the role of lithospheric flexure in the landscape evolution of the wilkes subglacial basin and transantarctic mountains east antarctica reconstructions of the bedrock topography of antarctica since the eocene oligocene boundary ca 34 ma provide important constraints for modelling antarctic ice sheet evolution this is particularly important in regions where the bedrock lies below sea level since in these sectors the overlying ice sheet is thought to be most susceptible to past and future change here we use 3d flexural modelling to reconstruct the evolution of the topography of the wilkes subglacial basin wsb and transantarctic mountains tam in east antarctica we estimate the spatial distribution of glacial erosion beneath the east antarctic ice sheet and restore this material to the topography which is also adjusted for associated flexural isostatic responses we independently constrain our post 34 ma erosion estimates using offshore sediment stratigraphy interpretations our reconstructions provide a better defined topographic boundary condition for modelling early east antarctic ice sheet history we show that the majority of glacial erosion and landscape evolution occurred prior to 14 ma which we interpret to reflect more dynamic and erosive early ice sheet behaviour in addition we use closely spaced 2d flexural models to test previously proposed hypotheses for a flexural origin of the tam and wsb the pre 34 ma topography shows lateral variations along the length of the tam and wsb that cannot be explained by uniform flexure along the front of the tam we show that some of these variations may be explained by additional flexural uplift along the south western flank of the wsb and the rennick graben in northern victoria land

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

evidence for an earliest oligocene ice sheet on the antarctic peninsula there is growing consensus that development of a semipermanent ice sheet on antarctica began at or near the eocene oligocene e o boundary beyond ice rafted debris in oceanic settings however direct evidence for a substantial ice sheet at this time has been limited and thus far restricted to east antarctica it is unclear where glacier ice first accumulated and how extensive it was on the antarctic continent in the earliest oligocene sediments at the top of the eocene marine shelf section on seymour island antarctic peninsula include glacial marine deposits and a lodgment till with clasts derived from a variety of rock units on the peninsula dinoflagellate biostratigraphy and strontium isotope stratigraphy indicate an age at or very close to the e o boundary glacier ice extending to sea level in the northern peninsula at this time suggests the presence of a regionally extensive west antarctica ice sheet and thus an even more dramatic response to the forcing factors that facilitated high latitude ice expansion in the earliest oligocene

eocene oligocene global climate and sea level changes st stephens quarry alabama we integrate upper eocene lower oligocene lithostratigraphic magnetostratigraphic biostratigraphic stable isotopic benthic foraminiferal faunal downhole log and sequence stratigraphic studies from the alabama st stephens quarry ssq core hole linking global ice volume sea level and temperature changes through the greenhouse to icehouse transition of the cenozoic we show that the ssq succession is dissected by hiatuses associated with sequence boundaries three previously reported sequence boundaries are well dated here north twistwood creek cocoa 35 4 35 9 ma mint spring red bluff 33 0 ma and bucatunna chickasawhay the mid oligocene fall ca 30 2 ma in addition we document three previously undetected or controversial sequences midpachuta 33 9 35 0 ma shubuta bumpnose lowermost oligocene ca 33 6 ma and byram glendon 30 5 31 7 ma an 0 9 18 o increase in the ssq core hole is correlated to the global earliest oligocene oi1 event using magnetobiostratigraphy this increase is associated with the shubutabumpnose contact an erosional surface and a biofacies shift in the core hole providing a fi rst order correlation between ice growth and a sequence boundary that indicates a sea level fall the 18 o increase is associated with a eustatic fall of 55 m indicating that 0 4 of the increase at oi1 time was due to temperature maximum 18 o values of oi1 occur above the sequence boundary requiring that deposition resumed during the lowest eustatic lowstand a precursor 18 o increase of 0 5 33 8 ma mid chron c13r at ssq correlates with a 0 5 increase in the deep pacifi c ocean the lack of evidence for a sea level change with the precursor suggests that this was primarily a cooling event not an ice volume event eocene oligocene shelf water temperatures of 17 19 c at ssq are similar to modern values for 100 m water depth in this region our study establishes the relationships among ice volume 18 o and sequences a latest eocene cooling event was followed by an earliest oligocene ice volume and cooling event that lowered sea level and formed a sequence boundary during the early stages of eustatic fall

a new basis for recognizing the paleocene eocene boundary in western interior north america fossil pollen grains from paleocene eocene rocks of the bighorn basin of wyoming allow important sequences of terrestrial vertebrate fossils to be correlated with standard marine microfossil zonations the paleocene eocene boundary as based on pollen evidence falls within the wasatchian land mammal age much higher than the boundary used by some fossil mammal workers this discrepancy partly results from multiple definitions of the paleocene eocene boundary but may also indicate faulty mammal based correlations to the type sparnacian of france

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

the evolution of the subglacial landscape of antarctica the aim is to investigate the evolution of the subglacial landscape of antarctica using an ice sheet and erosion model we identify different stages of continental glaciation and model the erosion processes associated with each stage the model links erosion to the basal thermal regime and indicates that much of the antarctic interior may have been subject to less than 200 m of erosion the depth of erosion reflects the presence or absence of warm based ice and the consistency of ice flow direction this information linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography is used to generate a map of the subglacial antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the laurentian and scandinavian shields near the continental margins selective linear erosion has overdeepened pre existing river valleys by as much as 2 8 km high elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold based ice high erosion rates result from steep thermal gradients in basal ice mountain regions such as the gamburtsev mountains uplands in dronning maud land and massifs in west antarctica are likely to bear features of local alpine glaciation such landscapes may have been protected under cold based ice for the last 34 myrs or possibly longer

relative sea level rise around east antarctica during oligocene glaciation during the middle and late eocene 48 34 myr ago the earth s climate cooled and an ice sheet built up on antarctica the stepwise expansion of ice on antarctica induced crustal deformation and gravitational perturbations around the continent close to the ice sheet sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet here we identify the crustal response to ice sheet growth by forcing a glacial hydro isostatic adjustment model with an antarctic ice sheet model we find that the shelf areas around east antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed the inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice sheet margins consequently the coasts experienced a progressive relative sea level rise our analysis of sediment cores from the vicinity of the antarctic ice sheet are in agreement with the spatial patterns of relative sea level change indicated by our simulations our results are consistent with the suggestion that near field processes such as local sea level change influence the equilibrium state obtained by an ice sheet grounding line

calibration between eustatic estimates from backstripping and oxygen isotopic records for the oligocene eustatic estimates from the backstripping of oligocene sections are compared quantitatively with d 18 o data each of the nine oligocene d 18 o events maxima identified in previous studies correlates with a stratigraphically determined sea level lowstand oxygen isotopic records from planktonic foraminifers from western equatorial atlantic ocean drilling program odp site 929 indicate an isotopic increase of 0 16 per 10 m decrease in the depth of the ocean apparent sea level asl amplitudes of asl change also correlate with moderate and high resolution benthic foraminiferal d 18 o records from odp sites 803 western tropical pacific and 929 and from deep sea drilling project dsdp site 522 south atlantic ocean with an isotopic change of 0 22 per 10 m of asl change r 2 5 0 807 and 0 960 respectively and with records from odp site 689 southern ocean 0 13 per 10 m of asl change r 2 5 0 704 this correlation suggests that southern ocean deep water temperature changes were smaller than tropical sea surface temperature changes between million year scale glacials and interglacials it also suggests that the deep sea southern ocean records may provide the best means to calibrate sea level to oxygen isotopes

facies analysis and palaeoclimatic significance of ironstones formed during the eocene greenhouse lower and middle eocene ironstone sequences of the naqb and qazzun formations from the north east bahariya depression western desert egypt represent a proxy for early palaeogene climate and sea level changes these sequences represent the only palaeogene economic ooidal ironstone record of the southern tethys these ironstone sequences rest unconformably on three structurally controlled cenomanian palaeohighs for example the gedida harra and ghorabi mines and formed on the inner ramp of a carbonate platform these palaeohighs were exposed and subjected to subaerial lateritic weathering from the cenomanian to early eocene the lower and middle eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies the distribution of low energy ironstone facies is controlled by depositional relief these deposits consist of lagoonal burrow mottled mud ironstone and laterally equivalent tidal flat stromatolitic ironstones the agitated water ironstone facies consist of shallow subtidal intertidal nummulitic ooidal oncoidal and back barrier storm generated fossiliferous ironstones the formation of these marginal marine sequences was associated with major marine transgressive regressive megacycles that separated by subaerial exposure and lateritic weathering the formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features such as colloform texture and alveolar voids implies periods of humid and warm climate followed major marine regressions the formation of the lower to middle eocene ironstone succession and the associated lateritic palaeosols can be linked to the early palaeogene global warming and eustatic sea level changes the reworking of the middle eocene palaeosol and the deposition of the upper eocene phosphate rich glauconitic sandstones of the overlying hamra formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions

paleogene stable isotope events the oxygen isotope record in paleogene benthic foraminifera shows that at the base of the paleogene the ocean deep waters had a temperature of about 10 c rising to about 12 c at the base of the eocene and cooling between 51 ma and 49 ma to about 9 c the most dramatic event occurred just after the eocene oligocene boundary at about 35 8 ma when ocean deep waters cooled by several degrees within 104 105 yr probably in association with temporary glaciation in the antarctic region another more intense glacial event in antarctica may have occurred later in the oligocene at about 31 ma and a third near the top of the oligocene at 24 ma in the marine carbon isotope record a very rapid negative excursion occurred precisely at the cretaceous tertiary boundary a recovery to unusually positive values in the late paleocene was followed by a second negative excursion close to the paleocene eocene boundary that was even more extreme in magnitude although it was not as rapid these major carbon isotope events permit very accurate stratigraphic correlation there are many other smaller features in the carbon isotope record that will also prove useful for this purpose

