how do bedform patterns arise new views on the role of bedform interactions within a set of boundary conditions one explanation for bedform patterns is self organization in which the pattern emerges because of interactions among the bedforms themselves models remote images field studies and lab experiments have identified bedform interactions that involve whole bedforms only bedform defects or that are remote interactions between bedforms it is proposed that bedform interactions form a spectrum from constructive to regenerative in pattern development constructive interactions including merging lateral linking cannibalization and remote transfer of sediment push the system toward fewer larger more widely spaced bedforms regenerative interactions including bedform splitting defect creation and calving push the system back toward a more initial state other interactions including off center collision defect migration and bedform and defect repulsion cause pattern change but may not be strongly constructive or regenerative although bedform interactions are ubiquitous to any field of bedforms their dynamics flow field modification and impact upon measurable pattern parameters are yet poorly understood most bedform interactions span bedform types and fluids supporting the hypothesis that pattern emerges from dynamics at the bedform level in a hierarchy that includes lower levels of bedform flow and grain fluid interactions bedform interactions alone however cannot account for the rich diversity of bedform patterns in nature it is proposed that field diversity arises because of boundary conditions which are the environmental variables within which a field evolves conceptually boundary conditions modify the shape of the attractor toward which a field evolves possibly by altering the type and frequency of bedform interactions boundary conditions are broadly similar within system types but are unique for each bedform field so that no two are ever exactly alike although aeolian and fluvial systems share some types of boundary conditions flow depth is a unique boundary condition in shallow fluvial systems copyright 2009 john wiley sons ltd

failed predation in late ordovician gastropods mollusca from manitoulin island ontario canada shell repairs resulting from presumed failed predation are documented in gastropods from the late ordovician cincinnatian richmondian mid to upper kagawong submember of the georgian bay formation on manitoulin island ontario canada the bryozoan mollusc biota and associated sediments generally suggest nearshore shallow 10 m low energy lagoonal and perhaps mesotrophic to eutrophic conditions two sample sets from this unit have been studied for shell repair one of the more commonly applied estimates of shell repair frequencies involves division of the number of individuals with at least one scar by the total number of individuals in the sample the individuals with scars method using this calculation 207 specimens of lophospira trilineata ulrich and scofield yielded a shell repair frequency of 4 8 in 28 specimens of trochonemella sp the shell repair frequency was 35 7 repairs in trochonemella occur primarily in the larger size class suggesting that a size refuge was achieved by this

new models for the origin of valles marineris closed depressions current models for the formation of the abundant large closed depressions of valles marineris have serious shortcomings purely tectonic mechanisms are inconsistent with the morphology of many depressions and removal of large quantities of ground ice from the canyon walls is inconsistent with the observed strength of the walls accordingly we offer some alternatives one possibility involves decay of ice rich bodies occupying partially sediment choked ancient graben that predated the overlying cratered and ridged plains other possibilities involve the removal of massive equatorial carbonate deposits storing much of the planet s co2 inventory generated during greenhouse conditions on early mars solution by carbonic acid derived from the atmosphere analogous to terrestrial karst requires extensive recycling of the available water supply solution by various groundwater acids possibly derived from the tharsis magmas requires less water especially if only the smaller closed depressions are due to carbonate decay alternatively volume loss due to decarbonation of carbonate during early high heat flow or a later tharsis related heat pulse can produce extensive collapse especially if the carbonates have high silica content

basaltic lava flows covering active aeolian dunes in the parana basin in southern brazil features and emplacement aspects abstract burial of active aeolian dunes by lava flows can preserve the morphology of the dunes and generate diverse features related to interaction between unconsolidated sediments and lavas in the study area located in southern brazil burial of aeolian deposits by cretaceous basaltic lava flows completely preserved dunes and generate sand deformation features sand diapirs and peperite like breccia the preserved dunes are crescentic and linear at the main contact with basalts and smaller crescentic where interlayered with lavas the various feature types formed on sediment surfaces by the advance of the flows reflect the emplacement style of the lavas which are compound pahoehoe type four feature types can be recognized a type 1 features are related to the advance of sheet flows in dune interdune areas with slopes 5 b type 2 is formed where the lava flows advance in lobes and climb the stoss slope of crescentic dunes slopes 8 12 c type 3 is generated by toes that descend the face of linear dunes slopes 17 23 and d type 4 occurs when lava lobes descend the stoss slope of crescentic dunes slopes 10 15 the direction of the flows the disposition and morphology of the dunes and the ground slope are the main factors controlling formation of the features the injection of unconsolidated sand in lava lobes forms diapirs and peperite like breccias sand diapirs occur at the basal portion of lobes where the lava was more solidified peperite like breccias occur in the inner portion where lava was more plastic favoring the mingling of the components the generation of both features is related to a mechanical process the weight of the lava causes the injection of sand into the lava and the warming of the air in the pores of the sand facilitates this process the lava sediment interaction features presented here are consistent with previous reports of basalt lavas with unconsolidated arid sediments and additional new sand deformation features formed by lava breakouts and sand diapir injections are presented

morphology and composition of the surface of mars mars odyssey themis results the thermal emission imaging system themis on mars odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness implying temporal changes in the processes or environments during or after their formation kilometer scale exposures of bedrock are observed elsewhere airfall dust completely mantles the surface over thousands of square kilometers mars has compositional variations at 100 meter scales for example an exposure of olivine rich basalt in the walls of ganges chasma thermally distinct ejecta facies occur around some craters with variations associated with crater age polar observations have identified temporal patches of water frost in the north polar cap no thermal signatures associated with endogenic heat sources have been identified

mars global surveyor observations of martian fretted terrain the martian fretted terrain between latitudes 30 and 50 n and between 315 and 360 w has been reexamined in light of new mars orbiter camera moc and mars orbiter laser altimeter mola data from mars global surveyor much of the terrain in the 30 50 latitude belt in both hemispheres has a characteristic stippled or pitted texture at moc 1 5 m scale the texture appears to result from partial removal of a formerly smooth thin deposit as a result of sublimation and deflation a complex history of deposition and exhumation is indicated by remnants of a former thicker cover of layered deposits in some hollows and on some slopes particularly those facing the pole are smooth textured deposits outlined by an outward facing escarpment throughout the study area are numerous escarpments with debris flows at their base the escarpments typically have slopes in the 20 30 range at the base of the escarpment is commonly a deposit with striae oriented at right angles to the escarpment outside this deposit is the main debris apron with a surface that typically slopes 2 3 and complex surface textures suggestive of compression sublimation and deflation the presence of undeformed impact craters indicates that the debris flows are no longer forming fretted valleys contain lineated fill and are poorly graded they likely form from fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass wasting processes that formed the debris aprons slope reversals indicate that downvalley flow of the lineated fill is minor the ubiquitous presence of breaks in slope formed by mass wasting and the complex surface textures that result from mass wasting deflation and sublimation decreases the recognizability of the shorelines formerly proposed for this area

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

star and linear dunes on mars abstract a field containing 11 star and incipient star dunes occurs on mars at 8 8 s 270 9 w examples of linear dunes are found in a crater at 59 4 s 343 w while rare dune varieties that form in bi and multidirectional wind regimes are not absent from the surface of mars the occurrence of both of these dune fields offers new insight into the nature of martian wind conditions and sand supply the linear dunes appear to have formed through modification of a formerly transverse aeolian deposit suggesting a relatively recent change in local wind direction the 11 dunes in the star dune locality show a progressive change from barchan to star form as each successive dune has traveled up into a valley into a more complex wind regime the star dunes corroborate the model of n lancaster 1989 progr physical geogr 13 67 91 1989 sedimentology 36 273 289 for the formation of star dunes by projection of transverse dunes into a complex topographically influenced wind regime the star dunes have dark streaks emanating from them providing evidence that the dunes were active at or near the time the relevant image was obtained by the viking 1 orbiter in 1978 the star and linear dunes described here are located in different regions on the martian surface unlike most star and linear dunes on earth both martian examples are isolated occurrences neither is part of a major sand sea previously published mars general circulation model results suggest that the region in which the linear done field occurs should be a bimodal wind regime while the region in which the star dunes occur should be unimodal the star dunes are probably the result of localized complication of the wind regime owing to topographic confinement of the dunes local topographic influence on wind regime is also evident in the linear dune field as there are transverse dunes in close proximity to the linear dunes and their occurrence is best explained by funneling of wind through a topographic gap in the upwind crater wall

what makes a delta wave dominated river deltas low lying landforms that host high concentrations of human population and ecosystem services face a new and mostly unknown future over the coming decades and centuries even as some deltas experience decreased sediment supply from damming others will see increased sediment discharge from land use changes there are proposals to actively use riverine sediment supply to build new land and counteract delta loss we present a novel approach to understanding the morphology of deltas by quantifying the balance between river inputs and the largely overlooked ability of waves to spread sediments along the coast defining a fluvial dominance ratio river sediment input versus the potential maximum alongshore sediment transport away from the delta mouth allows a quantitative assessment of this sediment transport balance for a series of deltas on java indonesia that exhibit a large range of sediment loads but have a homogeneous drainage lithology and wave climate and for more eclectic global examples shoreline deflection increases along with this fluvial dominance ratio the fluvial dominance ratio also predicts the observed transition from cuspate wave dominated deltas to fluvially dominated deltas with protruding crenulated shorelines not only does this approach provide a more quantitative foundation for paleoenvironmental reconstructions and delta management perhaps more importantly this simple metric of fluvial dominance has a predictive application in determining potential morphology of deltas created by engineered sediment diversions

death of a sand sea an active aeolian erg systematically buried by the etendeka flood basalts of nw namibia here we report on a fossilized sand sea that was progressively engulfed by the basal etendeka flood basalts in nw namibia preserved relict aeolian landforms include transverse barchanoid dunes and isolated barchan dunes present day preferential erosion of the lava flows exhumes relict aeolian bedforms preserved in the position in which they were migrating at the time of burial c 133 ma a passive eruption style of inflated pahoehoe flows has preserved the bedforms without significant deformation the sediment interlayers record a decrease in sand supply and a change in palaeowind direction which may have been driven by the ongoing break up of west gondwana or may be a direct result of the widespread volcanism itself

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

spectroscopic study of the moses lake dune field washington determination of compositional distributions and source lithologies 1 source lithologies and transport histories of materials within the ephrata fan are investigated data were collected using a variety of remote sensing laboratory spectroscopic and field observations and techniques laboratory thermal emission spectra were collected of bedrock within the grand coulee dune samples and clast deposits factor analysis target transformation and end member recovery techniques were applied to the set of dune samples as well as a set of grain size fractions the dune sample spectra are composed of three components that represent basalt granodiorite and clay compositions the basalt and granodiorite components are similar to spectra of clast and bedrock samples from the grand coulee and the ephrata fan the clay component is similar to weathering surfaces located within the dune field the same components were recovered from the set of grain size fractions from a single dune sample demonstrating a relatively higher basalt concentration with grain sizes greater than 250 m thermal infrared multispectral scanner tims data display significant intradune compositional variation and no discernable interdune compositional variation indicating that the basalt and granodiorite components were likely deposited simultaneously and subsequently separated by wind based on grain size basalt and granodiorite bedrock units within the channeled scablands are source materials for the deposits within the ephrata fan and moses lake dune field the columbia river located 20 km west of the dune field is not a likely source of material

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

hadriaca patera insights into its volcanic history from mars express high resolution stereo camera 1 high resolution stereo camera hrsc images of hadriaca patera mars in combination with mars orbiter camera moc mars orbiter laser altimeter mola and thermal infrared imaging system themis data sets reveal morphologic details about this volcano and enable determination of a chronology of the major geologic events through new cratering age assessments new topographic measurements of the hadriaca edifice were also made from a hrsc based high resolution 125 m digital terrain model dtm and compared to the mola dtm we find evidence for a complex formation and erosional history at hadriaca patera in which volcanic fluvial and aeolian processes were all involved crater counts and associated model ages suggest that hadriaca patera formed from early shield building volcanic likely explosive pyroclastic eruptions at 3 7 3 9 ga with caldera formation no later than 3 5 ga a variety of geologic activity occurred in the caldera and on the northern flank and plains at 3 3 3 5 ga likely including pyroclastic flows that partially filled a large crater nw of the caldera and plains to the ne and differential erosion deposition by aeolian and or fluvial activity there were some resurfacing event s in the caldera and on the eastern flank at 2 4 2 6 ga in which the eastern flank s morphology is indicative of fluvial erosion the most recent dateable geologic activity on hadriaca patera includes caldera resurfacing by some process most likely differential aeolian erosion deposition in the amazonian period as recent as 1 5 ga this is coincident with the resurfacing of the heavily channeled south flank by fluvial erosion unlike the tharsis shields major geologic activity ended at hadriaca patera over a billion years ago

a late amazonian alteration layer related to local volcanism on mars hydrated minerals on mars are most commonly found in ancient terrains dating to the first billion years of the planet s evolution here we discuss the identification of a hydrated light toned rock unit present in one chasma of the noctis labyrinthus region stratigraphy and topography show that this alteration layer is part of a thin unit that drapes pre existing bedrock crism spectral data show that the unit contains hydrated minerals indicative of aqueous alteration potential minerals include sulfates such as bassanite caso4 1 2h2o or possibly hydrated chloride salts the proximity of a smooth volcanic plain and the similar crater model age late amazonian 100 myr of this plain and the draping deposits suggest that the alteration layer may be formed by the interaction of water with ash layers deposited during this geologically recent volcanic activity the alteration phases may have formed due to the presence of snow in contact with hot ash or eventually solid gas interactions due to the volcanic activity the relatively young age of the volcanic plain implies that recent alteration processes have occurred on mars in relation with volcanic activity but such local processes do not require conditions different than the current climate

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

light toned layered deposits in juventae chasma mars abstract we examine hypotheses for the formation of light toned layered deposits in juventae chasma using a combination of data from mars global surveyor s mars orbiter camera moc mars orbiter laser altimeter mola and thermal emission spectrometer tes as well as mars odyssey s thermal emission imaging system themis we divide juventae chasma into geomorphic units of i chasm wall rock ii heavily cratered hummocky terrain iii a mobile and largely crater free sand sheet on the chasm floor iv light toned layered outcrop llo material and v chaotic terrain using surface temperatures derived from themis infrared data and slopes from mola we derive maps of thermal inertia which are consistent with the geomorphic units that we identify llo thermal inertias range from 400 to 850 j m 2 k 1 s 1 2 light toned layered outcrops are distributed over a remarkably wide elevation range 5 8 km from the chasm floor to the adjacent plateau surface geomorphic features the absence of small craters and high thermal inertia show that the llos are composed of sedimentary rock that is eroding relatively rapidly in the present epoch we also present evidence for exhumation of llo material from the west wall of the chasm within chaotic and hummocky terrains and within a small depression in the adjacent plateau the data imply that at least some of the llo material was deposited long before the adjacent hesperian plateau basalts and that juventae chasma underwent and may still be undergoing enlargement along its west wall due to wall rock collapse chaotic terrain evolution and exposure and removal of llo material the new data allow us to reassess possible origins of the llos gypsum one of the minerals reported elsewhere as found in juventae chasma llo material forms only at low temperatures 60 c and thus excludes a volcanic origin instead the data are consistent with either multiple occurrences of lacustrine or airfall deposition over an extended period of time prior to emplacement of hesperian lava flows on the plateau above the chasm

styles and timing of volatile driven activity in the eastern hellas region of mars 1 recent analyses of mars global surveyor and mars odyssey data sets provide new insights into the geologic evolution of the eastern hellas region of mars in particular the role of volatiles here we present results of our recent work and integrate these with previous studies by various investigators to provide a synthesis of the history of volatile driven activity of the region we utilize high resolution images from the mars orbiter camera and thermal emission imaging system combined with mars orbiter laser altimeter digital elevation models and profiles to examine fluvial systems that dissect the circum hellas highlands to characterize stages in the development of the dao niger harmakhis and reull valles canyon systems and to evaluate evidence for ancient lakes in hellas planitia the occurrence of valley networks dissected highland crater rims and crater interior deposits such as layered plateaus suggests widespread ancient degradation of the circum hellas highlands canyon development which represents subsequent more localized activity may have included an early fluvial phase followed by the collapse and sapping dominated stages that along with recent wall erosion and floor resurfacing produced the currently observed morphologies the prominent role of collapse and sapping along the east rim of hellas along with the presence of numerous channels extending toward the basin and sequences of finely layered deposits along the basin rim suggests a volatile rich substrate across a broad depositional shelf the east rim of the basin was an accumulation zone for atmospheric volatiles and or the edge of volatile rich deposits associated with the basin floor this evidence combined with topographic data and cratered terrain preservation around the basin is consistent with a lacustrine period or periods in early martian history the style magnitude and spatial extent of volatile driven activity in eastern hellas have varied considerably with time and these variations may represent a transition from a water to an ice dominated surface environment

catastrophic flooding of an aeolian dune field jurassic entrada and todilto formations ghost ranch new mexico usa surveyed outcrops of the middle jurassic entrada sandstone at ghost ranch new mexico show the unusual occurrence of preserved aeolian dune palaeotopography buried beneath subaqueous strata the preserved dune remnants have relief up to 35 m trend nnw and show internal scalloped cross strata dipping to the wsw with small sets occurring as both topsets and bottomsets outcrop data are best satisfied in computer models by 50 m high sinuous bedforms that migrated to the wsw while the sinuosity migrated alongcrest to the nnw superimposed small dunes occurred upon the stoss slope and at the basal lee of the main bedform where they migrated alongslope to the nnw remnant dune palaeotopography is buried by onlapping subaqueous largely structureless sandstones believed to be derived by mass wasting of the upper portions of the dunes and deposited as sediment gravity flows that infilled between the dunes preservation of dune palaeotopography beneath mass flow deposits with no evidence for gradually rising water argues that flooding of the entrada dune field was geologically instantaneous the thickness and lithology of the overlying todilto formation conform to slight remnant palaeotopography on the entrada surface the todilto is a laminated limestone and thinnest over remnant dune crestal areas but thickens and increases in gypsum content downslope until it abruptly yields to a gypsum mound positioned over a remnant interdune hollow the todilto laminations are interpreted as seasonal varves deposited below wave base in a density stratified water body the flooding event that gave rise to the controversial todilto water body occurred during entrada time with todilto deposition occurring within an already substantial water body

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

martian pedestal craters marginal sublimation pits implicate a climate related formation mechanism 1 pedestal craters on mars are defined by an outward facing scarp forming a plateau perched tens of meters above the surrounding terrain their origin has been attributed to impact armoring of the surface and subsequent removal of inter crater terrain by either eolian deflation or sublimation of an ice rich substrate we identified 2696 pedestal craters between 60 n and 60 s latitude 98 are poleward of 33 n and 40 s the majority of pedestal crater margins are smoothly sloped but 3 concentrated in utopia planitia and malea planum display distinctive marginal pits these pedestal crater scarps are anomalously tall usually 80 100 m and the pits resemble sublimation depressions seen on earth and elsewhere on mars providing evidence for sublimation of volatiles in the scarp where the armored surface has tapered the pitted scarps provide insight into the origin of the general pedestal crater population favoring formation via deposition of a volatile rich substrate impact armoring and sublimation of intervening volatiles crater densities and overlapping pedestal craters suggest multiple periods of emplacement and loss of these climate related latitude dependent deposits throughout the amazonian

diverse mineralogies in two troughs of noctis labyrinthus mars two troughs in noctis labyrinthus display a diversity of mineral assemblages rarely seen spatially collocated on mars minerals identified from mars reconnaissance orbiter data within the troughs include polyhydrated and monohydrated sulfates an al clay e g kaolinite or beidellite fe mg smectites hydrated silica and or opal and a leached clay or jarosite mixture with a doublet absorption between 2 2 and 2 3 m units both pre date and post date smaller pits and depressions within the larger troughs indicating that deposition was coeval with continued extension collapse and erosion in the late hesperian to early amazonian 2 3 ga the strata within each trough display a mineralogic diversity consistent with active aqueous processes and or changing chemical conditions over time perhaps due to hydrothermal alteration of volcanic ash influxes of groundwater from nearby tharsis volcanism fumarole activity and melting snow and or ice the superposition of younger fe mg smectites over sulfates al clays and hydrated silica and or opal in both troughs indicates that this region is unique relative to most other locations on mars where the opposite progression is observed and the fe mg smectites are noachian older than 3 6 ga in age consequently these troughs may have been habitable regions on mars at a time when drier conditions dominated the surface

geologic evolution of the east rim of the hellas basin mars abstract geomorphic analyses and crater statistics indicate the distribution of materials on the east rim 27 5 42 5 s 260 275 w of the hellas basin and constrain the timing nature and interactions of geologic processes which have modified the hellas region the discernible geologic history of the area began with the formation of the impact basin and the emplacement of highlands that became heavily cratered during the noachian period the tectonic setting of the region was established at this time and basin structures promoted and influenced subsequent volcanic tectonic and fluvial activity degradation of the highland units by fluvial mass wasting and aeolian processes began in the noachian and continued into the hesperian and amazonian periods sedimentary plains covered low lying regions of the highlands their pitted surfaces in some areas suggest subsidence and the presence of volatiles emplacement of lobate debris aprons shed from highland peaks and possibly facilitated by ice creep occurred in the amazonian period the volcanic history of the east rim of the hellas basin began with the formation of the highland paterae the low dissected shields of hadriaca and tyrrhena paterae formed in the late noachian or early hesperian epochs and are older than or coeval with the ridged plains of hesperia planum volcanic activity continued throughout the hesperian period with the emplacement of the caldera filling materials at hadriaca patera and the lava flows of the flank flow unit of tyrrhena patera outflow channels and related channeled plains of the hesperian and amazonian periods suggest an extensive and complex history of volatile driven erosion and sedimentary deposition dao and harmahkis valles are interpreted to be collapsed regions of the older plains a combination of surface and subsurface flow has removed materials with deposition on the floor of the hellas basin the geologic evolution of the region determined from the observed surface morphology and stratigraphic relationships and refined by crater statistics indicates that a combination of diverse geologic processes acted in the degradation of the hellas basin the effects of volcanism and volatile driven processes were prominent throughout the hesperian and well into the amazonian periods the proposed transition from explosive to effusive volcanism in the hellas region is supported by the relative ages indicated by crater statistics the heat released by volcanism may have resulted in the melting of ground ice and contributed to the development of the channeled plains and outflow channels the presence of wrinkle ridges on units that are inferred to be relatively young from their crater size frequency distributions suggests deformation in the late hesperian or early amazonian epoch

periodic climate change on mars review of evidence and effects on distribution of volatiles abstract the polar regions of mars preserve in both their layering and their topography a record of recent climate changes because of the coincidence of the growth of the northern seasonal cap with global dust storms dust may be currently accumulating on the northern cap but conditions at the poles will alternate with the precessional cycle deposition is also modulated by changes in eccentricity and obliquity which interact complexly affecting initiation of global dust storms the stability of volatiles at the surface and global wind regimes formation of spiral valleys and low undulations on the surface of the layered deposits may result from prefential sublimation of volatiles on sunward facing slopes and condensation on the adjacent flats with the rates also modulated by astronomically caused insolation variations lack of impact craters on the surface and lack of interruption of the layers by impact scars suggest that the polar deposits are no more than a few million years old older deposits may have been periodically removed as indicated by etch pitted terrain at the south pole and by superposition relations around the periphery of the present layered deposits evidence of ancient periodic climate changes that occurred before formation of the present layered terrain is fragmentary but includes pedestal craters parallel moraine like ridges and etched ground at high latitudes perturbation of the orbital motions also results in adsorption and desorption of volatiles in the regolith which leads to variations in atmospheric pressure and partial dehydration of the equatorial near surface materials

oscillations of lake chad over the past 50 000 years new data and new hypothesis a recent sedimentological study of the chari deltas area allowed an evaluation of the oscillations of palaeolake chad over the past 50 000 years three maximum lake levels at circa 38 000 22 000 and between 12 000 and 8000 years b p have been described the levels reached by these large lakes were never very high and there has not been any major variation over the last 8000 years the hypothesis regarding a huge palaeolake chad of 320 000 km2 reaching the 320 m level at circa 6000 years b p instead of the present 279 5 282 m and approximatively 20 000 km2 is discussed and discarded on basis of stratigraphical sedimentological geomorphological hydrological and geophysical arguments taking into account geophysical data and the deep structures of the basin a new interpretation is proposed for the perilacustrine dune ridge which was considered to run along the shoreline of the 320 m level

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

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

bedform spacing from defect dynamics spacing is a time varying characteristic of bedform fields deriving from the behavior of defects ends of crest lines in the bedform pattern in a model based on this hypothesis crest line length is lost and spacing increases because bedform defects which are smaller in height and faster migrating than surrounding bedform crest lines merge with larger bedforms as defects migrate through bedform fields spacing in large bedform fields asymptotically increases with the logarithm of time as pairs of oppositely facing defects meet and annihilate spacing in small bedform fields such as flumes exponentially approaches a fixed value as defects are eliminated at the boundaries of the field model predictions are compatible with observed spacing of transverse bedforms ripples formed under waves and linear dunes calling into question the widespread assumption that bedform spacing approaches a steady state value characteristic of fluid flow and sediment transport over two dimensional bedforms

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

modeling emergent large scale structures of barchan dune fields in nature barchan dunes typically exist as members of larger fi elds that display striking enigmatic structures that cannot be readily explained by examining the dynamics at the scale of single dunes or by appealing to patterns in external forcing to explore the possibility that observed structures emerge spontaneously as a collective result of many dunes interacting with each other we built a numerical model that treats barchans as discrete entities that interact with one another according to simplifi ed rules derived from theoretical and numerical work and from fi eld observations 1 dunes exchange sand through the fl uxes that leak from the downwind side of each dune and are captured on their upstream sides 2 when dunes become suffi ciently large small dunes are born on their downwind sides calving and 3 when dunes collide directly enough they merge results show that these relatively simple interactions provide potential explanations for a range of fi eld scale phenomena including isolated patches of dunes and heterogeneous arrangements of similarly sized dunes in denser fi elds the results also suggest that 1 dune fi eld characteristics depend on the sand fl ux fed into the upwind boundary although 2 moving downwind the system approaches a common attracting state in which the memory of the upwind conditions vanishes this work supports the hypothesis that calving exerts a fi rst order control on fi eld scale phenomena it prevents individual dunes from growing without bound as single dune analyses suggest and allows the formation of roughly realistic persistent dune fi eld patterns

aeolian dune field self organization implications for the formation of simple versus complex dune field patterns abstract the interpretation of aeolian dune field patterns as self organizing complex systems is a new paradigm in which pattern evolution may be addressed computer simulations supported by field and experimental data indicate that a given wind regime produces a simple dune field pattern dune type and crest orientation are determined by wind regime and pattern ordering occurs through dune dune interactions over time because dunes reorient only at their crest terminations with a change in wind regime the rate of formation of a new pattern of small dunes is typically faster than the rate of reorientation of the existing pattern resulting in the superposition of simple patterns to give rise to complex patterns complex patterns are distinct from spatial changes in a simple pattern and from the type of superposition that characterizes compound complex dunes complex patterns necessarily indicate a rate of pattern formation that is rapid compared to the rate of sediment accumulation on the depositional surface

volcanic geology of hadriaca patera and the eastern hellas region of mars hadriaca patera is a low relief volcano in the southern highlands of mars northeast of the hellas basin layered friable deposits composing the extensive channeled flanks of the volcano surround a well defined summit caldera containing late stage eruptive products the morphologic characteristics of the channels suggest erosion by groundwater sapping and surface runoff the erosional morphology of the volcano the lack of lava flow features and the friable nature of the flank materials indicate that hadriaca patera consists predominantly of pyroclastic deposits gravity driven flow models demonstrate that the distribution of flank materials can be attributed to the emplacement of pyroclastic flows both magmatic and hydromagmatic eruption models are viable for the magmatic case the necessary mass eruption rates 107 108 kg s ejection velocities 400 m s and volatile contents 1 5 3 0 wt h2o are consistent with parameters derived for terrestrial plinian eruptions for the hydromagmatic case the required energy conversion efficiencies are comparable to those of laboratory experiments and the inferred permeability of the martian crust allows large amounts of groundwater to be transported rapidly at flow rates of 103 104 m3 s into the region models of cooling during emplacement indicate that welding of pyroclastic flows can occur at large distances hundreds of kilometers from a source vent on mars the layering within hadriaca patera could be attributed to welding of pyroclastic flows that would control its susceptibility to erosion morphologic similarities between hadriaca and tyrrhena paterae suggest a similar volcanic history with an early pyroclastic dominated shield building phase followed by effusive eruptions at their summit calderas and on the flank of tyrrhena patera the formation of the extensive ridged plains of hesperia planum following the formation of the highland paterae supports the interpretation of a transition from explosive to effusive volcanism in the eastern hellas region a progressive depletion of volatiles on mars is consistent with the morphologic properties of highland paterae and other central vent volcanoes a predominance of hydrovolcanic eruptions in the development of hadriaca and tyrrhena paterae would imply that the transition in volcanic eruption style can be attributed to a volatile depletion of the crust whereas magmatic eruptions at the paterae would be indicative of temporal changes in martian magmas

evidence for indurated sand dunes in the martian north polar region 1 we investigate the relevance of induration as an explanation for the occurrence of dunes of unusual morphology in the martian north polar region the evidence for induration of aeolian deposits on mars is reviewed an explanation for rounded elongated barchans in chasma boreale is presented the role played by induration in the formation of linear dunes is discussed our arguments are supported by the results of a computer simulation model

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

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

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

wind blown sandstones cemented by sulfate and clay minerals in gale crater mars gale crater contains mount sharp a 5km thick stratigraphic record of mars early environmental history the strata comprising mount sharp are believed to be sedimentary in origin but the specific depositional environments recorded by the rocks remain speculative we present orbital evidence for the occurrence of eolian sandstones within gale crater and the lower reaches of mount sharp including preservation of wind blown sand dune topography in sedimentary strata a phenomenon that is rare on earth and typically associated with stabilization rapid sedimentation transgression and submergence of the land surface the preserved bedforms in gale are associated with clay minerals and elsewhere accompanied by typical dune cross stratification marked by bounding surfaces whose lateral equivalents contain sulfate salts these observations extend the range of possible habitable environments that may be recorded within gale crater and provide hypotheses that can be tested in situ by the curiosity rover payload