the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

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

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

mercury deposition through the permo triassic biotic crisis abstract a 6 7 million year record of marine sedimentation through the permo triassic biotic crisis shows notable shifts in mercury concentrations that varied over an order of magnitude 0 002 to 0 116 g g mercury concentrations correlate strongly with total organic carbon showing both parallel increasing and decreasing trends over geologic time scales results suggest that changes in bioproductivity strongly influence mercury sequestration into marine sediment this may provide insight to potential marine response to modern anthropogenic hg loading and supports models that suggest enhanced bioproductivity that due to recent climate has increased hg sequestration over time

paleotemperature and paleosalinity inferences and chemostratigraphy across the aptian albian boundary in the subtropical north atlantic 1 geochemical analyses of extraordinarily well preserved late aptian early albian foraminifera from blake nose ocean drilling program site 1049 reveal rapid shifts of 18o 13c and 87sr 88sr in the subtropical north atlantic that may be linked to a major planktic foraminifer extinction event across the aptian albian boundary the abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0 8 1 4 million years at the boundary contact but the values before and after the hiatus indicate that major oceanographic changes occurred at this time 87sr 88sr increase by 0 000 200 13c values decrease by 1 5 to 2 2 and 18o values decrease by 1 0 planktics to 0 5 benthics across the hiatus further both 87sr 88sr ratios and 18o values during the albian are anomalously high the 87sr 88sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter basin differences in seawater 87sr 88sr during the albian or revision of the seawater curve for 18o planktic values in some aptian samples likely reflect a diagenetic overprint but preservation is excellent in the rest of the section in well preserved material benthic foraminiferal values are largely between 0 5 and 0 0 and planktic samples are largely between 0 0 to 1 0 with a brief excursion to 2 0 during oae 1b using standard assumptions for cretaceous isotopic paleotemperature calculations the 18o values suggest bottom water temperatures at 1000 1500 m of 8 10 c and surface temperatures of 10 14 c which are 4 6 c and 10 16 c cooler respectively than present day conditions at the same latitude the cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present because of their exquisite preservation whole scale alteration of the analyzed foraminifera is an untenable explanation our proposed solution is a high evaporative fractionation factor in the early albian north atlantic that resulted in surface waters with higher 18o values at elevated salinities than commonly cited in cretaceous studies a high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and like the sr isotopes implies limited connectivity among the individual basins of the early cretaceous proto atlantic ocean

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

biogeochemical formation of calyx shaped carbonate crystal fans in the subsurface of the early triassic seafloor abstract the kuh e dena sedimentary section in iran developed on the southwestern margin of the neotethys ocean the fossil and bioturbation lean early triassic section late dienerian to early smithian is typified by finely laminated calcareous shales that are interbedded with laterally extending carbonate beds which are mostly composed of calyx shaped carbonate crystal fans the calyxes consist of fibrous crystals that apparently formed within the subseafloor in soft water saturated sediment by displacive growth rare earth element and yttrium patterns indicate that calyx shaped crystals precipitated from anoxic pore waters biomarker patterns of the carbonate beds reveal major input of lipids from prokaryotes that typically occur within layered benthic microbial mats i e cyanobacteria anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea along their length the fibrous crystals of the calyxes reveal a trend of increasing 13 c carb values from 2 7 to 3 3 suggesting that archaeal methanogenesis affected the carbonate pool apart from the putative benthic prokaryotes molecular fossils of halophilic most likely planktic archaea were detected in the carbonate beds low pristane to phytane ratios 0 8 and the presence of halophilic archaea are in accord with the lack of bioclasts and bioturbation which likely reflects increased salinities the former presence of a benthic microbial mat with cyanobacteria underlain by anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea is in accordance with studies on living microbial mats in hypersaline low oxygen marine environments the early triassic subseafloor seems to have been a sink for carbon driven by biologically induced formation of secondary diagenetic carbonate

mercury in the bushveld complex south africa and the skaergaard intrusion greenland abstract we present mercury concentrations for layered mafic rocks of the bushveld complex the skaergaard intrusion morb and a karoo dolerite sill as determined by combustion atomic absorption spectroscopy combustion aas with gold amalgamation pre concentration mercury in the bushveld complex and the skaergaard intrusion is generally low with about 1 1 and 0 8 ppb hg on average respectively the karoo dolerite sill chill margins and morb have average hg concentrations of 2 5 and 6 4 ppb respectively the reason for the low whole rock hg concentrations in layered mafic intrusions is that the element is incompatible with respect to the cumulus mineral assemblages our results show far lower hg concentrations for the skaergaard cumulates than previous measurements and we find no evidence for preferential enrichment in plagioclase rich rocks as previously reported we attribute this difference to inaccurate analytical methodology of the early measurements there are hg enrichments in distinct levels in both intrusions mercury enrichments in the bushveld complex are observed near the top of the lower zone 2 4 ppb in the merensky reef at 8 6 ppb the platreef at 3 ppb average and in the upper zone near the main magnetitite layer 4 7 ppb these enrichments are due to the concentration of hg by sulfides as suggested by a positive correlation between cu and hg there is no upward increase in hg with stratigraphic height or positive correlation between hg and zr in the bushveld complex as would be expected if hg acted as an immobile incompatible element the lack of correlation is explained by periodic degassing of the bushveld magma chamber in which volatile elements including hg and s escaped in contrast the skaergaard intrusion probably did not degas and there is hg enrichment in the sandwich horizon 53 ppb because of the combination of the incompatibility and the presence of sulfides

precession driven monsoonal activity controlled the development of the early albian paquier oceanic anoxic event oae1b evidence from the vocontian basin se france abstract in the vocontian basin in southeastern france the aptian albian boundary is marked by the occurrence of four laminated black shales jacob kilian paquier leenhardt corresponding to oceanic anoxic event 1b oae1b equivalents of one or more of these intervals are also known from different regions in the tethys atlantic and pacific and correspond in time to major climatic and evolutionary perturbations here we performed an integrated multi proxy high resolution study on the section at l arboudeysse in the northwestern part of the vocontian basin including mineralogical whole rock and clay minerals and geochemical carbon and oxygen isotopes organic matter major and trace elements mercury contents analyses the aim of this study is to reconstruct the level of productivity and related state of oxygenation in addition to the weathering coditions on the adjacent continent during the paquier event modest enrichments in redox sensitive trace elements rste mo as v u ni associated with moderate total organic carbon contents between 0 57 and 5 52 wt indicate the development of suboxic anoxic conditions during deposition of the paquier level the strong enrichment of mo 10 229 relative to other rste

onshore quaternary geological surveys in the 21st century a perspective from the british geological survey abstract at the turn of the century the british geological survey has embarked on a major programme to construct a 3 dimensional geological model of the uk the reassessment of methodologies used to investigate quaternary deposits and processes forms an important part of this programme surveys of user requirements indicate that the collation of new data and the generation of new output are needed to meet the diverse needs of society such as information on the geometry of sediment bodies their lithologies geotechnical properties and permeability the rockhead surface slope stability land susceptible to flooding coastal sediments contaminated land and artificial deposits these initiatives are driven by the recognition that the dynamic quaternary record reflecting the effects of recent climate and neotectonic change has both short and long term relevance to the use of information on the natural environment in which we live

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

high resolution chemostratigraphy of the late aptian early albian oceanic anoxic event oae 1b from the poggio le guaine section umbria marche basin central italy an integrated study of multiple geochemical proxies 13ccarb 13corg toc hi caco3 trace elements al ratios of the late aptian early albian oceanic anoxic event oae 1b has been performed on the pelagic sedimentary sequence of poggio le guaine umbria marche basin central italy a comparison of the newly collected stable isotope carbon curve with the records from the vocontian basin se france dsdp site 545 and hole 1049c provided a reliable and precise identification of the four main prominent black shale levels 113 jacob kilian urbino paquier and leenhardt that characterize the oae 1b the studied record shows an increase in the marine organic carbon accumulation rate in particular in the 113 jacob and urbino paquier levels in the other black shales toc values are 1 with evidence of degraded marine organic matter completely anoxic conditions were never established during the sediment deposition although evidence of oxygen depletion at the bottom of the basin is clearly documented by the distribution pattern of redox sensitive trace metals the results suggest an increase in organic carbon burial rates during the oae 1b due to the effect of enhanced surface productivity as supported by a major increase in ba al and reduced bottom water ventilation notably the kilian and urbino paquier levels from the plg section are characterized by the absence of correlative shifts in 13ccarb and 13corg the increase in the 13corg values in these levels is explained by an increase in the relative contribution of 13c enriched marine planktonic archaeal biomass while the concomitant negative excursions recorded in the 13ccarb could reflect a major contribution of isotopically light terrestrial carbonate ions from increased continental runoff during documented more humid conditions

massive expansion of marine archaea during a mid cretaceous oceanic anoxic event biogeochemical and stable carbon isotopic analysis of black shale sequences deposited during an albian oceanic anoxic event 112 million years ago indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine nonthermophilic archaea the carbon 13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event indeed the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in earth history at which certain hyperthermophilic archaea adapted to low temperature environments

record of albian to early cenomanian environmental perturbation in the eastern sub equatorial pacific the present paper documents and discusses a new albian early cenomanian carbon isotope 13ccarb and 13corg curve from the subequatorial eastern pacific in peru chemostratigraphic evidences for the expression of the oae1b set and for oae1c and oae1d are presented this dataset is relevant inasmuch as previous work is strongly biased towards study sites in north america western interior basin in europe tethys and the pacific realm a comparison of the carbon isotope stratigraphy obtained in peru with published sections from the central and western pacific the western atlantic and northern and western tethys reveals an overall good agreement supporting the global nature of the isotope patterns described here the 13c from peru record is constrained by biostratigraphic evidence and 87sr 86sr isotope stratigraphy using well preserved oyster shells furthermore we document the development of a heterozoan epeiric neritic mixed carbonate siliciclastic ramp in the western platform of peru and its corresponding sedimentary facies associations this dataset was used to elucidate the complex interplay of climatic changes nutrient supply and platform drowning leading to the following conclusions i an upper aptian lower albian major change from siliciclastic dominated to carbonate sedimentation coincided with the impact of the kilian level ii a lower albian incipient platform drowning linked to the impact of the paquier level iii a lower middle albian major demise of neritic carbonate production that coincides with the leenhardt level followed by middle albian condensed sedimentation that reports prominent negative values in 13ccarb prior to the onset of oae1c and iv finally renewed carbonate ramp production during the upper albian lower cenomanian the data shown here represent the foundation for future work documenting the mid cretaceous of peru and its implications for the palaeoceanography of the se subequatorial pacific

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

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

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

reconstructing nutricline dynamics of mid cretaceous oceans evidence from calcareous nannofossils from the niveau paquier black shale se france abstract a high resolution calcareous nannofossil record is presented from the lower albian niveau paquier black shale from the vocontian basin se france the niveau paquier black shale represents the regional equivalent of the supraregionally distributed oceanic anoxic event 1b oae 1b to reconstruct surface water fertility a nutrient index based on zeugrhabdotus erectus discorhabdus rotatorius high fertility indicators and watznaueria barnesae low fertility indicator was established using principal component analysis in addition the distribution of nannoconus spp and absolute abundances of coccoliths coccoliths per gram were used for reconstructing nutricline dynamics of the surface waters high surface water fertility coincides with low percentages of nannoconids and vice versa moreover high percentages of nannoconids correlate with low absolute abundances of all other coccoliths based on the observed nannoplankton distribution pattern and a suggested similarity in ecological requirements between nannoconids and the modern taxon florisphaera profunda a model is proposed that couples nannoconid abundances with dynamics of the nutricline time series analyses of the nutrient index show fluctuations within the precessional band the precession controlled fluctuations of the surface water fertility may represent a monsoonal signal with the nutrient supply in the surface waters depending on the strength of monsoonal activity during periods of enhanced monsoonal activity which were characterized by humid conditions and stronger winds mixing of the upper water column was enhanced during that time the abundance of nannoconids decreased as a consequence of enhanced wind stress that improved vertical mixing and led to an entrainment of nutrients into the surface waters this resulted in an increase of primary production during periods of reduced monsoonal activity marked by drier conditions and reduced wind stress the surface waters were depleted in nutrients as a result of a deep nutricline and a reduced nutrient supply to the upper photic zone in a stratified water column percentages of nannoconids increased according to the mechanisms outlined above fluctuations of the nutrient index and nannoconid percentages have been used as a proxy for reconstructing the physical structure of mid cretaceous oceans steered by precession forced monsoonal activity the results of the study show that the formation of the lower albian oae 1b from the vocontian basin occurred under strongly fluctuating surface waters fertility

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