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

new constraints on the evolution of the mallina basin and their bearing on relationships between the contrasting eastern and western granite greenstone terranes of the archaean pilbara craton western australia abstract the northeast trending mallina basin in the central part of the archaean pilbara craton separates western and eastern granite greenstone terranes with significantly different structural histories and age distribution patterns the basin which is up to 70 km wide and has a strike length of more than 150 km is mainly composed of metamorphosed turbidites assigned to the de grey group in the north these rocks are in faulted contact with metamorphosed volcanosedimentary rocks of the whim creek group new shrimp u pb zircon dates show that the turbidite sequence and the whim creek group were deposited within the same period between ca 3010 and 2940 ma and that the basement to the mallina basin is as young as ca 3015 ma geochronological structural and stratigraphic data now mitigate against previous models which suggested that the whim creek group was significantly younger than the turbidite sequence and that the whim creek group evolved in a late ensialic pull apart basin the mallina basin reinterpreted to include at least part of the whim creek group is now believed to be an extensional basin containing an overlap sequence an ensialic setting is preferred in which the basement to the basin consisted of ca 3170 3020 ma granites and greenstones rifted by major northeast trending faults a continental block to the south and east of which the presently exposed east pilbara granite greenstone terrane is a remnant influenced sedimentation in most of the basin previous tectonostratigraphic models that correlated across and beneath the mallina basin and interpreted the entire granite greenstone terrane of the pilbara craton in terms of evolution during two cycles of arc accretion are not compatible with the new geochronological data and stratigraphic interpretations

hydrocarbon plumbing systems of salt minibasins offshore angola revealed by three dimensional seismic analysis analysis of three dimensional seismic data from the lower congo basin offshore angola reveals numerous fluid flow features in the miocene to holocene succession and the potential for large shielded traps underneath basinward overhanging salt structures the fluid flow evidence includes present day sea floor pockmarks clustered above salt structures pliocene pleistocene stacked paleopockmarks and miocene pockmark fields other fluid flow features include high amplitude cylindrical pipe structures 60 to 300 m 197 984 ft wide and 25 to 300 m 82 984 ft high within lower and middle miocene strata thick 150 m 492 ft high reflectivity zones within the pliocene succession associated with bottom simulating reflections and subvertical low amplitude chimneys originating from the deeper section 1 km 0 6 mi beneath the sea floor the miocene pockmark fields occur at a specific horizon suggesting a regional fluid expulsion event at ca 12 ma and the miocene fluid flow regime is interpreted to be dominated by thermogenic fluids supplied via carrier beds and leaking vertically above structural highs the pliocene pleistocene fluid flow regime was dominated by short distance vertical fluid migration and expulsion related to early stage diagenetic processes involving biogenic methane and pore water the present day fluid flow regime is inferred to be dominated by thermogenic fluids primarily controlled by kilometer scale salt flank controlled migration the study emphasizes the use of seismically imaged fluid flow features in hydrocarbon systems analysis by documenting the evolution of an overburden plumbing system through time involving several fluid types and flow regimes depending on the spatiotemporal availability of thermogenic and diagenetic fluids and the tectonostratigraphic occurrence of aquifers traps and seals

velocity structure of a gas hydrate reflector seismic reflection profiles across many continental margins have imaged bottom simulating reflectors bsrs parallel to the seabed these are often interpreted as the base of a zone in which methane hydrate ice is stable waveform inversion of seismic reflection data can be used to estimate from seismic data worldwide the velocity structure of a bsr and its thickness a test of this method at a drill site of the ocean drilling program predicts that sediment pores beneath the bsr contain free methane for approximately 30 meters the hydrate and underlying gas represent a large global reservoir of methane which may have economic importance and may influence global climate

a seafloor observatory to monitor gas hydrates in the gulf of mexico gas hydrates are solid structures composed of gas molecules encased in cages of water molecules most interesting to the energy community are hydrates that contain hydrocarbon gases in the northern gulf of mexico hydrates of this type form in water depths greater than 450 m and often occur in mounds located where faults intersect the seafloor typically these hydrates consist of seawater from which the salt has been excluded and gases that have migrated up faults from buried hydrocarbon reservoirs in addition to hydrates the mounds contain large amounts of calcium carbonate and various other minerals precipitated by microbes that extract energy from hydrocarbon fluids

multiple resolution seismic imaging of a shallow hydrocarbon plumbing system woolsey mound northern gulf of mexico abstract the northern gulf of mexico is dominated by salt tectonics resulting fracturing and numerous seafloor seeps and vents woolsey mound site of the gulf of mexico hydrates research consortium s seafloor observatory has been investigated extensively via surveys direct sampling and seafloor instrument systems this study presents an innovative approach to seismic data interpretation integrating three different resolution datasets and maximizing seismic coverage of the complex natural hydrocarbon plumbing system at woolsey mound 3d industry seismic data reveal the presence of a salt body at in the shallow subsurface that has generated an extended network of faults some extending from the salt body to the seafloor master faults higher resolution seismic data show acoustic wipe out zones along the master faults with expulsion features seafloor pockmarks and craters located immediately above them and associated in the subsurface with high amplitude negative anomalies at constant depth of 0 2 s twtt b s f interpreted as free gas since pockmarks and craters provide pathways for hydrocarbons to escape from depth into the water column related sub surface seismic anomalies may indicate free gas at the base of the gas hydrates stability zone ghsz fluid flow and gas hydrates formation are segmented laterally along faults gas hydrates formation and dissociation vary temporally in the vicinity of active faults and can temporarily seal them as conduits for thermogenic fluids periodic migrations of gases and other fluids may perturb the ghsz in terms of temperature and pressure producing the observed lack of classical bsrs

detecting hydrate and fluid flow from bottom simulating reflector depth anomalies methane hydrates ice like compounds that consist of water and methane represent a potentially enormous unconventional methane resource that may play a critical role in climate change and ocean acidification however it remains unclear how much hydrate exists here using a newly developed three dimensional 3 d thermal technique we reveal a novel method for detecting and quantifying methane hydrate the analysis reveals where fluids migrate in three dimensions across a continental margin and is used to quantify hydrate with meter scale horizontal resolution our study located at hydrate ridge offshore oregon united states suggests that heat flow and hydrate concentrations are coupled and that 3 d thermal analysis can be used to constrain hydrate and fluid flow in 3 d seismic data hydrate estimates using this technique are consistent with 1 d drilling results but reveal large previously unrecognized swaths of hydrate rich sediments that have gone undetected due to spatially limited drilling and sampling techniques used in past studies the 3 d analysis suggests that previous hydrate estimates based on drilling at this site are low by a factor of approximately three

massive vein filling gas hydrate relation to ongoing gas migration from the deep subsurface in the gulf of mexico abstract a gas hydrate mound that contains massive vein filling structure ii gas hydrate occurs on the upper continental slope 540 m water depth of the gulf of mexico southwest of the mississippi delta the mound is located in the green canyon gc block 185 adjacent to jolliet field in gc 184 jolliet field contains oil and gas that filled fault traps caused by salt deformation during late pleistocene holocene time in contrast to reservoir oil in jolliet field which shows bacterial oxidation effects the c 1 c 5 reservoir gas is unaltered by bacterial oxidation disassociated gas is assumed to have recently entered from the subsurface hydrocarbon system vertical migration of gas along faults is ongoing manifested on the sea floor by gas vents gas hydrate complex chemosynthetic communities and by a large gas plume that extends from the vents to the sea surface the isotopic properties of c 1 c 5 hydrocarbons from reservoirs gas vents and gas hydrate correlate closely although outcropping gas hydrate is transiently stable because of variations in seawater temperature the bulk of buried gas hydrate at gc 185 is stable and perhaps increasing in volume because of the copious gas flux the massive accumulation of gas hydrate at the gc 185 site is attributed to the gas that has recently entered the vents largely from jolliet field and to the synchronous activation of fault conduits allowing gas migration to the sea floor synchronous late gas charge and faulting could also explain the wide distribution of gas hydrate across the upper gulf slope

archaean boninite like rocks in an intracratonic setting abstract boninites and high mg norites show considerable compositional overlap while the petrogenesis of both may involve large ion lithophile element lile replenishment of a mantle source boninites appear restricted to convergent margin settings while many high mg norite suites intrude intracratonic rifts rocks with boninitic compositions are extremely rare in archaean terranes where they are also interpreted to have formed at convergent margins high mg lile enriched basaltic rocks form a ca 2950 ma sub volcanic sill within the 3010 2935 ma mallina basin of the pilbara craton northwest australia they are spatially associated with low ti tholeiitic intrusions and a high mg diorite sanukitoid suite they have a strong boninitic affinity with high sio 2 52 54 wt mg 62 67 and al 2 o 3 tio 2 62 73 low tio 2 0 24 0 28 wt and strong lile enrichments primitive mantle normalised la gd and gd yb ratios of 4 5 and 0 6 respectively produce prominent u shaped normalised trace element patterns despite such close compositional affinity to boninite these rocks probably formed more than 40 myr after regional magmatism and 60 myr after the last regional event linked to subduction geological evidence suggests that the mallina basin formed in an intracontinental setting not at a convergent margin and so high mg norite provides a more realistic analogy for the mallina boninite like rocks in terms of tectonic setting in old terranes the tectonic setting of rocks with boninite like compositions must be interpreted with caution trace element modelling shows that contamination by felsic crust is a plausible explanation for lile enrichments in the mallina boninite like rocks but the scarcity of suitable contaminants makes this explanation unlikely petrogenesis of the boninite like rocks was closely associated with that of the high mg diorite sanukitoid suite lile enrichments in high mg diorite require that the mantle beneath the entire mallina basin was variably metasomatically enriched by an earlier subduction event at or before ca 3015 ma the refractory source for the boninite like rocks may have also been enriched during this event

serpentinization of oceanic peridotites 1 a high sensitivity method to monitor magnetite production in hydrothermal experiments 1 a new method using the magnetic properties of magnetite fe 3 o 4 was developed to monitor experimental serpentinization the saturation remanent magnetization signal jrs was measured during the course of experiments designed to react san carlos olivine mg 0 91 fe 0 09 2 sio 4 with water at 250 to 350 c and 500 bars at the end of the experiments the ratio with saturation magnetization jrs js ratio allowed to convert each successive jrs measurement into an in situ amount of magnetite produced by the serpentinization reaction water weight loss was also measured on the end product to determine the final degree of serpentinization the application of this procedure to a series of experiments performed at 300 c 500 bars for various run duration 9 to 514 days and starting olivine grain size 1 to 150 mm shows a linear relationship between magnetite production and reaction progress this relationship can be safely transposed to other experimental conditions using thermochemical modeling and or the fe content of the product phases we show that this high sensitivity magnetic method is a powerful tool to precisely monitor serpentinization kinetics in fe bearing systems it represents in addition a new indirect mean for monitoring the production of hydrogen which is bound to magnetite production rate citation malvoisin b j carlut and f brunet 2012 serpentinization of oceanic peridotites 1 a high sensitivity method to monitor magnetite production in hydrothermal experiments

spatial distribution of gas hydrates from high resolution seismic and core data woolsey mound northern gulf of mexico abstract integration of new jumbo piston cores with high resolution seismic reflection data provides the first documentation on the subsurface distribution of gas hydrates at a deep water cold seep the study area woolsey mound is a carbonate hydrate mound of thermogenic origin in the northern gulf of mexico where salt tectonics dominate the regional structure two typologies of unconventional seismo acoustic data were used in this study 1 surface source deep receiver ssdr data and 2 auv borne chirp sub bottom profiler data correlation of the coring results with seismic interpretations supports the hypothesis that distinctive seismic brightening high frequency scattering present in the ssdr records may indicate the presence of solid hydrates this suggests that such unconventional seismic survey may be prospective for mapping gas hydrates in complex deep water settings coring results revealed the nature of the shallow gas hydrate system to be dominated by fine grained sediments gas hydrates were found exclusively in fracture porosity in the vicinity of a major active fault we present a model for woolsey mound where shallow gas hydrates are systematically distributed along segments of faults intersected by transit of thermogenic hydrocarbons this dual nature of the faults being both gas hydrate reservoirs and gas migration routes suggests a very dynamic hydrate stability field for this site

electrical anisotropy due to gas hydrate filled fractures in 2006 the indian national gas hydrate program expedition01 ornghp 01 discoveredgashydrateasfillinnearvertical fractures in unconsolidated sediments at several drillingsitesontheindiancontinentalmargins thesegashydrate filled fractures were identified on logging while drilling resistivity images the gas hydrate filled fracture intervals coincide with high measured resistivity at the nghp 01 sites high measured resistivity translates into high hydrate saturationsviaarchie sequation however thesehighsaturations contradict lower gas hydrate saturations determined from pressure core and chlorinity measurements also in intervalswithnear verticalgashydrate filledfractures thereis considerable separation between phase shift and attenuation resistivity logs with 2 mhz resistivity measurements being significantly higher than 400 khz resistivity measurements we modeled the sensitivity of the propagation resistivity measurements in the gas hydrate filled fracture intervals at nghp 01 sites 5 and 10 near vertical hydrate filled fracturescancausetheabnormallyhighresistivitymeasurements in vertical holes due to electrical anisotropy the model suggests the gas hydrate saturations in situ are usually significantlylowerthanthosecalculatedfromarchie sequation in addition these modeled gas hydrate saturations generally agree with the lower gas hydrate saturations obtained from pressure core and chlorinity measurements at nghp 01 sites5and10

geophysical characterization of a fine grained gas hydrate reservoir in the shenhu area northern south china sea integration of seismic data and downhole logs abstract high concentrated gas hydrate deposits in fine grained sediment are proved to be eligible for exploitation with the current technology nevertheless new insights and more understandings of the accumulation of gas hydrate and characterization of hydrate reservoir in fine grained sediment are required which can facilitate the commercial production of gas hydrate in the future combining seismic data and downhole logs here we investigate a fine grained gas hydrate reservoir in the shenhu area northern south china sea scs gas hydrate with saturations of 10 45 occurs in fine grained sediment besides the typical bottom simulating reflectors bsrs and high amplitude reflection below bsr a high amplitude positive reflector referred to as the top of gas hydrate reservoir reflector tghr exists at the top of high concentrated fine grained gas hydrate reservoir according to the result of acoustic impedance inversion the tghr is considered to represent a transitional zone from the overlying water saturated sediment to the underlying high concentrated gas hydrate occurrence zone ghoz discontinuous bsrs beneath the traditional bsrs are also discovered in the study area which are interpreted as the seismic evidence of the sii gas hydrate in the shenhu area fluid flow features such as chimney structures and faults are found on the ridges where gas hydrate occurs indicating that gas migration plays a critical role in the formation of gas hydrate in the fine grained sediment our results provide valuable geophysical indications for detecting the presence of gas hydrate in fine grained sediments

microbial activity in surficial sediments overlying acoustic wipeout zones at a gulf of mexico cold seep 1 down core concentration gradients of dissolved methane and sulfate isotope gradients of methane dissolved inorganic carbon and authigenic carbonate and organic matter elemental ratios are incorporated into a vent evolution model to describe spatial and temporal variability of sedimentary microbial activity overlying acoustic wipeout zones at mississippi canyon mc 118 gulf of mexico we tested the hypothesis that these zones indicate areas where sediments are exposed to elevated fluid flux and therefore should contain saturated methane concentrations and enhanced microbial activity from sulfate reduction sr anaerobic oxidation of methane aom and methanogenesis mp thirty surficial cores between 22 and 460 cm deep were collected from sediments overlying and outside the wipeout zones and analyzed for pore water and solid phase constituents outside the wipeout zones sulfate and methane concentrations were similar to overlying water values and did not vary with depth indicating low microbial activity above the wipeouts nine cores showed moderate activity with gently sloping sulfate and methane concentration gradients methane concentrations 20 m and isotope depth gradients indicative of organic matter oxidation in stark contrast to this moderate activity four cores showed high microbial activity where sulfate concentrations were depleted by 50 cm below seafloor maximum methane concentrations in the decompressed cores were above 4 mm and down core profiles of 13c ch4 and 13c dissolved inorganic carbon dic indicated distinct depth zones of sr aom and mp bulk organic matter analysis suggested that the high activity was supported by an organic source that was enriched in carbon c n 15 and depleted in 15n and 13c compared to other activity groups possibly due to the influx of petroleum or chemosynthetically fixed carbon within high activity cores the 13c dic values were similar to the 13c caco3 values a result expected for authigenic carbonate recently precipitated however these values were dissimilar in moderate activity cores suggesting that microbial activity was higher in the past this study provides evidence that the fluid flux at mc 118 varies over time and that the microbial activity responds to such variability it also suggests that sediments overlying wipeout zones are not always saturated with respect to methane which has implications for the formation and detection of gas hydrate

characteristics of short period wavelike features near 87 km altitude from airglow and lidar observations over maui 1 small scale less than 15 km horizontal wavelength wavelike structures known as ripples are a common occurrence in oh airglow images recent case studies attribute their origin to the presence of either convective or dynamical instabilities however little is known about their frequency of occurrence and period the maui malt observatory located at mt haleakala is instrumented with a na wind temperature lidar which allows the determination of whether the atmosphere is dynamically or convectively unstable and a fast oh airglow camera which takes images every 3 s with a sensitivity high enough to see the ripples this study reports on 2 months of observations in october november 2003 and in august 2004 eight nights of which also included na lidar measurements the imager results suggest that instability features occur in the 85 to 90 km region of the atmosphere for around 20 of the time the nominal observed period for the ripples is between 2 and 4 min while there are clear night to night variations the average observed period is similar for both the 2003 and 2004 observations in addition a few of the small scale structures are not ripples caused by instabilities but rather have features consistent with their being short horizontal wavelength evanescent waves their fractional intensity fluctuations are as large or larger than those of the ripple instabilities unlike the instabilities the origin of the evanescent waves is not determined

mesoscale biogeophysical characterization of woolsey mound northern gulf of mexico a new attribute of natural marine hydrocarbon seeps architecture abstract located on the continental slope in 900 m of water woolsey mound dominates seafloor morphology at mississippi canyon 118 the carbonate hydrate mound is the site of the gulf of mexico hydrates research consortium s seafloor observatory to investigate and monitor hydrographic geophysical geological geochemical and biological processes of the hydrocarbon system northern gulf of mexico innovative survey and monitoring systems sensors and tools have been developed to extract samples and data to unravel the history character and composition of the site many hours of visual data have been collected to investigate benthic communities thriving at the cold seep site associated with the mound these communities habitats are described here for the first time in terms of faunal assemblage substrate nature and presence absence of chemosynthetic species based on these factors we grouped them into four benthic meso habitats we speculate that the spatial distribution of these meso habitats is large enough to make this characteristic comparable to the geophysical response of the seismo acoustic systems we have tested this hypothesis carefully analyzing the relationship between benthic habitats zonation and the geophysical response of side scan sonar chirp subbottom surface source deep receiver ssdr vertical incidence profiler and 3 d oil industry multichannel data we observe that the geophysical response is not unique a single habitat may correlate with many geophysical attributes or a single geophysical attribute may span many habitats however we find that geophysical data can predict seep locations they can also convey some information concerning community composition and complexity that function as proxies for seep duration age while specific community components are believed to reflect composition of seep fluids although preliminary this approach represents a novel classification characterization for seafloor hydrocarbon seeps one that reflects a historical component

fault system and thermal regime in the vicinity of site nghp 01 10 krishna godavari basin bay of bengal abstract drilling coring activities onboard joides resolution for hydrate resource estimation have confirmed gas hydrate in the continental slope of krishna godavari kg basin bay of bengal and the expedition recovered fracture filled gas hydrate at the site nghp 01 10 in this paper we analyze high resolution multi channel seismic mcs high resolution sparker hrs bathymetry and sub bottom profiler data in the vicinity of site nghp 01 10 to understand the fault system and thermal regime we interpreted the large scale fault system 5 km predominantly oriented in nnw sse direction near nghp 01 10 site which plays an important role in gas hydrate formation and its distribution the increase in interval velocity from the baseline velocity of 1600 m s to 1750 1800 m s within the gas hydrate stability zone ghsz is considered as a proxy for the gas hydrate occurrence whereas the drop in interval velocity to 1400 m s suggest the presence of free gas below the ghsz the analysis of interval velocity suggests that the high concentration of gas hydrate occurs close to the large scale fault system we conclude that the gas hydrate concentration near site nghp 01 10 and likely in the entire kg basin is controlled primarily by the faults and therefore has high spatial variability we also estimated the heat flow and geothermal gradient gtg in the vicinity of nghp 01 10 site using depth and temperature of the seafloor and the bsr we observed an abnormal gtg increase from 38 c km to 45 c km at the top of the mound which remarkably agrees with the measured temperature gradient at the mound nghp 01 10 and away from the mound nghp 01 03 we analyze various geological scenarios such as topography salinity thermal non equilibrium of bsr and fluid gas advection along the fault system to explain the observed increase in gtg the geophysical data along with the coring results suggest that the fluid advection along the fault system is the primary mechanism that explains the increase in gtg the approximate advective fluid flux estimated based on the thermal measurement is of the order of few tenths of mm yr 0 37 0 6 mm yr

a seismic study of methane hydrate marine bottom simulating reflectors multichannel seismic reflection data have been analyzed from an area of clear bottom simulating reflectors bsrs on the northern cascadia subduction zone margin off vancouver island the reflector at a depth of about 300 m subbottom is interpreted to represent the base of a layer of methane hydrate or clathrate the shallow water depth of 1300 m and the 3600 m long hydrophone array have allowed bsr amplitude versus offset and high resolution velocity analysis as well as modelling of vertical incidence data the results of all three types of analysis can be best explained by a 10 to 30 m thick high velocity layer located immediately above the bsr about 300 m below the seafloor having a sharp base and transitional top in the layer about one third of the sediment pore spaces must be filled with hydrate ice there is no seismically detectable free gas beneath the bsrs these results put important constraints on models for the distribution and formation of bsr hydrate

rare earth element variations in mid archean banded iron formations implications for the chemistry of ocean and continent and plate tectonics abstract abundances of major and rare earth elements rees are reported for mid archean 3 3 3 2 gyr sedimentary rocks including banded iron formations bifs and ferruginous siliceous mudstone from the cleaverville area in the pilbara craton western australia geological lithological and geochemical lines of evidence indicate that these sedimentary rocks preserve a continuous record of depositional environments ranging from that typical of mid oceanic spreading centers to convergent plate boundary settings a range of environments most likely caused by plate movements except for the mudstone the ree content of these sedimentary rocks changes gradually from the lower to upper stratigraphic horizons europium anomalies decrease up section eu eu values normalized to nasc change from 3 5 to 1 1 as the ree contents and lree hree ratios increase the striking similarity in these ree signatures of bifs and modern hydrothermal sediments leads us to propose that the bifs were in situ hydrothermal precipitates near a mid ocean ridge significant amounts of terrigenous materials contributed to the siliceous and ferruginous mudstone of the uppermost horizon the observation that the source of the sediments shifted from proximal hydrothermal through distal hydrothermal to terrigenous suggests that plate tectonics dominated by horizontal movement was already operating in the mid archean distal hydrothermal sediments without a eu anomaly when normalized to nasc suggest that mid archean seawater had already been strongly influenced by a riverine flux from an upper continental crust and that this component bore no eu anomaly i e it had a negative eu anomaly when normalized to chondrite in addition to an absence of a eu anomaly mid archean seawater did not have a ce anomaly suggesting less oxic conditions in the mid archean than in the modern ocean

heat flow regimes and the hydrate stability zone of a transient thermogenic fault controlled hydrate system woolsey mound northern gulf of mexico abstract this study aims to constrain the base of the hydrates stability field in structurally complexsites using the case of woolsey mound a fault controlled transient thermogenic hydrates system in mississippi canyon block 118 northern gulf of mexico we have computed the base of the hydrates stability field integrating results from a recent heat flow survey designed to investigate geothermal anomalies along fault zones which exhibit different fluid flux regimes an advanced compositional simulator was used to model hydrate formation and dissociation at woolsey mound and addresses the following hypotheses 1 migrating thermogenic fluids alter thermal conditions of the hydrate stability zone hsz so heat flow reflects fault activity 2 gas hydrate formation and dissociation vary temporally at active faults temporarily sealing conduits for migration of thermogenic fluids 3 high salinity and inclusion of thermogenic gases with higher molecular weight than methane produce opposite effects on the depth to the bottom of the hydrate stability zone applications of results include identifying and quantifying hydrate deposits in shallow sediments using an interdisciplinary approach that includes multiple resolution seismic data evaluation geological and geochemical groundtruthing and heat flow analyses as a proxy for activity along faults

north cascadia heat flux and fluid flow from gas hydrates modeling 3 d topographic effects the bottom simulating reflector bsr of gas hydrate is well imaged from two perpendicular seismic grids in the region of a large carbonate mound informally called cucumber ridge off vancouver island we use a new method to calculate 3 d heat flow map from the bsr depths in which we incorporate 3 d topographic corrections after calibrated by the drilling results from nearby integrated ocean drilling program site 889 and site u1327 we then estimate the associated fluid flow by relating it to the topographically corrected heat flux anomalies in the midslope region a heat flux anomaly of 1 mw m2 can be associated with an approximate focused fluid flow rate of 0 09 mm yr around cucumber ridge high rates of focused fluid flow were observed at steep slopes with values more than double the average regional diffusive fluid discharge rate of 0 56 mm yr as well in some areas of relatively flat seafloor the focused fluid flow rates still exceeded 0 5 mm yr on the seismic lines the regions of focused fluid flow were commonly associated with seismic blanking zones above the bsr and sometimes with strong reflectors below the bsr indicating that the faults fractures provide high permeability pathways for fluids to carry methane from bsr depths to the seafloor these high fluid flow regions cover mostly the western portion of our area with gas hydrate concentration estimations of 6 based on empirical correlations from hydrate ridge in south off oregon significantly higher than previously recognized values of 2 5 in the eastern portion determined from site u1327

subsurface methane sources and migration pathways within a gas hydrate mound system gulf of mexico 1 geochemical profiles were coupled with seismic information to examine subsurface hydrocarbon source migration and fate at a gulf of mexico carbonate gas hydrate mound woolsey mound three seafloor features were investigated in detail 1 major faults resulting from a rising salt body 2 an acoustic backscatter anomaly and 3 a pockmark associated with a major fault we analyzed sulfate chloride dissolved inorganic carbon and hydrocarbon concentrations and carbon isotopes in pore water extracted from 20 m piston cores to characterize gas source and calculate methane flux dissolved biogenic methane dominated the off fault sites while the contribution of thermogenic methane increased near a major fault where thermogenic gas hydrates were recovered within the pockmark methane concentrations were low and isotopes indicated a biogenic source since pockmarks are typically formed from expulsive fluid flow this suggests that either the pockmark is the legacy of a conduit that has become plugged or that the expulsed fluid is confined within the fault walls at the acoustic anomaly nonsteady state sulfate profiles suggested temporal variability in methane flux estimates from 75 gravity cores collected across woolsey mound since 2002 were mapped to display the spatial variability in methane flux relative to the faults methane flux to the seafloor was generally low but increased several fold near the faults suggesting that the faults may provide conduits for hydrocarbons to bypass the microbial biofilter and cross the sediment water interface

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

trapping and migration of methane associated with the gas hydrate stability zone at the blake ridge diapir new insights from seismic data abstract the blake ridge diapir is the southernmost of a line of salt diapirs along the carolina trough diapirs cause faulting of the superjacent sediments creating pathways for migration of fluids and gas to the seafloor we analyzed reflection seismic data from the blake ridge diapir which is located in a region with known abundant gas hydrate occurrence a striking feature in these data is a significant shallowing of the base of gas hydrate stability bghs over the center of the diapir the seafloor is warped up by about 100 m above the diapir from about 2300 m to about 2200 m the bghs as indicated by a bottom simulating reflection bsr is about 4 5 s off the flanks of the diapir rising to about 4 15 s at the center above the diapir a fault system appears to rise vertically from the bghs to about 0 05 s below the seafloor 40 50 m it then diverges into several steeply dipping faults that breach the seafloor and cover an area 700 m in diameter other secondary faults diverge from the main fault or emerge directly from the bghs near the crest of the diapir gas and other fluids may migrate upward through the faults we performed complex trace analysis to compare the reflection strength and instantaneous frequency along individual reflections a low frequency anomaly over the center of the diapir indicates high seismic attenuation this is interpreted to be caused by migration of fluids probably methane along fault pathways the migration of gas i e probably mainly methane through the gas hydrate stability zone is not yet understood we speculate that pore fluids in the faults may be too warm and too salty to form gas hydrate even at depths where gas hydrate is stable away from the diapir alternatively gas hydrates may seal the fault walls such that water supply is too low to transform all the gas into gas hydrates the shallowing of the bsr may reflect increased heatflow above the diapir either caused by the high thermal conductivity of the underlying salt or by advective heat transport along with fluids high pore water salinity shifts the gas hydrate stability to lower temperatures and may also play a significant role in bsr shallowing we therefore investigated the possible effect of pore water salinity on shallowing of the bsr we found that bsr shallowing may theoretically be entirely caused by increased salinity over the diapir although geologically this would not be reasonable this observation demonstrates the potential importance of pore water salinity for lateral variations of bsr depths in particular above salt structures

bsrs estimated heat flow hydrate related gas volume and their implications for methane seepage and gas hydrate in the dongsha region northern south china sea abstract to investigate the relationship among methane seepage subsurface gas hydrate and heat flow and estimate hydrate related gas amount in the dongsha region northeastern south china sea in this study we first identified bottom simulating reflector bsr using multi channel seismic data collected in 2004 subsequently the thickness of gas hydrate stability zones ghsz was calculated from the observed bsr using time depth conversion ranging from 60 to 300 m in seawater depths of 600 1200 m additionally a seismic feature of double bsrs is locally observed in this region which is possibly caused by either the presence of mixed gas source thermogenic and biogenic or migration of a pre existing base of ghsz geothermal gradient heat flow and hydrate related gas volume are calculated based on the thickness of ghsz the estimated geothermal gradient and heat flow varies from 20 to 100 c km with an average of 48 c km and from 20 to 120 mw m 2 with an average of 54 mw m 2 respectively both estimated geothermal gradient and heat flow are generally consistent with those from measurements high geothermal gradient up to 60 c km and heat flow anomaly up to 80 mw m 2 are present in one methane seepage site where bsr is clear and reliable high heat flow could result in thin ghsz in the continental slope in this case gas hydrate could form in the shallow sediments making dissolved gas from hydrate and or free deep seated gas easy to migrate upwards to seafloor through faults and thus resulting in the occurrence of methane venting the hydrate related gas volume is estimated as 6 10 11 m 3 over an area of 400 km 2 with possible occurrence of bsr this finding would shed lights on understanding potential amount of subsurface methane in the dongsha region and place useful constraints for modeling ghsz from measured heat flow data especially in regions where no bsrs are present

drivers of focused fluid flow and methane seepage at south hydrate ridge offshore oregon usa methane seepage at south hydrate ridge offshore oregon united states one of the best studied examples of gas venting through gas hydrates is the seafloor expression of a vigorous fluid flow system at depth the seeps host chemosynthetic ecosystems and release significant amounts of carbon into the ocean with new three dimensional seismic data we image strata and structures beneath the ridge in unprecedented detail to determine the geological processes controlling the style of focused fluid flow numerical fluid flow simulations reveal the influence of free gas within a stratigraphic unit known as horizon a beneath the base of gas hydrate stability bghs free gas within horizon a increases the total mobility of the composite water gas fluid resulting in high fluid flux that accumulates at the intersection between horizon a and the bghs this intersection controls the development of fluid overpressure at the bghs and together with a well defined network of faults reveals the link between the gas hydrate system at depth and methane seepage at the surface

noritic dykes of southern west greenland early proterozoic boninitic magmatism two major swarms of early proterozoic ca 2 1 ga basic dykes occur within the archaean craton of southern west greenland one swarm comprises ophitic and sub ophitic tholeiitic dolerites while the other the bn dyke swarm constitutes mainly norites in which pyroxenes and olivine are enclosed by plagioclase oikocrysts the close geochemical similarity between a quenched norite and the coarser grained varieties indicates that the composition of the latter type has not been significantly modified by crystal accumulation the bn dykes are geochemically distinctive most having high mgo ca 16 cr and ni contents in conjunction with relatively high sio2 light rare earth ree and large ion lithophile lil element concentrations the texture mineral chemistry and petrochemistry of the quenched noritic dyke all bear strong resemblances to those features in modern boninitic lavas the bn dykes also correspond to proposed parental liquids of the bushveld complex and other major layered basic igneous intrusions the two dyke swarms are petrogenetically distinct the tholeiitic dolerites were derived from a relatively undepleted primordial mantle while the noritic dykes originated from a metasomatized harzburgitic source the wide spread distribution of similar proterozoic intrusions suggests crustal underplating by harzburgitic mantle on a world wide scale at this time