shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

long term evolution of transient liquid water on mars 1 liquid water is not currently stable on the surface of mars however transient liquid water ice melt may occur if the surface temperature is between the melting and boiling points such conditions are met on mars with current surface pressures and obliquity due to the large diurnal range of surface temperatures this yields the potential for transient nonequilibrium liquid water a general circulation model is used to undertake an initial exploration of the variation of this transient liquid water potential tlwp for different obliquities and over a range of increased pressures representing progressively earlier phases of martian geological history at higher obliquities and slightly higher surface pressures 50 mbar tlwp conditions are met over a very large fraction of the planet as the surface pressure is increased above about 50 100 mbar however increased atmospheric thermal blanketing reduces the diurnal surface temperature range essentially eliminating the possibility of even transient liquid water at high enough pressures the mean temperature is sufficiently elevated to allow stable liquid water thus the potential for liquid water on mars has not decreased monotonically over planetary history as the atmosphere was lost instead a distinct minimum in tlwp the dead zone will have occurred during the extended period for which pressures were in the middle range between about 0 1 and 1 bar this has direct and restrictive implications for chemical weathering and life the fundamental conclusion of this study is largely insensitive to invocation of brines and to more detailed treatment of atmospheric radiative processes

diagenetic stabilization of aragonite and low mg calcite i trace elements in rudists abstract cretaceous rudists with thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of meteoric diagenesis on their textural and chemical attributes the original fine compact prismatic or cellular prismatic microstructures of low mg calcitic layers have been preserved frequently despite the vagaries of their subsequent diagenetic histories these layers usually suffered only partial recrystallization which caused fusion of crystal units rounding of prism comers and partial cementation confined to intercrystalline and intraparticle pore spaces in contrast the originally aragonitic parts of the shell usually suffered either complete dissolution or at best retained some vestiges of their crossed lamellar or complex crossed lamella microstructures synsedimentary submarine diagenetic events such as borings by endolithic fauna internal micritic and or peloidal sedimentation and submarine aragonite and or high mg calcite cements within the primary inter and intraparticle pore spaces were coeval with rudist accretion the subsequent meteoric cementation has been characterized by the formation of bladed and equant ferroan calcites which occluded the residual primary and secondary porosities diagenetic stabilization of aragonite to diagnetic low mg calcite and low mg calcite to diagenetic low mg calcite is believed to have been a two stage process initially sr and na have been partially depleted during an early meteoric diagenetic phase calcitization of metastable phases with expulsion of sr at a slower rate than that of na this stage is followed by incorporation of more mn fe and mg due to precipitation of late ferroan calcite stabilization of aragonite causes more pronounced trace element repartitioning than the stabilization of low mg calcite however the degree of repartitioning depends not only on mineralogy but also on the structural buildup of a given shell layer suggesting that factors such as water rock ratio surface kinetics are of considerable sig ificance for the process of diagenetic stabilization rudist skeletal components with preserved original mineralogy and texture have trace element chemical signatures analogous to holocene marine bivalves this similarity argues for comparable chemical composition of the cretaceous and holocene seawater as well as for similar modes of incorporation of trace elements into mollusc shells

chemical and isotopic architecture of the belemnite rostrum abstract macrofossil calcite is of great importance for quantitative reconstructions of palaeoenvironment and palaeoseasonality the calcite rostra of belemnites jurassic to cretaceous marine invertebrates are especially suited for such investigations because they are comparatively large and are structured by growth bands despite their use in chemostratigraphic and palaeoenvironmental studies much of the internal variability of geochemical signatures in rostra is poorly understood here multiple profiles through a belemnite rostrum of passaloteuthis bisulcata 183 myr old were analyzed for 13c and 18o values as well as mg ca sr ca and mn ca ratios geochemical signatures of the central 1 2 mm of the profiles indicate diagenetic cementation along the apical zone for which original porosity of up to 40 can be inferred the overall 13c and 18o values of the other well preserved parts of the belemnite fluctuate by 1 per mil but are nearly uniform within single growth bands in contrast sr ca and mg ca in the well preserved parts show growth rate and crystal shape related variability close to the central apical zone strongly bent calcite crystals are enriched in mg up to 70 and sr up to 50 through the remainder of the rostrum higher calcite precipitation rate can account for mg depletion of 15 and sr enrichment of 15 with respect to co genetic calcite precipitated at a slower rate no indication for temperature control on mg ca or sr ca is detected in the investigated specimen overall the new findings indicate that 13c and 18o analyses of belemnite rostra produce consistent results regardless of the sampling area within the rostrum and that growth rate effects on element incorporation are minor with respect to the control exerted by secular changes in seawater composition through time additionally the central part of the rostrum where strong calcite crystal bending is observed should be avoided for sampling when studying elemental composition of the calcite for palaeoenvironmental reconstructions

toarcian oceanic anoxic event an assessment of global causes using belemnite c isotope records from black shales markingthe toarcian oceanic anoxic event t oae the first explanation envisions recycling of dissolved inorganiccarbon dic with a light isotopic signature into the photic zone from the lower levels of a salinity stratifiedwater mass essentially requiring a regional paleoceanographic driver of the carbon cycle the second involvesthe rapid and massive dissociation of methane from gas hydrates that effectively renders the t oae a globalperturbation of the carbon cycle we present c isotope records from belemnites d

climatic ups and downs in a disturbed jurassic world the tropical warm and equable climate of the jurassic world is regularly challenged by geoscientists especially since oxygen isotopes 18 o of fossil hardparts have been used to reconstruct the paleotemperature history of seawater by applying the innovative sizer sig nifi cant zero crossings of the derivatives statistical approach to a newly compiled 18 o data base for the jurassic we demonstrate the occurrence of major and multiscale 18 o changes mainly related to climate disturbances for the fi rst time two long term anomalies in 18 o are identifi ed during the toarcian and the late jurassic in conjunction with intensive volcanism in large igneous provinces these results support a strong infl uence of repeated volcanic pulses on the modulation of pco 2 temperatures and polar ice cap volumes over protracted periods at shorter time scales 13 relatively rapid 0 5 1 m y and signifi cant warming and cooling events are identifi ed the causes of which include transient fl uctuations in greenhouse gas con centrations related to still debated mechanisms

miocene to pliocene changes in south african hydrology and vegetation in relation to the expansion of c4 plants the miocene expansion of c4 plants mainly tropical grasses between 8 and 4 million years ma remains an enigma since regional differences in the timing of the expansion rules out decreased co2 pco2 as a dominant forcing e g tipple and pagani 2007 the early origins of terrestrial c4 photosynthesis annu rev earth planet sci 35 435 461 other environmental factors such as low latitude aridity and seasonality have been proposed to explain the low tree versus grass ratio found in savannahs and tropical grasslands of the world but conclusive evidence is missing here we use pollen and stable carbon 13c and hydrogen d isotope ratios of terrestrial plant wax from a south atlantic sediment core odp site 1085 to reconstruct miocene to pliocene changes of vegetation and rainfall regime of western southern africa our results reveal changes in the relative amount of precipitation and indicate a shift of the main moisture source from the atlantic to the indian ocean during the onset of a major aridification 8 ma ago we emphasize the importance of declining precipitation during the expansion of c4 and cam mainly succulent vegetation in south africa we suggest that the c4 plant expansion resulted from an increased equator pole temperature gradient caused by the initiation of strong atlantic meridional overturning circulation following the shoaling of the central american seaway during the late miocene

paleoceanographic changes of the late pliensbachian early toarcian interval a possible link to the genesis of an oceanic anoxic event abstract secular records of the elemental and isotopic composition of belemnite calcite were studied in pliensbachian and toarcian sections from the yorkshire coast uk and southern germany to investigate oceanographic change during an interval prior to and including the toarcian oceanic anoxic event oae records from southern germany are correlated to the uk stratigraphy using strontium isotope stratigraphy the geochemical trends measured from belemnite calcite are consistent between the two sections and are interpreted in terms of temperature and salinity of the northwest european epi continental sea the data suggest that a dramatic environmental change coincided with the toarcian oae belemnite mg ca sr ca and na ca ratios increase by a factor of between 1 7 and 2 coincident with a 3 negative shift in 18o from the mid tenuicostatum zone until the lower falciferum zone of the uk ammonite biostratigraphy a period of 0 6 0 7 myr taken at face value the mg ca and 18o data argue for an abrupt warming of 6 7 c and substantial freshening during this interval global warming accompanied by an accelerated hydrological cycle and increased runoff is proposed to explain these changes prior to these events data from lower in the yorkshire section suggest a possible cooling accompanied by a shift to more saline waters during the period from the upper pliensbachian margaritatus zone to the toarcian lower tenuicostatum zone this earlier event may also have been important in causing density stratification in the northwest european epi continental sea

