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

quantitative reconstruction of middle and late eocene paleoclimate based on palynological records from the huadian basin northeastern china evidence for monsoonal influence on oil shale formation abstract the eocene was an interval of climate evolution when the extreme high temperatures of the earliest cenozoic gave way to a global cooling trend fine grained lacustrine sediments of eocene age from northeastern china represent an excellent archive to study long term environmental and climatic changes at high resolution the huadian basin is a cenozoic fault bounded basin in jilin province northeastern china though small in area it contains numerous oil shale and coal bearing layers which provide an abundant middle to late eocene palynoflora eighty five palynomorph genera and one hundred palynomorph species were identified in the huadian formation allowing to distinguish 4 palynozones the nearest living relatives of the recovered palynomorph taxa suggest the presence of subtropical evergreen and deciduous broad leaved forests during deposition of the huadian formation using the coexistence approach ca we calculated seven paleoclimatic parameters which indicate a subtropical warm and humid climate with a mean annual temperature above 13 6 c and a mean annual precipitation of at least 887 mm however the climate became cooler and drier during the transition from the lower oil shale member to the upper carbonaceous shale member palaeoclimatic data from the various middle and late eocene basins of northeastern china i e the huadian fushun yilan hunchun and jishu basins were compared with data from north american and european basins middle eocene climate in the northern hemisphere was generally warm and humid and the mean annual temperature and precipitation in northeastern china were similar to those in north america though slightly lower than those of europe similar trends in temperature and precipitation on different continents support the existence of a global mid eocene cooling event this paper is the first systematic study of middle to late eocene seasonality in the huadian basin our results show an apparent differentiation in both temperature and precipitation between summer and winter supporting the view that the east asian monsoon was established in northeastern china already during the middle to late eocene this middle and late eocene monsoon was likely driven by the development of pacific trade winds and an alternating seasonal high and low pressure system over siberia the climatic changes observed in our dataset especially the precipitation changes appear to have played an important role in controlling oil shale formation in the huadian basin a warmer and more humid climate with abundant precipitation and high subsidence rates formed a deeper huadian depositional lake high productivity and stable stratification provided the abundant organic matter and favorable preservation conditions necessary for oil shale accumulation

opening of the australia antarctica gateway as dated by nannofossils abstract the opening of the tasmanian gateway between australia and antarctica has long been considered a critical element in the initiation of the antarctic circumpolar current thermal isolation of antarctica and cenozoic global cooling the timing for the opening of the gateway to shallow water circulation and subsequently to deep water circulation was poorly known however and the dating of these events was a major objective of odp leg 189 nannofossil data from leg 189 sites and dsdp site 281 in the tasmanian gateway suggest a 41 42 ma age for the initiation of widespread glauconite deposition in the region which coincided with a sharp drop in sedimentation rate this is interpreted to be the opening of the gateway to shallow water circulation which occurred within the middle of the 51 33 ma long term cooling the change from siliciclastic sediments to pelagic carbonates the most conspicuous sedimentological and paleontological change in the region for the last 70 ma and presumably the indicator for the opening of the gateway to deep water circulation is dated at about 31 ma this event is more than 2 my younger than the major high latitude cooling in the earliest oligocene and thus cannot be the cause for the latter

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

changes in calcareous nannofossil assemblages during the middle eocene climatic optimum clues from the central western tethys alano section ne italy we present a study focused on changes in calcareous nannofossil assemblages of the alano section during the middle eocene climatic optimum meco this warming event is characterized by a prominent perturbation both in oxygen and carbon stable isotopes around the chron c18r c18n transition ca 40 ma and lasting ca 500 600 kyr semi quantitative analyses on calcareous nannofossil assemblages have been carried out our results show that the meco interval coincides with a significant shift in the relative abundance of calcareous nannofossil taxa suggesting a relationship between biotic changes and stable isotope shifts paleoecological studies at species level and or based on morphometric criteria i e small placoliths sometimes show the opposite behaviour between changes observed at the genus level and those observed at lower taxonomic levels for instance a taxon thought to be better adapted to oligotrophic warm waters e g sphenolithus shows a prominent decrease if analyzed at genus level but an increase was instead recorded for s spiniger moreover taxa preferentially thriving in eutrophic cold waters as for instance small reticulofenestrids increase remarkably in abundance during this warming phase while medium large placoliths do not show any significant trend an increase in reworked mainly cretaceous specimens is also observed during the meco these lines of evidence are consistent with a transient enrichment in dissolved nutrients in warmer sea surface waters suggesting that an enhanced nutrient availability could have driven the make up of the calcareous nannofossil assemblages the increase in reworking may indicate an increase in terrigenous input due to increased chemical weathering likely produced by an enhanced hydrological cycle

