sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

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

mid cretaceous oceanic red beds in the umbria marche basin central italy constraints on paleoceanography and paleoclimate abstract detailed studies of the mid cretaceous sedimentary strata in the umbria marche basin in italy revealed that aside from several well known organic rich black shale horizons that record oaes several varicolored mainly reddish horizons indicate oxic conditions at the ocean bottom eight such horizons have been identified in aptian cenomanian sequences in the umbria marche basin the dysoxic oxic beds alternate regularly but not cyclically and seem to be the result of non random processes their occurrence is not a completely random process the duration of deposition of these oceanic red beds orbs varies from 0 13 my orb4 recorded in the ticinella primula zone to 4 54 my for orb1 which spans the globigerinelloides ferreolensis zone to the ticinella bejaouaensis zone in the piobbico core mid cretaceous orbs are not a local phenomenon because they occur in the tethyan deposits in the southern and austrian alps the carpathians the northern caucasus the central north atlantic in northeastern england and in the western himalayas they provide evidence for periodic changes in redox conditions at the ocean bottom such changes could have been caused by changes in bioproductivity basin geometry sedimentation rates paleocirculation and or production of bottom waters with higher content of dissolved oxygen in response to changes in paleoclimate we suggest that the periodic inflow of colder more oxygenated bottom waters was the probable cause of orbs development either as a result of changes in the ocean bottom topography or as a result of brief cool climate periods however reliable proxies for changes in deep ocean circulation are still lacking if orbs were the result of the paleoclimate and therefore indirectly caused by changes in co2 in atmosphere they document the increased sensitivity and instability of the mid cretaceous climate thus changes in ocean dynamics were on a scale of several hundred thousand years to several million years which has not been considered by most theories of co2 cycling mid cretaceous greenhouse paleoclimate and paleocean dynamics

plate tectonic paleoceanographic hypothesis for cretaceous source rocks and cherts of northern south america new paleocontinental reconstructions show a northern migration of the south american plate with respect to the paleoequator from the jurassic to the late cretaceous this movement caused the northern margin of south america to migrate from a position south to a position north of the paleoequator ekman transport generated net surface water movement towards the south during times when northern south america was south of the paleoequator this situation favored downwelling and prevented jurassic and earliest cretaceous marine source rocks from being deposited when northern south america was north of the paleoequator ekman transport forced net water movement to the north favoring upwelling paleoproductivity and the deposition of one of the best marine source rocks known the la luna villeta and equivalents this plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern south america the stratigraphic record reflects this increase in paleoproductivity through time this can be observed in facies non calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages followed by stressed foraminifer populations and finally by radiolarians total organic carbon and source rock quality were affected by this longmore term increase in paleoproductivity but also and more markedly by a punctuated sequence stratigraphic record dominated by low frequency changes in relative sea level the magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon less

palaeoenvironmental analysis of late cretaceous dinoflagellate cyst assemblages using high resolution sample correlation from the western interior basin usa abstract the cretaceous geological record of the western interior seaway of north america is one of the most thoroughly studied in the world extensive work on the lithostratigraphy biostratigraphy and geochemistry has resulted in a high resolution chronostratigraphic framework allowing precise bed by bed correlation between sections hundreds of kilometres apart late cenomanian to early turonian marine strata from five sites along a transect from arizona to kansas have been analysed for their palynological assemblages at the time of deposition the sites are thought to have been palaeoenvironmentally very different in terms of shoreline proximity bathymetry and salinity precise correlation of samples between the sites using the high resolution stratigraphy has provided a valuable testing ground for a comparison of the dinoflagellate cyst assemblages a number of species are determined to have palaeoenvironmental preferences in terms of salinity and shoreline proximity and this is supported by integration with the lithostratigraphy macropalaeontology micropalaeontology and geochemistry previous palaeoenvironmental interpretations suggest that one kansas site had comparatively much higher levels of primary productivity and this is reflected in the high ratio at this site of peridinioid to gonyaulacoid cysts the high resolution correlation also shows that a number of the biostratigraphically useful dinoflagellate cyst taxa had synchronous or near synchronous range tops and bases across the basin this integrated high resolution study with tight chronostratigraphic control supports the use of dinoflagellate cysts not only as biostratigraphic tools but also for palaeoenvironmental and palaeoecological interpretation

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

black shale deposition and faunal overturn in the devonian appalachian basin clastic starvation seasonal water column mixing and efficient biolimiting nutrient recycling integrated geochemical data suggest that black shale deposition in the devonian geneseo formation of western new york was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water column stratification and mixing once established however black shale deposition was maintained through efficient recycling of biolimiting nutrients which enhanced primary productivity recycling efficiency was achieved through a positive feedback loop of oscillating benthic redox conditions that enhanced n and p regeneration from sediments sustained high primary productivity by returning nutrients to the photic zone during mixing and ensured a downward flux of organic matter that drove or enhanced the episodic development of benthic anoxia during stratification this feedback was ultimately disrupted by rising siliciclastic influx which diluted organic matter and restored benthic redox stability the abrupt overturn of diverse long standing appalachian basin marine communities may have been the result of trophic resource destabilization during geneseo deposition

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

early diagenesis in sediments from danish coastal waters microbial activity and mn fe s geochemistry abstract depth distributions of bacterial respiration of o2 no3 and so42 were compared with geochemical data for mn fe and s in coastal sediments from water depths between 26 and 520 m as water depth increased the zone of so42 respiration was found deeper in the sediment and was eventually separated from the surface located activity of o2 and no2 respiration at the deepest station additional so42 reduction activity was observed in small detrital aggregates on the sediment surface dissolved mn2 and fe2 appeared between the o2 plus no3 containing surface layer and the h2s plus fes containing sediment below this was a result of mn and fe reductions coupled to either the oxidation of sulfide or the mineralization of organic matter tracer experiments showed that both fes fes2 and s0 were important radiolabelled products of sulfate respiration in this intermediate zone in the same zone the overall degradation of organic matter seemed to be underestimated by the assay of so2 4 respiration and additional mineralization by mn and fe reductions was likely

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

surface ocean variability at galapagos from 1936 1982 calibration of geochemical tracers in corals a variety of geochemical tracers has been developed in reef corals as a means of reconstructing the natural variability of the tropical surface ocean over wide ranging time frames the purpose of this paper is to calibrate the performance of five of these tracers in a modern coral colony over an extended period a 47 year growth interval 1936 1982 in a colony of pavona clavus taken from san cristobal island galapagos islands was sectioned into 187 quarterly intervals and analyzed for 18o 13o ba ca cd ca and mn ca the resulting time series are compared with eastern pacific sea surface temperatures one of few instrumental data bases available for calibration over this time period linear least squares regressions of four of the tracers 18o 13o ba ca cd ca against peruvian sst show highly significant correlations p 0 0001 over the annual biennial and enso 3 8 years frequency bands cross spectral comparisons show even stronger coherency with sst frequently accounting for 70 80 of the variance in these tracers these results as well as the phase relationships determined from the spectral analyses suggest that the coupling between sst and 18o and the nutrientlike tracers ba and cd is controlled principally by seasonal upwelling cycles and interannual interruptions of these cycles brought about by el nino and anti el nino phenomena an inverse relationship between sst and 13c has its primary origins in the co occurrence of the warm sst phase with high light levels during the first half of the calendar year the association with sunlight derives from the photosynthetic response of algal symbionts which results in fractionation of light and heavy carbon isotopes between soft tissues and caco3 skeleton the fifth tracer the transition metal mn exhibits poorer correlations against both sst and the other tracers slight shifts in phasing of the historical mn ca annual cycle suggest that the general water column distribution of this tracer which is the reverse of a nutrient may not be stable the erratic behavior of mn illustrates how complex hydrography near galapagos may influence tracers with diverse source signatures

seasonal and interannual variability of the mid holocene east asian monsoon in coral δ18o records from the south china sea understanding the full range of past monsoon variability with reference to specific monsoon seasons is essential to test coupled climate models and improve their predictive capabilities we present a 54 year long high resolution skeletal oxygen isotope 6180 record extracted from a well preserved massive porites sp coral at hainan island south china sea to investigate east asian monsoon variability during summer and winter similar to 4400 calendar yr ago analysis of modem coral 6180 confirms that porites from hainan island are well positioned to record winter monsoon forcing of sea surface temperature sst as well as the influence of summer monsoon rainfall on sea surface salinity sss the coral record for similar to 4400 yr ago shows similar to 9 amplification of the annual cycle of 6 delta o 18 in good agreement with coupled ocean atmosphere models showing higher summer rainfall lower coral 618 0 and cooler winter ssts higher coral delta o 18 in response to greater northern hemisphere insolation seasonality during the middle holocene mean ssts in the south china sea during the mid holocene were within 0 5 degrees c of modem values yet the mean 6 180 for the fossil coral is similar to 0 6 parts per thousand higher than that for the modem coral suggesting that the 6 180 of surface seawater was higher by at least similar to 0 5 parts per thousand relative to modem values the o 18 enrichment is likely to be driven by greater advection of moisture towards the asian landmass enhanced monsoon wind induced evaporation and vertical mixing and or invigorated advection of saltier o 18 enriched pacific water into the relatively fresh south china sea the o 18 enrichment of the northern south china sea similar to 4400 yr ago contributes to mounting evidence for recent freshening of the tropical western pacific today winter sst and summer sss variability in the south china sea reflect the interannual influence of enso and the biennial variability inherent to monsoon precipitation spectral analysis of winter ssts similar to 4400 yr ago reveals a strong enso cycle at 6 7 y which is significantly longer than the average 3 6 y cycle observed since 1970 the results suggest that the influence of enso on winter ssts in the south china sea was well established by similar to 4400 yr ago however spectral analysis of summer sss similar to 4400 yr ago shows no significant enso cycle suggesting that teleconnections between enso and summer monsoon rainfall were restricted taken together the results indicate marked differences in enso monsoon interactions during the winter and summer monsoon seasons in the past the fossil coral delta o 18 record also shows that the amplitude of interannual sst and sss variability was stronger similar to 4400 yr ago despite enso variability being significantly weaker in the pacific region thus it appears that the strengthened mid holocene monsoon was sensitive to forces other than enso that acted as alternative drivers of interannual monsoon variability if this is the case greater interannual climate variability could accompany the strengthening of the asian monsoon predicted to occur during the 21st century as transient greenhouse warming preferentially warms eurasia even if enso perturbations remain relatively stable c 2005 elsevier b v all rights reserved

trace elemental derived paleoceanographic and paleoclimatic conditions for pleistocene eastern mediterranean sapropels abstract eastern mediterranean sediments are characterized by cyclic deposition of organic rich sediments known as sapropels enhanced primary productivity combined with bottom water oxygen depletion are thought to be the main drivers for sapropel deposition we selected sapropel layers from a suite of odp leg 160 cores and applied a set of geochemical proxies to determine paleo productivity variations redox conditions of the water column during deposition and provenance of detrital material high sedimentary ba al and corg contents indicate enhanced primary production whereas the sedimentary la lu ratio points to an enhanced contribution from a north african riverine source during sapropel formation these features are especially pronounced on sapropels s5 and s7 deposited during a particularly warm climatic interval this indicates a more intense north african drainage weathering and consequently run off for those sapropels that have the most enhanced expression of productivity too correspondingly the latter has also resulted in bottom water redox conditions that have been more severe during these sapropels than during others deepwater formation from adriatic and aegean areas thought to be mainly controlled by sustained cooling of preconditioned surface waters triggers the onset of bottomwater ventilation thus sapropel duration our data therefore suggest that the intensity of sapropel formation is determined by the north african monsoonal system whereas their duration is directed by northern borderlands climatic conditions

temporal and spatial variability of the oxygen isotopic composition of massive corals from the south china sea influence of the asian monsoon coral colonies of porites lutea and p lobata were collected from areas to the east and south offshore of hainan island south china sea oxygen isotope ratios o 18 o 16 were analyzed along the major axis of growth at a resolution of 25 28 samples within an annual band from three colonies giving data series lengths of 15 20 and 30 years coral delta o 18 correlates well with sea surface temperature sst throughout most years particularly when the asian winter monsoon prevails over the region due to the same seasonal phases of sst and sea surface salinity sss it is estimated that most of the seasonal features of coral delta o 18 are controlled by changes in sst with a significant contribution of sss this indicates the importance of temperature as determined by the asian winter monsoon as a control on seasonal coral delta o 18 variations in the south china sea given the fact that annual sss maxima show minor inter annual changes the inter annual change of annual coral delta o 18 maximum mainly reflects the sst induced by the winter monsoon while the coral delta o 18 is mainly controlled by sst deviations of the delta o 18 from sst correlate statistically with sea surface salinity particularly for summer extreme events when sst reaches its annual maximum with minor inter annual change therefore we suggest that the inter annual variation of the annual coral delta o 18 minima is mainly controlled by seawater composition seawater composition analysis indicates that its delta o 18 and salinity are simultaneously affected by freshwater inputs primarily from precipitation which is mainly supplied by the asian summer monsoon thus seasonal alternations of the winter and summer monsoon mainly control the coral delta o 18 thereby allowing reconstruction of these monsoonal variables the three coral records consistently reveal clear inter decadal trends in delta o 18 a gradual increase from 1968 to 1987 and a subsequent decrease from 1987 to 2003 these inter decadal trends are roughly consistent with salinity changes but not with temperature and precipitation suggesting that seawater composition controlled by freshwater inputs from distant source areas rather than from local precipitation is responsible for the trends in seawater composition and coral delta o 18 over the last 30 years comparison of the three coral records indicates that spatial variations in coral delta o 18 coincide with variations in seawater salinity and local precipitation but not with temperature this confirms the dominant role of seawater composition mainly controlled by monsoonal precipitation on the spatial variability of coral delta o 18 in the south china sea c 2006 elsevier b v all rights reserved

carbon sulfur plots to show diagenetic and epigenetic sulfidation in sediments abstract organic carbon vs sulfide sulfur plots are now being used regularly by many geochemists to help understand recent and ancient depositional environments and diagenetic processes usually these plots are useful to recognize nonmarine vs marine environments or oxic vs anoxic vs euxinic depositional environments however c vs s plots can also indicate diagenetic and epigenetic events that produce excess sulfide four new examples are presented and discussed

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

dinoflagellate cysts paleoproductivity and upwelling systems a late cretaceous example from israel abstract diverse assemblages of dinoflagellate cysts occur in coniacian maastrichtian sedimentary sequences in israel which represent the inner shallower and outer deeper seaward belt of a late cretaceous upwelling system along the margin of the southern tethys the assemblages are composed mainly of peridinioid p and gonyaulacoid g cysts in varying concentrations it is suggested that the observed fluctuations in the numerical peridinioid gonyaulacoid p g cyst ratio reflect mainly changes in upwelling intensity and productivity in the studied area high p g values represent a higher productivity and vice versa thep g curve indicates a generally high productivity during the campanian followed by a decrease during the maastrichtian the inner part of the upwelling region is characterized by higherp g values representing a higher productivity the similarity between thep g ratio curve and the foraminiferal based paleoproductivity curve from the same sections supports the utility of thep g ratio as a reliable productivity indicator applied here for the first time to upper cretaceous sediments

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part ii direct and indirect components of the response the wintertime atmospheric circulation responses to observed patterns of north atlantic sea surface temperature and sea ice cover trends in recent decades are studied by means of experiments with an atmospheric general circulation model here the relationship between the forced responses and the dominant pattern of internally generated atmospheric variability is focused on the total response is partioned into a portion that projects onto the leading mode of internal variability the indirect response and a portion that is the residual from that projection the direct response this empirical decomposition yields physically meaningful patterns whose distinctive horizontal and vertical structures imply different governing mechanisms the indirect response which dominates the total geopotential height response is hemispheric in scale with resemblance to the north atlantic oscillation or northern hemisphere annular mode and equivalent barotropic in the vertical from the surface to the tropopause in contrast the direct response is localized to the vicinity of the surface thermal anomaly sst or sea ice and exhibits a baroclinic structure in the vertical with a surface trough and upper level ridge in the case of a positive heating anomaly consistent with theoretical models of the linear baroclinic response to extratropical thermal forcing both components of the response scale linearly with respect to the amplitude of the forcing but nonlinearly with respect to the polarity of the forcing the deeper vertical penetration of anomalous heating compared to cooling is suggested to play a role in the nonlinearity of the response to sst forcing

the toarcian oceanic anoxic event in the western saharan atlas algeria north african paleomargin role of anoxia and productivity we used an integrated analysis of benthic foraminiferal assemblages geochemical proxies paleoproductivity redox and detrital proxies and c and o stable isotopes to characterize the toarcian oceanic anoxic event along the north african paleomargin more precisely in the saharan atlas algeria special emphasis was placed on time intervals previous to the anoxic event and the recovery of normal conditions after this event the fisher9s alpha diversity of the foraminiferal assemblages decreased with respect to the end of the pliensbachian in the polymorphum zone with lower values of shallow infaunal forms and an increase in opportunists reinholdella lenticulina and eoguttulina this indicates fluctuations in the oxygenation degree of the infaunal microhabitat in the polymorphum zone despite the fact that redox proxies do not show any fluctuations indicating that dysoxic conditions were not reached the lower part of the levisoni zone reflects an abrupt paleoenvironmental change evidenced by the extinction of foraminifera enrichment in redox sensitive elements increase in detrital and paleoproductivity proxies and fluctuations of 13 c and 18 o an anoxic or strongly dysoxic event happened by the polymorphum levisoni zone boundary in the western saharan atlas coincident with increasing eolian detrital input and paleoproductivity the upper part of the levisoni zone represents a return to normal oxic conditions and the slow recovery of benthic foraminiferal assemblages dominated by opportunistic forms lenticulina eoguttulina and reinholdella of low diversity the toarcian oceanic anoxic event occurred in a generalized transgression that may have favored water stratification and confinement of bottom waters in the subbasins developed in the atlasic domain this research demonstrates the potential of the integration of data from foraminiferal assemblages and a wide range of geochemical proxies for understanding anoxic events during the mesozoic

pyrite framboid size distribution as a record for relative variations in sedimentation rate an example on the toarcian oceanic anoxic event in southiberian palaeomargin the early toarcian oceanic anoxic event t oae represents one of the major alterations of the carbon cycle of the mesozoic period despite being globally recognized and particularly represented within the tethys realm its expression in the sedimentary record is highly variable depending on the studied section which suggests local environmental factors exert a major control on the resulting lithological appearance of the event we investigated the fuente vidriera section in the eastern external subbetic of the betic cordillera spain where the lower jurassic is represented by alternate layers of marls and many limestones and the t oae is identified by a major delta c 13 excursion micropalaeontological ichnofacies and geochemical evidences 1 for this study we analyzed pyrite framboid size distribution of the sedimentary sequence in fuente vidriera the outcome according to previous studies on pyrite framboid distribution is contradictory when compared to all other evidences suggesting oxygen depletion during the t oae the results have been reinterpreted in the light of crystal size distribution theory and we conclude that not only growth time but also geochemical environment controls pyrite formation since growth time is directly related to burial rates this approach allows us to reconstruct relative variations of sedimentation rates during the early jurassic in this location based on the obtained results we provide new evidences for wide spread transgression during the early toarcian in the south iberian palaeomargin which induced low sedimentation rate and lower energetic conditions as well as favored oxygen impoverished bottom waters c 2015 elsevier b v all rights reserved less

astronomical calibration and global correlation of the santonian cretaceous based on the marine carbon isotope record high resolution records of bulk carbonate carbon isotopes have been generated for the upper coniacian to lower campanian interval of the sections at seaford head southern england and bottaccione central italy an unambiguous stratigraphic correlation is presented for the base and top of the santonian between the boreal and tethyan realms orbital forcing of carbon and oxygen isotopes at seaford head points to the boreal santonian spanning five 405 kyr cycles sa1 to sa5 correlation of the seaford head time scale to that of the niobrara formation western interior basin permits anchoring these records to the la2011 astronomical solution at the santonian campanian sa ca boundary which has been recently dated to 84 19 0 38 ma among the five tuning options examined option 2 places the sa ca at the 84 2 ma 405 kyr insolation minimum and appears as the most likely this solution indicates that minima of the 405 kyr filtered output of the resistivity in the niobrara formation correlate to 405 kyr insolation minima in the astronomical solution and to maxima in the filtered 13c of seaford head we suggest that variance in 13c is driven by climate forcing of the proportions of caco3 versus organic carbon burial on land and in oceanic basins the astronomical calibration generates a 200 kyr mismatch of the coniacian santonian boundary age between the boreal realm in europe and the western interior due either to diachronism of the lowest occurrence of the inoceramid cladoceramus undulatoplicatus between the two regions or to remaining uncertainties of radiometric dating and cyclostratigraphic records

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

high resolution isotopic records from corals using ocean temperature and mass spawning chronometers abstract we present a 6 year long 1978 1984 18 o and 13 c record from a great barrier reef pandora reef porites lutea coral based on near weekly sample intervals a sampling technique was designed to minimise any smoothing or distortion of the isotopic record due to complex coral growth calyx architecture and calcification at depth within the tissue layer the arrival time of the mid winter minimum sea surface temperature is very consistent 2 weeks near pandora reef and provides an annual time marker offering more precision than the traditional density band chronometer the improved chronology and high resolution record demonstrate that signal distortion in porites due to calcification within the tissue layer and variable intra annual coral extension is generally negligible also confirmed is that the arrival time of monsoonal floods is precisely preserved 1 week within the skeleton of porites the sensitivity of weekly sampling allows the detection of a subtle warm to cool sea surface temperature anomaly which preceded by more than one year a similar temperature anomaly associated with the 1982 83 el nin o in the east pacific sharply higher 13 c values coincide with the time of the annual coral mass spawning event in the great barrier reef recognition of this mass spawning signal should simplify the interpretation of coral 13 c records and provides an additional precise time marker with which to adjust chronologies when intra annual coral extension is not constant

coral δ18o records as an indicator of winter monsoon intensity in the south china sea we have used correlative analysis between mean december january february winter wind velocities measured at the xisha meteorological observatory 16degrees50 n 112degrees20 e in the middle of the south china sea and mean 518 0 data for the corresponding month from porites lutea coral collected in longwan waters 19degrees20 n 110degrees39 e to obtain a linear equation relating the two datasets this winter wind velocity for the south china sea wmiiscs can then be correlated to the coral delta 18 o by the equation wmiiscs 1 213 1 351 delta 18 o parts per thousand pdb r 0 60 n 40 p 0 01 from this the calculated wmiiscs delta18o series from 1944 to 1997 tends to decrease during the 1940s to the 1960s it increases slightly during the 1970s and then decreases again in the 1980s and 1990s the calculated decadal mean wmiiscs delta18o series had a obvious decrease from 5 92 to 4 63 m s during the period of 1944 1997 the calculated yearly mean wmiiscs delta18o value is 5 58 m s from 1944 to 1976 and this decreases to 4 85 m s from 1977 to 1998 that is the opposite trend to the observed yearly mean sst variation the yearly mean sst anomaly is 0 27degrees from 1943 to 1976 and this increases to 0 16degrees from 1977 to 1998 spectral analysis used on a 54 year long calculated wmiiscs delta18o series produces spectral peaks at 2 4 7 yr which can be closely correlated with the quasibiennial oscillation band qbo band 2 2 4 yr and the el nino southern oscillation band enso band 3 8 yr hence most of the variability of the winter monsoon intensity in the middle of the south china sea is mainly constrained by changes in the thermal difference between the land and the adjoining sea area perhaps due to global warming c 2003 elsevier science usa all rights reserved

the cenomanian turonian boundary event oae2 and palaeoenvironmental change in epicontinental seas new insights from the dinocyst and geochemical records abstract organic walled dinoflagellate cyst dinocyst and geochemical records across the cenomanian turonian boundary ctb are presented for the nw european reference section at eastbourne england dinocyst and nannofossil fertility indexes indicate that an upwelling driven productivity pulse accompanied a eustatic sea level fall that preceded by at least 40 kyr the global rise in 13 c values that marks the onset of oceanic anoxic event 2 oae2 and the deposition of black shales in the deep ocean a marine productivity collapse in the latest cenomanian is evidenced by the falling absolute and relative abundance of peridinioid dinocysts believed to be the product of heterotrophic dinoflagellates this biotic change accompanied transgression and sharply rising sea surface temperatures following an atlantic wide episode of short lived cooling geochemical tracers provide evidence of caribbean colombian plateau volcanism the increase in water depth caused by the latest cenomanian transgression resulted in less eutrophic waters in epicontinental seas where ctb biotic turnover was driven largely by water mass changes rather than oxygen depletion the species richness absolute abundance ratio of dinocysts is proposed as a water mass stability proxy

a 173 year stable isotope record from a tropical south pacific coral 0 we have generated a 173 year long time series a d 1806 to 1979 of changes in the 18 o and 13 c composition of a coral head platygyra lamellina to investigate environmental change in the climatologically sensitive region of the tropical south pacific little is known about decadal and centennial scale climate change at sea level in this region our coral is from near the south coast of espiritu santo island 15 s 167 e republic of vanuatu the stable isotope record from this coral is consistent with meteorological and oceanographic records during the period of overlap in the records 1964 1978 18 o values positively correlate with sst r 0 77 and 13 c values are highly coherent with rainfall r 0 82 at the annual cycle these relations suggest that the 18 o signal in this coral is a function of variations in sst and rainfall induced changes in sss whereas the 13 c signal may be related to rainfall and cloud cover modulation of photosynthesis in the coral 18 o and 13 c values are positively correlated over the entire length of the record r 0 65 a relation that is even stronger between 1806 and 1866 r 0 81 i e prior to the time of possible anthropogenic influence on the 13 c record because of the positive correlation between temperature and rainfall in this region we interpret the long term record of 18 o in terms of joint variations of these two variables the most significant cool dry excursion in the santo record occurs during the nineteenth century 1832 1866 and ends abruptly in 1866 with a change to modern values superimposed on this pattern is a slight 0 2 cooling drying toward the end of the twentieth century cross spectral analysis of the 18 o and 13 c records indicates a strong concentration of variance at the quasi biennial 2 years and el nino southern oscillation enso 4 5 years frequency bands in addition to a 15 year peak found also in global temperature records cross spectral analysis of coral isotope records from santo and the philippine sea indicate a concentration of variance at enso 4 5 years frequency bands however comparison of the santo coral isotope record with high latitude northern hemisphere temperature records indicates that the major cool dry excursion in the santo record 1832 1866 is not seen in the northern hemisphere record if verified in other tropical south pacific coral records the results have implications concerning the global scale of cooling for little ice age events

palaeoenvironmental changes in the northwestern tethys during the late campanian radotruncana calcarata zone implications from stable isotopes and geochemistry abstract this paper investigates the palaeoceanographic setting and evolution of two biostratigraphically well constrained upper cretaceous sections in the eastern alps of austria the duration of the investigated time interval is confined by the total range zone of radotruncana calcarata which was a very short lived 806 000 yrs species as calibrated using orbital parameters this results in a precise time frame for paleoenvironmental interpretations within this interval stable isotope stratigraphy links both sections to published records the two studied sections are located at the passive northern margin of the european foreland and at the active southern margin of a northwestern tethys ocean branch respectively we use mineralogy clay mineralogy element geochemistry carbonate associated elements and element ratios sr isotope stratigraphy and stable c and o isotopes to characterize the profiles mn sr ratios as well as stable c and o isotopes indicate that the sediments are largely diagenetically unaltered both sections have a similar history concerning their sea level evolution i e a gradual third order regression with short fourth order transgressive intervals the inferred water temperature increases at both locations and the overall primary production and nutrient availability increased slightly with time predominately suboxic conditions are confined to the southern profile and were interrupted by oxic spells of 50 kyr duration and even shorter periods of increases in primary production we also found evidence of a strong aeolian influence on the cyclic deposition of marl limestone couplets in the southern profile the similar history at both geodynamic settings indicates that the southern block close to the subduction zone was relatively stable for the duration of r calcarata total range zone

itcz controls on late cretaceous black shale sedimentation in the tropical atlantic ocean 1 this study presents high resolution organic and inorganic proxy records for coniacian to santonian black shale on the demerara rise odp site 1261 in the western tropical atlantic off south america we integrate these records with approximately time equivalent geochemical data from the eastern tropical atlantic off tropical africa odp site 959 to extract the underlying relationships of intertropical convergence zone itcz dynamics and black shale formation in the tropical cretaceous atlantic at orbital time scales the geochemical records from the demerara rise show repetitive fluctuations in productivity ocean redox conditions and clastic sediment supply consistent with a dynamic paleo upwelling regime off tropical south america upwelling intensity most likely was driven by shifts of the mean annual position of the itcz which connects the large scale precipitation and wind field patterns of the hadley cells upwelling was strongest off south america and burial of oil prone organic matter most pronounced when the itcz was in its southernmost position which maximized the impact of ne trade winds on the inner tropical part of the northern hadley cell geochemical records from the deep ivorian basin equatorial atlantic suggest that source rock formation occurred in phase with regions north of the equator off tropical africa however black shale formation was primarily driven by regional rainfall and nutrient export the results of this study provide a conceptual framework that explains the formation distribution and quality of petroleum source rocks below the tropical component of the hadley cells on orbital time scales

degree of pyritization of iron as a paleoenvironmental indicator of bottom water oxygenation abstract a new method is presented for recognizing the degree of bottom water oxygenation in organic carbon bearing rock the method uses the parameter degree of pyritization dop which is the ratio of pyritic fe to pyritic fe acid soluble fe sediments with ages ranging from devonian to cretaceous have been classified on paleoecological and sedimentological criteria as having been deposited in aerobic conditions deposited in fully oxygenated bottom waters restricted marine conditions deposited in waters with low oxygen concentrations or inhospitable bottom conditions where little or no oxygen is present and h2s may be continually or intermittently present aerobic dop

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

evaluation of sampling resolution in coral stable isotope records a case study using records from new caledonia and tarawa we have generated a 40 year long monthly stable isotope record from a porites lutea coral collected offshore of amedee new caledonia 22 s 167 e to investigate the relation between sampling resolution in coral isotope studies and retrieval of sea surface environmental information we interpret the high correlation between our oxygen isotope record and a twenty year long sea surface temperature record at the monthly timescale r 0 88 to indicate that our coral isotope record is an accurate monitor of environmental conditions offshore of amedee the character of the signal and the percent variance explained in the record at the annual band at the quasi biennial oscillation band qbo 2 0 2 4 years and at the el nino southern oscillation band enso 3 8 years changes little in response to a reduction in sampling density from monthly to bimonthly to quarterly similar results have been obtained in a reanalysis of a coral isotope record from tarawa kiribati our results indicate that a significant amount of the information obtained from high density sampling can also be retrieved from lower density sampling in particular bimonthly sampling yields virtually no drop off in variance explained and quarterly sampling is satisfactory for resolving interannual and decadal scale trends in time series the proposed sampling approach may enable a more rapid filling in of numerous spatial holes in coral sampling sites needed for reconstruction of long term decadal scale variations in climate

redox conditions associated with organic carbon accumulation in the late devonian new albany shale west central kentucky illinois basin abstract factors affecting organic carbon accumulation in marine basins may include surface water productivity enhanced preservation due to bottom water anoxia protection by and adsorption onto clays and variations in sediment supply in this study geochemical proxies for the new albany shale of the illinois basin were examined for ten cores from the outcrop belt in west central kentucky in an attempt to evaluate redox conditions associated with organic carbon enrichment in these cores the late devonian new albany shale is represented by the clegg creek camp run morgan trail and the blocher members specifically c s relationships degree of pyritization dop t and c s fe relationships along with redox sensitive trace elements e g v and mo and ratios ni co v cr and v v ni were used to assess redox conditions in addition organic carbon to total phosphorus ratios c org p tot were used to assess levels of paleoproductivity that were possibly enhanced by the productivity anoxia feedback mechanism results suggest variable bottom water conditions existed during accumulation of the new albany shale of west central kentucky including predominantly anoxic conditions for the clegg creek member dysoxic conditions for the camp run and morgan trail members and dysoxic to oxic conditions for the blocher member however throughout deposition all members exhibited some variability in redox conditions thus overall lowest oxygen levels were likely experienced during deposition of the clegg creek followed by the camp run and morgan trail members the blocher member was probably deposited under conditions closer to normal marine yet still dysoxic at most times high c p ratios observed in these members suggest regeneration of p enhanced productivity and sequestration of organic carbon as described by the productivity anoxia feedback paf mechanism during anoxic periods variations in redox indications obtained from different proxies suggest that multiple parameters should be utilized rather than relying on a single proxy reasonably good agreement is seen between c s dop t c s fe and mo levels ni co and v cr tend to agree well with each other but suggest higher oxygen levels than the other proxies values for v v ni tend to be an outlier suggesting more anoxic to euxinic conditions compared to other proxies

sedimentation rate dilution preservation and total organic carbon some results of a modelling study abstract a modelling exercise was undertaken to evaluate the positive preservational and negative diluent effects of sedimentation rate sr on the total organic carbon toc content of marine sediments and to use multiple regression analysis of modern data to predict toc data presented show the predicted marine toc using the carbon burial efficiency be versus sr relationship of betts and holland betts j n holland h d 1991 the oxygen content of ocean bottom waters the burial efficiency of organic carbon and the regulation of atmospheric oxygen palaeogeography palaeoclimatology palaeoecology global and planetary change section 97 5 18 calculated for a range of sr water depths primary productivities and four fixed be values the results suggest that the preservation effect of sr only enhances toc at 5 cm ka in oxic regimes after which dilution occurs if carbon supply is held constant above 35 cm ka there is no appreciable difference in toc regardless of whether the sea floor is anoxic or not below 10 cm ka there is a strong divergence in oxic and anoxic toc values observed positive correlations of sr and toc at 5 cm ka are largely an artefact of including sites from shallower depths and or higher productivities multiple regression analysis mra of modern marine sediment data suggests that once re scaled to allow for their non linear effect dissolved oxygen values may be a significant additional variable in determining the toc predicting an approximately 2 5 4 0 times higher toc in anoxic facies compared with fully oxic ones 4 ml l dissolved oxygen all other things being equal the mra also indicates a generally negative partial correlation between carbon delivery flux and be in modern sediments producing a significant moderating effect on the predicted toc

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

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

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

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

source rock potential and depositional environment of upper cretaceous sedimentary rocks abu gharadig basin western desert egypt an integrated palynological organic and inorganic geochemical study abstract the abu gharadig basin in the northern part of the western desert egypt is among the most important petroleum provinces in egypt here cenomanian to santonian rocks of bahariya formation and abu roash a g members from the gpt 3 well were investigated for their depositional environment kerogen quality petroleum generation potential and thermal maturity by geochemical petrological and palynological methods the sediments of the bahariya and abu roash formations excluding the abu roash f member represent variable shallow marine environments with poor preservation of marine organic matter whereas there is an excellent preservation in the abu roash f member the basal part of this member is characterized by anoxic carbonate rich depositional conditions high toc values up to 7 high hi up to 700 mghc gtoc and liptinite dominated organic matter depletion of iron leads to sulfur incorporation into organic matter which is reflected in high thiophene benzene ratios above sediments are enriched in terrestrial elements fe ti as well as k and mn this pattern and the occurrence of the fresh brackish water algae botryococcus suggests a regression phase during deposition the upper part of the abu roash f member is again characterized by fully marine suboxic conditions and a lower thiophene benzene ratio the source rock section demonstrates lower thermal maturity compared to the above and below sections based on all microscopic pyrolysis and biomarker data this indicates thermal maturity retardation suppression most likely due to a different organic facies and early diagenetic transformation of kerogen as indicated by the geochemical and palynological data the source rock heterogeneity indicates a relatively shallow marine environment where the changes in bottom water conditions are very sensitive to sea level fluctuations residual oil characterization reveals two reservoir compartments which are in the abu roash d and c members the abu roash f source rocks are compared with time equivalent sediments in the tarfaya basin in morocco which represent more distal settings the more proximal group a is characterized by s fe ratios between 0 57 and 0 67 indicating suboxic conditions it has toc and hi values not exceeding 4 and 600 mghc gtoc respectively at variable caco3 contents the more distal tarfaya sediments group b have higher toc and hi as well as high organic sulfur contents group a is higher in terrigenous element concentrations the tmax of immature source rocks ranges from 410 to 415 c in organic sulfur rich samples and from 420 to 430 c in organic sulfur poor samples revealing an important impact of organic facies on maturity parameters furthermore there is an inverse relationship between s fe and al2o3 toc which might become an important tool in paleoenvironmental reconstructions as well as petroleum source rock studies

the effect of colony topography on climate signals in coral skeleton the stable oxygen isotope composition of the aragonitic skeleton of hermatypic corals is a potential archive of paleotemperature and rainfall data biological processes also influence coral 18o although it has been difficult to determine which processes are involved and whether or not they dominate the stable isotope signal we show here that colony topography or surface bumpiness is associated with significant differences in 18o 13c and the timing of high density band formation between same age corallites in the central and fastest growing region of a coral colony these differences reflect changes experienced by individual corallites as they grow from the summit of a bump toward the bottom of a valley corallites on the bump record isotopic temperatures more than 1 c higher and accrete high density skeleton about 2 months earlier than their valley counterparts just 20 mm away we propose that these changes are not caused by corallite aging but rather by changes in the overall rate and timing of light enhanced calcification which is lower and occurs later in shaded valleys than it does on exposed bumps although we conclude that sea temperature is the dominant influence on 18o values in our coral our results show that significant isotopic variations may be expected over a small surface area in a single colony the production of accurate and reproducible coral based climate records thus requires an understanding of the complexities of coral growth processes and incorporation of this knowledge into sampling strategies and interpretation of data