thermal genesis of dissolution caves in the black hills south dakota jewel cave 118 km of mapped passages beneath an area of 2 7 km 2 and wind cave 70 km beneath 1 8 km 2 are respectively the fourth and tenth longest known cave systems and the world9s foremost examples of three dimensional rectilinear networks of solutional passages other caves in the black hills are similar they occur in 90 140 m of well bedded mississippian limestone and dolomite walls throughout jewel cave are lined with euhedral calcite spar as much as 15 cm thick wind cave displays lesser encrustations and remarkable calcite boxwork since 1938 opinion has favored cave excavation by slowly circulating meteoric waters in artesian confinement similar to that surrounding the black hills we believe that the caves were developed by regional thermal waters focusing on paleospring outlets in outlying sandstones four sets of criteria are evaluated 1 morphological the three dimensional one phase maze form having convectional features is similar to known and supposed thermal caves in europe 2 petrographic and mineralogical study of the chief precipitates shows a record of carbonate solution calcite precipitation consonant with a model of cooling then degassing waters 3 a thermal anomaly at regional hot springs is shown to extend beneath wind cave where basal lake water samples show chemical and isotopic affinities with the thermal waters and 4 13 c and 18 o measurements place all suspected paleothermal water precipitates in the domain of thermal calcites reported by others and being deposited at the modern hot springs finally u series dates show that the wind cave deposits are quaternary and that the cave is still draining jewel cave is truly relict and divorced from the modern thermal ground water system its great calcite spar sheets are probably older than 1 25 1 50 ma

the thermal history of the bowen basin queensland australia vitrinite reflectance and clay mineralogy of late permian coal measures abstract the thermal history of the bowen basin queensland australia has been investigated using vitrinite reflectance data and clay mineralogy vitrinite reflectance data combined with a study of clay mineral reactions indicates that the maximum temperatures which induced organic maturation of the bowen basin coals and extensive clay mineralisation are not related to deep burial metamorphism during the latest middle triassic earliest late triassic as previously believed the results of the present study indicate that the development of a zone of high heat flow in the latest late triassic had a major control on the thermal history of the bowen basin high palaeogeothermal gradients estimated in the northern bowen basin are interpreted to result from convective heat transfer during a hydrothermal event variable heat distributions due to localised fracture enhanced permeable zones acting as hot reservoirs in the deeper part of the basin may have been responsible for some significant local thermal anomalies in the lower coal measures the estimated palaeogeothermal gradients in the southern bowen basin also indicate high heat flow in the lower sections of the stratigraphy sections in the southern bowen basin however are believed to reflect a rock dominated semi closed system with low water rock ratio where rocks are impervious to circulating fluids and thus heat transfer may have occurred by conduction the correlation between vitrinite reflectance and clay mineralogy shows a delay in illitisation reaction relative to organic maturity for many illite smectite i s mixed layer clays in the northern bowen basin this phenomenon can be explained as a result of insufficient time for the completion of mineral reactions and a variable potassium supply in relatively impermeable rocks the relationship between i s expandability and vitrinite reflectance for the bowen basin data compared to basins with known tectonic regimes suggests a thermal history in a rift setting for the bowen basin the effect of thin igneous intrusions on clay mineral reactions is very limited intensive illitisation due to heating of intrusions can only be observed in narrow zones immediately adjacent to intrusive bodies this further demonstrates that mineral reactions are too slow to record the effect of extremely short heating duration in contrast to organic maturity indicators these differences between mineral and organic parameters aid in the identification of local contact metamorphic effects

three dimensional normal faulting models of the valles marineris mars and geodynamic implications inversion of martian topography using a three dimensional boundary element model permits revised estimates of fault dip angle depth of faulting paleogeothermal gradient and extensional strain in the valles marineris region the major normal faults dip at 40 55 to depths of 60 75 km with comparatively small footwall uplifts 500 m for throws to 10 km implying that paleogeothermal gradients during faulting were 10 k km 1 or less assuming relatively rapid strain rates appropriate to the extending martian crust accumulation of dip slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs the magnitudes of the predicted vertical and horizontal displacements outside the troughs as well as extensional strains are spatially variable depending on both cross and along strike position relative to the troughs the predicted displacements and strains attain maximum values at the troughs and decay to background values at cross strike distances of 250 km corresponding to 3 4 times the depth of faulting with an average province wide strain of 4 15 by implication the aggregate strain field surrounding tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields each associated and scaling in size with an individual graben from the smallest structures through the largest valles marineris troughs

salt tectonics and collapse of hebes chasma valles marineris mars a photogeologic and physical modeling study indicates that hebes chasma mars formed by collapse of the megaregolith local heating facilitated drainage of 10 5 km 3 of brines and entrained particulates through fractures in the chasma floor and into a regional aquifer a megaregolith rich in salts and water is implied by massive low gradient allochthonous flows that terminate in deep pits and troughs by emergent diapirs and by arching of hebes mensa these structures are consistent with plastic and viscous deformation but inconsistent with collapse of basalt flows and or tephra spectral measurements confirm that hydrated sulfate salts are spatially associated with allochthonous flows from depth and light toned deposits collapse features and flows are present in many other chasmata in valles marineris suggesting that widespread salt tectonics and dissolution may have shaped the region

new models for the origin of valles marineris closed depressions current models for the formation of the abundant large closed depressions of valles marineris have serious shortcomings purely tectonic mechanisms are inconsistent with the morphology of many depressions and removal of large quantities of ground ice from the canyon walls is inconsistent with the observed strength of the walls accordingly we offer some alternatives one possibility involves decay of ice rich bodies occupying partially sediment choked ancient graben that predated the overlying cratered and ridged plains other possibilities involve the removal of massive equatorial carbonate deposits storing much of the planet s co2 inventory generated during greenhouse conditions on early mars solution by carbonic acid derived from the atmosphere analogous to terrestrial karst requires extensive recycling of the available water supply solution by various groundwater acids possibly derived from the tharsis magmas requires less water especially if only the smaller closed depressions are due to carbonate decay alternatively volume loss due to decarbonation of carbonate during early high heat flow or a later tharsis related heat pulse can produce extensive collapse especially if the carbonates have high silica content

reply to comment of smith and pallasser on factors controlling the origin of gas in australian bowen basin coals firstly we wish to acknowledge the leadership and contribution that smith and his various coworkers have made over the last three decades to the understanding of the origin of natural gas and coal seam gas particularly through the use of stable isotopes our intention was in no way to criticise their views rather as expressed in boreham et al 1998 our view was and remains that the origin of coal seam gases especially methane is not as straightforward as previously thought indeed smith 1999 has recently o ered an alternative abiogenic origin for methane and co2 via decomposition of acetic acid smith et al 1998 the essence of our paper was that laboratory studies using open system pyrolysis methods with extrapolation to geological heating rates demonstrate that a carbon isotope composition heavier than y50 for methane is consistent with a thermogenic origin secondly we acknowledge the incorrectness of a statement in boreham et al 1998 which credited smith and pallasser 1996 as reporting that they have argued for a predominantly microbiological origin for methane based on reduction of co2 sourced from a magmatic origin by methanogenic bacteria we inadvertently included the phrase sourced from magmatic origin which has lead to this rebu on the part of smith and pallasser we acknowledge the proposition in smith and pallasser 1996 and re stated in smith 1999 and ahmed and smith 1999 that the origin of the isotopically light methane in the coal seam gases is from the biogenic reduction of co2 dc y23 where the source of the co2 is organic derived from decarboxylation of the coal the view of smith and pallasser 1996 p 891 is that the magmatic derived co2 dc 7 2 and 10 mol is inert to attack by methanogens however we have di culty with this model since it is hard to see how a microorganism can distinguish the source of co2 although smith 1999 has o ered some possible reasons another weakness of the smith and pallasser 1996 model is that they attribute the downhole increase in the c content of methane to an increasing mix of heavy methane dc y5 relative to the isotopically light biogenic methane however they o er no source for this unusually heavy methane the main concern expressed in the comment of smith and pallasser is our handling of data appearing in smith and pallasser 1996 and references therein and reproduced by boreham et al 1998 in their fig 2 and table 1 this gure presented a rayleigh model t to the data to show that the data in smith and pallasser 1996 are inconsistent with a closed system approach with this model the small systematic isotopic changes in the carbon isotopic compositions of the product methane and the residual co2 cannot be reconciled with the large kinetic isotope e ect generally associated with the methanogenic process as noted above smith and pallasser 1996 p 891 have argued that there is no genetic relationship between co2 of magmatic origin and isotopically light methane speci cally they state where it co2 occurs in seam gas in highly variable proportions the relatively constant isotopic composition of the ch4 shows that neither reduction of co2 to ch4 nor isotopic equilibration between co2 and ch4 has occurred however this observation is also consistent with microbial reduction of magmatic co2 where the kinetic isotope e ect is 55 and the co2 availability is non limiting i e an open system additionally coal seam gases in the sydney basin fig 1 with co2 contents 10 mol show