the mmco eot conundrum same benthic δ18o different co2 knowledge on climate change during the cenozoic largely stems from benthic 18o records which document combined effects of deep sea temperature and ice volume information on co2 is expanding but remains uncertain and intermittent attempts to reconcile 18o sea level and co2 by studying proxy data suffer from paucity of data and apparent inconsistencies among different records one outstanding issue is the difference suggested by proxy co2 data between the eocene oligocene boundary eot and the middle miocene climatic optimum mmco while similar levels of 18o are shown during these times this conundrum implies changing relations between 18o co2 and temperature over time here we use a coupled climate ice sheet model forced by two different benthic 18o records to obtain continuous and mutually consistent records of 18o co2 temperature and sea level over the period 38 to 10 myr ago we show that the different co2 levels between the eot and mmco can be explained neither by the standard configuration of our model nor by altering the uncertain ablation parametrization on the east antarctic ice sheet however we offer an explanation for the mmco eot conundrum by considering erosion and or tectonic movement of antarctica letting the topography evolve over time a decreasing height of the antarctic continent leads to higher surface temperatures reducing the co2 needed to maintain the same ice volume this also leads to an increasing contribution of ice volume to the 18o signal this result is however dependent on how the topographic changes are implemented in our ice sheet model

taphonomy of vertebrate assemblages from the paleogene of northwestern wyoming and the neogene of northern pakistan abstract we compare the taphonomy of vertebrate assemblages from two long continental records the early paleogene of the bighorn basin wyoming and the neogene siwalik sequence of northern pakistan both sequences contain a similar array of fluvial facies and the abundance of these facies differs among formations we document environments of preservation of vertebrate localities over time to determine comparability of fossil assemblages within and between sequences changes in sample size and species richness are noted to reveal potential sampling effects on patterns of faunal turnover preservational history determined the environment sample size quality of specimens taxonomic composition and spatial and temporal resolution of fossil assemblages and thereby the quality of the fossil record and its suitability for further analyses in both sequences changes in prevailing taphonomic processes reflect changes in lithofacies and habitat distribution correlated changes are found in fossil productivity species richness and faunal composition both sequences contain some episodes of apparent faunal change in which appearances and disappearances of rare taxa can be attributed principally to changes in sample size the paleogene record has high taxonomic resolution i e to genus or species for most mammalian fossil remains temporal and spatial averaging of paleogene fossil assemblages changes with lithofacies the neogene record has higher taxonomic resolution for remains of small mammals different preservational circumstances impose different constraints on paleocological and evolutionary analyses the best opportunities for paleocommunity reconstruction are provided by high taxonomic resolution large samples nd varied environments of preservation these circumstances are found in limited portions of each record the best opportunities for documenting evolution within lineages and species replacement patterns are provided by high taxonomic resolution high temporal resolution and consistent preservational context these taphonomic attributes pertain to the more common paleogene mammals particularly from the rich paleosol localities of the willwood formation and to the more common neogene small mammals from abandoned channel fills of the siwalik record

paleogene geochronology an integrated approach geochronology is the conceptual division of continuous time as measured geochronometry by the progression in an ordinal series of events this is best achieved by an approach which integrates four independent data sets magnetostratigraphy seafloor spreading magnetic lineation patterns biostratigraphy and isotopic ages this integrated approach results in an ordinal framework which can measure time with greater resolution though perhaps less accuracy than a radiometric approach alone a comparative analysis of two recently proposed paleogene geochronologic time scales is presented

mammalian generic diversity and turnover in the late paleocene and early eocene of the bighorn and crazy mountains basins wyoming and montana usa abstract patterns of mammalian generic turnover richness and faunal composition were investigated for faunas from 17 biostratigraphic zones in middle paleocene through early eocene deposits of the bighorn and clarks fork basins of northern wyoming and the crazy mountains basin of south central montana significance of turnover was evaluated 1 by comparison of observed turnover to expected turnover calculated from the multiple regression of turnover on zone duration and generic richness and 2 by comparison of observed turnover to a bootstrapped turnover distribution patterns of turnover and richness also were assessed in light of relative sampling quality of each faunal zone the analysis identified four intervals of significant faunal change the torrejonian tiffanian transition the late tiffanian the earliest wasatchian and the middle to late wasatchian the first interval was characterized by a high number of last occurrences in the latest torrejonian resulting in a decrease in standing generic richness in the earliest tiffanian but no major changes in ordinal composition during the next interval of significant turnover the late tiffanian higher than expected first occurrences resulted in an increase in standing richness and a change in faunal composition most probably reflecting the immigration of taxa from outside north america the third and most dramatic interval of significant generic turnover took place in the earliest wasatchian and was distinguished by a high number of first occurrences but relatively few last occurrences this led to a marked increase in generic richness a pattern similar to that for the early wasatchian of north america as a whole the major change in faunal composition as in the late tiffanian was largely composed of immigrants from other continents the pattern of faunal change during the early wasatchian of the bighorn basin along with evidence for global warming at the paleocene eocene boundary supports previous interpretations associating this episode in mammalian evolution with the opening of high latitude intercontinental dispersal routes during the fourth interval of interest the middle to late wasatchian the bighorn basin fossil record shows a drop in generic richness this differs from the overall north american pattern and may be in part an artifact of still inadequate sampling for the latest part of the stratigraphic sequence in the bighorn basin

late paleocene early eocene tethyan carbonate platform evolution a response to long and short term paleoclimatic change abstract the early paleogene experienced the most pronounced long term warming trend of the cenozoic superimposed by transient warming events such as the paleocene eocene thermal maximum petm the consequences of climatic perturbations and associated changes on the evolution of carbonate platforms are relatively unexplored today modern carbonate platforms especially coral reefs are highly sensitive to environmental and climatic change which raises the question how sub tropical reef systems of the early paleogene reacted to gradual and sudden global warming eutrophication of shelf areas enhanced co 2 levels in an ocean with low mg ca ratios the answer to this question may help to investigate the fate of modern coral reef systems in times of global warming and rising co 2 levels here we present a synthesis of tethyan carbonate platform evolution in the early paleogene 59 55 ma concentrating on coral reefs and larger foraminifera two important organism groups during this time interval we discuss and evaluate the importance of the intrinsic and extrinsic factors leading to the dissimilar evolution of both groups during the early paleogene detailed analyses of two carbonate platform areas at low egypt and middle spain paleolatitudes and comparison with faunal patterns of coeval platforms retrieved from the literature led to the distinction of three evolutionary stages in the late paleocene to early eocene tethys stage i late paleocene coralgal dominated platforms at low to middle paleolatitudes stage ii a transitional latest paleocene platform stage with coralgal reefs dominating at middle paleolatitudes and larger foraminifera dominated miscellanea ranikothalia assilina platforms at low paleolatitudes and stage iii early eocene larger foraminifera dominated alveolina orbitolites nummulites platforms at low to middle paleolatitudes the onset of the latter prominent larger foraminifera dominated platform correlates with the paleocene eocene thermal maximum the causes for the change from coral dominated platforms to larger foraminifera dominated platforms are multilayered the decline of coralgal reefs in low latitudes during platform stage ii is related to overall warming leading to sea surface temperatures in the tropics beyond the maximum temperature range of corals the overall low occurrence of coral reefs in the paleogene might be related to the presence of a calcite sea at the same time larger foraminifera started to flourish after their near extinction at the cretaceous paleogene boundary the demise of coralgal reefs at all studied paleolatitudes in platform stage iii can be founded on the effects of the petm resulting in short term warming eutrophic conditions on the shelves and acidification of the oceans hampering the growth of aragonitic corals while calcitic larger foraminifera flourished in the absence of other successful carbonate producing organisms larger foraminifera were able to take over the role as the dominant carbonate platform inhabitant leading to a stepwise tethyan platform stage evolution around the paleocene eocene boundary this szenario might be also effective for threatened coral reef sites

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

evidence for a heavily glaciated antarctica during the late oligocene warming 27 8 24 5 ma stable isotope records from odp site 690 high 18o values 3 0 from a 9 kyr resolution benthic foraminiferal stable isotope record from the ocean drilling program odp site 690b located on the maud rise antarctica indicate a heavily glaciated antarctic continent during late oligocene 27 8 24 5 ma values ranging 2 5 3 0 during interglacial periods and 3 0 3 6 during glacial intervals are consistent with an ice sheet near or larger than modern size in addition this record does not exhibit the long term late oligocene warming trend seen in records from low latitude drill sites oxygen isotope values from 26 0 24 5 ma are comparable ranging between 2 5 and 3 3 to values that preceded the 18o event oi2b at 26 7 ma indicating no significant glacial collapse occurred during the late oligocene a gradient between ocean basins during the oligocene has already been linked to the development of a modern multi layered ocean and worked to bathe the low to mid latitude deep sea records with a warmer water mass we suggest this masked the significant antarctic glaciation in low latitude paleoceanographic records additionally we propose a resolution for conflicting lines of evidence from some antarctic proximal records suggesting significant glaciation and others suggesting reduced glaciation during the late oligocene by allowing a modern sized ice sheet to grow on an antarctic continent as more land surface area existed above sea level during this time this could allow at least some portions of the antarctic coastline to remain ice free during glacial minima while still maintaining modern or near modern ice volume

