eocene climate record of a high southern latitude continental shelf seymour island antarctica a high resolution record of eocene paleotemperature variation is preserved within the high southern latitude marine shelf succession of the la meseta formation on seymour island off the ne side of the antarctic peninsula 87 sr 86 sr ratios of bivalve shell carbonate indicate that the la meseta formation spans virtually the entire eocene and suggest the presence of an early middle eocene unconformity paleoclimatic and paleoceanographic inferences are based on the stable oxygen and carbon isotope values of two genera of bivalves collected with a high degree of stratigraphic resolution within the formation and with multiple replicate samples from each horizon 18 o data indicate roughly 10 c of cooling from the early eocene climatic optimum 15 c through the end of the eocene minimum 5 c much of which took place in two comparatively short intervals at ca 52 and ca 41 ma many features of the isotope curves generated from this eocene shelf section are apparent in 18 o and 13 c data from the southern and global oceans including warm intervals that likely correspond to the early and middle eocene climatic optima eeco and meco a rapid middle eocene shift to much more positive values is the most signifi cant in the section and refl ects a drop to universally cooler temperatures in the late middle and late eocene that might also be associated with a short lived glacial advance however even using a somewhat depleted value for 18 o of seawater in the antarctic peninsular region average seymour island shelf water paleotemperatures did not reach freezing before the end of the eocene 13 c data similarly refl ect the documented middle eocene surface ocean enrichment followed by more negative values but depletion is much more pronounced on seymour island and persists for the remainder of the eocene suggesting a combination of upwelling metabolic effects and or atypical carbon cycling on the shelf in this region isotope data capture information about changes in the paleoenvironment that also had consequences for the biota as published paleontological records document marked change in the nature of terrestrial and marine biota at this time the fact that middle eocene cooling and biotic turnover in the peninsular region correspond well in time to the proposed initial opening of drake passage suggests that the formation of gateways in addition to changes in pco 2 had signifi cant consequences for the earth s climate system during the paleogene

dinoflagellate cysts sea level changes and planktonic foraminifers across the cretaceous tertiary boundary at el haria northwest tunisia abstract dinoflagellate cysts and planktonic foraminifers have been studied from the cretaceous tertiary k t boundary interval at el haria northwest tunisia a high resolution integrated biostratigraphy is presented the k t boundary is drawn at the level of extinction of cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species danea californica the final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay this reduction is coeval with reported anomalies in siderophyle elements and 13 c values in the same area dinoflagellate cysts do not show accelerated rates of extinction at k t time associations of dinoflagellate cysts however change drastically and parallel changes in relative numbers of sporomorphs spores and pollen and in the quantity of land derived organic matter jointly these changes reflect a rapidly falling sea level during the final 17 kyr of the mesozoic which culminates at the level of the k t boundary this steep sea level fall at k t time represents a peak regressive pulse at the end of the well documented latest cretaceous regressive trend this short term sea level fall might show to be a wide spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas since deep waters in cretaceous oceans were primarily produced in shallow marginal seas the rate of formation of deep water might have been minimized at k t time minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients consequently phytoplankton productivity rapidly diminished which in combination with a weakened thermal gradient pushed the highly depth stratified cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions the oscillating rise in sea level at the beginning of the cenozoic reinforced the upward mixing of relatively cool and nutrient rich deeper water steepened the thermocline and replenished the photic layer with nutrients concomitant niche differentiation in the photic layer progressively stimulated morphological innovation amongst early cenozoic planktonic foraminifers the final return of normally sized planktonic foraminifers and of stable and well balanced dinoflagellate cyst associations at about 125 kyr after the k t boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels the earliest cenozoic planktonic foraminiferal species globoconusa minutula and parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

palaeoenvironmental analysis of late cretaceous dinoflagellate cyst assemblages using high resolution sample correlation from the western interior basin usa abstract the cretaceous geological record of the western interior seaway of north america is one of the most thoroughly studied in the world extensive work on the lithostratigraphy biostratigraphy and geochemistry has resulted in a high resolution chronostratigraphic framework allowing precise bed by bed correlation between sections hundreds of kilometres apart late cenomanian to early turonian marine strata from five sites along a transect from arizona to kansas have been analysed for their palynological assemblages at the time of deposition the sites are thought to have been palaeoenvironmentally very different in terms of shoreline proximity bathymetry and salinity precise correlation of samples between the sites using the high resolution stratigraphy has provided a valuable testing ground for a comparison of the dinoflagellate cyst assemblages a number of species are determined to have palaeoenvironmental preferences in terms of salinity and shoreline proximity and this is supported by integration with the lithostratigraphy macropalaeontology micropalaeontology and geochemistry previous palaeoenvironmental interpretations suggest that one kansas site had comparatively much higher levels of primary productivity and this is reflected in the high ratio at this site of peridinioid to gonyaulacoid cysts the high resolution correlation also shows that a number of the biostratigraphically useful dinoflagellate cyst taxa had synchronous or near synchronous range tops and bases across the basin this integrated high resolution study with tight chronostratigraphic control supports the use of dinoflagellate cysts not only as biostratigraphic tools but also for palaeoenvironmental and palaeoecological interpretation

covarying sedimentary and biotic fluctuations in lower middle eocene pyrenean deep sea deposits palaeoenvironmental implications abstract analyses of expanded 1975 to 3330 m thick deep marine ypresian lutetian successions from the pamplona and basque basins w pyrenees demonstrate a recurring pattern of coeval sedimentary and biotic changes intervals rich in resedimented deposits are typified by high latitude planktonic foraminiferal indices whereas intervals devoid of large scale resedimented deposits megabreccias are characterized by low latitude planktonic foraminiferal indices data from the megabreccia free intervals record a reasonably good correlation between the vertical trend of planktonic foraminiferal indices from the two pyrenean basins and the global curve of oxygen isotopes from deep sea records for instance the early eocene climatic optimum and the long lasting late ypresian lutetian cooling are respectively recorded in the studied successions by an increase and by a progressive decline in abundance in low latitude planktonic foraminiferal indices this correlation may support the assumption that changes of planktonic foraminiferal indices in the megabreccia free intervals were forced by global climatic changes the dominance of high latitude planktonic foraminiferal indices in the megabreccia bearing intervals is more difficult to interpret such dominance might record global cooling episodes that resulted in eustatic lowstand resedimentation events however the climatic cooling and sea level fall do not fully explain the characteristics of these intervals a reasonable scenario is that tectonically induced resedimentation processes resuspended large volumes of mud and organic matter which led to the eutrophication of seawater such eutrophication would preferentially affect low latitude oligotrophic planktonic foraminiferal species and lead to a relative or absolute increase in the cosmopolitan opportunistic species that typify high latitude groups

numerical simulations of tidal and wind driven circulation in the cretaceous interior seaway of north america twenty two numerical experiments using a multi layer numerical model of turbulent flow in shallow seas better define fluid circulation and sediment transport paths in the cretaceous interior seaway of north america each experiment consists of a different combination of paleogeography paleobathymetry coriolis acceleration boundary tidal amplitudes wind stresses and bed friction the paleogeographies and paleobathymetries represent three seaway configurations a seaway of intermediate size and depth 200 m during a transgressive peak t5 in late albian time a seaway of maximum size and depth 400 m during peak transgression t6 in early turonian time and a seaway of minimum size and depth 100 m during a peak regression r8 in the campanian values for the other key model parameters are m 2 co oscillating boundary tides of 0 1 to 0 2 m range at the arctic ocean boundary and 0 5 to 1 m range at the proto gulf of mexico boundary coriolis accelerations corresponding to 30 n 45 n and 60 n latitude chezy friction factors ranging from 31 to 70 m s 1 and average winter winds and two winter storms computed by the community climate model at the national center for atmospheric research for paleogeographic conditions during the late albian results of the numerical experiments and comparison of these results with geologic observations allow the following conclusions 1 circulation in the seaway was generally storm dominated 2 typical winter storms crossing the seaway from west to east generated 0 3 m s 1 shore parallel geostrophic currents on the shelves north of arizona at first flowing weakly to the north but later during the storm flowing strongly to the south 3 extreme storms could have produced 0 8 m s 1 currents over the shelves and 0 3 m s 1 currents in 200 m of water 4 co oscillating tides propagated into the seaway as progressive kelvin waves and therefore tidal ranges in the seaway were mesotidal to macrofdal along the southeastern margin but microtidal everywhere else 5 significant deep water wave heights and periods of the fully developed wave field are predicted to have been 5 to 6 m high and 10 s respectively the northwestern shore of the seaway would have experienced these storm waves approaching from the north and thus net sediment drift should have been to the south limited available field data support these conclusions

milankovitch forcing of bioturbation intensity in deep marine thin bedded siliciclastic turbidites abstract trace fossils have been used to infer a milankovitch type control on pelagic and hemipelagic sediments but there have been no comparable studies in deep marine siliciclastic turbidite successions here we present the results of a quantitative analysis of trace fossil abundance and intensity in an essentially continuous middle eocene 230 m long well a6 core comprising very thin and thin bedded siliciclastic turbidites in the deep marine ainsa basin spanish pyrenees after removing the sediment slides and debris flow deposits as these represent geologically instantaneous events approximately two orders of magnitude thicker than the typical laminated turbiditic sediments in the core spectral analysis was conducted on the bioturbation intensity data spectral analysis of bioturbation intensity in the a6 core suggests for the first time from a siliciclastic turbidite succession at a tectonically active plate margin thrust top basin in a foreland basin a cyclicity that is interpreted to reflect the 41 kyr and an 112 kyr possibly an average of the 95 and 125 kyr milankovitch frequencies we propose that this drove environmental changes in bottom water conditions in the ainsa basin most likely leading to critically varying levels of oxygenation stratification of bottom waters our age model for the ainsa basin 4 km of deep marine sediments in 10 myr yields an average sediment accumulation rate of 40 cm kyr 1 that is consistent with that inferred from the spectral analysis 30 cm kyr 1 for fine grained sedimentation an implication of these results is that global environmental change probably glacio eustasy acted as a driver on deep marine siliciclastic sedimentation patterns during the middle eocene

calibration between eustatic estimates from backstripping and oxygen isotopic records for the oligocene eustatic estimates from the backstripping of oligocene sections are compared quantitatively with d 18 o data each of the nine oligocene d 18 o events maxima identified in previous studies correlates with a stratigraphically determined sea level lowstand oxygen isotopic records from planktonic foraminifers from western equatorial atlantic ocean drilling program odp site 929 indicate an isotopic increase of 0 16 per 10 m decrease in the depth of the ocean apparent sea level asl amplitudes of asl change also correlate with moderate and high resolution benthic foraminiferal d 18 o records from odp sites 803 western tropical pacific and 929 and from deep sea drilling project dsdp site 522 south atlantic ocean with an isotopic change of 0 22 per 10 m of asl change r 2 5 0 807 and 0 960 respectively and with records from odp site 689 southern ocean 0 13 per 10 m of asl change r 2 5 0 704 this correlation suggests that southern ocean deep water temperature changes were smaller than tropical sea surface temperature changes between million year scale glacials and interglacials it also suggests that the deep sea southern ocean records may provide the best means to calibrate sea level to oxygen isotopes

onset of cenozoic antarctic glaciation abstract this paper considers the wide range of evidence both direct and indirect for the onset of cenozoic antarctic glaciation it distinguishes two useful phases of antarctic glacial onset an initial phase of mountain glaciation from which ice streams occasionally and in isolated locations reached sea level and a subsequent phase of full glaciation with an ice sheet as large as today s extending everywhere to sea level according to direct evidence generally proximal from the continent itself or surrounding southern ocean the first of these occurred probably during the late eocene while the second developed at the eocene oligocene boundary indirect evidence mainly involving proxy measurements from dsdp and odp sites remote from the southern ocean suggests that middle and late eocene glaciations may have been full also ice sheets possibly even larger than today s but short lived and that the e o boundary onset differed from these mainly in producing a stable ice sheet in pursuing the notion of glacial onset we examined the direct record separately for east antarctica west antarctica and the antarctic peninsula the different sub ice topography and geographic positions of which suggest that their glacial histories could have been different the direct record for an initial middle or late eocene phase is very sparse only the rare occurrence of ird at southern ocean dsdp and odp sites suggests the possibility of early ice and all three regions include mountains that could have hosted such ice although the indirect record and climate modelling in combination suggest that full glaciation of each region was probably synchronous we find differences in the available direct evidence there is abundant evidence that east antarctica became fully glaciated in the earliest oligocene but certain evidence of glaciation of a similar age extending to sea level is sparse for the antarctic peninsula and is not found until the late oligocene for west antarctica high resolution direct evidence is required to resolve uncertainties in glacial history

no extreme bipolar glaciation during the main eocene calcite compensation shift major ice sheets were permanently established on antarctica approximately 34 million years ago1 2 3 close to the eocene oligocene boundary at the same time as a permanent deepening of the calcite compensation depth in the world s oceans4 until recently it was thought that northern hemisphere glaciation began much later between 11 and 5 million years ago1 2 3 5 this view has been challenged however by records of ice rafting at high northern latitudes during the eocene epoch6 7 and by estimates of global ice volume that exceed the storage capacity of antarctica8 at the same time as a temporary deepening of the calcite compensation depth 41 6 million years ago9 here we test the hypothesis that large ice sheets were present in both hemispheres 41 6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial atlantic ocean these records allow at most an ice budget that can easily be accommodated on antarctica indicating that large ice sheets were not present in the northern hemisphere the records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled ocean temperatures increased and carbon isotope values decreased in the equatorial atlantic the nature of these changes around 41 6 million years ago implies common links in terms of carbon cycling with events at the eocene oligocene boundary4 and with the hyperthermals of the early eocene climate optimum3 10 11 our findings help to resolve the apparent discrepancy between the geological records of northern hemisphere glaciation6 7 8 and model results12 13 that indicate that the threshold for continental glaciation was crossed earlier in the southern hemisphere than in the northern hemisphere

constraints on glaciation in the middle eocene 46 37 ma from ocean drilling program odp site 1209 in the tropical pacific ocean the presence of glacial ice in the late middle eocene has been vigorously debated recently published sedimentary data from the high latitudes is suggestive of episodic cooling events and near freezing sea surface temperatures during parts of the late middle eocene constraints on ice volumes and the significance of excursions in open ocean foraminifera and seawater 18o reconstructions are less clear and there are few high resolution 18o records we present a new detailed record of benthic foraminiferal 18o from site 1209 that exhibits variations 18o benthic of 0 6 1 3 different approaches have previously been used to interpret 18o benthic including 1 an a priori assumption of a 50 contribution of temperature similar to what is reconstructed for the last glacial maximum recent change 2 applying oligocene calibrations between apparent sea level asl and 18o benthic or 3 assuming temperature and seawater 18o contributions can be partitioned through comparison with benthic mg ca using assumption 1 the record from site 1209 indicates changes in seawater 18o of 0 3 0 7 equivalent to 33 72 m m of asl assuming mean ice 18o of 45 using assumption 2 and two different end member calibrations the 18o benthic record implies changes in asl of 23 50 m or 50 108 m the third approach yields changes in seawater 18o of up to 0 6 to 1 4 we explore the compatibility of the results of each of these approaches with other studies that discuss evidence for ephemeral glaciations during the middle eocene with variable ice storage at one or both poles

orbital scale climate change and glacioeustasy during the early late ordovician pre hirnantian determined from δ18o values in marine apatite this study focuses on the 10 m y before the latest ordovician hirnantian glaciation we test whether orbital scale climatic fluctuations controlled the growth and melting of continental glaciers resulting in glacioeustatic sea level changes and the development of widespread marine sedimentary cycles 18o values of conodont apatite from 14 late ordovician katian cycles range from 17 to 21 isotopic values decrease and are lowest in the deepest water facies and increase and are highest in shallow water facies supporting the hypothesis that glacioeustasy was the dominant control on water depth changes measured intracycle 18o changes of 0 7 2 5 were controlled by changes in ice volume 60 m sea level changes sea surface temperatures 5 c and potentially local increases in seawater evaporation during drier and or windier glacial stages these interpreted orbital scale climate changes and resultant large glacial ice volume changes support recent interpretations of a dynamic and prolonged ordovician greenhouse to icehouse transition

concepts and methods of high resolution event stratigraphy modern geological analyses involving sedimentary rocks require a high resolution system of dating integrating and correlating diverse strati graphic geochemical and paleontological data that also takes into account the possibility that short term phenomena 100 kyr or less exercise a strong control on sedimentation such phenomena may be extraterrestrial tectonic volcanic oceanographic climatic sedimentologic and or bio logic in origin some reflect unpredictable perturbations of local to global scale but most short term phenomena are predictable and may be either autocyclic locally regulated with limited stratigraphic continuity or allo cyclic in nature regionally to globally regulated with extensive strati graphic continuity beerbower 1964 a stratigraphic system based on short term phenomena would ideally be chronostratigraphic involving the identification and regional tracing of time lines isochronous surfaces or very thin event deposits and easily integrated with refined independently derived biostratigraphic and geochronologic systems an intensive search for such a new and revolutionary system of stratig raphy has been prompted in many parts of the phanerozoic by attain ment of plateaus in stratigraphic resolution utilizing the more standard tools of magnetostratigraphy biostratigraphy and geochronology most magnetic reversals have been identified biostratigraphic systems can be no more refined than the maximum evolutionary rates of component taxa and their major structures known for many favored groups and geo chronology is regulated by the analytical confidence limits of radiometric

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

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

reconstruction of tertiary progradation and clinoform development on the new jersey passive margin by 2 d backstripping we have reconstructed the oligocene to middle miocene paleobathymetry and stratigraphy of the new jersey margin using a modified backstripping technique by analyzing the geometry of the margin through time we investigate its response to fluctuating sea level changing climate and variable sediment supply during the tertiary the reconstructions reveal a change in the margin morphology from a more steeply dipping 1 300 to 1 500 carbonate ramp in the eocene to a flatter shelf with a sharp shelf edge at present this was accomplished by an increase in the terrigenous sediment supply that filled available accommodation and caused progradation across the margin we link the increase in sediment flux with climatic cooling rather than tectonic processes the progradation is evidenced by a series of clinoforms whose formation was modulated by sea level and which extend over 100 km across the shelf the height and dip of the clinoforms increased as they extended onto the deeper parts of the earlier ramp the miocene clinoform rollovers at the new jersey margin had water depths of60 130 m and are interpreted as the edge of a new continental shelf built over the older ramp sea level fall was probably insufficient to drive the miocene shorelines past the shelf breaks thus measurements of sea level amplitude based upon coastal onlap over the clinoforms are not reliable 1999 elsevier science b v all rights reserved

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

calcareous nannofossil paleoecology of the mid cretaceous western interior seaway and evidence of oligotrophic surface waters during oae2 abstract analysis of calcareous nannofossils total organic carbon toc values and carbon isotope records from outcrop and drill cores in the central colorado and kansas and southern texas western interior basin wib indicates predominantly oligotrophic surface water conditions during the late cenomanian turonian oceanic anoxic event 2 oae2 high resolution bio chemostratigraphy of this interval allows for detailed correlation of changes in nannofossil assemblages and toc across the wib and aids comparison with other global records prior to and at the onset of oae2 the a interval in the 13c positive excursion identified by pratt and threlkeld 1984 mesotrophic to eutrophic nannofossil taxa biscutum and zeugrhabdotus are relatively high in abundance and foraminiferal assemblages record a high diversity benthonic zone toc sharply declines at the start of oae2 despite evidence of high surface productivity and benthic diversity implying that the seafloor was briefly oxygenated during a period of enhanced mixing in the expanding western interior seaway during the latter two thirds of oae2 intervals b and c in the excursion toc periodically increases suggesting that anoxic conditions returned at the substrate despite persistently low abundances of biscutum and zeugrhabdotus implying oligotrophic surface water conditions the divergence of these two proxies suggests a highly stratified water column in the wib not higher productivity which resulted in anoxic conditions during oae2 if productivity was not the primary cause of increased carbon burial in the wib it is probable that increased terrestrial runoff and incursion of warm saline tethyan waters from the south led to salinity stratification in the absence of mixing warm and saline bottom waters would have been isolated from freshened boreal currents and become stagnant allowing for preservation of greater amounts of organic material in the substrate nannofossil records from cuba ks are an exception and reveal relatively high productivity throughout suggesting that occasional mixing of nutrients to the surface may have continued along the eastern margin of the central wib

high resolution calibration of eocene strata 40ar 39ar geochronology of biotite in the green river formation the sixth tuff of the wilkins peak member of the green river formation is an important potential calibration point for magnetic stratigraphy mammalian evolution and lacustrine processes however two recent 40 ar 39 ar ages based on laser fusion of biotite from this important bed are not in agreement with one other most large euhedral biotite from the basal 1 cm give concordant age spectra when incrementally heated however some crystals yield discordant age spectra and have plateau and integrated ages that are scattered toward both older and younger apparent ages electron probe microanalysis indicates that intergrown alteration phases occur in a small fraction of sixth tuff biotite crystals and likely contributed to open system processes that led to the observed discordance and age scatter a new age of 49 62 0 10 ma is obtained from 22 concordant incremental heating experiments this age agrees with a new 49 78 0 08 ma age for the sanidine from the layered tuff which is stratigraphically 24 m below the sixth tuff

drake passage and cenozoic climate an open and shut case drake passage opening has often been viewed as a single discrete event possibly associated with abrupt changes in global circulation and climate at or near the eocene oligocene boundary a new plate tectonic model based on recent reinterpretations of the opening history of basins in the scotia sea suggests that an effective ocean gateway may have developed even earlier during the middle eocene this is consistent with a growing body of evidence from sediment core proxy data for eocene changes in southern ocean circulation and biological productivity the period between earliest opening after 50 ma and the latest eocene was characterized by the evolution of various current pathways across the subsiding continental shelves and intervening deep basins this shallow opening may have caused important changes in southern ocean circulation contributing to eocene cooling and the growth of antarctic ice sheets

the k pg boundary at brazos river texas usa an approach by marine palynology two cores and one outcrop section from the cretaceous palaeogen k pg boundary interval at the brazos river area texas usa have been high resolution sampled and analysed fully quantitatively by marine palynology the results have been compared and integrated with data from micropalaeontology sedimentology and isotope geochemistry from the same sections within all three sections the k pg boundary defined as the base of the p0 foraminifera zone and the onset of a negative carbon isotope anomaly closely corresponds to the appearance of lowermost danian organic walled dinocysts based on various palynological proxies as well as on sedimentologic features a sequence stratigraphic subdivision of the sections is proposed from a synopsis of all three sections a long term punctuated drop of relative sea level is indicated starting at about the top of the upper cretaceous cf2 foraminifera zone and reaching a minimum within the upper p1a zone of the lower palaeogene this is followed by a prominent transgression starting within the p1a p1b boundary interval the event deposit ed a siliciclastic unit located well below the base of the p0 foraminifera zone in the present sections most probably represents a combination of both episodic relative sea level fall and lag deposit due to initial transgression it is preceded by significant fluctuations of climatic boundary conditions with cool climates correlating to heavier 13c values and increased p g ratio of dinocysts suggestive of higher marine primary productivity across the k pg boundary a prominent increase and spike of the warm temperate waters dinocysts fraction is documented represented mainly by trithyrodinium evittii which is accompanied by climatic warming and an episodic relative sea level rise thus prominent paleo environmental changes and sea level fluctuations precede and coincide with the k pg boundary proper these data are inconsistent with a single catastrophic impact as the cause for the k pg boundary event but suggest relative longer term environmental stress as finally leading to end cretaceous crisis of the biosphere between the ed and the k pg boundary proper the gradual increase to peak abundance in trilete spores demonstrates a significant time lag between these two horizons according to the distinct distribution of this peak abundance it cannot be excluded that an impact tsunami event is related to the lower portion of the ed in contrast no significant changes within most palynologic proxies are documented across the yellow clay layer below the ed documented within one of the sections and recently suggested as the original chicxulub impact ejecta horizon this questions the impact origin of this horizon or at least suggests only little consequences of this event on the ecosystem

dinoflagellate cysts paleoproductivity and upwelling systems a late cretaceous example from israel abstract diverse assemblages of dinoflagellate cysts occur in coniacian maastrichtian sedimentary sequences in israel which represent the inner shallower and outer deeper seaward belt of a late cretaceous upwelling system along the margin of the southern tethys the assemblages are composed mainly of peridinioid p and gonyaulacoid g cysts in varying concentrations it is suggested that the observed fluctuations in the numerical peridinioid gonyaulacoid p g cyst ratio reflect mainly changes in upwelling intensity and productivity in the studied area high p g values represent a higher productivity and vice versa thep g curve indicates a generally high productivity during the campanian followed by a decrease during the maastrichtian the inner part of the upwelling region is characterized by higherp g values representing a higher productivity the similarity between thep g ratio curve and the foraminiferal based paleoproductivity curve from the same sections supports the utility of thep g ratio as a reliable productivity indicator applied here for the first time to upper cretaceous sediments

exploring uncertainties in the relationship between temperature ice volume and sea level over the past 50 million years over the past decade efforts to estimate temperature and sea level for the past 50 ma have increased in parallel efforts to model ice sheet changes during this period have been ongoing we review published paleodata and modeling work to provide insights into how sea level responds to changing temperature through changes in ice volume and thermal expansion to date the temperature to sea level relationship has been explored for the transition from glacial to interglacial states attempts to synthesize the temperature to sea level relationship in deeper time when temperatures were significantly warmer than present have been tentative we first review the existing temperature and sea level data and model simulations with a discussion of uncertainty in each of these approaches we then synthesize the sea level and temperature data and modeling results we have reviewed to test plausible forms for the sea level versus temperature relationship on this very long timescale there are no globally representative temperature proxies and so we investigate this relationship using deep sea temperature records and surface temperature records from high and low latitudes it is difficult to distinguish between the different plausible forms of the temperature to sea level relationship given the wide errors associated with the proxy estimates we argue that for surface high latitude southern hemisphere temperature and deep sea temperature the rate of change of sea level to temperature has not remained constant i e linear over the past 50 ma although the relationship remains ambiguous for the available low latitude surface temperature data a nonlinear form between temperature and sea level is consistent with ice sheet modeling studies this relationship can be attributed to 1 the different glacial thresholds for southern hemisphere glaciation compared to northern hemisphere glaciation and 2 the ice sheet carrying capacity of the antarctic continent

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

deconvolving tectono climatic signals in deep marine siliciclastics eocene ainsa basin spanish pyrenees seesaw tectonics versus eustasy the eocene deep marine siliciclastic fill of the ainsa basin spanish pyrenees gives unprecedented temporal resolution of the causes and timing of coarse clastic sediment supply to a deep marine basin early eocene tectonic subsidence linked to pyrenean orogenesis created the ainsa basin with water depths of similar to 400 800 m above a foundered shallow marine mixed carbonate and clastic shelf the similar to 25 sandbodies or channelized submarine fans in the basin were controlled by the similar to 400 k y milankovitch frequency with modes at similar to 100 k y and similar to 41 k y possibly stacked similar to 23k y influencing bottom water conditions in the basin causing periodic stratification in the water column across a submarine sill at the western basin margin early boltana anticline intrabasinal tectonics defined and controlled the position of eight sandy systems and their constituent fans in a process of seesaw tectonics by 1 westward lateral offset stacking of sandy fans due to growth of the eastern side of the basin represented today by the mediano anticline and 2 eastward orogenward back stepping of the depositional axis of each sandy system due to phases of relative uplift of the boltana anticline during basin infill uplift of the boltana anticline led to increasing basin narrowing and depositional confinement unlike the earlier depositional systems the youngest deep marine system was fed from a more southern sediment source between the growth anticlines as was the overlying deltaic system all the older deep marine sandy systems were fed from southeast point sources from canyons and erosional lower slope channels eroding the growing mediano anticline the depositional style outlined in this paper might be common to other active margins where siliciclastic basins evolve between active thrusts

a point sourced calciclastic submarine fan complex eocene anotz formation western pyrenees facies architecture evolution and controlling factors a complete transect of a fossil carbonate ramp slope has been reconstructed using outcrop data from the lower middle eocene anotz formation in the western pyrenees the anotz formation contains four calciclastic mostly bioclastic members encased within hemipelagic marl limestone alternations each calciclastic member representing a submarine fan system individual fans are composed of a gullied upper slope a leveed feeder channel a channelized lobe area an unconfined lobe zone and a peripheral lobe fringe that grades downcurrent into basinal deposits quantitative data on the dimensions and degree of lateral continuity and vertical connectivity of the anotz calciclastic fan elements are presented these data provide information for a better understanding of the intrinsic nature of calciclastic submarine fans and to model their reservoir potential the long term evolution of the anotz carbonate slope was generally progradational as evidenced by the four discrete episodes of calciclastic fan development the location of the fans was controlled by the synsedimentary tectonic activity of the pamplona fault which created a slope valley along which the reworked shallow water calciclastic sediments were funnelled in addition episodic basinward tilting of the shallow water carbonate ramp linked to the development of the south pyrenean foreland basin switched on and off the process of calciclastic resedimentation and determined the growth or abandonment of the fan systems

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

the respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the eocene oligocene transition the continental scale initiation of the antarctic ice sheet at the eocene oligocene boundary eocene oligocene transition eot 34 ma is associated with a global reorganization of the climate if data studies have assessed the precise timing and magnitudes of the ice steps modeling studies have been unable to reproduce a transient ice evolution during the eocene oligocene transition in agreement with the data here we simulate this transition using general circulation models coupled to an ice sheet model our simulations reveal a threshold for continental scale glaciation of 900 ppm 100 to 150 ppm higher than previous studies this result supports the existence of ephemeral ice sheets during the middle eocene as similar co 2 levels 900 1000 ppm have been reached episodically during this period transient runs show that the ice growth is accurately timed with eot 1 and oi 1 the two 18 o excursions occurring during the transition we show that co 2 and orbital variations are crucial in initiating these steps with eot 1 corresponding to the occurrence of low summer insolation whereas oi 1 is controlled by a major co 2 drop the two 18 o steps record both ice growth and temperature representing some 10 30 m eustatic sea level fall and 2 4 c cooling at eot 1 and 70 20 m and 0 2 c for oi 1 the simulated magnitude of the ice steps 10 m for eot 1 and 63 m for oi 1 and the overall cooling at various locations show a good agreement with the data which supports our results concerning this critical transition

on the origin of cenozoic and mesozoic third order eustatic sequences abstract the origin of third order eustatic sequences is reviewed by comparing recent sequence stratigraphic data to the latest best constrained astronomical model middle eocene to holocene icehouse sequences correspond to 1 2 myr obliquity cycles constraints from oxygen isotope records highlight the link between icehouse sea level lowerings sequence boundaries and 1 2 myr obliquity nodes mesozoic greenhouse sequences show some relation with the 2 4 myr eccentricity cycles suggesting that orbital forcing contribute to sea level change we suggest that during the icehouse large ice sheets associated with significant glacioeustatic changes 25 m up to 120 m changes were mainly governed by obliquity forcing during icehouse worlds obliquity forcing was the stongest control on global sea level and depositional sequences additionally during the middle eocene third order sequences were glacioeustatically driven in tune with 1 2 myr obliquity cycle suggesting that the presence of significant ice sheets is earlier than previously supposed i e early eocene in contrast during greenhouse worlds e g ephemeral small to medium sized or no ice sheets 0 25 m glacioeustatic changes the expression of obliquity in the sedimentary record is weak and intermittent instead the eccentricity signature which is the modulator of climatic precession is documented moreover we presume that greenhouse sequences on the myr scale are global and hence cannot be caused by regional tectonism e g intraplate stress or mantle hot blobs instead the eccentricity link implies a weaker glacioeustatic control because thermoeustasy is too small to explain the sea level changes stratigraphically well documented fourth order sequences may be linked to the astronomically stable strongest amplitude 405 kyr eccentricity cycle and possibly to 160 200 kyr obliquity modulation cycles fifth order sequences to the short 100 kyr eccentricity cycles and finally sixth order sequences to the fundamental obliquity 40 kyr and climatic precession 20 kyr cycles these astronomical cycles could be preserved in the sedimentary record and have been demonstrated to control sea level changes accordingly by placing depositional sequence orders into a high resolution temporal framework i e orbital periodicities standardization of eustatic sequence hierarchy may be possible

filling the north european early middle eocene ypresian lutetian boundary gap insights from the pyrenean continental to deep marine record abstract the early middle eocene ypresian lutetian transition is represented by a hiatus in many north european sections including those in which the classic stratotypes were originally defined however the global stratotype section and point of the lutetian stage which is still pending definition should be placed at a globally correlatable event included within that unrepresented interval the pyrenean eocene outcrops display sedimentary successions that offer the rare opportunity to analyse the ypresian lutetian boundary interval in almost continuous sections and in very different settings seven reference stratigraphic sections were selected on the basis of their quality and correlated by means of biomagnetostratigraphic data this correlation framework casts light on the sequence of chronostratigraphic events that characterize the ypresian lutetian boundary interval which may prove useful in defining the main correlation criterion of the base of the lutetian all of the pyrenean sections show a similar sedimentary evolution despite being up to 350 km apart from each other containing deposits of different origins intrabasinal carbonate sediments siliciclastic sediments sourced from the iberian plate and terrigenous sediments sourced from the uplifting pyrenees and despite having been accumulated in different sedimentary environments from continental to deep marine and in different geodynamic settings piggy back basin foreland basin and cratonic margin this common evolution can be readily interpreted in terms of a sea level driven depositional sequence whose lowstand and transgressive systems tracts are included within the ypresian lutetian boundary interval the pyrenean ypresian lutetian depositional sequence can reasonably be correlated with depositional sequences from classic north european areas shedding light on the palaeoenvironmental history which in those areas has not been recorded furthermore these depositional sequences may possibly correlate with others from the antarctic ocean and from new jersey as well as with oceanic temperature variations suggesting that they might be the result of climatically driven glacioeustatic sea level changes should this hypothesis prove correct it would confirm previous suggestions that the onset of antarctic glaciations needs to be backshifted to the late ypresian at least

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

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

the contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation in this study we reconstruct the timing of the onset of northern hemisphere glaciation this began in the late miocene with a significant build up of ice on southern greenland however progressive intensification of glaciation did not begin until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia were glaciated at approximately 2 74 ma 40 ka before the glaciation of alaska 2 70 ma and about 200 ka before significant glaciation of the north east american continent 2 54 ma we also review the suggested causes of northern hemisphere glaciation tectonic changes such as the uplift of the himalayan and tibetan plateau the deepening of the bering strait and the emergence of the panama isthmus are too gradual to account entirely for the speed of northern hemisphere glaciation we therefore postulate that tectonic changes may have brought global climate to a critical threshold but the relatively rapid variations in the earth s orbital parameters and thus insolation triggered the intensification of northern hemisphere glaciation this theory is supported by computer simulations which despite the relative simplicity of the model and the approximation of some factors e g using a linear carbon dioxide scenario neglecting the geographical difference between the pliocene and the present suggest that it is possible to build up northern hemisphere ice sheets between 2 75 and 2 55 ma by varying only the insolation controlled by the orbital parameters c 1998 elsevier science ltd all rights reserved

orbital forcing in turbidite accumulation during the eocene greenhouse interval the influence of astronomically driven short term climate change milankovitch cycles on deep marine turbidite systems is not well known particularly in the case of long term greenhouse intervals with no significant glacio eustatic sea level fluctuations this study carried out at the gorrondatxe section global stratotype section and point for the base of the lutetian stage in the western pyrenees demonstrates that the characteristics of lower middle eocene fan fringe basin plain turbiditic and pelagic deposits varied in line with orbitally forced fluctuations in seasonal rainfall runoff and terrigenous input to the sea reduced turbiditic activity during the formation of pelagic limy precessional hemicouplets indicates subdued seasonality and low terrigenous input conversely turbidity currents were more frequent had greater energy and were more voluminous during the formation of pelagic marly hemicouplets suggesting precessional hemicycles with strong seasonality and heavy summer rainfall these differences at precessional time scales were enhanced at maximum eccentricity because turbiditic activity was most intense when boreal summer occurred at perihelion i e maximum seasonality but declined when it occurred at aphelion at minimum eccentricity with relatively weak seasonality throughout one or more than one precessional cycle 21 kyr turbiditic activity remained relatively low the pattern observed at the gorrondatxe fan fringe basin plain succession implies that the orbitally forced environmental changes must also have affected the inner and middle parts of the submarine fan the astronomical influence on terrigenous sediment input also determined the changing characteristics of the pelagic sedimentation thus terrigenous sediment contribution to pelagic sedimentation fluctuated by a factor of five during opposite precessional situations at maximum eccentricity whereas there was almost no fluctuation at minimum eccentricity

early and middle eocene radiolarian assemblages in the eastern equatorial pacific ocean iodp leg 320 site u1331 faunal changes and implications for paleoceanography abstract quantitative faunal analyses of radiolarians were used to reconstruct paleoceanographic conditions spanning the interval from zones rp8 early eocene to rp16 middle eocene in pelagic sequences recovered at integrated ocean drilling program iodp site u1331 in the eastern equatorial pacific ocean on the basis of relative abundance data from the low to high latitudes reported in the previous literature paleoceanographic indices were identified 1 species indicative of warmer conditions include stylosphaera coronata coronata phormocyrtis embolum dendrospyris didiceros phormocyrtis cf proxima and thyrsocyrtis triacantha 2 species indicative of cooler conditions include the lophocyrtis aspera group the lithocyclia ocellus group hexacontium sp a hexacontium sp b thecosphaerella glebulenta and lithelius sp a two warming and at least six cooling events in the early to middle eocene were identified from radiolarian assemblage variations the paleoclimatic trends can be summarized as follows warming in c23n 2n to c21r 51 5 49 0 ma and c18n 40 2 39 0 ma cooling in c21r 48 5 47 8 ma lower c20r 46 2 45 2 ma top c20r to c20n 44 0 43 0 ma top c20n to c19r 43 0 41 7 ma c19n to c18r 41 7 40 2 ma and c18n 1n 39 0 38 5 ma these cooling events corresponded to the eli and bli events which were identified in benthic foraminiferal 18 o of the southern ocean in general radiolarian and opal mass accumulation rates mars in the eastern equatorial pacific had higher values in cooling conditions during the middle eocene the changes in biological productivity in the eastern equatorial pacific were associated with cooling of tropical surface water the change in relative abundance of radiolarians and caco 3 content at site u1331 indicated that middle eocene carbonate events carbonate accumulation events caes lyle et al 2005 coincided with the cooling events of tropical surface water at least cae 2 and cae 3 were associated with high biological productivity as well as cooling

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

glacioeustatic changes in the early and middle eocene 51 42 ma shallow water stratigraphy from odp leg 189 site 1171 south tasman rise and deep sea δ18o records sequence boundary ages determined in shallow water sediments obtained from odp ocean drilling program leg 189 site 1171 south tasman rise compare well with other stratigraphic records new jersey united states and northwestern europe and 1 8 o increases from deep sea records indicating that significant 10 m eustatic changes occurred during the early to middle eocene 51 42 ma sequence boundaries were identified and dated using lithology bio and magnetostratigraphy water depth changes caco 3 content and physical properties e g photospectrometry they are characterized by a sharp bioturbated surface low caco 3 content and an abrupt increase in glauconite above the surface foraminiferal biofacies and planktonic benthic foraminiferal ratios were used to estimate water depth changes ages of six sequence boundaries 50 9 49 2 48 5 47 8 47 1 44 5 and 42 6 ma from site 1171 correlate well to the timings of 1 8 o increases and sequence boundaries identified from other eocene studies the synchronous nature of sequence boundary development from globally distal sites and 1 8 o increases indicates a global control and that glacioeustasy was operating in this supposedly ice free world this is supported by previous modeling studies and atmospheric co 2 estimates showing that the first time co 2 levels decreased below a threshold that would support the development of an antarctic ice sheet occurred at ca 51 ma estimates of sea level amplitudes range from 20 m for the early eocene 51 49 ma and 25 m to 45 m for the middle eocene 48 42 ma using constraints established for oligocene 1 8 o records

antarctic climate southern ocean circulation patterns and deep water formation during the eocene we assess early to middle eocene seawater neodymium nd isotope records from seven southern ocean deep sea drill sites to evaluate the role of southern ocean circulation in long term cenozoic climate change our study sites are strategically located on either side of the tasman gateway and are positioned at a range of shallow 500 m to intermediate deep 1000 2500 m paleowater depths unradiogenic seawater nd isotopic compositions reconstructed from fish teeth at intermediate deep indian ocean pelagic sites ocean drilling program odp sites 738 and 757 and deep sea drilling project dsdp site 264 indicate a dominant southern ocean sourced contribution to regional deep waters end t 9 3 1 5 iodp site u1356 off the coast of adelie land a locus of modern day antarctic bottom water production is identified as a site of persistent deep water formation from the early eocene to the oligocene east of the tasman gateway an additional local source of intermediate deep water formation is inferred at odp site 277 in the sw pacific ocean end t 8 7 1 5 antarctic proximal shelf sites odp site 1171 and site u1356 reveal a pronounced erosional event between 49 and 48 ma manifested by 2 end unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites this erosional event coincides with the termination of peak global warmth following the early eocene climatic optimum and is associated with documented cooling across the study region and increased export of antarctic deep waters highlighting the complexity and importance of southern ocean circulation in the greenhouse climate of the eocene

oligocene miocene biostratigraphy magnetostratigraphy and isotopic stratigraphy of the western north atlantic magnetostratigraphic records from western north atlantic deep sea drilling project dsdp sites 563 and 558 are correlated with the geomagnetic polarity time scale gpts berggren et ai 1984a 1984b using marine magnetic anomalies and selected biostratigraphic datum levels the magnetochronology established is used to make direct magnetobiostratigraphic correlations that agree with previous oligocene early miocene studies however we show that zones nn8 partim and nn9 and associated epoch 11 correlate with magnetic anomaly 5 chron csn this contrasts with previous indirect correlations of epoch 11 with anomaly sa and requires an upward adjustment of 1 5 2 0 m y for middle late miocene calcareous nannofossil zones we correlate the middle late miocene boundary with zone nn8 and earliest chron csn 10 4 ma

eocene sea temperatures for the mid latitude southwest pacific from mg ca ratios in planktonic and benthic foraminifera abstract we have used laser ablation inductively coupled plasma mass spectrometry la icp ms to measure elemental mg ca al ca mn ca zn ca sr ca and ba ca ratios of 13 species of variably preserved early to middle eocene planktonic and benthic foraminifera from new zealand the foraminifera were obtained from ashley mudstone mid waipara river south island which was deposited at bathyal depth ca 1000 m on the northern margin of the east facing canterbury basin at a paleo latitude of ca 55 s la icp ms data yield trace element depth profiles through foraminifera test walls that can be used to identify and exclude zones of surficial contamination and infilling material resulting from diagenetic coatings mineralisation and detrital sediment screened mg ca ratios from 5 species of foraminifera are used to calculate sea temperatures from late early to early middle eocene ca 51 to 46 5 ma a time interval that spans the termination of the early eocene climatic optimum eeco during this time sea surface temperatures sst varied from 30 to 24 c and bottom water temperatures bwt from 21 to 14 c comparison of mg ca sea temperatures with published 18o and tex86 temperature data from the same samples hollis et al 2009 shows close correspondence indicating that la icp ms can provide reliable mg ca sea temperatures even where foraminiferal test preservation is variable agreement between the three proxies also implies that mg ca temperature calibrations for modern planktonic and benthic foraminifera can generally be applied to eocene species although some species e g v marshalli show significant calibration differences the mg ca ratio of the eocene ocean is constrained by our data to be 35 50 lower than the modern ocean depending on which tex86 temperature calibration kim et al 2008 liu et al 2009 is used to compare with the mg ca sea temperatures sea temperatures derived from 18o analysis of foraminifera from waipara show amplified variability relative to the mg ca and tex86 proxies this amplified variability is probably a diagenetic effect although it is possible that this eocene 18o record contains an ice volume component the amplification signalling that temperature changes may have been accompanied by growth and collapse of ephemeral polar ice sheets on timescales of ca 0 5 myr

sequence stratigraphy and sea level history of oligocene strata of the northern aral sea region kazakhstan implications for glacioeustatic reconstructions we have applied sequence stratigraphic techniques to the upper eocene to oligocene strata of the region north of the aral sea and northern usturt plateau western kazakhstan and compared the inferred sea level history with other records derived from different parts of the world during late eocene to early miocene time the entire region of study was within the northeastern part of the paratethys sea clastic and carbonate deposition occurred in a range of environments from fluvial and lacustrine in coastal plains northern priaral to relatively deep marine in the north usturt trough stratal geometries and sedimentation rates indicate that the deposition of the northern priaral sections occurred under tectonically quiet conditions whereas noticeable syndepositional subsidence took place in the central part of the north usturt trough the same oligocene sequences have been identified in these areas despite significant spatial variations in tectonic subsidence and sediment supply rates we therefore conclude that eustasy played a major role in controlling sedimentation in the region of study especially in the northern priaral through sequence stratigraphic analysis we identified four sequence boundaries resulting from regional sea level falls two major sea level falls are identified in the earliest oligocene and at the early late oligocene boundary and two smaller sea level falls took place in late early oligocene and latest oligocene time each of these events can be correlated to peaks in the global 18 o record in addition paleoclimatic data from the region indicate that regional periods of cooling are coincident with the intervals of inferred sea level falls we therefore conclude that global glacioeustasy represents the main controlling force for the sea level record we observe in the northern priaral and north usturt trough this makes the region of study very useful for reconstruction of eustatic history for late eocene oligocene time

climatic cyclicity and terrigenous sediment influx to the early turonian greenhorn sea southern utah abstract rhythmically alternating beds of limestone and shale in pelagic deposits of the cenomanian turonian north american western interior seaway have been widely attributed to climatic cyclicity in the milankovitch band whether these rhythmic beds record cycles of terrigenous dilution or of productivity remains controversial we present results of a study of early turonian strata of the tropic shale and tununk member of the mancos shale in southern utah aimed at testing the dilution model in a prodeltaic environment within 130 km of the paleoshoreline the study transect consisted of four localities spaced along a 110 km onshore offshore transect in each of the four sections we studied a stratigraphic interval characterized by beds of limestone or marlstone that alternate with beds of marly shale or calcareous shale along the transect content of quartz sand and coarse silt in each of the beds generally decreases and content of calcium carbonate increases in each section quartz sand and coarse silt content varies antithetically with calcium carbonate content these observations suggest that the limestone marlstone beds accumulated during times when rates of terrigenous sediment transport to offshore sites were relatively slow conversely the shaly beds were deposited during times of enhanced terrigenous sediment flux these ob ervations support the hypothesis that limestone shale bedding rhythms record wet and dry phases of climate cycles in utah the limestone marlstone beds contain smaller proportions of mixed layer illite smectite clays than do the shaly beds climatic cyclicity apparently led to cyclic variations in the proportions of clay minerals supplied to the prodeltaic environments or to variation in the loci of accumulation of different clay minerals analysis of intensity of bioturbation and preservation of fecal pellets also indicates that the limestone marlstone beds accumulated under more oxic benthic conditions than did the shaly beds detailed examination of the alternating beds of limestone marlstone and shale in southern utah indicates that the deposits are characterized by a distinctive succession of facies these deposits are better interpreted as bedding cycles composed of three gradational lithologies than as bedding rhythms composed of two alternating lithologies data on grain size and calcium carbonate content suggest that the bedding cycles correspond to shoaling upward parasequences that developed in response to small scale changes in relative sea level our study suggests that climatically modulated changes in fresh water discharge and terrigenous sediment supply were mainly responsible for these sea level changes and for cyclic variations in benthic oxygenation in prodeltaic environments of the earl turonian western interior seaway

climate response to orbital forcing across the oligocene miocene boundary spectral analyses of an uninterrupted 5 5 million year my long chronology of late oligocene early miocene climate and ocean carbon chemistry from two deep sea cores recovered in the western equatorial atlantic reveal variance concentrated at all milankovitch frequencies exceptional spectral power in climate is recorded at the 406 thousand year ky period eccentricity band over a 3 4 million year period 20 to 23 4 my ago ma as well as in the 125 and 95 ky bands over a 1 3 million year period 21 7 to 23 0 ma of suspected low greenhouse gas levels moreover a major transient glaciation at the epoch boundary approximately 23 ma mi 1 corresponds with a rare orbital congruence involving obliquity and eccentricity the anomaly which consists of low amplitude variance in obliquity a node and a minimum in eccentricity results in an extended period approximately 200 ky of low seasonality orbits favorable to ice sheet expansion on antarctica

high resolution stratigraphy of an underfilled lake basin wilkins peak member eocene green river formation wyoming u s a abstract lakes tend to respond noticeably to minor changes in sediment and water balance driven by climatic tectonic or geomorphic processes this unique behavior of lacustrine basins can provide a high resolution record of geologic processes within the continental setting far from the globally averaged record of marine strata the wilkins peak member of the eocene green river formation in wyoming usa is dominated by aggradation of repetitive sedimentary facies successions recording distinct lacustrine expansions and contractions these lacustrine cycles consist of up to four successive facies associations littoral profundal sublittoral palustrine and salt pan because they comprise disparate facies that may never have been simultaneously deposited in the basin wilkins peak member cycles are non waltherian successions that do not readily equate to any established sequence stratigraphic unit the completeness of the stratigraphic record in the wilkins peak member varies continuously across the basin at least 126 cycles are present in the erda white mountain 1 core near the basin depocenter whereas only about one third as many are recognizable 53 km north nearer to the basin margin cycle boundaries terminate northward by gradual amalgamation into palustrine facies reflecting the interplay between varying lake levels and a south dipping deposition gradient evidence for complete desiccation and hiatuses is commonplace even near the basin center a truly complete record may not be present anywhere based on recent 40ar 39ar geochronology of tuffs the average cycle duration in the white mountain 1 core is approximately 10 000 years however the true average duration is shorter due to the presence of lacunae and the time required for deposition of the thinnest cycles may have been less than 1000 years no external driving mechanism is presently known for eocene cycles of such short duration raising the possibility that they are instead autogenic cycles related to geomorphic instability of the surrounding landscape evaporite deposition corresponded closely in time and space to maximum differential subsidence suggesting that tectonic influences on drainage patterns and basin accommodation exerted a primary control differential accommodation was most pronounced during deposition of the lower wilkins peak member and became progressively less so after that time based on structural and stratigraphic observations a period of increased tectonic uplift commenced concurrent with deposition of the lower wilkins peak member

origin of the cretaceous bridge creek cycles in the western interior united states abstract alternating beds of burrowed limestone and laminated organic carbon rich marlstone in the bridge creek member of the greenhorn formation were deposited during maximum transgression of the cenomanian turonian sea in the western interior of the united states one view of the origin of the bridge creek limestone marlstone rhythms holds that they represent dilution cycles produced by alternating climates within the western interior the marlstones recording wet episodes when high runoff produced a sediment laden brackish lid on the seaway and the limestones recording dry episodes when runoff was low and the water column well mixed a second view holds that the rhythms represent productivity cycles the limestones representing times of high productivity of calcareous planktonic skeletons and the marlstones representing times of low productivity in this view the rhythms were produced by alternations in vertical circulation that characterized much of the world ocean at the time the productivity origin of the rhythms is supported by the presence of abundant calcispheres in the limestone beds the concentration of clay size quartz in many of the limestone beds the comparatively high 18 o and low 13 c in limestone beds the similarity in proportion of clay minerals in marlstone and limestone beds the pelagic depositional rate of the bridge creek member and by the discovery that bridge creek deposition began with a marlstone and not a limestone bed the dilution model is not consistent with these features and it has not been supported by modeling of paleoclimates and lithofacies that were predicted from it nor by macrofaunal distributions within the seaway the dilution model is not consistent with the occurrence of diverse and abundant planktonic foraminifera in both marlstone and limestone beds which indicate that near normal marine salinities prevailed during deposition of both bed by bed analysis of the bridge creek member may provide an analog for events in the tethys that are poorly recorded in deposits from the deep sea itself

early eocene climatic optimum environmental impact on the north iberian continental margin the early eocene climatic optimum which constituted the peak of the long term early cenozoic global warming had a significant impact on the environmental evolution of terrestrial and oceanic areas surprisingly however its influence on continental margins is poorly known new insights are provided from a sedimentological stable isotope mineralogical and micropaleontological study of an 1100 m thick lower middle eocene deep marine succession that accumulated on the north iberian continental margin the early eocene climatic optimum is represented by a 410 m thick interval characterized by scarcity of hemipelagic limestones abundance of dark marls which record a reduction in calcium carbonate content and an increase in kaolinite and the occurrence of conspicuous red layers with high siderite and pyrite content series of stratigraphically significant events frame the early eocene climatic optimum based on this analysis the environmental influence of the early eocene climatic optimum started at 52 6 ma and lasted 2 3 m y its onset is marked by rapid drops in 13c and 18o which record the addition of 13c depletedcarbon into the ocean atmosphere system for 80 k y and a concomitant warming a hotter climate and a perennial rainfall regime increased the supply of terrestrial clays organicmatter and iron oxides into the sea eventually these changes affected the deepsea bottom 270 k y after the onset of the early eocene climatic optimum creating conditions in which opportunistic benthic foraminifera thrived and leading to increased methanogenesis in the subsurface which caused the formation of siderite a subsequent gradual recovery culminated abruptly at 50 3 ma with a global cooling episode which is locally recorded by the accumulation of lowstand resedimentation deposits 2015 geological society of america

calcareous nannofossil paleoceanography of the cretaceous greenhorn sea two distinctive laterally traceable bentonite beds were used to construct three isochronous time slices through the marine sediments of the upper cretaceous greenhorn cyclothem of the western interior basin calcareous nannofossil assemblages from these time slices were analyzed from 40 localities to examine the paleoceanographic conditions in the basin deposition of the lower time slice x bentonite approximately corresponded to the time at which free communication between the basin and open oceanic systems first occurred the most striking trend is the presence of common to abundant nannofossils in the center of the basin and their absence from the eastern and western margins this indicates that open oceanic conditions conducive to large standing crops of calcareous nannoplankton existed only in a narrow centrally located channel conditions at the basin margins were probably unsuitable for large populations due to salinity constraints multivariate analyses indicate two distinct biofacies northern and southern which are interpreted to represent distinct surface water masses the geometry of the water mass boundary suggests that the northern surface water mass actively flowed southward into or over the relatively passive southern water mass the upper time slice hl 3 bentonite samples the nannofossil distributions at or near the maximum transgression of the greenhorn sea in this time slice nannofossils occur beyond the limits of the study area except in proximity to the frontier delta system diversities are significantly higher indicating water mass conditions more similar to those in open oceanic settings multivariate analyses indicate three distinct surface water masses northern southern and western the northern and southern water masses exhibit relationships similar to those during the x bentonite time slices the interaction between the northern and southern water masses promoted vertical stratification of the water column and resultant sediment anoxia the western biofacies may be indicative of a surface water mass with significant contributions from nearby fresh water influx

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

long periodic variations in the earth s obliquity and their relation to third order eustatic cycles and late neogene glaciations abstract evolutive spectra of four high resolution climatic proxy records reveal that the spectral power in the obliquity frequency band increases during five well defined intervals in the last 5 3 million years these intervals correspond to periods of high amplitude variations in the tilt obliquity of the earth s axis connected with a 1 2 myr cycle and to sea level lowstands of third order eustatic cycles in the haq et al 1987 curve this implies that the development of major plio pleistocene glaciations proceeded episodically and that third order cycles are glacio eustatically controlled in at least two of these intervals sinistrally coiled neogloboquadrinids entered the mediterranean at times of glacial periods one interval starts around 2 8 ma and is characterized by the first occurrence of n atlantica s another interval begins at the plio pleistocene boundary around 1 8 ma and is characterized by the common occurrence of sinistrally coiled n pachyderma also during the late miocene third order cycles correlate well with the 1 2 myr cycle of obliquity a significant drop in the third order eustatic curve starting at the tortonian messinian boundary for instance coincides with a period of high amplitude variations in the obliquity time series connected with the 1 2 myr cycle

cenozoic climate changes a review based on time series analysis of marine benthic δ18o records the climate during the cenozoic era changed in several steps from ice free poles and warm conditions to ice covered poles and cold conditions since the 1950s a body of information on ice volume and temperature changes has been built up predominantly on the basis of measurements of the oxygen isotopic composition of shells of benthic foraminifera collected from marine sediment cores the statistical methodology of time series analysis has also evolved allowing more information to be extracted from these records here we provide a comprehensive view of cenozoic climate evolution by means of a coherent and systematic application of time series analytical tools to each record from a compilation spanning the interval from 4 to 61 myr ago we quantitatively describe several prominent features of the oxygen isotope record taking into account the various sources of uncertainty including measurement proxy noise and dating errors the estimated transition times and amplitudes allow us to assess causal climatological tectonic influences on the following known features of the cenozoic oxygen isotopic record paleocene eocene thermal maximum eocene oligocene transition oligocene miocene boundary and the middle miocene climate optimum we further describe and causally interpret the following features paleocene eocene warming trend the two step long term eocene cooling and the changes within the most recent interval miocene pliocene we review the scope and methods of constructing cenozoic stacks of benthic oxygen isotope records and present two new latitudinal stacks which capture besides global ice volume also bottom water temperatures at low less than 30 and high latitudes this review concludes with an identification of future directions for data collection statistical method development and climate modeling

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

two dimensional paleoslope modeling a new method for estimating water depths of benthic foraminiferal biofacies and paleoshelf margins abstract a new method developed for estimating water depths of benthic foraminifers was implemented for oligocene foraminiferal biofacies from the new jersey coastal plain we combined benthic foraminiferal biofacies and two dimensional flexural backstripping to construct a two dimensional paleoslope model the original depositional geometry of new jersey oligocene strata was reconstructed by calculating the effects of sediment accumulation and flexural loading paleodepth estimates for benthic foraminiferal biofacies were calibrated to inner neritic facies along the resulting nonlinear profile e g with clinoforms paleodepth estimates for ten foraminiferal biofacies ranged from 20 10 m to 115 30 m and were consistent with more qualitative estimates based on other methods e g foraminiferal abundances and species diversity applying this method to the new jersey coastal plain for the oligocene showed clear distributional patterns of benthic foraminiferal biofacies this enabled paleobathymetry to be determined for the reconstructed new jersey margin as well as significant stratal surfaces within sequences i e systems tracts and condensed sections paleodepth estimates ranged from nearshore 20 10 m up to 85 25 m for deposits landward of the clinoform rollover of the underlying sequence boundary and from middle neritic to outer neritic 50 20 m to over 100 30 m on the slopes of the clinoforms during earliest transgressive systems tracts paleodepths immediately seaward of the clinoform slope ranged from inner neritic 100 m at downdip sites during early highstands paleobathymetry ranged from 45 10 to 85 25 m landward of the clinoform rollover to 85 25 m to over 100 30 m on the slope seaward of the developing prograding sedimentary wedge while during late hsts paleodepths shoaled to as shallow as 25 10 m near the clinoform rollover this method can be applied to other continental passive margins to reconstruct the stratal geometry of and estimate water depths on the shelf furthermore by extending this process relative sea level and eustatic timings and amplitudes could be evaluated

global implications of lower to middle eocene sequence boundaries on the new jersey coastal plain the icehouse cometh wedocumentninelower middleeocenesequencesonthenewjerseycoastalplainand comparethemwithglobal d 18 oandhaqetal records earlyeocenehiatusesdonotmatch d 18 ochanges anditisunlikelythattheyaretheresultofglacioeustasy consistentwithan ice free early eocene early middle eocene 49 43 ma evidence for a link between sequencesand d 18 oisequivocal andthepresenceoflargeicesheetsisuncertain beginning in the late middle eocene 43 42 ma concomitant increases in planktonic and benthic d 18 o records coincide with the timing of hiatuses on the new jersey coastal plain and a change from carbonate dominated to siliciclastic dominated sedimentation these represent the development of the antarctic ice cap and the beginning of the icehouse world of the 14 sequences predicted by haq et al for this interval 9 are resolvable on the new jersey margin and the other 5 appear to be combined with others we conclude that although ice volume changes controlled sequences since at least 42 ma mechanisms for sea level change prior to then are still not fully understood

a coupled climate ice sheet modeling approach to the early cenozoic history of the antarctic ice sheet abstract the sudden widespread glaciation of antarctica and the associated shift toward colder temperatures near the eocene oligocene boundary 34 ma represents one of the most fundamental reorganizations of the global climate system recognized in the geologic record this glacial inception and the subsequent evolution of the early east antarctic ice sheet eais are simulated using a new coupled global climate dynamical ice sheet model accounting for the paleogeography greenhouse gas concentrations changing orbital parameters and varying ocean heat transport suites of long 105 yr climate ice sheet simulations are used to investigate the effects of declining atmospheric co2 compared to those of the tectonic opening of southern ocean gateways and the timing of mountain uplift in the antarctic interior in contrast to the established paradigm for the glaciation of antarctica which centers on the opening of the southern ocean gateways and the thermal isolation of the continent our results show that declining cenozoic pco2 may have played the dominant role first small isolated ice caps formed on the highest antarctic plateaus then as a co2 threshold between 3 and 2 pre industrial level pal was crossed height mass balance feedbacks were initiated during orbital periods with cold austral summers triggering much larger highly dynamic terrestrial ice sheets as co2 continued to decline these isolated ice caps eventually merged into a permanent continental scale eais in our model neither the opening of the southern ocean gateways nor mountain uplift significantly affected the timing of the major ice sheet transition given a scenario of gradually declining co2 from 4 to 2 pal over 10 million years around the eocene oligocene boundary

large scale facies change in the middle eocene south pyrenean foreland basin the role of tectonics and prelude to cenozoic ice ages abstract the present study reports a sedimentological analysis of the guara limestone formation deposited during the lutetian in the sierras exteriores in the south pyrenean foreland basin we provide a detailed facies analysis of the carbonates to precise the paleoenvironmental context during their deposition we show that those limestones are mainly composed of shallow water foraminifers and were deposited in relative shallow water environments

coupled manganese and carbon isotopic events in marine carbonates at the cenomanian turonian boundary abstract the boundary interval between the cenomanian and turonian stages of the upper cretaceous shows a positive excursion in the carbon isotopic composition of organic matter and carbonate in many epicontinental and oceanic sections of the atlantic tethyan realm some of the studied epicontinental sections contain an excursion in the manganese content of carbonates coincident with the shift in carbon isotopic values in a key reference section at pueblo colorado the stratigraphic position and magnitude of the manganese excursion are described with respect to the carbon isotopic excursion coincident excursions in manganese contents and carbon isotopic values are verified for a section in normandy france the depositional setting for these two sections is persistently to intermittently we l oxygenated with the accumulation of interbedded chalky and marly sediments no shift in manganese values was detected through the isotopic excursion in a section from northern nebraska where fossils are preserved only as bedding plane impressions due to extensive early diagenetic dissolution of carbonate the carbon isotopic and manganese excursions begin at the same stratigraphic position but manganese contents return to background values within the lower half of the carbon isotopic excursion the relative timing and duration of these signals suggest the existence of a large manganese reservoir that was rapidly mobilized transfer of manganese from deep sea oxides mn4 to epicontinental carbonates mn2 is inferred to have occurred during expansion of oceanic oxygen minimum zones with associated changes in redox gradients and boundaries simultaneous excursions in carbon isotopic values and manganese contents can occur at sites of carbonate accumulation when the carbon and manganese cycles are linked through the reducing potential of widespread oxygen deplete water masses

geochemical and palynological sea level proxies in hemipelagic sediments a critical assessment from the upper cretaceous of the czech republic geochemical and palynological records are presented for an expanded turonian coniacian hemipelagic succession in the central bohemian cretaceous basin a high resolution stratigraphic framework is provided by biostratigraphy and organic carbon stable isotope 13corg chemostratigraphy a short term 100 kyr sea level curve has been derived from high resolution transgressive regressive maxima shore proximity data established from basin wide sediment geometries the viability of geochemical and palynological parameters as potential sea level proxies is tested against this independently derived sea level record elemental chemostratigraphy is demonstrated to offer a reliable means of identifying medium to long term 0 4 2 4 myr sea level trends manganese maxima are associated with periods of high sea level and troughs with intervals of low sea level falling mn contents accompany regression and rising values transgression major transgressive events associated with medium term sea level change are marked by sharp increases in ti al ratios but short term 100 kyr sea level cycles are not consistently identified long term 13corg variation and dinoflagellate cyst species richness are positively correlated and show similarities to the sea level curve baseline trends have a cycle duration close to the 2 4 myr long eccentricity cycle dinocyst species richness closely follows short term changes in sea level with marked increases in dinocyst diversity coincident with most short term flooding events periods of rapid sea level rise caused an influx of a more diverse outer shelf assemblage into the study area together with the addition of shallower water species some of which may have been transported into the central basin by hypopycnal flows changes in the proportion and abundance of peridinioid dinoflagellate cysts principally palaeohystrichophora infusorioides were controlled principally by changing nutrient levels proximity proxies derived from geochemical and palynological data are not always consistent with the independent sea level model this exemplifies the need to understand all factors influencing elemental geochemical and palynological proxies before making simplistic sea level interpretations

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher

groundwater geochemistry of a small reservoir catchment in central tunisia abstractdue to the scarcity of water resources in semiarid sedimentary basins hill reservoirs are often constructed torechargegroundwaterandlimitruno inducedwaterloss theimpactofsuchreservoirsongroundwaterchemistryisinvestigatedintheaquifersoftheelgouazinewatershed centraltunisia threegroundwatertypesarerecognised ca hco 3 na clandca so 4 thestrongsimilaritybetweenhostrockandgroundwaterchemistriesindicatessig ni cantrock waterinteraction a owpath alongwhichthechemicalcompositionofthegroundwaterevolves canbeidenti ed using the contrast in stable isotope signature between upstream and downstream groundwater shallowupstreamgroundwaterisrechargedbythein ltrationofrainwaterwiththerateofrechargestronglylinkedtothepermeability of the host lithology calcium and hco 3 are supplied to an alluvial aquifer from a more rapidlyrechargedlimestoneaquiferwiththeconcentrationofcaandhco 3 ionsdecreasingbydilution thealluvialaquiferisalsoenrichedincaandso 4 duringthedownstream owofgroundwaterthroughgypsiferousmaterials thereisevi dence of mixing between meteoric groundwater and evaporated reservoir water below the reservoir and partlyresponsibleforreservoirleakageisasandyaquifer formedbyweatheringanderosionofasandstonehostwhichalsosupplieswatertothealluvialaquifer 2002elsevierscienceltd allrightsreserved 1 introductiona perennial problem for farmers and herdsman insemiaridareaswithoutpermanentriversisthescarcityofwaterowingtothelowanderraticrainfall inthelastcentury globalpopulationexpansionhastremendouslyincreased the pressure on water resources to securewater supply and intensify agricultural production water harvesting is traditionally used to combat theproblemsofvaryingrainfallratesandpopulationden sities one technique of water harvesting oodwater har vesting fwh alsocalledlargecatchmentwaterhar vesting or spate irrigation is widely developed when oodwaterisharvestedinthestreambed thewater owisdammedandstoredintemporaryorpermanentsur face reservoirs water is forced to in ltrate and asaresult torechargetheaquifer withrechargeconcentratedmainly in the valley downstream from the reservoir prinz 1999 fwhisarelativelyinexpensivetechniqueprovidingwaterforthedevelopmentofagricultureandagroforestry and reducing the use of other valuablewater resources such as groundwater water supply isnotalwaysevenandsecureduringtheyeardependingontheclimaticvariability largeevaporationlossesandlossofstoragebysiltationandpollutionarethemainlimitations of fwh social problems like con ictbetweenwaterusersareafurtherdrawbacktothisstyleofwaterharvesting inthemediterraneanbasin waterharvestingplayedan important role in ancient civilisations such as theromanandegyptianempires prinz 1999 duringthe20thcentury moderntechniques groundwaterdrilling largereservoirconstructionetc whicharefavouredbygovernmentpolicy slowlyreplacedtraditionalharvest ing techniques high demands for water during theagricultural growing season which coincides with thedryperiodofthemediterraneanclimate hasresultedinthe depletion of the groundwater table in some areas thelowrenewalrateofgroundwaterresourcesandthe