microbial origin of australian coalbed methane bituminous coal seam gases from the permian sydney and bowen basins australia are characterized by 1 methane ethane ratios greater than or equal to 1000 2 dgr13c and dgrd values for methane of 60 10 pmil pdb and 217 17 pmil smow respectively 3 carbon dioxide contents of less than 5 and 4 dgr13c co 2 ch4 values of 55 10 pmil pdb these data suggest that microbial reduction of co2 rather than traditional thermogenic reactions is mainly responsible for gas composition invasions by co2 of deep seated external origins are readily recognized by their isotopic compositions 7 2 pmil pdb

are there carbonate deposits in the valles marineris mars the thick sequences of layered deposits found in the valles marineris have recently been determined by s s nedell s w squyres and d w andersen 1987 icarus 70 409 441 to contain a minimum of 105 km3 of material we suggest that this material could be derived from the precipitation of 30 mbar of atmospheric co2 as carbonates in lakes as surface temperatures fell on mars the presence of an insulating ice cover would have allowed liquid water to exist fed by transitory surface melting atmospheric co2 would have accumulated in such lakes enhancing carbonate precipitation support for this hypothesis comes from processes that occur in the perennially frozen lakes in the dry valleys of antarctica where the mean temperature is 253 k and the lake water is supersaturated with atmospheric gases a search of the recently reissued mariner 6 7 infrared spectrometer data in the wavelength region between 2 and 6 m failed to confirm the presence of carbonates due to the fact that no spectral footprints appear to directly overlie the layered deposits and that deposits may be blanketed by an eolian mantle this negative result is inconclusive we feel that the canyon deposits are still a prime site for future searches for carbonates on mars

stable isotope geochemistry of authigenic clay minerals from late permian coal measures queensland australia implications for the evolution of the bowen basin oxygen and hydrogen isotope analyses were carried out on authigenic clay minerals from late permian coal measures of the bowen basin australia in the northern bowen basin the oxygen isotope compositions of the mixed layer illite smectite show significant irregular variations with respect to depth which parallel the changes in the extent of the illitisation reaction and are interpreted as reflecting changes in water rock ratio in turn related to permeability the o and d values of illite smectite and kaolinite in the northern bowen basin and the calculated fluid isotopic composition o 3 to 1 d 70 to 90 in equilibrium with these clays are considerably lower than those typically reported for deeply buried sedimentary basins these stable isotope data together with relatively high inferred palaeotemperatures up to 235 c and abnormally high geothermal gradients are consistent with a hydrothermal origin for clay mineral formation in the northern bowen basin the hydrothermal system is interpreted to be a result of the late triassic extensional tectonic regime which developed in large parts of eastern australia and affected the northern part of the bowen basin in the southern bowen basin by contrast clays are more enriched in o and deuterium which is explained by lower temperatures in the shallow coal measures and a significant enrichment in the fluid isotopic composition o 3 6 to 5 6 d 66 to 35 under low water rock ratio conditions especially in deeper pelitic rocks c 2000 elsevier science b v all rights reserved

underlying structural control of small scale faults and fractures in west candor chasma mars 1 orientations of small scale faults and fractures within the interior layered deposits of west candor chasma were measured to investigate what information about the geologic history of valles marineris they can contribute deformational features were separated into six categories based on morphology and their orientations were analyzed the elevations at which the deformational features formed are recorded as a proxy for stratigraphic level deformational features occur over a continuous range of elevations and display regionally consistent preferred orientations indicating their formation was controlled by a regional stress regime the two most abundant preferred orientations of 35 and 110 are approximately parallel to the chasma walls and the inferred underlying normal faults the alignment of three populations of small faults at 140 consistent with the morphology of release faults indicates a large scale fault underlying the southeastern border of ceti mensa the preferred orientations imply these small scale deformational features formed from a continuation of the same imposed stresses responsible for the formation of valles marineris indicating these stresses existed past the formation of the interior layered deposits the origins of a fourth preferred orientation of 70 is less clear but suggests the study area has undergone at least two periods of deformation

geochemical evolution of the northern plains of mars early hydrosphere carbonate development and present morphology it is likely that early in mars history abundant liquid water was available under a thick several bars carbon dioxide atmosphere this water could have formed an ocean located primarily in the lowlands of the northern hemisphere an equilibrium geochemical model of this ocean and its interactions with the atmosphere and regolith of mars was developed and the results of this model were used to discuss the evolution of the volatile budget of mars including the deposition of large carbonate beds on the northern plains differential solutional weathering of these carbonate beds may have caused the formation of some of the enigmatic features seen on the northern plains of mars such as the thumbprint terrain and enclosed depressions

valles marineris mars wet debris flows and ground ice abstract detailed study of the valles marineris equatorial troughs suggests that the landslides in that area contained water and probably were gigantic wet debris flows one landslide complex generated a channel that has several bends and extends for 250 km further support for water or ice in debris masses includes rounded flow lobes and transport of some slide masses in the direction of the local topographic slope differences in speed and emplacement efficiency between martian and terrestrial landslides can be attributed to the entrainment of volatiles on mars but they can also be explained by other mechanisms support that the wall rock contained water comes from the following observations 1 the water within the landslide debris must have been derived from wall rock 2 debris appears to have been transported through tributary canyons 3 locally channels emerged from the canyons 4 the wall rock apprarently disintegrated and flowed easily and 5 fault zones within the troughs are unusually resistant to erosion the study further suggests that in the equatorial region of mars material below depths of 400 800 m was not desiccated during the time of landslide activity within the last billion years of martian history therefore the martian ground water or groundice reservoir if not a relic from ancient times must have been replenished

the formation of valles marineris 2 stress focusing along the buried dichotomy boundary 1 although valles marineris is widely regarded as an extensional tectonic feature the source of stress responsible for its formation remains unknown this study argues that the tensile stresses that triggered valles marineris tectonism are a result of its location south of and subparallel to the buried crustal dichotomy boundary beneath tharsis the emplacement of the tharsis volcanic load straddling the pre existing topographic step of the crustal dichotomy boundary would have resulted in an abrupt change in the thickness of the load causing differential subsidence and extension across the boundary thin shell flexural models predict a narrow belt of focused tensile stresses south of the buried dichotomy boundary coinciding with the location of present day valles marineris the interaction of these boundary generated stresses with the competing stress fields associated with tharsis loading can explain the formation of noctis labyrinthus in the west and the deflection of the valles marineris troughs away from the buried boundary toward the east finite element models demonstrate that the magnitudes and vertical variations of stress at valles marineris are sensitive to the timing of loading and flexure in tharsis the incremental loading and flexure expected for a large volcanic rise results in the maximum tensile stress at valles marineris occurring at depth with tensile stresses through the majority of the lithospheric column dikes forming within this tensile stress belt would propagate through the full vertical extent of the lithosphere due to the stress release associated with the dilation of the dikes playing a crucial role in the formation of the valles marineris troughs

mars regolith versus snc meteorites possible evidence for abundant crustal carbonates abstract viking xrf analyses of the martian regolith are compared with typical igneous rocks of the earth the moon the eucrite parent asteroid and especially the shergottites nakhlites and chassigny snc meteorites which are suspected to be basalts and mafic cumulates from mars a striking feature of the martian regolith compared to igneous rocks with similar molar mg fe si ratios is its extraordinarily low ca si ratio the regolith s low ca si ratio is probably not a result of simple mixing isochemical weathering of snc like rocks with other igneous rocks unless the regolith contains a large component of rock with an improbable combination of extremely low ca si and mg fe si and yet low k 2 o and zr several other models might conceivably account for the low ca si ratio but i suggest that most of the missing ca was removed from the regolith as ca carbonate formation of a mass of carbonate equivalent to a global shell 20 m thick would suffice to remove 1000 mbar of co 2 from the martian atmosphere thus the peculiar ca si ratio of the martian regolith tends to support the hypothesis that the climate of mars was once far warmer and wetter than it is today

viscosity of rock ice mixtures and applications to the evolution of icy satellites theory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix for typical conditions encountered in icy satellites this ratio is of order ten or possibly larger depending on unknown factors such as the particle size distribution it is shown that even this modest increase in viscosity may be enough to have caused a failure of solid state convective self regulation early in the evolution of a homogeneous rock water ice satellite provided the satellite is large enough and sufficiently silicate rich the criteria for this failure are satisfied by ganymede and are marginal for callisto if the silicates are hydrated failure of self regulation means that the viscosity is too high for the interior to remain completely solid and eliminate the heat production of long lived radioisotopes by solid state convection partial melting of the ice then occurs it is further shown that satellites of this size may then undergo runaway differentiation into a rock core and almost pure ice mantle because the gravitational energy release is sufficient to melt nearly all the ice and the rayleigh taylor instability time scale is short although the high pressure phases of ice melt the resulting water quickly refreezes at a higher level it is conjectured that these results explain the striking surface dissimilarity of ganymede and callisto if these satellites accreted cold and undifferentiated ganymede may have gone supercritical melted and differentiated because of a failure of self regulation whereas callisto remained undifferentiated to the present day like all proposed explanations for the ganymede callisto dichotomy this conjecture cannot be quantified with confidence because of inadequate or incomplete observations theory and experimental data

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

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

the stable isotope geochemistry of australian coals abstract d h 13 c 12 c 18 o 16 o and 34 s 32 s ratios in the organic matrix and organic solvent extracts of australian coals and in the fluids and minerals associated with these coals are reported and reviewed against similar isotopic data for coals from other regions where coals are immature original isotopic differences between macrolithotypes and between solvent extracts lipid concentrates and insoluble residues are largely preserved however with increasing maturity these characteristic differences particularly those between macrolithotypes are rapidly erased conversely where as indicated by low total sulfur contents coals of cretaceous to permian age were deposited under essentially freshwater conditions 34 s values for the organically bound sulfur remain remarkably constant at 4 3 relative to meteoritic sulfur in similar younger tertiary coals the organic sulfur is markedly enriched in 34 s five distinctive isotopic patterns which may be interpreted in terms of the environment of sulfate reduction can be recognized from 34 s 32 s ratio measurements on the various forms of sulfur in australian coals isotopic studies of seam gas hydrocarbons collected in situ show these to be unexpectedly strongly depleted in the heavier isotopes of hydrogen and carbon relative to natural gases from proposed humic sources furthermore no pronounced increase in the 13 c content in methane with increase in rank of the parent coal was observed in addition several sources of associated carbon dioxide have been delineated including normal maturation processes invasion of the seams by magnetic carbon dioxide and interaction of the coal with intrusive magma isotopic exchange between free seam gases is not accepted as an explanation for some unusual isotopic fractionations seen rather the data suggest that these gases may be formed in a state approaching isotopic equilibrium this argument also satisfactorily explains the isotopic compositions of primary siderite and secondary calcite associated with bituminous coal seams however where seams are invaded and permeated with externally derived carbon dioxide usually of magnetic origin carbonates are frequently absent presumably as a result of the action of carbonic acid

a volcanotectonic survey of ascraeus mons mars 1 ascraeus mons is one of the largest volcanoes on mars it is replete with well preserved features that can be used to understand its volcanotectonic evolution previous studies of this volcano focused on specific features and were limited by the quality and coverage of contemporary data our objective is to review and enhance the existing developmental model for ascraeus by considering all endogenic surface features on the volcano we surveyed the volcano s caldera complex flank terraces pit structures sinuous rilles arcuate grabens and small vents we report the spatial and temporal distributions of these features appraise their proposed formation mechanisms in light of our mapping results and propose a detailed geological history for ascraeus mons an initial shield building phase was followed by the formation of a summit caldera complex and small parasitic cones while compression due to flexure of the supporting basement led to extensive terracing of the shield flanks an eruptive hiatus followed ending with the construction of expansive rift aprons to the northeast and southwest against later extensive flank resurfacing in the late amazonian continued flexure formed arcuate grabens concentric to the edifice localized eruption and surface flow of a fluid agent lava and or water from within the volcano then produced a population of rilles on the lower flanks finally in a change of flank tectonic regime from compression to extension pit crater chains and troughs developed on the main shield and rift aprons eventually coalescing to form large embayments at the northeast and southwest base of the volcano

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

stable isotope geochemistry of coal bed and shale gas and related production waters a review coal bed and shale gas can be of thermogenic microbial or of mixed origin with the distinction made primarily on the basis of the molecular and stable isotope compositions of the gases and production waters methane ethane carbon dioxide and nitrogen are the main constituents of coal bed and shale gases with a general lack of c2 hydrocarbon species in gases produced from shallow levels and more mature coals and shales evidence for the presence of microbial gas include 13c ch4 values less than 50 covariation of the isotope compositions of gases and production water carbon and hydrogen isotope fractionations consistent with microbial processes and positive 13c values of dissolved inorganic carbon in production waters the co2 reduction pathway is distinguished from acetate methyl type fermentation by somewhat lower 13c ch4 and higher d ch4 but can also have overlapping values depending on the openness of the microbial system and the extent of substrate depletion crossplots of 13c ch4 versus 13c co2 and d ch4 versus 13c h2o may provide a better indication of the origin of the gases and the dominant metabolic pathway than the absolute carbon and hydrogen isotope compositions of methane in the majority of cases microbial coal bed and shale gases have carbon and hydrogen isotope fractionations close to those expected for co2 reduction primary thermogenic gases have 13c ch4 values greater than 50 and 13c values that systematically increase from c1 to c4 and define a relatively straight line when plotted against reciprocal carbon number although coals and disseminated organic matter in shales represent a continuum as hydrocarbon source rocks current data suggest a divergence between these two rock types at the high maturity end in deep basin shale gas reversals or rollovers in molecular and isotopic compositions are increasingly reported in what is effectively a closed shale system as opposed to the relative openness in coal measure environments detailed geochemical studies of coal bed and shale gas and related production waters are essential to determine not only gas origins but also the dominant methanogenic pathway in the case of microbial gases

mars the regolith atmosphere cap system and climate change abstract a new model for predicting the behavior of the martian regolith atmosphere cap co 2 regime and describing its role in climate change is derived the model describes the time temperature histories of 90 regolith chunks on a latitude depth grid accounting for co 2 exchange by means of laboratory derived expressions relating temperature co 2 pressure p co 2 and adsorbed co 2 mass co 2 polar cap formation and sublimation is accounted for subject to the constraint of constant total co 2 in the atmosphere regolith cap system the influence of differences in regolith adsorption laws for basalt and clay and the influence of variations in regolith depth with latitude regolith thermal diffusivity and total exchangeable co 2 inventory on predicted variations in atmospheric pressure and cap mass are examined the following results are indicated 1 the atmosphere acts as a low capacity conduit through which flows between 10 and 100 times the current atmospheric mass of co 2 between two reservoirs a regolith ocean of adsorbed co 2 and a polar cap cryosphere 2 exchange between these reservoirs is driven by variations of obliquity with the polar cap the dominant co 2 sink at low and the regolith dominating at high atmospheric pressure ranges between 0 1 low and 15 mbar high pressures of up to 25 mbar could result from pre tharsis variations pressure up to 40 mbarare achieved only in models which also call for a huge quasi permanent present co 2 cap which is not apparent 3 at high the atmospheric pressure is buffered by the regolith and satisfies adsorption equilibrium for the 90 chunks as well as conservation of co 2 mass at low a potetially large co 2 cap appears and the atmospheric pressure is buffered by the cap not the regolith 4 the periodic reservoir flushing can account for the observation of simultaneous nonenrichment of 18 o and enrichment of 13 n 5 mars climate history may be divided into three parts a post tharsis formation history as described above b pre tharsis formation with qualitatively similar processes but larger oscillations between reservoirs and larger atmospheric pressure and cap mass variation and c the very early period of channel formation 6 the nature of the response of the three part regolith atmosphere polar cap martian climate system to surface insolation variations may be analogous to that of earth s ocean atmosphere cryosphere system

stable isotope and water quality analysis of coal bed methane production waters and gases from the bowen basin australia abstract coal bed methane cbm is a significant growing industry in queensland s energy sector it is however a relatively new industry with little local water quality data and stable isotope compositions of production waters and gases available in the public domain this study aims to determine whether water quality and stable isotope data can be correlated with gas and groundwater production and flow pathways and identify zones of recharge and water mixing stable isotope analysis and accessory water quality tests were conducted on cbm production gas and water samples collected from two cbm producing bituminous coal seams within a single field in the bowen basin in the production field the reservoir seams are gently folded with eastwardly dipping fold axes and compartmentalised by an ene normal fault on the flank of a broad central anticline that contains minor faults for one seam splitting and a change in coal quality parallels the fault and fold axes although virgin reservoir conditions were similar differing production performance north and south of the main fault suggests it acts as a barrier to water and gas flow along strike the stable isotope analysis on the production water showed that waters with more positive d and 18o compositions were associated with areas of higher water production and shallower depths whereas more negative d and 18o compositions were associated with lower water production and high gas production the gas isotope analysis showed that production gases had both biogenic and thermogenic origins and that secondary biogenic gas generated through co2 reduction comprises a significant portion of the cbm produced from this field more negative ch4 13c values characterize the zones of meteoric recharge in shallow up dip areas gas production data and co2 13c values suggest that this may result from 13ch4 stripping by the recharge waters and or increased biogenic activity in this area smaller co2 ch4 carbon isotopic fractionation values characterized zones of meteoric recharge whereas higher isotopic fractionation values characterized the high gas production domain

origin and evolution of the layered deposits in the valles marineris mars abstract thick sequences of layered deposits are found in the martian valles marineris they exhibit fine nearly horizontal layering and are present as isolated plateaus of what may have once been more extensive deposits individual sequences of layered deposits are as thick as 5 km the greatest total thicknesses of deposits are found in candor ophir and melas chasmata individual layer thicknesses range from about 70 to 300 m some tilting of sequences is observed but at the best image resolutions no angular unconformities are detectable in the layers the sequences of events in the canyons as deduced from morphologic and stratigraphic evidence was 1 graben formation in response to the tharsis uplift 2 canyon wall retreat and canyon enlargement roughly contemporaneous with formation of the layered deposits 3 deep erosion of the layered deposits 4 landsliding of the canyon walls and 5 eolian erosion of the layered deposits perhaps continuing up to the present we consider four hypotheses for the origin of the layered deposits they are eolian deposits they are remnants of the material that makes up the canyon walls they are deposits of explosive volcanic eruptions or they were deposited in standing bodies of water the rhythmic nature of the layers and their lateral continuity horizontality great thickness and stratigraphic relationships with other units in the canyons all appear most consistent with deposition in an aqueous environment if standing bodies of water existed in the valles marineris they were almost certainly ice covered there are three ways in which sediment could have entered an ice covered lake down through the ice cover up from the lake bottom or in from the lake margins layers of sediment could have been transported downward through an ice cover by foundering or rayleigh taylor instabilities but it is not clear whether there was a viable mechanism for repeatedly accumulating thick sediment layers on top of the ice cover subaqueous volcanic eruption on the lake bottom does not suffer from many of the morphologic arguments that make origin by subaerial volcanism seem improbable while this mechanism is attractive there are no eruptive centers observed and there is no other direct evidence to support it because canyon enlargement took place at roughly the same time as layer deposition debris from the canyon walls is an obvious and likely source for some of the material in the layered deposits however the volume of material removed from the canyon walls may be insufficient to account for all of the presently observed material we conclude that there are several geologically feasible but as yet unproven mechanisms that could have led to formation of thick deposits in ice covered paleolakes in the valles marineris present data are insufficient to choose conclusively among the various possibilities several types of data from the mars observer mission will be useful in further characterizing the deposits and clarifying the process of their origin the deposits should be considered important targets for a future mars sample return mission

obsidian hydration dating of volcanic events abstract obsidian hydration dating of volcanic events had been compared with ages of the same events determined by the 14c and k ar methods at several localities the localities ranging in age from 1200 to over 1 million yr include newberry craters oregon coso hot springs california salton sea california yellowstone national park wyoming and mineral range utah in most cases the agreement is quite good a number of factors including volcanic glass composition and exposuretemperature history must be known in order to relate hydration thickness to age the effect of composition can be determined from chemical analysis or the refractive index of the glass exposure temperature history requires a number of considerations enumerated in this paper