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

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

biostratigraphic characterization and quaternary microfossil palaeoecology in sediment drifts west of the antarctic peninsula implications for cyclic glacial interglacial deposition abstract the sedano project recovered 19 gravity cores on sediment drifts from the pacific continental margin of the antarctic peninsula camerlenghi et al 1997a high resolution terrigenous sedimentary record of the sediment drifts on the antarctic peninsula pacific margin in ricci c a ed the antarctic region museo nazionale dell antartide siena pp 705 710 fifteen cores were sampled with the aim of developing an integrated biostratigraphy and palaeoecology based on calcareous nannofossils diatoms planktonic and benthic foraminifera framed in a depositional process reconstruction barren gray laminated and brown bioturbated hemipelagic sediments characterize glacial and interglacial cycles respectively analyses from both intervals allow comparison between microfossil occurrence in glacial and interglacial cycles the unit boundaries were drawn more accurately by means of the microfossil distribution on the basis of micropalaeontological and sedimentological evidence interglacial unit c is correlated to oxygen isotope stage 5 thus dating the unit boundaries at 127 and 70 ka peaks in diatom abundance correlate well with interglacial units and indicate high productivity and an open ocean environment a calcareous nannofossil cold taxa association is present in most cores examined and its consistent distribution within interglacial unit c indicates key environmental relationships the occurrence of calcareous nannofossils has been related to temperature tolerance sea ice cover reduction nutrient availability and factors limiting primary productivity our results confirm that coccolithophorids occurred at southern high latitudes in the western marginal basins of the antarctic peninsula during short periods of the late quaternary a foraminiferal assemblage made up of sinistral neogloboquadrina pachyderma and few benthics occurs only in interglacial units correlation of microfossil occurrences with climatic cycles adds information on their palaeoecology and palaeoproductivity in the southern high latitudes

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

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

tectonic setting and terrane accretion of the archean zimbabwe craton the archean zimbabwe craton is made of a number of distinct tectonostratigraphic terranes assembled by plate tectonic processes the central tokwe terrane consists of 3 5 2 95 ga gneissic rocks and structurally complex inliers of possibly older greenstone belts these are overlain unconformably by a 2 9 2 8 ga assemblage of mafic and felsic volcanic rocks and conglomerates and a separate 3 0 2 7 ga southeastward thickening platform sequence of sandstone shale and limestone 2 7 ga greenstone belts form two distinctly different domains flanking the central terrane northwest of the ancient gneissic terrane ca 2 7 ga greenstone belts comprise a series of calc alkaline lavas and intercalated sedimentary rocks intruded by syn volcanic plutons southeast of the ancient gneissic complex 2 7 ga greenstone belts consist of thick piles of tholeiitic basalts overlying ultramafic lavas resting allochthonously over the shallow water platform sequence and older gneissic terrane this division of the zimbabwe craton is interpreted to show that the central tokwe terrane had a continental magmatic arc built on its northwestern edge as its southeastern margin rifted from another fragment forming the sea of umtali a passive margin sedimentary wedge formed on the rifted southeastern edge of this ancient continent and prograded onto the craton during sedimentary and tectonic loading of the craton margin the southeastern greenstone belts formed as thick oceanic crust oceanic plateau in this back arc basin and were later obducted on to the rift and passive margin sequence as the sea of umtali closed ca 2 7 ga this was followed by intrusion of granitic plutons of the chilimanzi suite ca 2 6 ga in a tectonic regime of intracontinental strike slip faulting representing a response to the zimbabwe kaapvaal continent continent collision crustal and lithospheric thickening during intrusion of these late granites may have played a role in stabilizing the zimbabwe craton and forming the lithospheric root

