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

the global martian volcanic evolutionary history abstract viking mission image data revealed the total spatial extent of preserved volcanic surface on mars one of the dominating surface expressions is olympus mons and the surrounding volcanic province tharsis earlier studies of the global volcanic sequence of events based on stratigraphic relationships and crater count statistics were limited to the image resolution of the viking orbiter camera here a global investigation based on high resolution image data gathered by the high resolution stereo camera hrsc during the first years of mars express orbiting around mars is presented additionally mars orbiter camera moc and thermal emission imaging system themis images were used for more detailed and complementary information the results reveal global volcanism during the noachian period 3 7 ga followed by more focused vent volcanism in three tharsis elysium and circum hellas and later two tharsis and elysium volcanic provinces finally the volcanic activity became localized to the tharsis region about 1 6 ga ago where volcanism was active until very recently 200 100 ma these age results were expected from radiometric dating of martian meteorites but now verified for extended geological units mainly found in the tharsis montes surroundings showing prolonged volcanism for more than 3 5 billions years the volcanic activity on mars appears episodic but decaying in intensity and localizing in space the spatial and temporal extent of martian volcanism based on crater count statistics now provides a much better database for modelling the thermodynamic evolution of mars

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

deltaic deposits at aeolis dorsa sedimentary evidence for a standing body of water on the northern plains of mars a fundamental long standing question regarding mars history is whether the flat and low lying northern plains ever hosted an ocean the best opportunity to solve this problem is provided by stratigraphic observations of sedimentary deposits onlapping the crustal dichotomy here we use high resolution imagery and topography to analyze a branching network of inverted channel and channel lobe deposits in the aeolis dorsa region just north of the dichotomy boundary observations of stacked cross cutting channel bodies and stratal geometries indicate that these landforms represent exhumed distributary channel deposits observations of depositional trunk feeder channel bodies a lack of evidence for past topographic confinement channel avulsions at similar elevations and the presence of a strong break in dip slope between topset and foreset beds suggest that this distributary system was most likely a delta rather than an alluvial fan or submarine fan sediment transport calculations using both measured and derived channel geometries indicate a minimum delta deposition time on the order of 400 years the location of this delta within a thick and widespread clastic wedge abutting the crustal dichotomy boundary unconfined by any observable craters suggests a standing body of water potentially 105 km2 in extent or greater and is spatially consistent with hypotheses for a northern ocean

evidence for the episodic erosion of the medusae fossae formation preserved within the youngest volcanic province on mars we use orbital shallow radar sharad sounder data to three dimensionally visualize the subsurface structure of elysium planitia the youngest volcanic province on mars our results reveal an emplacement history consisting of multiple groups of overlapping lava flow units originating from different sources the uniquely complex radar stratigraphy of elysium planitia relative to other volcanic regions requires a distinct mechanism to generate the numerous reflectors observed in sharad data sedimentary deposits interbedded with successive batches of lava flows could account for the elaborate pattern of reflectors we infer that widespread rapidly emplaced material sourced from the enigmatic medusae fossae formation mff creates these sedimentary layers this implies that episodes of atmospheric activity perhaps linked with the obliquity of mars periodically erode and redeposit material from the mff across a large region

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

combining seismic and electric methods for predicting bedrock depth along a mediterranean soil toposequence abstract bedrock depth provides important information for many environmental and agricultural applications such as shallow groundwater monitoring the determination of soil water availability and the estimation of crop production potential direct estimates of bedrock depth from destructive soil observations are discontinuous and too expensive to be used in large areas geophysical methods are often cited as possible alternatives however their ability to provide reliable estimations of bedrock depth is known to depend greatly on local site characteristics therefore combining geophysical methods based on different physical parameters may help to provide better predictions this study examines the ability of the spectral analysis of surface waves sasw method combined with the classical high resolution electrical resistivity tomography ert method to predict soil depths in a 500 m ranged mediterranean hillslope southern france with increasing soil depths along the slope sasw was performed using the data measured in the field with classical seismic equipment impulse source and geophones distributed along a line in the same place eight transects of ert wenner schlumberger array 1 m electrode spaced were measured under wet and dry conditions to calibrate the geophysical measurements 81 boreholes from two to 5 m deep were interpreted to determine the bedrock depth which was defined as the occurrence in the depth of heterogeneous marine miocene loose sandstone with centimetric laminations ert and sasw were found to have highly variable performances for predicting separately the bedrock depth along the hillslope sasw correctly predicted the bedrock depth in the lower part of the hillslope whereas the data from ert were disrupted by shallow permanent groundwater conversely ert correctly predicted bedrock depth within the upper part of the hillslope whereas a high variability of sasw data near the topsoil caused difficulties for bedrock depth prediction from these results it was possible to define an estimator of bedrock depth according to the presence of shallow groundwater which varies along the slope such that more importance is given to ert estimates in the upper part of the hillslope and more importance is given to sasw in the lower part this study shows the usefulness of such a sensor combination to estimate soil properties when the uncertainties of making predictions vary according to the geophysical methods

medusae fossae formation new perspectives from mars global surveyor 1 the nature and origin of the medusae fossae formation mff on mars has been debated since the return of the first viking images the mff s young age distinctive surface texture and lack of obvious source have prompted multiple hypotheses for its origin this study uses data from the mars global surveyor mgs mission to examine the mff at all available scales we discuss and quantify observations from mars orbiter laser altimeter mola topography and mars orbiter camera moc images to better constrain the origin of the mff topographic grid estimates yield a present extent of 2 1 106 km2 and a volume of 1 4 106 km3 however remnant yardang deposits observed far from the thicker lobes of mff material suggest that it may have once covered up to 5 106 km2 we do not find compelling evidence for extensive fluvial reworking of the mff however in several regions buried channels are apparent in the mff because the formation is draped over underlying topography layering is apparent at all scales from submeter to hundreds of meters with variable resistance to weathering continuity of layers appears to be local to regional but not likely formation wide yardangs form both parallel and bidirectional patterns with resistant layers and jointing probably influencing their orientations a comparative study of mff regional topography and surface expression indicates that the mff is quantitatively dissimilar to martian polar layered deposits the material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin

occurrence and origin of rhythmic sedimentary rocks on mars sedimentary rocks preserved on the surface of mars represent a natural archive of past climate conditions although the details of their formation often remain poorly constrained the recent detection of rhythmic bedding patterns in the arabia terra region suggests the influence of orbital variations on sedimentary deposition here we detail a number of new sites which exhibit quasiperiodic stratigraphic variations demonstrating their occurrence throughout the equatorial region of the planet we characterize these recorded signals as well as the local geomorphic context and structural attributes two cyclic units are identified within gale crater the landing site of the mars science laboratory mission enabling estimation of possible formation timescales for the geologic units that may be studied in situ by the rover we find a general lack of fluvial features in connection with rhythmic geologic units contrasting these sites with the aperiodic deltaic stratigraphy found at eberswalde crater possible formation scenarios and their climatic implications are discussed for the diverse set of quasiperiodic sedimentary units we propose multiple depositional pathways for recording cyclic climate changes including repeated evaporitic precipitation from groundwater discharge in topographic lows as well as largely anhydrous accumulation of atmospheric dust for deposits outside of confined basins the preservation of orbital signals in sediments distributed across a wide range of geographic settings suggests a pervasive influence on martian climate conditions through time

errors in martian paleodischarges skew interpretations of hydrologic history case study of the aeolis dorsa mars with insights from the quinn river nv abstract changes in martian fluvial geomorphology with time stratigraphic age including decreases in paleochannel widths suggest waning paleodischarges through time where fluvial landforms do not preserve paleochannel widths e g meander deposits other landform dimensions i e radius of curvature may be used to estimate paleodischarges in the aeolis dorsa region topographically inverted and stacked fluvial deposits wide meander point bars overlain by thin channel fills preserve ostensible evidence of decreasing paleodischarges through time however a robust paleohydraulic analysis of these distinct deposits requires knowledge of the accuracy of a terrestrial based empirical relationship that estimates channel width from point bar radius of curvature we assess the accuracy of this radius width relationship by applying it to a well studied terrestrial analog the quinn river nevada we find that radii of curvature from the quinn river exceed the values predicted from the empirical relationship these anomalously high radii are associated with greater resistance in the channel cut banks indicating that bank strength is a confounding factor in the radius width relationship some deposits in the aeolis dorsa include irregular meander morphologies suggesting variably resistant channel banks and overestimates of both paleochannel widths and paleodischarges furthermore the morphometry of the overlying thin channel fills suggests their widths have been eroded such that their paleodischarges are underestimates these overestimates and underestimates when considered together suggest little change in paleodischarge during the stratigraphic transition from meander deposits to channel fills this work demonstrates the importance of terrestrial analog studies for revealing confounding factors in martian fluvial systems and cautions against simplistic interpretations of martian fluvial history the discovered inaccuracies of paleodischarge estimates expose sources of uncertainty in the extant paleodischarge data that bias inferences toward waning hydrologic activity through time

ignimbrites of amazonis planitia region of mars a series of postulated ignimbrite units is mapped in the amazonis memnonia and aeolis quadrangles of mars the units cover about 2 2 106 km2 within a broad but discontinuous and irregular belt trending east west along the highland lowland boundary the ignimbrites overlie parts of the western and southern aureole materials of olympus mons but are embayed in places by the lava plains of the lowlands stratigraphic relations between the basalt flows from the tharsis montes region and the ignimbrites are not clearly defined crater counts suggest that the younger ignimbrites postdate the lava flows crater counts per square kilometer for the ignimbrites range from 7 29 1 95 10 4 to 6 36 2 01 10 5 for craters larger than 1 km in diameter the ignimbrite materials form thick 100 m extensive relatively flat sheets that are smooth to grooved or gently undulating grooved surfaces appear to be yardangs and in most places are not alined with prevailing wind directions the seven mapped ignimbrite units are characterized by morphologic expression stratigraphic position and crater counts similarities to ignimbrites in the pancake range of central nevada include 1 rounded patches of smooth high albedo nonwelded material superposed on jointed low albedo welded material 2 local complementary joint sets in welded materials and 3 thick flow sheets of great areal extent that follow but subdue underlying topography four major eruptive centers occur in areas where units are thickest and where a dominant nnw sse structural trend is expressed locally by unit margins elongate collapse features and normal faulting a minimum volume of 3 85 106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations

greater contrast in martian hydrological history from more accurate estimates of paleodischarge correlative width discharge relationships from the missouri river basin are commonly used to estimate fluvial paleodischarge on mars however hydraulic geometry provides alternative and causal width discharge relationships derived from broader samples of channels including those in reduced gravity submarine environments comparison of these relationships implies that causal relationships from hydraulic geometry should yield more accurate and more precise discharge estimates our remote analysis of a martian terrestrial analog channel combined with in situ discharge data substantiates this implication applied to martian features these results imply paleodischarges of interior channels of noachian hesperian 3 7 ga valley networks have been underestimated by a factor of several whereas paleodischarges for smaller fluvial deposits of the late hesperian early amazonian 3 0 ga have been overestimated thus these new paleodischarges significantly magnify the contrast between early and late martian hydrologic activity width discharge relationships from hydraulic geometry represent validated tools for quantifying fluvial input near candidate landing sites of upcoming missions

comparing orbiter and rover image based mapping of an ancient sedimentary environment aeolis palus gale crater mars this study provides the first systematic comparison of orbital facies maps with detailed ground based geology observations from the mars science laboratory msl curiosity rover to examine the validity of geologic interpretations derived from orbital image data orbital facies maps were constructed for the darwin cooperstown and kimberley waypoints visited by the curiosity rover using high resolution imaging science experiment hirise images these maps which represent the most detailed orbital analysis of these areas to date were compared with rover image based geologic maps and stratigraphic columns derived from curiosity s mast camera mastcam and mars hand lens imager mahli results show that bedrock outcrops can generally be distinguished from unconsolidated surficial deposits in high resolution orbital images and that orbital facies mapping can be used to recognize geologic contacts between well exposed bedrock units however process based interpretations derived from orbital image mapping are difficult to infer without known regional context or observable paleogeomorphic indicators and layer cake models of stratigraphy derived from orbital maps oversimplify depositional relationships as revealed from a rover perspective this study also shows that fine scale orbital image based mapping of current and future mars landing sites is essential for optimizing the efficiency and science return of rover surface operations

rafted pumice a new model for the formation of the medusae fossae formation mars abstract the medusae fossae formation mff mars could be deposits of materials originally formed as hyaloclastites erupted from vents which formed the basal units of olympus mons volcano and subsequently collapsed as landslides to form the aureole materials these low density hyaloclastites subsequently floated on the northern sea as pumice rafts and drifted to the southwest where they encountered the boundary of the southern highlands to form the mff

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

a candidate methane clathrate destabilisation event on mars a model for sub millennial scale climatic change on earth abstract methanogenic explosion of siberian permafrost mounds over the last three years questions whether this new phenomenon is the first sign of cascading release under climatic warming identical mounds occur in their millions on mars but are uniformly interpreted as ancient volcanic structures a geomorphic paradigm whose geological basis continues to escape objective observation here i show that thousands of mars mounds have recently exploded onto overlying aeolian dunes and are thus active and climatogenic the time lag between formation and synchronous explosion naturally explained by a trigger of climatic origin time transgressive mass explosion of a multi billion year aged source has no parallel in rock forming processes and points to regional scale mobilisation of volatiles this abrupt destabilisation event having immediate implications for hypothesised cascading releases from terrestrial clathrate reservoirs whether the siberian explosions are new or simply newly discovered is uncertain but their spatial density is 20 000 times lower than on mars inconsistent with ongoing multi millennial scale process we should therefore consider the possibility that they are just beginning and irrespective of volatile involved we now have a scaleable example of how they might end were the clathrates of the east siberian arctic shelf to degas on the density and frequency of mars then the entire reservoir would be depleted and unstoppable runaway warming initiated

crust stratigraphy and heterogeneities of the first kilometers at the dichotomy boundary in western elysium planitia and implications for insight lander abstract insight landed on mars on november 26 2018 in western elysium planitia the mars crust beneath the lander is subject to complex geologic history next to the great topographic and crustal dichotomy of mars understanding this part of the martian crust in the subsurface would aid future investigations of the internal structure of the planet based on seismic datasets collected by the seismic experiment for interior structure seis instrument here we investigate the subsurface structure and composition from the analysis of mineralogy and morphology of exposures in impact craters as well as on scarps and knobs in the general region of elysium planitia using a combination of orbital datasets we identify exposures of subsurface materials with distinct composition and physical properties we find olivine and pyroxene detections associated with small impact craters 1 5 7 km rim in the vicinity of insight lander as well as in the transition unit and elysium volcanic unit fe mg phyllosilicates have been identified in the central peak of the 51 km diameter kalpin crater and on knobs in the transition unit between the dichotomy and the plains in addition eroded meter scale layered unit subject to erosion has been identified in six impact craters to the north east of the landing site including kalpin crater massive bedrock and layered weak materials co occur in the transition unit indicating a complex origin these results together suggest both materials with altered composition and layered deposit occur as distinct geologic units beneath the basaltic lava flow units through analogy with terrestrial sedimentary rocks or clay bearing sediments we suggest physically weak materials exist beneath the lava flow units in the general region of elysium planitia the spatial distribution and continuity of these materials are unclear due to the lack of exposures within the lava flow unit where the insight lander is located these subsurface materials of distinct physical properties may result in increased attenuation or reverberations of seismic waves to be collected by seis the findings suggest a close investigation of the potential effects of subsurface stratigraphy on seismic data would help inform future data interpretation and understanding of the internal structure of mars

redefinition of the crater density and absolute age boundaries for the chronostratigraphic system of mars abstract for the boundaries of each chronostratigraphic epoch on mars we present systematically derived crater size frequencies based on crater counts of geologic referent surfaces and three proposed standard crater size frequency production distributions as defined by a a simple 2 power law b neukum and ivanov c hartmann in turn these crater count values are converted to model absolute ages based on the inferred cratering rate histories we present a new boundary definition for the late hesperian early amazonian transition our fitting of crater size frequency distributions to the chronostratigraphic record of mars permits the assignment of cumulative counts of craters down to 100 m 1 km 2 km 5 km and 16 km diameters to martian epochs due to differences in the standard crater size frequency production distributions a generalized crater density based definition to the chronostratigraphic system cannot be provided for the diameter range used for the boundary definitions the resulting model absolute age fits vary within 1 5 for a given set of production function and chronology model ages crater distributions translated to absolute ages utilizing different curve descriptions can result in absolute age differences exceeding 10

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

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

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

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

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

hirise images of yardangs and sinuous ridges in the lower member of the medusae fossae formation mars abstract hirise images of the lower member of the medusae fossae formation mff were used to identify characteristics of two specific landforms that are well expressed in this particular geologic unit yardangs and sinuous ridges yardangs are wind eroded ridges that are usually confined to arid environments where the bedrock materials can be easily eroded by windblown sand yardangs are common in the lower member of mff where many individual yardangs show evidence of a caprock unit overlying a more friable unit most consistent with an ignimbrite origin for these mff deposits heights of the yardangs in the lower member materials are generally less than a few tens of meters in contrast to yardangs in the thicker middle member mff materials to the east of the study area the yardangs may form in materials comprised of discrete depositional units and there is good evidence that at least a dozen such depositional events contributed to the emplacement of the lower member of mff the lower member yardang heights indicate aeolian erosion has removed at least 19 000 km 3 of lower member mff materials sinuous ridges are elongate positive relief landforms that have been attributed to a variety of possible fluvial flow processes on mars sinuous ridges are very common within exposures of the lower member of mff multiple ridge types are present but all forms seen at hirise scale are most consistent with some form of aqueous channel flow rather than other possible origins the results from this initial examination of hirise images indicate the potential utility of comparing yardangs and sinuous ridges in the lower member to other members of mff although it remains to be determined if sinuous ridges are abundant in the younger mff members

roughness and near surface density of mars from sharad radar echoes 1 we present a technique for estimating mars topographic roughness on horizontal scales from about 10 m to 100 m using shallow radar sharad sounding data our results offer a view of surface properties complementary to mars orbiter laser altimeter mola pulse width or baseline roughness maps and can be compared to sharad peak echo properties to infer deviations from the average near surface density latitudinal averaging of sharad derived roughness over arabia and noachis terrae shows good agreement with mola derived roughness and provides clear evidence for latitude dependent mantling deposits previously inferred from image data in northwestern gordii dorsum we find that bulk density in at least the upper few meters is significantly lower than in other units of the medusae fossae formation we observe the same behavior indicative of low near surface density in wind eroded crater fill in the southern highlands combining surface properties analysis subsurface sounding and high resolution optical images we show that the pavonis mons fan shaped deposit differs significantly from lobate debris aprons which sharad has shown to be ice cored there are no internal radar reflections from the smooth facies portion of the pavonis mons fan shaped deposit and we suggest that these deposits are either quite thin or have little dielectric i e density contrast with the underlying terrain future application of these techniques can identify other low density units across mars assist in the mapping of regional volatile rich mantling units and provide new constraints on the physical properties of the polar layered terrain

the birth and death of transverse aeolian ridges on mars transverse aeolian ridges tars are small bright windblown deposits found throughout the martian tropics that stand a few meters tall and are spaced a few tens of meters apart the origin of these features remains mysterious more than 20 years after their discovery on mars this paper presents a new hypothesis that some of the tars could be indurated dust deposits emplaced millions of years ago during periods of higher axial obliquity it suggests that these tars are primary depositional bed forms that accumulated in place from dust carried by the winds in suspension perhaps in a manner comparable to antidunes on earth and were subsequently indurated and eroded to their current states by eons of sandblasting it points out examples of modern dust drifts and dune like features that appear to have been recently formed by dust accumulating directly onto the surface from atmospheric suspension it shows how these pristine dust deposits could evolve to explain the range of morphologies of the tars finally it explains how the known properties of many tars are consistent with this hypothesis including their composition thermal behavior and distribution

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

geochemical diversity in first rocks examined by the curiosity rover in gale crater evidence for and significance of an alkali and volatile rich igneous source the first four rocks examined by the mars science laboratory alpha particle x ray spectrometer indicate that curiosity landed in a lithologically diverse region of mars these rocks collectively dubbed the bradbury assemblage were studied along an eastward traverse sols 46 102 compositions range from na and al rich mugearite jake matijevic to fe mg and zn rich alkali rich basalt hawaiite bathurst inlet and span nearly the entire range in feo and mno of the data sets from previous martian missions and martian meteorites the bradbury assemblage is also enriched in k and moderately volatile metals zn and ge these elements do not correlate with cl or s suggesting that they are associated with the rocks themselves and not with salt rich coatings three out of the four bradbury rocks plot along a line in elemental variation diagrams suggesting mixing between al rich and fe rich components chemcam analyses give insight to their degree of chemical heterogeneity and grain size variations in trace elements detected by chemcam suggest chemical weathering li and concentration in mineral phases e g rb and sr in feldspars we interpret the bradbury assemblage to be broadly volcanic and or volcaniclastic derived either from near the gale crater rim and transported by the peace vallis fan network or from a local volcanic source within gale crater high fe and fe mn in et then likely reflect secondary precipitation of fe 3 oxides as a cement or rind the k rich signature of the bradbury assemblage if igneous in origin may have formed by small degrees of partial melting of metasomatized mantle

composition and organic maturity of middle jurassic coals north east greenland evidence for liptinite induced suppression of huminite reflectance abstract middle jurassic coals from kuhn o north east greenland may contain up to 85 vol liptinite principally resinite up to 68 6 vol the coals are thus petrographically comparable to the middle jurassic muslingebjerg formation coals at hochstetter forland approximately 40 50 km to the north and they are inherently excellent petroleum source rocks liptinite poor 6 0 vol coal samples from both kuhn o and hochstetter forland yield mean random huminite reflectance values of 0 49 0 53 ro implying a rank of sub bituminous a above a threshold value somewhere between 3 and 24 vol resinite and 6 and 35 vol total liptinite significant reflectance suppression is induced and between 24 and 69 vol resinite and 35 and 85 vol total liptinite a nearly linear inverse relationship exists between the content of liptinite resinite and the mean random reflectance values at the highest liptinite resinite contents reflectance suppression may be up to 0 23 ro the reflectance suppression is related to bitumen adsorption caused by bitumen expulsion from resinite and total reflectance distributions of the huminite fractions suggest that the reflectance of all huminite macerals is lowered with increasing liptinite resinite content