microbial sulfate reduction in deep sea sediments at the guaymas basin hydrothermal vent area influence of temperature and substrates abstract microbial sulfate reduction was studied by a 35 s tracer technique in sediments from the hydrothermal vent site in guaymas basin gulf of california mexico in situ temperatures ranged from 2 7 c in the overlying seawater to 120 c at 30 cm depth in the hydrothermal sediment sulfate reduction was measured in intact cores of hydrothermal sediment at 3 20 35 50 70 and 90 c the maximum rates of sulfate reduction were found in the upper 0 2 cm of the sediment and ranged from 32 nmol cm 3 d 1 at 90 c to 1563 nmol cm 3 d 1 at 70 c the rates of sulfate reduction rapidly decreased with depth in the upper 0 10 cm of the sediment and the maximal depth integrated rate 0 10 cm was 70 3 mmol so 4 2 m 2 d 1 at 70 c in comparison the sulfate reduction rate in nonhydrothermal sediment from the vent area was 0 85 mmol m 2 d 1 at the in situ temperature of about 3 c the high subsurface rates of sulfate reduction in the hydrothermal vent area was attributed to an enhanced local substrate availability in slurries of hydrothermal sediment incubated at 10 120 c microbial sulfate reduction extended to 102 c and different temperature groups of microbial sulfate reducers had optimum temperatures at around 34 70 and 80 88 c the overall temperature response of thermophilic sulfate reduction was similar in hydrothermal sediment sampled at different sites addition of short chain fatty acids and yeast extract to the sediment slurries stimulated sulfate reduction rates at all incubation temperatures no sulfate reduction was detected in the temperature range from 102 120 c microbial rather than thermochemical sulfate reduction could be a possible source of h 2 s in sulfide deposits with formation temperatures at about 100 c

origin and palaeomagnetism of the mesoproterozoic gangau tilloid basal vindhyan supergroup central india abstract the stratigraphic position and claimed glacial origin of the diamictitic gangau tilloid in central india have long been controversial our study shows that the 50 m thick tilloid overlies the palaeoproterozoic bijawar group with angular unconformity and forms the base of the mesoproterozoic 1200 1400 ma vindhyan semri group the tilloid contains clasts up to 1 m across virtually all of stable siliceous lithologies like those of the bijawar group supported by a fine grained haematitic matrix glacially faceted and striated clasts were not observed the tilloid displays much disruption of beds and pebble sized clasts of lamellar and nodular chert quartz underwent brittle fracture and plastic puckering during deposition values are high for sio2 68 8 85 5 and fe2o3 7 73 20 1 and low for al2o3 1 03 5 50 and other elements the composition of the tilloid is similar to that of laterites formed on sandstone bedrock thermal step demagnetisation of 91 core samples from seven sites spanning the tilloid revealed three components a low temperature tertiary component a an intermediate temperature steep downward component b and more rarely a high temperature less steep component c haematite is the likely carrier of the remanence interpreted as chemical remanent magnetisation c may be older than b and date from near the time of deposition bedding corrected c has a direction of d 161 4 i 63 2 a95 12 7 that gives a pole at 18 2 s 93 4 e dp 15 8 dm 20 0 the pole plots near 1200 ma on the australian precambrian apparent polar wander path using the veevers et al 1991 reconstruction for east gondwanaland the sedimentology composition and geochemistry of the gangau tilloid accord with deposition by continental debris flows derived mainly from a ferruginous regolith formed on sedimentary rocks zoned chert quartz bodies may have been precipitated in shrinkage cracks and voids in the lower saturated zone of the regolith and possibly also as thin beds or crusts of silica within the drainage system the inferred ferruginous weathering in the source area favours warm and humid conditions with a dry season and precipitation of silica in the regolith implies seasonal or longer wet and dry intervals debris flow activity indicates brief episodes of abundant runoff there is no evidence of glaciation production of abundant ferric iron in the source regolith implies the presence of appreciable atmospheric oxygen by 1200 1400 ma

low temperature hydrothermal maturation of organic matter in sediments from the atlantis ii deep red sea abstract hydrocarbons and bulk organic matter of two sediment cores no 84 and 126 chain 61 cruise located within the atlantis ii deep have been analyzed although the brines overlying the coring areas were reported to be sterile microbial inputs and minor terrestrial sources represent the major sedimentary organic material this input is derived from the upper water column above the brines both steroid and triterpenoid hydrocarbons show that extensive acid catalyzed reactions are occurring in the sediments in comparison with other hydrothermal guaymas basin or intrusive systems cape verde rise the atlantis ii deep exhibits a lower degree of thermal maturation this is easily deduced from the elemental composition of the kerogens and the absence of polynuclear aromatic hydrocarbons of a pyrolytic origin in the bitumen the lack of carbon number preference among the n alkanes suggests especially in the case of the long chain homologs that the organic matter of atlantis ii deep sediments has undergone some degree of catagenesis however the yields of hydrocarbons are much lower than those observed in other hydrothermal areas the effect of lower temperature and poor source rock characteristics appear to be responsible for the differences

first evidence of benthic communities based on chemosynthesis on the napoli mud volcano eastern mediterranean abstract some molluscan valves attributed to myrtea sp lucinidae vesicomya sp and another undetermined vesicomydae were sampled in 1993 cruise ttr3 leg2 and 1994 cruise um94 by coring on the top of the napoli dome a mud volcano located on the mediterranean ridge at about 1900 m of water depth these bivalves belong to an unknown apparently rich benthic community associated to the sulphides and methane rich emissions that characterize the napoli dome outside the mediterranean deep sea lucinidae and vesicomyidae are associated with cold seeps and hydrothermal vents and are known to be sustained by bacterial chemosynthetic activity based on sulphide and or methane oxidation the same explanation is given for this newly discovered deep mediterranean fauna firstly described here

carbon isotope systematics of individual hydrocarbons in hydrothermal petroleum from middle valley northeastern pacific ocean abstract individual aliphatic hydrocarbons in samples of bulk hydrothermal petroleum from middle valley odp site 858 were submitted to compound specific isotope analysis to trace their origins the c isotope compositions of the n alkanes and isoprenoid hydrocarbons means n alkanes 30 1 1 01 858a 28 3 1 7 858c and 24 8 1 4 858d isoprenoids 26 0 2 7 858c and 27 9 0 4 858d respectively reflect mixed marine and terrestrial organic matter sources biphytane from thermophiles has a 13 c value of 21 0

sedimentary geochemistry of hydrothermal vents in guaymas basin gulf of california mexico abstract surface sediments from 4 contrasting environmental settings in the southern trough of guaymas basin were analysed to determine their texture total organic matter tom p tp and n tn content as well as the spatial variation in their c n p atomic ratios in hydrothermally altered sediments particle size analysis revealed a marked spatial heterogeneity among sites cores taken at beggiatoa bacterial mats and at clam fields contained significant silt and clay content while those obtained near venting sites had sand and gravel as the main components because no fine sedimentary materials are deposited at these sites fine grain sediments were common farther away from vents high levels of organic c 3 4 to 12 4 were recorded in the upper 8 cm but no clear trends of decreasing toc with depth were noted the presence of hydrothermally generated petroleum in some cores increased the organic c content between 8 and 12 cm tn was generally high 456 3 4356 g g and sustained a significant correlation with tom r 0 834 p beggiatoa or vesicomyd clams are predominant

vent type taxa in a hydrocarbon seep region on the louisiana slope recent discoveries on the northern gulf of mexico continental slope have altered our understanding of biological and chemical processes occurring in the deep ocean a biological community of hydrothermal vent type organisms was recently discovered at the base of the florida escarpment1 where the fauna are apparently nourished by hydrogen sulphide rich hypersaline water seeping out onto the sea floor dense colonies of deep living chemosynthetic benthic organisms were first discovered during investigations of warm water anomalies along the axis of the galapagos rift in the pacific ocean in 19772 4 and this first discovery of clusters of clams tube worms and other filter feeders in the immediate proximity of warm water vents has been followed by the discovery of a number of other hydrothermal vent sites for example guaymas basin east pacific rise at 21 n the dense population assemblages at these sites are apparently restricted to small areas of the ocean floor where hydrogen sulphide rich water is escaping from spreading centres but the florida escarpment discovery indicates that these communities can also exist on passive margins here we report the discovery of dense biological communities associated with regions of oil and gas seepage on the louisiana continental slope these communities of large epi and infaunal organisms are similar to those associated with the vents of the pacific and the hypersaline brine seeps of the florida escarpment carbon isotope analyses suggest that these communities are chemosynthetic and derive their energy from hydrogen sulphide and or hydrocarbons similar communities may be widely distributed on the sea floor in other oil producing regions of the ocean

