seismically generated hydroplastic deformation structures in the late miocene lacustrine deposits of the malatya basin eastern turkey abstract the late miocene succession of continental deposits in the malatya basin eastern anatolia comprises alluvial fan lacustrine and fluvial facies associations this fault bounded basin formed in a tectonically active region notorious for strong earthquakes still today the lacustrine deposits in the northern part of the basin show several isolated horizons of soft sediment deformation including such structures as slump folds load and flame features sand dikes and small scale synsedimentary reverse faults with associated folds there is no direct evidence supporting instabilities due to unequal loading or overloading wave induced cyclical and or impulsive stresses sudden changes in groundwater level or bioturbation capable of producing these deformation structures the soft sediment deformation structures described in the lacustrine deposits are interpreted as having developed as a result of seismic activity taking place along the malatya fault zone based on the tectonic setting of the basin the lateral extent of the soft sediment deformation structures over hundreds of metres their confinement by undeformed layers the presence of complex structures and similarities with structures interpreted as being seismically induced in other areas and those obtained experimentally

an integrated model of extrusive sand injectites in cohesionless sediments clastic injection and surface expression of subsurface sediment remobilization is a phenomenon which is becoming increasingly recognized however understanding of the physical mechanisms that control these features remains limited dominated by inference from outcrop and seismic studies here this limitation is addressed through a set of experiments focused on the development and evolution of fluidization features in non cohesive bedded sequences fluidization and the onset of piping are shown to occur progressively through a sequence of discrete phases with initial void formation development of infiltration horizons rupture and finally pipe formation critically the style of piping the stability of piping and the temporal evolution of venting are shown to exhibit considerable variability in particular pipes may either be stable or very mobile migrating laterally over large distances these produce deposits that are typically interpreted in outcrop as being the product of en masse liquefaction rather than localized dynamic fluidization these differing elements are synthesized to produce a model of sand extrudites in addition the implications of this model are explored

radar imagery of mercury s putative polar ice 1999 2005 arecibo results abstract we present an updated survey of mercury s putative polar ice deposits based on high resolution 1 5 km imaging with the upgraded arecibo s band radar during 1999 2005 the north pole has now been imaged over a full range of longitude aspects making it possible to distinguish ice free areas from radar shadowed areas and thus better map the distribution of radar bright ice the new imagery of the south pole though derived from only a single pair of dates in 2005 improves on the pre upgrade arecibo imagery and reveals many additional ice features some medium size craters located within 3 of the north pole show near complete ice coverage over their floors central peaks and southern interior rim walls and little or no ice on their northern rim walls while one large 90 km crater at 85 n shows a sharp ice cutoff line running across its central floor all of this is consistent with the estimated polar extent of permanent shading from direct sunlight some craters show ice in regions that though permanently shaded should be too warm to maintain unprotected surface ice owing to indirect heating by reflected and reradiated sunlight however the ice distribution in these craters is in good agreement with models invoking insulation by a thin dust mantle comparisons with goldstone x band radar imagery indicate a wavelength dependence that could be consistent with such a dust mantle more than a dozen small ice features have been found at latitudes between 67 and 75 all of this low latitude ice is probably sheltered in or under steep pole facing crater rim walls although since most is located in the mariner unimaged hemisphere confirmation must await imaging by the messenger orbiter these low latitude features are concentrated toward the cold longitudes possibly indicating a thermal segregation effect governed by indirect heating the radar imagery places the corrected locations of the north and south poles at 7 w 88 35 n and 90 w 88 7 s respectively on the original mariner based maps

mercury radar imaging evidence for polar ice the first unambiguous full disk radar mapping of mercury at 3 5 centimeter wavelength with the goldstone 70 meter antenna transmitting and 26 antennas of the very large array receiving has provided evidence for the presence of polar ice the radar experiments conducted on 8 and 23 august 1991 were designed to image the half of mercury not photographed by mariner 10 the orbital geometry allowed viewing beyond the north pole of mercury a highly reflective region was clearly visible on the north pole during both experiments this polar region has areas in which the circular polarization ratio pt was 1 0 to 1 4 values 0 1 are typical for terrestrial planets such high values of have hitherto been observed in radar observations only from icy regions of mars and icy outer planet satellites

stability of polar frosts in spherical bowl shaped craters on the moon mercury and mars following svitek martian water frost control of global distribution by small scale processes ph d thesis california institute of technology 1992 analytic solutions are presented for the effective albedo the effective emissivity and the radiative equilibrium temperature in the shadowed portions of a spherical bowl shaped crater the model assumes that the surface is a lambert scatterer with visual albedo and infrared emissivity each independent of wavelength across their respective spectral ranges absorption emission and multiple scattering from the walls of the crater are treated rigorously to all orders for airless bodies whose surfaces are in radiative equilibrium all shadowed portions of any individual crater have the same temperature whose value depends on four quantities the insolation product of the solar constant and the sine of the solar elevation angle the depth diameter ratio of the crater the visual albedo and the infrared emissivity as long as the crater is deep enough to have shadows the lowest temperatures are for the shallowest crater those with the smallest depth diameter ratio the model is applied first to the moon and mercury using a depth diameter ratio of 0 2 which is typical of the lunar highlands according to pike geophys res lett 1 291 294 1974 in impact and explosion cratering roddy et al eds pp 489 509 pergamon new york 1977 for mercury and the moon temperatures in shadows in polar craters are below 102 k so the sublimation rate of water ice calculated according to the model of watson et al j geophys res 66 3033 3015 1961 is less than 1 cm per byr the latitudinal extent of the cold zone on the moon is greater than that on mercury although temperatures at the poles of the two planets are similar the other application is to polar frosts on mars illuminated water frosts in radiative equilibrium grow rougher because the average temperature of a depression is greater than that of flat ground subliming co 2 frosts which are always at the same temperature grow rougher at low solar elevation angles because the heat flux absorbed by a depression is greater than that for a flat surface at high insolation rates high sun near perihelion the average heat flux to a depression is less than for a flat surface the latter evaporates faster which makes the average surface smoother and leads to a high average albedo this behavior helps explain the fact that the south co 2 cap which receives its greatest insolation near perihelion has a higher effective albedo and therefore can survive the summer whereas the north co 2 cap has a lower effective albedo and disappears each year around summer solstice

mercury full disk radar images and the detection and stability of ice at the north pole the first full disk radar images of mercury were obtained on august 8 and 23 1991 these images were constructed using the very large array vla in socorro new mexico to receive and map radar flux at 3 5 cm x band which was continuously transmitted from the 70 m jet propulsion laboratory deep space network antenna at goldstone california approximately 77 of the surface was imaged at resolutions as good as 150 km about half of the hemisphere photographed by mariner 10 was imaged as well as most of the hemisphere which has not previously been photographed at the time of the observations the north pole was visible and the feature with the highest same sense ss circular reflectivity in the images is near the nominal polar position the peak ss reflectivity of this feature was 7 9 and the circular polarization ratio throughout much of the feature is 1 our best estimate of the size of the feature is that its diameter is 350 km we interpret the feature to be indicative of the presence of ices because of the signal strength and polarization characteristics the ices must be very clean and were thus probably deposited in a relatively short time period the most likely place to find these ices is in any permanently shadowed areas in the polar regions which would be very cold in comparison to absolute reflectivities of other icy bodies and regions in the solar system the reflectivity of the north polar feature is slightly depressed this is probably because the ices do not fill an observational resolution cell i e there is incomplete areal coverage or are covered by a layer of dust or soil which absorbs some of the incoming and outgoing radar energy or both a covering layer would also protect any ices from erosion by energetic sources other prominent features on the unphotographed hemisphere correspond to positions where atmospheric sodium enhancements have been measured from earth this may indicate that these locations are large basins similar to the caloris basin where an atmospheric potassium enhancement has been measured which may be the result of increased degassing in the disrupted surface and near surface direct comparison of the radar echoes from our features with those from the caloris basin are hard to make as caloris was not imaged by us in a favorable geometry features on the photographed hemisphere are smaller and mostly associated with craters and crater complexes most notably the kuiper crater and its environs

analyzing the ages of south polar craters on the moon implications for the sources and evolution of surface water ice abstract surface water ice in the permanently shadowed polar regions of the moon has a patchy surficial distribution and is not found within all available cold trapping areas to date it is not well understood when the ice was delivered which has important implications for the surficial characteristics of the ice as well as for possible delivery mechanisms here we present absolute model ages for 20 south polar craters that host surface water ice providing maximum estimates of the ages of surface ice contained within these craters we quantify the amount of available cold trapping surface area that is occupied by water ice in order to examine the relationship between the patchiness of ice within each crater and the age of each host crater the majority of surface ice is contained in old craters 3 1 gyr where the majority of cold trapping area on the pole exists the ice is these ancient craters is very patchy in surficial distribution occupying siegler et al 2016 if true polar wander did occur on the moon then the ages of ice bearing craters presented here set an upper limit for the age of post true polar wander hydrogen emplacement of 4 1 0 1 gyr

physical modelling of sand injectites abstract sand injectites are structures that result from intrusion of fluidized sand into fractures we have studied them in the tampen spur area of the north sea and have reproduced them experimentally by driving compressed air through layers of sand glass microspheres and silica powder the silica powder was cohesive and capable of hydraulic fracturing whereas the sand and glass microspheres were almost non cohesive and therefore able to fluidize the models were dynamically similar to their natural counterparts for as long as equilibrium was static when the processes became dynamic so that inertial forces were significant the scaling was approximate and the corresponding reynolds numbers differed the experimental apparatus was a square box 1 m 1 m wide resting on a grid of fluid diffusers during the experiments the fluid pressure increased until it attained and surpassed the weight of overburden flat lying hydraulic fractures containing air formed within cohesive and least permeable layers heterogeneities in material properties and layer thicknesses were responsible for localizing fracture networks when any one network broke through to the surface rapid flow of air through the fractures fluidized the underlying mobile materials and even depleted some of the layers some of the fluidized material extruded at the surface through vents forming volcanoes and sheets the remainder lodged at depth forming sand injectites or laccoliths conical sand injectites formed preferentially where layers had high resistance to bending laccoliths formed nearer the surface where overlying layers had low resistance to bending the experimental sand injectites were broadly similar to those in the tampen spur area of the north sea as well as other areas

effects of orbital evolution on lunar ice stability 1 many regions near the lunar poles are currently cold enough that surface water ice would be stable against sublimation losses for billions of years however most of these environments are currently too cold to efficiently drive ice downward by thermal diffusion leaving impact burial as the primary means of protection from surface loss processes in this respect most of the present near surface thermal environments on the moon may actually be quite poor traps for water ice this was not always the case long term orbital changes have dramatically altered the lunar polar thermal environment we develop a simple model of the evolution of the lunar orbit and spin axis to examine the thermal environments available for volatile deposition and retention in the past our calculations show that some early lunar polar environments were in the right temperature regime to have collected subsurface ice if a supply were available however a high obliquity period which occurred when the moon was at about half its present distance from the earth would either have driven this ice out into space or deep into the lunar subsurface since that time as the lunar obliquity has slowly decreased to its present value environments have undergone their own thermal evolution and each of the current cold traps experienced a period when they were most efficient at thermally burying ice we examine the thermal history of a lunar polar crater to provide a framework for examining other processes effecting volatiles in the moon s near surface cold traps

sand injectites network as a marker of the palaeo stress field the structural framework and the distance to the sand source example in the vocontian basin se france a large sand injectite network is very well exposed in the area of bevons southeast france the associated sandstone turbiditic channel fill and the host marls are the aptian albian rocks of the vocontian basin the sand injection network is composed of dykes sills and sedimentary laccoliths ranging in thickness from mm to pluri m the dykes and sills have vertical and horizontal lengths of up to and over 100 m and 1 km respectively outcrop observations show that the architecture and morphology of the sand injectites in the marls is governed by the local stress field during injection pre existing faults the host rock lithology compaction and distance to the potential sand source s the main set of dykes is oriented n50 60 perpendicular to the minimum compressive stress 3 during sand injection two other sets of dykes are intruded along pre existing syn sedimentary faults oriented n140 150 set 2 and n90 set 3 during the apto cenomanian interval sills and dykes thin laterally away from their potential sand sources and thin laterally away from them the vertical thickness variations of the dykes and wings are more complex as thinning away from the sand sources is often compensated by thickening toward the palaeo surface based on field observations and measurements we characterized the 3d architecture of the sand injectites and showed that the injectites probably formed due to a forceful injection from an overpressured sand body sealed by low permeability lithologies

heavy mineral sorting in downwards injected palaeocene sandstone siri canyon danish north sea abstract post depositional remobilization and injection of sand are often seen in deep water clastic systems and have been recently recognised as a significant modifier of deep water sandstone geometry large scale injectite complexes have been interpreted from borehole data in the palaeocene siri canyon near the danish central graben of the north sea hydrocarbon province the emplacement of large scale injectite complexes has been commonly attributed to seismic activity and consequent sand liquefaction however due to very small differences in textural and compositional properties and the lack of depositional structures in deep water sandstones the distinction between in situ and injected or remobilized sandstones is often ambiguous large scale heavy mineral sorting in 10 m thick units is observed in several reservoir units in the siri canyon and has been interpreted to represent the depositional sorting in this study we describe an example of effective shear zone sorting of heavy minerals in a thin downwards injected sandstone dyke which was encountered in one of the cores in the cecilie field siri canyon differences in sorting pattern of heavy minerals are suggested as a tool for petrographic geochemical distinction between in situ sandstones and their related injectites especially where primary sedimentary structures are removed by fluidization or minor remobilization

persistently illuminated regions at the lunar poles ideal sites for future exploration abstract the lunar reconnaissance orbiter camera lroc provides multi temporal and high resolution imaging of the north and south polar regions these images delimit illuminated areas from those in shadow and are used to analyze the illumination environment of the polar regions over the course of a lunar year the wide angle camera wac provides repeat imaging of the north and south pole at a frequency of roughly 2 h with a ground sampling distance of 100 m the lroc narrow angle camera nac acquires images with a ground sampling distance of 0 5 2 0 m providing the means to construct high resolution maps that reveal illuminated terrain under varying lighting conditions with the multi temporal coverage provided by the wac and the high resolution images from the nac the lroc dataset enables a more comprehensive analysis of the illumination conditions near the lunar poles than any previous image based dataset furthermore these images are used to validate previously published numerical models that simulate polar illumination conditions from our analysis of the lroc images we identified localized regions where the lunar surface remains illuminated for nearly 94 of the year with the longest eclipsed period lasting only 43 h we also identified small illuminated peaks tens of meters across in areas previously modeled to be in shadow together the wac and nac dataset provide direct high resolution observations of the actual surface illumination environment of potential exploration sites near the lunar poles

sediment accumulation rates and carbon burial in the bottom sediment in a high productivity area gerlache strait antarctica abstract recent 100 yr sediment carbon and nitrogen accumulation rates have been assessed at six different sites along a high productivity area gerlache strait antarctica organic carbon oc content in the sampled sediments along the strait accounted for more than 90 of the total carbon which ranged from 0 7 to 1 2 of the total mass dry weight apparent mean sediment accumulation rates sar varied between 630 30 and 1750 80 g m 2 yr 1 0 65 0 03 3 11 0 14 mm yr 1 bottom sediment from the eastern part of the strait had the highest mean oc content and apparent mean sar the oc sedimentation rates were significant and fluctuated between 5 and 23 g m 2 yr 1 the highest values corresponded to the centre of the strait the eastern half of the strait is the deposit area of both locally produced material and that generated farther to the west due to bottom topography together with hydrographical and biological controls between 71 and 83 of the oc originally deposited in the surface sediment remained below the surface mixed layer the preservation ratio remnant oc in the sediment column primary production rates in the local euphotic zone ranged from 1 to 6 these ratios are comparable to other from antarctic areas such as the ross sea nevertheless the amount of primary produced oc buried in the gerlache strait sediment is higher than in other areas such as the bransfield strait or the ross sea the gerlache strait can be considered as a carbon sink area and it is able to export particulate oc to the adjacent western bransfield strait

craters hosting radar bright deposits in mercury s north polar region areas of persistent shadow determined from messenger images 1 radar bright features near mercury s poles were discovered in earth based radar images and proposed to be water ice present in permanently shadowed areas images from messenger s one year primary orbital mission provide the first nearly complete view of mercury s north polar region as well as multiple images of the surface under a range of illumination conditions we find that radar bright features near mercury s north pole are associated with locations persistently shadowed in messenger images within 10 of the pole almost all craters larger than 10 km in diameter host radar bright deposits there are several craters located near mercury s north pole with sufficiently large diameters to enable long lived water ice to be thermally stable at the surface within regions of permanent shadow craters located farther south also host radar bright deposits and show a preference for cold pole longitudes thermal models suggest that a thin insulating layer is required to cover these deposits if the radar bright material consists predominantly of long lived water ice many small 10 km diameter and low latitude extending southward to 66 n craters host radar bright material and water ice may not be thermally stable in these craters for 1 gy even beneath an insulating layer the correlation of radar bright features with persistently shadowed areas is consistent with the deposits being composed of water ice and future thermal modeling of small and low latitude craters has the potential to further constrain the nature source and timing of emplacement of the radar bright material

indicators of propagation direction and relative depth in clastic injectites implications for laminar versus turbulent flow processes clastic injectites are widely recognized in deep water stratigraphic successions although their sediment transport processes propagation direction and depth of injection are poorly constrained understanding how they form is important as injectites are increasingly being recognized as significant components of sedimentary basin fills yet are not predicted by standard sedimentary facies models here analysis of features on the margins of exhumed clastic sills and dikes and clasts within them enables their genesis to be determined a diverse array of diagnostic structures is found on the margins of injectites in the karoo basin south africa where the net direction of injection and position of the parent sand are well constrained injectite margin features include mudstone clast rich surfaces planar or smooth surfaces blistered surfaces and parallel and plumose ridged surfaces combined these features are critical in distinguishing injected sands where injectites are strata concordant from those of primary deposition all features are indicative of propagation through brittle very fine grained sediments at depths where the applied shear stress is at least four times the tensile strength of the host rock additionally the presence of parallel ridges plumose ridges and steps allows local fracture propagation to be constrained and in turn injection direction the features described provide evidence that sands were injected at considerable depth in closed fractures with limited capacity for flow dilution and turbulence enhancement calculated reynolds numbers lack of erosion at injectite walls and the presence of mud clasts at the top and base of sills indicate that many flows were likely fully laminar during injection the sedimentary features of these confined relatively deep laminar flow induced injectites are very different from injectites that reach the surface and produce extrudites surface linked injectites are associated with open conduits where a greater fraction of carrier fluid to particles can be accommodated enabling highly turbulent lower concentration flows

morphometry of impact craters on mercury from messenger altimetry and imaging abstract data acquired by the mercury laser altimeter and the mercury dual imaging system on the messenger spacecraft in orbit about mercury provide a means to measure the geometry of many of the impact craters in mercury s northern hemisphere in detail for the first time the combination of topographic and imaging data permit a systematic evaluation of impact crater morphometry on mercury a new calculation of the diameter d t at which craters transition with increasing diameter from simple to complex forms and an exploration of the role of target properties and impact velocity on final crater size and shape measurements of impact crater depth on mercury confirm results from previous studies with the exception that the depths of large complex craters are typically shallower at a given diameter than reported from mariner 10 data secondary craters on mercury are generally shallower than primary craters of the same diameter no significant differences are observed between the depths of craters within heavily cratered terrain and those of craters within smooth plains the morphological attributes of craters that reflect the transition from simple to complex craters do not appear at the same diameter instead flat floors first appear with increasing diameter in craters at the smallest diameters followed with increasing diameter by reduced crater depth and rim height and then collapse and terracing of crater walls differences reported by others in d t between mercury and mars despite the similar surface gravitational acceleration on the two bodies are confirmed in this study the variations in d t between mercury and mars cannot be adequately attributed to differences in either surface properties or mean projectile velocity

