reading the climate record of the martian polar layered deposits abstract the martian polar regions have layered deposits of ice and dust the stratigraphy of these deposits is exposed within scarps and trough walls and is thought to have formed due to climate variations in the past insolation has varied significantly over time and caused dramatic changes in climate but it has remained unclear whether insolation variations could be linked to the stratigraphic record we present a model of layer formation based on physical processes that expresses polar deposition rates of ice and dust in terms of insolation in this model layer formation is controlled by the insolation record and dust rich layers form by two mechanisms 1 increased summer sublimation during high obliquity and 2 variations in the polar deposition of dust modulated by obliquity variations the model is simple yet physically plausible and allows for investigations of the climate control of the polar layered deposits pld we compare the model to a stratigraphic column obtained from the north polar layered deposits npld fishbaugh k e hvidberg c s byrne s russel p s herkenhoff k e winstrup m kirk r 2010a geophys res lett 37 l07201 and show that the model can be tuned to reproduce complex layer sequences the comparison with observations cannot uniquely constrain the pld chronology and it is limited by our interpretation of the observed stratigraphic column as a proxy for npld composition we identified however a set of parameters that provides a chronology of the npld tied to the insolation record and consistently explains layer formation in accordance with observations of npld stratigraphy this model dates the top 500 m of the npld back to 1 million years with an average net deposition rate of ice and dust of 0 55 mm a 1 the model stratigraphy contains a quasi periodic 30 m cycle similar to a previously suggested cycle in brightness profiles from the npld laskar j levrard b mustard f 2002 nature 419 375 377 milkovich s head j w 2005 j geophys res 110 but here related to half of the obliquity cycles of 120 and 99 kyr and resulting from a combination of the two layer formation mechanisms further investigations of the non linear insolation control of pld formation should consider data from other geographical locations and include radar data and other stratigraphic datasets that can constrain the composition and stratigraphy of the npld layers

hydrogen content of sand dunes within olympia undae neutron currents measured using the mars odyssey neutron spectrometer seasonally varying temperatures measured using the thermal emission spectrometer and visible images measured using the high resolution imaging science experiment hirise are studied to determine the water content and stratigraphy of olympia undae both the neutron and thermal infrared data are best represented by a two layered model having a water ice equivalent hydrogen content of 30 5 in a lower semi infinite layer buried beneath a relatively desiccated upper layer that is 9 6g cm 2 thick about 6 cm depth at a density of 1 5 g cm 3 a model that is consistent with all three data sets is that the dunes contain a top layer that is relatively mobile which overlays a niveo aeolian lower layer the geomorphology shown by the hirise images suggests that the bottom layer may be cemented in place and therefore relatively immobile

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

models of climate cycles recorded in martian polar layered deposits abstract layered strata observed in orbital images of polar sedimentary terrains on mars have been hypothesized to contain information about recent variations in the martian climate celestial mechanicians have determined that mars has experienced large amplitude quasi periodic variations in obliquity and eccentricity planetary meteorologists have inferred that the resulting changing patterns of solar heating must have had dramatic effects on martian climate accordingly it might be possible to link the known recent history of orbit axial variations with the physical characteristics of the most recently deposited strate determined from orbital imagery our paper explores that possibility quantitatively for various models of the formation of the polar layered deposits and the layering developed within them we modeled the formation of polar layered deposits during the past 10 my for two general classes of model uniform deposition rate udr models assume that the major constituent of the layered deposits is deposited at a uniform rate and that layering is established by climate induced variations in the concentration of a minor constituent climate modulated deposition rate cmdr models assume that the deposition rate of the major constituent is controlled by climate and that layer boundaries correspond to intervals of nondeposition in both models abrupt changes in deposition regime occur when a function of the orbit axial parameters crosses a threshold value detailed physical mechanisms for the control of sedimentation by orbit axial variations were developed for two specific models of the cmdr type in one model the deposits are assumed to be primarily composed of dust in the other they are assumed to be predominantly water ice we calculated the times at which abrupt changes in deposition regime occur and determined the relative thicknesses of successive layers which can be compared against layer thicknesses made from orbital imagery in all these models obliquity variations exert the dominant influence on the sequential variations in layer thickness although eccentricity and precession index longitude of perihelion may take recognizable contributions as well the layer patterns for the north and south polar deposits are identical for the dust model and only slightly different for the ice model but this is at least partly a consequence of simplifying assumptions the sequential variation in layer thickness is also very sensitive to those model parameters which control the fraction of time for which deposition occurs when the climate threshold for deposition is low deposition occurs a large fraction of the total time and characteristic patterns form with one thick layer and a number of much thinner ones such patterns would be easily recognized in photogeological measurements of layer thickness when the threshold for deposition lies in the mid range with respect to excursions of the climate function deposition occurs approximately half of the time and there is only slight modulation of layer thickness when the threshold for deposition is high deposition occurs only a small fraction of the total time and groups of layers form which are separated form other groups by long periods of nondeposition the stratigraphic unconformities that separate groupings of five to ten layers in the polar deposits may indicate that the martian polar region has experienced such a depositional history the feasibility of using these model results to verify the theory of climate control of polar stratigraphy on mars and to gain additional insights into the significant processes is considered the stratigraphy issues raised here are also explored in the context of recent work on the interpretation of stratigraphy of ocean margins from this comparison there emerge some valuable insights into the stratigraphic effects of periods of nondeposition and the uncertaintiesin interpreting images of exposed polar strata on mars

thermal behavior and ice table depth within the north polar erg of mars abstract we fully resolve a long standing thermal discrepancy concerning the north polar erg of mars several recent studies have shown that the erg s thermal properties are consistent with normal basaltic sand overlying shallow ground ice or ice cemented sand our findings bolster that conclusion by thoroughly characterizing the thermal behavior of the erg demonstrating that other likely forms of physical heterogeneity play only a minor role and obviating the need to invoke exotic materials thermal inertia as calculated from orbital temperature observations of the dunes has previously been found to be more consistent with dust sized materials than with sand since theory and laboratory data show that dunes will only form out of sand sized particles exotic sand sized agglomerations of dust have been invoked to explain the low values of thermal inertia however the polar dunes exhibit the same darker appearance and color as that of dunes found elsewhere on the planet that have thermal inertia consistent with normal sand sized basaltic grains whereas martian dust deposits are generally lighter and redder the alternative explanation for the discrepancy as a thermal effect of a shallow ice table is supported by our analysis of observations from the mars global surveyor thermal emission spectrometer and the mars odyssey thermal emission imaging system and by forward modeling of physical heterogeneity in addition our results exclude a uniform composition of dark dust sized materials and they show that the thermal effects of the dune slopes and bright interdune materials evident in high resolution images cannot account for the erg s thermal behavior

meter scale morphology of the north polar region of mars mars north pole is covered by a dome of layered ice deposits detailed 30 centimeters per pixel images of this region were obtained with the high resolution imaging science experiment on board the mars reconnaissance orbiter mro planum boreum basal unit scarps reveal cross bedding and show evidence for recent mass wasting flow and debris accumulation the north polar layers themselves are as thin as 10 centimeters but appear to be covered by a dusty veneer in places which may obscure thinner layers repetition of particular layer types implies that quasi periodic climate changes influenced the stratigraphic sequence in the polar layered deposits informing models for recent climate variations on mars

dielectric constant estimation of the uppermost basal unit layer in the martian boreales scopuli region abstract an electromagnetic inversion model has been applied to echoes from the subsurface sounding shallow radar sharad to retrieve the dielectric properties of the uppermost basal unit bu beneath the north polar layered deposits of mars sharad data have been carefully selected to satisfy the assumption of the inversion model which requires a stratigraphy consisting of mostly plane parallel layers the resulting values of the dielectric constant have been interpreted in terms of a variable percentage of dust in an ice dust mixture through the use of a mixing model for dielectric properties the resulting dust content exceeds 65 reaching perhaps 95 depending on the permittivity values assumed for the dust such a concentration is higher than that obtained by selvans et al selvans m m plaut j j aharonson o 2010 j geophys res 115 e09003 this discrepancy could be justified considering that our observations refer to the uppermost bu layer whereas selvans et al selvans m m plaut j j aharonson o 2010 j geophys res 115 e09003 probed the bu full thickness moreover if the bu is considered spatially inhomogeneous with very different dust content and thickness tanaka k l skinner j a fortezzo c m herkenhoff k e rodriguez j a p bourke m c kolb e j okubo c h 2008 icarus 196 318 358 the discrepancy could be furtherly reconciled

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

crater population and resurfacing of the martian north polar layered deposits present day accumulation in the north polar layered deposits npld is thought to occur via deposition on the north polar residual cap understanding current mass balance in relation to current climate would provide insight into the climatic record of the npld to constrain processes and rates of npld resurfacing a search for craters was conducted using images from the mars reconnaissance orbiter context camera one hundred thirty craters have been identified on the npld 95 of which are located within a region defined to represent recent accumulation high resolution imaging science experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal a classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth diameter ratios were determined the temporal and spatial distribution of crater degradation is interpreted to be close to uniform through comparison of the size frequency distribution of these craters with the expected production function the craters are interpreted to be an equilibrium population with a crater of diameter d meters having a lifetime of 30 75d 1 14 years accumulation rates within these craters are estimated at 7 2d 0 14 mm yr which corresponds to values of 3 4 mm yr and are much higher than rates thought to apply to the surrounding flat terrain the current crater population is estimated to have accumulated in the last 20 kyr or less

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

density and lithospheric structure at tyrrhena patera mars from gravity and topography data the tyrrhena patera highland volcano mars is associated with a relatively well localized gravity anomaly and we have carried out a localized admittance analysis in the region to constrain the density of the volcanic load the load thickness and the elastic thickness at the time of load emplacement the employed admittance model considers loading of an initially spherical surface and surface as well as subsurface loading is taken into account our results indicate that the gravity and topography data available at tyrrhena patera is consistent with the absence of subsurface loading but the presence of a small subsurface load cannot be ruled out we obtain minimum load densities of 2960 kg m 3 minimum load thicknesses of 5 km and minimum load volumes of 0 6 106 km3 photogeological evidence suggests that pyroclastic deposits make up at most 30 of this volume such that the bulk of tyrrhena patera is likely composed of competent basalt best fitting model parameters are a load density of 3343 kg m 3 a load thickness of 10 8 km and a load volume of 1 7 106 km3 these relatively large load densities indicate that lava compositions are comparable to those at other martian volcanoes and densities are comparable to those of the martian meteorites the elastic thickness in the region is constrained to be smaller than 27 5 km at the time of loading indicating surface heat flows in excess of 24 mw m 2

physical properties of martian meteorites porosity and density measurements martian meteorites are fragments of the martian crust these samples represent igneous rocks much like basalt as such many laboratory techniques designed for the study of earth materials have been applied to these meteorites despite numerous studies of martian meteorites little data exists on their basic structural characteristics such as porosity or density information that is important in interpreting their origin shock modification and cosmic ray exposure history analysis of these meteorites provides both insight into the various lithologies present as well as the impact history of the planets surface we present new data relating to the physical characteristics of twelve martian meteorites porosity was determined via a combination of scanning electron microscope sem imagery image analysis and helium pycnometry coupled with a modified archimedean method for bulk density measurements our results show a range in porosity and density values and that porosity tends to increase toward the edge of the sample preliminary interpretation of the data demonstrates good agreement between porosity measured at 100 and 300 magnification for the shergottite group while others exhibit more variability in comparison with the limited existing data for martian meteorites we find fairly good agreement although our porosity values typically lie at the low end of published values surprisingly despite the increased data set there is little by way of correlation between either porosity or density with parameters such as shock effect or terrestrial residency further data collection on additional meteorite samples is required before more definitive statements can be made concerning the validity of these observations

