global distribution of late paleogene hiatuses six global late paleogene hiatuses pha to phe have been identified from deep sea sequences these hiatuses occurred at the middle late eocene boundary late eocene eocene oligocene boundary late early oligocene late oligocene and oligocene miocene boundary horizons paleodepth distribution of hiatuses shows hiatus maxima characterized by major mechanical erosion below 4800 m at mid depth between 2000 and 3000 m and in shallower water above 1600 m paleodepth the geographic distribution and paleodepth of these hiatus maxima suggest that flow paths of major water masses and currents are the principal cause widespread short hiatuses due to carbonate dissolution or nondeposition occurred primarily during global cooling trends or climatic instability and appear to correlate to sea level transgressions or onlap sequences these hiatuses may have been caused by basin shelf fractionation of carbonates

biogeographic gradients of middle eocene oligocene calcareous nannoplankton in the south atlantic ocean middle eocene oligocene calcareous nannoplankton have been analyzed quantitatively for eight dsdp and odp sites ranging from the equatorial zone to 65 s latitude in the south atlantic ocean there is a general decrease in calcareous nannoplankton species diversity from the middle eocene through the oligocene and species diversity also decreases towards the higher latitudes similar to findings of other studies the drop of the species diversity of calcareous nannoplankton across the eocene oligocene boundary is not drastic delineation of latitudinal distribution patterns of individual species or groups and r mode cluser analysis permit the classification of warm water taxa coccolithus formosus discoasters helicosphaerids and sphenoliths temperate water taxa coccoliths pelagicus cyclicargoliths floridanus group reticulofenestra bisecta reticulofenestra samodurovii reticulofenestra umbilica and cool water taxa chiasmoliths isthmolithus recurvus and reticulofenestra daviesii the abundance of warm water taxa plummets whereas the abundance of cool water taxa sharply increases across the eocene oligocene boundary at the middle and high latitude sites reflecting a profound cooling event in these areas polar ordination and similarity analyses reveal that steep latitudinal biogeographic gradients had been established at least by the middle eocene the gradient greatly increases near the eocene oligocene boundary indicating more severe and permanent cooling at the high latitudes the biogeographic gradient data of this study conflict with the widely accepted inference from the oxygen isotopic data that the thermal gradients between mid latitudes and high latitudes are low or nearly flat for the paleogene oceans lower surface water salinities in the high latitudes may have lowered the 18o values of the planktonic microfossils but apparently did not have significant effect on latitudinal distribution patterns of calcareous nannoplankton which offers an independent means for estimating latitudinal thermal gradients

cenozoic palaeotemperature changes and planktonic foraminiferal speciation the interaction of plate movements and progressive climatic deterioration produced a constantly changing oceanic environment during the cenozoic the destruction of the tethyan seaway and the severing of low latitude oceanographic connections during the past 65 myr ref 1 coupled with the initiation of unrestricted circum antarctic circulation in the middle to late oligocene2 provided the necessary boundary conditions for the development of a global ocean marked by steep latitudinal temperature gradients this is in contrast to the rather mild climate of the mesozoic which was characterized by an ocean with a homogeneous thermal structure and weak latitudinal temperature gradients1 throughout the cenozoic marine plankton were constantly adapting to major changes in the oceanic environment this can be seen for example in the continual development of latitudinal provincialization as a response to polar coolings1 3 here i attempt to evaluate the relationship between palaeotemperature change and planktonic foraminiferal speciation during the past 65 myr

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

eocene to oligocene benthic foraminiferal isotopic record in the bay of biscay we present here oxygen and carbon isotopic records of eocene to oligocene benthic f oraminif era from two bay of biscay deep sea drilling project dsdp sites 119 and 401 18o of benthic foraminifera increases 1 9 from a middle eocene minimum zones p10 p11 to an earliest oligocene maximum zone np21 approximately 1 4 of the increase in benthic foraminiferal 18o occurs during the late eocene to earliest oligocene zones p15 16 np21 previous results from other north atlantic dsdp sites 400a and 398 have significantly lower 18o values of benthic foraminifera some by as much as 2 refs 1 3 we believe that these differences result from diagenetic alteration of the sediments in the deeper buried sites 400a and 398

oxygen isotope ranking of late eocene and oligocene planktonic foraminifers implications for oligocene sea surface temperatures and global ice volume abstract oxygen isotope analyses of late eocene and oligocene planktonic foraminifers from low and middle latitude sites in the atlantic basin show that different species from the same samples can yield significantly different isotopic values the range of isotopic values observed between species is greatest at low latitudes and declines poleward many planktonic foraminifers exhibit a systematic isotopic ranking with respect to each other and can therefore be grouped on the basis of their isotopic ranking the isotopic ranking of some taxa however appears to vary geographically and or through time isotopic and paleontologic data from dsdp site 522 indicate that commonly used isotopic temperature scales underestimate oligocene sea surface temperatures we suggest these temperature scales require revision to reflect the presence of oligocene glaciation comparison of isotopic and paleontologic data from sites 522 511 and 277 suggests cold low salinity surface waters were present in high southern latitudes during the early oligocene lowsalinity high latitude surface waters could be caused by eocene oligocene paleogeography or by the production of warm saline bottom water

the eocene oligocene boundary event in the deep sea analysis of middle eocene to early oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the eocene oligocene boundary biotic changes in the late paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the eocenel oligocene boundary