core top calibration of b ca in pacific ocean neogloboquadrina incompta and globigerina bulloides as a surface water carbonate system proxy abstract practical methods for reconstructing past ocean carbonate chemistry are needed to study past periods of ocean acidification and improve understanding of the marine carbonate system s role in the global climate cycles planktic foraminiferal b ca may fill this role but requires better understanding and improved proxy calibrations we used pacific ocean core top sediments to generate new calibrations of the b ca proxy for past carbonate system parameters in two upwelling subpolar species of asymbiotic planktic foraminifera globigerina bulloides and neogloboquadrina incompta both species show significant positive correlation of b ca with calcite saturation calcite and carbonate ion concentration co 3 2 across a broad range of environmental conditions this suggests a calcification rate control on b ca incorporation as calcite regulates calcification rate in agreement with recent inorganic calcite studies this is also consistent with a surface entrapment model of trace element incorporation into caco3 in neither species is b ca significantly correlated with ph suggesting that ph does not directly regulate boron incorporation and that calculation of ph directly from foraminiferal b ca is not suitable correlations between b ca and b oh 4 b oh 4 hco3 and b oh 4 dic are weaker than with calcite boron partition coefficients k d b ca solid b oh 4 hco 3 seawater show little or no correlation with co32 or temperature and vary widely providing no support for application of kd to calculate carbonate system parameters from b ca we also discuss potential effects of depth related dissolution temperature and salinity on b ca these empirical calibrations linking foraminiferal calcite b ca with calcite provide a strong tool for reconstructing the past ocean carbonate system and improve our understanding of the proxy s geochemical basis

high albedo dune features suggest past dune migration and possible geochemical cementation of aeolian sediments on mars high albedo features are identified in association with barchan dunes in an equatorial inter crater dune field on mars using images from the mro mission this paper describes the morphometric properties of these features and their association with the present barchan dune field we propose that these features are cemented aeolian deposits that form at the foot of the dune avalanche face a possible terrestrial analog exists at white sands national monument in south central new mexico usa the presence of these features suggests past episodes of dune migration in inter crater dunefields and liquid water in the near sub surface in sufficient quantity to cause the cementation of aeolian dune sediment

automatic detection of particle aggregation in particle code simulations of rock deformation we explore whether it is possible to determine the initial stages of localization of deformation during a numerical experiment on a virtual rock purely through observation and interpretation of geometrical rearrangements of the particles we study the spatial arrangements of particle via two tools first by viewing the virtual rock as a network we look for local clusters of edges particle contacts second by analyzing the distribution of the directions of motion of the particles we recognize that the main particle aggregations are characterized by directions which are statistically meaningful more important the locations of edge clusters and particle aggregations coincide suggesting that the tools presented could be routinely used to detect emergent structures in particle assemblages

an isotopic appraisal of the late jurassic greenhouse phase in the russian platform abstract oxygen and carbon isotope ratios have been determined from late jurassic callovian volgian belemnites from three locations on the russian platform gorodischi khanskaya gora and marievka all samples were examined by means of trace element geochemistry and petrography in order screen for diagenetic alteration oxygen and carbon isotopes from well preserved belemnites range from 2 24 to 0 09 and 0 57 to 1 77 respectively oxygen isotopes if interpreted in terms of temperature reveal a rise of temperatures during the oxfordian early kimmeridgian and indicate a prolonged episode of warmth during the kimmeridgian volgian the isotope data only equivocally reflect a number of significant changes in boreal tethyan ammonite assemblages a positive carbon isotope excursion is observed within the volgian but not seen within composite carbon isotope stratigraphies of the western tethys hence the jurassic may have been characterised by regional 13 c excursions related to non simultaneous organic matter deposition resulting from localised ponding semi restricted ocean circulation and a lack of tidal mixing

u th systematics and 230th ages of carbonate chimneys at the lost city hydrothermal field the lost city hydrothermal field lchf is a serpentinite hosted vent field located 15 km west of the spreading axis of the mid atlantic ridge in this study uranium thorium u th geochronological techniques have been used to examine the u th systematics of hydrothermal fluids and the 230th ages of hydrothermally precipitated carbonate chimneys at the lchf fluid sample analyses indicate that endmember fluids likely contain only 0 0073 ng g u or less compared to 3 28 0 03 ng g of u in ambient seawater for fluid samples containing only 2 21 ambient seawater 1 1 11 mmol kg mg th concentration is 0 11 0 13 pg g and surrounding seawater concentrations average 0 133 0 016 pg g the 230th 232th atomic ratios of the vent fluids range from 1 10 10 6 to 11 5 10 6 are less than those of seawater and indicate that the vent fluids may contribute a minor amount of non radiogenic 230th to the lchf carbonate chimney deposits chimney 238u concentrations range from 1 to 10 g g and the average chimney corrected initial 234u is 147 2 0 8 which is not significantly different from the ambient seawater value of 146 5 0 6 carbonate 232th concentrations range broadly from 0 0038 0 0003 to 125 16 ng g and 230th 232th atomic ratios vary from near seawater values of 43 8 10 6 up to 530 25 10 3 chimney ages corrected for initial 230th range from 17 6 yrs to 120 13 kyrs the youngest chimneys are at the intersection of two active steeply dipping normal faults that cut the atlantis massif the oldest chimneys are located in the southwest portion of the field vent deposits on a steep fault bounded wall on the east side of the field are all 4 kyrs old indicating that mass wasting in this region is relatively recent comparison of results to prior age dating investigations of submarine hydrothermal systems shows that the lchf is the most long lived hydrothermal system known to date it is likely that seismic activity and active faulting within the atlantis massif and the atlantis fracture zone coupled with volumetric expansion of the underlying serpentinized host rocks play major roles in sustaining hydrothermal activity at this site the longevity of venting at the lchf may have implications for ecological succession of microorganisms within serpentinite hosted vent environments

radiaxial fibrous calcites a new look at an old problem abstract marine radiaxial fibrous and fascicular optic calcites are very common but poorly understood pore filling cements in paleozoic and mesozoic marine neritic and upper bathyal limestones the main diagnostic feature of these cements is their converging or diverging crystal c axis respectively the reasons for this anomalous texture are at present unknown another controversy is due to the relative lack of occurrences in cenozoic strata and their apparent absence in quaternary marine limestones despite these uncertainties marine fibrous cements are thought by some to be amongst the best proxies for the geochemistry of ancient oceans because of the absence of metabolic effects during their precipitation applying electron backscatter diffraction analysis we here for the first time document radiaxial fibrous and subordinate fascicular optic fibrous biominerals from well preserved jurassic and cretaceous low mg calcite belemnite rostra the finding of fibrous biogenic calcites in combination with the recent description of holocene and modern fibrous calcites in stalagmites represents in the view of the authors a significant advance in carbonate research here these findings are placed in their wider processes oriented context and the significance of biogenic and speloan fibrous calcite for their marine counterparts is assessed comparing the physico chemical and organomineralic properties of different precipitation sites indicates that the diagnostic variations in the crystal c axis orientation are not related to a specific nucleation environment or substratum in contrast preliminary crystallographic analyses suggest that kinetic factors during nucleation or subtle gradients in the statistical replacements of ca 2 by mg 2 in the crystal structure may lead to local strain resulting in converging or diverging crystal c axes

diagenetic stabilization of aragonite and low mg calcite ii stable isotopes in rudists abstract cretaceous rudists having thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of phreatic vadose meteoric diagenesis on their microstructural and isotopic attributes rudist skeletal components with preserved original mineralogy of aragonite and low mg calcite and with preserved microstructures have isotopic signatures analogous to holocene marine bivalves this similarity argues for a comparable isotopic composition of the cretaceous and holocene seawater as well as for a similar mode of incorporation of stable isotopes into their shells diagenetic stabilization of rudist shells appears to have been a two stage process with low mg calcite diagenetic calcite lmc dlmc and particularly aragonite diagenetic calcite a dlmc transformation as the first step and cementation as a later development the direct a dlmc mineralogical transformation calcitization results in initial depletion in 18o of 2 and the subsequent diagenetic precipitation of ferroan calcite spar causes depletion in 13c as well as an additional decrease in 18o the former due to introduction of organically derived co2 into the diagenetic aquifer in contrast 13o and 13c isotopic depletions in the originally lmc skeletal components are both related to the precipitation of the late diagenetic ferroan sparry calcite cement the earlier calcitization stage being of subordinate importance only

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

recent aeolian dune change on mars previous comparisons of martian aeolian dunes in satellite images have not detected any change in dune form or position here we show dome dunes in the north polar region that shrank and then disappeared over a period of 3 04 mars years 5 7 earth years while larger neighboring dunes showed no erosion or movement the removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on mars but that any sand that is available for transport is likely to be moved dunes that show no evidence of change could be crusted indurated or subject to infrequent episodes of movement

