the method. Most of these methods can be applied to a palaeoclimatic reconstruction for the interior of North America during the early Eocene, which is thought to be the warmest interval of global climate in the Cenozoic. Most of the data indicate warm equable climates with little frost. Rainfall was variable, but strong aridity was local or absent. The inferred palaeoclimate is very different from the present climate of the region and from model simulations for the Eocene. This suggests that models fail to incorporate forcing factors that were present at that time, that they treat the heat regime of continents unrealistically, and/or that model inputs such as sea surface temperature gradients or palaeotopography are incorrect.

  16. Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition.

    PubMed

    Goldner, A; Herold, N; Huber, M

    2014-07-31

    Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future. PMID:25079555

  17. A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales.

    PubMed

    Bajpai, S; Gingerich, P D

    1998-12-22

    Himalayacetus subathuensis is a new pakicetid archaeocete from the Subathu Formation of northern India. The type dentary has a small mandibular canal indicating a lack of auditory specializations seen in more advanced cetaceans, and it has Pakicetus-like molar teeth suggesting that it fed on fish. Himalayacetus is significant because it is the oldest archaeocete known and because it was found in marine strata associated with a marine fauna. Himalayacetus extends the fossil record of whales about 3.5 million years back in geological time, to the middle part of the early Eocene [ approximately 53.5 million years ago (Ma)]. Oxygen in the tooth-enamel phosphate has an isotopic composition intermediate between values reported for freshwater and marine archaeocetes, indicating that Himalayacetus probably spent some time in both environments. When the temporal range of Archaeoceti is calibrated radiometrically, comparison of likelihoods constrains the time of origin of Archaeoceti and hence Cetacea to about 54-55 Ma (beginning of the Eocene), whereas their divergence from extant Artiodactyla may have been as early as 64-65 Ma (beginning of the Cenozoic).

  18. Eocene primates of South America and the African origins of New World monkeys.

    PubMed

    Bond, Mariano; Tejedor, Marcelo F; Campbell, Kenneth E; Chornogubsky, Laura; Novo, Nelson; Goin, Francisco

    2015-04-23

    The platyrrhine primates, or New World monkeys, are immigrant mammals whose fossil record comes from Tertiary and Quaternary sediments of South America and the Caribbean Greater Antilles. The time and place of platyrrhine origins are some of the most controversial issues in primate palaeontology, although an African Palaeogene ancestry has been presumed by most primatologists. Until now, the oldest fossil records of New World monkeys have come from Salla, Bolivia, and date to approximately 26 million years ago, or the Late Oligocene epoch. Here we report the discovery of new primates from the ?Late Eocene epoch of Amazonian Peru, which extends the fossil record of primates in South America back approximately 10 million years. The new specimens are important for understanding the origin and early evolution of modern platyrrhine primates because they bear little resemblance to any extinct or living South American primate, but they do bear striking resemblances to Eocene African anthropoids, and our phylogenetic analysis suggests a relationship with African taxa. The discovery of these new primates brings the first appearance datum of caviomorph rodents and primates in South America back into close correspondence, but raises new questions about the timing and means of arrival of these two mammalian groups.

  19. Ecological Turnover of Shallow Water Carbonate Producers Following the Paleocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Weiss, A.; Martindale, R. C.

    2015-12-01

    Modern coral reef ecosystems are under threat from global climate change (and associated, synergistic stresses) and local environmental degradation. Therefore, it is important for ecologists to understand how ecosystems adapt and recover from climate change. The fossil record provides excellent case studies of similar events, such as the Paleocene-Eocene Thermal Maximum (PETM). Although Paleocene and Eocene shallow water carbonates have not received the same degree of attention as the deep-water record, the PETM provides an opportunity to study the role of alternative stable states in maintaining the health and diversity of shallow water carbonate environments. It is generally accepted that during the PETM there is a transition from reef systems to foraminiferal shoals as the dominant shallow water carbonate producers. In fact, previous work has documented this interval as one of the major metazoan reef collapses of the Phanerozoic. This study fills an important gap in the shallow-water PETM record by quantitatively measuring the changes in carbonate production and ecology of 15 localities as they shift from coral reefs to foraminiferal shoal. The quantitative and semi-quantitative analysis is accomplished by using data from the PaleoReefs database and a simple carbonate production calculation to estimate the productivity of the shallow water system. Ecological data are gathered through a literature review of the localities. The results of this study will enable a better understanding of how modern reefs may react to global climate and environmental change.

  20. Micro-Halocline Enabled Nutrient Recycling May Explain Extreme Azolla Event in the Eocene Arctic Ocean

    PubMed Central

    van Kempen, Monique M. L.; Smolders, Alfons J. P.; Lamers, Leon P. M.; Roelofs, Jan G. M.

    2012-01-01

    In order to understand the physicochemical mechanisms that could explain the massive growth of Azolla arctica in the Eocene Arctic Ocean, we carried out a laboratory experiment in which we studied the interacting effects of rain and wind on the development of salinity stratification, both in the presence and in the absence of a dense Azolla cover. Additionally, we carried out a mesocosm experiment to get a better understanding of the nutrient cycling within and beneath a dense Azolla cover in both freshwater and brackish water environments. Here we show that Azolla is able to create a windproof, small-scale salinity gradient in brackish waters, which allows for efficient recycling of nutrients. We suggest that this mechanism ensures the maintenance of a large standing biomass in which additional input of nutrients ultimately result in a further expansion of an Azolla cover. As such, it may not only explain the extent of the Azolla event during the Eocene, but also the absence of intact vegetative Azolla remains and the relatively low burial efficiency of organic carbon during this interval. PMID:23166833

  1. Early Eocene tectonics and sedimentation in Northern Fossil basin, Wyoming Overthrust Belt

    SciTech Connect

    Hurst, D.J.; Steidtmann, J.R.

    1984-07-01

    The Tunp Member of the early Eocene Wasatch Formation in southwestern Wyoming was shed from rising thrust sheets as debris flows containing abundant, very poorly sorted to unsorted, coarse clastic material in a mudstone matrix. Deposition occurred on the margins of the northern Fossil basin as coalesced alluvial fans and fan deltas. Small braided streams traversed the surface of these fans and reworked debris flow material, but the resultant fluvial deposits are volumetrically minor. Tunp Member deposits are preserved in three north-south-trending belts around the periphery of the northern Fossil basin. Each belt had a separate source in discrete highlands created by early Eocene motion on the Absaroka, Tunp, and Crawford thrust faults. These thrusts possessed unique characteristics of uplift style, provenance, and duration of in-situ weathering that are reflected by differences in clast lithology, size and rounding, as well as thickness and areal extent of the deposits resulting from each thrust. The results of this study have several important implications about thrust belt development: (1) passive rotation of older thrusts by younger ones can provide an uplifted source for syntectonic sediments, (2) the tenet that major thrusts young in the direction of tectonic transport may be violated by the Tunp and Crawford thrusts in the Fossil basin area, and (3) those heretical faults (i.e., Tunp and Crawford) possess a similar geometry that is distinct from other thrust faults in the area.

  2. Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum

    PubMed Central

    Wright, James D.; Schaller, Morgan F.

    2013-01-01

    The Paleocene/Eocene thermal maximum (PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE’s onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). These couplets have corresponding δ18O cycles that imply a climatic origin. Seasonal insolation is the only regular climate cycle that can plausibly account for δ18O amplitudes and layer counts. High-resolution stable isotope records show 3.5‰ δ13C decrease over 13 couplets defining the CIE onset, which requires a large, instantaneous release of 13C-depleted carbon. During the CIE, a clear δ13C gradient developed on the shelf with the largest excursions in shallowest waters, indicating atmospheric δ13C decreased by ∼20‰. Our observations and revised release rate are consistent with an atmospheric perturbation of 3,000-gigatons of carbon (GtC). PMID:24043840

  3. Palaeoclimatic evolution during Eocene and its influence on oil shale mineralisation, Fushun basin, China

    NASA Astrophysics Data System (ADS)

    Meng, Qingtao; Liu, Zhaojun; Bruch, Angela A.; Liu, Rong; Hu, Fei

    2012-02-01

    The Fushun basin is a small, explored, coal and oil shale-bearing, Cenozoic fault basin in the Liaoning Province, northeast China. The basin mainly consists of Eocene swamp to lacustrine deposits of the Guchengzi to Xilutian Formation, and contains the biggest opencast oil shale mine in Asia. This mine has provided an ideal opportunity to undertake palaeoclimate reconstruction in this basin based on a single geological profile and the analyses of 93 samples, using various approaches, namely field geological observation, clay mineralogical and geochemical (Sr/Ba, Sr/Cu, stable C and O isotope) analyses, all of which were compared with palaeobotanical data. The Eocene climate of Fushun basin evolved from warm temperate to north subtropical, and generally changed from warm humid to subhumid-semiarid. Paleoclimatic and geochemical parameters shows that the very warm and humid climate during Jijuntun Formation increased the initial productivity of lake water, and caused a steady stratification of the lake water, then caused oxygen lack in the bottom of water. Productivity of the lake provides the mean origin of organic matters for oil shale formation, and steady anoxic environment is beneficial for the conservation of organic matters.

  4. The influence of extraterrestrial material on the late Eocene marine Os isotope record

    NASA Astrophysics Data System (ADS)

    Paquay, François S.; Ravizza, Greg; Coccioni, Rodolfo

    2014-11-01

    A reconstruction of seawater 187Os/188Os ratios during the late Eocene (∼36-34 Ma), based upon bulk sediment analyses from the sub-Antarctic Southern Atlantic Ocean (Ocean Drilling Program (ODP) Site 1090), Eastern Equatorial Pacific Ocean (ODP Sites 1218 and 1219) and the uplifted (land-based) Tethyan section (Massignano, Italy), confirms that the previously reported abrupt shift to lower 187Os/188Os is a unique global feature of the marine Os isotope record that occurs in magnetochron C16n.1n. This feature is interpreted to represent the change in seawater 187Os/188Os caused by the Popigai impact event. Higher in the Massignano section, two other iridium anomalies previously proposed to represent additional impact events do not show a comparable excursion to low 187Os/188Os, suggesting that these horizons do not record multiple large impacts. Comparison of records from three different ocean basins indicates that seawater 187Os/188Os begins to decline in advance of the Popigai impact event. At Massignano this decline coincides with a previously reported episode of elevated 3He flux, suggesting that increased influx of interplanetary dust particles (IDPs) contributed to the pre-impact shift in 187Os/188Os and not to the longer-term latest Eocene 187Os/188Os decline that occurred ∼1 million year after the Popigai impact event.

  5. Late Eocene to early Oligocene quantitative paleotemperature record: evidence from continental halite fluid inclusions.

    PubMed

    Zhao, Yan-jun; Zhang, Hua; Liu, Cheng-lin; Liu, Bao-kun; Ma, Li-chun; Wang, Li-cheng

    2014-01-01

    Climate changes within Cenozoic extreme climate events such as the Paleocene-Eocene Thermal Maximum and the First Oligocene Glacial provide good opportunities to estimate the global climate trends in our present and future life. However, quantitative paleotemperatures data for Cenozoic climatic reconstruction are still lacking, hindering a better understanding of the past and future climate conditions. In this contribution, quantitative paleotemperatures were determined by fluid inclusion homogenization temperature (Th) data from continental halite of the first member of the Shahejie Formation (SF1; probably late Eocene to early Oligocene) in Bohai Bay Basin, North China. The primary textures of the SF1 halite typified by cumulate and chevron halite suggest halite deposited in a shallow saline water and halite Th can serve as an temperature proxy. In total, one-hundred-twenty-one Th data from primary and single-phase aqueous fluid inclusions with different depths were acquired by the cooling nucleation method. The results show that all Th range from 17.7°C to 50.7°C,with the maximum homogenization temperatures (ThMAX) of 50.5°C at the depth of 3028.04 m and 50.7°C at 3188.61 m, respectively. Both the ThMAX presented here are significantly higher than the highest temperature recorded in this region since 1954 and agree with global temperature models for the year 2100 predicted by the Intergovernmental Panel on Climate Change. PMID:25047483

  6. Description of a Well Preserved Fetus of the European Eocene Equoid Eurohippus messelensis

    PubMed Central

    Franzen, Jens Lorenz; Aurich, Christine; Habersetzer, Jörg

    2015-01-01

    The early Middle Eocene locality of Grube Messel, near Darmstadt (Germany), is famous for its complete vertebrate skeletons. The degree of preservation of soft tissues, such as body silhouettes, internal organs and gut contents, is frequently remarkable. The present specimen was analyzed for remnants of the reproductive system. Classic anatomy and osteology and high-resolution micro-x-ray were applied to describe the fetus of the European Eocene equoid Eurohippus messelensis. Scanning electronic microscopy (SEM) was used for determination of soft tissue remnants. The fetus is the earliest and best-preserved fossil specimen of its kind. The postcranial fetal skeleton is almost complete and largely articulated, allowing the conclusion that the pregnant mare was in late gestation. The apparent intrauterine position of the fetus is normal for the phase of pregnancy. Death of mare and fetus were probably not related to problems associated with parturition. Soft tissue interpreted as the uteroplacenta and a broad uterine ligament are preserved due to bacterial activity and allow considerations on the evolutionary development of the structures. PMID:26445456

  7. Late Eocene to early Oligocene quantitative paleotemperature record: evidence from continental halite fluid inclusions.

    PubMed

    Zhao, Yan-jun; Zhang, Hua; Liu, Cheng-lin; Liu, Bao-kun; Ma, Li-chun; Wang, Li-cheng

    2014-01-01

    Climate changes within Cenozoic extreme climate events such as the Paleocene-Eocene Thermal Maximum and the First Oligocene Glacial provide good opportunities to estimate the global climate trends in our present and future life. However, quantitative paleotemperatures data for Cenozoic climatic reconstruction are still lacking, hindering a better understanding of the past and future climate conditions. In this contribution, quantitative paleotemperatures were determined by fluid inclusion homogenization temperature (Th) data from continental halite of the first member of the Shahejie Formation (SF1; probably late Eocene to early Oligocene) in Bohai Bay Basin, North China. The primary textures of the SF1 halite typified by cumulate and chevron halite suggest halite deposited in a shallow saline water and halite Th can serve as an temperature proxy. In total, one-hundred-twenty-one Th data from primary and single-phase aqueous fluid inclusions with different depths were acquired by the cooling nucleation method. The results show that all Th range from 17.7°C to 50.7°C,with the maximum homogenization temperatures (ThMAX) of 50.5°C at the depth of 3028.04 m and 50.7°C at 3188.61 m, respectively. Both the ThMAX presented here are significantly higher than the highest temperature recorded in this region since 1954 and agree with global temperature models for the year 2100 predicted by the Intergovernmental Panel on Climate Change.

  8. Late Eocene to early Oligocene quantitative paleotemperature record: Evidence from continental halite fluid inclusions

    PubMed Central

    Zhao, Yan-jun; Zhang, Hua; Liu, Cheng-lin; Liu, Bao-kun; Ma, Li-chun; Wang, Li-cheng

    2014-01-01

    Climate changes within Cenozoic extreme climate events such as the Paleocene–Eocene Thermal Maximum and the First Oligocene Glacial provide good opportunities to estimate the global climate trends in our present and future life. However, quantitative paleotemperatures data for Cenozoic climatic reconstruction are still lacking, hindering a better understanding of the past and future climate conditions. In this contribution, quantitative paleotemperatures were determined by fluid inclusion homogenization temperature (Th) data from continental halite of the first member of the Shahejie Formation (SF1; probably late Eocene to early Oligocene) in Bohai Bay Basin, North China. The primary textures of the SF1 halite typified by cumulate and chevron halite suggest halite deposited in a shallow saline water and halite Th can serve as an temperature proxy. In total, one-hundred-twenty-one Th data from primary and single-phase aqueous fluid inclusions with different depths were acquired by the cooling nucleation method. The results show that all Th range from 17.7°C to 50.7°C,with the maximum homogenization temperatures (ThMAX) of 50.5°C at the depth of 3028.04 m and 50.7°C at 3188.61 m, respectively. Both the ThMAX presented here are significantly higher than the highest temperature recorded in this region since 1954and agree with global temperature models for the year 2100 predicted by the Intergovernmental Panel on Climate Change. PMID:25047483

  9. Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum

    USGS Publications Warehouse

    Sluijs, A.; Schouten, S.; Pagani, M.; Woltering, M.; Brinkhuis, H.; Damste, J.S.S.; Dickens, G.R.; Huber, M.; Reichart, G.-J.; Stein, R.; Matthiessen, J.; Lourens, L.J.; Pedentchouk, N.; Backman, J.; Moran, K.; Clemens, S.; Cronin, T.; Eynaud, F.; Gattacceca, J.; Jakobsson, M.; Jordan, R.; Kaminski, M.; King, J.; Koc, N.; Martinez, N.C.; McInroy, D.; Moore, T.C.; O'Regan, M.; Onodera, J.; Palike, H.; Rea, B.; Rio, D.; Sakamoto, T.; Smith, D.C.; St John, K.E.K.; Suto, I.; Suzuki, N.; Takahashi, K.; Watanabe, M. E.; Yamamoto, M.

    2006-01-01

    The Palaeocene/Eocene thermal maximum, ???55 million years ago, was a brief period of widespread, extreme climatic warming, that was associated with massive atmospheric greenhouse gas input. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition. We show that sea surface temperatures near the North Pole increased from ???18??C to over 23??C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations, but the absolute polar temperatures that we derive before, during and after the event are more than 10??C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms-perhaps polar stratospheric clouds or hurricane-induced ocean mixing-to amplify early Palaeogene polar temperatures. ?? 2006 Nature Publishing Group.

  10. Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum.

    PubMed

    Sluijs, Appy; Schouten, Stefan; Pagani, Mark; Woltering, Martijn; Brinkhuis, Henk; Sinninghe Damsté, Jaap S; Dickens, Gerald R; Huber, Matthew; Reichart, Gert-Jan; Stein, Ruediger; Matthiessen, Jens; Lourens, Lucas J; Pedentchouk, Nikolai; Backman, Jan; Moran, Kathryn

    2006-06-01

    The Palaeocene/Eocene thermal maximum, approximately 55 million years ago, was a brief period of widespread, extreme climatic warming, that was associated with massive atmospheric greenhouse gas input. Although aspects of the resulting environmental changes are well documented at low latitudes, no data were available to quantify simultaneous changes in the Arctic region. Here we identify the Palaeocene/Eocene thermal maximum in a marine sedimentary sequence obtained during the Arctic Coring Expedition. We show that sea surface temperatures near the North Pole increased from 18 degrees C to over 23 degrees C during this event. Such warm values imply the absence of ice and thus exclude the influence of ice-albedo feedbacks on this Arctic warming. At the same time, sea level rose while anoxic and euxinic conditions developed in the ocean's bottom waters and photic zone, respectively. Increasing temperature and sea level match expectations based on palaeoclimate model simulations, but the absolute polar temperatures that we derive before, during and after the event are more than 10 degrees C warmer than those model-predicted. This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms--perhaps polar stratospheric clouds or hurricane-induced ocean mixing--to amplify early Palaeogene polar temperatures.

  11. A fossil primate of uncertain affinities from the earliest late Eocene of Egypt.

    PubMed

    Seiffert, Erik R; Simons, Elwyn L; Boyer, Doug M; Perry, Jonathan M G; Ryan, Timothy M; Sallam, Hesham M

    2010-05-25

    Paleontological work carried out over the last 3 decades has established that three major primate groups were present in the Eocene of Africa-anthropoids, adapiforms, and advanced strepsirrhines. Here we describe isolated teeth of a previously undocumented primate from the earliest late Eocene ( approximately 37 Ma) of northern Egypt, Nosmips aenigmaticus, whose phylogenetic placement within Primates is unclear. Nosmips is smaller than the sympatric adapiform Afradapis but is considerably larger than other primate taxa known from the same paleocommunity. The species bears an odd mosaic of dental features, combining enlarged, elongate, and molariform premolars with simple upper molars that lack hypocones. Phylogenetic analysis across a series of different assumption sets variously places Nosmips as a stem anthropoid, a nonadapiform stem strepsirrhine, or even among adapiforms. This phylogenetic instability suggests to us that Nosmips likely represents a highly specialized member of a previously undocumented, and presumably quite ancient, endemic African primate lineage, the subordinal affinities of which have been obscured by its striking dental autapomorphies. Discriminant functions based on measurements of lower molar size and topography reliably classify extant prosimian primates into their correct dietary groups and identify Nosmips and Afradapis as omnivores and folivores, respectively. Although Nosmips currently defies classification, this strange and unexpected fossil primate nevertheless provides additional evidence for high primate diversity in northern Africa approximately 37 million years ago and further underscores the fact that our understanding of early primate evolution on that continent remains highly incomplete.

  12. Inducement of heterochronic variation in a species of planktic foraminifera by a Late Eocene impact event

    NASA Technical Reports Server (NTRS)

    Macleod, N.; Kitchell, J. A.

    1988-01-01

    While it is well known that the cosmic impact event at or near the Cretaceous-Tertiary boundary coincides with an interval of mass extinction, a similar impact (or series of impacts) near the Eocene-Oligocene boundary presents a more complex picture, in terms of associated fluctuations in marine biotic diversity. Tektites, microtektites, and mineral grains exhibiting features of shock metamorphism found in Eocene sediments of the western N. Atlantic, Caribbean, and Gulf of Mexico (comprising the North American microtektite strewn field) offer compelling evidence for a catastrophic impact event. Despite the magnitude of this event, however, few extinctions in the planktic marine fauna are known to have occurred coincident with this event. Instead, changes in relative abundance, morphology, and development occurred. Cosmic impacts generally have been interpreted as influencing the course of evolution through the wholesale elimination of significant portions of standing biotic diversity. Indeed, extinction traditionally has been viewed as the negative side of evolution. In some instances, it is suggested such impact events can serve instead to increase, rather than decrease, morphological and ecological diversity, by altering the developmental programs within species at the level of the local population.

  13. Paleocene/Eocene boundary changes in atmospheric and oceanic circulation: A Southern Hemisphere record

    SciTech Connect

    Hovan, S.A.; Rea, D.K. )

    1992-01-01

    Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocene boundary, the most complete mid-latitude sequence from a Southern Hemisphere location in the Indo-Pacific area. The events of this transition occurred during a span of about 1.2 m.y. Oxygen isotope values derived from benthic foraminiferal calcite decrease by about 1.0{per thousand}, a decrease most likely related to warming of deep ocean waters. Turnovers of benthic foraminifera accompany {delta}{sup 18}O changes and culminate in the predominant extinction event at the end of the Paleocene Epoch. Carbon isotope ratios also shift dramatically toward lighter values near the end of the Paleocene, beginning about 0.45 m.y. after oxygen isotope values start to change. The intensity of Southern Hemisphere atmospheric circulation as recorded by grain sizes of eolian particles shows a large and rapid reduction beginning another 0.45 m.y. later. A significant reduction of zonal wind strength at the Paleocene/Eocene boundary, until now observed only at Northern Hemisphere locations, appears to have been a global phenomenon related to decreased latitudinal thermal gradients occasioned by more effective poleward heat transport via the deep ocean.

  14. Micro-halocline enabled nutrient recycling may explain extreme Azolla event in the Eocene Arctic Ocean.

    PubMed

    van Kempen, Monique M L; Smolders, Alfons J P; Lamers, Leon P M; Roelofs, Jan G M

    2012-01-01

    In order to understand the physicochemical mechanisms that could explain the massive growth of Azolla arctica in the Eocene Arctic Ocean, we carried out a laboratory experiment in which we studied the interacting effects of rain and wind on the development of salinity stratification, both in the presence and in the absence of a dense Azolla cover. Additionally, we carried out a mesocosm experiment to get a better understanding of the nutrient cycling within and beneath a dense Azolla cover in both freshwater and brackish water environments. Here we show that Azolla is able to create a windproof, small-scale salinity gradient in brackish waters, which allows for efficient recycling of nutrients. We suggest that this mechanism ensures the maintenance of a large standing biomass in which additional input of nutrients ultimately result in a further expansion of an Azolla cover. As such, it may not only explain the extent of the Azolla event during the Eocene, but also the absence of intact vegetative Azolla remains and the relatively low burial efficiency of organic carbon during this interval. PMID:23166833

  15. The Toms Canyon structure, New Jersey outer continental shelf: A possible late Eocene impact crater

    USGS Publications Warehouse

    Poag, C.W.; Poppe, L.J.

    1998-01-01

    The Toms Canyon structure [~20-22 km wide] is located on the New Jersey outer continental shelf beneath 80-100 m of water, and is buried by ~1 km of upper Eocene to Holocene sedimentary strata. The structure displays several characteristics typical of terrestrial impact craters (flat floor; upraised faulted rim: brecciated sedimentary fill), but several other characteristics are atypical (an unusually thin ejecta blanket; lack of an inner basin, peak ring, or central peak; bearing nearly completely filled with breccia). Seismostratigraphic and biostratigraphic analyses show that the structure formed during planktonic foraminiferal biochron P15 of the early to middle late Eocene. The fill unit is stratigraphically correlating with impact ejecta cored nearby at Deep Sea Drilling Project (DSDP) Site 612 and at Ocean Drilling Program (ODP) Sites 903 and 904 (22-35 km southeast of the Toms Canyon structure). The Toms Canyon fill unit also correlates with the Exmore breccia, which fills the much larger Chesapeake Bay impact crater (90-km diameter; 335 km to the southwest). On the basis of our analyses, we postulate that the Toms Canyon structure is an impact crater, formed when a cluster of relatively small meteorites approached the target site bearing ~N 50 E, and struck the sea floor obliquely.

  16. Cool-water carbonates in an Eocene palaeoestuary, Norseman Formation, Western Australia

    NASA Astrophysics Data System (ADS)

    Clarke, Jonathan D. A.; Bone, Yvonne; James, Noel P.

    1996-02-01

    Numerous palaeovalleys formed extensive drowned estuaries during Eocene transgressions along the southwestern part of the southern margin of Australia. The Tertiary sediments of the Cowan palaeovalley have been extensively drilled, revealing deposition of the Norseman Formation during the Middle Eocene Tortachilla transgression. Initial deposition occurred during transgression of the valley to form a drowned estuary. Sediments consisted of coarse-grained muddy, lithic, iron and glauconite-rich sands and gravels of mixed carbonate and quartz. Pure carbonates accumulated during the highstand, produced by a typical shallow temperate water assemblage of bryozoans, coralline algae, echinoids and molluscs and were swept into shoals by strong tidal currents. Minor "tropical" components in the form of large benthic foraminifers and dasycladacean algae are present. Coarse bryozoan and trough cross-bedded carbonate sands accumulated in the margins of the estuary and fine bryozoan sands in the deeper parts. Rhodoliths accumulated to form shoals in sheltered localities. The Spencer Gulf and Gulf St. Vincent of South Australia provide close modern analogues to the Cowan palaeovalley and the Norseman Formation. Modern carbonate sediments off Esperance on the south coast of Western Australia contain "tropical" faunal elements within an otherwise temperate skeletal assemblage and also provide a modern analogue. The Norseman Formation thus provides an excellent example of cool-water carbonate deposition in near-shore, tide-dominated environments. This study complements and contrasts existing cool-water shelf facies models based on Tertiary carbonates deposited on deep shelves elsewhere in southern Australia.

  17. Radio-isotopic calibration of the Late Eocene - Early Oligocene geomagnetic polarity time scale

    NASA Astrophysics Data System (ADS)

    Sahy, Diana; Fischer, Anne U.; Condon, Daniel J.; Terry, Dennis O.; Hiess, Joe; Abels, Hemmo; Huesing, Silja K.; Kuiper, Klaudia F.

