constraints on the geologic history of home plate materials provided by clast morphology and texture 1 we quantified and classified the size shape roundness and texture of 333 loose surface particles clasts along the spirit rover traverse from martian solar days 750 to 1889 these data provided clues to origin transport mechanisms association with geologic units and other alteration processes clasts average 15 mm in size and 0 73 sphericity and display a low degree of roundness textures include vesicular smooth and rough flat faceted and granular platy clasts characteristics are comparable to those for clasts outside the home plate region mapped geologic units around home plate are characterized by distinctive clast morphologic parameters and only minor adjustments were made to unit boundaries and definitions mapped by others no new units are suggested by the data consistent roundness values seen from unit to unit coupled with the correlation between unit boundaries and clast characteristics in and outside home plate indicate that no appreciable transport has occurred subsequent to fragmentation from outcrop and emplacement rather clasts have been emplaced through volcanic activity and or impact and have been subjected to weathering processes since that time we interpret vesicular and flat faceted clasts texture types 1 3 to be derived from mitcheltree ridge basalts and the presence of these clasts to provide a general outline of the original extent of this unit platy granular textured clasts texture type 5 are derived from the upper home plate unit

shale gas transport model in 3d fractal porous media with variable pore sizes abstract a model for gas transport in shale is proposed by accounting for three major fluid flow mechanisms in shale stratum which is modeled as a 3d fractal media the proposed apparent permeability of shale is an analytical expression that also accounts for heterogeneous pore sizes in shale stratum and is verified using experimental datasets for methane and helium flow in shale results of sensitivity analysis indicate that surface diffusion of adsorbed gas plays an important role specifically in smaller pores while surface diffusion would be negligible in larger pores further the proposed model shows that flow due to surface diffusion decreases moderately with the increase of isosteric adsorption heat while it increases significantly with the increase of the maximum adsorption capacity one of the key novelties of the proposed permeability model is that it accounts for pore size distribution to reveal novel insights on gas transport in shale that can be used to optimize gas production by operational controls e g controlling reservoir pressure as flow regimes change with time

the subsidence history of conoco well 15 30 1 central north sea abstract the depth of deposition of the sediments from north sea well conoco 15 30 1 is determined using faunal and sedimentary evidence the effects of sedimentary load corrected for compaction and variations in water depth and sea level are removed to obtain the subsidence of the basement when covered by water only a crustal stretching and lithospheric thinning of 25 35 1 35 can account for both the initial fault controlled subsidence and the later uniform subsidence

modelling stress dependent permeability in fractured rock including effects of propagating and bending fractures the influence of in situ stresses on flow processes in fractured rock is investigated using a novel modelling approach the combined finite discrete element method femdem is used to model the deformation of a fractured rock mass the fracture wall displacements and aperture changes are modelled in response to uniaxial and biaxial stress states the resultant changes in flow properties of the rock mass are investigated using the complex systems modelling platform csmp csmp is used to model single phase flow through fractures with variable aperture and a permeable rock matrix the study is based on a geological outcrop mapping of a low density fracture pattern that includes the realism of intersections bends and segmented features by applying far field boundary stresses to a square region geologically important phenomena are modelled including fracture dependent stress heterogeneity the re activation of pre existing fractures i e opening closing and shearing the propagation of new fractures and the development of fault zones flow anisotropy is investigated under various applied stresses and matrix permeabilities in situ stress conditions that encourage a closing of fractures together with a more pervasive matrix dominated flow are identified these are compared with conditions supporting more localised flow where fractures are prone to dilatational shearing and can be more easily exploited by fluids the natural fracture geometries modelled in this work are not perfectly straight promoting fracture segments that dilate as they shear we have demonstrated the introduction of several realistic processes that have an influence on natural systems fractures can propagate with wing cracks there is the potential for new fractures to connect with existing fractures thus increasing the connectivity and flow blocks can rotate when bounded by fractures bent fractures lead to locally different aperture development highly heterogeneous stress distributions emerge naturally results presented in this work provide a mechanically rigorous demonstration that a change in the stress state can cause reactivation of pre existing fractures and channelling of flow in critically stressed fractures

