the nature of shallow water carbonate lithofacies thickness distributions carbonate lithofacies thickness distributions are of fundamental importance to understanding shallow water carbonate deposystems because they record evidence of the lateral distribution and migration of lithofacies elements as well as evidence for the various other intrinsic and extrinsic controls on stratal geometries and accumulation rates previous analyses of lithofacies thickness data led to the suggestion that exponential distributions are ubiquitous in the ancient record this has been interpreted to indicate deposition by stochastic poisson process lithofacies mosaics to further investigate these ideas statistical analysis of 56 outcrop and core examples was performed the kolmogorov smirnov test was used to identify the degree to which measured lithofacies thicknesses are well represented by a theoretical exponential distribution results from this analysis show that 16 of the 56 examples can be confidently shown to be exponential while 28 are very probably not exponential this indicates that stochastic poisson processes are a plausible explanation for many carbonate successions but they do not explain all of those tested here suggesting that other non poisson processes either stochastic or deterministic in nature or both must also be important thus lithofacies planform geometries and the processes controlling vertical stacking in ancient carbonate platform top deposystems were likely more diverse than has been suggested requiring significant further quantitative analysis and numerical forward modeling to properly understand

facies mosaics across the persian gulf and around antigua stochastic and deterministic products of shallow water sediment accumulation abstract among broadly different types of sedimentary successions those that accumulate in nearshore settings are perhaps unique in that a very wide range of rock types recurs with high frequency over relatively short stratigraphic intervals this vertical lithofacies heterogeneity suggests that deposition of any sedimentary unit at any site was short lived that many different sediment types existed within a complex mosaic over the depositional surface and that this facies montage repeatedly moved across surfaces of accumulation in response to eustatic sedimentologic and or tectonic forcing data on numbers and thicknesses of lithofacies units from several dozen such sequences define the size frequency distribution expected if horizons of lithologic change occur randomly within sedimentary successions walther s law suggests that the amount of vertical lithologic heterogeneity manifest in a sedimentary sequence should reflect the degree of lateral heterogeneity in sediment composition that existed across depositional surfaces if so this repetition should also be manifest in sizes and areal distributions of sediment patches constituting the depositional mosaic in order to examine size frequency relations of sediment bodies across surfaces of sediment accumulation we tabulated numbers and areal extents of lithotopes across two rather dissimilar settings across the persian gulf and around the caribbean island of antigua although compositions and lateral extents of different sediment types exhibit broad lateral variation across interior to margin transects in either area lithotope abundances and areal extents define frequency distributions that are in excellent agreement with those anticipated for a facies mosaic of elements whose mean linear widths constitute an exponential frequency distribution these are the size frequency distributions one would expect if mosaic element boundaries occur randomly across regions of sediment accumulation and suggest that distributions of lithotope areas from holocene surfaces are directly analogous to lithofacies thickness frequencies from ancient successions in addition to the fact that both of the size frequency distributions attest to the importance of stochastic processes during sediment deposition they also afford numerical descriptors of abundances and areal extents of holocene lithosomes that can then be used as controlling parameters in computational models of sediment accumulation importantly results derived from such simulations are based not on inference of water depth varying in response to change in subsidence sea level and rate of sediment accumulation but on statistical attributes intrinsic to modern and ancient marginal marine successions

orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

evolution and depositional environments of the eberswalde fan delta mars the eberswalde crater and its contributing basins have been analyzed in detail in order to reconstruct the geological evolution of the water related landforms with particular focus on the eberswalde delta like feature based on a complex strata organization characterized by a topset foreset bottomset geometry typical of delta progradation on earth we interpret the eberswalde feature to be a fan delta associated with a lacustrine system depositional sub environments have been recognized and mapped and the sedimentary processes discussed a sequence stratigraphy approach has been used to evaluate the system which we interpret to result from three depositional sequences these sequences suggest relative water level fluctuations and a longer trend over time towards decreasing water content inside the basin

is scaling in turbidite deposition consistent with forcing by earthquakes abstract two hypotheses have been suggested to explain the statistical distribution of bed thickness in turbidite sequences that it is a reflection of turbidite triggering by earthquakes occurring haphazardly in time and that it is controlled by the intrinsic nonlinear dynamics of a sedimentary system composed of many downslope transport events that are correlated over a broad range of scales of length and time in an attempt to distinguish between these hypotheses we have applied five tests to two previously described oligocene turbidite sequences from the izu bonin basin of the western pacific ocean we conclude that turbidite deposition in the izu bonin region is not the outcome of a self organized process nor of a low dimensional chaotic system but rather is consistent with turbidite emplacement by flows triggered by earthquakes at least some recent turbidites are known to have been deposited by such flows and the tests we have applied demonstrate that no other process is required to explain the statistics of the thickness and the timing of emplacement of beds in turbidite sequences if turbidites are indeed related to earthquakes then changes in the rate of turbidite emplacement may be used to place important constraints on paleoseismicity

complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

dynamic river channels suggest a long lived noachian crater lake on mars 1 recent images of the noachian age holden northeast crater show spectacular meandering channels that form a complex 150 meter thick lacustrine river delta deposit confined to the northwest margin of the crater we identify 11 major avulsion events in the topmost layer and suggest an avulsion frequency of a few hundred years the meandering nature of the channels and numerous avulsions is incompatible with deposition on an alluvial fan and clearly reflects a complex history of multiple sustained flows assuming an average sedimentation rate of 1mm year we suggest that holden ne crater contained a lake that persisted for at least 150 000 years our analysis is incompatible with this feature being the result of a major bolide impact that would have released a catastrophic flood by groundwater sapping and supports the hypothesis that early mars was both warmer and wetter during the noachian

spectral and geological study of the sulfate rich region of west candor chasma mars sulfates have been discovered by the omega spectrometer in different locations of the planet mars they are strongly correlated to light toned layered deposits in the equatorial regions west candor chasma is the canyon with the thickest stack of layers and one with the largest area covered by sulfates a detailed study coupling mineralogy derived from omega spectral data and geology derived from hrsc imager and other datasets leads to some straightforward issues the monohydrated sulfate kieserite is found mainly over heavily eroded scarps of light toned material it likely corresponds to a mineral present in the initial rock formed either during formation and diagenesis of sediments or during hydrothermal alteration at depth because it is typically found on outcrops that are eroded and steep polyhydrated sulfates that match any ca na fe or mg sulfates with more than one water molecule are preferentially present on less eroded and darker outcrops than outcrops of kieserite these variations can be the result of a diversity in the composition and or of the rehydration of kieserite on surfaces with longer exposure the latter possibility of rehydration in the current or recent atmosphere suggests the low surface temperatures preserve sulfates from desiccation and also can rehydrate part of them strong signatures of iron oxides are present on sulfate rich scarps and at the base of layered deposits scarps they are correlated with tes gray hematite signature and might correspond to iron oxides present in the rock as sand size grains or possibly larger concretions that are eroded and transported down by gravity at the base of the scarp pyroxenes are present mainly on sand dunes in the low lying terrains pyroxene is strongly depleted or absent in the layered deposits when mixed with kieserite local observations favor a spatial mixing with dunes over layered deposits sulfates such as those detected in the studied area require the presence of liquid water to form by precipitation either in an intermittent lacustrine environment or by hydrothermal fluid circulation both possibilities require the presence of sulfur rich groundwater to explain fluid circulation the elevation of the uppermost sulfate signatures suggests the presence of aquifers up to 2 5 km above datum only 1 km below the plateau surface

mid infrared spectroscopy of refractory inclusions cais in cv and co chondrites we present laboratory mid infrared absorption spectra 2 5 m to 16 0 m of powdered calcium aluminum rich inclusions cais and matrix separated from the carbonaceous chondrites allende cv3 2 vigarano cv3 3 and ornans co3 3 two groups of spectra with different features were found for the cai in the first group spectra are dominated by spinel pyroxene and sodalite nepheline where main features occur at 9 3 m 10 3 m and 11 3 m in the second group characteristic minerals are spinel and melilite with typical band maxima at 11 0 m and 12 3 m and a broad feature between 14 0 m and 15 0 m the position of the broad spinel feature probably depends on its iron content comparison of band positions in spectra from the cai components to observed circumstellar emission spectra indicates the potential occurrence of cai like material pyroxene and spinel rich features could occur in spectra of dust around the herbig ae star hd104237 the t tauri star hen3 600 and the post agb star r sge melilite and spinel rich components possibly appear in the spectrum of hd104237 hen3 600 04187 1927 r sge and the planetary nebula hb 12 there is also indication for a spinel component in dust from the herbig ae be star hd179218 the spectra of the agb stars r cas and aps show no features of cai type spinel

