PP33B-1534
Re-Os Geochronology Pins Age and Os Isotope Composition of Middle Triassic Black Shales and Seawater, Barents Sea and Spitsbergen (Svalbard)
Absolute age control throughout the Triassic is extraordinarily sparse. Two "golden spikes" have been added recently (http://www.stratigraphy.org/cheu.pdf) within the otherwise unconstrained Triassic, but ages of stage boundaries remain controversial. Here we report two Re-Os isochrons for Anisian (Middle Triassic) black shales from outcrop in western Svalbard and drill core from the Svalis Dome about 600 km to the SE in the Barents Sea. Black shales of the Blanknuten Member, Botneheia Formation, from the type section at Botneheia, western Spitsbergen (Svalbard), have total organic carbon (TOC) contents of 2.6 to 6.0 wt%. Rock-Eval data suggest moderately mature (Tmax = 440-450° C) Type II-III kerogens (Hydrogen Index (HI) = 232-311 mg HC/g TOC). Re-Os data yield a well-constrained Model 3 age of 241 Ma and initial 187Os/188Os (Osi) of 0.83 (MSWD = 16, n = 6). Samples of the possibly correlative Steinkobbe Formation from IKU core hole 7323/07-U-04 into the Svalis Dome in the Barents Sea (at about 73°30'N, 23°15'E) have TOC contents of 1.4 to 2.4%. Rock-Eval data suggest immature (Tmax = 410-430°) Type II-III kerogens (HI = 246-294 mg HC/g TOC). Re-Os data yield a precise Model 1 age of 239 Ma and Osi of 0.776 (MSWD = 0.2, n = 5). The sampled section of Blanknuten shale underlies a distinctive Frechitas (formerly Ptychites) layer, and is therefore assumed to be middle Anisian. The Steinkobbe core was sampled at 99-100 m, just above the Olenekian-Anisian transition. It is therefore assumed to be lower Anisian. The two isochron ages overlap within uncertainty, and fall within constraints provided by biozones and the current ICS-approved stage boundary ages. The Re-Os ages support the correlation of the Botneheia and Steinkobbe formations. The nearly identical Osi ratios suggest regional homogeneity of seawater and provide new information for the Os seawater curve, marking a relatively high 187Os/188Os ratio during profound ocean anoxia in the Middle Triassic.
PP33B-1535
Milankovitch Modulation of the Ecosystem Dynamics of Fossil Great Lakes
Triassic and Early Jurassic lacustrine deposits of eastern North American rift basins preserve a spectacular record of precession-related Milankovitch forcing in the Pangean tropics. The abundant and well-preserved fossil fish assemblages from these great lakes demonstrate a sequence of cyclical changes that track the permeating hierarchy of climatic cycles. To detail ecosystem processes correlating with succession of fish communities, we measured bulk δ13Corg through a 100 ky series of Early Jurassic climatic precession-forced lake level cycles in the lower Shuttle Meadow Formation of the Hartford rift basin, CT. The deep-water phase of one of these cycles, the Bluff Head bed, has produced thousands of articulated fish. We observe fluctuations in the bulk δ13Corg of the cyclical strata that reflect differing degrees of lake water stratification, nutrient levels, and relative proportion of algal vs. plant derived organic matter that trace fish community changes. We can exclude extrinsic changes in the global exchangeable reservoirs as an origin of this variability because molecule-level δ13C of n-alkanes of plant leaf waxes from the same strata show no such variability. While at higher taxonomic levels the fish communities responded largely by sorting of taxa by environmental forcing, at the species level the holostean genus Semionotus responded by in situ evolution, and ultimately extinction, of a species flock. Fluctuations at the higher frequency, climatic precessional scale are mirrored at lower frequency, eccentricity modulated, scales, all following the lake-level hierarchical pattern. Thus, lacustrine isotopic ratios amplify the Milankovitch climate signal that was already intensified by sequelae of the end-Triassic extinctions. The degree to which the ecological structure of modern lakes responds to similar environmental cyclicity is largely unknown, but we suspect similar patterns and processes within the Neogene history of the East African great lakes, which may be modified in the future by anthropogenic CO2-driven intensification of the hydrological cycle.
PP33B-1536
Change of a Paleoecosystem Reef Associated with Variations in the Carbon Cycle
How variations in the carbon cycle affect marine ecosystems is an important question for understanding the consequences of the present day increases in atmospheric CO2. At the present time, coral reefs and their associated fauna have some of the largest marine biodiversity on the planet and therefore represent ecosystems of particular importance. Recent observations suggest that the temperatures associated with the increased atmospheric concentration of greenhouse gases may contribute to an increase in coral bleaching events. Moreover, the increase of CO2 concentration in the atmosphere and seawater is believed to inhibit biogenic calcification. High atmospheric CO2 concentration is believed to enhance oceanic evaporation and contribute to increased precipitation, which in turn favors sediment transfer from continent to ocean. The specific effects of changes in atmospheric CO2concentration on the dynamics of marine faunal communities are as yet not well understood. Here we report an analysis of an Upper Jurassic (Oxfordian, Transversarium zone) reef system in the northern margin of the Atlantic-Tethys Ocean related with a perturbation of the carbon cycle. In the studied sections reproducible carbon isotope shifts are observed in biogenic carbonate. The reef construction is mainly composed of organisms specialized in suspension feeding and microsolenid corals. We observe four fossil-communities matching distinct stages of colonization. The colonization of palaeo-sea bottom begins with a community mainly composed by annelids and soft-bottom bivalves. Then a fossil community characterized by Ostreidae and small-sized corals with low diverse morphology colonized the sea bottom. A third fossil community characterized by calcareous sponges is associated with minimum δ13C values (~ 1 - 1.5 ‰) suggesting enhanced input of dissolved nutrients in the platform under oxidizing conditions. Finally the fourth fossil community is characterized by large-sized corals, an increase of morphotypes and high δ13C values (from 2.5 to 3.5 ‰), probably associated with a diminution of sediment and nutrient supply and therefore more transparent seawater enhancing photosynthetic carbonate production. Simultaneously in the northern margin of the Tethys-Atlantic Ocean, a general trend of the opening up of the platform and connection to open marine waters was observed. Positive δ13C values are interpreted as a result of important accelerated extraction of light carbon from the ocean reservoir that occurred possibly during periods of warm and dry climate. The fossil communities characterize a reef construction in an environment associated with important sediment and nutrient supplies. Similar fossil assemblages identical in age are also observed on the northern margin of the Tethys-Atlantic Ocean. They represent typical biolithostratigraphic succession associated with high CO2 concentration in the atmosphere. During the time of greenhouse atmosphere, high temperatures cause increased evaporation from the oceans, and greater amounts of precipitation, which enhances erosion on, emerged lands. Enhanced siliclastic and nutrient influxes from continent drives the evolution of a reef system dominated by suspension feeding organisms.