the rasc method for ranking and scaling of biostratigraphic events abstract the rasc method for ranking and scaling of biostratigraphic events was developed by the authors and associates during the past 20 years the purpose of ranking is to create an optimum sequence of events observed in different wells or sections subject to stratigraphic inconsistencies in the direction of the arrow of time these inconsistencies which result in crossovers of lines of correlation between sections are due to various sampling errors and other sources of uncertainty including reworking and misclassification they can be resolved by statistical averaging combined with stratigraphic reasoning subsequent scaling of the events can be carried out by estimating intervals between successive events along a relative time scale this results in the scaled optimum sequence either the ranked optimum sequence or the scaled optimum sequence can be used for biozonation and for correlation between sections with error bars to denote precision of the correlation the observed positions in the sections of different biostratigraphic events can have different degrees of precision these differences can be evaluated by analysis of variance other types of stratigraphic events including logmarkers can be integrated and incorporated with the biostratigraphic events the purpose of this review paper is to provide a succinct description of rasc as it is today using the cretaceous microfossil example of gradstein et al gradstein f m kaminski m a agterberg f p 1999 biostratigraphy and paleoceanography of the cretaceous seaway between norway and greenland earth science reviews for illustration

stress dependent permeability of a de mineralised fracture in shale abstract the paper presents the results of laboratory direct shear tests on the hydro mechanical behaviour of an extensional fracture in shale the tests were conducted on fracture specimens obtained by mechanically splitting blocks of a naturally fractured shale along the cemented fracture and dissolving the calcite fracture filling with a strong acid the experiments consisted of radial fluid flow tests from a single fluid source along the fracture surface fracture samples were tested under different levels of effective normal stress and shear displacement the experimental results show significant reduction of fracture permeability during increasing contact normal stress across the fracture and after shearing of the fracture under constant high normal stress however the tested fractures never completely closed even under normal stresses close to or higher than the unconfined compressive strength of the intact shale the fracture permeability remained much higher than the intact shale or matrix permeability even when the fracture surface has undergone some gouge formation from local asperity failure during shearing the results indicate that fractures once created are difficult to close by mechanical loading in tight formations like shales fractures will always be conduits for fluid flow unless closed by cementation currently it is widely assumed that fractures in sedimentary basins stay open only when there is an overpressure which could keep the fractures hydraulically parted however the results presented here indicate that given a sufficient hydraulic gradient fluid can still flow along a fracture even in the absence of large overpressures

effects of rock mineralogy and pore structure on stress dependent permeability of shale samples we conducted pulse decay permeability experiments on utica and permian shale samples to investigate the effect of rock mineralogy and pore structure on the transport mechanisms using a non adsorbin

how synchronous are neogene marine plankton events an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username andguest as the password go to the right directory by typing cdapend type ls to see what files are available type get and thename of the file to get it finally type exit to leave the system paper 94pa01456 how synchronous are neogene marine planktonevents by c spencer cervato h r thierstein d b lazarus andj p beckmann diskette may be ordered from american geophysicalunion 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order we analyzed the synchrony and diachrony of commonly used neogene biostratigraphic events from data published in the initial reports of the deep sea drilling project dsdp and in the proceedings of the ocean drilling program odp on the basis of the combined biostratigraphic and magnetostratigraphic evidence new neogene age models were constructed for 35 globally distributed dsdp and odp holes biostratigraphic events from the four major plankton groups calcareous nannofossils diatoms planktonic foraminifera and radiolarians were compiled from dsdp and odp reports after the elimination of possible sources of error such as stratigraphic hiatuses and reworking of specimens 124 biostratigraphic events that occurred in at least four holes were analyzed in detail for each event a biochronologic age estimate was derived by projection of the depth of the event onto the line of correlation of each hole and from these a global mean age for each event was calculated together with its standard deviation average standard deviations for event ages by fossil group are calcareous nannofossil first appearance datums fads 0 57 m y 21 events calcareous nannofossil last appearance datums lads 0 60 m y 25 events diatom fads 0 57 m y 7 events diatom lads 0 85 m y 14 events planktonic foraminifera fads 0 88 m y 22 events foraminifera lads 0 68 m y 16 events radiolarian fads 0 30 m y 9 events radiolarian lads 0 31 m y 10 events since the average sample spacing in the sites used for this analysis is only 0 185 m y we have examined the data for true patterns of diachrony and for other biases diachrony is more frequent among cosmopolitan than among endemic taxa thus there is a general trade off between the obtainable age precision and the geographic extent of a bioevent precision of age calibrations also decreases with increasing age although some of these features may be due to investigator bias they appear in part to be real phenomena and thus could also provide opportunities for further exploration of important paleobiological processes such as change in environmental gradients through time evolutionary adaptation of species populations and migration due to water mass changes

