aragonite crystal fans in neoproterozoic cap carbonates a case study from brazil and implications for the post snowball earth coastal environment abstract neoproterozoic cap carbonates are characterized by anomalous sedimentary features including sea floor precipitates represented by aragonite pseudomorph cement crusts and crystal fans these features are found in restricted periods of geological history and their generation in the context of the neoproterozoic has been attributed to very specific postglacial conditions leading to alkalinity oversaturation new sedimentary and geochemical results on well preserved neoproterozoic deposits of aragonite pseudomorph crystal fans at the base of the sete lagoas formation bambui group central brazil are reported the micrite settling facies shows the highest abundance of crystal fans arranged in centimeter scale layers interfingered with the micrite matrix this facies is interpreted as a result of postglacial calcium carbonate oversaturation in restricted areas characterized by marine dysoxic waters a numerical model constrains the kinetics of formation of aragonite crystals or micrite by calculating the induction times and precipitation rates of both carbonate species for postglacial conditions of elevated temperature and high atmospheric pco2 in these conditions the mg ca ratio of the neoproterozoic seawater is calculated at ca 1 2 alkalinity oversaturation is monitored by a variable evaporation degree aragonite formation is kinetically favored and the discrepancy between calcite and aragonite precipitation rate is greater as atmospheric pco2 hence alkalinity is higher these modeling conditions do not preclude the contribution of incomplete organic matter degradation to alkalinity as suggested by negative carbon isotope signatures in addition the large number of aragonite micrite pairs suggests a seasonal or paleoclimatic forcing other cases of abiotic aragonite precipitation through time are also briefly examined by comparison

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

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

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

carbon isotopic evidence for coupled sulfate reduction methane oxidation in amazon fan sediments abstract carbon isotope ratios of dissolved inorganic carbon were measured on porewaters from amazon fan sediments collected on ocean drilling program leg 155 values as low as 49 6 vs pdb were recorded with the lowest values coinciding with the base of the sulfate reduction zone at each site the values indicate that on the order of 50 85 of sulfate reduction in amazon fan sediments takes place by methane oxidation estimated rates of methane oxidation range from 0 3 1 0x10 5 moles l yr the reasons for the high percentage of sulfate reduction taking place by methane oxidation are thought to be the large decrease in fan sedimentation rates in the early holocene and the terrestrial source of organic matter in fan sediments

stratigraphy and magnetic polarity of the high terrace remnants in the upper ohio and monongahela rivers in west virginia pennsylvania and ohio abstract a synthesis of previous work and new data on the stratigraphy of high terraces of the ohio and monongahela rivers upstream from parkersburg west virginia indicates a correspondence between terrace histories in the ancient teays and pittsburgh drainage basins four terraces are identified in each sediments of the lower three alluvial and slackwater terraces correlated with illinoian early wisconsin and late wisconsin glacial deposits have been traced along the modern ohio river through the former divide between the teays and pittsburgh basins sediments in the fourth terrace the highest well defined terrace in each basin were deposited in two ice dammed lakes separated by a divide near new martinsville west virginia some deposits of the highest slackwater terrace in both the teays and pittsburgh basins have reversed remanent magnetic polarity this and the stratigraphic succession in the two basins suggests that both were ponded during the same glaciation reversed polarity in these terrace sediments restricts the age of the first ice damming event for which stratigraphic evidence is well preserved to a pre illinoian early pleistocene glaciation prior to 788 000 yr ago in contrast slackwater sediments in the monongahela river valley upstream from an outwash gravel dam at the allegheny monongahela confluence have normal remanent magnetic polarity corroborating correlation with an illinoian ponding event

controls on marine carbonate cement mineralogy review and reassessment abstract commonly cited models for controls on variations in carbonate mineralogy are only partly successful in accounting for natural mineralogical trends this limited success may result in part from a failure to recognize or address the ramifications of assumptions inherent to such models in general changes from calcite to aragonite or vice versa and variations in mgco3 incorporation in calcite are interpreted as resulting from 1 kinetic rather than thermodynamic effects 2 the effects of fluid chemistry rather than hydrologic biological or substrate effects 3 the effects of single parameters of fluid chemistry rather than the interactive or aggregate effects of several components and or 4 inorganic rather than organic parameters of fluid chemistry recent laboratory data suggest the necessity of a new approach to modeling controls on mineralogy these data indicate that no single fluid parameter is likely to be a sole or dominant control on carbonate mineralogy in natural environments in some cases thermodynamic stability differences may be as important as kinetic factors in determining mineralogy furthermore the effects of substrate hydrologic and biological factors and of organic compounds cannot be ruled out for most natural situations although at present reliable data are lacking to quantify the influence of these factors on mineralogy future models of controls on carbonate mineralogy need to consider the aggregate and interdependent effects of all of these factors

microbial methane turnover at mud volcanoes of the gulf of cadiz the gulf of cadiz is a tectonically active area of the european continental margin and characterised by a high abundance of mud volcanoes diapirs pockmarks and carbonate chimneys during the r v sonne expedition gap gibraltar arc processes so 175 in december 2003 several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes captain arutyunov bonjardim ginsburg gemini and a newly discovered mud volcano like structure called no name show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed the presence of a distinct sulphate methane transition zone smt overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor anaerobic oxidation of methane aom and sulphate reduction sr rates show maxima at the smt which was found between 20 and 200 cm below seafloor at the different mud volcanoes in comparison to other methane seeps aom activity 383 mmol m 2 year 1 and diffusive methane fluxes 321 mmol m 2 year 1 in mud volcano sediments of the gulf of cadiz are low to mid range corresponding lipid biomarker and 16s rdna clone library analysis give evidence that aom is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria srb in the studied mud volcanoes little is known about the variability of methane fluxes in this environment carbonate crusts littering the seafloor of mud volcanoes in the northern part of the gulf of cadiz had strongly 13c depleted lipid signatures indicative of higher seepage activities in the past however actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor no active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes and biogeochemical measurements indicate a complete methane consumption in the seafloor our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present

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

origins of hydrocarbon gas seeping out from offshore mud volcanoes in the nile delta abstract this paper discusses the origin of gas seepages free gas or dissolved gas in ground water or brine sampled with the nautile submarine during the nautinil cruise at the seafloor of the deep water area of the nile turbiditic system on different mud volcanoes and brine pools generally the gas is wet and includes c1 c2 c3 ic4 nc4 co 2 these gas samples show no evidence of biodegradation which is not the case of the gas present in the deep hydrocarbon accumulations at depth it indicates that the gas expelled by the mud volcanoes is not issued from direct leakages from deep gas fields the collected gas samples mainly have a thermogenic origin and show different maturities some samples show very high maturities indicating that these seepages are sourced from great depths below the messinian salt moreover the different chemical compositions of the gas samples reflect not only differences in maturity but also the fact that the gas finds its origin in different deep source rocks carbon dioxide has an organic signature and cannot result from carbonate decomposition or mantle fluids the crustal derived radiogenic isotopes show that the analyzed gas samples have suffered a fractionation processes after the production of the radiogenic isotopes due either to oil occurrence at depth interacting with the flux of gas and or fractionation during the fluid migration

an integrated view of the methane system in the pockmarks at vestnesa ridge 79 n accepted manuscript version published version available at https doi org 10 1016 j margeo 2017 06 006 accepted manuscript version licensed cc by nc nd 4 0

fluid seepage associated with slope destabilization along the zambezi margin mozambique abstract evidences for active fluid seepages have been discovered along the zambezi continental slope offshore southern mozambique these seepages are mostly associated with pockmarks which are aligned along a trend parallel to the slope and running closely upstream of the headwall scarp of a wide zone of slope destabilization fluid seepages are interpreted as a potential trigger for the slope destabilization acoustic anomalies within the water column have been interpreted as related to moderate bubble seepages mostly located outside and only punctually inside the destabilization zone exploration with the scampi towed camera system in the widest pockmark diameter 200 m wide has shown fluid seepages associated to authigenic carbonate crusts and possibly bacterial mats these fluid seepages are also associated to the presence of chemiosynthetic organisms vesicomyidae and thyasiridae bivalves siboglinidae tubeworms the sampled gas in the sediment corresponds mainly to ch4 of microbial origin generated by hydrogenotrophic methanogenesis from a substrate of organic origin i e a conventional process of genesis of microbial gas in the marine domain no evidence for thermogenic gas was detected another type of pockmarks has been observed within the core of the slope destabilization zone most of these pockmarks are inactive in terms of fluid seepage at present time and are associated to carbonate buildups forming chimney geometries they probably correspond to diagenetic chimneys of former fluid migration pathways that have been exhumed during the mass sliding and the surrounding depression are related to recurrent activity of strong lateral slope currents which have scoured the sediments around the spatial organization of the slope destabilization features is considered as representative of the temporal evolution of the landslide giving information about the dynamics of slope instability processes this proposed evolution started by scattered seepages of formation water with dissolved gas then free gas seepages appeared notably in the upper part of the slope this was followed by progressive shallow deformation in the sediments downslope of the main gas seepages finally the whole slope was destabilized forming imbricated landslides exhuming locally former diagenetic chimneys

coupled organic and inorganic carbon cycling in the deep subseafloor sediment of the northeastern bering sea slope iodp exp 323 abstract we studied microbially mediated diagenetic processes driven by carbon mineralization in subseafloor sediment of the northeastern bering sea slope to a depth of 745 meters below seafloor mbsf sites u1343 u1344 and u1345 were drilled during integrated ocean drilling program iodp expedition 323 at water depths of 1008 to 3172 m they are situated in the high productivity green belt region with organic carbon burial rates typical of the high productivity upwelling domains on western continental margins the three sites show strong geochemical similarities the downward sequence of microbially mediated processes in the sediment encompasses 1 organoclastic sulfate reduction 2 anaerobic oxidation of methane aom coupled to sulfate reduction and 3 methanogenesis the sediment contains two distinct zones of diagenetic carbonate formation located at the sulfate methane transition zone smtz and between 300 and 400 mbsf the smtz at the three sites is located between 6 and 9 mbsf the upward methane fluxes into the smtz are similar to fluxes in smtzs underlying high productivity surface waters off chile and namibia our bering sea results show that intense organic carbon mineralization drives high ammonium and dissolved inorganic carbon dic production rates 4 2 mmol m 3 y 1 in the uppermost 10 mbsf and strongly imprints on the stable carbon isotope composition of dic driving it to a minimum value of 27 vpdb at the smtz pore water calcium and magnesium profiles demonstrate formation of diagenetic mg rich calcite in the smtz below the smtz methanogenesis results in 13c enrichment of pore water dic with a maximum value of 11 9 the imprint of methanogenesis on the dic carbon isotope composition is evident down to a depth of 150 mbsf below this depth slow or absent microbially mediated carbon mineralization leaves dic isotope composition unaffected ongoing carbonate formation between 300 and 400 mbsf strongly influences pore water dic and magnesium concentration profiles the linked succession of organic carbon mineralization and carbonate dissolution and precipitation patterns that we observe in the bering sea slope sediment may be representative of passive continental margin settings in high productivity areas of the world s ocean

anaerobic oxidation of methane in a cold water coral carbonate mound from the gulf of cadiz the gulf of cadiz is an area of mud volcanism and gas venting through the seafloor in addition several cold water coral carbonate mounds have been discovered at the pen duick escarpment amidst the el arraiche mud volcano field on the moroccan margin one of these mounds named alpha mound has been studied to examine the impact of the presence of methane on pore water geochemistry potential sulphate reduction sr rate and dissolved inorganic carbon dic budget of the mound in comparison with off mound and off escarpment locations pore water profiles of sulphate sulphide methane and dic from the on mound location showed the presence of a sulphate to methane transition zone at 350 cm below the sea floor this was well correlated with an increase in sr activity 13c depleted dic at the transition zone 21 9 vs vienna pee dee belemnite indicated that microbial methane oxidation significantly contribute to the dic budget of the mound the alpha mound thus represents a new carbonate mound type where the presence and anaerobic oxidation of methane has an important imprint on both geochemistry and dic isotopic signature and budget of this carbonate mound

microbial methane oxidation and sulfate reduction at cold seeps of the deep eastern mediterranean sea abstract the eastern mediterranean hosts a variety of active cold seep systems such as gas chimneys mud volcanoes and pockmarks in water depths of 500 to 3200 m as part of the nautinil expedition in 2003 the sediments of cold seeps on the nile deep sea fan ndsf were sampled for the first time for biogeochemical and microbiological analyses here we compare rates of the anaerobic oxidation of methane aom and sulfate reduction sr as well as the microbial community structure of a variety of cold seep systems including mud volcanoes pockmarks and brine seeps our results revealed strong differences in microbial activity among the different seep systems of the eastern central and western provinces of the ndsf as well as the olimpi field central mediterranean ridge integrated over a sediment depth of 10 cm below the seafloor sr rates ranged from 0 1 66 mmol m 2 d 1 and aom rates from 0 1 3 6 mmol m 2 d 1 sr was often considerably higher than methane oxidation indicating that electron donors other than methane were utilized in general the lowest rates were associated with pockmarks and carbonate pavements and highest rates with bacterial mats above the gassy sediments of mud volcano centers 16s rrna gene analysis and fluorescence in situ hybridization fish revealed the presence of all known groups of marine methane oxidizing archaea i e anme 1 2 3 and also of methane oxidizing bacteria i e methylobacter sp and relatives in some seep sediments presumably syntrophic sulfate reducing bacterial partners of anmes were also detected in association with the anmes several anmes formed consortia with unknown bacterial partners the microbial community structure reflected the presence of typical seep microorganisms at all sites investigated but differed to varying extents between the different types of seeps despite the high availability of methane and sulfate methanotrophic microbial activity and biomass were lower at the seeps of the eastern mediterranean compared to those of other continental margins for unknown reasons

last glacial emplacement of methane derived authigenic carbonates in the sea of japan constrained by diatom assemblage carbon 14 and carbonate content abstract we studied diatom assemblages and caco 3 contents of methane derived authigenic carbonates from the eastern margin of the sea of japan and assessed the formation time of these samples radioactive 14 c date was determined in selected samples to obtain the maximum age of the time the results of our study suggest mass formation of carbonate nodules in a glacial period within 40 ky consistent with a published u th dating result of carbonate nodules in the study area diatom assemblages and contents in the carbonate nodules abundance of 10 6 g dominance of neritic littoral species warm cold water species ratio lower than 25 differ from the near seafloor sediments in the study area which have characteristics of holocene sediments in the sea of japan and suggest cementation of glacial sediments laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi enclosed ocean similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules glacial sediments with oceanic cold water species as low as holocene sediments restricts the sediment age to before 20 cal ky bp carbonate contents higher than 78 wt suggest the cementation of poorly compacted sediments near the seafloor and the date of carbonate cementation is therefore close to that of the cemented sediments most carbonate nodule samples in this study were formed in a glacial period and detection of 14 c restricts this period to within 40 ky

the chimney forest of the deep montenegrin margin south eastern adriatic sea a spectacular field of columnar carbonates has been discovered on the montenegrin margin in the southern adriatic sea at a depth of about 450 m the site exposes many columnar carbonates protruding from the substrate or abated on the bottom such carbonates attain maximum visible lengths of ca 60 cm with diameters up to 20 cm display an annular growth and are either hollow or plugged by indurated sediment petrographic and geochemical analyses document the pervasive presence of dolomite and 13c values as low as 30 vpdb these chimneys are therefore interpreted as former conduits related to hydrocarbon expulsion in this sector of the adriatic basin however available data suggest that hydrocarbon flows at this site have ceased our results show that chimneys formed inside the local depositional units glacial pleistocene shelf shelly rich muddy sediment and were successively exhumed from the host sediment today the chimneys offer substrate to benthic life including cold water corals and sponges the u series dating of these carbonate concretions is complicated by the presence of a significant fraction of detrital sediment which represents a major source of initial 230th ams 14c and 87sr 86sr dating of shells embedded in one of the chimney provided ages beyond the range of radiocarbon dating and 600 kyrs indicating a pleistocene age of the host sediment uncorrected u series dating of the carbonate chimneys yielded and age of ca 250 270 kyrs providing a temporal upper limit for conduit formation driven by lithification caused by the degradation of seeping hydrocarbons in addition u th dating of cold water coral bases settled on chimneys indicates a holocene age for their first exposure after exhumation and subsequent function as hard substrate for benthic organisms the montenegrin chimney forest is a rare case where many such carbonate columnar concretions are still in their original vertical position

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

u th dating and post depositional alteration of a cold seep carbonate chimney from the campos basin offshore brazil abstract dating authigenic cold seep carbonates allows determining the timing of active seepage of hydrocarbon rich fluids at continental margins and ultimately the detection of the geological factors affecting it u th dating has been selected in this study the method having been successfully used before however incorporation of initial thorium in substantial amounts of detrital material due to the precipitation of carbonates within the seabed and post depositional alteration potentially pose a major problem violating the basic assumptions of the method here we report results from several samples from the campos basin off the coast of brazil they are unusual in their high 13 c values mean of 10 0 vpdb high detrital contents and being dominantly dolomite elevated 230 th 238 u activity ratios indicate that most of the carbonates lost uranium during diagenesis isochrones are obtained from the unaffected samples yielding an age of 140 4 3 1 ka vertical growth of the chimney must have been short and rapid since results from the top and bottom parts of the chimney concur within analytical uncertainties furthermore profiles of u th radioisotope specific activity 234 u and 232 th specific activity on two quarter slices of a carbonate chimney reveal the occurrence of three distinct diagenetic processes u loss u exchange with seawater and th gain

mud volcanoes and gas hydrates in the anaximander mountains eastern mediterranean sea abstract detailed multibeam sedimentological and geophysical surveys provide ample new data to confirm that the anaximander mountains eastern mediterranean are an important area for active mud volcanism and gas hydrate formation more than 3000 km of multibeam track length was acquired during two recent missions and 80 gravity and box cores were recovered morphology and backscatter data of the study area have better resolution than previous surveys and very detailed morphology maps have been made of the known targeted mud volcanoes amsterdam kazan and kula especially the amsterdam crater and the related mud breccia flows gas hydrates collected repeatedly from a large area of amsterdam mud volcano at a sub bottom depth of around 0 3 1 5 m resemble compacted snow and have a rather flaky form new gas hydrate sites were found at amsterdam mud volcano including the mud flow sloping off to the south gas hydrates sampled for the first time at kazan mud volcano are dispersed throughout the core samples deeper than 0 3 m and display a rice like appearance relative chronology and ams dating of interbedded pelagic sediments late holocene hemipelagic sapropel layer s1 and ash layers within the mud flows indicate that successive eruptions of kula mud volcano have a periodicity of about 5 10 kyrs new mud volcanoes identified on the basis of multibeam backscatter intensity were sampled documented as active and named athina and thessaloniki gas hydrates were sampled also in thessaloniki mud volcano the shallowest 1264 m among all the active mediterranean sites at the boundary of the gas hydrate stability zone biostratigraphical analyses of mud breccia clasts indicated that the source of the subsurface sedimentary sequences consists of late cretaceous limestones paleocene siliciclastic rocks eocene biogenic limestones and miocene mudstones rough estimations of the total capacity of the anaximander mud volcanoes in methane gas are 2 56 6 40 km3

biomarker indicators for anaerobic oxidizers of methane in brackish marine sediments with diffusive methane fluxes the anaerobic oxidation of methane aom is a major methane sink in marine sediments and plays a crucial role in mitigating methane fluxes to the overlying water column we investigated biomarker distributions and compound specific isotopic signatures in sediments from sites on the northern european continental margin that are characterized by a diffusive flux of methane at all sites the organic matter om is predominantly derived from terrestrial higher plants with subordinate abundances of algal biomarkers but biomarkers for archaea and bacteria are also present the co occurrence of the archaeal lipids archaeol sn 2 hydroxyarchaeol and 2 6 10 15 19 pentamethylicosane pmi with non isoprenoidal glycerol diethers inferred to derive from sulfate reducing bacteria srb is similar to microbial biomarker assemblages observed at cold seeps the archaeal and inferred srb biomarker concentrations typically reach maxima close to the sulfate methane transition zone smtz where archaeal biomarkers are depleted in 13c the 16s rrna gene sequences from the smtz of the aarhus bay sediment core indicate the occurrence of anme 1 archaea consistent with inferences derived from biomarker distributions the observations suggest that aom in these diffusive settings is mediated by consortia of archaea and bacteria similar to those found at many seep and methane hydrate sites around the world

preliminary video spatial analysis of cold seep bivalve beds at the base of the continental slope of israel palmahim disturbance abstract seafloor video surveys were carried out with the rov max rover in the palmahim disturbance pd area offshore israel in september 2016 during the eurofleets2 semseep cruise on board the r v aegaeo preliminary observations of distribution and frequencies of bivalve accumulations show that they are mostly composed by lucinoma kazani shells valves are distributed mainly along the base of authigenic carbonate crusts in association with bacterial mats and inside inactive chimney like structures sometimes associated with crabs and living tubeworms however no living molluscs were observed the relation between distribution of bivalve beds and seepage activity is not straightforward in the pd area however the presence of these accumulations and the size of l kazani suggest that seepages may have lasted for at least one decade before its reduction cessation that induced l kazani mortality the presence of few articulated valves of this species indicates that they were alive up to one year before the rov observations and their different preservation state may imply different seepage phases this research shows that chemosymbiotic benthic communities may be used as a proxy for better understanding the past dynamics of fluid emissions at the seafloor however further quantitative studies are needed to confirm these observations

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

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

taphonomic degradation of molluscan remains during thirteen years on the continental shelf and slope of the northwestern gulf of mexico abstract in 1993 sseti shelf and slope experimental taphonomy initiative deployed shells of a suite of molluscan species in a variety of environments of preservation eops covering a range of depths and sediment types on the gulf of mexico continental shelf and upper slope with the goal of measuring taphonomic rates over an extended period of time sseti retrieved shells from these eops after 2 8 and 13 years the degree of shell degradation was significantly influenced by species elapsed time since deployment and eop a suite of physical taphonomic processes such as dissolution abrasion discoloration and edge alteration increased in severity over the 13 years fragmentation occurred in some species dissolution proceeded apace however the incidence of chalkiness declined from high levels observed after a few years while the more extreme levels of dissolution such as the development of a soft or deeply dissolved surface rose significantly in frequency the incidence of original color declined while fading of original color increased brown to red and green discoloration rose rapidly in the first eight years and then declined leaving a faded shell surface between habitat differences in degradation rate were significant for most taphonomic attributes between species differences were minor in comparison thus taphofacies the product of the independent actions of a suite of taphonomic processes originate from and provide information on environmental conditions species composition has a lesser inherent influence on the outcome not uncommonly the rates of change in shell condition differed significantly between eops although the direction of change was coincident this was particularly true of the summary indices such as maximum discoloration or the average degree of dissolution the taphonomic process is nonlinear in time nonlinearity is eop dependent becoming a defining attribute leading to disparate taphofacies types some taphonomic processes cannot proceed expeditiously without prior alteration of the shell through other taphonomic means some taphonomic conditions such as chalkiness can be intermediate states the presumption that similar taphonomic characteristics between eops indicate similar environmental processes operating at similar rates is falsified by sseti sites in which similar taphonomic indices at year 13 accrued from different time varying degradational rates during the preceding years

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

lipid biomarkers preserved in hydrate associated authigenic carbonate rocks of the gulf of mexico anaerobic oxidation of methane aom is common in ocean margin sediments where it is mediated by consortia of archaea and bacteria and can result in the formation of authigenic carbonate including extensive carbonate crusts previous work indicates that aom is associated with gulf of mexico hydrocarbon seeps and is mediated by similar organisms as identified in other settings however biological investigations have not been done on the associated 13c depleted carbonates here we show that 13c depleted archaeal and bacterial biomarkers are abundant in gulf of mexico authigenic carbonate rocks revealing that aom mediating organisms are closely associated with carbonate authigenesis moreover the rocks share general characteristics of the background soft sedimentary archaeal and bacterial community inferred from biomarker analysis suggesting that the organisms associated with carbonate authigenesis are the same as those that live elsewhere in the hydrocarbon seep environment this provides further evidence that aom by archaea and sulfate reducing bacteria can result in the sequestration of significant quantities of methane derived carbon in carbonate rocks

trace element systematics in cold seep carbonates and associated lipid compounds abstract seeping of methane rich fluids at submarine cold seeps drives intense microbial activity and precipitation of authigenic carbonates some trace elements play an important role in the biogeochemical processes operating at cold seeps especially as specific enzymatic co factors related to methanogenesis and the anaerobic oxidation of methane aom however it is unclear whether microbial trace metal utilization can be traced by the geochemical composition of seep carbonates in this study we analyzed a series of authigenic carbonate samples recovered from various seep settings worldwide and report for the first time trace element concentrations for total lipid fractions combined with biomarker analyses and determination of elemental abundances in associated inorganic mineral phases carbonate phases sulfides organic compounds and detrital fractions our results indicate marked enrichments of co ni cu mo and w in the archaeal and bacterial lipids associated with authigenic carbonates which can all be ascribed to previously identified enzymatic pathways in addition to the microbial communities involved in aom which most likely control specific lipid bound enrichments of co ni mo and w in seep carbonates cu was found to display higher concentrations in the lipid fractions extracted from a few authigenic carbonate samples formed closer to the sediment water interface hence possibly related to the presence of aerobic methane oxidizing bacterial assemblages in the near seafloor environment while the above mentioned trace metals are relatively enriched in all studied inorganic and organic fractions the very low w concentrations measured in carbonate phases combined with their pronounced enrichment in associated lipid fractions and inferred microbial requirement suggest that tungsten depletion in pore waters could possibly act as a limiting factor on aom at cold seeps finally two other trace elements li and ti also displayed particular enrichments in studied lipid fractions which despite no reported evidence could possibly indicate that they are also involved as metalloenzymes in microbial methane oxidation processes at cold seeps

lipid biomarker patterns reflect different formation environments of mussel and tubeworm dominated seep carbonates from the gulf of mexico atwater valley and green canyon abstract mussels and tubeworms thriving at many methane seeps typically live in symbiosis with chemosynthetic chiefly methanotrophic or thiotrophic bacteria it has been shown that the activities of chemosymbiotic animals can result in large differences in the sedimentary environments of their habitats here we put forward the concept that such environmental variability can be archived in the lipid biomarker inventories of authigenic carbonates forming in different locally confined environments at seeps mussel beds and tubeworm bushes in this case to test this hypothesis lipid biomarker patterns of carbonates from mussel and tubeworm environments from two seep sites atwater valley 340 and green canyon 852 of the gulf of mexico were analyzed previous work revealed stronger carbon isotope fractionation between the methane source and biomarkers of anaerobic methane oxidizing archaea 2 anme 2 sulfate reducing desulfosarcina desulfococcus dss consortia than for anme 1 dss consortia both performing anaerobic oxidation of methane aom similar 13cmethane values were found at the mussel and tubeworm sites from the same seeps and the local microbial consortia also appear to be largely similar based on the observed aom biomarker inventories yet a large average offset of 32 between the 13c values of molecular fossils of sulfate reducing bacteria srb involved in aom was observed with lower values typifying tubeworm carbonates than mussel carbonates this pattern is interpreted to reflect local effects on isotope fractionation caused by the chemosymbiotic metazoans at mussel and tubeworm dominated sites at tubeworm dominated sites the excess sulfate produced by thiotrophic symbionts of tubeworms and pumped down into the sediment results in persistent production of aom derived bicarbonate and the enrichment of 12c in sub surface sediments interestingly tubeworm carbonates also contain high amounts of non isoprenoidal dialkyl glycerol diethers dages with extreme 13c depletions representing compounds that derived from non dss cluster srb most likely 13c depleted aom derived organic intermediates were used as carbon sources by the dage producing non dss cluster srb possibly performing organoclastic sulfate reduction our study identifies significant variation in biomarker patterns between mussel and tubeworm carbonates at two seep sites in the gulf of mexico such variation allows to characterize different habitats at seeps which are shaped by the interaction of chemosymbiotic seep metazoans and their symbionts with the local environment metazoan community composition apparently controls geobiological interaction in seep ecosystems to a large degree which may allow tracing of the effects of chemosymbiosis into the rock record

trace element behaviour at cold seeps and the potential export of dissolved iron to the ocean seawater samples were collected by submersible above methane seeps in the gulf of guinea regab and baboon pockmarks in order to investigate the behaviour of iron fe manganese mn and rare earth elements ree during fluid seepage our aim was to determine whether cold seeps may represent potential sources of dissolved chemical species to the ocean dissolved 0 45 m filtered samples and total dissolvable unfiltered samples concentrations were determined over 50 m long vertical transects above the seafloor and at various discrete locations within the pockmarks we show that substantial amounts of fe and mn are released into seawater during seepage of methane rich fluids mn is exported almost quantitatively in the dissolved form more than 90 of total mn mean mndiss 12 11 nmol kg 12 11 nmol kg although a significant fraction of fe is bound to particulate phases the dissolved iron pool still accounts on average for approximately 20 percent of total iron flux at vent sites mean fediss 22 11 nmol kg 22 11 nmol kg this dissolved fe fraction also appears to remain stable in the water column in contrast there was no evidence for any significant benthic fluxes of pore water ree associated with fluid seepage at the studied sites overall our results point towards distinct trace element behaviour during fluid seepage with potential implications for the marine geochemical budget the absence of any dissolved ree enrichments in bottom waters clearly indicates effective removal in sub surface sediments most likely precipitation of authigenic mineral phases at cold seeps i e carbonates represents a net sink for these elements while mn appears to behave near conservatively during fluid seepage the observed relative stability of dissolved fe in the water column above seepage sites could be explained by complexation with strong organic ligands and or the presence of fe bearing sulfide nanoparticles as reported previously for submarine hydrothermal systems considering the ubiquitous occurrence of methane vents at ocean margins cold seeps could represent a previously unsuspected source of dissolved fe to the deep ocean

characterizing lipid biomarkers in methanotrophic communities of gas hydrate bearing sediments in the sea of okhotsk abstract we studied specific lipid biomarkers of archaea and bacteria that are associated with the anaerobic oxidation of methane aom in a cold seep environment as well as the origin of sedimentary organic matter on the continental slope off ne sakhalin in the sea of okhotsk the organic geochemical parameters demonstrated that most of the sedimentary organic matter containing hydrate layers could be derived from marine phytoplankton and bacteria except for a station lv39 29h which was remarkably affected by terrestrial vascular plant specific methanotrophic archaea biomarkers was vertically detected in hydrate bearing cores lv39 40h coinciding with the negative excursion of the 13corg at core depths of 90 100 cm below the seafloor these results suggest that methane provided from gas hydrates are already available substrates for microbes thriving in this sediment depth in addition the stable isotope mass balance method revealed that approximately 2 77 3 41 of the total organic carbon or 0 036 0 044 dry weight sediment was generated by the activity of the aom consortium in the corresponding depth of core lv39 40h on the other hand the heavier 13c values of archaeol in the gas hydrate stability zone may allow ongoing methanogenesis in deeper sediment depth

archaeal and bacterial lipids in authigenic carbonate crusts from eastern mediterranean mud volcanoes abstract we investigated the distributions and 13 c values of lipid biomarkers in authigenic methane related carbonate crusts formed on eastern mediterranean mud volcanoes a highly diverse suite of microbial membrane lipids was detected strongly 13 c depleted lipids diagnostic for archaea include isoprenoid glycerol diethers isoprenoid glycerol dialkyl glycerol tetraethers and several c 20 c 35 isoprenoid hydrocarbons bacterial lipids mainly consist of dialkyl glycerol diethers branched fatty acids and hopanoids showing important 13 c depletions albeit less than archaeal lipids the data provide further evidence for the involvement of archaea and bacteria in the anaerobic oxidation of methane aom and in the sequestration of methane derived carbon in authigenic carbonate crusts varying distributions and isotopic compositions of 13 c depleted lipids argue for heterogeneous aom related microbial consortia expanding on existing work at cold seeps distinctive biomarker features and inferred microbial assemblages are observed in these crusts in agreement with available phylogenetic data for the samples our results support the potential of lipids for distinguishing methanotrophic communities despite the observed variances conservative features in the abundances and isotopic offsets of microbial biomarkers occur likely reflecting the overall relationships between archaea and bacteria and the nature of carbon flow between them

carbonate formation by anaerobic oxidation of methane evidence from lipid biomarker and fossil 16s rdna carbonate chimneys and other carbonate structures occur widespread in the gulf of cadiz and probably reflect the presence of cold seeps and associated release of methane in the geological past possibly in the early pleistocene but it is unclear under what conditions and by which processes these carbonates were formed we studied a fossil methane related carbonate crust collected from the kidd mud volcano in the gulf concentrations of microbial lipids their stable carbon isotope composition sequences of fossil 16s rrna genes of anaerobic methanotrophic archaea in combination with mineralogical and carbon and oxygen isotopic composition of carbonate were obtained for seven different horizons of the crust this combination of organic and inorganic geochemical techniques with molecular ecological methods gave a consistent view on processes resulting in the formation of the crust and indicated that it took place in two phases and in a downward direction archaeal lipid biomarkers and fossil 16s rrna gene sequence data revealed the dominance of archaeal anme 2 group and elevated methane partial pressures during the formation of the top part of the crust the lower part of the carbonate was likely formed in an environment with reduced methane fluxes as revealed by the dominance of fossil remains of anme 1 archaea the combination of these methods can be used as an effective tool to reconstruct in unprecedented detail the palaeo biogeochemical processes resulting in the formation of carbonate fabrics this interdisciplinary strategy may also be applied for other fossil methane derived carbonates generating new concepts and knowledge about past methane related carbonate systems

cold seep deposits of beauvoisin oxfordian southeastern france and marmorito miocene northern italy microbially induced authigenic carbonates the relation of two well known ancient carbonate deposits to hydrocarbon seepage was confirmed by this study archaea are found to be associated with the formation of oxfordian seep carbonates from beauvoisin and with a miocene limestone from marmorito tube worm limestone carbonates formed due to a mediation by archaea exhibit extremely positive or extremely negative 13ccarbonate values respectively highly positive values 15 reflect the use of 13c enriched co2 produced by methanogenesis low 13c values of the marmorito carbonates 30 indicate the oxidation of seepage derived hydrocarbons likewise the 13c content of specific tail to tail linked isoprenoids biomarkers for archaea was found to be strikingly depleted in these samples as low as 115 the isotopic signatures corroborate that archaea were involved in the cycling of seepage derived organic carbon at the ancient localities another miocene limestone marmorito limestone shows a strong imprint of methanotrophic bacteria as indicated by 13c values of carbonate as low as 40 and biomarker evidence epifluorescence microscopy and field emission scanning electron microscopy revealed that bacterial biofilms were involved in carbonate aggregation in addition to lucinid bivalves previously reported from both localities we infer that sponges from beauvoisin and tube worms from marmorito depended on chemosynthesis as well low 13c values of nodules related to sponge taphonomy 27 indicate that sponges might have been linked to an enhanced hydrocarbon oxidation tube worm fossils from marmorito closely resemble chemosynthetic pogonophoran tube worms from recent cold seeps and are embedded in isotopically light carbonate 13c 30

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

distributions and carbon isotopic compositions of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abstract we investigated the distributions and 13c values of lipid biomarkers in authigenic carbonate crusts from the nordic margin norwegian sea abundant highly 13c depleted archaeal and bacterial biomarkers revealed that anaerobic oxidation of methane aom is associated with carbonate authigenesis at the hakon mosby mud volcano hmmv and the nyegga pockmark field no conclusive evidence for aom was found in the crust sample from the storegga slide anme 2 methanotrophic archaea and sulfate reducing bacteria from the desulfosarcina desulfococcus cluster were inferred from lipid fingerprints distinct patterns of 13c depleted non isoprenoid dialkyl glycerol diethers dages are possibly associated with unknown microbial partners in the aom

structural controls on seepage of thermogenic and microbial methane since the last glacial maximum in the harstad basin southwest barents sea the harstad basin is a structural block on the continental shelf of sw barents sea where gas hydrates likely occurred below the grounded ice sheet during the last glaciation and it hosts active gas seepage at numerous seafloor sites we present an integrated study of fluid flow systems in the harstad basin by combining seismic profile interpretations and gas flare mapping data with the geochemical results obtained on seafloor seeping gas and methane derived carbonate crusts more than 190 acoustic gas flares were registered in water column many of them in association with pockmarks and carbonate crust fields however weak or absent seepage observed during remotely operated underwater vehicle transects across many pockmarks and crust fields suggests that seepage activity may have decreased since the last deglaciation in the western harstad basin seeps of microbial methane occur mainly above tertiary formations that are pinching out below the glacial sediments high amplitude seismic anomalies suggest the presence of gas pockets at the base of the glacial sediments and within tertiary deposits in contrast gas seeping in the eastern harstad basin originates from a biodegraded thermogenic source tentatively connected to the deeply faulted mesozoic rocks occurring below glacial sediments this spatial variability in fluid sources is also recorded in the carbon isotope data of seafloor carbonate crusts with 13 c values typically between 55 and 42 and 40 and 20 vpdb for carbonate crusts associated with microbial and thermogenic fluids respectively u th chronology combined with the stable isotope data suggests that this discrepancy in fluid sources over a distance of about 20 km has been stable since the last glaciation and highlights the significance of regional underlying geology in mediating fluid supply to the seafloor

increased fluid flow activity in shallow sediments at the 3 km long hugin fracture in the central north sea the north sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species such as methane from the earth s interior to its exterior here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered 3 km long hugin fracture in the central north sea although venting of gas bubbles was not observed concentrations of dissolved methane were significantly elevated up to six times background values in the water column at various locations above the fracture and microbial mats that form in the presence of methane were observed at the seafloor seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane sediment porewaters recovered in close proximity to the hugin fracture indicate the presence of fluids from two different shallow 500m sources i a reduced fluid characterized by elevated methane concentrations and or high levels of dissolved sulfide up to 6 mmol l 1 and ii a low chlorinity fluid cl 305 mmol l 1 that has low levels of dissolved methane and or sulfide the area of the seafloor affected by the presence of methane enriched fluids is similar to the footprint of seepage from other morphological features in the north sea

fluid source and methane related diagenetic processes recorded in cold seep carbonates from the alvheim channel central north sea integrated petrography mineralogy geochronology and geochemistry of cold seep carbonate crusts and free gas from the alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central north sea free gas isotope characteristics coupled with carbonate 13c values as low as 66 vpdb indicate a predominantly microbial methane source with minor thermogenic contribution we estimate that 70 of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane the early stage of crust growth is represented by microcrystalline aragonite and mg calcite 10 to 40 mol mgco3 cementing seafloor sediments consisting of clays quartz feldspar and minor detrital low mg calcite and dolomite typical association of aragonite cement with coarse grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction the later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts in contrast to early generation cements late generation cavity infills have rare earth elements and y patterns with small negative ce anomalies similar to seawater consistent with carbonate precipitation in a more open seawater dominated system aragonite u th ages indicate carbonate precipitation between 6 09 and 3 46 kyr bp in the northern part of the channel whereas in the southern part precipitation occurred between 1 94 and 0 81 kyr bp reflecting regional changes in fluid conduit position

u th chronology and formation controls of methane derived authigenic carbonates from the hola trough seep area northern norway abstract we investigated methane derived authigenic carbonate mdac crusts and nodules from a cold seep site on the northern norwegian continental shelf in ca 220 m water depth to determine the timing and mode of their formation gas bubbling observed during remotely operated vehicle rov assisted sampling of mdac crusts revealed ongoing seep activity authigenic carbonates were present as crusts on the seafloor and as centimetre size carbonate cemented nodules at several intervals within an adjacent sediment core aragonite dominated mineralogy of the mdac crusts suggests formation close to the seafloor at higher rates of sulphate dependent anaerobic oxidation of methane aom in contrast dolomite cemented nodules are consistent with the formation at the sulphate methane transition zone deeper within the sediment at lower rates of aom the 13c carbonate values of bulk rock and of micro drilled aragonite samples vary between 22 2 and 34 6 vpdb we interpret the carbon in aragonite to be mainly derived from the anaerobic oxidation of thermogenic methane with a minor contribution from seawater dissolved inorganic carbon dic aom activity is supported by high concentrations of aom related biomarkers of archaea archaeol and 2 sn hydroxyarchaeol and sulphate reducing bacteria iso and anteiso c15 0 fatty acids in the crusts the dolomite nodules exhibit higher 13c carbonate values 12 vpdb suggesting a smaller amount of methane derived carbon presumably due to the contribution of dic migrating from depth and lower aom rates the latter is supported by orders of magnitude lower concentrations of archaeol and sn 2 hydroxyarchaeol in the sediment interval containing the largest dolomite nodules 18o values of pure aragonite samples and dolomite nodules indicate the precipitation of carbonate close to isotopic equilibrium with seawater and no influence of gas hydrate derived water u th dating of two mdac crusts shows that they formed between 1 61 0 02 and 4 39 1 63 ka bp and between 2 65 0 02 and 4 32 0 08 ka bp we infer both a spatial and temporal change in methane flux and related mdac formation at this seep site these changes might be caused by regional seismic events that can affect pore pressure or re activation of migration pathways thus facilitating fluid flow from deep sources towards the seabed

molecular and isotopic analysis of anaerobic methane oxidizing communities in marine sediments convergent lines of molecular carbon isotopic and phylogenetic evidence have previously indicated hinrichs k u hayes j m sylva s p brewer p g delong e f 1999 methane consuming archaebacteria in marine sediments nature 398 802 805 that archaea are involved in the anaerobic oxidation of methane in sediments from the eel river basin offshore northern california now further studies of those same sediments and of sediments from a methane seep in the santa barbara basin have confirmed and extended those results mass spectrometric and chromatographic analyses of an authentic standard of sn 2 hydroxyarchaeol hydroxylated at c 3 in the sn 2 phytanyl moiety have confirmed our previous tentative identification of this compound but shown that the previously examined product was the mono tms rather than di tms derivative further analyses of 13 c depleted lipids appreciably more abundant in samples from the santa barbara basin have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in 13 c these are additional glycerol ethers and fatty acids the alkyl substituents in the ethers mostly monoethers with some diethers are non isoprenoidal the carbon number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar suggesting strongly that they are produced by the same organisms their structures n alkyl and methyl branched n alkyl require a bacterial rather than archaeal source the non isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic sulfate and nitrate reducing organisms which lie near the base of the rrna based phylogenetic tree based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate it appears likely that the non archaeal 13 c depleted lipids are products of one or more previously unknown sulfate reducing bacteria which grow syntrophically with the methane utilizing archaea their products account for 50 of the fatty acids in the sample from the santa barbara basin at all methane seep sites examined the preservation of aquatic products is apparently enhanced because the methane oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column

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

cold seep driven carbonate deposits at the central american forearc contrasting evolution and timing in escarpment and mound settings continuous surface cores of cold seep carbonates were recovered offshore pacific nicaragua and costa rica from 800 to 1 500 m water depths meteor 66 3 in order to decipher their evolution and methane enriched fluid emanation in contrasting geological settings cores from the mounds iguana perezoso baula v and from the jaco scarp escarpment were used for a multi method approach for both settings aragonite was revealed as dominant authigenic carbonate phase in vein fillings and matrix cementation followed by mg calcite as second most abundant this common precipitation process of caco3 polymorphs could be ascribed as indirectly driven by chemical changes of the advecting pore water due to anaerobic oxidation of methane a more direct influence of seep related microbial activity on the authigenic mineral assemblage in both settings is probably reflected by the observed minor amounts of dolomite and a dolomite like camg carbonate mgco3 42 13c data of jaco scarp samples are significantly lower 43 to 56 pdb than for mound samples 22 to 36 pdb indicating differences in fluid composition and origin noteworthy 18o values of scarp samples correlate most closely with the ocean signature at their time of formation documenting the archive potential a high resolution case study of a mound core implies at least 40 changes in fluid supply within a time interval of approximately 14 ky as most striking difference the age data indicate a late stage downward progressing cementation front for all three mound cap structures approx 2 5 cm ky but a significantly faster upward carbonate buildup in the bulging sediments on top of the scarp environment approx 120 cm ky the latter data set leads to the hypothesis of chemoherm carbonate emplacement in accord with reported sedimentation rates until decompression of the advective fluid system probably caused by the jaco scarp landslide and dating this to approximately 13 000 years ago