north polar deposits of mars extreme purity of the water ice 1 the polar layered deposits are the largest reservoir of water on the surface of mars the physical properties of the ice and their spatial distribution are largely unknown 140 000 data points from the sounding radar sharad on the mars reconnaissance orbiter were analyzed over the gemina lingula region one fourth of the north polar layered deposits area maps of the dielectric properties of the bulk ice were drawn up there is no basal melting signature a drop of the dielectric constant in north west of gemina lingula could be explained by an abrupt 250 meter uplift of the base the bulk ice of the studied region has an average dielectric constant of 3 10 0 12 and a loss tangent 0 0026 0 0005 analytic interpretations shown the volume of ice is pure at 95 the impurities have a radial distribution with higher concentrations at margins

recent aeolian dune change on mars previous comparisons of martian aeolian dunes in satellite images have not detected any change in dune form or position here we show dome dunes in the north polar region that shrank and then disappeared over a period of 3 04 mars years 5 7 earth years while larger neighboring dunes showed no erosion or movement the removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on mars but that any sand that is available for transport is likely to be moved dunes that show no evidence of change could be crusted indurated or subject to infrequent episodes of movement

massive co2 ice deposits sequestered in the south polar layered deposits of mars shallow radar soundings from the mars reconnaissance orbiter reveal a buried deposit of carbon dioxide co2 ice within the south polar layered deposits of mars with a volume of 9500 to 12 500 cubic kilometers about 30 times that previously estimated for the south pole residual cap the deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior co2 volatile release if released into the atmosphere at times of high obliquity the co2 reservoir would increase the atmospheric mass by up to 80 leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling

origin and characteristics of the mars north polar basal unit and implications for polar geologic history building upon previous studies we have used mars orbiter camera and mars orbiter laser altimeter data to characterize in detail the newly discovered north polar basal unit lying stratigraphically between the polar layered deposits from which it is likely separated by an unconformity and the vastitas borealis formation this unit has introduced new complexity into north polar stratigraphy and has important implications for polar history exposures of the basal unit in olympia planitia and chasma boreale reveal relatively dark layers which exhibit differential erosion eroded primarily by wind the basal unit may be the major if not sole source for the north polar dunes and ergs and has contributed material to the lower polar cap layers we investigate four possible origins for the basal unit outflow channel oceanic deposits basal ice paleopolar deposits and eolian deposits the patchy layering within the unit its likely sandy grain size and presence only in the north polar basin suggest that it is primarily an eolian deposit supporting byrne and murray s 2002 earlier conclusion this implies that at some time during the early to late amazonian migrating sand was mixed with water ice forming a relatively dark sandy deposit during this time either no classic polar layered deposits were forming or smaller caps were growing and shrinking possibly adding material to the basal unit

surface ages and resurfacing rates of the polar layered deposits on mars interpretation of the polar stratigraphy of mars in terms of global climate changes is complicated by the significant difference in surface ages between the north and south polar layered terrains inferred from crater statistics we have reassessed the cratering record in both polar regions using viking orbiter and mariner 9 images no craters have been found in the north polar layered terrain but the surface of most of the south polar layered deposits appears to have been stable for many of the orbital axial cycles that are thought to have induced global climate changes on mars the inferred surface age of the south polar layered deposits about 10 ma is two orders of magnitude greater than the surface age of the north polar layered deposits and residual cap at most 100 ka similarly modeled resurfacing rates are at least 20 times greater in the north than in the south these results are consistent with the hypotheses that polar layered deposit resurfacing rates are highest in areas covered by perennial ice and that the differences in polar resurfacing rates result from the 6 4 km difference in elevation between the polar regions deposition on the portion of the south polar layered deposits that is not covered by the perennial ice cap may have ceased about 5 million years ago when the obliquity of mars no longer exceeded 40

density of martian north polar layered deposits implications for composition mariner 9 and viking orbiter observations of the topography and mass of layered deposits in the north polar region of mars suggest a density of about 1 gm cm consideration of the self compaction of these deposits further suggests that this low density cannot be explained by a high porosity sediment rather a significant component of ice is probably required to account for the low value the density further implies that the silicate fraction regardless of its density i e its composition represents a volumetrically almost negligible component of the deposit the most likely values 5 silicate dust and 95 ice agree well with a theoretical model for the formation of the deposits through cyclic incorporation of the perennial polar ice cap additional tests of this model may be posed in advance of future spacecraft missions to mars

constraints on the composition of the martian south polar cap from gravity and topography abstract the polar caps of mars have long been acknowledged to be composed of unknown proportions of water ice solid co 2 dry ice and dust gravity and topography data are here analyzed over the southern cap to place constraints on its density and hence composition using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading the best fit density of the volatile rich south polar layered deposits is found to be 1271 kg m 3 with 1 limits of 1166 and 1391 kg m 3 the best fit elastic thickness of this geologically young deposit is 140 km though any value greater than 102 km can fit the observations the best fit density implies that about 55 dry ice by volume could be sequestered in these deposits if they were completely dust free alternatively if these deposits were completely free of solid co 2 the dust content would be constrained to lie between about 14 and 28 by volume the bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust however even if a moderate quantity of solid co 2 were present as horizontal layers the bulk thermal conductivity of the polar cap would be significantly reduced reasonable estimates of the present day heat flow of mars predict that dry ice beneath the thicker portions of the south polar cap would have melted depending on the quantity of solid co 2 in these deposits today it is even possible that water ice could melt where the cap is thickest if independent estimates for either the dust or co 2 content of the south polar cap could be obtained and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not it would be possible to use these observations to place tight constraints on the present day heat flow of mars

internal structure of planum boreum from mars advanced radar for subsurface and ionospheric sounding data 1 an investigation of the internal structure of the ice rich planum boreum pb deposit at the north pole of mars is presented using 178 orbits of mars advanced radar for subsurface and ionospheric sounding data for each radargram bright laterally extensive surface and subsurface reflectors are identified and the time delay between them is converted to unit thicknesses using a real dielectric constant of 3 results include maps of unit thickness for pb and its two constituent units the stratigraphically older basal unit bu and the stratigraphically younger north polar layered deposits npld maps of the individual units surface elevation are also provided estimates of water ice volume in each unit are 1 3 0 2 106 km3 in pb 7 8 1 2 105 km3 in the npld and 4 5 1 0 105 km3 in the bu no lithospheric deflection is apparent under pb in agreement with previous findings for only the gemina lingula lobe which suggests that a thick elastic lithosphere has existed at the north pole of mars since before the emplacement of the bu the extent of bu material in the olympia planum lobe of pb is directly detected providing a more accurate map of bu extent than previously available from imagery and topography a problematic area for mapping the bu extent and thickness is in the distal portion of the 290 e 300 e region where marsis data show no subsurface reflectors even though the bu is inferred to be present from other lines of evidence

dune field pattern formation and recent transporting winds in the olympia undae dune field north polar region of mars high resolution imaging science experiment hirise imagery of the central olympia undae dune field in the north polar region of mars shows a reticulate dune pattern consisting of two sets of nearly orthogonal dune crestlines with apparent slipfaces on the primary crests ubiquitous wind ripples areas of coarse grained wind ripples and deflated interdune areas geomorphic evidence and dune field pattern analysis of dune crest length spacing defect density and orientation indicates that the pattern is complex representing two constructional generations of dunes the oldest and best organized generation forms the primary crestlines and is transverse to circumpolar easterly winds gross bed form normal analysis of the younger pattern of crestlines indicates that it emerged with both circumpolar easterly winds and ne winds and is reworking the older pattern mapping of secondary flow fields over the dunes indicates that the most recent transporting winds were from the ne the younger pattern appears to represent an influx of sediment to the dune field associated with the development of the olympia cavi reentrant with ne katabatic winds channeling through the reentrant a model of the pattern reformation based upon the reconstructed primary winds and resulting secondary flow fields shows that the development of the secondary pattern is controlled by the boundary condition of the older dune topography

the thermal evolution of an earth with strong subduction zones it is commonly supposed that plate tectonic rates are controlled by the temperature dependent viscosity of earth s deep interior if this were so a small decrease in mantle temperature would lead to a large decrease in global heat transport this negative feedback mechanism would prevent mantle temperatures from changing rapidly with time we propose alternatively that convection is primarily resisted by the bending of oceanic lithosphere at subduction zones because lithospheric strength should not depend strongly on interior mantle temperature this relationship decreases the sensitivity of heat flow to changes in interior mantle viscosity and thus permits more rapid temperature changes there the bending resistance is large enough to limit heat flow rates for effective viscosities of the lithosphere greater than about 1023 pa s and increases with the cube of plate thickness as a result processes that affect plate thickness such as small scale convection or subduction initiation could profoundly influence earth s thermal history

porosity and packing of holocene river dune and beach sands the porosity and packing of 174 samples of surficial and shallowly buried to 17 m unconsolidated holocene sands medium to coarse grained were determined by point counting the upper surface of thin sections of epoxy impregnated samples in reflected light average depositional porosity for 124 surficial sands from beaches river point bars and braid bars and eolian dunes respectively is 47 48 and 49 the porosity values range between 40 and 58 beach sands exhibit an average packing value ci contact index of 0 79 fluvial sands an average ci of 0 91 and eolian sands an average ci of 1 02 beach sands typically contain 5 5 oversized pores river sands 3 8 oversized pores and eolian dune sands 4 0 oversized pores most oversized pores are depositional packing defects although trapped air bubbles are common in some beach sands extrapolation of our data for buried samples indicates depositional oversized pores are destroyed at a depth of less than 100 m average porosity is 46 for eolian ripple strata 50 for grain fall strata and 51 for grain flow strata differences in packing are significant for grain flow versus grain fall strata and for ripple versus grain flow strata for samples of similar grain size porosity is more uniform within individual beds from a river and a beach than among different beds at the same localities porosity of ancient sandstones from a particular bed or facies may be as uniform as sampled holocene sands unless cements having patchy distribution such as carbonate or anhydrite are present compaction associated with burial to 17 m is minor packing is tighter but our technique of measuring porosity is not sensitive enough to show any decrease in porosity changes in packing and porosity upon burial to common hydrocarbon reservoir depths will depend on individual histories of cementation compaction and secondary porosity development however if only physical compaction of quartzose river dune and beach sands takes place porosity would approach a limiting value of 26 and ci would approach 5 5

planum boreum basal unit topography mars irregularities and insights from sharad shallow radar investigations of planum boreum mars basal unit bu deposit have revealed multiple reentrants morphologic irregularities and thickness trends that differ from those of the overlying north polar layered deposits we present detailed subsurface maps for these features and offer explanation for genesis of the deposit s morphologic asymmetry expressed in different erosional characteristics between 0 e 180 e and 180 e 360 e additionally this work revealed a depression in the basal unit that may have provided a site for spiral trough initiation interpretations of the findings suggest that antecedent bu topography has a marked impact on modern morphology and that aeolian forces have been the dominant driver of polar deposit accumulation since at least the end of rupes unit emplacement we find no results requiring explanation beyond common martian surface processes including aeolian erosion and impact armoring to add to the detailed morphologic study of the bu we mapped the variability of the bu radar reflection character combining generalized katabatic wind flow with the radar mapping results suggests that rupes unit material sourced the younger cavi we present clear evidence that while compositionally distinct from the overlying layered deposits the bu and its morphology are intimately linked to the morphology of the north polar layered deposits combining geologic evidence with paleoclimate modeling the deposits contain evidence for a long history of aeolian emplacement and modification

tectonic controls on the hydrocarbon habitats of the barito kutei and tarakan basins eastern kalimantan indonesia major dissimilarities in adjoining basins abstract the barito kutei and tarakan basins are located in the eastern half of kalimantan borneo island indonesia the basins are distinguished by their different tectonic styles during tertiary and pleistocene times in the barito basin the deformation is a consequence of two distinct separate regimes firstly an initial transtensional regime during which sinistral shear resulted in the formation of a series of wrench related rifts and secondly a subsequent transpressional regime involving convergent uplift reactivating old structures and resulting in wrenching reverse faulting and folding within the basin presently nne ssw and e w trending structures are concentrated in the northeastern and northern parts of the basin respectively in the northeastern part the structures become increasingly imbricated towards the meratus mountains and involve the basement the western and southern parts of the barito basin are only weakly deformed in the kutei basin the present day dominant structural trend is a series of tightly folded nne ssw trending anticlines and synclines forming the samarinda anticlinorium which is dominant in the eastern part of the basin deformation is less intense offshore middle miocene to recent structural growth is suggested by depositional thinning over the structures the western basin area is uplifted large structures are evident in several places the origin of the kutei structures is still in question and proposed mechanisms include vertical diapirism gravitational gliding inversion through regional wrenching detachment folds over inverted structures and inverted delta growth fault system in the tarakan basin the present structural grain is typified by nne ssw normal faults which are mostly developed in the marginal and offshore areas these structures formed on older nw se trending folds and are normal to the direction of the basin sedimentary thickening suggesting that they developed contemporaneously with deposition as growth faults and may be the direct result of sedimentary loading by successive deltaic deposits older structures were formed in the onshore basin characterized by the n s trending folds resulting from the collision of the central range terranes to the west of the basin hydrocarbon accumulations in the three basins are strongly controlled by their tectonic styles in the barito basin all fields are located in west verging faulted anticlines the history of tectonic inversion and convergent uplift of the meratus mountains isostatically have caused the generation migration and trapping of hydrocarbons in the kutei basin the onshore samarinda anticlinorium and the offshore mahakam foldbelt are prolific petroleum provinces within which most indonesian giant fields are located in the offshore very gentle folds also play a role as hydrocarbon traps in association with stratigraphic entrapment these structures have recently become primary targets for exploratory drilling in the tarakan basin the prominent nw se anticlines fragmented by ne sw growth faults have proved to be petroleum traps the main producing pools are located in the downthrown blocks of the faults diverse tectonic styles within the producing basins of kalimantan compel separate exploration approaches to each basin to discover new opportunities in exploration it is important to understand the structural evolution of neighbouring basins

viscous relaxation of craters within the martian south polar layered deposits abstract the south polar layered deposits pld are of fundamental importance to martian climatology as they may comprise the largest reservoir of near surface water on mars the south pld exhibit relatively young crater retention surface ages which are widely attributed to recent resurfacing however we show that both constructional and destructional resurfacing mechanisms such as dust deposition and water ice sublimation respectively are inconsistent with the size depth and spatial distributions of south pld craters we demonstrate that another process viscous creep relaxation of dusty water ice is more compatible with the observed cratering of south pld surfaces the results of our finite element relaxation simulations suggest that despite their apparent youthfulness the pld have been stable for at least several hundred million and perhaps even over a billion years consequently our modeling implies that the time scales for the formation and preservation of the layers characteristic of the south and possibly north pld are much longer than generally assumed

subsurface structure of planum boreum from mars reconnaissance orbiter shallow radar soundings abstract we map the subsurface structure of planum boreum using sounding data from the shallow radar sharad instrument onboard the mars reconnaissance orbiter radar coverage throughout the 1 000 000 km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits npld a dome shaped zone of diffuse reflectivity up to 12 s 1 km thick underlies two thirds of the npld predominantly in the main lobe but also extending into the gemina lingula lobe across chasma boreale we equate this zone with a basal unit identified in image data as amazonian sand rich layered deposits byrne s murray b c 2002 j geophys res 107 5044 12 pp doi 10 1029 2001je001615 fishbaugh k e head j w 2005 icarus 174 444 474 tanaka k l rodriguez j a p skinner j a bourke m c fortezzo c m herkenhoff k e kolb e j okubo c h 2008 icarus 196 318 358 elsewhere the npld base is remarkably flat lying and co planar with the exposed surface of the surrounding vastitas borealis materials within the npld we delineate and map four units based on the radar layer packets of phillips et al phillips r j and 26 colleagues 2008 science 320 1182 1185 that extend throughout the deposits and a fifth unit confined to eastern gemina lingula we estimate the volume of each internal unit and of the entire npld stack 821 000 km3 exclusive of the basal unit correlation of these units to models of insolation cycles and polar deposition laskar j levrard b mustard j f 2002 nature 419 375 377 levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 is consistent with the 4 2 ma age of the oldest preserved npld obtained by levrard et al levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 we suggest a dominant layering mechanism of dust content variation during accumulation rather than one of lag production during periods of sublimation

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick