stable organic carbon isotope stratigraphy across oceanic anoxic event 2 of demerara rise western tropical atlantic ocean drilling program odp leg 207 recovered expanded sections of organic carbon rich laminated shales on demerara rise western tropical atlantic high resolution organic carbon isotope and total organic carbon toc records are presented which span the cenomanian turonian boundary interval ctbi including the oceanic anoxic event oae 2 from four sites oriented along a nw striking depth transect these records represent the first high resolution carbon isotope records across oae 2 from the south american margin of the tropical atlantic due to the scarcity of age significant fossils the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the ctbi across the depth transect and to tie this to biostratigraphically well defined sections in the western interior basin pueblo usa boreal shelf seas eastbourne england and western tethys oued mellegue tunisia all four sections studied document a 6 increase of 13corg values at the base of the ctbi which is followed by an interval of elevated 13corg values and a subsequent decrease our results supply an important stratigraphic base for subsequent paleoceanographic studies on late cenomanian to early turonian sediments from demerara rise and elsewhere

organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

a study on the regulation of the concentrations of some trace metals rb sr zn pb cu v cr ni mn and mo in saanich inlet sediments british columbia canada abstract bulk metal concentrations were measured in the sediments of saanich inlet in an attempt to establish the occurrence of trace metal enrichment in the anoxic central basin ba ni v cr zn pb cu and mo were found to be enriched in the anoxic ooze over the possible contributions from lithogenic sources spatial and seasonal variations in the chemical composition of the settling particulates collected with interceptor traps gave further indications of the mode of incorporation of these metals biogenic ba and cr appeared to be associated with opaline silica although alternative explanations are also possible particularly for ba zinc seemed to be added to the sediment essentially in association with planktonic materials while cu required an additional source directly linked to the anoxic environment similarly ni v and mo were added to the anoxic sediments by reactions occurring at the sediment water interface in the nearshore environment studied here these metals particularly ni and mo were not associated to any significant extent with planktonic materials of all the elements analyzed mo showed the largest enrichment in the anoxic sediments of saanich inlet

detecting volcanism on titan and venus with microwave radiometry the detection by spaceborne instrumentation of infrared thermal emission from volcanic eruptions is well established on earth but is challenged on venus and titan by their optically thick atmospheres microwave radiometry in principle offers the ability to detect emission from surface thermal anomalies on these worlds due to greater atmospheric transparency microwaves also offer the prospect of sensing the shallow subsurface and thus may detect warmth from lava flows for longer than surface infrared emission however satellite microwave instruments typically have low spatial resolution 10s of km so volcanic heat is diluted in the wide instrument footprint we examine the prospects for the detection of volcanic deposits by microwave given likely planetary eruption rates and lava flow deposit geometries using mt etna as a template nondetection of prominent hotspots in cassini data may imply that the resurfacing rate is lower than 2 km3 yr five times smaller than the expression of an earth like fraction of geothermal heat flow as latent heat in extrusive volcanism

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

characterization of the unconventional tuscaloosa marine shale reservoir in southwestern mississippi usa insights from optical and sem petrography abstract this study presents new optical petrography and electron microscopy data interpreted in the context of previously published petrophysical geochemical and mineralogical data to further characterize the tuscaloosa marine shale tms as an unconventional reservoir in southwestern mississippi the basal high resistivity zone has a higher proportion of type ii sedimentary organic matter than the overlying tms indicating it is more prone to oil generation optical petrography and electron microscopy reveal a heterogeneous clay matrix with ubiquitous pyrite grains quartz feldspar glaucony foraminifera shell fragments and rarer occurrences of apatite and crinoid fragments as well as liptinite alginite inertinite and vitrinite our petrographic observations suggest that higher abundances of detrital quartz grains coupled with minimal authigenic cements result in higher porosity and permeability however the tms is also more clay rich than other unconventional shale oil and gas plays which can impair the effectiveness of hydraulic fracture stimulation thin section observations reveal alternating clay and calcium carbonate laminae that are interpreted to reflect changes in sediment flux planktonic foraminifera indicate an overlying oxygenated water column while benthic inoceramid fragments and pervasive authigenic pyrite suggest anoxic or dysoxic bottom water conditions apatite fragments in thin section suggest mixing events and an influx of nutrient rich sediments overall these observations suggest that a variety of paleodepositional environments occurred in the tms and the lithofacies diversity resulting from these small scale depositional cycles makes it difficult to determinatively identify areas conducive to enhanced economic hydrocarbon recovery

venus crater related radar dark parabolas and neighboring terrains a comparison of 1 μm emissivity and microwave properties abstract this work presents a comparative study of microwave properties and 1 m emissivity for five venus crater associated radar dark parabolas along with neighboring plains and some other geologic units craters of interest are adivar bassi bathsheba sitwell and du chatelet with nearby crater caccini having non parabolic radar dark halo microwave properties under study include emissivity fresnel reflectivity decameter scale surface roughness and radar cross section from the magellan mission 1 m emissivity was derived using venus monitoring camera vmc measurements on board of venus express vex results of our analysis show that 1 m emissivity which characterizes the uppermost hundreds microns thick layer of parabola mantles usually relates to microwave properties as following the lower 1 m emissivity the lower fresnel reflectivity the higher microwave emissivity for loose mantles having the same composition lower 1 m emissivity indicates smaller particles differences in bulk properties of parabola units showing the same 1 m emissivity appear to reflect differences in a packing style of mantles consisting of particles having similar sizes properties of radar bright inner parabola parts observed within the three of five studied parabolas possibly indicate more turbulent comparing to radar dark parts deposition environment thinner parabola mantles and or partial coverage of the underlying surface the non parabolic halo of the crater caccini exhibits characteristics close to dark parabolas suggesting that in a process of shrinking of a parabolic like deposit into non parabolic one parabola mantle properties remain mainly unchanged observed differences in microwave emissivity and fresnel reflectivity between parabolas and adjacent plains may indicate highly weathered loose parabola material with oxidation of their iron into hematite that is more easily accessible for atmospheric gases studied properties of tessera terrains confirmed suggestions of earlier works for a possible non basaltic composition of tesserae material the distinctive from plains composition of tesserae also could indicates an effective down slope movement of these material uncovering new portions of pristine tessera material otherwise considered in this work horizontal transportation of the very thin layer of surface material would equalize the observed properties

