toarcian carbon isotope shifts and nutrient changes from the northern margin of gondwana high atlas morocco jurassic palaeoenvironmental implications the early toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes these coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial and culminate in the so called toarcian oceanic anoxic event it is believed that the environmental crisis was triggered by the activity of the karoo ferrar large igneous province in order to further document the early toarcian palaeoenvironmental perturbations carbon isotope total organic matter calcareous nannofossils and phosphorus content of the amellago section in the high atlas rift basin of morocco were investigated this section is extremely expanded compared to the well studied european sections its position along the northern margin of the gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western tethyan realm the carbon isotope curve shows two negative excursions of equal thickness and amplitude at the pliensbachian toarcian boundary and at the transition from the polymorphum to the levisoni zone this confirms the supra regional nature of these shifts and highlights the possible condensation of the first boundary shift in european sections phosphorus content is used to trace palaeo nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels confirming that these episodes are related to enhanced continental weathering probably due to elevated greenhouse gases in the atmosphere in the high atlas basin the increase in nutrient levels at the pliensbachian toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the saharan carbonate platform a middle toarcian event centered on the boundary between the bifrons and gradata zones characterized by a positive carbon isotope excursion and nutrient level rise is documented in the amellago section

the early toarcian and cenomanian turonian anoxic events in europe comparisons and contrasts two intervals of mesozoic time are demonstrably of sufficient geological brevity to qualify readily for the term anoxic event the earlyfalciferum zone orexaratum subzone of the toarcian and thewhiteinella archaeocretacea interval zone that straddles the cenomanian turonian boundary both periods of time saw regional deposition of anomalously organic rich strata black shales accompanied by a positive 2 pdb carbon isotope excursion in coeval biogenic carbonates and significant faunal change the duration of both events was probably less than half a million years and both were preceded by regional erosion and possible upwelling coincident sea level rise and transgression is likely a european view of these events however spotlights some significant differences whereas thefalciferum zone organic matter is generally more concentrated and more hydrogen rich on the palaeo european shelf than on the tethyan continental margins the reverse holds true for the black shales formed during thewhiteinella archaeocretacea interval zone furthermore the carbon isotope composition offalciferum zone organic matter from both north european and tethyan sites is anomalously negative compared to that developed in thewhiteinella archaeocretacea interval zone differing planktonic organisms may have been involved and their possible diverse ecological requirements may go some way to explaining the nature and distribution of facies deposited during these two events

mapping and geochemical characterization of the toarcian organic matter in the mediterranean tethys and middle east organic matter from toarcian outcrops and boreholes in several basins around the mediterranean sea and middle east has been studied rock eval pyrolysis elemental analyses of kerogens and gas chromatography of chloroform extracts within these different basins have been used to determine the amount petroleum potential and type of the organic matter the results have been used to compile a mapping of the organic matter for the toarcian stage which shows heterogeneities in the distribution and type of organic matter 1 1 marine organic matter type ii occurs in different environments of deposition whereas high contents 5 total organic carbon correspond to thick deposits within the west european realm great britain north sea paris basin and germany the organic matter is less abundant in the mediterranean area where lower concentrations 1 2 toc preserved in lower toarcian thin levels are limited only to restricted basins northern italy greece 2 2 the predominance of continental organic matter type iii along the northern margin of the tethys corresponds to a deltaic environment 3 3 there is a predominance of altered organic matter within the carbonated platforms around the mediterranean tethys these results supplemented with the data issuing from the literature add a geochemical dimension to the paleogeography of the tethys

detectability of martian carbonates from orbit using thermal neutrons numerical simulations of martian neutron leakage flux spectra are made in order to explore the detectability of magnesium and calcium carbonate deposits using neutron spectroscopic techniques from orbit the primary signature of such deposits is found to be an enhanced thermal amplitude although this enhancement is weakened by 1 partial burial beneath an aeolian regolith blanket 2 admixture with regolith on a microscopic centimeter or macroscopic tens of centimeters scale and 3 reduction in the areal size of the deposit near surface stratigraphies of carbonates hypothesized by some authors as possible on mars are still detectable by simple neutron sensors from orbit however the large variations in the magnitude of the thermal neutron enhancements caused by different carbonate deposit configurations found in this study require a combined gamma ray and neutron analysis for their unique specification

an organic geochemical profile of the toarcian anoxic event in northern italy abstract a suite of black shales calcareous shales and limestones representing the toarcian anoxic event jurassic 192 ma was collected from a 14 m length of core taken from the belluno trough northern italy and examined in detail to assess variations in depositional environment during this interval geochemical and optical data indicate organic matter of algal and bacterial origin with only trace contribution from terrestrial sources detailed biological marker data interpreted with the aid of multivariate statistics demonstrate fluctuations in primary producers and bacterial populations during black shale deposition the onset of the anoxic event was not abrupt but characterized by an apparent gradual development of anoxia and consequent enhanced organic matter preservation different hopane biomarkers proved especially useful in recognizing preservation potential in the section and correlate well with other preservation indicators increased oxygenation at the end of the event may have been associated with changes in primary productivity

toarcian anoxic event in europe an organic geochemical study abstract a total of 48 sediment samples comprising both black shales and associated organic poor interbeds were examined from toarcian organic rich sections throughout europe despite being contemporaneous deposits of a single oceanic anoxic event oae the molecular organic geochemical characteristics particularly the steroidal hydrocarbons of the black shales are highly variable this suggests different depositional environments in different regions although the sedimentary organic matter is dominantly of marine origin in all areas environmental conditions apparently varied considerably arguing against a simple oxygen minimum layer model for the accumulation of organic rich sediments furthermore molecular evidence of hypersaline conditions at two sites suggests that salinity stratification may have been an important factor for black shale deposition in some areas a more complex model for the widespread deposition of organic rich sediments during the toarcian oae is presented in the light of results arising from the present organic geochemical investigation

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

palaeoenvironmental significance of toarcian black shales and event deposits from southern beaujolais france new sedimentological biostratigraphical and geochemical data recording the toarcian oceanicanoxicevent t oae arereportedfromamarginalmarinesuccessioninsouthernbeaujolais france the serpentinum and bifrons ammonite zones record black shales with high 1 10 wt total organic carbon contents toc and dysoxia tolerant benthic fauna typical of the schistes carton facies well documented in contemporaneous nearby basins the base of the serpentinum ammonite zone however differs from coeval strata of most adjacent basinal series in that it presents several massive storm beds particularly enriched in juvenile ammonites and the dysoxia tolerant miniaturized gastropod coelodiscus this storm dominated interval records a marked negative 5 carbonate and organic carbon isotope excursion being time equivalent with that recording storm and mass flow deposits in sections of the lusitanian basin portugal pointing to the existence of a major tempestite turbidite event over tropical areas during the t oae although several explanations remain possible at present we favour climatically induced changes in platform morphology and storm activity as the main drivers of these sedimentological features in addition we show that recent weathering most probably due to infiltration of o2 rich meteoric water resulted in the preferential removal of 12 c enriched organic carbon dramatic toc loss and total destruction of the lamination of the black shale sequence over most of the studied exposure these latter observations imply that extreme caution should be applied when interpreting the palaeoenvironmental significance of sediments lacking toc enrichment and lamination from outcrops with limited surface exposures

3d stratigraphic forward numerical modelling approach for prediction of organic rich deposits and their heterogeneities abstract the source rock characteristics e g thickness lateral extension richness are known to be highly variable in both time and space the lower jurassic formations of north western europe contain source rocks with organic rich intervals showing different characteristics from one region to another the paris basin differs from the south east basin of france but organic content and hydrogen index also vary within a single basin during the early jurassic the overall depositional environment of north western europe corresponded to an epicontinental domain at the western extremity of the tethys ocean the early transgressive phase of the jurassic induced flooding of this european realm because of the evolution of the connections and threshold of the european basins and their associated sedimentary settings this domain occupied a key position for the deposition of organic rich layers using a forward modelling approach we aim to predict the heterogeneous characteristics of such sediments it is widely accepted that primary productivity and preservation are key factors favouring the accumulation of organic rich layers however the roles of these factors remain to be assessed and the processes leading to accumulation and preservation need to be quantified we focus on the lower jurassic hettangian to toarcian in france since this provides a vast amount of data to calibrate the 100 kyr time step model in terms of an accurate framework including paleogeography stratigraphy lithology palaeontology mineralogy and geochemistry results show that favourable conditions for the deposition of organic rich sediment can occur even with moderate primary productivity and without requiring anoxic conditions these windows are firstly dependent on internal factors directly linked to the basin morphology such as sedimentation rate bathymetry and distance from the coastline we do not need to evoke external factors such as oceanic anoxic events or enhancement of primary production to account for the deposition of organic rich sediments

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

abundance and size changes in the calcareous nannofossil schizosphaerella relation to sea level the carbonate factory and palaeoenvironmental change from the sinemurian to earliest toarcian of the paris basin abstract abundance and size changes in the calcareous nannofossil schizosphaerella are investigated throughout the upper sinemurian to lowermost toarcian of the sancerre couy core paris basin measurements from 116 samples are compared to 487 and 411 measurements of caco3 content and total organic carbon toc content respectively our results confirm that schizosphaerella was better adapted to proximal areas than coccoliths as expressed by the stepwise rise in abundance of schizosphaerella followed later on by the rise in abundance of coccoliths during the major transgression of the sinemurian the new results show that changes in the size of schizosphaerella were mostly a response to early jurassic temperature variations coldhouse greenhouse changes large average sizes of schizosphaerella correspond mostly to proximal cool environmental conditions of the late sinemurian medium average sizes correspond to more distal conditions and cool surface waters whereas small average sizes are associated with warm episodes these results suggest that the size response of schizosphaerella to the early toarcian oceanic anoxic event and to preceding environmental perturbations of the early jurassic was probably not a physiological response to lower calcification but rather represent changes in abundances of different ecophenotypes or sub species related to climate change the contribution of schizosphaerella carbonate caco3schizo to the total carbonate bulk caco3 in the paris basin was minor

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

polar record of early jurassic massive carbon injection abstract the toarcian oceanic anoxic event t oae ca 182 myr early jurassic represents one of the best recognized examples of greenhouse warming decreased seawater oxygenation and mass extinction the leading hypothesis to explain these changes is the massive injection of thermogenic or gas hydrate derived 13 c depleted carbon into the atmosphere resulting in a 3 per mil negative carbon isotope excursion cie accelerated nutrient input and dissolved oxygen consumption in the oceans nevertheless the lack of a precisely dated record of the t oae outside low latitudes has led to considerable debate about both its temporal and spatial extent and hence concerning its underlying causes here we present new isotopic and lithological data from three precisely dated n siberian sections which demonstrate that mass extinction and onset of strong oxygen deficiency occurred near synchronously in polar and most tropical sites and were intimately linked to the onset of a marked 6 negative cie recorded by bulk organic carbon rock eval pyrolysis data from siberia and comparisons with low latitudes show that the cie cannot be explained by the extent of stratification of the studied basins or changes in organic matter sourcing and suggest that the negative cie reflects rapid 13 c depleted carbon injection to all exchangeable reservoirs sedimentological and palynological indicators show that the injection coincided with a change from cold abundant glendonites and exotic boulder sized clasts to exceptionally warm conditions dominance of the thermophyllic pollen genus classopollis in the arctic which likely triggered a rapid possibly partly glacioeustatic sea level rise comparisons with low latitude records reveal that warm climate conditions and poor marine oxygenation persisted in continental margins at least 600 kyr after the cie features that can be attributed to protracted and massive volcanic carbon dioxide degassing our data reveal that the t oae profoundly affected arctic climate and oceanography and suggest that the cie was a consequence of global and massive 13 c depleted carbon injection

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

calibrating the magnitude of the toarcian carbon cycle perturbation sedimentary rocks recording the toarcian oceanic anoxic event t oae are marked by a negative carbon isotope excursion cie reaching up to 7 and ranking among the largest known in the phanerozoic these records suggest a dramatic perturbation of the carbon cycle that has been linked to the transfer of juvenile carbon from the endogenic to the exogenic reservoirs nevertheless the magnitude of the toarcian cie varies significantly from one substrate to another hence complicating mass balance evaluation of the potential driving mechanisms here we show using high resolution paired records of 13ctotal organic carbon toc and hydrogen index from the denkingen core and dotternhausen quarry germany that the amplitude of the negative cie in marine organic matter is considerably exaggerated by changes in organic matter sourcing our corrected 3 4 cie implies a constant carbon isotope fractionation between organic and carbonate carbon across the t oae and may point to a prominent role of cyanobacteria as organic matter producers during the early jurassic these results also suggest that the difference between inorganic and organic carbon isotope values in marine strata constitutes a poor proxy of pco2 levels across the t oae moreover this corrected 3 4 cie together with evidence for 5 c seawater warming across the t oae point to the input of 25 000 gt c with much more 13c enriched signature than previously modeled our results thus allow reconciling inorganic and organic 13c records of the t oae and have important implications for the evaluation of their causal mechanisms

sedimentary organic matter and early toarcian environmental changes in the lusitanian basin portugal abstract the objective of this study is to investigate the relationship between early toarcian climatic events and the composition of kerogen assemblages in the lusitanian basin portugal in particular we aim to understand how the pliensbachian toarcian event pl toa event and toarcian oceanic anoxic event toae affected the continental areas of the western iberian margin and how possible variations in continental sources of organic matter om were expressed in marginal marine and hemipelagic depositional environments during the early toarcian we present here a characterisation total organic carbon toc total sulphur ts 13c in kerogen concentrate 13ckerogen and palynofacies of kerogen assemblages from several uppermost pliensbachian emaciatum ammonite zone lower toarcian sections in the lusitanian basin western iberian margin including the peniche section which contains the toarcian gssp in all sections toc concentration is low average 0 4 wt with the highest values reaching up to 2 1 wt in a discrete level located approximately 10 5 m above the base of the levisoni zone at peniche the toae negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni zone throughout the basin palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity with the dominance of the phytoclast group and terrestrial palynomorphs and with punctual increases in amorphous organic matter freshwater e g botryococcus sp and marine microplankton dinoflagellate cysts acritarchs and prasinophyte algae in specific stratigraphic intervals a change in palynofacies assemblages associated with the toae is observed around the base of levisoni zone although with slight differences between sections the toae interval records an increase in non opaque translucent phytoclasts nop and cuticle fragments and is also associated with an increased contribution of terrestrial palynomorphs increase in sporomorphs and classopollis in tetrads and agglomerates and decrease in marine palynomorphs the increases in nop and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial om into marine environments during the early toarcian especially during the toae in the western iberian margin understanding the impact of the early toarcian climatic events on land based ecosystems may provide important insights into current climate change

recent advances in petroleum geochemistry applied to hydrocarbon exploration this paper presents a critical review of recent advances in the study of generation maturation and migration of petroleum the different source potentials for generating hydrocarbons depend on the type of kerogen in addition to the classic types i ii and iii a residual oxidized organic matter is also observed which has no potential for hydrocarbon generation coal is widely considered as a potential source for gas but some coals may generate sizeable amounts of oil as well the development of routine analytical tools particularly pyrolysis makes possible the preparation of geochemical logs that are the basis for screening samples and for interpreting other analyses among optical techniques the major subjects of discussion concern the nature of amorphous organ c matter which may encompass different chemical types of kerogen and the applicability of vitrinite reflectance techniques to type i and ii kerogens following important advances in identification of biological markers in sediments and crude oils these markers are used for oil source rock correlation and proposed for reconstruction of depositional environment and subsequent thermal evolution migration of hydrocarbons is now better understood and the importance of a hydrocarbon phase migration is widely recognized overpressuring of pore fluids is mainly responsible for expulsion of petroleum geologic models of basin evolution subsidence compaction thermal history and geochemical models hydrocarbon generation and migration become progressively available their integration int a comprehensive model should be one of the major developments in future petroleum exploration

effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow rock fragments on soil surfaces can have a variety of contrasting effects on the hydraulics of overland flow and soil erosion this makes modeling soil erosion difficult systematic studies are needed to assess the effects of rock fragments on the hydraulics of overland flow and to specifically relate these hydraulics to sediment yield therefore flume experiments were conducted in which overland flow was applied to a highly erodible sediment surface covered by various percentages of rock fragments high local turbulence was caused by horseshoe vortex erosion around individual rock fragments for a given discharge and slope the dimension of the scour was affected by the space between the rock fragments for low cover percentages the scour can develop undisturbed and sediment yield increases with percent of rock fragment cover up to about 20 sediment yield then declines as percent cover increases above 20 beyond a cover threshold value of 20 the larger opportunity for scour hole development is counteracted by limited inter rock fragment space that does not allow scour holes to develop to their full extent as sediment yield varies nonmonotonically with rock fragment cover percent sediment yield cannot be predicted by spatially averaged flow hydraulics

the toarcian black shale event in northern italy abstract during the early toarcian jurassic c 192 ma organic rich sediments were deposited in many areas of europe this paper reports the major findings of the first part of an organic geochemical investigation of the toarcian oceanic anoxic event oae thirty two black shales and associated lithologies were studied from seven localities in the southern alps of northern italy toarcian organic rich sediments up to 4 3 toc were deposited in various palaeoceanographic settings within the lombardy belluno and julian basins and on the trento plateau results of biomarker analyses indicates that in all sections mixed contributions from algae and bacteria dominate a variable but generally minor terrigenous input the preservation of significant quantities of marine derived organic matter and the typically well developed sedimentary lamination suggest that the black shales accumulated under oxygen deficient conditions in all palaeoceanographic settings molecular evidence suggests that the algal derived components of the sedimentary organic matter is partially degraded in many of the basinal samples this observation is here interpreted as being the result of aerobic decomposition of algal debris during transport through the water column other lines of evidence indicate that oxygen depletion intensified during the later stages of the toarcian oae with enhanced preservation of authochthonous organic matter in the light of these results the preferred model for the accumulation of black shales on the tethyan southern margin incorporates anoxic basin bottom waters overlain by a relatively well oxygenated water column