response of nannoplankton to early eocene ocean destratification abstract nannoplankton play a significant role in the global carbon cycle changes in the composition of the assemblage can influence primary productivity carbon burial and ultimately climate here counts of nannofossils in eocene samples document one of the largest nannoplankton assemblage turnovers of the cenozoic era this event is marked by the global expansion of reticulofenestra at the termination of the early eocene climatic optimum eeco and continues through the progressive cooling to the earliest oligocene glaciation to understand the mechanisms driving this assemblage shift we use multivariate statistical techniques and carbon and oxygen isotope records from localities worldwide we find that the turnover in the global nannofossil assemblage is tied to thermal destratification of the ocean and a coincident decrease in the efficiency of the oceanic biologic pump at the height of the eeco we propose that increased vertical mixing and increased nutrient supply to surface waters during the eeco caused a shift in the trophic structure towards enhanced productivity influencing the global nannoplankton population

calcareous nannofossil zonation of the jurassic cretaceous boundary interval and correlation with the geomagnetic polarity timescale abstract calcareous nannofossil stratigraphy has been investigated in six european land sections and at two deep sea drilling project sites 391c and 534a ranging from the upper kimmeridgian to the lower valanginian most of the sections contain a continuous record of the jurassic cretaceous boundary interval a time of rapid increase in nannofossil abundance and diversity and allow development of a revised nannofossil zonation scheme for this period numerous nannofossil lineages have been studied in detail and the results help to increase potential stratigraphic resolution in this interval the proposed scheme consists of six zones which are units recognizable in all sections regardless of nannofossil preservation and eleven subzones determinable in all but the most poorly preserved material thirty eight additional biohorizons are proposed based on the stratigraphy of the two dsdp sites these can be accurately established only in moderately well preserved material but spotty occurrences of these taxa in other sections may be stratigraphically useful most of the sections studied have been investigated magnetostratigraphically and the results of this study allow correlation between nannofossil zonation and the geomagnetic polarity time scale magnetostratigraphy indicates that many nannofossil events can be quite precisely determined and are not significantly time transgressive finally the magnetostratigraphic definitions of two stage boundaries are refined the kimmeridgian tithonian and berriasian valanginian boundaries are placed within chrons cm22n and cm15n respectively two new genera faviconus and umbria and seven new species are described umbria granulosa rhagodiscus nebulosus cretarhabdus octofenestratus faviconus multicolumnatus nannoconus infans nannoconus compressus and nannoconus wintereri eight subspecies and three taxonomic emendations are also described

deep sea carbonates reading the carbon isotope signal the carbon isotope signal in deep sea sediments reflects a mix of 1 global changes in the rates of exchange of the ocean s carbon reservoir with biosphere soil and sediments 2 global and regional changes in surface water productivity 3 internal shifts in water mass structure and circulation basin basin fractionation oxygen minimum development and 4 organism specific fractionation effects due to changes in micro habitat and or ontogenic fractionation vital effects additional complications arise from differential preservation it is impossible to entirely isolate these various factors as a rule of thumb long period signals that are parallel for planktonic and benthic data reflect external global fractionation patterns whilst short period signals are more likely tied to internal patterns water mass fractionation the various approaches to interpretation are illustrated with three case studies the glacial holocene transition the messinian carbon shift and the miocene monterey excursion

comparison of pleistocene and holocene barrier island beach to offshore sequences georgia and northeast florida coasts u s a abstract well exposed vertical sequences of pleistocene shoreline deposits are rare on the coastal plain of the southeastern united states an important exception is an exposure along the st mary s river on the georgia florida state line this outcrop contains an excellent depositional strike section of a prograding offshore shoreface foreshore and backshore sequence with well preserved physical and biogenic sedimentary structures offshore sediments are composed of highly bioturbated muddy fine sand distinct burrows and bedding become progressively more abundant upward through a transition zone into shoreface deposits the shoreface is dominated by the trace fossil ophiomorpha nodosa and physical sedimentary structures are poorly preserved foreshore sediments contain low angle seaward dipping beds high angle landward dipping beds and ripple laminae heavy mineral accumulations in the backshore accentuate bedding and biogenic structures such as ghost crab and insect burrows and bioturbation by amphipods direct correlation of most primary physical and biogenic sedimentary structures and textures can be made between the pleistocene and holocene beach to offshore facies assemblages however our studies of the pleistocene indicate that the existing holocene vertical sequence model for the georgia coast needs to be modified to account for biogenically produced post depositional effects

biogeography of planktonic foraminifera and regional carbon isotope variations productivity and water masses in late cretaceous europe the first appearances of species of marginotruncana planktonic foraminifera are found stratigraphically earlier in boreal northwestern germany than in the tethys helvetoglobotruncana helvetica bolli is rare in northwestern germany and common in the tethys its stratigraphic range is probably comparable between both areas the biogeographic patterns are discussed with respect to influences of water depths based on isotope evidence for the depth distribution of species of hedbergella praeglobotruncana and rotalipora and water temperatures the regional variation of 13c values of cenomanian turonian pelagic carbonates was mapped for the european epicontinental basins and the southern european shelf helvetic zone of the alps the highest 13c values up to 5 were found in northwestern germany and the eastern north sea and are coincident with an upwelling zone numerically predicted by three independent climate models intermediate values in france and england 2 4 correspond to predicted weak upwelling lowest values occur in the alpine helvetic zone and the south german regensburg area 1 2 and coincide with predicted absence of upwelling the 13c values are interpreted as indicators of increased biogenic productivity in the upwelling zone semiquantitative nannofossil data suggest abundance patterns influenced by latitude neritic oceanic gradients and productivity observations agree with east to west wind driven surface current systems regional differences in nutrient supply and subsequently different primary productivity could have been a major factor controlling the evolution and the biogeographic distribution of planktonic foraminifera in cenomanian turonian europe

calcareous nannofossil response to late cretaceous climate change in the eastern tethys zagros basin iran abstract coniacian to maastrichtian changes in calcareous nannofossil assemblages have been investigated in the eastern tethyan shahneshin section central zagros basin iran the nannofossil assemblages are mainly composed of watznaueria spp avg 54 retecapsa spp avg 7 9 cribrosphaerella ehrenbergii avg 7 7 and micula spp avg 5 7 throughout the late campanian there is a trend to lower abundances in watznaueria spp together with increasing abundances of c ehrenbergii and arkhangelskiella cymbiformis which are considered in this basin as the main cool water taxa our results reveal that despite a diagenetic impact on calcareous nannoflora a number of primary paleoecological trends are preserved which depict well features of the progressive late cretaceous cooling the first pronounced cooling episode occurs across the late campanian to early maastrichtian the onset of pronounced cooling in the eastern tethys appears to occur prior to the campanian maastrichtian boundary event cmbe 13c negative excursion in contrast with the boreal realm where pronounced cooling only occurs in the early maastrichtian postdating the onset of the cmbe the coincidence of this earlier cooling in the zagros basin with an interval characterized by a significant increase in benthic foraminifera suggests an amplified response of the assemblage due to a change to shallower environments hence the late campanian calcareous nannofossil assemblage turnover in central zagros is either a response to an early cooling trend in the eastern tethys or to sea level fall or both the mid maastrichtian warming and late maastrichtian cooling episodes are also delineated in the nannofossil assemblage of shahneshin and likely correlate with similar episodes in the boreal realm

calcareous nannofossil assemblages of oceanic anoxic event 2 in the equatorial atlantic evidence of an eutrophication event the calcareous nannofossils of the cenomanian turonian boundary interval of sites 1258 and 1260 ocean drilling program leg 207 have been studied in order to understand the depositional environment during oceanic anoxic event 2 oae2 in the equatorial atlantic nannofossil assemblages show a significant change in relative abundances during the positive 13 corg excursion interval the strong increase of the high productivity indicator zeugrhabdotus erectus and the simultaneous decrease of the oligotrophic taxa watznaueria barnesiae and watznaueria fossacincta are indicative of enhanced fertility the decrease of eprolithus floralis may be attributed to the surface water temperature increase during oae2 which is however not very significant 2 3 c as suggested by published tex86 data it seems more likely that the decrease of e floralis during oae2 was evoked by the breakdown of water column stratification indicating it as a deep dwelling species which prefers stratified waters with a deep nutricline prediscosphaera spp and retecapsa ficula which show a significant increase in relative abundances during oae2 seem to prefer eutrophic environments while amphizygus brooksii and zeugrhabdotus noeliae lower surface water fertility gartnerago segmentatum broinsonia spp watznaueria biporta and seribiscutum gaultensis decrease in abundances during oae2 it is not clear if they preferred an oligotrophic environment cooler surface waters or if they were inhabitants of the lower photic zone published geochemical data suggest that enhanced fertility and higher temperatures during oae2 may have been caused by submarine volcanic activity through the release of biolimiting micronutrients into the ocean and carbon dioxide into the atmosphere the breakdown of water column stratification may have increased further nutrient availability 2007 elsevier b v all rights reserved

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

using magnetic resonance imaging and petrographic techniques to understand the textural attributes and porosity distribution in macaronichnus burrowed sandstone abstract magnetic resonance images are paired with petrographic data to evaluate the textural characteristics of rocks dominated by macaronichnus segregatis a trace fossil that is commonly associated with rocks deposited in shallow marginal marine sedimentary environments mri techniques used revealed the three dimensional geometry of the trace fossil burrows are typically horizontal and in plan view range between straight sinuous meandering and spiral geometries changes in burrow morphology may be related to population density and patchy resource distribution the pairing of mri and petrographic data helped map the distribution of porosity in the burrowed rock because mri images represent complex composites of nuclear spin density and mr relaxation times each of which is related to pore size stronger mr signals must be calibrated to known porous zones by integrating petrographic data with mr data the complex distribution of porosity and its relationship to the matrix show that this fabric represents a dual porosity permeability system and may affect the resource reservoir or aquifer quality of similarly burrowed sedimentary rocks future research should elaborate upon the porosity permeability model for this and similar fabrics

influence of paleoenvironmental factors on preservation of organic matter in middle cretaceous greenhorn formation pueblo colorado sedimentological and geochemical studies of the upper cretaceous hartland shale and overlying bridge creek limestone members of the greenhorn formation reveal close associations between abundance of current induced sedimentary structures extent of bioturbation and type of preserved organic matter abundant hydrogen rich organic matter 4 5 wt and low sulfur to organic carbon ratios are characteristic of the laminated facies which lack current induced sedimentary structures sparse hydrogen poor organic matter 0 1 0 5 wt and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies which contain numerous sedimentary structures indicative of currents the concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively by currents rather than by the rate of oxygen consumption by decomposition thus paleoclimatic and paleo oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units it is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen depleted bottom water and high preservation of organic matter thus accounting for the intermittent widespread deposition of organic rich strata during maximum transgression and depth of the greenhorn sea the lateral association of voluminous deltaic deposits with dee water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the hartland shale and bridge creek limestone members

calcareous nannofossils of the cenomanian turonian boundary interval from the boreal realm wunstorf northwest germany abstract the cenomanian turonian boundary interval ctbi is marked by an intense climatic warming presumably caused by large magmatic eruptions this warming was characterised by one of the most prominent mesozoic perturbations of the carbon cycle the oceanic anoxic event 2 oae2 which is marked by a well pronounced positive carbon isotope excursion cie sediments of the oae2 interval often consist of organic rich black shales suggesting widespread bottom water anoxia during the ctbi this study focuses on calcareous nannofossils from the ctbi of a european section wunstorf core northwest germany a total of 105 samples were examined for calcareous nannofossils using the settling technique eight bioevents last occurrences corollithion kennedyi lithraphidites acutus first occurrences rotelapillus biarcus corollithion exiguum eprolithus octopetalus eprolithus eptapetalus quadrum gartneri eiffellithus eximius have been recognised throughout the middle cenomanian to middle turonian interval with the exception of eleven samples preservation is moderate to good calcareous nannofossils are abundant mean 2 0 billion specimens g sediment and highly diverse mean 58 species sample assemblages are dominated by watznaueria spp 32 3 prediscosphaera spp 13 4 zeugrhabdotus spp 11 2 and biscutum spp 10 5 pre oae2 and also post oae2 nannofossil assemblages show high abundances of biscutum spp 20 indicative for stable mesotrophic conditions the assemblages of the oae2 itself are marked by high values for watznaueria spp and low frequencies of biscutum spp making oligotrophic conditions during the oae2 likely high absolute abundances of organic walled dinoflagellates and the occurrence of frequent stress tolerant nannofossil genera like retecapsa spp in the organic rich intervals suggest however a deposition of black shales enhanced by high primary productivity thus dinoflagellates and calcareous nannofossils are interpreted to reflect different seasonal signals during the time of black shale deposition short term high fertile seasons allowed the blooming of the organic walled dinoflagellates whereas calcareous nannofossils dominated the longer oligotrophic seasons the black shale deposition was supported by the formation of large amounts of organic matter during fertile seasons as well as by surface water stagnation during oligotrophic seasons

calcareous nannofossils from the great australian bight iodp site u1512 as a record of the peak and early decline of the mid cretaceous super greenhouse abstract international ocean discovery program drilling in the great australian bight site u1512 provides a record of turonian to santonian hemipelagic sedimentation deposited in an elongate epicontinental basin that opened westward to the southern ocean during the peak and the early decline of the cretaceous hot greenhouse despite its relatively high paleolatitude at about 60 s the biostratigraphy of calcareous nannofossils from this succession is directly correlative to low latitude zonation schemes throughout the turonian to santonian these calcareous nannofossil assemblages are somewhat restricted in species composition lacking some elements generally found in late cretaceous assemblages e g holococcoliths in addition two biostratigraphically important high latitude taxa thiersteinia ecclesiastica and zeugrhabdotus kerguelenesis have biostratigraphic ranges notably shorter than elsewhere indicating range truncation through local extirpation quantitative paleoecological analysis of the calcareous nannofossil assemblages indicates that the major change in the paleoenvironment was the evolution from conditions that were quite warm and had relatively elevated surface water fertility in the turonian to cooler and possibly more oligotrophic conditions in the coniacian santonian the first cooling began at about 92 ma accelerated at about 91 2 ma and then continued to gradually cool during the coniacian santonian this paleotemperature scenario is consistent with those documented from other localities globally

campanian carbon isotope calibrated paleofertility estimates from northwestern tunisia inferences from calcareous nannofossils abstract the 13c calibrated campanian upper part of cc17 uc13 to cc23a uc16 zones calcareous nannofossil assemblages were analyzed to reconstruct paleofertility paleoenvironment and sea level changes from the jebil section north western tunisia seven globally recognized 13c events are noted three positive santonian campanian boundary event scbe early campanian event ece mid campanian event mcae and four negative excursions pillula event conica event late campanian event lce epsilon event or the c1 event the nannofossil assemblage is dominated by watznaueria barnesae 28 lucianorhabdus cayeuxii 8 micula decussata 6 cyclagelosphaera reinhardtii 5 and micula concava 4 in spite of the dominance of w barnesiae range 33 46 5 the signal given by the nannofossil assemblage is primary all species based proxies the percentage abundances of stressed opportunistic taxa high and low fertility taxa cool and warm watermass taxa and nannoconus spp along with the inferred paleotemperature index suggests a cooling trend for the campanian data suggests that oligotrophy was a greater influencing factor than paleotemperature for the observed changes within the nannofossil assemblage as a result of this extreme oligotrophy a distinct assemblage is recorded that is marked by the absence of biscutum reduced abundances of prediscosphaera 0 7 retecapsa 2 3 and zeugrhabdotus 1 8 but with the dominance of w barnesiae

calcareous nannofossil biostratigraphy and assemblages of the cenomanian turonian boundary interval implications for the origin and timing of oceanic anoxia a detailed nannofossil zonation has been derived for the cenomanian turonian boundary interval consisting of three zones two subzones and nine additional biohorizons this biostratigraphy based on the investigation of numerous sections from europe north america and africa allows accurate correlation of sections from shelf and deep sea environments the increased resolution helps solve several pertinent paleoceanographic and sedimentologic problems in this time period facies patterns are variable in this interval for numerous reasons a widespread hiatus occurred in the latest cenomanian and earliest turonian in much of northwest europe and may have been an indirect result of peak marine transgression in parts of the deep tethys dissolution of carbonate took place in undersaturated bottom waters or during early diagenesis only a few boundary sections mostly within the western interior united states are characterized by continuous carbonate deposition in many sections a 13c excursion which has been associated with the burial of large amounts of marine organic matter coincides with a facies change lower ratios of coccolith carbonate to micrite and poorer nannofossil preservation this excursion therefore may be strongly overprinted by diagenesis numerous nannofossil events indicate that the carbon excursion is slightly diachronous between sequences of the western interior and that the shift occurred distinctly later in this region than in northwest germany the data obtained do not invalidate the concept of a cenomanian turonian ocean wide anoxic event but show how local tectonic climatic and oceanographic perturbations have masked the global scenario in particular they indicate that carbon shifts may be basinal and not always oceanic phenomena a conclusion which can be rationalized with overall sluggish middle cretaceous circulation nannofossil assemblages in almost all sequences observed contain exceptionally high abundances of two dissolution resistant taxa in particular samples eprolithus floralis and broinsonia sp however the overall composition of assemblages does not change dramatically in the boundary interval in contrast to the macrofossils and foraminifera which suffered widespread extinctions

biogenic chaos cryptobioturbation and the work of sedimentologically friendly organisms abstract biogenic chaos from an ichnological point of view can be defined as total bioturbation of sediment by infaunal organisms such that the original sedimentary fabric and associated sedimentary structures are entirely destroyed the truth however is that not all forms of thorough bioturbation are purely destructive as improbable as it initially sounds sediment can be pervasively potentially 100 bioturbated and yet have suffered remarkably little distortion of the original bedding in nature there exist many different levels of organism communities historically the study of any natural system begins with the most obvious attention grabbing elements only later do the more innocuous aspects come to be discovered and appreciated ichnology shows a similar historical pattern the most obvious aspects of the science the discrete burrow or track forms have been well studied for many years only recently have more subtle biogenic disturbances such as micro borings bacterial trails meiofaunal burrows infaunal tiering etc gained attention likewise another level of bioturbation cryptobioturbation exists and is becoming more evident in the rock record owing to its diminutive and obscure nature cryptobioturbation has not received widespread attention as the name implies cryptobioturbation is characteristically small in scale and exceedingly subtle in expression what sets it apart from other forms of bioturbation however is its tendency to preserve rather than to destroy the sediment s primary physical structure the fabric that results from cryptobioturbation can have significant influence on resulting permeability and porosity trends in some systems where both cryptically bioturbated sandstone and generally unburrowed sandstone are present mini permeameter measurements show that numerous heterogeneities are retained in the unburrowed sandstone resulting in a wide range of permeabilities in contrast cryptically bioturbated sandstone intervals show that these heterogeneities are less pronounced and the resulting permeability curve is more uniform the effect of cryptobioturbation does not result in enhanced permeabilities but rather diminishes internal heterogeneities leading to a more uniform permeability distribution

a paleoceanographic model for the early evolutionary history of planktonic foraminifera the first major radiations of planktonic foraminifera occurred during the mid cretaceous however this period of great diversification was interrupted by two intervals of pronounced paleoceanographic paleoecologic change one during the latest aptian early albian and a second associated with the cenomanian turonian boudary both of these times corresponded with widespread organic carbon burial during intervals commonly referred to as oceanic anoxic events oae 1 and 2 respectively this synthesis focuses on the evolutionary history of aptian early cenomanian planktonic foraminifera and the relationship with oae 1 dynamic paleoceanographic changes controlled the course of planktonic foraminiferal evolution during the mid cretaceous heightened plate tectonic activity a major long term rise of global sea level and an overall increase of global temperatures characterized aptian albian time as proposed here the evolutionary history of aptian early cenomanian planktonic foraminifera was influenced most strongly by changes in the density structure and stability of the upper water column via changes in the sites and rates of water mass production through time and perhaps by subtle changes in oceanic productivity including trophic structure and shifts in productivity centers with rising sea level the creation and growth of epicontinental seas played a major role in regional climate change water mass production and water column structure epicontinental seas were also an important factor in creating vast new niche space and increased biotic diversity for many marine organisms the amplified seasonality and instability of epicontinental seas resulted in habitation of the upper water column by morphologically simple eurytopic planktonic foraminifera several new species of epicontinental sea dwelling planktonic foraminifera appeared during the mid cretaceous however much of the diversification of morphologic form took place in oceanic areas during times of oceanic stability and upper water column stratification during mid to late aptian and late albian time a decline in diversity and return to simple morphotypes occurred when oceanic stability was disrupted and the upper water column was poorly stratified during latest aptian early albian time

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

palaeoceanography of organic rich rocks of the loma chumico formation of costa rica late cretaceous eastern pacific the late cretaceous late cenomanian campanian loma chumico formation consists of laminated to massive bedded siliceous shales cherts ash fall tuffs volcanic glass beds and volcaniclastic sandstones the loma chumico formation is at least 630 m thick core data in the tempisque basin and can be subdivided in the subsurface into organic rich and organic lean total organic carbon 1 facies rock eval total organic carbon toc data show that toc in the organic rich facies averages 15 5 with values as high as 33 inorganic geochemical petrological and sedimentological analyses indicate that all the lithologies of the loma chumico formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc the organic geochemistry and palaeontology of the loma chumico formation help constrain the factors that controlled biological productivity in the region during the late cretaceous biomarkers identified in organic rich facies by gas chromatography mass spectrometry gc ms show a high abundance of total steranes relative to hopanes in the morote 1 core indicating algal dominated organic input the hopane to sterane ratio of the extract from the manzanillo 1 core indicates a relatively high bacterial component to the organic matter upwelling and extrusive volcanism were the most important factors that controlled nutrient supply including silica flux and biological productivity within the loma chumico formation depositional system episodic radiolarian dinoflagellate or diatom blooms instigated by rapid infusions of volcanogenic silica may have resulted in expansion of the oxygen minimum zone omz enhancing the preservation of organic matter productivity appears to have been uniform even during deposition of the organic lean facies the findings of this study suggest that ocean wide anoxia in the eastern pacific was unlikely during the late cretaceous high toc contents of organic rich radiolarites from central caribbean deep sea drilling project dsdp sites may be related to upwelling produced in the eastern pacific by convergence of the easterly trade winds eastern pacific equatorial upwelling zone or may be part of a more complex pacific atlantic ocean interaction the end of deposition of organic rich rocks began near the end of the latest santonian earliest campanian in the central caribbean and costa rica palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the north atlantic south atlantic seaway may explain this observation this may represent the influx of a previously unrecognized source of colder oxygenated intermediate bottom water proto antarctic intermediate water into the late cretaceous central atlantic and eastern pacific oceans

response of calcareous nannoplankton to the late cretaceous oceanic anoxic event 2 at oued bahloul central tunisia abstract oued bahloul is a reference section for the cenomanian turonian that was located on the north african palaeomargin where oceanic anoxic event 2 oae2 is represented by black limestones and grey marls biostratigraphic study allowed the identification of calcareous nannofossil uc3 to uc6 zones quantitative analyses of calcareous nannofossil assemblages indicate that high fertility surface water conditions predominated throughout most of the oae2 interval the most eutrophic conditions probably developed during deposition of the lowermost part of the whiteinella archaeocretacea zone uc3 to uc4 zones where nannofossil derived fertility indices reach high values and the small zeugrhabdotus gr predominates over biscutum spp the temperature index based on calcareous nannofossil assemblages indicates a warming at the beginning of the oae2 followed by progressive cooling the same trend indicated by 18 o bulk values the significant proportion of holococcoliths suggests high stress conditions in surface waters during most of the oae2 interval the enrichment in redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicates dysoxic conditions both in the deep water column and sea bottom at the beginning of the oae2 w archaeocretacea zone geochemical detrital proxies indicate an enhanced rate of terrigenous supply during the oae2 interval resulting from increased riverine influx related to a more humid climate enhanced fluvial run off increased nutrient input to marine surface waters contributing to eutrophication recorded by calcareous nannoplankton and planktic foraminifera plankton consumption of surface water nutrients increased organic matter production whose decay contributed to the decrease in dissolved oxygen generating increasingly dysoxic anoxic conditions and favoring preservation of organic matter although low latitude nannofossil assemblages such as those of oued bahloul reflect an increase in nutrient availability during the oae2 interval assemblages from mid latitude areas record a decreased nutrient content

the significance of palynofacies fluctuations in the greenhorn formation cenomanian turonian of the western interior basin usa abstract in the greenhorn limestone formation of the pueblo section colorado the palynofacies in the hartland shale member is remarkably homogeneous this is in marked contrast to that of the overlying bridge creek limestone member in which the alternating limestones and marlstones are characterized by rhythmic variations in the terrestrial phytoclasts such variations appear to be related to milankovitch cycles as well as to both the dilution and productivity models the marine palynofacies includes three dinocyst associations and scytinascia foraminiferal linings changes in the marine palynofacies do not appear to be related to the cyclical limestone marlstone deposits however the alternating dinocyst associations suggest mesotrophic oligotrophic rhythms in the surface waters the discrepancy between the dinocyst cycles and the lithological couplets could reflect the modulation of the sea level rises in the milankovitch frequency band by a barrier during deposition of the hartland shale member within the second order t6 transgression of kauffman the discrepancies between the foraminifer nannofossil and dinocyst fluctuations are interpreted as reflecting specific responses by each planktic group to global oceanographic changes and diagenesis

integrated paleoenvironmental analysis of the niobrara formation cretaceous western interior seaway northern colorado abstract this study presents a regional chronostratigraphic framework and paleoenvironmental reconstruction of the niobrara formation in northern colorado based upon multidisciplinary biostratigraphic and lithostratigraphic data a local biostratigraphic zonation is described for the coniacian to earliest campanian of this region of the western interior seaway based primarily upon the distribution of calcareous nannofossils three key paleoenvironmental packages are also identified and linked to the evolution of regional sedimentary facies during the early to late coniacian tethyan water masses interacted with boreal surface currents to produce regional upwelling along tectonically controlled bathymetric highs a well mixed relatively well oxygenated water column with warm surface water temperatures and high fertility sustained a rich microflora fauna and promoted higher carbonate production enhanced fluvial input and a weakening of tethyan influence during the early santonian mark the onset of a regional environmental shift this period of transition extends through the middle santonian and is characterized by pulses of transported material and relatively frequent turnover of faunal associations increased terrigenous runoff likely produced eutrophic surface waters and intensified water column stratification leading to a general deterioration of the bottom water environment in a progressively dysoxic setting continued strengthening of fluvial input during the late santonian to early campanian resulted in surface water freshening and sustained primary productivity this surface water environment in conjunction with stifled vertical mixing promoted the development of a stagnant and intensely stratified water column the basin was therefore severely dysoxic possibly anoxic and corrosive with chemically reducing bottom waters and an expanded oxygen minimum zone thereby limiting biotic development and causing the deposition of finely laminated mud rich carbonate poor seciments

evolution of mid cretaceous radiolarians in response to oceanic anoxic events in the eastern tethys southern tibet china abstract oceanic anoxic events oaes are well known from their widespread black shale and carbon isotopic excursions in the western and eastern tethys and atlantic ocean however the weakest link in the studies of the oaes is biological evolution sedimentological biostratigraphical and geochemical data from albian to coniacian strata in southern tibet recorded turnover events and fluctuations in diversity of the radiolarian fauna within the eastern tethys during oae 1d and oae 2 abundant radiolarian fossils were obtained from the gyabula formation with 93 species from 43 genera identified and assigned to the mid to upper cretaceous acaeniotyle umbilicata archaeospongoprunum tehamaensis crucella cachensis alievium superbum and dictyomitra formosa zones the association of carbon isotopic excursions black shale and radiolarian turnover indicates extensive changes in the ocean climate system nutrients are made increasing available to the marine plankton through submarine volcanic activity and rising sea level which were a likely cause of radiolarian turnover at or near the oaes active submarine tectonism volcanism leads to the expansion of the hypoxic zone and may cause many deeper dwelling forms to become extinct whereas most of the shallower dwelling radiolarians survive radiolarian evolution thus provides a useful record with which to seek understand relationships between climate paleoceanographic processes and plankton evolution

foraminiferal and nannofossil paleoecology and paleoceanography of the cenomanian turonian eagle ford shale of southern texas article i nfo the uppercretaceous of central texas isdominated by a broad shallow carbonate platformcalled thecomanche platform that occupies an important gateway between the epeiric western interior seaway wis of north america to the open marine gulf of mexico tethys we investigated the cenomanian turonian eagle ford shale on and adjacent to the comanche platform to determine whether the eagle ford shale has an affinity with the western interior and if so determine where the transition from western interior to open ocean is located we were also interested in the relationship if any between the organic rich facies of the eagle ford and oceanic anoxic event 2 oae2 our work is based on quantitative foraminiferal population counts and associated sedimentary particles including inoceramid prisms sand glauconite and pyrite grains calcareous nannofossil assemblages carbon isotopes and total organic carbon toc from three sites across a range of paleowater depths an outcrop in lozier canyon in terrell county west of langtry tx an outcrop at bouldin creek outside of austin tx and swift energy s fasken a 1h core in webb county tx the highest toc intheeagle ford occurs beforethe onset of oae2 6 at loziercanyon 7 atboth bouldincreek and the fasken core and then declines steadily through the rest of the section except for a small increase at the end of oae2 at lozier and a fairly large post oae2 increase at bouldin creek nannofossil paleoproductivity indicators zeugrhabdotusand biscutum track tocatbouldincreekandinthefaskencoreanddisplaysimilar trends to those observed inthe western interior seawayto the north benthic foraminiferalabundances increase astoc decreasesand the lithology shifts from laminatedblack shale to bioturbatedlight gray shale low oxygen tolerant infaunal neobulimina spp appear first and gradually increase in abundance epifaunal benthics appear soon after this oxygenation trend continues through the oae2 interval and the upper eagle ford contains a diverse epi and infaunal benthic foraminiferal assemblage and macrofossil assemblage this trend of decreasing toc and nannofossil paleoproductivity indicators coupled with increasing benthic foraminiferal abundance and diversity and seafloor oxygenation corresponds to rising sea level based on foraminiferal and nannofossil events toc trends and changes in lithology both platform sites have a strong affinity with the western interior with lozier canyon being the most similar the fasken core bears all the characteristics of an open ocean site except for the fact that peak toc occurs before oae2 this suggests that the oceanographic boundary between wis and tethys can be placed on the edge of the comanche platform productivity was likely driven by bathymetry induced upwelling caused by restriction between the wisand tethys during times of low sea level as sea level rose upwelling diminished and productivity decreased this explains why the fasken core adjacent to the platform margin and in the center of this upwelling zone displays the same toc trends as the platform sites organic carbon content in the seaway was controlled by stratification and enhanced preservation but this was also reduced by rising sea level which is why the two areas show parallel trends

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

stable isotopic fractionation among particles in quaternary coccolith sized deep sea sediments oxygen and carbon isotopic ratios of individual grain size splits of the 38 m fraction of deep sea carbonate particles vary systematically with size over a range of 1 25 4 0 most splits are dominated by just a few coccolith taxa and other types of particles the 18o and 13c values of individual splits are linearly related to each other with a slope of 1 5 13c 18o in all holocene and glacial samples analyzed although the observed variability is less than predicted from culture experiments of individual components compositional variations can significantly influence the stable isotopic stratigraphies measured on the nannofossil fraction

evidence of increasing surface water oligotrophy during the campanian maastrichtian boundary interval calcareous nannofossils from dsdp hole 390a blake nose abstract the latest cretaceous campanian maastrichtian is characterized by several global cooling and intermittent warming events these climatic changes influenced the palaeoceanography substantially including changes of the deep water sources and surface water currents one of the most prominent episodes of climatic cooling occurred during the campanian maastrichtian transition this study focuses on the palaeoclimate and palaeoceanography of the campanian maastrichtian transition by analysing the calcareous nannofossils of dsdp hole 390a 139 92 126 15 mbsf blake nose for the examination of calcareous nannofossils sixty samples were processed using the settling technique biostratigraphical index taxa broinsonia parca constricta uniplanarius trifidus and tranolithus orionatus suggest a late campanian age for the major part of the studied section the calcareous nannofossils are well preserved highly abundant 6 80 billion specimens gram sediment and diverse 80 species sample the assemblages are dominated by prediscosphaera spp 20 5 watznaueria spp 20 3 and retecapsa spp 9 8 cool water taxa ahmuellerella octoradiata gartnerago segmentatum and kamptnerius magnificus however appear less frequently and do not exceed more than 1 due to their rarity these cool water taxa do not support the existence of an intense cooling phase during the campanian maastrichtian transition at dsdp hole 390a around 133 mbsf several nannofossil taxa however show a distinctive turnover mesotrophic species like discorhabdus ignotus zeugrhabdotus bicrescenticus and zygodiscus exmouthiensis are abundant below 133 mbsf whereas oligotrophic taxa like watznaueria spp eiffellithus spp and staurolithites flavus become common above this level these changes imply a decrease in the input of nutrients perhaps caused by a reorganization of ocean currents palaeo gulf stream and reduced upwelling

