discrepancies between different organic maturity indicators in a coal series affected by an abnormal thermal event visean niger abstract classical petrographical and geochemical approaches have been used to study visean coal seams sampled in two areas 50 km apart in northern niger t max values given by rock eval pyrolysis and individual molecular ratios determined on hopanes and steranes are in agreement with the burial history of the two sets of samples studied the difference of maturity of the two sample sets revealed by these various parameters is consistent with their current difference in burial depth 400 m only small changes of these parameters with depth were observed owing to the small depth interval sampled at both sites 15 and 40 m these variations also appear to be related to normal burial diagenesis no maturity differences between the two sample sets are revealed by vitrinite reflectance data and atomic h c ratios which are in the same range at both sites but display very large variations with depth r v 0 60 1 40 and h c at 0 80 0 90 to 0 55 these data indicate rapid entrance into the oil window this conclusion also being supported by microspectrofluorimetric observations showing oil production and expulsion and by the presence of pyrobitumens containing large devolatilization vacuoles in the deepest samples the abnormally high maturity gradient could have been caused by a hydrothermal event the present observations on coals confirm and supplement previous conclusions drawn from the study of organic materials disseminated in zn pb sulfide ore bearing sedimentary rocks the difference in sensitivity shown by the various maturity indicators is considered very likely to be due to differences in the kinetics of the transformations on which they each depend

mineralogical and isotopic record of biotic and abiotic diagenesis of the callovian oxfordian clayey formation of bure france abstract the callovian oxfordian cox clayey unit is being studied in the eastern part of the paris basin at depths between 400 and 500 m depth to assess of its suitability for nuclear waste disposal the present study combines new mineralogical and isotopic data to describe the sedimentary history of the cox unit petrologic study provided evidence of the following diagenetic mineral sequence 1 framboidal pyrite and micritic calcite 2 iron rich euhedral carbonates ankerite sideroplesite and glauconite 3 limpid calcite and dolomite and celestite infilling residual porosity in bioclasts and cracks 4 chalcedony 5 quartz calcite pyrite in bioturbations shows a wide range of 34s 38 to 34 5 providing evidence of bacterial sulphate reduction processes in changing sedimentation conditions the most negative values 38 to 22 measured in the lower part of the cox unit indicate precipitation of pyrite in a marine environment with a continuous sulphate supply the most positive pyrite 34s values 14 up to 34 5 in the upper part of the cox unit indicate pyrite precipitation in a closed system celestite 34s values reflect the last evolutionary stage of the system when bacterial activity ended however its deposition cannot be possible without sulphate supply due to carbonate bioclast dissolution the 87sr 86sr ratio of celestite 0 706872 0 707040 is consistent with deposition from jurassic marine derived waters carbon and oxygen isotopic compositions of bulk calcite and dolomite are consistent with marine carbonates siderite only present in the maximum clay zone has chemical composition and 18o consistent with a marine environment its 13c is however lower than those of marine carbonates suggesting a contribution of 13c depleted carbon from degradation of organic matter 18o values of diagenetic chalcedony range between 27 and 31 suggesting precipitation from marine derived pore waters late calcite crosscutting a vein filled with chalcedony and celestite and late euhedral quartz in a limestone from the top of the formation have lower 18o values 19 suggesting that they precipitated from meteoric fluids isotopically close to present day pore waters of the formation finally the study illustrates the transition from very active biotic diagenesis to abiotic diagenesis this transition appears to be driven by compaction of the sediment which inhibited movement of bacterial cells by reduction of porosity and pore sizes rather than a lack of inorganic carbon or sulphates

martian north polar cap summer water cycle abstract a key outstanding question in martian science is are the polar caps gaining or losing mass and what are the implications for past current and future climate to address this question we use observations from the compact reconnaissance imaging spectrometer for mars crism of the north polar cap during late summer for multiple martian years to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer we establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap we show that in a key region in the interior of the north polar cap the absorption band depths grow until l s 120 when they begin to shrink until they are obscured at the end of summer by the north polar hood this behavior is transferable over the entire north polar cap where in late summer regions flip from being net sublimating into net condensation mode this transition or mode flip happens earlier for regions closer to the pole and later for regions close to the periphery of the cap the observations and calculations presented herein estimate that on average a water ice layer 70 microns thick is deposited during the l s 135 164 period this is far larger than the results of deposition on the south pole during summer where an average layer 0 6 6 microns deep has been estimated by brown et al 2014 earth planet sci lett 406 102 109