geophysical consequences of planetary scale impacts into a mars like planet all planetary bodies with old surfaces exhibit planetary scale impact craters vast scars caused by the large impacts at the end of solar system accretion or the late heavy bombardment here we investigate the geophysical consequences of planetary scale impacts into a mars like planet by simulating the events using a smoothed particle hydrodynamics sph model our simulations probe impact energies over two orders of magnitude 2 10 27 6 10 29 j impact velocities from the planet s escape velocity to twice mars orbital velocity 6 50 km s and impact angles from head on to highly oblique 0 75 the simulation results confirm that for planetary scale impacts surface curvature radial gravity the large relative size of the impactor to the planet and the greater penetration of the impactor contribute to significant differences in the geophysical expression compared to small craters which can effectively be treated as acting in a half space the results show that the excavated crustal cavity size and the total melt production scale similarly for both small and planetary scale impacts as a function of impact energy however in planetary scale impacts a significant fraction of the melt is sequestered at depth and thus does not contribute to resetting the planetary surface complete surface resetting is likely only in the most energetic 6 10 29 j slow and head on impacts simulated a crater rim is not present for planetary scale impacts with energies 10 29 j and angles 45 but rather the ejecta is more uniformly distributed over the planetary surface antipodal crustal removal and melting is present for energetic 10 29 j fast 6 km s and low angle 45 impacts the most massive impactors with both high impact energy and low velocity contribute sufficient angular momentum to increase the rotation period of the mars sized target to about a day impact velocities of 20 km s result in net mass erosion from the target for all simulated energies and angles the hypothesized impact origin of planetary structures may be tested by the presence and distribution of the geochemically distinct impactor material

assessment of aeolis palus stratigraphic relationships based on bench forming strata in the kylie and the kimberley regions of gale crater mars abstract the stratigraphic context of rock layers is a critical piece of information needed for accurate reconstruction of their geologic history although sedimentary rocks are widespread in gale crater efforts to deduce stratigraphic relationships of rocks were challenging early in the mars science laboratory mission because vertical bedrock exposures were relatively rare along the first 3 km the rover traversed across aeolis palus potential insights into the three dimensional configuration of rock layers were made once the rover passed dingo gap especially in the informally named kylie and kimberley regions here the terrain exhibits low relief 75 m curiosity mastcam and navcam images show that the cliffs are capped by resistant bench forming rock layers corresponding to two facies a poorly sorted weakly stratified pebble conglomerate and a massive dark toned vuggy sandstone in places the inclination of the topographic surface northward 2 to 3 is similar to the apparent dip of the underlying strata suggesting the presence of dip slopes in an area inferred to be generally flat lying conformable rock units further we assessed potential strata correlations via plane fitting exercises and a regional comparison to other capping strata we speculate that bench forming strata in the study region could be part of a widespread package of draping strata the siccar point group that post dates deposition and exhumation of the lower strata of mount sharp

bed thickness distributions on mars an orbital perspective studies on earth show that sedimentary bed thickness and bed thickness distributions record information about the processes controlling sediment deposition high resolution digital terrain models dtms such as those derived from the high resolution imaging science experiment hirise now provide the opportunity to quantify bed thickness properties on mars over several orders of magnitude down to the submeter scale this study uses hirise dtms and visible images to measure bed thickness distributions at 10 deposits on mars with the aim of determining whether statistical techniques can provide useful criteria for distinguishing sedimentary depositional processes basic statistics including mean thickness and range are examined as are histograms cumulative frequency plots and log log plots statistical tests interrogate these deposits for thinning or thickening upward trends and the presence of normal lognormal and exponential distributions although there are challenges associated with these methods the statistical analysis of bed thickness coupled with morphological and mineralogical interpretations has the potential to be a powerful tool for characterizing and classifying sedimentary rocks on mars in particular bed thickness statistics are particularly well suited for examining changes in sediment supply and accommodation within martian sedimentary sequences

multispectral remote sensing as stratigraphic and structural tool wind river basin and big horn basin areas wyoming stratigraphic and structural analyses of the wind river basin and big horn basin areas of central wyoming are in progress one result has been the development of an approach to stratigraphic and structural analysis that uses photogeologic and spectral interpretation of multispectral image data to characterize the attitude thickness and lithology of strata new multispectral systems that have only been available since 1982 are used with topographic data to map upper paleozoic and mesozoic strata exposed on the southern margin of the bighorn mountains landsat acquired thematic mapper tm data together with topographic data are used to map lithologic contacts measure dip and strike and develop a stratigraphic column that is correlated with conventional surface and subsurface sections aircraft acquired airborne imaging spectrometer ais and thermal infrared multispectral scanner tims data add mineralogic information to the tm column including the stratigraphic distribution of quartz calcite dolomite smectite and gypsum results illustrate an approach that has general applicability in other geologic investigations that could benefit from remotely acquired information about areal variations in attitude sequence thickness and lithology of strata exposed at the earth s surface application of our methods elsewhere is limited primarily by availability of multispectral and topographic data and quality of bedrock exposures

an analysis of sinuous ridges in the southern argyre planitia mars using hirise and ctx images and mola data 1 a suite of sinuous ridges with branching and braided morphologies forms an anastomosing network in southern argyre planitia mars several modes of origin have been proposed for the argyre ridges imagery from the high resolution imaging science experiment hirise and context camera ctx aboard mars reconnaissance orbiter mro and mars orbiter laser altimeter mola topographic data sets from mars global surveyor mgs are used to constrain processes involved in formation of the argyre ridges we find the characteristics of the ridges and associated layered deposits consistent with glaciofluvial lacustrine processes and conclude that the ridges are most likely eskers in particular variations in ridge height appear to be related to the surrounding surface slope ridge height increases with descending slopes and decreases with ascending slopes this characteristic is observed in terrestrial eskers and is related to subice flow processes the nature of some eroding beds in the ridges suggests induration if the argyre ridges are indeed eskers the southern argyre basin was once covered by the margin of a large thick stagnating or retreating ice deposit that extended for hundreds of kilometers or more during ridge formation water flowed on top within or beneath the ice deposit the continuity and preservation of the ridges suggests that flow was primarily at the base of the ice the dimensions up to hundreds of meters tall and several kilometers wide aspect ratio and extent hundreds of kilometers of the ridges as well as preliminary calculations of discharge suggest that a significant amount of water was available

morphology stratigraphy and mineralogical composition of a layered formation covering the plateaus around valles marineris mars implications for its geological history an extensive layered formation covers the high plateaus around valles marineris mapping based on hirise ctx and hrsc images reveals these layered deposits lds crop out north of tithonium chasma south of ius chasma around west candor chasma and southwest of juventae chasma and ganges chasma the estimated area covered by lds is not vert similar42 300 km2 they consist of a series of alternating light and dark beds a 100 m in total thickness that is covered by a dark unconsolidated mantle possibly resulting from their erosion their stratigraphic relationships with the plateaus and the valles marineris chasmata indicate that the lds were deposited during the early to late hesperian and possibly later depending on the region before the end of the backwasting of the walls near juventae chasma and probably before louros valles sapping near ius chasma their large spatial coverage and their location mainly on highly elevated plateaus lead us to conclude that lds correspond to airfall dust and or volcanic ash the surface of lds is characterized by various morphological features including lobate ejecta and pedestal craters polygonal fractures valleys and sinuous ridges and a pitted surface which are all consistent with liquid water and or water ice filling the pores of lds lds were episodically eroded by fluvial processes and were possibly modified by sublimation processes considering that lds correspond to dust and or ash possibly mixed with ice particles in the past lds may be compared to dissected mantle terrains currently observed in mid to high latitudes on mars which correspond to a mantle of mixed dust and ice that is partially or totally dissected by sublimation the analysis of crism and omega hyperspectral data indicates that the basal layer of lds near ganges chasma exhibits spectra with absorption bands at not vert similar1 4 m and not vert similar1 9 m and a large deep band between not vert similar2 21 and not vert similar2 26 m that are consistent with previous spectral analysis in other regions of lds we interpret these spectral characteristics as an enrichment of lds in opaline silica or by al phyllosilicate rich layers being overlain by hydroxylated ferric sulfate rich layers these alteration minerals are consistent with the aqueous alteration of lds at low temperatures

a lake in uzboi vallis and implications for late noachian early hesperian climate on mars abstract uzboi vallis centered at 28 s 323 e is 400 km long and comprises the southernmost segment of the northward draining uzboi ladon morava ulm meso scale outflow system that emerges from argyre basin bond and holden craters blocked the valley to the south and north respectively forming a late noachian to hesperian paleolake basin that exceeded 4000 km 3 limited crism data suggest lake deposits in uzboi and underlying basin floor incorporate relatively more mg clays and more fe clays respectively the short lived lake overflowed and breached holden crater s rim at an elevation of 350 m and rapidly drained into the crater fan deltas in holden extend 25 km from the breach and incorporate meter sized blocks and longitudinal grooves along the uzboi basin floor are hundreds of meters long and average 60 m wide suggesting high discharge drainage of the lake precipitation derived runoff rather than regional groundwater or overflow from argyre dominated contributions to the uzboi lake although the failure of most tributaries to respond to a lowering of base level indicates their incision largely ended when the lake drained the uzboi lake may have coincided with alluvial and or lacustrine activity in holden eberswalde and other craters in southern margaritifer terra where fluvial lacustrine activity may have required widespread synoptic precipitation rain or snow perhaps associated with an ephemeral global hydrologic system during the late noachian into the hesperian on mars