    2013-04-01

    The Geomagnetic Polarity Time Scale (GPTS) has been the subject of several revisions over the last few decades, with a trend toward increasing reliance on astronomically tuned age models over traditional radio-isotopic calibration. In the 2012 Geological Time Scale (GTS12) a comparison between radio-isotopic and astronomical age models for the GPTS yielded partially divergent results, with discrepancies of up to 0.4 Myr in the age of magnetic reversals around the Eocene - Oligocene transition (Vandenberghe et al., 2012). Radio-isotopic constraints on the age of Late Eocene - Early Oligocene magnetic reversals are available from two key sedimentary successions which host datable volcanic tuffs: the marine record of the Umbria-Marche basin in Italy, and the terrestrial White River Group of North America, however concerns have been raised regarding both the accuracy of dates obtained from these successions, and the reliability of their magnetic polarity records (Hilgen and Kuiper, 2009). Here we present a fully integrated radio-isotopic and magnetostratigraphic dataset from the Late Eocene - Early Oligocene North American terrestrial succession with the aim of assessing the accuracy and precision of numerical ages derived from the GPTS. We developed a magnetic polarity record for two partially overlapping sections: Flagstaff Rim in Wyoming and Toadstool Geologic Park in Nebraska, which together provide coverage for the time interval between 36-31 Myr (C16n.2n - C12n) and calibrated this record using an age model based on 14 Pb/U weighted mean ID-TIMS dates obtained on zircons from primary air fall tuffs. The uncertainty of our age model includes random and systematic components for all radio-isotopic tie-points, as well as estimated uncertainties in the stratigraphic position of both the magnetic reversals and the dated tuffs. Our Pb/U dates are 0.4 - 0.8 Myr younger than previously published Ar/Ar data (Swisher and Prothero,1990, recalculated to 28.201 Myr for Fish

  18. Eocene sea retreat out of Asia: paleogeography, controlling mechanisms and environmental impacts

    NASA Astrophysics Data System (ADS)

    Dupont-Nivet, Guillaume; Bosboom, Roderic; Proust, Jean-Noël; Mandic, Oleg; Villa, Giuliana; Grothe, Arjan; Stoica, Marius; Guo, Zhaojie; Krijgsman, Wout; Yang, Wei; Bougeois, Laurie; Aminov, Jovid; Ormukov, Cholponbec; Huang, Wentao

    2014-05-01

    The sediments of the Central Asian basins include the remnants of the easternmost extent of a large epicontinental sea. Before it retreated westward and eventually separated as the Paratethys Sea following the Eocene-Oligocene transition (EOT), this shallow marine sea extended across the Eurasian continent from the Mediterranean Tethys in the west to the Tarim Basin in western China in the east. However, the paleogeography and the timing of the westward retreat of the proto-Paratethys Sea are too poorly constrained to identify its proposed controlling mechanisms and paleoenvironmental impacts. The sea supposedly entered Central Asia in the Cretaceous and five third-order marine incursions have been recognized from the Cretaceous-Paleogene sedimentary record, of which the last two transgressions are documented here. We studied the sea retreat in the Tarim Basin in western China, the Alai Valley and Ferghana Basin in southern Kyrgyzstan and the Afghan-Tajik Basin in south-western Tajikistan. Integrated bio-magnetostratigraphic dating shows that the sea retreated westward from the Tarim Basin in stepwise fashion. The major fourth transgression occurred during the Lutetian, after which the sea retreated from the southwest Tarim Basin paleodepocenter at ~41 Ma (base C18r). The last and fifth transgression was restricted to the westernmost margin of the Tarim basin and occurred during latest Bartonian-early Priabonian (base C17n.3n-base C16n.1n). At the level of precision of our dating, each of these marine incursions is apparently synchronous across the Tarim Basin suggesting rapid regional transgression/regression cycles in these shallow epicontinental basins with limited diachroneity. The shallow marine near-shore sediments of these last two transgressions can be convincingly correlated by litho- and biostratigraphy across Central Asia, showing for the first time that the sea may have largely retreated from Central Asia in the late Eocene. The lack of apparent

  19. Biotic Response in Aquatic Reptiles (Testudines) during Earliest Eocene Climatic Warming

    NASA Astrophysics Data System (ADS)

    Holroyd, P. A.; Hutchison, J. H.

    2010-12-01

    The earliest Eocene is marked by significant events of global warming: the Paleocene-Eocene Thermal Maximum (PETM) at ~55.8 Ma and two short-lived events (ETM2 or Elmo and H2) approximately 2 Ma later. These environmental changes induced strong responses in the continental biota. Noteworthy changes in North American mid-latitude faunas and floras that are temporally correlated with earliest Eocene warming events include: increased diversity; turnover; and significant range changes, comprising both northward shifts in ranges of North American taxa as well as intercontinental dispersal across Holarctica. Evidence for these biotic changes comes directly from the fossil record and indirectly from phylogeographic analyses of molecular phylogenies of extant biota. To date, the stratigraphic record of biotic change has only been examined for the flora and terrestrial mammals. Data on reptiles and for continental aquatic systems are particularly lacking. In order to assess the impact of climate-mediated faunal change in aquatic systems during early Paleogene warming, we have focused on developing a detailed record of fossil turtles (Testudines) from the Bighorn Basin of Wyoming, where these records can be directly compared to similarly studied mammalian and floral data and to isotopic studies that provide independent proxies of climate change. Using genus-level occurrence data from more than 450 stratigraphically-constrained localities spanning ~2.5 Ma, we calculated first and last appearances, taxonomic richness, and relative abundance as measured by presence-absence (site occupancy). Among turtles, taxonomic richness increased episodically through the earliest Eocene with two new taxa appearing at the PETM, two immediately following it, and two at Biohorizon B, an interval associated with the younger hyperthermals. These new, immigrant taxa eventually comprised 40% of known generic richness. Phylogenetically, the inferred biogeographic source regions are southern North

  20. Long-distance longitudinal transport of gravel across the Cordilleran thrust belt of Montana and Idaho

    NASA Astrophysics Data System (ADS)

    Janecke, Susanne U.; Vandenburg, Colby J.; Blankenau, James J.; M'gonigle, John W.

    2000-05-01

    Two newly identified middle Eocene paleovalleys (≥ 100 km long) preserved on top of the southwest Montana reentrant of the Cordilleran fold-and-thrust belt indicate long-lived longitudinal flow across the thrust belt and resolve a long-standing debate about the source of the voluminous quartzite debris in the Upper Cretaceous to lower Tertiary Divide, Harebell, and Pinyon conglomerates of Montana, Idaho, and Wyoming. Geologic mapping, stratigraphic, provenance, and geochronologic studies revealed that Eocene volcanic and sedimentary rocks in the paleovalleys are as thick as 2 km, onlap preexisting bedrock, and interfinger with well-rounded conglomerate derived from formations exposed only to the west. The middle Eocene paleovalleys are the youngest expression of a major paleoriver system that transported sediment toward the foreland during the Sevier orogeny. An Eocene subcrop map shows that the headwaters of the Eocene paleovalleys coincided with structural culminations in the thrust belt that supplied sediment to the Divide conglomerate of the Upper Cretaceous to lower Tertiary Beaverhead Group. Ultimately, the Lemhi Pass and Hawley Creek paleovalleys provided several thousand cubic kilometers of quartzite debris to the Pinyon and Harebell conglomerates of northwest Wyoming 200 350 km away, and formed the northwest half of a giant longitudinal drainage system. Sevier contraction, not the rising Idaho batholith, first uplifted vast culminations beneath the headwaters of this river system.

  1. Estimates of late middle Eocene pCO2 based on stomatal density of modern and fossil Nageia leaves

    NASA Astrophysics Data System (ADS)

    Liu, X. Y.; Gao, Q.; Han, M.; Jin, J. H.

    2016-02-01

    Atmospheric pCO2 concentrations have been estimated for intervals of the Eocene using various models and proxy information. Here we reconstruct late middle Eocene (42.0-38.5 Ma) pCO2 based on the fossil leaves of Nageia maomingensis Jin et Liu collected from the Maoming Basin, Guangdong Province, China. We first determine relationships between atmospheric pCO2 concentrations, stomatal density (SD) and stomatal index (SI) using "modern" leaves of N. motleyi (Parl.) De Laub, the nearest living species to the Eocene fossils. This work indicates that the SD inversely responds to pCO2, while SI has almost no relationship with pCO2. Eocene pCO2 concentrations can be reconstructed based on a regression approach and the stomatal ratio method by using the SD. The first approach gives a pCO2 of 351.9 ± 6.6 ppmv, whereas the one based on stomatal ratio gives a pCO2 of 537.5 ± 56.5 ppmv. Here, we explored the potential of N. maomingensis in pCO2 reconstruction and obtained different results according to different methods, providing a new insight for the reconstruction of paleoclimate and paleoenvironment in conifers.

  2. Sedimentary model for Eocene exotic blocks of carbonates and turbiditic carbonate deposits in the South Sistan Basin, SE Iran

    NASA Astrophysics Data System (ADS)

    Mohammadi, Ali; Burg, Jean-Pierre; Bernoulli, Daniel

    2016-04-01

    The N-S-trending Sistan Suture Zone in east Iran results from collision of the Lut Block to the west with the Afghan Block to the east. Extensive Eocene turbiditic sequences with numerous exotic carbonate olistholiths and carbonate debris flows in the southern part of the Sistan Basin (so-called Neh Accretionary Wedge) were deposited in a deep-marine environment. Litho-biostratigraphy of the exotic carbonate blocks and carbonate debris flows with surrounding sandstones aims to develop a paleoenvironmental model for the South Sistan sedimentary basin. The olistholiths, of Early to Middle Eocene age, are derived from one or more carbonate platforms including inner shelf (protected platform), shelf margin (coral reefs, skeletal sand bars) and upper slope deposits. In addition, the terrigenous turbidites that form the background sediments of the basinal deposits are interlayered with carbonate mass-flow deposits, lime turbidites and scarcer pelagic limestones with planktonic foraminifera of Eocene age showing that the mass-flow events contemporaneous with platform evolution. The absence of terrigenous detritus and of volcanic material in the platform limestones and related mass-flow deposits suggests that the carbonate platform was presumably located on the Kuh-e-Birk passive margin, to the southwest of the Sistan Basin. Key words: South Sistan Basin, sedimentary model, Eocene, olistostrome, carbonate platform

  3. A new Late Eocene primate from the Krabi Basin (Thailand) and the diversity of Palaeogene anthropoids in southeast Asia

    PubMed Central

    Chaimanee, Yaowalak; Chavasseau, Olivier; Lazzari, Vincent; Euriat, Adélaïde; Jaeger, Jean-Jacques

    2013-01-01

    According to the most recent discoveries from the Middle Eocene of Myanmar and China, anthropoid primates originated in Asia rather than in Africa, as was previously considered. But the Asian Palaeogene anthropoid community remains poorly known and inadequately sampled, being represented only from China, Myanmar, Pakistan and Thailand. Asian Eocene anthropoids can be divided into two distinct groups, the stem group eosimiiforms and the possible crown group amphipithecids, but the phylogenetic relationships between these two groups are not well understood. Therefore, it is critical to understand their evolutionary history and relationships by finding additional fossil taxa. Here, we describe a new small-sized fossil anthropoid primate from the Late Eocene Krabi locality in Thailand, Krabia minuta, which shares several derived characters with the amphipithecids. It displays several unique dental characters, such as extreme bunodonty and reduced trigon surface area, that have never been observed in other Eocene Asian anthropoids. These features indicate that morphological adaptations were more diversified among amphipithecids than was previously expected, and raises the problem of the phylogenetic relations between the crown anthropoids and their stem group eosimiiforms, on one side, and the modern anthropoids, on the other side. PMID:24089342

  4. Late Paleocene-early Eocene carbon isotope stratigraphy from a near-terrestrial tropical section and antiquity of Indian mammals

    NASA Astrophysics Data System (ADS)

    Samanta, A.; Sarkar, A.; Bera, M. K.; Rai, Jyotsana; Rathore, S. S.

    2013-02-01

    Late Paleocene to early Eocene (~56 to 51 Ma) interval is characterized by five distinct transient warming (hyperthermal) events (Paleocene-Eocene thermal maximum (PETM), H1/ETM2/ELMO, H2, I1 and I2) in a super greenhouse globe associated with negative carbon isotope excursions (CIEs). Although well-documented marine records exist at different latitudes, terrestrial PETM sections are rare. In particular, almost no terrestrial records of either the PETM or early Eocene hyperthermals (EEHs) are yet available from the tropics. Further, evolution of modern order of mammals near the PETM has been recorded in many northern continents; however, the response of mammals in the tropics to these warming events is unknown. A tropical terrestrial record of these hyperthermal/CIE events, encompassing the earliest modern order mammal bearing horizon from India, can therefore be vital in understanding climatic and biotic evolution during the earliest Cenozoic time. Here, for the first time, we report high resolution carbon isotope ( δ 13C) stratigraphy, nannofossil, and Sr isotope ratio of marine fossil carbonate from the Cambay Shale Formation of Western India. The record shows complete preservation of all the above CIE events, including the PETM, hitherto unknown from the equatorial terrestrial records. δ 13C chemostratigraphy further suggests that at least the present early Eocene mammal-bearing horizon, recently discovered at Vastan, does not support the `out of India' hypothesis of earliest appearance of modern mammals and subsequent dispersal to the Holarctic continents.

  5. Molecular and Morphological Evidence Challenges the Records of the Extant Liverwort Ptilidium pulcherrimum in Eocene Baltic Amber.

    PubMed

    Heinrichs, Jochen; Scheben, Armin; Lee, Gaik Ee; Váňa, Jiří; Schäfer-Verwimp, Alfons; Krings, Michael; Schmidt, Alexander R

    2015-01-01

    Preservation of liverworts in amber, a fossilized tree resin, is often exquisite. Twenty-three fossil species of liverworts have been described to date from Eocene (35-50 Ma) Baltic amber. In addition, two inclusions have been assigned to the extant species Ptilidium pulcherrimum (Ptilidiales or Porellales). However, the presence of the boreal P. pulcherrimum in the subtropical or warm-temperate Baltic amber forest challenges the phytogeographical interpretation of the Eocene flora. A re-investigation of one of the fossils believed to be P. pulcherrimum reveals that this specimen in fact represents the first fossil evidence of the genus Tetralophozia, and thus is re-described here as Tetralophozia groehnii sp. nov. A second fossil initially assigned to P. pulcherrimum is apparently lost, and can be reassessed only based on the original description and illustrations. This fossil is morphologically similar to the extant North Pacific endemic Ptilidium californicum, rather than P. pulcherrimum. Divergence time estimates based on chloroplast DNA sequences provide evidence of a Miocene origin of P. pulcherrimum, and thus also argue against the presence of this taxon in the Eocene. Ptilidium californicum originated 25-43 Ma ago. As a result, we cannot rule out that the Eocene fossil belongs to P. californicum. Alternatively, the fossil might represent a stem lineage element of Ptilidium or an early crown group species with morphological similarities to P. californicum. PMID:26536603

  6. Stable isotope paleoclimatology of the earliest Eocene using kimberlite-hosted mummified wood from the Canadian Subarctic

    NASA Astrophysics Data System (ADS)

    Hook, B. A.; Halfar, J.; Gedalof, Z.; Bollmann, J.; Schulze, D.

    2014-11-01

    The recent discovery of well-preserved mummified wood buried within a subarctic kimberlite diamond mine prompted a paleoclimatic study of the early Eocene "hothouse" (ca. 53.3 Ma). At the time of kimberlite eruption, the Subarctic and Artic were warm and humid producing a temperate rainforest biome well north of the Arctic Circle. Previous studies have estimated mean annual temperatures in this region were 4-20 °C in the early Eocene, using a variety of proxies including leaf margin analysis, and stable isotopes (δ18O) of fossil cellulose. Here, we examine stable isotopes of tree-ring cellulose at subannual to annual scale resolution, using the oldest viable cellulose found to date. We use mechanistic models and transfer functions to estimate earliest Eocene temperatures using mummified cellulose, which was well preserved in the kimberlite. Multiple samples of Piceoxylon wood within the kimberlite were crossdated by tree-ring width. Multiple proxies are used in combination to tease apart likely environmental factors influencing the tree physiology and growth in the unique extinct ecosystem of the Polar rainforest. Calculations of interannual variation in temperature over a multidecadal time-slice in the early Eocene are presented, with a mean temperature estimate of 11.4 °C (1σ = 1.8 °C) based on δ18O. Dual-isotope spectral analysis suggests that multidecadal climate cycles similar to the modern Pacific Decadal Oscillation likely drove temperature and cloudiness trends on 20-30 year timescales.

  7. Molecular and Morphological Evidence Challenges the Records of the Extant Liverwort Ptilidium pulcherrimum in Eocene Baltic Amber.

    PubMed

    Heinrichs, Jochen; Scheben, Armin; Lee, Gaik Ee; Váňa, Jiří; Schäfer-Verwimp, Alfons; Krings, Michael; Schmidt, Alexander R

    2015-01-01

    Preservation of liverworts in amber, a fossilized tree resin, is often exquisite. Twenty-three fossil species of liverworts have been described to date from Eocene (35-50 Ma) Baltic amber. In addition, two inclusions have been assigned to the extant species Ptilidium pulcherrimum (Ptilidiales or Porellales). However, the presence of the boreal P. pulcherrimum in the subtropical or warm-temperate Baltic amber forest challenges the phytogeographical interpretation of the Eocene flora. A re-investigation of one of the fossils believed to be P. pulcherrimum reveals that this specimen in fact represents the first fossil evidence of the genus Tetralophozia, and thus is re-described here as Tetralophozia groehnii sp. nov. A second fossil initially assigned to P. pulcherrimum is apparently lost, and can be reassessed only based on the original description and illustrations. This fossil is morphologically similar to the extant North Pacific endemic Ptilidium californicum, rather than P. pulcherrimum. Divergence time estimates based on chloroplast DNA sequences provide evidence of a Miocene origin of P. pulcherrimum, and thus also argue against the presence of this taxon in the Eocene. Ptilidium californicum originated 25-43 Ma ago. As a result, we cannot rule out that the Eocene fossil belongs to P. californicum. Alternatively, the fossil might represent a stem lineage element of Ptilidium or an early crown group species with morphological similarities to P. californicum.

  8. Molecular and Morphological Evidence Challenges the Records of the Extant Liverwort Ptilidium pulcherrimum in Eocene Baltic Amber

    PubMed Central

    Heinrichs, Jochen; Scheben, Armin; Lee, Gaik Ee; Váňa, Jiří; Schäfer-Verwimp, Alfons; Krings, Michael; Schmidt, Alexander R.

    2015-01-01

    Preservation of liverworts in amber, a fossilized tree resin, is often exquisite. Twenty-three fossil species of liverworts have been described to date from Eocene (35–50 Ma) Baltic amber. In addition, two inclusions have been assigned to the extant species Ptilidium pulcherrimum (Ptilidiales or Porellales). However, the presence of the boreal P. pulcherrimum in the subtropical or warm-temperate Baltic amber forest challenges the phytogeographical interpretation of the Eocene flora. A re-investigation of one of the fossils believed to be P. pulcherrimum reveals that this specimen in fact represents the first fossil evidence of the genus Tetralophozia, and thus is re-described here as Tetralophozia groehnii sp. nov. A second fossil initially assigned to P. pulcherrimum is apparently lost, and can be reassessed only based on the original description and illustrations. This fossil is morphologically similar to the extant North Pacific endemic Ptilidium californicum, rather than P. pulcherrimum. Divergence time estimates based on chloroplast DNA sequences provide evidence of a Miocene origin of P. pulcherrimum, and thus also argue against the presence of this taxon in the Eocene. Ptilidium californicum originated 25–43 Ma ago. As a result, we cannot rule out that the Eocene fossil belongs to P. californicum. Alternatively, the fossil might represent a stem lineage element of Ptilidium or an early crown group species with morphological similarities to P. californicum. PMID:26536603

  9. Eocene sea retreat out of Asia: paleogeography, controlling mechanisms and environmental impacts

    NASA Astrophysics Data System (ADS)

    Dupont-Nivet, Guillaume; Bosboom, Roderic; Proust, Jean-Noël; Mandic, Oleg; Villa, Giuliana; Grothe, Arjan; Stoica, Marius; Guo, Zhaojie; Krijgsman, Wout; Yang, Wei; Bougeois, Laurie; Aminov, Jovid; Ormukov, Cholponbec; Huang, Wentao

    2014-05-01

    The sediments of the Central Asian basins include the remnants of the easternmost extent of a large epicontinental sea. Before it retreated westward and eventually separated as the Paratethys Sea following the Eocene-Oligocene transition (EOT), this shallow marine sea extended across the Eurasian continent from the Mediterranean Tethys in the west to the Tarim Basin in western China in the east. However, the paleogeography and the timing of the westward retreat of the proto-Paratethys Sea are too poorly constrained to identify its proposed controlling mechanisms and paleoenvironmental impacts. The sea supposedly entered Central Asia in the Cretaceous and five third-order marine incursions have been recognized from the Cretaceous-Paleogene sedimentary record, of which the last two transgressions are documented here. We studied the sea retreat in the Tarim Basin in western China, the Alai Valley and Ferghana Basin in southern Kyrgyzstan and the Afghan-Tajik Basin in south-western Tajikistan. Integrated bio-magnetostratigraphic dating shows that the sea retreated westward from the Tarim Basin in stepwise fashion. The major fourth transgression occurred during the Lutetian, after which the sea retreated from the southwest Tarim Basin paleodepocenter at ~41 Ma (base C18r). The last and fifth transgression was restricted to the westernmost margin of the Tarim basin and occurred during latest Bartonian-early Priabonian (base C17n.3n-base C16n.1n). At the level of precision of our dating, each of these marine incursions is apparently synchronous across the Tarim Basin suggesting rapid regional transgression/regression cycles in these shallow epicontinental basins with limited diachroneity. The shallow marine near-shore sediments of these last two transgressions can be convincingly correlated by litho- and biostratigraphy across Central Asia, showing for the first time that the sea may have largely retreated from Central Asia in the late Eocene. The lack of apparent

  10. The marine 187Os/ 188Os record of the Eocene-Oligocene transition: the interplay of weathering and glaciation

    NASA Astrophysics Data System (ADS)

    Ravizza, G.; Peucker-Ehrenbrink, B.

    2003-05-01

    Osmium (Os) isotope analyses of bulk sediments from the South Atlantic, Equatorial Pacific, and the Italian Apennines yield a well-dated and coherent pattern of 187Os/ 188Os variation from the late Eocene to the early Oligocene. The resulting composite record demonstrates the global character of two prominent features of the low-resolution LL44-GPC3 Os isotope record [Pegram and Turekian, Geochim. Cosmochim. Acta 63 (1999) 4053-4058]. These are: (1) a pronounced minimum in 187Os/ 188Os (0.22-0.27) in the late Eocene, between 34 and 34.5 Ma, and (2) a subsequent rapid increase in 187Os/ 188Os, to approximately 0.6 by 32 Ma. An ultramafic weathering event and an increased influx of extraterrestrial particles to the Earth are discussed as alternative explanations for the late Eocene 187Os/ 188Os minimum. Comparison of the 187Os/ 188Os to benthic foraminiferal oxygen isotope records demonstrates that the nearly three-fold increase in 187Os/ 188Os from the late Eocene minimum coincides with the growth and decay of the first large ice sheet of the Oligocene (Oi1 [Miller et al., J. Geophys. Res. 96 (1991) 6829-6848]). The fine structure of the Os isotope record indicates that enhanced release of radiogenic Os, unrelated to the recovery from late Eocene minimum, lagged the initiation of the Oi1 event by roughly 0.5 Myr. This record, in conjunction with weathering studies in modern glacial soils [Blum, in: W.F. Ruddiman (Ed.), Tectonic Uplift and Climate Change, Plenum Press, New York, 1997, pp. 259-288; Peucker-Ehrenbrink and Blum, Geochim. Cosmochim. Acta 62 (1998) 3193-3203], suggests that exposure of freshly eroded material during deglaciation following Oi1 enhanced chemical weathering rates, and may have contributed to ice sheet stabilization by drawing down atmospheric carbon dioxide. The improved temporal resolution and age control of the refined Eocene-Oligocene Os isotope record also makes it possible to illustrate the late Eocene Os isotope excursion as a tool for

  11. A Backarc Basin Origin for the Eocene Volcanic Rocks North of Abbas Abad, East of Shahrud, Northeast Iran

    NASA Astrophysics Data System (ADS)

    Khalatbari Jafari, M.; Mobasher, K.; Davarpanah, A.; Babaie, H.; La Tour, T.

    2008-12-01

    The region in northeastern Iran, bordered by the Miami fault and the Doruneh fault, mainly exposes the Eocene volcanic and Tertiary sedimentary rocks and sporadic outcrops of pre- Jurassic metamorphic rocks such as gneiss and mica-schist. We have divided the volcanic and volcanic-sedimentary rocks into six main units: E1 through the youngest E6. North of Abbas Abad, the Lower Eocene is conglomerate, sandstone, and red shale with lenses of nummulite-bearing limestone at the base, and dacitic lava (E1) at the top. The nummulites give an Early Eocene age for the limestone lenses. The E2 unit includes vesicular basalt, intercalated, intraformational conglomerate, and lenses of nummulite-bearing limestone. E3 is volcanic- sedimentary, and is made of green tuff, tuffite, shale, and nummulite bearing limestone. E4 includes basalt and vesicular trachy-basalt, and E5 is mostly sedimentary, made of tan marl, sandstone, shale, and lenses of Middle Eocene nummulite-bearing limestone. The E6 unit is the most extensive, with at least three levels of nummulite-bearing limestone lenses which give a Middle to Early Eocene age. The volcanic rocks of the E6 unit include few hundred meters of epiclastic to hyaloclastic breccia, with intercalations of lava at the base. These are overlain by four horizons of aphyric olivine basalt and basalt, and phyric trachy-andesite and trachy-basalt. The volume of the aphyric lavas decreases, and that of the phyric lavas increases upsection. The Eocene volcanic sequence is covered by turbidite; the marl washings give an Eocene-Oligocene age range. Chondrite-normalized multi-element plots indicate enrichment of the Eocene Abbas Abad volcanic rocks in the LILE elements, with variable ratios of La/Yb (4.36-19.33) and La/Sm (3.10-7.91). These plots show a gentle slope, and the volcanic rocks in the E1 to E4 units are less enriched than those in the E6 unit, probably reflecting the difference in the original source for the melt. The multi-element plots

  12. Petrology and Geochemistry of the Eocene Volcanic Rocks in the Kahrizak Mountains, Central Iran

    NASA Astrophysics Data System (ADS)

    Yazdani, S.; Castillo, P.; Tutti, F.

    2013-12-01

    The Eocene volcanic rocks in the Kahrizak (KH) Mountains in the northern part of Central Iran were mainly formed by magmatism that accompanied block-faulting tectonism in the region. In the KH area, the volcanic rocks are nonconformably overlain by Oligocene-Pliocene sedimentary deposits, suggesting that the Eocene magmatic activity in the region was followed by a sequence of uplift and shallow marine regression. The volcanic rocks consist of pyroclastics (tuff and ignimbrites) and lava flows (basalt, basaltic trachyandesite, trachyandesite, and rhyolite); superposition indicates an earlier explosive volcanic phase that caused the widespread distribution of rhyolitic ignimbrites and tuffs, and this was followed by a quieter phase of lava eruptions. Petrographic evidence such as mineral zoning, sieve texture and rounded crystals of plagioclase and pyroxene phenocrysts indicate non-equilibrium conditions between melt and crystals during magma cooling. These textures suggest magma mixing, although these may also be due to rapid decompression, where heat loss is minor relative to the ascent rate. The geochemistry of KH samples indicates their subalkaline to alkaline affinity. In terms of trace element contents, most samples exhibit the distinct geochemical trait of arc volcanism, i.e., Nb and Ta depletions relative to LILE (e.g., Ba, Rb) enrichment and positive Sr anomaly; however, Zr and Ti depletions are not prominent. The samples have a light-REE enriched but flat heavy-REE pattern and negative Eu anomaly in the rhyolites and trachyandesites. They have a ~narrow to ~moderate range of Pb isotopic ratios (206Pb/204Pb ~18.6-18.9, 207Pb/204Pb ~15.5-15.6, and 208Pb/204Pb ~38.5-38.8), with basaltic rocks somewhat higher than rhyolitic rocks. Available geochemical and isotopic data suggest a complex origin and evolution of the KH magmas. The magmas originated from an intrinsically ~heterogeneous source and, in addition to fractional crystallization, some of the

  13. Paleoceanography of the Eocene Central Arctic Basin Based on Geochemical Measurements of Biogenic Matter

    NASA Astrophysics Data System (ADS)

    Takahashi, K.-; Ogawa, Y.-; Onodera, J.-

    2006-12-01

    The IODP Leg 302 Arctic Coring Expedition retrieved approximately 120 m long continuous Eocene section from the Lomonosov Ridge in the central Arctic for the first time. The Eocene section is lithologically classified into Unit 2 with the assigned age of ~49-44Ma below and Unit 1/6 with 44Ma above the unit boundary. Unit 2 consists of very dark gray mud bearing siliceous ooze and Unit 1/6 consists of very dark gray silty clay to clayey silt. Biogenic opal (293 samples), organic carbon, nitrogen, and sulfur (150 samples) were measured. The sample resolutions are approximately 16 kyrs for Unit 2 and 8 kyrs interval for Unit 1/6, respectively. In Unit 2 biogenic opal ranged from 40 to 70% whereas in Unit 1/6, it decreased down to 10-20%, except for a peak of 37% at approximately 203 mbsf. Organic carbon consistently showed high values such as 1.4-5.7% both in Units 2 and 1/6. C/N ratios ranged from 15 to 20. Sulfur values ranged 2.6-7.7% in Unit 2 and it significantly increased to 4.0-19.4% in Unit 1/6. Based on the presence of abundant framboidal pyrites and the observed extremely low C/S ratios of <1.2 clearly indicate that the basin was under euxinic marine condition with sluggish bottom water circulation. Siliceous plankton mainly contributed to the biological productivity from 250 to 220 mbsf in Unit 2 and from 216 to 207 mbsf in Unit 1/6, judging from positive correlations of %biogenic opal vs %organic carbon. In other parts of the section such a positive correlation was not seen, implying something else other than siliceous plankton mainly contributed the total productivity. From Unit 2 to Unit 1/6, three rather drastic environmental changes are suggested: decrease of siliceous plankton productivity, increase of sulfate availability, and intensification of the euxinic conditions. In Unit 1/6 where sulfur values significantly increased, an increase of marine water inflow from the North Atlantic suggested by a study on silicofragellates assemblages. The marine

  14. Upper Paleocene-Lower Eocene biostratigraphy of Darb Gaga, Southeastern Kharga Oasis Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Ouda, Khaled; Berggren, William A.; Abdel Sabour, Ayman