calcium sulfate veins characterized by chemcam curiosity at gale crater mars the curiosity rover has analyzed abundant light toned fracture fill material within the yellowknife bay sedimentary deposits the chemcam instrument coupled with mastcam and chemcam remote micro imager images was able to demonstrate that these fracture fills consist of calcium sulfate veins many of which appear to be hydrated at a level expected for gypsum and bassanite anhydrite is locally present and is found in a location characterized by a nodular texture an intricate assemblage of veins crosses the sediments which were likely formed by precipitation from fluids circulating through fractures the presence of veins throughout the entire similar to 5 m thick yellowknife bay sediments suggests that this process occurred well after sedimentation and cementation lithification of those sediments the sulfur rich fluids may have originated in previously precipitated sulfate rich layers either before the deposition of the sheepbed mudstones or from unrelated units such as the sulfates at the base of mount sharp the occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively nonacidic conditions

a model of thermal conductivity for planetary soils 2 theory for cemented soils 1 a numerical model of heat conduction through particulate media made of spherical grains cemented by various bonding agents is presented the pore filling gas conductivity volume fraction and thermal conductivity of the cementing phase are tunable parameters cement fractions 0 001 0 01 in volume have small effects on the soil bulk thermal conductivity a significant conductivity increase factor 3 8 is observed for bond fractions of 0 01 to 1 in volume in the 1 to 15 bond fraction domain the conductivity increases continuously but less intensely 25 100 conductivity increase compared to a 1 bond system beyond 15 of cements the conductivity increases vigorously and the bulk conductivity rapidly approaches that of bedrock the composition of the cements i e conductivity has little influence on the bulk thermal inertia of the soil especially if the volume of bond 10 these results indicate that temperature measurements are sufficient to detect cemented soils and quantify the amount of cementing phase but the mineralogical nature of the bonds and the typical grain size are unlikely to be determined from orbit on mars a widespread surface unit characterized by a medium albedo 0 19 0 26 and medium high thermal inertia 200 600 j s 0 5 m 2 k 1 has long been hypothesized to be associated with a duricrust the fraction of cement required to fit the thermal data is less than 1 5 by volume this small amount of material is consistent with orbital observations confirming that soil cementation is an important factor controlling the thermal inertia of the martian surface

mahli at the rocknest sand shadow science and science enabling activities 1 during martian solar days 57 100 the mars science laboratory curiosity rover acquired and processed a solid sediment sample and analyzed its mineralogy and geochemistry with the chemistry and mineralogy and sample analysis at mars instruments an aeolian deposit herein referred to as the rocknest sand shadow was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions during first time activities the mars hand lens imager mahli was used to support both science and engineering activities related to sample assessment collection and delivery here we report on mahli activities that directly supported sample analysis and provide mahli observations regarding the grain scale characteristics of the rocknest sand shadow mahli imaging confirms that the rocknest sand shadow is one of a family of bimodal aeolian accumulations on mars similar to the coarse grained ripples interrogated by the mars exploration rovers spirit and opportunity in which a surface veneer of coarse grained sediment stabilizes predominantly fine grained sediment of the deposit interior the similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on mars we suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation where winnowing of the fine sediment fraction results in a relatively low sediment load and a preferential increase in the coarse grained fraction of the sediment load the compositional similarity of martian aeolian deposits supports the potential for global redistribution of fine grained components combined with potential local contributions

