tem study of in situ organic matter on continental margins occurrence and the monolayer hypothesis abstract tem photomicrographs show that organic matter in the continental margin sediments that we have examined is primarily patchy in distribution and occurs as 1 discrete discontinuous blebs and micro blebs of differentiated and undifferentiated protoplasm 2 bacterial cells and associated muco polysaccharide networks and 3 localized smears generally associated with clay minerals and domain junctions in clay rich flocs not as thin uniform grain coatings or as infillings of nicks or etch pits on sediment grains with high degrees of surface roughness this occurrence contradicts recent assertions that most organic matter in continental margins occurs as monolayer or monolayer equivalent coatings on mineral grains and inorganic bioclastic particles our results are based on tem photomicrographs of samples from the northern california continental slope that fall within the monolayer equivalent envelope defined by mayer 1994 marine snow from the overlying nepheloid layer and sediments from eckernforde bay in the baltic sea these samples were prepared specifically to preserve and image in situ sediment fabric and organic constituents textural evidence suggests that low permeabilities caused by the interaction between the organic inorganic and biologic components of the clay size fraction play a major role in determining organic matter preservation on continental margins

bottom simulating reflections and geothermal gradients across the western svalbard margin seismic reflection data reveal prominent bottom simulating reflections bsrs within the relatively young 0 78 ma sediments along the west svalbard continental margin the potential hydrate occurrence zone covers an area of c 1600 km2 the hydrate accumulation zone is bound by structural tectonic features knipovich ridge molloy transform fault vestnesa ridge and the presence of glacigenic debris lobes inhibiting hydrate formation upslope the thickness of the gas zone underneath the bsr varies laterally and reaches a maximum of c 150 ms using the bsr as an in situ temperature proxy geothermal gradients increase gradually from 70 to 115 c km 1 towards the molloy transform fault anomalies only occur in the immediate vicinity of normal faults where the bsr shoals indicating near vertical heat fluid flow within the fault zones amplitude analyses suggest that sub horizontal fluid migration also takes place along the stratigraphy as the faults are related to the northwards propagation of the knipovich ridge long term disturbance of hydrate stability appears related to incipient rifting processes

regional variations in deformation mechanisms and structural styles in the central appalachian orogenic belt orogenic belts such as the central appalachian fold and thrust belt consist of distinct tectonic provinces characterized by different structural styles as a result of deformation under different physical conditions a quantitative study of deformation mechanisms was undertaken for quartzites and sandstones of the central appalachian orogenic belt in order to understand the controls of different physical parameters on the relative importance of these mechanisms and on the geometry and mechanics of formation of structures in the different provinces in the blue ridge province the dominant deformation mechanisms are pressure solution dislocation creep and extension fracturing with some accompanying grain boundary sliding and recrystallization the proportion of dislocation creep to pressure solution strain increases both with temperature and deviatoric stress an axial plane slaty cleavage which contains the maximum and intermediate principal directions of the strain ellipsoid maintains a uniform orientation in both the blue ridge and the great valley provinces folds in the blue ridge province have a similar geometry formed by progressive flattening of parallel folds due to internal deformation ductile deformation zones on the overturned limbs of folds acted as precursors for the propagation of thrust faults in the late stages of folding in the valley and ridge and massanutten synclinorium important deformation mechanisms in the sandstone units include pressure solution plastic deformation cataclasis brecciation extension fracturing and slip along minor faults and bedding planes major folds are strongly disharmonic and show variations between concentric and angular geometries they are associated with thrust ramps that propagated through progressively developing folds in the late stages of folding brittle deformation zones characterized by high intensities of extension fractures and cataclastic bands formed on the steep forelimbs these features are interpreted to be the result of layer parallel extension and the propagation of splay faults through these limbs cleavage developed during layer parallel shortening prior to the onset of folding and was rotated to its present fanned geometry during folding on the basis of the results of this study the central appalachian orogenic belt can be subdivided into two deformational provinces dominated by different deformation mechanisms and characterized by different geometries and mechanics of formation of the structures for orthoquartzites the tectonite front which separates the tectonites of the hinterland from the non tectonites of the foreland is located along the blue ridge front for carbonates and argillaceous sandstones the tectonite front is located along the north mountain fault

ocean temperature variability for the past 60 years on the norwegian svalbard margin influences gas hydrate stability on human time scales 1 the potential impact of future climate change on methane release from oceanic gas hydrates is the subject of much debate we analyzed world ocean database quality controlled data on the norwegian svalbard continental margin from the past 60 years to evaluate the potential effect of ocean temperature variations on continental margin gas hydrate reservoirs bottom water temperatures in the norwegian svalbard margin were subject to significant cooling until 1980 by 2 c offshore nw svalbard and in the barents sea followed by a general bottom water temperature increase until 2010 0 3 c in deep water areas offshore nw svalbard and mid norwegian margin and 2 c in the shallow areas of the barents sea and prins karls forland bottom water warming in the shallow outer shelf areas triggered the gas hydrate stability zone ghsz retreat toward upper continental slope areas potentially increasing methane release due to gas hydrate dissociation ghsz responses to temperature changes on human time scales occur exclusively in shallow water and only if near surface gas hydrates exist the responses are associated with a short time lag of less than 1 year temperatures in the bottom water column seem to be partly regulated by the north atlantic oscillation nao with positive nao associated with warm phases however cooling events in the surface water offshore nw svalbard might be associated with el nino events of 1976 1977 1986 1987 and 1997 1998 in the pacific such ocean cooling if long enough may delay ocean temperature driven gas hydrate dissociation and potential releases of methane to the ocean

gas hydrate systems in petroleum provinces of the sw barents sea abstract 3d seismic data of the sw barents sea provided information about the existence of structure ii gas hydrates and shallow gas in marine sediments gas hydrates and shallow gas exist in the sw barents sea in conjunction with deep hydrocarbon reservoir leakage available conventional 3d seismic data show acoustic chimneys that extend to depths 1700 ms two way travel time below the seafloor the location of the chimneys coincides with structural boundaries and fault complexes cutting through mostly jurassic and triassic strata vertical fluid flow through these chimneys transports thermogenic gas to the gas hydrate stability zone causing the formation of a bottom simulating reflector bsr in addition variations of fluid flux across deep seated fault complexes cause changes in heat flow which explains the shoaling of the bsr and the formation of a tilted bsr tbsr at the border between the ringvassoya fault complex and the loppa high the stability model using thermogenic gas composition type i and ii shows gas hydrates are stable at 225 m 345 m depth corresponding to variation in the geothermal gradient for upper bsr 28 7 c km and 37 c km and lower bsr levels 23 4 c km and 28 3 c km these lateral changes in the temperature gradient can be reconciled with changes in upward fluid flow rates of 1 8 2 2 mm yr 1 such gas hydrate and fluid flow systems on arctic continental margins especially in shallow water depths are potential gas emitters due to their sensitivity to warming ocean temperatures

gas hydrate distribution and hydrocarbon maturation north of the knipovich ridge western svalbard margin a bottom simulating reflector bsr occurs west of svalbard in water depths exceeding 600 m indicating that gas hydrate occurrence in marine sediments is more widespread in this region than anywhere else on the eastern north atlantic margin regional bsr mapping shows the presence of hydrate and free gas in several areas with the largest area located north of the knipovich ridge a slow spreading ridge segment of the mid atlantic ridge system here heat flow is high up to 330 mw m 2 increasing towards the ridge axis the coinciding maxima in across margin bsr width and heat flow suggest that the knipovich ridge influenced methane generation in this area this is supported by recent finds of thermogenic methane at cold seeps north of the ridge termination to evaluate the source rock potential on the western svalbard margin we applied 1d petroleum system modeling at three sites the modeling shows that temperature and burial conditions near the ridge were sufficient to produce hydrocarbons the bulk petroleum mass produced since the eocene is at least 5 kt and could be as high as 0 2 mt most likely source rocks are miocene organic rich sediments and a potential eocene source rock that may exist in the area if early rifting created sufficiently deep depocenters thermogenic methane production could thus explain the more widespread presence of gas hydrates north of the knipovich ridge the presence of microbial methane on the upper continental slope and shelf indicates that the origin of methane on the svalbard margin varies spatially

rare earth element characteristics of paleoproterozoic cap carbonates pertaining to the sausar group central india implications for ocean paleoredox conditions abstract the paleoproterozoic era is marked by significant changes in the level of oxygen in the atmosphere and chemistry of the ocean and the presence of world wide glaciation geochemistry of chemogenic sediments provide clues to these changes the sausar group 2478 2250 ma of central india is one of the few places in the world where paleoproterozoic glacial unit overlained by a cap carbonate horizon has been identified major trace and rare earth element ree contents of paleoproterozoic cap carbonates of the sausar group have been analysed for their implications for ocean redox conditions during interglacial periods of the huronian glaciation the la la gd gd lusn lasn and y ho ratios of the cap carbonate reflect their pristine marine nature conspicuous ce anomaly ce ce up to 1 75 accompanied by the enrichment of fe mn zn and u provides insight into the redox state of the ocean at the time of deposition of the cap carbonate succession based on these observations we infer anoxic depositional conditions in the basin during the interglacial period of the paleoproterozoic glaciation before the great oxidation event goe and the level of oxygen in the atmosphere fluctuating between 10 5 and 10 2 of the present atmospheric level pal

gas hydrate reservoir and active methane venting province in sediments on 20 ma young oceanic crust in the fram strait offshore nw svalbard seafloor pockmarks are common indicators for vertical fluid flow and frequently associated with methane discharge through the gas hydrate stability zone ghsz the present day flux through these degassing systems is presumably at a low level on most rifted continental margins a pockmark field on the nw svalbard passive margin is located on young ocean crust 20 ma and shows evidence of ongoing episodic degassing new geophysical data from the vestnesa ridge 79 n a mounded and elongated sediment drift in the eastern fram strait reveal a gas hydrate free gas and venting system that is exceptionally more dynamic than documented elsewhere along the northeastern north atlantic margin the prominent bottom simulating reflection bsr about 200 mbsf separates anomalously high p wave velocities in the ghsz from a remarkable underlying low velocity zone indicating the presence of gas hydrate and gas in the pore space inversion of p wave velocity data using the differential effective medium theory yields a two dimensional concentration model of methane hydrate and free gas the model predicts saturations of up to 11 in the hydrate reservoir which due to the seafloor topography forms a large anticlinal permeability barrier below in the low velocity zone i e 1350 1500 m s up to 3 of free gas is predicted across the apex of the vestnesa ridge and in the immediate vicinity of extensional faults a conservative estimate indicates that 225 kg m2 of pure methane is stored in hydrate and gas in the upper 230 m of the sedimentary column an elongated pockmark field consisting of 100 individual pockmarks up to 600 m wide systematically aligns the apex of the vestnesa ridge active vigorous degassing from the topography controlled pressure valve system was evident from a 750 m high and 150 m wide gas flare observed in the water column during a cruise with r v jan mayen in october 2008 the gas flare documents dynamic degassing through the corresponding chimney which penetrates the entire ghsz and into the underlying free gas zone cruises in 2006 and 2007 did not detect active gas venting above the pockmark field accordingly vigorous degassing may operate in an episodic mode where hydrothermal circulation systems through young ocean crust may play a significant role

migration of brines in the basement rocks of the athabasca basin through microfracture networks p patch u deposit canada abstract the unconformity type uranium deposits of the athabasca basin saskatchewan canada are hosted near the unconformity between a middle proterozoic intracratonic sedimentary basin and an archean to paleo proterozoic metamorphic and plutonic basement these deposits which are considered to be the richest u deposits in the world are the result of massive basinal fluid migrations in the basement rocks this study shows that basinal brines have strongly penetrated into the basement not only through faults and major pathways but also by way of dense networks of microfractures which favoured the percolation of fluids down to considerable depths hundred metres below the unconformity and their chemical modification salinity increase by interaction with basement lithologies these processes are one of the major causes of uranium mobility within the basement rocks and the formation of unconformity type mineralization microfracture networks which opened during the basinal brine stage ca 1600 1400 ma are interpreted as sets of mode i cracks corresponding to a specific stage of deformation and occur as fluid inclusion planes after healing the stress field at that stage 1 n130 150 e subvertical partly reopened the earlier microcrack networks 1 n80 110 e and n130 150 e subvertical issued from the trans hudson orogeny late retrograde metamorphic stage ca 1795 1720 ma the circulation of the two types of fluids carbonic and brines occurs thus at two distinct events trans hudson orogeny late retrograde metamorphism for carbonic fluids and maximal burial diagenesis for brines but the same main microfissure geometry was used by the fluids this demonstrates the existence of a similar stress field direction acting before and after the basin formation moreover the brine circulations in the basement acted in a wider volume than the clay rich alteration halo surrounding the u ores generally considered as the main envelope of fluid percolation outside the fault systems the data on the chemistry of the fluids and on the geometry of their migration at various scales emphasise the fundamental role of the basement in the chemical evolution of highly saline brines linked to unconformity related uranium mineralization in the athabasca basin

microfracturing paleostress and the growth of faults abstract we have analyzed the microfractures in samples taken near one thrust fault and five normal faults of known displacement to test the dependence of microfracture density and distribution on fault slip we have also recorded the orientation of microfractures as a function of distance from the associated fault surface in order to control as many parameters as possible shallow faults with similar lithologies were chosen they showed the same kind of deformation namely microfracturing without block rotation recrystallization extensive granulation or crystal plasticity the results of over 8000 microfracture measurements suggest that maximum microfracture density is independent of net slip we interpret this relationship as indicating that the preponderance of microfracturing occurs in proximity to the propagating fault tip the angular relationship between the shear plane and microfractures was commonly found to be between 5 and 20 significantly less than the 30 expected between the far field maximum principal stress and the shear surface this low angle between microfracture orientation and shear plane orientation is predicted for a local stress field associated with a propagating mode ii fault tip other possible explanations for the small angle for tensional microfractures and the shear surface are 1 the effective confining pressure was very low or 2 shear strength at failure was much larger than expected

methane generated pockmarks on young thickly sedimented oceanic crust in the arctic vestnesa ridge fram strait acoustic backscatter imagery in the fram strait between greenland and spitzbergen reveals a 1 3 km wide 50 km long belt of 50 pointlike backscatter objects decorating the 1300 m deep crest of vestnesa ridge a 1 2 km thick sediment drift possibly underlain by a transform parallel oceanic basement ridge crustal ages 3 14 ma a 3 5 khz seismic reflection profile indicates that at least some objects are pockmarks 100 200 m in diameter and 10 20 m deep the pockmarks possibly also mud diapirs may have been formed by evolution of methane generated by the decomposition of marine organic matter in the vestnesa ridge sediment drift the ridge may be underlain by an anticlinal carapace of methane hydrate calculated to be 200 300 m thick comparable to the hydrate thickness measured just to the south the rising methane would collect in the ridge crest trap intermittently escaping to the sea floor this hypothesis is supported by multichannel evidence for bright spots and bottom simulating reflectors in the area the pockmark belt may also be located above a transcurrent fault sediment slumps on the flanks of vestnesa ridge and northeast of molloy ridge may have been triggered by plate boundary earthquakes and facilitated by methane hydrates

controls on gas hydrate system evolution in a region of active fluid flow in the sw barents sea abstract the location and stability of gas hydrates in the sw barents sea is poorly constrained due to complex geological geochemical and geophysical conditions including poor controls on regional heat flow and gas chemistry understanding the stability of gas hydrates in this region is important as recent studies suggest destabilizing hydrates may lead to methane discharge into the ocean and possibly in to the atmosphere here we use high resolution 3d p cable seismic data combined with 3d heat flow and fluid flow models to place new constraints on gas hydrate stability in this region the 3d p cable seismic data acquired in 2009 west of loppa high show cross cutting reverse polarity high amplitude reflectors interpreted as the base of gas hydrate stability to constrain heat flow fluid flow and gas hydrate stability within the 3d seismic volume we use a 3d steady state finite difference diffusive thermal model that incorporates regional bottom water temperature from ctd casts expected geothermal gradients and gas composition derived from well data in general modelled bottom simulating reflectors are deeper than observed bsrs our analysis weighs multiple factors that might explain the discrepancy between observed and modelled bottom simulating reflector depths from this analysis we propose that the most significant discrepancies in bsr depth are likely related to changes in regional fluid heat flow and fluid geochemistry the anomalously shallow bottom simulating reflectors can be explained via vertical fluid flow that might include ensuing potential effects on gas composition pore water salinity and temperature our estimate suggest that a maximum vertical fluid flux of approximately 12 mm y is necessary to explain the most significant anomalies our study provides new insight into regional heat flow geochemistry and end member vertical fluid flux rates in the barents sea moreover it documents that the fluid flow system is active and most likely very dynamic

geological controls on shallow gas distribution and seafloor seepage in an arctic fjord of spitsbergen norway abstract this study integrates high resolution shallow and deep geophysical datasets to study the seabed seepage systems linked to subsurface shallow gas and geological features influencing the fluid flow in nordfjorden central spitsbergen arctic norway this is one of the tributary fjords of the isfjorden fjord system in spitsbergen which has the highest density of pockmarks ranging up to 20 km2 the 535 pockmarks identified manually in the 300 km2 large study area have diameters ranging from 10 m to 212 m and depth varying between 1 m and 8 m sub surface seep related acoustic features such as enhanced reflections acoustic blanking and turbidity zones recorded on 55 km of new high resolution sub bottom acoustic data suggest shallow gas free and or dissolved occurrences in the marine sediments beneath the pockmarks structural features thrust faults and associated folds belonging to the palaeogene west spitsbergen fold and thrust belt and early cretaceous igneous sills have been interpreted on 2d multichannel seismic data in the triassic and permian successions some of these faults and igneous sills form seafloor ridges where pockmark density is high and they are typically aligned acoustic flares attributed to active gas seepage from the seafloor were imaged in the water column in the southern part of nordfjorden above the sub surface shallow gas occurrences and thrust faults the integrated analysis of these geophysical datasets suggests that the near seafloor tectonically deformed stratum plays an important role in the up dip propagation of fluids liquids and or gas distribution of shallow gas in marine sediments and seepage at the seafloor

subsurface fractures and their relationship to stress history in east texas basin sandstone abstract subsurface fractures were sampled with more than 400 m of core from the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 600 m thick that was deposited in the gradually subsiding gulf coast basin depth to the top of the formation in east texas now ranges between 1800 and 2900 m fractures in sandstone exhibit features that are due to intermittent fracturing and sealing crack seal which suggest that the fractures are the result of episodes of fluid pressure in excess of hydrostatic correlation of the vein mineral precipitation sequence with the diagenetic history and the results of previous 18 o studies of quartz cement indicates that fractures propagated at depths of between 900 and 1500 m during the migration of quartz precipitating fluids fracture permeability provides a mechanism for the passage of large fluid volumes recorded by the precipitation of extensive quartz cement in the formation fractures stopped propagating before maximum burial depth was achieved during approximately 1500 m of subsequent burial fractures either remained partly open or were sealed by postkinematic ankerite and clay minerals

seepage in isfjorden and its tributary fjords west spitsbergen abstract this study analyses pockmark morphology and their spatial distribution in isfjorden relative to seabed morphology bedrock geology fault systems glacial landforms and processes using multibeam bathymetric data it provides insight into the possible mechanisms of pockmark formation high density pockmark field evolution and fluid migration pathways a total of 1304 pockmarks occur in the isfjorden at water depths of 40 to 320 m varying from circular to elongate in plan view their diameter ranges from 14 to 265 m and their depths from 1 to 11 m elongate pockmarks are dominant in the isfjordbanken and outer isfjorden where the seafloor is influenced by the west spitsbergen current the west spitsbergen fold and thrust belt and other fault systems sub cropping at the isfjorden seafloor correlate spatially with the high density pockmark zones the pockmarks are preferentially located on the marine sediments draping the bedrock of isfjorden fjord system they are most abundant in the areas underlain by jurassic cretaceous and the triassic lower jurassic bedrock pockmarks found ahead of submarine slope failures may have formed due to dewatering of soft sediments as a result of rapid increase of overpressure caused by deposition of glacigenic debris lobes fault conduits potential source rock and thin postglacial sediment layers are found to be crucial for the formation of pockmarks modeling results of the near shore subsea permafrost and potential gas hydrate stability zone imply thawing permafrost and gas hydrate dissociation as additional possible mechanisms for pockmark formation in isfjorden

acoustic evidence for a gas migration and release system in arctic glaciated continental margins offshore nw svalbard abstract high resolution 3d and 2d seismic data offshore nw svalbard west of prins karls forland provide geophysical evidence for geologically controlled fluid migration pathways gas hydrate occurrence and an active seabed gas expulsion system the investigated seabed area covers 1600 km2 and lies between kongsfjorden cross shelf trough in the north and isfjorden cross shelf trough in the south ranging in water depths from 200 m on the shelf to 800 m on the upper continental slope acoustic evidence for present day methane release from the seabed to the water column comes from more than 220 gas flares at the outer shelf while past methane release activity at the mid shelf area is evident from pockmarks without flares the fluid migration pathways towards the seabed can be drawn from sub seabed acoustic anomalies fluid migration towards the upper slope occurs mostly along strata in upslope direction and largely prevails over vertical focused migration fluids accumulate in the uppermost part of the slope just westward of the shelf break where they are trapped beneath the prograding glacigenic sequence which is not permeable enough for fluids to migrate through fluids are expelled on the shelf where the base of the glacigenic sequence outcrops some gas charged fluids may originate from deep seated hydrocarbon reservoirs and can be temporally stored in gas hydrates in the shallow subsurface though evidence for hydrates on the uppermost slope is missing the seismic data from the lower slope clearly suggest the occurrence of gas hydrate

near surface hydrocarbon anomalies in shelf sediments off spitsbergen evidences for past seepages 1 as global warming occurs the dissociation of bound methane on arctic shelves due to ocean current temperature changes may become a major contributor to the global methane budget and thus contribute to strong positive climate feedback mechanisms however little is known about the magnitude and fate of methane emissions from shallow submarine sediments to the atmosphere in the peculiar area in this paper we present one of the first direct evidences for seepage on the northwestern barents sea shelf by studying the molecular and isotopic signatures of low molecular weight hydrocarbons in seawater near surface sediment pore space and the sediment matrix at 26 locations we provide a detailed view on the partitioning of gaseous hydrocarbons in the sediment water interface off spitsbergen in the free gas phase low concentration of methane 28 ng g wet sediment paired with constantly high isotopic values 65 is consistent with high impact of methane oxidation on the isotopic composition in contrast high concentrations of adsorbed ch4 up to 5292 ng g wet 63 m and c2 ethane through pentane up to 1724 ng g wet 63 m in the sediment matrix suggest that the adsorbed gas is reasonably well protected against microbial degradation moreover the isotopic and molecular signatures of adsorbed ch4 38 60 100 5300 ng g wet 63 m and c2h6 20 36 30 1700 ng g wet 63 m indicate an integrated but strongly varying signal of historic thermally derived hydrocarbon plumes plus in situ adsorbed gas of biological origin this suggests a minimal exchange and unlike histories of free and adsorbed gas the majority of gaseous hydrocarbons in the adsorbed pool may be the result of past seepages past upward flow of thermogenic gas and impregnation with mature hydrocarbons was particularly strong along tectonic lineaments active petroleum source rocks along the continental margin and migration of gaseous hydrocarbons at re activated fault systems might explain the anomalies along these conduits

tsunami modeling of a submarine landslide in the fram strait the present geological setting west of svalbard closely parallels the situation off mid norway after the last glaciation when crustal unloading by melting of ice induced very large earthquakes today on the modern svalbard margin increasing bottom water temperatures are destabilizing marine gas hydrates which are held in continental margin sediments consisting of interlayered contourite deposits and glacigenic debris flows both unloading earthquakes and hydrate failure have been identified as key factors causing several megalandslides off norway during early holocene deglaciation the most prominent event was the storegga slide 8200 years b p which caused a tsunami up to 23 m high on the faroe and shetland islands here we show by numerical tsunami modeling that a smaller submarine landslide west of svalbard 100 m high and 130 km wide would cause a tsunami capable of reaching northwest europe and threatening coastal areas a tsunami warning system based on tiltmeters would give a warning time of 1 4 h

surface geochemical studies in the norwegian barents sea comparison with drilling results during the last 4 years a number of surface geochemical studies have been undertaken in the barents sea acreage in all of the areas has subsequently been licensed for exploration sampling for surface geochemistry has been undertaken using a gravity corer where samples were taken 2 m below the seafloor the sampling grids were either regular or irregular based on known geological features in the areas or a combination of the two the samples were analyzed for interstitial gas adsorbed gas grain size distribution organic and inorganic carbon content fluorescence of the hexane extract and heavy hydrocarbons in the hexane extract the results from the different areas ranged from barren i e no indication of petrogenic hydrocarbons at the surface anomalies of petrogenic hydrocarbons i e indicating the generation of gas condensate or oil to extremely strong anomalies of oil interpreted as indicators of direct leakage from source rocks or a defective caprock

geochemical signatures of intense episodic anaerobic oxidation of methane in near surface sediments of a recently discovered cold seep kveithola trough nw barents sea abstract at cold seep environments the detection of large 34s enrichments within bulk sulphide minerals has been frequently used as a proxy to infer the vertical migrations of the sulphate methane transition zone smtz processes related to the oxidative part of the sulphur cycle can alter the original stable sulphur isotope composition 34s of the solid sulphur phases in particular at the sediment water interface identification of paleo and present positions of methane fronts in the sedimentary records requires the use of multiple geochemical proxies authigenic enrichment of mo has been demonstrated to represent a valid and durable tracer of the past smtz depth fluctuations and of the intensities of the related methane seepages this study is based on two closely spaced short cores collected from the main drift of the kveithola trough a glacially carved depression located in northwestern barents sea active fluid seepage has been recently reported in this area and a gas flare was specifically observed in proximity of the sampling sites where the cores object of our study were retrieved in order to collect evidences of the possible occurrence of anaerobic oxidation of methane aom at the sediment water interface of the investigated area and infer the entity of the associated methane flux we combined the analyses of reduced sulphur species 34s total organic carbon and redox sensitive elements the negative 34s values within the extracted solid sulphur phases up to 49 1 for pyritic sulphur show that organoclastic sulphate reduction osr coupled with disproportionation of sulphur intermediates are the only active processes in the near surface sediments however moderate to strong enrichments of mo detected in the relatively organic carbon poor intervals of both cores and the lack of concurrent enrichments of co cu ni v and zn usually associated to osr dominated environment suggested that the sulphidic conditions favouring the mo enrichments were produced by aom therefore we infer that high methane flux events characterized the drift area of the kveithola occasionally moving upward the smtz and thus inducing intense aom in proximity of the sediment water interface of this part of the trough our results confirmed the validity of sedimentary mo as an indicator of the occurrence and intensity of past methane seepages

triggering of the hinlopen yermak megaslide in relation to paleoceanography and climate history of the continental margin north of spitsbergen 1 on the basis of the detailed sedimentological record of the key core ps66 309 1 and a review of open literature we present an assessment of the paleoenvironmental conditions as well as trigger mechanism of the hinlopen yermak megaslide north of spitsbergen the svalbard archipelago is characterized by strong inflow of atlantic water accompanied by rapidly falling sea level rapidly growing svalbard barents sea ice sheet and associated increasing glaciotectonic activity during the time window around 30 calendar kyr b p of this catastrophic failure event thus the potential trigger mechanisms include sediment buoyancy and excess pore pressure hydrate stability and tectonic glaciotectonic processes while the common scenarios seem to fail to explain this unique submarine megaslide we focus on glacial processes and their consequences for the regional tectonic framework we conclude that the hinlopen yermak megaslide has been the consequence of the rapid onset of late weichselian glaciation resulting in a drastic sea level drop asymmetrical ice loading and a forebulge development leading to enhanced tectonic movements along the hinlopen fault zone as the final trigger we assume a strong earthquake positioned below or close to the se sophia basin

fingerprinting stress stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding the case of the monte nero anticline in the apennines italy in this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold and thrust belt first we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion second we use our new approach to present a high resolution deformation and stress history that affected meso cenozoic limestone strata in the monte nero anticline during its late miocene pliocene growth in the umbria marche arcuate ridge northern apennines italy in this area an extensive stylolite joint vein network developed during layer parallel shortening lps as well as during and after folding stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during lps the stress regime oscillated between strike slip and compressional during lps before ultimately becoming strike slip again during late stage fold tightening our case study shows that high resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses beyond regional implications this study validates our approach as a new powerful toolbox to high resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques

diagenetic relationships of methanogenesis nutrients acoustic turbidity pockmarks and freshwater seepages in eckernforde bay abstract high organic loading 4 5 wt and sedimentation rates 1 4 mm yr 1 in eckernforde bay sediments lead to anaerobic conditions within the uppermost 15 cm intense bacterial sulphate reduction 0 011 0 15 mm so 4 red 2 yr 1 exhausts dissolved sulphate around 150 cm sediment depth resulting in methanogenesis at greater sediment depth by carbonate reduction 1 8 8 5 m ch 4 yr 1 extensive regions of eckernforde bay are characterized by acoustically turbid sediments 300 cm sediment depth resulting from deeper sediments supersaturated in methane forming free gas accumulation zones methane migrating upward into the sulphate reduction zone is effectively consumed by sulphate reducing bacteria at rates 3 10 times greater than methanogenesis i e 46 95 m ch 4 ox yr 1 the pathways of methane formation and anaerobic oxidation are confirmed by stable carbon and hydrogen isotope evidence pockmarks i e shallow surface depressions in some eckernforde bay sediments are not associated with gas ebullition rather these physical features result from the expulsion of freshwater these episodic springs or seepages of groundwater from the underlying holocene glacial lags and sands into the basin at pockmark sites have characteristic low chloride and methane concentrations the geochemical evidence indicates that the commercial accumulation of petroleum in the lower cretaceous dogger beta hauptsandstein schwedeneck field in eckernforde bay 1500 mbsf has no surface manifestation and does not influence either the occurrence of acoustic turbidity or pockmarks

microfractures and their role in deformation of a quartz arenite from the central appalachian foreland abstract microfractures are pervasive in the massanutten sandstone a quartz arenite exposed in a doubly plunging synclinorium in the central appalachian foreland they are present as fluid inclusion planes fips and microveins parallel the fips fips occur in three orthogonal sets horizontal vertical and normal to the fold axis and vertical and parallel to the fold axis the geometry distribution and age of fips relative to other microstructures shows that microfractures developed during folding microfracturing followed layer parallel shortening by dislocation flow and was coeval with the peak of pressure solution that marked the final stages of folding microfracture densities are extremely high 160 mm 1 in many samples rapid closure of microfractures suppressed brecciation and prevented microfractures from propagating unstably to form joints microfracture opening accounts for significant finite strain with extensional strains of up to 11 1 and associated volume increases of over 16 0 the general lack of shortening microstructures indicates that a net volume increase is likely and that the massanutten sandstone may have served as a sink for dissolved phases from adjacent units undergoing volume loss deformation

fluid inclusion constraints on the kinematics of footwall uplift beneath the brenner line normal fault eastern alps dynamic models of isostatic footwall uplift in response to normal faulting can be divided into those in which uplift is accomplished by flexural failure and those in which uplift occurs via subvertical simple shear each class of model predicts a different incremental strain history that should be recorded in the footwall in the tauern window eastern alps postmylonitic structures in the footwall of the brenner line normal shear zone predominantly consist of closely spaced steep west down and east down microfaults formation of the west down faults before and at greater depths than the east down faults would be consistent with unroofing via subvertical simple shear in contrast formation of the two fault types as a conjugate set would be more indicative of unroofing via elastic processes the field data alone do not provide a sufficient test of the two hypotheses because crosscutting relations are only rarely observed and there is no control on the depth at which the structures formed however both depth and timing constraints on the formation of the late structures can be obtained by correlating the orientations of fluid inclusion lined microfaults with the macroscopic west down and east down faults obtaining density data for the inclusions and correlating these data with previously obtained geochronologic data the results indicate that the west down structures formed at depths of 10 20 km and temperatures 450 c in the mid to late oligocene and that the east down structures formed at 2 to 10 km depth and temperatures of 300 50 c in the mid miocene these data support the hypothesis that a rolling hinge was present in the footwall of the brenner line and that isostatically driven footwall deformation was accomplished predominantly by subvertical simple shear the depths at which west down and east down faulting occurred coupled with the angle of dip of the brenner line yield a minimum lateral displacement on the fault of 15 26 km approximately coeval ductile shearing and brittle faulting at depths of 15 20 km and temperatures in excess of 400 c may reflect local variations in strain rate as the footwall rocks entered the zone of rolling hinge deformation

hydrocarbons from near surface sediments of the barents sea north of svalbard indication of subsurface hydrocarbon generation abstract the barents sea is considered as an important target for oil and gas exploration but the petroleum potential of its shelf and slope regions is unknown here we present results of a research cruise to the northern hinlopen margin at the transition to the southern nansen basin and the eastern yermak plateau multichannel reflection seismic data acquisition heat flow measurements and geochemical analyses of near surface sediments obtained by gravity coring were conducted to study the northern barents sea shelf and the early opening of the nansen basin and decipher their petroleum potential seismic data indicate high thicknesses of up to 2000 m of cenozoic sediments heat flow density values in the study area range between 67 and 108 mw m 2 the sediment samples were analysed for bulk geochemistry and sorbed hydrocarbon gases and for two sites for extractable hydrocarbons data from extractable n alkanes n c 25 and bulk hi and oi from rock eval organic matter demonstrate predominantly terrigenous organic material most likely derived from ice transported allochthonous sediments none of the sediments revealed substantial amounts of methane in pore waters arguing against active hydrocarbon seepage in the studied areas however thermogenic gases sorbed to the sediment matrix clay minerals organic matter and or carbonates were found in concentrations of up to 600 ppb on sediment wet wt basis for the samples from the northern hinlopen margin and particularly from the adjacent nansen basin a paleo fluid flow of thermogenic gas is indicated and accompanied by higher n alkanes with a modal petroleum like distribution 13 c values of methane ethane and propane and gas compositions point at a mainly marine source rock origin of all studied gases with early oil window maturities of the associated rocks 0 6 0 9 vr from this data an admixture of type iii derived thermogenic gases is indicated for some of the yermak plateau sediments for which also the lowest abundances of sorbed gases 50 100 ppb were observed gas geochemical characteristics in the samples with low gas abundances can partially be explained by an input of gases through ice transport of allochthonous hydrocarbons which were bound to mature organic matter for a site on the northern hinlopen margin ne of svalbard right at the southern termination of the nansen basin a different situation is indicated in this area the highest concentrations of sorbed gases most likely derived from sediments with an early oil window maturity and a marine kerogen type ii typical isotopic distribution at this location a pseudo well was constructed from 2d seismic data for reconstruction of thermal and maturity evolution the simulation results indicate that an early to middle eocene source rock would be in the early oil window since the early miocene a possible source rock here and in the circum arctic region could have been formed by azolla algae and other flourishing primary producers

are fluid inclusion planes useful in structural geology abstract quantification of deformation or stresses in structural geology is often difficult due to the uncertainity of the paleodepth or fluid pressure the best records of fluid percolation are paleofluids trapped as fluid inclusions in healed microcracks of the rock forming minerals fluid inclusion planes fip are mode i cracks which form in sets with a predominant orientation perpendicular to the least principle stress 3 however the repeated microfracturing and healing of the rock forming minerals yield complex superimposed patterns of healed microcracks such patterns are often difficult to interpret due to the lack of suitable chronological criteria these problems have been recently documented and solved by coupling deformation studies detailed examination at all scales of the relationships between trapped fluids and their host structures and studies of fluid inclusions this paper summarizes recent advancements in fip analysis and suggests further ways for research

modelling persistent methane seepage offshore western svalbard since early pleistocene abstract recent observations of extensive methane release into the oceans and atmosphere have raised concern as to whether rising temperatures across the arctic could drive rapid destabilization of gas hydrate reservoirs here we report modelling results from hydrate modulated methane seepage from vestnesa ridge offshore western svalbard suggesting that continuous leakage has occurred from the seafloor since the early pleistocene up until today sustained by modelled deep subsurface thermogenic sources of miocene age large scale hydrocarbon fluid migration started 6 million years ago and reached the seafloor some 4 million years later the modelling results indicate that widespread methane seepage offshore western svalbard commenced in earnest during early pleistocene significantly older than late holocene as previously reported we propose that the onset of vertical hydrocarbon migration is the response of rapid burial of potential hydrocarbon sources induced by increased sediment deposition following the onset of northern hemisphere glaciations 2 7 million years ago from the modelling results we propose that source rock intervals capable of generating hydrocarbons and hydrocarbon reservoirs buried kilometers deep have continuously fueled the gas hydrate system off western svalbard for the past 2 million years it is this hydrocarbon system that primarily controls the thermogenic methane fluxes and seepage variability at the seabed over geological times

diverse fracture properties and their impact on performance in conventional and tight gas reservoirs saudi arabia the unayzah south haradh case study the upper permian carboniferous unayzah formation in south haradh saudi arabia includes two major mechanical and petrophysical layers that are separated by shale rich zones open tectonic fracture clusters are rare and not essential for fluid flow in the unayzah a zone which has high porosity and permeability however such fracture clusters are essential to and impact the production performance in the unayzah b c tight gas reservoir the occurrence of the tectonic fractures in the unayzah formation is linked to the rock mechanical properties which vary with porosity shale volume cement type and texture the b c unit is more fractured than the a unit but its layers vary in the degree of fracturing the variation in fracture development within the b c unit results in differences in fracture enhanced permeability based on production profiles where flow is restricted to preferentially fractured mechanical layers that lack effective vertical fluid communication with other layers we identify two tectonic fracture systems an older subordinate fully mineralized system and a younger primary mostly open system early extensional fractures including joints and faults developed parallel to the basement faults during the opening of the neotethys these are fully mineralized and have little or no function as fluid conduits the younger system includes open fracture clusters that are predominantly parallel or nearly parallel to the regional east northeast west southwest maximum horizontal stress of the zagros that has been active since the late cretaceous and is independent of local structures therefore these fractures are controlled by remote stresses instead of the basement rooted forced folds and faults in this article we demonstrate that in the unayzah b c natural fractures are essential to permeability and in some areas to porosity and thence to reservoir performance the results of this study are being implemented in well placement and completion design to optimize the intersection of open fracture clusters with positive preliminary results

distribution of subsurface hydrocarbon seepage in near surface marine sediments hydrocarbon seeps in surficial marine sediments are of two types active and passive active seeps occur where gas bubbles pockmarks or bright spots are visible on seismic profiles and where chemosynthetic communities are present in conjunction with large concentrations of migrated hydrocarbons macroseeps these generally occur where generation and migration of hydrocarbons from source rocks are ongoing today at maximum burial or where significant migration pathways have developed from recent tectonic activity passive seeps occur where concentrations of migrated hydrocarbons are usually low microseeps with few or no geophysical anomalies these occur typically in areas where generation and expulsion is relict no longer at maximum burial or regional seals prevent significant vertical migration the type of seepage controls the distribution of migrated hydrocarbons in the near surface sediments and should dictate the sampling equipment and approach used to detect seeps active seeps are usually detected near the water sediment interface in the water column or at the sea surface and at relatively large distances from major leak points most conventional sediment and water samplers can capture active seeps the gulf of mexico santa barbara channel and parts of the north sea have active hydrocarbon seeps passive seeps can only be detected relatively far below the water sediment interface and require samples to be collected near leak points sampling equipment must penetrate the zone of maximum disturbance or any shallow migration barriers in areas where surficial sediments are coarse grained or compacted conventional gravity corers will not work other options for subsurface sampling include vibracores jet cores and rotary cores precise location of samples site specific using seismic profiles to locate leak points is critical to detect passive hydrocarbon seeps the beaufort and bering seas offshore alaska and parts of the north sea contain passive seeps

fluid percolations in a fault zone a study of fluid inclusion planes in the st sylvestre granite northwest massif central france abstract a method for relating fluid flow evolution direction of fluid percolation to the bulk brittle network microfracture system at each state in a sequence of deformational events is presented fluids percolating through cracks are generally trapped as fluid inclusion planes alignment of fluid inclusions the method involves the use of fluid inclusions not only as a tool for the establishment of the physico chemical conditions under which fluids were entrapped but also as a microstructural marker of the geometry of permeability the study shows that through the determination of the paleopressures for each stage of fluid migration the chronology of the cracks and p t conditions prevailing during each crack formation can be established this methodology has focussed on a granitic example from the french massif central but may be applied to other geological environments

dynamic analysis of deformed quartz grains from the folded middle miocene momonoki subgroup of central japan origin of healed microcracks abstract dynamic analyses have been performed on quartz detrital grains from the sandstones of folded middle miocene strata momonoki subgroup found along the itoigawa shizuoka tectonic line istl central japan these quartz grains contain numerous deformation lamellae kink bands and healed microcracks in this study in addition to the dynamic analysis using deformation lamellae the arrow method of carter and friedman the c axis preferred orientations of kinked and unkinked grains and the preferred orientations of healed microcracks in individual grains are analyzed in order to test if these fabrics can be used to determine the palaeostress field in the case of basal a slip being dominant which probably holds for the analyzed quartz the principal stress axes can be inferred from the c axis preferred orientations of kinked and unkinked grains referred to as the kink method here because the preferred orientations indicate the favourable and unfavourable orientations respectively under stress for basal a slip results of the dynamic analyses of deformed quartz by the arrow method and by the kink method are consistent with each other and presumably indicate the palaeostress field associated with the macroscopic folding of the momonoki subgroup although the origin and timing of healed microcracking in the deformed quartz are not completely resolved the preferred orientation of poles to healed microcracks seems to consist of two or three sets of orthogonally disposed maxima whose directions coincide with the principal stress axes responsible for the crystal plasticity i e the lamellae and kinks in the quartz it is suggested that the successive release of residual tectonic stresses in the principal stress directions led to this orthogonal orientation pattern of healed microcracks in the present study then combined dynamic analyses of deformed quartz using deformation lamellae kink bands and healed microcracks provide a more complete quantitative picture of the bulk stress field during deformation particularly the combination of the arrow method with the kink method the latter applied to naturally deformed quartz for the first time in this study provides an indication of the relative magnitude of principal stresses finally in the context of the influence of fluids on the deformation processes in rocks i would like to stress that microcracking in crystalline or consolidated rocks is essential for the incorporation of enough fluid into the constituent crystals to activate fluid assisted deformation processes such as solution precipitation creep and that the regional development of microcracks may be controlled by the stress field associated with the fold development in layered consolidated rocks

microhabitat preferences of live benthic foraminifera and stable carbon isotopes off sw svalbard in the presence of widespread methane seepage abstract to constrain the use of and better calibrate benthic foraminiferal carbon isotope based proxies 13c we analyzed live rose bengal stained benthic foraminifera from fjords outer shelves and the upper continental slope of sw svalbard we further investigated whether the presence of widespread methane seepage altered benthic foraminiferal 13c the one to one relationship between the 13c of cibicidoides wuellerstorfi and cibicides lobatulus tests and the 13cdic of bottom water in nordic seas was reconfirmed we also confirmed an almost constant 13c of live specimens of infaunal species melonis zaandamae nonion labradoricum and globobulimina affinis independent of their subbottom sampling depth and pore water 13cdic at any given site this is in contrast to the wide range of intraspecific 13c values of both epifaunal as well as infaunal species observed between sites we did not find significant correlations between foraminiferal 13c minus site specific 13cdic 13cfor dic of the investigated species and the total organic carbon toc contents of surface sediments on the contrary a distinct relationship is observed between high marine organic carbon moc contents and low 13cfor dic values of n labradoricum and to a lesser extent g affinis these findings are important because on the one hand they confirm a systematic influence of the availability of labile moc on deep infaunal species 13c whereas on the other hand they document the independence of epifaunal and infaunal species 13c of toc contents in well ventilated bottom water and organic rich surface sediment generally species mean 13c reflects their average living depths ald5 such that epifaunal and shallow infaunal species depict highest and deep infaunal species lowest 13c values mean 13cfor dic values of neither epifaunal c lobatulus and c wuellerstorfi 0 05 0 06 nor of infaunal m zaandamae 2 40 0 07 n labradoricum 2 69 0 13 and g affinis 3 48 0 15 seem to be significantly influenced by strongly elevated methane concentrations in the water column widespread gas seepage at the sea floor and low pore water 13cdic the latter possibly partly due to methanotrophic oxidation the 13c values of deep infaunal n labradoricum and g affinis minus epifaunal 13c values 13cnlab cib and 13cgaff cib seem to decrease with increasing toc and moc contents however only the 13cnlab cib values correlate significantly with moc contents and thus marine primary productivity dissolved oxygen concentrations estimated on the basis of 13cgaff cib values of 230 mol kg are in accordance with reported well oxygenated bottom water conditions at all stations

depositional environment and source rock potential of miocene strata from the central fram strait introduction of a new computing tool for simulating organic facies variations abstract organic rich sediments were recognized in early miocene strata from the norwegian greenland sea during odp leg 151 three organic geochemical subunits were distinguished in hole 909c using detailed organic geochemical and microscopic analyses toc up to 3 wt hi up to 200 mg hc g toc and 13corg values 24 26 indicate the predominance of terrestrial type iii organic matter in subunit 3 18 16 2 ma biomarker and vitrinite reflectance values r0 0 5 point to rather fresh immature terrestrial organic matter supplied by river discharge from adjacent vegetated coastal areas although the sediments of subunit 3 have a fair to good source rock potential they are insufficiently mature to generate significant amounts of oil or gas to test if the moderate generation potential and source rock quality of subunit 3 are applicable to the entire area the computer software of mod was applied several modelling runs testing the most probable depositional scenarios result even under conservative assumptions in the formation of good to excellent source rocks towards the basin margins

carbon isotopic distribution of methane in deep sea hydrothermal plume myojin knoll caldera izu bonin arc implications for microbial methane oxidation in the oceans and applications to heat flux estimation the concentration and stable carbon isotopic composition 13c of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the myojin knoll caldera izu bonin arc in the western north pacific the hydrothermal end member concentrations and 13c of methane show near homogeneity among vents 41 2 mol kg and 16 3 0 8 pdb respectively while those in the effluent plume are stratified in the caldera and vertically exhibit a large variation 2 1 11 nmol kg and 29 0 to 11 3 pdb respectively comparison of concentration and 13c data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume assuming steady state emission of methane from the vents 1 kinetic isotope effect due to the microbial oxidation k12 k13 2 methane flux from the vents fvents 3 heat flux from the vents q and 4 average turnover time of hydrothermal methane tall are estimated to be k12 k13 1 005 0 001 fvents 90 340 mol d q 30 110 mw and tall 60 240 d respectively the estimated turnover times however are not uniform within the water column around the vents a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean while those at the distant points correspond to values more typical for deep ocean water

near surface in situ stress 3 correlation with microcrack fabric within the new hampshire granites we studied the correlation between near surface in situ stress and the preferred orientation of microcracks at two quarries in the milford granite and one quarry in the conway granite new hampshire the orientation of in situ stress was determined by overcoring doorstoppers and from the strike of induced borehole fractures produced by a pressurized packer the preferred orientation of vertical microcracks was determined using ultrasonic measurements to determine p wave velocity vp on core and in situ and from thin section analyses in situ vp anisotropy was determined from interborehole travel time data at all three sites directions of maximum compressive stress 1 and induced borehole fractures are aligned with the preferred orientation of open microcracks determined from core vp and thin section data an analysis of the microcracking sequence within each pluton suggests 1 that the quarry grain resulted from cooling induced thermal stresses and 2 a method of distinguishing the paleostress axes at the time of cooling from contemporary stress

light hydrocarbon gases in shallow sediments in the northern north sea abstract large amounts of data on hydrocarbons in shallow marine sediments 0 6 m below sea floor have been gathered on the norwegian sector in conjunction with surface exploration for petroleum seepage in this paper some results from a re investigation of five surveys is presented the surveys include a total of 2136 shallow cores and cover mainly the stord basin and the viking graben areas offshore western norway adsorbed gases interstitial gases headspace gases grain size and inductively coupled argon plasma elemental data have been investigated table 1 the adsorbed methane ranges from 10 to 5000 ppb it has a uni modal distribution with a median concentration of 504 ppb weight weight the interstitial methane ranges from less than 1 to 500 ppb it has a uni modal distribution with a median concentration of 13 4 ppb there are two classes of headspace methane samples a normal class comprising about 90 of the samples lies in the range 0 1 to 500 ppb with a median of 2 1 ppb the second class lies in the range 500 to more than 100 000 ppb with a median of 6990 ppb the ratio of unsaturated to saturated alkane homologues in the interstitial and headspace gasses is on average equal to one and show positive correlation this rules out thermogenic hydrocarbons as a direct source for the headspace and interstitial gasses the proportion of unsaturated hydrocarbons in the adsorbed gas is much lower the highest interstitial methane contents are found in sediments with high contents of coarse material principal component analysis show that the yields dryness and isotopic composition of adsorbed methane correlate positively with the contents of calcium and strontium the sr ca ratio in the sediments and the proportion of silt size material in the sediments we infer from this that a major component in the adsorbed gas is cogenetic with carbonates in the fine fraction probably resulting from in situ bacterial degradation of organic matter distinct and unquestionable regional headspace gas anomalies are found within the quaternary kleppe senior kse formation of soft silty marine glaciomarine clays outside of kse only background levels of headspace methane is observed some of the most prominent headspace gas anomalies correlate very well with a shallow gas accumulation in a sand body just 10 20 m below sea floor we conclude that gas found at the surface has migrated upwards from this sand body the 1 3 c 1 2 c isotopic ratio for the anomalous methane 51 to 100 ppt and its extremely dry characteristics are typical for a biogenic origin we speculate that shallow biogenic gas may be a secondary form of carbon related to leakage from petroleum deposits at depth in this very prolific area

gas hydrate and associated free gas in the dongsha area of northern south china sea abstract a large ongoing cold seep named jiulong methane reef was discovered in the dongsha area of northern south china sea scs in 2004 to understand links among seafloor methane seepage subsurface gas hydrate origin of gas source and structural styles controlling the formation and accumulation of gas hydrate high resolution multi channel seismic data were interpreted in this region bottom simulating reflectors bsrs known as the base of gas hydrate stability zone were identified and mapped additionally seismic attributes interval velocity model and acoustic p wave impedance were obtained to better delineate the spatial distribution of gas hydrate hydrate bearing sediments are characterized by weak reflection i e blanking zone above bsrs high velocities and relatively small acoustic impedance differences while enhanced reflection low frequency and low velocities beneath bsrs suggest the presence of underlying free gas beneath solid hydrate a number of faults mud diapirs and a possible submarine landslide were observed in seismic profiles both faults and mud diapirs are useful conduits allowing methane gas to migrate upward and linking free gas zones beneath bsrs hydrate zones and seafloor methane seepage a submarine landslide with a length scale of 10 km is observed in a seismic profile the landslide may trigger dissociation of gas hydrate accounting for the occurrence of jiulong methane seepage seismic observations and estimated heat flow coupled with geochemical analyses suggest that gas source of methane in this region probably originates from mixture of biogenic and thermogenic methane this study would not only help to understand gas hydrate system in the dongsha area but also provide insights to geological hazards associated with the dissociation of gas hydrate

stress state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein types high ardenne slate belt germany abstract in the frontal part of the rhenohercynian fold and thrust belt high ardenne slate belt germany two successive types of quartz veins oriented normal and parallel to bedding respectively are interpreted to reflect the early variscan compressional tectonic inversion of the ardenne eifel sedimentary basin fracturing and sealing occurred in lower devonian siliciclastic multilayers under very low grade metamorphic conditions in a brittle upper crust a geometrical and microthermometric analysis of these veins has helped to constrain the kinematic and pressure temperature conditions of both vein types allowing the reconstruction of the stress state evolution in a basin during tectonic inversion it is demonstrated that bedding normal extension veins which developed under low differential stresses and repeatedly opened and sealed crack seal under near lithostatic fluid pressures reflect the latest stage of an extensional stress regime bedding parallel veins which developed at differential stresses that were still low enough to allow the formation of extension veins cross cut the bedding normal veins and preceded the regional fold and cleavage development these veins show a pronounced bedding parallel fabric reflecting bedding normal uplift and bedding parallel shearing under lithostatic to supra lithostatic fluid pressures during the early stages of a compressional stress regime this kinematic history corroborates that fluid overpressures are easy to maintain during compressional tectonic inversion at the onset of orogeny

fracture abundance and patterns in the subandean fold and thrust belt devonian huamampampa formation petroleum reservoirs and outcrops argentina and bolivia abstract opening mode fractures in devonian sandstones in outcrop and in several fields in the subandean ranges of southern bolivia and northern argentina compose two fracture sets i and ii that strike west northwest and north northeast respectively abundant set i fractures are at a high angle to local andean structural trends and set ii is aligned with fold axes crosscutting relations and quartz textures in fractures suggest that although set i is locally older these sets may have opened partly contemporaneously sets comprise both macroscopic fractures and more abundant millimeter scale microfractures fractures with opening displacement of less than 0 1 mm are typically sealed with quartz but wider fractures are lined with quartz and contain connected fracture porosity microfractures are more abundant than macrofractures and size distributions can be interpreted to approximate power laws microfracture strain is an efficient method of quantifying fracture abundance both sets record small fracture strains of 0 00016 0 0083 in backlimbs set i strain is higher in brittle quartz rich sandstones set ii strain varies markedly and is generally high in hinges and steep forelimbs of asymmetric anticlines for individual samples set i ii strains in fold hinges and forelimbs are comparable consistent with concurrent set i ii growth open fractures that could augment permeability are present both on and off structure but microfractures document fracture abundance that varies with structural position and sandstone quartz content that could account for variations in production outcomes

norwegian margin outer shelf cracking a consequence of climate induced gas hydrate dissociation a series of en echelon cracks run nearly parallel to the outer shelf edge of the mid norwegian margin the features can be followed in a 60 km long and 5 km wide zone in which up to 10 m deep cracks developed in the seabed at 400 550 m water depth the time of the seabed cracking has been dated to 7350 14c years bp 8180 cal years bp which corresponds with the main storegga slide event 8100 250 cal years bp reflection seismic data suggest that the cracks do not appear to result from deep seated faults but it cannot be ruled out completely that tension crevices were created in relation to past movements on the headwall of the storegga slide the cracking zone corresponds well to the zone where the base of the hydrate stability zone bhsz outcrops evidence of fluid release in the bhsz outcrop zone comes from an extensive pockmark field we suggest that post glacial ocean warming triggered the dissociation of gas hydrates while the interplay between dissociation overpressure and sediment fracturing on the outer shelf remains to be understood

late cenozoic seismic stratigraphy and glacial geological development of the east greenland and svalbard barents sea continental margins abstract the european program on the late cenozoic evolution of the polar north atlantic margins ponam running from 1990 to 1994 resulted in a wealth of seismic data and sediment cores particularly from the svalbard and barents sea continental margin but also from areas of the east greenland margin deep sediment coring was undertaken on both margins during odp legs 152 and 162 this paper uses the ponam generated information as well as previous and subsequent seismic and core data to review our present understanding of the glacial geological development of these regions four main depositional facies have been identified these are represented by hemipelagic glaciomarine sediments sandy silty debris flows diamictic debris flows and tills deposited directly beneath grounded ice the temporal and spatial distribution of these four facies determines the architecture and seismic character of the two continental margins the two regions show significant differences with regard to both the timing of initial glaciation and the response of the ice sheets to climatic variability glacial deposition has taken place on the east greenland margin at least since 7 ma but apparently only since 2 5 ma on the svalbard barents sea margin significant glacial expansion across the continental shelf probably occurred in the early and late pliocene in east greenland whereas the glaciers on svalbard and the barents sea did not reach the shelf edge until the early pleistocene despite a shorter glacial period average glacial sedimentation rates are 2 3 times higher on the svalbard barents sea margin than on the studied parts of the east greenland margin the svalbard barents sea ice sheet has advanced and retreated much more frequently during the plio pleistocene than the greenland ice sheet glacial regime polar on greenland and polythermal to temperate in svalbard and the barents sea and the more easily erodible preglacial bedrock of svalbard and the barents sea are thought to be main factors responsible for the differences in ice sheet behavior and consequently glacial sediment production

quantification of co occurring reaction rates in deep subseafloor sediments net rates of biogeochemical reactions in subseafloor sediments can be quantified from concentration profiles of dissolved reactants or products and physical properties of the sediment to study net rates of microbial activities in deep sediments we developed a robust approach that is well suited to use over a broad range of sediment depths our approach is based on a finite difference solution to a continuity equation that considers molecular diffusion sediment burial fluid advection and reaction under the assumption of steady state numerical procedures are adopted to identify the maximum number of depth intervals with statistically different reaction rates the approach explicitly considers downcore variation in physical properties and sample spacing uncertainties in the rate estimates are quantified using a monte carlo technique we tested our approach using synthetic concentration profiles generated from analytical solutions to the continuity equation we then applied the approach to concentration profiles of dissolved sulfate sulfide methane and manganese in the 420 m thick sediment column of eastern equatorial pacific ocean drilling program site 1226 our results indicate that i sulfate reduction and iron reduction occur at most sediment depths ii net methane production occurs in discrete depth intervals and iii manganese reduction occurs near the seafloor and deep in the sediments these results provide quantitative evidence that multiple respiration pathways co exist in the same depth intervals of these deep subseafloor sediments

holocene mass transport activity and climate in outer isfjorden spitsbergen marine and subsurface evidence the analyses of high resolution seismic data swath bathymetry data and sediment cores from the basin svensksunddjupet in isfjorden spitsbergen reveal the deposits of repeated slope failures most of the slope failures occurred during three periods at c 9650 cal bp 8350 8200 cal bp and 3000 cal bp suggested factors causing instability of the slopes include earthquake activity resulting from rapid isostatic uplift excess pore pressure caused by relative sea level fall and or the presence of gas as well as climatic changes mass transport deposits at the mouth of an incision at the southern slope of svensksunddjupet are suggested to mainly relate to runoff from the land based glacier vardebreen the increase of the mass transport activity may indicate that vardebreen either formed or increased in size at c 7000 cal bp

geochemical surface exploration for hydrocarbons in north sea approximately 350 sediment samples were taken in the central part of the north sea and hydrocarbon composition methane c1 and ethane c2 yields and carbon isotope composition of the methane dgr13c1 adsorbed in the sediment were determined methane generation or oxidation by bacterial activity can not be deduced from the analytical data this fact is explained by the assumption of a threshold of methane concentration in sediments below which methane oxidizing bacteria are inactive and that this threshold was not reached in the area investigated background gases in the surface sediments characterized by low c1 yields and dgr13c1 37 ppt can be distinguished from thermal sediment g ses which are obviously derived from a hydrocarbon generating source rock in the subsurface source rock data obtained from several wells situated on a cross section through the investigated area were compared to the geochemical patterns of the sediment gases and used to define profile sections with good dgr13c1 approx 40 ppt yield c1 approx 217 ppb and poor source rock properties dgr13c1 approx 33 ppt yield c1 approx 24 ppb an assessment of the source rock potential of the whole area under investigation has been carried out using the geochemical data of the surface sediment gases and taking into account that the c1 and c2 yields are generally higher in clay sediments than in sand samples the number of producing wells was related to the number of all wells 271 in the areas characterized by surface geochemistry as good or poor source rock areas the comparison showed that the relative number of producing wells is higher in areas geochemically characterized as good hydrocarbons in surface sediments of good north sea areas are not generated by bacteria at shallow depth they are formed thermally from the organic carbon of deep source rocks and migrate to the surface therefore they are indicative of thermal hydrocarbon generation in the subsurface

thermal evolution of the north central gulf coast the subsidence history of the north louisiana salt basin determined from well data indicates that the region underwent extension during rifting and has since passively subsided due to conductive cooling of the lithosphere timing of the rifting event is consistent with opening of the gulf of mexico during late triassic to early jurassic time crustal extension by a factor of 1 5 to 2 was computed from tectonic subsidence curves however data from the early subsidence history are insufficient to distinguish between uniform and nonuniform extension of the lithosphere the magnitude of extension is in good agreement with total sediment and crustal thicknesses from seismic refraction data in the adjacent central mississippi salt basin the temperature distribution within the sediments is calculated using a simple heat conduction model temperature and subsidence effects of thermal insulation by overlying sediments are included the computed temperature distribution is in good agreement with bottom hole temperatures measured in deep wells temperature histories predicted for selected stratigraphic horizons within the north louisiana salt basin suggest that thermal conditions have been favorable for hydrocarbon generation in the older stata results from a two dimensional heat conduction model suggest that a probable cause for the early formation of the adjacent uplifts is lateral heat conduction from the basin rapid extension of the lithosphere underneath areas with horizontal dimensions of 50 100 km produces extremely rapid early subsidence due to lateral heat conduction the moderate subsidence rate observed in the north louisiana salt basin during the jurassic and early cretaceous suggests slow extension over a long period of time

the biogeochemistry of sorbed methane in marine sediments abstract sorption of volatile hydrocarbon gases vhcs to marine sediments is a recognized phenomenon that has been investigated in the context of petroleum exploration however little is known about the biogeochemistry of sorbed methane and higher vhcs in environments that are not influenced by thermogenic processes this study evaluated two different extraction protocols for sorbed vhcs used high pressure equipment to investigate the sorption of methane to pure clay mineral phases and conducted a geochemical and mineralogical survey of sediment samples from different oceanographic settings and geochemical regimes that are not significantly influenced by thermogenic gas extraction of sediments under alkaline conditions yielded higher concentrations of sorbed methane than the established protocol for acidic extraction application of alkaline extraction in the environmental survey revealed the presence of substantial amounts of sorbed methane in 374 out of 411 samples 91 particularly high amounts up to 2 1 mmol kg 1 dry sediment were recovered from methanogenic sediments carbon isotopic compositions of sorbed methane suggested substantial contributions from biogenic sources both in sulfate depleted and sulfate reducing sediments carbon isotopic relationships between sorbed and dissolved methane indicate a coupling of the two pools while our sorption experiments and extraction conditions point to an important role for clay minerals as sorbents mineralogical analyses of marine sediments suggest that variations in mineral composition are not controlling variations in quantities of sorbed methane we conclude that the distribution of sorbed methane in sediments is strongly influenced by in situ production

mode i microfracturing and fluid flow in damage zones the key to distinguishing faults from slides abstract we have examined the distribution of microfractures in arenites and the evolution of vein forming fluids in the matrix of carbonate breccias within the damage zones of large detached blocks in order to characterize their modes of emplacement previous studies of microfractures in the damage zone associated with tectonic faulting have shown a clear pattern of increasing density as the fault is approached previous studies of carbonate breccia within damage zones of tectonic faults typically document evidence of multiple fluid events representing repeated rupture healing processes however in this study we find no change in the microfracture density with distance from the 45 km displaced gravity driven slide block at heart mountain wyoming in a previous study of the same massive slide block there was no evidence of multiple fluid infiltration events related to emplacement we interpret these observations as indicating the absence of rupture cycling that would be expected in the development of a process zone instead being consistent with catastrophic emplacement of gravity driven slide blocks we use this distinct pattern of microfracture density and fluid infiltration to demonstrate that several large 1 km2 detached blocks in the basin and range previously thought to be allochthons related to hyperextension detachment faults are actually slide blocks whose detachment surfaces represent no crustal extension

identification of fluid inclusions in relation to their host microstructural domains in quartz by cathodoluminescence abstract the geometry of fluid trapping in relation to microfracture healing or filling was investigated using massive quartz vein samples characterized by multistage deformation and fluid trapping the multidisciplinary approach used in this study includes 1 mapping of oriented thin sections of quartz using the cathodoluminescence cl mode of a scanning electron microscope sem sem cl images display areas of different intensities from dark to white which correspond to the intensity of the cl and are caused by trace elements present in the quartz microfracture healing by newly formed quartz crystallization may occur under physical chemical conditions different from those which characterized the early quartz matrix formation thus evidences of linear cathodoluminescent markers have been searched and identified by paralleling sem cl images and transmitted light microphotographs data show that cathodoluminescence makes clearly visible the healed crack networks which are only detected in part by transmitted light microscopy the technique is essential to establish the microcrack chronology and to estimate the width affected by healing along a fluid inclusion trail such data are useful for the estimation of the microfracture permeability changes throughout the history of fluid migration 2 systematic and statistical analysis of the microstructural markers in horizontal and oriented planes using an interactive videographic analyzer which gives the geometry of the paleofluid pathways orientation dip and width of the veinlets fluid inclusion trails and cathodoluminescent microdomains 3 microthermometric and raman analyses of fluid inclusions in selected fluid inclusions for the determination of the p v t x conditions of fluid migration in a specific microcrack network studied quartz samples come from au mineralized quartz veins from the french massif central and some quartz samples from the cassiar mountains in british columbia have been observed for comparison in all samples the quartz matrix exhibits intense microfracturing suggesting strong brittle deformation which postdates the main stage of quartz lens formation the quartz veins are characterized by multistage quartz crystallization healed microfractures clear quartz bands as well as quartz comb veinlets were studied as functions of the physicochemical conditions in relation to stages of deformation and ore deposition this study shows that systematic measurements of microstructural marker orientations together with detailed fluid inclusion and mineral petrography and microthermometry may lead to a precise determination of ore fluid pathways and chronology

cementation and burial history of a low permeability quartzarenite lower cretaceous travis peak formation east texas fine grained quartzarenites and subar koses in the lower cretaceous travis peak formation were extensively modified during burial diagenesis timing of diagenetic events can be constrained by combining petrographic and geochemical data with data on subsidence and thermal history the geothermal gradient in the east texas study area is 38 c km now but it may have been as high as 44 c km when the travis peak was deposited because of elevated heat flow caused by crustal stretching associated with rifting of the gulf of mexico illite rims and dolomite were the first authigenic minerals to precipitate in travis peak sandstones dolomite probably formed soon after deposition at about 25 c from water with a 18 o composition near smow next extensive quartz cement averaging 17 of the rock volume in well sorted sandstones occluded much of the primary porosity the average 18 o composition of the quartz overgrowths indicates that they precipitated from meteoric fluids at temperatures of between 55 and 75 c at depths of 1 to 1 5 km dissolution of orthoclase and albitization of plagioclase followed quartz cementation and occurred prior to mid cretaceous movement of the sabine uplift illite chlorite and ankerite precipitated after feldspar diagenesis the ankerite may have precipitated over a range of temperatures from about 80 to 125 c from fluids with 18 o composition of about 2 smow 2 is the average present composition of travis peak water most diagenesis ended when oil migrated into the travis peak later de asphalting of the oil by solution of gas filled much of the remaining porosity with reservoir bitumen in some zones near the top of the formation

hydrocarbon plumbing systems above the snohvit gas field structural control and implications for thermogenic methane leakage in the hammerfest basin sw barents sea abstract based on the analysis of the high resolution 3d seismic data from the sw barents sea we study the hydrocarbon plumbing system above the snohvit and albatross gas field to investigate the geo morphological manifestation and the dynamics of leakage from the reservoir fluid and gas escape to the seafloor is manifested in this area as mega pockmarks 1 2 km wide large pockmarks

fluid inclusions tectonic indicators abstract during the first half of the 20th century fluid inclusions have been studied in ore geology in order to determine the chemistry and physical parameters density of the mineralising fluids apart from a few pioneering works in the middle of the century fluid inclusions were not used as structural markers before the late 1980s during the same time experiments as well as observations of natural samples have shown that the volume shape and density of fluid inclusions may change when submitted to pressure temperature conditions different from their trapping isochores in view of these experiments and based on natural examples from the higher himalaya metamorphic rocks it is evident how fluid inclusions can be used as thermobarometric structural and tectonic markers points of interest for further studies on fluid inclusions in nature and experiments are also stressed

microfracturing and regional stress field a study of the preferred orientations of fluid inclusion planes in a granite from the massif central france abstract a study of the deformation of a granitic massif indicates a relationship between palaeostress fields and the geometry of microfractures as defined by fluid inclusion trails that is healed microfractures a statistical study of the distribution of the trails leads to the following conclusions trails exhibit several distinct preferred orientations on the scale of a grain which may be observed in many samples the orientations of the trails are similar to those of micro and mesoscale fractures in the granite and the dominant trail direction is parallel to the main direction of regional shortening thus fluid inclusion trails are mode i cracks which can be used as excellent markers of palaeostress fields

evidence of fluid seepage in gronfjorden spitsbergen implications from an integrated acoustic study of seafloor morphology marine sediments and tectonics abstract this study integrates high resolution surface and sub surface geophysical data to investigate possible fluid gas and or liquids migration pathways to the seafloor in gronfjorden west spitsbergen gronfjorden is an n s aligned tributary fjord located in the western part of the isfjorden fjord system pockmarks were identified on the bathymetric data in the southern and northern parts of the fjord three types of shallow seep related acoustic features have been identified in the marine sediments i enhanced reflections ii acoustic turbid zones and iii acoustic blankings they occur beneath some of the pockmarks and circular patches of high backscatter on the seafloor in the central part of the fjord which are potential seep related seafloor features 6 8 km long nnw sse striking ridges have been identified in the southern part of the study area thrust faults were interpreted on 2d multichannel seismic data truncating the triassic jurassic and cretaceous successions of western isfjorden located north of gronfjorden a possible link has been found between these fault systems and the seafloor ridges which strike in a similar direction further a normal fault has been identified within the shallow marine sediments which drapes the bedrock of the fjord the fractured bedrock of the fjord and faults associated with the west spitsbergen fold and thrust belt could possibly represent major conduits for fluid migration from deeper stratigraphy to shallow marine sediments and the seafloor

correlation between deformation lamellae microfractures macrofractures and in situ stress measurements white river uplift colorado dynamic analyses of quartz deformation lamellae and microfractures in lower paleozoic quartzites from the white river uplift record a northwest direction of compression which can be related to joint and fault orientations and in situ stress determinations crystallographic orientations of deformation lamellae resemble those formed in the subbasal i relatively nonselective domain microfractures in quartz grains form orthogonal sets of generally north northeast and west northwest trending fracutres which are approximately normal to bedding the strongest set of microfractures in most samples lies in the 2 plane deduced from deformation lamellae analyses suggesting that the microfractures are extensional features maxima of microfractures correspond to maxima of joints measured at adjacent locations the strikes of prominent west northwest sets of microfractures and joints are subparellel to the dominant northwest strike of faults on the uplift in situ stress measurements conducted in the piceance basin and rangely colorado areas indicate principal stress orientations similar to those determined from quartz deformation lamellae microfractures and joints which are pre uplift to early uplift late laramide fabric elements

fluxes and fate of dissolved methane released at the seafloor at the landward limit of the gas hydrate stability zone offshore western svalbard widespread seepage of methane from seafloor sediments offshore svalbard close to the landward limit of the gas hydrate stability zone ghsz may in part be driven by hydrate destabilization due to bottom water warming to assess whether this methane reaches the atmosphere where it may contribute to further warming we have undertaken comprehensive surveys of methane in seawater and air on the upper slope and shelf region near the ghsz limit at 400 m water depth methane concentrations are highest close to the seabed reaching 825 nm a simple box model of dissolved methane removal from bottom waters by horizontal and vertical mixing and microbially mediated oxidation indicates that 60 of methane released at the seafloor is oxidized at depth before it mixes with overlying surface waters deep waters are therefore not a significant source of methane to intermediate and surface waters rather relatively high methane concentrations in these waters up to 50 nm are attributed to isopycnal turbulent mixing with shelf waters on the shelf extensive seafloor seepage at 100 m water depth produces methane concentrations of up to 615 nm the diffusive flux of methane from sea to air in the vicinity of the landward limit of the ghsz is 4 20 mol m 2 d 1 which is small relative to other arctic sources in support of this analyses of mole fractions and the carbon isotope signature of atmospheric methane above the seeps do not indicate a significant local contribution from the seafloor source

a large methane plume east of bear island barents sea implications for the marine methane cycle a pockmark field extending over 35 km2 at 74 54 n 27 3 e described by solheim and elverhoi 1993 was re surveyed and found to be covered with more than 30 steep sided craters between 300 and 700 m in diameter and up to 28 m deep the craters are thought to have been formed by an explosive gas eruption anomalously high concentrations of methane in the shelf waters around the craters suggest that a strong methane source near this area is still active today methane enrichment more than 10 km away from the crater field indicates the large dimensions of a plume and the amount of gas released from sources below the seafloor of the barents sea shelf from the characteristic vertical decrease of methane towards the sea surface it is concluded that biota are extensively using this energy pool and reducing the methane concentration within the water column by about 98 between 300 m depth and the sea surface degassing to the atmosphere is minimal based on the shape of the methane concentration gradient nevertheless the net flux of methane from this area of the barents sea is about 2 9 104 g ch4 km 2 yr 1 and thus in the upper range of the presently estimated global marine methane release this flux is a minimum estimate and is likely to increase seasonally when rough weather leads to more effective vertical mixing during autumn and winter the amount of methane consumed in the water column however is about 50 times greater and hence should significantly contribute to the marine carbon inventory

fractures generated during folding of the palmerton sandstone eastern pennsylvania a syncline of devonian palmerton sandstone exposed in a quarry in the fold thrust belt of eastern pennsylvania contains a set of fractures that are perpendicular to bedding and strike parallel to the fold axis fracture spacing is between 0 25 and 30 cm these fractures are zones of cataclasis that have striated shear surfaces displacement on fractures where measurable is less than 1 cm sparse kinematic evidence suggests that slip on fractures could have contributed to growth of the fold petrographic evidence shows that slip is in part localized along pre existing mineralized fractures which probably formed during burial lithification and diagenesis of the palmerton sandstone in an extensional structural setting the unusual shear fracture pattern illustrated by the palmerton sandstone may result from slip on these early fractures during thnist sheet displacement along a thrust ramp this exposure also illustrates the operation of contrasting deformation mechanisms in sandstone and in vertically ad

a method to detect natural fracture strike in sandstones in siliciclastic hydrocarbon reservoir rocks economic gas and oil production may depend on the attributes of natural fractures and with the advent of horizontal drilling fractures are increasingly exploration and development targets yet reliable information on such key fracture attributes as orientation strike is sparse because few fractures intersect vertical well bores this paper describes how fracture strike can be documented on a bed by bed basis even in well bores where few or no visible fractures are directly sampled quartz lined opening mode microfractures lengths of microns to millimeters in quartz cemented sandstones commonly are not visible using standard petrographic methods but systematic mapping of these microfractures is possible using photomultiplier based electron beam induced luminescence scanned cathodoluminescence imaging as shown by observations primarily from three natural gas plays and one oil play in the united states microfracture strike is a good guide to the strike of large fractures macrofractures that formed concurrently because microfractures are widespread and small specimens can be used to get accurate fracture strike data this approach can be applied to samples obtained from wireline conveyed rotary drilled sidewall coring devices as well as to samples from full diameter core

contourites in the fram strait abstract multichannel seismic reflection profiles from the fram strait show many features that can be attributed to bottom current influence on the sediments by comparison with well known contourite sequences elsewhere a greater than 2 km thick contourite drift with a smooth internal reflection pattern is observed northwest of svalbard the currents here have probably been controlled by local topography we interpret sequences with abundant diffractions in the broader basins to be current related probably deposited during periods of intensified circulation the continental slopes on the svalbard side have fairly continuous sequences whereas the younger sequences on the greenland lower slope onlaps the lowermost one this can be attributed to differences in current regime sediment supply or margin subsidence the contourites of the lower slope in the northeastern part of the strait about 1000 m water depth can be explained by long term influence of the west spitsbergen current but current influenced patterns down to 3000 m water depth are not compatible with the weak deep water circulation observed at present the oldest contourites west of svalbard are estimated to be of late miocene to pliocene age between 10 and 3 ma based on correlation to the dsdp site 344 and inferred basement ages near the present plate boundary hiatuses may be present beneath the contourites the onset of currents may be related to opening of the gateway between greenland and svalbard to climatic cooling and to palaeogeographic changes outside the fram strait contourite deposition has continued through the late neogene and quaternary but vertical changes in the pattern suggest that current intensities have decreased through time

gas hydrate stability zone modelling in areas of salt tectonics and pockmarks of the barents sea suggests an active hydrocarbon venting system the barents sea seabed exhibits an area of major glacial erosion exposing parts of the old hydrocarbon basins in this region we modelled the gas hydrate stability field in a 3d perspective including the effects of higher order hydrocarbon gases we used 3d seismic data to analyse the linkage between fluid flow expressions and hydrate occurrences above old sedimentary basin systems and vertical faults pockmarks showed a relation to fault systems where some of them are directly connected to hydrocarbon bearing sedimentary formations the influence of bottom water temperature pore water salinity and geothermal gradient variation on gas hydrate stability zone ghsz thickness is critically analysed in relation to both geological formations and salt tectonics our analysis suggests a highly variable ghsz in the barents sea region controlled by local variations in the parameters of stability conditions recovery of gas hydrate sample from the region and presence of gas enhanced reflections below estimated bsr depths may indicate a prevalent gas hydrate stable condition

evolution of solution structures in a deformed quartz arenite geometric changes related to permeability changes abstract quartz arenite of the silurian keefer sandstone at a site in west virginia u s a records an early pervasive solution related deformation by grain interpenetration volume losses measured by the pss method show shortening directions from both diagenetic compaction and early tectonic layer parallel shortening later solution related tectonic deformation during folding formed transgranular stylolites along pre existing faults or in rock volumes with abundant microfractures thus the geometry of solution related deformation changed progressively from pervasive at grain scale to focused along transgranular surfaces we propose that this geometric change resulted from intense porosity and permeability reduction during diagenetic cementation and early layer parallel shortening which required fluids to exploit tectonically created pathways along faults or networks of microfractures during later deformation

thermogenic hydrocarbons in surface sediments of the bransfield strait antarctic peninsula antarctica is the only continent from which petroleum deposits have not been encountered despite the occurrence of potential hydrocarbon basins onshore and around its margins we have discovered thermogenic hydrocarbons in unconsolidated recent sediments from the king george basin bransfield strait west antarctica these sediments possessed a marked petroliferous smell throughout the length of the 8 6 m gravity core the basin sediments are glacial marine deposits dominated by turbidites and contain abundant autochthonous organic matter as a result of high seasonal primary productivity in this most fertile part of the circumpolar ocean1 the maturation of this material into hydrocarbons may have been accelerated by the high geothermal gradient in the basin associated with back arc spreading created by the subduction of the drake plate into the south shetland trench2 sediments in this rifted basin are frequently intruded by volcanic sills and dykes3 giving rise to acoustic features shown in fig 1 the presence of these thermogenic hydrocarbons provides the first demonstration of active source rocks in antarctica

linked fluid and tectonic evolution in the high himalaya mountains nepal fluid inclusions were studied in a quartz lens from the structurally highest unit of the himalaya mountains in nepal from a textural geometrical chemical and isotopic point of view six types of fluid inclusions were distinguished one of these types consists of annular inclusions this shape is attributed to a confining pressure increase in a non isotropic stress field two successive stress fields were deduced from the orientation of the inclusion planes relative to the schistosity the bulk composition of the fluid was dominated by co2 84 mol and h2o the composition remained constant during the whole history of the sample indicating that it was buffered by the carbonaceous host rock and or that one single fluid was reworked in situ by decrepitation stable isotope of fluids and minerals indicate 1 that fluids were buffered by surrounding rocks for o and c and 2 that at least two types of water metamorphic and meteoric were involved finally a p t t e path is proposed for the sample taking into account the southward thrusting along the main central thrust the northward tectonic denudation of the himalaya mountains inducing tectonic burying below the annapurna range and lastly rapid uplift

the sensitivity of gas hydrate reservoirs to climate change perspectives from a new combined model for permafrost related and marine settings abstract gas hydrate reservoirs store large quantities of gas in sediments on continental margins in deep lakes and in continental and relic sub shelf permafrost the gas hydrate structure is only stable at sufficiently low temperature and high pressure and may therefore collapse under changing climatic conditions if a temperature rise or pressure drop e g through falling sea level is effective enough to dissociate hydrate deposits methane the most common gas component in hydrates and a potent greenhouse gas is released from the hydrate structure and may eventually enter into the atmosphere this may generate a positive feedback effect as resulting enhanced greenhouse gas levels would additionally warm the atmosphere and hence maintain or reinforce hydrate dissociation the significance of this mechanism has been debated over the past decades often within the framework of geologically rapid quaternary climatic oscillations and present day climate warming an extensive set of studies has addressed the climate sensitivity of gas hydrate reservoirs in various study areas and geological settings and by means of various approaches no real consensus has yet been reached on the matter in this study we seek to evaluate the sensitivity of gas hydrate reservoirs to changes in global climate from a more general perspective by firstly reviewing the available literature and secondly developing a new numerical model to quantify gas hydrate destabilization under changing environmental conditions qualities of the model include the wide applicability to both marine and permafrost related hydrate reservoirs and the integrative approach combining existing hydrate formation models with a dissocation model that accounts for the consumption of latent heat during hydrate dissociation to determine which settings are most vulnerable and to acquire insight into the extent fashion and rates of hydrate dissociation we apply the model to four distinct types of hydrate reservoirs across a hypothetic high latitude continental margin under two specific cases of climate change the last deglaciation following the last glacial maximum and present day climate warming the simulations indicate that hydrates on the upper continental slope and in association with thin sub shelf permafrost are most sensitive to the imposed climatic variations whereas deepwater and onshore permafrost related reservoirs react in a more stable way however the deep i e at several tens to hundreds of meters subsurface depth stratigraphic type hydrates considered in this study constitute by far the largest fraction of the global gas hydrate volume but dissociate on slow timescales of thousands to hundreds of thousands of years even in the most sensitive environments in contrast shallow i e at or a few meters below the surface or seafloor structural type hydrates are able to respond to climatic variations on sub millennial timescales but the volumes of gas they may release are probably insignificant to the global carbon cycle and climate quaternary and present day climate change do affect the stability of gas hydrate reservoirs but at long timescales where hydrate volumes are large and on short timescales where hydrate volumes are small consequently gas hydrates dissociate to an extent that is too small or at a pace that is too slow to create a strong positive feedback effect while the release of methane from the disintegration of gas hydrates is observed on different margins today it is not likely to have played a leading role in quaternary climatic variations or to become a significant process in the coming centuries as a result of present day rising temperatures

mechanical and fracture stratigraphy using examples from core studies this article shows that separate identification of mechanical stratigraphy and fracture stratigraphy leads to a clearer understanding of fracture patterns and more accurate prediction of fracture attributes away from the wellbore mechanical stratigraphy subdivides stratified rock into discrete mechanical units defined by properties such as tensile strength elastic stiffness brittleness and fracture mechanics properties fracture stratigraphy subdivides rock into fracture units according to extent intensity or some other observed fracture attribute mechanical stratigraphy is the by product of depositional composition and structure and chemical and mechanical changes superimposed on rock composition texture and interfaces after deposition fracture stratigraphy reflects a specific loading history and mechanical stratigraphy during failure because mechanical property changes reflect diagenesis and fractures evolve with loading history mechanical stratigraphy and fracture stratigraphy need not coincide in subsurface studies current mechanical stratigraphy is generally measurable but because of inherent limitations of sampling fracture stratigraphy is commonly incompletely known to accurately predict fractures in diagenetically and structurally complex settings we need to use evidence of loading and mechanical property history as well as current mechanical states

methane in shallow subsurface sediments at the landward limit of the gas hydrate stability zone offshore western svalbard offshore western svalbard plumes of gas bubbles rise from the seafloor at the landward limit of the gas hydrate stability zone llghsz 400 m water depth it is hypothesized that this methane may in part come from dissociation of gas hydrate in the underlying sediments in response to recent warming of ocean bottom waters to evaluate the potential role of gas hydrate in the supply of methane to the shallow subsurface sediments and the role of anaerobic oxidation in regulating methane fluxes across the sediment seawater interface we have characterised the chemical and isotopic compositions of the gases and sediment pore waters the molecular and isotopic signatures of gas in the bubble plumes c1 c2 1 104 13c ch4 55 to 51 d ch4 187 to 184 are similar to gas hydrate recovered from within sediments 30 km away from the llghsz modelling of pore water sulphate profiles indicates that subsurface methane fluxes are largely at steady state in the vicinity of the llghsz providing no evidence for any recent change in methane supply due to gas hydrate dissociation however at greater water depths within the ghsz there is some evidence that the supply of methane to the shallow sediments has recently increased which is consistent with downslope retreat of the ghsz due to bottom water warming although other explanations are possible we estimate that the upward diffusive methane flux into shallow subsurface sediments close to the llghsz is 30 550 mmol m 2 yr 1 but it is 20 mmol m 2 yr 1 in sediments further away from the seafloor bubble plumes while anaerobic oxidation within the sediments prevents significant transport of dissolved methane into ocean bottom waters this amounts to less than 10 of the total methane flux dissolved gas into the shallow subsurface sediments most of which escapes aom as it is transported in the gas phase

deep seismic transects across the sheared western barents sea svalbard continental margin abstract we have used recently acquired deep seismic reflection and refraction profiles together with a large amount of conventional mcs data to study the 1000 km long sheared western barents sea svalbard margin with the objective of determining its crustal structure and tectonic history the margin developed from a megashear zone which linked the norwegian greenland sea and the eurasia basin during the eocene opening the margin is composed of two large shear segments and a central rifted margin segment associated with volcanism the continent ocean boundary is confined within a narrow zone 10 20 km at the sheared margin segments but is more obscure and partly masked by volcanics at the rifted margin the crustal structure and tectonic history differ significantly between the three margin segments in the north across the hornsund fault zone the crustal thickness changes abruptly from more than 30 km thick continental crusy on the svalbard platform to 6 8 km thick oceanic crust in the greenland sea this margin segment experienced oblique continent continent and partly continent ocean shear with both transtensional and transpressional component during eocene time while post eocene extension caused crustal stretching west of svalbard the volcanic province at the central rifted margin segment probably comprises an outer part of thick oceanic crust and an inner part of thinned continental crust covered by a mixture of volcanics and sediments this formed at a releasing bend in the margin in response to eocene oligocene extension and two phases of volcanism in the south the crustal thinning occurs over a wider area landward of the senja fracture zone here the margin bounds a basinal province in which as much as 18 20 km of sediments cover a highly attenuated crystalline crust the senja fracture zone evolved due to eocene transtensional continent continent shear followed by continent ocean shear and has been passive since earliest oligocone time we conclude that the first order crustal structure along the margin and its tectonic development is mainly the result of three controlling parameters 1 1 the pre breakup structure 2 2 the geometry of the plate boundary at opening and 3 3 the direction of relative plate motion the interplay between the direction of plate motion and the geometry of the plate boundary gave rise to striking differences in the structural development of the different margin segments

paleostress directions from the preferred orientation of closed microfractures fluid inclusion planes in sandstone east texas basin u s a abstract closed extensional microfractures are useful indicators of paleostress directions in shallowly buried quartz cemented quartz arenites of the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 670 m thick that was deposited in the gradually subsiding northern gulf of mexico basin the closed microfractures are syndiagenetic fluid inclusion rich planes that have an ene strike that is subparallel to contemporary quartz filled extension veins and regional normal faults indicating that closed microfractures contain the maximum paleostress direction these microstructures are potentially useful for mapping paleostress trajectories in passive margin and platform settings particularly where samples are obtained from core previous experimental studies of microfracture closure suggest that microfractures evolved into fluid inclusion planes by dendritic quartz precipitation in east texas microfracture closure may have occurred at temperatures as low as 85 c and depths as shallow as 1500 m

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

microfractures within the fault damage zone record the history of fault activity 1 for faults without sedimentary covers there is no robust method to obtain paleoseismic data that is crucial for the prediction of future damaging earthquake events sudden failure along faults during earthquakes induces off fault damage surrounding such basement faults we showed that the quaternary active fault has the damage zone characterized by a fracture density that decays exponentially with distance from the fault for both healed and open microfractures in contrast quaternary inactive faults contain only healed microfracture damage zone cross cutting relationships between microfractures and a minimum healing temperature of 100 c suggest that healed microfractures formed before and at deeper levels than did unhealed microfractures the damage zone defined by open microfractures reflects the recent fault movement during exhumation associated with erosion and regional uplift from the maximum depth at which microfractures may remain unhealed microfracture analysis can therefore be used to examine the history of basement fault activity

origin of near surface hydrocarbon gases bound in northern barents sea sediments abstract in the southern part of the norwegian barents sea extensive hydrocarbon exploration and drilling has led to several oil and gas discoveries yet little is known on the petroleum systems and potential hydrocarbon reservoirs in the northern norwegian barents sea if hydrocarbons generated by thermogenic processes deep in the subsurface migrate to the surface traces of these hydrocarbons can remain in the near surface sediments and provide indirect information on potential petroleum systems near surface hydrocarbon prospecting is a method frequently used in hydrocarbon exploration of frontier areas where no direct geochemical information from drilling is available to improve knowledge of subsurface structures and the evolution of potential petroleum systems in the northern barents sea seismic data and near surface sediment samples were collected analysis of bound hydrocarbon gases extracted from these sediments revealed concentrations significantly above background in areas along the hornsund knollega fault complex as well as near margins of the olga basin generally the compositional and stable carbon isotope signatures of bound gases indicate thermogenic origins from source rocks of oil window maturity for near surface gases with anomalous high concentrations whereas for sediments with low concentration of bound gases mixture of thermogenic and microbial gas is indicated amount and composition of bound gas extracted from source rock samples from spitsbergen indicate that contribution of transported material may have influenced the bound gas in near surface marine sediment of the barents sea in areas where presence of mature organic matter is indicated in the knolegga fault complex near the western barents sea margin high concentrations of thermogenic gas in near surface sediments are associated with fault bound basins and most likely originate from the paleocene eocene torsk formation in the olga basin higher bound gas concentrations occur near the southern border of the basin corresponding to sub cropping late jurassic early cretaceous shales whereas elevated concentrations in the northern olga basin are associated with reactivated faults reaching close to the surface sediments above the center of the basin show significantly lower bound gas concentrations these observations indicate that the jurassic shales act as a regional seal for hydrocarbons and that reactivated faults at the basin margin represent pathways for migration to the surface 1d basin and petroleum systems modeling for the olga basin indicates that early to middle triassic sediments reached oil window maturity and represent the most likely source for thermogenic near surface gas in that area