pantasma evidence for a pleistocene circa 14 km diameter impact crater in nicaragua the circa 14 km diameter pantasma circular structure in oligocene volcanic rocks in nicaragua is here studied for the first time to understand its origin geomorphology field mapping petrographic and geochemical investigations all are consistent with an impact origin for the pantasma structure observations supporting an impact origin include outward dipping volcanic flows the presence of former melt bearing polymict breccia impact glass with lechatelierite and low h 2 o 10 km found in the americas

geochemical and geological characteristics of the es3l lacustrine shale in the bonan sag bohai bay basin china abstract although extensive studies have been conducted on unconventional shale oil resources in recent years little work has been performed on the resource potential of lacustrine shales the es3l lower sub member of the third member of the eocene shahejie formation shale of the bonan sag a set of thick lacustrine deposited sediments offers a good example for furthering the understanding of these rocks geochemical and mineralogical investigations were carried out on a large sample set from the 220 m thick sequence of well luo69 in total 200 core samples were analyzed for total organic carbon toc and rock eval pyrolysis and 421 core samples were analyzed for mineral compositions the es3l shales have a very high toc content with type i lacustrine oil prone kerogen in the early oil generation stage rock eval tmax suppression is evident in the lower part of the es3l member associated with a rise in pi production index with respect to fracability or brittleness the content of brittle minerals in the es3l shale is generally higher than that of marine shales in the usa with higher calcite mineral averaging 51 82 wt and lower clay content averaging 18 86 wt interparticle pores in minerals grains or clay aggregates intraparticle pores intercrystalline dolomite and pyrite framboid and four types of fractures tectonic fractures abnormal pressure fractures clay shrinkage fractures and inter laminar fractures are developed in the es3l shale organic matter pores are not present in the studied samples probably due to lower maturity tectonic fracture may play an important role in hydrocarbon migration and accumulation the results of this study suggest that the es3l shale in the bonan sag has very good shale oil potential especially in the lower section

ice lubricated gravity spreading of the olympus mons aureole deposits abstract gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of olympus mons detachment sliding could have occurred around the volcano if either pore fluid pressures were exceptionally high greater than 90 or the rocks had very low resistance to shear about 1 105 pa or 1 bar because of the vast areal extent and probable shallow depth of the detachment zone development of ubiquitous high pore fluid pressures beneath aureole forming material was unlikely however a zone of sufficiently weak material consisting of about 10 interstitial or interbedded ice could have been present if so a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer according to this model extensional deformation would have occurred near the shield and compressional deformation in its distal parts proximal grabens and distal corrugations on aureole surfaces support this model a submarine slide at kitimat arm british columbia is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits ground ice processes have been considered the cause of many geologic features on mars a 3 average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere ice may have been deposited in higher concentrations below the aureole forming material the source of the ice could have been juvenile water circulated hydrothermally by olympus mons volcanism the basal scarp of olympus mons apparently demarcates the transition between the upper stable part of the shield and its lower part that decoupled and formed the aureole deposits this transition may reflect a change in the bulk shear strength of the shield caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano other martian volcanoes exhibit virtually no evidence of similar large scale gravity spreading and basal scarps perhaps such evidence if it existed has been buried by lava flows or perhaps the smaller size of other volcanoes did not permit the development of these features

organic molecules formed in a primordial womb primordial organic molecules may have evolved in seafloor hydrothermal systems by mineral catalysis most organic compounds decompose in 300 c vent fluid however we show that smectite type clays can protect and promote development of diverse organic compounds that may be precursors to biomolecules smectite provides a safe haven for the synthesis of organic molecules essentially like a primordial womb our experiments simulated seafloor hydrothermal conditions 300 c 100 mpa and reacted common clays montmorillonite saponite illite with dilute methanol as a source of c montmorillonite reacts under these conditions to illite while the other clays do not change we observed increased organic synthesis over time with montmorillonite during mineralogical reaction approaching equilibrium smectite contracts and organic molecules are expelled organic compounds unstable in hot fluid where the smectite reacts may survive in cooler waters outside the vent

the shape of mars before global surveyor results from reanalysis of the viking control point network three dimensional coordinates of 3739 globally distributed control points derived from photogrammetric analysis of viking orbiter image data are studied with respect to the shape and large scale morphology of mars spheres spheroids spherical functions and a digital terrain model dtm of 50 km grid spacing are fitted to the data prominent topographic features in the terrain model include the tharsis volcanoes olympus mons alba patera and prominent mare and highland regions as well as the major impact basins while the global dichotomy is clearly visible in our data our model does not reveal any distinct signature associated with the presumed dichotomy boundary at this global scale rather it suggests a smooth topographic transition from southern to northern hemisphere this model is unique among existing topographic data sets for mars as it combines global coverage a spatial resolution sufficient to resolve regional topography and absolute elevation data more accurate than in previous control point network analyses formal errors and a comparison with the first released topographic profiles obtained by mars global surveyor s laser altimeter mola suggest that 70 and 90 of the dtm grid elements represent the topography of the planet to better than 1000 m and 2000 m respectively

clay organic association as a control on hydrocarbon generation in shale abstract programmed pyrolysis experiments investigating the influence of the mineral matrix on hydrocarbon generation from organic compounds have shown inconclusive results in past studies this study tests the hypothesis that the inhibitory vs catalytic influence of clay minerals is dependent on the physical association of the mineral matrix with organic compounds by comparing natural samples from two shale formations with different mineral organic associations samples from the miocene monterey formation have a greater area of surface contact between organic matter and mineral surfaces when compared to the more particulate texture and discrete nature of the organic matter in the samples from the permian stuart range formation comparison of kerogen extracts to the whole rock containing mineral and organic matter samples during programmed pyrolysis shows higher hydrocarbon generation from isolated kerogen compared to the whole rock sample it was extracted from in both the monterey and the stuart range formation samples the difference between extracted kerogen and whole rock samples is greater and more variable 56 210 mghc gtoc in the stuart range than the monterey formation 85 142 mghc gtoc implying greater hydrocarbon retention by the free mineral surfaces the temperature of maximum hydrocarbon generation rock eval t max is greater in whole rock than kerogen isolates 20 c mean in the monterey formation samples but shows negligible difference 2 c mean in the samples from the stuart range formation standard kerogen typing using rock eval pyrolysis data places the same kerogen as type ii to type iii on a modified van krevelen diagram depending whether it is isolated or pyrolysed with its mineral host this study identifies that not only the bulk mineralogy and kerogen type but also the degree of surface contact of the phases influence hydrocarbon generation

the early environment and its evolution on mars implication for life there is considerable evidence that the early climate of mars was very different from the inhospitable conditions there today this early climate was characterized by liquid water on the surface and a dense atmosphere composed predominantly of co2 the duration of these warm initial conditions on the surface of mars is uncertain but theoretical models suggest that they could have persisted for hundreds of millions up to a billion years from studies of the earth s earliest biosphere we know that by 3 5 gyr ago life had originated on earth and reached a fair degree of biological sophistication surface activity and erosion on earth make it difficult to trace the history of life before the 3 5 gyr time frame if mars did maintain a clement environment for longer than it took for life to originate on earth then the question of the origin of life on mars follows naturally the fossil evidence of early life on earth provides clues as to what form fossils on mars might take of particular interest are stromatolites macroscopic layered structures that result from the anchoring of sediments by microorganisms living in the photic zone since over two thirds of the martian surface is more than 3 5 gyr old the possibility exists that mars may hold the best record of the events that led to the origin of life even though there may be no life there today

saqqar a 34 km diameter impact structure in saudi arabia here we present the first proof of an impact origin for the saqqar circular structure in northwestern saudi arabia neville et al 2014 with an apparent diameter of 34 km centered at 29 35 n 38 42 e the structure is formed in cambrian devonian siliciclastics and is unconformably overlain by undeformed cretaceous and paleogene sediments the age of impact is not well constrained and lies somewhere between 410 and 70 ma the subsurface structure is constrained by 2 d reflection seismic profiles and six drilled wells first order structural features are a central uplift that rises approximately 2 km above regional datums surrounded by a ring syncline the crater rim is defined by circumferential normal faults the central uplift and ring syncline correspond to a bouguer gravity high and an annular ring like low respectively the wells were drilled within the central uplift the deepest among them exceed 2 km depth sandstone core samples from these wells show abundant indicators of a shock metamorphic overprint planar deformation features pdfs were measured with orientations along 0001 103 and less frequently along 101 and 104 planar fractures pfs predominantly occur along 0001 and 101 and are locally associated with feather features ffs in addition some shocked feldspar grains and strongly deformed mica flakes were found the recorded shock pressure ranges between 5 and 15 gpa the preserved level of shock and the absence of an allochthonous crater fill suggest that saqqar was eroded by 1 2 km between the devonian and maastrichtian the documentation of unequivocal shock features proves the formation of the saqqar structure by a hypervelocity impact event

bias corrected population size distribution and impact hazard for the near earth objects abstract utilizing the largest available data sets for the observed taxonomic binzel et al 2004 icarus 170 259 294 and albedo delbo et al 2003 icarus 166 116 130 distributions of the near earth object population we model the bias corrected population diameter limited fractional abundances of the taxonomic complexes are a 0 2 c 10 d 17 o 0 5 q 14 r 0 1 s 22 u 0 4 v 1 x 34 in a diameter limited sample 30 of the neo population has jovian tisserand parameter less than 3 where the d types and x types dominate the large contribution from the x types is surprising and highlights the need to better understand this group with more albedo measurements combining the c d and x complexes into a dark group and the others into a bright group yields a debiased dark to bright ratio of 1 6 overall the bias corrected mean albedo for the neo population is 0 14 0 02 for which an h magnitude of 17 8 0 1 translates to a diameter of 1 km in close agreement with morbidelli et al 2002 icarus 158 2 329 342 coupling this bias corrected taxonomic and albedo model with the h magnitude dependent size distribution of stuart 2001 science 294 1691 1693 yields a diameter distribution with 1090 180 neos with diameters larger than 1 km as of 2004 june the spaceguard survey has discovered 56 of the neos larger than 1 km using our size distribution model and orbital distribution of stuart 2001 science 294 1691 1693 we calculate the frequency of impacts into the earth and the moon globally destructive collisions 10 21 j of asteroids 1 km or larger strike the earth once every 0 60 0 1 myr on average regionally destructive collisions with impact energy greater than 4 10 18 j 200 m diameter strike the earth every 56 000 6000 yr collisions in the range of the tunguska event 4 8 10 16 j occur every 2000 3000 yr these values represent the average time between randomly spaced impacts actual impacts could occur more or less closely spaced solely by chance as a verification of these impact rates the crater production function of shoemaker et al 1990 geological society of american special paper 247 has been updated by combining this new population model with a crater formation model to find that the observed crater production function on both the earth and moon agrees with the rate of crater production expected from the current population of neos

