sandstone matrix olistostrome deposited on intra subduction complex serpentinite franciscan complex western marin county california abstract detailed field mapping in the franciscan complex in western marin county california offers insight into the origins and development of melanges as well as accretionary complex architecture from structurally high to low the study area units comprise a structurally high sandstone matrix olistostrome serpentinite a structurally intermediate sandstone matrix olistostrome early cretaceous nicasio reservoir terrane greenstone and coherent cretaceous greywacke all exhibiting prehnite pumpellyite burial metamorphism the structurally high sandstone matrix olistostrome includes volcanic blocks up to 700 m in diameter and chert blocks up to 100 m in diameter whereas the structurally intermediate olistostrome unit comprises a lithic rich sandstone matrix enclosing volcanic blocks 1 20 m in diameter the youngest detrital zircons in the high olistostrome and the coherent greywacke have u pb ages of 20 m y older than the inferred depositional ages of the units themselves suggesting that the bulk of the detritus comprising these units was derived by exposure and sedimentary recycling of significantly older previously accreted sediments the matrix of both olistostrome units exhibits minimal strain with weak local development of pressure solution cleavage these findings demonstrate introduction of franciscan exotic blocks and development of franciscan block in matrix fabrics through sedimentary sliding and support sedimentary interpretations for more highly strained shale and serpentinite matrix melanges additionally these data suggest that sandstone matrix olistostromes melange may constitute a larger part of the franciscan and other accretionary complexes than previously believed the structurally high olistostrome preserves a depositional contact on serpentinite verifying an intra subduction complex origin for the serpentinite the serpentinite lacks block in matrix structure and likely represents a tectonically emplaced unit derived from the subducting plate as a coherent nappe rather than a sedimentary serpentinite deposit multi kilometer scale west vergent overturned folds with subhorizontal fold axes deform the nappes of the field area and a later generation of open northeast trending folds overprints the earlier folds

converted phases analysis of the campi flegrei caldera using active seismic data abstract we applied a type of depth migration for converted seismic phases to active and passive seismic data sets from the campi flegrei volcanic region in southern italy the migration method is based on the diffraction summation migration technique travel times to grid points in a volume were calculated in smooth p and s velocity models and trace energy near the calculated converted phase time was stacked over multiple sources at one receiver weighting factors based on snell s law at an arbitrarily oriented local interface were applied to better focus trace energy pp reflection images from the active data set provide increased detail to images of the caldera rim from other studies the migrated images also show features near 2 3 km in depth beneath pozzuoli city which may be associated with an over pressured gas volume as suggested by other geophysical investigations possible deeper features near 4 km depth may be related to the presence of the carbonate basement or may image a previously undetected feature such as a small body of strongly thermometamorphosed volcanic rock the current passive earthquake data set from the 1984 ground uplift episode was not well suited to the converted phases analysis due to narrow p s windows and high noise levels in the traces however two stations provide confirmation and extension of imaged features in the active data

charging of the neogene penglai 19 3 field bohai bay basin china oil accumulation in a young trap in an active fault zone the penglai 19 3 pl19 3 oil field the largest offshore oil field in china was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl19 3 anticline was not finally formed until about 2 0 ma and is cut by densely distributed faults source rock and crude oil samples from the pl19 3 field were analyzed to determine the origin and formation mechanisms of this large oil field three organic rich oil prone source rock intervals exist in the bozhong subbasin each of which has a distinct biomarker assemblage oil samples from different wells have different biomarker associations and three source related oil classes were identified within the pl19 3 field based on biomarker compositions and multivariate analysis of the data the pl19 3 field displays considerable compositional heterogeneity the compositional heterogeneity within the field and comparison between oil samples from the pl19 3 field and those from nearby structures suggest three field filling directions which is consistent with the results of migration pathway modeling the pl19 3 field was charged in the north by oil generated from dongying formation source rocks in the eastern bozhong depression and bodong depression in the southeast by oil generated from shahejie formation source rocks in the miaoxi depression and in the northwest by oil generated from shahejie formation source rocks in the central bozhong depression oil charge from multiple source rock intervals and multiple generative kitchens and focusing of oil originating from a large area of the bozhong depression into the same trap resulted in rapid oil accumulation in the pl19 3 structure and the formation of this large oil field in a very young trap within an active fault zone

detrital zircon evidence for progressive underthrusting in franciscan metagraywackes west central california we present new u pb ages for detrital zircons separated from six quartzose metagraywackes collected from different franciscan complex imbricate nappes around san francisco bay all six rocks contain a broad spread of late jurassic cretaceous grains originating from the klamath sierra nevada volcanic plutonic arc units young structurally downward consistent with models of progressive underplating and offscraping within a subduction complex the youngest specimen is from the structurally lowest san bruno mountain sheet at 52 ma it evidently was deposited during the eocene none of the other metagraywackes yielded zircon ages younger than 83 ma zircons from both el cerrito units are dominated by ca 100 160 ma grains the upper el cerrito also contains several grains in the 1200 1800 ma interval these samples are nearly identical to 97 ma metasedimentary rock from the hunters point shear zone zircon ages from this melange block exhibit a broad distribution ranging from 97 to 200 ma with only a single pre mesozoic age the albany hill specimen has a distribution of pre mesozoic grains from 1300 to 1800 ma generally similar to that of the upper el cerrito sheet however it contains zircons as young as 83 ma suggesting that it is significantly younger than the upper el cerrito unit the skaggs spring schist is the oldest studied unit its youngest analyzed grains were ca 144 ma and it is the only investigated specimen to display a significant paleozoic detrital component sedimentation and subduction accretion of this tract of the trench complex took place along the continental margin during early to early late cretaceous time and perhaps into eocene time franciscan and great valley deposition attests to erosion of an andean arc that was active over the entire span from ca 145 to 80 ma with an associated accretionary prism built by progressive underthrusting we use these new data to demonstrate that the eastern franciscan complex in the northern and central coast ranges is a classic accretionary prism where younger structurally lower allochthons are exposed on the west and older structurally higher allochthons occur to the east in the heavily studied san francisco bay area

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

application of organic facies studies to sedimentary basin analysis a case study from the yitong graben china abstract an organic facies is defined in this paper as a mappable stratigraphic unit containing organic matter om of a particular genetic type in certain abundance several concepts concerning organic facies are proposed and their significance in basin analysis is discussed in detail a combined sedimentological and organic geochemical investigation has been carried out in the yitong graben and four organic facies and one organic parafacies have been recognized distinct organic basin fill sequences obfs and organic facies association ofa were developed in different sub units of this graben which indicates that the yitong graben had undergone two tectonic subsidence cycles such tectonic subsidence patterns could not have been found out without detailed organic facies analysis confirming that organic facies especially obfs and ofa study is a very useful tool not only for prediction and three dimensional mapping of petroleum source rocks but also for sedimentary basin analysis

provenance of synorogenic foreland basin strata in southwestern montana requires revision of existing models for laramide tectonism north american cordillera

three dimensional seismic tomography from p wave and s wave microearthquake travel times and rock physics characterization of the campi flegrei caldera 1 the campi flegrei cf caldera experiences dramatic ground deformations unsurpassed anywhere in the world the source responsible for this phenomenon is still debated with the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes a multidisciplinary approach dealing with three dimensional delay time tomography and rock physics characterization has been followed selected seismic data were modeled by using a tomographic method based on an accurate finite difference travel time computation which simultaneously inverts p wave and s wave first arrival times for both velocity model parameters and hypocenter locations the retrieved p wave and s wave velocity images as well as the deduced v p v s images were interpreted by using experimental measurements of rock physical properties on cf samples to take into account steam water phase transition mechanisms affecting p wave and s wave velocities also modeling of petrophysical properties for site relevant rocks constrains the role of overpressured fluids on velocity a flat and low v p v s anomaly lies at 4 km depth under the city of pozzuoli earthquakes are located at the top of this anomaly this anomaly implies the presence of fractured overpressured gas bearing formations and excludes the presence of melted rocks at shallow depth a high v p v s anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase finally maps of the v p v s product show a high v p v s horseshoe shaped anomaly located at 2 km depth it is consistent with gravity data and well data and might constitute the on land remainder of the caldera rim detected below sea level by tomography using active source seismic data

time dependent spatial amplitude patterns of harmonic tremor at arenal volcano costa rica seismic wave interferences seismograms recorded at the receivers of a small aperture seismic array usually display very similar waveforms and amplitudes as a consequence of their close proximity during the analysis of the volcanic tremor wave field at arenal volcano costa rica we detected significant differences in the amplitudes of harmonic tremor recorded at the stations of a small aperture 210 m seismic array the amplitude distributions are geometrically complex and characterized by strong gradients they occur just for harmonic tremors any other type of seismic event produces nearly uniform amplitudes across the array this suggests some relation with harmonic frequency content moreover the spatial amplitude patterns change with time some of these observations could be explained by an extreme combination of source path and site effects but they also could be produced by interference of different components of the seismic wave field we use numerical calculations to investigate the amplitude pattern generated by two interfering plane waves and are able to reproduce the main features of the observed amplitude patterns we propose mechanisms that might generate seismic wave fields with multiple components and conclude that interference can explain the complexity and variability of the harmonic tremor wave field at arenal volcano online material wave field animation

u th pb and rb sr geochronology of middle proterozoic granite and augen gneiss salmon river mountains east central idaho coarsely porphyritic granite and augen gneiss in east central idaho have been dated by the u th pb zircon method when plotted on concordia diagrams the results give nonlinear data arrays that indicate the presence of at least one component of inherited radiogenic lead as well as postcrystallization probably recent episodic lead loss nevertheless a systematic relationship between zircon size and convergence of the 207 pb 206 pb ages for the 100 and 100 150 mesh fractions from several samples are interpreted to provide a valid age of about 1 370 m y for these plutons a single sample which is free of inheritance for all size fractions confirms this conclusion rb sr whole rock samples are highly enriched in radiogenic strontium but do not define an isochron probably because the system did not remain closed following crystallization of the plutons intrusive contacts of the granitic rocks indicate that deformation and regional metamorphism of the host yellowjacket formation occurred prior to 1370 ma rather than prior to 1500 ma as previously suggested by others this refinement of the geochronology 1 removes the necessity that the yellowjacket formation and overlying proterozoic metasedimentary rocks of central and east central idaho be pre belt in age 2 permits the traditional age correlation of the east central idaho metasedimentary sequence yellowjacket through lawson creek formations with the belt supergroup and 3 suggests that a re evaluation is in order for paleogeographic models of central idaho especially the proposed topographic high known as the salmon river arch

