the paleocene eocene transition at mead stream new zealand a southern pacific record of early cenozoic global change mead stream in marlborough new zealand exposes a spectacular 650 m thick stratigraphic section of well bedded micritic limestone chert and marl that was deposited on a south pacific upper continental slope from late cretaceous to middle eocene the 200 m upper paleocene lower eocene succession was examined for its lithology bulk carbonate carbon isotopes and assemblages of radiolarians calcareous nannoplankton and foraminifera so that it could be placed into a global context the interval displays several prominent carbon isotope anomalies and is correlated with south pacific radiolarian zones rp5 to rp9 and calcareous nannofossil zones np6 8 to np12 additionally planktic foraminiferal zones p4 to p6b are identified in uppermost paleocene and lower eocene strata mead stream has a near continuous paleocene lower eocene sediment record and three globally significant climate events the late paleocene carbon isotope maximum pcim the initial eocene thermal maximum ietm and the early eocene climatic optimum eeco have obvious expressions the pcim is a 50 m thick interval of biosiliceous micritic limestone in which 13c is 3 the lower part contains two organic rich biosiliceous mudstone units that may represent expansion of an oxygen minimum zone omz during a global increase in marine biological productivity the ietm is a 4 m thick interval in which 13c drops below 1 5 in a pattern seen at other locations the basal 2 4 m is a distinctive recessed marl rich unit that is defined herein as the dee marl the ietm is marked by a rapid decline in the nannoplankton genus fasciculithus short lived occurrences of discoaster cf araneus and morozovella aequa aequa and significant radiolarian faunal turnover owing to impoverished benthic faunas the benthic foraminiferal extinction event bfee is poorly defined the onset of the eeco is marked by a 1 negative 13c excursion a transition from limestone rich to marl rich facies and a marked decrease in radiolarian abundance compacted sedimentation rates vary between 1 4 2 7 cm kyr for upper paleocene lower eocene strata at mead stream although individual beds with average thickness of 10 cm were deposited too fast to directly represent cycles in orbital parameters time series analysis of bed thicknesses suggests that groups of beds may record milankovitch scale periodicity perhaps with a significant obliquity component thus the relative frequency and thickness of marl and limestone beds in this section is shown to be strongly influenced by climatic changes at a wide range of temporal scales from suborbital and orbital cycles to aberrant short term events and long term trends predominance of marl in ietm and eeco intervals indicates that episodes of extreme global warming resulted in reduced oceanic productivity and increased terrestrial discharge in the high latitude southwestern pacific

changing depth distribution of hiatuses during the cenozoic the differential effects of climate change sea level and water mass circulation on deposition erosion of marine sediments can be constrained from the distribution of unconformities in the world s oceans i identified temporal and depth patterns of hiatuses hiatus events from a large and chronologically well constrained stratigraphic database of deep sea sediments the paleogene is characterized by few several million year long hiatuses the most significant cenozoic hiatus event spans most of the paleocene the neogene is characterized by short frequent hiatus events nearly synchronous in shallow and deep water sediments epoch boundaries are characterized by peaks in deep water hiatuses possibly caused by an increased circulation of corrosive bottom water and sediment dissolution the plio pleistocene is characterized by a gradual decrease in the frequency of hiatuses future studies will focus on the regional significance of the hiatus events and their possible causes

paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

effects of diagenesis on the isotopic record of late paleogene tropical sea surface temperatures abstract oxygen isotope records of planktonic foraminifera indicate that late eocene and oligocene tropical sea surface temperatures were as much as 8 c lower than present at a time when high latitude sea surface temperatures were higher than present using a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate the effects of diagenesis on bulk carbonate 18 o records for the cenozoic are quantified for four tropical sites most of the observed variations in measured 18 o values at all sites can be accounted for by diagenetic effects there are no systematic trends that support substantial variations in tropical sea surface temperatures beyond diagenetic effects with the possible exception of the early eocene for which the data are consistent with slightly higher sea surface temperatures reconstructions based on oxygen isotope records of planktonic foraminifera which indicate cooler tropical sea surface temperatures for the eocene and oligocene may be artifacts of diagenetic recrystallization as such records are particularly sensitive to diagenetic effects

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

silica burp in the eocene ocean the eocene was a time of greatly increased silica accumulation in the ocean and the peak was in the early middle eocene at about 50 ma the responsible geohistorical configuration included the following elements extensive volcanism about 4 m y earlier as part of the chron 24 plate reorganization early eocene warming with deep weathering to high latitudes and accumulation of the released silica in a sluggish ocean and sharp cooling in the earliest middle eocene stimulating oceanic upwelling and biosilicification it is possible on the evidence of carbon and oxygen isotopic patterns that the trigger for the exhalation of silica was a reverse greenhouse effect

atmospheric carbon dioxide and early eocene climate a general circulation modeling sensitivity study abstract the early eocene was the warmest time interval of the past 65 million years we have investigated the hypothesis that the warm climate of the early eocene may have been caused by higher than present levels of atmospheric carbon dioxide co2 we have used an atmospheric general circulation model the ncar genesis model coupled to a land surface model and a mixed layer ocean to examine the sensitivity of early eocene climate to varying levels of atmospheric co2 model cases contained a description of the early eocene earth and included either 300 560 or 1680 ppm atmospheric co2 climate responses to increased atmospheric co2 include 1 increased mean annual global temperature by 2 6 c and decreased latitudinal surface temperature gradients 2 maximum warming at high latitudes especially in the winter season 3 increased mean global precipitation 4 increased high latitude clouds in comparison with geological paleoclimate data the climate response to increased co2 does not appear to explain completely the early eocene latitudinal surface temperature gradient for example with the 1680 ppm co2 case high latitude oceans and continents are minimally warm enough to match paleoclimate data while low latitude regions are overly warm when compared to sea surface temperature reconstructions we conclude that co2 was very likely at least double the present level during the early eocene and contributed to the overall character of early eocene climate however consideration of increased poleward oceanic heat transport and or other factors may be required to produce model results that more closely agree with marine and terrestrial paleoclimate data especially at low latitudes

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

mesozoic alpine facies deposition as a result of past latitudinal plate motion the fragmentation of pangaea as a consequence of the opening of the atlantic ocean is documented in the alpine mediterranean region by the onset of widespread pelagic sedimentation1 shallow water sediments were replaced by mainly pelagic limestones in the early jurassic period radiolarian cherts in the middle late jurassic period and again pelagic limestones in the late jurassic cretaceous period1 during initial extension basin subsidence below the carbonate compensation depth ccd is thought to have triggered the transition from early jurassic limestones to middle late jurassic radiolarites1 it has been proposed that the transition from radiolarites to limestones in the late jurassic period was due to an increase in calcareous nannoplankton abundance when the ccd was depressed below the ocean floor1 but in modern oceans sediments below the ccd are not necessarily radiolaritic here we present palaeomagnetic samples from the jurassic cretaceous pelagic succession exposed in the lombardian basin italy on the basis of an analysis of our palaeolatitudinal data in a broader palaeogeographic context we propose an alternative explanation for the above facies tripartition we suggest that the lombardian basin drifted initially towards and subsequently away from a near equatorial upwelling zone of high biosiliceous productivity our tectonic model for the genesis of radiolarites adds an essential horizontal plate motion component to explanations involving only vertical variations of ccd relative to the ocean floor it may explain the deposition of radiolarites throughout the mediterranean and middle eastern region during the jurassic period

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

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

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

paleomagnetism of the late paleozoic slide mountain terrane northern and central british columbia paleomagnetic samples were collected from mid pennsylvanian to lower permian red argillaceous cherts at two localities of the slide mountain terrane 18 sites from the sylvester allochthon in northern british columbia and 11 sites from sliding mountain in central british columbia a secondary component of natural remanent magnetization in the sylvester samples yields a paleomagnetic pole that can be brought into coincidence with the jurassic portion of the north american apparent polar wander path by inferring vertical axis rotation during obduction of the allochthon both localities yield a characteristic component chrm with unblocking temperatures from 650 to 680 c after structural correction for bedding tilt all inclinations of chrm are negative consistent with magnetization during a reversed polarity interval in the northern hemisphere site mean chrm directions show consistent inclinations but distinct stratigraphic groupings of declinations inclination only statistics indicate that the chrm p

paleogene tropical pacific clues to circulation productivity and plate motion 1 stratigraphic data from 63 deep sea drilling project and ocean drilling program odp sites that sample the lower neogene and paleogene sediments of the tropical pacific have been compiled and put on the biostratigraphic and paleomagnetic timescale refined by odp leg 199 scientists sediment accumulation rates have been calculated for ten intervals ranging in age from 10 to 56 ma and have been plotted for the midpoint of each interval at the associated paleoposition for each site used a fixed hot spot model was used for reconstruction of the pacific lithospheric plate all such reconstructed intervals show the development of a tongue of high accumulation rates associated with the oceanographic divergence at the geographic equator the development of this equatorial band is weakest between 46 and 56 ma the time of the peak warmth in paleogene climate possible motion of the hawaiian hot spot or true polar wander between 46 and 56 ma appears to have had little effect on the plate rotation estimate of the position of the equator in addition to temporal changes in the calcite compensation depth and in productivity the biggest change in the patterns of sediment accumulation rates in the eastern tropical pacific was the development of a relatively strong divergence between 6 and 10 n near the region of divergence between the modern north equatorial current and the north equatorial counter current changes in the equatorial circulation appear to be associated in time with the opening and closing of oceanic gateways particularly the complex closing of the caribbean pacific gateway

effect of global ocean temperature change on deep ocean ventilation 1 a growing number of paleoceanographic observations suggest that the ocean s deep ventilation is stronger in warm climates than in cold climates here we use a general ocean circulation model to test the hypothesis that this relation is due to the reduced sensitivity of seawater density to temperature at low mean temperature that is at lower temperatures the surface cooling is not as effective at densifying fresh polar waters and initiating convection in order to isolate this factor from other climate related feedbacks we change the model ocean temperature only where it is used to calculate the density to which we refer below as dynamic temperature change we find that a dynamically cold ocean is globally less ventilated than a dynamically warm ocean with dynamic cooling convection decreases markedly in regions that have strong haloclines i e the southern ocean and the north pacific while overturning increases in the north atlantic where the positive salinity buoyancy is smallest among the polar regions we propose that this opposite behavior of the north atlantic to the southern ocean and north pacific is the result of an energy constrained overturning

equatorial ocean circulation in an extremely warm climate 1 the warm climates of the early paleogene and the associated diminished near surface winds should have resulted in a reduction in near surface ocean circulation one check on this deduction is the delineation of biogenic sediments associated with an equatorial current system of the early eocene pacific a latitudinal seismic reflection transect across the tropical pacific along early paleogene ocean crust reveals a basal high amplitude reflection package that we take to be the lower eocene section this unit varies in thickness by a factor of about two with the thickest portion forming a low mound some 3 4 north of the 56 ma paleoequator this mound may represent the position of a divergence generated in the frontal region between two currents flowing in opposite directions and its position suggests that the wind driven equatorial circulation of the early eocene was one without a pronounced equatorial divergence

late cretaceous eocene nannofossil and magnetostratigraphic correlations near gubbio italy abstract using a modified sample preparation technique we have been able to establish a detailed lower campanian to upper eocene nannofossil stratigraphy in the bottaccione and contessa highway sections near gubbio appearance and extinction levels of virtually all the commonly used calcareous nannofossil zonal markers have been recognized and can now be closely correlated with the planktonic foraminifera zonation and the magnetic reversal stratigraphy previously established in these sections comparisons with the nannofossil calibrations of the oceanic magnetic anomaly sequence in deep sea drilling project dsdp sites suggest that magmetic subchrons c17n and c25n are missing in the bottaccione section the observed variability of the relative stratigraphic position of most plankton events is confirmed to less than one magnetic subchron absolute abundance paleobiogeographic restriction and differential preservation render some of the traditionally used biostratigraphic events less reliable than others

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

eocene biostratigraphy and magnetic stratigraphy from possagno italy the calcareous nannofossil response to climate variability a study of quantitative calcareous nannofossil biostratigraphy and magnetostratigraphy of a 68 m thick marine limestone section of late paleocene middle eocene age outcropping at possagno in northern italy shows that the section encompasses nannofossil zones np9 np15 equivalent to cp8 cp13b and chrons c24r c21n the paleocene eocene boundary was placed at the base a of d 13 c negative excursion from the literature that was found virtually coincident with the base of zone np9b the base of the middle eocene lutetian was placed at the base of chron c21r biostratigraphic events were generally found to be consistent with parallel events in recent time scales several potentially useful new events are also described in particular we detected the earliest specimens of dictyococcites at the base of chron c22r np12 np13 zonal transition which is several million years older than previous estimates correlation of possagno data to the oxygen isotope record from the literature allowed us to describe the temporal relationships between climate variability and calcareous nannofossil assemblages modifications in the nannofossil assemblage coeval to both the paleocene eocene thermal maximum petm and the early middle eocene long term climatic trend are recognized the short lived petm was coeval to provisional adaptations malformations and or ecophenotypes in the coccolithophores communities that were reabsorbed upon return to long term varying climatic conditions the early middle eocene long term climatic trend was instead coeval to true evolutionary trends with the appearance of the very successful noelaerhabdaceae clade whose offsprings include the most important bloom forming coccolithophorids in the modern ocean the early middle eocene can thus be considered the time in which nannoplankton communities set course toward modern structure triggering a reconfiguration of the global ocean life chain d 2005 elsevier b v all rights reserved

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

sequences of silica phase transitions effects of na mg k al and fe ions abstract hydrothermal experiments on silica phase transitions in artificial solutions tested the effects of dissolved aluminum and iron on the evolution of solution composition and the mineral compositions of solid phases dissolved aluminum and iron come from detrital aluminosilicate phases including their coatings aluminosilicate phases retard formation of opal ct a metastable silica phase but they may promote transformation of opal ct to quartz the stable phase the four starting solutions all had alkalinity greater than seawater either 90 or 8 mm the four solutions were dominated by different cations one solution contained magnesium ion one magnesium and sodium ions one potassium ion and one sodium ion compositions of the solutions changed within 4 weeks quartz formed under a higher initial alkalinity of 90 mm with or without magnesium minor phases including opal ct clay minerals and melanophlogite were also observed in some experiments opal ct formed in the presence of magnesium and an initial alkalinity above 8 mm dissolved aluminum or iron reduced concentrations of dissolved silica causing precipitation of an initially more ordered opal ct in the presence of magnesium and quartz in its absence these effects influence the rates and sequences of silica diagenesis

evidence for deep water production in the north pacific ocean during the early cenozoic warm interval the deep ocean circulation is responsible for a significant component of global heat transport in the present mode of circulation deep waters form in the north atlantic and southern oceans where surface water becomes sufficiently cold and dense to sink polar temperatures during the warmest climatic interval of the cenozoic era approximately 65 to 40 million years myr ago were significantly warmer than today and this may have been a consequence of enhanced oceanic heat transport however understanding the relationship between deep ocean circulation and ancient climate is complicated by differences in oceanic gateways which affect where deep waters form and how they circulate here i report records of neodymium isotopes from two cores in the pacific ocean that indicate a shift in deep water production from the southern ocean to the north pacific approximately 65 myr ago the source of deep waters reverted back to the southern ocean 40 myr ago the relative timing of changes in the neodymium and oxygen isotope records indicates that changes in cenozoic deep water circulation patterns were the consequence not the cause of extreme cenozoic warmth

implications for the history of cenozoic opal deposition from a quantitative model in addition to being a time of enhanced crustal activity and a warmer climate the eocene also saw prolonged periods of silica accumulation on the ocean floor the peak of this accumulation occurred at approximately 50 ma creating horizon ac a layer of silica rich sediments spanning approximately 4 my horizon ac is comparatively isolated in time from known silicic acid addition processes leading mcgowran 1989 mcgowran b 1989 silica burp in the eocene ocean geology 17 pp 857 860 to suggest a novel mechanism the silica burp hypothesis that centres on the temporal decoupling of silicic acid supply and burial by climatic variation here we examine this hypothesis using a quantitative biogeochemical model of the silicon cycle our results unequivocally show that mcgowran s hypothesis is unable to account for horizon ac the model s residence time and ocean capacity for silicic acid are insufficient to permit the degree of temporal decoupling proposed by mcgowran inverting the model s results suggests that instead the sediment record may be a useful proxy for silicic acid additions to the ocean

stratigraphic and regional distribution of fractures in barremian aptian carbonate rocks of eastern oman outcrop data and their extrapolation to interior oman hydrocarbon reservoirs the carbonates of the barremian to aptian qishn formation are outcrop equivalents to major hydrocarbon reservoirs in the middle east and in oman specifically the rocks are exposed in the haushi huqf area of eastern oman where they are affected by pervasive jointing and localized folding and faulting information gathered in the huqf outcrops can be used to formulate predictions on fracture patterns in adjacent reservoirs systematic joints are confined to few meters thick intervals of widely differing lithologies which can be correlated over hundreds of square kilometers over the entire area systematic joints are typically more than tens of meters long have spacings of 4 18 cm and homogeneous morphologies these joints are interpreted to be of late aptian age the dominant set of joints strikes consistently nw se and developed parallel to the causative maximum horizontal compression sh the direction of compression is at an high angle to the two major tectonic domains of the region the subsiding oman interior basins and the elevated haushi huqf high nw se compression is proposed to have caused crustal lithospheric buckling and thereby to have controlled jurassic to early tertiary patterns of vertical movements in such a scenario the direction of compression is predicted to be constant over the entire domain it is thus expected that qishn carbonates in the subsiding oman interior basins also experienced nw se compression and developed systematic joints similar to those observed in the huqf region in the neogene with the establishment of the zagros stress field the maximum horizontal compression became roughly n s thereby possibly leading to the closure of pre existing joint systems

palaeoclimatology communication arising tropical temperatures in greenhouse episodes we agree with zachos and colleagues that much can be learned about transient climate events from well dated carbonate sediments from the deep ocean and that the problem of recrystallization of such sediments when tens of millions of years old means that constraining relative temperature changes from oxygen isotope data is more appropriate than attempting to measure absolute values

eocene magnetic stratigraphy at gubbio italy and its implications for paleogene geochronology the sequence of polarity zones established by alvarez and others for the cretaceous and paleocene in the scaglia formation in the bottaccione gorge at gubbio has now been extended through the uppermost paleocene into the upper eocene globigerinatheka semiinvoluta zone anomaly 18 the relationships between the standard paleogene foraminiferal zones and the sea floor anomalies are defined with the exception of the mid eocene zones of morozovella lehneri orbulinoides beckmanni and the base of the truncorota loides rohri zone which are obscured by inadequate preservation and a fault gap the base of the eocene lies above anomaly 25 the lower to middle eocene contact base lutetian lies in the upper part of anomaly 22 the base of the bartonian lies below the base of anomaly 18 and the base of the priabonian upper eocene lies within anomaly 18 radiometric ages appear to diverge systematically from a geochronology based on steady sea floor spreading rates suggesting that spreading may have been as much as a factor of 3 slower in the paleocene and the late eocene than in the early and middle eocene

new evidence for the hawaiian hotspot plume motion since the eocene abstract a thick mound of fossiliferous sediments reflecting high biogenic productivity at the equator can be used to determine latitudinal motion of the pacific lithospheric plate plate motion estimates based on the latitudinal movement of equatorial facies are independent of paleomagnetic data and hotspot tracks and thus permit further testing of kinematic models we have determined the northward motion of the pacific plate for the last 53 myr based on the position of the paleoequator as shown by equatorial sediment facies between 26 and 69 dsdp and odp sites sample the past 53 myr in the tropical pacific based on the mapped patterns of accumulation rates in these sites we were able not only to determine the position of the paleoequator but also to estimate the equatorial great circle and hence the relative position of the spin axis since the early eocene the northward motion of the pacific plate inferred from the change in latitude of dated hawaiian chain seamounts relative to the hawaiian hotspot is consistently higher than that deduced from the analyses of equatorial sediment facies such a difference results from a latitudinal shift of the hawaiian hotspot during the last 53 myr all together our observations and recent paleomagnetic results from the detroit nintoku and koko seamounts j a tarduno r a duncan d w scholl r d cottrell b steinberger t thordarson b c kerr c r neal f a frey m torii m c carvallo the emperor seamounts southward motion of the hawaiian hotspot plume in earth s mantle science 301 2003 1064 1069 1 are consistent with a progressive southward motion of the hawaiian mantle plume since the late cretaceous our results suggest that the hawaiian hotspot moved at 32 mm yr to the se during the past 43 million years and that the pacific plate moved 12 northward since 53 ma at an average rate of 25 mm yr

biostratigraphic implications of mid latitude palaeocene eocene radiolarian faunas from hole 1051a odp leg 171b blake nose western north atlantic

deposition of franciscan complex cherts along the paleoequator and accretion to the american margin at tropical paleolatitudes red radiolarian cherts from three localities within the franciscan subduction complex of northern california contain three components of remanent magnetization which are best isolated by progressive thermal demagnetization the first component usually removed by 300 c has an in situ direction similar to the present axial dipole field and is probably a recently acquired thermoviscous overprint a second component generally removed between 300 and 630 c has constant normal polarity and direction within each section and is interpreted to have been acquired by low temperature chemical alteration during subduction and accretion at the continental margin the third component isolated between 560 and 680 c has both normal and reversed polarities passes a fold test and is inferred to have been acquired during or soon after deposition the available paleomagnetic biostratigraphic and geochemical data indicate deposition of these cherts along the paleoequator 0 2 n or s paleolatitude between pliensbachian and oxfordian time as the oceanic plate moved eastward relative to north america beneath the equatorial zone of high biologic productivity between bathonian and cenomanian time the chert sequences apparently moved progressively away from the paleoequator 2 15 n or s and were soon after accreted to the american continental margin plate reconstruction models for the farallon plate corroborate low paleolatitude trajectories from ridge crest to subduction zone for example from 3 s to 11 n and they imply subsequent northward translation of the franciscan complex 4 000 km by strike slip faulting related to relative motions between the farallon kula pacific and north american plates

paleogene magnetic stratigraphy in umbrian pelagic carbonate rocks the contessa sections gubbio the umbrian sequence of pelagic carbonate rocks provides an opportunity for precise correlation between paleogene biostratigraphy and geomagnetic polarity history the red to pink paleocene to middle eocene scaglia rossa limestone the varicolored upper eocene scaglia variegata limestone and the gray green oligocene scaglia cinerea marlstone form a 250 m thick continuous exposure in the contessa valley near gubbio italy magnetostratigraphic lithostratigraphic and biostratigraphic investigations in three sections covering the entire paleogene have confirmed and dated the geomagnetic reversal sequence for most of this period the ferromagnetic mineral in the scaglia cinerea is magnetite and af demagnetization to peak fields of 20 mt is sufficient to define the characteristic remanent magnetization the scaglia variegata and pink scaglia rossa samples contain an additional hematite component which is very pronounced in dark red paleocene scaglia rossa samples changes of magnetic mineralogy take place in these limestones during heating especially above 500 c however thermal demagnetization is effective in isolating the characteristic remanence vectors which form almost antipodal clusters of directions representing normal and reversed polarities the directions are rotated counterclockwise partly due to post oligocene tectonism paleontological zonations of planktic foraminifera and calcareous nannofossils were hampered by poor preservation but the major epoch and stage 29 as in the gubbio bottaccione section paleocene eocene just above anomaly 25 eocene oligocene between anomalies 13 and 15 oligocene miocene just below anomaly 6c these correlations require slight modifications to previous conclusions on paleogene sea floor spreading rates

sea floor hydrothermal activity links climate to tectonics the eocene carbon dioxide greenhouse two important findings of recent ocean floor drilling in the southeast pacific deep sea drilling project leg 92 are i that sea floor hydrothermal activity may fluctuate through time by as much as an order of magnitude and ii that episodes of greatest hydrothermal flux correspond to times when ridge transform plate boundaries are undergoing major changes in their configuration rather than to known times of increased spreading rate or volcanism evidence is presented here in support of the hypothesis that heightened hydrothermal activity induced by the eocene tectonic activity caused a global greenhouse effect which may represent the long sought after historical analog to the carbon dioxide induced global warming expected to occur by the middle of the next century

palaeoclimatology communication arising tropical temperatures in greenhouse episodes reconstruction from oxygen isotope data of global sea surface temperatures ssts that prevailed during periods when greenhouse gas levels were higher than at present that is in the early eocene and cretaceous epochs indicates that temperatures were significantly warmer than present in mid to high latitudes but similar to or slightly cooler in the tropics however pearson and colleagues1 claim on the basis of oxygen isotope data from planktonic foraminifers recovered from clay beds in tanzania and other localities that the tropics were warm during the eocene attributing the discrepancy between these and previous tropical sst estimates to the effects of diagenetic overprinting of the latter here we note some potential flaws in their interpretation of the new oxygen isotope data

widespread formation of cherts during the early eocene climate optimum radiolarian cherts in the tethyan realm of jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates however the widespread occurrence of cherts in the eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones in a new survey of the global spatio temporal distribution of cenozoic cherts in deep sea drilling project dsdp and ocean drilling program odp sediment cores we found that cherts occur most frequently in the paleocene and early eocene with a peak in occurrences at 50 ma that is coincident with the time of highest bottom water temperatures of the early eocene climatic optimum eeco when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity cherts occur less commonly during the subsequent eocene global cooling trend primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation this timing of peak eocene chert occurrence which is supported by detailed stratigraphic correlations contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and or volcanism in a supposedly sluggish ocean of the eeco followed during the subsequent middle eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification with the formation of chert as a result of biosilica transformation during diagenesis instead we suggest that basin basin fractionation by deep sea circulation could have raised the concentration of eeco dissolved silica especially in the north atlantic where an alternative mode of silica burial involving widespread direct precipitation and or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling deficient conditions of the eeco cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones 2007 elsevier b v all rights reserved

secular distribution of biogenic silica through the phanerozoic comparison of silica replaced fossils and bedded cherts at the series level abstract the modern marine silica cycle is dominated by silica secreting phytoplankton principally diatoms but this cycle has evolved considerably during the phanerozoic we analyzed the temporal distribution of silica replaced fossils and bedded chert to determine the influence of factors such as extinctions and climate change on siliceous facies trends in silica replacement of fossils match faunal radiations during the ordovician and siluro devonian with peaks in silica replacement in the late ordovician and middle devonian corresponding to peaks in the abundance and diversity of siliceous sponges sharp drops in the abundance of silica replaced fossils and or bedded cherts coincide with four of the five major mass extinctions no discernible decrease marks the extinction at the end of the triassic we expected peaks in bedded chert deposition during glacial episodes because enhanced ocean circulation should favor more and stronger upwelling orogenic episodes which may trigger continental glaciati

in situ dissolution experiment of radiolaria in the central north pacific ocean abstract monospecific phaeodarian radiolarian assemblages of castanidium longispinum were suspended in plastic cages built with 225 m nylon mesh at different water depths from 378 to 5582 m in the central north pacific weight losses of these samples after a suspension period of 61 days were used to determine dissolution rates the highest weight losses were observed at 378 m where samples lost 90 of their initial weight through the main thermocline weight losses decreased from 90 to 60 and reached a constant value of 40 below it these weight losses are roughly an order of magnitude higher than those reported by earlier workers the higher weight losses can be attributed in part to the more soluble nature of the phaeodarian radiolarian skeletons and in part to the improved experimental technique kinetic considerations show that temperature is the major factor that controls silica dissolution rates in the ocean using an arrehnius plot for the apparent rate constants it can be shown that in surface water dissolution rats should be two orders of magnitude higher than in deep water below the main thermocline