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

high molecular weight polycyclic aromatic hydrocarbons in hydrothermal petroleums from the gulf of california and northeast pacific ocean hydrothermal petroleums and heavy tars have been analyzed for polycyclic aromatic hydrocarbons pah with molecular weights greater than that of coronene 300 da samples from the hydrothermal systems in the guaymas basin gulf of california and in the escanaba trough and middle valley northeastern pacific were analyzed by gas chromatography mass spectrometry and high pressure liquid chromatography with diode array absorbance detection mass spectra and fluorescence spectra were used to characterize the compounds several large pahs with six and more rings were identified among the heavy pah production routes via one ring build up and scholl condensation are proposed to explain the observed structures the variations in pah concentrations and distributions between samples from different locales are a consequence of the hydrothermal conditions of generation migration and post depositional alteration

neoproterozoic deformation at a boundary zone between the nellore khammam schist belt and pakhal basin se india strain analysis of deformed pebbles abstract in the kinnerasani area in southeastern india the terrain boundary between the archean nellore khammam schist belt and the proterozoic pakhal supergroup overlying the dharwar bastar cratons can be observed we analyzed the mesoscopic and microscopic structural features of the highly deformed pebbles in the basal conglomerate bed of the pakhal supergroup that occurs at the terrain boundary the results of the analysis of the pebbles suggest that 1 deformation of pebbles resulted from ductile deformation during peak metamorphism 2 the mode of strain is plane strain to constrictive and maximum elongation located to be vertical and 3 the apparent stretch of the pebbles is up to 300 in the nellore khammam schist belt quartz grains constituting the quartz layer of the feldspathized gneiss folded by the last phase deformation also show vertical maximum stretching in constrictive strain this observation suggests that the deformational features at least the mode of strain during the last phase deformation is comparable to the deformation forming elongated pebbles of the pakhal conglomerate the last phase deformation structures of the nellore khammam schist belt are well observed near the terrain boundary this indicates that the pakhal deformation overprinted the rocks of the nellore khammam schist belt near the boundary and that their tectonic juxtaposition occurred during or before this deformation period because the pakhal deformation took place during or soon after the peak metamorphism of the pakhal supergroup which is known to be 1000 ma and the last metamorphism of the nellore khammam schist belt in the khammam area were reported to be 1100 ma the tectonic juxtaposition between the pakhal supergroup and nellore khammam schist belt was around 1000 1100 ma

survey of hydrothermally generated petroleums from the guaymas basin spreading center abstract the guaymas basin spreading center and hydrothermal system are generating an assortment of petroleum like bitumens by pyrolysis of organic matter in the overlying uncosolidated sediments samples collected by d s v alvin from hydrothermal fields in the southern trough exhibit large variations in the quantities and character of the solvent soluble organic materials various pyrolytic regimes combined with fluctuating thermal gradients and migration velocities may impart a compositional fractionation possibly by differential gaseous solubilization and hydrodynamic alteration of the multi component fluids the data suggest that differential condensation solidification biodegradation and water washing cause selective removal of components at the seabed many hydrothermal oils are unlike normal reservoir petroleums because they contain significant concentrations of polar material due to their rapid genesis and transport and probable solubilization or advection of polar immature components the biomarker distributions confirm high temperature pyrolysis at depth with variable entrainment of less thermally mature bitumens during transport data for shallow core samples from the northern trough indicate that those locations experienced variable influx predominantly volatiles of a low temperature pyrolysate

deep biological communities in the subduction zone of japan from bottom photographs taken during nautile dives in the kaiko project abstract twenty seven dives of the submersible nautile in the subduction zone around japan conducted in the french japanese project kaiko proved that fairly luxuriant benthic communities dominated by deep sea giant clams of the genus calyptogena family vesicomyidae were consistently present on the accretionary prism at abyssal depths benthic communities characterized by three hitherto undescribed bivalves of the genus calyptogena were found between depths of about 3800 and 4020 m at the mouth of tenryu canyon and at the top of basement swell of the zenisu ridge both situated in the eastern nankai subduction zone sporadic but discrete patches of organisms characterized by one more undescribed bivalve belonging to the genus calyptogena were observed and collected between depths of 5130 and 5960 m on the landward wall of the japan and kouriles trenches photographic inventories were prepared semiquantitatively using each series of bottom photographs taken in these areas with bow cameras of the submersible nautile observations on the sporadic but dense distribution of the clams and other characteristic associated organisms match well with the scheme that communities sustained by chemosynthetic energy sources can be present at connate water seepages in subduction zones these are to date the deepest record of benthic communities supposedly associated with chemosynthetic processes

progressive incision of the channeled scablands by outburst floods the surfaces of earth and mars contain large bedrock canyons that were carved by catastrophic outburst floods reconstructing the magnitude of these canyon forming floods is essential for understanding the ways in which floods modify planetary surfaces the hydrology of early mars and abrupt changes in climate flood discharges are often estimated by assuming that the floods filled the canyons to their brims with water however an alternative hypothesis is that canyon morphology adjusts during incision such that bed shear stresses exceed the threshold for erosion by a small amount here we show that accounting for erosion thresholds during canyon incision results in near constant discharges that are five to ten fold smaller than full to the brim estimates for moses coulee a canyon in the channeled scablands which was carved during the pleistocene by the catastrophic missoula floods in eastern washington usa the predicted discharges are consistent with flow depth indicators from gravel bars within the canyon in contrast under the assumption that floods filled canyons to their brims a large and monotonic increase in flood discharge is predicted as the canyon was progressively incised which is at odds with the discharges expected for floods originating from glacial lake outbursts these findings suggest that flood carved landscapes in fractured rock might evolve to a threshold state for bedrock erosion thus implying much lower flood discharges than previously thought

crustal processes at spreading centers recent discoveries and research on mid ocean ridges mor s in the last four years have greatly increased our knowledge of this fundamental type of plate boundary the last iugg review of mor research was in 1975 aumento et al 1975 and its omission as a topic in 1978 may have reflected a feeling that spreading centers were reasonably well understood since that time however there has been a surfeit of important new observations and exciting research and there is now a turmoil of innovative ideas about the processes which create and leave their imprint on two thirds of the earth s crust new seismic measurements have been made and interpreted as evidence for the existence of shallow axial magma chambers amc beneath intermediate total opening rate 5 9 cm yr and fast 9 18 cm yr spreading centers fig 1 yet there is controversy as to whether they are steady state whether they persist beneath slow ridges as well in the steady state what the dimensions and shape of the chamber are its relation to oceanic crustal stratigraphy and its relation to observations in ophiolites black smoker hydrothermal vents have been discovered in the pacific spewing forth 350 c fluids blackened by polymetallic sulfide precipitates this discovery is embroiled in debate as to how long the vents last whether they occur at slow spreading rates as well whether the enormous heat flux of the vents freeze the magma chamber even at fast spreading rates their influence on geochemical balances in the ocean and the value of the sulfide deposits commercially it has been found that our initial view of mor s as two dimensional linear structures has served us well as an initial working model but must be significantly modified to account for variations in tectonic volcanic and hydrothermal activity along strike as well as for episodicity of these processes deep sea drilling project dsdp samples have raised fundamental questions about formation of the magnetic source layer hydrothermal circulation and fault mechanisms along the mor spreading centers which penetrate existing lithosphere along strike as propagating rifts have modified our views of how plate boundaries reorient themselves and how v shaped magnetic and topographic trends are formed we have also found that transform faults may modify spreading center processes for some distance away from their intersections with mor s and that rigid plate transform faults may fail to develop at fast spreading centers under certain conditions resulting in en echelon overlapping of spreading centers this review will focus on these developments and several others only example references to these topics will be given in the text and many important topics will not be discussed directly e g petrology and geochemistry mantle convection research on lithosphere older than 1 m y however i have tried to compile and have included an extensive bibliography for u s research on a broader range of mor topics for mid 1978 to mid 1982 which is the main purpose of this report pre 1978 references are occasionally included where appropriate abstracts are not included

petroleum generation an easy and widespread process in hydrothermal systems an overview abstract the conversion of organic matter to petroleum products by hydrothermal activity is an easy process occurring in nature in many types of environments geologically immature organic matter of marine sediments has been shown to be altered to petroleum products by this process in the guaymas basin escanaba trough bransfield strait and atlantis ii deep and this process probably occurs elsewhere in active sedimented rift systems contemporary organic detritus and or viable microorganisms are also converted in part to petroleum like products when they become entrained by turbulent mixing into hydrothermal vent waters resulting in their instantaneous hydrous pyrolysis this latter case occurs in hydrothermal vent fields without a sedimentary cover emanating directly from oceanic ridges as for example on the east pacific rise at 13 n and 21 n and on the mid atlantic ridge at 26 n this process is probably also ubiquitous for all actively venting sediment starved oceanic ridges the hydrocarbon products generated in these areas have been compared in terms of composition organic matter sources and analogy to reservoir petroleum they represent a major carbon source for chemosynthetic assimilation by vent biota and are compositionally similar to normal petroleum

spatial distribution of diverse cold seep communities living on various diapiric structures of the southern barbados prism three sectors of the south barbados prism between 1000 and 2000 m depth were explored by the french submersible nautile chemosynthesis based benthic communities were discovered on several structures affected by diapirism including mud volcanoes domes and an anticlinal ridge the communities are associated with the expulsion of methane rich fluids which is a wide spread process in the area these communities are dominated by large bivalves and vestimentiferans which harbour chemoautotrophic symbiotic bacteria the symbiotic bivalves include two species of mytilidae and one of vesicomyidae with dominance of a methanotrophic mussel cartography of the benthic communities interpretation of thermal measurements and observation of sedimentary patterns have been used to define the life habits of each of the three species of symbiotic bivalves each species has a characteristic preference for different conditions of edaphic and fluid flow the dominant methanotrophic mussel appears to require high velocity vents and hard substratum the vesicomyids and the other species of mussel are able to take up sulfide from the sediments and so are associated with low seepages but also require soft sediment the three bivalve species are assumed successively to colonize the top of a diapiric ridge in a succession related to the temporal evolution of fluid flow and sedimentation the composition of the bivalve assemblages their densities and biomasses all differ between the several mud volcanoes and domes studied and these parameters are thought to be related to the spatial and temporal variations of fluid expulsion through the structures and the lithification processes linked to fluid expulsion one very active dome is at present colonized by an exceptionally large and dense population of the methanotrophic mussel in contrast communities in another area on the domes and volcanoes that are currently inactive were colonized by only a few living vesicomyids and mussels both associated with sulfur oxydizing bacteria and there were numerous empty shells the densities and biomasses of symbiotic bivalves were far greater in the area studied than in a deeper mud volcano field on the same prism that had been studied previously this is consistent with a report that methane production is greater in the southern region of this accretionary prism than in the northern numerous non symbiotic organisms were observed in and around the areas of the seeps some are endemic to the seep communities including some gastropods and shrimps others are either colonists or vagrants from the surrounding deep sea floor filter feeders were very abundant and some of these like the serpulids and large sponges may also be dependent on the chemosynthetic production faunistic composition of both symbiotic and non symbiotic taxa of the assemblages around these cold seeps is closely related to that reported for communities living on hydrocarbon seeps in the gulf of mexico

