a paleoslope model of late albian to early turonian foraminifera of the western atlantic margin and north atlantic basin abstract a paleoslope model of albian to turonian benthic foraminifera reveals seven successive biofacies which are associated with increasing paleodepth the paleoslope model indicates that the biofacies occupied inner neritic to abyssal environments of deposition 10 m to 3500 m water depth biofacies 1 and 2 characterize paleodepths of less than 60 m the biofacies contain abundant species of epistomina and gavelinella and exhibit a rapid stratigraphic alternation in response to local sea level change which considerably aids in the identification of depositional sequences species of globorotalites eggerellina and neobulimina characterize biofacies 3 which principally occurs between 60 m and 130 m paleodepth biofacies 3 is the only biofacies to occur in both the new jersey coastal plain and the baltimore canyon trough biofacies 4 is composed of species of gavelinella gyroidinoides and valvulineria and is abundant in outer neritic to middle bathyal paleodepths of 130 m to 600 m it is largely replaced by biofacies 5 during times of maximum flooding during sea level rise a diverse assemblage of species of lingulogavelinella and lenticulina characterize biofacies 5 paleodepths of 600 m to greater than 3500 m contain abundant species of osangularia pleurostomella praebulimina pseudopatellinella and quadrimorphina which define biofacies 6 and 7 in addition four biofacies of much more limited distribution are recognized biofacies 1 characterizes shallow water open marine paleoenvironments of the north atlantic and is composed of spirillinids and species of epistomina turonian dysaerobic environments are indicated by biofacies dsa and dsb which are composed mostly of agglutinated species dysaerobic environments expanded rapidly from middle bathyal to outer neritic depths in the early turonian on the western atlantic margin biofacies daa represents disturbed benthic environments and is dominated by species of psammosphaera and reophax biostratigraphy and species composition of the studied biofacies are similar to previously described european and south atlantic assemblages major speciation events occur among the genera gavelinella lingulogavelinella and valvulineria well defined neritic and bathyal biofacies formed during a rapid late albian species diversification concomitant with the first major cretaceous flooding of continental margins

resolving a late oligocene conundrum deep sea warming and antarctic glaciation abstract changes in ice volume and resulting changes in sea level were determined for the late oligocene 26 23 ma astronomical timescale ats by applying 18 o to sea level calibrations to deep sea 18 o records from odp sites 689 690 929 1090 and 1218 our results show that maximum global ice volume occurred during two late oligocene 18 o events oi2c 24 4 ma and mi1 23 0 ma inferred glacioeustatic lowering with volumes up to 25 greater than the present day east antarctic ice sheet eais ice volume during glacial minima was on the order of about 50 of the present day eais this is supported by late oligocene stratigraphic records from antarctica that contain evidence of cold climates and repeated episodes of glaciation at sea level and grounding lines of glacial ice on the antarctic continental shelf in the ross sea and prydz bay in contrast composite deep sea 18 o records show a significant decrease 1 between 26 7 and 23 5 ma which have long been interpreted as bottom water warming combined with deglaciation of antarctica however a close examination of individual 18 o records indicates a clear divergence after 26 8 ma between records from southern ocean locations i e ocean drilling program sites 689 690 744 and those of other ocean basins high 18 o values 2 9 3 3 from these southern ocean 18 o records are consistent with an ice sheet on the east antarctic continent equivalent to present day values and cold bottom water temperatures 2 0 c these differences suggest a reduction in deep water produced near the antarctic continent i e proto antarctic bottom water proto aabw which were quickly entrained and mixed with warmer and presumably more saline bottom water originating from lower latitudes expansion of a warmer deep water mass and the weakening of the proto aabw may explain the large intra basinal isotopic gradients that developed among late oligocene benthic 18 o records these conclusions are also supported by ocean modeling suggesting a reduction of deep water formed in the southern ocean strengthening of deep water from the northern hemisphere and decreasing temperatures in high southern latitudes occurred as the drake passage opened to deep water low 18 o values reported from deep sea locations other than the southern ocean are shown to bias estimates of antarctic ice volume calling for a re evaluation of the notion that antarctic ice volume was significantly reduced during the late oligocene

ocean circulation and calcareous nannoplankton evolution during the jurassic and cretaceous abstract spatial and temporal distribution of calcareous nannoplankton aid in the reconstruction of ocean circulation during the cretaceous biogeographic patterns of calcareous nannoplankton during the late cretaceous are mostly zonal reflecting mostly latitudinal gradients of surface water temperature during the middle cretaceous calcareous nannofossil assemblages are more strongly affected by surface water fertility concentration of limiting nutrients especially in a wide tropical belt between 50 and 45 n latitudes major upwelling regions off northwest africa in the south atlantic and the equatorial pacific divergence are apparent temporal changes in the composition of middle cretaceous nannofloras are indicative of changes in surface water fertility and vertical mixing at frequencies of tens to hundreds of kiloyears ka changes in the intensity of atmospheric circulation with frequencies close to the milankovitch cycles appear to be the ultimate cause of these minor changes in the circulation of the upper ocean calcareous nannofossil preservation patterns show that during the middle cretaceous deep waters were quite homogeneous with respect to carbonate saturation in the atlantic ocean but not in the indo pacific ocean where a more distinctive calcite compensation depth ccd is apparent water mass structure of the major oceans during the mesozoic was thus quite different taxonomic evolution of calcareous nannofossils was also strongly affected by ocean circulation and fertility major peaks in the rates of diversification coincide with anoxic events that is periods of increased preservation of organic carbon in the oceans which coincide with high sea level stands during anoxic events ocean circulation was sluggish vertical mixing was slow deep ocean ventilation poor and the concentration of limiting nutrients in surface waters was low increased competition for limiting nutrients and possibly preferential cropping of the dominant forms by zooplankton resulted in increased rates oof speciation during anoxic events periods of major production of nannofossil carbonate coincided with low sea level stands when oceans were more vigorously stirred and surface waters were more fertile the first such period was the latest jurassic when calcareous nannoplankton invaded the open oceans and became the major carbonate producers in the pelagic realm during the mesozoic the frequency of peaks and troughs in evolutionary rates is on the order of 10 30 ma and appears to be irregular the coincidence of periods of anoxia with high sea level stands which in turn appear to be caused by more rapid sea floor spreading indicates that the ultimate diving forces of nannoplankton evolution are processes in the earth s mantle these major tectonically driven fluctuations in ocean atmosphere circulation with frequencies of a few million to a few tens of millions of years are hereby named fischer cycles superimposed astronomically driven milankovitch cycles affected relative abundance patterns but not taxonomic evolution of calcareous nannoplankton rates of nannoplankton extinction are about five times higher than background rates at the end of the jurassic and orders of magnitude higher in the latest cretaceous possibly indicating a terrestrial or extraterrestrial catastrophe

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

contourite drifts on early passive margins as an indicator of established lithospheric breakup the albian cenomanian breakup sequence bs offshore northwest iberia is mapped described and characterised for the first time in terms of its seismic and depositional facies the interpreted dataset comprises a large grid of regional 2d seismic reflection profiles complemented by industry and odp dsdp borehole data within the bs are observed distinct seismic facies that reflect the presence of a black shales and fine grained turbidites b mass transport deposits mtds and coarse grained turbidites and c contourite drifts borehole data show that these depositional systems developed as mixed carbonate siliciclastic sediments proximally and as organic carbon rich mudstones black shales distally on the northwest iberia margin mtds and turbidites tend to occur on the continental slope frequently in association with large scale olistostromes distally these change into interbedded fine grained turbidites and black shales showing widespread evidence of deep water current activity towards the top of the bs current activity is expressed by intra bs erosional surfaces and sediment drifts the results in this paper are important as they demonstrate that contourite drifts are ubiquitous features in the study area after aptian albian lithospheric breakup therefore we interpret the recognition of contourite drifts in northwest iberia as having significant palaeogeographic implications contourite drifts materialise the onset of important deep water circulation marking the establishment of oceanic gateways between two fully separated continental margins as a corollary we postulate the generation of deep water geostrophic currents to have had significant impact on north atlantic climate and ocean circulation during the albian cenomanian with the record of such impacts being preserved in the contourite drifts analysed in this work

middle and late albian geography oceanography and climate and the setting of the kirchrode i and ii borehole sites abstract the paper reviews the literature on the geography oceanography and climate belts during the middle and late albian emphasis is placed on the northern hemisphere and the lower saxony basin the middle and late albian represents a time with a greenhouse climate the n s temperature gradient and the temperature gradient between the shallow and deep waters of the oceans were lower than at present meaning higher temperatures especially at middle and high latitudes a more sluggish ocean circulation than today and the absence of polar ice caps warming from the early to late albian is documented in the marine sediments by oxygen isotope studies and the poleward expansion of rudist dominated carbonate platforms in the terrigenous sediments of the northern hemisphere it is documented by northward migration of low latitude relatively arid flora the opening north atlantic was still narrow at the beginning of the albian it widened and deepened through the albian a shallow seaway between the south atlantic and the western tethys developed during the late albian wide shelf seas existed on the continental plates with rising sea level the basins of the western epicontinental seas of eurasia became increasingly connected and sedimentation gradually became more calcareous nevertheless these basins received a large clastic input from the land documenting the weathering conditions on the surrounding land masses they received also a considerable biogenic particle flux from the surface waters documenting productivity of the marine plankton because of these different origins of the sediment components as well as the connections with neighbouring seas the sediments in these shelf basins were expected to document changes in climate as well as palaeo oceanographic changes earlier interpretations based on ammonite studies that indicate changing connections between the arctic ocean and the tethys during the albian can thus be tested the lower saxony basin was a shelf sea in the southern part of the warm humid climate belt at mid latitudes in the northern hemisphere in which thick deposits of hemipelagic sediments accumulated mapping previous to our study indicated that a complete undisturbed albian basinal sequence ca 400 m thick is present below a thin quaternary cover in a sub basin between the nne ssw trending benthe and lehrte salt structures in the central part of the lower saxony basin the boreholes at the kirchrode i and ii sites 52 22 35 n 9 49 87 e and 52 22 16 n 9 49 12 e respectively in hannover were drilled into this sub basin the high sedimentation rates known for the albian of the lower saxony basin are ideal for studying climatic changes with a cyclicity of a few ten thousand to a few hundred thousand years milankovitch cyclicity

mineralogical evidence for warm and dry climatic conditions in the neo tethys eastern turkey during the middle eocene abstract minerals in stratigraphic sections are valuable tools for reconstructing past environmental conditions given the state of preservation of clay minerals it is possible to determine under what conditions they formed which provides clues about continental weathering inherited minerals and geochemical conditions in the water column or pore waters neoformed or transformed of the sedimentary environment this study presents new mineralogical and chemical data from the baskil section a well preserved middle eocene neo tethys sequence from eastern turkey greater terrigenous input is marked by the increase of silicate minerals e g phyllosilicates quartz and albite in the section from 40 5 to 40 ma which diluted the marine carbonate content this period is correlative with the global middle eocene climatic optimum meco event authigenic palygorskite increased from the middle to the uppermost portion 40 to 37 3 ma of the section indicating dryer conditions in the continent and availability of si and mg in the water column and pore waters favorable for its formation additionally we suggest a stratified water column with warmer and more saline conditions at greater depths e g 200 m after 40 ma favoring palygorskite and possibly authigenic dolomite precipitation the mineralogical variations and element chemistry of rocks in the baskil section reflect how detrital sources and weathering regimes changed in this area during the middle eocene and how these changes can be related to global regional and local processes

paleocene oceanography of the eastern subtropical indian ocean an integrated magnetobiostratigraphic and stable isotope study of odp hole 761b wombat plateau surface and deep water circulation patterns in the eastern indian ocean during the paleocene epoch are inferred based on an integrated magnetobiostratigraphic and stable isotope investigation of ocean drilling program hole 761b drilled on the wombat plateau a combination of magnetostratigraphy biostratigraphy and isotope stratigraphy demonstrates that numerous deep sea sites that have been considered to show continuous or nearly continuous sedimentation through the paleocene are punctuated by a series of hiatuses some of which exceeding a duration of 1 myr therefore our study is based on a detailed temporal interpretation of the stratigraphic successions we used for paleoceanographic reconstructions we compare detailed planktonic and benthic foraminiferal carbon and oxygen isotope records from hole 761b with several temporally correlative records published from different oceanic provinces in order to distinguish between local and global patterns within the eastern indian ocean although site 761 was situated at low latitudes during the paleocene its surface waters were predominantly influenced by circulation originating from the southern ocean as indicated by inferred cool sea surface temperatures and reduced surface to deep water temperature gradients we suggest that deep waters in the eastern indian ocean were not directly fed by the southern or tethys oceans rather the more negative n 13 c composition of the bottom waters recorded by benthic foraminifera implies the presence and or active contribution of aged deep waters from the pacific during this time at least prior to v60 2 ma and subsequent to v59 0 ma the indian continent ninetyeast ridge kerguelen plateau and broken ridge may have played a significant role as submarine barriers to deep water circulation during the paleocene 2002 elsevier science b v all rights reserved

alluvial sandstone composition and paleoclimate ii authigenic mineralogy abstract various empirical and theoretical arguments suggest that early formed cement in sandstone is a product of meteoric water whose chemistry is controlled by climate the nature and distribution of early silicate cement in gondwana fountain and cutler sandstone support this supposition sandstones from all three units have experienced a broadly similar diagenetic history characterized by two stages of authigenesis stage i was typified by neomorphic development of kaolinite chlorite smectite quartz and additionally in the cutler formation laumontite stage ii was dominated by replacement reactions involving the production mostly of illite iron oxide carbonate minerals and mostly in the gondwana sandstone a second generation of quartz thermodynamic relations hydrologic constraints and radiometric dating of the late stage illite indicate that early authigenesis took place within a few million years of deposition at burial depths measured in hundreds of meters consequently the nature of the silicate cement was a function of the groundwater chemistry as controlled by climate during times of relative aridity ionic concentration of the groundwater was high and high proportions of smectite chlorite and more rarely laumontite formed such was the case in petrofacies i iv v of the gondwana supergroup for a definition of gondwana petrofacies see part i of this study in the cutler fm and in the upper 150 m of the fountain fm during times of high precipitation pore water was dilute which promoted authigen c formation of kaolinite and quartz this is represented by sandstones in petrofacies ii and vi of the gondwana and by sandstones in the lower 200 m of the fountain fm illite is especially abundant as a pseudomorphic replacement of kaolinite in the older gondwana sandstones illitization apparently began at burial depths of about 1 600 m at a temperature of about 75 c illite is not common in the cutler formation and is present only in subordinate amounts in the fountain formation from the study area the 18o values of early clay cement in the gondwana sandstones range systematically from base to top from 5 00 to 13 20 the systematic variation in 18o value of gondwana clay reflects the gradual migratory drift of the gondwana harm toward lower latitudes through time average 18o values for cutler cement 13 23 and fountain cement 19 82 are greater than the analogous values for gondwana cements this is consistent with the lower latitude setting of deposition for the cutler and fountain relative to the latitudinal location of the gondwana basins however the values are anomalously lower than what have been observed in modern day neoformed clays in weathering profiles from low latitudes

past co2 changes and tropical sea surface temperatures the relationship between past co2 variations and tropical climate change on time scales of millions of years is reviewed explanations for cretaceous and early cenozoic climate change often involve higher atmospheric co2 levels climate models predict that such increases should have been associated with warmer tropical sea surface temperatures ssts however sparse mid cretaceous 18o based sst estimates from low latitude calcareous plankton are 1 0 1 5 heavier than predicted initial evaluations indicate that changes in salinity may not alleviate model data discrepancies for calcareous 18o and that interpretation of altered latitudinal 18o gradients in terms of increased poleward heat transport due to warm saline bottom water wsbw formation would require very large levels of wsbw production at least 60 sv calcareous 18o records may not always record true sst patterns as 18o analyses from phosphatic groups which are less sensitive to diagenesis indicate ssts 5 c higher this latter conclusion is supported by a number of other fossil groups which indicate temperatures warmer than those estimated from calcareous 18o in order to more rigorously test the paleo co2 hypothesis and indeed the models used to forecast future climates it is desirable to intensify investigations of past climate change in low latitudes in order to determine whether these preliminary conclusions stand the test of further scrutiny

sea level variations global sedimentation rates and the hypsographic curve sea level changes during the neozoic have been estimated by two different methods the first involves measuring the amount of present day land area which was flooded during the past and using the present day hypsographic curve to estimate the amount of sea level rise necessary to produce this flooding the second involves the estimation of the changing volume of mid oceanic ridges through time and estimating sea level changes after having allowed for isostatic adjustment a difference in sea level of 170 m is obtained from the two methods for the cretaceous 80 100 m y b p this is equivalent to a difference in continental flooding of 24 mm 2 using the present day hypsographic curve we attempt to explain this difference firstly by allowing for the fact that the present day ocean basins have more sediment in them than did the cretaceous ocean basins this produces a sea level change in the opposite direction to that produced by the reduction in mid ocean ridge volume since the cretaceous secondly we suggest another large factor in producing the difference is that the present day hypsographic curve is not the correct one to use when studying sea level stands in the cretaceous present day average continental heights are closely related to continental areas accepting this principle if continents are joined together in the past their average height must be greater and so their hypsographic curve must be steeper a given sea level rise would produce less continental flooding during times of continental aggregation than it would today

recurrent depletion of benthic oxygen with 4th order transgressive maxima in the cretaceous western interior seaway abstract a study was designed to investigate the relationship between depletion of benthic oxygen and 4th order sea level change within the cretaceous western interior seaway of north america three 4th order sea level change cycles were studied in strata belonging to the tropic shale and the tununk shale member of the mancos shale in utah these sedimentary deposits accumulated within prodeltaic environments in utah strata belonging to all three 4th order cycles exhibit evidence for depletion of benthic oxygen at times of peak 4th order transgression and development of condensed sections the evidence includes decreased intensities of bioturbation increased cr al ni al and zn al ratios and decreased mn fe ratios the data also suggest that depletion of benthic oxygen in the distal section preceeded that in the more proximal one and thus may reflect episodic expansion of an oxygen depleted water mass es from the pelagic to the prodeltaic environment of the seaway evidence for subsequent increases in benthic oxygen level with the onset of 4th order regressions is interpreted to reflect either aggradation of the seafloor above the oxygen poor water due to sediment accumulation or contraction of the oxygen depleted water mass from the prodeltaic part of the seaway or a combination of the two s organic c ratios of strata interpreted to have been deposited under conditions of depleted benthic oxygen are distinctly below 0 4 and thus were not useful for recognition of paleo oxygen levels in the prodeltaic environment this study highlights the importance of depletion of benthic oxygen as a mechanism for enhancing preservation of organic carbon in condensed sections on a hundred thousand year time scale our results underline the potential for source rock formation in similar prodeltaic deposits of other epicontinental seaways during periods of relatively high sea level and global depletion of benthic oxygen

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

planktic foraminiferal diversity as indicator of ocean environments abstract the combination of the number of species simple diversity an information function shannon diversity and a measure of equitability is used to characterize modern ocean environments based on planktic foraminiferal faunas regional environmental conditions can be recognized as deviations from the global latitudinal trend simple diversity number of species offers relatively little resolution itself because it is sensitive to the addition of rare species variable conditions such as the highly productive spring bloom and upwelling are characterized by relatively low diversity and equitability values relatively high diversity and a lesser increase in equitability are found in mixing zones of adjacent water masses in extreme conditions diversity is low whereas equitability is intermediate to high modern patterns can be applied to fossil sections to reconstruct regional paleoceanographic conditions thus relatively low shannon diversity with low equitability in maastrichtian heterohelicid faunas from el kef tunisia is interpreted as indicating variable conditions an increase in simple diversity mostly traces evolution of the heterohelicids as a group which diversified during the maastrichtian the number of species through time is a function of available niches and as such related to oceanic circulation on a global scale therefore when applying modern patterns to fossil sections a distinction has to be made between global diversity trends and regional environmental change the correlation between cenozoic stable isotope record and number of planktic foraminiferal species suggest indeed that simple diversity registers changes in global circulation maximum number of species occurred in the maastrichtian the middle eocene and the early middle miocene in these three instances the maxima are found after the start of a cooling trend and are interpreted as transition periods between two modes of ocean circulation causing the temporary coexistence of old and new species

the paleocene eocene transition in the antarctic indian ocean inference from planktic foraminifera isotopic depth stratification and relative abundance studies of planktic foraminifera at odp site 738 reveal three major faunal turnovers during the latest paleocene and early eocene reflecting the climatic and structural changes in the antarctic surface ocean faunal event 1 occurred near the paleocene eocene boundary and is characterized by a faunal turnover in deep dwellers decreased relative abundance in intermediate dwellers and increased relative abundance in surface dwellers this event marks a temporary elimination of the vertical structure in the surface ocean over a period of more than 63 000 years that is apparently associated with the sudden shutdown of the antarctic intermediate water production the appearance of morozovellids before this event suggests that polar warming is the cause for the shutdown in the production of this water mass at this time warm saline deep water may have formed at low latitudes faunal event 2 occurred near the ap5a ap5b subzonal boundary and is characterized by a faunal turnover in deep dwellers with no apparent change in surface and intermediate dwellers increased individual size wall thickness and relative abundance in deep dwelling chiloguembelinids suggests the formation of a deep oxygen minima in the antarctic oceans during the maximum polar warming possibly as a result of upwelling of nutrient rich deep water faunal event 3 occurred in subzone ap6 and is characterized by a faunal turnover in surface dwellers and a delayed diversification in deep dwellers this event marks the onset of antarctic cooling a drastic decrease in the 13c 18o values of the deep assemblage in zone ap7 suggests an intensified thermocline and reduced upwelling following the polar cooling

reconstruction of mid cenomanian orbitally forced palaeoenvironmental changes based on calcareous dinoflagellate cysts abstract mid cenomanian precession controlled 21 ka chalk marl couplets of the cap blanc nez section anglo paris basin have been studied with focus on the effects which milankovitch cycles have had on the palaeoenvironment in this paper we present micropalaeontological and lithological proxies that enable the reconstruction of both the cycle architecture and the transformation of the orbitally forced signal into the sediment a palaeoecological reconstruction based on changes in calcareous dinoflagellate cysts c dinocysts assemblages was carried out in which two characteristic ecological assemblages of c dinocysts were identified gradual changes in absolute and relative abundance of the cyst species in these assemblages over several couplets depict a bundling pattern which is interpreted to reflect the modulation of the intensity of the precession cycle by the eccentricity cycle 100 ka the stacking pattern in the natural gamma ray signal and the carbonate and toc content has the same period and provides lithological support of the bundling a shelf basin circulation model is proposed to explain the relation between orbitally forced climate change its palaeoenvironmental consequences and the resulting sedimentary cyclicity variations in surface water circulation are reflected in the sediment by the chalk marl couplets the most distinctive couplets ocurring at the base and top of the bundles while the chalks reflect well mixed surface water conditions the marls particularly those at the bundle boundaries can be interpreted as the sedimentary expression of stratified water masses during deposition of these marls reduced oceanic mixing due to low seasonality during strong precession maxima at the eccentricity maxima caused periods of water column stratification that in turn led to nutrient depletion and decreased productivity in the surface water masses

translating milankovitch climate forcing into eustatic fluctuations via thermal deep water expansion a conceptual link sedimentological evidence indicates metre scale cyclic changes in global sea level during mesozoic greenhouse climates the cyclicity is thought to be due to milankovitch forcing the absence of continental ice caps requires other mechanisms than glacier build up to explain these variations we propose that thermal expansion of the entire oceanic water column may partly explain the observed sea level variations on milankovitch timescales using existing climate model results we show that an increase in deep water temperature of 2 c and a corresponding sea level rise of 1 7 m by thermal expansion can be induced by milankovitch forcing via increased formation of warm deep waters in low latitudes

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

stable isotopes in late middle eocene to oligocene foraminifera oxygen and carbon isotope ratios in eocene and oligocene planktonic and benthic foraminifera have been investigated from atlantic indian and pacific ocean locations the major changes in eocene oligocene benthic foraminiferal oxygen isotopes were enrichment of up to l in 18o associated with the middle late eocene boundary and the eocene oligocene boundary at locations which range from 1 to 4 km paleodepth although the synchronous eocene oligocene 18o enrichment began in the latest eocene most of the change occurred in the earliest oligocene the earliest oligocene enrichment in 18o is always larger in benthic foraminifera than in surface dwelling planktonic foraminifera a condition that indicates a combination of deep water cooling and increased ice volume planktonic foraminiferal 18o does not increase across the middle late eocene boundary at our one site with the most complete record deep sea drilling project site 363 walvis ridge this pattern suggests that benthic foraminiferal 18o increased 40 m y ago because of increased density of deep waters probably as a result of cooling although glaciation cannot be ruled out without more data stable isotope data are averaged for late eocene and earliest oligocene time intervals to evaluate paleoceanographic change average 18o of benthic foraminifera increased by 0 64 from the late eocene to the early oligocene 18o maximum whereas the average increase for planktonic foraminifera was 0 52 this similarity suggests that the eocene oligocene boundary 18o increase was caused primarily by increased continental glaciation coupled with deep sea cooling by as much as 2 c at some sites average 18o of surface dwelling planktonic foraminifera from 14 upper eocene and 17 lower oligocene locations when plotted versus paleo latitude reveals no change in the latitudinal 18o gradient the oligocene data are offset by 0 45 also believed to reflect increased continental glaciation at present there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from eocene to oligocene time using oxygen isotopes

upper kellwasser carbon isotope excursion pre dates the f f boundary in the upper devonian lennard shelf carbonate system canning basin western australia abstract here we report four high resolution carbon isotope records in addition to trace element data for the frasnian famennian f f boundary interval in the lennard shelf carbonate system of the canning basin western australia this region lacks the characteristic black shale horizons associated with the global late devonian kellwasser extinction events yet still exhibits a trend in carbon isotope character similar to what has been reported from elsewhere in the world two positive 13c excursions with 3 4 amplitudes enrichments in select trace element ratios suggest that both excursions are related to periods of oxygen deprivation and perhaps increased biological productivity given the continuous and stratigraphically expanded nature of lennard shelf sections together with high density sampling constrained by both conodont biostratigraphy and magnetostratigraphy we observe that the upper kellwasser isotope excursion maximum 13c values and associated trace element enrichments occur distinctly lower than the f f boundary level these results have implications for the paleoenvironmental conditions leading up to the late devonian mass extinction in terms of ocean chemistry and circulation patterns this data set allows for a rare detailed look at the temporal relationship between the kellwasser events and the f f boundary and constrains the pattern of carbon isotope perturbations at the intra zonal scale

deep water in the late maastrichtian ocean 1 stable isotopic data from benthic foraminifera indicate the occurrence of at least three deepwater masses in the late maastrichtian ocean given mean oceanic 18ow of 1 0 the temperature of the coolest intermediate depth waters was 5 7 c that of the deepest waters was 10 c and that of the warmest intermediate waters was 13 15 c the cool intermediate depth water mass probably originated in the high latitude southern ocean the deepest waters originated at least partly in the northern atlantic the source region for the warmest intermediate depth water mass is unknown although much of the late maastrichtian deep water was probably preconditioned for winter sinking by low or middle latitude evaporation no more than 11 of late maastrichtian deep water could have been directly actuated by low latitude sea surface evaporation at least in the southern atlantic and indian oceans heat transport by upwelling of deep water was not the primary cause of mild sea surface and coastal temperatures

orbital forcing of low frequency glacioeustasy the role of orbital forcing in glacioeustasy has long presented a major problem regarding the reconciliation of data oriented seismic sequence stratigraphy with process oriented dynamic stratigraphy dynamic stratigraphy commonly cites orbital forcing periods of approximately 20 000 years precession 40 000 years tilt and 100 000 years eccentricity which are too fine scale to be resolved consistently by seismic sequence stratigraphy seismic sequence stratigraphy consistently identifies seemingly eustatic events on a scale of millions of years which have no heretofore easily identifiable causal mechanisms in this paper we propose a geologic mechanism and realistic quantitative construct to explain how antarctic ice volume varies as a function of orbital forcing in the tertiary we demonstrate that this mechanism which has a nonlinear response to long period modulation of the orbital forcing time series can produce major glacioeustatic events with quasi periodicities of the order of 2 m y we use a fortran program strata various to construct a two dimensional forward model demonstrating that this proposed mechanism can produce a synthetic sequence stratigraphy which bears strong resemblance to the generalizations of seismic sequence stratigraphy we acknowledge important achievements of seismic sequence stratigraphy nevertheless we propose that the seismic sequence stratigraphy concepts of long term and short term eustatic curves be replaced by independent estimates of tectonoeustasy and glacioeustasy based upon data sets which are wherever possible independent of seismic sequence stratigraphy likewise we propose that qualitative generalizations be replaced with explicit forward models as the targets for model data convergence

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

climate change on tectonic time scales abstract observational and modeling studies relevant to climate change on tectonic time scales are reviewed probably the most significant climate result from this time scale involves inferences about nearly ice free conditions for some intervals of earth history some additional results suggest relatively rapid transitions between climate states modeling studies indicate that although tectonic changes significantly modify the atmosphere and ocean circulation in most cases such modifications do not appear to be sufficient to explain ice free climates increased atmospheric co2 levels 5 10 presentvalues may be needed to completely reconcile models and data although the co2 paradigm has received widespread attention in the last few years the results summarized herein indicate that co2 is only one of several important factors influencing climate i believe the time is appropriate for contemplating climate change on tectonic time scales in terms of a post co2 synthesis in which direct tectonic factors are approximately equal in importance to co2 fluctuations in the last few years modeling studies have progressed from a state of virtually no work on the topic to one where the models are in some respect ahead of the observations in the sense that data have not been compiled to test even some of the most basic model predictions in particular information is needed on past atmospheric co2 levels tropical sea surface temperatures seasonality of continental interiors and locations and production rates of deep waters initial steps are being taken to integrate observational and modeling activities on tectonic time scales and some of these shortcomings may be rectified over the next few years

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

paleoceanographic changes across the jurassic cretaceous boundary the calcareous phytoplankton response abstract calcareous nannoplankton experienced rapid diversification at the jurassic cretaceous boundary including the appearance of several highly successful and long ranging cretaceous genera this study examines at high resolution calcareous nannofossil assemblages and bulk rock oxygen and carbon isotopes of lower tithonian to lower berriasian 151 to 142 ma sediments recovered in deep sea drilling project hole 534a central atlantic ocean the results show major changes in assemblage composition and abundance of three genera conusphaera nannoconus and polycostella conusphaera dominates the nannolith assemblage in the late middle tithonian conusphaera world while the nannoconid dominance nannoconus world began in the berriasian the acme peak of the genus polycostella in the late tithonian partially superimposes that of conusphaera although these genera are indicators of warm oligotrophic surface waters stable isotope data suggest that the individual taxa may flourish in slightly different ecological regimes nannoconus flourished under warmer and possibly more nutrient depleted surface waters than polycostella a genus that thrived in relatively cooler waters these findings imply paleoceanographic changes across the j k boundary interval with a cooling in the late tithonian followed by a temperature increase in the berriasian because the transfer of these heavily calcified nannolith taxa to the seafloor is more efficient than that of average coccolithophorids the j k evolutionary event changed carbonate cycling and burial in the oceans

patterns and processes of alteration in the lavas and dykes of the troodos ophiolite cyprus alteration patterns in the lavas and dykes of the troodos ophiolite cyprus record a complex history of axial hydrothermal alteration crustal aging and subsequent uplift and emplacement of the ophiolite field mapping shows that distribution of five alteration zones each with distinct mineralogical geochemical and hydrologie characteristics is influenced by igneous stratigraphy structure and the nature and thickness of the overlying sediments paragenetic sequences of secondary minerals indicate that alteration conditions changed progressively as the crust cooled and moved off axis along spreading axes low temperatures 50 c were maintained by the rapid flow of seawater in and out of the lavas and only minimal alteration took place in contrast lower water rock ratios and higher temperatures 200 c in the dykes promoted extensive seawater rock interaction although the sharp rise in temperature between the two regimes generally coincides with the lava dyke transition late stage intrusions or hydrothermal upwelling zones locally cause high temperature alteration to extend upward into the lavas as a segment of crust moved off axis temperatures remained low in the lavas and progressively decreased from 250 to 80 c in the dykes high permeability in the uppermost lavas led to the downward migration of an oxidative alteration front whose thickness and spatial distribution was dependent upon the rate and nature of sedimentation and thus the original seafloor morphology although field relations show that alteration has a consistent vertical pattern in troodos the alteration zones are not laterally continuous and the stratigraphie depth of their boundaries varies considerably

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

paleoceanographic significance of high resolution carbon isotope records across the cenomanian turonian boundary in the western interior and new jersey coastal plain usa carbon isotope measurements have been made on bulk carbonate and organic matter in three sections across the cenomanian turonian boundary the stratigraphy records the positive carbon isotopic excursion that is associated with the major oceanic anoxic event oae2 comparison of toc and isotopic data in sections from a range of different environments suggests that the positive excursion is a response to increased burial of organic matter in the deep ocean the lack of coupled negative shifts in 13corg and 13ccarb records at the onset of oae2 does not support a causal role for volcanism or methane hydrate dissociation

tectonic control of chemical and isotopic composition of ancient oceans the impact of continental growth a numerical model that couples carbon sulfur strontium and atmospheric oxygen cycles is used here to explore the impact of continental growth on the long term or 10 8 yrs evolution of the isotopic composition of seawater three growth scenarios are tested big bang generation of continents shortly after the accretion of the earth and two more gradual scenarios with a major growth episode around the archean proterozoic boundary the corresponding 87 sr 86 sr delta 34 s and delta 13 c of seawater and the sizes of the respective crustal sedimentary reservoirs are calculated for each scenario and compared to the available data the gradual continental growth scenarios yield a better fit to the existing 87 sr 86 sr and delta 34 s isotope data for ancient seawater than does the big bang model and can be in agreement also with the measured seawater delta 13 c providing c org participates in carbon subduction flux over the earth history these scenarios also generate a progressive oxygenation of the ocean atmosphere system with a large po 2 rise coincident with and due to the major continental growth event around the archean proterozoic transition in accord with the geologic record that indicates a major oxidation event in the early proterozoic the advancing oxygenation of the planetary exogenic system may therefore be a consequence of tectonic evolution rather than of biological innovations such as the photosystem 2 the latter may have predated considerably the impact of oxygenation visible in the geologic record in contrast to the above isotope systematics the model does not approximate well experimental observations of large delta 18 o variations at 10 8 yrs time scales at least during the phanerozoic the reason for this discrepancy may depend on the model structure that permits large variations in the oxygen isotopic composition of seawater only on time scales of 10 9 yrs

nannofossil assemblages fine fraction stable isotopes and the paleoceanography of the valanginian barremian early cretaceous north sea basin calcareous nannofossil assemblages have been investigated in three sections from around the margins of the early cretaceous north sea basin both absolute number of nannofossils per gram and relative percent of the assemblage of different taxa abundance data have been collected absolute abundances up to 10 billion nannofossils per gram are somewhat higher than those reported previously from other stratigraphic intervals stratigraphic correlation of trends in assemblage data in different sections points toward the existence of large uniform water masses stable over long 0 5 to 1 m y time periods these water masses contained a characteristic nannoplankton which appears to have been driven largely by variations in fertility possibly tied to changes in sources of surface waters which in turn may have been controlled by relative sea level fine fraction isotopic data show fluctuations on shorter time periods 0 1 to 0 5 m y we postulate that some of these isotopic fluctuations were controlled by relative changes in sea level which affected the balance of surface waters derived from runoff and those imported from the boreal sea these oceanographic changes appear to have affected nannofossil assemblages only in discrete intervals data are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p95 001 2 50 payment must accompany order

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

the impact of paleocene eocene boundary events on middle neritic benthic foraminiferal assemblages from egypt abstract a 25 m upper paleocene to lower eocene marly sequence exposed at gebel duwi quseir red sea coast of egypt provides a good opportunity for studying paleocene eocene p e boundary stratigraphy and events various bio eco and isotope stratigraphic correlations accurately delineate the position of the p e boundary i e the level of stable isotopic excursions and deep sea benthic extinctions in the middle part of this section within zones p5 and np9 in this paper the impact of p e boundary environmental perturbations on benthic foraminiferal communities of the shallow tethyan shelf is examined benthic foraminiferal assemblages from gebel duwi characterized by large frondicularia phosphatica and f nakkadyi in addition to a number of other neritic taxa but without any typical outer neritic bathyal taxa suggest middle neritic 75 100 m deposition throughout the studied interval and only minor relative sea level variations perhaps some 10 20 m across the boundary sea level appears to have been stable yet a distinct faunal turnover marks the p e boundary of this shallow site which in contrast to deep sea records is less abrupt being preceded by a gradual diversity decrease starting some four meters below the boundary moreover most exits are either local or just temporary and thus not true extinctions many lazarus taxa reappear at some point above the boundary while all but one of the disappearing taxa are known from other lower eocene neritic deposits in egypt in general benthic foraminiferal assemblages display low diversities and high dominance values notably anomalinoides aegyptiacus up to 74 suggesting high levels of environmental stress at the sea floor in combination with occasionally very high p b ratio s up to 98 p and generally laminated sediments the character of the benthic assemblage points to a strong influence of recurrent dysoxia and or anoxia we suggest that these resulted from surface eutrophication by intermittent coastal upwelling and reduced ventilation of the bottom environment although these conditions prevailed during most of the time interval studied they were most severe during the latest paleocene and early eocene when eutrophication intensified and the organic carbon flux to the sea floor increased enhanced atmospheric contrasts between the tethys seaway and the african continent resulting in intensified longshore tradewinds may have controlled these changes at the p e boundary the bottom environment became minimally ventilated perhaps due to reduced oxygen advection from deeper waters three meters above the boundary a succession of increasingly diverse assemblages indicate a gradual decrease of environmental stress and a return to more normal conditions although the organic carbon flux to the sea floor remained high

extinction survivorship and evolution of planktic foraminifera across the cretaceous tertiary boundary at el kef tunisia an expanded sediment record at el kef shows that the k t boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary ir anomaly to 7 cm above species extinctions appear sequential with complex large ornate forms disappearing first and smaller less ornate forms surviving longer the 14 species extinctions below the boundary appear unrelated to an impact event cretaceous species survivorship is greater than previously assumed about 10 species survive 22 into subzone p1a globigerina eugubina all cretaceous survivors are small primitive forms which are generally smaller than their ancestors in cretaceous sediments species evolution after the k t event occurs in two pulses the first new paleocene species evolve in the basal black clay zone po immediately after the major cretaceous extinctions evolving species are small and primitive similar to cretaceous survivors the second pulse in species evolution occurs in the lower part of subzone p1b with the appearance of larger more diverse species the first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300 000 years after the k t event the species extinctions prior to the generally assumed impact event implied by the ir anomaly and the long recovery period of the ecosystem thereafter cannot be explained by a single impact but suggest that multiple causes may be responsible such as climatic changes volcanism a sea level drop production of warm saline bottom water and the chemical consequences associated with increased salinity

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

oxygen isotope variations in phosphate of biogenic apatites iii conodonts abstract the method for measurement of the isotopic composition of oxygen in phosphates has been improved and adapted for analysis of small quantities of apatite down to 10 mg this extension enables one to analyze hand picked conodont samples with an analytical reproducibility better than 0 5 1 46 samples of conodonts ranging from the ordovician to the pennsylvanian of north america were analysed some insoluble phosphatic residues ichthyoliths and inarticulate brachiopods of the same time range were also measured the range of the 18o values of the analysed conodonts is between 15 and 19 it shows a general trend of decreasing d18o with increasing age from an average value of about 19 in the pennsylvanian to 17 in the ordovician this trend parallels that previously detected in marine phosphorites for the time range between the devonian and pennsylvanian our data are in agreement with independent paleoclimatic information specifically we detect maximum18o enrichment at the end of the pennsylvanian and minimum enrichment at the end of the devonian the difference between these two extremes is equivalent to about 10 c from about 40 to 30 c assuming constant isotopic composition of ocean water the success of oxygen isotopic analysis of conodonts raises the possibility of their use in paleozoic paleo oceanography in a similar way to foraminifera in the mesozoic cenozoic

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

global patterns in opal deposition from late cretaceous to late miocene biogenic silica accumulation rates were calculated at deep sea drilling project dsdp sites from legs 1 44 and were plotted on global reconstructions at seven 10 m y intervals these data were then contoured because of the correlation between opaline sediments and upwelling these maps may be used to trace paleocirculation patterns through time they demonstrate a gradual transition from the cretaceous circum global equatorial current to the modern circum antarctic divergence as tethys closed and australia and south america separated from antarctica modern bottom water circulation tends to concentrate opaline sediments in the pacific and carbonate sediments in the atlantic basinal opal fluxes were measured for each interval and in combination with carbonate compensation depth ccd histories reveal four lagoonal versus estuarine exchange reversals from the late cretaceous to the present these reversals can be directly related to the development of new bottom water sources with changing climatic and tectonic conditions

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

possible role of oceanic heat transport in early eocene climate increased oceanic heat transport has often been cited as a means of maintaining warm high latitude surface temperatures in many intervals of the geologic past including the early eocene although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically determining how additional oceanic heat transport would take place has yet to be accomplished that the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked using early eocene climate as an example we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early eocene conditions our interpolation of early eocene paleotemperature data indicate that an approximately 30 increase in poleward heat transport would be required to maintain eocene high latitude temperatures this increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early eocene rates either oceanic processes were very different from those of the present to produce the early eocene climate conditions or oceanic heat transport was not the primary cause of that climate we believe that atmospheric processes with contributions from other factors such as clouds were the most likely primary cause of early eocene climate