paleoclimatology and paleoecology across the eocene oligocene boundary thrace basin northeast aegean sea greece abstract the detailed biostratigraphic and ichnological analysis of the upper eocene lower oligocene forearc sedimentary sequence in the southern greek part of the thrace basin on lemnos island reveals a relationship between eco sedimentary factors and the base level dynamics influencing calcareous nannofossils and trace fossil assemblages the lower part of the 350 m thick succession was deposited in a sand rich submarine fan system and upper part in a shelf environment it contains nannofossil assemblages and distributions typical of the np19 np21 biozones the eocene oligocene e o boundary top of np20 biozone is clearly distinguished within the upper parts of the turbidite system where a decrease in water temperature salinity nutrient supply and oxygenation level is also revealed additionally 19 ichnospecies mostly graphoglyptids typical of deep sea fan deposits have been distinguished the trace fossil diversity and abundance decrease upward reflecting the impact of the changing depositional environments from basin floor fans to slope systems and then shelfal environments the regional basin fill history rather than global climatic changes was probably the fundamental controlling factor on the distribution of graphoglyptids and other trace fossils across the e o boundary

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

lithium saltworks of the salar de atacama a model for mgso 4 free ancient potash deposits abstract potash basins similar to those in the geological past no longer exist at present there are only hypersaline lakes such as those in the tibetan plateau where carnallite kcl mgcl2 6h2o precipitates given that the purpose of common saltworks is to obtain nacl the halitic stage is not exceeded by contrast saltworks extracting lithium by solar evaporation reach more advanced stages of brine evolution and saline precipitation in the salar de atacama saltworks with a relative humidity commonly below 30 monthly average salts precipitate following a sequence of halite nacl sylvite kcl carnallite and bischofite mgcl2 6h2o and display a useful model of evolution similar to that which gave rise to mgso4 free potash deposits in the past prismatic acicular gypsum caso4 2h2o the main accessory mineral is transformed into a less hydrated calcium sulfate probably anhydrite caso4 during carnallite precipitation mineral crystal size and annual sedimentary thickness of each paragenesis are compared with those in ancient potash deposits the behavior of sylvite and carnallite as cements is observed at the onset of their precipitation in ponds where both minerals coexist with previous halite millimeter cyclicity due to day night thermal variations is observed in these saltworks whereas cm and mm cyclicities have been interpreted in ancient sites as annual regular and intra annual irregular respectively conditions similar to those existing at the salar de atacama were necessary to preserve carnallite which is commonly the most evolved mineral in the ancient deposits the development of potash deposits in the south pyrenean foreland basin and the rhine graben near the eocene oligocene boundary is attributed to global aridity and cooling and to the basin restriction associated with a decrease in the ocean level caused by the spread of the antarctic ice cap

the eocene oligocene preglacial glacial transition in the atlantic sector of the southern ocean odp site 690 abstract high resolution interdisciplinary analyses of the clay and coarse 40 m fractions of odp leg 113 site 690 eocene oligocene sediments on the flank of the maud rise provide information on paleoproductivity water masses paleoclimate and erosion in the antarctic range as well as on the cyclicity of these processes three time intervals are distinguished 1 1 the middle eocene characterized by a nearly pure smectites b productivity varying between relatively high values in the 42 44 ma interval to very low values after 42 ma and c cyclic variations which correspond to changes in clay mineral associations a warm saline deep water mass is inferred to have protected carbonate shells against dissolution at site 690 we interpret the abundant mica in the coarse fraction as distributed by intermediate currents 2 2 the latest middle eocene late eocene characterized by low productivity values increasing with time kaolinite and illite concentrations also increase since the middle late eocene boundary mixing in the water column which starts during a cooling event causes similar clay mineral assemblages at site 690 and at site 689 on top of maud rise 3 3 the oligocene separated from the eocene by a hiatus is characterized by high productivity highly increased amounts of illite and other minerals originating from erosion and physical weathering of antarctica and by cyclic variations of clay mineral indices which appear to be synchronous with productivity variations with a 400 450 kyr cyclicity six periods of strong carbonate dissolution associated with low productivity levels are attributed to incursions of cold carbonate aggressive bottom water of a proto aabw type

shifting ocean carbonate chemistry during the eocene oligocene climate transition implications for deep ocean mg ca paleothermometry to date no conclusive evidence has been identified for intermediate or deep water cooling associated with the 1 parts per thousand benthic delta o 18 increase at the eocene oligocene transition eot when large permanent ice sheets first appeared on antarctica interpretation of this isotopic shift as purely ice volume change necessitates bipolar glaciation in the early oligocene approaching that of the last glacial maximum to test this hypothesis it is necessary to have knowledge about deep water temperature which previous studies have attempted to reconstruct using benthic foraminiferal mg ca ratios however it appears likely that contemporaneous changes in ocean carbonate chemistry compromised the mg ca temperature sensitivity of benthic foraminifera at deep sites new geochemical proxy records from a relatively shallow core odp site 1263 estimated paleodepth of 2100 m on the walvis ridge reveal that carbonate chemistry change across the eot was not limited to deep sites but extended well above the lysocline critically limiting our ability to obtain reliable estimates of deep ocean cooling during that time benthic li ca measurements used as a proxy for co32 suggest that co32 increased by similar to 29 mu mol kg at site 1263 across the eot and likely impacted benthic foraminiferal mg ca a co32 benthic mg ca relationship is most apparent during the early eot when the overall increase in co32 is interrupted by an apparent dissolution event planktonic d18o and mg ca records suggest no change in thermocline temperature and a delta o 18 seawater increase of up to 0 6 parts per thousand at this site across the eot consistent with previous estimates and supporting the absence of extensive bipolar glaciation in the early oligocene

