concentrations en uranium et desequilibres radioactifs iou en mediterranee orientale discussion sur l origine des sapropeles abstract sedimentation rates of the oxidized sediments from the eastern basin of the mediterranean sea are about a few centimetres per 1000 years not very different from the sedimentation rates of the western basin the sapropels levels show strong u enrichment from 10 to 30 times and ionium 230 th daughter of 238 u is in radioactive equilibrium with u at these levels these facts together with the high surficial productivity and or conservation factor implied by the strong organic material concentration of the sediments are hardly explained if sapropels are formed in the sea it seems that they are largely made up by continental material debris accumulated during propitious epochs of vegetation growth they would be expelled massively from the continent lagoons or closed seas when the sea level goes down causing the ablation of continental or coastal formations by the running waters then deposited onto the sea floor sapropel s 5 for instance could be made up by material from the last interglacial rich in organic matter but dispatched to the sea at the beginning of the glacial era

holocene sedimentation rates on the hellenic outer ridge a comparison by 14c and 230thexcess methods abstract an examination of the most recent eastern mediterranean sapropel s 1 or a is made by 14 c and 230 th excess techniques to test the observation mangini and dominik 1979 that sapropels in this area often represent periods of slower than average sedimentation two cores from the hellenic outer ridge with long clear cut sapropel sections were analysed together the 230 th excess and 14 c data are equivocal and suggest a complex sedimentation process the 14 c ages call for high sedimentation rates in the sapropel sections while the estimated 230 th excess values in the sapropel sections are relatively high and would normally be taken to indicate a slower sedimentation rate than in the overlying carbonate ooze the 14 c ages are more direct and ought to be valid for the core sites from consideration of a model based on water column supply of 230 th excess however it is suggested that the sapropel in the local area as a whole probably accumulated at a rate similar to or slightly higher than the carbonate ooze subsequently deposited

unusual lithospheric structure beneath the hyderabad granitic region eastern dharwar craton south india abstract using multiparametric geological and geophysical data the evolutionary history of the lithosphere beneath the late archean early proterozoic hyderabad granitic region hgr of the eastern dharwar craton of south indian shield has been attempted our study reveals that the entire granitic region and the surroundings 200 km 200 km is being neotectonically uplifted possibly due to a major intrusive body situated at sub crustal depth leading to changes in river courses and also erosion of several kilometers 10 km from its upper crustal column beneath this region the moho is elevated 32 33 km the reduced heat flow is of the order of 28 mw m2 and the asthenosphere is located at shallow depths of about 124 km i e far less than 200 400 km depth found in precambrian shield areas of the globe the cratonic mantle lithosphere beneath hgr contains a highly conductive 15 m hydrous and seismically anisotropic metasomatic zone between depth of 90 and 100 km where the estimated temperatures could be in the range of 900 1000 c the surface granitic layer containing unusually high radioactivity 5 25 w m3 appears very thin probably a kilometer or so beneath which the entire crustal column seems to be differentiated and made up of low radioactive granulite facies rocks of acid to intermediate composition persistent episodic thermal reactivations during the last 2 6 gega years and continuous uplifting seems to have played a major role towards making its crustal column unusual

variation of radiogenic heat production rate in 2 8 1 8 ga old rocks in the central fennoscandian shield abstract we present results of a geochemical survey based on 1150 outcrop samples for heat production studies in a e w oriented band 120 km 500 km located approximately between 62 and 63 n in finland the central fennoscandian shield the results provide representative averages of heat production rate in the studied tectonic units but also demonstrate the heterogeneity and spatial variation in radiogenic heat production rate of the precambrian lithosphere the study area covers formations from the archaean granite greenstone terrain in the east via a palaeoproterozoic mobile belt to a major granitoid complex surrounded by schist belts in central and western finland in this study we review the heat production rates as calculated from the u th and k total analyses and densities of the samples and the relations of heat production rate values with major tectonic setting lithological types major composition and petrophysical properties of rocks the data is further correlated with heat flow values measured in boreholes and applied in a lithospheric heat production model in the central part of the shield generally heat production rate increases from archaean to proterozoic rocks in e w direction but this trend is relatively weak and often overrun by lithological variations the arithmetic means are 1 1 1 3 w m 3 in the archaean domain 1 3 0 6 w m 3 in the hoytiainen autochthonous proterozoic domain 1 2 0 5 w m 3 in the suvasvesi domain characterized by allochthonous proterozoic cover 1 0 0 6 w m 3 in the proterozoic raahe ladoga mobile belt 1 3 1 1 w m 3 in the proterozoic rantasalmi haukivuori domain 1 6 0 8 w m 3 in the central finland granitoid complex and 1 4 0 8 w m 3 in the bothnian schist belt the standard deviations of the mean values are considerable and reflect the heterogeneity of heat production all distributions overlap heat production rate shows spatial variations which range in scale from kilometres to tens of kilometres well defined systematic variations of heat production rate values with either sio2 content density or p wave velocity could not be found although the correlations are statistically significant at 1 risk level the correlations are weak and scattered and sometimes opposite in sign in the major rock groups plutonic metavolcanic and metasedimentary heat flow density measured in boreholes increases with increasing heat production rate but the present data do not support a strict linear dependence between the variables and the regression line parameters vary depending on the applied heat production values drill core analyses versus hole site averages from the present study this indicates that the heat production rate is spatially heterogeneously distributed in the scale of the boreholes and their formations a lithospheric heat production model was constructed using data from the present study for the upper crust literature data for lower crustal xenoliths in the study area and a xenolith derived heat flow density value for the mantle the total crustal contribution to the surface heat flow density 37 mw m 2 from radiogenic heat sources is calculated as 26 mw m 2 and the contributions from the lower middle and upper crust are 4 11 and 11 mw m 2 respectively

