eolian deposition in the northeast pacific ocean cenozoic history of atmospheric circulation the mass accumulation rate and grain size distribution of the total eolian component of north pacific pelagic clays have been used to evaluate changes in eolian sedimentation and in the intensity of atmospheric circulation that have occurred during the past 70 m y eolian deposition was relatively low approximately 12 mg cm2 1 000 yr in the late cretaceous and paleocene reflecting an increasingly humid environment a peak in accumulation rates across the paleocene eocene boundary may be the result of episodic volcanism in mexico a sharp decrease in grain size across the paleocene eocene boundary is not readily interpreted fine eolian grain size and the low accumulation rates averaging 8 mg cm2 1 000 yr in the eocene and early oligocene are in agreement with low early tertiary thermal gradients and less vigorous atmospheric circulation large increases in grain size between 37 and 30 m y ago 20 and 10 m y ago and 5 m y ago to the present suggest that atmospheric circulation intensified by a factor of 1 5 1 8 and 1 4 respectively at these times eolian accumulation rates increased from 8 mg cm2 1 000 yr at the eocene oligocene boundary to approximately 25 mg cm2 1 000 yr at the end of the miocene with significant changes at 25 and 13 m y ago increased rates about 25 m y ago probably reflect movement of the core site into the influence of the westerlies and the increase 13 m y ago appears to be a response to steepening thermal gradients and intensifying atmospheric circulation resulting from major expansion of antarctic ice in the mid miocene along with a general increase in global aridity in the late cenozoic an order of magnitude increase in eolian accumulation rates 25 to 226 mg cm2 1 000 yr in pliocene pleistocene time coincides with the onset of northern hemisphere glaciation and consequent climatic deterioration the large increase in accumulation rates in pliocene pleistocene time coincides with a relatively smal increase in the intensity of atmospheric circulation compared to that in oligocene and miocene time suggesting that the increased deposition rates were the result of an increase in global aridity in glacial times rather than a further increase in the vigor of the global wind systems

abyssal circulation and benthic foraminiferal changes near the paleocene eocene boundary a major change in cenozoic deep sea benthic foraminifera occurred in the atlantic indian and pacific oceans near the paleocene eocene boundary benthic foraminiferal abundance changes began at about 61 5 ma at pacific deep sea drilling project dsdp site 577 a major extinction event followed at 58 57 ma between zones p6a and p6b and a series of first appearances continued until circa 55 5 ma zone p6c these faunal changes occurred during a 6 c warming of pacific bottom water and may indicate that the primary cause was changing temperature other potential causes of the faunal turnover include global changes in surface ocean productivity and changing bottom water source regions comparison of benthic and planktonic 13c records requires no change in the ratio of oceanic phosphorous to carbon during the late paleocene to early eocene which weakens the case for but does not disprove a change in surface ocean productivity at this time interbasinal comparisons of benthic foraminiferal 13c records document that water with high 13c values filled the cape basin during the late paleocene and possibly the early eocene circa 61 57 ma but apparently did not extend into the western basins of the atlantic this pattern suggests a supply of antarctic source water for the cape basin and possible tectonic isolation of the western atlantic basins during at least part of the late paleocene carbon isotope comparisons show that bottom water supply to the cape basin was reduced in the early eocene eolian grain size data suggest that a decrease in zonal wind intensity occurred at the end of the paleocene these late paleocene climatic changes bottom water warming and decreased wind intensity correspond with evidence for an important global tectonic reorganization and extensive subaerial volcanism which may have contributed to climatic warming through increased supply of co2

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

flexural constraints on the denudation of assymetric mountain belts the regional excavation of metamorphic rocks from mid and lower crustal levels is the consequence of erosion driven denudation of mountain belts that are in permanent isostatic equilibrium if the erosion process occurs at different rates in different parts of a topographically asymmetric mountain belt then the flexural properties of the lithosphere need to be considered in order to describe the features of the isostatic rebound such a situation is given in plateaulike mountain ranges which are likely to erode only at their steeply sloping edges whereas erosion on top stagnates this paper investigates the flexural isostatic response of a plate that is unloaded due to the continuous retreat of an erosional escarpment the isostatic response is tested for two limiting model cases 1 for a plate with a broken edge and 2 for a continuous plate with variable flexural rigidity it is shown that for both cases the rate of topography development on the exposed plate is not linear with the retreatrate of the escarpment this feature is utilized to predict the nature of the subsequent erosion of the newly formed topography and ultimately of the denudation of the plate geological limitations of the theoretical model and its relevance to plateaulike topographies in southern africa and the eastern highlands of australia are then discussed in these areas the origin of the apparently cyclic rebound forces creating stairlike topography at their continental margins and the old age of their present surface topography has previously been unexplained within the presented model these features can be explained satisfactorily two important conclusions may be drawn 1 the distance of flexural swells from great escarpments and the origin of subsequent stair like topographies may be explained by simple flexural considerations 2 the flexural rebound forces uplifting a plate exposed by a retreating escarpment are cyclic excavation times of metamorphic rocks under such mountain belts may therefore be prolonged not only by the nature of erosion of their initial topography but also by the nature of the subsequent isostatic rebound and ultimately their denudation history

cenozoic ice volume history development of a composite oxygen isotope record to view cenozoic ice volume and ocean temperature history a composite 18 o time series was constructed for tropical shallow dwelling planktonic foraminifers and for deep water benthic foraminifers we conclude that cenozoic benthic 18 o primarily reflect considerable deep ocean temperature variation and that tropical planktonic 18 o afford the best record of cenozoic ice volume the planktonic composite indicates the presence of a significant ice budget for the past 40 m y the difference between the benthic and planktonic 18 o composites suggests that low latitude production of warm saline bottom water dominated tertiary thermohaline circulation

sedimentary trace element constraints on the role of north atlantic igneous province volcanism in late paleocene early eocene environmental change abstract a growing body of geologic evidence suggests that emplacement of the north atlantic igneous province naip played a major role in global warming during the early paleogene as well as in the transient paleocene eocene thermal maximum petm event a 5 million year record of major and trace element abundances spanning 56 to 51 ma at deep sea drilling project sites 401 and 549 confirms that the majority of naip volcanism occurred as subaerial flows thus the trace element records provide constraints on the nature and scope of the environmental impact of the naip during the late paleocene early eocene interval subaerial volcanism would have injected mantle co2 directly into the atmosphere resulting in a more immediate increase in atmospheric greenhouse gas abundances than co2 input through submarine volcanism the lack of significant hydrothermalism contradicts recently proposed mechanisms for thermally destabilizing methane hydrate reservoirs during the petm any connection between naip volcanism and petm warming had to occur through the atmosphere

climate and bioproductivity control on carbonate turbidite sedimentation paleocene to earliest eocene gulf of biscay zumaia spain abstract the paleocene to lowermost eocene zumaia series situated along the basque coast northern spain consists of pelagic limestones and marlstones with interbedded mixed calcarenite turbidites we have compared the composition and frequency of turbidite beds in time as well as the clay mineral and bulk rock carbon isotope composition of the pelagic beds to discern the factors controlling turbidite deposition the pelagic beds are coccolithic mudstones with mainly planktic foraminifera the sources of detrital material to turbidites were the carbonate producing shelves bearing foramol associations around the evolving bay of biscay and to a minor extent the incipient pyrenean chain for siliciclastic components we have found close relationships between variations of turbidite facies and depositional rates with clay mineral assemblages and carbon isotopes in the pelagic beds the latter are in line with global trends it appears that in the early bay of biscay climate and nutrient availability controlled turbidite sedimentation the bulk rock late paleocene np 5 np 9 positive carbon isotope excursion coincides with a period of relatively cool and dry climate characterized by the highest frequency of turbidity flow we propose that during this period globally enhanced latitudinal temperature gradients and strong thermohaline ocean circulation increased bioproductivity in surface waters by upwelling and or by wind driven ekman pumping in contrast warm perennially wet periods such as the early paleocene np 1 np 4 and the paleocene eocene transition upper np 9 np 10 are characterized by low frequency of turbidity flow in the basin this may have been caused by sluggish thermohaline circulation and low carbonate productivity during this time period

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

a significant correlation between fluctuations in seafloor spreading rates and evolutionary pulsations this report presents the results of a detailed correlation analysis which reveals a remarkable correspondence between variations in seafloor spreading rates and marine taxonomic diversity the implications of this analysis are that the evolution of some biota was influenced by tectonic processes operative in the ocean basins such a conclusion suggests the need to seek a terrestrial explanation for extinction crises an indirect link via tectonism rise axis hydrothermal activity and the carbon dioxide cycle may provide a partial explanation

magnetic polarity stratigraphy and biostratigraphy of paleocene and lower eocene continental deposits clark s fork basin wyoming paleomagnetic samples were collected at 273 sites within a 2012 m continental sedimentary sequence in the clark s fork basin near powell wyoming the lower 1158 m is in the polecat bench fm while the upper 854 m is within the willwood fm although significant secondary components of magnetization were present alternating field demagnetization to 300 oe peak field revealed the polarity of the primary component of the natural remanent magnetism a well defined polarity zonation is observed the polecat bench fm is dominantly of reversed polarity but does contain two normal polarity zones the willwood fm in this section is entirely of reversed polarity abundant tiffanian clarkforkian and wasatchian faunas indicate that the age range of the sediments is from late paleocene through early eocene these age constraints along with the characteristic polarity sequence allow the magnetic polarity sequence to be correlated with the magnetic polarity time scale the section correlates with the magnetic polari

paleoceanography of the eastern indian ocean from odp leg 121 drilling on broken ridge broken ridge in the eastern indian ocean is overlain by about 1 600 m of middle cretaceous to pleistocene tuffaceous and carbonate sediments that record the oceanographic history of southern hemisphere mid to high latitude regions prior to about 42 ma broken ridge formed the northern part of the broad kerguelen broken ridge plateau during the middle eocene this feature was split by the newly forming southeast indian ocean ridge since then broken ridge has drifted north from about 55 to 31 s the lower part of the sedimentary section is characterized by turonian to santonian tuffs that contain abundant glauconite and some carbonate the tuffs record a large but apparently local volcanic input that characterized the central part of broken ridge into the early tertiary maestrichtian shallow water several hundred to 1 000 m depth limestones and cherts accumulated at some of the highest rates ever documented from the open ocean 4 to 5 g cm 2 10 3 yr 1 a complete with all biostratigraphic zones cretaceous tertiary boundary section was recovered from site 752 the first 1 5 m y of the tertiary is characterized by an order of magnitude reduction in the flux of biogenic sediments indicating a period of sharply reduced biological productivity at 55 s following which the carbonate and silica sedimentation rates almost reach the previous high values of the latest cretaceous we recovered a complete section through the paleocene that contains all major fossil groups and is more than 300 m thick perhaps the best pelagic paleocene section encountered in ocean drilling about 42 ma broken ridge was uplifted 2 500 m in response to the intra plateau rifting event subsequent erosion and deposition has resulted in a prominent eocene angular unconformity atop the ridge an oligocene disconformity characterized by a widespread pebble layer probably represents the 30 ma sea level fall the neogene pelagic ooze on broken ridge has been winnowed and thus its grain size provides a direct physical record of the energy of the southern hemisphere drift current in the indian ocean for the past 30 m y

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

late pliocene onset of glaciation ice rafting and diatom stratigraphy of north pacific dsdp cores abstract the revised diatom biostratigraphy for the north pacific allows the timing of ice rafting as recorded in deep sea drilling project cores to be determined significant ice rafting began at the time of the matuyama gauss reversal boundary about 2 48 ma other bio and lithostratigraphic data from the pacific atlantic and arctic oceans and the black sea all indicate that northern hemispherical cooling and the accumulation of continental ice began at 2 4 2 5 ma we interpret all these data to indicate northern hemisphere ice cap formation at that time if so the closing of the isthmus of panama approximately 3 2 m y ago was not the immediate cause of the plio pleistocene glaciations

eocene reorganization of the pacific farallon spreading center north of the mendocino fracture zone during a 1984 sea beam and magnetics survey in the north pacific we collected data in the area north of the mendocino fracture zone where a change in the direction of seafloor spreading occurred between magnetic anomalies 24 and 21 and also conducted detailed surveys of the bends in the surveyor and mendocino fracture zones associated with this change in plate motion we have analyzed these data combined with all available magnetics and bathymetric data from previous cruises to determine whether the ridge reorientation and reorganization occurred by way of rift propagation or rift rotation through differential asymmetric spreading the reorganization began just after anomaly 24 to the north of the surveyor fracture zone but did not begin between the mendocino and surveyor fracture zones until the time of anomaly 22 a 2 5 m y delay produced by the old mendocino transform trend constraining the farallon plate lithosphere between the mendocino and surveyor transforms to move in the old spreading direction until the fracturing through of a new mendocino transform fault in the new orientation most of the reorientation of spreading rift segments occurs within 2 3 m y the entire reorganization requires about 7 m y we find direct evidence for seven propagation episodes accounting for the primary reorientation of 75 of the length of the ridge system and nowhere is the data more consistent with rift rotation than with rift propagation as the principal means of reorientation we conclude that the primary mechanism by which the reorganization occurred was rift propagation assuming that rift propagation can account for all of the ridge reorganization we present forward models of magnetic anomaly profiles which succeed in fitting the data well we then present a model for the tectonic evolution of the reorganization which fits the data well using 11 episodes of both northward and southward propagation

higher temperatures and lower oceanic pco2 a climate enigma at the end of the paleocene epoch one of the largest and most abrupt climatic warming events documented in the geologic record occurred at the end of the paleocene epoch oceanic deep waters warmed to 10 c and high latitude surface waters warmed from 10 c to 20 c within several thousand years this coincided with weakened atmospheric circulation and the extinction of 50 of deep sea benthic foraminiferal species it has been suggested that this warm excursion was forced by higher atmospheric pco2 and greenhouse effects caused by a pulse of hydrothermal activity and or volcanism stable isotopic evidence is presented from two widely separated locations that suggest this warming was associated with a drop in oceanic pco2 rather than an increase oceanic pco2 change across this event was estimated using a model of 13c fractionation in photosynthate organic carbon versus co2aq with solubility constants for co2 and stable isotopic paleotemperature estimates to derive a well preserved record for surface ocean 13c change the organic carbon bound within the calcite lattice of well preserved planktonic foraminifera was extracted for isotopic analysis with allowance for uncertainty in the isotopic differences between phytoplankton and foraminiferal organic matter the initial results indicate a drop in surface ocean pco2 at high and low latitudes from 600 700 parts per million ppm to 200 ppm lower pco2 persisted for at least 10 000 years the duration of the pco2 excursion was long enough for the ocean and atmosphere to have reached a new steady state condition there is no evidence of increased organic carbon burial in the deep sea during this period two alternative explanations are presented to account for such a rapid drop in oceanic pco2 one involves reduced upwelling induced by diminished wind stress as atmospheric circulation weakened in response to climate warming this would have reduced the rate of metabolic co2 recycling into the surface ocean it will be necessary to obtain data from regions outside potential upwelling zones in order to evaluate this the second involves a readjustment of carbonate equilibria in the ocean to higher co3 in the surface ocean particularly at high latitudes where surface waters warmed to approximately 20 c such a shift in carbonate equilibria would have lowered the ocean s capacity to take in co2 if the initial results presented here do accurately reflect a change in the global ocean co2aq the paleocene eocene boundary event may provide clues about the ocean s physical and biological response to rapid large scale perturbations in atmospheric pco2 and to global warming

variations in the strontium isotope composition of seawater during the paleocene and early eocene from odp leg 208 walvis ridge we refined the strontium isotope seawater curve for the paleocene and early eocene by analysis of samples recovered from the walvis ridge during ocean drilling project odp leg 208 the highest sr 87 sr 86 values occurred in the earliest paleocene at similar to 65 ma and generally decreased throughout the paleocene reaching minimum values between 53 and 51 ma in the early eocene before beginning to increase again at similar to 50 ma a plausible explanation for the sr 87 sr 86 decrease between 65 and 51 ma is increased rates of hydrothermal activity and or the eruption and weathering of large igneous provinces e g deccan traps and north atlantic strontium isotope variations closely parallel sea level and benthic delta o 18 changes during the late paleocene and early eocene supporting previous studies linking tectonic reorganization and increased volcanism to high sea level high co2 and warm global temperatures

chronology of the wasatchian land mammal age early eocene magnetostratigraphic results from the mccullough peaks section northern bighorn basin wyoming a discussion netic polarity time scale and estimated the time durations of the mammal zones the purpose of this discussion is to show that their placement of the paleocene eocene boundary at the clarkforkian wasatchian boundary the base of mammal zone wa0 as in many previous vertebrate paleontologic studies is significantly older than the paleocene eocene boundary originally defined in northwest europe and generally used in marine biostratigraphy failure to recognize this causes miscorrelations between terrestrial and marine records e g the significant climatic biotic and isotopic events near the paleocene eocene boundary would appear to be strongly diachronous between terrestrial and marine records data avail

late cretaceous and paleogene tectonic evolution of the north pacific ocean the late cretaceous history of the northern pacific ocean has not been adequately deciphered largely because a major plate reorganization occurred during the cretaceous magnetic quiet interval using primary data to reconstruct plate motions from fracture zone trends and late cretaceous seafloor spreading magnetic anomalies allows formulation of a reasonable sequence of events that accounts for all the geologic features of that region especially the emperor and chinook troughs the primary event in our reconstruction is the subduction of the old northwest pacific triple junction new relative plate motions imposed by formation of convergent boundaries along both the northern pacific and farallon plates caused the farallon plate to crack this subdivision occurred 82 m y ago and resulted in the formation of the kula and chinook plates the chinook plate was bounded on the north by the chinook kula ridge the western arm of the great magnetic bight on the west by the southern emperor trough a slowly spreading rift valley on the south by the mendocino transform and on the east by the chinook farallon ridge the northern emperor trough formed the initial western boundary of the kula plate from 82 m y ago to 50 m y ago this configuration was stable the chinook plate expanded the chinook kula ridge migrated north and the kula plate was subducted with the subduction of this ridge the chinook plate adhered to the pacific plate and the pacific farallon ridge became the north south trending feature reflected by anomalies 22 and younger this reconstruction obviates the awkward late cretaceous shifting of triple junctions found in other proposed histories and provides reasonable explanations for the several structural features of the region to achieve closure of vector triangles representing the relative late cretaceous plate motions some extension must occur presumably across the eastern mendocino fracture zone between the northern and southern portions of the farallon plate these two plates apparently were independent units between 105 and 50 m y ago the initiation and cessation of rapid north farallon north american convergence 82 and 50 m y ago may have determined the nature and duration of the laramide orogeny

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

stable isotope stratigraphy and paleoclimatology of the paleogene bighorn basin wyoming usa abstract climatic warming from the late paleocene into the early eocene had profound effects on atmospheric and marine circulation marine thermal gradients and benthic biota in addition marine carbon isotope values decreased substantially in both surface and deep waters because carbon is rapidly exchanged between reservoirs at the earth s surface such as marine surface water the atmosphere land plants and materials that obtain carbon from plants e g soil minerals and herbivores carbon isotope fluctuations provide time lines linking the marine and continental records we analyzed the carbon isotope composition of paleosol carbonates and mammalian tooth enamel from stratigraphic sections in northwestern wyoming carbon isotope correlation demonstrates that a short interval of extreme high latitude warming coincided precisely with the first appearance of several important modern mammalian orders in addition oxygen isotope analyses of fossils and paleosol carbonates provide information about climatic conditions on land in the paleogene we reconstructed the oxygen isotope composition of local meteoric water using biogenic minerals paleocene eocene meteoric water was significantly 18 o depleted indicating substantial loss of water vapor during its transport to the region soil temperature was calculated as a proxy for mean annual temperature assuming oxygen isotope equilibrium between soil carbonate and meteoric water calculated temperatures were plausible 10 25 c but highly variable prohibiting high resolution analysis of local temperature variations in response to global climatic warming

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

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

stratigraphic and climatic implications of clay mineral changes around the paleocene eocene boundary of the northeastern us margin abstract kaolinite usually is present in relatively small amounts in most upper paleocene and lower eocene neritic deposits of the northern us atlantic coastal plain however there is a short period less than 200 000 k y in the latest paleocene upper part of calcareous nannoplankton zone np 9 when kaolinite dominated clay mineral suites replaced the usual illite smectite dominated suites during this time of global biotic and lithologic changes kaolinite increased from less than 5 of the clay mineral suite to peak proportions of 50 60 of the suite and then returned to less than 5 in uppermost paleocene lowermost eocene strata this kaolinite pulse is present at numerous localities from southern virginia to new jersey these sites represent both inner and middle neritic depositional environments and reflect input from several river drainage systems thus it is inferred that kaolinite rich source areas were widespread in the northeastern us during the latest paleocene erosion of these source areas contributed the kaolinite that was transported and widely dispersed into shelf environments of the salisbury embayment the kaolinite increase which occurred during a time of relatively high sea level probably is the result of intensified weathering due to increased temperature and precipitation the southern extent of the kaolinite pulse is uncertain in that uppermost paleocene beds have not been identified in the southern atlantic coastal plain the late paleocene kaolinite pulse that consists of an increase to peak kaolinite levels followed by a decrease can be used for detailed correlation between more upbasin and more downbasin sections in the salisbury embayment correlations show that more upbasin paleocene eocene boundary sections are erosionally truncated they have varying portions of the kaolinite increase and if present at all discontinuous portions of the subsequent kaolinite decrease as these truncated sections are disconformably overlain by lower eocene strata rapid erosional removal of large parts of the most kaolinite rich p e boundary clay deposits occurred by early eocene time erosion of the kaolinite rich p e boundary beds was enhanced during times of sea level fall when kaolinite rich sediments were redeposited to produce kaolinite spikes in basal beds of lower and middle eocene sequences that have little or no kaolinite elsewhere in the sequence in contrast more downbasin sites document only the upper decreasing part of the kaolinite pulse the absence of strata documenting the earlier kaolinite increase is attributed to slow sedimentation condensed interval as a result of a significant sea level rise that ponded most sediments in shallower waters combined with the probable subsequent erosional removal of these thin downbasin deposits by oceanic currents

magnetic polarity stratigraphy and biostratigraphy of middle late paleocene continental deposits of south central montana exposures of the fort union formation on the divide between hunt creek and cub creek in the northern clark s fork basin carbon county montana were selected for magnetostratigraphic study of the transition between the torrejonian and tiffanian land mammal ages paleomagnetic samples were collected from 25 sites within a 160 m thick section of the fort union formation at that location rock magnetic analyses indicate that alternating field demagnetization to peak fields in the 10 to 40 mt interval successfully removed secondary components of natural remanent magnetism nrm characteristic nrm directions define three polarity zones a 50 m thick normal polarity zone bracketed by two reversed polarity zones the cub creek local faunule cc 2 to 3 or ti 1 occurs within the upper portion of the normal polarity zone cub creek local faunules cc 1 cc 3 and eagle quarry all ti 1 occur in the upper reversed polarity zone these data along with faunal and magnetostratigraphic data from the san

environmental impact of volcanic margin formation late rift stage uplift and subsequent massive transient volcanism during breakup of rifted volcanic continental margins constrain paleoenvironments by modifying basin geometry and the composition of the atmosphere hydrosphere and thus biosphere on regional and global scales the early tertiary north atlantic breakup history shows that lava emplacement was accompanied by regional ashfalls and that extrusive complexes influenced paleogene oceanic and continental margin circulation and sedimentation temporal correspondence with the terminal paleocene deep sea extinction event and the earliest eocene greenhouse suggests a global impact possibly by enhanced atmospheric co 2 levels leading to polar warming and thereby changing patterns of deep water formation in this context transient subaerial volcanism at continental margins should be considered with the much discussed continental flood basalt provinces and oceanic plateaus

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

calcareous nannofossil assemblages of the upper miocene to pliocene shimajiri group on okinawa jima ryukyu islands southwestern japan abstract we investigated the calcareous nannofossil biostratigraphy and paleoceanography of the shimajiri group in two exploratory wells depths 1243 and 1800 m drilled on southern okinawa jima ryukyu islands southwestern japan three late miocene to pliocene datum planes were identified the first occurrence of amaurolithus spp 7 42 ma the last occurrence of discoaster quinqueramus 5 59 ma and the first occurrence of ceratolithus rugosus 5 12 ma these datum planes were also identified in two other deep wells on southern okinawa jima nutrient levels reconstructed from the relative abundances of small reticulofenestra spp and the relative abundances of discoaster spp plus sphenolithus abies suggest that deposition of the shimajiri group

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

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

the mid cretaceous super plume carbon dioxide and global warming carbon dioxide releases associated with a mid cretaceous super plume and the emplacement of the ontong java plateau have been suggested as a principal cause of the mid cretaceous global warming the authors developed a carbonate silicate cycle model to quantify the possible climatic effects of these co sub 2 releases utilizing four different formulations for the rate of silicate rock weathering as a function of atmospheric co sub 2 they find that co sub 2 emissions resulting from super plume tectonics could have produced atmospheric co sub 2 levels from 3 7 to 14 7 times the modern pre industrial value of 285 ppm based on the temperature sensitivity to co sub 2 increases used in the weathering rate formulations this would cause a global warming of from 2 8 to 7 7c over today s global mean temperature altered continental positions and higher sea level may have been contributed about 4 8c to mid cretaceous warming thus the combined effects of paleogeographic changes and super plume related co sub 2 emissions could be in the range of 7 6 to 12 5c within the 6 to 14c range previously estimated for mid cretaceous warming co sub 2 releases from oceanic plateaus alone are unlikely to have been directly responsible for more than 20 of the mid cretaceous increase in atmospheric co sub 2

two cretaceous volcanic episodes in the western pacific ocean stratigraphic analyses of cores recovered by the deep sea drilling project from the western pacific ocean confirm that cretaceous volcanic activity in that region was common and that two separate major episodes of activity can be distinguished the older episode aptian to cenomanian in age resulted in the formation of most of the oceanic plateaus in the western pacific in the younger santonian to maastrichtian episode several island and seamount chains formed especially those in the west central pacific that trend north northwest these volcanic events among the most extensive in the marine geologic record covered an area of at least 30 10 6 km 2 possibly the older episode was responsible for a cretaceous sea level high and concomitant epi continental transgression the younger episode of volcanism certainly covered an extensive area but its effect upon sea level may not have been as great as that of the older event

latest on the absolute age of the paleocene eocene thermal maximum petm new insights from exact stratigraphic position of key ash layers 19 and 17 abstract we constructed a precise early eocene orbital cyclostratigraphy for dsdp site 550 leg 80 goban spur north atlantic utilizing precession related cycles as represented in a high resolution x ray fluorescence based barium core log based on counting of those cycles we constrain the exact timing of two volcanic ash layers in site 550 which correlate to ashes 19 and 17 of the fur formation in denmark the ashes relative to the onset of the paleocene eocene thermal maximum petm are offset by 862 kyr and 672 kyr respectively when combined with published absolute ages for ash 17 the absolute age for the onset of the petm is consistent with astronomically calibrated ages using the current absolute age of 28 02 ma for the fish canyon tuff fct standard for calibrating the absolute age of ash 17 is consistent with tuning option 2 in the astronomically calibrated paleocene time scale of westerhold et al 2008 westerhold t rohl u raffi i fornaciari e monechi s reale v bowles j and evans h f 2008 astronomical calibration of the paleocene time palaeogeography palaeoclimatology palaeoecology v 257 p 377 403 using the recently recalibrated absolute age of 28 201 ma for the fct standard is consistent with tuning option 3 in the astronomically calibrated paleocene time scale the new results do not support the existence of any additional 405 kyr cycle in the early paleocene astronomically tuned time scale

effect of sea surface temperature configuration on model simulations of equable climate in the early eocene abstract a major challenge in paleoclimate modeling studies is reproducing the equable climate conditions recorded by proxy climate data this challenge has long been a focus in studies of eocene paleoclimate climate models consistently overestimate mean annual temperature range matr relative to proxy data interpretations and produce minimum temperatures that are far lower than proxy estimates we hypothesize that the lack of accurate sea surface temperatures ssts and a complete annual cycle definition is responsible for some of these model data discrepancies in eocene comparisons to test this hypothesis we developed two eocene annual cycle sst data sets as boundary conditions for model experiments and ran full annual cycle and abbreviated cycle perpetual cases when a perpetual case is replaced by a full annual cycle of sst values the january 0 c isotherm freezeline over north america shifts poleward by 5 latitude and matr is reduced by 5 c a change from one annual sst cycle to another equally plausible annual sst cycle results in a further latitudinal migration 5 of the freezeline and another 5 c change in continental interior matr overall the global mean annual and cold month mean temperatures show little sensitivity to the forcing while matr shows larger sensitivity in some continental regions our results suggest that the annual cycle of ssts and the actual sst values incorporated into experiments are major sources of the model data continental temperature discrepancies reported in past paleoclimate modeling studies we also find that the relatively coarse spatial resolution of the topography incorporated into paleoclimate models is an additional source of the discrepancy

magnetostratigraphic re calibration of the paleocene eocene boundary interval in holes 550 and 549 goban spur eastern north atlantic a magnetostratigraphic reinvestigation of the paleocene eocene boundary intervals in dsdp holes 550 and 549 goban spur has removed uncertainties associated with the previously published magnetostratigraphic information for these chronostratigraphically important sections in hole 550 levels assigned to nannoplankton zones np4 and 5 previously considered to be of normal polarity carry a reverse polarity characteristic magnetisation which is correlated with geomagnetic chron c26r unconformably overlying these levels is a thin interval of reversely magnetised sediment which records the latter part of chron c25r chron c25n is redefined and its lower upper boundaries are placed respectively at 425 08 and 422 12 mbsf in hole 550 chron c24r extends upwards62 4 m respectively the start and end of chron c24n 3n are placed at 359 69 and 349 41 mbsf in this hole within core 28 just above c24n 3n is a record of chron c24n 2n as well as interval of indeterminate polarity within c24n 2r the problematic issue of assigning numerical ages to the various events associated with the paleocene eocene transition in hole 550 is then discussed the remanence in hole 549 is difficult to interpret because magnetic inclinations in the interval previously assigned to chrons c25n and c24r are typically 20o compared with the60o expected for the paleogene sediments at this site acknowledging the complexities of this record we have constructed the magnetostratigraphy for this hole based on results from the present study and previous work h a townsend the paleomagnetism of sediments acquired from the goban spur on the deep sea drilling project leg 80 in p c de graciansky c w poag et al eds initial reports dsdp 80 1985 389 410 contrary to the previous study we are not able to fix the base of chron c25n it is located either in the lower part of core 18 where the core pieces are too small to be used reliably for paleomagnetic studies or in the gap between cores 18 and 19 the chron c25n 24r boundary is blurred 351 to 353 mbsf because of the shallow inclination problem chron c24n 3n which is characterised by inclinations of35o has its lower upper boundaries at318 and 307 62 mbsf respectively an apparent record of chron c24n 2n based on two samples is present between 305 53 and 304 65 mbsf 1998 elsevier science b v all rights reserved

the paleocene eocene thermal maximum as recorded by tethyan planktonic foraminifera in the forada section northern italy abstract the forada section in the venetian pre alps of northern italy represents an expanded record of the paleocene eocene thermal maximum petm at a depositional paleodepth of about 1 km 0 5 km high resolution planktonic foraminiferal analysis of this section in a time interval of approximately 1 3 myr across the paleocene eocene boundary reveals striking faunal changes that allow the identification of eight phases a h the late paleocene was represented by stable warm and oligotrophic surface water conditions phase a unstable environmental conditions start well before the onset of petm ca 150 kyr phase b and involved a change towards eutrophy as marked by the increase of subbotina and the concomitant decrease of morozovella this step is also characterized by enhanced fragmentation and dissolution the interval corresponding to the main body of the carbon isotope excursion cie is characterized by a marked increase of acarinina though with some differences in the species composition and relative abundance both in high and low latitudes particularly in the tethyan area forada is no exception to this pattern however at forada two prominent peaks in abundance of acarininids are recorded ca 30 kyr prior to the onset of the cie thus suggesting an increase in temperature heralding the onset of the petm phase c interestingly the lower peak in abundance of acarinina just precedes the 1 carbon isotope negative shift occurring below the onset of the main cie the basalmost eocene corresponding to the lower part of cie curve is represented by intense planktonic foraminiferal dissolution implying an extraordinary rise of the ccd this interval has an estimated duration of about 16 kyr phase d the dominance of acarininids in the lower part of the cie phase e f ca 14 and 22 5 kyr is interpreted as a consequence of the extreme warmth coupled with eutrophic conditions characterizing the forada depositional environment at that time these acarininids include at forada also the temporally constrained acarinina sibaiyaensis and a africana the morphological similarity between these peculiar species with the radially elongated chambered forms characterizing the cretaceous anoxic events suggests the hypothesis that depletion of oxygen in the upper water column might have been one of the factors causing their conspicuous occurrence at the petm the recovery in abundance of the specialized morozovellids and of other planktonic foraminiferal groups e g biserials globanomalinids igorinids planorotalids and pseudohastigerinids occurring in the middle part of the cie ca 30 kyr after the onset of the petm indicates an initial environmental recovery phase g a new stable state is definitely reached in the upper part of the forada section where the relative proportions of the main component of planktonic foraminiferal assemblages move towards values similar to those of the late paleocene conditions phase h however the perturbation during the petm produced significant changes in the ocean geochemistry that endured after the petm event as testified by the prominent high carbonate dissolution characterizing the marly levels and the large variability in relative abundance among different components of the planktonic foraminiferal assemblages these striking oscillations were not present in the latest paleocene

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

late tertiary history of hydrothermal deposition at the east pacific rise 19 s correlation to volcano tectonic events commonly it is assumed that the intensity of mid ocean ridge hydrothermal activity should correlate with spreading rate since high spreading rates are an indication of large subcrustal heat sources needed for intense hydrothermal activity we have tested this hypothesis by modeling the deposition of hydrothermal precipitates from cores from deep sea drilling project leg 92 taken on the west flank of the east pacific rise at 19 s although spreading rates at the east pacific rise and its predecessor the mendoza rise have varied by only 50 in the last 30 million years we found certain episodes at about 25 18 14 and 9 million years ago of hydrothermal manganese deposition as much as a factor of 20 higher than equivalent holocene accumulation these eposides do not correlate with spreading rate changes and instead seem to occur at times of major tectonic reorganizations we propose that ridge jumps and changes of ridge orientation may substantially increase hydrothermal activity by fracturing the ocean crust and providing seawater access to deep seated heat sources

early eocene palaeoceanography and palaeoclimatology of the eastern north atlantic stable isotope results for dsdp hole 550

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

a 9 million year long astrochronological record of the early middle eocene corroborated by seafloor spreading rates the early middle eocene ca 56 41 ma is recorded in the pelagic scaglia rossa and variegata formations of the umbria marche basin central italy geochemical and magnetostratigraphic alignment between the bottaccione section gubbio central italy and the smirra core cagli central italy allows us to generate a continuous and wellpreserved new record that combined with previously published data from the same area creates a continuous high resolution record from the paleocene eocene thermal maximum ca 56 ma to the lower part of chron c21n comparison with carbon isotope records from ocean drilling program sites 1258 and 1263 reveals a satisfactory match providing further evidence of the global significance of the long term trend and superposed perturbations captured by the 13c records the identification of astronomically forced geochemical cycles allows us to develop a 405 k y tuned age model thereby extending the astrochronology from ca 56 0 to ca 47 5 ma marine magnetic anomaly profiles from major oceanic basins characterized by high seafloor spreading rates were used to independently test the astronomical polarity time scale associated with our tuning as well as other polarity time scales our age model suggests the existence of periods of relatively constant seafloor spreading rates separated by rapid changes while the other time scales generate more gradual variations and also include large and short term deviations in spreading rates that occur simultaneously in different oceanic basins implying errors in polarity reversal ages the umbria marche age model further contributes to the closure of the middle eocene gap in the astronomical time scale

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

the impact of paleocene eocene boundary events on middle neritic benthic foraminiferal assemblages from egypt abstract a 25 m upper paleocene to lower eocene marly sequence exposed at gebel duwi quseir red sea coast of egypt provides a good opportunity for studying paleocene eocene p e boundary stratigraphy and events various bio eco and isotope stratigraphic correlations accurately delineate the position of the p e boundary i e the level of stable isotopic excursions and deep sea benthic extinctions in the middle part of this section within zones p5 and np9 in this paper the impact of p e boundary environmental perturbations on benthic foraminiferal communities of the shallow tethyan shelf is examined benthic foraminiferal assemblages from gebel duwi characterized by large frondicularia phosphatica and f nakkadyi in addition to a number of other neritic taxa but without any typical outer neritic bathyal taxa suggest middle neritic 75 100 m deposition throughout the studied interval and only minor relative sea level variations perhaps some 10 20 m across the boundary sea level appears to have been stable yet a distinct faunal turnover marks the p e boundary of this shallow site which in contrast to deep sea records is less abrupt being preceded by a gradual diversity decrease starting some four meters below the boundary moreover most exits are either local or just temporary and thus not true extinctions many lazarus taxa reappear at some point above the boundary while all but one of the disappearing taxa are known from other lower eocene neritic deposits in egypt in general benthic foraminiferal assemblages display low diversities and high dominance values notably anomalinoides aegyptiacus up to 74 suggesting high levels of environmental stress at the sea floor in combination with occasionally very high p b ratio s up to 98 p and generally laminated sediments the character of the benthic assemblage points to a strong influence of recurrent dysoxia and or anoxia we suggest that these resulted from surface eutrophication by intermittent coastal upwelling and reduced ventilation of the bottom environment although these conditions prevailed during most of the time interval studied they were most severe during the latest paleocene and early eocene when eutrophication intensified and the organic carbon flux to the sea floor increased enhanced atmospheric contrasts between the tethys seaway and the african continent resulting in intensified longshore tradewinds may have controlled these changes at the p e boundary the bottom environment became minimally ventilated perhaps due to reduced oxygen advection from deeper waters three meters above the boundary a succession of increasingly diverse assemblages indicate a gradual decrease of environmental stress and a return to more normal conditions although the organic carbon flux to the sea floor remained high

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

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

the climate of the eocene ocean oxygen isotope palaeotemperature estimates are presented for a number of deep sea sediment samples of eocene age covering a wide geographical area these are plotted on a geographical reconstruction for 50 ma the latitudinal temperature gradient at that time was less than half its present value surface temperature at high latitudes was about 10 c and at low latitudes little over 20 c it is concluded that ocean currents must have contributed a greater proportion of the poleward transport of heat than they do at present

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

sea floor hydrothermal activity links climate to tectonics the eocene carbon dioxide greenhouse two important findings of recent ocean floor drilling in the southeast pacific deep sea drilling project leg 92 are i that sea floor hydrothermal activity may fluctuate through time by as much as an order of magnitude and ii that episodes of greatest hydrothermal flux correspond to times when ridge transform plate boundaries are undergoing major changes in their configuration rather than to known times of increased spreading rate or volcanism evidence is presented here in support of the hypothesis that heightened hydrothermal activity induced by the eocene tectonic activity caused a global greenhouse effect which may represent the long sought after historical analog to the carbon dioxide induced global warming expected to occur by the middle of the next century

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

eocene equator to pole surface ocean temperatures a significant climate problem eocene surface ocean paleotemperature data which illustrate a reduced equator to pole temperature gradient cooler tropical sea surface temperatures and a relatively small global temperature warming 2 c present a significant climatic enigma if the reconstructions are correct such a temperature distribution can be achieved through greater poleward heat transport by the ocean however the mechanism for a greater oceanic role is uncertain in addition the results from climate models for conditions of a substantially greater poleward heat transport by the oceans indicate a weak atmospheric circulation and highly seasonal continental interior climates the weak atmospheric circulation is consistent with the record of continent derived eolian sediment recovered in deep sea cores however the eocene paleobotanical evidence from continental interiors indicates a very mild seasonality the lack of consistency between model results oceanic data and terrestrial data defines the nature of the problem of eocene climates the solution must involve reinterpretation of at least one major source of information