patterns in the distribution of aptian rudists and corals within a sequence stratigraphic framework maestrat basin e spain abstract the ecological zonation of and environmental controls on rudist and coral assemblages on carbonate platforms of the old world have received more attention for late cretaceous examples than for their early cretaceous counterparts this study accordingly investigates the vertical and lateral distribution of aptian rudist bivalves and scleractinian corals on a carbonate platform succession from the western maestrat basin e iberian peninsula here colonial corals grew profusely on an isolated platform top environment during an earliest highstand stage of a long term trend of relative sea level as well as on marly slope settings during higher frequency transgressive pulses during the later highstand stage within a longer term relative sea level cycle a facies belt dominated by autochthonous rudist bivalves overlaid the coral meadow that had developed on the isolated platform top the internal part of this carbonate platform with rudists is dominated by slender elevator caprinids such as caprina parvula whereas requieniids and polyconitids predominate in the external zone the abundance of caprinids in the internal platform is remarkable given that caprinid lithosomes of late early aptian age are usually rare in the northern margin of the tethys the proliferation of caprinids in this case was probably favoured by the apparently more isolated nature of the carbonate platform on the slopes the coral communities that flourished during higher frequency transgressive pulses are overlain by carbonates with rudists mainly requieniids shed from the platform top during normal and forced regressive higher frequency changes of relative sea level accordingly the vertical change from coral dominated to rudist dominated facies in both platform top and slope settings records progradation to decipher the long term relative sea level changes that controlled the deposition of this carbonate succession a sequence stratigraphic analysis was performed two depositional sequences including a late early aptian intra dufrenoyia furcata zone forced regressive stage of relative sea level which subaerially exposed and incised the early aptian succession to a depth of 21 m were recognised the incisions were back filled with peritidal deposits during the subsequent marine onlap the rudist and coral bearing carbonates were deposited along platform top to slope profiles lacking a barrier margin and hence lagoon environments

observed evolution of linear and nonlinear effects at the dahan downhole array taiwan analysis of the september 21 1999 m 7 3 chi chi earthquake sequence in this paper the site characteristics of the dahan downhole array are studied by analyzing the september 21 1999 m 7 3 chi chi earthquake sequence including the main shock and some aftershocks the four level array 0 m 50 m 100 m and 200 m is located to the north of hualien city in eastern taiwan polarization analysis is used to check the orientation errors of the seismometers at different levels of depth if the surface instrument is chosen as reference the angle between the major polarization axes of the surface and any downhole records is the orientation error that must be corrected for the downhole accelerographs the orientation errors at depths of 50 m 100 m and 200 m are 32 120 and 84 after the corrections the coherency between the surface and downhole records is substantially improved spectral ratio analysis shows that the predominant frequency of the chi chi main shock shifts to a lower frequency we also simulate ground motions at different depths by using the haskell method with a linear velocity structure model the record at surface is chosen as the input motion compared with the observed data ground acceleration can be well reproduced for the aftershocks weak motion events of the september 21 1999 m 7 3 chi chi earthquake however for the chi chi main shock the synthetic waveform cannot match well with the observation neither in amplitude nor in phase this indicates that large ground shaking probably induced the nonlinear site effect at that time and the model used cannot support it

high resolution chemo and biostratigraphic records of the early aptian oceanic anoxic event in cantabria n spain palaeoceanographic and palaeoclimatic implications abstract during the early aptian major palaeoenvironmental changes occurred leading to an oceanic anoxic event oae 1a and a perturbation of the global carbon cycle new detailed litho bio and chemostratigraphic toc 13ccarb 13corg records of two superbly exposed and expanded lower aptian sections in cantabria la florida and cuchia allow to recognize the expression of the oae 1a in shallow shelf environments of northern spain the succession consists of shallow platform limestones that include a marly unit patrocinio formation the deposition of which occurred mostly at the onset of the oae 1a 120 5 ma this study presents a new integrated biostratigraphy based on ammonites planktonic foraminifera calcareous nannofossils and palynomorphs that allows an accurate age resolution of the succession the marly unit records an abrupt negative 13c excursion in both bulk organic matter up to 5 and carbonate up to 6 mean 3 as has been already observed at the onset of the oae 1a in other lower aptian deposits worldwide in detail however the negative excursion presents two minima in the studied sections this negative spike is confidently attributed to the upper half of the hayesites irregularis nannofossil zone to the upper part of the blowiella blowi foraminiferal zone and to the middle upper part of the deshayesites weissi ammonite zone a third negative excursion occurs at the base of the rhagodiscus angustus nannofossil zone which may be correlatable with the dufrenoyia furcata ammonite zone this data set refines the age of the oae 1a and reveals the existence of a stratigraphic gap in the westernmost margin of the basque cantabrian basin that covers at least a portion of the upper part of the early aptian sedimentary facies and quantitative analysis of palynomorphs and nannofossils document significant environmental changes associated with the oae 1a compositional changes of neritic carbonates and calcareous nannofossils data indicate the occurrence of a biocalcification crisis inferred to have been related to co2 induced changes in seawater chemistry and palynomorphs identify a thermal maximum followed by a cooling phase the latter show a classopollis maximum during the oae 1a which is followed by a decrease in classopollis and an increase of bisaccate pollen after the event

episodes of high productivity and cooling in the early aptian alpine tethys a palynological and organic geochemical study of the early aptian selli unit oceanic anoxic event 1a of the western tethys provides new information about paleoceanography and documents pronounced changes in the regional climate pattern it also emphasizes the role of oxic degradation of organic matter even at horizons with the highest rates of organic carbon corg accumulation the absence of anoxia indicates that enhanced primary production is the main reason for these organic carbon accumulations and variations in preservation are related to pulses in primary production and nutrient recycling despite the high productivity character of the selli unit black shales the 13ccarb values are not marked by a positive shift but by an interval of unchanged values warm climatic conditions for deposition of the selli unit are inferred from the presence of southern provenance pollen and low 18o values for the interval above the selli unit changes in the pollen spectrum and an increase in 18o values reflect a hitherto undocumented late early aptian cooler and more humid climate and or a reorganization of the tethyan oceanographic circulation pattern

high resolution carbon isotope records of the aptian to lower albian from se france and the mazagan plateau dsdp site 545 a stratigraphic tool for paleoceanographic and paleobiologic reconstruction high resolution carbon isotope stratigraphy is established for the aptian to lower albian of the vocontian basin se france and correlated to the carbon isotope record of the mazagan plateau dsdp site 545 the carbon isotope stratigraphy of the vocontian basin is proposed as a standard reference curve for the aptian to lower albian due to the completeness and high temporal resolution of the stratigraphic succession the good biostratigraphical time control and the frequent occurrence of regional to global black shale horizons including oceanic anoxic events 1a oae 1a of the lower aptian and oae 1b of the lower albian the carbon isotope record appears better suited for long distance short term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types however the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography and to correlate regional to global black shale horizons in different marine environments this combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species based on the demonstrated diachroneity of important biostratigraphic markers of the aptian albian boundary the globally observed break point between the end of the uppermost aptian positive carbon isotope excursion and the onset of the pronounced negative shift of 13c values is an alternative criterion the distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the aptian to lower albian

a plate tectonic mechanism for methane hydrate release along subduction zones negative carbon isotope excursions from a new record of terrestrial organic carbon d 13 corg 2 3x and from marine carbonate d 13 ccarb 0 8x were used to calculate a methane hydrate release of 1137 gt of carbon over 1 myr during the early aptian early cretaceous we show how the coincident and sudden near cessation of subduction along the northern boundaries of the farallon plate resulted in uplift along the continental margin by up to 4 0 km which may have triggered the release we conservatively estimated the amount of methane hydrate carbon likely to have been destabilized during the uplift and found it to be within 20 of the amount of carbon implied by the isotopic records within the same 1 myr time frame linking subduction triggered destabilization with isotopic evidence for methane release reveals a plate tectonic mechanism for the incorporation of methane hydrate release into long term carbon cycling d 2005 elsevier b v all rights reserved

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

geochemical and paleoenvironmental record of the early to early late aptian major episodes of accelerated change evidence from sierra del rosario northeast mexico abstract the lower to lower upper aptian succession of northern mexico documents the drowning of the shallow water cupido cupidito carbonate platform system followed by deposition of the deep water sediments of the la pena formation using 13 c stratigraphy geochemical and mineralogical information coupled with previous microfacies paleontological and total organic carbon toc data from a stratigraphic section which includes such lithological change this study identifies distinctive episodes of accelerated global environmental change and determines the paleoenvironmental conditions conducive to the deposition of toc rich intervals within the cupidito unit the oceanic anoxic event 1a oae 1a is recorded near the base of the section and the intra furcata negative excursion in the topmost beds of the unit the upper part of the section within the la pena formation is correlatable with the noire level organic carbon rich intervals occur in the lower and middle part of the oae 1a upper part of the cupidito unit base of the la pena formation and in the noire level equivalent reducing conditions within the sediment and oxic dysoxic at the seafloor locally controlled persisted both before and during oae 1a interval in the cupidito lagoon oxygen depleted conditions dysoxic anoxic were more permanent and stronger during the deposition of the base of the la pena formation and the noire equivalent level it is proposed here that deposition of the lower middle part of the oae 1a and the base of the la pena formation was influenced by climate controlled increases in detrital and accompanying nutrient influx that supplied especially biolimiting nutrients fe p fostering marine productivity and toc burial upwelling of nutrient rich deeper waters and minor arrival of nutrients from runoff both account for the domination of radiolaria and organic carbon burial during the noire level equivalent record of the oae 1a time equivalent facies in the cupidito lagoonal sediments confirms the diachronism of the cupidito la pena flooding heterozoan carbonate production in the cupidito ramp was uninterrupted during and after oae 1a periodic arrival of detrital components and nutrients during warmer humid periods accelerated platform drowning which peaked during the diachronic deposition of the la pena formation

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

pulsating subsidence during a rift episode stratigraphic and tectonic consequences aptian albian northern spain backstripping analysis has been carried out on nine outcrop sections of the basque cantabrian aptian and albian of northern spain which consist of shallow water marine deposits up to 7000 m thick it reveals four main pulses of common accelerated subsidence i early aptian ii early albian iii lower late albian and iv uppermost late albian separated by tectonic quiescent intervals tectonic subsidence rates of 70 m myr 1 for the aptian and 101 m myr 1 for the albian were recorded sopuerta section the calculated stretching factor referred to a pre rift continental crust of 35 km is bs 1 32 and represents approximately 8 5 km of crustal thinning points of change towards lesser subsidence rate in the curves are correlated with major unconformities in the sections in the basque cantabrian basin and in boreal europe suggesting geodynamic changes related with the opening of bay of biscay minor variations of spreading direction and intensity are proposed to explain the subsidence pulses

climatic evolution across oceanic anoxic event 1a derived from terrestrial palynology and clay minerals maestrat basin spain studies dealing with the response of the continental biosphere to the environmental perturbations associated with cretaceous oceanic anoxic events oaes are comparatively rare here a quantitative spore pollen record combined with clay mineral data is presented which covers the entire early aptian oae 1a interval forcall formation maestrat basin east spain the well expressed oae 1a carbon isotope anomaly is paralleled by changes in the clay mineral assemblage and by a stepwise decline in the normalized frequency of classopollis pollen produced by xerophytic cheirolepidiaceae with lowest contents occurring during the positive 13 c shift in contrast araucariacites and inaperturopollenites pollen show a pronounced increase in relative abundance from low background values to become a significant component of the palynological assemblage during the classopollis minimum the observed changes in clay minerals and pollen distribution patterns are interpreted to reflect a major change in the composition of the hinterland vegetation of the maestrat basin most probably due to short lived but pronounced climatic cooling and changes in humidity temperature anomalies driven by organic carbon burial and associated co 2 decline have been postulated for all major mesozoic oaes the palynomorph record from the iberian maestrat basins indicates that the climax of this cooling episode was significantly delayed in comparison to the end of organic carbon rich deposition in the world oceans

chemostratigraphic correlation of barremian and lower aptian ammonite zones and magnetic reversals based on carbon isotope stratigraphy we correlate the ammonite dated barremian reference section near angles se france with the magneto and biostratigraphically dated succession at cismon northern italy the results confirm the previous correlation of the lower barremian ammonite and magnetostratigraphy by channell et al 1995 and show that the base of cm0 selected as the stage boundary between the aptian and the barremian coincides with the stage boundary defined by ammonite stratigraphy the upper barremian carbon isotope record of the cismon section displays two positive 13c excursions whereas the data from angles show only one shift towards more enriched values the absence of the second upper barremian 13c excursion at angles indicates that up to 50 of the barremian stage is missing in the selected reference section the gap occurs most probably within the giraudi ammonite zone and is related to the 12d maximum flooding surface of jacquin et al 1998

expression of the late aptian cold snaps and the oae1b in a highly subsiding carbonate platform aralar northern spain abstract cretaceous climate records provide evidence that major volcanic pulses with duration of 103 to several 105 yr triggered changes in climate and oceanography black shales of oceanic anoxic event 1b ca 113 109 ma are regarded as signatures of late aptian greenhouse pulses associated with volcanic episodes new tex86 paleotemperature record indicates that warm aptian climate was interrupted by repeated cold snaps alternating with described greenhouse pulses an extraordinary thick shallow water carbonate succession of the aralar platform from the southeastern basque cantabrian basin in spain provides a unique opportunity to test the hypothesis that cold phases interrupted warm climate in the aptian platform evolution is traced through time of the proposed aptian cold snaps alternating with greenhouse episodes new high resolution c isotope records established in the studied upper aptian platform carbonates serve as chemostratigraphic tool providing a link between carbonate platform evolution basinal black shale formation and associated changes in open ocean palaeotemperatures the late aptian cold snaps find their expression in a remarkably reduced neritic succession punctuated by several emersion horizons formed during sea level lowstands the studied section bears evidence for several episodes of choked carbonate production related to increased runoff at times of sea level rise during which orbitolinids bloomed in a sediment loaden lagoonal setting these intervals coincide with the deposition time of organic rich kilian and leenhardt levels belonging to oae1b

early aptian paleoenvironmental evolution of the bab basin at the southern neo tethys margin response to global carbon cycle perturbations across ocean anoxic event 1a 1 lower aptian carbonates in the bab basin at the southern neo tethys margin record significant environmental changes across oceanic anoxic event 1a oae1a a long lasting negative shift of carbon isotope ratios 13c associated with a distinct decrease in oxygen isotope ratios 18o in orbitolinid rich carbonates characterizes the onset of oae1a livello selli supporting a hypothesis that a long lasting volcanic co2 emission is the main cause of oae1a inducing global warming a bloom of microencrusters lithocodium and bacinella across the proto bab basin occurred synchronously at the beginning of the subsequent positive 13c excursion responding to the global carbon cycle perturbations the carbonates formed during the oae1a show higher strontium isotope ratios 87sr 86sr compared with those of global seawater this was likely caused by a local influx of isotopically heavier strontium along with nutrients into the proto bab basin these biotic proliferations were triggered by an increased nutrient supply induced by intensified continental weathering due to the global warming suggested by the increase in 18o values spatial variations in the 13c values among sites in the bab basin and its surrounding platform are related to local environmental factors such as the degree of mixing of basin water with ocean water and local removal of 12c by metabolic activity at the platform top the 13c profile of the studied core indicates global removal of organic carbon of oae1a began during the early stage of the second order transgression and lasted until the early stage of the highstand after the oae1a the livello selli corresponds to the early stage of this transgression

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

a volcanic co2 pulse triggered the cretaceous oceanic anoxic event 1a and a biocalcification crisis 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 characterized by the deposition of organic carbon rich sediments oaes reflect major perturbations in the global carbon cycle evidenced by sedimentary carbon isotope records however the triggering mechanisms for oaes remain controversial here we present a bulk rock and molecular marine and terrestrial bio markers c isotope record at unprecedented time resolution from the cismon section of northern italy that shows that oae1a conditions were reached over a period of several thousands of years through a stepwise perturbation of the carbon cycle the documented sequence of events is most compatible with a trigger associated with increased co 2 emissions possibly leading to a doubling of p co 2 which in turn caused larger c isotope fractionation in marine and terrestrial organisms and a major biotic crisis in the calcareous nannoplankton our data also show that a release of isotopically light carbon from partial methane hydrate dissociation probably played a minor role in the oae1a carbon cycle perturbation

stable isotopic ratios and origins of the carbonates associated with cold seepage at the eastern nankai trough two types of cold seeps were located at the eastern nankai trough 1 seeps on sediment covered seafloor of 3800 3600 m in depth at the toe of the accretionary prism and 2 those between 1900 and 2100 m situated on the backthrust of the accretionary prism covered with rough outcrops of calcareous sandstones fragments of sandstone pipes or chimneys cemented with calcite were recovered from type 1 seeps whereas in type 2 seeps massive carbonate cemented sandstones and silty sandstones were obtained many of which contain cemented fragments of different lithologies and textures including dense aggregates of fossilcalyptogena type clam shells the carbon isotopic ratios of the carbonates in these sediments range from 36 to 56 pdb the carbonates formed by mixing between isotopically light carbonate ions derived from biogenic methane carried from depth in advecting fluids and heavy marine sedimentary carbonates sharp isotopic gradients in carbon and sometimes also in oxygen from the mixing processes are still retained across the walls of the sandstone pipes from type 1 seeps whereas the isotopic ratios of the samples from type 2 seeps exhibit variation patterns related to lithologies and textures and confirm the presence of several generations of carbonate cement within a single specimen these facts and the oxygen isotopic ratios of live and fossil clam shells recovered from the survey areas suggest that the cold seeps started at least during the last glaciation and have experienced repeated destruction and reformation due to episodic supply of methane rich fluid of different isotopic ratios and or temperature

mesozoic climates and oceans a tribute to hugh jenkyns and helmut weissert the study of past greenhouse climate intervals in earth history such as the mesozoic is an important relevant and dynamic area of research for many sedimentary geologists geochemists palaeontologists and climate modellers the mesozoic sedimentary record provides key insights into the mechanics of how the earth system works under warmer conditions providing examples of natural climate change and perturbations to ocean chemistry including anoxia that are of societal relevance for understanding and contextualizing ongoing and future environmental problems furthermore the deposition of widespread organic carbon rich sediments black shales during the mesozoic means that this is an era of considerable economic interest in july 2015 an international group of geoscientists attended a workshop in ascona switzerland to discuss all aspects of the mesozoic world and to celebrate the four decade long contributions to our understanding of this fascinating era in earth history made by hugh jenkyns university of oxford and helmut weissert eth zurich this volume of sedimentology arose from that meeting and contains papers inspired by and co authored by hugh and helmi here a brief introduction to the volume is provided that reviews aspects of hugh and helmi s major achievements contextualizes the papers of the thematic issue and discusses some of the outstanding questions and areas for future research this article is protected by copyright all rights reserved

the madotz urgonian platform aralar northern spain paleoecological changes in response to early aptian global environmental events abstract sudden addition of carbon dioxide to the atmosphere can reduce the caco3 saturation and weaken the biocalcification potential of marine organisms in shallow water and in open marine settings in this study the response of an aptian neritic carbonate environment to sudden addition of carbon dioxide at the beginning of oceanic anoxic event 1a is investigated the beginning of the oae1a was coupled with a major perturbation on the carbon cycle as indicated by a negative carbon isotope excursion in the sedimentary record this isotope anomaly is regarded as a proxy for massive addition of volcanic or methane derived co2 to the atmosphere within only a few 104 years the impact of a rapid change in atmospheric pco2 on biocalcifiers in low latitude shallow water settings can be studied in a well preserved aptian carbonate shelf succession cropping out today in the aralar mountains ne spain the madotz section n spain preserves a continuous shallow water record that was deposited on a mid latitude atlantic oriented mixed siliciclastic carbonate ramp lower aptian sediments consist of two neritic limestone successions separated by orbitolinid rich marlstone enriched in organic matter the lower neritic limestone succession ends with a submarine hardground and the transition from the lower neritic limestone to the orbitolinid marlstone coincides with a negative spike in the organic carbon isotope record this negative spike can be correlated with the negative carbon isotope anomaly marking the base of oae1a the paleoecological change coinciding with the base of oae1a occurred at a time of sea level rise and it coincided with a demise of heavily calcified nannoconids in the tethys and pacific oceans the paleoecological change observed in the madotz section corresponds to a comparable change seen in the more distal and more expanded carbonate ramp section igaratza at the aralar mountains ocean acidification caused by sudden increase in pco2 may explain reduced calcification potential of some shallow water calcifiers calcification crisis was amplified by rising sea level increasing temperatures and increased flux of detrital material and nutrients from continents into coastal seas

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

a volcanically induced climate warming and floral change preceded the onset of oae1a early cretaceous the aptian oceanic anoxic event 1a oae1a is preceded by a prominent negative c isotope excursion ncie attributed to major volcanism on the ontong java plateau that is supposed to lead to a pco2 increase and a climate change lower aptian sporomorph assemblages in two pelagic sections from the southern tethys margin n italy were analysed in order to test if the postulated climate changes affected the terrestrial vegetation at the base of the ncie the sporomorph assemblages comprise abundant bisaccate pollen reflecting a warm temperate climate several tens of kiloyears ka after the start of the ncie decreasing bisaccate pollen and increasing classopollis spp and araucariacites spp suggest the beginning of a long term temperature rise palynomorphs indicate that maximum temperatures were reached several tens of ka after the end of the ncie and the onset of oae1a the highest temperatures coincide with arid conditions which could reflect a northward shift of the hot arid northern gondwana floral province as a result of an increasing pco2 over 200 ka after the onset of oae1a reduced volcanic activity and or increased black shale deposition allowed for a drawdown of most of the excess co2 and a southward shift of floral belts

organic geochemistry stable isotopes and facies analysis of the early aptian oae new records from spain western tethys abstract the early aptian oceanic anoxic event oae1a is a time interval characterized by increased organic carbon accumulation in marine sediments notable sedimentary and biotic changes and abrupt carbon isotope excursions indicative of significant major palaeoenvironmental changes linked to a perturbation in the global carbon cycle here we present the study of four sections recording the oae1a early aptian in spain which are located in two broad basins respectively located in the south and the north of iberia the southern iberian palaeomargin carbonero la frontera and cau sections and the basque cantabrian basin puentenansa section which represent depositional settings ranging from shallow marine distal ramp cau and drowned platform puentenansa to pelagic environments carbonero la frontera biomarker compositions c isotope profiles biostratigraphic data and facies analysis from the four sections are correlated and integrated the c isotope curves all present a clear negative excursion followed by a positive shift the integration of the c isotope curves with the biostratigraphic data has been used to correlate the studied sections and to tentatively identify the eight segments formerly proposed from the alpine domain and subsequently identified in sections worldwide four main groups of compounds are present in all sections n alkanes isoprenoids hopanes and steranes n alkanes and acyclic isoprenoids pristane and phytane are dominant in most samples the hopanes are represented by a range of c 27 to c 35 components with the specific isomers varying amongst the sections due to differences in thermal maturity steranes occur as a range of c 27 c 28 and c 29 isomers whereas diasteranes only occur in the most thermally mature section carbonero other compounds of interest include gammacerane and dinosterane differences in thermal maturity appear to be the first order control on different biomarker assemblages amongst the studied sections the carbonero section is thermally mature whereas the nearby la frontera and cau sections are immature puentenansa has intermediate values organic matter is derived from a range of terrestrial marine and bacterial sources the dominance of the c 29 sterane isomers in all sections suggests a strong contribution from higher plants the presence of gammacerane indicates water column stratification and high c 29 c 30 hopane ratios suggest anoxia at the water sediment interface respectively sedimentologic analysis also suggests anoxic conditions during sedimentation but evidence for strong and persistent water column anoxia is equivocal the correlation of the sections reveals that sedimentation of organic rich facies started earlier in pelagic and later in the shallow marine settings which can be related to an expansion of the favorable conditions for organic matter accumulation and preservation from deep marine waters to shallower platform environments during the development of oae1a

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

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

latitudinally different responses of tethyan shoal water carbonate systems to the early aptian oceanic anoxic event oae 1a ocean wide anoxic events represent intensively investigated anomalies in the global carbon cycle most previous research has focussed on hemipelagic and pelagic settings and on the relationship between black shale deposition and carbon isotope excursions the study of ocean wide anoxic events and coeval shallow water settings is now increasingly seen as an interesting complementary approach but one that is not without problems whereas platform drowning characterizes the early aptian of the northern tethyan margin lithocodium bacinella rich facies and ongoing shoal water sedimentation at the southern tethyan margin oman bears important information on potential causes of carbon cycle perturbations the present paper seeks to test the supra regional relevance of the oman data by investigating coeval central tethyan limestones three lower aptian shoal water sections in istria croatia deposited on the isolated adriatic carbonate platform are investigated applying chemostratigraphy carbon and strontium and detailed sedimentological analysis the focus is on peritidal to lagoonal facies characterized by mass occurrences of lithocodium bacinella an enigmatic microencruster community lithocodium bacinella facies occurs predominantly in layers ranging from one to several centimetres in stratigraphic thickness with several layers merging to metre thick packages growth fabrics within the layers include oncoidal morphotypes lumps interconnected patches and columns layers and rare nodular to massive bindstone facies these growth patterns show a remarkable regional extent and consistency over study sites distributed several kilometres apart this widespread distribution suggests that specific lithocodium bacinella morphotypes might serve as regional stratigraphic markers the high resolution carbon isotope chemostratigraphy presented here is based on pristine rudist shells and matrix micrite samples and calibrated against strontium isotope data obtained from screened rudist low mg calcite the chemostratigraphic data are consistent with existing biostratigraphic data and place the studied strata at the onset of early aptian oceanic anoxic event 1a moreover results indicate the near coeval nature of lithocodium bacinella bloom facies in istria and oman the outcomes of this study point to latitudinally different responses of tethyan shoal water carbonate systems platform drowning versus lithocodium bacinella blooms to the ocean wide anoxic event 1a

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

carbon isotope stratigraphy and ammonite faunal turnover for the middle jurassic in the southern iberian palaeomargin variations in the stable carbon isotope ratio of marine and continental sediments can reflect changes in sink and flux modifications of the palaeocarbon cycle here we report carbon isotope compositions of middle jurassic marine carbonates from the betic cordillera southern spain which represents an ideal region to link the stable carbon isotope curves directly to ammonite zones and subzones and thereby for the first time achieve an accurate chronostratigraphic calibration the five sections studied represent basin and high swell deposits of the southern iberian palaeomargin we find a similar 13 c of carbonates between different oceanic areas suggesting a homogeneous carbon isotope oceanic reservoir through the middle jurassic the aalenian bajocian transition is a critical period in ammonite evolution hence the early jurassic fauna are replaced by new ammonite families which become dominant throughout the middle and late jurassic for this reason we compared the 13 c values of carbonates with ammonite diversity and extinction rates at different taxonomical levels in order to explore the possible relationship between the carbon cycle and ammonite evolution the carbon isotope values of carbonates are not exactly linearly correlated with the extinction rate and ammonite diversity but the main faunal turnovers follow minimum 13 c values where extinct taxa are replaced by new ones likewise radiation episodes are associated with increasing 13 c values and with transgressive sea level rise all these data support the idea that perturbations in the global carbon cycle reflect rapid palaeoenvironmental changes we made detailed analyses of these faunal turnovers using them as a proxy to identify major palaeoenvironmental crises in their ecosystems forced by modification in the carbon cycle

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

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

compositional and isotopic characteristics of organic matter for the early aptian oceanic anoxic event at shatsky rise odp leg 198 the occurrence of intervals of enhanced sequestration of organic matter om during the mid cretaceous collectively termed oceanic anoxic events oae reflect abrupt changes in global carbon cycling these episodes raise questions about the causes for such perturbations and their linkages to fluctuations in climate marine biota and ocean geochemistry preserved in the sedimentary record detailed assessment of the early aptian event oae1a in the pacific has been precluded by the limited recovery of this stratigraphic interval in contrast to the many records from the tethyan realm the recovery of pelagic sequences of om rich sediments at site 1207 on shatsky rise odp leg 198 corresponding to oae1a has enabled recognition of high resolution temporal variations in the elemental and isotopic compositions of this event in the pacific however the continuous 45 cm om rich interval recovered is likely only the initiation of oae1a rather than a complete section based on natural gamma and uranium logs which suggest that the full thickness of this interval is 1 2 m exceedingly high organic carbon corg 20 and total sulfur ts 5 contents among the highest ever recorded for pelagic cretaceous sequences attest to the enhanced sequestration of om during oae1a 13corg values are lowest 27 7 at the base of the recovered om rich interval followed by a 2 4 positive shift this isotopic profile resembles part of the 13ccarb record at resolution guyot and is comparable with segments c3 and c4 of the cismon 13corg record low 15n values 2 provide evidence for nitrogen fixation perhaps coupled with elevated cyanobacterial populations that suggest that the marine nitrogen cycle in the cretaceous was different from the modern overall the temporal fluctuations in elemental and isotopic data through oae1a at shatsky rise describe differences in production and preservation of om that likely reflect variations in ocean conditions associated with both local and global environmental changes

estimating the impact of early diagenesis on isotope records in shallow marine carbonates a case study from the urgonian platform in western swiss jura the poor preservation of sedimentological and geochemical evidence often hampers the identification of subaerial exposure surfaces in carbonate platform successions such discontinuities may represent significant time gaps justifying the quest for diagnostic indications we investigated a lower hauterivian to upper barremian sedimentary succession from switzerland to highlight the stratigraphic impact of meteoric diagenesis on platform carbonates petrographic observations revealed the presence of five generations of calcitic cements spot measurement of carbon and oxygen stable isotope compositions 13c and 18o values respectively measurements relate them to specific diagenetic environments selected blocky calcite cements exhibit an enrichment in light isotopes 12c 16o indicative of meteoric eogenesis whereas very negative 18o values link the last phase of cementation to mesogenesis meteoric calcitic cements formed during karstification of the top of the upper barremian succession burial diagenetic phases overlap these eogenetic phases which thus cannot be related to recent telogenesis we estimated the ratio of early meteoric versus burial cements within the studied succession its stratigraphic repartition reveals that lower aptian eogenesis influenced the geochemistry of platform carbonates as deep as 45 m below the exposure surface in this interval negative whole rock 13c values do not reflect contemporaneous variations of the 13c curves documented in sections devoid of strong diagenetic impact such an impact is a function of the amount of meteoric cement filling pore space as well as of the primary carbon isotope composition of the carbonate sediments and of the meteoric cement the vertical influence of a karst event is not restricted to the first metres directly below the exposure surface although meteoric diagenesis may not significantly alter microfacies it may strongly perturb isotope systems building onto this case study the application of 13c chemostratigraphy to platform carbonates can only be performed with great caution and after a careful examination of diagenetic features

high resolution ammonite and carbon isotope stratigraphy across the triassic jurassic boundary at new york canyon nevada the triassic jurassic boundary is generally considered as one of the major extinctions in the history of phanerozoic the high resolution ammonite correlations and carbon isotope marine record in the new york canyon area allow to distinguish two negative carbon excursions across this boundary with different paleoenvironmental meanings the late rhaetian negative excursion is related to the extinction and regressive phase the early hettangian 13corg negative excursion is associated with a major floristic turnover and major ammonite and radiolarian radiation the end triassic extinction early jurassic recovery is fully compatible with a volcanism triggered crisis probably related to the central atlantic magmatic province the main environmental stress might have been generated by repeated release of so2 gas heavy metals emissions darkening and subsequent cooling this phase was followed by a major long term co2 accumulation during the early hettangian with development of nutrient rich marine waters favouring the recovery of productivity and deposition of black shales

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

synchronous negative carbon isotope shifts in marine and terrestrial biomarkers at the onset of the early aptian oceanic anoxic event 1a evidence for the release of 13c depleted carbon into the atmosphere 1 a common feature of records of the early aptian oceanic anoxic event oae 1a is the sharp negative 13c excursion displayed in both carbonate and organic matter at the onset of this event a synchronous negative 13c excursion has also been noted for terrestrial organic matter this negative excursion has been attributed to either an injection of 13c depleted light carbon into the atmosphere or in case of marine sediments recycling of 13c depleted co2 however most studies were done on separate cores and no information on the relative timing of the negative spikes in terrestrial versus marine records has been obtained here we examine early aptian core sections from two geographically distal sites italy and the mid pacific to elucidate the causes and relative timing of this negative spike at both sites increased organic carbon corg and decreased bulk carbonate contents characterize the interval recording oae 1a variously referred to as the selli event the organic material within the selli level is immature and of autochthonous origin measured 13c values of marine and terrestrial biomarkers largely covary with those of bulk organic carbon with lowest values recorded at the base of the organic rich section by contrast sediments enveloping the selli level exhibit very low corg contents and their extractable corg is predominantly of allochthonous origin hydrous pyrolysis techniques used to obtain an autochthonous pre selli 13c value for algal derived pristane from corresponding sample material yielded a negative 13c shift of up to 4 a negative 13c shift of similar magnitude was also measured for the terrigenous n alkanes the results are collectively best explained by means of a massive syndepositional rapid input of 13c depleted carbon into the atmosphere and surface oceans likely delivered either via methane produced from the dissociation of sedimentary clathrates or perhaps by widespread thermal metamorphism of corg rich sedimentary rocks

rudists and carbonate platforms in the aptian a case study on biotic interactions with ocean chemistry and climate variations in aptian carbonate platform growth and associated turnover among rudists are reviewed and the results synthesized with evidence for climate change to yield an explanatory model extensive platform growth throughout the atlantic tethys low palaeolatitude pacific seamount belt in the earliest aptian was accompanied by prolific rudist diversification especially among the predominantly aragonitic caprinids occupying platform margins it was ubiquitously interrupted in the mid early aptian in tandem with major perturbations of the global carbon cycle that culminated in oceanic anoxic event 1a although the causal linkages remain contentious platform growth terminated along most of the northern tethyan margin and maybe also in the new world meanwhile lithocodium bacinella or similar microbial encrustations became widespread in lower palaeolatitudes recovery of tethyan platforms in the late early aptian was limited to lower palaeolatitudes caprinid rich platform margin facies again prevailed in central and southern tethyan areas but gave way to those dominated by rudists with a thickened calcitic outer shell layer polyconitids and requieniids in marly successions around iberia the end of the early aptian saw the lazarus style disappearance of caprinids and renewed tethyan platform growth in the late aptian was dominated by calcite rich rudists although rudists remained scarce in the new world until the terminal aptian this study postulates that sea water acidification influenced both the mid early aptian platform debacle and the subsequent late early aptian geographical restriction of platform recovery although in contrasting atmospheric regimes at first it was forced by the increasing atmospheric levels of volcanically derived co2 with mitigation in low latitudes from thermal expulsion of aqueous co2 here termed the kettle effect due to greenhouse warming however subsequent cooling due to drawdown of atmospheric co2 by organic carbon burial could have sustained acidification of platform waters in higher latitudes by reducing the protective kettle effect there caprinid susceptibility to such assaults may have been as much due to exposure on their preferred outer platform habitats as to their mineralogy the increased calcite aragonite ratio among rudists through the aptian resulted largely from this taxonomic turnover

interactions between environmental change and shallow water carbonate buildup along the northern tethyan margin and their impact on the early cretaceous carbon isotope record 1 the evolution of the early cretaceous northern tethyan carbonate platform was not only influenced by changes in sea level detrital influx and surface water temperature but also by changes in trophic levels we distinguish between phases of carbonate production dominated by oligotrophic photozoan communities and by mesotrophic and eventually colder water heterozoan communities superimposed on this bimodal trend in platform evolution were phases of platform demise for which we provide improved age control based on ammonite biostratigraphy the initial phase of these episodes of platform demise corresponds in time to episodes of oceanic anoxic events and environmental change in general on the basis of a comparison between the temporal changes in an early cretaceous ammonite calibrated d 13 c record from southeastern france and coeval changes in the platform record we suggest that the history of carbon fractionation along the northern tethyan margin was not only influenced by changes in the oceanic carbon cycle such as in the rate of production and preservation of organic and carbonate carbon and in the size of the oceanic dissolved inorganic carbon reservoir but it was also influenced by the above mentioned changes in the ecology and geometry of the adjacent carbonate platform phases of photozoan carbonate production induced positive trends in the hemipelagic carbonate d 13 c record phases of heterozoan carbonate production pushed the d 13 c system toward more negative values platform drowning episodes implied an initial increase in d 13 c values followed by a longerterm decrease in d 13 c values

drowning events development and demise of carbonate platforms and controlling factors the late barremian early aptian record of southeast france abstract in provence and languedoc se france four drowning events were identified in platform carbonates of late barremian bedoulian age their timing referred to ammonite zones or subzones is as follows 1 late barremian d1 at the gerhardtia sartousiana imerites giraudi boundary 2 middle bedoulian d2 at the deshayesites weissi deshayesites deshayesi boundary 3 mid late bedoulian d3 in correspondence with the roloboceras hambrovi subzone and 4 late bedoulian d4 at the deshayesites grandis dufrenoya furcata transition notwithstanding their relatively wide regional lateral continuity the depositional hiatus linkage with exposure paleobathymetric range and offset and geographical extent of drowning discontinuities are not uniform the late barremian drowning d1 is marked either by the development of a permanent intra shelf basin with ammonites associated with the re organization of platform basin relationships or by the wide extent of palorbitolina heteraster facies which develops to the detriment of the antecedent rudist facies the drowning event is followed by platform recovery during the early bedoulian but the corresponding development of shallow water carbonates is subsequently interrupted by the emergence of an uplifted bulge trending sub parallel to the provence languedoc margin the middle bedoulian drowning d2 is concurrent with the sealing of the antecedent paleotopography and the wide development of palorbitolina facies then bioclastic and coral facies tend to recover the mid late bedoulian drowning d3 is characterized by an overall deepening phase with ammonite bearing marly facies or cherty limestones shallow bioclastics being locally present the late bedoulian drowning d4 records the deposition of deep water marls evidence is lacking that global sea level changes or transgressive regressive cycles had a significant impact on drowning events and some evidence that changes in temperature and productivity of the ocean may have contributed to these phenomena in conjunction with other factors though distension fault activity is regarded as a major controlling factor for the origin of the late barremian deepening event its associated paleogeographic re organization ensuing emergence of the provence languedoc marginal bulge and its subsequent detumescence coeval with the middle bedoulian drowning associated changes in facies types from rudist to palorbitolina reflect sea water deepening coupled with trophic modifications as agents of differential subsidence tectonic phenomena are also testified by the contrasting regional patterns of paleobathymetric offsets combined with drowning events they are a clue for understanding thickness changes and coeval modifications in the overall orientation of the progradational polarity of the platform system towards the adjacent basinal areas environmental changes essentially the two main oae1a subevents are regarded as significant agents of the mid late and late bedoulian drownings whereas tectonic processes are also involved in the corresponding deepening however the effects of the oae events on the functioning of the shallow carbonate factory are poorly understood and still need to be investigated the rise in atmospheric carbon dioxide pressure and as a consequence the reduction of the calcification potential of benthic organisms both reported in the literature are not clearly reflected in the composition of the biota aragonite dominated organisms such as caprinid rudists thrive throughout the bedoulian the role of acidification in platform demise is therefore questionable

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

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