assessment of mars pathfinder landing site predictions remote sensing data at scales of kilometers and an earth analog were used to accurately predict the characteristics of the mars pathfinder landing site at a scale of meters the surface surrounding the mars pathfinder lander in ares vallis appears consistent with orbital interpretations namely that it would be a rocky plain composed of materials deposited by catastrophic floods the surface and observed maximum clast size appears similar to predictions based on an analogous surface of the ephrata fan in the channeled scabland of washington state the elevation of the site measured by relatively small footprint delay doppler radar is within 100 m of that determined by two way ranging and doppler tracking of the spacecraft the nearly equal elevations of the mars pathfinder and viking lander 1 sites allowed a prediction of the atmospheric conditions with altitude pressure temperature and winds that were well within the entry descent and landing design margins high resolution 38 m pixel viking orbiter 1 images showed a sparsely cratered surface with small knobs with relatively low slopes consistent with observations of these features from the lander measured rock abundance is within 10 of that expected from viking orbiter thermal observations and models the fractional area covered by large potentially hazardous rocks observed is similar to that estimated from model rock distributions based on data from the viking landing sites earth analog sites and total rock abundance the bulk and fine component thermal inertias measured from orbit are similar to those calculated from the observed rock size frequency distribution a simple radar echo model based on the reflectivity of the soil estimated from its bulk density and the measured fraction of area covered by rocks was used to approximate the quasi specular and diffuse components of the earth based radar echos color and albedo orbiter data were used to predict the relatively dust free or unweathered surface around the pathfinder lander compared to the viking landing sites comparisons with the experiences of selecting the viking landing sites demonstrate the enormous benefit the viking data and its analyses and models had on the successful predictions of the pathfinder site the pathfinder experience demonstrates that in certain locations geologic processes observed in orbiter data can be used to infer surface characteristics where those processes dominate over other processes affecting the martian surface layer

heat flow and heat generation in the archaean dharwar cratons and implications for the southern indian shield geotherm and lithospheric thickness abstract we report terrestrial heat flow density measurements from 11 new sites in the archaean eastern and western dharwar cratons of the southern indian shield the new values together with already published data have yielded a mean heat flow of 40 3 4 s d mw m 2 n 11 for the eastern dharwar craton which is a predominantly gneiss granite terrain the mean heat flow in the archaean supracrustal belts of western dharwar craton which is a granite greenstone terrain is 31 4 1 s d mw m 2 n 4 the observed difference in surface heat flow between the two cratons is ascribed to differences in radiogenic heat production in upper crustal layers inferred to be related to different crust forming processes it has been argued that low heat production appears to be an inherent characteristic of the crust similar to that of the western dharwar craton which evolved during the early archaean and suffered depletion of the lithophile elements of its lower crust prior to the late archaean radiogenic heat production measurements were carried out on borehole core samples for one heat flow site sortur and data have been compiled from the literature on three other sites and on a variety of rocks of the southern indian shield heat flow and radiogenic heat production for sortur when combined with the published data define a linear relation r 0 97 with a slope of 11 5 km and an intercept of 23 mw m 2 the thickness of the thermal lithosphere beneath the dharwar cratons is over 200 km thereby indicating beneath the cratons the existence of deep continental roots a concept which is also supported by teleseismic p wave travel time data the geothermal data has clearly demonstrated that the archaean dharwar cratons of the indian landmass are associated with low mean surface heat flow 37 7 mw m 2 reduced heat flow moho heat flux 12 17 mw m 2 and a cool and thick lithosphere all characteristics of many archaean early proterozoic terrains of other shields it is inferred that the thermal structure of the south indian lithosphere is identical with that of other cratons

humic substances in an arabian shelf sediment and the s1 sapropel from the eastern mediterranean abstract the molecular size distribution of humic substances has been investigated in sediment from two different geographical sites two depth horizons in a core sample taken from the arabian sea upwelling region age limits of 700 3000 yr have been analysed together with samples of the s 1 sapropel and the underlying grey marl deposit from the eastern mediterranean the extractable humic substances account for 20 of the total organic c in the sapropel 50 in the grey marl and 76 and 58 in the arabian sea sediments the humic compounds are described on the basis of their molecular weight distribution elemental composition and ir spectra results are considered in relation to the likely sources of organic c at each site the age of the sediment and the sedimentary environment the results obtained indicate that in both areas during the formation of the organic rich deposits the major source of organic c was planktonic the humic and fulvic acid distributions being dominated by high molecular weight humic acids

is the indian shield hotter than other gondwana shields abstract geothermal data on various precambrian terrains from the african australian indian and south american brazil only gondwana landmasses have been compiled synthesised and statistically analysed the results do not support the prevailing notion that the indian shield is hotter than other shields the study clearly shows that the mean surface heat flow values from the various precambrian cratons and mobile belts of the indian landmass for which the data have become available are either equal to or even lower in some cases than that in similar terrains from other gondwana continents further on the basis of available data it is found that the moho and the reduced heat flow values and moho temperatures in the south indian south african western australian and brazilian shields fall within a narrow range thus indicating within the error limits of the estimation the similarity of these shields in terms of these characteristics in conclusion it is shown that the indian landmass is not hotter than the other gondwana landmasses including even the presently immobile african continent and that the super mobility of the indian landmass does not appear to be associated with its thermal characteristics the cause of the latter lies elsewhere

the occurrence of high molecular weight humic material in recent organic rich sediment from the namibian shelf abstract the molecular size distribution of humic substances has been investigated in two recent sediment samples of different ages taken from a single core sample collected off walvis bay south west africa extractable humic acids were found to be by far the major form of organic carbon in both sediments the near surface younger sample containing predominantly high molecular weight 100 000 molecular weight humic acids and little fulvic acids whilst the deeper older sample contained relatively less humic acid and relatively more fulvic acid of a range of molecular weights a significant age difference was found between the 300 000 molecular weight and the the data suggest that in this rapidly accumulating organic rich sediment the first step en route from the planktonic matter to the humic complexes is direct and rapid incorporation of the biogenic material into high molecular weight humic acids

the scaling of complex craters the empirical relation between the transient crater diameter dg and final crater diameter dr of complex craters and basins is estimated using cumulative terrace widths central uplift diameters continuous ejecta radii and transient crater reconstructions determined from lunar and terrestrial impact structures the ratio dg dr is a power law function of dr decreasing uniformly from unity at the diameter of the simple complex crater morphology transition to about 0 5 for large multiring basins like imbrium on the moon the empirical constants in the dg dr relation are interpreted physically to mean that the position of the final rim relative to the transient crater and hence the extent of collapse is controlled or greatly influenced by the properties of the zone of dissociated material produced by the impact shock the continuity of the dg dr relation over the entire spectrum of morphologic types from complex craters to multiring basins implies that the rims of all these structures form in the same tectonic environment despite morphologic differences

thermal history and extension of the lithosphere in the mannar basin and realization its hydrocarbon potential offshore sri lanka abstract data on the structure of the sedimentary blanket and the composition of its rocks measurements of deep temperatures and vitrinite reflectance published in the open press were used for the numerical 1 d reconstructions of the thermal evolution of the mannar basin and the history of its tectonic subsidence near wells pearl 1 dorado north pseudo mannar deep and barracuda analysis of variations in the basin s tectonic subsidence and published geophysical data on the modern depth of the moho boundary made it possible to numerically estimate the degree of stretching of the basin s lithosphere at different stages of its evolution our analysis shows that a significant part of the lithosphere extension occurred before the start of the formation of the basin s sedimentary cover the moderate lithosphere extension with amplitude 1 15 1 25 accompanied the thermal activation of the basin lithosphere during the second stage of the basin rifting in the late cretaceous our modeling suggests a more moderate history of changes in the thermal regime of the basin s lithosphere and lower degree of maturity and realization of hydrocarbon potential in sedimentary sections of the pearl 1 dorado north pseudo mannar deep and barracuda wells than those reconstructed numerically in recent studies of the mannar basin

late quaternary mediterranean sapropels ii organic geochemistry and palynology of s1 sapropels and associated sediments six s1 sapropel samples from the eastern mediterranean were investigated organic geochemically to study the lateral variation within this organic rich layer five of these samples were also analyzed palynologically in addition some sediment samples from below and overlying the sapropel intervals were investigated for their organic geochemical characteristics organic matter of s1 sapropels is of a mixed marine terrigenous and bacterial origin a trend of relatively increasing amounts of continentally derived organic matter towards more seaward and deeper realms can be observed from both palynological and organic geochemical data this trend is supported to some extent by 13c values of the organic matter the sapropelic intervals deposited on the nile cone are characterized by expanded thicknesses and a diluted organic carbon content due to a higher sedimentation rate the environmental conditions in terms of preservation during sapropel formation over the eastern mediterranean were probably not uniform at site 29 the conditions were favourable for the deposition of sapropel with a higher organic carbon content than at the other locations this might have been caused by better preservation conditions an increasing discharge from the river nile seems to be the driving force for formation of the s1 sapropels based on this assumption a model for sapropel formation is proposed although not all the data could be explained properly by this model most phenomena can be explained

stress field and seismicity in the indian shield effects of the collision between india and eurasia intraplate stresses and intraplate seismicity in the indian subcontinent are strongly affected by the continued convergence between india and eurasia the mean orientation of the maximum horizontal compression in the indian subcontinent is subparallel to the direction of the ridge push at the plate boundary as well as to the direction of compression expected to arise from the net resistive forces at the himalayan collision zone indicating that the intraplate stresses in the subcontinent including the shield area are caused by plate tectonic processes spatial distribution of historic and instrumentally recorded earthquakes indicate that the seismic activity is mostly confined to linear belts while the remaining large area of the shield is stable the available conventional heat flow data and other indicators of heat flow suggest hotter geotherms in the linear belts leading to amplification of stresses in the upper brittle crust many of the faults in these linear belts which happen to be 200 80 m y old are being reactivated either in a strike slip or thrust faulting mode the reactivation mechanisms have been analyzed by taking into consideration the amplification of stresses pore pressures geological history of the faults and their orientation with respect to the contemporaneous stress field the seismicity of the indian shield is explained in terms of these reactivation mechanisms

geochemical studies of the recent sapropel and associated sediment from the hellenic outer ridge eastern mediterranean sea i mineralogy and chemical composition abstract the mineralogy major and minor element geochemistry and the accumulation rate of a single kastenlot core from the eastern mediterranean is reported the sapropel is similar mineralogically and in its major element composition to the associated marl ooze and calcareous clay it differs from these sediments in having higher concentrations of ba cr cu mo ni sr and zn and lower concentrations of mn the enrichments are explained by increased fertility ba organic matter or sulphide association cr cu mo ni and zn and the presence of aragonitic pteropods sr the organic material has a marine origin based on the carbon isotopic value 13 c 20 and c n ratio 10 the sapropel accumulated 3 to 5 times faster than the associated sediments in this particular core the evidence is consistent with the formation of this sapropel by an increased flux of carbon to the sea floor this would have been caused by increased marine primary production in the eastern mediterranean during periods of reversed circulation brought about by high post glacial runoff primarily from northern africa the additional carbon flux would have lowered the oxygen levels of the bottom waters but it is not known whether anoxic conditions ensued or whether they would have been necessary to preserve the deposited carbon

the changing picture of volatiles and climate on mars many questions still remain unanswered about the climate history and possible past biological activity on mars in their perspective jakosky et al 1 discuss recent results from space probes and other studies that are changing scientists views of martian climate observations of holes in the frozen carbon dioxide layer suggest that underlying water ice is being exposed on seasonal cycles and models indicate that frost deposition may not be driven entirely by local energy balance axial obliquity the tilt of mars rotational axis that gives rise to planetary seasons may also be having a bigger effect than previously thought and geological mapping shows features that may be glacial in origin implying a wet past despite the large uncertainties such studies will be important in understanding whether biological activity was part of mars history 1 http www sciencemag org cgi content full 310 5753 1439

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

a refined chronology of catastrophic outflow events in ares vallis mars abstract we investigate the geomorphology and chronology of catastrophic flooding in a major martian outflow channel ares vallis we use recently acquired stereo and colour images and derived topographic data with grid spacing of 50 m from the high resolution stereo camera hrsc onboard mars express to constrain the detailed flood geomorphology of proximal ares vallis we identify morphologic evidence for 6 distinct erosion surfaces that were likely formed by multiple episodes of catastrophic flooding these surfaces occur at distinct topographic levels exhibit multiple sets of flood grooves and contain distinct post flood crater populations crater count statistics on the flood eroded surfaces from mro context camera ctx and thermal emission imaging system themis visible images indicate that flooding was initiated during the late noachian early hesperian at 3 6 ga the morphology data confirm that the oldest flooding events occurred on the topographically highest erosion surfaces while subsequent floods abandoned the upper surfaces and continued to modify craters in the topographically lowest main channel of ares vallis into the late hesperian early amazonian 2 5 ga our results suggest that release of water to ares vallis likely occurred at repeated intervals over a long period of geological time thus supporting recent numerical modelling studies that suggest a recharging water source

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

evaluation of indian coastal response an integrated approach abstract since its separation 130 ma from the mainland the indian subcontinent has experienced major evolutionary changes a comparison of the structure evolution and tectonic elements of the east and west coast reveals characteristic differences thus while the eastern coast shows significant anomalous behaviour in all geophysical observations in contrast the corresponding observations on the western coast are relatively devoid of such anomalies in this investigation available magsat gravity electromagnetic gds and heatflow data have been utilized to search for a possible coherent cause for these different anomalies and thereby some inferences are sought to relate these causes to the geodynamics of this part of the indian plate

surficial sediments of the arabian sea abstract coarse grained low carbonate sediments with high abundances of quartz and feldspar in the northerly areas of the arabian sea close to land reflect significant terrigenous sediment in fluxes primarily from the indus river and to some extent from other sources carbonate content of sediments increases gradually from the northernmost areas to about 18 21 n and reflects the waning influence of terrigenous sediment supply southward in areas farther from significant terrigenous influences the carbonate distribution also clearly reflects bathymetric control thus whereas the caco3 content is high on ridges it becomes less than 10 at about 4800 m ccd in the arabian basin a low carbonate band extends from the areas opposite the indus river to the deep areas 2000 3000 m southward and is confined to the easternmost indus fan valley relatively high bottomwater turbidities in this valley suggest that the low carbonate band may result in part from dilutions due to the influxes of terrigenous sediments transported and deposited by deep turbid water flows although high amounts of organic matter occur in the sediments of westerly northerly and easterly areas close to land it is along the indian continental margin at 200 1500 m water depths that the highest organic carbon values 5 10 are observed however high nutrient abundances in the surface waters and high contents of opal and siliceous fossil remains in the sediments off the arabian peninsula gulf of aden clearly reflect higher biogenic productivities in this region than along the indian margin the high organic matter content in the sediments of the indian margin is primarily due to its preservation which results from the impingement of low oxygenated waters on the sea floor at 200 1500 m water depths and from the high sedimentation rates calculations suggest that the degree of preservation of organic matter along the indian margin is about 15 80 times higher than that in the region off the arabian peninsula

surface heat flow and probable evolution of deccan volcanism abstract in the light of surface heat flow observations as well as other related geological and geophysical data the origin of the deccan basalts has been examined the indian lithosphere after its detachment from gondwanaland apparently traversed a rising plume at la reunion which virtually bored through the lithosphere to emerge as the deccan trap volcanism on the surface subsequent volcanic and plutonic activity appears to have continued not only up to the oligocene as is indicated by the alkaline magmatic activity observed near the junction of the three prominent features the west coast faults the narmada son tapti lineament and the cambay graben but also up to the mio pliocene as indicated by the heat flow and gravity data over the cambay graben the dyke swarms and sills which are mostly post trappean evolved from the lithosphere after the indian plate moved away from the hot spot

late noachian to hesperian climate change on mars evidence of episodic warming from transient crater lakes near ares vallis 1 the ares vallis region is surrounded by highland terrain containing both degraded and pristine large impact craters that suggest a change in climate during the late noachian early hesperian from warmer wetter conditions to colder dryer conditions however the regional occurrence of hesperian age crater outlet channels indicates that this period on mars was characterized by episodic climate fluctuations that caused transient warming facilitating the stability of liquid water at the surface an extensive survey of the morphology and topography of 75 impact basins in the region indicates that of the largest degraded craters 4 were identified with single outlet channels that suggest the former presence of water infill these basins lack inlets indicating that water influx was likely derived from sapping of groundwater a comparison of measured crater rim heights to modeled rim heights suggests that the bulk of the depth diameter reduction on these craters was the result of infilling possibly by sediments crater statistics indicate that crater degradation and infill occurred during a short 200 ma interval in the late noachian from 3 8 ga to 3 6 ga craters that formed after 3 6 ga exhibit a near pristine morphology our results support the hypothesis of rapid climate change at the end of the noachian period however geologic relationships between the crater outlet channels and ares vallis indicate that drainage occurred only after the period of intense crater modification during the hesperian 3 5 2 9 ga this suggests a delay between the time of infill of the craters and the time of drainage

what we know about mars from its impact craters martian impact craters provide insights into formation ages of terrain units nearsurface properties and the planet s degradational history crater size frequency distribution analyses allow determination of terrain unit relative ages and extrapolation of the lunar crater chronology can provide estimates of absolute ages for these units such analyses indicate that mars has been geologically active throughout its history but it also retains extensive regions dating back to ca 4 ga higher cratering rates during the late heavy bombardment lhb helped to create the martian regolith and formation of large impact basins helped to erode the initially denser martian atmosphere and may have created the hemispheric dichotomy low global degradation rates since the end of lhb ca 3 8 ga resulted in well preserved impact crater morphologies the presence of layered ejecta blankets and central pits associated with fresh to moderately eroded craters suggests a volatile rich crust impact crater depth diameter relationships allow estimation of the vertical extent of crustal volatiles to depths greater than those probed by current spacecraft instrumentation temporal changes in subsurface ice reservoir depths are revealed by differences in layered ejecta onset diameter as a function of crater age an understanding of the morphology and morphometry of pristine impact craters facilitates efforts to determine the amount and types of degradation and the periods over which they operated impact craters therefore play a major role in unraveling the climatic and geologic history of mars

polar basal melting on mars if ice is present throughout the cryosphere anywhere on mars thermodynamic considerations suggest that it is most likely at the poles given this condition the deposition of dust and h2o at the polar surface will ultimately result in a situation where the equilibrium depth to the melting isotherm has been exceeded melting ice at the base of the cryosphere until thermal equilibrium is once again established should deposition persist the polar deposits will ultimately reach a thickness where melting will occur at their actual base at this point the cap may reach a state of equilibrium where the deposition of any additional ice is balanced by geothermal melting thermal calculations yield basal melting thicknesses that are consistent with the inferred 4 6 km thickness of the present north polar cap however in the south the deposits appear sufficiently thin 1 2 km that geothermal melting is likely to be relegated to a depth that lies well below the regolith polar cap interface similar conclusions are reached from consideration of the polar caps theoretical equilibrium profiles in the north a basal yield stress characteristic of ice at or near the melting point is indicated while in the south it appears the cap has yet to achieve the necessary height for significant deformation to occur at its base the potential importance of basal melting is illustrated through the discussion of four examples 1 the origin of the major polar reentrants 2 the removal and storage of an ancient martian ice sheet 3 the mass balance of the polar terrains and 4 the possibility of basal melting at temperate latitudes this analysis suggests that the process of basal melting may play a key role in understanding the evolution of the martian polar terrains and the long term climatic behavior of water on mars

tectonics and thermal structure of western satpura india abstract increased seismicity and occurrences of hot springs having surface temperature of 36 58 c are observed in the central part of india 74 81 e 20 25 n where the ne trending middle proterozoic aravalli mobile belt meets the ene trending satpura mobile belt earlier deep seismic sounding dss studies along thuadara sendhwa sindad profile in the area has showed mesozoic sediments up to around 4 km depth covered by deccan trap and the moho depth with a boundary velocity p n of 8 2 km s in the present study surface heat flow of 48 4 mw m 2 has been estimated based on p n velocity which agrees with the value of heat flow of 52 4 mw m 2 based on curie point isotherms estimates the calculated temperature depth profile shows temperature of 80 120 c at the basement which is equivalent to oil window temperature in mesozoic sediments and around 570 635 c at moho depth of 38 43 km and the thermal lithosphere is about 110 km thick which is comparatively higher than those of adjoining regions the present study reveals the brittle ductile transition zone at 14 41 km depth temperature around 250 600 c where earthquake nucleation takes place

evolution of temperature maturation level and realization of hydrocarbon potential in subtrappean sedimentary complex of the bombay offshore results of 1 d basin modeling abstract the modified galo program package for basin modeling is used to calculate the temperature and vitrinite reflectance distributions with depth at any time before during and after the decan trap formation an assessment of hydrocarbon generation by kerogen of type iii is carried out for burial history of probable source rocks in the subtrappean sedimentary complex of the western passive margin of india near the bombay offshore duration of trap formation is most critical and indefinite parameter in construction of maturity aureole in the subtrappean sedimentary complex the analysis in the frame of the model of continuous formation of traps suggests that a maturation level of organic matter in sedimentary rocks under the trap depends strongly on duration of the trap formation even for traps thickness of 1 5 km or more maturity level of organic matter in the rocks located on the 100 500 m below the base of the trap can be rather moderate if the trap has been formed over fairly a long time

sedimentary history and mass flow structures of chryse and acidalia planitiae mars geologic mapping and crater counting in chryse and acidalia planitiae cap reveal five major sedimentary deposits of hesperian to early amazonian age including 1 a mass flow deposited during the early hesperian near deuteronilus mensae northeast of the map region that may have resulted from the carving of kasei valles 3000 km southwest of the exposed part of the deposit 2 knobby plains material consisting of channel likely from simud and tiu valles and possibly ares and shalbatana valles and mass wasting deposits in central and eastern cap 3 material largely from maja and ares valles emplaced in at least western and southern cap outcrops in southern chryse planitia developed thermokarst 4 a thin mass flow covering much of southern chryse planitia that emanated from simud and tiu valles and 5 a thick extensive perhaps 3500 km across mass flow deposit in central and northern cap derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature various associated landforms appear to be consistent with the mass flow interpretations including lobate and linear scarps along deposit edges fractures related to desiccation of thick sediments troughs and ridges near the edges of the deposit indicative of secondary mass movement and deformation pitted domes and fissure fed flows possibly formed by sedimentary mud eruptions and longitudinal channel grooves perhaps formed by roller vortices no convincing evidence for paleoshorelines or stagnant ice sheets is found in cap these findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow channel dissection in cap elsewhere in the northern plains similar landforms are prevalent the mass flow interpretation does not require either multiple episodes of extraordinarily high water discharge rates achieved by freeing huge volumes of water from the crust repetitive recycling of immense volumes of water into highland aquifers at the heads of chryse channels or profound climate change mars pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of simud and tiu valles

heat flow in the indian peninsula its geological and geophysical implications abstract the distribution of surface heat flow in the various geological units of the indian peninsula is presented and discussed in the light of other related geodata the heat flow data show a large variation 26 to 107 mw m 2 but indicate in general a thermal regime characteristic of stable continental areas the dharwar schist belts greenstone belts and greenstone like geosynclinal piles arc characterised by low heat flow it appears very probable a that favourable conditions for the generation of the earth s crust and the melting near the surface developed at the very early stages of the earth s evolution and b that true greenstone belts which represent the relics of the primitive basic ultrabasic crust may have been more or less continuous once it is our contention that their association with low surface heat flow is primarily due to their initial evolution and growth the low heat flow values in green stone belts show a general increase in archaean proterozoic granitic and gneisic terrains the average heat flow in archaean areas is significantly lower than in proterozoic parts of the indian shield in general the average heat flow shows an inverse relation with the age of precambrian orogeny further the proterozoic geosynclinal belts in which sedimentation and mobility continued up to upper proterozoic have been found to mark the highest heat flow areas of precambrian india surprisingly the deccan traps the cretaceous paleocene basic effusives are associated with low heat flow values 40 mw m 2 the observed high heat flow in the northern part of a basin in which a full sequence of tertiary to recent sediments overlie the deccan traps has been ascribed to a shallow basic crustal miocene pliocene intrusive body the gondwanas which occur in intracratonic small isolated elongate trough like and semi elliptical depressions show a contrasting geothermal character with many zones of high surface heat flow for which there is no clear explanation at present most of the indian peninsula is comprised of three cratons the dharwar the aravallis and the singhbhum the dharwar craton appears to be associated with the lowest surface heat flow and the heat flow from the mantle and the lower crust is q r 23 mw m 2 this is followed by q r 30 mw m 2 for the aravalli craton and about 38 mw m 2 for the singhbhum craton thus for the same surface radioactivity and heat flow crustal temperatures are lowest in the dharwar craton for this craton the temperatures at the base of the crust are similar to those in the western australian shield and in the superior province of the canadian shield we further suggest that u th and k in the top radioactive layer probably do not follow the same concentration depth pattern i e the characteristic depth d for these heat producing radioactive elements is most likely different and is the main cause of a wide scatter in the values of q r for various heat flow heat production pairs within a heat flow province we demonstrate that it is not worthwhile to study the correlation of surface heat flow to the gravity anomaly in the indian peninsula without removing the effects of the pronounced indian ocean gravity low from the gravity anomalies surface heat flow q s and crustal thickness zm as obtained from dss and earthquake data show a positive slightly exponential correlation which is compatible with crustal properties and dynamics it is demonstrated that the correlation between q s and zm in precambrian shields can be positive or negative or even negligible depending upon their past geological history

hydrographs of a martian flood from a breached crater lake with insights about flow calculations channel erosion rates and chasma growth 1 the elaver vallis channels provide a unique opportunity to develop calibrated hydrographs for a martian flood groundwater filled morella crater until the enclosed lake overtopped the rim confirming that the groundwater potentiometric surface exceeded 1771 m the overtopping flow rapidly breached the crater wall catastrophically drained the lake and eroded a broad scabland and two main channels laser altimeter data were used to calculate a preflood lake volume of 2 216 1012 m3 dam breach methods were used to develop hydrographs of discharge and lake stage over time the peak discharge was in the range of 1 94 107 to 3 51 107 m3 s 1 depending on the underlying breach erosion scenario approximately 95 of the drainable lake volume discharged in 6 4 to 7 5 days the 240 m deep southern channel entirely formed in 1 to 1 7 days indicating a mean erosion rate of 0 10 to 0 17 m min 1 the volume of material eroded from the channels was 0 45 of the flood volume but the actual eroded fraction was probably greater because distant channel reaches were obliterated by the postflood growth of ganges chasma for comparison flow calculations were performed using open channel methods channel energy slopes had to be corrected for a postflood tectonic tilt in the regional surface comparing the hydrographs to the open channel calculations reveals that the northern elaver vallis channel as seen today never flowed bank full or even at half its maximum depth because the implied flows would have exceeded the peak discharges

retreat of a giant cataract in a long lived 3 7 2 6 ga martian outflow channel we describe the evolution of an similar to 600 m deep tributary outflow channel to ares vallis mars high resolution topography image analysis and crater statistics indicate that this tributary canyon developed by the upstream migration of a large similar to 300 m tall cataract during multiple flood events that span similar to 1 b y of mars history 3 7 2 6 ga issuing from hydapsis chaos these floods were initiated at a similar time and occurred over a similar time range to flooding in ares vallis suggesting a potential regional control on flood initiation and chaos formation in addition we provide evidence that cataract retreat and significant incision within the tributary canyon occurred only after a series of downcutting events within ares vallis topography data and crater statistics taken from the floor of ares vallis indicate an similar to 300 m base level drop that coincides temporally with an early amazonian ca 2 6 ga flood event and cataract formation within the tributary canyon the results both confirm the hypothesis of long term multiple flood events within martian outflow channels and demonstrate the influence of base level change on their incision

late quaternary mediterranean sapropels i on the origin of organic matter in sapropel s7 abstract at least twelve organic rich layers so called sapropels s1 s12 occur in late quaternary sediments from the eastern mediterranean organic matter in sapropel s7 organic carbon up to 11 is characterized in detail by gas chromatography gc and gas chromatography mass spectrometry gcms lipids were thus separated to obtain information about their mode of occurrence this procedure separates the lipids into three classes 1 free lipids extracted by soxhlet extraction 2 residual bound lipids extracted after saponification of the soxhlet extracted residue and 3 residual bound lipids extracted after acid treatment of the saponified residue in addition an extract was obtained after saponification of the free lipids the organic matter investigated is of a mixed marine e g dinoflagellates coccolithophorids terrigenous e g cuticles and bacterial origin with the former predominating the formation of sapropel s7 is probably caused by a combination of stagnation and high productivity both induced by a large input of fresh riverine water carrying nutrients and terrigenous organic material

hydrographs of a martian flood from the breach of galilaei crater abstract spectacular floods were spawned on mars when large craters filled to overtopping and catastrophically breached the wealth of data now available permits quantitative analysis of these ancient floods galilaei crater is examined here along with the likely sources of its water and the processes that formed tana vallis its 1 km deep outflow channel laser altimetry data stereo photogrammetry and scaled images are used to reconstruct the lake volume and the geometry of the preserved breach it is theorized that surface flows from hydaspis chaos eroded the rim and floor of galilaei crater and partly filled the basin leading to degradation of the underlying cryosphere groundwater released from a confined aquifer then slowly filled galilaei crater until the enclosed lake overtopped its rim the resulting flood breached the crater wall rapidly drained the lake and eroded tana vallis the drainable lake volume was 1 110 1013 m3 based on laser altimetry data from mars global surveyor this volume was 90 of the volume in lake superior in the great lakes using the reconstructed breach and channel geometry methods used to analyze terrestrial dam breaches were applied to produce hydrographs of lake stage and discharge peak flood discharge in tana vallis likely ranged from 1 5 to 4 7 107 m3 s 1 mean channel incision rates are estimated at 0 333 0 133 and 0 0667 m min 1 for scenarios in which tana vallis formed in 2 5 and 10 days for the 5 day breach erosion scenario stream power per unit streambed area at the time of peak discharge was estimated at 3 5 105 w m 2 the volume of material eroded to form the vallis was only 3 of the lake volume that drained in 5 days open channel calculations were performed to compare with the dam breach hydrographs for tana vallis the channel as seen today never flowed bank full or even at three fourths its maximum depth because the implied flows would have exceeded peak discharges from the crater breach i also evaluate an alternative model catastrophic ice lake collapse for the morphology and breach of aram chaos a large crater near galilaei crater that model has fundamental difficulties because of improbable assumptions and inadequate consideration of the knowledge base of terrestrial basalt hydrology the model of ice lake collapse fails to explain the breach and outflow of crater lakes like those that existed in aram chaos and galilaei crater the present analysis supports a simpler model of groundwater inflow that fills a crater to overtopping this model harmonizes with the low elevations of aram chaos and galilaei crater and is more consistent with extensive evidence of fluid breakouts in this region and with theoretical and terrestrial knowledge

martian subsurface volatile concentrations as a function of time clues from layered ejecta craters 1 martian layered ejecta morphologies are characterized using a new preservation classification system and through measurement of ejecta mobility em ratios em the ratio of ejecta extent to crater radius is believed to provide information about ejecta material fluidity during emplacement this study compares em and preservation classification to determine if subsurface volatile concentrations have changed measurably over time results from both regional and local analyses suggest that concentrations of subsurface volatiles have remained approximately constant at the depths and over the time periods recorded by these craters

geothermal studies in the hyderabad granitic region and the crustal thermal structure of the southern indian shield based on temperature measurements in three boreholes one specially drilled for the purpose and thermal conductivity determinations heat flow density values were determined for three sites in the archaean hyderabad granitic batholith a mean heat flow density value of 40 1 s d mw m 2 has been obtained the heat generation in its rocks 5 57 w m 3 is significantly higher than in average crustal rocks it has been proposed that the hyderabad batholith has a layered structure with a thin 1 km surface layer of high radioactivity these results together with the already reported data have been used to estimate the conductive steady state temperature within and at the base of the crust of the southern indian shield yielding values of the same order as found in the western australian shield

distributions and origins of clay minerals and quartz in surface sediments of the arabian sea abstract mineral distributions in surface sediments of the arabian sea north of 5 n reflect several sedimentary origins and processes smectite and quartz rich sediments occurring along the indian margin have been derived from the western regions of peninsular india in the northern and western most areas of the arabian sea sediments probably have been derived from several sources indus river iran makran region arabian peninsula and somalia these different sediment sources appear to have characteristically high amounts of quartz illite chlorite or palygorskite in addition smectite becomes a significant component in the sediments off somalia horn of africa the sediments derived from the peninsular india and indus river may have been dispersed by prevailing surface oceanic irculation in the region sediments from other sources probably have been transported by wind the sediments of the distal indus fan appear to be a mixture of sediments derived from the indus river iran makran and arabia somalia regions palygorskite clays from the arid regions of arabia somalia appear to have been transported by winds eastward to as far as the indian continental margin in the southernmost region of study relatively high kaolinite derived from the tropical soils of africa madagascar and southern india characterize the sediments

characterization of humic and fulvic acids isolated from baltic sea sediments using 13c and 1h nuclear magnetic resonance spectra abstract the 13 c and 1 h nmr spectra of marine humic and fulvic acids isolated from baltic sea sediments were obtained using the pulse fourier transform mode and cross polarization magic angle spinning techniques aliphatic structures were found to constitute a much larger fraction of the humic acids than previously expected the fulvic acids in contrast to the humic acids contain significant amounts of polysaccharide like substances the aromatic content of the humic and fulvic acids was found to be lower than expected suggesting that some of the humic substances in these five basins of the baltic sea are of marine origin