the cenomanian turonian oceanic anoxic event in the south atlantic new insights from a geochemical study of dsdp site 530a abstract one of the key objectives of deep sea drilling project dsdp leg 75 was to shed light on the underlying causes of cretaceous oceanic anoxia in the south atlantic by addressing two major hypotheses productivity productivity driven anoxia vs enhanced ocean stratification leading to preservation of organic matter and black shale deposition here we present a detailed geochemical dataset from sediments deposited during the cenomanian turonian c t transition and the global oceanic anoxic event 2 oae 2 at dsdp site 530a located off shore namibia southeast angola basin north of walvis ridge to characterise the succession of alternating black and green shales at this site and to reconstruct the evolution of their paleoenvironmental setting we have combined data derived from investigations on bulk organic matter biomarkers and the inorganic fraction the location of the c t boundary itself is biostratigraphically not well constrained due to the carbonate poor but organic matter rich facies of these sediments the bulk 13corg record and compound specific 13c data in combination with published as well as new biostratigraphic data enabled us to locate more precisely the c t boundary at dsdp site 530a the compound specific 13c record is the first of this kind reported from c t black shales in the south atlantic it is employed for paleoenvironmental reconstructions and chemostratigraphic correlation to other c t sections in order to discuss the paleoceanographic aspects and implications of the observations at dsdp site 530a in a broader context e g with regard to the potential trigger mechanisms of oae 2 global changes in black shale deposition and climate on a stratigraphic level an approximation and monitoring of the syndepositional degree of oxygen depletion within the sediments bottom waters in comparison to the upper water column is achieved by comparing normalised concentrations of redox sensitive trace elements with the abundance of highly source specific molecular compounds these biomarkers are derived from photoautotrophic and simultaneously anoxygenic green sulphur bacteria chlorobiacea and are interpreted as paleoindicators for events of photic zone euxinia in contrast to a number of other oae 2 sections that are characterised by continuous black shale sequences dsdp site 530a represents a highly dynamic setting where newly deposited black shales were repeatedly exposed to conditions of subtle bottom water re oxidation presumably leading to their progressive alteration into green shales the frequent alternation between both facies and the related anoxic to slight oxygenated conditions can be best explained by variations in vertical extent of an oxygen minimum zone in response to changes in a highly productive western continental margin setting driven by upwelling

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

early holocene vegetation in the ayllon massif central system range spain based on macroremains a paleoecological approach abstract we present a palaeoecological study of well preserved vegetal macroremains in spain which age range 10 025 5371 cal yr bp confers it an outstanding interest because for the first half of the holocene palaeobotanical data are extremely scarce in the iberian central system range we found for the first time in the easternmost zone of the central system range macroremains belonging to the genus pinus these have specifically been identified as pinus cf sylvestris and pinus gr sylvestris these findings provide valuable information on the role of the genus pinus regarding the natural character of these pine forests in this relatively unknown region in the larger wood samples we measured tree rings and cross dated growth series which represent a 75 increase in the number of floating fossil chronologies and increase the time span by almost 1750 years in the centre of the iberian peninsula remarkably this is the first time in spain and in southern europe that some of the floating chronologies have been successfully crossdated creating four composite chronologies furthermore we discuss some palaeoclimatic inferences comparing with different sites in southern europe and provide new data for best knowing the palaeoecological characteristics of the first half of the holocene in spain likewise we found two bones belonging to aurochs bos primigenius one of these also dating from the first half of the holocene with valdojos constituting the only site with this taxon for this period in the central system range and surrounding areas

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

sedimentological evidence concerning the paleoceanography of the cretaceous western north atlantic ocean abstract black clays developed as a result of progressively intensifying intermittent anoxic conditions from the early through mid cretaceous the preservation of primary sedimentary structures of authigenic minerals such as pyrite and siderite and of significant amounts of organic carbon testify to the stagnant conditions intermittent anoxic conditions prevailed in the deepest portion of the basin resulting from vertical migration of an intrasediment anoxic interface middle aptian variegated clays within the black clay sequence at several low latitude sites suggest a widespread oxygenation event of short duration occurred there greater thicknesses of black clays accumulated in low latitudes implying that surface or intermediate depth currents redistributed the sediments south ward millimeter scale laminae characterizing the early and mid cretaceous sediments represent seasonal sediment input where seasons during the cretaceous had durations measured in years cenomanian variegated clays succeeded the black clay interval and represent deposition under totally oxygenated conditions thus the sluggish and stagnant conditions present in the early and mid cretaceous were followed by increased current activity these currents were derived from more northern latitudes as iberia was rifted from north america cooler temperatures presumably increased the oxygen capacity of the water and its ability to sink into the deep basin to relieve the stagnant conditions present the late cenomanian through late campanian was a time of widespread marine transgression resulting in the deep ocean becoming a sediment starved basin clastics and carbonates accumulated on the shelves as the calcite compensation depth ccd shallowed appreciably the late campanian through maastrichtian interval is characterized by calcium carbonate accumulation throughout much of the deep basin a significant lowering of sea level paralleled by a deepening ccd caused this sedimentation pattern

integrated palynological organic geochemical and sequence stratigraphic analyses of the middle to upper cenomanian hydrocarbon reservoir source abu roash g member a depositional model in northwestern egypt abstract the current investigation provides further insight into the petroliferous characteristics of the abu roash g member which is regarded as an important rock unit for the egyptian oil industry forty seven samples covering the g member were selected from the bed 14 1 and bed 2 4 wells in the abu gharadig basin and from the abu tunis 1x well in the matruh basin both of which are located in the north western desert an independent dating of the g rocks of bed 2 4 by benthic foraminifera and ostracods in addition to palynological dating suggests a middle late cenomanian age and provides the biochronostratigraphic framework for the sequence stratigraphic analysis analysis of the vertical distribution of particulate organic matter defines three palynofacies types pf pf 1 represents the basal g where shales of the bed wells and calcareous shale of abu tunis 1x were deposited during a relative sea level rise in an outer middle shelf environment that experienced a notable high primary productivity prevailing reducing suboxic anoxic conditions supported preservation of very high amounts of amorphous organic matter aom in pf 1 pf 2 is equated to shales of the middle g of bed 14 1 and bed 2 4 and to calcareous shales and limestone of the upper g in abu tunis 1x pf 2 was deposited during a relative sea level fall in an inner middle shelf setting under better developed suboxic anoxic conditions pf 3 corresponds to the upper g of bed 14 1 and bed 2 4 and represents the shallowest setting where sandy and silty shales were deposited during a pronounced sea level fall in an inner shelf environment the same suboxic anoxic conditions were prevailing during deposition of pf 3 three bioevents were recorded which could be of palaeoecological and or biostratigraphic significance these are senegalinium aenigmaticum dinopterygium cladoides peak dinopterygium cladoides dinopterygium alatum peak and an acme of classopollis brasiliensis sequence stratigraphy of a transect of the four studied sections was carried out to understand the response of the particulate organic matter distribution and depositional system to the sea level changes three third order depositional genetic sequences were recognized and correlated with the global sea level curve kce 2 kce 3 and kce 4 the early highstand systems tract ehst of the genetically related kce 3 in all wells is characterized by relatively rich organic matter where combined remarkably low water circulation and insignificant dilution of organic matter with coarse terrigenous material probably supported good preservation of organic matter spatial distribution of the g rocks shows lateral facies changes this was inferred from sedimentation of an organic poor avg 0 8 toc wt coarse clastic sandy shales facies in the studied area in abu gharadig basin sedimentation changes laterally into a northeast and northwest organic rich finer clastic shale calcareous shales and argillaceous limestone facies in the western matruh basin the robust anoxic conditions and very low dilution of organic matter by terrigenous influx enhanced the organic richness avg 2 4 toc wt of these rocks which resulted in the formation of promising hydrocarbon source rocks thus for a successful hydrocarbon exploration in the north western desert the promising source section of the g member would be associated with shales calcareous shales and argillaceous limestone lithologies its depositional environment is mainly confined to outer middle and inner middle shelf settings that have widespread suboxic anoxic conditions and show ehst pattern in contrast the regressive intervals that are denoted by the lowstand systems tract lst and or the late hst lhst typify the relatively coarse clastics as good quality reservoir rocks that are characterized by poor organic richness due to dilution with terrigenous influx

an offset in tex86 values between interbedded lithologies implications for sea surface temperature reconstructions abstract the tex 86 tetraether index of tetraethers consisting of 86 carbon atoms sea surface temperature sst proxy is based on the distribution of isoprenoid glycerol dialkyl glycerol tetraether gdgt membrane lipids of pelagic thaumarchaeota that are preserved in marine sediments it is a valuable tool for reconstructing past ssts from sedimentary archives however there are still major uncertainties as to the effects of variables other than temperature on the proxy here we present the first study of gdgt variability across early cretaceous interbedded pelagic and shelf sourced turbiditic sediments from two deep sea drilling project dsdp sites in the western north atlantic the results indicate that a small but consistent offset in tex 86 ratios equivalent to 1 2 c of temperature difference occurs between interbedded lithologies of a similar age the offset can be attributed to spatial differences in sea surface temperatures or thaumarchaeotal populations between the shelf and the open ocean or to secondary diagenetic effects related to oxic degradation of the gdgts of these a difference in either thaumarchaeotal taxa or ecology between those living in the shelf and ocean areas seems most plausible regardless of the root cause of the offset these findings highlight the necessity of careful sample selection prior to tex 86 analysis to ensure robust interpretation of palaeotemperature trends

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

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

palynofacies investigation of callovian middle jurassic sediments from dsdp site 534 blake bahama basin western central atlantic abstract during the extension of deep sea drilling project dsdp leg 76 a new and previously unpenetrated lithological unit composed mainly of claystones was cored above basalt basement at site 534 in the blake bahama basin the callovian part of the new unit contains interbedded black shales which were hitherto unexpected in this part of the section this paper presents a brief palynological examination of lithofacies kerogen relationships in these sediments and shows that their organic content is almost entirely a function of the re deposition of terrestial and marine organic matter versus the ambient redox conditions of the depositional environment allochthonous organic matter inputs are highest in the interbedded turbidites and decline progressively toward the pelagic black shales in which marine organic matter is comparatively well preserved the significance of various kerogen and palynomorph indices are discussed the study emphasizes the absolute necessity for sedimentologically aware sampling in all palynological and geochemical work on lithologically heterogeneous sequences

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

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

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

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

the stratigraphic and palaeogeographic setting of the late cenomanian anoxic event the late cenomanian carbon isotope excursion can be shown to be synchronous over most areas of the globe where micropalaeontological data are adequate the sedimentological variations seen in these different areas are thought to be due to palaeobathymetry the relationship between this anoxic event and the major faunal change in the late cenomanian is described

evolution of middle to late cretaceous oceans a 55 m y record of earth s temperature and carbon cycle a new 55 m y global compilation of benthic foraminifera 13 c and 18 o for the middle to late cretaceous shows that there was widespread formation of bottom waters with temperatures 20 c during the cretaceous greenhouse world these bottom waters filled the silled north atlantic and probably originated as thermocline or intermediate waters in the tropical oceans carbon burial during the cretaceous oceanic anoxic events produced a positive 13 c shift in global carbon reservoirs but this is not particularly large especially by comparison with the remarkable late paleocene carbon maximum the interbasin 13 c gradient was unusually large during the cretaceous hot greenhouse probably because the north atlantic sills prevented the free exchange of waters in the deep basin the hot greenhouse ended when the equatorial atlantic gateway opened sufficiently to flood the deep north atlantic with relatively cool polar waters formed in the southern ocean

organic matter variations in transgressive and regressive shales abstract organic matter in the upper cretaceous mancos shale adjacent to the tocito sandstone in the san juan basin of new mexico was characterized using organic petrology and organic geochemistry differences in the organic matter found in these regressive and transgressive offshore marine sediments have been documented and assessed within a sequence stratigraphic framework the regressive lower mancos shale below the tocito sandstone contains abundant well preserved phytoclasts and correspondingly low hydrogen indices total organic carbon values for the regressive shale are low sediments from the transgressive systems tract tocito sandstone and overlying upper mancos shale contain less terrestrially derived organic matter more amorphous non structured protistoclasts higher hydrogen indices and more total organic carbon advanced stages of degradation are characteristic of the phytoclasts found in the transgressive shale amorphous material in the transgressive shale fluoresces strongly while that found in the regressive shale is typically non fluorescent data from pyrolysis gas chromatography confirm these observations these differences are apparently related to the contrasting depositional styles that were active on the shelf during regression and subsequent transgression it is suggested that data from organic petrology and organic geochemistry provide greater resolution in sedimentologic and stratigraphic interpretations particularly when working with basinward fine grained sediments petroleum source potential for the regressive lower mancos shale below the tocito sandstone is poor based on abundant fluorescent amorphous material high hydrogen indices and high total organic carbon the transgressive upper mancos shale above the tocito sandstone possesses excellent source potential this suggests that appreciable source potential can be found in offshore fine grained sediments of the transgressive systems tract below the condensed section and associated downlap surface organic petrology can be used to accurately predict petroleum source potential the addition of simple fluorescence microscopy greatly enhances this predictive ability because non generative amorphous material is generally non fluorescent organic petrology must also be used to properly evaluate the utility of t max from programmed pyrolysis as a thermal maturity indicator organic matter dominated by autochthonous amorphous protistoclasts exhibits lower t max values than that which is composed of mostly phytoclasts

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

palynological palynofacies paleoenvironmental and organic geochemical studies on the upper cretaceous succession of the gptsw 7 well north western desert egypt abstract the present study of the abu roash and bahariya formations in well gptsw 7 refines our understanding of the subsurface cretaceous of the north western desert of egypt our investigations are based on the palynological analyses of 71 cuttings samples of which 24 have also been analyzed for geochemistry in addition to 3 sidewall cores analyzed for vitrinite reflectance r o four palynological zones and three subzones in addition to a poorly fossiliferous interval ranging in age from coniacian santonian to early cenomanian are proposed these include a poorly fossiliferous interval coniacian santonian dinogymnium vozzhennikovae interval zone late to middle turonian ephedripites ambiguus ephedripites multicostatus foveotricolpites giganteus foveotricolpites gigantoreticultus assemblage zone early turonian classopollis brasiliensis interval zone late to middle cenomanian and afropollis jardinus interval zone early cenomanian the succeeding subzones are afropollis kahramanensis interval subzone elaterosporites klaszii interval subzone and cretacaeiporites densimurus interval subzone all of early cenomanian age total organic carbon toc and rock eval pyrolysis and palynofacies analyses indicate that the bahariya formation and the abu roash g member are primarily of kerogen iii type and hence gas prone suggesting a strong influence of hydrogen enriched organic matter the abu roash a c e members may also be gas prone type iii kerogen and appear to contain highly oxidized terrestrial organic matter in contrast the abu roash f member has very high toc and hi values and contains a very high proportion of amorphous organic matter aom indicating a highly oil prone facies while this finding is not unexpected for anoxic black shale it contrasts with earlier studies that suggest a gas prone nature r o measurements show that the bahariya formation represents an immature early genesis dry gas phase this is also true for all investigated samples from the abu roash and bahariya formations based on their low thermal alteration index tai quantitative and qualitative analyses of both the palynoflora and palynofacies show that the abu roash a and c members b is missing both of coniacian santonian age represent oxic proximal and distal shelf environment the abu roash d and e members dated as turonian represent oxic proximal shelf whereas the cenomanian abu roash f member was deposited in a distal suboxic anoxic basin the cenomanian abu roash g member and the bahariya formation were deposited in a shallow marine and shallow marine to fluvio deltaic setting respectively the senonian palmae province is recognized in the palynoflora by the presence of proteacidites auriculiidites reticulatus ariadnaesporites gabonisporis vigourouxii on the other hand the albian cenomanian elaterates province is characterized by the presence of steevesipollenites gnetaceaepollenites elaterocolpites elaterosporites elateroplicites senegalosporites sofrepites afropollis and cretacaeiporites

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

ostracod diversity and sea level changes in the late cretaceous of southern england abstract the available data of ostracod ranges for the cenomanian campanian and maastrichtian stages of the late cretaceous of the northern part of the anglo paris basin were examined and combined with new data from the turonian santonian and coniacian stages a new cumulative species diversity curve is presented for the ostracoda of the late cretaceous of britain the results obtained challenge the method of chronoecologic charts to determine sea level from diversity when a more complete data set is applied and compared with published sea level curves the result is the inverse of that previously predicted by employing chronoecologic charts a model is presented of changing sea levels in s e england from the cenomanian through to the santonian which integrates the new diversity data with published sea level changes and curves of stable isotopes of oxygen and carbon in the earliest cenomanian low diversity is associated with a deeper water depositional environment and warmer temperatures the mid cenomanian diversity maximum corresponds to a regressive trough and cooler water over the cenomanian turonian boundary interval the diversity minimum is correlated with global sea level and temperature maxima the proportion of ostracods possessing eye tubercles falls to a minimum over this period after the diversity crash the cenomanian fauna was replaced by the new turonian fauna east west migrations into the anglo paris basin were facilitated by the sea level rise overcoming marginal basin highs the pattern seen in the mid cenomanian is also present at the turonian coniacian boundary interval that of high diversity corresponding with a regressive trough on a long term regressive trend with cooling conditions the model for this northern part of the anglo paris basin then associates high diversity with regressive cooler conditions and low diversity with deeper and warmer water

models for the deposition of mesozoic cenozoic fine grained organic carbon rich sediment in the deep sea the widespread occurrence of organic carbon rich strata black shales in certain portions of jurassic cretaceous and cenozoic sequences has been well documented from deep sea drilling project sites in the atlantic and pacific oceans and from sequences now exposed on land originally deposited in the tethyan ocean these ancient black shales usually have been explained by analogy with examples of modern deep sea sediments in which organic matter locally is preserved by 1 increasing the supply of organic matter 2 increasing the rate of sedimentation and or 3 decreasing the oxygen content of the bottom water however detailed examination of many black shales reveals characteristics that cannot be explained by simple local models including their approximate coincidence in time globally their occurrence in a variety of different environments including open oxygenated oceans restricted basins deep and shallow water their interbedding with organic carbonpoor strata which often dominate a so called black shale sequence their deposition by pelagic hemipelagic turbiditic and other processes and the variations in type and amount of organic matter that occur even within the same sequence a more complex model for the origin of black shales therefore appears most appropriate in which the cyclic preservation of organic matter depends on the interplay of the three main variables namely supply of organic matter sedimentation rate and deep water oxygenation each of which varies independently to some extent the variation and relative importance of these parameters in individual basins and widespread black shale deposition in general are linked globally and temporally by changes in global sea level climate and related changes in oceanic circulation an important and often overlooked factor for the supply of organic matter to deep basin sediments is the frequency and magnitude of redepositional processes the interplay of these variables is discussed in relation to the middle cretaceous and cenozoic organic carbon rich strata in particular which show marked differences in the relative importance of the different variables

interaction between injection points during hydraulic fracturing 1 we study the geomechanical stress interaction between two injection points during hydraulic fracturing hydrofracking and how this interaction in combination with disorder influences the fracturing process to this end we develop an effective continuum model of the hydrofracking of heterogeneous poroelastic media that captures the coupled dynamics of the fluid pressure and the fractured rock matrix and models both the tensile and shear failure of the rock for injection points that are separated by less than a critical correlation length our numerical simulations show that the fracturing process around each point is strongly correlated with the position of the neighboring point the magnitude of the correlation length depends on the degree of heterogeneity of the rock and is on the order of 30 45 m for rocks with low permeabilities in the strongly correlated regime we predict a novel effective fracture force that attracts the fractures toward the neighboring injection point

sedimentary and geochemical indicators of productivity and oxygen contents in modern and ancient basins the holocene black sea as the type anoxic basin data on the accumulation rates of organic carbon total phosphorus and reduced sulfur over the past 7000 yr from modern abyssal black sea sediments are examined as geochemical monitors of variations in biologic productivity and the development of deep water masses variations in organic carbon accumulation rates at both intermediate and deep water sites are believed to be controlled by the combined effects of enhanced preservation of organic matter under anoxic bottom conditions and the regulation of primary productivity in surface waters by nutrient availability estimates of variations in water column and pore water organic carbon consumption by sulfate reducing bacteria can be made using average carbon and sulfur accumulation rates for various depositional episodes and are examined in the light of changes in the thickness of the h2s zone in the water column the amount of available sulfate within this zone and the reactiveness of particulate organic matter sulfur and phosphorus accumulation rates are used to estimate the maximum amount of phosphorus regenerated from organic matter during bacterial sulfate reduction processes total phosphorus accumulation rates are found to markedly increase over the part 1000 yr and are not proportionally paralled by organic carbon accumulation rates these accelerated phosphorus accumulation rates appear to stem from organic matter degradation adsorption on surfaces of caco3 and perhaps diffusion into sediments from bottom waters and authigenic precipitation of phosphate minerals accumulation rates of organic carbon and phosphorus in black sea sediments are low in comparison to those typical of modern highly productive upwelling zones peru south west africa namibia accumulation rates of reduced sulfur and the ratios of reduced sulfur to organic carbon burial may be higher in anoxic basins than in oxic ones knowledge of accumulation rates therefore rather than concentrations alone may help to differentiate black shales which resulted from enhanced organic matter preservation under anoxic conditions from those resulting from high biologic productivity with or without accompanying oxygen deficiencies

the middle cenomanian event in the equatorial atlantic the calcareous nannofossil and benthic foraminiferal response abstract in addition to oceanic anoxic event 2 oae2 other perturbations of the carbon cycle occurred during the cenomanian and turonian of which the middle cenomanian event mce is the most prominent one in palaeoecological publications however this event is strongly underrepresented in contrast to the well studied oae2 in order to fill this gap we have studied early cenomanian to late turonian calcareous nannofossil and benthic foraminiferal assemblages of ocean drilling program site 1260 at demerara rise western equatorial north atlantic in order to decipher biotic changes throughout this interval and especially across the mce our data show distinctive changes in the relative abundance of certain calcareous nannofossil taxa and a drastic decrease in benthic foraminiferal diversities and abundances associated with the mce in the lower part of the studied section and prior to the mce a mixed water column with high nutrient availability in the upper photic zone is suggested based on very high relative abundances of the mesotrophic eutrophic nannofossil species biscutum constans around the mce interval certain nannofossil taxa e g rhagodiscus asper show a distinctive decrease in relative abundance while others become more dominant taxa which increase in relative abundance after the mce e g eprolithus floralis are interpreted as either having favoured less eutrophic surface waters or having inhabited deeper parts of the photic zone in a well stratified water column this interpretation is supported by published oxygen isotope and tex86 data which suggest increased water column stratification starting with the mce and lasting to the end of the cenomanian stage as a result of the implementation of a saline intermediate to deep water mass during this interval our study shows that the mce was a significant biotic event in the cenomanian turonian equatorial atlantic characterised by a lasting change of surface and bottom water ecosystems

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