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

a comparison of early paleogene export productivity and organic carbon burial flux for maud rise weddell sea and kerguelen plateau south indian ocean 1 marine biological productivity has been invoked as a possible climate driver during the early paleogene through its potential influence on atmospheric carbon dioxide concentrations however the relationship of export productivity the flux of organic carbon c from the surface ocean to the deep ocean to organic c burial flux the flux of organic c from the deep ocean that is buried in marine sediments is not well understood we examine the various components involved with atmosphere to ocean c transfer by reconstructing early paleogene carbonate and silica production using carbonate and silica mass accumulation rates mars export productivity using biogenic barium bio ba mars organic c burial flux using reactive phosphorus p mars redox conditions using uranium and manganese contents and the fraction of organic c buried relative to export productivity using reactive p to bio ba ratios our investigations concentrate on paleocene eocene sections of sites 689 690 from maud rise and site 738 from kerguelen plateau in both regions export productivity organic c burial flux and the fraction of organic c buried relative to export productivity decreased from the paleocene early eocene to the middle eocene a shift is indicated from an early paleogene two gyre circulation in which nutrients were not efficiently recycled to the surface via upwelling in these regions to a circulation more like the present day with efficient recycling of nutrients to the surface ocean export productivity was enhanced for kerguelen plateau relative to maud rise throughout the early paleogene possibly due to internal waves generated by the plateau regardless of gyre circulation

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

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

middle eocene to late oligocene antarctic glaciation deglaciation and southern ocean productivity during the eocene oligocene transition earth cooled significantly from a greenhouse to an icehouse climate nannofossil assemblages from southern ocean sites enable evaluation of paleoceanographic changes and hence of the oceanic response to antarctic ice sheet evolution during the eocene and oligocene a combination of environmental factors such as sea surface temperature and nutrient availability is recorded by the nannofossil assemblages of and can be interpreted as responses to the following changes a cooling trend started in the middle eocene was interrupted by warming during the middle eocene climatic optimum and by short cooling episodes the cooling episode at 39 6 ma preceded a shift toward an interval that was dominated by oligotrophic nannofossil assemblages from 39 1 to 36 2 ma we suggest that oligotrophic conditions were associated with increased water mass stratification low nutrient contents and high efficiency of the oceanic biological pump that in turn promoted sequestration of carbon from surface waters which favored cooling after 36 2 ma we document a large synchronous surface water productivity turnover with a dominant eutrophic nannofossil assemblage that was accompanied by a pronounced increase in magnetotactic bacterial abundance this turnover reflects a response of coccolithophorids to changed nutrient inputs that was likely related to partial deglaciation of a transient antarctic ice sheet and or to iron delivery to the sea surface eutrophic conditions were maintained throughout the oligocene which was characterized by a nannofossil assemblage shift toward cool conditions at the eocene oligocene transition finally a warm nannofossil assemblage in the late oligocene indicates a warming phase

carbonate dissolution in recent sediments of the eastern equatorial indian ocean preservation patterns and carbonate loss above the lysocline abstract multiple dissolution indices from 45 sediment samples show that the foraminiferal lysocline is near 3800 m in the eastern equatorial indian ocean close to the saturation horizon with respect to calcite in the water column below the lysocline the increase in foraminiferal fragmentation decrease in absolute abundance and progressive modification of planktic foraminiferal assemblages with depth is accompanied by an increasing rate of loss of carbonate from the sediments above the lysocline some dissolution must occur in order to produce the dramatic reduction in foraminiferal numbers up to 60 and the pattern of increased fragmentation with depth however the amount of carbonate actually lost from supralysoclinal sediments reaches at most 20 30 of the total at the depth of the lysocline the principal driving force behind supralysoclinal dissolution is most likely the oxidation of organic matter incorporated into the sediments dissolution above the lysocline has a greater apparent impact on relative preservation in the coarse 150 m fraction than it does on total carbonate loss because of redistribution of carbonate to the finer size fractions as fragments though the effects of dissolution on foraminiferal preservation are clearly visible at all depths the lysocline itself does appear to mark the local onset of large scale loss of dissolved carbonate from the sediments such an interpretation is broadly consistent with models regarding the saturation state of the overlying waters as the principal driving force behind the preservation or dissolution of recent carbonate sediments on the sea floor

middle eocene to early oligocene paleoceanography of the antarctic ocean maud rise odp leg 113 site 689 change from a low to a high productivity ocean the sediment record from the middle eocene about 45 ma to the early oligocene about 33 ma on maud rise site 689 weddell sea paleodepth 1400 1650 m has been studied by means of a coarse fraction analysis in order to reconstruct variations in surface water productivity and bottom water masses productivity has been estimated using carbonate dissolution and accumulation rates of radiolaria diatoms benthonic and planktonic foraminifers sponge debris ostracods and echinoids accumulation rates of bolboforma spp vary parallel to these proxies productivity increased with time three episodes were found in which productivity increased sharply and productivity varied cyclically with a period of 430 ky the middle eocene ca 45 44 37 26 ma was a period of generally low productivity no opal was deposited and carbonate preservation was excellent during periods of a slight increase in productivity accumulation rates of benthonic and planktonic foraminifers ostracods and echinoids increased in spite of an increase in carbonate dissolution in the period ca 41 62 43 07 ma productivity rose in three distinct pulses clinoptilolite formed from biogenous opal is a common mineral in these sediments these three productivity maxima coincide with a mica rich unit mica probably originated from erosion on antarctica and was transported by an intermediate water depth current in the late eocene ca 36 9 34 95 ma productivity increased considerably and opal skeletons were deposited carbonate dissolution increased but planktonic foraminifer accumulation rates were not markedly decreased in periods of higher productivity because productivity increase exceeded or equalled rises in dissolution rates increasing opal accumulation rates coincided with increases in the rates for benthonic foraminifers sponge debris ostracods and echinoids in the late eocene early oligocene period 34 95 33 05 ma a further increase in productivity led to a strong dissolution of planktonic foraminifers in high productivity periods the productivity increase is probably due to the increasing pole equator temperature gradient which led to stronger atmospheric and oceanic turnover and mixing in the oceans in the uppermost late eocene two unusual layers suggest changes in bottom water masses affecting the seafloor at site 689 a sediment interval with especially well preserved carbonate microfossils underlies an interval that has poor carbonate preservation despite evidence of low productivity these intervals suggest a change in bottom water conditions from warm saline deep water wsdw which favors carbonate preservation to antarctic bottom water aabw which promotes carbonate dissolution cooling of surface waters over a period of 300 ky led to a thickening of the deep aabw layer and an upward shift of the overlying wsdw until the aabw finally reached the top of the maud rise in the area of site 689 this period of aabw influence on top of the maud rise lasted 200 ky

evolution of deep sea sediments across the paleocene eocene and eocene oligocene boundaries abstract the composition and distribution of deep sea sediments is the result of a multitude of climatic biotic and oceanic conditions relating to biogeochemical cycles and environmental change here we utilize the extensive sediment archives of the international ocean discovery program iodp and its predecessors to construct maps of deep sea sediment type across two critical but contrasting boundaries in the paleogene one characterised by an interval of extreme warmth paleocene eocene and the other by global cooling eocene oligocene ocean sediment distribution shows significant divergence both between the latest paleocene and paleocene eocene thermal maximum petm across the eocene oligocene transition eot and in comparison to modern sediment distributions carbonate sedimentation in the latest paleocene extends to high southern latitudes disappearance of carbonate sediments at the petm is well documented and can be attributed to dissolution caused by significant ocean acidification as a result of carbon cycle perturbation biosiliceous sediments are rare and it is posited that the reduced biogenic silica deposition at the equator is commensurate with an overall lack of equatorial upwelling in the early paleogene ocean in the southern ocean we attribute the low in biosiliceous burial to the warm deep water temperatures which would have impacted biogenic silica preservation in the late eocene our sediment depositional maps record a tongue of radiolarian ooze in the eastern equatorial pacific enhanced biosiliceous deposits in the late eocene equatorial pacific and south atlantic are due to increased productivity and the spin up of the oceans our compilation documents the enhanced global carbonate sedimentation in the early oligocene confirming that the drop in the carbonate compensation depth was global

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

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

carbonate sedimentation beneath the antarctic circumpolar current during the late quaternary abstract calcium carbonate content and planktonic foraminiferal fragmentation have been studied in four late quaternary eltanin piston cores e48 22 e48 28 e49 18 and e49 23 taken from the southeast indian ridge between 3200 and 3400 m waterdepth beneath the antarctic circumpolar current the calcium carbonate records in the two southernmost cores e49 18 and e49 23 show distinct glacial interglacial cycles with the glacial intervals and intermediate cool intervals having low carbonate values relative to the interglacial times however the carbonate records of e48 22 and e48 28 are largely independent of the paleoclimatic records and may be influenced by input of volcanic ash from the st paul or amsterdam islands located less than 700 km upwind of the cores planktonic formainiferal fragmentation considered to be a dissolution index indicates that dissolution generally increased during glacial intervals relative to the interglacial intervals in e49 18 and e49 23 in e48 22 and e48 28 the dissolution records do not follow glacial interglacial patterns but instead dissolution was greatest during oxygen isotope stage 9 the stage 9 8 boundary the early part of stage 8 and during stage 7 no relationship exists between benthonic formainiferal changes and the fragmentation records in three cores e48 22 e48 28 and e49 23 indicating that deep water circulation changes had minimal or no influence on these dissolution records however in e49 18 the benthonic foraminiferal and the dissolution records are closely matched from oxygen isotope stages 12 to 5 t 440 000 120 000 yrs b p deep water circulation changes may have influenced the dissolution record in e49 18 or the two variables may be unrelated but may have independently responded to glacial interglacial climatic changes

late cainozoic ostracod faunas and paleoenvironmental changes at odp site 1148 south china sea ostracod faunas from odp site 1148 in the south china sea have been analyzed quantitatively in order to understand paleoenvironmental changes in the late cainozoic deep water more than 2000 core samples were taken from the oligocene to quaternary section of which 725 contained ostracods and yielded at least 100 species krithe dominates the faunas throughout the oligocene quaternary sequences indicating that deep sea conditions had existed since the earliest oligocene ca 34 5 ma this suggests that the spreading of the south china sea basin predates the oligocene three distinct ostracod assemblages have been recognized and their respective faunal turnover reflects a change in paleodepth from the upper bathyal 2500 m since the late middle miocene 14 ma to the present intervals when ostracods become very rare are at 28 5 27 20 18 2 and 13 2 8 ma the earliest of these intervals was probably related to the high surface productivity and the depletion of oxygen content in bottom water while intervals were the product of enhanced carbonate dissolution measures of evolutionary activity origination extinction and diversity have been applied to detecting the environmental change and their relationship to global events five peaks of evolutionary activity occurred in the oligocene p18 p21a and p22 and in the earlier mid miocene n8 and late pliocene quaternary n21 n22 respectively the peaks in p18 and p21a are the possible response respectively to the global cooling events oi 1 and oi 2 which occurred in the early oligocene the marked increase in extinction origination and diversity was synchronous with the major enrichment in benthic 18o in the late pliocene n21 suggesting a reaction of the ostracod faunas to the rapid cooling of the bottom water and the initiation of the north hemispheric glaciation during the period of 3 2 5 ma

distribution and mixing of intermediate water masses in the channel of sicily mediterranean sea 1 the channel of sicily which represents the only connection between the western and the eastern mediterranean sea can be described as a three layer system where fresher water of atlantic origin modified atlantic water flows eastward in the upper layer levantine intermediate water liw leaves the eastern basin at around 250 350 m and an outflow of transitional ionian deep water tidw is identified below the liw synoptic mesoscale plankton experiment data collected during four surveys in the channel of sicily show that liw and tidw are subject to major modifications when crossing the eastern sill a significant bernoulli aspiration is found there and the bottom water at the sill is composed of modified deep ionian waters coming from 800 m an analysis of the water mass composition proves that liw mixes essentially with tidw and that the tidw flow through the channel must be larger than the expected 0 5 sv the presence of a secondary circulation related to the bottom boundary layer is demonstrated to be the primary factor leading to the dilution and cooling of liw

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

geochemistry and origin of basaltic lavas from society islands french polynesia south central pacific ocean the society islands of french polynesia south central pacific ocean are formed predominatly by basaltic lavas of alkaline affinities these intraplate rocks are either ne or hy normative ne normative basaltic lavas are lower in si and heavy rare earth elements and higher in ti v and sr than hy normative the differences are attributed to the contrasting behaviour of amphibole during melting of the upper mantle which in turn may be related to the variation in the depth of melting compared to pyrolite the upper mantle source of the lavas was enriched in incompatible elements

middle eocene to early oligocene paleoceanography from agulhas ridge southern ocean ocean drilling program leg 177 site 1090 1 the agulhas ridge off the tip of africa between the atlantic and indian oceans is ideally located to capture the evolution of paleogene early neogene circulation patterns associated with global cooling multiproxy records of productivity biogenic barium baex opal caco3 mass accumulation rates mars nutrient and organic carbon burial reactive phosphorus pr mars and redox state of deep waters u enrichment from ocean drilling program odp site 1090 reflect hydrographic shifts in this region between the middle eocene and early oligocene 39 33 ma several peaks in increased export productivity and burial of organic matter occurred within the late eocene 36 5 34 and 33 7 ma which along with surface hydrologic conditions favoring opaline organisms over calcareous organisms could have aided in the draw down of pco2 to a threshold level that facilitated large ice sheet development on antarctica in the earliest oligocene our multiproxy approach illustrates the importance of vertical as well as spatial hydrographic reorganization in amplifying or driving climatic cooling of the middle eocene to early oligocene by facilitating increases in the relative or absolute burial of organic carbon

bryozoan beds in northern italy as a shallow water expression of environmental changes during the oligocene isotope event 1 abstract shifts in carbonate producing biotic communities in the geological record provide evidence of past environmental changes in the neritic realm the shallow marine calcare di nago formation exposed in the san valentino section northern italy covers the late eocene and earliest oligocene the succession is characterized by the occurrence of light dependent biota such as coralline algae and larger benthic foraminifera in the uppermost part of the section however the fossil association is dominated by bryozoans which are filter feeder organisms this ca 12 m thick interval locally contains up to 86 bryozoans while coralline algae as well as larger benthic foraminifera are absent coralline algae and nummulitid foraminifera recover in the upper part of the bryozoan beds whereas orthophragminids do not recover the gradual disappearance of larger foraminifera and coralline algae within the bryozoan dominated deposits is coeval with a pronounced positive shift in 13c based on its biostratigraphic position this positive shift is interpreted to be linked to the positive shift in 13c recognized in deep sea records shortly above the eocene oligocene boundary which in turn is associated to the positive shift in 18o leading to the oi 1 oligocene isotope event 1 cooling phase total phosphorus content increases in the bryozoan beds suggesting enhanced nutrient supply to the neritic ecosystem this phosphorous peak is coeval with the globally recognized increment in ocean productivity around the oi 1 and 13c positive shift thus disappearance of light dependent biota and the dominance of bryozoans in the platform carbonates studied are interpreted to result not necessarily from a deepening of the depositional environment but from the combination of lower sea surface temperatures and the deterioration of underwater light conditions on account of elevated turbidity in surface waters resulting from enhanced primary productivity as bryozoan beds occur in several italian localities around the eocene oligocene boundary they are interpreted to represent the regional expression of neritic carbonate depositional systems to global environmental changes occurring at the dawn of an ice house earth

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

pattern of first and last appearance in diatoms oceanic circulation and the position of polar fronts during the cenozoic 1 first and last occurrences of 389 diatom species from the first global cenozoic record are used to reconstruct the position of major oceanographic boundaries first appearances and extinctions group in three latitudinal bands middle to high northern latitudes equatorial region and high southern latitudes sparse paleogene occurrences were limited to southern high latitudes along the equivalent of the modern antarctic polar front its late middle eocene to middle miocene position varied within 10 and within a 20 band from middle miocene to present suggesting an association with global cooling first and last occurrence events appear in the two remaining latitudinal regions during the eocene and increase in a stepwise fashion mimicking significant cooling events at about 16 ma first and last appearances shift from the north atlantic to the north pacific low latitude data suggest low surface water productivity prior to 40 ma while increased abundance from the middle miocene correlates with expansion of the east antarctic ice sheet

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

eocene to miocene magnetostratigraphy biostratigraphy and chemostratigraphy at odp site 1090 sub antarctic south atlantic at ocean drilling program odp site 1090 lat 42854 89s long 8854 09e located in a water depth of 3702 m on the agulhas ridge in the sub antarctic south atlantic 300 m of middle eocene to middle miocene sediments were recovered with the advanced piston corer apc and the extended core barrel xcb u channel samples from the 70 230 meters composite depth mcd interval provide a magnetic polarity stratigraphy that is extended to 380 mcd by shipboard whole core and discrete sample data the magnetostratigraphy can be interpreted by the fit of the polarity zone pattern to the geomagnetic polarity time scale gpts augmented by isotope data and bioevents with documented correlation to the gpts three normal polarity subchrons c5dr 1n c7ar 1n and c13r 1n not included in the standard gpts are recorded at site 1090 the base of the sampled section is correlated to c19n middle eocene although the interpretation is unclear beyond c17r the top of the sampled section is correlated to c5cn late early miocene although in the uppermost 10 m

chemical and physical erosion rhythms of the west african cenozoic morphogenesis the 39 ar 40 ar dating of supergene k mn oxides chemical weathering and mechanical erosion are first order processes of long term tropical morphogenesis which is still poorly deciphered for lack of time constraints we address this issue by laser probe 39ar 40ar dating of generations of cryptomelane k1 2mn8o16 nh2o from the manganese ore deposit of tambao in northern burkina faso this mn deposit results from the supergene weathering of carbonate and silicate mn protores underneath lateritic palaeolandsurfaces it consists of an upper cryptomelane rich domain and a lower domain where pyrolusite b mno2 is the dominant mn oxide the oldest 39ar 40ar ages 59 45 ma are obtained on surface outcrops while the youngest ones characterize deep oxidation fronts 3 4 2 9 ma apparent correlations of 39ar 40ar age groups with d18o and eustatic curves allow definition of the different stages of morphogenesis paleocene eocene ages 59 45 ma bracket a greenhouse period propitious to bauxitic weathering the lack of significant ages between 45 and 29 ma characterizes a period dominated by mechanical erosion during which detrital sediments including lateritic materials were accumulated in intracratonic basins allowing the exhumation of a new lateritic landsurface two major weathering periods separated by a second erosion episode 24 18 ma are also depicted at the end of oligocene 29 24 ma and lower to mid miocene 18 11 5 ma in the upper domain during which newly shaped land surfaces conspicuously weathered the shorter weathering and erosion episodes recorded in the lower domain from 18 to 2 9 ma led to the final geomorphic changes that were conducive to the formation of glacis the preservation of old cryptomelane 59 45 ma in the upper part of the ore deposit indicates a cenozoic denudation limited to the erosion of previous bauxites and partly of ferricretes

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

cenozoic history of phosphogenesis recorded in the ferromanganese crusts of central and western pacific seamounts implications for deepwater circulation and phosphorus budgets abstract ages of seamount phosphatization episodes have been revised for 14 mid plate seamounts in the western and central pacific using the most up to date marine sr isotope curve and 87 sr 86 sr data from the literature the new ages provide a composite geologic history of phosphatization consistent with cenozoic climate history phosphatization on mid pacific seamounts took place only between 36 and 12 ma and it peaked at the eocene oligocene e o transition 34 ma the unprecedented appearance of prominent amounts of phosphorites at the e o transition and frequent recurrences of it afterwards suggests that a new mechanism came into play at that time namely the intensification of the advective flow of bottom water which accelerated the phosphorus cycle in contrast the absence of phosphorites younger than 12 ma suggests another fundamental change in process associated with the shift to a dry and cold climate that probably resulted in a decrease in the riverine input of labile phosphorus the drastic decrease in the frequency of hiatuses in ocean floor depositional records also indicates weakened bottom currents as a possible explanation for the absence of seamount phosphorite since 12 ma a phosphorus flux is a critical variable in modeling the response of the earth system to climate forcing in the geologic past thus the changes in phosphorus flux across the e o boundary and around 12 ma justify further study

climate forcing of fine grained deep marine systems in an active tectonic setting middle eocene ainsa basin spanish pyrenees abstract a multi proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m long middle eocene core from the ainsa basin spanish pyrenees representing deep marine siliciclastic sediments using detailed sedimentary logging high resolution multi element xrf geochemistry total organic carbon and stable carbon isotopes the well a6 was drilled as part of an industry university consortium through siltstones fine very fine grained sandstone turbidites and hemipelagic structureless mudstones that were deposited as overbank and off axis deposits from a sandy submarine fan and interfan deposits for comparative mineralogy between the sandstone turbidites and siltstones scanning electron microscopy sem and x ray diffraction xrd were undertaken on selected samples the sandstone turbidites show enrichment of detrital elements such as si zr and ti that can be linked to greater quartz and heavy mineral content compared with adjacent siltstones structureless hemipelagic mudstones comprise mainly clay minerals and carbonate we interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge whilst hemipelagic mudstones resulted from the suspension fall out of hypopycnal flows cyclostratigraphic analysis of the core reveals milankovitch cyclicity at frequencies of 0 03 cycles m short eccentricity 0 09 cycles m obliquity 0 15 cycles m precession couplet and 0 19 cycles m precession couplet orbital parameters appear to have controlled the cyclic delivery of coarser grained sediment by turbidity currents two equally plausible depositional models both as milankovitch driven can explain the cyclical changes in the deep marine sediments 1 climatic cycles with humid periods of enhanced chemical weathering increased storminess and greater riverine run off leading to high sediment flux to the deep basin as sandstone turbidites 2 climatic cycles with cooler conditions linked to high frequency small scale eustatic sea level fluctuations with lowstand shelf edge delta progradation resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows this study provides an insight into the likely depositional effects of orbitally induced climate change on the nature and delivery of terrigenous sediment into deep marine environments

testing for ice sheets during the mid cretaceous greenhouse using glassy foraminiferal calcite from the mid cenomanian tropics on demerara rise the mid cretaceous is widely considered the archetypal ice free greenhouse interval in earth history with a thermal maximum around cenomanian turonian boundary time ca 90 ma however contemporaneous glaciations have been hypothesized based on sequence stratigraphic evidence for rapid sea level oscillation and oxygen isotope excursions in records generated from carbonates of questionable preservation and or of low resolution we present new oxygen isotope records for the mid cenomanian demerara rise that are of much higher resolution than previously available taken from both planktic and benthic foraminifers and utilizing only extremely well preserved glassy foraminifers our records show no evidence of glaciation calling into question the hypothesized ice sheets and rendering the origin of inferred rapid sea level oscillations enigmatic simple mass balance calculations demonstrate that this cretaceous sea level paradox is unlikely to be explained by hidden ice sheets existing below the limit of 18 o detection

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

paleoceanographic and paleoclimatic evolution in the weddell sea antarctica during the middle eocene late oligocene from a coarse sediment fraction and clay mineral data odp site 689 abstract paleoceanographic and paleoclimatic variations from the middle eocene to the late oligocene in the antarctic area atlantic sector have been deduced from a coarse fraction and clay mineral analysis of odp site 689 leg 113 sediments in the middle eocene smectite rich sediments were a consequence of warm climate with alternating wet and dry seasons on the antarctic margins productivity in the maud rise area of the southern ocean was low no opal was deposited preservation of carbonate is very good carbonate preservation shows cyclic changes clinoptilolite is a common mineral at the middle late eocene boundary 40 8 ma productivity suddenly increased enough to allow preservation of opal skeletons clinoptilolite disappeared where opal appeared illite appearance points to cooling of antarctic climates the presence of detrital kaolinite indicates a change in oceanic circulation in the late eocene cyclic changes in productivity cycle length 0 42 ma were associated with clay mineral compositional variations sediments from colder highly productive periods generally contain more illite and less smectite than warmer ones the early oligocene was a period of very high productivity highest opal accumulation rates correspond to strongest carbonate dissolution cyclic changes in productivity with a mean cycle duration of 0 4 0 5 myr were associated with cyclic changes in clay mineral composition highest productivity intervals are generally those with highest smectite content because of strong erosion of sediments of the antarctic margins sediments from less productive warmer periods most of the time contain more illite in the late oligocene the intensity of physical weathering on antarctica was stronger as documented by increasing fluxes of illite muscovite amphiboles and talc ice expanded on the east antarctic continent lower productivity than in the early oligocene is indicated by lower accumulation rates of opal and weaker carbonate dissolution cyclic variations in productivity correlate to cyclic variations in illite and smectite contents as in the early oligocene

what controls opal preservation in tropical deep sea sediments measurements of opal preservation in deep sea sediment cores have been presented in three ways the opal concentration as a fraction of total dry weight opaltot the opal concentration normalized to calcite free dry weight opalcalcite free and me opal accumulation rate opal mar it is tempting to interpret changes in these indices as indicators of rates of biological production in past oceans based on theoretical constraints we argue that in typical tropical and subtropical sediments both opalcalcite free and opal mar reflect a significant artifact of dilution by other phases thus the band of high opalcalcite free in the equatorial pacific appears to be caused in large part by the high calcite in that region rather than by high opal productivity the best candidate for a reliable paleoproductivity proxy appears to be opaltot unfortunately present day opaltot data from tropical and subtropical regions show little or no systematic trend with the rain rate of opal pore water silica concentration data reveal that the apparent pore water opal solubility is not constant but correlates regionally with the rain rate of opal to the seafloor a model that treats opal as a single homogeneous phase with a single well defined solubility product predicts a strong dependence of opal concentration on rain rate in stark contrast to the data and a constant asymptotic pore water si two models representing opal as multiple heterogeneous phases with different solubilities are able to reproduce the observed asymptotic pore water si rain rate relationship but not the lack of rain rate trend in the opal concentration data only by assuming a systematic trend in the quality of opal i e the solubility as a function of opal production can we reproduce the observed pattern of opal preservation the implication of this study is that changes in opal preservation in the geologic record cannot simply be interpreted in terms of changes in surface ocean productivity until our understanding of opal diagenesis can be improved

cenozoic deep sea benthic foraminifers tracers for changes in oceanic productivity from late middle eocene through earliest oligocene high latitude regions cooled and by the end of the period continental ice sheets existed in antarctica diversity of planktonic microorganisms declined and modern groups of terrestrial vertebrates originated coeval faunal changes in deep sea benthic foraminifers have been related to cooling of deep waters and increased oxygenation cooling however occurred globally whereas species richness declined at high latitudes and not in the tropics the late eocene and younger lower diversity high latitude faunas typically contain common epistominella exigua and alabaminella weddellensis opportunistic phytodetritus exploiting species that indicate a seasonally fluctuating input of organic matter to the sea floor we speculate that the species richness gradient and increase in abundance of phytodetritus exploiting species resulted largely from the onset of a more unpredictable and seasonally fluctuating food supply especially at high latitudes

eocene oligocene calcareous nannofossils from maud rise and kerguelen plateau antarctica paleoecological and paleoceanographic implications abstract the evolution of the southern ocean climate during the late eocene late oligocene interval is examined through high resolution quantitative calcareous nannofossil analyses on samples from the southern ocean sections on maud rise and kerguelen plateau we determined the abundance patterns of the counted species to clarify the biostratigraphy which we correlated with high resolution magnetostratigraphy roberts a p bicknell s j byatt j bohaty s m florindo f harwood d m 2003a magnetostratigraphic calibration of southern ocean diatom datums from the eocene oligocene of kerguelen plateau ocean drilling program sites 744 and 748 in florindo f cooper a k o brien p a eds antarctic cenozoic palaeoenvironments geologic record and models palaeogeogr palaeoclimatol palaeoecol 198 145 168 florindo f roberts a p in press eocene oligocene magnetobiochronology of odp sites 689 and 690 maud rise weddell sea antarctica geol soc am bull and used this data to interpret paleoceanographic changes through the late eocene to late oligocene percentage plots of the individual species compared with r mode principal component and cluster analysis results allowed us to divide the assemblages into three groups temperate water taxa cool water taxa and no temperature affinity taxa we attempt correlations between these paleoecological groups and the major sea surface temperature sst variations with tectonic and paleoceanographic changes in the southern ocean during the late eocene the nannofossil assemblage data reveal that there were several minor sst decreases coolings from 36 to 34 ma before the eocene oligocene e o boundary a sharp cooling event dated at 33 54 ma earliest oligocene occurred about 160 kyr after the e o boundary which is dated at 33 7 ma relatively stable cool conditions are interpreted to persist until the latest oligocene when an increase in abundance of temperate water taxa which corresponds to an antithetical decrease in abundance of cool water indicators is recorded on the basis of our dating the opening of the drake passage allowing shallow water circulation began by 33 54 ma at the latest while the establishment of deep water connections through the tasmanian gateway occurred at 33 ma as suggested by exon et al proc odp init rep 189 2001 1

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

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

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

quasi static eocene oligocene climate in patagonia promotes slow faunal evolution and mid cenozoic global cooling abstract new local regional climatic data were compared with floral and faunal records from central patagonia to investigate how faunas evolve in the context of local and global climates oxygen isotope compositions of mammal fossils between c 43 and 21 ma suggest a nearly constant mean annual temperature of 16 3 c consistent with leaf physiognomic and sea surface studies that imply temperatures of 16 18 c carbon isotopes in tooth enamel track atmospheric 13 c but with a positive deviation at 27 2 ma and a strong negative deviation at 21 ma combined with paleosol characteristics and reconstructed leaf area indices rlais these trends suggest aridification from 45 ma c 1200 mm yr to 43 ma c 450 mm yr quasi constant map until at least 31 ma and an increase to 800 mm yr by 21 ma comparable map through most of the sequence is consistent with relatively constant floral compositions rlai and leaf physiognomy abundance of palms reflects relatively dry adapted lineages and greater drought tolerance under higher p co2 pedogenic carbonate isotopes imply low p co2 430 300 ppmv at the initiation of the eocene oligocene climatic transition arid conditions in patagonia during the late eocene through oligocene provided dust to the southern ocean enhancing productivity of silicifiers drawdown of atmospheric co 2 and protracted global cooling as the antarctic circumpolar current formed and earth cooled wind speeds increased across patagonia providing more dust in a positive climate feedback high tooth crowns hypsodonty and ever growing teeth hypselodonty in notoungulates evolved slowly and progressively over 20 ma after initiation of relatively dry environments through natural selection in response to dust ingestion a ratchet evolutionary model may explain protracted evolution of hypsodonty in which small variations in climate or dust delivery in an otherwise static environment drive small morphological shifts that accumulate slowly over geologic time

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

eocene oligocene mammalian faunal turnover in the hampshire basin uk calibration to the global time scale and the major cooling event a new high resolution c 1 ma mammalian record in continental eocene oligocene strata in the hampshire basin is used to investigate the nature and timing of the major europe wide mammalian faunal turnover termed the grande coupure whether this was caused by climate change or by competition with taxa dispersing from asia is controversial the mammalian faunas in this record after rarefaction analysis show a sharp reduction in diversity only after the grande coupure improved correlation of nw european successions to global events confirms the grande coupure as earliest oligocene it shows that a c 350 ka hiatus interrupts the hampshire and paris basin sequences prior to the first record of post grande coupure asian taxa hiatus bridging faunas from elsewhere in europe record mainly post grande coupure taxa suggesting that the turnover occurred early in the hiatus minimizing bias to the turnover pattern a previously unrecorded second smaller turnover involving european mammals only immediately precedes the grande coupure in the hampshire basin coinciding with vegetational change this turnover is judged not to represent cooling it is concluded that the grande coupure coincides with the earliest oligocene oi 1 glaciation and that climate change combined with competition to produce the turnover

eocene oligocene transition in the southern ocean history of water mass circulation and biological productivity high resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the eocene oligocene section at ocean drilling program site 689 maud rise weddell sea paleodepth about 1500 m were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper water column the benthic foraminiferal abundance and isotope records show short term fluctuations at periodicities of 100 and 400 ka implying orbitally driven climatic variations both records suggest that intermediate depth water chemistry and primary productivity changed in response to climate during the eocene productivity increased during cold periods and during cold to warm transitions possibly as a result of increased upwelling of nutrient rich waters in the oligocene in contrast productivity maxima occurred during intervals of low d18o values presumably warmer periods when a proto polar front moved to the south of the location of site 689 this profound transition in climate productivity patterns occurred around 37 ma coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger amplitude d18o fluctuations therefore we infer that at this time temperature fluctuations increased and a proto polar front formed in conjunction with the first distinct pulsations in size of the antarctic ice sheet we speculate that this major change might have resulted from an initial opening of the drake passage at 37 ma at least for surface and intermediate water circulation

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

the early opening between broken ridge and kerguelen plateau abstract reconstructions to total closure of the australia antarctic continents causes an unacceptable overlap of broken ridge and kerguelen plateau this has been partially resolved in the past by supposing that the northern part of kerguelen that is principally involved in the overlap is younger than the remainder we have revised the early reconstructions using a newly proposed breakup chronology of australia and antarctica which suggests that opening began at least 90 m y b p at an initially slow rate this eliminates the overlap problem without invoking major age differences within the kerguelen plateau we also suggest that the northeastern flank of kerguelen plateau may be underlain by the missing westward continuation of the diamantina zone it may have been isolated on the antarctic plate by a ridge crest jump at about anomaly 24 time that also formed the ob trench

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

first 40ar 39ar geochronology of lateritic manganiferous pisolites implications for the palaeogene history of a west african landscape abstract a pisolitic superficial formation deriving from the geochemical degradation of a previous massive manganiferous crust has been investigated in west africa using 40 ar 39 ar laser probe analysis on different generations of cryptomelane from fe mn pisolites and their embedding lateritic matrices prior to the 40 ar 39 ar geochronological analysis a detailed petrographical study has allowed the identification of successive assemblages from mn pisolites to fe mn pisolites embedded in mn rich and fe rich matrices respectively the age spectra obtained for pisolites including cores cortices and matrices enables the definition of three age clusters around 56 59 44 47 and 24 27 ma the first two age clusters with the petrographical and geochemical results obtained on the different assemblages indicate that the development of the pisolitic crust first induced mn leaching and fe al accumulations due to warmer and wetter climatic conditions in the age interval 56 47 ma that characterizes the tertiary greenhouse effect period propitious to bauxite formation in west africa the absence of 40 ar 39 ar ages between 44 and 27 ma only means that geochemical conditions for cryptomelane crystallisation were not fulfilled but could still be favourable to fe and or al oxy hydroxides formation before drier climatic conditions became rather effective at the oligocene period to sustain mechanical erosion rather than chemical weathering processes the age cluster 24 27 ma indicates however a reactivation of the manganiferous lateritic weathering late oligocene the 40 ar 39 ar dating results are discussed in terms of climatic condition changes during the palaeogene that were favourable to the genesis of either al and fe or mn oxy hydroxides in the course of development and evolution of the pisolitic formation the 40 ar 39 ar dating also provides a new highlight to large scale geomorphological patterns of west africa

late eocene oligocene paleoceanography in the southern indian ocean odp site 744 the late eocene through oligocene changes in the paleoceanography of the southernmost indian ocean have been reconstructed by means of a coarse fraction analysis of closely spaced samples 20 cm about 20 kyr from odp site 744 kerguelen plateau surface water productivity reconstructed from accumulation rates of opal skeletons and benthic foraminifers is low in the early late eocene increases at about 36 ma and shows a sharp increase to maximum values in the earliest oligocene in the early late oligocene it decreases gradually to a minimum and increases again to a maximum in the latest oligocene beside this general trend productivity varies in short term cycles of a duration of about 400 kyr 340 kyr in the latest oligocene with maxima in productivity in warmer oligocene periods these productivity variations are reflected by strong variations in carbonate dissolution changes in bottom water mass chemistry have been deduced from the degree of carbonate dissolution and it s relation to productivity proxies following kennett and stott 1990 it is suggested that a proto antarctic bottom water proto aabw and an overlying warm saline deep water wsdw from low latitudes shifted vertically and latitudinally with time and exerted their influence on the sediments of site 744 proto aabw is detected by means of strong carbonate dissolution when productivity is low wsdw is detected by means of an excellent carbonate preservation despite high productivity terrigenous material occurs as very coarse ice rafted detritus ird in the late eocene 167 168 5 mbsf and after a main shift in oxygen isotopes in the early oligocene very low amounts of 40 125 m sized mica and very few quartz grains occur only in high productivity periods and at the transition from low to high productivity periods these occurrences are attributed to wind current supply during warmer oligocene intervals

eocene to miocene terrigenous inputs and export production geochemical evidence from odp leg 177 site 1090 abstract changes in ocean circulation and climate during the cenozoic led to the development of the antarctic circum polar current acc and permanent antarctic ice sheets however the timing of the opening of the drake passage and the establishment of the acc is poorly constrained we present geochemical proxies of terrigenous inputs and export production at a single site in the southeastern atlantic ocean that suggest the drake passage had opened to intermediate and deep water by 32 8 ma two separate styles of sedimentation and geochemical composition of terrigenous material are observed with the change in sediment geochemical characteristics occurring at 32 8 ma middle to late eocene records are highly variable while latest eocene to early miocene records exhibit cyclic variations in elemental records and terrigenous material based on al ti ratios metal sources change from continental crust to oceanic crust sources at the eocene oligocene transition which we suggest reflects a change in deep water circulation phosphorus metal ratios indicate that there are two distinct intervals of enhanced export production one in the middle eocene and one throughout the eocene oligocene transition elevated al ti ratios greater than any lithic source in the middle eocene provide evidence of particulate scavenging and thus increased export production barium ratios further support changes in productivity in the middle eocene and at the eocene oligocene transition permanent changes in the ba concentration record in the early oligocene further support a change in deep water circulation due to the opening and deepening of the drake passage at 32 8 ma

diatom biomarkers during the eocene oligocene transition in the il pinskii peninsula kamchatka russia abstract marine strata of the il pinskii section northeastern kamchatka russia expose the complete eocene oligocene e o succession although diatom fossils are very poorly preserved in these mudstones and carbonate concretions oligocene mudstones contain typical diatom biomarkers the c 25 highly branched isoprenoids hbis in concentrations that rise markedly above the e o boundary the abundance of the dinoflagellate biomarkers known as dinosteranes decreases through the late eocene to oligocene interval a rise in the abundance of hbis through this time interval suggests that the post e o diatom community of the northwest pacific region was dominated by the genus rhizosolenia hbis in sedimentary rocks spanning the e o transition may show the appearance of the oligocene marine diatom rhizosolenia oligocaenica and may therefore be useful as biomarkers in regional biostratigraphic correlation of the northwest pacific during this interval an e o boundary in the il pinskii section is proposed based on hbi distribution

carbonate dissolution and abyssal hydrography in the atlantic ocean abstract surface sediment samples from two regions in the eastern atlantic angola basin and cape verde basin and two regions in the western atlantic brazil basin and vema channel were examined to evaluate the relationship among carbonate dissolution abyssal hydrography and carbonate chemistry of the water column at each of these locations the position of the lysocline was determined carbonate saturation 1 was calculated and major deep water mass boundaries were identified as previously observed the correlation among these variables is strikingly different between the eastern and western atlantic in the vema channel and the brazil basin there is a first order correlation among the position of the lysocline the benthic thermocline aabw nadw boundary and the transition from saturation to undersaturation with respect to carbonate this relationship breaks down in the eastern atlantic where there is no noticeable benthic thermocline and the lysocline occurs significantly deeper than the saturation undersaturation transition

early cenozoic glaciation antarctic weathering and seawater 87sr 86sr is there a link abstract stable and radiogenic isotopic and sedimentological data from sub antarctic deep sea sediment cores reveal a temporal link between changes in seawater 87 sr 86 sr ratios and major episodes of late eocene early oligocene climate change the 87 sr 86 sr records show two major inflections one at 38 39 ma near the middle late eocene boundary followed by another at 33 4 ma similarly the oxygen isotope ice rafted debris and clay assemblage records indicate two important climatic events the appearance of alpine glaciers and or small ice sheets on antarctica in the late eocene at 38 39 ma followed by a rapid transition to larger and more permanent temperate ice sheets in the early oligocene at 33 4 ma moreover during the early oligocene 30 33 ma three to four inferred peaks in glacial activity appear to coincide with subtle steps in the 87 sr 86 sr record the coupled variations in climate and seawater sr isotope ratios during the eocene oligocene imply a strong causal link between the two either changes in climate directly influenced patterns of continental weathering and hence seawater chemistry and or a tectonic event e g uplift as reflected in weathering and seawater chemistry triggered relatively abrupt changes in global climate