hydrocarbon generation migration alteration entrapment and mixing in the central and northern north sea abstract there is little doubt that sediments of upper jurassic to lowermost lower cretaceous age particularly those of the kimmeridge clay formation and its equivalents are the source of the vast bulk of the oil in the central and northern north sea this is true both of oil in conventional mesozoic plays and in tertiary clastic reservoirs the timing of oil generation and migration ranges from the late cretaceous through to the present the oil productivity of the kimmeridge clay formation in the central graben moray firth and south viking graben areas of the north sea is estimated to be in excess of 250 billion barrels of which about 25 is accounted for in accumulations discovered to date there is strong areal differentiation between oil trapped in mesozoic reservoirs as opposed to upper cretaceous chalk and tertiary reservoirs this paper is particularly concerned with hydrocarbons in tertiary reservoirs which have a wide range of compositions and appear to have complex accumulation and degradation histories migration to chalk and younger tertiary reservoirs occurs often through thick shale sequences the evidence for the timing and mechanism of this process is considered and a preferred model for the vertical migration and subsequent lateral migration mixing and degradation is proposed

mineralogical and stable isotopic characterization of authigenic carbonate from a hydrocarbon seep site gulf of mexico slope possible relation to crude oil degradation abstract one of the characteristic features on the cold deep seafloor on atwater valley at block 425 1930 m water depth in the gulf of mexico is the occurrence of seepage of crude oil and hydrocarbon gases associated with thermogenic gas hydrate and authigenic carbonate deposits mineralogical petrographic and isotopic analyses revealed that the precipitation of these carbonates was related to the microbial oxidation of hydrocarbons carbonate deposits are composed of heavily oil stained small nodules to large cobbles of dense limestones of fine grained textures other carbonate fragments are composed of small intraclasts pellets and some bivalve shell fragments cemented together by aragonite cement xrd analysis and petrographic investigations revealed that the authigenic carbonate is predominantly composed of aragonite that occurs as microcrystalline matrix and cement microcrystalline sparitic and botryoidal acicular aragonite crystals are observed as void filling cement the 18o values of the authigenic carbonate 3 80 to 4 16 v pdb suggest that the precipitating fluid has equilibrated with the cold bottom seawater the calculated 18o values 0 18 to 0 54 smow of the precipitating fluid show subtle deviation from the values reported for the present bottom seawater this is attributed possibly to the precipitation from pore water with temperature ranged from 3 3 to 1 7 c which is less than the measured bottom seawater 4 c however the mixing of the marine pore water with some deep hydrocarbon rich brines or hydrate water would provide a source of 18o enrichment fluid for the precipitation of the authigenic carbonates based on the predominance of aragonite with botryoidal and clotted fabric the occurrence of pyrite and from the oxygen isotopic data it is plausible that the authigenic carbonates may have formed near the sediment water interface in an oxygen depleted environment with low temperature the narrow range of the 13c values of the authigenic carbonate 23 88 to 28 62 v pdb suggests that a single source of carbon is predominant based on the moderately low 13c values and the occurrence of spots of crude oil coatings of the carbonate samples in addition to the application of a carbon isotope mass balance model the carbon involving in the formation of the carbonates of the at 425 seep site could be mainly derived from microbial degradation of crude oil microbial oxidation of non methane thermogenic hydrocarbon gases such as ethane propane and isobutane would play some role as a source of carbonate carbon

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

seeping hydrocarbons and related carbonate mineralisations in sediments south of lihir island new ireland fore arc basin papua new guinea hydrocarbon gases have been sampled from both cold seeping and heat venting areas in the new ireland fore arc basin in the vicinity of lihir island highest concentrations of up to 10 l l ch4 with a 13cch4 value of 54 9 pdb have been measured in the deep ocean water within a long and narrow deep sea basin located between edison seamount and an uplifted structure named mussel cliff surface sediments of the seep area were covered with chemoautotrophic deep sea fauna such as calyptogena species and tube worms large authigenic calcite concretions occur in the sediments between 50 and 200 cm sediment depth the carbon isotopes of the carbonates in the concretions range from 15 to 40 pdb indicating a mixture of two co2 sources normal marine inorganic carbon fixed in biogenic shells and co2 from anaerobe bacterial oxidation processes of methane accordingly 14c ams dating suggests that authigenic calcite mineralisation incorporated relatively young carbon from methane oxidation in contrast the c1 c2 ratio of 234 and the 13cch4 value of 24 1 pdb in the hot hydrothermal vent of lihir harbour indicates a mixture of a major abiogenic carbon source for methane formation related to magmatism associated with lihir volcano the observed variable fluid characteristics within only 20 km distance between hot hydrothermal venting and the methane seeping deep sea area indicates highly variable heat flow situations and or sediment distributions which control the gas geochemical characteristics in the new ireland fore arc basin

radiocarbon dating peatland development key steps in reconstructing past climate in the central appalachian mountains abstract canaan valley in west virginia contains a greater area of peatlands than any other locality in the mid atlantic highlands extensive fieldwork focused on peat stratigraphy combined with high resolution radiocarbon dating was used to evaluate five peatlands within canaan valley national wildlife refuge cvnwr one hundred soil cores were profiled and described 30 with laboratory analysis including 52 radiocarbon dates calibrated basal peat dates from the five peatlands indicate the onset of peat genesis ranged from 18 600 to 15 200 cal yr bp basal peat dates on the two oldest cores are 1800 to 2200 years older than published dates on peat initiation in any other appalachian mountain peatlands peat accumulation rates varied from 0 02 mm yr to 1 34 mm yr with a mean of 0 14 mm yr results of age depth profiles for six well dated cores consistently exhibit rapid accumulation during the late pleistocene heinrich stadial 1 bolling allerod interstadial and younger dryas cold stadial lower accumulation rates in the early holocene greenlandian age even lower accumulation rates during the mid holocene northgrippian age and the most rapid peat accumulation at the onset of the late holocene early meghalayan age a paucity of shallow peat dating younger than 2000 bp may reflect a reduction in peat accumulation or mixing of surface vegetation into near surface soil horizons soil cores from cvnwr suggest a somewhat different peat development history than the process of terrestrialization previously proposed for other peatland ecosystems in the region

ch 4 consuming microorganisms and the formation of carbonate crusts at cold seeps to understand the role played by microorganisms in the formation of cold seep carbonates we conducted an integrated microbial mineralogical and organic geochemical study of methane related authigenic carbonate crusts formed on eastern mediterranean mud volcanoes we show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane combined lipid biomarker analysis and 16s rrna gene surveys identified a highly diversified methane consuming archaeal community possibly comprising novel species implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation moreover pore water sulphate gradients produced by co occurring methane based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation we propose that this may be the dominant mode of carbonate crust formation at cold seeps world wide in agreement with aquatic chemistry predictions and explaining carbonate mineralogy

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

inferred gas hydrates and clay diapirs near the storegga slide on the southern edge of the voring plateau offshore norway this paper presents a new data set including single channel airgun seismic lines okean long range side scan sonar data and gravity cores acquired on the edge of the voring plateau and in the region of the storrega slide the data acquisition was part of the 8th training through research ttr 8 expedition with r v professor logachev the acoustic profiles clearly show two laterally separated zones characterised by the presence of bottom simulating reflectors bsrs at about 350 ms twt subbottom depth the lower bsr zone is located on the slope of the voring plateau in the immediate vicinity of the northern headwall of the storegga slide and in some places below the slide deposits this zone runs parallel to the general trend of the continental slope the spatial distribution of the upper bsr zone located upslope in an area where diapir like structures are found does not demonstrate any topographic control interpretation of high backscatter patches on the okean sonographs associates the observed structures with fluid escape features on the seabed most of them are pockmarks but in a few places diapirs are cropping out and form dome like elevations after analysing the behaviour of the bsr sometimes crosscutting and its acoustic characteristics reversed polarity and after applying seismic inversion processing to estimate the acoustic velocity change across the bsr this reflector is interpreted to represent the base of the local gas hydrate stability field ghsf this information was used to derive the regional geothermal gradient spatial variations of the inferred geothermal field appeared to be negligible the observation of two separated bsr zones suggests different environmental controls for the growth of the hydrates enhanced reflectors observed in the intermediate zone can be explained by the presence of strata bound free gas accumulations and migration combined with overlying permeability barriers therefore a model for gas hydrate formation in relation to directional fluid migration processes fluid escape features and the presence of diapiric structures is proposed in this paper our model is supported by sedimentological analyses of seafloor samples which demonstrate the presence of stiff clays with evidence of gas migration and by paleontological studies of the cores retrieved from the pockmarks the presence of a bsr in the sedimentary section within the slide scar area implies the repositioning of hydrates to newly established equilibrium conditions after the slide event this observation allows us to simply estimate an upper limit of the fluid migration velocity in the order of several cm year finally the effect of hydrate dissociation on slope instability is considered assuming that the in situ decomposition of hydrates due to instantaneous depressurisation is slow enough to permit the excess volume of released gas and water to be re distributed through the whole sedimentary section above the paleo bsr with consuming heat and increasing pore pressure dissociation tends to shift the pt conditions back to equilibrium values it appears that the dissociation of hydrates due to sliding would cause only 0 2 increase of the pore pressure which would hardly contribute to further slope instability

the nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems in accretionary wedges often morphologically similar sedimentary intrusions when observed by remote geophysical means may have one of two quite different driving mechanisms and a highly variable significance for the regional hydrogeologic picture for example mud diapirs are driven by buoyancy forces that arise from bulk density contrasts in them mud and pore fluid upwell en masse and fluid migration is a related sometimes important but generally subsidiary process in contrast diatremes contain sediments fluidized during rapid fluid advection and are forcibly and directly driven by the hydrogeologic system the nature of fluid input from local and exotic source regions can therefore strongly affect sedimentary intrusive processes and vice versa this complicates the process of defining the main features of the hydrogeological systems operating in accretionary wedges focused vertical advection through steep sided piercement mud diapirs requires conduit systems otherwise flow will be diffuse and directed more horizontally out of the low permeability mud mass however where the permeability of the overburden is less than that of the diapir the whole diapir may act as a conduit apart from this special case conduits will be associated with highly anisotropic scaly fabrics that can sometimes develop in the marginal shear zone of diapirs scaly fabrics form during deformation and compaction of a mud matrix under conditions of constant or increasing effective stress however the effective stress path can be complex as it is both controlled by the relative rates of upward intrusion and burial by sedimentation and or structural thickening and the hydrogeologic system due to this it appears likely that even in a geographically related group of diapirs effective stress histories will vary widely between intrusions so that some can form advective pathways for fluids and some cannot mixed systems of behavior may also be present with local diatremes developing within diapirs above the terminations of conduit systems and rapidly expanding methane gas pockets the potentially heterogeneous near surface behavior may be why the surface manifestations of sedimentary intrusions are so variable when observed in the field diatremes can also form separately as large primary features above any structural or stratigraphic conduit that rapidly expels water or gas into the base of an unlithified sediment column when active large diatremes require enormous quantities of fluid water or gas to drive them particularly if they are long lived features and hence are a direct indication of at least an episodically vigorous hydrogeologic system

fluid flow in and around a mud volcano field seaward of the barbados accretionary wedge results from manon cruise a field of mud diapirs and mud volcanoes situated in the barbados trench at 13 50 n and extending along an old oceanic fracture zone mercurus was investigated during the manon cruise using both surface ship and nautile submersible sampling and measurements the entire zone from 13 50 n up to 14 20 n has an anomalously high heat flow which implies that fluids are drained into it from a segment of the accretionary wedge a few hundred kilometers wide two structures interpreted as diatremes atalante and cyclops expell large amounts of water and methane we propose that they were formed from the release of a light fluid when gas hydrates were dissociated in the sediment as the result of the circulation of warm fluid in the area however they expell only a small fraction of the incoming fluid implying that disperse flow is the dominant mode of expulsion in this area the chemoautotrophic communities on the surface of the structures rely mostly on sulfides submersible observations temperature measurements in the sediment and the chemistry of the pore fluid indicate that convection of seawater occurs within the first few meters of sediment through high permeability channels such as cemented carbonate conduits we propose that this convection is driven by the density difference between the pore fluid and seawater but fresh water released by the dissolution of shallow hydrates may also contribute this shallow convection may be a frequent process in cold seep environments

a climatic trigger for the giant troll pockmark field in the northern north sea abstract pockmarks are seafloor craters usually formed during methane release on continental margins however the mechanisms behind their formation and dynamics remain elusive here we report detailed investigations on one of the world s largest pockmark fields located in the troll region in the northern north sea seafloor investigations show that 7000 pockmarks are present in a 600 km2 area a similar density of pockmarks is likely present over a 15 000 km2 region outside our study area based on extensive monitoring coring geophysical and geochemical analyses no indications of active gas seepage were found still geochemical data from carbonate blocks collected from these pockmarks indicate a methanogenic origin linked to gas hydrate dissociation and past fluid venting at the seafloor we have dated the carbonates using the u th method in order to constrain the pockmark formation the carbonates gave an isochron age of 9 59 1 38 ka i e belonging to the initial holocene moreover radiocarbon dating of microfossils in the sediments inside the pockmarks is consistent with the ages derived from the carbonates based on pressure and temperature modelling we show that the last deglaciation could have triggered dissociation of gas hydrates present in the region of the northern part of the norwegian channel causing degassing of 0 26 mtch4 km2 at the seafloor our results stress the importance of external climatic forcing of the dynamics of the seafloor and the role of the rapid warming following the younger dryas in pacing the marine gas hydrate reservoir

cenozoic evolution of the northern voring margin the northern voring volcanic margin was initiated by late campanian paleocene rifting culminating with massive breakup related igneous activity near the paleocene eocene transition paleocene uplift of the central rift zone led to subaerial erosion and deposition in a restricted basin west of the fles fault complex the western source area was active toward the end of eocene time in the east the low relief land surface underwent modest relative uplift which led to the construction of an early oligocene delta system on the trondelag platform this event was followed by a period of margin subsidence and modest sedimentation until late pliocene time although miocene and early pliocene biosiliceous hemipelagic sediments dominate on the outer margin the influx of ice rafted detritus records the climatic deterioration and the establishment of glaciers in late miocene and early pliocene time since ca 2 6 ma ongoing epeirogenic uplift of fennoscandia and the onset of northern hemisphere glaciation increased the erosion potential a huge prograding wedge of glacial sediments was constructed from ca 2 6 to 1 0 ma when the glacial mode changed from moderate relatively stable icecaps to distinct glacial interglacial cycles the wedge overlies the base of the late pliocene horizon which marks pronounced changes in lithology and physical sediment properties and corresponds to a distinct regional velocity inversion the differential glacial sediment load over unconsolidated and mobile biosiliceous oozes may have caused abundant small offset faulting and diapirism in the western voring basin

pockmarks and methanogenic carbonates above the giant troll gas field in the norwegian north sea abstract acoustic imaging has revealed more than 7000 pockmarks on the seafloor above the troll east gas field in the norwegian north sea we present the first comprehensive study conducted on one of the world s largest pockmark fields complementing the acoustic data with extensive sampling geochemical and petrographical studies specifically we aimed at detecting possible active seepage still present over this vast area the pockmarks are present as isolated structures on average 35 m wide and up to 100 m in size in addition smaller satellite pockmarks surround some of the pockmarks in contrast to the muddy surroundings parts of the investigated pockmarks contain laterally extensive carbonate deposits or meter sized carbonate blocks these blocks provide shelter to abundant colonies of benthic megafauna the carbonate blocks are comprised of micritic mg calcite and calcite micritic aragonite and botryoidal aragonite framboidal pyrite is also commonly present carbon isotopic values of the carbonates are 13c depleted 13c as low as 59 7 and with 18o up to 4 5 indicating a methanogenic origin possibly linked to gas hydrate dissociation pore water extracted from shallow cores from the centre and the flanks of the pockmarks show similar cl and so4 profiles as the reference cores outside the pockmarks ruling out active methane seepage this conclusion is also supported by seafloor video observations that did not reveal any evidence of visual fluid seepage and by the absence of microbial mats and by the fact that the carbonate blocks are exposed on the seafloor and party oxidized on the surface we conclude that methane seepage formed this extensive gas field following to gas hydrate dissociation

methane related carbonate cements in pockmarks of the north sea abstract some pockmarks on the norwegian continental shelf contain patches of cemented sediment that can provide hardgrounds attractive to a variety of benthonic organisms detailed examination of a sandstone sample from a pockmark in norwegian block 25 7 in the north sea has revealed the presence of mg calcite and aragonite cements some of the latter forming botryoids all cement types are characterized by extremely light carbon isotopic compositions with a mean 13c value of 56 1 pdb which shows that the cements contain carbonate produced by oxidation of biogenic methane oxidation occurred in both the oxic and anoxic diagenetic zones trace amounts of interstitial methane mean 13c 40 8 and higher hydrocarbon gases up to c5 with a c1 cn ratio of 0 855 0 874 in the pockmark sediments indicate that some thermogenic methane may be mixed with the biogenic gas

methane related authigenic carbonates from the black sea geochemical characterisation and relation to seeping fluids during ttr11 cruise 2001 three areas of active fluid venting and mud volcanism were investigated in the black sea below the oxic zone at depths varying between 800 and 2200 m authigenic carbonates often associated with microbial mats were recovered from the sea floor and the shallow subsurface structural and petrographic observations allowed the distinction of five different types of authigenic carbonates three of these consist of carbonate cemented layered hemipelagic sedimentary units while the other two consist of carbonate cemented mud breccia sediment and authigenic micrite slabs the carbonate cements consist predominantly of micritic mg calcite their d 13 ccaco3 varies between 8 5x and 46 9x at the different sampling locations indicatingthatauthigenic carbonatesincorporate variableproportions ofcarbonderivedfromthe anaerobicoxidationof methane aom the oxidation of organic matter and from sea water methane is the dominant component among other hydrocarbon gases in these sediments its relative amount varies from 99 9 to 95 1 of total hydrocarbon gases and its d 13 c values range fromi40xtoi74x methane in sediments associated with the carbonate crusts shows carbon isotopic values 25 30x lighter than the authigenic carbonates at all the studied sites indicating that methane present in the seeping fluids confers a distinct isotopic signature to the carbonate deposits at each location models proposed for the formation of carbonate slabs in the subsurface imply methane seepage impeded by homogenous clayey laminae or by pre existing slabs coupled with microbial activity oxidising methane and organic matter present in the sediment mud breccia crust pavements on the sea floor form by carbonate cementation of methane charged sediment gas saturation of the sediment is confirmed by the presence of gas hydrates whose shape indicates an association with authigenic carbonates supporting the idea that sedimentary structures can control gas distribution

geochemistry bubbles from the deep a study suggests that hydrocarbons released from sedimentary basins formed part of a climatic feedback mechanism that exacerbated global warming during the eocene epoch

the geochemical characteristics of the hydrate bound gases from the nyegga pockmark field norwegian sea the nyegga pockmark field located south east of the voring plateau norwegian sea was investigated on the uob cruises gs07 148 2007 and gs08 155 2008 remotely operated vehicle rov monitoring and successful recovery of gas hydrate give insights to the origin of the hydrocarbon gases in the complex pockmark feature named g11 isotope values of methane 13c ranging from 72 4 to 66 2 and d from 202 0 to 198 0 in the hydrate bound gas suggest that the methane is microbially produced and originates from co2 reduction it is proposed that the ethane from the gas hydrate has mixed thermogenic and microbial contributions which is supported by the fact that the gas hydrate also contains propane and isobutane the composition of the hydrate bound gas thus leads to small inclusions of structure ii sii in the hydrate while the major part is structure i si the isotope data and gas composition together with the geological setting suggest that the hydrate bound gas originated predominantly from a free gas system located beneath the gas hydrate stability zone and accumulated under glaciated debris formations the free gas system is mainly microbial methane from in situ production however a contribution of thermogenic gas from deeper polygonal faults to the free gas system seems evident from the composition of the gas the rov monitoring strengthens previous suggestions that the fauna in the complex pockmark g11 are supported by ongoing micro seepage

comparison and implications from strikingly different authigenic carbonates in a nyegga complex pockmark g11 norwegian sea authigenic carbonates sampled in a complex pockmark g11 from the nyegga area south western voring basin reveal strikingly different morphologies a comparative study of macro and micro features of these neighbouring samples was approached in order to attempt a reconstruction of the pockmark dynamics the carbonate morphologies include thin 1 cm platy carbonate crusts blocky and massive carbonate ridges up to several metres in size and irregularly shaped carbonate deposits consisting of interconnected tubular and uneven intervals displaying high porosity our observations indicate that three distinct mechanisms of fluid seepage and carbonate precipitation occurred within the pockmark petrography studies reveal that the samples contain three generations of predominantly aragonitic cements in addition zoned crystals with coexisting mg calcite and dolomite are abundant in one sample suggesting a trend of gradual increase of the sulphate concentrations in the pore fluids during carbonate precipitation isotope measurements on bulk carbonate cements show consistent values with 13 c as low as 52 1 18 o as high as 6 4 and 87 86 sr of 0 7092 anaerobic oxidation of methane close to seafloor conditions can explain these isotope data the carbonates have a common carbon source despite the differences in morphology methane probably originated from the dissolution of gas hydrates as supported from calculated 18 o enrichment in the pore fluids and the methanogenic carbon we propose a model where the differences in bulk carbonate morphology are related to local sediment properties depth of carbonate precipitation and the flow rate of the seeping fluids

fluid sediment interactions at eastern mediterranean mud volcanoes a stable isotope study from odp leg 160 abstract pore fluids from two odp sites at eastern mediterranean mud volcanoes have been analyzed for their cl concentration and their 18o and d isotopic composition the cl data span a wide range of concentrations from extremely depleted with respect to seawater as low as 60 mm at the crest of milano dome site 970 to strongly enriched up to 5 4 m at napoli dome site 971 chloride enrichment is known to be due to dissolving messinian evaporites whereas the source of the low cl fluid is deduced from stable isotope data presented here the isotopic composition of the endmember fluid is found to be 10 for 18o and 32 for d for low as well as for high cl waters from this signature it can be concluded that neither gas hydrates nor meteoric water play a significant role in the freshening of the pore water several other processes altering the 18o d composition of pore waters are discussed and considered to be of only negligible influence the process characterizing the isotopic composition of the fluid is found to be clay mineral dehydration mainly smectite illite transformation corresponding to a depth range of 3 5 7 km and an elevated temperature of about 120 165 c a quantitative estimate shows that this reaction is capable of producing the observed extreme cl depletion

paleocene methane seep and wood fall marine environments from spitsbergen svalbard abstract here we describe a paleocene aged methane seep locality and an associated layer of sunken wood from fossildalen on spitsbergen svalbard hosted in offshore to prodelta siltstones of the basilika formation van mijenfjorden group the fossiliferous seep carbonates were first identified in museum collections from expeditions in the 1920s and 1970s and subsequently sampled as ex situ blocks in the field in 2015 the isotopically light composition 13c values approaching 50 v pdb and characteristic petrographic textures of the carbonates combined with the isotopically light archaeal lipids are consistent with their formation at fossil hydrocarbon seep environment the invertebrate fauna within the carbonates is of moderate diversity 17 species and has a shallow water affinity wood specimens within the carbonates contain the borings and shells of wood boring bivalves the seep fauna is dominated by a species of the thyasirid genus conchocele common to other seeps of similar age the data shed new light onto the history of methane seepage on svalbard and the evolution and ecology of seep and wood fall faunas during the latest cretaceous earliest paleogene time interval

evidence from three dimensional seismic tomography for a substantial accumulation of gas hydrate in a fluid escape chimney in the nyegga pockmark field offshore norway in recent years it has become evident that features commonly called gas chimneys provide major routes for methane to pass through the methane hydrate stability zone in continental margins and escape to the ocean one of many such chimneys lying beneath pockmarks in the southeastern voring plateau off norway was investigated with a high resolution seismic experiment employing a 2 d array of sixteen 4 component ocean bottom seismic recorders at approximately 100 m separation and a dense network of shots to define the 3 d variation of the chimney s structure and seismic properties the tomographic model derived from p wave travel times shows that p wave velocity inside the chimney is up to 300 m s higher than in the surrounding strata within the methane hydrate stability zone the zone of anomalously high velocity about 500 m wide near its base narrowing to about 200 m near the seabed extends to a depth of 250 m below the seafloor the depth extent of this zone and absence of high velocity beneath the base of the methane hydrate stability field make it more likely that it contains hydrate rather than carbonate if a predominantly fracture filling model is appropriate for the formation of hydrate in low permeability sediment the maximum hydrate concentration in the chimney is estimated to be 14 27 by total volume depending on how host sediment properties are affected by hydrate formation doming of the strata penetrated by the chimney appears to be associated with the emplacement of hydrate accompanying the invasion of the gas hydrate stability zone by free gas

origin of carbonate cemented beds on the naglfar dome voring basin norwegian sea abstract lower eocene sediments cored north in the voring basin include calcite cemented beds with unusual microstructures the origin of these beds has been interpreted on the basis of optical microscopy sem microprobe analyses and stable isotope analyses the calcite cement includes perfect pseudomorphs of vesicular ash and lapilli and a few micro sized 0 1 mm remains of unaltered sideromelane were discovered the sideromelane has the composition of relatively alkali rich tholeiitic basalt similar to lower eocene plagioclase basalt from dsdp site 342 on the voring marginal high the earliest phase of diagenesis in the marine environments was associated with palagonitisation and glauconitisation of volcanic glass and growth of smectite and zeolites an early diagenetic origin is also inferred for the more extensive growth of calcite and pyrite cement stable isotope analyses of the calcite cement show very light 13 c values between 55 and 28 4 and with the largest negative values in beds with pseudomorphic textures after ash lapilli such low 13 c values are consistent with a carbon source associated with oxidation of methane within the upper levels of the sediment body close to the sediment water interface the metastable basalt glass acted as a source for ca 2 and fe 2 ions required for calcite and pyrite growth whereas sulphur for pyrite formation may have been supplied from accompanying sulphate reduction the combined occurrence of volcaniclastic deposits and methane seepage as documented in the voring basin may have implications for more widespread formation of calcite cemented beds in the offshore tertiary sediments

integrated petrographic and geochemical record of hydrocarbon seepage on the voring plateau authigenic carbonate crusts nodules and chemoherms were sampled from pockmarks and mud diapirs on the southern part of the voring plateau during the ttr 8 and ttr 10 marine expeditions a petrographic and geochemical study was carried out to investigate their possible relationship with the seepage of hydrocarbon fluids all authigenic carbonates are depleted in 13 c 31 6 13 c 18 o 18 o 4 6 18 o 18 o rich fluid the occurrence of different carbonate mineral phases aragonite calcite dolomite is possibly related to varying dissolved sulphate concentrations in the diagenetic environment fluid inclusion microthermometry and raman spectroscopy indicate the presence of an aqueous hydrocarbon mixture inside the inclusions this seepage mixture was almost certainly immiscible resulting in heterogeneous trapping

biogeochemical processes controlling authigenic carbonate formation within the sediment column from the okinawa trough abstract authigenic carbonates are one type of conspicuous manifestation in seep environments that can provide long term archives of past seepage activity and methane cycling in the oceans comprehensive investigations of the microbial community functional structure and their roles in the process of carbonate formation are however lacking in this study the mineralogical geochemical and microbial functional composition were examined in seep carbonate deposits collected from the west slope of the northern section of the okinawa trough ot the aim of this work was to explore the correspondence between the mineralogical phases and microbial metabolism during carbonate deposit formation the mineralogical analyses indicated that authigenic carbonate minerals aragonite magnesium rich calcite dolomite ankerite and siderite and iron bearing minerals limonite chlorite and biotite were present in these carbonate samples the carbon and oxygen isotopic values of the carbonate samples varied between 51 1 to 4 7 and 4 8 to 3 7 respectively a negative linear correlation between carbon and oxygen isotopic compositions was found indicating a mixture of methane derived diagenetic low 13c high 18o carbonates and detrital origin high 13c low 18o carbonates at the ot geochip analyses suggested that various metabolic activities of microorganisms including methanogenesis methane oxidation sulfite oxidation sulfate reduction and metal biotransformations all occurred during the formation process on the basis of these findings the following model for the methane cycle and seep carbonate deposit formation in the sediment column at the ot is proposed 1 in the upper oxidizing zone aerobic methane oxidation was the main way of methane consumption 2 in the sulfate methane transition zone sulfate dependent aom anaerobic oxidation of methane consumes methane and authigenic minerals such as aragonite magnesium calcite and sulfide minerals precipitate 3 in the underlying sulfate depleted zone the presence of iron oxides supplied by hydrothermal fluids and terrestrial inputs created thermodynamically favorable conditions for fe dependent aom to consume methane and dolomite and siderite ankerite precipitate in this zone

suspected gas associated clay diapirism on the seabed off mid norway abstract on the continental shelf off mid norway at water depths ranging from 150 to 350 m large areas of the seabed consist of plastic clays with a rugged surface topography and an amorphous opaque subsurface acoustic appearance five topographic side scan sonar and shallow seismic examples are presented and discussed many of the mounds and ridges are suspected to be of a clay diapiric nature numerous gas seepages originating from opaque clays have also been found off mid norway a tentative formation model for the ridges and dome shaped features is proposed the model is based on suspected differential gas charging of subsurface sediments and clay diapirism caused by differential clay buoyancy

mid cretaceous hydrothermal vents and authigenic carbonates in a transform margin basque cantabrian basin western pyrenees a multidisciplinary study a comprehensive study of authigenic carbonates and associated fauna in late albian organic rich deep water deposits the black flysch group reveals that carbonate precipitation was a by product of the anaerobic oxidation of hydrocarbon rich hydrothermal fluids the authigenic carbonates are exposed along the kardala and alkolea sea cliffs in the western pyrenees the two vent carbonates occur 1 km apart adjacent to the synsedimentary right reverse mutriku fault but in contrasting structural domains the kardala carbonates occur on a structural ridge hangingwall and the alkolea carbonates are positioned at the base of an erosional scarp folded downward footwall the similarity in pattern of the carbonate phases and complex paragenetic events for both vent precipitates implies that hydrothermal fluid generation processes and pore water evolution during early and late diagenesis were similar nevertheless a comparison of the geochemistry fossil fauna and morphology of carbonate structures of both precipitates suggests that the vented hydrocarbon type flow intensity and temperature of hydrothermal fluids were different at the kardala vent intense focused flow of hot up to 109 c oil rich fluids were generated allowing the development of a relatively abundant chemosynthesis based fauna in contrast at the alkolea vent diffuse flows of warm thermogenic methane rich fluids were expelled to the sea floor and no chemosynthetic fauna developed these differences are related to the contrasting structural setting of each locality similar d 13 corg values for both pyrobitumen fills and host unit organic matter suggest that the hydrocarbon source was the black flysch group contact alteration of these organic rich sediments by syndepositional hydrothermal fluids generated hydrothermal petroleum oil and gas hydrocarbons which probably migrated updip to the sea floor by contemporary compression tectonics

surface expression of fluid venting at the toe of the nankai wedge and implications for flow paths abstract cold seeps have been observed with manned submersibles at many sites on the tokai margin most sites are found on the hanging wall of major thrust faults within 1 2 km of their outcrop few sites relate to purely erosional features this relationship between thrusting and venting may be explained either by fluid flow along fault zones by fluid flow along permeable layers outcropping at the fault scarp or by diffuse upward flow of fluids released during footwall compaction we use deep towed side scan sonar and sediment sounder profiles acquired at the toe of the nankai accretionary wedge to identify the context of seepage at a smaller scale modes of fluid expulsion inferred from observations in this zone include flow channelling along strata along thrusts along gravity faults and along joint fractures as well as diffuse flow we then combine visual observation and monitoring of electrochemical potential eh to assess the relative importance of seepage sites we show that bacterial mats are better visual indicators of active seepage than bivalve beds and that the most active seepage sites correlate with outcrops of coarse turbidites cemented by authigenic carbonates these were sampled and have permeability high enough to channel fluid flow 1 4 10 14 m2 we suggest they are the main conduits near the seafloor however seepage sites are also observed directly on the outcrop of major thrusts indicating that they do play a role as fluid conduits we observe negative polarity seismic reflections on these faults below 1 km depth and wonder about their significance

seismic character of bottom simulating reflectors examples from the mid norwegian margin three classes of bottom simulating reflectors bsr cross cut the post breakup sediments of the mid norwegian margin the first class is caused by free gas at the base of the pressure and temperature dependent gas hydrate stability zone the second class of bsr is caused by the diagenetic transition from opal a to opal ct the third class of bsr is always observed underneath the opal a opal ct transition but heat flow data and the amplitude characteristics of this arrival exclude one of the known silicate diagenetic transitions or gas hydrates as the explanation for this reflector odp site 643 drilling results from the voring plateau suggest two possible processes as the reason for this third bsr a smectite illite conversion or b a sudden increase in the abundance of authigenic carbonates the genesis of both is pressure and temperature dependent and could potentially result in a cross cutting seismic reflector the data are not conclusive as to which process is causing the third class of observed bsr

chemistry and mineralogy of pyrite enriched sediments at a passive margin sulfide brine seep abyssal gulf of mexico pyrite is rapidly accumulating at the contact between the cretaceous limestones of the florida platform and the hemipelagic sediments of the abyssal gulf of mexico sediments sampled with the submersible alvin in 3266 m of water are associated with a dense community of organisms that depend on chemosynthetic primary production as a food source analysis of the chemistry mineralogy and textural composition of these sediments indicate that iron sulfide mineralization is occurring at the seafloor within an anoxic micro habitat sustained by the advection of hydrogen sulfide charged saline brines from the adjacent platform the chemosynthetic bacteria that directly overlie the sediments oxidize hydrogen sulfide for energy and provide elemental sulfur that reacts with iron monosulfide to form some of the pyrite the sediments are mixtures of pyrite 30 wt basr sulfates 4 wt clays and locally derived biogenic carbonates and are progressively being cemented by iron sulfides oxidation of hydrogen sulfide produces locally acidic conditions that corrode the adjacent limestones potential sources of s h2s fe ba and sr are discussed

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

brachiopods and chemosymbiotic bivalves in phanerozoic hydrothermal vent and cold seep environments a compilation of 37 fossiliferous phanerozoic marine deposits interpreted to represent ancient hydrothermal vent or cold seep habitats reveals that articulate brachiopods particularly rhynchonellides and terebratulides were relatively common constituents of these chemosynthetic settings from the devonian through the early cretaceous but were rare in such paleoenvironments from the late cretaceous to the present late devonian vent and seep settings were dominated by rhynchonellides dzieduszyckia eoperegrinella morphologically similar to cretaceous seep restricted peregrinella all of which are purported to be closely related phylogenetically bivalve genera with extant chemosymbiotic descendants first appeared in vent seep deposits during the late jurassic and were prevalent therein after the early cretaceous these bivalves include members of five families vesicomyidae mytilidae solemyidae thyasiridae lucinidae lucinids and thyasirids are the dominant groups represented ancient hydrothermal vent and cold seep settings may provide clues to delineate better which factors e g biotic interactions differential recovery following the permian triassic mass extinction have influenced overall evolutionary patterns of dominance among brachiopods and bivalves through the phanerozoic

fluid migration directions inferred from gradient of time surfaces of the sub seabed the role of sub seabed topographically controlled fluid migration is assessed to improve our understanding of distributions of acoustic chimneys at the nyegga pockmark field on the mid norwegian continental margin 3d seismic data interpretations resulted in topographic gradients of seismic time surfaces and rms amplitude maps topographical gradient maps and flow tracing allowed identifying migration pathways and trapping locations for free gas within the shallow sub seabed the occurrence of acoustic chimneys pockmarks and mounds correlate with identified fluid migration pathways and gas trapping locations an important factor that controls the trapping locations and the lateral distribution of seeps on the seabed at nyegga is the variation through time of the depth of the base of the gas hydrate stability zone bghsz fluids can derive from gas hydrate systems that are suspected of being a biogenic source and or tertiary domes that are considered to show leakage of thermogenic fluids to the shallow geosphere

mud volcano field seaward of the barbados accretionary complex a submersible survey we describe a 0 55 km2 semicircular mud pie and three adjacent diapiric mounds explored using the submersible nautile near 13 50 n 12 km seaward of the barbados accretionary complex deformation front this diapiric field had been previously explored with an acoustically navigated deep towed side scan sonar thus providing an accurate base map the mud pie is situated at a depth of 4938 m in addition to visual observations water rock sediment and biological sampling we measured temperature gradients and made geochemical analyses of the samples fluid venting associated with chemosynthetic animal communities is widespread on all four structures but is maximal in the central third of the mud pie the chemosynthetic life distribution on the mud pie displays a concentric zonation which we relate to an increase in venting activity toward the center as evidenced by thermal gradients recent mud flows are present in the centralmost part of the mud pie the simplest interpretation of the structure is that it is a mud lake covered by a mechanically resistant carbonate crust we determine that approximately 106 m3 of fluid are advected upward through the crust of the mud lake every year this large amount of fluid implies large scale lateral transport

nitrogen geochemistry as a tracer of fluid flow in a hydrothermal vent complex in the karoo basin south africa abstract we have investigated the n geochemistry of minerals and rocks from contact metamorphic aureoles and hydrothermal vent complexes hvc in the karoo basin in south africa the hvc formed during phreatic eruptions associated with rapid devolatilization and pressure build up in contact aureoles around early jurassic sill intrusions by combining outcrop data from a hvc and core data from contact aureoles we investigate the relationship between light element release during metamorphism and vertical fluid migration sandstone and breccia from the hvc contain early diagenetic ammonium nh 4 bearing feldspar buddingtonite and illite ammonium occupies up to 95 of the a site in feldspar corresponding to concentrations up to 5 2 wt n bulk rock n isotope data for rocks from inside and outside the hydrothermal vent complex fall into two distinct groups background samples have 15nair between 1 5 and 4 9 whereas minerals from the vent complex have 15n in the range 7 5 to 10 6 the n geochemistry of contact metamorphic shale from the lower stratigraphic units of the karoo basin shows that the vitrinite reflectance and 15n values are positively correlated shale with reflectivity values 4 ro are enriched in 15n with 15n values between 6 and 14 implying the release of isotopically light n into metamorphic fluids probably as n2 we suggest that the relatively high 15n values of the early diagenetic buddingtonite in the hvc reflect exchange of buddingtonite with n bearing fluids ascending from greater depth after their release during contact metamorphism and dehydration we present a qualitative model whereby hydrothermal vent complexes represent fluid flow structures after their formation focusing n bearing metamorphic fluids sourced in deeper levels of the basin the release of organic n from sediments at depth in volcanic basins could play a role in the geochemical cycle of n becoming particularly important during periods of intense volcanic activity

a comprehensive approach to the study of methane seep deposits from the lincoln creek formation western washington state usa a comprehensive approach using palaeontology petrography stable isotope geochemistry and biomarker analyses was applied to the study of seven small methane seep carbonate deposits these deposits are in the oligocene part of the lincoln creek formation exposed along the canyon and satsop rivers in western washington each deposit preserves invertebrate fossils many representing typical seep biota authigenic carbonates with 1 3 c values as low as 51 pdb reveal that the carbon is predominately methane derived carbonates contain the irregular isoprenoid hydrocarbons 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi lipid biomarkers diagnostic for archaea these lipids are strongly depleted in 1 3 c 1 3 c values as low as 120 pdb indicating that archaea were involved in the anaerobic oxidation of methane small filaments preserved in the carbonate may represent methanotrophic archaea archaeal methanogenesis induced the formation of a late diagenetic phase brownish calcite consisting of dumbbell shaped crystal aggregates that exhibit 1 3 c values as high as 7 pdb clotted microfabrics of primary origin point to microbial mediation of carbonate precipitation downward directed carbonate aggregation in the seeps produced inverted stromatactoid cavities large filaments interpreted as green algae based on their size shape arrangement and biomarkers imply that deposition occurred in places in water no deeper than 210 m

shallow water methane derived authigenic carbonate mounds at the codling fault zone western irish sea abstract methane derived authigenic carbonate mdac mound features at the codling fault zone cfz located in shallow waters 50 120 m of the western irish sea were investigated and provide a comparison to deep sea mdac settings carbonates consisted of aragonite as the major mineral phase with 13 c depletion to 50 and 18 o enrichment to 2 these isotope signatures together with the co precipitation of framboidal pyrite confirm that anaerobic oxidation of methane aom is an important process mediating methane release to the water column and the atmosphere in this region 18 o enrichment could be a result of mdac precipitation with seawater in colder than present day conditions or precipitation with 18 o enriched water transported from deep petroleum sources the 13 c depletion of bulk carbonate and sampled gas 70 suggests a biogenic source but significant mixing of thermogenic gas and depletion of the original isotope signature cannot be ruled out active seepage was recorded from one mound and together with extensive areas of reduced sediment confirms that seepage is ongoing the mounds appear to be composed of stacked pavements that are largely covered by sand and extensively eroded the cfz mounds are colonized by abundant sabellaria polychaetes and possible nemertesia hydroids which benefit indirectly from available hard substrate in contrast to deep sea mdac settings where seep related macrofauna are commonly reported seep specialist fauna appear to be lacking at the cfz in addition unlike mdac in deep waters where organic carbon input from photosynthesis is limited lipid biomarkers and isotope signatures related to marine planktonic production e g sterols alkanols were most abundant evidence for microbes involved in aom was limited from samples taken possibly due to this dilution effect from organic matter derived from the photic zone and will require further investigation

modeled patterns of late pleistocene glacier inception and growth in the southern and central rocky mountains usa sensitivity to climate change and paleoclimatic implications abstract high resolution modern climate data for the southern and central rocky mountains provide a starting point for analysis of climate changes necessary to produce regional late pleistocene glaciation a gis based model was used to assess the sensitivity of glaciation in different ranges to climatic change and the combinations of temperature and precipitation change necessary to sustain the last glacial maximum lgm extent of glaciation in each range extensive glaciation initiates first in the wind river range of wyoming under every climate change scenario tested in absence of precipitation change a summer temperature depression of 6 8 c would be necessary to maintain lgm ice extents in colorado and wyoming if precipitation was halved necessary summer temperature depression would be 8 10 c if precipitation was doubled a depression of 3 5 5 5 c would suffice given model uncertainties these values may underestimate necessary temperature depression by as much as 2 c under all scenarios tested lgm glaciation in utah particularly the wasatch range requires either more temperature depression for given precipitation change or more precipitation for a given temperature depression than is required in the colorado wyoming rockies a summer temperature depression of 7 c which would suffice to sustain lgm ice extent with little change from modern precipitation in the colorado wyoming rockies would need to be coupled with a near doubling of precipitation to maintain lgm ice extent in the wasatch range this difference appears to reflect lgm precipitation enhancement in the wasatch range and to a lesser degree the uinta mountains resulting from the presence of lake bonneville immediately upwind of these ranges

widespread venting of methane rich fluids in late cretaceous campanian submarine springs tepee buttes western interior seaway u s a from new mexico to montana campanian shales contain abundant submarine spring and seep deposits aligned along early laramide basement faults from spring conduit to sea floor characteristic lithofacies are a a vuggy pelletoid micrite core to 30 m height 5 m width b lucinoid bivalve coquina in pelletoid micrite or grainstone c carbonate slump breccias in shale d concretion bearing shale and e organic rich shale stable isotope analyses of early zoned marine core rock cements suggest a an oxidized methane source for the carbonate carbon b venting of methane charged fluids along active fracture zones and c methanogenesis in older and coeval organic carbon rich muds six consistently zoned foraminifer and macrofaunal communities suggest a strong environmental stress gradient over a few metres from spring vents to the adjacent sea floor these methane springs and their biotas were dynamic and episodically active over a 1 25 m y time span

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

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

archaea mediating anaerobic methane oxidation in deep sea sediments at cold seeps of the eastern aleutian subduction zone cold seeps in the aleutian deep sea trench support prolific benthic communities and generate carbonate precipitates which are dependent on carbon dioxide delivered from anaerobic methane oxidation this process is active in the anaerobic sediments at the sulfate reduction methane production boundary and is probably performed by archaea working in syntrophic co operation with sulfate reducing bacteria diagnostic lipid biomarkers of archaeal origin include irregular isoprenoids such as 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi as well as the glycerol ether lipid archaeol 2 3 di o phytanyl sn glycerol these biomarkers are prominent lipid constituents in the anaerobic sediments as well as in the carbonate precipitates carbon isotopic compositions of the biomarkers are strongly depleted in 13c with values of 13c as low as 130 3 pdb the process of anaerobic methane oxidation is also reflected in the carbon isotope composition of organic matter with 13c values of 39 2 and 41 8 and of the carbonate precipitates with values of 45 4 and 48 7 this suggests that methane oxidizing archaea have accumulated within the microbial community which is active at the cold seep sites the dominance of crocetane in sediments at one station indicates that probably due to decreased methane venting archaea might no longer be growing whereas high amounts of crocetenes found at other more active stations may indicate recent fluid venting and active archaea comparison with other biomarker studies suggests that various archaeal assemblages might be involved in the anaerobic consumption of methane the assemblages are apparently dependent on specific conditions found at each cold seep environment selective conditions probably include water depth temperature degree of anoxia and supply of free methane

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

evidence for long term instability in the storegga slide region off western norway abstract shallow seismic surveys around the storegga slide off western norway have allowed greater understanding of the development of this part of the european margin the northern flank of the scarp is formed of seismically well layered hemipelagic and distal glaciomarine deposits in which a variety of luid escape structures probably due to gas are locally abundant there is evidence of slides that substantially pre date the earliest slide previously recognized surveying on the north sea fan to the southwest of the storegga slide shows the markedly different nature of the autochthonous sediments on the southern flank of the storegga slide there is a predominance of glacigenic debris flows in the upper part of the sequence lesser maximum slopes and an apparent absence of interstitial gas and or hydrates this contrast has had considerable effect on slope stability and has influenced the position of the southwestern storegga slide boundary the north sea fan succession includes at least three major buried slides termed the vigra more and tampen slides all of which substantially pre date the storegga event and probably pre date predominantly glacigenic margin sedimentation post late weichselian slope failure is locally significant the region has a long but as yet chronologically poorly defined history of instability in which seismic triggering is considered to have been important

mineralogy geochemistry and petrography of methane derived authigenic carbonates from enza river northern apennines italy abstract a remarkable exposure of carbonate pipe like and slab concretions occurs along the enza riverbanks on the northern apennines foothills italy based upon geochemical and field evidences their genesis has been attributed to microbial governed carbonate precipitation from hydrocarbon enriched fluids the pipe like concretions are thus interpreted as former conduits chimneys marking sites of methane ascent onto the seafloor the resulting enza river chimney field is arranged in a palisade fashion a rare example of such mineralogical and petrographic analyses of some chimneys and slabs document that the dominant cement is dolomite although the chimneys show a rather homogeneous texture a clear zonation is observed in the relative distribution of major and minor elements in their internal and external parts the occurrence of sulphide minerals in the stratigraphically upper samples indicates possible renewal of fluids leakage after a major erosive event

gas venting and subsurface charge in the green canyon area gulf of mexico continental slope evidence of a deep bacterial methane source abstract questions as to the role of modern carbon in methanogenesis and the maximum depth of methane sources in the gulf of mexico continental slope remain unanswered a research submersible was used to sample mixed bacterial and thermal gas 13 c of methane 62 8 d 176 venting to the water column from the gulf slope in green canyon gc 286 the 14 c value of the methane 998 is consistent with fossil carbon another gas vent on gc 185 is 100 methane 13 c 62 9 d 155 and may be from a bacterial source the 14 c 997 of this bacterial methane is also consistent with fossil carbon fossil bacterial methane and thermal hydrocarbons are present in pliocene to pleistocene reservoirs 3509 4184 m of genesis field gc 205 161 160 oil in these reservoirs is biodegraded but gas is not suggesting that gas charge to reservoirs continues presently at 3 4 km depth mixed thermal and bacterial methane may charge the deep reservoirs and fossil methane from depth may ultimately vent on the sea floor at gc 286 and gc 185 results of this study of green canyon suggest that bacterial methane in gas vents and in reservoirs is from deep fossil sources

high resolution 3d seismic data indicate focussed fluid migration pathways above polygonal fault systems of the mid norwegian margin seismic attribute analysis and interpretation of high resolution 3d and 2d seismic data reveal focussed fluid flow processes through the gas hydrate stability zone ghsz at the northern flank of the giant storegga slide diffusive fluid migration predominantly starts from a widespread polygonal fault system in fine grained sediments of the miocene kai formation the overlying 600 700 m thick plio pleistocene naust formation shows spatially related soft sediment deformation and overlying fluid conduits a low relief antiform structure connects to an overlying 250 m high 300 m wide and 3 km elongated columnar zone where seismic signatures suggest self enhanced permeability i e natural hydraulic fracturing push down effects create an elongated depression caused by increased gas accumulations where a cluster of vertical cylindrical acoustic pipe structures originates these pipe clusters pierce the ghsz and indicate focussed fluid flow pathways originating from potentially overpressured sediments high seismic reflection amplitudes at the seafloor above the pipe structures may indicate pockmarks with authigenic carbonates and or gas hydrates the observed objects and seismic features presented are not stand alone indicators for fluid flow but a joint perspective illustrates that they are vertically tied together providing new insights to the effects of focussed fluid flow

tracing the evolution of seep fluids from authigenic carbonates green canyon northern gulf of mexico authigenic carbonates from hydrocarbon seeps are unique long term archives of past fluid flow the studied samples were collected from green canyon block 140 at a water depth of 260 m in the gulf of mexico petrography x ray diffraction stable isotopes and c 14 dating were applied to assess the evolution of seep activity and potential driving forces the carbonates are dominated by high mg calcite hmc and aragonite with a minor amount of low mg calcite lmc and dolomite petrographically peloids clotted microfabric acicular aragonite and a variable content of bioclasts were observed three types of carbonates are recognized structure i carbonates with c 14 ages from 46 5 ka to 25 8 ka bp are characterized by delta c 13 values from 23 2 parts per thousand to 5 1 parts per thousand suggesting multiple carbon sources that include thermogenic methane biodegraded crude oil seawater and residual co2 from methanogenesis at greater depth in contrast structure ii carbonates formed between 17 6 ka and 11 7 ka bp and have delta c 13 values varying from 22 2 parts per thousand to 8 8 parts per thousand suggesting carbon sources similar to those of structure i carbonates but with a negligible influence of residual co2 from methanogenesis in addition the presence of lmc in this type of carbonate may be associated with brine seepage structure iii carbonates among the youngest of the samples analyzed with c 14 ages of 1 2 ka bp these carbonates have the most negative delta c 13 values ranging from 36 1 parts per thousand to 26 8 parts per thousand suggesting that thermogenic methane is the primary carbon source the majority carbonates of both structure i and ii are slightly o 18 enriched which is most likely related to the incorporation of water from dehydration of clay minerals the considerable range of mineralogical and isotopic variations of the studied carbonates highlights the local control of the seepage flux it is proposed that factors affecting the activity of hydrocarbon seeps are sea level changes and salt movement the combination of petrography stable isotopes and dating approach used here highlights that these are valuable tools to assess the variability of past fluid flow at hydrocarbon seeps c 2013 elsevier ltd all rights reserved

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

authigenic minerals from the paola ridge southern tyrrhenian sea evidences of episodic methane seepage abstract paola ridge along the nw calabrian margin southern tyrrhenian sea is one of the few reported deep sea sites of precipitation of authigenic carbonates in the tyrrhenian sea here the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite siderite and other carbonate phases the occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate methane transition zone smtz concretions of authigenic minerals formed in the near sub bottom sediments of the paola ridge were investigated for their geochemical and isotopic composition these concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs the mud diapirs are dotted by pockmarks and dissected by normal faults and are known for having been a site of fluid seepage for at least the past 40 kyrs present day venting activity occurs alongside the two alleged mud volcanoes and is dominated by co2 rich discharging fluids this discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area in this study we used stable isotopes carbon and oxygen of carbonates coupled with rare earth element ree composition of different carbonate and non carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates the analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea water authigenic calcite aragonite concretions from surficial sediments on diapiric structures have depleted 13c isotopic composition and slightly positive 18o values by contrast siderite concretions generally found within the first 6 m of sediments on the alleged mud volcanoes yielded positive 13c and 18o values the siderite ree pattern shows consistent lree light ree fractionation mree medium ree enrichment and positive gd and la anomalies as shown by the ree distribution the 13c depleted composition and their association with chemosymbiotic fauna calcite aragonite precipitated at time of moderate to high methane flux close to the seafloor under the influence of bottom seawater authigenic siderite on the other hand formed in the subseafloor during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13c rich dissolved inorganic carbon dic and 18o rich water likely related to methanogenesis and intermittent venting of deep sourced co2

authigenic carbonates from the darwin mud volcano gulf of cadiz a record of palaeo seepage of hydrocarbon bearing fluids hydrocarbon rich fluids expelled at mud volcanoes mvs may contribute significantly to the carbon budget of the oceans but little is known about the long term variation in fluid fluxes at mvs the darwin mv is one of more than 40 mvs located in the gulf of cadiz but it is unique in that its summit is covered by a thick carbonate crust that has the potential to provide a temporal record of seepage activity in order to test this idea we have conducted petrographic chemical and isotopic analyses of the carbonate crust in addition a 1 d transport reaction model was applied to pore fluid data to assess fluid flow and carbonate precipitation at present the carbonate crusts mainly comprise of aragonite with a chaotic fabric exhibiting different generations of cementation and brecciation the crusts consist of bioclasts and lithoclasts peloids intraclasts and extraclasts immersed in a micrite matrix and in a variety of cement types microsparite botryoidal isopachous acicular radial and splayed fibrous the carbonates are moderately depleted in 13c 13c 8 1 to 27 9 as are the pore fluids 13c 19 1 to 28 7 which suggests that their carbon originated from the oxidation of methane and higher hydrocarbons like the gases that seep from the mv today the carbonate 18o values are as high as 5 1 and it is most likely that the crusts formed from 18o rich fluids derived from dehydration of clay minerals at depth pore fluid modelling results indicate that the darwin mv is currently in a nearly dormant phase seepage velocities are 0 09 cm yr 1 thus the thick carbonate crust must have formed during past episodes of high fluid flow alternating with phases of mud extrusion and uplift highlights results of pore fluid modelling indicate low seepage activity at localised sites pore fluids are supersaturated with respect to hydrocarbons of thermogenic origin aom supports vent fauna and results in the formation of authigenic carbonates the carbonate crust has a brecciated appearance and mainly consists of aragonite the crust formation seems to be regulated by changes in fluid and mudflow activity