constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

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

high resolution records of the late paleocene thermal maximum and circum caribbean volcanism is there a causal link two recently drilled caribbean sites contain expanded sedimentary records of the late paleocene thermal maximum a dramatic global warming event that occurred at ca 55 ma the records document significant environmental changes including deep water oxygen deficiency and a mass extinction of deep sea fauna intertwined with evidence for a major episode of explosive volcanism we postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the earth s environment

atmospheric carbon dioxide and early eocene climate a general circulation modeling sensitivity study abstract the early eocene was the warmest time interval of the past 65 million years we have investigated the hypothesis that the warm climate of the early eocene may have been caused by higher than present levels of atmospheric carbon dioxide co2 we have used an atmospheric general circulation model the ncar genesis model coupled to a land surface model and a mixed layer ocean to examine the sensitivity of early eocene climate to varying levels of atmospheric co2 model cases contained a description of the early eocene earth and included either 300 560 or 1680 ppm atmospheric co2 climate responses to increased atmospheric co2 include 1 increased mean annual global temperature by 2 6 c and decreased latitudinal surface temperature gradients 2 maximum warming at high latitudes especially in the winter season 3 increased mean global precipitation 4 increased high latitude clouds in comparison with geological paleoclimate data the climate response to increased co2 does not appear to explain completely the early eocene latitudinal surface temperature gradient for example with the 1680 ppm co2 case high latitude oceans and continents are minimally warm enough to match paleoclimate data while low latitude regions are overly warm when compared to sea surface temperature reconstructions we conclude that co2 was very likely at least double the present level during the early eocene and contributed to the overall character of early eocene climate however consideration of increased poleward oceanic heat transport and or other factors may be required to produce model results that more closely agree with marine and terrestrial paleoclimate data especially at low latitudes

water level changes in lake baikal siberia tectonism versus climate relative changes in the level of lake baikal amounting to hundreds of meters in quaternary time are well documented data presented here show that tectonic displacements of the lake outlet or former shoreline features are entirely sufficient to explain these relative lake level changes in contrast the morphology and hydrology of the lake make its level hydrologically insensitive to climate change available evidence indicates that throughout the past several hundred thousand years lake baikal was a dilute through flowing lake controlled by the level of its outlet on the basis of geologic data alone climatic effects on lake level whatever their magnitude are difficult to separate from those caused by active rift tectonism however consideration of 1 the hydrologic budget of the lake and 2 the configuration of the outlet suggests that potential lake level fluctuations due solely to climate change were less than about 2 m

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

oceanographic and climatic implications of the palaeocene carbon isotope maximum we have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope records from the palaeocene and early eocene successions at dsdp site 577 shatsky rise north pacific a composite section derived from dsdp leg 74 sites walvis ridge south atlantic and a composite section from odp leg 113 sites maud rise weddell sea the 13c records of palaeocene and early eocene foraminifera at site 577 and the leg 74 sites show that an increase in 13c values in surface waters at 64 ma end of zone p1 resulted in increased vertical carbon isotope gradients 13c between surface and deeper dwelling planktonic foraminifera and between surface dwelling planktonics and benthonic foraminifera which became progressively steeper until the iniddle late palaeocene zone p4 this steepening also occurs in the latest palaeocene of the composite leg 113 section and can be explained by an increase in surface ocean productivity this increase in productivity probably resulted in an expansion of the oxygen minimum zone omz benthonic 13c values increased during the late palaeocene in site 577 and the composite leg 74 section suggesting that the palaeocene carbon isotope maximum was composed of both within ocean reservoir increased surface water productivity and between reservoir organic carbon burial ftactionation effects the benthonic 13c increase lags the surface ocean 13c increase in the early palaeocene 63 64 ma suggesting that surface water productivity increase probably led an increase in the burial rate of organic carbon relative to carbonate sedimentation moreover inter site 13c comparisons suggest that the locus of deep to intermediate water formation for the majority of the palaeocene and the earliest eocene was more likely to have been in the high southern latitudes than in the lower latitudes oxygen isotope data show a decline in deeper water temperatures in the early and early late palaeocene followed by a temperature increase in the late palaeocene and across the palaeoceneeocene boundary we speculate that these changes in deeper water temperatures were related to the flux of co2 between the oceans and the atmosphere through a mechanism operating at the high southern latitudes