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

the mineralogy and potassium supplying power of some loessial and related soils of new zealand abstract sixteen pallic aqualfs ustalfs aquepts ochrepts and related soils collected from the north and south islands of new zealand were studied to determine if variations in nonexchangeable k supply could be explained by mineralogical composition a strong relationship was found which indicates that mica is weathering to vermiculite proportions of vermiculite and kandite are generally higher in the north island than in the south island dominance of either micas or vermiculite or kandite is determined by the stage of weathering and or the nature of parent materials soils that supplied more nonexchangeable k knex to ryegrass plants contained more mica in the clay fraction than soils that supplied less knex the results confirmed that use of a soil test that includes a measure of knex i e acid extractable k may be a vital part of identifying variations in plant available k status of the soils it is concluded that the k supplying power of the pallic and related soils is related directly to the amounts of mica present in clay fraction and that good k supplying soils will be transformed to k depleted soils as a result of increased weathering and leaching pedogenic factors and k exploitation in intensive farming systems

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

mars and earth comparison of cold climate features abstract on earth glacial and periglacial features are common in areas of cold climate on mars the temperature of the present day surface is appropriate for permafrost and the presence of water is suspected from data relating to the outgassing of the planet from remote sensing measurements over the polar caps and elsewhere on the martian surface and from recognition of fluvial morphological features such as channels these observations and the possibility that ice could be in equilibrium with the atmosphere in the high latitudes north and south of 40 latitude suggest that glacial and periglacial features should exist on the planet morphological studies based mainly on viking pictures indicate many features that can be attributed to the action of ice among these features are extensive talus aprons debris avalanches flows that resemble glaciers or rock glaciers ridges that look like moraines various types of patterned ground scalloped scarps and chaotically collapsed terrain that could be attributed to thermokarst processes and landforms that may reflect the interaction of volcanism and ice

geophysical and structural criteria for the identification of buried impact structures with reference to australia the discovery of large asteroid impact structures likely and possible impact structures onshore and offshore the australian continent woodleigh 120 km 360 ma gnargoo 75 km lower permian upper cretaceous tookoonooka 55 65 km 125 ma talundilly 84 km 125 ma mount ashmore 100 km end eocene and warburton twin structures 400 km pre end carboniferous requires re examination of the diagnostic criteria used for their identification bouguer anomalies of established impact structures chicxulub 170 km 64 98 0 05 ma woodleigh impact structure and gnargoo probable impact structure display a unique structural architecture where pre impact structural ridges are intersected and truncated by the outer ring of the circular structure seismic reflection data outline circular central uplift domes basement plugs and rim synclines sharp circular seismic tomography anomalies indicate low velocity columns under both the woodleigh impact structure and warburton probable impact hinting at deep crustal fracturing deformed curved and clouded intra crystalline planar deformation features in quartz qz pdfs displaying miller indices 10 11 10 12 10 13 diagnostic of shock metamorphism abound around exposed established impact structures vredefort 298 km 2023 4 ma sudbury 250 km 1850 3 ma charlevoix 54 km 342 15 ma manicouagan 100 km 214 1 ma tookoonooka and talundilly deformed qz pdfs allow recognition of shock metamorphism in buried impact structures where original qz pdfs were bent recrystallized and or clouded during formation of the central uplift and hydrothermal activity triggered by the impact planar deformation in quartz can also occur in explosive pyroclastic units but are limited to boehm lamella brazil twins with single lamella sets 0001 it has been suggested that a class of microstructures in quartz referred to as metamorphic deformation lamella qz mdl occur in endogenic tectonic metamorphic terrains however no type locality has been established for qz mdl of non impact origin

searching for evidence of hydrothermal activity at apollinaris mons mars a multidisciplinary approach involving various remote sensing instruments is used to investigate apollinaris mons a prominent volcano on mars as well as the surrounding plains for signs of prolonged hydrologic and volcanic and possibly hydrothermal activity the main findings include 1 evidence from laser altimetry indicating the large thickness 1 5 2 km at some locations of the fan deposits draping the southern flank contrary to previous estimates coupled with possible layering which point to a significant emplacement phase at apollinaris mons 2 corroboration of robinson et al robinson m s mouginis mark p j zimbelman j r wu s s c ablin k k howington kraus a e 1993 icarus 104 301 323 hypothesis regarding the formation of incised valleys on the western flanks by density current erosion which would indicate magma water interaction or alternatively volatile rich magmas early in the volcano s history 3 mounds of diverse geometric shapes many of which display summit depressions and occur among faults and fractures possibly marking venting 4 strong indicators on the flanks of the volcano for lahar events and possibly a caldera lake 5 ubiquitous presence of impact craters displaying fluidized ejecta in both shield forming flank and caldera materials and materials that surround the volcano that are indicative of water rich target materials at the time of impact 6 long term complex association in time among shield forming materials and medusae fossae formation the findings point to a site of extensive volcanic and hydrologic activity with possibly a period of magma water interaction and hydrothermal activity finally we propose that the mound structures around apollinaris should be prime targets for further in situ exploration and search for possible exobiological signatures

effect of the greenhouse gases co2 h2o so2 on martian paleoclimate there is general agreement that certain surface features on mars are indicative of the presence of liquid water at various times in the geologic past in particular the valley networks are difficult to explain by a mechanism other than the flow of liquid water it has been suggested in several studies that a thick co2 atmosphere on mars early in its history could have provided a greenhouse warming that would have allowed the flow of water either on the surface or just below the surface however we have examined this effect with a detailed radiation model and have found that if reduced solar luminosity early in the history of the solar system is taken into account even three bars of co2 will not provide sufficient greenhouse warming the addition of water vapor and sulfur dioxide both plausible gases that may have been emitted by martian volcanoes to the atmosphere also fail to warm the surface above 273k for reduced solar luminosity conditions the increase in temperature may be large enough however for the formation of these features by brines

thermal studies of martian channels and valleys using termoskan data the termoskan instrument on board the phobos 88 spacecraft acquired the highest spatial resolution thermal infrared emission data ever obtained for mars included in the thermal images are 2 km pixel midday observations of several major channel and valley systems including significant portions of shalbatana ravi al qahira and ma adim valles the channel connecting valles marineris with hydraotes chaos and channel material in eos chasma termoskan also observed small portions of the southern beginnings of simud tiu and ares valles and some channel material in gangis chasma simultaneous broadband visible reflectance data were obtained for all but ma adim vallis we find that most of the channels and valleys have higher thermal inertias than their surroundings consistent with previous thermal studies we show for the first time that the thermal inertia boundaries closely match flat channel floor boundaries also buttes within channels have inertias similar to the plains surrounding the channels suggesting the buttes are remnants of a contiguous plains surface lower bounds on typical channel thermal inertias range from 8 4 to 12 5 10 3 cal cm 2 s 1 2 k 1 352 to 523 in si units of j m 2 s 1 2 k 1 lower bounds on inertia differences with the surrounding heavily cratered plains range from 1 1 to 3 5 46 to 147 si atmospheric and geometric effects are not sufficient to cause the observed channel inertia enhancements we favor nonaeolian explanations of the overall channel inertia enhancements based primarily upon the channel floors thermal homogeneity and the strong correlation of thermal boundaries with floor boundaries however localized dark regions within some channels are likely aeolian in nature as reported previously most channels with increased inertias have fretted morphologies such as flat floors with steep walls eastern ravi and southern ares valles the only major channel sections observed that have obvious catastrophic flood bedforms do not have enhanced inertias therefore we favor fretting processes over catastrophic flooding for explaining the inertia enhancements we postulate that the inertia enhancements were caused either by the original fretting process or by a process involving the bonding of fines due to an increased availability of water either initially or secondarily

subkilometer martian volcanoes properties and possible terrestrial analogs kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of mars based on examination of more than 12 000 high resolution viking orbiter images most of these very small cones are located in parts of eastern acidalia and utopia isidis elysium planitia measurements of base and pit diameter for some 2000 well resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater cone diameter ratios this suggests that the small cones had a similar origin with only minor variations in local conditions the acidalia cones are generally larger more widely distributed and occur on a greater variety of terrains than those in utopia isidis elysium based on morphology distribution and the crater cone ratio histograms the smallest martian cones may be similar to icelandic pseudocraters somewhat larger steeper cones with smaller crater cone ratios which also occur in eastern acidalia may be analogs of terrestrial cinder cones

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

nonuniform cratering of the moon and a revised crater chronology of the inner solar system abstract we model the cratering of the moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system in order to refine the crater chronology method impact occurrences locations velocities and incidence angles are calculated semi analytically and scaling laws are used to convert impactor sizes into crater sizes our approach is generalizable to other moons or planets the lunar cratering rate varies with both latitude and longitude with respect to the global average it is about 25 lower at 65 n 90 e and larger by the same amount at the apex of motion 0 n 90 w for the present earth moon separation the measured size frequency distributions of lunar craters are reconciled with the observed population of near earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size frequency distributions we give a revised analytical relationship between the number of craters and the age of a lunar surface for the inner planets expected size frequency crater distributions are calculated that account for differences in impact conditions and the age of a few key geologic units is given we estimate the orientale and caloris basins to be 3 73 ga old and the surface of venus to be 240 ma old the terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 ma better knowledge of the orbital dynamics crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps from the observation of asteroids to the formation of craters our model may be inaccurate for periods prior to 3 5 ga because of a different impactor population or for craters smaller than a few kilometers on mars and mercury due to the presence of subsurface ice and to the abundance of large secondaries respectively standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3 5 ga ago and give self consistent estimates of the planetary cratering rates relative to the moon

the shallow structure of the martian lithosphere in the vicinity of the ridged plains wrinkle ridges in the smooth plains of the coprates and lunae planum regions of mars form linear or concentric patterns with a regular spacing of 25 50 km the authors test the hypothesis that the periodic development of deformation was a consequence of unstable horizontal compression that occurred prior to probable ridge related faulting of a strength stratified lithosphere which consists of a mechanically strong surface plains unit that successively overlies a weak megaregolith and a strong lithospheric basement results show that a range of models with both rigid and deformable megaregolith basement interface conditions yield solutions which can explain the ridge spacing within the constraint provided by the estimated thickness of the smooth plains materials in models that incorporate viscous and plastic rheologies uniform and exponentially varying vertical strength distributions and the presence or absence of interfacial slip at the base of the surface plains unit the ridge spacing is primarily controlled by the power law exponent of the lithosphere the megaregolith plains unit thickness ratio and the plains unit megaregolith strength contrast deformable basement models with a viscous rheology 1 le n approx le 3 can explain the ridge spacing if the megaregolith was thicker than and approximately 1 3 orders of magnitude weaker than themore plains unit similar models with a perfectly plastic n yields infinity rheology require plains unit thicknesses greater than 5 km which exceeds most observational estimates ridge spacing in the combined viscous and plastic models can be consistent with either a dry water rich or ice rich megaregolith at the time of ridge formation less

direct evidence for organic carbon preservation as clay organic nanocomposites in a devonian black shale from deposition to diagenesis abstract the burial of marine sourced organic carbon oc in continental margin sediments is most commonly linked to oceanographic regulation of bottom water oxygenation anoxia and or biological productivity here we show an additional influence in the devonian woodford shale in which oc occurs as nanometer intercalations with specific phyllosilicate minerals mixed layer illite smectite that we term organo mineral nanocomposites high resolution transmission electron microscopic hrtem images provide direct evidence of this nano scale relationship while discrete micron scale organic particles such as tasmanites algal cysts are present in some lamina a strong relation between total organic carbon toc and mineral surface area msa over a range of 15 toc indicate that the dominant association of organic carbon is with mineral surfaces and not as discrete pelagic grains consistent with hrtem images of nanocomposites where periods of oxygenation are indicated by bioturbation this relationship is modified by a shift to lower oc loading on mineral surfaces and reduced msa variability likely resulting from biological mixing and homogenization of the sediment oxidative burn down of oc and or stripping of oc from minerals in animal guts the toc msa relationship extends across a range of burial depths and thermal maturities into the oil window and persists through partial illitization where illitization occurs the loss of mineral surface area associated with the collapse of smectite interlayer space results in a systematic increase in toc msa and reorganization of organic carbon and clays into nano scale aggregates while the woodford shale is representative of black shale deposits commonly thought to record heightened marine productivity and or anoxia our results point to the importance of high surface area clay minerals for oc enrichment given that the vast majority of these clay minerals are formed in soils before being transported to continental margin settings their mineralogy and attendant preservative potential is primarily a function of continental climate and provenance making these deposits a sensitive recorder of land as well as oceanographic change

formation of melt droplets melt fragments and accretionary impact lapilli during a hypervelocity impact abstract we present a model that describes the formation of melt droplets melt fragments and accretionary impact lapilli during a hypervelocity impact using the isale hydrocode coupled to the aneos equation of state for silica we create high resolution two dimensional impact models to track the motion of impact ejecta we then estimate the size of the ejecta products using simple analytical expressions and information derived from our hydrocode models ultimately our model makes predictions of how the size of the ejecta products depends on impactor size impact velocity and ejection velocity in general we find that larger impactor sizes result in larger ejecta products and higher ejection velocities result in smaller ejecta product sizes we find that a 10 km diameter impactor striking at a velocity of 20 km s creates millimeter scale melt droplets comparable to the melt droplets found in the chicxulub ejecta curtain layer our model also predicts that melt droplets melt fragments and accretionary impact lapilli should be found together in well preserved ejecta curtain layers and that all three ejecta products can form even on airless bodies that lack significant volatile content this prediction agrees with observations of ejecta from the sudbury and chicxulub impacts as well as the presence of accretionary impact lapilli in lunar breccia

the stability of ground ice in the equatorial region of mars consideration of the partial pressure of h2o in the martian atmosphere and the range of mean annual temperatures at the martian surface suggests that the occurrence of ground ice in equilibrium with the atmosphere is restricted to latitudes poleward of 40 however there is a growing body of morphologic evidence that indicates that substantial quantities of ground ice may have been present in the equatorial regolith throughout martian geologic time the accepted explanation for this apparent contradiction has been that the h2o found near the equator is a relic emplaced very early in martian geologic history 3 5 b y ago and under substantially different climatic conditions it is generally believed that this fossil ground ice layer has been preserved to the present day by the diffusion limiting properties of a relatively shallow layer 10 m of fine grained regolith to evaluate this hypothesis the lifetime of a 200 m layer of ground ice buried below 100 m of ice free regolith has been examined for the latitudes between 30 on mars twelve model pore size distributions representative of silt and clay type soils found on earth were selected to simulate the pore structure of the martian regolith the parallel pore model of gaseous diffusion was then used to calculate the flux of escaping h2o molecules from the buried ground ice layer the potential effects of such factors as depth of burial the martian geothermal gradient regolith porosity adsorption surface diffusion and climatic change were also considered based on our analysis the most important factors affecting the stability of equatorial ground ice appear to be 1 soil structure 2 the magnitude of the geothermal gradient and 3 the climatic desorption of co2 from the regolith we conclude that while the conditions necessary for the long term survival of ground ice may exist in isolated regions within the equatorial regolith on the global scale it appears unlikely that a fossil ground ice layer has been preserved throughout martian geologic history if massive ground ice does presently exist in the equatorial regolith then its presence may imply the existence of some continuous or periodic process of replenishment

convection in a catastrophic flood deposit as the mechanism for the giant polygons on mars a formational mechanism for the large scale polygons that are defined by intersecting fractures in the northern plains of mars is proposed in this work the presented model is based on rayleigh convection of interstitial water driven by an unstable density temperature gradient within a saturated porous medium catastrophic emplacement of water rich sediments into the martian northern plain basins could have provided a thick sedimentary layer in which rayleigh convection could have occurred convection within this active layer is proposed to have differentially thawed an underlying ice rich permafrost layer that had been at the planet s surface before being rapidly buried the resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid liquid interface morphology produced in terrestrial convective flow visualization studies the exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells which are estimated to have had width to depth ratios of between 3 4 and 4 5 subsequent stresses e g gravity and bending stresses would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by mcgill and hills 1992 additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large scale polygonal fractures visible in the viking orbiter and mars global surveyor images of the martian northern plains

spherule layers records of ancient impacts abstract a large extraterrestrial object striking earth at cosmic velocity melts and vaporizes silicate materials which can condense into highly spheroidal sand size particles that get deposited hundreds to thousands of kilometers from the point of impact these particles known as impact spherules have been detected in great abundance in a relatively small number of thin discrete layers ranging in age from less than a million years to 3 47 billion years unaltered impact spherules consist entirely of glass microtektites or a combination of glass and crystals grown in flight microkrystites impact spherule layers form very rapidly and can be very extensive even global in extent e g the cretaceous tertiary k t boundary layer so they form excellent time stratigraphic markers because they are always found in a stratigraphic context spherule layers are probably superior to terrestrial craters and related structures for assessing the environmental and biotic effects of large impacts a reco

planetary exploration using a small electromagnetic sensor a prototype broadband electromagnetic em sensor gem 5 has been built and tested as a possible new probe for the future mars rover to seek an ice bonded layer at a given depth below the martian surface the sensor with a vertical coaxial coil configuration will measure the terrain resistivity and susceptibility to determine lateral variations in resistivity and magnetic susceptibility the lateral variations will indicate regions of resistivity susceptibility anomalies that may contain ice or water at depth the forward solution for the sensor geometry over a layered formation and inverse algorithms to convert the em data into the apparent susceptibility and resistivity are developed to investigate the ability of the sensor in detecting and resolving a buried wet ice layer in mars like geologic formations based on the simulated study we find that the prototype sensor design should be able to resolve the lateral variations in resistivity susceptibility under conditions of the martian subsurface

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

electromagnetic and geological transect across permafrost terrain mackenzie river delta canada the time domain electromagnetic tdem method provides a surface geophysical technique suitable for interpreting deep permafrost conditions this paper describes profiles collected in early spring in a transitional area of the mackenzie delta arctic canada with differing permafrost conditions and surficial geology these data augment previously published profiles and allow the construction of a 30 km long tdem transect from the holocene age mackenzie delta in the southwest to the pleistocene age tuktoyaktuk coastlands in the northeast the geoelectric section produced from the tdem data is interpreted in terms of permafrost distribution this interpretation provided a basis for inferring lithologic changes unconsolidated non ice bonded unfrozen sediment has resistivities less than 10 ohm m partially ice bonded sediment ranges in resistivity from 10 to 40 ohm m ice bonded frozen sediment has resistivities from 30 to 300 ohm m bedrock has low resistivities from 5 to 15 ohm m interpretation of the geoelectric section derived from both the shallow 500 m tdem data suggests that the main body of permafrost increases in thickness from 50 to 500 m over a few kilometers a horizontally persistent unfrozen zone talik is situated from 50 to 100 m in depth within the main body of permafrost ice bonding models derived from the tdem surveys provide constraints on the geologic history of the mackenzie delta

early archean spherule beds chromium isotopes confirm origin through multiple impacts of projectiles of carbonaceous chondrite type three early archean spherule beds from barberton south africa have anomalous cr isotope compositions in addition to large ir anomalies confirming the presence of meteoritic material with a composition similar to that in carbonaceous chondrites the extra terrestrial components in beds s2 s3 and s4 are estimated to be approx l 50 60 and 15 30 respectively these beds are probably the distal and possibly global ejecta from major large body impacts these impacts were probably much larger than the cretaceous tertiary event and all occurred over an interval of approx 20 m y implying an impactor flux at 3 2 ga that was more than an order of magnitude greater than the present flux

contribution to the study of thermal erosion on mars similar to the coldest terrestrial periglacial regions like yakutia siberia the planet mars exhibits wide outflow channels this analogy and the presence of permanent ground ice suggest that thermal erosion have existed during martian fluvial outbursts 3000 m y ago thermal erosion here is considered to be the result of ground thawing produced by heat transfer between the water flow and the frozen ground followed by a transport of unfrozen sediments this paper proposes a qualitative explanation of thermal erosion with the help of some physical models from the quantitative point of view two thermal mathematical models are proposed and discussed the zones undergoing the most efficient erosion are river banks the first model studied here describes extreme thermomechanical actions a constant thermal flux on the ground surface produces ground thaw and the unfrozen sediments are immediately removed by water flow it is an ablation model it allows a theoretical evaluation of the river bank recession validity of theoretical estimations is acquired by comparing the calculations to the observed backwearing of the banks of some siberian rivers which can reach 25 m yr 1 thermal erosion acting upon the bottom of wide rivers on mars or in siberia as well is a very complex mechanism indeed the mathematical modeling requires the study of interaction between thermal processes and transport of sediments laws these laws are not yet well defined and are very difficult to establish thus another model presented in this paper concerns only one dimensional thermal actions of water flow upon the bottom of wide rivers it considers fluvial flow at positive celsius temperature producing a thermal flux from the bottom to the initially frozen semi infinite ground this model considers a constant convective heat transfer coefficient and allows an estimation of the thickness of the thawed ground beneath the river talik calculated thickness of the melted ground is given in the paper for different periods of time

illitizing fluids as precursors of hydrocarbon migration along transfer and boundary faults of the jeanne d arc basin offshore newfoundland canada abstract illite content in mixed layer illite smectite i s and the degree of ordering in the fine fraction

where have all the craters gone earth s bombardment history and the expected terrestrial cratering record here we make the first quantitative estimates of the maximum total number of large terrestrial impact craters that can survive until the current era on earth our estimates of crater survival are made using the age of earth s crust and the expected flux of large extraterrestrial bodies striking earth this analysis neglects effects such as weathering and burial which tend to preferentially erase smaller craters thus our results represent the maximum number of craters we expect to exist on earth today although the constant recycling of crustal material creates a strong bias toward younger ages our model suggests that the terrestrial cratering record can be used to determine the size frequency distribution of the impactors that bombarded earth over the past 3 5 g y however our model suggests that the cratering record cannot be used to distinguish between scenarios with a constant flux of impactors over time and scenarios where the bombardment rate was considerably higher in earth s ancient history luckily layers of distal impact ejecta may act as records of impacts even when the source craters have been tectonically recycled we suggest that searches for these distal impact ejecta layers will be more fruitful for constraining the bombardment history of earth than searches for large craters

the experimental use of correspondence analysis to assess the relationship between soils and geomorphology in eastern zambia correspondence analysis an eigenvalue technique suitable for application to mainly qualitative data is used to display relationships between soils and geomorphic units using data derived from a reconnaissance soil survey in eastern zambia the survey involved the direct mapping of soil taxonomy subgroups and phases of subgroups within delineated geomorphic units of a national geomorphic legend the operation of correspondence analysis is described and correspondence plots presented primary association groups pags of soil classes associated with each geomorphic unit are derived from the plots and from accompanying tables of distances multivariate standard deviations between soil classes and geomorphic units the pags are shown to be ordered in horseshoe patterns reflecting the catenary sequence of the geomorphic units in the survey area confirming the normal operation of correspondence analysis on the data pag composition is discussed in relation to the geomorphic units and is evaluated to test the success of pilot detailed soil surveys in predicting soil geomorphic unit relationships in the overall reconnaissance survey area on the ba sis of the analyses undertaken the geomorphic approach to reconnaissance soil survey is judged a success

a comparison of the thermal and radar characteristics of mars abstract there is a correlation between martian thermal inertia and radar cross section data centered on 22 latitude the correlation is strongest with 70 cm radar except between longitudes 10 and 90 where there is a slight anticorrelation and gets progressively weaker at 12 5 and 3 8 cm wavelengths respectively a correlation is expected because of the dependence of both properties on density but an increase in the average particle size of the surface with increasing dielectric constant is also required in order to explain the data this may take the form of an increased number of small rocks the anticorrelation may result from either the effects of atmospheric dust on the surface temperature or from the effects on radar of local variations in large scale roughness or scattering by rocks the relative behavior between the wavelengths can be understood in terms of appropriately sized rocks which act as radar scatterers the trend of the correlation agrees with the dichotomy of the planet into two types of terrain as noted in other remote sensing data and is consistent with an erosional versus depositional surface nature variations in the surface dielectric constant inferred from the 3 8 cm radar data can explain discrepancies between 2 8 cm radio emission observations and a simple model based on the global distribution of thermal inertia and albedo

the number of impact craters on earth any room for further discoveries abstract only 128 impact craters exposed at earth s surface have been found so far while new craters are discovered occasionally taking into account the permanent consumption of craters by erosion we present the first estimate on the number of impact craters that should be present at earth s surface our study yields no evidence for any systematic incompleteness in the available inventory of the craters larger than about 6 km in diameter exposed at the surface in contrast more than 90 craters in the diameter range from 1 km to 6 km should still be waiting to be discovered and even more than 250 between 0 25 km and 1 km diameter the transition from a probably complete inventory above 6 km to a strongly incomplete record at smaller sizes may be related to the difference between simple and complex craters beyond these results on the terrestrial crater record our findings tentatively suggest that erosion rates on the 10 to 100 million year scale may be closer to present day erosion rates than previously assumed

influence of organic matter on smectite illitization a comparison between red and dark mudstones from the dongying depression china interactions between organic matter om and clay minerals have received considerable attention in previous studies the influence of om on smectite illitization has been analyzed primarily in simulation experiments rather than in diagenetic studies the present study explores the influence of om on smectite illitization during diagenesis thirty red and dark mudstone samples from the dongying depression were analyzed x ray diffraction xrd analyses revealed that the illite percentages in mixed layer illite smectite i s of both types of samples were dispersive above 3100 m and more convergent below this depth the stacking mode of i s in dark mudstones above 3100 m remained primarily at r0 r0 5 ordering with the average number of layers nave dispersively distributed between 2 and 4 5 in red mudstones the i s changed from the r0 to r0 5 mode with the nave increasing from 2 to 5 over this range the smectite illitization in dark mudstones was slower than that in red mudstones below 3100 m the i s stacking mode of dark mudstones changed from r0 5 to r3 ordering with the nave increasing sharply from 4 to 8 in red mudstones the i s displayed r1 5 and r3 ordering with the nave varying between 4 5 and 6 5 over this range the smectite illitization in dark mudstones accelerated rapidly whereas the process in red mudstones was retarded additionally the red mudstone samples contained little om whereas the dark mudstone samples contained abundant total organic carbon 0 17 4 43 thermo xrd near infrared nir as well as mid infrared mir spectroscopy analyses suggested that the om in dark mudstones exhibited a significant transition at 3100 m coincident with the illitization change above 3100 m the smectite illitization in dark mudstones was delayed due to the om pillar effect in the interlayer spaces of smectite below 3100 m the interlayer om became varied and desorbed discharging organic acid this led to the dissolution of smectite structural layers consequently illitization in the dark mudstone was accelerated this study revealed that the existence and occurrence of om could influence the smectite illitization in diagenesis further study on the interactions between om and clay minerals is needed to facilitate our understanding on the mechanism of smectite illitization as well as its geological applications

generation of martian chaos and channels by debris flows abstract a debris flow mechanism is proposed to account for the formation of chaos and the large channels debouching into chryse planitia from the adjacent southern uplands of mars the debris is thought to have originated through a mechanism of collapse in the chaotic terrains which exist at the head of these channels as well as locally along the channels this proposition is based on the detailed morphologic similarities between martian channel source areas and the heads of both subaerial and subaqueous terrestrial debris flows the downslope movement of the debris produced the channels through a modification of earlier collapse areas b active bed erosion and c loading induced collapse the large scale channel geometry and the assemblage of related morphologic features on mars correspond tto that observed in subaqueous debris flow chutes on the mississippi delta front through various mechanisms of strain dependent viscosity decrease the debris flow gained mobility downstream turned into a debris avalanche and moved onto chryse planitia at very high velocities this high velocity avalanche eroded a series of streamlined remnants near the channel mouths and deposited its load as a thin blanket over a large area of the basin creating virtually no depositional relief

variations of porosity in intermediate sized lunar impact basins abstract the moon is cratered with hundreds of well preserved impact basins and shared bombardment history with earth makes lunar basins a good proxy for the processes affecting early earth basin forming impact events alter the bulk density and porosity of the targeted crust and measurement of these quantities offers a means by which we can investigate the mechanisms of basin formation in this work we calculate the bulk density of the crust in the vicinity of 50 basins with diameters of 170 360 km a size range that has been neglected by previous studies with the goal of understanding the deformational mechanisms present during impact events our bulk density estimates are derived from gravity data from nasa s gravity recovery and interior laboratory grail mission and topography data from the lunar orbiter laser altimeter lola using a new technique similar to the nettleton method in terrestrial gravimetry by making assumptions about crustal compositions across the moon we can furthermore estimate porosity in and around the basins low porosity is observed in the interior of 76 of the basins studied and this trend becomes more apparent when basins in the feldspathic highlands terrane are observed alone overall impact events appear to decrease porosity inside basins and increase porosity outside basins suggesting the prevalence of impact melting within the basins and fracturing and ejecta deposition in the exteriors our results are seemingly inconsistent with previous studies that measured high porosity values inside basins from residual bouguer anomalies however these disparate results may be reconciled if impact melting processes are confined to the uppermost kilometers of the lunar crust and are underlain by heavy impact induced fracturing

critical considerations when assessing hydrocarbon plays using rock eval pyrolysis and organic petrology data data quality revisited abstract the dramatic increase in exploration for unconventional hydrocarbon resources has inherently fuelled the need for new source rock geochemical data the need for new data comes along with an increasing number of new users many of whom do not possess the background to interpret accurately and evaluate the quality of data sets generated by different geochemical screening techniques e g rock eval pyrolysis vitrinite reflectance here datasets from rock eval pyrolysis vitrinite reflectance and leco toc analyses are scrutinized and compared to show how failing to recognize good vs bad datasets can dramatically change interpretations during prospect or play appraisals detector saturation contamination of the sample with drilling fluid and suppression of both tmax and vitrinite reflectance are examples of complications that could compromise the validity of the results and the play or prospect reviews derived from them in addition misconceptions such as leco toc is better than rock eval 6 toc expressed by many users are a consequence of the lack of understanding of how different screening techniques and instrumentation work a solid understanding of these pitfalls and limitations can provide inexperienced geoscientists and engineers with the required support to improve risk maps for hydrocarbon charge analysis and source rock evaluations when using classic guidelines for interpreting results

the forms and availability to plants of soil potassium as related to mineralogy for upland oxisols and ultisols from thailand abstract potassium k deficiency is widespread in crops on highly weathered upland soils under a tropical monsoonal climate critical assessment of the forms of k in soils and of the ability of soils to release k for plant uptake is important for the proper management of k in crop production the relationships between different pools of k were investigated as a function of silt and clay mineralogy for 14 upland oxisols and 26 upland ultisols soils from thailand most soils contained no k minerals in the silt fraction xrd showed that kaolinite is the dominant clay mineral with variously minor or moderate amounts of illite hydroxy al interlayered vermiculite and smectite present in some soils for some soils both conventional and synchrotron xrd were unable to detect illite analytical tem including eftem of individual clay crystals showed that clay in the apparently illite free samples contained very small amounts of illite many kaolinite particles appear to contain k which may be present in illite interleaved with kaolinite crystals a glasshouse k depletion experiment was conducted to assess the k supply capacity and changes in chemical forms of k and k minerals using exhaustive k depletion by guinea grass panicum maximum potassium deficiency symptoms and mortality of plants occurred on light textured soils whereas plants survived for six harvests for oxisols with clay texture relatively high cec and higher nh4oac k exchangeable k plus water soluble k there is a strong linear relationship of unit slope between nh4oac k and cumulative k uptake by plants indicating that nh4oac k is a major form of k available to plants thus k bearing minerals contributed little k to plants over the time scale of the experiment and xrd patterns of whole soil samples silt and clay from soils after cropping mostly showed no change from those for the initial soil an exception was for a single surface soil clay where a minor amount of smectite was formed from illite by k release to plants

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

soil genesis and evolution on calanchi badland like landform of central italy abstract calanchi are badland like erosional landforms common in the mediterranean region which form from accelerated erosion processes the calanchi slopes naked or differently vegetated can be considered as formed by different ecological tesserae originated by the mutual interaction of several factors such as erosion geomorphology microclimatic conditions vegetation ground cover and pedogenesis however information about pedogenesis is rather scarce mainly because the soils developing on calanchi slopes are incessantly disturbed by erosion processes to understand the role of soil evolution on landslide erosion we considered three land facets each one made up of four tesserae t1 to t4 which represented the different steps of soil and vegetal evolution of calanchi the soil of each tessera was described sampled by genetic horizons and the samples were characterized for their physical mineralogical and chemical properties field observations and laboratory data suggest that pedogenesis in the calanchi badlands may progress until a critical threshold indeed advanced plant colonization and solum development improve soil structure increase soil organic matter and favor redistribution of nutrients along the profile the improvement of structure at depth fosters water storage and clay dispersion through soil leaching and reduction of ionic strength of the soil solution making soil less stable depending on the slope gradient the soil weight acquired during rainfall events may trigger landsliding mudflows or collapses that rejuvenate the surface

first detection of extraterrestrial material in ca 2 49 ga impact spherule layer in kuruman iron formation south africa thin layers rich in formerly molten spherules interpreted as distal ejecta from large impacts by extraterrestrial bodies have been found in 8 stratigraphic units deposited between ca 2 63 ga and 2 49 ga and attributed to a minimum of 4 separate impacts here we report geochemical evidence of extraterrestrial material in the only one of these spherule layers where it has not been previously reported the kuruman spherule layer ksl in the kuruman iron formation a banded iron formation bif in the griqualand west basin south africa we identified the ksl in 3 drill cores separated by as much as 350 km and analyzed 2 core samples that have a mean ir concentration of 12 9 ppb and nearly chondritic interelement ratios of platinum group elements ir ru pt and rh this suggests that the samples contain 1 3 by mass extraterrestrial material even though the spherules are highly diluted by ambient sediment our geochemical data strongly support the correlation of the ksl with the dales gorge spherule layer dgsl in a penecontemporaneous bif in the hamersley basin western australia the ksl and dgsl are close matches in terms of major and various trace element contents and the dgsl has a comparable ir content of 11 5 ppb therefore it is very likely the ksl and dgsl are distal ejecta from a ca 2 49 ga impact by a single extraterrestrial object 10 km across the lack of any significant changes in the stratigraphic succession in either basin also implies that large impacts alone are not sufficient to cause long term changes in earth s surface environments

an archaean heavy bombardment from a destabilized extension of the asteroid belt the late heavy bombardment lasted much longer than previously thought up to 1 7 billion years ago on earth with impacts on the moon and earth coming mostly from the e belt survivor hungaria asteroids the late heavy bombardment was a period of time generally put at about 4 1 billion to 3 8 billion years ago when the inner planets of the solar system were subjected to a high frequency barrage of asteroids this left its mark on the moon but on earth the craters quickly disappeared owing to tectonic processes and erosion in the first of two papers on the bombardment brandon johnson and jay melosh determine the properties of the asteroids by looking at spherule beds layers of debris ejected during the impacts the thickness of spherule layers is expected to vary according to the size of the impactor and the speed at which it hit earth this historical record of impacts indicates that the number of projectiles colliding with earth was substantially higher 3 5 billion years ago than it is today with a gradual decline in the number of strikes after the late heavy bombardment bottke et al modelled the evolution of an asteroid belt that extended farther towards mars than the present one they find that most of the impactors traced by the spherule beds probably originated in this e belt which was disrupted during migrations of some of the giant planets the barrage of comets and asteroids that produced many young lunar basins craters over 300 kilometres in diameter has frequently been called the late heavy bombardment1 lhb many assume the lhb ended about 3 7 to 3 8 billion years gyr ago with the formation of orientale basin2 3 evidence for lhb sized blasts on earth however extend into the archaean and early proterozoic eons in the form of impact spherule beds globally distributed ejecta layers created by chicxulub sized or larger cratering events4 at least seven spherule beds have been found that formed between 3 23 and 3 47 gyr ago four between 2 49 and 2 63 gyr ago and one between 1 7 and 2 1 gyr ago5 6 7 8 9 here we report that the lhb lasted much longer than previously thought with most late impactors coming from the e belt an extended and now largely extinct portion of the asteroid belt between 1 7 and 2 1 astronomical units from earth this region was destabilized by late giant planet migration10 11 12 13 e belt survivors now make up the high inclination hungaria asteroids14 15 scaling from the observed hungaria asteroids we find that e belt projectiles made about ten lunar basins between 3 7 and 4 1 gyr ago they also produced about 15 terrestrial basins between 2 5 and 3 7 gyr ago as well as around 70 and four chicxulub sized or larger craters on the earth and moon respectively between 1 7 and 3 7 gyr ago these rates reproduce impact spherule bed and lunar crater constraints

a geochemical model for the formation of hydrothermal carbonates on mars it is often argued that substantially more carbon dioxide and water were degassed from the martian interior than can be found at present in the atmosphere polar caps and regolith calculations have shown that atmospheric escape cannot account for all of the missing volatiles suggestions that carbon dioxide is stored as marine or lacustrine deposits are challenged by earth based and spacecraft remote sensing data moreover recent modelling of the martian atmosphere suggests that rainfall or open bodies of water are in any case unlikely to have persisted for extended periods of time hydrothermal carbonates therefore provide a possible solution to this dilemma using an accessible terrestrial system iceland as a guide to the underlying processes and a host rock composition inferred from the least altered martian meteorite we present a geochemical model for the formation of carbonates in possible martian hydrothermal systems our results suggest that an extensive reservoir of carbonate minerals equivalent to an atmospheric pressure of carbon dioxide of at least one bar could have been sequestered beneath the surface by widespread hydrothermal activity in the martian past

impact spherules from karelia russia possible ejecta from the 2 02 ga vredefort impact event spherule beds of possible impact origin have been discovered in two drill cores in the paleoproterozoic zaonega formation karelia northwest russia spherules are found within the dolomite matrix of in situ brecciated sedimentary dolostones spherules are millimeter size and generally round although teardrop and dumbbell morphologies are present spherules contain up to 0 75 ppb ir with a ru ir of 2 indicating a mixing of target rocks with a minor chondritic component the age of the zaonega formation is constrained between limits of 1 975 0 024 ga sm nd and 1 980 0 057 ga pb pb and 2 050 ga re os which brackets the age of the 2020 ma vredefort impact structure in south africa and suggests that the spherule beds could represent ejecta from that event if the link is confirmed the size of the spherules and thickness of the beds suggest that the distance from the impact site was 2500 km thereby constraining the paleogeographic distance between the fennoscandian shield and kaapvaal craton during the late paleoproterozoic

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

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

effect of pore structure on shale oil accumulation in the lower third member of the shahejie formation zhanhua sag eastern china evidence from gas adsorption and nuclear magnetic resonance abstract as shale oil occurs primarily in micro nano pores and fractures research about the effect of pore structure on shale oil accumulation has great significance for shale oil exploration and development the effect of pore structure on shale oil accumulation in the lower third member of the shahejie formation es 3 l zhanhua sag eastern china was investigated using gas adsorption soxhlet extraction nuclear magnetic resonance nmr analysis and field emission scanning electron microscope fe sem observation the results indicated that the samples contained a larger amount of ink bottle shaped and slit shaped pores after extraction than before extraction the pore volume and specific surface area of the samples were approximately 2 5 times larger after extraction than before extraction residual hydrocarbon occurred primarily in the free state form in pores with diameters of 10 1000 nm which can provide sufficient pore volume for free hydrocarbon accumulation therefore pores with diameters of 10 1000 nm were regarded as oil enriched pores which are effective pores for shale oil exploration whereas pores with diameters smaller than 10 nm were regarded as oil ineffective pores samples with only well developed small pores with diameters smaller than 1000 nm showed high oil saturation whereas samples with both small pores and also relatively large pores and micro fractures presented low oil saturation as the minimum pore size allowing fluid expulsion is 1000 nm pores with diameters greater than 1000 nm were considered as oil percolated pores large pores and micro fractures are generally interconnected and may even form a complex fracture mesh which greatly improves the permeability of shale reservoirs and is beneficial to fluid discharge

impact of hydrocarbon expulsion efficiency of continental shale upon shale oil accumulations in eastern china abstract core samples were taken from two formations the qingshankou formation in northern songliao basin and the third member of the shahejie formation of zhanhua sag to carry out a study of impact of hydrocarbon expulsion from continental shale upon shale oil accumulations in eastern china total organic carbon toc and pyrolysis data of these samples were used to establish an evaluation criterion with absolute and relative oil content indexes for determining oil potential of shale as a result a correspondence relationship between shale oil content and organic types was established factors that may affect oil content of shale were discussed through study of fractures pore development minerals and lithological assemblage of the samples the results show that oil content of mature petroleum source rocks is firstly controlled by fracture growth and secondly by pore development they played both negative and positive roles in hydrocarbon flow and accumulation in shale overpressure caused by hydrocarbon generation and existence of organic acid corrosion are two important factors affecting the formation of fractures and pores in shale respectively intervals with type i organic matter are not favorable shale oil exploration targets because they contain little oil shale with type i organic matter tends to generate large amount of hydrocarbon but these hydrocarbon will escape with a high efficiency through over pressurized fractures caused by hydrocarbon generation and lack of pore space which in turn is the result of absence of oxygen that is essential for forming organic acid to create secondary pores in shale on the contrary intervals with type ii organic matters are potential shale oil exploration targets for that they offered just right conditions for oil to stay inside higher content of oxygen that is helpful in forming organic acid moderate hydrocarbon generation capacity that will not cause over pressurized fractures in shale with secondary pores while intervals with type iii organic matter bear no exploration significance due to the fact that this type of kerogen produces less oil because of low hydrocarbon generation capacity and unfavorable molecular configuration shale intervals with thin sandstone interbeds provide favorable passageways for dissolved carbonate by organic acid to flow out avoiding secondary precipitation the pores left behind can be excellent space for generated hydrocarbon to linger around these interbeds are also favorable for later reservoir stimulation measures such as hydraulic fracturing shale oil exploration shall be focused on finding sweet spots with greater pores which are the main reservoir space

the influence of shale depositional fabric on the kinetics of hydrocarbon generation through control of mineral surface contact area on clay catalysis abstract accurately assessing the temperature and hence the depth and timing of hydrocarbon generation is a critical step in the characterization of a petroleum system clay catalysis is a potentially significant modifier of hydrocarbon generation temperature but experimental studies of clay catalysis show inconsistent or contradictory results this study tests the hypothesis that source rock fabric itself is an influence on clay mineral catalysis as it controls the extent to which organic matter and clay minerals are physically associated two endmember clay organic fabrics distinguish the source rocks studied 1 a particulate fabric where organic matter is present as discrete 5 m particles and 2 a nanocomposite fabric in which amorphous organic matter is associated with clay mineral surfaces at sub micron scale high resolution electron imaging and bulk geochemical characterisation confirm that samples of the miocene monterey formation california are representative of the nanocomposite source rock endmember whereas samples from the permian stuart range formation south australia represent the particulate source rock endmember kinetic experiments are performed on paired whole rock and kerogen isolate samples from these two formations using open system non isothermal pyrolysis at three different heating rates 0 7 2 and 5 k min to determine the effects of the different shale fabrics on hydrocarbon generation kinetics extrapolation to a modelled geological heating rate shows a 20 c reduction in the onset temperature of hydrocarbon generation in monterey formation whole rock samples relative to paired kerogen isolates this result is consistent with the monterey formations s nanocomposite fabric where clay catalysis can proceed because reactive clay minerals are intimately associated with organic matter by contrast there is no significant difference in the modelled hydrocarbon generation temperature of paired whole rock and kerogen isolates from the stuart range formation this is consistent with its particulate fabric where relatively large discrete organic particles have limited contact with the mineral matrix and the clay minerals are mainly diagenetic and physically segregated within pores while heating rate may have a control on mineral matrix effects this result shows that the extent to which organic matter and clay minerals are physically associated could have a significant effect on the timing of hydrocarbon generation and is a function of the depositional environment and detrital vs diagenetic origin of clay minerals in source rocks

organic matter sequestered in potential energy fields predicted by 3 d clay microstructure model abstract transmission electron microscopy tem observations confirm theoretical predictions of the location of organic matter om sequestered in fine grained sediment organo clay micro and nanoscale fabric images validate for the first time the protective adsorption model of om preservation preservation of om against enzymatic digestion is demonstrated predominately at locations consistent with our model of the potential energy field that is developed through interactions of clay minerals the om and pore water chemistry pores observed in 2 d fabric tem images of clay muds commonly appear to be totally encapsulated however the great majority of these pores are clearly demonstrated to be open in one or more directions when observed in rotated 3 d images despite the scarcity of completely closed pores om is preserved against enzymatic attack in those locations where the predicted 3 d potential energy of interaction between clay domains and om is attractive

smectite illitization difference of source rocks developed in saline and fresh water environments and its influence on hydrocarbon generation a study from the shahejie formation dongying depression china abstract samples of argillaceous source rocks from three sub members of the shahejie formation es in the dongying depression china were collected to investigate the differences in hydrocarbon generation among the sub members which developed in fresh es32 es33 and saline es41 water environments pyrolysis xrd and thermo xrd analyses were used to compare the characteristics of organic matter om clay minerals and om occurrences total organic carbon and hydrocarbon potential proxies suggest that the samples from es33 were much better than the other two intervals which agrees with previous studies the characteristics of clay minerals suggest that the samples from es41 have the most abundant illite with a maximum illite percentage in mixed layer illite smectite i sm and the best crystallinity of i sm with a main stacking mode of r1 5 however the stacking modes of i sm in es32 and es33 were primarily r0 and r1 respectively and the crystallinity was relatively poor thus the smectite illitization process was faster in es41 than in the other two intervals and a saline environment was a primary cause for the acceleration of the process moreover om occurrence indicates that the samples from es41 had the lowest amount of interlayer om whereas es33 had the largest amount therefore the rapid illitization in es41 caused abundant interlayer om to be desorbed and discharged which in turn caused the amount of residual interlayer om in es41 to be less than that in the other two intervals thus the source rocks of es41 made a more significant contribution to hydrocarbon generation than those of the other two units in conclusion the inconsistent illitization among these intervals was a major cause of the differences in hydrocarbon generation

impact spherules as a record of an ancient heavy bombardment of earth the fossilized remnants of vaporized asteroids called spherules can be used to infer that the flux of asteroid impacts on earth 3 5 billion years ago was much greater than it is now the late heavy bombardment was a period of time generally put at about 4 1 billion to 3 8 billion years ago when the inner planets of the solar system were subjected to a high frequency barrage of asteroids this left its mark on the moon but on earth the craters quickly disappeared owing to tectonic processes and erosion in the first of two papers on the bombardment brandon johnson and jay melosh determine the properties of the asteroids by looking at spherule beds layers of debris ejected during the impacts the thickness of spherule layers is expected to vary according to the size of the impactor and the speed at which it hit earth this historical record of impacts indicates that the number of projectiles colliding with earth was substantially higher 3 5 billion years ago than it is today with a gradual decline in the number of strikes after the late heavy bombardment bottke et al modelled the evolution of an asteroid belt that extended farther towards mars than the present one they find that most of the impactors traced by the spherule beds probably originated in this e belt which was disrupted during migrations of some of the giant planets impact craters are the most obvious indication of asteroid impacts but craters on earth are quickly obscured or destroyed by surface weathering and tectonic processes1 earth s impact history is inferred therefore either from estimates of the present day impactor flux as determined by observations of near earth asteroids or from the moon s incomplete impact chronology2 3 4 asteroids hitting earth typically vaporize a mass of target rock comparable to the projectile s mass as this vapour expands in a large plume or fireball it cools and condenses into molten droplets called spherules5 for asteroids larger than about ten kilometres in diameter these spherules are deposited in a global layer spherule layers preserved in the geologic record accordingly provide information about an impact even when the source crater cannot be found1 here we report estimates of the sizes and impact velocities of the asteroids that created global spherule layers the impact chronology from these spherule layers reveals that the impactor flux was significantly higher 3 5 billion years ago than it is now this conclusion is consistent with a gradual decline of the impactor flux after the late heavy bombardment