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

early east antarctic ice sheet growth recorded in the landscape of the gamburtsev subglacial mountains the gamburtsev subglacial mountains are regarded as a key nucleation site for the antarctic ice sheet and they retain a unique long term record of pre glacial and early glacial landscape evolution here we use a range of morphometric analyses to constrain the nature of early glaciation and subsequent ice sheet evolution in the interior of east antarctica using a new digital elevation model of the gamburtsev subglacial mountains derived from an extensive airborne radar survey we find that an inherited fluvial landscape confirms the existence of the gamburtsev subglacial mountains prior to the onset of glaciation at the eocene oligocene climate boundary ca 34 ma features characteristic of glaciation at a range of scales are evident across the mountains high elevation alpine valley heads akin to cirques identified throughout the mountains are interpreted as evidence for early phases of glaciation in east antarctica the equilibrium line altitudes associated with these features combined with information from fossil plant assemblages suggest that they formed at or prior to 34 ma it cannot be ruled out that they may have been eroded by ephemeral ice between the late cretaceous and the eocene 100 34 ma hanging valleys overdeepenings truncated spurs and steep sided linear valley networks are indicative of a more widespread alpine glaciation in this region these features represent ice growth at or before 33 7 ma and provide a minimum estimate for the scale of the east antarctic ice sheet between ca 34 and 14 ma when dynamic fluctuations in ice extent are recorded at the coast of antarctica the implications are that the early east antarctic ice sheet grew rapidly and developed a cold based core that preserved the alpine landscape the patterns of landscape evolution identified provide the earliest evidence for the development of the east antarctic ice sheet and can be used to test coupled ice climate evolution models

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

plant and mammal diversity in the paleocene to early eocene of the bighorn basin abstract abundant plant and vertebrate fossils have been recovered from fluvial sediments deposited in the bighorn basin wyoming during the first 13 m y of the tertiary here we outline and discuss changes in the composition and diversity of floras and faunas during this period which includes the recovery of terrestrial ecosystems from the k t boundary extinctions and later during the paleocene eocene transition the greatest global warming of the cenozoic floral diversity has been studied at three levels of spatial resolution sub local at individual collecting sites local along a single bed or stratigraphic horizon and basin wide regional sub local diversity shows a moderate increase from the early to late paleocene followed by a decrease across the paleocene eocene boundary then an increase into the later early eocene local heterogeneity was lower in paleocene backswamp floras although distinct groups of species dominated in different local fluvial settings such as backswamps and alluvial ridges heterogeneity of backswamp forests increased by about 65 from the early to late wasatchian early eocene the number of plant species inferred from the bighorn basin dataset rose gradually from the puercan to an early clarkforkian peak of about 40 species declined sharply to about 25 species by the clarkforkian wasatchian boundary then rose through the wasatchian to about 50 species a regional analysis of mammalian genera shows high turnover and a rapidly increasing number of genera within a million years of the k t boundary 10 50 genera a slight decline to 40 genera by the early clarkforkian then an increase from 40 to 75 genera by the late wasatchian our analyses found no major extinctions in mammals during the paleocene and early eocene in the bighorn basin but a one third decrease in the number of plant species at about the paleocene eocene boundary rates of taxonomic turnover were much higher for mammals than plants the diversity trends for plants and mammals show little congruence implying that the two groups responded in a very different manner to post k t extinction opportunities there is also little congruence between plant diversity levels and change in mean annual temperature mat as inferred from foliar physiognomy

paleoecology of an early eocene mammalian fauna from paleosols in the clarks fork basin northwestern wyoming u s a winkler d a 1983 paleoecology of an early eocene mammalian fauna from paleosols in the clarks fork basin northwestern wyoming u s a palaeogeogr palaeoclimmatol palaeoecol 43 261 298 the paleoecology and depositional history of an early eocene vertebrate assemblage dominated by small mammals is analyzed at a richly fossiliferous locality in the willwood formation northwestern wyoming systematic surface sampling using a quadrat net screen washing and quarrying of fresh sediment show that all vertebrate material in these fluvial deposits is contained in dark gray mudstones representing the a horizons of paleosols seven such paleosols occur in 22 m of stratigraphic section the fauna includes 34 species of mammals and also birds reptiles amphibians fishes and gastropods all vertebrate fossil material is fragmented but it shows no evidence of transportation or current sorting surface weathering and possibly carnivore activity are responsible for the fragmentation and for an overabundance of dense and compact skeletal elements detailed surface collections were made to obtain multiple samples from the different bone beds paleosols principle component analysis shows that differences in the type and abundance of fossils from the various collecting areas are related to differences between contained bone beds not differences along single bone beds one paleosol has a red b horizon and six have an orange b horizon the gray over red colored paleosol is faunally distinct from gray over orange paleosols it contains the only specimens of two large archaic mammals and no very small mammalian taxa cluster analysis on the occurrence of vertebrate taxa is used to define subsets of the fauna that may represent animals living in different habitats separate clusters are formed by a group of the most common terrestrial herbivorous mammals and the crocodilian allognathosuchus and by a group of small possibly arboreal herbivores and carnivores the relative abundance of each mammalian species was initially calculated from a sample representing a minimum of 300 individual animals collected from the surface the surface sample is dominated by mammals that are medium sized for the fauna screen washing yields a greater relative abundance of very small mammals than was found on the surface this indicates that the surface sample is biased against small forms corrected relative abundances based on both surface and washing samples show that the fauna is dominated numerically by very small mammals one multituberculate species and several insectivores screen washing of fresh matrix is the best means of sampling a locality for paleoecological purposes

tracer transport in the greenland ice sheet three dimensional isotopic stratigraphy abstract polar ice cores can provide both a record of climate history and a sharp test of the performance of numerical ice dynamics models the stratigraphic structure of an ice sheet is an expression of its full depositional and dynamic history and thus presents a greater challenge to computer models than merely matching the contemporary ice thickness and areal extent we describe a coupled model of ice and tracer dynamics that is realized by adding a semi lagrangian tracer transport scheme to a conventional thermomechanical ice dynamics model model skill is demonstrated by using ice core data from the grip site near summit greenland to successfully predict the isotopic stratigraphy of ice cores at other deep drilling sites the success of this effort indicates that when compensated for the effects of ice flow and elevation all the deep cores relate a coherent glacial history over the past 120 000 years according to the simulation results the oldest greenland ice lies beneath the grip gisp2 and northgrip sites although comparably old ice may also be found in north greenland and east central greenland

thurston island west antarctica between gondwana subduction and continental separation a multistage evolution revealed by apatite thermochronology

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

response of antarctic odp site 690 planktonic foraminifera to the paleocene eocene thermal maximum faunal evidence for ocean climate change 1 high resolution study of antarctic planktonic foraminiferal assemblages ocean drilling program site 690 weddell sea shows that these microplankton underwent a stepwise series of changes during the paleocene eocene thermal maximum petm initiation of this response coincides with the onset of the carbon isotope excursion cie but precedes the benthic foraminiferal mass extinction the top to bottom succession in the biotic response indicates that the surface ocean atmosphere was affected before the deep sea the earliest stage of the faunal response entailed a conspicuous turnover within the shallow dwelling genus acarinina and a succession of stratigraphic first appearances the genus morozovella large 180 m biserial planktonics and a wilcoxensis are all restricted to the lower cie within this petm section acarininid populations crashed as the ocean climate system ameliorated during the cie recovery reflecting atypical surface water conditions this transient decline in acarininids is paralleled by a marked increase in carbonate content of sediments it is postulated that this interval of carbonate enrichment and its unusual microfauna reflects enhanced carbon storage within reservoirs of the global carbon cycle other than the marine carbonate system sensu broecker et al 1993 ravizza et al 2001

turnover of larger foraminifera during the paleocene eocene thermal maximum and paleoclimatic control on the evolution of platform ecosystems the larger foraminifera turnover lft during the paleocene eocene transition constitutes an important step in paleogene larger foraminifera evolution involving a rapid increase in species diversity shell size and adult dimorphism a platform to basin transect in egypt provides new data on timing and causal mechanisms through correlation with planktic biozonations and through integration with regional paleoenvironmental data the lft coincides with the boundary between shallow benthic biozones sbz4 and sbz5 and closely correlates with the paleocene eocene thermal maximum petm enhanced oligotrophy from the late paleocene onward favored the diversification of k strategist larger foraminifera we suggest that a short term eutrophication during the petm led to a temporary decline of extreme k strategist larger foraminifera species providing opportunities for new taxa with different ecological strategies to develop during post petm oligotrophic conditions these new taxa were able to evolve rapidly and soon dominated early eocene larger foraminifera assemblages whereas many paleocene taxa gradually disappeared the success of larger foraminifera during the early paleogene appears climatically controlled because of the vulnerability of corals to high surface water temperatures the late paleocene to early eocene global warming may have favored larger foraminifera at the expense of corals as the main carbonate producing component on carbonate platforms at lower latitudes