    2016-06-01

    Paleontological studies on the Upper Paleocene-Lower Eocene succession at Darb Gaga, southeastern Kharga Oasis, Western Desert, Egypt document the changes associated with the Paleocene-Eocene Thermal Maximum (PETM), such as 1) a radical alteration of the relative and absolute abundance of planktonic foraminifera; 2) a massive occurrence of the excursion planktonic foraminiferal taxa; 3) a widespread deposition of calcarenite yielding atypical (extremely high) faunal abundance associated with the younger phase of warming; and 4) a concentration of coprolites associated with the middle phase of warming. We also document the Lowest Occurrence (LO) of dimorphic larger benthic and excursion foraminifera during the earlier phase of warming at Darb Gaga, as recorded in Bed 1 of the Dababiya Quarry Member. The absence of these faunas in Bed 1 at Dababiya (the GSSP for the P/E Boundary) is likely to be due to both intense deficiency in dissolved oxygen and massive carbonate dissolution. Only remains (fish remains) of faunas that can tolerate the toxicity produced by low oxygen conditions are found in the stratigraphic record of this (oldest) phase at Dababiya. The Dababiya Quarry Member (DQM) at Darb Gaga reflects the unfolding of the sedimentary and biotic changes associated with the PETM global warming at, and following, the Paleocene/Eocene boundary on the southern Tethys platform. The changes began with a rapid increase in bottom and "intermediate" water temperature. The temperature increase was accompanied by removal of oxygen during the early and middle stages of warming. This led to the absence of both subbotinids and calcareous benthic foraminifera in the early and second coprolite-bearing phases (Beds 2 and 3 of the DQM). Dissolution seems to have no role during these stages as shown by the unusual abundance and good preservation of the warm-tolerant Ac. sibaiyaensis. This species reaches its maximum abundance in Bed 2 where it exhibits a broad range of size (63

  15. The Eocene Arctic Azolla phenomenon: species composition, temporal range and geographic extent.

    NASA Astrophysics Data System (ADS)

    Collinson, Margaret; Barke, Judith; van der Burgh, Johan; van Konijnenburg-van Cittert, Johanna; Pearce, Martin; Bujak, Jonathan; Brinkhuis, Henk

    2010-05-01

    Azolla is a free-floating freshwater fern that is renowned for its rapid vegetative spread and invasive biology, being one of the world's fastest growing aquatic macrophytes. Two species of this plant have been shown to have bloomed and reproduced in enormous numbers in the latest Early to earliest Middle Eocene of the Arctic Ocean and North Sea based on samples from IODP cores from the Lomonosov Ridge (Arctic) and from outcrops in Denmark (Collinson et al 2009 a,b Review of Palaeobotany and Palynology 155,1-14; and doi:10.1016/j.revpalbo.2009.12.001). To determine the geographic and temporal extent of this Azolla phenomenon, and the spatial distribution of the different species, we have examined samples from 15 additional sites using material from ODP cores and commercial exploration wells. The sites range from the Sub-Arctic (Northern Alaska and Canadian Beaufort Mackenzie Basin) to the Nordic Seas (Norwegian-Greenland Sea and North Sea Basin). Our data show that the Azolla phenomenon involved at least three species. These are distinguished by characters of the megaspore apparatus (e.g. megaspore wall, floats, filosum) and the microspore massulae (e.g. glochidia fluke tips). The Lomonosov Ridge (Arctic) and Danish occurrences are monotypic but in other sites more than one species co-existed. The attachment to one another and the co-occurrence of megaspore apparatus and microspore massulae, combined with evidence that these spores were shed at the fully mature stage of their life cycle, shows that the Azolla remains were not transported over long distances, a fact which could not be assumed from isolated massula fragments alone. Our evidence, therefore, shows that Azolla plants grew on the ocean surfaces for approximately 1.2 million years (from 49.3 to 48.1 Ma) and that the Azolla phenomenon covered the area from Denmark northwards across the North Sea Basin and the whole of the Arctic and Nordic seas. Apparently, early Middle Eocene Northern Hemisphere middle

  16. Recognition of Early Eocene global carbon isotope excursions using lipids of marine Thaumarchaeota

    NASA Astrophysics Data System (ADS)

    Schoon, Petra L.; Heilmann-Clausen, Claus; Pagh Schultz, Bo; Sluijs, Appy; Sinninghe Damsté, Jaap S.; Schouten, Stefan

    2013-07-01

    The Paleocene-Eocene Thermal Maximum (PETM; ˜56 Ma) and Eocene Thermal Maximum 2 (ETM2; ˜53 Ma) are geological short (<200,000 years) episodes of extreme global warming and environmental change. Both the PETM and ETM2 are associated with the injection of 13C-depleted carbon into the ocean-atmosphere system as revealed through a globally recognized carbon isotope excursion (CIE) and massive dissolution of deep sea carbonate. However, the magnitude of these CIEs vary with the type of fossil matter, i.e. multiple carbonate phases, bulk organic matter, and terrestrial and marine biomarker lipids, making it difficult to constrain the actual CIE in atmospheric and oceanic carbon pools. Here we analyzed the stable carbon isotopic composition (δ13C) of glycerol dibiphytanyl glycerol tetraether lipids (GDGTs) derived from marine Thaumarchaeota in sediments deposited during the PETM in the North Sea Basin and ETM2 in the Arctic Ocean. The δ13C values of these lipids are potentially directly recording variations in δ13C dissolved inorganic carbon (DIC) and can thus provide a record of marine δ13C DIC across both these Eocene carbon cycle perturbations. Reconstructed pre-CIE δ13CDIC values are slightly lower (0.5-1‰) than modern day values, possibly because Thaumarchaeotal lipids are not only derived from surface waters but also from 13C-depleted subsurface waters. Their values decrease by ˜3.6 (±0.3) ‰ and ˜2.5 (±0.7)‰ during the PETM and ETM2, respectively. The CIE in crenarchaeol for ETM2 is higher than that in marine calcite from other locations, possibly because of the admixture of deep water 13C-depleted CO2 generated by the euxinic conditions that developed occasionally during ETM2. However, the reconstructed PETM CIE lies close to the CIE inferred from marine calcite, suggesting that the δ13C record of crenarchaeol may document changes in marine DIC during the PETM in the North Sea Basin. The δ13C of thaumarchaeotal lipids may thus be a novel tool to

  17. It's getting hot here - The Middle Eocene Climatic Optimum (MECO) in a terrestrial sedimentary record

    NASA Astrophysics Data System (ADS)

    Methner, K.; Wacker, U.; Fiebig, J.; Chamberlain, C.; Mulch, A.

    2013-12-01

    The Middle Eocene Climatic Optimum (MECO) represents an enigmatic global warming event during Cenozoic cooling that has been discovered in ocean drill cores from varying latitudes and oceanic basins. It is marked by a rapid negative shift in oxygen isotope ratios of foraminiferal calcite and thought to reflect the combined effects of freshwater input as well as an increase in sea surface and bottom water temperatures by up to 5 to 6 °C. MECO is therefore a temperature extreme during already warm Eocene climate. This makes the MECO to one of the hottest phases during Earth's climate history, yet it is largely unknown how MECO affected temperatures in the continental interiors as well as their rainfall and vegetation dynamics. Here, we present stable isotope (δ18O, δ13C) and clumped isotope temperature (Δ47) records from a middle Eocene (ca. 42.0 to 40.0 Ma) mammal fossil locality in southwestern Montana, USA. The sampled section (Upper Dell Beds, Sage Creek Basin) comprises about 60 m of stacked paleosols that were correlated to Chron C18r by paleomagnetics and biostratigraphy. δ18O values of pedogenic carbonate range from -12 to -18 per mil (SMOW) and to first-order follows the marine δ18O pattern. Low δ18O values coincide with peak-MECO conditions and show a relatively rapid ca. 5°C increase in soil temperatures reaching peak temperatures of ~27°C at the climax of MECO. Immediately after the MECO event temperatures drop rapidly by about 8°C. To our knowledge this is the first terrestrial MECO paleotemperature record that further provides insight into the precipitation dynamics deep within the North American continent during this early Cenozoic hyperthermal. Paleosol Δ47 temperatures are highly reproducible within and across individual soil sequences and provide a realistic temperature estimate prior, during and after the MECO event. The combined δ18O and Δ47 data therefore provide important insight into the isotopic evolution of precipitation and mean

  18. Early Eocene carbon isotope excursions and landscape destabilization at eccentricity minima: Green River Formation of Wyoming

    NASA Astrophysics Data System (ADS)

    Smith, M. Elliot; Carroll, Alan R.; Scott, Jennifer J.; Singer, Brad S.

    2014-10-01

    Repeated global reorganizations of carbon cycling and biotic, oceanic and terrestrial processes occurred during the Early Eocene, and appear to have been paced by cyclic variations in the eccentricity of the Earth's orbit. The phase relationship(s) between insolation variation, terrestrial paleoclimate, and atmospheric pCO2 during these events remains enigmatic however, due to their poorly constrained timing relative to specific orbital configurations. Here we use tiered interpolation between radioisotopic ages and paleomagnetic polarity chrons to compare high-resolution δ13C and lithofacies records from the Wilkins Peak Member of the Green River Formation of western North America to a Fe-intensity XRF record from the western Atlantic Ocean, and to numerical solutions for Earth's orbital configuration. Wilkins Peak Member lithofacies stacking patterns record cyclic geomorphic responses to insolation and climate fluctuations, spanning an interval of 1.8 Ma. Previous macrostratigraphic analyses using 40Ar/39Ar and U-Pb ash bed ages indicate that these cycles reflect long and short eccentricity modulation of precession. Hydrologic variance appears to have occurred inversely with intervals of maximum sediment advection, with carbonate- and evaporite-dominated lacustrine modes during eccentricity maxima, and siliciclastic-dominated alluvial modes during eccentricity minima. Stable carbon isotope analyses of 126 meters of Wilkins Peak Member strata reveal a regular ∼5 per mil oscillation between high-δ13C lacustrine modes and low-δ13C alluvial modes. Tiered interpolation between paleomagnetically characterized terrestrial ash beds facilitates the integration of 11 radioisotopic ages with the geomagnetic polarity timescale, resulting in significant expansion of chron C23 and shortening of chron C22 relative to timescales based on seafloor magnetic anomaly profiles. The new proposed timescale permits direct comparison of terrestrial and marine climate proxy records

  19. Environmental Change at the Time of the Paleocene-Eocene Biotic Turnover; a Palynological Perspective

    NASA Astrophysics Data System (ADS)

    Crouch, E. M.; Brinkhuis, H.; Dickens, G. R.; Heilmann-Clausen, C.; Adatte, T.; Morgans, H. E.; Visscher, H.

    2001-12-01

    Over the last 65 Ma, the most prominent Earth surface thermal and carbon cycle perturbations occurred during the Paleocene-Eocene thermal maximum (PETM), ca. 55 Ma. Manifestations of this aberrant warming event include a prominent negative carbon isotope excursion (CIE) in carbonate and organic matter, and a pronounced increase in the relative abundance of Apectodinium dinocysts at several locations. Indeed, recent studies have shown that the onset of Apectodinium-dominated assemblages globally coincides with the beginning of the CIE (Crouch et al., 2001). While motile representatives of Apectodinium are thought to be both thermophilic and heterotrophic, the underlying environmental conditions that resulted in this unique global acme are not well understood. Here, we present palynological and geochemical records across a PETM marine section at Tawanui, New Zealand, to provide insight into the cause of the Apectodinium acme. Changes in Apectodinium and δ 13C correspond with increased terrestrial palynomorphs, elevated C/N ratios, lower carbonate concentrations, higher SiO2 and Al2O3, and lower Ba/Al. The variations are best explained by an increase in delivery of terrigenous material to the Tawanui region. The results agree with the growing evidence for increased terrigenous input to the ocean during the PETM, most likely a result of enhanced weathering in response to a sudden and massive carbon injection to the ocean-atmosphere system. In addition, the dinocyst record from Tawanui is combined with several well-calibrated late Paleocene-early Eocene dinocyst records in other regions (e.g., Tethyan Basin, North Sea Basin) to better understand the global distribution and abundance of Apectodinium across the Paleocene-Eocene transition. The current knowledge of terrestrial plant response during the PETM is rather sparse. Terrestrial spore and pollen have also been examined across the PETM at Tawanui in order to detect to what extent vegetation in mid- to high

  20. Climatic and floral change during the Paleocene-Eocene Thermal Maximum in the Bighorn Basin (Invited)

    NASA Astrophysics Data System (ADS)

    Wing, S. L.

    2009-12-01

    The Paleocene-Eocene Thermal Maximum (PETM) is an interval of global warming lasting ~150 ka that occurred at the start of the Eocene, ~55.8 Ma. Globally, temperature rose 4-8 °C in association with carbon cycle changes attributed to the release of >5,000 Pg of C into the ocean-atmosphere system. Fossil plants from the PETM in the Bighorn Basin, northwestern Wyoming, show that latest Paleocene forests contained palms, deciduous taxodiaceous conifers, and a variety of deciduous and evergreen angiosperms, many belonging to lineages with north temperate distributions. Mean annual temperature (MAT) for the latest Paleocene inferred from leaf margin analysis is ~18 °C. Early and mid-PETM floras have a completely different composition. They lack conifers and broad-leaved deciduous taxa with north temperate distributions, and are dominated by palms, legumes, and other angiosperm taxa with living relatives in the dry tropical forests of Central and South America. Leaf margin analysis gives an MAT of ~23 °C. Floras of this type are known from a stratigraphic interval ~30 m thick that also produces geochemical and mammalian faunal indicators of the PETM. Floras from late PETM or earliest post-PETM time are composed largely of species that had been present in the latest Paleocene, with a few new species that are common in the early Eocene. The inferred MAT is ~18 °C. Leaf size data suggest that the PETM was drier than the immediately preceding and following times. Floral data from the Bighorn Basin indicate that the magnitude of temperature change in this mid-latitude continental interior was similar to that inferred for the surface ocean. Evidence for dryness or seasonal dryness during the PETM has been observed in sections in northern Spain as well as in Wyoming, raising the possibility of widespread water stress in the middle northern latitudes. Change in floral composition during the PETM is consistent with regional extinction in mid-latitude populations of plants

  1. Extreme (sub)Tropical Eocene oceanic warmth: Clumped isotope temperatures of shallow-dwelling large Benthic Foraminifera

    NASA Astrophysics Data System (ADS)

    Evans, D.

    2015-12-01

    The response of the tropical surface oceans to greater than modern atmospheric carbon dioxide is poorly constrained. Eocene climate modelling broadly indicates that the tropical surface ocean was 8-10°C warmer compared to pre-industrial simulations, at odds with much of the currently available proxy information which suggests low latitude sea surface temperatures (SST) no more than a few degrees warmer than at present. However, the accuracy of some of this proxy information, particularly the δ18O and Mg/Ca ratio of biogenic marine carbonates, is hampered by uncertainties regarding the secular evolution of seawater chemistry. Here, we present clumped isotope temperatures of modern and Eocene shallow-dwelling benthic foraminifera, a palaeothermometer independent of seawater isotopic composition. These organisms have photosymbionts and therefore inhabit the photic zone, within the depth range of planktic species considered to be surface dwelling. Specimens collected from the modern ocean precipitate calcite in agreement with the clumped isotope-temperature calibration of Zaarur et al. [2013]. Based on 11 tropical to mid-latitude localities from across the globe we demonstrate that the Eocene ocean was significantly warmer than suggested by much of the previous proxy data. Exceptionally-preserved samples from the mid-Eocene of Java indicate the West Pacific was characterised by mean annual SST of 34-37°C at this time, whilst mid-latitude northern hemisphere SST (from localities in the UK, France and Belgium) were 24-30°C throughout the Eocene. These data bring (sub)tropical SST in a high-CO2 world into much better agreement with climate models, indicating low-mid latitudinal SST gradients similar to modern.

  2. Fluvial baselevel changes in the lower part of the White River Group, Eocene-Oligocene, Badlands of South Dakota

    SciTech Connect

    Evans, J.E. . Dept. of Geology); Terry, D.O. Jr. . Dept. of Geology)

    1992-01-01

    The Chamberlain Pass Formation (CPF) is a Middle( ) to Late Eocene fluvial unit that represents the lower part of the White River Group in western South Dakota. The CPF consists of multistory channel sandstone and overbank mudstone, both overprinted by a distinctive paleosol unit, the Interior Paleosol Series. The CPF thickens from west to east, to a maximum channel-belt thickness [ge] 11 m. Paleoflow data indicates that deposition of the CPF was restricted to an asymmetric basin controlled by faults trending Se, away from the Black Hills uplift. Sandstones in the CPF contain a suite of resistant minerals derived from a recycled sedimentary rock source area. In contrast, the overlying Chadron Formation contains a suite of minerals and rock fragments consistent with a source area from the igneous and metamorphic core rocks of the Black Hills uplift. The deposition of the CPF brackets four significant changes in relative baselevel that occurred in this region during the Paleogene: (1) Late Cretaceous to Middle( ) Eocene baselevel fall, weathering and erosion of the Cretaceous Pierre Shale to form the Yellow Mounds Paleosol, and fluvial incision; (2) Middle( ) to Late Eocene baselevel rise and deposition of the CPF; (3) Late Eocene baselevel fall, weathering and erosion of the CPF to form the Interior Paleosol, and fluvial incision; and (4) late Eocene to Oligocene baselevel rise and deposition of the Chadron formation. The first event was eustatic, the second was controlled primarily by subsidence in a fault-controlled basin, the third records tectonic uplift and unroofing of the Black Hills, and the fourth was controlled by a combination of eustatic, tectonic, and paleoclimatic factors.

  3. Palynological Response to Middle Eocene Climate Variability in the North Atlantic Ocean: IODP Expedition 342, Newfoundland Ridge, Offshore Canada

    NASA Astrophysics Data System (ADS)

    Willard, D. A.

    2013-12-01

    Proxy records from Eocene hyperthermals provide evidence for rates and magnitudes of environmental changes associated with these events, as well as their impacts on terrestrial and marine ecosystems. The Middle Eocene Climatic Optimum (MECO) occurred ~40 Million years ago (Ma) and lasted ~500,000 years, and previous research has documented changes in marine and terrestrial biotas during and after this event. Cores collected in sediment drifts on Newfoundland Ridge off the coast of eastern Canada during IODP Expedition 342 recovered expanded sections of the middle Eocene, with sedimentation rates of 1-2 cm/kyr. We present results from pollen, palynofacies, and dinocyst analyses from Sites 1408 (41.438'N, 49.786'W, 3022 mwd), 1409 (41.296'N, 49.233'W, 3501 mwd), and 1410 (41.328'N, 49.170'W, 3387 mwd), spanning an interval that includes the MECO. Palynological assemblages are well preserved throughout the middle Eocene at Sites 1408 and 1410, whereas carbonate-rich samples from Site 1409 were completely barren of palynomorphs. Substantial variability in dinocyst species composition and diversity, pollen assemblages, and organic palynofacies were observed within the MECO event. Fluctuations in concentrations of opaque organic matter, insect fragments, and pollen and spores from terrestrial vegetation reflect changes in terrigenous influx, intensity of the hydrologic cycle, and source vegetation. Dinocyst assemblage shifts are correlated with changes in productivity, nutrient supply, and salinity. Integration of palynological data with other proxies will provide further insights into correlations between increased terrigenous input and eutrophication, leads and lags between terrestrial and marine responses to climate fluctuations, and environmental stability during the Middle Eocene.

  4. Middle-Eocene artiodactyls from Shanghuang (Jiangsu Province, Coastal China) and the diversity of basal dichobunoids in Asia

    NASA Astrophysics Data System (ADS)

    Metais, Grégoire; Qi, Tao; Guo, Jianwei; Beard, K. Christopher

    2008-12-01

    A new assemblage of basal dichobunoid artiodactyls from the middle-Eocene Shanghuang fissure fillings includes the diacodexeid Jiangsudon shanghuangensis gen. and sp. nov., a new species of the lantianine dichobunoid Elaschitotherium, Elaschitotherium crepaturus sp. nov., and an indeterminate suoid which is presently the earliest record of this clade. Diacodexeids are also represented by two forms provisionally referred to cf. Diacodexis sp. and to an indeterminate Diacodexeidae, respectively. The occurrence of diacodexeids in Shanghuang contrasts with the early and earliest middle-Eocene chronological range of the family in Europe and North America and suggests that the stratigraphic range of the family in Asia extends up to the middle Eocene. This may reflect particular habitats in coastal China that may have been relatively stable during the early and middle Eocene, thus preserving forest-dwelling artiodactyls that became extinct in the other Holarctic regions. Compared to other supposedly coeval North American, European, and Asian faunas, the Shanghuang mammalian assemblage is most similar to early Uintan faunas of North America but is also remarkable in recording forms close to taxa that are characteristic of the Wasatchian and Bridgerian North American Land Mammal Ages. The Irdinmanhan age of the Shanghuang fauna is supported by the mammalian assemblage recovered from the fissure D, but an Arshantan age cannot be completely ruled out at this point. Although the Shanghuang assemblage is biased towards preservation of small components of the mammalian fauna, the Shanghuang fauna provide an important and unique window into the Eocene diversity and early evolution of cetartiodactyls in eastern Asia.

  5. Eocene fossil is earliest evidence of flower-visiting by birds

    PubMed Central

    Mayr, Gerald; Wilde, Volker

    2014-01-01

    Birds are important pollinators, but the evolutionary history of ornithophily (bird pollination) is poorly known. Here, we report a skeleton of the avian taxon Pumiliornis from the middle Eocene of Messel in Germany with preserved stomach contents containing numerous pollen grains of an eudicotyledonous angiosperm. The skeletal morphology of Pumiliornis is in agreement with this bird having been a, presumably nectarivorous, flower-visitor. It represents the earliest and first direct fossil evidence of flower-visiting by birds and indicates a minimum age of 47 million years for the origin of bird–flower interactions. As Pumiliornis does not belong to any of the modern groups of flower-visiting birds, the origin of ornithophily in some angiosperm lineages may have predated that of their extant avian pollinators. PMID:24872461

  6. Gigantism in unique biogenic magnetite at the Paleocene-Eocene Thermal Maximum.

    PubMed

    Schumann, Dirk; Raub, Timothy D; Kopp, Robert E; Guerquin-Kern, Jean-Luc; Wu, Ting-Di; Rouiller, Isabelle; Smirnov, Aleksey V; Sears, S Kelly; Lücken, Uwe; Tikoo, Sonia M; Hesse, Reinhard; Kirschvink, Joseph L; Vali, Hojatollah

    2008-11-18

    We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene-Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 microm long and hexaoctahedral prisms up to 1.4 microm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability--a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming--drove diversification of magnetite-forming organisms, likely including eukaryotes.

  7. Preliminary Stratigraphic Cross Sections of Oil Shale in the Eocene Green River Formation, Uinta Basin, Utah

    USGS Publications Warehouse

    Dyni, John R.

    2008-01-01

    Oil shale units in the Eocene Green River Formation are shown on two east-west stratigraphic sections across the Uinta Basin in northeastern Utah. Several units have potential value for recovery of shale oil, especially the Mahogany oil shale zone, which is a high grade oil shale that can be traced across most of the Uinta Basin and into the Piceance Basin in northwestern Colorado. Many thin medium to high grade oil shale beds above the Mahogany zone can also be traced for many miles across the basin. Several units below the Mahogany that have slow velocities on sonic logs may be low grade oil shale. These may have value as a source for shale gas.

  8. Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific

    NASA Astrophysics Data System (ADS)

    Matthews, Kara J.; Dietmar Müller, R.; Whittaker, Joanne; Flament, Nicolas; Seton, Maria

    2013-04-01

    The late Cretaceous to mid Eocene history of the southwest and southernmost Pacific has been subject to starkly contrasting interpretations, ranging from relative tectonic quiescence with the Lord Howe Rise (LHR) being part of the Pacific plate to a dynamic subduction setting. In the first scenario the Tasman Sea would have formed as a consequence of divergence between the Pacific and Australian plates, whereas in the second scenario it would have formed as a marginal basin associated with subduction. The first scenario is supported by a number of arguments, including a lack of evidence for deformation and tectonic activity in New Zealand during this period and a geodynamic modelling inference, namely that the bend in the Hawaiian-Emperor chain can be better reproduced if the LHR is part of the Pacific plate. The second scenario is supported by regional plate kinematic models reconciling a variety of observations including back-arc basin formation and destruction through time and the history of arc-continent collisions. The primary problem with the first scenario is the use of a plate circuit that leaves relative motion between East and West Antarctica unconstrained, leading to an improbable history of periodic compression and extension. The main problem with the alternative scenario is a lack of sampled late Cretaceous volcanic arc rocks east of the LHR. We analysed available geological and geophysical data to constrain the locations of and movements along the plate boundaries in the southwest and southern Pacific from the late Cretaceous to mid Eocene, and assessed how Pacific plate motion is best quantified during this period. Geological and geophysical evidence suggests that a plate boundary separated the Pacific plate from the LHR. The distribution of lower mantle slab material that is imaged by seismic tomography beneath New Zealand is best explained if subduction occurred to the east of the LHR during the entire late Cretaceous to mid Eocene period. Rocks

  9. A siliceous microfossil view of middle Eocene Arctic paleoenvironments: A window of biosilica production and preservation

    NASA Astrophysics Data System (ADS)

    Stickley, Catherine E.; Koç, NalâN.; Brumsack, Hans-Jürgen; Jordan, Richard W.; Suto, Itsuki

    2008-03-01

    Integrated Ocean Drilling Program (IODP) Expedition 302, "The Arctic Coring Expedition" (ACEX), unearthed the most significant find of Paleogene siliceous microfossils in nearly 2 decades. 100 m of early middle Eocene, organic-rich, finely laminated sediments contain abundant marine and freshwater siliceous microfossils allowing intriguing insights into central Arctic paleoenvironments during the start of Cenozoic cooling. Largely endemic assemblages of marine diatoms and ebridians are preserved along with very high abundances of chrysophyte cysts, the endogenously formed resting stage of freshwater algae. An overall brackish environment is invoked, but variations in group dominance suggest episodic changes in salinity, stratification, and trophic status. With the backing of inorganic geochemistry we synthesize the sediment characteristics by hypothesizing an environmental model for the cooccurrence of these diverse siliceous microfossil groups. We also report on initial insights into the composition of some of the laminations, which may help explain the formation of this rich sediment archive.

  10. Paleogeographic reconstruction of northwestern Oregon based on Eocene freshwater deposition in accreted terrane

    SciTech Connect

    Ries, J.E.

    1989-03-01

    Freshwater deposits exposed in the Coast Range of Oregon have been identified by the absence of marine organisms, significant floral remains, and the identification of a freshwater fish assemblage. These facies have been correlated with foraminiferal and lithologic horizons from test wells from the Mist Gas field of northwestern Oregon. Consistent records of inner neritic and marginal marine deposition in the Narizian stage, upper Cowlitz Formation, suggest the existence of an Eocene volcanic archipelago. Foraminiferal correlation through this stage is complicated by the absence of stratigraphically significant species in several of the wells. Floral remains from exposed sections have provided diverse elements, allowing paleogeographic reconstruction. A sea level coastal swamp was dominated by a subtropical flora consisting of Sabalites, Platanophyllum, and Equisetum. The swamp was apparently backed by higher altitude volcanic uplands dominated by a more temperate flora including Cornus, Chamaecyparis, Ailanthus, Pinus, and Picea.

  11. Seafloor hydrothermal activity and spreading rates: the Eocene carbon dioxide greenhouse revisted.

    PubMed

    Kasting, J F; Richardson, S M

    1985-01-01

    A suggestion has been made that enhanced rates of hydrothermal activity during the Eocene could have caused a global warming by adding calcium to the ocean and pumping CO2 into the atmosphere (Owen and Rea, 1984). This phenomenon was purported to be consistent with the predictions of the CO2 geochemical cycle model of Berner, Lasaga and Garrels (1983) (henceforth BLAG). In fact, however, the BLAG model predicts only a weak connection between hydrothermal activity and atmospheric CO2 levels. By contrast, it predicts a strong correlation between seafloor spreading rates and pCO2, since the release rate of CO2 from carbonate metamorphism is assumed to be proportional to the mean spreading rate. The Ecocene warming can be conveniently explained if the BLAG model is extended by assuming that the rate of carbonate metamorphism is also proportional to the total length of the midocean ridges from which the spreading originates.

  12. Seafloor hydrothermal activity and spreading rates: the Eocene carbon dioxide greenhouse revisted

    NASA Technical Reports Server (NTRS)

    Kasting, J. F.; Richardson, S. M.

    1985-01-01

    A suggestion has been made that enhanced rates of hydrothermal activity during the Eocene could have caused a global warming by adding calcium to the ocean and pumping CO2 into the atmosphere (Owen and Rea, 1984). This phenomenon was purported to be consistent with the predictions of the CO2 geochemical cycle model of Berner, Lasaga and Garrels (1983) (henceforth BLAG). In fact, however, the BLAG model predicts only a weak connection between hydrothermal activity and atmospheric CO2 levels. By contrast, it predicts a strong correlation between seafloor spreading rates and pCO2, since the release rate of CO2 from carbonate metamorphism is assumed to be proportional to the mean spreading rate. The Ecocene warming can be conveniently explained if the BLAG model is extended by assuming that the rate of carbonate metamorphism is also proportional to the total length of the midocean ridges from which the spreading originates.

  13. Evidence for abundant isolated magnetic nanoparticles at the Paleocene-Eocene boundary.

    PubMed

    Wang, Huapei; Kent, Dennis V; Jackson, Michael J

    2013-01-01

    New rock magnetic results (thermal fluctuation tomography, high-resolution first-order reversal curves and low temperature measurements) for samples from the Paleocene-Eocene thermal maximum and carbon isotope excursion in cored sections at Ancora and Wilson Lake on the Atlantic Coastal Plain of New Jersey indicate the presence of predominantly isolated, near-equidimensional single-domain magnetic particles rather than the chain patterns observed in a cultured magnetotactic bacteria sample or magnetofossils in extracts. The various published results can be reconciled with the recognition that chain magnetosomes tend to be preferentially extracted in the magnetic separation process but, as we show, may represent only a small fraction of the overall magnetic assemblage that accounts for the greatly enhanced magnetization of the carbon isotope excursion sediment but whose origin is thus unclear.