dynamics of a stepped carbon isotope excursion ultra high resolution study of early toarcian environmental change abstract in the toarcian early jurassic 183 myr ago the ocean atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250 myr known as the toarcian oceanic anoxic event t oae this event was accompanied by a 6 negative carbon isotope excursion cie caused by massive injection of isotopically light carbon into the ocean atmosphere system possibly from destabilisation of gas hydrates this study reveals the pacing and sequence of events leading up to the cie and to widespread deposition of organic rich sediments the very high resolution isotopic record from exceptionally well preserved carbonate and organic matter from the paris basin enables recognition of increased co 2 levels 130 kyr in advance of the major negative cie an accelerated increase in the p co 2 is registered 25 kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the paris basin undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface dwelling calcifiers these environmental perturbations representing precursor phases of co 2 injection predate the first step towards relatively light carbon isotopes in carbonate and organic matter and are tentatively attributed to karoo ferrar magmatism this negative shift was registered slightly earlier in terrestrial carbon than marine carbonate subsequent global warming is credited with liberating isotopically light carbon and ultimately fostered anoxia in the paris basin the response of these cumulative inputs of carbon to the earth system isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative cie suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation 45 kyr after the first step of the cie this re establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

measurements of thermal properties of icy mars regolith analogs in a series of laboratory experiments we measure thermal diffusivity thermal conductivity and heat capacity of icy regolith created by vapor deposition of water below its triple point and in a low pressure atmosphere we find that an ice regolith mixture prepared in this manner which may be common on mars and potentially also present on the moon mercury comets and other bodies has a thermal conductivity that increases approximately linearly with ice content this trend differs substantially from thermal property models based of preferential formation of ice at grain contacts previously applied to both terrestrial and non terrestrial subsurface ice we describe the observed microphysical structure of ice responsible for these thermal properties which displaces interstitial gases traps bubbles exhibits anisotropic growth and bridges non neighboring grains we also consider the applicability of these measurements to subsurface ice on mars and other solar system bodies

a revised surface age for the north polar layered deposits of mars this work was funded by nasa grant nnx13ag72g m e l was supported by the national science foundation graduate research fellowship program grant dge 1143953 hirise images referenced are available on the instrument s public website https hirise lpl arizona edu the crater catalog used in this work is included with this paper as supporting information the authors thank s sutton for help with socet set software m m sori for useful discussion on viscous relaxation and m e banks for useful discussion on the impact population the authors additionally thank j a skinner p becerra d laikko m sori n barlow and an anonymous reviewer for helpful comments on the manuscript

the magnetization of clay rich rocks in sedimentary basins low temperature experimental formation of magnetic carriers in natural samples abstract rocks are often magnetically altered during burial thus providing a useful method to study their thermo chemical history in order to improve the understanding of burial diagenetic magnetization we experimentally synthesized magnetite in natural samples lower jurassic argillites from the paris basin were heated to 150 c under a confined atmosphere of argon when a magnetic field was applied during the heating a chemical remanent magnetization was acquired rock magnetism studies reveal that most of the newly formed magnetic carriers were magnetite using anhysteretic remanent magnetization as a measure of the quantity of magnetite an increase of up to 150 after heating was observed ferrimagnetic iron sulphide and hematite are observed to have formed in samples composed of less than 3 calcite and new magnetite is sometimes completely absent in samples containing less than 0 5 calcite hysteresis measurements suggest that the new magnetite is in the pseudo single domain state scanning electron microscope studies indicate that the new magnetic carriers are associated with pre existing pyrite the magnetic transformations during the experiments involved a fluid which reacted with iron bearing and sulfur bearing minerals in ways depending on local redox conditions this study shows that magnetite can be produced in argillaceous sediments at the normal temperatures and pressures found in sedimentary basins without any external supply from long range fluid flow

viscous flow rates of icy topography on the north polar layered deposits of mars we investigate the importance of viscous flow in shaping topography at the north polar layered deposits npld of mars by using finite element modeling to calculate the distribution of stresses and flow velocities present day impact craters on thenpldare too small and cold for viscous relaxation tohavebeen an important mechanism in controlling their current dimensions this effect may be ignored when analyzing crater size frequency distributions scarps at the npldmargins where avalanches of dust and carbon dioxide frost occur are sufficiently steep high andwarm to experience significant viscous flow we find flow velocities at the base of these steep scarps on the order of tens to hundreds of cm yr which are fast enough to significantly affect their slopeover kiloyear timescales alternatively the scarps could be close to steady state in which observed block falls provide a competing effect to viscous flow

geochemical disturbance and paleoenvironmental changes during the early toarcian in nw europe the early toarcian oceanic anoxic event oae is associated with a rapid and severe environmental change whose causes are still a matter of debate a new paleoenvironmental interpretation is proposed based on a multidisciplinary dataset chemical mineralogical and paleontological obtained from a borehole drilled by andra french national radioactive waste management agency in the lower toarcian of the eastern paris basin france during the earlymost toarcian tenuicostatumzone the presence ofwell oxygenated sea water is reflected by an abundant and diverse fauna alongwith paleoredox proxies u al mo al and v al typical of oxidizing conditions associated with predominant mechanical weathering on the continent at the base of the serpentinum zone an important paleoenvironmental change is marked by an initial phase of organic matter enrichment 12 toc during the negative shift of 13c carbon isotope excursion cie euxinic anoxic conditions indicated by cobalt enrichment and the development of framboidal pyrite lead to the disappearance of the benthic and pelagic fauna and alloworganic matter to be preserved in the sediments at this time the lowconcentration of paleoproductivity proxies cd p ni and zn suggests weak chemical weathering on the continent due to a rather arid climate low concentrations of sr and coccoliths are due to an input of fresh water probably coming from the arctic through the laurasian seaway thus the isolation of the paris basin from the tethyan realm and the influx of freshwater favour haline stratification and the preservation of organic matter following the cie oxygen concentration gradually increases up to amaximumflooding surface dated as coevalwith the serpentinum zone elegantulum subzone paleoproductivity proxies indicate a weak primary productivity the top of the lower toarcian is characterized by a second enrichment in organic matter 12 toc due to an important input of nutrients this enhanced primary production generates euxinic anoxic conditions in the sediment and in part of the water column leading to a high enrichment in paleoredox proxies mo u v co and causing the sudden disappearance of the benthic fauna and a progressive decline of the pelagic fauna the metal enrichment is related to intense chemical weathering on the continent due to a more humid climate

implications of spatial and temporal evolutions of thermal parameters in basin modelling this paper presents the paris basin numerical modelling at a high sequential resolution scale 1 5 my simulations were carried out from the computation of thermal gradients and conductivities varying with the burial of genetic units geologic heating rates are also calculated throughout the burial of the stratigraphic sequences thermal energies are then deduced the paris basin is well known for its hydrocarbon potential in liassic sediments this study is focused on an east west cross section through the basin the results show spatial and temporal variations of thermal parameters from the western to the eastern part of the profile the reactivation of hercynian fracture systems during the mesozoic may be responsible for the computed variations in thermal conductivities and thermal gradients major geodynamic events also played a role in the simulated thermal history variations of the thermal energy are observed and are well correlated with the burial history of the basin we suggest linking the simulated thermal energies to the thermal cracking of the organic matter our results are consistent with the prediction of hydrocarbon potential in the cretaceous period consequently this approach provides new insights to improve petroleum generation modelling issues

continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle toarcian in the paris basin abstract lower toarcian strata lower jurassic have been extensively studied with a view to understanding the oceanographic climatic and biological processes that drove the earth s system into an oceanic anoxic event oae for this time period the evolution of the european marine seaways is now relatively well constrained owing to multiple geochemical studies but investigations regarding climatic trends in the continental realm remain sparse in the present study we test the clay mineralogy as a continental climate sensitive proxy in the well documented sancerre core southern paris basin we compare variations in the kaolinite content with p co 2 fluctuations derived from paired carbon isotopes 13 c 13 c carb 13 c org taking advantage of the detailed chemostratigraphic palaeoenvironmental and sequence stratigraphy frameworks established for this core material the results indicate a substantial decrease in kaolinite abundance at the end of the pliensbachian which is compatible with a long term diminution in continental weathering and an inferred temperature decrease the early toarcian prior to the carbon cycle perturbation and deposition of black shale facies remained relatively cold with minima in both the proportion of kaolinite and reconstructed p co 2 the mineralogical and geochemical responses across the prominent negative carbon isotope excursion cie itself are not univocal the first of four steps that compose the negative limb of the cie at sancerre is associated with decreased kaolinite and p co 2 and increased carbonate oxygen isotope ratios taken together these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition conversely the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in yorkshire providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the cie relaxation in the intensity of continental weathering as suggested by resumed low kaolinite abundance is seen immediately after the cessation of co 2 input after the fourth step of the cie the interval spanning the upper portion of the early toarcian and the middle toarcian records a subsequent long term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment continued greenhouse conditions even after the recovery from the carbon isotope perturbation and regional black shale deposition are likely related to sustained co 2 emission by karoo ferrar volcanism through the considered interval

sedimentological evidence concerning the paleoceanography of the cretaceous western north atlantic ocean abstract black clays developed as a result of progressively intensifying intermittent anoxic conditions from the early through mid cretaceous the preservation of primary sedimentary structures of authigenic minerals such as pyrite and siderite and of significant amounts of organic carbon testify to the stagnant conditions intermittent anoxic conditions prevailed in the deepest portion of the basin resulting from vertical migration of an intrasediment anoxic interface middle aptian variegated clays within the black clay sequence at several low latitude sites suggest a widespread oxygenation event of short duration occurred there greater thicknesses of black clays accumulated in low latitudes implying that surface or intermediate depth currents redistributed the sediments south ward millimeter scale laminae characterizing the early and mid cretaceous sediments represent seasonal sediment input where seasons during the cretaceous had durations measured in years cenomanian variegated clays succeeded the black clay interval and represent deposition under totally oxygenated conditions thus the sluggish and stagnant conditions present in the early and mid cretaceous were followed by increased current activity these currents were derived from more northern latitudes as iberia was rifted from north america cooler temperatures presumably increased the oxygen capacity of the water and its ability to sink into the deep basin to relieve the stagnant conditions present the late cenomanian through late campanian was a time of widespread marine transgression resulting in the deep ocean becoming a sediment starved basin clastics and carbonates accumulated on the shelves as the calcite compensation depth ccd shallowed appreciably the late campanian through maastrichtian interval is characterized by calcium carbonate accumulation throughout much of the deep basin a significant lowering of sea level paralleled by a deepening ccd caused this sedimentation pattern

the state and future of mars polar science and exploration as the planet s principal cold traps the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of 10 6 km 2 and total as much as 3 4 km thick from the scarcity of superposed craters on their surface these layered deposits are thought to be comparatively young preserving a record of the seasonal and climatic cycling of atmospheric co 2 h 2o and dust over the past 10 5 10 8 years for this reason the martian polar deposits may serve as a rosetta stone for understanding the geologic and climatic history of the planet documenting variations in insolation due to quasiperiodic oscillations in the planet s obliquity and orbital elements volatile mass balance atmospheric composition dust storm activity volcanic eruptions large impacts catastrophic floods solar luminosity supernovae and perhaps even a record of microbial life beyond their scientific value the polar regions may soon prove important for another reason providing a valuable and accessible reservoir of water to support the long term human exploration of mars in this paper we assess the current state of mars polar research identify the key questions that motivate the exploration of the polar regions discuss the extent to which current missions will address these questions and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding

origin of mid cretaceous black shales in the benue through nigeria abstract black and dark gray laminated shales with large amounts of both terrestrial and marine organic material are common in upper cenomanian to lower santonian rocks of the benue trough these shales were deposited during global mid cretaceous marine transgressions when widespread high organic carbon sedimentation took place the benue trough in those times was the site of a shallow density stratified anoxic epeiric sea with estuarine type circulation from this reservoir nutrient rich oxygen depleted waters were fed into the northern parts of the south atlantic ocean

enhancement of accumulation and anoxic degradation of organic matter controlled by cyclic productivity a model abstract the aim of the study is to determine the relative influences of the genetic sources the export efficiency and the anaerobic degradation of organic carbon as factors controlling short term cyclic organic rich sedimentation in areas of high marine productivity a cyclic organic sequence of the kimmeridge clay formation of yorkshire u k was studied as an example of ancient sedimentation this formation outcropping in the cleveland basin near marton is known as a lateral equivalent of the major oil source rock unit of the north sea on the basis of petrographic and geochemical results a new model is proposed to explain the short term cyclic sedimentation of organic carbon under continuously anoxic bottom conditions the model assumes that the cyclicity is primarily controlled by variations of mineral free phytoplanktonic productivity such variations are thought to induce changes in carbon recycling in the photic zone so that the export efficiency of the metabolizable organic matter is modified a high sulphate reduction intensity relative to the organic matter flux is observed for the highest productivity periods which also reflects an enhancement of export efficiency as the redox conditions did not change significantly such variations in sulphate reduction intensity must be attributed not only to quantitative variations in the export productivity but also to its qualitative variations with more metabolizable organic matter reaching the anoxic domain during high productivity periods biosedimentary processes depending on productivity such as aggregation are thought to play an important role in reducing the transit time of metabolizable organic matter to the sediment finally the model implies that the amplitude of export productivity variations probably were larger than that of toc variations recorded in sediment which are mainly due to biologically refractory organic matter from plankton

if martian ice caps flow ablation mechanisms and appearance abstract assuming that the northern ice cap of mars is thick enough to flow like terrestrial ice sheets a model is presented that explains i the origins movement and spiral nature of the scarp trough complexes ii the reentrant valleys like chasma boreale and iii the layered terrain accumulation and ablation are discussed in relation to the scarps and a model is developed relating them to ice flow and scarp velocities and to the particle paths within the ice cap a brief summary of terrestrial ice sheet flow and mass balance is given in order to illustrate and clarify the concepts used to model the martian ice caps

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

isotopic diffusion in cold snow and firn molecular mixing in cold snow and firn is ordinarily controlled by vapor diffusion diffusion through or along the ice matrix is slow whereas diffusion from the air to within separate grains is comparatively rapid thus mixing occurs in the vapor phase and exchange with the local ice involves all the water molecules a quantification of these concepts is applied to the diffusion of oxygen isotopic depth profiles in southern greenland and at dome c antarctica it successfully describes the smoothing of measured profiles the smoothing rate is strongly dependent on temperature and density of the firn

north polar deposits of mars extreme purity of the water ice 1 the polar layered deposits are the largest reservoir of water on the surface of mars the physical properties of the ice and their spatial distribution are largely unknown 140 000 data points from the sounding radar sharad on the mars reconnaissance orbiter were analyzed over the gemina lingula region one fourth of the north polar layered deposits area maps of the dielectric properties of the bulk ice were drawn up there is no basal melting signature a drop of the dielectric constant in north west of gemina lingula could be explained by an abrupt 250 meter uplift of the base the bulk ice of the studied region has an average dielectric constant of 3 10 0 12 and a loss tangent 0 0026 0 0005 analytic interpretations shown the volume of ice is pure at 95 the impurities have a radial distribution with higher concentrations at margins

preservation of midlatitude ice sheets on mars national science foundation nsf dge 1143953 nasa earth and space sciences fellowship nessf nnx16ap09h nasa mars data analysis program mdap award nnx15am62g

ocean wide stagnation episode in the late cretaceous in this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid cretaceous here called the cenomanian turonian black shale horizon ctbsh the occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments the stratigraphic record above and below the ctbsh in environments as different as the deep north atlantic ocean and marginal and epicontinental seas over enormous areas in north america north africa and northwestern europe is characterized by a stratigraphic gap a disconformity or a continuous but strongly condensed stratigraphic section the anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2 no simple model has yet been found to explain the occurrence of the ctbsh in such a wide range of depth and palaeoenvironmental conditions

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

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

effect of the thermal gradient variation through geological time on basin modeling a case study the paris basin many studies investigated the thermal modeling of the paris basin for petroleum interests during the 1970s most of the softwares developed by oil companies or research centers were based on the assumption of a constant thermal gradient in order to take into consideration the variation of the thermal gradient during basin evolution we developed the thermo s visual basic 1d program we applied our model to twenty boreholes located along a cross section roughly running ew over 150 km in the center of the paris basin the numerical results were calibrated with organic matter maturity data thermo s simulates the amount of heat provided to the sedimentary organic matter the heat parameter simulated shows lateral variation along the cross section it decreases from rambouillet to trou aux loups boreholes 87 66 mw m2 at about 100 km more to the east whereas the heat flux value simulated is 73 mw m2 in st loup borehole the mean thermal gradient calculated for liassic horizons at 87 my for the rambouillet well is 50 4 c km this value is similar to previously published results by integrating the calculation of the thermal gradients and conductivities related to the burial of each stratigraphic sequence our approach points out variations in the thermal regimes the sedimentary organic matter som has been subjected to through geological time

constraints on the composition of the martian south polar cap from gravity and topography abstract the polar caps of mars have long been acknowledged to be composed of unknown proportions of water ice solid co 2 dry ice and dust gravity and topography data are here analyzed over the southern cap to place constraints on its density and hence composition using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading the best fit density of the volatile rich south polar layered deposits is found to be 1271 kg m 3 with 1 limits of 1166 and 1391 kg m 3 the best fit elastic thickness of this geologically young deposit is 140 km though any value greater than 102 km can fit the observations the best fit density implies that about 55 dry ice by volume could be sequestered in these deposits if they were completely dust free alternatively if these deposits were completely free of solid co 2 the dust content would be constrained to lie between about 14 and 28 by volume the bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust however even if a moderate quantity of solid co 2 were present as horizontal layers the bulk thermal conductivity of the polar cap would be significantly reduced reasonable estimates of the present day heat flow of mars predict that dry ice beneath the thicker portions of the south polar cap would have melted depending on the quantity of solid co 2 in these deposits today it is even possible that water ice could melt where the cap is thickest if independent estimates for either the dust or co 2 content of the south polar cap could be obtained and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not it would be possible to use these observations to place tight constraints on the present day heat flow of mars

hydrothermal origin for the 2 billion year old mount tom price giant iron ore deposit hamersley province western australia giant iron ore deposits such as those in the hamersley province of northwestern australia may contain more than a billion tonnes of almost pure iron oxides and are the world s major source of iron it is generally accepted that these deposits result from supergene oxidation of host banded iron formation bif accompanied by leaching of silicate and carbonate minerals new textural evidence however shows that formation of iron ore at one of those deposits mount tom price involved initial high temperature crystallisation of magnetite siderite iron silicate assemblages this was followed by development of hematite and ferroan dolomite bearing assemblages with subsequent oxidation of magnetite leaching of carbonates and silicates and crystallisation of further hematite preliminary fluid inclusion studies indicate both low and high salinity aqueous fluids as well as complex salt rich inclusions with the range of fluid types most likely reflecting interaction of hydrothermal brines with descending meteoric fluids initial hematite crystallisation occurred at about 250 c and high fluid pressures and continued as temperatures decreased although the largely hydrothermal origin for mineralisation at mount tom price is in conflict with previously proposed supergene models it remains consistent with interpretations that the biosphere contained significant oxygen at the time of mineralisation

age scale of the air in the summit ice implication for glacial interglacial temperature change the air occluded in ice sheets and glaciers has in general a younger age defined as the time after its isolation from the atmosphere than the surrounding ice matrix because snow is first transformed into open porous firn in which the air can exchange with the atmosphere only at a certain depth firn ice transition the pores are pinched off and the air is definitely isolated from the atmosphere the firn ice transition depth is at around 70 m under present climatic conditions at summit central greenland the air at this depth is roughly 10 years old due to diffusive mixing whereas the ice is about 220 years old this results in an age difference between the air and the ice of 210 years this difference depends on temperature and accumulation rate and did thus not remain constant during the past we used a dynamic firn densification model to calculate the firn ice transition depth and the age of the ice at this depth and an air diffusion model to determine the age of the air at the transition past temperatures and accumulation rates have been deduced from the 18o record using time independent functions we present the results of model calculations of two paleotemperature scenarios yielding a record of the age difference between the air and the ice for the greenland ice core project grip and the greenland ice sheet project two gisp2 ice cores for the last 100 000 years during the holocene the age difference stayed rather stable around 200 years while it reached values up to 1400 years during the last glaciation for the colder scenario the model results are compared with age differences obtained independently by matching corresponding climate events in the methane and 18o records assuming a very small phase lag between variations in the greenland surface temperature and the atmospheric methane the past firn ice transition depths are compared with diffusive column heights obtained from 15n of n2 measurements the results of this study corroborate the large temperature change of 20 to 25 k from the coldest glacial to holocene climate found by evaluating borehole temperature profiles

firn densification in a late noachian icy highlands mars implications for ice sheet evolution and thermal response abstract recent modeling of a thicker early co2 martian atmosphere and late noachian climate predicts that for pressures beyond a fraction of a bar atmosphere surface thermal coupling occurs resulting in adiabatic cooling of high areas across mars this promotes the transport of water ice from relatively warmer low lying areas to the highlands where deposition and accumulation of water ice result in an icy highlands late noachian mars deposits will remain stable in the highlands under nominal late noachian conditions but the potential exists for punctuated heating by both top down e g impacts volcanism and bottom up e g elevated geothermal heat flux processes important in understanding melt generation from these processes is the state of the accumulated snow and ice through modeling of the firn densification process in the icy highlands framework we assess 1 the nature of snow accumulation and the physical growth and evolution of the predicted ice deposits and 2 the implications for the thermal properties of the ice sheets and the response to heating events analysis of the firn densification process in the icy highlands context indicates that 1 the upper layers of the ice sheet will be more vulnerable to melting from top down heating processes because they are comprised of the least dense and least thermally conductive ice and 2 even with a low thermal conductivity firn layer basal melting is only likely to occur through a combination of top down and bottom up heating this is because at the nominal mean annual surface temperatures and estimated effective thermal conductivities the predicted ice sheet thicknesses do not produce enough basal warming to initiate melting for plausible geothermal heat fluxes variations in spin axis orbital parameters alone are not predicted to cause widespread ablation melting and sublimation of the icy highlands ice sheets

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

landscape evolution in martian mid latitude regions insights from analogous periglacial landforms in svalbard periglacial landforms on spitsbergen svalbard norway are morphologically similar to landforms on mars that are probably related to the past and or present existence of ice at or near the surface many of these landforms such as gullies debris flow fans polygonal terrain fractured mounds and rock glacier like features are observed in close spatial proximity in mid latitude craters on mars on svalbard analogous landforms occur in strikingly similar proximity which makes them useful study cases to infer the spatial and chronological evolution of martian coldclimate surface processes the analysis of the morphological inventory of analogous landforms on svalbard and mars allows the processes operating on mars to be constrained different qualitative scenarios of landscape evolution on mars help to better understand the action of periglacial processes on mars in the recent past

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

shallow radar sharad pedestal craters and the lost martian layers initial assessments 1 since their discovery martian pedestal craters have been interpreted as remnants of layers that were once regionally extensive but have since been mostly removed pedestals span from subkilometer to hundreds of kilometers but their thickness is less than 500 m except for a small equatorial concentration in the medusae fossae formation the nearly exclusive occurrence of pedestal craters in the middle and high latitudes of mars has led to the suspicion that the lost units bore a significant fraction of volatiles such as water ice recent morphological characterizations of pedestal deposits have further supported this view here we employ radar soundings obtained by the shallow radar sharad to investigate the volumes of a subset of the pedestal population in concert with high resolution imagery to assist our interpretations from the analysis of 97 pedestal craters we find that large pedestals diameter 30 km are relatively transparent to radar in their majority with sharad being able to detect the base of the pedestal deposits and possess an average dielectric permittivity of 4 0 5 in one of the cases of large pedestals in malea planum layering is detected both in sharad data and in high resolution imagery of the pedestal margins we find that clutter is a major issue in the analysis of radar soundings for smaller pedestals and tentative detection of the basal reflection occurs in only a few of the cases examined these detections yield a higher average permittivity of 6 the permittivity value derived for the larger pedestals for which a basal reflection is unambiguous is higher than that of pure water ice but lower than that of most silicate materials a mixture of ice and silicates or an ice free porous silicate matrix can explain a permittivity of 4 and radar alone cannot resolve this nonuniqueness data from the compact reconnaissance imaging spectrometer crism tentatively confirms a mafic component in at least one pedestal in malea planum interpretation of sharad results can support either a mixture of ice and silicates or a porous silicate the former is compatible with a model where nonpolar ice is periodically deposited in the midlatitudes as a result of obliquity variations the latter is compatible with ash deposits at least in where pedestals appear in volcanic centers such as malea planum

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

organic facies of middle cretaceous black shales in deep north atlantic the middle cretaceous black shales of the deep north atlantic consist of alternating layers of sediment rich in total organic carbon toc that contains abundant amorphous types of organic matter and sediment poor in toc that contains mostly woody and coaly types of organic matter the amorphous materials are derived mostly from marine organisms in the eastern north atlantic off africa in the caribbean and on the demerara rise off surinam and from higher land plants in the western north atlantic and off europe marine amorphous material is important off africa because this was an area of upwelling and highly productive surface water amorphous marine organic matter was deposited across the entire north atlantic basin in the cenomanian in response to an ocean wide upwell ng event connected with the opening of the equatorial atlantic the difference between the toc rich and background toc layers reflects deposition of the former under reducing conditions which allowed the preservation of labile amorphous materials of marine and terrestrial orgin and of the latter under oxidizing conditions when nearly all that was preserved was refractory organic material

sedimentation de la matiere organique dans le nord est du bassin de paris consequences sur le depot des argilites carbonees du toarcien inferieur organic matter sedimentation in the northeast of the paris basin consequences on the deposition of the lower toarcian black shales abstract a borehole realised by the agence nationale pour la gestion des dichets radioactifs andra near the village of montcomet aisne in the paris basin allowed to core about 1 km of jurassic series the organic matter om associated to the drilled series has been characterised by various well proven methods rock eval pyrolysis palynofacies study and saturated hydrocarbon analysis the series received variable but notable amounts of inputs of om of terrestrial origin during all the jurassic these inputs probably originated from the ardennes massif near the study area the conditions of preservation of these inputs being poor during the early jurassic improved markedly at the beginning of the domerian and then apparently remained rather constant at least up to the callovian during three distinct and rather well limited periods important amounts of algae derived om added to the background of terrestrial om the most important and the best known of these episodes corresponds to the black shales of the base of the lower toarcian lateral equivalent of the well known schistes carton these results suggest that in the paris basin the deposition of om rich sediments occurred during episodes of high planktonic production happening when medium conditions were favourable to om preservation the quantitative and qualitative fluctuations of the om all along the studied series accompany and describe three of the large transgression regression cycles recently evidenced in the paris basin guillocheau 1991 late carnian toarcian aalenian bathonian and callovo oxfordian one episode of accumulation of planktonic om appears to have occurred in each of these cycles in the neighbourhood of transition transgression regression in the present state of knowledge only the confinement behind sills in a structured basin seems capable of explaining the triggering of episodes of planktonic production in the paris basin these conditions of confinement appear to have mainly resulted from a notable structuration of the platforms and of the adjacent troughs due to 1 subsidence during the tectonic cycles and 2 to distensive tectonic activity during tectono eustatic cycles

densification of water ice deposits on the residual north polar cap of mars abstract understanding the density evolution of any ice deposits on the martian north polar residual cap is key to understanding whether the cap contains a climate record in the form of occluded samples of past atmospheres we present a physical model for densification of water ice deposits on the cap due to gravity driven sintering and temperature gradient driven vapor transport the model predicts the steady state profile of porosity versus depth in the ice cap for specified time independent mass accumulation rate and surface deposition density and for surface temperatures with specified diurnal and seasonal variations that comprise an invariant annual cycle we find that in contrast to the analogous situation on earth vapor transport dominates densification in the current martian climate this mechanism can produce very low porosity near surface ice even when accumulation rates are small but positive comparable to those presently thought to occur thus recent inferences of high thermal inertia on the cap may not necessarily imply that the cap is ablating the model predicts a sharp transition between temperature and accumulation conditions under which a deep firn column results and those characterized by very low surface porosity finally we derive a temporal frequency dependent thermal inertia for a vertically inhomogeneous medium observations of this quantity are at least in principle useful for remote estimation of the ice cap density variations within about 10 m of the surface

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

vertical and lateral changes in organic matter from the mesozoic eastern paris basin france variability of sources and burial history abstract the callovian oxfordian claystones located at 500 m depth in the eastern paris basin are currently being investigated by andra the french national radioactive waste management agency for long term geological nuclear waste disposal for this purpose a recent 2000 m deep well was drilled close to the andra underground research laboratory this borehole penetrated the mesozoic sedimentary series for a detailed study of the sediments located beneath the target formation it also provides the opportunity to study the vertical evolution of the sedimentary organic matter and its thermal maturity in this part of the basin where the thickness of sedimentary eroded cover is poorly constrained to extend this study at the scale of the eastern paris basin 5 more wells and numerous outcrops were sampled sedimentary organic matter characterization was performed on kerogen rock eval pyrolysis organic petrography and mean huminite and vitrinite reflectance measurements and on the extractible organic fraction gas chromatography mass spectrometry results show that inputs of organic matter during the mesozoic were essentially of terrigenous origin except during the toarcian where marine contributions are predominant the major macerals present are huminite ulminite vitrinite collotelinite and inertinite inertodetrinite and fusinite vitrinite shows a regular increase of reflectance with depth in the 2000 m depth well correlations between t max vitrinite reflectance and biomarker data define the thermal maturity of the mesozoic sediments maturity is reached at 1300 1500 m present day depth in the 2000 m well in the upper triassic at the regional scale the organic matter maturity of each sedimentary formation decreases towards the eastern part of the basin probably in relation to a decrease of the jurassic and or cretaceous cover thickness which is now eroded all results indicate the lack of hydrocarbon generation in the mesozoic series in this part of the basin

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

sedimentary and metamorphic lithofacies of the lower negaunee iron formation marquette district michigan usa the base of the proterozoic negaunee iron formation is exposed in the open pit at tilden mine marquette michigan juxtaposed against the archean aged palmer gneiss it is bounded by the regional scale southern shear zone and cut by two sets of dykes an older chloritic and schistose set and a younger 1 1 ga keweenawan set tilden mine is dominated by a 100 m scale plunging northwest anticline and is cut by a growth fault locally termed the tower hill fault that intersects the southern shear zone the base of the exposed iron formation is composed of three lithofacies including lower clastics that grade into the overlying banded iron formation that in turn grades upward into granular iron formation this succession is capped by chloritic metadiabases locally termed the summit hill sill and pillar intrusive petrographic and mineral chemical investigations document primary or early diagenetic hematite siderite and possibly ferri hydrite metamorphic and related hydrothermal magnetite chlorite late mar

h2o grain size and the amount of dust in mars residual north polar cap in mars north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and h2o grains of comparable size and abundance however metamorphism of such material will gradually lower its albedo by increasing the size of the h2o grains only if the cap is undergoing net annual sublimation as inferred from water vapor observations late summer observations should be of old ice with h2o grain sizes of 100 microns or more ice of this granularity containing 30 percent fine dust has a reflectivity similar to that of dust alone the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less the brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by viking and aged for thousands of years the residual cap surface cannot be old dirty ice it could be old coarse and clean or it could be young fine and dirty this brings into question both the source of the late summer water vapor and the formation rate of laminated terrain

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

lineations on the white accumulation areas of the residual northern ice cap of mars their relation to the accublation and ice flow hypothesis abstract mars orbiter camera moc images of the whiter areas of the residual north polar cap p c thomas et al 2000 nature404 161 164 show a gentle hummocky pitted surface that has been popularly called cottage cheese terrain the pits are 1 or 2 m deep and tens of meters across they are typically joined in roughly linear strings or long depressions and these features are referred to here as lineations the lineations tend to have one or occasionally two preferred directions we have examined the moc imagery for the north cap and using high resolution images that have good wide angle context images were able to determine the lineation angles for 31 sites scattered over most of the ice cap we propose a process that will produce linear features in the white areas then relate the orientation of the lineations over much of the north cap to these processes and the inferred ice flow direction there is first order agreement between the measured sign of the lineation angles and those predicted assuming ice flow higher accumulations and velocities are predicted in the catchment for ice that flows into chasma boreale this comes from the indications that katabatic winds are concentrated in this catchment