first high resolution stratigraphic column of the martian north polar layered deposits 1 this study achieves the first high spatial resolution layer scale measured stratigraphic column of the martian north polar layered deposits using a 1m posting dem the marker beds found throughout the upper north polar layered deposits range in thickness from 1 6 m 16 0 m 1 4 m and 6 of 13 marker beds are separated by 25 35 m thin layer sets have average layer separations of 1 6 m these layer separations may account for the spectral power peaks found in previous brightness profile analyses marker bed layer thicknesses show a weak trend of decreasing thickness with depth that we interpret to potentially be the result of a decreased accumulation rate in the past for those layers however the stratigraphic column reveals that a simple rhythmic or bundled layer sequence is not immediately apparent throughout the column implying that the relationship between polar layer formation and cyclic climate forcing is quite complex

pyroclastic activity at home plate in gusev crater mars home plate is a layered plateau in gusev crater on mars it is composed of clastic rocks of moderately altered alkali basalt composition enriched in some highly volatile elements a coarse grained lower unit lies under a finer grained upper unit textural observations indicate that the lower strata were emplaced in an explosive event and geochemical considerations favor an explosive volcanic origin over an impact origin the lower unit likely represents accumulation of pyroclastic materials whereas the upper unit may represent eolian reworking of the same pyroclastic materials

north polar cap of mars polar layered deposit characterization and identification of a fundamental climate signal of the cap 6 10 5 km 2 in the 13 images analyzed to date 3 assessment of geometric relationships shows that layers are not horizontal but rather have an apparent dip of approximately 0 5 degrees we interpret these results as follows 1 the fundamental 30 m signal is interpreted as a climate signal that may correspond to a 51 kyr insolation cycle 2 the lateral correlation and broad distribution of these layer sequences strongly imply that layer accumulation processes are widespread across the cap rather than confined within a single trough or region 3 local to regional variability in individual layer thicknesses and thus accumulation and sublimation rates is typically less than a factor of 2 5 providing the ability to study regional trends but often making it difficult to correlate visually the vertical sequences in individual cores finally initial examination of layers located deeper in the stratigraphic sequence within the north polar cap than the 300 m thick zone 1 provides evidence for a unit less than 100 m thick zone 2 in which the fundamental 30 m sequence is not detected we interpret this as a deposit having formed during a recent high obliquity phase of mars during which time polar volatiles underwent mobilization and were transport equatorward leaving a polar lag of dust rich material the most recent ice age 0 5 2 ma offers a plausible candidate for this period of ice cap removal and lag deposit formation an underlying zone 3 200 m contains a dominant 35 m signal and a lowermost zone 4 200 m contains multiple signals but no dominant one together these four zones represent 800 m of vertical stratigraphic section about one fourth of the total thickness of the cap these findings support earlier interpretations that orbital parameter variations could cause significant erosion and possibly complete removal of the polar caps the interpreted crater retention ages of the layered terrain are consistent with the correlations and vertical sequences described here suggesting that the polar caps wax and wane throughout geological history depending on the evolution of orbital parameters definition of the 30 m unit signal holds promise for determining 1 the detailed origin of individual layer types 2 the nature of deposition and sublimation processes and their relation to insolation geometry across the polar cap and 3 correlation with and comparison to the south polar layered terrain record

stratal thickness frequencies and the prevalence of orderedness in stratigraphic sequences assuming the existence of discernable hierarchies in the thickness and or temporal recurrence of stratal units within sedimentary sequences has become an increasingly important axiom of sequence and cyclostratigraphic studies and multiple orders of stratigraphic cyclicity are now commonly associated with inferred durations and magnitudes of rhythmic variation in global sea level beyond the desire to establish an informal nomenclature relating stratigraphic thickness to periodicity of eustatic change an assumption of stratigraphic orderedness also supports the inference that groups of sedimentary units with distinct modal dimensions in fact do occur with some generally distinct frequency in stratigraphic sequences in contrast to such perceived patterns of stratigraphic order many groupings of sedimentary units exhibit lognormal frequency distributions wherein most of the population has an exponentially increasing frequency of occurrence with linearly decreasing class size such thickness distributions

mineralogy microtexture and composition of shock induced melt pockets in the los angeles basaltic shergottite analytical electron microscopy of shock features in the basaltic shergottite los angeles stone 1 reveals 1 shock recorded in the bulk sample and 2 localized pressure and temperature excursions that have generated melt pockets up to 4 mm in diameter bulk shock effects include microfaulting offsets 1 200 mm mosaicism deformed exsolution lamellae and planar fracturing in pyroxene undulose extinction in whitlockite mechanical twinning in titanomagnetite and ilmenite and the transformation of plagioclase to maskelynite 4 remnant reduced birefringence the pressure estimates for bulk shock are 35 40 gpa localized shock excursions have generated three types of discrete melt zones 0 07 1 3 mm to 3 0 3 5 mm apparent diameter possessing glassy to microcrystalline groundmasses these melt pockets are differentiated on the basis of size clast volume and degree of crystallization and vesiculation melt veins and melt dikelets emanate from the melt pockets up to 3 mm into the host rock but do not necessarily connect with other melt pockets the melt pockets were generated by pressure temperature excursions of 60 80 gpa and 1600 2000 c resulting in discrete melting of adjacent host rock minerals at grain boundary margins concentric zoning in the margins of clinopyroxenes coincides with a progressive reduction in birefringence as melt pockets are approached this suggests that the shock excursions were focused as point sources in the wake of the shock front that induced bulk damage

poisson processes of carbonate accumulation on paleozoic and holocene platforms abstract cambro ordovician carbonate lithofacies units in the elbrook and conococheague formations exposed at wytheville virginia as well as those in many other phanerozoic peritidal sequences exhibit exponential thickness frequency distributions that is occurrence frequency decreases exponentially with linear increase in unit thickness such distributions are characteristic of waiting times between independent poisson events this relative frequency of spaces of different size between horizons of lithologic change is what one would expect if the horizons were distributed randomly throughout carbonate successions abundances of different lithologies both as net stratigraphic thickness and as number of occurrences also decreases exponentially among successively rare sediment types with each lithology being about 60 as plentiful as the next more abundant rock type relations between net thickness and number of occurrences for each facies define a linear trend coincident with a mean thickness for all wytheville units of 0 48 m a relation indicating that thickness distribution is independent of facies type similar relations are apparent for the horizontal extent of carbonate sediment bodies from the holocene florida bahama platform areal extents of individual facies units lithotopes are described by a frequency distribution in agreement with that anticipated for a population of equidimensional facies elements whose diameter distribution follows an exponential frequency distribution although regional gradients in sediment texture and composition are also apparent along most transects from platform margin to interior such frequency distributions indicate that lateral extents of individual sediment reflect a largely stochastic distribution of facies boundaries across this holocene surface lithotope abundances also yield trends of exponentially decreasing dominance among successively subordinate facies with each being about 70 as extensive the next more abundant sediment type relations between areas and abundances for all lithotopes define a covariant trend corresponding to a mean area of 2 2 103 km2 for all florida bahamas lithotopes we consider several numerical models of stochastic carbonate accumulation although not demonstrably unique scenarios incorporating the sequential superposition of randomly placed coniform lithotopes result in thickness and area frequency distributions that are the same as those observed in ancient and modern platform deposits such simulations of poisson processes of sediment accumulation are in general agreement with stochastic models of lithologic heterogeneity that have been more widely applied to petroleum reservoirs and groundwater aquifers to the as yet unknown degree that peritidal lithofacies area and thickness are correlated data from paleozoic and holocene platforms suggest that carbonate units should exhibit length height ratios of approximately 105 given the decimeter scale over which facies are designated in most paleozoic peritidal successions these relations predict mean lateral extents on the order of several tens of kilometers a value in general agreement with the few data that exist on spatial continuities of peritidal lithotopes in paleozoic carbonate sequences

