from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

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

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

long distance correlations by sequence stratigraphy and cyclostratigraphy examples and implications oxfordian from the swiss jura spain and normandy the oxfordian sedimentary successions studied in the swiss jura in normandy and in the soria and cazorla regions of spain display complex facies evolution and stacking patterns based on bio stratigraphy and absolute age dating it is suggested that the shallow water depositional settings in the jura normandy and the soria region as well as the deeper water environments in the cazorla region recorded climatic and sea level fluctuations in the milankovitch frequency band beds and bedsets corresponding to 20 100 and 400 ka cyclicities can be identified facies evolution inside such small scale sequences and also in the larger sequences of million year scale is interpreted in terms of sequence stratigraphy superposition of high frequency cyclicity on a longer term sea level trend led to multiplication of diagnostic surfaces se quence boundary and maximum flooding zones in the large scale sequences can thus be defined these zones are correlated between closely spaced sections but also from the swiss jura to normandy and to spain the narrow time lines given by milankovitch cyclicity then allow comparison of facies evolution in the di erent regions on a scale of 100 ka or less by filtering out local e ects of di erential subsidence and sediment supply a long term sea level curve valid for the northwestern margin of the tethys ocean can be reconstructed for the middle to late oxfordian di erential subsidence is implied from varying thicknesses of the sequences as well as from the distribution of siliciclastics which have been channelized through depressions tilted blocks reduced sedimentation or increased input of siliciclas tics appearing at the same time in all study areas point to a widespread regional tectonic event distribution through the sequences of climate dependent facies components such as corals ooids palynomorphs and siliciclastics indicates that climate changes were depen dent on atmospheric circulation patterns and thus on paleolatitude rainy periods and related increase of siliciclastics in the swiss jura were more abundant during low sea level stands whereas in the soria region they coincided with sea level highs through the com bination of high resolution sequence stratigraphy and cyclostratigraphy and supported by biostratigraphy and absolute dating it becomes possible to analyze paleoenvironmental changes in a very narrow time framework

classification and analysis of palynodebris from the palaeocene sediments of the forties field sedimentary organic matter behaves as sedimentary particles and this study attempts to interpret its occurrence in the palaeocene sands and mudstones of the forties field of the north sea new nomenclature and classification of this palynodebris are presented and are used to make quantitative counts of the palynodebris from nearly 600 samples of known sedimentary character the new categories are further refined by objective testing of the data by principal components analysis and cluster analysis it is argued that two types of sedimentary organic matter are of particular value because they are preferentially deposited in different environments palynowafers are most commonly deposited in the submarine fan lobes and channel complexes and amorphous matter occurs mostly in the lower energy basin plain sediments

use of palynofacies analysis to define lower jurassic sinemurian to pliensbachian genetic stratigraphic sequences in the wessex basin england

palynofacies prediction of distance from sediment source a case study from the upper cretaceous of the pyrenees quantitative variations in the size shape and preservation state of microscopic plant debris assemblages correlate with the actual distance of the sample site from the coastal siliciclastic sediment source a case study from a shelf to basin transect in the upper cretaceous of the spanish pyrenees reveals that 1 the diameter of equant black wood phytoclasts 2 the ratio of equant to lath shaped black wood phytoclasts and 3 several other parameters show predictable changes over a 55 km onshore offshore transect these parameters primarily reflect sedimentological sorting based on particle size and density rather than paleoecological gradients when only samples from the transgressive systems tract are considered multiple regression models predict the distance from the source with a standard error of 5 km r 2 0 84 0 93 these parameters also allow the maximum flooding surface to be more precisely located within mudstone dominated sections by applying the lateral regression relationship to stratigraphic data a quantitative estimate can also be made for the scale of lateral facies shifts through depositional sequences here 10 km

paleo oxygenation in tertiary epeiric seas evidence from dinoflagellate cysts the dinoflagellate cyst record from an epeiric setting in the oligocene of southwest germany exhibits major changes associated with variations in paleo oxygenation inferred from benthic foraminifera dinoflagellate cyst diversity and equitability strongly decline in the case of extreme oxygen depletion the relative abundance of the dinoflagellate cyst thalassiphora pelagica inversely correlates with the availability of benthic oxygen the t pelagica spectrum consists of different morphotypes which are considered to represent different stages within the cystal part of the t pelagica life cycle following the concept of benedek and gocht the distribution of these morphotypes is also linked to oxygen availability horizons with highest t pelagica abundances are characterized by the occurrence of t pelagica specimens representing an early stage in cyst formation a model is proposed that uses t pelagica as a proxy to assess oxygenation both at the sediment surface and in the water column the occurrence of t pelagica specimens representing an early stage in cyst formation is interpreted to reflect the extension of oxygen depletion upwards into the water column because t pelagica is an easily recognized globally distributed element of paleogene and early neogene dinoflagellate cyst assemblages the application of this model may be of importance in the reconstruction of paleo oxygenation in epeiric settings from these times its sensitivity to changes in benthic oxygenation can be as high as if not higher than that of the approach based on foraminifera moreover it is applicable to decalcified sediments

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

seasonal cycle variations on the supercontinent of pangaea the seasonal cycle of temperatures on pangaea early late permian configuration is simulated with a two dimensional energy balance climate model results indicate that the annual range of temperatures in the southern hemisphere of pangaea was considerably larger than any occurring at present maximum mean monthly summer temperatures are 38 c daytime highs probably exceed 45 c in some regions however summer temperatures in polar regions are considerably lower 0 5 c and are favorable for persistence of ice in eastern australia and glaciation in siberia conditions that receive some support from geologic data these simulations suggest that very high summer temperatures and a large annual range are major features of supercontinent environments such conditions may have significantly influenced the distribution of terrestrial permian biota our results are difficult to reconcile with postulated equable climates for some supercontinent configurations

delineating sequence stratigraphic patterns in deeper ramp carbonates quantitative palynofacies data from the upper jurassic kimmeridgian of southwest germany abstract the delineation of sequence stratigraphic patterns in deeper ramp carbonates is notoriously difficult using sedimentological criteria hence in an effort to better understand the processes controlling the formation of deeper water carbonate ramps fully quantitative palynofacies analyses were carried out on two cores from the upper jurassic kimmeridgian of the swabian marl basin sw germany to eliminate the effect of variable carbonate content absolute palynoclast abundances i e particles per gram of sediment were calculated with respect to the non carbonate fraction of the original sediment the palynofacies data were supplemented by bulk sediment oxygen isotope data and sedimentological information terrestrial and marine palynoclast groups show in phase cyclical absolute abundance patterns in both cores investigated highest carbonate adjusted absolute abundances of terrigenous palynoclasts are interpreted to indicate sea level lowstands and vice versa the in phase distribution of marine and terrestrial palynoclast groups points towards a coupling between the terrestrial and marine realms increased absolute abundances of terrigenous palynoclasts are interpreted to represent intervals of enhanced land derived nutrient input into the marine system such higher nutrient availability would have caused higher phytoplankton productivity as evidenced in increased absolute abundances of marine palynomorphs hence marine productivity in the epeiric setting of the swabian marl basin was strongly controlled by the nutrient flux from the surrounding landmasses in the palynofacies and bulk sediment 18o records two hierarchies of sequences are recognized well pronounced medium scale sequences with thicknesses of 5 20 m are built by the stacking of smaller scale sequences with thicknesses of 3 7 m heavier 18o values coincide with high absolute abundances of terrigenous palynoclasts based on this observation a model for environmental fluctuations is proposed time intervals with high sea level were characterized by relatively high water temperatures whereas time intervals with low sea level coincided with relatively low water temperatures estimates of ammonite zone ages available from the literature were used to constrain the duration of medium scale sequences when taking into account the range of dating uncertainties the obtained value of ca 370 kyr appears reasonably close to the duration of the 400 kyr eccentricity cycle we speculate that the formation of medium scale sequences as evidenced in our palynoclast and 18o records may be related to eccentricity driven insolation changes that caused sea level changes with higher insolation leading to a sea level rise this would imply that the regional record of sea level and temperature fluctuations within the epeiric swabian marl basin reflects climatic changes that occurred on a more global scale the integration with sedimentological data shows that marl dominated intervals were deposited during early sea level rise and under cooler conditions whereas limestone dominated intervals formed during intervals of high sea level and under warmer conditions

fabric development as the key for forming ductile shear zones and enabling plate tectonics abstract lithospheric deformation on earth is localized under both brittle and ductile deformation conditions as high temperature ductile rheologies are fundamentally strain rate hardening the formation of localized ductile shear zones must involve a structural or rheological change or a change in deformation conditions such as an increase in temperature in this contribution i develop a localization potential that quantifies the weakening associated with these changes the localization potential corresponds to the increase in strain rate resulting from that change under constant stress conditions i provide analytical expressions for the localization potential associated with a temperature increase grain size reduction an increase in water fugacity melt content or the abundance of a weak mineral phase i show that these processes cannot localize deformation from a mantle convection scale 103 km to a ductile shear zone scale 1 km to achieve this is it necessary to invoke a structural transition whereby the weak phase in a rock forms interconnected layers this process is efficient only if one phase is much weaker than the others or if the weakest phase has a highly non linear rheology micas melt and fine grained aggregates unless dry rheologies are used have the necessary characteristics as none of these phases is expected to be present in the dry lithosphere of venus this concept can explain why venus unlike the earth does not display a global network of plate boundaries the diffuse plate boundary in the central indian ocean may be as yet non localized because serpentinization has not reached the ductile levels of the lithosphere

stratigraphic architecture and gamma ray logs of deeper ramp carbonates upper jurassic sw germany abstract the objective of this paper is to contribute to the development of sequence stratigraphic models for extensive epicontinental carbonate systems deposited over cratonic areas epicontinental carbonates of the sw german upper jurassic were analysed in terms of microfacies sedimentology and sequence stratigraphy based on 2 5 km of core 70 borehole gamma ray logs and 24 quarries facies analysis revealed six major facies belts across the deeper parts of the carbonate ramp situated generally below fair weather wave base and mostly below average storm wave base but in the reach of occasional storm events observed stratigraphic patterns differ in some aspects from widely published sequence stratigraphic models 1 elementary sedimentary cycles are mostly more or less symmetrical and are thus referred to as genetic sequences or genetic units aaapg bull 55 1971 1137 frazier d e 1974 depositional episodes their relationship to the quaternary stratigraphic framework in the northwestern portion of the gulf basin university of texas austin bureau of economic geology geologicalo circular 71 1 aapg bull 73 1989 125 galloway w e hobday d k 1996 terrigenous clastic depositional systems 489 pp springer cross t a baker m r chapin m s clark m s gardner m h hanson m s lessenger m a little l d mcdonough k j sonnenfeld m d valasek d w williams m r witter d n 1993 applications of high resolution sequence stratigraphy to reservoir analysis edition technip 1993 11 33 bull cent rech explor prod elf aquitaine 16 1992 357 homewood p mauriaud p lafont f 2000 best practices in sequence stratigraphy elf ep mem 25 81 pp homewood p eberli g p 2000 genetic stratigraphy on the exploration and production scales elf ep mem 24 290 pp in contrast to the asymmetrical shallowing upward parasequences of the exxon approach 2 neither sequence boundaries nor maximum flooding surfaces could be clearly delineated cycle boundaries are generally not represented by sharp stratal surfaces but are always transitional and thus referred to as turnarounds nor pet soc spec publ 8 1998 171 several types of genetic sequences were delineated both major types of facies and sequences show characteristic gamma ray log signatures based on the cycle stacking and the gamma ray patterns a hierarchy of sequences was recognized probably driven in part by 100 000 and 400 000 year milankovitch signals the cyclicity allowed regional correlations across various depositional environments such as sponge microbial bioherms and coeval basins the basin wide correlation revealed evidence for a subtle clinoform type stratigraphic architecture along very gentle slopes rather than a so far assumed simple layer cake pattern

shallow water aragonite recorded in bundles of limestone marl alternations the upper jurassic of sw germany abstract characteristically limestone marl alternations are conspicuous in outcrop because of differential weathering the marls being predisposed to stronger deterioration superimposed on the bedding rhythms are in many cases lower frequency meter scale rhythms so called bundles these bundles are eye catching from a distance and are typified by variations in thickness of limestone beds and marl interbeds the palaeoenvironmental significance of the bundles received markedly less attention in the literature than the origin of the small scale couplets here we focus on the palaeoenvironmental significance of the bundles by reconstructing the initial mineralogical composition as an example we present a classical limestone marl alternation from the upper jurassic oxfordian kimmeridgian of sw germany that is typified by two orders of bundles superimposed on the limestone marl couplets our method of reconstruction of the original mineralogical composition of the precursor sediment of limestone marl alternations is based on a diagenesis model that assumes dissolution of aragonite and reprecipitation as calcite cement as the major mechanism of early diagenesis calculated initial clay aragonite and calcite contents show rhythmic variations on a scale of several meters that correspond to the bundles as seen in the outcrop limestone dominated parts of the bundles correspond to intervals of elevated aragonite content in the precursor sediment but not necessarily to elevated calcite contents additionally an overlain fluctuation in initial mineralogy on the order of tens of meters mega bundles reflecting the former local subdivision of the sw german upper jurassic into weisjura alpha beta and gamma is observed the limestone dominated weisjura beta lower kimmeridgian is the interval with highest initial aragonite content our new method allows for quantification of initial mineralogical composition as aragonite and calcite usually have different sources shallow water benthic versus planktic this approach potentially adds significant new possibilities for palaeoceanographic interpretation of calcareous rhythmites in the jurassic example the observed variations in reconstructed aragonite content are interpreted as variations in flooding events and related export of aragonitic material from marginal shallow water platforms

high resolution stable isotope stratigraphy from bulk sediment a high quality 18 o record has been obtained from a deep sea core in the somali basin in a water depth of 4020 m well below the foraminiferal lysocline by analyzing bulk sediment instead of picked foraminifera in some areas this may be a valuable tool for extending the applicability of the 18 o stratigraphy for obtaining data by a less laborintensive procedure and for conserving valuable core material additionally we draw attention to the need for more data on 6 3c in bulk carbonate if we are to fully utilize the ocean 6 3c record either in relation to long term global carbon budget or in relation to changes in carbon cycling in the ocean and its effect on atmospheric pco 2

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

third order depositional sequences reflecting milankovitch cyclicity the origin of third order depositional sequences remains debatable and in many cases it is not clear whether they were controlled by tectonic activity and or by eustatic sea level changes in oxfordian and berriasian valanginian carbonate dominated sections of switzerland france germany and spain high resolution sequence stratigraphic and cyclostratigraphic analyses show that the sedimentary record reflects milankovitch cyclicity orbitally induced insolation changes translated into sea level fluctuations which in turn controlled accommodation changes beds and bedsets formed in rhythm with the precession and 100 kyr eccentricity cycles whereas the 400 kyr eccentricity cycle contributed to the creation of major depositional sequences biostratigraphical data allow the correlation of many of the 400 kyr sequence boundaries with third order sequence boundaries recognized in european basins this implies that climatically controlled sea level changes contributed to the formation of third order sequences furthermore this cyclostratigraphical approach improves the relative dating of stratigraphic intervals

stratigraphical and lateral distribution of sedimentary organic matter in upper jurassic carbonates of se france abstract a detailed analysis of sedimentary organic matter som has been carried out in upper jurassic deep water marls and carbonates of the vocontian basin se france its main purpose is to analyse the vertical and lateral trends of som distribution in order to better understand processes and factors controlling the accumulation and preservation of organic constituents in basinal environments the vocontian basin is characterized by widespread oxic depositional environments in the upper jurassic as confirmed by the very low total organic carbon content less than 0 25 wt for such organic poor deposits palynofacies analysis represents the best tool to investigate som stratigraphic analysis of palynofacies trends has been performed within a pre established sequence stratigraphic framework defined by means of field sedimentology and subsequently complemented through lateral correlations biostratigraphical constraints and geochemistry this approach highlights the vertical signatures which are directly related to relative sea level changes furthermore lateral correlations of palynofacies trends at the scale of 3rd and 2nd order cyclicity permit the signatures observable at basin scale to be distinguished from those detectable only at local scale the former are controlled by factors affecting the whole basin such as eustasy regional tectonics and climate the palynofacies signatures at the scale of 3rd order cyclicity reflect relative sea level changes and the degradation state of som taking into account the preservation state of organic constituents leads to a better understanding of the relationship between som and sequence stratigraphy usually condensed sections about maximum flooding surfaces are characterized by a decrease in the relative proportion of the terrestrial organic constituents as far as sequence boundaries are concerned they are marked by an increase in the relative proportion of continental organic matter which results from a renewal of the erosion related to relative sea level fall an increase in fresh woody debris has not been systematically observed at sequence boundaries nevertheless the abundance of fresh woody debris tends to decrease stratigraphically towards maximum flooding intervals and laterally in a distal direction the vertical palynofacies signatures at the scale of 2nd order cyclicity appear to be controlled by tectonics in the upper oxfordian to lower kimmeridgian interval these signatures confirm the hypothesis of a regional uplift of the hinterland and or a differential basin subsidence related to the intense rifting activity in the proto atlantic or to the westward opening of the tethys

reconstruction of short term palaeoceanographic changes during the formation of the late albian niveau breistroffer black shales oceanic anoxic event 1d se france the niveau breistroffer black shale succession in the vocontian basin se france is the regional equivalent of the widely distributed late albian oceanic anoxic event 1d the studied black shale rich interval at the col de palluel section is 6 28 m thick and comprises four black shale units with up to 2 5 wt total organic carbon toc intercalated with marlstones calcareous nannofossil palynomorph planktic foraminifera and stable isotopic data from the niveau breistroffer succession suggest that short term climate changes influenced its deposition with relatively warm and humid climate during black shale formation in comparison with relatively cool and dry climatic conditions during marlstone deposition an increase in the terrigenous marine ratio of palynomorphs indicates enhanced humidity and higher runoff during black shale formation a nutrient index based on calcareous nannofossils and the abundance pattern of small 63 125 m hedbergellid foraminifera show short term changes in the productivity of the surface water surface water productivity was reduced during black shale formation and increased during marlstone deposition a calcareous nannofossil temperature index and bulk rock oxygen isotope data indicate relative temperature changes with warmer surface waters for black shale samples at these times warm humid climate and reduced surface water productivity were accompanied by greater abundances of subsurface dwelling calcareous nannofossils nannoconids and planktic foraminifera rotaliporids these taxa presumably indicate more stratified surface water conditions we suggest that the formation of the niveau breistroffer black shales occurred during orbitally induced increase in monsoonal activity that led to increasing humidity during periods of black shale formation this in turn caused a decrease in low latitude deep water formation and probably an increase in surface water stratification the combination of these two mechanisms caused depleted o 2 concentrations in the bottom water that increased the preservation potential of organic matter