geochemical anomalies at the cenomanian turonian boundary northwest new mexico a high resolution section of 64 carbonates and calcareous shales from northwest new mexico spanning the cenomanian turonian c t boundary is examined for selected elemental concentrations as well as carbon isotopic and molecular distributions spatial and temporal sampling resolutions for the entire sample set are 1 spl 19 cm and 1 spl 33 ka respectively in proximity to the c t boundary respective spatial and temporal resolutions increase to 1 spl 10 cm and 1 spl 17 ka results show the occurrence of several geochemical anomalies all with coincident maxima at about 0 5 m below the c t boundary stable carbon isotope ratios of the kerogen and the aliphatic and aromatic hydrocarbon fractions increase by approximately 4 within 20 m of the boundary this entire c t boundary event isotope anomaly occured over approximately 2 5 ma a 5 fold increase in the concentrations of u and th occurs synchronous with the isotope excursion although this u th spike occurs over a period of only 0 2 0 3 ma elevated u and th concentrations at this spike co occur with a the highest 20s 20s 20r sterane epimer ratios b c27 c27 30 sterane homolog ratios and c the lowest n alkane yields in kerogen pyrolyzates these observations suggest an effect of radiogenic heat production on the organic matter in the section the origin of the carbon isotope excursion is attributed as in previous studies to atmospheric co2 drawdown in latest cenomanian time caused by rapid burial of organic matter due to a global marine transgression the u and th spike is probably secondary perhaps resulting from adsorption of these elements onto clays concentrated at the c t boundary although the occurrence of coeval maxima for these isotopic and elemental anomalies suggests a common cause extrapolation of the co2 drawdown model to explain the u th anomaly is unwarranted at this time ongoing mineralogical analysis of clays and carbonates close to the c t boundary in the red wash section may ultimately explain the occurrence of this u and th spike

geochemical and palaeontological studies of the δ13c anomaly in boreal and north tethyan cenomanian turonian sediments in germany and adjacent areas in two sections of the upper cenomanian and lower turonian of northwest germany boreal realm north sea basin and southeast germany north tethys regensburg area stable isotopes 13c 18o acid soluble manganese carbonate contents and foraminifera were investigated in addition other sections across norttwest and middle europe are reviewed with respect to the detailed stratigraphy of a positive 13c anomaly which was found earlier to be of global importance in the archaeocretacea foraminiferal zone cenomanian turonian transition the 13c excursion was found to be isochronous with the lower limit marked by the extinction of the foraminiferal genus rotalipora the upper limit is found immediately above the entry of the foraminiferal praeglobotruncana helvetica bolli in the macrofossil zonation the base is marked by the occurrence of the belemnite actinocamax plenus blainville in the upper part the metoicoceras geslinianum ammonite zone the upper limit falls in the watinoceras coloradoense ammonite zone just above the entry of the inoceramid genus mytiloides in some cases the 13c excursion refers to a maximum of a more or less well expressed oscillation of the 13c values with minima in the lowermost cenomanian and the upper turonian in other cases 13c is constant with a marked spike at the position of the anomaly the locally different structures of the 13c trends point to incomplete mixing of water masses between basins in northwest europe a manganese anomaly associated with the 13c excursion in the anglo paris basin was found at a higher position in northwest germany and is apparently absent from the german north tethys in both cases high mn contents appear to be associated with a markedly increased terrigenous input expressed by an increase in grainsize of the acid insoluble residue the stratigraphical value of the mn anomaly is therefore limited the palaeoecological conditions are discussed in terms of foraminiferal diversity and the occurrences of macrofossils a shift to higher 18o values coincident with the 13c excursion is possibly a response to cooling of ocean water for which evidence is provided by a low diversity globular planktonic assemblage the correlation of 18o and foraminiferal diversity is suggested to provide a tool for bathymetric interpretations of sections but needs further investigations

the cenomanian turonian boundary at eastbourne sussex uk a proposed european reference section the cenomanian turonian boundary ctb section at eastbourne sussex england is the thickest at outcrop in the anglo paris basin is rhythmic throughout rich in macro micro and nanno fossils and shows less diagenetic alteration than other sections in nw europe geochemical and biostratigraphic data are all related to detailed rhythmic lithostratigraphy allowing correlation with the global boundary stratotype section to within 20 000 years and accurate estimates of rates of changes very detailed stable isotope curves for oxygen and carbon are presented and show that the build up phase of the ctb carbon excursion had two portions separated by a trough patterns of occurrence of coarse fraction benthic foraminifera 250 mm show two peaks of extinction corresponding to the two build up phases of the carbon excursion benthic and planktic foraminifera ostracods and calcareous nannofossils all show declines in diversity and abundance across the ctb foraminifera also decline significantly in size key biomarker events for the ctb include first occurrences of the ammonites fagesia catinus and mammites nodosoides the bivalve mytiloides the planktic foraminifera helvetoglobotruncana praehelveticaand marginotruncana renzi and the calcareous nannofossils quadrum intermedium q gartneri and eprolithus octopetalus and last occurrences of the ammonite sciponoceras the planktic foraminifera rotalipora greenhornensis and r cushmani the calcareous nannofossils corolithion kennedyi axopodorhabdus albianus lithraphidites acutus rhagodiscus asperand microstaurus chiastius cyclostratigraphy allows very precise correlation of isotopic and bioevents with other sections in europe and north america eastbourne is recommended as a nw european standard section 1999 elsevier science b v all rights reserved

pioneer nannofossil assemblages from the initial transgression of the niobrara seaway in the turonian san juan basin new mexico usa abstract nannofossils of the north american late cretaceous western interior seaway have been extensively studied but these investigations have primarily focused on the diverse communities of the niobrara and greenhorn sea level highstands we lack a firm understanding of the nature of early nannofossil communities from the initial stages of the transgression and of how the diverse assemblages of the coniacian santonian became established we investigated nannofossils in a core from the san juan basin new mexico with concentrated sampling across this transgression we then compared nannofossil assemblages from the initial transgression of the seaway to the more established cosmopolitan assemblages of the niobrara highstand the initial stages of transgression were characterized by unusual low diversity assemblages dominated by holococcoliths and seldom reported and previously undescribed species of hetero and holococcoliths herein we describe five new species and one new genus from these assemblages ahmuellerella frankiae sp nov gartnerago waszczakii sp nov orastrum schollei sp nov pharus clarescopoli sp nov and wisea sanjuanensis gen et sp nov these initial assemblages transitioned to more cosmopolitan higher diversity assemblages coincident with an unconformity that likely represents subaqueous erosion or prolonged non deposition above this unconformity the nannoplankton were abundant diverse and characterized by open marine cosmopolitan taxa that persisted through the coniacian and santonian x ray fluorescence data collected from the core show a high abundance of the detrital elements al and ti in the section indicating substantial detrital clay input into the area coincident with deposition of the holococcolith dominated assemblages the detrital influence lessened as cosmopolitan nannoplankton became more abundant in the area we suggest that the initial holococcolith rich assemblages are representative of a shallow marine potentially hyposaline turbid or unstable environment such assemblages have been observed from the late turonian elsewhere in northern new mexico and may represent typical pioneer nannofloras of the late cretaceous western interior marine transgressions our integrated investigation of nannofossils and x ray fluorescence geochemistry adds to the meager knowledge base of pioneer nannofloral communities in the initial phases of continental marine transgression

ocean wide stagnation episode in the late cretaceous in this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid cretaceous here called the cenomanian turonian black shale horizon ctbsh the occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments the stratigraphic record above and below the ctbsh in environments as different as the deep north atlantic ocean and marginal and epicontinental seas over enormous areas in north america north africa and northwestern europe is characterized by a stratigraphic gap a disconformity or a continuous but strongly condensed stratigraphic section the anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2 no simple model has yet been found to explain the occurrence of the ctbsh in such a wide range of depth and palaeoenvironmental conditions

global and local controls influencing the deposition of the la luna formation cenomanian campanian western venezuela bulk and molecular geochemical micropalaeontological and carbon isotopic data are used to address the different local and global factors influencing the environment of sedimentation of the la luna formation cenomanian campanian approximate palaeolatitude 15 n in a single section in western venezuela based on the constructed chronostratigraphic framework oxygen depleted bottom water conditions and black shale deposition started in western venezuela well before the widespread occurrence of organic rich sediments in higher palaeolatitude regions such as the tethys and the north atlantic near or at the cenomanian turonian boundary in the la luna formation palaeoenvironmental conditions that allowed the preservation of organic matter mainly of marine origin prevailed until santonian times in a distal platform facies with very low siliciclastic input changes in lithology appear to reflect the local response to eustatic sea level variations and the presence of a migrating upwelling belt affecting the bioproductivity of silica and carbonate a marked 13corg isotopic excursion is recognised in the middle part of the section and is apparently unrelated to local palaeoenvironmental changes in bioproductivity and oxygen depletion biological marker data show no variations in association with the isotopic excursion being mainly controlled by local fluctuations in organic matter input and preservation

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

sequence stratigraphy and ichnology of early cretaceous reservoirs gadvan formation in southwestern iran abstract the siliciclastic gadvan formation from abadan plain southwestern iran is highly bioturbated and allows relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high resolution sequence stratigraphic framework relying on the sedimentary and ichnological characteristics the siliciclastic succession is divided into two facies associations a wave dominated offshore shoreface complex and a tide river influenced delta the first includes facies that have been deposited in shelf offshore upper offshore lower shoreface and upper middle shoreface environments the latter includes facies that have been deposited in prodelta and delta front integrated ichnologic and sedimentologic studies of the gadvan formation allow distinction between prodelta and delta front and open marine deposits with the identification of maximum flooding and ravinement surfaces as bounding surfaces of the stratal units detailed analysis on systematic changes in the stacking pattern cycle thickness cycle type and facies proportion are made eight ichnocoenoses could be differentiated in the studied sections the positions of the ichnocoenoses within genetically related stratal units genetically related ichnocoenoses indicate three large scale cycles ds1 to ds3 from oldest to youngest the cyclical nature of the gadvan formation is attributed to low amplitude eustasy in greenhouse conditions formed under interaction of eustatic high frequency cycles and longer term tectonically driven sea level variations during the long term transgressive sea level trend of the early cretaceous stratigraphic architectural style of sequences ds1 to ds3 which includes scarce evidence of lowstand deposits partial or total truncation of the hst and predominance of thick transgressive deposits is remarkably similar to long term transgressive sea level trend of the early cretaceous across the arabian plate this study suggests a more relatively seaward position of the siliciclastic successions of the gadvan formation of abadan plain than the mesopotamian basin upper zubair formation equivalent in western iraq and kuwait which would be concordant with the prevailing view of an easterly prograding coastline across the arabian plate this study reveals important sedimentological and ichnological features and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical significance of trace fossil assemblages that can be readily compared or translated to analogous depositional systems worldwide the ichnological analysis is based on cores and can be especially applied to evaluate the applicability of current ichnological models to the study of cretaceous reservoirs of western iraq kuwait and western saudi arabia

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

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

new morphologic information on cretaceous nannofossils from the niobrara formation upper cretaceous of kansas outcrops of the niobrara formation from northwestern kansas have yielded horizons of well preserved calcareous nannofossils scanning electron and light microscopy have revealed not only several new taxa but also an extraordinary cylindrical coccosphere not previously described from the fossil record this unusual cylindrical form of a species of biscutum black also differs from the characteristic spherical coccosphere by the arrangement of its coccoliths in an ordered and repetitive fashion a new term coccocylinder is proposed here as a more appropriate descriptive term than coccosphere for the cylinder a stagnant anoxic benthic environment prevalent during intervals of niobrara deposition enhanced the preservation of monospecific coccolith clusters which represent coccospheres that settled to the bottom often via fecal pellets before disarticulating these clusters representing 34 different species provide information on the minimum number of coccoliths originally present on the living cell such data may be valuable for determining the total biomass of the living populations on the basis of the abundances of individual coccoliths in the fossil record

valanginian to aptian calcareous nannofossil stratigraphy and correlation with the upper m sequence magnetic anomalies abstract calcareous nannofossil stratigraphy has been investigated in lower cretaceous italian sections at gorgo a cerbara presale and frontale all in the umbrian apennines and at cismon southern alps a modified sample preparation technique has allowed a thorough stratigraphic study of the well lithified maiolica limestone and although nannofossil preservation is generally quite poor the major valanginian to aptian marker species can be detected nine nannofossil events can be determined and correlated to magnetic stratigraphies previously established in these sections nannofossil stratigraphy confirms most magnetostratigraphic correlations made between sections and allows a more precise correlation of magnetic chrons m 0 to m 11 with the valanginian hauterivian barremian and aptian stages the results obtained differ considerably from previous timescales nannofossil events recorded in the various sections may be time transgressive by as much as one magnetic chron probably due to differential preservation

molecular fossil constraints on the water column structure of the cenomanian turonian western interior seaway usa abstract bulk geochemical and biomarker molecular fossil data were collected for four cenomanian turonian sections in the western interior basin usa the four sections represent a 900 km wide transect across the basin from kansas to new mexico rock eval and biomarker analyses indicate an east west thermal maturity trend due to progressive deeper burial associated with the tectonic flexure of the foreland basin since the cenonamian turonian at each site the source of extractable organic matter is dominantly marine with minor terrestrial contribution the presence of isorenieratene derivatives in samples from bunker hill ks pueblo co and red wash nm indicates the presence of the green sulfur bacterium chlorobium in the water column and shows that the southern part of the western interior seaway wis experienced events of photic zone anoxia at maximum transgression sedimentary features indicative of water column oxygenation occur within single beds with geochemical evidence of photic zone anoxia this is consistent with a scenario in which bottom waters experienced alternating oxic dysoxic and anoxic conditions these so called intermittent anoxic events underline the high variability in redox conditions in the wis the distribution of isorenieratene derivatives shows a dynamic water column structure of the wis and indicates that anoxia was a permanent feature of the transgressive and regressive intervals of the greenhorn cyclothem rather than at maximum transgression hence the oceanographic circulation is dominated by near field effects inherent to the seaway rather than by direct proto atlantic elements such as the oceanic anoxic event oae

geology of the strata exposed on the florida escarpment three sampling and observational transects were made during five dives in the research submersible alvin on the steep lower flanks of the florida escarpment from 3280 m twelve other dives were conducted at the base of the escarpment which provided additional rock samples and observations the face of the escarpment consists of steep to vertical limestone cliffs with intervening gently sloping sediment covered terraces flat lying beds ranging up to several meters in thickness are truncated at the face along joint planes sixty rock samples were collected on submersible transects up the face of the escarpment together with fifteen additional samples from near the base of the escarpment the sampled strata which contain sparse early aptian and late cenomanian nannofossil floras are dominated by limestone facies which indicate lagoonal or low energy intertidal depositional environments these facies are indicative of deposition at some distance from the original platform edge suggesting that the original shallow water cretaceous margin has been lost to erosion although erosion is suggested by the exposure of truncated nearly horizontally bedded interior platform limestone facies at the escarpment face the data do not indicate when or how much erosion has occurred however the exposed surfaces of most rocks are not heavily corroded or bored many of the rock samples have smooth surfaces and angular edges rocks are covered with a veneer of iron and manganese oxides which are typically 0 1 mm thick on the lower steep face of the escarpment paleogene and most miocene nannofossils are missing in the pore fillings of the sampled mesozoic strata although 55 of the samples contained biologically penetrated surfaces the frequency of rock surfaces that are biologically penetrated decreases with depth the truncated outcrops display fresh surface characteristics which suggest that episodic physical collapse of the lower escarpment face progressively exposes fresh rock surfaces strata with weathered surfaces and more than 0 1 mm of femn coatings are more common at shallower depths thus the face of the present escarpment is not a preserved mesozoic platform flank but a morphological feature which is undergoing episodic active erosion

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

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

the northern gulf of mexico during oae2 and the relationship between water depth and black shale development despite their name oceanic anoxic events oaes are not periods of uniform anoxia and black shale deposition in ancient oceans shelf environments account for the majority of productivity and organic carbon burial in the modern ocean and this was likely true in the cretaceous as well however it is unlikely that the mechanisms for such an increase were uniform across all shelf environments some like the northwest margin of africa were characterized by strong upwelling but what might drive enhanced productivity on shelves not geographically suited for upwelling to address this we use micropaleontology carbon isotopes and sedimentology to present the first record of oceanic anoxic event 2 oae2 from the northern gulf of mexico shelf here oae2 occurred during the deposition of the well oxygenated inner neritic lower estuarine lower tuscaloosa sandstone the overlying organic rich oxygen poor marine tuscaloosa shale is entirely turonian in age we trace organic matter enrichment from the spinks core into the deepwater gulf of mexico where wireline log calculations and public geochemical data indicate organic enrichment and anoxia throughout the cenomanian turonian boundary interval redox change and organic matter preservation across the gulf of mexico shelf were driven by sea level rise prior to the early turonian highstand which caused the advection of nutrient rich oxygen poor waters onto the shelf this results in organic matter mass accumulation rates 1 2 orders of magnitude lower than upwelling sites like the nw african margin but it likely occurred over a much larger geographic area suggesting that sea level rise was an important component of the overall increase in carbon burial during oae2

stepwise mass extinctions the case for the late cenomanian event the various extinctions of marine taxa in the late cenomanian can be shown as conforming to the step wise extinction model the order of such extinctions is however compatible with the presence of an expanded oxygen minimum zone in the world ocean the occurrence of iridium anomalies at this level in the succession may however indicate a volcanogenic control on the global environment detailed time analysis of the late cenomanian event has been used to produce a correlation of some key successions

comet showers as a cause of mass extinctions if at least some mass extinctions are caused by impacts why do they extend over intervals of one to three million years and have a partly stepwise character the solution may be provided by multiple cometary impacts astronomical geological and palaeontological evidence is consistent with a causal connection between comet showers clusters of impact events and stepwise mass extinctions but it is too early to tell how pervasive this relationship may be

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

density magnetic susceptibility and the characterization of ordinary chondrite falls and showers bulk and grain densities of 132 ordinary chondrites from the vatican observatory collection were measured and compared with their magnetic susceptibility for the most part using previously measured values ten new susceptibility measures were taken for this study grain density and magnetic susceptibility combined provide a reliable method of classifying un weathered ordinary chondrites unlike traditional chemical tests this method is fast nondestructive and characterizes the whole rock making it especially appropriate for surveying large collections the system is less viable for finds extensive weathering of metallic iron in an h chondrite can cause it to plot among l chondrites while heavily weathered l chondrites plot among the ll group this system has revealed outlier stones that may be misclassified meteorites or mislabeled samples in every case where the magnetic susceptibility of a meteorite does not fit its putative classification the grain density is also found to be in disagreement in a manner consistent with either severe weathering or misidentification an analysis of stones from five showers shows that excluding outliers these samples tend to cluster tightly within their appropriate groups in a plot of grain versus magnetic susceptibility

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

production and preservation of organic matter the significance of iron 1 iron fertilization has been previously recognized as a potential mechanism for enhanced organic matter burial in marine sediments however the singular view of iron as a control on primary production overlooks its role in sedimentary diagenesis a factor that must be evaluated when considering organic matter accumulation this study examines the role of iron as a buffer of pore water sulfide and its implications for marine organic matter burial biogeochemical model experiments indicate that dissolved sulfide buildup in surficial marine sediments is highly sensitive to reactive iron concentration a reduction in reactive iron concentration can initiate dissolved sulfide accumulation the consequences of which include inhibition of bioturbation bioirrigation a decrease in oxygen exposure time and enhanced organic matter burial alternatively an increase in reactive iron concentration can serve to decrease organic matter burial the coupling of iron and phosphorous cycling within marine sediments provides an important positive feedback and therefore this mechanism is designated the sulfide buffer phosphorous trap hypothesis given sufficient organic carbon supply carbonate rich and opal rich sediments should be especially prone to the development of sulfidic conditions because of a deficiency in terrigenous iron widespread chalk and marl deposition during the cretaceous in association with the evolutionary expansion of calcareous plankton may have predisposed many benthic marine environments to the accumulation of toxic hydrogen sulfide and fostered the development of oceanic anoxic events comparison of model results with proxy data from oceanic anoxic event ii middle cretaceous suggests a complex role of iron as a control on both organic matter production and preservation

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

a quantitative analysis of calcareous nannofossil bioevents of the late cretaceous late cenomanian coniacian western interior seaway and their reliability in established zonation schemes abstract calcareous nannofossil assemblages from 8 localities in the upper cenomanian coniacian strata of central colorado and kansas and southern texas western interior seaway usa were analyzed to produce a new high resolution biostratigraphic framework for the greenhorn formation eagle ford formation and basal austin chalk eighteen datasets from coeval successions around the world including the global stratotype section and point gssp at pueblo co and proposed reference sections for the base of the turonian and candidate gssps for the base of the coniacian in germany poland and new mexico were incorporated from literature sources additional discussion is devoted to the basal turonian and coniacian boundaries as they reflect paleoceanographic phenomena e g oae2 widespread late turonian regression where high resolution biostratigraphy has academic as well as industrial application ranking and scaling of 48 selected bioevents produces a quantitatively derived optimum sequence of first and last occurrences scaling of events along a relative time scale reveals an 8 9 evolutionary turnover during oae2 comparison with the qualitatively developed nannofossil zonations known as the cc zonation of perch nielsen and uc zonation of burnett reveals inconsistencies largely due to the recognition of new amended species concepts discrepancies near the turonian coniacian boundary reflect changes to its placement in recent revisions to the geologic timescale a recently documented sequence of bioevents provides an accurate proxy for the boundary in the absence of the inoceramid index fossil cremnoceramus deformis erectus meek fifteen bioevents from the optimum sequence are given greater priority based on their interpreted reliability between the sections examined and the cc and uc zonations

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

patterns of local and global redox variability during the cenomanian turonian boundary event oceanic anoxic event 2 recorded in carbonates and shales from central italy careful evaluation of the local geochemical conditions in past marine settings can provide a window to the average redox state of the global ocean during episodes of extensive organic carbon deposition these comparisons aid in identifying the interplay between climate and biotic feedbacks contributing to and resulting from these events well documented examples are known from the mesozoic era which is characterized by episodes of widespread organic carbon deposition known as oceanic anoxic events this organic carbon burial typically leads to coeval positive carbon isotope excursions geochemical data are presented here for several palaeoredox proxies cr ti v mo zn mn fe speciation i ca and sulphur isotopes from a section exposed at furlo in the marche umbrian apennines of italy that spans the cenomanian turonian boundary here oceanic anoxic event 2 is represented by a ca 1 m thick radiolarian rich millimetre laminated organic rich shale known locally as the bonarelli level iron speciation data for thin organic rich intervals observed below the bonarelli level imply a local redox shift going into the oceanic anoxic event with ferruginous conditions i e anoxic with dissolved ferrous iron transiently developed prior to the event and euxinia i e anoxic and sulphidic bottom waters throughout the event itself pre oceanic anoxic event enrichments of elements sensitive to anoxic water columns were due to initial development of locally ferruginous bottom waters as a precursor to the event however the greater global expanse of dysoxic to euxinic conditions during the oceanic anoxic event greatly reduced redox sensitive trace metal concentrations in seawater pyrite sulfur isotopes document a positive shift leading into the oae carbonate i ca ratios were generally low suggesting locally reduced bottom water oxygen conditions preceding the event and relatively increased o2 concentrations post event combined the furlo geochemical data suggest a redox stratified water column with oxic surface waters and a shallow chemocline overlying locally ferruginous bottom waters preceding the event globally widespread euxinic bottom waters during the oceanic anoxic event followed by chemocline shallowing but sustained local redox stratification following the event this article is protected by copyright all rights reserved

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

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

testing the precision of bioevents deciding which of two bioevents is the less diachronous is a common problem in biostratigraphy the most accurate correlation uses the finest timescale available chemostratigraphy or cyclostratigraphy offer a potential precision of about 10 ka graphic correlation can then be used to test the precision of bioevents and to quantify any mismatch it can also be used to determine in which section any event occurs earlier application of these ideas to correlation of the cenomanian turonian and coniacian santonian boundaries demonstrates that some bioevents are as precise as chemo and cyclostratigraphy but that most are not two problems occur with bioevents first they may not be recognizable in all sections second where they are recognizable they may be diachronous in the former case calculating confidence intervals on known ranges in sections where the relevant fossil has been recorded is an alternative test large confidence intervals suggest that both first and last occurrences of a fossil may be diachronous bioevents at the cenomanian turonian boundary the following bioevents in stratigraphic order appear to be reliable time planes for international correlation the last occurrences of 1 corolithion kennedyi 2 rotalipora greenhornensis 3 axopodorhabdus albianus 4 rotalipora cushmani 5 lithraphidites acutus 6 microstaurus chiastius and 7 the first occurrence of quadrum gartneri at the coniacian santonian boundary only the first and last occurrences of platyceramus undulatoplicatus and the first occurrences of platyceramus cycloides and lucianorhabdus cayeuxii have been identified as potentially reliable bioevents

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

the cenomanian turonian boundary event in central poland abstract stable isotopes 13c 18o caco3 content carbon content insoluble in hcl corg and in the carbonates ccarb and foraminifers have been investigated in the cenomanian turonian boundary interval rotalipora cushmani zone and lower whiteinella archaeocretacea zone in southeast central poland a higher content of corg in the uppermost rotalipora cushmani zone and lowermost whiteinella archaeocretacea zone a 13c and 18o stable isotope anomaly in the uppermost cenomanian and substantial changes in the foraminiferal assemblages have been recorded a major carbon stable isotope excursion with a shift of up to 1 6 pdb recorded in the lower part of the whiteinella archaeocretacea zone within the marly limestone in the uppermost cenomanian a late cenomanian expanding oxygen minimum zone is thought to be responsible for changes in foraminiferal assemblages

middle and late cenomanian oceanic anoxic events in shallow and deeper shelf environments of western morocco the response of shallow water sequences to oceanic anoxic event 2 and mid cenomanian events 1a and 1b was investigated along the west african margin of morocco north of agadir azazoul and correlated with the deep water sequence of the tarfaya basin mohammed beach based on biostratigraphy mineralogy phosphorus and stable isotopes in the deeper mohammed beach section results show double peaks in 13corg for mid cenomanian events 1a and 1b rotalipora reicheli biozone lower cc10a biozone the characteristic oceanic anoxic event 2 13c excursion rotalipora cushmani extinction top of cc10a biozone and laminated anoxic black shale in the shallow environment north of agadir a fluctuating sea level associated with dysoxic brackish and mesotrophic conditions prevailed during the middle to late cenomanian as indicated by oyster biostromes nannofossils planktonic and benthonic foraminiferal assemblages anoxic conditions characteristic of oceanic anoxic event 2 for example laminated black shales did not reach into shallow water environments until the maximum transgression of the early turonian climate conditions decoupled along the western margin of morocco between mid cenomanian event 1b and the cenomanian turonian boundary as also observed in eastern tethys north of agadir alternating humid and dry seasonal conditions prevailed whereas in the tarfaya basin the climate was dry and seasonal this climatic decoupling can be attributed to variations in the intertropical convergence zone and in the intensity of the north east trade winds in tropical areas

the geochemistry of the plenus marls at dover england evidence of fluctuating oceanographic conditions and of glacial control during the development of the cenomanian turonian δ13c anomaly

early turonian pelagic sedimentation at moria umbria marche italy primary and diagenetic controls on lithological oscillations abstract the upper cretaceous of the umbria marche basin italy consists of an alternation of calcareous and siliceous fine grained sedimentary rocks in which the calcareous lithologies are predominant the cenomanian succession is dominated by white micritic limestones and contains a black shale horizon bonarelli level in its uppermost part which is the regional expression of oceanic anoxic event 2 in the turonian the rocks gradually become red upwards and are referred to as cretaceous oceanic red beds the lithological variability in the succession reflects the local response of sedimentary systems to varying local and global environmental conditions in this study local processes behind the transition from black shale to red bed deposition and in particular behind lithological oscillations within the lowermost turonian are studied and placed in their global context sediment colour composition geochemistry and nannofossil content were studied using samples of the scaglia formation at moria umbria marche basin the results show that following the cenomanian turonian boundary terrigenous input decreased and its composition was different in calcareous and siliceous oozes organic productivity was high during the deposition of siliceous ooze due to upwelling and varied on orbital timescales the alternation between the siliceous and calcareous ooze was further controlled by carbonate dissolution small fluctuations in the calcite compensation depth ccd had a significant impact on sediment composition because depositional depth was between the lysocline and the ccd diagenesis resulted in the segregation of carbonate and silica in the concentration of terrigenous material in smarl interbeds and in the enhancement of bedding after the earliest turonian ocean circulation patterns changed seawater temperatures declined slowly and seawater became better oxygenated productivity and terrigenous input also declined and the resulting combination of oxygen demand in the sediments and sedimentation rates favoured the formation of authigenic haematite in the sediments which led to their reddening

chemostratigraphy versus biostratigraphy data from around the cenomanian turonian boundary a detailed isotopic profile is presented for a stratigraphically expanded cenomanian turonian boundary section in chalk facies exposed at eastbourne sussex and compared with data from pueblo colorado in both sections macro and micropalaeontological markers first appearances and disappearances are well constrained and their relative positions and relationship to the structure of the carbon isotope curve are identical this consistent relationship between two independent phenomena one geochemical the other biostratigraphical is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon isotope excursion in these two areas this interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon isotope excursion in europe and north america

the first 150 million years history of calcareous nannoplankton biosphere geosphere interactions abstract the mesozoic evolution of calcareous nannoplankton is here compared to global changes in the earth system to derive possible causal links between biosphere geosphere interactions the late triassic appearance of nannofossils represents an innovation that affected the marine carbonate system the global carbon cycle and the ocean atmosphere co2 nannofossil biodiversity generally increases through the jurassic and cretaceous with development of approximately 30 coccolith nannolith families speciations mass extinctions diversifications and turnovers correlate with global changes in the geosphere hydrosphere and atmosphere suggesting that the evolutionary patterns are intimately linked to environmental modifications coccolithophore biocalcification involves conversion of ca2 and co32 ions into caco3 when high fluxes of ca2 and inorganic c from the external environment into the cell are maintained seawater co2 availability and nutrient type and abundance are also important for the functioning of photosynthesis and calcification the role of coccolith secretion with respect to photosynthesis remains uncertain current dating of events suggests that pco2 and chemistry of the oceans ca2 mg ca ratio are instrumental in coccolith and particularly nannolith appearance and development whereas climate and sea level apparently play a secondary role availability of nutrients and biolimiting metals certainly influence nannoplankton evolution it is suggested here that there is a causal link between levels of co2 and calcite secretion by nannoplankton namely when pco2 in the ocean atmosphere system is minimum production of heavily calcified coccoliths nannoliths might provide sufficient co2 inside the cell to sustain photosynthesis on the contrary excess carbon dioxide makes calcification less indispensable or even inhibits calcite production smaller and less calcified coccoliths become dominant natural variations in atmospheric co2 are essentially triggered by igneous activity that also controls the ocean chemistry and nutrient cycling in particular the seawater mg ca ratio is related to seafloor spreading and hydrothermal processes high production of ocean crust results in high ca2 concentrations low mg2 concentrations and low mg ca ratio and vice versa accordingly the phanerozoic is subdivided into intervals of calcite and aragonite seas the appearance of calcareous nannoplankton and its maximum diversification indeed correlate with the shift from the paleozoic triassic aragonite sea to the jurassic paleogene calcite sea and the core of the latter respectively although there is a logical connection between pco2 and ca2 concentration and nannofossil diversity species richness alone cannot measure the productivity production of coccolithophores through time absolute abundances are necessary to interpret and model the distribution of calcareous nannofossils relative to the environment and quantify positive and negative feedbacks of coccolithophore biocalcification improved chronology of paleobiological and geological events will be crucial for the understanding of evolutionary processes

trace element abundances in the rock canyon anticline pueblo colorado marine sedimentary section and their relationship to caribbean plateau construction and oxygen anoxic event 2 1 rapid eruption of submarine lava flows during formation of the caribbean plateau correlates closely with ocean anoxic event 2 oae2 which bracketed the cenomanian turonian boundary 93 5 ma these events also correspond with a positive excursion in carbon isotopic composition of seawater hydrothermal activity associated with large scale submarine volcanism may have been responsible for this abrupt change in ocean chemistry we determined the distribution of major minor and trace element abundances in the rock canyon marine sedimentary section pueblo colorado after normalizing element concentrations to zr to remove the variable contribution of terrigenous material to these sediments we detected an interval of concentrated metal abundance anomalies that coincides with the abrupt beginning of the positive 13c isotope excursion the metal abundance anomalies indicate that intermittent hydrothermal activity in the form of both water rock exchange and magmatic degassing introduced large concentrations of trace metals into the cretaceous ocean at the same time that extinctions of benthic species turnover in plankton communities and increases in isotopically light organic carbon burial occurred the stratigraphic position of this interval of trace metal anomalies matches events associated with oae2 and indicates that intermittent hydrothermal activity on a massive scale triggered abrupt changes in carbon burial and deep ocean oxygen contents

sequence architecture and carbonate platform configuration late cenomanian santonian sinai egypt relative sea level changes on the mixed carbonate siliciclastic platform of sinai are manifested in shifts of distinct facies belts deep water facies highenergy subtidal shallow subtidal lagoon shallow shoreface siliciclastics supratidal and are interpreted in terms of sequence stratigraphy eight sedimentary sequences are recognized for the upper cenomanian to santonian their correlation along a north south transect reveals distinct changes in lithofacies and progradation retrogradation patterns within the individual systems tracts the number and stratigraphy of the sequence boundaries of sinai correlate well with those from adjacent areas patterns of increased subsidence are documented for the central sinai basin since the late cenomanian by increased thickness of the stratal packages post cesin 7 hst post tusin 1 lst and hst post tusin 2 lst and are balanced by varying accumulation rates based on new sedimentological and biostratigraphic data large scale palaeogeographic maps and cross sections show the 1 temporal and spatial evolution of the central sinai basin e g its latest cenomanian initial formation lower turonian deep water facies middle turonian to coniacian synsedimentary subsidence 2 drowning of the cenomanian platform coinciding with the latest cenomanian to early turonian relative sea level rise 3 re establishment of the platform in middle late turonian times and 4 a coniacian basin and swell morphology

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes