gas hydrates clathrates causing pore water freshening and oxygen isotope fractionation in deep water sedimentary sections of terrigenous continental margins the occurrence of gas hydrates in deep water sections of the continental margins predicted from anomalous acoustic reflectors on seismic profiles has been confirmed by recent deep sea drilling results on the pacific continental slope off guatemala gas hydrates were brought up for the first time from two holes 497 498a drilled during leg 67 of the dsdp in water depths of 2360 and 5500 m respectively the hydrates occur in organic matter rich pleistocene to miocene terrigenous sediments in the hydrate bearing zone a marked decrease in interstitial water chlorinities was observed starting at about 10 20 m subbottom depth pore waters at the bottom of the holes near 400 m subbottom have as little as half the chlorinity of seawater i e 9 similar but less pronounced trends were observed during previous legs of the dsdp in other hydrate prone segments of the continental margins where recharge of fresh water from the continent can be excluded e g leg 11 the crystallization of hydrates like ice excludes salt ions from the crystal structure during burial the dissolved salts are separated from the solids subsidence results in a downward motion of the solids including hydrates relative to the pore fluids thawing of hydrates during recovery releases fresh water which is remixed with the pore fluid not involved in hydrate formation the volume of the latter decreases downhole thus causing downward decreasing salinity chlorinity hydrate formation is responsible for oxygen isotope fractionation with18o enrichment in the hydrate explaining increasingly more positive 18o values in the pore fluids recovered after hydrate dissociation with depth

microbial fabrics from neogene cold seep carbonates northern apennine italy abstract a number of hydrocarbon seep carbonate masses are hosted within miocene and pliocene siliciclastic units along the apennine range and sicily and are mainly composed of micritic and microsparitic textures geomicrobiological analysis of some of these deposits shows that preserved microbial processes are few and the contribution of microbe derived textures to their construction is volumetrically very limited in the carbonate groundmass of two northern apennine miocene and pliocene seep carbonate deposits uncommon and well preserved features suggest direct and indirect evidence of microbial activity some of these features are interpreted as the mineralization products of microbial textures and include complex alveolar textures and fossilized biofilms that line and fill microconduits pores and other voids similar to living bacterial aggregations recovered in modern seep carbonates other mineral structures such as spheroids and rhombs with concentric fabrics composed of calcite dolomite alternations abound as cement components and suggest a nucleation via bacterial sulfate reduction processes a similar origin is also assumed for the acicular aragonite bundles that in the miocene seep carbonate mass enclose dense clusters of millimeter size filamentous morphologies of biological origin

seep carbonates in a thrust related anticline at the leading edge of an orogenic wedge the case of the middle late miocene salsomaggiore ridge northern apennines italy abstract seep carbonates are important indicators of submarine fluid expulsion and dewatering of sediments along convergent margins and accretionary prisms in the northern apennine compressional wedge seep carbonates usually occur in pelitic successions from different settings of the middle late miocene foreland basin system in serravallian foredeep deposits of the salsomaggiore area seep carbonates cemented and or encrusted coarse grained sandstones and conglomerates fluid expulsion strictly related to variable intensities in tectonic stresses generated seep carbonate facies and sediment instabilities depending on the position of the fluid pathway feeders within the salsomaggiore ridge a middle late miocene intra basinal high at the leading edge of the apenninic orogenic wedge this site provides a unique opportunity for analyzing depositional characters and the three dimensional distribution and evolution of a seepage system in a thrust related anticline the resulting evolutionary model shares common features with recent ridges in other accretionary wedges in this model a strict relationship between tectonics seepage and sediment instability during a major tectonic phase is outlined

unraveling tectonic and climatic controls on synorogenic growth strata northern apennines italy we develop a new high resolution stratigraphic age model to unravel the contributions of tectonic and climatic processes on early to late pleistocene synorogenic growth strata we capitalize on excellent continuous exposures along the flank of the po foreland in northern italy to elucidate hydrologic geomorphic and sedimentologic processes that are regularly attributed to but rarely proven to be caused by glacial interglacial climatic changes and unsteady rock uplift we perform our analysis on the enza section a succession of marine and terrestrial strata exposed along the enza river between parma and reggio emilia northern italy bedding in the enza section displays synorogenic growth strata geometry with bedding dips that range from 2 to 55 that becomes progressively shallower upsection we develop an age model that incorporates biostratigraphy magnetostratigraphy rock magnetic cyclostratigraphy cosmogenic radionuclide burial dating and optically stimulated luminescence dating and shows that the enza section spans the interval between 0 04 and 1 65 ma furthermore the age model pins the time of deposition for several lithostratigraphic units of regional significance and shows that sediment accumulation was unsteady ranging from 14 31 cm k y in the marine part of the section to 5 362 cm k y in the overlying littoral and terrestrial part of the section unsteady deposition is most pronounced in the terrestrial deposits where thick fluvial gravel packages accumulated in short 10 15 k y time periods that coincide with quaternary glacial intervals there is direct evidence for a dominant tectonic control in the older marine part of the section here sediment accumulation rates on the limb of the fold growing along this portion of the northern apennine mountain front show that between 1 07 and 1 65 ma repetitive progradation of neritic sand units directly followed pulses of rapid punctuated uplift in contrast the cyclic terrestrial facies variations in the enza section reveal that once the section became emergent at ca 1 ma and uplift slowed climate was the dominant control on sediment production and deposition

a new approach to discern the hydrocarbon sources oil vs methane of authigenic carbonates forming at marine seeps abstract numerous marine hydrocarbon seeps have been discovered in the past three decades the majority of which are dominated by methane rich fluids however an increasing number of modern oil seeps and a few ancient oil seep deposits have been recognized in recent years oil seepage exerts significant control on the composition of the seep dwelling fauna and may have impacted the marine carbon cycle through geological time to a greater extent than previously recognized yet distinguishing oil seep from methane seep deposits is difficult in cases where 13ccarb values are higher than approximately 30 due to mixing of different carbon sources here we present a comparative study of authigenic carbonates from oil dominated site gc232 and methane dominated site gc852 seep environments of the northern gulf of mexico aiming to determine the geochemical characteristics of the two types of seep carbonates we analyzed 1 major and trace element compositions of carbonates 2 total organic carbon toc total nitrogen tn and carbon isotope 13ctoc of residue after decalcification 3 sulfur isotope signatures of chromium reducible sulfur crs 34scrs and residue after crs extraction 34stos as well as 4 sulfur contents tos of residue after crs extraction carbonates from the studied oil seep are dominated by aragonite and exhibit lower 34scrs values suggesting carbonate precipitation close to the sediment surface in addition oil seep carbonates are characterized by higher toc and tos contents and higher toc tn ratios as well as less negative 13ctoc values compared to methane seep carbonates probably reflecting a contribution of residual crude oil enclosed in oil seep carbonates very low 13ctoc values as low as 68 7 vpdb and low toc tn ratios of methane seep carbonates indicate that the enclosed organic matter is derived mainly from the biomass of methanotrophic biota this study presents new geochemical data that will allow the discrimination of oil seep from methane seep deposits although some of the geochemical patterns are likely to be affected by late diagenesis if applied with caution such patterns can be used to discern the two end member types of seepage oil seeps and methane seeps in the geological record

light toned salty soils and coexisting si rich species discovered by the mars exploration rover spirit in columbia hills 1 light toned soils were exposed through serendipitous excavations by spirit rover wheels at eight locations in the columbia hills their occurrences were grouped into four types on the basis of geomorphic settings at three major exposures the light toned soils are hydrous and sulfate rich the spatial distributions of distinct types of salty soils vary substantially with centimeter scaled heterogeneities at paso robles dead sea shredded and champagne penny a well mixed nature for light toned soils occurring near and at the summit of husband hill and relatively homogeneous distributions in the two layers at the tyrone site aeolian fumarolic and hydrothermal fluid processes are suggested to be responsible for the deposition transportation and accumulation of these light toned soils in addition a change in pancam spectra of tyrone yellowish soils was observed after being exposed to current martian surface conditions for 175 sols this change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface si rich nodules and soils were observed near the major exposures of s rich soils they possess a characteristic feature in pancam visible near infrared vis nir spectra that may be diagnostic of hydrated species and this spectral feature can be used to search for additional si rich species the exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the neutron spectrometer on mars odyssey

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

ice 5g and ice 6g models of postglacial relative sea level history applied to the holocene coral reef record of northeastern st croix u s v i investigating the influence of rotational feedback on gia processes at tropical latitudes abstract fossil coral reefs along the northeastern coast of st croix in the caribbean sea provide an 8000 year record of dated and interpreted holocene sea level change we herein compare this record with the predictions of models of glacio hydro isostatic adjustment for st croix and for additional sites at similar latitudes in the greater and lesser antilles region rsl predictions are based upon the model ice 5g vm2 and with a modified model ice 6g vm5a both including and excluding the influence of rotational feedback misfits between the modeled sea levels and the local geologic data are most apparent for models without rotational feedback particularly in the prediction of a 2 to 4 m unsupported mid holocene misfit at 4 ka as well as a small amplitude highstand that extends from 2 5 to 1 5 ka incorporation of the influence of rotational feedback provides the best fit to the data largely eliminating the unsupported mid holocene misfit between the data field and the sea level histories predicted by the models without rotational feedback and fitting data older than 5 kyr more closely than a previously published latitudinally averaged sea level curve for the western atlantic the st croix data therefore demonstrate that rotational influence extends at least 27 further south from its 45 n mid latitude extremum along the us east coast and identifies tropical latitudes as influenced by proglacial forebulge collapse implications for reef based sea level reconstruction include the ability to accurately model sea levels at specific tropical sites with partial holocene chronologies using the ice 6g vm5a model with rotational feedback latitudinally averaged sea level curves are therefore of limited use in understanding the relative importance of contributing physical influences on postglacial sea level history

a genetic model of hydrocarbon derived carbonate chimneys in shelfal fine grained sediments the enza river field northern apennines italy abstract methane derived authigenic carbonate mdac concretions have been recently exposed in the pleistocene argille azzurre fm outcropping along the enza riverbanks northern apennines foothills italy the relations between the sediment deposition the coeval tectonic deformation and the mdac concretions have been investigated to unravel the mechanism of methane migration through the sediments and the processes leading to mdac occurrence the biogenic methane responsible for the formation of mdac chimneys and slabs has been generated in the organic rich pliocene sediments located in the po plain subsurface the gas migrated up dip towards the northern apennines foothills the mdac cements are mainly composed of dolomite whose precipitation requires thousand years and the absence of so 4 in the pore fluids according with the sedimentation rates of the mdac hosting pleistocene succession the sulphate methane transition zone migrated upwards faster than time required for dolomite precipitation therefore the connate water migrating together with the methane could have acted as second dic source allowing the mdac formation also in the methane rich zone

effect of injection rate on hydraulic fracturing in naturally fractured shale formations a numerical study this paper studies the effect of fluid injection rate on hydraulic fracturing in pre existing discrete fracture network dfn formations a flow stress damage coupling approach has been used in an initial attempt toward how reservoir responses to injection rate under different dfn connected configuration states the simulation results show that injection rate has an significant influence on the hydraulic fractures hf and dfn interaction and hydraulic fracturing effectiveness which can be characterized by the total interaction area stimulated dfn length stimulated hf length and leak off ratio for the sparse dfn model stimulated hf length increases with increasing injection rate and the stimulated dfn length decreases with the increasing injection rate for the medium dfn model stimulated hf and dfn length both increase with increasing of injection rate for the dense dfn model length of stimulated hf deceases with increasing injection rate however the stimulated dfn length increases with the increasing injection rate the effect of injection rate on hydraulic fracturing is closely related to formation characteristics which are strongly affected by the dfn connected configuration for the studied fracture network the sparse dfn model gets the optimal hydraulic fracturing effectiveness with lower injection rate however the dense dfn model has the best hydraulic fracturing effectiveness with higher injection rate this work strongly links the production technology and hydraulic fracturing effectiveness evaluation and aids in the understanding and optimization of hydraulic fracturing simulations in naturally fractured reservoirs

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

cenozoic dolomites of carbonate islands their attributes and origin abstract dolomites found on and below carbonate islands atolls and oceanic platforms provide useful insights into the origin of dolomite insights that may not be attainable from the study of more ancient cratonic dolomites for this reason they have been the subject of study for decades a critical mass of case studies now exist and some significant conclusions can be drawn from the cumulative data in most cases the association with an island is causal and not genetic nevertheless these dolomite occurrences are referred to herein as island dolomites one type of dolomite on carbonate islands is penecontemporaneous dolomite a phase that forms while the host sediment is in its original depositional setting island examples are holocene in age occur in holocene sediments and originate as a direct precipitate from either normal or evaporated seawater these are microcrystalline poorly ordered ca rich 18o enriched and geochemically unstable phases that are susceptible to recrystallization in the setting in which they formed post depositional dolomite is the other type of dolomite associated with carbonate islands this type of dolomite replaces older precursors and forms as cement distinctive characteristics include a dominance of fabric preserving texture pore lining cement rims that may exhibit micron scale banding with low mg calcite and formation in association with precursor dissolution sr isotopic dating indicates that all examples are neogene or quaternary in age those formed during the middle miocene through pliocene are massive laterally continuous and often multigenerational in contrast younger examples tend to be localized partial replacements of a single generation sr isotope ages also suggest global synchroneity in many dolomitization events which suggests a connection between dolomitization global eustacy and or global climatic factors geochemical attributes of post depositional island dolomites are ca enrichment positive 18o and 13c low sr contents 150 300 ppm and low fe global similarity in petrography and geochemistry of replacive island dolomites argues for a similar origin inferred origins however depend primarily on how 18o and sr data are interpreted values for 18o and dsr must be assumed due to uncertainties in oxygen isotope fractionation and sr partitioning there is no consensus or uniformity in those assumptions thus interpretations can vary and be biased to a desired result covariant trends in 13c and 18o some negative 13c values and high sr all favor a mixing zone origin but examples with these attributes are few lack of covariance in the isotopes mean 18o of 2 0 to 3 5 and low sr future studies should standardize the type of data collected and the analytical techniques employed multiple geochemical attributes should be measured on microsampled components and quantitative modeling should be employed in order to constraint interpretations as much as possible also needed are a better understanding of the kinetic processes that form these dolomites more careful assessment of their recrystallization status and an improved understanding of dsr and 18o at low temperature

methane derived carbonate conduits from the late aptian of salinac marne bleues vocontian basin france petrology and biosignatures abstract peculiar carbonate bodies occur in distinct marl layers of the marnes bleues formation aptian albian vocontian basin southern france the carbonate conduits exhibit pipe or sausage like forms and a central channel their sizes range between 30 and 60 cm in length and 5 10 cm in diameter the conduit carbonates consist of automicrite authigenically formed within the sediment millimeter sized aggregates of framboidal pyrite are abundant within the conduit automicrites probably representing former colonies of sulfate reducing bacteria the central channel reflects former pathways of reduced fluids in the carbonate conduit ni enrichments at the margins of the central cavity are may be due to the activity of methane related metabolism as ni is an important bio element for respective microbes light stable carbon isotope ratios of the conduit automicrites 25 86 to 23 10 vpdb point to carbonate precipitation linked to anaerobic oxidation of methane aom while less depleted stable carbon isotope ratios of microspar in marginal zones of the central opening 8 96 vpdb are in line with microbial sulfate reduction a methane related origin of the conduit carbonates is confirmed by the presence of authigenic lipid biomarkers tentatively sourced by archaea most of which are characterized by strong 13 c depletions 13 c values down to 104 the presence of organically bound sulfur is well in line with microbial sulfate reduction isorenieratane potentially point to the presence of brown pigmented green sulfur bacteria the methane was probably sourced by older oae black shales which are known to contain isotopically 13 c heavy biomarkers of archaea as reported elsewhere

authigenic carbonate formation and its impact on the biomarker inventory at hydrocarbon seeps a case study from the holocene black sea and the plio pleistocene northern apennines italy carbonates are widespread at methane and petroleum seeps and are often precipitated as consequence of an alkalinity increase due to the anaerobic oxidation of methane aom or less often reported of higher hydrocarbons these carbonates are taphonomic windows into earth s history because they excellently protect the in situ formed microbial signatures e g lipid biomarkers from diagenetic destruction a complication for paleoreconstructions however is that seep carbonates also encapsulate variable amounts of allochthonous organic matter sometimes even completely obscuring authigenic microbial signatures seep carbonates from the holocene black sea the pleistocene enza river and the pliocene san lorenzo both northern apennines italy provide hints to better understand i the importance of processes other than aom for the formation of seep carbonates and ii the controls of allochthonous and autochthonous contribution of biomarkers to organic matter in seep carbonates biomarker distributions in different parts of a black sea carbonate clearly demonstrate that high allochthonous organic matter is entrapped if aom carbonates are formed intrasedimentary particularly if methane supply is relatively low and external organic matter input high high allochthonous contributions were also found in the biomarker inventory of ancient seep carbonates from the italian northern apennines enza river and san lorenzo pointing at their precipitation within the sediment specific and complex conditions were indicated from our data for the enza river location carbonate facies and particularly biomarker compositions with abundant signatures of sulfate reducing bacteria suggest that sulfate reduction using alkaline and eventually sulfate and higher hydrocarbon enriched fluids triggered the growth of these seep carbonates our and other data suggest that this process has to be more considered if interpreting seep settings particularly where microbial processes rely on rising fluids from deep petroleum reservoirs

authigenic carbonates in upper miocene sediments of the tertiary piedmont basin nw italy vestiges of an ancient gas hydrate stability zone a wide array of carbonate rich rocks has been recognized in the tertiary piedmont basin nw italy hosted in lower messinian slope deposits carbonate cements show negative 13 c values and positive 18 o values suggesting that carbonate precipitation was induced by microbial degradation of methane produced from gas hydrate destabilization two groups of rocks have been distinguished 1 lucina bearing mud breccias representing the seafloor product of an ancient seepage site and 2 lucina free concretions originating below the sediment water interface within this group two subtypes have been further distinguished stratiform concretions and cylindrical concretions stratiform concretions result from precipitation of dolomite in the pores of muddy sediments some of them display a brecciated structure others show a network of septarian like cracks that are empty filled with sediments or zoned carbonate cements their internal features are related to the formation of gas hydrates within the sediments and to their destabilization thus these rocks mark a portion of the sedimentary column located within a paleo gas hydrate stability zone cylindrical concretions represent ancient fluid conduits related to the upward migration of ch 4 rich fluids subsequent to gas hydrate destabilization the carbonate rich rocks of the tertiary piedmont basin stand as one of the first examples of methane derived rocks that record successive episodes of dissociation and re formation of gas hydrates and they provide precious elements to model the general evolution of a portion of the sedimentary column located within the hydrate stability zone

carbon oxygen and strontium isotopic constraints on fluid sources temperatures and biogeochemical processes during the formation of seep carbonates secchia river site northern apennines abstract understanding authigenic seep carbonate formation provides clues for hydrocarbon exploration and insights into contributions to gas budgets of marine environments and the atmosphere seep carbonates discovered in the outcropping succession along the secchia riverbanks near modena italy belong to the argille azzurre formation of early pleistocene age deposited in an upper shelf environment overlying the miocene foredeep successions which include hydrocarbon fields the fluid migration from the hydrocarbon fields up to the surface is presently active on land and started in the marine succession during the late miocene authigenic globular carbonate concretions and carbonate chimneys are interspersed along the strata throughout the section a comprehensive geochemical characterisation of the carbonates has been carried out to understand the processes leading to their formation the carbonate concretions are the record of past hydrocarbon vents linked to the miocene petroleum system of the northern apennines the samples are composed of 50 microcrystalline dolomite the 13 c signatures identify two groups in the samples according to different type of formation processes globular concretions have positive values that suggest an influence of co 2 associated to secondary methanogenesis due to microbial degradation of higher hydrocarbons the analysed chimney with negative 13 c values is interpreted as former conduit where carbonate precipitation is promoted by anaerobic oxidation of methane coupled with sulfate reduction the 18 o range coupled with 87 86 sr signatures indicate that the contribution of deep connate water from the miocene reservoirs is up to 23 during the formation of the globular concretions the connate water occurrence is also documented by higher ambient temperatures the different isotope signatures in seep carbonates result from the relative contribution of the recognised gas and water components linked to different plumbing systems and fluid supply from a well defined hydrocarbon field the seep carbonate characteristics have enlightened variations in biogeochemical processes which can be rarely quantified in ancient and present day marine environments

a study of the chemistry of pore fluids and authigenic carbonates in methane seep environments kodiak trench hydrate ridge monterey bay and eel river basin analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the kodiak trench hydrate ridge monterey bay clam flats and the eel river basin coupled with the studies of the chemistry of the pore fluids have shown that these carbonates have grown within the sediment column geochemical profiles of pore fluids show that in deep water seeps kodiak trench 4450 m monterey bay 1000 m hydrate ridge 650 m 13c dic values are low isotopically light whereas in the eel river area 350 500 m 13c dic values are much higher isotopically heavier in all cases the 13c values indicate that processes of methane oxidation associated with sulfate reduction are dominant in the shallow sediments data on the isotopic composition of authigenic carbonates found at sites in kodiak trench eel river basin south and eel river basin north indicate a variable composition and origin in different geochemical environments some of the authigenic carbonates from the study sites show a trend in their 13c values similar to those of the pore fluids obtained in their vicinity suggesting formation at relatively shallow depths but others indicate formation at greater sediment depths the latter usually consist of high magnesium calcite or dolomite which from their high values of 13c up to 23 and 18o up to 7 5 suggest formation in the deeper horizons of the sediments in the zone of methanogenesis these observations are in agreement with observations by other workers at hydrate ridge in monterey bay and in the eel river basin

terrestrial methane seeps and mud volcanoes a global perspective of gas origin abstract a global database of gas composition and methane stable isotopes of 143 terrestrial mud volcanoes from 12 countries and 60 seeps independent from mud volcanism from eight countries was compiled and examined in order to provide the first worldwide statistics on the origin of methane seeping at the earth s surface sixteen seep data were coupled with their associated subsurface reservoirs the surface seepage data indicate that at least 76 of the mud volcanoes release thermogenic gas with only 4 biogenic and 20 with mixed character the average 201 data of methane concentration and methane carbon isotope ratios 13 c 1 of mud volcanoes are 90 v v and 46 4 respectively the other types of seeps which are independent from mud volcanism have an average 13 c 1 value that is slightly higher 42 9 gases from mud volcanoes are generally lighter more methane less ethane and propane than their associated reservoir gases suggesting a molecular fractionation during advective fluid migration other types of seeps especially dry seeps maintain the reservoir c 1 c 2 c 3 bernard ratio mud volcanoes behave like a natural refinery and the origin of gas more isotopically enriched than 50 and with c 1 c 2 c 3 500 should be attributed to a thermogenic source rather than partial oxidation of biogenic gas some data that appear biogenic in the bernard diagram can be explained by molecular fractionation of mixed gas consequently the bernard parameter may be misleading when applied to mud volcanoes since it does not always reflect the original gas composition the mechanisms of the molecular advective segregation should be studied quantitatively by specific models and experiments

when did the northern apennine become a mountain chain abstract the purpose of the present paper is to bracket the age of the initial uplift of the northern apennine chain by means of all the available evidence the collected data show that the age of the lacustrine or fluvio lacustrine units which have aggraded in the intramontane basins is late pliocene in the northwestern tip of the northern apennine and mostly early pleistocene elsewhere the age of the oldest terraced fluvial deposits showing the initiation of incision is mostly middle pleistocene the uplift of the summit areas of low relief most likely took place during the middle pleistocene it is concluded that the uplift occurring during middle and upper pleistocene caused an area of rather low relief to become the northern apennine mountain chain an eastward shift of the uplift through time is likely

productivity generated annual laminae in mid pliocene sapropels deposited during precessionally forced periods of warmer mediterranean climate abstract paleoproductivity estimates for a sequence of five mid pliocene mediterranean sapropels illustrate the importance of insolation maxima in enhancing organic carbon accumulation well laminated sapropelitic intervals in the northern apennines have been studied by a combination of sedimentological and micropaleontological analysis detailed electron microscope description bulk chemical composition carbon isotopic composition and elemental ratios each sapropel formed during precessional minima lasted 7 5 to 10 kyr which is the same duration calculated for coeval counterparts in odp sites in the eastern mediterranean the organic carbon mass accumulation rates of the studied sapropels show the same values of those calculated in the coeval mediterranean sapropels suggesting that the same productivity conditions were controlling sapropel formation in the whole mediterranean despite the differences in depositional setting and the strong variations in sedimentation rate mat forming diatoms play an important role in increasing the settling velocity allowing rapid sinking of organic matter and preventing bacterial remineralization in the water column the consequent partial oxygen depletion at the seafloor increases preservation which is therefore considered an effect rather than a cause of the organic carbon accumulation

petroleum exploration in italy a review abstract petroleum exploration in italy began in the second half of the 19th century but the first consistent discoveries were only made after world war ii at present the original reserves of the italian petroleum fields amount to about 160 million tons of oil and 720 billion cubic metres of gas domestic production in 1990 was 4 6 million tons of oil and 17 3 billion cubic metres of gas the lithology of the italian sedimentary sequences was controlled by the geodynamic evolution of the western margin of the adria plate the permian triassic continental and shallow water environments pre dating the break up of pangea were followed by subsiding carbonate platforms and basins in the mesozoic tertiary compressive tectonics induced by the subduction of the adria continental margin produced a complex thrust belt bordered by a migrating foredeep filled with clastic sediments most of the oil and a minor part of the gas were generated by middle triassic lower jurassic shaly and carbonate source rocks most of the gas was sourced by pliocene pleistocene clays in the foredeep turbiditic deposits and has a bacterial origin a short review integrated with some actual examples of typical fields cortemaggiore costa molina settala agostino porto garibaldi barbara candela palino rospo vega exemplifies the different plays in the main tectonic domains

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

fission track reconstruction of the front of the northern apennine thrust wedge and overlying ligurian unit in the northern apennines foreland the marnoso arenacea formation ma fm records post depositional burial temperatures overlapping with those of the zone of partial annealing of apatite fission tracks because the stratigraphy sedimentology petrography and structural evolution of this turbidite succession has been intensively studied over the last 40 years the ma fm provides an ideal case to apply the apatite fission track method the data show a general decrease of the maximum paleotemperature undergone by the ma samples toward the foreland area the maximum burial calculated using a geothermal gradient of 20 c km spans from more than 5 km to less than 2 5 km and indicates that the reconstructed total thickness of the ma succession is not enough to justify the determined burial values stratigraphic data indicates that the missing section consisted of a lower component foredeep successions and an upper allocthonous component composed of disrupted and chaotic oceanic sediments and minor ophiolites ligurian unit the ligurian unit overrode the foredeep succession during deposition its advancement toward the foreland area was associated with subsidence and only locally contrasted by thrust growth the reconstructed wedge shape of the ligurian unit in its final and pre erosional configuration at time of the maximum bunal of the ma succession shows a flat upper surface which corresponds to a paleosurface of early pliocene age this surface marks at 4 to 5 ma the onset of the exhumation phase which occurred at a mean rate of 1 2 mm yr

role of deep sourced fluids on the initiation and growth of isolated carbonate build ups abstract the relative role of the various mechanisms responsible for the formation of isolated carbonate build ups occurring on the seafloor along continental margins is still uncertain the interpretation of an extensive seismic dataset in the central vulcan sub basin nw australia allowed to evaluate the possible role of migration and seepage of deep sourced fluids during the initial growth of isolated carbonate build ups the neogene tectonic activity along the margin generated extensional fault systems that commonly displaced the seafloor thus apparently creating a substratum to the initiation of various carbonate build ups during the pleistocene the seismic data show reflections with enhanced amplitude respect to background values which are associated with both isolated carbonate build ups and normal faults the seismic character of these reflections supports the presence of fluids that migrated within the sedimentary pile throughout the investigated area the interpreted occurrence of methane derived authigenic carbonates mdac on the seismic surface upon which the carbonate build ups lay suggests that seepage of hydrocarbons likely occurred at the time of their initial formation the fluid migration appears focused in the areas above extensional faults which breached the seals of the mesozoic reservoirs combined tectonic activity and seepage are suggested to support the initial growth of the carbonate build ups various smaller buried carbonate build ups developed contemporaneously to those on the present day seafloor in sites that lack evidence of past hydrocarbon seepage their shorter life compared to those on the present day seafloor suggests their inability to keep up with the frequent relative sea level variations during the quaternary and the importance of deep sourced fluids for the carbonate build ups growth in the central vulcan sub basin the initiation of the numerous carbonate build ups documented along continental margins worldwide must be explained considering the complex and dynamic interplay of all factors potentially involved such as geological and oceanographic settings and an active petroleum system in particular the migration and seepage of deep sourced fluid can have an important role in controlling the genesis and growth of isolated carbonate build ups

morphostructural evidence of late quaternary tectonics at the po plain northern apennines border lombardy italy abstract the landscape of foreland basins adjacent to active mountain ranges evolves under the control of basinward tectonic propagation of the structural fronts in competition with climate dynamics the resulting palimpsest landscapes record the sequence of geomorphic evolutionary steps and the spatial temporal relations between the active geological processes however a precise evolutionary sequence is hard to decipher from low relief settings like the wide alluvial plains worldwide about these topics we investigate the sequence of tectonic and climate driven processes which shaped the palimpsest landscape of a large quaternary foreland basin the po plain in northern italy above the average glacio fluvial and alluvial plain of the basin late quaternary intra basin reliefs emerge owing to syndepositional ramp folding and uplift driven by n wards propagation of the outermost thrust fronts of the active n apennine chain the incremental tectono morphological and depositional history of the region permits to describe the propagation of the structural front as a polyphase process involving uplift wrenching and late collapse of the reliefs this history is documented by relicts of uplifted planation surfaces covered by latest pleistocene weathered loess units polygonal facets landslides and slope wedges along faults delineating the slopes of the largest among the intra basin reliefs san colombano hill hydrographic anomalies on the relief network river diversions piracy and perching of valleys paleovalley fills river diversions and cross cut relations on the adjacent alluvial plain these features testify the thrust fold related pre lgm uplift of the late pleistocene alluvial stratigraphy the subsequent segmentation of the relief in differently uplifting blocks along riedel faults owing to activation of a transfer fault zone and the lgm extensional collapse of the relief along inherited fault systems a late post glacial outwards propagation of the apennine thrusts was buttressed by the opponent alpine thrust belt front and induced the entrenchment of the river network river diversions on the plain were controlled by the orientation of the san colombano hill fault systems the distribution of historical earthquakes and the present day geodetic data are coherent with this evolution the study documents how in foreland basins the syndepositional propagation of blind orogenic fronts shapes the palimpsest landscape with superimposed morphological tectonic and stratigraphic features of paleoseismic significance and permits comparisons with the other low relief basin settings worldwide

biodetrital carbonates on the adriatic continental shelf imprinted by oxidation of seeping hydrocarbons abstract the gas productive bonaccia area located at ca 80 90 m below sea level offshore ancona central adriatic sea is site of hydrocarbon derived carbonate production the carbonates include large dm sized slabs bryozoan limestone smaller concretionary aggregates mudstones and pipes the mudstones and botryoidal aragonite cements within limestones show 13c values as low as 47 8 vpdb consistent with seepage of isotopically light hydrocarbons e g methane these hydrocarbon derived carbonates commonly incorporate abundant shell remains deriving from the prevalently coarse bioclastic rich muddy deposits from post glacial transgressive units it is therefore hypothesized that hydrocarbon rich fluids permeated the post glacial sediments resulting in seafloor seeps that were inhabited by chemosymbiotic lucinid bivalves and burrowing callianassid shrimps fossils and traces of which have been found in the bonaccia carbonates microbial oxidation of the reduced compounds contained in the seep fluids led to a locally patchy carbonate cementation of the sediments at the seep sites the pipes are interpreted as decapod burrows that subsequently served as conduits for hydrocarbon leakage seepage is probably still active at present as testified by gas production at the study site interestingly seep carbonates exhumed by erosion served as hard substrate for fouling benthos i e bryozoans oysters and red algae in the holocene the main products of the processes at the bonaccia study site are composite bryozoan dominated limestones whose multi step and complex history was unfold thank to radiocarbon dating of key components and precise stratigraphic control the bonaccia case study can serve as a model for the interpretation of ancient analogs such as bryozoan dominated limestones and mudstones of paleozoic to mesozoic age which are not uncommon in the geological record it further calls for caution in assuming that the presence of dominant macrobenthic fossil in old hydrocarbon derived limestones implies its ecological connection to active seepage

a new active tectonic model for the construction of the northern apennines mountain front near bologna italy 1 we integrate existing and new geologic data retreating trench extension and accretion tectonics retreat project particularly on the origin growth and activity of the mountain front at bologna italy into a new model that explains apennine orogenesis in the context of a slab rollback upper plate retreat process the bologna mountain front is an actively growing structure driving rock uplift 1 mm year cored by a midcrustal flat ramp structure that accommodates ongoing shortening driven by adria subduction at a rate of 2 5 mm year the data we use are assembled from river terraces and associated pleistocene growth strata geodesy including releveling surveys reinterpretation of published reflection lines and a new high resolution reflection line these data constrain a simple trishear model that inverts for blind thrust ramp depth dip and slip apennine extension is recognized both in the foreland as high angle normal faults and modest stretching in the carapace of the growing mountain front and in the hinterland with larger normal faults that accomplish some crustal thinning as the upper plate retreats this coevolution of extension and shortening shares some notable characteristics with other basement involved collisional orogens including the early tertiary laramide orogeny in the american west and the oligocene to miocene evolution of the alps we propose a possible relationship between underplating and the development of the po as a sag basin as a quaternary phenomenon that may also apply to past periods of apennine deformation tortonian continued shortening on the structure beneath the bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern apennines

mineralogical footprints of microbial life earth s geosphere is intimately tied to its biosphere a major link between the two lies in the microbial realm microorganisms grow in and upon rocks and minerals often relying on their substratum for critical compounds needed in order to produce cellular energy the presence of a metabolizing cell on a mineral substrate has a significant effect on the mineral texture and on the geochemistry of the surrounding microenvironment in nature microorganisms exist in microbial commu nities as mats or biofilms growing upon a solid substrate as such they cover a vast surface area both within and below the surface of earth s land and sea the following review will provide a glimpse into the latest findings in the field of geomicrobiology and is intended to convey a sense of the profound influence microorganisms can have upon the geological environment they inhabit

a new model of the petroleum system in the northern apennines italy a geochemical study on fluids from selected spontaneous seepages and drilled wells was carried out together with geologic investigation and deep cross sections reconstruction to examine the petroleum system in the western northern apennines foothills the hydrocarbons occurring in the miocene foredeep units that form the reservoirs are commonly interpreted as generated in a source reservoir system however the low total organic carbon its elevated dilution in the sediment pile and the limited amount of successions that entered in the oil window indicate a low potential for the hydrocarbons generation the structures deformation in the northern apennines foothills is mainly late miocene to pliocene in age and involves successions that are progressively younger towards southeast the earlier structure forms the salsomaggiore anticline in the western sector the comparison of the fluids from the wells and the mud volcanoes shows high geochemical and thermal history similarities saline waters originate from the connate pore water entrapped in the miocene reservoir rocks during their deposition the gaseous hydrocarbons are a mixture of secondary biogenic methane and primary and secondary thermogenic gases the associated oils show both early and late maturities these evidences account for different generation and migration steps depending on burial conditions and deformation time the various reservoirs appear confined by the thrust detachment at different depths and by the occurrence of reactivated lateral ramps these results suggest the occurrence of a common source rock deeper than the tertiary reservoir units which progressively entered in the oil window this source rock could have wide lateral extension at least comparable with the width of the studied area and represent a prime exploration target to evaluate the undiscovered oil and gas resources

isotopic compositions of diagenetic dolomites in the tortonian marls of the western mediterranean margins evidence of past gas hydrate formation and dissociation abstract previous studies in the lorca basin s e spain sediment geol 2002 have shown that the diagenetic dolomitic concretions from the tortonian marls are related to the past occurrence of gas hydrates which were rapidly dissociated when the sea level dropped during the messinian salinity crisis these conclusions were based on the oxygen and carbon isotopic compositions of these dolomites which indicated that the carbonate diagenesis occurred either in 13 c rich 18 o poor solutions as it is typical in gas hydrate systems or in 13 c poor 18 o rich solutions generated during gas hydrate decomposition we have recently discovered similar dolomitic nodules in other tortonian marly successions from s e spain and northern morocco the oxygen and carbon isotopic compositions of the diagenetic dolomites from these areas in spain and morocco are very similar to those from the lorca basin this demonstrates that the dolomitic nodules from the tortonian marls of the betic and rifian basins were all related to the same diagenetic environments where pore fluids were modified by gas hydrate formation dissociation processes these overall observations in s e spain and northern morocco suggest that the dissociation of gas hydrates during the messinian salinity crisis was not a local phenomenon but corresponded to a major event which affected both sides of the western mediterranean margins it might have been initiated during the first major restriction step that started around 6 7 ma in the mediterranean sea and probably climaxed at 5 9 ma when the mediterranean sea level dropped by more than 1000 m during the salt deposition stage

microbially influenced formation of mg calcite and ca dolomite in the presence of exopolymeric substances produced by sulphate reducing bacteria some species of sulphate reducing bacteria srb are known to mediate the formation of dolomite and mg calcite however their exact role in the mineralization process remains elusive here we present the result of a laboratory experiment that was designed to test whether formation of carbonate minerals by srb can occur in the absence of living cells through passive mineralization of their exopolymeric substances eps srb capable of mediating dolomite were cultivated in the laboratory allowing them to secrete eps microbial activity within the cultures was subsequently inhibited with antibiotics only after this step ca2 and mg2 were added to the solution and carbonate minerals could form mg calcite and disordered ca dolomite precipitated in association with eps the mol of mg2 in the crystals increased with longer incubation times this result demonstrates that organic compounds produced by srb can mediate the formation of ca mg carbonates in the absence of an active metabolism

strike slip faults mediate the rise of crustal derived fluids and mud volcanism in the deep sea we report on newly discovered mud volcanoes located at 4500 m water depth 90 km west of the deformation front of the accretionary wedge of the gulf of cadiz and thus outside of their typical geotectonic environment seismic data suggest that fluid flow is mediated by a 400 km long strike slip fault marking the transcurrent plate boundary between africa and eurasia geochemical data cl b sr 87 sr 86 sr d 18 o dd reveal that fluids originate in oceanic crust older than 140 ma on their rise to the surface these fluids receive strong geochemical signals from recrystallization of upper jurassic carbonates and clay mineral dehydration in younger terrigeneous units at present reports of mud volcanoes in similar deep sea settings are rare but given that the large area of transform type plate boundaries has been barely investigated such pathways of fluid discharge may provide an important yet unappreciated link between the deeply buried oceanic crust and the deep ocean

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

the place of tubular concretions in hydrocarbon cold seep systems late miocene urenui formation taranaki basin new zealand the late miocene urenui formation cropping out on the eastern margin of taranaki basin currently new zealand s only commercially exploited hydrocarbon basin is dominated by siliciclastic slope mudstone 5 carbonate that locally includes a variety of tubular concretions 50 85 carbonate dominated by commonly large pipe and bulbous varieties as much as 0 5 to more than 10 m 1 6 to 33 ft long and 5 to 70 cm 2 to 28 in across these concretions formed from the precipitation of fine grained calcite or dolomite cement within siliciclastic mud in the shallow subsurface likely 100 m burial most support a central conduit that may be empty or filled with sediment or multiple generations of post shallow burial carbonate cements depleted 13c values of the concretionary calcite cements 40 to 25 pdb indicate that their carbon was sourced from oxidized methane in contrast enriched 13c values of the concretionary dolomite cements 10 to 11 pdb indicate that their carbon was derived from methanogenic co2 and or extensive methane oxidation the range of 18o values for the concretionary cement types 2 to 5 pdb supports precipitation from fluids both depleted and enriched with respect to new zealand miocene marine waters which are suggested to reflect episodes of gas hydrate formation and dissociation respectively the tubular carbonate concretions are interpreted to mark the subsea floor pathways of focused methane infused upward fluid escape and as such they represent a part of the shallow subsurface plumbing system of a cold seep system developed on the continental margin bounding the taranaki basin in the late miocene this margin has been strongly influenced by periodic movements along the major taranaki fault thrust system which coincidentally directly underlies the urenui concretion occurrences and was probably the most likely avenue for active fluid migration within the hydrocarbon seep system the tubular concretions experienced periodic intervals of exhumation and burial caused by margin failure because of greater slope instability from injected fluids and resulted in conglomeratic channel fill deposits within the urenui formation that include mass transported tubular concretions

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

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

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

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

sr and nd isotopes of cold seep carbonates from the northern south china sea as proxies for fluid sources abstract in this study sr isotopes combined with nd isotopes of modern cold seep carbonates were studied to provide reliable proxies for sources and pathways of seep fluids we presented sr and nd isotopes together with stable carbon and oxygen isotope data of cold seep carbonates recovered from the northern continental slope of the south china sea scs based on the evidence for negligible detrital contamination and diagenetic alteration carbonate samples are considered dependable archives which record sr and nd isotope signals of the original pore waters from which carbonates have precipitated excellent correlation between 87sr 86sr ratios and 1 sr observed in carbonate samples indicates two end members with distinct sr isotopic signatures including modern seawater as a major source and a lesser contribution from methane rich seep fluid driven from a deep source besides these two end members release of nd from organic matter and fe mn oxyhydroxide is an additional contribution to pore water nd furthermore sr and nd isotopic compositions suggest water rock interactions between upward seep fluid and detrital component in sediments which resulted in the isotopic shift towards pronounced 143nd depleted and slightly 87sr enriched in the fluid phase this study provides insight into the knowledge for tracing seepage fluid circulation by sr nd isotope system at modern seep systems

fluid sources and stable isotope signatures in authigenic carbonates from the northern apennines italy abstract authigenic carbonates are frequently associated with methane cold seep systems which extensively occur in various geologic settings worldwide of interest is the relation between the fluids involved in their formation and the isotopic signals recorded in the carbonate cements along the northern apennines foothills italy hydrocarbons and connate waters still seeping nowadays are believed to be the primary sources for the formation of fossil authigenic carbonate found in plio pleistocene marine sediments four selected outcrops of dolomitic authigenic carbonates were analysed to compare signature of seeping fluids with fractionation of stable carbon and oxygen isotopes recorded in the carbonate along the foothills deep methane rich fluids spontaneously rise to the surface through mud volcanoes or are exploited in wells drilled nearby to the fossil plio pleistocene authigenic carbonates the plumbing system providing fluids to present day cold seeps was structurally achieved in late miocene and plio pleistocene 13 c values of methane which vary from 51 9 to 43 0 vpdb indicate that gas composition from the deep hydrocarbon reservoirs is relatively uniform along the foothills on the contrary 13 c in fossil authigenic carbonates strongly varies among different areas and also within the same outcrop the different carbon sources that fed the investigated carbonates were identified and include thermogenic methane from the deep miocene reservoirs 13 c enriched co 2 derived from secondary methanogenesis and microbial methane from pliocene successions buried in the po plain the 13 c variability documented among samples from a single outcrop testifies that the authigenic carbonates might represent a record of varying biogeochemical processes in the hydrocarbon reservoirs the sources of stable oxygen isotopes in authigenic carbonates are often ascribed to marine water oxygen isotopic fractionation in the dolomite cements indicates that marine pore water couldn t be the sole source of oxygen 18 o values provide a preliminary evidence that connate waters had a role in the carbonates precipitation the concomitant occurrence of active cold seepages and fossil record of former plumbing systems suggests that generation and migration of hydrocarbons are long lasting and very effective processes along the northern apennines foothills

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

topographic expression of active faults in the foothills of the northern apennines abstract active faults that rupture the earth s surface leave an imprint on the topography that is recognized using a combination of geomorphic and geologic metrics including triangular facets the shape of mountain fronts the drainage network and incised river valleys with inset terraces we document the presence of a network of active high angle extensional faults collectively embedded in the actively shortening mountain front of the northern apennines that possess unique geomorphic expressions we measure the strain rate for these structures and find that they have a constant throw to length ratio we demonstrate the necessary and sufficient conditions for triangular facet development in the footwalls of these faults and argue that rock type exerts the strongest control the slip rates of these faults range from 0 1 to 0 3 mm yr which is similar to the average rate of river incision and mountain front unroofing determined by corollary studies the faults are a near surface manifestation of deeper crustal processes that are actively uplifting rocks and growing topography at a rate commensurate with surface processes that are eroding the mountain front to base level

pliocene and pleistocene exhumation and uplift of two key areas of the northern apennines application of different thermochronological methods to two areas of pronounced relief apuane alps and mt falterona of the northern apennines chain documents an average exhumation rate of about 0 7m m yr this result suggests that the general exhumation of the chain is driven mainly by erosion nevertheless the long term exhumation trend seems to be perturbed by shortterm events at higher exhumation rates the time of increased exhumation rates coincides with onset of intramontane sedimentation documenting a contribution of tectonics local normal faulting to the surface uplift the data indicate an eastward shifting of the onset of topographic relief early pliocene in the apuane alps and early pleistocene in the mt falterona area r 2002 elsevier science ltd and inqua all rights reserved

origin of the gypsum veins associated with the diagenetic dolomite nodules from the neogene marls of south east spain abstract the late neogene marls from the lorca murcia and vera basins in s e spain contain abundant dolomite nodules that were formed due to intense methane rich fluid migration the pathways for these fluids are evidenced by dense networks of fractures that are crossing the sedimentary layers and eventually the dolomite nodules the fractures are generally filled by secondary fibrous gypsum that form veins of a few cm thick the oxygen and sulfur isotopic compositions of the gypsum veins exhibit wide ranges 2 2

mineralogical geochemical and isotopic characterization of authigenic carbonates from the methane bearing sediments of the bering sea continental margin iodp expedition 323 sites u1343 u1345 abstract during expedition 323 of the integrated ocean drilling program to the bering sea july 5 september 4 2009 three sites were drilled along the bering sea northeastern continental margin u1343 down to 745 meters below sea floor mbsf u1344 745 mbsf u1345 150 mbsf diagenetic carbonates are present at all sites within the clayey diatom rich oozes of the bering sea where pore waters are also characterized by extremely high methane concentrations we here present mineralogical elemental and isotopic data obtained from the authigenic carbonate rich intercalations within the clay rich pleistocene sediments deposited along the bering sea continental margin the mineralogy of the authigenic carbonates is generally represented by composite mixtures of very small crystals of magnesian calcite dolomite and iron rich carbonates with the latter phases occurring below 260 mbsf at site u1343 below 200 mbsf at site u1344 and below 130 mbsf at site u1345 element geochemistry shows that ca mg fe ba mn sr and u are enriched in the carbonate rich intercalations relative to the background sediments due to their incorporation into the carbonates and into other authigenic phases e g barite and pyrite the oxygen and carbon isotopic compositions of the authigenic carbonate minerals show that they were sequentially precipitated from pore waters at different temperatures i e different burial depths and with different isotopic compositions of dissolved inorganic carbon dic the authigenic mg calcite precipitated early during diagenesis and shallow burial from a 13 c depleted dic pool whereas dolomite and fe rich carbonates formed during later diagenesis and deeper burial from a 13 c enriched dic pool these authigenic carbonate occurrences are interpreted as resulting from microbial sulfate reduction combined with anaerobic oxidation of methane and methanogenesis that was intimately linked to the alteration of silicates especially iron rich clay minerals