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

early diagenesis of eolian dune and interdune sands at white sands new mexico abstract the degree of early diagenesis in eolian dune and interdune sands at white sands new mexico is largely a function of the relationship between sand location and the water table most active and vegetation stabilized dune sands are in the vadose zone whereas interdune sands are in the capillary fringe and phreatic zones crystallographically controlled dissolution of the framework gypsum grains results in elongate prismatic etch pits on sand grains from the capillary fringe and phreatic zones whereas dissolution of sand grains in the vadose zone is slight causing minute irregularities on grain surfaces vadose water percolating through the sand is manifest as meniscus layers consequently dune sands in the vadose zone are cemented mainly by meniscus shaped gypsum at grain contacts pendant cements formed on the lower margins of some sand grains cementation in the capillary fringe and the phreatic zone is more extensive than the vadose regardless of strata type typically well developed gypsum overgrowths form along the entire edge of a grain or may encompass the entire grain complex diagenetic histories are suggested by multiple overgrowths and several episodes of dissolution on single grains attesting to changing saturation levels with respect to gypsum in the shallow ground water these changes in saturation are possibly due to periods of dilution by meteoric recharge alternating with periods of concentration of ions and the formation of cement due to evaporation through the capillary fringe

determination of both chemical and stable isotope composition in milligramme size carbonate samples abstract isotopic analysis of carbonates involves dissolution of the sample in 100 phosphoric acid analysis of the acid after reaction using inductive coupled plasma source spectrometry gives the chemical composition of the same sample molar fractions of cations in carbonate minerals can be determined to about 0 1 for ca 0 04 for mg 0 06 for fe 60 ppm for mn and 90 ppm for sr even the minor carbonate component in shales can be analyzed if a correction for leaching of clay minerals is made by reference to the al content of the solution however loss in accuracy ensues because of the uncertainty in the correction

deformation of rock a pressure sensitive dilatant material permanent plastic deformation of rock materials in the brittle regime cataclastic flow is modelled here in terms of mohr coulomb behaviour in which all three of the parameters cohesion friction angle and dilation angle follow hardening or softening evolution laws with both plastic straining and increases in confining pressure the physical basis for such behaviour is provided by a sequence of uniaxial shortening experiments performed byedmond andpaterson 1972 at confining pressures up to 800 mpa on a variety of materials including gosford sandstone and carrara marble these triaxial compression experiments are important for the large range of confining pressures covered and for the careful recording of data during deformation particularly volume change of the specimens both materials are pressure sensitive and dilatant it is therefore possible to derive from these experiments a set of material parameters which allow a preliminary description of the deformation behaviour in terms of a non associated mohr coulomb constitutive model thus providing the first constitutive modelling of geological materials in the brittle ductile regime these parameters are used as input to a finite difference numerical code flac with the aim of investigating how closely this numerical model simulates real material behaviour upon breakdown of homogeneous deformation the mechanical and macrostructural behaviour exhibited by the numerical model is in close agreement with the physical results in that the stress strain curves are duplicated together with localization behaviour the results of the modelling illustrate how the strength of the upper crust may be described by two different but still pressure dependent models the linear shear stress normal stress relationship of amontons that is byerlee s law and a non linear mohr coulomb constitutive model both include parameters of friction and both describe brittle deformation behaviour consideration of the non linear bulk material model allows investigation of the geologic regimes which favour localization of the deformation over a continuing homogeneous deformation more complex models are required to describe the deformation of rock with increasing depth and temperature as the behaviour becomes increasingly temperature sensitive and rate dependent

barchan dune asymmetry observations from mars and earth barchan dune asymmetry refers to the extension of one barchan limb downwind it is a common dune form on earth and also occurs on mars and titan a new classification of barchan limbs is presented where three types of limb morphology are identified linear kinked and beaded these along with other dune scale morphological signatures are used to identify three of the causes of barchan asymmetry on mars bi directional winds dune collision and the influence of inclined topography the potential for specific dune asymmetric morphologies to indicate aspects of the formative wind regime on planetary surfaces is shown for example the placement of dune limbs can indicate the general direction and relative strength of formative oblique winds an extreme barchan limb length may indicate a long duration oblique wind a kinked limb may be evidence of the passage of a storm beaded limbs may represent surface wave instabilities caused by an increase in wind energy parallel to the dune a preliminary application of these signatures finds evidence for bi modal winds on mars however these and other morphological signatures of wind direction and relative strength should be applied to planetary landforms with caution as more than one process e g bi modal winds and collision may be operating together or sequentially on the dunefield in addition analysis should be undertaken at the dunefield scale and not on individual dunes finally morphological data should be acquired from similar scale dunes within a dunefield in addition to bi modal wind regimes on mars the frequent parallel alignment of the extended barchan limb to the dune suggests that dune collision is also an important cause of asymmetry on mars some of the more complex dunefield patterns result from a combination of dune collision limb extension and merging with downwind dunes dune asymmetric form does not inhibit dune migration in the namib desert or on mars data from the namib suggest that dune migration rates are similar for symmetric and asymmetric dunes further modeling and field studies are needed to refine our understanding of the potential range of limb and dune morphologies that can result from specific asymmetry causes

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

crystal growth rate effect on mg ca and sr ca partitioning between calcite and fluid an in situ approach abstract partition coefficients of mg and sr kmg and ksr between calcite and fluid were determined in crystals grown under different rates v where v is defined as the crystal extension per unit of time nm s addition of rare earth elements ree into the fluid leads to ree preservation in the calcite this preservation allows for a direct determination of the values of v by measuring the widths of the ree spiked zones the edge to edge spot analyses of mg ca sr ca and ree ca in the individual crystals were conducted using secondary ion mass spectrometry sims the mg ca and sr ca ratios in the fluids from which calcites precipitated were also measured with inductively coupled plasma atomic emission spectroscopy icp oes this allowed for the first time to evaluate kmg in situ in the individual crystals without averaging the data from the multiple calcite crystals results show that ksr increases by a factor of six with increasing calcite growth rate from 0 001 to 4 nm s kmg decreases by a factor of three with the same increase of v values these ksr and kmg behaviors were described quantitatively using a growth entrapment model gem according to the gem simulations sr is enriched and mg is depleted in the near surface layer of calcite relative to the bulk lattice this distinct outermost region of the crystal may be fully or partially captured by its lattice during rapid growth this process causes disequilibrium partitioning of sr and mg through growth entrapment

reconstructing the palaeoenvironment of the middle russian sea during the middle late jurassic transition using stable isotope ratios of cephalopod shells and variations in faunal assemblages abstract oxygen and carbon isotope data of well preserved belemnite rostra and ammonite shells are presented from the callovian oxfordian boundary uppermost lamberti to lowermost cordatum zones of the dubki section near saratov in the russian platform palaeotemperatures calculated for nektobenthic belemnites averages of 5 c and 8 c for cylindroteuthids and belemnopseids respectively show the presence of cold bottom waters in the central part of the middle russian sea during the studied interval palaeotemperatures calculated for ammonites which are assumed to have lived in near surface waters are considerably higher average 13 c the presented data show a vertical thermal gradient in the middle russian sea the belemnite oxygen isotope record and the relative abundances of ammonite families in the dubki section do not correlate with each other probably as a result of different depth habitats of ammonites and belemnites a review of literature isotope data shows the climatic zonation in european seas at the middle late jurassic transition despite the flux of cold polar waters to the middle russian sea and the area of scotland there is no evidence for glaciation at the middle late jurassic transition changes in water circulation during a sea level highstand were likely a source of spreads of cold bottom waters and cardioceratid ammonite fauna in this time period the belemnite isotope record of the callovian oxfordian boundary in the russian platform is characterized by significant scatter of 13c values no temporal carbon isotope trend is observed the 13c values of russian belemnite rostra average 2 6 vpdb being 1 to 2 higher than the values of coeval lower oxfordian belemnites from the area of the submediterranean ammonite province higher than submediterranean 13c values of russian belemnite rostra are likely related to high biologic productivity and or high organic matter burial in semi isolated boreal subboreal marine basins

reconstruction of late bajocian bathonian marine palaeoenvironments using carbon and oxygen isotope ratios of calcareous fossils from the polish jura chain central poland abstract oxygen and carbon isotope analyses were carried out on upper bajocian bathonian calcitic belemnite rostra and oyster shells as well as aragonitic ammonite nautiloid and trigoniid shells from the ore bearing czestochowa clay formation in south central poland all samples were studied by means of cathodoluminscence microscopy trace element x ray and scanning electron microscope sem analysis in order to select best preserved material sem studies allowed classifying some aragonitic ammonite and nautiloid shells 99 aragonite as diagenetically altered average 18o values of oysters belemnites and trigoniids translate into relatively low palaeotemperatures of 10 1 9 2 and 7 4 c respectively the comparable 18o values of bivalves and belemnites indicate that belemnites had a nectobenthic lifestyle and did not record surface water temperatures the ammonite fauna is interpreted to have been nektonic however palaeotemperatures derived from ammonite 18o around 18 6 c may be overestimated due to a lower than normal marine salinity of surface waters the reduced salinity is inferred as well from sedimentological observations and faunal composition the obtained 18o values indicate cool climatic conditions during the late bajocian bathonian in south central poland which may have been linked with the occurrence of a cold climatic episode despite the fact that all studied shells were not precipitated in carbon isotope equilibrium with ambient waters the 13c shell values enabled us to roughly estimate isotope composition of dissolved inorganic carbon dic in the late bajocian bathonian sea of south central poland water 13cdic values calculated from ammonite 13c are lower in comparison to 13cdic values calculated from oyster and belemnite carbon isotope ratios which in conjunction with ammonite 18o values indicates lower salinity of surface or shallow near coastal waters

paleotemperature variations of early jurassic seawater recorded in geochemical trends of belemnites from the basque cantabrian basin northern spain abstract here we present new o isotope mg ca and sr ca data of early jurassic belemnites from the basque cantabrian basin of northern spain a succession deposited in a periodically anoxic restricted hemipelagic basin nearly 200 pliensbachian lower toarcian belemnites were collected and examined using optical cathodoluminescence and chemical techniques to constrain the effects of potential diagenetic alteration after a precise diagenetic screening of samples 176 belemnites were selected to provide records of changes in seawater geochemistry and temperature the records show a fairly good correlation of 18o with mg ca ratios r 0 65 and a weak correlation of 18o with sr ca ratios r 0 34 the oxygen isotope data if interpreted in terms of paleotemperature have revealed a period of relatively uniform and warm seawater temperatures during the early pliensbachian followed by a sharp temperature drop during the late pliensbachian earliest toarcian the onset of this cooler period occurred within the protogrammoceras celebratum subzone and the coolest seawater temperatures were reached at the end pliensbachian pleuroceras spinatum zone this was followed by a rapid seawater warming during the harpoceras serpentinus zone of the early toarcian in addition the data set provides new information regarding paleoceanographic conditions for anoxic events in a critical region of connection between the boreal and tethys realms it is the background to relatively high 18o values that prevailed during the anoxic episodes concerning the impact of the early toarcian anoxic event in northern spain the detected 18o and mg ca excursions reached their minimum and maximum respectively during the lower h serpentinus zone while the anoxic black shale interval developed earlier during the upper dactylioceras tenuicostatum lowermost h serpentinus zones

defrosting dark flow features and dune activity on mars example in russell crater 1 defrosting processes observed on mars are among the most unusual features described on high resolution images a defrosting sequence has been observed near the crest of the megadune located in the russell crater on new high resolution images obtained from the hirise instrument and on hyperspectral cubes obtained from crism instrument both on board mro hyperspectral images show that frost overlaps the entire megadune in middle winter this frost is composed mainly of co2 and of a small amount of water ice the deepest ice signatures are mainly located near the crest of the megadune the defrosting sequence monitored by crism reveals spatial heterogeneity and refrosting processes on the morphological counterpart the defrosting sequence starts with the development of dark spots similar to those described in the cryptic regions after few sols we observe the emplacement of dark linear flow features that start from the dark spots downward of the main slope of the dune these linear flow features are 1 to 2 m wide and 50 to 100 m long they settle on the small rills visible on the frost cover they are interpreted as avalanches of a mixing of sand dust and unstable co2 gas released under pressure the avalanches would be triggered by the eruption of the dark spots the flux of material transported by the flow features has been estimated to 0 25 to 0 5 m3 by meter width each year on the megadune this flux is larger than flux transported by wind these dark flow features are thus very efficient to transport material on slopes located in frosted areas

southern high latitude dune fields on mars morphology aeolian inactivity and climate change in a study area spanning the martian surface poleward of 50 s 1190 dune fields have been identified mapped and categorized based on dune field morphology dune fields in the study area span 116 400 km2 leading to a global dune field coverage estimate of 904 000 km2 far less than that found on earth based on distinct morphological features the dune fields were grouped into six different classes that vary in interpreted aeolian activity level from potentially active to relatively inactive and eroding the six dune field classes occur in specific latitude zones with a sequence of reduced activity and degradation progressing poleward in particular the first signs of stabilization appear at 60 s which broadly corresponds to the edge of high concentrations of water equivalent hydrogen content observed by the neutron spectrometer that have been interpreted as ground ice this near surface ground ice likely acts to reduce sand availability in the present climate state on mars stabilizing high latitude dunes and allowing erosional processes to change their morphology as a result climatic changes in the content of near surface ground ice are likely to influence the level of dune activity spatial variation of dune field classes with longitude is significant suggesting that local conditions play a major role in determining dune field activity level dune fields on the south polar layered terrain for example appear either potentially active or inactive indicating that at least two generations of dune building have occurred on this surface many dune fields show signs of degradation mixed with crisp brinked dunes also suggesting that more than one generation of dune building has occurred since they originally formed dune fields superposed on early and late amazonian surfaces provide potential upper age limits of 100 my on the south polar layered deposits and 3 ga elsewhere at high latitudes no craters are present on any identifiable dune fields which can provide a lower age limit through crater counting assuming all relatively stabilized dune fields represent a single noncontiguous surface of uniform age their estimated crater retention age is 10 000 years an average sized uncratered dune field 94 km2 has a crater retention age 8 my this apparent youth suggests that present day climate conditions are responsible for the observed degradation and reduced level of aeolian activity a lack of observed transport pathways and the absence of large dune fields in the largest basins hellas and argyre planitiae are consistent with the previously proposed idea that dune sands are not typically transported far from their source regions on mars

partial diagenetic overprint of late jurassic belemnites from new zealand implications for the preservation potential of δ7li values in calcite fossils the preservation potential and trends of alteration of many isotopic systems e g li mg ca that are measured in fossil carbonates are little explored yet extensive paleoenvironmental interpretations have been made on the basis of these records here we present a geochemical dataset for a late jurassic 153 ma belemnite belemnopsis sp from new zealand that has been partially overprinted by alteration we report the physical pathways and settings of alteration the resulting elemental and isotopic trends including 7li values and li ca ratios and assess whether remnants of the primary shell composition have been preserved or can be extrapolated from the measured values the 18o and 13c values as well as sr ca and mn ca ratios were analysed along two profiles in addition 6 samples were analysed for 87sr 86sr sr ca and mn ca ratios five samples from the same specimen and 2 from the surrounding sediment were analysed for 7li values li ca sr ca and mn ca ratios and are compared to results for 6 other late jurassic belemnite rostra belemnopsis sp andhibolithes sp from the same region the 87sr 86sr ratios are lower less radiogenic in the most altered part of the rostrum whereas 7li values become more positive with progressive alteration the direction and magnitude of the trends in the geochemical record indicate that one main phase of alteration that occurred in the late cretaceous caused most of the diagenetic signature in the calcite despite relatively deep burial down to 4 km and thus elevated temperatures this diagenetic signature has subsequently been preserved even for the highly mobile element lithium suggesting that primary lithium isotope values can be maintained over geological timescales at least in thick macrofossil shells our best 7li estimate for pristine late jurassic 155 148 ma belemnites is 27 1 which points to a late jurassic seawater 7li of 29 32 compatible with the modern value of 31

effect of a jurassic oceanic anoxic event on belemnite ecology and evolution the toarcian oceanic anoxic event t oae 183 million y ago is possibly the most extreme episode of widespread ocean oxygen deficiency in the phanerozoic coinciding with rapid atmospheric pco2 increase and significant loss of biodiversity in marine faunas the event is a unique past tipping point in the earth system where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic c isotope records modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the t oae here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early toarcian belemnites we combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early toarcian global exogenic carbon cycle perturbation and belemnite paleoecology the organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation environmental change and biotic response during the t oae we infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia

frictional behaviour of sandstone a sample size dependent triaxial investigation abstract frictional behaviour of rocks from the initial stage of loading to final shear displacement along the formed shear plane has been widely investigated in the past however the effect of sample size on such frictional behaviour has not attracted much attention this is mainly related to the limitations in rock testing facilities as well as the complex mechanisms involved in sample size dependent frictional behaviour of rocks in this study a suite of advanced triaxial experiments was performed on gosford sandstone samples at different sizes and confining pressures the post peak response of the rock along the formed shear plane has been captured for the analysis with particular interest in sample size dependency several important phenomena have been observed from the results of this study a the rate of transition from brittleness to ductility in rock is sample size dependent where the relatively smaller samples showed faster transition toward ductility at any confining pressure b the sample size influences the angle of formed shear band and c the friction coefficient of the formed shear plane is sample size dependent where the relatively smaller sample exhibits lower friction coefficient compared to larger samples we interpret our results in terms of a thermodynamics approach in which the frictional properties for finite deformation are viewed as encompassing a multitude of ephemeral slipping surfaces prior to the formation of the through going fracture the final fracture itself is seen as a result of the self organisation of a sufficiently large ensemble of micro slip surfaces and therefore consistent in terms of the theory of thermodynamics this assumption vindicates the use of classical rock mechanics experiments to constrain failure of pressure sensitive rocks and the future imaging of these micro slips opens an exciting path for research in rock failure mechanisms

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

groundwater salinity as a control on development of eolian landscape an example from the white sands of new mexico abstract the white sands of southern new mexico form the largest field of gypsum dunes in the world the juxtaposition of several different types of dunes within the field has long been recognized and has generally been attributed to changes in the rate of sand transport across the dune field however steven fryberger fryberger s g 2003 geology of white sands national monument web page www2 nature nps gov geology parks whsa recently hypothesized however that a primary control is groundwater salinity the white sands dune field is underlain by saline waters fryberger proposed that parabolic dunes could form in topographic highs that accumulated a lens of fresher water derived from precipitation water with lower salinity allowed vegetation to grow and stabilized the sand except for the active noses of the parabolic dunes this study is a test of that hypothesis a study transect was established across the boundary between parabolic and barchan dunes groundwater and soil at six sites were sampled during december 2004 and march may and june of 2005 two sites were established in the parabolic field two in the barchans and two in the transition zone between them groundwater was found to be three times more saline in the barchan area conductivity and chloride decreased across the transition zone a gps topographic survey revealed two abrupt topographic steps one at the boundary between the barchans and the transition zone and a second at the edge of the parabolic field a second larger topographic step was found outside the study area defining a higher parabolic dune field these data indicate that fryberger s 2003 hypothesis is correct and groundwater is controlling the dune field morphology the dune field did not begin to form until the mid holocene 6500 years ago a compilation of dates shows that the parabolic dune field has probably been stable for the last 3500 years in contrast the barchan area has been recently deflated and exposed 2000 year old sediment near the surface

the mars global digital dune database mgd3 global patterns of mineral composition and bedform stability abstract we present an expansion to the mars global digital dune database mgd3 describing 1 bulk dune field composition determined by fitting a mineral spectral library to thermal emission spectra tes data and 2 a morphologic stability index that measures the degree of non aeolian modification that has eroded and stabilized each dune field this paper describes results for these two components providing insight into global patterns of dune sand sources postdepositional alteration and mineral maturity consistent with the work of others the main mineral components of each analyzed dune field are feldspar pyroxene and high silica phases with minor amounts of olivine and possibly sulfate minerals subtle global scale spatial variations in olivine and feldspar abundances correspond with previously observed trends in surface mineralogy suggesting that dune sand is reflective of its regional setting and thus that aeolian sand has typically not traveled far

evaluating mg ca in belemnite calcite as a palaeo proxy the mg ca sr ca 18o and 13c compositions are given for well preserved specimens of ten belemnite species genera from three stratigraphic intervals the data help assess the use of these proxies for palaeo oceanography samples are from dorset uk pliensbachian 5 species cambridgeshire uk callovian 1 species and the vocontian basin se france valanginian 4 genera in none of these belemnite populations at species or genera level does mg ca correlate with 18o neither do values of 18o correlate with mg ca along a microsampled radial profile across a single specimen of cylindroteuthis puzosiana callovian the use of mg ca is therefore considered to be unreliable as a palaeo temperature indicator for these belemnite species and genera

orientation and distribution of recent gullies in the southern hemisphere of mars observations from high resolution stereo camera mars express hrsc mex and mars orbiter camera mars global surveyor moc mgs data 1 geologically recent small gullies on mars display morphologies consistent with erosion by water or by debris flows suggested formation models are divided into two main categories 1 groundwater or 2 melting of near surface ice snow sourced from the atmosphere we have measured location and orientation and recorded the local contexts of gullies to constrain the likely models of gully formation more than 22 000 mars orbiter camera narrow angle moc na and 120 mars express high resolution stereo camera hrsc images in the southern hemisphere were searched for gullies discrete gullied slope sections with consistent orientation were recorded rather than individual gullies slope setting impact crater valley wall etc location and orientation were recorded for each slope section more than 750 moc images with gullies 900 distinct gullied slope sections and more than 40 hrsc images 380 distinct gullied slope sections were identified from both moc and hrsc gullies were found to be most common between 30 and 50 degrees latitude and to have an overall pole facing preference the preferred gully orientation for hrsc is southeast rather than south in moc owing to illumination effects that make gullies difficult to detect on south to southwest facing slopes in hrsc in both moc and hrsc surveys higher latitude gullies show less preference for pole facing than those at mid latitudes both data sets produced similar results demonstrating that our data are reliable we suggest that the observed latitudinal and orientation distributions of gullies show that insolation and atmospheric conditions play a key role in gully formation

white sands dune field new mexico age dune dynamics and recent accumulations abstract the white sands dune field situated within the tularosa basin in southern new mexico is thought to have been largely derived by a stepwise progressive deflation of pleistocene lake otero strata with the onset of regional aridity optically stimulated luminescence osl dating of samples from a core that penetrated the gypsum accumulation of the dune field confirm a time of origin at 7000 yr dune sediment is characterized as lagged influx from previously stored lake otero sediment and contemporaneous influx derived from subsequent playas sediment became available for aeolian transport and dune field construction because of a falling water table driven by the regional aridity the current dune field is primarily a wet aeolian system in which the behavior of the accumulation surface over time is a function of the water table although surface cementation by gypsum also imparts aspects of a stabilizing system dune crests are oriented borderline transverse to the annual transport resultant and a monitored dune and its cross strata show that transverse winds from the sw during the late winter and spring account for most of the crest normal migration but a significant along crest component of migration of dune sinuosity occurs with fall and winter winds from the nw and n that strike the crests obliquely trenches across three interdune areas show dune sets and interdune strata climbing at about 0 1 depth of interdune scour increases with interdune streamwise length which acts to enhance the probability of dune cross strata deflation during arid years but also increases the probability of interdune accumulation because the water table shows a net rise over time within the trenches dune sets show a bundling of foresets between reactivation surfaces interpreted as annual cycles that reveal lee face reworking by the oblique nw and n winds and slipface progradation fostered by transverse winds from the sw a progression from grainflow dominated to wind ripple dominated cross strata within a single set revealed in the longest trench is consistent with along crest migration of dune sinuosity interdune laminations show light dark couplets interpreted as annual varves reflecting dry wet portions of the year the number of laminations preserved in vertical sections across an interdune area shows that the record is incomplete and endorses the interpretation of periods of interdune deflation a calculation of the current accumulation rate as based upon the climbing strata within the trenches is significantly greater than the long term accumulation rate determined by osl dates taken from the core in addition to compaction and possible dissolution of gypsum as partial explanations the long term accumulation rate may reflect significant variation in the accumulation rate over time short term deflation of accumulations on a regular basis and or the presence of unconformities within the gypsum body

preservation of delta 18 o and delta 13 c in belemnite rostra from the jurassic early cretaceous successions stratigraphic collection of 263 belemnite rostra guards from jurassic to lower cretaceous sediments in the moscow area of russia northern germany england new zealand and morocco were analyzed to determine temporal variations in their delta 18 o and delta 13 c as a proxy for isotopic composition of surface seawater internal structures of the rostra were studied using cathodoluminescence and sem techniques their trace element fe mn mg and sr and the stable carbon and oxygen isotope compositions the average stratigraphic resolution is about 1 ma these samples represent a broad range of paleolatitudes and paleoceanographic settings ranging from 42 degrees n to 82 degrees s covering boreal to subtropical brackish to open marine shelf paleoenvironments the rostra originally contained domains enriched in organic matter that were later replaced by luminescent diagenetic calcite thereby generating an impression of seasonal growth rings diagenetic calcite accounts for up to 6 8 percent of the rostrum the trace element content of the rostra range from 227 to 3935 ppm for mg 379 to 1514 ppm for sr and up to 305 and 3662 ppm for mn and fe respectively however selective drilling of only primary calcitic domains resulted in 90 percent of all analyzed samples to fall within the range of trace element values typical for modern low mg calcite shells the chemical and textural data suggest that the primary calcite of the rostra is well preserved as is its isotopic signature the delta 13 c and delta 18 o measurements define oscillating temporal bands of about 3 to 4 per mil width around more or less modern marine values of 2 and 1 per mil respectively oxygen isotopes in the well preserved rostra most likely reflect temperature variations within a approximately 14 or 8 degrees c range the observed 3 to 4 per mil spread of values between contemporaneous specimens which is comparable to the scatter of data reported for modern low mg calcitic brachiopod shells probably reflects the diversity of local ecosystems although some of the spread may be due to real short term temporal variations within single biozones the delta 13 c values of the rostra define a band similar to that of the oxygen isotopes and the temporal oscillations of both isotope curves are commonly in phase the above dataset complemented by the results of jones jenkyns and hesselbo 1994 and jones and others 1994 yields a composite delta 18 o and delta 13 c variations in belemnite guards for the entire jurassic early cretaceous interval for delta 18 o the oscillating band indicates that the most negative values occur at times of independently postulated global and or regional anoxic events such as those in the toarcian and kimmeridgian as well as the aptian these oaes appear to be characterized by up to 10 degrees c higher seawater temperatures than the intervening background times the delta 13 c record shows 13 c depletion for the kimmeridgian event but enrichment for the other two suggesting that the delta 13 c temporal oscillations and oaes are not simply a reflection of surficial productivity due to operation of the biological pump but rather of changing oceanic circulation patterns due to variations in latitudinal surface temperature gradients

physical abrasion of mafic minerals and basalt grains application to martian aeolian deposits abstract sediment maturity or the mineralogical and physical characterization of sedimentary deposits has been used to identify sediment sources transport medium and distance weathering processes and paleoenvironments on earth mature terrestrial sands are dominated by quartz which is abundant in source lithologies on earth and is physically and chemically stable under a wide range of conditions immature sands such as those rich in feldspars or mafic minerals are composed of grains that are easily physically weathered and highly susceptible to chemical weathering on mars which is predominately mafic in composition terrestrial standards of sediment maturity are not applicable in addition the martian climate today is cold and dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering due to these large differences in weathering processes and composition martian sediments require an alternate maturity index this paper reports the results of abrasion tests conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted well rounded spherical polycrystalline materials such as basalt volcanic glass is also likely to persist in a mechanical weathering environment while more fragile and chemically altered products are likely to be winnowed away a modified sediment maturity index is proposed that can be used in future studies to constrain sediment source paleoclimate mechanisms for sediment production and surface evolution this maturity index may also provide insights into erosional and sediment transport systems and preservation processes of layered deposits

belemnite taphonomy upper jurassic western tethys part ii fossil diagenetic analysis including combined petrographic and geochemical techniques abstract fossil diagenetic features were analyzed on 56 belemnite rostra from the pozo canada section external prebetic as well as 31 belemnite rostra from the rio segura internal prebetic both from the upper oxfordian lower kimmeridgian they mainly correspond to hibolithes and secondarily to belemnopsis fossil diagenetic processes were analyzed in each specimen using petrographic conventional cathodoluminescence epifluorescence and scanning electron microscopy and geochemical elemental and stable isotopes techniques the most common fossil diagenetic processes are dissolution calcite cementation and recrystallization of the apical zone and outer growth rings of belemnite rostra these processes may appear enhanced by fracturing and stylolite formation petrographic study also reveals that the alternation of cloudy and clear concentric growth areas displayed by many belemnite rostra corresponds to an early diagenetic feature in origin however an original concentric growth pattern is also observed under epifluorescent microscopy and bsem this growth pattern fits with changes in the mg and s content of the rostra although fossil diagenetic processes typically make specimens non suitable for paleoenvironmental interpretations microsampling of petrographically altered and non altered areas from the same specimens performed directly from thin sections after petrographic study allowed us to obtain excellent geochemical results suitable for paleoenvironmental interpretations these geochemical analyses moreover demonstrates that caution should be taken if elemental analyses are used as the most significant criteria for discriminating diagenetically altered and non altered belemnite samples

amalgamated interdune deposits white sands new mexico abstract cores taken by mckee and moiola 1975 from white sands dune field indicate that interdune areas are underlain by 7 0 10 4 m of clastic gypsum deposits clean sand bodies as much as 4 5 m thick are separated by thin beds of silly sand mckee and moiola interpreted the sequence to be the product of climbing bed forms interdune silty sands were interpreted to be deposited upon truncated dune sands and to be soon buried by the next wave of advancing dunes if the dunes are climbing in such a manner a pinchout of interdune sediments downwind across interdune surfaces is required the thickness of the silly sands should be related to the size of the interdune area and the rate of dune migration we tested this autocyclic hypothesis by trenching the length of the interdune areas in both t e barchanoid and transverse dunes trenches revealed that interdune deposits form flat lying sheets which extend uninterrupted to positions directly beneath the windward slopes of dunes at the downwind end of each interdune area this relationship precludes the possibility that under present conditions thick dune sands are being preserved because there is little or no net accumulation of dune sand interdune deposits are being amalgamated thin lenses of dune sediment exposed on the wall of one trench show that a minimum of three interdune deposits have been fused to form the uppermost 30 cm of the interdune deposit clean sand in the cores may have accumulated during periods when sediment supply was greater than at present silly sediments accumulated during periods when as in the p esent sand supply was limited and dunes did not climb appreciably future studies of modern and ancient eolian sediments should attempt to document whether the interdune deposits represent deposition within single interdune areas or amalgamation of several discrete deposits

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

stable isotope records from sepia officinalis a key to understanding the ecology of belemnites abstract the stable isotope ratios 1 8 o 1 3 c of the aragonite of cuttlebones of sepia officinalis were measured on a high resolution scale where every septum was measured our studies aim at understanding whether variations of the isotope signature are controlled by ontogenetic and or ecological factors five specimens were reared from eggs under known water temperatures a sixth specimen was caught in the german part of the north sea the data suggest that the oxygen isotope composition is in isotopic equilibrium with the surrounding seawater and reflects ambient temperature migration and seasonal temperature changes are visible in the acquired data set the carbon isotope signature shows signs of biofractionation and no direct correlation to the oxygen signature as far as ontogeny and ecology are concerned

dynamic polar climates in a greenhouse world evidence from clumped isotope thermometry of early cretaceous belemnites sub arctic cretaceous berriasian late valanginian ca 145 134 ma marine temperatures obtained from fossil mollusks belemnites are determined using carbonate clumped isotope thermometry an approach based on the clumping of 13 c and 18 o in the carbonate mineral lattice into bonds with each other from our analyses we infer sub arctic early cretaceous marine temperatures ranging from 10 c to 20 c these possibly seasonally biased warm sub arctic temperatures are warmer than present mean summer water temperatures at 60 65 n and are therefore consistent with a warmer greenhouse world featuring a shallow equable latitudinal temperature gradient our combined temperature and 18 o belemnite data imply seawater 18 o values that have a remarkably modern character in that they are similar to modern high latitude seawater but more positive than modeled cretaceous seawater we identify a cooler late valanginian interval ca 134 ma with temperatures consistent with polar regions a few degrees above freezing and also coincident with increased 18 o seawater values thus we find evidence of intervals when polar ice was unlikely and also when polar ice was plausible both scenarios support the view of generally warm but dynamic polar climates during greenhouse intervals that were punctuated by periods of ice growth

the cenozoic cooling continental signals from the atlantic and pacific side of eurasia a b s t r a c t the evolution of cenozoic continental climate signals from the atlantic and pacific side of eurasia can be assessed for the first time by comparing climate records obtained for two mid latitudinal regions for the west a detailed climate record over the past 45 ma based on palaeofloras from two northern german cenozoic basins mosbrugger et al 2005 r evealed major trends and shorter term events throughout the cenozoic cooling thus testifying the close correlation of continental and marine temperature evolution as derived from oxygen isotopes zachos et al 2008 using the same methodology we analyze a total of 14 floral horizons originating from continental strata of southern primory e russia in order to study the evolution at the eastern side of the continent the primory e record spans the middle eocene to early pleistocene as the coeval record for the atlantic side it reflects major global signals of cenozoic climate change such as the temperature decline throughout the late eocene coinciding with the growth of antarctic ice sheets warming during the mid miocene climatic optimum and step wise cooling throughout the later neogene the comparison of both records reveals differing regional patterns the considerable longitudinal temperature gradient currently existing between both study areas already began to evolve during the aquitanian and was very significant during the mid miocene climatic optimum the temperature offset between east and west is likely attributable to an effective north atlantic current already operational from the late early miocene onwards bringing about mild winters and low seasonality in western europe while in primory e seasonality steadily increased from the late oligocene on the strong late pliocene decline of cold month mean temperatures recorded in primory e is supposed to coincide with the establishment of the siberian high as semi permanent structure of the northern hemisphere circulation pattern when comparing the precipitation records obtained for both study areas an unexpected co variability at the longer term in the order of 5 20 ma is noted pointing to continent wide hydrological changes the steady decline of mean annual precipitation in the primory e record beginning in the bartonian and culminating in the aquitanian coincides with an aridity increase reported from coeval chinese inland localities of the mid latitudes the seasonality patterns of rainfall point to progressive intensification of the east asian summer monsoon in primory e since the later tortonian while the post zanclean decline of the precipitation of the dry season can be related to an increasing impact of the winter monsoon 2015 elsevier b v all rights reserved

sulfates in the north polar region of mars detected by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer observed the northern circumpolar regions of mars at a resolution of a few kilometers an extended region at 240 e 85 n with an area of 60 kilometers by 200 kilometers exhibits absorptions at wavelengths of 1 45 1 75 1 94 2 22 2 26 and 2 48 micrometers these signatures can be unambiguously attributed to calcium rich sulfates most likely gypsum this region corresponds to the dark longitudinal dunes of olympia planitia these observations reveal that water alteration played a major role in the formation of the constituting minerals of northern circumpolar terrains

recent debris flows on mars seasonal observations of the russell crater dune field 1 debris flows occur on slopes in the russell crater dune field the morphology of the erosion features resembles terrestrial viscous slurry flows mudflows and suggests that a flow of fine grained material mixed with liquid water might have been responsible for their formation seasonal mgs tes and moc imagery based observations of the dune field show 1 an annual frosting and defrosting cycle and 2 that liquid h2o could be stable within a limited time period in the summer of the southern hemisphere these observations lead to the conclusion that debris flows in the russell crater dune field may form under current climatic conditions by episodic or seasonal melting of small amounts of autumn winter condensed water ice

aeolian slipface dynamics and grainflow morphologies on earth and mars abstract in 2015 an active dune field on mars was visited up close by the curiosity rover in gale crater providing the first high resolution ground images of fine scale windblown features not previously resolved from orbital based imagery for the first time these images allow for direct comparison with terrestrial aeolian dynamics and provide critical ground truth data to bridge the gap between model predictions and satellite observations the image data from the slipface on the namib dune within the bagnold dune field shows grainflow morphologies that are similar to dunes on earth quantitative estimates of flow thickness based on shadow length are presented for the grainflows on the namib dune slipface and compared to grainflow characteristics measured by terrestrial laser scans from the maspalomas dune field located in gran canaria spain using observations from maspalomas to support interpretations of martian slipface dynamics we discuss implications for the local wind regime style of grainflow seasonal activity and dune migration the presence of multiple large magnitude grainflows on the namib slipface suggests an active aeolian environment capable of delivering enough sediment to the slipface to initiate these flows and transport sediment to the bottom of the lee slope however the thinness of grainflows on the namib dune the formation of smaller grainflows directly below the dune brink and limited grainfall suggest a lower wind energy environment at least for the most recent slipface activity large actively migrating stoss ripples obliquely oriented to the dune crest regularly deposit sediment on to the upper slipface and may be a mechanism in which larger grainflow occur during seemingly low energy wind events this mechanism of sediment delivery may also explain the existence of a variety of slipface morphologies both young and old which are otherwise quickly erased on earth due to sediment redistribution and grainfall

extraterrestrial dunes an introduction to the special issue on planetary dune systems abstract aeolian dune fields have been described on earth mars venus and titan the plethora of data returned from recent planetary missions has enabled a new era in planetary geomorphic studies much of our understanding of planetary dune systems comes from the application of earth analogs wind tunnel experiments and modeling studies despite the range of atmospheric pressures composition and gravity many of the dune forms on extraterrestrial surfaces are similar to those on earth although some have notable differences in bedform scale and composition as an introduction to the special issue on planetary dune systems this paper summarizes the current state of knowledge of planetary dune studies and highlights outstanding questions that require further investigation

tectonic focusing of voluminous basaltic eruptions in magma deficient backarc rifts highlights shield type volcanoes in young backarc rifts may be linked to arc segmentation arc transverse faults act as magma conduits for voluminous basaltic eruptions the nifonea volcano hosts the first large lava lake described in a submarine backarc effusive eruptions produced short live hydrothermal venting and an event plume the coriolis troughs of the new hebrides subduction zone are among the youngest backarc rifts in the world they reach depths of 3 km despite their small size 100 km in length and only 25 45 km wide and their proximity to the arc front 50 km the narrow deep graben morphology is characteristic of magma deficient arc rifts in the early stages of backarc extension where the rate of extension and subsidence exceeds the magmatic input unexpectedly the youngest graben the vate trough contains a centrally located 1000 m tall and 14 km wide shield volcano with a large 5 8 km breached summit caldera the nifonea axial volcano has a volume of 126 km3 reflecting unusually high extrusion rates given its young age 3 ma and the summit caldera hosts the remnants of a large lava lake the first described from a submarine backarc setting extensive diffuse hydrothermal venting and several clusters of black smoker chimneys with the highest recorded fluid temperatures 368 c in the sw pacific occur on the youngest lava flows comparison with similar axial volcanoes on the mid ocean ridges suggests that the 46 106 m3 of sheet flows in the caldera could have been erupted in 30 hours the focusing of voluminous basaltic eruptions into an otherwise magma deficient backarc has been linked to strong left lateral transtension caused by clockwise rotation and segmentation of the southern portion of the arc after collision with d entrecasteaux ridge this study shows that the upper plate stresses can result in dramatic variability in magma supply and hydrothermal activity at the earliest stages of arc rifting and could explain the wide range of melt compositions volcanic styles and mineral deposit types found in nascent backarc rifts

bright dunes on mars seasonal changes observed on the surface of mars can in part be attributed to the transport of geological materials by wind1 images obtained by orbiting spacecraft in the 1970s showed large wind formed features such as dunes and revealed regional time varying albedos that could be attributed to the effects of dust erosion and deposition but the resolution of these images was insufficient to identify different types and sources of aeolian materials nor could they reveal aeolian deposits other than large dunes or extensive surface coverings that were redistributed by dust storms here we present images of mars with up to 50 times better resolution these images show that martian dunes include at least two distinct components the brighter of which we interpret to be composed of relatively soft minerals possibly sulphates we also find large areas of the martian surface that have several metres or more of aeolian mantle lacking obvious bedforms

testing palaeo environmental proxies in jurassic belemnites mg ca sr ca na ca δ18o and δ13c we test the hypothesis that the noise in belemnite records through time results from changing climate we do so by comparing palaeo proxies mg ca sr ca na ca 18o 13c in two species of toarcian belemnites acrocoelites odontobelus vulgaris 14 specimens and acrocoelites acrocoelites subtenuis 10 specimens deposited in a period of time that was short relative to the timescale of climate change the specimens are interpreted to have been regurgitated from the stomach of a marine predator and so were deposited together in a geological instant of early jurassic time in a o vulgaris isotopic and elemental palaeo proxies group tightly suggesting that this belemnite occupied a restricted environmental niche in a a subtenuis elemental and isotopic compositions spread more widely suggesting that this species occupied a greater range of habitats possible sexual dimorphism in a o vulgaris is reflected in bimodal mg ca and differing intra rostral distribution of mg in putative dimorphs concentrations decline by 30 from apical line to rim in specimens with high mg ca but are largely invariant radially in specimens with lower mg ca sexual dimorphism in a a subtenuis yields a bimodality in size mg ca and intra rostral distribution of mg larger specimens have a higher mg ca and mg concentrations that increase along radial traverses from apical line to rim whilst the smaller specimens show a mid rostral minimum in mg concentration radial profiles of concentrations for sr and na vary little in all forms toarcian belemnites of these species thus show strong biofractionation effects on mg ca and little or no observable biofractionation of sr ca or na ca it follows that much of the noise in belemnite records results from biofractionation and from a cosmopolitan life style of some belemnite species rather than climate change for toarcian belemnites we suggest that sr ca is the best indicator of palaeo temperature

elemental and oxygen isotope composition of early jurassic belemnites salinity vs temperature signals well preserved calcitic belemnite samples from the basque cantabrian basin of northern spain have been analyzed to improve our current understanding of the chemistry of seawater as an index of paleoceanographic changes during the early jurassic a period punctuated by times of oceanic anoxia and global mass extinctions because the oxygen isotope composition of calcite depends not only on temperature but also on salinity we present here a combination of sr ca mg ca and 18o analyses that helped us to evaluate both effects separately comparison between the temporal records and cross plots of these geochemical parameters shows a good correlation of mg ca with 18o and a weak correlation of sr ca with 18o comparison of our belemnite 18o record with coeval o isotope profiles from other paleogeographic domains suggests the existence despite differences in the absolute isotopic values of a major negative shift during the serpentinus zone that is regionally reproducible this event is linked to the early toarcian ocean anoxic event oae and suggests the existence of global changes in paleoclimatic and paleoceanographic conditions that are reflected largely in the geochemical composition of seawater compared to our results however other early toarcian 18o data reported from northern european basins are generally depleted 1 3 1 6 in contrast mg ca ratios display similar values these differences in 18o data suggest a salinity component for the northern european data and provide evidence for a north to south salinity gradient within the north european interior boreal seaway during the early jurassic this study suggests that the secular variation of mg ca is a useful proxy for discriminating between temperature and salinity effects on the oxygen isotope composition of fossil shells and highlights the prospect of using the mg ca ratios of belemnite calcite to calculate paleotemperatures independently of salinity the findings of our study may help to calibrate 18o curves in other basins by removing the salinity component of their 18o records which may help to calculate water density gradients between the jurassic seas of northern and southern europe

mars observer camera the mars observer camera moc is a three component system one narrow angle and two wide angle cameras designed to take high spatial resolution pictures of the surface of mars and to obtain lower spatial resolution synoptic coverage of the planet s surface and atmosphere the cameras are based on the push broom technique that is they do not take frames but rather build pictures one line at a time as the spacecraft moves around the planet in its orbit moc is primarily a telescope for taking extremely high resolution pictures of selected locations on mars using the narrow angle camera areas ranging from 2 8 km 2 8 km to 2 8 km 25 2 km depending on available internal digital buffer memory can be photographed at about 1 4 m pixel additionally lower resolution pictures to a lowest resolution of about 11 m pixel can be acquired by pixel averaging these images can be much longer ranging up to 2 8 500 km at 11 m pixel high resolution data will be used to study sediments and sedimentary processes polar processes and deposits volcanism and other geologic geomorphic processes the moc wide angle cameras are capable of viewing mars from horizon to horizon and are designed for low resolution global and intermediate resolution regional studies low resolution observations can be made every orbit so that in a single 24 hour period a complete global picture of the planet can be assembled at a resolution of at least 7 5 km pixel regional areas covering hundreds of kilometers on a side may be photographed at a resolution of better than 250 m pixel at the nadir such images will be particularly useful in studying time variable features such as lee clouds the polar cap edge and wind streaks as well as acquiring stereoscopic coverage of areas of geological interest the limb can be imaged at a vertical and along track resolution of better than 1 5 km different color filters within the two wide angle cameras permit color images of the surface and atmosphere to be made to distinguish between clouds and the ground and between clouds of different composition

late jurassic kimmeridgian tithonian stable isotopes δ18o δ13c and mg ca ratios new palaeoclimate data from helmsdale northeast scotland abstract the data presented here provide the first detailed stable isotope 18 o 13 c and geochemical mg ca investigation of kimmeridgian tithonian belemnites from the helmsdale coast scotland uk oxygen and carbon stable isotope values from well preserved specimens range from 2 8 to 0 3 and from 2 3 to 2 8 respectively the oxygen isotope data are consistent with palaeotemperatures of up to 24 c in the early kimmeridgian cymodoce zone and down to 11 c in the mid tithonian rotunda fittoni zones these estimates are strongly supported by the mg ca data which also indicate a cooling episode and very similar palaeotemperatures 11 22 c at this time the cooling event is associated with an approximately 5 decline in 13 c ratios this shift towards more negative 13 c values has also been recorded in the tethys and on the russian platform confirming that this event was of global origin such globally synchronous records can provide a valuable tool for stratigraphic correlation the helmsdale 13 c data are therefore combined here with other published belemnite isotope data from the jurassic of scotland from the callovian kimmeridgian of the isle of skye and the toarcian aalenian of raasay the resultant belemnite 13 c curve provides a detailed record of the toarcian tithonian british boreal realm that can be compared with coeval records to investigate regional differences in jurassic carbon isotope stratigraphy

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation

origin of terrestrial gypsum dunes implications for martian gypsum rich dunes of olympia undae abstract the estancia white sands guadalupe and cuatrocienegas dune fields are among the largest known aeolian gypsum sand dune accumulations on earth and occupy closed drainage basins within the rio grande rift high sedimentation rates of lacustrine gypsum occur in topographic depressions within the closed basins the gypsum accumulations result from long term complex interaction between tectonism climate and a hydrologic cycle that involves geochemical recycling of sulfur from older sedimentary rocks flanking and underlying the basins gypsum precipitation in lacustrine environments is strongly controlled by local groundwater bedrock interaction the ranges of 34s values per mil vs vcdt for gypsum sand in the white sands dune field 12 1 to 13 9 guadalupe dune field 10 2 to 12 5 and cuatrocienegas dune field 14 6 to 15 9 indicate that the main sources of dissolved sulfate are evaporite strata of lower permian middle permian and cretaceous ages respectively a spatial increase of 34s values across the white sands dune field in the direction of prevailing winds matches well with a stratigraphically upward increase of 34s values recorded in lake otero an ancient lake in the basin strata this finding supports previous suggestions that white sands dune field evolved as a result of the step wise deflation of previously stored sediments in lake otero the modern gypsum dune fields are primarily wet eolian systems in which dune accumulation is controlled by a near surface groundwater table which promotes early cementation of the dune accumulations early cementation in the interdune surfaces and to a lesser degree on the dune surfaces reduces the amount of sand available for transport and slows rates of dune migration based on an average migration rate of 2 m year the time needed for a dune at white sands to migrate the downwind distance of the dune field is approximately 6500 years which matches well with other estimates of the initiation of the dune field at approximately 7000 years ago and indicates that white sands likely evolved as a wet aeolian system as on earth gypsum rich dune fields apparently are rare on mars gypsum has been identified only within the olympia undae dune field which encircles a portion of the martian north polar residual ice cap analogous to terrestrial gypsum dunes the gypsum within the olympia undae gypsum rich dunes might have originated from transport and deposition via aeolian processes in this model gypsum rich source sediment could have been formed by confined groundwater or surface water activity and later transported by the wind any subsequent gypsum precipitation in the source area could have been initiated by episodic melting of the martian polar ice cap it is likely that the gypsum was deposited in the olympia undae dunes after the main deflation events that led to formation of the siliciclastic components of the dune field

the role of biogeography and ecology on the isotope signature of cuttlefishes cephalopoda sepiidae and the impact on belemnite studies abstract calcitic belemnite guards are often used for temperature reconstructions of ancient seawater by using oxygen isotope thermometry these geochemical studies discuss diagenesis and vital effects but neglect ecological or biogeographic effects on the isotope signature to estimate the impact of seasonal temperature variations short term salinity changes and biogeography on the isotope signals we compare the 18o and 13c signals of ten cuttlebones with local water temperatures the cuttlebones aragonitic internal shells come from five different species of recent cuttlefish sepiidae sepia sp from seven different regions north sea baltic sea mediterranean red sea angola north australia and tasmania all analysed specimens reflect the temperature characteristics of their habitat perfectly the 18o signal and calculated temperatures follow annual temperature changes of up to 15 c the 13c values show no clear pattern and are thought to be controlled by vital effects freshwater influence is recognizable in the negative 18o and 13c values of the baltic sea specimen although sudden short term salinity changes are not reflected by the signatures

strontium isotope profile of the early toarcian jurassic oceanic anoxic event the duration of ammonite biozones and belemnite palaeotemperatures we profile 87sr 86sr 13c 18o sr ca mg ca and na ca in belemnites through pliensbachian and toarcian strata on the yorkshire coast uk which include the early jurassic oceanic anoxic event the 87sr 86sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30 the lower jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in yorkshire which contains the anoxic event is condensed by a factor of between 6 5 and 12 2 times relative to adjacent strata using our 87sr 86sr profile the resolution in correlation and dating attainable in the interval is between 1 5 m and 15 m of section and better than 0 25 myr in parts of the sequence this stratigraphic resolution equals that attainable with ammonites a new age model is provided for late pliensbachian and early toarcian time that is based on the 87sr 86sr profile through the sequence the sr ca mg ca na ca and 18o of belemnite carbonate covary suggesting that elemental ratios may be useful for palaeotemperature measurement our 13cbelemnite data splits into three the previously reported positive isotope excursion to 6 5 in the early toarcian we speculate that the excursion s resulted from addition to surface waters of isotopically heavy co2 via ebullition of methanogenic co2 from the sediment during early burial of organic rich 10 toc sediments