geochemical identification of marine and terrigenous condensates a case study from the sichuan basin sw china abstract condensates are extensively produced from the marine lower permian maokou formation and the lower triassic jialingjiang formation the main marine condensate producing strata in southern sichuan basin and also in the terrigenous upper triassic xujiahe formation in the central and southern sichuan basin based on the analyses of light hydrocarbons biomarkers and stable carbon isotopic compositions of marine and terrigenous condensates and the light hydrocarbon composition of natural gases in the jialingjiang fm and xujiahe fm in the sichuan basin the following conclusions are drawn a condensates produced from the carbonate reservoirs of jialingjiang fm and the maokou fm marine condensates belong to a single oil family and the condensates from the terrigenous xujiahe fm terrigenous condensates belong to another family b marine condensates were generated from sapropelic organic matter in the late stage of high maturation and the biomarker composition indicates that they were derived from the lower silurian shale and the lower permian carbonate while the terrigenous condensates were generated from mature humic source rocks c most of the marine condensates and gases encountered in the lower permian maokou fm and lower triassic jialingjiang fm were generated from the same source and a few of the gases in the jialingjiang fm contain admixtures of coal derived gas while terrigenous condensates and gases were generated from the xujiahe fm humic source rocks d effects that could be related to evaporative migration and biodegradation are not evident in the examined condensates

benthos communities in oxygen deficient shelf and upper slope areas of the peruvian and chilean pacific coast and changes caused by el nino

classification of sea floor features associated with methane seeps along the gulf of cadiz continental margin abstract based on recently gathered swath bathymetry high to ultra high resolution seismic and underwater camera data along with dredging and coring samples this paper examines the relationship between sea floor features and the nature of hydrocarbon enriched fluid and gas leaks from degassing of deeply buried sediments along the continental margin of the gulf of cadiz eastern central atlantic a classification into three main groups is proposed on the basis of the morphology and nature of deposits 1 mud volcanoes 2 methane derived authigenic carbonates mdac mounds and 3 crater like pockmarks mud volcanoes are topographically cone shaped sea floor edifices built up from catastrophic mud and fluid degassing intercalated with periods of inactivity so far more than 25 mud volcanoes have been discovered in the gulf of cadiz named in memory of deceased colleagues e g ginsburg and baraza or researchers birth places e g faro cibeles almazan san petersburgh yuma rabat bonjardim coruna gades these structures range from 800 to 2500 m in diameter and tower 150 300 m above the seabed the volcanoes consistently feature a well defined outer ring or circular terrace and an inner dome all mud volcanoes are built up of episodes of mud breccia flows intercalated with deep current deposits with evident indications of gas saturation degassing structures a strong h2s smell and chemosynthetic fauna such as pogonophora sp tube worms and calyptogena sp commonly observed carbonate crusts and slabs overlying some mud volcanoes are thought to have been formed by slow diffuse venting during periods of inactivity or slower rates of fluid venting following the ejection of mud a fermentation process the result of microbial mediated oxidation of hydrocarbon enriched fluids seems to play an important role in the growth of large deep water carbonate mounds and chimneys during periods of low methane seep fluid pressure more than 400 crater like pockmarks a common sea floor feature in the tasyo field have been observed their seabed diameter ranges from 500 to 3000 m with steep slopes ranging from 12 to 35 according to their internal structure pockmarks can be grouped into 1 pockmarks with low central mounds and 2 crater like pockmarks apparently collapse structures lacking central mounds with a flat to slightly undulating sea bottom surrounded by steep slopes up to 25

highly isotopically depleted isoprenoids molecular markers for ancient methane venting abstract we propose that organic compounds found in a miocene limestone from marmorito northern italy are source markers for organic matter present in ancient methane vent systems cold seeps the limestone contains high concentrations of the tail to tail linked acyclic c20 isoprenoid 2 6 11 15 tetramethylhexadecane crocetane a c25 homolog 2 6 10 15 19 pentamethylicosane pme and a distinctive glycerol ether lipid containing 3 7 11 15 tetramethylhexadecyl phytanyl moieties the chemical structures of these biomarkers indicate a common origin from archaea their extremely 13c depleted isotope compositions 13c 108 to 115 6 pdb suggest that the respective archaea have directly or indirectly introduced isotopically depleted methane derived carbon into their biomass we postulate that a second major cluster of biomarkers showing heavier isotope values 13c 88 is derived from sulfate reducing bacteria srb the observed biomarkers sustain the idea that methanogenic bacteria in a syntrophic community with srb are responsible for the anaerobic oxidation of methane in marine sediments marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined two membered bacterial consortium 1 archaea that perform reversed methanogenesis by oxidizing methane and producing co2 and h2 and 2 srb that consume the resulting h2 furthermore the respective organic molecules are unlike other compounds tightly bound to the crystalline carbonate phase the marmorito carbonates can thus be regarded as cold seep microbialites rather than mere authigenic carbonates

the puguang gas field new giant discovery in the mature sichuan basin southwest china the giant puguang gas field with a proven original in place gas volume of 350 109 m3 12 36 tcfg was discovered in 2003 in the eastern sichuan fold thrust belt of the mature sichuan basin southwest china the field is a combination structural stratigraphic trap closed by lateral depositional change and fault closure the trap evolved from a paleo oil reservoir originating in the triassic jurassic the entrapment of thermal gas which was derived from lower middle silurian and permian source rocks occurred during deep burial in the jurassic cretaceous tertiary quaternary compression transformed the paleotrap into the present gas reservoir gas is contained in the lower triassic feixianguan and the upper permian changxing reservoirs which consist predominantly of dolomitized oolites deposited in shelf and platform margin shoal and backreef environments reservoir quality is characterized by porosity of 1 29 and permeability of 0 01 9664 md with buried depth greater than 5000 m 16 400 ft the discovery of the puguang field exemplifies the successful application of a new play concept and new technology in a mature basin the discovery resulted from a shift in exploration strategy from structures to stratigraphic traps in reef and shoal dolomites and benefited from advanced high resolution seismic techniques the discovery will not only broaden the exploration scope in the sichuan basin but also provide an excellent analog for exploration in other fold thrust belts worldwide

concretionary methane seep carbonates and associated microbial communities in black sea sediments abstract gas seeps in the euxinic northwestern black sea provide an excellent opportunity to study anaerobic methane based ecosystems with minimum interference from oxygen dependent processes an integrated approach using fluorescence and electron microscopy fluorescence in situ hybridization lipid biomarkers stable isotopes 13c and petrography revealed insight into the anatomy of concretionary methane derived carbonates currently forming within the sediment around seeps some of the carbonate concretions have been found to be surrounded by microbial mats the mats harbour colonies of sulphate reducing bacteria dss group and archaea anme 1 putative players in the anaerobic oxidation of methane isotopically depleted lipid biomarkers indicate an uptake of methane carbon into the biomass of the mat biota microbial metabolism sustains the precipitation of concretionary carbonates significantly depleted in 13c the concretions consist of rectangularly orientated rod to dumbbell shaped crystal aggregates made of fibrous high mg calcite the sulphate reducing bacteria exhibit intracellular storage inclusions and magnetosomes with greigite fe3s4 indicating that iron cycling is involved in the metabolism of the microbial population transfer of fe3 into the cells is apparently mediated by abundant extracellular vesicles resembling known bacterial siderophore vesicles marinobactine in size 20 to 100 nm and structure

mud volcanism in the gulf of cadiz results from the ttr 10 cruise a new deep water mud volcano field between 2000 and 3500 m water depth was discovered in the deep south portuguese margin as well as several new mud volcanoes in the south spanish and western moroccan margins of the gulf of cadiz during the ttr 10 training through research unesco ioc cruise in july august 2000 this work followed the discovery of a large mud volcano field in the gulf of cadiz first investigated during the ttr 9 cruise gardner 2001 geophys res lett 28 339 342 kenyon et al 2000 ioc technical series no 56 the discoveries were made based on a seamap side scan sonar mosaic and multibeam bathymetry seabeam collected in the area by the naval research laboratory nrl washington dc usa in 1992 kindly released for this purpose single channel seismics long range side scan sonar okean tv controlled grab hull mounted 3 5 khz profiler and coring were used to investigate several seafloor features observed on the side scan sonar imagery in the south iberia spanish and moroccan margins of the gulf of cadiz which were confirmed to be mud volcanoes the typical structures related to fluid venting in the gulf of cadiz are essentially represented by conical mud volcanoes with diameters ranging from several tens of meters to 4 km and heights that can reach 200 m some of these structures appear to be aligned along major conjugate ne sw and nw se trending faults that can be identified on the side scan sonar imagery the new field discovered in the south portuguese margin is the deepest in the gulf of cadiz area and includes three new mud volcanoes bonjardim olenin and carlos ribeiro which seem to be quite active with near surface gas hydrate occurrence and a high saturation in h2s and hydrocarbon gases mainly methane in the mud breccia and overlying pelagic sediments gas hydrates were recovered from the bonjardim mud volcano an intensely gassified mud breccia with one fragment of semi consolidated claystone with a thin bituminous veneer at the surface was recovered from the carlos ribeiro mud volcano the fauna recovered consists mainly of pogonophoran worms belonging to several species and undetermined species of foraminifera three new mud volcanoes were also discovered in the nw moroccan margin rabat student and jesus baraza these show a richer fauna that includes several species of molluscs polychaetes pogonophoran worms crustaceans echinoderms and some fragments of dead coral madrepora and lophelia carbonate crusts were recovered from the student mud volcano the ginsburg mud volcano discovered during the previous ttr 9 cruise was revisited and gas hydrates recovered once again a new mud volcano was also discovered in the spanish margin tasyo where evidence was found of coral build ups on the hard substratum of the mud volcanic edifice

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

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

the pliocene age stirone river hydrocarbon chemoherm complex northern apennines italy abstract the stirone river section in the italian northern apennines hosts a rare example of pliocene age hydrocarbon imprinted carbonates in the mediterranean basin associated with deep water hemipelagic lithologies these include meter sized dolomite cemented chimneys micritic brecciated limestones lucina mudstones and chemosymbiotic bivalve shells some such chimneys show 13 c values as low as 37 5 vpdb suggesting subsurface precipitation of authigenic dolomite induced by anaerobic oxidation of methane triggered by consortia of sulphate reducing bacteria these carbonates are interpreted as part of the plumbing system related to hydrocarbon expulsion onto the seafloor resulting from hydrocarbon enriched defluidization processes dated at an interval at 3 6 3 3 ma and associated with the thrust related salsomaggiore structure

quantitative analyses of porosity evolution in tight grainstones a case study of the triassic feixianguan formation in the jiannan gas field sichuan basin china abstract tight grainstones although widespread throughout the lower triassic feixianguan formation in the sichuan basin have received little attention in part due to their lower porosity and greater heterogeneity relative to their dolostone counterparts based on data from cores and thin sections as well as petrophysical properties the feixianguan grainstones representing a major gas reservoir in the jiannan gas field were systemically analysed to better understand porosity evolution in tight carbonates that have experienced original oil accumulation and subsequent thermal cracking during progressive burial the grainstones were divided into two types according to whether pyrobitumen was present and their porosity evolutions were quantitatively reconstructed taking 40 as the original porosity the grainstones without pyrobitumen which were ineffective palaeo oil reservoirs lost 21 94 and 3 13 of their porosities through marine and burial calcite cementation respectively and 13 34 by compaction and have a current porosity of 1 59 thus allowing them to serve as major present day gas reservoirs comparatively pyrobitumen bearing grainstones which were once palaeo oil reservoirs lost 23 96 and 2 36 of their porosities through marine and burial calcite cementation respectively 11 4 by compaction and 1 44 by pyrobitumen and have a current porosity of 0 84 thus making them ineffective gas reservoirs this study provides a quantitative understanding of the close association between porosity evolution and reservoir effectiveness for the palaeo oil charge and present day gas accumulation with respect to diagenetic history which is useful for the future exploration in tight gas limestone reservoirs

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

seabed morphology and hydrocarbon seepage in the gulf of cadiz mud volcano area acoustic imagery multibeam and ultra high resolution seismic data abstract extensive mud volcanism mud diapirism and carbonate chimneys related to hydrocarbon rich fluid venting are observed throughout the spanish portuguese margin of the gulf of cadiz all the mud volcanoes and diapirs addressed in this paper lie in the region of olistostrome accretionary complex units which were emplaced in the late miocene in response to nw directed convergence between the african and eurasian plates the study area was investigated by multibeam echo sounder high and ultra high resolution seismic profiling dredging and coring the structures observed on multibeam bathymetry at water depths between 500 and 1300 m are dominated by elongate mud ridges mud cones mud volcanoes and crater like collapse structures ranging in relief from 50 to 300 m and size from 0 8 to 2 km in diameter the main morphotectonic features named the guadalquivir diapiric ridge gdr and the cadiz diapiric ridge cdr are longitudinally shaped diapirs which trend ne sw and consist of lower middle miocene plastic marly clays the gdr field and the tasyo field which consist of mud volcanoes and extensive fluid venting related to diapiric ridge development are described in this paper the gdr field is characterised by numerous single sub circular mud volcanoes and mud cones the single mud volcanoes are cone shaped features with relatively gentle slopes of 3 6 consisting of several generations of mud breccia deposition with indications of gas saturation degassing structures and the presence of h2s the mud cones have asymmetric profiles with steep slopes of up to 25 and contain large surficial deposits of hydrocarbon derived carbonate chimneys and slabs the tasyo field is characterised by an extensive concentration of small sub circular depressions oval and multi cone mud volcanoes and large sediment slides mud volcanoes in this area are characterised by moderate slopes 8 12 have bathymetric relief ranging from 100 to 190 m and consist of sulphide rich mud breccia calcite chimneys carbonate crusts and chemosynthetic fauna pogonophora tube worms we propose that all these hydrocarbon seepage structures are related to lateral compressional stress generated at the front of the olistostromic accretionary wedge this stress results in the uplifting and squeezing plastic marly clay deposits additionally the compressional stress at the toe of the olistostrome forms overpressurised compartments which provide avenues for hydrocarbon enriched fluids to migrate

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

gas charged sediments and large pockmark like features on the gulf of cadiz slope sw spain abstract gassy sediments and large seafloor pockmarks are identified from seismic profiles in the gulf of cadiz slope gas charged sediments are represented by zones of acoustic turbidity and other acoustic anomalies on seismic profiles most of the gas is believed to be biogenic in origin resulting from the decay of organic matter contained within rapidly developed regressive shelf margin deltas a group of large asymmetric seafloor pockmarks also occurs downslope of the gassy area both on the seafloor surface and deeply buried in the sediment column sediment sorting by the mediterranean undercurrent seems to act as a controlling factor for the development of each type of gas originated feature the area where the strong mediterranean undercurrent outflow impinges the seafloor is covered by sandy sediments of high porosity which allow the interstitial gas to escape through the sediment pores whereas the areas affected by weaker currents are covered by clays and the gas tends to accumulate in the sediment beneath impermeable horizons

structure and evolution of the olistostrome complex of the gibraltar arc in the gulf of cadiz eastern central atlantic evidence from two long seismic cross sections reflection profiles characterize the structure and the upper mesozoic to cenozoic deposits of the gulf of ca diz region two long ene wsw multichannel seismic lines ca 400 500 km long are analyzed to study the evolution of the area from the continental shelf to the horseshoe and seine abyssal plains the huge allochthonous deposits emplaced in this region the socalled olistostrome of the gulf of cadiz are described in terms of three different domains on the basis of the seismic architecture the main tectonic features and the nature of the basement oceanic or continental the eastern domain extends along the continental shelf and upper and middle slope and corresponds to the offshore extension of the betic rifean external front it is characterized by salt and shale nappes later affected by extensional collapses the central domain develops along the lower slope between the betic rifean front and the abyssal plains and is characterized by a change in dip of the allochthonous basal surface and the basement the allochthonous masses were emplaced by a combined gravitational and tectonic mechanism the northern boundary of this domain is marked by the occurrence of an outstanding wnw ese trending thrust fault with a strike slip component termed here as the gorringe horseshoe fault the westernmost domain corresponds to the abyssal plains where the distal emplacement of the allochthonous body takes place it is characterized by thrust faults affecting both the sedimentary cover and the oceanic basement the allochthonous masses show a less chaotic character and the thickness decreases notably these domains represent different evolutionary steps in the mechanisms of emplacement of the allochthonous units the eastern domain of the allochthonous units was emplaced as part of the pre messinian orogenic wedge related to the collision that gave rise to the betic rifean belt whereas the allochthonous wedge of the central and western domains were emplaced later as a consequence of the ne sw late miocene compression that continues in present times

sulfur and carbon isotopic compositions of the permian to triassic tsr and non tsr altered solid bitumen and its parent source rock in ne sichuan basin abstract reservoir solid bitumens from the permian to triassic and potential source rocks in the northeastern sichuan basin were measured for elemental and stable carbon 13c and sulfur 34s isotopic compositions to determine the chemical and isotopic composition of non tsr and tsr altered solid bitumen and to develop proxies to reflect the extent of bitumen alteration by tsr non tsr altered reservoir bitumen samples showed s c atomic ratios 0 03 and had 13c values closer to longtan formation p3l kerogen than to the lower silurian and cambrian kerogens and 34s values slightly more enriched than p3l kerogens the tsr altered solid bitumens have incorporated significant amounts of tsr derived h2s resulting in s c atomic ratios 0 047 0 074 and 34s values 13 4 24 0 being significantly higher than those of the solid bitumen not altered by tsr s c 0 013 0 030 34s 5 8 9 6 and the potential source rock kerogen the incorporation has produced a decrease in n c ratio and negative shift of 2 7 in 13c values that resulted from increasing tsr h2s back reactions with 12c rich n alkanes from the gas phase soluble solid bitumen or paleo oil to generate organic sulfur compounds such as ethanethiol that were incorporated into the solid bitumens which is followed by further aromatization and polymerization the solid bitumens show positive relationships of s c ratios and 34s values to the associated gas h2s h2s c1 6 or tsr extents and thus the s c ratios and 34s values can be used as proxies to reflect tsr extents

microbial processes controls on the shape and composition of carbonate concretions abstract shape size and mineralogical chemical compositions of carbonate concretions vary considerably the questions to be answered are why do they form at all what processes are involved why do they so often form as regular spheroids why do they sometimes form laterally extensive bands what controls whether the mineral composition is calcite dolomite rhodochrosite or siderite or mixtures of them the questions are addressed and the answers illustrated by selected examples carbonate precipitation is the result of the sedimentary system exploiting the potential energy provided by juxtaposing oxidised detrital input with reducing agents organic matter microbes take advantage of the energy source and are believed to be involved in most of the various processes pore waters in steadily accumulated sediments show a depth related succession of chemical and carbon stable isotope compositions this results from degradation of organic matter proceeding via an orderly succession of processes during burial each mediated by a specific microbial group aerobic oxidation using dissolved oxygen occurs first followed by mn iv reduced to mn ii as the oxidant fe iii reduction and sulphate reduction are probably more significant methanogenesis is the final deepest microbial process the common product of all these reactions is co 2 or dissolved hco 3 which can result in carbonate supersaturation the specific process controls the chemical and isotopic compositions of pore water and leads to a characteristic mineralogy of any carbonate precipitated however the processes may not proceed successively and localised micro environments occur recent work on siderite concretions in very young salt marsh sediments norfolk u k has shown that microbial populations are not homogeneously distributed and that these localise and control concretionary growth concretions in ancient rocks can be described in terms of the same processes observed in modern sediments laterally extensive siderite bands in bullhouse quarry westphalian u k resulted from interaction of two sets of complementary processes shallow manganese and iron reduction coupled with deeper methanogenesis and decarboxylation the model is supported by a mass and charge balance calculation similar complementary processes formed spheroidal concretions gammon shale usa but there is evidence that the outer shell of the concretion formed before the inner core and in the absence of a core the shell was crushed by burial compaction the spheroidal form resulted from diffusion of reactive components controlled by the relative rates of the contributory processes calcite or dolomite analogues of the siderite concretions are formed by similar processes but inhibition of carbonate precipitation makes it impossible to use an equilibrium mass balance model kimmeridge bay uk dolomite ledges are marine analogues to the bullhouse examples for the pyrite rimmed calcite jet rock concretions early jurassic yorkshire u k the rate of production of sulphide from sulphate reduction locally exceeded availability of fe ii to precipitate pyrite outward diffusion of sulphide produced the characteristic spheroidal shape of the concretion because of their developmental pattern bedded concretions are more likely to preserve a sequence of diagenetic cements which record the history of pore water evolution however all represent an expression in ancient rocks of microbiological processes similar to those operating today

structural evolution of organic matter and implications for graphitization in over mature marine shales south china abstract to characterize the degree of organic matter graphitization in the over mature lower paleozoic marine shales from south china a suite of kerogen samples covering different maturity ro ranging from 1 2 to 4 2 were analyzed by laser raman microprobe lrm transmission electron microscope tem and fourier transform infrared spectroscopy ftir techniques chemical structures and related major changes caused by thermal evolution history were systematically discussed the results indicate that with the thermal maturity increasing the aliphatic side chains fall off gradually and the aromatic rings increase continuously the ordered structure of shales continues to enhance leading to the increasing of graphitization degree the parameters of lrm i e position of g and d bands peak position difference rbs full width at half maximum fwhm and intensity ratio id ig highlight the turning point at maturity level around rmcro 3 5 which represents the chemical structure jump of the kerogen this chemical structure jump can be characterized by the continuous decreasing of amorphous carbon before the rmcro exceeded 3 5 and the sharp increasing degree of aromatic conjugation after that point tem analysis indicates that the carbon layers of shale samples with rmcro exceeds 3 5 show better ordering and continuity than that of low maturity shale samples the ftir analysis suggests that there are relatively high aromatics c c chains and very few aromatic c h chains in the high maturity samples this critical chemical structure jump at rmcro 3 5 could be interpreted as the structure of organic matter begins to transform from amorphous carbon to crystalline graphite in shales due to the increasing degree of graphitization graphitized shale is characterized by stable chemical structure condensed and orderly carbon layer constructure and ultra low resistivity

large scale slope failure involving triassic and middle miocene salt and shale in the gulf of cadiz atlantic iberian margin sheets of salt and ductile shale advancing beyond the thrust front of the gibraltar arc iberian moroccan atlantic continen tal margin triggered downslope movements of huge allochth onous masses these allochthons represent the cadiz nappe which detached from the gibraltar arc along low angle normal faults and migrated downslope from the iberian and moroccan continental margins towards the atlantic ocean extensional tectonics initiated upslope salt withdrawal and downslope diapirism during large scale westward mass wasting from the shelf and upper slope low angle salt and shale detachments bound by lateral ramps link extensional structures in the shelf to folding thrusting and sheets of salt and shale in the gulf of cadiz from backstripping analyses carried out on the depo centres of the growth fault related basins on the shelf we infer two episodes of rapid subsidence related to extensional collapses these were from late tortonian to late messinian 200 400 m myr 1 and from early pliocene to late pliocene 100 150 m myr 1 the extensional events that induced salt movements also affected basement deformation and were probably associated with the westward advance of frontal thrusts of the gibraltar arc as a result of the convergence between africa and eurasia the complexities of salt and or shale tectonics in the gulf of cadiz result from a combination of the deformations seen at convergent and passive continental margins

iron oxyhydroxide and sulphide mineralization in hydrocarbon seep related carbonate submarine chimneys gulf of cadiz sw iberian peninsula this paper aims to investigate the iron mineralization hosted in the submarine hydrocarbon seep related carbonate chimneys from the gulf of cadiz continental slope sw iberia chimneys are made of a general fine groundmass of major fe rich dolomite ankerite and calcite small grains of quartz and phyllosilicates and some foraminifer tests and ostracod shells primary porosity is frequently generated inside foraminifer chambers and ostracod shells and is filled with closely packed microcrystals of iron oxyhydroxide and sulphide minerals forming framboids some extremely peculiar multiframboidal textures are also detected corresponding to microcrystal groups spherical framboids and euhedral crystals without framboidal texture the mineralogy observed is mainly goethite pyrite pseudomorphs traces of tiny grains of pyrite were also observed cubic octahedral and pyritohedral are the habits observed in both minerals chemical analyses of framboids and euhedral crystals display high often erratic amounts of as co ni and mo in oxyhydroxides and mo pb v and co in sulphides versus almost always negligible concentrations of cu and zn a textural geochemical and mineralogical evolution is proposed to explain the coexistence of different morphologies in the multiframboidal texture a growth and aggregation of microcrystals as typical framboidal type mineralogical associations b development of euhedral habits c coalescence and homogenization of the microcrystal into large size euhedral to anhedral crystals and d formation of euhedral crystals or polycrystalline masses with complete loss of framboidal texture along this process an increase of the concentration of fe s mn and ti linked to a decrease in mg si al as p ca and v was observed the study of the iron mineralization in the gulf of cadiz is a first and can give clues to understand the complex geobiological interactions in this and other similar extreme hydrocarbon bearing submarine ecosystems

tectonics and mud volcano development in the gulf of cadiz many structures associated with fluid escape including mud volcanoes mud carbonate mounds pockmarks and slides have been identified and characterized in the gulf of cadiz most of the mud volcanoes following ne sw and nw se main trends are found at 350 2000 m depth in the eastern domain of the gulf of cadiz which corresponds to the betic rifean margin scattered mud volcanoes have also been recognized on the lower slope at 2300 3900 m depth the major tectonic structures are thrust faults extensional faults strikeslip faults and diapirs all these tectonic structures have provided escape pathways for overpressured material and fluids or have favoured upward fluid movement along the sedimentary column and eventually the build up of mud volcanoes in this work we present images of the mud volcano plumbing systems and the relationship between regional tectonics and mud volcano development seismic profiles acquired during the tasyo 2000 and mvseis ttr 15 cruises are used to image and interpret the link between the mud volcano edifices and the subsurface tectonic structures

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

introduction to the special issue signatures of microbes and microbial mats and the sedimentary record abstract the present special issue originated from a session ssp4 5 at the egu general assembly 2010 vienna microbes and microbial mat signatures and the sedimentary record this special issue comprises a set of papers that focus on several aspects of microbial and microbial mat signatures grouped into four major fields 1 microbial biomineralisation 2 microbial communities and mat related structures 3 organo sedimentary accretion and microbial deposits and 4 processes and products in submarine cold seeps and terrestrial mud volcanoes

compositional changes of surface sediments and variability of manganese nodules in the peru basin abstract two types of manganese nodules were observed in the peru basin large botryoidal nodules in basins and small ellipsoidal nodules on slope positions the sediment in areas with large botryoidal nodules contains a thinner and weaker oxidation zone than the sediment under small ellipsoidal nodules indicating that diagenetic processes in the sediment which supply manganese nodules with metals for their growth are stronger in sediments on which large botryoidal nodules grow organic matter which activates remobilization of metals occurs mostly in the form of refractory lipidic compounds in the inner capsule of radiolaria this material needs bacterial degradation to act as a reducing agent easily oxidizable organic components could not be found in the sediments other changes in sediment composition do not have a link to manganese nodule growth biogenous components radiolarians organogenic barite and apatite increase towards the equatorial high productivity zone authigenous clay minerals nontronite as well as montmorillonite with high fe 3 incorporation on positions of ochtaedral al increase with distance from the continent the assessment of environmental impacts will have to take into account the regional differences in sediment composition and the small scale variability of manganese nodules

bacterially induced dolomite precipitation in anoxic culture experiments to study the process of microbial mediated dolomite formation growth experiments were carried out with selected bacterial cultures under anoxic environmental conditions simulating those found in lagoa vermelha a hypersaline lagoon in brazil where dolomite precipitation occurs specifically we report the isolation of a particular strain of sulfate reducing bacteria lvform6 from lagoa vermelha sediment which apparently promotes the formation of nonstoichiometric dolomite sulfate reducing bacteria grown in a synthetic liquid medium produced dolomite during 30 days incubation at 30 c the precipitates have morphologies similar to those observed in lagoa vermelha sediment our results demonstrate that sulfate reducing bacteria can influence dolomite precipitation under controlled lowtemperature anoxic conditions and imply that anaerobic microorganisms can play an important role in carbonate sedimentation they may have been particularly significant in earth s earliest history when a more reducing atmosphere existed

depositional environment and thermal maturity of the coal bearing longtan shale in southwest guizhou china implications for shale gas resource potential abstract significant knowledge has been assembled on the marine longmaxi shale in the sichuan basin over the past ten years however the distribution of shale gas resources on the periphery of the sichuan basin and in other source rock formations are still not sufficiently understood to improve our understanding on the depositional environment and thermal maturity and their relevance to the source rock quality and shale gas potential of the thick coal bearing longtan shale 36 organic rich shale samples were selected from a single borehole located in the southwestern guizhou province for geochemical and petrographic analysis total organic carbon toc contents are high with 7 7 wt on average reaching partly up to 28 21 wt while carbonate contents are low vitrinite reflectance vrr values and rock eval tmax temperatures range from 1 48 to 1 84 and 482 to 583 c respectively indicating a high thermal maturity which is in accordance with aromatic molecular parameters the remaining present day hydrocarbon generation potential rock eval s2 is rather low due to the high maturity microscopic investigations further show that the organic matter in the rocks is mainly composed of higher land plant particles present as large and poorly rounded vitrinite and inertinite particles indicating a rather short transport distance toc vs total sulfur ts relationships as well as specific hydrocarbon ratios e g pristane phytane and framboidal pyrite size distributions indicate a variable either marine or freshwater environment for the shales in the coal bearing sequence and suggest that original kerogen was either type iii or type ii iii bottom water during deposition was probably oxygen depleted but not anoxic high sedimentation rates can be assumed for the now 700 m thick compacted sequence favorable for the preservation of organic matter overall the present results are in accordance with previous studies of the longtan shale which initially had a high hydrocarbon mainly gas generation potential furthermore the thickness of the formation is much larger in the here studied southwestern part of the guizhou province than in the previously studied northern parts

origin and carbon isotope fractionation of co2 in marine sour gas reservoirs in the eastern sichuan basin abstract according to gas chemical and carbon isotopic compositions for 75 gas samples from the eastern sichuan basin c 1 c 3 gaseous hydrocarbons are dominant with high dryness coefficient c 1 c 1 3 0 99 1 0 despite the presence of various contents of h 2 s and co 2 a reasonably good positive correlation is exhibited when both contents are 5 the carbon dioxide in the natural gas in the eastern sichuan basin mainly originated from carbonate dissolution by acid gases and thermochemical sulfate reduction tsr the content of co 2 produced at the early stage of acid gas dissolution is commonly 13 c co2 value 2 content exceeds 5 the 13 c co2 values range from 8 to 2 and the co 2 and h 2 s contents demonstrated a positive correlation the majority of co 2 is generated via tsr as well as acid gas dissolution during the late uplift of the basin particularly the co 2 with 13 c co2 value 2 generated via the tsr after it was partially precipitated to form calcite while the co 2 with 13 c co2 value 3 is a mixture of the co 2 produced early via tsr and the co 2 produced by the subsequent carbonate rock dissolution by acid gases

molecular structure and origin of solid bitumen from northern sichuan basin abstract four natural solid bitumen samples were collected from the guangyuan area northwest sichuan basin southwest china to characterize their structure samples were ground to power 120 mesh purified by znbr2 solution to remove mineral and soluble impurities and analyzed using rock eval pyrolysis elemental analysis raman spectroscopy solid bitumen reflectance and solid state 13c nuclear magnetic resonance to determine the maturity degree of samples and obtain structural information results showed that guangyuan solid bitumen samples are in low maturity and three solid bitumen maturity detection methods are compared in this research with respect to the solid bitumen molecular structure less than 10 carbon atoms were determined in aliphatic chains and the solid bitumen aromatic clusters ranged from two to four rings which indicates that the solid bitumen comprises complex geological organic matter such as kerogen four molecular models were established in this research to reflect the basic molecular configuration of natural solid bitumen samples were classified into two types based on the structural information and models and the results imply that the solid bitumen samples may have been derived via different evolutionary processes this phenomenon indicates that structural studies could play an important role in the research of oxidation and carbon isotope changes in solid bitumen in summary this investigation provides an understanding of the evolutionary stages of guangyuan bitumen establishes associated molecular structure models and researches the role of structural information in bitumen source studies as the focus of this study the four molecular models were used to restore the structural characteristics of natural solid bitumen as possible and this study tried to find out the relationship between the solid bitumen structure information and it geology evolution as the carbon isotope may not accurately determine the source of solid bitumen because of oxidation molecular information could be used to research the solid bitumen source and associated evolution

formation of carbonate pipes in the northern okinawa trough linked to strong sulfate exhaustion and iron supply abstract the microbial anaerobic oxidation of methane aom a key biogeochemical process that consumes substantial amounts of methane produced in seafloor sediments can lead to the formation of carbonate deposits at or beneath the sea floor although fe oxide driven aom has been identified in cold seep sediments the exact mode by which it may influence the formation of carbonate deposits remains poorly understood here we characterize the morphology petrology and geochemistry of a methane derived fe rich carbonate pipe in the northern okinawa trough ot we detect abundant authigenic pyrites as well as widespread trace fe within microbial mat like carbonate veins in the pipe the in situ 34 s values of these pyrites range from 3 9 to 31 6 vcdt suggesting a strong consumption of seawater sulfate by sulfate driven aom at the bottom of sulfate reduction zone the positive 56 fe values of pyrite and notable enrichment of fe in the ot pipe concurrently indicate that the pyrites are primarily derived from fe oxides in deep sediments we propose that the fe rich carbonate pipe formed at the bottom of sulfate reduction zone below which fe driven aom rather than fe oxide reduction coupled to organic matter degradation might be responsible for the abundantly available fe 2 in the fluids from which pyrites precipitated the fe rich carbonate pipe described in this study probably represents the first fossil example of carbonate deposits linked to fe driven aom because fe rich carbonate deposits have also been found at other cold seeps worldwide we infer that similar processes may play an essential role in biogeochemical cycling of sub seafloor methane and fe at continental margins

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

lipid biomarker patterns of methane seep microbialites from the mesozoic convergent margin of california abstract in order to reconstruct biogeochemical pathways at mesozoic methane seeps a set of late jurassic tithonian to early cretaceous aptian albian 13 c depleted seep limestones from forearc strata in western california were subjected to detailed molecular isotopic biomarker analyses two of the microbial carbonate deposits are turbidite hosted fault related whereas one is hosted in serpentinite in a diapir related setting the limestones contain 13 c depleted archaeal lipid biomarkers such as crocetane 13 c 80 and pmi 100 indicative of an involvement of anaerobic oxidation of methane aom in carbonate precipitation isotopically depleted crocetane in the tithonian sample represents the oldest reported occurrence of this compound at methane seeps in the set of samples a series of strongly 13 c depleted regular c 21 to c 24 isoprenoids possibly results from diagenetic alteration of archaeal sesterterpanylglycerol diethers as suggested by the presence of the putative intermediate 3 7 11 15 19 pentamethylicosanoic acid 13 c depleted 17 h 21 h and 17 h 21 h hopanes c 30 c 34 with 22 s and 22 r isomer couplets c 31 are present in all samples in distributions indicative of a moderate thermal maturity low 13 c values 78 to 60 suggest that these are derived from anaerobic bacteria involved in aom notably 22 s isomers are consistently enriched in 13 c relative to their 22 r counterparts our samples represent 70 myr of seepage activity and aom along the mesozoic margin of western california filling the gap between the currently oldest methane seep biomarker record from the oxfordian late jurassic and the more widely recognised cenozoic examples

ecology of a polymetallic nodule occurrence gradient implications for deep sea mining abyssal polymetallic nodule fields constitute an unusual deep sea habitat the mix of soft sediment and the hard substratum provided by nodules increases the complexity of these environments hard substrata typically support a very distinct fauna to that of seabed sediments and its presence can play a major role in the structuring of benthic assemblages we assessed the influence of seafloor nodule cover on the megabenthos of a marine conservation area area of particular environmental interest 6 in the clarion clipperton zone 3950 4250 m water depth using extensive photographic surveys from an autonomous underwater vehicle variations in nodule cover 1 20 appeared to exert statistically significant differences in faunal standing stocks some biological diversity attributes faunal composition functional group composition and the distribution of individual species the standing stock of both the metazoan fauna and the giant protists xenophyophores doubled with a very modest initial increase in nodule cover from 1 to 3 perhaps contrary to expectation we detected little if any substantive variation in biological diversity along the nodule cover gradient faunal composition varied continuously along the nodule cover gradient we discuss these results in the context of potential seabed mining operations and the associated sustainable management and conservation plans we note in particular that successful conservation actions will likely require the preservation of areas comprising the full range of nodule cover and not just the low cover areas that are least attractive to mining

a rock physics model for characterizing the total porosity and velocity of shale a case study in fuling area china abstract the total porosity in a shale gas reservoir is the key parameter to evaluate its potential production capability petroleum geologists have been pursuing an accurate way of predicting total porosity in shale gas reservoirs from logging curves in the fuling area near chongqing in china we use core test data and well logging data in order to establish a logging response model for porosity through the analysis of the data we found that the porosity and the p sonic p velocity have a strong correlation by combining our results with previous research i e physical rock data we establish a new model which better predicts the total porosity of a given a shale reservoir than the models established in previous research in addition to total porosity mineral composition pore pressure pore fluid type and confining pressure affect p velocity by taking a series of artificial cores as test objects and systematic analysis of total porosity mineral composition and content pore fluid type and pressure on the p velocity we establish response templates between every individual parameter and p velocity to this end we further establish a multi parameter rock physical characterization equation for the total porosity and p velocity and analyze its applicable conditions using the rich geological and geophysical data of the lower silurian series in the fuling area we gradually improve the model for the total porosity and verify the results using well logging data finally a set of accurate methods are established to predict the total porosity in shale gas reservoirs by using well logging data

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

water mass circulation on the continental shelf of the gulf of cadiz acoustic doppler current profiler data collected during three successive surveys in the gulf of cadiz in may june 2001 have been used to analyse the surface circulation on the continental shelves of the gulf of cadiz and how this circulation matches the circulation in the ocean side of the gulf the wider and larger eastern continental shelf holds a cyclonic circulation bounded at the south by a shelf break jet that is identified with the huelva front the coastal current that closes the gyre at the north is identified with the warm counterflow mentioned in the literature under westerly winds this counter current recirculates toward the east while recent upwelled water near cape santa maria is advected downstream by the shelf break jet leaving the cold signature at the surface that has been identified historically with the huelva front under easterlies part of the coastal counterflow invades the western continental shelf while the remaining recirculates eastward to close the cyclonic cell the western continental shelf and slope is occupied by a larger scale cyclonic eddy that extends into the deep ocean this eddy has vertical length scale of hundreds of metres and is linked to the general wind forcing in the area both cyclonic structures are bounded at the south by a jet that enters in the gulf of cadiz moving around the second eddy and eastward to feed the atlantic inflow through the strait of gibraltar r 2006 elsevier ltd all rights reserved

jiulong methane reef microbial mediation of seep carbonates in the south china sea chemoherm carbonates as well as numerous other types of methane seep carbonates were discovered in 2004 along the passive margin of the northern south china sea lithologically the carbonates are micritic containing peloids clasts and clam fragments some are highly brecciated with aragonite layers of varying thicknesses lining fractures and voids dissolution and replacement is common mineralogically the carbonates are dominated by high magnesium calcites hmc and aragonite some hmcs with mgco3 contents of between 30 38 mol extreme hmc occur in association with minor amounts of dolomite all of the carbonates are strongly depleted in 13c with a range from 35 7 to 57 5 pdb and enriched in 18o 4 0 to 5 3 pdb abundant microbial rods and filaments were recognized within the carbonate matrix as well as aragonite cements likely fossils of chemosynthetic microbes involved in carbonate formation the microbial structures are intimately associated with mineral grains some carbonate mineral grains resemble microbes the isotope characteristics the fabrics the microbial structure and the mineralogies are diagnostic of carbonates derived from anaerobic oxidation of methane mediated by microbes from the succession of hmcs extreme hmc and dolomite in layered tubular carbonates combined with the presence of microbial structure and diagenetic fabric we suggest that extreme hmc may eventually transform into dolomites our results add to the worldwide record of seep carbonates and establish for the first time the exact locations and seafloor morphology where such carbonates formed in the south china sea characteristics of the complex fabric demonstrate how seep carbonates may be used as archives recording multiple fluid regimes dissolution and early transformation events

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

molecular and carbon isotopic variability of hydrocarbon gases from mud volcanoes in the gulf of cadiz ne atlantic investigations of molecular and carbon isotopic variability of hydrocarbon gases from methane through butanes pentanes have been performed on six mud volcanoes from two fluid venting provinces located in the gulf of cadiz ne atlantic the main aims were to define the basic gas types to describe their geochemical characteristics in relationship to their sources and to determine the secondary effects due to migration mixing and microbial alteration hydrocarbon gas data reveal two groups of gases despite the different maturation characteristics both gas groups are allochthonous to the erupted mud breccia and represent a complex of redeposited secondary migrated mixed and microbially altered hydrocarbons it may possibly imply the presence of hydrocarbon accumulations in the deep subsurface of the gulf of cadiz

chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the barbados accretionary wedge chemical isotopic and heat budgets are controlled by fluid flow and venting at convergent margins fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes which are common at the barbados convergent margin chemical and isotopic compositions of fluids collected from four mud volcanoes located east of the barbados deformation front at 13 50 n indicate venting is sufficiently rapid to prevent diffusion from seawater in sediments surrounding the mud volcanoes the rate of nonfocused fluid flow is 0 26 cm yr although this rate is 3 orders of magnitude slower than the flow from the mud volcanoes significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes chloride concentrations are depleted to a minimum of 211 mm 45 of seawater value primarily by mixing diagenetically altered pore fluids with an 18o enriched fresh water released from the dissociation of methane hydrate this reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes the geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions 1 clay mineral dehydration which releases h2o and influences a range of chemical and isotopic compositions 2 organic matter regeneration which increases alkalinity nh4 and br and decreases so42 concentrations 3 cation exchange with clay minerals which increases na and decreases nh4 concentrations 4 carbonate recrystallization and precipitation which decrease ca2 but increase sr2 concentrations and 5 conversion of volcanic ash to clay minerals which utilizes h2o and decreases mg2 concentrations the geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from 75 to 115 c thus at the regional geothermal gradients of 27 to 40 c km these temperatures indicate that the source regions are at 2 to 4 5 km depth

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

branched alkanes from ancient and modern sediments isomer discrimination by gc ms with multiple reaction monitoring abstract linked scanning of a tandem sector mass spectrometer has been used to identify abundant first field free region ffr1 unimolecular fragmentations in branched and isoprenoid hydrocarbons the most intense structure specific reactions were selected to establish multiple reaction monitoring mrm parameters for gc ms analysis this methodology has been used to study the identity of co eluting and closely eluting hydrocarbon biomarkers from modern and ancient sediments anand from extant micro organisms some sediments of cambrian and proterozoic age have been found to contain suites of monomethylalkanes with all possible isomers present and with little apparent preference for the site of branching

the el arraiche mud volcano field at the moroccan atlantic slope gulf of cadiz the el arraiche field is a new mud volcano field discovered near the moroccan shelf edge in the gulf of cadiz that consists of 8 mud volcanoes in water depths from 200 to 700 m the largest mud volcano in the field al idrissi mud volcano is 255 m high and 5 4 km wide the cluster was discovered during a survey with the rv belgica and studied further during leg 2 of the ttr 12 survey onboard the r v prof logachev the 2002 surveys yielded detailed multibeam bathymetry over a 700 km 2 study area dense grids of high resolution seismic data deep tow sub bottom profiles sidescan sonar mosaics over the major structures selected video imagery lines video guided grab samples dredge samples gravity cores and box cores were collected for groundtruthing purposes eight mud volcanoes in water depths from 200 to 700 m cluster around two sub parallel anticlines and associated active extensional faults rock clasts and regional seismic data locate the el arraiche field over a late miocene pliocene extensional basin the onset of mud volcanic activity is estimated at about 2 4 ma and probably roots in the cretaceous miocene accretionary wedge stacked outflows are visible up to a depth of about 500 m below the sea floor the occurrence of long lived mud volcanoes bear witness to continued overpressure generation at depth either by in situ oil and gas generation or by focussed flow and accumulation in the area geochemical analyses of pore water from cores demonstrate the presence of thermogenic hydrocarbon processes the activity of the mud volcanoes is indicated by the thickness of hemi pelagic sediments covering extruded mud breccia the

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

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

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

origin of light volatile hydrocarbon gases in mud volcano fluids gulf of cadiz evidence for multiple sources and transport mechanisms in active sedimentary wedges widespread mud volcanism across the thick 7000 between sites mixing of shallow biogenic and deep thermogenic gases cannot account for the observed compositions which instead result mainly from extensive migration of thermogenic gases in the deeply buried sediments possibly associated with biodegradation of c2 homologues and secondary methane production at captain arutyunov and carlos ribeiro mvs at the deep water bonjardim olenin and carlos ribeiro mvs generation of c2 enriched gases is probably promoted by high heat flux anomalies which have been measured in the western area of the wedge at porto mv gases are highly enriched in ch4 having delta c 13 ch4 similar to 50 parts per thousand as at most sites but markedly lower delta h 2 ch4 values 250 parts per thousand suggesting that it is not generated by thermal cracking of n alkanes but rather that it has a deep archaeal origin the presence of petroleum type hydrocarbons is consistent with a thermogenic origin and at sites where ch4 is predominant support the suggestion that gases have experienced extensive transport during which they mobilized oil from sediments similar to 2 4 km deep these fluids then migrate into shallower thermally immature muds driving their mobilization and extrusion at the seafloor at porto mv the limited presence of petroleum in mud breccia sediments further supports the hypothesis of a predominantly deep microbial origin of ch4 c 2009 elsevier b v all rights reserved

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

ectosymbiosis associated with cidaroids echinodermata echinoidea promotes benthic colonization of the seafloor in the larsen embayments western antarctica ice shelf collapses in the larsen a and b embayments along the weddell side of the antarctic peninsula resulted in new open water areas that are likely reorganizing benthic communities it is a natural laboratory to assess colonization of the sea bottom under new conditions we tested the hypothesis that the epibionts associated to cidaroid echinoids could promote or enhance the colonization of hard surfaces in fact being vagile cidaroids might improve dispersal capabilities of the sessile animals that are attached to their spines e g promoting the colonization of areas where the fauna has been eradicated by iceberg scouring if this hypothesis is correct pioneer sessile species present locally on stones might have affinities with ectosymbionts on cidaroids and the sessile fauna present both on cidaroids and stones should be more similar in the larsen embayments than in undisturbed areas we therefore compared sessile species living on cidaroids with those living on stones in three areas larsen a and b embayments and two undisturbed and geographically different areas atka bay and elephant island overall richness evaluated as morphotypes richness was lower in the larsen area than in other areas but levels of species diversity were similar among the three zones the estimate of similarity between assemblages using the c 22 index of chao et al 2008 also suggests that cidaroid epibionts are either species specific or specific to cidaroids while the composition of sessile fauna on stones is more variable and probably dependent on local factors in the two undisturbed areas sessile fauna are highly different between stones and cidaroids this contrasts with the larsen embayments where cidaroids share more than 80 of epibionts with the surrounding stones these results suggest that ectosymbioses linked to cidaroids strongly contribute to benthic colonization of the seafloor in the larsen enbayments with time secondary successions are expected to occur increasing the difference between epibiotic communities on cidaroids and those on stones and lead to the situations observed in unperturbed sites

vast fields of hydrocarbon derived carbonate chimneys related to the accretionary wedge olistostrome of the gulf of cadiz we report the first discovery and sampling of vast fields of hydrocarbon derived carbonate chimneys along the gulf of cadiz continental slope at depths between 500 and 1200 m a large variety of carbonate chimneys more than 200 samples were recovered from four different areas named the diasom tasyo gbf guadalquivir basin and esf east moroccan fields observations from an underwater camera revealed a spectacular high density of pipe like chimneys some of them longer than 2 m lying over the sea floor and some protruding from muddy sediment local fissures and alignment of isolated chimneys were also observed suggesting that their distribution is controlled by fault planes chimneys collected show a wide range of morphological types spiral cylindrical conical mushroom like and mounded with numerous nodule protuberances and ramified fluid channelways the chimneys are mainly composed of authigenic carbonates ankerite fe bearing dolomite and calcite with abundance of iron oxides forming agglomerates of pseudo pyrite framboids n 18 o isotopic values vary from 0 7 to 5 5x whereas n 13 c values indicate that chimney carbonates are moderately depleted in 13 c ranging from 346x to 320x pdb interpreted as formed from a mixture of deep thermogenic hydrocarbons and shallow biogenic methane these vast fields of carbonate chimneys imply new considerations on the importance of hydrocarbon fluid venting in the gulf of cadiz and moreover on the active role of the olistostrome accretionary wedge of the gibraltar arc b 2003 elsevier science b v all rights reserved

the large scale environmental impact experiment discol reflection and foresight it is now accepted that environmental impact studies should accompany society s growing interest in exploiting deep sea resources a large scale experiment discol disturbance and recolonisation experiment in a manganese nodule area of the deep south pacific was conducted to evaluate potential impacts from mining on the deep sea bed discol was the first of a series of projects aimed at better understanding impacts of industrial scale mining of polymetallic nodules upon the seafloor and its biological community a schedule of biological work including a disturbance scheme and sampling patterns for another 12 year period is described that builds on the discol results but is strictly valid only for this area however future experiments may use estimates from the discol data as a first approximation in their planning phase but will need to conduct site specific sampling to establish a baseline

hydrocarbon derived ferromanganese nodules in carbonate mud mounds from the gulf of cadiz mud breccia sediments and clasts as nucleation sites abstract more than 500 fe mn nodules were sampled during the anastasya 01 cruise tasyo project along the continental margin of the gulf of cadiz eastern central atlantic at the confluence of the mediterranean sea with the atlantic ocean where extensive nodule fields were discovered based on wide previous studies that included swath bathymetry multi channel and very high resolution seismic reflection gravimetry magnetism and underwater photography surveys nodules were collected at water depths ranging from 850 to 1000 m associated with hydrocarbon derived ankerite and dolomite chimneys and crusts thirty six selected samples among the various morphological types were used for the laboratory analysis of physical properties morphology colour surface texture sphericity weight and size mineralogy xrd optical and electronic microscopy and geochemistry xrf aas icp ms epma gc ms s c and o isotopes nodules show a wide range of sizes densities weights and morphologies nodules are formed of multiple millimetre thick layers of fe and mn oxyhydroxides surrounding the nucleus composed of early middle miocene plastic marl the textures developed by the fe and mn oxyhydroxides layers are massive laminated detrital and mottled to dendritic goethite lepidocrocite mn oxides 7 a manganates and 10 a manganates quartz and phyllosilicates are the main components accessory minerals are calcite dolomite siderite rhodochrosite kutnohorite pyrite chalcopyrite potassium feldspar zircon rutile ilmenite and chlorite fe mn carbonates from the siderite rhodochrosite continuous series are forming part of the marl nuclei framboidal filamentous and globular textures are observed in fe mn oxides and pyrite suggesting biogenic origin nodules show a high mean abundance of fe 38 6 moderate mn 6 0 and low contents of trace metals and rees compared to the average content of deep seabed polymetallic nodules from other oceanic areas the mn fe ratio ranges from 0 07 to 0 25 the studied nodules hold in their oxide layers hydrocarbons n alkanes derived from marine bacterial activity aromatic hydrocarbons in the form of phenanthrene are also present which is characteristic of mature petroleum the structure mineralogy and chemical composition in the studied nodules are similar to those of diagenetic hydrogenetic continental margin nodules rather than deep sea nodules we suggest that the formation of this type of nodule occurred through a combined diagenetic hydrogenetic growth process involving fluid venting from deep seated hydrocarbon reservoirs bio mineralization processes and bottom current erosion

re establishment of an abyssal megabenthic community after experimental physical disturbance of the seafloor the suitability of deep sea megafauna as indicators of environmental change has been demonstrated by a large scale and long term disturbance and recolonisation experiment discol established in the deep peru basin in 1989 the experiment was designed to show what effects physical disturbances such as those caused by future commercial deep sea mining might have on the seafloor and its inhabitants a plough harrow was used to create a large scale disturbance on the seafloor it destroyed megafauna within the plough tracks to a large extent and buried the manganese nodules in the area as a result fauna that lived attached to the nodules disappeared the soft bottom community however did show signs of recovery in the seven years of the study the repopulation of the disturbed areas by highly motile and scavenging animals started shortly after the area was ploughed seven years later hemisessile animals had returned to the disturbed areas but the total abundance of soft bottom taxa was still low compared to the pre impact study nearby reference areas not impacted by the experiment showed natural changes in animal densities during the study the ploughing activities created a sediment plume that resettled in the surrounding areas in these not directly impacted areas animal densities declined immediately after the ploughing event but later appeared to be greater than in the reference areas of the pre impact study possible reasons for this are discussed

tracing organic compounds in aerobically altered methane derived carbonate pipes gulf of cadiz sw iberia abstract the primary geochemical process at methane seeps is anaerobic oxidation of methane aom performed by methanotrophic archaea and sulfate reducing bacteria srb the molecular fingerprints biomarkers of these chemosynthetic microorganisms can be preserved in carbonates formed through aom however thermal maturity and aerobic degradation can change the original preserved compounds making it difficult to establish the relation between aom and carbonate precipitation here we report a study of amino acid and lipid abundances in carbonate matrices of aerobically altered pipes recovered from the seafloor of the gulf of cadiz sw iberian peninsula this area is characterized by a complex tectonic regime that supports numerous cold seeps studies so far have not determined whether the precipitation of carbonate pipes in the gulf of cadiz is a purely chemical process or whether microbial communities are involved samples from this site show signs of exposure to oxygenated waters and of aerobic alteration such as oxidation of authigenic iron sulfides in addition the degradation index calculated from the relative abundance of preserved amino acids indicates aerobic degradation of organic matter although crocetane was the only lipid identified from methanotrophic archaea the organic compounds detected n alkanes regular isoprenoids and alcohols are compatible with an origin from aom coupled with bacterial sulfate reduction bsr and subsequent aerobic degradation we establish a relation among aom bsr and pipe formation in the gulf of cadiz through three types of analysis 1 stable carbon and oxygen isotopic composition of carbonate minerals 2 carbonate microfabrics and 3 mineralogical composition our results suggest that carbonate pipes may form through a process similar to the precipitation of vast amounts of carbonate pavements often found at cold seeps our approach suggests that some organic compound patterns in combination with additional evidence of aom and bsr may help indicate the source of altered methane derived carbonates commonly occurring in ancient and modern deposits

mudrock hosted carbonate concretions a review of growth mechanisms and their influence on chemical and isotopic composition existing interpretations of cement textures and isotopic compositions may significantly under estimate the depth and duration of concretionary growth minus cement porosities can commonly under estimate depths of concretionary growth for some or all of the following reasons i cements might not passively replace host sediment porosity ii non cement carbonate phases such as replaced bioclastic carbonate can be significant iii sediment compaction models over estimate rates of porosity loss at shallow carbon isotope data from modern sediments show that dissolved carbonate in the methanogenic zone has a continuum of values from 30 to 15 and thus overlaps 13 c depleted values normally considered characteristic of sulphate reduction many concretions previously thought to have grown entirely during sulphate reduction may therefore have continued cementation during methanogenesis indicating a deeper and more prolonged cementation history the necessary carbonate supersaturation for concretionary growth could either occur throughout the porewaters the equilibrium model or be generated in situ by organic matter decay the local equilibrium model or created where external fluids are introduced the fluid mixing model

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

distribution and circulation of water masses in the gulf of cadiz from in situ observations from data collected during golfo 2001 survey a study was conducted on the circulation and distribution of water masses in the gulf of cadiz in the spring of 2001 the general surface circulation in the gulf of cadiz is anticyclonic with

evaluation of the environmental consequences of polymetallic nodule mining based on the results of the tusch research association abstract realising a need for increased general knowledge of the deep sea for environmental impact assessments related to the permanent storage of waste products and mining of metal resources the german bundesministerium fur bildung und forschung has funded targeted research in the deep sea for more than 10 years the research was carried out in an area in the southeast pacific ocean close to and within a german mining claim to match the interests of german deep sea polymetallic nodule mining enterprises and the developing mining code of the preparatory commission for the international seabed authority and the international tribunal for the law of the sea the tusch abbreviation for tiefsee umweltschutz deep sea environmental protection research association with members from various university and governmental institutions was part of the atesepp effects of technical interventions into the ecosystem of the deep sea in the southeast pacific ocean project between 1996 and 1998 geotechnical sedimentological geochemical hydrographic numerical modelling and ecological studies relevant to environmental impact assessment studies of polymetallic nodule mining were undertaken since general oceanographic knowledge of the deep sea is rather limited these various projects also have increased our general understanding of this region this paper describes the potential impacts of mining processes on the seafloor and the near bottom water layer as well as on bathyal and abyssal pelagic zones that will receive processed water sediment and abraded nodule fines tailings discharged after nodule transport to the mining vessel at the ocean surface the tusch research association defined various recommendations to keep the unavoidable impacts to a minimum such as limited penetration of the mining system into the sediment confining intensive resedimentation to the area behind the miner minimising transport of sediment to the ocean surface and discharging all tailings at great depths ideally close to the seafloor the recommendations are not new but the present studies have improved them from precautionary to scientifically based statements

bioturbation coefficients of deep sea sediments from the peru basin determined by gamma spectrometry of 210pbexc abstract in the investigation of the impact of deep sea mining on the ecosystem the radioactive disequilibrium between 210pb and 226ra was studied in 16 surface sediment cores from the peru basin to obtain a quantitative measure of bioturbation gamma spectrometry was used as a fast non destructive simultaneous assay of 210pb and 226ra buried manganese nodules and geochemical anomalies affect the depth profiles of these two radioisotopes the calculated bioturbation coefficients show a high lateral variability this made it impossible to detect a significant difference in bioturbation between two different study areas

petroleum geology and geochemistry of the middle proterozoic mcarthur basin northern australia iii composition of extractable hydrocarbons abstract middle proterozoic organic rich sediments from the mcarthur basin in northern australia contain abundant hydrocarbons which are derived from syngenetic kerogen and hence are representative of the organic remains of microorganisms living at that time the major classes of hydrocarbons identified were n alkanes monomethyl branched alkanes cyclohexyl alkanes and acyclic isoprenoids there were also low abundances of pentacyclic triterpanes comprising hopanes and methyl hopanes low concentrations of steranes were present in most samples but like the triterpanes they were only easily detected in the least thermally altered sediments and hence were of limited use in detailed assessments of thermal maturity the presence of steranes in sediments of this age is strong evidence for the existence of eukaryotic organisms as far back as 1690 ma although the relatively high abundances of branched alkanes indicates that most of this primitive organic matter was probably derived from prokaryotes