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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. Compound paleovalley fills in the Lower Pennsylvanian New River Formation, West Virginia, USA

    NASA Astrophysics Data System (ADS)

    Korus, Jesse T.; Kvale, Erik P.; Eriksson, Kenneth A.; Joeckel, R. M.

    2008-07-01

    Ancient paleovalley fills are typically interpreted in the rock record using over-generalized models without carefully considering modern analogs, especially in light of recent discoveries. It is now known that many Quaternary paleovalleys are compound in origin, exhibit considerable stratigraphic complexity, contain multiple incisions, and can be orders of magnitude larger than their putative ancient counterparts. Compound paleovalley fills in the Lower Pennsylvanian New River Formation (NRF) are directly comparable to these Quaternary analogs, stimulating a paradigm shift in the interpretation of ancient paleovalleys. In the NRF, multiple laterally- and vertically-juxtaposed fill successions, separated by incision surfaces, record high-frequency fluvial responses to external controls within lower-order sequences. Lowstand incision and sediment bypass, as predicted in sequence stratigraphy, is largely discounted by the available evidence and the definition of regional sequence boundaries is not straightforward. The identification of genetic sequences may be the most effective approach to understanding the NRF and, by inference, many other ancient paleovalleys. Results from this study of the NRF promote a revised model for ancient paleovalleys that incorporates: 1) the pre-eminence of compound architecture, 2) periodic episodes of incision and subaerial exposure occurring in response to high-frequency changes in climate or relative sea level, 3) fluvial downcutting as the primary cause of paleovalley incision, although some sediments are still preserved in a net-erosional regime, and 4) composite, time-transgressive sequence boundaries that may be difficult or impossible to correlate regionally.

  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. Stratigraphy and Structure of Late Oligocene-Early Miocene Ignimbrite-filled Paleovalleys, Northern Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Rood, D. H.; Busby, C. J.; Wagner, D.

    2003-12-01

    Mapping of a Late Oligocene-Early Miocene (31-25 Ma) paleovalley system filled with ignimbrites erupted from calderas in present-day Nevada provides relationships necessary to deduce paleotopographic vs. structural controls on the paleogeography of the Sierra Nevada and its transition into the Basin and Range in Early Tertiary time. A paleovalley filled with five distinctive ignimbrites is well-exposed in the Diamond Mountains about 2 -3 km west of the Honey Lake fault zone, a segment of the northern Walker Lane fault zone. We map a N-S trending paleovalley approximately 7.2 km wide, using ignimbrite distributions and thicknesses of ignimbrites and sedimentary rocks, as well as compaction foliation, cooling joints, welding zonation and lateral variations within each ignimbrite. Paleotopographic relief in the metamorphic and granitic basement reaches approximately 223 m; metamorphic roof pendants form steep-sided paleo-ridges and spires, while the granitic basement forms stepped relief controlled by pre-existing joints. The five ignimbrites are composed of at least nine mappable cooling units that vary laterally, from ca. 260 m thick paleovalley axis deposits to ca. 70 m thick paleovalley wall deposits, with dramatic thickening of vitrophyres toward paleovalley walls. The lowest three ignimbrites are confined to the paleovalley, the fourth passes upward from confined to unconfined, and the fifth is entirely unconfined. All of the ignimbrites are cut by two N-S trending, steeply W-dipping faults; the first, near the axis of the paleovalley, shows maximum 85 m of dip-slip displacement, and the second, near the eastern margin of the paleovalley, shows ca. 40 m of dip slip displacement. These N-S faults parallel the paleovalley and are oblique to the modern (NW-trending) Honey Lake fault zone, suggesting they may be older. Evidence for syndepositional faulting is present along the paleovalley axis fault, where sedimentary rocks between ignimbrites 3 and 4 thicken from

  6. 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

  7. Temporal stability of a coarse sediment community in the Central Eastern English Channel Paleovalleys

    NASA Astrophysics Data System (ADS)

    Lozach, Sophie; Dauvin, Jean-Claude

    2012-07-01

    The natural variation of the benthic community of eastern Channel paleovalleys was investigated over a four-year period in the context of an aggregate extraction licence for the French side of the English Channel. Six surveys were conducted: twice a year (mid-April: pre-recruitment and the end of August: post-recruitment) in 2007, 2009 and 2010. The area showed similar features of community structural parameters, to other coarse sediment areas in the eastern English Channel. This area also presented an outstanding constancy over time. The baseline obtained allows the identification of cause-effect relationships between the impact of aggregate dredging and environmental changes and also highlights the consequences of dredging on key ecological attributes. The long-term biological recovery rate will thereby be easier to assess. The use of this baseline is discussed in terms of implications for future management of the study area.

  8. Resolving environmental signatures from a paleovalley sedimentary sequence from arid northwest Australia

    NASA Astrophysics Data System (ADS)

    Rouillard, Alexandra; Skrzypek, Grzegorz; Dogramaci, Shawan; Grierson, Pauline

    2014-05-01

    Sediments from paleolakes can retain invaluable archives of past environmental conditions. However, deciphering a depositional signal from digenetic processes can be challenging in arid environments owing to extremely variable rainfall and saline groundwaters, which result in aggressive chemical conditions that often limit the preservation of traditionally used proxies. We investigated the development of hydroclimatic proxies based on sediment geochemistry from the Fortescue Marsh, in the arid Pilbara region of northwest Australia. The Marsh lies in a paleovalley that acts as a terminal basin for the upper part of the Fortescue River and consists of a ~1000 km2 contiguous floodplain with freshwater pools episodically inundated during intense rainfall events. The paleovalley is bound by mountain ranges that contain some of the most Fe-ore rich and ancient deposits on Earth, which we expected to confer unique geochemical characteristics to the sediments. We used a sonic rig to retrieve a 25 m core from one of the deepest sedimentary sections of the Fortescue Marsh (86 m to bedrock). We combined δ34S and δ18O stable isotopes analyses with scanning μXRF and reflectance spectroscopy to quantitatively map the elemental and mineralogical composition of the sedimentary sequence and to identify underlying mechanisms relating to paleoclimate. We found that Fe, Ca and Sr were the most abundant elements identified by μXRF. Typically, layers of up to 1 m that were almost exclusively Fe-dominated alternated with layers of 0.3-2.4 m thickness dominated by Ca and/or Sr, with at least five intervals with distinct peaks in Sr. As expected, the hyperspectral characterization confirmed that Fe oxides were most abundant during the Fe-rich intervals. While clay minerals including kaolinite and montmorillonite were also indicated from the spectral data, this assessment is contradicted by the low relative abundance of Al and Si. Peaks in Sr don't appear to reflect carbonates nor Sr

  9. 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.).

  10. 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.

  11. 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

  12. 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

  13. Silica burp in the Eocene ocean

    NASA Astrophysics Data System (ADS)

    McGowran, Brian

    1989-09-01

    The Eocene was a time of greatly increased silica accumulation in the ocean, and the peak was in the early middle Eocene at about 50 Ma. The responsible geohistorical configuration included the following elements: extensive volcanism about 4 m.y. earlier, as part of the Chron 24 plate reorganization; early Eocene warming, with deep weathering to high latitudes and accumulation of the released silica in a sluggish ocean; and sharp cooling in the earliest middle Eocene, stimulating oceanic upwelling and biosilicification. It is possible, on the evidence of carbon and oxygen isotopic patterns, that the trigger for the exhalation of silica was a reverse greenhouse effect.

  14. 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., Jr.; 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.

  15. 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.

  16. Eocene continental climates and latitudinal temperature gradients

    NASA Astrophysics Data System (ADS)

    Greenwood, David R.; Wing, Scott L.

    1995-11-01

    Global climate during the Mesozoic and early Cenozoic is thought to have been warmer than at present, but there is debate about winter temperatures. Paleontological data indicate mild temperatures even at high latitudes and in mid-latitude continental interiors, whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels. Foliar physiognomy and floristic composition of 23 Eocene floras from the interior of North America and Australia indicate cold month means generally >2 °C, even where the mean annual temperature (MAT) was <15 °C. Reconstructed Eocene latitudinal gradients of MAT are curvilinear but are about 0.4 °C per 1° of latitude in continental interiors at mid-latitudes, much less than the 0.8 1.0 °C per 1° of latitude observed in eastern and central North America today, but similar to modern gradients in the Southern Hemisphere mid-latitudes and on the west coast of North America. Latitudinal temperature gradients reconstructed here are broadly representative of Eocene climates, showing that the discrepancy between proxy data and simulations will not be resolved by regional adjustments to paleogeography or reinterpretation of individual fossil assemblages. Similar discrepancies between proxy data and general circulation model simulations for other time periods suggest that there is a basic flaw with the way climate models simulate heat transport to, or loss from, continental surfaces.

  17. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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. 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.

  20. Extreme Seasonality During Early Eocene Hyperthermals

    NASA Astrophysics Data System (ADS)

    Plink-Bjorklund, P.; Birgenheier, L.

    2012-12-01

    An outcrop multi-proxy dataset from the Uinta Basin, Utah, US indicates that extreme seasonality occurred repeatedly during the Early Eocene transient global warming events (hyperthermals), during the Palaeocene-Eocene Thermal Maximum (PETM) as well as during the six consequent younger hyperthermals. In this multi-proxy analysis we have investigated the precipitation distribution and peakedness changes during Early Eocene hyperthermals. This dataset is different from previously published terrestrial climate proxy analyses, in that we fully utilize the sedimentary record itself, and especially the hydrodynamic indicators within the river strata. We combine these high-resolution sedimentologic-stratigraphic analyses, with analyses of terrestrial burrowing traces, and the conventional palaeosol and stable carbon isotope analyses. With this approach, we are able to better document hydroclimatologic changes, and identify climate seasonality changes, rather than just long-term mean humidity/aridity and temperature trends. For this study we analyzed over 1000 m of Palaeocene and Early Eocene river and lake strata in the Uinta Basin, Utah, US (Figs. 1 and 2). The sedimentologic-stratigraphic analyses of outcrops included measuring detailed stratigraphic sections, analyzing photopanels, a spatial GPS survey, and lateral walk-out of stratigraphic packages across an area of 300 km2, with additional data across an area of ca 6000 km2 (Fig. 2). Continental burrowing traces and palaeosols were analyzed along the measured sections. For geochemical analysis 196 samples of mudrock facies were collected along the measured sections and analyzed for total organic carbon (Corg), total nitrogen (Ntot), and δ13C values of bulk organic matter. Biostratigraphy (25), radiometric dates, and carbon isotope stratigraphy, using bulk δ13C of organic matter in floodplain siltstones confirm the position of the PETM and the 6-8 post-PETM hyperthermals in the studied strata The seasonality

  1. 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.

  2. 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.

  3. Geodynamics of Sundaland since the Eocene

    NASA Astrophysics Data System (ADS)

    Yang, T.; Gurnis, M.

    2014-12-01

    Sundaland is the continental core of southeast Asia bounded by subduction zones since early Mesozoic. Many Sundaland basins, extensional in origin, have formed since Late Eocene. These rift basins experienced extensive inversion since early Miocene. The basins and the adjacent continental crust subsided with a regional sea level rise during a period of basin inversion and falling global sea level, suggesting control beyond eustasy and lithospheric deformation. The mechanism of this large-scale synchronous inversion and subsidence is not well understood. We use four dimensional dynamic models that explicitly assimilate the plate tectonic history and additional geological and geophysical data to investigate the underlying causes for the enigmatic evolution of Cenozoic Sundaland basins. The assimilation method honors both empirical data at the surface (including the seafloor age, plate motion velocity, subduction history) and mantle dynamics at depth and predicts mantle structure, surface topography and intraplate stress. These later expressions are compared against independent observations. With continuously closing plates, we embed deforming plates into the conventional rigid plate models in GPlates, thus enabling us to model continental deformation and mantle dynamics jointly. Models are initiated in the early Eocene with the temperature field derived from the backward integration of the present temperature field synthesized from seismic models. The velocity-temperature perturbation scaling ratio and depth and temperature dependent viscosity are derived by fitting the geoid. Our models are consistent with a slab avalanche occurring beneath Sundaland in the early Miocene. The slab avalanche induced large scale subsidence and compression across the southern Sundaland region, which correspond to the synchronous marine inundation and basin inversion since early to middle Miocene regionally. The model results suggest that the evolution of Sundaland basins is dominated

  4. 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.

  5. 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.

  6. Ectomycorrhizas from a Lower Eocene angiosperm forest.

    PubMed

    Beimforde, Christina; Schäfer, Nadine; Dörfelt, Heinrich; Nascimbene, Paul C; Singh, Hukam; Heinrichs, Jochen; Reitner, Joachim; Rana, Rajendra S; Schmidt, Alexander R

    2011-12-01

    The development of mycorrhizal associations is considered a key innovation that enabled vascular plants to extensively colonize terrestrial habitats. Here, we present the first known fossil ectomycorrhizas from an angiosperm forest. Our fossils are preserved in a 52 million-yr-old piece of amber from the Tadkeshwar Lignite Mine of Gujarat State, western India. The amber was produced by representatives of Dipterocarpaceae in an early tropical broadleaf forest. The ectomycorrhizas were investigated using light microscopy and field emission scanning electron microscopy. Dissolving the amber surrounding one of the fossils allowed ultrastructural analyses and Raman spectroscopy. Approx. 20 unramified, cruciform and monopodial-pinnate ectomycorrhizas are fossilized adjacent to rootlets, and different developmental stages of the fossil mycorrhizas are delicately preserved in the ancient resin. Compounds of melanins were detectable in the dark hyphae. The mycobiont, Eomelanomyces cenococcoides gen. et spec. nov., is considered to be an ascomycete; the host is most likely a dipterocarp representative. An early ectomycorrhizal association may have conferred an evolutionary advantage on dipterocarps. Our find indicates that ectomycorrhizas occurred contemporaneously within both gymnosperms (Pinaceae) and angiosperms (Dipterocarpaceae) by the Lower Eocene. PMID:22074339

  7. 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.

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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

  13. 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.

  14. Climate stability across the Eocene-Oligocene transition, southern Argentina

    NASA Astrophysics Data System (ADS)

    Kohn, Matthew J.; Josef, Jennifer A.; Madden, Richard; Kay, Richard; Vucetich, Guiomar; Carlini, Alfredo A.

    2004-07-01

    Fossil mammal teeth from mid-latitude southern Argentina (˜46°S) that closely bracket the Eocene-Oligocene transition show no resolvable change in oxygen isotope compositions. In combination with paleofloral observations and geographic considerations, this finding implies not only that climate was essentially constant, despite interpretations elsewhere for major mid- and high-latitude cooling, but also that evolution of hypsodonty did not coincide with climate change during the Eocene-Oligocene transition. One possible explanation for Eocene-Oligocene transition climatic stability is that southern high-latitude cooling increased latitudinal temperature gradients and strengthened ocean circulation gyres, including the southward-flowing Brazil Current in the western South Atlantic. Regionally increased heat transport in the western Atlantic offset global cooling, producing a nearly constant temperature in southern South America. A more radical interpretation, supported by some marine data, is that the paradigm of major global cooling at the Eocene-Oligocene transition is largely false, in that mean sea-surface temperatures changed very little.

  15. 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.

  16. 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

  17. Equatorial Pacific productivity changes near the Eocene-Oligocene boundary

    NASA Astrophysics Data System (ADS)

    Moore, T. C.; Wade, Bridget S.; Westerhold, Thomas; Erhardt, Andrea M.; Coxall, Helen K.; Baldauf, Jack; Wagner, Meghan

    2014-09-01

    There is general agreement that productivity in high latitudes increased in the late Eocene and remained high in the early Oligocene. Evidence for both increased and decreased productivity across the Eocene-Oligocene transition (EOT) in the tropics has been presented, usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the EOT itself. A complete record of the Eocene-Oligocene transition was obtained at three drill sites in the eastern equatorial Pacific Ocean (ODP Site 1218 and IODP Sites U1333 and U1334). Four paleoproductivity proxies that have been examined at these sites, together with carbon and oxygen isotope measurements on early Oligocene planktonic foraminifera, give evidence of ecologic and oceanographic change across this climatically important boundary. Export productivity dropped sharply in the basal Oligocene (~33.7 Ma) and only recovered several hundred thousand years later; however, overall paleoproductivity in the early Oligocene never reached the average levels found in the late Eocene and in more modern times. Changes in the isotopic gradients between deep- and shallow-living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early Oligocene that, on average, affected accumulation rates of barite, benthic foraminifera, and opal, as well as diatom abundance near 33.5 Ma. An interval with abundant large diatoms beginning at 33.3 Ma suggests an intermediate thermocline depth, which was followed by further shoaling, a dominance of smaller diatoms, and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera.

  18. Arctic Climate during Eocene Hyperthermals: Wet Summers on Ellesmere Island?

    NASA Astrophysics Data System (ADS)

    Greenwood, D. R.; West, C. K.; Basinger, J. F.

    2012-12-01

    Previous work has shown that during the late Paleocene to middle Eocene, mesothermal conditions (i.e., MAT ~12-15° C) and high precipitation (MAP > 150cm/yr) characterized Arctic climates - an Arctic rain forest. Recent analyses of Arctic Eocene wood stable isotope chemistry are consistent with the annual and seasonal temperature estimates from leaf physiognomy and nearest living relative analogy from fossil plants, including the lack of freezing winters, but is interpreted as showing that there was a summer peak in precipitation - modern analogs are best sought on the summer-wet east coasts (e.g., China, Japan, South Korea) not the winter-wet west coasts of present-day northern temperate continents (e.g., Pacific northwest of North America). Highly seasonal 'monsoon-type' summer-wet precipitation regimes (i.e., summer precip./winter precip. > 3.0) seem to characterize Eocene hyperthermal conditions in several regions of the earth, including the Arctic and Antarctic, based on both climate model sensitivity experiments and the paleoclimate proxy evidence. The leaf physiognomy proxy previously applied to estimate Arctic Paleogene precipitation was leaf area analysis (LAA), a correlation between mean leaf size in woody dicot vegetation and annual precipitation. New data from modern monsoonal sites, however demonstrates that for deciduous-dicot dominated vegetation, summer precipitation determines mean leaf size, not annual totals, and therefore that under markedly seasonal precipitation and/or light regimes that summer precipitation is being estimated using LAA. Presented here is a new analysis of a leaf macrofloras from 3 separate florules of the Margaret Formation (Split Lake, Stenkul Fiord and Strathcona Fiord) from Ellesmere Island that are placed stratigraphically as early Eocene, and likely fall within Eocene thermal maximum 1 (ETM1; = the 'PETM') or ETM2. These floras are each characterized by a mix of large-leafed and small-leafed dicot taxa, with overall

  19. 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. PMID:23720311

  20. 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.

  1. 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

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Marty, Richard; Dunbar, Robert; Martin, Jonathan B.; Baker, Paul

    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 CaCO3, have a diverse and abundant radiolarian fauna, and possess varved-massive and millimetre- and metre-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.

  5. 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.

  6. High plant diversity in Eocene South America: evidence from Patagonia.

    PubMed

    Wilf, Peter; Cúneo, N Rubén; Johnson, Kirk R; Hicks, Jason F; Wing, Scott L; Obradovich, John D

    2003-04-01

    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 approximately 47 degrees 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. PMID:12677065

  7. Transient Middle Eocene atmospheric CO₂ and temperature variations.

    PubMed

    Bijl, Peter K; Houben, Alexander J P; Schouten, Stefan; Bohaty, Steven M; Sluijs, Appy; Reichart, Gert-Jan; Sinninghe Damsté, Jaap S; Brinkhuis, Henk

    2010-11-01

    The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO(2)). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO(2) and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO(2) indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO(2) trends during the MECO suggests that elevated pCO(2) played a major role in global warming during the MECO. PMID:21051636

  8. 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).

  9. 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

  10. Paleomagnetism of Eocene volcanic rocks, Talkeetna Mountains, Alaska

    SciTech Connect

    Panuska, B.C. ); Stone, D.B.; Turner, D.L. )

    1990-05-10

    Previous paleomagnetic studies of Eocene rocks deposited in the Talkeetna Mountains on the northern edge of the combined Peninsular, Wrangellia, and Alexander terranes (the southern Alaska superterrane (SAS)) yield a paleolatitude of 76{degree}N, while Late Cretaceous rocks on the southern edge of the SAS record a 32{degree}N paleolatitude. At face value, these drastically different paleolatitudes imply that Wrangellia moved 44{degree} to the north in only 20 m.y., requiring a northward component of velocity of about 24 cm/yr. Alternatively, the discrepancy might be explained by postulating an unrecognized tectonic boundary separating the two localities, allowing different emplacement ages. The authors have tested the unrecognized tectonic boundary hypothesis by sampling Eocene volcanic rocks deposited near the southern edge of the SAS in the Talkeetna Mountains. The data set comprises measurements from 97 oriented cores collected from 26 lava flows and two tuffs distributed over a distance of 50 km. A primary remanence is indicated by positive fold tests and penecontemporaneous intrusion tests. Age control is provided by nine new K-Ar whole rock age determinations ranging from 38.8 to 53.6 Ma. The mean paleomagnetic pole calculated for this study is not significantly different from the pole derived from the Eocene flows to the north and gives a paleolatitude of 78{degree}, thus ruling out the hypothesis of an unrecognized suture accommodating major post-Eocene displacement. This result has prompted a reevaluation of the data. The bulk of the evidence suggests northward displacement from lower latitudes; however, the error limits are such that the dramatic velocities previously postulated are not required.

  11. 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

  12. 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

  13. 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. PMID:26131767

  14. 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

  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. Eocene tidal deposits, northern San Diego County, California

    SciTech Connect

    Eisenberg, L.I.; Abbott, P.L.

    1985-02-01

    A transgressive-regressive sedimentation sequence is recorded in a band of middle Eocene strata a few miles wide. An abundance of primary sedimentary structures, along with interfingering relationships and paleontology, define 12 lithofacies representing depositional environments including nearshore shelf, outer and inner barrier island, tidal flats and channels, lagoon and lagoonal delta. Tide-influenced sedimentary features are well defined and include meandering and abandoned tidal channels, oppositely inclined superimposed cross-strata, interlaminated mud and sand along the basal and lateral accretion surfaces of migrating tidal channels, flaser and wavy bedding, and storm-deposited strata. The first sedimentary half cycle was transgressive and documents the compression of dominantly tidal-flat and lagoonal environments against a steep, hilly coastline by the overall rising sea level of early and medial middle Eocene time. The inboard tidal-flat and lagoonal mudstones (Delmar and Friars Formations) and outboard tidal flat, channel and bar sandstones (Torrey Sandstone and Scripps Formation) interfinger in a landward-climbing, 3-dimensional sedimentary mass that parallels and meets the basement with a pronounced unconformity. The second half cycle was regressive and occurred in the medial and late middle Eocene. It formed due to the influx of coarser, more angular sediment from the adjacent basement into the narrowed paralic zone. This westward (seaward) progradation of lagoonal delta and inner tidal-flat sandy sediments occurred despite the still-rising sea level.

  17. 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.

  18. Orbital Forcing of Paleocene-Eocene Hyperthermal Events

    NASA Astrophysics Data System (ADS)

    Galeotti, S.

    2013-05-01

    The Late Paleocene to Early Eocene records a succession of short-term negative carbon isotope excursions in marine carbonates and organic carbon. At least three of these episodes, including the Eocene Thermal Maximum (ETM)1 at ca. 55.5, the ETM2 at ca. 53.5 Ma and the ETM3 at ca. 52 Ma, were associated with rapid warming and widespread dissolution of marine carbonate forced by shoaling of the carbonate lysocline and lowering of the carbonate saturation state. Cyclostratigraphic analyses of marine sequences suggest that these episodes are part of a continuum of C-cycle anomalies and were triggered by changes in local climates at high latitudes. The frequency and magnitude of related dissolution events is controlled by long-term modulations of orbital parameters, including long eccentricity (400 kyr) and a ~1 million year modulation. Highest frequency of events - at the orbital scale - is observed across the Early Eocene Climatic Optimum, which provides an observational basis to validate theoretical models predicting a threshold effect resulting from orbital forcing superimposed on gradually changing mean global boundary conditions.

  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. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. Geologic history indicated by the fossiliferous deposits of the Wilcox group (Eocene) at Meridian, Mississippi

    USGS Publications Warehouse

    Berry, Edward Wilber

    1917-01-01

    The presence of erosion intervals at several horizons in the Eocene of the Gulf States has been pointed out in a recent paper, and the evidence of an erosion interval between the period of deposition of the sediments of the Wilcox group (lower Eocene) and that of the Claiborne group (middle Eocene) was reviewed in some detail in a general discussion of the extensive flora of the Wilcox group of that region.

  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. 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., Jr.; 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.

  8. Discovery of an embrithopod mammal (Arsinoitherium?) in the late Eocene of Tunisia

    NASA Astrophysics Data System (ADS)

    Vialle, Nicolas; Merzeraud, Gilles; Delmer, Cyrille; Feist, Monique; Jiquel, Suzanne; Marivaux, Laurent; Ramdarshan, Anusha; Vianey-Liaud, Monique; Essid, El Mabrouk; Marzougui, Wissem; Ammar, Hayet Khayati; Tabuce, Rodolphe

    2013-11-01

    Dental and postcranial remains (an atlas, carpus and metacarpus elements, and a part of the pelvic girdle) of an embrithopod mammal are described from Bir Om Ali, Tunisia, a new late Eocene locality. The enamel microstructure of a tooth fragment found in association shows 'arsinoitheriid radial enamel', an enamel condition which is characteristic of Arsinoitherium (Arsinoitheriidae, Embrithopoda). Although the postcranial elements slightly differ in size and morphology from those of Arsinoitherium zitteli (late Eocene to early Oligocene), we tentatively refer this new Eocene Tunisian material to that genus. These fossils represent the first known embrithopod from the Eocene of Tunisia.

  9. 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.

  10. 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

  11. 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

  12. Climatic conditions governing extensive Azolla bloom during the Middle Eocene

    NASA Astrophysics Data System (ADS)

    Dekker, Rolande; Speelman, Eveline N.; Barke, Judith; Konijnendijk, Tiuri; Sinninge Damste, Jaap S.; Reichart, Gert-Jan

    2010-05-01

    Enormous amounts of intact mega- and microspores from the free floating aquatic fern Azolla were found in sediments recovered during Integrated Ocean Drilling Program expedition 302, indicating that Azolla grew and reproduced in situ in the Eocene Arctic Ocean. In general, the Early/Middle Eocene is characterized by enhanced greenhouse conditions with elevated sea surface temperatures (SSTs) in the Arctic (~10°C), while tropical sea surface temperatures (SSTs) were only a little warmer than today (with a mean annual temperature (MAT) of 32-34 °C) (Pearson et al., 2007). The consequently reduced temperature gradient between the equator and the poles and the presence of freshwater at the North Pole as indicated by the presence of the freshwater fern Azolla (Brinkhuis et al., 2006) provide important boundary conditions for understanding the hydrological cycle and latent heat transport during this interval. Here we reconstruct variations in SST and mean annual air temperature using the TEX86 and MBT temperature proxies for the Azolla interval. Sediments from around the Arctic Basin have been analyzed, including samples from Alaska, the Mackenzie Basin, Greenland (IODP core 913b), and Denmark. Furthermore, a high resolution sea surface temperature record for the Azolla interval has been constructed from sediment samples from the Lomonosov Ridge, showing a cyclic signal. Model experiments have shown that the here confirmed low equator-to-pole temperature gradient modulated the hydrological cycle. Since the growth of Azolla is restricted to low salinity conditions, changes in the hydrological cycle are proposed to coincide with the cyclic occurrence of Azolla throughout the interval. To confirm the overlapping presence of high quantities of Azolla and increased precipitation, changes in the hydrogen cycle are reconstructed by creating a high resolution hydrogen isotope record throughout the interval. By performing compound specific analyses (δD) on terrestrial derived

  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. PMID:15273387

  14. 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

  15. 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.

  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. 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

  18. Sequence stratigraphy of the Misoa Formation (Eocene) Lake Maracaibo, Venezuela

    SciTech Connect

    Marais-Gilchrist, G.; Higgs, R. )

    1993-02-01

    A preliminary sequence analysis of the Misoa Formation has been done in the Maraven concession area, Lake Maracaibo, using well logs supported by palynological and seismic data. The Misoa Formation is interpreted to comprise a lower transgressive unit containing at least four third-order cycles (lithostratigraphic units C7 to C3, approximately), and an upper dominantly regressive unit consisting of six third-order cycles (approximately C2 to B1). A major flooding surface (gamma-ray log maximum) provides a marker near the top of the lower unit, almost coincident with the important N-M local pollen zone. A tentative correlation can be achieved with the Haq-Vail coastal onlap curves for the Tejas A 2.3 to 3.3 third-order cycles, 55 to 44 ma. The maximum flooding surface would correlate with the maximum Eocene onlap at 52.5 ma. These ages broadly agree with the local pollen zonation. Incised valley fill units interpreted on the basis of blocky log character in some wells could have accumulated during global Eocene sea level falls, particularly those between 55 and 54 ma. The sequences gradually onlap onto the Paleocene unconformity and converge in a southwestward (landward) direction. Although north-south-oriented high-angle sinusoidal events are evident on some seismic lines, these are thought to indicate rotated listric fault-bounded blocks formed during an extensional episode, possibly syn-Misoa. The study should aid exploration for stratigraphic traps in the lake area.

  19. Episodic fresh surface waters in the Eocene Arctic Ocean.

    PubMed

    Brinkhuis, Henk; Schouten, Stefan; Collinson, Margaret E; Sluijs, Appy; Sinninghe Damsté, Jaap S; Dickens, Gerald R; Huber, Matthew; Cronin, Thomas M; Onodera, Jonaotaro; Takahashi, Kozo; Bujak, Jonathan P; Stein, Ruediger; van der Burgh, Johan; Eldrett, James S; Harding, Ian C; Lotter, André F; Sangiorgi, Francesca; van Konijnenburg-van Cittert, Han; de Leeuw, Jan W; Matthiessen, Jens; Backman, Jan; Moran, Kathryn

    2006-06-01

    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 (approximately 50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an approximately 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 approximately 10 degrees C to 13 degrees 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. PMID:16752440

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. Episodic fresh surface waters in the Eocene Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Brinkhuis, Henk; Schouten, Stefan; Collinson, Margaret E.; Sluijs, Appy; Damsté, Jaap S. Sinninghe; Dickens, Gerald R.; Huber, Matthew; Cronin, Thomas M.; Onodera, Jonaotaro; Takahashi, Kozo; Bujak, Jonathan P.; Stein, Ruediger; van der Burgh, Johan; Eldrett, James S.; Harding, Ian C.; Lotter, André F.; Sangiorgi, Francesca; Cittert, Han Van Konijnenburg-Van; de Leeuw, Jan W.; Matthiessen, Jens; Backman, Jan; Moran, Kathryn; Expedition 302 Scientists

    2006-06-01

    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 (55-45Myr 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 (~50Myr 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.

  5. 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

  6. 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.

  7. Eocene Tibetan plateau remnants preserved in the northwest Himalaya

    NASA Astrophysics Data System (ADS)

    van der Beek, Peter; van Melle, Jérémie; Guillot, Stéphane; Pêcher, Arnaud; Reiners, Peter W.; Nicolescu, Stefan; Latif, Mohammad

    2009-05-01

    The northwest Himalaya shows strongly contrasting relief. Deeply incised mountain ranges that are characterized by extremely rapid exhumation and some of the highest peaks in the world are in contrast with high-elevation, low-relief areas such as the Deosai plateau in northern Pakistan, which lies at an altitude of 4,000m. The origin and evolution of such plateau regions at the convergence of the most active continental collision in the world remain elusive. Here we report low-temperature thermochronology data from the Deosai plateau and use thermal history modelling to show that the plateau has undergone continuous slow denudation at rates below 250mMyr-1 for the past 35Myr at least. This finding suggests tectonic and morphologic stability of the plateau since at least Eocene times, only 15-20Myr after the onset of the India-Asia collision. Our work contradicts the hypothesis that widespread low-relief surfaces in the northwest Himalaya result from efficient kilometre-scale glacial erosion during Quaternary times. We show that similarly stable surfaces exist throughout the entire northwest Himalaya and share common morphologic characteristics and denudation histories, which are comparable to those of the western Tibetan plateau. Our results suggest that these surfaces are preserved remnants of an Eocene southwestern Tibetan plateau that was more extensive than today.

  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. 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.

  10. 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.

  11. Constraining carbon input for early-middle Eocene 'hyperthermals'

    NASA Astrophysics Data System (ADS)

    Kirtland, S. E.; Sexton, P. F.; Ridgwell, A.; Norris, R. D.

    2010-12-01

    The past ten years have witnessed the continuing discovery of short-lived warming events (‘hyperthermals’) smaller in size and shorter in duration than the Paleocene-Eocene Thermal Maximum (PETM). For example, a 2.4 Myr-long benthic foraminiferal stable isotope record from Demerara Rise has revealed the occurrence of multiple short-lived ‘hyperthermals’ across the early to middle Eocene transition (47.6 to 50 Myr ago). While the PETM is widely attributed to a massive injection of carbon into the oceans-atmosphere from a buried, sedimentary source, the size, duration, and shape of these less-extreme events suggests that their genesis may not require the release of sedimentary-sourced carbon. Instead, redistribution of carbon from readily exchangeable surficial carbon reservoirs could provide a source consistent with the magnitude and shape of these events. Here we use GENIE (Gride Enabled Integrated Earth system model) to evaluate how details of the shape and magnitude of these observed isotopic excursions in both bulk and benthic records relate to the source and quantity of carbon input. In particular, we test competing mechanisms and carbon sources to explain the relatively rapid recovery of these events.

  12. 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.

  13. 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.

  14. Reconnaissance paleomagnetic study of the Eocene Admiralty Island volcanics, southeast Alaska: evidence for pre-late Eocene accretion

    SciTech Connect

    Panuska, B.C.; Decker, J.

    1985-01-01

    Paleomagnetic data have shown that many of the terranes in southern and southeastern Alaska originated in equatorial paleolatitudes. The ages(s) of accretion of these terranes is much debated and paleomagnetic studies constraining this age are limited. As part of a larger study, reconnaissance samples of the Admiralty Island Volcanics (Eocene) were collected at Deepwater Point and Little Pybus Bay on the southern coast of Admiralty Island. Thermal or AF cleaning effectively isolated stable magnetic components in most specimens. Homoclinal dip of the flows precludes a fold test and reversals were not observed. However, 3 penecontemporaneous feeder dikes have magnetic directions which are statistically different from the magnetic directions of the flows they intrude (baked contact test). In addition, the flows have not been affected by a regional overprinting observed in most pre-Tertiary rocks. Thus, these magnetic directions are provisionally interpreted as primary. Assuming a reversed geomagnetic polarity during the eruption of the flows, the mean direction is not significantly different than the expected North American direction. Although more data are necessary to prove a primary remanence and to insure that secular variation has been averaged out, the preliminary evidence suggests that the Southern Alaska superterrane had accreted to North American by Eocene time. These results are similar to findings in south central Alaska, which also suggest that the major terrane translation and had been completed by the early Tertiary.

  15. Reconstruction of the Eocene Arctic Ocean Using Ichthyolith Isotope Analyses

    NASA Astrophysics Data System (ADS)

    Gleason, J. D.; Thomas, D. J.; Moore, T. C.; Waddell, L. M.; Blum, J. D.; Haley, B. A.

    2007-12-01

    Nd, Sr, O and C isotopic compositions of Eocene fish debris (teeth, bones, scales), and their reduced organic coatings, have been used to reconstruct water mass composition, water column structure, surface productivity and salinities of the Arctic Ocean Basin at Lomonosov Ridge between 55 and 44 Ma. Cleaned ichthyolith samples from IODP Expedition 302 (ACEX) record epsilon Nd values that range from -5.7 to -7.8, distinct from modern Arctic Intermediate Water (-10.5) and North Atlantic Deep Water. These Nd values may record some exchange with Pacific/Tethyan water masses, but inputs from local continental sources are more likely. Sr isotopic values are consistent with a brackish-to-fresh water surface layer (87Sr/86Sr = 0.7079-0.7087) that was poorly mixed with Eocene global seawater (0.7077-0.7078). Leaching experiments show reduced organic coatings to be more radiogenic (>0.7090) than cleaned ichthyolith phosphate. Ichthyolith Sr isotopic variations likely reflect changes in localized river input as a function of shifts in the Arctic hydrologic cycle, and 87Sr/86Sr values might be used as a proxy for surface water salinity. Model mixing calculations indicate salinities of 5 to 20 per mil, lower than estimates based on O isotopes from fish bone carbonate (16 to 26 per mil). Significant salinity drops (i.e., 55 Ma PETM and 48.5 Ma Azolla event) registered in oxygen isotopes do not show large excursions in the 87Sr/86Sr data. Carbon isotopes in fish debris record a spike in organic activity at 48.5 Ma (Azolla event), and otherwise high-productivity waters between 55 and 44 Ma. The combined Sr-Nd-O-C isotopic record is consistent with highly restricted basin-wide circulation in the Eocene, indicative of a highly stratified water column with anoxic bottom waters, a "fresh" water upper layer, and enhanced continental runoff during warm intervals until the first appearance of ice rafted debris at 45 Ma.

  16. The Eocene to Oligocene Landscape of the Northern Sierra Nevada

    NASA Astrophysics Data System (ADS)

    Cassel, E. J.; Graham, S. A.

    2007-12-01

    To gain a better understanding of the Cenozoic tectonic and landscape evolution of the northern Sierra Nevada, well-preserved Eocene to Oligocene sedimentary and volcanic units form the focus of a detailed stratigraphic study which incorporates geochemical and stable isotopic analyses. Widespread silicic ash-flow tuffs (31-28 Ma) crop out across the northern Sierra from near paleo-sea level at the eastern edge of the Great Valley across the modern crest of the range into Nevada. On the western flank of the northern Sierra, they cap Eocene prevolcanic fluvial sediments of the ancestral Yuba and Feather Rivers. The Eocene fluvial system was dominantly controlled by bedrock structure, consisting of two types of coeval valley morphologies: steep, narrow high-energy valley segments and broader, lower-gradient braided stream valley segments. The braided fluvial sequence contains four upward-fining cycles: coarse lower intervals consist of gravel-sand dunes and lateral accretion elements deposited within higher energy channels; upper fine intervals consist of 1-5 m thick lignite-bearing clay and silt marsh deposits. Full-valley width exposures of clay eliminate the possibility of autocyclic controls, indicating that the multiple upward-fining cycles reflect base-level change. Two distinctive overlying ash-flow tuffs were identified and correlated by trace and rare earth element composition of volcanic glass and lithologic criteria. Hydrated glass was used as a proxy for hydrogen isotopic composition of precipitation to determine the paleoelevation gradient in the Oligocene. The δD of ancient meteoric waters, which scales at a predictable rate with change in elevation, decreases steadily across a range-perpendicular transect, from -125‰ ± 1‰ in the west to -160‰ ± 4‰ in the east. This 35‰ decrease in the δD of precipitation is similar to the compositional gradient of the range today, and reflects an increase in ancient mean elevation along the transect. These

  17. Eocene Tibetan Plateau remnants preserved in the Northwest Himalaya

    NASA Astrophysics Data System (ADS)

    van der Beek, P. A.; van Melle, J.; Guillot, S.; Pêcher, A.; Reiners, P. W.; Nicolescu, S.; Latif, M.

    2009-04-01

    The northwest Himalaya shows strongly contrasting relief, opposing deeply incised mountain ranges characterized by extremely rapid exhumation and some of the highest peaks in the world (i.e., the Karakorum range and Nanga Parbat massif) to high-elevation, low-relief areas such as the 4000-m high Deosai plateau in northern Pakistan and the 5000-m high Tso Morari in Indian Ladakh. The origin and evolution of such plateau regions in the syntaxis of the most active continental collision in the world remain elusive. Here, we report the first low-temperature thermochronology (apatite fission-track, apatite and zircon (U-Th)/He) data from the Deosai plateau and use thermal history modelling to show that it has undergone continuous slow (≤ 200 m/Myr) denudation and has thus remained tectonically stable for the last 35 Myr at least. The inferred history of constant slow denudation of the plateau contradicts the hypothesis that widespread low-relief surfaces in the northwest Himalaya result from efficient, km-scale glacial erosion during Quaternary times; such erosion would have been recorded as a phase of rapid recent denudation that is not observed in the data. Slow continuous denudation since Eocene times, i.e. only 15-20 Myr after the onset of India-Asia collision implies that the Deosai plateau surface developed early in the Himalayan history and limits the phase of orogenic relief growth in the Ladakh-Kohistan arc to the early Paleogene. Although thermochronology data do not directly record surface uplift, the simplest explanation for the inferred constant denudation rates is that the plateau had reached its present-day elevation already during the Eocene, as a later phase of surface uplift would have triggered an erosional response that would have been recorded by the thermochronology data. We use morphological analyses to characterise such plateaux and identify them at the scale of the entire northwest Himalaya and compare our thermochronological data with

  18. 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

  19. Radiative forcing by forest and subsequent feedbacks in the early Eocene climate

    NASA Astrophysics Data System (ADS)

    Port, U.; Claussen, M.; Brovkin, V.

    2015-03-01

    Using the Max Planck Institute for Meteorology Earth System Model, we investigate the forcing of forests and the feedback triggered by forests in the pre-industrial climate and in the early Eocene climate (about 54 to 52 million years ago). Other than the interglacial, pre-industrial climate, the early Eocene climate was characterised by high temperatures which led to almost ice-free poles. We compare simulations in which all continents are covered either by dense forest or by bare soil. To isolate the effect of soil albedo, we choose either bright soils or dark soils, respectively. Considering bright soil, forests warm in both, the early Eocene climate and the current climate, but the warming differs due to differences in climate feedbacks. The lapse-rate and water-vapour feedback is stronger in early Eocene climate than in current climate, but strong and negative cloud feedbacks and cloud masking in the early Eocene climate outweigh the stronger positive lapse-rate and water-vapour feedback. In the sum, global mean warming is weaker in the early Eocene climate. Sea-ice related feedbacks are weak in the almost ice-free climate of the early Eocene leading to a weak polar amplification. Considering dark soil, our results change. Forests cools stronger in the early Eocene climate than in the current climate because the lapse-rate and water-vapour feedback is stronger in the early Eocene climate while cloud feedbacks and cloud masking are equally strong in both climates. The different temperature change by forest in both climates highlights the state-dependency of vegetation's impact on climate.

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. Late Eocene Hydrological Conditions on the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Feakins, S. J.; Deconto, R. M.; Warny, S.

    2013-12-01

    The late Eocene to Oligocene transition (EOT) witnessed a major ice advance on Antarctica. Little is known about hydrological conditions in the Antarctic Peninsula during the late Eocene prior to the major ice advance. Here we explore the hydrological conditions with proxy reconstructions from marine sediment core NBP0602A-3C, adjacent to the tip of the Antarctic Peninsula, with sediments dated to approximately 35.9 × 1.1 Ma providing a snapshot of conditions prior to the EOT. We combine plant leaf wax hydrogen isotopic evidence paired with previously-published evidence from pollen assemblages from the marine core, and compare to results of climate model experiments. The pollen from late Eocene sediments of NBP0602A-3C indicate a Nothofagidites (southern beech) dominated landscape. In the same sediments, leaf wax hydrogen isotope (δDwax) values average -202×7‰ (1σ, n=22) for the C28 n-alkanoic acid. Based on an estimated net fractionation of -100‰, these values suggest paleoprecipitation δD values on the order of -118×8‰. The similarity between Late Eocene precipitation isotopic reconstructions (with no ice on what was then an island) and in situ modern isotopic values (while ice-covered) is surprising as ice-free conditions should imply warmer temperatures which would normally imply more enriched isotopic values. Convergent isotopic compositions during demonstrably different environments require a dynamical test to evaluate this validity of this isotopic result. In order to test the isotopic response to an expanding Antarctic ice sheet across the EOT, we conducted experiments with an isotope-enabled GCM. We simulated conditions before, during, and after the transition by systematically decreasing carbon dioxide levels from 1000 to 560 ppm while increasing ice volume to represent an ice-free to fully glaciated continent. Model experiments predict changes in vegetation cover from mixed forest to tundra biomes, reductions in austral summer temperature of

  8. Eocene Structural Development of the Valhalla Complex, Southeastern British Columbia

    NASA Astrophysics Data System (ADS)

    Carr, Sharon D.; Parrish, Randall R.; Brown, Richard L.

    1987-04-01

    The Valhalla complex, a Cordilleran metamorphic core complex, is a 100 km by 30 km structural culmination within the Omineca belt of southeastern British Columbia. It comprises sheets of granitic orthogneiss ranging in age from 100 to 59 Ma with intervening paragneiss of uncertain age and stratigraphic correlation. The complex is roofed by the ductile Valkyr shear zone and the ductile/brittle Slocan Lake fault zone; the upper plate comprises lower grade metasedimentary rocks intruded by middle Jurassic plutons. The Valkyr shear zone and the Slocan Lake fault zone deform 62 and 59 Ma granitic sheets in their footwalls. The easterly directed Valkyr shear zone is a 2 to 3 km thick zone of distributed ductile strain which is arched over the complex and is exposed around the periphery on the northern, western, and southern margins. The shear zone was active between 59 and 54 Ma under amphibolite facies conditions. The juxtaposition of upper and lower plates with different structural and metamorphic histories indicates that the Valkyr shear zone is a significant structure with large displacement. There is evidence to support an easterly rooting direction consistent with an extensional origin; its surface breakaway is suggested to be west of the Valhalla complex. The Slocan Lake fault zone on the eastern side of the complex is a gently (30°), easterly dipping ductile/brittle normal fault which roots to the east. It was active between 54 and approximately 45 Ma and truncates the Valkyr shear zone. Timing and structural relationships indicate that the Valkyr shear zone and the Slocan Lake fault zone are genetically related. Movement on the ductile Valkyr shear zone, arching of the complex, and displacement on the Slocan Lake fault zone occurred as a continuum in Early to Middle Eocene time. This paper documents the presence of significant Eocene ductile strain in the Valhalla complex and suggests that the role of extension in this region is more profound than had been

  9. 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.

  10. Widanelfarasia, a diminutive placental from the late Eocene of Egypt

    PubMed Central

    Seiffert, Erik R.; Simons, Elwyn L.

    2000-01-01

    The lower dentition of Widanelfarasia (new genus), a diminutive late Eocene placental from the Fayum Depression in Egypt, is described. Widanelfarasia exhibits a complex of features associated with incipient zalambdodonty and at least three unequivocal apomorphies [loss of P1, an enlarged I2 (relative to I3), and a basal cusp on I2], which provide weak support for its placement as a possible sister taxon of either a tenrecid–chrysochlorid clade or of solenodontids. The former hypothesis gains additional support from biogeographical evidence, but both scenarios are currently tenuous as Widanelfarasia is clearly not truly zalambdodont. Phylogenetic hypotheses positing affinities with tenrecids alone or chrysochlorids alone must invoke either convergent acquisition of zalambdodonty in these taxa or autapomorphic reversal in Widanelfarasia. Given these considerations, a relationship with more generalized taxa from the Laurasian Paleogene (e.g., geolabidids, nyctitheriids, leptictids) cannot yet be ruled out. Comparisons with other Paleogene Afro-Arabian forms are generally inconclusive. A relationship with the earlier Eocene Chambilestes from Tunisia—currently represented by a single specimen preserving P4–M3—seems possible based on the geometry and predicted occlusal relationships of these teeth, but cannot be confidently determined until these two taxa come to be represented by common diagnostic elements. Todralestes (late Paleocene, Morocco) exhibits general phenetic similarities to Widanelfarasia, but it is not yet known whether this taxon shares any of Widanelfarasia's unequivocal dental apomorphies. Pending the recovery of more informative material, we tentatively refer Widanelfarasia to Placentalia incertae sedis. Truly zalambdodont placentals remain conspicuously absent from the Paleogene of Afro-Arabia. PMID:10694573

  11. 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

  12. Microfloral diversity patterns of the late Paleocene Eocene interval in Colombia, northern South America

    NASA Astrophysics Data System (ADS)

    Jaramillo, Carlos A.; Dilcher, David L.

    2000-09-01

    The late Paleocene early Eocene interval was characterized by a long period of global warming that culminated with the highest temperatures of the Tertiary. This interval was also associated with plant extinctions and a subsequent increase in plant diversity in temperate latitudes. However, tropical regions remain largely unknown. We compare the microfloral diversity of the late Paleocene with the late early to middle Eocene in flood plain, coastal plain, and estuarine facies of a section in the Colombian eastern Andes. Several techniques such as range-through method, rarefaction, bootstrap, detrended correspondence analysis, and Simpson index were used to assess the significance of the diversity pattern observed throughout the section. The microfloral record indicates a distinct, diverse Paleocene flora declining toward the end of the Paleocene, being replaced by a different and much more diverse Eocene flora. It is uncertain, however, how these floral changes correlate with the latest Paleocene thermal maximum and Eocene thermal maximum events.

  13. 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

  14. 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

  15. 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

  16. A structural intermediate between triisodontids and mesonychians (Mammalia, Acreodi) from the earliest Eocene of Portugal.

    PubMed

    Tabuce, Rodolphe; Clavel, Julien; Antunes, Miguel Telles

    2011-02-01

    A new mammal, Mondegodon eutrigonus gen. et sp. nov., is described from the earliest Eocene locality of Silveirinha, Portugal. This species shows dental adaptations indicative of a carnivorous diet. M. eutrigonus is referred to the order Acreodi and considered, along with the early Paleocene North American species Oxyclaenus cuspidatus, as a morphological intermediate between two groups of ungulate-like mammals, namely, the triisodontids and mesonychians. Considering that triisodontids are early to early-late Paleocene North American taxa, Mondegodon probably belongs to a group that migrated from North America towards Europe during the first part of the Paleocene. Mondegodon could represent thus a relict genus, belonging to the ante-Eocene European mammalian fauna. The occurrence of such a taxon in Southern Europe may reflect a period of isolation of this continental area during the Paleocene/Eocene transition. In this context, the non-occurrence of closely allied forms of Mondegodon in the Eocene North European mammalian faunas is significant. This strengthens the hypothesis that the mammalian fauna from Southern Europe is characterized by a certain degree of endemism during the earliest Eocene. Mondegodon also presents some striking similarities with an unnamed genus from the early Eocene of India which could represent the first Asian known transitional form between the triisodontids and mesonychians. PMID:21181109

  17. A structural intermediate between triisodontids and mesonychians (Mammalia, Acreodi) from the earliest Eocene of Portugal

    NASA Astrophysics Data System (ADS)

    Tabuce, Rodolphe; Clavel, Julien; Antunes, Miguel Telles

    2011-02-01

    A new mammal, Mondegodon eutrigonus gen. et sp. nov., is described from the earliest Eocene locality of Silveirinha, Portugal. This species shows dental adaptations indicative of a carnivorous diet. M. eutrigonus is referred to the order Acreodi and considered, along with the early Paleocene North American species Oxyclaenus cuspidatus, as a morphological intermediate between two groups of ungulate-like mammals, namely, the triisodontids and mesonychians. Considering that triisodontids are early to early-late Paleocene North American taxa, Mondegodon probably belongs to a group that migrated from North America towards Europe during the first part of the Paleocene. Mondegodon could represent thus a relict genus, belonging to the ante-Eocene European mammalian fauna. The occurrence of such a taxon in Southern Europe may reflect a period of isolation of this continental area during the Paleocene/Eocene transition. In this context, the non-occurrence of closely allied forms of Mondegodon in the Eocene North European mammalian faunas is significant. This strengthens the hypothesis that the mammalian fauna from Southern Europe is characterized by a certain degree of endemism during the earliest Eocene. Mondegodon also presents some striking similarities with an unnamed genus from the early Eocene of India which could represent the first Asian known transitional form between the triisodontids and mesonychians.

  18. 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

  19. 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

  20. 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.

  1. Arctic Ocean circulation during the anoxic Eocene Azolla event

    NASA Astrophysics Data System (ADS)

    Speelman, Eveline; Sinninghe Damsté, Jaap; März, Christian; Brumsack, Hans; Reichart, Gert-Jan

    2010-05-01

    The Azolla interval, as encountered in Eocene sediments from the Arctic Ocean, is characterized by organic rich sediments ( 4wt% Corg). In general, high levels of organic matter may be caused by increased productivity, i.e. extensive growth of Azolla, and/or enhanced preservation of organic matter, or a combination of both. Anoxic (bottom) water conditions, expanded oxygen minimum zones, or increased sedimentation rates all potentially increase organic matter preservation. According to plate tectonic, bathymetric, and paleogeographic reconstructions, the Arctic Ocean was a virtually isolated shallow basin, with one possible deeper connection to the Nordic Seas represented by a still shallow Fram Strait (Jakobsson et al., 2007), hampering ventilation of the Arctic Basin. During the Azolla interval surface waters freshened, while at the same time bottom waters appear to have remained saline, indicating that the Arctic was highly stratified. The restricted ventilation and stratification in concert with ongoing export of organic matter most likely resulted in the development of anoxic conditions in the lower part of the water column. Whereas the excess precipitation over evaporation maintained the freshwater lid, sustained input of Nordic Sea water is needed to keep the deeper waters saline. To which degree the Arctic Ocean exchanged with the Nordic Seas is, however, still largely unknown. Here we present a high-resolution trace metal record (ICP-MS and ICP-OES) for the expanded Early/Middle Eocene section capturing the Azolla interval from Integrated Ocean Drilling Program (IODP) Expedition 302 (ACEX) drilled on the Lomonosov Ridge, central Arctic Ocean. Euxinic conditions throughout the interval resulted in the efficient removal of redox sensitive trace metals from the water column. Using the sedimentary trace metal record we also constrained circulation in the Arctic Ocean by assessing the relative importance of trace metal input sources (i.e. fluvial, eolian, and

  2. 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.

  3. 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

  4. Sea surface salinity of the Eocene Arctic Azolla event using innovative isotope modeling

    NASA Astrophysics Data System (ADS)

    Speelman, E. N.; Sewall, J. O.; Noone, D.; Huber, M.; Sinninghe Damste, J. S.; Reichart, G. J.

    2009-04-01

    With the realization that the Eocene Arctic Ocean was covered with enormous quantities of the free floating freshwater fern Azolla, new questions regarding Eocene conditions facilitating these blooms arose. Our present research focuses on constraining the actual salinity of, and water sources for, the Eocene Arctic basin through the application of stable water isotope tracers. Precipitation pathways potentially strongly affect the final isotopic composition of water entering the Arctic Basin. Therefore we use the Community Atmosphere Model (CAM3), developed by NCAR, combined with a recently developed integrated isotope tracer code to reconstruct the isotopic composition of global Eocene precipitation and run-off patterns. We further addressed the sensitivity of the modeled hydrological cycle to changes in boundary conditions, such as pCO2, sea surface temperatures (SSTs) and sea ice formation. In this way it is possible to assess the effect of uncertainties in proxy estimates of these parameters. Overall, results of all runs with Eocene boundary conditions, including Eocene topography, bathymetry, vegetation patterns, TEX86 derived SSTs and pCO2 estimates, show the presence of an intensified hydrological cycle with precipitation exceeding evaporation in the Arctic region. Enriched, precipitation weighted, isotopic values of around -120‰ are reported for the Arctic region. Combining new results obtained from compound specific isotope analyses (δD) on terrestrially derived n-alkanes extracted from Eocene sediments, and model outcomes make it possible to verify climate reconstructions for the middle Eocene Arctic. Furthermore, recently, characteristic long-chain mid-chain ω20 hydroxy wax constituents of Azolla were found in ACEX sediments. δD values of these C32 - C36 diols provide insight into the isotopic composition of the Eocene Arctic surface water. As the isotopic signature of the runoff entering the Arctic is modelled, and the final isotopic composition of

  5. 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.

  6. Primate postcrania from the late middle Eocene of Myanmar.

    PubMed

    Ciochon, R L; Gingerich, P D; Gunnell, G F; Simons, E L

    2001-07-01

    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

  7. 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. PMID:20962843

  8. 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.

  9. Water isotopes and the Eocene. A tectonic sensitivity study

    NASA Astrophysics Data System (ADS)

    Legrande, A. N.; Roberts, C. D.; Tripati, A.; Schmidt, G. A.

    2009-04-01

    The early Eocene (54 Million years ago) is one of the warmest periods in the last 65 Million years. Its climate is postulated to have been the result of enhanced greenhouse gas concentration, with CO2 roughly 4 times pre-industrial and methane 7 times pre-industrial concentrations. One interesting feature of this period to emerge recently is the intermittent presence of fossilized Azolla, a type of freshwater fern, in the Arctic Ocean. Synchronous (within dating error) with this appearance were major changes in the restriction of the Arctic Ocean and the other global oceans. We investigate this time period using the Goddard Institute for Space Studies ModelE-R, a fully coupled atmosphere-ocean general circulation model that incorporates water isotopes throughout the hydrologic cycle, making it an ideal model to test hypotheses of past climate change and to compare to paleoclimate proxy data. We assess the impact of tectonic variability by using minimal and maximal levels of restriction for the Arctic Ocean seaways. We find that the modulation of connectivity of these basins dramatically alters global salinity distribution, leading to large changes in ocean circulation. Greater restriction of the Arctic Basin is associated with fresh and relatively warmer conditions. The same mechanisms responsible for this redistribution of salt also change the global distribution of water isotopes, and can alias (water isotope) proxy climate signals of warmth.

  10. 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

  11. 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'.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. Investigating Seasonal Isotopic Variability along an Early Eocene Shallow Shelf

    NASA Astrophysics Data System (ADS)

    Sessa, J. A.; Ivany, L. C.; Schlossnagle, T. H.

    2009-12-01

    While the bulk of paleotemperature estimates are derived from microfossils in the open ocean, shelf settings can also provide detailed records of climatic and oceanographic parameters. Molluscs live in a variety of habitats, but are especially common in shallow-water shelf environments, where microfossil preservation may be rare. Isotope thermometry using mollusc shells has been the subject of considerable study and the accretionary process is generally well understood. Because shells accrete more or less continuously over a lifespan, their chemistry can additionally provide estimates of mean annual range of temperature (MART), or seasonality, a valuable complement to mean annual temperature (MAT) estimates derived from open ocean microfossils. Studies of paleotemperature through time in shelf settings typically employ a sampling scheme designed to maximize temporal coverage, with one or a few shells from each stratigraphic horizon. However, few have assessed the degree to which spatial and/or environmental variability may confound temperature estimates. Because shelf environments are affected by local processes such as runoff and evaporation, spatial variability may bias temporal trends when specimens from only one locality per temporal bin are used. Even controlling for facies through time may not be enough, as processes that typically influence oxygen isotopic composition, such as freshwater influx, can be transient events in shelf settings and hence may not be reflected in sediment composition. Here, we document the spatial variability in oxygen isotopes (and therefore MAT and MART) along an inner shelf environment in the early Eocene (~55 Ma) of the Gulf Coastal Plain (GCP; Alabama, Georgia, Mississippi and Texas) of the United States. The GCP was a shallow, mixed carbonate-siliciclastic shelf during the Paleogene. Geochemical data are derived from the aragonitic shells of the common GCP bivalve genus Venericardia, collected from the Bashi Marl and its

  2. Atmospheric carbon dioxide through the Eocene-Oligocene climate transition.

    PubMed

    Pearson, Paul N; Foster, Gavin L; Wade, Bridget S

    2009-10-22

    Geological and geochemical evidence indicates that the Antarctic ice sheet formed during the Eocene-Oligocene transition, 33.5-34.0 million years ago. Modelling studies suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels (pCO2atm) fell below a critical threshold of approximately 750 p.p.m.v., but the timing and magnitude of pCO2atm relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania to estimate pCO2atm before, during and after the climate transition. Our data suggest that are reduction in pCO2atm occurred before the main phase of ice growth,followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, pCO2atm was between approximately 450 and approximately 1,500 p.p.m.v., with a central estimate of approximately 760 p.p.m.v. The ice cap survived the period of pCO2atm recovery,although possibly with some reduction in its volume, implying (as models predict) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining pCO2atm in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling) and help to constrain mechanisms and feedbacks associated with the Earth's biggest climate switch of the past 65 Myr. PMID:19749741

  3. 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.

  4. Calcareous nannoplankton and diatoms from the Eocene/Pliocene sediments, Fayoum depression, Egypt

    NASA Astrophysics Data System (ADS)

    Zalat, Abdelfattah A.

    1995-04-01

    Different assemblages of calcareous nannofossil and diatom taxa are detected in samples collected from sections at Shaqluf, Siela and Qaret El Faras in the Fayoum area. Five calcareous nannoplankton biozones are recorded: the Middle Eocene Discoaster tanii nodifer Zone, the Discoaster saipanensis Zone; the early, Late Eocene Chiasmolithus oamaruensis Zone; the Late Eocene Isthmolithus recurvus Zone and the Early Pliocene Reticulofenestra pseudoumbilicus Zone. Diatoms are recorded for the first time in the sections studied. The gradual changes in diatom composition from marine to brackish, ending with a well-developed, freshwater flora at the top of the Pliocene Shaqluf section, indicate changes in the palaeoecological conditions in the area during that time. In the Pliocene Siela and Qaret El Faras sections, all the identified diatom taxa belong to the freshwater assemblage together with some brackish water forms. The predominance of freshwater diatoms suggests that these taxa were introduced to the area with the sediments of the Palaeonile river during the Late Pliocene.

  5. The case for dynamic subsidence of the U.S. east coast since the Eocene

    NASA Astrophysics Data System (ADS)

    Spasojević, Sonja; Liu, Lijun; Gurnis, Michael; Müller, R. Dietmar

    2008-04-01

    The dynamic subsidence of the United States east coast is addressed using the discrepancy between regional and global estimates of sea level, elevation of paleoshorelines, and adjoint models of mantle convection that assimilate plate motions and seismic tomography. The positions of Eocene and Miocene paleoshorelines are lower than predicted by global sea levels, suggesting at least 50 m, and possibly as much as 200 m of subsidence since the end of the Eocene. Dynamic models predict subsidence of the east coast since the end of Eocene, although the exact magnitude is uncertain. This subsidence has been occurring during an overall global sea-level fall, with the eustatic change being larger than the dynamic subsidence; this results in a regional sea-level fall in the absence of land subsidence. Dynamic subsidence is consistent with the difference between eustasy and regional sea level at the New Jersey coastal plain.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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).

  12. 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.

  13. 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

  14. 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

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

    USGS Publications Warehouse

    Gibson, T.G.

    1965-01-01

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

  16. Hydrogen Isotopes in Eocene River Gravels and Paleoelevation of the Sierra Nevada

    NASA Astrophysics Data System (ADS)

    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. 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. PMID:16825568

  18. Early Eocene perturbed parameter simulations: multiple methods of proxy-model comparison

    NASA Astrophysics Data System (ADS)

    Sagoo, N.; Valdes, P. J.; Flecker, R.

    2012-04-01

    Geological proxy data for the early Eocene, ~55 million years ago, indicate widespread greenhouse conditions across the Earth. High latitude early Eocene temperature estimates inferred from a variety of proxy data are much warmer than their modern counterparts (~10-20°C), whilst low latitude early Eocene temperature estimates where available (~30-35°C) are only slightly warmer than their modern equivalent. This implies a reduced pole to equator temperature gradient during the early Eocene. Climate models are unable to simulate the low latitudinal temperature gradients seen in the early Eocene. The mechanisms for transporting and maintaining heat at high latitudes in order to achieve these reduced gradients are still uncertain although several hypotheses have been proposed. We are interested in reducing this model-data discrepancy by considering both climate model and proxy data uncertainty. A comprehensive study by Murphy et al. 20041 identified a subset of 29 parameters within the UK Hadley centre climate model (HadCM3) whose values cannot be accurately determined from observations. These 29 parameters were identified as being responsible for controlling key physical characteristics of sub-grid scale atmospheric and surface processes by modelling experts. Using a subset of 12 of the uncertain parameters identified by Murphy et al. 2004, we have run climate model experiments perturbing these parameters singly and jointly, within a realistic range, in order to understand the spectrum of climates that result. We use the model, FAMOUS (Fast Met Office/UK Universities Simulator), a low resolution emulator of HadCM3 for our experiments. The relatively low computing time of FAMOUS makes it ideal for long paleoclimate studies. We use an early Eocene paleogeography and run our simulations at 560 ppm, (2 x pre-industrial CO2.) The solar constant for the early Eocene is set to 1359.5 Wm-2. The climate proxy dataset (terrestrial and marine) available for the early Eocene is

  19. Monophyly and extensive extinction of advanced eusocial bees: Insights from an unexpected Eocene diversity

    PubMed Central

    Engel, Michael S.

    2001-01-01

    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. PMID:11172007

  20. 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

  1. 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. PMID:11172007

  2. Analysis of Eocene depositional environments - Preliminary TM and TIMS results, Wind River Basin, Wyoming

    NASA Technical Reports Server (NTRS)

    Stucky, Richard K.; Krishtalka, Leonard; Redline, Andrew D.; Lang, Harold R.

    1987-01-01

    Both Landsat TM and aircraft Thermal IR Multispectral Scanner (TIMS) data have been used to map the lithofacies of the Wind River Basin's Eocene physical and biological environments. Preliminary analyses of these data have furnished maps of a fault contact boundary and a complex network of fluvial ribbon channel sandstones. The synoptic view thereby emerging for Eocene fluvial facies clarifies the relationships of ribbon channel sandstones to fossil-bearing overbank/floodplain facies and certain peleosols. The utility of TM and TIMS data is thereby demonstrated.

  3. Stratigraphy and paleoenvironment of the Danish Eocene Azolla event

    NASA Astrophysics Data System (ADS)

    Heilmann-Clausen, Claus; Beyer, Claus; Snowball, Ian

    2010-05-01

    Spores (massulae and megaspores) of the freshwater fern Azolla are recorded in several Danish Eocene outcrops and boreholes. The Azolla-bearing interval is 0.5 - ca. 3 m thick and occurs within the L2 Bed, a unit in the lower part of the hemipelagic, bathyal Lillebælt Clay Formation deposited in the central and eastern parts of the North Sea Basin. Intervals of organic-rich clay, usually including two distinctive, black sapropels, are present in the lower part of Bed L2, indicating a generally reduced oxygen content in the bottom waters during this time, with at least two episodes of severe, basinwide stagnation. The oxygen-deficit points to reduced circulation and/or enhanced marine productivity in the North Sea Basin. Azolla occurs in the upper part of this mainly organic-rich interval. The frequency of Azolla spores relative to marine dinoflagellate cysts fluctuates within the interval. The Azolla interval has previously been correlated to levels near the Ypresian/Lutetian transition in Belgium, based on dinoflagellate stratigraphy. Calibration of a new magnetostratigraphic study of the lower Lillebælt Clay with the dinoflagellate biostratigraphy suggests that Bed L2 spans the upper part of Chron 22r, C22n and lower part of C21r. The Azolla pulse spans the upper part of C22n and lowermost part of C21r. The combined bio-magnetostratigraphy from Denmark allows a detailed comparison with published data from the northern part of the Norwegian-Greenland Sea (ODP Hole 913B). The correlation confirms earlier assumptions, which were based on biostratigraphy alone, that the marine Azolla pulse in the two areas, and therefore probably over the whole Norwegian-Greenland Sea - North Sea region, is of the same age. An ongoing palynological study of the L2 Bed has so far revealed no indication for freshwater episodes or brackish waters in the basin during the Azolla pulse, except perhaps for Azolla itself. It is, therefore, suggested that the Azolla spores were transported

  4. 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.

  5. Orbital pacing of Eocene climate during the Middle Eocene Climate Optimum and the chron C19r event: Missing link found in the tropical western Atlantic

    NASA Astrophysics Data System (ADS)

    Westerhold, Thomas; Röhl, Ursula

    2013-11-01

    A high-resolution stratigraphy is essential toward deciphering climate variability in detail and understanding causality arguments of events in earth history. Because the middle to late Eocene provides a perfect testing ground for carbon cycle models to reconstruct the transition from a hothouse to an icehouse world, an accurate time scale is needed to decode climate-driving mechanisms. Here we present new results from ODP Site 1260 (Leg 207) which covers a unique expanded middle Eocene section (magnetochrons C18r to C20r, late Lutetian to early Bartonian) of the tropical western Atlantic including the chron C19r transient hyperthermal event and the Middle Eocene Climate Optimum (MECO). To establish a detailed cyclostratigraphy we acquired iron intensity records by XRF scanning Site 1260 cores. We revise the shipboard composite section, establish a cyclostratigraphy and use the exceptional eccentricity modulated precession cycles for orbital tuning. The new astrochronology revises the age of magnetic polarity chrons C19n to C20n, validates the position of very long eccentricity minima at 40.2 and 43.0 Ma in the orbital solutions and extends the Astronomically Tuned Geological Timescale back to 44 Ma. For the first time the new data provide clear evidence for an orbital pacing of the chron C19r event and a likely involvement of the very long (2.4 myr) eccentricity cycle contributing to the evolution of the MECO.

  6. 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

  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. 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.

  10. The Middle Eocene Paleoceanography of the Arctic Ocean Based on Silicoflagellates and Ebridians

    NASA Astrophysics Data System (ADS)

    Onodera, J.; Takahashi, K.

    2006-12-01

    The early middle Eocene Arctic samples, which were obtained by IODP Expedition 302 (ACEX), were studied for the siliceous microfossils of silicoflagellates and ebridians in order to decipher the paleoceanographic changes of the upper water column. The presence of low salinity waters in the Eocene Arctic is suggested from the co-occurrence of freshwater and blackish water microfossils. Changes of characteristic assemblages with age are probably due to the habitat modulation governed by the extent of mixing of significantly different water masses between the low salinity waters derived from the Arctic region and relatively high salinity waters supplied from the outside of the semi-closed paleo-Arctic basin. The freshwater is attributed to the rainfall and river influx during the rainy Eocene Arctic summers. According to the basin to basin fractionation model of Berger (1970), the Eocene Arctic Ocean probably corresponds to an estuarine type, which includes the Black Sea or the Baltic Sea today. The significantly high abundance of ebridians may reflect the presence of H2S boundary within the euphotic layer based on the extant ebridian ecology of Hermesinum adriaticum with symbiotic algae, which is present in the Black Sea today.

  11. Late middle Eocene epoch of Libya yields earliest known radiation of African anthropoids.

    PubMed

    Jaeger, Jean-Jacques; Beard, K Christopher; Chaimanee, Yaowalak; Salem, Mustafa; Benammi, Mouloud; Hlal, Osama; Coster, Pauline; Bilal, Awad A; Duringer, Philippe; Schuster, Mathieu; Valentin, Xavier; Marandat, Bernard; Marivaux, Laurent; Métais, Eddy; Hammuda, Omar; Brunet, Michel

    2010-10-28

    Reconstructing the early evolutionary history of anthropoid primates is hindered by a lack of consensus on both the timing and biogeography of anthropoid origins. Some prefer an ancient (Cretaceous) origin for anthropoids in Africa or some other Gondwanan landmass, whereas others advocate a more recent (early Cenozoic) origin for anthropoids in Asia, with subsequent dispersal of one or more early anthropoid taxa to Africa. The oldest undoubted African anthropoid primates described so far are three species of the parapithecid Biretia from the late middle Eocene Bir El Ater locality of Algeria and the late Eocene BQ-2 site in the Fayum region of northern Egypt. Here we report the discovery of the oldest known diverse assemblage of African anthropoids from the late middle Eocene Dur At-Talah escarpment in central Libya. The primate assemblage from Dur At-Talah includes diminutive species pertaining to three higher-level anthropoid clades (Afrotarsiidae, Parapithecidae and Oligopithecidae) as well as a small species of the early strepsirhine primate Karanisia. The high taxonomic diversity of anthropoids at Dur At-Talah indicates either a much longer interval of anthropoid evolution in Africa than is currently documented in the fossil record or the nearly synchronous colonization of Africa by multiple anthropoid clades at some time during the middle Eocene epoch. PMID:20981098

  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. 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.

  14. 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.

  15. Eocene plant diversity at Laguna del Hunco and Río Pichileufú, Patagonia, Argentina.

    PubMed

    Wilf, Peter; Johnson, Kirk R; Cúneo, N Rubén; Smith, M Elliot; Singer, Bradley S; Gandolfo, Maria A

    2005-06-01

    The origins of South America's exceptional plant diversity are poorly known from the fossil record. We report on unbiased quantitative collections of fossil floras from Laguna del Hunco (LH) and Río Pichileufú (RP) in Patagonia, Argentina. These sites represent a frost-free humid biome in South American middle latitudes of the globally warm Eocene. At LH, from 4,303 identified specimens, we recognize 186 species of plant organs and 152 species of leaves. Adjusted for sample size, the LH flora is more diverse than comparable Eocene floras known from other continents. The RP flora shares several taxa with LH and appears to be as rich, although sampling is preliminary. The two floras were previously considered coeval. However, (40)Ar/(39)Ar dating of three ash-fall tuff beds in close stratigraphic association with the RP flora indicates an age of 47.46+/-0.05 Ma, 4.5 million years younger than LH, for which one tuff is reanalyzed here as 51.91+/-0.22 Ma. Thus, diverse floral associations in Patagonia evolved by the Eocene, possibly in response to global warming, and were persistent and areally extensive. This suggests extraordinary richness at low latitudes via the latitudinal diversity gradient, corroborated by published palynological data from the Eocene of Colombia. PMID:15937744

  16. 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

  17. Salinity of the Eocene Arctic Ocean from oxygen isotope analysis of fish bone carbonate

    NASA Astrophysics Data System (ADS)

    Waddell, Lindsey M.; Moore, Theodore C.

    2008-03-01

    Stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle Eocene samples (˜55 to ˜45 Ma) recently recovered from the Lomonosov Ridge by Integrated Ocean Drilling Program Expedition 302 (the Arctic Coring Expedition). The δ18O values of the Eocene samples ranged from -6.84‰ to -2.96‰ Vienna Peedee belemnite, with a mean value of -4.89‰, compared to 2.77‰ for a Miocene sample in the overlying section. An average salinity of 21 to 25‰ was calculated for the Eocene Arctic, compared to 35‰ for the Miocene, with lower salinities during the Paleocene Eocene thermal maximum, the Azolla event at ˜48.7 Ma, and a third previously unidentified event at ˜47.6 Ma. At the Azolla event, where the organic carbon content of the sediment reaches a maximum, a positive δ13C excursion was observed, indicating unusually high productivity in the surface waters.

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

    PubMed

    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

    2012-04-01

    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

  19. 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

  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. 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

  2. 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.

  3. 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.

  4. Stable isotope paleoaltimetry of Eocene core complexes in the North American Cordillera

    NASA Astrophysics Data System (ADS)

    Mulch, A.; Teyssier, C.; Cosca, M. A.; Chamberlain, C. P.

    2007-08-01

    The hydrogen isotope composition of Eocene muscovite in mylonitic quartzite from the Kettle and Shuswap metamorphic core complexes (Washington and British Columbia) permits estimates of paleoaltimetry of the North American Cordillera at the onset of post-collisional lithospheric extension. Coupled oxygen, hydrogen, and 40Ar/39Ar isotope data indicate that meteoric water penetrated to significant depths during normal faulting along the Columbia River Detachment bounding both Kettle and Shuswap metamorphic core complexes. Synkinematic muscovite attains δDmuscovite values as low as -135‰ and -157‰, respectively, consistent with δDwater values of -115 ± 5‰ and -135 ± 5‰. In context with stable isotope data from Eocene sedimentary basins of continental North America, these data constrain the isotopic composition of precipitation from which paleoelevation estimates can be made. Stable isotope paleoaltimetry indicates that during detachment formation (49-47 Ma), orogen-parallel variations in topography existed, and mean elevations decreased from ≥4000 m at the latitude of the Shuswap core complex to ≥3000 m in the Kettle core complex. In addition, these data indicate a net decrease in mean surface elevation by ˜1000 m since the Eocene. Our results for the Kettle core complex are consistent with paleoelevation estimates based on fossil floral physiognomy in the Eocene Republic basin (Washington), indicating that high elevations characterized not only the frontal escarpment near the crustal-scale detachment but continued into the Okanogan highlands further west. Collectively, the stable isotope, geochronological, and paleofloral data support tectonic models of high Eocene surface elevations contemporaneous with magmatism and lithospheric extension.

  5. Paleocene-Eocene magnetostratigraphy and climate-driven rock-magnetism from the Belluno Basin (Italy)

    NASA Astrophysics Data System (ADS)

    Muttoni, G.; Dallanave, E.

    2012-12-01

    The magnetostratigraphy and rock-magnetism of the Paleocene-Eocene interval has been studied in the recent years in several Tethyan marine sections of the Belluno Basin of NE Italy (Possagno, Cicogna, South Ardo, Alano). The paleomagnetic results, integrated with calcareous nannofossil biostratigraphy, allowed the recovery of a virtually continuous ~27 Myr-long interval of time spanning from the K/Pg boundary (~65 Ma) at the South Ardo section up to the middle-late Eocene boundary (~38 Ma) at the Alano GSSP candidate, and bracketing some of the most extreme climate conditions of the Cenozoic such the Early Eocene climatic optimum (EECO) and the Paleocene-Eocene thermal maximum (PETM). The rock-magnetic data indicate that the magnetic mineralogy of the sediments generally consists of variable proportions of magnetite-maghemite-hematite, which are iron oxides characterized by different oxidation states and crystal structures. We reconstructed the rock-magnetic variability across the investigated interval, and placed it on a temporal reference frame using a CK95-based age-depth function for comparison with oxygen isotope data from the literature. The rock-magnetic data indicate that relatively warmer climate periods (i.e. the PETM and the early Eocene warming trend leading to EECO) are associated with high contents of detrital hematite relative to magnetite-maghemite, while relatively cooler climates (i.e. the Paleocene) are associated with a relative increase in magnetite-maghemite. We speculate that the increase of detrital hematite observed during warm periods is due to intensified chemical weathering rates of land silicates under warm and humid climates. We therefore show that rock-magnetic properties can be useful proxies to study the efficiency of the silicate weathering negative feedback mechanism to stabilize long-term Earth's surface temperatures.

  6. The silicoflagellates and ebridians from the central Arctic Ocean in the early middle Eocene

    NASA Astrophysics Data System (ADS)

    Onodera, J.; Takahashi, K.

    2007-12-01

    The early middle Eocene sediments from the central Arctic Ocean obtained by IODP Expedition 302 (ACEX) were studied for the siliceous microfossils of silicoflagellates and ebridians in order to establish the biostratigraphy and to decipher the paleoceanographic changes of the upper water column. Seven silicoflagellate taxa of the total of 56 taxa and three ebridian taxa of the total of 30 taxa were previously unknown and they were newly described as new species. Silicoflagellate and ebridian assemblages in lower part of Lithologic Unit 2 are endemic compared to the assemblages of the outside of the Eocene Arctic Ocean. Temporal intervals of the silicoflagellate and ebridian assemblages were categorized to several assemblage groups according to the variation in the assemblage characteristics. Changes in characteristic assemblage is probably due to the habitat modulation governed by the extent of mixing of significantly different water masses between the low salinity waters derived from the Arctic region and relatively high salinity waters supplied from the outside of the Arctic Ocean. The low salinity water in the Eocene Arctic is suggested from the co-occurrence of freshwater and blackish water microfossils. The origin of the freshwater is attributed to the rainfall and river influx during the rainy Eocene Arctic summer. The circulation of the Arctic Ocean in the early middle Eocene probably corresponds to an estuarine type, which includes the Black and the Baltic Seas today. The high abundance of ebridians may reflect the presence of hypoxic waters in or near the euphotic layer based on the extant ebridian ecology of Hermesinum adriaticum with symbiotic algae, which is present in the Black Sea today.

  7. 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

  8. Multiple States in the Vegetation-Atmosphere System during the Early Eocene

    NASA Astrophysics Data System (ADS)

    Port, U.; Claussen, M.

    2014-12-01

    Model simulations suggest that different initial conditions can lead to multiple stable vegetation-atmosphere states in the present-day Sahara. Here, we explore the stability of the vegetation-atmosphere system in the warm, nearly ice-free early Eocene climate. Using the MPI-ESM, we simulate the early Eocene vegetation starting from two different states: Continents are either completely covered by forest or completely barren, devoid of any vegetation. The soil albedo is similar to vegetation albedo. Hence, the albedo effect of vegetation is negligible. Without the albedo effect, the Charney effect which is suggested to cause multiple stable vegetation states in the present-day Sahara is absent. In our simulations, the hydrological effect of vegetation plays the major role. We perform the same simulations with preindustrial conditions to compare the stability of the vegetation-atmosphere system in both climate states. A desert evolves in Central Asia in both early Eocene simulations. This Asian desert is larger when the simulation starts from bare soil instead forest. Bare soil causes a dry climate in Central Asia in the beginning of the simulation. In the dry climate, vegetation does not establish. Forest enhances evaporation relative to bare soil leading to a stronger Asian monsoon and higher precipitation rates. The increased precipitation sustains plant growth and a smaller Asian desert evolves than in the simulation started from bare soil. Moreover, the stronger Asian monsoon affects global climate. Therefore, the two vegetation states in Central Asia accompany two globally different vegetation-atmosphere states. In the preindustrial climate, the Sahara is larger when the initial vegetation is bare soil instead of forest. The same hydrological effect causes the multiple vegetation states the Sahara as in the early Eocene Asian desert. However, the multiple stable vegetation states in the Sahara do not affect the global climate. This result emphasises that the

  9. 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

  10. 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.

  11. 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. PMID:24043872

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. Early Eocene rodents (Mammalia) from the Subathu Formation of type area (Himachal Pradesh), NW sub-Himalaya, India: Palaeobiogeographic implications

    NASA Astrophysics Data System (ADS)

    Gupta, Smita; Kumar, Kishor

    2015-08-01

    Based on isolated upper cheek teeth, two new early Eocene rodents (Subathumys solanorius gen. et sp. nov. and Subathumys globulus gen. et sp. nov.) and three others (Birbalomys cf. sondaari, Birbalomys sp., cf. Chapattimys sp.) are recorded from the lower-middle part of the Subathu Formation of the type area in Himachal Pradesh, northwestern sub-Himalaya (India). The new rodents exhibit morphological features most similar to the unified ctenodactyloid family Chapattimyidae (including Yuomyidae), which is also represented in the assemblage from the upper part (middle Eocene) of the Subathu Formation. The associated lower cheek teeth are provisionally described as three indeterminate chapattimyid taxa. The new Subathu rodents are somewhat younger than the previously documented early Eocene assemblages from the Indian subcontinent, and are chronologically intermediate between the early Eocene ailuravines from Gujarat in the western peninsular India and the middle Eocene chapattimyids from northwestern India and Pakistan. They suggest that chapattimyids originated in the sub-Himalayan region during the Ypresian, which is earlier than previously believed. The absence of ailuravines in this as well as younger rodent assemblages from the subcontinent seems to suggest that ailuravines (Ischyromyidae), within a relatively short time after their appearance in the peninsular India in the early Eocene, may have been replaced by the indigenous chapattimyids. The co-occurrence in the early Eocene Subathu assemblage of three or more chapattimyids indicates their early radiation and dominance during the early and middle Eocene. This record of rodents opens the possibility of recovery of other small mammal remains in older levels of the Subathu Formation, which will be important for understanding linkage with early Eocene faunas from peninsular India, Europe and North America.

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

    USGS Publications Warehouse

    Seal, R.R., II; 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

  18. 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.

  19. 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

  20. Insights into the early Eocene hydrological cycle from an ensemble of atmosphere-ocean GCM simulations

    NASA Astrophysics Data System (ADS)

    Carmichael, M. J.; Lunt, D. J.; Huber, M.; Heinemann, M.; Kiehl, J.; LeGrande, A.; Loptson, C. A.; Roberts, C. D.; Sagoo, N.; Shields, C.; Valdes, P. J.; Winguth, A.; Winguth, C.; Pancost, R. D.

    2015-07-01

    Recent studies, utilising a range of proxies, indicate that a significant perturbation to global hydrology occurred at the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma). An enhanced hydrological cycle for the warm early Eocene is also suggested to have played a key role in maintaining high-latitude warmth during this interval. However, comparisons of proxy data to General Circulation Model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised, despite significant differences in simulated surface temperatures. In this work, we undertake an intercomparison of GCM-derived precipitation and P-E distributions within the EoMIP ensemble (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 preindustrial. This is primarily due to elevated atmospheric paleo-CO2, although the effects of differences in paleogeography/ice sheets are also of importance 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 a number of GCMs underestimate precipitation rates at high latitudes. Models which warm these regions, either via elevated CO2 or by varying

  1. Insights into the early Eocene hydrological cycle from an ensemble of atmosphere-ocean GCM simulations

    NASA Astrophysics Data System (ADS)

    Carmichael, Matthew; Lunt, Daniel; Pancost, Richard

    2015-04-01

    Recent studies utilising a range of geochemical proxies have indicated that a significant perturbation to global hydrology occurred at the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma). An enhanced hydrological cycle for the warm early Eocene is also suggested to have played a key role in maintaining high-latitude warmth during this interval. Comparisons of proxy data to General Circulation Model (GCM) simulated hydrology have not widely been made however, and inter-model variability remains poorly characterised despite significant differences in simulated surface temperatures. In this work, we address this by undertaking an intercomparison of GCM-derived precipitation distributions within the EoMIP ensemble (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 is simulated for all Eocene simulations relative to preindustrial. This is primarily due to elevated atmospheric paleo-CO2, although the effects of differences in paleogeography/ice sheets are also of importance in some models. For a given CO2 level, globally-averaged precipitation rates vary widely between models, largely as a result of different climate sensitivities (dT/dCO2) and differing parameterisation schemes. Despite this, models with similar global precipitation sensitivities (dP/dT) display different regional responses for a given temperature change. Regions which are particularly model sensitive include the South Pacific, tropical Africa and the Tethys and may represent targets for future proxy acquisition. A comparison of leaf-fossil-derived precipitation estimates with GCM data illustrates that models tend to unanimously underestimate early Eocene precipitation rates at high latitudes. Models which warm these regions via elevated CO2 or by utilising alternative parameterisations are most

  2. 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

  3. 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.

  4. Evidence for reactivation of Eocene joints and pre-Eocene foliation planes in the Okanagan core-complex, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Eyal, Yehuda; Osadetz, Kirk G.; Feinstein, Shimon

    2006-11-01

    We studied the brittle deformational history of the Okanagan metamorphic core complex, and its hanging wall carapace, in the Canadian Cordillera, in southern British Columbia by an extensive structural investigation at mesoscopic scale. The deformational history reveals that the transition from ductile to brittle deformation occurred during the early-middle Eocene and was associated with cooling due to tectonic and/or extensive erosional unroofing of the Okanagan portion of the Sushwap metamorphic core complex. Our study is based on mesostructures because in this region macro-structures are rarely exposed, although their existence can be deduced from field relationships. Measured fault systems that are either perpendicular to bedding, or which were sub-vertical to inferred paleohorizontal and with very small dispersion of strike are interpreted as faulted joints, i.e. joints that were reactivated by subsequent shear due to a relative change in stress orientation. The faulted joints are similar to observed open-mode I fracture system that exhibit no evidence for subsequent reactivation. In this study we suggest that fault sets characterized by consistent attitude with a very small dispersion can be interpreted as faulted joints using only their stereographic projection pattern relative to the inferred paleohorizontal. The first brittle deformation was a pervasive open-mode fracturing in the hanging wall carapace of both Eocene sedimentary and volcanic rocks and Eocene and older igneous rocks characterized by a N-S trend, with a very small dispersion, which formed either perpendicular to bedding or was sub-vertical with respect to the inferred paleohorizontal. These fractures are of similar trend to a middle Eocene dyke swarm in part of the study area and beyond. The Okanagan core complex metamorphic rocks exhibit brittle fractures that are interpreted as metamorphic foliation planes which were reactivated as faults in response to the same E-W extension recorded by

  5. 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.

  6. 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.

    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.

  7. 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.

  8. 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.

  9. Orbital chronology of Early Eocene hyperthermals from the Contessa Road section, central Italy

    NASA Astrophysics Data System (ADS)

    Galeotti, Simone; Krishnan, Srinath; Pagani, Mark; Lanci, Luca; Gaudio, Alberto; Zachos, James C.; Monechi, Simonetta; Morelli, Guia; Lourens, Lucas

    2010-02-01

    High-resolution geochemical analyses of the Lower Eocene Contessa Road section (Italy) reveal orbitally controlled fluctuations in the percent concentration of calcium carbonate (wt.% CaCO 3) that include the ETM2 (Elmo) and ETM3 ("X") hyperthermal events. Patterns of increased dissolution, negative carbon isotope excursions, and warmer global climates are intimately linked to maxima in insolation, through the global carbon cycle. Extraction of short- and long-eccentricity orbital periodicities of the wt.% CaCO 3 record provides a relative cyclochronology for the interval ranging from ˜ 52 to ˜ 55.5 Ma. The Contessa Road section is easily accessible and offers a continuous integrated stratigraphic record (stable isotopes, standard calcareous plankton biostratigraphy, magnetostratigraphy, and cyclostratigraphy), thus providing a potential type succession for the study of Early Eocene hyperthermals.

  10. 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.

  11. 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.

  12. 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.

  13. Species diversity and postcranial anatomy of eocene primates from Shanghuang, China.

    PubMed

    Gebo, Daniel L; Dagosto, Marian; Ni, Xijun; Beard, K Christopher

    2012-11-01

    The middle Eocene Shanghuang fissure-fillings, located in southern Jiangsu Province in China near the coastal city of Shanghai (Fig. 1), contain a remarkably diverse array of fossil primates that provide a unique window into the complex role played by Asia during early primate evolution.1 Compared to contemporaneous localities in North America or Europe, the ancient primate community sampled at the Shanghuang fissure-fillings is unique in several ways. Although Shanghuang has some typical Eocene primates (Omomyidae and Adapoidea), it also contains the earliest known members of the Tarsiidae and Anthropoidea (Fig. 2), and some new taxa that are not as yet known from elsewhere. It exhibits a large number of primate species, at least 18, most of which are very small (15-500 g), including some of the smallest primates that have ever been recovered. PMID:23280920

  14. 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.

  15. 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. PMID:25295875

  16. Bizarre tubercles on the vertebrae of Eocene fossil birds indicate an avian disease without modern counterpart

    NASA Astrophysics Data System (ADS)

    Mayr, Gerald

    2007-08-01

    Remains of fossil birds with numerous bony tubercles on the cervical vertebrae are reported from the Middle Eocene of Messel in Germany and the Late Eocene of the Quercy fissure fillings in France. These structures, which are unknown from extant birds and other vertebrates, were previously described for an avian skeleton from Messel but considered a singular feature of this specimen. The new fossils are from a different species of uncertain phylogenetic affinities and show that tuberculated vertebrae have a wider taxonomic, temporal, and geographic distribution. In contrast to previous assumptions, they are no ontogenetic feature and arise from the vertebral surface. It is concluded that they are most likely of pathologic origin and the first record of a Paleogene avian disease. Their regular and symmetrical arrangement over most of the external vertebral surface indicates a systemic disorder caused by factors that do not affect extant birds, such as especially high-dosed phytohormones or extinct pathogens.

  17. 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

  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. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. The case for dynamic subsidence of the United States east coast since the Eocene (Invited)

    NASA Astrophysics Data System (ADS)

    Spasojevic, S.; Liu, L.; Gurnis, M.

    2009-12-01

    We developed inverse mantle convection models to investigate dynamic effects of Farallon slab subduction in North America (NAM) from Late Cretaceous to the present. The models are constrained by seismic tomography, plate motions and stratigraphic data (reconstructed paleo shorelines, sediment isopachs and borehole tectonic subsidence), and past mantle structure is recovered through the backward integration of the adjoint equation. During Late Cretaceous, the Farallon slab is flat to shallow lying under the western NAM, creating long-wavelength dynamic topography low and resulting in widespread flooding in the Western Interior Seaway. As the Farallon slab continues sinking into the lower mantle during the Cenozoic, NAM moves westward, while dynamic topography low moves to the east. Consequently, western NAM experiences dynamic uplift, while eastern NAM experiences dynamic subsidence. For the east coast of the United States, we investigate dynamic subsidence by analyzing results of inverse geodynamic models, elevation of Eocene and Miocene paleoshorelines, and discrepancies between regional (New Jersey) and global sea-level estimates. All inverse models we analyzed predict continuous subsidence of the east coast, with total magnitudes on the order of hundreds of meters since the Eocene. Present-day elevation of reconstructed Eocene and Miocene paleo shorelines is lower than the sea level at those times, suggesting overall subsidence, with a maximum magnitude of up to 200 m since the end of Eocene. The dynamic subsidence has been occurring during the overall fall of sea level, with the eustatic signal potentially being larger than the dynamic signal, resulting in the absence of observed land subsidence. This dynamic subsidence can potentially explain the difference between the regional sea level reconstructed for New Jersey coastal margin and other published sea-level curves. Improvements of seismic data quantity and quality with USArray should result in a better

  5. 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.

  6. 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)

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. State of the Hydrological Cycle during the Eocene: Model-Data Comparison

    NASA Astrophysics Data System (ADS)

    Krishnan, S.; Huber, M.; Pagani, M.

    2011-12-01

    The early Eocene was much warmer compared to modern conditions and represents the warmest time interval of the Cenozoic. In addition to determining the character of regional temperature change during globally warm conditions, a clear understanding of how the hydrological cycle was impacted is a fundamental pursuit. The isotopic composition of precipitation is a fundamental signal that relates to the character of the hydrologic system - dependent on distance of transport, number of rainout events, amount of rainfall, and evapotranspiration. Terrestrial biomarkers, such as higher plant n-alkanes can be used to track the hydrogen isotopic composition (δD) of precipitation and have been applied to interpret hydrological changes during the Paleocene Eocene Thermal Maximum. That work concluded that rapid, global warming was associated with increased rainout at the poles with the probability of relative drying across the mid-latitudes. Several other n-alkane δD records for the early Eocene have already been generated including Cicogna (Italy), MAR-2X (Venezuela), and Tawanui (New Zealand). In this study, we present results from the water isotope enabled version of National Center for Atmospheric Research (NCAR) Community Atmospheric Model version 3, the atmospheric component of Community Climate System Model (CCSM) with Eocene boundary conditions, two different pCO2 levels (2240 and 4480 ppm). Modeling results are evaluated and compared with existing n-alkane δD records. Preliminary results suggest that the model qualitatively reproduces the latitudinal trend observed in the data, with the most D-enriched values observed at the tropics and depletion towards the poles. However, the model predicts values that appear more D-enriched than the proxy records, by up to 40 per mil in the high latitudes. Reasons for this discrepancy along with uncertainties in the proxy records and modeling results are discussed. These results will be useful for validating models and

  12. 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

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Going subsurface: Reconciling proxy and model estimates of early Eocene marine temperatures

    NASA Astrophysics Data System (ADS)

    Ho, Sze Ling; Laepple, Thomas

    2015-04-01

    The early Eocene (50-55 million years ago) is a time interval characterized by elevated surface temperatures and atmospheric CO2, and a flatter than-present latitudinal surface temperature gradient. The multi-proxy derived flat temperature gradient has been a challenging feature to reproduce in model simulations, especially the subtropical warmth inferred from the archaeal lipid-based palaeothermometry, namely TEX86H, for both poles. Although widely applied on marine and lacustrine sediments, archaeal lipid paleothermometry is not without uncertainties, especially in the water depth origin of the lipids. Here we take an alternative approach to constrain this uncertainty, by comparing the temperature variability inferred from multiple proxies over a broad range of time-scales (millennial to multi-million years). Our analysis shows that the widely used TEX86H overestimates the amplitude of past temperature changes and suggests that the archaeal temperature signals originate from greater depths. A recalibration of the TEX86H thermometry, using the independent estimates of past temperature variability as a constraint, strongly improves the model-proxy comparison of Eocene warming at water depths corresponding to the calibration. This finding implies that the subtropical Eocene warmth inferred from TEX86H for both poles, which is not reproducible in climate models, are likely an artefact due to the fundamental bias in the applied calibration. This study emphasizes that learning from model-data comparisons needs an in-depth understanding of the proxy as well as the model uncertainty.

  2. 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

  3. Climate deterioration on the Asian continent after the Middle Eocene Climatic Optimum (MECO)

    NASA Astrophysics Data System (ADS)

    Dupont-Nivet, G.; Bosboom, R. E.; Hemmo, A.; Hoorn, C.; van den Berg, B.; Guo, Z.

    2012-12-01

    Cenozoic global climate cooling leading from greenhouse to icehouse conditions, occurred mainly during a peculiar interval referred to as the 'doubthouse' from the early Eocene (~50 Ma) until permanent Antarctic ice-sheet formation at the ~34 Ma Eocene-Oligocene transitions (EOT). Understanding this critical interval characterized by periodic polar ice-sheet formations as well as short-lived warming events (hyperthermals), of which the Middle Eocene Climatic Optimum (MECO) is most noticeable, requires high resolution records that are being gathered in marine basins but are still lacking in the terrestrial realm. Here, we analyze the lithofacies and palynological changes within four lacustrine sedimentary sections from the central Asian continent (Xining Basin, NW China), precisely dated with magnetostratigraphy between ~43 and ~36 Ma. We show that a permanent regional aridification and a shift to obliquity-dominated cyclicity is, within uncertainty, concomitant with peak warming of the MECO records in the marine realm at ~39.3 Ma (basal part of chron C18n.2n). We interpret our results to indicate that incipient polar ice sheet formation in association with higher climate variability started directly following the MECO, marking the onset of a major cooling step leading to the EOT. The permanent - rather than transient - expression of the MECO in Asian terrestrial paleoenvironments suggests this warming event marks the crossing of a critical threshold for atmospheric conditions in their course from greenhouse to icehouse conditions.

  4. 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

  5. Studies in Neotropical paleobotany. XIV. A palynoflora from the Middle Eocene Saramaguacan Formation of Cuba.

    PubMed

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

    2000-10-01

    An assemblage of 46 fossil pollen and spore types is described from a core drilled through the middle Eocene Saramaguacán Formation, Camagüey 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 paleoclimate 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 Saramaguacán 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. PMID:11034928

  6. 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

  7. 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

  8. 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).

  9. 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.

  10. 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.

  11. An Early Middle Eocene Orbital Scale Benthic Isotope Record From IODP Site 1408, Newfoundland Rise

    NASA Astrophysics Data System (ADS)

    Wu, F.; Lawler, N.; Penman, D. E.; Zachos, J. C.; Kirtland Turner, S.; Norris, R. D.; Wilson, P. A.; Hull, P. M.

    2014-12-01

    The long-term Paleogene global cooling trend and eventual glaciation of Antarctica has been attributed to a reduction in greenhouse gas levels as well as changes in the configuration of high-latitude oceanic gateways. This major trend in climate and forcing is known to have initiated in the early middle Eocene, between 44-49 Mya, yet our understanding of the detailed evolution of climate and oceanic circulation and carbon chemistry of this critical interval has been limited for lack of high-resolution proxy climate records. Integrated Ocean Drilling Program (IODP) Expedition 342, designed in part to address this deficiency, successfully recovered highly expanded sequences of middle Eocene sediment from multiple sites in the western North Atlantic, with several sites characterized by high sedimentation rates (>2.8 cm/kyr) and pronounced lithologic cycles. Using samples from cores recovered at one of these sites, 1408, located on Southeast Newfoundland Ridge, we are reconstructing the first orbital-scale deep sea δ18O and δ13C records spanning a ~1.6 million year interval (~Chron 20r) of the middle Eocene. Based on analyses of benthic foraminifer N. truempyi, our preliminary data reveal distinct high-frequency cycles with periods matching those of the orbital cycles, particularly precession and obliquity. Cross spectral analysis of δ18O, δ13C and lithologic records reveal a high degree of coherency, implying a high sensitivity in local sediment fluxes and bottom water chemistry (and circulation) to orbital forcing. Also, given the location and depth (~2600 m at 50 Ma), Site 1408 constrains the end-member composition of northern component bathyal bottom waters so that comparison with benthic isotope records from the south Atlantic and other basins can be used to assess ocean circulation patterns in the mid-Eocene. In general, bottom water temperatures appear to have been warmer, and DIC δ13C lower than observed elsewhere. Thus, our preliminary results are

  12. 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

  13. 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

  14. 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

  15. 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.

  16. Rethinking Controls on the Long-Term Cenozoic Carbonate Compensation Depth: Case Studies across Late Paleocene - Early Eocene Warming and Late Eocene - Early Oligocene Cooling

    NASA Astrophysics Data System (ADS)

    Greene, S. E.; Ridgwell, A. J.; Schmidt, D. N.; Kirtland Turner, S.; Paelike, H.; Thomas, E.

    2014-12-01

    The carbonate compensation depth (CCD) is the depth below which negligible calcium carbonate is preserved in marine sediments. The long-term position of the CCD is often considered to be a powerful constraint on palaeoclimate and atmospheric CO2 concentration due to the requirement that carbonate burial balance riverine weathering over long timescales. The requirement that weathering and burial be in balance is clear, but it is less certain that burial compensates for changes in weathering via shoaling or deepening of the CCD. Because most carbonate burial occurs well above the CCD , changes in weathering fluxes may be primarily accommodated by increasing or decreasing carbonate burial at shallower depths, i.e., at or near the lysocline, the depth range over which carbonate dissolution markedly increases. Indeed, recent earth system modelling studies have suggested that the position of the CCD is relatively insensitive to changes in atmospheric pCO2. Additionally, studies have questioned the nature and strength of the relationship between the CCD, carbonate saturation state in the water column, and lysocline. To test the relationship between palaeoclimate and the location of the CCD, we reconstructed the global, long-term CCD behaviour across major Cenozoic climate transitions: the late Paleocene - early Eocene long-term warming trend (study interval ~58 to 49 Ma) and the late Eocene - early Oligocene cooling and glaciation (study interval ~38 to 27 Ma). We use Earth system modelling (GENIE) to explore the links between atmospheric pCO2 and the CCD, isolating and teasing apart the roles of total dissolved inorganic carbon, temperature, circulation, and productivity in determining the CCD.

  17. 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.

  18. 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.

  19. A biomarker isotope record of hydrologic change in NE Spain from the late Eocene to early Oligocene

    NASA Astrophysics Data System (ADS)

    Patros, K.; Hren, M. T.

    2014-12-01

    The Eocene-Oligocene transition (EOT) (34-33.5 Ma) is one of the most dramatic climatic changes in the Cenozoic and represents a shift from global "hothouse" to "icehouse" conditions. Climatic and hydrologic data from across the globe indicate a high degree of heterogeneity in the terrestrial climatic response to this global cooling, with the largest changes observed at high latitudes. Recent data from northern Europe shows cooling across this interval associated with major faunal turnover. However, paleosol data from northeastern Spain suggests only modest changes to temperature and precipitation associated with this transition. We measured the hydrogen isotopic composition of higher plant-derived normal alkanes in Eocene to Oligocene sediments of Northeastern Spain to quantify changes to climate and isotope hydrology across this transition. Hydrogen isotopes of plant waxes provide a record of isotopes of precipitation and/or factors that influence stomatal regulation. Our data show a small increase in the average chain length of higher plant waxes across the EOT cooling event, which may reflect changes in water availability or ecosystem type. Hydrogen isotopes of higher plant waxes show a small positive shift in δD from the late Eocene to early Oligocene, but high-frequency variability prior to and after the Eocene-Oligocene transition. In total, when coupled with other paleoclimate proxy data, these suggest minimal changes to the hydrologic cycle in NE Spain from the late Eocene to early Oligocene.

  20. 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.

  1. 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

  2. Declining moisture availability in late Eocene Antarctica as deduced from Nothofagus sporopollenin δ13C

    NASA Astrophysics Data System (ADS)

    Griener, K. W.; Nelson, D. M.; Warny, S.

    2012-12-01

    Palynological data demonstrate that significant changes in vegetation and climate occurred at the Eocene-Oligocene (E-O) Boundary on the Antarctic Peninsula. These changes include decreases in terrestrial palynomorph abundance and diversity as well as dinoflagellate assemblages that reflect colder sea surface temperatures and increased glaciation (Warny and Askin, 2011). Understanding the factors controlling these changes in climate and vegetation is a topic of great interest. One area of remaining uncertainty is how the hydrologic regime varied during Antarctica's shift from greenhouse to icehouse conditions. For example, estimates of Antarctic precipitation from around the E-O boundary based on plant leaf margins (e.g. Francis et al., 2008), clay mineralogy (e.g. Christian and Kennett, 1997), and models (Thorn and DeConto 2006) are vastly different. We used a moving-wire device interfaced with an isotope-ratio mass spectrometer (Sessions et al., 2005; Nelson et al., 2008) to analyze δ13C of small quantities of Nothofagus sporopollenin extracted from Antarctic Eocene SHALDRIL cores from ~35.9 Mya, just prior to the E-O Boundary (Bohaty et al., 2011). We also analyzed δ13C of modern Nothofagus sporopollenin from herbaria specimens and related these results to historical climate data. Our modern data show that carbon isotope discrimination (Δ) of Nothofagus sporopollenin is positively correlated with mean annual and growing-season precipitation, consistent with prior studies that demonstrate a strong relationship between Δ and water availability in C3 plants. Eocene Nothofagus Δ values progressively decreased through time, implying a decline in moisture availability. There is a close correlation between Nothofagus palynomorph abundance (Warny and Askin, 2011) and Δ, indicating that Nothofagus abundance declined in response to decreasing moisture availability. We consider changes in sea surface temperatures as well as increased glaciation as possible causes

  3. 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.

  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. 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.

  6. Late Cretaceous and Eocene volcanism in the southern Line Islands and implications for hotspot theory

    NASA Astrophysics Data System (ADS)

    Haggerty, Janet A.; Schlanger, Seymour O.; Premoli Silva, Isabella

    1982-08-01

    Rocks dredged from a seamount 100 km northwest of Caroline Island, at the southern end of the Line Islands chain, contain Late Cretaceous fossils associated with volcanic debris. This association is evidence for the existence of a reef-bearing volcanic edifice with a minimum age of Late Cretaceous, 70 to 75 m.y., near Caroline Island. With the discovery of this seamount, the known occurrences of Late Cretaceous, reef-capped, volcanic edifices now extend a distance of 2,500 km, from Deep Sea Drilling Project Site 165 to 100 km northwest of Caroline Island. The apparent synchroneity of Late Cretaceous volcanism over this distance argues against the proposition that a single hotspot of the Hawaiian-Emperor type produced the Line Islands chain. Biochronologic data from the Line Islands indicate that the chain is not the temporal equivalent of the Emperor chain. Volcanic edifices of Cretaceous age are now known to extend from the Line Islands through the Mid-Pacific Mountains to the Marshall Islands and the western margin of the Pacific plate from Japan to the Marianas. A volcanic event occurred in the southern Line Islands during middle Eocene time; Eocene sediments were engulfed and altered by a volcanic eruption. The occurrence of both Cretaceous and Eocene volcanism in the southern Line Islands indicates that the history of the Line Islands is similar to that of the Marshall Islands. *Present addresses: (Haggerty) Department of Geosciences, University of Tulsa, Tulsa, Oklahoma 74104; (Schlanger) Department of Geological Sciences, Northwestern University, Evanston, Illinois 60201

  7. 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.

  8. The Eocene Arctic Azolla bloom: environmental conditions, productivity and carbon drawdown.

    PubMed

    Speelman, E N; Van Kempen, M M L; Barke, J; Brinkhuis, H; Reichart, G J; Smolders, A J P; Roelofs, J G M; Sangiorgi, F; de Leeuw, J W; Lotter, A F; Sinninghe Damsté, J S

    2009-03-01

    Enormous quantities of the free-floating freshwater fern Azolla grew and reproduced in situ in the Arctic Ocean during the middle Eocene, as was demonstrated by microscopic analysis of microlaminated sediments recovered from the Lomonosov Ridge during Integrated Ocean Drilling Program (IODP) Expedition 302. The timing of the Azolla phase (approximately 48.5 Ma) coincides with the earliest signs of onset of the transition from a greenhouse towards the modern icehouse Earth. The sustained growth of Azolla, currently ranking among the fastest growing plants on Earth, in a major anoxic oceanic basin may have contributed to decreasing atmospheric pCO2 levels via burial of Azolla-derived organic matter. The consequences of these enormous Azolla blooms for regional and global nutrient and carbon cycles are still largely unknown. Cultivation experiments have been set up to investigate the influence of elevated pCO2 on Azolla growth, showing a marked increase in Azolla productivity under elevated (760 and 1910 ppm) pCO2 conditions. The combined results of organic carbon, sulphur, nitrogen content and 15N and 13C measurements of sediments from the Azolla interval illustrate the potential contribution of nitrogen fixation in a euxinic stratified Eocene Arctic. Flux calculations were used to quantitatively reconstruct the potential storage of carbon (0.9-3.5 10(18) gC) in the Arctic during the Azolla interval. It is estimated that storing 0.9 10(18) to 3.5 10(18) g carbon would result in a 55 to 470 ppm drawdown of pCO2 under Eocene conditions, indicating that the Arctic Azolla blooms may have had a significant effect on global atmospheric pCO2 levels through enhanced burial of organic matter. PMID:19323694

  9. 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.

  10. 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.

  11. Aridification in continental Asia after the Middle Eocene Climatic Optimum (MECO)

    NASA Astrophysics Data System (ADS)

    Bosboom, Roderic E.; Abels, Hemmo A.; Hoorn, Carina; van den Berg, Bas C. J.; Guo, ZhaoJie; Dupont-Nivet, Guillaume

    2014-03-01

    Global climate cooling from greenhouse to icehouse conditions occurred across an enigmatic transitional interval during the Eocene epoch characterized by incipient polar ice-sheet formation as well as short-lived warming events, of which the Middle Eocene Climatic Optimum (MECO) is most noticeable. Understanding this critical period requires high-resolution records that are being gathered in marine basins, but are still lacking in the terrestrial realm. Here, we provide a precisely-dated terrestrial record crossing the MECO time interval from the Xining Basin (NW China). We document a rapid aridification step and the onset of obliquity-dominated climate cyclicity indicated by lithofacies and pollen records dated at 40.0 Ma at the base of magnetochron C18n.2n. This shift is concomitant - within error - with the MECO peak warming in Ocean Drilling Program Site 1258 for which we reassessed the magnetostratigraphic age at 40.0 Ma (also at base of magnetochron C18n.2n). The rapidity of the shift observed in the Xining Basin and the region-wide aridification and monsoonal intensification reported around 40 Ma suggests Asian paleoenvironments were responding to global climate changes associated with the MECO. However, the Xining records show only the permanent shift but not the transient peak warming observed in marine MECO records. We thus relate this permanent aridification to occur during the post-MECO cooling. We propose the mechanisms linking global climate to Asian paleoenvironments may be eustatic fluctuations driving the stepwise retreat of the proto-Paratethys epicontinental sea or simply global cooling reducing moisture supply to the continental interior. In any case, Eocene global climate cooling from greenhouse to icehouse conditions seem to have played a primary role in shaping Asian paleoenvironments.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. Palaeoclimate reconstruction within the upper Eocene in central Germany using fossil plants

    NASA Astrophysics Data System (ADS)

    Moraweck, Karolin; Kunzmann, Lutz; Uhl, Dieter; Kleber, Arno

    2013-04-01

    The Eocene has been commonly called "The world`s last greenhouse period" covering the Paleocene-Eocene Thermal Maximum (PETM) as well as the Eocene-Oligocene turnover. In the mid-latitudes of Europe this turnover was characterized by pronounced climatic changes from subtropical towards temperate conditions that were accompanied by significant vegetational changes on land. Fossil plants are regarded as excellent palaeoenvironmental proxies, because leaf physiognomy often reflects climate conditions. The study site, the Paleogene Weißelster basin in central Germany, including fluvial, estuarine and lacustrine deposits, provides several excellently preserved megafloras for reconstructions of terrestrial palaeoclimate. For our case study we used material from different stratigraphic horizons within the late Eocene Zeitz megafloral assemblage recovered from the open-cast mines of Profen and Schleenhain. These horizons cover a time interval of ca. 3 Ma. The Zeitz megafloral assemblage ("Florenkomplex") was characterized by mainly evergreen, notophyllous vegetation, consisting of warm-temperate to subtropical elements. Tropical species are present but very rare. To infer the regional climatic conditions and putative climate changes from these fossil plants we compare proxy data obtained by the application of standard methods for quantitative reconstruction of palaeoclimate data: the coexistence approach (CA), leaf margin analysis (LMA) and Climate Leaf Analysis Multivariate Program (CLAMP).Before the CA was applied to the material the list of putative nearest living relative species (NLR) was carefully revisited and partly revised. In case of the LMA approach information of so-called "silent taxa" (fossil species preserved by diaspores, leaf margin state is inferred from NLR data) were partly included in the data set. The four floras from the Zeitz megafloral assemblage show slightly different floral compositions caused by various taphonomic processes. An aim of the

  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. Asian Winter Monsoons in the Eocene: Evidence from the Aeolian Dust Series of the Xining Basin

    NASA Astrophysics Data System (ADS)

    Licht, A.; Adriens, R.; Pullen, A. T.; Kapp, P. A.; Abels, H.; van Cappelle, M.; Vandenberghe, J.; Dupont Nivet, G.

    2014-12-01

    The aeolian dust deposits of the Chinese Loess Plateau are attributed to spring and winter monsoonal storms sweeping clastic material from the deserts of the Asian interior into central China and are reported to begin 25-22 million years (Myr) ago. The beginning of aeolian dust sedimentation has been attributed to the onset of central Asia desertification and winter monsoonal circulation, and are commonly linked to development of high topographic relief associated with the Tibetan-Himalayan orogenic system. However, recent papers suggest that the core of the Tibetan Plateau may have reached significant elevation since the earliest phases of the India-Asia collision 55 Myr ago. Here, we extend the sedimentary record of the Chinese Loess Plateau at its western margin to include the late Eocene - late Oligocene deposits of the Xining Basin, which were deposited between 41 and 25 Myr ago based on detailed magnetostratigraphy. The particle size, shape, and surface microtexture of quartz grains in these deposits display textures indicative of prolonged aeolian transport; grain-size distributions show a bimodal distribution similar to Miocene through Quaternary deposits of the Chinese Loess Plateau. The clay mineralogy of the finer fraction and U/Pb zircon ages of the coarser fraction from Xining Loess sediments sampled along three sections spanning the whole studied interval are also similar to those observed in Quaternary and Neogene aeolian deposits of the Chinese Loess Plateau and thus suggest similar sources located in central China. However, slight differences in Eocene U/Pb zircon ages, such as the lack of Cenozoic ages or the scarcity of zircons older than 2000 Myr, suggest that the Tibetan Plateau may have contributed little to the aeolian dust deposition, in favor of sources located further north and west (Kunlun and Tian Shan Ranges). The Xining deposits are thus the first direct evidence that winter monsoonal winds were active 15 Myr earlier than previously

  3. 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

  4. 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.

  5. 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

  6. 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

  7. Eonandeva gen. nov., a new distinctive genus from Eocene Baltic amber (Diptera: Chironomidae).

    PubMed

    Zakrzewska, Marta; Giłka, Wojciech

    2015-01-01

    A new fossil genus, Eonandeva gen. nov., with two new species: E. helva sp. nov. (type for the genus) and E. latistyla sp. nov., is described from Eocene Baltic amber (~45-40 Ma). Adult males of both new species show the wing venation pattern, shape and chaetotaxy typical for the tribe Tanytarsini. The characters defined as prior apomorphies for the new genus--the gonostylus with a subapical flattened lobe and the stout, strongly elongated superior volsella--separate Eonandeva from the closely related extant genus Nandeva Wiedenbrug, Reiss et Fittkau, 1998. PMID:26624727

  8. 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

  9. Palaeo-altimetry of the late Eocene to Miocene Lunpola basin, central Tibet.

    PubMed

    Rowley, David B; Currie, Brian S

    2006-02-01

    The elevation history of the Tibetan plateau provides direct insight into the tectonic processes associated with continent-continent collisions. Here we present oxygen-isotope-based estimates of the palaeo-altimetry of late Eocene and younger deposits of the Lunpola basin in the centre of the plateau, which indicate that the surface of Tibet has been at an elevation of more than 4 kilometres for at least the past 35 million years. We conclude that crustal, but not mantle, thickening models, combined with plate-kinematic solutions of India-Asia convergence, are compatible with palaeo-elevation estimates across the Tibetan plateau. PMID:16467830

  10. An exceptionally well-preserved Eocene dolichopodid fly eye: function and evolutionary significance

    PubMed Central

    Tanaka, Gengo; Parker, Andrew R.; Siveter, David J.; Maeda, Haruyoshi; Furutani, Masumi

    2008-01-01

    The exceptionally preserved eyes of an Eocene dolichopodid fly contained in Baltic amber show remarkable detail, including features at micrometre and submicrometre levels. Based on this material, we establish that it is likely that the neural superposition compound eye existed as far back as 45 Ma. The ommatidia have an open rhabdom with a trapezoidal arrangement of seven rhabdomeres. Such a structure is uniquely characteristic of the neural superposition compound eye of present-day flies. Optical analysis reveals that the fossil eyes had a sophisticated and efficient optical system. PMID:19129103

  11. Orbital forced sea level fluctuations during the Middle Eocene (ODP site 1172, East Tasman Plateau)

    NASA Astrophysics Data System (ADS)

    Warnaar, J.; Stickley, C.; Jovane, L.; Roehl, U.; Brinkhuis, H.; Visscher, H.

    2004-12-01

    Ocean Drilling Program leg 189 was undertaken to test and refine the hypothesis (by Kennett et al., 1975), that the reconfiguration of continents around Antarctica (e.g.: the opening of the Tasmanian Gateway and Drake passage) led to the onset of the Antarctic Circumpolar Current that, in turn, would cause thermal isolation and hence cooling of Antarctica. This would possibly even cause global cooling, as suggested by the 33.3 Ma Oi1 event. The cores of leg 189, site 1172 on the eastern side of the Tasmanian Gateway provided a nearly complete succession of Eocene and Oligocene sediments. Cyclostratigraphic analysis based on XRF derived Ca and Fe records indicates distinct Milankovitch cyclicity between 40 and 36 Ma. (Röhl et al, in press). In the core-section representing magnetochron 18n-1n, the Ca record shows precession cycles in combination with obliquity, suggested to reflect sea level fluctuations (Röhl et al, in press). New datasets include microfossil data (organic-walled dinoflagellate cysts, pollen/spores and diatoms), loss-on-ignition measurements, magnetic data (environmental magnetics - ARM). Here, we aim to further investigate the proposed relationship between astronomical forcing and sea-level fluctuations. Additionally, we aim to obtain insight in the palaeoecology of the distinct endemic circum-Antarctic late Middle to Late Eocene dinoflagellate cyst assemblages. Results corroborate the concept that the cyclicity recorded by Ca and Fe measurements is the result of sea-level fluctuations. This implies that during late Middle Eocene times, astronomical forcing has modulated sea level - most likely through Antarctic ice buildup and meltdown. In turn, this would indicate the presence of significant, though probably modest, ice masses already ~40 Ma ago, well before the onset of the Antarctic Circumpolar Current. Kennett, J. P., R. E. Houtz, et al. (1975). Development of the circum-Antarctic current. Science 186: 144-147. Röhl, U.; H. Brinkhuis, C

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. The Alba field - a middle Eocene deepwater channel in the UK North Sea

    SciTech Connect

    Mattingly, G.A.; Bretthauser, H.H. )

    1990-09-01

    The Alba field is located in the Witch Ground Graben between the Fladen Ground Spur to the north and the Renee Ridge to the south, entirely in UKCS in Block 16/26. In 1985, oil was discovered in the middle Eocene sandstones of the Horda Formation at a depth of 6,100 ft subsea. Twelve additional wells, including sidetracks, have been drilled to appraise the discovery. This drilling indicates the Alba field is a stratigraphic trap covering an area of 3,400 ac. The Alba sands represent a brief interruption in the hemipelagic sedimentation that dominated this part of the Witch Ground Graben during the middle Eocene. Sediment was supplied intermittently from a shelf to the northwest into a deep-water environment. Well correlations, seismic facies analysis, and core analysis indicate that these sands were deposited as part of a constructional channel/levee complex within a mudrich, shelf-sourced submarine fan system. The cap, updip, and lateral seals to the reservoir are shale. The Alba reservoir is predominantly a homogeneous, fine-grained, unconsolidated sandstone. The average reservoir porosity is 33% and the average permeability is 2.8 d. Oil in place is estimated to be 1.1 billion bbl of 20{degree} API crude.

  17. Alba field - middle Eocene deep-water channel in U. K. North Sea

    SciTech Connect

    Winter, S.R.; Bretthauer, H.H.; Mattingly, G.A.

    1989-03-01

    The Alba field is located in the Witch Ground graben between the Fladen Ground spur to the north and the Renee Ridge to the south, entirely in UKCS Block 16/26. In 1985, oil was discovered in the middle Eocene sands of the Horda formation at a depth of 6100 ft subsea. Twelve additional wells, including sidetracks, have been drilled appraise the discovery. This drilling indicates the Alba field is a stratigraphic trap covering an area of 3600 ac. The Alba sands represent a brief interruption in the hemipelagic sedimentation that dominated this part of the Witch Ground graben during the middle Eocene. Sediment was supplied intermittently from a shelf area to the northwest into a deep-water environment. Well correlations, seismic facies analysis, and core analysis indicate that these sands were deposited as part of a constructional channel/levee complex within a mud-rich, shelf-sourced submarine fan system. The cap and the updip and lateral seals to the reservoir are shale. The Alba reservoir is predominantly a homogeneous, fine-grained, unconsolidated sand. The average reservoir porosity is 33% and the average permeability is 2.8 darcys. Oil in place is estimated to be 1.1 billion bbl of 20/degrees/ API crude.

  18. Late Eocene-Middle Miocene paleoclimates of the south-west Pacific: oxygen isotopic evidence

    SciTech Connect

    Kennett, J.P.; Murphy, M.G.

    1985-01-01

    High resolution oxygen isotopic stratigraphy is presented for Late Eocene-Middle Miocene sequences in a traverse of 6 DSDP sites from the southwest Pacific at water depths ranging from 1300 to 2000 m and from the warm subtropics to the cool temperature water masses. The data record the progressive increase of latitudinal temperature gradients from the late Eocene. A pattern of increasing isotopic offset between the latitudinally distributed sites is linked to the establishment and strengthening of the circum-Antarctic Current. The intensification of this current system progressively decoupled the warm subtropical gyres from cool polar circulation, in turn leading to Antarctic glaciation. Enriched oxygen isotopic values clustering in the middle Oligocene, are interpreted to represent accumulations of Antarctic ice, although this must have been temporary and of relatively low volume. This Antarctic ice must have disappeared by the Early Miocene when delta/sup 18/O values were relatively depleted, reaching minimum values during the late Early Miocene (19.5 to 16.5), the climax of Neogene warmth. This climatic optimum was immediately followed by a major enrichment in benthic delta/sup 18/O values between approx. 16.5 and 13.5 Ma, which is interpreted to represent major, permanent accumulation of the East Antarctic ice sheet and cooling of bottom waters.

  19. 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., Jr.; 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.

  20. 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

  1. Storm-generated accumulation of nummulite banks in Eocene of Cairo, Egypt

    SciTech Connect

    Aigner, T.

    1983-03-01

    Nummulite banks which are common in neritic and shelf-edge facies in many parts of the Tethyan Eocene have been mainly regarded as reef-type buildups so far. However, stratification and biofabrics of such banks in the middle Eocene around Cairo demonstrate the importance of physical processes in molding nummulitic sediment bodies. Initiation of a nummulite bank at the Giza Pyramids Plateau is localized by a preexisting paleohigh, inherited from Late Cretaceous tectonism. On this submarine swell (about 1 x 1.5 km wide), ecological conditions were optimal for a flourishing Nummulites gizehensis-community, resulting in greater sediment production than in adjacent environments. Growth of the nummulite bank into a sediment body over 30 m (98 ft) in thickness and more than 1 km (.62 mi) in length is strongly enhanced by mechanical concentration of nummulite tests into coquinal packstones. These are interpreted to be a product of storm-generated winnowing. Paleoecological evidence shows that nummulite banks are largely an in-situ lag deposit. Periods of nummulite settlement are episodically disturbed by catastrophic storm events, which result in winnowing and local accumulation of the heavier bioclasts. During shallowing, patch reefs and a back-bank lagoon formed on the landward side of the bank. This facies association may be regarded as a model for hydrocarbon reservoirs. The high intraparticle porosity in nummulite tests (54%) makes the banks a potential reservoir, while adjacent and overlying lagoonal mudstone and wackestone may serve as source and cap rocks.

  2. 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.

  3. 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.

  4. Agerinia smithorum sp. nov., a new early Eocene primate from the Iberian Peninsula.

    PubMed

    Femenias-Gual, Joan; Minwer-Barakat, Raef; Marigó, Judit; Moyà-Solà, Salvador

    2016-09-01

    The new species Agerinia smithorum (Adapiformes, Primates) from the early Eocene of the Iberian Peninsula is erected in this work. An emended diagnosis of the genus is provided, together with a broad description of the new species and comparisons with other samples assigned to Agerinia and other similar medium-sized cercamoniines. The new species is based on the most complete specimen of this genus published to date, a mandible preserving the alveoli of the canine and P1 , the roots of the P2 and all teeth from P3 to M3 . It was found in Casa Retjo-1, a new early Eocene locality from Northeastern Spain. The studied specimen is clearly distinguishable from other cercamoniines such as Periconodon, Darwinius, and Donrussellia, but very similar to Agerinia roselli, especially in the similar height of P3 and P4 and the general morphology of the molars, therefore allowing the allocation to the same genus. However, it is undoubtedly distinct from A. roselli, having a less molarized P4 and showing a larger paraconid in the M1 and a tiny one in the M2 , among other differences. The body mass of A. smithorum has also been estimated, ranging from 652 to 724 g, similar to that of A. roselli. The primitive traits shown by A. smithorum (moderately molarized P4 , large paraconid in the M1 and small but distinct in the M2 ) suggest that it could be the ancestor of A. roselli. PMID:27306700

  5. Inducement of heterochronic variation in a species of planktic foraminifera by a Late Eocene impact event

    NASA Astrophysics Data System (ADS)

    MacLeod, N.; Kitchell, J. A.

    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.

  6. 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.

  7. 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

  8. 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.

  9. New Early Eocene Basal tapiromorph from Southern China and Its Phylogenetic Implications

    PubMed Central

    Bai, Bin; Wang, Yuanqing; Meng, Jin; Li, Qian; Jin, Xun

    2014-01-01

    A new Early Eocene tapiromorph, Meridiolophus expansus gen. et sp. nov., from the Sanshui Basin, Guangdong Province, China, is described and discussed. It is the first reported Eocene mammal from the basin. The new taxon, represented by a left fragmentary mandible, is characterized by an expanded anterior symphyseal region, a long diastema between c1 and p1, a rather short diastema between p1 and p2, smaller premolars relative to molars, an incipient metaconid appressed to the protoconid on p3, a prominent entoconid on p4, molar metaconid not twinned, cristid obliqua extending mesially and slightly lingually from the hypoconid, inclined metalophid and hypolophid, and small hypoconulid on the lower preultimate molars. Meridiolophus is morphologically intermediate between basal Homogalax-like taxa and derived tapiromorphs (such as Heptodon). Phylogenetic analysis indicates Equidae is more closely related to Tapiromorpha than to Palaeotheriidae, although the latter is only represented by a single species Pachynolophus eulaliensis. ‘Isectolophidae’, with exception of Meridiolophus and Karagalax, has the closest affinity with Chalicotherioidea. Furthermore, the majority rule consensus tree shows that Meridiolophus is closer to Karagalax than to any other ‘isectolophid’, and both genera represent stem taxa to crown group Ceratomorpha. PMID:25353987

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  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. Environmental precursors to rapid light carbon injection at the Palaeocene/Eocene boundary.

    PubMed

    Sluijs, Appy; Brinkhuis, Henk; Schouten, Stefan; Bohaty, Steven M; John, Cédric M; Zachos, James C; Reichart, Gert-Jan; Sinninghe Damsté, Jaap S; Crouch, Erica M; Dickens, Gerald R

    2007-12-20

    The start of the Palaeocene/Eocene thermal maximum--a period of exceptional global warming about 55 million years ago--is marked by a prominent negative carbon isotope excursion that reflects a massive input of 13C-depleted ('light') carbon to the ocean-atmosphere system. It is often assumed that this carbon injection initiated the rapid increase in global surface temperatures and environmental change that characterize the climate perturbation, but the exact sequence of events remains uncertain. Here we present chemical and biotic records of environmental change across the Palaeocene/Eocene boundary from two sediment sections in New Jersey that have high sediment accumulation rates. We show that the onsets of environmental change (as recorded by the abundant occurrence ('acme') of the dinoflagellate cyst Apectodinium) and of surface-ocean warming (as evidenced by the palaeothermometer TEX86) preceded the light carbon injection by several thousand years. The onset of the Apectodinium acme also precedes the carbon isotope excursion in sections from the southwest Pacific Ocean and the North Sea, indicating that the early onset of environmental change was not confined to the New Jersey shelf. The lag of approximately 3,000 years between the onset of warming in New Jersey shelf waters and the carbon isotope excursion is consistent with the hypothesis that bottom water warming caused the injection of 13C-depleted carbon by triggering the dissociation of submarine methane hydrates, but the cause of the early warming remains uncertain. PMID:18097406

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. Oxygen isotopes of marine mollusc shells record Eocene elevation change in the Pyrenees

    NASA Astrophysics Data System (ADS)

    Huyghe, Damien; Mouthereau, Frédéric; Emmanuel, Laurent

    2012-09-01

    Constraining paleoaltimetry of collisional orogens is critical to understand the dynamics of topographic evolution and climate/tectonics retroactions. Here, we use oxygen stable-isotope record on oyster shells, preserved in marine foreland deposits, to examine the past elevation of the Pyrenees during the Eocene. Our approach is based on the comparison with the Paris basin, an intracratonic basin not influenced by orogenic growth. The finding of a shift of 1.5‰ between 49 and 41 Ma, indicating more negative δ18Oc in the south Pyrenean foreland, is interpreted to reflect the inflow of river water sourced from higher elevation in the Pyrenees. To test this and provide paleoelevation estimate, we adopt a morphologic-hydrological model accounting for the hypsometry of drainage basin. Our best fitting model shows that the Pyrenees rose up to 2000 m. This indicates that the Pyrenees reached high elevation in the Eocene, thus providing new critical constraints on their long-term orogenic development. δ18O of marine mollusc shells are proved potentially attractive for paleoelevation studies, especially for mountain belts where elevated continental surfaces have not been preserved.

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

    USGS Publications Warehouse

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

    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.

  5. 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

  6. 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

  7. 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.

  8. 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

  9. 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.

  10. Sudden spreading of corrosive bottom water during the Palaeocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Alexander, Kaitlin; J. Meissner, Katrin; J. Bralower, Timothy

    2015-06-01

    The Palaeocene-Eocene Thermal Maximum, approximately 55 million years ago, was a period of rapid warming linked to a massive release of carbon to the ocean-atmosphere system. This warming event was also marked by widespread dissolution of carbonates at the sea floor. The acidification of deep waters was generally more extensive and severe in the Atlantic and Caribbean, with more modest changes in the Southern and Pacific oceans. Here we use the UVic ESCM global climate model to show that corrosive deep water spreading from the North Atlantic can explain the spatial variations in carbonate dissolution during the Palaeocene-Eocene Thermal Maximum. In our simulations, highly corrosive waters accumulate in the deep North Atlantic at the onset of the event. Several thousand years after an imposed atmospheric carbon release, warming of the deep ocean destabilizes the North Atlantic water column and triggers deep-water formation. This deep convection causes the corrosive bottom water to spill over an equatorial sill into the South Atlantic. The bottom water then spreads through the Southern and Pacific oceans, progressively gaining alkalinity. We conclude that the pattern of sediment dissolution simulated along the path taken by the corrosive water is consistent with most dissolution estimates from the sediment record.

  11. Quantifying the Eocene to Pleistocene topographic evolution of the southwestern Alps, France and Italy

    NASA Astrophysics Data System (ADS)

    Fauquette, Séverine; Bernet, Matthias; Suc, Jean-Pierre; Grosjean, Anne-Sabine; Guillot, Stéphane; van der Beek, Peter; Jourdan, Sébastien; Popescu, Speranta-Maria; Jiménez-Moreno, Gonzalo; Bertini, Adele; Pittet, Bernard; Tricart, Pierre; Dumont, Thierry; Schwartz, Stéphane; Zheng, Zhuo; Roche, Emile; Pavia, Giulio; Gardien, Véronique

    2015-02-01

    We evaluate the topographic evolution of the southwestern Alps using Eocene to Pleistocene pollen data combined with existing sedimentological, petrographic and detrital geo- and thermochronological data. We report 32 new pollen analyses from 10 sites completed by an existing dataset of 83 samples from 14 localities situated across the southwestern Alps, including both the pro- and the retro-foreland basins. The presence of microthermic tree pollen (mainly Abies, Picea) indicates that this part of the mountain belt attained elevations over 1900 m as early as the Oligocene. Inferred rapid surface uplift during the mid-Oligocene coincided with a previously documented brief phase of rapid erosional exhumation, when maximum erosion rates may have reached values of up to 1.5-2 km/Myr. Slower long-term average exhumation rates of ∼0.3 km/Myr since the Late Oligocene helped maintaining the high Alpine topography of the southwestern Alps until today. The relative abundances of meso-microthermic tree pollen (Cathaya, Cedrus and Tsuga) and microthermic tree pollen (Abies, Picea) in the pro- and retro-foreland basin deposits, indicate that the present-day asymmetric topography, with a relatively gentle western flank and steeper eastern flank, was established early in the southwestern Alps, at least since the Early Miocene, and possibly since the Oligocene or Late Eocene. Therefore, the high topography and asymmetric morphology of this part of the Alps has been maintained throughout the past ∼30 Ma.

  12. 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

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

    Seal, Robert R., II; Rye, Robert O.

    1993-03-01

    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. The oxygen and hydrogen isotope compositions of meteoric waters vary because of changes in climatic variables such as mean annual temperature of precipitation, relative humidity, origin and history of air masses, and the isotope composition of the oceans. Inclusion fluids found in fluorite (CaF2) are especially useful because their host is devoid of oxygen or hydrogen, thus precluding postentrapment isotope exchange. Fluorite-hosted fluid inclusions from the Eocene (51-50 Ma) epithermal deposits of the Bayhorse mining district, northeastern Idaho, have low salinities, most less than 0.6 equivalent wt% NaCl, and low to moderate homogenization temperatures (98 to 146 °C), 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. This conclusion supports the climate modeling of Sloan and Barron, who suggested that the climates of continental interiors do not reflect the magnitude of warming preserved by the deep-ocean paleoclimate record during the Eocene.

  19. 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

  20. 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

  1. 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

  2. The Middle and Upper Eocene sections of the Omsk trough, West Siberian Platform: Palynological, stratigraphic, hydrologic, and climatic aspects

    NASA Astrophysics Data System (ADS)

    Zaporozhets, N. I.; Akhmetiev, M. A.

    2013-01-01

    The thorough analysis and correlation of Middle-Upper Eocene sections in the Omsk trough (southern West Siberian Platform) recovered by Borehole 9 in its axial part near the Chistoozernoe Settlement (Novosibirsk region) and Borehole 8 on the southern limb near the Russkaya Polyana Settlement (southern Omsk region) revealed hiatuses at the base and top of the Russkaya Polyana Beds, a lithostratigraphic unit defined in the Lyulinvor Formation based on its substantially fine-grained composition and poor siliceous microplankton fossil remains. The overlying Tavda Formation (Middle-Upper Eocene) is traditionally accepted to consist of two subformations. The last formation was deposited in the West Siberian inner sea isolated from the Arctic basin. Particular attention is paid to eustatic sea level fluctuation especially during the period marked by accumulation of Azolla Beds under considerable desalination of surface waters in the basin. The curve of variations in the open sea factor based on the quantitative ratio between organic-walled phytoplankton fossils and higher plant palynomorphs is correlated with the modified version of the wellknown Vail curve. It is established that the West Siberian sea level experienced a brief rise in the terminal late Eocene prior to its complete desiccation at the Eocene-Oligocene transition because of global regression in response to glaciation in Antarctica.

  3. 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.

  4. 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.

  5. Evidence for Atlantic thermal differentiation in the late middle Eocene to early Oligocene, eastern equatorial Atlantic DSDP Site 366

    NASA Astrophysics Data System (ADS)

    Rabideaux, N. M.; Cramer, B. S.; Katz, M.

    2011-12-01

    The Eocene-Oligocene climate transition marked a pronounced shift in global climate from greenhouse to icehouse conditions. We present new late middle to late Eocene (~33-39 Ma) benthic foraminiferal stable isotope records (δ18O, δ13C), including Oi-1, from DSDP Site 366 on the Sierra Leone Rise (04°40.70'N, 19°51.10'W) that extend published latest Eocene-early Oligocene Site 366 records (Miller et al. 1989), in an attempt to identify the influence Northern Component Water (NCW) and Southern Component Water (SCW), and possibly Tethyan Outflow Water (TOW), had on deepwater circulation in the Atlantic at this time. Site 366 provides constraints on eastern equatorial Atlantic deepwaters (~2700m paleodepth) during this time. Comparisons with published isotope records (Cramer et al., 2009) indicate a distinct δ18O offset between ODP Site 689 (Deister-Haass and Zahn, 1996) and Site 366 indicating cooler waters in the Southern Ocean than in the eastern equatorial Atlantic. South Atlantic δ18O records generally fall between the Site 689 and Site 366 values throughout the late middle Eocene-early Oligocene, and may indicate relative contributions of northern- and southern-sourced deepwater.

  6. 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

  7. Eocene Topography of the Northern Sierra Nevada: Direct Paleoelevation Evidence from Hydrogen Isotopes in Kaolinite of Paleostream Channels

    NASA Astrophysics Data System (ADS)

    Mulch, A.; Graham, S. A.; Chamberlain, C. P.

    2005-12-01

    The links and feedbacks among topography, tectonics, and climate remain a poorly understood yet important problem in Earth Sciences. Large mountains and high-elevation plateaux exert a strong control on global climate and it is, therefore, critical to understand their topographic history. Despite its importance to global climate change relatively little is known of the Cenozoic topographic development of the western North America. For example, there is considerable debate as to when the Sierra Nevada developed as a mountain range, with one view that the bulk of elevation gain took place in the last 3-5 Ma and the other that it already existed as a major topographic feature throughout much of the Cenozoic. To address this debate we examined the hydrogen isotope composition of kaolinite from weathered Eocene fluvial sediments. These sediments, well known because of past gold mining, occur within Eocene river channels cut into the western flank of the northern Sierra Nevada and are found from paleo-sea level upstream into the modern range. Our results show that the deltaD of kaolinite along paleoslopes decreases systematically by up to 25 per mil within different paleodrainage systems from a high of -80 per mil in sediments deposited at the current base of the Sierra to -106 per mil about 60 km eastward on the flank of the Sierra Nevada. The observed isotopic difference between downstream and upstream samples suggests that the highest altitude samples, collected at ca. 1600 m current elevation, were deposited at Eocene elevations of 1100 m to 1300 m. Thus, Eocene topographic gradients may have been lower than todays, but still reflect mountainous topography, consistent with pebble- to cobble-sized clasts that dominate the Eocene fluvial deposits. Viewed in context of other isotopic and geomorphic studies, we therefore suggest that mountainous topography characterized the Eocene northern Sierra Nevada whose western flank was occupied by high discharge river systems

  8. Major Transient Floral Change During the Paleocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Wing, S. L.; Harrington, G. J.; Bloch, J. I.; Boyer, D. M.; Smith, F.

    2004-12-01

    New continental sections representing the Paleocene-Eocene Thermal Maximum (PETM) have been discovered in the southern Bighorn Basin, Wyoming. Three localities preserving leaves and fruits are the first megafossil record of plants from this geologically short (about 150ky) period of intense warming. The localities produce fossil pollen and spores as well. The plant remains are in sections that preserve vertebrate fossils characteristic of the Wa-0 faunal zone that elsewhere is restricted to the period of negative carbon isotopic values that occurred during the PETM. The megaflora and palynoflora from the three localities contain a small number of long-ranging taxa that are common in many late Paleocene and early Eocene localities from the Bighorn Basin (e.g., Macginitiea, Caryapollenites, Ulmipollenites, Alnipollenites), however they also produce up to 10 taxa that have not been seen before in either the Paleocene or Eocene of this area. In the palynoflora, several of these previously unrecorded taxa (e.g, Labropollis, cf. Bombax, and a distinctive large tricolpate grain) are common in the Gulf Coastal Plain Paleogene. Although the number of dicot leaf species so far is too small to produce a robust physiognomic estimate of temperature or precipitation, it is notable that one locality near the base of the PETM is dominated by small-leaved legumes, and another near the top by an undetermined dicot leaf with an extremely long drip-tip. Preliminary analysis of the floral data strongly suggests that some types of plants extended their ranges up to 1500 km northward during the PETM, where they became sympatric with native mid-latitude taxa. These range extensions are restricted to the PETM. Furthermore, PETM floral change was essentially synchronous with the better-known mammalian turnover event. The unusual physiognomy of PETM fossil leaves raises the possibility of major changes in seasonality or amount of precipitation. We plan to measure stable carbon isotope ratios

  9. 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

  10. 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

  11. 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

  12. Characterization and genesis interpretation of charcoal-bearing concretions from the early Eocene Ione Formation, CA

    NASA Astrophysics Data System (ADS)

    Bair, D.; Aburto, F.

    2013-12-01

    Charcoal core concretions have been discovered in the kaolinitic soil horizons of the Ione formation (early Eocene epoch ~52Ma BP). It is thought that the Ione Formation in the Ione Basin was deposited in delta and estuarine waters that were subsequently exhumed and exposed to a warmer, humid, tropical-like environment during the early Eocene. The formation of concretions is indicative of seasonal dryness, and the charcoal cores are evidence of wildfires and of the existence of a forest ecosystem. The mineral outer shells of the concretions have been characterized by powder X-ray diffraction, Electron Microprobe and Laser Ablation Quadruple Mass Spectrometry (LA-ICP-MS). Micro-computed tomography (MCT) scans indicate that these concretions have at least three distinct shells and a inner core with fragments of charcoal without apparent internal organization. The outer shell is mainly composed of a layered mix of kaolinite, quartz, goethite, hematite and birnessite. Some pyrite and jarosite have also been found, which could indicate that goethite may be post-depositional and a product of the bacteria-mediated oxidation of pyrite. The central shell has a similar composition, but with a higher content of iron oxyhydroxides and jarosite. The inner cores of the concretions are mainly composed of a mixture of kaolinite and quartz which correspond to the layer in which the concretions were found. The concretion cores contain loose charcoal fragments in a unsolidified kaolinite matrix. The charcoal fragments have been characterized by Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), C/N isotope analysis, and Synchrotron radiation FTIR (SR-FTIR). Analysis of the ATR-FTIR spectra showed significant absorbance peaks at wavenumbers that coincided with the chemical functionality of other wood biochars. Charcoal from different concretions display (n =12) extremely similar spectra which suggest that they were originated from similar species and

  13. Terrestrial astronomical age model for Eocene Thermal Maximum 2 and H2 hyperthermal events

    NASA Astrophysics Data System (ADS)

    Abels, Hemmo; Lourens, Lucas; Gingerich, Philip

    2013-04-01

    Knowledge of the duration and the rates of onset and recovery of early Paleogene hyperthermal events is crucial for understanding Earth's system response to massive input of greenhouse gases into the exogenic carbon pool. The second largest hyperthermal, Eocene Thermal Maximum 2 (ETM2), and its immediate successor H2 occur around 54 million years ago. Relative chronologies have been constructed for ETM2 and H2 in deep-sea records at Walvis Ridge in the southern Atlantic Ocean (Stap et al. 2009). Here, we construct an independent astronomical age model for these hyperthermals in terrestrial successions in the Bighorn Basin, Wyoming (Abels et al. 2012). We first generated parallel carbon isotope records of the ETM2-H2 interval in the Creek Star Hill, West Branch, and Purple Butte sections located between 1 and 3 km of the previously analyzed Upper Deer Creek (UDC) section. The carbon isotope patterns in the three new sections mimic both in time and magnitude the ETM2-H2 carbon isotope patterns from the UDC section. This confirms the reproducibility of the carbon isotope time series in these floodplain successions. The four sections were subsequently correlated by lateral tracing of distinctive paleosol horizons representing time lines at the sub-precession time scale. The correlation was confirmed by overbank-avulsion sedimentation cycles coevally occurring in the four sections. The constructed stratigraphic fence panel allows disentangling local fluvial variability in sedimentation from the regional signal. Coeval overbank-avulsion cyclicity at the precession time scale (Abels et al. 2013) are then used to construct an astronomical age model for the ETM2-H2 hyperthermal events. References Abels, H.A., W.C. Clyde, P.D. Gingerich, F.J. Hilgen, H.C. Fricke, G.J. Bowen, L.J. Lourens, 2012. Terrestrial carbon isotope excursions and biotic change during Palaeogene hyperthermals. Nature Geoscience 5, 326-329. Abels, H.A., M.J. Kraus, P.D. Gingerich, 2013. Precession

  14. 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

  15. 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

  16. Early Eocene changes in the frequency and spatial distribution of extreme precipitation events

    NASA Astrophysics Data System (ADS)

    Carmichael, Matthew; Lunt, Daniel; Pancost, Richard

    2015-04-01

    Global warming over the next 100 years is likely to result not only in changes to the spatial distribution of mean annual precipitation, but also to the seasonality of precipitation and the frequency of hydrological extremes, with far-reaching socio-economic and ecological impacts. The study of the sensitivity of the hydrological cycle to episodes of global warmth in the geologic past is receiving increased attention from the paleoclimate community, but our understanding of the occurrence of hydrological extremes remains limited. The warming associated with the Paleocene-Eocene Thermal Maximum (PETM) hyperthermal (~56 Ma) has received widespread attention given its global nature, rapid onset and transient nature. A range of geomorphological, microfossil and biomarker proxies suggest significant hydrological changes occurred at the PETM which have traditionally been interpreted in terms of changes in mean annual precipitation; recently changes in the frequency of hydrological extremes at the PETM have also been suggested. In this work, we seek to better understand whether numerical climate models run with boundary conditions appropriate for the early Eocene (56 - 49 Ma) are capable of simulating changes in the frequency of intense precipitation ('storm') events by analysing GCM-simulated precipitation rates at an hourly frequency. Our Eocene simulations are performed at x2 and x4 preindustrial CO2 using a coupled atmosphere-ocean GCM, HadCM3L. Differences in climatology between high and low CO2 may be considered analogous to the changes which occurred at the PETM. Our results indicate significant changes occur in the precipitation intensity-frequency relationships at locations which correspond to sites from which PETM proxies exist. The percentage of time during which precipitation occurs and the overall number of events lasting longer than an hour declines in the high-CO2 model. These changes tend to occur with an associated increase in mean storm precipitation

  17. Understanding long-term carbon cycle trends: The late Paleocene through the early Eocene

    NASA Astrophysics Data System (ADS)

    Komar, N.; Zeebe, R. E.; Dickens, G. R.

    2013-12-01

    The late Paleocene to the early Eocene (˜58-52 Ma) was marked by significant changes in global climate and carbon cycling. The evidence for these changes includes stable isotope records that reveal prominent decreases in δ18O and δ13C, suggesting a rise in Earth's surface temperature (˜4°C) and a drop in net carbon output from the ocean and atmosphere. Concurrently, deep-sea carbonate records at several sites indicate a deepening of the calcite compensation depth (CCD). Here we investigate possible causes (e.g., increased volcanic degassing or decreased net organic burial) for these observations, but from a new perspective. The basic model employed is a modified version of GEOCARB III. However, we have coupled this well-known geochemical model to LOSCAR (Long-term Ocean-atmosphere Sediment CArbon cycle Reservoir model), which enables simulation of seawater carbonate chemistry, the CCD, and ocean δ13C. We have also added a capacitor, in this case represented by gas hydrates, that can store and release13C-depleted carbon to and from the shallow geosphere over millions of years. We further consider accurate input data (e.g., δ13C of carbonate) on a currently accepted timescale that spans an interval much longer than the perturbation. Several different scenarios are investigated with the goal of consistency amongst inferred changes in temperature, the CCD, and surface ocean and deep ocean δ13C. The results strongly suggest that a decrease in net organic carbon burial drove carbon cycle changes during the late Paleocene and early Eocene, although an increase in volcanic activity might have contributed. Importantly, a drop in net organic carbon burial may represent increased oxidation of previously deposited organic carbon, such as stored in peat or gas hydrates. The model successfully recreates trends in Earth surface warming, as inferred from δ18O records, the CCD, and δ13C. At the moment, however, our coupled modeling effort cannot reproduce the magnitude of

  18. 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

  19. 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.

  20. Tectonic and climatic significance of a late Eocene low-relief, high-level geomorphic surface, Colorado

    NASA Technical Reports Server (NTRS)

    Gregory, Kathryn M.; Chase, Clement G

    1994-01-01

    New paleobotanical data suggest that in the late Eocene the erosion surface which capped the Front Range, Colorado was 2.2-2.3 km in elevation, which is similar to the 2.5-km present elevation of surface remnants. This estimated elevation casts doubt on the conventional belief that the low-relief geomorphic surface was formed by lateral planation of streams to a base level not much higher than sea level and that the present deeply incised canyons must represent Neogene uplift of Colorado. Description of the surface, calculations of sediment volume, and isostatic balance and fluvial landsculpting models demonstrate that while the high elevation of the erosion surface was due to tectonic forces, its smoothness was mostly a result of climatic factors. A sediment balance calculated for the Front Range suggests that from 2 to 4 km of material were eroded by the late Eocene, consistent with fission track ages. This amount of erosion would remove a significant portionof the 7 km of Laramide upper crustal thickening. Isostatic modeling implies that the 2.2-3.3 km elevation was most likely created by lower crustal thickening during the Laramide. A numerical model of fluvial erosion and deposition suggests a way that a late Eocene surface could have formed at this high elevation without incision. A humid climate with a preponderance of small storm events will diffusively smooth topography and is a possible mechanism for formation oflow-relief, high-level surfaces. Paleoclimate models suggest a lack of large strom events in the late Eocene because of cool sea surface temperatures in the equatorial region. Return to a drier but stormier climate post-Eocene could have caused the incision of the surface by young canyons. By this interpretation, regional erosion surfaces may represent regional climatic rather than tectonic conditions.

  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. 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.

  3. Middle-Eocene artiodactyls from Shanghuang (Jiangsu Province, Coastal China) and the diversity of basal dichobunoids in Asia.

    PubMed

    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. PMID:18719875

  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. 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

  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. PMID:18936486

  7. 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

  8. 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

  9. Evolution of the earliest horses driven by climate change in the Paleocene-Eocene Thermal Maximum.

    PubMed

    Secord, Ross; Bloch, Jonathan I; Chester, Stephen G B; Boyer, Doug M; Wood, Aaron R; Wing, Scott L; Kraus, Mary J; McInerney, Francesca A; Krigbaum, John

    2012-02-24

    Body size plays a critical role in mammalian ecology and physiology. Previous research has shown that many mammals became smaller during the Paleocene-Eocene Thermal Maximum (PETM), but the timing and magnitude of that change relative to climate change have been unclear. A high-resolution record of continental climate and equid body size change shows a directional size decrease of ~30% over the first ~130,000 years of the PETM, followed by a ~76% increase in the recovery phase of the PETM. These size changes are negatively correlated with temperature inferred from oxygen isotopes in mammal teeth and were probably driven by shifts in temperature and possibly high atmospheric CO(2) concentrations. These findings could be important for understanding mammalian evolutionary responses to future global warming. PMID:22363006

  10. 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

  11. 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.

  12. The Eocene/Oligocene benthic foraminiferal turnover at ODP Site 647, southern Labrador Sea

    NASA Astrophysics Data System (ADS)

    Kaminski, Michael A.; Ortiz, Silvia; Bown, Paul

    2010-05-01

    The biostratigraphical record of ODP Hole 647A in the southern Labrador Sea is exceptional in the northern Atlantic, because it provides the only direct calibration of the benthic foraminiferal biostratigraphy to the standard chronostratigraphy by means of a well-constrained age model. Moreover, it is the only site in the western North Atlantic that recovered a reasonably complete Eocene/Oligocene boundary interval, whereas at other sites the boundary is present as a hiatus. Palaeobathymetrically, it was the deepest site in the northwestern Atlantic and was in the pathway of bottom water flowing through the Charlie Gibbs Fracture Zone, thereby giving unique insight into the nature of the abyssal biofacies and changes in bottom water properties over the boundary interval. Our high-resolution study of the faunal record at Site 647 confirms earlier findings (e.g. Van Couvering et al. 1981, Kaminski et al., 1989) that the E/O transition was an interval of significant faunal change among benthic foraminifera. The E/O transition in Hole 647A is characterised by a major extinction event among deep-water agglutinated foraminiferal species (DWAF), especially among taxa that use organic cement to constrict their tests. In total, 90 DWAF species and generic groupings are observed in our record. Species diversity falls from ca. 25 DWAF species/sample in the uppermost Eocene to 3 - 5 species across the E/O boundary interval. The uppermost Eocene is characterised by an acme in large suspension-feeding tubular forms such as Psammatodendron and Bathysiphon, suggesting increased bottom water activity and improved ventilation. The boundary interval in Core 647A-30R is nearly devoid of DWAF, with only the calcareous-cemented DWAF surviving. This interval also displays the first appearance of the calcareous benthic species Turrilina alsatica and a major acme of Nuttallides umbonifer (up to 70% of the assemblage) suggesting the sudden appearance of a southern hemisphere water mass

  13. 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.

  14. 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

  15. 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. PMID:21071667

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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

    2014-01-01

    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. PMID:25410701

  3. 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

  4. 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

  5. The circum-Antarctic sedimentary record; a dowsing rod for Antarctic ice in the Eocene

    NASA Astrophysics Data System (ADS)

    Scher, H.

    2012-12-01

    Arguments for short-lived Antarctic glacial events during the Eocene (55-34 Ma) are compelling, however the paleoceanographic proxy records upon which these arguments are based (e.g., benthic δ18O, eustatic sea level, deep sea carbonate deposition) are global signals in which the role of Antarctic ice volume variability is ambiguous. That is to say, the proxy response to ice volume may be masked other processes. As a result broad correlations between proxies for ice volume are lacking during suspected Eocene glacial events. I will present a more direct approach for detecting Antarctic ice sheets in the Eocene; utilizing provenance information derived from the radiogenic isotopic composition of the terrigenous component of marine sediments near Antarctica. The method relies on knowledge that marine sediments represent a mixture derived from different basement terrains with different isotopic fingerprints. A key issue when using sedimentary deposits to characterize continental sediment sources is to deconvolve different sources from the mixed signal of the bulk sample. The pioneering work of Roy et al. (2007) and van de Flierdt et al. (2007) represents a major advance in Antarctic provenance studies. It is now known that the isotopic composition of neodymium (Nd) and hafnium (Hf) in modern circum-Antarctic sediments are distributed in a pattern that mimics the basement age of sediment sources around Antarctica. For this study I selected two Ocean Drilling Program (ODP) sites on southern Kerguelen Plateau (ODP Sites 738 and 748) because of their proximity to Prydz Bay, where Precambrian sediment sources contribute to extremely nonradiogenic isotopic signatures in modern sediments in the Prydz Bay region. New detrital Nd isotope records from these sediment cores reveal an Nd isotope excursion at the Bartonian/Priabonian boundary (ca. 37 Ma) that coincides with a 0.5 ‰ increase in benthic foram δ18O values. Detrital sediment ɛNd values are around -12 in intervals

  6. 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

  7. Environment of deposition of an Eocene lignite-bearing sedimentary sequence in northeast Rusk County, Texas

    SciTech Connect

    Cole, W.F.; Kersey, D.G.; Mathewson, C.C.

    1984-04-01

    The stratigraphy and environment of deposition of the undivided Wilcox Group (lower Eocene) and Carrizo Formation (Eocene) were studied in an 88 km/sup 2/ (34 mi/sup 2/) area in northeastern Rusk County, Texas. Seven cores and 300 boreholes logs were used in the study. The undivided Wilcox Group is the predominant geologic unit in the study area and consists of poorly lithified, interlaminated sandstones, siltstone, claystones, and lignite seams. Lignite seams range in thickness from 0.1 to 2.2 m (4 in. to 7 ft) and are conformable with the overlying and underlying strata. Subtle coarsening-upward sequences, 1.8-31.3 m (6-103 ft) thick, occur between lignite seams; however, the individual sandstone units, 0.3-1.8 m (4 in.-6 ft) thick, within these sequences fine upward. The fine-grained rocks of the Wilcox Group are overlain unconformably by well-sorted, medium to coarse-grained sandstones of the Carrizo Formation. The small-scale sedimentary structures, fine-grain size, and matrix-rich nature of the undivided Wilcox units are characteristic of fluvial overbank deposits. Peat beds probably accumulated in interchannel swamps on a lower alluvial plain, distal from overbank discharge. As streams meandered across the area, overbank discharge buried the swamps. The coarsening-upward sequences between lignite seams indicate overbank deposition from a prograding stream. Swamps were reestablished as the stream was abandoned or migrated away. Fining-upward trends in grain size and the upward decrease in scale of sedimentary structures indicate the Carrizo Formation was deposited in fluvial channels.

  8. 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. PMID:16906647

  9. 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.

  10. Eocene to Pleistocene magmatic evolution of the Delarof Islands, Aleutian Arc

    NASA Astrophysics Data System (ADS)

    Schaen, Allen J.; Jicha, Brian R.; Kay, Suzanne M.; Singer, Brad S.; Tibbetts, Ashley

    2016-03-01

    The Delarof Islands in the Aleutian Arc near 179º W record ˜37 million years of discontinuous arc magmatism along a SW-NE cross-arc transect from near the trench to the active volcanic front. Geochemical and geochronologic data from the pre-Pleistocene volcanic record in this region are limited and the 40Ar/39Ar, isotopic, and trace element data presented here are the first from units older than the Pleistocene-Holocene volcanoes (Tanaga, Gareloi). Twenty-two new 40Ar/39Ar ages establish a temporal framework for geochemical data and reveal that magmatism in the Delarof region was coincident with two arc-wide magmatic flare ups in the late Eocene/early Oligocene and latest Miocene/Pliocene. Mafic lavas and plutons in the southern Delarofs give 40Ar/39Ar plateau ages ranging from 36.8 ± 0.2 to 26.9 ± 0.6 Ma on Amatignak Island and 37.0 ± 0.2 to 29.3 ± 1.0 Ma on Ulak Island. To the north 25 km, 40Ar/39Ar ages from the central Delarof Islands, Kavalga, Ogliuga, and Skagul are late Miocene (6.28 ± 0.04 Ma) to Pliocene (4.77 ± 0.18 Ma) with younger ages to the northeast. A significant transition in arc chemistry occurs in the Pleistocene where lavas from active volcanoes Gareloi and Tanaga exhibit higher sediment and hydrous fluid signatures (Th/La, Cs/Ta, La/Sm, LILE abundances) and lower 143Nd/144Nd than older Delarof Island units closer to the trench. Similar findings from Eocene-Miocene lavas from Amchitka to Adak suggest that a previously minor sediment melt component became more pronounced in the Quaternary.

  11. 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.

  12. Biomarker Constraints on Arctic Surface Water Conditions During the Middle Eocene

    NASA Astrophysics Data System (ADS)

    Speelman, E. N.; Reichart, G.; Brinkhuis, H.; Sinninghe Damste, J. S.; de Leeuw, J. M.; van Kempen, M.

    2007-12-01

    Through analyses of unique microlaminated sediments of Arctic drill cores, recovered from the Lomonosov Ridge in the central Arctic Ocean during Integrated Ocean Drilling Program (IODP) Expedition 302, it has been shown that enormous quantities of the free floating freshwater fern \\textit {Azolla} grew and reproduced in situ in the Arctic Ocean during the middle Eocene (Brinkhuis et al., Nature, 2006).The presence of the freshwater fern Azolla, both within the Arctic Basin and in all Nordic seas, suggests that at least the sea surface waters were frequently dominated by fresh- to brackish water during an interval of at least 800 kyr. However, to which degree the Arctic Basin became fresh and what the consequences of these enormous Azolla blooms were for regional and global nutrient cycles is still largely unknown. Comparing samples of extant Azolla, including its nitrogen fixing symbionts, with samples from the Arctic Azolla interval revealed the presence of a group of highly specific biomarkers. These biomarkers are closely related to similar organic compounds that have been suggested to play a crucial role in the biogeochemistry of nitrogen fixing bacteria. This finding, therefore, potentially implies that this symbioses dates back to at least the middle Eocene. Furthermore, this particular symbiosis was probably crucial in triggering basin wide Azolla blooms. We now aim to measure compound specific stable hydrogen isotope values of these biomarkers which should provide insight into the degree of mixing between high salinity (isotopically heavy) deeper and low salinity surface water (isotopically light). The results of these compound specific isotope analyses will be extrapolated using calibrations from controlled growth experiments and subsequently evaluated using climate modeling experiments.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. Changes in benthic ecosystems and ocean circulation in the Southeast Atlantic across Eocene Thermal Maximum 2

    NASA Astrophysics Data System (ADS)

    Jennions, S. M.; Thomas, E.; Schmidt, D. N.; Lunt, D.; Ridgwell, A.

    2015-08-01

    Eocene Thermal Maximum 2 (ETM2) occurred ~1.8 Myr after the Paleocene-Eocene Thermal Maximum (PETM) and, like the PETM, was characterized by a negative carbon isotope excursion and warming. We combined benthic foraminiferal and sedimentological records for Southeast Atlantic Sites 1263 (1500 m paleodepth) and 1262 (3600 m paleodepth) to show that benthic foraminiferal diversity and accumulation rates declined more precipitously and severely at the shallower site during peak ETM2. As the sites are in close proximity, differences in surface productivity cannot have caused this differential effect. Instead, we infer that changes in ocean circulation across ETM2 may have produced more pronounced warming at intermediate depths (Site 1263). The effects of warming include increased metabolic rates, a decrease in effective food supply and increased deoxygenation, thus potentially explaining the more severe benthic impacts at Site 1263. In response, bioturbation may have decreased more at Site 1263 than at Site 1262, differentially affecting bulk carbonate records. We use a sediment-enabled Earth system model to test whether a reduction in bioturbation and/or the likely reduced carbonate saturation of more poorly ventilated waters can explain the more extreme excursion in bulk δ13C and sharper transition in wt % CaCO3 at Site 1263. We find that both enhanced acidification and reduced bioturbation during the ETM2 peak are needed to account for the observed features. Our combined ecological and modeling analysis illustrates the potential role of ocean circulation changes in amplifying local environmental changes and driving temporary, but drastic, loss of benthic biodiversity and abundance.

  20. Arctic hydrology during global warming at the Palaeocene/Eocene thermal maximum

    NASA Astrophysics Data System (ADS)

    Pagani, Mark; Pedentchouk, Nikolai; Huber, Matthew; Sluijs, Appy; Schouten, Stefan; Brinkhuis, Henk; Sinninghe Damsté, Jaap S.; Dickens, Gerald R.; Expedition 302 Scientists; Backman, Jan; Clemens, Steve; Cronin, Thomas; Eynaud, Frédérique; Gattacceca, Jérôme; Jakobsson, Martin; Jordan, Ric; Kaminski, Michael; King, John; Koc, Nalân; Martinez, Nahysa C.; McInroy, David; Moore, Theodore C., Jr.; O'Regan, Matthew; Onodera, Jonaotaro; Pälike, Heiko; Rea, Brice; Rio, Domenico; Sakamoto, Tatsuhiko; Smith, David C.; St John, Kristen E. K.; Suto, Itsuki; Suzuki, Noritoshi; Takahashi, Kozo; Watanabe, Mahito; Yamamoto, Masanobu

    2006-08-01

    The Palaeocene/Eocene thermal maximum represents a period of rapid, extreme global warming ~55million 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.

  1. 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.

  2. 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

  3. Stromatolites As Fine Records of Terrestrial Environmental Conditions: Examples from the Eocene Green River Formation (Wyoming)

    NASA Astrophysics Data System (ADS)

    Frantz, C. M.; Corsetti, F. A.; Petryshyn, V. A.; Wagner, M.; Tripati, A.

    2014-12-01

    Stromatolites are layered structures that form subaqueously, thereby recording chemical information about their formation environment. As such, these accretionary structures are useful tools for fine-timescale environmental reconstructions. High-resolution geochemical analyses of stromatolites that formed in paleolake Gosiute (Eocene Green River Formation) provided novel information about terrestrial environmental variability during the Early Eocene Climatic Optimum (EECO), the period with the highest temperatures and atmospheric CO2 levels in the Cenozoic. Stromatolites from the ~51 Ma Rife Bed of the Tipton Shale Member of the Green River Formation record dramatic changes in lake volume (and correspondingly, water depth and shoreline) indicating the environment during the peak of the EECO was more variable than previously appreciated. A second set of stromatolites from the ~49 Ma Lower Laclede Bed of the Laney Member of the Green River Formation record transient periods of basin closure during a time when the basin is generally considered to have been balanced-filled. In addition, the results reveal that basin filling after desiccation was not continuous, but fluctuated before becoming an open system, further indicating local climate variability during the EECO. In both cases, major environmental changes are reflected not only in the recorded chemistry, but also in changes in stromatolite microfabric. In addition, clumped isotope paleothermometry provided estimates of water temperature from the evolving lake, which for most of its existence was so massive that it would have influenced regional climate. These and other studies demonstrate that stromatolite laminae can be used to understand fine-scale environmental variability in ancient lacustrine systems.

  4. Occurrence of gigantic biogenic magnetite during the Paleocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Schumann, D.; Raub, T. D.; Kopp, R. E.; Guerquin-Kern, J. L.; Wu, T. D.; Rouiller, I.; Smirnov, A. V.; Sears, S. K.; Lücken, U.; Tikoo, S. M.; Hesse, R.; Kirschvink, J. L.; Vali, H.

    2009-04-01

    The Paleocene-Eocene Thermal Maximum (PETM) is one of the most severe climatic events of the Cenozoic Era. A massive injection of light carbon into the oceans and atmosphere over a few thousand of years triggered drastic perturbation of Earth's climate resulting in abrupt global warming of ~5-9oC [Sluijs et al., 2007] that persisted for ~180,000 years. This episode is marked by the diversification and radiation of terrestrial plants and mammals while in the marine realm numerous deep-sea benthic foraminifera species disappeared and new forms evolved. Sediments deposited during the PETM are clay-rich and contain distinct evidence of these climatic changes. Kopp et al., (2007) and Lippert & Zachos (2007) report an extraordinary magnetofossil ‘Lagerstätte' in lowermost Eocene kaolinite-rich clay sediments deposited at subtropical paleolatitude in the Atlantic Coastal Plain of New Jersey, USA. Magnetofossils are magnetic particles produced most abundantly by magnetotactic bacteria. Kopp et al. (2007) and Lippert & Zachos (2007) used ferromagnetic resonance (FMR) spectroscopy, other rock magnetic methods, and transmission electron microscopy (TEM) of magnetic separates to characterize sediments from boreholes at Ancora (ODP Leg 174AX) and Wilson Lake, NJ, respectively. These sediments contain abundant ~40- to 300-nm cuboidal, elongate-prismatic and bullet-shaped magnetofossils, sometimes arranged in short chains, resembling crystals in living magnetotactic bacteria. Despite the scarcity of intact magnetofossil chains, the asymmetry ratios of the FMR spectra reflects a profusion of elongate single domain (SD) crystals and/or chains. Here we address both conundrums by reporting the discovery from these same sediments of exceptionally large and novel biogenic magnetite crystals unlike any previously reported from living organisms or from sediments. Aside from abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite

  5. 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

  6. A "tropical" Early Eocene marine environment on the Antarctic margin: TEX86 results from IODP expedition 318

    NASA Astrophysics Data System (ADS)

    Bendle, J. A.; Bijl, P.; Toney, J. L.; Pross, J.; Contreras, L.; Schouten, S.; Roehl, U.; Tauxe, L.; Huber, M.; Brinkhuis, H.; Scientific Team of IODP Drilling Leg 318

    2011-12-01

    The early Eocene was characterised by high pCO2 (ca.1,000 to more than 2,000ppm) and mean global temperatures that reached a long-term maximum. Relative to the present day, meridional temperature gradients were unusually low, with warmer equatorial regions and much warmer subtropical Arctic and mid-latitude climates. Yet global climatic conditions during this pre-glacial interval have remained poorly constrained, as only a few temperature records are available portraying the Cenozoic climatic evolution of the high southern latitudes. Here we present dinoflagellate cyst assemblages and organic geochemical tetraether based sea-surface temperature estimates from IODP expedition 318, extracted from bio- and magnetostratigraphically dated, late early to early middle Eocene sediments recovered at Site U1356. For the first time, we reconstruct marine temperatures and ecological conditions from the Eocene Greenhouse world in direct proximity to the Antarctic continent. Early Eocene dinocyst assemblages are dominated by tropical dinocyst genus Apectodinium, whilst TEX86 results indicate persistent and remarkable warmth, with the magnitude of the reconstructed SSTs dependent on the applied calibration: TEX86-L = 20 - 26°C (Av. 23°C); TEX86-H = 27 - 33°C (Av. 32°C). Our marine based proxies are just several strands from multiple independent lines of evidence emerging from the Early Eocene of the Wilkes Land Antarctic margin, including: pollen, terrestrial biomarkers (e.g. MBT/CBT-MAT estimates of 22 - 27°C , Av. 26°C), compound specific plant wax D/H measurements and clay minerals. Taken together, this evidence of very high temperatures, thermophilic fauna, an invigorated hydrological cycle, chemically weathered soils and well developed wetlands gives a very compelling picture of environmental conditions comparable to the modern tropics. These results confirm that exceptionally warm polar-regions are a feature common to reconstructed Greenhouse periods. Such

  7. Eocene sea temperatures for the mid-latitude southwest Pacific from Mg/Ca ratios in planktonic and benthic foraminifera

    NASA Astrophysics Data System (ADS)

    Creech, John B.; Baker, Joel A.; Hollis, Christopher J.; Morgans, Hugh E. G.; Smith, Euan G. C.

    2010-11-01

    We have used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to measure elemental (Mg/Ca, Al/Ca, Mn/Ca, Zn/Ca, Sr/Ca, and Ba/Ca) ratios of 13 species of variably preserved early to middle Eocene planktonic and benthic foraminifera from New Zealand. The foraminifera were obtained from Ashley Mudstone, mid-Waipara River, South Island, which was deposited at bathyal depth ( ca. 1000 m) on the northern margin of the east-facing Canterbury Basin at a paleo-latitude of ca. 55°S. LA-ICP-MS data yield trace element depth profiles through foraminifera test walls that can be used to identify and exclude zones of surficial contamination and infilling material resulting from diagenetic coatings, mineralisation and detrital sediment. Screened Mg/Ca ratios from 5 species of foraminifera are used to calculate sea temperatures from late Early to early Middle Eocene ( ca. 51 to 46.5 Ma), a time interval that spans the termination of the Early Eocene Climatic Optimum (EECO). During this time, sea surface temperatures (SST) varied from 30 to 24 °C, and bottom water temperatures (BWT) from 21 to 14 °C. Comparison of Mg/Ca sea temperatures with published δ 18O and TEX 86 temperature data from the same samples (Hollis et al., 2009) shows close correspondence, indicating that LA-ICP-MS can provide reliable Mg/Ca sea temperatures even where foraminiferal test preservation is variable. Agreement between the three proxies also implies that Mg/Ca-temperature calibrations for modern planktonic and benthic foraminifera can generally be applied to Eocene species, although some species (e.g., V. marshalli) show significant calibration differences. The Mg/Ca ratio of the Eocene ocean is constrained by our data to be 35-50% lower than the modern ocean depending on which TEX 86 - temperature calibration (Kim et al., 2008; Liu et al., 2009) - is used to compare with the Mg/Ca sea temperatures. Sea temperatures derived from δ 18O analysis of foraminifera from Waipara show

  8. 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

  9. 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.

  10. Shocked Quartz, Ir, Sr, and OS Anomalies Found in the Late Eocene at Massignano (Ancona, Italy): Clear Evidence of a Bolide Impact

    NASA Astrophysics Data System (ADS)

    Clymer, A. K.; Vonhof, H. B.; Meisel, T.; Bice, D. M.; Montanari, A.

    1996-03-01

    Shock metamorphosed quartz grains coincident with a positive Ir anomaly of 199 +/- 19 ppb, a positive 87Sr/88Sr anomaly, and a negative 1870s/1880s anomaly of about 0.35 have been found in a marry layer of the Late Eocene Scaglia Variegata formation at Massignano (Ancona), which clearly indicates a large impact with an interpolated radiometric age of 35.7 +/- 0.4 Ma. The Popigai crater (Siberia, ~ 100 km diameter) and the recently discovered Chesapeake Bay Crater (Eastern U. S., ~80 km diameter) are the only known giant craters from the Late Eocene and are prime candidates for the event that distributed the shocked quartz and geochemical anomalies found at Massignano. Although the Middle and Late Eocene are characterized by significant stepwise extinctions, the only evidence of a biotic response at Massignano to an impact is a cooler water shift in the dinocyst assemblage associated with the impact layer. Therefore the effects of the impact on this region of the Late Eocene Tethys appears mild, and the global ramification s of the Late Eocene impacts on climate and life remains unclear. However, the tight age control of the Massignano impact layer presents a correlation potential that is a critical step in our understanding of the Late Eocene impact scenario.

  11. 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.

  12. "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

  13. Eocene to Miocene Southern Ocean Deep Water Circulation Revealed From Fossil Fish Teeth Nd Isotopes

    NASA Astrophysics Data System (ADS)

    Scher, H.; Martin, E. E.

    2001-12-01

    We have evaluated Nd and Sr isotopic compositions of cleaned fossil fish teeth for the late Eocene to early Miocene from ODP site 1090 (43° S, 9° E, 3599 m) in the Atlantic sector of the Southern Ocean. Using an age model based on biostratigraphy and paleomagnetics, Sr isotopic values from the fossil fish teeth tend to plot slightly below the seawater curve. This offset may be due to early diagenetic reactions, but overall the seawater trace metal chemistry appears to be well preserved in these samples. At site 1090, \\epsilonNd values increase from ~-7.5 at 39 Ma to ~-6 at 35 Ma and stay at this value until ~28.5 Ma. A high resolution Nd isotope record demonstrates steadily decreasing \\epsilonNd values from -6 to -8 between 28.5 and 23 Ma. Sampling during this interval reveals two rapid oscillations (<.5 Myr) in \\epsilonNd values superimposed on this decreasing trend; a one \\epsilonNd unit decrease at ~26 Ma and a one \\epsilonNd unit increase at ~23 Ma. Bottom water Nd composition is controlled by deep-water circulation, dissolved and particulate riverine inputs, and eolian inputs. In the late Eocene, bottom waters at site 1090 became increasingly radiogenic as benthic \\delta18O values began to reflect cooler deep-sea temperatures and the growth of ice sheets on Antarctica. It has been speculated that deep water in the Southern Ocean during the Eocene may have had a Tethyan origin. The shift toward radiogenic values at Site 1090 may reflect decreasing flow of nonradiogenic seawater from this low latitude deepwater source (modern Mediterranean \\epsilonNd ~-9). It may also be a result of the emergence of ice sheets on Antarctica, which reduced chemical weathering of nonradiogenic material into Southern Ocean. Although we anticipated that the opening of Drake Passage would introduce radiogenic Pacific waters into the Southern Atlantic, decreasing \\epsilonNd values coincide with age estimates for the opening based on geophysical data. Ocean circulation models

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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

  19. Paleomagnetic and rock magnetic study of the IODP Site U1332 sediments - relative paleointensity during Eocene and Oligocene

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Acton, G.; Channell, J. E.; Palmer, E. C.; Richter, C.; Yamazaki, T.

    2011-12-01

    Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321 recovered sediment cores from equatorial Pacific. Cores were taken at eight Sites (U1331-U1338) and onboard measurements showed that those from Sites U1331, U1332, U1333 and U1334 covered Eocene and/or Oligocene (Expedition 320/321 Scientists, 2010). Although many efforts have been made to reveal relative geomagnetic paleointensity variations in geologic time, those prior to ca. 3 m.y. have been not yet reported except a few studies (e.g. ca. 23-34 Ma, Tauxe and Hartl, 1997). This study concentrates on paleomagnetic and rock magnetic measurements on the Site U1332 sediment core. The measurements include stepwise alternating field demagnetization of the natural remanent magnetization (NRM), the anhysteretic remanent magnetization (ARM) and the isothermal remanent magnetization (IRM). The magnetostrartigraphy constructed from the NRM data show that the sedimentary section extends from the early Oligocene to middle Eocene (23.030-41.358 Ma). Intensity variation of ARM and IRM is within about a factor of six throughout the core. Magnetic grain size proxy, ARM/IRM, differ between Eocene (about 0.11) and Oligocene (about 0.14). These suggest that relative paleointensity (RPI) estimation is basically possible if we divide the core into Eocene and Oligocene periods. RPI estimates have been done by using ARM and IRM as normalizers for NRM. RPIs by ARM and IRM generally show consistent variations. However, several experimental results imply that RPI by IRM may be more preferable. We will compare the U1332 RPI record with the U1331, U1333 and U1334 RPI records.

  20. The respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the Eocene-Oligocene transition

    NASA Astrophysics Data System (ADS)

    Ladant, Jean-Baptiste; Donnadieu, Yannick; Lefebvre, Vincent; Dumas, Christophe

    2014-08-01

    The continental scale initiation of the Antarctic ice sheet at the Eocene-Oligocene boundary (Eocene-Oligocene transition (EOT), 34 Ma) is associated with a global reorganization of the climate. If data studies have assessed the precise timing and magnitudes of the ice steps, modeling studies have been unable to reproduce a transient ice evolution during the Eocene-Oligocene transition in agreement with the data. Here we simulate this transition using general circulation models coupled to an ice sheet model. Our simulations reveal a threshold for continental scale glaciation of 900 ppm, 100 to 150 ppm higher than previous studies. This result supports the existence of ephemeral ice sheets during the middle Eocene, as similar CO2 levels (900-1000 ppm) have been reached episodically during this period. Transient runs show that the ice growth is accurately timed with EOT-1 and Oi-1, the two δ18O excursions occurring during the transition. We show that CO2 and orbital variations are crucial in initiating these steps, with EOT-1 corresponding to the occurrence of low summer insolation, whereas Oi-1 is controlled by a major CO2 drop. The two δ18O steps record both ice growth and temperature, representing some 10-30 m eustatic sea level fall and 2-4°C cooling at EOT-1 and 70 ± 20 m and 0-2°C for Oi-1. The simulated magnitude of the ice steps (10 m for EOT-1 and 63 m for Oi-1) and the overall cooling at various locations show a good agreement with the data, which supports our results concerning this critical transition.

  1. Reconstruction of Tertiary palaeovalleys in the South Alpine Foreland Basin of France (Eocene-Oligocene of the Castellane arc)

    NASA Astrophysics Data System (ADS)

    Grosjean, Anne-Sabine; Pittet, Bernard; Ferry, Serge; Mahéo, Gweltaz; Gardien, Véronique

    2012-11-01

    The dynamics of depositional environments and the spatial deformation of drainage networks in foreland basins reflect the tectonic and erosional dynamics associated with the development of mountain belts. The spatial and temporal organization of the Eocene-Oligocene (40-25 Ma) sedimentation in the external part of the South Alpine Foreland Basin of France was reconstructed using an integrated cartographic, sedimentological and petrographic analysis of the Tertiary sedimentary successions. The depositional geometries and variations in facies and thickness of the Palaeogene Nummulitic succession, as well as the observed flow directions in various continental and marine sediments, suggest that the Barrême, Blieux and Taulanne synclines were present as palaeovalleys since the Eocene. The sedimentological analysis of the Nummulitic succession allows the identification of three depositional sequences separated by transgressive surfaces that are recognized in the Barrême, Blieux and Taulanne synclines. Correlation of these sequences between the three synclines suggests that these palaeovalleys were connected by a local valley network that recorded the same sea-level fluctuations during the marine Nummulitic sedimentation. The palaeovalley network was structurally controlled by the east-west axes of the Blieux and Taulanne synclines and the north-south axis of the Barrême syncline formed during the "Pyrenean-Provençal" (Late Cretaceous-Middle Eocene) shortening and the first stage of the Alpine history (Middle Eocene) respectively. Later on, the westward "Alpine" compression (since the Early Oligocene) induced local depocenter migration and reversal in flow direction. However, compared to the modern river pattern, the palaeovalley orientation highlights a geometrical stability since their formation (about 40 Ma), suggesting a long-term stability of the early structures in the foreland basin. This constancy can be explained by the location of the study area in a piggy

  2. 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.

  3. 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.

  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. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. Tropical/subtropical Upper Paleocene Lower Eocene fluvial deposits in eastern central Patagonia, Chile (46°45'S)

    NASA Astrophysics Data System (ADS)

    Suárez, M.; de la Cruz, R.; Troncoso, A.

    2000-11-01

    A succession of quartz-rich fluvial sandstones and siltstones derived from a mainly rhyolitic source and minor metamorphic rocks, located to the west, represent the first Upper Paleocene-Early Eocene deposits described in Chilean eastern central Patagonian Cordillera (46°45'S). This unit, exposed 25 km south of Chile Chico, south of lago General Carrera, is here defined as the Ligorio Márquez Formation. It overlies with an angular unconformity Lower Cretaceous shallow marine sedimentary rocks (Cerro Colorado Formation) and subaerial tuffs that have yielded K-Ar dates of 128, 125 and 123 Ma (Flamencos Tuffs, of the Divisadero Group). The Ligorio Márquez Formation includes flora indicative of a tropical/subtropical climate, and its deposition took place during the initial part of the Late Paleocene-Early Eocene Cenozoic optimum. The underlying Lower Cretaceous units exhibit folding and faulting, implying a pre-Paleocene-Lower Eocene contractional tectonism. Overlying Oligocene-Miocene marine and continental facies in the same area exhibit thrusts and normal faults indicative of post-Lower Miocene contractional tectonism.

  20. Benthonic foraminiferal assemblages and microfacies analysis of Paleocene Eocene carbonate rocks in the Kastamonu region, Northern Turkey

    NASA Astrophysics Data System (ADS)

    Özgen-Erdem, Nazire; İnan, Nurdan; Akyazı, Mehmet; Tunoğlu, Cemal

    2005-06-01

    The Kastamonu region, NW Turkey, is known for its rich foraminiferal marine biota and variety of deposits from Paleocene to Eocene times. The focus of this study is on the foraminiferal assemblages and microfacies analysis of the sediments. Usually Paleocene shallow water limestones overlie Maastrichtian rocks conformably. They are characterized by benthic foraminifera such as Laffitteina mengaudi (Astre) Anomalina sp., Eponides sp., Rotalia sp., Mississippina sp., Haurenidae in the lower strata and numerous rotaliid such as Pseudocuvillierina sireli İnan, Rotalia perovalis Terquem, R. trochidiformis (Lamarck), Kathina selveri Smout, Kathina major Smout, Smoutina? subspherica (Sirel), Miscellanea primitiva Rahaghi in the upper strata. The Eocene clayey limestones, limestones and marls, which generally conformably overlie the Paleocene, are commonly characterized by benthic foraminifera of Orbitolites complanatus Lamarck, Asterigerina rotula (Kaufmann), Gyroidinella magna (Le Calvez), Fabiania cassis (Oppenheim), Nummulites minervensis Schaub, Nummulites burdigalensis de la Harpe, Nummulites millecaput Boubee, Assilina placentula (Deshayes), Assilina exponens (Sowerby). Microfacies analyses of the Paleocene-Eocene carbonate rocks were carried out with respect to the distribution of depositional components and biota. The Danian, Selandian and Thanetian units are characterized by reefal (organic buildup), shelf lagoon, shelf and tidal flat paleoenvironments. The Ilerdian units are represented by reefal and shelf lagoon environments, while the Cuisian units are characterized by shelf lagoon and deep shelf settings. The Lutetian units indicate platform margin through fore-slope to deep marine shelf paleoenvironments.

  1. 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

  2. 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.

  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. A large mimotonid from the middle Eocene of China sheds light on the evolution of lagomorphs and their kin.

    PubMed

    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

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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

  10. 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

  11. Salinity of the Early and Middle Eocene Arctic Ocean From Oxygen Isotope Analysis of Fish Bone Carbonate

    NASA Astrophysics Data System (ADS)

    Waddell, L. M.; Moore, T. C.

    2006-12-01

    Plate tectonic reconstructions indicate that the Arctic was largely isolated from the world ocean during the early and middle Eocene, with exchange limited to shallow, and possibly intermittent, connections to the North Atlantic and Tethys (via the Turgay Strait). Relative isolation, combined with an intensification of the hydrologic cycle under an Eocene greenhouse climate, is suspected to have led to the development of a low- salinity surface water layer in the Arctic that could have affected deep and intermediate convection in the North Atlantic. Sediment cores recently recovered from the Lomonosov Ridge by the IODP 302 Arctic Coring Expedition (ACEX) allow for the first assessment of the salinity of the Arctic Ocean during the early and middle Eocene. Stable isotope analysis performed on the structural carbonate of fish bone apatite from ~30 samples between the ages of ~55 and ~44 myr yielded δ18O values between -6.84‰ and -2.96‰ VPDB, with a mean value of -4.89‰. From the δ18O values we calculate that the Arctic Ocean was probably brackish during most of the early and middle Eocene, with an average salinity of 19 to 24‰. Negative excursions in the δ18O record (<-6‰) indicate three events during which the salinity of the Arctic surface waters was severely lowered: the Paleocene Eocene Thermal Maximum (PETM), the Azolla event at ~49 Ma, and a third previously unidentified event at ~46 Ma. During the PETM, low salinities developed under conditions of increased regional precipitation and runoff associated with extreme high latitude warmth and possible tectonic uplift in the North Atlantic. During the other two low-salinity events, sea level was lowered by ~20-30 m, implying a possible severing of Arctic connections to the world ocean. The most positive δ18O value (-2.96‰) occurs at ~45 Ma, the age of the youngest dropstone discovered in the ACEX sediments, and may therefore correspond to a climatic cooling rather than a high salinity event.

  12. 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

  13. Eocene lake basins in Wyoming and Nevada record rollback of the Farallon flat-slab beneath western North America

    NASA Astrophysics Data System (ADS)

    Smith, M. E.; Cassel, E. J.; Jicha, B. R.; Singer, B. S.; Carroll, A.

    2014-12-01

    Numerical and conceptual models of flat-slab rollback predict broad initial dynamic subsidence above the slab hinge then uplift and volcanism triggered by the advection of asthenosphere beneath the overriding plate. These predicted surface effects provide a viable but largely untested explanation for lake basin formation in Cordilleran-type orogenies. We argue that the hydrologic closure of both the foreland (early Eocene) and hinterland (late Eocene) of the North American Cordillera were caused by a trenchward-migrating wave of dynamic and thermal topography resulting from progressive removal of the Farallon flat-slab. Two major episodes of hydrologic drainage closure are recorded by Eocene terrestrial strata in the western United States. The first occurred in the retroarc foreland during the early Eocene, and resulted in the deposition of the Green River Fm. The second occurred in the hinterland during the late Eocene and resulted in accumulation of the Elko Fm. In both regions, lake strata overlie fluvial strata and become progressively more evaporative up-section, and are overlain by volcaniclastic strata. Both successions were then truncated by regional unconformities that extend until the Oligocene. We interpret these stratigraphic successions to record trenchward propagation of a regional topographic wave, caused by slab rollback. Migration of the slab-hinge initially caused dynamic subsidence and initiation of lacustrine deposition. Regional surface uplift followed, and was associated with scattered volcanism. Uplift promoted formation of endorheic basins and ultimately the development of regional unconformities. The height of the uplift can be roughly approximated by the preserved thickness of lacustrine and other nonmarine deposits at both locations (0.2-1.0 km). The 40Ar/39Ar and U-Pb geochronology of Green River Fm ash beds indicate that this surface topographic wave migrated trenchward (SW) across the foreland from 53 to 47 Ma at a velocity of ~6 cm

  14. Palynostratigraphy and depositional environment of Vastan Lignite Mine (Early Eocene), Gujarat, western India

    NASA Astrophysics Data System (ADS)

    Rao, M. R.; Sahni, Ashok; Rana, R. S.; Verma, Poonam

    2013-04-01

    Early Eocene sedimentary successions of south Asia, are marked by the development of extensive fossil-bearing, lignite-rich sediments prior to the collision of India with Asia and provide data on contemporary equatorial faunal and vegetational assemblages. One such productive locality in western India is the Vastan Lignite Mine representing approximately a 54-52 Ma sequence dated by the presence of benthic zone marker species, Nummulites burdigalensis burdigalensis. The present study on Vastan Lignite Mine succession is based on the spore-pollen and dinoflagellate cyst assemblages and documents contemporary vegetational changes. 86 genera and 105 species belonging to algal remains (including dinoflagellate cysts), fungal remains, pteridophytic spores and angiospermous pollen grains have been recorded. On the basis of first appearance, acme and decline of palynotaxa, three cenozones have been recognized and broadly reflect changing palaeodepositional environments. These are in ascending stratigraphic order (i) Proxapertites Spp. Cenozone, (ii) Operculodinium centrocarpum Cenozone and (iii) Spinizonocolpites Spp. Cenozone. The basal sequence is lagoonal, palm-dominated and overlain by more open marine conditions with dinoflagellate cysts and at the top, mangrove elements are dominant. The succession has also provided a unique record of fish, lizards, snakes, and mammals.

  15. Fossil legumes from the Middle Eocene (46.0 Ma) Mahenge Flora of Singida, Tanzania.

    PubMed

    Herendeen, P S; Jacobs, B F

    2000-09-01

    Middle Eocene age caesalpinioid and mimosoid legume leaves are reported from the Mahenge site in north-central Tanzania. The Mahenge flora complements a sparse Paleogene tropical African fossil plant record, which until now consisted of a single macrobotanical assemblage, limited palynological studies in West Africa and Egypt, and fossil wood studies primarily from poorly dated deposits. Mahenge leaf macrofossils have the potential to add significantly to what is known of the evolutionary history of extant African plant groups and to expand our currently limited knowledge of African Paleogene environments. The site is associated with a kimberlite eruption and demonstrates the potential value of kimberlite-associated lake deposits as much-needed resources for African Paleogene floras. In this report we document a relatively diverse component of the flora consisting of the leaves of at least five species of Leguminosae. A new species of the extant genus Acacia (Mimosoideae), described herein, is represented by a bipinnate leaf. Another taxon is described as a new species of the extant genus Aphanocalyx (Caesalpinioideae), and a third leaf type may be related to the extant genus Cynometra (Caesalpinioideae). Two additional leaf types are less well understood: one appears to be referable to the Caesalpinioideae and subfamily affinities of the other taxon are unknown. PMID:10991905

  16. The origin of Chubutolithes Ihering, ichnofossils from the Eocene and Oligocene of Chubut Province, Argentina.

    USGS Publications Warehouse

    Brown, T.M.; Ratcliffe, B.C.

    1988-01-01

    The distinctive trace fossil Chubutolithes gaimanensis n. ichnosp. occurs in Casamayoran (early Eocene) and Colhuehaupian (late Oligocene) alluvial rocks of the Sarmiento Formation in eastern Chubut Province, Argentina. Though known for nearly 70 years, its origin has remained obscure. Examination of new specimens and comparisons with modern analogs demonstrate that specimens of Chubutolithes represent the fossil nests of a mud-dauber (Hymenoptera: Sphecidae). Virtually identical nests are constructed today by mud-daubers in areas as disparate as southern Santa Cruz Province, Argentina, and Nebraska, confirming that quite similar trace fossils can be produced by several different taxa in a higher taxonomic clade. No satisfactory ethological term exists for trace fossils that, like Chubutolithes, were constructed by organisms above, rather than within, a substrate or medium. The new term aedificichnia is proposed. Chubutolithes occurs in alluvial paleosols and is associated with a large terrestrial ichnofauna. These trace fossils include the nests of scarab beetles, compound nests of social insects, and burrows of earthworms. -Authors

  17. 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.

  18. Halophilic archaea cultivated from surface sterilized middle-late eocene rock salt are polyploid.

    PubMed

    Jaakkola, Salla T; Zerulla, Karolin; Guo, Qinggong; Liu, Ying; Ma, Hongling; Yang, Chunhe; Bamford, Dennis H; Chen, Xiangdong; Soppa, Jörg; Oksanen, Hanna M

    2014-01-01

    Live bacteria and archaea have been isolated from several rock salt deposits of up to hundreds of millions of years of age from all around the world. A key factor affecting their longevity is the ability to keep their genomic DNA intact, for which efficient repair mechanisms are needed. Polyploid microbes are known to have an increased resistance towards mutations and DNA damage, and it has been suggested that microbes from deeply buried rock salt would carry several copies of their genomes. Here, cultivable halophilic microbes were isolated from a surface sterilized middle-late Eocene (38-41 million years ago) rock salt sample, drilled from the depth of 800 m at Yunying salt mine, China. Eight unique isolates were obtained, which represented two haloarchaeal genera, Halobacterium and Halolamina. We used real-time PCR to show that our isolates are polyploid, with genome copy numbers of 11-14 genomes per cell in exponential growth phase. The ploidy level was slightly downregulated in stationary growth phase, but the cells still had an average genome copy number of 6-8. The polyploidy of halophilic archaea living in ancient rock salt might be a factor explaining how these organisms are able to overcome the challenge of prolonged survival during their entombment. PMID:25338080

  19. Large-scale phylogeny of chameleons suggests African origins and Eocene diversification

    PubMed Central

    Tolley, Krystal A.; Townsend, Ted M.; Vences, Miguel

    2013-01-01

    Oceanic dispersal has emerged as an important factor contributing to biogeographic patterns in numerous taxa. Chameleons are a clear example of this, as they are primarily found in Africa and Madagascar, but the age of the family is post-Gondwanan break-up. A Malagasy origin for the family has been suggested, yet this hypothesis has not been tested using modern biogeographic methods with a dated phylogeny. To examine competing hypotheses of African and Malagasy origins, we generated a dated phylogeny using between six and 13 genetic markers, for up to 174 taxa representing greater than 90 per cent of all named species. Using three different ancestral-state reconstruction methods (Bayesian and likelihood approaches), we show that the family most probably originated in Africa, with two separate oceanic dispersals to Madagascar during the Palaeocene and the Oligocene, when prevailing oceanic currents would have favoured eastward dispersal. Diversification of genus-level clades took place in the Eocene, and species-level diversification occurred primarily in the Oligocene. Plio-Pleistocene speciation is rare, resulting in a phylogeny dominated by palaeo-endemic species. We suggest that contraction and fragmentation of the Pan-African forest coupled to an increase in open habitats (savannah, grassland, heathland), since the Oligocene played a key role in diversification of this group through vicariance. PMID:23536596

  20. The terminal Eocene event - Formation of a ring system around the earth

    NASA Technical Reports Server (NTRS)

    Okeefe, J. A.

    1980-01-01

    It is suggested that the formation of a ring system about the earth by particles and debris related to the North American strewn tektite field is responsible for the terminal Eocene event of 34 million years ago, in which severe climatic changes accompanied by widespread biological extinctions occurred. Botanical data is cited which implies a 20-C decrease in winter temperature with no change in summer temperature, and evidence of the correlation of the North American tektite fall, which is estimated to have a total mass of 10 to the 9th to 10 to the 10th tons, with the disappearance of five of the most abundant species of radiolaria is presented. The possible connection between the tektites and climatic change is argued to result from the screening of sunlight by an equatorial ring of trapped particles of extraterrestrial origin in geocentric orbit which would cut off sunlight only in the winter months. Such a ring, located at a distance of between 1.5 and 2.5 earth radii (the Roche limit) is estimated to have a lifetime of a few million years.