nutrients as the dominant control on the spread of anoxia and euxinia across the cenomanian turonian oceanic anoxic event oae2 model data comparison 1 the cenomanian turonian oceanic anoxic event oae2 is characterized by large perturbations in the oxygen and sulfur cycles of the ocean potentially resulting from changes in oxygen supply via oxygen solubility and ocean circulation and in marine productivity we assess the relative impact of these mechanisms comparing model experiments with a new compilation of observations for seafloor dysoxia anoxia and photic zone euxinia the model employed is an intermediate complexity earth system model which accounts for the main ocean dynamics and biogeochemistry of the cretaceous climate the impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations the model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with oae2 observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content responsible for 85 of the change higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation the model also shows that the presence of seafloor anoxia as suggested by black shale deposition in the proto north atlantic ocean before the event might be the result of the silled shape and lack of deep water formation of this basin at the late cretaceous overall our model data comparison shows that oae2 anoxia was quasi global spreading from 5 of the ocean volume before the event to at least 50 during oae2

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

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

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

anoxic events productivity rhythms and the orbital signature in a mid cretaceous deep sea sequence from central italy albian pelagic sediments from the umbrian apennines exhibit rhythmic bedding in outcrop high temporal resolution 4 kyr spacing sampling of carbonate si and al along a 1 6 m y interval of core demonstrates that changes in accumulation rate of calcareous and siliceous microorganisms were controlled by insolation cycles optical densitometry logging correlates variations of geochemical parameters to episodes of deep sea anoxia indicated by numerous black laminated zones black shales harmonic analysis of data shows oscillations at three frequencies which correspond closely in estimated duration and ratio to the modern eccentricity and precessional orbital cycles as in pleistocene marine sequences the eccentricity approximately 100 kyr term dominates the sedimentary variance in the umbrian cycles anoxic episodes occur in phase with a limestone marl repetition and reflect minima of the precessional 21 kyr cycle the covariance of carbonate and silica with estimates of foraminiferal abundances suggest that carbonate cycles are the result of changes in surface productivity of calcareous organisms rather than an effect of dissolution or diagenesis recognition of orbital cyclicity provides a tool for making quantitative estimates of these changes productivity during anoxic events was uniformly low 0 4 0 5 g cm2 kyr carbonate 0 05 g cm2 kyr silica but it rose to high levels during oxygenated periods 1 2 5 g cm2 kyr carbonate 0 1 0 3 g cm2 kyr silica vertical overturning and organic carbon flux decreased during anoxic episodes but decreased oxygenation of the deep water led to enhanced preservation of the organic matter delivered the degree of paleoceanographic variability indicated by this study requires that accepted notions of climate stability and oceanic quiescence during nonglacial times be reassessed

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

sources and deposition of organic matter in cretaceous passive margin deep sea sediments a synthesis of organic geochemical studies from deep sea drilling project site 603 outer hatteras rise abstract the results of organic geochemical studies of rock samples from cretaceous strata at site 603 on the outer hatteras rise are reviewed and integrated with their lithostratigraphic information although most of the strata contain little organic carbon black shales enriched in organic matter were found in two settings these rocks exist as claystones in the aptian to turonian hatteras formation and as marlstones in the neocomian blake bahama formation terrigenous organic matter predominates in these deposits except in cenomanian and valanginian rocks where marine material becomes dominant organic carbon concentrations in cenomanian black claystones are higher than any previously reported from the western north atlantic but lower than the concentrations found in the eastern north atlantic black shales at site 603 appear to result from downslope transport and rapid reburial of coastal and ocean margin sediments by turbidity flows deep basin anoxia is not a major factor except during the cenomanian turonian when the entire atlantic ocean may have briefly become anoxic organic matter in the sediments from all locations is thermally immature

organic rich and manganese sedimentation during the cenomanian turonian boundary event in the outer carpathian basins a new record from the skole nappe poland abstract upper cenomanian lower turonian strata in the splawa section of the skole nappe outer carpathians poland provide a detailed palaeoenvironmental record of the oceanic anoxic event oae 2 from a deep water basin below the ccd at the northern margin of the western tethys the oae 2 succession consists of black parallel laminated radiolarian shales enriched in organic matter of mainly marine origin toc up to 8 organic carbon isotope variations together with microfossil datum events allowed to correlate the studied organic rich facies with other black shale successions along the outer carpathians and other areas of the western tethys the mean values of sedimentation rate 3 5 5 5 mm kyr and organic matter accumulation rate 0 5 g m2 year calculated for the oae 2 interval in the outer carpathian basins are comparable to the values from other deep water marginal basins in the western tethys the average redox sensitive trace metal contents and their enrichment factors indicate water column anoxia in the outer carpathian basins intensified during the interval of the largest shift in 13c values the periods of bottom anoxia were interrupted by intervals of variable eh conditions with sedimentation of hemipelagic green shales including poor agglutinated foraminiferal assemblages an increase in productivity of organic and siliceous plankton during the oae 2 is documented based on increased values of silica and barium enrichments this closely corresponds to an interval of the largest positive stable carbon isotope excursion related to the beginning of the largest sea level rise linked with intensive coastal upwelling extremely low sedimentation rate or even hiatuses and the increase in deep water circulation causing basin oxygenation resulted in precipitation of two ferromanganese layers their formation was related to changes in hydrodynamic conditions at the basin floor expressed by precipitation of fe mn carbonates some chemical indices seem to suggest that the primary metal enrichments could be related to hydrothermal activity however the concentrations of some elements show also on hydrogenic to diagenetic influences in these metalliferous sediments the precipitation of these fe mn sediments was probably synchronous with the manganese enrichment across the c t transition recorded in other western tethyan basins and in the adjacent epicontinental seas

tracking the key parameters stimulating organic carbon productivity accumulation rate and preservation based on foraminiferal proxies in the subsurface miocene sediments in north sinai egypt abstract productivity redox conditions and sedimentation rate constrain the enrichments of organic matters and under suitable conditions they can trigger larger enrichments these parameters are tracked in the subsurface miocene sediments in four wells on east to west transect across north sinai these wells are abu roda 1 misfaq 1 teffah 1 and einab 1 the miocene sections cover the aquitanian burdigalian langhian serravalian and tortonian the tracking is based on the proxies of planktonic and benthic foraminifera that offer many solutions in the application of the equations used to calculate these parameters the first of these parameters is the sedimentation rate which is calculated for different time segments based on the planktonic foraminifera bioevents the sedimentation rates are correlated throughout the basin the second parameter is the water depth that is obtained from conversion of the scores of component 1 resulted during the routine statistical analysis of the benthic foraminifera by cluster and principal component analyses these analyses are used also in assessment of redox condition and eutrophication the sedimentation rates and water paleobathymetry alongside the measured corg are used to calculate the paleoproductivity and to determine four stratigraphic sequences seq1 seq2 seq3 and seq4 the tracking of these parameters reveal higher productivity levels in the seq1 aquitanian and burdigalian accompanied with dysoxic and mesotrophic conditions however the lower sedimentation rates are not optimum to stimulate enough burial efficiency that reduced values of corg in the younger sequences seq2 4 the higher sedimentation rates increase the burial efficiency and values of corg despite the lower paleoproductivity and oxic oligotrphic conditions

history of atmospheric co2 constraints from the deep sea record the carbon chemistry of deep ocean water is quantitatively reflected in carbonate preservation and in the 13c values of foraminifera by using benthic 13c ranges to estimate total dissolved co2 and correcting for the aging effect of deep water back aging the pco2 of the atmosphere can be reconstructed data at hand are insufficient for detailed studies but allow the calculation of an upper limit of pco2 for selected periods within the last 100 million years the limit is probably near a factor of 2 5 times present atmospheric co2 for post eocene time and below a factor of 10 for the late cretaceous

nutrient enriched waters and the early skeletal fossil record this paper examines the role of stratified oxygen depleted and nutrient enriched water masses new in transforming the fossil record over the precambrian cambrian boundary interval the following may serve as markers for the encroachment of new over low latitude cratons trace element enriched black shales stone coals and hydrocarbon source rocks phosphorites phosphatized shells and organic matter sponge spicule cherts early appearance of silica and phosphatic skeletons appearance of anabarites and coleoloides biofacies peak diversity of phosphatic species occurrence of black shale lagerstatten and light 13 c values of carbonates nutrient depleted waters ndw are inferred over inner cratonic areas and nutrient starved waters nsw may well have developed over deeper waters at times through the later cambrian related to the effects of sea level rise and salinity stratification carbon isotopic fluctuations are suggested to record the history of these water masses with major changes in carbon burial and palaeoproductivity the latter may well imply episodes of greenhouse climate with globally raised levels of carbon dioxide and relatively high ocean temperatures

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

the hydrochemistry of a semi arid pan basin case study sua pan makgadikgadi botswana this study presents results on the fluid and salt chemistry for the makgadikgadi a substantial continental basin in the semi arid kalahari the aims of the study are to improve understanding of the hydrology of such a system and to identify the sources of the solutes and the controls on their cycling within pans sampling took place against the backdrop of unusually severe flooding as well as significant anthropogenic extraction of subsurface brines this paper examines in particular the relationship between the chemistry of soil leachates fresh stream water salty lake water surface salts and subsurface brines at sua pan botswana with the aim of improving the understanding of the system s hydrology occasionally during the short wet season december march surface water enters the saline environment and precipitates mostly calcite and halite as well as dolomite and traces of other salts associated with the desiccation of the lake the hypersaline subsurface brine up to tds 190 000 mg l is homogenous with minor variations due to pumping by botash mine botswana ash pty ltd which extracts 2400 m 3 of brine h from a depth of 38 m notable is the decrease in tds as the pumping rate increases which may be indicative of subsurface recharge by less saline water isotope chemistry for sr 87 sr 86 sr average 0 722087 and s d 34 s average 34 35 suggests subsurface brines have been subject to a lithological contribution of undetermined origin recharge of the subsurface brine from surface water including the nata river appears to be negligible

sedimentological geochemical and microfaunal responses to environmental changes around the cenomanian turonian boundary in the outer carpathian basin a record from the subsilesian nappe poland abstract sedimentological micropalaeontological and geochemical data from the upper cenomanian lower turonian zasan section outer carpathians subsilesian nappe poland provide new insights into the sedimentary environment and its changes in a basin at the northern margin of the western tethys a global oceanic event oae2 has been identified on the basis of lithology and radiolarian stratigraphic data this event is marked by a series of organic rich toc up to 5 non calcareous shales practically devoid of benthic microfossils indicative of bottom water anoxia the marine type of organic matter and the occurrence of radiolarian rich layers with abundant small opportunistic forms suggest that coastal upwelling was probably the main driving force for the accumulation of organic matter during the latest cenomanian the early diagenetic ferromanganese nodules followed by a 30 cm thick series of manganese rich non calcareous variegated shales and bentonites directly overlie the black facies of oae2 the fe mn nodules formed in two stages reflecting changes in bottom water dynamics across the c t boundary during the first stage the fe mn carbonate nodules were precipitated in presence of anoxic pore and or bottom water that could be episodically oxygenated later an increase in deep water circulation led to strong oxygenation of the bottom and pore water causing diagenetic modification of the nodule carbonate into ferromanganese oxides and hydroxides the manganiferous sediments recorded in the zasan section represent an isochronous horizon within the outer carpathian basin probably concurrent with manganese enrichments in many other epicontinental seas and deep water basins coinciding with the end of the carbon isotope excursion close to the base of the turonian the manganese event may have been related to increased deep water circulation associated with the maximum flooding of the late cenomanian early turonian transgression the mn event may have also been enhanced as a result of remobilization of mn 2 dissolved in anoxic bottom and pore waters in the organic rich sediments directly underlying the manganese sediments the lower turonian succession records increasing but not completed oxygenation of bottom water the oxygenation was interrupted by periods of anoxia marked by a few intervals of dark laminated black shales strongly enriched in organic matter toc up to 10 their marine origin and the occurrence of radiolarian rich layers demonstrate enhanced primary productivity and a low clastic supply during the sea level high stand frequency of radiolarian rich layers increases up section reflecting an increase in upwelling circulation at the northern margin of the carpathian basin during the early turonian

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

formation of the late aptian niveau fallot black shales in the vocontian basin se france evidence from foraminifera palynomorphs and stable isotopes abstract we present paleoceanographic models for the formation of the marlstone facies and the most prominent black shale intervals of the late aptian niveau fallot black shale succession from the vocontian basin se france in the lower part of the succession the composition of benthic foraminiferal assemblages of the niveau fallot 2 and 2 black shales suggests an enhanced burial of organic matter due to more eutrophic conditions and resulting low oxygen conditions at the seafloor in the upper part of the succession including niveau fallot 3 and 4 a third order sea level fall indicated by a decrease in the stable carbon isotope values may have resulted in a reduced water mass exchange between the vocontian basin and the western tethyan ocean this may have led to dysoxic conditions at the seafloor of the vocontian basin and may have favored the formation of organic rich sediments as shown by benthic foraminiferal assemblages decreased evaporation however is proposed as the most important mechanism causing a restriction of deep water formation within the basin which finally led to the formation of the niveau fallot 3 and 4 black shales based on our investigations the formation of the niveau fallot black shales was caused by different factors the most prominent ones include sea level fluctuations increasing productivity and changes in precipitation and evaporation rates furthermore niveau fallot 3 can probably be correlated with the thalmann black shale event in california and a dark horizon at the mazagan plateau dsdp site 545

progressive palaeoenvironmental change during the late barremian early aptian as prelude to oceanic anoxic event 1a evidence from the gorgo a cerbara section umbria marche basin central italy abstract during oceanic anoxic event 1a oae 1a 120 ma li et al 2008 organic carbon rich layers were deposited in marine environments under anoxic conditions on a global scale in this study palaeoenvironmental conditions leading to this event are characterised by studying the upper barremian to the lower aptian succession of the gorgo a cerbara section central italy for this an integrated multi proxy approach 13ccarb 13corg 18o phosphorus total organic carbon toc bulk rock mineralogy as well as redox sensitive trace elements rstes has been applied during the late barremian thin organic rich layers occur episodically and associated corg ptot ratios indicate the presence of intermittent dysoxic to anoxic conditions coarse correlations are observed between toc p and biogenic silica contents indicating links between p availability productivity and toc preservation however the corresponding 13ccarb and 18o records remain quite stable indicating that these brief periods of enhanced toc preservation did not have sufficient impact on the marine carbon reservoir to deviate 13c records around the barremian aptian boundary toc enriched layers become more frequent these layers correlate with negative excursions in the 13ccarb and 13corg records possibly due to a warming period as indicated by the 18o record during the earliest aptian this warming trend is reverted into a cooling trend which is then followed by an important warming step near the onset of oceanic anoxic event 1a oae 1a during this time period organic rich intervals occur which are characterised by the progressive increase in rste the warming step prior the onset of oae 1a is associated with the well known negative spike in 13ccarb and 13corg records an important peak in p accumulation rste enrichments and corg ptot ratios indicating the prevalence of anoxic conditions the selli level itself may document a cooling phase rste enrichments and corg ptot ratios confirm the importance of anoxic conditions during oae 1a at this site the gorgo a cerbara section is interpreted to reflect the progressive impact of palaeoenvironmental change related to the formation of the ontong java plate basalt plateau which started already around the barremian aptian boundary and culminated into oae 1a

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

model for prediction of organic carbon content in possible source rocks abstract a quantitative model has been developed to improve the prediction of the occurrence of marine siliciclastic source rocks and their likely organic carbon content the input parameters of this quantitative model are organic matter supply in the surface layer of the ocean photic zone water depth calculation of the carbon flux sedimentation rate and preservation conditions presence or absence of oxygen at the sediment water interface to handle the difficulties in the quantification of input parameters a probabilistic approach is applied depending on the available data or the interpretation of the kind of environment different risk distribution functions are used to describe the possible range of each input parameter the calculation is then carried out using the monte carlo simulation technique resulting in a probability distribution of the total organic carbon content which forms the basis of the analysis different scenarios currently under debate e g high primary productivity or the possible effects of enhanced preservation under anoxic bottom water conditions and the influence of varying water depth and sedimentation rate can be tested very quickly using examples of recent peru continental margin and ancient lower toarcian shale germany organic rich marine shales the potential of this tool is demonstrated firstly to quantify souce rock quality in this case total organic carbon content only secondly to assess quantitatively the uncertainties in source rock prediction e g evaluation of organic matter supply water depth and sedimentation rates and thirdly to determine source quality risk values to be used in the appraisal of sedimentary basins and prospects

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

sequestration of 12c in the deep ocean during the early wenlock silurian positive carbon isotope excursion abstract marine carbonates from three biostratigraphically well dated silurian sections from the mid continent of north america were analyzed for carbon isotopic 13 c carb study the early wenlock positive carbon isotope excursion ireviken excursion is recorded in three sections from tennessee iowa and ohio with values of 4 5 this global shift in the carbon isotopic ratio of marine waters began during a protracted extinction event ireviken event that spanned the llandovery wenlock boundary although several oceanographic models have been developed to account for the coincident changes in lithology biology and carbon isotope stratigraphy during this interval of the silurian their proposed causal connections among glaciation oceanography primary productivity and the global carbon cycle remain a matter of debate this investigation provides carbon isotopic and lithologic evidence that the ireviken excursion occurred during a time of relatively oligotrophic conditions a third order transgressive regressive cycle and increased carbonate production throughout the mid continent of north america the ireviken excursion is recorded in relatively pure carbonate sequences and is immediately preceded by a significant unconformity in each of the measured sections it is proposed that the ireviken excursion was the product of sequestration and burial of 12 c in deep water as a result of altered deep ocean circulation

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

seismic attenuation in porous rocks with random patchy saturation saturation of porous rocks with a mixture of two fluids has a substantial effect on seismic wave propagation in particular partial saturation causes significant attenuation and dispersion of the propagating waves due to the mechanism of wave induced fluid flow such flow arises when a passing wave induces different fluid pressures in regions of rock saturated by different fluids most models of attenuation and dispersion due to mesoscopic heterogeneities imply that fluid heterogeneities are distributed in a regular way however recent experimental studies show that mesoscopic heterogeneities have less idealized distributions and that the distribution itself affects attenuation and dispersion based on an approximation for the coherent wavefield in random porous media we develop a model which assumes a continuous distribution of fluid heterogeneities as this continuous random media approach assumes that there will be a distribution of different patch sizes it is expected to be better suited to modelling experimental data we also show how to relate the random functions to experimentally measurable parameters

rare earth element evolution of phanerozoic seawater recorded in biogenic apatites rare earth element ree contents of marine biogenic apatites have been shown to record seawater compositions a data base of available and newly acquired rare earth element ree contents of marine biogenic apatites has been created to assess the past seawater ree compositions to ensure that this data base contains only the pristine ree signals altered samples characterized by very low la sm n ratios where n stands for ree ratios normalized to the nasc composition gromet et al 1984 geochim cosmochim acta 48 1984 2469 acquired during apatite recrystallization are not included in the database these data reveal a change in the tethyan seawater composition between 110 and 80 ma after the end of the cretaceous the ree chemistry of seawater remains constant until present day this seawater composition change is likely due to concurrent changes in ree scavenging processes a strong correlation between decreasing sm yb n ratios and increasing ce anomalies for samples deposited during the 80 110 ma period is observed as ce anomalies are attributed to ocean water redox conditions changes in ree scavenging could reflect an evolution from stratified and poorly oxygenated waters towards well mixed and oxygenated waters this could have resulted from changing current patterns stemming from the contemporaneous opening of the atlantic ocean a major change in middle and late cretaceous oceanic circulation linked to plate tectonics would have favored the colonization of pelagic environments

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

sequence stratigraphy and condensed pelagic sediments an example from the rosso ammonitico veronese northeastern italy abstract correlation between eustatic and sedimentary cycles in the jurassic rosso ammonitico veronese suggests that the existence of a genetic link between them should be explored the red nodular limestones of this formation were deposited on a current swept submarine plateau pertaining to the south alpine passive continental margin in this setting of fault bounded blocks shelf derived sediments were trapped in the intervening troughs and only the very slow particle by particle rain of planktonic organisms took place the corresponding rock bodies typically show frequent omission surfaces of variable range current activity seems to be the prime controlling factor which affects the degree of winnowing early cementation and reworking and is decisive in bringing about all lithologic changes this hydrodynamic effect greatly depends on ocean circulation patterns which in turn are controlled by climatic and sea level changes highstands lead to equable climates and hence to a weak regime of currents impinging on sea bottoms the opposite happens during the following lowstands which reactivate ocean circulation through deteriorated climatic conditions it is envisaged that even though most of the geometric and sedimentologic criteria commonly used on shelf slope sediments are lacking depositional sequences i e physically the stratigraphic record of complete eustatic cycles may be recognized also in condensed pelagic successions they consist of thin rock units deposited during periods of sea level highstand when a slowed down current activity allows the preservation of the pelagic input and are bounded by lowstand induced hard grounds when accelerated winnowing prevent deposition these unconformities consequently don t correlate with condensed sections on shelves

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

organic carbon accumulation in bannock basin evaluating the role of productivity in the formation of eastern mediterranean sapropels abstract three sediment cores from bannock basin a hypersaline anoxic basin in the eastern mediterranean have been studied to evaluate the importance of productivity on organic carbon accumulation and sapropel formation in this region organic carbon accumulation rates were determined for two cores from within the anoxic hypersaline zone and for one core from the oxygenated portion of this basin organic carbon accumulation rates are higher by an order of magnitude in the surficial sediments of the anoxic zone due to better preservation an empirically derived preservation factor which allows calculation of paleoproductivity during the deposition of the most recent sapropel si indicates that productivity increased by an order of magnitude during the formation of si we conclude that increased productivity was coupled with a density stratification and a circulation reversal in the eastern mediterranean which together led to sapropel formation

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

anatomy of the organic carbon related to the miocene syn rift dysoxia of the rudeis formation based on foraminiferal indicators and palynofacies analysis in the gulf of suez egypt abstract the syn rift deposits from the gulf of suez witness different episodes of anoxia and dysoxia conditions in many areas the sediments of rudeis formation that represent the deposition in the time of maximum rift subsidence are considered as the principal organically rich and oil prone sources while in other areas they are not these differences are attributed to relative positions to the location of the syn rift dysoxia and amounts of the carbon flux during active paleoproductivity time in the present study an extensive analysis of the syn rift dysoxia and paleoproductivity during the miocene is conducted in burdigalian rudeis formation in ramadan 1 well to determine their influence on the accumulation of organic carbon the analysis depends on the statistical investigation of the benthic foraminiferal assemblages the foraminiferal assemblages are discriminated into two biofacies in r mode suboxic and dysoxic and three biotopes in q mode suboxic s dysoxic da and db sample groups the sediments are divided into three stratigraphic sequences five oxygen minimum zones are determined at the extreme oxygen depletion intervals and they are defined by suboxic s and dysoxic da sample groups in descendent order of oxygen depletion intensity and mostly coincide with the high sea levels the distribution of the organic matter showed large enrichment with partial fluorescence amorphous organic matter indicating kerogen type ii in the three biotopes as clarified from palynofacies analysis the organic carbon enrichment from the studied samples ranged from fair to very good 0 51 and 2 38 wt and the relatively larger enrichments are found to be correlated with dysoxic sample group da of intermediate oxygen depletion the pyrolysis gas chromatography pgc specifies the algal rich type i kerogen that deposited in oxygen depleted marine environment the mathematical calculation of the paleoproductivity oligotrophic to eutrophic range 106 352 gcm 2yr 1 carbon flux 13 77 and 36 19 gcm 2yr 1 indicates that higher levels of organic productivity are correlated with dysoxic sample group da the larger organic carbon values are found in the rudeis formation when the dysoxic conditions from the deeper topographic lows extend to the higher tectonic position of ramadan 1 well during the sea level rise that furthermore enhances the paleoproductivity

distribution of deep sea black shales of cretaceous age in the eastern equatorial atlantic from seismic profiling abstract the presence of thick 200 m carbonaceous shales of cretaceous age in the deep waters of the eastern equatorial atlantic was first revealed by drilling at dsdp sites 367 and 368 near the cape verde islands more recent seismic investigations show that black shales are widely distributed in this region in the gambia basin they are associated with a group of seismic reflectors lying at depths of 400 600 m below the sea floor these can be traced southwards from the drill sites into the sierra leone basin and eastwards beneath the african continental rise to depths at which ambient temperatures fall within the oil generation window in the gambia basin the reflectors continue westwards from the cape verde archipelago before terminating on turonian oceanic basement 92 ma south of the guinea fracture zone near 10 n extension of the same seismic sequence on to younger oceanic crust indicates that deep sea carbonaceous deposits formed close to the present equator as late as the early campanian 80 ma long after a series of oceanic anoxic events in the aptian albian oae1 and over the cenomanian turonian boundary oae2 led to widespread accumulation of black shales this late period of deposition may correspond to the more locally developed oae3 high surface productivity in equatorial upwelling zones during the late cretaceous probably played an important role in delivering large amounts of organic carbon to the sea floor when meridional movement of deep water between the south and north atlantic was restricted by closely spaced east west fracture zones in some areas seismic data show that the black shales level out rather than drape pre existing topography implying significant downslope transport of organic rich material from upwelling cells near the african margin

fluctuations in epeiric sea carbonate production during silurian positive carbon isotope excursions a review of proposed paleoceanographic models positive excursions in the carbon isotopic ratio of marine carbonates 13ccarb are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains the notion that high 13ccarb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings what is surprising is that major positive carbon isotope excursions during the silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas in fact silurian 13ccarb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally this discrepancy has sparked considerable debate among silurian carbon isotope specialists but has offered a valuable opportunity to re examine the intricate connections among nutrients primary productivity carbonate sedimentology and the global carbon cycle in the lower paleozoic here we consider several sedimentological and geochemical features of one of these silurian positive carbon isotope 13ccarb excursions and discuss the broader implications of current silurian 13ccarb models to the interpretation of lower paleozoic carbonate sequences

hot shale in an ice world paleoceanographic evolution of the northern gondwana margin during the early paleozoic tanezzuft formation tunisia abstract the tanezzuft formation deposited in marine periglacial conditions on the northern gondwana margin during the end of the ice house climate that characterized the lowermost silurian the basal part of this sedimentary sequence is characterized by organic rich facies with locally very high measured total organic carbon toc content up to values greater than 20 while deposition of organic rich sediments during greenhouse time interval is well known deposition of black shales during ice house conditions is poorly documented the extraordinary paleoceanographic conditions that led to the accumulation and preservation of enormous amounts of organic matter in periglacial settings makes this formation an atypical example of black shales deposition the study area is situated on the north african platform in southern tunisia on the northern flank of the ghadames basin petrophysical logs biostratigraphic organic and inorganic geochemical data from nine wells are here integrated with the aim of reconstructing the depositional history of the tanezzuft formation and the role played by organic matter production preservation and dilution through time data indicate that dilution that is depositional style and framework had an important control on lateral and vertical distribution of the c organic rich facies toc and hydrogen index hi maxima are found in correspondence of the main transgressive phases with repetitive stacking patterns strongly associated with source rock properties organic matter production as observed by detailed palynofacies analysis was mainly marine in nature with important contribution by amorphous organic matter leiosphaeridia tasmanaceae and minor amounts of graptolites fragments geochemical data indicate that the organic richest interval hot shale of the tanezzuft formation deposited under severe anoxic conditions that resulted in enhanced organic matter preservation at the sea floor of mod 3d an organic facies modelling software tool by sintef is used in order to reconstruct and quantify the peculiar processes that controlled the exceptional accumulation of organic matter at the time of deposition modelling results indicate that water stratification was the most plausible process that drove organic matter sedimentation under mesotrophic conditions density stratification was probably controlled by the deglaciation phase after the hirnantian glaciation and or by the flooded complex basin physiography that induced an inefficient circulation of the water masses the complete recovery from these extreme paleoceanographic conditions implied progressive processes that took several hundred thousand years

benthic microbial mats a possible major component of organic matter accumulation in the lower aptian oceanic anoxic event oceanic anoxic events oaes throughout the cretaceous were periods of high organic carbon burial leading to drawdown of atmospheric carbon dioxide and lowering of bottom water oxygen concentration thereby enhancing the preservation of organic matter om two dynamic depositional models have been proposed for these events in the tethyan domain one is based on strong thermohaline stratification and low surface productivity the other on high surface productivity with intensified deep water circulation here we propose another explanation for the concentration of om derived essentially from microscopical observations scanning electron microscope and transmission electron microscope in the organic richest interval of an early aptian oae in central italy oae1a or selli level 116 ma this high resolution microscopical study of om highlights benthic microbial mats as the possible source of organic rich samples where amorphous om is the major organic constituent these mats could be more common in oae black shales than previously thought

carbon sulfur iron relationships and δ13c of organic matter for late albian sedimentary rocks from the north atlantic ocean paleoceanographic implications abstract cores from six deep sea drilling project sites 367 369 137 386 387 and 603 of the late albian north atlantic ocean were investigated for organic carbon content 13c values of the kerogens maceral composition of the organic matter c s ratios fe toc s relationships and framboidal pyrite size distribution in order to evaluate processes that led to the accumulation of organic matter rich black shale deposits the results show a clear separation of the albian north atlantic into an anoxic eastern part and a mostly oxic western part the eastern north atlantic is dominated by organic matter rich deposits sulfate reduction occurred in an oxygen free water column and resulted in characteristic c s ratios fe toc s relationships and framboidal pyrite size distribution patterns elevated productivity anoxia and high sedimentation rates supported the formation of black shale deposits for most of the western and central parts organic matter sedimentation took place through an oxygenated water column the accumulated organic matter is dominantly of terrigenous origin the deposition of marine derived organic matter was most likely controlled by productivity paleobathymetry and low sedimentation rates

origin and age of phosphorite from the last glacial maximum to holocene transgressive succession off the orange river south africa a major erosional unconformity between upper cretaceous sediments and the last glacial maximum lgm transgressive succession occurs on the inner continental shelf off the orange river vibracores from 122 m water depth consist of upper pleistocene shelly phosphatic sands deposited in a high energy shoreface environment during the lgm lowstand between 22 and 19 ka the gravel rich shoreface sand grades into condensed shell rich delta front sands as sea level rose between 19 and 14 3 ka an abrupt facies transition to prodelta muddy sands corresponds to the rapid rise in sea level associated with melt water pulse mwp 1a at 14 3 ka and the facies transition to clayey silt corresponds to mwp 1b at around 11 ka a large decrease in macro and microfossil diversity indicates low oxygen conditions as the sea level rose phosphorite recovered from throughout the succession includes large interior mollusc moulds sand size peloids and friable nodules sr derived ages of the phosphorite range from early miocene to quaternary x ray amorphous friable ca phosphate nodules occur in organic rich holocene mud deposits quaternary sediment on the shelf represents a complex condensed section in which reworked phosphorite pebbles show multiple episodes of phosphogenesis often separated by millions of years within individual pebbles the phosphorite indicates that organic rich mud deposition on the shelf was prevalent during the early to middle miocene marine transgressions and sea level highstands that were associated with increased upwelling as indicated by the extensive early to middle miocene eolianites of the tsondab sandstone formation most friable phosphorite that formed during quaternary marine transgressions and highstands was probably fragmented and transported off shelf during succeeding marine regressions

impact of early aptian carbon cycle perturbations on evolution of a marine shelf system in the basque cantabrian basin aralar n spain abstract the aptian oceanic anoxic event 1a oae1a ca 120 ma ago is one of the most prominent of a series of geologically brief intervals in the cretaceous reflecting a major perturbation in the global carbon cycle this carbon cycle perturbation is recorded in the c isotope stratigraphy in this study we present a new carbonate and organic carbon isotope record across oae1a from expanded shallow marine sections igaratza and iribas in the basque cantabrian basin n spain the sediments studied were accumulated on a mixed carbonate siliciclastic and carbonate shelf the 13 c carb and 13 c org curves obtained show a pronounced negative spike in the deshayesites weissi zone and a subsequent positive excursion within the newly described d deshayesi d furcata transition zone approximately equivalent to the upper d deshayesi zone of other sections specific changes in facies patterns and a reduction in neritic carbonate production predate the negative c isotope perturbation these changes coincide with global carbonate crises in neritic and pelagic environments corresponding with the beginning of oae1a selli level a condensed interval rich in ammonites is observed this horizon is linked to a major transgression with high biodiversity the ammonite bloom suggests enhanced primary productivity in the surface waters of the basque cantabrian basin at improving environmental conditions for selected biocalcifiers the ultimate recovery of shelf carbonate deposition occurred after oae1a and it coincided in time with the most positive values of the carbon isotope excursion based on carbon isotope stratigraphy it has been deduced that black shales corresponding to selli level are missing in aralar so that anoxia is not recorded in the studied sections of the marine shelf environment an organic rich interval aparein level postdates the early aptian major positive excursion the aparein event should be considered in the future research of oaes

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

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

production and preservation of organic matter during deposition of the bakken formation late devonian and early mississippian williston basin abstract the organic rich up to 35 toc lower and upper black mudstone members of the bakken formation late devonian and early mississippian accumulated in response to both increased productivity and enhanced preservation that resulted from unique palaeogeographic palaeoceanographic and palaeoclimatic conditions during bakken deposition the semi isolated williston basin was located close to the equator 5 to 10 n in a zone of prevailing east to west winds a pattern of estuarine like marine circulation between the williston basin and open ocean conditions at the western craton edge of north america is proposed surface water discharged from the basin was replaced by nutrient rich deeper water sourced from the equatorial undercurrent in the pacific basin undercurrent flow into the williston basin upwelled providing a potentially sustainable source of nutrients to enhance productivity in the surface photic zone during black mudstone deposition in response to increased productivity that led to a high rate of organic sedimentation and quiescent deep water conditions due primarily to the geographic isolation of the basin and the restriction of estuarine like circulation to the upper water column anoxic bottom water developed on the basin floor as sea level rose during lower and upper black mudstone deposition anoxic bottom water expanded across the basin enhancing organic matter preservation conditions in the williston basin demonstrate that both increased productivity and improved preservation can be essential and complementary factors affecting organic rich mud deposition these results have potentially important implications for the accumulation of similarly organic rich deposits across the north american interior during late devonian and early mississippian time

elevated primary productivity of calcareous nannoplankton associated with ocean anoxic event 1b during the aptian albian transition early cretaceous 1 previous isotopic investigations of aptian albian oceanic anoxic event oae 1b from the western north atlantic blake nose posited that increased sea surface temperatures and decreased salinity led to stratification of the upper water column resulting in lowered dissolved oxygen and enhanced organic matter preservation we examined calcareous nannofossils from the same site in the western north atlantic blake nose to evaluate changes in surface water conditions prior to during and after the aptian albian oae1b the results of our analysis conflict somewhat with the previous interpretation that oae1b at blake nose was linked to water column stratification the signal from calcareous nannofossils indicates that in the late aptian prior to oae1b oligotrophic conditions in the surface waters were replaced by mesotrophic conditions that persisted throughout the oae event and into the early albian we speculate that increased surface water productivity facilitated to some degree the development of oae1b at blake nose

organic geochemical characteristics of atlantic ocean cretaceous and jurassic black shales abstract organic rich black shales have been observed in mesozoic strata penetrated by the deep sea drilling project dsdp these black shales represent a major carbon sink in the geologic record of paramount importance in establishing the origin of the black shales is the character and level of preservation of the organic matter within the north and south atlantic sample suite three types of organic matter were identified well preserved marine organic matter moderately well preserved terrestrial material and severely altered and or recycled organic matter the spatial and temporal distribution of the three types of organic matter suggest that the organic rich shales are not of a single origin these shales have developed as a result of high continental runoff from regions rich in sedimentary carbon and or elevated terrestrial productivity or high marine productivity and preservation in part due to rapid deposition by turbidity currents or mass slumping a detailed analysis of individual and closely spaced dsdp sites further documents that anoxia was probably not the result of synchronous major expansions of anoxic bottom water masses but represents isolated occurrences

ecology of extant nummulitids and other larger benthic foraminifera applications in palaeoenvironmental analysis abstract larger benthic foraminifera lbf are important contributors to modern and ancient tropical shallow marine sediments over the past 30 years a substantial body of literature has built up on the ecology of modern lbf especially in terms of their environmentally sensitive depth distribution reproductive strategy and morphology and the symbiotic relationship between many larger foraminifera and photosynthetic algae over the same period the extinct genus nummulites which is abundant in eocene sediments of southern europe north africa and the arabian peninsula has increasingly been studied principally because significant volumes of hydrocarbons have been discovered reservoired within nummulitic limestones offshore tunisia and libya the modern ecological studies of lbf provide a powerful tool with which to develop palaeoecological models for fossil nummulites and other symbiont bearing larger foraminifera in the rock record

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

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

bedding rhythms and cyclic sequences as documented in organic carbon carbonate patterns upper cretaceous western interior u s abstract a three component sedimentation model is introduced for estimating the relative effects of major changes in sediment flux coupled organic carbon carbonate changes reflecting different dilution concentration styles are utilized to detect the changing flux between the carbonate siliciclastic and organic matter components the three component model is then applied to upper cretaceous rhythmically bedded units of the greenhorn and niobrara cycles of the western interior seaway the cycles are related to third order sea level changes the western interior seaway was sensitive to small scale climatic cycles only during periods of maximum flooding due to combined variations in carbonate productivity redox conditions and siliciclastic supply from continental sources rhythmic deposition is different for different parts within the periods of maximum flooding for each of the two investigated third order sea level cycles section intervals reflecting peak flooding show variations in carbonate productivity and variations in redox conditions slightly more regressive intervals show variations in calcareous productivity and siliciclastic dilution with stagnant dysaerobic bottom waters for most of the investigated bedding rhythms persistent dysaerobic bottom waters are largely uninfluenced by variations in pelagic carbonate productivity except for section intervals representing peak flooding this suggests the existence of a circulation pattern in which a mixed surface water zone was underlain by more stratified oxygen depleted water masses with slow circulation

biotic recovery after mass extinction the role of climate and ocean state in the post glacial late ordovician early silurian recovery of the conodonts

origin of rhythmic albian black shales piobbico core central italy calcareous nannofossil quantitative and statistical analyses and paleoceanographic reconstructions 1 the mid cretaceous 120 90 ma was a time of excess atmospheric co2 greenhouse climate and widespread o2 deficiency in the ocean the albian is punctuated by brief intermittent episodes of anoxia dysoxia recorded as cyclic black shales in the western tethys and atlantic oceans the albian section of the piobbico core central italy contains 30 m 10 ma of rhythmic black shales that were sampled at a high resolution and examined for calcareous nannofossil assemblages and c and o stable isotopes unlike oceanic anoxic events productivity was not the primary factor controlling the deposition of albian rhythmic black shales it is suggested that during warm humid climatic cycles higher temperatures and or increased precipitation and runoff produced density stratification at a regional scale recurrent lowered salinity in the early albian and warming in the late albian are credited with causing development of a pycnocline resulting in slower rates of deep water renewal and consequent anoxia

the mid cretaceous north atlantic nutrient trap black shales and oaes organic rich sediments are the salient marine sedimentation product in the mid cretaceous of the ocean basins formed in the mesozoic oceanic anoxic events oaes are discrete and particularly organic rich intervals within these mid cretaceous organic rich sequences and are defined by pronounced carbon isotope excursions marine productivity during oaes appears to have been enhanced by the increased availability of biolimiting nutrients in seawater due to hydrothermal alteration of submarine basalts in the pacific and proto indian oceans the exact mechanisms behind the deposition of organic rich sediments in the mid cretaceous are still a matter of discussion but a hypothesis which is often put forward is that their deposition was a consequence of the coupling of a particular paleogeography with changes in ocean circulation and nutrient supply in this study we used a global coupled climate model to investigate oceanic processes that affect the interbasinal exchange of nutrients as well as their spatial distribution and bioavailability we conclude that the mid cretaceous north atlantic was a nutrient trap as a consequence of an estuarine circulation with respect to the pacific organic rich sediments in the north atlantic were deposited below regions of intense upwelling we suggest that enhanced productivity during oaes was a consequence of upwelling of pacific derived nutrient rich seawater associated with submarine igneous events

changes in paleoenvironments in the atlantic ocean during cretaceous times results from black shales studies large parts of the cretaceous atlantic ocean are characterized by the wide spread deposition of organic carbon rich sediments black shales with a maximum occurrence during aptian albian and cenomanian turonian times in order to explain the origin of these black shales changes in the amount and type of organic matter in relation to changes in paleogeography paleoceanic circulation and paleoclimate have been investigated in detail the study is mainly based on calculation of accumulation rates of marine and terrigenous organic carbon organic carbon sedimentation rate relationships and estimates of paleoproductivity