the coexistence approach a method for quantitative reconstructions of tertiary terrestrial palaeoclimate data using plant fossils abstract the coexistence approach is introduced as a method for quantitative terrestrial palaeoclimate reconstructions in the tertiary it is based on the assumption that tertiary plant taxa have similar climatic requirements to their nearest living relatives the aim of the coexistence approach is to find for a given fossil flora and a given climate parameter the climatic interval in which all nearest living relatives of the fossil flora can coexist for this purpose we have developed a data base climbot containing for over 800 tertiary plant taxa the nearest living relatives and their climatic requirements and an algorithm for analysis climst for all types of fossil floras the coexistence approach thus allows the rapid quantitative reconstruction of 10 different climate parameters including the mean annual temperature temperature of the warmest month temperature of the coldest month mean annual precipitation maximum monthly precipitation minimum monthly precipitation precipitation of the warmest month relative humidity potential evaporation as well as the ratio of mean annual precipitation over potential evaporation the reliability and resolution of the coexistence approach are tested with various techniques and proved to be reasonably good for instance the resolution with respect to the mean annual temperature can be up to 1 c applications to various modern and fossil floras are illustrated and the advantages and disadvantages of the coexistence approach are discussed

magnetostratigraphy across the wasatchian bridgerian nalma boundary early to middle eocene in the western green river basin wyoming abstract new paleomagnetic and biostratigraphic data from the western green river basin of wyoming provide a magnetobiostratigraphic framework to correlate the late wasatchian through early bridgerian north american land mammal ages nalma to the geomagnetic polarity time scale gpts three hundred and twelve paleomagnetic samples were collected from 73 sites within a 350 m continuously exposed flat lying section the section is characterized by alternating packages of well developed paleosol mudstone horizons wasatch formation and lacustrine shale limestone horizons green river formation fossil mammal assemblages are known from various levels within the section and constrain the location of the wasatchian bridgerian nalma boundary to lie between 60 and 120 m paleomagnetic results of paleosol horizons are generally characterized by two components a present day field component with low unblocking temperatures up to 400 c and a characteristic component with unblocking temperatures up to 680 c cha

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

biozonation diagenesis and evolution of radiolarians in the lower carboniferous of germany abstract based on radiolarian faunas recovered from sequences of siliceous shales and dark claystones in the lower carboniferous of the rheinisches schiefergebirge germany a radiolarian biozonation is proposed diagenetic alteration of faunas is documented and the stratigraphic distribution of more resistent taxa is given for closely spaced samples a gradual shift of morphotype abundance has been found for albaillella cartalla in the visean but no gradual transition between species of albaillella has been found

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

orbital forcing and eocene continental temperatures abstract the ability to define terrestrial paleotemperatures is a key issue for understanding past climate states and the processes that produced them paleotemperatures are defined ideally by proxy data interpretations and supported by theoretical modeling results that provide physical explanations for the temperatures such explanations are especially critical for paleoclimates substantially warmer than present for which we have no modern or recent examples model results and geologic data describing continental mean annual temperatures for the warm early eocene earth as well as other time periods are generally in agreement however there are persistent discrepancies between climate model results and proxy data interpretations for temperature seasonality estimates in this paper we test the idea that orbital forcing and resulting distributions of solar radiation played a role in determining continental interior temperatures during the eocene specification of extreme values of orbital parameters within the range of calculated pleistocene values produces a wide range of continental temperatures these include cooler northern hemisphere continental summer temperatures and milder winter temperatures by up to 30 and an annual temperature range reduced by 75 relative to temperatures produced at the same location with modern orbital configuration temperature responses to the specified orbital forcing are most evident at middle and high latitudes the results produced with one specification of extreme orbital configurations are more similar to proxy data interpretations than any previous results of these temperature parameters we suggest that orbital variation and resulting insolation responses must be included in paleoclimate modeling studies that aim to explain proxy data and paleoclimate conditions for specific times in earth s history