detailed stratigraphy and bed thickness of the mars north and south polar layered deposits the mars polar layered deposits pld likely hold an extensive record of recent climate during a period of high amplitude orbit and obliquity cycles previous work has detected limited evidence for orbital signatures within pld stratigraphy but data from the high resolution imaging science experiment hirise permit renewed analysis of pld stratigraphy at sub meter scale topography derived from hirise images using stereogrammetry resolves beds previously detectable only as alternating light and dark bands in visible images we utilize these data to measure the thickness of individual beds within the pld corrected for non horizontal bed orientation stratigraphic columns and bed thickness profiles are presented for two sites within the npld and show several sets of finely bedded units 1 2 m thick isolated marker beds 3 4 m thick and undifferentiated sections bed thickness measurements for three sites within the spld exhibit only one bed type based on albedo and morphology and bed thicknesses have a larger mean and variance compared to measurements for the npld power spectra of brightness and slope derived along the measured stratigraphic sections confirm the regularity of npld fine bed thickness and the lack of a dominant spld bed thickness the regularity of fine bed thickness of the npld is consistent with quasiperiodic bed formation albeit with unknown temporal period the spld thickness measurements show no such regularity

stratal order in peritidal carbonate sequences abstract speculation on the depositional origins and geological significance of meter scale cycles in peritidal carbonates is becoming an increasingly prominent facet of sequence stratigraphic theory the understanding of which bears directly on their appropriateness as chronostratigraphic entities as well as their usefulness as records of periodic extrabasinal forcing during sediment accumulation in spite of the generally wide acceptance of the stratigraphic importance and interpretational significance of meter scale parasequences little has been done to quantitatively document the stratigraphic nature of regularly recurring lithologic associations or to verify the predominance of such cyclicity in shallow water limestone dolostone sequences in order to determine the statistical extents and stratigraphic scales of stratal order in such sequences we have examined several long sections of peritidal carbonate both with respect to the presence or absence of markovian lithologic transitions and with respect to the upward shallowing character of lithofacies associations in contrast to common wisdom these measures of stratal order suggest that lithologic manifestation of meter scale cyclicity is relatively uncommon all of the several sequences deemed cyclic via qualitative inspection in fact contain relatively few intervals of demonstrable lithologic order and even fewer exhibit any tendency for contained units to shallow upsection in reality most parts of most shallow water carbonate sequences exhibit little more str tal order than would be apparent in random sequences of peritidal lithologies on the basis of these considerations we suggest that discrimination of meter scale cyclicity in epicratonic carbonates is perhaps more perceptional artifact than stratigraphic reality imminent and future efforts intended to fruitfully evaluate the importance of intrabasinal versus extrabasinal processes of sedimentation in shallow low latitude settings should perhaps eschew more generic perceptions of periodic paleoclimatic forcing in favor of a less regimented view toward the importance of stochastic processes of carbonate accumulation

thin skinned deformation of sedimentary rocks in valles marineris mars deformation of sedimentary rocks is widespread within valles marineris characterized by both plastic and brittle deformation identified in candor melas and ius chasmata we identified four deformation styles using hirise and ctx images kilometer scale convolute folds detached slabs folded strata and pull apart structures convolute folds are detached rounded slabs of material with alternating dark and light toned strata and a fold wavelength of about 1 km the detached slabs are isolated rounded blocks of material but they exhibit only highly localized evidence of stratification folded strata are composed of continuously folded layers that are not detached pull apart structures are composed of stratified rock that has broken off into small irregularly shaped pieces showing evidence of brittle deformation some areas exhibit multiple styles of deformation and grade from one type of deformation into another the deformed rocks are observed over thousands of kilometers are limited to discrete stratigraphic intervals and occur over a wide range in elevations all deformation styles appear to be of likely thin skinned origin crism reflectance spectra show that some of the deformed sediments contain a component of monohydrated and polyhydrated sulfates several mechanisms could be responsible for the deformation of sedimentary rocks in valles marineris such as subaerial or subaqueous gravitational slumping or sliding and soft sediment deformation where the latter could include impact induced or seismically induced liquefaction these mechanisms are evaluated based on their expected pattern scale and areal extent of deformation deformation produced from slow subaerial or subaqueous landsliding and liquefaction is consistent with the deformation observed in valles marineris

emplacement of the youngest flood lava on mars a short turbulent story abstract recently acquired data from the high resolution imaging science experiment hirise context ctx imager and compact reconnaissance imaging spectrometer for mars crism onboard the mars reconnaissance orbiter mro spacecraft were used to investigate the emplacement of the youngest flood lava flow on mars careful mapping finds that the athabasca valles flood lava is the product of a single eruption and it covers 250 000 km 2 of western elysium planitia with an estimated 5000 7500 km 3 of mafic or ultramafic lava calculations utilizing topographic data enhanced with mro observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks this is the first well documented example of a turbulently emplaced flood lava anywhere in the solar system however mro data suggest that this same process may have operated in a number of martian channel systems the magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision

an effect of seiche on groundwater seepage rate into lake biwa japan numerical analyses of seiche and continuous measurements of water level and groundwater seepage rates into lake biwa japan were made to evaluate interactions between surface and subsurface waters an automatic seepage meter was used to obtain continuous groundwater seepage rates analyses of the fluctuations of seepage rate and water level in the lake were done using the fast fourier transform method the finite element method was used for analysis of the seiche in the lake dominant periods of fluctuations of the groundwater seepage rate into lake biwa agree well with those of fluctuations of water levels in the lake the dominant fluctuations of the groundwater seepage rate are caused by the seiche in lake biwa

light toned strata and inverted channels adjacent to juventae and ganges chasmata mars 1 light toned layered deposits on the plains adjacent to juventae and ganges chasmata have been identified and analyzed with several instruments onboard the mars reconnaissance orbiter including hirise ctx and crism beds exhibit variations in brightness color polygonal fracturing and erosional properties that are not seen in light toned layered deposits within the chasmata at both juventae and ganges the light toned layered deposits along the plains have associated features we interpret as fluvial including sinuous ridges inverted channels that exhibit light toned layering and an extensive valley system for the ganges deposit the strong correlation between the inverted channels and light toned layered deposits suggests an association with fluvial lacustrine processes although pyroclastic and eolian activity may also be involved in their emplacement the identification of potential fluvial lacustrine layered deposits and associated valley networks suggests surface water flow in the valles marineris region that occurred for sustained periods during the hesperian 3 7 3 0 gyr

recent and episodic volcanic and glacial activity on mars revealed by the high resolution stereo camera the large area coverage at a resolution of 10 20 metres per pixel in colour and three dimensions with the high resolution stereo camera experiment on the european space agency mars express mission has made it possible to study the time stratigraphic relationships of volcanic and glacial structures in unprecedented detail and give insight into the geological evolution of mars here we show that calderas on five major volcanoes on mars have undergone repeated activation and resurfacing during the last 20 per cent of martian history with phases of activity as young as two million years suggesting that the volcanoes are potentially still active today glacial deposits at the base of the olympus mons escarpment show evidence for repeated phases of activity as recently as about four million years ago morphological evidence is found that snow and ice deposition on the olympus construct at elevations of more than 7 000 metres led to episodes of glacial activity at this height even now water ice protected by an insulating layer of dust may be present at high altitudes on olympus mons

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

volcanic rilles streamlined islands and the origin of outflow channels on mars 1 the widely accepted view that catastrophic flow of liquid water was the dominant process involved in formation of outflow channels on mars has as part of its foundation the assumption that the flow of lava could not have formed martian features such as streamlined islands and anastamosing channels however lunar and venusian channels believed to have formed through volcanic processes in the absence of water are indeed associated with such features additionally many lunar and venusian rilles head at topographic depressions a common characteristic of martian outflow channels lunar rilles typically lack positive relief accumulations of volcanic deposits at their mouths suggesting that contrary to previous assertions absence of such accumulations at the mouths of martian outflow channels is not incompatible with a common mode of formation consistent with an igneous origin for outflow channels and certain valley systems on mars volcanic processes can produce a wide range of landforms that are similar to those normally associated with the flow of water including channel terraces and complex channel networks the simplest interpretation of martian channels that extend from volcanic source regions onto volcanic plains is as conduits formed by the flow of lava channel formation hypotheses requiring major changes in martian atmospheric properties or repeated catastrophic flow of water from volcanic features appear needlessly exotic alongside the igneous hypothesis for channel formation in light of these points future investigations of martian outflow channels should more actively consider volcanic processes as candidate mechanisms for channel formation

opaline silica in young deposits on mars high spatial and spectral resolution reflectance data acquired by the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism instrument reveal the presence of h 2o and sioh bearing phases on the martian surface the spectra are most consistent with opaline silica and glass altered to various degrees confirming predictions based on geochernicall experiments and models that amorphous silica should be a common weathering product of the basaltic martian crust these materials are associated with hydrated fe sulfates including h 3o bearing jarosite and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the valles marineris canyon system stratigraphic relationships place the formation age of these deposits in the late hesperian or possibly the amazonian implying that aqueous alteration continued to be an important and regionally extensive process on mars during that time

scaling in turbidite deposition abstract we propose that the distribution of layer thicknesses of turbidite deposits that show minimal erosional truncation and amalgamation should obey the power law n h h b where n h is the number of layers of thickness greater than h and b 1 we support this proposal with two sets of observations one from formation microscanner images obtained in offshore wells that penetrate tertiary fore arc turbidites hiscott et al 1992 and the other from our own field measurements of turbidites in the neoproterozoic kingston peak formation deposited in a glacially influenced rift basin both sets of observations show roughly the same power law distribution above a small h cutoff otivated by the possible generality of these results and given strong geological and sedimentological contrasts between the two data sets we consider the available theoretical and experimental evidence that could support or deny these observations we tentatively conclude that the power law is generic in data sets characterized by minimal erosional truncation and amalgamation but emphasize that further study is required for a definitive statement proceeding from the assumption that the scaling law is valid for arbitrarily thin layers we derive an upper bound for b we then detail simple and plausible assumptions that provide a theoretical estimate of b we discuss possible ramifications of this analysis for the interpretation of further data

formation of mesosiderites by fragmentation and reaccretion of a large differentiated asteroid we propose that mesosiderites formed when a 200 400 km diameter asteroid with a molten core was disrupted by a 50 150 km diameter projectile to test whether impacts can excavate core iron and mix it with crustal material we used a low resolution smoothed particle hydrodynamics computer simulation for 50 300 km diameter differentiated targets we found that significant proportions of scrambled core material and hence potential mesosiderite metal material could be generated for near catastrophic impacts that reduce the target to 80 of its original diameter and about half of its original mass the proportion of scrambled core material would be about 5 vol equivalent to 10 vol of mesosiderite like material the paucity of olivine in mesosiderites and the lack of metal poor or troilite rich meteorites from the mesosiderite body probably reflect biased sampling mesosiderites may be olivine poor because mantle material was preferentially excluded from the metal rich regions of the reaccreted body molten metal globules probably crystallized around small cool fragments of crust hindering migration of metal to the core if mantle fragments were much hotter and larger than crustal fragments little metal would have crystallized around the mantle fragments allowing olivine and molten metal to separate gravitationally the rapid cooling rates of mesosiderites above 850 c can be attributed to local thermal equilibration between hot and cold ejecta very slow cooling below 400 c probably reflects the large size of the body and the excellent thermal insulation provided by the reaccreted debris we infer that our model is more plausible than an earlier model that invoked an impact at 1 km s to mix projectile metal with target silicates if large impacts cannot effectively strip mantles from asteroidal cores as we infer we should expect few large eroded asteroids to have surfaces composed purely of mantle or core material this may help to explain why relatively few olivine rich a type and metal rich asteroids m type are known some s type asteroids may be scrambled differentiated bodies

stratigraphy and paleohydrology of delta channel deposits jezero crater mars abstract the jezero crater open basin lake contains two well exposed fluvial sedimentary deposits formed early in martian history here we examine the geometry and architecture of the jezero western delta fluvial stratigraphy using high resolution orbital images and digital elevation models dems the goal of this analysis is to reconstruct the evolution of the delta and associated shoreline position the delta outcrop contains three distinct classes of fluvial stratigraphy that we interpret from oldest to youngest as 1 point bar strata deposited by repeated flood events in meandering channels 2 inverted channel filling deposits formed by avulsive distributary channels and 3 a valley that incises the deposit we use dems to quantify the geometry of the channel deposits and estimate flow depths of 7 m for the meandering channels and 2 m for the avulsive distributary channels using these estimates we employ a novel approach for assessing paleohydrology of the formative channels in relative terms this analysis indicates that the shift from meandering to avulsive distributary channels was associated with an approximately four fold decrease in the water to sediment discharge ratio we use observations of the fluvial stratigraphy and channel paleohydrology to propose a model for the evolution of the jezero western delta the delta stratigraphy records lake level rise and shoreline transgression associated with approximately continuous filling of the basin followed by outlet breaching and eventual erosion of the delta our results imply a martian surface environment during the period of delta formation that supplied sufficient surface runoff to fill the jezero basin without major drops in lake level but also with discrete flooding events at non orbital e g annual to decadal timescales

on the frequency distribution of turbidite thickness the frequency distribution of turbidite thickness records information on flow hydrodynamics initial sediment volumes and source migration and is an important component of petroleum reservoir models however the nature of this thickness distribution is currently uncertain with log normal or negative exponential frequency distributions and power law cumulative frequency distributions having been proposed by different authors a detailed analysis of the miocene marnoso arenacea formation of the italian apennines shows that turbidite bed thickness and sand interval thickness within each bed have a frequency distribution comprising the sum of a series of log normal frequency distributions these strata were deposited predominantly in a basin plain setting and bed amalgamation is relatively rare beds or sand intervals truncated by erosion were excluded from this analysis each log normal frequency distribution characterizes bed or sand interval thickness for a given basal grain size or basal bouma division measurements from the silurian aberystwyth grits in wales the cretaceous great valley sequence in california and the permian karoo basin in south africa show that this conclusion holds for sequences of disparate age and variable location the median thickness of these log normal distributions is positively correlated with basal grain size the power law exponent relating the basal grain size and median thickness is different for turbidites with a basal a or b division and those with only c d and e divisions these two types of turbidite have been termed thin bedded and thick bedded by previous workers a change in the power law exponent is proposed to be related to i a transition from viscous to inertial settling of sediment grains and ii hindered settling at high sediment concentrations the bimodal thickness distribution of thin bedded and thick bedded turbidites noted by previous workers is explained as the result of a change in the power law exponent this analysis supports the view that a and b divisions were deposited from high concentration flow components and that distinct grain size modes undergo different depositional processes summation of log normal frequency distributions for thin and thick bedded turbidites produces a cumulative frequency distribution of thickness with a segmented power law trend thus the occurrence of both log normal and segmented power law frequency distributions can be explained in a holistic fashion power law frequency distributions of turbidite thickness have previously been linked to power law distributions of earthquake magnitude or volumes of submarine slope failure the log normal distribution for a given grain size class observed in this study suggests an alternative view that turbidite thickness is determined by the multiplicative addition of several randomly distributed parameters in addition to the settling velocity of the grain sizes present

spectral reflectance and morphologic correlations in eastern terra meridiani mars the mars express observatoire pour la mineralogie l9eau les glaces et l9activite omega hyperspectral image data covering eastern terra meridiani indicate the ubiquitous presence of molecular water in etched terrain materials that disconformably overlie heavily cratered terrains and underlie the hematite bearing plains explored by the opportunity rover identification of crystalline water in kieserite mgso4 h2o is linked to materials exposed in a valley and plateau to the north of hematite bearing plains the mineralogical similarities between the etched terrain deposits examined with omega data and the layered rocks examined by opportunity imply that the ancient aqueous environments inferred from analyses of the rover data extend over regional scales

mineralogy of juventae chasma sulfates in the light toned mounds mafic minerals in the bedrock and hydrated silica and hydroxylated ferric sulfate on the plateau 1 juventae chasma contains four light toned sulfate bearing mounds denoted here as a d from west to east inside the trough mafic outcrops at the base of the mounds and in the wall rock and light toned layered deposits of opal and ferric sulfates on the plateau hyperspectral visible near infrared compact reconnaissance imaging spectrometer for mars crism spectra were used to identify monohydrated and polyhydrated sulfate phs outcrops of layered material on the bright mounds most of the monohydrated sulfate signatures closely resemble those of szomolnokite feso4 h2o characterized by a water band near 2 08 m while some areas exhibit spectral features more similar to those of kieserite mgso4 h2o with a band centered closer to 2 13 m the largest phs outcrops occur on the top of mound b and their spectral features are most consistent with ferricopiapite melanterite and starkeyite but a specific mineral cannot be uniquely identified at this time coordinated analyses of crism maps mars orbiter laser altimeter elevations and high resolution imaging science experiment images suggest that mounds a and b may have formed together and then eroded into separate mounds while mounds c and d likely formed separately mafic minerals low ca pyroxene high ca pyroxene and olivine are observed in large 2 10 km wide outcrops in the wall rock and in smaller outcrops 50 500 m across at the floor of the canyon most of the wall rock is covered by at least a thin layer of dust and does not exhibit strong features characteristic of these minerals the plateau region northwest of juventae chasma is characterized by an abundance of light toned layered deposits one region contains two spectrally unique phases exhibiting a highly stratified terraced pattern crism spectra of one unit eroded into swirling patterns with arc like ridges exhibit a narrow 2 23 m band assigned to hydroxylated ferric sulfate a thin layer of a fractured material bearing an opaline silica phase is observed at the contact between the older plateau unit and the younger hydroxylated ferric sulfate bearing light toned layered deposits hydrothermal processes may have produced an acidic environment that fostered formation of the hydrated silica and hydroxylated ferric sulfate units

martian layered fluvial deposits implications for noachian climate scenarios 1 fluvial deposits in a basin north of holden crater exhibiting a sinuous anabranching pattern are of deltaic or fan origin channel width and meander wavelength indicate persistent flow magnitudes of about 700 m3 s if these flows were produced by quasi periodic climate episodes involving typical terrestrial style precipitation the deposit required thousands to millions of years to accumulate however a scenario of deposition during a few short episodes of constant heavy precipitation resulting from large impacts cannot be excluded

surface water groundwater interaction near shallow circular lakes flow geometry in three dimensions steady flow regimes for three dimensional lake aquifer systems are studied via idealized mathematical models that are extensions of earlier simplified vertical section models of interaction between shallow lakes and underlying aquifers the present models apply to a shallow circular lake at the surface of a rectangular aquifer of finite depth yielding a truly three dimensional representation of the resulting flow system flux boundary conditions are applied at the ends of the aquifer with net vertical recharge or evapotranspiration at the water table the lake is defined by a region with constant head by determining and visualizing solutions to the discretized saturated flow equations a range of possible flow regimes is identified and their topological properties are studied tools for analyzing flow regimes are described including a method for locating and mapping three dimensional dividing surfaces within steady flow fields results show strong similarities between two and three dimensional systems including a large number of flow through recharge and discharge regimes and reverse flow cells flow lines calculated on a vertical plane through the middle of a lake resemble but are not identical to two dimensional streamlines for a range of aquifer flow and recharge conditions estimates of the widths and depths of capture and release zones for various lake aquifer geometries are asymptotic to earlier results for two dimensional systems numerical predictions are compared with analytical results for certain limiting flow regimes

origin of the structure and planform of small impact craters in fractured targets endurance crater at meridiani planum mars we present observations and models that together explain many hallmarks of the structure and growth of small impact craters forming in targets with aligned fractures endurance crater at meridiani planum on mars diameter 150 m formed in horizontally layered aeolian sandstones with a prominent set of wide orthogonal joints a structural model of endurance crater is assembled and used to estimate the transient crater planform the model is based on observations from the mars exploration rover opportunity a bedding plane orientations and layer thicknesses measured from stereo image pairs b a digital elevation model of the whole crater at 0 3 m resolution and c color image panoramas of the upper crater walls this model implies that the crater s current shape was mostly determined by highly asymmetric excavation rather than long term wind mediated erosion we show that modal azimuths of conjugate fractures in the surrounding rocks are aligned with the square component of the present day crater planform suggesting excavation was carried farther in the direction of fracture alignments this was previously observed at barringer crater in arizona and we show the same relationship also holds for tswaing crater in south africa we present models of crater growth in which excavation creates a stellate transient cavity that is concave cuspate in planform these models reproduce the lenticular crescentic layering pattern in the walls of some polygonal impact craters such as endurance and barringer craters and suggest a common origin for tear faults and some crater rays we also demonstrate a method for detailed error analysis of stereogrammetric measurements of bedding plane orientations

testing evidence of recent hydration state change in sulfates on mars the east candor interior layered deposit ild has signatures of mono and polyhydrated sulfate in alternating layers that give insight into the processes which formed these layered deposits and on the environmental conditions acting on them since then we use orbital data to explore multiple hypotheses for how these deposits formed 1 sulfate bearing ilds experience hydration changes on seasonal to a few years timescales under current mars environmental conditions 2 the deposits experience hydration under recent mars conditions but require the wetter climate of high obliquity and 3 the kieserite could be an original or diagenetic part of a complex evaporite mineral assemblage modeled climatology shows recent mars environmental conditions might pass between multiple sulfate fields however comparison of observatoire pour la mineralogie l eau les glaces et l activite omega and compact reconnaissance imaging spectrometer crism observations of the same ild do not show changes in hydration over 2 mars years low temperatures might slow the kinetics of that transition it is likely that more clement conditions during periods of high obliquity are needed to overcome mineral metastability and hydrate kieserite bearing deposits we find the alternate model that the deposit is a cyclic evaporite sequence of mono and polyhydrated sulfates also plausible but with an unexplained dearth of fe sulfates

a theoretical analysis of seepage flow of the confined groundwater into the lake bottom with a gentle slope recently in japan a new interest has been shown to the specific discharge of groundwater from the lake bottom in order to elucidate its influence on the quality and quantity of lake water using conformal mapping techniques the authors describe analytically the steady two dimensional groundwater flow in an idealized confined aquifer which extends infinitely with uniform thickness and constant inclination and is exposed to the lake bottom surface with a gentle slope the techniques enable analytical calculation of the head and stream functions of groundwater in the aquifer and also the distribution of specific discharge at lake bottom surface from the results of calculation it is found that most of the aquifer water flows into the lake through the upper part of the surface of contact between lake and aquifer this analysis may be useful in the evaluation of the role of groundwater seepage in the water balance of large lakes

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

evaluating the meaning of layer in the martian north polar layered deposits and the impact on the climate connection abstract using data from the high resolution imaging science experiment hirise aboard the mars reconnaissance orbiter we reassess the methods by which layers within the north polar layered deposits npld can be delineated and their thicknesses measured apparent brightness and morphology alone are insufficient for this task high resolution topographic data are necessary from these analyses we find that the visible appearance of layers depends to a large degree on the distribution of younger mantling deposits which in turn is partially influenced by inherent layer properties and on the shape and location of the particular outcrop this younger mantle partially obscures layer morphology and brightness and is likely a cause of the gradational contacts between individual layers at this scale high resolution images reveal that there are several layers similar in appearance to the well known marker bed discovered by malin m edgett k 2001 j geophys res 106 23429 23570 the morphology thicknesses 4 8 2 m and separation distances 5 32 2 m of these marker beds as gleaned from a high resolution stereo digital elevation model lend insight into the connection between stratigraphy and climate

dust from collisions a way to probe the composition of exo planets abstract in order to link infrared observations of dust formed during planet formation in debris disks to mid infrared spectroscopic data of planetary materials from differentiated terrestrial and asteroidal bodies we obtained absorption spectra of a representative suite of terrestrial crustal and mantle materials and of typical martian meteorites a series of debris disk spectra characterized by a strong feature in the 9 0 9 5 m range hd23514 hd15407a hd172555 and hd165014 is comparable to materials that underwent shock collision or high temperature events these are amorphous materials such as tektites sio2 glass obsidian and highly shocked shergottites as well as inclusions from mesosiderites group a a second group bd 20307 beta pictoris hd145263 id8 hd113766 hd69830 p1121 and eta corvi have strong pyroxene and olivine bands in the 9 12 m range and is very similar to ultramafic rocks e g harzburgite dunite group b this could indicate the occurrence of differentiated materials similar to those in our solar system in these other systems however mixing of projectile and target material as well as that of crustal and mantle material has to be taken into account in large scale events like hit and run and giant collisions or even large scale planetary impacts this could explain the olivine dominated dust of group b the crustal type material of group a would possibly require the stripping of upper layers by grazing style hit and run encounters or high energy events like evaporation condensation in giant collisions in tidal disruptions or the involvement of predominantly icy water bodies the resulting mineral dust would originate mainly in one of the involved planetesimals this could allow attributing the observed composition to a specific body such as e g eta corvi

statistical analysis of turbidite cycles in submarine fan successions tests for short term persistence abstract to statistically test and evaluate the significance of asymmetric upward thickening and thinning trends and other cyclic patterns in turbidite successions 28 bed by bed sections with a wide coverage in geological time tectonic settings facies characteristics and depositional environments were measured and described first 286 sandstone packets were selected from the 28 turbidite sections through statistically based segmentation then these packets were examined by three powerful correlation tests kendall s spearman s and pearson s correlation tests and four tests for randomness only 34 11 9 of the sandstone packets pass tests designed to identify asymmetry at the 10 significance level monte carlo simulation and calculation of cumulative binomial probabilities indicate that the number of asymmetric cycles identified in the original set of sandstone packets is indistinguishable from the number expected to result from random processes eighty six sandstone packets from five sections were tested for upward coarsening and fining trends forty two of these packets were from channel deposits and the rest from lobes and basin plain deposits only 25 29 of the 86 packets coarsen or fine upward however 33 50 of packets from coarse grained channel fills show asymmetric grain size trends mostly as upward fining cycles 15 of the 42 tested packets from channel deposits these upward fining trends in channel deposits are interpreted as the result of channel filling or the stacking of onlapping deposits at a channel mouth results from this study strongly suggest that asymmetric bed thickness cycles have essentially no statistical significance in turbidite successions and therefore cannot provide a key criterion for identification of sub environments in submarine fan systems it follows that models for submarine fans based on the widely publicized hypothesis of common asymmetric cycles should be reconsidered instead other criteria such as specific facies characteristics large scale geometry and degree of sand bed clustering may provide the best tools for discrimination of submarine fan sub environments in natural systems the disordered vertical arrangement of thicker and thinner beds likely results from irregular variations in flow volumes concentrations and precise pathways of turbidity currents over the short time scales represented by tens of meters of section most submarine fans are built by aggradation not progradation so that facies shifts are controlled mostly by channel switching and avulsion and not by progressive basinward or landward advance or retreat of one sub environment over another aggradation does not tend to generate asymmetric trends in bed thickness the same arguments are believed to hold for grain size trends in submarine fan packets except in the case of coarse grained channel deposits where upward fining is conspicuous

clustered streamlined forms in athabasca valles mars evidence for sediment deposition during floodwater ponding a unique clustering of layered streamlined forms in athabasca valles is hypothesized to reflect a significant hydraulic event the forms interpreted as sedimentary are attributed to extensive sediment deposition during ponding and then streamlining of this sediment behind flow obstacles during ponded water outflow these streamlined forms are analogous to those found in depositional basins and other loci of ponding in terrestrial catastrophic flood landscapes these terrestrial streamlined forms can provide the best opportunity for reconstructing the history of the terrestrial flooding likewise the streamlined forms in athabasca valles may provide the best opportunity to reconstruct the recent geologic history of this young martian outflow channel

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

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

use of fischer plots to define third order sea level curves in ordovician peritidal cyclic carbonates appalachians fischer plots in which cumulative cycle thickness corrected for linear subsidence is plotted against time were originally used in the study of triassic peritidal sequences to define short duration departures in relative sea level in the milankovitch range 104 to 105 yr however they also provide a means of assessing magnitude of third order 1 to 10 m y fluctuations in sea level which on the basis of their regional correlatability we ascribe to eustatic events

stratigraphic correlation by integrating photostratigraphy and remote sensing multispectral data an example from jurassic eocene strata northern somalia integrated analyses of aerial photographs and multispectral remote sensing images were used for stratigraphic correlation in mainly carbonate and evaporitic rocks these rocks crop out in an area of northern somalia characterized by an arid climate by the aerial photo analysis we recognized photostratigraphic logs and stratal patterns and established correlations based on the tracing of physical surfaces with chronostratigraphic significance such as photohorizons and photostratigraphic discontinuities a limited number of field sections provided the lithological interpretation of the packages of strata delineated in aerial photos by satellite multispectral landsat thematic mappertm data analysis we identified image facies that represent packages of strata with different lithological characteristics to interpret the image facies we compared the responses in the thematic mapper tm bands with the laboratory spectroscopic properties of rock samples from the study area and interpreted the absorption features by p trographic analysis the mesozoic and tertiary strata analyzed herein are part of several formations deposited on a passive margin preceding the oligocene miocene gulf of aden rifting and initial drifting following this approach a number of stratigraphic units were recognized and mapped on aerial photos and a framework of photostratigraphic correlation surfaces was delineated over significantly wide areas these surfaces approximate time surfaces and are traced both within and across the lithostratigraphic units improving existing maps this method represents a mapping tool preliminary to more detailed field work and is particularly useful in areas of difficult access

the effect of remote sensing resolution limits on aeolian sandstone measurements and the reconstruction of ancient dune fields on mars numerical experiment using the page sandstone earth the distribution of cross set thicknesses is important field collected data for reconstructing ancient aeolian dune fields from the strata they accumulated but most aeolian strata on mars must be observed with remote sensing we hypothesize that remote sensing resolution limits will affect cross set thickness measurements and the dune field reconstructions that follow here we test this hypothesis using a numerical experiment mimicking the effects of remote sensing resolution limits performed on a distribution of aeolian cross set thicknesses measured in the field from the page sandstone arizona usa page set thicknesses are exponentially distributed representing the accumulations of dry no water table dune fields in a state of net sediment bypass set thickness measurements are progressively blended into adjacent sets based on the map view distance between their upper and lower bounding surfaces on exposures with different dips this is termed the exposure distance of a cross set and in this experiment is a function of 1 set thickness 2 the dip of the outcrop surface and 3 assumptions of the number of remote sensing image pixels required to detect a set detection limit using outcrop dips from 1 to 60 and detection limits from 3 to 10 hirise pixels gently sloping surfaces 13 allow most of the page sandstone sets to be measured conserving the bypass interpretation made from the true set thicknesses at all detection limits although these results are specific to the page they can be used as a rule of thumb for future mars work

mars reconnaissance orbiter observations of light toned layered deposits and associated fluvial landforms on the plateaus adjacent to valles marineris abstract we have used data from the mars reconnaissance orbiter to study 30 80 m thick light toned layered deposits on the plateaus adjacent to valles marineris at five locations 1 south of ius chasma 2 south of western melas chasma 3 south of western candor chasma 4 west of juventae chasma and 5 west of ganges chasma the beds within these deposits have unique variations in brightness color mineralogy and erosional properties that are not typically observed in light toned layered deposits within valles marineris or many other equatorial areas on mars reflectance spectra indicate these deposits contain opaline silica and fe sulfates consistent with low temperature acidic aqueous alteration of basaltic materials we have found valley or channel systems associated with the layered deposits at all five locations and the volcanic plains adjacent to juventae ius and ganges exhibit inverted channels composed of light toned beds valleys channels and light toned layering along the walls of juventae and melas chasmata are most likely coeval to the aqueous activity that affected the adjacent plateaus and indicate some hydrological activity occurred after formation of the chasmata although the source of water and sediment remains uncertain the strong correlation between fluvial landforms and light toned layered deposits argues for sustained precipitation surface runoff and fluvial deposition occurring during the hesperian on the plateaus adjacent to valles marineris and along portions of chasmata walls

spectral analysis of the middle triassic latemar limestone abstract the middle triassic latemar limestone in the dolomites region northern italy consists of hundreds of vertically stacked meter scale platform carbonate cycles each cycle is composed of a shallow marine subtidal carbonate unit with a thin centimeter scale vadose diagenetic dolomite cap these latemar couplets are the products of repeated episodes of submergence emergence with durations estimated at 20 000 yr the couplets are arranged in upward thinning bundles of five indicating the presence of a 100 000 year modulating component we examined this high frequency cycling in the platform buildup using a variety of classical and advanced spectral analysis techniques we found si nificant evidence for the presence of a milankovitch forcing signal in this cycling we also present evidence that the adjacent coeval basinal facies the livinallongo formation exhibits a similar bundling pattern in its cm scale hemipelagic carbonate shale alternations we conclude that milankovitch forced small amplitude sea level oscillations were the most likely cause of these middle triassic carbonate rhythms

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

condensation evaporation melting and crystallization in the primitive solar nebula experimental data in the system mgo sio 2 h 2 to 1 0x10 super 9 bar and 1870 degrees c with variable oxygen fugacity

the lunar magma ocean reconciling the solidification process with lunar petrology and geochronology abstract the moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded ages of anorthositic crust range over at least 200 million years the model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine 1 the final thickness of flotation crust generated by a fractionally solidifying magma ocean 2 the timescale of crystallization before plagioclase is a stable phase 3 the timescale of solidification after the formation of the plagioclase flotation crust and 4 the post overturn lunar mantle composition and structure we find that magma oceans of as much as 1000 km depth are consistent with creating an anorthositic crust 40 to 50 km in thickness solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000 years and complete solidification would require additional ten to tens of millions of years reconciling these short model timescales with radiometric dates of crustal samples requires either a very late forming moon combined with finding older crustal ages to be incorrect or calling on tidal heating of the crust by the early earth to prolong solidification gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar mg suite of crustal rocks further we find that upon crystallization the moon likely began with an azimuthally heterogeneous gravitationally stable mantle after magma ocean cumulate overturn this result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials

variation in bed thickness in a turbidite succession dezadeash formation jurassic cretaceous yukon canada evidence of thinning upward and thickening upward cycles abstract analysis of the vertical variation in thickness of turbidites in an 883 in thick stratigraphic section of the dezadeash formation jurassic cretaceous yukon canada indicates that the turbidites are comprised of alternating sequences of thick beds and thin beds visual inspection reveals that 40 thick bedded cycles or megasequences are present fourier analysis indicates 38 cycles five different methods i e freehand signs of differences test correlation analysis least squares and moving averages used to determine the trend in bed thickness of the megasequences demonstrate that asymmetric cycles are present and most of these methods show that thickening upward trends are more common than thinning upward trends the best objective method for determining the asymmetry of megasequences appears to be correlation analysis viz pearson s spearman s and kendall s correlation coefficients and possibly the least squares method this particular section of the dezadeash formation is characterized by asymmetric cycles that are both common and statistically convincing and thickening upward sequences are more plentiful than thinning upward sequences

hirise imaging of impact megabreccia and sub meter aqueous strata in holden crater mars high resolution imaging science experiment hirise images of holden crater mars resolve impact megabreccia unconformably overlain by sediments deposited during two noachian age phases of aqueous activity a lighter toned lower unit exhibiting phyllosilicates was deposited in a long lived quiescent distal alluvial or lacustrine setting an overlying darker toned and often blocky upper unit drapes the sequence and was emplaced during later high magnitude flooding as an impounded uzboi vallis lake overtopped the crater rim the stratigraphy provides the first geologic context for phyllosilicate deposition during persistent wet and perhaps habitable conditions on early mars

constraints on the role of impact heating and melting in asteroids received 1996 august 30 accepted in revised form 1997 january 30 abstract imaging of asteroids gaspra and ida and laboratory studies of asteroidal meteorites show that im pacts undoubtedly played an important role in the histories of asteroids and resulted in shock metamorphism and the formation of breccias and melt rocks however in recent years impact has also been called upon by numerous authors as the heat source for some of the major geological processes that took place on asteroids such as global thermal metamorphism of chondrite parent bodies and a variety of melting and igneous events the latter were proposed to explain the origin of ureilites aubrites mesosiderites the eagle station pallasites acapulcoites lodranites and the iab iiicd and iie irons we considered fundamental observations from terrestrial impact craters combined with results from laboratory shock experiments and theoretical consider ations to evaluate the efficiency of impact heating and melting of asteroids studies of terrestrial impact craters and relevant shock experiments suggest that impact heating of aster oids will produce two types of impact melts 1 large scale whole rock melts total melts not partial melts at high shock pressure and 2 localized melts formed at the scale of the mineral constituents mineral specific or grain boundary melting at intermediate shock pressures the localized melts form minuscule amounts of melt that quench and solidify in sifu thus preventing them from pooling into larger melt bodies partial melting as defined in petrology has not been observed in natural and experimental shock metamor phism and is thermodynamically impossible in a shock wave induced transient compression of rocks the total impact melts produced represent a minuscule portion of the displaced rock volume of the parent crater internal differentiation by fractional crystallization is absent in impact melt sheets of craters of sizes that can be tolerated by asteroids and impact melt rocks are usually clast laden thermal metamorphism of country rocks by impact is extremely minor experimental and theoretical considerations suggest that 1 single dis ruptive impacts cannot raise the average global temperature of strength or gravity dominated asteroids by more than a few degrees 2 cumulative global heating of asteroids by multiple impacts is ineffective for asteroids less than a few hundred kilometers in diameter 3 small crater size low gravity and low impact velocity suggest that impact melt volume in single asteroidal impacts is a very small 0 014 1 fraction of the total displaced crater volume 4 total impact melt volume formed during the typical lifetime of an asteroid is a small fraction 0 001 of the volume of impact generated debris and 5 much of the impact melt generated on asteroidal targets is ejected from craters with velocities greater than escape velocity and thus not retained on the asteroid the inescapable conclusion from these observations and calculations is that impacts cannot have been the heat source for the origin of the meteorite types listed above and we must turn to processes other than impact such as decay of short lived radionuclides or electromagnetic induction during an early t tauri phase of the sun to explain heating and melting of the parent bodies of these meteorites

hydrogen isotope analyses of alteration phases in the nakhlite martian meteorites abstract secondary alteration phases such as carbonates smectite clays and fe oxides are found within the martian meteorites if these meteorites were seen to fall the assumption can be reasonably made that the secondary phases have a martian origin however for martian meteorite finds this is not the case deuterium hydrogen d h ratio analysis can be used to distinguish between terrestrial and martian secondary alteration phases the martian atmosphere is currently five times enriched in deuterium compared to terrestrial seawater producing a deuterium enrichment in the martian alteration phases large enough to be detected with modern ion microprobe techniques we aimed to measure the d h ratio of the iddingsite like alteration veins in the nakhlite martian meteorites nakhla mil 03346 mil 090030 and y 000593 to help confirm the martian origin of this material and determine the relative amounts of terrestrial contamination in each meteorite as an observed fall nakhla is nominally uncontaminated by terrestrial alteration and shows elevated d values in its alteration veins however even the highest of these values is much below that of the martian atmosphere indicating that terrestrial contamination probably combined with fractionation effects between the martian atmosphere and the alteration material have reduced the d values of these veins the speed of hydrogen isotope exchange in the nakhlite iddingsite like alteration veins is demonstrated by the purely terrestrial d values in the veins of nakhla 110 a thin section exposed to the terrestrial atmosphere since its preparation in 1998 mineralogical heterogeneity also affects the hydrogen isotope exchange rate in these veins the wide variation in d within the veins of nakhla and y 000593 appears to be due to the heterogeneous nature of the vein material where some phases exchange hydrogen with the atmosphere at a faster rate than others

stratigraphic analysis of the distributary fan in eberswalde crater using stereo imagery the eroded remains of a fluvial distributary network in eberswalde crater are uniquely well preserved among similar structures on mars a quantitative analysis of the exposed stratigraphy has been performed to investigate the internal structure of the deposit using topographic information derived from stereo pairs of high resolution mars orbiter camera images we have for the first time quantified the orientation of individual layers exposed along the distal end of the distributary network in combination with topographic data from the mars orbiter laser altimeter we have examined plausible scenarios for the formation of this structure we find that the evidence is inconsistent with formation both as an alluvial fan and as a progradational delta instead we find that an aggradational delta best fits the observed characteristics of the channel network and the eberswalde basin as a whole we conclude that the delta likely formed not in a stable long lived lake but over the course of a small number of shorter lacustrine episodes which were not sustained at equilibrium conditions

submarine fan environment inferred from turbidite thickness distributions recent studies of turbidite bed thickness distributions have demonstrated power law as well as log normal statistical distributions the different distributions may reflect different fan processes and environments and therefore could be used as a quantitative method to help identify those environments including those devoid of sequential patterns the cumulative distributions of well known turbidite deposits spanning a range of interpreted fan subenvironments are used to illustrate the potential correlation between cumulative distribution and environments assuming that power law distributions may for some systems be the primary input signal one dimensional modelling allows semi quantitative characterization of the effects of different fan processes such as erosion and bed amalgamation environments indicative of different fan processes may be characterized based on the degree to which processes have acted as a filter to modify the assumed power law distribution systematically this model of the effect of fan processes on the power law distribution is used to help to account for bed thickness distributions observed in several field sites

the high resolution imaging science experiment hirise during mro s primary science phase psp the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro acquired 8 terapixels of data in 9137 images of mars between october 2006 and december 2008 covering 0 55 of the surface images are typically 5 6 km wide with 3 color coverage over the central 20 of the swath and their scales usually range from 25 to 60 cm pixel nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models dtms completed these data have led to some of the most significant science results new methods to measure and correct distortions due to pointing jitter facilitate topographic and change detection studies at sub meter scales recent results address noachian bedrock stratigraphy fluvially deposited fans in craters and in or near valles marineris groundwater flow in fractures and porous media quasi periodic layering in polar and non polar deposits tectonic history of west candor chasma geometry of clay rich deposits near and within mawrth vallis dynamics of flood lavas in the cerberus palus region evidence for pyroclastic deposits columnar jointing in lava flows recent collapse pits evidence for water in well preserved impact craters newly discovered large rayed craters and glacial and periglacial processes of particular interest are ongoing processes such as those driven by the wind impact cratering avalanches of dust and or frost relatively bright deposits on steep gullied slopes and the dynamic seasonal processes over polar regions hirise has acquired hundreds of large images of past present and potential future landing sites and has contributed to scientific and engineering studies of those sites warming the focal plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions

stratigraphy and structure of interior layered deposits in west candor chasma mars from high resolution stereo camera hrsc stereo imagery and derived elevations 1 interior layered deposits ilds within western candor chasma were studied by mapping lithologies measuring layer attitudes and comparing the stratigraphy of two adjacent mounds layering tends to dip in the same direction as the local topographic slope although at different angles regionally consistent attitudes do exist suggesting postdepositional block rotations the stratigraphy of two adjacent mounds correlates but the thicknesses of the units differ most layered material appears to have been deposited conformably with one late major unconformity several fault populations are identified and correlate well with regional faults associated with the formation of valles marineris the data suggest that here the ilds predate the faulting and may be early basin fill according to our model for ild formation ilds are deposited syntectonically during early basin collapse subsequent subsidence of surrounding areas accompanied by little or no sedimentation left the early deposits as individual mounds remnants of the former subbasins stratigraphic differences between mounds resulted from different subsidence rates of subbasins a significant change in depositional environment from depositional to a near cessation of deposition and the onset of a major erosion event possibly coincided with the opening of the main valles marineris troughs we further suggest that groundwater played an important role in the formation of sulfates the youngest unit identified not including surficial deposits is likely the result of a posttectonic regionally limited volcanic event if basin collapse continued following the cessation of deposition this model can also account for mounds within closed basins such as hebes