the simud tiu valles hydrologic system a multidisciplinary study of a possible site for future mars on site exploration abstract when looking for traces of past life on mars we have to look primarily for places where water was present possibly for long time intervals the simud and tiu valles are two large outflow channels connected to the north with the chryse basin oxia palus quadrangle the area carved by water during the noachian early hesperian is characterized by a complex geological evolution the geomorphological analysis shows the presence of fluvial and alluvial structures interpreted as fluvial channels and terraces debris flow fronts and short lasting small water flows coexisting with maar diatremes and mud volcanoes several morphological features indicate a change in water flux direction after the main erosive phase during this period water originated from the masursky crater and flown southwards into the hydraotes chaos this phenomenon caused the studied area to become a depocenter where fine grained material deposition took place possibly in association with ponding water this setting is potentially quite valuable as traces of life may have been preserved the presence of water at various times over a period of about 1 ga in the area is corroborated by mineralogical analyses of different areas that indicate the possible presence of hydrated minerals mixtures such as sulfate bearing deposits given the uniqueness of the evolution of this region the long term interactions between fluvial volcanic and tectonic processes and its extremely favorable landing parameters elevation slope roughness rock distribution thermal inertia albedo etc we decided to propose this location as a possible landing site for the esa exomars 2018 the nasa mars 2020 and future on site missions

organic chemistry in a co 2 rich early earth atmosphere the emergence of life on the earth has required a prior organic chemistry leading to the formation of prebiotic molecules the origin and the evolution of the organic matter on the early earth is not yet firmly understood several hypothesis possibly complementary are considered they can be divided in two categories endogenous and exogenous sources in this work we investigate the contribution of a specific endogenous source the organic chemistry occurring in the ionosphere of the early earth where the significant vuv contribution of the young sun involved an efficient formation of reactive species we address the issue whether this chemistry can lead to the formation of complex organic compounds with co2 as only source of carbon in an early atmosphere made of n2 co2 and h2 by mimicking experimentally this type of chemistry using a low pressure plasma reactor by analyzing the gaseous phase composition we strictly identified the formation of h2o nh3 n2o and c2n2 the formation of a solid organic phase is also observed confirming the possibility to trigger organic chemistry in the upper atmosphere of the early earth the identification of nitrogen bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the early earth

geology of xanthe terra outflow channels and the mars pathfinder landing site the mars pathfinder landing site mpls was selected for its location at the mouths of ares and tiu valles outflow channels on mars where sediments from a variety of geologic units could have accumulated in a lacustrine environment recent geologic mapping at 1 2 m scale of the xanthe terra channels and chryse planitia near mpls reveals a progression of fluvial erosion and deposition throughout the hesperian period from the geology the watersheds of the channels were inferred and a sequence of paleogeologic maps was produced three outflow episodes are recognized 1 broad sheetwash during the early hesperian emanating from eastern valles marineris and equatorial chaos regions with initial erosion into highland plateau basement 2 early channel formation and 3 subsequent flooding which deepened the channels to their current morphologies the most recent flooding issued from simud and tiu valles during the late hesperian indicated by stratigraphic superposition striations along the floor of the channel and the orientation of streamlined islands in the flood direction this suggests that surface sediments deposited at mpls are most likely to have come from these channels and to a lesser extent from ares vallis a ranking scheme was developed to assess the potential origins for the sediments found at mpls the most abundant materials are inferred to have come from the noachian and hesperian highland plains and reworked sediments from previous floods underlying materials from earlier floods could also be found at mpls as ejecta from nearby impact craters

glacial sediments and erosional pavements near the cambrian precambrian boundary in western henan province china exceptionally well preserved glaciated pavements and a variety of glacigenic sediments comprising the luoquan formation in henan province central china are believed to have formed close to the cambrian precambrian boundary they may therefore be younger than the better known sinian tillites representing the changan and nantuo ice ages they perhaps belong to a distinct glacial epoch that is recorded elsewhere in china and in other continents but for which there is less evidence than for earlier late proterozoic glacial periods lithofacies represented in the luoquan formation are massive diamictite signifying deposition as lodgement or melt out till bedded diamictite waterlain till or glaciomarine glaciolacustrine sediments with dropstones rhythmites with dropstones glaciolacustrine or fjord deposits possibly varves tabular conglomerates and sandstones outwash deltaic or sub aqueous mass flow deposits lens shaped breccia deposits sub aqueous mass flow deposits and gravel sand wedges frost contraction crack infillings the glaciated pavements reveal well preserved striations grooves often intersecting 9plastically moulded9 forms crescentic gouges and steps on a regional scale the linear features are of variable orientation but they indicate a dominant ice flow direction towards the southeast all this evidence points to upland glaciation with erosion followed by deposition in a terrestrial glacial and glaciolacustrine environment

3d structure of the gusev crater region abstract gusev crater lies within the aeolis quadrangle of mars at the boundary between the northern lowlands and southern highlands the ancient valley ma adim vallis dissects the highlands south of gusev crater and is thought to have fed the crater with sediments high resolution stereo camera data and digital elevation models were used to construct a geologic geomorphic map 173 5 178 5 e 10 18 s and cross sections complemented by data from mars orbiter camera mars orbiter laser altimeter and thermal emission imaging system three geologic domains are recognised the highlands in the south gusev crater and lowlands in the north twelve units are mapped with thicknesses ranging from hundred meters to several kilometres thicknesses of units and their bedding attitude are estimated combining the geologic map and topographic information relative ages are determined from crater counts ranging from early noachian for highland units to middle amazonian for units in gusev crater and in lowlands episodes of intense geologic activity deposition volcanism deformation occur at around 4 0 ga 3 7 ga and 3 5 ga comparing the geometry of the gusev crater with similar sized filled and un filled martian craters suggests that the columbia hills are relics of the original central peak of gusev crater

nature and characteristics of the flows that carved the simud and tiu outflow channels mars 1 geomorphic and topographic relations of higher and lower levels of dissection within the simud and tiu valles outflow channels on mars reveal new insights into their formational histories we find that the water floods that carved the higher channel floors were primarily sourced from hydaspis chaos the floods apparently branched into distributaries downstream that promoted rapid freezing and sublimation of water and limited discharge into the lowlands in contrast we suggest that the lower outflow channels were carved by debris flows from hydraotes chaos surges within individual debris flows possessed variable volatile contents and led to the deposition of smooth deposits marked by low relief longitudinal ridges lower outflow channel discharges resulted in widespread deposition within the simud tiu valles as well as within the northern plains of mars

late pleistocene depositional systems of metropolitan toronto and their engineering and glacial geological significance the municipality of metropolitan toronto area 480 km2 population 2 15 million is centrally located on the late pleistocene sedimentary infill of the laurentian channel a broad bedrock low up to 115 km wide connecting the huron and ontario basins this channel forms part of a relict late tertiary drainage network the laurentian river modified by pleistocene glacial erosion and infilled by over 100 m of glacial and interglacial sediments the subsurface stratigraphy of the channel fill below metropolitan toronto has been established from many different data sources and is depicted in this paper as a series of cross sections with a total length of nearly 105 km the subsurface stratigraphy has been divided provisionally into five depositional complexes which have been mapped in the subsurface along several transects these are 1 a glacial complex of illinoian age 2 a lacustrine complex of sangamon interglacial and earliest wisconsinan sediments 120 000 75 000 bp 3 a glaciolacust

outflow channel sources reactivation and chaos formation xanthe terra mars abstract the undulating warped and densely fractured surfaces of highland regions east of valles marineris located north of the eastern aureum chaos east of the hydraotes chaos and south of the hydaspis chaos resulted from extensional surface warping related to ground subsidence caused when pressurized water confined in subterranean caverns was released to the surface water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of ares tiu and simud valles of the eastern part of the circum chryse outflow channel system progressive surface subsidence and associated reduction of the subsurface cavernous volume and or episodes of magmatic driven activity led to increases of the hydrostatic pressure resulting in reactivation of both catastrophic and non catastrophic outflow activity ancient cratered highland and basin materials that underwent large scale subsidence grade into densely fractured terrains collapse of rock materials in these regions resulted in the formation of chaotic terrains which occur in and near the headwaters of the eastern circum chryse outflow channels the deepest chaotic terrain in the hydaspis chaos region resulted from the collapse of pre existing outflow channel floors the release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow basal warming related to dike intrusions thermokarst activity involving wet sediments and or dissected ice enriched country rock permafrost exposed to the atmosphere by extensional tectonism and channel incision and or the injection of water into porous floor material may have enhanced outflow channel floor instability and subsequent collapse in addition to the possible genetic linkage to outflow channel development dating back to at least the late noachian clear disruption of impact craters with pristine ejecta blankets and rims as well as preservation of fine tectonic fabrics suggest that plateau subsidence and chaos formation may have continued well into the amazonian period the geologic and paleohydrologic histories presented here have important implications as new mechanisms for outflow channel formation and other fluvial activity are described and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation and thus chaotic terrains mark prime locations for future geologic hydrologic and possible astrobiologic exploration

initiation of martian outflow channels related to the dissociation of gas hydrate we propose that the disruption of subpermafrost aquifers on mars by the thermal or pressure induced dissociation of methane hydrate may have been a frequent trigger for initiating outflow channel activity this possibility is raised by recent work that suggests that significant amounts of methane and gas hydrate may have been produced within and beneath the planet s cryosphere on earth the build up of overpressured water and gas by the decomposition of hydrate deposits has been implicated in the formation of large blowout features on the ocean floor these features display a remarkable resemblance in both morphology and scale to the chaotic terrain found at the source of many martian channels the destabilization of hydrate can generate pressures sufficient to disrupt aquifers confined by up to 5 kilometers of frozen ground while smaller discharges may result from the water produced by the decomposition of near surface hydrate alone

related magma ice interactions possible origins of chasmata chaos and surface materials in xanthe margaritifer and meridiani terrae mars abstract we examine here the close spatial and temporal associations among several unique features of xanthe and margaritifer terrae specifically the valles marineris troughs or chasmata and their interior deposits chaotic terrain the circum chryse outflow channels and the subdued cratered material that covers xanthe margaritifer and meridiani terrae though previous hypotheses have attempted to explain the origin of individual features or subsets of these we suggest that they may all be related all of these features taken together present a consistent scenario that includes the processes of sub ice volcanism and other magma ice interactions results of intrusive events during late noachian to early amazonian times

comments and reply on sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada reply

martian surface paleotemperatures from thermochronology of meteorites the temporal evolution of past martian surface temperatures is poorly known we used thermochronology and published noble gas and petrographic data to constrain the temperature histories of the nakhlites and martian meteorite alh84001 we found that the nakhlites have not been heated to more than 350 c since they formed our calculations also suggest that for most of the past 4 billion years ambient near surface temperatures on mars are unlikely to have been much higher than the present cold 0 c state

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

comments on using the viscoelastic relaxation of large impact craters to study the thermal history of mars karimi et al 2016 icarus 272 102 113 and studying lower crustal flow beneath mead basin implications for the thermal history and rheology of venus karimi and dombard 2017 icarus 282 34 39 abstract two recent papers by karimi et al 2016 icarus 272 102 113 and karimi and dombard 2017 icarus 282 34 39 tried to deduce paleo heat flows for respectively mars and venus from modeling the viscoelastic relaxation of large impact craters indeed crater relaxation would be consequence of the flow of the lower crust and uppermost mantle this flow is dependent on temperature permitting the link with the calculation of thermal profiles and heat flows both papers used conductive thermal profiles and constant thermal conductivities for both the crust and upper mantle equivalent to using linear thermal gradients given there were no mention to crustal or mantle heat sources and appropriate rheological laws in the present discussion we show that the background heat flows contemporaneous to impact craters formation and relaxation obtained by karimi and co workers when used along with the assumptions made by these authors lead to temperatures that produce massive even total lower crust melting in all and at least a substantial part of the cases for respectively venus and mars it is clear that the heat flow results presented by karimi and co workers suffer of inconsistency between model requirements explicitly indicated a crust free of melting and the implications of the obtained basal heat flows a lowermost crust partially or totally molten thus we consider that the papers by karimi and co workers do not give reliable information on the thermal history of mars and venus

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

lacustrine ostracodes in the late pleistocene sunnybrook diamicton of southern ontario canada two opposing interpretations have been made on the depositional origin of the late pleistocene sunnybrook diamicton in the metro toronto region of southern ontario the traditional view holds this deposit to be a till but more recent arguments advocate a glaciolacustrine origin by suspension deposition and ice rafting the discovery of a low diversity ostracode fauna consisting of candona subtriangulata candona caudata and darwinula stevensoni in the sunnybrook diamicton suggests a lacustrine origin excellent preservation of thin fragile shells and a mixture of juveniles and adults in sediments of varying texture clayey silt to silty clay indicate that there has been little winnowing or selective sorting and that the ostracodes are in situ indications are that the sunnybrook diamicton was deposited in a large deep and cold lake these new palaeontological observations call for a reassessment of the quaternary stratigraphy of the ontario basin and suggest that the laurentide ice sheet in the eastern

headward growth of chasmata by volatile outbursts collapse and drainage evidence from ganges chaos mars 1 the nature and significance of collapse processes in capri eos and ganges chasmata remain poorly understood using ganges chasma as a type locality these chasmata are interpreted to be the result of clustering and assimilation of multiple chaotic terrains which primarily formed by localized depressurization induced or thermally triggered dissociation of buried gas clathrate hydrates and explosive eruption of gas saturated ground water such crustal destabilization could have been triggered by 1 deep fracture propagation from the martian surface 2 magmatic intrusions and associated heating and inflation induced terrain fracturing and or 3 climatic thaw and thinning weakening of the permafrost over the clathrate and gas rich groundwater zones volume increases associated with release of gases contributed to the expulsion of groundwater and fluidized sediments at the surface thereby carving the higher outflow channels peripheral to the chasmata and the lower outflow channel floors of the chasmata and outflow channels

simulation of martian chaotic terrain and outflow channels abstract outflow channeling and associated chaotic terrain were created under temperature and pressure conditions suggested for a diluvian period on mars 3 5 to 0 5 by ago pressures under which both features were formed ranged from 130 to 34 mbar at a constant ambient temperature of 266 k analogs of the collapse structures and channels evolved in a high altitude low temperature chamber are found on the martian surface similarities exist not only in their overall morphology but in the finer details of the megastructures themselves the critical factor that allowed channelized flow to occur was the sudden release of liquid water derived from melting of subsurface ground ice and ice layers under the low atmospheric pressure and temperature conditions within the chamber experimentation may indicate the existence of substantially thick water ice layers beneath the martian regolith prior to the outflow channeling episode

evidence for extensive denudation of the martian highlands high resolution topographic data from the mars orbiter laser altimeter reveal evidence for widespread denudation from margaritifer sinus to northern arabia terra an area of 1 107 km2 a major resurfacing event is indicated by 1 a heavily degraded landscape hosting numerous inliers 2 truncation or absence of valley networks and 3 a break in slope at the edge of early to middle noachian plateau materials geomorphic mapping was completed on the type locale of denudation 0 30 s 0 30 w superposition relations and crater counts for geomorphic units indicate that large scale resurfacing took place in the late noachian eroding the martian highlands and resulting in transportation and deposition of 4 5 106 km3 of sediment in the northern plains this is equivalent to a 120 m thick uniform layer of sediment on the surface of mars north of 30 n geomorphic mapping and crater counts limit the timing of denudation to the late noachian an interval of 350 500 m y using this limit we estimate a minimum rate of denudation of 2 0 m yr comparable to denudation of typical slopes in a temperate maritime climate on earth the morphology rate of denudation and extensive nature of upland degradation suggest that precipitation fed surface runoff is the most likely geomorphic agent capable of such a process indicative of a warm wet mars during the late noachian epoch

on the orbital forcing of martian water and co2 cycles a general circulation model study with simplified volatile schemes 1 variations in the martian water and co2 cycles with changes in orbital and rotational parameters are examined using the geophysical fluid dynamics laboratory mars general circulation model the model allows for arbitrary specification of obliquity eccentricity and argument of perihelion as well as the position and thickness of surface ice exchange of co2 between the surface and atmosphere is modeled generating seasonal cycles of surface ice and surface pressure water is allowed to exchange between the surface and atmosphere cloud formation is treated and both cloud and vapor are transported by modeled winds and diffusion exchange of water and co2 with the subsurface is not allowed and radiative effects of water vapor and clouds are not treated the seasonal cycle of co2 is found to become more extreme at high obliquity as suggested by simple heat balance models maximum pressures remain largely the same but the minima decrease substantially as more co2 condenses in the more extensive polar night vapor and cloud abundances increase dramatically with obliquity the stable location for surface ice moves equatorward with increasing obliquity such that by 45 obliquity water ice is stable in the tropics only ice is not spatially uniform but rather found preferentially in regions of high thermal inertia or high topography eccentricity and argument of perihelion can provide a second order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles further model simulations reveal the robustness of these distributions for a variety of initial conditions our findings shed light on the nature of near surface ice rich deposits at midlatitudes and low latitudes on mars

a refined chronology of catastrophic outflow events in ares vallis mars abstract we investigate the geomorphology and chronology of catastrophic flooding in a major martian outflow channel ares vallis we use recently acquired stereo and colour images and derived topographic data with grid spacing of 50 m from the high resolution stereo camera hrsc onboard mars express to constrain the detailed flood geomorphology of proximal ares vallis we identify morphologic evidence for 6 distinct erosion surfaces that were likely formed by multiple episodes of catastrophic flooding these surfaces occur at distinct topographic levels exhibit multiple sets of flood grooves and contain distinct post flood crater populations crater count statistics on the flood eroded surfaces from mro context camera ctx and thermal emission imaging system themis visible images indicate that flooding was initiated during the late noachian early hesperian at 3 6 ga the morphology data confirm that the oldest flooding events occurred on the topographically highest erosion surfaces while subsequent floods abandoned the upper surfaces and continued to modify craters in the topographically lowest main channel of ares vallis into the late hesperian early amazonian 2 5 ga our results suggest that release of water to ares vallis likely occurred at repeated intervals over a long period of geological time thus supporting recent numerical modelling studies that suggest a recharging water source

possible precipitation of ice at low latitudes of mars during periods of high obliquity most of the old cratered highlands of mars are dissected by branching river valleys that appear to have been cut by running water1 2 yet liquid water is unstable everywhere on the martian surface in the equatorial region where most of the valleys are observed even ice is unstable3 4 it has been suggested therefore that mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water5 here we suggest instead that during periods of very high obliquities ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards at low latitudes the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed the mechanism is efficient only at the very high obliquities that occurred before formation of tharsis very early in the planet s history but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet s history partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system

formation and evolution of the chaotic terrains by subsidence and magmatism hydraotes chaos mars the origin of the martian chaotic terrains is still uncertain and a variety of geologic scenarios have been proposed we provide topographic profiles of different chaos landscapes notably aureum and hydraotes chaos showing that an initial shallow ground subsidence occurred at the first step of the chaos formation we infer that the subsidence was caused by intrusion of a volcanic sill which could have produced consequent melting as well as release of ground water from disrupted aquifer signs of a volcanic activity are observed on the floor of hydraotes chaos a complex and deep depression located at the junction of three channels the volcanic activity is represented by small 0 5 to 1 5 km diameter rounded cones with summit pits the cone s size and morphology as well as the presence of possible surrounding lava flows suggest that they are primary volcanic cones similar to terrestrial cinder cones the identification of volcanic activity on the deepest chaos where the lower crustal thickness and the faults fractures system contributed to the magma rising reveals that magmatic activity proved by the cones and possibly help by structural activity has been a major factor in the formation of chaotic terrains

melt and collapse of buried water ice an alternative hypothesis for the formation of chaotic terrains on mars chaotic terrains and the associated massive outflow channels are some of the most enigmatic features on mars over hundreds of kilometres of rock units are fractured tilted and have subsided forming chaotic terrain basins sharp 1973 large quantities of water emanated from these chaotic terrains in short periods of time in the hesperian epoch 3 7 3 3ga carving huge outflow channels thousands of kilometres long and more than 1km deep baker 2001 however the subsurface mechanism by which chaotic terrains form and thereby suddenly produce very large quantities of water 10 5 km 3 is poorly understood here we explore if these features can form by melting and collapse of buried water ice in a confined basin 2d thermal modelling using boundary conditions derived from the geology of aram chaos demonstrates that a buried ice unit will start melting when 1 2km of overburden has accumulated the thickness of the liquid subsurface layer depends primarily on the crustal heat flux the thermal conductivity of the overburden sediments and the surface temperature a subsurface liquid water layer of 1 to 2km can be achieved under present day surface temperature conditions and a crustal heat flux of 15 30mwm 2 to a first order the geological features of chaotic terrains and their outflow channels are consistent with a scenario in which a subsurface lake forms by melting of buried water ice followed by collapse and rapid outflow of water if correct this hypothesis suggests that subsurface lakes on mars may have existed for extensive 100ma periods of time such subsurface lakes would be of major interest for astrobiology 2010 elsevier b v

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

mineralogical composition structure morphology and geological history of aram chaos crater fill on mars derived from omega mars express data 1 aram chaos is a crater 280 km in diameter centered at 2 5 n 338 5 e it is filled by chaotic terrains overlain by a dome shaped layered 900 m thick formation displaying spectral signatures of ferric oxides on thermal emission spectrometer tes and observatoire pour la mineralogie l eau les glaces et l activite omega medium spatial resolution data we describe in detail the mineralogical composition structure and morphology of this crater fill using high resolution data omega mars orbiter laser altimeter mars orbiter camera tes thermal emission imaging system and high resolution imaging science experiment we infer the following formation scenario the crater was first filled by a geological formation the composition of which remains unclear because it is covered by dust widespread fracturing of this formation led to the development of chaotic terrains later a second layered formation presently dome shaped was emplaced unconformably on the chaotic terrains this younger unit is composed of a bright poorly consolidated material that contains both monohydrated sulfates and ferric oxides according to omega data the surface of this formation is partially covered by dust and displays landforms indicating that the bright material has been mobilized by wind during or after its deposition after its emplacement this formation has been grooved down to various depths by large eolian erosion corridors in these corridors eolian removal of the bright material with a sulfate rich matrix has left debris fans sand sheets and dunes which display some of the strongest spectral signatures of ferric oxides on mars similar residual deposits enriched in ferric oxides overlying a layered formation containing both ferric oxides and sulfates have been observed by the opportunity rover in meridiani planum suggesting a common formation process

control of impact crater fracture systems on subsurface hydrology ground subsidence and collapse mars 1 noachian layered materials are pervasively exposed throughout the highlands of mars the layered deposits in places many kilometers thick exhibit impact craters of diverse morphologic characteristics ranging from highly degraded to pristine most of which formed during the period of heavy bombardment in addition exhumed impact craters ancient channels and fluvial and alluvial fans are visible in the layered deposits through moc imagery these features are more abundant in noachian terrains which indicates relatively high erosion rates during ancient mars that competed with heavy meteoritic bombardment the noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation here we propose that impact craters buried and exposed and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic driven hydrothermal activity in and surrounding the tharsis region for example the formation of chaotic terrains the source regions of the circum chryse outflow channel system and a large diversity of collapse structures including impact crater moats and pit chains appear to be the result of enhanced hydrothermal activity

effect of obliteration on crater count chronologies for martian surfaces 1 the density of impact craters calibrated against lunar data is currently the only quantitative measure of surface age for terrestrial planetary surfaces unlike the moon however mars has been weathered and eroded obliterating some small 10 km diameter craters a phenomenon addressed in the mariner viking days of mars exploration but commonly overlooked in recent studies we present a quantitative model that extends this earlier work to assess the effect of erosion and infilling on surface ages inferred from crater frequency distributions our work affirms that small cratersizedistributionscanbeinterpretedquantitatively in terms of effects of erosion and crater infilling at rates comparable to those reported for mars a reanalysis of prior studies indicates that low to moderate long term rates of erosion and crater infilling can mask an ancient age and result in small crater populations similar to those offered as evidence for young and geologically significant surface activity citation smith m r a r gillespie and d r montgomery 2008 effect of obliteration on crater count chronologies for martian surfaces geophys res lett 35 l10202 doi 10 1029 2008gl033538

methane and climate during the precambrian era abstract the sun was substantially less bright in the distant past yet earth s surface temperature remained above freezing higher concentrations of the greenhouse gases co 2 and ch 4 were likely responsible for keeping the early climate warm ch 4 concentrations of 1000 ppm or higher are predicted for the late archean paleoproterozoic atmosphere prior to the rise of o 2 photolysis of this ch 4 may have created an optically thin organic haze during much of this time the rise of o 2 at 2 3 ga eliminated most of the methane and probably triggered the paleoproterozoic glaciations ch 4 concentrations could have remained elevated throughout much of the proterozoic however as a consequence of low concentrations of dissolved o 2 and sulfate in the deep oceans and a corresponding increase in organic matter recycling by fermentation and methanogenesis

resurfacing history of the northern plains of mars based on geologic mapping of mars global surveyor data 1 geologic mapping of the northern plains of mars based on mars orbiter laser altimeter topography and viking and mars orbiter camera images reveals new insights into geologic processes and events in this region during the hesperian and amazonian periods we propose four successive stages of lowland resurfacing likely related to the activity of near surface volatiles commencing at the highland lowland boundary hlb and progressing to lower topographic levels as follows highest elevations indicated stage 1 upper boundary plains early hesperian 2 0 to 2 9 km stage 2 lower boundary plains and outflow channel dissection late hesperian 2 7 to 4 0 km stage 3 vastitas borealis formation vbf surface late hesperian to early amazonian 3 1 to 4 1 km and stage 4 local chaos zones early amazonian 3 8 to 5 0 km at acidalia mensa stage 2 and 3 levels may be lower 4 4 and 4 8 km respectively contractional ridges form the dominant structure in the plains and developed from near the end of the early hesperian to the early amazonian geomorphic evidence for a northern plains filling ocean during stage 2 is absent because one did not form or its evidence was destroyed by stage 3 resurfacing remnants of possible amazonian dust mantles occur on top of the vbf the north polar layered deposits appear to be made up of an up to kilometer thick lower sequence of sandy layers early to middle amazonian in age overlain by late amazonian ice rich dust layers both units appear to have outliers suggesting that they once were more extensive

hydrographs of a martian flood from the breach of galilaei crater abstract spectacular floods were spawned on mars when large craters filled to overtopping and catastrophically breached the wealth of data now available permits quantitative analysis of these ancient floods galilaei crater is examined here along with the likely sources of its water and the processes that formed tana vallis its 1 km deep outflow channel laser altimetry data stereo photogrammetry and scaled images are used to reconstruct the lake volume and the geometry of the preserved breach it is theorized that surface flows from hydaspis chaos eroded the rim and floor of galilaei crater and partly filled the basin leading to degradation of the underlying cryosphere groundwater released from a confined aquifer then slowly filled galilaei crater until the enclosed lake overtopped its rim the resulting flood breached the crater wall rapidly drained the lake and eroded tana vallis the drainable lake volume was 1 110 1013 m3 based on laser altimetry data from mars global surveyor this volume was 90 of the volume in lake superior in the great lakes using the reconstructed breach and channel geometry methods used to analyze terrestrial dam breaches were applied to produce hydrographs of lake stage and discharge peak flood discharge in tana vallis likely ranged from 1 5 to 4 7 107 m3 s 1 mean channel incision rates are estimated at 0 333 0 133 and 0 0667 m min 1 for scenarios in which tana vallis formed in 2 5 and 10 days for the 5 day breach erosion scenario stream power per unit streambed area at the time of peak discharge was estimated at 3 5 105 w m 2 the volume of material eroded to form the vallis was only 3 of the lake volume that drained in 5 days open channel calculations were performed to compare with the dam breach hydrographs for tana vallis the channel as seen today never flowed bank full or even at three fourths its maximum depth because the implied flows would have exceeded peak discharges from the crater breach i also evaluate an alternative model catastrophic ice lake collapse for the morphology and breach of aram chaos a large crater near galilaei crater that model has fundamental difficulties because of improbable assumptions and inadequate consideration of the knowledge base of terrestrial basalt hydrology the model of ice lake collapse fails to explain the breach and outflow of crater lakes like those that existed in aram chaos and galilaei crater the present analysis supports a simpler model of groundwater inflow that fills a crater to overtopping this model harmonizes with the low elevations of aram chaos and galilaei crater and is more consistent with extensive evidence of fluid breakouts in this region and with theoretical and terrestrial knowledge

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

implications of present day abiogenic methane fluxes for the early archean atmosphere 1 during earth s early history greenhouse warming by atmospheric methane helped to maintain elevated surface temperatures here we estimate the present day abiogenic ch4 flux generated by mineral alteration serpentinization at mid ocean ridges volcanic emissions and geothermal sources in addition we assess the impact that abiogenic methane may have had on greenhouse warming during the early prebiotic archean based on estimates of the rate of seafloor spreading and the degree of serpentinization within the oceanic crust the flux of methane generated by serpentinized lithosphere is calculated to be 1 35 mt ch4 y 1 while volcanic and geothermal sources are estimated to contribute 0 1 and 0 9 mt ch4 y 1 respectively furthermore it is shown that if atmospheric co2 partial pressures were above 0 01 bar the present day level of abiogenic methane production could have been sufficient to maintain above freezing surface temperatures during the archean the very high temperatures 70 c that have been suggested for the early archean however would have required extremely high methane fluxes or more likely greatly elevated atmospheric co2 levels

formation of martian outflow channels by catastrophic dewatering of evaporite deposits geological mapping based on topographic analysis of mars orbiter laser altimeter mola data together with photointerpretation of mars orbiter camera moc images and thermodynamic and heat flow considerations frame a new hypothesis for the formation of martian outflow channels through catastrophic dewatering of evaporite deposits mola transects across valles marineris show that the valley is located at the crest of a 3 km high topographic bulge on the flank of the much larger tharsis rise interpretation of moc images showing layered deposits within valles marineris as unconformably underlying hesperian age lava flows means that these thick deposits thought to contain hydrous sulfates were heated by an increased geothermal gradient due to development of tharis increased temperatures adequate to dehydrate hydrous evaporites would trigger significant volumetric expansion and catastrophically release tremendous amounts of overpressured water