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

evidence for oligocene middle miocene abyssal circulation changes in the western north atlantic previous studies of benthic foraminiferal isotopic composition have demonstrated that a latest eocene earliest oligocene benthic foraminiferal 18o increase occurred in the pacific southern and atlantic oceans1 9 a middle miocene 18o increase has been noted in the pacific southern and south atlantic oceans1 3 7 10 11 and tentatively identified in the north atlantic12 13 due to the incomplete nature of the north atlantic stratigraphical record14 15 however the oligocene to middle miocene isotopic record of this ocean is poorly understood in the modern ocean the north atlantic and its marginal seas has a critical role in abyssal circulation influencing deep and bottom water hydrography as far away as the north pacific16 18 we now report oxygen isotope measurements on oligocene to middle miocene 12 36 myr bp benthic foraminifera in the western north atlantic which show two periods of enriched 18o values early oligocene and early middle miocene these enriched intervals are interpreted as resulting in part from the build up of continental ice sheets the oligocene to middle miocene 13c record shows three cycles of enrichment and depletion of large enough magnitude to be useful for time stratigraphical correlations within the biostratigraphical age resolution 18o and 13c records correlate with records from other oceans helping to establish a useful tertiary isotopic stratigraphy an atlantic pacific 13c contrast of 0 3 0 9 during the latest oligocene to middle miocene 12 26 myr bp indicates north atlantic deep and bottom water production analogous to modern north atlantic deep water nadw

paleogene calcareous nannofossil magnetobiochronology results from south atlantic dsdp site 516 abstract the detailed study of an expanded paleogene section with abundant moderate to well preserved calcareous nannofossils from south atlantic dsdp site 516 has resulted in a precise correlation of most calcareous nannofossil markers with the magnetostratigraphy many nontraditional datums have also been documented and correlated to the magnetostratigraphy comparison of the results from site 516 with those of previous studies from other areas enables a critical evaluation of the accuracy synchroneity or diachroneity of the species events over geographically long distances of special significance is the correlation for the first time of the stratigraphic ranges of chiasmolithus gigas and rhabdosphaera gladius with the magnetostratigraphy other important results include the following first occurrence fo of cruciplacolithus primus 66 3 ma fo chiasmolithus danicus 65 6 66 0 ma fo prinsius martinii 65 5 66 0 ma fo heliolithus kleinpellii 59 8 61 6 ma probably diachronous last occurrence lo of tribrachiatus orthostylus 51 0 54 8 ma unreliable fo chiasmolithus gigas 47 4 ma fo reticulofenestra umbilica 44 6 ma lo chiasmolithus gigas 44 4 46 8 ma diachronous lo nannotetrina fulgens 44 2 ma lo chiasmolithus grandis 40 0 41 6 ma probably diachronous fo chiasmolithus oamaruensis 39 8 40 4 ma unreliable fo isthmolithus recurvus 39 5 ma lo reticulofenestra reticulata 37 6 ma lo discoaster saipanensis 36 4 ma end acme of ericsonia subdisticha diachronous fo and lo sphenolithus distentus unreliable and lo reticulofenestra bisecta 24 0 ma

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

paleo oceanographic utility of oxygen isotopic measurements on planktic foraminifera indian ocean core top evidence abstract isotopic analyses have been performed on narrow size ranges of seven species of planktic foraminifera picked from 43 core top locations in the indian ocean comparison of observed 18o for each species with calculated profiles of equilibrium 18o at each location yield three distinct depth habitat preferences for surface dwelling species globigerinoides ruber and globigerina bulloides observed oxygen isotopic compositions are in close agreement with the seasonal range of calculated 18o for calcite precipitated in surface waters observed 18o values for orbulina universa neogloboquadrina dutertrei and pulleniatina obliquiloculata are consistently enriched relative to calculated 18o for surface conditions in the northern indian ocean test precipitation for o universa n dutertrei and p obliquiloculata occurs over a narrow range of temperature 22 c 24 c with no systematic relationship with sea water t in contrast globorotalia inflata and g truncatulinoides observed 18o apparently reflect temperature and salinity variation along the 26 8 t isopycnal

the salinity contrast between the atlantic and pacific oceans during glacial time in today s ocean the salinity of low latitude surface waters in the pacific is on the average 1 per mil lower than in the atlantic oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for pacific surface water during glacial time if so the transport of water vapor from the atlantic to the pacific must have been as strong as or even stronger to balance the tendency toward salt buildup the atlantic would have had to export during glacial time waters saltier than it received from the other oceans

morphometry of the eocene nannofossil reticulofenestra umbilicus lineage and its biochronological consequences abstract morphometruc measurements of eocene and early oligocene reticulofenestrids from dsdp site 523 in the south atlantic show that a 90 size increased led to the appearance of reticulofenestra umbilicus this increase occurred between about 45 2 ma and 42 9 ma the attempts made to recognize r umbilicus during this period of change as a distinct subpopulation among the reticulofenestrid assemblages did not yield any tenable conclusions however using a lower size limit of 14 m for recognition of the r umbilicus morphovariant resulted in an easily identified first appearance event which occurred during chron 19r at an age of about 44 4 44 5 ma from a morphometric point of view the two morphovariants r hillae and r umbilicus could not be distinguished as two distinct subpopulations the oligocene assemblages show markedly smaller 10 central opening placolith length ratios as compared to the eocene forms but for several reasons it seems difficult to use this decrease biostratigraphically

stepwise mass extinctions and impact events late eocene to early oligocene abstract species ranges and relative abundances of dominant planktonic foraminifers of eight late eocene to early oligocene deep sea sections are discussed to determine the nature and magnitude of extinctions and to investigate a possible cause effect relationship between impact events and mass extinctions late eocene extinctions are neither catastrophic nor mass extinctions but occur stepwise over a period of about 1 2 million years four stepwise extinctions are identified at the middle late eocene boundary the upperglobigerapsis semiinvoluta zone theg semiinvoluta globorotalia cerroazulensis zone boundary and at the eocene oligocene boundary each stepwise extinction event represents a time of accelerated faunal turnover characterized by generally less than 15 species extinct and in itself is not a significant extinction event relative species abundance changes at each stepwise extinction event however indicate a turnover involving 60 of the population implying major environmental changes there microtektite horizons are present in late eocene sediments one in the upperg semiinvoluta zone 38 2 ma and two closely spaced layers only a few thousand years apart in the lower part of thegloborotalia cerroazulensis zone 37 2 ma each of the three impact events appears to have had some effect on microplankton communities however the overriding factor that led to the stepwise mass extinctions may have been the result of multiple causes as there is no evidence of impacts associated with the step preceding or the step following the deposition of the presently known microtektite horizons

middle oligocene cooling from equatorial pacific dsdp site 77b an apparently complete 150 m oligocene sequence of pelagic sediment at equatorial pacific deep sea drilling project site 77b has been analyzed for stable isotope and quantitative planktonic foraminiferal studies lower abundance of inferred warm water species and enrichment of 18 o and 12 c in foraminiferal tests during the interval 29 to 32 m y ago suggest cooler climate lowered sea level and significant volume of continental ice compared to earlier and later times in the oligocene

paleogene sea levels and climates u s a eastern gulf coastal plain abstract biostratigraphic zonation of the paleogene formations in the eastern gulf coastal plain of the u s a based on calcareous nannoplankton allows a reassessment of the timing and pattern of changing sea levels and climates in the region general similarity is recognizable between the gross pattern of paleogene transgressions regressions in the eastern gulf coastal plain and the recently published vail et al 1977 scheme of eustatic sea level changes local tectonism and sedimentation have however overprinted intra cycle shoreline fluctuations on the eustatic pattern a hiatus spanning at least calcareous nannoplankton zone np 11 exists between the early eocene hatchetigbee and tallahatta formations another significant hiatus representing most or all of np 23 exists between the early oligocene bucatunna clay and the late oligocene chickasawhay limestone nannoplankton assemblages suggest temperate sea surface waters during the early and early late paleocene followed by subtropical sea surface conditions from latest paleocene to earliest oligocene climatic conditions were cooler during the remainder of the early oligocene

landscape antiquity and cenozoic drainage development of southern yukon through restoration modeling of the tintina fault the impact of tintina fault displacement on the development of the yukon river and drainage basins of central yukon is investigated through geophysical and hydrological modeling of digital terrain model data regional geological evidence suggests that the age of the planation of the klondike plateau is at least late cretaceous rather than neogene as previously assumed and that surprisingly there has been little net incision in the region since the late mesozoic the tintina fault has been previously interpreted to have experienced 430 km of dextral displacement primarily during the eocene however the alignment of river channels across the fault at specific displacements coupled with recent seismic events and related fault activity suggests that the fault may have moved in stages over a longer time span topographic restoration and hydrological models show that the drainage of the yukon river northwestward into alaska via the ancestral kwikhpak river was only possible at restored displacements of u

multiple microtektite horizons in upper eocene marine sediments no evidence for mass extinctions microtektites have been recovered from three horizons in eight middle eocene to middle oligocene marine sediment sequences five of these occurrences are coeval and of latest eocene age 37 5 to 38 0 million years ago three are coeval and of early late eocene age 38 5 to 39 5 million years ago and three are of middle oligocene age 31 to 32 million years ago in addition rare probable microtektites have been found in sediments with ages of about 36 0 to 36 5 million years the microtektite horizon at 37 5 to 38 0 million years can be correlated with the north american tektite strewn field which has a fission track age minimum of 34 to 35 million years and a paleomagnetic age of 37 5 to 38 0 million years there is no evidence for mass faunal extinctions at any of the microtektite horizons many of the distinct faunal changes that occurred in the middle eocene to middle oligocene can be related to the formation of the antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large scale dissolution of calcium carbonate and erosion which created areally extensive hiatuses in the deep sea sediment records the occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle eocene to middle oligocene time

characterizing riverbed sediment using high frequency acoustics 2 scattering signatures of colorado river bed sediment in marble and grand canyons in this the second of a pair of papers on the statistical signatures of riverbed sediment in high frequency acoustic backscatter spatially explicit maps of the stochastic geometries length and amplitude scales of backscatter are related to patches of riverbed surfaces composed of known sediment types as determined by georeferenced underwater video observations statistics of backscatter magnitudes alone are found to be poor discriminators between sediment types however the variance of the power spectrum and the intercept and slope from a power law spectral form termed the spectral strength and exponent respectively successfully discriminate between sediment types a decision tree approach was able to classify spatially heterogeneous patches of homogeneous sands gravels and sand gravel mixtures and cobbles boulders with 95 88 and 91 accuracy respectively application to sites outside the calibration and surveys made at calibration sites at different times were plausible based on observations from underwater video analysis of decision trees built with different training data sets suggested that the spectral exponent was consistently the most important variable in the classification in the absence of theory concerning how spatially variable sediment surfaces scatter high frequency sound the primary advantage of this data driven approach to classify bed sediment over alternatives is that spectral methods have well understood properties and make no assumptions about the distributional form of the fluctuating component of backscatter over small spatial scales

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation

paleoclimatic analyses of middle eocene through oligocene planktic foraminiferal faunas quantitative faunal analyses and oxygen isotope ranking of individual planktic foraminiferal species from deep sea sequences of three oceans are used to make paleoceanographic and paleoclimatic inferences species grouped into surface intermediate and deep water categories based on 18o values provide evidence of major changes in water mass stratification and individual species abundances indicate low frequency cool warm oscillations these data suggest that relatively stable climatic phases with minor cool warm oscillations of 0 5 m y frequency are separated by rapid cooling events during middle eocene to early oligocene time five major climatic phases are evident in the water mass stratification between middle eocene through oligocene time phase changes occur at p14 p15 p15 p16 p20 p21 and p21 p22 zone boundaries and are marked by major faunal turnovers rapid cooling in the isotope record hiatuses and changes in the eustatic sea level a general cooling trend between middle eocene to early late oligocene is indicated by the successive replacement of warm middle eocene surface water species by cooler late eocene intermediate water species and still cooler oligocene intermediate and deep water species increased water mass stratification in the latest eocene p17 indicated by the coexistence of surface intermediate and deep dwelling species groups suggest that increased thermal gradients developed between the equator and poles nearly coincident with the development of the psychrosphere this pattern may be related to significant ice accumulation between late eocene and early late oligocene time

isomerization and aromatization of hydrocarbons in stretched sedimentary basins we have calculated the progress of two reactions both involving biological marker compounds which occur in shales rich in organic matter both reactions are associated with the early stages of oil generation one of these reactions is an isomerization reaction of a sterane1 2 the other involves the aromatization of monoaromatic steroid hydrocarbons3 4 both reactions have recently been discussed by mackenzie et al 5 we demonstrate that the observed progress of these reactions within two basins formed by extension the north sea and the pannonian basin can be reproduced in some detail by a simple model of basin formation6 we used samples from basins formed by stretching the lithosphere because both the subsidence history and the variation of heat flux with time is principally controlled by the amount of extension6 10 in contrast the subsidence of the other major class of sedimentary basins which are formed by flexure of the continental lithosphere11 13 can only be modelled when the geological history of the region is known in detail13 and such models do not constrain the history of the heat flux

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