global mantle heterogeneity and its influence on teleseismic regional tomography abstract a new global p wave tomography model is determined using a flexible grid parameterization this new model better reveals the mantle structure under the polar regions than the previous tomographic models the subducting slabs are generally imaged clearly as high velocity high v zones the young slabs are still subducting in the upper mantle and the mantle transition zone mtz whereas the old and ancient slabs are either stagnant in the mtz or have subducted down to the lower mantle even reaching the core mantle boundary low velocity low v anomalies are generally revealed in the mantle under the hotspot regions it seems that a variety of mantle upwelling plumes exist some strong plumes are visible in the whole mantle under the long living hotspots such as those in south central pacific africa hawaii and iceland whereas weak plumes are visible in only some depth range under the minor hotspots under the intraplate volcanoes in east eurasia bering sea and west alaska significant low v anomalies are revealed in the upper mantle which may reflect hot and wet upwelling associated with corner flows in the big mantle wedge bmw above the stagnant pacific slab in the mtz and perhaps deep slab dehydration as well the subduction triggered magmatism in the bmw may be a new class of mantle plumes we also used the new global model to investigate the influence of whole mantle heterogeneity on the determination of upper mantle tomography under japan with a teleseismic inversion method the results show that the mantle heterogeneities outside the target volume of regional tomography can cause significant changes 0 2 0 4 s to the observed relative travel time residuals of a distant earthquake the pattern of regional tomography remains the same even after correcting for the whole mantle heterogeneity but there are some changes in the amplitude of velocity anomalies in the regional tomography hence it is necessary to correct for the mantle heterogeneities outside the target volume so as to obtain a better regional tomography

planktic foraminiferal turnover and δ13c isotopes across the paleocene eocene transition at caravaca and zumaya spain abstract biostratigraphic and faunal analysis of planktic foraminifera and benthic foraminiferal isotopes at zumaya and caravaca sections in spain indicate that zumaya has a continuous record with high sediment accumulation rates across the paleocene eocene transition whereas caravaca has a hiatus with the uppermost zone p4 zone p5 and the lower part of zone p6 missing both sections contain nearly continuous and expanded records of the global 13c excursion at zumaya and caravaca respectively the 13c excursion is associated with dark grey shale deposition in a dysaerobic benthic environment this 13c event is associated with a major planktic foraminiferal turnover marked by the gradual extinction and evolution of 33 and 18 of the species respectively a rapid change in the relative abundances of these taxa occurs at the 13c excursion coincident with the extinction of 50 of the small benthic foraminiferal taxa the entire water column was affected by this faunal turnover surface intermediate deep dwellers but in contrast to benthic foraminifera there was no net loss of habitats since species extinctions of planktic foraminifera were largely replaced by originations

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

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

heat flow on hot spot swells evidence for fluid flow 1 we examine variability observed in heat flow determinations collected on hot spot swells we find substantial scatter in heat flow at wavelengths of a few hundred kilometers and less at both hawaii and reunion where closely spaced data exist and large variability in the regional heat flow surveys at cape verde bermuda and crozet our preferred interpretation is that the observed variability is due to fluid flow the presence of fluid flow admits the possibility that some heat is lost through advection such that the mean observed heat flow is less than the actual mantle flux if so the full magnitude of sublithospheric thermal variations may not be observed this interpretation has important implications for understanding heat flow determinations made on hot spot swells and resulting geodynamic inferences we suggest fluid flow may be masking variations in sublithospheric heat flux making available surface heat flow values a poor discriminator between geodynamic models for hot spot swells future field programs methods of data analysis and models should be designed to help extract a low frequency mantle flux disguised by a high noise surface filter

thermal and mechanical properties of the cape verde rise the cape verde rise represents an extreme case of the process of oceanic midplate volcanism the regional depth and geoid anomalies relative to the plate model are the largest observed peaking at 2 4 km and 12m respectively the late tertiary volcanoes rest on mesozoic aged seafloor indicating that the lithosphere was about 130 m y old when loaded depth and geoid anomalies in the cape verde region are examined using both forward filtering and admittance techniques to determine the thermomechanical properties of the swell the effective elastic thickness for the plate supporting the volcanoes is 28 4 km and the compensation depth for the broad swell is 69 10 km these two results combined with heat flow observations from the rise are consistent with a model for reheating of the lithosphere beneath cape verde such that the average thermal gradient is increased by 35 while there is no doubt that the cape verde lithosphere has been reheated it is unlikely that the entire depth anomaly is explained by thermal anomalies confined to the lithosphere a linear programming inversion of the geophysical data places an upper bound of 1 7 km on the portion of the depth anomaly due to lithospheric reheating there are no permissible thermal models fitting all of the geophysical data that do not require either dynamic support from or elevated temperature within the asthenosphere

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

the influence of burial heating on the u th he system in apatite grand canyon case study article history thermochronological data can constrain the cooling paths of rocks exhumed through the uppermost 1 2 km of earth s crust and have thus been pivotal in illuminating topographic development over timescales 0 1 ma however in some cases different methods have led to conflicting conclusions about timing of valley scale exhumation here we investigate the case of western grand canyon usa where different thermochronological datasets have been interpreted to record very different timings of canyon incision 70 ma versus 5 ma we present a method to assess key assumptions in these constraints and demonstrate that burial heating conditions of basement rocks in the mesozoic can result in incomplete annealing of radiation damage in apatite in turn this has a dramatic effect on the temperature sensitivity of the apatite u th he system and its ability to record post burial exhumation the possibility of incomplete annealing resolves the apparent conflict in time temperature paths inferred over the last 70 ma although it requires temperatures during burial that are lower than predicted by apatite fission track data a refinement of parameters that prescribe the kinetics of damage annealing and related control on 4 he diffusivity in apatite would account for this discrepancy specifically if alpha recoil damage anneals at a lower rate than fission tracks at a given temperature these effects will be important for any application of the apatite u th he system in geologic settings that experienced prolonged residence 10 ma between 50 150 c the approaches developed here provide means to assess these effects

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

paleoceanography of the cretaceous tertiary boundary event inferences from stable isotopic and other data we report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction whole rock and benthic foraminifers caco3 and coarse fraction percentage determinations and trace element sr analyses on carbonate constituents across the cretaceous tertiary k t boundary in deep sea drilling project dsdp sites 47 2 356 384 and 577 and compare them with published results from k t boundary sections in other dsdp sites we used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study the 18o data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late maestrichtian followed by somewhat fluctuating temperatures in the early paleocene however there is no indication of either a significant warming or cooling at or following the k t boundary several sites do exhibit somewhat heavier 18o values by about 0 5 across the boundary which might suggest a 2 3 c cooling at most however we interpret these somewhat heavier 18o values as reflecting slightly better preservation of 18o of carbonate constitutents in relatively clay rich intervals e g lower diagentic potential characteristic of the k t boundary the 13c values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary the surface water and deepwater 13c values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest paleocene are consistent with a major decrease in productivity across the k t boundary the decrease in caco3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters the low productivity episode lasted at least 1 m y beyond the k t boundary crisis suggesting that hypothesized catastrophic events alone such as impact of an apollo object are not the only explanation for the observed long term decrease in productivity there is also an indication in the 13c curves from several sites that the surface water 13c decrease began in the latest maestrichtian suggesting that the decrease in productivity may have been independent of a hypothesized impact event

the late palaeocene early eocene and toarcian early jurassic carbon isotope excursions a comparison of their time scales associated environmental changes causes and consequences although the earth9s environment is constantly changing there have been a few unusual episodes over the last c 200 ma when change was extreme in terms of its rapidity severity long lasting consequences and unpredictability the geochemical and biotic records for two of these episodes the palaeocene eocene thermal maximum and the toarcian oceanic anoxic event early jurassic possess many significant similarities each event was associated with a major carbon isotope excursion significant levels of biotic extinctions severe global warming an enhanced hydrological cycle and evidence for widespread seawater anoxia both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations based on a detailed comparison the palaeocene eocene thermal maximum may have been an incipient oceanic anoxic event the geochemical and biotic changes during these two events are most readily explained by the abrupt large scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere indicating that ancient events such as these may usefully serve as analogues for present day environmental change

equatorial pacific deep sea benthic foraminifera faunal changes before the middle miocene polar cooling data on the composition of benthic foraminiferal faunas at deep sea drilling project site 575 in the eastern equatorial pacific ocean were combined with benthic and planktonic carbon and oxygen isotope records and caco 3 data changes in the composition of the benthic foraminiferal faunas at site 575 predated the middle miocene period of growth of the antarctic ice cap and cooling of the deep ocean waters by about 2 m y and thus were not caused by this cooling as has been proposed the benthic faunal changes may have been caused by increased variability in corrosivity of the bottom waters possibly resulting from enhanced productivity in the surface waters

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

structure of axisymmetric mantle plumes results of high resolution numerical calculations of axisymmetric thermal plumes in an infinite prandtl number fluid with thermally activated viscosity are used to infer the structure of axisymmetric subsolidus thermal plumes in the earth s lower mantle we calculate the velocity and temperature distribution for axisymmetric convection above a heated disk in an incompressible fluid cylinder 2400 km in height and 1200 km in diameter initially at a uniform temperature t the lower boundary representing the plume source region near the core mantle boundary is stress free and maintained at temperature tc t the upper boundary is permeable allowing the plume to escape the cylinder we determine the sensitivity of plume structure to viscosity variations c ranging from 102 to more than 104 and temperature differences t tc t in the range 400 850 k starting plumes consist of a large leading diapir and a trailing conduit connected to the thermal boundary layer above the heated surface the leading diapir expands during ascent to about 400 km diameter at 2200 km height in steady state the plume consists of a narrow high velocity conduit imbedded within a broader thermal halo the width of both these structures is proportional to height above the heated boundary and inversely proportional to t and the viscosity ratio heat transport in the plume is nearly independent of viscosity variations a simplified boundary layer model yields a heat transfer law nu ra where nu is the plume nusselt number and ra is the rayleigh number based on t and the radius of the heated circular region feeding the plume calculated steady state plume heat transports fit this law to within a few percent we present several calculations of plumes with heat transport in the range 100 400 gw similar to the advective heat transport by the hawaiian hotspot at the top of the lower mantle plumes with large viscosity variations have high velocity conduits 50 60 km in diameter and 125 km diameter thermal halos a centerline temperature anomaly of about 500 k and a centerline velocity of about 75 cm yr 1 plumes with weak viscosity variations are approximately twice as broad and have centerline temperature anomalies less than 160 k at the same height and much smaller velocity large viscosity variations and a minimum heat transport are both

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

paleocene eocene thermal maximum environmental change in the new jersey coastal plain benthic foraminiferal biotic events abstract the environmental impact of the paleocene eocene thermal maximum petm has been intensively studied in the new jersey coastal plain but the benthic foraminiferal response reflecting bottom water conditions has not been documented at high resolution we use benthic foraminiferal data across the paleocene eocene boundary in cores from wilson lake wl and bass river br to recognize 5 foraminiferal associations based on species clusters their varying abundances allow the identification of a stratigraphic succession of 8 distinct biofacies across the studied interval uppermost paleocene biofacies 1 corresponds to the glauconitic sands of the vincentown formation and contains rare small planktic foraminifera and a diverse benthic fauna sediments accumulated slowly in a sufficiently oxygenated outer neritic setting depth 100 110 m at wl 140 150 m at br under fairly oligotrophic conditions the embayment was storm dominated and influenced by strong currents inhibiting deposition of suspended fine particles e g planktic foraminifera clay and enhancing re suspension no significant pre petm environmental changes are detected in the benthic foraminiferal assemblages deposition of the fine grained silty clays of the marlboro clay started at the onset of the petm with transitional lithology present at wilson lake gavelinella beccariiformis common at deep shelfal to bathyal abyssal depths is the only taxon to become extinct at this level water depth increased during the petm to a maximum of 130 150 m at wl planktic foraminifera increased strongly in abundance while the benthic foraminiferal assemblage changed to a more opportunistic less diverse assemblage dominated by stress tolerant taxa tappanina selmensis pulsiphonina prima and anomalinoides acutus biofacies 2 increased riverine influence may have reduced vertical mixing initiating stratification of the water column and establishment of a continuously dysoxic mud belt benthic diversity then gradually increased indicating environmental recovery biofacies 3 and 4 40 95 kyr post petm onset riverine influence probably became more variable generating peak abundances of specialized taxa in a mud belt system with increased accumulation rates the latest petm biofacies 5 95 kyr post onset contains a poorly diverse bulimina callahani assemblage indicative of reoxygenated but still eutrophic bottom water conditions with renewed vertical mixing the lower eocene glauconitic sandy clays of the manasquan formation contain an outer neritic benthic fauna biofacies 6 8 depth 100 135 m at wl indicative of persistent high primary production with return of more vigorous currents higher abundances of buliminids may have been triggered by upwelling along frontal zones our environmental interpretations indicate relatively stable benthic foraminiferal ecosystems at persistently outer neritic water depths 100 150 m despite distinct temporary changes during the petm including eustatic sea level rise of up to 30 m and widespread establishment of dysoxic conditions

frequency dependence of the visibility and depths of mantle seismic discontinuities the visibility and apparent position of a seismic gradient zone depends on the seismic wave frequency at which it is observed which we illustrate by showing how the visibility and depth of the olivine phase transformation 410 km discontinuity change as temperature varies temperature variations change bottomside reflection coefficients by factors of 2 4 in the 0 5 1 0 hz frequency band which can explain spatial variability in short period p 410p observations and the small apparent variability in observed 410 km discontinuity depths discontinuity depths inferred from the time lags of these reflections are also frequency dependent leading to a frequency dependence of estimates of mantle lateral thermal variability based on discontinuity displacements the frequency dependent seismic clapeyron slopes for the olivine phase change we compute are 2 04 mpa k 1 at 0 2 hz and 2 12 mpa k 1 at 0 05 hz and differ significantly from thermodynamic slope for the mg2sio4 end member

the paleocene eocene transition in the antarctic indian ocean inference from planktic foraminifera isotopic depth stratification and relative abundance studies of planktic foraminifera at odp site 738 reveal three major faunal turnovers during the latest paleocene and early eocene reflecting the climatic and structural changes in the antarctic surface ocean faunal event 1 occurred near the paleocene eocene boundary and is characterized by a faunal turnover in deep dwellers decreased relative abundance in intermediate dwellers and increased relative abundance in surface dwellers this event marks a temporary elimination of the vertical structure in the surface ocean over a period of more than 63 000 years that is apparently associated with the sudden shutdown of the antarctic intermediate water production the appearance of morozovellids before this event suggests that polar warming is the cause for the shutdown in the production of this water mass at this time warm saline deep water may have formed at low latitudes faunal event 2 occurred near the ap5a ap5b subzonal boundary and is characterized by a faunal turnover in deep dwellers with no apparent change in surface and intermediate dwellers increased individual size wall thickness and relative abundance in deep dwelling chiloguembelinids suggests the formation of a deep oxygen minima in the antarctic oceans during the maximum polar warming possibly as a result of upwelling of nutrient rich deep water faunal event 3 occurred in subzone ap6 and is characterized by a faunal turnover in surface dwellers and a delayed diversification in deep dwellers this event marks the onset of antarctic cooling a drastic decrease in the 13c 18o values of the deep assemblage in zone ap7 suggests an intensified thermocline and reduced upwelling following the polar cooling

crustal structure of western hispaniola haiti from a teleseismic receiver function study haiti located at the northern caribbean plate boundary records a geological history of terrane accretion from cretaceous island arc formations to the eocene to recent oblique collision with the bahamas platform little is presently known about the underlying crustal structure of the island we analyze p waveforms arriving at 27 temporary broadband seismic stations deployed over a distance of 200 km across the major terrane boundaries in haiti to determine the crustal structure of western hispaniola we compute teleseismic receiver functions using the extended time multi taper method and determine crustal thickness and bulk composition vp vs using the h stacking method three distinctive and fault bounded crustal domains defined by their characteristic moho depth distributions and bulk crustal vp vs are imaged across haiti we relate these domains to three crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the caribbean plate and are presently being deformed in a localized fold and thrust belt in the northern domain made up of volcanic arc facies the crust has a thickness of 23 km and vp vs of 1 75 0 1 typical of average continental crust the crust in the southern domain is part of the caribbean large igneous province caribbean lip and is 22 km thick with vp vs of 1 80 0 03 consistent with plume related rocks of late cretaceous age significantly thicker the crust in central haiti has values of moho depths averaging 41 km and with vp vs of 1 80 0 05 we propose that the central domain is likely constructed of an island arc upper crust with fragments of dense material originating from mafic lavas or lip material we produce a crustal profile along a n s transect across haiti accounting for the surface geology shallow structural history and new seismological constraints provided by variations of crustal thickness and bulk composition

changes in composition of neogene benthic foraminiferal faunas in equatorial pacific and north atlantic thomas e 1986 changes in composition of neogene benthic foraminiferal faunas in equatorial pacific and north atlantic palaeogeogr palaeoclimatol palaeoecol 53 47 61 deep sea benthic foraminiferal faunas were studied from three dsdp sites in the equatorial pacific leg 85 depth about 4 5 kin and two dsdp sites in the north atlantic leg 94 depth 3 5 and 2 5 km for the interval between 25 and 0 ma the number of first appearances fa s and last appearances la s of taxa in the early to middle miocene was similar at all sites despite differences in location and depth specific events however were rarely coeval at several sites even within the pacific changes in faunal composition began earlier at about 18 ma in the equatorial pacific than in the north atlantic about 15 5 ma these changes affected between about 20 and 30 of the total fauna there is no simple globally valid correlation between the changes in composition of the benthic foraminiferal faunas and events in oxygen and carbon isotopic records the fa of cibicidoides wuellerstorfi however appears to be coeval with the increase in oxygen isotopic ratios in the early middle miocene

arctic late paleocene early eocene paleoenvironments with special emphasis on the paleocene eocene thermal maximum lomonosov ridge integrated ocean drilling program expedition 302 we reconstruct the latest paleocene and early eocene 57 50 ma environmental trends in the arctic ocean and focus on the paleocene eocene thermal maximum petm 55 ma using strata recovered from the lomonosov ridge by the integrated ocean drilling program expedition 302 the lomonosov ridge was still partially subaerial during the latest paleocene and earliest eocene and gradually subsided during the early eocene organic dinoflagellate cyst dinocyst assemblages point to brackish and productive surface waters throughout the latest paleocene and early eocene dinocyst assemblages are cosmopolitan during this time interval suggesting warm conditions which is corroborated by tex86 reconstructed temperatures of 15 18 c inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower eocene spectral analysis reveals that the cyclicity recorded in x ray fluorescence scanning fe data from close to eocene thermal maximum 2 53 ma presence confirmed by dinocyst stratigraphy is related to precession within the lower part of the petm proxy records indicate enhanced weathering runoff anoxia and productivity along with sea level rise on the basis of total organic carbon content and variations in sediment accumulation rates excess organic carbon burial in the arctic ocean appears to have contributed significantly to the sequestration of injected carbon during the petm

climate model and proxy data constraints on ocean warming across the paleocene eocene thermal maximum article constraining the greenhouse gas forcing climatic warming and estimates of climate sensitivity across ancient large transient warming events is a major challenge to the palaeoclimate research community here we provide a new compilation and synthesis of the available marine proxy temperature data across the largest of these hyperthermals the paleocene eocene thermal maximum petm this includes the application of consistent temperature calibrations to all data including the most recent set of calibrations for archaeal lipid derived palaeothermometry this compilation provides the basis for an informed discussion of the likely range of petm warming the biases present in the existing record and an initial assessment of the geographical pattern of petm ocean warming to aid interpretation of the geographic variability of the proxy derived estimates of petm warming we present a comparison of this data with the patterns of warming produced by high pco2 sim ulations of eocene climates using the hadley centre atmosphere ocean general circulation model aogcm hadcm3l on the basis of this comparison and taking into account the patterns of intermediate water warming we estimate that the global mean surface temperature anomaly for the petm is within the range of 4 to 5 c

two lips and two earth system crises the impact of the north atlantic igneous province and the siberian traps on the earth surface carbon cycle the links between the siberian traps and the end permian mass extinction and between the north atlantic igneous province naip and the paleocene eocene thermal maximum petm demonstrate a critical role for large igneous provinces lips in the disruption of the earth surface carbon cycle escc high precision ages for both volcanic provinces and the associated environmental crises show that in both cases the crisis was contemporaneous with the volcanism the naip comprises two phases the earlier phase 1 c 61 ma and the much more voluminous phase 2 c 56 ma linked to the opening of the ne atlantic the latter triggered the petm the largest cenozoic hyperthermal the siberian traps are significantly more voluminous than the naip and triggered the end permian mass extinction the masses of volcanic co 2 emitted from these provinces may have been much greater than previously suggested as substantial gas may come from intrusive bodies deep within the crust precursory warming due to the accumulation of volcanic co 2 in the atmosphere likely triggered the release of low 13 c methane hydrate although the masses of methane hydrate alone may have been insufficient to account for the observed temperature rises the organic c was likely strongly supplemented by magmatically derived carbon and thermogenic carbon released during emplacement of sills and dykes into c rich sedimentary units more data are required on the volcanic flux rates in order to refine the cause effect relationships between lips and the escc

stable isotopes in late middle eocene to oligocene foraminifera oxygen and carbon isotope ratios in eocene and oligocene planktonic and benthic foraminifera have been investigated from atlantic indian and pacific ocean locations the major changes in eocene oligocene benthic foraminiferal oxygen isotopes were enrichment of up to l in 18o associated with the middle late eocene boundary and the eocene oligocene boundary at locations which range from 1 to 4 km paleodepth although the synchronous eocene oligocene 18o enrichment began in the latest eocene most of the change occurred in the earliest oligocene the earliest oligocene enrichment in 18o is always larger in benthic foraminifera than in surface dwelling planktonic foraminifera a condition that indicates a combination of deep water cooling and increased ice volume planktonic foraminiferal 18o does not increase across the middle late eocene boundary at our one site with the most complete record deep sea drilling project site 363 walvis ridge this pattern suggests that benthic foraminiferal 18o increased 40 m y ago because of increased density of deep waters probably as a result of cooling although glaciation cannot be ruled out without more data stable isotope data are averaged for late eocene and earliest oligocene time intervals to evaluate paleoceanographic change average 18o of benthic foraminifera increased by 0 64 from the late eocene to the early oligocene 18o maximum whereas the average increase for planktonic foraminifera was 0 52 this similarity suggests that the eocene oligocene boundary 18o increase was caused primarily by increased continental glaciation coupled with deep sea cooling by as much as 2 c at some sites average 18o of surface dwelling planktonic foraminifera from 14 upper eocene and 17 lower oligocene locations when plotted versus paleo latitude reveals no change in the latitudinal 18o gradient the oligocene data are offset by 0 45 also believed to reflect increased continental glaciation at present there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from eocene to oligocene time using oxygen isotopes

foraminiferal turnover across the eocene oligocene transition at fuente caldera southern spain no cause effect relationship between meteorite impacts and extinctions we studied planktic and small benthic foraminifera from the fuente caldera section southern spain across the eocene oligocene transition benthic foraminifera indicate lower bathyal depths for the late eocene and earliest oligocene detailed highresolution sampling and biostratigraphical data allowed us to date precisely layers with evidence for meteorite impact ni rich spinel which occur in the lower part of the planktic foraminiferal globigerapsis index biozone and in the middle part of the small benthic foraminiferal cibicidoides truncanus bb4 biozone middle priabonian late eocene major turnovers of foraminifera occur at the eocene oligocene boundary only the impact did not occur at a time of planktic or benthic foraminiferal extinction events and the late eocene meteorite impacts did thus not cause extinction of foraminifera the most plausible cause of the eocene oligocene boundary extinctions is the significant cooling which generated glaciation in antarctica and eliminated most of the warm and surface dwelling foraminifera d 2005 elsevier b v all rights reserved

atlantic eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography reconstruction of atlantic ocean vertical and meridional water characteristics is based on combined synoptic fossil census data stable isotope records and measurements of individual planktonic foraminiferal species correlations between planktonic foraminiferal indices and specific water types and or chemical conditions are used to trace seven stages in the history of atlantic circulation during eocene climatic changes 1 warm equable probably saline productive ocean of the early eocene characterized by lowest meridional and vertical thermal gradients and the maximal extent of tropical surface water 2 early middle eocene expansion of subtropical waters and faunas accompanying the first climatic cooling and eutrophication of equatorial surface waters 3 maximal partitioning of water types faunas and bioprovinces in middle eocene zone p11 accompanying maximum planktonic foraminiferal diversity accelerated near surface and deepwater cooling and intensified upwelling 4 latest middle eocene zone p14 maximal planktonic foraminiferal evolutionary overturn during accelerated cooling deep and surface water ventilation and transformation of tropical surface water habitat with the expansion of temperate water types and faunas this accompanied the reduction of meridional heat transport in boundary currents 5 late eocene bottom water and middle latitude cooling broadening of meridional temperature gradients and expanded oxygen minimum but faunal homogenization following the decreased import of mediterranean water ourflow 6 weakening and or shoaling of the nutricline an oxygen minimum and the thermocline preceding a diminution of primary productivity at the eocene oligocene boundary and 7 earliest oligocene low productivty ocean marked by diminished vertical thermal contrasts and homogeneous foraminiferal faunas dominated by small sized individuals the increased areal extent of upwelling with the outcropping of cooler waters over large geographic regions provides an important climatic forcing mechanism in the latest middle and late eocene

very low shear wave velocity at the base of the mantle under the south pacific superswell abstract s wave velocity heterogeneity at the base of the mantle beneath the south pacific superswell has been examined using skks sks and s sdiff sks differential travel times the residuals of skks sks and s sdiff sks with respect to the preliminary reference earth model prem are compared to the residuals predicted using recently published three dimensional s wave velocity models we have obtained a three dimensional model that explains the s sdiff sks residuals well and applied this model to the correction of the skks sks residuals the corrected skks sks residuals beneath the south pacific superswell remain large and positive forward modeling reveals that these residuals can be accounted for by a 5 7 low velocity region with a lateral extent of about 500 km in the lowermost 200 km of the mantle although the magnitude of the velocity reduction and the thickness of the anomalous region trade off against one another and cannot be uniquely determined the existence of a very low s wave velocity region at the base of the mantle is a robust feature this feature lies close to the ultra low velocity zone ulvz identified by p velocity data beneath the southwestern pacific and is located just below a 2 3 low s velocity body in the lower mantle at depths of 2300 2700 km beneath the south pacific superswell

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

planktic foraminiferal turnover across the paleocene eocene transition at dsdp site 401 bay of biscay north atlantic abstract planktic foraminifera across the paleocene eocene transition at dsdp site 401 indicate that the benthic foraminiferal mass extinction occurred within subzone p 6a of berggren and miller 1988 or p5 of berggren et al 1995 and coincident with a sudden 2 0 excursion in 13c values the benthic foraminiferal extinction event bfee and 13c excursion was accompanied by a planktic foraminiferal turnover marked by an influx of warm water species morozovella and acarinina a decrease in cooler water species subbotina a sudden short term increase in low oxygen tolerant taxa chiloguembelina and no significant species extinctions these faunal changes suggest climatic warming expansion of the oxygen minimum zone and a well stratified ocean water column oxygen isotope data of the surface dweller m subbotina suggest climate warming beginning with a gradual 0 5 decrease in 18o in the 175 cm preceding the benthic foraminiferal extinction event followed by a sudden decrease of 1 4 c at the bfee the 13c excursion occurred over 27 cm of sediment and assuming constant sediment accumulation rates represents a maximum of 23 ka recovery to pre excursion gd13c values occurs within 172 cm or about 144 ka climate cooling begins in subzone p 6c as indicated by an increase in cooler water subbotinids and acarininids with rounded chambers and a decrease in warm water morozovellids

topography of the transition zone seismic discontinuities phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities nominally at 410 520 and 660 km depth thermodynamic principles govern phase transformations making them sensitive to changes in the mantle s ambient conditions through the thermodynamic response changes in temperature or composition shift the transformation to a different pressure creating topography on a level discontinuity with this use as an exploratory tool for the mantle in mind we review the basic seismological and phase equilibrium concepts underlying the detection and interpretation of the seismic wave arrivals associated with the transition zone discontinuities reviewing the evidence for and against the phase transition model we conclude that it is viable and describe how discontinuities have been and can be used to probe the physical and chemical state of the transition zone

anomalous shifts in tropical pacific planktonic and benthic foraminiferal test size during the paleocene eocene thermal maximum paleocene eocene warming and changes in oceanic hydrography should have significantly impacted the ecology of marine microorganisms both at the surface and on the seafloor we analyzed several key characteristics of foraminifera from two shatsky rise odp leg 198 cores spanning the p e boundary including the maximum test diameters of the largest calcareous trochospiral benthic foraminifera and largest shallow dwelling planktonic foraminifera and the stable carbon and oxygen isotope ratios of benthic foraminifera and bulk samples we also qualitatively constrained changes in bottom water dissolved oxygen concentrations by quantifying changes in benthic species abundances we find warming synchronous with an unusual increase in the size of surface water planktonic in contrast to deep water benthic foraminifera which decrease in size we suggest that a decline in bottom water dissolved oxygen is the primary mechanism responsible for the size reduction of pacific deep sea benthic foraminifera whereas the contemporaneous size increase of surface water planktonic foraminifera is attributed to an increase in thermal stratification and decrease in local nutrient supply

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

on dating the magmatism of maio cape verde islands conventional k ar and40ar 39ar studies of mesozoic ocean floor basalts and tertiary plutonic and volcanic rocks from maio cape verde islands have been determined to elucidate the magmatic evolution of this ocean island pillow lavas of the basement complex yield a minimum age of 113 8 ma though thermal overprinting of their formation age by the younger central intrusive complex cic and subsequent sheet intrusions is in some cases almost total activity in the cic began before 20 ma and plutons continued to develop until about 8 ma the youngest ages possibly indicating a cooling history of more than 2 ma for these bodies relative to their volcanic counterparts sheet intrusion occurred throughout the period 20 to 9 ma though the peak of this activity probably occurred 11 ma ago field relations allow the time of thrusting s on the monte branco thrust to be bracketed between 9 and 7 ma volcanic activity began in the tertiary probably before 12 ma and culminated in the development of a stratovolcano at 7 ma

transition zone structure under a stationary hot spot cape verde abstract we report on a two year seismic deployment in the cape verde islands one goal of which was to study the upper mantle to determine its structure under a hot spot that is stationary in the hot spot reference frame we find from analysis of p to s receiver functions estimated from broadband seismic recordings that within uncertainty the time separation between the 410 and 660 km discontinuities is normal compared to radial earth models thus to exist even stationary hot spots do not require vertical thermal anomalies from deep melting sources anchored in the lower mantle or at the core mantle boundary or their anomalies are narrower than 250 km in the upper mantle

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

chemostratigraphic implications of spatial variation in the paleocene eocene thermal maximum carbon isotope excursion se bighorn basin wyoming 1 the paleocene eocene thermal maximum petm is marked by a prominent negative carbon isotope excursion cie of 3 5 that has a characteristic rapid onset stable body and recovery to near pre cie isotopic composition although the cie is the major criterion for global correlation of the paleocene eocene boundary spatial variations in the position and shape of the cie have not been systematically evaluated we measured carbon isotope ratios of bulk organic matter 13corg and pedogenic carbonate 13ccarb at six petm sections across a 16 km transect in the se bighorn basin wyoming bed tracing and high resolution floral and faunal biostratigraphy allowed correlation of the sections independent of chemostratigraphy the onset of the cie in bulk organic matter at all six sections occurs within a single laterally extensive geosol the magnitude of the cie varies from 2 1 to 3 8 the absolute and relative stratigraphic thickness of the body of the cie in bulk organic matter varies significantly across the field area and underrepresents the thickness of the petm body by 30 80 the variations cannot be explained by basinal position and instead suggest that 13corg values were influenced by local factors such as reworking of older carbon the stratigraphic thickness and shape of the cie have been used to correlate sections estimate timing of biotic and climatic changes relative to the presumed carbon isotope composition of the atmosphere and calculate rates of environmental and biotic change localized controls on 13corg values place these inferences in question by influencing the apparent shape and duration of the cie

topography of the mantle discontinuities beneath the south pacific superswell as inferred from broadband waveforms on seafloor we analyzed seismic waveforms recorded by the broadband ocean bottom seismographs deployed in the south pacific superswell to determine the depths of the mantle discontinuities using a receiver function method we estimated the thickness of the mantle transition zone mtz to be 245 km on average beneath the superswell region which is close to the global average the mtz is found to be thinned locally beneath the society hot spot by 30 km temperature anomalies computed from the thinned transition zone and the clapeyron slope of the olivine phase transformations are 150 200 k beneath the society hot spot previous studies using land based data suggested the presence of a hot mtz beneath the pitcairn hot spot the locally hot transition zone beneath the hot spots is attributed to narrow mantle plumes probably rising from the lower mantle the normal average thickness obtained from the present study indicates that there is no broad upwelling across the transition zone beneath the entire superswell region at present

40ar 39ar geochronology of santo antao cape verde islands santo antao the northernmost island of the cape verde archipelago consists entirely of silica undersaturated volcanic products and minor intrusions 40ar 39ar incremental heating experiments have been carried out on 24 samples that cover the entire exposed chronological sequence the oldest lavas 7 57 0 56 ma representing an older volcanic basement are exposed about 620 m above mean sea level after an interval of quiescence of up to 4 3 ma the volcanic activity resumed and continued at low eruption rates the older basement is unconformably overlain by a ca 810 m thick lava sequence that spans an age range from 2 93 0 03 to 1 18 0 01 ma this sequence is cut by many dykes and sills simultaneous volcanic activity occurred in the northeastern central and eastern part of the island a phonolitic pumice deposit that forms a noteworthy feature over most of the island has an estimated age of 0 20 ma this predates volcanic activity that formed the highest point of the island tope de coroa which has an age of 0 17 0 02 ma the most recent eruption on the island formed nephelinitic lavas in the porto novo region at 0 09 0 03 ma the oldest volcanism exposed on santo antao which took place about 7 6 ma ago was simultaneous with waning activity on maio at the eastern end of the cape verde archipelago

expanded oxygen minimum zones during the late paleocene early eocene hints from multiproxy comparison and ocean modeling anthropogenic warming could well drive depletion of oceanic oxygen in the future important insight into the relationship between deoxygenation and warming can be gleaned from the geological record but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions we use i ca in benthic foraminifera to reconstruct late paleocene through early eocene bottom and pore water redox conditions in the south atlantic and southern indian oceans and compare our results with those derived from mn speciation and the ce anomaly in fish teeth we conclude that waters with lower oxygen concentrations were widespread at intermediate depths 1 5 2 km whereas bottom waters were more oxygenated at the deepest site in the southeast atlantic ocean 3 km epifaunal benthic foraminiferal i ca values were higher in the late paleocene especially at low oxygen sites than at well oxygenated modern sites indicating higher seawater total iodine concentrations in the late paleocene than today the proxy based bottom water oxygenation pattern agrees with the site to site o2 gradient as simulated in a comprehensive climate model community climate system model version 3 but the simulated absolute dissolved o2 values are low 35 mol kg while higher o2 values 60 100 mol kg were obtained in an earth system model grid enabled integrated earth system model multiproxy data together with improvements in boundary conditions and model parameterization are necessary if the details of past oceanographic oxygenation are to be resolved

an uplift history of the colorado plateau and its surroundings from inverse modeling of longitudinal river profiles 1 it is generally agreed that a region encompassing the colorado plateau has been uplifted by sub crustal processes admittance calculations tomographic studies and receiver function analyses suggest that dynamic support is generated by some combination of convective upwelling and lithospheric thickness changes notwithstanding advances in our understanding of present day setting uplift rate histories are poorly constrained and debated an improved history will aid discrimination between proposed models here we show that a regional uplift rate history can be obtained by inverting longitudinal river profiles we assume that the shape of a river profile is controlled by uplift rate and moderated by erosion in our model uplift rate is allowed to vary smoothly as a function of space and time upstream drainage area is invariant with time simultaneous inversion of river profiles from the colorado rio grande columbia and mississippi catchments shows that three phases of regional uplift occurred the first phase occurred between 80 and 50 myrs when 1 km of uplift was generated at a rate of 0 03 mm yr a second phase occurred between 35 and 15 myrs when 1 5 km of uplift was generated at a faster rate of 0 06 mm yr a final phase of uplift commenced 5 myrs ago these distinct phases of late cretaceous and oligocene uplift are corroborated by stratigraphic considerations by thermochronometric data and by stratigraphic evidence of periodic clastic efflux delivered into the gulf of mexico an episodic uplift history is consistent with staged removal of thick lithospheric mantle beneath a large region which is currently centered on yellowstone

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

an oceanwide view of palaeogene plate tectonic events abstract the tectonic events taking place during the palaeogene are discussed ocean by ocean three predominant periods of tectonic changes are determined separating periods of continuous stable seafloor spreading these periods of change occur at the palaeocene eocene boundary 56 53 m y at the eocene oligocene boundary 42 35 m y and during the early middle eocene 35 30 m y during the course of writing this review it became very evident how much marine surveying and data analysis took place during the early 1970s this decade showed great leaps forward in our understanding of seafloor anatomy and tectonics

latest cretaceous early neogene oxygen and carbon isotopic record at dsdp sites in the indian ocean abstract stable isotopic data of calcareous nannofossil monogeneric and monospecific planktic and benthic foraminifera from five indian ocean dsdp sites 212 217 220 237 and 253 leads to the following paleoclimatic and paleoceanographic conclusions the latest cretaceous oxygen isotopic record implies a cooling 3 4 c during the maastrichtian at the cretaceous tertiary boundary only a minor warming about 2 c has been recorded the parallel 13 c decrease of more than 1 indicates a significant decrease in productivity during the latest paleocene a positive 13 c excursion was detected in sites 217 and 237 this transient enrichment in 13 c may be due to productivity changes on continents and or a change in the storage rate of organic matter in marginal basins or shelf areas the most striking feature in the oxygen isotopic record is noted at the early middle eocene transition the shift towards more positive values which were probably enhanced to a certain extent by a preceding diagenetic alteration delineates a dramatic climatic deterioration at high and mid latitudes during the earlier tertiary near the eocene oligocene boundary a cooling is evident within the latest eocene interval during the earliest oligocene time a hiatus at sites 217 and 253 partially obscures the climatic record several climatic fluctuations have been noted during the oligocene a cooling at the base of zone np 23 a warming at the top of zone np 23 through np 24 and a cooling during zone np 25 the miocene oxygen isotopic record is dominated by changes in surface and bottom water environments during zone nn5 the decreasing and then increasing 18 o values together with the subsequent steepening of the vertical 18 o gradient point towards major climatic instabilities these events coincide with the mid miocene build up of antarctic ice sheets during the latest miocene to the earliest pliocene the 18 o record of planktic foraminifera indicates a significant warming of the indian ocean at mid latitudes the 13 c record during the oligocene and miocene reveals several cycles 13 c enrichments np 24 nn2 nn5 nn9 and base nn 11 which are most likely related to changes in storage rates of organic matter and biological productivity due to climatic changes and transgression regression cycles in addition changes in the circulation patterns may also have influenced the carbon isotopic record

explanations of the tertiary global cooling trend abstract a series of general circulation model experiments are performed to examine the role of paleogeography as an explanation of the tertiary global cooling trend systematic long term variations in topography and land sea distribution are potential causes of long term climate change however climate model sensitivity experiments indicate a geographically related cooling during the last 20 million years but not a long term cenozoic trend coarse resolution changes in geography throughout the tertiary may not be the explanation of the tertiary global cooling trend either a series of events some geographically related or another forcing factor most probably atmospheric co2 concentration are offered as alternative explanations of the tertiary global cooling trend

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

latest paleocene benthic foraminiferal extinction and environmental changes at tawanui new zealand a major extinction of intermediate water 500 1000 m benthic foraminiferal species coincided with a major decrease in 13c 2 8 of terrestrial organic matter n c29 alkane and 34s 20 of whole rock sulfide in a continuous siltstone sequence in the tawanui section 46 s paleolatitude along the akitio river southeastern north island new zealand in the middle part of the uppermost paleocene nannofossil zone cp8 the benthic extinction 25 of species occurred over 3 kyr at 55 5 ma increases in kaolinite illite and kaolinite smectite ratios and in terrestrial organic carbon percentages started 3 kyr before the major benthic extinctions lasted over 40 kyr and probably reflect warmer climate and increased rainfall the productivity of planktonic foraminifera and calcareous nannoplankton decreased 3 kyr prior to the major extinctions and recovered at the time of benthic extinctions these events that started 3 kyr before the extinction can be best explained by warming increased rainfall reduced salinity of surface waters and increased influence of warm saline deep water wsdw benthic foraminiferal oxygen indices indicate a strong decrease in dissolved oxygen levels within the intermediate water from low oxic 1 5 3 0 ml l o2 to suboxic 0 3 1 5 ml l o2 conditions coinciding with the benthic extinctions increases in total organic carbon toc and in the hydrocarbon generating potential of kerogen measured as the hydrogen index hi agree with the interpretation of decreased dissolved oxygen levels of the intermediate water the lowest oxygen conditions lasted 40 kyr and coincided with a decrease in calcareous benthic foraminiferal productivity highest toc levels and lowest 13c of terrestrial organic carbon dominant formation of wsdw or sluggish intermediate water circulation caused by warming and high rainfall in high latitude areas most likely led to the 3 kyr time lag between events on land and in surface waters preceeding the extinction and the development of dysaerobia in the sea coinciding with the major benthic extinction and decrease in 13c and 34s in new zealand global warming of deep and intermediate waters may have caused decomposition of methane hydrate in sediments resulting in a strongly decreased 13c of marine carbonates promoting dysaerobia in the ocean and warming global climate by increased methane concentrations in the atmosphere upwelling of wsdw occurring soon after it became dominant in high latitude areas is likely responsible for the recovery of normal salinity and the concomitant recovery of planktonic foraminifera and calcareous nannoplankton productivity in high latitude surface waters minor benthic foraminiferal extinctions 9 of species occurred 40 kyr after the major extinctions lasted 6 kyr and coincided with the initiation of environmental recovery

early cenozoic benthic foraminiferal isotopes species reliability and interspecies correction factors 1 oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions with those of benthic foraminifera providing information on the deep oceans reconstructions are complicatedby interspecies isotopic offsets that result from microhabitat preferences carbonate precipitation in isotopically distinct environments and vital effects species specific metabolic variation in isotopic fractionation we provide correction factors for early cenozoic benthic foraminifera commonly used for isotopic measurements cibicidoides spp nuttallides truempyi oridorsalis spp stensioina beccariiformis hanzawaia ammophila and bulimina spp showing that most yield reliable isotopic proxies of environmental change the statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies interspecies isotopic offsets appear to have changed through the cenozoic either 1 as a result of evolutionary changes or 2 as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies regardless of the reason the assumption that isotopic offsets have remained constant through the cenozoic has introduced an 1 2 c uncertainty into deep sea paleotemperature calculations in addition we compare multiple species isotopic data from a western north atlantic section that includes the paleocene eocene thermal maximum to determine the most reliable isotopic indicator for this event we propose that oridorsalis spp was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time it may be the best recorder at other locations and for other extreme events also

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