glaciation across the oligocene miocene boundary in southern mcmurdo sound antarctica new chronology from the ciros 1 drill hole few palaeogene and neogene sediment cores from the antarctic continental margin have been dated with sufficient precision to enable establishment of direct linkages between glacial events on the antarctic continent and marked events in deep sea delta 18o records as a result much of our knowledge of the gradual but stepwise shift from greenhouse climates of the cretaceous to the ice house climates of the quaternary is inferred from well dated and more continuously deposited deep sea sediments in this study we present new magnetostratigraphic results from the ciros 1 drill core from mcmurdo sound antarctica along with a reinterpretation of a published diatom biostratigraphic zonation that is constrained by correlation to a high precision age model from the nearby crp 2 2a drill core our results suggest that most of the upper 350 m of the ciros 1 drill core represents rapid sediment accumulation during a short time interval spanning the oligocene miocene boundary chronostratigraphic control is precise enough to enable correlation of this interval of glacimarine sedimentation with the mi 1 deep sea delta 18o event which confirms that the mi 1 event was related to a major expansion of antarctic ice a major unconformity at 366 m in the ciros 1 drill core which is widely observed in regional seismic reflection studies represents 9 myr of missing time this unconformity can be traced offshore into the ross sea using seismic stratigraphy and is interpreted to indicate significant east antarctic ice sheet development during the mi 1 glaciation the stratigraphic expression of this 400 kyr glacial event is evidently multiphase and complex in the victoria land basin probably because it was punctuated by higher frequency orbitally induced glacial oscillations the presence of nothofagidites pollen throughout the ciros 1 drill core and the presence of a nothofagus southern beech leaf within the early miocene portion of the core indicate that antarctic mean summer temperatures did not decrease below 5 deg c throughout the mi 1 glaciation these temperatures are significantly warmer than present day mean summer temperatures at sea level in mcmurdo sound the persistence of a nothofagus forest in coastal southern victoria land throughout this time interval suggests that the present state of deep refrigeration was not reached until some time after the mi 1 glaciation

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

environmental magnetic record of antarctic palaeoclimate from eocene oligocene glaciomarine sediments victoria land basin summary the onset of continent wide glaciation in antarctica is still poorly understood despite being one of the most important palaeoclimatic events in the cenozoic the eocene oligocene boundary interval has recently been recognized as a critical time for antarctic climatic evolution and it may mark the preglacial glacial transition magnetic susceptibility intensity of natural and artificial remanences hysteresis parameters and magnetic anisotropy of the lower half late eocene early oligocene of the ciros 1 core from mcmurdo sound antarctica reveal alternating intervals of high and low magnetic mineral concentrations that do not correspond to lithostratigraphic units in the core pseudo single domain magnetite is the main magnetic mineral throughout the sequence and sharp changes in magnetite concentration match changes in clay mineralogy beneath and at the eocene oligocene boundary the detrital magnetite originated from weathering of the ferrar group which comprises basic extrusive and intrusive igneous rocks weathering processes and input of magnetite to the victoria land basin were intense during periods when the antarctic climate was warmer than today but during intervals when the climate was relatively cool chemical weathering of the ferrar group was suppressed and input of detrital magnetite to the victoria land basin decreased our results also indicate that a cold and dry climate was not established in antarctica until the eocene oligocene boundary with major ice sheet growth occurring at the early late oligocene boundary some earlier cold intervals are identified which indicate that climate had begun to deteriorate by the middle late eocene boundary

evidence of surface water oligotrophy during the paleocene eocene thermal maximum nannofossil assemblage data from ocean drilling program site 690 maud rise weddell sea 1 nannoplankton assemblages at ocean drilling program site 690 maud rise weddell sea experienced an abrupt and dramatic transformation at the onset of the paleocene eocene thermal maximum petm at 55 m y the major assemblage shift suggests a change from colder more productive surface waters to warmer more oligotrophic conditions significant restructuring of assemblages during the later part of the petm indicates that nannoplankton communities were not stable and that surface water conditions changed although they remained warm and oligotrophic combined with benthic foraminiferal assemblage data nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean although the petm was a short lived event it appears to have had long term effects on nannoplankton leading to the extinction of fasciculithus a dominant paleocene genus

magnetostratigraphic calibration of southern ocean diatom datums from the eocene oligocene of kerguelen plateau ocean drilling program sites 744 and 748 ocean drilling program holes 744a and 748b represent key sections for calibration of southern ocean eocene oligocene biostratigraphic zonations sites 744 and 748 were above the carbonate compensation depth throughout this time interval and contain good planktonic foraminiferal calcareous nannofossil and diatom biostratigraphic records in particular the southern ocean diatom biostratigraphic zonation for the oligocene critically hinges on calibration of these two holes previous low resolution magnetostratigraphic studies at these sites were hampered by limited sampling and technical difficulties which prompted our high resolution reinvestigation of the magnetostratigraphy magnetic polarity zonations for holes 744a and 748b were constructed after inspection of vector component plots at 1 cm stratigraphic intervals from continuous u channel measurements the magnetizations are generally stable and a robust polarity stratigraphy has been obtained for both holes the increased resolution of our study and identification of persistent secondary overprints which were not recognised in previous studies suggests that the previously published interpretations need to be revised our magnetostratigraphic interpretations for both holes are constrained by foraminiferal and calcareous nannofossil datums as well as by sr isotope ages we have calibrated four diatom datums which are synchronous at the two studied sites to the geomagnetic polarity timescale including the first occurrence fo of lisitzinia ornata 27 8 ma the fo of rocella vigilans var b 27 8 ma the fo of cavitatus jouseanus 30 9 ma and the fo of rhizosolenia oligocaenica 33 8 ma the synchroneity of these datums suggests that diatom biostratigraphy has considerable potential for palaeogene biostratigraphic correlation in the southern ocean although the ages of some datums are obscured by an unconformity in hole 744a our age model from hole 748b suggests age estimates for the last common occurrence of rocella vigilans var a 29 0 ma the fo of rocella vigilans var a 30 0 ma and the fo of rhizosolenia antarctica 33 2 ma it should also be noted that the last occurrence of the calcareous nannofossil chiasmolithus altus occurs in chron c8r rather than c8n in our revised magnetostratigraphic interpretation which indicates that this datum is not diachronous between low and mid latitudes as had previously been suggested significant unconformities are documented in both holes in the middle oligocene and in the middle late oligocene respectively which probably resulted from periods of enhanced circumpolar deep water circulation

inorganic geochemistry of the type caradoc series sandbian to middle katian upper ordovician onny valley shropshire uk the geochemistry and petrology of the type section of the caradoc series in the onny valley indicate that it was deposited on a marginal basin continental shelf similar to the western side of the present sea of japan the lower beds form a transgressive regressive sequence in which the rocks become less mature upwards all the coarser sediments above the basal quartzites and conglomerates are greywackes in which the apparent muddy and ferrous matrix is due to the breakdown of unstable minerals and particles higher values of na 2 o and na k ratios are found in the coarser shallow water sandstones of the horderley sandstone formation and decrease markedly in the succeeding beds accompanied by an increase in k 2 o higher values of carbonate corrected and hence related other major and minor elements like sio 2 cao p 2 o 5 mno and most trace elements correlate with the transgressive systems and maximum flooding surfaces of the three sequences recognized where they are related to condensation at those horizons chemical indices of alteration cia suggest that the horderley sandstone formation underwent greater predepositional physical weathering than lower and higher beds which is compatible with the petrography and were deposited during a cool phase within overall warm sandbian katian times trace element ratios suggest an oxic to suboxic depositional environment

biotic signals from nannoflora across the iridium anomaly in the upper eocene of the massignano section evidence from statistical analysis abstract strong evidence for a major late eocene impact including an iridium rich layer and shocked quartz has been found in the massignano section central italy stratotype of the eocene oligocene boundary quantitative calcareous nannofossils analyses have been performed and classical and multivariate statistical techniques have been applied to assess the paleonvironmental effect of this impact on the nannoflora abundance patterns indicate 1 a warming episode just above the iridium layer 2 a subsequent slight cooling trend probably related to the global cooling during late eocene to early oligocene 3 marked fluctuations in the trophic resources and an increase in near shore taxa in the upper part of the interval 4 increase in low nutrient taxa in biotite rich layers just above the iridium level possibly related to lowered productivity linked to volcanic activity all these signals appear most likely to be the result of long term climatic changes rather than to short term effects of extraterrestrial impact in addition cluster analysis was performed on the assemblage data this delineated similarities among different taxa and grouped samples with similar assemblages several groups related to temperature trophic and unknown preference conditions have been distinguished a consistent difference in the abundances of the taxa and in their correlation has been detected between samples above and below the iridium level this change appears to be related to two important sedimentary features which are found in the interval above the iridium occurrence 1 the presence of biotite rich layers linked to increasing volcanism and 2 a conspicuous color transition from reddish to greenish related to changes in sedimentary environments e g variations in trace element abundance these environmental changes rather than the impact may have affected the nannoflora assemblages

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

evolution of cenozoic seaways in the circum antarctic region abstract a complete circum antarctic seaway did not open until both the south tasman rise cleared the oates land coast of east antarctica and drake passage opened between the southern tip of south america and the northern end of the antarctic peninsula major plate motions based on dated seafloor spreading anomalies and distinct fracture zone lineations constrain the age of the opening of a seaway between the south tasman rise and antarctica as very close to the eocene oligocene boundary with an unrestricted opening deeper than 2000 m dating from 32 ma timing of the opening of drake passage is more circumstantial because the exact motions of certain micro continental fragments are not known the motion of africa with respect to south america as well as the motion of east antarctica with respect to africa are well constrained for the cenozoic these major plate motions are used with the reasonable assumption of no cenozoic motion of the antarctic peninsula with respect to east antarctica to constrain the location of the antarctic peninsula with respect to the southern tip of south america for the critical period of late eocene to late oligocene uncertainty of motion of the south georgia and south orkney microcontinents and other possible continental fragments make an exact time for opening of drake passage difficult to ascertain even so the early oligocene position of the antarctic peninsula with respect to south america requires a through going deep water seaway to have been open at drake passage prior to 28 ma even given the unconstrained motion of various high standing crustal fragments in the scotia sea with reasonable assumptions concerning motion of the crustal fragments in the western and central scotia sea it is likely that drake passage or passage through powell basin was open to deep water circulation by 31 2 ma

the middle miocene climatic transition in the southern ocean evidence of paleoclimatic and hydrographic changes at kerguelen plateau from planktonic foraminifers and stable isotopes abstract middle miocene 14 8 11 9 ma deep sea sediments from odp hole 747a kerguelen plateau southern indian ocean contain abundant well preserved and diverse planktonic foraminiferal assemblages a detailed study of the climatic and hydrographic changes that occurred in this region during the middle miocene climatic transition led to the identification of an intense cooling phase the middle miocene shift abundance fluctuations of planktonic foraminiferal species with different paleoclimatic affinities and oxygen and carbon stable isotopes have been integrated in a multi proxy approach reconstruction of changes in foraminiferal faunal composition and diversity through time were the basis for identification of three foraminiferal biofacies the most prominent faunal change took place at 13 8 ma when a fauna with warm water affinity marked by high abundance of globorotalia miozea group and globoturborotalita woodi plexus was replaced by an oligotypic opportunistic fauna with typical polar characters and dominated by neogloboquadrinids this faunal change is interpreted as the result of foraminiferal migration from adjacent bioprovinces caused by modifications in climate and hydrography a positive 2 0 shift in 18o interpreted as the mi3 event and a related positive 1 0 shift in 13c corresponding to the cm6 event accompanied this faunal turnover these are interpreted to reflect substantial reorganization of southern ocean waters the northward migration of the polar front and a strong increase in primary productivity the second faunal change took place at 12 9 ma and was characterized by the gradual decrease in abundance of the neogloboquadrinids and the recovery of globorotalia praescitula scitula group and globigerinita glutinata a positive 1 5 shift in 18o interpreted as the mi4 event and a concurrent gradual negative shift in 13c accompanied this faunal change witnessing further modifications of the climate ocean system variations in sea surface temperature considered as the main factor causing changes of surface hydrography at the kerguelen plateau seem to have been driven by obliquity and long term eccentricity thus suggesting a key role played by the astronomical forcing on the evolution of southern ocean dynamics during the middle miocene also an evident 1 2 myr modulation of the 13c record suggests a main control of the long term obliquity cycles on the carbon cycle dynamics particularly the mi3 cm6 events exactly fit with a node of the 1 2 myr modulation cycles this confirms the key role played by orbital parameters on high latitude temperatures and antarctic ice volume and indirectly on global carbon burial and or productivity this climatic transition was marked also by changes in surface hydrography from 14 8 to 13 8 ma an intermediate strength thermocline controlled by seasonality developed just below the photic zone weaker seasonality characterized the interval from 13 8 to 12 9 ma when the thermocline became shallower and sharper and favored intermediate water foraminifers from 12 9 ma seasonality increased again and an intermediate strength thermocline re developed

the middle pleistocene glacial evolution of northern east anglia uk a dynamic tectonostratigraphic parasequence approach the middle pleistocene glacial history of northern east anglia is a controversial topic with differing opinions surrounding chronology provenance and the relative stratigraphic framework reconciling the stratigraphic framework of the region is an essential first step to developing onshore offshore geological models and a robust event driven chronological framework within this study a dynamic tectonostratigraphic parasequence methodology is applied to deposits traditionally attributed to the anglian glaciation marine isotope stage 12 this approach offers an insight into ice bed coupling during glaciation and how evolving boundary conditions influenced glacier dynamics six major tectonostratigraphic parasequence assemblages a1 a6 are recognized in northern east anglia and correlate with successive advances into the region of north sea or pennine lobes of the british ice sheet individual tectonostratigraphic parasequence assemblages are bound at their base by a sedimentary contact or more commonly a glacitectonic zone the geometry and structural characteristics of these glacitectonic zones reflect temporal and spatial variations in ice bed coupling traction a function of substrate rheology and in turn variations in lithology porewater availability and thermo mechanical properties the role of permafrost may also be significant promoting proglacial ice marginal thrust stacking in front of advancing ice and enhanced ice bed decoupling during subsequent overriding and subglacial till accretion 2016 british geological survey nerc journal of quaternary science 2016 john wiley sons ltd

the enigma of oligocene climate and global surface temperature evolution falling atmospheric co2 levels led to cooling through the eocene and the expansion of antarctic ice sheets close to their modern size near the beginning of the oligocene a period of poorly documented climate here we present a record of climate evolution across the entire oligocene 33 9 to 23 0 ma based on tex86 sea surface temperature sst estimates from southwestern atlantic deep sea drilling project site 516 paleolatitude 36 s and western equatorial atlantic ocean drilling project site 929 paleolatitude 0 combined with a compilation of existing sst records and climate modeling in this relatively low co2 oligocene world 300 to 700 ppm warm climates similar to those of the late eocene continued with only brief interruptions while the antarctic ice sheet waxed and waned ssts are spatially heterogenous but generally support late oligocene warming coincident with declining atmospheric co2 this oligocene warmth especially at high latitudes belies a simple relationship between climate and atmospheric co2 and or ocean gateways and is only partially explained by current climate models although the dominant climate drivers of this enigmatic oligocene world remain unclear our results help fill a gap in understanding past cenozoic climates and the way long term climate sensitivity responded to varying background climate states

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

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

neritic southern extratropical foraminifera and the terminal eocene event abstract if the terminal eocene event tee records a major bolide impact or other extraterrestrial happening then there ought to be disruption of benthonic foraminiferal communities especially in rather shallow neritic environments we record the arrivals and departures of 180 species in a composite succession through the later middle eocene late eocene and earliest oligocene in southern australia the rate of new arrivals increases at each of several transgressions each of which also marks a climatic amelioration the sharpest increase in rate of departure is found at a regional regression within the latest eocene there is no evidence of major disruption of the fauna at the end of the eocene the tee on this data was not extraterrestrial in origin and was hardly cataclysmic the study suggests instead that the origins of late eocene biotic change should be sought through earthly configurations of climate and sea level

coccolithus pelagicus a productivity proxy related to moderate fronts off western iberia abstract the traditional interpretation of coccolithus pelagicus as a cold water proxy is examined based on its distribution patterns in the water column off the portuguese coast using data from eleven cruises and in holocene surface sediment samples and quaternary cores from the same region coccolithus pelagicus is common in the portuguese upwelling system an area where surface waters are predominantly of subtropical origin although revealing an affinity for low temperature upwelled waters the species was found in waters up to 18 c associated with riverine plume and shelf break fronts c pelagicus seemed to consistently occupy a particular ecological niche between other phytoplankton groups related to moderate turbulence conditions combined with nutrient availability from this behaviour it is proposed that c pelagicus can be used as a tracer of the periphery of areas of enhanced productivity coccolithus pelagicus preferences for fronts of moderate temperature and salinity gradients are tentatively used to explain particular features of its sedimentary record the repeated increase of c pelagicus in thanatocoenoses surface sediment assemblages close to three river mouths on the portuguese shelf are interpreted as a positive response to the development of riverine plumes on the other hand inconsistencies in the correlation between sea surface cooler glacial and warmer interglacial isotope stages and the relative abundance pattern of c pelagicus during the late quaternary as registered in two galicia bank piston cores 42 n are tentatively explained in terms of shifts in the extent of the outer limit of the local palaeoproductivity belt off the iberian peninsula

magnetotactic bacterial abundance in pelagic marine environments is limited by organic carbon flux and availability of dissolved iron article i nfo article history magnetotactic bacteria intracellularly biomineralize magnetite of an ideal grain size for recording palaeomagnetic signals however bacterial magnetite has only been reported in a few pre quaternary records because progressive burial into anoxic diagenetic environments causes its dissolution deep sea carbonate sequences provide optimal environments for preserving bacterial magnetite due to low rates of organic carbon burial and expanded pore water redox zonations such sequences often do not become anoxic for tens to hundreds of metres below the seafloor nevertheless the biogeochemical factors that control magnetotactic bacterial populations in such settings are not well known we document the preservation of bacterial magnetite which dominates the palaeomagnetic signal throughout eocene pelagic carbonates from the southern kerguelen plateau southern ocean we provide evidence that iron fertilization associated with increased aeolian dust flux resulted in surface water eutrophication in the late eocene that controlled bacterial magnetite abundance via export of organic carbon to the seafloor increased flux of aeolian iron bearing phases also delivered iron to the seafloor some of which became bioavailable through iron reduction our results suggest that magnetotactic bacterial populations in pelagic settings depend crucially on particulate iron and organic carbon delivery to the seafloor

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

eocene oligocene magnetobiochronology of odp sites 689 and 690 maud rise weddell sea antarctica magnetostratigraphic studies of paleogene sediments piston cored on maud rise weddell sea odp sites 689 and 690 are a cornerstone of southern ocean paleogene and neogene chronostratigraphy however parts of previous magnetostratigraphic interpretations have been called into question and recent reinvestigation of the upper paleocene middle eocene portion of site 690 suggested that the records might be contaminated by spurious magnetizations which raises doubts about the reliability of these important records we undertook a high resolution magnetostratigraphic study of eocene oligocene u channel samples from odp holes 689b 689d 690b and 690c in order to address these concerns a pervasive overprint appears to be present below the middle eocene which compromises magnetobiostratigraphic interpretations for the upper cretaceous and lower paleogene nevertheless our new results provide a robust record of geomagnetic field behavior from 38 5 to 25 ma and confirm the reliability of these sediments for calibration of biostratigraphic datum events during a crucial phase of earth history when major antarctic ice sheets developed also comparison of magnetozone thicknesses in multiple holes at the same site indicates that 1 2 1 8 m of the stratigraphic record is missing at each core break which corresponds to time breaks of 120 360 k y lack of a continuous record within a single hole renders useless spectral analyses for investigating long geomagnetic and paleoclimatic time series this observation reinforces the need for coring of multiple offset holes to obtain continuous paleoceanographic records sedimentary hiatuses have been identified only at the deeper of the two investigated sites site 690 which could mark a local response to the onset of the antarctic circumpolar current

middle eocene to early oligocene calcareous nannofossil stratigraphy at leg 177 site 1090 semi quantitative and quantitative analyses on nannofossil assemblages were carried out on the middle eocene to early oligocene interval of site 1090 hole b several biozones were recognized according to the schemes of martini 1971 okada and bukry 1980 and wei and wise 1990a between the fo of reticulofenestra reticulata and the lo of reticulofenestra umbilica based on nannofossil biostratigraphy our proposed interpretation of shipboard magnetic inclination data recognizes magnetic chrons from c12 to c19 according to the geomagnetic polarity time scale of berggren et al 1995 the eocene oligocene boundary is placed between the last occurrences of reticulofenestra oamaruensis and discoaster saipanensis within chron c13r on the basis of the correlation between magnetostratigraphy and biostratigraphy a new biochronology is proposed for some nannofossil events the age of fo of reticulofenestra circus was estimated at 33 39 ma no previous biochronology is available in the literature for this event an age depth curve is constructed on the basis of the correlation between nannofossil biostratigraphy and the gpts of berggren et al 1995 a very low value of sedimentation rate 0 5 m ma characterizes the upper part of the study site from the last occurrence of ericsonia formosa to the last occurrence of r umbilica the presence of a hiatus or a condensed interval may occur at this level it may be related to the mid oligocene marshall paraconformity and the inception of the antarctic circumpolar current which contributed to the modification of the nannoflora composition and sedimentation in this sector of the south ocean 9 2002 elsevier science b v all rights reserved