sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

u th systematics and ages of authigenic carbonates from hydrate ridge cascadia margin recorders of fluid flow variations uranium u concentrations and activity ratios 234u of authigenic carbonates are sensitive recorders of different fluid compositions at submarine seeps of hydrocarbon rich fluids cold seeps at hydrate ridge off the coast of oregon usa the low u concentrations mean 1 3 0 4 g g and high 234u values 165 317 of gas hydrate carbonates reflect the influence of sedimentary pore water indicating that these carbonates were formed under reducing conditions below or at the seafloor their 230th 234u ages span a time interval from 0 8 to 6 4 ka and cluster around 1 2 and 4 7 ka in contrast chemoherm carbonates precipitate from marine bottom water marked by relatively high u concentrations mean 5 2 0 8 g g and a mean 234u ratio of 166 3 their u isotopes reflect the 234u ratios of the bottom water being enriched in 234u relative to normal seawater simple mass balance calculations based on u concentrations and their corresponding 234u ratios reveal a contribution of about 11 of sedimentary pore water to the bottom water from the u pore water flux and the reconstructed u pore water concentration a mean flow rate of about 147 68 cm a can be estimated 230th 234u ages of chemoherm carbonates range from 7 3 to 267 6 ka 230th 234u ages of two chemoherms alvin and se knoll chemoherm correspond to time intervals of low sealevel stands in marine isotope stages mis 2 4 5 6 7 and 8 this observation indicates that fluid flow at cold seep sites sensitively reflects pressure changes of the hydraulic head in the sediments the 18o pdb ratios of the chemoherm carbonates support the hypothesis of precipitation during glacial times deviations of the chemoherm 18o values from the marine 18o record can be interpreted as to reflect temporally and spatially varying bottom water and or vent fluid temperatures during carbonate precipitation between 2 6 and 8 6 c

hydrocarbon potential and depositional environments of oligo miocene rocks in the eastern carpathians vrancea nappe romania abstract the oligocene to early miocene fine grained succession in the eastern carpathians includes from base to top the lower menilite lmm bituminous marl bmm lower dysodilic shale ldsm and upper dysodilic shale udsm members these stratigraphic units constituting the main hydrocarbon source rocks in the eastern carpathians have been studied in an outcrop section to determine its depositional environment and hydrocarbon potential the lmm contains high amounts of toc but because of low thickness its source potential is limited the organic matter of the overlying bmm is mainly derived from autochthonous marine organisms including bacterial biomass toc contents are moderate because of dilution by carbonate minerals calcareous nannoplankton dates the bmm into nannoplankton zones np21 22 salinity and redox conditions varied from reduced to slightly enhanced and from strictly anoxic to dysoxic the ldsm contains carbonate free black shale and sandstone beds deposited in a depositional lobe under anoxic conditions despite of high hi values land plants form a significant part of the organic matter channel fill sediments form the top of the ldsm the lower part of the early miocene udsm accumulated in a lobe whereas its upper part represents a basin plain setting mttc ratios reflect a trend from slightly enhanced to slightly decreased normal marine salinity the presence of aryl isoprenoids suggests a temporary photic zone anoxia controlled by salinity variations both marine and terrestrial biomass contributed to the organic matter a major change towards oxic conditions occurred at the boundary between the udsm and the overlying gura soimului formation the studied succession can generate 6 t of hydrocarbons per square meter all members are oil prone but yield oil with different biomarker characteristics this allows the identification of oil generated from different lithostratigraphic units

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

gas hydrate reservoirs and gas migration mechanisms in the terrebonne basin gulf of mexico highlights identify new fine grained hydrate filled fracture units in the terrebonne basin identify new hydrate bearing thin sands mostly within fractured muds present detailed seismic amplitude maps of the new hydrate bearing units discuss methane migration mechanisms and hydrate formation in thin sands identify and discuss source reservoir relationships between thick muds and thin sands abstract the interactions of microbial methane generation in fine grained clay rich sediments methane migration and gas hydrate accumulation in coarse grained sand rich sediments are not yet fully understood the terrebonne basin in the northern gulf of mexico provides an ideal setting to investigate the migration of methane resulting in the formation of hydrate in thin sand units interbedded with fractured muds using 3d seismic and well log data we have identified several previously unidentified hydrate bearing units in the terrebonne basin two units are 100 m thick fine grained clay rich units where gas hydrate occurs in near vertical fractures in some locations these fine grained units lack fracture features and they contain 1 4 m thick hydrate bearing sands in addition several other thin sand units were identified that contain gas hydrate including one sand that was intersected by a well at the location of a discontinuous bottom simulating reflector using correlation of well log data to seismic data we have mapped and described these new units in detail across the extent of the available data allowing us to determine the variation of seismic amplitudes and investigate the distribution of free gas and or hydrate we present several potential source reservoir scenarios between the thick fractured mud units and thin hydrate bearing sands we observe that hydrate preferentially forms within thin sand layers rather than fractures when sands are present in larger marine mud units based on regional mapping showing the patchy lateral extent of the thin sand layers we propose that diffusive methane migration or short migration of microbially generated methane from the marine mud units led to the formation of hydrate in these thin sands as discontinuous sands would not be conducive to long range migration of methane from deeper reservoirs

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

early oligocene dinoflagellate cysts from the upper rhine graben sw germany paleoenvironmental and paleoclimatic implications using principal component analysis and cyst diversity and equity trends we can recognize four distinct dinoflagellate cyst dinocyst assemblages from four rupelian early oligocene cores in the mainz embayment of the northern rhine graben sw germany these assemblages are the spiniferites ramosus pc1 thalassiphora pelagica pc2 homotryblium tenuispinosum pc3 and vozzhennikovia spinula pc4 assemblages the four cores provide an onshore offshore transect in the mainz embayment the h tenuispinosum assemblage shows high factor loadings in proximal to intermediate cores which is interpreted to reflect temporary high salinity conditions mean dinocyst diversity and equity increase with distance from the mid rupelian shoreline indicating increasingly stable paleoenvironmental conditions towards the center of the mainz embayment within individual cores changes in dinocyst assemblages through time are related to paleoenvironmental and paleoclimatological changes the three proximal to intermediate cores show dominance of the h tenuispinosum assemblage repeatedly alternating with high factor loadings of the t pelagica assemblage in both cases dinocyst diversity and equity tend to be reduced highest factor loadings of the s ramosus assemblage occur in intervals where neither of the above assemblages is dominant and tend to coincide with dinocyst diversity and equity maxima we interpret this distribution pattern to denote different paleoceanographic conditions reflecting drier and more humid phases in the early oligocene of central europe during relatively dry periods increased salinity conditions prevailed in proximal to intermediate settings of the mainz embayment as reflected by the dominance of the h tenuispinosum assemblage during more humid periods increased runoff led to higher nutrient availability and the formation of a pycnocline separating slightly less saline surface waters from higher saline deeper waters thus impeding vertical circulation these environmental conditions are documented in high loadings of the t pelagica assemblage which is indicative of increased eutrophication and or oxygen depleted bottom waters transitions between drier and more humid periods i e episodes of normal marine conditions are characterized by high loadings predominantly of the s ramosus assemblage as well as increased dinocyst diversity and equity values we propose that the alternations between drier and more humid phases may be related to variations in the ocean atmosphere moisture flux from the north atlantic into central europe bearing a high latitude climate signal 2002 elsevier science b v all rights reserved

finite fault inversion of dinsar coseismic displacement of the 2009 l aquila earthquake central italy 1 we define the geometric and kinematic characteristics of the fault activated during the mw 6 3 6 april 2009 l aquila earthquake from the modeling of envisat and cosmo skymed the first ever x band interferogram inverted for a coseismic dislocation study dinsar interferograms our best fit solution for the main shock is represented by a normal fault 16 km long and 12 km wide with a small right lateral component dipping 47 sw with a maximum slip of 90 cm although the seismic dislocation probably ended at 1 km depth the updip projection of the fault plane corresponds to the northern segment of the mapped paganica s demetrio fault where alignment of surface breaks was observed in the field the absence of this fault in existing seismic source catalogues suggests that an improved approach involving detailed surface and subsurface geological and geophysical investigations is needed for a better assessment of the seismic hazard at the local scale

thermodynamic and pore water halogen constraints on gas hydrate distribution at odp site 997 blake ridge abstract marine sediment sequences with ch4 hydrate are characterized by an atypical depth profile in dissolved cl squeezed from pore space a shallow subsurface cl maximum overlies a lengthy and pronounced cl minimum this pore water cl profile represents a combination of multiple processes including glacial interglacial variations in ocean salinity advection and diffusion of ions that are excluded during gas hydrate formation at depth and release of fresh water from dissociation of hydrate during core recovery in situ quantities of gas hydrate can be determined from a measured pore water cl profile provided the in situ pore water signature prior to core recovery can be separated ocean drilling program odp site 997 was drilled into a large ch4 hydrate reservoir on the blake ridge in the western atlantic ocean previously we have constructed a high resolution pore water cl profile at this location here we present a coupled chloride hydrate numerical model to explain basic trends in the cl profile and to isolate in situ cl concentrations the model is based on thermodynamic and ecological considerations and uses established equations for describing chemical behavior in marine sediment pore water systems the model incorporates four key concepts 1 most gas hydrate is formed immediately below the so42 reduction zone 2 fluid dissolved ions and gas advect upward through the sediment column 3 ch4 hydrate dissociates at the base of hydrate stability conditions and 4 seawater salinity fluctuates during glacial interglacial cycles of the late pliocene and quaternary rates of upward advection in the model are sufficient to account for measured br and i concentrations as well as ch4 oxidation at the base of the so42 reduction zone in situ pore water cl inferred from the model is similar to that determined by limited direct sampling in situ ch4 hydrate amounts inferred from the model an average of about 4 of porosity are broadly consistent with those determined by direct gas sampling and indirect geophysical techniques the model also predicts production of substantial quantities of free ch4 gas bubbles 2 5 of porosity at a depth immediately below the lowest accumulation of ch4 hydrate in the sediment column our explanation for the pore water cl profile at site 997 is important because it provides a theoretical mechanism for understanding the distribution of interstitial water cl gas hydrate and free gas in a marine sediment column

chemostratigraphy of the posidonia black shale sw germany ii assessment of extent and persistence of photic zone anoxia using aryl isoprenoid distributions aquatic depositional environments where anoxic conditions extend from bottom waters into the photic zone occurred frequently during the geologic past periods of photic zone anoxia pza can be recognized by the presence of specific lipids produced exclusively by the green sulphur bacteria chlorobiaceae that are preserved in the sedimentary record chlorobiaceae perform anoxygenic photosynthesis that requires light penetration into h2s saturated waters sediment samples integrate paleoenvironmental conditions over time intervals ranging from at best a few decades to more commonly several millennia photic zone anoxia recognized in paleoenvironmental analyses is thus defined as episodic with no further interpretation on the duration and persistence of the anoxic events we provide here a high resolution multiproxy chemostratigraphy study for the toarcian posidonia black shale from the dotternhausen section in sw germany in order to assess duration and seasonal fluctuation of photic zone anoxia based on the relative abundance of derivatives of chlorobiaceae lipids we assess the variability in the degree and persistence of photic zone anoxia using an aryl isoprenoid ratio air obtained by calculating the proportion of the short chain c13 17 versus the intermediate chain c18 22 aryl isoprenoids higher relative abundance of the short chain analogues is interpreted as indicating more intensive aerobic degradation of aryl isoprenoids air varies between values of 0 5 indicative of persistent pza phases and 3 0 for short termed episodic pza events absolute concentration of aryl isoprenoids is negatively correlated with the air which is in agreement with a progressive diagenetic breakdown of aryl isoprenoids the air decreases are validated using independent palecological and geochemical redox indicators for the posidonia shale in sw germany d 2004 elsevier b v all rights reserved

spatial and temporal variability of paleocene miocene organofacies of the kura basin eastern azerbaijan and implications for basin evolution and petroleum generation abstract fine grained paleocene miocene strata of eastern azerbaijan record the evolution of the kura basin from an open marine system connecting the south caspian basin to the paratethys of eastern europe to an isolated epicontinental sea tectonic uplift associated with the greater caucasus mountains in azerbaijan resulted in exposure of these strata over much of the northeastern part of the basin allowing detailed observation and sampling over a broad area four hundred paleocene miocene samples collected in eastern azerbaijan demonstrate spatial and temporal geochemical heterogeneity within the predominately mudstone succession indicating a complex evolution of this elongate basin through detailed organic geochemical analysis of samples trends can be seen in the distribution of total organic carbon toc pyrolysis characteristics and biomarker results from a subset of twenty four samples in addition to confirming the well documented regional basin restriction during the oligocene to early miocene deposition of the maikop series heterogeneity of these geochemical indicators across the study area shows spatial variability in oxicity and terrestrial organic input within the basin on a sub regional scale observed geochemical variability suggests a complex evolutionary history of the kura basin during the paleocene miocene and this has important implications for hydrocarbon prospectivity in the region within the 400 collected samples total organic carbon toc values range from 0 3 to 6 3 with oligocene miocene samples showing average values of 1 4 compared to lower toc values found in paleocene eocene strata average 0 3 rock eval pyrolysis shows that the majority of strata are organic lean immature and mixed oil gas to gas prone type ii iii to type iii with a smaller group of latest eocene early miocene samples having better oil prone source potential gas chromatography and biomarker analysis of 24 samples reinforces the immaturity of most samples shows varying levels of terrestrial input in all samples suggests well oxygenated waters prevailed with periodic suboxic to dysoxic anoxic events highlights gross differences between the paleocene eocene and oligocene miocene stratigraphic intervals and shows generally good lateral correlation between samples these interpretations reinforce what is seen through inorganic geochemical evaluation of trace metals bulk composition and stable isotopic ratios and offer more detail as to the evolution of this basin and the implications for oil and gas prospectivity of the region

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

generalization of gas hydrate distribution and saturation in marine sediments by scaling of thermodynamic and transport processes gas hydrates dominated by methane naturally occur in deep marine sediment along continental margins these compounds form in pore space between the seafloor and a sub bottom depth where appropriate stability conditions prevail however the amount and distribution of gas hydrate within this zone and free gas below can vary significantly at different locations to understand this variability we develop a one dimensional numerical model that simulates the accumulation of gas hydrates in marine sediments due to upward and downward fluxes of methane over time the model contains rigorous thermodynamic and component mass balance equations that are solved using expressions for fluid flow in compacting sediments the effect of salinity on gas hydrate distribution is also included the simulations delineate basic modes of gas hydrate distribution in marine sediment including systems with no gas hydrate gas hydrate without underlying free gas and gas hydrate with underlying free gas below the gas hydrate stability zone for various methane sources the results are scaled using combinations of dimensionless variables particularly the peclet number and damkohler number such that the dependence of average hydrate saturation on numerous parameters can be summa rized using two contour maps one for a biogenic source and one for upward flux from a deeper source simulations also predict that for systems at steady state large differences in parameters like seafloor depth seafloor temperature and geothermal gradient cause only small differences in average hydrate saturation when examined with scaled variables although important caveats exist our model presents a unified picture of hydrate accumulations that can be used to understand well characterized gas hydrate systems or to predict steady state average hydrate saturation and distribution at locations for which seismic or core data are not available

permeability evolution during the formation of gas hydrates in marine sediments 1 fluxes of gas energy and fluid water with dissolved gas are known to control the distribution of gas hydrate and free gas in gas hydrate reservoirs but theoretical studies have so far not focused on the effect of sediment properties e g permeability on these fluxes during the formation of gas hydrate deposits using a transient one dimensional two phase gas hydrate and fluid numerical model based on a coupled conservation approach we examine permeability clogging during gas hydrate formation in end member porous media and fractures initially lacking hydrate and determine the resulting changes in fluid and advective energy flux gas hydrate accumulates most rapidly at depth in both systems a result consistent with borehole logging and seismic studies on the blake ridge consideration of the ratio of surface area to fluid volume explains model results that imply more rapid permeability reduction in the porous media system and more uniform hydrate formation as a function of depth in the fracture system depending on fluid flux fracture aperture or pore sizes and other factors the timescale for permeability clogging due to the accumulation of gas hydrate ranges from thousands to millions of years regenerating gas hydrate to a concentration of 10 15 of pore space in marine settings with fluid fluxes characteristic of hydrate ridge or blake ridge requires 103 105 years meaning that hydrate deposits in these settings cannot be viewed as a naturally renewable resource these results also imply that significant time is required to reestablish gas hydrate deposits after large scale dissociation events associated with global scale climate change

sediment petrography mineralogy and geochemistry of the miocene islam dag section eastern azerbaijan implications for the evolution of sediment provenance palaeo environment and post depositional alteration patterns

methylhopanoids molecular indicators of ancient bacteria and a petroleum correlation tool abstract methylhopanoids are organic compounds synthesized by certain bacteria that when preserved in sediments act as molecular fossils or biomarkers for organic matter inputs from specific bacterial sources two series of methylhopanoids occur each mainly deriving from a distinct bacterial source cyanobacteria 2 methyl and methanotrophic bacteria 3 methyl the abundance and composition of methylhopanoids within sediments of modern depositional environments varies widely apparently due to different bacterial communities contributing to the sedimentary organic matter comparable molecular characteristics are found in oils and their source rocks consequently methylhopanoids are valuable in oil oil and oil source rock correlations distinguishing between samples related to different depositional environments in particular abundant 3 methylhopanoids from methanotrophic bacteria or an additional unknown bacterial source are characteristic of some modern alkaline saline lake environments comparable compositional features in the methylhopanes of oils allow the assignment of lacustrine oils offshore west africa to two distinct lacustrine source rock facies and to distinguish between different marine source facies thus refining oil source rock correlation

abruzzo italy earthquakes of april 2009 heterogeneous fault slip models and stress transfer from accurate inversion of envisat insar data abstract the seismic sequence that occurred in the abruzzo apennines near l aquila italy in april 2009 caused extensive damage and a large number of casualties more than 300 the earthquake struck an area in the italian apennines chain where several faults belonging to adjacent seismotectonic domains create a complex tectonic regime resulting from the interaction among regional stress buildup local stress changes caused by individual earthquakes and viscous elastic stress relaxation understanding such complex interaction in the apennines can lead to a large step forward in the seismic risk mitigation in italy the abruzzo earthquake has been very well recorded by interferometric synthetic aperture radar insar data much better than the first italian earthquake ever recorded by satellites namely the 1997 umbria marche earthquake envisat environmental satellite data for the abruzzo earthquake are in fact very clear and allow an accurate reconstruction of the faulting mechanism we present here an accurate inversion of vertical deformation data obtained by envisat images aimed to give a detailed reconstruction of the fault geometry and slip distribution the resulting fault models are then used to compute by a suitable theoretical model based on the elastic dislocation theory the stress changes induced on the neighboring faults the correlation of the subsequent mainshocks and aftershocks of the abruzzo sequence with the volumes undergoing increasing coulomb stress clearly evidence the triggering effect of coseismic stress changes on further seismicity moreover this analysis put in evidence which seismotectonic domains have been more heavily charged by stress released by the abruzzo mainshocks the most important faults significantly charged by the abruzzo sequence belong to the sulmona and avezzano tectonic domains taking into account the average regional stress buildup in the area the positive coulomb stress changes caused by this earthquake can be seen as anticipating the next earthquakes in the neighboring domains of 15 20 yr

coseismic deformation of the destructive april 6 2009 l aquila earthquake central italy from gps data 1 on april 6 2009 01 32 39 gmt the city of l aquila was struck by a mw 6 3 earthquake that killed 307 people causing severe destruction and ground cracks in a wide area around the epicenter four days before the main shock we augmented the existing permanent gps network with five gps stations of the central apennine geodetic network cageonet bordering the l aquila basin the maximum horizontal and vertical coseismic surface displacements detected at these stations was 10 39 0 45 cm and 15 64 1 55 cm respectively fixing the strike direction according to focal mechanism estimates we estimated the source geometry with a non linear inversion of the geodetic data our best fitting fault model is a 13 15 7 km2 rectangular fault sw dipping at 55 3 1 8 consistent with the position of observed surface ruptures the estimated slip 495 29 mm corresponds to a 6 3 moment magnitude in excellent agreement with seismological data

the impact of lithologic heterogeneity and focused fluid flow upon gas hydrate distribution in marine sediments gas hydrate and free gas accumulation in heterogeneous marine sediment is simulated using a two dimensional 2 d numerical model that accounts for mass transfer over geological timescales the model extends a previously documented one dimensional 1 d model such that lateral variations in permeability k become important various simulations quantitatively demonstrate how focused fluid flow through high permeability zones affects local hydrate accumulation and saturation simulations that approximate a vertical fracture network isolated in a lower permeability shale kfracture kshale show that focused fluid flow through the gas hydrate stability zone ghsz produces higher saturations of gas hydrate 25 70 and free gas 30 60 within the fracture network compared to surrounding shale simulations with a dipping high permeability sand layer also result in elevated saturations of gas hydrate 60 and free gas 40 within the sand because of focused fluid flow through the ghsz increased fluid flux a deep methane source or both together increase the effect of flow focusing upon hydrate and free gas distribution and enhance hydrate and free gas concentrations along the high permeability zones permeability anisotropy with a vertical to horizontal permeability ratio on the order of 10 2 enhances transport of methane charged fluid to high permeability conduits as a result gas hydrate concentrations are enhanced within these high permeability zones the dip angle of these high permeability structures affects hydrate distribution because the vertical component of fluid flux dominates focusing effects hydrate and free gas saturations can be characterized by a local peclet number localized vertical focused and advective flux relative to diffusion relative to the methane solubility gradient somewhat analogous to such characterization in 1 d systems even in lithologically complex systems local hydrate and free gas saturations might be characterized by basic parameters local flux and diffusivity

organofacies and paleoenvironment of the oligocene maikop series of angeharan eastern azerbaijan the maikop formation deposited in eastern azerbaijan during oligocene and early miocene times contains prolific source rocks with primarily type ii organic matter paleontological analyses of dinoflagellate cysts revealed a lower to upper oligocene age for the investigated succession near angeharan a major contribution of aquatic organisms diatoms green algae dinoflagellates chrysophyte algae and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n alkane distribution patterns composition of steroids and 13c of hydrocarbon biomarkers microbial communities included heterotrophic bacteria cyanobacteria chemoautotrophic bacteria as well as green sulfur bacteria higher inputs of terrigenous organic matter occurred during deposition of the upper oligocene units of the maikop formation from angeharan mountains the terpenoid hydrocarbon composition argues for angiosperm dominated vegetation in the shamakhy gobustan area high primary bioproductivity resulted in a stratified water column and the accumulation of organic matter rich sediments in the lower oligocene units of the maikop formation organic carbon accumulation during this period occurred in a permanently salinity stratified mesohaline environment with free h2s in the water column this is indicated by low pristane phytane ratios of all sediments varying from 0 37 0 69 lower methylated trimethyltridecyl chromans ratio in the lower units and their higher contents of aryl isoprenoids and highly branched isoprenoid thiophenes subsequently the depositional environment changed to normal marine conditions with oxygen deficient bottom water the retreat of the chemocline towards the sediment water interface and enhanced oxic respiration of om during deposition of the upper oligocene maikop sediments is proposed parallel depth trends in 13c of total om n alkanes isoprenoids and steranes argue for changes in the regional carbon cycle associated with the changing environmental conditions increased remineralisation of om in a more oxygenated water column is suggested to result in low toc and hydrocarbon contents as well as 15n enriched total nitrogen of the upper oligocene units

reducing the risk of finding a working petroleum system using sar imaging sea surface slick sampling and geophysical seafloor characterization an example from the eastern black sea basin offshore georgia abstract as new plays emerge in deepwater settings sea surface slicks are often overlooked as a source of geochemical information to help define potential petroleum systems to demonstrate how sea surface hydrocarbon slicks can be used a case study is presented from the eastern black sea in the rioni basin offshore republic of georgia there source rocks of oligo miocene age maikop are suspected of charging upper miocene deepwater channel levee sands in fold and thrust system traps to reduce exploration risk direct evidence of hydrocarbon generation and migration was sought using sea surface slicks observed there to provide confirmation of charge a collection of diverse data was used first synthetic aperture radar satellite images were utilized to verify the presence of large recurring sea surface slicks over prospective structures these slicks were then sampled for later analysis during the acquisition of 3 d seismic data to verify that the slicks were related to the subsurface expulsion seafloor bathymetric and amplitude data were extracted from the 3 d seismic volume and used to identify potential seafloor features consistent with hydrocarbon seepage some of these seafloor features were found to be coincident with the apparent sea surface origins of the slicks seismic imaging was also used to demonstrate potential migration pathways which may link suspected deep subsurface traps and the seafloor and finally geochemical analysis showed that the compositional characteristics of the slicks hydrocarbons were similar to known maikop sourced oils in the region this combination of data provided a high level of confidence that the seismically imaged traps in offshore republic of georgia are charged suggesting a working petroleum system was present what it cannot tell us is how much petroleum may be in these structures that question can only be answered by the drill bit

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

relationship between rank and composition of aromatic hydrocarbons for coals of different origins distributions of di and tricyclic aromatics were determined for upper carboniferous to oligocene coals of various origins in addition to upper carboniferous ruhr coals wealden lower creataceous coals from north west germany lower cretaceous coals from western canada and tertiary coals from japan and colombia were studied the coals ranged from sub bituminous to anthracite in rank and showed vitrinite reflectance from 0 4 to 4 9 rm the previously established relationship between the rank of coal in terms of vitrinite reflectance and the distribution patterns of individual aromatic hydrocarbon isomers has been verified and refined it is demonstrated how the above relationships can be used to calculate vitrinite reflectance from the methylphenanthrene index mpi 1 the chemical rank levels of coals can now be defined in terms of the calculated vitrinite reflectance rc

stratigraphy and geochemical characterization of the oligocene miocene maikop series implications for the paleogeography of eastern azerbaijan abstract the oligocene miocene maikop series is a world class source rock responsible for much of the oil and gas found in the south caspian basin it is composed of up to 3 km of marine mudstone and contains a nearly continuous record of deposition during progressive tectonic closure of the basin as the arabian peninsula converged northward into eurasia historically the stratigraphy of this interval has been difficult to define due to the homogenous nature of the fine grained clay dominated strata outcrop exposures in eastern azerbaijan allow direct observation and detailed sampling of the interval yielding a more comprehensive stratigraphic context and a more advanced understanding of syndepositional conditions in the eastern paratethys sea specifically the present investigation reveals that coupling field based stratigraphic characterization with geochemical analyses e g bulk elemental geochemistry rock eval pyrolysis bulk stable isotope geochemistry yields a more robust understanding of internal variations within the maikop series samples from seven sections located within the shemakha gobustan oil province reveal consistent stratigraphic and spatial geochemical trends it is proposed that the maikop series be divided into three members based on these data along with lithostratigraphic and biostratigraphic data reported herein when comparing rupelian early oligocene and chattian late oligocene strata the rupelian age strata commonly possess higher toc values more negative 15 n tot values more positive 13 c org values and higher radioactivity relative to chattian age rocks the trace metals mo and v normalized to al are positively correlated with toc with maximum values occurring at the rupelian chattian boundary and overall higher average values in the rupelian across the oligocene miocene boundary a slight drop in v al mo al ratios is observed along with drops in s and toc these results indicate that geochemical signatures of the maikop series are regional in nature and furthermore that analogous fine grained sections may be better characterized and subdivided using similar techniques in general geochemical indicators suggest that the basin was in limited communication with the tethys sea throughout the oligocene early miocene with suboxic to anoxic conditions present during the oligocene and to a lesser extent in the miocene this increased isolation was likely due to tectonic uplift to both the south and north of the study area and greatly enhanced by global sea level fluctuations these data serve as the basis for a more detailed understanding of the tectonic evolution of the region and support a standardized chemostratigraphic division of the important petroleum source interval

response of the san andreas fault to the 1983 coalinga nunez earthquakes an application of interaction based probabilities for parkfield 1 the parkfield cholame section of the san andreas fault site of an unfulfilled earthquake forecast in 1985 is the best monitored section of the world s most closely watched fault in 1983 the m 6 5 coalinga and m 6 0 nunez events struck 25 km northeast of parkfield seismicity rates climbed for 18 months along the creeping section of the san andreas north of parkfield and dropped for 6 years along the locked section to the south right lateral creep also slowed or reversed from parkfield south here we calculate that the coalinga sequence increased the shear and coulomb stress on the creeping section causing the rate of small shocks to rise until the added stress was shed by additional slip however the 1983 events decreased the shear and coulomb stress on the parkfield segment causing surface creep and seismicity rates to drop we use these observations to cast the likelihood of a parkfield earthquake into an interaction based probability which includes both the renewal of stress following the 1966 parkfield earthquake and the stress transfer from the 1983 coalinga events we calculate that the 1983 shocks dropped the 10 year probability of a m 6 parkfield earthquake by 22 from 54 22 to 42 23 and that the probability did not recover until about 1991 when seismicity and creep resumed our analysis may thus explain why the parkfield earthquake did not strike in the 1980s but not why it was absent in the 1990s we calculate a 58 17 probability of a m 6 parkfield earthquake during 2001 2011 index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 7260 seismology theory and modeling keywords coalinga earthquake parkfield stress change earthquake probability seismicity rate

analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope cascadia margin sediments contain a rich reservoir of carbon derived both from terrestrial input and sea surface productivity a portion of this carbon exists as solid gas hydrate within sediment pore spaces which previous studies have shown to be a methane reservoir of substantial size on both the vancouver island and oregon portions of the cascadia margin multichannel seismic reflection profiles on the cascadia margin show the widespread presence of bottom simulating reflectors bsrs within the sediment column indicating the gas hydrate reservoir extends from the deformation front at 3000 m depth to the upper limit of gas hydrate stability near 500 m water depth in this study we compile an inventory of methane bubble plume sites on the cascadia margin identified in investigations carried out for a range of interdisciplinary goals that also include sites volunteered by commercial fishermen high plume density anomalies are associated with both the continental shelf 180 m and the depth of the upper limit of methane hydrate stability depth mhsd that occurs near 500 m in the ne pacific the observed anomalies on the cascadia slope may be due to the warming of seawater at intermediate depths suggesting that modern climate change has begun to destabilize the climate sensitive hydrate reservoir within the cascadia margin sediments reanalysis of similar plume images on the north american atlantic slope suggests a lack of correlation between observed plume depths and the mhsd for much of the latitudinal range

the origin of hydrocarbon source rocks in the austrian molasse basin eocene oligocene transition organic rich rocks schoneck formation from five wells representing a section across the northern paleo slope of the austrian molasse basin were studied using a multi method approach including petrography x ray diffraction organic and inorganic geochemistry and c and n isotopes of the organic material organic matter accumulation commenced during the latest eocene and was dependent on variations of currents salinity organic productivity and nutrient supply initial marl deposition and phosphorite formation under dysoxic conditions was followed by organic rich mud deposition associated with benthic and photic zone anoxia this paleoceanographic situation resembles the first isolation of the western central paratethys deposition of organic rich rocks terminated during lower oligocene time when changing current patterns and decreasing salinity caused a breakdown of water column stratification even though the schoneck formation is an excellent source rock major differences exist in the petroleum potential of the schoneck formation deposited in upper and lower basin slope settings the schoneck formation from the upper slope is characterised by toc contents up to 12 and hi values between 500 and 600 mghc gtoc in the lower slope settings toc values are generally below 2

the 2009 l aquila central italy mw6 3 earthquake main shock and aftershocks 1 a m w 6 3 earthquake struck on april 6 2009 the abruzzi region central italy producing vast damage in the l aquila town and surroundings in this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks the distribution of aftershocks 712 selected events with m l 2 3 and 20 with m l 4 0 defines a complex 40 km long nw trending extensional structure the main shock fault segment extends for 15 18 km and dips at 45 to the sw between 10 and 2 km depth the extent of aftershocks coincides with the surface trace of the paganica fault a poorly known normal fault that after the event has been quoted to accommodate the extension of the area we observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes

correlated transient fluid pulsing and seismic tremor in the costa rica subduction zone continuous measurements of fluid flow were made over a six month period across the nicoya peninsula costa rica pacific convergent margin utilizing osmotically driven fluid flow meters designed to quantify both inflow and outflow rates on the order of 10 5 to 3 cm d significant transience in flow was observed through the surface of the forearc three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out of sequence thrust oost zone over along margin strike distances of 30 km amplitudes of ground velocity recorded on collocated ocean bottom seismometers obs increase during the three correlated flow events the seismic signal has frequency characteristics that resemble volcanic and non volcanic tremor we hypothesize that repeated plate boundary slow slip events potentially originating at the up dip limit of the seismogenic zone generate the observed signals within the toe of the forearc we propose a model in which the poro elastic stress strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments the former generates the seismic tremor like noise recorded by the obss and the latter generates the flow transients recorded by the fluid flow meters we suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible d 2005 elsevier b v all rights reserved

the effectiveness of a distant accelerometer array to compute seismic source parameters the april 2009 l aquila earthquake case history the 6 april 2009 mw 6 3 l aquila earthquake central italy has been recorded by the irpinia seismic network isnet about 250 km southeast of the epicenter up to 19 three component accelerometer stations could be used to infer the main source parameters with different seismological methods we obtained an approximate location of the event from arrival times and array based back azimuth measurements and estimated the local magnitude 6 1 from an at tenuation relation for southern italy assuming an omega square spectral model we inverted s wave displacement spectra for moment magnitude 6 3 corner frequency 0 33 hz stress drop 2 5 mpa and apparent stress 1 6 mpa waveform modeling using a point source and an extended source model provided consistent moment tensors with a centroid depth around 6 km and a prevalently normal fault plane solution with a dominant directivity toward the southeast the relatively high corner frequency and an overestimated moment magnitude of 6 4 from moment tensor inversions are attributed to the rupture directivity effect to image the rupture geometry we implemented a beamforming technique that back projects the recorded direct p wave amplitudes into the earthquake source region a northwest southeast striking rupture of 17 km length is imaged propagat ing with an average velocity up to 3 km s this value is significantly higher than our estimate of 2 2 km s from s wave spectra our case study demonstrates that the use of array techniques and a dense accelerometer network can provide quick and robust estimates of source parameters of moderate sized earthquakes located outside the network

the oligocene maikop series of lahich eastern azerbaijan paleoenvironment and oil source rock correlation abstract the maikop formation deposited in eastern azerbaijan during oligocene and early miocene represents a prolific source unit for the oils found within the southern gobustan area and the kura depression based on biomarker characteristics the oils are believed to have originated from a clastic source rock deposited in an anoxic to suboxic transitional marine environment with low to moderate input of terrigenous organic matter however due to the thermal immaturity of accessible maikop rocks oil source rock correlation based on biomarker fingerprints is hampered the results from a sedimentary succession sampled in the shemakha gobustan area near the village of lahich revealed the presence of marginally mature rr 0 6 0 7 maikop rocks based on lithology geochemical data and paleontological analyses the sampled section contains upper eocene and lower oligocene sediments palynological analyses of dinoflagellate cysts indicate an early rupelian to early chattian oligocene age for the upper part of the investigated maikop succession however the stratigraphic position of the middle and lower part of the succession remains unclear maceral composition as well as biomarker and stable isotope c n data indicate a major contribution of aquatic organisms and variable inputs from macrophytes and land plants to organic matter deposition during the oligocene microbial communities most probably included heterotrophic bacteria and cyanobacteria as well as green sulfur bacteria higher inputs of terrigenous organic matter occurred during deposition of the lower part of the succession increased remineralisation of organic matter in the water column is suggested to result in low toc and hydrocarbon contents as well as 15n enriched total nitrogen of the eocene to earliest oligocene sediments organic carbon accumulation during the oligocene occurred in a stratified episodically euxinic environment this is indicated by low toc s ratios and higher contents of aryl isoprenoids in several samples from the upper units a moderate to good oil source rock correlation with oils from the kura depression is indicated by sterane and triterpane fingerprints as well as carbon isotopic composition of hydrocarbon fractions

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

the 1984 abruzzo earthquake italy an example of seismogenic process controlled by interaction between differently oriented synkinematic faults the evolution of the seismogenic process associated with the ms 5 8 sangro valley earthquake of may 1984 abruzzo central italy is closely controlled by the quaternary extensional tectonic pattern of the area this pattern is characterised by normal faults mainly nnw striking whose length is controlled by pre existing mio pliocene n100f10j left lateral strike slip fault zones these are partly re activated as right lateral normal oblique faults under the quaternary extensional regime and behave as transfer faults integration of re located aftershocks focal mechanisms and structural features are used to explain the divergence between the alignment of aftershocks wsw ene and the direction of seismogenic fault planes defined by the focal mechanisms nnw sse of the main shock and of the largest aftershock ms 5 3 the faults that appear to be involved in the seismogenic process are the nnw sse barrea fault and the e w m greco fault there is field evidence of finite quaternary deformation indicating that the normal barrea fault re activates the m greco fault as right lateral transfer fault no surface faulting was observed during the seismic sequence the apparently incongruent divergence between aftershocks and nodal planes may be explained by interpreting the m greco fault as a barrier to the propagation of earthquake rupturing the rupture would have nucleated on the barrea fault migrating along strike towards nnw the sharp variation in direction from the barrea to the m greco fault segments would have represented a structural complexity sufficient to halt the rupture and subsequent concentration of post seismic deformation as aftershocks around the line of intersection between the two fault planes fault complexities similar to those observed in the sangro valley are common features of the seismic zone of the apennines we suggest that the zones of interaction between nw se and nnw sse plio quaternary faults and nearly e w transfer faults extending for several kilometres in the same way as m greco does might act as barriers to the along strike propagation of rupture processes during normal faulting earthquakes this might have strong implications on seismic hazard especially for the extent of the maximum magnitude expected on active faults during single rupture episodes d 2002 elsevier science b v all rights reserved

integrated stratigraphy of the oligocene pelagic sequence in the umbria marche basin northeastern apennines italy a potential global stratotype section and point gssp for the rupelian chattian boundary the oligocene represents an important time period from a wide range of perspectives and includes significant climatic and eustatic variations the pelagic succession of the umbria marche apennines central italy includes a complete and continuous sequence of marly limestones and marls with volcaniclastic layers that enable us to construct an integrated stratigraphic framework for this time period we present here a synthesis of detailed biostratigraphic magnetostratigraphic and chemostratigraphic studies along with geochronologic results from several biotite rich volcaniclastic layers which provide the means for an accurate and precise radiometric calibration of the oligocene time scale from this study the interpolated ages for the rupelian chattian stage boundary located in the upper half of chron 10n at meter level 188 in the monte cagnero section and corresponding to the o4 o5 planktonic foraminiferal zonal boundary are 28 36 ma paleomagnetic interpolation 28 27 0 1 ma direct radioisotopic dating and 27 99 ma astrochronological interpolation these ages appear to be slightly younger than those reported in recent chronostratigraphic time scale compilations the monte cagnero section is a potential candidate for defining the chattian global stratotype section and point gssp and some reliable criteria are here proposed for marking the rupelian chattian boundary according to international union of geological sciences iugs recommendations

origin of the oligocene manganese deposit at obrochishte bulgaria insights from c o fe sr nd and pb isotopes abstract the large manganese mn deposit at obrochishte ne bulgaria is part of a cluster of similar early oligocene deposits located around present day black sea they collectively constitute the earth s second largest endowment of mn after the kalahari manganese field in africa we have employed a battery of isotopic techniques c o fe sr nd pb to help understand the genesis of this deposit carbon isotope data indicates that some sections of the mn ore layer have diagenetic mnco3 mineralization formed by reaction of mn oxides with organic carbon corg whereas other sections have mnco3 precipitated directly from the seawater column oxygen isotopes show that the high grade mn mineralization had seawater as the fluid source whereas some lower grade sections had a mix of ground water and seawater as fluid sources sr and nd isotope values of ore leachates also indicate that the mn deposition occurred in normal early oligocene seawater nd and pb isotope values suggest that the clastic host sediments were sourced from continental bedrock rather than younger arc volcanic rocks to the west iron isotope composition of the mn ore implies deposition in a redox stratified basin similar to the modern black sea with much of the fe sequestered in deep anoxic euxinic water as sulfides similar to the modern black sea most of the detrital fe was transferred from shallow oxic sediments into deep anoxic euxinic water by an iron shuttle and remobilized mn sequestered in the upper suboxic water layer however during the oligocene the iron shuttle operated intermittently due to the chemocline falling mostly below the shelf break thereby limiting the efficiency of the shuttle mechanism we propose a model for the lower oligocene strata in which intense weathering during the eocene weathering phase produced a thick lateritic crust on the southern european continent the drastic sea level drop at the end of the eocene initiated downcutting of streams through this weathered material transferring fe and mn oxides to the redox stratified western black sea here these oxides were partly or entirely dissolved in the suboxic mn oxides partly fe oxyhydroxides entirely dissolved and anoxic euxinic mn oxides entirely dissolved dissolved fe2 re precipitated water layers eventually fe was re precipitated as sulfide in the deep anoxic euxinic water while mn accumulated in the suboxic water layer transgression in the early oligocene brought this mn rich water onto the shallow shelf where it precipitated as mn oxide then converted to mn carbonates during early diagenesis some mn was also contributed by submarine groundwater discharge further transgression brought lower oxygen water onto the shelf and mn carbonate precipitated directly from the water column the findings from this work provide insights about the unique oligocene geochemical event in the region that lead to the formation of the 2nd largest cluster of mn deposits in the world

on two phase relative permeability and capillary pressure of rough walled rock fractures this paper presents a conceptual and numerical model of multiphase flow in fractures the void space of real rough walled rock fractures is conceptualized as a two dimensional heterogeneous porous medium characterized by aperture as a function of position in the fracture plane portions of a fracture are occupied by wetting and nonwetting phase respectively according to local capillary pressure and accessibility criteria phase occupancy and permeability are derived by assuming a parallel plate approximation for suitably small subregions in the fracture plane for log normal aperture distributions a simple approximation to fracture capillary pressure is obtained in closed form it is found to resemble the typical shape of leverett s j function wetting and non wetting phase relative permeabilities are calculated by numerically simulating single phase flows separately in the wetted and non wetted pore spaces illustrative examples indicate that relative permeabilities depend sensitively on the nature and range of spatial correlation between apertures it is also observed that interference between fluid phases flowing in a fracture tends to be strong with the sum of wetting and nonwetting phase relative permeabilities being considerably less than 1 at intermediate saturations

the mechanics of intermittent methane venting at south hydrate ridge inferred from 4d seismic surveying sea floor methane vents and seeps direct methane generated by microbial and thermal decompositions of organic matter in sediment into the oceans and atmosphere methane vents contribute to ocean acidification global warming and providing a long term e g 500 4000 years powell et al 1998 life sustaining role for unique chemosynthetic biological communities however the role methane vents play in both climate change and chemosynthetic life remains controversial primarily because we do not understand long term methane flux and the mechanisms that control it milkov et al 2004 shakhova et al 2010 van dover 2000 vents are inherently dynamic and flux varies greatly in magnitude and even flow direction over short time periods hours to days often tidally driven boles et al 2001 tryon et al 1999 but it remains unclear if flux changes at vents occur on the order of the life cycle of various species within chemosynthetic communities months years to decades leifer et al 2004 torres et al 2001 and thus impacts their sustainability here using repeat high resolution 3d seismic surveys acquired in 2000 and 2008 we demonstrate in 4d that hydrate ridge a vent off the oregon coast has undergone significant reduction of methane flow and complete interruption in just the past few years in the subsurface below a frozen methane hydrate layer free gas appears to be migrating toward the vent but currently there is accumulating gas that is unable to reach the seafloor through the gas hydrate layer at the same time abundant authigenic carbonates show that the system has been active for several thousands of years thus it is likely that activity has been intermittent because gas hydrates clog the vertical flow pathways feeding the seafloor vent back pressure building in the subsurface will ultimately trigger hydrofracturing that will revive fluid flow to the seafloor the nature of this mechanism implies regular recurring flow interruptions and methane flux changes that threaten the viability of chemosynthetic life but simultaneously and enigmatically sustains it

post seismic relaxation following the great 2004 sumatra andaman earthquake on a compressible self gravitating earth summary the mw 9 0 2004 december 26 sumatra andaman and mw 8 7 2005 march 28 nias earthquakes which collectively ruptured approximately 1800 km of the andaman and sunda subduction zones are expected to be followed by vigorous viscoelastic relaxation involving both the upper and lower mantle because of these large spatial dimensions it is desirable to fully account for gravitational coupling effects in the relaxation process we present a stable method of computing relaxation of a spherically stratified compressible and self gravitating viscoelastic earth following an impulsive moment release event the solution is cast in terms of a spherical harmonic expansion of viscoelastic normal modes for simple layered viscoelastic models which include a low viscosity oceanic asthenosphere we predict substantial post seismic effects over a region several 100s of km wide surrounding the eastern indian ocean we compare observed gps time series from ten regional sites mostly in thailand and indonesia beginning in 2004 december with synthetic time series that include the coseismic and post seismic effects of the 2004 december 26 and 2005 march 28 earthquakes a viscosity structure involving a biviscous burgers body rheology in the asthenosphere explains the pattern and amplitude of post seismic offsets remarkably well

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

seismic and ground deformation monitoring in the seismogenetic region of the southern apennines italy abstract the 23 november 1980 magnitude m s 6 9 southern italy earthquake has been associated by crosson et al 1986 with a faulting system consisting predominantly of two high angle sub perpendicular normal faults forming the corner of down dropped crustal block this model was inferred from a detailed analysis of the space time distribution of aftershocks and their focal mechanisms some features of the acceleration field the focal mechanism of the main shock and the observed displacements along two leveling profiles quantitative modelling of ground displacements which amounted to up to 70 cm was performed through a forward analysis with a dislocation source consisting of several fault segments and by inverse methods with a priori information allowing the parameters of a multiple rectangular fault system to be retrieved quantitative modeling of vertical displacements observed in a nearby seismic region showed a similar mechanism with coseismic movements of up to 12 cm which are consistent with uniform dislocation on two rectangular faults coinciding with the focal mechanism location and magnitude of the earthquakes which occurred in august 1962 m s 5 7 6 1 and 5 4 a system for monitoring ground displacements and related seismic activities has been in place since 1982 in this region and has recently been improved on the basis of our knowledge of the seismic source mechanisms the aim is to study the stress regime during interseismic phases to gain a better understanding of the physics of earthquake processes and to discover any patterns in earthquake occurrences in the seismogenetic regions of the apennines

origin and evolution of fracture hosted methane hydrate deposits 1 fracture hosted methane hydrate deposits exist at many sites worldwide these sites often have hydrate present as vein and fracture fill as well as disseminated through the pore space we estimate that thousands to millions of years are required to form fracture systems by hydraulic fracturing driven by occlusion of the pore system by hydrate this time scale is a function of rates of fluid flow and permeability loss low permeability layers in a sedimentary column can reduce this time if the permeability contrast with respect to the surrounding sediments is of order 10 or greater additionally we find that tensile fracturing produced by hydrate heave around hydrate lenses is a viable fracture mechanism over all but the lowermost part of the hydrate stability zone with our coupled fluid flow hydrate formation model we assess fracture formation at four well studied hydrate provinces blake ridge offshore south carolina hydrate ridge offshore oregon keathley canyon block 151 offshore louisiana and the krishna godavari basin offshore india we conclude that hydraulic fracturing due to pore pressure buildup is reasonable only at hydrate ridge and the krishna godavari basin owing to sediment age constraints and that hydrate filled fractures observed at blake ridge and keathley canyon block 151 are formed either by hydrate heave or in preexisting fractures our findings offer new insight into the processes and time scales associated with fracture hosted hydrate deposits which help further our understanding of hydrate systems

transient hydraulic fracturing and gas release in methane hydrate settings a case study from southern hydrate ridge episodic seafloor methane venting is associated with focused fluid flow through fracture systems at many sites worldwide we investigate the relationship between hydraulic fracturing and transient gas pressures at southern hydrate ridge offshore oregon usa two colocated seismic surveys acquired 8 years apart at hydrate ridge show seismic amplitude variations interpreted as migration of free gas in a permeable conduit horizon a feeding an active methane hydrate province the geophysical surveys also reveal transients in gas venting to the water column we propose that episodic gas migration and pressure fluctuations in the reservoir underlying the regional hydrate stability zone rhsz at southern hydrate ridge influence methane supply to the rhsz and are linked with periodic fracturing and seafloor methane venting we model the effect of pore pressure variations within the deep methane source on fracturing behavior with a 1d model that couples multiphase flow hydrate accumulation and pore pressure buildup as the reservoir pressure increases fractures open when the pore pressure exceeds the hydrostatic vertical effective stress gas then flows through the fractures and vents at the seafloor while hydrate precipitates in the fracture system we show that active seafloor gas venting occurs for approximately 30 years and that the available methane reservoir is exhausted 30 to 55 years after the onset of pressure buildup this provides important constraints on the time scale of transient fluid flow at southern hydrate ridge and illustrates how pore pressure pulses affect fluid flow and fracturing behavior in active methane hydrate provinces

quantification of loss of calcite pyrite and organic matter due to weathering of toarcian black shales and effects on kerogen and bitumen characteristics abstract comparison of geochemical data on posidonia shale early toarcian from a shallow unweathered core and from adjacent weathered exposures of the same fades was performed results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering due to this process of weathering the bulk composition of organic matter especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles are changed estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

evidence of paleo cold seep activity from the bay of bengal offshore india 1 we report evidence of paleo cold seep associated activities preserved in methane derived carbonates in association with chemosynthetic clams calyptogena sp from a sediment core in the krishna godavari basin bay of bengal visual observations and calculations based on high resolution wet bulk density profile of a core collected on board r v marion dufresne may 2007 show zones of sharp increase in carbonate content 10 55 vol within 16 20 meters below seafloor mbsf the presence of calyptogena clam shells chimneys shell breccias with high mg calcite cement and pyrite within this zone suggest seepage of methane and sulfide bearing fluid to the seafloor in the past highly depleted carbon isotopic values 13c ranges from 41 to 52 vpdb from these carbonates indicate carbon derived via anaerobic oxidation of methane extrapolated mean calendar age 58 7 ka b p of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the u th based depositional age 46 2 3 7 and 53 0 1 6 ka of authigenic carbonates sampled from this level thereby constraining the younger age limit of the carbonate deposition methane expulsion events the observed carbonate deposition might have resulted from the flow of methane enriched fluids through the fracture network formed because of shale diapirism

deep petroleum occurrences in the lower kura depression south caspian basin azerbaijan an organic geochemical and basin modeling study abstract high sedimentation rates as much as 2500 m ma during pliocene pleistocene with a resultant undercompacted section as thick as 10 000 m and lower than normal geothermal gradients are the main characteristics which have created all the means for generation and preservation of oil at deep layers in the lower kura depression oils collected from eight different oil fields for analyses seem to have originated from a common source rock which probably is clastic deposited in relatively subanoxic to suboxic transitional marine environment receiving low to moderate input of terrestrial organic matter oils from shallow a computer aided basin modeling study has been carried out to outline the spatial variation of the oil window and thus help in further identification of possible source rocks for the reservoired oil in the lower kura depression results suggest that the potential hydrocarbon source horizons of the miocene and pliocene red bed series of the so called productive succession are even at depocenter areas immature with respect to oil generation and thus are very unlikely to have been source rocks for the reservoired oils however the oligocene lower miocene maykop rocks are marginally mature to mature depending on locality and the eocene and older rocks are mature with respect to oil generation at all representative field locations oil generation commenced at the end of pliocene and continues at present at depths between 6000 and 12 000 m an unusually deep 10 000 m oil window in the depocenter areas has been caused by the depressed isotherms due to extremely high sedimentation rates up to 3000 m ma for the last two million years the main phase of oil generation is taking place at depths greater than what most of the wells in the study are have reached

geochemical evaluation of hydrocarbons and their potential sources in the western south caspian depression republic of azerbaijan abstract the western south caspian depression located in offshore azerbaijan contains significant accumulations of oil and gas in upper tertiary fluvial deltaic sediments the active tertiary hydrocarbon system is a product of unique paleogeographic and tectonic events that led to paleogene deposition of organic rich source rocks rapid pliocene subsidence concurrent with voluminous supply of clastic sediments and development of anticlinal traps with abundant shale diapirs molecular characterization of selected oil samples indicates most of the oils are sourced from similar organic facies the molecular characteristics are consistent with oils sourced from a tertiary slightly calcareous marine clastic facies examination of oil molecular characteristics oil oil correlations molecular characteristics of selected source rock samples maturation models and potential migration pathways suggests the oil is not syngenetic but most likely sourced from deeper miocene and older marine shales most of the oils have low to moderate organic maturities vre 0 75 0 85 relative to conventional peak generation windows significant variations in oil gravity and whole oil gas chromatogram character suggest post emplacement bacterial and fractionation alteration several oils display characteristics consistent with multiple phases of trap charging the bulk of reservoired gases examined in this study have been sourced from mixed terrestrial marine kerogen generated at organic maturities of vre 0 80 1 00 with some biogenic low maturity mixing none of the gases examined were sourced from the thermal destruction of liquid hydrocarbons we postulate multi stage hydrocarbon emplacement into evolving structural traps the first phase of emplacement occurred in the middle pliocene when tectonic movement and increased subsidence initiated early trap reservoir formation hydrocarbon generation and migration late rapid subsidence from quaternary tectonic activity produced additional hydrocarbons to replenish older depleted traps and charge newly formed traps this late tectonic activity also extensively redistributed hydrocarbon accumulations degassed some that were breached by faults and destroyed other oil pools thermal disequilibrium from the rapid subsidence delayed hydrocarbon generation and increased the minimum depth required for the onset of liquid hydrocarbon generation

perylene as an indicator of conifer fossil wood degradation by wood degrading fungi the occurrence of perylene in middle jurassic fossil wood and miocene xylites from poland is described along with its correlation with unsubstituted polycyclic aromatic hydrocarbons pahs as well as cellulose content both middle jurassic and miocene wood remnants were of relatively low maturity ca 0 2 0 3 vitrinite reflectance rr had excellent preservation of biomarkers and biomolecules and in the case of the middle jurassic fossil wood samples generally good preservation of anatomical structures due to early diagenetic mineralisation the results from 42 middle jurassic and 8 miocene most taxonomically defined fossil wood fragments demonstrated a negative correlation between the concentration of perylene and those of generally typical conifer biomarkers e g cadalene dehydroabietane simonellite and retene in addition good correlation r2 0 81 was observed between the ratio of perylene to the above conifer biomarkers and the ratio of pahs phenanthrene and fluoranthene and pyrene to the conifer biomarkers this implies that the high concentration of perylene in fossil wood indicate its extensive degradation during decay transport and early diagenesis we defined a conifer wood degradation index as cwdi perylene perylene cadalene retene simonellite dehydroabietane cwdi perylene perylene cadalene retene simonellite dehydroabietane and observed a wide range of values 0 001 for less degraded wood to 0 95 for highly degraded samples anatomical wood preservation was associated with cwdi values in most of the samples characterised by poorly preserved anatomy high cwdi values were observed while anatomically well preserved samples generally had lower cwdi values we determined similar 13c values for perylene from the fossil wood samples 26 4 to 27 8 whereas the values for the conifer biomarkers were slightly higher and varied from 25 6 to 26 6 in contrast pyrene was depleted in 13c 27 5 to 28 2 the carbon isotope values of perylene are consistent with an origin from wood degrading fungi

seismic imaging of a fractured gas hydrate system in the krishna godavari basin offshore india gas hydrate was discovered in the krishna godavari kg basin during the india national gas hydrate program nghp expedition 1 at site nghp 01 10 within a fractured clay dominated sedimentary system logging while drilling lwd coring and wire line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect three dimensional 3d seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures a system of two fault sets was identified part of a typical passive margin tectonic setting the lwd derived fracture network at hole nghp 01 10a is to some extent seen in the seismic data and was mapped using seismic coherency attributes the fractured system around site nghp 01 10 extends over a triangular shaped area of 2 5 km2 defined using seismic attributes of the seafloor reflection as well as seismic sweetness at the base of the gas hydrate occurrence zone the triangular shaped area is also showing a polygonal nearly hexagonal fault pattern distinct from other more rectangular fault patterns observed in the study area the occurrence of gas hydrate at site nghp 01 10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source the triangular shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits additionally the fault associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone it is proposed that there are additional locations in the kg basin with possible gas hydrate accumulation of similar tectonic conditions and one such location was identified from the 3d seismic data 6 km nw of site nghp 01 10

the geneses of sedimentary organic matter with anomalous 13c enriched isotopic composition in saline and freshwater lakes a case study of lacustrine source rocks from dongpu and qikou sags bohai bay basin eastern china abstract the carbon isotopic composition of sedimentary organic matter 13com is notably important for the genetic identification of source rock and its products the sapropelic organic matter mostly plankton with high hydrogen index is generally depleted in 13c as compared to humic organic matter mainly higher plants with lower hydrogen index however some lacustrine sediments contain sapropelic source rocks with anomalous 13c enriched isotopic ratios especially reported in freshwater lakes the purpose of this study is to discuss the geneses of lacustrine sedimentary organic matter characterized by anomalous 13c enriched ratios in saline and freshwater sediments to this end we integrate the detailed organic geochemical data including rock eval analysis data total organic carbon contents total organic carbon isotopic compositions biomarkers and trace element concentrations of 64 saline lake sediments and 39 freshwater lake sediments obtained from the paleogene shahejie formation of dongpu sag and qikou sag separately in bohai bay basin of eastern china both sags exist samples with high hydrogen index values hi 400 mg g and high total organic carbon contents toc 2 but anomalous 13c enriched isotopic ratios up to 21 1 in qikou sag the 13com values of sapropelic kerogen correlate positively with toc contents the anomalous enrichment of 13c in organic matter is associated with extremely high productivity of algae such as algae bloom in dongpu sag the enrichment of 13c in organic matter is attributed to the significant increase of drought and salinity high salinity and aridity climate may lead to the abundance of c4 plants and chlorobium as well as the enrichment of 13c in plankton

depositional environment and hydrocarbon source potential of the oligocene ruslar formation kamchia depression western black sea abstract the oligocene ruslar formation is a hydrocarbon source rock in the kamchia depression located in the western black sea area depositional environment and source potential of the predominantly pelitic rocks were investigated using core and cuttings samples from four offshore wells in these wells the ruslar formation is up to 500 m thick based on lithology and well logs the ruslar formation is subdivided from base to top into units i vi dysoxic to anoxic conditions and mesohaline to euhaline salinities prevailed during deposition of the ruslar formation relatively high oxygen contents occurred during early solenovian times lower part of unit ii when brackish surface water favoured nannoplankton blooms and the deposition of bright marls solenovian event anoxic conditions with photic zone anoxia were established during late oligocene times units iii and iv and probably reflect a basin wide anoxic event in the eastern paratethys during kalmykian times organic carbon content in the ruslar formation is up to 3 autochthonous aquatic and allochthonous terrigenous biomass contribute to the organic matter relatively high amounts of aquatic organic matter occur in the lower part of the ruslar formation units i and ii and in its upper part unit vi diatoms are especially abundant in the lower part of unit vi the kerogen is of type iii and ii with hi values ranging from 50 to 400 mghc gtoc units i and ii pshekian lower solenovian are characterized by a fair to good potential to produce gas and oil but potential sources for gas and oil also occur in the upper oligocene units iv vi

stable carbon isotopes of amorphous kerogens from phanerozoic sedimentary rocks amorphous kerogens from phanerozoic sedimentary rocks may be divided into two groups on the basis of their 13c values h amorphous kerogens have isotopic values in the range of 24 to 20 per mil and l amorphous kerogens have isotopic values in the range of 35 to 26 per mil the occurrence of amorphous kerogens in the intermediate isotopic range from one rock unit in the data set suggests a weak continuum may exist between these two groups phytoplankton and to a lesser extent zooplankton and bacteria are considered to be the precursors for both kerogen types a plausible explanation for this dichotomy may be found in the source of co2 utilized by phytoplankton which is considered to be controlled by environmental factors h amorphous kerogens are expected to occur in silled basins that are overlain by expansive well circulated deep 500 m water where the prevailing source of carbon in the photic zone is atmospheric derived co2 conversely l amorphous kerogens are expected to occur in restricted basins that are overlain by stratified shallow 200 m water where the prevailing source of carbon in the photic zone may be organic derived co2

capillary effects on hydrate stability in marine sediments 1 we study the three phase liquid gas hydrate stability of the methane hydrate system in marine sediments by considering the capillary effects on both hydrate and free gas phases the capillary pressure a measure of the pressure difference across a curved phase interface exerts a key control on the methane solubility in liquid hydrate l h and liquid gas l g systems by calculating the l h and l g solubilities as a function of water depth pressure and pore size interface curvature we show how the solubility requirements for forming both gas hydrate and free gas can be met in a three phase zone the top of the three phase zone shifts upward in sediments as the water depth increases and the mean pore size decreases the thickness of the three phase zone increases as the distribution of pore sizes widens the top of the three phase zone can overlie or underlie the bulk three phase equilibrium depth at blake ridge we predict that the three phase zone is 27 7 m thick and that the top of the three phase zone lies 13 m above the predicted bulk equilibrium depth this reconciles the observation of the bottom simulating reflector bsr at blake ridge that is shallower than the predicted bulk equilibrium depth in contrast at hydrate ridge where water depth is shallower we predict that the three phase zone is 20 4 m thick and that the top of the three phase zone lies 0 7 m below the predicted bulk equilibrium depth our model which predicts an upward shift in the top of free gas occurrence with increasing water depth pressure is compatible with worldwide observations that the bsr is systematically shifted upward relative to the bulk equilibrium depth as water depth pressure is increased

gas invasion into water saturated unconsolidated porous media implications for gas hydrate reservoirs abstract gas transport through unconsolidated porous media has been a recent focus in studies of hydrate reservoir dynamics and is important in numerous other geophysical contexts we conduct experiments to examine the controls on gas invasion through sieved sands that are suspended within the water column as air is injected slowly from below we monitor the thickness of the free gas column that accumulates beneath the sand to gauge the difference between the gas and liquid pressure or overpressure just prior to gas invading and passing through the sand layer comparing the threshold overpressures for initial gas invasion using different particle sizes our experiments demonstrate the control of capillary forces when the effective stress supported by particle contacts is sufficiently large at lower effective stresses smaller sediment overburdens we observe gas invasion before the capillary controlled threshold overpressure is reached these results demonstrate a transition from capillary invasion at high effective stresses to fracture dominated invasion at low effective stresses moreover video documentation reveals evidence for transitions from capillary to fracture dominated behavior within single invasion episodes as the rising gas nears the sediment surface after the initial invasion episode in each experiment we infer that observed reductions in the overpressure needed for subsequent invasions are caused by bubble break up and retention within the sediment column these experiments highlight the importance of effective stress and pore size in determining the mode of gas passage through unconsolidated sediments we discuss the implications of our findings for the dynamics of gas hydrate reservoirs and other geophysical systems

the irpinia italy 1980 earthquake detailed analysis of a complex normal faulting a detailed analysis of near source strong motion and leveling data together with the results of teleseismic waveform modeling by westaway and jackson 1987 and aftershock studies by deschamps and king 1984 allows a satisfactory kinematic description of the complex normal faulting associated with the magnitude ms 6 9 november 23 1980 irpinia earthquake southern italy the three main rupture episodes starting at about 0 20 and 40 s are here associated with better constrained source parameters than in previous studies we first evaluated the triggering time for the 11 closest accelerometers by using the well recorded 40 s strong motion phases this gave the absolute time and location of the dominant episodes of faulting the first rupture propagated mainly toward the northwest on a ne dipping normal fault at a mean velocity close to 3 km s for about 20 km and continued 15 km further on smaller subfaults it was associated with surface breakage in the southeastern part the second rupture started from the southeastern end of the first rupture about 18 s after it and propagated about 20 km toward the southeast on a low angle normal fault dipping 20 ne it was associated with secondary faulting on steeper planes reaching the surface the third and last episode at 39 s nucleated near the first hypocenter at shallower depth and the rupture possibly propagated on a 10 to 15 km long normal fault striking se antithetic to the first activated fault a clear correlation appears between the strength of the geological formations and the existence of surface breakage and shallow aftershock activity

seismic moment summation for historical earthquakes in italy tectonic implications tectonic deformation rates in and around the apennine mountains of italy are studied using seismic moments estimated from macroseismic effects of historical earthquakes northeastward extension in the northern apennines north of 42 5 n accompanies shortening along their northeast flank since the seventeenth century the sparse seismicity in these two zones has included no earthquake with magnitude 6 5 or seismic moment above 6 1018 n m their spatially averaged deformation rates are only 0 3 mm yr 1 but are equal such that the extension and shortening balance with no relative motion between their external surroundings in contrast the numerous historical earthquakes in the central and southern apennines with magnitude 7 and seismic moment 20 1018 n m require northeastward relative velocity across the deforming zone up to 5 mm yr 1 matching the expected relative motion of their surroundings this relative velocity is taken up in part by extension and in part by strike slip depending on the trend of the deforming zone and is not accompanied by en echelon shortening elsewhere in italy the northern apennines thus show different senses and rates of deformation from localities farther south and are thus technically distinct at present in contrast with previous interpretations

the marine photosynthetic carbon isotopic fractionation remained constant during the early oligocene abstract the oligocene has recently been suggested as a time of drastic decrease of marine photosynthetic carbon isotopic fractionation mphcif leading to a separation of 13 c depleted 13 c pre neogene and 13 c rich 13 c 24 neogene quaternary marine kerogen a more exact timing of this change in fractionation is hindered by the scarcity of well preserved marine kerogen in oligocene sedimentary records we have analyzed 13 c values of about 40 kerogen samples from the often anoxic early oligocene sediments of the hungarian paleogene basin and the carpathian flysch belt the bulk of the well preserved marine kerogen covering a time span between 35 0 and 31 5 m y has 13 c values more negative than 26 5 while marine kerogens from the boundary of early and late oligecene 30 5 m y representing a local ephemerous anoxic event have 13 c values between 23 1 and 23 3 the unambiguously low 13 c values of the early oligocene marine kerogens prove that the recently suggested global decrease of the mphcif could not have begun before the end of the early oligocene the high 13 c values of marine kerogens from the early late oligocene boundary may have been caused by a decrease in mphcif at the end of the early oligocene alternatively they may indicate a local depletion of hco 3 in the photic zone

pressure core based study of gas hydrates in the ulleung basin and implication for geomechanical controls on gas hydrate occurrence pressure coring technology enables the recovery of natural gas hydrate bearing sediments without pressure release and thus without gas hydrate dissociation a total of 21 pressure cores were successfully recovered from the ulleung basin east sea korea during the second gas hydrate drilling expedition in the ulleung basin ubgh2 recovered pressure core samples were utilized to characterize hydrate occurrences and formation mechanisms with non destructive physical property scans x ray ct scans and controlled degassing experiments findings include 1 the p wave velocity in mud rich sediments with grain displacing hydrate increases with decreasing bulk density since hydrate displaces sediment grains and lowers the bulk density 2 the p wave velocity in sand with pore filling hydrate is mostly affected by hydrate saturation rather than bulk density 3 the p wave velocity trend with hydrate saturations for pore filling hydrates follows pore filling model at low hydrate saturations and gradually deviates from pore filling model toward cementation model as hydrate saturation increases 4 gas recovery times during controlled core degassing experiments are proportional to both hydrate saturations and porosities 5 at site ubgh2 3 the thickness of both sub horizontal and sub vertical grain displacing hydrates decreases with depth while the number of sub vertical hydrates does not decrease with depth implying that the formation mechanisms of sub horizontal and sub vertical hydrates differ while growth mechanisms are similar to each other in different growth directions 6 the angle and thickness of grain displacing hydrate bearing fractures are a function of the overburden stress and the hydraulic conductivity but the main governing factor is the overburden stress

temporal variation of methane flares in the ocean above hydrate ridge oregon abstract while bubble plumes have been acoustically imaged in the water column above marine gas hydrate deposits in many studies little is known about the temporal variation in plume intensity in july 2008 we conducted surveys using 3 5 and 12 khz echosounders and a 75 khz acoustic doppler current profiler adcp over the northern and southern summits of hydrate ridge on the cascadia continental margin our study included multiple surveys at both sites including a survey of the northern summit that was repeated 16 times in 19 h seafloor depth at the northern summit is 600 m well within the hydrate stability zone hsz which was below 510 m during our survey based on ctd data three distinct flares a term used to denote the acoustic signature of bubble plumes were detected at northern hydrate ridge nhr and one was detected at southern hydrate ridge shr coincident with where flares were observed a decade ago indicating that the supply of gas is stable on this time scale high resolution bathymetric surveys of nhr and shr acquired with an autonomous underwater vehicle auv flown 50 m above the seafloor indicate that flare locations are correlated with a distinctive pattern of short wavelength seafloor roughness supporting the inference of long term stability in the location of bubble expulsion sites as in previous studies at hydrate ridge flares were not detected with the 3 5 khz echosounder but were clearly imaged at 12 khz by reprocessing routine shipboard adcp data we show that they are also observed in at 75 khz indicating that a wide range of bubble sizes is present the intensity of the flares varied strongly with time two primary sources for flares were observed one located on the regional topographic high showed continuous activity with two times periods of particularly strong flares that are not correlated with tidal height the other located on a local topographic high shows a pulse of increased backscatter that occurred on a falling tide while the time period of observation is not enough to constrain the effect of tidal changes in seafloor pressure on venting the data suggest that tides are not the dominant factor controlling release of bubbles from the seafloor the data support previously suggested models in which temporary sealing of vents by gas hydrate formation and breaking of these barriers as gas pressure builds up is responsible for burp like pulses of gas expulsion we also report the first observations of flares originating within the hsz that extend well above the hsz with little loss of backscatter intensity these represent a new source of methane injection into the upper ocean and possibly the atmosphere flare extension above the hsz may be due to coating of some bubbles by oil or biofilms or to inclusion of particulate matter possibly including floating pieces of hydrate in the plumes although this study provides tantalizing new information on both short term variability in gas expulsion rate and long term stability of vent sites longer well calibrated observations that integrate bubble flux over entire vent fields as a function of time are needed to develop accurate models for the flux of methane into the ocean and atmosphere from seafloor methane vents

the type section of the maikop group oligocene lower miocene at the belaya river north caucasus depositional environment and hydrocarbon potential the type section of the oligocene to lower miocene maikop group considered the main source rock in the eastern paratethys has been studied using geochemical proxies to gain insights into depositional setting and hydrocarbon potential the maikop group at the type section is approximately 600 m 2000 ft thick deposition commenced after a major late eocene sea level drop and a subsequent early oligocene sea level rise the maikop group is composed mainly of carbonate free pelitic rocks calcareous rocks are limited to the lower oligocene succession including the polbian bed that forms a basin wide marker horizon deposited during a time with significantly decreased salinity solenovian event anoxic conditions prevailed and were only interrupted for longer periods during deposition of the lower part of the lower oligocene pshekha formation the polbian bed and the lower miocene olginskaya formation total organic carbon toc contents range up to 3 5 wt hydrogen index values are typically less than 300 mg hydrocarbons hc g toc but reach 420 mg hc g toc in black shales overlying the polbian bed lower morozkina balka formation organic richness of this level approximately 10 m 33 ft thick is controlled by low salinity and high bioproductivity the maikop group could generate approximately 2 0 t hc m2 surface area a significant part 0 45 t m2 comes from the lower morozkina balka formation which generates a high wax paraffinic naphthenic aromatic mixed oil the pshekha upper morozkina balka and batalpashinsk formations would generate low wax oil or condensate the hydrocarbon generation potential of the overlying formations is minor overall the generation potential of the maikop group is surprisingly low

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

effects of multiphase methane supply on hydrate accumulation and fracture generation 1 we simulate methane hydrate formation with multiphase flow and free gas within the regional hydrate stability zone rhsz we find that hydrate distribution and fracture behavior are largely determined by the phase of the methane supply we allow free gas to enter the rhsz when porewater salinity increases to the value required for three phase equilibrium fractures nucleate when the excess pore pressure exceeds the vertical hydrostatic effective stress at hydrate ridge where methane supply is dominantly free gas hydrate saturation increases upwards and fractures nucleate high within the rhsz eventually allowing gas to vent to the seafloor at blake ridge where methane supply is dominantly in the dissolved phase hydrate saturation is greatest at the base of the rhsz fractures nucleate here and in some cases could propagate through the rhsz allowing methane charged water to vent to the seafloor

rupture history of the 2009 l aquila italy earthquake from non linear joint inversion of strong motion and gps data 1 we image the rupture history of the 2009 l aquila central italy earthquake using a nonlinear joint inversion of strong motion and gps data this earthquake ruptured a normal fault striking along the apennines axis and dipping to the sw the inferred slip distribution is heterogeneous and characterized by a small shallow slip patch located up dip from the hypocenter 9 5 km depth and a large deeper patch located southeastward the rupture velocity is larger in the up dip than in the along strike direction this difference can be partially accounted by the crustal structure which is characterized by a high velocity layer above the hypocenter and a lower velocity below the latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km the imaged slip distribution correlates well with the on fault aftershock pattern as well as with mapped surface breakages

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

prolonged post seismic deformation of the 1960 great chile earthquake and implications for mantle rheology 1 contemporary crustal deformation of the southern andean margin shows an interesting feature while nearly all coastal gps sites move landward consistent with inter seismic deformation near a locked subduction fault sites 300 400 km landward of the rupture region of the mw9 5 1960 chile earthquake are moving in the opposite direction we attribute the seaward motion of these inland sites to a prolonged crustal deformation due to mantle stress relaxation following the 1960 great earthquake in order to reproduce the observed seaward motion using a three dimensional finite element model we need to incorporate a mantle viscosity of about 3 1019 pa s the possibility that the seaward motion is caused by a silent slip event on the plate interface at large depths cannot be completely excluded and our analysis provides a working model for future field tests

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

organic matter maturity and hydrocarbon potential of the lower oligocene menilite facies in the eastern flysch carpathians tarcău and vrancea nappes romania abstract bulk organic geochemical and molecular composition data have been used to analyse the hydrocarbon potential and organic matter maturity of the lower oligocene menilite facies from two adjacent tectonic units of the eastern flysch carpathians tarc u and vrancea nappes romania due to the importance of these source rocks in hydrocarbon exploration in entire paratethys realm the data show strong variability in organic matter quantity and quality organic carbon content reaches peak values in the siliceous facies of the lower menilite member up to 8 6 wt toc which contains type ii kerogen with increasing contribution of flysch sedimentation mixed type ii iii kerogen gains importance the biomarker distribution reveals strong variation in the supplied organic matter common for flysch influenced sedimentary environments terrigenous input is marked by epicuticular wax imprint in n alkane distribution and occurrence of conifer biomarkers while marine organic matter origin is expressed by the occurrence of short chain n alkanes and hopanes especially in the siliceous facies thus these source rocks can be classified as oil prone and subordinately mixed oil gas prone the maturity in the outer tectonic unit vrancea is low t max 425 c r o 0 4 but increases towards the inner tarc u nappe t max 430 c r o 0 5 reaching onset of hydrocarbon generation the studied rocks have good petroleum potential but hydrocarbons were generated only in more mature tarc u nappe where solid bitumen veins were observed bitumen impregnation of numerous vitrinite grains possibly suppressed vitrinite reflectance thus leading to more accurate maturity assessment based on molecular proxies biomarker maturity indices the observed difference in maturity levels between the nappes results from the more inner position of the sampled tarc u nappe succession within the orogen relative to the vrancea unit this is related to different burial histories as well as variation in subsequent erosion and exhumation levels the actual hydrocarbon potential in the studied area varies due to local interplay of these critical factors

surface faulting in the southern italian campania basilicata earthquake of 23 november 1980 the campania basilicata earthquake of 23 november 1980 was the largest ms 6 9 and most destructive earthquake that has occurred in this region of southern italy for over 100 years killing more than 3 000 people the consensus among seismologists geologists and earthquake engineers who have studied1 10 this event is in keeping with previous italian earthquakes that it did not produce faulting at the surface this has led to the establishment of a number of models2 3 11 13 requiring an unusual tectonic setting for the southern apennines however on a recent visit to the epicentral region of the earthquake may 1984 we discovered more than 10 km of surface faulting that is consistent with focal mechanisms for this event based on first motion polarities2 4 5 12 and long period waveform studies14 16 which show that it involved normal faulting with one nodal plane dipping at 60 towards the north east our observations of this the first well documented earthquake fault break to be reported in italy suggest that the deformation associated with earthquakes in the southern apennines takes place in the upper 10 15 km of the earth s crust on steep planar normal faults which break the surface as is widely observed in other areas of active extension outside italy

stress triggering and earthquake probability estimates 1 stress triggering and fault interaction concepts are beginning to be incorporated into quantitative earthquake probability estimates however the current methods are limited in their range of compatible earthquake nucleation models i introduce a new general method for translating stress changes into earthquake probability changes which can potentially be used with any physical fault model given the large uncertainties in earthquake probability calculations it is unclear whether the small probability changes resulting from stress transfer are significant and meaningful for the purposes of seismic hazard assessment i present a case study of the effect of the 1992 m7 3 landers california earthquake on the probability of a major earthquake on the san andreas fault in southern california this is a large event in a well studied region which should maximize the probability change signal and minimize the uncertainty even for this scenario the earthquake probability change for a 30 year period is not significant with respect to the initial uncertainty in the earthquake probability this example comparisons with other studies and exploration of parameter space imply that the probability changes due to stress triggering are significant only for time intervals which are short compared to the repeat time of the target fault therefore stress change calculations will be useful in long term seismic hazard assessment only for low slip rate faults otherwise stress triggering calculations are best utilized in the short term immediately following a major earthquake

patterns of subsurface fluid flow at cold seeps the hikurangi margin offshore new zealand based on multichannel seismic geoacoustic and methane sensor data four different areas along the hikurangi margin show multiple indications for seep activity including bright spots transparent zones vertical chimneys and the occurrence and distribution of bottom simulating reflectors locations where these features reach the seafloor are characterised by high backscatter intensity on sidescan sonar images and transparent zones in sediment echosounder profiles while methane sensors show episodic elevated methane concentrations near the seep sites methane discharge is facilitated by reduced hydrostatic pressure during low tides the greatest number of seeps at opouawe bank correlates with the highest methane activity along the hikurangi margin high heat flow values on flanks of ridges and low heat flow values on anticlines reflect a topographic effect on subsurface temperatures elevated heat flow occurs in the vicinity of seeps on opouawe bank we propose that there are two drivers behind methane seepage with respect to the migration pathways of methane through the gas hydrate stability zone ghsz to the seafloor 1 structurally controlled and 2 stratigraphically controlled in the structural model vertical chimneys are the major pathways for methane through the ghsz part of the upwardly migrating methane forms gas hydrate within the chimney in the stratigraphic model methane migration is stratigraphically controlled beneath seeps that are located on bathymetric highs and or where subsurface anticlines occur beneath seeps the structurally controlled seeps produce higher methane escape at the seafloor than those that are stratigraphically controlled a combination of both driving mechanisms results in the highest methane seepage rates at the tui seep on opouawe bank

a variable slip fault model for the 1908 messina straits italy earthquake by inversion of levelling data summary a variable slip fault model is presented for the 1908 december 28 messina italy earthquake it has been obtained by inversion of levelling data using a gradient method fault location and mechanism are consistent with an approximately n s orientation and normal faulting on a low angle plane dipping 39 with about 45 of strike slip component the main difference from a homogeneous slip model is represented by a higher slip area up to 3 m located close to the city of reggio calabria it is interpretable as a major asperity which is related to the main fracture episode this is in agreement with some macroseismic evidence and the same structure could be responsible for the nearby recent seismic activity the area which effectively slipped is all confined within the messina straits this result differs from the homogeneous slip model recently proposed by capuano et al 1988

fracture networks and hydrate distribution at hydrate ridge oregon abstract analysis of resistivity at the bit rab images acquired during ocean drilling program odp leg 204 to southern hydrate ridge oregon reveals changes in the distribution and orientation of resistive fractures between the different hydrologic provinces sampled fractures on the ridge crest at sites 1247 1248 and 1250 are typically high angle 60 with isotropically distributed strikes while those on the ridge flanks at sites 1244 1246 have lower dips 20 60 and strike parallel to the trend of the ridge the eastern slope basin site 1251 lacks significant fracturing these differences indicate that the minimum principal stress 3 direction rotates to horizontal at the ridge crest as a result of topographically driven extension and gravitational collapse of the ridge chaotic fracturing on the ridge crest results from the interaction of the stress state and free gas migration which is confined to high permeability sediments and fracture zones by capillary pressure constraints in contrast on the ridge flanks well ordered fractures that agree with stress orientations determined from borehole breakouts result from an obliquely dipping 3 and the predominance of aqueous rather than gaseous flow

depositional environment and hydrocarbon potential of the oligocene menilite formation in the western carpathians a case study from the loucka section czech republic abstract the eocene oligocene boundary in the paratethys area represents a period associated with a major extinction event followed by anoxic events a good understanding of the factors controlling the formation of organic rich layers is a key for prediction of source rock distributions an excellent opportunity to study these factors is provided by the loucka section situated in the silesian unit of the czech republic the menilite formation is subdivided into the subchert member chert member dynow marlstone and sitbo ice member and comprises non calcareous shales marlstones and cherts the lithological variations reflect strongly depositional environment which caused strong changes in geochemical parameters and source rock potential the ratio of total organic carbon to total sulphur toc ts and methylated 2 methyl 2 trimethyltridecyl chroman mttc ratios supported by paleontological evidence show normal marine to brackish water conditions pr ph ratios indicate strictly anoxic conditions during deposition of the upper part of the subchert member and the lower part of the chert member very low steranes hopanes ratios reflect strong bacterial activity during deposition of the chert member very high hi values 600 mg hc g toc and the apparent absence of terrestrial macerals suggest that high amounts of c29 steranes and long chain n alkanes in this member result from the input of algal material the menilite formation contains mainly type ii kerogen and typically holds a good source rock potential hi values 600 mg hc g toc are observed in the chert member while values the source potential index spi of the entire succession of the menilite formation is about 1 25 t hc m2 which is significantly lower than spi determined for the polish and ukrainian carpathians but mainly due to the lower thickness

facies evolution and stratigraphic correlation in the early oligocene tard clay of hungary as revealed by maceral biomarker and stable isotope composition abstract hydrocarbon source rocks i e tard clay formation containing type ii organic matter were deposited in the hungarian paleogene basin during lower oligocene a major contribution of aquatic organisms green algae dinoflagellates chrysophyte algae and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n alkane distribution patterns composition of steroids and 13c of hydrocarbon biomarkers microbial communities included heterotrophic bacteria cyanobacteria chemoautotrophic bacteria as well as green sulphur bacteria the presence of methanotrophic bacteria is indicated by 13c depleted hop 17 21 ene higher inputs of terrestrial organic matter occurred during deposition of the lower and uppermost units of the tard clay formation the terpenoid hydrocarbon composition argues for angiosperm dominated vegetation in the area of the hungarian paleogene basin diterpenoid hydrocarbons derived from the resins of conifers are about 2 3 enriched in 13c compared to the angiosperm biomarkers environmental conditions changed from marine to brackish accompanied by oxygen depletion in the lower parts of the water column organic carbon accumulation during this period was a consequence of stagnant bottom water conditions in the hungarian paleogene basin due to salinity stratification this is indicated by low pristane phytane ratios varying from 0 27 to 1 44 enhanced ratios of dimethylated versus trimethylated mttcs 0 14 0 59 and the presence of aryl isoprenoids from 0 4 to 14 1 g g toc a major marine incursion is evidenced by stable isotope ratios of organic matter and carbonates in the uppermost member of the tard clay a transition from brackish towards normal marine conditions is proposed up to 3 anoxic cycles are recognized in the drill core sections separated by minima in pristane phytane ratios and maxima in the depth trends of di tri methylated mttcs and aryl isoprenoid concentrations in combination with the position of maxima of 13c of carbonate and organic matter and an abrupt decrease in perylene concentrations the cycles can be used for intra formational correlation of the tard clay