withdrawn petrographic and origin of authigenic carbonate minerals and the associated fluid evolution in the lacustrine carbonate siliciclastic mudrocks a case from the low cretaceous of the erennaoer sag erlian basin ne china

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

using iron speciation in authigenic carbonates from hydrocarbon seeps to trace variable redox conditions abstract seepage of hydrocarbon rich fluids out of the marine sedimentary column is characterized by temporal changes of flow intensity and resultant spatially variable redox conditions authigenic carbonates at marine hydrocarbon seeps provide excellent geological and geochemical archives that serve to explore seepage dynamics over time in this study we investigated the potential of mossbuaer spectroscopy and fe contents of seep related authigenic carbonates from the congo fan the gulf of mexico and the black sea for reconstructing past redox conditions and fluid seepage activity at cold seeps the fe speciation observed by mossbauer spectroscopy and fe contents suggest that 1 the congo fan carbonates precipitated in a sulfidic environment 2 the formation conditions of seep carbonates were variable at the gulf of mexico seep site ranging from oxic to suboxic and anoxic and even spanning into the methanogenic zone and 3 the stratified water column of the black sea or suboxic condition resulted in low fe contents of black sea carbonates the study reveals that fe speciation can provide constraints on the wide range of redox conditions that imprinted seep carbonates during the life span of seepage similarly mossbauer spectroscopy particularly when used in combination with the analysis of redox sensitive elements is a promising tool to trace variable redox conditions in marine paleoenvironments other than seeps

fabric and formation of grapestone concretions within an unusual ancient methane seep system eocene bulgaria terra nova 23 56 61 2011 abstract authigenic carbonates at methane seeps provide valuable information on the evolution of seepage dynamics in this study we report on an unusual type of 13c depleted 13c 44 8 to 8 3 v pdb vienna peedee belemnite calcite cemented grapestone concretion composed of small spheroidal nodules 0 1 15 cm across associated with an ancient seep setting in eocene marine sediments pobiti kamani area ne bulgaria field observations suggest that the nodules started to grow close to the ancient sea floor and apparently were agitated by fluid flow promoting their spheroidal shape the precipitation of calcite between sand grains started at multiple closely spaced nucleation sites induced by locally elevated calcite supersaturation in response to anaerobic microbial consumption of ascending methane consecutive nodule growth continued deeper in the sediment with the formation of dark and light concentric bands surrounding one or more nodule cores the occurrence of similar grapestone concretions at seeps might indicate changing redox conditions at the seep site

stable isotopes and rare earth element compositions of ancient cold seep carbonates from enza river northern apennines italy implications for fluids sources and carbonate chimney growth abstract cold seep carbonates are remarkable fossil records of hydrocarbon seepage and related conduits in the present research we analysed the carbon and oxygen isotopes rare earth element ree and trace element content of carbonate chimneys and concretions in the pleistocene argille azzurre formation northern apennines italy strong 13 c depletions values as low as 40 3 observed in both carbonate concretions and chimneys indicate that anaerobic oxidation of biogenic methane played a major role in the formation of these carbonates slightly higher 13 c values mostly found in the outer layers of the carbonate chimneys reflect a contribution of inorganic carbon from seawater ree patterns reveal the carbonates formed under mostly anoxic pore water conditions combined ree and trace element data reveal the growth of chimneys occurred from the outside in with the outer chimney walls experiencing rapid growth excellent correlations between ce ce ree contents and la n sm n and y ho ratios observed in the chimney walls provide additional evidence for the influence of seawater in the formation of the chimneys meanwhile o isotopic compositions of the samples suggest an 18 o depleted fluid was involved in carbonate precipitation this study has major implications for tracking fluid sources of seep carbonates and patterns of carbonate chimney growth

controls on rare earth element distributions in ancient organic rich sedimentary sequences role of post depositional diagenesis of phosphorus phases abstract the processes that dictate the formation and preservation of rare earth element ree signatures in ancient marine black shales are incompletely understood thus potentially limiting the utility of the rees as geochemical tracers here we report on whole rock ree analyses of six black shale formations from different ages and depositional settings which fall within three general groupings group 1 is characterized by low whole rock ree content ree n la n n la n n la n 2 yb n la n 250 g g and moderately middle ree enriched patterns gd n la n 1 5 2 5 yb n la n 1 representative samples from these groups were selected from the marcellus and hushpuckney shales and subjected to a multi step leaching procedure to isolate four extractable p phases reducible authigenic carbonate associated detrital apatite organic in group 1 samples with low carbonate content 3 rees were hosted mainly in the organic 50 of ree and siliciclastic fractions 37 whereas in samples with greater carbonate content 25 caco 3 rees were hosted mainly in carbonate associated phases 53 in group 2 rees were hosted mainly in the carbonate associated 64 and organic fractions 30 and in group 3 rees were hosted mainly in the carbonate associated 60 detrital apatite 23 and siliciclastic fractions 16 authigenic phases include minerals such as carbonate fluorapatite and authigenic calcite that if present tend to dominate the whole rock ree inventory in the absence of carbonate whole rock ree content depends on the relative ree contributions of the organic and siliciclastic fractions

the effects of diagenetic processes and fluid migration on rare earth element and organic matter distribution in seep related sediments a case study from the south china sea abstract methane seepage is an important factor governing microbial activity in marine sediments although its impact on the distribution of rare earth elements rees and organic matter in sediments is unclear here we report isotope signatures of organic 13ctoc and inorganic 13ctic carbon as well as total rees contents of core sediments collected from a well characterized seep area on the northern south china sea previous studies have identified sediments corresponding to three methane release events mres in the studied core mre i at 4 0 5 5 m mre ii at 7 4 8 2 m and mre iii at 10 0 11 5 m depth intervals increased methane flux and reducing bottom waters during mre i resulted in a higher accumulation of marine sourced organic matter as indicated by lower c n ratios and higher 13ctoc values compared with those of mres ii and iii sediments deposited during mre i have relatively low total ree contents which may be related to reduced ree adsorption on mn oxyhydroxides however the absence of ce anomaly at mre i is more likely due to the detrital input that obscures the original ce anomaly in the mre iii sediments a weak negative eu anomaly relative to that in the mre i and ii may be attributed to the reduction of eu3 to eu2 under strongly reducing conditions that caused by intense methane seepage these observations demonstrate that fluid flow may have an important effect on the distribution of both organic matter and rees in methane rich marine sediments

mud volcanoes at the front of the makran accretionary complex pakistan abstract conical mounds 1 1 5 km in diameter and up to 65 m high were mapped at the foot of the active makran continental margin the mounds developed seaward of the accretionary front in a relatively planar zone where the beginning of build up of tectonic pressure initiates deformation based on shallow high resolution 4 khz sediment echosounding the sedimentary sequence in this area is generally well stratified as indicated by closely spaced horizontal reflections however in the vicinity of the mounds the sediment is characterised by many acoustically transparent zones which are 100 300 m in diameter and cut near vertically through the horizontal reflectors two sediment cores from the top of the largest cone and a neighbouring acoustically transparent zone reveal small scale post depositional deformation in a stratified sequence and methane concentrations up to 40 000 ng g this deformation and disruption of potential reflectors provides a clue to explain the acoustic transparency we interpret it as caused by the rise of charged fluids and mud leading initially to the slight disturbance of the generally good acoustic reflectors and eventually to the formation of conical mud mounds mud volcanoes mcs data showing a buried mound in an analogous structural position support the idea of tectonically induced mud fluid expulsion seaward of the accretionary front

changing redox conditions at cold seeps as revealed by authigenic carbonates from alaminos canyon northern gulf of mexico anaerobic oxidation of methane in anoxic sediments at cold seeps often leads to formation of authigenic carbonates close to the seafloor along continental margins recent work however indicated that the redox conditions in sediments may vary to some degree during seepage activity in order to shed new light on the extent of this variability authigenic carbonates from alaminos canyon lease block 645 of the northern gulf of mexico have been characterized by means of inorganic and organic geochemistry the carbonates were collected from seep deposits representing various seafloor morphologies including extensive pavements mounds fractured carbonate slabs surrounded by dense bivalve shells and vestimentiferan tubeworm colonies the deposits almost entirely consist of aragonite the 18o values of aragonite vary from 2 6 to 5 8 v pdb suggesting precipitation in slight disequilibrium with the surrounding pore fluids the 13c values of aragonite between 33 9 and 20 4 v pdb agree with variable amounts of carbonate derived from oxidation of thermogenic methane and crude oil methane was primarily oxidized in an anaerobic process as revealed by the presence of 13c depleted molecular fossils of methane oxidizing archaea 13c values as negative as 118 and sulfate reducing bacteria 13c values as negative as 97 the syntrophic partners in the anaerobic oxidation of methane the observed inventories of molecular fossils in the authigenic carbonates mirror those of known consortia of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria namely the anme 2 desulfosarcina desulfococcus dss and anme 3 desulfobulbus dbb consortia in contrast the same carbonates exhibit shale normalized rare earth elements patterns that all display real negative ce anomalies ce ce 0 78 suggesting that at least temporarily oxic conditions prevailed the episodic occurrence of oxic conditions is confirmed by the presence of molecular fossils of aerobic methanotrophic bacteria including 4 methylcholesta 8 14 24 dien 3 ol and two bacteriohopanepolyols aminotetrol and aminotriol the 13c values of the biomarkers of aerobic methanotrophs are as negative as 58 and are consequently less 13c depleted than the molecular fossils of the prokaryotes performing anaerobic oxidation of methane a pattern in accord with culture experiments overall our results suggest that redox conditions at cold seeps are variable this variability probably reflects changes in seepage flux the combination of an inorganic and an organic geochemical approach used here is promising to better assess the variability and diversity of past fluid and gas expulsion at seeps

large scale sediment underplating in the makran accretionary prism southwest pakistan field relations in the emergent part of the makran accretionary prism show that a mid miocene to early pliocene slope and shelf sedimentary sequence was deposited directly on abyssal plain turbidites without any detectable stratigraphic or structural discordance sedimentological evidence for rapid shoaling however indicates that the underlying sediment column was tectonically thickened by a factor of between two and three during this period this can be explained by large scale underthrusting and underplating of sediment a mode of accretion that is also favored by mass balance considerations the visible deformation in the coastal makran occurred when the region was 70 100 km north of the contemporary prism front

seasonal to decadal modes of global sea level variability derived from merged altimeter data abstract motivated by the first availability of more than 16 years 1992 2009 of merged altimeter data from up to four concurrent satellite missions with topex poseidon ers 1 and 2 envisat jason 1 and geosat follow on the global sea level is reexamined with special emphasis on its distinctive scales of variability the global sea level variability is dominated by eleven statistically significant and geographically robust principal modes at seasonal to decadal timescales the identified modes can be divided into four regimes i e the seasonal regime with two principal components at 3 and 6 months the annual regime with a single 12 month component of global dominance the interannual regime with seven principal components at 1 55 1 74 1 94 2 34 3 07 4 20 and 5 40 years as well as the decadal regime with a 9 28 year subdecadal component the frequency dispersion of the identified modes is found to be at 0 level for the annual regime at 5 level for the seasonal and interannual regimes and at 10 level for the decadal regime in the space domain the locations of principal modes are found to be geographically correlated the seasonal regime is characterized by a small number of localized amplitude highs in regional seas the annual regime is associated with major western boundary currents of the gulf stream and kuroshio for the interannual regime mode active zones are observed in the western pacific warm pool wpwp el nino and western indian ocean regions among which the wpwp has a well defined two core structure and the northern core coincides with the most energetic zone of the decadal regime another interesting finding is that east west zonal and equatorial extratropical meridional teleconnections are evident for the major signals in a rather symmetric and systematic pattern joint spatiotemporal analysis reveals that multi modality at a given location and multi regionality for a given mode are fundamental features in global sea level variability

evolutions of water stable isotopes and the contributions of cryosphere to the alpine river on the tibetan plateau the significant changes of cryosphere on the tibetan plateau tp are an important cause of concern for the huge population in asia which depends on the glacier permafrost feed rivers up to now little is known about the response of runoff to the cryospheric changes under a warming climate taking an example of a typical alpine river hereafter named klr river in kunlun mountains pass on the tp to investigate the hydrological processes and quantify the potential recharge sources using stable isotopes and electrical conductivities the results showed significantly temporal variations in isotopes of precipitation and river water deviations in the precipitation isotopes indicated that precipitation in kunlun mountains pass during summer months mainly originated from local recycled moisture and slightly influenced by monsoon the klr river was separated into three hydrological components which include precipitation meltwater of glacier and meltwater of subsurface ground ice on average the meltwater of glacier accounted for 56 64 of total flow whereas the meltwater of subsurface ground ice contributed 37 44 and only 5 92 was supplied by precipitation evidently the contributions of glacier and thawing permafrost are up to as high as 94 the cryosphere played a crucial role on the hydrological cycle on the tp which would be important to understand the water resource distribution in permafrost regions on the tp under the global warming

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

rare earth elements in cold seep carbonates from the southwestern dongsha area northern south china sea the circulation of methane rich fluids at cold seeps often leads to the precipitation of seep carbonates close to the seafloor along continental margins which can be used as records of past fluid seepage rare earth element ree concentrations in seep carbonates have been used to trace fluid sources and provide information on associated biogeochemical processes at cold seeps the ree concentrations of a series of carbonates collected from cold seeps in the southwestern dongsha area of the northern south china sea are analyzed in this study the total ree contents sigma ree of the seep carbonates analyzed show a wide variation from 17 ppm to 523 ppm with an average sigma ree value of 54 ppm which are higher than the carbonates from other cold seep areas a positive correlation between fe mn content and sigma ree was observed these results suggest that the seep carbonates of this study were primarily controlled by the methane derived fluid from which they precipitated the fe rich dolomite and siderite which are the main components of the carbonates are responsible for the enrichment of the ree a slight positive ce anomaly observed in the shale normalized ree patterns of the studied seep carbonates suggests that they formed in anoxic conditions and the correlations between ce ce and la n sm n ce ce and dy n sm n ce ce and sigma ree further reveal that the ree characteristics of most seep carbonate samples preserve the original redox conditions in which they precipitated and late diagenesis has had little effect on the ree however the ree characteristics of sub samples ds2 2b ds1 6a and ds1 7a are very different from those of the other sub samples indicating a greater impact of late diagenesis and post oxidation favored ree enrichment c 2014 elsevier ltd all rights reserved

oxygenated conditions in the aftermath of the lomagundi jatuli event the carbon isotope and rare earth element signatures of the paleoproterozoic zaonega formation russia abstract the c 2 0 ga zaonega formation of the onega basin nw russia has been central in efforts to understand what led to the initial rise great oxidation event goe and postulated fall in free atmospheric oxygen and associated high amplitude carbon cycle excursions the lomagundi jatuli event lje and subsequent shunga event during paleoproterozoic time the formation accumulated shortly after the lje and encompasses both the recovery in the carbon cycle and hypothesised contraction of the oceanic oxidant pool however interpreting the correct environmental context recorded by geochemical signatures in the zaonega rocks is difficult due to a complex depositional and diagenetic history in order to robustly constrain that history we undertook a multiproxy study mineralogy petrography carbon isotope and rare earth element composition of carbonate beds in the upper part of the zaonega formation recovered in the 102 m composite section of the onzap drill cores our findings differentiate primary environmental signatures from secondary overprinting and show that i the best preserved carbonate beds define an upwards increasing 13ccarb trend from c 5 4 to near 0 and that ii large intra bed 13ccarb variations reflect varying contributions of methanotrophic dissolved inorganic carbon dic to the basinal dic pool rare earth element and yttrium reysn patterns confirm a marine origin of the carbonate beds whereas a consistent positive eusn anomaly suggests a strong high temperature hydrothermal input during accumulation of the zaonega formation importantly the presence of a negative cesn anomaly in the reysn pattern indicates an oxygenated atmosphere ocean system shortly after the lje and indicates that models invoking a fall in oxygen at that time require reassessment

rare earth elements in the nw indian ocean abstract dissolved rare earth element ree distributions have been determined at three stations in the high productivity nw indian ocean nwio upwelling zone dissolved ree distributions within the well oxygenated surface waters and deep portions of the water column are similar to those reported previously from other open ocean locations at depth dissolved ree concentrations are intermediate between those of the atlantic and pacific oceans consistent with the continuous regeneration and enrichment of the strictly trivalent rees in and the progressive oxidative removal of ce from the deep ocean within the mid depth oxygen minimum zone dissolved ree concentrations exhibit a notable enrichment superimposed upon these typical oceanic profiles further dissolved ce concentrations are preferentially enriched within the suboxic horizon compared to the rest of the series indicating the reduction of insoluble ce iv to dissolved ce iii at these depths by analogy with our previous studies of ree distributions in anoxic basins we propose that the more modest enrichments of the strictly trivalent rees observed in the nwio suboxic zone must derive from uptake through scavenging within the well oxygenated portions of the water column and regeneration from sediments and settling particles within the more reducing conditions of the oxygen minimum zone

effective use of cerium anomalies as a redox proxy in carbonate dominated marine settings abstract rare earth elements and yttrium rey have a distinct distribution pattern in seawater and this pattern may be faithfully preserved in carbonate sediments and rocks anomalous concentrations of redox sensitive cerium ce compared with neighbouring rey originate in oxic water column conditions and as such ce anomalies can provide a potentially useful redox proxy in carbonate dominated marine settings the methods used to extract rey from carbonates vary widely and may suffer from widespread leaching of rey from accessory non carbonate minerals and organic matter limiting the application of ce anomalies for palaeo redox reconstruction we have systematically compared different methods on 195 carbonate samples with varying purity carbonate from both modern and ancient environments we used sequential leaching experiments in nitric acid to identify the most seawater like portion of the carbonate sample where contributions from non carbonate minerals and organic matter are minimised we also compared the results of sample dissolution in different types and strengths of acid our results confirm that rey concentrations can be inadvertently contaminated by partial leaching of clays and fe oxyhydr oxides during a single step digestion and we suggest a pre leach of 20 of the sample followed by a partial leach of 40 of the sample to selectively dissolve carbonate we suggest that rey studies are optimised in carbonates with 85 caco 3 and show that dolomites behave differently during the leaching process and must be treated separately we present rey patterns for modern carbonate rich sediments from a range of environments and show that seawater rey are faithfully preserved in some non skeletal carbonate but modified leaching procedures are necessary for impure unlithified or organic rich carbonate sediments we combine rey with fe speciation data to identify how fe oxides and clays contribute to the rey signal and explore how the two proxies can be used together to provide a complex and high resolution redox reconstruction in carbonate dominated marine environments

internal deformation and compaction of the makran accretionary wedge the makran accretionary wedge is one of the largest on earth a 7 km thick column of sands and quartzolithic turbidites are incorporated into this wedge in a series of deformed thrust sheets we present the results of prestack depth migration and focusing error analysis migration velocity analysis performed on a profile across the makran wedge the depth section shows the deformation style of the accreted sediments and the migration velocities allow us to estimate porosity variations in the sediments the thrust sheets show evidence of fault propagation folding with a long wavelength of deformation 12 km and secondary thrusting in the kink bands of the folds such that the central part of each thrust sheet is elevated to form an additional ridge this deformation style and the 15 steep surface slope of the first ridge suggest a high degree of consolidation porosities were calculated from the seismic migration velocities and the ratio of fluid pressure to lithostatic pressure was estimated for 5 locations along the profile rather than being undercompacted and overpressured as in most accretionary wedges the sedimentary input is normally compacted exponential porosity decay throughout almost the whole wedge however a slight increase in porosity and at depth with respect to the normal compaction curve indicates that the turbiditic sequence might be overpressured landward of the deformation front

the paleoenvironmental evolution of the cambrian longwangmiao formation stage 4 toyonian on the yangtze platform south china petrographic and geochemical constrains abstract during the cambrian period stage 4 biodiversity and biomass declined rapidly and globally in an event known as the botomian toyonian crisis to gain a better understanding of the paleoenvironment in south china during this stage we present and interpret complex multi parameter carbonate analyses petrography carbon and oxygen isotopic composition and major trace and rare earth elements from the toyonian longwangmiao formation in the bandenggou section the longwangmiao formation comprises primarily carbonate deposits with massive detrital mineral occurrences in its lower middle sequence principal component analysis of the minerals and oxides leads to the definition of two intervals i and ii interval i is composed mainly of dolostones interbedded with sandstones and contains exceedingly high amounts of terrestrial original minerals and oxides as well as high ree y th and sc concentrations interval ii which is composed primarily of limestones has trace amounts of terrestrial original minerals and oxides and low ree y th and sc concentrations the 13c and 18o values show a significant positive shift from interval i to interval ii after eliminating the effects of diagenesis contributions through the analyses of diagenesis sensitive indexes 18o values mgo cao mn sr and fe sr ratios and the correlations of 13c 18o 18o eu eu eu eu ce ce and eu eu feo the sr and na concentrations of calcites in interval i are extremely high exceeding even the corresponding ranges of marine aragonites while calcites from interval ii have low sr and na concentrations that are within the range of marine low mg calcite however both show strong positive correlations between ca sr ca na and sr na the different calcite elemental behaviors in intervals i and ii suggest different carbonate precursors associated with seawater temperature and climate furthermore the sr ca ratios are negatively correlated with 13c and 18o values and the 13c values also negatively correlated with sio2 content these features indicate a significant change in the depositional environment during the cambrian toyonian stage from an early restricted marine environment under a warm and arid climate with massive terrestrial influxes to a later relatively open marine environment under a cool and humid climate with negligible terrestrial influxes this shift likely resulted in the observed changes in biomass and biodiversity

microbial utilization of rare earth elements at cold seeps related to aerobic methane oxidation abstract a major breakthrough in the field of rare earth element ree geochemistry has been the recent discovery of their utility to microbial life as essential metalloenzymes catalyzing the oxidation of methanol to formaldehyde lanthanide dependent bacteria are thought to be ubiquitous in marine and terrestrial environments but direct field evidence of preferential microbial utilization of ree in natural systems is still lacking in this study we report on the ree and trace element composition of the tube of a siboglinid worm collected at a methane seep in the gulf of guinea a tube dwelling annelid that thrives in deep sea chemosynthetic ecosystems high resolution trace element profiles along the chitin tube indicate marked enrichments of lanthanum la and cerium ce in its oxic part resulting in ree distribution patterns that depart significantly from the ambient seawater signature combined with various geochemical and microbiological evidence this observation provides direct support for an active consumption of light ree at cold seeps associated with the aerobic microbial oxidation of methane to further evaluate this hypothesis we also re examine the available set of ree data for modern seep carbonates worldwide while most carbonate concretions at cold seeps generally display ree distribution patterns very similar to those for reduced pore waters in marine sediments we find that seafloor carbonate pavements composed of aragonite commonly exhibit pronounced light ree enrichments as inferred from high shale normalized la gd ratio 0 8 interpreted here as possibly reflecting the signature of lanthanide dependent methanotrophic activity this finding opens new perspectives for revisiting ree systematics in ancient seep carbonates and other microbialites throughout the earth s history in particular the geochemical imprint of aerobic methane oxidation could be possibly traced using ree in archaean stromatolites and other archives of precambrian seawater chemistry potentially providing new insights into the oxygenation of early earth s oceans and associated microbiogeochemical processes

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

geochemical evidence from marine carbonate for enhanced terrigenous input into seawater during the ediacaran cambrian transition in south china abstract high resolution carbon and oxygen analyses along with residue contents major and trace element concentrations were carried out for marine dolostone from a profile through the upper ediacaran to the lower cambrian strata in south china the results provide geochemical evidence for enhanced input of terrigenous material into seawater in this period four positive and four negative carbon isotope excursions are identified in this profile the first remarkably negative 13c excursion exhibits the lowest value down to 2 at the ediacaran to cambrian boundary ecb in agreement with the global 13c and stratigraphy correlation the second remarkably negative 13ccarb excursion is as low as 1 81 subsequent to a positive 13ccarb excursion as high as 1 74 in the lower cambrian the ecb position in the stratigraphic profile is constrained by carbon isotope correlations the decreases of dolostone 18o and 13c values are synchronous across the ecb suggesting a change of the seawater composition at that time the increase of residue contents is concordant with decreases of y ho ratios and 18o values for the dolostone across the ecb suggesting the increase of terrigenous input in this period the relatively smooth ree y patterns of dolostone suggest its deposition in the environment of continental platform an integrated interpretation of these geochemical data including the major and trace element concentrations mn sr and mg ca ratios and the well preserved dolostone 13c and 18o values indicates that the terrigenous material from the continental weathering is rich in nutrients and 13c depleted organic matter which would have contributed to the negative 13ccarb excursion of dolostone at the stratigraphic boundaries the strong positive 13ccarb excursion in the lower cambrian may be linked to the biological radiation with lots of organic matter buried from the seawater in this period the fall and rise of sea level during different periods in the same region may result in differential input of terrigenous materials including freshwater into marine carbonates recording the coupling between regional tectonism and paleoclimatic change on the continental platform

stable isotope patterns of coexisting pyrite and gypsum indicating variable methane flow at a seep site of the shenhu area south china sea aggregates of authigenic pyrite and gypsum were found at site hs373 in the shenhu seepage area south china sea most of the pyrite occurs as tubes consisting of framboids gypsum aggregates are mainly represented by rosettes and some of them grew over pyrite revealing that gypsum precipitation postdated pyrite formation at seeps extensive sulfate driven anaerobic oxidation of methane aom commonly leads to the accumulation of 34s enriched sulfide resulting in the formation of 32s depleted pyrite the sulfur isotopic composition of pyrite at site hs373 reveals a great variability of 75 5 in 34s values spanning from 37 6 to 37 9 v cdt with a distinct trend towards higher values with increasing depth this trend indicates an increase of the effect of sulfate driven aom with depth whereas pyrite at shallow depth apparently resulted mostly from organiclastic sulfate reduction to date reports on coexisting pyrite and gypsum in seep environments are limited and therefore the mechanism of gypsum formation is insufficiently understood this is the first time that the sulfur and oxygen stable isotope composition of gypsum has been analyzed to understand its formation at seeps the 34s values of gypsum vary from 24 5 to 0 9 revealing a similar trend with depth like pyrite the 18ogypsum values range from 5 3 to 12 3 v smow with a scattered trend to lower values with depth the combined evidence reveals that gypsum formation was linked to the establishment of more oxidizing conditions probably caused by waning seepage this led to the oxidation of pyrite and the associated increase in pore water sulfate and acidity which favored carbonate mineral dissolution providing the calcium ions required for gypsum formation the observed isotopic variability of gypsum suggests that oxidation occurred by different mechanisms at different depth whereby pyrite oxidation was dominated by aerobic processes at shallow depth involving dissolved molecular oxygen and by anaerobic processes at greater depth involving electron acceptors like ferric iron taken together the stable isotope compositions of pyrite and gypsum suggest that the redox conditions within the studied sediments were variable such variability was controlled by complex factors among which changes in seepage activity have been instrumental for the vertical displacement of the sulfate methane transition zone

rare earth elements in seep carbonates as tracers of variable redox conditions at ancient hydrocarbon seeps marine hydrocarbon seeps are dynamic systems which are typically reflected in complex lithologies of limestones forming at these sites in order to test if seep limestones with their multiple generations of carbonate phases reflect variable redox conditions the rare earth element ree patterns of limestones from five ancient hydrocarbon seep localities hollard mound middle devonian iberg mississippian beauvoisin oxfordian canyon and satsop river oligocene and marmorito miocene have been investigated the total ree contents vary widely 0 3 43 7 p p m early microcrystalline phases tend to show higher contents than spatially associated later phases microspar sparite and blocky cement the shale normalized ree patterns of the carbonates show both negative and positive ce anomalies even for individual deposits suggesting that the redox conditions varied significantly it is apparent that in addition to anoxic conditions oxic conditions were common in some ancient seep environments intermittent oxygenation is presumed to have resulted from abrupt changes in fluid flow

tracing the composition and origin of fluids at an ancient hydrocarbon seep hollard mound middle devonian morocco a nd ree and stable isotope study abstract for the first time nd isotope signatures combined with rare earth element ree concentrations were used in investigations of ancient seep carbonates the study was performed on the fossil hydrocarbon seep deposit of the middle devonian hollard mound eastern anti atlas morocco where nd isotopes ree concentrations and carbon and oxygen isotope ratios were measured to investigate the origin former migration pathways and composition of fluids relatively high end values compared to local eifelian seawater as well as consistently appearing positive eu anomalies in mree enriched shale normalized ree patterns of the seep carbonates provided evidence for interaction between the seeping fluids and the lower devonian basaltic volcaniclastics underlying the studied seep deposit strongly reducing conditions and increased temperature of methane formation could have constituted an additional factor in the eu enrichment of the investigated carbonate phases the presence of exclusively negative ce anomalies in these carbonates is in line with observations of other workers that seep limestones may not necessarily display positive ce anomalies indicative of precipitation under anoxic conditions the negative ce anomalies are attributed here to mixing between anoxic pore waters and oxic ce depleted seawater necessary to enable carbonate precipitation at seeps the methane rich fluids ascended most likely from below the volcaniclastic unit and inherited the enriched end signatures and positive eu anomalies due to fluid rock interactions during their seepage to the seafloor the carbon isotope data are most consistent with thermogenic origin of methane although contribution of abiotic and biogenic methane sources cannot be excluded our results indicate that neodymium isotope and rare earth element analyses constitute one of the most valuable tools for reconstructing former fluid migration patterns the study shows also that nd isotopes and eu anomalies can serve as sensitive tracers of fluid rock interactions at submarine springs

biogeochemical formation of calyx shaped carbonate crystal fans in the subsurface of the early triassic seafloor abstract the kuh e dena sedimentary section in iran developed on the southwestern margin of the neotethys ocean the fossil and bioturbation lean early triassic section late dienerian to early smithian is typified by finely laminated calcareous shales that are interbedded with laterally extending carbonate beds which are mostly composed of calyx shaped carbonate crystal fans the calyxes consist of fibrous crystals that apparently formed within the subseafloor in soft water saturated sediment by displacive growth rare earth element and yttrium patterns indicate that calyx shaped crystals precipitated from anoxic pore waters biomarker patterns of the carbonate beds reveal major input of lipids from prokaryotes that typically occur within layered benthic microbial mats i e cyanobacteria anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea along their length the fibrous crystals of the calyxes reveal a trend of increasing 13 c carb values from 2 7 to 3 3 suggesting that archaeal methanogenesis affected the carbonate pool apart from the putative benthic prokaryotes molecular fossils of halophilic most likely planktic archaea were detected in the carbonate beds low pristane to phytane ratios 0 8 and the presence of halophilic archaea are in accord with the lack of bioclasts and bioturbation which likely reflects increased salinities the former presence of a benthic microbial mat with cyanobacteria underlain by anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea is in accordance with studies on living microbial mats in hypersaline low oxygen marine environments the early triassic subseafloor seems to have been a sink for carbon driven by biologically induced formation of secondary diagenetic carbonate

geochemical assessment of hydrocarbon migration phenomena case studies from the south western margin of the dead sea basin abstract calcite veins with fluid and solid bitumen inclusions have been discovered in the south western shoulder of the dead sea rift within the masada zohar block where hydrocarbons exist in small commercial gas fields and non commercial fields of heavy and light oils the gas liquid inclusions in calcite are dominated either by methane or co2 and aqueous inclusions sometimes bear minor dissolved hydrocarbons the enclosed flake like solid bitumen matter is a residue of degraded oil which may be interpreted as dead carbon about 2 3 of this matter is soot like amorphous carbon and 1 3 consists of n c8 c18 carboxylic acids and traces of n alkanes light dicarboxylic acids and higher molecular weight c20 branched and or cyclic carboxylic acids both bitumen and the host calcites show genetic relationship with mature maastrichtian chalky source rocks mcsrs evident in isotopic compositions 13c 34s and 18o and in ree y patterns the bitumen precursor may have been heavy sulfur rich oil which was generated during the burial compaction of the mcsr strata within the subsided blocks of the dead sea graben the 18o and 13c values and ree y signatures in calcites indicate mixing of deep buried fluids equilibrated with post mature sediments and meteoric waters the temperatures of fluid generation according to mg li geothermometer data range from 55 to 90 corresponding to the 2 5 4 0 km depths and largely overlap with the oil window range 60 90 in the dead sea rift hunt 1996 gvirtzman and stanislavsky 2000 buryakovsky et al 2005 the bitumen rich vein calcites originated in the course of late cenozoic rifting and related deformation when tectonic stress triggers damaged small hydrocarbon reservoirs in the area produced pathways and caused hydrocarbon bearing fluids to rise to the subsurface the fluids filled open fractures and crystallized to calcite with entrapped bitumen the reported results are in good agreement with the existing views of maturation migration and accumulation of hydrocarbons as well as basin fluid transport processes in the dead sea area

paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite abstract rare earth element concentrations in biogenic apatite of conodonts fish debris and inarticulate brachiopods were determined in over 200 samples from cambrian to modern sediments tests for experimental bias caused by the chemicals used to separate fossils from the rock matrix and for interlaboratory interexperiment or interspecies related variations clearly show that no resolvable fractionation of ree occurs incorporation of ree in biogenic apatite of recent fish debris occurs near the sediment water interface soon after deposition and reflects characteristics of seawater the original ree signature apparently survives subsequent burial and diagenesis cerium variations in fish debris from modern environments are controlled by redox potential ce is fractionated by co precipitation with metallic oxides under oxidizing conditions this fractionation produces a negative ce anomaly ce anom in seawater that is reflected in the sedimented fish debris conversely no fractionation of ce occurs under reducing conditions resulting in ce concentrations that are normal to enriched in anoxic seawater and fish debris deposited under local or basinwide anoxic conditions extrapolation of observations of the redox control of ce anom in modern oceans to fossil apatite indicates that anoxic conditions were prevalent in lower paleozoic and lower triassic oceans whereas in the upper paleozoic the world ocean was generally oxidizing

the effect of diagenesis and fluid migration on rare earth element distribution in pore fluids of the northern cascadia accretionary margin analytical challenges in obtaining high quality measurements of rare earth elements rees from small pore fluid volumes have limited the application of rees as deep fluid geochemical tracers using a recently developed analytical technique we analyzed rees from pore fluids collected from sites u1325 and u1329 drilled on the northern cascadia margin during the integrated ocean drilling program iodp expedition 311 to investigate the ree behavior during diagenesis and their utility as tracers of deep fluid migration these sites were selected because they represent contrasting settings on an accretionary margin a ponded basin at the toe of the margin and the landward tofino basin near the shelf s edge ree concentrations of pore fluid in the methanogenic zone at sites u1325 and u1329 correlate positively with concentrations of dissolved organic carbon doc and alkalinity fractionations across the ree series are driven by preferential complexation of the heavy rees simultaneous enrichment of diagenetic indicators doc and alkalinity and of rees in particular the heavy elements ho to lu suggests that the heavy rees are released during particulate organic carbon poc degradation and are subsequently chelated by doc ree concentrations are greater at site u1325 a site where shorter residence times of poc in sulfate bearing redox zones may enhance ree burial efficiency within sulfidic and methanogenic sediment zones where ree release ensues cross plots of la concentrations versus cl li and sr delineate a distinct field for the deep fluids z 75 mbsf at site u1329 and indicate the presence of a fluid not observed at the other sites drilled on the cascadia margin changes in ree patterns the presence of a positive eu anomaly and other available geochemical data for this site suggest a complex hydrology and possible interaction with the igneous crescent terrane located east of the drilled transect

the mud volcanoes of pakistan marine geologic investigations on the arabian sea by bundesanstalt fur geowissenschaften und rohstoffe bgr in 1995 and 1998 and land expeditions in 1998 and 1999 to the coastal regions of the makran desert pakistan have extended the knowledge of the aerial distribution of mud volcanoes these structures rise from under compacted formations within the regional accretionary prism which is built by the subduction of the oceanic crust of the arabian sea and its km thick sedimentary load the occurrence of mud volcanoes is limited to the abyssal plain near the accretionary front to the coastal region of the makran desert and to a region in the interior of the desert to the south to southeast of the so called hinglay synform the location of mud volcanoes in pakistan is clearly tied to fault systems mud volcanoes are conspicuously absent on the lower slope of the accretionary prism where thick gas hydrate layers have developed the presence of large gas plumes emerging from the seafloor landward of the gas hydrate stability zone at water depths of less than 800 m points to a redirection of fluids from depth which might explain the absence of mud volcanoes along the lower slope

authigenic carbonates from methane seeps of the northern congo fan microbial formation mechanism abstract authigenic carbonates were collected from methane seeps at hydrate hole at 3113 m water depth and diapir field at 2417 m water depth on the northern congo deep sea fan during rv meteor cruise m56 the carbonate samples analyzed here are nodules mainly composed of aragonite and high mg calcite abundant putative microbial carbonate rods and associated pyrite framboids were recognized within the carbonate matrix the 13c values of the hydrate hole carbonates range from 62 5 to 46 3 pdb while the 13c values of the diapir field carbonate are somewhat higher ranging from 40 7 to 30 7 pdb indicating that methane is the predominant carbon source at both locations relative enrichment of 18o 18o values as high as 5 2 pdb are probably related to localized destabilization of gas hydrate the total content of rare earth elements ree of 5 hno3 treated solutions derived from carbonate samples varies from 1 6 ppm to 42 5 ppm the shale normalized ree patterns all display positive ce anomalies ce ce 1 3 revealing that the carbonates precipitated under anoxic conditions a sample from hydrate hole shows a concentric lamination corresponding to fluctuations in 13c values as well as trace elements contents these fluctuations are presumed to reflect changes of seepage flux

formation of methane derived carbonates during the last glacial period on the northern slope of the south china sea abstract methane derived carbonates with blocky and chimney morphologies were collected on the northern slope of the south china sea the studies of petrography geochemistry and chronology show that the blocky carbonate has a microcrystalline structure with numerous of biogenic tests whereas the carbonate chimney has a cryptocrystalline structure with scarce biogenic tests aragonite can be detected in the carbonate chimney which indicates that it formed at the shallow sediments or on the seafloor the 13c and 18o values of the blocky carbonate range from 46 8 to 28 8 vpdb and 2 2 to 3 5 vpdb respectively the 13c and 18o values of the carbonate chimney range from 45 0 to 22 9 vpdb and 2 8 to 3 1 vpdb respectively the carbon isotopic values indicate that these carbonates are related to the anaerobic oxidation of methane aom the oxygen isotopic values show that the gas hydrate dissociation contributed the 18o enrich fluid to a certain degree during the authigenic carbonate formation according to the rare earth element results the carbonate chimney precipitated in stable anoxic conditions because of the la enriched influence the formation environment of the blocky carbonate is ambiguous the u th chronology results indicate that these authigenic carbonates precipitated during the last glacial period primarily marine isotopic stage 3 of low sea level stand

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

evidence for a thick free gas layer beneath the bottom simulating reflector in the makran accretionary prism abstract seismic reflection data from the makran continental margin indicate the presence of a strong and widespread bottom simulating reflector bsr we apply a nonlinear full waveform inversion technique to multichannel reflection data from this area to investigate the detailed velocity structure and hence the origin of the bsr our result shows an abrupt decrease in the compressional wave velocity from 2 2 to 1 3 km s at a depth of 500 m below the sea bed the low velocity zone is unusually thick 200 350 m and may contain large quantities of free gas similar to some of the recently drilled blake ridge sites of odp leg 164 the voluminous free gas may have been generated by the dissociation of gas hydrates as a consequence of the upward movement of the base of gas hydrate stability field relative to the sediment column due to uplift and sedimentation in the accretionary wedge

temporal variability of gas seeps offshore new zealand multi frequency geoacoustic imaging of the wairarapa area hikurangi margin cold seeps on opouawe bank situated in around 1000 m water depth on the hikurangi margin offshore north island new zealand were investigated using multibeam bathymetry 75 and 410 khz sidescan sonar imagery and 2 8 khz chirp sediment echosounder data towed video camera observations allowed ground truthing the various geoacoustic data at least eleven different seep locations displaying a range of seep activity were identified in the study area the study area consists of an elongated northward widening ridge that is part of the accretionary hikurangi margin and is well separated from direct terrigenous input by margin channels surrounding the ridge the geoacoustic signature of individual cold seep sites ranged from smooth areas with slightly elevated backscatter intensity resulting from high gas content or the presence of near surface gas hydrates to rough areas with widespread patches of carbonates at the seafloor five cold seeps also show indications for active gas emissions in the form of acoustic plumes in the water column repeated sidescan sonar imagery of the plumes indicates they are highly variable in intensity and direction in the water column probably reflecting the control of gas emission by tides and currents although gas emission appears strongly focused in the wairarapa area the actual extents of the cold seep structures are much wider in the subsurface as is shown by sediment echosounder profiles where large gas fronts were observed

rare earth elements in cold seep carbonates from the niger delta abstract the circulation of methane rich fluids at cold seeps often leads to precipitation of authigenic carbonates mediated by microbial activity which can be used as archives of fluid seepage on continental margins in this study we have investigated the potential of using rare earth element ree concentrations in authigenic carbonates for tracing fluid sources and providing information on associated biogeochemical processes at cold seeps we have examined various chemical procedures for the analysis of ree in authigenic carbonates and present a robust method using dilute acetic acid solution that allows the extraction of ree from carbonate phases with reduced contamination from fe mn oxides and detrital minerals using this method we analysed a series of carbonate samples collected at various deep sea sites of active fluid seepage on the niger delta for their ree and trace element concentrations 13c and 18o values and 87sr 86sr isotope compositions we show that the ree composition of cold seep carbonates is controlled primarily by that of the fluid from which they have precipitated our results also suggest that significant ree fractionation can occur during carbonate precipitation which can be related to various degrees of ree complexation by organic versus carbonate ligands in response to changing pore water chemical composition for parameters such as carbonate alkalinity

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

petrographic and geochemical characterization of seep carbonate from bush hill gc 185 gas vent and hydrate site of the gulf of mexico abstract authigenic carbonates are common at cold seep sites as a result of microbial oxidation of hydrocarbons seep carbonate samples were collected from the surface of the bush hill green canyon block 185 gulf of mexico a mound containing gas hydrate the carbonates consisted of oily porous limestone slabs and blocks containing bioclasts and matrix analysis by x ray diffraction shows that aragonite is the dominant mineral 89 99 wt with an average of 94 wt in the matrix of seep carbonate this cement occurs in microcrystalline microspar and sparite forms the moderate 13 c depletion of the seep carbonate the most depleted one has 13 c value of 29 4 and 26 of 38 subsamples have 13 c values 20 0 indicates that the non methane hydrocarbons was incorporated during seep carbonate precipitation relative enrichment of 18 o may be related to localized destabilization of gas hydrate or derived from 18 o enriched pore water originated from smectite illite transition in the deep sediments the total content of rare earth elements ree of the 5 hno 3 treated solution of the carbonates is from 0 40 ppm to 30 9 ppm the shale normalized ree patterns show varied ce anomalies from significantly negative slightly negative and no to positive ce anomalies variable content of trace elements total ree and ce anomalies in different samples and even in the different carbonate mineral forms microcrystalline microspar and sparite of the same sample suggest that the formation condition of the bush hill seep carbonate is variable and complex which is possibly controlled by the rate of fluid flux

a deep fluid source of radiogenic sr and highly dynamic seepage conditions recorded in miocene seep carbonates of the northern apennines italy abstract the 87sr 86sr ree and mo u systematics were investigated in miocene seep carbonates formed on accretionary ridges at the front of the northern apennine wedge here we evaluate fluid sources seepage intensity and redox conditions during carbonate precipitation micrite matrix and early calcite cements lining cavities are the main authigenic carbonate phases and show negligible diagenetic alteration their aom related anaerobic oxidation of methane origin is evident from 13c values ranging from 38 7 to 25 7 the 87sr 86sr ratios in carbonates vary between 0 708659 and 0 709132 most micrite values fall within the range of middle miocene seawater langhian mnn5a biozone in agreement with the biostratigraphy of the host sediments thus reflecting precipitation of seep carbonates close to the seafloor highly radiogenic 87sr 86sr ratios of early calcite cements and micrite from conduit rich facies at the base of carbonate bodies likely derived from the interaction of fluids with detrital clays during the fault controlled upward migration through the underlying terrigenous turbidite successions strong mo and u enrichments in carbonates with moef and uef up to 233 5 and 86 6 respectively coupled with mo u ef ratios ranging between 0 7 and 9 7 indicate dynamic redox conditions episodically sulfidic and restricted to porewaters this interpretation is also supported by enrichments in mree of micrites and a general absence of negative ce anomalies these new data provide an indirect indication of rates and temporal variability of aom at fossil methane seeps developed on a thrust related anticline and help to constrain the complex interaction between fluid migration pathways seepage intensity and environmental conditions as observed in modern seep analogues

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

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

corrosion patterns of seep carbonates from the eastern mediterranean sea terra nova 23 206 212 2011 abstract porous seep carbonates are exposed at mud volcanoes in the eastern mediterranean sea the 13c depleted aragonitic carbonates formed as a consequence of the anaerobic oxidation of methane in a shallow sub surface environment besides the macroscopically visible cavernous fabric extensive carbonate corrosion was revealed by detailed analysis after erosion of the background sediments the carbonates became exposed to oxygenated bottom waters that are periodically influenced by the release of methane and upward diffusion of hydrogen sulphide we suggest that carbonate corrosion resulted from acidity locally produced by aerobic oxidation of methane and hydrogen sulphide in the otherwise with respect to aragonite oversaturated bottom waters although it remains to be tested whether the mechanisms of carbonate dissolution suggested herein are valid this study reveals that a better estimate of the significance of corrosion is required to assess the amount of methane derived carbon that is permanently fixed in seep carbonates

morphotectonics and mechanics of the central makran accretionary wedge off pakistan abstract swath bathymetry images and 3 5 khz data acquired during rv sonne cruise 123 in autumn 1997 are the base for analysing the morphology and deformation styles of the huge makran accretionary wedge the continental slope off pakistan is characterised by three morphological provinces a the lower slope is built of a sequence of imbricate thrust slices which form long and narrow accretionary ridges with flanks locally as steep as 20 and between 10 and 20 on average while the regional slope is only 1 2 b the nearly flat mid slope terrace is present in the central east part of the margin narrows significantly towards the east and is absent east of 63 45 and c the upper slope up to the shelf has a regionally uniform slope as steep as about 8 and comprises a very rough topography with many gullies and canyons and evidence for mass wasting two meandering canyons crossing the entire margin down to the abyssal plain at about 63 15 63 30 can be correlated with onshore rivers they have been formed by episodic erosion through turbidity flows and are characterised by erosional and depositional portions sinuosity of the canyons is exclusively caused by the accretionary ridges functioning as obstacles for flow to be directly downhill application of coulomb rheology to the frontal part of the makran wedge implies that the mid level decollement is intrinsically extraordinary weak with a great strength contrast to the overlying sediments comparison with nankai cascadia and the western mediterranean ridge reveals new insights in the parameters controlling the shape of an accretionary wedge and the role of a mid level decollement

authigenic carbonates from seeps on the northern continental slope of the south china sea new insights into fluid sources and geochronology seep carbonates represent excellent archives of seepage activities near seafloors in order to provide insights on sources of seeping fluids stable carbon and oxygen isotopes and sr 87 sr 86 ratios were applied to seep carbonates from shenhu sw dongsha and ne dongsha on the northern continental slope of the south china sea u th dating was selected to constrain the time involved in carbonate formation and the potential driving force the delta c 13 values of the shenhu and ne dongsha carbonates vary from 52 3 parts per thousand to 32 6 parts per thousand v pdb indicating that biogenic methane is the primary carbon source at both locations the delta c 13 values of the sw dongsha carbonates are much higher ranging from 18 8 parts per thousand to 11 parts per thousand v pdb suggesting that thermogenic methane is the predominant carbon source in this region a relatively deep origin of thermogenic methane for the sw dongsha seeps is also supported by somewhat lower sr 87 sr 86 ratios of the samples from 0 709025 to 0 709097 the delta o 18 values of the shenhu and ne dongsha carbonates vary from 1 4 to 5 1 v pdb while the delta o 18 values of the sw dongsha carbonates range from 2 5 to 3 4 v pdb many samples from shenhu and ne dongsha demonstrate an o 18 enriched fluid source that most likely originated from waters released from the dissociation of locally abundant gas hydrate u th ages of the shenhu carbonates show a large range from 330 ka to 152 ka bp and the ne dongsha carbonates have ages from 77 ka to 63 ka bp interestingly u th ages of most samples are either within times of sea level lowstands or correspond to periods when the sea level was falling taken together our data suggest that in the south china sea gas hydrate dissociation during sea level lowstands or falling stages resulted from reduced hydrastastic pressures which in turn enhanced the seep activities and promoted the formation of authigenic carbonates close to the seafloor c 2013 elsevier ltd all rights reserved

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

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

establishing criteria to distinguish oil seep from methane seep carbonates hydrocarbon seeps harbor copious chemosynthesis dependent life the traces of which are preserved in the fossil record within authigenic carbonates these environments are mostly characterized by seepage of methane rich fluids yet numerous crude oil dominated seeps have been discovered in recent years oil seepage has a profound influence on the local fauna but recognizing such seeps in the rock record remains elusive this study presents new geochemical data that will allow for a more confident identification of ancient oil seep deposits geochemical data from modern and ancient seep limestones reveal that oil dominated seep carbonates are enriched in rare earth elements and uranium compared to their methane dominated counterparts these trace element patterns have the potential to serve as a basis for an improved understanding of the adaptation of chemosynthetic life to oil seepage and to better constrain the marine carbon cycle in the geologic past

cold seep status archived in authigenic carbonates mineralogical and isotopic evidence from northern south china sea abstract cold seep carbonates are precipitated under high alkalinity conditions created by the anaerobic oxidation of methane in cold seep sites multiple ca mg carbonate phases are identified including aragonite low mg calcite lmc high mg calcite hmc protodolomite and dolomite these phases result from different conditions that are related with cold seep activities here we report on the relationship between the ca mg carbonate phases and the cold seep status authigenic carbonates were sampled from northern slope of south china sea carbon isotopic compositions of samples from shenhu area are lower than 40 indicating methane derived carbon the 13c values of samples from southwest sw taiwan area range from 30 to 20 which is the result of the mixture of methane carbon and seawater carbon carbonate phases were identified according to the composition and structure results samples from shenhu area are composed of protodolomite and hmc three zones were discovered from the center to the rim of the cross section of the tube like sample from sw taiwan area from the external to the internal zones the carbonate phases are hmc lmc and protodolomite hmc respectively the intensity of superstructure reflections of the protodolomite from shenhu area is stronger than that from sw taiwan area indicating higher mgco3 content based on the formation conditions of ca mg carbonates from lmc to dolomite those with higher mgco3 content are formed in more active cold seep environment according to the distribution of carbonate phases in each sample the cold seep flux was high in shenhu area and was sustained for a long time by contrast the flux in sw taiwan area was relatively low and not stable it once became higher but finally returned to low

paleo cold seep activity in the southern south china sea evidence from the geochemical and geophysical records of sediments abstract over the past decade more than 30 cold seep sites have been reported along the continental slope of the south china sea scs these seep sites have all been located in the northern scs and no methane seepage has been discovered in the southern scs here we report on the analysis results of the geochemical and geophysical of the marine core sediments 58s collected from the southern continental slope of the scs we suggest that the sedimentary total sulfur ts total inorganic carbon tic 34scrs values of chromium reducible sulfur crs and carbonate 13ctic values of the bulk sediments coupled with the ratio of nrmaf60mt nrmaf80mt nrm can be used to trace the methane release events in a methane rich environment at least two methane release events were identified at depths of 5 5 6 2 m and 6 8 7 2 m moreover according to the characteristic of the ts toc and nrmaf60mt nrmaf80mt nrm ratio of sediments we suggest the methane flux has changed episodically this inference is supported by the occurrence of the strongly negative carbonate 13ctic values of bulk sediments and the positive 34scrs values which indicate the occurrence of anaerobic oxidation of methane aom and the location of a past or present sulfate methane transition zone smtz respectively ultimately these new data suggest that the combined geochemical and geophysical study of marine sediments provides a valuable tool with which to infer the temporal variations in methane seepage in a marine environment

sediment compaction and fluid migration in the makran accretionary prism the makran continental margin in the gulf of oman forms the seaward extremity of an accretionary sediment prism which extends several hundred kilometers inland a recently acquired multichannel seismic reflection profile shot across the margin imaged the structure of the prism in greater detail than was previously possible and allowed us to investigate the relationship between deformation and pore fluid motion in the region velocity analyses of the common midpoint gathers reveal a marked change in velocity structure at the toe of the accretionary wedge as seen in previous sonobuoy wide angle data accreted sediments show significantly higher vertical velocity gradients than those of sediments entering the prism this change is interpreted as due to porosity reduction as pore fluids are squeezed out of the compacting sediment a prominent bottom simulating reflector appears 500 800 m beneath the sea bed several lines of evidence suggest that this reflector represents the base of a gas hydrate zone underlain by widespread free gas which may be exsolved from pore water migrating from deep within the sediment pile up permeable fault planes imaged in the profile the hydrate reflector appears to shallow in the region of some faults suggesting a temperature anomaly due to the presence of warm pore fluids a heat flow profile derived from the depth of the hydrate reflector does not show the expected landward decrease as the sediment pile thickens simple thermal modeling suggests that advective heat flow within the prism may explain this anomaly the inferred presence of overpressured pore fluids in the makran suggests that accreted sediments have a low permeability the seismic evidence suggests a two stage compaction process with rapid initial dewatering through intergranular permeability as sediment enters the prism followed by a buildup of pore pressure as the permeability decreases and fluid migration is restricted to fault zones

differentiating marine vs hydrothermal processes in devonian carbonatemounds using rare earth elements kess kess mounds anti atlas morocco abstract petrological and geochemical analyses were carried out on early devonian kess kess mound limestones of the seheb el rhassel group exposed in the hamar laghdad ridge tafilalt platform eastern anti atlas morocco in order to evaluate marine vs hydrothermal processes for the origin of the mounds hydrothermal fluid circulation affected limestone deposition resulting in the formation of a plumbing system preserved in the mound facies and inter mound facies as cavities veins and dykes shale normalized rare earth element ree patterns for limestones display pronounced light ree depletion compared to middle ree average prsn dysn 0 46 and heavy ree average prsn ybsn 0 55 a super chondritic y ho ratio up to 87 and positive la anomaly consistent with precipitation from normal marine seawater within our data set the ce anomaly as well as u and other trace element concentrations vary with facies providing evidence for variable redox conditions the presence of positive ce anomaly in carbonates of the plumbing system is consistent with precipitation under anoxic condition samples from mound facies and quartz veinlets in the upper part of the group show ree patterns consistent with precipitation from hydrothermal fluids early devonian hypothetical seawater ree patterns were calculated from samples showing normal marine ree patterns i e inter mound facies and from samples with weaker marine signature i e fossiliferous mound limestones and plumbing system deposits hypothetical patterns are slightly enriched in ree compared to modern open ocean seawater this study reveals that ree analysis is a powerful tool for understanding polygenetic carbonate systems it sheds light into the genesis of the kess kess mounds by reconstructing fluid pathways and palaeo redox conditions

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

rare earth elements in authigenic methane seep carbonates as tracers for fluid composition during early diagenesis abstract authigenic carbonates forming at an active methane seep on the makran accretionary prism mainly consist of aragonite in the form of microcrystalline cryptocrystalline and botryoidal phases the 13 c carbonate values are very negative 49 0 to 44 0 v pdb agreeing with microbial methane as dominant carbon source the 18 o carbonate values are exclusively positive 3 0 to 4 5 v pdb and indicate precipitation in equilibrium with seawater at bottom water temperatures the content of rare earth elements and yttrium ree y determined by laser ablation inductively coupled plasma mass spectrometry la icp ms and solution icp ms varies for each aragonite variety with early microcrystalline aragonite yielding the highest cryptocrystalline aragonite intermediate and later botryoidal aragonite the lowest ree y concentrations shale normalised ree y patterns of different types of authigenic carbonate reflect distinct pore fluid compositions during precipitation microcrystalline aragonite shows high contents of middle rare earth elements mree reflecting ree patterns ascribed to anoxic pore water cryptocrystalline aragonite exhibits a seawater like ree y pattern at elevated total ree y concentrations indicating higher concentrations of rees in pore waters which were influenced by seawater botryoidal aragonite is characterised by seawater like ree y patterns at initial growth stages followed by an increase of light rare earth elements lree with advancing crystal growth reflecting changing pore fluid composition during precipitation of this cement conventional sample preparation involving micro drilling of carbonate phases and subsequent solution icp ms does not allow to recognise such subtle changes in the ree y composition of individual carbonate phases to be able to reconstruct the evolution of pore water composition during early diagenesis an analytical approach is required that allows to track the changing elemental composition in a paragenetic sequence as well as in individual phases high resolution analysis of seep carbonates from the makran accretionary prism by la icp ms reveals that pore fluid composition not only evolved in the course of the formation of different phases but also changed during the precipitation of individual phases

authigenic carbonates derived from oxidized methane vented from the makran accretionary prism off pakistan we report the first discovery and sampling of a methane hydrogen sulfide rich cold seep from the makran accretionary prism off pakistan arabian sea a variety of cm to m scale pockmarks and gas seepage structures were identified from underwater tv photo sled profiles crossing the oxygen minimum zone omz related to highresolution seismic parasound records from the seeps isotopically light bacterially formed methane is emanating that is partly oxidized to hco3 in the bacterial sulfate reduction zone this results in the precipitation of irregular dark gray to black crusts of indurated authigenic carbonates mainly cryptocrystalline magnesian calcite and ca rich dolomite near the sediment seawater interface within the omz downcore the crusts grade into hemipelagic carbonate poor silty clays with transitional lithologies in between similar to the pockmark carbonates from the oregon margin and in the north sea the authigenic carbonates are extremely depleted in 13c 13ccarbonate 40 this suggests that they were derived from bacterial methane 13cmethane 77 8 that was oxidized under anaerobic conditions the authigenic carbonates are associated with white fluffy mats of chemoautotrophic h2s oxidizing bacteria small pockmarks appear to be concentrated at small scale escarpments suggesting focussed fault controlled pore fluid expulsion due to the tectonic dewatering and degassing of the accretionary prism whereas diffuse discharge of pore fluids is inferred from the widespread occurrence of tiny gas bubble tubes

trace elements and ree geochemistry of middle devonian carbonate mounds maider basin eastern anti atlas morocco implications for early diagenetic processes abstract trace and rare earth elements rees have proven their utility as tools for assessing the genesis and early diagenesis of widespread geological bodies such as carbonate mounds whose genetic processes are not yet fully understood carbonates from the middle devonian conical mud mounds of the maider basin eastern anti atlas morocco have been analysed for their ree and trace element distribution collectively the carbonates from the maider basin mud mounds appear to display coherent ree patterns three different geochemical patterns possibly related with three different diagenetic events include i dyke fills with a normal marine ree pattern probably precipitated in equilibrium with seawater ii mound micrite with a particular enrichment of overall ree contents and variable ce anomaly probably related to variation of ph increase of alkalinity or dissolution remineralization of organic matter during early diagenesis and iii haematite rich vein fills precipitated from venting fluids of probable hydrothermal origin our results reinforce the hypothesis that these mounds were probably affected by an early diagenesis induced by microbial activity and triggered by abundance of dispersed organic matter whilst venting may have affected the mounds during a later diagenetic phase

origin of dolomites in the lower cambrian xiaoerbulak formation in the tarim basin nw china implications for porosity development abstract dolomites occur pervasively in the cambrian strata in the tarim basin nw china although the cambrian strata have been deeply buried and affected by multiple phases of dolomitization some intervals in the upper part of the lower cambrian xiaoerbulak formation developed high porosity the goal of this study is to understand the origin of different types of dolomites and the formation mechanism of the porosity in the xiaoerbulak formation the geochemistry of matrix dolomites suggests that they formed from middle rare earth element mree enriched anoxic pore fluids close to or within the zone of iron reduction the similar ree y patterns and overlapping 13 c values between pore filling and matrix dolomites indicate that the fluids that were responsible for the precipitation of pore filling dolomite apparently inherited the signatures of the formation waters that were stored in the host strata low 18 o values coupled with high ba zn and rare earth element ree content of pore filling dolomites indicate that pore filling dolomites were formed at elevated temperatures the precipitation of authigenic quartz and saddle dolomites and high mn content in pore filling dolomites indicate that hydrothermal fluids that mostly originated from cambrian basinal clastic units or basement rocks were involved the mixture of formation water and external hydrothermal fluids is the most likely explanation for the formation of significant porosity and precipitation of pore filling dolomites at depth breccia dolomite zebra dolomite and saddle dolomite occur mostly in areas that are close to faults which suggests that hydrothermal fluids passed through strike slip faults in this area when these faults were activated the development of permeable layers in the upper part of the xiaoerbulak formation overlain by impermeable layers of the wusongger formation suggests a possible potential diagenetic trap when the faults were activated high pressure and high temperature fluids flowed up through faults and hit low permeability beds at the base of the wusongger formation then the hydrothermal fluids flowed laterally into permeable dolomite strata at the top of the xiaoerbulak formation and encountered the formation brines large volumes of secondary porosity formed when host dolomite was leached by the mixing fluids and pore filling dolomites and other minerals formed soon afterward both the faults and original host facies exerted important influences on the lateral extent of the dissolution

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

a methane derived carbonate build up at a cold seep on the crimean slope north western black sea abstract a unique chimney shaped carbonate build up was produced by microbially mediated anaerobic oxidation of methane at a deep sea cold seep the build up was sampled from 1600 m water depth in the area of the lomonosov rise nw black sea crimean shelf slope the carbonate chimney grew free into the anoxic water column with its base attached to a steep slope composed of plagiogranite and void of sediments the perfectly preserved 1 5 m high chimney stores reliable records of the diversity of mineralogy geochemistry and stable isotope composition of deep sea methane related carbonates never studied before the build up consists of mg calcite mgco 3 9 13 mol with minor aragonite the carbonate matrix encloses organic matter and emiliania huxleyi coccoliths as well as minor framboidal pyrite gypsum barite and diatomite fragments the contribution of detrital silicate material is negligible micritic mg calcite in the inner zone of the chimney forms obtuse rhombohedrons clustered in hemispherical aggregates clots and hosts isolated prismatic aragonite 1 vol in the outer zone mg calcite exists as foliated crystals and spherulites while aragonite spherulites are restricted to the top surface the carbon isotope compositions of carbonates 13 46 5 to 33 0 vpdb and remnant bacterial mats 13 76 9 to 81 6 vpdb provide evidence of a biogenic methane source for the build up formation oxygen came mainly from sea water judging by a narrow range of 18 o values in carbonates 0 2 to 1 3 vpdb the prevalence of mg calcite throughout the build up indicates an anme 2 sbr consortium being the main component of the bacterial mats living at the seep aragonite grew mostly late in the seep history which hints to environmental changes and the ensuing predominance of the anme 1 sbr consortium the observed relationship between the prokaryotic communities and the main carbonate phases is common to the microbial mats of the black sea but is actually opposed to the pattern of aom community and aom related carbonates found in sediments different morphologies of carbonates in the outer and inner zones of the build up point to variations in the methane flux gradient which controlled the biomass density of the aom consortia the ree y patterns of mg calcite from the inner zone are typical of carbonates crystallised in a freshened sea water environment while both mg calcite and aragonite from the outer zone show distinct sea water signatures inasmuch as the time span of build up growth radiocarbon ages from 9000 180 to 7500 180 year bp overlaps the period when the black sea lake reconnected to the mediterranean sea the progressive arrival of sulphate rich waters can be inferred to be another possible control of ree y patterns in seep carbonates besides the methane flux gradient and related activity of aom consortia

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

original sediment composition of the lower cretaceous lacustrine tight oil mudstone and influences on diagenesis and organic matter content the erennaoer sag in erlian basin ne china abstract the original sediment composition is of great value to providing an understanding of depositional environment and hydrocarbon generation potential but it is easily altered by diagenesis and difficult to recognize in this study we examine carbonate rich tight oil mudstones of the lower cretaceous arshan formation in the erennaoer sag of the erlian basin as an example based on analyses of mineralogy stable carbon and oxygen isotopes and trace rare earth elements the original composition of the arshan mudstones has been reconstructed results show that the original arshan mudstone composition was mainly siliciclastic detritus tuffaceous and clay matrix which has a major impact on diagenesis and organic matter content the erupted volcanic ashes were beneficial to the introduction of nutrients an increase in biomass and an associated increase in to the preservation of organic matter which has been suggested by an improvement of toc of arshan tuffaceous mudstones with average contents of 2 82 the volcanic ashes in the studied mudstones had also enhanced methanogensis during the shallow burial additionally the early alteration products of authigenic minerals include analcime or zeolite most of which is entirely altered to analcime and chlorite the formation of major eogenetic carbonate cements include early dolomite and calcite which were related to volcanic materials and methanogenesis at shallow depths

chemoherms on hydrate ridge unique microbially mediated carbonate build ups growing into the water column two active chemoherm build ups growing freely up into the oceanic water column the pinnacle and the south east knoll chemoherms have been discovered at hydrate ridge on the cascadia continental margin these microbially mediated carbonate formations rise above the seafloor by several tens of meters and display a pinnacle shaped morphology with steep flanks the recovered rocks are pure carbonates dominated by aragonite based on fabric and mineralogic composition different varieties of authigenic aragonite can be distinguished detailed visual and petrographic investigations unambiguously reveal the involvement of microbes during the formation of the carbonates the fabric of the cryptocrystalline and fibrous aragonite can be described as thrombolitic fossilized microbial filaments in the microcrystalline aragonite indicate the intimate relationship between microbes and carbonates the strongly 13c depleted carbon isotope values of the samples as low as 48 1 pdb are characteristic of methane as the major carbon source for the carbonate formation the methane rich fluids from which the carbonates are precipitated originate most probably from a gas reservoir below the bottom simulating reflector bsr and rise through fault systems the 18o values of the aragonitic chemoherm carbonates are substantially higher as high as 5 0 pdb than the expected equilibrium value for an aragonite forming from ambient seawater 3 5 pdb as a first approximation this indicates formation from glacial ocean water but other factors are considered as well a conceptual model is presented for the precipitation of these chemoherm carbonates based on in situ observations and the detailed petrographic investigation of the carbonates this model explains the function of the consortium of archaea and sulfate reducing bacteria that grows on the carbonates performing anaerobic oxidation of methane aom and enabling the precipitation of the chemoherms above the seafloor surrounded by oxic seawater beggiatoa mats growing on the surface of the chemoherms oxidize the sulfide provided by sulfate dependent anaerobic oxidation of methane within an oxic environment the contact between beggiatoa and the underlying microbial consortium represents the interface between the overlying oxic water column and an anoxic micro environment where carbonate formation takes place

complex flow patterns through hydrate ridge and their impact on seep biota our recent measurements of long term fluid flux rates and output fluid chemistry at seep sites on hydrate ridge cascadia suggest that the mechanisms driving fluid flow in gas hydrate bearing forearc settings may be significantly more complex than previously thought temporal changes in the polarity and magnitude of flow and in seep fluid chemistry were observed the nature of flow appears to generate a strong response in the chemosynthetic seep community ecology we document here 1 the frequency and range of temporal variability in flow rates 2 the relatively rapid changes in outflow composition 3 strong outflow of seawater like fluids 4 the association of calyptogena sp clams with oscillatory and inflow settings and 5 microbial mat communities associated with strong advection of altered fluids these results suggest that a reappraisal may be required of the nature of the hydrologic system and its effect on related processes such as benthic seep community ecology and biogeochemical cycles

distribution and interpretation of rare earth elements and yttrium in cenozoic dolostones and limestones on cayman brac british west indies abstract the cenozoic carbonate succession on cayman brac a small island 19 km long and 1 5 to 3 km wide located in the caribbean sea has been dolomitized to varying degrees the rare earth element ree and yttrium y concentrations ree y of 134 carbonate samples 127 from cayman brac and 7 supplementary samples from grand cayman vary from 0 2 to 7 5 ppm average 2 8 ppm n 134 the shale normalized ree y patterns of the carbonate samples akin to those of oxygenated seawater are characterized by 1 lree depletion relative to hree average dy n sm n 1 7 n 125 2 positive la anomalies 3 negative ce anomalies average ce ce 0 4 n 133 and 4 superchondritic y ho molar ratios average y ho 85 n 86 the lack of correlation between the dolomite content of the samples and their ree y dy n sm n la n nd n ce ce or y ho indicates that dolomitization did not have a major impact on ree y signatures and that dolomitization was probably mediated by seawater like fluids the shale normalized patterns e g dy n sm n la n nd n ce ce and y ho vary from formation to formation for samples from the cayman formation the pedro castle formation and the ironshore formation there are subtle but gradual changes in dy n sm n la n nd n ce ce with depth in contrast there are marked changes in la n nd n ce ce y ho and sm nd across the brac unconformity which forms the boundary between the lower oligocene brac formation and the overlying miocene cayman formation variations in the ree y patterns reflect diagenetic processes e g dy n sm n and possibly secular changes in the ree y composition of seawater e g la n nd n y ho and sm nd

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

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

pore water geochemistry at two seismogenic areas in the sea of marmara within the sea of marmara the highly active north anatolian fault naf is responsible for major earthquakes mw 7 and acts as a pathway for fluid migration from deep sources to the seafloor this work reports on pore water geochemistry from three sediment cores collected in the gulfs of izmit and gemlik along the northern and the middle strands of the naf respectively the resulting data set shows that anaerobic oxidation of methane aom is the major process responsible for sulfate depletion in the shallow sediment in the gulf of gemlik depth concentration profiles of both sulfate and alkalinity exhibit a kink type profile the sulfate methane transition zone smtz is located at moderate depth in the area in the gulf of izmit the low concentrations observed near the seawater sediment interface for sulfate calcium strontium and magnesium result from rapid geochemical processes aom and carbonate precipitation occurring in the uppermost part of the sedimentary column and sustained by free methane accumulation barite dissolution and carbonate recrystallization have also been identified at deeper depth at the easternmost basin of the gulf of izmit this is supported by the profile of the strontium isotope ratios 87sr 86sr as a function of depth which exhibits negative anomalies compared to the modern seawater value the strontium isotopic signature also shows that these carbonates had precipitated during the reconnection of the sea of marmara with the mediterranean sea finally a first attempt to interpret the sulfate profiles observed in the light of the seismic activity at both sites is presented we propose the hypothesis that seismic activity in the areas is responsible for the transient sulfate profile and that the very shallow smtz depths observed in the gulf of izmit is likely due to episodic release of significant amount of methane