sedimentology and stratigraphy of thetownsend tuff bed lower old red sandstone in south wales and the welsh borders the townsend tuff bed has a highly distinctive internal stratigraphy which allows it to be recognized at a large number of localities scattered over the welsh borders and south wales it is a group of 3 almost directly superimposed normally graded air fall tuffs that originated in distant but powerful plinian eruptions centre unknown and became spread over extensive but practically featureless coastal mud flats the bed occurs in a barren interval within the early lower old red sandstone between a silurian invertebrate vertebrate fauna below and an already devonian vertebrate assemblage above the base of the devonian system in south wales and the welsh borders is accordingly defined as occurring at a regionally uniform lithological contact within the townsend tuff bed

compact reconnaissance imaging spectrometer for mars crism north polar springtime recession mapping first 3 mars years of observations 1 we report on mapping of the north polar region of mars using data from the compact reconnaissance imaging spectrometer for mars crism instrument we have observed 3 mars years 28 30 of late winter and spring recessions ls 304 92 our investigations have led to the following observations 1 we classify the retreat of the north polar seasonal cap into presublimation early spring asymmetric and stable periods according to the prevalent h2o ice grain size distributions 2 during the early spring the signatures of co2 ice at the edge of the cap are obscured by h2o ice which increases the apparent size of the h2o ice annulus around the seasonal co2 cap at this time at around ls 25 this process changes into an asymmetrical distribution of h2o deposition covering co2 signatures more rapidly in the longitude range from 90 to 210 e 3 we detect signatures of pure co2 ice in extremely limited locations in lomonosov crater even in midwinter h2o ice signatures appear everywhere in the retreating co2 seasonal cap in contrast with the south polar seasonal cap 4 we find that average h2o ice grain sizes continuously increase from northern midwinter to the end of springtime this is the inverse of the behavior of co2 ice grain sizes in the southern springtime

martian north polar cap summer water cycle abstract a key outstanding question in martian science is are the polar caps gaining or losing mass and what are the implications for past current and future climate to address this question we use observations from the compact reconnaissance imaging spectrometer for mars crism of the north polar cap during late summer for multiple martian years to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer we establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap we show that in a key region in the interior of the north polar cap the absorption band depths grow until l s 120 when they begin to shrink until they are obscured at the end of summer by the north polar hood this behavior is transferable over the entire north polar cap where in late summer regions flip from being net sublimating into net condensation mode this transition or mode flip happens earlier for regions closer to the pole and later for regions close to the periphery of the cap the observations and calculations presented herein estimate that on average a water ice layer 70 microns thick is deposited during the l s 135 164 period this is far larger than the results of deposition on the south pole during summer where an average layer 0 6 6 microns deep has been estimated by brown et al 2014 earth planet sci lett 406 102 109

north polar region of mars topography of circumpolar deposits from mars orbiter laser altimeter mola data and evidence for asymmetric retreat of the polar cap we have used high resolution mars orbiter laser altimeter mola data to analyze the topography morphology stratigraphy and geologic history of the martian north circumpolar deposits the present polar deposits are offset about toward 0 w from the rotational pole an arc of irregular topography concentric to olympia planitia and the cap consists of polar material remnants depressions which we interpret to be kettles frost covered and residual ice filled craters and frost patches olympia planitia originally thought to be a flat sand covered plain is characterized by a convex upward topography contiguous with the polar cap we interpret olympia planitia to represent a now dune covered extension of the polar materials together olympia planitia and the outlying deposits delineate a former extent of the polar cap topographic data have clarified relationships among the circumpolar deposits contributors to these deposits include local volcanics fluvial and aqueous sediments from outflow channels and a possible standing body of water pyroclastic ash sublimation lag from the olympia lobe and eolian reworked materials significant events in the history of the region include 1 formation of the northern lowlands 2 emplacement of volcanic plains fluvial and aqueous sedimentation and subsequent desiccation forming polygonal patterns which in part underlie the present polar layered deposits 3 formation of the polar cap composed primarily of layered deposits 4 asymmetric retreat of the olympia lobe resulting in sublimation lag deposits polar remnants and kettles and 5 continued collection and reworking of sediments by eolian processes the cause of the asymmetrical retreat of the olympia lobe is unknown

absorption and scattering properties of the martian dust in the solar wavelengths a new wavelength dependent model of the single scattering properties of the martian dust is presented the model encompasses the solar wavelengths 0 3 to 4 3 m at 0 02 m resolution and does not assume a particular mineralogical composition of the particles we use the particle size distribution shape and single scattering properties at viking lander wavelengths presented by pollack et al 1995 we expand the wavelength range of the aerosol model by assuming that the atmospheric dust complex index of refraction is the same as that of dust particles in the bright surface geologic units the new wavelength dependent model is compared to observations taken by the viking orbiter infrared thermal mapper solar channel instrument during two dust storms the model accurately matches afternoon observations and some morning observations some of the early morning observations are much brighter than the model results the increased reflectance can be ascribed to the formation of a water ice shell around the dust particles thus creating the water ice clouds which colburn et al 1989 among others have predicted

on the icy edge at louth and korolev craters abstract the modern climate of mars has been well characterized from over a decade of orbiting spacecraft in situ measurements via landers rovers and theoretical advances in climate modeling nonetheless important questions remain unanswered including the present day mass balance of the north polar residual cap and its icy outliers exposed water ice mounds are found in craters and extend as far equatorward as 70 2 n due to their southerly location these ice mounds are likely more sensitive to ongoing changes in climate we analyze high resolution images of the louth crater ice mound and employ a coupled 1 d thermal and atmospheric model to estimate annual mass balance of both louth and korolev water ice we incorporate the effects of shallowly sloping surfaces and seasonally dependent water ice albedo no clear trend in the advance or retreat of louth crater water ice is observed in over 4 mars years of repeat high resolution images secular changes are either sufficiently small as to not be detected or the ice is in equilibrium modeled mass balance ranges from 6 to 2 mm of water ice per mars year at both sites with nominal cases being in near equilibrium

mapping of the water ice content within the martian surficial soil on the periphery of the retreating seasonal northern polar cap based on the tes and the omega data 1 analysis of seasonal data from the mars global surveyor thermal emission spectrometer tes shows a significant increase in thermal inertia during autumn winter and spring in the middle and high latitudes of mars at each stage of the northern seasonal polar cap s recession in spring a distinct high thermal inertia hti annulus arises around the cap s edge within this annulus we estimated and mapped the springtime water ice content in the daily thermal skin depth layer using spring and summer values of the thermal inertia in tes surface footprints the results show that the average water content in the surface soil within the hti annulus varies from 5 vol at the early stages of the seasonal polar cap retreating ls 340 360 to 1 vol at later stages ls 60 70 maximum values of water ice content within the hti annulus occur at ls 0 20 2 6 vol and ls 20 40 4 10 vol we analyzed the temporal and spatial relationship between the hti annuli and the water ice wi annuli at the edge of the northern seasonal polar cap the water ice within the wi annuli was mapped using a water ice spectral index the absorption band depth at the 1 5 m wavelength derived from the omega observatoire pour la mineralogie l eau les glaces et l activite imaging spectrometer aboard the mars express spacecraft recent omega observations show that the wi annuli formation arises only around the retreating northern seasonal polar cap never around the retreating southern seasonal cap for this reason our study is confined only to the northern hemisphere the observed relationship between the hti and wi annuli in the northern hemisphere of mars indicates a close physical interdependence between these two phenomena our results confirm that the seasonal permafrost exposed by the retreating northern polar cap within the hti annuli is actively involved today in the condensation and sublimation processes in the modern water cycle on mars the water abundance in this annual condensation sublimation cycle within the active layer may be an order of magnitude higher than all the annual water vapor abundance in the martian atmosphere our results are consistent with existence of the positive mass balance of the northern permanent polar cap in the modern climatic period

compact reconnaissance imaging spectrometer for mars observations of northern martian latitudes in summer 1 this paper brings together initial results obtained of the high northern latitudes in mars years 28 and 29 between october 2006 and october 2008 these measurements confirm many previous models and shed new light on the nature of polar surface materials particularly in intermediate albedo units of the polar layered deposits many of which are found to be ice rich we identify hydrated non ice materials present in many low albedo troughs as well as in the circumpolar erg that was previously associated with gypsum we identify icy outlier deposits that may be related to subsurface thermophysical properties and permafrost new observations of the gypsum rich dune material constrain models for its formation and distribution intrinsic properties of ice content and grain size are found to be independent of the albedo of fine layered units and may provide a novel method for stratigraphic identification and correlation