PP33B-1537
Paleoclimatic Studies of the Cretaceous Banyawol Stromatolite: A Review of the Microstructure and Cyclicity
In the Cretaceous Gyeongsang Basin, SE Korea, the Banyawol lacustrine stromatolite shows rare microtextural characteristics. Gypsum layers occur as first-order cycles, separating dolomicrospar and dolomicrite in the lower part of the stromatolite while fibrous calcite/microbial micrite couplets form second- order cycles in the upper part. Gypsum and dolomite are not common minerals that are usually interlaminated within stromatolites, thus the mineralogy and microstructure of the stromatolites in the Banyawol Formation is an uncommon example. Petrographic and geochemical analyses display both textural and isotopic differences in the lower and upper parts. Couplets in the upper part mostly show depletions in /delta18O and /delta13C values from fibrous calcite to micrite. A generally increasing 18O trend characterizes the lower part and 13C depletions within the 2nd-order cycles are very consistent. Increases in 18O within the 2nd-order cycles are more conspicuous just before the gypsum layers marking the end of 1st-order cycles. This trend confirms the documented highly arid climate that prevailed when the stromatolites were formed.
PP33B-1538
Drastic Shrinking of the Hadley circulation in the Mid-Cretaceous Supergreenhouse
Understanding the behaviour of the global climate system during extremely warm periods is one of the major targets of paleoclimatology. Paleo-SST proxy data demonstrate that the equator-to-pole temperature gradient was much lower than the present during the mid-Cretaceous gsupergreenhouseh period, implying larger meridional heat transport either by atmospheric and/or oceanic circulation. However, reconstruction of the atmospheric circulation during the Cretaceous has been hampered by the lack of appropriate data sets with reliable proxies. Desert distribution directly reflects the position of subtropical high pressure belt, and prevailing surface wind pattern preserved in the desert deposits gives the information on the exact position of its divergent axis that marks the poleward flank of the Hadley circulation. We reconstruct temporal changes in latitude of the subtropical high pressure belt and its divergent axis during the Cretaceous based on the spatio-temporal changes in latitudinal distribution of deserts and prevailing surface wind patterns recorded in the Asian interior (Gobi basin of Mongolia; Ordos, Subei, Jianguan, Sichuan, Simao basins of China; Khorat basin of Thailand). The results reveal poleward shift of the subtropical high pressure belt during the early and late Cretaceous periods, suggesting poleward expansion of Hadley circulation, whereas equatorward shift of such belt during the mid-Cretaceous gsupergreenhouseh period, suggesting drastic shrinking of the Hadley circulation. These results in conjunction with recent observations suggest that the Hadley circulation gradually expands poleward in response to the increase in global temperatures and atmospheric pCO2, and when global temperatures and atmospheric pCO2 exceed a certain threshold, the Hadley circulation shrinks drastically.
PP33B-1539
Late Cretaceous Subtropical Paleotemperatures from 'Glassy' Foraminifera in East Africa and implications for sensitivity in Greenhouse Climates Models
Coring in southern coastal Tanzania has recovered extended Late Cretaceous intervals containing diverse planktonic foraminiferal assemblages exhibiting 'glassy' preservation (preservation where there is no apparent test recrystallization at the submicron scale). Previous δ18O data for specimens with 'glassy' preservation from Tanzania and elsewhere have demonstrated Late Cretaceous tropical temperatures were sometimes much higher than temperatures in the modern tropics. However, these data come largely from short stratigraphic intervals and/or from samples with unusual lithologic and faunal characteristics raising the possibility that the results reflect temperatures or seawater compositions that were not typical for the time. We are attempting to address this uncertainty by generating long records from multiple taxa preserved in unremarkable outer shelf claystones and silty claystones. For a section spanning most of the Turonian (Whitinella archaeocretacea through Helvetoglobotruncana Helvetica Zones), δ18O results are relatively stable with warmest temperatures estimated at ~34°C (assuming a seawater δ18O value of - 1‰SMOW). The planktic δ18O gradient is <1‰ among most samples. Species of Whitinella consistently yield relatively low values whereas species of Dicarinella yield relatively high values. Our warmest calculated paleotemperatures are several degrees cooler than some Cretaceous tropical temperature estimates but are still ~6°C warmer than summer seawater temperatures in comparable modern settings. The data show no coordinated δ18O shifts that might indicate a Turonian glacial episode. In terms of the Cretaceous greenhouse climate, model experiments reproducing the temperatures calculated require atmospheric CO2 and/or CH2 higher than most estimates for the Cretaceous atmosphere supporting the conclusion that sensitivity to greenhouse gas forcing, at least on long time scales, is too low in the current climate models.
PP33B-1540
Blake Nose Stable Isotopic Evidence against the Mid-Cenomanian Glaciation Hypothesis
To rigorously test a glaciation hypothesis during the mid-Cretaceous greenhouse, detailed multi-taxon stable isotope data and coccolith fraction Sr/Ca data have been obtained from the middle Cenomanian of Ocean Drilling Program Site 1050, Blake Nose, western North Atlantic. The δ18O and δ13C values of each taxon analyzed (surface- to deep-dwelling planktonic foraminifera, benthic foraminifera, coccoliths) show small intra-specific variation, and the inter-taxon offsets are remarkably consistent. Chemostratigraphy by means of a twin δ13C excursion "MCE Ia" and "MCE Ib" in the Rotalipora reicheli Zone facilitates high-resolution correlation of Site 1050 with the European reference sections, allowing the interpretation of the Atlantic middle Cenomanian δ18O record within the context of sea-level change as deduced from sequence stratigraphy. Across MCE Ia, to which a major glacioeustatic regression has been proposed, all the planktonic δ18O signals are essentially constant. Absence of mean seawater δ18O shift at MCE Ia, together with Sr/Ca evidence for the uniform extent of diagenesis, does not support the hypothesized mid-Cenomanian glaciation episode. The benthic δ18O records show significant fluctuation at MCE Ia, and this is likely a result of change in Atlantic deep-water property. A dramatic planktonicbenthic δ18O covariation by ~+1‰ found at MCE Ib is attributed to selective diagenesis based on SEM study of foraminifera and attendant Sr/Ca decrease.
PP33B-1541
Bioapatite epsilonNd Record across the Mid-Cenomanian Event of Demerara Rise and Implications for Tropical North Atlantic Intermediate-Water Circulation
Records of epsilonNd from fish teeth and debris at Demerara Rise (western tropical North Atlantic) show excursions across the mid-Cenomanian event (MCE) with patterns that differ as a function of water depth. The MCE was a significant episode in the Late Cretaceous associated with a major perturbation to the global carbon cycle and marked changes in the sedimentological and biological records. The MCE shows less extreme changes than the more widely documented Oceanic Anoxic Event 2, but the two events have a number of similarities. On Demerara Rise, at both Site 1260 (600 m water paleodepth) and Site 1258 (1,500 m water paleodepth), the Cenomanian sequence exhibits delta13Corg background values of around - 28permil to -29permil and the MCE interval, which is represented by the same organic-rich, finely laminated claystones as the overlying and underlying intervals, shows positive peaks in delta13Corg of up to 4.0permil at Site 1260 and 2.0permil at Site 1258. Similar to other Demerara data, the average epsilonNd(T) signals along the Cenomanian sequence are quite low (-13.9 in Site 1260 and -15.0 in Site 1258) suggesting the epsilonNd of Demerara bottom waters was dominated by inputs from the Guyana Shield with little or no mixing with other North Atlantic intermediate waters. Across the MCE interval, Site 1260 epsilonNd(T) values show positive excursions (up to -11.1) that are inversely correlated to delta13Corg. In contrast, Site 1258 exhibits less radiogenic epsilonNd(T) values (-15.9 to -14.4) across the MCE with excursions that are positively correlated to delta13Corg. The out of phase correlation at Site 1260 is also accompanied by higher epsilonNd(T) variability compared to Site 1258. Analyses are underway to improve sampling resolution, but these preliminary data suggest a decoupling between upper bathyal and lower bathyal waters occurred during the MCE at Demerara Rise. Decoupling could indicate increased water column stratification which is difficult to reconcile with the recently proposed hypothesis of an interval of warm saline water delivery to the bottom of the western tropical North Atlantic around the time of the MCE.
PP33B-1542
The Nd Isotopic Composition of Southern Ocean mid-Late Cretaceous Deep Waters
Considerable uncertainty exists concerning the role that meridional overturning circulation patterns played in poleward heat transport during the middle to Late Cretaceous. It is widely assumed that ventilation in ancient deep ocean basins occurred in a manner similar to the modern: deep convection of surface waters that subsequently circulated as deep- and bottom-water masses. However, model simulations and proxy evidence for warm bottom-water temperatures has led to the concept of warm, saline deep-water formation in low- latitudes ("halothermal" mode) during greenhouse climates rather than a high-latitude thermohaline mode. The only mechanism by which the oceans can transport heat poleward of the Subtropical Front is through polar downwelling, a process that draws surface waters across the frontal boundary. In contrast, oceanic circulation characterized by downwelling in low latitude regions would not enable heat transport into polar regions. Thus, the identifying the fundamental location of deep-water formation is integral to understanding the nature of oceanic heat transport. The first step in testing the hypothesis that deep-water formation at high latitudes ventilated the deep-ocean during the middle to Late Cretaceous is to reconstruct the composition of surface, intermediate, and deep- waters in the various sectors of the Southern Ocean. Here we present Nd isotopic records (143Nd/144Nd expressed as ε Nd) of fish teeth and bones generated from Southern Ocean Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) Sites 361, 511, 530, 690, 763, 765, and 766 (the Atlantic and Indian sectors of the Southern Ocean). The Atlantic sector ε Nd values range from ~ -6 to -7 during the late Campanian and the Indian sector values changed from ~ -9 to -11 from the Cenomanian to the Campanian. The difference in composition likely reflects a difference in Nd inputs to the respective portions of the Southern Ocean as well as limited communication between the Atlantic and Indian sectors due to tectonic barriers such as the Kerguelen Plateau.
PP33B-1543
Depth Related Differences in Nd Isotopes During the Late Cretaceous at Demerara Rise
Late Cretaceous Nd isotopic data derived from fossil fish teeth and debris from Demerara Rise (tropic North Atlantic) illustrate depth-related differences in the distribution of Nd isotopes during Ocean Anoxic Event 2 (OAE2) at the Cenomanian-Turonian. In contrast, values are very similar across depth both before and after the event. Data are reported for Ocean Drilling Program Sites 1258 (3192 m), 1260 (2549 m) and 1261(1899 m) with paleowater depths estimated to range from ~1500 to 600 m, respectively. Cenomanian through Turonian (Site 1258 and 1260) or Santonian (Site 1261) sediments at these sites are composed of organic- rich black shales, which are separated from Campanian and Maastrichtian chalky marls by a hiatus. With the exception of OAE2, the Mid-Cenomanian Event, and a newly documented shift starting within the Maastrichtian, εNd(t) values for the late Cretaceous at all three sites range between -14 to - 16. These background values are distinctly lower than values for other deep sea sites in the North Atlantic, which range from -6 to -10. The lack of structure over ~1000 m of water depth and the unusually low εNd values argue for a distinct Demerara bottom water mass, perhaps locally formed and incorporating Nd from the neighboring Guyana Shield. Consistently low εNd values over tens of millions of years (excursions notwithstanding) suggests that this mode of intermediate water formation was typical of the Late Cretaceous and shows no apparent response to opening of the equatorial Atlantic gateway. Our high resolution records of Nd isotopes throughout OAE2 average one sample every 25 ky and illustrate a dramatic positive excursion at all three sites spanning ~1 km of depth. This excursion is largest and reaches peak values most rapidly at the deepest site, where values peak at -7.5 εNd units at approximately the same level as the first peak in δ13C. In comparison, a peak value of -8.5 εNd units is not achieved in the shallowest site until approximately midway through the δ13C excursion. These depth-related differences can be explained by changes in circulation patterns of intermediate waters during OAE2, with the deepest site responding more quickly and completely to the influence of other North Atlantic intermediate waters. These results suggest enhanced communication between the Demerara region and the rest of the North Atlantic during OAE2 and argue against deep sea stagnation as the cause of enhanced carbon burial. Alternatively, the direction of the excursion at OAE2 is also consistent with introduction of Nd derived from the Caribbean Large Igneous Province (LIP) into an ocean characterized by anoxia. However, preliminary trace element data at Demerara Rise do not indicate enrichments of elements that should accompany changes in ocean chemistry associated with submarine volcanism, and it is unclear why Nd sourced from the Caribbean LIP would produce depth-related gradients in Nd isotopes.
PP33B-1544
Deep To Shallow, Time Transgressive Shift In The Source Of Bottom Waters On Demerara Rise Inferred From Neodymium Isotopes In Fish Debris
Between the Campanian and Danian, εNd values of fish debris from four sites on Demerara Rise (tropical North Atlantic) shift by ~5 units from -16 to -11. Low values from Campanian and early Maastrichtian samples are similar to values measured on most other Late Cretaceous samples from Demerara sites, whereas the post-shift values are similar to Late Cretaceous and Paleogene values observed at a number of other North Atlantic deep sea sites. In addition, at the two relatively deep sites studied (Ocean Drilling Program [ODP] Sites 1258 and 1260), the shift begins near the base of the Maastrichtian Abathomphalus mayaroensis planktonic foraminifera Zone and values increase over an interval representing several million years of deposition. In two relatively shallow sites (OSP Sites 1259 and 1261), on the other hand, εNd values remain low through the highest Cretaceous samples measured, which are from near the top of the Abathomphalus mayaroensis Zone. Therefore, low values persist for several million years longer at the shallower sites. At Site 1259, no Paleogene samples have been analyzed yet, but at Site 1261 values shift from ~-16.5 to ~-13 in samples separated by ~3.5 m and bracketing the Cretaceous/Paleogene (K/T) boundary. Unfortunately, the K/T boundary is not complete at Site 1261, so the relationship to the K/T event is unclear. Ongoing work is focused on constraining the relationship between εNd shifts and the K/T boundary using the more complete record at Site 1259 and at examining whether there is any high frequency variation superimposed on the gradual trends observed, especially at the deeper sites. Regardless of the outcome of the these analyses, assuming the low εNd values characteristic of most the Late Cretaceous on Demerara Rise are the signature of a locally formed intermediate water mass, the existing data already indicate that the importance of downwelling in the tropical North Atlantic began to wane in the mid- Maastrichtian and had apparently ceased by the earliest Paleogene.
PP33B-1545
Exploring the implications of a dynamic Ca cycle in the Cenozoic
Recent work measuring the Ca isotopic composition of Cenozoic marine sediments has resulted in a variety of Ca isotope curves and related interpretations. Such isotope records may be interpreted as representing changes in the Ca isotopic composition of either seawater or the output flux (e.g., nannofossil ooze, foraminiferal tests, or barite). Variability in surface ocean temperature and/or the mode of carbonate deposition in the ocean, as they affect the fractionation factor between seawater and the primary sedimentation flux, have been suggested as causes of change. Within the context of the global Ca cycle, the levers that drive change are the isotopic composition of the weathering flux and the balance between the Ca input and output fluxes to and from the ocean. In many cases, it is quite reasonable to explain the observed variations in the Ca isotope record as being due to imbalances in the weathering (FW) and sedimentation (FSed) fluxes. The current work offers a critical analysis of the hypothesis that imbalances between the weathering and sedimentation fluxes affects the Ca isotopic of the ocean over million-year time scales. Employing numerical models of various complexities, this study addresses the major questions surrounding the interpretation of Ca isotopes as a relative weathering proxy: (1) can the Ca flux into the ocean due to weathering be significantly greater than or less than the sedimentation flux on long time scales, (2) do imbalances in the relative weathering flux (FW/FSed) result in reasonable changes in ocean alkalinity, and (3) over what time scales are changes in the fractionation factor visible in either a tracer proxy (e.g., barite) or a primary component of the output flux (e.g., nannofossil ooze)? These questions must be resolved if Ca isotopes are to be used as a robust proxy for past temperature and/or weathering regime. Simple box models coupling the Ca and C cycles show that FW/FSed decreases of 5 to 10% over tens of thousands of years can drive ocean alkalinity to zero. This is not a realistic scenario, requiring a more in-depth look at Ca cycling and the chemistry of the ocean. This study, therefore, evaluates existing Ca isotope records in the context of temperature change, hydrothermal exchange, and varying contributions to the terrestrial weathering flux.
PP33B-1546
Sediment Fluxes and Provenance for the Paleocene Eocene Thermal Maximum (PETM) at Walvis Ridge; Constraints From Helium Isotopes
We report a high-resolution helium stable isotope stratigraphy spanning the latest Paleocene into the early Eocene section of ODP Site 1266 and an extended %CaCO3 and d13Cbulk record. Helium extracted from deep-sea sediments can be considered a mixture of 3He enriched extraterrestrial and 3He poor terrestrial endmembers. By assuming a constant flux of extraterrestrial 3He, 3HeET, to the seafloor we have constructed a high-resolution age model for the Paleocene Eocene Thermal Maximum, PETM. Trends in 3HeET concentrations replicate those observed at ODP site 690 by Farley and Eltgroth (2003) and imply similar but less extreme changes in sedimentation rates. An excursion in the concentration of terrestrial 4He, 4HeTerr, within the non-carbonate sediment fraction indicates a shift in provenance of terrigenous material buried at Walvis Ridge from 20 to 150 kyr after the onset of the carbon isotope excursion (CIE). The carbonate content remains high through the full recovery of the PETM and only gradually declines after the recovery of the CIE. The observed pattern of a spike in the non-carbonate fraction (NCF), while the concentration of 3HeET in the non-carbonate fraction, [3HeET]NCF, and 3He/4He ratio remain constant is consistent with a carbonate dissolution event and supports a constant flux of helium bearing extraterrestrial material to the sea floor throughout this interval.
PP33B-1547
Dynamics of Carbon Burial in the Coastal Oceans through the Paleocene-Eocene Thermal Maximum
Climatic recovery from the Paleocene-Eocene boundary thermal maximum (PETM) involved the rapid burial of thousands of petagrams of carbon, a significant fraction of which may have been sequestered in marginal marine sediments. This burial flux may have been modulated by changes in climate, biology, sea level, and sediment flux, but the primary pathways and controls on excess carbon burial have remained speculative to this point. Using the global PETM carbon isotope excursion and C/N ratios as tracer of organic carbon source, we investigated preservation of organic carbon through the PETM as particulate organic carbon (POC) and mineral-bound carbon (MBC) at three coastal ocean sites (Tawanui, New Zealand; IODP leg 302, Arctic Ocean; and Wilson Lake, NJ, USA). We show that an increase in total organic carbon burial during the PETM is dominated by burial of young (<10,000 year old), land-derived POC, but that elevated POC burial was limited to sites with high sedimentation rates through the event (ca. 5 cm/kyr). In contrast, MBC sources were more variable, both among sites and through the PETM, and although there was no conclusive evidence for reburial of kerogen-derived MBC at the study sites the carbon isotope data suggest that a fraction of the MBC at each site may have had a long (>10,000 years) residence time prior to burial. MBC dominated the organic burial flux only at the low sedimentation-rate site (Tawanui), but also contributed significantly to changes in total burial at the Arctic site where bottom water anoxia or suboxia has been inferred during the PETM. Our results demonstrate that changes in total carbon burial rates in marginal marine sediments were determined by decoupled responses of the POC and MBC burial pathways that varied substantially among locations, and that the strongest feedbacks on PETM climate involved changes in the transfer of sediment and particulate organic carbon from the continents to the coastal oceans.
PP33B-1548
Sedimentology and Carbon Isotope in Lower Tertiary Sediments of Rajasthan:Implication to Post Paleocene/Eocene Thermal Maximum Event
The Paleocene-Eocene thermal maxima (PETM; ~55 My.), identified as the most abrupt and transient climatic events in Cenozoic era, associated with pronounced warming of ocean and atmosphere, change in ocean chemistry, and perturbation of global carbon cycle. Catastrophic (~5° -6° C) rise in the deep sea temperature and oxygen deficiency might cause 30-50% extinction of benthic foraminifera, increase in sea surface temperature by ~8° C at high latitude (lesser amount towards equator) affected the planktonic biota, and this global warming event led to a pulse of speciation or migration of mammal. PETM is characterized by a prominent drop in carbon isotope values by ~3-4 per mil in both marine and terrestrial sediments in less than 10 ka. The source and triggering mechanism of PETM event are still raging debate. Input of massive amount of greenhouse gas from the dissociation of 13C poor methane hydrate from the continental slop as well as from the terrestrial biosphere is currently the most acceptable explanation for the warming and the negative carbon isotope excursion (CIE). Like other catastrophic events the post-PETM recovery was gradual. Interestingly, δ13C of both carbonate and organic matter shifted towards positive during the recovery period possibly as a combined effect of increased organic burial and silicate weathering. Compared to most studied PETM and post-PETM sections of subtropical to high latitudes, data for equatorial regions and marginal marine are scanty. The marginal marine are important as the effect of silicate weathering or increased burial of shallow marine organic matter will be more pronounced here. The lower Tertiary marginal marine successions of Rajasthan (Akli formation; Giral lignite mine) (paleolatitude ~5° S) shed light on the PETM and post-PETM events and the response of the events on equatorial marginal marine environment. Sedimentological studies suggest that the Akli formation was deposited in a lagoonal environment occasionally inundated by marine incursions. High resolution δ13C Bulk organic matter profile in these lignitic beds and its comparison with the oceanic foraminiferal carbonate δ13C profile reveals that the upper part of the Akli formation was deposited during Early Eocene or recovery phase of PETM. This inference is also supported by the presence of larger benthic foraminifera Nummulites burdigalensis (~52My) in the sand beds. The preliminary data (presence of lignites and C/N Values) suggest that substantial organic carbon burial in shallow seas world over could have been responsible for atmospheric CO2 reduction and enriched δ13C values during the early Eocene period.
PP33B-1549
Late Paleocene to Early Eocene Magneto-Biostratigraphy of the Cicogna section (Belluno Basin, NE Italy)
During the Late PaleoceneEarly Eocene (~60 Ma to 50 Ma), Earth's climate experienced a warming trend that culminated at the Early Eocene Climatic Optimum (EECO). The EECO was characterized by warm conditions at even extreme high latitudes, subdued latitudinal temperature gradients, and virtually nonexistent polar ice sheets. A persistent cooling trend occurred during the Middle and Late Eocene and eventually drove the Earth climate into the current glacial mode. The early Paleogene long-term climate was punctuated by several short-lived hyperthermal events, the most prominent of which is the Paleocene Eocene Thermal Maximum (PETM). Here we present paleomagnetic and calcareous nannofossil data from the Tethyan marine Cicogna section (Belluno Basin, NE Italy). The paleomagnetic results, integrated with calcareous nannofossil biostratigraphy, indicate that the Cicogna section extends from Chron C25r to Chron C23r spanning the NP7/NP8-NP12 nannofossil Zones with a relatively constant sediment accumulation rate of ~18 m/My. To extend the magnetic property characterization of the Belluno Basin sediments in the Early and Middle Eocene, we integrated the Cicogna magnetic analysis results with data from the neighboring Possagno section. Rock-magnetic data show a gradual relative increase in pigmentary (fine-grained) hematite within the sediments that peaked at ~4950 Ma. This datum is interpreted as related to enhanced continental weathering processes under EECO warm climate conditions. The Middle-Late Eocene cooling trend following the EECO was than characterized by a gradual relative decrease of the fine-grained hematite content of the sediments toward pre-warming values. Our findings contribute to the understanding of the coupling between long-term Earth's climate and silicate weathering processes during the Eocene.
PP33B-1550
Astronomical pacing of ecosystem function in the Green River Formation of Utah and Colorado
Part of one of the largest petroleum reserves in the world, the Green River Formation of the Uinta and Piceance Creek basins of Utah and Colorado, formed in a huge Eocene lake system during the warmest, most equable period in recent Earth history. Despite the unit's great potential economic importance and correspondingly large number of geochemical analyses and the preeminent role of these strata in Milankovitch theory (Bradley, 1929), there are surprisingly few systematic studies of the geochemistry of the characteristic permeating cyclicity. Here, we report multiple proxies of lacustrine ecosystem dynamics including oil shale yields, sedimentary facies, carbon and nitrogen isotopes, and molecule-level carbon isotopes from the most oil-rich parts (including the Mahogany oil shale zone) from a series of cores and outcrops in a transect across the Uinta and Piceance Creek basins spanning ~500 m stratigraphically and 3.2 m.y. temporally. Our initial results show covariation in sedimentary facies, oil shale yield, TOC, C/N ratios, and δ13Corg in the expected Milankovitch periodicities, although significant lateral and vertical changes in accumulation make the relative spectral power in the precessional range rather weak. There are, however, differences in the mode of response with oil shale yield, TOC, and sedimentary facies showing more power in the precessional range, while C/N ratios track the 100 ky cycle. C/N ratios tend to be high through multiple precessional cycles dominated by kerogen derived from microbial organic matter suggesting persistent anoxia and a large resulting pool of hypolimnetic ammonium. This pool was eliminated during low lake stands and C/N values then fluctuate through several precession controlled steps. The δ13Corg record, while showing a signal coherent with that of other proxies, has a rather complicated relationship with other proxies, the analysis of which is in its early stages. Molecule-level δ13Corg analysis of n-alkanes suggests mixing of carbon from different sources of varying isotopic composition, and presents a dramatically different pattern from that seen in published studies of the saline facies of the formation. Based on our results, the Milankovitch cyclostratigraphy of these cores in concert with that from the rest of the Uinta and Piceance basin sections, can provide a basis for a time scale for continental environments and pivotal mammalian evolution during the hot-house Eocene.
PP33B-1551
The Paleoecology of Eocene Nannoplankton and Global Oceanographic Variability During the Early-Middle Eocene
The greenhouse to icehouse transition during the Eocene denotes the shift from the highest global temperatures since the Cretaceous to the onset of Antarctic glaciation. The initiation of this transition is marked by a significant overturn in global nannoplankton assemblages as well as changes in the biologic pump and water column stratification as indicated by stable isotopes. The similarity in the timing of these events suggests a connection between plankton populations and water column conditions. Between 50 and 45 Ma, the genus Reticulofenestra dramatically increased in abundance and retained its dominance through the Eocene/Oligocene boundary. This trend is global, including low latitude settings where the evidence for the cooling of surface waters during this transition has been contested. The niche space occupied by Reticulofenestra was previously held by genera conventionally labeled as eutrophic. Traditionally, the paleoecology of calcareous nannofossils has been based upon biogeographic distributions and inferences of temperature and nutrient levels. Here we use multivariate statistics with variables such as latitude, ocean basin, and water column stratification to piece together a quantitative evaluation of major Eocene nannofossil taxa ecology. By combining the abundances of nannofossils with geochemical data, we can begin to understand the complex processes occurring during this critical time interval, relate changes in the water column to the plankton record, and determine how nannoplankton populations respond to climate change and their environment.
PP33B-1552
High resolution Mg/Ca and calcareous nannofossil records from middle Eocene of Blake Nose, ODP Site 1052
Significant short-term, cyclic variations have been identified in the δ18O record of middle Eocene planktonic foraminifera from Blake Nose, subtropical western North Atlantic. The causes of the variations (e.g., the nature of the environmental change) are not well understood. To constrain the nature of the environmental change as well as the response of phytoplankton communities to these changes, we generated high resolution planktonic foraminifera Mg/Ca and calcareous nannofossil absolute abundance data. Planktonic foraminiferal Mg/Ca values increased from ~5.0 mmol/mol at 37.85 Ma to ~5.7 mmol/mol at 37.78 Ma, followed by a gradual decrease to ~4.0 mmol/mol at 37.50 Ma. This translates to a decrease in temperature from ~ 34°C to 28°C, a cooling of ~6°C over 280 ky, and is consistent with the gradual global cooling during the middle Eocene. However, this result is inconsistent with the previously published δ18O data that showed an overall decrease through this interval. This suggests that salinity, not temperature, is the major factor influencing the oxygen isotope record. The nannofossil assemblage at Blake Nose is diverse with 55 taxa identified, and is composed mainly of small Reticulofenestra (0-6μm), Pemma spp., Coccolithus pelagicus, Reticulofenestra bisecta, Reticulofenestra reticulata, Discoaster barbadiensis, Zygrhablithus bijugatus and Discoaster saipanensis. Other less common taxa include Braarudosphaera spp., Calcidiscus protoannulus, Sphenolithus moriformis, Discoaster tanii, and Coccolithus formosus. We compared the nannofossil absolute abundance data with the Mg/Ca paleotemperatures. No single taxa showed a direct similarity with the Mg/Ca paleotemperature trend suggesting that other factors such as salinity and nutrient level could be affecting their abundance.
PP33B-1553
Mechanisms for Early Eocene Warmth: A Downscaling Approach Utilizing the Weather Research and Forecasting Model
The mechanisms for maintaining Early Eocene high-latitude warmth are poorly understood, especially during the long, dark winter months. Climate models have been unable to resolve these mechanisms due to their coarse resolution. This project provides a new tool for use in paleoclimate studies by utilizing a downscaling approach. The mesoscale Weather Research and Forecasting (WRF) model is initialized with both boundary and initial conditions provided from output from an early Eocene experiment with the NCAR Community Climate System Model (CCSM3.0). Ten years of atmosphere model output at 6 hourly intervals was time filtered using Fourier analysis. Since water vapor is believed to be the prime contributor to maintaining warmth, large positive anomalies in specific humidity at the 992mb level were identified and extracted for input into WRF. The WRF model was then run on a 200 X 200 grid at 45km grid spacing centered over the North Pole, with a nested domain on a 181 X 121 grid at 15km spacing centered over northern Canada. The high resolution and advanced physics schemes in WRF help identify weather patterns not previously possible in coarse resolution climate models.
PP33B-1554
An atmosphere-ocean GCM modelling study of the climate response to changing Arctic seaways in the early Cenozoic.
The report of fossil Azolla (a freshwater aquatic fern) in sediments from the Lomonosov Ridge suggests low salinity conditions occurred in the Arctic Ocean in the early Eocene. Restricted passages between the Arctic Ocean and the surrounding oceans are hypothesized to have caused this Arctic freshening. We investigate this scenario using a water-isotope enabled atmosphere-ocean general circulation model with Eocene boundary conditions including 4xCO2, 7xCH4, altered bathymetry and topography, and an estimated distribution of Eocene vegetational types. In one experiment, oceanic exchange between the Arctic Ocean and other ocean basins was restricted to two shallow (~250 m) seaways, one in the North Atlantic, the Greenland-Norwegian seaway, and the second connecting the Arctic Ocean with the Tethys Ocean, the Turgai Straits. In the restricted configuration, the Greenland-Norwegian seaway was closed and exchange through the Turgai Straits was limited to a depth of ~60 m. The simulations suggest that the severe restriction of Arctic seaways in the early Eocene may have been sufficient to freshen Arctic Ocean surface waters, conducive to Azolla blooms. When exchange with the Arctic Ocean is limited, salinities in the upper several hundred meters of the water column decrease by ~10 psu. In some regions, surface salinity is within 2-3 psu of the reported maximum modern conditions tolerated by Azolla (~5 psu). In the restricted scenario, salt is stored preferentially in the North Atlantic and Tethys oceans, resulting in enhanced meridional overturning, increased poleward heat transport in the North Atlantic western boundary current, and warming of surface and intermediate waters in the North Atlantic by several degrees. Increased sensible and latent heat fluxes from the North Atlantic Ocean, combined with a reduction in cloud albedo, also lead to an increase in surface air temperature of over much of North America, Greenland and Eurasia. Our work is consistent with previous findings on the potential influence of Arctic gateways on ocean overturning and also suggests that Northern Hemisphere climate, particularly in the North Atlantic, was very sensitive to changes in Arctic seaways. This result is of particular significance when considered in the context of the Paleocene Eocene Thermal Maximum (PETM). Volcanic activity prior to the PETM may have been responsible for the formation of a sub-aerial barrier in the North Atlantic, and consequently may have driven warming of intermediate waters sufficient to destabilize methane clathrates. Evidence for freshening of Arctic ocean waters prior to the PETM would support this hypothesis.
PP33B-1555
Evidence From Svalbard for Cool Episodes in Early Tertiary Arctic Climate
The Arctic is a climatically sensitive and important region. However, very little is known about the climatic and oceanographic evolution of the area, particularly prior to the Neogene. Until recently, the Arctic was assumed to be characterized by relatively warm conditions during the early Cenozoic. The Early Tertiary sedimentary sequence on Svalbard contains several layers with coal seams and broad-leaved plants which were commonly accepted as indicators of a generally temperate-warm climate. Here we report on the intermittent occurrence of certain temperature indicators in the succession, which may represent the first northern high- latitude record of near-freezing temperatures for the early Cenozoic. Besides the findings of probably ice- rafted erratic clasts in the Paleocene and Eocene sandstones and shales, we note especially the occurrence of glendonites which are pseudomorphs of calcite after ikaite (calcium carbonate hexahydrate). Stratigraphic control for the most important glendonite layers was improved by paleomagnetic investigations on the host sediment. We measured the chemical composition of Svalbard glendonites which is almost identical to that of similar pseudomorphs from the Lower Cretaceaous of Northern Canada. Mass spectrometric analyses of the glendonite calcite gave very low carbon isotope values. These values suggest a provenance of the calcium carbonate from marine organic carbon and connect our glendonites to the precursor mineral ikaite which has similar low values. Since a variety of studies has demonstrated that ikaite is stable only at temperatures close to freezing point, we have to infer low temperatures also for the deepositional environment of which the sediments were deposited that now hold glendonites. These results imply the occurrence of cooling phases episodically during the warm background climate of the Paleocene and Eocene, suggesting that temperature variability was much greater than previously recognized.
PP33B-1556
Evaluating the Input of Iceberg-Rafted vs. Sea Ice-Rafted Debris Using Surface Texture Analyses of Quartz Grains From the ACEX Central Arctic Middle Eocene Marine Sediment Record
The temporal accumulation pattern of terrigenous sand in IODP Expedition 302 (ACEX) cores from the Lomonosov Ridge is evidence of a long ice-rafting history for the central Arctic, one that is well established by 46 Ma (St. John, 2008). However, the type of ice sea ice or icebergs that transported the terrigenous debris (i.e., ice-rafted debris, or IRD) remains a question. Both sea ice and icebergs are known to transport sand size grains in the abundances measured from the ACEX cores. A previous Arctic study (Duhill, 1998) indicated that sea ice and iceberg rafted grains can be distinguished based on certain surface texture characteristics, including mechanical abrasion and chemical dissolution and precipitation features. Assuming the textural characteristics of the Dunhill (1998) classification are correct, we have applied this method to a preliminary set of ACEX IRD samples. Sixteen IRD samples from the IODP 302 core 55X were selected for surface texture analysis. Core 55X has good age control and was already shown to have a middle Eocene ice-rafting record that is cyclic and corresponds to obliquity forcing (Sangiorgi et al., 2008). A subset of quartz grains from each sample were examined using a checklist approach with 30 surface texture categories and SEM imaging. Preliminary analyses of this initial data set using Principle Component Analyses and Discriminant Analysis indicate that some stratigraphic patterns seem to emerge. Sea ice appears to be the dominant mechanism for the early ice transport. A spike in iceberg transport occurs at 240.53 mbsf, and there is generally greater iceberg transport above this level in core 55X. Lastly, cyclic peaks in overall IRD abundance correspond to increased iceberg IRD vs. sea ice IRD.
PP33B-1557
The 10,000 Year-scale Paleoceanography Based on Silicoflagellate and Ebridian Assemblages in the Middle Eocene Arctic Ocean
IODP Exp. 302 (Arctic Coring Expedition - ACEX) revealed that the paleo-geography of the Arctic Ocean in the early middle Eocene was a semi-closed basin similar to the modern Black and the Baltic Seas, based on many paleoceanographic proxies. The primary composition of the microfossil assemblages of the middle Eocene ACEX cores included silicoflagellates and ebridians in addition to abundant diatoms. Because that the silicoflagellates and ebridians are abundantly observed in coastal waters, which sometime includes the eutrophic suboxic waters in the euphotic layer, the analysis of these siliceous microfossils on their abundances and assemblage changes appears to indicate the extent of surface water connections between the Arctic and the Atlantic Oceans. The silicoflagellate and ebridian assemblages in the studied ACEX cores were usually unique, suggesting the limited surface water mixing between the neighboring oceans probably due to the salinity front. However, the assemblage similarities were not always consistent between the Arctic and the Atlantic Oceans. The studied sediments were deposited in the anoxic deep waters without bioturbation, and thus a high resolution study has been hereby accomplished in order to decipher the Milankovich Cycle. While our previous publications on the silicoflagellate and ebridian assemblages were based on the chronological resolution of approximately every 40 kyrs, here we present our temporally significantly improved results based on the sample sets of approximately every 10 kyr resolution.
PP33B-1558
Large Variations in Ice Volume During the Middle Eocene "Doubthouse"
The onset of glacial conditions in the Cenozoic is widely held to have begun ~34 million years ago, coincident with the Eocene-Oligocene boundary1. Warm and high pCO2 'greenhouse' intervals such as the Eocene are generally thought to be ice-free2. Yet the sequence stratigraphic record supports the occurrence of high-frequency sea-level change of tens of meters in the Middle and Late Eocene3, and large calcite and seawater δ18O excursions (~0.5-1.0 permil) have been reported in foraminifera from open ocean sediments4. As a result, the Middle Eocene is often considered the intermediary "doubthouse". The extent of continental ice during the 'doubthouse' is controversial, with estimates of glacioeustatic sea level fall ranging from 30 to 125m2,3,5. We present a new δ18Osw reconstruction for Ocean Drilling Project (ODP) Site 1209 in the tropical Pacific Ocean. It is the first continuous high-resolution record for an open-ocean site that is not directly influenced by changes in the carbonate compensation depth, which enables us to circumvent many of the limitations of existing records. Our record shows increases of 0.8 ± 0.2 (1 s.e) permil and 1.1 ± 0.2 permil at ~44-45 and ~42-41 Ma respectively, which suggests glacioeustatic sea level variations of ~90 m during the Middle Eocene. Modelling studies have shown that fully glaciating Antarctica during the Eocene should drive a change in seawater (δ18Osw) of 0.45 permil, and lower sea level by ~55 m6. Our results therefore support significant ice storage in both the Northern and Southern Hemisphere during the Middle Eocene 'doubthouse'. 1.Miller, Kenneth G. et al., 1990, Eocene-Oligocene sea-level changes in the New Jersey coastal plain linked to the deep-sea record. Geological Society of America Bulletin 102, 331-339 2.Pagani, M. et al., 2005, Marked decline in atmospheric carbon dioxide concentrations during the Paleogene. Science 309 (5734), 600-603. 3.Browning, J., Miller, K., and Pak, D., 1996, Global implications of Eocene Greenhouse and Doubthouse sequences on the New Jersey coastal plain; the Icehouse cometh. Geology 24 (7), 639-642. 4.Tripati, A.K., Backman, J., Elderfield, H., and Ferretti, P., 2005, Eocene bipolar glaciation associated with global carbon cycle changes. Nature 436 (7049), 341-346. 5.Edgar, K.M., Wilson, P.A., Sexton, P.F., and Suganuma, Y., 2007, No extreme bipolar glaciation during the main Eocene calcite compensation shift. Nature 448 (7156), 908-911. 6.DeConto, R. and Pollard, D., 2003, Rapid Cenozoic glaciation of Antarctic induced by declining atmospheric CO2. Nature 421, 245-249.
PP33B-1559
Organic Carbon Burial Following the Middle Eocene Climatic Optimum (MECO) a Mechanism for Global Cooling?
Long-term cooling through the Eocene was interrupted ~40 Ma by a ~500 kyr long climatic warming event in the Middle Eocene known as the Middle Eocene Climatic Optimum (MECO). Here, we present coupled trace metal geochemistry and stable isotope data for the Alano di Piave section, NE Italy over the MECO interval. Originally documented at several deep sea sites in the Southern Ocean (Bohaty and Zachos, 2003), we confirm the widespread extent of MECO from a marginal basin in the western Teyths. The initiation of the isotope excursion, interpreted to be the MECO event, occurs within magnetochron C18r at ~40.5 Ma with minimum δ18O and δ13C values achieved at the base of C18n.2n ~40.13Ma, which are interpreted to represent peak warming conditions. Trace element geochemistry is coupled with bulk stable isotopes, δ18O, inorganic carbon (δ13Ccc) and organic carbon (δ13Corg), and both CaCO3 and organic carbon sediment content (TOC) to investigate this significant paleoenvironmental change following the MECO. Two organic rich intervals (up to 3% TOC) are associated with increases in the concentration of sulphur, and redox-sensitive trace metals, very low concentrations of Mn and the occurrence of pyrite. Together these changes imply low bottom water O2 conditions, possibly anoxic to dysoxic during this interval. At the same time nannofossil assemblages shift from oligotrophic to eutrophic suggesting increased nutrient input and surface ocean productivity. As do negative δ13Corg excursions and positive δ13Ccc excursions coincident with the organic rich intervals. Increases in terrigenous and organic marine matter to the sediment precede the first organic rich interval and may provide a driving mechanism for the development of anoxic conditions. Furthermore the rapid burial of organic carbon will have lowered global pCO2 and returned the climate system to the general Eocene cooling trend. Bohaty, S. M., & J. C. Zachos, (2003) Geology, 31, 1017-1020
PP33B-1560
Eocene-Oligocene Transition Across the Indian Ocean: Nitrogen Isotopes and Bottom Water Oxic/Anoxic Pulses
The Eocene-Oligocene Transition (EOT; Pearson et al., 2008) marks a period of rapidly expanding continental glaciation on Antarctica. Coevally, the Antarctic Circumpolar Current was establishing, and it is postulated that the Antarctic bottom waters were feeding deep water into the tropical Indian Ocean (as occurs in modern day). Also, during this interval increased productivity is reported from the southern high latitudes, as a result of increased detrital nutrient flux and cooling-enhanced upwelling. In this study, sites from southern Tanzania and Java, Indonesia were sampled across the Eocene-Oligocene Boundary (EOB). These sites represent outer-shelf to slope environments, recorded in dark, organic-rich clays with less than 10% CaCO3. Nitrogen isotopes and major and trace elements were analysed from these well-preserved, thermally immature sediments. Results from the Tanzanian EOT show two cycles of increased productivity, beginning at the Eocene- Oligocene Boundary. We also detect the onset of rapid changes in the oxic/anoxic conditions at the sediment-water interface. These rapid oscillations occur throughout the EOT but return to pre-EOT values after 33.5 Ma. These data may be explained by productivity changes through the transition, coupled with changing ocean thermal dynamics relating to the 'turning on' of the circum-Antarctic currents. The results from Java will allow us to see if these changes are ocean-wide, or if they are restricted to specific regions. Current studies indicate that productivity changes were widespread, possibly global, and occurred at all latitudes. This dataset may lend further support to this hypothesis, and will certainly allow for a better understanding of globabl productivity changes during the Eocene-Oligocene Transition.