methane fluxes and carbonate deposits at a cold seep area of the central nile deep sea fan eastern mediterranean sea abstract high acoustic seafloor backscatter signals characterize hundreds of patches of methane derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the nile deep sea fan ndsf in the eastern mediterranean sea during a high resolution ship based multibeam survey covering a 225 km2 large seafloor area in the central province of the ndsf we identified 163 high backscatter patches at water depths between 1500 and 1800 m and investigated the source composition turnover flux and fate of emitted hydrocarbons systematic parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies flares indicative of gas bubble streams above 8 of the high backscatter patches in echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution visual inspection of three high backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter volume estimates considering results from high resolution autonomous underwater vehicle auv based multibeam mapping were used to calculate the amount of carbonate bound carbon stored in these slabs additionally the flux of methane bubbles emitted at one high backscatter patch was estimated 0 23 to 2 3 106 mol a 1 by combined auv flare mapping with visual observations by remotely operated vehicle rov another high backscatter patch characterized by single carbonate pieces which were widely distributed and interspaced with sediments inhabited by thiotrophic chemosynthetic organisms was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption 0 1 to 1 106 mol a 1 and dissolved methane flux 2 to 48 106 mol a 1 our comparison of dissolved and gaseous methane fluxes as well as methane derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo bio and hydrosphere at cold seeps

u th dating of carbonate nodules from methane seeps off joetsu eastern margin of japan sea abstract we performed u th radioactive disequilibrium analyses of carbonate nodules and sediment samples recovered from methane seep sites off joetsu of the eastern margin of japan sea to decipher the active period of the methane seep the carbonates contain 230th part of which is located in detritus such as silicate and organics at the time of precipitation the initial 230th renders accurate dating with u th radioactive disequilibrium method difficult we assessed the feasibility of correction using radioactive disequilibrium data of ambient sediment to overcome this difficulty a 230th 232th 234u 232th isochron drawn by three chips divided from a carbonate nodule pc05 04 50 passed through data points of local sediments we conclude that the problem of initial 230th can be resolved by measurements of local sediments results show that carbonate nodules include local sediment as impurities furthermore the results of trace element analyses such as rb zr nb ree pb and th also support the idea in all 18 carbonate samples were dated with correction of initial 230th using the mean value of local sediment in this study the u th correction ages show 12 35ka with an isochron age of 26 3ka results indicate that during the time interval of u th ages from 12ka to 35ka environmental conditions must have been favorable for enhanced methane flux through sediment the extensive methane flow period at 20ka accords with the lowest stand sea level during the last glacial age results of this study also suggest that u th ages of carbonate are useful as a reliable chronometer with regard to methane seep activation in order to acquire u th ages of carbonate at methane seep sites however it is important to evaluate the amount of initial 230th accurately using the value of sediment

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

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

the cenozoic ch4 derived carbonates of monferrato nw italy a solid evidence of fluid circulation in the sedimentary column abstract two types of methane derived carbonates each with different lithological and paleontological signatures have been distinguished in the oligocene miocene sediments of monferrato nw italy 1 irregularly shaped metre sized rock bodies characterized by the widespread occurrence of remains of large bivalves lucina sp these bodies include two subtypes differing in the lithological characteristics of the cemented sediments a lucina rich marly limestones encased in langhian outer shelf marls they document a slow seepage of ch4 rich fluids at the paleo sea floor b lucina bearing cemented mud breccias found either as cemented masses in the original stratigraphic position or as redeposited blocks within upper messinian chaotic block in matrix sediments these carbonate bodies document the activity of submarine mud volcanoes during the late messinian in particular they document intermittent fluid emission ranging from violent eruptive phases responsible for the extrusion of soft mud breccias at the sea floor to quiet degassing phases that promoted colonization by chemosymbiotic communities and localized cementation 2 very irregularly shaped strongly cemented mainly coarse grained clastic sediments reaching the lateral extent of few hundred meters and the thickness of few tens of meters they occur within oligocene to messinian sediments lack remains of chemosymbiotic taxa and are highly fractured with fractures filled with sediments and cements these carbonate cemented masses here referred to as macroconcretions result from the precipitation of carbonate cements within buried sediments flushed by ascending ch4 rich fluids they document a complex fluid circulation pattern in the sedimentary column in which so4 rich waters were drawn from surrounding sediments by the fast and prolonged flow of ch4 rich fluids and promoted anaerobic oxidation of methane and the precipitation of carbonate cements the polyphase network of clastic dykes and veins that characterize macroconcretions is related to an intermittent fluid flow regime dykes formed during fast upward flows of sediment rich fluids whereas carbonate filled veins formed during slower degassing phases the local lithostratigraphic and structural framework allow to correlate genetically and chronologically the macroconcretions to lucina bearing mud breccias consequently macroconcretions are here regarded as the result of cementation along fluid conduits feeding messinian mud volcanoes at the sea floor the massive release of fluids could have played a role in triggering large scale mass wasting events responsible for the emplacement of sedimentary melanges including ch4 derived rocks in the messinian

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

intraseasonal oscillations in the global atmosphere part ii southern hemisphere abstract in part ii of this two part article we complete the systematic examination of oscillatory modes in the global atmosphere by studying 12 years of 500 mb geopotential heights in the southern hemisphere as in part i for the tropics and northern hemisphere extratropics the data were band pass filtered to focus on intraseasonal is phenomena and spatial eofs were obtained the leading principal components were subjected to singular spectrum analysis ssa in order to identify nonlinear is oscillations with high statistical confidence in the southern hemisphere the dominant mode has a period of 23 days with spatial patterns carried by the second and third winter eof of the is band it has a zonal wavenumber four structure the 40 day mode is second and dominated by wavenumbers three and four while a 16 day mode is too weak to separate its spatial behavior from the previous two the is dynamics in the southern hemisphere is more complex and dominated by shorter wavenumbers than the northern

changes in depositional systems and sequences in response to basin evolution in a rifted and inverted basin an example from the neogene niigata shin etsu basin northern fossa magna central japan abstract the niigata shin etsu basin which occurs along the eastern margin of the sea of japan was generated in middle miocene time as a failed rift basin in relation to the backarc opening of the japan arc and was converted to a compressional basin in late miocene time the basin filling succession can be divided into four tectonostratigraphic units stages based on characteristics of depositional systems depositional sequences tectonic subsidence rate and sediment supply these units coincide in time with major tectonic events during backarc rifting and subsequent basin inversion unit i 16 13 5 ma represents a syn rift stage characterized by rapid basin subsidence the rate of accommodation exceeded the rate of accumulation resulting in a retrogradational stacking pattern of muddy slope to basin floor systems unit ii 13 5 6 5 ma represents a post rift thermal subsidence stage the rate of accommodation nearly equaled the rate of accumulation resulting in an aggradational stacking pattern of five third order depositional sequences mainly comprising submarine fan turbidite systems affected by supply of coarse clastics unit iii 6 5 1 ma represents the basin inversion stage showing no subsidence or uplift the accumulation rate exceeded the rate of accommodation resulting in rapid progradation of depositional sequences composed of slope shelf shallow marine delta and fluvial systems unit iv 1 ma present represents an intense compressional stress field sedimentation has been restricted to a synclinal area due to syndepositional folding and uplift changes in basin subsidence rate and sediment supply resulting from tectonics and climate change in the basin and the provenance strongly affected characteristics of the depositional systems and sequences the change in basin subsidence also created a basinwide depositional cycle whereas eustasy affected relative sea level changes created higher order depositional sequences during relatively stable phases of tectonics

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

time integrated variation of sources of fluids and seepage dynamics archived in authigenic carbonates from gulf of mexico gas hydrate seafloor observatory article i nfo authigenic carbonate rocks recovered from the gulf of mexico gas hydrate seafloor observatory in mississippi canyon block 118 mc118 at approximately 900 m water depth were studied using mineralogical bulk geochemical and lipid biomarker analyses carbonate rocks occurred as fractured blocks and nodular masses incorporated in carbonate breccias the carbonates were comprised mainly of high mg calcite and aragonite the stable carbon isotope composition

patterns of carbonate authigenesis at the kouilou pockmarks on the congo deep sea fan abstract different types of seep carbonates were recovered from the kouilou pockmarks on the congo deep sea fan in approximately 3100 m water depth the carbonate aggregates are represented by pyritiferous nodules crusts and slabs tubes and filled molds the latter are interpreted to represent casts of former burrows of bivalves and holothurians the nodules consisting of high mg calcite apparently formed deeper within the sediments than the predominantly aragonitic crusts and slabs nodule formation was caused by anaerobic oxidation of methane dominantly involving archaea of the phylogenetic anme 1 group whereas aragonitic crusts resulted from the activity of archaea of the anme 2 cluster evidence for this correlation is based on the distribution of specific biomarkers in the two types of carbonate aggregates showing higher hydroxyarchaeol to archaeol ratios in the crusts as opposed to nodules formation of crusts closer to the seafloor than nodules is indicated by higher carbonate contents of crusts probably reflecting higher porosities of the host sediment during carbonate formation this finding is supported by lower 18 o values of crusts agreeing with precipitation from pore waters similar in composition to seawater the aragonitic mineralogy of the crusts is also in accord with precipitation from sulfate rich pore waters similar to seawater moreover the interpretation regarding the relative depth of formation of crusts and nodules agrees with the commonly observed pattern that anme 1 archaea tend to occur deeper in the sediment than members of the anme 2 group methane represents the predominant carbon source of all carbonates 13 c values as low as 58 9 v pdb and the encrusted archaeal biomarkers 13 c values as low as 140 v pdb oxygen isotope values of some nodular carbonates ranging from 3 9 to 5 1 v pdb are too high for precipitation in equilibrium with seawater probably reflecting the destabilization of gas hydrates which are particularly abundant at the kouilou pockmarks

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

simulation of long term feedbacks from authigenic carbonate crust formation at cold vent sites fluid flow at cold vent sites is usually driven by the ascent of overpressured fluids from subsurface reservoirs porosity changes in surface sediments due to precipitation and dissolution of authigenic carbonates affects fluid flow and biogeochemical turnover from observations it is known that carbonate precipitates often occur in distinct layers in high concentrations surrounded by layers with low carbonate content using a non steady state model we simulate aragonite and calcite precipitation and dissolution in a 2 m long sediment column located under a bacterial mat at hydrate ridge cascadia accretionary margin assuming a constant pressure gradient over 7000 years fluid flow anaerobic oxidation of methane aom rates and carbonate precipitation and dissolution rates show strong oscillations evoked by changes in permeability and fluid flow over time the porosity reaches values below 0 35 in the carbonate layers that reduce the fluid flow velocity from an initial value of 30 cm a 1 to a minimum value of about 2 cm a 1 these significant changes in the fluid flow system displace the depth of sulfate penetration the simulation predicts cycles of carbonate crust formation and dissolution with a duration of 2000 2700 years resulting in several distinct carbonate layers during periods of high fluid flow aom reaches rates over 1000 mol cm 1 a 1 and methane fluxes out of the sediment reach 200 mol cm 1 a 1 during periods of low fluid flow aom is about 450 mol cm 1 a 1 and the methane flux into the bottom water vanishes completely the oscillations are dampened so that fluid flow and biogeochemical turnover slowly approach steady state after about 7000 years towards the end of the simulation period showing a 1 m thick area at the surface with carbonate concentrations of about 25 wt flow oscillations may also impact the colonization of chemoautotrophic larva and bacteria in and on the sediment the frequency of precipitation dissolution cycles of 2000 2700 years is long enough for vent biota to react to changes in the sediments for example explaining the occurrence of buried calyptogena and acharax mussel shells at former vent sites that are not presently active the evaluation of side scan sonar data reveals large areas of cemented sediments and carbonate pavements north of the investigated site the situation found in the investigated core may be characterized as intermediate stage of carbonate cementation this ongoing process will also form a solid carbonate pavement at this site in the future

marine cold seeps and their manifestations geological control biogeochemical criteria and environmental conditions characteristics of cold seeps at different geologic settings are the subject of this review primarily based on results of the research consortium sfb 574 criteria are drawn from examples on the erosive convergent margin off costa rica the accretionary margin off chile supplemented by examples from the transform margin of the golf of cadiz and the convergent hikurangi margin off new zealand others are from well studied passive margins of the black sea the golf of mexico the eastern mediterranean sea and the south china sea seeps at all settings transport water and dissolved compounds to the ocean through the seafloor by different forcing mechanism and from different depths of the submerged geosphere 10s of meters to 10s of km the compounds sustain oasis type ecosystems by providing bioactive reductants sulfide methane and hydrogen hereby the interaction between fluid composition flux rates and biota results in a diagnostic hydrocarbon metazoan microbe carbonate association currently well over 100 active sites are known the single most important reaction is microbially mediated anaerobic oxidation of methane with secondary reactions involving s biogeochemistry and carbonate mineral precipitation seep fluids and their seafloor manifestations provide clues as to source depth fluid sediment rock interaction during ascent lifetime and cyclicity of seepage events but less so on the magnitude of return flow at erosive margins cl depleted and b enriched fluids from clay dehydration provide criteria for source depth and temperature the upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth at accretionary margins fluids are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate they are emitted through thrust faults at highly sedimented margins organic rich and evaporite containing strata when present determine the final fluid composition by emitting characteristically gas hydrate derived methane brine associated non methane hydrocarbons or leached elements and their isotopes li 7li b ba from host sediments smectite illite transformation and associated cl depletion from release of interlayer water is a pervasive process at these margins rare earth element pattern in conjunction with redox sensitive metals retained in seep carbonates indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids clear environmental characterization though currently remains inconclusive more deeply sourced fluids as in transform margins may be characterized by their 87sr 86sr ratios from interaction with oceanic crustal rocks below quantification of flow and reliable estimates of total volatile output from fore arcs remain a challenge to seep research as does understanding the role of geologically derived methane in the global methane cycle

significance of aragonite cements around cretaceous marine methane seeps abstract detailed petrography and geochemistry of carbonate precipitates in cretaceous cold seep mounds from the canadian arctic show spectacular early diagenetic products some still preserved splays and isopachous layers of fine acicular aragonite and large botryoids and crusts of low magnesium calcite showing unusual entanglement of former fibrous calcite and aragonite the latter mineralogy is suggested by clear flat terminated cathodoluminescence patterns interpreted as ancient crystal growth steps and the former by rhombohedral terminations the early cement phases very likely precipitated in cold arctic water dominated by bicarbonates derived from bacterially oxidized methane these cements have d13c values around 44 and d18o values of 1 8 to 0 1 pdb coexistence of calcite and aragonite early cements in the cretaceous seep mounds is unusual because precipitation occurred in high latitude cold water settings and during a so called calcite sea mode as in modern marine hydrocarbon seeps the chemistry of the cretaceous system was apparently controlled by chemosynthetic bacterial activity resulting in high ahco3 that promoted precipitation of carbonates we suggest that locally fluctuations in ahco3 aso42 resulted in oscillating aragonite or calcite supersaturation and hence controlled the mineralogy of the early precipitates

carbon isotopic compositions of prokaryotic lipids as tracers of carbon cycling in diverse settings recent work has highlighted the ubiquity of bacteria and archaea and continues to affirm their significance in diverse biogeochemical processes the 13c values and distributions of diagnostic lipids derived from such microorganisms can provide insights into prokaryotic processes in modern settings and are one of the few means by which past prokaryotic processes in depositional settings can be elucidated here we present a brief review of prokaryotic lipids commonly observed in sediments and the controls on their carbon isotopic compositions we then present two case studies one of mediterranean cold seeps at which anaerobic oxidation of methane occurs and one of a holocene peat deposit in which a variety of aerobic and anaerobic microorganisms govern the degradation of organic matter these two studies illustrate the potential utility of compound specific carbon isotope analyses to deconvolute pathways of carbon flow in microbial communities

diffusive methane seepage in ancient deposits examples from the neogene shin etsu sedimentary basin central japan abstract along continental margins various types of methane seeps with a variety of flux rates spatial extents and durations occur although numerous studies have investigated spatially extensive high flux rate seeps seeps with ephemeral and or weak flows known as diffusive seeps have received less attention this study investigates ancient diffusive methane seeps in the shin etsu sedimentary basin central japan aiming to deduce their spatial extent and their sedimentological paleontological and geochemical properties the seeps were identified as centimeter scale carbonate concretions in two outcrops of neogene siltstones in the basin a comprehensive examination of the spatial distribution of the carbonates their associated molluscan fossils petrography carbon and oxygen isotopic compositions and lipid biomarker contents of the concretions revealed that they originated from the anaerobic oxidation of methane aom and formed via a weak diffusive fluid flow the small size and irregular or burrow shaped morphologies of the concretions indicate that methane bearing fluids diffused through small pore spaces such as burrows associated molluscan fossils consist of vesicomyids and other bivalves typical of methane seeps fossils of predator species were also identified but epifaunal seep organisms are notably absent the carbonate concretions are composed of strongly 13c depleted micrite 13c values as low as 46 0 vs vpdb with minor 13c rich void filling sparry cements the presence of lipid biomarkers pentamethylicosane pmi with 13c values as low as 119 and biphytane and the absence of crocetane suggests that the aom was performed by an anme 1 dominated archaeal community the insights of diffusive methane seepage in the geological record gained from this study can help to better understand depositional processes of seep deposits and variations in fluid flows in both ancient and modern methane seeping systems

miocene tubular concretions in east coast basin new zealand analogue for the subsurface plumbing of cold seeps the uplifted accretionary prism of east coast basin in hikurangi margin north island new zealand exposes late miocene slope mudrocks whangaehu mudstone 10 carbonate in coastal cliffs north of cape turnagain that contain conspicuous tubular carbonate concretions 50 85 carbonate supporting near central conduits pipe and bulbous morphologies dominate ranging in exposed length up to 5 m and up to 1 m in diameter the concretions were formed by the precipitation of micritic dolomite and calcite cement within the host mudstone at shallow burial depths 100 m 13c values of the cement range from 22 to 13 pdb and are interpreted to reflect carbonate precipitation from either the extensive anaerobic oxidation of methane aom and or mixing of microbial methane and methanogenic co2 aom is confirmed by lipid biomarker evidence indicating that methane oxidation occurred in the sediments at the time of carbonate precipitation the mixed dolomite calcite mineralogies and the trend of 13c in the tubular concretions from strongly negative to strongly positive values are interpreted to reflect methane oxidation from the onset of ascent through to the end of a migration event depleted and enriched 18o values suggest an evolved fluid source influenced by the dissociation of gas hydrates collectively our results indicate that the tubular concretions within the upper slope mudstones delineate parts of the subsurface plumbing network of a cold seep system on the late miocene paleo hikurangi margin in which the fluids were sourced from ascending methane the intermediate location of the whangaehu concretions between older early miocene seep carbonates to the west and modern ones offshore to the east indicates a progressive eastwards shift with time of a long lived if only periodically active seep system the concretionary plumbing features at whangaehu provide a conceptual model for subsurface fluid pathways and seep related processes beneath the modern hikurangi margin seabed and possibly also for other modern and ancient cold seep carbonate systems

hydrocarbon seep carbonates of a miocene forearc east coast basin north island new zealand an ancient hydrocarbon seep province of 14 isolated authigenic carbonate deposits has been identified in fine grained deep marine siliciclastic strata of the miocene east coast basin north island new zealand these forearc sediments have been uplifted and complexly deformed into accretionary ridges adjacent to the still active hikurangi convergent margin older active and passive margin strata mid cretaceous to oligocene in age underlie the neogene sequence and contain oil and gas prone source rocks older mesozoic meta sedimentary rocks constitute the backstop against which the current phase of subduction related sedimentation has accumulated 24 ma present the seep carbonates up to 10 m thick 200 m across archive methane signatures in their depleted carbon isotopes to 13c 51 7 pdb and contain chemosynthesis based paleocommunities e g worm tubes bathymodioline mussels and vesicomyid lucinid and thyasirid bivalves typical of other cenozoic and modern seeps northern and southern sites are geographically separated and exhibit distinct lithological and faunal differences structural settings are variable seep associated lithologies also are varied and suggest carbonate development in sub seafloor seafloor and physically reworked diapiric expansion gas explosion gravity slide or debris flow settings similar to italian apennine seep deposits of overlapping ages peculiar attributes of the new zealand miocene seep deposits are several including digitate thrombolites of clotted microbial micrite encased in thick isopachous horizons and botryoids of aragonite seep plumbing features are also well exposed at some sites displaying probable gas explosion breccias filled with aragonite tubular concretions fluid conduits and carbonate cemented thin sandstone beds and burrows within otherwise impermeable mudstones a few seeps were large enough to develop talus debris piles on their flanks which were populated by lucinid bivalves and terebratulid brachiopods firmgrounds and hardgrounds were common as evidenced by trace fossil associations or caryophyllid coral thickets atop some seep carbonate deposits thus the new zealand examples show strong evidence of formation in sediments at or just beneath the seafloor but some were clearly exhumed by erosion to sustain later non seep epifaunal and boring paleocommunities

seep deposits from northern istria croatia a first glimpse into the eocene seep fauna of the tethys region three isolated limestone deposits and their fauna are described from a middle eocene flysch succession in northwestern istria croatia the limestones are identified as ancient methane seep deposits based on fabrics and characteristic mineral phases 13 c carbonate values as low as 42 2 and 13 c depleted lipid biomarkers indicative of methane oxidizing archaea the faint bedding of the largest seep deposit the great dominance of authigenic micrite over early diagenetic fibrous cement as well as biomarker patterns indicate that seepage was diffusive rather than advective apart from methanotrophic archaea aerobic methanotrophic bacteria were present at the eocene seeps as revealed by 13 c depleted lanostanes and hopanoids the observed corrosion surfaces in the limestones probably reflect carbonate dissolution caused by aerobic methanotrophy the macrofauna consists mainly of chemosymbiotic bivalves such as solemyids acharax thyasirids thyasira and lucinids amanocina the middle eocene marks the rise of the modern seep fauna but so far the fossil record of seeps of this age is restricted to the north pacific region the taxa found at buje originated during the cretaceous period whereas taxa typical of the modern seep fauna such as bathymodiolin mussels and vesicomyid clams are absent although this is only a first palaeontological glimpse into the biogeography during the rise of the modern seep fauna it agrees with biogeographic investigations based on the modern vent fauna indicating that the dominant taxa of the modern seep fauna first appeared in the pacific ocean

geological imprint of methane seepage on the seabed and biota of the convergent hikurangi margin new zealand box core and grab carbonate results abstract short box cores to 30 cm bsf and seafloor carbonate grab samples were acquired at mapped hydrocarbon seep sites 600 1200 m water depths during the 2007 rv sonne so191 cruise on the hikurangi margin offshore eastern north island new zealand to evaluate the influence of methane seepage on sedimentologic biotic mineralogic and stable isotopic attributes of seabed sediments sedimentary horizons in the box cores consist of siliciclastic silts and sands shell beds and nodular microcrystalline aragonite bands up to 15 cm thick the megafauna is dominated by infaunal to semi infaunal chemosymbiotic bivalves calyptogena lucinoma and acharax as well as associated worms and carnivorous and grazing gastropods burrows in silts some occupied by worms or juvenile acharax mainly have simple morphologies more typical of high energy nearshore settings than deep sea environments while a few are large and sparsely branched with wall scratch marks inferred to be of decapod crustacean origin the box core silts and nodular carbonate samples vary in toc content from 0 2 to 0 9 wt carbonate content from 4 to 78 and 13 c and 18 o values from 50 3 to 0 6 pdb and 0 77 to 3 2 pdb respectively low carbonate content silt samples have the most enriched 13 c values implying a seawater source for their pore water bicarbonate negative 13 c and positive 18 o values typify the nodular microcrystalline aragonite bands indicating formation during microbially mediated sulphate dependent anaerobic oxidation of methane aom in a cold near seafloor environment as is also supported by lipid biomarker data a clear isotopic mixing trend of decreasing 13 c and increasing 18 o and carbonate content in the fine seafloor grab carbonate samples show greater textural variability and are divided into two types fresh appearing grey to white blocks yield similar mineralogic isotopic and biomarker signatures to the nodular carbonate bands in the cores a largely seep related epifauna affiliated with these grab samples include chemosymbiotic bathymodiolin mussels siboglinid tube worms methanotrophic suberitid sponges and grazing limpets which in places are entombed within the carbonate by contrast some dark reddish to brown iron stained microcrystalline dolomitic slabs and tubular concretions support abundant non seep epifaunal encrusters from the surrounding deep sea indicative of long exposure on the seafloor distinct stable isotopic signatures of these exhumed dolostones 13 c c 20 pdb 18 o up to 7 pdb suggest derivation from an oxidised methane pool and pore fluid freshening by gas hydrate dissociation or from mobilized burial fluids that have undergone clay mineral dehydration

late cretaceous maastrichtian shallow water hydrocarbon seeps from snow hill and seymour islands james ross basin antarctica fossil hydrocarbon seeps are present in latest cretaceous maastrichtian volcaniclastic shallow shelf sediments exposed on snow hill and seymour islands james ross basin antarctica the seeps occur in the snow hill island formation on snow hill island and are manifest as large sized cement rich carbonate bodies containing abundant thyasirid bivalves and rarer ammonites and solemyid bivalves these bodies have typical seep cement phases with 13c values between 20 4 and 10 7 and contain molecular fossils indicative of terrigenous organic material and the micro organisms involved in the anaerobic oxidation of methane including methanotrophic archaea and sulphate reducing bacteria on seymour island the seeps occur as micrite cemented burrow systems in the lopez de bertodano formation and are associated with thyasirid solemyid and lucinid bivalves and background molluscan taxa the cemented burrows also have typical seep cement phases with 13c values between 58 0 and 24 6 there is evidence from other data that hydrocarbon seepage was a common feature in the james ross basin throughout the maastrichtian and into the eocene the snow hill and seymour island examples comprise the third known area of maastrichtian hydrocarbon seepage but compared to most other ancient and modern seep communities the james ross basin seep fauna is of very low diversity being dominated by infaunal bivalves all of which probably had thiotrophic chemosymbionts but which were unlikely to have been seep obligates absent from the james ross basin seep fauna are typical obligate seep taxa from the cretaceous and the cenozoic reasons for this may have been temporal palaeolatitudinal palaeobathymetric or palaeoecological

outcrop analogues of pockmarks and associated methane seep carbonates a case study from the lower cretaceous albian of the basque cantabrian basin western pyrenees abstract late albian deep water sediments of the black flysch group in the basque cantabrian basin western pyrenees preserve a fossil pockmark field including methane seep carbonates and associated macrofauna the geometry of the pockmarks is reconstructed from repeated lens shaped turbidite deposits with centrally located carbonate bodies early diagenetic carbonate phases such as clotted micrite and yellow calcite with 13c values as low as 41 6 and hydrocarbon biomarkers e g 2 6 10 15 19 pentamethylicosane with strong depletions in 13c indicate that the carbonates precipitated due to anaerobic oxidation of methane the pockmarks probably formed due to subsidence induced by dewatering and degassing of the gas charged seabed perhaps enhanced by the weight of the carbonate bodies the macrofauna resembles that of other late mesozoic deep water methane seeps world wide and is dominated by large lucinid and caspiconcha bivalves and hokkaidoconchid gastropods during late diagenesis the carbonate 18o values were reset to a narrow range of 12 to 10 the remaining pore spaces and fissures were filled with pyrobitumen and additional carbonate phases precipitated potentially due to thermochemical sulfate reduction processes

measurements of transience and downward fluid flow near episodic methane gas vents hydrate ridge cascadia aqueous flux measurements within cold seep regions on northern hydrate ridge cascadia indicate a high degree of variability with extended periods of downflow and reversals of flow direction over periods of weeks to months local episodic venting of free methane gas was also observed the instruments recorded similar changes in hydrologic flow patterns both on and off clam fields the magnitude of the flow rates decreasing away from the clam field the coincidence of episodic gas venting with nearby highly variable aqueous fluid flow suggests that they may be coupled we propose that these observations are consistent with the action of a gas driven pump that operates somewhat like a geyser the hypothesis of gas driven pumping of seawater through northern hydrate ridge has important ramifications for the mass fluxes through this region

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

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

the beast burrowed the fluid followed crustacean burrows as methane conduits abstract an extensive pockmark field with associated methane seep carbonates has recently been reported from the late albian lower cretaceous ubidepea mudstone of the black flysch group in the basque country northern spain but the exact pathways of the migrating methane rich fluids remained elusive here we provide petrographic stable carbon and oxygen isotope evidence that abundant crustacean burrows in the surrounding mudstone preserved as the trace fossil thalassinoides and the seep carbonates themselves have acted as long lasting fluid conduits in this system the thalassinoides infill generations show a diagenetic parasequence often starting with a distinctive lining followed by one to several phases of cementing of the burrow walls and burrow infills and finally late diagenetic sparry calcite that filled the remaining open cavities and conduits the micrite cementing the burrow walls shows negative 13 c values similar to those reported from the seep carbonates indicating that methane oxidation was involved in their precipitation rather than or in addition to the oxidation of other organic matter even the late diagenetic sparry calcite shows 13 c values as low as 30 4 versus pdb providing evidence that these burrows served as fluid conduits for an extended period of time our study supports the growing body of evidence that crustacean burrows play an important role in channeling seeping fluids in such systems we anticipate that this phenomenon is much more widespread than currently appreciated especially in examples where other types of fluid conduits are absent

formation of seep carbonates along the makran convergent margin northern arabian sea and a molecular and isotopic approach to constrain the carbon isotopic composition of parent methane abstract authigenic carbonate deposits have been sampled with the remotely operated vehicle marum quest 4000 m from five methane seeps between 731 and 1823 m water depth along the convergent makran continental margin offshore pakistan northern arabian sea two seeps on the upper slope are located within the oxygen minimum zone omz ca 100 to 1100 m water depth the other sites are situated in oxygenated water below the omz below 1100 m water depth the carbonate deposits vary with regard to their spatial extent sedimentary fabrics and associated seep fauna within the omz carbonates are spatially restricted and associated with microbial mats whereas in the oxygenated zone below the omz extensive carbonate crusts are exposed on the seafloor with abundant metazoans bathymodiolin mussels tube worms galatheid crabs aragonite and mg calcite are the dominant carbonate minerals forming common early diagenetic microcrystalline cement and clotted to radial fibrous cement the 18 o carbonate values range from 1 3 to 4 2 v pdb indicating carbonate precipitation at ambient bottom water temperature in shallow sediment depth extremely low 13 c carbonate values as low 54 6 v pdb point to anaerobic oxidation of methane aom as trigger for carbonate precipitation with biogenic methane as dominant carbon source prevalence of biogenic methane in the seepage gas is corroborated by 13 c methane values ranging from 70 3 to 66 7 v pdb and also by back calculations considering 13 c methane values of carbonate and incorporated lipid biomarkers these calculations 13 c methane carbonate 13 c anme methane 13 c mox methane prove to be useful to assess the carbon stable isotope composition of seeping methane if this has not been determined in the first place such an approach represents a useful tool to reconstruct fluid composition of ancient seeps aom is also revealed by lipid biomarkers of anaerobic methane oxidizing archaea such as crocetane pentamethylicosane pmi and sn2 hydroxyarchaeol strongly depleted in 13 c 13 c values as low as 127 v pdb biomarkers of sulphate reducing bacteria are also abundant showing slightly less negative 13 c values but still significantly 13 c depleted average values as low as 101 other bacterial biomarkers such as bacteriohopanepolyols bhps hopanols and hopanoic acids are detected in most carbonates but are particularly common in seep carbonates from the non omz sites the bhp patterns of these carbonates and their low 13 c values resemble patterns of aerobic methanotrophic bacteria in the shallower omz sites bhps revealed much lower contents and varying compositions most likely reflecting other sources than aerobic methanotrophic bacteria 230 th u carbonate ages indicate that aom induced carbonate precipitation at the deeper non omz seeps occurred mainly during the late pleistocene holocene transition i e between 19 and 15 ka before present when the global sea level was lower than today

eocene deep sea communities in localized limestones formed by subduction related methane seeps southwestern washington densely populated communities of soft bottom dwelling taxa similar to those found today along subduction zones off the coasts of japan and oregon have been discovered in very localized deep water limestones of late middle to late eocene age along the southwestern margin of washington subduction was prevalent in this area during this time and compressive forces squeezed subsurface methanerich waters onto the ocean floor where opportunistic bivalves especially modiolus calyptogena and thyasira vestimentiferan tube worms serpufid tube worms siliceous sponges very small limpets trochid and turbinid archaeogastropods and other macrobenthos colonized these assemblages are the earliest recorded biologic communities formed in response to methane seeps in subduction zones

new age constraints on the western betic intramontane basins a late tortonian closure of the guadalhorce corridor several gateways connected the mediterranean with the atlantic during the late miocene but the timing of closure and therefore their role prior to and during the messinian salinity crisis 5 97 5 33 ma is still under debate the timing of closure of the guadalhorce corridor is especially disputed as the common lack of marine microfossils hampers precise age determination here we present new biostratigraphic age constraints on the sediments of the ronda antequera and arcos regions which formed the northern part of the guadalhorce corridor the general presence of globorotalia menardii 4 in the youngest deep marine sediments of all three regions indicates a late tortonian age older than 7 51 ma we conclude that the guadalhorce corridor closed during the late tortonian well before the onset of the messinian salinity crisis and that the late tortonian tectonic uplift of the eastern betics extended into the western betics

a miocene chemosynthetic community from the ogaya formation in joetsu evidence for depth related ecologic control among fossil seep communities in the japan sea back arc basin abstract two large carbonate bodies within deep water sediments of the uppermost middle miocene ogaya formation at kita kuroiwa niigata prefecture central japan are identified as an ancient hydrocarbon seep site based on petrographic features such as acicular and sparry calcite cements and clotted micrite with 13c values as low as 38 0 vs vpbd and a low diversity fauna of vesicomyid and mytilid bivalves and provannid gastropods compared to well studied coeval seep communities from the japan sea back arc basin species diversity is particularly low at the kita kuroiwa site while the percentage of seep obligate taxa taxa that are restricted to this type of environment is very high largely due to the absence of predatory gastropods such as naticids and buccinids modern seep communities show a decrease in species diversity and an increase in seep obligate taxa with depth due to the lower abundance and diversity of background colonists entering cold seep habitats likewise depth is here considered as the most likely cause for the observed differences in community structure because the kita kuroiwa seep site was located in considerably deeper water 1000 2000 m than the comparable coeval seep sites in the japan sea back arc basin

new records of oligocene diffuse hydrocarbon seeps northern cascadia margin abstract fossil methane seeps are preserved in late eocene through pliocene marine sedimentary units of the cascadia margin of the northeastern pacific all cascadia fossil seeps are situated in the uplifted accretionary wedge that overlies extensive middle eocene coal bearing units and the paleocene early eocene siletzia large igneous province this study describes eight previously unrecorded oligocene seeps all of which are identified by small scattered carbonates with or without accompanying characteristic seep macrofauna from both inner and outer shelf depths we interpret these deposits as reflecting spatially and temporally diffuse seepage of hydrocarbon enriched fluids sourced from various carbon sources within the actively deforming accretionary prism and term them diffuse seeps 13c and 18o values from foraminiferal carbonate from the studied stratigraphic units have broad variability authigenic carbonates occurring as nodules blebs burrow fill and fracture fill indicated microbial and thermogenic methane and multiple fluid flow pathways from within the actively deforming accretionary wedge it is apparent that the complex fluid flow regime observed in modern seeps of the cascadia margin is a continuation of one established in the late eocene

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

mineralized conduits are part of the uppermost plumbing system of oligocene methane seep deposits washington state usa abstract plumbing systems of marine seeps are complex pathways along which hydrocarbon rich fluids move upward through the sedimentary column in the shallow subsurface seep plumbing systems may become successively filled by methane derived authigenic carbonates resulting in mineralized conduits this work investigates mineralized conduits in the uppermost plumbing network of oligocene seep deposits from the lincoln creek formation in washington state that consist of a paragenetic sequence of authigenic mineral phases at two study sites the pipes grade into the base of seep deposits the studied samples of concentrically mineralized conduits are cylindrical in shape measure 2 3 cm in diameter and are up to 15 cm in length the mineralized conduits are referred to as pipes hereafter the earliest mineral phase in the paragenetic sequence is matrix micrite making up the outer part of the pipes toward their centers the pipes are filled by two intercalated cement phases 1 clear banded and botryoidal aragonite and 2 micro to cryptocrystalline yellow aragonite the innermost portions of the pipes are filled by brownish calcite microspar or pipe filling micrite the observed paragenetic sequences archive successions of biogeochemical processes the 13 c values of clear and yellow aragonite cements range from 50 6 to 41 2 suggesting that their main carbonate source was provided by anaerobic oxidation of methane in contrast the later phases brownish calcite microspar pipe filling micrite are relatively enriched in 13 c 13 c values 2 3 to 3 9 pointing to carbonate precipitation from fluids affected by methanogenesis the size and morphology of the pipes suggest that initial excavation was caused by burrowing organisms the burrows subsequently acted as preferred fluid pathways suggesting that the transport of fluids within near surface sediments at the oligocene seeps was strongly influenced by the activity of the local fauna possible producers of the burrows were sediment dwelling crustaceans specifically callianassid decapods as well as bivalves

aerobic methanotrophy at ancient marine methane seeps a synthesis abstract the molecular fingerprints of the chemosynthesis based microbial communities at methane seeps tend to be extremely well preserved in authigenic carbonates the key process at seeps is the anaerobic oxidation of methane aom which is performed by consortia of methanotrophic archaea and sulphate reducing bacteria besides the occurrence of 13 c depleted isoprenoids and n alkyl chains derived from methanotrophic archaea and sulphate reducing bacteria respectively 13 c depleted triterpenoids have been reported from a number of seep deposits in order to evaluate the significance of these apparently non aom related molecular fossils the biomarker inventories of one campanian and two miocene methane seep limestones are compared these examples provide strong evidence that methane was not solely oxidized by an anaerobic process structural and carbon isotope data reveal that aerobic methanotrophy was common at some ancient methane seeps as well the miocene marmorito limestone contains abundant 3 methylated hopanoids 13 c 100 most likely 3 methylated hopanepolyols prevailing in aerobic methanotrophs were the precursor lipids of these compounds a series of isotopically depleted 4 methylated steranes lanostanes 13 c 80 to 70 and similarly isotopically depleted 17 h 21 h 32 hopanoic acid in the miocene pietralunga seep limestone also are derived probably from aerobic methanotrophs lanosterol which is known to be produced by aerobic methanotrophs is the most likely precursor of 4 methylated steranes less obvious is the origin of 8 14 secohexahydrobenzohopanes 13 c 110 to 107 in late cretaceous seep limestones these hopanoids probably reflect early degradational products of precursor lipids locally produced by seep endemic aerobic methanotrophs

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures