comparison of water column co2aq with sedimentary alkenone based estimates a test of the alkenone co2 proxy 1 the stable carbon isotopic compositions of alkenones have been used to interpret the long term history of the partial pressure of atmospheric carbon dioxide pco2 although extensive water column and culture studies document the potential utility and limitations of this approach to date the accuracy of pco2 values derived from sedimentary alkenones remains untested for this study we establish holocene aged alkenone based co2aq estimates co2aq alk from 20 sites along a central pacific ocean transect and compare them against both observed modern water column co2aq and estimated preindustrial concentrations at the depth of alkenone production at each site although the co2aq alk track measured water column values they are conspicuously lower than modern values across the subtropics this offset likely reflects the contributions of anthropogenic co2 in modern surface waters relative to preindustrial concentrations at the time of alkenone production when a model based estimate of anthropogenic co2 is removed from the modern observed values a majority 84 of co2aq alk falls within 20 of modeled preindustrial values consistency between the modeled and alkenone based estimates of preindustrial co2 levels points to the relative accuracy of the alkenone co2 method across a wide range of ocean and biogeographic regimes provided that phosphate concentrations at the depth of haptophyte production are reasonably constrained it further suggests that light limited growth and or active carbon uptake if they occur have a negligible effect on reconstructed co2aq

organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

organic matter source and thermal maturity within the late cretaceous niobrara formation u s western interior abstract the late cretaceous sedimentary record of the north american western interior seaway is characterized by cyclic deposition of organic carbon rich sediments one notable interval during the late coniacian santonian is recorded by the niobrara formation the organic carbon rich interval within the niobrara formation has been identified as oceanic anoxic event oae 3 understanding the reason for this distribution of organic carbon within the niobrara formation requires a refined understanding of the source and maturity of the organic matter in this study we present lipid biomarker records from the usgs portland 1 core canon city co to constrain the thermal maturity of the organic matter and the differing contributions of organic matter sources sterane and hopane thermal maturity indices indicate that the samples are somewhat immature with respect to oil formation and that there is strong agreement between different proxies for thermal maturity based on the distribution of n alkanes steranes and hopanes there is a significant increase in the contribution of algal organic matter during and after oae 3 coeval with increased organic carbon accumulation although a consistent terrestrial contribution is observed it is only a minor source of organic matter at the portland core location and does not drive increased organic matter accumulation during oae 3 of particular note is the consistent influence of even over odd predominantly mid chain length c21 to c25 organic matter this observation within the brackish to marine not methanogenic wis represents an expansion of the depositional settings in which even over odd predominance has been observed in mid chain length n alkanes pristane pr and phytane ph abundances are inconsistent with a redox control on pr ph ratios and suggest an increase in the delivery and or preservation of phototrophic organic matter as the source for pristane and phytane in the portland core

modeling phosphorus cycling and carbon burial during cretaceous oceanic anoxic events article i nfo in the greenhouse world of the cretaceous there were episodes of oxygen depletion in the deep ocean associated with enhanced organic carbon burial in sediments black shale formation in this study we use a box model of the oceanic phosphorus p organic carbon orgc and oxygen cycles to explore the hypothesis that variations in marine p availability control deep ocean oxygen depletion anoxia and the formation of black shales under cretaceous ocean conditions we find that for the cretaceous ocean with large continental shelves slow oceanic overturning and high sea surface temperatures oceanic anoxic events oaes can be triggered by enhanced p supply from land and that the system is particularly sensitive to oceanic mixing in our baseline scenario the deep sea becomes completely anoxic while the shelves attain only partial anoxia sedimentary burial differs between the shelves and open ocean while organic carbon burial is enhanced in both regions deep sea reactive p burial decreases dramatically under anoxia but not on the shelves where oxygen depletion is not complete furthermore our model results imply that oaes can be sustained by p recycling from sediments under low oxygen conditions ultimately however the feedbacks which result in the accumulation of atmospheric oxygen terminate the anoxic event atmospheric oxygen is modulated by land processes such as forest fires and oxidative weathering which limit the rise of atmospheric o2 our model findings are corroborated by p burial data from the geological record for oae2 approximately 94 myr bp through a sensitivity analysis we identify two necessary criteria for oaes low mixing of surface and deep waters poor ocean ventilation and enhanced sedimentary p recycling under low oxygen conditions when these criteria are met ocean anoxia is a robust result to a mild increase of continental supply of phosphorus under a wide range of environmental conditions

the benthic boundary biofacies model hartland shale member greenhorn formation cenomanian western interior north america abstract well laminated predominantly non burrowed strata of the mid cretaceous western interior basin contain in situ epifaunal body fossils indicative of dysaerobic benthic oxygen levels a gradient of increasing ecological complexity in these dysaerobic faunas is identifiable and reflects improvements in benthic conditions using these faunal assemblages a benthic boundary biofacies model is developed in which the critical redox boundary is in dynamic equilibrium at the sediment water interface variations in bottom water oxygenation as well as substrate characteristics are cited as the controlling factors in the position of this boundary and thus control benthic colonization the model describes a background of low oxygen tolerant flat clam communities which were predominant during deposition of the late cenomanian hartland shale member superimposed on this background a history of brief episodic colonization and sedimentation events reveals a dynamic climate ocean system in the western interior sea which maintained a delicate balance of oxygen deficiency at the sediment water interface

marine 187os 188os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during oceanic anoxic event 2 high resolution osmium os isotope stratigraphy across the cenomanian turonian boundary interval from 6 sections for four transcontinental settings has produced a record of seawater chemistry that demonstrates regional variability as a function of terrestrial and hydrothermal inputs revealing the impact of palaeoenvironmental processes in every section the 187os 188os profiles show a comparable trend radiogenic values in the lead up to oceanic anoxic event 2 oae 2 an abrupt unradiogenic trend at the onset of oae 2 an unradiogenic interval during the first part of oae 2 and a return to radiogenic values towards the end of the event above the cenomanian turonian boundary the unradiogenic trend in 187os 188os is synchronous in all sections previous work suggests that activity of the caribbean lip large igneous province was the source of unradiogenic os across the oae 2 and possibly an instigator of anoxia in the oceans here we assess this hypothesis and consider the influence of activity from other lips such as the high arctic lip a brief shift to high radiogenic 187os 188os values occurred in the western interior seaway before the onset of oae 2 we evaluate this trend and suggest that a combination of factors collectively played critical roles in the initiation of oae 2 differential input of nutrients from continental and volcanogenic sources coupled with efficient palaeocirculation of the global ocean and epeiric seas enhanced productivity due to higher nutrient availability which permitted penecontemporaneous transport of continental and lip derived nutrients to trans equatorial basins

impact of suboxia on sinking particulate organic carbon enhanced carbon flux and preferential degradation of amino acids via denitrification fluxes of particulate organic carbon poc through the oxygen deficient waters in the eastern tropical north pacific were found to be relatively less attenuated with depth than elsewhere in the eastern north pacific the attenuation coefficient b for the flux was found to be 0 40 versus the composite value of 0 86 determined by martin et al 1987 to examine this further sinking poc was collected using sediment traps and allowed to degrade in oxic and suboxic experiments using a kinetic model it was found that degradation proceeded at similar rates roughly 0 8 day 1 under oxic and suboxic conditions but a greater fraction of bulk poc was resistant to degradation in the suboxic experiments 61 vs 23 amino acids accounted for 37 of poc collected at 75m but following degradation the value dropped to 17 and 16 in the oxic and suboxic experiments respectively poc collected from 500m was 10 amino acids the non aa component of poc collected at 75m was not degraded under suboxic conditions while under oxic conditions it was these results suggest that microbes degrading oc under suboxic conditions via denitrification preferentially utilize nitrogen rich amino acids this preferential degradation of amino acids suggests that 9 more nitrogen may be lost via water column denitrification than is accounted for when a more redfieldian stoichiometry for poc is assumed

evaluating late cretaceous oaes and the influence of marine incursions on organic carbon burial in an expansive east asian paleo lake abstract expansive late cretaceous lacustrine deposits of east asia offer unique stratigraphic records to better understand regional responses to global climate events such as oceanic anoxic events oaes and terrestrial organic carbon burial dynamics this study presents bulk organic carbon isotopes 13 c org elemental concentrations xrf and initial osmium ratios 187 os 188 os os i from the turonian coniacian qingshankou formation a 5 ma lacustrine mudstone succession in the songliao basin of northeast china a notable 13 c org excursion 2 5 in organic carbon lean qingshankou members 2 3 correlates to oae3 in the western interior basin wib of north america within temporal uncertainty of high precision age models decreases in carbon isotopic fractionation 13 c through oae3 in the wib and songliao basin suggest that significantly elevated global rates of organic carbon burial drew down pco 2 likely cooling climate despite this os i chemostratigraphy demonstrates no major changes in global volcanism or weathering trends through oae3 identification of oae3 in a lake system is consistent with lacustrine records of other oaes e g toarcian oae and underscores that terrestrial environments were sensitive to climate perturbations associated with oaes additionally the relatively radiogenic os i chemostratigraphy and xrf data confirm that the qingshankou formation was deposited in a non marine setting organic carbon rich intervals preserve no compelling os i evidence for marine incursions an existing hypothesis for generating member 1 s prolific petroleum source rocks based on our results we present a model for water column stratification and source rock deposition independent of marine incursions detailing dominant biogeochemical cycles and lacustrine organic carbon burial mechanisms

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

unraveling the onset of cretaceous oceanic anoxic event 2 in an extended sediment archive from the tarfaya laayoune basin morocco we investigated the onset and development of cretaceous oceanic anoxic event 2 oae2 in a newly drilled core sn degrees 4 from the tarfaya basin southern morocco where this interval is unusually expanded high resolution centimeter scale equivalent to centennial analysis of bulk organic and carbonate stable isotopes and of carbonate and organic carbon content in combination with xrf scanner derived elemental distribution reveal that the ocean climate system behaved in a highly dynamic manner prior to and during the onset of oae2 correlation with the latest orbital solution indicates that the main carbon isotope shift occurred during an extended minimum in orbital eccentricity similar to 400 kyr cycle shorter term fluctuations in carbonate and organic carbon accumulation and in sea level related terrigenous discharge were predominantly driven by variations in orbital obliquity negative excursions in organic and carbonate delta c 13 preceded the global positive delta c 13 shift marking the onset of oae2 suggesting injection of isotopically depleted carbon into the atmosphere the main delta c 13 increase during the early phase of oae2 in the late cenomanian was punctuated by a transient plateau maximum organic carbon accumulation occurred during the later part of the main delta c 13 increase and was associated with climate cooling events expressed as three consecutive maxima in bulk carbonate delta o 18 the extinctions of the thermocline dwelling keeled planktonic foraminifers rotalipora greenhornensis and rotalipora cushmani occurred during the first and last of these cooling events and were likely associated with obliquity paced ocean wide expansions and intensifications of the oxygen minimum zone affecting their habitat space on a global scale

depositional and organic carbon controlled regimes during the coniacian santonian event first results from the southern tethys egypt abstract geochemical and palynological proxies were determined for 31 samples representing the upper coniacian lowermost campanian abu roash a member collected from the bed2 3 well this was done to assess the prevailing paleoredox conditions productivity levels and water column settings to 1 understand controls and mechanisms related to accumulation of organic carbon within the sedimentary record 2 assess principal environmental processes that triggered the preservation of organic matter poor calcareous shale and limestone facies of the abo roash a member and 3 to interpret the paleoceanographic settings and confirm the occurrence of either oceanic anoxic event 3 oae3 or cretaceous oceanic red beds corbs within the abu gharadig basin in the southern part of the tethyan ocean egypt sedimentation rates were reconstructed based on the biostratigraphic age constraints of marine dinoflagellate cysts dinocysts trace elements based ratios and relationships were used in order to study the role of clastic terrestrial input three groups of dinocysts and freshwater pediastrum algae were used to study the water column conditions results showed that the abu roash a member was deposited under oxic to intermittently dysoxic conditions in a distal inner to middle neritic environment with varying sedimentation rates from 32 to 119 mm kyr 1 productivity appeared to be a significant factor for determining magnitudes of the organic carbon accumulation however low productivity was prevalent during deposition carbonate content was high which resulted in dilution of organic matter during varied rates of sediment input such results indicate that the paleoceanographic conditions in the southern tethys witnessed the absence of prevalent oceanic anoxia i e the coniacian santonian oae 3 and deposition of the corbs as in several parts of the tethys the pacific and the indian oceans

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

concepts and methods of high resolution event stratigraphy modern geological analyses involving sedimentary rocks require a high resolution system of dating integrating and correlating diverse strati graphic geochemical and paleontological data that also takes into account the possibility that short term phenomena 100 kyr or less exercise a strong control on sedimentation such phenomena may be extraterrestrial tectonic volcanic oceanographic climatic sedimentologic and or bio logic in origin some reflect unpredictable perturbations of local to global scale but most short term phenomena are predictable and may be either autocyclic locally regulated with limited stratigraphic continuity or allo cyclic in nature regionally to globally regulated with extensive strati graphic continuity beerbower 1964 a stratigraphic system based on short term phenomena would ideally be chronostratigraphic involving the identification and regional tracing of time lines isochronous surfaces or very thin event deposits and easily integrated with refined independently derived biostratigraphic and geochronologic systems an intensive search for such a new and revolutionary system of stratig raphy has been prompted in many parts of the phanerozoic by attain ment of plateaus in stratigraphic resolution utilizing the more standard tools of magnetostratigraphy biostratigraphy and geochronology most magnetic reversals have been identified biostratigraphic systems can be no more refined than the maximum evolutionary rates of component taxa and their major structures known for many favored groups and geo chronology is regulated by the analytical confidence limits of radiometric

trace metal evidence for changes in the redox environment associated with the transition from terrigenous clay to diatomaceous sediment saanich inlet bc abstract we measured the concentrations of redox sensitive trace metals mn v mo u cd and re in sediments from odp leg 169s hole 1033b in saanich inlet british columbia to determine changes in redox conditions associated with the onset of laminated sediments at 12 5 kyr the most striking result is a large peak in authigenic re along with detrital levels of mo at the glacial terrigenous clay diatomaceous sediment transition in contrast the underlying glacial terrigenous clay which extends throughout the bottom section of the core is chemically similar to detrital concentrations either cowichan river particulates or average shale values these data suggest a period of oxic bottom waters but reducing pore waters this could be due to the dramatic transformation of saanich inlet during the late deglaciation from an open bay to an inlet which restricted circulation and slowed bottom water oxygen renewal a peak and gradual increase in authigenic mn in younger sediments subsequent to the re peak suggests that increasingly oxic conditions followed the authigenic enrichment in re these conditions could be connected to the younger dryas cooling period which was coincident with an increase in well oxygenated upwelled waters on the west coast of north america that form the bottom waters of saanich inlet metal concentrations in a gray clay bed 11 kyr are similar to their concentrations in the glacial terrigenous clay implying that they have a common source authigenic enrichments of re with little authigenic mo and cd suggest that before the deposition of this bed bottom waters were oxic and pore water oxygen was consumed in the top centimeter or less laminations above the clay layer suggest anoxic conditions which are also indicated by higher authigenic mo and cd and slightly lower re mo ratios in these sediments the basin remained mostly anoxic after the gray clay was emplaced as seen by continuous authigenic enrichment of the redox sensitive trace metals these results are consistent with increased stratification of the water column brought about by an influx of fresh water to the basin by a large flood

new tools for seismic stratigraphic interpretation stratal convergence and instantaneous isochron attribute cubes derived from volumetric flattening of experimental strata interpreting seismic data requires inferences to be made from the geometry character and spatial association of seismic reflections seismic attributes that highlight such associations are essential for understanding basin fill histories in this article we describe two novel attributes obtained from an automatic full volume flattening algorithm and apply them to a synthetic seismic volume of experimental strata the stratal convergence attribute colors reflections according to their degree of convergence which is commonly high in areas where strata thin because of erosion or nondeposition the instantaneous isochron attribute measures thickness between reflections and is therefore generally proportional to sediment accumulation rate these attributes distinguish bounding surfaces and depocenter migration in well constrained experimental strata by showing the diagnostic value of each attribute our study motivates field based applications of full volume flattening and attribute co rendering for seismic stratigraphic interpretation

modelling oceanic carbon and phosphorus fluxes implications for the cause of the late cenomanian oceanic anoxic event oae2 a two box ocean model with a coupled carbon and phosphorus cycle is used to test which processes can realistically generate a rapid positive 2 13c excursion in the global carbon reservoir internal oceanic processes enhanced preservation of organic matter under anoxic conditions enhanced upwelling cannot produce a substantial 13c excursion under the assumption that burial rates of c and p are coupled loss of nutrients to the sediment acts as a negative feedback mechanism that prevents a substantial perturbation of the carbon cycle a large and renewable source of nutrients is needed either from increased continental weathering or from enhanced regeneration of sedimentary organic phosphorus under anoxic conditions measurements of total phosphorus and organic carbon in sediments from the tarfaya basin morocco suggest that a large decrease in p burial occurred relative to organic carbon at the base of the cenomanian turonian oceanic anoxic event oae2 with the right magnitude to quantitatively explain a 2 shift in 13c it is concluded that the main underlying mechanism that allowed and sustained enhanced carbon burial during the mid cretaceous was a perturbation of the oceanic phosphorus cycle

greenhouse crises of the past 300 million years proxies of past co 2 and climate over the past 300 m y now reveal multiple global climate change events in unprecedented detail evidence for past co 2 spikes comes from expanded and refined data on stomatal index of fossil ginkgo and related leaves new evidence for synchronous climatic change comes from paleosols in montana utah and neighboring states each co 2 spike was coeval with unusually clayey red and decalcified paleosols which can be traced throughout the colorado plateau spikes in atmospheric co 2 also were coeval with increases in paleosol alkali depletion as an indication of high temperature and spikes in paleosol base depletion and depth to calcic horizons as indications of high precipitation in the colorado plateau times of warmer climate were also more humid perhaps due to greater moisture potential of warmer air seasonality of climate did not increase during warm wet spikes the mesozoic greenhouse was not persistently hot with cool spells but warm with hot flashes these data furnish power laws predicting the sensitivity and magnitude of change in mean annual temperature mat and mean annual precipitation map due to rising co 2 in a mid latitude mid continental region the magnitude of the coming anthropogenic greenhouse pales in comparison with past greenhouse spikes at times of global mass extinctions

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

stratification and paleocirculation of the late cretaceous western interior seaway of north america paleotemperature and salinity profiles for the western interior seaway are reconstructed by use of oxygen and carbon isotopic signatures of shell material data have been gathered on different groups of molluscs distributed in three distinct habitat types infaunal benthonic epifaunal benthonic and nektonic isotopic variations and inferred environmental tolerances of the organisms were used to determine upper and lower temperature boundaries for each habitat group and therefore water depth zones water density for each temperature salinity combination within a habitat range was calculated and used to develop a physically stable stratification model the results clearly show that the water column consisted of denser more saline warm bottom layers that were overlain by and decoupled from cooler less saline intermediate layers it is proposed that this profile originated due to a surface current transporting runoff water from the western highlands toward the eastern shallow border of the seaway where evaporation and heating of surface water in a warm humid atmosphere caused increased density and sinking followed by westward return flow of the warm saline bottom water this model is compatible with known climatic and oceanographic information for the cretaceous

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

organic carbon production and preservation in response to sea level changes in the turonian carlile formation u s western interior basin abstract a primary sea level control over the distribution of total organic and carbonate carbon and organic matter type can be inferred in the early to middle turonian carlile formation fm western interior basin united states the conceptual model relies on chemo and lithostratigraphic correlations of lower to mid turonian strata in the central kwis supported by ammonite biostratigraphy and is based primarily on lithologic gamma ray spectrometric and geochemical facies analysis of the usgs portland no 1 core from central colorado the amoco rebecca bounds no 1 core from western kansas and the hawarden core from northwestern iowa sedimentation in the central marine axial basin of the cretaceous western interior seaway kwis during the turonian mostly reflects deposition by pelagic settling and from nepheloid layers with winnowing by bottom currents relatively high total organic carbon toc carbonate caco3 and rock eval pyrolysis hydrogen index hi values correspond to transgressive or highstand episodes within the overall regressive sequence whereas low values of these parameters characterize regressive intervals the lower fairport shale member of the carlile fm and coeval strata in iowa were deposited during a second order sea level highstand the waning stages of the greenhorn cyclothem an overall shallowing and coarsening upward sequence characterizes the overlying majority of the carlile fm this trend is punctuated by a short term transgressive episode with associated retrograde facies and a disconformity earlier studies document relatively high productivity during the turonian nutrient input to the seaway required to sustain water column productivity is difficult to account for solely by riverine inputs thus a model of transgressive flooding of preconditioned oxygen deficient nutrient rich water from the global ocean into the kwis is invoked this advection of nutrients and low oxygen water also helped to create broadly distributed dysoxic to anoxic conditions in the seaway which would otherwise have been difficult to maintain in a relatively well mixed shallow sea as the seaway regressed river supplied sea surface nepheloid layers provided sufficient nutrient inputs and occasionally established temporary stratification of the water column and thus contributed to maintaining an environment poised to produce and preserve organic matter

interregional correlation of disconformities in upper cretaceous strata western interior seaway biostratigraphic and sequence stratigraphic evidence for eustatic change we are pleased to have this opportunity to address the main points raised by krause and braunberger 2015 1 in 1964 scott and cobban in their study of the peck creek section noted that the top of bed 29 was very smooth a description not applied by them to any other bed in the fort

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

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

modeling organic carbon burial during sea level rise with reference to the cretaceous after three decades of research on the correlation between sea level and various proxies there has been very little quantification of the first order influence of sea level change on nutrient inventory marine productivity and burial of organic carbon we present a model aimed at quantifying the burial of organic carbon as a function of sea level rise the biogeochemical model explicitly considers the mean surface area distribution of the earth as a function of elevation also included is dissolved inorganic phosphate dip liberated from coastal sediments during transgression we quantify how sea level rise of magnitudes inferred for the mid cretaceous influences the phosphorus cycle and burial of organic carbon the burial efficiency is greater on the shelf therefore in the model the larger shelf area under high sea level results in more efficient burial of marine organic carbon for a given dip concentration and associated new production of organic matter np with a late cretaceous model shelf area the residence time of dip decreases by 60 relative to the present day reference thus in the final steady state dip and np in the open ocean are reduced compared to today when the biologically reactive phosphorus preac fluxes to the ocean from land are held constant the lower new production reduces the oxygen demand for respiration and results in a significant oxygenation of the global ocean finally the global organic carbon burial decreases by 30 relative to today in the model this decrease results from feedbacks between the flux of organic carbon to the seafloor and the ratio of organic carbon to preac in buried sediments in contrast during sea level rise coastal erosion may increase the preac flux to the ocean by up to 20 relative to today and cause a temporary increase in dip concentration in the ocean the resulting increase in organic carbon burial is equivalent to a carbon isotope event of 0 5 to 1 larger carbon isotope events can be triggered by sea level rise only when the ocean is sufficiently close to anoxia in the oxygen minimum zone just prior to the sea level rise

contrasting molybdenum cycling and isotopic properties in euxinic versus non euxinic sediments and sedimentary rocks refining the paleoproxies abstract the redox sensitive transition element molybdenum is present in the earth s crust at trace concentrations but is abundant in seawater marine sediments and ancient sedimentary rocks these occurrences have led to the development of a suite of paleoredox proxies based on the bulk concentration of mo its isotopic composition and the covariation of mo with total organic carbon toc in ancient black shales however these proxies have almost exclusively targeted the identification and interpretation of euxinic environments where bottom waters are both anoxic and sulfidic here we present a discussion of the mo geochemistry of non euxinic sediments where hydrogen sulfide is sometimes present yet always restricted to pore waters we propose a new paleoredox application that uses mo concentrations to help distinguish between environments where sulfide was present in the bottom waters and environments where sulfide was restricted to pore waters under ideal conditions it is also possible to infer the presence of mn oxides recycling in non euxinic paleoenvironments based on the mo isotope composition of ancient black shales providing a critical constraint on bottom water oxygenation

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

the cenomanian turonian boundary interval deep sea deposits in the zagros basin sw iran bioevents carbon isotope record and palaeoceanographic model abstract the cenomanian turonian c t boundary interval spanning the upper part of the sarvak formation in the zagros basin izeh zone has been studied to determine the timing and the possible cause of biotic turnovers coinciding with the intense environmental perturbations during the oceanic anoxic event 2 oae2 the upper cenomanian strata in the study section composed of light colour marlstone organic rich marlstone and shale bedding couplets record fluctuations in microfossil assemblages and organic carbon contents we suggest that the organic poor layers characterized by high abundance of radiolarians were deposited during cold periods under surface water eutrophication upwelling and ventilated seafloor in contrast water column stratification during warm periods enhanced organic matter preservation and allowed deposition of organic rich strata continued stratification and also increased runoff and primary productivity during warm intervals of oae2 led to expansion of oxygen minimum zone omz which may have caused extinctions of deep followed by intermediate water planktic foraminifera such conditions may have led to significant decreases in the abundance and diversity of planktic foraminifera and dominance of the biserial genus planoheterohelix heterohelix shift event the 13c curve in the study interval reveals the diagnostic features of global c t boundary carbon isotope record including three positive peaks a b and c within the whiteinella archaeocretacea biozone these carbon isotope features and the most important bioevents in the study section are stratigraphically listed below 1 highest occurrences hos of th greenhornensis and th deeckei 2 ho of r cushmani and 13c peak a 3 ho of g bentonensis 4 onset of heterohelix shift event 5 13c peak b 6 13c peak c 7 filament event 8 lowest occurrence lo of h helvetica and 9 holywell event

millennial to centennial scale record of african climate variability and organic carbon accumulation in the coniacian santonian eastern tropical atlantic ocean drilling program site 959 off ivory coast and ghana millennial to centennial scale geochemical records of coniacian to santonian deposits from the deep ivorian basin are used to develop a model for the accumulation of black shales in equatorial regions during the final of the cretaceous oceanic anoxic events oae proxy records from ocean drilling program site 959 document a strong precessional signal in the occurrence of black shales the abundance of quartz and clay mineralogy during oae 3 we hypothesize that this signal reflects changes in atmospheric circulation patterns which in turn caused latitudinal shifts of continental climate belts across western africa furthermore we propose that the periodic deposition of black shales occurred in response to adjustments of oceanic circulation in the deep ivorian basin resulting from climate controlled fluctuations in continental runoff a new high resolution cyclostratigraphic framework allowed us to estimate a rapid change within 1000 yr from dysoxic background to anoxic or euxinic black shale environmental conditions followed by black shale deposition for 10 k y and a gradual return to the initial dysoxic conditions our findings imply a highly dynamic late cretaceous atmosphere ocean system

a critical review of marine sedimentaryδ13corg pco2 estimates new palaeorecords from the south china sea and a revisit of other low latitude δ13corg pco2 records in an attempt to understand better the local biogeochemistry of the south china sea scs and to unravel the contribution of this marginal low latitude basin to changes in atmospheric co2 concentrations we analyzed the carbon isotopic composition of organic matter 13corg in four sediment cores from throughout the scs covering the last 220 kyr higher values around 19 5 to 20 5 mark glacial stages while lower values around 21 to 22 5 are characteristic of interglacials following well established procedures the 13corg records are converted to local pco2 estimates on the basis of these and other low latitude 13corg pco2 estimates from the literature we present a critical evaluation of the use of 13c of bulk sedimentary organic matter to hindcast past changes in local co2 aq three crucial pitfalls are identified 1 given the present inability to quantify precisely the time varying amount of terrigenous corg input to marine sediments absolute values of pco2 estimates based on bulk sedimentary corg are questionable 2 none of the low latitude sedimentary 13corg pco2 records shows the expected correlation between temporal changes in upwelling intensity and co2 estimates most likely due to the antagonistic influences of co2 aq and phytoplankton growth rate on 13corg 3 a detailed comparison of marine 13corg pco2 records with the vostok co2 record reveals significant differences in phasing specifically at the end of the last deglaciation and during the oxygen isotope stage 5 4 transition however in areas where equilibrium between oceanic and atmospheric co2 occurs for example the scs and the mediterranean the timing of changes in 13corg should agree with the co2 record from ice cores if 13corg is a reliable proxy for changes in co2 aq taken together the compilation of records presented here cautions the use of 13corg as an unambiguous tracer of dissolved molecular co2 in the surface ocean and calls for a re evaluation of the role of the low latitude ocean on temporal changes in atmospheric co2

periodic mid cretaceous oceanic anoxic events linked by oscillations of the phosphorus and oxygen biogeochemical cycles 1 a series of oceanic anoxic events oaes occurred in the mid cretaceous warm period 120 80 ma that have been linked with high rates of organic carbon burial warm high and low latitude temperatures and sea level changes oaes have been studied individually but a causal mechanism that connects them has been lacking we show that peaks in phosphorus accumulation in marine sediments broadly coincide with oaes 1a 1b 1d 2 and 3 and exhibit a 5 6 myr periodicity which for reactive p is prominent over 100 80 ma oxic anoxic oscillations of this frequency are also found in a model of the coupled n p c and o2 biogeochemical cycles these oscillations are maintained by positive feedbacks between phosphate concentration biological productivity and anoxia in the global ocean and counteracting but slower negative feedbacks involving changes in atmospheric oxygen an increase in phosphorus weathering rate above a critical threshold can shift the system into self sustaining oscillation this could have been caused by tectonic and volcanic forcing increasing atmospheric co2 and global warmth 120 80 ma augmented by the rise of flowering plants around 100 ma with a plausible forcing scenario we are able to reproduce the approximate timing of oaes 1a 1b 1d 2 and 3 in the model

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

a critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for late cretaceous global correlation abstract climate variability is driven by a complex interplay of global scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter regional correlation which in most cases cannot be obtained with biostratigraphic methods alone chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high resolution correlation over large distances but complications arise from a multitude of possible influences from local differences in biological diagenetic and physico chemical factors on individual 13c records that can mask the global signal to better assess the global versus local contribution in a 13c record it is necessary to compare numerous isotopic records on a global scale as a contribution to this objective this paper reviews bulk sediment 13ccarb records from the late cretaceous in order to identify differences and similarities in secular 13c trends that help establish a global reference 13c record for this period the study presents a global scale comparison of twenty 13c records from sections representing various palaeo latitudes in both hemispheres and different oceanic settings from the boreal tethys western interior indian ocean and pacific ocean and with various diagenetic overprinting the isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute 13c values and variation in amplitude between the sites these differences reflect the varying local influences e g from depositional settings bottom water age and diagenetic history whereas the concordant patterns in 13c shifts might represent 13c fluctuations in the global seawater dissolved inorganic carbon the latter is modulated by variations in organic matter burial relative to re mineralization in the global scale formation of authigenic carbonate and in partitioning of carbon between organic carbon and carbonate sinks these variations are mainly controlled by changes in climate and eustasy additionally some globally synchronous shifts in the bulk 13ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and thus can be globally synchronized by fluctuations in eustasy atmospheric and oceanic oxygen levels or in large scale oceanic circulation because the influence of early diagenetic cements on the bulk 13ccarb signal can but need not be synchronized chemostratigraphy should not be used as a stand alone method for trans continental correlation and especially minor isotopic shifts have to be interpreted with utmost care nevertheless the observed consistency of the 13c correlations confirms global scale applicability of bulk sediment 13c chemostratigraphy for the late cretaceous including sediments that underwent lithification and burial diagenesis such as the sediments from the himalayan and alpine sections limitations arise from increased uncertainties 1 in sediments with very low carbonate content 2 from larger 13c variability in sediments from very shallow marine environments 3 from unrecognized hiatuses or strong changes in sedimentation rates and 4 in sections with short stratigraphic coverage or with few biostratigraphic marker horizons the combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes facies or provincialism of key fossils by using an iterative approach to stepwise increase precision of the correlations isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested which helps to improve biostratigraphic zonations to assess zonal boundary ages and to identify useful criteria for defining late cretaceous stage boundaries many of which are still not formally defined the presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid cretaceous sea level high whereas diachroneity appears to be more pronounced during the late campanian and maastrichtian global sea level fall a similar pattern is observed for trans continental consistency in the 13c shifts graphic correlation of isotopic shifts magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo and magnetostratigraphy finally an attempt of a global average 13c stack is presented for the turonian through maastrichtian

nannoplankton productivity fluctuations and rhythmically bedded pelagic carbonates of the greenhorn limestone upper cretaceous abstract comparison of calcareous nannofossil assemblages from rhythmically interbedded calcareous shales and adjacent bioturbated chalks of the greenhorn limestone cenomanian turonian of the western interior basin indicate significant changes in phytoplankton paleocommunity structure between lithotypes significantly higher shannon diversity and evenness values in the chalk assemblages indicate more stable surface water conditions with lower fertility three taxa indicative of high surface water fertility are significantly more abundant in marlstone assemblages which suggests that calcareous shale marlstone deposition corresponded with fluctuating surface water conditions with relatively high fertility the higher surface fertility and concomitant production of organic matter resulted in sediment anoxia during marlstone deposition leading to high rates of organic carbon storage reduced phytoplankton production during chalk deposition allowed oxygenation of the sea floor and establishment of diverse benthic invertebrate communities

cenomanian to campanian carbon isotope chemostratigraphy from the western interior basin u s a abstract late cretaceous carbon isotope curves generated for localities in europe asia and the deep sea records have provided the foundation for development of a contiguous intercontinental chemostratigraphic framework despite the development of carbon isotope records from selected stratigraphic intervals in the western interior basin however a comprehensive 13c record comparable to those developed in europe and asia and from odp sites had not yet been completed this study reports a new high resolution cenomanian to campanian carbon isotope record for the central western interior basin of north america that makes a key contribution to the intercontinental correlation the curve is correlated to the well developed molluscan biostratigraphic framework for the western interior basin as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the 13c data were derived the new 13c record reflects not only major perturbations in the global carbon cycle such as the mid cenomanian event and the cenomanian turonian ocean anoxic event 2 but also smaller excursions that have been recognized in records from europe and asia this shows that the western interior shallow epeiric sea was not isolated for any appreciable part of cenomanian to early campanian time it consistently recorded changes in the global marine carbon cycle observed elsewhere a critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised late cretaceous time scale assignment of revised ages to western interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the western interior where similar carbon isotope records have been generated this chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

oceanic front in the greenhorn sea late middle through late cenomanian an abrupt lithofacies change between calcareous shale and noncalcareous shale occurs in strata deposited in the mid cretaceous greenhorn seaway in the southeastern corner of montana the facies were correlated lithostratigraphically using bentonites and calcarenites the lithocorrelations were then refined using ammonites foraminifera and calcareous nannofossils twenty five time slices were defined within the upper middle and lower upper cenomanian strata biofacies analysis indicate that lithofacies changes record the boundary or oceanic front between two water masses with distinctly different paleoceanographic conditions one water mass entered the seaway from the arctic and the other from the gulf of mexico tethys the microfauna and microflora permit interpretation of the environmental conditions in each water mass at times when the front was near vertical the two water masses were of the same density but of different temperatures and salinities

sedimentary environments and mechanisms of organic matter enrichment in the mesoproterozoic hongshuizhuang formation of northern china abstract the mesoproterozoic hongshuizhuang formation in jixian northern china is a hydrocarbon source unit containing abundant organic matter we investigated the mechanisms controlling this organic matter accumulation by analyzing the sedimentology and geochemistry of the qinghe section in the kuancheng region of northern china trace element geochemistry suggests that organic matter accumulation was controlled primarily by marine productivity which was the main determinant of redox conditions elevated marine productivity and consequent anoxic sulfidic bottom water conditions were coincident with accumulation of the organic rich toc 1 0 lower part of the hongshuizhuang formation deposition of the organic lean upper hongshuizhuang formation appears to have been coeval with diminished productivity and a transition to oxic suboxic redox conditions enhanced organic matter accumulation in the lower hongshuizhuang formation was promoted by a warm humid paleoclimate and submarine hydrothermal activity average rb sr ratios 3 42 and negative carbon isotope excursion reflect a warm climate likely caused by the release of volcanogenic co 2 warm conditions would have promoted continental weathering and increased the flux of nutrients into the oceans enhancing marine productivity an increased supply of nutrients and enhanced marine productivity would have depleted oxygen in the bottom water environment and favored the proliferation of sulfate reducing bacteria leading to anoxic sulfidic conditions the relative stability of 13 c carb values suggests that organic matter enrichment in the hongshuizhuang formation reflects changes in surface water productivity and redox conditions caused by climate induced sea level fluctuations shale normalized rare earth element ree distributions show a depletion in light rees and enrichment in heavy rees positive eu anomalies and mean y ho and ba sr ratios of 33 2 and 9 91 respectively suggesting that deposition of the hangshuizhuang formation was accompanied by submarine hydrothermal activity

phosphorus cycling from the margin to abyssal depths in the proto atlantic during oceanic anoxic event 2 abstract phosphorus p burial during the cenomanian turonian oceanic anoxic event oae 2 93 55 ma was studied using sediment records from four sites in the proto atlantic ocean the sites represent a variety of depositional settings from the continental margin and slope to the abyssal plain strong links between changing marine conditions during oae 2 and p cycling were observed in black shale sections on the continental margin and slope sedimentary p contents and p mars increased around the onset of oae 2 which may reflect enhanced productivity and p burial partly in the form of biogenic apatite fish debris during the main stage of oae 2 phosphorus was efficiently regenerated from the sediment resulting in p depleted sediments and high organic c corg total p ratios the increased availability of dissolved p may have helped to sustain high productivity during oae 2 the termination of oae 2 was associated with a strong recovery of p burial efficiency in the sediment sedimentary records from the two deep sites do not reveal such close links between different stages of oae 2 and the characteristics of p cycling here oae 2 was a period with maximum deposition of relatively thin black shale intervals that alternate with more oxic deep sea sediments the black shale layers record enhanced p regeneration from organic matter and in some cases p enrichment relative to the oxic sediments detailed chemical p fractionation was performed on sediment from all sites but the results were found to mostly reflect diagenesis and sample handling artifacts in these ancient sediments total p concentrations and the corg total p ratio appear to be the most robust indicators of p cycling and regeneration

phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2 four sections documenting the impact of the late cenomanian oceanic anoxic event oae 2 were studied in basins with different paleoenvironmental regimes accumulation rates of phosphorus p bound to iron organic matter and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of oae 2 with an associated increase in 13 c values accumulation rates of p return to preexcursion values in the interval where the 13 c record reaches its fi rst maximum an offset in time between the maximum in p accumulation and peaks in organic carbon burial hydrogen indices and corg preact molar ratios is explained by the evolution of oae 2 in the following steps 1 an increase in productivity increased the fl ux of organic matter and p into the sediments the preservation of organic matter was low and its oxidation released p which was predominantly mineralized 2 enhanced productivity and oxidation of organic matter created dysoxic bottom waters the preservation potential for organic matter increased whereas the sediment retention potential for p decreased 3 the latter effect sustained high primary productivity which led to an increase in the abundance of free oxygen in the ocean and atmosphere system after the sequestration of co 2 in the form of black shales this oxygen helped push the ocean back into equilibrium terminating black shale deposition and removing bioavailable p from the water column

euxinia and primary production in late cretaceous eastern equatorial atlantic surface waters fostered orbitally driven formation of marine black shales 1 oceanic anoxic events oae in the cretaceous represent major perturbations in the global climate and ocean system characterized by widespread deposition of organic carbon in the ocean the causes and effects of these events are poorly constrained mainly because of the lack of high resolution marine records here we report the distribution of molecular markers from a millennial scale record of coniacian santonian black shale oae 3 from ocean drilling program site 959 in the deep ivorian basin in the eastern equatorial atlantic highly branched isoprenoids and alkenone derived organic compounds indicate that diatoms and calcareous nanoplankton were important primary producers changes in redox sensitive trace metal accumulation and biomarkers of green sulfur bacteria provide evidence for extreme variations in redox conditions with intervals of lower photic zone euxinia pze accordingly oxygen in the coniacian santonian tropical atlantic was absent as during the cenomanian turonian boundary oae 2 but over more restricted geographic area and more limited time intervals we hypothesize that pze was a common phenomenon typical in large areas of tropical continental margins these conditions fostered sequestration of atmospheric co2 and thus helped cause the positive excursion in 13c of carbonate documented in higher latitude marine records

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

integrating 40ar 39ar u pb and astronomical clocks in the cretaceous niobrara formation western interior basin usa this study revises and improves the chronostratigraphic framework for late turonian through early campanian time based on work in the western interior u s and introduces new methods to better quantify uncertainties associated with the development of such time scales building on the unique attributes of the western interior basin which contains abundant volcanic ash beds and rhythmic strata interpreted to record orbital cycles we integrate new radioisotopic data of improved accuracy with a recently published astrochronologic framework for the niobrara formation new 40ar 39ar laser fusion ages corresponding to eight different ammonite biozones are determined by analysis of legacy samples as well as newly collected material these results are complemented by new u pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry ages from four biozones in the study interval when combined with published radioisotopic data from the cenomanian turonian boundary paired 206pb 238u and 40ar 39ar ages spanning cenomanian to campanian time support an astronomically calibrated fish canyon sanidine standard age of 28 201 ma stage boundary ages are estimated via integration of new radioisotopic data with the floating astrochronology for the niobrara formation the ages are determined by anchoring the long eccentricity bandpass from spectral analysis of the niobrara formation to radioisotopic ages with the lowest uncertainty proximal to the boundary and adding or subtracting time by parsing the 405 k y cycles the new stage boundary age determinations are 89 75 0 38 ma for the turonian coniacian 86 49 0 44 ma for the coniacian santonian and 84 19 0 38 ma for the santonian campanian boundary the 2 uncertainties for these estimates include systematic contributions from the radioisotopic measurements astrochronologic methods and geologic uncertainties related to stratigraphic correlation and the presence of hiatuses the latter geologic uncertainties have not been directly addressed in prior time scale studies and their determination was made possible by critical biostratigraphic observations each methodological approach employed in this study new radioisotopic analysis stratigraphic correlation astrochronology and ammonite and inoceramid biostratigraphy was critical for achieving the final result

redox sensitivity of p cycling during marine black shale formation dynamics of sulfidic and anoxic non sulfidic bottom waters abstract a high resolution geochemical record of a 120 cm black shale interval deposited during the coniacian santonian oceanic anoxic event 3 odp leg 207 site 1261 demerara rise has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo redox conditions high contents of organic matter sulfur and redox sensitive trace metals cd mo v zn as well as continuous lamination point to deposition under consistently oxygen free and largely sulfidic bottom water conditions however rapid and cyclic changes in deep ocean redox are documented by short term 15 20 ka intervals with decreased total organic carbon toc s and redox sensitive trace metal contents and in particular pronounced phosphorus peaks up to 2 5 wt p associated with elevated fe oxide contents sequential iron and phosphate extractions confirm that p is dominantly bound to iron oxides and incorporated into authigenic apatite preservation of this fe p coupling in an otherwise sulfidic depositional environment as indicated by fe speciation and high amounts of sulfurized organic matter may be unexpected and provides evidence for temporarily non sulfidic bottom waters however there is no evidence for deposition under oxic conditions instead sulfidic conditions were punctuated by periods of anoxic non sulfidic bottom waters during these periods phosphate was effectively scavenged during precipitation of iron oxyhydr oxides in the upper water column and was subsequently deposited and largely preserved at the sea floor after 15 25 ka sulfidic bottom water conditions were re established leading to the initial precipitation of cds zns and pyrite subsequently increasing concentrations of h2s in the water column led to extensive formation of sulfurized organic matter which effectively scavenged particle reactive mo complexes thiomolybdates at site 1261 sulfidic bottom waters lasted for 90 100 ka followed by another period of anoxic non sulfidic conditions lasting for 15 20 ka the observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface to mid waters from the south atlantic resulting in a lowering of the oxic anoxic chemocline in the water column alternatively sea water sulfate might have been stripped by long lasting high rates of sulfate reduction removing the ultimate source for hs production

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

iron limitation in the western interior seaway during the late cretaceous oae 3 and its role in phosphorus recycling and enhanced organic matter preservation the sedimentary record of the coniacian santonian oceanic anoxic event 3 oae 3 in the north american western interior seaway is characterized by a prolonged period of enhanced organic carbon oc burial this study investigates the role of fe in enhancing organic matter preservation and maintaining elevated primary productivity to sustain black shale deposition within the coniacian santonian aged niobrara formation in the usgs 1 portland core iron speciation results indicate the development of a reactive fe limitation coeval with reduced bioturbation and increased organic matter preservation suggesting that decreased sulfide buffering by reactive fe may have promoted enhanced organic matter preservation at the onset of oae 3 an fe limitation would also provide a feedback mechanism to sustain elevated primary productivity through enhanced phosphorus recycling additionally our results demonstrate inconsistencies between fe based and trace metal redox reconstructions iron indices from the portland core indicate a single stepwise change whereas the trace metal redox proxies indicate fluctuating redox conditions during and after oae 3 using fe speciation to reconstruct past redox conditions may be complicated by a number of factors including fe sequestration in diagenetic carbonate phases and efficient sedimentary pyrite formation in a system with limited fe supply and high levels of export production

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

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

cretaceous rhythmic bedding sequences a plausible link between orbital variations and climate abstract simple oscillation cycles have been recognized in cretaceous pelagic sequences as a marked periodicity in carbonate and or organic carbon content the estimated periodicities of these cycles resemble milankovitch type variations in orbital elements however during warm geologic periods the nature of the link between orbital variations and the sedimentary record has been problematic climate model studies show that the intensity of continental margin precipitation in specific low latitude regions is a function of land sea thermal contrast which is sensitive to orbital variations cretaceous climate model simulations are characterized by regions of intense precipitation the locations of which are controlled by geographic configuration in particular in the model simulation the northern margin of the tethys ocean has all the climatic characteristics necessary to exhibit a sensitivity to orbital variations detailed studies of the biota sedimentology and geochemistry of the bedding rhythms in greenhorn cyclothem in the western interior seaway of north america are best interpreted in terms of variations in precipitation runoff and stable stratification of the seaway combined the geologic and model studies support a link between orbital periodicities variations of intense precipitation associated with specific paleogeographic situations and cretaceous bedding patterns this hypothesis has important implications for the sensitivity of the atmosphere hydrosphere lithosphere system to external forcing

why are the δ13corg values in phanerozoic black shales more negative than in modern marine organic matter the 13corg values of phanerozoic black shales average 27 whereas those of modern marine organic matter average 20 the black shale isotopic values mimic those of continental organic matter yet their organic geochemical properties mandate that they contain predominantly marine organic matter hypotheses that proposed to explain the low 13c values of black shales include diagenetic losses of isotopically heavier organic matter components releases of isotopically light carbon from methane clathrates or extensive magmatic events greater photosynthetic discrimination against 13c during times of higher atmospheric pco2 and greenhouse climate stratification of the surface ocean that magnified photic zone recycling of isotopically light organic matter although the last possibility seems contrary to the vertical mixing that leads to the high productivity of modern oceanic upwelling systems it is consistent with the strongly stratified conditions that accompanied deposition of the organic carbon rich pliocene pleistocene sapropels of the mediterranean sea because most phanerozoic black shales contain evidence of photic zone anoxia similar to the sapropels well developed surface stratification of the oceans was likely involved in their formation existence of isotopically light land plant organic matter during several episodes of extensive magmatism that accompanied black shale deposition implies massive release of mantle co2 that added to the greenhouse conditions that favored oceanic stratification the 13c depletion common to most phanerozoic black shales apparently resulted from a greenhouse climate associated with elevated atmospheric pco2 that led to a strongly stratified ocean and photic zone recycling of organic matter in augmented by magmatic co2 releases

nitrogen cycling during the cretaceous cenomanian turonian oceanic anoxic event ii low 15n values ranging from 1 2 to 3 9 and atomic carbon nitrogen c n ratios of 25 50 are characteristic of black shales deposited during the cenomanian turonian boundary interval and oceanic anoxic event ii oae ii an observed antithetic relationship between c n ratios and 15n could suggest a predominance of terrestrially derived organic matter or a diagenetic control on 15n variability shifting bulk 15n values lower however hydrogen indices hi generally 450 and a positive correlation of hi with c n mitigates against a significant terrestrial organic matter fraction high c n values are likely the result preferential degradation of labile n rich compounds during early diagenesis and loss of n as ammonium from sediments through time a hypothetical model that considers the degradation of a 15n enriched labile protein fraction yields only small 1 2 negative shifts in 15n however 15n depletion during diagenesis is contrary to normal isotope kinetics which should result in 15n enrichment of bulk organic matter therefore we conclude that the bulk 15n values in this study reflect primary changes in the nitrogen cycle the 15n data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient nitrogen poor phosphorus replete waters during oae ii and from the mid cenomanian to santonian at demerara rise the low 15n values which are significantly lower than bulk 15n values in modern regions where nitrogen fixation is known to be important probably result from a more significant fraction of dissolved inorganic nitrogen being produced by nitrogen fixation during the peak of oae ii a marked shift to lower 15n values is observed this shift possibly reflects greater utilization of 15n depleted ammonium during a chemocline upward excursion cue dominance of low 15n values from other periods of more widespread marine anoxia is likely the result of similar processes

paleoceanographic and paleoclimatic similarities between mediterranean sapropels and cretaceous black shales pliocene quaternary sapropels of the mediterranean sea and mid cretaceous black shales share many distinctive properties organic carbon concentrations that often exceed 5 in both types of sequences record episodes of exceptional accumulation of organic matter although both are rich in marine organic matter they have high c n ratios that mimic those of land plant organic matter which suggests less efficient organic matter recycling than in the modern ocean the coupled presence of isorenieratene derivatives and low 15n values that result from microbial primary productivity indicates that photic zone anoxia existed during their formation and implies strong stratification of the surface ocean enrichments of redox sensitive metals and sediment laminations indicate that anoxia existed deeper in the water column and at the seafloor multiple proxies indicate freshening of surface waters of the mediterranean and imply periods of wetter climate during times of sapropel deposition episodes of black shale deposition similarly coincide with times of wetter climate these comparisons suggest that the wetter climate created similar conditions of surface salinity stratification that enhanced microbial primary production and magnified organic matter export during deposition of both the mediterranean sapropels and mid cretaceous black shales

detection quantification and significance of hiatuses in pelagic and hemipelagic strata temporal gaps in the stratigraphic record have important implications for the interpretation of stratigraphically rapid geochemical and paleobiologic changes for the development of high resolution time scales e g orbital time scales and for deciphering the response of depositional systems to climatic change and basin evolution e g accommodation space vs sediment supply in ancient pelagic and hemipelagic strata the identification of relatively short hiatus 10 3 10 6 years is commonly challenged by the resolution limits of geochronologic techniques in this study a quantitative method is developed to identify and quantify hiatuses in strata where milankovitch orbital cycles are documented the new method is based on the interpretation of evolutive harmonic analysis eha results and permits estimation of minimum durations for the temporal gaps application of this technique to an optical densitometry data series derived from the cenomanian turonian c t bridge creek limestone member permits quantification of hiatus within the unit and addresses important questions about abrupt changes in biogeochemical proxy records across the boundary interval integration of the new method with stratigraphic data and geochemical burial flux estimates permits a detailed reconstruction of the controls on sediment delivery and hiatus generation including a refined analysis of the orbital scale linkages between climate and sedimentation d 2004 elsevier b v all rights reserved

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

cyclostratigraphy of the upper cretaceous niobrara formation western interior u s a a coniacian santonian orbital timescale abstract the turonian campanian niobrara formation of the western interior basin u s a is characterized by decimeter scale rhythmic alternations of chalk and marl beds and decameter scale oscillations of chalky and marly facies this study applies recent advances in quantitative cyclostratigraphic analysis to high resolution geophysical records in order to test for an orbital signal we studied records of the entire formation 85 m from two wells in colorado 40 17 n 104 38 w 40 14 n 104 41 w the study utilized high resolution time series of borehole resistivity measured from formation microimager tools fmi advanced spectral techniques indicate the presence of eccentricity obliquity and precession periodicities throughout the study interval deviations of bundling ratios in the lower fort hays member from those predicted by simple eccentricity modulation of precession previously reported in the literature are likely due to the influence of obliquity deconvolution and frequency tracking of orbital components were used to reconstruct sedimentation rates for the niobrara formation and thus develop a high resolution orbital timescale which permits calculations of accumulation rates for sedimentary components and the duration of inclusive stages substages and in some cases biozones the niobrara formation in the studied cores appears to be hiatus free and therefore provides a continuous record of rhythmic deposition for astronomical timescale development the relationship between carbonate content and sedimentation rate throughout the niobrara formation indicates that the decameter scale oscillations of chalk and marl are dominantly driven by variations in siliciclastic flux dilution the duration derived from the orbital timescale between the turonian coniacian and coniacian santonian boundaries is 3 40 0 13 myr which is generally consistent with radiometric estimates for the coniacian the orbitally derived duration of the santonian stage is 2 39 0 15 myr which is very similar to estimates based on curve fitting between radiometric dates development of high resolution orbital chronometers provides excellent time resolution in intervals that lack radiometric time control or where control points are widely spaced

formation of sedimentary bedding couplets in the western interior seaway of north america implications from climate system modeling we use global climate simulations across one precessional cycle to investigate the effect of orbitally induced climatic changes on sedimentation in the western interior seaway wis of north america at the cenomanian turonian boundary the simulations include a control run with no orbital eccentricity and hence no precession cycle and four runs with varying precession with an eccentricity of 0 05 having 1 northern spring equinox at perihelion 2 northern winter solstice at perihelion 3 northern fall equinox at perihelion and 4 northern summer solstice at perihelion these numeric climate simulations and field observations suggest that the wis at the cenomanian turonian boundary can be divided into three latitudinal units 1 a northern unit alberta montana between 51 n and 71 n paleolatitude where conditions remained constant under the influence of steady inflow of low salinity cool waters which were devoid of calcareous plankton flowed in from the arctic preventing the development of bedding couplets 2 a central unit wyoming colorado between 41 n and 51 n paleolatitude where runoff from western north america wna was reduced by more than half when the northern hemisphere winter solstice coincided with perihelion where bedding couplets are well developed the central part of the wis was characterized by warm saline waters with abundant calcareous plankton however it experienced high summer surface runoff from the sevier highlands to the west during all orbital configurations except when the winters were unusually warm with the northern hemisphere winter solstice occurring at perihelion seasonal dilution of the surface waters of the seaway may have resulted in formation of a fresh water lid with stratification of the water column throughout most of the precession cycle when the northern hemisphere winter solstice was at perihelion reduced runoff would promote vertical mixing concomitantly a steady detrital sediment supply would occur in summer throughout the precession cycle except when the nh winter solstice was at perihelion when it would be much reduced thus the marlstone of the limestone marlstone couplets would represent most of the time of the precession cycle and the limestone layers would represent the time when the nh winter solstice was near perihelion 3 a southern region new mexico northern mexico from 21 to 42 n paleolatitude where the detrital sediment supply was much reduced and couplets are thicker and less well developed

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

water mass characteristics in the cenomanian us western interior seaway as indicated by stable isotopes of calcareous organisms abstract stable oxygen isotopes taken from taxon specific planktic foraminifera are potential sources of water mass density proxy data and paleoclimate information material suitable for stable isotope analysis is uncommon in the middle to late cenomanian strata of the western interior of the usa however well preserved material from 17 correlative horizons at five localities across se montana and ne wyoming has provided an opportunity to obtain reliable 18 o data from foraminiferal samples fine fraction carbonate e g calcareous nannofossils and inoceramid prisms with the exception of inoceramids which for a benthic organism have stable isotopic compositions resembling surface dwelling calcareous organisms these data indicate that the water column was vertically stratified and water masses were anomalously depleted in 18 o within samples planktic and benthic foraminifera display strong vertical gradients in 18 o and 13 c of several per mil the vertical gradient of 18 o ranges from more negative nearer the sea surface to less negative at the sea floor with a gradient of about 4 this implies less saline warmer waters near the surface with increasingly more saline colder waters with depth this isotopic distribution indicates a stably stratified water column at least seasonally in addition a persistent vertical carbon isotope gradient of 2 3 suggests a strong nutrient gradient that if mixed would result in high surface water fertility preservation of high amounts of organic carbon in the sediments corroborates this inference although the water column was stratified overall the nutrients necessary to promote high productivity were clearly renewed at least seasonally nutrient renewal could have been achieved by 1 winter cooling of the upper layer allowing deeper seasonal mixing with nutrient rich deep waters 2 seasonal shallowing of the pycnocline into the photic zone 3 entrainment and decomposition of organic matter at the previously proposed frontal convergence 4 upwelling of nutrient rich deep waters along the previously proposed oceanic front or 5 mixing of shelf waters with more oceanic waters across an oceanic front

stratigraphic and spatial distribution of ochre and ochre processing tools at porc epic cave dire dawa ethiopia abstract reassessment of the archaeological assemblages recovered by kenneth d williamson in 1975 and 1976 at porc epic cave dire dawa ethiopia demonstrates that the middle stone age msa levels of this site yielded one of the richest known collections of ochre and ochre processing tools from this period in terms of quantity we analyze the vertical and horizontal distribution of all ochre fragments n 4213 and ochre processing tools n 23 of known provenance and compare them with the distribution of other categories of archaeological remains our results suggest that no major post depositional reworking occurred at the site virtually no ochre fragments and processing tools are recorded in the superficial levels of the site 0 60 cm below datum concomitant and statistically significant changes in the location of ochre and ochre processing tool concentrations are observed at various depth intervals in deeper levels interpreted as changes in the location of the area devoted to ochre processing comparison of the vertical distributions of ochre fragments and lithics highlights that in most cases ochre and lithics covary the vertical distribution of gastropod opercula interpreted by other authors as ornaments and of ochre fragments throughout the sequence also follows the same trends however concentrations of ochre and ochre processing tools do not coincide with that of the opercula spatially 14c determinations obtained at porc epic indicate a relatively short chronology for the accumulation of the main archaeological deposits and date to ca 40 ka cal bp the levels containing most of the ochre this is consistent with the fact that no significant typo technological variations in the lithics are observed throughout the sequence and argues in favour of the site reflecting a phase of the transition from the middle stone age to the later stone age lsa in this region of africa

米国 西部内陸 上部白亜系niobrara層のサイクロ層序学 コニアシアン サントニアン軌道時間尺度

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

marine carbon burial flux and the carbon isotope record of late cretaceous coniacian santonian oceanic anoxic event iii abstract episodes of widespread distribution of organic rich marine facies within relatively narrow stratigraphic intervals have been interpreted as oceanic anoxic events oaes there are a number of such intervals in the upper cretaceous some of which also exhibit significant positive excursions in carbon isotope records as a result a general model of the relationship between enhanced organic carbon burial and positive c isotope shifts has emerged carbon isotope stratigraphy has therefore developed the dual utility of a chronostratigraphic tool and a means to help identify and define intervals of exceptional organic matter burial and preservation however variations in regional carbon isotope records of globally documented events suggest that the relationship between organic carbon burial flux and magnitude of carbon isotope excursion may not be entirely straightforward for example strata of coniacian santonian age have long been recognized for enhanced organic content in many areas but the designation of oceanic anoxic event iii for this interval has been rather equivocal in the literature mostly due to the weak positive 13 c excursion 0 5 yet in some areas organic carbon accumulation rates for coniacian santonian strata are roughly double that of the older oae ii which is marked by a 2 4 shift in 13 c interestingly the burial flux of carbonate which leads to depletion rather than enrichment of the c isotope signal is also significantly elevated during coniacian santonian time in this study the role of variations in organic carbon and carbonate accumulation rates on carbon isotopic expression are explored through application of data on the composition accumulation rate and areal distribution of end member facies types to the development of a global carbon isotopic mass balance model the results are used to explore the hypothesis that net organic carbon burial during oae iii was not accurately represented in the carbon isotopic record these results have important implications for interpretation of c isotope records related to past perturbations of the global carbon cycle

isotopic evaluation of ocean circulation in the late cretaceous north american seaway the role of the north american seaway in creating and maintaining late cretaceous global greenhouse conditions has been unclear an isotopic analysis of marine turtle and fish fossils from western kansas and the mississippi embayment reveals that the inflow of tethyan surface waters to the seaway was limited during the mid and late cretaceous period north america was split by the north south oriented western interior seaway its role in creating and maintaining late cretaceous global greenhouse conditions remains unclear different palaeoceanographic reconstructions portray diverse circulation patterns1 2 3 the southward extent of relatively cool low salinity low 18o surface waters critically distinguishes among these models but past studies of invertebrates could not independently assess water temperature and isotopic compositions here we present oxygen isotopes in biophosphate from coeval marine turtle and fish fossils from western kansas representing the east central seaway and from the mississippi embayment representing the marginal tethys ocean our analyses yield precise seawater isotopic values and geographic temperature differences during the main transition from the coniacian to the early campanian age 87 82 myr and indicate that the seaway oxygen isotope value and salinity were 2 and 3 lower respectively than in the marginal tethys ocean we infer that the influence of northern freshwater probably reached as far south as kansas our revised values imply relatively large temperature differences between the mississippi embayment and central seaway explain the documented regional latitudinal palaeobiogeographic zonation4 5 and support models with relatively little inflow of surface waters from the tethys ocean to the western interior seaway2 3

comparison of organic and inorganic carbon isotope patterns across the frasnian famennian boundary abstract the carbon isotopic composition of organic matter is reported for two frasnian famennian boundary sections from the rheinische schiefergebirge germany during the late frasnian 13 c org values commonly range from 27 5 to 26 highest 13 c org values around 24 are encountered immediately above and below the kellwasser horizons all samples from the kellwasser horizons are depleted in 13 c org by 2 5 to 4 7 this depletion is explained by a higher proportion of biomass derived from isotopically depleted chemoautotrophic bacteria a comparison of the positive 13 c excursions shows that the 13 c org shifts precede the 13 c carb shifts by some 10 5 years consequently 13 c values document a shift towards lower values below the upper kellwasser horizon a contribution of terrestrial organic matter as well as a thermal alteration of the 13 c org signals do not provide compelling explanations for the earlier 13 c org shift increases in primary productivity or carbon burial rate will change the co 2 aq content of surface waters affect the carbon isotope fractionation during photosynthetic carbon uptake and thus enrich organic carbon in 13 c however both processes cannot account for the earlier onset of the 13 c org shift because the 13 c carb record should document the resulting 13 c enrichment in surface waters as well a reduction in the calcium carbonate precipitation rate due to the global extinction of the reef ecosystem may have played an important role in reducing the co 2 aq content of surface waters without changing the isotopic composition of surface waters whether this process or other factors such as a rise in sea surface temperature or a change in the phytoplankton association account for the earlier onset of the positive shift in the 13 c org curve must be determined by further studies that may be able to confirm the global significance of the reported 13 c org pattern in frasnian famennian boundary sections from other parts of the globe

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

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

orbital time scale and new c isotope record for cenomanian turonian boundary stratotype previous time scales for the cenomanian turonian boundary ctb interval containing oceanic anoxic event ii oae ii vary by a factor of three in this paper we present a new orbital time scale for the ctb stratotype established independently of radiometric biostratigraphic or geochemical data sets update revisions of ctb biostratigraphic zonation and provide a new detailed carbon isotopic record for the ctb study interval the orbital time scale allows an independent assessment of basal biozone ages relative to the new ctb date of 93 55 ma gts04 the d 13 corg data document the abrupt onset of oae ii significant variability in d 13 corg values and values enriched to almost 222 these new data underscore the difficulty in defining oae ii termination using the new isotope curve and time scale estimates of oae ii duration can be determined and exported to other sites based on integration of well established chemostratigraphic and biostratigraphic datums the new data will allow more accurate calculations of biogeochemical and paleobiologic rates across the ctb

redox controlled preservation of organic matter during oae 3 within the western interior seaway during the cretaceous widespread black shale deposition occurred during a series of oceanic anoxic events oaes multiple processes are known to control the deposition of marine black shales including changes in primary productivity organic matter preservation and dilution oaes offer an opportunity to evaluate the relative roles of these forcing factors the youngest of these events the coniacian to santonian oae 3 resulted in a prolonged organic carbon burial event in shallow and restricted marine environments including the western interior seaway new high resolution isotope organic and trace metal records from the latest turonian to early santonian niobrara formation are used to characterize the amount and composition of organic matter preserved as well as the geochemical conditions under which it accumulated redox sensitive metals mo mn and re indicate a gradual drawdown of oxygen leading into the abrupt onset of organic carbon rich up to 8 deposition high hydrogen indices hi and organic carbon to total nitrogen ratios c n demonstrate that the elemental composition of preserved marine organic matter is distinct under different redox conditions local changes in 13c indicate that redox controlled early diagenesis can also significantly alter 13corg records these results demonstrate that the development of anoxia is of primary importance in triggering the prolonged carbon burial in the niobrara formation sea level reconstructions 18o results and mo total organic carbon ratios suggest that stratification and enhanced bottom water restriction caused the drawdown of bottom water oxygen increased nutrients from benthic regeneration and or continental runoff may have sustained primary productivity

integrated biostratigraphy and carbon isotope stratigraphy for the upper cretaceous kanguk formation of the high arctic sverdrup basin canada