petroleum characteristics of the oil in a guaymas basin hydrothermal chimney abstract extensive petroleum shows have been sampled from the seabed of guaymas basin these petroleums were generated at depth by hydrothermal activity from immature sedimentary organic matter and migrated to the sea floor there the heavy ends solodify due to the temperature drop and the volatiles are emitted as plumes thus it is of interest to determine the petroleum characteristics of such oils for comparison with normal reservoir petroleums an oil saturated sample of a chimney alvin dive 1630 emitting water at 200 c was studied in contained 21 7 solvent extractable oil and 19 2 s moisture the oil has an api gravity of 27 6 a specific gravity at 20 c of 0 8891 and contains 0 99 s the astm distillation yields vol are gasoline 3 0 ibp 149 c ibp 300 f intermediates 149 315 c 300 660 f 61 0 gas oil 315 538 c 660 1000 f 21 0 and residue 538 c 1000 f 15 0 gas chromatography and ft infrared spectrometry indicate that this oil is similar to typical reservoir petroleum but with the low ends and aromatics depleted due to water washing mild thermal conditions are indicated by the absence of cracking products

magnitudes and implications of peak discharges from glacial lake missoula new field evidence and discharge calculation procedures provide new estimates of maximum late pleistocene glacial lake missoula flood discharges for two important reaches along the flood route within the spokane valley near the point of release the peak discharge probably exceeded 17 3 million m3 sec 1 downstream at wallula gap a major point of flow convergence peak discharge was about 10 2 5 million m3sec 1 flow duration was on the order of several days these are the largest known terrestrial fresh water flows consideration of these discharge values constrains models for the failure of glacial lake missoula the maximum discharges estimated here are larger than theoretical and empirical predictions of maximum subglacial jokulhlaup style releases for lake missoula we postulate consistent with geological relations in the glacial lake missoula basin and in the channeled scabland that the largest late wisconsinan missoula flood resulted from a cataclysmic failure of the impounding ice dam of glacial lake missoula this large release may have been the result of a complete rupture of the ice dam subsequent multiple flows of lesser magnitude may have resulted from repeated subglacial releases from the lake

depositional character of a dry climate alluvial fan system from palaeoproterozoic rift setting using facies architecture and palaeohydraulics example from the par formation gwalior group central india abstract the 20 m thick coarse grained clastic succession in the basal part of palaeoproterozoic par formation gwalior group has been investigated using process based sedimentology and deductive palaeohydraulics bounded between granitic basement at its base and shallow marine succession at the top the studied stratigraphic interval represents products of an alluvial fan and its strike wise co existent braided river system that possibly acted as a tributary for the fan detailed facies facies association analysis allowed identification of two anatomical parts for the fan system viz proximal and mid fan while thin proximal fan is represented by products of rock avalanche and hyperconcentrated flows with widely varying rheology the mid fan is represented by products of sheet floods and flows within streamlets the interpretation found support from palaeoslope estimation carried out on the fluvial part of the mid fan that plot dominantly within the alluvial fan field demarcated by blair and mcpherson 1994 dry climatic condition suggested from dominance of stream flow over mass flow deposition within the par alluvial fan strike wise the fan is discontinuous and juxtaposed with a braid plain system in contrast to the fluvial part of fan system the palaeoslope data from the braid plain system dominantly plot within the natural depositional gap defined by blair and mcpherson a raised palaeoslope for the river systems as suggested from proterozoic braid plain deposits around the globe is found valid for the par braid plain system as well from preponderance of granular and sandy sediments within the alluvial fan and braid plain systems and a pervasive north westward palaeocurrent pattern within the fluvial systems the present study infers a gently sloping bevelled source area in the south southeast of the basin with occurrence of steep cliffs only locally

seafloor facies related to upward methane flux within a giant pockmark of the lower congo basin the origin of the cold fluid venting from a giant pockmark within the lower congo basin has been elucidated based upon results of precise mapping submersible dives gravity coring and isotopic analyses realized under a total ifremer cooperative project zaiango and biozaire projects during four dives of the ifremer rov victor 6000 the bottom was filmed hard and soft samples were lifted from the sediment and water samples were collected with a ctd rosette system the detailed dip map shows that the 800 m wide giant pockmark is a composite feature due to the coalescence of multiple 100 m wide depressions that displays a broad range of biological mineralogical and chemical features on the seafloor leading to a seafloor anomaly recorded on the multibeam imagery methane rich fluids migrating through the sedimentary column from a buried palaeochannel clearly react with the sulphate rich circulating sea water to produce hydrogen sulphide and bicarbonate ions this situation leads to a concentrical arrangement of the sedimentary facies with methane related features in the centre and sulphide related features at the periphery this organization is correlated with high levels of methane up to 20 mol l measured in the centre of the giant pockmark responsible for the crystallization of gas hydrates at the bottom in this model the concentrical organization of mineralogical and biological features reflects a geochemical partitioning related to the peripheral progressive mixing of the methane flux

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

deep water hydrocarbon seeps in guaymas basin gulf of california abstract acoustically discovered hydrocarbon seeps along a transform fault zone on the sonoran margin of guaymas basin and in the southern trough of guaymas basin were examined and sampled during dives of dsv alvin seepage of methane and heavier hydrocarbons occurs through shallow pockmarks along the eroding crest of a steep anticline 1600 m below sea level extensive ledges of aragonite crop out around the rims of the pockmarks isotopic analysis indicates that carbonate precipitation is a result of methane oxidation seepage zones within the pockmarks support dense communities of calyptogena half buried in the mud tubeworms lamellibracheae sp have colonized many of the aragonite outcrops though the margin site is only a few kilometers from a high temperature sulfide precipitating and petroleum discharging vent system at a nearby center its structural setting is more akin to pockmarks described from continental shelves and its chemosynthetic fauna is more like that around low temperature seeps on other continental slopes and margins e g oregon u s a and japan the seep in the southern trough is a condensate type petroleum c 1 c 40 and rises as a plume from a young vent mound system about 2000 m below sea level

evidence from fluid seeps atop serpentine seamounts in the mariana forearc clues for emplacement of the seamounts and their relationship to forearc tectonics abstract the mariana forearc is a non accretionary forearc with numerous seamounts dredge hauls from these seamounts are composed primarily of serpentinite indicating a non volcanic origin in addition dredged carbonate samples reveal 1 the presence of aragonite in water depths greater than the aragonite compensation depth 2 unusual porosity and cement types 3 light carbon and heavy oxygen isotopic compositions and 4 an unusual trace element geochemistry of aragonite and calcite these mineralogic petrologic and geochemical characteristics formed the basis of a prediction that methane bearing fluids are venting from these seamounts subsequent to this prediction submersible dives on a mariana forearc seamount found and sampled chimneys seeping cool water that contains dissolved methane the serpentine substrate beneath the chimneys appears to form from cold gravitational flows of serpentine material fluid inclusion contents of chimney samples also show an earlier history of methane as well as longer chain hydrocarbons aromatics and acetate ions drilling into the flank and the summit of this seamount by the ocean drilling program during leg 125 confirmed the presence of methane other light alkanes and organic acids in the present day interstitial pore fluid of the cores the presence of aromatic compounds and organic acids if derived from the maturation of organic compounds indicates a thermogenic origin for these volatiles strontium isotopic ratios of the aragonitic chimney samples and of the present day interstitial waters range from present day seawater values to significantly lower values the strontium isotopic ratios of the pore waters within the seamount trend toward a relatively less radiogenic composition with increasing depth below the seafloor this strontium isotopic signature is probably not the consequence of near surface processes but more likely a contribution from an igneous source deeper in the lithosphere the lack of a large accretionary prism in the mariana forearc removes the complication of fluid contribution from dewatering of the prism by compression during convergence as in the oregon washington or barbados margins the organic compounds in the fluid inclusions and interstitial pore fluids as well as the isotopic and the geochemical composition of the carbonates and the dissolved constituents suggest that fluids are derived from dewatering compression and dehydration of subducted sediments and the subducting plate furthermore the composition of the fluid is influenced by thermal maturation of organics in subducted sediments as well as by a contribution from a deep igneous source

surficial evidence of fluid expulsion from the costa rica accretionary prism the nature and distribution of authigenic carbonates chemosynthetic bacterial mats and unique macrobenthic chemosynthetic communities of bivalves and tube worms are important for evaluating and reconstructing present and past fluid venting of accretionary complexes this paper describes the authigenic carbonates chemosynthetic fauna and fluid venting observed at the four tectonic regions of the costa rica accretionary wedge in february 1994 during an alvin diving program of 20 submersible dives we found no surficial evidence of highly focused fluid venting at the toe of the prism outermost 3 km as implied by the absence of authigenic carbonates and chemosynthetic fauna the absence of vent communities on the lower 3 km of the prism and the relatively elevated heat flow with respect to the adjacent incoming cocos plate langseth and silver this issue suggests diffuse rather than focused flow through the toe of the prism twelve active and relict vent sites marked by small clusters of live vesicomyid clams are localized at the bases and tops of out of sequence thrusts implicating fracture permeability as the fluid conduit in the lower slope region but upslope from the toe vast authigenic carbonates and seven active and relict vent sites marked by large dense clusters of chemosynthetic organisms predominate the largest mud diapir in the mid slope region fluid expulsion appears to be more restricted on the upper slope with only 2 small but dense vents marked by chemosynthetic fauna observed at one wall of one canyon

