eocene bipolar glaciation associated with global carbon cycle changes the transition from the extreme global warmth of the early eocene greenhouse climate 55 million years ago to the present glaciated state is one of the most prominent changes in earth s climatic evolution it is widely accepted that large ice sheets first appeared on antarctica 34 million years ago coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world s oceans and that glaciation in the northern hemisphere began much later between 10 and 6 million years ago here we present records of sediment and foraminiferal geochemistry covering the greenhouse icehouse climate transition we report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical pacific and south atlantic oceans from 42 million years ago with a permanent deepening 34 million years ago the most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1 5 per mil suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres variations in benthic carbon isotope ratios of up to 1 4 per mil occurred at the same time indicating large changes in carbon cycling we suggest that the greenhouse icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago between 55 and 34 million years ago earth switched from a warm greenhouse ocean climate system to the icehouse that we now enjoy frustratingly the few oceanographic datasets that exist for this key period are of low resolution tripati et al now present measurements of sediment and foraminiferal geochemistry that provide the first continuous high resolution records for this period the data suggest that northern hemisphere glaciation started 34 million years ago rather than between 10 and 8 million years ago as previously thought

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

late eocene to early oligocene dinoflagellate cysts from the priabonian type area northeast italy biostratigraphy and paleoenvironmental interpretation abstract marginal marine late eocene through early oligocene dinoflagellate cyst successions have been studied from the type area of the priabonian stage northeast italy the results allow the recognition of dinoflagellate zones previously defined in bio and magnetostratigraphically well calibrated pelagic sequences from central italy thus providing a first order correlation of the priabonian stage to the standard chronostratigraphic scale with unprecedented precision within this detailed biostratigraphic framework successive shifts in the composition of the dinoflagellate cyst assemblages are interpreted in terms of sea level and sea surface temperature sst fluctuations the evaluation of ecologically and sedimentary controlled changes in the composition of dinoflagellate cyst assemblages in combination with sequence stratigraphic analysis allows the reconstruction of third and fourth order sea level fluctuations the third order sea level fluctuations appear to correspond to exxon cycles ta4 1 4 5 the stratigraphically and palaeoenvironmentally important late eocene dinoflagellate cyst species glaphyrocysta priabonensis sp nov is formally described

magnetostratigraphy of eocene oligocene boundary sections in italy no evidence for short subchrons within chrons 12r and 13r abstract the marine magnetic polarity record shows many small scale anomalies that could be due to short normal polarity subchrons within chrons 12r and 13r new examination of published magnetostratigraphic results from a section near gubbio shows that suspected short chrons in this section are probably not real the eocene oligocene boundary in the stratotype section at massignano lies just above a tentatively identified normal magnetozone that might correlate with a possible short normal subchron within chron 13r in a new investigation of the weathered marlstones in this section acquisition and thermal demagnetization of irm reveal a magnetic mineralogy dominated by magnetite with minor amounts of maghemite and hematite vector analysis of the natural remanent magnetization discloses a complex structure in some samples at least two and up to four components were isolated the magnetostratigraphy based on a magnetite component correlates well to the main features of the chron 13n 16n polarity sequence no short polarity subchrons are found although the resolution is inadequate to exclude the possibility that they exist in particular we did not find a short normal polarity magnetozone previously located close to the eocene oligocene boundary the results of this study favour the interpretation that low amplitude magnetic anomalies represent geomagnetic intensity fluctuations rather than unresolved short polarity intervals

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

frequency dependence of q in the mantle underlying the shield areas of eurasia part 11 analyses of long period data summary long period multiple s and scs phases observed in northern europe were analysed to determine mantle attenuation in the 0 02 to 0 2 liz range under the eurasian shield two groups of events were used deep fareastern earthquakes and large earthquakes near the edges of the shield areas of eurasia the q of the upper mantle under the eurasian shield region was estimated in the time domain by taking amplitude ratios and in the frequency domain by taking spectral amplitude ratios among various arrivals under shield regions ss s amplitude ratios and multiple scs amplitude ratios give ti 2 5 3 0 s in the 0 02 to 0 20 hz band the results show that the upper mantle q under this shield area is higher than the global average but less than the q values inferred from our studies of short period data in the same area preliminary results suggest significantly higher under tectonic regions in the same frequency band

similarities between planktonic and larger foraminiferal evolutionary trends through paleogene paleoceanographic changes abstract the paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may in part reflect changes in nutrient flux to surface waters following the terminal cretaceous extinctions faunas were dominated by a few cosmopolitan opportunistic species more specialized k strategists in both groups diversified during the paleocene dominating into the early eocene consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters high latitude cooling intensified in the middle eocene promoting diversification of less specialized taxa characteristic of cooler and deeper waters higher latitudes meridional upwelling zones and boundary currents geographic ranges of warm water taxa diminished and fragmented yet many species survived thus global diversities during the middle eocene were the highest in the cenozoic as cooling and increased rates of nutrient flux further intensified in the late eocene extinction rates of warm water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms so diversity dropped to intermediate levels where it remained through the late eocene and oligocene previous observations that planktonic foraminiferal faunas dominated by warm water taxa are often replaced by cool water faunas even though oxygen isotopes only recorded relatively minor cooling can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction as well as to temperature change itself

carbon isotope stratigraphy in shallow water carbonates implications for cretaceous black shale deposition a barremian to albian succession on mount kanala part of a tethyan isolated carbonate platform was investigated for its 13c variations the limestone sequence is composed of a series of peritidal shallowing upward cycles with clear petrographic evidence for strong early diagenetic overprinting related to repeated subaerial exposure despite significant impact of diagenesis the observed changes in 13c can be very well correlated with deep water sections from different ocean basins and shallow water carbonate platforms in the middle east this lends further support to the applicability of 13c variations for stratigraphic purposes in shallow water limestones using the 13c signal time resolution in lower cretaceous platform carbonates can be significantly increased independent of bio zonations often hampered by ecological variability cyclostratigraphic analysis of the aptian part of the section shows that strong positive excursions of the cumulative departure from mean cycle thickness of the peritidal shallowing upward cycles coincide with global positive 13c excursions this and the fact that positive shifts in the 13c record are preserved within shallow water limestones provide evidence that black shale accumulation in the ocean basins occurred during sea level rise and flooding of platform tops integration of carbon isotope cyclo and sequence stratigraphic results from different carbonate platforms indicate that strong positive global 13c shifts and concurrent organic carbon burial during black shale deposition are ultimately caused by rapid rises of eustatic sea level hence the rate of change of eustatic sea level is considered to play a crucial role in black shale accumulation in the global ocean basins during the cretaceous

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

strontium isotope stratigraphy in the upper cenomanian shallow water carbonates of the southern apennines short term perturbations of marine 87sr 86sr during the oceanic anoxic event 2 abstract strontium isotope stratigraphy of shallow water carbonates from the southern apennines italy indicates that the late cenomanian early turonian evolution of marine 87sr 86sr is not accurately depicted by the marine reference curve using the low mg biotic calcite of well preserved rudist shells as a study material and carbon isotope stratigraphy for correlation to the standard ammonite biozonal scheme of northern europe new 87sr 86sr values are proposed for four different stratigraphic levels the middle and uppermost part of the guerangeri zone the lower and upper part of the geslinianum zone the southern apennines data suggest that a sharp positive shift at the onset of oceanic anoxic event 2 precedes the well known sr isotope negative shift the positive shift is interpreted in terms of enhanced rates of chemical weathering driven by global warming forced by volcanogenic co2 outgassing a stratified ocean is invoked to reconcile the high gradient and the short lag time of the perturbation with estimates of present day total mass and residence time of strontium in the ocean the sharp switch to the negative shift is related to the collapse of water column density gradient driven by thermal instability during a late cenomanian cool event more active ocean circulation suddenly delivered to surface waters the signal of increased submarine volcanism that had accumulated in deep waters

glacioeustasy during the middle eocene insights from the stratigraphy of the hampshire basin uk the sedimentary strata of the hampshire basin constitute some of the best preserved palaeogene sequences worldwide and include the traditional unit stratotype for the bartonian 36 9 41 4 ma the barton clay formation at alum bay on the isle of wight iow was studied to assess the evidence for middle eocene sea level variation in records of grain size sediment properties faunal assemblage foraminiferal diversity indices and foraminiferal stable isotopes sedimentary cycles of 1 10 myr third order and 0 2 0 5 myr fourth order duration are reported and interpreted to reflect 20 60 metre variations in water depth additionally an integrated magneto bio chemostratigraphical age model for the succession at alum bay is presented and new and published litho and bio stratigraphical markers are used to correlate additional successions based on this age model it appears that during the late lutetian and early bartonian 42 38 ma water depth variation identified within the basin was synchronous sedimentary and fossil evidence supports episodic uplift in the eastern part of the hampshire basin during the bartonian which at present precludes the calculation of eustatic sea level however the amplitude and frequency of water depth variations identified in the barton clay formation and correlations to published sea level curves are consistent with a component of these changes being glacioeustatic during the middle eocene there is also evidence for a large excursion delta 18o 1 per mille sign in the mono specific benthic foraminiferal oxygen isotope record alum bay 39 9 ma which is correlated to the isotope excursion at the middle eocene climatic optimum previously reported in the southern ocean and other localities a contemporaneous water depth increase of 40 m at alum bay may indicate that a component of this global oxygen isotope excursion results from a reduction in continental ice storage

late pleistocene and holocene cool water carbonates of the western mediterranean sea post glacial neritic cool water carbonates of the western mediterranean sea were examined by means of hydroacoustic data sediment surface sampling and vibrocoring to unravel geometries and to reconstruct sedimentary evolution in response to the last sea level rise the analysed areas located on the alboran ridge in the bay of oran and at the southern shelf of the island of mallorca are microtidal and bathed by oligotrophic to weakly mesotrophic waters seasonal water temperature varies between 13 c and 27 c echosounder profiles show that the bay of oran and the southern shelf of mallorca are distally steepened ramps while the alboran ridge forms a steep flanked rugged plateau around the alboran island in the three areas an up to 10 m thick post glacial sediment cover overlies an unconformity in oran and mallorca stacked lowstand wedges occur in water depths of 120 to 130 m on the alboran ridge and in the bay of oran highstand wedges occur at 35 to 40 m up to 5 m long cores of upper pleistocene to holocene successions were recovered in water depths between 40 and 81 m deposits contain more than 80 carbonate with mixed carbonate volcaniclastics in the lower part of some cores in alboran the carbonates consist of up to 53 of aragonite and up to 83 of high magnesium calcite radiocarbon dating of bivalve shells coralline algae and serpulid tubes indicates that deposits are as old as 12 400 cal yr bp the carbonate factories in the three areas are dominated mostly by red algae but some intervals in the cores are richer in bivalves a facies rich in the gastropod turritella reflecting elevated surface productivity is restricted to the mallorca shelf rhodoliths occur at the sediment surface in most areas at water depths shallower than 70 m they form a 10 to 20 cm thick veneer overlying rhodolith poor bioclastic sediments which nonetheless contain abundant red algal debris this rhodolith layer has been developing for the past 800 to 1000 years similar layers at different positions in the cores are interpreted as reflecting in situ growth of rhodoliths at times of reduced net sedimentation sedimentary successions in the cores record the post glacial sea level rise and the degree of sediment exposure to bottom currents deepening upward trends in the successions are either reflected by shallow to deep facies transitions or by a corresponding change of depth indicative red algae there are only weak downcore variations of carbonate mineralogy which indicate that no dissolution or high magnesium to low magnesium calcite neomorphism occurs in the shallow subsurface these new data support the approach of using the recent facies distribution for interpretation of past cool water low energy microtidal carbonate depositional systems hydroacoustic data show that previous pleistocene transgressive and highstand inner ramp deposits and wedges were removed during sea level lowstands and accumulated downslope as stacked lowstand wedges this suggests that under conditions of high amplitude sea level fluctuations the stratigraphic record of similar cool water carbonates may be biased

sr isotope stratigraphy of the upper jurassic of central portugal lusitanian basin based on oyster shells strontium isotope stratigraphy was performed on oyster shells from the late jurassic of the lusitanian basin central portugal this represents the first approach to obtain numerical ages for these strata the new chronostratigraphic data provide a more precise age determination of several units after a basin wide hiatus sedimentation in the late jurassic is proven in the cabo mondego and cabacos formations to resume as early as the middle oxfordian the alcobaca formation can be placed in the latest late oxfordian to late kimmeridgian while data from the upper part of the abadia formation indicate an early to late kimmeridgian age the farta pao formation ranges from the latest kimmeridgian to the latest tithonian the largely synchronous sobral arranho i and arranho ii members are overlain by the late early to late tithonian freixial member the brief local carbonate incursion of the arranho i member marks the kimmeridgian tithonian boundary oysters are shown once more to be suitable for strontium isotope studies their calcitic shells are often unaffected by diagenesis in particular for marginal marine jurassic and cretaceous strata where belemnites are usually absent oysters may serve as a valuable tool for isotope stratigraphy

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

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

dinoflagellate cyst stratigraphy of the eocene oligocene transition in central italy abstract eight dinoflagellate cyst zones based on the massignano and monte cagnero sections in central italy provide high resolution control for the eocene oligocene e o transition most of these zones have been recognized in the time equivalent contessa highway section and are calibrated against previously established magneto and biostratigraphies the invasion of the mediterranean area by several higher latitude dinoflagellate taxa marks the e o boundary as characterized by the last occurrence of the hantkeninids planktic foraminifers calibrated against a horizon just above the youngest normal polarity event within chron c1 3r quantitative and qualitative dinoflagellate events across the e o boundary allow the recognition of warmer and cooler successive intervals of sea surface temperature in addition to apparent sea level fluctuations our data indicate that latest eocene warm conditions and a sea level highstand were rapidly replaced by short term cooler conditions and a lowstand across the e o boundary horizon following a shortterm warmer interval and a highstand during the earliest oligocene a second cool and lowstand episode occurred this cool interval was of greater magnitude and duration than the one at the e o boundary horizon and may correspond to the globally recognized cooling event reported from the basal part of chron c1 3n

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

strontium isotopes in early jurassic seawater abstract the analysis of well preserved well dated belemnites and oysters from the jurassic of great britain has resulted in a well constrained detailed seawater strontium isotope curve for the early jurassic the preservation of fossil low mg calcite was monitored using mn fe 13 c and 18 o iron was the most useful indicator with about 75 of the samples containing more than 150 ppm fe showing 87 sr 86 sr ratios elevated relative to adjacent points on the curve high mn concentrations less often correlated with elevated 87 sr 86 sr ratios however low mn concentrations 87 sr 86 sr 13 c and 18 o proved to be insensitive to diagenesis as it affects 87 sr 86 sr the principal features of the strontium isotope curve include a rise to about 0 70772 in the latest triassic and earliest jurassic hettangian from the hettangian the curve begins a roughly linear descent through the sinemurian and pliensbachian following a small levelling off and increase in the late pliensbachian the curve falls rapidly to its early jurassic minimum of 0 70706 it then gently increases through the toarcian until the falciferum zone where it shows an apparently abrupt increase to 0 70719 before continuing its slow increase to 0 70728 in the aalenian bajocian middle jurassic this reversal of the downwards trend established in the sinemurian and pliensbachian had not been previously identified the sinemurian and pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones 0 5 to 1 ma

neritic isotope and sedimentary records of the eocene oligocene greenhouse icehouse transition the calcare di nago formation northern italy in a global context abstract from the middle eocene to early oligocene the earth experienced the most significant climatic cooling of the cenozoic era the eocene oligocene transition eot represents the culmination of this climatic cooling leading to the onset of the antarctic glaciation and consequently to the beginning of the present day icehouse world whereas the response of deep sea systems to this climate transition has been widely studied its impact on the shallow water carbonate realm is poorly constrained here the sedimentary expression of the eot in two shallow marine carbonate successions nago and san valentino northern italy belonging to the calcare di nago formation is presented the chronostratigraphic framework was constructed by integrating litho bio and isotope stratigraphic data c and sr isotopes allowing to correlate these shallow marine successions with pelagic sections in central italy massignano tanzania tdp sites 12 and 17 and the indian ocean odp site 744 within several sections in northern italy including nago and san valentino a priabonian late eocene transgression is recorded oxygen isotopes of odp site 744 show a coeval negative shift of 0 4 suggesting a glacio eustatic origin for this transgression in the nago and san valentino sections no prominent sequence boundary has been detected that would indicate a rapid sea level drop occurring together with the positive shift in 18o defining the eot 1 cooling event instead a gradual shallowing of the depositional environment is observed at tdp sites 12 and 17 the eot 1 is followed by a negative shift in 18o of around 0 4 which correlates with a relative deepening of the environment in the studied sections and suggests a melting pulse between eot 1 and the oligocene isotope event 1 oi 1 the positive 18o shift related to the oi 1 translates in san valentino into a change in carbonate factory from a photozoan association dominated by larger benthic foraminifera corals and red algae to a heterozoan association dominated by bryozoans the same bryozoan facies occurs in several italian localities near the eocene oligocene boundary this facies is interpreted to represent an analogue of modern cool water carbonates and results from a cooling pulse of at least regional scale associated to the oi 1 event

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

ecology of extant nummulitids and other larger benthic foraminifera applications in palaeoenvironmental analysis abstract larger benthic foraminifera lbf are important contributors to modern and ancient tropical shallow marine sediments over the past 30 years a substantial body of literature has built up on the ecology of modern lbf especially in terms of their environmentally sensitive depth distribution reproductive strategy and morphology and the symbiotic relationship between many larger foraminifera and photosynthetic algae over the same period the extinct genus nummulites which is abundant in eocene sediments of southern europe north africa and the arabian peninsula has increasingly been studied principally because significant volumes of hydrocarbons have been discovered reservoired within nummulitic limestones offshore tunisia and libya the modern ecological studies of lbf provide a powerful tool with which to develop palaeoecological models for fossil nummulites and other symbiont bearing larger foraminifera in the rock record

marine biotic signals across a late eocene impact layer at massignano italy evidence for long term environmental perturbations the eocene oligocene transition marks the passage from greenhouse conditions to an icehouse state with progressive global cooling starting in the early middle eocene the late eocene presents substantial evidence for extraterrestrial impacts whose effects on living organisms and climatic changes are still not completely clear a high resolution microfloral and faunal investigation has been carried out in a 4 m thick segment of the massignano global stratotype section and point for the eocene oligocene boundary the studied interval includes a late eocene 35 7 0 4 myr old impactoclastic layer containing several cosmic signatures the impact event recorded at massignano had no abrupt dramatic effects on marine biota in terms of extinction however significant quantitative changes in the calcareous plankton and dinoflagellate cyst assemblages occurred 60 kyr after the impact event the observed pattern is intepreted as reflecting a long term re organization of water structure

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

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

multiproxy record of abrupt sea surface cooling across the eocene oligocene transition in the gulf of mexico the eocene oligocene transition eot ca 33 34 ma was a time of pronounced climatic change marked by the establishment of continental scale antarctic ice sheets the timing and extent of temperature change associated with the eot is controversial here we present multiproxy eot climate records 15 34 k y resolution from st stephens quarry alabama usa derived from foraminiferal mg ca d18o and tex86 we constrain sea surface temperatures ssts in the latest eocene and early oligocene and address the issue of climatic cooling during the eot paleotemperatures derived from planktic foraminifera mg ca and tex86 are remarkably consistent and indicate late eocene subtropical ssts of 28 c there was substantial and accelerated cooling of ssts 3 4 c through the latest eocene precursor d18o shift eot 1 prior to oligocene isotope 1 oi 1 our multispecies planktic foraminiferal d18o records diverge at the e o boundary 33 7 ma signifying enhanced seasonality in the earliest oligocene in the gulf of mexico