characteristics of pebble and cobble sized clasts along the curiosity rover traverse from sol 100 to 750 terrain types potential sources and transport mechanisms abstract we combine the results of orbitally derived morphologic and thermal inertia data with in situ observations of abundance size morphologic characteristics and distribution of pebble to cobble sized clasts along the curiosity rover traverse our goals are to characterize rock sources and transport history and improve our ability to predict upcoming terrain there are ten clast types with nine types interpreted as sedimentary rocks only type 3 clasts had morphologies indicative of significant wear through transport thus most clast types are indicative of nearby outcrops or prior presence of laterally extensive sedimentary rock layers consistent with the erosional landscape a minor component may reflect impact delivery of more distant material types 1 and 4 are heavily cemented sandstones likely associated with a caprock layer types 5 and 6 and possibly 7 are pebble rich sandstones with varying amounts of cement leading to varying susceptibility to erosion wear type 3 clasts are rounded pebbles likely transported and deposited alluvially then worn out of pebbly sandstone conglomerate types 9 and 10 are poorly sorted sandstones with type 9 representing fragments of square top type layers and type 10 deriving from basal or other mt sharp layers types 2 8 and 9 are considered exotics there are few clear links between clast type and terrain surface roughness particularly in identifying terrain that is challenging for the rover to navigate orbital data may provide a reasonable prediction of certain end member terrains but the complex interplay between variables that contribute to surface characteristics makes discriminating between terrain types from orbital data problematic prediction would likely be improved through higher resolution thermal inertia data

gale crater and impact processes curiosity s first 364 sols on mars abstract impact processes at all scales have been involved in the formation and subsequent evolution of gale crater small impact craters in the vicinity of the curiosity msl landing site and rover traverse during the 364 sols after landing have been studied both from orbit and the surface evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate and disrupted fractured sedimentary layers which are not obviously displaced by erosion impact ejecta blankets are likely to be present but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary volcaniclastic breccia and conglomerate deposits the occurrence of individual blocks with diverse petrological characteristics including igneous textures have been identified across the surface of bradbury rise and some of these blocks may represent distal ejecta from larger craters in the vicinity of gale distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material possible examples of impactites in the form of shatter cones shocked rocks and ropy textured fragments of materials that may have been molten have been observed but cannot be uniquely confirmed modification by aeolian processes of craters smaller than 40 m in diameter observed in this study are indicated by erosion of crater rims and infill of craters with aeolian and airfall dust deposits estimates for resurfacing suggest that craters less than 15 m in diameter may represent steady state between production and destruction the smallest candidate impact crater observed is 0 6 m in diameter the observed crater record and other data are consistent with a resurfacing rate of the order of 10 mm myr considerably greater than the rate from impact cratering alone but remarkably lower than terrestrial erosion rates

insights on why graphic correlation shaw s method works in 1964 a b shaw presented a method of correlating fossiliferous sedimentary rocks based on interpretation of graphic plots of first and last occurrences of taxa because there is no way to determine the true total ranges of fossil taxa it is instructive to test the accuracy of the method using hypothetical datasets the dataset used here consists of 16 taxa in six sections with differing known rates of rock accumulation in all graphs a single straight line correlation was a reasonable interpretation the resulting ranges after the first and third rounds of compositing reproduce the true ranges but with small errors slight errors in the positioning of individual correlation lines are more likely to lengthen ranges artificially than to shorten them shaw s method works well because whereas actually sampled ranges will be shorter than true ranges errors in correlation will be likely to extend some ranges this or any exercise using simulated data is useful only if the hypothetical situation resem

quantitative determination of tertiary sediment supply to the north sea basin sediment supply comprises a major family of regime variables that influence geomorphic surface grade spatial and temporal changes in total sediment supply and sediment texture gravel sand mud ratio will cause reconfiguration of depositional and erosional profiles potentially creating or influencing the sequence stratigraphic framework of the basin sequence grain volume which is defined as the volume of sedimentary grains in an individual stratigraphic sequence total sequence volume minus cement and porosity volume has been quantitatively determined for each of 16 genetic stratigraphic sequences in the north sea basin rates of total sediment supply to the basin in both time and space were then calculated sand grain volume and sand mud ratio were also calculated for each sequence these data define four principal episodes of tertiary sediment supply the most significant episode occurred in the late paleocene and was followed by secondary episodes in the eocene and oligocene a fourth neogene episode extends through the present all episodes correlate to source terrain tectonic pulses related to evolution of the north atlantic basin to intraplate stress changes associated with successive phases of the alpine orogeny or to the late cenozoic epeirogenic uplift of scandinavia the major episodes in turn contain secondary sequence to sequence variations that correspond to changes in spatial or temporal values of one or both of the supply regime variables again most changes closely reflect details within the histories of the principal tectonic phases the history of changing source area relief and resulting topographic grades and related changes in sediment yield into the basin was a principal control on north sea cenozoic sequence development source basin relief in turn was largely determined by regional tectonism

