snow grain size profiles deduced from microwave snow emissivities in antarctica spaceborne microwave radiometers are an attractive tool for observing antarctic climate because their measurements are related to the snow temperature however the conversion from microwave emission to snow temperature is not simple and strongly depends on the emissivity through snow properties this difficulty in predicting the snow property profile for antarctic conditions is the main bottleneck in the retrieval of accurate climate information from microwave radiometers we attempt to explain the vertically polarized emissivity at 19 3 and 37 ghz derived from brightness temperatures acquired by the special sensor microwave imager ssm i and physical temperature from the era 40 re analysis in antarctica the snow emissivities at 19 3 and 37 ghz are nearly equal although a decrease with frequency is expected to explain this we consider various profiles of snow grain size and density and predict their emissivity using a dense medium radiative transfer dmrt model the results show that the emissivities cannot be explained by constant profiles of grain size and density heterogeneous snowpacks need to be considered we first test random variations of snow density and grain radius with depth and then monotonic and continuous variations in the snow grain radius in both cases we show that an overall increase of the snow grain radius with depth is required to match the observed emissivity in antarctica in addition two parameters characterizing the snow grain profiles are retrieved and compared with 1 in situ measurements of grain size at various locations in east antarctica 2 grain size estimated using visible spaceborne radiometers and 3 a semi empirical relationship for grain growth

gravity field of the moon from the gravity recovery and interior laboratory grail mission spacecraft to spacecraft tracking observations from the gravity recovery and interior laboratory grail have been used to construct a gravitational field of the moon to spherical harmonic degree and order 420 the grail field reveals features not previously resolved including tectonic structures volcanic landforms basin rings crater central peaks and numerous simple craters from degrees 80 through 300 over 98 of the gravitational signature is associated with topography a result that reflects the preservation of crater relief in highly fractured crust the remaining 2 represents fine details of subsurface structure not previously resolved grail elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies

sediment dewatering in the makran accretionary prism abstract sediments within the makran accretionary prism are considerably more compacted than the material entering the subduction zone due to the additional tectonic stresses resulting from plate convergence and accretionary processes tectonic compaction of the offscraped sediments has been documented by deriving in situ porosities in the upper 4 km from their seismic velocities wide angle seismic reflection refraction profiles were analysed from a transect crossing both the makran accretionary prism and the undeformed abyssal plain sediments to the south the 6 7 km thick abyssal plain sediments exhibit normal compaction with depth the sediments incorporated into the accretionary prism have higher seismic velocities at all depths corresponding to reductions in porosity of 30 40 mapping the porosity depth gradient across the prism shows that there is a marked change in porosity at the seaward toe of the prism the frontal fold there is then little further change until further folding begins to occur 70 km landward of the toe the dewatering and consolidation of the sediments is an important control on deformation occurring within the sedimentary prism

paleobiogeography of miocene equinae of north america a phylogenetic biogeographic analysis of the relative roles of climate vicariance and dispersal article i nfo the horse subfamily equinae underwent a major radiation during the miocene in north america diversifying from one species parahippus leonensis to 70 species this radiation has been linked to climatic and vegetation changes that occurred in north america during this time however the relationship between climate change and speciation has not previously been studied quantitatively using phylogenetic biogeography distribution and age range data were collected for all north american species within eighteen equine genera through a literature review and use of the paleobiology database fitch parsimony analysis of the taxon area cladogram indicate that speciation by dispersal allopatry model ii was more common in the evolution of the clade than speciation by vicariance allopatry model i distribution data were analyzed using the lieberman modified brooks parsimony analysis lbpa to determine patterns of vicariance and geodispersal using four constrained biogeographic regions within north america in the analysis the great plains the southwest the gulf coast and the southeast resulting general area cladograms are congruent with geological events such as uplift of the rocky mountains and climatic conditions such as the change from a warm and moist to cool and arid climate during the miocene well supported vicariance and geodispersal trees derived from the lbpa analysis are largely congruent with each other indicating that cyclical events in particular climate change during the miocene influenced the radiation of the clade

working models for spatial distribution and level of mars seismicity 1 we present synthetic catalogs of mars quakes intended to be used for performance assessments of future seismic networks on the planet we have compiled a new inventory of compressional and extensional tectonic faults for the planet mars comprising 8500 faults with a total length of 680 000 km the faults were mapped on the basis of mars orbiting laser altimeter mola shaded relief hence we expect to have assembled a homogeneous data set not biased by illumination and viewing conditions of image data updated models of martian crater statistics and geological maps were used to assign new maximum ages to all faults on the basis of the fault catalog spatial distributions of seismicity were simulated using assumptions on the available annual seismic moment budget the moment frequency relationship and a relation between rupture length and released moment we have constructed five different models of martian seismicity predicting an annual moment release between 3 42 1016 nm and 4 78 1018 nm and up to 572 events with magnitudes greater than 4 per year as upper limit end member case most events are expected on the tharsis shield but minor seismic centers are expected south of hellas and north of utopia planitia

anomalous density and elastic properties of basalt at high pressure reevaluating of the effect of melt fraction on seismic velocity in the earth s crust and upper mantle independent measurements of the volumetric and elastic properties of columbia river basalt glass were made up to 5 5 gpa by high pressure x ray microtomography and ghz ultrasonic interferometry respectively the columbia river basalt displays p and s wave velocity minima at 4 5 and 5 gpa respectively violating birch s law these data constrain the pressure dependence of the density and elastic moduli at high pressure which cannot be modeled through usual equations of state nor determined by stepwise integrating the bulk sound velocity as is common practice we propose a systematic variation in compression behavior of silicate glasses that is dependent on the degree of polymerization and arises from the flexibility of the aluminosilicate network this behavior likely persists into the liquid state for basaltic melts resulting in weak pressure dependence for p wave velocities perhaps to depths of the transition zone modeling the effect of partial melt on p wave velocity reductions suggests that melt fraction determined by seismic velocity variations may be significantly overestimated in the crust and upper mantle

modeling the thermal and physical evolution of mount sharp s sedimentary rocks gale crater mars implications for diagenesis on the msl curiosity rover traverse gale crater the mars science laboratory msl landing site contains a central mound named aeolis mons informally mount sharp that preserves 5 km of sedimentary stratigraphy formation scenarios include 1 complete filling of gale crater followed by partial sediment removal or 2 building of a central deposit with morphology controlled by slope winds and only incomplete sedimentary fill here we model temperature time paths for both scenarios compare results with analyses provided by msl curiosity and provide scenario dependent predictions of temperatures of diagenesis along curiosity s future traverse the effects of variable sediment thermal conductivity and historical heat flows are also discussed modeled erosion and deposition rates are 5 37 m yr consistent with previously published estimates from other mars locations the occurrence and spatial patterns of diagenesis depend on sedimentation scenario and surface paleotemperature for 1 temperatures experienced by sediments decrease monotonically along the traverse and up mount sharp stratigraphy whereas for 2 temperatures increase along the traverse reaching maximum temperatures higher up in mount sharp s lower units if early mars surface temperatures were similar to modern mars mean 50 c only select locations under select scenarios permit diagenetic fluids in contrast if early mars surface temperatures averaged 0 c or brines had lowered freezing points diagenesis is predicted in most locations with temperatures 225 c comparing our predictions with future msl results on diagenetic textures secondary mineral assemblages and their spatial variability will constrain past heat flow mount sharp s formation processes the availability of liquid water on early mars and sediment organic preservation potential

evolution of structural and physical parameters of clays during experimental compaction abstract to provide a better understanding of sedimentary basin geological history it is important to describe correctly the evolution of the various physical mechanical and hydraulic properties of clayey rocks as a function of burial depth as a contribution to this field a programme of experimental studies on reworked clay samples compacted under various load pressures in oedometric conditions has been set up the evolution of samples under compaction was followed with microscopic and macroscopic measurements in a specially designed oedometric cell samples are compacted under different total stresses from 0 1 to 50 mpa in this cell cylindrical cores are submitted to progressive loading from both ends under controlled pore pressure conditions the symmetrical loading allows more even deformation about the midplane of the sample this device allows the evolution of hydraulic pressure radial stress displacement and expelled pore fluid to be followed as a function of time in a first step kaolinite was chosen because it retains a high permeability compared with other clays such as illite or smectite which allows compaction tests to be performed within a few days a complete set of measurements was performed after the tests these measurements are 1 micro structures investigated by means of transmission electron microscopy tem mercury porosimetry water removal under low water vapour pressure granulometry and specific area measured by ethylene glycol adsorption and 2 various physical parameters measured including hydraulic conductivity and thermal conductivity tem gives an understanding of the arrangement of particles it was found that each particle is composed of several crystal units each unit formed by 25 individual kaolinite layers during compaction these particles remain undeformed but are rotated the angular distribution of grain orientation is a function of the applied effective stress this reorientation is in agreement with the observed decrease in porosity and pore size it also explains the occurrence of a strong anisotropy in the thermal conductivity and hydraulic permeability the combination of these experimental results allows a qualitative and quantitative understanding of the behaviour of kaolinite with respect to parameters such as permeability porosity mechanical and thermal properties the knowledge of which are necessary for basin modelling

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

thermophysical properties along curiosity s traverse in gale crater mars derived from the rems ground temperature sensor abstract the rems instrument onboard the mars science laboratory rover curiosity has measured ground temperature nearly continuously at hourly intervals for two mars years coverage of the entire diurnal cycle at 1 hz is available every few martian days we compare these measurements with predictions of surface atmosphere thermal models to derive the apparent thermal inertia and thermally derived albedo along the rover s traverse after accounting for the radiative effects of atmospheric water ice during fall and winter as is necessary to match the measured seasonal trend the rems measurements can distinguish between active sand other loose materials mudstone and sandstone based on their thermophysical properties however the apparent thermal inertias of bedrock dominated surfaces 350 550 j m 2 k 1 s are lower than expected we use rover imagery and the detailed shape of the diurnal ground temperature curve to explore whether lateral or vertical heterogeneity in the surface materials within the sensor footprint might explain the low inertias we find that the bedrock component of the surface can have a thermal inertia as high as 650 1700 j m 2 k 1 s for mudstone sites and 700 j m 2 k 1 s for sandstone sites in models runs that include lateral and vertical mixing although the results of our forward modeling approach may be non unique they demonstrate the potential to extract information about lateral and vertical variations in thermophysical properties from temporally resolved measurements of ground temperature

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

a surface gravity traverse on mars indicates low bedrock density at gale crater gravimetry the precise measurement of gravitational fields can be used to probe the internal structure of earth and other planets the curiosity rover on mars carries accelerometers normally used for navigation and attitude determination we have recalibrated them to isolate the signature of the changing gravitational acceleration as the rover climbs through gale crater the subsurface rock density is inferred from the measured decrease in gravitational field strength with elevation the density of the sedimentary rocks in gale crater is 1680 180 kilograms per cubic meter this value is lower than expected indicating a high porosity and constraining maximum burial depths of the rocks over their history

elasticity of marine sediments rock physics modeling we offer an effective medium model for the elastic moduli of high porosity ocean bottom sediments the elastic constants of the dry sediment frame depend on porosity elastic moduli of the solid phase and effective pressure the model connects two end points in the elastic modulus porosity plane the hertz mindlin modulus of a dense elastic sphere pack at critical porosity and zero at 100 porosity the elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation unlike the suspension model our model assigns non zero elastic constants to the dry sediment frame and can predict the shear wave velocity unlike various modifications of the travel time average equation it is first principle based and contains only physical parameters we justify this model by matching sonic data in shallow marine sediments and in an odp well

observations of an aeolian landscape from surface to orbit in gale crater abstract landscapes derived solely from aeolian processes are rare on earth because of the dominance of subaqueous processes in contrast aeolian derived landscapes should typify mars because of the absence of liquid water the long exposure times of surfaces and the presence of wind as the default geomorphic agent using the full range of available orbital and mars science laboratory rover curiosity images wind formed features in gale crater were cataloged and analyzed in order to characterize the aeolian landscape and to derive the evolution of the crater wind regime over time inferred wind directions show a dominance of regional northerly winds over geologic time scales but a dominance of topography driven katabatic winds in modern times landscapes in gale crater show a preponderance of aeolian features at all spatial scales interpreted processes forming these features include first cycle aeolian abrasion of bedrock pervasive deflation organization of available sand into bedforms abundant cratering and gravity driven wasting all of which occur over a background of slow physical weathering the observed landscapes are proposed to represent a spectrum of progressive surface denudation from fractured bedrock to retreating bedrock capped mesas to remnant hills capped by bedrock rubble to desert pavement plains this model of landscape evolution provides the mechanism by which northerly winds acting over 3 ga excavated tens of thousands of cubic kilometers of material from the once sediment filled crater thus carving the intra crater moat and exhuming mount sharp aeolis mons the current crater surface is relatively sand starved indicating that potential sediment deflation from the crater is greater than sediment production and that most exhumation of mount sharp occurred in the ancient geologic past

growth of greenland ice sheet interpretation an observed 0 23 m year thickening of the greenland ice sheet indicates a 25 to 45 excess ice accumulation over the amount required to balance the outward ice flow the implied global sea level depletion is 0 2 to 0 4 mm year depending on whether the thickening is only recent 5 to 10 years or longer term 100 years if there is a similar imbalance in the northern 60 of the ice sheet area the depletion is 0 35 to 0 7 mm year increasing ice thickness suggests that the precipitation is higher than the long term average higher precipitation may be a characteristic of warmer climates in polar regions

evidence for hydraulic fracturing at gale crater mars implications for burial depth of the yellowknife bay formation abstract nasa s curiosity rover identified a formerly habitable environment within strata informally known as the yellowknife bay formation the stratigraphic relationship and thus depositional age of these rocks relative to other geologic units in gale crater is not clear from orbital data alone if part of lower aeolis mons informally known as mount sharp the yellowknife bay rocks have been deeply buried and exhumed prior to 3 2 3 3 ga if part of younger alluvial fan deposits however they likely have never experienced more than 100 m of burial knowledge of burial history can thus constrain the stratigraphic placement of yellowknife bay and the habitable environment preserved therein the mechanics of natural hydraulic fractures observed in mudstone at ykb allow us to evaluate its burial history and imply a minimum burial depth of 1 2 km this is consistent with burial by the entirety of lower mount sharp and a depositional age of 3 6 3 8 ga providing observation based evidence that mount sharp was once much more laterally extensive than its present form rocks of the yellowknife bay formation thus represent the oldest strata that curiosity will encounter during its journey in gale crater and any additional habitable environments discovered along curiosity s future path represent conditions at younger times

velocity anisotropy of shales and depth estimation in the north sea basin it is known that in the north sea basin the depths to major reflectors as determined from surface seismic data are often larger than the well log depths from a study of data sets which tie 21 wells i found a strong correlation between the occurrence of the depth error and the presence of shales in the subsurface assuming that the error is caused by elliptical velocity anisotropy in shales i measured the anisotropy from a comparison of the well log sonic data and the interval velocity profile obtained from the surface seismic data and also from a comparison of the seismic depth and the well log depth it was found that the two methods of measurements agree with each other and also agree qualitatively with the previous laboratory measurements of anisotropy in shale samples the results strongly suggest that the depth anomaly in the north sea basin is caused by the velocity anisotropy of shales a simple method to correct the seismic depth is given

petrological constraints on the density of the martian crust new insights into the chemistry of the martian crust have been made available since the derivation of crustal thickness maps from mars global surveyor gravity and topography data that used a conservative range of density values 2700 3100 kg m3 a new range of crustal density values is calculated from the major element chemistry of martian meteorites 3100 3700 kg m3 igneous rocks at gusev crater 3100 3600 kg m3 and from the surface concentration of fe al ca si and k measured by the gamma ray spectrometer on board mars odyssey 3250 3450 kg m3 in addition the density of mineral assemblages resulting from low pressure crystallization of primary melts of the primitive mantle are estimated for plausible conditions of partial melting corresponding to the noachian to amazonian periods 3100 3300 kg m3 despite the differences between these approaches the results are all consistent with an average density above 3100 kg m3 for those materials that are close to the surface the density may be compatible with the measured mass of mars and the moment of inertia factor but only if the average crustal thickness is thicker than previously thought approaching 100 km a thicker crust implies that crustal delamination and recycling could be possible and may even control its thickness globally or locally alternatively and considering that geoid to topography ratios argue against such a thick crust for the highlands our results suggest the existence of a buried felsic or anorthositic component in the southern hemisphere of mars

effective elastic properties of solid clays clay minerals are perhaps the most abundant materials in the earth s upper crust as such their elastic properties are extremely important in seismic exploration seismic reservoir characterization and sonic log interpretation because little exists in the literature on elastic properties of clays we have designed a method of measuring effective elastic properties of solid clays clays without pores in this method clay minerals are mixed with a material with known elastic properties to make composite samples elastic properties of these clay minerals are then inverted from the measured elastic properties of the composite samples using the weighted hashin shtrikman average using this method we have measured 66 samples of 16 types of clays in this paper we present a comprehensive data set of elastic properties of solid clays that commonly occur in or are related to petroleum reservoirs although uncertainties up to 10 exist the data set reported here is by far the most comprehensive set of e

spatial and temporal characterization of hoar formation in central greenland using ssm i brightness temperatures the summertime formation and burial of low density coarse grained hoar layers in the snow of central greenland can be mapped using satellite passive microwave data variations in a signal derived from special sensor microwave imager ssm i brightness temperature trends correlate temporally and spatially with hoar complex evolution over 120 000 km of the greenland ice sheet s dry firn facies observations at the greenland ice sheet project ii gisp2 site indicate that changes in surface conditions and brightness temperatures correspond to four hoar events over two summers as expected from theory following a snowfall the smooth high density surface reflects some emitted 37 ghz horizontally polarized h radiation but little vertically polarized v radiation progressive surface roughness increases and density decreases during hoar formation cause a gradual decrease in h reflection formation and burial of a hoar layer thus causes a slow decrease followed by an abrupt increase in the v h ratio hoar layers have been used to date the gisp2 ice core through the entire holocene archived microwave data now can be used to assess the timing and frequency of the formation of these stratigraphic markers in central greenland

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

redox stratification of an ancient lake in gale crater mars introduction the primary goal of nasa s curiosity rover mission is to explore and quantitatively assess a local region on mars surface as a potential habitat for past or present life a necessary component of that assessment involves an investigation of the surface chemical conditions and paleoclimate of ancient mars gale crater was selected as the landing site for curiosity it hosts a 5 km tall mountain of layered sedimentary rock the rocks of mount sharp preserve a long duration record of martian environmental conditions geological reconstructions from curiosity rover data have revealed an ancient habitable lake environment that was sustained for tens of thousands to tens of millions of years by rivers draining into the crater rationale we seek to constrain the chemical environment within the lake in gale crater as well as short and long term climate variations in and around gale crater we focus on fine grained sedimentary rocks that carry information about sediment provenance the environment of deposition the conversion of sediment to rock during burial i e lithification and the chemical conditions of later modification i e diagenesis these were investigated during the first 1300 martian solar days sols of rover operations in gale crater using bulk geochemical and mineralogical analysis techniques combined with high resolution color imagery at a variety of scales results two mudstone units have been recognized both deposited in lakes the sheepbed member of the yellowknife bay formation an older set of strata defining the base of the stratigraphic section and the murray formation of relatively younger age and positioned higher in the stratigraphic section the chemical index of alteration cia paleoclimate proxy increases by up to 10 to 20 cia units expressed in from the sheepbed member to the murray formation on the basis of mineralogy geochemistry textural properties and stratigraphic relationships the murray formation can be subdivided into two sedimentary associations or facies the hematite phyllosilicate hp facies and the magnetite silica ms facies the hp facies is characterized by abundant fe 3 oxides accompanied by phyllosilicates as well as indications of mn oxidation and trace metal concentration these properties are consistent with deposition in an oxidizing environment the ms facies is recognized by a near complete absence of pure fe 3 minerals and high concentrations of silica accompanied by magnetite consistent with deposition in an anoxic environment both facies were affected by a saline overprint after burial and lithification conclusion the observed variations in cia are consistent with modest short term fluctuations in the ancient climate between cold dry conditions and relatively warmer wetter conditions these changes occurred during the deposition of lake bed mudstones in an environment that was conducive to the presence of a long lived lake in gale crater we propose that the distinct properties of the two murray facies were developed as a result of i fractionation of river borne detritus into coarser denser materials in shallow water close to shore and finer lower density materials offshore in deeper water as a result of deceleration of river flow as it entered the lake and ii redox stratification of the lake water body caused by depth dependent variations in the concentration of atmospheric oxidants and dissolved groundwater derived solutes resulting in oxidizing conditions in shallow water and anoxia in deeper water the addition of saline minerals during a later phase of brine migration through the section records longer term changes in martian climate at gale crater perhaps driven by global atmospheric escape processes the recognition of redox stratification in the lake in gale crater adds new detail to our understanding of ancient martian aquatic environments previously reported detections of organic carbon compounds nitrogen phosphate minerals and fe and s minerals in a variety of redox states combined with the evidence presented here for relatively stable climate conditions and gradients in fluid oxidation state provide compelling evidence that all of the physical chemical and energetic conditions necessary to establish a habitable environment were present on mars between 3 8 billion and 3 1 billion years ago

magnetic stratigraphy and a test for block rotation of sedimentary rocks within the san andreas fault zone mecca hills southeastern california a 500 m section of the palm spring formation in the southern mecca hills located within the san andreas fault zone in southeastern california has been paleomagnetically sampled to determine possible tectonic rotation in this area and to establish time stratigraphic control this work was partly stimulated by the fact that 80 km farther south previous studies demonstrated 35 of postdepositional rotation in the palm spring formation of the vallecito fish creek basin east of the elsinore fault several lines of evidence suggest that hematite is the main magnetic carrier of the mecca hills samples large anhedral hematite grains observed in magnetic extracts and a positive fold test imply a detrital origin of the remanence the polarity reversal patterns together with earlier vertebrate paleontologic studies restrict the time span for deposition of this unit to the middle late matuyama chron 2 0 0 75 myr ago thus of uppermost pliocene and early pleistocene age characteristic directions of best least squares fit for 73 samples suggest little or no overall rotation despite the severe late quaternary tectonic activity demonstrated by the intense deformation of these strata

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

compactional behavior of fine grained sediments examples from deep sea drilling project cores laboratory experiments statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep sea sediments which are in compaction equilibrium with the overburden a revised and generalized version of athy s law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles surfaces especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces the sediments analyzed almost range from systems of suspended grains to nearly perfect colloidal systems the methods and equations required to derive the relevant parameters are given for both downhole porosity density measurements and laboratory experiments

radar measurements of melt zones on the greenland ice sheet surface based microwave radar measurements were performed at a location on the western flank of the greenland ice sheet here firn metamorphosis is dominated by seasonal melt which leads to marked contrasts in the vertical structure of winter and summer firn this snow regime is also one of the brightest radar targets on earth with an average backscatter coefficient of 0 db at 5 3 ghz and an incidence angle of 25 by combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter s snow pack this observation has important implications for monitoring and understanding changes in ice sheet volume using space borne microwave sensors

compaction behavior of argillaceous sediments as function of diagenesis the paper presents the results of laboratory compaction tests on samples of kimmeridge clay taken from two different locations in the uk the main objective of the laboratory tests is to determine how diagenesis affects the hydro mechanical properties and compaction behavior of argillaceous sediments the two kimmeridge clays used in the tests are essentially from the same parent material but have undergone different degrees of mechanical and chemical diagenesis the laboratory tests are designed to determine the effects of mechanical loading and chemical processes on changes in porosity permeability compressibility strength and effective horizontal stress in argillaceous materials another objective of the study is to investigate the adequacy of soil mechanical constitutive models in predicting the response of argillaceous materials to conditions corresponding to burial depths in sedimentary basins the tests on kimmeridge clay are carried out to as high as 150 mpa effective vertical stress corresponding to about 9 km in burial the results indicate that mechanical compaction and burial depth cannot explain the differences in the hydro mechanical behavior of the tested materials the differences in hydro mechanical response are attributed to chemical diagenesis by precipitation of minerals in the pores of the sediment other observed effects of chemical diagenesis on hydro mechanical behavior of lithified sediments are 1 increase in apparent pre consolidation stress 2 decrease in compressibility 3 decrease in permeability and 4 decrease in effective horizontal stress implications of the results to fluid flow and overpressure development in sedimentary basins are discussed

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

simple quantitative evaluation of porosity of argillaceous sediments at various depths of burial abstract relationship of porosity to depth of burial d in m geologic age a in millions of years and lithology ratio of thickness of shales total thickness of terrigenous deposits r has been developed by the writers which gives satisfactory results 0 exp 0 014 13 3 log a 83 25 log r 2 79 10 3 d where 0 initial porosity of the argillaceous sediment a nomogram has been prepared for an easy solution of the above equation

geochronology of hemphillian blancan aged strata guanajuato mexico and implications for timing of the great american biotic interchange abstract we present new geochronologic magnetostratigraphy fission track and 40ar 39ar radioisotopic dates biostratigraphy data constraining the age of three separate sequences and a composite section from guanajuato mexico those data make this one of the most complete and precisely age calibrated sequences in north america spanning the hemphillian blancan north american land mammal age nalma boundary interval and the data further constrain the timing and pattern of the great american biotic interchange gabi in total 196 samples 77 sites were used to construct the magnetic polarity stratigraphies with eight fission track analyses and four new 40ar 39ar radioisotopic dates the sections sampled are possibly latest miocene to late pliocene in age spanning about 2 7 m yr 5 5 2 7 ma from chrons c3n 4n or c3r to c2an 1n the radioisotopic dates and magnetostratigraphic correlations indicate the hemphillian blancan nalma boundary at guanajuato in central mexico is 4 7 4 8 ma and it pro

mineralogy of an ancient lacustrine mudstone succession from the murray formation gale crater mars the mars science laboratory curiosity rover has been traversing strata at the base of aeolis mons informally known as mount sharp since september 2014 the murray formation makes up the lowest exposed strata of the mount sharp group and is composed primarily of finely laminated lacustrine mudstone intercalated with rare crossbedded sandstone that is prodeltaic or fluvial in origin we report on the first three drilled samples from the murray formation measured in the pahrump hills section rietveld refinements and fullpat full pattern fitting analyses of x ray diffraction patterns measured by the msl chemin instrument provide mineral abundances refined unit cell parameters for major phases giving crystal chemistry and abundances of x ray amorphous materials our results from the samples measured at the pahrump hills and previously published results on the buckskin sample measured from the marias pass section stratigraphically above pahrump hills show stratigraphic variations in the mineralogy phyllosilicates hematite jarosite and pyroxene are most abundant at the base of the pahrump hills and crystalline and amorphous silica and magnetite become prevalent higher in the succession some trace element abundances measured by apxs also show stratigraphic trends zn and ni are highly enriched with respect to average mars crust at the base of the pahrump hills by 7 7 and 3 7 times respectively and gradually decrease in abundance in stratigraphically higher regions near marias pass where they are depleted with respect to average mars crust by more than an order of magnitude in some targets the mn stratigraphic trend is analogous to zn and ni however mn abundances are close to those of average mars crust at the base of pahrump hills rather than being enriched and mn becomes increasingly depleted moving upsection minerals at the base of the pahrump hills in particular jarosite and hematite as well as enrichments in zn ni and mn are products of acid sulfate alteration on earth we hypothesize that multiple influxes of mildly to moderately acidic pore fluids resulted in diagenesis of the murray formation and the observed mineralogical and geochemical variations the preservation of some minerals that are highly susceptible to dissolution at low ph e g mafic minerals and fluorapatite suggests that acidic events were not long lived and that fluids may not have been extremely acidic ph 2ph 2 alternatively the observed mineralogical variations within the succession may be explained by deposition in lake waters with variable eh and or ph where the lowermost sediments were deposited in an oxidizing perhaps acidic lake setting and sediments deposited in the upper pahrump hills and marias pass were deposited lake waters with lower eh and higher ph

relationship between p and s wave velocities and geological properties of near surface sediments of the continental slope of the barents sea seismic velocities v p and v s of compressional p and shear s waves are important parameters for the characterization of marine sediments with respect to their sedimentological and geotechnical properties p and s wave velocity data of near surface marine sediments upper 9 m of the continental slope of the barents sea are analysed and correlated to sedimentological and geotechnical properties the results show that the s wave velocity is much more sensitive to changes in lithology and mechanical properties than the p wave velocity which is characterized by a narrow range of values the correlation coefficients between s wave velocity and silt and clay content wet bulk density porosity water content and shear strength are higher than 0 5 while the correlation coefficients of p wave velocity and the same parameters are always lower than 0 4 although the relationship between v s and clay content has been widely described the data show that v s is better correlated with silt content than with clay content for the sediments of the area investigated however they show different trends while v s increases with increasing clay content it decreases with increasing silt content

rock lithology and porosity determination from shear and compressional wave velocity data examined in this study are previously published laboratory shear s and compressional p wave velocity measurements on water saturated sandstone calcareous sandstone dolomite and limestone cores as well as laboratory porosity measurements on the sandstone and limestone cores sandstone and limestone porosities range from 092 to 299 and from 006 to 229 respectively differential pressure was varied from 500 to 6000 psi corresponding to approximate burial depths from 290 to 3460 m respectively sandstone limestone and dolomite are effectively separated by poisson s ratio or equivalently by the ratio of p to s wave velocity separation of sandstone and limestone appears to result from the difference in of the matrix material namely quartz 056 and calcite 316 respectively an empirical function 1 v a b was fit by regression analysis to sandstone and limestone velocity vs and vp versus porosity values at each differential pressure in this equation a and b are const

velocity porosity clay content systematics of poorly consolidated sandstones compressional velocities have been measured as a function of confining pressure for 14 west delta block louisiana sandstone cores the dry velocity data for these poorly consolidated sandstones at 10 mpa confining pressure plot on a linear velocity density trend with well consolidated sandstones but not loose sands the dry velocity data also show linear trends of decreasing velocity with increasing porosity along contours of constant clay content similar to those obtained at 40 mpa by tosaya and nur 1982 for saturated sandstones the spacing between clay contours indicates that a large portion of the velocity variation with clay content is due to microporosity which is not included in point counting within the clays the slope of the velocity porosity trends indicates that cementation increases with decreasing porosity

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

variations in snowpack melt on the greenland ice sheet based on passive microwave measurements a simple microwave emission model is used to simulate 37 ghz brightness temperatures associated with snowpack melt conditions for locations across the greenland ice sheet the simulated values are utilized as threshold values and compared to daily gridded smmr and ssm i passive microwave data in order to reveal regions experiencing melt the spatial extent of the area classified as melting is examined on a daily monthly and seasonal may august basis for 1979 91 the typical seasonal cycle of melt coverage shows melt beginning in late april a rapid increase in the melting area from mid may to mid july a rapid decrease in melt extent from late july through mid august and cessation of melt in late september seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3 8 annually significant at the 95 confidence interval this increase is dominated by statistically significant positive trends in melt coverage during july and august in the west and southwest of the ice sheet we find that a linear correlation between microwave derived melt extent and a surface measure of ablation rate is significant in june and july but not august so caution must be exercised in using the microwave derived melt extents in august nevertheless knowledge of the variability of snowpack melt on the greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the arctic and examining the impact of climate change on the ice sheet

uniaxial compressive strengths of rocks drilled at gale crater mars measuring the physical properties of geological materials is important for understanding geologic history yet there has never been an instrument with the purpose of measuring mechanical properties of rocks sent to another planet the mars science laboratory msl rover employs the powder acquisition drill system pads which provides direct mechanical interaction with martian outcrops while the objective of the drill system is not to make scientific measurements the drill s performance is directly influenced by the mechanical properties of the rocks it drills into we have developed a methodology that uses the drill to indicate the uniaxial compressive strengths of rocks through comparison with performance of an identically assembled drill system in terrestrial samples of comparable sedimentary class during this investigation we utilize engineering data collected on mars to calculate the percussive energy needed to maintain a prescribed rate of penetration and correlate that to rock strength

mars high resolution gravity fields from mro mars seasonal gravity and other dynamical parameters abstract with 2 years of tracking data collection from the mro spacecraft there is noticeable improvement in the high frequency portion of the spherical harmonic mars gravity field the new jpl mars gravity fields mro110b and mro110b2 show resolution near degree 90 additional years of mgs and mars odyssey tracking data result in improvement for the seasonal j 3 gravity changes which compares well to global circulation models and odyssey neutron data and mars rotation and precession 7594 10 mas year once atmospheric dust is accounted for in the spacecraft solar pressure model solutions for mars solar tide are consistent between data sets and show slightly larger values k2 0 164 0 009 after correction for atmospheric tide compared to previous results further constraining core models an additional 4 years of mars range data improves the mars ephemeris determines 21 asteroid masses and bounds solar mass loss dgmsun dt

mechanical behaviour of fine grained sediments experimental compaction and three dimensional constitutive model abstract the usual undimensional description of deformations of sediments based on a phenomenological relationship between porosity and the vertical effective stress does not give information about the horizontal stress and moreover is irrelevant for sedimentary structures in which deformation process is not only vertical modelling three dimensional deformation processes in sedimentary basins requires a three dimensional mechanical constitutive model for sediments a special dometric cell was conceived in g 3s this cell allows the measurement of the lateral stress during dometric compaction and so enables us to elaborate a three dimensional model of mechanical behaviour four varieties of fine grained sediments were studied by this cell in a large scale of strain and stresses the modified cam clay model was used for fitting the experimental data and it was shown that this model can reproduce the mechanical compaction of sediments up to 50 mpa of vertical effective stress about 3 km burial depth if its parameters are deduced from dometric zero lateral strain data

stratigraphy and paleoceanography of pliocene deposits of karaginsky island eastern kamchatka u s s r abstract the lithology and paleontology of pliocene deposits from karaginsky island off eastern kamchatka peninsula u s s r are described in order to provide a paleoceanographic reconstruction of this region of the eastern north pacific ocean the stratigraphic sequence is divided into three suites the limimtevayamian the ust limimtevayamian and the tusatuvayamian which correspond to three standard pacific diatom zones the thalassiosira oestrupii neodenticula koizumi n kamtschatica and n koizumi the entire sequence is further subdivided into six members and 18 distinct beds on the basis of molluscan assemblages and three members and seven beds on the basis of benthic foraminiferal assemblages marine ostracodes are described from the limimtevayamian suite the marine invertebrate assemblages from karaginsky island provide evidence that 1 ocean water temperatures were warmer than today about 4 ma and again about 3 5 3 0 ma 2 several arctic atlantic species of molluscs and ostracodes migrated to the eastern north pacific between 4 2 3 0 ma presumably through the proto bering strait 3 many species found in the karaginsky island pliocene represent pacific taxa which migrated through the arctic into the north atlantic during the late pliocene

the gravitational signature of martian volcanoes by modeling the elastic flexure of the martian lithosphere under imposed loads we provide a systematic study of the old and low relief volcanoes 3 2 ga 0 5 to 7 4 km and the younger and larger prominent constructs within the tharsis and elysium provinces 3 2 ga 0 5 to 7 4 km and the younger and larger constructs clustered in the tharsis and elysium provinces 3 ga 5 8 to 21 9 km the observed topography is used to define the load and to derive a simulated gravity field that is compared to the observed gravity the bulk density of the lava that composes all volcanoes is found to be 3 200 kg m 3 which is representative of iron rich basalts as sampled by the martian basaltic meteorites the elastic part of the lithosphere that is the part maintaining loads over geologic time is found to have been thin when the small old volcanoes formed which implies that the lithosphere was hot early in geologic history conversely larger volcanoes are found to have been emplaced on a cold and thicker elastic lithosphere

subsurface density structure of taurus littrow valley using apollo 17 gravity data the traverse gravimeter experiment tge from the apollo 17 mission was the first and only successful gravity survey on the surface of the moon revealing the local gravity field at taurus littrow valley tlv tlv is hypothesized to be a basalt filled graben oriented radial to serenitatis basin we implemented modern 3d modeling techniques using recent high resolution lunar reconnaisance orbiter topography and image datasets to reinvestigate the subsurface structure of tlv and constrain the volcanic and tectonic history of the region updated topography led to significant improvements in the accuracy of free air bouguer and terrain corrections to determine the underlying geometry for tlv we tested a range of possible thicknesses dips and wall positions for the graben fill we found that the thickness and position previously determined by talwani et al 1973 represent our preferred model for the data but with walls with dips of 30 rather than 90 talwani et al 1973 we found large model misfits due to unmodelled 3d structure and density anomalies as well as parameter trade offs we performed a sensitivity analysis to quantify the parameter trade offs in an ideal future survey assuming dominantly 2d geological structure at the tge survey noise level 2 5 mgal the fill thickness was constrained to 150 m the wall angle to 5 20 and the wall positions to 1 km of the preferred model this information can be used to inform the design of future lunar gravimetry experiments in regions similar to tlv

a physical model for shear wave velocity prediction the clay sand mixture model of xu and white is shown to simulate observed relationships between s wave velocity or transit time porosity and clay content in general neither s wave velocity nor s wave transit time is a linear function of porosity and clay content for practical purposes clay content is approximated by shale volume in well log applications in principle the model can predict s wave velocity from lithology and any pair of p wave velocity porosity and shale volume although the predictions should be the same if all measurements are error free comparison of predictions with laboratory and logging measurements show that predictions using p wave velocity are the most reliable the robust relationship between s and p wave velocities is due to the fact that both are similarly affected by porosity clay content and lithology moreover errors in the measured p wave velocity are normally smaller than those in porosity and shale volume both of which are subject to errors introduced by imperfect models and imperfect parameters when estimated from logs because the model evaluates the bulk and shear moduli of the dry rock frame by a combination of kuster and toksoz theory and differential effective medium theory using pore aspect ratios to characterize the compliances of the sand and clay components the relationship between p and s wave velocities is explicit and consistent consequently the model sidesteps problems and assumptions that arise from the lack of knowledge of these moduli when applying gassmann s theory to this relationship making it a very flexible tool for investigating how the v p v s relationship is affected by lithology porosity clay content and water saturation numerical results from the model are confirmed by laboratory and logging data and demonstrate for example how the presence of gas has a more pronounced effect on p wave velocity in shaly sands than in less compliant cleaner sandstones

metamorphic signature of snow revealed in ssm i measurements brightness temperatures 19 22 37 85 ghz measured by the special sensor microwave imager ssm i are analyzed using data from the snow monitoring network within the former soviet union during the 1987 1988 winter period it is shown that in the beginning of winter the ssm i measurements display the classical snow scattering signature i e the brightness temperatures decrease with increasing depth and the largest decrease occurs at the highest frequency dramatic deviations from this pattern are observed in the middle of winter where the brightness temperature approaches a minimum and then begins to increase despite the fact that the snow depth remains constant or continues to grow the two stream radiative transfer model is combined with results from dense media theory to help explain the phenomenon model results suggest that the increase in brightness temperature is due to a decrease of the single scattering albedo as the snowpack ages this decrease of the albedo is related to changes in the snow crystalline structure due to metamorphism consequences for the interpretation of satellite measurements and development of algorithms for deriving snow water equivalent are discussed

shear wave velocity estimation in porous rocks theoretical formulation preliminary verification and applications shear wave velocity logs are useful for various seismic interpretation applications including bright spot analyses amplitude versus offset analyses and multicomponent seismic interpretations measured shear wave velocity logs are however often unavailable we developed a general method to predict shear wave velocity in porous rocks if reliable compressional wave velocity lithology porosity and water saturation data are available the precision and accuracy of shear wave velocity prediction are 9 and 3 respectively the success of our method depends on 1 robust relationships between compressional and shear wave velocities for water saturated pure porous lithologies 2 nearly linear mixing laws for solid rock constituents 3 first order applicability of the biot gassmann theory to real rocks we verified these concepts with laboratory measurements and full waveform sonic logs shear wave velocities estimated by our method can improve formation evaluation our method has been successfully tested with data from several locations

interior structure of terrestrial planets modeling mars mantle and its electromagnetic geodetic and seismic properties 1 we present a new procedure to describe the one dimensional thermodynamical state and mineralogy of any earth like planetary mantle with mars as an example the model parameters are directly related to expected results from a geophysical network mission in this case electromagnetic geodetic and seismological processed observations supplemented with laboratory measurements we describe the internal structure of the planet in terms of a one dimensional model depending on a set of eight parameters for the crust the thickness and the mean density for the mantle the bulk volume fraction of iron the olivine volume fraction the pressure gradient and the temperature profile and for the core its mass and radius currently available geophysical and geochemical knowledge constrains the range of the parameter values in the present paper we develop the forward problem and present the governing equations from which synthetic data are computed using a set of parameter values among all martian models fitting the currently available knowledge we select eight candidate models for which we compute synthetic network science data sets the synergy between the three geophysical experiments of electromagnetic sounding geodesy and seismology is emphasized the stochastic inversion of the synthetic data sets will be presented in a companion paper

velocity anisotropy and attenuation of shale in under and overpressured conditions the seismic velocity and attenuation of fully saturated shales were measured for the first time under overpressured conditions using the ultrasonic reflection technique shale cores from naturally overpressured horizons in the north sea were tested in the laboratory at confining and pore pressures relevant to in situ conditions a single frequency tone burst pulse wave was used to determine the seismic wave velocities and quality factors of the shale samples with errors less than 0 3 and 0 1 db cm respectively at a frequency of 0 75 mhz sample length changes with varying confining and pore pressure were measured and the pore pressure equilibration time was monitored for each sample the anisotropy of the seismic attributes vp vs qp and qs was determined over a range of differential pressures from 5 to 60 mpa with respect to the predominant foliation the ultrasonic velocity data followed a transversely isotropic pattern depending on the direction of wave propagation with respect to the laminations the poisson s ratio was found to rise by 5 as the shale material progressed from a normally pressured to an overpressured state the quality factor q characteristics were interpreted in terms of pore geometry and connectivity as well as the directional permeability of the transversely isotropic shale material the results were converted to bulk and shear loss modulus defects and a positive bulk loss was observed for waves propagating perpendicular to the lamination plane even above differential pressures of 20 mpa this indicates different levels of biot flow and squirt flow attenuation mechanisms acting within the shale structure depending on the wave propagation and vibration directions

formation and erosion of layered materials geologic and dust cycle history of eastern arabia terra mars 1 eastern arabia terra is mantled in a layer of dust a few centimeters to a meter thick yet contains morphologic features that suggest a history of multiple events of deposition and consolidation of fine grained material and a significant amount of erosion early in martian history this region was affected by volcanic and fluvial activity but has since been dominated by aeolian processes five craters in this region contain interior mound material that ranges in height from 1600 to 2100 m above the crater floor the fluted erosional pattern and the thermal inertia are suggestive of a weakly indurated material and the extensive layering implies that these mounds were formed by a repeated process or processes although these materials primarily occur within craters there are materials outside craters that have similar erosional features and fine laminations suggesting a more extensive deposit the most likely process to form this material is the deposition and cementation of air fall dust and is potentially related to martian obliquity changes the significant amount of erosion of the intracrater mounds unit indicates a dramatic change from a depositional environment to an erosional regime over the past 106 108 years currently dust is accumulating in this region in years with planet encircling dust events but global circulation model results indicate that dust devils may be removing slight amounts of dust from arabia terra these observations suggest that the thickness of the dust mantle may not be currently increasing and may instead be in equilibrium

shear wave velocity anisotropy in sedimentary rocks a laboratory study a systematic laboratory study of shear wave velocity anisotropy in sedimentary rocks has been carried out as a function of both hydrostatic and uniaxial stress the presence of shear wave velocity anisotropy in sedimentary rocks was confirmed by transmitting a polarized shear wave in a rock sample and receiving a signal on an orthogonally polarized receiver the magnitude of the observed velocity anisotropy is dependent upon the magnitude and nature of the applied stress and the lithology of the rock sample shales exhibit significant velocity anisotropy independent of both uniaxial and hydrostatic stress which suggests the presence of preferentially aligned minerals sandstones also exhibit significant velocity anisotropy but the anisotropy is strongly dependent upon the stress hydrostatic stress was found to diminish the velocity anisotropy and uniaxial stress was found to enhance it this implies the presence of preferentially oriented cracks limestones exhibit weak velocity anisotropy these laboratory observations may be helpful in in situ identification of lithology

diagenetic silica enrichment and late stage groundwater activity in gale crater mars diagenetic silica enrichment in fracture associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of aeolis mons in gale crater mars the diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger unconformably draping aeolian sandstone implying that diagenetic silica enrichment postdates the detrital silica enrichment a causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock although absolute timing is uncertain the observed diagenesis likely represents some of the most recent groundwater activity in gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of aeolis mons were deposited

the spirit rover s athena science investigation at gusev crater mars the mars exploration rover spirit and its athena science payload have been used to investigate a landing site in gusev crater gusev is hypothesized to be the site of a former lake but no clear evidence for lacustrine sedimentation has been found to date instead the dominant lithology is basalt and the dominant geologic processes are impact events and eolian transport many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration any lacustrine sediments that may exist at this location within gusev apparently have been buried by lavas that have undergone subsequent impact disruption

sediment compaction and fluid migration in the makran accretionary prism the makran continental margin in the gulf of oman forms the seaward extremity of an accretionary sediment prism which extends several hundred kilometers inland a recently acquired multichannel seismic reflection profile shot across the margin imaged the structure of the prism in greater detail than was previously possible and allowed us to investigate the relationship between deformation and pore fluid motion in the region velocity analyses of the common midpoint gathers reveal a marked change in velocity structure at the toe of the accretionary wedge as seen in previous sonobuoy wide angle data accreted sediments show significantly higher vertical velocity gradients than those of sediments entering the prism this change is interpreted as due to porosity reduction as pore fluids are squeezed out of the compacting sediment a prominent bottom simulating reflector appears 500 800 m beneath the sea bed several lines of evidence suggest that this reflector represents the base of a gas hydrate zone underlain by widespread free gas which may be exsolved from pore water migrating from deep within the sediment pile up permeable fault planes imaged in the profile the hydrate reflector appears to shallow in the region of some faults suggesting a temperature anomaly due to the presence of warm pore fluids a heat flow profile derived from the depth of the hydrate reflector does not show the expected landward decrease as the sediment pile thickens simple thermal modeling suggests that advective heat flow within the prism may explain this anomaly the inferred presence of overpressured pore fluids in the makran suggests that accreted sediments have a low permeability the seismic evidence suggests a two stage compaction process with rapid initial dewatering through intergranular permeability as sediment enters the prism followed by a buildup of pore pressure as the permeability decreases and fluid migration is restricted to fault zones

assessment of β the compression coefficient of mudstones and its relationship with detailed lithology abstract the mechanical compaction of soils and fine grained sediments is commonly described in soil mechanics by a relationship between void ratio and effective stress the relationship is defined by two parameters derived from the slope of the line relating void ratio and log effective stress and e the void ratio at a chosen effective stress e g 100 kpa and e are strongly correlated and are related to the atterburg liquid limit which is itself related in a general way to the grain size and mineralogy of the sediment in general finer grained sediments have higher initial void ratios and compact faster than coarser sediments porosity depth trends for mudstones in sedimentary basins are therefore strongly influenced by lithology steps or changes in the slope of porosity depth trends can be caused by lithological change rather than changes in the pressure regime a method is presented to evaluate for mechanically compacted mudstones using porosities determined from the density log fdc and based on the relationship between effective stress and void ratio developed in soil mechanics the method allows one to obtain rapidly approximate values for materials for which it is essentially impossible to obtain compaction parameters experimentally calculated values for mudstones in wells 8 3 2 and 30 2 1 on the norwegian margin vary between 0 2 and 0 65 the values correlate positively with the clay particle content of the mudstones which we have determined for 50 mudstone samples from the same wells the strong link between mudstone lithology and suggests that a downhole log may be a useful way to visualize downhole variations in mudstone lithology the log also shows how lithology affects the rate of porosity loss with depth or effective stress for example porosity in mudstones within both wells 8 3 2 and 30 2 1 is essentially constant over 700 m sections of normally pressured mudstones the log and grain size data indicate that this reflects changes in the lithological character and of the muds and not as commonly inferred a change in the pressure regime

blancan hemphillian land mammal ages and late cenozoic mammal dispersal events vertebrate fossils have produced a reliable and useful framework for interpreting geologic history during the cenozoic era and for unraveling the complex evolution of mammals this framework was formalized for north america in 1941 as the north american provincial land mammal ages wood et ai 1941 during the last 40 years that framework has been revised extended and calibrated so that land mammal ages are now the prime chronologie standard for terrestrial deposits of the cenozoic land mammal ages have been calibrated and resolved because of numerous studies relating mammal fossils and fossil sites to modern systematic analyses detailed biostratigraphic analyses new radiometric dating

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

late miocene washhouse climate in europe abstract we present two eight million year long proxy records of precipitation for southwest and central europe covering the middle to late miocene 5 3 13 ma at a temporal resolution of about 60 kyr and 150 kyr respectively the estimates of precipitation are based on the ecophysiological structure of herpetological assemblages amphibians and reptiles from 13 0 ma until about 9 ma both records show a similar trend evolving from a long dry period 13 11 ma into a washhouse climate 10 2 9 8 ma characterized by global warm conditions and several times more precipitation than present the transition from washhouse to a dryer climate between 9 7 and 9 5 ma and the concomitant cooling episode appear to have triggered a severe biotic event known as the vallesian crisis which included the extinction of hominoids in western europe a second washhouse period 9 0 8 5 ma coeval with a global warm episode was unprecedentedly intense in southwest europe but less pronounced in central europe from 8 ma onward a divergence in the two precipitation records is observed with southwest europe staying wetter and central europe becoming dryer than present both precipitation records are combined into a common run off curve as a measure of the relative intensity of the hydrological cycle for moderate latitudes of continental europe the run off curve shows a remarkable positive correlation with atlantic deep water temperatures from ceara rise by lear et al 2003 which are significantly higher up to 3 c during the two washhouse periods and show no other positive excursion of comparable magnitude we discuss potential links and the role of the coeval temporary restriction of the central american seaway on ocean and atmosphere circulation

magnetic polarity stratigraphy and possible differential tectonic rotation of the miocene pliocene mammal bearing san timoteo badlands southern california abstract the san timoteo badlands consisting of the mt eden beds conformably overlain by the san timoteo beds is a 3000 m thick sequence of nonmarine sediments deposited in a tectonically active region in southern california paleomagnetic samples were collected from 132 sites within these badlands a composite magnetostratigraphic section for this sequence correlates to the mpts from the late part of chron c3an 1n to the early part of chron c2r 2r between about 6 and 2 3 ma the classic late hemphillian late miocene mt eden fossil mammal quarry occurs near the base of the composite section within chron c3r between 5 8 and 5 3 ma although the overall unit mean declinations indicate negligible or slight counterclockwise ccw vertical axis rotation 8 8 4 9 analysis of declination subsets from different parts of the section suggest possible differential small block rotation within the san timoteo badlands prior to 3 5 ma represented by the mt eden beds there is negligible rotation the overlying portion of the san timoteo badlands represented by the lower san timoteo beds dated between 3 5 and 2 3 ma chrons c2an 3n to c2r 2r indicate significant apparent ccw rotation r r of 20 7 5 2 these data suggest decoupling of the upper part of the san timoteo badlands and independent ccw vertical axis rotation relative to the lower part of this sequence

windsat passive microwave polarimetric signatures of the greenland ice sheet windsat has systematically collected the first global fully polarimetric passive microwave data over both land and ocean as the first spaceborne polarimetric microwave radiometer it was designed to measure ocean surface wind speed and direction by including the third and fourth stokes parameters which are mostly related to the asymmetric structures of the ocean surface roughness although designed for wind vector retrieval windsat data are also collected over land and ice and this new data has revealed for the first time significant land signals in the third and fourth stokes parameter channels particularly over greenland and the antarctic ice sheets the third and fourth stokes parameters show well defined large azimuth modulations that appear to be correlated with geophysical variations particularly snow structure melting and metamorphism and have distinct seasonal variation the polarimetric signatures are relatively weak in the summer and are strongest around spring this corresponds well with the formation and erosion of the sastrugi in the dry snow zone and snowmelt in the soaked zone in this paper we present the full polarimetric signatures obtained from windsat over greenland and use a simple empirical observation model to quantify the azimuthal variations of the signatures in space and time

evolution of microstructures and of macroscopic properties of some clays during experimental compaction abstract in order to understand the evolution of clay sediments during their burial to three or four kilometers depth remoulded and non remoulded clay samples were oedometrically consolidated under loads ranging from 0 1 50 mpa and their microstructural mechanical and transport properties were studied for this study four clays were selected on mineralogical grounds a kaolinite st austell clay two illitic clays la bouzule clay and salins 14 clay and an illite smectite mixed clay marais poitevin clay among those materials two are almost pure clays st austell clay and salins 14 clay and were compacted in a remoulded state the other two have a clay fraction about 60 and were studied in non remoulded state for marais poitevin clay and both remoulded and non remoulded for la bouzule clay the oedometric tests have been performed in classical oedometers and in a new oedometric cell specially designed to measure lateral stresses and to perform hydraulic conductivity measurements under compaction load the two pure clays show an evolution of their void ratio differing from what is expected considering their liquid limits the behaviour seems to be governed by the size of the clay particles around 1 m for st austell clay and around 0 1 m for salins 14 clay marais poitevin clay very slightly compacted in its natural state and remoulded la bouzule clay have consolidation coefficients cc and void ratios consistent with their liquid limits a relationship reported in soil mechanics literature skempton 1944 burland 1990 nagaraj et al 1994 the natural la bouzule clay shows very low void ratios and cc due to overconsolidation the microstructure observed by tem showed that clay particles are platy and made of aggregates of individual crystals except for salins 14 clay where individual crystals do not aggregate the evolution of the microstructure with applied stress shows no change in the particles structure but a progressive reorientation of the particles perpendicular to the load axis these microstructural observations explain the transport properties measured and their evolution the thermal conductivity of kaolinite measured in the axial and radial direction reflects the evolution of anisotropy with compaction observed on particles orientation the different hydraulic conductivities observed on the various samples are compared to those obtained with the kozeny carman formula using two types of specific surface determination this comparison emphasizes the importance of inter and intraparticule pore size and of their intimate organisation

interpretation of ssm i measurements over greenland multispectral brightness temperature t sub b measurements over greenland are obtained from the special sensor microwave imager ssm i which are flown aboard the dmsp satellites this paper examines the different spectral characteristics over greenland throughout the year although snow covers the vast majority of greenland the southern regions rarely exhibit the spectral characteristics associated with snowcover i e t sub b decreases at higher frequencies in fact the ssm i polarization and frequency measurements over southern greenland are more indicative of water than a snow covered surface i e t sub b increases at higher frequencies a simplified physical model is developed to help explain the anomalous measurements over southern greenland model results indicate that high frequency radiation is mainly scattered by snow grains residing above the subsurface ice layers whereas low frequency radiation is scattered throughout a much greater depth since low frequencies are scattered throughout a greater volume they are depressed relative to high frequencies and the typical snowcover signature is absent

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

a hematite bearing layer in gale crater mars mapping and implications for past aqueous conditions oversampled compact reconnaissance imaging spectrometer for mars crism visible and near infrared hyperspectral data over mount sharp in gale crater mars were used to generate spatially sharpened maps of the location of red crystalline hematite within the uppermost stratum of an 6 5 km long ridge on the mound s northern flank finely layered strata underlie the ridge to the north and have dips consistent with the nearby mount sharp sedimentary sequence fe mg smectites are exposed in a valley to the south of the ridge emplacement of the hematite is hypothesized to result either from exposure of anoxic fe 2 rich groundwater to an oxidizing environment leading to precipitation of hematite or its precursors or from in place weathering of precursor silicate materials under oxidizing conditions these hypotheses and implications for habitability will be testable with in situ measurements by the mars rover curiosity when it reaches mount sharp

evidence for the overflow origin of the grand canyon abstract the colorado river s course through grand canyon and across the topographic high imposed by the kaibab plateau represents one of the most well known transverse drainages only four processes allow a river to flow across a topographic obstruction antecedence superimposition piracy and overflow since powell first described the canyon in 1875 various authors have repeatedly proposed variations of all four mechanisms to explain the formation of the grand canyon and this paper does not review or try to refute this prior scholarship this paper s purpose rests in providing a detailed evaluation of evidence associated with overflow upstream across and downstream of the east kaibab monocline paleodivide upstream of the paleodivide we re interpreted the bidahochi formation the older units of this formation represent a fluctuating system between playa and lacustrine deposition fed by multiple localized tributaries entering a topographically barred basin the younger bidahochi units signify the abrupt arrival of an additional drainage with a distinctive geochemical signature into the basin roughly 6 8 ma supported by three lines of evidence 1 an order of magnitude increase in depositional rates from 3 m ma in the older units to 50 m ma in the younger units that buried the paleo landscape at least locally up to an elevation of at least 2250 m 7380 ft 2 new evidence of an elevated 87sr 86sr ratio in the younger units when compared to the older units and the modern colorado river and 3 fossil evidence of the existence of large freshwater lakes and rivers in the bidahochi basin during deposition of the younger units newly re evaluated evidence at the east kaibab paleodivide focuses on a southern bend of the colorado river s path across the kaibab plateau as well as the confluence of the colorado and the little colorado rivers at the junction of the kaibab plateau and cedar ridge both lines of evidence at the paleodivide focus on the impact of topography on grand canyon incision and both lines of evidence are consistent only with an overflow process evidence downstream of the paleodivide includes the abrupt arrival of river water with an elevated 87sr 86sr ratio followed by colorado river sediment into a series of successively lower downstream basins that integrated via overflow new 10be 9be geochemistry data support the relative timing of deposition of the bidahochi formation followed soon after by deposition of the bouse formation downstream of the grand canyon we conclude that newly presented and re evaluated available evidence supports an overflow process for the colorado river s transverse section across the kaibab plateau ultimately resulting in incision of the grand canyon

ultrasonic velocities in sands revisited ultrasonic compressional and shear wave velocities of isotropic sands are shown to be dependent on their mineralogy their porosity their fluid content and their state of consolidation under fixed temperature and pressure conditions this leads to a distinction between two broad classes of sands those that are well consolidated and those that are loosely consolidated changes in elastic velocities reflect changes in the ratio of bulk and shear moduli to density in response to lithologic variations we decouple the two effects by examining changes in elastic moduli with respect to changes in lithology and we observe three main points 1 for consolidated sandstones the effects of mineralogy and porosity can be approximated both empirically and theoretically by a modified isostrain theory the dry bulk and shear moduli of the rock aggregate follow a mixing law being linear combinations of the respective moduli of the individual constituents the dry elastic moduli of families of clean sands and s

estimation of marine sediment bulk physical properties at depth from seafloor geophysical measurements a combination of geophysical techniques can yield estimates of several physical properties versus depth an example is presented for a thick sequence of sediments in middle valley near the present spreading axis of the juan de fuca ridge we have computed the porosity temperature and thermal conductivity versus depth by combining the results of seafloor electrical and heat flow surveys the electrical resistivity of the sediments is empirically related to the porosity of the medium and to the pore fluid electrical conductivity which is in turn sensitive to the temperature the temperature profile is determined from the heat flow and the thermal conductivity the latter is determined from calculated porosity and estimates of the constituent mineral and pore fluid thermal conductivities the measured surface heat flow is assumed to be and the resistivity has been determined to be approximately constant with depth the computation of the variation of temperature porosity and thermal conductivity with depth yields physically realistic and reasonable results other physical properties void ratio bulk density water content compressional wave velocity are estimated from the porosity the shear wave velocity is calculated empirically from the compressional wave velocity and poisson s ratio is then computed from the compressional and shear wave velocities the results are in good agreement with values derived for similar rapidly deposited sediment sequences elsewhere but the model calculations indicate that deep sea drilling project measurements may be biased toward higher porosity samples

the seismic signatures of recently formed impact craters on mars we investigated the seismic signatures of recent impact crater clusters on mars that would be recorded by the interior exploration using seismic investigations geodesy and heat transport insight seismometers we used a database of 77 measured and dated impact sites with craters with diameters between 2 1 and 33 8 m along with inferred impact angle bolide trajectory and varying target material properties to empirically scale for the momentum expected seismic source function and radiation pattern of impacts the impact source is simulated in a local 3 d finite difference wave propagation code and coupled to teleseismic distances by scaling the spectra of 1 d global synthetic seismograms we use the insight seismometer noise floors to estimate detectability of impact s across azimuth and distance our experiments reveal that impact clusters have a higher peak corner frequency resulting from energy contributed by smaller craters to the power spectrum we also find that the time separation between individual impacts in a cluster is small 100 hz to resolve individual impacts within the cluster two of the clusters in our database 20 m effective diameter would have been detectable by insight with the assumptions that the martian background noise and seismic attenuation are both low joint detection of surface changes from newly formed crater s in images and by insight will provide precise source locations that are crucial for constraining the internal structure of mars

the expansion of c4 grasses and global change in the late miocene stable isotope evidence from the americas j3c values in paleosols and fossil teeth have been used to document the expansion of c plants in south asia africa and north america during the late miocene however the exact timing and rate of expansion of c vegetation is unclear outside the old world because of a lack of high resolution records we present a high resolution record from northwest argentina in which the s13c values of soil carbonate rise above a threshold of 8 0 suggesting the presence of c plants starting at 7 3 6 7 ma sr3c values of fossil teeth from well dated sections in south and north america display a concomitant increase of c plants in the diets of large herbivores these results show that the late miocene expansion of c plants was global but occurred at different rates in each region while it is has been suggested that declining pc0 levels during the late neogene caused c plant expansion climate change such as an increase in summer dominated rainfall regimes globally is an alternative explanation the 6 0 soil carbonate records from south asia east africa and now also northwest argentina all show an increase of at least 3 4 in the late neogene either the result of climate change or of greater evaporation in average grassland soils

velocity anisotropy in shales a petrophysical study using ultrasonic velocity and anisotropy measurements on a variety of shales with different clay and kerogen content clay mineralogy and porosity at a wide range of effective pressure we find that elastic anisotropy of shales increases substantially with compaction the effect is attributed to both porosity reduction and smectite to illite transformation with diagenesis a means of kerogen content mapping using velocity versus porosity crossplot for shales is shown matrix anisotropy of shales dramatically increases with kerogen reaching the maximum values of about 0 4 at total organic carbon toc 15 20 a strong chemical softening effect was found in shales containing even minor amounts of swelling smectite clay when saturated with aqueous solution this effect results in a significant p wave anisotropy reduction as compared to dry and oil saturated shales since mature black shales are normally oil wet this effect can only have a local significance restricted to the wellbore wall accurate measurements of phase velocities including velocities at a 45 direction to the bedding plane allow us to immediately calculate elastic stiffnesses and anisotropic parameters intrinsic high pressure properties of shales display an e 0 relation introduction of the bedding parallel microcracks in overpressured shales results in a decrease when fully fluid saturated and a increase when partially gas saturated with a characteristic effect on the shape of the p wave velocity surface at small angles of incidence filtering the contribution of the intrinsic anisotropy of shales it is possible to estimate the pore fluid phase microcrack density and aspect ratio parameters using seismic anisotropy measurements

experimental compaction of na montmorillonite clay mixed with crude oil and seawater abstract the mechanism of primary migration of generated petroleum from source rocks to reservoirs is still poorly understood to investigate some of problems involved in primary migration of oil na montmorillonite clay mixed with seawater and crude oil was compacted for 25 days under a pressure of 1000 kg cm 2 and a temperature of 60 c the amount of expelled liquid from the clay was large at the early stage of compaction and decreased gradually as compaction progressed the proportion of oil in the expelled liquid gradually increased with increasing time of compaction porosity of the compacted sample decreased from 81 of original clay to 26 this may indicate that the primary migration of oil from source to reservoir rocks will occur chiefly during the late compaction stage 10 30 by the effect of capillary pressure of continuous oil flow

sharad soundings and surface roughness at past present and proposed landing sites on mars reflections at phoenix may be attributable to deep ground ice we use the shallow radar sharad on the mars reconnaissance orbiter to search for subsurface interfaces and characterize surface roughness at the landing sites of viking landers 1 and 2 mars pathfinder the mars exploration rovers spirit and opportunity the phoenix mars lander the mars science laboratory curiosity rover and three other sites proposed for curiosity only at the phoenix site do we find clear evidence of subsurface radar returns mapping out an interface that may be the base of ground ice at depths of 15 66 m across 2900 km2 in the depression where the lander resides at the opportunity spirit and candidate curiosity sites images and altimetry show layered materials tens to hundreds of meters thick extending tens to hundreds of kilometers laterally these scales are well within sharad s resolution limits so the lack of detections is attributable either to low density contrasts in layers of similar composition and internal structure or to signal attenuation within the shallowest layers at each site we use the radar return power to estimate surface roughness at scales of 10 100 m a measure that is important for assessing physical properties landing safety and site trafficability the strongest returns are found at the opportunity site indicating that meridiani planum is exceptionally smooth returns of moderate strength at the spirit site reflect roughness more typical of mars gale crater curiosity s ultimate destination is the smoothest of the four proposed sites we examined with holden crater eberswalde crater and mawrth vallis exhibiting progressively greater roughness

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in