high density bioturbated sandstones in the mississippian mauch chunk formation eastern pennsylvania usa implications for continental ecospace exploitation abstract continental communities represented by complex rapidly evolving invertebrate ecosystems first appeared during the early palaeozoic era and are recorded in surface and subsurface bioturbation the mississippian age mauch chunk formation contains several high density bioturbated fine grained sandstones that are preserved as erosively based fluvial channel fills several of these channel sandstone bodies are almost completely homogenized by subsequent bioturbation throughout their entire thickness up to a maximum depth of 1 6 m the mauch chunk ichnofossil record demonstrates that high density bioturbation occurred at least 30 my prior to the permian and well before its widespread distribution in the triassic hence the late mississippian high density bioturbated sandstones demonstrate a much earlier high density exploitation of the continental subsurface ecospace than previously known

sublimation and transport of water from the north residual polar cap on mars several features of the viking mars atmospheric water detection observations have suggested that the residual north polar cap on mars is a major source of atmospheric water during northern summer and that the water it supplies to the atmosphere is transported equatorward to low northern latitudes by summer s end we have explored the role of the north residual cap in the current martian water cycle by constructing models to assess the ability of the cap to supply water to the atmosphere and the ability of the atmosphere to transport it out of the polar regions from our sublimation model we conclude that the residual cap can sublime the 7 1014 g of water that appears in the atmosphere after ls 80 provided surface winds are high 10 m s the cap emissivity is low 0 9 or the exposed soil in polar regions contains ice that is accessible to the atmosphere in our view these requirements seem unlikely and we are drawn to the conclusion that other sources of water exist this conclusion is further supported by the results of two dimensional transport simulations which show that most of the water sublimed from the cap remains at high latitudes the polar circulation simply lacks the intensity and scale to move water very far from the cap a weak circulation places additional constraints on cap sublimation rates since abundant clouds and significant ice deposits would form just equatorward of the cap edge according to the model if the cap is allowed to sublime 7 1014 g of water such predictions are inconsistent with available data we suggest that the nature of the additional source is water desorbing from the nonpolar regolith

ichnology paleosols and palimpsests surfaces in the tinat member of the nuayyim formation unayzah group subsurface saudi arabia trace fossils and genetic stratigraphy in continental settings abstract the nuayyim formation of the unayzah group is widespread in subsurface central saudi arabia and constitutes a laterally variable stratigraphic unit with a complex mosaic of facies sedimentation for the tinat member took place majorly in a continental setting dominated by aeolian processes that resulted in dunes interdunes ephemeral stream deposits terminating with regional development of paleosols facies ichnofacies and palynological analysis suggest an arid to semi arid setting with biogenic activity in the form of continental fauna and plants in deposits associated with pedogenetical alteration in paleosol horizons therein burrowing exhibits elements of the scoyenia ichnofacies in beds with sparse to abundant bioturbation tectonic uplift and subaerial exposure resulted in the exhumation of previously buried substrates leading to the formation of burrowed palimpsests surfaces associated with paleosols at the end of unayzah deposition prior to the onset of the khuff formation progressive thermal updoming is interpreted to have occurred during the latest portion of the unayzah group sedimentation cycle in the arabian plate culminating in the regional pre khuff unconformity at the top of this megacycle recognized in this study by biogenically demarcated diastems ichnological and sedimentological observations outlined in this study are significant because they i refine existing interpretations of the paleoenvironmental history in the study area ii document diastems marking breaks in sedimentation and iii outline several soil forming cycles that allowed the establishment of a trace fossil suite with continental affinities thus demarcating the end of an entire sedimentation cycle the recognition and delineation of burrowed horizons associated with paleosols provides a tool to understand the tectono stratigraphic evolution of similar successions in the rock record

stratigraphic relationships within martian polar cap deposits abstract deposits of layered ice and dust accumulate on the smooth and banded terrains of the north and south polar cap deposits while erosion of equator facing slopes of layered terrain expose these layers banded terrain occurs at exposures of irregular layers resulting from slight erosion of the feather edges of layers deposited on pole facing trough walls these deposits unconformably overlap onto adjacent layered terrain stripping of layers occurs in areas of strong multidirectional wind forming striped terrain local wind scour has also produced steep scarps with crescentic planform often associated with dune fields positioned immediately downwind unconformities are common within layered deposits in areas of complex topography at the north pole these indicate that episodes of deposition of 5 10 layers alternate with slight erosion of pole facing trough walls troughs that strike north south alternate between erosional widening and deepening and depositional infilling creating multiple unconformities troughs near the equatorward limit of polar deposits increase in relief by deposition on adjacent smooth terrain and locally by erosional deepening troughs may migrate poleward replacing the relief increase by depositional infilling when they near the poles

monitoring the perennial martian northern polar cap with mgs moc abstract we have used the mars global surveyor mars orbiter camera wide angle mgs moc wa dataset to study albedo trends on the martian northern residual cap six study regions were selected the chasma boreale source region three regions near the center of the cap fish hook region latitude 87 bottle opener region latitude 87 steep shallow region latitude 85 and two lower latitude regions crater latitude 77 and polar outlier latitude 82 and the albedos of these six regions were examined these regions were chosen due to their good temporal coverage in the moc dataset as well as having been studied by other researchers bass et al 2000 icarus 144 382 396 calvin and titus 2004 lunar planet sci xxxv abstract 1455 the picture which emerges is complex most areas experience a combination of darkening and brightening through the northern summer only one area consistently brightens the polar outlier region a good deal of interannual repeatability in each region s albedo behavior is seen however possible causes for the observed complex behaviors include dust deposition from late summer storms sintering of frost grains over the course of the summer and cold trapping of volatiles on bright cold surfaces

ice sublimation and rheology implications for the martian polar layered deposits it has been suggested that the martian polar layered deposits are composed largely of water ice if true then sublimation and deformation creep of the ice are important processes simple models indicate that sublimation will occur at a rate inconsistent with current estimates of the deposit s age and viking observations of the atmospheric water abundance suggesting that when considering the formation evolution and structure of the deposits one must include a mechanism by which sublimation is inhibited a surface layer of dust seems the most likely possibility additionally over the age of the deposits flows of at least 1 km are expected at viking resolution 150 m no obvious flow features are observed assuming that martian features would be similar to those that occur on the earth this limits the maximum flow rates possible and suggest the deposits need to be more than 90 ice or less than about 40 ice by volume the mars observer spacecraft will be able to constrain the ice abundance further by both searching for flow features and clarifying the nature of the deposit s surface and near surface

astronomical theory of the pleistocene ice ages a brief historical review abstract this paper traces the evolution of the astronomical theory of the pleistocene ice ages from its origin in the work of adhemar and croll through its quantitative transformation in the hands of milankovitch to its current renaissance emphasis is given to the interplay between climatic theory and geologic observation from 1941 when milankovitch published his final version of the theory until the early 1970s most attempts to test the theory empirically were carried out in the time domain by comparing the geologic record of climate with predicted climate curves these attempts ran into serious difficulties particularly the inaccuracy of the geologic time scale and the ambiguity of climate predictions early attempts to evaluate the theory with simple radiation balance models appeared to indicate that the climatic response to secular changes in the orbit would be too small to be observed geologically but by the mid 1970s the advent of an improved time scale for pleistocene marine deposits and the availability of long closely sampled records made it possible to arrange generalized but unambiguous tests of the theory in the frequency domain by comparing orbital and climatic spectra these results decisively confirmed the idea that orbital variations significantly influenced the earth s climate during the pleistocene but they did not tell us how this influence was exercised the emphasis of current work has therefore shifted to the identification and quantitative modeling of physical mechanisms by which the climate system responds so dramatically to the predicted rather subtle changes in radiative boundary conditions

winter and spring evolution of northern seasonal deposits on mars from omega on mars express the omega visible near infrared imaging spectrometer on mars express has observed the retreat of the northern seasonal deposits during martian year 27 28 from the period of maximum extension close to the northern winter solstice to the end of the retreat at l s 95 we present the temporal and spatial distributions of both co 2 and h 2o ices and propose a scenario that describes the winter and spring evolution of the northern seasonal deposits during winter the co 2 rich condensates are initially transparent and could be in slab form a water ice annulus surrounds the sublimating co 2 ice extending over 6 of latitude at l s 320 decreasing to 2 at l s 350 and gradually increasing to 4 5 at l s 50 this annulus first consists of thin frost as observed by the viking lander 2 and is then overlaid by h 2o grains trapped in the co 2 rich ice layer and released during co 2 sublimation by l s 50 h 2o ice spectrally dominates most of the deposits in order to hide the still several tens of centimeters thick co 2 ice layer in central areas of the cap we propose the buildup of an optically thick top layer of h 2o ice from ice grains previously embedded in the co 2 ice and by cold trapping of water vapor from the sublimating water ice annulus the co 2 ice signature locally reappears between l s 50 and 70 what emerges from our observations is a very active surface atmosphere water cycle these data provide additional constraints to the general circulation models simulating the martian climate copyright 2011 by the american geophysical union

variability of mars north polar water ice cap i analysis of mariner 9 and viking orbiter imaging data abstract previous studies interpreted differences in ice coverage between mariner 9 and viking orbiter observations of mars north residual polar cap as evidence of interannual variability of ice deposition on the cap however these investigators did not consider the possibility that there could be significant changes in the ice coverage within the northern residual cap over the course of the summer season our more comprehensive analysis of mariner 9 and viking orbiter imaging data shows that the appearance of the residual cap does not show large scale variance on an interannual basis rather we find evidence that regions that were dark at the beginning of summer look bright by the end of summer and that this seasonal variation of the cap repeats from year to year our results suggest that this brightening was due to the deposition of newly formed water ice on the surface we find that newly formed ice deposits in the summer season have the same red to violet band image ratios as permanently bright deposits within the residual cap we believe the newly formed ice accumulates in a continuous layer to constrain the minimum amount of deposited ice we used observed albedo data in conjunction with calculations using mie theory for single scattering and a delta eddington approximation of radiative transfer for multiple scattering the brightening could have been produced by a minimum of 1 a 35 m thick layer of 50 m sized ice particles with 10 dust or 2 a 14 m thick layer of 10 m sized ice particles with 50 dust

the effects of martian orbital variations upon the sublimation and relaxation of north polar troughs and scarps abstract the north polar layered deposits pld of mars are climatologically significant because they represent the largest actively exchanging reservoir of martian water the kilometer scale topography of the north pld is dominated by troughs and scarps which exhibit highly correlated surface slopes and total depths the most widespread theories of pld evolution presume that the asymmetrical nature of north pld troughs characterized by equatorward facing slopes that are generally steeper than poleward facing slopes is the result of preferential h 2 o sublimation from equatorward facing trough walls however our orbitally modulated simulations indicate that there is no long term sublimation advantage of equatorward facing trough walls because of the effects of obliquity upon the slope dependence of sublimation rate in contrast we propose that viscous relaxation of subsurface water is consistent with the slope and depth distributions of north pld troughs and scarps the results of our finite element simulations suggest that a mere 2 k difference in the subsurface temperatures of opposing trough walls is sufficient to produce the observed slope disparity due to the slower rate of uplift of colder poleward facing trough walls both our sublimation and relaxation simulations indicate that present day north pld troughs have formed since 5 ma and are not sites of long term deposition additionally our results imply that glacial flow may govern the large scale evolution of the north pld especially at high obliquity

mariner 9 television calibration revisited improved processing of the mariner 9 television data allows more accurate photometric analysis of the images returned in 1971 1972 by the first successful mars orbiting spacecraft these data include good synoptic coverage of the planet and the highest resolution images yet obtained of the south polar region errors in calibration are comparable to but still greater than those of the viking orbiter cameras calibration data and software are now available to interested parties as part of the planetary image cartography system through the u s geological survey in flagstaff arizona

a wireless subglacial probe for deep ice applications we present the design and first results from two experiments using a wireless subglacial sensor system wise that is able to transmit data through 2500 m thick ice energy consumption of the probes is minimized enabling the transmission of data for at least 10 years in july 2010 the first prototype of the system was used to measure subglacial pressure at the base and a temperature profile consisting of 23 probes in two 600 m deep holes at russell glacier a land terminating part of the west greenland ice sheet near kangerlussuaq the time series of subglacial pressure show very good agreement between data from the wise system and the wired reference system the wireless measured temperature data were validated by comparison with the theoretical decrease of melting point with water pressure inside the water filled hole directly after installation to test the depth range of the wise system a second experiment using three different probe types and two different surface antennas was performed inside the 2537 m deep hole at neem it is demonstrated that with the proper combination of transmission power and surface antenna type the wise system transmits data through 2500 m thick ice

martian north polar cap recession 2000 mars orbiter camera observations abstract the wide angle cameras of the mars orbiter camera moc on the mars global surveyor have recorded the 2000 recession of the seasonal co 2 cap in the north polar region from l s 330 to 90 in stark contrast to the asymmetric behavior of the south seasonal cap the seasonal north cap remains relatively circular and uniform until mid spring when the retreat reaches the circum polar dune field which is the one major nonuniformity in the cap the recession of cap edge latitude versus areocentric longitude l s is very well represented as a linear function until late spring there is no evidence for the plateau or standstill in the recession curve that has been observed in some prior years the lambert albedo of the seasonal frost deposits in the north polar region demonstrates the increase with insolation first observed by paige in 1985 increasing to approximately 0 57 at l s 40 the north polar cap near solstice visually appears smaller than that observed by moc at the start of mapping in 1999 but later images acquired in summer show the residual cap returning to its more usual shape the most likely explanation for these changes in albedo is precipitation and subsequent removal of dust on the cap as a result of frequent dust storms near the cap edge

viking bistatic radar experiment summary of first order results emphasizing north polar data abstract bistatic radar observations of mars north polar region during 1977 1978 showed surface rms slope ranging from 1 to 6 these values apply to horizontal scales of 1 100 m values of roughness tend to decrease with increasing latitude especially over 65 80 n but there are many exceptions the smoothest surfaces 1 appear to be inclusions within generally rougher 3 terrain rather than broad expanses of very smooth material the permanent north polar cap is relatively uniform with 2 5 3 0 considerable structure has been found in echo spectra indicating a heterogeneous and perhaps anisotropic scattering surface echo spectra obtained from the same region but several months apart 1 l s

color and albedo of the south polar layered deposits on mars five color albedo units including polar frost have been recognized and mapped in the southern layered deposits on mars atmospheric dust scattering was measured in shadows and modeled in order to remove the component of brightness in mars images due to the atmosphere and quantify the albedo and color of the surface the layered deposits appear to be mantled by red dust except where eolian stripping has exposed the underlying bedrock frost and bare ground are mixed below the resolution of the images in many areas adjacent to the polar cap some of which appear to be younger than the surrounding layered terrain dark material has been deposited in topographic depressions in much of the south polar region including the layered deposits the available observational data suggest that the layered deposits are composed of bright dust ice and a small amount of dark material if the dark material is sand a periodic change in polar winds seems required in order to transport the sand poleward into the layered terrain in any case the observations are not consistent with the layered deposits being composed only of bright dust and ice the mars observer camera and infrared instruments should be particularly useful in this investigation

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

introduction to the 4th mars polar science and exploration conference special issue five top questions in mars polar science abstract as an introduction to this icarus special issue for the 4th mars polar science and exploration conference we discuss five key questions in mars polar science gleaned from plenary discussions and presentations held at the conference these questions highlight major unknowns in the field 1 what are the physical characteristics of the polar layered deposits pld and how are the different geologic units within beneath and surrounding the pld related 2 how old are the pld and what are their glacial fluvial depositional and erosional histories 3 what are the mass and energy budgets of the pld and what processes control these budgets on seasonal and longer timescales 4 what chronology compositional variability and record of climatic change is expressed in the stratigraphy of the pld 5 how have volatiles and dust been exchanged between polar and non polar reservoirs and how has this exchange affected the past and present distribution of surface and subsurface ice

occurence of the trace fossil beaconites antarcticus in the lower carboniferous fluviatile rocks of county mayo ireland abstract large straight curved or sinuous endichnial burrows with a meniscus pattern of infilling are described from lower carboniferous red beds of county mayo ireland the burrows have been identified as beaconites antarcticus the burrows show a strong facies association being concentrated in the upper parts of sandstones deposited during floods in shallow possibly ephemeral stream channels they appear to be absent from the overlying non red fluvial sandstones which show evidence for deeper more sinuous and more permanent channels it is suggested that burrowing was related to varying moisture content of the sediment the burrows were probably formed by locomotory back packing of arthropods or vertebrates but the precise nature of the producer remains unknown

distribution and state of h2o in the high latitude shallow subsurface of mars abstract a quantitative model of the state distribution and migration of water in the shallow martian regolith is presented reported results are confined to the region of the planet greater than 40 lat the calculations take into account 1 expected thermal variations at all depths latitudes and times resulting from seasonal and astronomically induced insolation variations 2 variations in atmospheric ph2o and pco2 resulting from polar insolation variations and regolith adsorptive equilibria 3 feedback effects related to latent heat and albedo variations resulting from condensation of atmospheric constituents 4 two possible regolith mineralogies 5 variable total h2o content of the regolith 6 kinetics of h2o transport through the martian atmosphere and regolith and 7 equilibrium phase partitioning of h2o between the condensed adsorbed and vapor phases results suggest that the adsorptive capacity of the regolith is important in controlling the state and distribution of high latitude h2o unweathered mafic silicates favor the development of shallow ground ice at all temperate and polar latitudes while heavily weathered clay like regolith materials leads to a deeper ground ice interface and far more extensive quantities of adsorbed h2o the capacity of the high latitude regolith for storage of h2o and the total mass of h2o exchanged between the atmosphere polar cap and subsurface over an obliquity cycle is found to be relatively independent of mineralogy the maximum exchanged volume is found to be 3 0 104 km3 of ice per cycle implications for the history of the polar caps and the origin of the layered terrain are discussed results also suggest that seasonal thermal waves act to force adsorbed h2o into the solid phase over a wide variety of latitude obliquity conditions seasonal phase cycling of regolith h2o is most common at high latitudes and obliquities such phase behavior is highly dependent on regolith mineralogy in a highly weathered regolith adsorbed h2o is annually forced into the solid phase at all latitudes 40 at obliquities greater than approximately 25 seasonal adsorption freezing cycles which are predicted here may produce geomorphologic signatures not unlike those produced by terrestrial freeze thaw cycles

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

patterning instability on the mars polar ice caps 1 we present a mathematical theory to study the origin of large scale spiral troughs on the mars residual polar caps starting with the hypothesis that atmospheric circulation governs the planform of the troughs via an instability that operates in the flow direction of surface winds this concept can explain why the troughs spiral at each pole in an opposite sense to that expected for coriolis deflected winds the instability arises from interactions on water ice assumed to contain dust and depends on how the exchange of atmospheric dust and moisture h2o with the polar cap surface controls its albedo and mass and energy balance our model predicts spatial patterns to form when moisture is carried by wind over the surface owing to unstable coupling between the albedo and the h2o vapor pressure the resulting albedo pattern causes an alternating accumulation ablation mass balance so that an undulating topography develops which resembles the dark troughs and their adjacent bright smooth terrains on the polar caps because the albedo patterning process is fast whereas topographic evolution is slow we suggest that an ancient imprint in the surface albedo preconditions today s trough morphology

topography and stratigraphy of martian polar layered deposits abstract topography and stratigraphy of young sediments in the martian north polar region are being studied from high resolution viking orbiter images to test and constrain theories of terrain evolution driven by cyclical climate change several steepened slopes upon which layers are exposed in section were found to have local relief of 200 to 800 m and slopes ranging from 1 to 8 first attempts to calculate average layer thicknesses from portions of sections yielded results ranging from 14 to 46 m linearly correlated with slope in some cases under the assumption of short range lateral continuity a greater number of layers was inferred to be present than was actually resolved on a particular section when apparent layer thickness are revised accordingly the correlation with slope is destroyed we conclude that images of the shallowest sloping sections of layered deposits should yield the most stratigraphic information and layers thinner than 14 m may occur indeed they may even be common or typical because of the sensitivity of summer frost distribution to local slope and other properties of exposed strata interseasonal comparisons of images promise to enhance the capability to detect layers and differentiate them by material properties

summer evolution of the north polar cap of mars as observed by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega visible infrared imaging spectrometer extensively observed regions of mars with latitudes above 70 n in late 2004 heliocentric longitude from ls 93 to ls 127 the extent of water ice at the surface and the size of ice grains were monitored as a function of time bright small grained frost which initially covered a large fraction of the polar cap waned in favor of large grained ice in outlying regions dominated by large grained ice the albedo increased over the period evaluating the dust content was model dependent however contamination of ice by dust was low

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

ichnology and sedimentology of the trace fossil bearing fluvial red beds from the lowermost member of the paleocene funing formation in the jinhu depression subei basin east china abstract the lowermost member of the paleocene funing formation which is composed of bioturbated fluvial red beds is extensively distributed throughout the jinhu depression subei basin east china despite its economic value as one of the most important oil bearing reservoirs in the subei basin the sedimentology ichnology and paleoenvironment of this formation in the jinhu depression remain poorly understood in this work we investigated the ichnofossils and sedimentary facies analyzed the ichnofacies and potential tracemakers and reconstructed the paleoenvironment of the jinhu depression based on cores from the lowermost member of the paleocene funing formation this formation contains a moderately diverse ichnofauna 9 ichnotaxa of the scoyenia ichnofacies that includes meniscate burrows taenidium barretti taenidium satanassi and beaconites coronus simple horizontal cylindrical burrows palaeophycus tubularis palaeophycus heberti and planolites isp simple vertical or subvertical burrows skolithos linearis and skolithos isp and plant root traces the other complex branched and chambered burrows are left in open nomenclature these ichnofossils are widespread throughout the three facies associations identified in this study 1 ephemeral fluvial channel 2 crevasse splay and 3 distal floodplain facies associations multiple lines of sedimentological and ichnological evidence namely the predominance of massive and upper flow regime structures the occurrence of invertebrate burrows e g skolithos and taenidium in the lower and middle parts of the channel deposits and the dramatic changes in the color and mottling in channel and overbank sediments indicate that the river discharge was short lived and that the water table was highly variable the variations in the discharge and water level are attributed to the influence of seasonal rainfall the cyclic nature of intense rainfall events and dry periods suggests that the subei basin was likely located in a semiarid region with a seasonal rainfall pattern during the early paleocene this study also reveals that the ephemeral fluvial channel is the facies association with the highest potential to yield oil bearing reservoirs in the paleocene red beds of the jinhu depression additionally the influence of bioturbation on the reservoir quality in this region should be considered in future research

fluvial sedimentation in the lower carboniferous of clew bay county mayo ireland abstract a succession of about 300 m of fluvial sediments from the lower carboniferous of northwest ireland is described and interpreted a lower mainly red formation contains fluvial channel deposits dominated by flat laminated sandstone these are separated by interbedded sandstones and mudrocks with local caliche horizons and abundant mudcracks interpreted as levee and flood basin deposits an upper mainly non red formation contains fluvial channel deposits with common trough cross stratification and epsilon cross stratification also separated by interbedded sandstones and mudrocks evidence of desiccation is less common in the uppermost beds which pass transitionally upwards into marine sediments the change in fluvial channel style is interpreted as due to increasing sinuosity and permanence of flow which may have been partly temporally and partly spatially controlled the predominance of coarse sediments is thought to be largely controlled by limited subsidence the lower carboniferous transgression was the major overall control of alluviation

sand dune materials and polar layered deposits on mars abstract the relationship of dark sand dunes to the polar layered deposits of mars is investigated by mapping the colors and morphologic settings of the dunes in and near the polar deposits in the north polar region the dunes have restricted sources in the layered deposits that are associated with are arcuate scarps 10 50 km in length and

modeling the martian seasonal water cycle ever since the observations of percival lowell the annual cycle of martian water has been a fascinating topic in planetary exploration observations by the viking orbiter supplemented by earth based microwave and infrared observations have given us a reasonable picture of this cycle we are now also able to model the cycle using our mars climate model a simplified atmospheric general circulation model designed specifically for this purpose we find that a thin adsorbing layer of the martian regolith plays a fundamental role in the water cycle limiting the lower atmospheric relative humidity and preventing the formation of widespread ice deposits at low latitudes we are thus able to estimate a large scale average value of the specific soil surface area of this regolith water which evaporates from the permanent north polar ice cap during summer is returned by a process of repeated evaporation and precipitation on the retreating seasonal cap the following spring so that the global inventory of water outside the polar caps ranges within narrow limits there is a small net annual deposition of water ice at the south polar cap which is always at dry ice temperatures if ice on the residual south polar cap is exposed during the summer it rapidly sublimes generating vapor amounts similar to those observed in northern summer recovery to normal dry conditions in the southern atmosphere occurs very rapidly in the next year such an event could explain the otherwise anomalous earth based pre viking observations of a wet southern summer if southern ice deposits at lower latitudes are exposed the vapor can be transferred irreversibly through the strong hadley cell to the north polar cap we therefore speculate that the asymmetry of mars current orbit is responsible for the asymmetry of the present water distribution with extensive permanent water ice deposits located only in the colder aphelion summer northern hemisphere