thermal stability of volatiles in the north polar region of mercury thermal models for the north polar region of mercury calculated from topographic measurements made by the mercury surface space environment geochemistry and ranging messenger spacecraft show that the spatial distribution of regions of high radar backscatter is well matched by the predicted distribution of thermally stable water ice messenger measurements of near infrared surface reflectance indicate bright surfaces in the coldest areas where water ice is predicted to be stable at the surface and dark surfaces within and surrounding warmer areas where water ice is predicted to be stable only in the near subsurface we propose that the dark surface layer is a sublimation lag deposit that may be rich in impact derived organic material

deep sea volcaniclastic sedimentary systems an example from la fournaise volcano reunion island indian ocean a volcaniclastic sedimentary fan extending to water depths of 4000 m is characterized using gravity cores camera surveys high resolution sonar images seismic records and bathymetry from the submarine portion of la fournaise volcano reunion island a basaltic shield volcano in the sw indian ocean three main areas are identified from the study 1 the proximal fan extending from 500 m water depth down to 2000 m water depth 2 the outer fan extending from 2000 m water depth down to 3600 m water depth 3 the basin extending beyond 3600 m water depth within these three main areas seven distinct submarine environments are defined the proximal fan is characterized by volcanic basement outcrops sedimentary slides deep water deltas debris avalanche deposits and eroded floor in the valley outlets the outer fan is characterized by a discontinuous fine grained sedimentary cover overlying coarse grained turbidites or undifferentiated volcanic basement the basin is characterized by hemipelagic muds and fine grained turbidites interbedded with sandy and gravelly turbidite lobes the evolution of the deep sea volcaniclastic fan is strongly influenced by sector collapses such as the one which occurred 0 0042 ma ago this collapse produced a minimum of 6 km3 of debris avalanche deposit in the proximal area the feeding regime of the deep sea fan is alluvial dominated before the occurrence of any sector collapse and lava dominated after the occurrence of a sector collapse the main deep water lava fed delta is prograding among the blocks of the debris avalanche deposits as a result of turbidity flows occurring on the delta slope these turbidity flows are triggered routinely by wave action earthquakes and accumulation of new volcanic debris on top of the deltas both turbidity currents triggered on the deep water delta slope and those triggered by debris avalanche reworked volcaniclastic material as far as 100 km from the shore line

syndepositional tectonics recorded by soft sediment deformation and liquefaction structures continental lower permian sediments southern alps northern italy stratigraphic significance abstract the lower permian succession of the central southern alps lombardy northern italy was deposited in fault controlled continental basins probably related to transtensional tectonics we focussed our study on the stratigraphic record of the lower permian orobic basin which consists of a 1000 m thick succession of prevailing continental clastics with intercalations of ignimbritic flows and tuffs pizzo del diavolo formation pdv resting on the underlying prevailing pyroclastic flows of the cabianca volcanite the pdv consists of a lower part composed of conglomerates passing laterally to sandstones and distally to silt and shales a middle part pelitic with carbonates and an upper part alternating sandstone silt and volcanic flows syndepositional tectonics during the deposition of the pdv is recorded by facies distribution thickness changes and by the presence of deformation and liquefaction structures interpreted as seismites deformation is recorded by both ductile structures ball and pillow plastic intrusion disturbed lamination convolute stratification and slumps and brittle structures sand dykes and autoclastic breccias both the sedimentological features and the geodynamic setting of the depositional basin confidently support the interpretation of the described deformation features as related to seismic shocks the most significant seismically induced deformation is represented by a slumped horizon about 4 m thick on average which can be followed laterally for more than 5 km the slumped bed consists of playa lake deposits alternating pelites and microbial carbonates associated with mud cracks and vertebrate tracks the lateral continuity and the evidence of deposition on a very low angle surface along with the deformation liquefaction of the sediments suggest that the slump was triggered by a high magnitude earthquake the stratigraphic distribution of the seismites allows us to identify time intervals of intense seismic activity which correspond to rapid and basin wide changes in the stratigraphical architecture of the depositional basin and or to the reprise of the volcanic activity the nature of the structures and their distribution suggest that the magnitude of the earthquakes responsible for the observed structures was likely higher than 5 in order to produce sediment liquefaction and probably reached intensity as high as 7 or more the basin architecture suggests that the foci of these earthquakes were located close to the fault controlled borders of the basin or within the basin itself

seismic scale funnel shaped collapse features from the paleocene eocene of the north west shelf of australia abstract a multi tiered cluster of funnel shaped seismic anomalies can be observed over 11 000 km2 in the lower tertiary of the carnarvon basin nw shelf of australia the lithology is dominated by deep water carbonates and marls individual funnel shaped depressions typically have a diameter exceeding 1 km and a depth of a few hundred meters the strata inside some of the anomalies can be correlated with surrounding layers in the best documented example the correlation shows that the infill has foundered into the funnel shaped depression the collapse appears to have removed about 1 km3 below sedimentary cover the anomalies were emplaced in deep water when gas was actively migrating in the basin and above a structural high based on this context and using recently described hydrate pockmarks as live analogs the following model is proposed for the emplacement of these collapsed features 1 thermogenic gas migrated up into the fine grained paleogene series and froze up into hydrates upon entering the gas hydrate stability zone 2 the correlative volume increase resulted in conical failure of the overburden and gas migrating along the failure impregnated the surrounding sediments with hydrates 3 as the hydrate stability zone moved up hydrate dissolution dissociation expelled gas and associated liquefied sediment from the cone while the non impregnated core foundered towards the bottom of the cone three such episodes are recorded in the study area during the paleogene two of them lie in close temporal vicinity to the main hyperthermal events of this period volume calculations indicate that the amount of gas released in our study area is two orders of magnitude lower than what would be needed to trigger the paleocene eocene thermal maximum event suggesting that the anomalies are rather developed as a consequence of global hyperthermal events

age constraints of mercury s polar deposits suggest recent delivery of ice abstract surface ice at the poles of mercury appears as several m thick deposits that are composed of nearly pure water we provide new age estimates of the surfaces of mercury s polar deposits from combined analyses of poisson statistics and direct observations of crater densities within permanently shadowed radar bright regions imaged by the messenger spacecraft these age estimates conservatively suggest that ice was delivered to mercury within the last 330 myr the geologically young ages suggest that the surfaces have been recently refreshed and this may be accomplished by the delivery of ice in a young impactor or impactors a single recent impactor is more consistent with the relative purity of the ice as suggested by the earth based radar observations in contrast to ice on mercury observations of the lunar poles are suggestive of a highly patchy distribution of surface frost the patchiness of lunar polar deposits is consistent with long exposure times to the space weathering environment given enough time the polar deposits on mercury may age into a more heterogeneous spatial distribution similar to that on the moon

areas of permanent shadow in mercury s south polar region ascertained by messenger orbital imaging 1 radar bright features near mercury s poles have been postulated to be deposits of water ice trapped in cold permanently shadowed interiors of impact craters from its orbit about mercury messenger repeatedly imaged the planet s south polar region over one mercury solar day providing a complete view of the terrain near the south pole and enabling the identification of areas of permanent shadow larger in horizontal extent than approximately 4 km in mercury s south polar region all radar bright features correspond to areas of permanent shadow application of previous thermal models suggests that the radar bright deposits in mercury s south polar cold traps are in locations consistent with a composition dominated by water ice provided that some manner of insulation such as a thin layer of regolith covers many of the deposits

extent age and resurfacing history of the northern smooth plains on mercury from messenger observations abstract messenger orbital images show that the north polar region of mercury contains smooth plains that occupy 7 of the planetary surface area within the northern smooth plains nsp we identify two crater populations those superposed on the nsp post plains and those partially or entirely embayed buried the existence of the second of these populations is clear evidence for volcanic resurfacing the post plains crater population reveals that the nsp do not exhibit statistically distinguishable subunits on the basis of crater size frequency distributions nor do measures of the areal density of impact craters reveal volcanically resurfaced regions within the nsp these results suggest that the most recent outpouring of volcanic material resurfaced the majority of the region and that this volcanic flooding emplaced the nsp over a relatively short interval of geologic time perhaps 100 my or less stratigraphic embayment relationships within the buried crater population including partial crater flooding and the presence of smaller embayed craters within the filled interiors of larger craters and basins indicate that a minimum of two episodes of volcanic resurfacing occurred from the inferred rim heights of embayed craters we estimate the nsp to be regionally 0 7 1 8 km thick with a minimum volume of volcanic material of 4 10 6 to 10 7 km 3 because of the uncertainty in the impact flux at mercury the absolute model age of the post plains volcanism could be either 3 7 or 2 5 ga depending on the chronology applied

the thermal stability of water ice at the poles of mercury recent radar observations of mercury have revealed the presence of anomalous radar reflectivity and polarization features near its north and south poles thermal model calculations show that despite mercury s proximity to the sun the temperatures of flat low reflectivity surfaces at mercury s poles are not expected to exceed 167 kelvin the locations of the anomalous polar radar features appear to be correlated with the locations of large high latitude impact craters maximum surface temperatures in the permanently shadowed regions of these craters are expected to be significantly colder as low as 60 kelvin in the largest craters these results are consistent with the presence of water ice because at temperatures lower than 112 kelvin water ice should be stable to evaporation over time scales of billions of years

radar images of mars full disk images of mars have been obtained with the use of the very large array vla to map the radar reflected flux density the transmitter system was the 70 m antenna of the deep space network at goldstone california the surface of mars was illuminated with continuous wave radiation at a wavelength of 3 5 cm the reflected energy was mapped in individual 12 minute snapshots with the vla in its largest configuration fringe spacings as small as 67 km were obtained the images reveal near surface features including a region in the tharsis volcano area over 2000 km in east west extent that displayed no echo to the very low level of the radar system noise the feature called stealth is interpreted as a deposit of dust or ash with a density less than about 0 5 gram per cubic centimeter and free of rocks larger than 1 cm across the deposit must be several meters thick and may be much deeper the strongest reflecting geological feature was the south polar ice cap which was reduced in size to the residual south polar ice cap at the season of observation the cap image is interpreted as arising from nearly pure co 2 or h 2o ice with a small amount of martian dust less than 2 percent by volume and a depth greater than 2 to 5 m only one anomalous reflecting feature was identified outside of the tharsis region although the elysium region was poorly sampled in this experiment and the north pole was not visible from earth

imaging mercury s polar deposits during messenger s low altitude campaign images obtained during messenger s low altitude campaign in the final year of the mission provide the highest spatial resolution views of mercury s polar deposits images for distinct areas of permanent shadow within 35 north polar craters were successfully captured during the campaign all of these regions of permanent shadow were found to have low reflectance surfaces with well defined boundaries additionally brightness variations across the deposits correlate with variations in the biannual maximum surface temperature across the permanently shadowed regions supporting the conclusion that multiple volatile organic compounds are contained in mercury s polar deposits in addition to water ice a recent large impact event or ongoing bombardment by micrometeoroids could deliver water as well as many volatile organic compounds to mercury either scenario is consistent with the distinctive reflectance properties and well defined boundaries of mercury s polar deposits and the presence of volatiles in all available cold traps

near surface ice on mercury and the moon a topographic thermal model abstract a thermal model that can be easily adapted to craters of arbitrary shape is developed and applied to high latitude impact craters on mercury and the moon chao meng fu crater at 87 5 l on mercury an unnamed bowl shaped crater at 86 7 l on mercury and peary crater at 88 6 l on the moon for an assumed input topography and grid of surface elements the model computes for each element the irradiation from direct insolation and reflected and emitted radiation from other elements taking into account shadowing by the walls of the crater partial obscuration of the solar disk near the poles and the diurnal orbital and seasonal cycles temperatures are computed over the surface grid as functions of depth and time from the surface to a specified depth and over the pertinent astronomical cycles including the effects of direct and indirect surface irradiation infrared radiation heat conduction and interior heating vapor fluxes and ice recession times are computed as functions of ice depth over the surface grid temperatures profiles vapor fluxes and ice recession times were computed for flat surfaces not associated with craters near the poles of mercury and the moon it was found that water ice could have existed throughout geologic time within the maximum radar detection depth of recent observation of mercury j k harmon and m a slade 1992 science 258 640 643 poleward of 87 88 l on mercury and poleward of 73 l on the moon for chao meng fu crater it was found that 40 of the crater floor is permanently shadowed from direct solar insolation while the remainder of the crater floor is periodically illuminated by a partially obscured sun temperatures at the upper levels of the south wall can slightly exceed 550 k surface temperatures in the permanently shadowed region of the crater floor are under 130 k which could have allowed water ice to exist throughout geologic time within the radar detection depth of recent observation of mercury for the small bowl shaped crater on mercury it was found that most of the crater is permanently shadowed from direct solar radiation except for a narrow semicircular band bordering the north rim however temperatures in the permanently shadowed region periodically reach a maximum near 315 k due to efficient heating of the small crater by thermal emission and reflection from the small sunlit region which periodically reaches temperatures exceeding 630 k water ice could not have existed throughout geologic time anywhere in this crater within the radar detection depth for peary crater on the moon the entire crater floor is permanently shadowed from direct solar insolation with maximum temperatures under 120 k the upper level of the north wall periodically reaches a maximum temperature near 310 k the low temperatures on the crater floor would have allowed water ice to exist near the surface throughout geologic time provided that the moon s obliquity was always as low as it is at present

high resolution radar imaging of mercury s north pole abstract the recently upgraded arecibo s band 12 6 cm radar was used to make delay doppler images of mercury s north polar region where earlier observations had shown strong echoes from putative ice deposits in craters the image resolution of 1 5 3 km is a substantial improvement over the 15 km resolution of the older arecibo images j k harmon et al 1994 nature 369 213 215 the new observations confirm all the original polar features and reveal many additional features including several at latitudes as low as 72 75 n and several from craters less than 10 km in diameter all of the new features located on the mariner imaged side of the planet can be matched with known craters or other shaded areas we find the north pole to be located 65 km from the original mariner based pole and 15 km from the new mariner based pole of m s robinson et al 1999 j geophys res 104 30 847 30 852 the improved resolution reveals fine structure in the radar features and their respective host craters including radar shadowing highlighting by central peaks and rim walls rim terracing and preferential concentration of radar bright deposits in shaded southern floor areas the radar features high brightness circular polarization inversion c 1 25 and confinement to regions permanently shaded from direct sunlight are all consistent with volume scattering from a cold trapped volatile such as clean water ice the sizes and locations of most of the features show good agreement with the thermal model of a r vasavada d a paige and s e wood 1999 icarus 141 179 193 for insulated buried water ice although the problems of explaining radar features in small craters and the rapid burial required at lower latitudes suggest that other factors may be suppressing ice loss after emplacement

soft sediment deformation in a tectonically active area the plio pleistocene zarzal formation in the cauca valley western colombia abstract the plio pleistocene zarzal formation corresponds to fluvio lacustrine sediments deposited in an intramontane depression within the colombian andes associated with the cauca romeral fault system it crops out mainly in the cauca valley where numerous field sections have permitted the mapping of the vertical and lateral lithological variations lacustrine deposits of sands silts clays and diatomites are interbedded with fluvial sand and gravel beds and fluvio volcanic mass flows derived from the volcanic central cordillera numerous soft sediment deformation structures are encountered in this formation particularly in fine to medium grained sands silts and clays load structures load casts flame structures pseudonodules water escape structures water escape cusps dish and pillar and pocket and pillar structures soft sediment intrusions clastic sills and dykes disturbed laminites convolute laminations slumps and synsedimentary faulting deformation mechanisms and driving forces are related essentially to gravitational instabilities dewatering liquidization and brittle deformations field and regional geological data show that most of these deformations are related to seismicity and can be interpreted as seismites this area has a geological and recent seismic history and outcrops show both syn and post depositional faulting related to the transpressional regime of this part of the colombian andes which generates strike slip faults and associated local normal faults the drainage pattern within the zarzal formation shows the signature of neotectonics moreover the fine to coarse grained sands of the zarzal formation are lithologies prone to liquefaction when affected by seismic waves the intercalation of the deformed intervals within undisturbed strata confirms the catastrophic nature of the events finally the large areal extent of the deformations and the type of structures are compatible with seismites consequently the existence of seismites in the zarzal formation represents corroboration of tectonic activity in this area during the pleistocene earthquakes with a magnitude higher than 5 can be postulated based upon the proximity of active faults and the types of deformations

radar mapping of mercury full disk images and polar anomalies a random code technique has been used at arecibo to obtain delay doppler radar images of the full disk of mercury anomalously bright features were found at the north and south poles the north polar feature is oblong 4 by 8 and offset from the pole the smaller south polar feature is mostly confined to the floor of the crater chao meng fu the polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice the images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers some of these appear to have an impact origin

bright and dark polar deposits on mercury evidence for surface volatiles measurements of surface reflectance of permanently shadowed areas near mercury s north pole reveal regions of anomalously dark and bright deposits at 1064 nanometer wavelength these reflectance anomalies are concentrated on poleward facing slopes and are spatially collocated with areas of high radar backscatter postulated to be the result of near surface water ice correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice whereas dark regions are consistent with a surface layer of complex organic material that likely overlies buried ice and provides thermal insulation impacts of comets or volatile rich asteroids could have provided both dark and bright deposits

investigating mercury s south polar deposits arecibo radar observations and high resolution determination of illumination conditions there is strong evidence that mercury s polar deposits are water ice hosted in permanently shadowed regions in this study we present new arecibo radar observations of mercury s south pole which reveal numerous radar bright deposits and substantially increase the radar imaging coverage we also use images from messenger s full mission to determine the illumination conditions of mercury s south polar region at the same spatial resolution as the north polar region enabling comparisons between the two poles the area of radar bright deposits in mercury s south is roughly double that found in the north consistent with the larger permanently shadowed area in the older cratered terrain at the south relative to the younger smooth plains at the north radar bright features are strongly associated with regions of permanent shadow at both poles consistent with water ice being the dominant component of the deposits however both of mercury s polar regions show that roughly 50 of permanently shadowed regions lack radar bright deposits despite some of these locations having thermal environments that are conducive to the presence of water ice the observed uneven distribution of water ice among mercury s polar cold traps may suggest that the source of mercury s water ice was not a steady regular process but rather that the source was an episodic event such as a recent large impact on the innermost planet

submarine slope systems processes and products understanding of the processes operating on submarine slopes the preserved deposi tional products and post depositional modifications to sediment body geometries through instabil ity and remobilization requires integration of data from modern slopes with information derived from seismic and outcrop studies of ancient slope successions although local factors are important key generic concepts that aid in predicting submarine slope processes and products include 1 shelf accommodation lateral sediment supply variations on sediment delivery 2 the spatial tem poral distribution of characteristic styles intensities of sediment instability and remobilization and 3 a generalized model for the stratigraphic development of slope channel complexes slope fans and the temporal relationships between these major components of slope stratigraphy key remaining problems include bridging the gap between the timescales sampled by recent to late quaternary studies and those represented by ancient slope successions moreover present day highstand conditions may not provide a good analogue for lowstand slope settings future research efforts will also concentrate on better calibration of seismic facies to rock facies and linking of physical and numerical process and forward modelling techniques at different scales to observa tional datasets the future lies in integration of these complementary research directions

near surface temperatures on mercury and the moon and the stability of polar ice deposits abstract in order to assess the thermal stability of polar ice deposits we present model calculated temperatures of flat surfaces and surfaces within bowl shaped and flat floored polar impact craters on mercury and the moon our model includes appropriate insolation cycles realistic crater shapes multiple scattering of sunlight and infrared radiation and depth and temperature dependent regolith thermophysical properties unshaded water ice deposits on the surface of either body are rapidly lost to thermal sublimation a subsurface water ice deposit is stable within 2 latitude of the moon s poles meter thick water ice deposits require billions of years to sublime if located in the permanently shaded portions of flat floored craters within 10 latitude of the poles of mercury and 13 latitude of the poles of the moon results for craters associated with radar features on mercury are consistent with the presence of stable water ice deposits if a thin regolith layer thermally insulates deposits at lower latitudes and within smaller craters a regolith cover would also reduce losses from diffusion ion sputtering impact vaporization and h ly and is implied independently by the radar observations permanently shaded areas near the moon s poles are generally colder than those near mercury s poles but the moon s obliquity history its orbit through earth s magnetospheric tail and its radar opaque regolith may limit the volume and radar detectability of ice deposits there

illumination conditions of the lunar polar regions using lola topography abstract we use high resolution altimetry data obtained by the lunar orbiter laser altimeter instrument onboard the lunar reconnaissance orbiter to characterize present illumination conditions in the polar regions of the moon compared to previous studies both the spatial and temporal extent of the simulations are increased significantly as well as the coverage fill ratio of the topographic maps used thanks to the 28 hz firing rate of the five beam instrument we determine the horizon elevation in a number of directions based on 240 m resolution polar digital elevation models reaching down to 75 latitude the illumination of both polar regions extending to 80 can be calculated for any geometry from those horizon longitudinal profiles we validated our modeling with recent lunar reconnaissance orbiter wide angle camera images we assessed the extent of permanently shadowed regions psrs defined as areas that never receive direct solar illumination and obtained total areas generally larger than previous studies 12 866 and 16 055 km2 in the north and south respectively we extended our direct illumination model to account for singly scattered light and found that every psr does receive some amount of scattered light during the year we conducted simulations over long periods several 18 6 years lunar precession cycles with a high temporal resolution 6 h and identified the most illuminated locations in the vicinity of both poles because of the importance of those sites for exploration and engineering considerations we characterized their illumination more precisely over the near future every year a location near the shackleton crater rim in the south polar region is sunlit continuously for 240 days and its longest continuous period in total darkness is about 1 5 days for some locations small height gains 10 m can dramatically improve their average illumination and reduce the night duration rendering some of those particularly attractive energy wise as possible sites for near continuous sources of solar power

the thickness of radar bright deposits in mercury s northern hemisphere from individual mercury laser altimeter tracks the discovery of mercury s radar bright deposits has expanded our understanding of volatiles in the solar system key to deciphering the history and origin of the radar bright deposits is an estimate of the volume of radar bright material that in turn requires a measure of the average thickness of the deposits in this study we investigate changes in topography across radar bright deposits hosted in flat floored complex craters using individual edited mercury laser altimeter mla tracks we compare the difference in heights of radar bright regions and non radar bright regions of the crater floor and the difference of similarly sized and located regions in non radar bright craters and show that the two populations cannot be distinguished the similarity of topography in these two sets of craters allows an upper limit of 15 m to be placed on the thickness of the radar bright deposits

illumination conditions at the lunar south pole recent remote sensing data strongly suggest that deposits of ice occur in permanently shadowed regions at the lunar poles clementine by providing the first contiguous coverage of the moon has enabled the production of an illumination map of the south pole this map shows the extent of the areas of permanent darkness during winter in this region as well as identifying places on the lunar surface that receive illumination for more than 50 of the lunar day the permanently dark areas are prime candidates for locations of ice deposits while regions that are illuminated for anomalous periods are possible sites for lunar bases in this paper we study in detail the illumination history during a lunar day of some of these sites while we find no area that receives permanent illumination we do find two areas only 10 km apart which collectively receive sunlight for over 98 of the time

borehole evidence for wing like clastic intrusion complexes on the western norwegian margin abstract data from a borehole on the norwegian margin indicate that a strata concordant amplitude anomaly within the upper cretaceous succession represents a 15 m thick sandbody that was either intruded in the subsurface or extruded on the palaeo seabed this observation implies that spatially related strata discordant anomalies are the seismic expression of sandstone dykes thereby supporting previous geometry based interpretations of the origin of these amplitude anomalies furthermore this study indicates that thickness of an intrusion may be overestimated if based solely on seismic reflection mapping and that this may lead to erroneous calculation of the ratio between depositional and intruded sandstone

the alba field ocean bottom cable seismic survey impact on development alba field in the central north sea uk block 16 26 consists of eocene age high porosity unconsolidated turbidite channel sands sealed by low permeability shales at an average subsea depth of 1900 m the main channel is approximately 9 km long and 1 5 km wide and can be up to 100 m thick figure 1 the channel contains discrete bodies of intrareservoir shales that can cause significant drilling completion and production problems immediately overlying the main alba sand channel several wells have encountered thin discontinuous oil saturated brioc sands

submarine slope systems submarine slopes provide the critical link between shallow water and deep water sedimentary environments they accumulate a sensitive record of sediment supply accommodation creation destruction and tectonic processes during basin filling there is a complex stratigraphic response to the interplay between parameters that control the evolution of submarine slope systems e g slope gradient topographic complexity sediment flux and calibre base level change tectonic setting and post depositional sediment remobilization processes the increased understanding of submarine slope system has been driven partly by the discovery of large hydrocarbon fields in morphologically complex slope settings such as the gulf of mexico and offshore west africa and has led to detailed case studies and improved generic models for their evolution this volume brings together research papers from modern outcrop and subsurface settings to highlight these recent advances in understanding of the stratigraphic evolution of submarine slope systems

images of surface volatiles in mercury s polar craters acquired by the messenger spacecraft images acquired by nasa s messenger spacecraft have revealed the morphology of frozen volatiles in mercury s permanently shadowed polar craters and provide insight into the mode of emplacement and evolution of the polar deposits the images show extensive spatially continuous regions with distinctive reflectance properties a site within prokofiev crater identified as containing widespread surface water ice exhibits a cratered texture that resembles the neighboring sunlit surface except for its uniformly higher reflectance indicating that the surficial ice was emplaced after formation of the underlying craters in areas where water ice is inferred to be present but covered by a thin layer of dark organic rich volatile material regions with uniformly lower reflectance extend to the edges of the shadowed areas and terminate with sharp boundaries the sharp boundaries indicate that the volatile deposits at mercury s poles are geologically young relative to the time scale for lateral mixing by impacts and either are restored at the surface through an ongoing process or were delivered to the planet recently

planetary science constant illumination at the lunar north pole thinking of a property on the moon the northern rim of peary crater could be the place to be an illumination map of the moon s north pole based on images obtained by the clementine spacecraft reveals areas around the peary crater that are in permanent sunlight these are prime locations for lunar outposts as well as abundant solar energy temperatures are relatively benign and nearby regions in permanent shadow may conveniently contain water ice images returned by the spacecraft clementine have been used to produce a quantitative illumination map of the north pole of the moon revealing the percentage of time that points on the surface are illuminated during the lunar day we have used this map to identify areas that are constantly illuminated during a lunar day in summer and which may therefore be in permanent sunlight all are located on the northern rim of peary crater close to the north pole permanently sunlit areas represent prime locations for lunar outpost sites as they have abundant solar energy are relatively benign thermally when compared with equatorial regions and are close to permanently shadowed regions that may contain water ice

high resistant sand injected marl and low resistant damaged marl to locate and characterize the thenia fault zone in boumerdes city north central algeria the purpose of this study was to locate and characterize the thenia fault zone tfz in the urban area of boumerdes city geological and electrical resistivity tomography surveys have targeted the plaisancian marl and its quaternary cover as a whole data indicate a complex near vertical fault zone with an asymmetric and zoned internal structure of at least 150 m wide and with a straight n120 overall trending the fault zone is traversed with two elongated parallel fault branches fb1 and fb2 generally 70 m distant from each other these fault branches locate two intense damage zones idzs of 10 15 m thick each situated at the margin of two damage zones each having a thickness of several tens of meters downward sand injections into idzs during pleistocene epoch possible pulverization of plaisancian marl rocks systematic deflection of actual stream channels and vertical displacement of at least 30 m affecting quaternary alluvial deposits show that the area would have undergone active tectonic driven by the tfz

radar mapping of mercury s polar anomalies ground based radar observations of mercury have revealed unusually strong highly depolarized echoes from the north1 2 and south2 poles these anomalous echoes have been cited as evidence of polar ice deposits1 5 thermal studies3 5 suggest that the permanently shaded floors of large polar craters are cold enough to preserve water ice in a stable state over aeons in spite of mercury s proximity to the sun here we present high resolution radar maps of mercury s polar regions derived from delay doppler measurements we have resolved the north and south polar anomalies into numerous crater sized features and we have been able to identify the source craters for many of these features after making small corrections to the pole positions on the mariner 10 images the coincidence with crater locations together with other properties of the radar features are consistent with the polar ice hypothesis

did the late ordovician african ice sheet reach europe abstractpaleovalleys and their in lling successions are described from outcrops and drill cores of the cantabrian range northern spain a hirnantia fauna and associated diamictites with striated lonestones indicate that the paleovalleys are related to the hirnantian latest ordovician glacial event based on overall geometry depositional facies and associated deformation structures the paleovalleys are interpreted as subglacial tunnel valleys they were most likely related to the north gondwana ice sheet the ice sheet therefore reached the ibero armorican domain that was still attached to the gondwana landmass at least until the latest ordovician introduction the hirnantian glacial record documents one or several ice sheets throughout africa arabia and south america the extents of which are still controversial ghienne et al 2007 schonian and egenhoff 2007 although glaciomarine strata are widespread in european peri gondwa nan terranes robardet and dore 1988 brenchley et al 1991 they do not precisely indicate the presence of glaciers at those localities because a number of these terranes would have been attached to the gondwana land mass during the late ordovician e g robardet 2003 the gondwanan ice sheet may have reached some of them the hirnantian paleovalleys of the cantabrian range northwest spain are the rst glacial valleys to be recognized outside the gondwana landmass they may be related to a gondwanan ice sheet lobe or to a peri gondwana satellite ice cap

arecibo radar imagery of mars ii chryse xanthe polar caps and other regions abstract we conclude our radar imaging survey of mars which maps spatial variations in depolarized radar reflectivity using arecibo s band 12 6 cm observations from 2005 2012 whereas our earlier paper harmon et al 2012 arecibo radar imagery of mars the major volcanic provinces icarus 220 990 1030 covered the volcanic regions of tharsis elysium and amazonis this paper includes non volcanic regions where hydrologic and impact processes can be the dominant resurfacing agents affecting radar backscatter many of the more prominent and interesting radar bright features outside the major volcanic provinces are located in and around chryse planitia and xanthe terra these features are identified with a basin in northeast lunae planum containing the combined deposits from maja vallis and ganges catena outflows channel outwash plains in western and southern chryse basin plateaus bordering chasma chaos zones where surface modification may have resulted from hydrologic action associated with incipient chaos formation and some bright ejecta craters in chryse basin of a type otherwise rare on mars dark halo craters have also been identified in chryse and elsewhere that are similar to those seen in the volcanic provinces although the cratered highlands are relatively radar bland they do exhibit some bright depolarized features these include eroded crater rims several unusual ejecta flows and impact melts and terrain softened plains the rims of large impact basins hellas argyre isidis show a variety of radar bright features provisionally identified with massif slopes erosion sediments eroded pyroclastics impact melts and glacial deposits the interiors of these basins are largely radar dark which is consistent with coverage by rock free sediments tempe terra and acheron fossae show bright features possibly associated with rift volcanism or eroded tectonic structures and northwest tempe terra shows one very bright feature associated with glacial or other ice processes in the dichotomy boundary region the first delay doppler images of the radar bright features from the north and south polar icecaps are presented both poles show the circular polarization inversion and high reflectivity characteristic of coherent volume backscatter from relatively clean ice the south polar feature is primarily backscatter from the residual co 2 icecap with a lesser contribution from the polar layered deposits whose finite optical depth probably accounts for the feature s strong s x band wavelength dependence conversely the north polar radar feature appears to be mostly backscatter from the h 2 o ice rich polar layered deposits rather than from the thin residual h 2 o cap the north polar region shows additional radar bright features from korolev crater and a few other outlying circumpolar ice deposits

comparison of areas in shadow from imaging and altimetry in the north polar region of mercury and implications for polar ice deposits earth based radar observations and results from the messenger mission have provided strong evidence that permanently shadowed regions near mercury s poles host deposits of water ice messenger s complete orbital image and topographic datasets enable mercury s surface to be observed and modeled under an extensive range of illumination conditions the shadowed regions of mercury s north polar region from 65 n to 90 n were mapped by analyzing mercury dual imaging system mdis images and by modeling illumination with mercury laser altimeter mla topographic data the two independent methods produced strong agreement in identifying shadowed areas all large radar bright deposits those hosted within impact craters 6 km in diameter collocate with regions of shadow identified by both methods however only 46 of the persistently shadowed areas determined from images and 43 of the permanently shadowed areas derived from altimetry host radar bright materials some sizable regions of shadow that do not host radar bright deposits experience thermal conditions similar to those that do the shadowed craters that lack radar bright materials show a relation with longitude that is not related to the thermal environment suggesting that the earth based radar observations of these locations may have been limited by viewing geometry but it is also possible that water ice in these locations is insulated by anomalously thick lag deposits or that these shadowed regions do not host water ice

mercury s global color mosaic an update from messenger s orbital observations abstract we report an update to the photometric correction used to produce global color mosaics of mercury derived from an analysis of photometric observations acquired during the orbital phase of messenger s primary mission comparisons between versions of the color mosaic produced with photometric corrections derived from flyby and orbital data indicate that areas imaged at high incidence and emission angles 50 are better standardized to a common illumination and viewing geometry with the orbit derived corrections seams between images taken at very different illumination geometries however are still present at visually detectable levels further improvements to the photometric correction await updates to the radiometric calibration that will enable data retrieval over a larger range of photometric angles