  14. Furrowed outcrops of Eocene chalk on the lower continental slop offshore New Jersey

    USGS Publications Warehouse

    Robb, James M.; Kirby, John R.; Hampson, John C., Jr.; Gibson, Patricia R.; Hecker, Barbara

    1983-01-01

    A sea bottom of middle Eocene calcareous claystone cut by downslope-trending furrows was observed during an Alvin dive to the mouth of Berkeley Canyon on the continental slope off New Jersey. The furrows are 10 to 50 m apart, 4 to 13 m deep, linear, and nearly parallel in water depths of 2,000 m. They have steep walls and flat floors 3 to 5 m wide, of fine-grained sediment. Mid-range sidescan-sonar images show that similarly furrowed surfaces are found on nearby areas of the lower continental slope, not associated with canyons. The furrows are overlain in places by Pleistocene sediments. Although they show evidence of erosional origin, they do not appear to be related to observed structures, and their straight, parallel pattern is not well understood. A general cover of flocky unconsolidated sediments implies that bottom-current erosion is not active now.

  15. Seafloor hydrothermal activity and spreading rates: the Eocene carbon dioxide greenhouse revisted.

    PubMed

    Kasting, J F; Richardson, S M

    1985-01-01

    A suggestion has been made that enhanced rates of hydrothermal activity during the Eocene could have caused a global warming by adding calcium to the ocean and pumping CO2 into the atmosphere (Owen and Rea, 1984). This phenomenon was purported to be consistent with the predictions of the CO2 geochemical cycle model of Berner, Lasaga and Garrels (1983) (henceforth BLAG). In fact, however, the BLAG model predicts only a weak connection between hydrothermal activity and atmospheric CO2 levels. By contrast, it predicts a strong correlation between seafloor spreading rates and pCO2, since the release rate of CO2 from carbonate metamorphism is assumed to be proportional to the mean spreading rate. The Ecocene warming can be conveniently explained if the BLAG model is extended by assuming that the rate of carbonate metamorphism is also proportional to the total length of the midocean ridges from which the spreading originates. PMID:11539654

  16. Groundwater pollution risk mapping for the Eocene aquifer of the Oum Er-Rabia basin, Morocco

    NASA Astrophysics Data System (ADS)

    Ettazarini, Said

    2006-11-01

    Sustainable development requires the management and preservation of water resources indispensable for all human activities. When groundwater constitutes the main water resource, vulnerability maps therefore are an important tool for identifying zones of high pollution risk and taking preventive measures in potential pollution sites. The vulnerability assessment for the Eocene aquifer in the Moroccan basin of Oum Er-Rabia is based on the DRASTIC method that uses seven parameters summarizing climatic, geological, and hydrogeological conditions controlling the seepage of pollutant substances to groundwater. Vulnerability maps were produced by using GIS techniques and applying the “generic” and “agricultural” models according to the DRASTIC charter. Resulting maps revealed that the aquifer is highly vulnerable in the western part of the basin and areas being under high contamination risk are more extensive when the “agricultural” model was applied.

  17. Gigantism in unique biogenic magnetite at the Paleocene–Eocene Thermal Maximum

    PubMed Central

    Schumann, Dirk; Raub, Timothy D.; Kopp, Robert E.; Guerquin-Kern, Jean-Luc; Wu, Ting-Di; Rouiller, Isabelle; Smirnov, Aleksey V.; Sears, S. Kelly; Lücken, Uwe; Tikoo, Sonia M.; Hesse, Reinhard; Kirschvink, Joseph L.; Vali, Hojatollah

    2008-01-01

    We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene–Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 μm long and hexaoctahedral prisms up to 1.4 μm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability—a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming—drove diversification of magnetite-forming organisms, likely including eukaryotes. PMID:18936486

  18. Effects of rapid global warming at the Paleocene-Eocene boundary on neotropical vegetation.

    PubMed

    Jaramillo, Carlos; Ochoa, Diana; Contreras, Lineth; Pagani, Mark; Carvajal-Ortiz, Humberto; Pratt, Lisa M; Krishnan, Srinath; Cardona, Agustin; Romero, Millerlandy; Quiroz, Luis; Rodriguez, Guillermo; Rueda, Milton J; de la Parra, Felipe; Morón, Sara; Green, Walton; Bayona, German; Montes, Camilo; Quintero, Oscar; Ramirez, Rafael; Mora, Germán; Schouten, Stefan; Bermudez, Hermann; Navarrete, Rosa; Parra, Francisco; Alvarán, Mauricio; Osorno, Jose; Crowley, James L; Valencia, Victor; Vervoort, Jeff

    2010-11-12

    Temperatures in tropical regions are estimated to have increased by 3° to 5°C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.

  19. Evidence for abundant isolated magnetic nanoparticles at the Paleocene–Eocene boundary

    PubMed Central

    Wang, Huapei; Kent, Dennis V.; Jackson, Michael J.

    2013-01-01

    New rock magnetic results (thermal fluctuation tomography, high-resolution first-order reversal curves and low temperature measurements) for samples from the Paleocene–Eocene thermal maximum and carbon isotope excursion in cored sections at Ancora and Wilson Lake on the Atlantic Coastal Plain of New Jersey indicate the presence of predominantly isolated, near-equidimensional single-domain magnetic particles rather than the chain patterns observed in a cultured magnetotactic bacteria sample or magnetofossils in extracts. The various published results can be reconciled with the recognition that chain magnetosomes tend to be preferentially extracted in the magnetic separation process but, as we show, may represent only a small fraction of the overall magnetic assemblage that accounts for the greatly enhanced magnetization of the carbon isotope excursion sediment but whose origin is thus unclear. PMID:23267095

  20. The termites of Early Eocene Cambay amber, with the earliest record of the Termitidae (Isoptera).

    PubMed

    Engel, Michael S; Grimaldi, David A; Nascimbene, Paul C; Singh, Hukam

    2011-01-01

    The fauna of termites (Isoptera) preserved in Early Eocene amber from the Cambay Basin (Gujarat, India) are described and figured. Three new genera and four new species are recognized, all of them Neoisoptera - Parastylotermes krishnai Engel & Grimaldi, sp. n. (Stylotermitidae); Prostylotermes kamboja Engel & Grimaldi, gen. et sp. n. (Stylotermitidae?); Zophotermes Engel, gen. n., with Zophotermes ashoki Engel & Singh, sp. n. (Rhinotermitidae: Prorhinotermitinae); and Nanotermes isaacae Engel & Grimaldi, gen. et sp. n. (Termitidae: Termitinae?). Together these species represent the earliest Tertiary records of the Neoisoptera and the oldest definitive record of Termitidae, a family that comprises >75% of the living species of Isoptera. Interestingly, the affinities of the Cambay amber termites are with largely Laurasian lineages, in this regard paralleling relationships seen between the fauna of bees and some flies. Diversity of Neoisoptera in Indian amber may reflect origin of the amber deposit in Dipterocarpaceae forests formed at or near the paleoequator.

  1. Isotopic compositions and probable origins of organic molecules in the Eocene Messel shale

    NASA Technical Reports Server (NTRS)

    Hayes, J. M.; Takigiku, Ray; Ocampo, Ruben; Callot, Enry J.; Albrecht, Pierre

    1987-01-01

    It is shown here that the carbon isotopic compositions of biomarkers from the Eocene Messel shale, accumulated 47 + or - 2 million years ago in anaerobic waters at the bottom of a lake, allow identification of specific sources for some materials and reconstruction of carbon flows within the lake and its sediments. The C-13 content of organic matter synthesized by lacustrine primary producers can be estimated from the observed C-13 content of the geoporphyrins derived from their chlorophylls. Total organic material in the shale is depleted in C-13 by six parts per thousand relative to that input. This difference cannot be explained by selective loss of components enriched in C-13, nor, as shown by isotopic compositions of other biomarkers, by inputs from land plants surrounding the lake or from methanogenic bacteria.

  2. Whales originated from aquatic artiodactyls in the Eocene epoch of India.

    PubMed

    Thewissen, J G M; Cooper, Lisa Noelle; Clementz, Mark T; Bajpai, Sunil; Tiwari, B N

    2007-12-20

    Although the first ten million years of whale evolution are documented by a remarkable series of fossil skeletons, the link to the ancestor of cetaceans has been missing. It was known that whales are related to even-toed ungulates (artiodactyls), but until now no artiodactyls were morphologically close to early whales. Here we show that the Eocene south Asian raoellid artiodactyls are the sister group to whales. The raoellid Indohyus is similar to whales, and unlike other artiodactyls, in the structure of its ears and premolars, in the density of its limb bones and in the stable-oxygen-isotope composition of its teeth. We also show that a major dietary change occurred during the transition from artiodactyls to whales and that raoellids were aquatic waders. This indicates that aquatic life in this lineage occurred before the origin of the order Cetacea.

  3. Pristine Early Eocene wood buried deeply in kimberlite from northern Canada.

    PubMed

    Wolfe, Alexander P; Csank, Adam Z; Reyes, Alberto V; McKellar, Ryan C; Tappert, Ralf; Muehlenbachs, Karlis

    2012-01-01

    We report exceptional preservation of fossil wood buried deeply in a kimberlite pipe that intruded northwestern Canada's Slave Province 53.3±0.6 million years ago (Ma), revealed during excavation of diamond source rock. The wood originated from forest surrounding the eruption zone and collapsed into the diatreme before resettling in volcaniclastic kimberlite to depths >300 m, where it was mummified in a sterile environment. Anatomy of the unpermineralized wood permits conclusive identification to the genus Metasequoia (Cupressaceae). The wood yields genuine cellulose and occluded amber, both of which have been characterized spectroscopically and isotopically. From cellulose δ(18)O and δ(2)H measurements, we infer that Early Eocene paleoclimates in the western Canadian subarctic were 12-17°C warmer and four times wetter than present. Canadian kimberlites offer Lagerstätte-quality preservation of wood from a region with limited alternate sources of paleobotanical information.

  4. Pristine Early Eocene Wood Buried Deeply in Kimberlite from Northern Canada

    PubMed Central

    Wolfe, Alexander P.; Csank, Adam Z.; Reyes, Alberto V.; McKellar, Ryan C.; Tappert, Ralf; Muehlenbachs, Karlis

    2012-01-01

    We report exceptional preservation of fossil wood buried deeply in a kimberlite pipe that intruded northwestern Canada’s Slave Province 53.3±0.6 million years ago (Ma), revealed during excavation of diamond source rock. The wood originated from forest surrounding the eruption zone and collapsed into the diatreme before resettling in volcaniclastic kimberlite to depths >300 m, where it was mummified in a sterile environment. Anatomy of the unpermineralized wood permits conclusive identification to the genus Metasequoia (Cupressaceae). The wood yields genuine cellulose and occluded amber, both of which have been characterized spectroscopically and isotopically. From cellulose δ18O and δ2H measurements, we infer that Early Eocene paleoclimates in the western Canadian subarctic were 12–17°C warmer and four times wetter than present. Canadian kimberlites offer Lagerstätte-quality preservation of wood from a region with limited alternate sources of paleobotanical information. PMID:23029080

  5. Resolving tectonic, climatic, and geomorphologic signatures in the Eocene Green River Formation, Western U.S

    NASA Astrophysics Data System (ADS)

    Smith, M. E.; Carroll, A. R.

    2011-12-01

    Tectonic lake basins are windows into the co-evolution of terrestrial climate and topography, but the stratigraphic responses to these drivers are complex and incompletely understood. Coring Quaternary lake basins has provided excellent temporal resolution, but is limited to one-dimensional archives of relatively short duration. Conversely, outcrop-based studies of older deposits can elucidate complex lateral facies relationships and longer time periods, but temporal resolution is often poor due to the lack of marine fossils. However, recent advances in radioisotopic dating have produced highly-resolved records of older lacustrine strata, provided volcanic ash beds are present. The Eocene Green River Formation in Wyoming, Colorado, and Utah is such a record, containing numerous 40Ar/39Ar-dated ash horizons with c.a. ±200 ky 2σ uncertainties. At the scale of individual Members of the Green River Formation (100-400 m), lithofacies and faunas differentiate five distinct lake-type intervals: Luman-Scheggs (fluviolacustrine), Rife (saline), Wilkins Peak (hypersaline-alluvial), Lower LaClede (saline), and Upper LaClede (fluviolacustrine). Although published explanations implicate tectonic and/or climatic control of these changes, both lack significant correlation to bulk lithofacies. While stratal geometries imply that the Uinta Mountains were the principle Eocene driver of flexural subsidence for the Greater Green River Basin (GGRB), conglomerate compositions reveal progressive Paleocene through Eocene unroofing rather than a discreet Early Eocene pulse of Laramide tectonism. Similarly, paleofloral evidence for climatic changes is equivocal. Instead, regional provenance and paleoflow patterns suggest that lake-type changes resulted from progressive hydrologic isolation of the GGRB from orogenic highlands to the west, hydrologic closure, then subsequent integration. From ~53 to ~51.5 Ma, Lake Gosiute expanded from a restricted freshwater to expansive saline lake

  6. Evidence for abundant isolated magnetic nanoparticles at the Paleocene-Eocene boundary.

    PubMed

    Wang, Huapei; Kent, Dennis V; Jackson, Michael J

    2013-01-01

    New rock magnetic results (thermal fluctuation tomography, high-resolution first-order reversal curves and low temperature measurements) for samples from the Paleocene-Eocene thermal maximum and carbon isotope excursion in cored sections at Ancora and Wilson Lake on the Atlantic Coastal Plain of New Jersey indicate the presence of predominantly isolated, near-equidimensional single-domain magnetic particles rather than the chain patterns observed in a cultured magnetotactic bacteria sample or magnetofossils in extracts. The various published results can be reconciled with the recognition that chain magnetosomes tend to be preferentially extracted in the magnetic separation process but, as we show, may represent only a small fraction of the overall magnetic assemblage that accounts for the greatly enhanced magnetization of the carbon isotope excursion sediment but whose origin is thus unclear. PMID:23267095

  7. Aeolian dust deposition during the Eocene-Oligocene in central to eastern Asia

    NASA Astrophysics Data System (ADS)

    Vandenberghe, Jef; Abels, Hemmo; van Cappelle, Marijn

    2015-04-01

    Aeolian dust deposition during the Eocene-Oligocene in central to eastern Asia Jef Vandenberghe1, Hemmo Abels2 and Marijn van Cappelle3 1Dept. of Earth Sciences, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands 2Dept. of Earth Sciences, Universiteit Utrecht, 3584 CD, Utrecht, The Netherlands 3Dept. of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, U.K. The deposition of loess is generally attributed to a monsoonal climate system. Recently it has been shown that such a system existed already at the end of the Eocene on the northeastern Tibetan Plateau (Licht et al., 2014). One of the main arguments to prove the supply of loess by monsoonal winds is the use of grain size properties. The lower part of the Shuiwan section (Eocene) consists of metre-scale alternations of mudstone and gypsum beds; the upper part (Oligocene) is mainly mudstone (Dupont-Nivet et al., 2007; Abels et al., 2010). Sediments are categorized in six grain-size types based on the grain-size distribution and the mode of the silt grain sizes as measured using laser diffraction. Sediments of type 1, the only type with a unimodal grain-size distribution, consist exclusively of clay-sized particles (modal value of 2-2.5 µm). Types 2-6 have a multimodal composition. They contain an additional silt-sized fraction with a modal size of c. 16 µm in type 2; c. 26 µm in type 3 and c. 31 µm in type 4. Type 5 is a mixture of previous types, and type 6 contains in addition a slight amount of sand. Similar bimodal grain-size distributions occur in the Neogene Red Clay and in the Pleistocene loess of the Chinese Loess Plateau. All three silt fractions (with modal sizes 16, 26 and 31 µm) represent typical loess sediments, transported by dust storms in suspension at different altitudes. Their exact grain size depends on wind velocity, source material and transport distance. The 'clay component' may have settled from high suspension clouds in the air down to dry ground or to

  8. Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India.

    PubMed

    Rose, Kenneth D; Holbrook, Luke T; Rana, Rajendra S; Kumar, Kishor; Jones, Katrina E; Ahrens, Heather E; Missiaen, Pieter; Sahni, Ashok; Smith, Thierry

    2014-11-20

    Cambaytheres (Cambaytherium, Nakusia and Kalitherium) are recently discovered early Eocene placental mammals from the Indo-Pakistan region. They have been assigned to either Perissodactyla (the clade including horses, tapirs and rhinos, which is a member of the superorder Laurasiatheria) or Anthracobunidae, an obscure family that has been variously considered artiodactyls or perissodactyls, but most recently placed at the base of Proboscidea or of Tethytheria (Proboscidea+Sirenia, superorder Afrotheria). Here we report new dental, cranial and postcranial fossils of Cambaytherium, from the Cambay Shale Formation, Gujarat, India (~54.5 Myr). These fossils demonstrate that cambaytheres occupy a pivotal position as the sister taxon of Perissodactyla, thereby providing insight on the phylogenetic and biogeographic origin of Perissodactyla. The presence of the sister group of perissodactyls in western India near or before the time of collision suggests that Perissodactyla may have originated on the Indian Plate during its final drift toward Asia.

  9. Pristine Early Eocene wood buried deeply in kimberlite from northern Canada.

    PubMed

    Wolfe, Alexander P; Csank, Adam Z; Reyes, Alberto V; McKellar, Ryan C; Tappert, Ralf; Muehlenbachs, Karlis

    2012-01-01

    We report exceptional preservation of fossil wood buried deeply in a kimberlite pipe that intruded northwestern Canada's Slave Province 53.3±0.6 million years ago (Ma), revealed during excavation of diamond source rock. The wood originated from forest surrounding the eruption zone and collapsed into the diatreme before resettling in volcaniclastic kimberlite to depths >300 m, where it was mummified in a sterile environment. Anatomy of the unpermineralized wood permits conclusive identification to the genus Metasequoia (Cupressaceae). The wood yields genuine cellulose and occluded amber, both of which have been characterized spectroscopically and isotopically. From cellulose δ(18)O and δ(2)H measurements, we infer that Early Eocene paleoclimates in the western Canadian subarctic were 12-17°C warmer and four times wetter than present. Canadian kimberlites offer Lagerstätte-quality preservation of wood from a region with limited alternate sources of paleobotanical information. PMID:23029080

  10. Dinocyst taphonomy, impact craters, cyst ghosts, and the Paleocene-Eocene thermal maximum (PETM)

    USGS Publications Warehouse

    Edwards, Lucy E.

    2012-01-01

    Dinocysts recovered from sediments related to the Chesapeake Bay impact structure in Virginia and the earliest Eocene suboxic environment in Maryland show strange and intriguing details of preservation. Features such as curled processes, opaque debris, breakage, microborings and cyst ghosts, among others, invite speculation about catastrophic depositional processes, rapid burial and biological and chemical decay. Selected specimens from seven cores taken in the coastal plain of Virginia and Maryland show abnormal preservation features in various combinations that merit illustration, description, discussion and further study. Although the depositional environments described are extreme, many of the features discussed are known from, or could be found in, other environments. These environments will show both similarities to and differences from the extreme environments here.

  11. Chromium-Isotope and iridium-Abundance Measurements for Late Eocene Impact-Derived Spherule Deposits

    NASA Astrophysics Data System (ADS)

    Kyte, F. T.; Shukolyukov, A.; Hildebrand, A. R.; Lugmair, G. W.; Hanova, J.

    2004-05-01

    The late Eocene (approx. 35 Ma) was a time of multiple large body impacts superimposed within an interval of dust accretion. At least two spherule layers are preserved in deep sea sediments: North American microtektites and the slightly older cpx spherules. The two largest impact structures in the Cenozoic, the 45 km Chesapeake Bay structure and the 100 km Popigai structure, are indicated as the respective spherule sources. Enhanced 3He concentrations extending across a 3 m.y. duration in upper Eocene sediments from the Massignano quarry in Italy indicate accretion of <50 micron dust over this time interval. To characterize one of the impactors we have analyzed splits from the 125-250 micron cpx spherules from ODP 709C, and two fractions from the Massignano layer. Splits of each sample were analyzed for minor and trace elements by instrumental activation analysis (INAA) including Ir, Cr, Fe, Ni, and Co. Additional splits were analyzed for their Cr-isotopic composition, using thermal ionization mass spectrometry. Significant concentrations of Ir were found in all samples, with the highest levels in the Massignano coarse sample and the lowest in the 709C sample. In all cases, element/Ir ratios are much higher than in chondritic meteorites; this may reflect elemental fractionation due to preferential concentration of Cr in spinel growing in the impact fireball. The Cr-isotopic compositions of the 709C and Massignano coarse samples are both non-terrestrial with a positive epsilon 53, indicating a 53Cr/52Cr ratio higher than in terrestrial materials. Microprobe surveys showed that the Massignano samples had significant fine grained oxide grains (mixed with the spherules in the coarse sample) that were not Ni- or Cr-rich, including Ti-rich spinels (likely terrestrial contaminants). In contrast, the ODP 709C sample is a pure extract of generally well-preserved cpx spherules composed of clinopyroxene in a glass matrix. Both the Massignano coarse and the 709C cpx samples

  12. Eocene fossil is earliest evidence of flower-visiting by birds.

    PubMed

    Mayr, Gerald; Wilde, Volker

    2014-05-01

    Birds are important pollinators, but the evolutionary history of ornithophily (bird pollination) is poorly known. Here, we report a skeleton of the avian taxon Pumiliornis from the middle Eocene of Messel in Germany with preserved stomach contents containing numerous pollen grains of an eudicotyledonous angiosperm. The skeletal morphology of Pumiliornis is in agreement with this bird having been a, presumably nectarivorous, flower-visitor. It represents the earliest and first direct fossil evidence of flower-visiting by birds and indicates a minimum age of 47 million years for the origin of bird-flower interactions. As Pumiliornis does not belong to any of the modern groups of flower-visiting birds, the origin of ornithophily in some angiosperm lineages may have predated that of their extant avian pollinators.

  13. Sedimentologic and biostratigraphic implications for early Eocene lacustrine systems, eastern Great Basin, Nevada

    SciTech Connect

    Dubiel, R.F.; Potter, C.J.; Snee, L.W. ); Good, S.C. )

    1993-04-01

    A multidisciplinary study integrating sedimentology, molluscan paleontology and paleoecology, structural and geologic mapping, and [sup 40]Ar/[sup 39]Ar dating of volcanic flows indicates the White Sage Formation north of the Deep Creek Range on the NV-UT border was deposited during the early Eocene in marginal-lacustrine, lacustrine, freshwater-marsh, and minor terrestrial settings. Sedimentary facies include wave-reworked, locally derived Paleozoic carbonate-clast basal conglomerates in contact with bedrock; carbonate tufa mounds; organic-rich mudstones; and laminated to medium-bedded carbonates. The wave-reworked conglomerate implies a broad lake with considerable fetch to generate large waves, but one with only small drainage basins with sharp relief to supply the locally-derived clasts. There is a striking lack of any fluvial, deltaic, or alluvial-fan deposits that would indicate development of substantial drainage areas. The large tufa mounds indicate a high-wave-energy shoaling environment with stable substrate and topography. The profusion of lacustrine carbonates indicates dominantly chemical- or biochemical-induced deposition in a carbonate-saturated lake. The aquatic molluscan fauna indicates shallow, quiet lacustrine conditions with emergent vegetation. The limpets inhabited areas of rooted aquatic vegetation, and the terrestrial gastropods indicate marshes adjacent to the lacustrine system. The molluscan assemblage constrains the age of the White Sage as early Eocene, indicating a lacustrine system equivalent to the Sheep Pass Formation and to outcrops near Illipah, NV that have similar facies and molluscan faunas and that also lack significant fluvial, deltaic, or alluvial fan deposits. The data are consistent with a model wherein the White Sage, Sheep Pass, and Illipah carbonates were deposited in a large lake superimposed on preexisting topography with low relief and little or no syndepositional extension.

  14. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation.

    PubMed

    Simmons, Nancy B; Seymour, Kevin L; Habersetzer, Jörg; Gunnell, Gregg F

    2008-02-14

    Bats (Chiroptera) represent one of the largest and most diverse radiations of mammals, accounting for one-fifth of extant species. Although recent studies unambiguously support bat monophyly and consensus is rapidly emerging about evolutionary relationships among extant lineages, the fossil record of bats extends over 50 million years, and early evolution of the group remains poorly understood. Here we describe a new bat from the Early Eocene Green River Formation of Wyoming, USA, with features that are more primitive than seen in any previously known bat. The evolutionary pathways that led to flapping flight and echolocation in bats have been in dispute, and until now fossils have been of limited use in documenting transitions involved in this marked change in lifestyle. Phylogenetically informed comparisons of the new taxon with other bats and non-flying mammals reveal that critical morphological and functional changes evolved incrementally. Forelimb anatomy indicates that the new bat was capable of powered flight like other Eocene bats, but ear morphology suggests that it lacked their echolocation abilities, supporting a 'flight first' hypothesis for chiropteran evolution. The shape of the wings suggests that an undulating gliding-fluttering flight style may be primitive for bats, and the presence of a long calcar indicates that a broad tail membrane evolved early in Chiroptera, probably functioning as an additional airfoil rather than as a prey-capture device. Limb proportions and retention of claws on all digits indicate that the new bat may have been an agile climber that employed quadrupedal locomotion and under-branch hanging behaviour. PMID:18270539

  15. An extinct Eocene taxon of the daisy family (Asteraceae): evolutionary, ecological and biogeographical implications

    PubMed Central

    Barreda, Viviana D.; Palazzesi, Luis; Katinas, Liliana; Crisci, Jorge V.; Tellería, María C.; Bremer, Kåre; Passala, Mauro G.; Bechis, Florencia; Corsolini, Rodolfo

    2012-01-01

    Background and Aims Morphological, molecular and biogeographical information bearing on early evolution of the sunflower alliance of families suggests that the clade containing the extant daisy family (Asteraceae) differentiated in South America during the Eocene, although palaeontological studies on this continent failed to reveal conclusive support for this hypothesis. Here we describe in detail Raiguenrayun cura gen. & sp. nov., an exceptionally well preserved capitulescence of Asteraceae recovered from Eocene deposits of northwestern Patagonia, Argentina. Methods The fossil was collected from the 47·5 million-year-old Huitrera Formation at the Estancia Don Hipólito locality, Río Negro Province, Argentina. Key Results The arrangement of the capitula in a cymose capitulescence, the many-flowered capitula with multiseriate–imbricate involucral bracts and the pappus-like structures indicate a close morphological relationship with Asteraceae. Raiguenrayun cura and the associated pollen Mutisiapollis telleriae do not match exactly any living member of the family, and clearly represent extinct taxa. They share a mosaic of morphological features today recognized in taxa phylogenetically close to the root of Asteraceae, such as Stifftieae, Wunderlichioideae and Gochnatieae (Mutisioideae sensu lato) and Dicomeae and Oldenburgieae (Carduoideae), today endemic to or mainly distributed in South America and Africa, respectively. Conclusions This is the first fossil genus of Asteraceae based on an outstandingly preserved capitulescence that might represent the ancestor of Mutisioideae–Carduoideae. It might have evolved in southern South America some time during the early Palaeogene and subsequently entered Africa, before the biogeographical isolation of these continents became much more pronounced. The new fossil represents the first reliable point for calibration, favouring an earlier date to the split between Barnadesioideae and the rest of Asteraceae than previously

  16. Dynamic, Large-Magnitude CCD Changes in the Atlantic During the Middle Eocene Climatic Optimum

    NASA Astrophysics Data System (ADS)

    Kordesch, W.; Bohaty, S. M.; Palike, H.; Wilson, P. A.; Edgar, K. M.; Agnini, C.; Westerhold, T.; Roehl, U.

    2015-12-01

    The Middle Eocene Climatic Optimum (MECO; ~40.1 Ma) is a transient global warming event that abruptly reversed the long-term Eocene cooling trend. The primary driving mechanism(s) must be linked to a CO2 increase; however, geochemical modeling experiments show that prevailing hypotheses are incompatible with the paleoclimate record. To further examine changes in deep-sea carbonate burial, we identify the MECO for the first time at ODP Site 929 (Equatorial Atlantic; ~3935 m paleodepth) and present new lithological and geochemical data for this site, including benthic foraminiferal stable isotopes (δ18O and δ13C), XRF scanning data, and an orbitally tuned age model. We combine these records with data from a suite of Atlantic sites to form a depth transect between ~2-4 km (DSDP Site 523, ODP Site 1260 and 1263, IODP Site U1404) representing the first detailed record of carbonate dissolution in the Atlantic spanning the MECO. This compilation reveals dissolution at water depths as shallow as ~2 km (>1 km shallower than previous estimates) with multiple and discrete short-lived (<100 kyr) phases of carbonate compensation depth (CCD) shoaling during and after the event. Careful reevaluation of the Pacific CCD records combined with new results suggests similar short-term variability and magnitude of shoaling globally. These data provide new constraints on carbon release history during the MECO and, potentially, the forcing mechanisms for warming. The transient CCD shoaling events indicate multiple pulses of carbon input and acidification decoupled from deep-sea δ18O and δ13C records, indicating that these events must not have been driven directly by changes in temperature or carbon burial/storage - potentially reconciling some of the data-model discrepancies.

  17. Basalt of Summit Creek: Eocene Magmatism Associated with Farallon Slab Break Off

    NASA Astrophysics Data System (ADS)

    Kant, L. B.; Tepper, J. H.; Eddy, M. P.

    2015-12-01

    In the Pacific Northwest the Early-Middle Eocene was a time of widespread magmatism and tectonic reorganization that included accretion of the Siletzia terrane, Challis volcanism, and establishment of the modern Cascade arc. Although individual events are well documented our knowledge of the underlying tectonic framework is incomplete. To better understand the tectonic changes that occurred during this interval we studied the ~48 Ma Basalt of Summit Creek (BSC), a 1500m section of lavas located south of Mt. Rainier that erupted during the critical time period between the docking of Siletzia and the initiation of the modern Cascade arc. The BSC consists mainly of tholeiitic basalts (wt. % SiO2 = 45.54-63.45, Mg# = 0.68-0.30) with EMORB traits (La/YbN = 1.2-5.9; 206Pb/204Pb = 19.005-19.102; 207Pb/204Pb = 15.538-15.593; 208Pb/204Pb = 38.560-38.714). These lavas lack arc signatures (e.g., HFSE depletions) but overlap in elemental and isotopic composition with oceanic basalts of the Crescent Formation (part of Siletzia) located ~100 km to the west. We suggest that emplacement of lavas that lack arc traits in what was the forearc was a response to break off of the Farallon slab, which occurred as a result of the accretion of Siletzia at ~49 Ma (Wells et al., 2014). Break off opened a gap in the subducted slab, allowing upwelling and subsequent decompression melting. BSC lavas are consistent in age, location and composition with this model. After break off subduction resumed outboard of Siletzia, initiating the Cascade arc. Thus, BSC provides evidence of Farallon slab break off and furthers our understanding of the tectonic transition from widespread magmatism of the Early-Middle Eocene to the Cascade arc.

  18. Arctic hydrology during global warming at the Palaeocene/Eocene thermal maximum.

    PubMed

    Pagani, Mark; Pedentchouk, Nikolai; Huber, Matthew; Sluijs, Appy; Schouten, Stefan; Brinkhuis, Henk; Damsté, Jaap S Sinninghe; Dickens, Gerald R

    2006-08-10

    The Palaeocene/Eocene thermal maximum represents a period of rapid, extreme global warming 55 million years ago, superimposed on an already warm world. This warming is associated with a severe shoaling of the ocean calcite compensation depth and a >2.5 per mil negative carbon isotope excursion in marine and soil carbonates. Together these observations indicate a massive release of 13C-depleted carbon and greenhouse-gas-induced warming. Recently, sediments were recovered from the central Arctic Ocean, providing the first opportunity to evaluate the environmental response at the North Pole at this time. Here we present stable hydrogen and carbon isotope measurements of terrestrial-plant- and aquatic-derived n-alkanes that record changes in hydrology, including surface water salinity and precipitation, and the global carbon cycle. Hydrogen isotope records are interpreted as documenting decreased rainout during moisture transport from lower latitudes and increased moisture delivery to the Arctic at the onset of the Palaeocene/Eocene thermal maximum, consistent with predictions of poleward storm track migrations during global warming. The terrestrial-plant carbon isotope excursion (about -4.5 to -6 per mil) is substantially larger than those of marine carbonates. Previously, this offset was explained by the physiological response of plants to increases in surface humidity. But this mechanism is not an effective explanation in this wet Arctic setting, leading us to hypothesize that the true magnitude of the excursion--and associated carbon input--was greater than originally surmised. Greater carbon release and strong hydrological cycle feedbacks may help explain the maintenance of this unprecedented warmth.

  19. Constraining early to middle Eocene climate evolution of the southwest Pacific and Southern Ocean

    NASA Astrophysics Data System (ADS)

    Dallanave, Edoardo; Bachtadse, Valerian; Crouch, Erica M.; Tauxe, Lisa; Shepherd, Claire L.; Morgans, Hugh E. G.; Hollis, Christopher J.; Hines, Benjamin R.; Sugisaki, Saiko

    2016-01-01

    Studies of early Paleogene climate suffer from the scarcity of well-dated sedimentary records from the southern Pacific Ocean, the largest ocean basin during this time. We present a new magnetostratigraphic record from marine sediments that outcrop along the mid-Waipara River, South Island, New Zealand. Fully oriented samples for paleomagnetic analyses were collected along 45 m of stratigraphic section, which encompasses magnetic polarity Chrons from C23n to C21n (˜ 51.5- 47 Ma). These results are integrated with foraminiferal, calcareous nannofossil, and dinoflagellate cyst (dinocyst) biostratigraphy from samples collected in three different expeditions along a total of ˜80 m of section. Biostratigraphic data indicates relatively continuous sedimentation from the lower Waipawan to the upper Heretaungan New Zealand stages (i.e., lower Ypresian to lower Lutetian, 55.5 to 46 Ma). We provide the first magnetostratigraphically-calibrated age of 48.88 Ma for the base of the Heretaungan New Zealand stage (latest early Eocene). To improve the correlation of the climate record in this section with other Southern Ocean records, we reviewed the magnetostratigraphy of Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau) and Integrated Ocean Drilling Program (IODP) Site U1356 (Wilkes Land Margin, Antarctica). A paleomagnetic study of discrete samples could not confirm any reliable magnetic polarity reversals in the early Eocene at Site 1172. We use the robust magneto-biochronology of a succession of dinocyst bioevents that are common to mid-Waipara, Site 1172, and Site U1356 to assist correlation between the three records. A new integrated chronology offers new insights into the nature and completeness of the southern high-latitude climate histories derived from these sites.

  20. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation.

    PubMed

    Simmons, Nancy B; Seymour, Kevin L; Habersetzer, Jörg; Gunnell, Gregg F

    2008-02-14

    Bats (Chiroptera) represent one of the largest and most diverse radiations of mammals, accounting for one-fifth of extant species. Although recent studies unambiguously support bat monophyly and consensus is rapidly emerging about evolutionary relationships among extant lineages, the fossil record of bats extends over 50 million years, and early evolution of the group remains poorly understood. Here we describe a new bat from the Early Eocene Green River Formation of Wyoming, USA, with features that are more primitive than seen in any previously known bat. The evolutionary pathways that led to flapping flight and echolocation in bats have been in dispute, and until now fossils have been of limited use in documenting transitions involved in this marked change in lifestyle. Phylogenetically informed comparisons of the new taxon with other bats and non-flying mammals reveal that critical morphological and functional changes evolved incrementally. Forelimb anatomy indicates that the new bat was capable of powered flight like other Eocene bats, but ear morphology suggests that it lacked their echolocation abilities, supporting a 'flight first' hypothesis for chiropteran evolution. The shape of the wings suggests that an undulating gliding-fluttering flight style may be primitive for bats, and the presence of a long calcar indicates that a broad tail membrane evolved early in Chiroptera, probably functioning as an additional airfoil rather than as a prey-capture device. Limb proportions and retention of claws on all digits indicate that the new bat may have been an agile climber that employed quadrupedal locomotion and under-branch hanging behaviour.

  1. High Arctic Forests During the Middle Eocene Supported by ~400 ppm Atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Maxbauer, D. P.; Royer, D. L.; LePage, B. A.

    2013-12-01

    Fossils from Paleogene High Arctic deposits provide some of the clearest evidence for greenhouse climates and offer the potential to improve our understanding of Earth system dynamics in a largely ice-free world. One of the most well-known and exquisitely-preserved middle Eocene (47.9-37.8 Myrs ago) polar forest sites, Napartulik, crops out on eastern Axel Heiberg Island (80 °N), Nunavut, Canada. An abundance of data from Napartulik suggest mean annual temperatures of up to 30 °C warmer than today and atmospheric water loads 2× above current levels. Despite this wealth of paleontological and paleoclimatological data, there are currently no direct constraints on atmospheric CO2 levels for Napartulik or any other polar forest site. Here we apply a new plant gas-exchange model to Metasequoia (dawn redwood) leaves to reconstruct atmospheric CO2 from six fossil forests at Napartulik. Individual reconstructions vary between 405-489 ppm with a site mean of 437 ppm (337-564 ppm at 95% confidence). These estimates represent the first direct constraints on CO2 for polar fossil forests and suggest that the temperate conditions present at Napartulik during the middle Eocene were maintained under CO2 concentrations ~1.6× above pre-industrial levels. Our results strongly support the case that long-term climate sensitivity to CO2 in the past was sometimes high, even during largely ice-free periods, highlighting the need to better understand the climate forcing and feedback mechanisms responsible for this amplification.

  2. Tectono-climatic implications of Eocene Paratethys regression in the Tajik basin of central Asia

    NASA Astrophysics Data System (ADS)

    Carrapa, Barbara; DeCelles, Peter G.; Wang, Xin; Clementz, Mark T.; Mancin, Nicoletta; Stoica, Marius; Kraatz, Brian; Meng, Jin; Abdulov, Sherzod; Chen, Fahu

    2015-08-01

    Plate tectonics and eustatic sea-level changes have fundamental effects on paleoenvironmental conditions and bio-ecological changes. The Paratethys Sea was a large marine seaway that connected the Mediterranean Neotethys Ocean with Central Asia during early Cenozoic time. Withdrawal of the Paratethys from central Asia impacted the distribution and composition of terrestrial faunas in the region and has been largely associated with changes in global sea level and climate such as cooling associated with the Eocene/Oligocene transition (EOT). Whereas the regression has been dated in the Tarim basin (China), the pattern and timing of regression in the Tajik basin, 400 km to the west, remain unresolved, precluding a test of current paleogeographic models. Here we date the Paratethys regression in Tajikistan at ca. 39 million years ago (Ma), which is several million years older than the EOT (at ca. 34 Ma) marking the greenhouse to icehouse climate transition of the Cenozoic. Our data also show a restricted, evaporitic marine environment since the middle-late Eocene and establishment of desert like environments after ca. 39 Ma. The overall stratigraphic record from the Tajik basin and southern Tien Shan points to deposition in a foreland basin setting by ca. 40 Ma in response to active tectonic growth of the Pamir-Tibet Mountains at the same time. Combined with the northwestward younging trend of the regression in the region, the Tajik basin record is consistent with northward growth of the Pamir and suggests significant tectonic control on Paratethys regression and paleoenvironmental changes in Central Asia.

  3. Environmental forcing of terrestrial carbon isotope excursion amplification across five Eocene hyperthermals

    NASA Astrophysics Data System (ADS)

    Bowen, G. J.; Abels, H.

    2015-12-01

    Abrupt changes in the isotope composition of exogenic carbon pools accompany many major episodes of global change in the geologic record. The global expression of this change in substrates that reflect multiple carbon pools provides important evidence that many events reflect persistent, global redistribution of carbon between reduced and oxidized stocks. As the diversity of records documenting any event grows, however, discrepancies in the expression of carbon isotope change among substrates are almost always revealed. These differences in magnitude, pace, and pattern of change can complicate interpretations of global carbon redistribution, but under ideal circumstances can also provide additional information on changes in specific environmental and biogeochemical systems that accompanied the global events. Here we evaluate possible environmental influences on new terrestrial records of the negative carbon isotope excursions (CIEs) associated with multiple hyperthermals of the Early Eocene, which show a common pattern of amplified carbon isotope change in terrestrial paleosol carbonate records relative to that recorded in marine substrates. Scaling relationships between climate and carbon-cycle proxies suggest that that the climatic (temperature) impact of each event scaled proportionally with the magnitude of its marine CIE, likely implying that all events involved release of reduced carbon with a similar isotopic composition. Amplification of the terrestrial CIEs, however, does not scale with event magnitude, being proportionally less for the first, largest event (the PETM). We conduct a sensitivity test of a coupled plant-soil carbon isotope model to identify conditions that could account for the observed CIE scaling. At least two possibilities consistent with independent lines of evidence emerge: first, varying effects of pCO2 change on photosynthetic carbon isotope discrimination under changing background pCO2, and second, contrasting changes in regional

  4. Eocene Kashmar granitoids (NE Iran): Petrogenetic constraints from U-Pb zircon geochronology and isotope geochemistry

    NASA Astrophysics Data System (ADS)

    Shafaii Moghadam, Hadi; Li, Xian-Hua; Ling, Xiao-Xiao; Santos, Jose F.; Stern, Robert J.; Li, Qiu-Li; Ghorbani, Ghasem

    2015-02-01

    Kashmar granitoids outcrop for ~ 100 km along the south flank of the Sabzevar ophiolite (NE Iran) and consist of granodiorite and monzogranite along with subordinate quartz monzonite, syenogranite and aplitic dikes. These granitoids intruded Early to Middle Eocene high-K volcanic rocks and can spatially be grouped into eastern and western granitoids. Five samples of granite have identical zircon U-Pb ages of ca. 40-41 Ma. The granitoids have quite high K2O (~ 1.3-5.3 wt.%) and Na2O (~ 1.1-4.6 wt.%) with SiO2 ranging between ~ 62 and 77 wt.%. They are metaluminous to peraluminous, calc-alkaline and I-type in composition. Their chondrite-normalized REE patterns are characterized by LREE enrichment and show slight negative Eu anomalies. Kashmar granitoids have low whole rock εNd (- 0.43 to - 2.3), zircon εHf values (- 1.9 to + 7.2), and somewhat elevated δ18O (+ 6.1 to + 8.7‰) in the range of I-type granites. The Kashmar granitoids show Early Neoproterozoic zircon second-stage Hf and bulk rock Nd model ages at ca. 500-1000 Ma (associated with ca. 640 Ma old inherited zircons). Bulk rock Nd-Sr isotopic modeling suggests that 10-20% assimilation of Cadomian lower crust by juvenile mantle melts and then fractional crystallization (AFC process) can explain the Sr-Nd isotopic compositions of Kashmar granitoids. Kashmar granitoids are products of crustal assimilation by mantle melts associated with extension above the subducting Neotethyan Ocean slab beneath SW Eurasia. Similar subduction-related extension was responsible for the flare-up of Eocene-Oligocene magmatism across Iran, associated with core complex formation in central Iran.

  5. Paleocene-eocene lignite beds of southwest Alabama: Parasequence beds in highstand systems tracts

    SciTech Connect

    Mancini, E.A.; Tew, B.H. ); Carroll, R.E. )

    1993-09-01

    In southwest Alabama, lignite beds are present in at least four stratigraphic intervals that span approximately 8 m.y. of geologic time. Lignite is found in the Paleocene Oak Hill Member and Coal Bluff Member of the Naheola Formation of the Midway Group and the Paleocene Tuscahoma Sand and the Eocene Hatchetigbee Formation of the Wilcox Group. Lignite beds range in thickness from 0.5 to 11 ft and consist of 32-53% moisture, 13-39% volatile matter, 4-36% fixed carbon, and 5-51% ash. These Paleocene and Eocene lignite beds occur as parasequence deposits in highstand systems tracts of four distinct third-order depositional sequences. The lignite beds are interpreted as strata within highstand systems tract parasequences that occur in mud-dominated regressive intervals. Lignite beds were deposited in coastal marsh and low-lying swamp environments as part of deltaic systems that prograded into southwestern Alabama from the west. As sediment was progressively delivered into the basin from these deltas, the effects of relative sea level rise during an individual cycle were overwhelmed, producing a net loss of accommodation and concomitant overall basinward progradation of the shoreline (regression). Small-scale fluctuations in water depth resulting from the interaction of eustasy, sediment yield, and subsidence led to cyclical flooding of the low-lying coastal marshes and swamps followed by periods of progradational and regression. Highstand systems tract deposition within a particular depositional sequence culminated with a relative sea level fall that resulted in a lowering of base level and an abrupt basinward shift in coastal onlap. Following sea level fall and the subsequent accumulation of the lowstand deposits, significant relative sea level rise resulted in the marine inundation of the area previously occupied by coastal marshes and swamps and deposition of the transgressive systems tract of the overlying sequence.

  6. Volutidae (Mollusca: Gastropoda) of the Lakhra Formation (Earliest Eocene, Sindh, Pakistan): systematics, biostratigraphy and paleobiogeography.

    PubMed

    Merle, Didier; Pacaud, Jean-Michel; Métais, Grégoire; Bartolini, Annachiara; Lashari, Rafiq A; Brohi, Imdad A; Solangi, Sarfraz H; Marivaux, Laurent; Welcomme, Jean-Loup

    2014-06-27

    The paleobiodiversity of the Volutidae (Mollusca: Gastropoda) of the Ranikot Group (Sindh, Pakistan) and particularly of the Lakhra Formation (SBZ 5 biozone, Earliest Eocene), is reconsidered on the basis of new material collected during recent field trips. Ten new species are described (Mitreola brohii sp. nov., Lyrischapa vredenburgi sp. nov., L. brevispira sp. nov., Athleta (Volutopupa) citharopsis sp. nov., A. (Volutocorbis) lasharii sp. nov., Volutilithes welcommei sp. nov., V. sindhiensis sp. nov., Pseudaulicina coxi sp. nov., Sindhiluta lakhraensis sp. nov. and Pakiluta solangii sp. nov.) and one species is in open nomenclature (Lyria sp.). Three new genera are described: Lyriopsis gen. nov. [Volutinae, ?Lyriini, type species: Lyriopsis cossmanni (Vredenburg, 1923)], Sindhiluta gen. nov. [Volutilithinae, type species: Sindhiluta lakhraensis n. sp.] and Pakiluta gen. nov. [?Volutodermatinae, type species: Pakiluta solangii n. sp.]. Two new combinations are proposed: Lyriopsis cossmanni (Vredenburg, 1923) comb. nov. and Athleta (Volutopupa) intercrenatus (Cossmann & Pissarro, 1909) comb. nov. Lectotypes are designated for Lyria cossmanni Vredenburg, 1923, L. feddeni Vredenburg, 1923, Volutospina noetlingi Cossmann & Pissarro, 1909, V. intercrenata Cossmann & Pissarro, 1909 and Athleta (Volutocorbis) victoriae Vredenburg, 1923. With 21 species, this volutid fauna is the most diverse recorded from the Tethys Ocean during Earliest Eocene time. The assemblage is characterized by a strong turnover marked by regional speciation and the appearance of many western Tethyan invaders. Although at the species level, the assemblage documents a strong provincialism, at the genus level, the high number of shared genera between Eastern Tethyan and Old World Tethyan realms begins a phase of long-term homogeneity of volutid assemblages from the Tethyan paleobiogeographic province.

  7. Decreased Temperate but not Polar Fish Productivity Across the Eocene-Oligocene Transition: Insights from Ichthyoliths

    NASA Astrophysics Data System (ADS)

    Zill, M.; Sibert, E. C.; Norris, R. D.

    2015-12-01

    The Eocene-Oligocene Transition (EOT, 38-28 Ma) was a period of global cooling and increased nutrient delivery to the ocean. It is associated with the onset of permanent ice sheet on Antarctica, and the beginning of a highly productive polar ecosystem, dominated by diatoms and favoring short, efficient food chains. In a highly efficient, large phytoplankton-dominated ecosystem, we would expect to see higher abundances of consumers, as fewer trophic steps means more carbon available to upper trophic level groups. Here we use the accumulation rate of ichthyoliths (fish teeth and dermal scales) to measure the relative export production of fish through this time period of changing climate. Records from the South Atlantic gyre (DSDP Site 522) the South Pacific Gyre (DSDP Site 596) and the Southern Ocean (DSDP Site 689) show a 50% reduction in ichthyolith accumulation rate in the vicinity the Eocene Oligocene boundary. However, this drop in fish production occurs just after the E/O in the Atlantic, 4 million years before the E/O in the Pacific and 6 million years prior to the E/O in the Southern Ocean. Since the EOT is generally associated with an increase in productivity and diatom blooms in the Southern Ocean and tropical Pacific, we would expect that the abundance of fish would increase across the transition. Our results are surprisingly the inverse of this expectation, and suggest that the transition from greenhouse to icehouse did not produce increase in forage fish or even a response of any kind during the climatological transition into the icehouse world. Indeed, it seems that ichthyolith accumulation rate and primary productivity are not perfectly linked, and it may be that ichthyolith accumulation is responding more to another factor, such as ocean temperature or prey availability that is not linked to the increased diatom production during the EOT.

  8. Late Eocene Antarctic glacial events revealed by radiogenic isotope records from the Kerguelen Plateau

    NASA Astrophysics Data System (ADS)

    Smith, B. W.; Munn, G. H.; Bohaty, S. M.; Scher, H. D.

    2011-12-01

    Oxygen isotope measurements of benthic foraminifera in ODP Hole 738B (Kerguelen Plateau, Southern Ocean) show a 0.6% shift toward more positive values at ca. 37.1 Ma, near the middle/late Eocene boundary. The δ18O values during this cool event reach 2.2%, which may reflect a combination of both intermediate deep-water cooling and partial glaciation of East Antarctica. We conducted neodymium (Nd) isotope measurements of the terrigenous detrital fraction (i.e., decarbonated and leached) from the same samples used to construct the stable isotope record. Our results reveal a shift in the Nd isotope composition of fine-grained material deposited on Kerguelen Plateau that coincides with the δ18O excursion. The background ɛNd values (i.e., before and after the δ18O shift) are -12 ɛNd, consistent with regionally sourced sediment from along the East Antarctica margin (e.g., Wilkes Land, Prydz Bay). During the δ18O excursion at 37.1 Ma, there is transient decrease in ɛNd values to -15.5. These results strongly indicate that Kerguelen Plateau received an influx of detrital material from ancient sediment sources (i.e., with low ɛNd values), such as those found in nearby Prydz Bay. Our results support an increase in continental ice volume in East Antarctica during this event, resulting in enhanced rates of mechanical weathering. We have also documented a second cool event ca. 36.7 Ma, approximately 400 kyr after the 37 Ma event. Future efforts will focus on determining the timing of middle-to-late Eocene cooling episoides and further documenting changes in weathering during each of these events.

  9. The Jianchuan Basin, Yunnan: Implications on the Evolution of SE Tibet During the Eocene

    NASA Astrophysics Data System (ADS)

    Gourbet, L.; Mahéo, G.; Leloup, P. H.; Jean-Louis, P.; Sorrel, P.; Eymard, I.; Antoine, P. O.; Sterb, M.; Wang, G.; Cao, K.; Chevalier, M. L.; Lu, H.

    2015-12-01

    The Jianchuan basin, Yunnan Province, China, is the widest continental Cenozoic sedimentary basin in the southeastern Tibetan plateau. It is located ~10 km east of the Red River fault zone. Climatic simulations and palaeoenvironment studies suggest that SE Asia has experienced a variable intensity monsoon system for 40 Ma. Because sediments can record deformation, climate and environment changes, the Jianchuan basin provides the opportunity to assess the relative role of climate and tectonics on the Tibetan plateau formation. Sediments consist of floodplain siltites, massive fluvial sandstone, few carbonate levels, coal and volcanosedimentary deposits. U/Pb dating of zircons from dykes, volcanodetrital deposits and lava flows respectively cutting and interbedded within the sediments was performed by in-situ LA-ICPMS. All ages range from 38 to 35 Ma. Such absolute dating is confirmed by palaeontological evidence. Dental remains of Zaisanamynodonwere found in coal deposits. This giant Rhino lived in Asia during the Ergilian (late Eocene). Our data allow us to propose a revised stratigraphy for the Jianchuan basin: contrary to what was suggested by previous studies, i.e. a continuous sedimentation from the Paleocene to the Miocene, nearly no sedimentation occurred after 34 Ma. Combined with a sedimentological analysis, the data indicate that during the late Eocene, the Jianchuan area was covered by a large (>15 km) braided river system that coexisted with local transient lakes, in a moderate-slope and semi-arid environment. This major sedimentation event was followed by a period of more humid conditions that may be related to an intensification of the monsoon. The end of the sedimentation seems to be contemporaneous with the Ailao Shan-Red River fault activation. The new stratigraphy has also implications for regional studies that need robust age constraints, for example for reconstructing palaeoelevation or provenance of sediments.

  10. Stable isotope paleoclimatology of the earliest Eocene using kimberlite-hosted mummified wood from the Canadian Subarctic

    NASA Astrophysics Data System (ADS)

    Hook, B. A.; Halfar, J.; Gedalof, Z.; Bollmann, J.; Schulze, D. J.

    2015-10-01

    The recent discovery of well-preserved mummified wood buried within a subarctic kimberlite diamond mine prompted a paleoclimatic study of the early Eocene "hothouse" (ca. 53.3 Ma). At the time of kimberlite eruption, the Subarctic was warm and humid producing a temperate rainforest biome well north of the Arctic Circle. Previous studies have estimated that mean annual temperatures in this region were 4-20 °C in the early Eocene, using a variety of proxies including leaf margin analysis and stable isotopes (δ13C and δ18O) of fossil cellulose. Here, we examine stable isotopes of tree-ring cellulose at subannual- to annual-scale resolution, using the oldest viable cellulose found to date. We use mechanistic models and transfer functions to estimate earliest Eocene temperatures using mummified cellulose, which was well preserved in the kimberlite. Multiple samples of Piceoxylon wood within the kimberlite were crossdated by tree-ring width. Multiple proxies are used in combination to tease apart likely environmental factors influencing the tree physiology and growth in the unique extinct ecosystem of the Polar rainforest. Calculations of interannual variation in temperature over a multidecadal time-slice in the early Eocene are presented, with a mean annual temperature (MAT) estimate of 11.4 °C (1 σ = 1.8 °C) based on δ18O, which is 16 °C warmer than the current MAT of the area (-4.6 °C). Early Eocene atmospheric δ13C (δ13Catm) estimates were -5.5 (±0.7) ‰. Isotopic discrimination (Δ) and leaf intercellular pCO2 ratio (ci/ca) were similar to modern values (Δ = 18.7 ± 0.8 ‰; ci/ca = 0.63 ± 0.03 %), but intrinsic water use efficiency (Early Eocene iWUE = 211 ± 20 μmol mol-1) was over twice the level found in modern high-latitude trees. Dual-isotope spectral analysis suggests that multidecadal climate cycles somewhat similar to the modern Pacific Decadal Oscillation likely drove temperature and cloudiness trends on 20-30-year timescales, influencing

  11. Stratigraphic and climatic implications of clay mineral changes around the Paleocene/Eocene boundary of the northeastern US margin

    USGS Publications Warehouse

    Gibson, T.G.; Bybell, L.M.; Mason, D.B.

    2000-01-01

    Kaolinite usually is present in relatively small amounts in most upper Paleocene and lower Eocene neritic deposits of the northern US Atlantic Coastal Plain. However, there is a short period (less than 200,000 k.y.) in the latest Paleocene (upper part of calcareous nannoplankton Zone NP 9) when kaolinite-dominated clay mineral suites replaced the usual illite/smectite-dominated suites. During this time of global biotic and lithologic changes, kaolinite increased from less than 5% of the clay mineral suite to peak proportions of 50-60% of the suite and then returned to less than 5% in uppermost Paleocene/lowermost Eocene strata. This kaolinite pulse is present at numerous localities from southern Virginia to New Jersey. These sites represent both inner and middle neritic depositional environments and reflect input from several river drainage systems. Thus, it is inferred that kaolinite-rich source areas were widespread in the northeastern US during the latest Paleocene. Erosion of these source areas contributed the kaolinite that was transported and widely dispersed into shelf environments of the Salisbury embayment. The kaolinite increase, which occurred during a time of relatively high sea level, probably is the result of intensified weathering due to increased temperature and precipitation. The southern extent of the kaolinite pulse is uncertain in that uppermost Paleocene beds have not been identified in the southern Atlantic Coastal Plain. The late Paleocene kaolinite pulse that consists of an increase to peak kaolinite levels followed by a decrease can be used for detailed correlation between more upbasin and more downbasin sections in the Salisbury embayment. Correlations show that more upbasin Paleocene/Eocene boundary sections are erosionally truncated. They have varying portions of the kaolinite increase and, if present at all, discontinuous portions of the subsequent kaolinite decrease. As these truncated sections are disconformably overlain by lower

  12. Geology and paleoecology of the Cottonwood Creek delta in the Eocene Tipton Tongue of the Green River Formation and a mammalian fauna from the Eocene Cathedral Bluffs Tongue of the Wasatch Formation, Southeast Washakie Basin, Wyoming

    SciTech Connect

    Roehler, H.W.; Hanley, J.H.; Honey, J.G.

    1988-01-01

    Nonmarine mollusks are used to interpret paleoenvironments and patterns of sedimentation of a fan delta on the east margin of Eocene Lake Gosiute. The delta is composed of a lens of quartzose sandstone intertongued with oil shale. Delta morphology is illustrated by cross sections and paleogeographic maps. A fossil fauna representing five mammalian orders is described and used to establish the age of parts of the Wasatch and Green River formations. There are three chapters in this bulletin.

  13. A partial skeleton of Proteopithecus sylviae (Primates, Anthropoidea): first associated dental and postcranial remains of an Eocene anthropoidean

    NASA Astrophysics Data System (ADS)

    Simons, Elwyn L.; Seiffert, Erik R.

    1999-12-01

    Recent excavation in the Late Eocene quarry L-41 (Fayum Depression, Egypt) revealed two tibiae and a femur in direct association with a mandible of Proteopithecus sylviae, arguably the most generalized African anthropoidean known from cranial remains. This discovery represents the first association of dental and postcranial material belonging to an Eocene anthropoidean, and provides new insights into the functional anatomy and phylogenetic position of Proteopithecus. The hindlimb morphology of Proteopithecus is most similar to small-bodied platyrrhines among living and extinct primates and is consistent with a locomotor repertoire that included a considerable amount of running and pronograde leaping. In certain dental and postcranial features, Proteopithecus differs from the other Fayum anthropoideansand shows a greater resemblance to living and extinct platyrrhines, but it is unclear whether these features are of particular phylogenetic significance.