patterns of faunal turnover and diversity in the neogene siwaliks of northern pakistan abstract the fluvial neogene siwalik formations of northern pakistan contain a long and richly fossiliferous sequence of terrestrial vertebrate faunas in which patterns of faunal turnover and changes in diversity can be documented and analyzed for intervals having durations of 0 5 m y the complete sequence extends from circa 18 5 to 1 ma but the part between 18 5 and 5 5 ma is best sampled and most intervals within it are well represented thirteen orders of siwalik mammals have been identified with well sampled intervals having 50 or more species most siwalik mammals however are either rodents or artiodactyls bovids are the most common and most speciose of the larger mammals while murid and cricetid rodents dominate the small mammal assemblages between 18 5 and 5 5 ma species diversity varied considerably among artiodactyls and rodents the number of species first increased between 15 and 13 ma and then fell data on stratigraphic ranges of rodents and artiodactyls show that faunal change in the siwaliks was episodic occurring during short intervals with high turnover followed by longer periods with considerably less change maxima of first appearances occurred at approximately 13 5 and 8 5 ma while maxima of last occurrences were at 12 5 and 8 0 ma some of the observed faunal events can be correlated to climatic and environmental changes the middle miocene diversification occurred during a period of global cooling while the latest miocene decline in diversity and increased turnover accompanied oxygen and carbon isotopic changes that correlate to globally increasing seasonality and aridity other correlations are ambiguous the marked decrease in diversity and the major turnover events between 13 and 8 ma do not correspond to known local or global events the neogene siwaliks and paleogene bighorn crazy mountains sequence in wyoming and montana share many similarities they have equivalent levels of temporal resolution and similar levels of completeness of their fossil records siwalik ordinal abundance and diversity patterns differ markedly from those of the paleogene but generic and probably species diversity was approximately the same although the siwalik faunas may have been slightly less diverse over time changes in diversity were of comparable magnitude with monotonic trends persisting for more than 5 million years the magnitude of faunal turnover was also similar ranging from less than half to 3 5 times that expected in both sequences faunal change appears to have been episodic with strong pulses between intervals of low turnover the siwaliks in contrast to the paleogene sequence may have had more distinct pulses and longer intervals between pulses neither sequence has peaks of first occurrences coinciding with peaks of last occurrences

stepwise transition from the eocene greenhouse to the oligocene icehouse the eocene oligocene transition is the largest global cooling in the cenozoic period a comparison of three independent proxies from the continental shelf and deep ocean reveals a three step transition to cold glacial conditions with ice sheets 25 larger than their present size

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

antarctic glaciation caused ocean circulation changes at the eocene oligocene transition a climate model is used to show that the growth of the antarctic ice sheet at about 34 myr ago drove changes in ocean circulation but the opening of ocean gateways had relatively little impact antarctica developed an ice sheet about 34 million years ago following a period of ice free conditions known as the super greenhouse climate previous research has suggested that ice sheet growth was driven by either the thermal isolation of antarctica arising from the opening of ocean gateways or by progressively lower atmospheric co2 content matt huber and colleagues now use a climate model to show that the growth of the ice sheet forced by changes in co2 drove the changes in ocean circulation in contrast the opening of the gateways had relatively little impact on ocean circulation 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 opening1 2 3 4 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 opening2 4 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

preglacial to glacial sediment thickness grids for the southern pacific margin of west antarctica circum antarctic sediment thickness grids provide constraints for basin evolution and paleotopographic reconstructions which are important for paleo ice sheet formation histories by compiling old and new seismic data we identify sequences representing pre glacial transitional and full glacial deposition processes along the pacific margin of west antarctica the pre glacial sediment grid depicts 1 3 to 4 0 km thick depocenters relatively evenly distributed along the margin the depocenters change markedly in the transitional phase at or after the eocene oligocene boundary when the first major ice sheets reached the shelf full glacial sequences starting in the middle miocene indicate new depocenter formation north of the amundsen sea embayment and localized eastward shifts in the bellingshausen sea and antarctic peninsula basins using present day drainage paths and source areas on the continent our calculations indicate an estimated observed total sedimentary volume of 10 x 106 km3 was eroded from west antarctica since the separation of new zealand in the late cretaceous of this 4 9 x 106 km3 predates the onset of glaciation and need to be considered for a paleotopography reconstruction of 34 ma whereas 5 1 x 106 km3 postdate the onset of glaciation of which 2 5 x 106 km3 were deposited in post mid miocene full glacial conditions this article is protected by copyright all rights reserved

correlation between isotope records in marine and continental carbon reservoirs near the palaeocene eocene boundary changes in the isotope content of the large marine carbon reservoir can force shifts in that of the smaller carbon pools in the atmosphere and on land the carbon isotope compositions of marine carbonate sediments from the late palaeocene vary considerably exhibiting a sudden decrease close to the palaeocene eocene boundary which coincides with deep sea benthic extinctions1 and with changes in ocean circulation here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel in using palaeosol carbonates to reconstruct the co2 content of the ancient atmosphere2 isotope shifts of this sort will have to be taken into account the sharp decrease in 13c 12c ratios in the late palaeocene provides a datum for precise correlation of marine and continental records and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals

sampling and faunal turnover in early eocene mammals badgley c and gingerich p d 1988 sampling and faunal turnover in early eocene mammals palaeogeogr palaeoclimatol palaeoecol 63 141 157 faunal turnovers in the fossil record are episodes of synchronous appearance and disappearance of species from a community often resulting in net change in species richness we studied the biostratigraphic record of faunal turnover involving early wasatchian early eocene mammals from the clark s fork basin wyoming u s a two faunal turnovers occur in this record one at the base of the wasatchian comprised mainly of appearances of taxonomically and ecologically distinctive species and a later one biohorizon a of schankler 1980 comprised mainly of disappearances especially of carnivorous species this study focuses on biohorizon a in the record of the clark s fork basin biohorizon a may be an artifact of sampling sample size and species richness are highly correlated r 0 95 throughout this record moreover sample size and species richness fluctuate markedly between successive stratigraphic intervals peaks of appearances coincide with large sample sizes and peaks of disappearances with low sample sizes the peaks and valleys in fossil productivity over time mask the real timing of appearances and disappearances of species changes in fossil productivity in the stratigraphic section may result from changes in exposure area taphonomic factors or ecological factors evaluation of the effects of sampling is a necessary prerequisite for investigating the chronological and ecological significance of faunal turnovers

planktic foraminiferal and 13 c isotopic changes across the paleocene eocene boundary at possagno italy the interval spanning the paleocene eocene p e transition in the possagno section consists of 1 m of red marls including a 4 cm thick dark red dissolution clay which represents the paleocene eocene boundary event the possagno section is much more condensed than other tethyan and north atlantic sections previously studied however in this section the most significant biotic isotopic and sedimentological events across the p e boundary can be recognized the possagno section spans the following planktic foraminiferal subzones upper part of m gracilis subzone a berggreni subzone a sibaiyaensis subzone and probably lowermost part of p wilcoxensis subzone the quantitative analysis indicates a major increase of low latitude acarininids including compressed tropical acarininids just above the boundary clay this acarininid incursion begins just below the boundary clay but reaches its maximum just above the clay the planktic foraminiferal faunal turnover is gradual except for the acarininid incursion the isotopic results show a negative excursion in 13c values at the small benthic foraminifera mass extinction event the acarininid maximum diversity coincides with this isotopic excursion and reflects an increase in surface seawater temperature despite being very condensed the possagno section allows us to further confirm that the different biotic isotopic and sedimentological events recognized in the spanish sections alamedilla campo caravaca zumaya are not local in nature and allows the establishment of a detailed chronostratigraphic framework to define the p e boundary stratotype

organic rich sedimentation in the south pacific ocean associated with late paleocene climatic cooling abstract a distinctive organic rich marine mudstone of late paleocene age occurs in most of new zealand s sedimentary basins and has been identified as a potential source rock for oil and gas identified as the waipawa formation in the east coast basin and the tartan formation in the great south and canterbury basins the unit is a relatively uniform massive mudstone that varies greatly in thickness 2 70 m and grades laterally into distinctive facies equivalents notably greensand and a thin bedded siliceous mudstone all these facies are characterised by relatively high toc 0 5 10 wt and 13 c enrichment 13 c toc 24 and we refer to them collectively as waipawa organofacies our detailed stratigraphic and geochemical studies refine the age 58 7 to 59 4 ma distribution and nature of the waipawa organofacies we have determined that deposition occurred in continental margin settings throughout much of the southwest pacific under cool dysoxic conditions associated with a significant influx of terrestrial organic matter high marine productivity a global fall in sea level and a regional unconformity across shallow and deep marine settings the combination of cool temperatures lowered sea level and bathyal erosion suggests that deposition was linked to short lived growth of an antarctic ice sheet in the earliest late paleocene 59 ma

west antarctic paleotopography estimated at the eocene oligocene climate transition 1 one generally recognized limitation of models for rapid growth of antarctic ice near the eocene oligocene transition is that they are based on present topography corrected only for removal of modern ice for west antarctica this results in large areas below sea level that would not readily host ice in the recently active west antarctic rift system other factors may have contributed to significant vertical motions since the eocene additional corrections for thermal contraction resulting from tectonic extension and for erosion and sedimentation since 34 ma restore most of west antarctica to above sea level increasing total antarctic land area by 10 20 because ice sheets have convex slopes the potential increase in ice volume is larger than the increase in land area accounting for large changes in west antarctic topography may resolve conflicts between ice models and data by demonstrating the possibility of an early large west antarctic ice sheet

the respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the eocene oligocene transition 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 co 2 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 18 o excursions occurring during the transition we show that co 2 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 co 2 drop the two 18 o 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

the pikermian event temporal and spatial resolution of the turolian large mammal fauna in se europe abstract during the turolian late miocene the eastern mediterranean region is considered to have been part of a single major ecological area supporting a particular savanna type large mammal community referred to as the pikermian biome analysis of the timing turnover patterns biogeographic relations and palaeoecological profile of the turolian large mammal faunas from either sides of the aegean sea failed however to confirm the presence of a homogeneous mammal community isotropically behaving through time for most of the turolian the large mammal assemblages from southern balkans and anatolia appear to have existed under different environmental conditions partly isolated by natural barriers overall climatic changes and regional physico geographic factors around 7 2 my allowed the southern balkan biogeographic region to be temporarily part of the sub paratethyan bioprovince as a result significant faunal reorganizations and interchanges triggered the emergence and expansion of the pikermian mammal fauna which collapsed soon after 7 0 my as a consequence of the early messinian global changes the pikermian large mammal event seems to follow known procedures related with contemporaneous marine and land faunal episodes across the mediterranean

evidence of surface water oligotrophy during the paleocene eocene thermal maximum nannofossil assemblage data from ocean drilling program site 690 maud rise weddell sea 1 nannoplankton assemblages at ocean drilling program site 690 maud rise weddell sea experienced an abrupt and dramatic transformation at the onset of the paleocene eocene thermal maximum petm at 55 m y the major assemblage shift suggests a change from colder more productive surface waters to warmer more oligotrophic conditions significant restructuring of assemblages during the later part of the petm indicates that nannoplankton communities were not stable and that surface water conditions changed although they remained warm and oligotrophic combined with benthic foraminiferal assemblage data nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean although the petm was a short lived event it appears to have had long term effects on nannoplankton leading to the extinction of fasciculithus a dominant paleocene genus

structural evolution and deformation near a tertiary salt weld willouran ranges south australia abstract we combine insights from subsurface studies and published numerical models to propose a three phase conceptual model that considers the potential deformation patterns that form during the emplacement evacuation and welding and post welding phases of tertiary weld formation the proposed model aims to 1 help establish the timing of deformation adjacent to a tertiary weld based on the geometry of deformation patterns and 2 serve as a guide for future work that examines deformation adjacent to tertiary welds and beneath allochthonous salt we apply the model along with new 1 10 000 scale geological mapping and mesostructural analysis of deformation patterns along the kingston tertiary salt weld and contiguous witchelina breaden hill salt canopy in the willouran ranges of south australia to constrain the evolution of the allochthonous salt system and the style extent and timing of adjacent deformation deformation near the weld is dominated by opening mode fractures that exhibit spatial heterogeneity in their orientation both along the strike of allochthonous salt and in suprasalt versus subsalt strata a halokinetic drape fold decimeter to decameter scale folding and localized debris flow deposits are present in subsalt strata whereas no evidence of thrust imbricates or laterally continuous shear and or rubble zones was observed anywhere below the canopy weld complex we hypothesize that remnant evaporite distribution and the juxtaposition of units exert the primary largest scale control on the hydrological behavior of tertiary welds the influence of deformation occurs at a much smaller scale and is more heterogeneous and difficult to predict higher resolution models and additional field studies are required to identify and rank the many variables that control this deformation

a case for a comet impact trigger for the paleocene eocene thermal maximum and carbon isotope excursion abstract we hypothesize that the rapid onset of the carbon isotope excursion cie at the paleocene eocene boundary 55 ma may have resulted from the accretion of a significant amount of 12c enriched carbon from the impact of a 10 km comet an event that would also trigger greenhouse warming leading to the paleocene eocene thermal maximum and possibly thermal dissociation of seafloor methane hydrate indirect evidence of an impact is the unusual abundance of magnetic nanoparticles in kaolinite rich shelf sediments that closely coincide with the onset and nadir of the cie at three drill sites on the atlantic coastal plain after considering various alternative mechanisms that could have produced the magnetic nanoparticle assemblage and by analogy with the reported detection of iron rich nanophase material at the cretaceous tertiary boundary we suggest that the cie occurrence was derived from an impact plume condensate the sudden increase in kaolinite is thus thought to represent the redeposition on the marine shelf of a rapidly weathered impact ejecta dust blanket published reports of a small but significant iridium anomaly at or close to the paleocene eocene boundary provide supportive evidence for an impact

widespread antarctic glaciation during the late eocene marine sedimentary rocks drilled on the southeastern margin of the south orkney microcontinent in antarctica ocean drilling program leg 113 site 696 were deposited between 36 5 ma to 33 6 ma across the eocene oligocene climate transition the recovered rocks contain abundant grains exhibiting mechanical features diagnostic of iceberg rafted debris sand provenance based on a multi proxy approach that included petrographic analysis of over 275 000 grains detrital zircon geochronology and apatite thermochronometry rule out local sources antarctic peninsula or the south orkney islands for the material instead the ice transported grains show a clear provenance from the southern weddell sea region extending from the ellsworth whitmore mountains of west antarctica to the coastal region of dronning maud land in east antarctica this study provides the first evidence for a continuity of widespread glacier calving along the coastline of the southern weddell sea embayment at least 2 5 million yrs before the prominent oxygen isotope event at 34 33 5 ma that is considered to mark the onset of widespread glaciation of the antarctic continent

modeling the oxygen isotope composition of the antarctic ice sheet and its significance to pliocene sea level recent estimates of global mean sea level based on the oxygen isotope composition of mid pliocene benthic foraminifera vary from 9 to 21 m above present which has differing implications for the past stability of the antarctic ice sheet during an interval with atmospheric co 2 comparable to present here we simulate the oxygen isotope composition of the antarctic ice sheet for a range of configurations using isotope enabled climate and ice sheet models we identify which ice sheet configurations are consistent with the oxygen isotope record and suggest a maximum contribution from antarctica to the mid pliocene sea level highstand of 13 m we also highlight that the relationship between the oxygen isotope record and sea level is not constant when ice is lost from deep marine basins which has important implications for the use of oxygen isotopes as a sea level proxy

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

post mid cretaceous tectonic and topographic evolution of western marie byrd land westantarctica insights from apatite fissiontrack and u th sm he data

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

the onset of the paleocene eocene thermal maximum petm at sites 1209 and 1210 shatsky rise pacific ocean as recorded by planktonic foraminifera abstract high resolution biostratigraphic and quantitative studies of subtropical pacific planktonic foraminiferal assemblages ocean drilling program leg 198 shatsky rise sites 1209 and 1210 are performed to analyse the faunal changes associated with the paleocene eocene thermal maximum petm at about 55 5 ma at shatsky rise the onset of the petm is marked by the abrupt onset of a negative carbon isotope excursion close to the contact between carbonate rich ooze and overlying clay rich ooze and corresponds to a level of poor foraminiferal preservation as a result of carbonate dissolution lithology planktonic foraminiferal distribution and abundances calcareous plankton and benthic events and the negative carbon isotope excursion allow precise correlation of the two shatsky rise records results from quantitative analyses show that morozovella dominates the assemblages and that its maximum relative abundance is coincident with the lowest 13c values whereas subbotinids are absent in the interval of maximum abundance of morozovella the excursion taxa acarinina africana acarinina sibaiyaensis and morozovella allisonensis first appear at the base of the event comparison between the absolute abundances of whole specimens and fragments of genera demonstrate that the increase in absolute abundance of morozovella and the decrease of subbotina are not an artifact of selective dissolution moreover the shell fragmentation data reveal subbotina to be the more dissolution susceptible taxon the upward decrease in abundance of morozovella species and the concomitant increase in test size of morozovella velascoensis are not controlled by dissolution these changes could be attributed to the species response to low nutrient supply in the surface waters and to concomitant changes in the physical and chemical properties of the seawater including increased surface stratification and salinity comparison of the planktonic foraminiferal changes at shatsky rise to those from other petm records sites 865 and 690 highlights significant similarities such as the decline of subbotina at the onset of the event and discrepancies including the difference in abundance of the excursion taxa the observed planktonic foraminifera species response suggests a warm oligotrophic scenario with a high degree of complexity in the ocean structure

a new global paleocene eocene apparent polar wandering path loop by stacking magnetostratigraphies correlations with high latitude climatic data a new apparent polar wander path apwp from the beginning of the paleocene 65 ma to the middle of the mid eocene 42 ma is shown to be correlated with polar climatic data of the same time period rather than applying the classical method based on analysis of site based poles we stacked the apwps obtained from magnetostratigraphies magnetostratigraphies have the advantage of displaying an unbroken record of local apwps through time and for a magnetozone defined as the a combination of normal and reversed polarity intervals the instantaneous poles are synchronous seven magnetostratigraphies located on 4 different plates covered sufficient time to be used in the analysis an average apwp was then determined with respect to age at the magnetozone level for the african plate which was arbitrarily chosen as a reference frame virtual geomagnetic poles were transferred onto the african plate using ocean kinematic euler rotations the calculated apwp is characterized by a loop with two main changes of direction at magnetozones 26 25 61 5 56 5 ma and 24 22 56 5 48 6 ma distinct at a 95 level of probability and indistinct poles related to magnetozones 29 27 65 5 61 5 ma and 21 19 48 6 40 6 ma we also show that the implied rapid shift of the lithosphere with respect to the geographic pole possibly an episode of true polar wander was coeval with the time evolution of vertebrate occurrence on ellesmere island canadian arctic and with the tree ring growth rate in western antarctica

tracer derived freshwater composition of the siberian continental shelf and slope following the extreme arctic summer of 2007 we investigate the freshwater composition of the shelf and slope of the arctic ocean north of the new siberian islands using geochemical tracer data 18o ba and po 4 collected following the extreme summer of 2007 we find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of pacific derived surface water in the westernmost part of the makarov basin we also find larger quantities of meteoric water near lomonosov ridge than were found in 1995 dissolved barium is depleted in the upper layers in one region of our study area probably as a result of biological activity in open waters increasingly ice free conditions compromise the quantitative use of barium as a tracer of river water in the arctic ocean

