ventifacts at the pathfinder landing site about half of the rocks at the mars pathfinder ares vallis landing site appear to be ventifacts rocks abraded by windborne particles comparable resolution images taken by the imager for mars pathfinder imp camera and the viking landers show that ventifacts are more abundant at the pathfinder site the ventifacts occur in several forms including rocks with faceted edges finger like projections elongated pits flutes grooves and possible rills the trends of elongated pits flutes grooves and rills cluster at 280 330 clockwise from north and generally dip 10 30 away from their trend direction these orientations are indicative of southeast to northwest winds and differ from the trend of wind tails at the landing site the direction of local wind streaks and predictions of the global circulation model all of which indicate northeast to southwest winds the disparity between these data sets strongly suggests that local circulation patterns have changed since the abrasion of the ventifacted rocks the greater number of ventifacts at the pathfinder site compared to either of the viking sites is most easily explained as being due to a larger supply of abrading particles composed of either sand sized grains or indurated dust aggregates and higher surface roughness which should increase the momentum of saltating grains the pathfinder ventifacts may have formed shortly after the deposition of outflow channel sediments nearly 2 gry ago when a large local supply of abrading particles should have been abundant and atmospheric conditions may have been more conducive to rock abrasion from saltating grains based on how ventifacts form on earth the several ventifact forms seen at the pathfinder site and their presence on some rocks but not on others are probably due to local airflow conditions original rock shape exposure duration rock movement and to a lesser extent rock lithology the abundance of ventifacts at the pathfinder site together with other evidence of weathering indicates that unaltered rock surfaces are rare on mars

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

true polar wander driven by late stage volcanism and the distribution of paleopolar deposits on mars article i nfo the areal centroids of the youngest polar deposits on mars are offset from those of adjacent paleopolar deposits by 5 10 we test the hypothesis that the offset is the result of true polar wander tpw the motion of the solid surface with respect to the spin axis caused by a mass redistribution within or on the surface of mars in particular we consider the possibility that tpw is driven by late stage volcanism during the late hesperian to amazonian there is observational and qualitative support for this hypothesis in both north and south observed offsets lie close to a great circle 90 from tharsis as expected for polar wander after tharsis formed we calculate the magnitude and direction of tpw produced by mapped late stage lavas for a range of lithospheric thicknesses lava thicknesses eruption histories and prior polar wander events we find that if tharsis formed close to the equator the stabilizing effect of a fossil rotational bulge located close to the equator leads to predicted tpw of b2 too small to account for observed offsets if however tharsis formed far from the equator late stage tpw driven by low latitude late stage volcanism would be 6 33 similar to that inferred from the location of paleopolar deposits a volume of 4 4 1 3 10 19 kg of young erupted lava can account for the offset of the dorsa argentea formation from the present day south rotation pole this volume is consistent with prior mapping based estimates and would imply a mass release of co2 by volcanic degassing similar to that in the atmosphere at the present time the south polar layered deposits are offset from the present rotation pole in a direction that is opposite to the other paleopolar deposits this can be explained by either a sequential eruption of late stage lavas or an additional contribution from a plume beneath elysium we predict that significant volcanic activity occurred during the time interval represented by the basal unit planum boreum unconformity planum boreum postdates the promethei lingula lobe and that the north polar deposits span a substantial fraction of solar system history if the additional contribution to tpw from plumes is small then we would also predict that tharsis montes formation postdates the promethei lingula lobe of the south polar layered deposits we conclude with a list of observational tests of the tpw hypothesis

four climate regimes on a land planet with wet surface effects of obliquity change and implications for ancient mars abstract series of numerical experiments are performed using a general circulation model to gain insights on the hydrologic cycle on ancient mars since the state of the ancient mars atmosphere is not well constrained we did not try to simulate an ancient mars climate under warm and wet condition in stead we used an idealized model and tried to extract general features of the hydrologic cycle by modeling an ideal land planet that has no ocean on its surface four different climate regimes warm upright warm oblique frozen upright and frozen oblique regimes are recognized depending on the inclination of the spin axis obliquity and average surface temperature the period of active hydrologic cycle suggested from the geomorphology on mars seems to be consistent with that at the warm oblique regime which appears at warm above freezing environment with high obliquity higher than about 30 condition

reply to a discussion of evidence for resetting of fluid inclusion temperatures from quartz cements in oilfields by osborne and haszeldine 1993

petroleum geology of the cusiana field llanos basin foothills colombia cusiana field is located in the llanos foothills 150 mi 240 km northeast of bogota colombia light oil gas and condensate in cusiana occur at drilling depths that average 15 000 ft 4575 m in an asymmetric hanging wall anticlinal trap 15 mi 25 km long and 3 4 mi 5 6 km across formed during the miocene holocene deformation of the eastern cordillera top and lateral seals are provided by marine mudstones of the oligocene carbonera group and support a hydrocarbon column of over 1500 ft 460 m biomarker data from the hydrocarbons indicate a marine mudstone source interpreted to be the turonian coniacian gacheta formation over 50 of the reserves occur in upper eocene mirador formation sandstones which were deposited predominantly in estuarine environments additional deeper reservoirs include estuarine sandstones of the paleocene barco formation and the shallow marine santonian campanian upper guadalupe sandstone porosity in cusiana is relatively low good permeability is retained however because the reservoirs are pure quartz cemented quartzarenites that lack permeability reducing authigenic clays and carbonate cements core and well test analyses indicate matrix permeability not fracture permeability provides the high deliverability of cusiana wells cusiana hydrocarbon phases exist in a near miscible critical point state reservoir simulation indicates very high liquid hydrocarbon recoveries should be possible from all reservoirs by using the reinjection of produced gas to maintain reservoir pressure and to vaporize residual liquids the field contains up to 1 5 mstb footnote of hydrocarbon liquid reserves and 3 4 tcf footnote of gas

dune forming winds on titan and the influence of topography abstract numerous extended dunes on saturn s moon titan detected by the cassini radar constrain the long term pattern of surface winds we analyse the statistics of surface wind speed and direction and their spatial and temporal variability predicted by a general circulation model gcm in order to constrain surface wind predictions of this gcm by dune observations the model shows that modern winds are sufficient for saltation and dune formation at low latitudes in agreement with the presence of dunes there the best condition for the dune forming wind occurs with a threshold friction speed of 0 02 m s 1 or slightly less the equatorial region is conducive to longitudinal dunes because of a combined effect of a high sand drift potential and obtuse bimodal wind pattern oblique to the equator caused by the seasonal reversal of the hadley circulation the cross equatorial wind is steady and is characterised by a high weibull shape parameter k 4 the wind pattern at higher latitudes is more complex and gusty and neither longitudinal nor transversal dunes would be able to form putative large scale topography is found to have a profound influence on the near surface wind pattern generally mountains cause a convergence and speeding up on the flank while basins weaken the wind and cause a divergent flow longitudinal dunes can be deflected on the foot of mountains by up to 90 if xanadu is a hypothetical large mountain a wind pattern converging in xanadu that entirely disagrees with the dune observations is predicted if instead xanadu is a large basin the wind arcs clockwise north of xanadu and anti clockwise west and southwest of xanadu in agreement with the dune orientations in the vicinity of xanadu the albedo pattern has comparatively little influence on the wind field isolated mountain chains cause only local scale change in the wind pattern however the persistent surface easterlies in belet which are in conflict with the dune orientations do not disappear by any combination of large scale topography

estimation of active earth pressure against rigid retaining walls considering arching effects it is known that the distribution of active earth pressure against a translating rigid wall is not triangular but nonlinear owing to arching effects in the backfill in the present paper a new formulation is proposed for calculating the active earth pressure on a rigid retaining wall undergoing horizontal translation it takes into account the arching effects that occur in the backfill or retained soil mass in order to check the accuracy of the proposed formulation the predictions from the equation are compared with both existing full scale test results and values from existing equations the comparisons between calculated and measured values show that the proposed equations satisfactorily predict both the earth pressure distribution and the lateral active earth force on the translating wall in order to facilitate calculation of active earth pressures using the proposed equations a modified active pressure coefficient and an effective height of application of the lateral active force are also prov

mars pathfinder landing site evidence for a change in wind regime from lander and orbiter data surface features related to the wind are observed in the vicinity of the mars pathfinder mpf landing site data from the lander and in data from orbit by the viking orbiter and mars global surveyor missions features seen from the surface include wind tails associated with small rocks barchanoid duneforms ripplelike patterns and ventifact flutes cut into some rocks features seen from orbit include wind tails associated with impact craters ridges inferred to be duneforms and modified crater rims interpreted to have been eroded and mantled by windblown material the orientations of these features show two prevailing directions one is inferred to represent winds from the northeast which is consistent with strongest winds predicted by a general circulation model to occur during the martian northern winter under current conditions a second wind blowing from the ese was responsible for modifying the crater rims and cutting some of the ventifacts the two wind regimes could reflect a change in climate related to mars obliquity or some other unknown factor regardless of the cause the mpf area has been subjected to a complex pattern of winds and supply of small particles and the original surface formed by sedimentary processes from tiu and ares vallis flooding events has been modified by repeated burial and exhumation