  14. Metre-scale cyclicity in Middle Eocene platform carbonates in northern Egypt: Implications for facies development and sequence stratigraphy

    NASA Astrophysics Data System (ADS)

    Tawfik, Mohamed; El-Sorogy, Abdelbaset; Moussa, Mahmoud

    2016-07-01

    The shallow-water carbonates of the Middle Eocene in northern Egypt represent a Tethyan reef-rimmed carbonate platform with bedded inner-platform facies. Based on extensive micro- and biofacies documentation, five lithofacies associations were defined and their respective depositional environments were interpreted. Investigated sections were subdivided into three third-order sequences, named S1, S2 and S3. Sequence S1 is interpreted to correspond to the Lutetian, S2 corresponds to the Late Lutetian and Early Bartonian, and S3 represents the Late Bartonian. Each of the three sequences was further subdivided into fourth-order cycle sets and fifth-order cycles. The complete hierarchy of cycles can be correlated along 190 km across the study area, and highlighting a general "layer-cake" stratigraphic architecture. The documentation of the studied outcrops may contribute to the better regional understanding of the Middle Eocene formations in northern Egypt and to Tethyan pericratonic carbonate models in general.

  15. "Kasserine Island" boundaries variations during the Upper Cretaceous-Eocene (central Tunisia)

    NASA Astrophysics Data System (ADS)

    Kadri, Ali; Essid, El Mabrouk; Merzeraud, Gilles

    2015-11-01

    The emergent domain known as "Kasserine Island" in central Tunisia, to the West of the North-South Axis, was emerging during the Turonian. This area has undergone several changes during the Cretaceous-Eocene period. In the present study, the compilation of surface and sub-surface data provided new information about the boundaries variations of the emerged domain. The analysis of paleogeographic maps allowed the identification of three distinct stages of evolution. The first stage extents from the Middle Turonian to the Lower Maastrichtian where the emergent domain covers the area extending from Jebels Selloum-Sidi Aich in the West to Jebel Bouhedma in the East. The boundaries of this area coincide with the E-W Kasserine fault to the North, the N-S Lessouda-Boudinar fault in the East and the N 120 el Mech-Souinia flexure at the South. This emersion contemporaneous with a high eustatic level is most likely related to tectonic activity. The extensional tectonic regime that is characterized by a NE-SW minimal horizontal stress, has reactivated border faults with a normal component. The interference of the tilting of these border faults was at the origin of the emergence of this domain. The ascent of the Triassic salt may also have contributed in this uplift. In the second stage, the emerged domain has reached its maximum expansion to the North, the West and the South during the Middle Maastrichtian-Paleocene period. Its northern limit is irregular, while the southern limit coincides with the N120 Gafsa fault and the E-W fault of Jebels Orbata-Bouhedma. The N-S Lessouda-Boudinar fault forms the eastern limit. This expansion is mostly related to the global eustatic fall that is well characterized during this period, and partly to the compressive tectonic activity. The Lower Eocene is characterized by a marine transgression that has interested the northern edge of the Island, where the Ypresian deposits are discordant on older series. This edge was irregular and marked by

  16. Late Cretaceous to Middle Eocene Geological Evolution of the Northwestern Caribbean - Constraints from Cuban Data

    NASA Astrophysics Data System (ADS)

    Cobiella, J.; Hueneke, H.; Meschede, M.; Sommer, M.

    2006-05-01

    Cuba acts as the northwestern boundary of the Caribbean Sea. However it is not part of the Caribbean plate, its geological development is deeply related to the plate history. In fact, its Cretaceous volcanic arc rocks tightly correlate with coeval sections in Hispaniola and Puerto Rico, and the same probably occurs with the ophiolites. The early Palaeogene events in Cuba were also involved in the Caribbean plate history. In general, two principal structural levels can be distinguished in the geological structure of Cuba. The rocks belonging to the upper level (Eocene to Quaternary) are little disturbed and can be referred to as the cover. Below it occurs the great complex of the Cuban orogenic belt, which consists mainly of rocks of Jurassic to Eocene age. In addition, small outcrops of Proterozoic metamorphic rocks also occur in north central Cuba. The Palaeocene-Eocene section contains volcanic arc sequences in SE Cuba and northward thrusted piggy back and foreland basins in central and western Cuba. The Mesozoic rocks lies unconformably below. The contacts between the major Mesozoic elements are always tectonic. With the exception of the rocks of the passive Mesozoic margin of North America in northern Cuba, the remaining units represent tectonostratigraphic terranes extending parallel to the axis of the present main island of Cuba. The northernmost unit is the Mesozoic passive continental margin of North America. It consists of a Jurassic- Cretaceous mainly marine sedimentary sequence now exposed as a thrust and fold belt along the northern edge of the Cuban mainland. The other units are, from north to south: the Northern Ophiolitic Belt, the Volcanic Arc Terrane and the Southern Metamorphic Terranes. The ophiolites and the Cretaceous volcanic arc terranes belong to the Proto-Caribbean plate and were accreted to the palaeomargin during Late Cretaceous and early Palaeogene episodes. Some constrains to Caribbean plate origin and evolution according to data from

  17. Fragments of Late Eocene Earth-impacting asteroids linked to disturbance of asteroid belt

    NASA Astrophysics Data System (ADS)

    Schmitz, Birger; Boschi, Samuele; Cronholm, Anders; Heck, Philipp R.; Monechi, Simonetta; Montanari, Alessandro; Terfelt, Fredrik

    2015-09-01

    The onset of Earth's present icehouse climate in the Late Eocene coincides with astronomical events of enigmatic causation. At ∼36 Ma ago the 90-100 km large Popigai and Chesapeake Bay impact structures formed within ∼ 10- 20 ka. Enrichments of 3He in coeval sediments also indicate high fluxes of interplanetary dust to Earth for ∼ 2 Ma. Additionally, several medium-sized impact structures are known from the Late Eocene. Here we report from sediments in Italy the presence of abundant ordinary chondritic chromite grains (63-250 μm) associated with the ejecta from the Popigai impactor. The grains occur in the ∼ 40 cm interval immediately above the ejecta layer. Element analyses show that grains in the lower half of this interval have an apparent H-chondritic composition, whereas grains in the upper half are of L-chondritic origin. The grains most likely originate from the regoliths of the Popigai and the Chesapeake Bay impactors, respectively. These asteroids may have approached Earth at comparatively low speeds, and regolith was shed off from their surfaces after they passed the Roche limit. The regolith grains then settled on Earth some 100 to 1000 yrs after the respective impacts. Further neon and oxygen isotopic analyses of the grains can be used to test this hypothesis. If the Popigai and Chesapeake Bay impactors represent two different types of asteroids one can rule out previous explanations of the Late Eocene extraterrestrial signatures invoking an asteroid shower from a single parent-body breakup. Instead a multi-type asteroid shower may have been triggered by changes of planetary orbital elements. This could have happened due to chaos-related transitions in motions of the inner planets or through the interplay of chaos between the outer and inner planets. Asteroids in a region of the asteroid belt where many ordinary chondritic bodies reside, were rapidly perturbed into orbital resonances. This led to an increase in small to medium-sized collisional

  18. Basin Evolution of the Cretaceous-Early Eocene Xigaze Forearc, Southern Tibet

    NASA Astrophysics Data System (ADS)

    Orme, D. A.; Carrapa, B.; Kapp, P. A.; Gehrels, G. E.; Reiners, P. W.

    2013-12-01

    An understanding of the processes which control the evolution of forearc basins is important for deciphering the tectonic development of a convergent margin prior to continent-continent suturing. This study presents sedimentologic, modal petrographic and geo-thermochronologic data from the Xigaze forearc basin, preserved along ~ 600 km of the Indus-Yarlung Suture Zone in southern Tibet. From late Cretaceous to early Cenozoic time, subduction of Neo-Tethyan oceanic crust beneath the southern margin of Asia accommodated the northward motion of the Indian craton and formed the Xigaze forearc basin. Following collision with India in the early Cenozoic, the basin transitioned from predominantly marine to non-marine sedimentation and was subsequently uplifted to a mean elevation of 5000 m. Thus, the sedimentary record in the Xigaze forearc preserves information regarding the tectonic evolution of the Indo-Asia continental margin prior to and following collision. We present new measured sections and geo-thermochronologic data from Early Cretaceous to Early Eocene clastic and carbonate sedimentary rocks, preserved in two previously unexplored regions of the forearc, (1) at its western most extent, northwest of Saga, and (2) north of Lhatse. In turn, we compare our results with previously published data in order to synthesize our current understanding of forearc evolution. Strata preserved in the Lhaste region record an initial shallow marine phase of forearc sedimentation (Aptian), but quickly transition to deep marine slope and distal fan turbidite facies (Albian-Campanian). In contrast, facies preserved in the Saga region record a younger shoaling upward marine sequence (Maastrichtian-Ypresian), with the uppermost ~ 400 m consisting of fluvial channel sandstones and red-green paleosols. Facies and depositional environments in the Saga region are highly variable along strike, with turbidites, shelf limestones, estuarine siliciclastics and thick paleosols sequences all

  19. Effects of Extreme Monsoon Precipitation on River Systems Form And Function, an Early Eocene Perspective

    NASA Astrophysics Data System (ADS)

    Plink-Bjorklund, P.; Birgenheier, L.

    2013-12-01

    Here we document effects of extreme monsoon precipitation on river systems with mountainous drainage basin. We discuss the effects of individual extreme monsoon seasons, as well as long-term changes in Earth surface system's form and function. The dataset spans across 1000 m of stratigraphy across ca 200 km of Paleocene and Early Eocene river deposits. The excessive 3-dimensional outcrops, combined with our new Carbon isotope, ichnological and paleosols record allow reconstruction of long-term river system's evolution during the Paleocene-Eocene Thermal Maximum (PETM) ca 56 million years ago, the transient global warming events during Early Eocene Climate Optimum (EECO) ca 53 to 51.5 million years ago, as well as the effects of highly peaked precipitation events during single monsoon seasons. On the single season scale, the increase in precipitation peakedness causes high discharge flooding events that remove large quantities of sediment from the drainage basin, due to stream erosion and landslide initiation. The initiation of landslides is especially significant, as the drainage basin is of high gradient, the monsoon intensification is accompanied by significant vegetation decline, as the monsoon cycle changes to multi-year droughts interrupted by extreme monsoon precipitation. These large discharge floods laden with sediment cause rapid deposition from high-velocity currents that resemble megaflood deposits in that they are dominated by high-velocity and high deposition rate sedimentary structures and thick simple depositional packages (unit bars). Such high deposition rates cause locally rapid channel bed aggradation and thus increase frequency of channel avulsions and cause catastrophic high-discharge terrestrial flooding events across the river basin. On long time scales, fluvial megafan systems, similar to those, e.g. in the Himalayan foreland, developed across the ca 200 km wide river basin, causing significant sediment aggradation and a landscape with high

  20. Missing organic carbon in Eocene marine sediments: Is metabolism the biological feedback that maintains end-member climates?

    NASA Astrophysics Data System (ADS)

    Olivarez Lyle, Annette; Lyle, Mitchell W.

    2006-06-01

    Ocean chemistry is affected by pCO2 in the atmosphere by increasing the dissolution of solid calcium carbonate and elevating the dissolved inorganic carbon concentrations in seawater. Positive feedbacks between the ocean and atmosphere can maintain high atmospheric pCO2 and affect global climate. We report evidence for changes in the oceanic carbon cycle from the first high-quality organic carbon (Corg) data set of Eocene sediments beneath the equatorial Pacific upwelling region (Leg 199 of the Ocean Drilling Program). Eocene Corg mass accumulation rates (MARs) are 10 times lower than Holocene rates, even though expected Corg MARs estimated from biogenic-barium MARs (an indicator of biological production) equal or exceed modern fluxes. What happened to the missing Corg? Recent advances in ecology and biochemical kinetics show that the metabolism of nearly all animals, marine and terrestrial, is positively correlated by first principles to environmental temperatures. The approximately 10°C abyssal temperature difference from Eocene to Holocene should have radically reduced pelagic Corg burial, as we observe. We propose that higher basal metabolism and nutrient utilization/recycling rates in the Eocene water column and surface sediments precluded Corg sediment burial in the pelagic ocean. Increased rates of metabolism, nutrient utilization, and lowered Corg sedimentation caused by increased temperature may have acted as a biological feedback to maintain high atmospheric pCO2 and hothouse climates. Conversely, these same parameters would reverse sign to maintain low pCO2 when temperatures decrease, thereby maintaining "icehouse" conditions during cold climate regimes.

  1. Harpactoxanthopsis quadrilobata (Desmarest, 1822) from the Eocene of Slovakia and Italy: the phenomenon of inverted images of fossil heterochelous crabs

    PubMed Central

    Hyžný, Matúš

    2015-01-01

    This short note provides details on a specimen of Harpactoxanthopsis quadrilobata (Desmarest, 1822) deposited in the Natural History Museum of Slovak National Museum in Bratislava which was figured in the monograph by Lőrenthey and Beurlen (1929). The phenomenon of inverted images of fossil heterochelous crabs in the literature published in the 19th century is documented on the example of H. quadrilobata from the Eocene of Italy. PMID:25983384

  2. Low-temperature thermochronologic record of Eocene migmatite dome emplacement and late Cenozoic landscape development, Shuswap core complex, British Columbia

    NASA Astrophysics Data System (ADS)

    Toraman, Erkan; Teyssier, Christian; Whitney, Donna L.; Fayon, Annia K.; Thomson, Stuart N.; Reiners, Peter W.

    2014-08-01

    Exhumed mid-to-lower crustal rocks offer an opportunity to determine the mechanisms, conditions, timing, and consequences of the ascent of hot rocks from deep to shallow crustal levels. We used results of low-T thermochronology (zircon and apatite (U-Th)/He, apatite fission track) to document the very shallow emplacement (<2 km) of high-grade metamorphic rocks and to determine the timing and rates of Cenozoic cooling, exhumation, and subsequent incision of the Thor-Odin migmatite dome of the Shuswap metamorphic core complex, British Columbia (Canada). Samples collected at high elevation in the dome (>1800 m) have preserved Eocene fission-track ages and evidence of rapid cooling (≥60°C/Myr). This Eocene cooling event corresponds to rapid exhumation by upward flow of partially molten crust and final exhumation by detachment faulting. Samples collected below 1800 m in elevation display a wide range of apatite fission track ages (43-15 Ma) and track length distributions that reflect prolonged residence in the apatite partial annealing zone. These age-elevation relations imply that the dome rocks reached the near surface (<2 km) during initial upward flow and tectonic exhumation in the Eocene and that little erosion of the Eocene surface has occurred since that time. Thermal modeling of the lowest elevation samples (≤ ~600 m) and intrasample apatite (U-Th)/He age variations reveal enhanced erosion and relief production at the onset of continental glaciations at ~3 Ma. Our work illustrates the dynamic links between deep and shallow crustal processes and the evolution of topography in a deeply incised hot orogen.

  3. A late eocene-early Oligocene transgressive event in the Golfo San Jorge basin: Palynological results and stratigraphic implications

    NASA Astrophysics Data System (ADS)

    Paredes, José M.; Foix, Nicolás; Guerstein, G. Raquel; Guler, María V.; Irigoyen, Martín; Moscoso, Pablo; Giordano, Sergio

    2015-11-01

    A new Cenozoic dataset in the subsurface of the South Flank of the Golfo San Jorge Basin (Santa Cruz province) allowed to identify a non-previously recognized transgressive event of late Eocene to early Oligocene age. Below of a marine succession containing a dinoflagellate cyst assemblage that characterizes the C/G palynological zone of the Chenque Formation (early Miocene), a 80-110 m thick marine succession contains a palynological assemblage integrated by Gelatia inflata, Diphyes colligerum and Reticulatosphaera actinocoronata supporting the occurrence of a marine incursion in the basin during the Eocene-Oligocene transition (EOT). The new lithostratigraphic unit - here defined as El Huemul Formation - covers in sharp contact to the Sarmiento Formation, and become thinner from East to West; the unit has been identified in about 1800 well logs covering up to 3500 km2, and its subsurface distribution exceed the boundaries of the study area. The El Huemul Formation consists of a thin lag of glauconitic sandstones with fining-upward log motif, followed by a mudstone-dominated succession that coarsening-upward to sandstones, evidencing a full T-R cycle. Preservation of the El Huemul Formation in the subsurface of the South Flank has been favored by the reactivation of WNW-ESE late Cretaceous normal faults, and by the generation of N-S striking normal faults of Paleocene-Eocene age. Flexural loading associated to igneous intrusions of Paleocene?- middle Eocene age also promoted the increase of subsidence in the South Flank of the basin prior to the transgression.

  4. Ocean Response to Possible Southern Meltwater Pulses During Eocene-Oligocene Cooling Climate Trend: A Sensitivity Ocean Modeling Study

    NASA Astrophysics Data System (ADS)

    Haupt, B. J.; Seidov, D.

    2003-12-01

    Understanding ocean circulation and sea level change in the past (and foreseeable future) is one of the focal points of paleoceanography. Sea level may change due to several primary causes, including the meltdown of the major ice sheets, sea ice melting, and changes in the thermohaline structure of the oceans. The sensitivity of the past ocean circulation to meltwater impacts may have been different from the present-day. We still have only a vague understanding of how ocean basin geography may influence the freshwater impacts in different oceans; the role of geography is important for reconstructing variability of past climates with substantially different land-sea distributions. As freshwater impacts in past geologic eras having different basins configurations may have been different from the present-day pattern, the sensitivity of the ocean circulation to sea surface density impacts and climate change could have been different as well. We use the Eocene-Oligocene geometry and climate to address the past ocean and sea level long-term internal variability because this time slice provides a substantially different geometry and for a strong sea ice impact that can be seen in the geologic record. The Eocene epoch is crucial as a transition from the warm Cretaceous ocean to cooler oceans that may have been subject to bi-polar millennial-scale oscillations of the deep ocean circulation caused by freshwater pulses of the developing southern cryosphere. In a series of numerical experiments, sea ice melting and sea water freezing around Antarctica were simulated by superimposing freshwater layers over zonally-averaged sea surface salinity. Eocene sea surface temperature and sea surface salinity are specified based on the paleoclimatic record and modeling. In our simulations, the Eocene ocean circulation is indeed sensitive to freshwater impacts in the Southern Hemisphere. There are noticeable sea level changes caused by the restructuring of the deep ocean thermal and

  5. Description and correlation of Eocene rocks in stratigraphic reference sections for the Green River and Washakie basins, southwest Wyoming

    SciTech Connect

    Roehler, H.W.

    1992-01-01

    Stratigraphic reference sections of the Wasatch, Green River, and Bridger (Washakie) Formations were measured on outcrops in the Green River and Washakie basins adjacent to the Rock Springs uplift in southwest Wyoming. The Washakie basin reference section is 7,939 feet thick and consists of 708 beds that were measured, described, and sampled to evaluate the origin, composition, and paleontology of the rocks. The reference section in the Green River basin is 6,587 feet thick and consists of 624 beds that were measured and described but were not sampled. Columnar sections that have been prepared combine information on the stratigraphic nomenclature, age, depositional environments, lithologies, and fossils of each bed in the reference sections. Eocene strata in the Green River and Washakie basins have been correlated biostratigraphically, chronostratigraphically, and lithostratigraphically. The time boundaries of the lower, middle, and upper Eocene rocks in the reference sections are located partly from biostratigraphic investigations and partly from chronostratigraphic investigations. The time boundaries agree with North American land mammal ages. Major stratigraphic units and key marker beds correlated between the reference sections appeared similar in thickness and lithology, which suggests that most depositional events were contemporaneous in both basins. Rocks sampled in the Washakie basin reference section were examined petrographically and were analyzed using heavy mineral separations, X-ray techniques, and assays. The mineralogy suggests that source rocks in the lower part of the Eocene were mostly of plutonic origin and that source rocks in the upper part of the Eocene were mostly of volcanic origin. Economically significant beds of oil shale and zeolite were identified by the analyses. 51 refs., 31 figs., 5 tabs.

  6. The first fossil record of the Emesinae genus Emesopsis Uhler (Hemiptera: Heteroptera, Reduviidae) from Eocene Baltic amber.

    PubMed

    Popov, Yuri A; Chłond, Dominik

    2015-01-01

    Two new fossil representatives of the assassin bug family Reduviidae are described as new from Baltic amber (Upper Eocene), belonging to the genus Emesopsis of the tribe Ploiariolini (Emesinae): Emesopsis putshkovi sp. nov. and E. similis sp. nov. These representatives of the Emesinae are the oldest fossil bugs of the genus Emesopsis known so far, and reported for the first time. This genus is also briefly diagnosed. PMID:26624642

  7. Third contribution on Rovno amber silken fungus beetles: a new Eocene species of Cryptophagus (Coleoptera, Clavicornia, Cryptophagidae)

    PubMed Central

    Lyubarsky, G.Yu.; Perkovsky, E.E.

    2011-01-01

    Abstract Cryptophagus alexagrestis Lyubarsky & Perkovsky, sp. n. is described based on a fossil inclusion in Late Eocene Rovno amber (Ukraine). The new species is similar to the extant Cryptophagus skalitzkyi Reitter and Cryptophagus dilutus Reitter, differing from the latter by having a very transverse, short and dilated 10th antennal segment, and from the former by the very elongate segments of the flagellum. PMID:22259281

  8. Clumped Isotopes, trace elements, and δ18O of stromatolites from the Laney Member of the Green River Formation (Eocene): Implications for paleoenvironments during the Eocene Climatic Optimum

    NASA Astrophysics Data System (ADS)

    Corsetti, F. A.; Miller, H. M.; Asangba, A. E.; Johannessen, K. C.; Wang, D. T.; Petryshyn, V. A.; Tripati, A.; Shapiro, R. S.

    2013-12-01

    The Green River Formation, a large lacustrine deposit located across parts of Utah, Colorado, and Wyoming, was deposited during the Eocene Climatic Optimum (~50 Ma), a period of sustained high temperatures and high atmospheric CO2 levels that may provide a geologic analog for future climate scenarios. Large variations in basin hydrology, water chemistry, and paleotemperatures occurring on time scales of tens of thousands of years or longer have been documented in the sedimentary record. Here, we use stromatolites to investigate much finer-scale resolution of paleoenvironmental changes in the Green River Formation and paleo-Lake Gosiute. We studied the lower LaClede Bed, the base of the Laney Member of the Green River Formation, comprised of cyclic layers of oil shale and carbonate. The lower LaClede Bed represents the filling of the lake following an extended period of closure during deposition of the underlying Wilkins Peak Member. To characterize fluctuations in water chemistry and lake level at greater temporal resolution, we conducted micro-stratigraphic and chemostratigraphic analyses on 24 distinct mm-scale laminae in a single 10 cm carbonate stromatolite bed, including δ13C, δ18O, and trace elemental analyses (Mg, Mn, Fe, Si, K, Na, Al, Sr). Sub-cm-scale correlations between petrographic analyses, elemental composition, and carbonate δ13C and δ18O suggest that this stromatolite records both hydrologically-closed and -open periods in the history of Lake Gosiute. During periods of apparent basin closure, we used two models to investigate lake volume change: 1) a Rayleigh distillation model of water evaporation to estimate lake depth variations and 2) a conservative ion model based on Na incorporation into the stromatolites. In both models, lake depth fluctuated by up to 8 m; this represents up to 40km of shoreline change in Lake Gosiute during the deposition of this stromatolite layer. Interestingly, the modern Great Salt Lake experienced similar

  9. Middle Eocene Nummulites and their offshore re-deposition: A case study from the Middle Eocene of the Venetian area, northeastern Italy

    NASA Astrophysics Data System (ADS)

    Bassi, Davide; Nebelsick, James H.; Puga-Bernabéu, Ángel; Luciani, Valeria

    2013-11-01

    The Middle Eocene Calcari nummulitici formation from northeastern Italy, Venetian area, represents a shallow-marine carbonate ramp developed on the northern Tethyan margin. In the Monti Berici area, its main components are larger foraminifera and coralline red algal communities that constitute thick carbonate sedimentary successions. Middle ramp and proximal outer ramp environments are recognized using component relationships, biofacies and sedimentary features. The middle-ramp is characterized by larger flattened-lenticular Nummulites on palaeohighs between which rhodoliths formed. Larger Nummulites palaeohighs containing Nummulites millecaput, Nummulites crassus, Nummulites discorbinus and Nummulites cf. gizehensis developed more basin-wards. The following relatively quiet environments of basin-wards of the palaeohighs represent areas of maximum carbonate production. The transition between the distal middle- and the proximal outer-ramp settings is marked in the study area by a large erosional surface which is interpreted to have been formed as a result of an erosive channel body filled in by deposits re-sedimented from shallower depths. These off-shore re-sedimented channelized deposits, ascribed to the Shallow Benthic Zone SBZ 15, lying on hemipelagic marls (planktonic foraminiferal zone E9 (P11)) allow for a biostratigraphic correlation to the Late Lutetian. The studied deposits, represented by packstone to rudstones, were displaced whilst still unlithified. The Lutetian-Bartonian regression along with the local tectonic activity promoted the production of a high amount of biogenic shallow-water carbonates mainly produced in the Mossano middle-ramp settings. These prograded towards the basinal areas with high-sedimentation rate of carbonate deposits characterized by the larger Nummulites rudstones. Such high amounts of sediment led to sediment instability which potentially could be mobilized either by return currents due to occasional major storms or by

  10. Low palaeoelevation of the northern Lhasa terrane during late Eocene: Fossil foraminifera and stable isotope evidence from the Gerze Basin

    PubMed Central

    Wei, Yi; Zhang, Kexin; Garzione, Carmala N.; Xu, Yadong; Song, Bowen; Ji, Junliang

    2016-01-01

    The Lhasa terrane is a key region for understanding the paleoelevation of the southern Tibetan Plateau after India-Asia collision. The Gerze Basin, located in the northern part of the Lhasa terrane, is a shortening-related basin. We discovered Lagena laevis (Bandy) fossils in upper Eocene strata of the Gerze Basin. This type of foraminifera is associated with lagoon and estuarine environments, indicating that the northern part of the Lhasa terrane was near sea level during the late Eocene. We speculate that these foraminifera were transported inland by storm surges to low elevation freshwater lakes during times of marine transgressions. This inference is consistent with the relatively positive δ18O values in carbonate from the same deposits that indicate low palaeoelevations close to sea level. Considering the palaeoelevation results from the nearby Oligocene basins at a similar latitude and the volcanic history of the Lhasa terrane, we infer that large-magnitude surface uplift of the northern Lhasa terrane occurred between late Eocene and late Oligocene time. PMID:27272610

  11. Low palaeoelevation of the northern Lhasa terrane during late Eocene: Fossil foraminifera and stable isotope evidence from the Gerze Basin.

    PubMed

    Wei, Yi; Zhang, Kexin; Garzione, Carmala N; Xu, Yadong; Song, Bowen; Ji, Junliang

    2016-01-01

    The Lhasa terrane is a key region for understanding the paleoelevation of the southern Tibetan Plateau after India-Asia collision. The Gerze Basin, located in the northern part of the Lhasa terrane, is a shortening-related basin. We discovered Lagena laevis (Bandy) fossils in upper Eocene strata of the Gerze Basin. This type of foraminifera is associated with lagoon and estuarine environments, indicating that the northern part of the Lhasa terrane was near sea level during the late Eocene. We speculate that these foraminifera were transported inland by storm surges to low elevation freshwater lakes during times of marine transgressions. This inference is consistent with the relatively positive δ(18)O values in carbonate from the same deposits that indicate low palaeoelevations close to sea level. Considering the palaeoelevation results from the nearby Oligocene basins at a similar latitude and the volcanic history of the Lhasa terrane, we infer that large-magnitude surface uplift of the northern Lhasa terrane occurred between late Eocene and late Oligocene time. PMID:27272610

  12. New Cricetid Rodents from Strata near the Eocene-Oligocene Boundary in Erden Obo Section (Nei Mongol, China).

    PubMed

    Li, Qian; Meng, Jin; Wang, Yuanqing

    2016-01-01

    New cricetids (Eucricetodon wangae sp. nov., Eucricetodon sp. and Pappocricetodon siziwangqiensis sp. nov.) are reported from the lower and middle parts of the "Upper Red" beds of the Erden Obo section in Nei Mongol, China. Eucricetodon wangae is more primitive than other known species of the genus from lower Oligocene of Asia and Europe in having a single anterocone on M1, a single connection between the protocone and the paracone, the anterior metalophule connection in M1-2 and weaker anteroconid and ectomesolophid in lower molars. Pappocricetodon siziwangqiensis is more advanced than other species of the genus in permanently missing P4 and having posterior protolophule connection. These fossils suggest that the age of the "Upper Red" of the Erden Obo section is younger than the age of the Upper Eocene Houldjin and Caijiachong formations, but older than those containing the Shandgolian faunas; the "Upper Red" is most closely correlative to the Ergilian beds in age, and probably close to the Eocene/Oligocene boundary. Given the age estimate, Eucricetodon wangae provides the new evidence to support that cricetid dispersal from Asia to Europe occurred prior to the Eocene-Oligocene boundary. PMID:27227833

  13. Single-crystal sup 40 Ar/ sup 39 Ar dating of the Eocene-Oligocene transition in North America

    SciTech Connect

    Swisher, C.C. III ); Prothero, D.R. )

    1990-08-17

    Explanations for the causes of climatic changes and associated faunal and floral extinctions at the close of the Eocene Epoch have long been controversial because of, in part, uncertainties in correlation and dating of global events. New single-crystal laser fusion (SCLF) {sup 40}Ar/{sup 39}Ar dates on tephra from key magnetostratigraphic and fossil-bearing sections necessitate significant revision in North American late Paleogene chronology. The Chadronian-Orellan North American Land Mammal Age boundary, as a result, is shifted from 32.4 to 34.0 Ma (million years ago), the Orellan-Whitneyan boundary is shifted from 30.8 to 32.0 Ma, and the Whitneyan-Arikareean boundary is now approximately 29.0 Ma. The new dates shift the correlation of Chron C12R from the Chadronian to within the Orellan-Whitneyan interval, the Chadronian becomes late Eocene in age, and the North American Oligocene is restricted to the Orellan, Whitneyan, and early Arikareean. The Eocene-Oligocene boundary, and its associated climate change and extinction events, as a result, correlates with the Chadronian-Orellan boundary, not the Duchesnean-Chadronian boundary. 30 refs., 1 fig., 1 tab.

  14. Foraminifera from Paleocene -early Eocene rocks of Bir El Markha section (West Central Sinai), Egypt: Paleobathymetric and paleotemperature significance

    NASA Astrophysics Data System (ADS)

    Orabi, Orabi H.; Hassan, Hatem F.

    2015-11-01

    In the studied section, there is cooling event started during the earliest Paleocene Pα till P1b Subzones. The warming event started at P1c Subzone and continued till P2 Zone. Nevertheless, during the late Paleocene (Zone P3) there is a cooling trend. Zone P4 is characterized by a warming episode and reached its maximum at the latest Paleocene and continued till the earliest Eocene (Subzone P5b), which indicate that the Late Paleocene-Early Eocene was the warmest period of the Cenozoic. It was possible to recognize four sea-level cycles during the Paleocene/Eocene; the first cycle marks the upper part of P3a Zone and represents shallow depth to ∼50 m; the second cycle (P3b/P4) marks another stratigraphic gap at the top of this zonal boundary, the third sea-level cycle (Zone P5a) marks the greatest paleodepth of ∼600 m whereas the fourth cycle represents gradual return to middle-shallow outer neritic.

  15. Maastrichtian-Early Eocene litho-biostratigraphy and palægeography of the northern Gulf of Suez region, Egypt

    NASA Astrophysics Data System (ADS)

    Scheibner, C.; Marzouk, A. M.; Kuss, J.

    2001-02-01

    The Maastrichtian-Lower Eocene sediments on both sides of the northern Gulf of Suez can be subdivided into eight formal formations (including one group) and one informal formation that are described in detail. These lithostratigraphic units reflect three different environmental regimes of deposition or non-deposition. The first regime is characterised by uplift and erosion or non-deposition resulting mostly from the uplift of the Northern Galala/Wadi Araba structure, a branch of the Syrian Arc Foldbelt. The shallow water carbonate platform and slope deposits of the Late Campanian-Maastrichtian St Anthony Formation and the Paleocene-Lower Eocene Southern Galala and Garra Formations represent the second regime and are found north and south of the Northern Galala/Wadi Araba High. The third regime is represented by basinal chalks, marls and shales of the Maastrichtian Sudr Formation and of the Paleocene-Eocene Dakhla, Tarawan and Esna Formations, the Dakhla/Tarawan/Esna informal formation and the Thebes Group. The distribution and lateral interfingering of the above mentioned environmental regimes reflect different vertical movements, changing basin morphology, sea level changes and progradation of shallow water sediments and is illustrated on 11 palæogeographic maps.

  16. A large mimotonid from the Middle Eocene of China sheds light on the evolution of lagomorphs and their kin

    PubMed Central

    Fostowicz-Frelik, Łucja; Li, Chuankui; Mao, Fangyuan; Meng, Jin; Wang, Yuanqing

    2015-01-01

    Mimotonids share their closest affinity with lagomorphs and were a rare and endemic faunal element of Paleogene mammal assemblages of central Asia. Here we describe a new species, Mimolagus aurorae from the Middle Eocene of Nei Mongol (China). This species belongs to one of the most enigmatic genera of fossil Glires, previously known only from the type and only specimen from the early Oligocene of Gansu (China). Our finding extends the earliest occurrence of the genus by at least 10 million years in the Paleogene of Asia, which closes the gap between Mimolagus and other mimotonids that are known thus far from middle Eocene or older deposits. The new species is one of the largest known pre-Oligocene Glires. As regards duplicidentates, Mimolagus is comparable with the largest Neogene continental leporids, namely hares of the genus Lepus. Our results suggest that ecomorphology of this species was convergent on that of small perissodactyls that dominated faunas of the Mongolian Plateau in the Eocene, and probably a result of competitive pressure from other Glires, including a co-occurring mimotonid, Gomphos. PMID:25818513

  17. Single-Crystal 40Ar/39Ar Dating of the Eocene-Oligocene Transition in North America.

    PubMed

    Swisher, C C; Prothero, D R

    1990-08-17

    Explanations for the causes of climatic changes and associated faunal and floral extinctions at the close of the Eocene Epoch have long been controversial because of, in part, uncertainties in correlation and dating of global events. New single-crystal laser fusion (SCLF) (40)Ar/(39)Ar dates on tephra from key magnetostratigraphic and fossilbearing sections necessitate significant revision in North American late Paleogene chronology. The Chadronian-Orellan North American Land Mammal "Age" boundary, as a result, is shifted from 32.4 to 34.0 Ma (million years ago), the Orellan-Whitneyan boundary is shifted from 30.8 to 32.0 Ma, and the Whitneyan-Arikareean boundary is now approximately 29.0 Ma. The new dates shift the correlation of Chron C12R from the Chadronian to within the Orellan-Whitneyan interval, the Chadronian becomes late Eocene in age, and the North American Oligocene is restricted to the Orellan, Whitneyan, and early Arikareean. The Eocene-Oligocene boundary, and its associated climate change and extinction events, as a result, correlates with the Chadronian-Orellan boundary, not the Duchesnean-Chadronian boundary. PMID:17756788

  18. Single-Crystal 40Ar/39Ar Dating of the Eocene-Oligocene Transition in North America

    NASA Astrophysics Data System (ADS)

    Swisher, Carl C., III; Prothero, D. R.

    1990-08-01

    Explanations for the causes of climatic changes and associated faunal and floral extinctions at the close of the Eocene Epoch have long been controversial because of, in part, uncertainties in correlation and dating of global events. New single-crystal laser fusion (SCLF) 40Ar/39Ar dates on tephra from key magnetostratigraphic and fossil-bearing sections necessitate significant revision in North American late Paleogene chronology. The Chadronian-Orellan North American Land Mammal "Age" boundary, as a result, is shifted from 32.4 to 34.0 Ma (million years ago), the Orellan-Whitneyan boundary is shifted from 30.8 to 32.0 Ma, and the Whitneyan-Arikareean boundary is now approximately 29.0 Ma. The new dates shift the correlation of Chron C12R from the Chadronian to within the Orellan-Whitneyan interval, the Chadronian becomes late Eocene in age, and the North American Oligocene is restricted to the Orellan, Whitneyan, and early Arikareean. The Eocene-Oligocene boundary, and its associated climate change and extinction events, as a result, correlates with the Chadronian-Orellan boundary, not the Duchesnean-Chadronian boundary.

  19. New Cricetid Rodents from Strata near the Eocene-Oligocene Boundary in Erden Obo Section (Nei Mongol, China)

    PubMed Central

    Li, Qian; Meng, Jin; Wang, Yuanqing

    2016-01-01

    New cricetids (Eucricetodon wangae sp. nov., Eucricetodon sp. and Pappocricetodon siziwangqiensis sp. nov.) are reported from the lower and middle parts of the “Upper Red” beds of the Erden Obo section in Nei Mongol, China. Eucricetodon wangae is more primitive than other known species of the genus from lower Oligocene of Asia and Europe in having a single anterocone on M1, a single connection between the protocone and the paracone, the anterior metalophule connection in M1-2 and weaker anteroconid and ectomesolophid in lower molars. Pappocricetodon siziwangqiensis is more advanced than other species of the genus in permanently missing P4 and having posterior protolophule connection. These fossils suggest that the age of the “Upper Red” of the Erden Obo section is younger than the age of the Upper Eocene Houldjin and Caijiachong formations, but older than those containing the Shandgolian faunas; the “Upper Red” is most closely correlative to the Ergilian beds in age, and probably close to the Eocene/Oligocene boundary. Given the age estimate, Eucricetodon wangae provides the new evidence to support that cricetid dispersal from Asia to Europe occurred prior to the Eocene-Oligocene boundary. PMID:27227833

  20. Low palaeoelevation of the northern Lhasa terrane during late Eocene: Fossil foraminifera and stable isotope evidence from the Gerze Basin

    NASA Astrophysics Data System (ADS)

    Wei, Yi; Zhang, Kexin; Garzione, Carmala N.; Xu, Yadong; Song, Bowen; Ji, Junliang

    2016-06-01

    The Lhasa terrane is a key region for understanding the paleoelevation of the southern Tibetan Plateau after India-Asia collision. The Gerze Basin, located in the northern part of the Lhasa terrane, is a shortening-related basin. We discovered Lagena laevis (Bandy) fossils in upper Eocene strata of the Gerze Basin. This type of foraminifera is associated with lagoon and estuarine environments, indicating that the northern part of the Lhasa terrane was near sea level during the late Eocene. We speculate that these foraminifera were transported inland by storm surges to low elevation freshwater lakes during times of marine transgressions. This inference is consistent with the relatively positive δ18O values in carbonate from the same deposits that indicate low palaeoelevations close to sea level. Considering the palaeoelevation results from the nearby Oligocene basins at a similar latitude and the volcanic history of the Lhasa terrane, we infer that large-magnitude surface uplift of the northern Lhasa terrane occurred between late Eocene and late Oligocene time.

  1. Eocene high-latitude temperature gradients over time and space based on d18O values of fossil shark teeth

    NASA Astrophysics Data System (ADS)

    Zeichner, S. S.; Kim, S.; Colman, A. S.

    2015-12-01

    Early-Mid Eocene (56.0-33.9Mya) is characterized by a temperate Antarctic climate and shallower latitudinal temperature gradients than those in present day. The warmer waters off the coast of the Antarctic Peninsula provided suitable habitats for taxa (i.e., sharks) that live today at lower latitudes. Stable isotope analysis of Eocene shark teeth provides a proxy to understand high latitude temperature gradients. However, shark ecology, in particular migration and occupation of tidal versus pelagic habitats, must be considered in the interpretation of stable isotope data. In this study, we analyze d18OPO4 values from the enameloid of Striatolamia (synonymized with Carcharias) shark teeth from the La Meseta formation (Seymour Island, Antarctica) to estimate paleotemperature in Early-Mid Eocene Antarctica, and assess the impact of ecology versus environmental signals on d18OPO4 values. We compare the ranges and offsets between our measured shark tooth d18OPO4 and published bivalve d18OCO3 values to test whether shark teeth record signals of migration across latitudinal temperature gradients, or instead reflect seasonal and long-term temporal variation across La Meseta stratigraphic units.

  2. Multiple early Eocene hyperthermals: Their sedimentary expression on the New Zealand continental margin and in the deep sea

    NASA Astrophysics Data System (ADS)

    Nicolo, Micah J.; Dickens, Gerald R.; Hollis, Christopher J.; Zachos, James C.

    2007-08-01

    The Paleocene-Eocene thermal maximum (PETM) ca. 55.5 Ma was a geologically brief interval characterized by massive influx of isotopically light carbon, extreme changes in global climate, and profound variations in Earth system processes. An outstanding issue is whether it was an isolated event, or the most prominent example of a recurring phenomenon. Recent studies of condensed deep-sea sections support the latter, but this finding remains uncertain. Here we present and discuss lithologic and carbon isotope records across two lower Eocene outcrops on South Island, New Zealand. The PETM manifests as a marl-rich horizon with a significant negative carbon isotope excursion (CIE). Above, in sediment deposited between 54 and 53 Ma, are four horizons with similar though less pronounced expressions. Marl beds of all five horizons represent increased terrigenous sedimentation, presumably linked to an accelerated hydrological cycle. Five corresponding clay-rich horizons and CIEs are found in deep-sea records, although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution. The presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 C-depleted carbon during the early Eocene.

  3. Revised magnetic polarity time scale for the Paleocene and early Eocene and implications for Pacific plate motion

    SciTech Connect

    Butler, R.F.; Coney, P.J.

    1981-04-01

    Magnetostratiographic studies of a continental sedimentary sequence in the Clark's Fork Basin, Wyoming and a marine sedimentary sequence at Gubbio, Italy indicate that the Paleocene--Eocene boundary occurs just stratigraphically above normal polarity zones correlative with magnetic anomaly 25 chron. These data indicate that the older boundary of anomaly 24 chron is 52.5 Ma. This age is younger than the late Paleocene age assigned by LaBrecque et al. (1977) and also younger than the basal Eocene age assigned by Ness et al. (1980). A revised magnetic polarity time scale for the Paleocene and early Eocene is presented in this paper. Several changes in the relative motion system between the Pacific plate and neighboring plates occurred in the interval between anomaly 24 and anomaly 21. A major change in absolute motion of the Pacific plate is indicated by the bend in the Hawaiian--Emperor Seamount chain at approx.43 Ma. The revised magnetic polarity time scale indicates that the absolute motion change lags the relative motion changes by only approx.3--5 m.y. rather than by >10 m.y. as indicated by previous polarity time scales.

  4. Paleoenvironmental Interpretation of Quartz Surface Textures, from the Middle Eocene Central Arctic IRD Record

    NASA Astrophysics Data System (ADS)

    St John, K. K.; Passchier, S.; Kearns, L.

    2010-12-01

    The marine record of ice-rafted debris (IRD) is among the best paleoclimatic evidence for the former presence of glaciers at sea level. Calving icebergs transport terrigenous mineral and rock fragments to offshore marine settings; during melting the icebergs release their debris which settles to the seafloor. IRD records are typically more continuous than land-based glacial records, and their interpretation benefits from paleoceanographic age control and multiproxy correlations. The marine IRD record also has its complications, in that both icebergs and sea ice, forming in shallow coastal settings and then drifting with currents, transport IRD. Untangling these two transport mechanisms of IRD is important in paleoclimatic reconstructions because of the different roles that ice sheets and sea ice play in Earth system feedbacks (e.g., ice sheet expansion reduces sea level, sea ice expansion reduces ocean heat loss, and both increase albedo, Stickley et al., 2009). A previous study indicated that analysis of surface texture characteristic of ice-rafted quartz grains can aid in discriminating between iceberg IRD and sea ice IRD (Dunhill, 1998). Preliminary application of this method to a key interval of middle Eocene Arctic IRD record (IODP 302-2A-55X; ~236-242 mcd) showed promising results, including a dominance of sea ice IRD, an increase in iceberg IRD concurrent with the oldest dropstone, and increases in iceberg IRD that tended to track cyclic (Sangiorgi et al., 2008) increases in total IRD abundance (St. John, 2008; St. John et al., 2009). The interpretation that sea ice was present in the Arctic in the middle Eocene is consistent with a robust record of sea-ice dependent fossil diatoms (Stickley et al., 2009). Here we stratigraphically extend the IRD surface texture study down to the base of the ACEX IRD record. Approximately 20 randomly-selected quartz grains from each of 16 samples between 247 mcd and 273 mcd (cores 302-2A-57X3 to 302-2A-62X3) were included in

  5. The Rise of Flowering Plants and Land Surface Physics: The Cretaceous and Eocene Were Different

    NASA Astrophysics Data System (ADS)

    Upchurch, G. R.; Feild, T.

    2010-12-01

    The Cretaceous and Eocene have served as the poster children of past greenhouse climates. One difference between the two time periods is that angiosperms (flowering plants) underwent a major diversification and rise to dominance during the mid-Cretaceous to Paleocene. Flowering plants differ from all other living and fossil plants in having significantly higher rates of transpiration and photosynthesis, which in modern leaves correlate with the density of venation (Dv), a feature that can be measured directly from fossils. This increase in Dv, coupled with an increase in the abundance of angiosperms, is thought to have had major impact on the climate system. This is, in part, because transpiration plays an important role in determining the ratio of sensible to latent heat flux from the land surface and in determining precipitation rate in regions such as the equatorial rainforest. Analysis of Dv in fossil leaves indicates two phases of increase in transpiration rate for angiosperms during the Cretaceous-Paleocene. The oldest known angiosperms (Aptian-early Albian) have a low Dv characteristic of extant and fossil ferns and gymnosperms. At this time angiosperms are low-stature plants of minor importance in terms of relative abundance and diversity (<5%). The first phase of Dv increase occurs during the Late Albian to Cenomanian, where average Dv is 40% greater than that of conifers and ferns, and maximum Dv reaches levels characteristic of many trees from the temperate zone. This first phase coincides with the first local dominance of angiosperms, the first occurrence of moderate to large angiosperm trees (up to 1 m in diameter) , and the first common occurrence of angiosperms in the Arctic. The second phase of Dv increase occurs during the Maastrichtian to Paleocene, where average Dv reaches levels characteristic of modern tropical forests and maximum Dv reaches the level found in highly productive modern vegetation. This second phase coincides with the rise to

  6. Orbitally-forced Azolla blooms and middle Eocene Arctic hydrology; clues from palynology

    NASA Astrophysics Data System (ADS)

    Barke, Judith; Abels, Hemmo A.; Sangiorgi, Francesca; Greenwood, David R.; Sweet, Arthur R.; Donders, Timme; Lotter, Andre F.; Reichart, Gert-Jan; Brinkhuis, Henk

    2010-05-01

    The presence of high abundances of the freshwater fern Azolla in the early Middle Eocene central Arctic Ocean sediments recovered from the Lomonosov Ridge during IODP Expedition 302, have been related to the presence of a substantial freshwater cap. Azolla massulae, belonging to the newly described Eocene species Azolla arctica Collinson et al., have been found over at least a ~4 m-thick interval. There are strong indications that Azolla has bloomed and reproduced in situ in the Arctic Ocean for several hundreds of thousands of years. Possible causes for the sudden demise of Azolla at ~48.1 Ma include salinity changes due to evolving oceanic connections or sea-level change. Distinct cyclic fluctuation in the Azolla massulae abundances have previously been related to orbitally forced climate changes. In this study, we evaluate the possible underlying forcing mechanisms for these freshwater cycles and for the eventual demise of Azolla in an integrated palynological and cyclostratigraphical approach. Our results show two clear periodicities of ~1.3 and ~0.7 m in all major aquatic and terrestrial palynomorph associations, which we can relate to obliquity (41 ka) and precession (~21 ka), respectively. Cycles in the abundances of Azolla, freshwater-tolerant dinoflagellate cysts, and swamp vegetation pollen show co-variability in the obliquity domain. Their strong correlation suggests periods of enhanced rainfall and runoff during Azolla blooms, possibly associated with increased summer season length and insolation during obliquity maxima. Cycles in the angiosperm pollen record are in anti-phase with the Azolla cycles. We interpret this pattern as edaphically drier conditions on land and reduced associated runoff during Azolla lows, possibly corresponding to obliquity minima. The precession signal is distinctly weaker than that for obliquity, and is mainly detectable in the cold-temperate Larix and bisaccate conifer pollen abundances, which is interpreted as a response to

  7. Paleoenvironmental reconstruction of the Early Eocene Wind River Formation in the Wind River Basin, Wyoming

    NASA Astrophysics Data System (ADS)

    Hyland, E.; Fan, M.; Sheldon, N. D.

    2011-12-01

    Terrestrial basin systems provide important information on paleoclimatic, paleoecological, and paleoenvironmental factors and how they control and respond to global changes and spatio-temporal heterogeneity. Examining these dynamics is crucial for times of major global change like the broad-scale climatic trends (warm/wet/high-CO2 conditions) of the Early Eocene Climatic Optimum (EECO). As most climatic records of such events are derived from global marine datasets, regional terrestrial studies such as these provide a better model for understanding ecological responses and the localized effects of events like the EECO. The formation of the Wind River Basin (northwestern Wyoming) has been studied for decades, but its regional climatic, environmental, and ecological dynamics have been largely overlooked. Recent work in other contemporaneous sites in the Green River Basin has suggested that the dynamics and rapidity of climate change in terrestrial interiors during the EECO may have been significantly different than what is indicated by the marine record, so to address these issues on a more regional scale we examined paleosols preserved in the fluvial, basin-margin Wind River Formation preserved near Dubois, Wyoming. Field identification of the paleosols indicated a suite that includes primarily Inceptisols and Alfisols; most exhibited significant redoximorphic features and Bg horizons that indicate a ponded floodplain paleoenvironment, while others contained deep Bk horizons (>100 cm) consistent with more well-drained, but still sub-humid to humid conditions. Based on the identification of these well-developed soil features, along with distinct horizonation and root development, paleosols were robustly correlated and sampled throughout the Formation, and environmental descriptors were assigned. To further examine the question of regional terrestrial climate/environmental change, whole rock geochemistry (XRF) samples from paleosol depth profiles were analyzed for use

  8. Type Region of the Ione Formation (Eocene), Central California: Stratigraphy, Paleogeography, and Relation to Auriferous Gravels

    USGS Publications Warehouse

    Creely, Scott; Force, Eric R.

    2007-01-01

    The middle Eocene Ione Formation extends over 200 miles (320 km) along the western edge of the Sierra Nevada. Our study was concentrated in the type region, 30 miles (48 km) along strike. There a bedrock ridge forms the seaward western side of the Ione depositional tract, defining a subbasin margin. The eastern limit of the type Ione is locally defined by high-angle faults. Ione sediments were spread over Upper Mesozoic metamorphic and plutonic bedrock, fed by gold-bearing streams dissecting the western slope of the ancestral Sierra Nevada. By middle Eocene time, a tropical or subtropical climate prevailed, leading to deep chemical weathering (including laterization) and a distinctively mature mineral assemblage was fed to and generated within Ione deposits. The Ione is noted for its abundant kaolinitic clay, some of it coarsely crystalline; the clay is present as both detrital grains and authigenic cement. Quartz is abundant, mostly as angular grains. Heavy mineral fractions are dominated by altered ilmenite and zircon. Distribution of feldspar is irregular, both stratigraphically and areally. Non-marine facies are most voluminous, and include conglomerates, especially at the base and along the eastern margins of the formation where they pass into Sierran auriferous gravels. Clays, grading into lignites, and gritty sands are also common facies. Both braided and meandering fluvial facies have been recognized. Shallow marine waters flooded the basin probably twice. Tongues of sediment exhibiting a variety of estuarine to marine indicators are underlain and overlain by fluvial deposits. Marine body fossils are found at only a few localities, but burrows identified as Ophiomorpha and cf. Thalassinoides are abundant in many places. Other clues to marginal marine deposition are the occurrence of glauconite in one bed, typical relations of lagoonal to beach (locally heavy-mineral-rich) lithofacies, closed-basin three-dimensional morphology of basinal facies, and high

  9. Uncorking the bottle: What triggered the Paleocene/Eocene thermal maximum methane release?

    NASA Astrophysics Data System (ADS)

    Katz, Miriam E.; Cramer, Benjamin S.; Mountain, Gregory S.; Katz, Samuel; Miller, Kenneth G.

    2001-12-01

    The Paleocene/Eocene thermal maximum (PETM) was a time of rapid global warming in both marine and continental realms that has been attributed to a massive methane (CH4) release from marine gas hydrate reservoirs. Previously proposed mechanisms for this methane release rely on a change in deepwater source region(s) to increase water temperatures rapidly enough to trigger the massive thermal dissociation of gas hydrate reservoirs beneath the seafloor. To establish constraints on thermal dissociation, we model heat flow through the sediment column and show the effect of the temperature change on the gas hydrate stability zone through time. In addition, we provide seismic evidence tied to borehole data for methane release along portions of the U.S. continental slope; the release sites are proximal to a buried Mesozoic reef front. Our model results, release site locations, published isotopic records, and ocean circulation models neither confirm nor refute thermal dissociation as the trigger for the PETM methane release. In the absence of definitive evidence to confirm thermal dissociation, we investigate an alternative hypothesis in which continental slope failure resulted in a catastrophic methane release. Seismic and isotopic evidence indicates that Antarctic source deepwater circulation and seafloor erosion caused slope retreat along the western margins of the North Atlantic in the late Paleocene. Continued erosion or seismic activity along the oversteepened continental margin may have allowed methane to escape from gas reservoirs trapped between the frozen hydrate-bearing sediments and the underlying buried Mesozoic reef front, precipitating the Paleocene/Eocene boundary methane release. An important implication of this scenario is that the methane release caused (rather than resulted from) the transient temperature increase of the PETM. Neither thermal dissociation nor mechanical disruption of sediments can be identified unequivocally as the triggering mechanism

  10. Stable isotope and calcareous nannofossil assemblage record of the late Paleocene and early Eocene (Cicogna section)

    NASA Astrophysics Data System (ADS)

    Agnini, Claudia; Spofforth, David J. A.; Dickens, Gerald R.; Rio, Domenico; Pälike, Heiko; Backman, Jan; Muttoni, Giovanni; Dallanave, Edoardo

    2016-04-01

    We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81 m thick section of upper Paleocene-lower Eocene marine sedimentary rocks now exposed along the Cicogna Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multi-million-year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate δ13C profile for the Cicogna section, once placed on a common timescale, resembles that at several other locations across the world, and includes both a long-term drop in δ13C and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated δ13C records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the δ13C record at Cicogna, an interpretation supported by variations in bulk carbonate δ18O, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major differences before, during and after the Paleocene-Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially affected nannoliths or holococcoliths such as Discoaster, Fasciculithus, Rhomboaster/Tribrachiatus, Sphenolithus and Zygrhablithus, which underwent distinct variations in

  11. Sequence stratigraphic analysis of Eocene Rock Strata, Offshore Indus, southwest Pakistan

    NASA Astrophysics Data System (ADS)

    Khan, Natasha; Rehman, Khaista; Ahmad, Sajjad; Khokher, Jamil; Hajana, M. Iqbal; Hanif, M.

    2016-09-01

    In this study, seismic data from two wells (Pak G2-1 and Indus Marine-1C) and age diagnostic larger benthic foraminifera (LBF) within drill cuttings has been used for the first time to identify depositional sequences within the carbonates in the Offshore Indus Basin, Pakistan. The Offshore Indus is tectonically categorized as a passive continental margin where carbonates occur as shelf carbonates in the near offshore and on volcanic seamounts in deeper waters. Seismic data analysis has indicated the presence of minor faults and carbonate buildups above the igneous basement in the south. Patterns of the seismic reflections enabled definition of three seismic facies units identified as: Unit 1 basement, represented by chaotic, moderate amplitude reflection configuration; while parallel bedding and the drape of overlying strata is typical character of Unit 2, carbonate mound facies. The younger Miocene channels represent Unit 3. The diagnosis of Alveolina vredenburgi/cucumiformis biozone confirmed the Ilerdian (55-52 Ma) stage constituting a second order cycle of deposition for the Eocene carbonates (identified as Unit 2). The carbonate succession has been mainly attributed to an early highstand system tract (HST). The environmental conditions remained favorable leading to the development of keep-up carbonates similar to pinnacle buildups as a result of aggradation during late transgressive system tract and an early HST. The carbonate sequence in the south (Pak G2-1) is thicker and fossiliferous representing inner to middle shelf depths based on fauna compared to the Indus Marine-1C in the north, which is devoid of fossils. Three biozones (SBZ 5, SBZ 6 and SBZ 8) were identified based on the occurrence of LBF. The base of the SBZ 5 zone marks the larger foraminifera turnover and the Paleocene-Eocene (P-E) boundary. The LBF encountered in this study coincides with earlier findings for the P-E boundary. Our findings indicate that the entire Ilerdian stage ranges from 55

  12. High resolution taxonomic study of the late Eocene (~34 Ma) Florissant palynoflora, Colorado, USA

    NASA Astrophysics Data System (ADS)

    Bouchal, J. M.

    2012-04-01

    The Florissant Fossil Beds National Monument is located in Teller County in central Colorado, at approximate latitude 38°54'N and longitude 105°13'. The lithologies of the Florissant Formation consist of coarse-grained arkosic and volcanoclastic sandstones and conglomerates, finer shale, and tuffaceus mudstone and siltstone. It is divided into six units, mostly of lacustrine and fluvial origin with volcanic sediments interfingering and topping the strata. Volcanic units have been dated using the 40Ar/39Ar single-crystal method, giving an absolute age of ca. 34 Ma for the upper fossiliferous sedimentary unit. This pinpoints the formation of the Florissant sediments at the end of the Eocene, providing fruitful insight into the changing palaeoecosystem of the region at the dawn of the Oligocene. The formation is very well known for its rich fossil insect fauna and well preserved plant macrofossils found in the shale units, and the silicified tree stumps occurring in the lower mudstone unit. The sample used for this study originates from the upper shale unit, the fifth unit from the base of the formation. Previous studies on the plant macrofossils, mesofossils and the palynoflora have shown that during the late Eocene the surroundings of Florissant palaeo-lake were covered by diverse mixed broad-leaved evergreen/deciduous and needle-leafed forests. Until now pollen from the Florissant Formation has mostly been described according to conventional morphological nomenclature, using light microscopy (LM) only. In this study the same individual pollen grains are investigated using both LM and scanning electron microscopy (SEM), by means of single grain technique. This provides best exploitable results concerning a more detailed resolution regarding taxonomy and more accurate identifications. The main goal of this study is to compile a well resolved taxonomic species list based on the palynoflora, to clarify the generic and species diversity of selected families (e

  13. Discovery of coesite and shocked quartz associated with the upper Eocene cpx spherule layer

    NASA Technical Reports Server (NTRS)

    Liu, S.; Kyte, T.; Glass, B. P.

    2002-01-01

    At least two major impact ejecta layers have been discovered in upper Eocene strata. The upper layer is the North American microtektite layer. lt consists tektite fragments, microtektites, and shocked mineral grains (e.g., quartz and feldspar with multiple sets of PDFs, coesite and reidite (a high-pressure polymorph of zircon)). The slightly older layer contains clinopyroxene-bearing (cpx) spherules and microtektites associated with an Ir anomaly. The North American tektite layer may be derived from the Chesapeake Bay impact structure, and the cpx spherule layer may from the Popigai impact crater. A cpx spherule layer associated with a positive Ir anomaly was recently found at ODP Site 709, western Indian Ocean. A large sample (Hole 709C, core 31, section 4, 145-150 cm), originally used for a study of interstitial water by shipboard scientists, was acquired for the purpose of recovering a large number of spherules for various petrographic and geochemical studies. A split of the sample (50.35 g) was disaggregated and wet-sieved. More than 17,000 cpx spherules and several hundred microtektites (larger than 125 microns) were recovered from the sample. Rare white opaque grains were observed in the 125-250 micron size fraction after removal of the carbonate component using dilute HCI. Seven of the white opaque grains were X-rayed using a Gandolfi camera and six were found to be coesite (probably mixed with lechatelierite). Eighty translucent colorless grains from the 63-125 micron size fraction were studied with a petrographic microscope. Four of the grains exhibit one to two sets of planar deformation features (PDFs). The only other possible known occurrence of shocked minerals associated with the cpx spherule layer is at Massignano, Italy, where pancake-shaped clay spherules (thought to be diagenetically altered cpx spherules are associated with a positive Ir anomaly and Ni- rich spinel crystals. Shocked quartz grains with multiple sets of PDFs also occur at this site

  14. Highly fractionated Late Eocene (~ 35 Ma) leucogranite in the Xiaru Dome, Tethyan Himalaya, South Tibet

    NASA Astrophysics Data System (ADS)

    Liu, Zhi-Chao; Wu, Fu-Yuan; Ding, Lin; Liu, Xiao-Chi; Wang, Jian-Gang; Ji, Wei-Qiang

    2016-01-01

    The Xiaru dome is located in the middle section of the North Himalayan Gneiss Domes belt in southern Tibet. The leucogranite, which crops out in the core of the Xiaru dome, is a typical medium-grained garnet + tourmaline + muscovite leucogranite. U-(Th)-Pb dating of zircon and monazite from the leucogranite yielded ages of approximately 35 Ma. This finding supports a growing body of evidence indicating that an extensive magmatic event occurred during the late Eocene in the Himalayas. This leucogranite is strongly peraluminous with A/CNK values of 1.08-1.52 and characterized by evolved geochemical composition with high contents of SiO2 and alkali elements; low levels of CaO, MgO, TiO2, and FeOT; enriched large-ion lithophile elements (such as Rb); and depleted of high-field-strength elements (such as Nb, Zr, and Hf). The non-CHARAC (CHarge-And-Radius-Controlled) trace element behaviors, which are typical of a highly fractionated granite system, were recorded in the whole rock and the accessory minerals of the Xiaru leucogranite. Furthermore, the magmatic zircon overgrowths have extremely high content of Hf, consistent with those from the highly fractionated aqueous-like fluid system. In addition, whole-rock geochemical fractionation trends were observed, which can be explained by crystal fractionation of biotite, K-feldspar, zircon, xenotime, and monazite. These geochemical features indicate that the Xiaru leucogranite is a typical highly fractionated granite. The geochronological and geochemical features of the inherited zircons from the Xiaru leucogranite show a close affinity to those of the country rocks, suggesting a certain degree of assimilation from the country rocks during melt ascent and emplacement. Although a restricted range of εHf(t) values from - 12.8 to - 6.6 with Hf TDM2 model ages of 1.2-1.6 Ga was obtained from the late Eocene zircons, it is invalid to constrain the source of the parental magma due to the strong fractionation and assimilation

  15. Chicxulub Impact, Yucatan Carbonate Platform, Cretaceous-Paleogene Boundary and Paleocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Fucugauchi, J. U.; Perez-Cruz, L. L.

    2015-12-01

    Chicxulub formed 66 Ma ago by an asteroid impact on the Yucatan carbonate platform, southern Gulf of Mexico. Impact produced a 200 km diameter crater, platform fracturing, deformation and ejecta emplacement. Carbonate sedimentation restarted and crater was covered by up to 1 km of sediments. Drilling programs have sampled the Paleogene sediments, which record the changing sedimentation processes in the impact basin and platform. Here, results of a study of the Paleocene-Eocene sediments cored in the Santa Elena borehole are used to characterize the K/Pg and PETM. The borehole reached a depth of 504 m and was continuously cored, sampling the post-impact sediments and impact breccias, with contact at 332 m. For this study, we analyzed the section from ~230 to ~340 m, corresponding to the upper breccias and Paleocene-Eocene sediments. The lithological column, constructed from macroscopic and thin-section petrographic analyses, is composed of limestones and dolomitized limestones with several thin clay layers. Breccias are melt and basement clast rich, described as a suevitic unit. Section is further investigated using paleomagnetic, rock magnetic, X-ray fluorescence geochemical and stable isotope analyses. Magnetic polarities define a sequence of reverse to normal, which correlate to the geomagnetic polarity time scale from chrons 29r to 26r. The d13 C values in the first 20 m interval range from 1.2 to 3.5 %0 and d18 O values range from -1.4 to -4.8 %0. Isotope values show variation trends that correlate with the marine carbon and oxygen isotope patterns for the K-Pg boundary and early Paleocene. Positive carbon isotopes suggest relatively high productivity, with apparent recovery following the K-Pg extinction event. Geochemical data define characteristic trends, with Si decreasing gradually from high values in the suevites, low contents in Paleocene sediments with intervals of higher variability and then increased values likely marking the PETM. Variation trends are

  16. Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the Southwest Pacific

    NASA Astrophysics Data System (ADS)

    Pascher, K. M.; Hollis, C. J.; Bohaty, S. M.; Cortese, G.; McKay, R. M.

    2015-07-01

    The Eocene was characterised by "greenhouse" climate conditions that were gradually terminated by a long-term cooling trend through the middle and late Eocene. This long-term trend was determined by several large-scale climate perturbations that culminated in a shift to "ice-house" climates at the Eocene-Oligocene Transition. Geochemical and micropaleontological proxies suggest that tropical-to-subtropical sea-surface temperatures persisted into the late Eocene in the high-latitude Southwest Pacific Ocean. Here, we present radiolarian microfossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) Sites 277, 280, 281 and 283 from the middle Eocene to early Oligocene (~ 40-33 Ma) to identify oceanographic changes in the Southwest Pacific across this major transition in Earth's climate history. The Middle Eocene Climatic Optimum at ~ 40 Ma is characterised by a negative shift in foraminiferal oxygen isotope values and a radiolarian assemblage consisting of about 5 % of low latitude taxa Amphicraspedum prolixum group and Amphymenium murrayanum. In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift can be correlated to the Priabonian Oxygen Isotope Maximum (PrOM) event - a short-lived cooling event recognized throughout the Southern Ocean. Radiolarian abundance, diversity, and preservation increase during the middle of this event at Site 277 at the same time as diatoms. The PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. These high-latitude taxa also increase in abundance during the late Eocene and early Oligocene at DSDP Sites 280, 281 and 283 and are associated with very high diatom abundance. We therefore infer a~northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau towards the end of the late Eocene. In the early Oligocene (~ 33 Ma) there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms

  17. Seymour Island/Marambio Drilling Project: Drilling 40Ma (Campanian to Eocene) of high latitude Southern Hemisphere climate history.

    NASA Astrophysics Data System (ADS)

    Viereck-Gotte, Lothar; Francis, Jane E.; Vaughan, Alan P. M.; Mohr, Barbara A. R.; Marenssi, Sergio A.; Pekar, Stephen F.

    2010-05-01

    The aim of this project is to core a key geological section in the Antarctic Peninsula region. The James Ross Basin, east of the Antarctic Peninsula, contains the best high-latitude section in the world that spans more than 40 million years of geological history from the mid-Cretaceous to the mid-Cenozoic (~80-34Ma). More than 6500m of marine and estuarine sediments were deposited during the filling of the James Ross back-arc basin. The sedimentary succession is extremely fossiliferous, yielding diverse invertebrate, vertebrate and plant fossil assemblages, allowing detailed reconstructions and integration of both terrestrial and marine systems. The sequence also contains a key global reference section for the Cretaceous-Palaeocene extinction event at high latitudes. The sequence contains key intervals that provide details about past polar climates: Mid-Late Cretaceous Thermal Maximum (~80Ma) when tropical floras grew at ~65°S and greenhouse temperatures reached their peak across the globe; a possible phase of high-latitude glaciation within greenhouse times during the latest Cretaceous; the Cretaceous-Palaeocene extinction event at 65Ma; the Palaeocene-Eocene Thermal Maximum episode of rapid global warming at 55Ma (possibly an unconformity in Seymour Island but this can be better established in a drill core); early Eocene hothouse climates; a cooling phase during the Eocene, and the first signs of global cooling in the latest Eocene. Although the sedimentary sequence is reasonably well known from surface outcrop and a stratigraphy has been established, the unconsolidated and weathered nature of the outcrop prohibits high resolution studies. Drill cores will provide more consolidated sediments that can be logged and sampled at high resolution and provide an extremely detailed picture of environmental and climate evolution through this transition from greenhouse to icehouse climates. Three drill cores are planned in this time interval using a land-based rig with

  18. The Tectonic Event of the Cenozoic in the Tasman Area, Western Pacific, and Its Role in Eocene Global Change

    NASA Astrophysics Data System (ADS)

    Collot, J.; Sutherland, R.; Rouillard, P.; Patriat, M.; Roest, W. R.; Bache, F.

    2014-12-01

    The geometry and age progression of Emperor and Hawaii seamounts provide compelling evidence for a major change in Pacific plate motion over a short period of geological time at c. 50 Ma. This time approximately coincides with significant changes in plate boundary configuration and rate in the Indian Ocean, Antarctica, and with the onset of subduction zones in the western Pacific from Japan to New Zealand. This new subduction system that initiated during Eocene time can be divided into two sectors: The northern sector formed at the eastern boundary of the Philippine Sea plate and evolved into the Izu-Bonin-Mariana system. It has and is being extensively studied (2014 IODP expedition 351) to determine the magmatic products, but is limited in the record that is preserved because it is entirely intra-oceanic in character. The southern sector, the Tasman Area sector, borders continental fragments of Gondwana from Papua New Guinea, New Caledonia and New Zealand. This subduction zone evolved into the Tonga-Kemadec system. Because most of the southwest Pacific remained in marine conditions throughout Paleogene time and because rapid seawards roll-back of the subduction is inferred to have happened, it presents extensive well-preserved stratigraphic records to study the Eocene-Oligocene plate boundary evolution. The recent compilation of c. 100.000 km of 2D seismic data in the Tasman Frontier database has allowed us to describe, in the overriding plate of the proto subduction, stratigraphic evidence for large Cenozoic vertical movements (2-4 km) over a lateral extension of 2000 km (from New Caledonia to New Zealand), long-wavelength (~500 km) warping and large amounts of reverse faulting and folding near the proto-trench. These recent observations from the Lord Howe Rise, New Caledonia Trough and South Norfolk Ridge system reveal clear evidence for convergent deformation (uplift and erosion) and subsequent subsidence recorded in Eocene and Oligocene stratal relationships

  19. Paleoclimatological analysis of Late Eocene core, Manning Formation, Brazos County, Texas

    SciTech Connect

    Yancey, T.; Elsik, W.

    1994-09-01

    A core of the basal part of the Manning Formation was drilled to provide a baseline for paleoclimate analysis of the expanded section of siliciclastic sediments of late Eocene age in the outcrop belt. The interdeltaic Jackson Stage deposits of this area include 20+ cyclic units containing both lignite and shallow marine sediments. Depositional environments can be determined with precision and the repetitive nature of cycles allows comparisons of the same environment throughout, effectively removing depositional environment as a variable in interpretation of climate signal. Underlying Yegua strata contain similar cycles, providing 35+ equivalent environmental transacts within a 6 m.y. time interval of Jackson and Yegua section, when additional cores are taken. The core is from a cycle deposited during maximum flooding of the Jackson Stage, with deposits ranging from shoreface (carbonaceous) to midshelf, beyond the range of storm sand deposition. Sediments are leached of carbonate, but contain foram test linings, agglutinated forams, fish debris, and rich assemblages of terrestrial and marine palynomorphs. All samples examined contain marine dinoflagellates, which are most abundant in transgressive and maximum flood zones, along with agglutinated forams and fish debris. This same interval contains two separate pulses of reworked palynomorphs. The transgressive interval contains Glaphyrocysta intricata, normally present in Yegua sediments. Pollen indicates fluctuating subtropical to tropical paleoclimates, with three short cycles of cooler temperatures, indicated by abundance peaks of alder pollen (Alnus) in transgressive, maximum flood, and highstand deposits.

  20. A remarkable cranium of Plesiopithecus teras (Primates, Prosimii) from the Eocene of Egypt.

    PubMed Central

    Simons, E L; Rasmussen, D T

    1994-01-01

    Between 1991 and 1993 specimens of a highly distinctive primate, named Plesiopithecus teras [Simons, E.L. (1992) Proc. Natl. Acad. Sci. USA 89, 10743-10747], were found at site L-41 in late Eocene deposits of the Fayum Depression, Egypt. The most important of these specimens consists of a nearly complete skull, which facilitates the evaluation of affinities of this primate. Characteristics of the known material now demonstrate that Plesiopithecus is a prosimian, although mandibular molar morphology, in particular, bears similarity to that in molars of archaic members of Anthropoidea. Plesiopithecus has a postorbital bar but lacks postorbital closure, it has upper molars without hypocones, and it may retain four lower premolars. Its familial rank was considered incertae sedis by Simons [Simons, E.L. (1992) Proc. Natl. Acad. Sci. USA 89, 10743-10747]; it can now be demonstrated that Plesiopithecus justifies establishment of a new family and superfamily. The new superfamily apparently lies closer to the toothcomb prosimians (strepsirhines) than to any other known primate group. Under this interpretation the enlarged, procumbent tooth in the jaw of Plesiopithecus is homologous to either the lateral incisor or the canine of the prosimian toothcomb. Images PMID:7937923

  1. Warm tropical sea surface temperatures in the Late Cretaceous and Eocene epochs.

    PubMed

    Pearson, P N; Ditchfield, P W; Singano, J; Harcourt-Brown, K G; Nicholas, C J; Olsson, R K; Shackleton, N J; Hall, M A

    2001-10-01

    Climate models with increased levels of carbon dioxide predict that global warming causes heating in the tropics, but investigations of ancient climates based on palaeodata have generally indicated cool tropical temperatures during supposed greenhouse episodes. For example, in the Late Cretaceous and Eocene epochs there is abundant geological evidence for warm, mostly ice-free poles, but tropical sea surface temperatures are generally estimated to be only 15-23 degrees C, based on oxygen isotope palaeothermometry of surface-dwelling planktonic foraminifer shells. Here we question the validity of most such data on the grounds of poor preservation and diagenetic alteration. We present new data from exceptionally well preserved foraminifer shells extracted from impermeable clay-rich sediments, which indicate that for the intervals studied, tropical sea surface temperatures were at least 28-32 degrees C. These warm temperatures are more in line with our understanding of the geographical distributions of temperature-sensitive fossil organisms and the results of climate models with increased CO2 levels.

  2. Uniquely derived upper molar morphology of Eocene Amphipithecidae (Primates: Anthropoidea): homology and phylogeny.

    PubMed

    Coster, Pauline; Beard, K Christopher; Soe, Aung Naing; Sein, Chit; Chaimanee, Yaowalak; Lazzari, Vincent; Valentin, Xavier; Jaeger, Jean-Jacques

    2013-08-01

    The extinct Southeast Asian primate family Amphipithecidae is regularly cited in discussions of anthropoid origins, but its phylogenetic position remains controversial. In part, the lack of consensus regarding amphipithecid relationships can be attributed to uncertainty regarding the homology of upper molar structures in this group. Here, we describe a virtually pristine upper molar of Pondaungia cotteri from the late middle Eocene Pondaung Formation of Myanmar, which is the first example of a relatively unworn and well-preserved amphipithecid upper molar ever recovered. The distolingual upper molar cusp in this new specimen of Pondaungia appears to be a lingually displaced and enlarged metaconule, rather than a hypocone or pseudohypocone as previous workers have thought. Reassessment of the upper molar morphology of other amphipithecids and putative amphipithecids reveals a very similar pattern in Siamopithecus, Myanmarpithecus and Ganlea, all of which are interpreted as having upper molars showing many of the same derived features apparent in Pondaungia. In contrast, the upper molar morphology of Bugtipithecus diverges radically from that of undoubted amphipithecids, and the latter taxon is excluded from Amphipithecidae on this basis. Phylogenetic analyses of several character-taxon matrices culled from the recent literature and updated to reflect the new information on amphipithecid upper molar morphology yield similar results. Consensus tree topologies derived from these analyses support amphipithecid monophyly and stable relationships within Amphipithecidae. Amphipithecids appear to be stem members of the anthropoid clade.

  3. A new primate from the Eocene Pondaung Formation of Myanmar and the monophyly of Burmese amphipithecids.

    PubMed

    Beard, K Christopher; Marivaux, Laurent; Chaimanee, Yaowalak; Jaeger, Jean-Jacques; Marandat, Bernard; Tafforeau, Paul; Soe, Aung Naing; Tun, Soe Thura; Kyaw, Aung Aung

    2009-09-22

    The family Amphipithecidae is one of the two fossil primate taxa from Asia that appear to be early members of the anthropoid clade. Ganlea megacanina, gen. et sp. nov., is a new amphipithecid from the late middle Eocene Pondaung Formation of central Myanmar. The holotype of Ganlea is distinctive in having a relatively enormous lower canine showing heavy apical wear, indicating an important functional role of the lower canine in food preparation and ingestion. A phylogenetic analysis of amphipithecid relationships suggests that Ganlea is the sister taxon of Myanmarpithecus, a relatively small-bodied taxon that has often, but not always, been included in Amphipithecidae. Pondaungia is the sister taxon of the Ganlea + Myanmarpithecus clade. All three Pondaung amphipithecid genera are monophyletic with respect to Siamopithecus, which is the most basal amphipithecid currently known. The inclusion of Myanmarpithecus in Amphipithecidae diminishes the likelihood that amphipithecids are specially related to adapiform primates. Extremely heavy apical wear has been documented on the lower canines of all three genera of Burmese amphipithecids. This distinctive wear pattern suggests that Burmese amphipithecids were an endemic radiation of hard object feeders that may have been ecological analogues of living New World pitheciin monkeys.

  4. Taxonomic status of purported primate frontal bones from the Eocene Pondaung Formation of Myanmar.

    PubMed

    Beard, K Christopher; Jaeger, Jean-Jacques; Chaimanee, Yaowalak; Rossie, James B; Soe, Aung Naing; Tun, Soe Thura; Marivaux, Laurent; Marandat, Bernard

    2005-10-01

    Two isolated cranial fragments from the late middle Eocene Pondaung Formation of central Myanmar have previously been interpreted as frontal bones of the amphipithecid primate Amphipithecus mogaungensis. Aside from a few maxillary fragments, these specimens provide the only potential source of information currently available regarding the cranial anatomy of Amphipithecidae. Were this taxonomic attribution correct, these specimens would indicate that amphipithecids retained numerous primitive skull features, including the absence of a postorbital septum, the retention of a voluminous olfactory chamber, and strong separation between the forebrain and the orbital fossa. However, several anatomical details observable on these specimens are incompatible with their attribution to any primate and strongly suggest that they cannot be ascribed to Mammalia. Particularly problematic in this regard are the extreme thickness of the dermal bone, the odd structure of the alleged "frontal trigon," and the mediolateral orientation and uniquely robust construction of the descending process of the frontal bone (which partially segregates the orbital and temporal fossae). Because these isolated elements can no longer be attributed to Amphipithecus, the anatomical, phylogenetic, and behavioral inferences regarding amphipithecid paleobiology that have been drawn from these specimens can no longer be sustained.

  5. Evolution and extinction of Afro-Arabian primates near the Eocene-Oligocene boundary.

    PubMed

    Seiffert, Erik R

    2007-01-01

    Revised age estimates for the primate-bearing localities of the Jebel Qatrani Formation (Fayum area, northern Egypt) have provided a new perspective on primate response to early Oligocene climate change in North Africa. Environmental changes associated with early Oligocene cooling might have driven the local extinction of at least 4 strepsirrhine primate clades (adapids, djebelemurines, plesiopithecids and galagids). Contrary to previous suggestions, oligopithecid (and possibly proteopithecid) anthropoids persisted beyond the Eocene-Oligocene boundary (EOB) in the Fayum area, and the former group evidently continued to diversify through the early Oligocene at lower latitudes. Propliopithecids and parapithecine parapithecids first appear in the Jebel Qatrani Formation millions of years after the EOB, so their derived dental and gnathic features can no longer be interpreted as sudden adaptive morphological responses to earliest Oligocene climatic events. Evidence for latitudinal contraction of Afro-Arabian primate distribution through the early Oligocene suggests that the profound late Oligocene restructuring of Afro-Arabian primate communities is most likely to have occurred in equatorial and low-latitude tropical Africa.

  6. Banda-Celebes-Sulu basin - a trapped Cretaceous-Eocene oceanic crust

    SciTech Connect

    Lee, C.S.; McCabe, R.

    1985-01-01

    The Banda, Celebes and Sulu Basins are three poorly understood marginal seas that are located at the junction of the Eurasian, Indian-Australian, Pacific and Philippine Sea plates. The incomplete data sets from each of these three marginal basins, the complex geological arrangement of the surrounding islands, and the compound late Cenozoic evolutions involving subduction, rifting, transform faulting and island arc collision have complicated any tectonic interpretations of this region. On the bases of marine geophysical data and on-land geology, the authors propose that the Banda, Celebes and Sulu Basins are the remanents of a once-continuous Cretaceous to Eocene ocean basin. Magnetic anomalies from the Banda, Celebes and Sulu Basins show the similar trends of about N70/sup 0/E, N60/sup 0/E and N55/sup 0/E respectively. Their best fit to the reversal models are as follows: (1) anomalies M1-M11 in the Banda Basin, (2) anomalies 30-33 in the Celebes Basin and (3) anomalies 17-20 in the Sulu Basin. The heat flow data from each of these basins is consistent with the relationship of our assigned magnetic ages. The on-land geology of this region is complicated by numerous land masses which dissect this old oceanic basin into the present configuration of marginal seas. The authors argue that each of these land masses arrived at its present location by either late Tertiary tectonic movements or has been built in place upon this older oceanic basement.

  7. Model simulations of early westward flow across the Tasman Gateway during the early Eocene

    NASA Astrophysics Data System (ADS)

    Sijp, Willem P.; von der Heydt, Anna S.; Bijl, Peter K.

    2016-04-01

    The timing and role in ocean circulation and climate of the opening of Southern Ocean gateways is as yet elusive. Recent micropalaeontological studies suggest the onset of westward throughflow of surface waters from the SW Pacific into the Australo-Antarctic Gulf through a southern shallow opening of the Tasman Gateway from 49-50 Ma onwards, a direction that is counter to the present-day eastward-flowing Antarctic Circumpolar Current. Here, we present the first model results specific to the early-to-middle Eocene where, in agreement with the field evidence, southerly shallow opening of the Tasman Gateway indeed causes a westward flow across the Tasman Gateway. As a result, modelled estimates of dinoflagellate biogeography are in agreement with the recent findings. Crucially, in this situation where Australia is still situated far south and almost attached to Antarctica, the Drake Passage must be sufficiently restricted to allow the prevailing easterly wind pattern to set up this southerly restricted westward flow. In contrast, an open Drake Passage, up to 517 m deep, leads to an eastward flow, even when the Tasman Gateway and the Australo-Antarctic gulf are entirely contained within the latitudes of easterly wind.

  8. Evolution of reef and atoll margin carbonates, upper Eocene through lower Miocene, Enewetak, Marshall Islands

    SciTech Connect

    Saller, A.H.; Schlanger, S.O.

    1988-01-01

    Two wells drilled along the margin of Enewetak Atoll penetrated approximately 1,000 m of upper eocene, Oligocene, and lower Miocene carbonates. STrontium isotope stratigraphy indicates relatively continuous deposition of carbonate from 40 Ma to 20 Ma. Depositional environments show a gradual basinward progradation of facies with slope carbonates passing upward into fore-reef, reef, back-reef, and lagoonal carbonates. Slope strata contain wackestones and packstones with submarine-cemented lithoclasts, coral, coralline algae fragments, benthic rotaline forams, planktonic forams, and echinoderm fragments. Fore-reef strata are dominantly packstones and boundstones containing large pieces of coral, abundant benthic forams, coralline algae fragments, stromatoporoids(.), and minor planktonic forams. Reef and near-reef sediments include coralgal boundstones and grainstones with abundant benthic forams. Halimeda and miliolid forams are common in lagoonward parts of the back reef. Sponge borings, geopetal structures, and fractures are common in reef and fore-reef strata. Lagoonal strata are wackestones and packstones with common mollusks, coral, coralline algae, and benthic forams (rotaline and miliolid). Diagenesis has extensively altered strata near the atoll margin. Aragonite dissolution and calcite cements (radiaxial and cloudy prismatic are abundant in fore-reef, reef, and some back-reef strata). Petrographic and geochemical data indicate arogonite dissolution and calcite cementation in seawater at burial depths of 100 to 300 m. Dolomite occurs in slope and deeply buried reefal carbonates.

  9. Migratory and braided channels in Eocene submarine fan deposits in the French maritime Alps

    SciTech Connect

    Bouma, A.H.

    1988-08-01

    Large- and small-scale (10-0.5 m) foresets in submarine fan sandstones, with internal bedding or lamination dipping roughly perpendicular to the paleocurrent direction, were observed in Eocene deposits in the Peira-Cava area, French Maritime Alps. The large-scale foresets require that major outcrops be observable. These features can be understood if compared with fluvial point bars. The smaller features can be interpreted in many ways, ranging from small, laterally accreting point bars of small channels in a broader channel complex to festoon-bedded bedforms in braided channels. Large scallops, about 0.5-1 km wide and 30-60 m deep, eroded in underlying shales and filled with nearly horizontal bedding, are present in the Annot and Peira-Cava areas. These erosional scours occur in downdip as well as lateral directions. All of these phenomena can be related to the accretionary channelized part of a submarine fan where large, high-energy sediment flows can result in major downcutting of the channels. The deposits represent all scales of channels from small to large and channel complexes with both meandering and braided characteristics. Recognition of such complexities helps them understand the difficulties in well-log correlations and variations in the depth of the oil-water contact in deep-sea fan reservoirs.

  10. The Paleocene - Eocene Thermal Maximum: Temperature and Ecology in the Tropics

    NASA Astrophysics Data System (ADS)

    Frieling, J.; Gebhardt, H.; Adekeye, O. A.; Akande, S. O.; Reichart, G. J.; Middelburg, J. J. B. M.; Schouten, S.; Huber, M.; Sluijs, A.

    2014-12-01

    Various records across the Paleocene - Eocene Thermal Maximum (PETM) have established approximately 5 °C of additional surface and deep ocean warming, superimposed on the already warm latest Paleocene. The PETM is further characterized by a global negative stable carbon isotope excursion (CIE), poleward migration of thermophilic biota, ocean acidification, increased weathering, photic zone euxinia and intensified hydrological cycle. Reconstructed temperatures for the PETM in mid and high-latitudes regularly exceed modern open marine tropical temperatures. Constraints on absolute tropical temperatures are, however, limited. We studied the PETM in a sediment section from the Nigerian sector of the Dahomey Basin, deposited on the shelf near the equator. We estimate sea surface temperatures by paired analyses of TEX86, and Mg/Ca and δ18O of foraminifera from the Shagamu Quarry. These show Palaeocene temperatures of ~33 °C and SSTs rose by 4 °C during the PETM based on TEX86. During the PETM, intermittent photic zone euxinia developed based on the presence of the biomarker isorenieratane. Interestingly, during peak warmth, dinoflagellate cyst abundances and diversity are remarkably low. From our new data and evidence from modern dinoflagellate experiments, we conclude that thermal stress was the main driver for this observation. We derive that endothermal and most ectothermal nektonic and planktonic marine eukaryotic organisms could not have lived in the surface waters in this part of the tropics during the PETM.

  11. Sedimentology and paleoecology of an Eocene Oligocene alluvial lacustrine arid system, Southern Mexico

    NASA Astrophysics Data System (ADS)

    Beraldi-Campesi, Hugo; Cevallos-Ferriz, Sergio R. S.; Centeno-García, Elena; Arenas-Abad, Concepción; Fernández, Luis Pedro

    2006-10-01

    A depositional model of the Eocene-Oligocene Coatzingo Formation in Tepexi de Rodríguez (Puebla, Mexico) is proposed, based on facies analysis of one of the best-preserved sections, the Axamilpa Section. The sedimentary evolution is interpreted as the retrogradation of an alluvial system, followed by the progressive expansion of an alkaline lake system, with deltaic, palustrine, and evaporitic environments. The analysis suggests a ch