early eocene biotic and climatic change in interior western north america imprecise correlation of the marine and terrestrial fossil records has been a major obstacle to understanding migration and extinction of continental biotas and early cenozoic climate change new sup 40 ar sup 39 ar data from the willwood formation in the bighorn basin of wyoming establish an age of 52 8 plus minus 0 3 ma for earliest lostcabinian late wasatchian faunas and coeval early eocene floras strata just beneath earliest wasatchian faunas can be correlated with the np9 np10 boundary in marine sedimentary units which has an interpolated age of approximately 55 7 ma this new information allows the authors to estimate the durations of the wasatchian approximately 5 m y and the lostcabinian approximately 2 m y and shows that the continental biotas are coeval with the acme of cenozoic warmth inferred from delta sup 18 o measurements of foraminifera from 58 to 50 ma paleoclimate in the continental interior at about 45 degree n was warm and equable but patterns of temperature change inferred from continental floras do not track precisely the marine delta sup 18 o record

new quantitative palaeocolimate data for the late cretaceous arctic evidence for a warm polar ocean abstract physiognomic analysis of four taphofloras one from the coniacian of n alaska one from the coniacian of kamchatka one from the turonian of kamchatka and one from the turonian of novaya sibir island using the clamp technique of wolfe 1993 yielded quantitative data on the mean annual warm month mean and cold month mean temperatures the length of the growing season mean annual precipitation mean growing season precipitation mean monthly growing season precipitation and the precipitation during the three consecutive driest months these new results represent the first application of multivariate statistical analysis of foliar physiognomy to determine palaeoclimatic parameters clamp to arctic cretaceous floras and demonstrate its robustness even in the context of vegetation which has no living analogues these new estimates were comparable to those from previous quantitative or qualitative sedimentological or palaeobotanical data where they were available but offer greater measurable precision the results also suggest that an arctic ocean with a winter surface temperature of approximately 6 c maintained n alaska coastal temperatures above freezing locally reversing the equator to pole temperature gradient a phenomenon not seen in the northern proto pacific this anomalously warm arctic ocean could have been produced by marine poleward heat transport precipitation in alaska kamchatka and novaya sibir island was predicted to have been high e g 1760 mm yr in the coniacian of n alaska reflecting a very weak polar high pressure cell and substantially different precipitation patterns to present

fossil crocodilians as indicators of late cretaceous and cenozoic climates implications for using palaeontological data in reconstructing palaeoclimate abstract that the earth s climate has cooled over the last 100 million years has been recognized since the early nineteenth century the transition from the hot house world of the cretaceous a time interval without significant polar icesheets to the ice house world in which we now live today the dynamics process responsible for this change are being examined using computer models especially general circulation models gcm s through such work our understanding of the dynamics of the earth system improves and our ability to predict future trends is enhanced but the success of modelling experiments can only be assessed by comparing results with observations the pattern which for palaeoclimate are drawn exclusively from the geological record palaeoclimate interpreted from geological data is invariably based on analogy with the recent the validity of which depends on corroboration from multiple lines of evidence this requires the compilation and investigation of large global datasets of well constrained geological climate proxies this study uses the palaeodistribution of fossil crocodilians to examine the spatial distribution of palaeoclimate during this transition fossil crocodilians have a relatively good fossil record and are climatically limited in the recent they also provide a manageable global dataset with which to investigate other issues that impinge on the use of geologic data for reconstructing palaeoclimate taphonomy sampling effects time averaging tectonics and for fossils palaeobiogeography and evolution as such this study provides a possible template for examining other climate proxies in order to validate and hone palaeoclimatic interpretations an analysis of modern crocodilians indicates that temperature is the principal influence on their global distribution with the coldest month mean temperature cmm of 5 5 c marking the minimum thermal limit for the group corresponding today to a minimum mean annual temperature mat of 14 2 c the duration of warmth during the year partly indicated by the mean annual range of temperature mart is also important as this affects early juvenile development and survival the presence of standing water provides an essential thermal buffer against temperature extremes by analogy the palaeodistribution of fossil crocodilians suggests the following during the late cretaceous and early palaeogene mat s in excess of 14 2 c cmm s 5 5 c permeated throughout mid latitudes and coastal regions in high latitudes during the oligocene the restriction of fossil crocodilians to low latitudes suggests high latitude cooling as indicated by numerous other lines of evidence coeval restriction of crocodilians to coastal regions in mid latitude north america and much of asia consistent with increased seasonality and aridification in continental interiors may reflect local orographic changes as well as global climate change during the miocene fossil crocodilians return to the great plains of north america but do not reoccupy the continental interior of asia by the pliocene crocodilians are again restricted to low latitudes and coastal regions in mid latitudes coincident with further high latitude cooling and aridification and cooling of mid latitude continental interiors minor distributional changes during the holocene may reflect human effects

equable climates during the early eocene significance of regional paleogeography for north american climate the character of continental interior paleoclimate at mid latitudes especially the aspect of temperature has been a major source of debate in modeling and paleontologic communities over the past few years a recent climate modeling study provides new insight into the issue of climatic conditions of early eocene north america model cases with six times the present level of co 2 or with doubled present co 2 and a large lake in western north america produced results most similar to proxy paleoclimate interpretations it is significant that the north american continental interior climate responded as strongly to the existence of the lake as to the atmospheric co 2 level the large lake deflects the winter freeze line poleward of the region containing most paleoclimate data site locations producing above freezing winter temperatures and providing a possible solution to the minimum temperature difference that exists between models and data the effect of the lake upon regional climate is significant and proves to be critical to reproducing the early eocene climate of north america

paleocene and eocene kaolinite distribution in the south atlantic and southern ocean antarctic climatic and paleoceanographic implications abstract clay mineral associations of paleocene and eocene age have been examined in six drilled sequences from the southern south atlantic and southern ocean these sites are located to provide three depth transects across intermediate water masses widespread abundance of pedogenic smectite at all locations suggests globally warm climates and alternating wet and dry seasons on the adjacent continental margins including antarctica as was the case during the late cretaceous remarkably kaolinite is observed only in paleocene eocene sediments at the highest latitudes of these sites and must have originated from antarctica the restriction of kaolinite to the antarctic region is inferred to have resulted from especially higher rainfall there during the paleocene eocene relative to the lower latitude areas examined this inferred high rainfall is considered to have resulted from globally warm temperatures that increased poleward latent heat transport compensating for a strong heat deficit in the antarctic region relative to the tropics kaolinite was not observed in the latest cretaceous maastrichtian sediments of maud rise antarctica kaolinite first appears in the clay mineralogical assemblages in the earliest paleocene 64 to 64 5 ma at a time of relatively cool intermediate waters and before a warming trend of surface waters currents at intermediate water depths transported fine terrigenous sediments from the antarctica during the latest paleocene and early eocene 59 to 52 ma at a time when the oxygen isotopic strongly in east antarctica during the latest paleocene and early eocene 59 to 59 ma at a time when the oxygen isotopic data indicate maximum warmth of surface and intermediate waters of the southern ocean these are interpreted to reflect a paleocene maximum of antarctic rainfall this development peaked at 57 3 m close to the paleocene eocene boundary a time of maximum warmth based on oxygen isotopic data increased illite content and associated chlorite and random mixed layer clays at the end of the middle eocene 41 ma suggest local development of poorly weathered soils on antarctica favored by a cooling of the southern ocean coeval extension of kaolinite into shallower water depths and similar clay mineral associations in shallower and deeper sites indicate the development of cooler conditions led to an increasing influence of antarctic environments upon intermediate water masses at high latitudes

estimation of rainfall variables from leaf characters in tropical africa abstract regression models are defined for leaf physiognomic and climate variables from 30 modern equatorial african plant communities herbarium specimens provide physiognomic data for published species lists for the 30 sites climate data are from a variety of published sources by limiting the sampled region to equatorial africa where annual amount and seasonality of rainfall are critical determinants of vegetation leaf physiognomy is found to be related linearly to moisture variables principal components analysis demonstrates that the pattern of variation among leaf variables is primarily a function of mean annual and wet months total of all months with 50 mm rainfall multiple regression models are derived for mean annual rainfall wet months rainfall and the number of dry months accuracy of each model is tested by comparing the adjusted predicted values the value for a case when it is not included in calculation of the regression line to the actual climate values at the 30 sites leaf size is the strongest correlate of moisture the mesophyll size class has the most significant positive relationship with annual and wet months rainfall entire margined species increase with wet months rainfall and temperature acuminate tip and length width ratio are also positively related to mean annual and wet months rainfall rounded base emarginate tip and acute tip are inversely related to rainfall variables regression models derived from modern plants and climate can be used to reconstruct seasonal and annual rainfall from cenozoic african leaf fossils

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

depositional subenvironments in an arid closed basin the wilkins peak member of the green river formation eocene wyoming u s a the wilkins peak member of the green river formation is a non marine dolomitic deposit that formed in an arid hydrologically closed basin a transect from the margin to the centre of the wilkins peak basin was examined in outcrop exposures in the south eastern corner of the basin and was supplemented with published core descriptions the rocks were divided into seven facies based upon lithology layering style and sedimentary fabrics 1 af facies quartzose conglomerates and sandstones representing sandy alluvial fans coming from the uinta mountains 2 sf facies quartzose peloidal dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans 3 dm facies irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat 4 el facies dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds 5 pl facies finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes 6 sm facies trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology these represent a central salt pan and the surrounding saline mudflat 7 as facies arkosic sandstones siltstones and mudstones which represent braided river and more basinal deltaic plain deposits the five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations there are at least forty 3 4 m thick cycles in the wilkins peak and one large scale cycle comprising the whole member which mimics the facies changes of the smaller cycles this is compatible with the transitions of the wilkins peak member to the tipton and laney members as climatic responses and not shifts in drainage the sheet flood sandstones actively aggrading subaerial mudflats and bedded evaporites of the wilkins peak are apparently unique within the green river formation they reflect the unusual provenance and hydrology of the wilkins peak and suggest chemical and sedimentary models established for the other green river members will not be applicable

late paleocene early eocene climate changes in southwestern wyoming paleobotanical analysis the warmest global temperatures of the cenozoic era occurred in early eocene time following a warming trend that started in late paleocene time the greater green river basin of southwestern wyoming is one of the best areas in the rocky mountains for paleobotanical investigation of the paleocene eocene climatic transition intensive sampling has resulted in the recovery of an estimated 189 species of plant macrofossils from the tiffanian clarkforkian wasatchian and bridgerian land mammal ages the leaf morphologies and taxonomic affinities of these fossils were used in combination with other indicators to evaluate paleocene eocene climates following cool humid conditions in the tiffanian the clarkforkian was humid and subtropical and several plant families with modern tropical affinities appeared however as in the tiffanian clarkforkian floras had low diversity and were dominated by a single species in the birch family mean annual temperature mat rose from an estimated 12 c in the tiffanian to 19 c in the clarkforkian while mean annual precipitation map for the tiffanian and clarkforkian is estimated to have been 130 150 cm little fossil plant material is preserved from the latest clarkforkian or the earliest wasatchian which is thought to have contained an interval of cooling and drying followed by renewed warming by the middle wasatchian the time of the cenozoic thermal maximum the inferred mat was about 21 c and the map was near 140 cm a second influx of plant families with tropical affinities appeared in the area and diversity increased significantly but most plant families known from the clarkforkian persisted species turnover from the clarkforkian to the wasatchian was greater than 80 a second turnover of more than 80 of species but not families from the wasatchian to the early bridgerian accompanied drying and increased seasonality of precipitation the early bridgerian mat is inferred to have been near 20 c and the map to have been about 80 cm except for the tiffanian and possibly portions of the early wasatchian paleoclimates during the study interval were predominantly frost free although the moderating influence of the green river lake system has been suggested as a possible explanation for mild eocene winters in wyoming this study shows that virtually frostfree climates existed in the area prior to and independent of significant lake development

winter and summer temperatures of the early middle eocene of france from turritella δ18o profiles the mean annual range of temperature is from a climatological point of view at least as important as the mean annual temperature in order to examine intra annual temperature variations in the warm early cenozoic we have analyzed stable oxygen and carbon isotopes along the transect of growth on excellently preserved specimens of the gastropod turritella imbricataria and the bivalve venericardia imbricata from sedimentary rocks of early middle eocene age ca 46 ma in the paris basin turritella shell growth is fast throughout the year and the isotopic records give the first detailed information about early middle eocene seasonal variations the oxygen isotope profiles indicate winter temperatures of about 14 c and summer temperatures of up to 28 c i e a seasonality indistinguishable from the present situation but an annual temperature some 10 c higher our results contradict the opinion that the climate during this period was more equable than that of today