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

diagenetic origin of nodules in the sheepbed member yellowknife bay formation gale crater mars the sheepbed member of the yellowknife bay formation in gale crater contains millimeter scale nodules that represent an array of morphologies unlike those previously observed in sedimentary deposits on mars three types of nodules have been identified in the sheepbed member in order of decreasing abundance solid nodules hollow nodules and filled nodules a variant of hollow nodules whose voids have been filled with sulfate minerals this study uses mast camera mastcam and mars hand lens imager mahli images from the mars science laboratory curiosity rover to determine the size shape and spatial distribution of the sheepbed nodules the alpha particle x ray spectrometer apxs and chemcam instruments provide geochemical data to help interpret nodule origins based on their physical characteristics spatial distribution and composition the nodules are interpreted as concretions formed during early diagenesis several hypotheses are considered for hollow nodule formation including origins as primary or secondary voids the occurrence of concretions interpreted in the sheepbed mudstone and in several other sedimentary sequences on mars suggests that active groundwater systems play an important role in the diagenesis of martian sedimentary rocks when concretions are formed during early diagenetic cementation as interpreted for the sheepbed nodules they have the potential to create a taphonomic window favorable for the preservation of martian organics

stress dependence of the permeability and porosity of sandstone and shale from tcdp hole a abstract we utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of pliocene to pleistocene sedimentary rocks from a 2000 m borehole experiments were conducted by first gradually increasing the confining pressure from 3 to 120 mpa and then subsequently reducing it back to 3 mpa the permeability of the sandstone remained within a narrow range 10 14 10 13 m2 the permeability of the shale was more sensitive to the effective confining pressure varying by two to three orders of magnitude than the sandstone possibly due to the existence of microcracks in the shale meanwhile the sandstone and shale showed a similar sensitivity of porosity to effective pressure whereby porosity was reduced by about 10 20 when the confining pressure was increased from 3 to 120 mpa the experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship to extrapolate the permeability or porosity under larger confining pressure e g 300 mpa using a straight line in a log log plot might induce unreasonable error but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range part of the permeability and porosity decrease observed during loading is irreversible during unloading

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

effect of tortuosity on the stress dependent permeability of tight sandstones analytical modelling and experimentation abstract accurately modelling stress dependent permeability is of great significance to predicting the oil gas production of unconventional tight sandstone reservoirs with time dependent pressure depletion the classic theory indicates that the porosity exponents of the capillary tube model and the fracture model are 2 and 3 respectively however experimental results demonstrate that the value of the porosity exponent usually varies greatly the effect of the nonuniform distribution of tortuosity on stress dependent permeability is rarely studied assuming that tight sandstones with natural microfractures can be represented by a bundle of tortuous capillary tubes and parallel plate fractures a new stress dependent permeability model of tight sandstones is proposed based on fractal theory considering the tortuosity effect the research results show that the porosity exponents of the tortuous capillary tube model and the tortuous plate fracture model are 3 d t 2 and 2 d t respectively here d t is the tortuosity fractal dimension for the capillary tube model and the plate fracture model without tortuosity d t 1 their porosity exponents can be simplified to 2 and 3 respectively the tortuosity fractal dimension is one of the reasons causing the porosity exponent to deviate from the classic theoretical value the newly developed stress dependent permeability model is verified with experimental data determined using tight sandstone core samples from the yanchang formation in the ordos basin china the average error of the permeability prediction under different effective stresses is only 3 78 thus the newly developed model can accurately predict the stress dependent permeability of tight sandstones

geohistory analysis of bombay high region abstract geohistory diagrams have been constructed for three representative sites in the bombay high region offshore west coast india the model curve for 60 lithospheric injection matches the intitial part of a thermo tectonic curve for one of the sites where a complete tertiary sequence is developed the study suggests that the four paleogene unconformities recognised in this region were caused by eustatic falls a distinct phase of active subsidence occurred during the late middle late miocene probably due to more active spreading at the mid indian ocean ridge

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

global distribution of bedrock exposures on mars using themis high resolution thermal inertia 1 we investigate high thermal inertia surfaces using the mars odyssey thermal emission imaging system themis nighttime temperature images 100 m pixel spatial sampling for this study we interpret any pixel in a themis image with a thermal inertia over 1200 j m 2 k 1 s 1 2 as bedrock which represents either in situ rock exposures or rock dominated surfaces three distinct morphologies ranked from most to least common are associated with these high thermal inertia surfaces 1 valley and crater walls associated with mass wasting and high surface slope angles 2 floors of craters with diameters 25 km and containing melt or volcanics associated with larger high energy impacts and 3 intercrater surfaces with compositions significantly more mafic than the surrounding regolith in general bedrock instances on mars occur as small exposures less than several square kilometers situated in lower albedo 350 j m 2 k 1 s 1 2 and relatively dust free dust cover index 0 95 regions however there are instances that do not follow these generalizations most instances are concentrated in the southern highlands with very few located at high latitudes poleward of 45 n and 58 s suggesting enhanced mechanical breakdown probably associated with permafrost overall mars has very little exposed bedrock with only 960 instances identified from 75 s to 75 n with likely 3500 km 2 exposed representing 1 ofthe total surface area these data indicate that mars has likely undergone large scale surface processing and reworking both chemically and mechanically either destroying or masking a majority of the bedrock exposures on the planet

volumetric estimates of ancient water on mount sharp based on boxwork deposits gale crater mars while the presence of water on the surface of early mars is now well known the volume distribution duration and timing of the liquid water have proven difficult to determine this study makes use of a distinctive boxwork rich sedimentary layer on mount sharp to map fluid based cementation from orbital imagery and estimate the minimum volume of water present when this sedimentary interval was formed the boxwork structures on mount sharp are decameter scale light toned polygonal ridges that are unique compared to previous observations of martian fractured terrain because they are parallel sided ridges with dark central linear depressions this texture and the sedimentary setting strongly imply that the ridges are early diagenetic features formed in the subsurface phreatic groundwater zone high resolution orbital imagery was used to map the volume of light toned cemented ridges based on the cemented volume a minimum of 5 25 105 m 3 of cement was deposited within the fractures using a brine composition based on observations of other martian cements and modeling the degree of evaporation each volume of cement requires 800 6700 pore volumes of water so the mapped boxwork ridge cements require a minimum of 0 43 km 3 of water this is a significant amount of groundwater that must have been present at the 3620 m level 1050 m above the current floor of gale crater providing both a new constraint on the possible origins of mount sharp and a possible future science target for the curiosity rover where large volumes of water were present and early mineralization could have preserved a once habitable environment

the simulation of the sedimentary fill of basins an interactive computer simulation which erects models of sedimentary geometries by filling in a two dimensional basin from both sides with a combination of clastic sediment and or in situ and transported carbonate sediments is described the simulation program is implemented in c using graphical plotting functions data entry including the initial basin configuration the local tectonic behavior the sea level curves the amount and source direction of clastic sediment and the growth rates of carbonates as a function of water depth is performed interactively geometries of clastic and carbonate sediments evolve through time and respond to tectonic movement eustasy and sedimentation clastic modeling includes sedimentary bypass and erosion and sedimentation in alluvial and coastal plains marine shelf basin slope and basin floor settings carbonate modeling includes progradation the development of hard grounds downslope aprons keep up catch up back step and drowned reef settings as well as lagoonal and epeiric settings also included in the model are extensional vertical faulting of the basin sediment compaction and isostatic response to sediment loading sediment geometries are plotted on a graphics terminal as they are computed so the user can immediately view the results based on these observations parameters can be changed and the program rerun until the user is satisfied with the resultant geometry this paper includes output showing the simulation s sensitivity to eustatic sea level variations and variations in sedimentation and subsidence rates also shown are outputs demonstrating the modeling of some examples from the geologic section in the permian basin of west texas and the upper permian of the sichuan basin

recent developments in quantitative stratigraphy abstract during the past 10 years about 150 scientists in 25 countries have collaborated under the auspices of the international geological correlation programme project no 148 evaluation and development of quantitative stratigraphical correlation techniques this paper reviews mathematical methods of stratigraphical correlation mainly in biostratigraphy but also in chronostratigraphy and lithostratigraphy sequencing methods treat the relative order of stratigraphic events such as the highest occurrences of fossil taxa as observed in many sections intervals between successive events in an ordered sequence can be estimated and the results expressed in linear time if a subgroup of the stratigraphical events can be dated recently such methods have been used to develop a new deep water benthic foraminiferal zonation for the cenozoic strata of the central and viking grabens north sea several regional hiatuses of 2 to 5 m y in duration can be recognized and matched to changes in sea level the same methods have been used for automated isochron contouring with error bars in depth or time units in cenozoic and cretaceous basins off eastern canada such information may be used for automated basin history analysis time successive assemblages of fossils can be established by using multivariate methods applied to co occurrences of events or by the method of unitary associations in conjunction with graph theory on the overlap of stratigraphical ranges other methods for stratigraphical correlation reviewed in this paper include the composite standard method and estimation of the age of chronostratigraphical boundaries using maximum likelihood and cubic spline interpolations attractions of quantitative stratigraphy are the use of rigorous methodology which highlights many properties of the data the ability to handle large and complex data bases in an objective manner and statistical evaluation of the uncertainty in the results generally little conceptual orientation is required in order to use these methods and thereby gain more information from a particular dataset

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

quantitative morphology of rocks at the mars pathfinder landing site 1 we adapt and test a standard terrestrial technique of assessing morphology quantitatively for use with sites on mars based on two dimensional equations and particle outlines whereby images of particles obtained remotely may yield dimensionless numerical shape and roundness values consistent with previous knowledge of the lithology and sedimentary transport history our test site was the particle rich rock garden at the mars pathfinder landing site a location where the primary geologic processes and lithology have been determined by other means a total of 575 particles were assessed in terms of size sphericity elongation and roundness qualitative roundness was determined for 460 particles particles are mostly pebble to cobble sized and have an average sphericity of 0 75 elongation of 0 63 and relative roundness of 0 083 69 of particles are subangular or subrounded particle sphericity is unimodal with a size sphericity profile matching trends for terrestrial populations of similar lithology and elongations nearly identical to those for particles at vikings 1 and 2 this matches the predictions for a site with the single overall lithology implied from other analyses roundness data indicate one or possibly two particle populations representing the primary processes that likely affected particle roundness most strongly impact and catastrophic flooding finally we tested a hypothesis suggesting that darker smaller more angular particles comprise a population transported through impact cratering while larger less dark more rounded particles are associated with catastrophic flood transport the opposite result is seen larger particles throughout the rock garden are more angular than smaller ones

observations and preliminary science results from the first 100 sols of msl rover environmental monitoring station ground temperature sensor measurements at gale crater we describe preliminary results from the first 100 sols of ground temperature measurements along the mars science laboratory s traverse from bradbury landing to rocknest in gale the ground temperature data show long term increases in mean temperature that are consistent with seasonal evolution deviations from expected temperature trends within the diurnal cycle are observed and may be attributed to rover and environmental effects fits to measured diurnal temperature amplitudes using a thermal model suggest that the observed surfaces have thermal inertias in the range of 265 375 j m 2 k 1 s 1 2 which are within the range of values determined from orbital measurements and are consistent with the inertias predicted from the observed particle sizes on the uppermost surface near the rover ground temperatures at gale crater appear to warm earlier and cool later than predicted by the model suggesting that there are multiple unaccounted for physical conditions or processes in our models where the mars science laboratory msl descent engines removed a mobile layer of dust and fine sediments from over rockier material the diurnal temperature profile is closer to that expected for a homogeneous surface suggesting that the mobile materials on the uppermost surface may be partially responsible for the mismatch between observed temperatures and those predicted for materials having a single thermal inertia models of local stratigraphy also implicate thermophysical heterogeneity at the uppermost surface as a potential contributor to the observed diurnal temperature cycle

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

martian fluvial conglomerates at gale crater observations by the mars science laboratory mast camera mastcam in gale crater reveal isolated outcrops of cemented pebbles 2 to 40 millimeters in diameter and sand grains with textures typical of fluvial sedimentary conglomerates rounded pebbles in the conglomerates indicate substantial fluvial abrasion chemcam emission spectra at one outcrop show a predominantly feldspathic composition consistent with minimal aqueous alteration of sediments sediment was mobilized in ancient water flows that likely exceeded the threshold conditions depth 0 03 to 0 9 meter average velocity 0 20 to 0 75 meter per second required to transport the pebbles climate conditions at the time sediment was transported must have differed substantially from the cold hyper arid modern environment to permit aqueous flows across several kilometers

flow through fractures flow through fractures is often idealized as flow between two parallel plates plane poiseuille flow the opening or aperture between parallel plates is unambiguous and its relation to flowrate is well known however fractures in rock have uneven walls and a variable aperture a model for flow in a fracture is proposed wherein the fracture is represented by a set of parallel plate openings with different apertures the model leads to a modified poiseuille equation for flow which includes an aperture frequency distribution for the fracture any arbitrary aperture distribution can be used in order to simplify computation and demonstrate the properties of the model a log normal form of distribution is assumed even when an analytical form of the distribution is assumed two parameters rather than a single value representing aperture size are required to determine flowrate models of aperture change for a fracture undergoing compression fracture walls deforming and extension fracture walls separating are developed which constrain the additional parameter and allow calculation of flowrate as a function of mean aperture the theoretical relationships developed between mean aperture and flowrate can be used to interpret published laboratory data for single fractures

elemental geochemistry of sedimentary rocks at yellowknife bay gale crater mars sedimentary rocks examined by the curiosity rover at yellowknife bay mars were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts no evidence of chemical weathering is preserved indicating arid possibly cold paleoclimates and rapid erosion and deposition the absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature circumneutral ph rock dominated aqueous conditions analyses of diagenetic features including concretions raised ridges and fractures at high spatial resolution indicate that they are composed of iron and halogen rich components magnesium iron chlorine rich components and hydrated calcium sulfates respectively composition of a cross cutting dike like feature is consistent with sedimentary intrusion the geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of mars

the probable range concept applied to the biostratigraphy of marine microfossils the probable range of a taxon is its most frequently observed range defined for a set of geologic sections the probable range concept is defined and demonstrated using two applications both based on deep sea drilling project data the first uses a cenozoic and mesozoic north atlantic ocean data set calcareous nannoplankton 228 taxa 55 sections the major result is a standardized rangechart at a definable level of minimum confidence for the data set that shows excellent correlation when compared with published range data the second application uses a pacific ocean data set calcareous nannoplankton planktonic foraminifera radiolaria 330 taxa 32 sections the application results in an estimated maximum attainable resolution of 100 000 years for the tertiary the quantitative application of the probable range concept offers the improvement of resolution beyond the 100 000 year level equally reliable alternatives to standard biostratigraphic zonations and objective limits of confidence or risk o

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

aeolian processes in proctor crater on mars sedimentary history as analyzed from multiple data sets 1 proctor crater is a 150 km diameter crater in noachis terra within the southern highlands of mars the analysis leading to the sedimentary history incorporates several data sets including imagery elevation composition and thermal inertia mostly from the mars global surveyor mission the resulting stratigraphy reveals that the sedimentary history of proctor crater has involved a complex interaction of accumulating and eroding sedimentation aeolian features spanning much of the history of the crater interior dominate its surface including large erosional pits stratified beds of aeolian sediment sand dunes erosional and depositional streaks dust devil tracks and small bright bed forms that are probably granule ripples long ago up to 450 m of layered sediment filled the crater basin now exposed in eroded pits on the crater floor these sediments are probably part of an ancient deposit of aeolian volcaniclastic material since then some quantity of this material has been eroded from the top layers of the strata small bright dune forms lie stratigraphically beneath the large dark dune field relative to the large dark dunes the bright bed forms are immobile although in places their orientations are clearly influenced by the presence of the larger dunes their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill dust devil tracks form during the spring and summer following a west southwesterly wind early in the spring the dust devils are largely restricted to dark patches of sand as the summer approaches dust devil tracks become more plentiful and spread to the rest of the crater floor indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils the dark dunes contain few dust devil tracks suggesting that accumulated dust is swept away directly by saltation rather than by the passage of dust devils spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt like materials the average thermal inertia calculated from thermal emission spectrometer bolometric temperatures is 277 17 j m 2 s 0 5 k 1 leading to an effective grain size of 740 170 mm which is consistent with coarse sand and within the range expected for martian sand the coarse sand that composes the large dune field may have originated from outside the crater saltating in from the southwest most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried the sand was transported to the east center of the crater floor where beneath the present day dunes a 50 m high mound of sand has accumulated dune slip faces indicate a wind regime consisting of three opposing winds some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms the combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime which produces the large reversing transverse and star dunes that dominate the dune field the dark dunes have both active slip faces and seemingly inactive slip faces suggesting that the dunes vary spatially in their relative activity nevertheless the aeolian activity that has dominated the history of proctor crater still continues today index terms 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5410 planetology solid surface planets