precessional climate cyclicity in late cretaceous early tertiary marine sediments a high resolution chronometer of cretaceous tertiary boundary events we report well dated late cretaceous and early tertiary precessional climatic cycles recorded by rhythmic carbonate maxima and minima in south atlantic deep sea sites spectral analyses of digitized sediment color a suitable carbonate proxy show prominent regularities in the spacing marl carbonate beds magnetostratigraphic dating over a number of magnetic chrons constrains the duration of the cycles which can be detected over at least 20 myr of sedimentation at 7 coring locations their mean absolute period of23 5 4 4kyr agrees closely with the predicted late cretaceous precessional period of 20 8 kyr because they can be matched to a physical forcing mechanism with a known repeat time the cycles offer a new high resolution tool to measure rates of climate change before and after the cretaceous tertiary k t boundary from counts of carbonate cycles we derive the position of the k t boundary within c29r at 350 kyr after the base of the reversal the constancy of cycle thickness linearly related to sedimentation rate and amplitude up to the boundary clay does not give evidence for climate instability preceding the boundary orbital chronometry records a step function decrease in sediment accumulation rate at the cretaceous tertiary boundary that is consistent with a geologically instantaneous event

latitudinal temperature gradient during the cretaceous upper campanian middle maastrichtian y18o record of continental vertebrates latitudinal variations in model biogenic apatite d18o values were calculated using fractionation equations of vertebrates and weighted rainfall y18o values along with mean annual air temperatures provided by iaea wmo meteorological stations the reference equation obtained was used to compute a continental temperature gradient for the late campanian middle maastrichtian interval by using published and new d18o values of phosphate from vertebrates samples are mainly tooth enamel from crocodilians and dinosaurs that lived at paleolatitudes ranging from 83 4 n alaska to 32 3 s madagascar the temperature gradient was less steep 0 4 0 1 c latitude than the present day one 0 6 c latitude with temperatures that decreased from about 30 c near the equator to about 5 c at the poles above 30 of paleolatitude air temperatures were higher than at present the validity of these results is discussed by comparison with climatic criteria inferred from paleontological paleobotanical and sedimentological data the latitudinal distribution of oxygen isotope compositions of continental vertebrates is potentially a powerful tool for quantifying mesozoic terrestrial climates

assessing the impact of diagenesis on δ11b δ13c δ18o sr ca and b ca values in fossil planktic foraminiferal calcite the geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo climatic oceanographic and ecological changes however dissolution of biogenic calcite and precipitation of inorganic calcite overgrowth and recrystallization at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test biasing any resulting paleoenvironmental reconstruction the 11b of planktic foraminiferal calcite is a promising ocean ph proxy but the effect of diagenesis is still poorly known here we present new 11b 13c 18o sr ca and b ca data from multiple species of planktic foraminifera from time equivalent samples for two low latitude sites clay rich tanzanian drilling project tdp site 18 from the indian ocean containing well preserved glassy foraminifera and carbonate rich ocean drilling program odp site 865 from the central pacific ocean hosting recrystallized frosty foraminifera our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis planktic foraminiferal 18o and 13c records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration sr ca and b ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa in contrast 11b values indicate no large differences between well preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the 11b of biogenic calcite appears robust potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing caco3 our finding may remove one potential source of uncertainty in 11b based ph reconstructions and provide us with greater confidence in our ability to reconstruct ph in the ancient oceans from at least some recrystallized foraminiferal calcite however further investigations should extend this approach to test the robustness of our findings across a range of taphonomies ages and burial settings

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

paleoceanographic modeling of temperature salinity profiles from stable isotopic data temperature salinity t s profiles in ancient seawater can be estimated from oxygen isotopic compositions of well preserved calcitic fossils sampled from known paleodepth gradients the proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition given estimates of average salinity isotopic composition and net global hydrologic fractionation for ancient oceans increasing density with depth constrains those combinations to narrow ranges this graphic method superposes curves for density and isotopic composition in t s space to reveal possible ancient t s profiles application of this method to oxygen isotope data from ordovician brachiopods deposited on the eastern continental slope of north america demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer more saline deep waters

efficacy of δ18o data from pliocene planktonic foraminifer calcite for spatial sea surface temperature reconstruction comparison with a fully coupled ocean atmosphere gcm and fossil assemblage data for the mid pliocene sea surface temperature sst estimates using the 18o composition of fossil planktonic foraminifer calcite within the time slice 3 12 to 3 05 ma pliocene kaena subchron c2an1r are assessed for nine atlantic ocean sites these are compared with sst estimates from fossil assemblages for the time slab 3 29 2 97 ma and with estimates from a fully coupled ocean atmosphere general circulation model gcm for the same time interval most sst estimates derived from the 18o data indicate a cooler ocean surface than at present through the latitudinal range 69 25 n to 46 88 s at some sites the temperature difference is greater than 5 c cooler than at present this contrasts with sst estimates from fossil assemblages that give warmer than present temperatures at mid to high latitudes and similar temperatures in the tropics and with the gcm which predicts ssts warmer than at present across all latitudes for this time interval difficulties interpreting the ecology of fossil foraminifer assemblages and inaccurate estimates of mid pliocene seawater 18o composition 18osw at some sites may partly produce the temperature discrepancy between isotope based and fossil based sst estimates but do not adequately explain the cool signal of the former we interpret the cool sst estimates from the 18o data to be the product of a calcite formed at a level deep within or below the ocean mixed layer during the life cycle of the foraminifera b secondary calcite with higher 18o formed in the planktonic foraminifer tests in sea bottom pore waters although these effects differ between sites secular and temporal oceanographic trends are preserved in the primary calcite formed in the mixed layer near the ocean surface witnessed by the latitudinal variation in estimated ssts reconstructing accurate mid pliocene ssts with much of the existing published oxygen isotope data probably requires a detailed re assessment of taphonomy particularly at tropical sites this study also indicates that methods for estimating atlantic pliocene 18osw need to be refined

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

past climate and the role of ocean heat transport model simulations for the cretaceous a series of general circulation model experiments using global environmental and ecological simulation of interactive systems genesis were executed to evaluate the sensitivity of simulated mid cretaceous climate to small perturbations in ocean heat transport three experiments were performed 1 mixed layer ocean with no ocean heat transport zeroq 2 ocean heat transport specified as required for genesis to best match modern observations oneq and 3 doubled ocean heat transport twoq the oneq experiment represents an ocean heat transport which is actually about 15 of the values given by carissimo et al 1985 from modern observations as a sensitivity experiment these model simulations represent a doubling of the role of the ocean however relative to the observations they represent small perturbations to the total poleward heat transport in the model with the exception of the tropics no major changes in the structure of the general circulation of the atmosphere resulted from the modification of the ocean heat transport however relatively small increases in ocean heat transport resulted in a number of significant differences between simulations including tropical cooling polar warming weakened equator to pole surface temperature gradients weakened midlatitude jets decreased land sea pressure contrast and decreased midlatitude storminess the experiments indicate that changes in ocean heat transport which are well within the realm of possibility for earth history can have significant climatic impact although ocean heat transport may be a significant factor in explaining cretaceous polar warmth the changes specified in these experiments alone are not sufficient to explain the polar warmth of the cretaceous

conflicting isotopic and biotic evidence for tropical sea surface temperatures during the tertiary abstract the biotic evidence from a varied group of shallow water organisms including mangroves zooxanthellate corals mainly reefal and larger foraminifera suggests that sea surface temperatures at low latitudes during the tertiary from at least the early eocene to the middle miocene were subtropical to tropical in nature and similar to temperatures prevailing at low latitudes at the present day 20 28 c in a recent paper shackleton 1984 the suggestion is made on the basis of oxygen isotope studies of foraminiferal shells that low latitude sea surface temperatures during the palaeogene and much of the neogene were invariably lower than those in similar regions today with a stable temperature of around 18 c this paper discusses the conflicting evidence for sea surface temperatures obtained from palaeontological and isotopic sources and suggests that palaeotemperatures derived from some isotopic studies are too low to account for the distribution and diversity of many tertiary tropical and subtropical biotas

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

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

past co2 changes and tropical sea surface temperatures the relationship between past co2 variations and tropical climate change on time scales of millions of years is reviewed explanations for cretaceous and early cenozoic climate change often involve higher atmospheric co2 levels climate models predict that such increases should have been associated with warmer tropical sea surface temperatures ssts however sparse mid cretaceous 18o based sst estimates from low latitude calcareous plankton are 1 0 1 5 heavier than predicted initial evaluations indicate that changes in salinity may not alleviate model data discrepancies for calcareous 18o and that interpretation of altered latitudinal 18o gradients in terms of increased poleward heat transport due to warm saline bottom water wsbw formation would require very large levels of wsbw production at least 60 sv calcareous 18o records may not always record true sst patterns as 18o analyses from phosphatic groups which are less sensitive to diagenesis indicate ssts 5 c higher this latter conclusion is supported by a number of other fossil groups which indicate temperatures warmer than those estimated from calcareous 18o in order to more rigorously test the paleo co2 hypothesis and indeed the models used to forecast future climates it is desirable to intensify investigations of past climate change in low latitudes in order to determine whether these preliminary conclusions stand the test of further scrutiny

structural relationships and srnd isotope systematics of polymetamorphic granitic gneisses and granitic rocks from central rajasthan india implications for the evolution of the aravalli craton this paper reviews the state of structural and geochronological knowledge of precambrian cratonic rocks in part of central rajasthan india and contributes new observations and isotopic data on the structural features and age of granitic rocks in the area the granitic rocks comprise plutons of two suites bgc and sendra suites which intrude ortho and paragneisses the archean banded gneiss complex bgc and its inliers as well as the proterozoic delhi supergroup nearly all the plutons show a foliation and a lineation which are mostly the result of solid state deformation although a magmatic component of strain is apparent in some of them the intensity of these structural fabrics varies from weak to extremely strong samples of granitic rocks from the bgc suite yield ages from sm nd isotopic data which scatter around a 2 83 ga reference isochron nd t of 4 1 with depleted mantle model ages ranging from 2 6 to 3 0 ga scatter of the data suggests that the bgc is a composite group of gneisses and confirms the antiquity of the bgc within this part of the aravalli delhi orogenic belt rb sr isotopic data of the bgc suite lie on a 1 7 ga reference isochron indicating a thermal event at that time data from plutons of the sendra suite on the other hand show some scatter but define a model ii isochron with slope equivalent to an age of 0 966 250 ga initial 87sr86sr of 0 70390 0 01889 mswd 311 the scatter of data could reflect open system behavior during a subsequent thermal event malani volcanics although independent evidence for such is lacking in the study area ages calculated from our rb sr data are within the error of published results from previous workers structural observations on granitic rocks within the bgc inlier at ajmer suggest that the inlier could represent a remobilized diapiric ridge emplaced into the delhi supergroup during the 1 7 ga thermotectonic event contemporaneously with formation of d1 structures in the wall rock although the radiometric age of the latter structures is not well constrained microtexture mineralogy and field relations of granitic rocks of the sendra suite point to those plutons being emplaced into the delhi supergroup during the 0 966 ga thermotectonic event late syntectonic relative to d2 indicating that d2 is 0 96 1 0 ga d3 represents retrograde deformation synchronous with cooling of the regional thermal framework and local pluton cooling probably between 0 96 and 0 90 ga further geochronological geochemical and structural work on the plutons and wall rock of both suites is necessary to establish a rigorous thermotectonic chronology by which to accurately model the crustal evolution of this part of central rajasthan

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

cool tropics in the middle eocene evidence from the changchang flora hainan island china abstract the middle eocene lutetian bartonian 48 6 37 2 ma near equatorial megafossil flora from swamp and lacustrine facies of the lower changchang formation hainan island south china 19 631463 n 110 445049 e is highly diverse 200 taxa dominated by an unusual mixture of angiosperms typical of modern temperate subtropical and tropical evergreen and deciduous forms it is also rich in palms multivariate analysis of the architecture of minimally transported woody dicot leaves reveals a mean annual air temperature mat of 22 4 7 c with a marked thermal seasonality range of 21 c the year round humid climate lacked any monsoonal signature the overall climate signal is compatible with the growth characteristics exhibited by fossil wood but is warmer than the climate signal derived from pollen and spores using co existence analysis corrections for possible palaeoelevation of the basin bring the megafossil derived mat estimate in line with 54 52 ma sea surface and soil temperatures obtained from the gulf coast usa palaeolatitude 30 n using multiple geochemical proxies and supports the claim that the low latitude eocene climate was not uniformly warm this challenges previous conclusions based on 18 o analysis of unaltered calcareous microfossils our air temperature data also adds to the challenge of understanding heat transport away from the equator to higher latitudes during hothouse climate regimes

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

cretaceous sea surface temperature evolution constraints from tex86 and planktonic foraminiferal oxygen isotopes it is well established that greenhouse conditions prevailed during the cretaceous period 145 66 ma determining the exact nature of the greenhouse gas forcing climatic warming and climate sensitivity remains however an active topic of research quantitative and qualitative geochemical and palaeontological proxies provide valuable observational constraints on cretaceous climate in particular reconstructions of cretaceous sea surface temperatures ssts have been revolutionised firstly by the recognition that clay rich sequences can host exceptionally preserved planktonic foraminifera allowing for reliable oxygen isotope analyses and secondly by the development of the organic palaeothermometer tex86 based on the distribution of marine archaeal membrane lipids here we provide a new compilation and synthesis of available planktonic foraminiferal 18o 18opl and tex86 sst proxy data for almost the entire cretaceous period the compilation uses ssts recalculated from published raw data allowing examination of the sensitivity of each proxy to the calculation method e g choice of calibration and places all data on a common timescale overall the compilation shows many similarities with trends present in individual records of cretaceous climate change for example both sst proxies and benthic foraminiferal 18o records indicate maximum warmth in the cenomanian turonian interval our reconstruction of the evolution of latitudinal temperature gradients low 48 palaeolatitudes reveals temporal changes in the valanginian aptian the low to higher mid latitudinal temperature gradient was weak decreasing from 10 17 c in the valanginian to 3 5 c in the aptian based on tex86 ssts in the cenomanian santonian reconstructed latitudinal temperature contrasts are also small relative to modern 14 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts compared with 20 c for the modern in the mid campanian to end maastrichtian latitudinal temperature gradients strengthened 19 21 c based on low latitude tex86 and 18opl ssts minus higher latitude 18opl ssts with cooling occurring at low middle and higher palaeolatitude sites implying global surface ocean cooling and or changes in ocean heat transport in the late cretaceous these reconstructed long term trends are resilient regardless of the choice of proxy tex86 or 18opl or calibration this new cretaceous sst synthesis provides an up to date target for modelling studies investigating the mechanics of extreme climates

can humans force a return to a cretaceous climate abstract the modern pole to equator sea level temperature difference is about 50 c that of the mid cretaceous ranged from 30 c to as little as 24 c implying a much more equable climate this may have been caused by 1 reduction of the ice forced albedo of the polar regions 2 more efficient meridional energy transport by the atmosphere and ocean and 3 increased atmospheric greenhouse gas concentrations earth s icy polar regions stabilize its present inequable climate through the ice albedo feedback effect the polar ice results in permanent atmospheric highs that stabilize earth s wind systems in turn the stable winds drive the ocean currents and determine the location of the frontal systems that separate the low and high latitude oceanic gyre systems and bound the region where water sinks into the ocean interior as thermocline and intermediate water masses increased ocean heat transport can assist in making a more equable climate but unrealistic volume transports would be required to warm the polar regions to cretaceous levels the major factor forcing the equable climate of the cretaceous is now thought to be increased greenhouse gas concentrations dominated by co2 the modern rate of change in atmospheric concentration is greater than 200 ppmv per century and increasing this compares with 1 ppmv per century during the last deglaciation at current rates of fossil fuel burning atmospheric co2 levels will reach cretaceous levels of 2 times the pre industrial level about 2070 and 8 times the pre industrial level shortly after 2300 it is likely that cretaceous atmospheric co2 concentrations will last for many thousands to tens of thousands of years in addition to increased atmospheric greenhouse gas concentrations a return to climatic conditions resembling those of the cretaceous would require ice free poles and large changes in atmospheric and oceanic circulation arctic sea ice is melting much more rapidly than had been expected and the arctic ocean will soon be free of sea ice in summer the greenland ice sheet is melting more rapidly than expected because of greenhouse warming surface meltwater forms lakes and then flows down through crevasses and holes in the ice to lubricate the base allowing ice steams to flow much more rapidly the lifetime of the greenland ice sheet may be only a few hundred years the west antarctic ice sheet is inherently unstable being grounded on rock well below sea level the ice shelves blocking ice streams off west antarctica have begun to melt from beneath and break up as the southern ocean warms the east antarctic ice sheet has been regarded as highly stable but discovery of lakes beneath the ice and fast flowing ice streams raises questions about whether the ice sheet will ultimately succumb to global warming and disintegrate i conclude that a return to climatic conditions resembling those of the mid cretaceous is not only possible but also likely unless humanity can organize an effective campaign to stop co2 emissions to the atmosphere and remove some of the excess co2 already introduced

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

fish tooth δ18o revising late cretaceous meridional upper ocean water temperature gradients the oxygen isotope composition of fossil fi sh teeth a paleo upper ocean temperature proxy exceptionally resistant to diagenetic alteration provides new insight on the evolution of the low to middlelatitude thermal gradient between the middle cretaceous climatic optimum and the cooler latest cretaceous period the new middle cretaceous low to middle latitude thermal gradient agrees with that previously inferred from planktonic foraminifera 18o recovered from deep sea drilling project and ocean drilling program drilling sites although the isotopic temperatures derived from 18o of fish teeth are uniformly higher by 3 4 c in contrast our new latest cretaceous thermal gradient is markedly steeper than those previously published for this period fish tooth 18o data demonstrate that low to middle latitude thermal gradients of the middle cretaceous climatic optimum and of the cooler latest cretaceous are similar to the modern one despite a cooling of 7 c between the two periods our new results imply that no drastic changes in meridional heat transport are required to explain the late cretaceous climate based on climate models such a cooling without any change in the low to middle latitude thermal gradient supports an atmospheric co2 decrease as the primary driver of the climatic evolution recorded during the late cretaceous

in situ δ18o and mg ca analyses of diagenetic and planktic foraminiferal calcite preserved in a deep sea record of the paleocene eocene thermal maximum we report 18o and minor element mg ca sr ca data acquired by high resolution in situ secondary ion mass spectrometry sims from planktic foraminiferal shells and 100 500 m sized diagenetic crystallites recovered from a deep sea record odp site 865 of the paleocene eocene thermal maximum petm the 18o of crystallites 1 2 pee dee belemnite pdb is 4 8 higher than that of planktic foraminiferal calcite 3 6 pdb while crystallite mg ca and sr ca ratios are slightly higher and substantially lower than in planktic foraminiferal calcite respectively the focused stratigraphic distribution of the crystallites signals an association with petm conditions hence we attribute their formation to early diagenesis initially sourced by seafloor dissolution burndown ensued by reprecipitation at higher carbonate saturation the mg ca ratios of the crystallites are an order of magnitude lower than those predicted by inorganic precipitation experiments which may reflect a degree of inheritance from donor phases of biogenic calcite that underwent solution in the sediment column in addition sims 18o and electron microprobe mg ca analyses that were taken within a planktic foraminiferal shell yield parallel increases along traverses that coincide with muricae blades on the chamber wall the parallel 18o and mg ca increases indicate a diagenetic origin for the blades but their 18o value 0 5 pdb is lower than that of crystallites suggesting that these two phases of diagenetic carbonate formed at different times finally we posit that elevated levels of early diagenesis acted in concert with sediment mixing and carbonate dissolution to attenuate the 18o decrease signaling petm warming in whole shell records published for site 865

palaeoecology of late middle eocene planktic foraminifera and evolutionary implications the late middle eocene is marked by accelerated global cooling representing part of the long transitional interval separating the early eocene greenhouse and later oligocene icehouse climatic regimes this time interval is also regarded as having witnessed a decline in planktic foraminiferal diversity following the extinction of most of the muricate clade genera acarinina and morozovelloides at approximately 39 ma here we examine planktic foraminiferal assemblages recovered at odp site 1052 blake nose nw atlantic and by recording a high level of taxonomic diversity including several previously undocumented morphotypes we suggest that the diversity of late middle eocene planktic foraminifera may have been underestimated depth habitats of every species within these late middle eocene assemblages are reconstructed using oxygen and carbon stable isotope ratios furthermore because stable isotope analyses suggest that species of globoturborotalita appear to have generally calcified during winter months these taxa offer in combination with predominantly summer surface dwellers such as morozovelloides the potential to reconstruct patterns of seasonality during the late palaeogene using extremely well preserved glassy planktic foraminiferal calcite from a contemporaneous hemipelagic drill site detailed sem imaging of test microstructures and wall textures confirm that many modern features of foraminiferal ecology and test architecture had already evolved by the late middle eocene the common occurrence of the cancellate wall texture combined with the wide variety of reconstructed foraminiferal depth habitats indicates that there is no necessary relationship between foraminiferal wall textures and habitat and that wall textures are evolutionary conservative features of the foraminiferal test

deep water in the late maastrichtian ocean 1 stable isotopic data from benthic foraminifera indicate the occurrence of at least three deepwater masses in the late maastrichtian ocean given mean oceanic 18ow of 1 0 the temperature of the coolest intermediate depth waters was 5 7 c that of the deepest waters was 10 c and that of the warmest intermediate waters was 13 15 c the cool intermediate depth water mass probably originated in the high latitude southern ocean the deepest waters originated at least partly in the northern atlantic the source region for the warmest intermediate depth water mass is unknown although much of the late maastrichtian deep water was probably preconditioned for winter sinking by low or middle latitude evaporation no more than 11 of late maastrichtian deep water could have been directly actuated by low latitude sea surface evaporation at least in the southern atlantic and indian oceans heat transport by upwelling of deep water was not the primary cause of mild sea surface and coastal temperatures

size related stable isotope changes in late cretaceous planktic foraminifera implications for paleoecology and photosymbiosis abstract the paleoecology of cretaceous planktic foraminifera during the late cenomanian to coniacian period 95 86 ma remains controversial since much of the tropical marine record is preserved as chalk and limestone with uncertain geochemical overprints here we present 13c and 18o data from sieve size fractions of monospecific samples of exceptionally well preserved planktic foraminifera recovered during ocean drilling program leg 207 demerara rise western tropical atlantic our results suggest that all species studied hedbergella delrioensis heterohelix globulosa marginotruncana sinuosa whiteinella baltica grew primarily in surface waters and did not change their depth habitat substantially during their life cycle comparison of size related ontogenetic trends in 13c in cretaceous and modern foraminifera further suggests that detection of dinoflagellate photosymbiosis using 13c is confounded by physiological effects during the early stages of foraminifer growth raising doubts about previous interpretations of photosymbiosis in small foraminifera species we propose that obligate photosymbiosis involving dinoflagellates may not have evolved until the campanian or maastrichtian since our survey of cenomanian coniacian species does not find the 18o and 13c size related trends observed in modern foraminifer dinoflagellate symbioses

late cretaceous oceans and the cool tropic paradox oxygen isotopic proxies of paleo sea surface temperatures ssts suggest that maastrichtian about 66 million years ago tropical ssts were lower than those of today they also demonstrate that maastrichtian latitudinal sst gradients were much lower than those of the present the low maastrichtian sst gradients indicate that meridional heat transport was much greater or latitudinal differences in the balance of radiation to and from the sea surface were much less extreme during the latest cretaceous than they are today or that both conditions were true these findings challenge traditional interpretations of greenhouse late cretaceous climates

variability in late cretaceous climate and deep waters evidence from stable isotopes abstract strong climatic and temperature fluctuations mark the late campanian and maastrichtian as indicated by stable isotope records from the equatorial pacific site 463 and middle and high latitude south atlantic sites 525 689 and 690 the first major global cooling decreased intermediate water temperatures iwt by 5 6 c between 73 70 ma at the same time sea surface temperature sst decreased by 4 5 c in middle and high latitudes intermediate waters iw temporarily warmed by 2 c in low and middle latitudes between 70 68 5 ma global cooling resumed between 68 5 65 5 ma when iwt decreased by 3 4 c and sst by 5 c in middle latitudes about 450 ka before the cretaceous tertiary boundary rapid global warming increased iwt and sst by 3 4 c though sst in the tropics changed little during the last 200 ka of the maastrichtian climate cooled rapidly with iwt and sst decreasing by 2 3 c during the global cooling at 71 70 ma and possibly at 67 65 5 ma the sources of cold intermediate waters in the equatorial pacific indo pacific and south atlantic were derived from the high latitude north pacific in contrast during the global climate warming between 65 2 65 4 ma the middle latitude south atlantic was closest to the source of iw production and implies that the low latitude tethys played a major role in global climate change climate changes sea level fluctuations and associated restricted seaways appear to be the most likely mechanisms for the alternating sources of iw production

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

phytogeography and paleoclimatic interpretation of the maestrichtian abstract insight into the true nature of cretaceous climate can best be grained through a worldwide study of the preserved climatic indicators this study focuses on reconstructing the climate of the maestrichtian latest cretaceous based on the abundant published information from the geologic record specifically the approach taken was to reconstruct the general patterns of the terrestrial ecological biomes based on the fossil megaflora and pollen record once the biomes were delineated the climatic constraints on the present counterparts of these biomes were used to determine the prevailing climate of each region biome boundaries were recognized by discontinuities in the phytogeographic distributions of a variety of fossil plant groups detailed comparisons of fossil plant assemblages with present day climatic preferences of nearest living relatives allowed each region to be assigned to a modern biome further comparisons with fossil leaf physiognomic studies and tree ring studies integrated with an extensive database of climatically important sediments helped to refine the biomal and climatic assignments altogether 12 climatic zones corresponding to 7 major biome types have been recognized for the late cretaceous period

late albian dinoflagellate cyst paleobiogeography as indicator of asymmetric sea surface temperature gradient on both hemispheres with southern high latitudes warmer than northern ones abstract late albian temperature sensitive dinoflagellate cysts are characterized in order to better understand mid cretaceous sea surface temperature gradients distribution maps of thirty seven species recovered from one hundred fifty outcrops and deep sea drilling holes odp dsdp sites located from low and high paleolatitudes over the two hemispheres 75 n 70 s are encountered fifty years of published data available in eighty seven articles have been considered and synthesized using a database coupled with a geographical information system gis the continuous and disjoint biogeographic patterns of dinocyst species along latitudes define seven climatic belts four in the northern hemisphere high mid high mid low low latitude belts and three in the southern hemisphere low mid low mid high latitude belts dinocysts restricted along latitudes are temperature sensitive species limit ranges of temperature sensitive dinocysts of mid low and mid high latitude belts reveal mixing belts located at 40 45 n and 50 70 s they represent major palaeofrontal systems as paleosubtropical fronts with strongly mixed water column the northern frontal system 40 45 n was located as in the modern ocean the large southern frontal system 50 s 70 s was 10 20 poleward to antarctica semi quantitative temperature range limits for mid cretaceous dinoflagellates and sst gradients in the two hemispheres are suggested by setting dinocyst climatic belts against estimated 18o temperature curve from fish teeth a paleoecological classification is suggested latitudinal distribution of extant temperature sensitive dinoflagellate cysts follows the asymmetric modern temperature gradient asymmetric latitudinal ranges of late albian dinocyst species of mid low latitude belts restricted between 45 n and 70 s demonstrate asymmetric temperature gradients with southern high latitudes being warmer than northern high latitudes

palaeoclimate broken tropical thermostats during the early pliocene epoch tropical sea surface temperatures were thought to be similar to those of today even though global mean temperatures were several degrees warmer temperature reconstructions now suggest that the pliocene tropical warm pools were about two degrees warmer than those at present

ocean loading deformations caused by storm surges on the northwest european shelf 1 a model of the non tidal ocean loading deformations caused by storm surges on the northwest european shelf has been developed using the output from a 12 km grid storm surge model the spatial distributions of displacements and gravity variations caused by a typical storm surge event are computed in order to show the magnitudes of the effects that can be expected in space geodetic or gravity measurements a storm surge of just over 2 m in the southern north sea produces vertical displacements of 20 to 30 mm and increases of gravity of 6 to 8 gal in the coastal areas of denmark germany the netherlands and the east coast of england it is shown that the loading deformations due to surges affect a wide area of northwest europe and that high resolution non tidal loading models are required for correcting geodetic measurements made in areas near shallow continental shelves

seawater ph and isotopic paleotemperatures of cretaceous oceans abstract stable oxygen isotope ratios 18 o of foraminifera are widely used to reconstruct the climatic history of earth it is well known that temperature reconstructions based on 18 o are complicated by factors such as the unknown isotopic composition of the ocean in addition recent experimental and theoretical work has shown that the seawater ph has a marked effect on the 18 o of foraminifera here i employ this effect to demonstrate that reconstructions based on 18 o of foraminifera may underestimate sea surface temperatures in the geological past ocean surface temperatures for the mid cretaceous are estimated to have been 2 3 5 c higher than previously thought

oxygen isotopes in phosphatic fish remains from israel paleothermometry of tropical cretaceous and tertiary shelf waters the isotopic composition of oxygen in phosphate was measured on 24 fossil fishes from israel and jordan ranging in age from cretaceous to eocene from these the first paleotemperatures were calculated for shallow water cretaceous paleotropics the results were compared to those of fish from other mediterranean localities and to late cretaceous marine reptiles from israel 18o in the fish average 18 0 in the early cretaceous 17 8 in the cenomanian 18 3 in the coniacian 18 2 in the santonian 19 4 in the campanian 20 1 in the maastrichtian and 18 4 in the early eocene such variations suggest a warm cenomanian turonian cooling towards the end of the cretaceous and warming up again in the eocene the deduced temperatures for the cretaceous range between 20 c and 34 c which is about 10 higher than cretaceous water surface temperatures in northern europe apatite from marine reptile skeletons yields similar 18o to coexisting fish the good agreement between these and previously known paleotemperature data give further credence to the validity of paleotemperatures obtained by isotopic analysis of oxygen in phosphates the relatively large thermal gradient between middle and low paleolatitudes favors barron s 1983 coolest cretaceous model

tectonic forcings of maastrichtian ocean climate evolution a global compilation of deep sea isotopic records suggests that maastrichtian ocean climate evolution tvas tectonically driven during the early maastrichtian the atlantic intermediate deep ocean was isolated from the pacific indian and southern oceans deep water formed in the high latitude north atlantic and north pacific at the early late maastrichtian boundary a major reorganization of oceanic circulation patterns occurred resulting in the development of a thermohaline circulation system similar to that of the modem oceans a combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the south atlantic and the initiation of north south flow of intermediate and deep water in the atlantic the onset of laramide tectonism during the mid maastrichtian led to the concurrent draining of major epicontinental seaways together these events caused cooling increased latitudinal temperature gradients increased ventilation of the deep ocean and affected a range of marine biota

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

cool equatorial terrestrial temperatures and the south asian monsoon in the early eocene evidence from the gurha mine rajasthan india abstract early eocene 55 52 ma laminated lacustrine sediments overlying lignites in the gurha mine 27 87398 n 72 86709 e rajasthan india yield a diversity of fossil leaves flowers fruits seeds and insects clamp multivariate foliar physiognomic analysis of two horizons separated by an estimated several tens of thousands of years of deposition indicates cool equatorial 10 n temperatures and a pronounced monsoon signature a lower assemblage consisting of 54 leaf morphotypes and an upper assemblage of 57 leaf forms yielded mean annual temperatures mat of 24 7 and 23 9 c respectively the uncertainty 2 82 c means these temperature regimes are identical despite few similarities in the morphotypes between the two assemblages the mean annual range of temperature mart was approximately 9 7 c for both assemblages when corrected for evapotranspirational cooling these temperature regimes are similar to those experienced today at 10 n on the west coast of india and surprisingly cool for the tropics at a time of extreme global warmth growth was year round the tropical to paratropical fossil floras also suggest a moist regime 80 annual relative humidity and high mean annual precipitation of 1800 mm for both assemblages but with a pronounced wet dry seasonality indicative of a pronounced monsoonal regime the lower assemblage has a stronger monsoon index 11 8 than the upper assemblage 8 8 the two assemblages seem to have been deposited less than 100 ka apart this suggests that not only a pronounced south asian monsoon existed when india and asia first made contact but also a variation in monsoon strength existed that cannot be ascribed to tectonic drivers

preservation of benthic foraminifera and reliability of deep sea temperature records importance of sedimentation rates lithology and the need to examine test wall structure preservation of planktic foraminiferal calcite has received widespread attention in recent years but the taphonomy of benthic foraminiferal calcite and its influence on the deep sea palaeotemperature record have gone comparatively unreported numerical modeling indicates that the carbonate recrystallization histories of deep sea sections are dominated by events in their early burial history meaning that the degree of exchange between sediments and pore fluids during the early postburial phase holds the key to determining the palaeotemperature significance of diagenetic alteration of benthic foraminifera postburial sedimentation rate and lithology are likely to be important determinants of the paleoceanographic significance of this sediment pore fluid interaction here we report an investigation of the impact of extreme change in sedimentation rate a prolonged and widespread upper cretaceous hiatus in the north atlantic ocean on the preservation and 18o of benthic foraminifera of middle cretaceous age nannofossil zone nc10 uppermost albian lowermost cenomanian 99 ma ago from multiple drill sites at sites where this hiatus immediately overlies nc10 benthic foraminifera appear to display at least moderate preservation of the whole test however on closer inspection these tests are shown to be extremely poorly preserved internally and yield 18o values substantially higher than those from contemporaneous better preserved benthic foraminifera at sites without an immediately overlying hiatus these high 18o values are interpreted to indicate alteration close to the seafloor in cooler waters during the late cretaceous hiatus intersite differences in lithology modulate the diagenetic impact of this extreme change in sedimentation rate our results highlight the importance of thorough examination of benthic foraminiferal wall structures and lend support to the view that sedimentation rate and lithology are key factors controlling the paleoceanographic significance of diagenetic alteration of biogenic carbonates

the effect of geographic range and climate on extinction risk in the deep time amphibian fossil record abstract geographic range is of crucial importance concerning the extinction risk of species however our understanding of how the influence of this trait on extinction risk has varied through earth history and across different climate regimes is still rather unexplored this is especially true for taxa that are currently of strong interest in conservation biology displaying a strong mismatch between paleontological studies and modern efforts to quantify the extinction risk of threatened species we herein calculated a continuous measure for the connection of geographic range and extinction risk in the deep time amphibian fossil record furthermore we evaluated the impact of climate on this connection using two climate proxies derived from oxygen isotope data global relative temperature change and variations in the latitudinal temperature gradient we show that geographic ranges tended to be larger during times of comparatively small latitudinal temperature gradients moreover the strength of geographic range influencing extinction risk fluctuated temporally but remained positive at all times the variation in range size impact on extinction risk showed a strong connection with the latitudinal temperature gradient our findings indicate that geographic range persists as a factor influencing species extinction risk through all times however geographic range seemed less important during times of higher environmental variability reasons might be the restriction of species ranges due to environmental constraints causing ranges to become more similar and therefore lose relative importance in buffering for extinction risk while other factors gain in importance simultaneously similar ranges might be more prone to alteration by e g conservation biases related to sedimentary deposition and fossilization in relation to their real range size resulting in a smaller signal to noise ratio potentially affecting the correlation strength we show that trait extinction risk dynamics can vary in their intensity and that specifically the observed impact of geographic range on extinction risk can vary with climatic changes

modelling late oligocene c4 grasses and climate evidence suggests that c4 grasses adapted to conditions of low co2 high temperatures and water stressed environments expanded relatively quickly and in several geographically distinct regions during the late miocene approximately 9 7 ma using a variety of modelling tools we attempt to explain this expansion in terms of changes in global climate we use a fully coupled atmosphere ocean general circulation model aogcm hadcm3l to simulate global climate before and after the expansion the late oligocene 27 ma and pre industrial we then use the simulated climates to drive a process based global vegetation model lpj contrary to indications from palaeo data the vegetation model predicts a greater c4 distribution during the late oligocene than the pre industrial the principal reason for this is that the relatively high tropical temperatures which we predict for the late oligocene confer a competitive advantage on c4 grasses over c3 grasses which outweighs the disadvantage imposed by the higher co2 concentrations we find that this result is robust to prescription of different co2 levels in the late oligocene aogcm simulation and to the vegetation model used of the several possible explanations proposed for the model data discrepancy three seem most likely first that the vegetation models do not adequately represent certain processes under extreme climate conditions such as fire disturbance or key parameters related to the competition between c3 and c4 grasses second that there existed an evolutionary niche for c4 grasses prior to their expansion in the late miocene which for some reason was not filled third that we have not adequately modelled the late oligocene climate with the aogcm future research should concentrate on the collection and analysis of additional data for the assessment of palaeo tropical land temperatures and on further testing of the sensitivity of the aogcm results

lilliput effect in late maastrichtian planktic foraminifera response to environmental stress the lilliput effect marks morphologic and intraspecies size reductions in response to environmental stresses commonly associated with the aftermath of mass extinctions this study shows that the lilliput effect is a universal biotic response associated with greenhouse warming mesotrophic or restricted basins shallow marginal settings and volcanically active regions during the late maastrichtian sedimentary sequences analyzed from tunisia egypt texas argentina the south atlantic and indian ocean reveal that the biotic stress response appears uniform regardless of the cause varying only with the degree of biotic stress overall late maastrichtian environments span a continuum from optimum conditions to the catastrophic mass extinctions with a predictable set of biotic responses relative to the degree of stress induced by oxygen salinity temperature and nutrient variations as a result of climate and sea level changes and volcanism early stages of biotic stress result in diversity reduction and the elimination of large specialized species k strategists leading to morphologic size reduction via selective extinction disappearances and intraspecies dwarfing of survivors later stages of biotic stress result in the complete disappearance of k strategists intraspecies dwarfing of r strategists and dominance by low oxygen tolerant small heterohelicids at the extreme end of the biotic response are volcanically influenced environments which cause the same detrimental biotic effects as observed in the aftermath of the k t mass extinction including the disappearance of most species and blooms of the disaster opportunist guembelitria

the evolution of late cretaceous deep ocean circulation in the atlantic basins neodymium isotope evidence from south atlantic drill sites for tectonic controls 1 the south atlantic basins during the late cretaceous were characterized by overall expansion and the opening of deep water connections eventually permitting deep ocean circulation with the indian and north atlantic basins however the evolving pattern of deep ocean circulation through the late cretaceous particularly the timing of the connection between various basins is not well constrained here we present new neodymium isotope data from five sites in the south atlantic to reconstruct water mass chemistry and circulation patterns the new data combined with previously published data indicate deep water formation occurred in the high latitude south atlantic throughout the late cretaceous tectonic boundaries restricted the circulation of southern component water until the opening of the equatorial atlantic gateway and the subsidence of rio grande rise between 79 and 75 ma subsidence of these features permitted the northward flow of southern component water which then ventilated the deep north atlantic nd isotope data indicate that the south atlantic water column during the cenomanian to santonian was vertically stratified between intermediate and deep waters with increased mixing evident during the campanian and maastrichtian

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

testing the impact of diagenesis on the δ18o and δ13c of benthic foraminiferal calcite from a sediment burial depth transect in the equatorial pacific stable oxygen and carbon isotope 18o and 13c values measured in foraminiferal calcite are one of the primary tools used in paleoceanography diagenetic recrystallisation of foraminiferal calcite can act to reset primary isotopic values but its effects are typically poorly quantified here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial pacific ocean recovered during ocean drilling program odp leg 199 and integrated ocean drilling program iodp expedition 320 our selected sites form paleowater and burial depth transects with excellent stratigraphic control allowing us to confidently correlate our records we observe large inter site differences in the preservation state of benthic foraminiferal calcite implying very different recrystallisation histories but negligible inter site offsets in benthic 18o and 13c values we infer that diagenetic alteration of benthic foraminiferal calcite in sedimentary oozes must predominantly occur at shallow burial depths 100 m where offsets in both the temperature and isotopic composition of waters in which the foraminifera calcified and pore waters in which diagenesis occurs are small our results suggest that even extensive recrystallisation of benthic foraminiferal calcite results in minimal shifts from primary 18o and 13c values this finding supports the long held suspicion that diagenetic alteration of foraminiferal calcite is less problematic in benthic than in planktic foraminifera and that in deep sea sediments routinely employed for palaeoceanographic studies benthic foraminifera are robust recorders of stable isotope values in the fossil record

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

interspecies variation in stable isotopic signals of maastrichtian planktonic foraminifera we measured stable isotopic signals of the largest specimens of all abundant species of planktonic foraminifera in late maastrichtian samples from three atlantic mid latitude and high latitude sites each sample is marked by a relatively small interspecies range of 18o values 1 2 to 0 8 each also exhibits an interspecies range of 13c values that resembles those of modern assemblages at similar latitudes 2 8 to 0 9 with greater ranges at lower latitudes these results indicate that late cretaceous planktonic foraminifera inhabited water masses characterized by a relatively narrow range of temperatures but may have occupied an array of niches as ecologically diverse as that of modern taxa maastrichtian taxa exhibit more complex relationships between skeletal morphology and vertical and seasonal paleohabitat affinities than previous paleoecologic models have assumed for example keeled taxa were not limited to cold or deep habitats and serial taxa appear to have occupied both warm near surface niches and the coolest or most saline habitats the isotopic differences between species indicate that apparent variation in maastrichtian stable isotopic signals strongly depends on the taxa analyzed narrowly constrained size fractions of rugoglobigerina species may provide a good estimate of relative variation in isotopic equilibria of near surface summer paleoconditions at low and middle latitudes gublerina species laeviheterohelix species and planoglobulina multicamerata appear the likeliest candidates for consistently tracking relative variation in isotopic equilibria of the coldest or most saline paleohabitats of maastrichtian planktonic foraminifera these isotopic results suggest that upper water column thermal gradients may have been only 3 to 5 c in mid latitude and high latitude regions they also suggest that the western and central atlantic mid latitude summer seasurface may have been much cooler or saltier in the maastrichtian than it is today finally they corroborate previous estimates of 10 c surface water at southern high latitudes

the accuracy of mid pliocene δ 18 o based ice volume and sea level reconstructions abstract understanding the sensitivity of the polar ice caps to a modest global warming 2 3 c above preindustrial is of paramount importance if we are to accurately predict future sea level change knowledge that will inform both social and economic policy in the coming years however decades of study of the pliocene 2 6 5 3 ma an epoch in recent earth history characterized by atmospheric co2 levels similar to today have so far failed to provide definitive sea level and ice volume estimates for that time here we review the sources of uncertainty in the paired mg ca 18o methodology used to estimate past sea level ice volume and ocean temperature as well as discuss common assumptions that may bias our interpretation of ocean geochemical records including the lr04 benthic 18o stack a global compilation of 57 oxygen isotope records that forms the standard template of climate change history for the last 5 3 million years

high paleolatitude late cretaceous paleotemperatures new data from james ross island antarctica oxygen isotope analysis of well preserved macrofossils from the santonian campanian of james ross island and the maastrichtian of vega island antarctica indicates that cool high paleolatitude temperatures prevailed during the late cretaceous and suggests that cooling occurred between the santonian campanian and the maastrichtian although more than 50 of the material showed diagenetic alteration 52 unaltered aragonite and calcite samples were analyzed mean delta sup 18 o and calculated paleotemperature values were minus 0 23 per thousand and 13 6 c respectively for the santonian campanian and 0 66 per thousand and 11 7 c respectively for the masstrichtian in conjunction with recent late cretaceous paleoclimatic data from high northern paleolatitudes these data indicate the presence of cool polar regions with broad climatic zonation during the late cretaceous this may have partly controlled faunal distributions

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

record of albian to early cenomanian environmental perturbation in the eastern sub equatorial pacific the present paper documents and discusses a new albian early cenomanian carbon isotope 13ccarb and 13corg curve from the subequatorial eastern pacific in peru chemostratigraphic evidences for the expression of the oae1b set and for oae1c and oae1d are presented this dataset is relevant inasmuch as previous work is strongly biased towards study sites in north america western interior basin in europe tethys and the pacific realm a comparison of the carbon isotope stratigraphy obtained in peru with published sections from the central and western pacific the western atlantic and northern and western tethys reveals an overall good agreement supporting the global nature of the isotope patterns described here the 13c from peru record is constrained by biostratigraphic evidence and 87sr 86sr isotope stratigraphy using well preserved oyster shells furthermore we document the development of a heterozoan epeiric neritic mixed carbonate siliciclastic ramp in the western platform of peru and its corresponding sedimentary facies associations this dataset was used to elucidate the complex interplay of climatic changes nutrient supply and platform drowning leading to the following conclusions i an upper aptian lower albian major change from siliciclastic dominated to carbonate sedimentation coincided with the impact of the kilian level ii a lower albian incipient platform drowning linked to the impact of the paquier level iii a lower middle albian major demise of neritic carbonate production that coincides with the leenhardt level followed by middle albian condensed sedimentation that reports prominent negative values in 13ccarb prior to the onset of oae1c and iv finally renewed carbonate ramp production during the upper albian lower cenomanian the data shown here represent the foundation for future work documenting the mid cretaceous of peru and its implications for the palaeoceanography of the se subequatorial pacific

north atlantic warming during global cooling at the end of the cretaceous differences in regional responses to climate fluctuations are well documented on short time scales e g el nino southern oscillation but with the exception of latitudinal temperature gradients regional patterns are seldom considered in discussions of ancient greenhouse climates contrary to the expectation of global warming or global cooling implicit in most treatments of climate evolution over millions of years this paper shows that the north atlantic warmed by as much as 6 c 1 5 decrease in 18o values of planktic foraminifera during the maastrichtian global cooling interval we suggest that warming was the result of the importation of heat from the south atlantic decreasing north atlantic 18o values are also associated with increasing gradients in planktic 13c values suggesting increasing surface water stratification and a correlated strengthening of the north atlantic polar front if correct this conclusion predicts arctic cooling during the late maastrichtian beyond implications for the maastrichtian these data demonstrate that climate does not behave as if there is a simple global thermostat even on geologic time scales

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

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

application of the fujita ziegler paleoclimate model early permian and late cretaceous examples abstract the fujita ziegler model is a new semi quantitative technique for reconstructing atmospheric circulation and resulting rainfall patterns of the geological past using uniformitarian assumptions in this paper we evaluate the performance of the model when applied to geographic and climatic conditions that were significantly different from the recent a late cretaceous maastrichtian reconstruction permits a test of the performance of the technique during a time that apparently lacked polar ice caps and steep latitudinal temperature gradients an early permian sakmarian reconstruction is used to evaluate the performance of the technique when the equator to pole temperature gradient was steep more like today but all major land masses had merged to form one large supercontinent pangea for both the maastrichtian and sakmarian the model produced more detailed retrodictions of surface air pressure and precipitation continuity than previously published paleoclimate reconstructions the results compare favorably with the known distribution of climatically sensitive sediments such as coals evaporites and phosphorites although the model considers complex relationships among land and sea distribution air pressure surface winds ocean currents and specific precipitation mechanisms it is still relatively simple and easy to apply therefore it is an excellent learning tool for the student of paleoclimate and should be an important technique to complement other methods of paleoclimate reconstruction

some patterns of planktic foraminiferal assemblage turnover at the cretaceous tertiary boundary abstract three uppermost cretaceous through basal paleocene stratigraphic sequences are examined for planktic foraminiferal assemblage stability and temporal succession patterns these sequences are at mid latitude south atlantic dsdp site 528 then equatorial pacific dsdp site 577 and the tethyan shelf ben gurion section of the negev israel in order to better estimate biogeographic patterns and habitat preferences the results of these analyses are compared to previous cretaceous biogeographic studies and to previous analyses of cretaceous tertiary k t boundary shelf and epicontinental sections results indicate that immediately following the k t boundary the examined epicontinental and open ocean sites were exploited primarily by previously epicontinental planktic foraminiferal assemblages this pattern of k t boundary assemblage dominance suggests the geologically instantaneous break down of late cretaceous epicontinental and open ocean biogeographic provincialization this shift in open ocean foraminiferal assemblages is not consistent with models of non selective k t boundary extinctions but is consistent with models of extinction resistence and offshore expansion of near shore taxa the re establishment of stable biogeographic differences between open ocean and epicontinental planktic foraminiferal assemblages occurs by the basal parvularugoglobigerina eugubina zone at open ocean sites 528 and 577 and the outer shelf ben gurion section po and p eugubina zone faunal records are marked by a pronounced alternation between paleocene biserial and non biserial dominated assemblages this alternation appears strongly damped at shelf and epicontinental sections previously examined the first appearance and peak magnitude of abundant earliest paleocene trochospiral forms parvularugoglobigerina eoglobigerina morozovella globoconusa also vary from site to site and may depend closely on levels of primary carbonate productivity

maastrichtian foraminiferal and paleoceanographic changes on milankovitch timescales milankovitch scale alternations in maastrichtian hemipelagic strata from ocean drilling program hole 1050c blake nose provide a natural experiment of paleoceanography and foraminiferal paleoecology in a tropical subtropical greenhouse ocean cycles are 30 50 cm thick and thought to reflect the 21 kyr precessional cycle high planktic 18o values are correlated with high planktic but low benthic 13c values indicating that cooler and or more saline surface waters were associated with higher productivity high productivity intervals are also characterized by high ca concentrations enrichment in feldspar and kaolinite and high relative abundance of heterohelix spp globigerinelloides spp and laeviheterohelix glabrans conversely low productivity intervals have low planktic 18o values high fe and ti concentrations enrichment in quartz illite and chlorite and relative increases in globotruncana spp and pseudoguembelina spp potential forcing mechanisms for observed covariation include cyclic variation in water column stratification variation in continental nutrient fluxes and changes in the intensity of upwelling

low latitude vegetation and climate dynamics at the paleocene eocene transition a study based on multiple proxies from the jathang section in northeastern india abstract we present a multi proxy study of an upper paleocene lower eocene succession from the paleo equatorial region the study is carried out on a coal bearing shallow marine succession exposed at jathang east khasi hills meghalaya northeastern india the succession was deposited in a low energy coastal marsh bay complex dinoflagellate cyst biostratigraphy yields a late paleocene to early eocene age for the section the deposits of the lower part of the succession represent a transgressive systems tract tst defined by seven parasequences each starting with bay sediments deposited during transgression followed by a shallowing upward bay fill marsh deposit in the vertical succession each parasequence acquires an increasingly marine character culminating in a maximum flooding surface at the paleocene eocene boundary it is followed by four shallowing upward parasequences deposited in a highstand systems tract hst enhanced chemical weathering and high terrestrial supply are testified by raised sio2 and al2o3 contents and high percentages of terrestrial palynomorphs the pollen flora recovered from the jathang section was used for quantitative paleoclimate and vegetation reconstructions the coexistence approach was applied based on nearest living relatives nlrs of sixty fossil species recorded at different stratigraphic levels seven climate variables were determined for the fossil assemblages and as a measure of the seasonality of climate the number of dry months was estimated our study shows that during the paleocene there existed warm seasonally dry tropical climate conditions with mean annual temperature at ca 24 26 c and mean annual precipitation at ca 700 1800 mm and with a dry season of 5 6 months particularly warm and wet perhumid climate conditions with 26 27 c and 2200 3200 mm mean annual precipitation with a dry period of 2 3 months were reconstructed for the latest paleocene earliest eocene interval the study shows a distinct vegetational turnover from palm dominated seasonally dry tropical forest during the paleocene to highly diversified dicotyledonous megathermal rainforest during the latest paleocene early eocene the present study demonstrates that the reduced duration of the dry period during the latest paleocene earliest eocene due to a more active hydrological cycle played a major role in determining the climate and shaping the vegetation cover in the paleo equatorial region there is evidence from our data that seasonality of rainfall is the determining factor for the tropical forest vegetation pattern of the equatorial region rather than mean annual rainfall condition as the main trigger for the observed step wise changes of the hydrology along the studied succession the fast northward movement of the indian plate is inferred