the age of the medusae fossae formation evidence of hesperian emplacement from crater morphology stratigraphy and ancient lava contacts abstract the medusae fossae formation mff covering about 2 1 10 6 km 2 with an estimated volume of 1 4 10 6 km 3 and straddling the equatorial region of mars east of tharsis has historically been mapped and dated as amazonian in age analysis of the mff using a range of new observations from recent mission data at multiple resolutions reveals evidence that the formation is older than previously hypothesized with parts of the mff having formed in the hesperian and parts having been reworked and reformed throughout the amazonian up to the present ancient outcroppings of the mff edged with jagged yardangs became a mold for embaying hesperian aged lavas the erosion of the mff left solidified lava casts in the embaying lava unit this lava edge morphology permits the identification of ancient contacts between the mff and hesperian aged lava terrain additionally the flanking fan of the hesperian aged apollinaris patera volcano embays the formation at its foot indicating that parts of the mff were formed in the hesperian erosion has erased and inverted many of the superposed craters in the region showing that very young amazonian ages derived from impact crater size frequency distributions are resurfacing ages and not emplacement ages we find abundant evidence that the formation is extremely mobile and continuously reworked we conclude that a significant part of the mff may have originally been emplaced in the hesperian these observations place new constraints on the mode of origin of the mff

stratigraphy of aeolis dorsa mars stratigraphic context of the great river deposits unraveling the stratigraphic record is the key to understanding ancient climate and past climate changes on mars grotzinger j et al 2011 astrobiology 11 77 87 stratigraphic records of river deposits hold particular promise because rain or snowmelt must exceed infiltration plus evaporation to allow sediment transport by rivers therefore river deposits when placed in stratigraphic order could constrain the number magnitudes and durations of the wettest and presumably most habitable climates in mars history we use crosscutting relationships to establish the stratigraphic context of river and alluvial fan deposits in the aeolis dorsa sedimentary basin 10 e of gale crater at aeolis dorsa wind erosion has exhumed a stratigraphic section of sedimentary rocks consisting of at least four unconformity bounded rock packages recording three or more distinct episodes of surface runoff early deposits 700 m thick are embayed by river deposits 400 m thick which are in turn unconformably draped by fan shaped deposits 900 m thick unconformably drape all previous deposits river deposits embay a dissected landscape formed of sedimentary rock the river deposits are eroding out of at least two distinguishable units there is evidence for pulses of erosion during the interval of river deposition the total interval spanned by river deposits is 1 10 6 2 10 7 yr and this is extended if we include alluvial fan deposits alluvial fan deposits unconformably postdate thrust faults which crosscut the river deposits this relationship suggests a relatively dry interval of 4 10 7 yr after the river deposits formed and before the fan shaped deposits formed based on probability arguments yardang forming layered deposits unconformably postdate all of the earlier deposits they contain rhythmite and their induration suggests a damp or wet near surface environment the time gap between the end of river deposition and the onset of yardang forming layered deposits is constrained to 1 10 8 yr by the high density of impact craters embedded at the unconformity the time gap between the end of alluvial fan deposition and the onset of yardang forming layered deposits was at least long enough for wind induced saltation abrasion to erode 20 30 m into the alluvial fan deposits we correlate the yardang forming layered deposits to the upper layers of gale crater s mound mt sharp aeolis mons and the fan shaped deposits to peace vallis fan in gale crater alternations between periods of low mean obliquity and periods of high mean obliquity may have modulated erosion deposition cycling in aeolis this is consistent with the results from an ensemble of simulations of solar system orbital evolution and the resulting history of the obliquity of mars 57 of our 61 simulations produce one or more intervals of continuously low mean mars obliquity that are long enough to match our aeolis dorsa unconformity data

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

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

inversion of relief a component of landscape evolution inversion of relief occurs when materials on valley floors are or become more resistant to erosion than the adjacent valley slopes as erosion proceeds the valley floor becomes a ridge bounded by newly formed valleys on each side areas of lava flows contain many examples of inversion of relief but it is also common in areas of duricrusts inversion of relief is so widespread in some areas that it should be regarded as a general component in a model of landscape evolution inversion of relief has some important implications drainage lines will shift significantly over time slope soil relationships catenas have to be reassessed because the regolith on the upper part of a hill slope may have developed under very different conditions from those existing at present the resulting catena is not a simple expression of soils and response to landscape position this also has important implications for geochemistry where present day ridge tops were once valley floors geochemical signatures will reflect lateral water movement in the old landscape rather than simple in situ weathering and vertical redistribution in the present landscape finally inversion of relief can produce erosion surfaces of very low relief that cannot be termed peneplains pediplains or etchplains because they have a very different genesis this underlines the importance of determining the complexities of landscape evolution before such genetic terms are applied to any landscape

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

a contourite drift system on the baffin bay west greenland margin linking pliocene arctic warming to poleward ocean circulation terrestrial records from the canadian arctic archipelago indicate that a temperate and moist climate prevailed during the pliocene i e before the intensification of northern hemisphere glaciations but the controlling factors causing these conditions remains elusive here we present marine seismic reflection evidence of contiguous kilometer scale sedimentary drifts or contourites buried below the west greenland shelf which relates high latitude pliocene warmth to intense geostrophic currents along the eastern baffin bay margin seismic to borehole correlation indicates that enhanced current induced deposition began during the middle miocene ca 17 15 ma and terminated during the late pliocene onset of global cooling the transition from along slope sediment transport to trough mouth fan progradation designates the onset of greenland ice sheet glaciers advancing across the continental shelf and coincides with increasing iceberg productivity in baffin bay and the nordic seas from 3 3 to 2 7 ma our results suggest that the baffin bay west greenland margin formed a late neogene passageway for persistent ocean boundary currents and we infer that the pliocene high latitude warmth was to a significant extent caused or enhanced by advection of subtropical heat and moisture to the arctic regions attenuation of the poleward heat flux conveyed by the paleo current system may have been critical for allowing glacial buildup in the canadian arctic and northern greenland during the late pliocene we further surmise that vertical tectonic adjustments of the continental margin played a role in this attenuation which eventually caused the demise of meridional ocean circulation through baffin bay

terraces and gilbert type deltas in crater lakes in ismenius lacus and memnonia mars paleolacustrine environments have been widely recognized from landform associations on the surface of mars in contrast to paleolakes in more open areas putative crater lakes commonly display well developed sedimentary landforms especially wave formed terraces and gilbert type deltas this study focuses on terraces and deltas of western memnonia and ismenius lacus as on earth these landforms provide important indications of water dynamics and sedimentary processes the putative martian paleolakes must have been active for thousands of years to have permitted the water movement and wave formation necessary to form one or more terraces fan shaped landforms at the mouths of channels entering crater lake areas may indicate various channel water interaction of these gilbert type deltas are particularly informative their presence indicates multiple flooding events whereby the inlet channels conveyed coarse grained sediment to the crater lake both terraces and deltaic progradation indicate that the crater lakes of memnonia and ismenius lacus were active for long time periods at least for thousands of years during the post heavy bombardment period of the later martian history the unequivocal presence of standing bodies of water of relatively long durations indicates that climatic settings very different from those prevailing today must have occurred at least locally and temporarily during parts of the martian planetary history

sublacustrine depositional fans in southwest melas chasma two depositional fan complexes have been identified on the floor of southwest melas chasma the western fan complex is located near the center of an enclosed basin in southwest melas chasma and is composed of multiple lobes with dendritic finger like terminations these fans are very flat and have a morphology unlike any other fan that has been previously identified on mars on the basis of the morphologic similarity of the western fan complex to the mississippi submarine fan complex we suggest that it may be a deep subaqueous fan depositional system there are numerous channels on the surface of the western fan complex and measurements of channel length width and sinuosity are consistent with channels observed on terrestrial submarine fans the eastern melas depositional fans are less well preserved and may be of deltaic or sublacustrine origin recognition of the fans supports earlier suggestions for the presence of a former lake in melas chasma and indicates that a significant body of water was present and stable at the surface of mars for at least 10 2 to 10 4 years

conditions for branching in depositional rivers it is often taken for granted that rivers organize transport into a single active channel in some net depositional environments however flow of water and sediment is distributed in several stable channels such branching rivers may be confined in valleys anabranching or anastomosed or unconfined on deltas distributaries and their existence confronts us with the very basic question of what governs the spatial organization of channel patterns in sedimentary landscapes current models for equilibrium channel morphology cannot predict the occurrence of branching rivers because they do not consider dynamical processes such as avulsion i e the rapid abandonment of a channel in favor of a new path at lower elevation the requisite conditions for avulsion have been the subject of ongoing debate here we resolve the conditions leading to channel avulsion and show that branching rivers occur when avulsion is the dominant mechanism of lateral channel motion a compilation of field and laboratory data demonstrates that avulsion frequency scales with the time required for sedimentation on channel beds to produce a deposit equal to one channel depth from the relative rates of bank erosion and channel sedimentation we derive a dimensionless mobility number that accurately predicts the conditions under which anabranching and distributary channels occur results may be directly applied to modeling landscape evolution over human and geologic time scales and for inverting formative environmental conditions from channel deposits on earth and other planetary surfaces

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

morphometry of small recent impact craters on mars size and terrain dependence short term modification most recent studies of crater morphometry on mars have addressed large craters d 5 km using elevation models derived from laser altimetry in the present work we examine a global population of small 25 m d 5 km relatively well preserved simple impact craters using hirise stereo derived elevation models we find that scaling laws from prior studies of large simple craters generally overestimate the depth and volume at small diameters we show that crater rim curvature exhibits a strong diameter dependence that is well described by scaling laws for d 1 km above this diameter upper rim slopes begin to exceed typical repose angles and crater rims sharpen significantly this transition is likely the result of gravity driven collapse of the upper cavity walls during crater formation or short term modification in addition we identify a tendency for small craters d 500m to be more conical than large craters and we show that the average cavity cross section is well described by a power law with exponent 1 75 neither conical nor paraboloidal we also conduct a statistical comparison of crater subpopulations to illuminate trends with increasing modification and target strength these results have important implications for describing the initial condition of simple crater shape as a function of diameter and geological setting and for understanding how impact craters are modified on the martian surface over time

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

fluvial sedimentary deposits on mars ancient deltas in a crater lake in the nili fossae region 1 new spacecraft observations in the nili fossae region of mars reveal two valley networks 80 and 200 km long that each formed distributary fans as they entered an ancient 40 km diameter impact crater an outlet channel on the eastern crater rim lying at an elevation above the fans suggests these fans formed as subaqueous deltas in a crater lake water flowing in the valley networks entered the crater and deposited the fans and ponded to a maximum depth of about 450 m the lake then overtopped and breached the crater rim incising it and dropping the lake level by 100 m geological evidence combined with the volume of water necessary to fill the crater suggests the duration of flow through this system was prolonged the existence of the deposits described here implies that the early martian environment supported overland flow and ponding of water for an extended period of time

influence of growth faults on coastal fluvial systems examples from the late miocene to recent mississippi river delta abstract the details of how fluvial systems respond to spatial changes in land surface subsidence produced by active faulting remain incompletely understood here we examine the degree to which the positioning of individual channels and channel belts is affected by local maxima in subsidence associated with the hanging walls of growth faults the channel forms and faults are imaged using a seismic volume covering 1400 km2 of breton sound and barataria bay in southern louisiana usa we look at the consequences of interactions between channels channel belts and faults in late miocene to recent strata more than fifty individual channels that crossed the traces of active growth faults were examined of these channels only three appear to have been redirected by the faults there also appeared to be no systematic change in the cross sectional geometries of channels or channel belts associated with crossing a fault though the orientation of the channel belts appears to be more influenced by faulting than the orientation of individual channels seven out of ten mapped channel belts appear to have been steered by growth faults we propose that channel belts are more likely to be influenced by faults than individual channels because channel belts are longer lived features unlikely to shift their overall position before experiencing a discrete faulting event in addition the style of influence in the few cases where an individual channel is affected by a fault is different from that of larger systems while downstream of a fault channel belts generally become oriented perpendicular to fault strike the individual channels are directed along the hanging wall of the fault running parallel to the fault trace we relate this to the ratio of the length scale of fault rollover relative to the channel or channel belt width fluvial fault interactions with higher values for this ratio are more likely to be carried parallel to the fault trace than systems with lower ratio values

pacing early mars river activity embedded craters in the aeolis dorsa region imply river activity spanned 1 20 myr we find net sedimentation rate 13 200 m yr in the aeolis dorsa region mars using the frequency of crater river interactions this sets a lower bound of 1 20 myr on the total interval spanned by fluvial activity which we correlate to the noachian hesperian transition the main uncertainty is the impact flux at the time of deposition this result rules out basin filling by a single catastrophic episode such as a single impact induced water vapor greenhouse

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

origin of the medusae fossae formation mars insights from a synoptic approach 1 the geologic origin of the medusae fossae formation mff has remained a mystery despite three decades of research to better constrain its formation an in depth analysis of observations made in the literature was combined with a new survey of over 700 mars orbiter camera narrow angle images of the mff to identify morphologic characteristics and material properties that define this formation as a whole while previous work has identified clear agreement on some characteristics our analysis identifies yardangs collapse features and layering as pervasive features of the mff whereas collapse features and layering may implicate several different physical and chemical processes yardangs provide vital information on material properties that inform about mechanical properties of the mff lithology aspect ratios of megayardangs range from 3 1 to 50 1 and slope analyses reveal heights of up to 200 m with cliffs that are almost vertical other yardangs show lower aspect ratios and topographic profiles these characteristics coupled to the presence of serrated margins suggest that mff lithology must be of weakly to heavily indurated material that lends itself to jointing the characteristics and properties of the mff are inconsistent with those of terrestrial pyroclastic fall deposits or loess but are in common with large terrestrial ignimbrites a hypothesis that explains all key observations with a single mechanism yardang fields developed in regionally extensive ignimbrite sheets in the central andes display morphologic characteristics that correlate with degree of induration of the host lithology and suggest an origin by pyroclastic flow for the mff

deltaic deposits indicative of a paleo coastline at aeolis dorsa mars abstract recent work at aeolis dorsa mars has identified exposure of fluvial sedimentary outcrop deposited early in martian history likely during the late hesperian or earlier here we examine a 1200 km2 exposure of sedimentary outcrop in southeast aeolis dorsa total thickness of the stratigraphic section exceeds 100 m we identify eight discrete complexes each of which is primarily composed of branching channel filling fluvial deposits associated with a primary feeder or trunk channel deposit relative ages for the branching complexes are derived from observed stacking relationships and there is a pattern of eastward younging using digital elevation models derived from context camera ctx stereo pair images we measure the strike and dip of stratal surfaces mapped throughout the study area there is a trend of increasing dip magnitude from north to south the branching complexes are interpreted as exhumed remnants of the lobes of an aggrading river delta that shifted its depo center from west to east over time the increasing dip magnitude of stratal surfaces towards the south records topset foreset transitions an architectural feature associated with river deltas and indicates paleo transport was locally southward the interpreted deltaic lobes indicate that aeolis dorsa was a coastal region not presently bound by a modern crater basin and the studied outcrop is part of a larger set of coastal sedimentary deposits identified in the region

hesperian age for western medusae fossae formation mars the medusae fossae formation mff on mars is an intensely eroded deposit north of the cratered highlands it is widely thought that mff materials were emplaced through ignimbrite eruptions recent geologic mapping of western mff identified outliers of mff materials well beyond the previously mapped western extent for the deposit including outliers close to gale crater we report counts of impact craters on the mff units that have implications for our understanding of the general history of mff and the uppermost layered materials on the gale crater mound

ancient ocean on mars supported by global distribution of deltas and valleys the climate of early mars could have supported a complex hydrological system analysis of ancient deltaic deposits and valley networks reveals the presence of a planet wide equipotential surface in the northern lowlands indicative of the existence of a vast ocean on mars 3 5 billion years ago

clinoform development by advection diffusion of suspended sediment modeling and comparison to natural systems clinoforms are the building blocks of prograding stratigraphic sequences these sig moid shaped surfaces can be found forming today on modem deltas sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions with a maximum accumulation rate on the upper foreset region we pres ent a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river model clino form surfaces are generated using an equation for the conservation of suspended sediment concentration together with a conservation of fluid equation for simple time averaged flow velocity fields in the model suspended sediment is advected horizontally into a basin and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion in shallow water shear stresses are too large to allow deposition and sediment bypasses the topset region with increasing water depth near bed shear stresses decrease and sediment is allowed to deposit at the foreset region with gradually decreasing rates toward deeper water this sedimentation pattern leads to progradation of the clinoform surfaces through time the clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms these include the gradual slope rollover at the topset and bottomset steeper foreset slopes with increased grain size and an increase in foreset slope through time as clinoforms prograde into deeper water because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems the model is an important step toward unraveling the physical processes associated with these deposits

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

mosaicking of global planetary image datasets 1 techniques and data processing for thermal emission imaging system themis multi spectral data 1 the mosaicking of global planetary data sets allows for the examination of local regional and global scale processes on all planetary bodies processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image processing algorithm these techniques e g non uniformity correction running contrast stretches line and row correlated noise removal and random noise removal were originally developed for the 2001 mars odyssey thermal emission imaging system themis infrared multispectral imager data but can be adapted and applied to other data sets by the alteration of input parameters the techniques for mosaicking planetary image data sets e g image registration blending and normalization are also presented along with the generation of qualitative and quantitative products these techniques are then applied to generate themis daytime and nighttime infrared viking context imager ctx and mars orbiter camera moc visible mosaics using a variety of input and output types at a variety of scales by creating mosaics of the same area using different data sets such as those that illustrate compositional diversity thermophysical properties or small scale morphology it is possible to view the surface of the planet and geologic problems through many different perspectives in addition to the techniques used to create large scale seamless mosaics we also present the themis daytime and nighttime relative temperature global mosaics which are the highest resolution 100m pixel global scale data sets available for mars to date

pervasive aqueous paleoflow features in the aeolis zephyria plana region mars abstract a survey of themis visible wavelength images in the aeolis zephyria plana region over the two western lobes of the equatorial medusae fossae formation mff shows 150 sinuous ridges having a variety of morphologies and contexts to systematize investigation we use a classification scheme including both individual ridge and ridge network types as well as associations with impact craters and fan shaped features the morphology of the ridges their location downslope from higher topography e g crater rims and scarps and their association with fan shaped forms indicate that most sinuous ridges formed through overland aqueous flow analysis of observations by individual ridge type leads to interpretation of most of these sinuous ridges as inverted fluvial channels or floodplains and a few as possible eskers with the origin of the remaining ridges under continuing investigation about 15 of the sinuous ridges are associated with impact craters but data analysis does not support a genetic relationship between the craters and the sinuous ridges instead analysis of one sinuous ridge network associated with a crater indicates that the water source for the network was atmospheric in origin namely precipitation runoff the broad areal distribution of these 150 ridges and the network morphologies in particular the branched and subparallel types suggest that an atmospheric water source is generally applicable to the population of sinuous ridges as a whole this concentration of sinuous ridges is the largest single population of such landforms on mars and among the youngest these ridges are situated at a paleoscarp between cerberus palus and the aeolis highlands suggesting that the precipitation that formed them was orographic in origin the ages of the equatorial mff units in which this population of sinuous ridges is found imply that this orographic rain and or snow fell during some period from the late hesperian through the middle amazonian

channel slope reversal near the martian dichotomy boundary testing tectonic hypotheses abstract faults along the martian dichotomy boundary are evidence of tectonic activity which by analogy with terrestrial tectonism may cause changes in or even reversal of fluvial longitudinal profiles in the eastern hemisphere between 30 e and 150 e this tectonic activity has been hypothesized to result from lower crustal flow or from lithospheric flexure for which loading e g by material deposition of the northern lowlands is a possible cause watters 2003a nimmo 2005 the topographic slope changes resulting from these two different mechanisms are distinct and can provide a means for distinguishing between them although other processes may complicate interpretations of reversed longitudinal profiles two fan shaped networks of inverted channels are located near 150 e in the aeolis dorsa region just north of the dichotomy boundary their original flow directions inferred from planform morphology suggest flow to the northeast in contrast to their current longitudinal profiles sloping down to the southwest this contrast indicates slope reversal we investigate the lower crustal flow and flexure mechanisms for slope reversal by testing three different hypotheses 1 lower crustal flow 2 flexure caused by material erosion from the highlands and deposition in the lowlands and 3 flexure caused by highland erosion and deposition in the lowlands plus deposition of the medusae fossae formation in the lowlands we test these three hypotheses by comparing the inferred magnitudes of the slope reversals with predicted slope changes from geophysical models for these processes taking the possibility of non tectonic i e collapse processes into account our results suggest that among these three models the slope reversal is most consistent with the predicted tectonic response to erosion and deposition of highland material in conjunction with deposition of the medusae fossae formation contrary to previous findings our results do not support the mechanism of lateral crustal flow although they do not rule it out because lower crustal flow and erosion may both have been operating but on different time scales the result of this hypothesis testing provides insight into the evolution of the dichotomy boundary and martian crust in this location

inverted fluvial features in the aeolis zephyria plana region mars formation mechanism and initial paleodischarge estimates 1 a subset of the sinuous ridges srs in the aeolis zephyria plana azp region of mars has been previously hypothesized to be inverted fluvial features although the precise induration and erosion mechanisms were not specified morphological observations and thermal inertia data presented here support this hypothesis a variety of mechanisms can cause inversion and identification of the specific events that lead to fluvial sr formation can provide insights into the sedimentological geochemical and climatic processes of the region reconnaissance of two terrestrial lava capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on mars but these criteria are not satisfied by the majority of the azp fluvial srs armoring also appears inconsistent with terrestrial analogs layering and surface textures of fluvial srs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments and that the primary erosional mechanism that exposed the fluvial srs was aeolian abrasion this analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form discharge approach to which we have applied scaling for martian gravity for those fluvial srs meeting a set of criteria for accurate paleodischarge estimates paleodischarge values generally range between 101 and 103 m3 s 1 the largest of these initial estimates are comparable to paleodischarge estimates for some late stage noachian fluvial channels on mars and provide a constraint on the atmospheric conditions at this equatorial location during the late hesperian to early amazonian time frame

a minimum time for the formation of holden northeast fan mars 1 the recently discovered deposits of a channelized fan located northeast of holden crater preserve a history of vertical and lateral accretion and avulsion of many channels indicating water flowed freely across the surface of the fan during its construction these sedimentary deposits however do not unambiguously discriminate between a deltaic or purely riverine origin for the feature by using a numerical model describing fan construction solely by river channels we estimate a minimum formation time of several decades to centuries a minimum value for the total volume of transporting fluid required to construct the fan is modest 900 km3 and may not have required precipitation

modeling erosion of ice rich permafrost bluffs along the alaskan beaufort sea coast the arctic climate is changing inducing accelerating retreat of ice rich permafrost coastal bluffs along alaska s beaufort sea coast erosion rates have increased roughly threefold from 6 8 to 19 m yr 1 since 1955 while the sea ice free season has increased roughly twofold from 45 to 100 days since 1979 we develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice free season sea level water temperature nearshore wavefield and permafrost temperature in controlling erosion rates in this setting the model captures the processes of erosion observed in short term monitoring experiments along the beaufort sea coast including evolution of melt notches topple of ice wedge bounded blocks and degradation of these blocks model results agree with time lapse imagery of bluff evolution and time series of ocean based instrumentation erosion is highly episodic with 40 of erosion is accomplished during less than 5 of the sea ice free season among the formulations of the submarine erosion rate we assessed we advocate those that employ both water temperature and nearshore wavefield as high water levels are a prerequisite for erosion any future changes that increase the frequency with which water levels exceed the base of the bluffs will increase rates of coastal erosion the certain increases in sea level and potential changes in storminess will both contribute to this effect as water temperature also influences erosion rates any further expansion of the sea ice free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates

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

inverted fluvial features in the aeolis zephyria plana western medusae fossae formation mars evidence for post formation modification 1 the aeolis and zephyria plana contain the western most portion of the medusae fossae formation mff an enigmatic and extensive light toned deposit located in the martian equatorial region and dated from the hesperian to amazonian epochs this area hosts a large population of sinuous ridges srs interpreted as inverted fluvial features formed by precipitation indurated by chemical cementation buried by subsequent deposition and finally exhumed this interpretation of srs as uniformly fluvial represents a modification to an earlier hypothesis for one particular sr of possible glaciofluvial i e esker formation these srs provide a tool to investigate the degree and character of post fluvial modification processes in this region we combined digital terrain models made from context camera ctx and high resolution imaging science experiment hirise stereo image pairs with individual data points from the mars orbiter laser altimeter mola to estimate relief cross sectional profiles longitudinal profiles and slope directions of selected srs longitudinal profiles of several srs display undulations with amplitudes of up to order 100 m while some of the lower amplitude undulations may be due to differential erosion undulations having amplitudes in excess of sr relief require alternative explanations our combined morphologic and topographic analysis suggests that multiple post flow processes including compaction of the deposits and tectonic displacements have modified the original sr profiles specification of the type s and magnitudes of these modification processes will contribute to understanding both the potential of post flow modification of fluvial profiles elsewhere on mars as well as the nature and properties of the mff