large scale right slip displacement on the east san francisco bay region fault system california implications for location of late miocene to pliocene pacific plate boundary a belt of northwardly younging neogene and quaternary volcanic rocks and hydrothermal vein systems together with a distinctive cretaceous terrane of the franciscan complex the permanente terrane exhibits about 160 to 170 km of cumulative dextral offset across faults of the east san francisco bay region esfbr fault system the offset hydrothermal veins and volcanic rocks range in age from 01 ma at the northwest end to about 17 6 ma at the southeast end in the fault block between the san andreas and esfbr fault systems where volcanic rocks are scarce hydrothermal vein system ages clearly indicate that the northward younging thermal overprint affected these rocks beginning about 18 ma the age progression of these volcanic rocks and hydrothermal vein systems is consistent with previously proposed models that relate northward propagation of the san andreas transform to the opening of an asthenospheric window beneath the north american plate margin in the wake of subducting lithosphere the similarity in the amount of offset of the permanente terrane across the esfbr fault system to that derived by restoring continuity in the northward younging age progression of volcanic rocks and hydrothermal veins suggests a model in which 80 110 km of offset are taken up 8 to 6 ma on a fault aligned with the bloomfield tolay franklin concord sunol calaveras faults an additional 50 70 km of cumulative slip are taken up 6 ma by the rogers creek hayward and concord franklin sunol calaveras faults an alternative model in which the permanente terrane is offset about 80 km by pre miocene faults does not adequately restore the distribution of 8 12 ma volcanic rocks and hydrothermal veins to a single northwardly younging age trend if 80 110 km of slip was taken up by the esfbr fault system between 8 and 6 ma dextral slip rates were 40 55 mm yr such high rates might occur if the esfbr fault system rather than the san andreas fault acted as the transform margin at this time major transpression across the boundary between the pacific and north american plates at about 3 to 5 ma would have resulted in the transfer of significant slip back to the san francisco peninsula segment of the san andreas fault since that time the esfbr fault system has continued to slip at rates of 11 14 mm yr if this interpretation is valid the esfbr fault system was the pacific north american plate boundary between 8 and 6 ma and this boundary has migrated both eastward and westward with time in response to changing plate margin geometry and plate motions

accurate fault mechanism determinations for a 1984 earthquake swarm at campi flegrei caldera italy during an unrest episode implications for volcanological research we have analyzed 42 microearthquakes 1 ml 3 that occurred at campi flegrei volcanic area during an intense swarm like activity more than 500 events in half a day in the last period of strong ground uplift 1982 1984 focal mechanisms of these earthquakes have been computed by a probability method which uses p wave polarity and s wave polarization data composite focal mechanisms for different groups of earthquakes have also been computed by the same technique results show a well defined fault plane in agreement with the elongation of the epicentral pattern the orientation and dip of this fault plane together with other observations about hypocenter locations and focal mechanisms of the whole seismicity accompanying the ground uplift episode suggest the presence of an elliptical fracture system at the caldera center this fracture system dipping toward the center of the caldera should represent the limit of the most recent caldera collapse which is also indicated by a negative bouguer gravity anomaly moreover an important differential feature among various groups of earthquakes has been shown namely a rotation up to about 30 of the strike of the compressive stress axis between the easternmost and the westernmost events the resulting pattern indicates that the axis is always oriented towards the town of pozzuoli which roughly represents the very center of the caldera and also the center of symmetry of the ground deformation these observations strongly suggest that earthquakes are generated by the variation of the stress field associated with the deformation along prefractured zones because of their greater weakeness this study provides then the first direct evidence that both seismicity and ground deformations have a common origin

u pb zircon geochronology of rocks in the salinas valley region of california a reevaluation of the crustal structure and origin of the salinian block the salinian block in the salinas valley region of central california consists of arc granitic and metasedimentary rocks schist of sierra de salinas sandwiched between coeval high pressure low temperature melange belts u pb zircon ages of three granitic plutons from this region range from 88 to 82 ma and coexisting biotite yielded 4 0 ar 3 9 ar cooling ages of 76 75 ma the u pb ages from detrital zircons indicate derivation of the protolith of the schist from a 117 81 ma igneous provenance muscovite and biotite 4 0 ar 3 9 ar cooling ages of 72 68 ma from the nearby schist are distinctly younger than those from the granitic plutons these data indicate that deposition and metamorphism of the schist occurred after emplacement of adjacent granitic rocks contradicting the prevailing view that the schist comprises the local framework for the salinian arc we propose that the schist of sierra de salinas was thrust beneath the salinian magmatic arc along a campanian thrust fault that has not been recognized this hypothesis implies that the salinian arc originated as a klippe of basement rocks derived from the vicinity of the western mojave desert thrusting initiated southeastward migrating laramide tectonism of a style similar to that which formed the vincent thrust and the latest cretaceous and paleocene pelona and orocopia schists of southern california and southwestern arizona

organic facies of the asbian early carboniferous queensferry beds lower oil shale group south queensferry scotland and a brief comparison with other carboniferous north atlantic oil shale deposits abstract the 71 m foreshore exposure of the queensferry beds at south queensferry is currently the best accessible section of the oil shale group of the midland valley of scotland a combination of bulk organic geochemistry and kerogen microscopy palynofacies organic petrology is used to define four organic facies and one variant organic facies 1 occurs in silty mudstones has a mean toc of only 2 and type iii iv gas prone or inert kerogen hi 800 variant 3a is additionally characterised by an abundance of small 4 m spherical cells of possible cyanobacterial origin occurring in one sample adjacent to a stromatolitic limestone organic facies 2 is transitional between 1 and 3 organic facies 4 has atypically low c s ratios and corresponds to the pumpherston marine band these organic facies can also be distinguished using biomarker parameters pr ph oep c25 c15 predominant carbon number etc the hi is very strongly correlated with the relative fluorescence of the organic matter and strongly correlated with the aom phytoclast ratio and the botryococcus and total alginite contents it is inversely correlated with the diameter of black equant phytoclasts the organic rich shales thus correspond to distal lower energy anoxic conditions during periods of meromixis high preservation low dilution similar carboniferous lacustrine source rocks occur in eastern canada and east greenland all are characterised by large lateral extents 500 2 000 km2 a geographic and temporal association with strong syndepositional subsidence generally low botryococcus contents and a dominance of amorphous type ii kerogen

determination of critical parameters for evaluating coal measure shale gas in china abstract coal measure shale is one of the most abundant types of marine continental shales in china two sets of typical coal measure shales in china are developed in the shanxi formation ordos basin and in the longtan formation guizhou province in this study thermal simulation rock pyrolysis and x ray diffraction experiments were used to analyze four coal measure shale samples collected from typical areas of china based on the study of hydrocarbon generation process of the samples the lower limits of thermal maturity ro of favorable and target areas for coal measure shale were 1 8 and 2 5 respectively the threshold ro value of oil generation in coal measure shale was preliminarily inferred to be 0 6 the gaseous hydrocarbon production per unit of s1 s2 after the gas generation threshold was linearly and positively correlated with ro the lower limits of total organic carbon toc corresponding to the favorable and target areas were 2 45 wt and 2 84 wt respectively combined with x ray diffraction experiments the diagenetic stage and the hydrocarbon generation model of coal measure shale were established and could be divided into four evolutionary stages the results of this study have direct scientific and practical significance for the evaluation of gas content and selection of areas in china for the extraction of coal measure shale

source rock potential toc hydrogen index evaluation by integrating well log and geochemical data abstract evaluation of source rock potential using well log data alone e g density or sonic log is limited to the assessment of total organic carbon toc content well logs that directly measure the most important source quality parameter the hydrogen content of the kerogen do not exist therefore a method is proposed that combines log derived toc data with calibration schemes relating toc content to hydrogen index and maturity for individual source rock sets the method has been applied to the compositionally heterogeneous kimmeridge clay formation of the north sea and the homogeneous lower toarcian shale of n germany the combination of well log and geochemical data greatly improves the accuracy with which the lateral and vertical distribution of source rocks and their potential can be predicted on a basin and prospect level

late cretaceous truncation of the western idaho shear zone in the central north american cordillera the mesozoic boundary separating accreted oceanic rocks and continental north america in west central idaho forms a prominent right angle bend the origin and kinematic significance of which have had a great influence on models for the evolution of the north american cordilleran orogen based on structural and geochronologic relations we conclude that the bend in the steep crustal boundary is formed by the intersection of two shear zones with different ages structural fabrics of the north striking western idaho shear zone are overprinted by penetrative structures of the west northwest striking orofino shear zone u pb sensitive high resolution ion microprobe ages on metaplutonic rocks and late synkinematic leucocratic dikes constrain the age of deformation in the orofino shear zone to ca 90 70 ma distinctly younger than ca 120 90 ma magmatism and deformation within the western idaho shear zone the orofino shear zone is interpreted as a southwest vergent contractional relay structure that linked basement cored foreland thrusts of the middle and southern rocky mountains with the deep crustal duplex of the shuswap complex in the canadian rockies truncation ca 90 ma terminated late cretaceous margin parallel translation of terranes along the western idaho shear zone and required displacement to step outboard to poorly understood structures to the west

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

high resolution seismic imaging of the mw5 7 2002 molise southern italy earthquake area evidence of deep fault reactivation 1 we investigate the seismic structure of the mw5 7 2002 molise earthquake area in order to understand the role of e w trending strike slip faults in the tectonics of the southern apennines we apply an innovative seismic migration technique to a high quality data set of earthquakes recorded at a dense local network sp converted waves are migrated in depth to image the high impedance contrast of the apulian platform top buried under the apennines allochthonous cover the continuity of the migrated seismic horizon is broken by vertical steps that we systematically picked along 200 cross sections the best location points of these structures define two main tectonic features the first one is related to nw se oriented normal faults and is consistent with the sw flexure of the foreland lithosphere beneath the orogenic belt the second one indicates that shallow e w oriented trans tensional faults are concentrated directly above the deeper 10 20 km strike slip fault delineating the geometry of a negative flower type structure this fault system delimits a depressed sector of the apulian platform whose geometry is consistent with a pull apart basin inherited from a previous left lateral strike slip tectonic regime the buried structure is analogous to those outcropping in the apulian foreland and in the adriatic offshore to the east this correlation brings new support to the hypothesis of a regional e w trending shear zone cutting the adria plate and suggests that other earthquakes could occur on this or on parallel e w trending strike slip faults

an insight into the unrest phenomena at the campi flegrei caldera from vp and vp vs tomography high resolution vp and vp vs tomography of the campi flegrei caldera is obtained using active and passive seismic data we find a continuous ring of high vp anomaly that defines the caldera rim associated to the last collapse a sharp vp vs decrease is observed between 2 and 4 km depth suggesting the absence of magmatic fluids and the presence of rock volumes with over pressured gas within the source region of uplift atmospheric water penetrating within the caldera and deep co2 fluids are presumably heated by a magmatic body located at depth greater than 4 km nested within the limestone layer along the fractures bordering the shallow high vp rim deep gas and co2 fluids up raise and are released in the pozzuoli solfatara we hypothesize that the past unrest episode is more likely due to pressure changes within the shallow geothermal reservoir located at the top of the magma intrusion

multimode migration of scattered and converted waves for the structure of the hikurangi slab interface new zealand reflectivity imaging of local earthquake seismograms has revealed the structure of the hikurangi subduction interface at the location of two strong earthquakes that occurred in 1990 the earthquakes originated within the continental plate of the north island of new zealand and below in the subducting pacific slab we used seismograms from 500 well located events in two earthquake sequences recorded by a small temporary seismograph deployment to directly image the structure and multiphase reflectivity of the plate interface synthetic tests of the imaging method show the effects of the poor 3 d geometric coverage afforded by the seismometer array kirchhoff summation image sections computed from synthetics show accurate depth imaging of backscattering interfaces phase converting interfaces imaged with forward scattered waves are smeared by poor ray coverage to 5 km depth inaccuracy and are only imaged over a small range of their horizontal extent from the data we computed image sections for p p p s s p and s s scattering we mitigated imaging artifacts due to poor ray coverage with an obliquity factor an antialiasing criterion and enhancement by resampling statistics imaging used a sharply layered velocity model we tested for the effects of imaging with first arriving headwaves by imaging through smoothly varying velocity models for our ray geometry early arrival headwaves contribute little to the images the plate interface appears as a 3 5 km thick p p and possibly s s backscatterer with 5j nw dip offset 5 km down to the nw above a normal fault in the slab when illuminated from below a wedge of the interface on the downdip side of the slab fault forms a very prominent p p forward scatterer the edges of the wedge forward scatter some s p and s s energy but an order of magnitude less than the p p forward scattering the imbalances between forward scattering of p and s energy suggest a wedge of subducted sediment retaining significant porosity but with rigidity close to that of surrounding rocks d 2002 elsevier science b v all rights reserved

merging active and passive data sets in traveltime tomography the case study of campi flegrei caldera southern italy we propose a strategy for merging both active and passive data sets in linearized tomographic inversion we illustrate this in the reconstruction of 3d images of a complex volcanic structure the campi flegrei caldera located in the vicinity of the city of naples southern italy the caldera is occasionally the site of significant unrests characterized by large ground uplifts and seismicity the p and s velocity models of the caldera structure are obtained by a tomographic inversion based on travel times recorded during two distinct experiments the first data set is composed of 606 earthquakes recorded in 1984 and the second set is composed of recordings for 1528 shots produced during the serapis experiment in 2001 the tomographic inversion is performed using an improved method based on an accurate finite difference traveltime computation and a simultaneous inversion of both velocity models and earthquake locations in order to determine the adequate inversion parameters and relative data weighting factors we perform massive synthetic simulations allowing one to merge the two types of data optimally the proper merging provides high resolution velocity models which allow one to reliably retrieve velocity anomalies over a large part of the tomography area the obtained images confirm the presence of a high p velocity ring in the southern part of the bay of pozzuoli and extends its trace inland as compared to previous results this annular anomaly represents the buried trace of the rim of the campi flegrei caldera its shape at 1 5 km depth is in good agreement with the location of hydrothermalized lava inferred by gravimetric data modelling the vp vs model confirms the presence of two characteristic features at about 1 km depth a very high vp vs anomaly is observed below the town of pozzuoli and is interpreted as due to the presence of rocks that contain fluids in the liquid phase a low vp vs body extending at about 3 4 km depth below a large part of the caldera is interpreted as the top of formations that are enriched in gas under supercritical conditions

strontium content of ostracods indicates lacustrine palaeosalinity individual non marine ostracod valves contain sr in proportion to the sr content of their host lake water two commonly coexisting large planktonic species mytilocypris praenuncia and australocypris robusta have a sr distribution coefficient kd sr ca of 0 082 which is independent of temperature in the range 10 18 c if the relationship between salinity and the sr content of a hydrologically simple lake is known palaeosalinities can be calculated from fossil ostracods we present here palaeosalinities for the past 10 000 yr for lake keilambete victoria calculated from ostracod sr ca of fossil material which are in striking agreement with independent interpretations of palaeosalinity the range of salinity spans 14 95 we also show that a reliable quantitative continuous indicator of lacustrine palaeosalinity is important for the elucidation of continental palaeoenvironments for palaeoclimatology and archaeology and ocean continent climatic correlations and interactions

characteristics and origin of the gas and condensate in the yinggehai basin offshore south china sea evidence for effects of overpressure on petroleum generation and migration three superimposed pressure systems have developed in the yinggehai basin the strongly overpressured rocks have abnormally low vitrinite reflectance ro and rock eval tmax values and display abnormal c15 hydrocarbon distributions such organic maturity anomalies were confirmed to be the result of overpressure retardation commercial gas fields with carbon dioxide content up to 93 and gas shows with nitrogen content more than 50 have been found in the basin methane and carbon dioxide dominated gases have low c2 hydrocarbon contents less than 4 and heavy methane 13c and d values and the associated condensates have high diamondoid indices and very low c25 saturated hydrocarbon concentration at the same time the methane and carbon dioxide dominated gases have high branched and cyclic light hydrocarbon contents and associated condensates have abnormally low heptane and isoheptane values low sterane isomerization values and abnormally high concentrations of isoprenoid hydrocarbons relative to adjacent n paraffins these distinct characteristics seem to result from the effects of overpressure on both hydrocarbon generation and migration

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

charging history of paleogene deep gas in the qibei sag bohai bay basin china abstract the qibei sag qs at the western region of the bohai bay basin bbb eastern china has made significant progress in the deep gas exploration recently indicating that the deep gas reservoirs have good exploration prospects the deep gas reservoirs within the second member of the shahejie formation of the paleogene e2s2 are buried at approximately 5000 m the sources and hydrocarbon accumulation mechanisms were investigated by analyzing the regional structure integrating geologic and geochemical parameters of source rocks and natural gas analyzing results show that in the qs and adjacent areas qsaa three sets of source rocks e2s1 e2s2 e2s3 were developed which differ in organic chemical characters but have abundant organic matters in fair good standard affected by burial history e2s3 source rocks have entered into the high mature over mature stage and e2s1 source rocks are mainly in mature stage the methane content of natural gas 78 91 the methane carbon isotope value 41 3 34 6 and the positive carbon isotope sequence 13c1

history of earthquakes and vertical ground movement in campi flegrei caldera southern italy comparison of precursory events to the a d 1538 eruption of monte nuovo and of activity since 1968 abstract the record of felt earthquakes around naples bay in southern italy is probably complete since the mid 15th century according to this record intense earthquake swarms originating beneath campi flegrei an explosive caldera located along the north coast of naples bay have occurred only twice 1 before the only historical eruption in campi flegrei in 1538 and 2 from mid 1983 to december 1984 earthquake activity during the earlier period which began at least a few years and possibly as many as 30 years before the 1538 eruption damaged many buildings in the city of pozzuoli located near the center of campi flegrei minor seismic activity which consisted of only a few felt earthquakes occurred from 1970 to 1971 the second period of intense earthquake swarms lasted from mid 1983 to 1984 again damaging many buildings in pozzuoli two periods of uplift along the shoreline within campi flegrei have also been noted since the mid 15th century 1 during the few decades before the 1538 eruption and 2 as two distinct episodes since 1968 uplift of a few meters probably occurred a few decades before the 1538 eruption uplift of as much as 3 0 m has occurred in pozzuoli since 1968 these similarities strongly suggest that for the first time in 440 years the same process that caused intense local earthquake swarms and uplift in the early 1500 s and led to an eruption in 1538 has again occurred beneath campi flegrei though no major seismicity or uplift has occurred since december 1984 because of the large amount of extensional strain accumulated during the past two decades if a third episode of seismicity and rapid uplift occurs it may lead to an eruption within several months after the resumption of activity

multiscale imaging of complex structures from multifold wide aperture seismic data by frequency domain full waveform tomography application to a thrust belt summary an application of full waveform tomography to dense onshore wide aperture seismic data recorded in a complex geological setting thrust belt is presented the waveform modelling and tomography are implemented in the frequency domain the modelling part is solved with a finite difference method applied to the visco acoustic wave equation the inversion is based on a local gradient method only the p wave velocity is involved in the inversion the inversion is applied iteratively to discrete frequency components by proceeding from low to high frequencies this defines a multiscale imaging in the sense that high wavenumbers are progressively incorporated in images the linearized waveform tomography requires an accurate starting velocity model that has been developed by first arrival traveltime tomography after specific pre processing of the data 16 frequency components ranging between 5 4 and 20 hz were inverted ten iterations were computed per frequency component leading to 160 tomographic models the waveform tomography has successfully imaged southwest dipping structures previously identified from other geophysical data as being associated with high resistivity bodies the relevance of the tomographic images is locally demonstrated by comparison of a velocity depth function extracted from the waveform tomography models with a coincident vertical seismic profiling vsp log available on the profile moreover comparison between observed and synthetic seismograms computed in the starting traveltime and waveform tomography models demonstrates unambiguously that the waveform tomography successfully predicts for wide angle reflections from southwest dipping geological structures this study demonstrates that the combination of first arrival traveltime and frequency domain full waveform tomographies applied to dense wide aperture seismic data is a promising approach to quantitative imaging of complex geological structures indeed wide aperture acquisition geometries offer the opportunity to develop an accurate background velocity model for the subsequent waveform tomography this is critical because the building of the macromodel remains an open question when only near vertical reflection data are considered

formation and evolution of nonmarine petroleum in songliao basin china in large lake basins source rocks containing sapropelic kerogen have a high transformation ratio and a high potential for petroleum and they offer the material basis for the formation of a large nonmarine oil field on the basis of geologic and geochemical data and the results of thermal simulation of kerogen it is confirmed that the maturation sequence of kerogen is type i type ii and type iii

comprehensive assessment of source rocks in the bohai sea area eastern china the bohai sea area offshore of the bohai bay basin is one of the most petroliferous regions in china with proven original oil in place of approximately 2 4 109 m3 150 94 108 bbl and proven original gas in place of over 5 1012 m3 1 76 1013 ft3 cumulative oil production is over 50 million tons 3 5 108 bbl in this study using the limited data on source rock thickness core samples and rock eval pyrolysis along with sedimentary facies analysis source rock characteristics of different depositional settings were identified and the thickness richness organic matter type and thermal evolution of four sets of source rocks in the bohai sea area the second member of dongying formation e3d2 the third member of dongying formation e3d3 the first and second members of shahejie formation e2s1 2 and the third member of shahejie formation e2s3 were predicted and evaluated subsequently the intensity and history of hydrocarbon expulsion for different sags was systematically compared and analyzed the greatest thickness of the four sets of source rocks in the bohai sea area is 400 800 m 1300 2600 ft the average richness of the organic matter of these source rocks is 1 74 2 87 the e2s3 set has the highest organic matter abundance e2s1 2 has the lowest the organic matter of these source rocks is mainly type i and type ii but their evolutions differ the vitrinite reflectance of e3d2 is 0 5 1 0 that of e3d3 is 0 7 1 25 that of e2s1 2 is 0 75 1 75 and that of e2s3 is 0 75 2 0 the cumulative hydrocarbon expulsion of the four sets of rocks is 4 14 1010 t 2 90 1011 bbl the e2s1 2 set has the greatest expulsion amount 1 75 1010 t 1 22 1011 bbl the peak stages of hydrocarbon expulsion of the four sets of source rocks were during neogene minghuazhen formation 12 2 2 0 ma and neogene guantao formation 16 6 12 0 ma the bozhong sag expelled the most hydrocarbons followed by the liaozhong qikou and huanghekou sags

lithofacies and sequence stratigraphy of the barnett shale in east central fort worth basin texas ten barnett shale lithofacies have been recognized in a 223 ft 68 m long core from johnson county texas eight of these lithofacies match those previously identified in the main producing area of the newark east barnett shale field in the northern part of the fort worth basin but two new lithofacies have been identified in this core resedimented spiculitic mudstone lithofacies and lag deposits both of which are indicative of a relatively higher energy environment and downslope resedimentation of shallower water deposits the recognition of cyclical stacking patterns of the lithofacies condensed sections css and transgressive surfaces of erosion were the keys to establishing the sequence stratigraphic framework in these fine grained rocks which consists of seven stratigraphic intervals in the lower barnett shale and nine stratigraphic intervals in the upper barnett shale spectral gamma ray uranium and thorium logs aided in this objective and are recommended for future sequence stratigraphic studies of these and other shales the sequence stratigraphic framework reveals that the lower barnett shale in this area was deposited mainly in a low energy relatively deep water environment somewhat far from a terrigenous source area which probably lies to the northwest by contrast the upper barnett shale was deposited in an oxygenated shallower water environment which had a source area from the west and southwest sides of the basin the higher frequency of sea level fluctuation during development of the upper barnett shale most probably indicates periodic tectonic activity perhaps associated with a structural high that was susceptible to sea level fluctuations alternatively it could have resulted from the onset of glaciations in gondwanaland during this time this higher frequency may indicate that the upper barnett is chesterian in age because cyclicity was higher than during the osagean and meramecian stages if so there may be more high frequency cycles than recognized in this core siliceous sponge spicules are more common in this core than in more northerly cores so more brittle facies might prevail in the southern part of the fort worth basin high gamma ray log responses which are caused by a high total organic carbon and or in situ phosphate minerals are commonly found in css and can be used for regional correlations however high gamma ray phosphatic deposits that have been resedimented to downslope positions by sediment gravity flows are an exception to the previous statement correlation of the barnett stratigraphic intervals now provides a north to southeast stratigraphic framework along the fort worth basin relative hydrocarbon potential rhp is an organic geochemical parameter applied to this core and found to provide an indicator of marine transgressions and regressions we recommend continued testing and use of the rhp parameter for high frequency sequence stratigraphic analysis of unconventional gas shales

petrology of a suite of sedimentary rocks associated with some cole bearing basins in northwestern thailand abstract a number of basins in northwestern thailand contain thick sequences of cenozoic sedimentary rocks oil shales and coals are prominent lithologies within these sequences and occur together in some basins most of the sequences are however dominated by either oil shales or coals the major oil shale deposit is in the mae sot basin but oil shales also occur in the ban huay dua mae moh ban pa ka li mae teep ban na hong and jae hom basins drilling and detailed mapping in the mae sot basin indicate thick sequences of oil shales and organic petrological studies show that they contain abundant lamalginite trace amounts of telalginite liptodetrinite bitumen resinite and huminite inertinite are also present in some of the rocks the parts of the sequences rich in authigenic minerals are in general petrographically similar to green river formation lamosites where clay silt sized epiclastics are more abundant similarities exist to australian tertiary lamosites vitrinite reflectance date from the oil shales and associated coals indicate a low level of maturity oil shales from the other basins are petrographically similar to the mae sot lamosites however some differences do exist the mae sot and other lamosites were deposited in lacustrine environments that probably had highly variable water depths

reconstructing the palaeoecosystem and palaeodepositional environment within the upper devonian lower mississippian bakken formation a biomarker approach abstract biomarkers have been used extensively to correlate oil families oil source rock relationships and source inputs and to help identify the palaeodepositional environment for a given geological sedimentary unit despite their application in characterising the bakken formation shales a number of biomarkers still appear unable to provide us a consistent understanding regarding heterogeneity in source organic matter and palaeoenvironment here we infer the palaeodepositional environment within the bakken formation shales using a biomarker suite and biomarker depth profiles we also use the occurrence and abundance of biomarkers to define organic facies and to make inferences regarding biotic interactions drawn from modern analogues the variations and co occurrence of biomarkers is explained by the existence of a proposed complex algal bacterium bacteriovore palaeoecosystem this approach not only helps explain the depth variation in occurrence and concentration of biomarkers and the molecular composition of associated organic matter but also advances the use of biomarker analysis and biomarker associations to determine a complex environment sensitive palaeoecosystem

mechanisms of petroleum accumulation in the bozhong sub basin bohai bay basin china part 1 origin and occurrence of crude oils the origin of the fourteen major oil fields in the bozhong sub basin bohai bay basin was studied based on the results of rock eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples the three possible source rock intervals have different biomarker assemblages and were deposited in different environments the third member of the oligocene dongying formation e3d3 32 8 30 3 ma in age is characterized mainly by high c19 c23 tricyclic terpane 0 75 high c24 tetracyclic terpane c26 tricyclic terpane 2 5 low gammacerane c30 hopane 0 15 and low 4 methyl steranes c29 steranes 0 15 ratios and was deposited in sub oxic to anoxic environments with significant terrigenous organic matter input the first e2s1 35 8 32 8 ma and third e2s3 43 0 38 0 ma members of the eocene shahejie formation have low c19 c23 tricyclic terpane and low c24 tetracyclic terpane c26 tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input but have different abundances of 4 methyl steranes and gammacerane the hydrocarbon generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub basin and climate changes three oil families derived from e2s3 e2s1 and e3d respectively and three types of mixed oils have been identified all large oil fields in the bozhong sub basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens and or focusing of oils originated from a large area of a generative kitchen is essential for the formation of large oil fields in the bozhong sub basin e2s3 and e2s1 derived oils experienced relatively long distance lateral migration and accumulated in traps away from the generative kitchen e3d3 derived oils had migrated short distances and accumulated in traps closer to the generative kitchen such a petroleum distribution pattern has important implications for future exploration there is considerable exploration potential for dongying derived oils in the bozhong sub basin and traps close to or within the generative kitchens have better chance to contain oils generated from the dongying formation

seismicity associated with the 2004 2006 renewed ground uplift at campi flegrei caldera italy abstract following the significant ground uplift 1 8 m of the 1982 1984 bradyseismic crisis the recent history of campi flegrei volcanic complex italy has been dominated by a subsidence phase recent geodetic data demonstrate that the subsidence has terminated and that positive ground deformation renewed in november 2004 at a low but accelerating rate leading to about 4 cm of uplift by the end of october 2006 as in previous episodes ground uplift has been accompanied by swarms of micro earthquakes m 1 4 in three distinct episodes october 2005 october 2006 and december 2006 hypocenters of these earthquakes are mainly located beneath the solfatara volcano at depths ranging between 0 5 and 4 km inversion of s wave spectra indicates source radius and stress drop on the order of 30 60 m and 104 9 105 pa respectively fault plane solutions indicate predominantly normal mechanisms accompanying the october 2006 swarm we detected intense long period lp activity for about 1 week these signals consist of weak monochromatic oscillations whose spectra exhibit a main peak at frequency 0 8 hz this peak is common to all the stations of the network and not present in the noise spectra suggesting that it is a source effect about 75 of the detected lps cluster into three groups of mutually similar events adjustment of waveforms using cross correlation allows for precise alignment and stacking which enhances signal onsets and permits accurate absolute arrival picks and thus better absolute as well as relative locations locations associated with the three different clusters are very similar and appear to delineate the se rim of the solfatara volcano at a depth of about 500 m the most likely source process for the lp events involves the resonance of a fluid filled buried cavity quality factors of the resonator cluster in a narrow interval around 4 which is consistent with the vibration of a buried cavity filled with a water vapour mixture at poor gas volume fractions we propose a conceptual model to interpret the temporal and spatial patterns of the observed seismicity

lacustrine source rock deposition in response to co evolution of environments and organisms controlled by tectonic subsidence and climate bohai bay basin china three paleogene syn rift intervals from the bohai bay basin the most petroliferous basin in china were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions the third es3 and first es1 members of the eocene shahejie formation and the oligocene dongying formation ed display widely variable total organic carbon contents hydrogen indices and visual kerogen compositions suggesting changes in organic facies from deep to marginal sediments carefully selected deep lake facies samples from any interval however display fairly uniform biomarker composition these three intervals have distinctly different biomarker assemblages which indicate weakly alkaline freshwater lakes with a moderately deep thermocline during es3 deposition alkaline saline lakes with shallow chemocline during es1 deposition and acidic freshwater lakes with deep unstable thermocline during the deposition of the dongying formation such environmental changes corresponded to changes in subsidence rate and paleoclimate from rapid subsidence and wet climate during es3 deposition through slow subsidence and arid climate during es1 deposition to rapid subsidence and wet climate during ed deposition and resulted in synchronous changes in terrigenous organic matter input phytoplankton community and primary productivity the co evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn rift evolutions the models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins

mechanisms of activity and unrest at large calderas large caldera collapses represent catastrophic natural events second only to large meteoritic impacts in addition some calderas are densely populated making the risk extreme even for moderate eruptions understanding caldera mechanisms unrest and the danger of eruption is therefore a crucial challenge for earth sciences several key features of caldera behaviour have yet to be fully understood through a combination of case studies and theoretical modelling the following topics are addressed in this volume the conditions required to produce and to release large volumes of magma erupted during caldera formation how magmatic feeding systems evolve before and after a caldera has formed the processes that limit the behaviour of precursors to eruptions how pre emptive precursors can be distinguished from those that drive unrest without an eruption and given that post collapse eruptions may occur across a wide area the optimum procedures for designing hazard maps and mitigation strategies

a new seismic tomography of aigion area gulf of corinth greece from the 1991 data set summary an ew three dimensional delay traveltime tomography is performed to image the intermediate structure of the western gulf of corinth a large data set collected in 1991 during a two month passive tomographic experiment has been reanalysed for the reconstruction of detailed vp and vs images an improved tomography method based on an accurate traveltime computation is applied to invert simultaneously delayed p and s first arrival traveltimes for both velocity and hypocentre parameters we perform different synthetic tests to analyse the sensitivity of tomography results to the model parametrization and to the starting 1 d model selection the analysis of the retrieved vp and vs models as well as deduced vp vs and vp vs images allows us to interpret and delineate the distribution of lithological variation porosity crack content and fluid saturation in the upper 9 11 km of the crust beneath the gulf the tomographic models image a rather complex crustal structure which is characterized by a vertical change in both velocity features and seismicity distribution we identify a shallower zone of the crust 0 5 km depth in which velocity distributions seem to be controlled by the still active n s extensional regime and a deeper zone 7 11 km depth which matches the seismogenic zone the correlation between this latter and a specific unit of the hellenic mountain structure the pyllite quartzite series allows us to suggest a possible explanation for seismicity concentration in a narrow band at 7 9 km depth finally the occurrence of clusters showing low angle normal fault mechanisms in areas characterized by high vp vs values indicates a possible role of fluids in triggering brittle creep along the identified low angle normal faults

characteristic of source rocks and origin of crude oils in the raoyang sag and baxian sag bohai bay basin china insights from geochemical and geological analyses abstract three potential source rock intervals were evaluated based on the results of rock eval pyrolysis on nearly 700 rock samples and the origin of the twenty two oil fields was studied by the biomarker analysis on 62 source rock samples and 93 oil samples in the raoyang sag and baxian sag bohai bay basin the first member of the shahejie formation es was deposited in an anoxic and salted water column with the dominant contribution of algal organic matters reflected by its rock samples with high gammacerane c30 hopane high etr high c35 c34 hopane high steranes hopanes low pristane phytane low c27 diasterane c27 sterane and low c19 c23 tricyclic terpane characterized by higher c19 c23 tricyclic terpane higher pristane phytane lower steranes hopanes and lower c35 c34 hopane than the es1 rock samples the biomarkers of rocks suggest that the third and forth members of the es were deposited in the sub oxic to anoxic environments with a significant terrestrial organism input further studies suggest that the best source rock interval for oil generation is the es1 source rock interval in the raoyang sag and is the es3 source rock interval in the baxian sag by organic facies analysis of source rocks three source related oil groups have been identified there are two oil groups for the discovered oils in the raoyang sag group i oil dominated by the es1 derived oils has been found in all the oil fields in the raoyang sag and group ii oil mainly derived from the es3 source rock interval only distributes in the north east area and in the south end of the raoyang sag however the three oil groups have been found in the baxian sag but the es3 derived oils are dominant in them and have been found in the major oil fields in the east area and the wen an slope in the west area furthermore the es4 derived oils group iii oil mainly distribute in the baxian sag without any findings in the raoyang sag because of the absence of the es4 source rocks as our studies oils almost accumulate near their source rocks without a long distance migration except the slope areas in the raoyang sag and baxian sag therefore the source rock distribution is a key factor to oil accumulations in the raoyang sag and baxian sag especially the efficient source rock distributions which mainly developed in the organic facies a and b based on the geochemical and geological researches

geochemistry of hco 3 na thermal water from the gudian slope insights into fluid origin formation mechanism and circulation in the yitong basin northeast china abstract the goal of this paper is to systematically analyze the geochemical and isotopic characteristics 18o d t 13chco3 and doc of a hco3 na thermal water to determine its origin formation mechanism and circulation pattern in the gudian slope yitong basin northeast china schoeller diagrams and isotope data indicate that this thermal water is not connected to groundwater or river water and that its recharge source is immature water with low 18o and d values that originates from the changbaishan area this result was also confirmed by its doc 13c value approximately 24 which indicates that the c originates from c3 plants the analysis of na k mg diagrams indicates that the thermal waters except for one sample sjxk are fully equilibrated this observation combined with the results of the analysis for 18o d t and cation geothermometry data for the thermal water indicates that no water underwent mixing with cold water before arriving at the surface instead high temperature immature water flowed up from a deep reservoir and mixed with old formation water approximately 35 4 in the eocene reservoir these data indicate the occurrence of an interesting phenomenon in which the thermal water samples of the gd area exhibit a regression line with a negative slope and similar 18o values potentially due to the fractionation of co2 gas and a buffer of high hco3 concentrations rather than their short circulation times the high so4 cl b cl f cl and hco3 cl ratios and 13chco3 values ranging from 0 84 to 1 24 of these samples imply that magmatic volatiles have been dissolved in the thermal water however we cannot ignore the contributions of 13c from the leaching of limestone with a13c value of approximately 3 4 which is further supported by the br cl and hco3 cl ratios thus we analyzed the geological background and data collected from well chang 27 and deduced that a limestone stratum exists below the study area magmatic volatiles flow up through the lithospheric faults along the northwestern and southeastern edges of the basin encounter changbaishan area recharge water in the limestone reservoir form hot water with high concentrations of hco3 and then recharged into the eocene sandstone reservoir long term mineral hydrolysis and transformation reactions in the reservoir cause the concentrations of na to increase and lead to the formation of hco3 na water

organic facies variability in the posidonia black shale from luxembourg implications for thermal maturation and depositional environment abstract posidonia shale lias e lower toarcian schiste bitumineux samples were obtained from a well in southern luxembourg esch sur alzette elemental composition and organic facies were studied along the cores and accordingly the thermal maturity and depositional environment were evaluated the organic matter content is high with an average of 7 2 ranging between 2 8 and 13 5 the average vitrinite reflectance value is ca 0 55 indicating an early stage of oil generation several biomarker based maturity parameters support the low thermal maturity including oep values and c 29 5 14 17 h steranes 20s 20s 20r rock eval data and microscopy observations reveal that the organic matter is composed of hydrogen rich type ii kerogen derived from alginite small algal bodies derived from nannoplankton predominate but large telalginite tasmanales also occurs pyrites are abundant and fish bones are frequently observed characterizing a marine depositional environment where strong sulfate reduction occurred small amount of autochthonous vitrinite observed microscopically combined with predominance of short chain n alkanes over long chain n alkanes as well as a low terrigenous aquatic ratio tar indicate a low input of terrigenous organic matter sterane distribution is in good agreement with an origin from a marine carbonate depositional environment which corresponds to the general marlstone lithology additionally c 30 24 propyl 14 h 17 h cholestane 20r was detected supporting the marine origin the depositional environment was strongly oxygen depleted in bottom water as indicated by low concentrations of c 35 homohopane fair to low pr ph ratios slightly less than 1 0 and high sulfur content ca 3 wt on average and sulfur organic carbon ratios with only few interruptions of dysoxic to suboxic conditions during deposition of the posidonia shale in luxembourg gammacerane detected in low abundance reveals that a stratified water column existed and water salinity was slightly enhanced in the paleoenvironment the highest c 27 c 29 sterane ratio due to more algal input indicates a maximum flooding during the upper falciferum zone of the lower toarcian in luxembourg which fits well to the global sea level curve and might correspond to a productivity oceanic anoxic event p oae furthermore toarcian greenhouse climate led to generally low oxygen concentration in bottom water of the shallow sea

the 1997 umbria marche central italy earthquake sequence insights on the mainshock ruptures from near source strong motion records a small size foreshock and the two mainshocks of the umbria marche earthquake sequence which occurred on september 26 1997 have been recorded by two digital 3c accelerometers located at near source distances the close epicentral distance and azimuthal location relative to the fault orientation and geometry make these records relevant to look at the detail of the rupture kinematics s wave polarizations apparent source time duration and waveforms from strong motion records are used to constrain the location of the fracture origin point the fault geometry the final slip distribution size and mechanism of the events the final model shows that the seismic ruptures occurred along two adjacent sub parallel low angle dipping normal faults the relative timing location and geometry of the mainshock faults suggest the presence of a transfer zone barrier which has probably controlled the amplitude increase of local stress released by the first rupture at its nw edge which triggered about 9 hours later the second rupture

fluorescent microscopy of particulate organic matter sparta formation and wilcox group south central louisiana abstract particulate organic matter pom isolated from core samples of mudstones in the mid eocene sparta formation and the late paleocene early eocene wilcox group in louisiana was characterized using transmitted and fluorescent light microscopy and rock eval pyrolysis observations of maceral fluorescence combined with programmed pyrolysis results better define source potential than visual examination using transmitted white light alone transmitted light microscopic characterization of pom indicates that amorphous macerals of mixed terrestrial and marine origin dominate samples from both the lagoonal and shelf depositional environments microscopic examination under fluorescent light indicates that some of the amorphous matter including terrestrially derived material fluoresces to some degree hydrogen index values show a positive correlation with the total number of fluorescing particles in the isolate as well as with the relative fluorescence levels comparison of sparta and wilcox samples indicates that significant changes occur in the assemblages at levels of thermal maturation associated with the onset of petroleum generation thermally mature samples contain a higher percentage of moderately fluorescent particles and lesser percentages of highly and weakly fluorescent particles this phenomenon is readily apparent in specific particle types namely amorphous nonstructured protistoclasts miospores and dinoflagellate cysts

simple kinetic models of petroleum formation part i oil and gas generation from kerogen modern basin analysis uses kinetic models to predict the extent of petroleum generation within potential source rocks the global kinetic model presented here assigns kinetic parameters based on gross depositional environment and stratigraphic age this is useful in areas of low geochemical knowledge including exploration frontiers five kerogen kinetic organofacies each characterized by a specific organic matter input and early diagenetic overprint can broadly be related to sedimentary facies age associations even using seismic sequence stratigraphy alone a aquatic marine siliceous or carbonate evaporite any age b aquatic marine siliciclastic any age c aquatic non marine lacustrine phanerozoic d e terrigenous non marine ever wet coastal mesozoic and younger and f terrigenous non marine coastal late palaeozoic and younger routine pyrolysis data allow partitioning of organic carbon in the immature source rock into four initial components oil oil generative gas generative and inert separate kinetic parameters for the oil and gas generative fractions allow computation of the evolving concentration and composition of the products it was assumed that the activation energy distributions for each fraction were normally distributed non linear regression of large combined laboratory and field data sets varying by up to 12 orders of magnitude in heating rate established optimum values for the required ten 5 2 kinetic parameter sets a emean e differences in kinetic parameters can be reconciled with known chemical properties although our knowledge base is still inadequate to construct kinetic models from first principles mean activation energies governing oil generation increase systematically in the order a f causing a corresponding increase in generation temperature at a reference heating rate 2 c ma 1 the oil generation window 10 90 oil generative kerogen degraded increases from ca 95 135 c to 145 175 c organofacies c has the tightest energy distribution and narrowest oil generation window the gas generation window ranges from ca 105 155 c to 175 220 c thermal stress results from a combination of temperature and time an order of magnitude increase decrease in heating rate elevates depresses reaction temperatures by ca 15 c heating rates in subsiding sedimentary basins can vary by two orders of magnitude dramatic differences in generation temperature can result if the heating rate and organofacies effects compound thus global oil and gas generation temperature thresholds constitute blunt instruments with which to screen the petroleum potential of sedimentary basins because unexpelled oil provides a potential feedstock for oil to gas cracking in the source rock quantitative models of petroleum generation become really useful only when coupled with models of oil gas cracking and expulsion for example the frequently observed association between gas provinces and coals cannot be explained solely by their generation behaviour

long distance longitudinal transport of gravel across the cordilleran thrust belt of montana and idaho two newly identified middle eocene paleovalleys 100 km long preserved on top of the southwest montana reentrant of the cordilleran fold and thrust belt indicate long lived longitudinal flow across the thrust belt and resolve a long standing debate about the source of the voluminous quartzite debris in the upper cretaceous to lower tertiary divide harebell and pinyon conglomerates of montana idaho and wyoming geologic mapping stratigraphic provenance and geochronologic studies revealed that eocene volcanic and sedimentary rocks in the paleovalleys are as thick as 2 km onlap preexisting bedrock and interfinger with well rounded conglomerate derived from formations exposed only to the west the middle eocene paleovalleys are the youngest expression of a major paleoriver system that transported sediment toward the foreland during the sevier orogeny an eocene subcrop map shows that the headwaters of the eocene paleovalleys coincided with structural culminations in the thrust belt that supplied sediment to the divide conglomerate of the upper cretaceous to lower tertiary beaverhead group ultimately the lemhi pass and hawley creek paleovalleys provided several thousand cubic kilometers of quartzite debris to the pinyon and harebell conglomerates of northwest wyoming 200 350 km away and formed the northwest half of a giant longitudinal drainage system sevier contraction not the rising idaho batholith first uplifted vast culminations beneath the headwaters of this river system

the bay of naples southern italy constraints on the volcanic structures inferred from a dense seismic survey 1 the bays of naples and pozzuoli host volcanic areas that have been active within recent history in addition the vicinities areas around the vesuvius volcano and the campi flegrei caldera are extremely densely inhabited over the past decade this situation has prompted several active seismic experiments focused on the vesuvius volcano more recently the serapis active seismic survey covered the entire bay of naples with particular attention to pozzuoli bay the processed serapis p wave travel time collection extended with a previously acquired data set has allowed the computation of the most comprehensive three dimensional p wave velocity distribution for the bay of naples which includes a small scale high resolution model of the campi flegrei caldera the joint interpretation of the velocity distribution together with both the available gravity measurements and models and the geothermal drilling information has allowed us to locate and map lithological units at depths we propose a model of the campi flegrei caldera in relation to the underlying mesozoic limestone unit in this model no magma chamber exists in the upper 6 km beneath the bay of naples the feeding system of the campi flegrei caldera is directly controlled by the tectonic structures affecting the limestone unit beneath the bay of naples two ne sw normal faults run beneath the vesuvius volcano and campi flegrei which are related to the pre pleistocene apenninic tectonics

structure and evolution of the bay of pozzuoli italy using marine seismic reflection data implications for collapse of the campi flegrei caldera digital marine seismic reflection data acquired in 1973 in the bay of pozzuoli and recently reprocessed were used to study the volcanological evolution of the marine sector of campi flegrei caldera during the last 37 ka in order to gain more information interpretation also involved estimation of the pseudo velocity and the pseudo density from the resistivity logs of two onshore deep exploration wells the main results are 1 discovery of ancient pre 18 ka and post 37 ka submarine and mainly effusive volcanic activity along coeval emission centers located at the edges of campi flegrei caldera 2 confirmation that the caldera collapse in the marine sector of campi flegrei seems strongly controlled by regional ne sw and nw se structural discontinuities 3 the finding of at least two episodes of collapse in the bay and 4 identification of a post 18 ka volcanic deflation phase that has caused about 150 200 m of subsidence in the central sector of the bay of pozzuoli in the last 18 ka

the campanian plain and phlegrean fields structural setting from potential field data abstract a boundary analysis of the gravity and magnetic fields of the phlegrean fields volcanic area and of the surrounding campanian plain reveals a complex structural setting the campanian plain results well defined from sharp density boundaries a set of major e w lineaments occurs within the plain we derive a framework of the structural control to the volcanological evolution of campanian plain which appears strongly influenced by a set of ne sw lineaments bordering the acerra depression the density and magnetization boundaries of the phlegrean fields are significantly consistent both indicating for the collapsed phlegrean caldera an area considerably less extended than that based on previous geologically defined models many other structures are evidenced in the phlegrean area often with agreement between density and magnetization boundaries inside the caldera a strong consistence between the structures we identified and recent seismicity has been noted

3 d numerical modelling of methane hydrate accumulations using petromod highlights petromod is the 1st basin modelling software including methane hydrate simulation the gas hydrate module includes physical thermodynamic and kinetic properties petromod simulates the evolution over time of the ghsz petromod includes a kinetic for the organic matter degradation at low temperature abstract within the german gas hydrate initiative sugar a new 2 d 3 d module simulating the biogenic generation of methane from organic matter and the formation of gas hydrates has been developed and included in the petroleum systems modelling software package petromod typically petromod simulates the thermogenic generation of multiple hydrocarbon components oil and gas their migration through geological strata finally predicting oil and gas accumulations in suitable reservoir formations we have extended petromod to simulate gas hydrate accumulations in marine and permafrost environments by the implementation of algorithms describing 1 the physical thermodynamic and kinetic properties of gas hydrates and 2 a kinetic continuum model for the microbially mediated low temperature degradation of particulate organic carbon in sediments additionally the temporal and spatial resolutions of petromod were increased in order to simulate processes on time scales of hundreds of years and within decimetres of spatial extension in order to validate the abilities of the new hydrate module we present here results of a theoretical layer cake model the simulation runs predict the spatial distribution and evolution in time of the gas hydrate stability field the generation and migration of thermogenic and biogenic methane gas and its accumulation as gas hydrates

maturation and source rock evaluation of kimmeridge clay norwegian north sea using a slightly modified version of the lopatin method of determining the level of thermal maturation of source rocks it is found that major hydrocarbon generation from the kimmeridge clay began in the late cretaceous early paleocene along the deeper parts of the viking and central grabens throughout the tertiary maturation progressed as subsidence and deposition continued as the maturation in the deep graben areas passed from the oil generation stage into wet gas and or condensate generation and finally into the dry gas stage the areas of strong active oil generation migrated from the graben areas into shallower areas toward the continental craton applying the results of the maturity calculations in conjunction with chemical analyses of the kimmeridge clay allows computations of the original generative capacity hydrogen index total organic carbon kerogen type and the volume of hydrocarbons generated the kimmeridge clay is mainly characterized by type ii kerogen with type i kerogen occurring in the deeper graben areas and type iii in the platform areas it is heterogeneous as a source with original generative capacities ranging from essentially zero to over 35 000 ppm and averaging about 13 300 ppm

three dimensional kinematic depth migration of converted waves application to the 2002 molise aftershock sequence southern italy migration techniques currently used in seismic exploration are still scarcely applied in earthquake seismology due to the poor source knowledge and sparse irregular acquisition geometries at the crustal scale classical seismological studies often perform inversions based on the arrival time of primary phases p and s waves but seldom exploit other information included in seismic records here we show how migration techniques can be adapted to earthquake seismology for converted wave analysis as an example we used data recorded by a dense local seismic network during the 2002 molise aftershock sequence in october and november 2002 two moderate magnitude earthquakes struck the molise region southern italy followed by an aftershock sequence lasting for about one month local earthquake tomography has provided earthquake hypocenter locations and three dimensional models of p and s velocity fields strong secondary signals have been detected between first arrivals of p and s waves and identified as sp transmitted waves in order to analyse these waves we apply a prestack depth migration scheme based on the kirchhoff summation technique since source parameters are unknown seismograms are equalized and only kinematic aspects of the migration process are considered converted wave traveltimes are calculated in the three dimensional 3d tomographic models using a finite difference eikonal solver and back ray tracing in the migrated images the area of dominant energy conversion corresponds to a strong seismic horizon that we interpreted as the top of the apulia carbonate platform and whose geometry and position at depth is consistent with current structural models from existing commercial seismic profiles gravimetric and well data

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

organic geochemistry and petrology of posidonia shale lower toarcian western europe the evolution from immature oil prone to overmature dry gas producing kerogen abstract kerogen concentrates as well as whole rock samples of the lower jurassic posidonia shale representing a complete maturity series from immature to highly overmature were analyzed using organic petrography palynology bulk geochemical analysis ft ir and curie point pyrolysis gc ms cp py gc ms in order to investigate changes in kerogen composition with increasing maturation vitrinite reflectance vrr ranges from 0 5 to 3 hi values reflect the maturity trend very well with little scatter in contrast tmax oi and pi values show more scatter and greater differences between kerogen concentrates and whole rock samples ft ir spectra show a decrease in functional group bands with increasing maturation which has been quantified cp py gc ms analyses indicate an increase in hydrocarbons especially for short and medium length n alkanes with a strong predominance of short length alkanes at highest maturities about 3 vrr this effect however depends also on the applied pyrolysis temperature where higher temperatures 920 c as compared to 650 c favor generation of short length n alkanes especially for samples at high levels of maturation ratios of aromatic over aliphatic hydrocarbons or alkenes over alkanes show a non steady evolution depending also on the applied pyrolysis temperatures indicating that higher pyrolysis temperatures are needed for pyrolytic alkene formation with a maximum alkene formation for samples within early overmature maturities 1 4 vrr aromaticity first decreases but increases at high levels of maturation finally weathering of the highly overmature sample 3 vrr resulted in strong oxidation of organic matter with impact on rock eval ftir and curie point pyrolysis data

solid bitumen bituminite and thermal maturity of the upper jurassic lower cretaceous chia gara formation kirkuk oil field zagros fold belt kurdistan iraq abstract the upper jurassic lower cretaceous chia gara formation a proven marine source rock characterised by predominance of amorphous organic matter aom is known from few outcrops in ne iraq and a number of exploration wells in the zagros fold belt this study presents comprehensive organic petrographic and mineralogical investigations of the dispersed organic matter and rock forming minerals of the tithonian berriasian chia gara formation intersected by the kirkuk well k 109 drilled in the giant kirkuk oil field ne iraq the organic petrographic analyses including incident light microscopy and confocal laser scanning microscopy clsm were applied to carbonate source rocks with low to moderate organic carbon contents our data demonstrate the predominance of bituminite and solid bitumen among the examined dispersed organic matter followed by oil exudates and oil globule inclusions as well as the presence of minor contributions of alginite i e tasmanites and leiospheridia liptodetrinite and vitrinite based on optical characteristics and clsm spectral fluorescence measurements examinations of bituminite point towards the presence of bituminite type iii the bituminite type iii encloses dark orange fluorescent amorphous components suggesting a genetic relationship either with liptodetrinite and or with solid bitumen the qualitative assessment of solid bitumen reveals several dissimilar forms identified in the analysed samples the photometric and spectral fluorescence measurements point to distinct reflectance values ranging between 0 19 and 0 43 sbrr and lambda max values extending from 515 nm to 590 nm respectively the corresponding results of the solid bitumen exhibit 1 a lack of a relationship with depth and 2 suggest its poor property as a reliable maturity indicator for the examined samples the presence of oil exudates oil globule inclusions and their association with solid bitumen suggests a genetic relation with the examined residues of liquid hydrocarbon phase the performed thermal maturities assessments of dispersed organic matter point towards early mature to peak mature oil window with vitrinite reflectance values ranging between 0 52 vrr at 2801 m to 0 83 vrr at 3089 m depth mineralogical analyses revealed the predominance of calcite over dolomite in the examined limestone to marl lithofacies e g clear rimmed dolomite with localised intensive dolomitisation in the phyllosilicate rich matrix predominance of calcite and siderite is observed followed by zinc blende and pyrite the composition of organic matter in the examined chia gara formation with predominance of bituminite and solid bitumen makes the major marine source rock of iraq s cretaceous petroleum systems distinctive in terms of hydrocarbon generation and migration at an oil window stage as it provides suitable explanations for its generally low hydrogen index hi with only minor terrestrial input in addition the results presented herein can be helpful for future evaluation of thermal maturities and characterisation of optical appearances of dispersed organic matter in carbonates by incident light microscopy and especially by clsm during hydrocarbon prospecting

charging of oil fields surrounding the shaleitian uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract this paper discusses origin and charging directions of oil fields on the shaleitian uplift bohai bay basin the shaleitian uplift is a footwall uplift surrounded by three sags containing mature source rocks the origins of the four oil fields on the shaleitian uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions for 61 source rock samples and 27 oil samples hierarchical cluster analysis using 12 parameters known to be effective indicators of organic matter input and or depositional conditions allowed the identification of six oil types or classes these six oil classes could then be linked to three distinct source rock intervals ranging in age from 43 0 ma to 30 3 ma the third member 43 0 38 0 ma in age and first member 35 8 32 8 ma of the eocene shahejie formation and the third member of the oligocene dongying formation 32 8 30 3 ma each sourced one class of oil the other three classes represent mixtures of oil generated from multiple source rock intervals traps on the shaleitian uplift were charged in the east by oil generated from the eocene shahejie formation in the bozhong sag in the southeast by oil generated from the eocene shahejie and then oligocene dongying formations in the southwestern part of the bozhong sag and or in the eastern part of the shanan sag and in the southwest by oil generated from the eocene shahejie formation in the western part of the shanan sag the estimated migration distances range from less than 5 km to about 20 km the compositional heterogeneity within fields and multiple parameter comparisons between oils from nearby wells in different fields have proven to be a powerful tool to determine the in filling histories of oil fields in cases where multiple source rock intervals and multiple generative kitchens exist

holocene sedimentology of hypersaline lake urmia northwestern iran abstract a limnogeological expedition examined the sedimentary record of lake urmia one of the world s largest saline lakes located in a tectonically active arid intermontane plateau in northwestern iran near the cradle of western civilization lake urmia resembles the great salt lake u s a in many respects of morphology water chemistry and sediments the present lake area is about 5000 km 2 shallow 8 12 m and a perennial sodium chloride sulfate system 22 salts high resolution 3 5 khz seismic profiles show morphological relicts from a desiccation playa phase buried below only a few meters of sediments from lacustral phases in places around the deeper areas the lake floor is not smooth but covered with mounds aligned in prevailing current directions these are erosional relicts rather than bioherms sediments comprise aragonite chemical precipitates fecal pellet sands detrital clayey muds thin aragonite crusts oolites various gypsum types and occurrences of dolomite in peripheral areas organic matter characteristic of the present shorelines is not preserved at depth in basinal areas piston cores up to 6 m long penetrated a holocene sequence of hypersaline facies with laminated aragonite fecal pellet muds and bottomed in a playa mudflat facies with central gypsiferous muds and marginal terrigenous to dolomitic muds preliminary radiocarbon and pollen analyses suggest a playa stage prior to 9000 yr b p with saline lake deposition in a cool arid climate from 9000 to 7500 yr b p higher energy facies prevailed in a shallow saline lake and since then present day saline environments have persisted with evidence of numerous second order water level fluctuations the preliminary results suggest a lake system out of phase with north african and some other middle eastern lakes

linking zircon u pb and garnet sm nd ages to date loading and metamorphism in the lower crust of a cretaceous magmatic arc swakane gneiss wa usa abstract synorogenic basin development and subsequent collapse and loading provide important constraints on the late cretaceous crustal structure of the north america cordillera high grade metasedimentary rocks of the swakane gneiss in the north cascades have been interpreted to include ca 73 ma detrital zircon that requires a protolith age considerably younger than metamorphic ages of adjacent terranes this detrital interpretation requires rapid loading rates of 7 8 mm yr heating to 750 c in garnet preserves compositional evidence for growth during high pressure amphibolite facies metamorphism and little subsequent modification new garnet rock sm nd isochrons of 73 5 1 2 71 3 2 8 and 65 8 0 7 ma tightly constrain the timing of garnet growth swakane gneiss zircons preserve complex magmatic detrital and metamorphic histories most zircons have distinct cores and homogeneous overgrowths detrital zircon cores include significant proterozoic and mesozoic components with low u th ratios homogeneous metamorphic zircon rims have high u th 5 and define an array of concordant u pb dates from 75 to 63 ma the new zircon u pb and garnet sm nd ages establish that the youngest regional metamorphism was diachronous and occurred between 75 and 63 ma our dataset precludes post 73 ma deposition and instead suggests that sedimentation occurred after ca 91 ma and ended before ca 75 ma using these age constraints for deposition and metamorphism we propose new loading rates of 1 3 mm yr and conclude that the swakane gneiss protolith was likely deposited in a small short lived intra arc basin that subsided filled in and collapsed quickly due to overthrusting of arc crust

organic geochemistry of the woodford shale southeastern oklahoma how variable can shales be woodford shale samples obtained from a cored outcrop in southeastern oklahoma were geochemically analyzed to determine vertical variations of organic facies thermal maturity and an evaluation of their depositional environments total organic carbon values ranged from 5 01 to 14 81 indicating a good source rock potential in this area the woodford shale is marginally mature as indicated by vitrinite reflectance values rock eval data revealed that the samples are dominated by type ii kerogen biomarker ratios based on pristane phytane steranes and hopanes show a mix of marine and terrigenous organic matter high salinity conditions and water density stratification also prevailed during deposition of this formation as indicated by the presence of gammacerane the woodford shale was subdivided into lower middle and upper members based on the integration of geochemical and geologic data moreover the presence and extent of photic zone anoxia pza were determined by the presence of aryl isoprenoids the lower and upper woodford shale members were deposited under dysoxic to suboxic conditions and episodic periods of pza the middle member was deposited under anoxic conditions and persistent pza in addition aryl isoprenoids helped infer the position of the chemocline during deposition of the different members the relative hydrocarbon potential parameter was used in determining transgressive and regressive cycles within the woodford shale this study undoubtedly demonstrates the significant lithologic and chemical variability that occurs within shales the application of this workflow to regional studies can have a direct influence on exploration and production activities in shale gas systems

p sv conversions at a shallow boundary beneath campi flegrei caldera italy evidence for the magma chamber seismograms from an active seismic experiment carried out at campi flegrei caldera near naples italy show a large amplitude 5v polarized shear wave following by less than 1 5 s p waves reflected at wide angle from a deep crustal interface early arriving sv polarized waves with the same delay to direct p waves are also observed in seismograms from a regional 280 km deep magnitude 5 1 earthquake such short delays of s to p waves are consistent with a p sv conversion on transmission occurring at a shallow boundary beneath the receivers the large amplitude of the converted sv phase along with that the p waves are near vertical requires a boundary separating a very low rigidity layer from the upper caldera fill the converted phases are interpreted as a seismic marker of a magma chamber the top of this magma chamber is located slightly deeper than the deepest earthquakes observed during the 1982 1984 unrest of campi flegrei

experimental investigation of thermal maturation on shale reservoir properties from hydrous pyrolysis of chang 7 shale ordos basin abstract thermal maturity has a significant impact on hydrocarbon generation and the storage capacity within shales but explicit and quantitative characterization of that impact on continental shales is scarce to better understand how thermal maturation affects the organic and inorganic changes of the continental shale reservoirs hydrous pyrolysis was performed to simulate the maturation process toc rock eval and adsorption isotherms tests were used to obtain various geochemical parameters of the shale solid residues the results indicate that with pyrolysis temperature increasing from ambient temperature to 550 c the vitrinite reflectance increases from 0 5 to 2 5 ro and the toc total organic carbon loss weight reaches 25 regarding porosity the fraction of micro to meso pores in the shale increases with an increase in the pyrolysis temperature whereas the macro pores do not change significantly the total amount of gas adsorption does not necessarily increase as the toc is consumed but the gas adsorption capacity per unit of toc increases with increasing thermal maturity our finding provides theoretical modelling for identifying shale gas development prospective zones according to thermal maturity mapping and for predicting quantitatively the geochemical and inorganic changes that occur with thermal evolution

shallow water evaporitic environments and their source rock potential in the major evaporitic environments on the world s surface today most organic matter accumulates in shallow subaqueous to seasonally subaerially exposed algal mat sediments given the present depositional setting and the most likely flushing by oxidizing water it is unlikely this organic matter could be preserved to form source rocks however if we place such evaporite deposition into a geologic context then there are times in the past when source rocks could have formed in shallow water settings such settings were characterized by hydrological conditions which allowed the retention of hypersaline anoxic pore waters to depths where the organic material was buried deeply enough to generate hydrocarbons when deep basin shallow water evaporite successions were laid down in basins such as the mediterranean in the late miocene the michigan basin in the silurian and other large saline giants then conditions were right for the formation of source rocks within shallow water and salt flat evaporitic environments the evaporites in these saline giants were deposited under conditions of relatively shallow water 50 m the basin never appears to have dried out but water levels changed quickly nearly equal 10 000 years from shallow to deep continual water saturation coupled with saline pore fluids prevented the inflow of fresh oxidizing groundwater into the basin center of shallow water organic rich evaporites immature hydrocarbons derived from such rocks today drip from the 5 5 m y evaporites of sicily in active salt and sulfur mines organic rich sediments could also be preserved to generate hydrocarbons in rapidly subsiding rift basins in such basins rapid burial has prevented the entrance of fresher oxygenated waters and the associated degradation and destruction of the organic matter the early continental riff stage generates the source rocks the ephemeral streams wadis and dune fields generate the reservoirs and the subsequent evaporite stage seals the reservoir

four cordilleran paleorivers that connected sevier thrust zones in idaho to depocenters in california washington wyoming and indirectly alaska upper cretaceous sandstones from 17 localities from california to southeastern alaska united states contain unexpectedly large populations of detrital zircons with proterozoic u pb ages with age peaks at 1800 1650 and 1380 ma these peaks are indicative of a sediment source region in the southern part of the proterozoic belt supergoup basin in central idaho which hosts 1800 1650 ma detrital zircons and which was intruded by rift related 1380 ma bimodal plutons and sills belt rocks were strongly uplifted and eroded during late cretaceous sevier shortening and fed four paleoriver systems the lemhi pass hawley creek river system flowed east and sourced the beaverhead harebell pinyon nonmarine megafan in the cordilleran foreland basin the kione river flowed southwest to northern california where it sourced a very large ca 82 80 ma 600 m thick delta and submarine fan complex within the northern great valley forearc basin considerable kione detritus also transited the forearc basin to reach the franciscan trench sourcing a pulse of deposition and subduction accretion in central california and even part of southern california the swakane river flowed northwest out of idaho into washington sourcing the protolith for the high grade swakane gneiss more speculatively a yakutat river may have flowed northwest and deposited yakutat strata in a trench off washington or british columbia before those rocks were translated north to southeastern alaska recognition of a major source area in central idaho for zircons with an uncommon age of 1380 ma helps constrain the ca 85 65 ma paleogeography and paleotectonics of major sectors of the north american convergent margin orogen

the effect of organic matter type and organic carbon content on rock eval hydrogen index in oil shales and source rocks abstract the amount of gas prone kerogen woody fungal and inert and the organic carbon content toc are the two predominant factors affecting the hydrogen index hi in the 226 samples of lacustrine and marine oil shales and source rocks studied hi decreases as a function of the amount of gas prone kerogen and increases as a function of toc in addition the type of amorphous kerogen influences the hydrogen index and this can be roughly estimated from the fluorescence intensity of the amorphous kerogen nearly eighty percent of the variation in hi in these samples can be accounted for by the percentage of gas prone kerogen the toc content and the fluorescence of the amorphous kerogen in a multiple regression analysis hydrogen index increases as a function of toc up to about 10 toc the relationship can be approximated by a quadratic equation and then levels off a possible explanation for this is that the capability of a rock to generate and expel hydrocarbons during pyrolysis increases with toc when the retention capacity of the rock matrix is saturated at about 10 toc further increases in toc have no effect on hi it is also possible that the quality i e oil proneness of the amorphous kerogen is poorer in low toc samples than in high toc samples the samples came from the following oil shales and source rocks rundle queensland eocene miocene mae sot northwestern thailand eocene pliocene river river northwestern colorado eocene toolebuc western queensland late albian the posidonienschiefer southwestern germany toarcian an argentinian lacustrine deposit eocene miocene the kimmeridgian sections from four north sea wells blocks 21 30 and 210 monterey shale california miocene and sections from six wells from the alaskan tertiary north slope north aleutian shelf navarin basin norton sound most samples appear to be thermally immature t a i less than 1 8 ro less than 0 6 so they should be considered only potential source rocks the lacustrine oil shales have a higher conversion ratio yeild toc or s1 s2 toc than do the marine oil shales in samples with only amorphous and algal kerogen these in turn have a higher conversion ratio than the marine source rocks these differences are roughly reflected in the fluorescence intensity of the amorphous kerogen free hydrocarbons are higher in the marine source rocks than in the marine oil shales and are lowest in the lacustrine oil shales

the origin of oil in the cretaceous succession from the south pars oil layer of the persian gulf the origin of the oil in barremian hauterivian and albian age source rock samples from two oil wells spo 2 and spo 3 in the south pars oil field has been investigated by analyzing the quantity of total organic carbon toc and thermal maturity of organic matter om the source rocks were found in the interval 1 000 1 044 m for the kazhdumi formation albian and 1 157 1 230 m for the gadvan formation barremian hauterivian elemental analysis was carried out on 36 samples from the source rock candidates gadvan and kazhdumi formations of the cretaceous succession of the south pars oil layer spol this analysis indicated that the om of the barremian hauterivian and albian samples in the spol was composed of kerogen types ii and ii iii respectively the average toc of analyzed samples is less than 1 wt suggesting that the cretaceous source rocks are poor hydrocarbon hc producers thermal maturity and ro values revealed that more than 90 of oil samples are immature the source of the analyzed samples taken from gadvan and kazhdumi formations most likely contained a content high in mixed plant and marine algal om deposited under oxic to suboxic bottom water conditions the pristane nc17 versus phytane nc18 diagram showed type ii iii kerogen of mixture environments for source rock samples from the spol burial history modeling indicates that at the end of the cretaceous time pre permian sediments remained immature in the qatar arch therefore lateral migration of hc from the nearby cretaceous source rock kitchens toward the north and south of the qatar arch is the most probable origin for the significant oils in the spol

detrital zircon record of a mesozoic collisional forearc basin in south central alaska the tectonic transition from an oceanic to continental arc

hydrocarbon generation capability of sinian lower cambrian shale mudstone and carbonate rocks in the sichuan basin southwestern china implications for contributions to the giant sinian dengying natural gas accumulation the giant natural gas accumulation recently discovered within the neoproterozoic dengying formation in the sichuan basin of southwestern china represents a new and important supplement to the ancient neoproterozoic cambrian petroleum systems worldwide however the source of this gas is controversial because there are five possibilities based on geology from bottom to top including the lower sinian doushantuo mudstone the upper sinian dengying algal dolomite the mudstone of the third member of the dengying formation the lower cambrian maidiping argillaceous dolomite and the lower cambrian qiongzhusi shale to improve the understanding of this issue 33 samples from the five possible source rock units in the study area were investigated for their character and maturity via petrology total organic carbon toc pyrobitumen reflectance kerogen carbon isotope and biomarker analyses based on the results we address their hydrocarbon generation capabilities and contributions to the giant gas accumulation results show that present day toc values of the samples range from 0 03 to 2 36 and vary both regionally and stratigraphically with the qiongzhusi shales in the central basin and the weiyuan ziyang area ranking the highest in contrast the organic matter source and maturity within these rocks are relatively homogenous with slight variation throughout the study area the organic matter is predominantly derived from algae and bacteria with different compositions deposited in marine reducing environments the rocks range in thermal maturity from postmature to overmature these results imply that the generation capability of source rock had been high in the past and the gas in the study area is most likely originated from oil cracking and the late generation directly from the kerogen of source rocks with the qiongzhusi shales being the dominant source rock thus the hydrocarbon migration pattern in the study area is a lateral migration from deep seated and younger cambrian source rocks in sags to shallow seated and older sinian dolomite reservoirs in uplifts the migration process occurred in the oil phase with the oil being later cracked the differences in natural gas geochemistry may be controlled by complex factors e g thermal maturity the migration accumulation process and differing contributions from source rocks besides the dominant qiongzhusi regionally the central basin and the weiyuan ziyang area have had high hydrocarbon generation capability and thus should be considered as favorable targets for natural gas exploration in the future this study of china provides an additional example of neoproterozoic cambrian petroleum systems worldwide and thus can help to synthesize the systematics of such systems and understand the sedimentary transition across the precambrian cambrian boundary