deep water temperature carbonate ion and ice volume changes across the eocene oligocene climate transition 1 paired benthic foraminiferal stable isotope and mg ca data are used to estimate bottom water temperature bwt and ice volume changes associated with the eocene oligocene transition eot the largest global climate event of the past 50 myr we utilized odp sites 1090 and 1265 in the south atlantic to assess seawater 18o w antarctic ice volume and sea level changes across the eot 33 8 33 54 ma we also use benthic 13c data to reconstruct the sources of the deep water masses in this region during the eot our data together with previously published records indicate that a pulse of northern component water influenced the south atlantic immediately prior to and following the eot benthic 18o records show a 0 5 increase at 33 8 ma eot 1 that represents a 2 c cooling and a small 10 m eustatic fall that is followed by a 1 0 increase associated with oi 1 the expected cooling of deep waters at oi 1 33 54 ma is not apparent in our mg ca records we suggest the cooling is masked by coeval changes in the carbonate saturation state co32 which affect the mg ca data to account for this the bwt ice volume and w estimates are corrected for a change in the co32 of deep waters on the basis of recently published work corrected bwt at sites 1090 and 1265 show a 1 5 c cooling coincident with oi 1 and an average w increase of 0 75 the increase in ice volume during oi 1 resulted in a 70 m drop in global sea level and the development of an antarctic ice sheet that was near modern size or slightly larger

influence of the opening of the drake passage on the cenozoic antarctic ice sheet a modeling approach we evaluate the opening of the drake passage dp between antarctica and south america and associated changes in ocean circulation as forcing factor for the onset of antarctic glaciation near the eocene oligocene transition 34 million years ago in this paper this hypothesis is tested through sensitivity experiments using numerical models for the global ocean and atmosphere and for the antarctic ice sheet the response of the antarctic continent to the opening of the dp and to the establishment of the antarctic circumpolar current is examined two different climate states are reproduced with ocean gateway configurations similar to the late eocene and to the late oligocene before and after the opening of the dp a reduced southward heat flux and a decrease of surface temperature are found in the antarctic realm when the dp is open a more massive ice sheet develops on the continent in case of dp open compared to the configuration with closed dp

a biogenic origin for anomalous fine grained magnetic material at the paleocene eocene boundary at wilson lake new jersey 1 the paleocene eocene thermal maximum which occurred 55 5 ma was caused by a massive release of carbon as indicated by an 3 negative carbon isotope excursion recorded in the marine atmospheric and terrestrial reservoirs one suggested source for the carbon a cometary impactor is based on the sudden appearance and high concentration of single domain sd magnetite in paleocene eocene p e boundary cores from the north atlantic continental margin we evaluate the potential sources of sd magnetite at the p e boundary by presenting new magnetic hysteresis low temperature magnetic remanence and transmission electron microscopy data from the north atlantic coastal ocean our results show a similar increase in sd material but demonstrate that the magnetic material has a biogenic origin these findings indicate that the high concentrations of sd magnetite immediately above the p e boundary are the result of unusual accumulations and or preservation of magnetotactic bacteria such bacteria typically occupy the oxic anoxic transition zone near the sediment water interface or in the water column the high abundances of sd magnetite in sediments from across the shelf may be an artifact of nonsteady state redox conditions and exceptional preservation of sd magnetite it may also indicate that the oxic anoxic redox boundary shifted into the water column the latter explanation implies transient eutrophy of the coastal ocean in this region most likely due to seasonally enhanced runoff and increased stratification and nutrient loading

plio pleistocene fossil record of large predators in iberia diversity home range and climatic change abstract we investigated the patterns of change in diversity and home range size structure of the latest miocene pleistocene iberian carnivores to recognize the tempo and mode of the major shifts and place them in the context of late cenozoic climatic changes the database consists of 36 selected and taxonomically revised faunal lists a general pattern of carnivore diversity from iberia shows three maxima in diversity that can be correlated with major global changes the first coincides with the glacial trend during pliocene starting at 2 7 2 6 ma with the onset of glacial cycles of 41 ka second maximum happened at the beginning of the middle pleistocene and can be correlated with the switch at 1 ma third maximum in diversity occurs at the end of middle pleistocene when the amplitude of interglacials shifted from cooler to warmer interglacials the most significant shifts in carnivora diversity and home range size patterns were linked to dispersal phases that were tracked by a renovation of the carnivore guild from the patterns in home range size structure it seems that some multifaceted and not always straight interactions exist between ecological and climatic change and shifts in home range size the onset of the holocene home range size structure in iberian carnivores traces back to a high diversity pulse at the end of the middle pleistocene

preservational paleoecological and evolutionary patterns in the paleogene of wyoming montana and the neogene of pakistan abstract contributions to this special issue have compared the tectonic settings fluvial systems paleoclimates paleofloras and faunas vertebrate taphonomy and mammalian paleoecology and evolution from two long continental records of cenozoic ecosystems in this concluding paper we summarize highlights of earlier papers to provide an overview of similarities and differences between these paleogene and neogene records the relative influences of tectonic climatic and fluvial processes on lithofacies environments of fossil preservation and the productivity of the fossil record are compared for each sequence tectonism was the primary control on sediment accumulation rate and the distribution of major depositional environments in each basin fossil productivity species richness and the distribution of fossil localities among fluvial environments change across formation boundaries in each sequence the taxonomic temporal and spatial resolution of vertebrate assemblages varies among fluvial environments and differs between the two sequences as a result the paleogene record is better suited for detailed study of evolutionary change within local lineages and the neogene record for detailed paleocommunity reconstruction several aspects of biotic change are considered 1 the timing and magnitude of mammalian faunal turnover in relation to climatic change are evaluated in terms of three models of evolutionary change within ecosystems van valen s red queen model stenseth and maynard smith s stationary model and vrba s turnover pulse model in both records climatic change was accompanied by change in faunal composition and ecological structure but both pulsed and diachronous biotic change at a resolution of about 0 5 m y also occurred over periods when no significant climatic change was discernible this pattern best matches the predictions of the red queen model 2 in both records the rate of mammalian faunal turnover first and last appearances of taxa is not highly correlated with standing richness suggesting that paleocommunities were not a equilibrium richness on these time scales 3 in the paleogene record plant species richness declined while mammalian species richness increased 4 in each sequence some episodes of mammalian faunal turnover were in step with changes in size or trophic structure while other changes in faunal composition entailed no corresponding change in ecological structure while both records would benefit from improved paleoclimatic temporal species level and ecomorphological resolution this initial synthesis suggests that both physical and biotic factors were important influences on faunal composition the timing and rate of turnover and ecological structure in these paleocommunities

flat latitudinal gradient in paleocene mammal richness suggests decoupling of climate and biodiversity mammal faunas from western north america exhibit no significant change in species richness with latitude during the torrejonian ca 63 60 ma and tiffanian ca 60 58 ma north american land mammal ages in contrast to a strong richness gradient in modern mammalian faunas of the same region today the latitudinal gradient in oxygen isotope composition of mammalian bioapatite from the paleocene faunas is similar to that of modern meteoric and surface waters suggesting that the temperature gradient in the paleocene was similar to the modern one the flat richness gradient in the middle paleocene indicates either different responses to climatic gradients of faunas dominated by extinct clades of placental mammals or distinct ecological processes during the paleocene diversification of mammals following the end cretaceous mass extinction

the relationship between neogene dinoflagellate cysts and global climate dynamics abstract the neogene period 23 03 2 58 ma underwent a long term relatively gradual cooling trend culminating in the glacial interglacial climate of the quaternary palaeoclimate studies on the neogene have provided important information for understanding how modern patterns of atmospheric and oceanic circulation developed and how they may relate to wider environmental change here we use a newly created global database of neogene dinoflagellate cysts the tertiary oceanic parameters information system topis to investigate how dinoflagellate cysts recorded the cooling of neogene surface marine waters on a global scale species with warm and cold water preferences were determined from previously published literature and extracted from the database percentages of cold water species were calculated relative to the total number of species with known temperature preferences from each site and compared throughout the neogene at differing latitudes overall the percentage of cold water species increases gradually through the neogene this trend indicates a gradual global cooling that is comparable to that reported from other marine and terrestrial proxies this also demonstrates the use of dinoflagellate cysts in determining temperature change on both extended temporal and wide geographical scales the increase in the percentage of cold water species of dinoflagellate cysts recorded worldwide from the early and middle miocene to the late pliocene indicates a global scale forcing agent on neogene climate such as co2

dynamic antarctic ice sheet during the early to mid miocene geological data indicate that there were major variations in antarctic ice sheet volume and extent during the early to mid miocene simulating such large scale changes is problematic because of a strong hysteresis effect which results in stability once the ice sheets have reached continental size a relatively narrow range of atmospheric co2 concentrations indicated by proxy records exacerbates this problem here we are able to simulate large scale variability of the early to mid miocene antarctic ice sheet because of three developments in our modeling approach i we use a climate ice sheet coupling method utilizing a high resolution atmospheric component to account for ice sheet climate feedbacks ii the ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice cliff failure and ice shelf hydrofracture iii we account for changes in the oxygen isotopic composition of the ice sheet by using isotope enabled climate and ice sheet models we compare our modeling results with ice proximal records emerging from a sedimentological drill core from the ross sea andrill 2a that is presented in a companion article the variability in antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0 52 0 66 or a sea level equivalent change of 30 36 m for a range of atmospheric co2 between 280 and 500 ppm and a changing astronomical configuration this result represents a substantial advance in resolving the long standing model data conflict of miocene antarctic ice sheet and sea level variability

clay mineralogical constraints on weathering in response to early eocene hyperthermal events in the bighorn basin wyoming western interior usa series of transient greenhouse warming intervals in the early eocene provide an opportunity to study the response of rock weathering and erosion to changes in temperature and precipitation during greenhouse warming chemical weathering is thought to increase the uptake of carbon from the atmosphere while physical weathering and erosion control sediment supply a large ancient greenhouse warming event is the paleocene eocene thermal maximum at 56 ma in many coastal sites an increase in the abundance of kaolinite clay during the paleocene eocene thermal maximum is interpreted as the result of reworking from terrestrial strata due to enhanced runoff caused by increased seasonal precipitation and storminess during a time of decreased vegetation cover in the continental interior of north america paleocene eocene thermal maximum paleosols show more intense pedogenesis and drying which are indicated by deeply weathered and strongly oxidized soil profiles the weathering and oxidation could be related to temperature and precipitation changes but also to increased time available for weathering and increased soil permeability in coarser sediment here we provide evidence for enhanced climate seasonality increased erosion of proximal laterites and intrabasinal floodplain soils and a potential slight increase in chemical weathering during the smaller early eocene hyperthermals eocene thermal maximum 2 including h1 and h2 postdating the paleocene eocene thermal maximum for which no previous clay mineral data were available hyperthermal soil formation at the site of floodplain deposition causes a similar insignificant clay mineralogical change as occurred during the background climates of the early eocene by showing small increases in smectite and decreases in illite smectite and illite remarkably the detrital sediments during the hyperthermals show a similar pedogenic like increase of smectite and decreases of mixed layer illite smectite and illite while the kaolinite and chlorite proportions remained low and unchanged since sedimentation rates and provenance were similar during the events enhanced smectite neoformation during soil formation in more proximal settings and associated reworking is the likely process causing this clay mineralogical change the hundreds to thousands of year time scales at which individual paleosols were formed were probably too short for significant alteration of the rocks by in situ chemical weathering despite changing climates during the two post paleocene eocene thermal maximum greenhouse warming episodes the relatively small signal however raises the question of whether increased chemical weathering can indeed be a strong negative feedback mechanism to enhanced greenhouse gas warming over the time scales at which these processes act

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

continuous simulations over the last 40 million years with a coupled antarctic ice sheet sediment model abstract much of the knowledge of antarctic ice sheet variations since its inception 34 ma derives from marine sediments on the continental shelf deposited in glacimarine or sub ice environments by advancing and retreating grounded ice and observed today by seismic profiling and coring here we apply a 3 d coupled ice sheet and sediment model from 40 ma to the present with the goal of directly linking ice sheet variations with the sediment record the ice sheet model uses vertically averaged ice dynamics and parameterized grounding line flux the sediment model includes quarrying of bedrock sub ice transport and marine deposition atmospheric and oceanic forcing are determined by uniform shifts to modern climatology in proportion to records of atmospheric co2 deep sea core 18o and orbital insolation variations the model is run continuously over the last 40 myr at coarse resolution 80 or 160 km modeling post eocene ice landscape evolution and off shore sediment packages in a single self consistent simulation strata and unconformities are tracked by recording times of deposition within the model sediment stacks which can be compared directly with observed seismic profiles the initial bedrock topography is initialized to 34 ma geologic reconstructions or an iterative procedure is used that yields independent estimates of paleo bedrock topography preliminary results are compared with recognized cenozoic ice sheet variations modern sediment distributions and seismic profiles and modern and paleo bedrock topographies

paleoceanographic and paleoclimatic constraints on the global eocene diatom and silicoflagellate record abstract eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves the global distribution of eocene diatom silicoflagellate bearing sediments varies considerably reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events event 1 49 million years ago ma at the end of the early eocene climatic optimum eeco saw the cessation of diatom silicoflagellate deposition in epicontinental regions of the north sea region and in the northern russia and the onset of biosilica deposition in the arctic event 2 46 ma which coincided with intensification of the middle eocene cooling trend marked the widespread expansion of diatom silicoflagellate deposition in both the north and south atlantic a shift of diatom silicoflagellate deposition from the atlantic to the pacific began at event 3 at the end of the middle eocene climatic optimum meco 40 ma that was likely tied to the initial opening of the drake passage between antarctica and south america event 4 39 ma coincided with a major sea level fall and a widespread deep sea hiatus in the latest middle eocene late eocene diatom silicoflagellate deposition became more concentrated in middle to high latitude regions and coastal upwelling regions particularly in the pacific ocean 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

initiation of the west antarctic ice sheet and estimates of total antarctic ice volume in the earliest oligocene 1 reconstructions of antarctic paleotopography for the late eocene suggest that glacial erosion and thermal subsidence have lowered west antarctic elevations considerably since then with antarctic land area having decreased 20 a new climate ice sheet model based on these reconstructions shows that the west antarctic ice sheet first formed at the eocene oligocene transition 33 8 33 5ma e o in concert with the continental scale expansion of the east antarctica ice sheet and that the total volume of east and west antarctic ice 33 4 35 9 10 6 km 3 w as 1 4 times greater than previously assumed this larger modeled ice volume is consistent with a modest cooling of 1 2 c in the deep ocean during the e o transition lower than other estimates of 3 c cooling and suggests the possibility of substantial ice in the antarctic interior before the eocene oligocene boundary citation wilson d s d pollard r m deconto s s r jamieson and b p luyendyk 2013 initiation of the west antarctic ice sheet and estimates of total antarctic ice volume in the earliest oligocene geophys res lett 40 doi 10 1002 grl 50797

cenozoic climate changes a review based on time series analysis of marine benthic δ18o records the climate during the cenozoic era changed in several steps from ice free poles and warm conditions to ice covered poles and cold conditions since the 1950s a body of information on ice volume and temperature changes has been built up predominantly on the basis of measurements of the oxygen isotopic composition of shells of benthic foraminifera collected from marine sediment cores the statistical methodology of time series analysis has also evolved allowing more information to be extracted from these records here we provide a comprehensive view of cenozoic climate evolution by means of a coherent and systematic application of time series analytical tools to each record from a compilation spanning the interval from 4 to 61 myr ago we quantitatively describe several prominent features of the oxygen isotope record taking into account the various sources of uncertainty including measurement proxy noise and dating errors the estimated transition times and amplitudes allow us to assess causal climatological tectonic influences on the following known features of the cenozoic oxygen isotopic record paleocene eocene thermal maximum eocene oligocene transition oligocene miocene boundary and the middle miocene climate optimum we further describe and causally interpret the following features paleocene eocene warming trend the two step long term eocene cooling and the changes within the most recent interval miocene pliocene we review the scope and methods of constructing cenozoic stacks of benthic oxygen isotope records and present two new latitudinal stacks which capture besides global ice volume also bottom water temperatures at low less than 30 and high latitudes this review concludes with an identification of future directions for data collection statistical method development and climate modeling

a coupled climate ice sheet modeling approach to the early cenozoic history of the antarctic ice sheet abstract the sudden widespread glaciation of antarctica and the associated shift toward colder temperatures near the eocene oligocene boundary 34 ma represents one of the most fundamental reorganizations of the global climate system recognized in the geologic record this glacial inception and the subsequent evolution of the early east antarctic ice sheet eais are simulated using a new coupled global climate dynamical ice sheet model accounting for the paleogeography greenhouse gas concentrations changing orbital parameters and varying ocean heat transport suites of long 105 yr climate ice sheet simulations are used to investigate the effects of declining atmospheric co2 compared to those of the tectonic opening of southern ocean gateways and the timing of mountain uplift in the antarctic interior in contrast to the established paradigm for the glaciation of antarctica which centers on the opening of the southern ocean gateways and the thermal isolation of the continent our results show that declining cenozoic pco2 may have played the dominant role first small isolated ice caps formed on the highest antarctic plateaus then as a co2 threshold between 3 and 2 pre industrial level pal was crossed height mass balance feedbacks were initiated during orbital periods with cold austral summers triggering much larger highly dynamic terrestrial ice sheets as co2 continued to decline these isolated ice caps eventually merged into a permanent continental scale eais in our model neither the opening of the southern ocean gateways nor mountain uplift significantly affected the timing of the major ice sheet transition given a scenario of gradually declining co2 from 4 to 2 pal over 10 million years around the eocene oligocene boundary

comparative paleoecology of paleogene and neogene mammalian faunas trophic structure and composition abstract trophic structure and composition are examined in two important biotic records one the paleogene of wyoming and montana and the other from the neogene of pakistan the paleogene sequence spans approximately 10 million years and encompasses four north american land mammal ages torrejonian tiffanian clarkforkian and wasatchian the neogene sequence spans approximately 17 m y and includes most of the miocene and pliocene with the best documented interval spanning from 16 to 7 ma five basic trophic categories primary consumers herbivores frugivores omnivores secondary consumers insectivores carnivores are recognized for paleogene and neogene mammals based on tooth morphology body size and analogy with modern mammalian groups the paleogene mammalian biota is characterized as one in which both trophic structure and taxonomic composition change through the history of the record the neogene mammalian biota maintains a relatively consistent trophic structure through most of the record although taxonomic composition changes substantially through time based on comparisons of trophic structure from the paleogene and neogene records with that of selected modern mammalian faunas paleogene habitats fluctuated between closed humid forests and more open drier woodlands neogene trophic structure indicates that savanna woodlands were the typical habitat present through most of the sequence only after 7 ma did these woodlands give way to more open grasslands in pakistan

antarctic ice sheet variability across the eocene oligocene boundary climate transition about 34 million years ago earth s climate cooled and an ice sheet formed on antarctica as atmospheric carbon dioxide co2 fell below 750 parts per million ppm sedimentary cycles from a drill core in the western ross sea provide direct evidence of orbitally controlled glacial cycles between 34 million and 31 million years ago initially under atmospheric co2 levels of 600 ppm a smaller antarctic ice sheet ais restricted to the terrestrial continent was highly responsive to local insolation forcing a more stable continental scale ice sheet calving at the coastline did not form until 32 8 million years ago coincident with the earliest time that atmospheric co2 levels fell below 600 ppm our results provide insight into the potential of the ais for threshold behavior and have implications for its sensitivity to atmospheric co2 concentrations above present day levels

taphonomy of a late eocene microvertebrate locality wind river basin wyoming u s a abstract the taphonomic history of a late eocene micromammal assemblage badwater locality 20 wind river basin wyoming is examined using methods of data collection and analysis designed to elucidate three taphonomic processes death and initial accumulation transport and burial and postburial alteration the disarticulated fragmentary nature of the fossils and the low percentage of teeth and jaws in the taphonomic sample suggests that much of the assemblage was initially accumulated in predator scats or pellets nonpredator agents of mortality were responsible for an additional attritional component there is evidence that the bones were exposed for a short period of time before burial and that the assemblage represents a time lag soil accumulation there is no evidence either from orientation and surface characteristics of the bones or from the sediments that the fossils were hydraulically transported and deposited postburial alteration included breakage of small bones due to mechanical stress the greatest information loss occurred during initial accumulation little additional information was lost during burial or through postburial alteration this information loss primarily concerned the relative abundance structure of the mammalian community in contrast information concerning species richness appears to be only slightly altered

could changing ocean circulation have destabilized methane hydrate at the paleocene eocene boundary 1 during the paleocene eocene thermal maximum petm 55 ma marine and terrestrial carbon isotope values exhibit a negative shift of at least 2 5 indicative of massive destabilization of marine methane hydrates releasing 2000 gigatons of methane carbon the cause of the hydrate destabilization is unknown but has been speculated to be warming due to a change from high latitude to low latitude deepwater formation here we present results from a numerical ocean model indicating that a sudden switch of deepwater formation from southern to northern high latitudes caused middepth and deep ocean warming of 3 5 c the switch is caused by a slow increase in the intensity of the atmospheric hydrologic cycle as expected under increasing temperatures and consistent with petm sedimentary evidence deepened subtropical subduction prior to the thermohaline circulation switch causes warming of 1 4 c in limited areas at thermocline through upper intermediate depths which could destabilize methane hydrates gradually and at progressively greater depths warming accompanying a south to north switch in deepwater formation would produce sufficient warming to destabilize seafloor gas hydrates over most of the world ocean to a water depth of at least 1900 m

high concentrations of greenhouse gases and polar stratospheric clouds a possible solution to high latitude faunal migration at the latest paleocene thermal maximum high latitude faunal migrations have been documented during a rapid warming event near the paleocene eocene boundary the latest paleocene thermal maximum lptm the migrations are difficult to explain from a climate perspective climate along these routes is at present too harsh to support the migrations and no mechanism has yet proved adequate to explain the past high latitude warmth required by such migrations a large negative excursion in the 13c record at the lptm suggests that a large quantity of ch4 was released into the atmosphere at this time high concentrations of atmospheric ch4 have been linked to the formation of polar stratospheric clouds we used an atmospheric general circulation model to explore early cenozoic climate response to the combined effects of high atmospheric ch4 levels and polar stratospheric clouds a unique combination of forcing factors in paleoclimate modeling studies our interests are in understanding if the climate response to this forcing may explain the high latitude faunal migrations model results indicate that high latitude winter warming with high methane levels and polar stratospheric clouds is sufficient to facilitate the high latitude migrations temperatures along high latitude migration routes remained above freezing year round and thus permitted exchanges of fauna between asia north america and europe on the basis of our results we suggest that other paleogene migrations may be correlated with lptm like events with high concentrations of greenhouse gases and polar stratospheric clouds

evidence of a full west antarctic ice sheet back to the early oligocene insight from double dating of detrital apatites in ross sea sediments the west antarctic ice sheet is the most unstable component of the antarctic cryosphere its fluctuations are well documented since the pliocene but its behaviour over the last 35 ma is more controversial particularly during periods of past high global pco2 values similar to those predicted in future global climate scenarios here we present new u pb dating of detrital apatite grains previously dated by the fission track method from cape roberts project oligocene to pliocene marine sediments in the ross sea two past ice flow patterns were identified one formed by outlet glaciers sourcing short travelled apatites and one northerly directed bringing far travelled apatite grains the latter provides the first robust physical evidence for the presence and repeated expansion of an oligocene west antarctic ice sheet

antarctic topography at the eocene oligocene boundary we present a reconstruction of the antarctic topography at the eocene oligocene ca 34 ma climate transition this provides a realistic key boundary condition for modeling the first big antarctic ice sheets at this time instead of using the present day bedrock topography which has changed significantly from millions of years of tectonism and erosion we reconstruct topography using a set of tools including ice sheet erosion models models of thermal subsidence and plate movement erosion estimates are constrained with offshore sediment volumes estimated from seismic stratigraphy maximum and minimum topographic reconstructions are presented as indicators of the range of uncertainty our results point to a significant upland area in the ross sea marie byrd land and weddell sea sectors in addition east antarctic coastal troughs are much shallower than today due to the restoration of material that has been selectively eroded by the evolving ice sheets parts of east antarctica have not changed since the e o boundary because they were protected under non erosive cold based ice the reconstructions provide a better defined boundary condition for modeling that seeks to understand interaction between the antarctic ice sheet and climate along with more robust estimates of past ice volumes under a range of orbital settings and greenhouse gas concentrations

bolide summer the paleocene eocene thermal maximum as a response to an extraterrestrial trigger the standard paradigm that the paleocene eocene thermal maximum petm represents a threshold event intrinsic to earth s climate and connected in some way with long term warming has influenced interpretations of the geochemical climate and biological perturbations that occurred at this event as recent high resolution data have demonstrated that the onset of the event was geologically instantaneous attempts to account for the event solely through endogenous mechanisms have become increasingly strained the rapid onset of the event indicates that it was triggered by a catastrophic event which we suggest was most likely a bolide impact we discuss features of the petm that require explanation and argue that mechanisms that have previously been proposed either cannot explain all of these features or would require some sort of high energy trigger a bolide impact could provide such a trigger and in the event of a comet impact could contribute directly to the shape of the carbon isotope curve we introduce a carbon cycle model that would explain the petm by global warming following a bolide impact leading to the oxidation of terrestrial organic carbon stores built up during the late paleocene our intention is to encourage other researchers to seriously consider an impact trigger for the petm especially in the absence of plausible alternative mechanisms

the campo section pyrenees spain revisited implications for changing benthic carbonate assemblages across the paleocene eocene boundary abstract the campo section is a parastratotype section for the shallow water ilerdian and cuisian stages although a lot of work has been concentrated during the last years on biostratigraphy sequence stratigraphy magnetostratigraphy and geochemistry surprisingly little work has been published on the facies development here we evaluate the facies evolution with particular emphasis on the biogenic assemblages of the latest paleocene shallow benthic zonation 4 to the earliest eocene shallow benthic zonations 5 and 6 of the campo and the nearby serraduy section overall the facies show a deepening in the paleocene and the eocene interrupted by a terrestrial interval across the newly defined paleocene eocene boundary in the late paleocene altogether seven microfacies types were distinguished these are dominated by various algal taxa and subordinate corals and larger foraminifera the lower eocene carbonate platform is characterised by twelve microfacies types which are dominated by larger foraminifera such as alveolinids orbitolitids and nummulitids and subordinate corals this facies dichotomy recognized in the campo and serraduy sections can be extrapolated to the whole pyrenean region in the early paleogene and is even found in egypt the comparison of the two regions shows that the facies dichotomy is less pronounced in the pyrenean region this is interpreted to reflect a latitudinal trend where corals are absent in the low latitudes while in the middle latitudes they occur subordinately this gradient within the facies distribution can be explained by latitudinal temperature changes and by the long time warming in the early paleogene and the short time warming of the paleocene eocene thermal maximum hot temperatures in the low latitudes hamper the growth of temperature sensitive corals while in the middle latitudes the temperatures were still in a favourable temperature range

an early to middle miocene record of ice sheet and landscape evolution from the friis hills antarctica the friis hills 77 45 s 161 30 e in the mcmurdo dry valleys region antarctica is a 1 km high inselberg with early to middle miocene aged glacial deposits preserved on its upper surface lithology sedimentology and ice flow direction define three units within a 34 m thick sequence the friis i friis ii and cavendish drifts tills in friis i drift were deposited from alpine glaciers flowing to the sw an extensive tephra bed in the drift is 19 76 0 11 ma in age based on 40 ar 39 ar dating tills in friis ii drift were deposited from alpine glaciers flowing to the se fossiliferous fluvial and lacustrine beds in the drift indicate that vegetation and insects repeatedly recolonized the friis hills during periods of reduced ice the geographic distribution of modern descendants of the fossils specifies mean summer temperatures of 6 7 c and precipitation as much as 3000 mm during these interglacial periods the presence of fossils also indicates deposition of friis ii drift occurred before the mid miocene climate transition ca 14 1 ma after this eastward flowing ice partially eroded the friis i and ii drifts the ice also cut parallel troughs to the n and s topographically isolating the friis hills the cavendish drift represents renewed deposition but from eastward flowing outlet glaciers within the newly established troughs together the friis hills drifts register multiple stages in the evolution of the east antarctic cryosphere including the general growth of the system reorganizations of glacial drainage patterns and periods of major downcutting importantly they also provide constraints on terrestrial climate conditions during these stages the friis hills record is the first that can be directly compared with shallow marine records from the ross sea the record also provides new constraints for paleoglaciological models of the early east antarctic ice sheet based on lithologic and geomorphic arguments the friis hills drifts are younger than nearby sirius group tillites which predicates that the sirius group in the dry valleys region is at least early miocene or more probably oligocene in age