calcareous nannofossil assemblages of oceanic anoxic event 2 in the equatorial atlantic evidence of an eutrophication event the calcareous nannofossils of the cenomanian turonian boundary interval of sites 1258 and 1260 ocean drilling program leg 207 have been studied in order to understand the depositional environment during oceanic anoxic event 2 oae2 in the equatorial atlantic nannofossil assemblages show a significant change in relative abundances during the positive 13 corg excursion interval the strong increase of the high productivity indicator zeugrhabdotus erectus and the simultaneous decrease of the oligotrophic taxa watznaueria barnesiae and watznaueria fossacincta are indicative of enhanced fertility the decrease of eprolithus floralis may be attributed to the surface water temperature increase during oae2 which is however not very significant 2 3 c as suggested by published tex86 data it seems more likely that the decrease of e floralis during oae2 was evoked by the breakdown of water column stratification indicating it as a deep dwelling species which prefers stratified waters with a deep nutricline prediscosphaera spp and retecapsa ficula which show a significant increase in relative abundances during oae2 seem to prefer eutrophic environments while amphizygus brooksii and zeugrhabdotus noeliae lower surface water fertility gartnerago segmentatum broinsonia spp watznaueria biporta and seribiscutum gaultensis decrease in abundances during oae2 it is not clear if they preferred an oligotrophic environment cooler surface waters or if they were inhabitants of the lower photic zone published geochemical data suggest that enhanced fertility and higher temperatures during oae2 may have been caused by submarine volcanic activity through the release of biolimiting micronutrients into the ocean and carbon dioxide into the atmosphere the breakdown of water column stratification may have increased further nutrient availability 2007 elsevier b v all rights reserved

microwave signatures and surface properties of ovda regio and surroundings venus abstract magellan observations of horizontally and vertically polarized emissivity and radar specific cross sections are jointly modeled to separate dielectric constants from textural effects for lobate plains fractured plains fracture belts festoon flows and tessera in ovda regio and surroundings the model assumes surface emission and scattering dominate and that signatures are controlled by a combination of quasi specular and diffuse scale mechanisms textural parameters are found to correlate with geology whereas dielectric constants are found to depend on elevation a gradual increase in dielectric constant from rock like values 4 to 5 to a value of approximately 50 is evident over the interval from 6054 to 6056 km where elevations are derived from magellan altimetry observations stereo radargrammetric analyses demonstrate that a return to rock like values occurs over approximately 0 5 km above the terrain with highest dielectric constants the abrupt return to rock like values occurs independently of geology and reinforces the hypothesis of elevation control on dielectric constant values variations in dielectric constant with elevation are modeled using an 1000 ppm concentration of a ferroelectric mineral with a curie temperature of 707 k the model reproduces the abrupt change at highest elevations as the curie temperature is reached and the gradual change as lower elevations are encountered to our knowledge no other model explains the trends with such simplicity

diagenetic barium cycling in black sea sediments a case study for anoxic marine environments high resolution sedimentary records of major and minor elements al ba ca sr ti total organic carbon toc and profiles of pore water constituents view the mathml sourceso42 ch4 ca2 ba2 mg2 alkalinity were obtained for two gravity cores core 755 501 m water depth and core 214 1686 m water depth from the northwestern black sea the records were examined in order to gain insight into the cycling of ba in anoxic marine sediments characterized by a shallow sulfate methane transition smt as well as the applicability of barite as a primary productivity proxy in such a setting the ba records are strongly overprinted by diagenetic barite baso4 precipitation and remobilization authigenic ba enrichments were found at both sites at and slightly above the current smt transport reaction modeling was applied to simulate the migration of the smt during the changing geochemical conditions after the holocene seawater intrusion into the black sea based on this sediment intervals affected by diagenetic ba redistribution were identified results reveal that the intense overprint of ba and baxs ba excess above detrital average strongly limits its correlation to primary productivity these findings have implications for other modern and ancient anoxic basins such as sections covering the oceanic anoxic events which ba is frequently used as a primary productivity indicator our study also demonstrates the limitations concerning the use of baxs as a tracer for downward migrations of the smt due to high sedimentation rates at the investigated sites diagenetic barite fronts are buried below the smt within a relatively short period thus relict barite fronts would only be preserved for a few thousands of years if at all

carbon and phosphorus burial associated with modern phosphorite formation phosphorite formation plays a significant but poorly constrained role in the marine c and p cycles this report concerns a site of modern phosphorite formation on the upper continental slope off southern baja california mexico sta 6 380 m water depth 23 41 n 111 05 w at this site a series of six narrow 1 3 cm partially indurated phosphorite layers have formed authigenically during the last 15 000 years within a surficial section of slowly but steadily accumulating 3 8 10 3 cm year 1 organic rich mud a poorly oxygenated benthic environment has prevailed at the study site since approximately 8100 year b p probably helping to produce and preserve the pristine phosphorite layers the mean p burial flux 1 1 mol cm 2 year 1 recorded by these deposits agrees closely with the downward diffusive p flux 1 3 mol cm 2 year 1 attributed to active francolite growth such a coincidence implies that the phosphorite layers could have formed entirely under present conditions however a much larger upward diffusive p flux 4 2 mol cm 2 year 1 directed out of the sediment limits the efficiency of ongoing phosphorite formation and the most recently deposited sediment does not contain enough labile p to maintain the overall p regeneration rate indefinitely attendant burial fluxes of inorganic and especially organic c 7 7 and 6 6 mol cm 2 year 1 respectively do not accord with a depositional model of coastal upwelling suggesting that an alternative mechanism possibly fe redox cycling controls porewater p concentrations and hence phosphorite formation a comparison with previously published p burial fluxes for a wide variety of other modern marine settings reveals that phosphorite formation in general does not disproportionately affect the global p burial flux from these data we tentatively estimate a minimum global p burial flux of approximately 70 109 mol year 1 with almost 80 occurring on continental margins