sounding the subsurface of athabasca valles using marsis radar data exploring the volcanic and fluvial hypotheses for the origin of the rafted plate terrain 1 to test the volcanic and fluvial hypotheses for the origin of the rafted plate terrain observed in the vicinity of athabasca valles 5 n 150 e central elysium planitia we investigated the subsurface radar echo from the mars advanced radar for subsurface and ionosphere sounding marsis 5 mhz band data over this area the backscattered signal losses were compared to finite difference time domain fdtd simulations of those arising from three hypothetical geoelectrical subsurface models which differed in their assumed composition percentage basalt versus ice and assumed mode of origin fluvial discharge frozen sea mudflow and low viscosity lavas the dielectric values used in these models are derived from laboratory measurements of mars analog materials under mars like conditions fdtd simulations suggest that if the near surface environment is ice rich it will result in an average loss rate of 0 053 db m for massive ice having less than 1 of suspended particulates and 0 065 db m for a mudflow consisting of a 50 50 mixture of ice and basaltic dust whereas the losses associated with a lava flow model increase to 0 19 db m in comparison the actual signal losses experienced by marsis within this region were on the order of 0 18 db m within the first 160 m beneath the surface this suggests that propagation characteristics of athabasca s near subsurface are more consistent with a volcanic rather than a fluvial or mudflow origin of the rafted plate terrain although limitations on radar sounding depth in this region cannot rule out the possibility of more deeply buried massive ice deposits

rapid identification of dolomite using a fourier transform infrared spectrophotometer ftir a fast method for identifying heinrich events in iodp site u1308 this study demonstrates that fourier transform infrared spectrophotometry ftir provides a quick and relatively inexpensive method for identifying and quantifying dolomite in deep marine sediments ftir is used to determine concentrations of dolomite in the top 29 m of sediments recovered at iodp site u1308 some of these dolomite peaks can be reliably correlated with heinrich events h1 through h6 thus ftir appears to provide a fast and reliable method for identifying heinrich events in deep sea sediments

adsorption of mudstone source rock for shale oil experiments model and a case study abstract inorganic minerals were separated from mudstone and shale to investigate their oil adsorption potential a conceptual model was developed to reconstruct the oil adsorption capacity of underground mudrock shale by combining adsorption and organic matter swelling data the predictions for the free hydrocarbon oversaturation sorption zones in the well ny1 profile were taken as a case study the results suggest that the best depth for the shale oil prospect of the es4s member strata lies between 3400 and 3600 m in the dongying depression hydrocarbon starvation zones occur mainly at a depth of

deep sea record of impact apparently unrelated to mass extinction in the late triassic the 34 million year my interval of the late triassic is marked by the formation of several large impact structures on earth late triassic impact events have been considered a factor in biotic extinction events in the late triassic e g end triassic extinction event but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits here we report evidence for an impact event platinum group elements anomaly with nickel rich magnetite and microspherules from the middle norian upper triassic deep sea sediment in japan this includes anomalously high abundances of iridium up to 41 5 parts per billion ppb in the ejecta deposit which suggests that the iridium enriched ejecta layers of the late triassic may be found on a global scale the ejecta deposit is constrained by microfossils that suggest correlation with the 215 5 mya 100 km wide manicouagan impact crater in canada our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon and no contemporaneous faunal turnover is seen in other marine planktons however such an event has been reported among marine faunas and terrestrial tetrapods and floras in north america we therefore suggest that the manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm

impact crater lakes on mars the robotic search for life on mars centers on identifying accessible environments where the biological catalyst water has existed the formation of large impact craters on mars 65 km diameter may have resulted in the creation of ice covered impact crater lakes which would not freeze for thousands of years even under present climatic conditions water could be supplied from deep confined aquifers penetrated by the impact craters without the need for surface melt water freezing of the lakes is postponed owing to heat from impact generated melt bearing deposits from impact related uplift of hotter rocks from depth and from the latent heat of freezing of a deep crater lake abundant morphologic evidence for ancient crater lakes has not been found in viking images except for craters associated with outflow channels however ice covered crater lakes could have formed and further searches for evidence of these lakes are warranted the lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from mars

earth and moon impact flux increased at the end of the paleozoic the terrestrial impact crater record is commonly assumed to be biased with erosion thought to eliminate older craters even on stable terrains given that the same projectile population strikes earth and the moon terrestrial selection effects can be quantified by using a method to date lunar craters with diameters greater than 10 kilometers and younger than 1 billion years we found that the impact rate increased by a factor of 2 6 about 290 million years ago the terrestrial crater record shows similar results suggesting that the deficit of large terrestrial craters between 300 million and 650 million years ago relative to more recent times stems from a lower impact flux not preservation bias the almost complete absence of terrestrial craters older than 650 million years may indicate a massive global scale erosion event near that time

mineralogical and chemical distribution of the es3l oil shale in the jiyang depression bohai bay basin e china implications for paleoenvironmental reconstruction and organic matter accumulation abstract the es3l lower sub member of the third member of the eocene shahejie formation shale in the jiyang depression is a set of relatively thick and widely deposited lacustrine sediments with elevated organic carbon and is considered to be one of the most important source rocks in east china we can determine the mineralogy organic and inorganic geochemistry of the es3l shale and calculate paleoclimate indexes by using multiple geochemical proxies based on organic chemistry total organic carbon toc and rock eval pyrolysis major and trace elements x ray diffraction and carbon and oxygen isotope data from key wells alongside ecs elemental capture spectroscopy well log data these indicators can be used to analyze the evolution of the paleoenvironment and provide a mechanism of organic matter om accumulation the es3l oil shale has high toc abundance most samples 3 0 and is dominated by type i kerogens additionally the organic rich shale is rich in cao and enrichment in some trace metals is present such as sr ba and u the positive 13c and negative 18o values high sr ba b ga and ca ca fe ratios and low c s ratios indicate that the es3l shales were mainly deposited in a semi closed freshwater brackish water lacustrine environment the consistently low ti al and si al ratios reflect a restricted but rather homogeneous nature for the detrital supply many redox indicators including the th u v v ni and u ratios pyrite morphology and toc ts fe diagrams suggest deposition under dysoxic to suboxic conditions subsequently the brackish saline bottom water evolved into an anoxic water body under a relatively arid environment during which organic lean marls were deposited in the early stage later an enhanced warm humid climate provided an abundant mineral nutrient supply and promoted the accumulation of algal material om input from algal blooms reached a maximum during the deposition of the organic rich calcareous shale with seasonal laminations high p ti ratios and a strongly positive relationship between the p and toc contents indicate that om accumulation in the oil shale was mainly controlled by the high primary productivity of surface waters with help from a less stratified water column factors such as the physical protection of clay minerals and the dilution of detrital influx show less influence on om enrichment

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

explosive volcanism on hecates tholus mars investigation of eruption conditions evidence is presented supporting the identification of a discrete well preserved air fall deposit generated by explosive volcanism on mars the deposit is located immediately to the west of the summit caldera of hecates tholus 32on 209ow the northernmost of the three volcanic constructs in the elysium planitia region the absence of superposed impact craters larger than the resolution limit of the viking images 40 m per pixel indicates a very young age for this eruption which evidently postdates even the most recent collapse episode of the olympus mons caldera 300 m y b p neukum and hiller 1981 from the distribution of craters smaller than 2 km in diameter it appears that the air fall material mantles an area about 50 x 75 km in extent to an estimated thickness of about 100 m by adapting numerical models for terrestrial volcanic eruptions to the martian environment these dimensions imply an eruption cloud height of about 70 km in order to attain such an altitude the mass eruption rate must have been 107 kg s and the volatile content either 1 wt for h20 or 2 wt for co2 although it is not possible to distinguish between silicic and basaltic volcanism on hecates were the volatile species co2 the depth of most recent storage prior to eruption of the magma would have to be 50 100 km due to the solubility of co2 in the melt if h20 were the driving volatile a minimum depth of storage would be 0 2 4 km thereby permitting the possibility of ground water assimilation by the magma

organic matter induced mineralogical changes in clay sized phlogopite and muscovite in alfalfa rhizosphere weathering of micaceous minerals is the major source of potassium in soils many studies have shown the beneficial effects of organic matter om on soil physical chemical biological and nutritional properties however there is no information on the effect of om on the breakdown of k rich micaceous minerals the objective of this study was to investigate the transformation of muscovite and phlogopite as influenced by added om in the rhizosphere zone of alfalfa growth medium was a mixture of quartz sand micaceous mineral muscovite or phlogopite and om 0 0 5 and 1 cocopeat on a weight basis during 120 days of alfalfa cultivation plants were irrigated with either a complete or a k free nutrient solution and distilled water as needed at the end of the experiment plants were harvested and their k uptake was measured by flame photometer following dry ash extraction micas and their weathering products were separated from the quartz sand to analyze their clay fractions using x ray diffraction xrd results showed a significant increase in total k uptake in pots containing trioctahedral mica phlogopite and om as compared with non om treatments addition of om transformed phlogopite to 2 1 expanding clays but left dioctahedral mica muscovite intact with undetectable formation of any secondary minerals root activities and om decomposition appear to have increased rhizosphere acidity which in turn facilitated k release from trioctahedral mica phlogopite and induced the formation of vermiculite and a minor quantity of smectite and hydroxy interlayered vermiculite hiv in conclusion the influence of om on the formation of expanding clays greatly depends on the type of micaceous mineral

towards an understanding of the role of clay minerals in crude oil formation migration and accumulation this article reviews progress in the understanding of the role of clay minerals in crude oil formation migration and accumulation clay minerals are involved in the formation of kerogen catalytic cracking of kerogen into petroleum hydrocarbon the migration of crude oil and the continued change to hydrocarbon composition in underground petroleum reservoirs in kerogen formation clay minerals act as catalysts and sorbents to immobilize organic matter through ligand exchange hydrophobic interactions and cation bridges by the mechanisms of maillard reactions polyphenol theory selective preservation and sorptive protection clay minerals also serve as catalysts in acid catalyzed cracking of kerogen into petroleum hydrocarbon through lewis and bronsted acid sites on the clay surface the amount and type of clay mineral affect the composition of the petroleum bronsted acidity of clay minerals is affected by the presence and state of interlayer water and displacement of this water is a probable driver in crude oil migration from source rocks during crude oil migration and accumulation in reservoirs the composition of petroleum is continually modified by interaction with clay minerals the clays continue to function as sorbents and catalysts even while they are being transformed by diagenetic processes the detail of chemical interactions and reaction mechanisms between clay minerals and crude oil formation remains to be fully explained but promises to provide insights with broader application including catalytic conversion of biomass as a source of sustainable energy into the future

which 2 1 clay minerals are involved in the soil potassium reservoir insights from potassium addition or removal experiments on three temperate grassland soil clay assemblages field and laboratory observations based on x ray diffraction techniques suggest that 2 1 clay minerals behave as a k reservoir however 2 1 soil clay assemblages are most often composed of a mixture of different 2 1 clay mineral populations and the role of these different clay mineral populations in k absorption or k release are not fully understood this present work addressed this question through laboratory experiments by using an x ray pattern decomposition program to quantify peak area modifications of different clay mineral populations induced by k addition and k removal through plant action this study was performed on three typical temperate grassland soil clay assemblages containing illite interstratified illite smectite and soil vermiculite our results revealed that the quantities of well crystallized illite increased at the expense of soil vermiculite as a result of k absorption whereas the opposite trend was observed following k depletion this particular relationship between well crystallized illite and soil vermiculite suggests that they constitute a subgroup among 2 1 clay minerals poorly crystallized illite and interstratified clay minerals were also significantly affected by k absorption or removal indicating that they are also involved in soil k dynamics moreover we observed that these short term clay mineral modifications occurring at the day scale induced by root k extraction are reversible we also observed that the linear relationship between clay k content and the centre of gravity position of x ray diffraction patterns in the 2 1 clay mineral range seem to be a general property for soil clay assemblages dominated by illite and interstratified illite smectite materials our results support the view of 2 1 clay minerals as a k reservoir and specify the role of each of the 2 1 clay mineral populations in k absorption and release all the 2 1 clay minerals commonly found in temperate grassland soil clay assemblages take part in the soil k reservoir

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

ground ice on mars inventory distribution and resulting landforms abstract most 90 of the estimated original volume of outgassed water on mars cannot be satisfactorily accounted for by exospheric escape or storage in the atmosphere as frost or in the permanent north polar ice cap the balance may be stored as ground ice in the martian cryosphere a zone of permanently frozen ground that is protected from the atmosphere by a debris cover ground ice can exist throughout the entire cryosphere but it need not fill it if the ground ice does fill the cryosphere then excess water can exist in a confined aquifer the theoretical distribution of ground ice can be tested by identification of forms on the martian surface that may be related to the presence of subsurface ice the observed features that are most likely to reflect ground ice are thermokarst like pits and debris flows landforms with ambivalent origins include polygonally patterned ground lobate ejecta blankets craters with central pits and curvilinear features the most persuasive morphologic evidence for ground ice is thermokarst pits and debris flows the thermokarst pits are primarily located in the volcanic regions of tharsis and elysium the association of ice related features with these volcanic areas suggests that these forms are not directly latitude dependent activation by orbital variations could produce periodic multiple episodes of melting that are dependent upon latitude the presence of ice related features in both hemispheres and the equatorial region of mars indicates that ground ice may be or have been present over the entire planet as predicted by the cryosphere model

climate driven paleolimnological change controls lacustrine mudstone depositional process and organic matter accumulation constraints from lithofacies and geochemical studies in the zhanhua depression eastern china abstract the influence of paleoclimate on the depositional process of lacustrine mudstone and organic matter accumulation is important to both paleoclimate reconstruction and hydrocarbon exploration here we study the lower third member es3l of the eocene shahejie formation in the zhanhua depression bohai bay basin eastern china in order to understand how paleoclimate influenced depositional processes and organic matter accumulation of lacustrine organic rich mudstone by combining detailed core descriptions and microscopic observations and high resolution mineralogical and geochemical analyses we identified two major lithofacies including massive calcareous mudstone and laminated calcareous mudstone from the luo 69 drilling core the sedimentologic observations and changes of geochemical proxies including detritus index ln al2o3 na2o b ga and v v ni suggest that the massive calcareous mudstone was deposited in a small shallow salt lake that was dysoxic anoxic and the paleoclimate in the lake catchment was cool and arid and the laminated calcareous mudstone was deposited in a large and deep stratified lake which has anoxic highly saline bottom and oxic less saline surface water and the lake catchment was more humid and warm the dominant lithofacies changed from laminated calcareous mudstone to massive calcareous mudstone in the studied core suggesting that the lake became shallower and smaller when the paleoclimate became cooler and drier through time such a climate trend may be a response to global cooling during the middle eocene the average total organic content toc in both lacustrine highstand and lowstand are comparable even though the lake water chemistry and amount of terrigenous input are different we infer that the accumulation of organic matter within the lacustrine highstand was controlled by the combination of primary productivity carbonate production and preservation in anoxic bottom water while accumulation within lacustrine lowstand was only controlled by primary productivity

variability of clay mineralogy in two new zealand steep land topsoils under pasture the variability of the clay mineralogy in the topsoil of agricultural fields has rarely been examined although it is important to the construction of accurate potassium k availability models the variability of clay mineralogy and the relationship to plant available nonexchangeable k step k were examined in two steep land fields in the southern north island of new zealand the soils at the sites have developed from quartzo feldspathic mica bearing parent materials the mineralogy was examined using x ray diffraction xrd and differential thermal analysis dta the clay mineralogy consisted of mixtures of mica interlayered mica smectite ms vermiculite interlayered mica vermiculite mv hydroxy interlayered vermiculite hiv smectite quartz feldspar and kaolin minerals the c v of the content of 2 1 layer silicates ranged from 52 to 257 indicating large variability within the fields correspondence analysis identified an antagonistic relationship and a large negative correlation between the proportion of mica and ms compared to the proportion of vermiculite hiv mv and chlorite in the clay fraction in most locations there was a logical relationship between the mineralogy and the position of the soil in the landscape as an indicator of the extent of weathering an exception was the clay mineralogy of topsoils under well drained and heavily frequented animal campsites which was characterized by large mica and ms contents a lack of hiv and irregularly interstratified expanded 2 1 layer silicates a reversal of the 2 1 silicate weathering processes was indicated the large spatial variability of the clay mineralogy and the evidence of modifications to the mineralogy on the animal campsites indicated that fixed values based on reference profiles from soil orders would inaccurately represent the effect of clay mineralogy in k availability models clay mineralogy is expensive to measure however step k values were highly correlated to the 2 1 silicate clay mineralogy step k can therefore be sampled within a field to cost effectively represent clay mineralogy trends in k availability models d 2005 elsevier b v all rights reserved

the growth of the continent through geological time studied by nd isotope analysis of shales abstract we determined the nd isotopic composition and the sm nd ratios in a series of australian shales ranging from 0 2 gy to 3 3 gy the first result of this study is the constancy of the sm nd ratio in these shales as in granitoids secondly the initial 143nd 144nd ratio gives a regular curve decreasing through geological time both results confirm that shales are representative samples of the continental crust when insoluble elements like ree are studied we calculated their nd model ages of crustal differentiation the model ages regularly decrease with the stratigraphic ages and after 2 gy the curve flattens and tends to an asymptotic value at around 1 8 gy the significance of the shales is that they represent a mixture of continental materials and we consider the model age of such a mixture directly linked with the mean age of the continental portion feeding the sedimentary basin from these results we deduce a quantitative model of the growth curve of the continental source of the shales taking into account the effects of erosion which selectively sample recent mountains relative to shield areas we propose that the results obtained here are representative of the whole gondwana continent having studied the case of the australian shales we try to extend our study first we applied our quantitative approach to the recent results obtained by o nions et al on north atlantic provinces the continental growth curves obtained by our inversion procedure are quite distinct from the australian shales showing the regional character of shales with these two cases studied we try to compare our results with the already developed model for continental growth the consideration of the surface conservative versus surface non conservative models clearly show the non uniqueness of the geological interpretation of the growth curve on the other hand we have calculated for each case the recycling rate versus geological time by comparing the growth curve with the hurley rand province age curve such recycling increases with time in agreement with the data obtained on nd and sr initial ratios on granitoids

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

spherule layers crater scaling laws and the population of ancient terrestrial impactors abstract ancient layers of impact spherules provide a record of earth s early bombardment history here we compare different bombardment histories to the spherule layer record and show that 3 2 3 5 ga the flux of large impactors 10 100 km in diameter was likely 20 40 times higher than today the e belt model of early solar system dynamics suggests that an increased impactor flux during the archean is the result of the destabilization of an inward extension of the main asteroid belt bottke et al 2012 here we find that the nominal flux predicted by the e belt model is 7 19 times too low to explain the spherule layer record moreover rather than making most lunar basins younger than 4 1 gyr old the nominal e belt model coupled with a corrected crater diameter scaling law only produces two lunar basins larger than 300 km in diameter we also show that the spherule layer record when coupled with the lunar cratering record and careful consideration of crater scaling laws can constrain the size distribution of ancient terrestrial impactors the preferred population is main belt like up to 50 km in diameter transitioning to a steep distribution going to larger sizes