fault related biogenic mounds in the ceduna sub basin australia implications for hydrocarbon migration abstract the early cenozoic in the bight basin represents a transitional period from the slow to fast oceanic crust spreading of the southern ocean between australia and antarctica this period is characterised by widespread igneous activity and the occurrence of biogenic mound complexes in the proximal part of the ceduna sub basin these mound complexes thrive on local topographic highs exploiting the shut down in siliciclastic sediment supply during the eocene new interpretation of 2d and 3d seismic data from the central ceduna sub basin shows additional undrilled paleocene eocene biogenic mound complexes they display rugose morphology progradational and aggradational internal organisation and high impedance contrast with the surrounding sediments these mounds typically show a clear relationship with underlying reactivated fault segments these faults intersect potential oil mature cretaceous source rock intervals and therefore one plausible mechanism for the development of fault related mound complexes in the central ceduna sub basin relies on natural hydrocarbon seeps along faults supplying nutrients for a benthic chemosynthetic organisms and localised biogenic mound growth the presence of a sub bottom profile anomaly overlaid by a vertical water column acoustic contact in close vicinity of a mound complex support this model the occurrence of seep related biogenic mounds would validate the presence of mature source rock s and hydrocarbon charge in the central ceduna sub basin if confirmed the biogenic mounds would imply fluid migration occurrence until at least the eocene

a braided distributary system on the orinoco deep sea fan abstract a long range side scan sonar gloria survey has been made of part of the orinoco deep sea fan that abuts against the deformation front of the barbados outer ridge i e in a pre orogenic setting immediately east of the deformation front sinuous channels up to 65 m deep and 3 km wide extend downslope and become very shallow a few metres or less deep and branch into a pattern that resembles stream braiding near the foot of the slope here there is a possible suprafan lobe and an almost flat perched sediment pond dammed by a buried basement ridge in this locality many of the acoustic contrasts on the sonographs are primarily due to differences in sediment type and small scale roughness rather than to variations in slope angle possible debris flows aligned along some of the braided channels have been identified from high resolution profiles this braided system of shallow channels then converges into a single channel that overtops the dam because of their braided nature the internal structure of the resulting deposits is likely to be complex these deposits should eventually be incorporated into the barbados ridge complex in contrast to this pre orogenic setting gloria sonographs also suggest that some orinoco sediment moves down along synclinical axes of folds on the barbados ridge complex i e in a syn orogenic setting

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

from basins to rivers understanding the revitalization and significance of top down drainage integration mechanisms in drainage basin evolution abstract the top down drainage basin integration and drainage network evolutionary processes of lake overflow and aggradational spillover or aggradational piracy collectively referred to here as spillover are undergoing a revitalization in the literature to explain aspects of drainage basin evolution and transverse drainage development across the globe spillover processes are commonly unidentified or misidentified as other processes e g piracy capture via headward erosion superimposition antecedence commonly invoked arguments for stream piracy associated with headward erosion are discussed in the context of contemporary research highlighting the inefficiency of this process the term headward erosion in this context is often misconstrued and confused with headward propagating knickpoints in preexisting drainages that are actively evolving this term is therefore misused when discussing basin integration and the establishment of new transverse drainages we propose the term drainage head erosion to rectify this and recommend that headward erosion only be used when referring to real headward erosion when a preexisting stream has headward propagating knickpoints or a knickzone recent investigations have pointed to an engrained paradigm and pedagogical bias as a possible culprit for the lack of recognition of lake overflow and aggradational spillover despite this spillover is common in a variety of terrestrial and extraterrestrial settings including geomorphic and geographic settings ranging from post glacial drainage reorganization to drainage integration processes in extensional tectonic terrains the focus of this manuscript is to provide a summary of these processes as presented in the scientific literature and to highlight the revitalization of spillover in present research with focus on two prominent geomorphic settings where spillover processes commonly occur proglacial environments and extensional terrains like those of the southwestern united states

phenols in hydrothermal petroleums and sediment bitumen from guaymas basin gulf of california the aliphatic aromatic and polar nso fractions of seabed petroleums and sediment bitumen extracts from the guaymas basin hydrothermal system have been analyzed by gas chromatography and gas chromatography mass spectrometry free and silylated the oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolyzates that have migrated to the seafloor by hydrothermal fluid circulation the downcore sediments are representative of both thermally unaltered and thermally altered sediments the survey has revealed the presence of oxygenated compounds in samples with a high degree of thermal maturity phenols are one class of oxygenated compounds found in these samples a group of methyl dimethyl and trimethyl isoprenoidyl phenols c27 c29 is present in all of the seabed nso fractions with the methyl and dimethyl isoprenoidyl phenols occurring as major components and a trimethyl isoprenoidyl phenol as a minor component a homologous series of n alkylphenols c13 c33 has also been found in the seabed petroleums these phenols are most likely derived from the hydrothermal alteration of sedimentary organic matter the n alkylphenols are probably synthesized under hydrothermal conditions but the isoprenoidyl phenols are probably hydrothermal alteration products of natural product precursors the suites of phenols do not appear to be useful tracers of high temperature hydrothermal processes

influence of a turbidite deposit on the extent of pyritization of iron manganese and trace metals in sediments from the guaymas basin gulf of california mexico abstract a core collected in the guaymas basin contained an organic poor mn oxide rich and relatively fe oxide rich turbidite layer that affected the distribution of fe mn c s and trace metals results indicate that sediments not influenced by the turbidite layer achieved a 100 degree of pyritization and by extension that pyrite production is fe limited in these sediments in contrast the mud slide layer apparently supplied enough reactive fe to transfer essentially 98 of the total s present at the base of the turbidite 17 19 cm to the pyrite reservoir c s ratios showed rapid decreases with depth from a high of 38 close to the sediment water interface to minimum values of 2 8 at the lower limit of the turbidite layer a ratio equal to the average c s value of normal marine modern sediments where concentrations of organic c and pyrite supposedly have attained quasi steady values a significant part of the reactive mn was associated with carbonates 41 12 and to a much lower degree with pyrite 2 7 1 2 the turbidite layer is currently showing a depletion of mn relative to the host sediment it is possible that mn a major metal constituent in these sediments was initially present in high concentrations in the mud slide but was eventually mobilized and transferred either to the water column or to the sediments immediately below the turbidite layer metals associated with this element probably followed the same path affecting their incorporation into pyrite the turbidite layer apparently affected the distribution of most of the trace metals associated with pyrite except maybe cd pb and to a certain extent cr however cu cr zn ni and co were all found to be highly pyritized 80 in the sediments of the guaymas basin

geomorphology of ma adim vallis mars and associated paleolake basins 1 ma adim vallis one of the largest valleys in the martian highlands appears to have originated by catastrophic overflow of a large paleolake located south of the valley heads ma adim vallis debouched to gusev crater 900 km to the north the landing site for the spirit mars exploration rover support for the paleolake overflow hypothesis comes from the following characteristics 1 with a channel width of 3 km at its head ma adim vallis originates at two eastern and western gaps incised into the divide of the 1 1 m km2 enclosed eridania head basin which suggests a lake as the water source 2 the sinuous course of ma adim vallis is consistent with overland flow controlled by preexisting surface topography and structural control is not evident or required to explain the valley course 3 the nearly constant 5 km width of the inner channel through crater rim breaches the anastomosing course of the wide western tributary the migration of the inner channel to the outer margins of bends in the valley s lower reach a medial sedimentary bar 200 m in height and a step pool sequence are consistent with modeled flows of 1 5 106 m3 s peak discharges were likely higher but are poorly constrained by the relict channel geometry 4 small direct tributary valleys to ma adim vallis have convex up longitudinal profiles suggesting a hanging relationship to a valley that was incised quickly relative to the timescales of tributary development 5 the eridania basin had adequate volume between the initial divide and the incised gap elevations to carve ma adim vallis during a single flood 6 the eridania basin is composed of many overlapping highly degraded and deeply buried impact craters the floor materials of the six largest craters have an unusually high internal relief 1 km and slope 0 5 1 5 among degraded martian craters which are usually flat floored long term fluvial sediment transport appears to have been inhibited within these craters and the topography is inconsistent with basaltic infilling 7 fluvial valleys do not dissect the slopes of these deeper crater floor depressions unlike similar slopes that are dissected at higher levels in the watershed these characteristics 6 7 suggest that water mantled at least the lower parts of the eridania basin floor throughout the period of relatively intense erosion early in martian history the lake level increased and an overflow occurred near the close of the noachian age determined using 5 km crater counts initially the eridania basin debouched northward at two locations into the intermediate basin a highly degraded impact crater 500 km in diameter as this intermediate basin was temporarily filled with water erosion took place first along the lower northern reach of ma adim vallis debouching to gusev crater the western overflow point was later abandoned and erosion of the intermediate basin interior was concentrated along the eastern pathway subsequent air fall deposition impact gardening tectonism and limited fluvial erosion modified the eridania basin region so evidence for a paleolake is restricted to larger landforms that could survive post noachian degradation processes

oil source rock correlation of the lower paleozoic petroleum system in the baltic basin northern europe the correlation of lower paleozoic marine source rocks with reservoired oils by biomarkers is complex because of the uniform early phanerozoic biomass bacteria and algae and the lack of land plant and animal input accordingly the main source rocks for the most prolific oil province in the baltic basin are still a matter of debate the 10 source rocks and 15 oil samples from 5 northern european countries bordering the baltic sea basin were analyzed by gas chromatography gc with flame ionization detector gc mass spectrometry gcms and gcms ms to detect acyclic isoprenoids and aliphatic aromatic and nitrogen sulfur and oxygen biomarkers chemometric tools were applied to screen for meaningful source and age related biomarkers and to highlight genetics extended tricyclic terpane ratios c24 tetracyclic terpane c26 tricyclic terpane ratios and relative c29 sterane concentrations are considered the most promising biomarkers in differentiating llandovery shales from cambrian to ordovician alum shale and for correlation with expelled oil the uranium irradiation related c26 c28 triaromatic steroid concentrations provide possible distinguishing criteria for the source potential of the different alum shale units enhanced oil maturation by volcanic intrusion is highlighted by sterane biomarkers and polycyclic aromatic hydrocarbons the alum shale is here considered the main source rock for oil accumulations in lower paleozoic reservoirs of the baltic basin oil seepage occurring in ordovician limestone was mainly generated by the middle cambrian alum shale and middle cambrian sandstone reservoirs were mainly sourced by upper cambrian and lower ordovician alum shale with higher maturity considerations about the assessment of migration distance are based on carbazole concentrations and c29 sterane isomerization advanced studies to unravel detailed lower paleozoic oil source rock correlations are based on meaningful biomarkers offer approaches to significantly reduce the exploration risk in this area and could be applied to similar early paleozoic petroleum systems in other basins

igneous activity and organic maturation in the midland valley of scotland abstract the general relationship of erich stach s research work to the effects of igneous activity on organic maturation is briefly considered the geological history of the midland valley of scotland is then reviewed as a graben which developed in devonian old red sandstone times and continued to do so as lithospheric tensional stretching was maintained throughout the carboniferous a significant factor in relation to the development of organic maturation was the widespread igneous activity that persisted throughout much of upper palaeozoic times calc alkaline volcanic rocks are a major feature within the molasse type deposits of the old red sandstone after a period of quiescence in later old red sandstone times the continuing tensional stretching initiated or rejuvenated major crustal fractures extensive volcanic sill and dyke activity exercised an important influence on the predominantly shallow water deltaic deposits of the carboniferous alkaline olivine basalts were erupted in the early carboniferous while volcanic activity in the later carboniferous was essentially phreatic two major intrusive episodes occurred the first of alkaline sills in early to mid carboniferous times which were closely related to volcanic plugs and eruptive centres the second in post westphalian times when tholeiitic sills and dykes with no known relationships with any extrusive rocks were injected the effects of this igneous activity on organic maturation can be considered under four headings 1 1 although the general development of maturation of carboniferous organic matter which includes many coal seams and oil shales was controlled to some degree by burial history the regional pattern of igneous activity was also influential thus there is a gradual increase of coalification from east to west in the midland valley which corresponds with an increasing thickness of volcanic pile in the central and westerly parts of the graben suggesting that there may have been a greater regional heat sink in the west during the carboniferous the level of coalification is nowhere particularly high except where affected by intrusions and regional reflectance gradients generally vary between r oil vitrinite 0 2 km to 0 4 km without displaying any consistent pattern 2 2 the post westphalian tholeiitic quartz dolerite midland valley sill which underlies most of the central and eastern parts of the graben has produced extensive reflectance thermal aureoles in the organic matter above and below the intrusion the olivine dolerite and teschenite sills of namurian early westphalian times many of similar thickness to the quartz dolerite intrusions fail to produce significant reflectance thermal aureoles this major difference in organic matter response to the intrusions can only be explained in terms of the initial rank level of the organic matter differences in degree of compaction of the sediments and particularly in the amount of water the sediments contained at the time of intrusion 3 3 maturation of organic matter closely associated with extensive surtseyan type volcanic activity in the eastern part of the graben displays no relationship to the regionally developed coalification in associated sediments although some vitrinite clasts in the pyroclastic deposits have had their reflectances raised to meta anthracitic rank reflectance levels of clasts in tuffs and agglomerates are generally not much raised above the regional reflectance level suggesting incorporation of organic matter in ash streams in which water was an important cooling and protective component 4 4 the close relationship of organic matter of all kinds with volcanic and intrusive igneous rocks has led to a marked increase of parent polycyclic aromatic hydrocarbons pah in the aromatic fractions of organic extracts the source of these hydrocarbons is the combustion and or pyrolysis of organic matter caused by the high temperatures of the igneous materials whether volcanic or intrusive these pah may be directly generated or absorbed from the surrounding environment

composition and spatial organization of a cold seep community on the south barbados accretionary prism tectonic geochemical and sedimentary context abstract deep faunal assemblages were observed on cold seeps between 1000 and 2000m depth along the southern termination of the barbados accretionary prism during the caracolante ii and diapicar cruises faunal composition and microdistribution of a cold seep community were analyzed at one site using deep sea photographs and seismic 3 5 kz profiles the community is dominated by large mussels up to 20cm long possibly related to the genus bathymodiolus tiny vesicomyid clams and vestimentiferan clusters in which animals are up to 2m long there is a high density of sponges three species bryozoans and gorgonians other taxa occasionally associated with this assemblage include galatheid crabs anemones holothurians and possibly pennatulaceans which are numerous at boundaries of the site a typical deep sea fauna of fish asteroids and ophiuroids is also scattered about the vicinity this seep community is distributed as a band of discontinuous colonies 40 50m in width and more than 10km in length living colonies alternate with accumulations shells and bare areas the substratum is hard mud covered by a ferrugineous crust and cemented by carbonates the early diagenetic character of the bottom and the occurrence of biological assemblages indicate that seepages of sulphur and or methane which have been revealed along the decollement zone of the barbados prism must diffuse through the sea floor these biological and geological features are located on the crests of ne sw anticlinal ridges and mud volcanoes which have been built by diaprism

generation of short chain acid anions in hydrothermally altered sediments of the guaymas basin gulf of california an initial investigation of the concentration distribution of short chain organic acid anions in hydrothermally altered sediments of the guaymas basin reveals the presence of high concentrations of acetate and propionate relative to normal marine sediments acetate and propionate concentrations appear to vary as a function of sediment temperature and reach concentrations 1100 and 200 m respectively at temperatures 100 c as in previously studied oil field formation waters these acid anions probably play a key role in the generation of co2 and hydrocarbons gases hydrogen ion ph buffering the complexing of aqueous ions and mineral dissolution and precipatation at temperatures 100 c these and other acid anions should be important substrates for heterotrophic bacterial processes including sulfate reduction

sediment instability related to fluid venting in miocene authigenic carbonate deposits of the northern apennines italy chemosynthetic carbonates identified by isotopic palaeoecological and sedimentological features are concentrated in middle late miocene satellite and foredeep deposits of the northern apennines chemoherms in the foredeep are hosted in thick pelitic intervals probably deposited in intrabasinal structural highs which are entirely or partly involved in large slumps in many cases associated with extrabasinal slides sediment textures in carbonates and in the enclosing foredeep pelitic sediments indicate a link between hydrocarbon fluid venting sediment deformation and mobilisation and tectonics the intensity and style of fluid release phases directly influenced chemoherm typology and also determined overpressure conditions in low shear strength pelitic sediments favouring sediment mobilisation and influencing slope instability which widely affected the apennine foredeep chemosynthetic carbonates are associated with sites of tectonically fractured and compressed sediments in the apennine foredeep thrust belt system thus indicating a relation with the tectonic loading of the apennine thrust sheets which favoured fluid expulsion along forerunner faults possible gas hydrate contributions to fluid expulsion processes are discussed based on sediment textures compared with modern vent areas finally sediment instability may have facilitated a large amount of fluid escape thus stopping carbonate precipitation

topography of mars from global mapping by hrsc high resolution digital terrain models and orthoimages characteristics and performance abstract we report on the results of the mars express high resolution stereo camera hrsc experiment pertaining to one of its major aims mapping the surface of mars by high resolution digital terrain models dtm up to 50 m grid spacing and orthoimages up to 12 5 m resolution we introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation we also address the performance characteristics of the mapping project related to different aspects of internal accuracy accuracy with respect to the global reference system and regional aspects using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data a mean precision of the resulting 3d points of about 12 m is obtained exceeding the mean ground resolution of the stereo images using mars orbiter laser altimeter mola data the hrsc models are firmly tied to the global reference system at the scale of the hrsc dtm grid spacing in the lateral dimension and to within few meters vertically hrsc high resolution dtms are typically generated using a grid size of about 2 times the mean ground resolution but usually not larger than 3 times the mean ground resolution and not smaller than 3 times the precision of the integrated 3d points derived from stereo image analysis statistically every grid cell is based on at least one measured 3d point thus horizontal dtm resolution is well established with regard to the precision and density of the derived 3d points while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued comparison with the dtm derived from mola data allows us to identify specific advancements related to this updated view of martian topography we also address the mapping performance of hrsc in comparison to mola with respect to latitude and to different surface types and morphologies finally comparison with mola highlights typical complementarities of the two different approaches for mapping planetary surfaces

hot fluids burial metamorphism and thermal histories in the underthrust sediments at iodp 370 site c0023 nankai accretionary complex abstract drilling during international ocean discovery program iodp expedition 370 at site c0023 encountered instances of hydrothermal mineralization from 775 to 1121 m below seafloor fluid inclusion homogenization temperatures measured on barite veins within this interval indicate precipitation from fluids with temperatures up to 220 c and salinities ten times higher than interstitial water 16 25 c f 2 8 3 6 wt nacl patches of stratabound mineralization rhodochrosite calcite barite and anhydride are largely confined to the vicinity of veins and have vertical thicknesses and extents that can be explained by precipitation within the thermal aureoles of veins thermal maturities measured on petroleum biomarkers in underthrust sediments record a rise from pre oil window to early oil window thermal maturities basin models show that increases in thermal maturity can be explained by burial metamorphism and kinetic based calculations suggest that hot fluids would only have had a minimal effect on hydrocarbon generation however the movement of hot fluids still has geochemical implications and creates a complex thermal history where both short duration localized heating within fracture zones at hot temperatures 200 c for less than 1 yr and heating during burial over long durations 80 110 c for 0 5 2 myrs need to be considered

ketones in hydrothermal petroleums and sediment extracts from guaymas basin gulf of california the polar compound nso fractions of seabed petroleums and sediment extracts from the guaymas basin hydrothermal system have been analyzed by gas chromatography and gas chromatography mass spectrometry the oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolysates that have migrated to the seafloor by hydrothermal fluid circulation the downcore samples are representative of both thermally unaltered and thermally altered sediments the survey has revealed the presence of oxygenated compounds correlated with samples exhibiting a high degree of thermal maturity several homologous series of related ketone isomers are enriched in the interiors of the hydrothermal vent samples or in hydrothermally altered sequences of the downcore sediments dsdp holes 477 and 481a the n alkanones range in carbon number from c11 to c33 with a cmax from 14 to 23 distributions that are similar to those of the n alkanes the alkan 2 ones are usually in highest concentrations with lower amounts of 3 4 5 6 7 and higher alkanones and they exhibit no carbon number preference there is an odd carbon number preference of alkanones observed for downcore samples the alkanones are enriched in the interiors of the hydrothermal vent spires or in downcore hydrothermally altered sediments indicating an origin at depth or in the hydrothermal fluids and not from an external biogenic deposition minor amounts of c13 and c18 isoprenoid ketones are also present simulation of the natural hydrothermal alternation process by laboratory hydrous pyrolysis techniques provided information regarding the mode of alkanone formation hydrous pyrolysis of n c32h66 at 350 c for 72 h with water only or water with inorganic additives has been studied using a stainless steel reaction vessel in each experiment oxygenated hydrocarbons including alkanones were formed from the n alkane the product distributions indicate a reaction pathway consisting of n alkanes and olefins as primary cracking products with internal olefins and alkanones as secondary reaction products hydrous pyrolyses of messel shale spiked with molecular probes have been performed under similar time and temperature constraints to produce alkanone distributions like those found in the hydrothermal vent petroleums

geochemical study of hydrothermal core sediments and rocks from the guaymas basin gulf of california abstract a geochemical study of core sediments from the guaymas basin was undertaken by x ray analysis and showed minerals such as barite gypsum wurtzite chalcopyrite marcasite galena and calcite the random relation between metal concentration and core depth apparently reflects the chages in hydrothermal activity mineral grains with holes and cavities were observed by sem photomicrography these holes are probably due to degastification of the samples which can be related to the presence of the guaymas basin is due to active extensional tectonics the associated seismic activity in the southern rift valley and the high rate of sedimentation

hydrothermal petroleum generation in red sea sediments from the kebrit and shaban deeps abstract petroleum impregnated sediments and massive sulfides have been found in two deeps of the northerns red sea biological marker distributions in extracts and polar fraction degradation products were analyzed in order to elucidate the source of the petroliferous material two organic phases could be distinguished according to their source and maturity the amounts of n alkanes show a marked decrease with depth whereas the concentrations of various branched and cyclic hydrocarbons increase resulting in a humpof unresolvable compounds in a depth as shallow as 300 cm changes in concentrations and distributions of hopanoids in the kebrit deep sediments indicate a rapid increase of maturity with depth the deepest core section 300 cm and the masive sulfide reveal comparable maturation indices typical for mature oils by chemical degradation of the polar fractions a series of c 40 isoprenoids was obtained which reveals a considerable contribution from methanogenic and thermophilic archapbacteria to the immature organic matter the data suggest that petroliferous material ofthermogenic origin migrates through the younger sequences superimposes the autochthonous organic substances in the sediments and furthermore forms asphaltic impregnations in the massive sulfides

hydrothermal petroleum at the seafloor and organic matter alteration in sediments of middle valley northern juan de fuca ridge abstract sediments from high heat flow areas of middle valley northern juan de fuca ridge contain traces of bitumens with insignificant amounts of thermogenic components and mainly lipid material which has experienced accelerated diagenesis these sediments have been exposed to mild hydrothermal conditions 50 120 c based on their bitumen compositions the hydrothermal bitumen in a barite alteration products the aliphatic fraction represents the mildly transformed and immature matter and the major polynuclear aromatic hydrocarbons are the high temperature constituents 300 c the 14c age of this bitumen is about 29 000 abp reflecting rapid organic carbon cycling

origin of petroliferous bitumen from the buyuk menderes gediz geothermal graben system denizli saraykoy western turkey abstract the kb 5 well is located at the intersection of the geothermally active menderes and gediz graben systems in western turkey significant volumes of petroleum like material plm with its associated thermal water 120 c erupted onto the surface during drilling from a depth of 120 132 m i e from the claystone and marl rich early to middle pliocene kolonkoya formation the purpose of this paper is 1 to characterize this plm 2 to assess the source characteristics from which the plm was likely generated and 3 to recognize the generation mechanism considering the geothermal gradual versus the hydrothermal rapid processes analytical organic geochemistry using thin layer chromatographic separation followed by gas chromatography mass spectrometry gc ms was carried out the plm is composed primarily of polar nso compounds asphaltenes 77 this feature is similar to hydrothermal petroleums e g calcite springs yellowstone national park wyoming the plm shows n alkanes ranging from n c 19 to n c 38 i e with a maximum at n c 30 but n alkanes are depleted in n c 19 an absence of acyclic isoprenoids pristane and phytane and considerably large ucm unresolved complex mixture indicate that the plm has been subjected to a moderate degree of alteration possibly by the accompanying hot geothermal waters the source specific biomarkers i e low c 29 nh c 30 h ratio presence of gammacerane and 18 h oleanane high c 35 c 34 homohopane ratio and c 29 sterane concentration n c 28 n c 27 n c 29 c 28 27 29 r steranes c 29 r c 27 r suggest that the plm is a petroleum and was most likely generated from a tertiary source rock with a carbonate clay rich lithology the source organic matter was predominantly terrestrial and bacterial detritus deposited in relatively saline anoxic environmental conditions maturity sensitive biomarker parameters i e t m t s c 29 sterane 20 s 20 s 20 r 0 35 c 32 hopane 22 s 22 s 22 r 0 57 low diasterane regular sterane ratio correspond to a maturity level of approximately 0 50 0 60 r o this level of maturation could not be reached by such a young upper miocene lower pliocene and shallow sedimentary column max 600 m in the absence of instantaneous hydrothermal activity pahs are not detectable but series of alkylbenzenes alkyltoluenes alk 1 enes and triaromatic steranes are present the lack of organic richness and maturity in the drilled section of the kb 5 well indicates that the petroleum was generated in the deeper sections of the formation the temperature profile of the well and composition of the hydrocarbons in the petroleum suggest that the temperature of the hydrothermal activity during hydrocarbon generation was

precambrian sedimentary sequences of india their geochronology and correlation abstract there are several sedimentary sequences in india which show little or no metamorphism among them the most ancient appear to be the bijawar and gwalior groups older than 1800 ma and the cuddapah supergroup 1720 1200 ma old the kolhan group is possibly ca 1530 ma old the sedimentation in the vindhyan supergroup ranges from 1400 550 ma the pakhal supergroup appears to be older than 1275 ma and the sedimentation in the chhattisgarh group possibly started ca 650 ma ago

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

an association between organic matter and localised prehnite pumpellyite alteration at builth wells wales u k metcalfe r banks d and bottrell s h 1992 an association between organic matter and localised prehnite pumpellyite alteration at builth wells wales u k chem geol 102 1 21 the builth volcanic group of the builth wells ordovician inlier wales is a sequence of basic intermediate lavas and volcaniclastics which shows a unique association between pyrobitumen and localised domainal calc silicate alteration the pyrobitumens occur in calcite veins and disseminated throughout alteration domains which form haloes to these veins the pyrobitumens were emplaced by ordovician hydrothermal fluids which were also responsible for the domainal alteration combined petrographic gas chromatography and stable isotopic studies show that light organic gases c2 c5 were liberated into the hydrothermal fluids by devolatilisation of liquid petroleum to form the pyrobitumens these light organic gases mixed with methane characterized by 13c 13 o which was already present in the fluids this methane was most likely mantle derived or produced from inorganic synthesis the organic content of the fluids exerted an important control on the inorganic secondary assemblages a similar control of inorganic assemblages by organic matter might possibly occur deep within modern petroleum bearing hydrothermal systems such as the guaymas basin and escanaba trough hydrothermal systems

hydrocarbons in waters and particulate material from hydrothermal environments at the east pacific rise 13 n the fast spreading east pacific rise at 13 n consists of an active circulating hydrothermal system with associated massive sulfide deposits and large communities of animals clustered around hot smokers the main food source of these benthic organisms is supplied by symbiotic chemosynthetic activity of sulfur oxidizing bacteria biomarker lipids such as hydrocarbons were analyzed to describe their sources and composition and also the relationships among microorganisms biological communities and dissolved and particulate organic materials in this productive area the organic matter of vent waters is both quantitatively and qualitatively different from the non vent bottom water dissolved hydrocarbon concentrations in warm water t 15 c from fissures in basalts and hot clear water t 250 c from smokers are 100 and 400 times more concentrated respectively than the water outside active areas the biomarker compounds from hot clear water are characteristic of thermally mature organic matter as indicated by the 17 h 17 h hopane series and the dominance of 5 h 14 h 17 h steranes over the 5 h 14 h 17 h 20r steranes i e the biologically inherited configuration the dissolved hydrocarbons from the warm waters may be correlated with bacterial lipid residues as indicated by the presence of isoprenoid hydrocarbons pristane phytane and low molecular weight cyclic hydrocarbons the water column samples collected near hydrothermally active areas contain bicyclic alkanes with drimane and rearranged drimane skeletons and mature biomarkers 17 h hopanes and steranes these components probably derived from thermally altered microbial sources the dissolved lipid matter is found to be degraded more rapidly by microbial activity and thermal processes especially in the warm water effluent and in the water column around hydrothermal vents than the lipids of the particulate matter