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

a new approach for the determination of the age of partial or complete homogenization of pb isotopes example anchimetamorphic detrital sediments of the central iberian zone spain abstract pb isotope systematics are discussed for lowermost ordovician to devonian pelites of the almaden area central iberian zone of spain the rocks suffered a carboniferous anchimetamorphic overprint which variably reset the rb sr whole rock systems at 335 ma the weak metamorphic event partially homogenized the pb isotopes of pelites between 330 and 320 ma this time range of partial homogenization was deduced by stepwise age correction t1 206 pb 204 pb vs 207 pb 204 pb are determined for the individual data sets that were stepwise corrected for in situ radiogenic pb the worst correlation monitored by the lowest value of the correlation coefficient is then indicative for the time at which the pb isotopic homogenization reached its maximum degree applying the above described procedures partial or complete homogenization of pb isotopes during any magmatic metamorphic or metasomatic process may readily be detected in any suite of whole rock and or mineral systems thus we strongly recommend determinations of u and pb concentrations on a routine basis even if there exists the possibility of secondary u and or pb mobility

sedimentary organic carbon to phosphorus ratios as a redox proxy in quaternary records from the mediterranean abstract in this study organic carbon to organic phosphorus c org p org and total phosphorus c org p tot ratios as bottom water redox proxies are explored for two eastern mediterranean sediment records extending back 600 700 kyrs cores kc19c 19 6 m long 2750 m water depth and kc01b 37 0 m long 3643 m water depth contain numerous organic rich layers sapropels throughout the two cores variations found in the c org p ratios correspond to those for other redox proxies such as total s contents and v al ratios accordingly these are interpreted as variations in bottom water oxygenation and inter sapropel redox variability in core kc19c the original c org p signals seem to have been preserved despite intense post depositional sulfidization high resolution p fractionation data of sapropel s5 from a third core ps25pc 3304 m water depth showing high and relatively stable c org p org ratios indicate that sapropel s5 at this deep location was deposited under permanently reducing conditions while p regeneration from organic matter was intense net p burial increased in the sapropel due to enhanced burial of inorganic calcium phosphate likely biogenic ca p sediment p contents and c org p tot ratios in s5 are variable reflecting short term changes in marine conditions productivity redox and sediment chemistry the c org p org and c org p tot ratios thus provide valuable insight into paleoceanographic conditions and pathways of p cycling for mediterranean sediment records extending back at least 600 700 kyrs

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

hydrographic conditions of the devono carboniferous north american seaway inferred from sedimentary mo toc relationships abstract deepwater anoxia developed widely within a series of silled intracratonic basins in north america during the middle devonian to early carboniferous but the hydrographic factors contributing to this development are virtually unknown the present study demonstrates that the degree of enrichment of strongly hydrogenous elements such as molybdenum mo in the organic rich shales that accumulated in these basins has the potential to provide information about paleohydrographic conditions most of the study units 49 of 55 exhibit significant positive covariation between elemental mo and toc concentrations yet there is substantial variation in the statistical parameters that define these relationships specifically the regression lines characterizing mo toc covariation have slopes m ranging from 2 to 65 10 4 although a majority of the study units yield m values between 10 and 25 10 4 the parameter m exhibits systematic stratigraphic variation within individual basins and geographic variation among basins suggesting that mo toc relationships were controlled by slowly evolving watermass characteristics of the devono carboniferous north american seaway a recent study of modern anoxic silled basins algeo t j lyons t w 2006 mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions paleoceanography 21 pa1016 doi 10 1029 2004pa001112 demonstrated that m is closely linked to the degree of restriction of the subpycnoclinal watermass as reflected in aqueous mo concentrations mo aq and deepwater renewal times dw these relationships reflect control of sedimentary mo enrichment by both the amount of sedimentary organic matter i e host phase availability and the concentration of aqueous mo i e source ion availability when applied to black shales of the devono carboniferous north american seaway these relationships permit both qualitative and quantitative inferences regarding the degree of restriction of deepwaters in cratonic basins and the evolution of hydrographic conditions through time black shales associated with early stages of sea level rise commonly exhibit low m values 1000 yr higher sea level stands resulted in more open marine conditions and enhanced deepwater renewal leading to deposition of black shales with m values up to 65 equivalent to mo aq 70 of the normal seawater concentration and dw

a new approach for the determination of age of a partial or complete homogenisation of pb isotopes example anchimetamorphic detrital sediments of the central iberian zone spain comments

bottom water anoxia inoceramid colonization and benthopelagic coupling during black shale deposition on demerara rise late cretaceous western tropical north atlantic 1 the bulk rock geochemistry and inoceramid isotopic composition from cenomanian to santonian finely laminated organic rich black shales recovered during ocean drilling program leg 207 on demerara rise western tropical north atlantic suggest persistent anoxic free h2s conditions within the sediments and short term variations within a narrow range of anoxic to episodically dysoxic bottom waters over a 15 ma time interval in addition to being organic rich the 50 90 m thick sections examined exhibit substantial bulk rock enrichments of si p ba cu mo ni and zn relative to world average shale these observations point to high organic burial fluxes likely driven by high primary production rates which led to the establishment of intensely sulfidic pore waters and possibly bottom waters as well as to the enrichments of cr mo u and v in the sediments at the same time the irregular presence of benthic inoceramids and foraminifera in this facies demonstrates that the benthic environment could not have been continuously anoxic the 13c and 15n values of the inoceramid shell organics provide no evidence of chemosymbiosis and are consistent with pelagic rain as being a significant food source demerara rise inoceramids also exhibit well defined regularly spaced growth lines that are tracked by 13c and 18o variations in shell carbonate that cannot be simply explained by diagenesis instead productivity variations in surface waters may have paced the growth of the shells during brief oxygenation events suitable for benthic inoceramid settlement these inferences imply tight benthopelagic coupling and more dynamic benthic conditions than generally portrayed during black shale deposition by invoking different temporal scales for geochemical and paleontological data this study resolves recent contradictory conclusions e g sulfidic sedimentary conditions versus dysoxic to suboxic benthic waters drawn from studies of either sediment geochemistry or fossil distributions alone on demerara rise this variability may be relevant for discussions of black shales in general

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

an evaluation of inoceramid single prism sclerochronology abstract inoceramid prisms are among the most common microfossils that can be found in late cretaceous strata since these biomineral units were formed by sequential accretion in the outer shell layer of the bivalves they potentially serve as archives of short term circa annual paleowater temperature fluctuations in the present study we tested to what extent intra prismatic stable isotope variations of individual inoceramid prisms reflect sub annual 13c and the 18o patterns we obtained multiple carbonate samples from prisms recovered from the sediment and from a cross sectioned inoceramid shell fragment and compared data from these samples to data from classical sclerochronological sampling i e sequential drilling the analyzed shell material belonged to the species platyceramus platinus from the smoky hill chalk member niobrara formation kansas usa scanning electron microscopy sem was used to evaluate the diagenetic alteration of the studied prisms and allowed to identify suitable material for stable isotope analyses the 18o values of drilled carbonate samples 18odrill and of prisms 18oip compare very well to each other when temporally aligned r2 0 98 the stable carbon isotope values 13cdrill 13cip however show less agreement r2 0 28 which is likely attributable to different time averaging of the samples we discuss how to identify the most suitable prisms for sub annual paleotemperature reconstructions from disarticulated material using microgrowth patterns and geometrical features of the prisms as proxies for changing growth rates finally we apply the novel sampling strategy to naturally occurring disarticulated prisms from the sediment and compare their intra prismatic isotope values 13cips and 18oips to those of bulk analyzed prism fragments from the sediment 13cbps and 18obps sclerochronological analysis of the prisms from the sediment yields 18oips fluctuations of 1 89 virtually identical to the 18oip chronologies of the prisms extracted from the shell cross section 1 90 the overall ranges of the 18oip and 18oips values are identical 2 60 and capture very well the expected seasonal stable oxygen isotope oscillation derived from the 18odrill values 2 61 the range of the 18oips data is two fold larger than that of the 18obps values 1 19 suggesting a strong effect of time averaging on the stable oxygen isotope data of the bulk analyzed prisms fragments according to our novel statistical model the resolution of 18obps data can be increased by preferentially analyzing short ca 300 m individual prisms fragments at least n 20

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

cretaceous inoceramid biogeography a review abstract cretaceous inoceramid bivalves were widely distributed they did not thrive in very shallow or very warm seas and are therefore rare in tethyan shallow deposits in the berriasian barremian interval they occured mainly in the temperate seas and thier distribution is often bipolar in the albian cenomanian interval inoceramids were varied and numerous especially in clays and chalks but rare in the greensand type strata most inoceramid groups were cosmopolitan during this interval from the turonian onwards the north pacific province is characterized by endemic inoceramid faunas following the opening of the south atlantic ocean in the turonian new inoceramid lineages in the southern hemisphere from brazil to madagascar evolved in co occurrence with other cosmopolitan groups many coniacian and santonian species were widely distributed and short lived but in the campanian and maastrichtian a homogeneous fauna was apparently confined to eastern north america and western eurasia few of the last inoceramid species in the upper cretaceous have stratigraphic value and in contrast to the lower cretaceous they are common in warm water deposits for example in libya nigeria and tunisia

late turonian climate variability in the bohemian cretaceous basin a sclerochronological study of inoceramus hercules shells from the upohlavy quarry czech republic abstract the 18o record of well preserved shells of the inoceramid inoceramus hercules from the upohlavy working quarry czech republic provides an insight into the climate variability in the late turonian benthic environment of the bohemian cretaceous basin similar to modern bivalves this inoceramid species built its shell near equilibrium with the oxygen isotope value of the ambient water due to the nearly year round shell growth sequentially sampled 18o values allowed to estimate the narrowest sub annual temperatures fluctuations that prevailed during lifetime of the organisms in accordance with previous studies reconstructed temperatures suggest colder water conditions 19 0 0 9 c during the earliest late turonian coinciding with the hyphantoceras event also known as hitch wood event than during the later part of the substage 20 9 1 1 c climate warming however did not affect the sub annual temperature fluctuations evenly but predominantly affected the warmest part of the year at least 4 0 c on the contrary the coldest recorded temperatures remained more or less invariant varying not much more than 1 0 c across the studied time interval the observed changes in the benthic temperature estimates likely reflect shifts in seasonal sea surface temperature amplitudes in response to climate forcing given the widespread distribution of i hercules in the upper turonian lower coniacian hemipelagic strata of europe the present study sets the basis for future continent wide sub annually resolved climate reconstructions

volatile transport on venus and implications for surface geochemistry and geology the high vapor pressure of volatile metal halides and chalcogenides e g of cu zn sn pb as sb bi at typical venus surface temperatures coupled with the altitude dependent temperature gradient of 8 5 k km 1 is calculated to transport volatile metal vapors to the highlands of venus where condensation and accumulation will occur the predicted geochemistry of volatile metals on venus is supported by observations of cu zn sn pb as sb and bi minerals around terrestrial volcanic vents spectroscopic observations of cucl in volcanic gases at kilauea and nyiragongo and large enrichments of these and other volatile elements in terrestrial volcanic aerosols a one dimensional finite difference vapor transport model shows the diffusive migration of a thickness of 0 01 to 10 m yr of moderately to highly volatile phases e g metal halides and chalcogenides from the hot lowlands 740 k to the cold highlands 660 k on venus the diffusive transport of volatile phases on venus may explain the observed low emissivity of the venusian highlands hazes at 6 km altitude observed by two pioneer venus entry probes and the pioneer venus entry probe anomalies at 12 5 km

changes in north atlantic circulation at the end of the cretaceous greenhouse interval ocean circulation patterns during the late cretaceous greenhouse interval remain disputed marine sediment geochemistry suggests that the end of the greenhouse interval coincided with the onset or intensification of deep water formation in the north atlantic ocean

terrestrial quadstatic interferometric radar observations of mars a new technique for resolving the ambiguity inherent in delay doppler radar observations of mars has been developed and implemented using a suite of data collected during 2001 2003 and 2005 oppositions new recording systems processing techniques and most importantly the addition of a fourth receiving telescope allow for the high resolution mapping of mars radar properties in this paper we develop a maximum likelihood method to probabilistically estimate the contributions to the received radar signal from the ambiguous resolution cells our delay doppler interferometric radar observations are designed to map the radar properties of mars surface while disregarding the historically typical goal of measuring topography instead using mars topography as a priori knowledge example data from the september 27 2003 observation over mars southern highlands including ma adim vallis and gusev crater and the june 7 2001 observation crossing terra meridiani are presented to demonstrate the effectiveness of the technique analysis of these observations predicted a root mean square rms roughness or slopes for the mars exploration rover mer spirit landing site of 1 80 0 75 similarly analysis of the gusev crater landing site of mer opportunity predicted rms slopes of 1 1 0 1 both predictions were validated by analysis of in situ rover images

seawater as the source of minor elements in black shales phosphorites and other sedimentary rocks many of the minor elements in seawater today have a concentration depth profile similar to that of the biologically essential nutrients no 3 and po3 4 they show a relative depletion in the photic zone and enrichment in the deep ocean the difference between their surface and deep ocean values normalized to the change in po3 4 approaches the average of measured minor element p ratios in marine plankton although individual analyses of the latter show extreme scatter for a variety of reasons despite this scatter in the minor element analyses of plankton agreement between the two sets of data shows unequivocally that an important marine flux of many minor elements through the ocean is in the form of biogenic matter with a composition approaching that of plankton this interpretation is further supported by sediment studies particularly of sediments which accumulate in shelf slope environments where biological productivity in the photic zone is exceptionally high and organic carbon contents of the underlying sediment elevated the interelement relations observed for some of these sediments approach the average values of plankton these same interelement relations are observed in many marine sedimentary rocks such as metalliferous black shales and phosphorites rocks which have a high content of marine fractions e g organic matter apatite biogenic silica and carbonates many previous studies of the geochemistry of these rocks have concluded that local hydrothermal activity and or seawater with an elemental content different from that of the modern ocean was required to account for their minor element contents however the similarity in several of the minor element ratios in many of these formations to minor element ratios in modern plankton demonstrates that these sedimentary rocks accumulated in environments whose marine chemistry was virtually identical to that seen on continental shelf slopes or in marginal seas of the ocean today the accumulation of the marine fraction of minor elements on these ancient sea floors was determined largely by the accumulation of organic matter settling from the photic zone and with a composition of average plankton a second marine fraction of minor elements in these rocks accumulated through precipitation and adsorption from seawater the suite of elements in this fraction reflects redox conditions in the bottom water as determined by bacterial respiration for example high mn high cr v and high mo concentrations above those which can be attributed to the accumulation of planktonic matter characterize accumulation under bottom water oxidizing denitrifying and sulfate reducing conditions respectively

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

rotation period of venus estimated from venus express virtis images and magellan altimetry abstract the 1 02 m wavelength thermal emission of the nightside of venus is strongly anti correlated to the elevation of the surface the virtis instrument on venus express has mapped this emission and therefore gives evidence for the orientation of venus between 2006 and 2008 the magellan mission provided a global altimetry data set recorded between 1990 and 1992 comparison of these two data sets reveals a deviation in longitude indicating that the rotation of the planet is not fully described by the orientation model recommended by the iau this deviation is sufficiently large to affect estimates of surface emissivity from infrared imaging a revised period of rotation of venus of 243 023 0 002 d aligns the two data sets this period of rotation agrees with pre magellan estimates but is significantly different from the commonly accepted value of 243 0185 0 0001 d estimated from magellan radar images it is possible that this discrepancy stems from a length of day variation with the value of 243 023 0 002 d representing the average of the rotation period over 16 years

further studies of the nature composition and ages of contemporary phosphorite from the namibian shelf major and minor element and radiochemical data are examined for a set of phosphorite concretions and other phosphatic material from the namibian shelf the concretions were separated on a morphological basis from grab samples taken in a transect of shallowing depth over the diatomaceous ooze belt compositional data indicate that the samples are fairly pure carbonate fluorapatite and trend towards a maximum 32 p2o5 content a range of compositional variability similar to other samples from the namibian shelf is observed radiochemical systematics confirm that pelletal phosphorite and glauconitized pelletal phosphorite from depths 170 m are at radioactive equilibrium and are therefore old and reworked the concretions collected from depths shallower than 78 m are entirely recent with maximum ages in the range 500 3800 years they may be much younger despite distinct textural and small compositional differences similar ages are found for separates from the same grab samples of fish scales and an unidentified high magnesian phosphate mineral are also shown to have incorporated uranium recently

concentration oxidation state and particulate flux of uranium in the black sea abstract in contrast to its unreactive behavior in the open ocean uranium is removed from seawater to sediments of anoxic marine basins four biogeochemical processes have been proposed to account for this removal active uptake by organisms whose remains are preserved by the anoxic conditions of the sediments complexation of u vi by particulate organic matter chemical reduction of soluble u vi to insoluble u iv which is scavenged to the sediments by settling particles and precipitation of uranium within the sediments themselves the black sea is the largest anoxic marine basin in the world today waters below 150 200 m are anoxic and h2s levels build up to about 400 mol 1 1 in the bottom water maximum depth 2200 m concentrations of total u and the oxidation state of dissolved u were measured throughout the water column while particulate u fluxes were determined from time series sediment trap samples collected in the deep anoxic zone bottom waters were depleted in u by 40 relative to the initial u content of the water two independent methods gave residence times of dissolved u in the deep water column of about 103 years uranium occurred throughout the water column as soluble chemically labile reducible u vi rather than the thermodynamically favored u iv uranium is neither reduced to u iv by the high levels of h2s nor is it rapidly scavenged from the water column as would be expected for strongly hydrolyzed tetravalent actinides like u iv fluxes of particulate authigenic u measured with sediment traps are at least two orders of magnitude less than the rate of authigenic u burial in black sea sediments therefore the first three processes listed above contribute negligibly to the deposition of u in the sediments of anoxic marine basins such as the black sea the dominant removal process must involve precipitation of u in the sediments rather than scavenging from the water column

low radar emissivity signatures on venus volcanoes and coronae new insights on relative composition and age abstract multiple studies reveal that most of venus highlands exhibit anomalously high radar reflectivity and low radar emissivity relative to the lowlands this phenomenon is thought to be the result of atmosphere surface interactions in the highlands due to lower temperatures these reactions are a function of rock composition atmospheric composition and degree of weathering we examine the magellan radar emissivity altimetry and sar data for all major volcanoes and coronae on venus we characterize and classify edifices according to the pattern of the variation of radar emissivity with altitude the volcanic highlands can be classified into 7 distinct patterns of emissivity that correspond to at least 3 discrete types of mineralogy based on the altitude temperature of the emissivity anomalies the majority of emissivity anomalies support the hypothesis of a weathering phenomenon at high altitude 6053 km but we also find strong emissivity anomalies at lower altitudes that correspond spatially to individual lava flows indicating variations in mineralogy within an evolving volcanic system the emissivity signature of tallest volcanoes on venus are consistent with the presence of ferroelectric minerals in their rocks while volcanic edifices in western ishtar terra and eastern aphrodite terra are consistent with the presence of semiconductor minerals sapas mons and pavlova corona are also consistent with ferroelectrics but at a different curie temperature than the other volcanoes in atla regio the spatial distribution of radar emissivity classes correlates to different geologic settings indicating that different mantle source regions deep shallow plumes and possible convergence zones may contribute to differences in mineralogy for the studied edifices finally we show that the emissivity signatures of idunn maat and other volcanic edifices are consistent with relatively fresh and unweathered rocks indicating recent or possibly current volcanism on venus

accumulation and preservation of organic carbon in marine sediments the roles of anoxia vs production organic carbon enrichments in marine sediments and sedimentary rocks commonly are explained by the preferential preservation of the deposited organic matter under anoxic conditions the role of primary organic plankton production is seldom considered a review of the available information shows that modern marine sediment accumulating in oxic and anoxic basins in similar topographic and sedimentary settings have very similar carbon contents on continental slopes carbon maxima are apparently produced by the complex interplay between the supply of carbon to the sea floor the texture of the sediment the dilution of carbon by other sediment components and the decreasing settling flux of carbon in the deeper waters of the open ocean contrary to contemporary thought there is no causal relationship between such maxima and the position of the oxygen minimum the degradation of sedimentary organic matter by aerobes and by sulfate reducers is very similar where the supply of fresh organic matter to the sea floor is similar hence there is no evidence for the preferential preservation of organic matter under anoxic conditions terrestrial organic matter however appears to be degraded to a lesser extent by sulfate reducers the burial of carbon below the surficial oxygenated horizons of a sedimentmore removes the easily oxidized fractions leaving material that may be less susceptible to attack by sulfate reducers sedimentary carbon maxima in pleistocene glacial horizons are due to the increased settling flux of organic matter brought about by climatically induced increases in upwelling in the equatorial and marginal areas of the ocean changes in bottom water oxygen levels during these periods plays a minor role in producing these signals previous work that claimed that anoxic bottom waters were prevalent during the accumulation of organic rich black shales in the geological record should be reevaluated less

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

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

evidence for crater ejecta on venus tessera terrain from earth based radar images abstract we combine earth based radar maps of venus from the 1988 and 2012 inferior conjunctions which had similar viewing geometries processing of both datasets with better image focusing and co registration techniques and summing over multiple looks yields maps with 1 2 km spatial resolution and improved signal to noise ratio especially in the weaker same sense circular sc polarization the sc maps are unique to earth based observations and offer a different view of surface properties from orbital mapping using same sense linear hh or vv polarization highland or tessera terrains on venus which may retain a record of crustal differentiation and processes occurring prior to the loss of water are of great interest for future spacecraft landings the earth based radar images reveal multiple examples of tessera mantling by impact parabolas or haloes and can extend mapping of locally thick material from magellan data by revealing thinner deposits over much larger areas of particular interest is an ejecta deposit from stuart crater that we infer to mantle much of eastern alpha regio some radar dark tessera occurrences may indicate sediments that are trapped for longer periods than in the plains we suggest that such radar information is important for interpretation of orbital infrared data and selection of future tessera landing sites

bioevents and redox conditions around the cenomanian turonian anoxic event in central mexico abstract the xilitla section of central mexico western margin of the proto north atlantic is characterized by pelagic sediments enriched in marine organic matter using biostratigraphic and radiometric data it was dated at the latest cenomanian earliest turonian transition we identified an interval coeval with the faunal turnover associated with the oceanic anoxic event 2 oae 2 recording the heterohelix shift and the filament event for the first time in mexico an integral analysis of sedimentary facies pyrite and geochemical proxies reveals vertically variable redox conditions with prevailing anoxic to dysoxic bottom waters along with phosphorous and manganese depletion the highest content of total organic carbon and of certain redox sensitive trace elements rstes is found during part of the anoxic event confirming more uniform and constant oxygen depleted conditions this interval is also characterized by a significant enrichment in biogenic barium and elevated toc ntot ratios suggesting a link between productivity and anoxia sulfur isotope fractionation has a maximum value within the anoxic event favored by the increase in the flux of organic matter and intensified through sulfur recycling highly bioturbated beds representing short lived episodes of oxic conditions are intermittent within the oae 2 and become more frequent in the early turonian this study proposes a model similar to that of modern upwelling regions high marine productivity controlled organic matter burial and oxygenation at the seafloor varying between anoxic laminated facies with small pyrite framboids and dysoxic conditions bedding parallel bioturbated facies with inoceramid bivalves and large pyrite framboids interrupted by short term well oxygenated episodes thoroughly bioturbated facies with common benthic foraminifera general low oxygen conditions led to the formation of glauconite and pyrite bacterially mediated the enrichment of redox sensitive trace elements in sediments cd zn v and cr scavenged by organic matter and ni mo pb co and re by pyrite and resulted in mn and p depletion

integrated depositional model for the cenomanian turonian organic rich strata in north africa abstract during the late cenomanian early turonian c t oceanic anoxic event oae2 organic rich strata was deposited in rift shelf basins and slopes across north africa and in deep sea basins of the adjacent oceans based on a review of published and unpublished information this paper documents the distribution and organic richness of c t strata across the whole region within a palaeogeographic framework and systematically analyses the conditions and processes which controlled their deposition previously the c t in north africa has been most intensively studied in southern morocco tarfaya and tunisia only little data is availabe for other parts of north africa namely algeria libya and egypt because distribution of c t corg strata there becomes more patchy a general decrease in peak organic richness and black shale thickness occurs from west to east partly as a result of upwelling along the moroccan atlantic coast and the absence of upwelling in the eastern mediterranean area furthermore in the confined central atlantic the oxygen minimum zone omz in many places reached down to the deep sea floor 3 4 km while the lower limit of the omz along the north african tethys was much shallower and underlain by oxic water masses as documented by high resolution biostratigraphic and chemostratigraphic data c t black shale deposition in most areas outside the upwelling zone are restricted to a strong eustatic latest cenomanian transgressive phase triggered by this sea level rise the omz impinged onto the north african continental shelf and the margins of intrashelf basins which mostly formed during the early cretaceous as halfgrabens important units containing c t organic rich strata in the region are the atlantic tarfaya black shales morocco western sahara black shales and phtanites in the moroccan and algerian atlas the bahloul fm in the se constantine basin and in northern and central tunisia the etel fm in the sirte basin the al hilal fm in cyrenaica libya the abu roash fm in the abu gharadig and fayium basins western desert egypt the daliyya fm along the ne sinai palestine isreal coast and the shueib fm in west central jordan

fluctuations of the oxygen minimum zone at the end of oceanic anoxic event 2 reflected by benthic and planktic fossils the latest cenomanian to early turonian late cretaceous section at vallecillo mexico contains a continuous and highly fossiliferous sedimentary record across the late oceanic anoxic event oae 2 and shows similar distributions of benthic inoceramids and planktic foraminifers during this period of an expanded oxygen minimum zone omz we suggest that these synchronous abundance changes result from similar environmental vulnerability of planktotrophic larval stages of inoceramids and deeper dwelling planktic foraminifers and that these synchronous changes reflect the expansion of the omz the abundances of ammonites and fishes used as independent control groups do not correlate and rule out a preservational bias ammonites fishes and their hatchlings thus populated shallower water depths than inoceramid gametes and planktic foramininifers the improving conditions at the end of oae 2 resulted in the dispersal of new inoceramid and foraminiferal morphotypes

surface processes in the venus highlands results from analysis of magellan and arecibo data the highlands of venus are characterized by an altitude dependent change in radar backscatter and microwave emissivity likely produced by surface atmosphere weathering reactions we analyzed magellan and arecibo data for these regions to study the roughness of the surface lower radar backscatter areas at the highest elevations and possible causes for areas of anomalous behavior in maxwell montes arecibo data show that circular and linear radar polarization ratios rise with decreasing emissivity and increasing fresnel reflectivity supporting the hypothesis that surface scattering dominates the return from the highlands the maximum values of these polarization ratios are consistent with a significant component of multiple bounce scattering we calibrated the arecibo backscatter values using areas of overlap with magellan coverage and found that the echo at high incidence angles up to 70 from the highlands is lower than expected for a predominantly diffuse scattering regime this behavior may be due to geometric effects in multiple scattering from surface rocks but further modeling is required areas of lower radar backscatter above an upper critical elevation are found to be generally consistent across the equatorial highlands with the shift in microwave properties occurring over as little as 500 m of elevation these surfaces are not simply characterized however by the absence of a highly reflective component surface morphology and radar scattering properties suggest that a mantling deposit forms at the highest elevations most likely by in situ erosion of the original rock in ovda regio this process mantles or has removed surface festoon structure at the 1 to 10 m scale implying a significant depth for the weathered layer similar radar dark areas occur in maxwell montes but are apparently unrelated to the current topography of the region possible reasons for these observations include mass wasting from areas of steep slopes compositional or age differences within the montes vertical tectonic shifts of relict contacts local topographic effects on surface temperature or errors in the magellan topography data in the rugged terrain while there is evidence for some of these effects in the existing data no single model at present appears to satisfy all occurrences of high altitude radar dark terrain new measurements of the surface and lower atmosphere chemistry of venus are needed to further refine these conclusions

intra annual isotopic variation in venericardia bivalves implications for early eocene temperature seasonality and salinity on the u s gulf coast abstract stable isotope compositions were determined for 166 microsamples of aragonite from the bivalve venericardia hatcheplata collected from the early eocene hatchetigbee formation in southwestern alabama these were milled from two transects one across the left valve hinge plate and one along the growth axis amplitude and spacing of about nine years of seasonal variation is very regular with peaks and troughs occurring at equal intervals and reaching consistent compositions except for some attenuation in both parameters during the last three years of life assuming an ice free world with an ocean 18o value of about 1 0 and using the aragonite water fractionation equation of grossman and ku 1986 isotope derived paleotemperatures are somewhat warmer 31 c than temperatures presently recorded anywhere on the earth s surface and exhibit significantly greater seasonality 12 c than regions with the warmest mean temperatures it is therefore likely that these very negative and extremely seasonal 18o values reflect the influence of seasonal discharge of 18o depleted river water into the eocene gulf of mexico comparison of these data with 1 mean annual temperature versus seasonal temperature variation from modern climates 2 isotopic compositions reported from coeval molluscs and 3 isotopic compositions of global meteoric precipitation and united states rivers suggest that mean annual temperature along this portion of the eocene gulf coast was in fact about 26 c and varied seasonally from a winter low of about 25 c to a summer high of 27 c differences between these temperatures and those derived from direct conversion of oxygen isotope values reflect the influence of seasonal influx of fresh 18o value of 4 7 water during deposition of this portion of the hatchetigbee formation ambient water 18o values varied between winter values of about 1 0 to less than 3 5 during the summer freshwater discharge served to seasonally depress salinity to 10 to 16 ppt along this part of the gulf coast the early eocene was perhaps the warmest time interval of the past 65 million years primarily manifest as lower equator to pole temperature gradients in this context an eocene mean annual temperature of 26 c is not much higher than modern surface water temperatures of about 24 c at 29 30 n immediately off the modern alabama coast seasonal temperature variation of 2 to 3 c about a mean of 26 c however is significantly lower than that off coastal alabama 19 to 30 c and occurs only along modern equatorial coasts at latitudes less than 19 this implies that early eocene tropical conditions extended well beyond modern latitudinal limits

bioturbation inoceramid extinction and mid maastrichtian ecological change notable among the biological changes of the middle part of the maastrichtian age was a major pulse of extinction among inoceramid bivalves analysis of the distribution of inoceramid shell fragments suggests that the population of burrowing organisms increased across the same stratigraphic interval that the bivalve population decreased a global reorganization of ocean circulation that resulted in cooler better oxygenated bottom waters is proposed as an explanation for the observed changes in the deep sea other observations regarding the mid maastrichtian are consistent with this hypothesis

venus radar bright highlands different signatures and materials on ovda regio and on maxwell montes abstract venus highlands appear much brighter than its lowland plains in reflected radar which has been explained by several conflicting hypotheses we study this transition at higher spatial and elevation resolution than previously possible by combining magellan synthetic aperture radar sar images with magellan sar stereo elevations we confirm that sar backscatter over ovda regio 5 n to 15 s grades from low to high as elevation increases 2 4 5 km above the datum and then drops precipitously above 4 5 km t 702 k this pattern is consistent with presence of a substance that undergoes a phase transition from ferroelectric to normal dielectric at 700 k the mineral chlorapatite is a likely candidate this pattern is seen across ovda on other near equatorial highlands and on some shield volcanoes like the tepev montes we also confirm that maxwell montes 60 68 n shows a different pattern its surface transitions abruptly from low backscatter to high backscatter at 4 5 km above the datum and remains so to nearly its highest elevations 10 km this pattern is consistent with the presence of a semiconductor material either precipitated from the atmosphere e g a frost or produced by atmosphere surface interaction if a ferroelectric substance were in the rock at maxwell as at ovda it could be invisible beneath the coating of semiconductor material however the absence of a semiconductor material on ovda requires either that 1 the atmosphere compositions at maxwell and ovda are substantially different or 2 that the semiconductor at maxwell forms by atmosphere surface reaction not as an atmospheric precipitate and that the surface materials at ovda and maxwell are substantially different

comparative geochemistry of cadmium rhenium uranium and molybdenum in continental margin sediments the concentrations of authigenic phases of cd re u and mo increase with depth in four 45 cm long sediment box cores collected along the axis of the laurentian trough gulf of st lawrence average authigenic accumulation rates estimated from element inventories are similar to rates in other continental margin environments strong regional variations in sediment accumulation rate and sulfide concentration have little influence on the accumulation rates of cd and re this suggests that slow precipitation kinetics controls the accumulation of cd and re in these sediments the accumulation rate of authigenic u is more variable it may be tied to the kinetics of microbially mediated u reduction and be controlled by the availability of reactive organic matter authigenic mo is distinguished by a sharp subsurface concentration minimum above which mo cycles with manganese mo released to pore water upon reduction of mn oxides diffuses downward and enriches the subsurface sediment mo accumulates most rapidly in the sediment with the highest sulfide content slow conversion of molybdate to thiomolybdate may explain the much slower mo accumulation rate in the less sulfidic sediments a component of authigenic mo accumulates with pyrite in an approximately constant mo fe ratio the accumulation rate of pyrite and associated mo is insensitive to avs abundance pyrite formation may be limited by the reactivity of iron oxide minerals

volcanic deposits in shield fields and highland regions on venus surface properties from radar polarimetry 1 we compare arecibo dual polarization radar image data for venus to magellan images and emissivity data to investigate the physical properties of volcanic deposits radar waves can easily penetrate smooth mantling layers such as ash aeolian and crater derived deposits if a circularly polarized radar wave refracts into a surface that is smooth at wavelength scales the vertical component of the wave will be preferentially transmitted resulting in a net linear polarized echo component arecibo polarimetry data were used to create maps of the degree of linear polarization in the radar echo we find that some volcanic fields in plains regions on venus are associated with enhanced linear polarization these fields sometimes have nearby windstreaks which suggest fine grained surface material and we infer that the radar wave is penetrating into mantling deposits that are a few centimeters to 1 m thick enhanced linear polarization values are also correlated with specific lava flows these lava flows have emissivity values of 0 80 to 0 84 similar to many other flows on venus the enhanced linear polarization may be produced by penetration of the radar wave into very smooth lava flows with internal air gaps high reflectivity low emissivity areas near the summits of theia and tepev montes also have a linearly polarized echo component consistent with surface penetration by the radar wave the cause of the high linear polarization in summit regions remains uncertain but perhaps the radar wave is able to penetrate into high dielectric material in limited cases of very smooth surface texture

an upwelling model for the phosphoria sea a permian ocean margin sea in the northwest united states the permian phosphoria formation a petroleum source rock and world class phosphate deposit was deposited in an epicratonic successor basin on the western margin of north america we calculate the seawater circulation in the basin during deposition of the lower ore zone in the meade peak member from the accumulation rates of carbonate fluorapatite and trace elements the model gives the exchange rate of water between the phosphoria sea and the open ocean to the west in terms of an upwelling rate 84 m yr 1 and residence time 4 2 yr of seawater in the basin these hydrographic properties supported a mean rate of primary productivity of 0 87 g m 2 d 1 of carbon in the uppermost few tens of meters of the water column the photic zone and denitrifying redox conditions in the bottom water below approximately 150 m depth high rain rates onto the sea floor of the organic matter that hosted the phosphate and several trace elements contributed to the accumulation of phosphorite chert and black shales and mudstones evaporation in the goose egg basin to the east of the phosphoria basin ensured the import of surface seawater from the phosphoria sea budgets of water salt phosphate and oxygen plus the minor accumulation of the biomarker gammacerane show that exchange of water between the two basins was limited possibly by the shallow carbonate platform that separated the two basins