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

potential sand sources for the dune fields in noachis terra mars 1 no sand transport pathways are visible in a study performed in noachis terra a 60 35 region in the southern highlands of mars known for its many intracrater dune fields detailed studies were performed of five areas in noachis terra using mars orbiter camera moc wide angle mosaics thermal emission imaging system themis daytime and nighttime infrared mosaics mola digital elevation and shaded relief maps and moc narrow angle images the lack of observable sand transport pathways suggests that such pathways are very short ruling out a distant source of sand consistent dune morphology and dune slipface orientations across noachis terra suggest formative winds are regional rather than local e g crater slope winds a sequence of sedimentary units was found in a pit eroded into the floor of rabe crater some of which appear to be shedding dark sand that feeds into the rabe crater dune field the visible and thermal characteristics of these units are similar to other units found across noachis terra leading to the hypothesis that a series of region wide depositional events occurred at some point in the martian past and that these deposits are currently exposed by erosion in pits on crater floors and possibly on the intercrater plains thus the dune sand sources may be both regional and local sand may be eroding from a widespread source that only outcrops locally sand bearing layers that extend across part or all of the intercrater plains of noachis terra are not likely to be dominated by loess or lacustrine deposits glacial and or volcanic origins are considered more plausible

quantitative geomorphic modeling of martian bedrock shorelines 1 multiple researchers have identified shoreline features such as scarps on mars these features occur in both paleocrater lake basins and the northern hemispheric basin here we use a simple numerical model to investigate the viability of forming martian bedrock scarps via wind wave action we use the pierson moskowitz equation modified for martian gravity to generate wave fields under a variety of wind speeds and use those wave fields to drive a terrestrial bedrock shore erosion model modified for martian conditions our results indicate that even with conservative assumptions for the key parameters of wind speed slope and substrate it is difficult to form shoreline features of sufficient magnitude to be captured by spacecraft imaging under many combinations of reasonable initial conditions no shoreline features are formed in cases where shoreline features do develop the largest equilibrium scarp height is 5 m and the shorelines require nearly 2000 model years to form in light of these results and the difficulty of maintaining warm wet climates on mars it seems unlikely that the putative shoreline features identified in images are a result of water wave erosion and alternative hypotheses such as ice cover should be entertained

recent near surface wind directions inferred from mapping sand ripples on martian dunes abstract the high resolution imaging science experiment hirise provides the capability to obtain orbital images of mars that are of sufficient resolution to record wind ripple patterns on the surfaces of sand dunes ripple patterns provide valuable insights into aeolian erosion and deposition on earth and mars in this study we develop a systematic mapping procedure to examine sand ripple orientations and create surface process maps to evaluate the recent wind flow over the dunes as well as the interplay of wind and dune shape by carefully examining the morphology of the dunes and the location of grainflow and grainfall on dune slipfaces the recent near surface wind direction short term wind can be identified results from the analysis of three dune fields on the floors of craters west of hellas basin show regional n nw se and ese wind directions in the three adjacent dune fields surface process and flow maps suggest a complex wind pattern the comparison of short term wind with dune constructing wind long term wind shows ne and ese winds may be persistent at least for the past thousands of years the results also show that the orientation of inferred wind direction on linear dunes is correlated with the crestlines which suggest that form flow interaction may take place the results of local wind flow documentation should improve martian surface wind modeling and advance our understanding of sand transport as well as the rates of sand mobility on both mars and earth

martian surface winds insensitivity to orbital changes and implications for aeolian processes aeolian features observed on the surface of mars provide insight into current and potentially past surface wind systems in some cases the features are clearly transient and related to the lifting and settling of atmospheric dust other features like dunefields yardangs and ventifacts are more persistent and likely require significant time to form in this study we analyze the observed directions of selected aeolian features with the aid of the geophysical fluid dynamics laboratory mars general circulation model gcm initially we examine bright and dark streaks which have been observed to form in association with global dust storms the ability to match these features with mars gcm wind directions provides an important validation of the model more important we are able to define best fit seasons and local times for both types of features which provide the basis for extension and modification of the veverka et al 1981 model of bright and dark dust streak formation in addition these best fit times correspond well with the dark streak wind storm model of magalhaes and young 1995 the primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long term wind indicators for example the misalignment of rock tail and ventifact orientations at the mars pathfinder landing site specifically we assess whether changes in planetary obliquity precession or global dust opacity could significantly alter patterns of surface wind directions in all cases we find the seasonal and annual average wind direction patterns to be highly invariable while changes in the dust loading hence the partitioning of solar absorption between the surface and atmosphere and in the surface latitude of maximum solstitial insolation cause the vigor of the large scale circulation to increase especially the hadley cell the spatial patterns of the surface wind orientations remain essentially unchanged in the case of perihelion during northern summer opposite of the current perihelion position the northern summer hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere taken together these results cast significant doubt on orbital explanations for surface wind changes it is thus suggested that significant changes in topography e g tharsis uplift true polar wander or climate e g the existence of a significantly thicker atmosphere or an ocean at some point in the past are more likely explanations for long term wind indicators such as the ventifact orientations at the mars pathfinder landing site

meteorology of proposed mars exploration rover landing sites 1 a descriptive study of the near surface meteorology at three of the potential mars exploration rover mer landing sites terra meridiani gusev crater and melas chasma is presented using global and mesoscale models the mesoscale model provides a detailed picture of meteorology on scales down to a few kilometers but is not well constrained by observations away from the viking and pathfinder landing sites as such care must be taken in the interpretation of the results with there being high confidence that the types of circulations predicted will indeed occur and somewhat less in the quantitative precision of the predictions and the local time phasing of predicted circulations all three landing sites are in the tropics and are affected by hadley circulation by diurnal variations due to the global thermal tide and by planetary scale topography in these particular cases from tharsis elysium and the global topographic dichotomy boundary terra meridiani is least affected by large variations in local topography mean winds at terra meridiani during mer landing would be less than 10 m s with little vertical shear however these low wind speeds result from strong mixing in the early afternoon convective boundary layer which creates its own hazard in the horizontal variation of vertical winds of up to 8 m s both upward and downward in gusev crater the topography of ma adim vallis and the crater rim generates strong diurnally reversing channeling of wind in ma adim vallis and diurnally reversing radial flow in the crater associated with thermal slope winds on the crater rim the overturning circulation in gusev crater slightly suppresses the daytime convective boundary layer melas chasma in valles marineris provides an example of strong topographic forcing of near surface circulation of particular interest is the channeling of regional scale wind toward the center of the tharsis plateau during the evening this results in a surface level jet along the canyon of over 25 m s drainage of air from the plateau and into the canyon produces vertical winds down the canyon walls in the evening of over 5 m s in contrast during the early afternoon mer landing time horizontal winds at the proposed mer landing site are relatively calm with little mean shear with height this results from the proposed site being in a region of local divergence and the action of daytime convection the nature of flow in melas chasma results in an interesting dual maximum in boundary convection and depth with the usual daytime afternoon free convective maximum being joined by a mechanically forced nighttime boundary layer of almost 2 km depth

longitudinal dunes on mars relation to current wind regimes longitudinal dunes are extremely rare on mars but constitute a substantial fraction of terrestrial desert dunes we report finding isolated examples of longitudinal dunes on mars and relate their occurrence to expected sand transport regimes terrestrial longitudinal dunes form in bimodal and multimodal transport regimes general circulation models and streak data indicate that bimodal and multimodal transport of sand should be very rare on mars thus the dearth of longitudinal dunes on mars is consistent with their apparent formation conditions on earth

downslope windstorms in the lee of ridges on mars abstract the semianalytical theory of downslope windstorms originally developed to understand large increases in surface winds in the lee of major mountain chains on earth such as the famous windstorms in boulder colorado is applied to martian conditions the focus of this work is to assess whether this theory can help us understand dark erosional wind streaks downstream of ridges on the martian surface these streaks provide a well documented example of dust raising on mars however the formation of the streaks remains a mystery because atmospheric circulation models indicate surface friction velocities far lower than those required for the initiation of eolian activity downslope windstorms result from the interaction of topographically launched finite amplitude gravity waves with a level of zero wind which vertically traps the waves when this zero wind level is at the proper height large increases in downstream surface winds up to a factor of 4 can be produced during the martian night downslope windstorms can occur in the lee of quite small ridges heights tens of meters when a level of zero wind is present in the lowest few kilometers of the atmosphere three independent models of the martian atmospheric circulation indeed show levels of zero wind in the form of wind reversals at the appropriate height and season and at the locations where the ridge related dark streaks are concentrated the strong upstream downstream difference in surface winds produced by the downslope windstorm mechanism when a suitable wind reversal is present rather than a particularly strong upstream wind is what controls the occurrence of the ridge related dark streaks downslope windstorms also appear to be potentially useful in understanding the build up of dust in the atmosphere preceding the martian global dust storms

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

global distribution composition and abundance of olivine on the surface of mars from thermal infrared data 1 we used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of fo91 fo68 fo53 fo39 fo18 and fo1 olivine samples to mars global surveyor thermal emission spectrometer tes data over low albedo regions of mars the fo91 fo68 fo53 and fo39 spectral end members were confidently identified on mars a range of compositions wider than inferred from martian meteorites small less than hundreds of square kilometers occurrences of the fo91 spectral end member are present in the rims of the argyre and hellas impact basins and may represent martian mantle materials the fo68 spectral end member is common throughout the highlands chasmata outflow channels and nili fossae region the fo53 spectral end member occurs in eastern syrtis major the nili fossae region and smooth floored craters of the highlands although less abundant than fo68 and fo53 the distribution of the fo39 spectral end member suggests that some olivine on mars is more fe rich than olivine in martian meteorites global maps of olivine show that 1 materials containing 10 20 of olivine are common in the southern highlands of mars 2 olivine is most common near the topographic dichotomy boundary and 3 olivine becomes uncommon near the poles suggesting that it may be influenced by topography and or latitude climate olivine is found in early noachian to amazonian terrains some of which may be coeval with phyllosilicate and sulfate deposits detected by omega implying that any early noachian wet period of mars climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today

the dispersal of pyroclasts from ancient explosive volcanoes on mars implications for the friable layered deposits a number of voluminous fine grained friable deposits have been mapped on mars the modes of origin for these deposits are debated the feasibility for an origin by volcanic airfall for the friable deposits is tested using a global circulation model to simulate the dispersal of pyroclasts from candidate source volcanoes near each deposit it is concluded that the medusae fossae formation and electris deposits are easily formed through volcanic processes and that the hellas deposits and south polar pitted deposits could have some contribution from volcanic sources in specific atmospheric regimes the arabia and argyre deposits are not well replicated by modeled pyroclast dispersal suggesting that these deposits were most likely emplaced by other means

sublimation waves geomorphic markers of interactions between icy planetary surfaces and winds abstract sublimation waves are periodic linear and transverse bedforms that grow by sublimation of icy substrates under turbulent winds they occur in different environments of the earth and other planets where the climate is favorable to sublimation their morphological and kinematic characteristics wavelength migration velocity characteristic time of formation depend on the environmental conditions in which they develop atmosphere viscosity wind speed sublimation rate to highlight these relations we designed a theoretical model for their formation based on models previously designed for dissolution bedforms from a linear stability analysis of the model we derived a dispersion relation and three scaling laws these are validated by comparison with measurements available for two natural terrestrial examples blue ice areas of the antarctic ice sheets and ice caves and with new measurements in a laboratory experiment they are applied to linear bedforms of hitherto unknown origin that we identified on the martian north polar cap we thus demonstrate that sublimation waves are convenient geomorphic markers to constrain surface compositions atmospheric properties climates and winds on terrestrial ice sheets and other icy planetary surfaces

arching in granular soils experimental observations of deformation mechanisms understanding soil arching is an important component of predicting soil behaviour in cases such as the progressive displacements above sinkholes and when predicting loads on buried structures wher

the martian hadley circulation comparison of viscous model predictions to observations abstract the predictions of an analytical steady thermally forced viscous model for the zonally averaged global circulation of the martian atmosphere are compared to observations of atmospheric temperatures and eolian feature directions the temperature of the winter polar atmosphere is a sensitive indicator of the value of the mean eddy diffusivity v of the atmosphere for global dust storm season the observed large warming of the atmosphere over the winter north pole during the 1977b storm as well as the distribution and azimuths of type i b dust streaks can be well reproduced if v 10 7 10 8 cm 2 sec 1 observed northeasterly surface winds at high northern latitudes could be produced by plausible fluxes of co 2 from the northern polar cap the thermal structure at southern latitudes during this storm is satisfactorily produced but a major discrepancy exists between observations and predictions of the temperature structure at middle northern latitudes by comparing these results with those from previous inviscid models of the zonal mean circulation on mars we suggest v 10 7 cm 2 sec 1 at heights above 30 km and v 10 7 cm 2 sec 1 at lower altitudes may yield a meridional circulation which produces the dynamical warming necessary to account for the observed thermal structure at 0 6 mbar at all latitudes for late southern summer when the dust content of the atmosphere has decreased to levels characteristic of much of the martian year the lack of dynamical warming of the winter pole implies v 10 6 cm 2 sec 1 in addition the predicted surface wind azimuths at this season agree well with the observed azimuths of type i d dust streaks which are observed to form at this season the observed latitudinal concentration of the streaks is not explained by the model and may require additional processes which have not been included

martian aeolian features and deposits comparisons with general circulation model results the development of a general circulation model gcm of mars atmosphere allows questions to be addressed concerning the relationships between near surface winds and the distribution of wind related features and deposits predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks yardangs and rock abundance on the surface the occurrence and orientation of bright streaks are well accounted for by the gcm results suggest that bright streaks form during southern hemisphere summer by hadley cell circulation in which dust is raised in the southern hemisphere carried northward at high altitudes then deposited in the wake of craters and other topographic obstacles by the descending hadley cell the reduction in the number of bright streaks southward from 30 n is interpreted to reflect the depletion of dust by near surface winds blowing to the south although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by gcm simulations a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season southern hemisphere summer yardang orientations do not match the gcm simulations for any season their orientation is attributed to either structural control in the rocks such as joint patterns or to a change in wind patterns from the time when the yardangs formed the global distribution of rocks on the surface is correlated well with predicted wind stress particularly during dust storm season the rocky areas are sites of strong winds suggesting that fine material is swept away by the wind leaving rocks and coarser material behind

petrogenesis of graphitic cherts in the armorican segment of the cadomian orogenic belt nw france graphitic cherts are interbedded within terrigenous sediments in the cadomian orogenic belt of end proterozoic age in the armorican massif nw france the graphitic cherts are of two types massive cherts essentially composed of quartz sio2 96 and with rare sedimentary structures laminated cherts containing up to 3ae4 al2o3 and 92 98 sio2 sedimentary structures observed in the laminated cherts are indicative of a restricted hypersaline tidal or supratidal environment the origins of both types of chert are to be found in the diagenetic processes of silification of terrigenous and mixed terrigenousevaporitic facies these processes which could be mediated by the presence of organic matter were controlled by the migration of the freshwater saltwater mixing zone during periods of relative sea level change the proposed diagenetic origin for the cherts places a number of constraints on their use in the establishment of stratigraphic correlations

a comparison of methods used to estimate the height of sand dunes on mars the collection of morphometric data on small scale landforms from other planetary bodies is difficult we assess four methods that can be used to estimate the height of aeolian dunes on mars these are 1 stereography 2 slip face length 3 profiling photoclinometry and 4 mars orbiter laser altimeter mola results show that there is good agreement among the methods when conditions are ideal however limitations inherent to each method inhibited their accurate application to all sites collectively these techniques provide data on a range of morphometric parameters some of which were not previously available for dunes on mars they include dune height width length surface area volume and longitudinal and transverse profiles the utilization of these methods will facilitate a more accurate analysis of aeolian dunes on mars and enable comparison with dunes on other planetary surfaces

new views of mars eolian activity materials and surface properties three vignettes from the mars global surveyor mars orbiter camera prior to the mars global surveyor mgs mission a very general view had emerged in which martian surface materials were seen as consisting of a mixture of bright dust dark sand and rocks the configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on mars for centuries high spatial resolution images 1 4 20 m pixel obtained by the mgs mars orbiter camera moc between september 15 1997 and july 4 1999 provide new information about the physical nature of the windblown material on the martian surface and show that the pre mgs view was much too simple in addition to bright dust and dark sand moc images show evidence of bright sediment that can be transported by saltation e g sand and dark material that can be transported in suspension e g silt new views of eolian wind streaks in daedalia planum show that part of this region thought to be mantled by bright dust based upon viking and mariner observations is instead covered by a thin veneer of bright windblown sand moc images of sinus sabaeus and parts of syrtis major two regions thought to be sandy based upon viking era observations exhibit thick mantles that are inferred to consist of fine grained sediment deposited from eolian suspension low albedo wind streaks in western arabia terra are also dark mantles and their association with eroded crater floors and megaripples dunes on these floors suggest that these particular wind streaks are deposits of silt sized material that was only briefly suspended before settling to the surface moc images also show evidence that some eolian dunes are active on mars today i e in 1998 and 1999 the evidence for activity is largely based upon wind and avalanche induced streaks superposed on or eroded into seasonal frost on high latitude dune fields moc images show that some other dunes are inactive but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust inactive dunes are best identified by superposed features such as impact craters landslide deposits and yardangs

classification of wind streaks on mars abstract a classification of martian wind streaks has been developed to assist in investigations of eolian transport and related meteorological phenomena on mars streaks can be grouped by their albedo contrast with their surroundings and by the presence of either topographic obstacles or sediment deposits at their points of origin the vast majority of wind streaks can be included in three categories 1 bright streaks with no source deposit interpreted to be formed by preferential deposition of dust from suspension 2 dark streaks with no source deposit interpreted to be formed by preferential erosion of bright dust and its removal in suspension 3 dark streaks associated with deposits of sediment interpreted to be formed by deposition of dark material moved by saltation the orientations of the different streak types are distinctive and reflect both global flow patterns and slope controlled winds the wind directions derived from streaks and the geographical distribution of the features show a strong north south asymmetry consistent with the fact that perihelion and hence maximum wind activity occurs near southern summer solstice

the sedimentology and dynamics of crater affiliated wind streaks in western arabia terra mars and patagonia argentina abstract wind streaks comprise recent aeolian deposits that have been extensively documented on venus earth and mars martian wind streaks are among the most abundant surface features on the planet and commonly extend from the downwind margins of impact craters previous studies of wind streaks emerging from crater interior deposits suggested that the mode of emplacement was primarily related to the deposition of silt sized particles as these settled from plumes we have performed geologic investigations of two wind streaks clusters one situated in western arabia terra a region in the northern hemisphere of mars and another in an analogous terrestrial site located in southern patagonia argentina where occurrences of wind streaks emanate from playas within maar craters in both these regions we have identified bedforms in sedimentary deposits on crater floors along wind facing interior crater margins and along wind streaks these observations indicate that these deposits contain sand sized particles and that sediment migration has occurred via saltation from crater interior deposits to wind streaks in arabia terra and in patagonia wind streaks initiate from crater floors that contain lithic and evaporitic sedimentary deposits suggesting that the composition of wind streak source materials has played an important role in development spatial and topographic analyses suggest that regional clustering of wind streaks in the studied regions directly correlates to the areal density of craters with interior deposits the degree of proximity of these deposits and the craters rim to floor depths in addition some but not all wind streaks within the studied clusters have propagated at comparable yearly earth years rates extensive saltation is inferred to have been involved in its propagation based on the studied terrestrial wind streak that shows ripples and dunes on its surface and the martian counterpart changes orientation toward the downslope direction where it extends into an impact crater

wind streaks on mars meteorological control of occurence and mode of formation abstract why do some craters on mars produce depositional wind streaks while others produce erosional ones there is no evidence to suggest that crater morphology or topography plays the determining role some craters can form either type of streak at different times of the martian year suggesting that the controlling factor is meteorological we propose that atmospheric stability is the determining factor a stable atmosphere should lead to blocking of the wind flow by crater rims producing wind shadows over distances comparable to those of observed bright streaks such conditions should prevail in a belt about the equator at the time of major dust storms as the atmosphere becomes more transparent following the end of the dust storms the rate of surface heating increases and the stability of the atmosphere is reduced under such conditions blocking is not expected flow over obstacles results in increased surface stress downwind conditions which encourage the formation of erosional dark streaks these ideas are shown to be consistent with the seasons at which erosional and depositional streaks are formed as well as with their distribution on the planet specifically the scheme explains why craters which have both erosional and depositional streaks occur only within a very restricted latitude belt

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

low level jets in the nasa ames mars general circulation model previous simulations of the martian atmosphere have shown how topography acts to confine the low level hadley cell flow into intense jets on the eastern flanks of tharsis and syrtis major we now conduct detailed studies of these jets using the nasa ames mars general circulation model mgcm the structure of the flow is found to be sensitive to local topography as well as large scale diabatic heating patterns consistent with terrestrial studies and mgcm studies carried out with simplified topography the summer subtropical zonal winds associated with the hadley circulation also form spatially confined intense jet cores diurnal variations in heating affect jet structure in three distinct ways global tides interact with the jets resulting in effects such as the two reinforcing each other at the summer subtropics near midday leading to high winds and surface stresses at this time slope winds act to change the character of the jets during the course of a day especially at syrtis major and the hellas basin where slopes are large vertical mixing acts to decrease low level winds during the late afternoon the sensitivity of the results to atmospheric dust loading is examined we finally show how a decrease in boundary layer height due to dust loading actually augments mid afternoon jet strength near the surface the resulting increase in maximum surface stress indicates that this is a positive feedback to dust lifting

western boundary currents in the martian atmosphere numerical simulations and observational evidence western boundary currents hereafter wbcs are an intensification of meridional fluid flow along the eastward facing flank of a boundary they occur in the earth s oceans the best known instance being the gulf stream and in the terrestrial atmosphere an example of which is the east african jet we have investigated wbcs in numerical simulations of the martian atmosphere where they occur in the presence of large longitudinal topographical gradients combined with the effect we suggest that wbcs have already been simulated by other martian atmospheric models although not identified as such the intensity of these currents is dependent on basic model parameters notably surface drag we show that for physically reasonable values of drag frictional forces dominate the wbcs behavior the requirement of zero net cross equatorial time mean mass flow produces a return flow in simulations with relatively low surface drag which acts in opposition to the tharsis wbc we also show that the intense flow associated with wbcs advects potential vorticity across the equator although the presence of strong radiative damping inhibits low level inertial instabilities that might result from this slope winds are found to have a profound effect on wbc structure especially where they have a component parallel to the jet in these cases slope winds can cancel out or reinforce wbcs depending on their direction enhanced low level winds associated with wbcs may be a factor that influences the locations of dust storm generation the high vertical shear associated with wbcs may also play a role in the maintenance and subsequent decay of these dust storms some observational evidence may exist for wbcs in the form of the alignment of bright depositional dust streaks wave clouds and in wind measurements taken during the parachute descent phase of viking lander 1 through the planetary boundary layer

aeolian processes in proctor crater on mars mesoscale modeling of dune forming winds 1 both atmospheric modeling and spacecraft imagery of mars are now of sufficient quality that the two can be used in conjunction to acquire an understanding of regional and local scale aeolian processes on mars we apply a mesoscale atmospheric model adapted for use on mars the mars mm5 to proctor crater a 150 km diameter crater in the southern highlands proctor crater contains numerous aeolian features that indicate wind direction including a large dark dune field with reversing transverse and star dunes containing three different slipface orientations small and older bright bedforms that are most likely transverse granule ripples and seasonally erased dust devil tracks results from model runs spanning a martian year with a horizontal grid spacing of 10 km predict winds aligned with two of the three dune slipfaces as well as spring and summer winds matching the dust devil track orientations the primary most prevalent dune slipface orientation corresponds to a fall and winter westerly wind created by geostrophic forces the tertiary dune slipface orientation is caused by spring and summer evening katabatic flows down the eastern rim of the crater influencing only the eastern portion of the crater floor the dunes are trapped in the crater because the tertiary winds enhanced by topography counter transport from the oppositely oriented primary winds which may have originally carried sand into the crater the dust devil tracks are caused by light spring and summer westerly winds during the early afternoon caused by planetary rotation the secondary dune slipface orientation is not predicted by model results from either the mars mm5 or the geophysical fluid dynamics laboratory mars general circulation model the reason for this is not clear and the wind circulation pattern that creates this dune slipface is not well constrained the mars mm5 model runs do not predict stresses above the saltation threshold for dune sand of the appropriate size and composition as with previous work the calculated wind velocities are too low which may be caused by too large of a grid spacing

nodular silcretes of the cypress hills formation upper eocene to middle miocene of southern saskatchewan canada siliceous nodules in the upper eocene to middle miocene cypress hills formation in southern saskatchewan formed on the distal portions of an extensive braidplain the nodules are similar to silcretes described elsewhere in the literature but their morphology and occurrence suggests that they are of a rare variety the silcretes are discrete equant to disc shaped nodules 1 3 cm thick and up to 15 cm long the silicretes form horizontal discontinous layers parallel to bedding within an unweathered profile void spaces and fractures within the nodules are lined or filled with drusy quartz the silcretes contain less than 0 07 tio2 the tio2 sio2 al2o3 and tio2 sio2 fe2o3 ratios are similar to values obtained from nodules formed in an arid to semi arid environment based on comparison with modern silcretes this interpretation is confirmed by independent sedimentological and palaeontological climatic evidence for an arid to semi arid climate throughout oligocene time in the western canadian plains

high resolution atmospheric observations by the mars odyssey thermal emission imaging system high resolution observations of atmospheric phenomena by the mars odyssey thermal emission imaging system themis during its first mapping year are presented an atmospheric campaign was implemented on the basis of previous spacecraft imaging this campaign however proved of limited success this appears to be due to the late local time of the odyssey orbit the locations of activity at 4 6 p m appear to be different from those at 2 p m ironically images targeting the surface were more useful for study of the atmosphere than those images specifically targeting atmospheric features while many previously recognized features were found novel themis observations included persistent clouds in the southern polar layered deposits dust or condensate plumes on the northern polar layered deposits dust plumes as constituent parts of local dust storms and mesospheric clouds the former two features tend to be aligned parallel and normal to polar troughs respectively suggesting a wind system directed normal to troughs and radially outward from the center of the polar deposits this is consistent with katabatic drainage of air off the polar deposits analogous to flow off antarctica the observation of dust lifting plumes at unprecedented resolution associated with local dust storms not only demonstrates the importance of mean wind stresses as opposed to dust devils in initiation of dust storms but is also seen to be morphologically identical to dust lifting in terrestrial dust storms as odyssey moves to earlier local times we suggest that the atmospheric campaign from the first mapping year be repeated

a geosynthetic reinforcement solution to prevent the formation of localized sinkholes to prevent the appearance of localized sinkholes under roads and railway lines in areas at risk a research program testing a geosynthetic reinforcement solution was carried out by a group of labor

dust streaks on mars global mapping and photometry of selected areas on mars are used to investigate the nature of bright and dark wind streaks that extend from topographic obstacles occurrence of both bright and dark streaks is strongly latitude dependent and is only weakly correlated with surface properties such as albedo and thermal inertia data on the colors albedos and phase behavior of streaks are consistent with models of bright streaks as mosaics of plains material and brighter redder dust less than 20 of the ground need be covered by the optically thick dust in the brightest parts of the streaks the amount of dust in optically thick layers could be as little as 10 3 g cm2 dark streaks can be interpreted as erosional windows in a patchy dust cover our model of dust deposition in optically thick patches is sedimentologically different from scenarios involving the deposition of ubiquitous optically thin layers it has the advantage that large amounts of dust can be deposited without affecting regional albedos

global map of eolian features on mars ten basic categories of eolian features on mars were identified from a survey of mariner 9 and viking orbiter images the ten features mapped are 1 light streaks including frost streaks 2 dark streaks 3 sand sheets or splotches 4 barchari dunes 5 transverse dunes 6 crescentic dunes 7 anomalous dunes 8 yardangs 9 wind grooves and 10 deflation pits the features were mapped in groups not as individual landforms and recorded according to their geographic positions and orientations on maps of 1 12 5 million or 1 25 million scale in the north polar region light and dark streaks indicate winds from the west and northwest frost streaks show northeast and northwest winds barchan dunes show southwest and west winds transverse dunes show east and west winds local erosional features show winds from the northwest or southeast and northeast or southwest in the middle and low northern latitudes streaks show northeast winds yardangs and deflation pits show mostly easterly and northeasterly winds in the low southern latitudes light streaks and dunes record northwest and northeast winds dark streaks record southeast winds in high southern latitudes most streaks and dunes record southeast and east winds in the south polar region light and frost streaks record southwest and northwest winds whereas dark streaks and transverse dunes show southeast winds the patterns recorded for ephemeral features conform to global conditions of strong southern spring and summer northern fall and winter wind circulation erosional features in bedrock indicate long term and perhaps ancient wind trends whereas depositional features may record relatively more recent winds wind directions indicated by yardangs pits and other erosional features seldom correspond to those shown by streaks these erosional features indicating winds of different directions than those that formed the streaks may have been carved when the effective regional winds on mars were different due to relative hemisphere insolation differences which are related to obliquity variations alternatively many yardangs and pits may be largely controlled by structure and carved along surface structural patterns or features that channeled both ancient and present day winds deflation pits in the mantled terrain may contain the best record of ancient wind trends these pits seem to have stratigraphically related orientations different stratigraphic units composing the mantle contain wind erosion pits that possibly record large scale wind direction changes because of long term changes in the obliquity of the mars

mars global digital dune database mgd 3 global dune distribution and wind pattern observations abstract the mars global digital dune database mgd 3 is complete and now extends from 90 n to 90 s latitude the recently released south pole sp portion mc 30 of mgd 3 adds 60 000 km 2 of medium to large size dark dune fields and 15 000 km 2 of sand deposits and smaller dune fields to the previously released equatorial eq 70 000 km 2 and north pole np 845 000 km 2 portions of the database bringing the global total to 975 000 km 2 nearly all np dunes are part of large sand seas while the majority of eq and sp dune fields are individual dune fields located in craters despite the differences between mars and earth their dune and dune field morphologies are strikingly similar bullseye dune fields named for their concentric ring pattern are the exception possibly owing their distinctive appearance to winds that are unique to the crater environment ground based wind directions are derived from slipface sf orientation and dune centroid azimuth dca a measure of the relative location of a dune field inside a crater sf and dca often preserve evidence of different wind directions suggesting the importance of local topographically influenced winds in general however ground based wind directions are broadly consistent with expected global patterns such as polar easterlies intriguingly between 40 s and 80 s latitude both sf and dca preserve their strongest though different dominant wind direction with transport toward the west and east for sf derived winds and toward the north and west for dca derived winds

how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones observations and experiments observations and hydrothermal experiments were used to derive new information about how clay grain coats inhibit quartz cement and preserve porosity in deeply buried sandstones samples of deeply buried porous sandstones with different types of clay coats were split in two coats removed from one of each pair of splits and grain surfaces inspected with scanning electron microscopy quartz grains in a fluvial deltaic sandstone buried to 115c had no visible authigenic quartz on grain surfaces cleaned of diagenetic chlorite coats though well developed overgrowths occurred on nearby naturally uncoated grains however in similar sandstones buried to 164c quartz grain surfaces exposed by chlorite coat removal were covered with small 5 m mainly anhedral syntaxial quartz overgrowths similar overgrowths were observed under various detrital and diagenetic clay coats in porous eolian sandstones buried to temperatures up to 215c we conclude that clay coats may retard quartz nucleation at moderate temperatures but at high temperatures many coats permit quartz nucleation and preserve porosity by limiting cement growth to investigate cement growth limitation mechanisms samples with coats removed were subjected to quartz cementing conditions in a hydrothermal reactor during experiments the naturally occurring small overgrowths on clay cleaned grains coalesced and grew suggesting that clay particles in coats inhibit cement growth by forming barriers to early overgrowth coalescence although the fraction of grain surface coverage is the primary control on cement inhibition by coats cement growth interference textures vary with coat type providing a mechanism by which coat composition may be a secondary control on inhibitory effectiveness in deeply buried sandstones quartz cement can fill significant microporosity within diagenetic chlorite coats potentially affecting mechanical and petrophysical rock properties

earth aeolian wind streaks comparison to wind data from model and stations wind streak is a collective term for a variety of aeolian features that display distinctive albedo surface patterns wind streaks have been used to map near surface winds and to estimate atmospheric circulation patterns on mars and venus however because wind streaks have been studied mostly on mars and venus much of the knowledge regarding the mechanism and time frame of their formation and their relationship to the atmospheric circulation cannot be verified this study aims to validate previous studies results by a comparison of real and modeled wind data with wind streak orientations as measured from remote sensing images orientations of earth wind streaks were statistically correlated to resultant drift direction rdd values calculated from reanalysis and wind data from 621 weather stations the results showed good agreement between wind streak orientations and reanalysis rdd r 0 78 a moderate correlation was found between the wind streak orientations and the weather station data r 0 47 a similar trend was revealed on a regional scale when the analysis was performed by continent with r ranging from 0 641 in north america to 0 922 in antarctica at sites where wind streak orientations did not correspond to the rdds i e a difference of 45 seasonal and diurnal variations in the wind flow were found to be responsible for deviation from the global pattern the study thus confirms that earth wind streaks were formed by the present wind regime and they are indeed indicative of the long term prevailing wind direction on global and regional scales

cap structures as diagnostic indicators of silcrete origin abstract cap structures within silcretes have long been used as a diagnostic indicator of pedogenic silicification however a growing number of studies of the micromorphology of non pedogenic silcretes indicate that this may no longer be appropriate this paper presents the first systematic investigation of the micro fabric geochemistry and mineralogy of cap structures in groundwater silcretes through an analysis of conglomeratic varieties puddingstones from the southern uk our results suggest that cap structures in groundwater silcretes fall within a spectrum of types related to the degree of sorting in the inter gravel host sediment at one end of this spectrum are well defined caps within otherwise well sorted overgrowth dominated silcretes these caps exhibit a grain supported fabric are cemented by micro and or cryptocrystalline silica and contain floating silt sized quartz and ti oxide grains we propose that these structures developed mainly as a result of in washing of fine sediments that were subsequently silicified at the other end of the spectrum are silcretes with caps defined by concentrations of ti oxide grains as opposed to cement type and grain size these formed mainly as a result of the remobilisation and precipitation of ti during the silicification of gravels containing interstitial clay rich sandy sediment between these end members are silcretes with cap structures formed by a combination of in washing and redistribution of fines plus some local remobilisation of ti overall the cap structures in this study exhibit a simple micromorphology lacking the alternating ti and silica rich lamellae typical of pedogenic silcrete we conclude that the presence of cap structures alone should not be considered diagnostic of pedogenic silicification unless accompanied by other indicators such as a differentiated profile and abundant complex way up structures within the micro fabric

aeolian features and processes at the mars pathfinder landing site the mars pathfinder landing site contains abundant features attributed to aeolian or wind processes these include wind tails drift deposits duneforms of various types ripplelike features and ventifacts the first clearly seen on mars many of these features are consistant with formation involving sand size particles although some features such as dunes could develop from saltating sand size aggregates of finer grains the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline rather than aggregates excluding the ventifacts the orientations of the wind related features correlate well with the orientations of bright wind steaks seen on viking orbiter images in the general area they also correlate with wind direction predictions from the nasa ames general circulation model gcm which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209

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

micromorphology and geochemistry of groundwater silcretes in the eastern south downs uk groundwater silcretes have been recognised recently as major terrestrial silicon sinks and yet their origins are poorly understood this paper aims to further understanding of the micro fabric geochemistry and formation of groundwater silcretes through detailed analyses of silcrete boulders from the south downs sussex uk in depth petrological investigations of silcrete blocks identified three varieties of silcrete across the study area saccharoid hard and pebbly conglomeratic or silcrete breccia similar to those elsewhere in england silcrete fabrics were universally simple and preserved host material structures optically continuous quartz overgrowths were the dominant cement and developed on framework grains in the absence of silt and clay sized particles finer grained silica cements occurred in isolated patches and as vein or cap like geopetal features these caps and veins formed through the silicification of illuviated clay rich material that entered the host sediment prior to or in the early stages of overgrowth formation titanium contents were related to the amount of fine grained silica and appear to reflect variations in host material chemistry subsequent to silicification the silcretes were altered by at least two phases of ferrunginisation characterised by the ingress of iron minerals and partial fabric dissolution or replacement the study reveals strong similarities in the micromorphology and geochemistry of groundwater silcretes in the study area and those developed in sandy host sediments in neighbouring parts of northwest europe variations that do occur could be explained by differences in the host sediment geological setting or tectonic history of the respective basins or sub basins suggesting that there may be a common mechanism for silcrete formation across northwest europe silcrete development appears to be related to the release of silica accompanying acid leaching of the host material or adjacent strata in the south downs this probably resulted from oxidisation of pyrite in the argillaceous and lignitic sediments overlying the host sands it is envisaged that palaeoenvironmental conditions were of limited importance for silcrete development and that there was no specific era of formation with phased development accompanying landscape evolution through the neogene into the pleistocene

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

north and south subice gas flow and venting of the seasonal caps of mars a major geomorphological agent 1 dark polygons associated with fans and spots appear during the spring on the southern seasonal cap the basal sublimation of the translucent cap and the venting of the co2 gas are responsible for their formation as previously proposed for the spots and fans dark polygons appear when dark material emerges from elongated vents whereas spots and fans form from point sources a class of erosive features etched polygons is associated with depressions a few meters to tens of meters in diameters connected to a network of radiating troughs spiders spiders are shaped by the scouring action of the confined gas converging toward point sources whereas the etched polygons result from the forced migration of the co2 gas over longer distances the minimum age of the spiders is 104 years they result from one of the most efficient erosive processes on mars displacing 2 orders of magnitude more dust per year than a typical dust storm or than all the dust devils during the same time period in the north parts of the seasonal cap are translucent between ls 355 and ls 60 and are associated with spots fans dark polygons and possibly spiders suggesting that the basal sublimation and venting of the cap triggers a subice gas and dust flow that is modifying the morphology of the surface layer however perennial features are extremely uncommon on the north regolith indicating that the conditions for their formation or conservation are not met the reduced basal energy budget of the north cap compared to the south and the shorter seasonal life time of the north translucent ice may explain the relative scarcity of features in the north the polar layered deposits contain the stratigraphic record of climatic changes and catastrophic events both polar deposits may have been locally disrupted by the seasonal subice gas flow and the stratigraphic record may have been partially lost

dike indicators in the hadriaca patera promethei terra region mars abstract the eastern hellas basin rim has been highly modified by a multitude of both volcanic and fluvial processes it is covered by a large part of the circum hellas volcanic province consisting of the volcanic plains of hesperia planum and western promethei terra as well as the two central volcanoes hadriaca and tyrrhena patera and their associated lava flows large outflow channels of dao niger harmakhis reull and teviot valles dissect the wrinkle ridged plains postdating the major volcanic events the origin of these outflow channels is still ambiguous as the mobilization mechanism for the underground volatile reservoirs has yet to be revealed due to the proximity of the volcanic structures many previous studies have suggested via models that the released ice or ground water was mobilized due to endogenic heating from magmatic activity in the region to find evidence of this we conducted a systematic search for any magmatic intrusions at 50 m pixel resolution this paper provides detailed mapping of several areas where we found features which we interpret to be dikes and shows the overall distribution of such structures in the eastern hellas rim region the hadriaca patera volcano flanks exhibit a concentric pattern of linear ridges and fractures indicative of a vast ring dike system the dikes occupy mostly the area near the summit and the hellas facing flank extending there for over 400 km away from the caldera a hadriaca radial dike swarm pattern is observed extending southwards from the volcano composed of isolated parallel linear ridge group outcrops and cut by the valles canyons an additional isolated dike ridge group exists south of lower reull valles possibly controlled by the tyrrhena patera volcano some 1300 km away all dikes within the study region are roughly late hesperian in age either predating the valles formation or being roughly concurrent with them in total 500 dike segments were identified with a combined length of 2500 km since 90 of the dikes are ridges they suggest that the entire region has undergone large scale erosion of at least a few tens of meters to expose the dikes the dike orientations were most probably controlled by the volcanic centers and possibly partly by a hellas concentric fracture pattern

long term wind erosion on mars abstract wind erosion and deposition are powerful agents of surface change on mars erosion is sensitive to the atmospheric density so feedback between orbit variations and atmospheric density can enhance the sensitivity of erosion rates to orbital parameters we use statistics derived from a 1 gyr integration of the spin axis of mars coupled with runs of the nasa ames 3 d general circulation model gcm at a variety of orbital conditions and pressures to explore this feedback we find that wind erosion in the gcm is associated with two factors baroclinic zone winds and strong cross equator solstice flows both of these factors are influenced by topography producing an asymmetry in the erosion pattern between the north and the south the erosion model averaged over 1 gyr produces potential erosion rates of 1 7 10 5 m yr 1 in the north and 1 0 10 5 m yr 1 in the south which increase by an order of magnitude in an early 28 mbar atmosphere the stability of these potential erosion patterns over geological time indicates that the lowland regions of mars are continuously eroded and that wind is capable of revealing ancient sedimentary deposits or eroding substantial deposits that may have otherwise been preserved

observations of the initiation and evolution of the 2001 mars global dust storm 1 a global dust storm occurred on mars between june and october 2001 the storm began near hellas just before southern spring equinox ls 177 local storms likely forced by a combination of slope flow and ice cap thermal contrasts were observed to propagate along the northwestern rim of hellas apparently triggering the global storm cap edge storm activity for much of late southern winter was similar in 2001 to one mars year earlier however a very large storm propagated into the basin just after ls 177 subsequently the total area of storm activity in 2001 was roughly double that of the previous year for about 10 days dust lifting was limited to the hellas region as additional storms propagated into hellas activity built and extended northward into syrtis and eastward into hesperia it is not clear whether transport or spreading of lifting were of greatest importance for expansion at ls 185 the storm began to spread rapidly to the east along a line from the southern pole to the northern tropics essentially no storm propagation to the west occurred yielding strong zonal asymmetry of expansion as the dust storm reached the western edge of tharsis secondary dust lifting centers developed in daedalia and solis southeastern tharsis subsequently the storm rapidly encompassed the planet by ls 193 once fully global the syria solis daedalia lifting center appeared to dominate on the basis of cloud top morphology with hellas quiescent by ls 212 lifting could no longer be discerned thereafter dust haze appeared uniform and diffuse and decay appeared to have set in

a topographically forced asymmetry in the martian circulation and climate large seasonal and hemispheric asymmetries in the martian climate system are generally ascribed to variations in solar heating associated with orbital eccentricity as the orbital elements slowly change over a period of 10 4 years characteristics of the climate such as dustiness and the vigour of atmospheric circulation are thought to vary as should asymmetries in the climate for example the deposition of water ice at the northern versus the southern pole such orbitally driven climate change might be responsible for the observed layering in mars polar deposits by modulating deposition of dust and water ice most current theories assume that climate asymmetries completely reverse as the angular distance between equinox and perihelion changes by 180 here we describe a major climate mechanism that will not precess in this way we show that mars global north south elevation difference forces a dominant southern summer hadley circulation that is independent of perihelion timing the hadley circulation a tropical overturning cell responsible for trade winds largely controls interhemispheric transport of water and the bulk dustiness of the atmosphere the topography therefore imprints a strong handedness on climate with water ice and the active formation of polar layered deposits more likely in the north

constraints on mars recent equatorial wind regimes from layered deposits and comparison with general circulation model results aeolian modification has been a fundamental surface process on mars throughout the amazonian orientations of aeolian features such as bedforms and yardangs are controlled by the prevailing wind regime during the feature s formation therefore observation of recently formed bedform orientations provides a way to probe mars recent wind regime and constrain test general circulation models gcms we collect statistical distributions of transverse bedform and yardang azimuths at nine sites on mars and compare measured feature orientations to those predicted by using vector wind field output from the marswrf gcm we focus on layered deposits because their erodible nature makes them applicable to determination of mars modern wind regime our methods of mapping from the long term wind field to predicted feature orientations include consideration of wind stress thresholds for sand movement to occur sand flux equations and the direction of maximum gross bedform normal transport we find that all methods examined typically agree with each other to within 15 though there are some exceptions using high order wind stress weightings with multi directional annual wind fields generally use of higher wind stress thresholds produces improved matches to bedform orientations comparison of multiple yardang orientations to annually variable wind fields is accomplished by inspection of directional maxima in modelled wind vector frequency distributions yardangs match well to model predictions and sub populations in close proximity to each other are shown to match individual directional maxima in gcm output for a single site implying that topographic effects may produce very localised unidirectional wind fields unresolved by the gcm

distribution of the ices exposed near the south pole of mars using thermal emission imaging system themis temperature measurements 1 understanding the present and past water cycle on mars requires an accurate knowledge of the distribution and amount of h2o available near the surface in this article we present a map of the distribution of the surface material exposed between 87 s and 70 s in the summer e g co2 and h2o ices dust based on temperature measurements made by thermal emission imaging system themis our compositional map 100 m per pixel is in good agreement with spectral mapping returned by observatoire pour la mineralogie l eau la glace et l activite omega and compact reconnaissance imaging spectrometer for mars crism exposed water ice covers a total surface area of approximately 40 000 km2 a large fraction of the water ice is exposed at the periphery of the co2 cap an approximately 25 000 km2 large patch centered at 83 5 s and 345 e is discovered and represents the largest exposure of water ice in the southern hemisphere it is not located on the south polar layered deposits but on the surrounding mantled terrains themis vis moc and hirise images indicate that the surface roughness of exposed water ice terrains is typically lower than that of the surrounding dust polygonal patterns are observed on the water ice but not exclusively there is a strong correlation between the surface albedo the composition of the exposed material and the timing of the initial seasonal co2 frost deposition and final removal these exposed water ice outcrops are not stable in the present environment and lose a vertical layer of tens to hundreds of micrometer a year to the atmosphere the spike of water vapor above the south pole during the southern summer occurs while the water ice is still covered by a layer of seasonal co2 frost indicating that the sublimation of the exposed water ice is not the main contributor of vapor for the southern atmosphere as water ice is not stable it may indicate the past location of part of the co2 perennial cap that has been eroded

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

groundwater geochemistry and composition of hardpans in southwestern australian regolith the mineralogy and geochemistry of pedogenic and groundwater silcretes and ferricretes and associated groundwater geochemistry were investigated for deeply weathered highly kaolinised lateritic regolith in southwesternaustralia the silcretes and ferricretes form subsurface hardpans and impede movement of the highly saline acidic shallow groundwaters in lower valleys of the subdued ancient landscape these valleys are associated with the discharge of groundwater and the formation of saline seeps which host a variety of secondary minerals including amorphous silica opal ct goethite feooh hematite fe 2 o 3 akaganeite feooh jarosite kfe 3 so 4 2 oh 6 barite baso 4 gypsum caso 4 2h 2 o and halite nacl deep groundwater silcretes are commonly composed of silicified in situ lateritic pallid zone materials and saprolite that have developed from granitic rocks the matrix consists of amorphous silica diffused through a porous kaolin groundmass these materials were initially highly porous but the voids are now mostly occupied by amorphous silica and secondary anatase acid groundwater weathering has resulted in the dissolution of most primary silicates including feldspars and micas which has greatly elevated the concentration of dissolved silicon in groundwater isovolumetric weathering of feldspar initially produced highly porous assemblages of fine grained kaolin and minor halloysite which now contain high concentrations of amorphous silica up to about 50 wt occupying most of the pores alkali feldspars alter to kaolin pseudomorphs that are much more porous than vermicular kaolin pseudomorphs replacing mica minerals consequently these pseudomorphs contain much less amorphous silica geochemical modeling using phreeqc enabled prediction of the saturation state of minerals and indicated the dissolution and precipitation reactions occurring in the regolith groundwater environment acid moderately saline groundwaters were in near equilibrium with respect to amorphous silica while near neutral ph saline groundwaters corresponded to undersaturated conditions for extremely acid groundwaters ph 3 5 phreeqc predicted dissolution of kaolin goethite and hematite which is reflected in the elevated concentrations of iron up to 169 mg l and aluminium up to 389 mg l in the groundwater this study is important for the understanding of how groundwater geochemistry influences the precipitation of cementing minerals that form various hardpans in the southwest australian landscape

ground water silicification and leaching in sands example of the fontainebleau sand oligocene in the paris basin in the fontainebleau sand oligocene superposed lenses of quartzite are restricted to outcrops and structurally low zones of the formation the quartzite lenses result from a silicification process controlled by water table levels during the recent geomorphologic evolution of the landscape the quartzite lenses pinch out rapidly under the limestone capped plateaus and are related to the development of a bleached sand profile above the water table the sand is bleached and the former quartzite lenses are corroded along their margins moreover flint pebbles are dissolved and primary smectite and illite are weathered to kaolinite dissolved silica can thus reach supersaturated levels allowing quartz precipitation quartz grains are overgrown at the base of the profile in zones of ground water outflow related to spring lines the adjustment of the water table during the landscape incision led to formation of quartzite lenses at deeper levels this silicification process has no climatic significance but is dependent on the stability of the landscape and on its progressive dissection the rate of quartz cementation indicated by geomorphologic considerations is consistent with hydraulic and geochemical calculations it appears to be very rapid approximately 30 000 yr for a quartzite lens

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

influence of early diagenesis on reservoir quality of rotliegende sandstones northern netherlands reservoir quality of rotliegende sandstones lower permian in the northern netherlands was significantly affected by early diagenetic processes that are related to sedimentary facies in marginal desert playa lake environments in the past burial related products and processes have received more attention than early diagenetic processes neglecting the effects that early diagenesis can have on reservoir quality and well productivity of rotliegende sandstones shallow groundwater related diagenesis is a major factor affecting rotliegende reservoir sandstones the precipitation of the main porosity occluding cements dolomite anhydrite and quartz occurred early in the diagenetic history oxygen isotopes of dolomite d18o 18 4 to 23 4 smow suggest that meteoric water has played a major role throughout the diagenetic history and that precipitation of these cements occurred at low temperatures 80 c the strontium isotopes of dolomite cements 87sr 86sr 0 70935 0 71387 and the sulfur isotopes of anhydrite cements d34s 6 7 to 9 7 cdt rule out permian or younger seawater as a source for these cements and are consistent with formation from meteoric water within a continental basin an early diagenetic origin of the cements is also suggested by the fact that the majority of sandstone samples have lost more porosity due to cementation than through compaction most samples with high 20 amounts of porosity loss via cementation were affected by early dolomite and anhydrite the relative abundance of dolomite and anhydrite cements can be correlated with depositional environments wet depositional environments e g interdune and fluvial sandstones with water tables close to the surface show the highest amount of dolomite and anhydrite cements whereas dry environments with relatively deep water tables e g dune sandstones are characterized by low amounts of cements the precipitation of early diagenetic cements has strongly influenced the present day porosity patterns with depositional environments interpreted as drier showing less cements and significantly altering the porosity patterns formed during early diagenesis knowledge of the influence of sedimentology and paleogeography on the diagenetic patterns is a key element for improved understanding and prediction of reservoir quality in the rotliegende sandstones of the northern netherlands

the rock abrasion record at gale crater mars science laboratory results from bradbury landing to rocknest ventifacts rocks abraded by wind borne particles are found in gale crater mars in the eastward drive from bradbury landing to rocknest they account for about half of the float and outcrop seen by curiosity s cameras many are faceted and exhibit abrasion textures found at a range of scales from submillimeter lineations to centimeter scale facets scallops flutes and grooves the drive path geometry in the first 100 sols of the mission emphasized the identification of abrasion facets and textures formed by westerly flow this upwind direction is inconsistent with predictions based on models and the orientation of regional dunes suggesting that these ventifact features formed from very rare high speed winds the absence of active sand and evidence for deflation in the area indicates that most of the ventifacts are fossil features experiencing little abrasion today

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

unsteady saltation on mars abstract saltation is an important process on mars as it contributes to dust raising bedform dynamics and aeolian abrasion lander measurements and mesoscale meteorological models suggest that winds in the martian atmosphere rarely exceed the fluid threshold value that is necessary to aerodynamically initiate saltation a fact in stark contrast to the existence of dunes and ripples on the planet many of which are in an active state of migration in an attempt to reconcile these observations we perform an unsteady simulation with a simple turbulence model to calculate the saltation transport rate sinusoidal wind variations are imposed on the saltation layer the numerical simulations verify that gusty transport is one of the main manifestations of martian sediment transport events a formula for the saltation transport rate is reported q m u u it p where u and u it are the friction velocity and impact threshold friction velocity the power p varies in the range of 0 7 1 8 on mars and 1 5 on earth depending on the period and amplitude of the gusty inflow wind our results show that the law of martian and terrestrial transport rate are not universal and hence one should be cautious when trying to extrapolate existing terrestrial results to mars

patterns in mobility and modification of middle and high latitude southern hemisphere dunes on mars nasa mars data analysis program mdap nnx14ao96g mdap grant nnx12aj38g nnx16aj43g 123117

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

a 1 gyr climate model for mars new orbital statistics and the importance of seasonally resolved polar processes new results from a 1 gyr integration of the martian orbit are presented along with a seasonally resolved energy balance climate model employed to illuminate the gross characteristics of the long term atmospheric pressure evolution we present a new analysis of the statistical variation of the martian obliquity and precession prior to and subsequent to the formation of the tharsis uplift and explore the long term effects on the martian climate we find that seasonal polar cycles have a critical influence on the ability for the regolith to release co2 at high obliquities and find that the atmospheric co2 actually decreases at high obliquities due to the cooling effect of polar deposits at latitudes where seasonal caps form at low obliquity the formation of massive permanent polar caps depends critically on the values of the frost albedo afrost and frost emissivity frost using our model with values of afrost 0 67 and frost 0 55 matched to the nasa ames general circulation model gcm results haberle et al 1993 j geophys res 98 3093 3123 and haberle et al 2003 icarus 161 66 89 we find that permanent caps only form at low obliquities 13 suggesting that any permanent deposits on the surface of mars today may be residuals left over from a period of very low obliquity or are the result of mechanisms not represented by this model thus contrary to expectations the martian atmospheric pressure is remarkable static over time and decreases both at high and low obliquity also from our one billion year orbital model we present new results on the fraction of time mars is expected to experience periods of low obliquity and high obliquity

pleistocene cold climate groundwater silicification jbel ghassoul region missour basin morocco surficial silicifications have been long considered to be indicative of warm and dry climates here we describe various forms of supergene silicification in a miocene lacustrine sequence in the missour basin near jbel ghassoul morocco in a landscape with accentuated relief the silicification is almost exclusively limited to a 10 40 m wide zone from the edges of scarp and mesa landforms this distribution is interpreted to record the locations where groundwaters which produced the silicification discharged from a higher level palaeolandscape the main component of the silica was imported late and significantly post dates the deposition of the sediments this implies that significant volumes of silica bearing solutions flowed through these formations in response to a hydraulic gradient generated by relief silicification thus occurred only after uplift and incision of the sedimentary fill of the missour basin the zones of silicification of the jbel ghassoul sequence can be linked geomorphologically to remnants of high level pediments that have been dated in the literature to the early to middle pleistocene and interpreted to have been formed during cold climates low temperatures in outcrops near the discharge zones during cold periods are considered to be a key factor in silica precipitation from groundwaters

implications of pore microgeometry heterogeneity for the movement and chemical reactivity of co2 in carbonates abstractwe studied the heterogeneity of natural rocks with respect to their pore size distribution obtained from mercury intrusion capillary pressure micp tests at a scale about one fifth of the standard plug size 2 5 cm we investigated two fontainebleau sandstone and two limestone samples we found that at the scale of the micp tests heterogeneities are practically nonexistent still there are large differences in the capillary curves from one rock type to another also carbonate rocks unlike fontainebleau sandstone show heterogeneities at a scale smaller than the scale used in micp tests as seen by the complexity in the mercury saturation versus pressure curves we used this diversity between the capillary curves and this complexity within a single capillary curve to obtain information about the movement and chemical reactivity of co2 in carbonates the method consists of three steps first subdividing the carbonate pore system into microstructural facies each of them having a specific ra

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

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

comparison of remote sensing observations of planetary wind streaks abstract wind streaks are common aeolian features observed on terrestrial planets they were first identified on mars thus the associated terminology is based on mars related observations usually describing surface patterns with distinct albedos however terms related to reflected tones are only relevant to past knowledge for mars and not necessarily suitable for description of radar visible streaks located on venus titan or earth furthermore the sensor type used to observe wind streaks can influence the subsequent data analysis the purpose of this study was to examine the effects of sensor type on wind streak identification and interpretation six case studies featuring wind streaks on earth were performed using imaging by both radar and optical sensors the results indicate that wind streak identification is constrained to a specific combination of sensor settings appropriate for the local surface properties only half the optically visible wind streaks considered in this study were also radar visible but all the wind streaks observable in the radar images also appeared in the optical images furthermore bright and dark reflectance and backscatter are relative terms and should be used with caution these results suggest that the venusian wind streak database is most likely far from complete and that many more streaks exist

arching in granular soils limit state equilibrium one of the most critical assumptions in the application of arching theory is an accurate estimate of the coefficient of lateral stress k used to relate vertical and horizontal stresses on the ass

geologic settings of martian gullies implications for their origins 1 martian gullies are found on steep slopes of all origins on all sorts of terrains of all ages scattered across nearly all of mars gullies are observed on all manner of substrates layered massive shattered rubble with or without nearby mantling deposits gullies are most common in the southern midlatitudes but also occur in the northern hemisphere in near polar terrain on equatorial volcanoes and on northern plains most gullies in the southern hemisphere are on south facing slopes but they occur on slopes of all orientations gullies are among the youngest features on mars but locally are overlain by eolian deposits and cut by faults old or eroded gullies are rare and those found have been partially stripped from slopes leaving no rock debris behind most gully deposits contain no detectable rocks these data are inconsistent with published hypotheses of gully formation including seeps and breakouts of water or brine hydrothermal activity cryovolcanism and breakouts from liquid carbon dioxide the data are consistent with gullies being dry flows of eolian material dust and silt comparable to climax snow avalanches on earth eolian sedimentation should be correlated little with underlying geology cause of slope age of terrain type of terrain or the nature of the rocks eolian sedimentation should be correlated with wind deceleration which will cause suspended sediment to drop and areas with common gullies are those with strong wind deceleration predicted by global circulation model in such areas sediment will be deposited preferentially in the lee of obstacles for the gully rich areas of the southern midlatitudes winds blow from the nnw so that sediment is deposited on sse facing slopes i e poleward these predictions are in accord with observations