geochemical and biogeochemical observations on the biological communities associated with fluid venting in nankai trough and japan trench subduction zones we have studied the compositions and structure of the lamellibranchiacalyptogena sp associated with fluid venting in subduction zones off japan the gills of thecalyptogena are the habitat of symbiotic bacteria which develop owing to chemoautotrophy they most probably assimilate hydrogen sulfide methane and or carbon dioxide and reduce nitrogen the isotopic budget of methane uptake enables to establish the thermal diagenetic origin of the light hydrocarbons brought by the upwelling fluids the microscopic examination of thin sections of the bacteria enables to establish that their membranes are compatible with uptake of inorganic nutrients and to establish relations with the metabolism of archeobacteria

gold in sea floor polymetallic sulfide deposits bulk chemical analyses of 48 samples of hydrothermal precipitates from seven polymstallic sulfide deposits at sea floor spreading centers in the eastern pacific reveal distinct patterns of gold enrichment high gold contents are found in samples from two sulfide deposits the axial seamount 45057 n 130002 w and the southern explorer ridge 49045 6 n 130016 2 w a large 160 kg sample composed of silica barite and sphalerite from the top of the axial seamount deposit gives analyses up to 6 700 ppb au averaging 4 900 ppb au similar material from the southern explorer ridge gives analyses up to 1 500 ppb au averaging 660 ppb au detailed mineralogical studies together with bulk chemical analyses of a wide range of samples from these two sites reveal strong elemental associations and paragenetic controls on gold deposition gold at concentrations of about 200 ppb is associated with high cu 1 wt and mo up to 470 ppm at concentrations 800 ppb with high zn 10 wt ba 3 wt and sio 20 wt and at concentrations 1 200 ppb with high pb 0 1 wt ag 100 ppm as 300 ppm and sb 50 100 ppm samples with the highest gold values from both locations contain late sinterlike low temperature sulfosalts of pb as sb ag and s in a matrix of amorphous silica these sulfosalts are the probable repositories of the gold published analyses of au poor 300oc cu fe rich sulfides and subsequently remobilized by late sustained low temperature 250oc fluids and concentrated in sio ba zn rich precipitates near the surface suitable fluid chemistry is required to mobilize the gold and a favorable precipitation mechanism is needed to concentrate it these observations could explain the occurrence of high gold concentrations in selected ore types of some ancient massive sulfide deposits on land

a large paleolake basin at the head of ma adim vallis mars at 8 to 15 kilometers wide ma9adim vallis is one of the largest valleys in the martian highlands although a groundwater source was previously suggested the channel originates at a spillway in the divide of a 3 000 000 square kilometer closed drainage basin the interior morphology of this source basin including likely shoreline features following topographic contours suggests that ma9adim vallis was created through catastrophic overflow of a 1 100 000 square kilometer highland lake the size constant levels and interior morphology of three regional paleolake basins require a warmer paleoclimate and a long term recharged stable highland water table more than 3 5 billion years ago

hydrocarbons associated with hydrothermal minerals vent waters and talus on the east pacific rise and mid atlantic ridge two active hydrothermal vent sites on the east pacific rise epr at 13 n and 21 n have similar biogeochemicals they are characterized by large animal communities surrounding massive porous mixed mineral e g sulfide edifices venting hot water 200 350 c as black smokers an analogous vent system on the mid atlantic ridge mar at 26 n has also been studied sediment talus mound mineral and water samples from these areas were analyzed in terms of biological marker lipids such as normal and isoprenoid alkanes polynuclear aromatic hydrocarbons triterpanes steranes and fatty acids to describe their sources bacterially mediated transformation products and alteration by hydrothermal fluids the mixed interior exterior of a chimney at 21 n on the epr shows a series of iso and anteiso alkanes which are known constituents of high wax crude oils these alkanes coupled with the absence of triterpanes and steranes seem to indicate a higher temperature water soluble fraction from hydrothermal pyrolysis which is unfavorable for the preservation of the biomarkers chimney fragments with tube worm casts at 21 n contain products that are characteristic of immature biodegraded organic matter as indicated by microbial markers branched c15 and c17 fatty acids and low thermal alteration which enhanced formation of cholestene isomers and diacholestenes in comparisons a metalliferous sediment and sediment trap particles at 13 n on the epr contain a biomaker mixture namely recent biomarkers derived from early diagenetic transformations of biogenic compounds sterols squalene and more mature components 5 h 14 h 17 h steranes 20 r 20 s dominant 17 h hopane series both having the same origin hydrocarbons isolated from hydrothermal anhydrite chalcopyrite and sphalerite enriched samples from 26 n on the mar exhibit a high degree of thermal maturation compared to an fe oxide enriched sample as evidenced by the high abundance of low molecular weight n alkanes ranging from c14 to c25 with a broad distribution of naphthenes all these trace hydrothermally derived petroleums contain polycyclic aromatic hydrocarbons pah the fe oxide enriched sample has a lower content of pah than the other mineral samples however benzopyrenes and coronene are present at significant levels and a series of mature triterpanes is also detectable these trace levels of petroleum with the associated biomarkers and pah strongly suggest generation from contemporary organic detritus by hydrothermal activity and subsequent association with the minerals talus vent fluids and ambient water

a multidisciplinary study of middle miocene seep carbonates from the northern apennine foredeep italy several pelitic intervals are intercalated at various levels within the marly arenaceous turbiditic successions of the middle miocene northern apennine foredeep they range in thickness from 30 to 200 m and represent sedimentation on top of ephemeral structural highs related to blind faults sediments are made up of hemipelagites and fine grained turbidites and include 13c depleted carbonates related to the rising of methane rich fluids hydrocarbon seep carbonates large portions of pelitic intervals are involved in chaotic masses by soft sediment deformation slumps slides intraformational breccias revealing an intense sediment instability during middle miocene a stratigraphic mineralogic and geochemical study was conducted on two of these pelitic intervals castagno d andrea mt citerna in order to reconstruct carbonate development the composition of fluids and to document the connections between fluid seepage and syndepositional tectonics this multidisciplinary approach has allowed us to discriminate between the two examined pelitic intervals in terms of age depositional rates and conditions organic carbon and post depositional processes seep carbonates are characterized by chemosymbiotic fossil communities autoclastic fractures and brecciation carbonate bodies show complex facies relationships as indicative of different stages in chemoherm growth the compositional study evidences the peculiar chemistry of chemoherm carbonates calcite low in mg and sr compared with carbonates in associated enclosing pelites and with modern chemoherms in general the non carbonate components within the chemoherms are enriched in detrital minerals and depleted in phyllosilicates with respect to the enclosing pelites the mineralogical changes in the clay component within the brecciated unit of the castagno d andrea chemoherms suggest authigenic precipitation of the mg rich phases isotopic analyses show the distinct carbon signature in the chemoherms from the two examined intervals castagno d andrea chemoherms more depleted from 15 8 up to 41 3 pdb than mt citerna from 5 2 up to 16 7 and the transitional 13c depletion trend observed moving from chemoherms to the enclosing pelites moderately depleted and te bouma sequence turbidites in the range of marine carbonates a slight but significant enrichment in 18o up to 1 4 pdb is observed for all chemoherms when compared to values of carbonate phases present in enclosing pelites geochemical data indicate that the brecciated facies of seep carbonates are related to an explosive release of gaseous fluids probably associated with the rise of deep hypersaline fluids

geophysical survey of a mud volcano seaward of the barbados ridge accretionary complex a detailed geophysical investigation that included multibeam bathymetry 3 5 khz channel and single channel seismic profiles 20 heat flow measurements and four piston cores was made of a mud volcano located about 8 km seaward of the toe of the barbados ridge accretionary complex in the northern guiana basin the material erupted from the volcano covers an oval area about 3 9 km with its long axis oriented e w roughly perpendicular to the deformation front a flat topped mound on the western side of the feature is the currently active center acoustic stratigraphy suggests that mud volcanism began at the site about 200 000 ma a piston core taken on the flank of the active mound sampled deposits erupted 20 000 30 000 ma that contain late miocene nannofossils heat flow on the active mound is 4 times that in the surrounding basin one dimensional modeling of this anomaly supports a low level continuing flux of mud and water at rates of 2 5 cm yr the mud volcanism appears to have arisen from the combined action of overpressured water that comes from beneath the accretionary prism and existing overpressures in the oceanic section large east west trending basement escarpments underlie the two known mud volcanoes seaward of the barbados ridge accretionary complex and they probably play an important role in developing vertical pathways for fluid to escape and in determining the location where mud volcanism starts

the permian kupferschiefer of southwest poland a geochemical trap for migrating metal bearing solutions abstract the ore grade cu mineralization in southwest poland is associated with the presence of the rote faule zone that overlies the contact of saxothuringian and rhenohercynian zones in these areas the soluble organic matter in the kupferschiefer is altered strongly saturated hydrocarbons and alkylated aromatic compounds are depleted significantly in comparison to non altered shale samples of a similar maturation instead unsubstituted di and tricyclic aromatic hydrocarbons are the dominant components of the extractable bitumen the observed alteration points to late diagenetic oxiadtion reactions caused by upward migrated metalliferous solutions moreover polycyclic aromatic hydrocarbons pah associated with polycyclic aromatic sulphur hydrocarbons pash are abundant in some samples these compounds are considered to originate from the underlying carboniferous strata and were carried upward to the kupferschiefer zone which acted as a geochemical trap

mosaicking of global planetary image datasets 1 techniques and data processing for thermal emission imaging system themis multi spectral data 1 the mosaicking of global planetary data sets allows for the examination of local regional and global scale processes on all planetary bodies processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image processing algorithm these techniques e g non uniformity correction running contrast stretches line and row correlated noise removal and random noise removal were originally developed for the 2001 mars odyssey thermal emission imaging system themis infrared multispectral imager data but can be adapted and applied to other data sets by the alteration of input parameters the techniques for mosaicking planetary image data sets e g image registration blending and normalization are also presented along with the generation of qualitative and quantitative products these techniques are then applied to generate themis daytime and nighttime infrared viking context imager ctx and mars orbiter camera moc visible mosaics using a variety of input and output types at a variety of scales by creating mosaics of the same area using different data sets such as those that illustrate compositional diversity thermophysical properties or small scale morphology it is possible to view the surface of the planet and geologic problems through many different perspectives in addition to the techniques used to create large scale seamless mosaics we also present the themis daytime and nighttime relative temperature global mosaics which are the highest resolution 100m pixel global scale data sets available for mars to date

rapid formation of a modern bedrock canyon by a single flood event deep river canyons are thought to form slowly over geological time see for example ref 1 cut by moderate flows that reoccur every few years in contrast some of the most spectacular canyons on earth and mars were probably carved rapidly during ancient megaflood events quantification of the flood discharge duration and erosion mechanics that operated during such events is hampered because we lack modern analogues canyon lake gorge texas was carved in 2002 during a single catastrophic flood the event offers a rare opportunity to analyse canyon formation and test palaeo hydraulic reconstruction techniques under known topographic and hydraulic conditions here we use digital topographic models and visible near infrared aerial images from before and after the flood discharge measured during the event field measurements and sediment transport modelling to show that the flood moved metre sized boulders excavated 7 m of limestone and transformed a soil mantled valley into a bedrock canyon in just 3 days we find that canyon morphology is strongly dependent on rock type plucking of limestone blocks produced waterfalls inner channels and bedrock strath terraces whereas abrasion of cemented alluvium sculpted walls plunge pools and streamlined islands canyon formation was so rapid that erosion might have been limited by the ability of the flow to transport sediment we suggest that our results might improve hydraulic reconstructions of similar megafloods on earth and mars

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

40ar 39ar geochronolgy and neoproterozoic tectonics along the northern margin of the eastern ghats belt in north orissa india abstract the post 1100 950 ma cooling history of the northern margin of the high grade eastern ghats belt is determined from 40ar 39ar data collected from schist and gneiss samples the data define two groups of dates with distinct cooling histories between ca 700 and 420 ma the oldest group of ages define a slow apparent cooling path whereas a younger group of 40ar 39ar dates from the west and north margin of the eastern ghats belt and along the southern margin of the rengali province define a more rapid cooling path the younger 40ar 39ar dates are interpreted to reflect a variable and locally intense thermal event at ca 550 500 ma associated with reactivation of major shear zones final exhumation to current exposed levels occurred by ca 300 ma as constrained by unconformable permo triassic coal bearing sediments overlying the northern eastern ghats belt and northwestern rengali province dextral reverse reactivation after ca 950 ma and possibly prior to ca 700 ma along the kerajang and barakot fault zones was associated with regional shortening within the eastern ghats belt and rengali province further reactivation of major shear zones within the same shortening regime at ca 550 500 ma is indicated by the 40ar 39ar data resetting of the k ar system was locally more intense along the eastern ghats boundary fault and kerajang fault zones and was associated with ingress of high temperature fluids the resulting post grenvillian tectonic framework for northern orissa provides insight into the character of intra cratonic pan african tectonism within east gondwanaland

solid bitumens an assessment of their characteristics genesis and role in geological processes familiar since antiquity and subject in contemporary times to various characterization schemes the exact nature of solid bitumen is not yet fully known bitumens have random polymer like molecular structures are mobile as highly viscous fluids or were once fluids but have since turned into solids solid bitumens consist mainly of large moieties of polyclyclic aromatic hydrocarbons occasionally with finely admixed fine grained cryptocrystalline graphite solid bitumens are distinguished from kerogen which is the syngenetic and generally finely dispersed particulate organic matter in sedimentary rock that virtually does not migrate following its deposition occurrences of solid bitumens are relevant to petroleum exploration as well as the search for and evaluation of a variety of metallic mineral deposits genesis of bitumen is in many cases linked to the thermal and hydrothermal history of organic matter in sedimentary rock apparently bitumen or more specifically organic acids generated along with bitumen during diagenesis may alter porosity of reservoir rocks or otherwise prepare the ground for ore deposition bitumen is also relatively sensitive to alteration processes some of which such as oxidative weathering water leaching biodegradation contact metamorphism and ionizing radiation may likewise affect its nature elemental composition of bitumen commonly reflects the nature of mineral deposits is is possible that in petroleum exploration trace metal abundances of bitumen may eventually allow prediction of crude oil types and volumes anticipated from a given source rock beside transition elements notably ni and v highly anomalous concentrations of u pt and au occur in some solid bitumens during the generation of petroleum from kerogen the trend in 13c is toward lighter values the opposite seems to occur when liquid petroleum is subjected to thermal cracking and or related processes yielding solid bitumen enriched in 13c and isotopically light methane in fact except for deasphalting and possibly some irradiation processes the result of thermal cracking oxidation water leaching inspissation drying and bacterial degradation of crude oil is that lower molecular weight hydrocarbons are removed leaving bitumen residues enriched in aromatic hydrocarbons heteroatomic compounds nso and 13c such phenomena are relevant to bitumen paragenesis in petroleum reservoir rocks to certain phanerozoic occurrences of multiple generations of bitumens and to bitumens in mineral deposits

hydrothermal discharge and alteration in near surface sediments from the guaymas basin gulf of california abstract in the guaymas basin gulf of california hydrothermal fluids discharge onto the seafloor via both direct emanation through hydrothermal spires and diffusely through the sediments the latter mode is the focus of this study short 20 cm sediment cores were taken in zones of diffuse hydrothermal flow for chemical investigation of interstitial fluids and bulk solids the hydrothermal component of the pore fluids was quite variable indicating the heterogenous nature of the near surface flow regimes the bulk solids chemistry indicates that the suite of cores has encountered different amounts of cumulative hydrothermal exposure dissolution of biogenic silica and deposition of large amorphous silica clasts in the sediment are related to the extent of hydrothermal exposure surface enrichments in ba are formed as barite precipitates when ba rich hydrothermal fluids mix with sulfate rich seawater at the seafloor formation of pyrite and removal of mg from the solid phases are also observed effects of hydrothermal flow through these sediments

multibeam bathymetric survey and high resolution seismic investigations on the barbados ridge complex eastern caribbean a key to the knowledge and interpretation of an accretionary wedge abstract an important problem of active margin processes is the way accretionary wedges form in response to oceanic crust subduction new data have been obtained along the barbados ridge in front of the lesser antilles tertiary island arc they include high resolution multichannel seismic data and accurate sea beam bathymetric maps both have been used to propose a 3 dimensional interpretation of tectonic and sedimentary processes related to subduction such as oceanic off scraping ductile folding relative uplift and subsidence fore arc basin evolution and mud diapirism they all improved our knowledge of the evolution of accretionary prisms and more specifically of the barbados ridge development in plio quaternary time previous tectonic events are deduced from recently published geological data from barbados and the lesser antilles islands

liquefied vs stratified sediment mobilization processes insight from the south of the barbados accretionary prism this paper discusses the nature and origin of subsurface sediment mobilization processes in deep marine clay rich environments in the studied area of the southern barbados accretionary prism new geophysical acquisitions have emphasized the spectacular widespread development of mud volcanoes that are well developed along ramp anticlines and along sigmoidal rises with trends that are oblique to the axes of the main folds of the accretionary wedge on some active mud volcanoes heat flow measurements show high positive anomalies related to high fluxes of mud transfer the mobilized solid fraction expelled by the mud volcanoes does not originate from a unique source bed but from various formations pierced by the mud conduits and is driven by the water phase the area studied also exhibits trends of structures corresponding to sub circular massive local uplifts of deformed but well preserved stratified sediments turbidites and hemipelagics no piercing shale diapirs have been encountered in this area some of these local uplift structures are complicated by the development of collapses calderas and superimposed mud volcanoes mud volcanism corresponds fundamentally to fluid displacement water and gas whereas massive sedimentary uplift corresponds to large vertical displacements of stratified solid levels but for which the deep cause could be partly the intrusion of mud plugs both are dynamic phenomena controlled by the development of overpressure at depth contributing to sedimentary mobilizations

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

insights into surface runoff on early mars from paleolake basin morphology and stratigraphy we present observations on the morphology and stratigraphy of more than 400 paleolake basins on mars we show that there are two distinct classes of martian paleolake basins 1 paleolakes fed by regionally integrated valley networks n 251 and 2 paleolakes fed by isolated inlet valleys not integrated into broader regional drainage systems n 174 we conclude that valley network fed paleolakes primarily formed prior to approximately the noachian hesperian boundary ca 3 7 ga while isolated inlet valley paleolakes primarily formed later in martian history all 174 isolated inlet valley paleolakes are closed basin lakes however there are surprisingly few 31 valley network fed closed basin lakes compared to a large number 220 of valley network fed open basin lakes this observation is consistent with declining levels of fluvial activity over time on the martian surface our results imply that during the era of valley network formation 90 of topographic basins breached by an inlet valley had sufficiently high ratios of water influx to losses to fill overtop and form an outlet valley this conclusion provides an important constraint on the balance between surface runoff production and water losses on early mars that must be satisfied by any model of the early martian climate and hydrologic cycle

hydrocarbons in surface sediments from a guaymas basin hydrothermal vent site petroleum like materials found at the guaymas basin hydothermal vent site gulf of california are derived from pyrolysis of organic matter two characteristics surface sediment cores differing in temperature profiles and other parameters were collected by dsv alvin sectioned and analyzed for hydrocarbons the quantitative and qualitative composition of alkanes steranes diasteranes and triterpanes differed between these cores as well as within sections of the same core these differences apparent for scales of tens of centimeters are related to interactive physical chemical and microbial processes as well as the influence of multiple sources for the petroleum

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve